Polyimide film, metal-clad laminate and circuit board

Abstract

To provide a polyimide film having excellent flame retardancy while having excellent optical properties and appearance such as transparency and to provide a metal-clad laminate and a circuit board using the same.SOLUTION: There is provided a polyimide film having a plurality of polyimide layers, which satisfies the following conditions I and II: I) the thickness (T) is in the range of more than 10 μm and 50 μm or less; II) the total light transmittance is 70% or more, wherein the plurality of polyimide layers each have a first polyimide layer and a second polyimide layer on the outermost layer, the thickness (t1) of the first polyimide layer and the thickness (t2) of the second polyimide layer are both more than 2 μm, the ratio of the total thickness of t1 and t2 to T {(t1+t2) / T} is in the range of more than 20% and 60% or less, the first polyimide layer and the second polyimide layer are composed of a polyimide containing a tetracarboxylic acid residue and a diamine residue and the polyimide has an organic group represented by the general formula (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide film, a metal-clad laminate, and a circuit board that are useful as materials for electronic components, etc.

[0002] In recent years, with the advancement of miniaturization, weight reduction, and space-saving of electronic devices, there has been an increasing demand for flexible printed circuits (FPCs) that are thin, lightweight, flexible, and highly durable even when repeatedly bent. Because FPCs allow for three-dimensional, high-density packaging even in limited spaces, their applications are expanding to include wiring for moving parts in electronic devices such as hard disk drives (HDDs), DVD players, and smartphones, as well as for cables, connectors, and other components. Most FPCs are manufactured by wiring (patterning) the metal layer of a metal-clad laminate, which is made by laminating a metal layer using a metal foil or other substrate with an insulating resin substrate (insulating resin layer).

[0003] FPCs, especially those with excellent transparency, have characteristics such as being thin, lightweight, bendable, and unbreakable, and therefore in recent years, demand has been expanding for them as transparent antennas, for example, glass antennas formed on the surface of window glass to turn the window into a base station, for technology to embed antennas in displays for mobile applications, and for substrate applications in fields where the installation of large LED transparent displays, including electric boards and LED vision screens, is expected. For example, a resin film having multiple polyimide layers suitable for transparent FPCs, a metal clad laminate using the same, and a method for manufacturing the same have been proposed (Patent Document 1).

[0004] In recent years, there has been growing concern about the safety of such transparent FPCs and the applications to which they are applied, and excellent flame retardancy is also being required for actual use. However, when forming the resin film, for example, blending other components such as a flame retardant into polyimide may affect the optical properties and appearance of the resin film, such as transparency, and it is difficult to achieve both flame retardancy and optical properties and appearance such as transparency, and it cannot be said that sufficient consideration has been given to this approach.

[0005] In the invention described in Patent Document 1, the ratio of the thickness of the outermost polyimide layer to the thickness of the polyimide layers used in the resin film is small, which makes it easy for the flame retardancy to vary and further raises concerns about the influence on properties such as adhesiveness and heat resistance, leaving room for improvement. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 262450 [Patent Document 2] Japanese Patent Application Publication No. 2024-051579 Summary of the Invention [Problem to be solved by the invention]

[0007] As a result of intensive research into these problems, the inventors of the present application have found that, in a polyimide film having a plurality of polyimide layers, a polyimide film having excellent flame retardancy while also having good optical properties such as transparency and good appearance can be obtained by optimizing the thickness and thickness ratio of the outermost polyimide layer among the plurality of polyimide layers, optimizing a predetermined organic group and a linking group in the organic group contained in the outermost polyimide layer, and preferably optimizing a value obtained from a calculation formula based on the predetermined organic group and linking group as a parameter indicating flame retardancy, thereby completing the present invention.

[0008] Therefore, an object of the present invention is to provide a polyimide film that has excellent optical properties such as transparency and appearance, as well as excellent flame retardancy, and a metal-clad laminate and a circuit board using the polyimide film. Another object of the present invention is to provide a method for optimizing the value obtained from the calculation formula based on the predetermined organic group and linking group to a suitable range as a parameter indicating flame retardancy in the development of polyimide films and the like having such excellent properties.

[0009] In the prior art, a resin laminate has been proposed in which a first insulating resin layer, an adhesive layer, and a second insulating resin layer are laminated in this order in order to achieve both excellent dielectric properties and flame retardancy (Patent Document 2). However, this laminate is characterized by the use of a specific dimer acid type diamine in the adhesive layer and by controlling the amount of aliphatic skeleton derived from the dimer acid type diamine, and is not intended for application to transparent FPCs, and does not achieve the problems and objectives of the present invention described above. [Means for solving the problem]

[0010] That is, the gist of the present invention is as follows. [1] A polyimide film having a plurality of polyimide layers, Conditions I and II below; I) The thickness (T) is in the range of more than 10 μm and not more than 50 μm; II) Total light transmittance is 70% or more; Fulfilling the plurality of polyimide layers each have a first polyimide layer and a second polyimide layer as their outermost layers, the thickness (t1) of the first polyimide layer and the thickness (t2) of the second polyimide layer each exceed 2 μm, and the ratio of the total thickness of (t1) and (t2) to the thickness (T) [(t1+t2) / T] is in the range of more than 20% but not more than 60%, The first polyimide layer and the second polyimide layer are made of a polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component, and the polyimide is represented by the following general formula (1): [ka] [In general formula (1), the linking group X independently represents a divalent group selected from -O-, -S-, -SO2-, or -C(CF3)2-.] A polyimide film characterized by having an organic group represented by the formula: [2] The polyimide film according to [1], wherein a parameter B1 indicating the flame retardancy of the polyimide contained in the first polyimide layer, which is represented by the following formula (i), and a parameter B2 indicating the flame retardancy of the polyimide contained in the second polyimide layer, which is represented by the following formula (ii), are both 0.8 or more. B1=a1×a1' / b1 (i) B2=a2×a2' / b2 (ii) (where a1, a1', b1, a2, a2' and b2 are a1: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the first polyimide layer, a1': the number of linking groups X in the polyimide contained in the first polyimide layer, b1: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the first polyimide layer are derived and the molecular weights of all diamine components from which all diamine residues are derived, a2: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the second polyimide layer, a2': the number of linking groups X in the polyimide contained in the second polyimide layer, b2: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the second polyimide layer are derived and the molecular weights of all diamine components from which all diamine residues are derived, means.) [3] The polyimide film according to [1] or [2], characterized in that a parameter C indicating flame retardancy, represented by the following formula (iii), is 0.4 or more. C=(B1+B2)×(t1+t2) / T ···(iii) (wherein B1, B2, t1, t2 and T are defined as above.) [4] A third polyimide layer is provided between the first polyimide layer and the second polyimide layer, The polyimide film according to [3], characterized in that the parameter D, which indicates flame retardancy and is represented by the following formula (iv), of the polyimide contained in the third polyimide layer is 0.12 or more, or the ratio of C to D (C / D) is within the range of 3.0 or more and 10 or less.

number

[0011] According to the present invention, it is possible to provide a polyimide film that has excellent optical properties such as transparency and appearance, as well as excellent flame retardancy, and a metal-clad laminate and a circuit board using the same. Furthermore, the polyimide film of the present invention has excellent dimensional stability, flexibility, and adhesion to metal layers, and is therefore particularly suitable for use as an insulating material for producing electronic components such as FPCs, particularly transparent FPCs that require colorless transparency due to the mounting of semiconductor elements. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described.

