HK1192401A - Planar heat-generating body and method for manufacturing same - Google Patents

Description

Planar heating element and method for manufacturing same

Technical Field

The present invention relates to a planar heating element of a temperature self-control type which is attached to a mirror back surface of a rear view mirror or the like of an automobile, for example, and is used for defrosting and preventing fogging of a mirror, and a method for manufacturing the same.

Background

In a rear view mirror of an automobile, in order to remove frost and mist that may impair the view, a method of attaching a planar heating element to the rear surface of the mirror and removing the frost and mist by heating is widely used. As the planar heat generating element, a temperature self-control planar heat generating element having a positive temperature characteristic (PTC characteristic) is generally used without requiring an expensive temperature control device.

A temperature self-controlling planar heating element is generally produced by printing a conductive paste mainly containing silver powder on a base film made of a polyester film (エステルフィルム) or the like by screen printing or the like to form electrode patterns as a main electrode and a pectinate electrode, then heating and curing the electrode patterns to form an electrode, and then forming a heating element film (hereinafter referred to as a PTC heating element film) having a temperature self-controlling property so as to cover the electrode. The PTC heating element film is a mixture obtained by kneading a crystalline resin such as polyethylene (ポリエチレン) and carbon black (カーボンブラック), and has PTC characteristics in which the resistance value increases at the softening temperature or the vicinity of the melting point of the resin.

Fig. 3 shows an example of the structure of the planar heat-generating body manufactured as described above, in fig. 3, 11 denotes a base film, and 12 and 13 denote a pair of electrodes. The electrodes 12, 13 become main electrodes 12a, 13a and pectinate electrodes 12b, 13b, respectively, and the pectinate electrodes 12b, 13b of the two electrodes 12, 13 are arranged to alternately enter into mutual meshing between the pectinate teeth as shown in fig. 3. The PTC heater film formed so as to cover both the electrodes 12 and 13 is located between both the electrodes 12 and 13, and generates heat at a portion constituting the current flow path. In fig. 3, a dot region indicates a heat generating region 14 of the PTC heater film, and the heat generating region 14 is a partial region between the electrodes 12 and 13.

The planar heating element is further provided with a terminal for electrical connection with the outside, and a double-sided adhesive tape required for attaching the mirror is attached. In fig. 3, 15 denotes an eyelet for rivet fixing of a terminal. The terminal is hidden from view in fig. 3, but is located on the side opposite to the side where the eyelet 15 is located.

However, in the planar heating element described above, it is important to ensure a sufficiently large current capacity of the electrode. If the current capacity is insufficient, the electrode may generate heat abnormally, which may cause smoke generation and ignition.

The current capacity of the electrode is determined by the resistivity, film thickness, and width of the electrode material. The silver paste electrode can reduce the resistivity by mixing and dispersing silver powder with a resin material as a binder, but if the silver powder is too much, the fluidity as paste becomes small, and printing becomes difficult. Further, the film becomes brittle, and there is a problem that cracks occur. Thus, the resistivity0.5×10^-4The degree of Ω · cm is a limit, and the resistivity of a general metal itself such as Al, Cu, Ni, Ag, etc. is not achieved at present.

On the other hand, since an increase in film thickness leads to an increase in material cost, the current capacity is generally secured by the width of the electrode pattern without changing the electrode material and film thickness. In this case, since a voltage of 13.5V is applied to the rearview mirror of the automobile and a current of about 3A to 7A is passed, it is necessary that the width of the main electrode of the silver paste electrode is as wide as about 10mm to 20 mm. Since the composite resistivity is low in the region where the wide main electrode and the heater film overlap each other, the amount of heat generated in this region is small, and when frost or dew adheres to the mirror, the frost or dew remains in the wide main electrode region, which impairs the view line, and good defogging performance cannot be obtained (in the mirror, performance of eliminating y percent of the area of the mirror of frost or dew after x minutes).

On the other hand, instead of such a silver paste electrode, an aluminum foil may be used as an electrode material (for example, see patent document 1). The resistivity of the aluminum foil was 0.03X 10^-4Omega cm is about one tenth of that of silver paste electrode. Therefore, even in the case of using a silver paste electrode, for example, if the film thickness of the silver paste electrode is made as thick as about 20 μm to 30 μm in order to reduce the electrode resistance as much as possible, if an aluminum foil is used instead of the silver paste, the thickness thereof is made only about 10 μm which is generally easily available, and the electrode width can be reduced to about one third to one fifth of the silver paste electrode, and therefore, the main electrode width can be considerably reduced as compared with the silver paste electrode. This can solve the problem that the residual frost disturbs the sight. However, the width of the main electrode of the terminal region shown in patent document 1 is significantly larger than the width of the pectinate electrode, and there is no suggestion to reduce the width.

