JP7664566B2 - Manufacturing method of heater film for in-vehicle parts and insert molding - Google Patents

Description

This disclosure relates to a heater film for vehicle-mounted parts and a manufacturing method for insert-molded products, and more specifically, to a heater film for vehicle-mounted parts that includes a substrate layer, a heater circuit, and a protective circuit layer, and a manufacturing method for insert-molded products that use this heater film for vehicle-mounted parts.

Heater films for automotive parts are heaters that can be attached to the curved outer surfaces of parts in automobiles and the like by bending and stretching them, and are used, for example, as snow melting heaters. Such heater films are made by laminating a heater circuit formed using copper foil or the like on a base layer, and this heater circuit is covered with a thermoplastic resin or the like to create a module for use. This module is usually created by insert molding, in which thermoplastic resin is injected onto the heater circuit side of the heater film. However, in insert molding, high-temperature and high-pressure resin is injected directly onto the heater circuit, so depending on the molding conditions such as the mold shape, the temperature and pressure of the injected thermoplastic resin, the heater circuit wires may bend, tear, or the circuit may become exposed, destroying the heater circuit.

One method for preventing damage that occurs during insert molding is to form a surface protective layer. Patent Document 1 discloses a decorative sheet having a low-gloss pattern ink layer and a surface protective layer that covers it, in which the surface protective layer is formed by crosslinking and curing a resin composition containing an ionizing radiation curable resin and a thermoplastic resin in a ratio (mass ratio) of 75:25 to 25:75, the polystyrene-equivalent weight average molecular weight of the thermoplastic resin being in the range of 90,000 to 120,000 as measured by gel permeation chromatography (GPC), and the thickness of the surface protective layer being 1 to 1,000 μm.

JP 2009-132145 A

However, when manufacturing heater film modules for in-vehicle components, the strength of the heater circuit is weaker and the temperature and pressure of the injected resin are higher, so using the conventional surface protection layer materials described above does not prevent damage to the heater circuit and does not improve the injection molding resistance of the heater film.

The objective of this disclosure is to provide a heater film for vehicle-mounted parts that has excellent injection molding resistance, and a manufacturing method for insert-molded products using the same.

A heater film for an in-vehicle component according to one embodiment of the present disclosure includes a base layer, a heater circuit, and a circuit protection layer. The heater circuit is laminated on the base layer. The circuit protection layer is laid so as to surround the heater circuit. The 5% weight loss temperature of the circuit protection layer in a thermogravimetric differential thermal analysis is 300°C or higher. The tensile elastic modulus of the circuit protection layer is 1 GPa or higher and 300 GPa or lower at 25°C, and 10 MPa or higher at 300°C.

A method for manufacturing an insert molded product according to one aspect of the present disclosure includes the steps of placing the heater film for vehicle-mounted parts in a mold, injecting molten resin into the mold, and solidifying the resin.

This disclosure provides a heater film for automotive components that has excellent injection molding resistance, and a method for manufacturing an insert molded product using the same.

1A is a schematic cross-sectional view of a heater film for an in-vehicle part according to one embodiment of the present disclosure, and FIG. 1B is a schematic cross-sectional view of a heater film for an in-vehicle part according to another embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of an insert molded product according to one embodiment of the present disclosure. 3A and 3B are schematic diagrams showing a method for measuring the interfacial adhesion strength between a base material layer and a circuit protection layer in a die shear test. FIG. 4 is a schematic diagram showing a method for evaluating the injection molding resistance of a heater film for an in-vehicle part.

1. Overview The heater film for an in-vehicle component according to this embodiment includes a base layer, a heater circuit, and a circuit protection layer. The heater circuit is laminated on the base layer. The circuit protection layer is laid so as to surround the periphery of the heater circuit. The 5% weight loss temperature of the circuit protection layer in a thermogravimetric differential thermal analysis is 300°C or higher. The tensile elastic modulus of the circuit protection layer is 1 GPa or higher and 300 GPa or lower at 25°C, and 10 MPa or higher at 300°C.