[0013] 1. Polyimide film A polyimide film according to one embodiment of the present invention is a polyimide film having a plurality of polyimide layers, Conditions I and II below; I) The thickness (T) is in the range of more than 10 μm and not more than 50 μm; II) Total light transmittance is 70% or more; Fulfilling the plurality of polyimide layers each have a first polyimide layer and a second polyimide layer as their outermost layers, the thickness (t1) of the first polyimide layer and the thickness (t2) of the second polyimide layer each exceed 2 μm, and the ratio of the total thickness of (t1) and (t2) to the thickness (T) [(t1+t2) / T] is in the range of more than 20% but not more than 60%, The first polyimide layer and the second polyimide layer are made of a polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component, and the polyimide is represented by the following general formula (1): [ka] [In general formula (1), the linking group X independently represents a divalent group selected from -O-, -S-, -SO2-, or -C(CF3)2-.] The compound has an organic group represented by the formula:

[0014] [P1, P2 and P3] The polyimide film according to the present embodiment is a multilayer polyimide film, and must have a first polyimide layer (P1) and a second polyimide layer (P2) as outermost layers. P1 and P2 may be identical polyimide layers (e.g., in terms of composition, thickness, etc.). The polyimide film is not limited to any particular polyimide film, as long as it has P1 and P2 as outermost layers. It may also have one or more additional polyimide layers on the inner side of P1 and P2, or an additional layer of the same composition as P1 and P2 on the inner side. For example, a preferred embodiment has a third polyimide layer (P3) (described below) formed between P1 and P2 for the purposes of improving transparency, heat resistance, dimensional stability, mechanical properties, film formability, and other properties. That is, in a more preferred embodiment, the polyimide film according to the present embodiment comprises a polyimide layer P1 that contacts a metal layer used in producing a metal-clad laminate or a circuit board, as described below; a polyimide layer P2 that forms a polyimide surface as the outermost layer on the opposite side from the metal layer; and a polyimide layer P3 consisting of one or more layers formed between P1 and P2.

[0015] Here, although not limited thereto, examples of possible lamination pattern embodiments include the following: As described above, P1 and P2 may be the same polyimide layer (composition, thickness, etc.). ·Metal layer / P1 / P3 / P2 ·Metal layer / P1 / P3 / P1(orP2) / P3 / P2

[0016] As described above, the polyimide film of the present embodiment satisfies the conditions I and II; I) The thickness (T) is in the range of more than 10 μm and not more than 50 μm; II) Total light transmittance is 70% or more; It satisfies the following.

[0017] [Thickness (T)] Here, the thickness (T) of the polyimide film, which is condition I, must be within the above range from the viewpoints of processability, transportability, and supportability of the film itself during processing, but can be appropriately selected depending on the intended use. If T is less than the above lower limit, electrical insulation may not be ensured, and handling may be impaired during the manufacturing process due to reduced handleability. On the other hand, if T exceeds the above upper limit, the dimensional change before and after etching increases, and the yellow to yellowish-brown coloring becomes stronger, tending to reduce the visibility of the insulating resin layer. Therefore, the preferred range of T is greater than 10 μm and not more than 45 μm, more preferably greater than 10 μm and not more than 40 μm, even more preferably greater than 10 μm and not more than 35 μm, and even more preferably greater than 10 μm and not more than 30 μm.

[0018] [Total light transmittance] Furthermore, the total light transmittance, which is the condition II, must be within the above range, since it is preferable to have suitable light transmittance for applications such as FPCs, which require high transparency and visibility. It is preferable that the transparency is as close as possible to the total light transmittance, and the total light transmittance is preferably 75% or more, and more preferably 80% or more.

[0019] [Thickness and thickness ratio of P1 and P2] Furthermore, as described above, in the polyimide film of the present embodiment, the thickness (t1) of P1 and the thickness (t2) of P2 both exceed 2 μm. By making each of the thicknesses t1 and t2 exceed 2 μm, the dimensional stability, high transparency, and colorlessness of the entire polyimide film can be maintained, adhesion to the metal layer described below can be improved, and flame retardancy can be achieved. Furthermore, by setting the thickness within this range, sufficient adhesion can be ensured even when a metal layer is formed on the outermost polyimide-forming surface opposite the metal layer. Furthermore, this also has the effect of suppressing appearance defects such as streaks during the manufacturing process. The lower limit of each of the thicknesses t1 and t2 is preferably 2.5 μm or more, more preferably 3 μm or more. Meanwhile, the upper limit of t1 and t2 can be appropriately set taking into account the thickness T and the thickness ratio described below, but is typically preferably 10 μm or less.

[0020] Furthermore, as described above, in the polyimide film of the present embodiment, the ratio (t1 + t2) / T, which is the ratio of the total thickness of t1 and t2 to the thickness T, is in the range of more than 20% and not more than 60%. Having the ratio of t1 and t2 in the above range is preferable because, as described above, the dimensional stability, high transparency, and colorlessness of the entire polyimide film can be maintained, adhesion to the metal layer described below can be improved, and flame retardancy can be achieved. A preferred value for (t1 + t2) / T is more than 20% and not more than 55%, more preferably more than 20% and not more than 50%. In this regard, when a polyimide layer other than P1 and P2 is included, particularly when a polyimide layer (P3) described below is included, the ratio (t3 / T) of the thickness t3 of P3 to the thickness T of the polyimide film is preferably 40% or more and less than 80%, more preferably 45% or more and less than 80%, and even more preferably 50% or more and less than 80%.

[0021] [Organic group represented by formula (1) and composition of P1 and P2] (Organic group represented by formula (1)) In the polyimide film of the present embodiment, P1 and P2 are polyimides containing tetracarboxylic acid residues derived from a tetracarboxylic acid anhydride component and diamine residues derived from a diamine component, and the polyimide has an organic group represented by the general formula (1). The organic group has two benzene rings and a divalent X group connecting them, where the X group is a group containing an oxygen atom, sulfur atom, or fluorine atom, as described above. Organic groups with such structures have sufficient flexibility to prevent electron cloud overlap and suppress charge transfer (CT) transitions that cause coloration. They also exhibit good adhesion to the substrate in terms of molecular chain entanglement and chemical bonding. In addition, because they are adjacent to benzene rings, which are effective in exhibiting flame retardancy, and because they generate non-flammable gases upon combustion, including them in the polyimide structure, polyimide films can be obtained that have high transparency, excellent adhesion to the substrate, and excellent flame retardancy.

