WO2024071066A1

WO2024071066A1 - Metal-clad laminated plate

Info

Publication number: WO2024071066A1
Application number: PCT/JP2023/034815
Authority: WO
Inventors: 宏遠王; 知弥池田
Original assignee: 日鉄ケミカル＆マテリアル株式会社
Priority date: 2022-09-30
Filing date: 2023-09-26
Publication date: 2024-04-04

Abstract

The present invention provides a metal-clad laminated plate in which the haze of an insulating resin layer is low and which has excellent visibility and light transmission and also has excellent light fastness.　Provided is metal-clad laminated plate having a metal layer on one or both surfaces of an insulating resin layer, the metal-clad laminated plate being characterised in that: the insulating resin layer has a thickness in the range of 10 μm to 100 μm, a total light transmittance of 70% or more, a haze of 50% or less, and an absolute value of 30 or less for the difference in the yellowness index YI before and after irradiation with ultraviolet light; when the surface of the metal layer in contact with the insulating resin layer is measured through the insulating resin layer, the reflectance at 580 nm is 50% or less; and the metal-clad laminated plate is used for applications in which the width of wire comprising said metal layer is processed to be 500 μm or less.

Description

Metal-clad laminate

The present invention relates to a metal-clad laminate formed by laminating an insulating resin layer and a metal layer.

In recent years, with the progress of miniaturization, weight saving, and space saving of electronic devices, there has been an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and have excellent durability even when repeatedly bent. Because FPCs allow for three-dimensional, high-density mounting even in a limited space, their applications are expanding to include wiring for moving parts of electronic devices such as HDDs, DVDs, and smartphones, as well as components such as cables and connectors. Most FPCs are manufactured by forming circuits on the metal layer of a metal-clad laminate, which is made by laminating a metal layer using metal foil or the like with an insulating resin substrate (insulating resin layer).

FPCs, especially transparent FPCs, are thin, lightweight, flexible, and unbreakable, and in recent years, they have been used as transparent antennas on the surface of window glass to turn windows into base stations, and are being used in mobile applications to embed antennas in displays, as well as in substrate applications in fields where transparent LED vision displays, including large light-emitting boards and LED (Light Emitting Diode) displays, are expected to be installed. For these new applications, there are known techniques for forming thin wiring that is difficult to see with the naked eye, but since the visibility of the substrate is particularly important, there is a strong demand for the processed wiring to be as inconspicuous as possible when viewed from the opposite side of the film (the side visible to the user (insulating resin layer side)). This is because there is a risk that the contrast of the display will decrease due to specular reflection of the wiring. Currently, in these fields, copper-clad laminates in which copper foil is sputtered onto polyethylene terephthalate (PET) as an insulating resin layer are being used in some cases due to cost and transparency considerations, but this method may not provide sufficient adhesive strength for the copper foil, and PET has low heat resistance, making high-temperature mounting difficult in the process. Furthermore, when expanding into the new applications mentioned above, there are issues such as light resistance, especially when exposed to sunlight, and there is room for further consideration to ensure long-term reliability.

Here, metal-clad laminates suitable for transparent FPCs have been proposed, but in order to ensure the visibility and transparency of the insulating resin layer used (the insulating resin layer at the location where the metal layer is etched), a metal layer that was present on that surface is preferably one that is relatively less roughened (for example, Patent Document 1). This is because, when the metal layer is etched, the surface profile of the metal layer, such as the surface roughness, is carried over to the resin layer.

However, metals with little roughening have a smooth surface, which means there is less scattering of light and a tendency to increase light reflection (specular reflection), which raises concerns that the gloss, color, and presence of the metal used may become more prominent. For this reason, when applying to substrates for the above-mentioned purposes, it is important not only to take into account the reflection and color of the metal itself used, but also to adjust the hue (presence) of the metal layer when viewed from the opposite side of the film (the side visible to the user (insulating resin layer side)) in anticipation of actual use, and there was room for further consideration of transparency as a device overall, including such concerns.

Conventionally, in FPCs, touch panels, and the like, a technique has been disclosed in which, in consideration of the transparency of the film after etching of the copper foil and the visibility of the wiring, a copper foil that has been blackened to a lightness L ^* value of 30 or less is used as the roughened copper foil (e.g., Patent Document 2), and in consideration of the adhesion and visibility after the formation of a circuit pattern in the application of a wiring board, a technique has been disclosed in which a pure copper is roughened to reduce the diffuse reflectance (e.g., Patent Document 3). In addition, in a touch panel, a technique has been disclosed in which a transparent adhesive layer having a predetermined roughened surface is provided on the contact surface between the transparent substrate and the copper foil (e.g., Patent Document 4). However, none of these techniques have been considered for applications in which the presence of even very fine wiring is taken into consideration, such as LED transparent displays, etc.

On the other hand, a copper foil having a fine uneven structure formed by needle-like or plate-like convex portions with a maximum length of 500 nm or less and made of a copper composite compound containing cuprous oxide and cupric oxide has been disclosed as a copper foil used in forming extremely fine copper wiring of 10 μm or less as a fine wiring type transparent electrode (Patent Document 5). However, the ranges of the reflectance of the copper foil, the adhesion to the resin layer, and the haze (turbidity) of the resin layer after film formation are not specified, and such viewpoints were not taken into consideration.

International Publication No. WO2020/262450 International Publication No. WO2014/133164 Japanese Patent No. 5706026 JP 2015-157392 A International Publication No. WO2015/178455

The inventors of the present application therefore further investigated the resin films and metal-clad laminates that had been previously investigated from the above perspective, and as a result, they discovered a metal-clad laminate that is suitable as a substrate for various new applications to be processed into fine metal layers (wiring layers) by using an insulating resin layer in the metal-clad laminate that has low haze (turbidity), excellent visibility and light transmittance, and excellent light resistance, and by using a metal layer that has low reflectance measured through the insulating resin layer, they completed the present invention.

The object of the present invention is therefore to provide a metal-clad laminate that has low haze (turbidity), excellent visibility and light transmittance, and excellent light resistance, and is suitable as a substrate for a variety of new applications when processed into a fine metal layer (wiring layer).

That is, the present invention is as follows.
[1] A metal-clad laminate having a metal layer on one or both sides of an insulating resin layer,
the insulating resin layer has a thickness in the range of 10 μm to 100 μm, a total light transmittance of 70% or more, a haze of 50% or less, and an absolute value of a difference in yellowness index YI before and after ultraviolet irradiation of 30 or less;
a reflectance at 580 nm of a surface of the metal layer in contact with the insulating resin layer is 50% or less when measured through the insulating resin layer;
A metal-clad laminate characterized in that it is used in applications in which the wiring width of the metal layer is processed to 500 μm or less.
[2] The metal-clad laminate according to [1], wherein the absolute value of the difference in haze between before and after ultraviolet irradiation is 10% or less.
[3] The metal-clad laminate according to [1] or [2], characterized in that the solder heat resistance is 200°C or higher.
[4] The metal-clad laminate according to [1] or [2], characterized in that when the metal layer is processed to a width of 100 μm, the 180° peel strength between the metal layer and the insulating resin layer after the processing is 0.3 kN/m or more.
[5] The metal-clad laminate according to [1] or [2], characterized in that the maximum height Rz of the surface of the metal layer in contact with the insulating resin layer is 300 nm or less, and the a ^* of the L ^* a ^* b ^* color system is 20 or less.
[6] The metal-clad laminate according to [1] or [2], characterized in that the application in which the wiring width is processed to 500 μm or less is a transparent LED vision application.
[7] The metal-clad laminate according to [1] or [2], characterized in that the application in which the wiring width is processed to 500 μm or less is for a head-mounted display.
[8] The metal-clad laminate according to [1] or [2], characterized in that the application in which the wiring width is processed to 500 μm or less is for a transparent antenna.

According to the present invention, it is possible to obtain a metal-clad laminate having a low haze of the insulating resin layer, excellent visibility and light transmittance, and excellent light resistance. The metal-clad laminate of the present invention is processed into a fine metal layer (wiring layer) and is suitable for applications requiring high transparency, such as transparent LED vision, head-mounted displays, and substrate applications for transparent antennas.

The following describes an embodiment of the present invention.

<Metal-clad laminate>
The metal-clad laminate of the present invention comprises an insulating resin layer and a metal layer laminated on at least one side of the insulating resin layer, and may have the metal layer on one side of the insulating resin layer or on both sides of the insulating resin layer.

