JPH0513157A - Face heating element and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a face heating element excellent in flexibility and heat resistance by directly forming a heat resisting polymer having a determined glass transition temperature on a conductive heating element circuit formed from a metal foil through no adhesive. CONSTITUTION:On at least one surface of a conductive heating element circuit formed from a metal foil, a heat resisting polymer having a glass transition temperature of 250 deg.C or more is directly formed through no adhesive. Thus, a face heating element having excellent flexibility and heating resistance as resisting a continuous use at 200 deg.C or more, which element is useful for industrial heating furnace, can be provided at low cost.

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 which is flexible and has excellent heat resistance. More specifically, the present invention relates to a sheet heating element useful as an electric heater for industrial and domestic purposes.

[0002]

2. Description of the Related Art Conventionally, a carbon powder was used as a heating element, and a conductive sheet formed by a resin sheet containing the powder and a thin wire or foil made of a metal such as nickel alloy, chromium alloy, aluminum alloy was used as an adhesive. Although a planar heating element bonded to an insulating film via a sheet has been proposed, this method increases manufacturing costs, heat resistance is limited by a resin sheet or an adhesive, or flexibility is low. There is a problem that the application is limited due to insufficientness.

[0003]

As described above, the sheet heating element manufactured by the conventional technique has insufficient heat resistance and flexibility. Therefore, the problem to be solved by the present invention is 20
It is to inexpensively manufacture a flexible sheet heating element which can be used at a temperature of 0 ° C. or higher for a long period of time and can be adapted to various shapes depending on the application.

[0004]

Means for Solving the Problems The present inventors finally conducted the present invention as a result of intensive studies and research for solving the above problems. That is, the present invention is characterized in that a heat-resistant polymer having a glass transition temperature of 250 ° C. or higher is directly formed on at least one surface of a conductive heating element circuit formed of a metal foil without an adhesive. On one surface of the sheet heating element and the metal foil, an organic solvent solution of a heat resistant polymer having a glass transition temperature of 250 ° C. or higher is applied, dried, and
After the heat treatment at a temperature of ℃ or more, a part of the metal foil is etched to form a conductive heating element circuit, which is a method for manufacturing a planar heating element.

Examples of the heat-resistant polymer having a Tg of 250 ° C. or higher used in the present invention include polyimide, polyether imide, polyester imide, polyamide imide, etc., but their solubility in solvents, moldability, price, etc. From the above, polyamide imide is particularly preferable, and among polyamide imides, copolymerized polyamide imide containing 25 to 95 mol% of 3,3′dialkylbiphenyl residue as an amine residue is further preferable. The reason for this is that by introducing a rigid biphenyl structure into the polymer skeleton, the heat resistance is improved and the coefficient of thermal expansion is reduced, curling is suppressed when a laminate with a metal foil is formed, and the dimensions after etching are reduced. This is because it has the effect of reducing the change. If the copolymerization ratio of the 3,3'-dialkylbiphenyl residue is 25 mol% or less, such an effect is not sufficiently exhibited, and if it exceeds 95 mol%, the solubility in a solvent is deteriorated, which is not preferable.

The polyamide-imide used in the present invention is improved in practical heat resistance such as solder resistance and chemical resistance by being modified with an epoxy resin in advance. Any epoxy resin may be used as the epoxy resin as long as it is bifunctional or more, but in order to improve heat resistance and chemical resistance without impairing flexibility, a multifunctional phenol novolac type epoxy is used. 1 to 30% by weight of resin, preferably 2.5 to 20% by weight, based on polyamide-imide
It is better to use within the range. If it is less than 1% by weight, the crosslinking density is too low and the effect is insufficient. If it exceeds 30% by weight, gelation occurs at the time of modification or the polymer becomes too hard and flexibility is deteriorated, which is not preferable.

The polyamideimide used in the present invention can be synthesized by a usual method such as an isocyanate method or an acid chloride method. Raw materials used in the isocyanate method include trimellitic anhydride, 3,3 ′ dimethyldiphenyl 4,4 ′ diisocyanate, and 3,3′diethyldiphenyl 4,4 ′ diisocyanate.

