Laminate and method for manufacturing the same

Abstract

To provide a laminate of a metal substrate and a polyimide layer having excellent thermal uniformity and thermal conductivity in the surface direction, balanced with characteristics such as toughness and flexibility.SOLUTION: A laminate has a metal substrate made of metal foil and a polyimide layer containing inorganic insulation particles laminated on at least one surface of the metal substrate. The metal foil has a volume resistivity of 10 μΩ cm or more. The polyimide layer containing inorganic insulation particles has a thickness of 3-70 μm, a tear propagation resistance of 7 mN or more, and an edge tear resistance of 0.3 N / 20 mm or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a laminate having a metal substrate made of metal foil and an inorganic insulating particle-containing polyimide layer laminated on at least one surface of the metal substrate, and more particularly to a laminate suitable as a flexible planar heating element and a method for manufacturing the same. [Background technology]

[0002] Polyimide is a heat-resistant resin obtained by ring-closing polyamic acid, which is synthesized from tetracarboxylic anhydride and diamine as raw materials through a condensation reaction. Due to the rigidity of its molecular chains, resonance stabilization, and strong chemical bonding, it has excellent resistance to thermal decomposition, high durability against chemical changes such as oxidation or hydrolysis, and excellent flexibility, mechanical properties, and electrical properties. Polyimide is widely used as the insulating resin layer in flexible printed circuit boards (FPCs) commonly used in electronic devices.

[0003] Due to these properties of polyimide, polyimide resin has conventionally been suitably used as a material for constituting planar heating elements such as flexible heaters. For example, laminates have been proposed in which layers (films) of polyimide with or without fillers are formed on metal foils such as stainless steel foil or copper foil (for example, Patent Documents 1 to 7). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-26185 [Patent Document 2] Japanese Patent Publication No. 2015-79202 [Patent Document 3] Japanese Patent Publication No. 2012-134132 [Patent Document 4] Patent No. 5023667 [Patent Document 5] Patent No. 4536335 [Patent Document 6] Japanese Patent Publication No. 2021-30523 [Patent Document 7] Japanese Patent Publication No. 2008-224056 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] As described above, planar heating elements with polyimide layers (films) have been known for some time. However, planar heating elements are used not only for heating pipes, tubes, and irregularly shaped objects, but also as heating elements in fuel cells and for heat fixing of toner in copiers and laser printers, and therefore have many applications that require heat resistance, with many requiring heat resistance exceeding 200°C. Attempts have been made to improve the thermal conductivity in the thickness direction of the layer of heat-resistant resin such as polyimide by methods such as incorporating fillers or thinning the film. However, after diligent research by the inventors of this application, they found that, firstly, in methods of improving heat conduction by adding fillers, the relative content of the resin component decreases as the amount of filler increases, which may reduce the properties of the polyimide layer (film), such as toughness and flexibility. Secondly, they found that in conventional planar heating elements, there is a strong tendency for the temperature to drop rapidly along the planar direction from the heating element (metal foil, electrical resistance heating element), and that the uniformity of heat in the planar direction is significantly reduced. This suggests that uniformity of heat in the planar direction (thermal conductivity) is actually important.

[0006] In addition, in such planar heating elements, there is a requirement to make the wiring of the heating element as small (thin) as possible in order to improve the efficiency of power usage and heat generation. It is advantageous to ensure thermal uniformity while maintaining this design.

[0007] Therefore, in conventional planar heating elements using polyimide, there is generally room for improvement in terms of heat resistance, flexibility, and uniformity of in-plane temperature, given that these are important for applications requiring conformability to complex shapes and precise heating. In particular, there is a need to improve thermal uniformity in the planar direction while maintaining toughness and flexibility.

[0008] The present invention was made based on the above-mentioned findings, and its objective is to provide a laminate of a metal substrate and a polyimide layer that is excellent in thermal uniformity (especially thermal uniformity in the planar direction and thermal conductivity), as well as excellent in properties such as toughness and flexibility, and furthermore, has good efficiency in power consumption and heat generation, and in particular, to provide a laminate that is suitable for use in flexible planar heating elements. Furthermore, another object of the present invention is to provide a method for manufacturing such a laminate. [Means for solving the problem]