Documents of the prior art

Patent document

Patent document 1: japanese unexamined patent publication No. 2007-18989

Disclosure of Invention

Technical problem to be solved by the invention

As described above, an aluminum foil having a low resistivity is excellent in thermal conductivity and has an appropriate surface as an electrode of a planar heat generator, but the surface of the aluminum foil is easily oxidized, and the interface resistance with the PTC heat generator film gradually increases due to the oxidation, which causes a problem that the conductivity at the interface with the PTC heat generator film is lowered.

If the conductivity of the electrode and the PTC heater film is reduced, a desired amount of heat generation cannot be obtained, resulting in a reduction in heating performance. Further, if the conductivity is partially lowered, for example, the heat generation distribution becomes abnormal, which may cause smoke generation and ignition.

As a countermeasure against such a problem, a plating film of silver, nickel, or the like is applied to the surface of the aluminum foil to prevent a decrease in conductivity, but this plating film is very expensive and is not practical.

On the other hand, the surface of the aluminum foil may be mechanically or chemically polished to increase the contact area with the PTC heater film, thereby improving the conductivity, but the conductivity cannot be satisfied in long-term use.

In view of the above circumstances, the present invention has been made to provide a planar heat generating element and a method for manufacturing the same, which can obtain a good defogging performance by using an aluminum foil as an electrode, and can further suppress an increase in the interface resistance between the aluminum foil and a PTC heat generating body film due to oxidation, thereby suppressing a decrease in conductivity and obtaining a good heat generating performance for a long period of time.

Technical scheme for solving technical problem

According to the present invention, a temperature self-controlling planar heating element attached to a rear surface of a mirror includes: a base film; an electrode formed by patterning an aluminum foil on the base film; a conductive coating film formed on the surface of the electrode; the PTC heater film is formed by covering the electrodes with a conductive coating film, which is formed by mixing a conductive material with a phenol resin (フェノール resin or an epoxy resin (エポキシ resin).

According to the present invention, a method for manufacturing a temperature self-controlling planar heating element attached to a rear surface of a mirror includes: a step of thermally bonding an aluminum foil coated with a hot melt adhesive (ホットメルト) on one side to a base film; patterning the thermally bonded aluminum foil to form an electrode pattern; printing, heating and curing the electrode pattern except for the terminal portion to form a conductive coating; and a step of forming the PTC heater film so as to cover the electrode pattern via the conductive coating film, wherein a material obtained by kneading a conductive material into a phenol resin or an epoxy resin is used for forming the conductive coating film.

According to another aspect of the present invention, a method for manufacturing a temperature self-controlling planar heating element attached to a rear surface of a mirror includes: a step of thermally bonding an aluminum foil coated with a hot-melt adhesive on one surface to a base film; printing and forming a conductive coating on the surface of the thermally bonded aluminum foil except for the terminal portion; a step of forming an electrode pattern by peeling the conductive coating film and the aluminum foil together after the conductive coating film is pre-cured; and a step of forming a PTC heater film so as to cover the electrode pattern after the conductive coating is completely cured, wherein a material obtained by kneading a conductive material into a phenol resin or an epoxy resin is used for forming the conductive coating.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, by using an aluminum foil as an electrode, the electrode width can be narrowed while sufficiently securing the current capacity. Therefore, good defogging performance can be obtained.

Further, by providing a conductive coating film on the surface of the aluminum foil, it is possible to suppress a decrease in conductivity at the interface between the aluminum foil and the PTC heater film, and thus to obtain a good heat generation performance over a long period of time.

Drawings

FIG. 1 is a plan view showing a structure of one embodiment of a planar heat generating element according to the present invention.

FIG. 2 is a cross-sectional view for explaining the general structure of a planar heat generating element according to the present invention.

FIG. 3 is a plan view showing a conventional configuration example of a planar heat generating element.

Detailed Description

Embodiments of the present invention will be described with reference to the accompanying drawings.

Fig. 1 shows a planar structure of a planar heat generating element according to the present invention, and fig. 2 is a partial cross-sectional view of the planar heat generating element shown in fig. 1 along line XL.

A pair of electrodes 22, 23 are formed on a base film 21 made of a polyester film or the like having a thickness of about 50 to 150 μm. The electrodes 22 and 23 are composed of main electrodes 22a and 23a and pectinate electrodes 22b and 23b, respectively, and are formed by patterning aluminum foil having a thickness of about 5 to 20 μm. As shown in fig. 1, the pectinate electrodes 22b, 23b of the two electrodes 22, 23 are configured to interact into intermeshing. The pitch between the comb-teeth electrodes 22b and 23b engaged with each other is about 2mm to 10 mm. The preferred width of the main electrodes 22a, 23a is 1.5mm to 10mm, and the preferred width of the pectinate electrodes 22b, 23b is 0.5mm to 5 mm. By forming the electrodes 22, 23 from aluminum foil, the width of the main electrodes 22a, 23a can be made as narrow as shown in fig. 1.

