Polyamic acid composition, polyimide, polyimide film, metal-clad laminate, methods for producing the same, and circuit board

Abstract

To provide a polyamic acid composition which, in a state of a polyamic acid solution, allows setting of molecular weight, viscosity, and solid concentration of the polyamic acid mutually in a wide range.SOLUTION: A polyamic acid composition comprises: (a) a polyamic acid obtained by reacting a tetracarboxylic acid dianhydride component including a tetracarboxylic acid dianhydride and a diamine component including a diamine compound; and (b) an organic solvent. The component (a) has ketone groups in a molecule, where the ketone groups are derived from the tetracarboxylic acid dianhydride and / or the diamine compound and a molar ratio of the tetracarboxylic acid dianhydride component and the diamine component (tetracarboxylic acid dianhydride component / diamine component) is less than 0.985.SELECTED DRAWING: None

Description

【Technical Field】 【0001】 The present invention relates to a polyamic acid composition, a polyimide, a polyimide film, a metal-clad laminate, methods for producing them, and a circuit board, which can be used as materials such as circuit boards. 【Background Art】 【0002】 Aromatic polyimides are widely used in the field of electronic materials and the like due to their high heat resistance and dimensional stability. In Patent Document 1, a polyimide containing a predetermined amount of an acid dianhydride residue derived from a tetracarboxylic dianhydride having a high storage elastic modulus and having a ketone group (-CO-) in the molecule is proposed as an insulating resin layer of a flexible printed circuit (FPC). Further, in Patent Document 2, it is proposed to apply a polyimide containing a specific structural unit and having an increased tear propagation resistance as an insulating resin layer for FPCs and HDD suspensions. 【0003】 Aromatic polyimides are insoluble and infusible in solvents, so a two-step synthesis method is often used: first, a solution of the precursor polyamic acid is prepared, then a film is formed, and finally, the imidized polyimide is heat-treated to form the film. In the case of polyimide films produced by this two-step synthesis method, the molecular weight of the imidized polyimide is almost uniquely determined by the molecular weight of the precursor polyamic acid. Generally, not only with polyimides, but with polymer compounds in general, the higher the molecular weight, the stronger the film tends to be. However, since solutions of high molecular weight polyamic acid become highly viscous, there is a problem that the degree of freedom in the viscosity and solid content concentration of the polyamic acid solution relative to the molecular weight of the polyamic acid is limited when considering film formation properties. For example, when producing a thick film, a high solid content concentration is advantageous for coating, but if the molecular weight of the polyamic acid is increased to increase film strength, the viscosity at high solid content concentrations becomes too high, making coating difficult. On the other hand, when producing a thin film, if one tries to adjust the viscosity of a high molecular weight polyamic acid solution to a low viscosity, the solid content concentration must be greatly reduced, which can be a factor in degrading film formation properties. While reducing the molecular weight of polyamic acid can solve the above-mentioned problems with coating properties and film formation, it would result in insufficient film strength. 【0004】 Thus, in the production of aromatic polyimide films, the viscosity and solid content concentration of the polyamic acid solution must be adjusted to an appropriate range depending on the molecular weight of the polyamic acid. This limits the range of adjustment when considering coating properties and film-forming properties, such as making the viscosity low or the solid content high. From another perspective, if the viscosity and solid content concentration of the polyamic acid solution are set prioritizing coating properties and film-forming properties, the molecular weight of the polyamic acid is restricted, making it difficult to produce high-molecular-weight, high-strength aromatic polyimide films. [Prior art documents] [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2020-104340 [Patent Document 2] Patent No. 5009714 [Overview of the project] [Problems that the invention aims to solve] 【0006】 Therefore, the first object of the present invention is to provide a polyamic acid composition in which the molecular weight, viscosity, and solid content concentration of the polyamic acid can be widely adjusted in the state of polyamic acid solution, and the second object is to provide a polyimide film with high molecular weight and high strength by using the above polyamic acid composition. [Means for solving the problem] 【0007】 The inventors have discovered that by introducing specific functional groups into polyamic acid and controlling the ratio of the tetracarboxylic dianhydride component and the diamine component used as raw materials, a polyamic acid composition can be obtained in which viscosity and solid content concentration can be set over a wide range with respect to the molecular weight of the polyamic acid, thus completing the present invention. 【0008】 In other words, the polyamic acid composition of the present invention comprises the following components (a) and (b); (a) A polyamic acid obtained by reacting a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride with a diamine component containing a diamine compound. (b) Organic solvents, It contains the following. Furthermore, in the polyamic acid composition of the present invention, component (a) has a ketone group in its molecule, and the ketone group is derived from the tetracarboxylic dianhydride and / or the diamine compound. The present invention is characterized in that the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) is less than 0.985. 【0009】 The polyamic acid composition of the present invention may have a weight-average molecular weight (Mw) of the polyamic acid in the range of 10,000 to 500,000. 