JP2002313540A - Planar heating element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar heating element 1 that can make heat distribution uniform or almost uniform on the whole heating face 5 without forming electrode width so large in the planar heating element 1 in which electrodes 3, 4 are formed of material with high surface resistivity such as a silver paste. SOLUTION: The heating face 5 of the planar heating element 1 is divided in a plurality of blocks, and a voltage drop portion by electric resistance in each block is adjusted by a distance between branch electrodes and branch electrode width so that current density is constant or almost constant on the whole heating face 5.

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, and more particularly to a sheet heating element suitable for use as a door mirror heater or the like. The door mirror heater is mounted on the back side of the door mirror to prevent fogging and defrosting of the vehicle door mirror and the like.

[0002]

2. Description of the Related Art In a planar heating element in which an electrode is formed of a material having a high surface resistivity such as a silver paste (Ag paste), it is necessary to reduce the electrode resistance in order to suppress heat generation at the electrode. The electrode width is as large as several tens of mm.

However, the plane area of a planar heating element used as a heater for a door mirror or the like has an approximately constant limit. Therefore, if the electrode width is increased, the area of the heating section is reduced correspondingly, so that the heating temperature is reduced. It becomes difficult to control. On the other hand, when the electrode width is reduced, the electrode resistance increases, and heat is generated in the vicinity of the voltage application portion. However, in a portion away from the voltage application portion, the voltage drops and the heat generation property is significantly reduced.

As described above, it is very difficult for a sheet heating element in which an electrode is formed using a material having a high surface resistivity to exhibit efficient heating performance.

[0005] In spite of the fact that the surface resistivity of silver paste is higher than the surface resistivity of copper foil, for example, silver paste is frequently used as an electrode in the process of forming an electrode.
This is because the number of manufacturing steps of the silver paste is smaller than that of the copper foil.

[0006]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a planar heating element having a structure in which an electrode formed of a material having a high surface resistivity such as silver paste is superposed on a heating layer. It is an object of the present invention to provide a planar heating element that can make the heat generation distribution uniform or substantially uniform over the entire heat generation surface without being formed so large.

[0007]

According to a first aspect of the present invention, there is provided a planar heating element for forming an electrode using a material having a high surface resistivity, such as a silver paste. The heating surface of the planar heating element is divided into a plurality of blocks, and the voltage drop due to the electric resistance in each block is determined by the distance between the branch electrodes and the width of the branch electrode so that the current density is constant or substantially constant over the entire heating surface. It is characterized by the following.

According to a second aspect of the present invention, there is provided the planar heating element according to the first aspect of the present invention, wherein the distance between the branch electrodes is narrowed in accordance with the voltage drop, and the width of the branch electrode is reduced. Is characterized in that it is formed widely according to the voltage drop.

The sheet heating element according to the first aspect of the present invention having the above-mentioned structure is a sheet heating element in which an electrode is formed of a material having a high surface resistivity, such as silver paste, wherein the heating surface of the sheet heating element is formed. It is divided into a plurality of blocks (for example, several blocks), and the voltage drop due to the electric resistance in each block is adjusted by the distance between the branch electrodes and the width of the branch electrodes, so that the current density is constant or substantially constant over the entire heating surface. In addition, the relationship between the electrode width and the voltage drop rate is grasped in advance, the distance between the branch electrodes, the width of the branch electrodes are adjusted, and the electrode pattern in which the voltage drop is corrected is configured. Is what you do. In the above adjustment, as described in claim 2, the distance between the branch electrodes is reduced according to the voltage drop, and the branch electrode width is widened according to the voltage drop.

[0010] Target values are determined in advance for the product resistance and the electrode temperature, and the width of the main electrode of the electrode pattern is determined based on the values. The width of the stem electrode is also reduced at a portion away from the voltage application unit. Further, at the end of the electrode pattern, the heating surface of the planar heating element is divided into several blocks, for example, three blocks in the horizontal direction, and each block is also divided into three blocks in the vertical direction. By using the relationship between the width and the voltage drop rate, the distance between the branch electrodes and the width of the branch electrodes are adjusted, and an electrode pattern in which the voltage drop is corrected is formed.

In the above-mentioned prior art, the reason why the current density on the entire heating surface is not constant is that the resistance of the silver paste itself is large, so that the current flowing near the voltage application part and the part distant from the voltage application part are different. This is because the magnitude of the current was different from the current value in the vicinity of the voltage application part> the current value in the part away from the voltage application part.

On the other hand, as a result of intensive studies on the sheet heating element applied to the present invention, the relationship shown in FIG. 1 between “electrode width” and “voltage loss rate” and “current density” It has been found that there is a relationship shown in FIG. 2 between “electrode heating temperature”. In view of this, the present invention realizes a uniform temperature distribution (heat generation) of the sheet heating element by setting the current density to be constant in all of the heating sections of the sheet heating element from this relationship. It is.