[0009] In other words, the present invention is as follows: [1] A laminate comprising a metal substrate made of metal foil and an inorganic insulating particle-containing polyimide layer laminated on at least one surface of the metal substrate, The aforementioned metal foil has a volume resistivity of 10 μΩ·cm or more. The laminate is characterized in that the inorganic insulating particle-containing polyimide layer has a thickness of 3 to 70 μm, a tear propagation resistance of 7 mN or more, and an edge tear resistance of 0.3 N / 20 mm or more. [2] The inorganic insulating particle-containing polyimide layer has a thermal conductivity in the planar direction (λ xy The laminate according to [1], characterized in that the ) is 0.5 to 7.0 W / m·K. [3] The laminate according to [1] or [2], characterized in that the inorganic insulating particle-containing polyimide layer has an inorganic insulating particle content of 10 to 60 volume%. [4] The laminate according to any one of [1] to [3], characterized in that the inorganic insulating particles have an average particle diameter of 0.6 to 15 μm. [5] The inorganic insulating particles are one or more selected from the group consisting of aluminum oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, quartz, and magnesium oxide, and the laminate according to any one of [1] to [4]. [6] The laminate according to any one of [1] to [5], which is used as a flexible planar heating element. [7] A method for manufacturing the laminate according to any one of [1] to [6], A step of applying a precursor solution of polyimide containing inorganic insulating particles to the surface of a metal substrate that is a metal foil, After drying the precursor solution of the polyimide, it is cured under heating conditions where the temperature of 100 to 150 °C has an integrated time of 3 to 15 minutes and the temperature of 320 to 380 °C has an integrated time of 5 minutes or more, to form a polyimide layer having a thickness of 3 to 70 μm, a tear propagation resistance of 7 mN or more, and an end crack resistance of 0.3 N / 20 mm or more. A method for manufacturing a laminate, characterized by having. [Advantages of the Invention]

[0010] According to the present invention, a laminate of a metal substrate and a polyimide layer is obtained, which is particularly excellent in the thermal uniformity and thermal conductivity in the plane direction, and also has both properties such as toughness and flexibility. Such a laminate has good power usage and heat generation efficiency, and as a flexible planar heating element, for example, it is suitable not only for heating pipes, pipes, and irregularly shaped objects, but also for heating heaters for fuel cells, heating parts for heat fixing of toner in copiers and laser printers, etc. [Brief Description of the Drawings]

[0011] [Figure 1] FIG. 1 illustrates an outline of a wiring pattern in the evaluation (temperature evaluation, uniformity evaluation) of an example. [Figure 2] FIG. 2 is a diagram showing the measurement results by thermography of the laminate of Example 1. [Figure 3] FIG. 3 is a diagram showing the measurement results by thermography of the laminate of Example 2. [Figure 4]Figure 4 shows the thermographic measurement results of the laminate of Example 3. [Figure 5] Figure 5 shows the thermographic measurement results of the laminate of Comparative Example 1. [Figure 6] Figure 6 shows the thermographic measurement results of the laminate of Comparative Example 2. [Figure 7] Figure 7 shows the thermographic measurement results of the laminate of Comparative Example 5. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below.

[0013] <Laminate> The laminate of the present invention comprises a metal substrate made of metal foil and an inorganic insulating particle-containing polyimide layer laminated on at least one side of the metal substrate. The polyimide layer may be on one side of the metal substrate, or on both sides of the metal substrate. If the inorganic insulating particle-containing polyimide layer is on only one side, the opposite side of the metal substrate may not have anything laminated on it, depending on the application and purpose, or it may have a layer made of a material with good heat insulation properties to prevent heat from escaping from the metal substrate. Furthermore, the inorganic insulating particle-containing polyimide layer on one side may be formed of two or more layers, and it is not excluded to include layers made only of other polyimides that are not directly laminated on the metal substrate, or layers other than polyimide layers. Depending on the application, a resin layer such as silicone or epoxy may be included, but is not limited to these.

[0014] <Metal substrate> The metal substrate, made of metal foil, can generate heat through resistive heating when an electric current is passed through it. However, it must have high resistance per unit length, and from the viewpoint of ease of adjusting heating output and current flow, a metal foil with a volume resistivity of 10 μΩ·cm or more is used. It may also be an alloy. Preferably, the volume resistivity is 30 μΩ·cm or more, and more preferably 50 μΩ·cm or more. There is no particular upper limit, but while a higher volume resistivity increases heat generation, a higher resistivity also means that the required power increases depending on the length of the wiring, so it is preferable that the volume resistivity is 200 μΩ·cm or less. The volume resistivity value preferably satisfies the above at a temperature of 25°C.

[0015] Examples of metals having such volume resistivity include, but are not limited to, stainless steel alloys, iron-nickel alloys, nickel-chromium alloys, iron-chromium-aluminum alloys, and composites thereof. Among these, stainless steel alloys and iron-chromium-aluminum alloys are preferred, and stainless steel alloys are more preferred, for reasons of mechanical strength, heat resistance, and workability. As for stainless steel alloys, foils of any stainless steel alloy such as austenitic, austenitic-ferritic, ferritic, martensitic, or composites thereof can be used. Among these, SUS304 and iron-chromium-aluminum alloys are preferred, for reasons of mechanical strength, heat resistance, workability, heat generation, and cost.

[0016] The thickness of the metal foil (metal substrate) is not particularly limited, but from the viewpoint of flexibility and processability, it is preferably 10 to 100 μm, and more preferably 10 to 50 μm.