[0022] (Composition of Polyimide Layers P1 and P2) The tetracarboxylic acid anhydride component for obtaining P1 and P2 containing such an organic group represented by formula (1) is not limited, and known components can be used depending on the linking group X. Examples include 4,4'-oxydiphthalic anhydride (ODPA), 3,4'-oxydiphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride, 2,2',3,3'-diphenylsulfonetetracarboxylic acid dianhydride, 2,3,3',4'-diphenylsulfonetetracarboxylic acid dianhydride, and 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride.

[0023] Furthermore, the diamine component for obtaining P1 and P2 containing the organic group represented by formula (1) is not limited, and known components can be used depending on the linking group X. Examples include 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 1,3-bis(4-aminophenoxysulfide)benzene, 4,4'-bis(4-aminophenoxy)diphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and the like.

[0024] In forming P1 and P2, the tetracarboxylic acid anhydride component having an organic group represented by formula (1) is preferably used in an amount of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, based on the total tetracarboxylic acid anhydride components. Similarly, in forming P1 and P2, the diamine component having an organic group represented by formula (1) is preferably used in an amount of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more, based on the total diamine components. The type and amount (proportion) of these components having an organic group can be adjusted depending on the flame retardancy parameters described below.

[0025] In addition, in forming P1 and P2, other than the tetracarboxylic acid anhydride component having an organic group represented by formula (1) exemplified above, any other tetracarboxylic acid anhydride component that can generally be used in the synthesis of polyimides can be used, as long as it does not impair the effects and objects of the present invention. When using other tetracarboxylic acid anhydride components, they are used in an amount of preferably 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less of the total tetracarboxylic acid anhydride components. The same applies to the diamine component, and as long as the effects and objects of the present invention are not impaired, any other diamine component than the diamine component having an organic group represented by formula (1) exemplified above can be selected and used from all other diamine components that can generally be used in the synthesis of polyimides. When other diamine components are used, they are preferably used in an amount of 50 mol % or less, more preferably 30 mol % or less, and even more preferably 10 mol % or less of the total diamine components.

[0026] The polyimide constituting P1 and P2 having the above-described structure and composition is preferably a thermoplastic polyimide, which improves the adhesiveness of the polyimide film and makes it suitable for use as an adhesive layer with a metal layer. The thermoplastic polyimide constitutes a polyimide with high thermal expansion. Here, a high thermal expansion polyimide layer refers to a polyimide with a coefficient of thermal expansion (CTE) preferably in the range of 35 ppm / K or more and 80 ppm / K or less. By appropriately changing the combination of raw materials used, thickness, and drying and curing conditions, a polyimide with the desired CTE can be obtained.

[0027] Here, the thermoplastic polyimide generally refers to a polyimide whose glass transition temperature (Tg) can be clearly confirmed. In this embodiment, the storage modulus at 30°C measured by DMA is 1.0 × 10 9 Pa, and the storage modulus at 350°C is 1.0 × 10 8 Polyimides with a modulus of less than 1 Pa are also referred to as polyimides.

[0028] [Parameters indicating flame retardancy] Here, the content of the organic group represented by the formula (1) in the polyimide layers P1 and P2 is not limited as long as it does not impair the effects and objects of the present invention. However, in a preferred embodiment of P1 and P2, parameter B1, which indicates the flame retardancy of P1 represented by the following formula (i), and parameter B2, which indicates the flame retardancy of P2 represented by the following formula (ii), are both 0.8 or more. B1=a1×a1' / b1 (i) B2=a2×a2' / b2 (ii)

[0029] In the formulas (i) and (ii), a1, a1', b1, a2, a2', and b2 are defined as follows: a1: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the first polyimide layer (P1). a1': the number of linking groups X in the polyimide contained in the first polyimide layer (P1). b1: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues are derived and all diamine components from which all diamine residues are derived, contained in the first polyimide layer (P1). a2: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the second polyimide layer (P2). a2': the number of linking groups X in the polyimide contained in the second polyimide layer (P2). b2: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the second polyimide layer (P2) are derived and the molecular weights of all diamine components from which all diamine residues are derived.

[0030] In formulas (i) and (ii), the denominators "b1" and "b2" refer to the sum of the molecular weights of all tetracarboxylic anhydride components and all diamine components used to form the P1 and P2 layers, respectively. The sum of the molecular weights of all the components (monomers) used is used as appropriate. Meanwhile, the numerators "a1 × a1'" and "a2 × a2'" can be calculated as follows. That is, for a1 and a2, the molecular weight of only the portion of all tetracarboxylic anhydride components and all diamine components used that corresponds to the organic group represented by formula (1) is used, and the value obtained by multiplying this by the number of linking groups X is used. For example, when the linking group X is -O-, -S-, -SO2-, or -C(CF3)2-, examples of the organic group represented by formula (1) and its molecular weight (molecular weight) are shown below in A to D.

[0031] [ka]

[0032] The tetracarboxylic anhydride component or diamine component used may have multiple organic groups represented by formula (1). In that case, the molecular weight of each organic group is counted for each linking group X, and the resulting value is calculated by multiplying these values. In other words, as shown in the example of E below, when a single diamine component has two adjacent organic groups as shown in the dashed line, the organic group has two of the "A" structures, i.e., there are two cases where the linking group X is -O-. In this case, "a1 x a1'" or "a2 x a2'" is calculated as 170.21 x 2. In other words, since the molecular weight of the organic group is counted for each linking group X, the molecular weight of the central benzene ring is counted twice. Similarly, in the case of the example F below, where there are three adjacent organic groups as surrounded by dashed lines, there are two of the "A" structures and one of the "C" structures as organic groups, so the "A" structure is calculated as 170.21 x 2 and the "C" structure is calculated as 218.27 x 1, and the sum of these is used for "a1 x a1'" or "a2 x a2'". In other words, the molecular weights of the two central benzene rings are each counted twice.

[0033] [ka]

[0034] The B1 and B2 values ​​in formulas (i) and (ii) calculated in this manner represent the ratio of the molecular weight of all the organic groups, including the linking group X, to the sum of the molecular weights of all the tetracarboxylic acid anhydride components and all the diamine components in each of the polyimide layers P1 and P2. This corresponds to defining the mass ratio of the organic groups per mole (molecule) of polyimide in each of the polyimide layers P1 and P2. In other words, the higher the mass ratio of the organic groups represented by formula (1), the greater the presence of the organic groups in each layer. Therefore, by adjusting B1 and B2 to be higher, a polyimide film that can achieve the objectives and problems of the present invention can be obtained. In particular, satisfying these B1 and B2 values ​​in the outermost layers P1 and P2 of the polyimide film of the present invention allows for the production of a polyimide film that exhibits excellent adhesion to metal layers, flexibility, and excellent optical properties such as transparency, as well as excellent appearance and flame retardancy, making this a preferred embodiment.