In the metal-clad laminate of the present invention, the reflectance of reflected light at 580 nm when the surface of the metal layer in contact with the insulating resin layer of the metal-clad laminate is measured through the insulating resin layer (through the insulating resin layer) is 50% or less. Preferably, it is 45% or less, more preferably 40% or less, and even more preferably 30% or less. On the other hand, there is no particular limit to the lower limit, since it is preferable that there is no reflection. The reason for measuring at a wavelength of 580 nm is that this wavelength is in the yellow light region of the visible light wavelength, making it easy to see both the insulating resin layer and the copper foil as the metal layer, and is a wavelength that makes it easy to see the differences between samples, especially when viewing the copper foil through the insulating resin layer. The reflectance is preferably measured by the method described in the examples. Specifically, as shown in the examples described later, after the mirror side of the metal layer of the metal-clad laminate (one side) is attached to a glass plate, light (C light source) is irradiated from the insulating resin layer side, and the reflected light reflected from the metal layer surface through the insulating resin layer is measured at a viewing angle of 2° to measure the reflectance at 580 nm. The reflected light measured at this time is not limited to only the reflected light from the metal layer surface, but may also include light originating from the insulating resin layer.

In other words, an important feature of the metal-clad laminate of the present invention is that it takes into consideration the reflectance of reflected light measured when the metal layer is viewed through the insulating resin layer using light of 580 nm, which is in the visible light wavelength range representing yellow light. If the reflectance is within the above range, the presence of the metal layer is not noticeable when observed through the insulating resin layer, making it particularly preferable for FPC applications that require high transparency and visibility (such as transparent LED vision, which will be described later).

In addition, in the metal-clad laminate of the present invention, the L ^* of the L ^* a ^* b ^* color system of the reflected light when measured through the insulating resin layer (through the insulating resin layer) as described above is preferably 65 or less, and a ^* is preferably 15 or less. The reflected light measured at this time is not limited to only the reflected light from the metal layer surface as described above, and does not exclude the inclusion of light caused by the insulating resin layer. In this way, by considering the L ^* value and a ^* value of the reflected light measured when the metal layer is viewed through the insulating resin layer using light of 580 nm, which is a visible light wavelength region representing yellow light, not only the reflectance but also the reflection of the metal layer can be suppressed to make the presence less noticeable, which is desirable.

It is preferable that the L ^* is relatively low and blackened to suppress gloss, and it is more preferable that the L ^* measured by the above method is 45 or less, and even more preferable that it is 40 or less. On the other hand, there is no particular restriction on the lower limit, but from the viewpoint of ease of adjusting the balance between the color tone of the metal layer and the transparency of the film, it is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more.

In addition, a ^* is a chromaticity in which +a ^* represents the red direction and -a ^* represents the green direction. In the metal-clad laminate of the present invention, copper (copper foil) is often used as the metal layer, and the reflected light of the copper surface often has a relatively large a ^* and a reddish color tone. In addition, since reddish colors tend to be easily noticeable to the human eye, in consideration of these, in the present invention, it is preferable that the value of a ^* of the reflected light of the metal layer surface in the above-mentioned measurement method is small, the redness is suppressed, and the presence of the metal layer is not noticeable, and a ^* is preferably 15 or less. More preferably, a ^* is 10 or less, and even more preferably 5 or less. On the other hand, there is no particular restriction on the lower limit, but since the greenish color tone becomes stronger as the negative value of a ^* increases, it is preferably -10 or more, more preferably -5 or more, and even more preferably -2 or more.

In the above-mentioned measurement method, there is no particular limitation on b ^* for the reflected light from the metal layer surface, but since +b ^* is a chromaticity indicating a yellow direction and −b ^* is a chromaticity indicating a blue direction, it is preferable that the numerical value (absolute value) is small, and the upper limit is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less. On the other hand, the lower limit is preferably −15 or more, more preferably −5 or more, and even more preferably 0 or more.

The L ^* a ^* b ^* color system is measured in accordance with JIS Z 8781-4-2013. The L ^* , a ^* , and b ^* values measured at this time are values measured at a viewing angle of 2° or 10° using a D65 light source (JIS Z8720 daylight standard illuminant (light for color measurement)) or a C light source (JIS Z8720 daylight auxiliary illuminant) used when displaying the color of an object illuminated by daylight. Specifically, as shown in the examples described later, the metal layer mirror side of the metal-clad laminate (one side) is attached to a glass plate, and then light is irradiated from the insulating resin layer side, and the reflected light reflected from the metal layer surface through the insulating resin layer is measured at a viewing angle of 2°. The L ^* , a ^* , and b ^* values are measured.

<Metal Layer>
The material of the metal layer is not particularly limited, but examples thereof include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, the metal elements of copper, iron, or nickel, or indium tin oxide (ITO) are preferred, and copper (copper foil) is more preferred. As the copper foil, both electrolytic copper foil and rolled copper foil can be used. In addition, in selecting these metal layers, the metal layer is selected so as to exhibit the properties required for the intended use, such as the conductivity of the metal layer, the light transmittance of the polyimide layer, and the adhesion to the polyimide layer. There is no particular limit to the shape of the metal layer, but it may be processed appropriately depending on the application. A roll-shaped one formed in a long shape is preferably used.

The thickness of the metal layer is not particularly limited, but is preferably 100 μm or less, more preferably in the range of 0.1 to 50 μm, and even more preferably in the range of 1 to 35 μm.

In addition, from the viewpoint of the light transmittance of the insulating resin layer, the color tone of the metal layer, and the clarity of the image when used as a display, the surface roughness (maximum height roughness) Rz of the surface of the metal layer is preferably 300 nm or less, more preferably 200 nm or less, and even more preferably 180 nm or less. As for the lower limit, it is preferable that it is 20 nm or more, more preferably 40 nm or more, and even more preferably 50 nm or more, because it maintains adhesion with the insulating resin layer. In addition, it is preferable that the surface roughness (arithmetic mean roughness) Ra is 0.005 μm or more and 0.1 μm or less, more preferably 0.005 μm or more and 0.07 μm or less, and even more preferably 0.005 μm or more and 0.03 μm or less. By setting the Rz and Ra of the surface of the metal layer in the above range, the HAZE (turbidity) of the insulating resin layer after etching the metal layer can be relatively low, and various properties such as L ^* and a ^* of the metal layer described later can also be adjusted, which is preferable.

In addition, it is preferable to use a metal layer having L ^* , a ^* and b ^* in the L*a*b ^* color system in a predetermined range, because the L ^* , a ^* and b ^* of the metal layer measured through the insulating resin layer can be in a predetermined range. As shown in the examples described later, the L ^* ^, a ^* and b ^* of the metal layer are measured by the same measurement method as for the metal-clad laminate (one side) after ^the metal layer is used alone and its mirror side is attached to a glass plate.

The L ^* of the metal layer is preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less. On the other hand, the lower limit of L ^* is preferably 10 or more, more preferably 40 or more, and even more preferably 45 or more. A metal layer with a low L ^* is preferable because the brightness of the metal is reduced and it is not noticeable when viewed through the insulating resin layer.

Further, a ^* of the metal layer is preferably 20 or less, more preferably 18 or less, and further preferably 15 or less. On the other hand, the lower limit of a ^* is preferably 1 or more, more preferably 2 or more, and further preferably 3 or more.

The b ^* of the metal layer is preferably 20 or less, more preferably 15 or less, and even more preferably 12 or less, while the lower limit is preferably 2 or more, more preferably 5 or more, and even more preferably 7 or more.

For the same reasons as above, it is preferable that the surface of the metal layer itself has low light reflectance, and the reflectance at a wavelength of 580 nm is preferably 50% or less. More preferably, it is 45% or less, even more preferably 40% or less, and even more preferably 35% or less. On the other hand, there is no particular restriction on the lower limit, since it is preferable that there is no reflection. The reflectance is preferably measured by the method described in the examples.

<Insulating resin layer>
The insulating resin layer of the present invention must have suitable light transmittance for FPC applications (such as transparent LED vision described below) that require high transparency and visibility, and must have a total light transmittance of 70% or more. It is preferable that the insulating resin layer is closer to transparency, and the total light transmittance is preferably 75% or more, and more preferably 80% or more.

In addition, from the viewpoint of the requirement of such high visibility and light transmission, the insulating resin layer (insulating resin layer after the metal layer is removed by etching) must have a haze of 50% or less, preferably 30% or less, more preferably 10% or less, even more preferably 5% or less, even more preferably 4% or less, and most preferably 3% or less. There is no lower limit since it is desirable to have less haze.

The thickness of the insulating resin layer is set to a range of 10 to 100 μm from the viewpoints of processability during processing, transportability, and supportability of the film itself. It can be appropriately selected depending on the application, but since the film needs to be transparent, it is preferably 10 to 70 μm, and more preferably 10 to 50 μm.

Furthermore, the insulating resin layer in the present invention preferably has good light resistance and undergoes little change (deterioration) in optical properties such as visibility and transparency, even in outdoor applications such as transparent LED vision described below, and indoor applications such as transparent antennas described below where the layer is exposed to sunlight. That is, the insulating resin layer used in the present invention has an absolute value of the difference in yellowness index (YI) before and after ultraviolet (UV) irradiation of 30 or less. The absolute value of the difference in YI is preferably 10 or less, and more preferably 5 or less. Specifically, the UV irradiation conditions are preferably performed as described in the Examples.

From the same viewpoint, it is preferable that the absolute value of the difference in haze between before and after UV irradiation of the insulating resin layer in the present invention is 10% or less. More preferably, it is 3% or less, and even more preferably, it is 2% or less.