[0017] The shape of the metal foil (metal substrate) can be appropriately adopted depending on the application of the laminate, and may be in the form of a sheet, wire, string, tape, etc. It may also be processed by known methods, for example, it may be processed into a precise pattern by etching, as long as it does not impair the purpose of the present invention. Surface treatment may also be performed by known methods.

[0018] <Polyimide layer containing inorganic insulating particles> The inorganic insulating particle-containing polyimide layer of the present invention is formed by mixing and incorporating inorganic insulating particles as a thermally conductive filler within a layer made of polyimide resin.

[0019] The inorganic insulating particle-containing polyimide layer primarily serves to insulate the metal substrate, which acts as a heating element, and to provide uniform temperature distribution within the surface. Preferably, for use in planar heating elements, it is desirable that the layer has good conductivity for heat generated from the metal substrate, and therefore high thermal conductivity is preferred. Furthermore, to enable use in flexible planar heating elements, it is preferable that the layer has good flexibility and toughness.

[0020] Therefore, the polyimide layer containing inorganic insulating particles must have a high tear propagation resistance of 7 mN or more. Preferably, it should be 8 mN or more, and more preferably 10 mN or more. The upper limit is not particularly limited. Within this range, problems such as tearing during processing and use can be prevented.

[0021] Furthermore, the polyimide layer containing inorganic insulating particles has high edge tear resistance, and it is necessary that the edge tear resistance be 0.3 N / 20 mm or higher, based on a width of 20 mm in accordance with JIS standards. Preferably, it should be 0.4 N / 20 mm or higher, and more preferably 0.5 N / 20 mm or higher. There is no particular upper limit. Within this range, it is possible to prevent problems such as tearing during processing and use.

[0022] Furthermore, the inorganic insulating particle-containing polyimide layer needs to have a thickness in the range of 3 to 70 μm in order to provide thermal conductivity, toughness, flexibility, processability, and support for the film itself, and to satisfy the aforementioned tear propagation resistance and edge tear resistance. The thickness can be appropriately selected depending on the application, but it is preferably 10 to 30 μm. Here, the thickness of the inorganic insulating particle-containing polyimide layer refers to the thickness on one side of the metal substrate, and if the inorganic insulating particle-containing polyimide layer on one side of the metal substrate consists of multiple layers, it refers to the total thickness of the multiple layers.

[0023] Furthermore, the polyimide layer containing inorganic insulating particles has a thermal conductivity in the planar direction (λ xy The thermal conductivity λ is preferably 0.5 to 7.0 W / m·K. More preferably 0.8 to 5.0 W / m·K. xy By setting the thermal conductivity to be above the aforementioned lower limit, the thermal uniformity in the planar direction of the inorganic insulating particle-containing polyimide layer can be improved. As mentioned above, while thermal conductivity in the thickness direction has been studied conventionally, according to the findings of the inventors of this application, it is preferable to consider thermal conductivity in the planar direction for a planar heating element, as this is thought to improve the thermal uniformity of the planar heating element. Thermal conductivity λ xy Regarding the upper limit, a larger value is considered preferable for thermal conductivity and uniformity. However, conversely, excessive heat transfer (escape) to the inorganic insulating particle-containing polyimide layer is thought to delay the temperature rise on the metal substrate side and cause excessive current. Therefore, it is preferable to set it to the aforementioned upper limit. Thermal conductivity λ in the plane direction xy This can be appropriately adjusted by factors such as the type and content of inorganic insulating particles, the layer thickness, and the composition of the polyimide (for example, by selecting one with high thermal conductivity).

[0024] Here, the inorganic insulating particles are thermally conductive fillers and are not particularly limited as long as they have high thermal conductivity and are generally considered to be electrically conductive, but their volume resistivity must be 1.0 × 10⁻⁶. 6 A resistivity of Ω·cm or greater is preferably used. More preferably, a volume resistivity of 1.0 × 10⁻⁶ is used.10 Ω·cm or greater, more preferably 1.0 × 10 14 The resistivity must be greater than or equal to Ω·cm. There is no particular upper limit to the volume resistivity. Examples of such inorganic insulating particles include aluminum oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, quartz, magnesium oxide, etc., and mixtures thereof may also be used. The shape is not limited to spherical, powdery, fibrous, needle-shaped, or flaky.

[0025] From the viewpoint of thermal conductivity, compatibility with polyimide, coating properties, and processability, the inorganic insulating particles preferably have an average particle diameter of 0.6 to 15 μm, and more preferably 1.0 to 15 μm. Here, the average particle diameter can be determined from the value at which the cumulative value from the small particle side in the frequency distribution curve obtained by volume-based particle size distribution measurement using laser diffraction becomes 50%.

[0026] Regarding the inorganic insulating particle content in the inorganic insulating particle-containing polyimide layer, it is preferable that the inorganic insulating particle content be 10 to 60 volume%. While a higher inorganic insulating particle content is preferable to improve thermal conductivity, there is a resistance to a decrease in toughness and flexibility due to the relative decrease in the polyimide resin content, so the above range is preferable. More preferably, the inorganic insulating particle content is 20 to 50 volume%.