The inventors have found that when a module is manufactured by insert molding by injecting high-temperature and high-pressure resin from a heater film for vehicle-mounted components, which includes a heater circuit and a circuit protection layer laid so as to surround the heater circuit, there is a relationship between the injection molding resistance of the heater film and the heat resistance and tensile modulus of the circuit protection layer, as shown below. That is, by setting the 5% weight loss temperature of the circuit protection layer to 300°C or higher, decomposition of the circuit protection layer due to high-temperature molten resin during injection molding is suppressed. In addition, by setting the tensile modulus of the circuit protection layer at 25°C to 1 GPa or more and 300 GPa or less, the stress applied to the heater circuit 12 in the circuit protection layer 13 can be reduced, thereby suppressing destruction of the heater circuit 12 during injection molding. Furthermore, by setting the tensile modulus of the circuit protection layer 13 at 300°C to 10 MPa or more, deformation of the circuit protection layer 13 due to high-temperature molten resin and exposure of the heater circuit 12 are suppressed. As a result, even when high-temperature and high-pressure resin is injected during insert molding, damage to the heater circuit 12 and circuit protection layer 13 can be suppressed, and it is believed that the heater film can have excellent injection molding resistance.

2. Details <Heater film for automotive parts>
The heater film for vehicle-mounted parts according to the present embodiment (hereinafter, simply referred to as the heater film) is a planar heater used to warm or heat vehicle-mounted parts. The heater film is preferably used as a snow melting heater mounted on a vehicle such as an automobile. The heater film is preferably flexible so that it can be attached to a curved outer surface of the vehicle-mounted part.

The heater film according to this embodiment includes a base layer, a heater circuit, and a circuit protection layer. When the heater circuit is formed from a metal foil such as copper foil, the base layer of the heater film preferably has an adhesive portion 21 that adheres to the metal foil.

The heater film 1 in Fig. 1A includes a base material layer 11, a heater circuit 12, and a circuit protection layer 13. The heater film 1 in Fig. 1B includes a base material layer 11, a heater circuit 12, and a circuit protection layer 13, and the base material layer 11 has an adhesive part 21. In Fig. 1A and Fig. 1B, the heater circuit 12 is shown to have only two parts in the cross-sectional view, but in reality, the cross-sectional shape of the heater circuit 12 is not particularly limited.
Each component will be described below.

[Base layer]
As shown in FIGS. 1A and 1B, the base layer 11 is a member for laminating the heater circuit 12 in the heater film 1.

The shape of the substrate layer 11 is, for example, a film, a sheet, a plate, etc.

The dimensions of the base layer 11 in a plan view are not particularly limited. The thickness of the base layer 11 is appropriately selected depending on the desired flexibility of the heater film 1, and is preferably 1 μm or more and 5000 μm or less. In this case, the flexibility of the heater film 1 can be further improved. The thickness of the base layer 11 is more preferably 10 μm or more and 1000 μm or less, even more preferably 50 μm or more and 800 μm or less, and particularly preferably 100 μm or more and 500 μm or less.

The material of the base layer 11 is, for example, a resin, and preferably a thermoplastic resin. When the base layer 11 is made of a thermoplastic resin, it can be heat-sealed to an object such as a vehicle body. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; polycarbonate, polyamide, polyimide, polyamideimide, polyetherimide, polyethersulfide, polyethersulfone, polyetherketone, polyphenylene ether, polyphenylene sulfide, polyarylate, polysulfone, and liquid crystal polymers. Among these, polycarbonate is preferred from the viewpoints of crack resistance and transparency. The base layer 11 may contain materials other than resin, such as inorganic fillers.

It is preferable to use the same type of resin as the resin injected in the insert molding process described below as the material for the base layer 11. In this case, the strength of the module produced can be further improved.

(Adhesive part)
1B, the adhesive part 21 is a part of the base layer 11, and is a part that can be adhered to the metal foil when the heater circuit 12 is formed from a metal foil such as a copper foil. Since the base layer 11 of the heater film 1 has the adhesive part 21, even when the heater circuit 12 is formed from a metal foil, peeling of the heater circuit 12 from the base layer 11 can be further suppressed, and thus the injection molding resistance of the heater film 1 can be further improved.