Conductive coatings 24 are formed on the surfaces of the electrodes 22 and 23, and PTC heater films are formed so as to cover the entire electrodes 22 and 23 via the conductive coatings 24. In fig. 1 and 2, the dotted area indicates a heat generation area 25a of the PTC heater film 25. As shown in fig. 2, the conductive coating 24 is formed on the aluminum foils 22 and 23 except for the terminal portions (the positions of the eyelets 28 for mounting the terminals 27).

The PTC heating element 25 is formed by, for example, printing PTC heating element paste formed by kneading carbon black or the like with a crystalline resin such as polyethylene.

The conductive coating 24 is formed by printing a conductive paste obtained by kneading a conductive material into a phenol resin or an epoxy resin. By using these phenol resins and epoxy resins as binder resins, good adhesion and adhesion to the electrodes 22 and 23 made of aluminum foil can be obtained. Carbon black and graphite powder were kneaded as conductive materials. Instead of the carbon black and graphite powder, metal powder such as silver powder and nickel powder can be used.

The resistivity of the conductive coating 24 is selected to be in the range of 2.5 to 2500 times the resistivity of the PTC heater film 25, and the film thickness of the conductive coating 24 is selected to be in the range of 5 to 70 μm. When the thickness of the conductive coating 24 is thicker than this range, the conductive coating 24 itself generates heat, and desired heating characteristics cannot be obtained.

As a method for forming the conductive coating 24 on the surfaces of the electrodes 22 and 23, screen printing or roll coating can be employed. The screen printing is suitable for obtaining a film thickness of about 5 to 30 μm, and the roll coating is suitable for obtaining a conductive coating 24 having a film thickness of 30 μm or more.

The method for forming the conductive coating 24 includes: a method of thermally bonding an aluminum foil coated with a hot-melt adhesive on one side to the base film 21, peeling the aluminum foil with a cutter or patterning the aluminum foil by etching to form an electrode pattern, and then screen-printing only the electrode pattern with a conductive coating 24; a method in which a conductive coating film 24 is printed on the entire surface of the aluminum foil before peeling, and after precuring (60 ℃ C. -100 ℃ C., 5 minutes-10 minutes), the aluminum foil is peeled off together with the conductive coating film by a cutter.

As described above, after the electrodes 22 and 23, the conductive coating 24, and the PTC heater film 25 are formed on the base film 21, the terminal 27 is attached, and the double-sided adhesive tape 29 for attaching to the mirror is further attached.

The terminals 27 are mounted using eyelets 28. The terminal 27 is an L-shaped metal member, and one side 27a of the L is caulked and fixed by an eyelet 28. Two holes 27b are formed in one side 27a of the L-shape, and two caulking portions 28a of the eyelet 28 are inserted through holes formed in the electrodes 22 and 23 and the base film 21, and the tip ends of the holes 27b of the terminal 27 are caulked. The terminals 27 are attached to the base film 21 side, and a double-sided adhesive tape 29 is attached to the opposite PTC heater film 25.

The following describes details of various examples and results of environmental tests.

Example 1

A planar heating element test piece was produced in the following manner. After the aluminum foil with the hot melt adhesive was thermally adhered to the base film 21 made of a polyester film, the aluminum foil was peeled off by a cutter to form electrode patterns (electrodes 22 and 23). The width of the main electrodes 22a, 23a is 3mm, and the width of the pectinate electrodes 22b, 23b is 1 mm. Next, a conductive paste obtained by kneading carbon black and graphite powder into a phenol resin was screen-printed on the electrodes 22 and 23, and cured by heating (150 ℃, 5 to 10 minutes), thereby forming a conductive coating 24. The thickness of the conductive coating 24 was 10 μm. The resistivity of the conductive coating 24 at this time was 0.2 Ω · cm. Then, PTC heater paste (resistivity 50 Ω · cm) was printed to form a PTC heater film 25, a terminal 27 for energization was attached, and a double-sided adhesive tape 29 was attached to complete a planar heater test piece. The resistance value between the pair of terminals 27 was measured to be 19.9 Ω.

The sheet-like heating element test piece was placed at 60 ℃ in a high-temperature and high-humidity state at 90 to 95% RH, and the resistance value after 72 hours of measurement was 1.04 times the resistance value almost unchanged in the initial state.

In addition, repeated temperature cycling tests of-30 ℃ and +80 ℃ were carried out for the same test pieces. The resistance value after five cycles became 0.98 of the initial state, and hardly changed.