Furthermore, the YI of the insulating resin layer is preferably 50 or less, more preferably 40 or less, and even more preferably 35 or less. For example, it is preferable to satisfy this when the insulating resin layer is 25 μm thick. By controlling it within this range, the insulating resin layer can be made almost colorless. On the other hand, if the YI is outside the above range, the yellow to yellowish brown coloring becomes stronger, and the visibility of the insulating resin layer tends to decrease.

From the viewpoint that the greater the surface roughness of the insulating resin layer, the worse the haze becomes when light is irradiated and the lower the visibility of the display, it is preferable that the surface roughness Ra of the insulating resin layer is 0.1 μm or less, more preferably 0.07 μm or less, and even more preferably 0.03 μm or less. In addition, it is preferable that the surface roughness Rz is 0.5 μm or less, more preferably 0.4 μm or less, and even more preferably 0.3 μm or less.

The insulating resin layer is not particularly limited and can be appropriately selected depending on the application. Preferred examples include polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, liquid crystal polymer (LCP), perfluoroalkoxyalkane (PFA) resin, polymethyl methacrylate, cycloolefin polymer, polycarbonate, polyimide (PI) resin, etc. Among these, polyimide resin is preferably used because it has excellent heat resistance, adhesion, flexibility, etc., and can also be made highly transparent depending on the composition, etc.

The insulating resin layer may contain an inorganic filler as necessary, provided that the object of the present invention is not hindered. Specific examples include silicon dioxide, aluminum oxide, magnesium oxide, beryllium oxide, boron nitride, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, etc. These may be used alone or in combination of two or more.

Below, we will explain an embodiment in which polyimide resin is used as an example of a preferred insulating resin layer of the present invention.

As the polyimide resin (polyimide layer) used, a commercially available polyimide film can be used as it is, and there is no limitation, but the method of forming the polyimide layer as the insulating resin layer includes, for example, [1] a method of applying a polyamic acid solution to a supporting substrate (e.g., a metal layer) and drying it, and then imidizing it to produce a resin film (hereinafter, the casting method), [2] a method of applying a polyamic acid solution to a supporting substrate and drying it, and then peeling off the polyamic acid gel film from the supporting substrate and imidizing it to produce a resin film, etc. In addition, when the insulating resin layer is composed of multiple polyimide layers, the embodiment of the manufacturing method includes, for example, [3] a method of applying a polyamic acid solution to a supporting substrate and drying it multiple times, and then imidizing it (hereinafter, the successive coating method), and [4] a method of applying a polyamic acid laminate structure to a supporting substrate by multilayer extrusion and drying it at the same time, and then imidizing it (hereinafter, the multilayer extrusion method).
From the viewpoints of dimensional stability, adhesion between the insulating resin layer and the metal layer, and control of the haze or in-plane retardation of the insulating resin layer after etching the metal layer, it is preferable to form the insulating resin layer (metal-clad laminate) by a casting method or a sequential coating method.

The method for applying the polyimide solution (or polyamic acid solution) to the substrate is not particularly limited, and it is possible to apply it using a coater such as a comma, die, knife, or lip coater. When forming a multi-layer polyimide layer, a method in which the polyimide solution (or polyamic acid solution) is applied to the substrate and then dried is repeated is preferred. The polyimide layer may be formed from only a single layer, but a multi-layer structure is preferred in consideration of the adhesiveness between the polyimide layer and the metal layer, etc.

In the case of multiple polyimide layers, a two-layer structure may be used, with a polyimide layer (P1) laminated directly to the metal layer and a polyimide layer (P2) not laminated directly to the metal layer. Although not particularly limited, as shown in the examples of configurations 1 to 4 below, three layers are preferred, and more preferably, the third polyimide layer (P3) is laminated in the order of (P1)/(P2)/(P3). M1 and M2 represent metal layers, and M1 and M2 may be the same or different. The polyimide layer (P1) laminated directly to the metal layer and the third polyimide layer (P3) may be of the same composition. For example, when multiple polyimide layers are formed by a casting method, a two-layer structure may be formed in which a polyimide layer (P1) that is directly laminated on a metal layer from the cast surface side and a polyimide layer (P2) that is not directly laminated on a metal layer are laminated in this order, or a three-layer structure may be formed in which a polyimide layer (P1) that is directly laminated on a metal layer from the cast surface side and a polyimide layer (P2) that is not directly laminated on a metal layer and a third polyimide layer (P3) are laminated in this order. The "cast surface" referred to here refers to the surface on the support side when forming a polyimide layer. The support may be the metal layer of the metal-clad laminate of the present invention, glass, etc., or a support when forming a gel film, etc. In addition, the surface opposite to the cast surface of the multiple polyimide layers is described as the "lamination surface", but unless otherwise specified, a metal layer may or may not be laminated on the laminate surface.

Configuration 1: M1/P1/P2
Configuration 2: M1/P1/P2/P1 (or P3)
Configuration 3: M1/P1/P2/P1 (or P3)/M2 (or M1)
Configuration 4: M1/P1/P2/P1 (or P3)/P2/P1 (or P3)/M2 (or M1)

The polyimide constituting the polyimide layer (P1) and the polyimide layer (P3) is preferably a thermoplastic polyimide, which improves the adhesiveness as an insulating resin layer and is suitable for use as an adhesive layer with a metal layer.

A preferred embodiment of the insulating resin layer has a thermoplastic polyimide layer (P1) and a non-thermoplastic polyimide layer (P2) made of a non-thermoplastic polyimide, and at least one of the non-thermoplastic polyimide layers (P2) has a polyimide layer (P1) that becomes a thermoplastic polyimide layer. In other words, the polyimide layer (P1) is preferably provided on one or both sides of the non-thermoplastic polyimide layer.

The non-thermoplastic polyimide layer constitutes a polyimide layer with low thermal expansion, and the thermoplastic polyimide layer constitutes a polyimide layer with high thermal expansion. Here, the low thermal expansion polyimide layer refers to a polyimide layer with a coefficient of thermal expansion (CTE) preferably in the range of 1 ppm/K to 25 ppm/K, more preferably in the range of 3 ppm/K to 25 ppm/K. The high thermal expansion polyimide layer refers to a polyimide layer with a CTE preferably in the range of 35 ppm/K or more, more preferably in the range of 35 ppm/K to 80 ppm/K, and even more preferably in the range of 35 ppm/K to 70 ppm/K. The polyimide layer can be made to have a desired CTE by appropriately changing the combination of raw materials used, the thickness, and the drying and curing conditions.

The coefficient of thermal expansion (CTE) of the entire insulating resin layer is preferably within the range of 10 to 30 ppm/K. By controlling it within this range, deformation such as curling can be suppressed and high dimensional stability can be ensured. Here, CTE is the average value of the coefficient of thermal expansion of the insulating resin layer in the MD and TD directions.

Here, non-thermoplastic polyimide generally refers to polyimide that does not soften or exhibit adhesiveness even when heated, but in the present invention refers to polyimide having a storage modulus of 1.0×10 ^{9 Pa or more at 30° C. and a storage modulus of 1.0×10 9} ^Pa or more at 350° C., as measured using a dynamic mechanical analyzer (DMA). Thermoplastic polyimide (also referred to as "TPI") generally refers to polyimide whose glass transition temperature (Tg) can be clearly confirmed, but in the present embodiment refers to polyimide having a storage modulus of 1.0×10 ⁹ Pa or more at 30° C. and a storage modulus of less than 1.0×10 ⁸ Pa at 300° C., as measured using a DMA.

When the thickness of the polyimide layer (P1) in contact with the metal layer in the insulating resin layer is T1 and the thickness of the main polyimide layer is T2, the thickness of T1 is preferably in the range of 1 μm to 4 μm, and the thickness of T2 is preferably in the range of 4 μm to 30 μm. From another perspective, the thickness of T1 is preferably 20% or less of the thickness of the insulating resin layer. Here, "main" means that it has the largest thickness among the multiple polyimide layers that make up the insulating resin layer, and preferably has a thickness of 60% or more, more preferably 70% or more, and even more preferably 80% or more of the thickness of the insulating resin layer. The main polyimide layer is preferably composed of a non-thermoplastic polyimide.

In the case of an insulating resin layer made of a polyimide layer, the insulating resin layer has a 1% weight loss temperature (Td1) of 400°C or higher in a thermal decomposition test, preferably 430°C or higher, and more preferably 450°C or higher. By controlling it within this range, it has sufficient heat resistance even when used as a major component of an FPC.

In addition, the insulating resin layer made of a polyimide layer preferably has a heat resistance (solder heat resistance) of 190°C or higher in a solder heat resistance test, and more preferably 200°C or higher. The solder heat resistance is evaluated by the method described in the examples.

In addition, the insulating resin layer made of a polyimide layer preferably has a heat resistance of a glass transition temperature (Tg) of 210°C or higher. More preferably, it is 250°C or higher, and even more preferably, it is 300°C or higher.