A known adhesive can be used to form the adhesive portion 21, and from the viewpoint of ease of application to the substrate, a solvent-based adhesive is preferred, and an adhesive in which a base agent and a curing agent are mixed is preferred. Examples of adhesives include polyester-based adhesives, acrylic-based adhesives, polyamide-based adhesives, polyurethane-based adhesives, olefin-based adhesives, and EVA (ethylene-vinyl acetate copolymer)-based adhesives. Of these, at least one of polyester-based adhesives and acrylic-based adhesives is preferred, and polyester-based adhesives are more preferred, from the viewpoint of superior adhesion to metal.

The adhesive portion 21 is formed, for example, by first mixing the main agent and the curing agent of a solvent-based adhesive, applying it on the surface of the substrate, and drying it to form an adhesive coating. The drying temperature is, for example, 50°C to 200°C, and preferably 100°C to 140°C. The drying time is, for example, 5 seconds to 1 hour, and preferably 10 seconds to 3 minutes. Next, a metal foil such as copper foil is attached to the adhesive coating, and then heated and cured. The heating temperature is, for example, 30°C to 100°C, and preferably 40°C to 60°C. The heating time is, for example, 1 hour to 1000 hours, and preferably 50 hours to 300 hours. Heating may be performed at one temperature, or may be performed by increasing the temperature stepwise at two or more temperatures. Heating and curing forms the adhesive portion 21 to which the metal foil as the heater circuit 12 is adhered.

The dimensions of the adhesive portion 21 in a plan view are usually equal to or smaller than the dimensions of the substrate on which the adhesive portion 21 is formed, and preferably the same dimensions as the substrate. The thickness of the adhesive portion 21 is, for example, 0.1 μm to 100 μm, preferably 1 μm to 60 μm, and more preferably 3 μm to 20 μm.

[Heater circuit]
1A and 1B , the heater circuit 12 is laminated on a base material layer 11. The shape of the heater circuit 12 in a plan view is not particularly limited, and examples thereof include any wiring pattern shape such as a lattice shape, a mesh shape, a fan shape, a spiral shape, a meandering shape, etc.

The material of the heater circuit 12 is not particularly limited as long as it is conductive, but examples include metals such as gold, silver, copper, stainless steel, nickel, and aluminum, and alloys of two or more of these metals. Of these, copper is preferred.

Methods for forming the heater circuit 12 include a method of forming the heater circuit 12 by etching a metal foil, a method of forming the heater circuit 12 by vapor deposition of a metal, and a method of forming the heater circuit 12 by plating a metal. When forming the heater circuit 12 by etching, the heater circuit 12 is formed, for example, by laminating a metal foil such as copper foil onto a film of adhesive applied to a substrate, curing the adhesive to obtain a substrate layer with metal foil, and then removing unnecessary parts of the metal foil from the substrate layer with metal foil by a photoetching method or the like to form the desired wiring pattern.

When the heater circuit 12 has a planar shape, the thickness of the heater circuit 12 is typically 1 μm or more and 100 μm or less, preferably 5 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less.

[Circuit protection layer]
As shown in FIGS. 1A and 1B, the circuit protection layer 13 is laid so as to surround the periphery of the heater circuit 12.

In the heater film 1 according to this embodiment, the 5% weight loss temperature of the circuit protection layer 13 in thermogravimetric differential thermal analysis (TG-DTA) is 300°C or higher. This 5% weight loss temperature is preferably 320°C or higher, more preferably 350°C or higher, and even more preferably 370°C or higher. By setting the 5% weight loss temperature to the above value or higher, it is possible to further suppress the decomposition of the circuit protection layer 13 due to the high-temperature molten resin in injection molding, thereby further improving the injection molding resistance of the heater film 1. The upper limit of this 5% weight loss temperature is not particularly limited, but is preferably less than 500°C and 400°C or lower, for example. The "5% weight loss temperature" is the temperature at which the weight loss of the circuit protection layer material is 5% by mass, measured by a TG-DTA device under conditions of an air atmosphere and a heating rate of 10°C/min.

In the heater film 1 according to this embodiment, the tensile modulus of elasticity of the circuit protection layer 13 is 1 GPa or more and 300 GPa or less at 25°C. In addition, the tensile modulus of elasticity of the circuit protection layer 13 is 10 MPa or more at 300°C.