[0035] In the polyimide film according to the present embodiment, it is preferable to adjust the type and blending ratio of the tetracarboxylic anhydride component having an organic group represented by formula (1) and / or the diamine component so that P1 and P2 satisfy the above-mentioned B1 and B2 in all layers. It is a more preferable embodiment to adjust both the tetracarboxylic anhydride component having an organic group represented by formula (1) and the diamine component having an organic group represented by formula (1). The preferred ranges for B1 and B2 are 0.85 or more, more preferably 0.90 or more, and even more preferably 0.95 or more. While there are no upper limits for B1 and B2, taking into account the tetracarboxylic anhydride component and diamine component typically used and from the viewpoint of adjusting the balance between flame retardancy and adhesion, they are preferably 1.5 or less, and more preferably 1.2 or less. Note that in the polyimide film according to the present embodiment, either B1 or B2 may satisfy the above range, but it is a more preferable embodiment that both B1 and B2 satisfy the above range.

[0036] In addition, in a preferred embodiment of the polyimide film of the present invention, with respect to the above-mentioned B1 and B2, the parameter C, which indicates flame retardancy and is represented by the following formula (iii), is 0.4 or more. C=(B1+B2)×(t1+t2) / T ···(iii)

[0037] That is, in the polyimide film of the present invention, in addition to satisfying the parameters B1 and B2 indicating the flame retardancy of P1 and P2, a more preferred embodiment for providing excellent flame retardancy is to adjust the parameter C, which is the parameter when considering the thickness ratio [(t1 + t2) / T] of the P1 and P2 layer thicknesses for B1 and B2. By adjusting C to satisfy this range, the amount of organic groups represented by formula (1) present in P1 and P2 can be more accurately represented even when considering the entire polyimide film, and the amount of these organic groups present is increased, resulting in a polyimide film with excellent flame retardancy. That is, not only can the amount of organic groups represented by formula (1) be increased to increase B1 and B2, but the thickness ratio of P1 and P2 relative to the total thickness of these B1 and B2 layers can also be increased to increase the amount of these organic groups present, resulting in a polyimide film with excellent flame retardancy.

[0038] Here, C represented by formula (iii) is more preferably 0.45 or more, even more preferably 0.47 or more, and even more preferably 0.49 or more. On the other hand, although there is no upper limit for C, taking into consideration the thickness ratio of P1 and P2, etc., from the viewpoint of dimensional stability and heat resistance, it is preferably 1.8 or less, more preferably 1.5 or less.

[0039] [Polyimide layers other than P1 and P2] In a preferred embodiment, the polyimide film of the present invention has a third polyimide layer (P3) between P1 and P2 in addition to the outermost layers P1 and P2, for the purpose of improving properties such as transparency, heat resistance, dimensional stability, mechanical properties, and film formability. P3 may be a multi-layer structure. In this embodiment, P3 preferably has a parameter D, which indicates flame retardancy and is represented by the following formula (iv), of 0.12 or more. That is, in a preferred embodiment, P3 uses a polyimide having an organic group represented by formula (1).

[0040]

number

[0041] Here, in formula (iv), the polyimide layer constituting P3 consists of n layers (where n is an integer of 1 or more), and a k, a'k, bk, and t3 are defined as follows: k is an integer of 1 or more and n or less, and indicates any layer (the kth layer) in P3. ak: molecular weight of the organic group represented by formula (1) in the polyimide contained in the kth layer. a'k: the number of linking groups X in the polyimide contained in the kth layer. bk: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the kth layer are derived and the molecular weights of all diamine components from which all diamine residues are derived. t3: Thickness of the third polyimide layer (P3) [unit: μm].

[0042] Here, D in formula (iv) is synonymous with C in formula (iii) and represents a parameter that indicates flame retardancy taking into account the thickness ratio. D is calculated by multiplying the sum of the parameters for each kth layer (from the first to nth layer) by the thickness ratio (t3 / T) of P3, where P3 is composed of one or more polyimide layers. This parameter represents the proportion of the overall flame retardancy parameter of P3 in the entire polyimide film, and indicates the proportion of the organic group represented by formula (1) present in P3 in the entire polyimide film. A larger value of D indicates a greater degree of the organic group present, improving the flame retardancy of P3 throughout the entire polyimide film. This allows for the production of a polyimide film with excellent flame retardancy, making this a more preferred embodiment of the polyimide film of the present invention. The definition of the organic group represented by formula (1) and the method for determining the molecular weight are as described above. The upper limit of n can be adjusted within the scope of the present invention. However, in consideration of the desirable properties required for P3, n is typically preferably 5 or less, and more preferably 3 or less.

[0043] Here, D represented by formula (iv) is more preferably 0.15 or more, even more preferably 0.20 or more, and even more preferably 0.23 or more. On the other hand, the upper limit of D is not limited and can be appropriately selected depending on the thickness ratio (t3 / T) taking into consideration the dimensional stability and heat resistance required for P3, and the proportion of preferred components related to dimensional stability and heat resistance, such as PMDA used in the examples, but is preferably 0.50 or less, more preferably 0.40 or less, even more preferably 0.30 or less, and even more preferably 0.25 or less.

[0044] In a more preferred embodiment, instead of satisfying the range of D, the polyimide film according to the present embodiment has a ratio (C / D) of 3.0 or more to 10 or less of C, which is a parameter indicating flame retardancy for P1 and P2, to D, which is a parameter indicating flame retardancy for P3. By ensuring that the ratio (C / D) falls within the above range, the parameter indicating flame retardancy for P1 and P2 is three times or more the parameter indicating flame retardancy for P3, thereby demonstrating flame retardancy and reducing variation in flame retardancy between samples. On the other hand, if the ratio is too large, properties other than flame retardancy (e.g., heat resistance and high dimensional stability) tend to deteriorate, so the above range is necessary to achieve both flame retardancy and other properties.

[0045] P3 can also be selected from all tetracarboxylic acid anhydride components that can generally be used in the synthesis of polyimides, even if they are not tetracarboxylic acid anhydride components having an organic group represented by formula (1) as exemplified above, as long as the effects and objects of the present invention are not impaired. The same applies to the diamine component; as long as it does not impair the effects and objects of the present invention, it can be selected from all diamine components that can generally be used in the synthesis of polyimides, even if they are not diamine components having an organic group represented by formula (1) as exemplified above.

[0046] As described above, in a preferred embodiment in which P3 is provided between P1 and P2, P3 is preferably a non-thermoplastic polyimide for the purposes of heat resistance, dimensional stability, etc. Non-thermoplastic polyimides constitute polyimides with low thermal expansion, and refer to polyimides with a CTE preferably in the range of 1 ppm / K or more and 25 ppm / K or less.