Furthermore, it is preferable that the insulating resin layer made of a polyimide layer has an in-plane retardation of 1 nm or more and 100 nm or less. More preferably, it is 1 nm or more and less than 20 nm.

(Polyimide Layer Composition)
The composition of the polyimide layer used in the insulating resin layer in the present invention is not particularly limited, but it is preferable that the polyimide layer has the following composition.

The polyimide layer is made of a polyimide containing an acid anhydride residue and a diamine residue, and the polyimide constituting at least one polyimide layer (P1) contains 50 mol% or more, preferably 70 mol% or more, and more preferably 90 mol% or more of acid anhydride residues derived from an aromatic tetracarboxylic acid anhydride represented by general formula (1) relative to the total acid anhydride residues derived from the acid anhydride component. By setting the content in such a range, heat resistance and low retardation are easily exhibited. In addition, the polyimide contains 50 mol% or more of diamine residues derived from an aromatic diamine compound represented by general formula (2) relative to the total diamine residues contained in the polyimide. Preferably, the content is 70 mol% or more, and more preferably, the content is 90 mol% or more.

The aromatic tetracarboxylic anhydride represented by the general formula (1) imparts flexibility to the polyimide, reduces interactions such as π-π stacking between polymer chains, and makes charge transfer (CT) between the aromatic tetracarboxylic acid residue and the aromatic diamine residue difficult to occur, so that it is believed that the resulting polyimide can be made closer to colorless and transparent. In addition, the aromatic diamine compound represented by the general formula (2) has two or more benzene rings, and has amino groups and divalent linking groups Z directly bonded to at least two benzene rings, which increases the degree of freedom of the polyimide molecular chain and gives it high flexibility, which is believed to contribute to improving the flexibility of the polyimide molecular chain and promote high toughness. In the present invention, the acid anhydride residue refers to a tetravalent group derived from a tetracarboxylic dianhydride, and the diamine residue refers to a divalent group derived from a diamine compound.

The acid anhydride residue contained in the polyimide constituting the polyimide layer (P1) that is directly laminated to the metal layer is preferably an acid anhydride residue derived from an aromatic tetracarboxylic acid anhydride represented by the general formula (1).

In formula (1), X represents a divalent group selected from a single bond, --O--, or --C(CF ₃ ) ₂ --.

Examples of aromatic tetracarboxylic acid anhydrides represented by formula (1) include 4,4'-oxydiphthalic dianhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA). These aromatic tetracarboxylic acid anhydrides are preferred because they can impart strength and flexibility to the polyimide film, have excellent heat resistance and transparency, and can control the CTE within an appropriate range. Among these, ODPA and 6FDA are particularly preferred.

The diamine residue contained in the polyimide constituting the polyimide layer (P1) is preferably a diamine residue derived from an aromatic diamine compound represented by general formula (2).

In formula (2), Z independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -CO-, -COO-, -SO ₂ -, -NH-, or -NHCO-, and is preferably -O-. n ₂ represents an integer of 0 to 4, and is preferably 0 or 1. R is a substituent, and independently represents a halogen atom, an alkyl group or an alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or a phenoxy group which may be substituted with a monovalent hydrocarbon group or an alkoxy group having 1 to 6 carbon atoms. n ₁ independently represents an integer of 0 to 3, and is preferably 0 or 1. Here, "independently" means that in the above formula (2), a plurality of substituents R, a divalent group Z, and further an integer n ₁ may be the same or different. In the above formula (2), the hydrogen atoms in the two terminal amino _groups may be substituted, for example, _-NR3R4 (wherein _R3 and _R4 each independently represent an arbitrary substituent such as an alkyl group). The same applies to other diamine compounds.
However, when X in formula (1) is a single bond, Z in formula (2) independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )- or -NH-.

Examples of the aromatic diamine compound represented by formula (2) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,4'-diaminobenzophenone, (3,3'-bisamino)di Phenylamine, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[5 -Methyl-(1,3-phenylene)bisoxy]bisaniline, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)]benzophenone, bis[4,4'-(3-aminophenoxy)]benzanilide, 4-[3-[4-(4-aminophenoxy)] Examples of such bis(aminophenoxy)phenyl]aniline, 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP), 4,4'-diaminodiphenyl ether, etc. Among these, 1,3-bis(3-aminophenoxy)benzene (APB) and 1,3-bis(4-aminophenoxy)benzene (TPE-R) are preferred.

However, other acid anhydride residues may be contained as long as they do not impede the objective of the present invention. If other acid anhydride residues are contained, the amount is 50 mol % or less of the total acid anhydride residues, preferably less than 30 mol %, and more preferably less than 10 mol %.

Other acid anhydride residues include, for example, pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,3,3',4'-benzophenonetetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, and 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene. -1,2,5,6-tetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-2,3,6,7-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'-biphenyltetracarboxylic dianhydride, 2,3,3 ',4'-biphenyltetracarboxylic dianhydride, 3,3'',4,4''-p-terphenyltetracarboxylic dianhydride, 2,2'',3,3''-p-terphenyltetracarboxylic dianhydride, 2,3,3'',4''-p-terphenyltetracarboxylic dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)ether dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3.4-dicarboxyphenyl)methane dianhydride Anhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic 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, cyclopentane-1,2,3,4-tetracarboxylic dianhydride, pyrazine-2,3,5,6-tetracarboxylic dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, (trifluoromethyl)pyromellitic dianhydride, di(trifluoromethyl)pyromellitic dianhydride, di(heptafluoropropyl)pyromellitic dianhydride, pentafluoro Ethyl pyromellitic dianhydride, bis{3,5-di(trifluoromethyl)phenoxy}pyromellitic 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'-tetracarboxydiphenyl ether dianhydride, 5,5'-bis(trifluoromethyl)- 3,3',4,4'-Tetracarboxybenzophenone dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}trifluoromethylbenzene dianhydride, 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 Examples of suitable anhydride residues include those derived from bis(trifluoromethyl)dicarboxyphenoxy)biphenyl dianhydride, bis(trifluoromethyl)dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride, bis(trifluoromethyl)dicarboxyphenoxy)diphenyl ether dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, fluorenylidene bisphthalic anhydride, and 1,2,4,5-cyclohexane tetracarboxylic dianhydride. Among these, the acid anhydride residues derived from pyromellitic dianhydride or 3,3',4,4'-biphenyl tetracarboxylic dianhydride are preferred, since they can impart strength and flexibility to the polyimide film, and the coefficient of thermal expansion (CTE) of the polyimide film does not increase too much and can be controlled within an appropriate range.

Similarly, diamine residues derived from other diamine compounds may be contained as long as they do not impede the object of the present invention. When other diamine residues are contained, the amount is 50 mol % or less of the total diamine residues, preferably less than 30 mol %, and more preferably less than 10 mol %.

Other diamine residues include, for example, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), bis[4-(aminophenoxy)phenyl]sulfone (BAPS), 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,5,3',5'-tetramethyl-4,4'-diaminodiphenylmethane, 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, 2,2-Bis(4-aminophenoxyphenyl)propane, 2,2-Bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfide, 4,4'-Diaminodiphenyl sulfone, 3,3'-Diaminodiphenyl sulfone, 4,4'-Diaminodiphenyl ether, 3,3'-Diaminodiphenyl ether, 1,3-Bis(3-aminophenoxy)benzene, 1,3-Bis(4-aminophenoxy)benzene, 1,4-Bis(4-aminophenoxy)benzene, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl Phenyl, 3,3'-dimethoxybenzidine, 4,4"-diamino-p-terphenyl, 3,3"-diamino-p-terphenyl, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, 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-t-butyl)toluene, 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, 4-(1H,1H,11H-eicosafluoroundecanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-butanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-heptanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-octanoxy)-1,3-diaminobenzene, 4-pentafluorophenoxy-1,3-diaminobenzene, 4-(2,3,5,6-tetrafluorophenoxy)-1,3-diaminobenzene, 4-(4-fluorophenoxy)-1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1- 1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1-dodecanoxy)-1,3-diaminobenzene, (2,5)-diaminobenzotrifluoride, diaminotetra(trifluoromethyl)benzene, diamino(pentafluoroethyl)benzene, 2,5-diamino(perfluorohexyl)benzene, 2,5-diamino(perfluorobutyl)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, octafluorobenzidine, 4,4'-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(aniline 1,4-bis(anilino)hexafluoropropane, 1,4-bis(anilino)octafluorobutane, 1,5-bis(anilino)decafluoropentane, 1,7-bis(anilino)tetradecafluoroheptane, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3',5,5'-tetrakis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminobenzophenone, 4,4'-diamino-p-terphenyl, 1,4-bis(p-aminophenyl)benzene, p-(4-amino-2-trifluoromethylphenoxy)benzene, bis(amino 2,2-bis{4-(4-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(3-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(2-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(4-aminophenoxy)-3,5-dimethylphenyl}hexafluoropropane, 2,2-bis{4-(4-aminophenoxy)-3.5-ditrifluoromethylphenyl}hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)phenyl and diamine residues derived from 4,4'-bis(4-amino-3-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)diphenyl sulfone, 4,4'-bis(3-amino-5-trifluoromethylphenoxy)diphenyl sulfone, 2,2-bis{4-(4-amino-3-trifluoromethylphenoxy)phenyl}hexafluoropropane, bis{(trifluoromethyl)aminophenoxy}biphenyl, bis[{(trifluoromethyl)aminophenoxy}phenyl]hexafluoropropane, bis{2-[(aminophenoxy)phenyl]hexafluoroisopropyl}benzene, and 4,4'-bis(4-aminophenoxy)octafluorobiphenyl. Among these, from the viewpoint of producing a polyimide having high transparency and a low degree of coloration, diamine residues derived from diamine compounds such as 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-b bis(2-(trifluoromethyl)-4-aminophenoxy)biphenyl, 2,2-bis(4-(2-(trifluoromethyl)-4-aminophenoxy)phenyl)hexafluoropropane, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, and p-bis(2-trifluoromethyl)-4-aminophenoxy]benzene are preferred.