The terms are as follows. Surface resistivity One side is 1c in the electric resistance value between the opposite sides of the square.
Measured with a square of m (unit is Ω / □). Volume resistivity One side is 1c of the electric resistance value between the opposing surfaces of the cube.
Measured with a cube of m (unit is Ωcm). Current density Current intensity per unit area perpendicular to current.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments will be described below with reference to the drawings.

FIG. 3 is a plan view of a sheet heating element 1 according to an embodiment of the present invention. The sheet heating element 1 is configured as follows.

That is, first, a heat generating layer 2 formed in a predetermined plane shape according to the shape of a door mirror or the like using the planar heat generating element 1 as a heater is provided. A pair of electrodes 3 and 4 formed in a planar shape slightly smaller than the heat generating layer 2 are laminated and fixed.

Each of the pair of electrodes 3 and 4 is formed of a silver paste or the like having a relatively high surface resistivity, and includes the main electrodes 3a and 4a and the comb-shaped branch electrodes 3b and 4 respectively.
b are integrally formed, and are formed in a pattern in which the comb-shaped branch electrodes 3b and 4b are alternately combined. Further, each of the pair of electrodes 3 and 4 is provided with a terminal connection portion 3c and 4c as a voltage application portion, each of which is located at an upper left portion of the stem electrodes 3a and 4a in the drawing.

In the upper electrode 3 in FIG.
a is a first portion 3d extending rightward along the upper edge of the heat generating layer 2 from the terminal connection portion 3c, and a second portion extending downward along the right edge of the heat generating layer 2 from an end of the first portion 3d. 3
e, and a linear third portion 3f extending downward from the middle of the first portion 3d. In the upper and lower electrodes 4 in the figure, the main electrode 4a is heated by the terminal connection portion 4c. First portion 4d extending downward along the left edge of layer 2
A second portion 4e extending rightward from the end of the first portion 4d along the lower edge of the heating layer 2, and a linear third portion 4f extending upward from the end of the second portion 4e. have. This third portion 4f is located between the second and third portions 3e, 3f of the upper electrode 3. A large number of branch electrodes 3b, 4b are respectively directed to the left or right from the second and third portions 3e, 3f of the upper electrode 3 and the first and third portions 4d, 4f of the lower electrode 4. The plurality of branch electrodes 3b and 4b are arranged alternately in the vertical direction in a comb shape. The distance between the branch electrodes and the width of the branch electrodes are not constant, but are adjusted for each block as follows.

That is, in the sheet heating element 1,
The heat generating surface 5 is divided into a plurality of blocks. In the figure, the heat generating surface 5 is divided into three blocks vertically and horizontally to be divided into nine blocks A to I, and the current density is constant or substantially constant over the entire heat generating surface 5. As described above, the voltage drop due to the electric resistance in each block is adjusted by the distance between the branch electrodes and the width of the branch electrodes.

The adjustment method is as follows.

That is, the above-mentioned voltage loss rate [unit:%
/ 10 mm] is first determined by the width of the main electrodes 3a and 4a, and the loss rate decreases as the width increases. Therefore, first, the voltage loss rate until the current reaches each block (set the center of the block) is calculated.

[0022] For example, the electrode width _{x A} is 1mm at the closest A block terminal connections 3c, and 4c among the nine blocks of the A to I, when the inter-electrode distance _{y A} is 2 mm, numerical values in the A block B to I on the basis of
8 blocks are set one by one.

W = IV (1) where W: electric power (= heat generation) I: current V: voltage In the above equation (1), the current value I can be adjusted so as to change it. Since it is impossible, V = IR formula (2) where R = resistance I = V / R formula (3), that is, W = V ² / R formula (4) Since the resistance R can be adjusted so as to change the resistance, the resistance R is set to a certain value so that the calorific value becomes uniform.

For example, the setting of the B block located immediately below the A block is performed as follows.

Voltage loss rate at each electrode width per unit length ×
Distance to the center of the B block = voltage loss rate When voltage is applied from the terminal 4c, since the width of the main electrode is 10.5 mm, from the above “electrode width and voltage loss rate”, the voltage loss rate is 0.5% / 10 mm. The distance to the center of the B block is 20 mm, and when a voltage is applied from the terminal 3c, the width of the main electrode is 7.2 mm. Therefore, from the above “electrode width and voltage loss rate”, the voltage loss rate is 0.65% / 10 mm. Distance to the center of 20mm. From the above values, the average voltage loss rate from the terminal 3c and the terminal 4c is calculated as follows: (0.5 [% / 10 mm] × 2 [cm] +0.65 [%
/ 10 mm] × 2 [cm]) / 2 = 1.15 [%]. In consideration of this loss rate, the distance between the electrodes (this portion generates heat) is set to make the same voltage loss rate as that of the A block. Since the distance y _A between the electrodes of the A block is 2 mm, B
By between blocks of the electrode distance _{y B} is ^{2 × (1-0.0115 2) = 1.9543} , about 1.95mm, and the electrode width _{x B} becomes 3-1.95 = 1.05mm (this 3 is the electrode width _{x a} + electrode distance _y a = 3 mm of the a block).