[0047] Here, non-thermoplastic polyimide generally refers to polyimide that does not soften or exhibit adhesiveness even when heated. In this embodiment, however, the storage modulus at 30°C measured using a dynamic viscoelasticity measuring device (DMA) is 1.0 × 10 9 Pa or more, and the storage modulus at 350°C is 1.0 × 108 This refers to polyimides with a modulus of tensile strength of 100 Pa or more.

[0048] The polyimide film according to the present embodiment preferably has a coefficient of thermal expansion (CTE) of 40 ppm / K or less, more preferably in the range of 10 to 30 ppm / K. By controlling the CTE 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 coefficients of thermal expansion in the MD and TD directions of the polyimide film.

[0049] When P3 is used, it is preferable to use a fluorine atom-containing diamine component and / or a fluorine atom-containing tetracarboxylic acid anhydride component in P3, particularly to achieve a total light transmittance within a predetermined range. The fluorine atom-containing component has a bulky fluorine atom-containing group, which is thought to reduce interactions such as π-π stacking between polymer chains and make charge transfer (CT) between residues based on the tetracarboxylic acid anhydride component and residues based on the diamine component less likely to occur, thereby making the polyimide closer to colorless transparency.

[0050] Examples of fluorine-containing diamine components include 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.

[0051] In addition to the fluorine-containing diamine, a diamine having a siloxane skeleton may be used as another diamine component from the viewpoint of flexibility of the polyimide, such as low elasticity and low residual stress, etc. Examples of diamines having a siloxane skeleton include diaminopropyltetramethyldisiloxane and methylphenylsilicone modified with amino groups at both ends.

[0052] Furthermore, examples of fluorine atom-containing tetracarboxylic acid anhydride components that are preferably used for P3 include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA).

[0053] Furthermore, in order to control the CTE within the above range, P3 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, and more preferably in the range of 60 to 100 molar parts, relative to a total of 100 molar parts of all tetracarboxylic acid anhydride components. [ka]

[0054] The tetracarboxylic acid anhydride component used in P3 may be not only an aromatic tetracarboxylic acid anhydride component but also an alicyclic tetracarboxylic acid anhydride component, and preferred examples thereof include 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, fluorenylidene bisphthalic anhydride, 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, cyclotanone bisspironorbornane tetracarboxylic acid dianhydride, etc. Alicyclic tetracarboxylic acid anhydride components are preferred because they have excellent heat resistance and transparency and can control the CTE within an appropriate range.

[0055] [Heat resistance] The polyimide film according to the present embodiment preferably has excellent heat resistance, and its heat resistance (solder heat resistance) measured in a solder heat resistance test is preferably 190° C. or higher, more preferably 200° C. or higher, and even more preferably 230° C. or higher. The solder heat resistance is evaluated by the method described in the examples.

[0056] [Formation of Polyimide Film]

[0057] The polyimide film used can be a commercially available polyimide film as is and is not limited thereto, but methods for forming multiple polyimide layers include, for example, [1] a method in which a polyamic acid solution is applied to a supporting substrate (e.g., a metal layer) and dried multiple times, followed by imidization (hereinafter referred to as the sequential coating method), or [2] a method in which a polyamic acid laminate is simultaneously applied to a supporting substrate by multilayer extrusion, dried, and then imidization (hereinafter referred to as the multilayer extrusion method).From the viewpoints of dimensional stability and adhesion between the polyimide layer and the metal layer, it is preferable to form a polyimide film (metal-clad laminate) by the sequential coating method.

[0058] The method for applying the polyamic acid solution to the substrate is not particularly limited, and it is possible to apply it using, for example, a coater such as a comma coater, a die coater, a knife coater, a lip coater, etc. When forming multiple polyimide layers, a method in which the polyamic acid solution is applied to the substrate and then dried is repeated is preferred.

[0059] Next, a method for synthesizing the polyimide constituting the plurality of polyimide layers will be described. The polyimide constituting the polyimide film according to the present invention can be produced by reacting a tetracarboxylic anhydride component and a diamine component in a solvent to form a polyamic acid, followed by heating and ring-closing. For example, the tetracarboxylic anhydride component and the diamine component are dissolved in approximately equimolar amounts in an organic solvent and stirred at a temperature between 0°C and 100°C for 30 minutes to 24 hours to polymerize the polyamic acid, which serves as the polyimide precursor. During the reaction, the reactants are dissolved so that the resulting precursor is present in the organic solvent at a concentration of preferably 5% to 30% by weight, more preferably 10% to 20% by weight. Examples of organic solvents suitable for 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-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 organic solvents used is not particularly limited, but it is preferable to adjust the amount used so that the concentration of the polyamic acid solution (polyimide precursor solution) obtained by the polymerization reaction is about 5% by weight to 30% by weight.

[0060] In the synthesis of polyimide, the tetracarboxylic anhydride component and the diamine component may each be used alone or in combination of two or more. By selecting the type of tetracarboxylic anhydride component and the diamine component, or by selecting the molar ratio when two or more of each are used in combination, it is possible to control the thermal expansion, adhesiveness, glass transition temperature, and the like.

[0061] A terminal blocking agent may also be used for the polyimide. Monoamines or dicarboxylic acids are preferred as terminal blocking agents. The amount of terminal blocking agent to be introduced is preferably 0.0001 to 0.1 mol per 1 mol of the acid anhydride component, and particularly preferably 0.001 to 0.05 mol. Examples of monoamine terminal blocking agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, aniline, and 4-methylaniline. Of these, benzylamine and aniline are preferred. Dicarboxylic acid terminal blocking agents are preferably dicarboxylic acids, which may be partially ring-closed. Examples of recommended dicarboxylic acid terminal blocking agents include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid. Of these, phthalic acid and phthalic anhydride are preferably used.

[0062] 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. The method for imidizing polyamic acid is not particularly limited, and a suitable method is, for example, heat treatment in the solvent at a temperature of 80°C to 400°C for 1 to 24 hours.

[0063] The weight-average molecular weight of the polyamic acid is, for example, preferably in the range of 10,000 to 400,000, more preferably in the range of 30,000 to 350,000. If the weight-average molecular weight is less than 10,000, the film tends to be weak and 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 coating.

[0064] 2. Metal-clad laminate and manufacturing method of metal-clad laminate The metal-clad laminate according to the present embodiment includes an insulating resin layer having a plurality of polyimide layers and a metal layer laminated on at least one surface of the insulating resin layer, the insulating resin layer being made of the polyimide film described above. The metal-clad laminate may have the metal layer on one side of the insulating resin layer or on both sides of the insulating resin layer.