By selecting the types of the acid anhydride residues and diamine residues and the molar ratios of two or more types of acid anhydride residues or diamine residues, it is possible to control the toughness, thermal expansion, adhesion, glass transition temperature (Tg), etc.

In the resin film of the present invention, in particular to set the total light transmittance within a predetermined range, it is preferable that the main polyimide layer contains diamine residues derived from an aromatic diamine compound containing fluorine atoms and/or acid anhydride residues derived from an aromatic tetracarboxylic acid anhydride containing fluorine atoms.

The main polyimide preferably contains a fluorine-containing diamine residue. The fluorine-containing diamine residue has a group containing a bulky fluorine atom, which reduces interactions such as π-π stacking between polymer chains and makes charge transfer (CT) between aromatic tetracarboxylic acid residues and aromatic diamine residues less likely to occur, which is thought to make the polyimide closer to colorless and transparent.

Examples of fluorine-containing diamine residues include diamine residues derived from diamine compounds such as 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 3,4-diamino-2,2'-bis(trifluoromethyl)biphenyl, 4,4'-bis(2-(trifluoromethyl)-4-aminophenoxy)biphenyl, 2,2-bis(4-(2-(trifluoromethyl)-4-aminophenoxy)phenyl)hexafluoropropane, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, p-bis(2-trifluoromethyl)-4-aminophenoxy]benzene, and 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane.

Among the fluorine-containing diamine residues, it is more preferable to contain a diamine residue derived from a diamine compound represented by the following general formula (A1) (hereinafter, sometimes referred to as "A1 residue").

In general formula (A1), the substituents X each independently represent an alkyl group having 1 to 3 carbon atoms substituted with a fluorine atom, and m and n each independently represent an integer from 1 to 4.

The A1 residue is an aromatic diamine residue and has a biphenyl skeleton in which two benzene rings are connected by a single bond, which makes it easy to form an ordered structure and promotes in-plane orientation of the molecular chains, thereby suppressing an increase in the CTE of the main polyimide layer and improving dimensional stability. From this perspective, the main polyimide layer preferably contains 50 molar parts or more of A1 residues relative to a total of 100 molar parts of all diamine residues, and more preferably contains 50 molar parts or more and 100 molar parts or less.

Preferred specific examples of the A1 residue include diamine residues derived from diamine compounds such as 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl (TFMB) and 3,4-diamino-2,2'-bis(trifluoromethyl)biphenyl.

The main polyimide layer may contain, as diamine residues other than those mentioned above, diamine residues derived from diamine components generally used in the synthesis of polyimides.

The main polyimide layer preferably contains fluorine-containing acid anhydride residues. Fluorine-containing acid anhydride residues have groups that contain bulky fluorine atoms, which reduces interactions such as π-π stacking between polymer chains and makes charge transfer (CT) between aromatic tetracarboxylic acid residues and aromatic diamine residues less likely to occur, which is thought to make the polyimide closer to colorless and transparent.

Examples of fluorine-containing acid anhydride residues include acid anhydride residues derived from acid anhydride components such as 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA).

In addition, in order to control the CTE within the above range, the main polyimide layer preferably contains a tetravalent acid anhydride residue (hereinafter, sometimes referred to as "PMDA residue") derived from pyromellitic dianhydride (PMDA) represented by the following formula (B1). The PMDA residue is preferably contained in an amount of 50 molar parts or more, more preferably in the range of 60 molar parts to 100 molar parts, relative to a total of 100 molar parts of all acid anhydride residues. If the PMDA residue is less than 50 molar parts, the CTE of the polyimide layer (A) may become high and the dimensional stability may decrease.

The main polyimide layer may also contain, as an acid anhydride residue other than those mentioned above, an acid anhydride residue derived from an acid anhydride component generally used in the synthesis of polyimides. As such an acid anhydride residue, an aromatic tetracarboxylic acid residue is preferred. In addition, it may contain an alicyclic tetracarboxylic acid residue, and preferred examples thereof include acid anhydride residues derived from alicyclic tetracarboxylic acid dianhydrides such as 1,2,3,4-cyclobutane tetracarboxylic dianhydride, fluorenylidene bisphthalic anhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, and cyclotanone bisspironorbornane tetracarboxylic dianhydride.

When the third polyimide layer P3 is used, there is no particular limitation on the composition of the polyimide layer P3, and the layer P3 may have the same composition as the polyimide layer P1. When the layer P3 has a composition different from that of the polyimide layer P1, the layer P3 preferably contains 50 mol % or more of a diamine residue derived from an aromatic diamine compound represented by general formula (A3).

In the above formula (A3), Z independently represents a divalent group selected from -O-, -S-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, or -SO ₂ -, and is preferably -O-. n ₂ independently represents an integer of 0 to 4, and is preferably 0 or 1. R independently represents a substituent, and is independently a halogen atom, an alkyl group or alkoxy group having 1 to 6 carbon atoms which may be substituted with a halogen atom, or a phenyl group or phenoxy group which may be substituted with a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms. n ₁ independently represents an integer of 0 to 3, and is preferably 0 or 1.

The aromatic diamine compound represented by the above formula (A3) has two or more benzene rings, and since there are amino groups and divalent linking groups Z directly bonded to at least two of the benzene rings, the degree of freedom of the polyimide molecular chain is increased, resulting in high flexibility, which is thought to contribute to improving the flexibility of the polyimide molecular chain and promote adhesion and toughness.

When a different composition from that of the polyimide layer P1 is applied to the polyimide layer P3, it is preferable that the polyimide layer P3 contains 50 mol % or more of acid anhydride residues derived from the aromatic tetracarboxylic acid anhydride represented by the general formula (1) relative to the total acid anhydride residues, and contains 50 mol % or more of diamine residues derived from the aromatic diamine compound represented by the general formula (A3) relative to the total diamine residues contained in the polyimide.

Examples of the aromatic diamine compound represented by the above formula (A3) include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylpropane, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylpropane, 3,4'-diaminodiphenyl sulfide, 3,4'-diaminobenzophenone, (3,3 '-bisamino)diphenylamine, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 3-[4-(4-aminophenoxy)phenoxy]benzenamine, 3-[3-(4-aminophenoxy)phenoxy]benzenamine, 4,4'-[2-methyl-(1,3-phenylene)bisoxy]bisaniline, 4,4'-[4-methyl-(1,3-phenylene)bisoxy ]bisaniline, 4,4'-[5-methyl-(1,3-phenylene)bisoxy]bisaniline, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)]benzophenone, bis[4,4'-(3-aminophenoxy)]benzanilide, 4-[3-[4-(4-aminophenoxy Examples of such compounds include 4,4'-[oxybis(3,1-phenyleneoxy)]bisaniline, bis[4-(4-aminophenoxy)phenyl]ether (BAPE), bis[4-(4-aminophenoxy)phenyl]ketone (BAPK), bis[4-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)]biphenyl, 2,2-bis(4-aminophenoxyphenyl)propane (BAPP), and 4,4'-diaminodiphenyl ether. Among these, 1,3-bis(3-aminophenoxy)benzene (APB) and 1,3-bis(4-aminophenoxy)benzene (TPE-R) are preferred.