The tensile modulus of the circuit protection layer 13 at 25°C is preferably 1.1 GPa or more, more preferably 1.2 GPa or more, even more preferably 1.3 GPa or more, and particularly preferably 1.4 GPa or more. The tensile modulus of the circuit protection layer 13 at 25°C is preferably 100 GPa or less, more preferably 30 GPa or less, even more preferably 10 GPa or less, and particularly preferably 2 GPa or less. By setting the tensile modulus of the circuit protection layer 13 at 25°C within the above range, the stress applied to the heater circuit 12 in the circuit protection layer 13 can be further reduced, and the injection molding resistance of the heater film 1 can be further improved.

The tensile modulus of the circuit protection layer 13 at 300°C is preferably 11 MPa or more, more preferably 12 MPa or more, even more preferably 20 MPa or more, and particularly preferably 30 MPa or more. By making the tensile modulus of elasticity at 300°C equal to or more than the above value, deformation of the circuit protection layer 13 and exposure of the heater circuit 12 due to high-temperature molten resin can be further suppressed, thereby further improving the injection molding resistance of the heater film 1. The upper limit of the tensile modulus of elasticity at 300°C is not particularly limited, but 100 MPa is sufficient.

As the material for forming the circuit protection layer 13, any material can be used so long as the 5% weight loss temperature and tensile modulus at 25°C and 300°C of the formed circuit protection layer 13 are within the above ranges. For example, various thermosetting resins can be used, and those containing epoxy resin as the main component are preferable. That is, the circuit protection layer 13 preferably contains a cured product of a composition containing epoxy resin as the main component (hereinafter also referred to as composition (X)). The "main component" refers to the component with the largest mass ratio, for example, 50 mass% or more, preferably 70 mass% or more. By using composition (X) containing epoxy resin as the main component as the material for forming the circuit protection layer 13, the 5% weight loss temperature and tensile modulus at 25°C and 300°C can be adjusted to more appropriate values, and the injection molding resistance of the heater film 1 can be further improved.

Epoxy resins are compounds that have two or more epoxy groups in one molecule. Examples of epoxy resins include bisphenol-type epoxy resins, hydrogenated bisphenol-type epoxy resins, biphenyl-type epoxy resins, naphthalene ring-containing epoxy resins, alicyclic epoxy resins, dicyclopentadiene-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, triphenylmethane-type epoxy resins, aliphatic epoxy resins, triglycidyl isocyanurate, glycidyl group-containing silicone resins, and glycidylamine-type epoxy resins.

The proportion of the epoxy resin in composition (X) is, for example, 50% by mass or more and 100% by mass or less, preferably 60% by mass or more and 95% by mass or less, and more preferably 65% by mass or more and 90% by mass or less.

Composition (X) usually contains a curing agent for the epoxy resin, a curing accelerator, etc. Examples of the curing agent include phenolic curing agents, acid anhydrides, amines, imidazoles, hydrazides, polymercaptans, Lewis acid-amine complexes, etc. The equivalent of the curing agent relative to 1 equivalent of the epoxy resin is, for example, 0.6 to 1.4. The ratio of the curing agent to composition (X) is, for example, 1 to 50% by mass, preferably 5 to 40% by mass, and more preferably 10 to 35% by mass.

Examples of the curing accelerator include imidazoles such as 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, and 2-ethyl-4-methylimidazole; cycloamidines such as 1,8-diazabicyclo[5.4.0]undecene-7, 1,5-diazabicyclo[4.3.0]nonene-5, and 5,6-dibutylamino-1,8-diazabicyclo[5.4.0]undecene-7; tertiary amines such as 2-(dimethylaminomethyl)phenol, triethylenediamine, benzyldimethylamine, triethanolamine, dimethylaminoethanol, and tris(dimethylaminomethyl)phenol; tributylphosphine, methyldiphenylphosphine, and the like. Examples of the curing accelerator include organic phosphines such as phenylphosphine, triphenylphosphine, tris(4-methylphenyl)phosphine, diphenylphosphine, an addition reaction product of triphenylphosphine and parabenzoquinone, and phenylphosphine; tetra-substituted phosphonium and tetra-substituted borates such as tetraphenylphosphonium tetraphenylborate, tetraphenylphosphonium ethyltriphenylborate, and tetrabutylphosphonium tetrabutylborate; quaternary phosphonium salts having a counter anion other than borate; and tetraphenylboron salts such as 2-ethyl-4-methylimidazole tetraphenylborate and N-methylmorpholine tetraphenylborate. The ratio of the curing accelerator to the composition (X) is, for example, 0.1% by mass or more and 2% by mass or less.