[0027] The polyimide resin (polyimide layer) used is not particularly limited, and commercially available polyimide films containing inorganic insulating particles, such as Kapton MT type (product name) manufactured by Toray DuPont, can be used as is. For example, [1] a resin film formed by coating a metal substrate, which is the support substrate, with a solution of polyamic acid containing inorganic insulating particles, drying it, and then imidizing it (hereinafter referred to as the casting method), or [2] a resin film formed by coating a metal substrate, which is the support substrate, with a solution of polyamic acid containing inorganic insulating particles, drying it, peeling the polyamic acid gel film from the support substrate, and then imidizing it. In the case of multiple layers, for example, [3] a method in which a solution of polyamic acid containing inorganic insulating particles is repeatedly coated and dried onto a metal substrate, which is the support substrate, and then imidizing it (hereinafter referred to as the sequential coating method), or [4] a method in which a laminated structure of polyamic acid containing inorganic insulating particles is simultaneously coated and dried onto a metal substrate, which is the support substrate, by multilayer extrusion, and then imidizing it (hereinafter referred to as the multilayer extrusion method). Alternatively, the film may be formed by heat-pressing it together with or without the use of an adhesive. From the viewpoint of dimensional stability and adhesion to the metal substrate, products formed by the casting method or sequential coating method are preferred.

[0028] Furthermore, the inorganic insulating particle-containing polyimide layer preferably has a glass transition temperature (Tg) of 200°C or higher and a coefficient of linear expansion (CTE) of 0 to 40 ppm / K as its heat resistance properties.

[0029] <Polyimide composition, method for manufacturing laminates> The composition of the polyimide used in the inorganic insulating particle-containing polyimide layer in the present invention is not particularly limited, and known components can be used.

[0030] As is well known, polyimides are obtained by imidizing polyamic acids. Polyamic acids are composed of tetravalent tetracarboxylic acid residues derived from tetracarboxylic dianhydride components and divalent diamine residues derived from diamine components. When these components are linked together and considered as a single repeating unit, polyimides are composed of polymers of these repeating units. Except for containing inorganic insulating particles, both polyamic acids and polyimides can basically be produced using known methods.

[0031] For example, polyimide acids are typically produced by dissolving a predetermined tetracarboxylic dianhydride component and a diamine component in an organic solvent in nearly equimolar amounts, and then polymerizing the mixture by stirring at a temperature typically in the range of 0 to 100°C for 30 minutes to 24 hours to obtain polyamic acid, which is a precursor of polyimide. In the reaction, the reactants are dissolved in the organic solvent so that the resulting precursor is in the range of 5 to 30% by weight, preferably 10 to 20% by weight. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide, N,N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and γ-ptylolactone. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used in combination.

[0032] In the present invention, it is preferable to mix the polyamic acid with the inorganic insulating particles to obtain an inorganic insulating particle-containing polyamic acid. In this case, as described above, it is preferable that the inorganic insulating particles are prepared to be present in an amount of 10 to 60% by volume when formed as an inorganic insulating particle-containing polyimide layer.

[0033] In the synthesis of polyimide acids and polyimides, only one tetracarboxylic dianhydride component and one diamine component may be used, or two or more may be used in combination. By selecting the types of tetracarboxylic dianhydride and diamine components, and the molar ratio of each component when two or more acid anhydrides or diamines are used, physical properties such as thermal conductivity, thermal expansion, adhesion, and glass transition temperature can be controlled.

[0034] Here, any known diamine component used in the production of polyimide acids and polyimides can be used without limitation, but aromatic diamine compounds are preferred. Alicyclic diamine compounds may also be used. For example, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis(4-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)benzophenone (BABP), 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB), 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis[4-(3-aminophenoxy Examples include bis(4-(4-aminophenoxy)phenyl) sulfone, bis[4-(4-aminophenoxy)phenyl] sulfone, 3,7-diamino-2,8-dimethylbenzothiophenesulfone, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 2,2'-difluoro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether (4,4'-DAPE), 3,3-diaminodiphenyl ether, bis(p-β-amino-t-butylphenyl) ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), or 1,4-bis(4-aminophenoxy)benzene.More preferably, 4,4'-diaminodiphenyl ether (4,4'-DAPE), 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), or 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,6-dimethyl-m-phenylenediamine, 2,5- Dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-p-terphenyl, 3,3'-diamino-p-terphenyl, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino- Examples include t-butyltoluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diaminobenzanilide, 5-amino-2-(4-aminophenyl)benzimidazole, and 5-amino-2-(4-aminophenyl)benzoxazole.