Other diamine residues include, for example, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), bis[4-(aminophenoxy)phenyl]sulfone (BAPS), 4,6-dimethyl-m-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,5,3',5'-tetramethyl-4,4'-diaminodiphenylmethane, 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, 2,2-Bis(4-aminophenoxyphenyl)propane, 2,2-Bis[4-(4-aminophenoxy)phenyl]propane, 4,4'-Diaminodiphenyl sulfide, 3,3'-Diaminodiphenyl sulfide, 4,4'-Diaminodiphenyl sulfone, 3,3'-Diaminodiphenyl sulfone, 4,4'-Diaminodiphenyl ether, 3,3'-Diaminodiphenyl ether, 1,3-Bis(3-aminophenoxy)benzene, 1,3-Bis(4-aminophenoxy)benzene, 1,4-Bis(4-aminophenoxy)benzene, benzidine, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl Phenyl, 3,3'-dimethoxybenzidine, 4,4"-diamino-p-terphenyl, 3,3"-diamino-p-terphenyl, bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether, 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-t-butyl)toluene, 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, 4-(1H,1H,11H-eicosafluoroundecanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-butanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-heptanoxy)-1,3-diaminobenzene, 4-(1H,1H-perfluoro-1-octanoxy)-1,3-diaminobenzene, 4-pentafluorophenoxy-1,3-diaminobenzene, 4-(2,3,5,6-tetrafluorophenoxy)-1,3-diaminobenzene, 4-(4-fluorophenoxy)-1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1- 1,3-diaminobenzene, 4-(1H,1H,2H,2H-perfluoro-1-dodecanoxy)-1,3-diaminobenzene, (2,5)-diaminobenzotrifluoride, diaminotetra(trifluoromethyl)benzene, diamino(pentafluoroethyl)benzene, 2,5-diamino(perfluorohexyl)benzene, 2,5-diamino(perfluorobutyl)benzene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, octafluorobenzidine, 4,4'-diaminodiphenyl ether, 2,2-bis(4-aminophenyl)hexafluoropropane, 1,3-bis(aniline 1,4-bis(anilino)hexafluoropropane, 1,4-bis(anilino)octafluorobutane, 1,5-bis(anilino)decafluoropentane, 1,7-bis(anilino)tetradecafluoroheptane, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3',5,5'-tetrakis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 3,3'-bis(trifluoromethyl)-4,4'-diaminobenzophenone, 4,4'-diamino-p-terphenyl, 1,4-bis(p-aminophenyl)benzene, p-(4-amino-2-trifluoromethylphenoxy)benzene, bis(amino 2,2-bis{4-(4-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(3-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(2-aminophenoxy)phenyl}hexafluoropropane, 2,2-bis{4-(4-aminophenoxy)-3,5-dimethylphenyl}hexafluoropropane, 2,2-bis{4-(4-aminophenoxy)-3.5-ditrifluoromethylphenyl}hexafluoropropane, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)phenyl and diamine residues derived from 4,4'-bis(4-amino-3-trifluoromethylphenoxy)biphenyl, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)diphenyl sulfone, 4,4'-bis(3-amino-5-trifluoromethylphenoxy)diphenyl sulfone, 2,2-bis{4-(4-amino-3-trifluoromethylphenoxy)phenyl}hexafluoropropane, bis{(trifluoromethyl)aminophenoxy}biphenyl, bis[{(trifluoromethyl)aminophenoxy}phenyl]hexafluoropropane, bis{2-[(aminophenoxy)phenyl]hexafluoroisopropyl}benzene, and 4,4'-bis(4-aminophenoxy)octafluorobiphenyl. Among these, from the viewpoint of producing a polyimide having high transparency and a low degree of coloration, diamine residues derived from diamine compounds such as 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-bis(2-(trifluoromethyl)-4-aminophenoxy)biphenyl, 2,2-bis(4-(2-(trifluoromethyl)-4-aminophenoxy)phenyl)hexafluoropropane, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, 4,4'-bis(3-(trifluoromethyl)-4-aminophenoxy)biphenyl, and p-bis(2-trifluoromethyl)-4-aminophenoxy]benzene are preferred.

Next, a method for synthesizing the polyimide constituting the multiple polyimide layers will be described.
The polyimide of the present embodiment can be produced by reacting the acid anhydride and diamine in a solvent, generating polyamic acid, and then heating to close the ring. For example, the acid anhydride component and the diamine component are dissolved in an organic solvent in approximately equal moles, and the mixture is stirred at a temperature in the range of 0° C. to 100° C. for 30 minutes to 24 hours to polymerize, thereby obtaining polyamic acid, which is a precursor of polyimide. In the reaction, the reaction components are dissolved so that the precursor generated is in the range of 5% by weight to 30% by weight, preferably 10% by weight to 20% by weight, in the organic solvent. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide, N,N-dimethylacetamide (DMAC), N-methyl-2-pyrrolidone, 2-butanone, dimethylsulfoxide, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, and γ-butyrolactone. 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. The amount of such an organic solvent to be used is not particularly limited, but it is preferable to adjust the amount to be used so that the concentration of the polyamic acid solution (polyimide precursor solution) obtained by the polymerization reaction becomes about 5% by weight to 30% by weight.

In the synthesis of polyimide, the above-mentioned acid anhydrides and diamines can be used alone or in combination of two or more kinds. By selecting the types of acid anhydrides and diamines, or the molar ratios when using two or more types of acid anhydrides or diamines, it is possible to control the thermal expansion, adhesion, glass transition temperature, etc.

In addition, a terminal blocking agent may be used for the polyimide. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent introduced is preferably in the range of 0.0001 to 0.1 mol per 1 mol of the acid anhydride component, and more preferably in the range of 0.001 to 0.05 mol. As monoamine terminal blocking agents, for example, methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, aniline, 4-methylaniline, etc. are recommended. Of these, benzylamine and aniline are preferably used. As dicarboxylic acid terminal blocking agents, dicarboxylic acids are preferred, and some of them may be ring-closed. For example, phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, cyclopentane-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, etc. are recommended. Of these, phthalic acid and phthalic anhydride are preferred.

The synthesized polyamic acid is usually advantageously used as a reaction solvent solution, but it can be concentrated, diluted, or replaced with another organic solvent if necessary. Polyamic acid is also advantageously used because it generally has excellent solvent solubility. There are no particular limitations on the method for imidizing polyamic acid, and a suitable method is, for example, heat treatment in which the polyamic acid is heated in the solvent at a temperature in the range of 80°C to 400°C for 1 to 24 hours.

The weight-average molecular weight of the polyamic acid is preferably, for example, in the range of 10,000 to 400,000, and more preferably in the range of 50,000 to 350,000. If the weight-average molecular weight is less than 10,000, the strength of the film tends to decrease and it becomes easily brittle. On the other hand, if the weight-average molecular weight exceeds 400,000, the viscosity increases excessively, and defects such as uneven film thickness and streaks tend to occur during the coating process.

<Metal-clad laminate manufacturing method>
As described above, the metal-clad laminate of the present invention is preferably prepared by forming an insulating resin layer, particularly consisting of multiple polyimide resin layers, on a metal layer as a supporting substrate by a casting method or a sequential coating method from the viewpoint of dimensional stability, but is not particularly limited thereto. For example, the metal-clad laminate may be prepared by preparing an insulating resin layer (resin film) containing the polyimide of the present invention, sputtering a metal onto the insulating resin layer to form a seed layer, and then forming a metal layer by, for example, plating.

Alternatively, the insulating resin layer (resin film) containing the polyimide of the present invention may be prepared by laminating a metal foil onto the insulating resin layer (resin film) by a method such as thermocompression bonding.

In such cases, the surface of the resin film may be modified, for example by plasma treatment, to improve adhesion between the resin film and the metal layer.

In addition, when manufacturing a metal-clad laminate having metal layers on both sides, for example, the metal layer can be laminated by means of hot pressing or the like, directly on the polyimide layer of the single-sided metal-clad laminate obtained by the above method, or after forming an adhesive layer that does not inhibit the transparency of the insulating resin layer as necessary. The heat press temperature when hot pressing the metal layer is not particularly limited, but is preferably equal to or higher than the glass transition temperature of the polyimide layer adjacent to the metal layer used. The heat press pressure is preferably in the range of 1 to 500 kg/ ^m2 , depending on the type of press equipment used.

<Peel strength>
The 180° peel strength between the insulating resin layer and the metal layer in the metal-clad laminate of the present invention is preferably 0.3 kN/m or more, more preferably 0.5 kN/m, even when the wiring layer made of the metal layer is processed to a wiring width of 100 μm. As for the wiring width, 250 μm, 500 μm, 1 mm, etc. can be adopted depending on the application, etc., but in any case, the 180° peel strength between the insulating resin layer and the metal layer preferably satisfies the above range. The metal-clad laminate of the present invention is suitable for applications in which the wiring width is 500 μm or less, as described below.
In this specification, the physical properties and characteristic values are evaluated by measuring under the conditions described in the Examples, and unless otherwise specified, the values are measured at room temperature (23° C.).

In addition, similar to the heat resistance (solder heat resistance) of the insulating resin layer made of the polyimide layer as described above in a solder heat resistance test, the metal-clad laminate as a whole preferably has a solder heat resistance of 190°C or higher, and more preferably 200°C or higher. The solder heat resistance is evaluated by the method described in the examples.

<Applications>
The metal-clad laminate of the present invention is preferably used for applications in which the wiring layer made of the metal layer is processed to have a wiring width of 500 μm or less. As mentioned above, in recent years, applications using FPCs with increasingly excellent transparency have been expanded, and in such new applications, methods for forming thin wiring that is difficult to see with the naked eye are known. The wiring width is preferably 250 μm or less, more preferably 100 μm or less. By making the wiring width 100 μm or less, it is preferable because the wiring is difficult to see even if the visibility distance is several meters. As for the processing method of the metal layer (wiring layer), a known processing method of FPC can be used depending on the application.