Commercially available examples of composition (X) include CV5340E manufactured by Panasonic Corporation and TB2082C manufactured by ThreeBond Co., Ltd.

The dimensions of the circuit protection layer 13 in a plan view are not particularly limited as long as they are large enough to surround the heater circuit 12. The thickness of the circuit protection layer 13 is not particularly limited as long as it is larger than the thickness of the heater circuit 12. The thickness of the circuit protection layer 13 is, for example, 1.1 times or more, and preferably 1.2 times or more, the thickness of the heater circuit 12. The thickness of the circuit protection layer 13 is, for example, 5 μm or more larger, and preferably 10 μm or more larger than the thickness of the heater circuit 12. The thickness of the circuit protection layer 13 is, for example, 10 μm or more and 1000 μm or less, preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 200 μm or less.

The interfacial adhesion strength between the base material layer 11 and the circuit protection layer 13 in a die shear test is preferably 1 MPa or more at the mold temperature in insert molding. In this case, the injection molding resistance in insert molding can be further improved. The mold temperature in insert molding is usually 80°C or more and 150°C or less.

The interfacial adhesion strength between the base material layer 11 and the circuit protection layer 13 in a die shear test is preferably 1 MPa or more at 120°C. When the interfacial adhesion strength at 120°C, which is a typical mold temperature in insert molding, is equal to or greater than the above value, the injection molding resistance of the heater film 1 can be further improved. The interfacial adhesion strength at 120°C is more preferably 1.1 MPa or more, and even more preferably 1.2 MPa or more. There is no particular upper limit to the interfacial adhesion strength at 120°C, but 3 MPa is sufficient.

The method for measuring the interfacial adhesion strength between the substrate layer 11 and the circuit protection layer 13 in a die shear test will be described in the Examples section below. When the substrate layer 11 has an adhesive portion 21, the interfacial adhesion strength between the substrate layer 11 and the circuit protection layer 13 means the interfacial adhesion strength between the adhesive portion 21 and the circuit protection layer 13.

It is preferable that both the base layer 11 and the circuit protection layer 13 in the heater film 1 have transparency. In this case, it becomes possible to visually confirm the heater circuit 12 in the heater film 1.

The circuit protection layer 13 can be formed, for example, by applying a material for forming the circuit protection layer 13 onto the base material layer 11 on which the heater circuit 12 is laminated, and then curing the material.

<Insert molding>
The insert molded product according to this embodiment includes the above-mentioned heater film for vehicle-mounted parts and a resin formed by insert molding and bonded to the heater film for vehicle-mounted parts. Since the insert molded product according to this embodiment is manufactured using the above-mentioned heater film 1 having excellent injection molding resistance, the heater circuit in the insert molded product is prevented from being broken and maintains its shape. Therefore, the insert molded product according to this embodiment can exhibit excellent heater performance.

Figure 2 shows a cross-sectional view of an example of an insert molded product of this embodiment. The insert molded product 2 includes the heater film 1 shown in Figure 1B and resin 31. The resin 31 is formed by insert molding and is bonded to the heater film 1.

The shape of the insert molded product 2 may be, for example, a film, a sheet, or a plate.

The dimensions of the insert molded product 2 in a plan view are not particularly limited. The thickness of the insert molded product 2 is, for example, 10 μm to 100 mm, preferably 100 μm to 10 mm, and more preferably 1 mm to 5 mm. By setting the thickness in this range, the flexibility, etc. of the insert molded product 2 can be further improved.

It is preferable that the base layer 11, the circuit protection layer 13, and the resin 31 in the insert molded product 2 are all transparent. In this case, it becomes possible to visually confirm the heater circuit 12 in the insert molded product 2.

<Method of manufacturing insert molding>
The insert molded product 2 can be manufactured by a known method. For example, the insert molded product 2 can be simply and reliably manufactured by a manufacturing method including a step of placing the heater film 1 in a mold (step 1), a step of injecting molten resin into the mold (step 2), and a step of solidifying the molten resin (step 3).