Example 2

Two test pieces of a planar heating element were prepared in the following manner. The electrode patterns and the conductive coating 24 of the two test pieces were formed by the same procedure as in example 1. The resistivity of the conductive coatings 24 of the two test pieces was 0.02 Ω · cm and 20 Ω · cm, respectively, and the film thickness was 10 μm in total. PTC heating element paste (resistivity 50. omega. cm) was printed, and two planar heating element test pieces were completed through the same procedure as in example 1. The resistance values between the terminals 27 are 15.8 Ω and 31.0 Ω, respectively.

These test pieces of the planar heating element were left in the same high-temperature and high-humidity state as in example 1, and the resistance value after 72 hours was measured. The resistance values were 1.02 times and 1.05 times, respectively, and were almost unchanged from the initial state.

In addition, the same temperature cycle test as in example 1 was performed on two test pieces of the same sample. The resistance values were measured after five cycles and became 0.95 times and 0.93 times, respectively, with little change.

Example 3

Two test pieces of a planar heating element were prepared in the following manner. The electrode patterns and the conductive coating 24 of the two test pieces were formed by the same procedure as in example 1. The thicknesses of the conductive coatings 24 of the two test pieces were 5 μm and 70 μm, respectively, and the resistivity was 0.2. omega. cm in total. PTC heating element paste (resistivity 50. omega. cm) was printed, and two planar heating element test pieces were completed through the same procedure as in example 1. The resistance values between terminals 27 are 16.52 Ω and 15.64 Ω, respectively.

These planar heat-generating body test pieces were subjected to the same temperature cycle test as in example 1. The resistance values were measured after five cycles and became 0.98 times and 1.02 times, respectively, with little change.

[ comparative example ]

Electrode patterns of aluminum foil were formed as in example 1. A PTC heating element paste (resistivity 50 Ω · cm) was printed without forming a conductive coating, and a planar heating element test piece was completed in the same manner as in example 1. The resistance value between the terminals 27 is 45.5 Ω.

The sheet-like heat-generating body test piece was left in the same high-temperature and high-humidity state as in example 1, and the resistance value after 72 hours was measured and became 2.61 times.

The same temperature cycle test as in example 1 was carried out on the same test piece. The resistance value after five cycles became 1.36 times.

As is clear from the above test results, according to the planar heat-generating element of the present invention, it is possible to suppress a decrease in conductivity at the interface between the electrode made of aluminum foil and the PTC heat-generating film.

Claims (6)

1. A planar heating element of a temperature self-control type which is attached to a back surface of a mirror, comprising:

a base film;

an electrode formed by patterning an aluminum foil on the base film;

a conductive coating film formed on the surface of the electrode;

a PTC heater film formed so as to cover the electrode via the conductive coating film,

the conductive coating is formed by mixing a conductive material with a phenol resin or an epoxy resin.

2. A planar heat-generating body as described in claim 1,

the resistivity of the conductive coating film is 2.5 to 2500 times lower than that of the PTC heater film, and the thickness of the conductive coating film is 5 to 70 [ mu ] m.

3. A method for manufacturing a planar heat generating element which is attached to a back surface of a mirror and is of a temperature self-controlling type, comprising:

a step of thermally bonding an aluminum foil coated with a hot-melt adhesive on one surface to a base film;

patterning the thermally bonded aluminum foil to form an electrode pattern;

printing, heating and curing the electrode pattern except for a terminal portion to form a conductive coating;

a step of forming a PTC heater film so as to cover the electrode pattern via the conductive coating film,

in the formation of the conductive coating, a material obtained by kneading a conductive material into a phenol resin or an epoxy resin is used.

4. A sheet heating element manufacturing method as defined in claim 3, characterized in that,

the step of forming the electrode pattern is a step of forming an electrode pattern by peeling the aluminum foil with a cutter.

5. A sheet heating element manufacturing method as defined in claim 3, characterized in that,

the step of forming the electrode pattern is a step of forming an electrode pattern by etching the aluminum foil.

6. A method for manufacturing a planar heat generating element which is attached to a back surface of a mirror and is of a temperature self-controlling type, comprising:

a step of thermally bonding an aluminum foil coated with a hot-melt adhesive on one surface to a base film;

printing and forming a conductive coating on the surface of the thermally bonded aluminum foil except for a terminal portion;

a step of forming an electrode pattern by peeling the conductive coating film and an aluminum foil together after precuring the conductive coating film;

a step of forming a PTC heater film so as to cover the electrode pattern after the conductive coating film is completely cured,

in the formation of the conductive coating, a material obtained by kneading a conductive material into a phenol resin or an epoxy resin is used.