【0010】 The polyamic acid composition of the present invention may contain a ketone group in component (a) of 5 moles or more per 100 moles of the total of the acid dianhydride residue and the diamine residue. 【0011】 The polyimide of the present invention is obtained by reacting a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride with a diamine component containing a diamine compound. The polyimide of the present invention has a molar ratio (tetracarboxylic dianhydride component / diamine component) of less than 0.985 of the tetracarboxylic dianhydride component and the diamine component, and has an imine bond formed by a ketone group derived from the tetracarboxylic dianhydride and / or the diamine compound and an amino group derived from the diamine compound. 【0012】 The polyimide film of the present invention contains the above-mentioned polyimide as the main component of the resin. 【0013】 The metal-clad laminate of the present invention comprises an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer includes the polyimide film. 【0014】 The present invention's method for producing a polyimide film consists of the following steps I and II; I) A step of forming a polyamic acid coating film by applying the above polyamic acid composition onto a substrate and drying it. II) A step of forming a polyimide film by heat-treating the coated film and imidizing the polyamic acid, It includes. 【0015】 The present invention's method for manufacturing a metal-clad laminate involves the following steps i and ii; i) A step of forming a polyamic acid coating film by applying the above polyamic acid composition onto a substrate containing metal foil and drying it, ii) Forming a polyimide layer by heat-treating the coating film on a substrate containing a metal foil to imidize the polyamic acid. which includes 【0016】 Furthermore, the present invention provides a circuit board in which the metal layer of the aforementioned metal-clad laminate is processed into wiring. 【Advantages of the Invention】 【0017】 The polyamic acid composition of the present invention can widely set the molecular weight, viscosity, and solid content concentration of the polyamic acid independently of each other. Therefore, various polyimide films with different molecular weights, film thicknesses, etc. can be formed without sacrificing coating properties or film-forming properties. In particular, when forming a high molecular weight and high strength polyimide film, the adjustment range of the viscosity and solid content concentration of the polyamic acid composition can be widened, which is industrially advantageous. 【Brief Description of the Drawings】 【0018】 [Figure 1] It is a drawing showing the relationship between the weight average molecular weight (horizontal axis) in a general aromatic polyamic acid and the tear propagation resistance (vertical axis) of a polyimide film. [Figure 2] It is a drawing showing the relationship between the molar ratio (horizontal axis) of the tetracarboxylic dianhydride component and the diamine component in the aromatic polyamic acids of the examples, reference examples, and comparative examples, and the tear propagation resistance (vertical axis) of the polyimide film. [Figure 3] It is a drawing showing the relationship between the weight average molecular weight (horizontal axis) in the aromatic polyamic acids of the examples, reference examples, and comparative examples, and the tear propagation resistance (vertical axis) of the polyimide film. 【Modes for Carrying Out the Invention】 【0019】 Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. 【0020】 [Polyamic Acid Composition] The polyamic acid composition according to an embodiment of the present invention contains the following components (a) and (b); (a) A polyamic acid obtained by reacting a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride with a diamine component containing a diamine compound, and (b) Organic solvents, It contains. 【0021】 (Component (a): Polyamic acid) The polyamic acid of component (a) has a ketone group (-CO-) in its molecule. The ketone group originates from the tetracarboxylic dianhydride and / or diamine compound, which are the raw materials for the polyamic acid. That is, the polyamic acid contains acid dianhydride residues and diamine residues, and either one or both of the acid dianhydride residues or diamine residues contain a residue with a ketone group. In the present invention, "acid dianhydride residue" refers to a tetravalent group derived from tetracarboxylic dianhydride, and "diamine residue" refers to a divalent group derived from a diamine compound. When the tetracarboxylic dianhydride component, which contains the raw material tetracarboxylic dianhydride, and the diamine component, which contains the diamine compound, are reacted in approximately equimolar amounts, the types and molar ratios of acid dianhydride residues and diamine residues contained in the polyimide can be approximated to the types and molar ratios of the raw materials. Furthermore, the "diamine compound" may have hydrogen atoms substituted in the two terminal amino groups. 【0022】 Examples of acid dianhydride residues containing a ketone group include residues derived from "tetracarboxylic dianhydrides containing a ketone group in the molecule," such as 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 4,4'-(paraphenylenedicarbonyl)diphthalic anhydride, and 4,4'-(metaphenylenedicarbonyl)diphthalic anhydride. 【0023】 Examples of acid dianhydride residues other than those containing a ketone group include those shown in the examples below, as well as acid dianhydride residues derived from tetracarboxylic dianhydrides commonly used in the synthesis of polyimides. However, from the viewpoint of storage stability of the polyamic acid composition, it is preferable that the acid dianhydride residues consist only of aromatic acid dianhydride residues derived from aromatic tetracarboxylic acid compounds. 【0024】 Examples of diamine residues containing a ketone group include residues derived from "diamine compounds containing a ketone group in the molecule," such as 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis(4-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)benzophenone (BABP), 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB), 1,4-bis(4-aminobenzoyl)benzene, and 1,3-bis(4-aminobenzoyl)benzene. 