Monomers capable of forming other copolymerizable structural units in the production of the polyamideimide used in the present invention are exemplified below in the form of an acid component and an amine component. As the amine component, p-phenylenediamine, m
-Phenylenediamine, 4,4 'diaminodiphenyl ether, 4,4' diaminodiphenylmethane, 4,4 '
Diaminodiphenyl sulfone, 4,4 ′ diaminobenzophenone, 2,2 ′ bis (4 aminophenyl) propane, 2,4 tolylenediamine, 2,6 tolylenediamine, p-phenylenediamine, m-phenylenediamine, isophoronediamine, Hexamethylenediamine and the like can be mentioned.

As the acid component, terephthalic acid, isophthalic acid, 4,4'biphenyldicarboxylic acid, pyromellitic acid, 3,3 ', 4,4'benzophenonetetracarboxylic acid, 3,3', 4,4'biphenyl Examples thereof include sulfone tetracarboxylic acid, 3,3 ′, 4,4 ′ biphenyl tetracarboxylic acid, adipic acid, sebacic acid, maleic acid, fumaric acid, dimer acid, and stilbene dicarboxylic acid.

The following isocyanates can be used as the amine component. For example, 2,4 tolylene diisocyanate, 4,4 ′ diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate and the like can be mentioned. The following acid anhydrides and acid chlorides can be used as the acid component. Examples thereof include benzophenone tetracarboxylic acid anhydride, diphenyl sulfone tetracarboxylic acid anhydride, biphenyl tetracarboxylic acid anhydride, and pyromellitic acid anhydride.

The conductive metal foil used in the present invention may be selected from iron, aluminum, nickel-chromium alloy, nickel-chromium-iron alloy, nickel-copper alloy, etc. depending on the application and is not particularly limited. The thickness and circuit pattern of these metal foils are determined by the voltage supplied to the sheet heating element, the required amount of heat generation, etc., and the thickness is several μ to 1
The one of about 00 μ is used.

As a method for producing the sheet heating element of the present invention, a solution of a heat-resistant polymer in an organic solvent is applied to one side of a metal foil, dried and heat-treated at a temperature of 200 ° C. or higher, and then a part of the metal foil. Is etched to form a conductive heating element circuit.

The organic solvent for the heat-resistant polymer is not particularly limited, but when the heat-resistant polymer is polyamideimide, a polar solvent such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, dimethylurea is used. Is preferred. Further, in combination with these solvents, hydrocarbons such as toluene and xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, dioxane, ethylene glycol dimethyl ether, ethers such as tetrahydrofuran, ethyl acetate, n-butyl acetate. Alternatively, a γ-butyrolactone nadonoester-based solvent or the like may be mixed and used.

In the present invention, the method of applying the heat-resistant polymer solution to the metal foil is not particularly limited, and a conventionally used gravure coater, reverse coater, kiss coater or comma coater can be used.

The metal foil coated with the heat resistant polymer is immediately dried and then heat treated. In the present invention, the heat treatment temperature is 1
It is required to be 50 ° C. or higher, preferably 200 ° C. or higher. The reason is that if the heat treatment temperature is lower than 150 ° C., it takes an extremely long time to completely remove the solvent remaining in the coating film, which is economically disadvantageous, and epoxy-modified polyamideimide is used as a heat-resistant polymer. This is because the crosslinking reaction with epoxy may be insufficient when used.

In the present invention, the thickness of the heat resistant polymer layer is 5 to 50 μ, preferably 10 to 30 μ. If it is less than 5μ, it is too thin, resulting in insufficient reliability of electric insulation and film properties, and if it exceeds 50μ, the moldability deteriorates and the curl of the laminate with the metal foil after coating becomes large, resulting in steps after etching. It is not preferable because it deteriorates workability.

The heat-resistant polymer used in the present invention may contain additives such as an antioxidant, a colorant, a defoaming agent and an inorganic filler as long as the object of the present invention is not impaired. .

[0018]

The present invention is characterized in that the conductive heating element circuit has a Tg of 25.
The heat-resistant polymer having a temperature of 0 ° C. or higher is directly laminated without using an adhesive. Since no adhesive is used, the sheet heating element of the present invention can exhibit heat resistance capable of continuous use at 200 ° C. or higher.

[0019]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

The characteristics of the sheet heating element shown in the examples were evaluated by the following methods. Logarithmic viscosity: A solution of 0.5 g of polymer dissolved in 100 ml of N-methyl-2-pyrrolidone was measured at 25 ° C. Tg: Rigaku Denki Co., Ltd. TMA device, thickness 30
A 1 g load was applied to a film of a heat-resistant polymer having a width of μ and a width of 1 mm, and the inflection point of the expansion coefficient was measured when the temperature was raised at a rate of 5 ° C./min. Tensile strength and elongation: Tensilon manufactured by Toyo Baldwin Co., Ltd. was used, and the tensile speed was measured at 20 mm / min. Adhesion; using Tensilon manufactured by Toyo Baldwin,
The tensile speed was measured at 50 mm / min.