Therefore, specifically, thereafter, by setting the electrode width x and the inter-electrode distance y of the C to I blocks respectively by the above-described method, the heat generation distribution which is the object of the present invention can be made uniform. That is, the current density is constant for all portions of the heat generating portion 5 of the sheet heating element 1 based on the relationship between “electrode width and voltage loss rate” and “current density and electrode heat generation temperature”. By making appropriate settings, it is possible to achieve uniform heat generation distribution.

The sheet heating element 1 of FIG.
The adjustment is performed by the above method so that the current density is constant in all nine blocks A to I. When the heat generation state is measured, the heat generation state is made uniform as shown in FIG. Good results could be confirmed. On the other hand, as a comparative example, in the planar heating element 51 of the same width electrode pattern shown in FIG. 5, the heat generation state was non-uniform as shown in FIG.

That is, in FIG. 4, the heating temperature of the upper left block (block A) closest to the voltage application section (terminal section) is about 72 ° C., and the right side of the drawing farthest from the voltage application section (terminal section). In the lower block (I block), the heat generation temperature is about 74 to 75 ° C., and the temperature difference between both blocks is only about 2 to 3 ° C., whereas in FIG. The heating temperature is about 72 ° C. at the uppermost part on the drawing closest to the part (terminal part), and the heating temperature is 62 to 63 ° C. at the lowest part on the drawing farthest from the voltage application part (terminal part). And there is a temperature difference of about 10 ° C. Therefore, from the comparison results, it was confirmed that the heat generation temperature was made substantially uniform according to the present invention.

[0029]

The present invention has the following effects.

That is, in the planar heating element according to the first aspect of the present invention having the above structure, the planar heating element in which the electrode is formed of a material having a high surface resistivity, such as silver paste, is used. The heating surface is divided into a plurality of blocks, and the voltage drop due to the electric resistance in each block is adjusted by the distance between the branch electrodes and the width of the branch electrodes so that the current density is constant or substantially constant over the entire heating surface. In addition, even if the electrode width is not so large, that is, a relatively large amount of heat is secured, and the heat generation distribution can be made uniform or substantially uniform over the entire heat generating surface. Therefore, it is possible to provide a high-quality sheet heating element or a heater product having a relatively large heat value and a uniform or substantially uniform heat distribution over the entire heating surface.

In addition, in the planar heating element according to the second aspect of the present invention having the above configuration, in the adjustment according to the first aspect, the distance between the branch electrodes is formed to be narrow according to the voltage drop. At the same time, the width of the branch electrode is made wider in accordance with the voltage drop, so that a fine adjustment operation can be appropriately performed in each block.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an electrode width and a voltage loss rate.

FIG. 2 is a graph showing the relationship between current density and electrode heating temperature.

FIG. 3 is a plan view of a sheet heating element according to an embodiment of the present invention.

FIG. 4 is an explanatory view showing a heat generation state measurement test result of the planar heating element.

FIG. 5 is a plan view of a sheet heating element according to a comparative example.

FIG. 6 is an explanatory view showing a heat generation state measurement test result of the planar heating element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Planar heating element 2 Heating layer 2a One surface 3, 4 electrode 3a, 4a Trunk electrode 3b, 4b Branch electrode 3c, 4c Terminal connection part 3d, 3e, 3f, 4d, 4e, 4f Trunk electrode part 5 Heating surface

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[Procedure amendment]

[Submission Date] May 28, 2002 (2002.5.2)
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Claims (2)

[Claims] 1. A sheet heating element (1) for forming electrodes (3) and (4) with a material having a high surface resistivity such as silver paste, wherein a heating surface (5) of the sheet heating element (1) is formed. The method is characterized by dividing into a plurality of blocks and adjusting the voltage drop due to the electric resistance in each block by the distance between the branch electrodes and the width of the branch electrodes so that the current density is constant or substantially constant over the entire heating surface (5). And a sheet heating element. 2. The planar heating element according to claim 1, wherein the distance between the branch electrodes is formed to be narrow in accordance with the voltage drop, and the branch electrode width is formed to be wide in accordance with the voltage drop. And a sheet heating element.