In step 1, the heater film 1 is placed in the mold. In step 1, the heater film 1 is placed, for example, on one wall inside the mold with the surface of the base layer 11 opposite the heater circuit 12 attached.

In step 2, the molten resin is injected into the mold. As the resin, a thermoplastic resin is usually used. As the resin, it is preferable to use the same material as the base material layer 11. In this case, the strength of the insert molded product 2 can be further improved. As the resin, polycarbonate is preferable from the viewpoint of crack resistance and transparency. The mold temperature in step 2 is, for example, 80°C or more and 150°C or less, and preferably 100°C or more and 140°C or less. The temperature of the molten resin is, for example, 200°C or more and 400°C or less, and preferably 250°C or more and 350°C or less. The holding pressure in step 2 is, for example, 10 Pa or more and 100 Pa or less, and preferably 20 Pa or more and 60 Pa or less. The injection speed in step 2 is, for example, 10 mm/s or more and 200 mm/s or less, and preferably 50 mm/s or more and 150 mm/s.

In step 3, the molten resin is solidified. Step 3 can be performed, for example, by gradually lowering the mold temperature. This allows an insert molded product 2 including a heater film 1 to be obtained.

The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples.

<Preparation of heater film>
[Preparation of circuit-equipped substrate]
A transparent polycarbonate film having a thickness of 300 μm was used as the substrate.
The solvent-based adhesive to be applied to the surface of the substrate was prepared by mixing the base material "Dynaleo VA-3020" (manufactured by Toyo Ink Mfg. Co., Ltd.) and the curing agent "Dynaleo HD-701" (manufactured by Toyo Ink Mfg. Co., Ltd.) in a base material/curing agent (mass ratio) of 100/7. This solvent-based adhesive was then applied to the surface of the substrate in an amount of 3 g/ ^m2 and dried at 120°C for 1 minute to provide a transparent adhesive film with a thickness of 12 μm.
Next, a copper foil was attached to the surface of the formed adhesive film, and then the adhesive was cured by heating at 40° C. for 48 hours and at 60° C. for 96 hours to obtain a base layer with a copper foil. A copper foil with a thickness of 35 μm was used as the copper foil.
An unnecessary portion of the copper foil was removed from the base layer with the copper foil by photoetching, and an arbitrary wiring pattern was provided on the base layer, thereby producing a base layer with a heater circuit.

[Formation of Circuit Protection Layer]
The following materials were used for the circuit protection layer.
Example 1: Panasonic CV5340E
Example 2: TB2082C manufactured by ThreeBond Co., Ltd.
Comparative Example 1: TB3732 manufactured by ThreeBond Co., Ltd.
Comparative Example 2: LQM014 manufactured by Henkel
Comparative Example 3: Stretchable film manufactured by Panasonic Comparative Example 4: CV5390 manufactured by Panasonic

Two sheets of heat-resistant polyimide tape (7413D manufactured by 3M) were placed on the portion of the substrate layer with heater circuit where no circuit was formed, and attached to the edge of the substrate layer with heater circuit to form a frame with a thickness of 135 μm. Next, various circuit protection layer materials were placed on the substrate layer with heater circuit, and an aluminum rod with a diameter of 3 mm was placed so that both ends of the rod were hanging on the polyimide tape to which it was attached, and the aluminum rod was moved along the surface of the polyimide tape to spread the circuit protection layer material on the substrate layer with heater circuit, and a heater film with a circuit protection layer was formed by passing it through the specified curing conditions.

<Evaluation>
[5% weight loss temperature]
The circuit protection layer material was applied onto a release film, cured under a specified condition, and then the release film was peeled off to obtain a bulk film of the circuit protection layer material. A specified weight was cut out from the bulk film of the circuit protection layer material, and the temperature at which the weight loss of the circuit protection layer material was 5% was measured using a TG/DTA6300 manufactured by Seiko Instruments Inc. The measurement was performed under the conditions of an air atmosphere (flow rate 200 mL/min) and a heating rate of 10°C/min.

[Tensile modulus]
The circuit protection layer material was applied onto a release film, cured under a predetermined condition, and then the release film was peeled off to obtain a bulk film of the circuit protection layer material. The obtained bulk film of the circuit protection layer material was cut into a width of 5 mm, and the tensile modulus was measured at 25°C and 300°C using a dynamic viscoelasticity measuring device (DMS6100 manufactured by Seiko Instruments Inc.). At this time, the measurement was performed in a tensile mode with a frequency of 10 Hz and a temperature rise rate of 10°C/min from room temperature to 300°C.