[0035] Furthermore, the tetracarboxylic dianhydride component can be any known component used in the production of polyimide acids and polyimides without limitation, but aromatic tetracarboxylic dianhydrides are preferred. Alternatively, alicyclic tetracarboxylic dianhydrides may be used, such as alicyclic tetracarboxylic dianhydrides including 1,2,3,4-cyclobutanetetracarboxylic dianhydride, fluorenylidenebisphthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and cyclopentanonebisspironorbornanetetracarboxylic dianhydride. Examples of aromatic tetracarboxylic dianhydrides include 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-(paraphenylenedicarbonyl)diphthalic anhydride, 4,4'-(metaphenylenedicarbonyl)diphthalic anhydride, pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), p-phenylenebis(trimellitate anhydride), 4,4'-oxydiphthalic dianhydride (ODPA), bis(2,3-dicarboxyphenyl) ether dianhydride, 5,5'-bis( Trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}diphenyl ether dianhydride, bis{3,5-di(trifluoromethyl)phenoxy}pyromellitic acid dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}, bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride, 2,2-bis{(4-(3,4-Dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}bis(trifluoromethyl)biphenyl dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, naphthalene-2,3,6,7-tetracarboxylic acid dianhydride, naphthalene-1,2,5,6-tetracarboxylic acid dianhydride , naphthalene-1,2,6,7-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,2',3,3'-biphenyl Tracarboxylic acid dianhydride, 2,3,3',4'-biphenyltetracarboxylic acid dianhydride, 3,3'',4,4''-p-terphenyltetracarboxylic acid dianhydride, 2,2'',3,3''-p-terphenyltetracarboxylic acid dianhydride, 2,3,3'',4''-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane Dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 2,2',3,3'-diphenylsulfonetetracarboxylic acid dianhydride, 2,3,3',4'-diphenylsulfonetetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, perylene-2,3,8,9-tetracarboxylic acid dianhydride, perylene-3,4,9,10-tetracarboxylic acid dianhydride, perylene-4,5,10,11-tetracarboxylic dianhydride, perylene-5,6,11,12-tetracarboxylic dianhydride, phenanthrene-1,2,7,8-tetracarboxylic dianhydride, phenanthrene-1,2,6,7-tetracarboxylic dianhydride, phenanthrene-1,2,9,10-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, (trifluoromethyl)pyromellitic acid dianhydride, di(trifluoromethyl)pyromellitic acid dianhydride, di(heptafluoropropyl Examples include pyromellitic dianhydride, pentafluoroethylpyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone dianhydride, and trifluoromethylbenzene dianhydride. Among these, pyromellitic dianhydride (PMDA) is more preferable from the viewpoint of improving thermal conductivity in the planar direction.

[0036] Furthermore, while the polyamic acid is not limited, it is preferable to adjust the viscosity to a range of 1,000 to 50,000 cP by adjusting the concentration and Mw. If the viscosity is too high, it can be diluted by adding a solvent.

[0037] The synthesized polyamic acid is usually advantageous to use as a reaction solvent solution, but it can be concentrated, diluted, or replaced with other organic solvents as needed. Furthermore, polyamic acid is advantageous to use because it generally has excellent solvent solubility. The method for imidizing the polyamic acid is not particularly limited; for example, heat treatment such as heating in the aforementioned solvent at a temperature in the range of 80 to 400°C for 1 to 24 hours is preferably employed.

[0038] Specifically, the following steps can be listed. That is, it has a step of applying a solution of polyamic acid (a precursor of polyimide) containing inorganic insulating particles to a metal substrate, and after drying the applied solution, curing it under heating conditions where the temperature of 100 to 150 °C has an integrated time of 3 to 15 minutes and the temperature of 320 to 380 °C has an integrated time of 5 minutes or more.

[0039] The method for applying the polyimide solution (or polyamic acid solution) onto the substrate is not particularly limited. For example, it can be applied using a coater such as a comma coater, die coater, knife coater, lip coater, etc. When forming a multilayer polyimide layer, for example, a method of repeating the above-described operations of application, drying, and heating is preferred.

Examples

[0040] Hereinafter, the content of the present invention will be specifically described based on examples, but the present invention is not limited to the scope of these examples. Note that Example 1 is for reference only.

[0041] The abbreviations used in this example represent the following compounds. BTDA: 3,3’,4,4’-benzophenone tetracarboxylic dianhydride PMDA: pyromellitic dianhydride DAPE: 4,4’-diaminodiphenyl ether BAPP: 2,2-bis [4- (4-aminophenoxy ) phenyl ] propane DMAc: N,N-dimethylacetamide

[0042] Also, for each characteristic evaluated in the examples, the following evaluation methods were followed.

[0043] [Measurement of viscosity] The viscosity of the polyamic acid solution was measured at 25 °C using a cone plate viscometer (manufactured by Tokimec) equipped with a constant temperature water bath. at 25 °C.

[0044] [Measurement of volume average particle diameter D 50 ​ Using a laser particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac-Bell), the volume-average particle size was defined as the value at which the cumulative value in the frequency distribution curve obtained by volume-based particle size distribution measurement reached 50%. For the measurement, alumina was placed in a 0.2 mass% sodium hexametaphosphate aqueous solution and dispersed for 5 minutes at 40W using the ultrasonic device built into the analyzer, resulting in a refractive index of 1.76 for the alumina.