EXAMPLE 1 0.8 mol of trimellitic acid anhydride, 0.2 mol of benzophenone tetracarboxylic acid anhydride and 1 mol of o-tolidine diisocyanate were placed in a reaction vessel and N-methyl-2pyrrolidone 2K was added.
It was charged with g and heated to 180 ° C. in about 1 hour with stirring. Then, stirring was continued at 180 ° C. for about 3 hours to stop the reaction. The inherent viscosity of the obtained polymer was 1.45. This polymer solution was applied to an iron foil of 20 μm using an applicator so that the coating film thickness was 25 μm, dried at 100 ° C. for 5 minutes, and then heat-treated at 200 ° C. for 3 hours. Next, a photosensitive dry film was laminated on the iron foil, ultraviolet rays were radiated through a photomask, and after development, the iron foil was etched using a ferric chloride aqueous solution as a chemical etching agent to obtain a circuit pattern. After that, the dry film was removed with an alkaline solution. The adhesion between the iron foil and the polymer layer was 120 g / mm, the Tg of the heat-resistant polymer layer in the portion where the iron foil was removed by etching was 305 ° C., the tensile strength was 26 Kg / mm ² , and the tensile elongation was 55%. It was Further, no crack was observed even when the sheet heating element was bent along the circuit pattern, and the flexibility was good.

Example 2 To the polyamideimide solution synthesized in Example 1, 5% by weight of phenol novolac type epoxy resin was added to the polymer solid content, and the mixture was stirred at 100 ° C. for 2 hours for epoxy modification. The polymer obtained had an inherent viscosity of 1.51. A planar heating element was produced in the same manner as in Example 1 using this polymer solution. The adhesive force between the polymer layer and the iron foil was 138 g / mm, the Tg of the polymer layer was 303 ° C., the tensile strength was 28 Kg / mm ² , and the tensile elongation was 48%. In addition, this sheet heating element was placed in an oven at 200 ° C for 1 hour.
The adhesive strength after heat treatment for 0 days was as good as 135 g / mm.

Comparative Example 1 Acrylonitrile-butadiene rubber (Nipol 1001; Nippon Zeon Co., Ltd.) was added to the iron foil having a thickness of 20 used in Example 1.
And an epoxy resin (Epicote 828; Yuka Shell Co., Ltd.) were mixed in equal amounts, and 3 parts by weight of 2-ethyl-4-methylimidazole was added to 100 parts by weight of the epoxy resin to obtain an adhesive solution having a solid content concentration of 40% by weight. It was applied so that the film thickness would be 20μ, dried at 100 ° C. for 5 minutes, and then a 36μ biaxially stretched polyester film was pressure-bonded between heating rolls.
Heat treatment was performed at 140 ° C. for 3 hours. When the obtained laminate was processed into a sheet heating element in the same manner as in Example 1 and the adhesion was evaluated, the initial adhesion was excellent at 153 g / mm, but after heat treatment at 200 ° C. for 10 days Adhesion is 17g / m
The heat resistance was insufficient because it was drastically reduced to m.

[0024]

EFFECTS OF THE INVENTION In the sheet heating element of the present invention, no adhesive is used between the conductive heating element circuit and the insulating layer, and the insulating layer uses a heat resistant polymer having Tg of 250 ° C. or higher. Since it has heat resistance far superior to that of conventional sheet heating elements that can withstand continuous use at temperatures of 200 ° C or higher, and has excellent flexibility, it can be used in industrial heating furnaces. It is a great contribution to the industrial world.

Claims (2)

[Claims] 1. A heat-resistant polymer having a glass transition temperature of 250 ° C. or higher is directly formed on at least one surface of a conductive heating element circuit formed of a metal foil without an adhesive. Sheet heating element. 2. The glass transition temperature is 25 on one surface of the metal foil.
An organic solvent solution of a heat-resistant polymer of 0 ° C. or higher is applied, dried, and heat-treated at a temperature of 150 ° C. or higher, and then a part of the metal foil is etched to form a conductive heating element circuit. Method for manufacturing sheet heating element.