[Interface adhesion strength]
As shown in FIG. 3A, a copper foil-attached substrate having a size of 15×15 mm is etched to form an adhesive-attached substrate 42, and a film 43 using various circuit protection layer materials is formed on the adhesive-attached substrate 42. An aluminum rivet 44 is attached to the surface of the adhesive-attached substrate 42 via the circuit protection layer material 43, and the substrate 42 is cured for a predetermined time to produce a test piece 41. Using the prepared test piece 41, a die shear test was performed using a bond tester (4000 model manufactured by Dega Co., Ltd.) as shown in FIG. 3B to measure the interfacial adhesion strength between the adhesive portion (substrate layer) and the circuit protection layer. The bottom surface of the aluminum rivet 44 is a circle with a diameter of 6 mm. The width of the tool A used in the measurement was 9 mm, the height of the tool A (the distance between the adhesive-attached substrate 42 and the bottom end of the tool A) was 100 μm, and the speed of the tool A was 100 μm/sec. The stage on which the test piece 41 was placed was heated to 120° C. to perform the measurement.

[Injection molding resistance]
First, a heater film having a circuit protection layer was produced by an injection molding machine (Si-80 manufactured by Toyo Machinery & Metals Co., Ltd.). The heater film having the produced circuit protection layer was cut into a size of 30 mm x 30 mm and attached to a position directly under the gate of the mold. The production conditions of the test piece for evaluating the injection molding resistance were as follows: resin used: polycarbonate (Iupilon S-3000 manufactured by Mitsubishi Engineering Plastics Corporation), resin temperature 320 ° C., mold temperature 80 ° C., injection speed 80 mm / s, holding pressure 40 Pa, and gate width 7 mm. In this way, as shown in FIG. 4, a 100 mm square, 2 mm thick flat test piece 51 including a heater film 52 having a circuit protection layer was produced.
For the obtained test piece 51, the area of portion B adjacent to portion 53 corresponding to the gate and where the circuit protection layer was destroyed by the resin injected from the gate was calculated by overlaying a grid of 1 mm squares on the test piece.

The injection molding resistance was evaluated according to the following criteria based on the area of the portion B where the circuit protection layer was destroyed.
◎: 10mm ² or less 〇: 88mm ² or less ×: 88mm more than ²

The results in Table 1 show that the heater film of the embodiment has excellent injection molding resistance because the 5% weight loss temperature of the circuit protection layer and the tensile modulus at 25°C and 300°C are within a specific range. The heater film of the comparative example also shows that the injection molding resistance is poor because at least one of the 5% weight loss temperature of the circuit protection layer and the tensile modulus at 25°C and 300°C is outside the specific range.

Reference Signs List 1 Heater film for vehicle-mounted parts 2 Insert molding 11 Base material layer 12 Heater circuit 13 Circuit protection layer 21 Adhesive part

Claims (4)

A heater film for vehicle-mounted parts used in the manufacture of insert molded products by injection molding,
A base layer;
A heater circuit laminated on the base layer;
a circuit protection layer disposed so as to surround the heater circuit,
the circuit protection layer is in direct contact with the heater circuit,
The heater film for automotive parts, wherein the 5% weight loss temperature in a thermogravimetric differential thermal analysis of the circuit protection layer is 300°C or more and less than 500°C , and the tensile modulus of the circuit protection layer is 1 GPa or more and 300 GPa or less at 25°C and 10 MPa or more and 100 MPa or less at 300°C. The heater film for vehicle-mounted parts according to claim 1 , wherein the circuit protection layer comprises a cured product of a composition containing an epoxy resin as a main component. 3. The heater film for an in-vehicle part according to claim 1, wherein an interfacial adhesion strength between the substrate layer and the circuit protection layer in a die shear test is 1 MPa or more at 120°C. A step of placing the heater film for an in-vehicle part according to any one of claims 1 to 3 in a mold;
injecting molten resin into the mold;
solidifying the molten resin;
A method for manufacturing an insert molding comprising:

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