[0045] [Thermal conductivity in the plane (λ xy )] Polyimide resin film was cut to a size of 5 mm x 30 mm, and the thermal diffusivity in the plane direction was measured by optical AC method (Advanced Riko Co., Ltd., product name: Laser PIT device), specific heat by differential scanning calorimetry (DSC) (TA Instruments, product name: DSC25), and density by water displacement method. Based on these results, the thermal conductivity (W / m·K) and specific gravity (g / cm³) were determined. 3 ) × Specific heat (J / g·K) × Thermal diffusivity (mm 2 The calculation was performed using the formula ( / s). The measurement results are shown in Table 3.

[0046] [Tear propagation resistance (TPR)] A 63.5 mm x 50 mm polyimide resin film was used as a test specimen. A 12.7 mm long cut was made in the test specimen, and the tear propagation resistance was measured using a light-load tear tester manufactured by Toyo Seiki Co., Ltd.

[0047] [End tear resistance] In accordance with Method B of JIS C2151 (2019), the edge tear resistance was measured using a polyimide resin film measuring 20 mm wide x 200 mm long as a test specimen, employing a Strograph R1, manufactured by Toyo Seiki Co., Ltd.

[0048] [Workability] In polyimide layer-metal foil laminates, when a 20cm x 30cm metal foil was fully etched with an acid solution (ferric chloride solution at 40°C), samples showing film defects such as cracks or tears in the polyimide film were evaluated as ×, while samples showing a good film without defects were evaluated as ○.

[0049] [Temperature evaluation of planar heaters, evaluation of heater uniformity] The metal foil heating element was set to 200°C, and its surface temperature was measured using an infrared thermograph (NEC Avio) and a thermocouple thermometer (Keyence temperature measurement unit). In particular, the temperature distribution at a distance of 2 mm from the metal foil heating wiring was measured. If the temperature at a distance of 2 mm was 100°C or higher, it was marked as ○; if it was below 100°C, it was marked as × because the uniformity as a heater was poor.

[0050] (Synthesis Example 1) Under a nitrogen atmosphere, DAPE (17.26 g, 0.086 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask while stirring. Then, BTDA (27.73 g, 0.086 mol) was added. The solution was then stirred at room temperature for 3 hours to carry out the polymerization reaction, yielding a pale yellow, viscous polyamic acid solution A with a viscosity of 12000 cP.

[0051] (Synthesis Example 2) Similar to Synthesis Example 1, BAPP (29.23 g, 0.071 mol) was dissolved in 255 g of DMAc solvent in a 500 ml separable flask while stirring under a nitrogen stream. Then, PMDA (15.38 g, 0.071 mol) was added. The solution was then stirred at room temperature for 3 hours to carry out the polymerization reaction, yielding a pale yellow, viscous polyamic acid solution B with a viscosity of 10,000 cP.

[0052] (Combination example 1) 65.0 parts by weight of polyamic acid solution A with a solid content concentration of 15 wt%, and aluminum oxide particles [manufactured by Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle size D] as a thermally conductive filler (inorganic insulating particles; the same applies hereinafter). 50 5.0 parts by weight of [3.4 μm] were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution C containing a thermally conductive filler. The aluminum oxide particle content in the layer obtained by curing this filler-containing polyamic acid solution C was 15 volume% (vol%).

[0053] (Combination example 2) 59.0 parts by weight of a polyamic acid solution A with a solid content concentration of 15 wt%, and aluminum oxide particles [manufactured by Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle size D] as a thermally conductive filler. 50 11.0 parts by weight of [3.4 μm] were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution D containing a thermally conductive filler. The aluminum oxide particle content in the layer obtained by curing this filler-containing polyamic acid solution D is 30 vol%.

[0054] (Combination example 3) 48.7 parts by weight of polyamic acid solution A with a solid content concentration of 15 wt%, and aluminum oxide particles as a thermally conductive filler [Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle size D]. 50 3.4 μm [21.3 parts by weight] was mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution E containing a thermally conductive filler. The aluminum oxide particle content in the layer cured from this filler-containing polyamic acid solution E was 50 vol%.

[0055] (Combination example 4) 1.3 parts by weight of polyamic acid solution A with a solid content of 15 wt% and 8.7 parts by weight of boron nitride particles [manufactured by Showa Denko Corporation, product name: UHP-1, flaky shape, average major diameter 8 μm, particles larger than 25 μm removed by a classifier] as a thermally conductive filler were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution F containing thermally conductive filler. The boron nitride particle content in the layer cured from this filler-containing polyamic acid solution F was 30 vol%.

[0056] (Combination example 5) 59.0 parts by weight of polyamic acid solution B with a solid content concentration of 15 wt%, and aluminum oxide particles [manufactured by Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle size D] as a thermally conductive filler. 5011.0 parts by weight of [3.4 μm] were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution G containing a thermally conductive filler. The content of aluminum oxide particles in the insulating resin layer cured with this filler-containing polyamic acid solution G is 30 vol%.