Here, according to the metal-clad laminate produced by the casting method or the sequential coating method preferably exemplified above, the peel strength can be relatively high, so that it is excellent in processing fine line patterns. In addition, since a metal-clad laminate having a relatively thick metal layer (e.g., a copper thickness of 18 μm or more) can be produced, it can be applied to a wide range of applications. For example, since a large current is required for a large screen application, there are circumstances such as restrictions such as the need to use a thick metal layer (copper foil), and from such a viewpoint, it is preferable to use a metal-clad laminate produced by the casting method or the sequential coating method as described above.
Suitable applications of the metal-clad laminate of the present invention in which the wiring width is processed to 500 μm or less are as follows, but are not limited to these.

(Transparent LED vision)
The metal-clad laminate of the present invention can be suitably used as a circuit board for a transparent LED vision. Here, the transparent LED vision includes a wide variety of uses, from small household displays to relatively large displays installed on outdoor advertising and bulletin boards and windows and walls of buildings, and is capable of displaying digital images and videos using LEDs in combination, while having high transparency (transparency) of the display part and having such high transparency and visibility that the back side of the display part can be seen through when the LED is not lit. It is called by various names, but is not limited to them, such as "transparent LED display" and "see-through (transparent) type LED vision". The configuration of the transparent LED vision is, but is not limited to them, that when viewed from the back side of the display part, the LEDs are arranged in a lattice or blind shape, and the aperture ratio is high, so that the background of the display part can be seen through when the LED is not lit. In such a transparent LED vision, the metal-clad laminate of the present invention is, for example, incorporated into a display substrate of 100 cm x 50 cm size by processing copper foil wiring in a line and space shape of 100 μm/500 μm.

(Head-mounted display)
The metal-clad laminate of the present invention can be suitably used as a substrate for a head-mounted display (HMD). In recent years, the applications of HMDs have been increasingly expanded, and include all wearable digital display devices that are worn on the head. For example, hat-type and eyeglass-type wearing forms can be mentioned, and they are often used to cover part or all of the field of vision. Specifically, they include those that project virtual reality (VR), those that extend real space by superimposing digital information on real space as the main body and making it appear (Augmented Reality (AR)), or those that combine real space and virtual reality to allow computer graphics (CG) and holograms to be touched or switched to a different angle, such as cross reality (XR), which is an advanced technology that combines the real world and the virtual world. The HMD referred to in the present invention can include such usage forms and display technologies without any restrictions. In such HMDs, the metal-clad laminate of the present invention is, for example, processed into thin wires to cover the entire surface of the glasses, or is incorporated into a cover for protecting the light guide plate that displays images, or into a microphone built into the cover.

(Transparent antenna)
The metal-clad laminate of the present invention can be suitably used as a substrate for a transparent antenna. Here, the transparent antenna can be used as a "glass antenna" that can be installed on a window glass inside a room or a car to turn the window into a base station, or a technology for attaching or embedding an antenna in a mobile display such as a smartphone (so-called antenna-on-display). In such a transparent antenna, the metal-clad laminate of the present invention is, for example, processed into a copper foil wiring width of 100 μm, processed into a substrate size of 1 cm × 5 cm, and incorporated into a window so that radio waves can reach it.

(Transparent heater)
The metal-clad laminate of the present invention can be suitably used as a substrate for flexible planar heating elements such as transparent heaters. For example, it can be used as a substrate for applications requiring heating, but where visibility may be impaired. For example, it is used as a heater for exerting anti-fogging, snow melting, and sensitivity improvement functions in window glass, cameras used mainly outdoors, such as observation cameras, surveillance cameras, and vehicle cameras, vehicle headlights, traffic lights, roadway guide lights, etc. In such transparent heaters, the metal-clad laminate of the present invention is incorporated, for example, in front of the camera lens of an autonomous vehicle to remove fogging.

(LED light strip)
The metal-clad laminate of the present invention can be suitably used as a substrate for an LED light strip. Here, the LED light strip is an LED light tape or ribbon-shaped material used as decorative lighting or as a replacement for a filament in a light bulb. In such an LED light strip, the metal-clad laminate of the present invention is incorporated into a lighting fixture in which, for example, an FPC is wired with a line and space of 200 μm/400 μm, fabricated into a tape shape with a diameter of 1 mm, and inserted into a light bulb.

The present invention will be explained in detail below based on examples, but the present invention is not limited to the scope of these examples. In the following examples, various measurements and evaluations are as follows, unless otherwise specified.

[Calculation of light transmittance and yellowness index (YI)]
The resin film (also referred to as an insulating resin layer, the same applies below) (50 mm×50 mm) was measured for light transmittance and yellowness index (YI) using a UV-3600 spectrophotometer manufactured by Shimadzu Corporation.
1) Light Transmittance According to JIS Z 8722, the light transmittances (T400, T430 and T450) for light having wavelengths of 400 nm, 430 nm and 450 nm were calculated.
2) YI
In accordance with JIS Z 8722, calculation was performed based on the calculation formula represented by the following formula (1).
YI = 100 × (1.2879X - 1.0592Z) / Y ... (1)
X, Y, and Z: Tristimulus values of the test piece (absolute value of difference in YI before and after UV irradiation)
The absolute value of the difference in YI before and after UV irradiation is calculated as the difference between the YI measured after UV irradiation under the UV irradiation conditions described below and the YI before UV irradiation.

[Reflectance and hue evaluation]
Each of the single-sided metal-clad laminates of the Examples and Comparative Examples, and each of the copper foils used in the manufacture thereof, was attached to a glass plate (12.5 cm square) so that the mirror side of the copper foil was in contact with the glass plate. The resin side or the copper foil coated side of the substrate was irradiated with light using a Hitachi High-Technologies Corporation UH-4100, and the reflectance and hue (L ^* , a ^* , b ^* ) in the wavelength range of 380 to 780 nm were measured. The light source used was a C light source (2° field of view). The reflectance at 580 nm was used as the reflectance result.

[Measurement of coefficient of thermal expansion (CTE)]
A resin film (3 mm x 15 mm) was heated from 30°C to 280°C at a heating rate of 10°C/min while applying a load of 5.0 g in a thermomechanical analysis (TMA) device, and then cooled from 250°C to 100°C. The thermal expansion coefficient was measured from the elongation (linear expansion) of the resin film during cooling.

[Calculation of total light transmittance (T.T.) and HAZE (turbidity)]
The total light transmittance (TT) and haze (turbidity) of the resin film (50 mm x 50 mm) were measured in accordance with JIS K 7136 using a HAZE METER NDH500 manufactured by Nippon Denshoku Industries Co., Ltd.
(Absolute value of difference in haze before and after UV irradiation)
The absolute value of the difference in haze before and after UV irradiation is calculated as the difference between the haze measured after UV irradiation under the UV irradiation conditions described below and the haze before UV irradiation.

[UV irradiation conditions]
Using a DEEP UV irradiation device VUM-3073, irradiation was performed continuously for 4 hours at a wavelength of 200-350 nm with an output of 20 J/cm ² per hour.

[Viscosity measurement]
The viscosity of the polyamic acid solution obtained in the synthesis example was measured at 25° C. using a cone-plate viscometer equipped with a thermostatic water bath (manufactured by Tokimec Co., Ltd.).

[Measurement of glass transition temperature (Tg)]
A resin film (10 mm x 22.6 mm) was heated from 20°C to 400°C at a rate of 5°C/min using a dynamic thermomechanical analyzer, and the dynamic viscoelasticity was measured to determine the glass transition temperature (Tan δ maximum value: °C).

[Peel strength measurement]
Using a tension tester, the resin side of test samples having circuits with widths of 1 mm, 500 μm, 250 μm and 100 μm obtained from the laminate was fixed to an aluminum plate with double-sided tape, and the copper was peeled off in a 180° direction at a speed of 50 mm/min to determine the peel strength.

[Measurement of copper foil surface roughness]
The sample was cut into a size of about 10 mm square, fixed to a sample stage with double-sided tape, irradiated with soft X-rays, and the static electricity on the copper foil surface was removed, and then the surface roughness was measured. The arithmetic mean roughness Ra and maximum height Rz of the copper foil surface were measured using a scanning probe microscope (AFM, manufactured by Bruker AXS, product name: Dimension Icon type SPM) under the following measurement conditions. The measurement conditions are as follows.
Measurement mode: tapping mode Measurement area: 1 μm x 1 μm
Scan speed: 1Hz
Probe: Olympus AC160 Analysis software: NanoScope Analysis

[Measurement of solder heat resistance]
A commercially available photoresist film was laminated onto the metal layer side of each of the copper-clad laminates obtained in the Examples and Comparative Examples, and exposed to light (365 nm, exposure dose of about 500 J/ ^m2 ) using a predetermined pattern forming mask to harden and form a resist layer on the metal layer side in a circular pattern with diameters of 20 mm, 15 mm, 10 mm, 5 mm, 3 mm, 1 mm, and 0.5 mm.
Next, the hardened resist areas were developed (developing solution was a 1% NaOH aqueous solution), and the copper foil layer unnecessary for forming the specified pattern was etched away using an aqueous ferric chloride solution. Furthermore, the hardened resist layer was peeled off and removed with an alkaline solution to obtain samples with patterns formed thereon for evaluating heat resistance corresponding to lead-free solder (laminates with circular patterns with a diameter of 1 mm formed on the metal layer side of each metal-clad laminate).
The samples were immersed in molten solder baths of different temperatures for 10 seconds, and the presence or absence of deformation or blistering in the copper foil layer was observed. The maximum temperature of the solder bath at which the copper foil layer did not deform, blister, or peel off was determined as the solder heat resistance temperature.