[0065] The material of the metal layer is not particularly limited, but examples include copper, stainless steel, iron, nickel, beryllium, aluminum, zinc, indium, silver, gold, tin, zirconium, tantalum, titanium, lead, magnesium, manganese, and alloys thereof. Among these, copper, iron, or nickel metal elements, or indium tin oxide (ITO) are preferred, and copper (copper foil) is more preferred. Both electrolytic copper foil and rolled copper foil can be used as the copper foil. The metal layer is selected to exhibit the properties required for the intended use, such as the conductivity of the metal layer, the optical transparency of the polyimide layer, and adhesion to the polyimide layer. The shape of the metal layer is not particularly limited, and may be processed appropriately depending on the application. A long roll-shaped metal foil is preferably used.

[0066] 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.

[0067] As described above, the metal-clad laminate according to the present embodiment is preferably produced by a method of forming an insulating resin layer made of a plurality of polyimide layers on a metal layer as a supporting substrate by a sequential coating method from the viewpoint of dimensional stability, etc. However, this is not particularly limited. For example, the metal-clad laminate may be produced by preparing an insulating resin layer made of the polyimide film according to the present embodiment, sputtering a metal onto the insulating resin layer to form a seed layer, and then forming a metal layer by, for example, plating.

[0068] Alternatively, the insulating resin layer may be prepared by preparing an insulating resin layer made of the polyimide film according to the present embodiment and laminating a metal layer thereon by a method such as thermocompression bonding.

[0069] In these cases, in order to improve the adhesiveness between the insulating resin layer and the metal layer, the surface of the polyimide layer that will be the adhesive surface for the metal layer may be subjected to a modification treatment such as plasma treatment.

[0070] Furthermore, when producing a metal-clad laminate having metal layers on both sides, the metal layer can be laminated by means of thermocompression or the like, for example, directly onto the polyimide surface opposite the metal layer of the single-sided metal-clad laminate obtained by the above-mentioned method, or after forming an adhesive layer that does not impair the transparency of the insulating resin layer as needed. The heat-pressing temperature when thermocompressing the metal layer is not particularly limited, but it is preferably equal to or higher than the glass transition temperature of the polyimide layer adjacent to the metal layer used. The heat-pressing pressure is 1 to 500 kg / m, depending on the type of press equipment used. 2 It is desirable that the range is

[0071] [Peel strength] The 180° peel strength between the insulating resin layer and the metal layer in the metal-clad laminate according to this embodiment is preferably 0.5 kN / m or more, more preferably 0.7 kN / m. The wiring width can also be 250 μm, 500 μm, 1 mm, etc. depending on the application, but in any case, the 180° peel strength between the insulating resin layer and the metal layer preferably satisfies the above range. In this specification, the evaluation of physical properties and characteristic values ​​was carried out under the conditions described in the examples, and unless otherwise specified, the values ​​were measured at room temperature (23°C).

[0072] Similarly to the heat resistance (solder heat resistance) of the polyimide film in the solder heat resistance test described above, the metal-clad laminate as a whole preferably has a solder heat resistance of 190° C. or higher, more preferably 200° C. or higher, and even more preferably 230° C. or higher. The solder heat resistance is evaluated by the method described in the examples.

[0073] 3. Circuit board and method for forming circuit board The circuit board according to this embodiment comprises an insulating resin layer having a plurality of polyimide layers and a wiring layer laminated on at least one surface of the insulating resin layer, and the insulating resin layer is made of the polyimide film.

[0074] The circuit board may have a wiring layer on one side of the insulating resin layer, or may have wiring layers on both sides of the insulating resin layer. The wiring layer is obtained as a patterned metal layer by wiring processing the metal layer in the metal-clad laminate, and a preferred embodiment includes a step of forming such a patterned metal layer. The wiring processing method can be carried out according to a conventional method. For example, the desired wiring layer can be formed by circuit processing the metal layer into a desired pattern using photolithography technology and etching. [Example]

[0075] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Measurements and evaluations of various physical properties were carried out according to the following methods.

[0076] [Viscosity measurement] The polyamic acid solutions obtained in the synthesis examples were measured at 25°C using a cone-plate viscometer equipped with a thermostatic water bath (manufactured by Tokimec Co., Ltd.).

[0077] [Measurement of number average molecular weight (Mn) and weight average molecular weight (Mw)] Measurement was performed by gel permeation chromatography (manufactured by Tosoh Corporation, product name: HLC-8220GPC). Polystyrene was used as a standard substance, and N,N-dimethylacetamide was used as a developing solvent.

[0078] [Measurement of total light transmittance (TT)] The total light transmittance (TT) of the polyimide film (50 mm x 50 mm) was measured using a HAZE METER NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. in accordance with JIS K7136.

[0079] [Measurement of coefficient of thermal expansion (CTE)] A polyimide film (3 mm × 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 analyzer (TMA), and then cooled from 250°C to 100°C. The thermal expansion coefficient was measured from the elongation (linear expansion) of the polyimide film during cooling.

[0080] [Peel strength measurement] Using a tension tester, the polyimide layer side of a test sample with a 1 mm wide circuit obtained from a metal-clad laminate was fixed to an aluminum plate with double-sided tape, and the copper was peeled off in a 180° direction at a rate of 50 mm / min to determine the peel strength.

[0081] [Solder heat resistance test] The metal-clad laminate was immersed for 10 seconds in a solder bath set at each evaluation temperature from 200°C to 300°C in 10°C increments, and the adhesion state was observed to check for defects such as foaming, swelling, peeling, etc. If no defects were observed at 230°C, the evaluation was ◯ (good), and if defects were observed, it was rated × (bad).

[0082] [Appearance] In any area of ​​540 mm wide x 200 mm long on the metal-clad laminate, if there were no defects in appearance (streaks), it was rated as ◯ (good), and if there were three or more streaks, it was rated as × (bad).

[0083] [Flammability test] Flammability was measured using the following procedure. The copper foil of the metal-clad laminate was etched away using an aqueous ferric chloride solution to obtain a polyimide film, which was used as a flame retardancy evaluation sample (50 mm wide x 180 mm long). This sample was subjected to the UL94VTM thin material vertical test method, and the burning time (vt) after the first flame release was measured. Of the 15 samples, 10 to 15 with a vt of 0 to 1 second were rated "excellent," 6 to 9 with a vt of 0 to 1 second were rated "good," 1 to 5 with a vt of 0 to 1 second were rated "fail," and even one with a vt of more than 4 seconds was rated "fail."

[0084] The abbreviations used in the examples represent the following compounds. PMDA: Pyromellitic dianhydride 6FDA: 2,2-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride ODPA: 4,4'-oxydiphthalic dianhydride CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride AAPBZI: 5-amino-2-(4-aminophenyl)benzimidazole TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl BAPS: Bis[4-(4-aminophenoxy)phenyl]sulfone APB: 1,3-bis(3-aminophenoxy)benzene BY16-871: Diaminopropyltetramethyldisiloxane (Toray Dow Corning) (manufactured by Sigma-Aldrich, amine equivalent weight 125g / mol) DMAc: N,N-dimethylacetamide

[0085] Synthesis Example 1 To synthesize polyamic acid solution A, the solvent DMAc was added to a 300 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine components and tetracarboxylic acid anhydride components shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for two days to carry out a polymerization reaction, producing a viscous polyamic acid solution A. The viscosity was 26,950 cP.