[0057] (Combination example 6) 1.3 parts by weight of polyamic acid solution B6 with a solid content concentration of 15 wt% and 8.7 parts by weight of boron nitride particles [manufactured by Showa Denko Corporation, product name: UHP-1, flaky shape, average major diameter 8 μm, particles larger than 25 μm removed by a classifier] as a thermally conductive filler were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution H containing thermally conductive filler. The content of boron nitride particles in the insulating resin layer cured from this filler-containing polyamic acid solution H is 30 vol%.

[0058] (Combination example 7) 34.7 parts by weight of polyamic acid solution A with a solid content concentration of 15 wt%, and aluminum oxide particles as a thermally conductive filler [Sumitomo Chemical Co., Ltd., product name: AA-3, spherical, volume average particle size D]. 50 35.3 parts by weight of [3.4 μm] were mixed in a centrifugal stirrer until homogeneous to obtain filler-containing polyamic acid solution I containing a thermally conductive filler. The aluminum oxide particle content in the layer cured from this filler-containing polyamic acid solution I was 70 vol%.

[0059] (Combination example 8) 59.0 parts by weight of a polyamic acid solution A with a solid content concentration of 15 wt%, and aluminum oxide particles [manufactured by Sumitomo Chemical Co., Ltd., product name: AA-04, spherical, volume average particle size D] as a thermally conductive filler. 50 11.0 parts by weight of [0.5 μm] were mixed in a centrifugal stirrer until homogeneous to obtain a filler-containing polyamic acid solution J containing a thermally conductive filler. The aluminum oxide particle content in the layer obtained by curing this filler-containing polyamic acid solution J was 30 vol%.

[0060] [Table 1]

[0061] (Example 1) Polyamic acid solution C obtained in Formulation Example 1 was applied to SUS foil 1 (SUS304 manufactured by Nippon Steel Chemical & Material Co., Ltd., thickness: 30 μm) to a cured thickness of 20.0 μm, and the solvent was removed by heating and drying at 90 to 140°C. Subsequently, a polyimide / SUS foil 1 laminate with a polyimide layer on SUS foil 1 was fabricated by gradually increasing the temperature in the temperature range of 130 to 360°C over 30 minutes. To evaluate the properties of the polyimide layer in the laminate, SUS foil 1 was etched off to fabricate a polyimide resin film M1, and the planar thermal conductivity (λ) was evaluated. xy The following properties were evaluated: tear propagation resistance (TPR), edge tear resistance, and processability. In addition, SUS foil 1 in the laminate was etched for use as a planar heater to create heating wiring. A schematic of the wiring pattern is shown in Figure 1. In Figure 1, the width of each heating wiring section (symbol: 1) is 14.5 mm, and the spacing between wiring sections is 7.25 mm. The parts other than the heating wiring sections (symbol: 2) represent the non-wired sections (polyimide sections). Electricity was passed through the heating wiring to heat the SUS foil wiring sections, and the surface temperature of the planar heater was evaluated using infrared thermography and a thermocouple thermometer. The results are shown in Tables 2-3. The measurement results by thermography are shown in Figure 2.

[0062] (Examples 2 and 3) The type of polyamic acid solution used was changed, and polyimide resin films M2 and M3 were obtained in the same manner as in Example 1 and evaluated in the same manner. The results are shown in Tables 2 and 3. In addition, the thermographic measurement results for Example 2 are shown in Figure 3, and the thermographic measurement results for Example 3 are shown in Figure 4.

[0063] (Example 4) Polyamic acid solution D obtained in Formulation Example 2 was applied to SUS foil 2 (SUS344 manufactured by Nippon Steel Chemical & Material Co., Ltd., thickness: 30 μm) to a cured thickness of 20.0 μm, and the solvent was removed by heating and drying at 90 to 140°C. Subsequently, a polyimide / SUS foil 2 laminate with a polyimide layer on SUS foil 2 was fabricated by gradually increasing the temperature in the temperature range of 130 to 360°C over 30 minutes. To evaluate the properties of the polyimide layer in the laminate, SUS foil 2 was etched off to fabricate a polyimide resin film M4, and the planar thermal conductivity (λ) was evaluated. xy The tear propagation resistance (TPR), edge tear resistance, and processability were evaluated. In addition, SUS foil 2 in the laminate was etched for use as a planar heater, and heating wiring was created. Electricity was passed through the heating wiring to heat the SUS foil wiring, and the surface temperature of the planar heater was evaluated using infrared thermography and a thermocouple thermometer. The results are shown in Tables 2 and 3.

[0064] (Examples 5-7, Comparative Examples 1 and 2) The type of polyamic acid solution used was changed, and polyimide resin films M5 to M9 were obtained and evaluated in the same manner as in Example 1. The results are shown in Tables 2 and 3. The thermographic measurement results for Comparative Example 1 are shown in Figure 5, and the thermographic measurement results for Comparative Example 2 are shown in Figure 6.