The abbreviations used in the examples represent the following compounds.
APB: 1,3-bis(3-aminophenoxy)benzene TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl BAPS: bis[4-(aminophenoxy)phenyl]sulfone BAFL: 9,9-bis(4-aminophenyl)fluorene PMDA: pyromellitic dianhydride 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride BPDA: 3,3',4,4'-biphenyl tetracarboxylic dianhydride ODPA: 4,4'-oxydiphthalic dianhydride CBDA: 1,2,3,4-cyclobutane tetracarboxylic dianhydride DMAc: N,N-dimethylacetamide

Synthesis Example 1
To synthesize polyamic acid solution A, a DMAc solvent was added to a 200 ml separable flask under a nitrogen gas flow to a solids concentration of 15 wt%, and the diamine component and acid anhydride component shown in Table 1 were added and dissolved while stirring at room temperature. The solution was then stirred at room temperature for 8 hours to carry out a polymerization reaction, preparing a viscous polyamic acid solution A. The solution was then diluted to 12 wt% with the DMAc solvent. The viscosity after dilution was 3000 cP.

Synthesis Example 2
To synthesize polyamic acid solution B, a solvent, DMAc, was added to a 200 ml separable flask under a nitrogen gas flow so as to obtain a solid content concentration shown in Table 1, and the diamine component and acid anhydride component shown in Table 1 were dissolved by heating at 40° C. for 1 hour while stirring. The solution was then stirred at room temperature for 2 days to carry out a polymerization reaction, and a viscous polyamic acid solution B was prepared. The viscosity was 21,000 cP.

Synthesis Examples 3 to 6
Polyamic acid solutions C to F were prepared by changing the monomer types as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. Viscous solutions C to F of polyamic acid were prepared. The viscosities are shown in Table 1.

The types of copper foil used as the metal layer in this invention are shown in Table 2.

Example 1
On the copper foil I (electrolytic copper foil, manufactured by Mitsui Mining & Smelting Co., Ltd., trade name: TQ-M4-VSP, thickness: 12 μm), a solution of polyamic acid solution A was uniformly applied so that the thickness after curing was 2 μm, and then the solution was stepwise heated and dried in a temperature range up to 120 ° C. to remove the solvent. Next, a solution of polyamic acid solution B was uniformly applied thereon so that the thickness after curing was 23 μm, and then the solution was stepwise heated and dried in a temperature range up to 120 ° C. to remove the solvent. Furthermore, a solution of polyamic acid solution A was uniformly applied thereon so that the thickness after curing was 2 μm, and then the solution was stepwise heated and dried in a temperature range up to 120 ° C. to remove the solvent. In this way, after forming three polyamic acid layers, stepwise heat treatment was performed from 125 ° C. to 360 ° C. to complete imidization, and an insulating resin layer having a thickness of 27 μm consisting of polyimide layer A / polyimide layer B / polyimide layer A was formed, and a metal-clad laminate 1A (in the table, it is written as "metal laminate") was prepared.
The copper foil of the obtained single-sided metal-clad laminate 1A was etched away using an aqueous solution of ferric chloride to prepare a polyimide film 1a. The haze, T.T., YI, CTE, and Tg of the polyimide film 1a were measured. The results of these measurements are shown in Table 3.
The obtained film was irradiated with UV for 4 hours under the above UV irradiation conditions, and the haze and the yellow index (YI) of the film after UV irradiation were measured, and the difference between the haze and the yellow index (YI) before UV irradiation was calculated to calculate the rate of change. The results are shown in Table 3.
The reflectance and hue (L ^* , a ^* , b ^* ) of the obtained single-sided metal-clad laminate 1A were measured from the resin film side. The peel strength of the polyamic acid-coated surface of the copper foil I when the wiring was processed to 1 mm, 500 μm, 250 μm, and 100 μm was 0.5 to 0.6 kN/m as shown in Table 3. The solder heat resistance was 250° C. or higher.

Examples 2 to 4 and 6
Single-sided metal-clad laminates 2A to 4A and 6A were prepared, and polyimide films 2a to 4a and 6a were prepared in the same manner as in Example 1, except that the copper foil and polyamic acid solution shown in Table 3 were used. For the polyimide films 2a to 4a and 6a, HAZE, T.T., YI, CTE and Tg were measured, and the absolute values of the differences in YI and HAZE before and after UV irradiation were measured. In addition, for the single-sided metal-clad laminates 2A to 4A and 6A, reflectance, hue, peel strength and solder heat resistance were measured in the same manner as in Example 1.

Example 5
Two sheets of copper foil II (electrolytic copper foil, manufactured by Fukuda Metal Foil and Powder Co., Ltd., product name: CF-T9DA-SV, thickness: 17 μm) were cut to 15 cm x 15 cm, and the 4a film of Example 4 was sandwiched between them with the coated surfaces facing each other, and heat-pressed at 320 ° C./5 min with a press to prepare a double-sided metal-clad laminate. Only the copper foil on one side of the prepared double-sided metal-clad laminate was etched and removed using an aqueous ferric chloride solution to obtain a single-sided metal-clad laminate 5A. The copper foil of the obtained single-sided metal-clad laminate 5A was etched and removed using an aqueous ferric chloride solution to prepare a polyimide film 5a. The single-sided metal-clad laminate 5A and polyimide film 5a were used to evaluate the same items as in the above examples. Table 3 shows the evaluation results.

Comparative Example 1
Two sheets of copper foil II were cut to 15 cm x 15 cm, placed on both sides of a polyester film of the same size (manufactured by Toray Industries, Inc., product name: Lumirror 25S28L, thickness: 25 μm), sandwiched, and heat-pressed with a press to prepare a double-sided metal-clad laminate. Only the copper foil on one side of the prepared double-sided metal-clad laminate was etched and removed using an aqueous ferric chloride solution to obtain a single-sided metal-clad laminate 7A. The obtained single-sided metal-clad laminate 7A was etched and removed using an aqueous ferric chloride solution to prepare a resin film 7a. The single-sided metal-clad laminate 7A and polyimide film 7a were used to evaluate the same items as in the above examples. Table 4 shows the evaluation results.

Comparative Examples 2 to 3
Single-sided metal-clad laminates 8A to 9A and polyimide films 8a to 9a were prepared in the same manner as in Example 1, except that the copper foil and polyamic acid solution shown in Table 4 were used. These polyimide films 8a to 9a and single-sided metal-clad laminates 8A to 9A were evaluated in the same manner as in the previous Examples. The measurement results are shown in Table 4.

Claims

A metal-clad laminate having a metal layer on one or both sides of an insulating resin layer,
the insulating resin layer has a thickness in the range of 10 μm to 100 μm, a total light transmittance of 70% or more, a haze of 50% or less, and an absolute value of a difference in yellowness index YI before and after ultraviolet irradiation of 30 or less;
a reflectance at 580 nm of a surface of the metal layer in contact with the insulating resin layer is 50% or less when measured through the insulating resin layer;
A metal-clad laminate characterized in that it is used in applications in which the wiring width of the metal layer is processed to 500 μm or less.
The metal-clad laminate according to claim 1, characterized in that the absolute value of the difference in haze between before and after ultraviolet irradiation of the insulating resin layer is 10% or less.
The metal-clad laminate according to claim 1 or 2, characterized in that it has a solder heat resistance of 200°C or higher.
The metal-clad laminate according to claim 1 or 2, characterized in that when the metal layer is processed to a width of 100 μm, the 180° peel strength between the processed metal layer and the insulating resin layer is 0.3 kN/m or more.
3. The metal-clad laminate according to claim 1, wherein the maximum height Rz of the surface of the metal layer in contact with the insulating resin layer is 300 nm or less, and the a * of the L * a * b * color system is 20 or less.
The metal-clad laminate according to claim 1 or 2, characterized in that the application in which the wiring width is processed to 500 μm or less is a transparent LED vision application.
The metal-clad laminate according to claim 1 or 2, characterized in that the application in which the wiring width is processed to 500 μm or less is for use in a head-mounted display.
3. The metal-clad laminate according to claim 1, wherein the application in which the wiring width is processed to 500 μm or less is for a transparent antenna.