[0086] Synthesis Example 2 Polyamic acid solution B was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. A viscous polyamic acid solution B was prepared. The viscosity was 4223 cP.

[0087] Synthesis Example 3 To synthesize polyamic acid solution C, the solvent DMAc was added to a 300 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine components and tetracarboxylic anhydride components shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for one day to carry out a polymerization reaction, producing a viscous polyamic acid solution C. The viscosity was 22,384 cP.

[0088] Synthesis Example 4 To synthesize polyamic acid solution D, the solvent DMAc was added to a 500 ml separable flask under a nitrogen stream to a solids concentration of 15 wt %, and the diamine components and tetracarboxylic anhydride components shown in Table 1 were added and dissolved with stirring at 40°C. The solution was then stirred at room temperature for 10 hours to carry out a polymerization reaction, producing a viscous polyamic acid solution D. The viscosity was 3524 cP.

[0089] Synthesis Example 5 Polyamic acid solution E was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. A viscous polyamic acid solution E was prepared. The viscosity was 3025 cP.

[0090] Synthesis Example 6 Polyamic acid solution F was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. A viscous polyamic acid solution F was prepared. The viscosity was 2030 cP.

[0091] Synthesis Example 7 Polyamic acid solution G was prepared by changing the type of monomer as shown in Table 1 and carrying out polymerization in the same manner as in Synthesis Example 1. A viscous polyamic acid solution G was prepared. The viscosity was 4000 cP.

[0092] [Table 1]

[0093] Example 1 Polyamic acid solution G was uniformly applied to copper foil (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: CF-T9DA-SV18, thickness: 18 μm) to a thickness of 3 μm after curing, and then stepwise heated and dried in a temperature range up to 120 ° C to remove the solvent. Next, polyamic acid solution A was uniformly applied thereon to a thickness of 19 μm after curing, and then stepwise heated and dried in a temperature range up to 120 ° C to remove the solvent. Polyamic acid solution G was further uniformly applied thereon to a thickness of 3 μm after curing, and then stepwise heated and dried in a temperature range up to 120 ° C to remove the solvent. In this way, a three-layer polyamic acid layer was formed, and then stepwise heat treatment was performed from 130 ° C to 360 ° C to complete imidization, forming an insulating resin layer with a thickness of 25 μm consisting of polyimide layer G / polyimide layer A / polyimide layer G, and single-sided metal-clad laminate 1 was prepared.

[0094] The copper foil was removed from the single-sided metal-clad laminate 1 using an aqueous ferric chloride solution to prepare a polyimide film. The TT and CTE of this polyimide film were measured (Table 2). A combustion test was also conducted on 15 samples, and the results are shown in Table 3. In addition, Table 2 shows the results of measuring the peel strength of the polyamic acid coated surface when the obtained single-sided metal-clad laminate 1 was processed into wiring at 1 mm, as well as the results of a solder heat resistance test and evaluation of the appearance state.

[0095] Examples 2 to 6 To prepare single-sided metal-clad laminates 2 to 6 in the same manner as in Example 1, insulating resin layers were formed by varying the type of polyamic acid and the thickness after heat treatment as shown in Table 2. The copper foil was then removed by etching to prepare polyimide films. The TT and CTE of these polyimide films were measured (Table 2). Flammability tests were also conducted on 15 samples, and the results are shown in Table 3. In addition, Table 2 shows the results of measuring the peel strength of the polyamic acid coated surface when the obtained single-sided metal-clad laminates 2 to 6 were processed into 1 mm wiring, as well as the results of a solder heat resistance test and evaluation of the appearance.

[0096] Comparative Example 1 Polyamic acid solution C was uniformly applied to copper foil (electrolytic copper foil, manufactured by Fukuda Metal Foil & Powder Co., Ltd., product name: CF-T9DA-SV18, thickness: 18 μm) so that the thickness after curing would be 26 μm, and then the solution was dried by stepwise heating in a temperature range up to 120 °C to remove the solvent. After forming a single-layer polyamic acid layer in this way, stepwise heat treatment was performed from 130 °C to 360 °C to complete imidization, forming a 26 μm-thick insulating resin layer made of single-layer polyimide C, and single-sided metal-clad laminate 7 was prepared. The copper foil was removed from the single-sided metal-clad laminate 7 using an aqueous ferric chloride solution to prepare a single-layer polyimide film. The TT and CTE of this polyimide film were measured (Table 2). Flammability tests were also conducted on 15 samples, and the results are shown in Table 3. Additionally, Table 2 shows the results of measuring the peel strength of the polyamic acid coated surface when the resulting single-sided metal-clad laminate 7 was subjected to wiring processing to 1 mm, as well as the results of a solder heat resistance test and evaluation of the appearance.

[0097] Comparative Examples 2 and 3 An insulating resin layer was formed in the same manner as in Example 1, except that the polyamic acid shown in Table 2 was used and the thickness after heat treatment was changed. The copper foil was then removed by etching to prepare a polyimide film. The TT and CTE of this polyimide film were measured (Table 2). A combustion test was also conducted on 15 samples, and the results are shown in Table 3. Additionally, Table 2 shows the results of measuring the peel strength of the polyamic acid coated surface when the obtained single-sided metal-clad laminates 8 and 9 were subjected to wiring processing to 1 mm, as well as the results of a solder heat resistance test and evaluation of the appearance.

[0098] [Table 2]

[0099] [Table 3]

[0100] For Examples 1 to 6 and Comparative Examples 1 to 3, B1, B2, t1, t2, and T used in the calculation of formula (iii), parameter C calculated by formula (iii), parameter D calculated by formula (iv), and C / D are shown in Table 4. Taking Example 1 as an example, as mentioned above, each can be calculated as follows:

[0101] B1=a1×a1' / b1 (i) B2=a2×a2' / b2 (ii) C=(B1+B2)×(t1+t2) / T ···(iii)

[0102]

number

[0103] Calculation of B1 and B2 in formula (i): In Example 1, the first polyimide layer (P1) and the second polyimide layer (P2) are both G. The monomers contained in G are ODPA, BAPS, and APB. ODPA contains one of the structures "A" (linking group X=O) among the organic groups represented by formula (1). BAPS contains two of the structures "A" (linking group X=O) among the organic groups represented by formula (1) and one of the structures "C" (X=SO2). APB contains two of the structures "A" (X=O). Therefore, the first polyimide layer and the second polyimide layer each contain a total of five of the structures "A" (X=O) and one of the structures "C" (X=SO2), so a1'(X=O) = 5 and a1'(X=SO2) = 1.