[0065] (Comparative Example 3) A polyamic acid solution D obtained in Formulation Example 2 was applied to copper foil 1 (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., product name: CF-T4MDS-HD-35, thickness: 35 μm, Rz = 1.4 μm) so that the thickness after curing was 20.0 μm, and the solvent was removed by heating and drying at 90 to 140°C. Then, a laminate for flexible substrates having a polyimide layer on copper foil 1 was fabricated by gradually increasing the temperature in the temperature range of 130 to 360°C over 30 minutes. To evaluate the properties of the polyimide layer in the laminate for flexible substrates, copper foil 1 was etched off to fabricate a polyimide resin film M10, and the planar thermal conductivity (λ) was evaluated. xyThe following were evaluated: tear propagation resistance (TPR), edge tear resistance, and processability. In addition, copper foil 1 in the laminate was etched for use as a planar heater, and heating wiring was created. Electricity was passed through the heating wiring to heat the copper foil 1 wiring portion, and the surface temperature of the planar heater was evaluated using infrared thermography and a thermocouple thermometer. The results are shown in Tables 2 and 3.

[0066] (Comparative Examples 4 and 5) Films M11 and M12 were obtained and evaluated in the same manner as in Example 1 by changing the type of polyamic acid solution used and the polyimide thickness. The results are shown in Tables 2 and 3. The thermographic measurement results for Comparative Example 5 are shown in Figure 7.

[0067] [Table 2]

[0068] The results above are summarized in Table 3.

[0069] [Table 3]

[0070] Comparative Example 1 is a system without filler, but due to its low in-plane thermal conductivity, the temperature of the non-wired (non-heating) parts was low, resulting in a lack of uniformity as a planar heater. Comparative Example 2 is a system with a high concentration of 70 vol% high-thermal-conductivity filler added, but it was found to be very brittle, with poor edge crack resistance, tear propagation resistance, and processability. Comparative Example 3 uses copper foil in the heating element, but the resistivity of copper is 3 μΩ·cm, resulting in poor heating efficiency and failure to reach the target temperature. Comparative Example 4 uses high-thermal-conductivity filler with fine particle size, but filler aggregation was observed, causing problems with processability. Comparative Example 5 has a thick polyimide section of 75 μm. While edge crack resistance, tear propagation resistance, and strength were improved due to the thickness, it was found to break during processability and to be poor in flexibility. Furthermore, due to the thick polyimide section, the temperature of the non-wired (non-heating) parts was low, resulting in a lack of uniformity as a planar heater.

[0071] Although embodiments of the present invention have been described in detail above for illustrative purposes, the present invention is not limited to the above embodiments and various modifications are possible. [Explanation of Symbols]

[0072] 1…Heating wiring section, 2…Non-wiring section (polyimide section)

Claims

1. A laminate comprising a metal substrate made of metal foil and an inorganic insulating particle-containing polyimide layer laminated on at least one surface of the metal substrate, The aforementioned metal foil has a volume resistivity of 10 μΩ·cm or more. The aforementioned polyimide layer containing inorganic insulating particles is characterized by having an inorganic insulating particle content of 30 to 60 volume%, a thickness of 3 to 30 μm, a tear propagation resistance of 7 mN or more, and an edge tear resistance of 0.3 N / 20 mm or more.

2. The aforementioned polyimide layer containing inorganic insulating particles has a thermal conductivity in the planar direction (λ ｘｙ The laminate according to claim 1, characterized in that the ratio is 0.5 to 7.0 W / m·K.

3. The laminate according to claim 1 or 2, characterized in that the polyimide in the inorganic insulating particle-containing polyimide layer is composed of a tetracarboxylic acid residue derived from an aromatic tetracarboxylic dianhydride and a diamine residue derived from an aromatic diamine compound having an ether bond.

4. The laminate according to any one of claims 1 to 3, characterized in that the inorganic insulating particles have an average particle diameter of 0.6 to 15 μm.

5. The laminate according to any one of claims 1 to 4, characterized in that the inorganic insulating particles are one or more selected from the group consisting of aluminum oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, quartz, and magnesium oxide.

6. The laminate according to any one of claims 1 to 5, characterized in that it is used as a flexible planar heating element.

7. A method for manufacturing a laminate according to any one of claims 1 to 6, A process of applying a precursor solution of polyimide containing inorganic insulating particles to the surface of a metal substrate which is a metal foil, A method for producing a laminate, comprising the steps of drying the polyimide precursor solution, curing it under heating conditions of 100 to 150°C for an integrated time of 3 to 15 minutes, and 320 to 380°C for an integrated time of 5 minutes or more, to form a polyimide layer having a thickness of 3 to 30 μm, a tear propagation resistance of 7 mN or more, and an edge crack resistance of 0.3 N / 20 mm or more.

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