[0104] Furthermore, the molecular weight a1 (X=O) of the structure "A" is 170.21 g / mol, and the molecular weight a1 (X=SO2) of the structure "C" is 218.27 g / mol. In addition, the total molecular weight (b1) of ODPA, BAPS, and APB is 1035.05 g / mol. Therefore, when calculating the formula (i) for the first polyimide layer, B1=(5×170.21+1×218.27) / 1035.05=1.033. Similarly, when the second polyimide layer is calculated, B2=1.033.

[0105] Furthermore, when the third polyimide layer (P3) consisting of polyimide layer A was similarly calculated using the molecular weights and the number of linking groups (the number of organic groups in formula (1)) corresponding to formulas (i) and (ii), the monomers contained in polyimide layer A were PMDA, 6FDA, and TFMB. PMDA and TFMB do not have the organic group represented by formula (1), and 6FDA contains one of the organic groups represented by formula (1) with the aforementioned structure "D" (linking group X = C(CF3)2, molecular weight: 304.24). In addition, the total molecular weight of PMDA, 6FDA, and TFMB is 982.6 g / mol. Therefore, the calculation for the third polyimide layer is (1 × 304.24) / 982.6 = 0.310, which is the value obtained from the part of the formula (iv) represented by the sigma symbol (this is referred to as "B3").

[0106] Regarding the calculation of C represented by formula (iii): In Example 1, the thicknesses (t1, t2) of the first polyimide layer and the second polyimide layer were each 3 μm, and the total thickness (T) of all layers was 25 μm. (t1+t2) / T=(3+3) / 25×100=0.24(24%). Since both B1 and B2 were 1.033, calculating equation (iii) gives: C = (1.033 + 1.033) × 0.24 = 0.496.

[0107] Regarding the calculation of D represented by formula (iv): The thickness t3 of the third polyimide layer in Example 1 is 19 μm, and T is 25 μm, so the thickness ratio is t3 / T=19 / 25=0.76 (76%). And, since B3 was 0.310, when we calculate formula (iv), we get D = 0.310 x 0.76 = 0.235.

[0108] Using the above C and D, C / D is calculated as 0.496 / 0.235=2.107.

[0109] Similarly, the formulas (i) to (iv) were calculated for Examples 2 to 6 and Comparative Examples 2 and 3, and the results are shown in Table 4. Note that for Example 5 and Comparative Example 2, in which polyimide C having no organic group represented by formula (1) was used as the third polyimide layer (P3), the parameters B, D, and C / D related to P3 were not calculated as significant values, and therefore are indicated by "-". Furthermore, since Comparative Example 1 is a single-layer PI, it does not have a polyimide layer defined as P1 as the outermost layer, and therefore formulas (i) to (iv) for P1 and P2 were not calculated. Also, since polyimide C, which does not have an organic group represented by formula (1), is used as a single layer (third polyimide layer (P3)), the parameters B, D, and C / D related to polyimide C were not calculated, as in the above. Therefore, the parts that were not calculated are all indicated by "-".

[0110] [Table 4]

Claims

1. A polyimide film having a plurality of polyimide layers, Conditions I and II below: I) The thickness (T) is in the range of more than 10 μm and not more than 50 μm; II) total light transmittance is 70% or more; Fulfilling the plurality of polyimide layers each have a first polyimide layer and a second polyimide layer as their outermost layers; a thickness (t1) of the first polyimide layer and a thickness (t2) of the second polyimide layer each exceed 2 μm, and a ratio [(t1+t2) / T] of the total thickness of the (t1) and the (t2) to the thickness (T) is in the range of more than 20% but not more than 60%, The first polyimide layer and the second polyimide layer are made of a polyimide containing a tetracarboxylic acid residue derived from a tetracarboxylic acid anhydride component and a diamine residue derived from a diamine component, and the polyimide is represented by the following general formula (1): 【Chemistry 1】 [In the general formula (1), the linking group X is independently —O—, —S—, or —SO ２ - or - C(CF ３ ) ２ - represents a divalent group selected from the group consisting of A polyimide film characterized by having an organic group represented by the formula:

2. 2. The polyimide film according to claim 1, wherein a parameter B1 indicating the flame retardancy of the polyimide contained in the first polyimide layer and a parameter B2 indicating the flame retardancy of the polyimide contained in the second polyimide layer and represented by the following formula (i) are both 0.8 or more: B1=a1×a1' / b1...(i) B2=a2×a2' / b2...(ii) (where a1, a1', b1, a2, a2' and b2 are a1: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the first polyimide layer, a1′: the number of linking groups X in the polyimide contained in the first polyimide layer, b1: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues are derived and all diamine components from which all diamine residues are derived, which are contained in the first polyimide layer; a2: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the second polyimide layer, a2′: the number of linking groups X in the polyimide contained in the second polyimide layer, b2: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the second polyimide layer are derived and the molecular weights of all diamine components from which all diamine residues are derived, means.)

3. 3. The polyimide film according to claim 1, wherein a parameter C indicating flame retardancy, represented by the following formula (iii), is 0.4 or more: C=(B1+B2)×(t1+t2) / T...(iii) (wherein B1, B2, t1, t2 and T are defined as above.)

4. a third polyimide layer between the first polyimide layer and the second polyimide layer; 4. The polyimide film according to claim 3, wherein the polyimide contained in the third polyimide layer has a parameter D, which indicates flame retardancy and is represented by the following formula (iv), of 0.12 or more, or a ratio of C to D (C / D) in the range of 3.0 to 10: [Equation 1] (Here, the polyimide layer constituting the third polyimide layer is composed of n layers (where n is an integer of 1 or more), and ak, a'k, bk and t3 are ak: the molecular weight of the organic group represented by formula (1) in the polyimide contained in the kth layer, a′k: the number of linking groups X in the polyimide contained in the kth layer, bk: the sum of the molecular weights of all tetracarboxylic acid anhydride components from which all tetracarboxylic acid residues contained in the kth layer are derived and the molecular weights of all diamine components from which all diamine residues are derived, t3: thickness of the third polyimide layer [unit: μm], means.)

5. In addition to the above conditions I and II, the following condition III is further satisfied: III) a coefficient of thermal expansion (CTE) of 40 ppm / K or less; 3. The polyimide film according to claim 1, wherein the polyimide film satisfies the following conditions:

6. A metal-clad laminate comprising an insulating resin layer having a plurality of polyimide layers and a metal layer laminated on at least one surface of the insulating resin layer, A metal-clad laminate, wherein the insulating resin layer is made of the polyimide film according to claim 1 or 2.

7. 7. The metal-clad laminate according to claim 6, wherein the 180° peel strength between the insulating resin layer and the metal layer is 0.5 kN / m or more.

8. A circuit board comprising an insulating resin layer having a plurality of polyimide layers and a wiring layer laminated on at least one surface of the insulating resin layer, 3. A circuit board, wherein the insulating resin layer is made of the polyimide film according to claim 1.

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