【0025】 Other diamine residues besides those containing a ketone group include, for example, those shown in the examples below, as well as diamine residues derived from diamine compounds commonly used in the synthesis of polyimides. However, from the viewpoint of storage stability of the polyamic acid composition, it is preferable that the diamine residues consist only of aromatic diamine residues derived from aromatic diamine compounds, and not include aliphatic diamine residues derived from aliphatic diamine compounds. 【0026】 The amount of ketone groups (as -CO-) present in the polyamic acid is preferably 5 moles or more, and more preferably in the range of 10 to 50 moles, per 100 moles of the total amount of acid dianhydride residues and diamine residues. If the ketone group content in the polyamic acid is less than 5 moles, the imination reaction during thermal imidation may not proceed sufficiently, and the desired film strength may not be obtained. There is no particular upper limit on the amount of ketone groups, but preferably keeping it at 50 moles or less per 100 moles of the total amount of acid dianhydride residues and diamine residues increases the degree of freedom in molecular design of the polyimide and makes it easier to control its physical properties. 【0027】 In this embodiment, a polyamic acid is used, preferably one in which most of the terminals are amino groups, and more preferably one in which all of the terminals are amino groups. Thus, a polyamic acid rich in amino terminals can be formed by adjusting the molar ratio of the two components such that the diamine component is in excess of the tetracarboxylic dianhydride component in the raw materials. Specifically, by adjusting the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) to less than 0.985, preferably in the range of 0.930 to 0.980, and more preferably in the range of 0.970 to 0.980, the majority of the synthesized polyamic acid can be made to be a polyamic acid having amino terminals (-NH2). While setting the molar ratio of the tetracarboxylic dianhydride component to the diamine component to less than 0.985 tends to result in a lower molecular weight of the polyamic acid, making the film brittle after imidation, in this invention, the imination reaction during thermal imidation makes it possible to increase the molecular weight at the polyimide stage, thereby achieving sufficiently high film strength. Thus, the effects of the present invention are particularly evident when the molar ratio of the tetracarboxylic dianhydride component to the diamine component is less than 0.985. When the charging ratio of the tetracarboxylic dianhydride component to 1 mole of the diamine component is 0.985 moles or more, the polyamic acid itself becomes high molecular weight, and a tough film is often obtained after imidation regardless of whether or not an imination reaction occurs during thermal imidation, making it difficult for the effects of the invention to be exhibited. On the other hand, if the charging ratio of the tetracarboxylic dianhydride component to the diamine component is too small, the high molecular weight of the polyamic acid does not proceed sufficiently. Therefore, the charging molar ratio of the tetracarboxylic dianhydride component to 1 mole of the diamine component should be, for example, 0.930 or more, preferably in the range of 0.930 to 0.980, and more preferably in the range of 0.970 to 0.980. 【0028】 (Synthesis of polyamic acid) Polyamic acid can be produced by reacting the above-mentioned tetracarboxylic dianhydride component and diamine component in a solvent. For example, polyamic acid can be obtained by dissolving the tetracarboxylic dianhydride component and diamine component in an organic solvent in the above-mentioned molar ratio and carrying out a polymerization reaction by stirring at a temperature in the range of 0 to 100°C for 30 minutes to 24 hours. In the reaction, it is preferable to dissolve the reaction components so that the amount of polyamic acid produced in the organic solvent is in the range of 5 to 30% by weight, preferably in the range of 10 to 20% by weight. Examples of organic solvents used in the polymerization reaction include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, and the like. Two or more of these solvents can be used in combination, and aromatic hydrocarbons such as xylene and toluene can also be used. While there are no particular restrictions on the amount of such organic solvents used, it is preferable to adjust the amount used so that the concentration of the polyamic acid solution obtained by the polymerization reaction is approximately 5-30% by weight. Synthesized polyamic acids generally exhibit excellent solvent solubility and are therefore usually advantageous when used as reaction solvent solutions; however, they can be concentrated, diluted, or substituted with other organic solvents as needed. 【0029】 In the synthesis of polyamic acids, either one tetracarboxylic dianhydride or a diamine compound may be used, or two or more may be used in combination. By selecting the types of tetracarboxylic dianhydrides and diamine compounds, and the molar ratios of each when two or more tetracarboxylic dianhydrides or diamine compounds are used, the physical properties of the polyimide, such as its elastic modulus, mechanical strength, thermal expansion, adhesion, and glass transition temperature, can be controlled. Furthermore, in the polyamic acid of this embodiment, if there are multiple structural units, they may exist as blocks or randomly, but random arrangement is preferable. The same applies to the polyimide described later. 【0030】 (Weight-average molecular weight of polyamic acid) The weight-average molecular weight (Mw) of the polyamic acid is preferably in the range of 10,000 to 500,000, and can be adjusted to an appropriate Mw within this range depending on the purpose. If the Mw is less than 10,000, the strength of the film tends to decrease and it becomes more prone to embrittlement. On the other hand, if the weight-average molecular weight exceeds 500,000, the viscosity increases, and defects such as uneven film thickness and streaks tend to occur during the coating process. 【0031】 (Component (b): Organic solvent) The organic solvent for component (b) can be the same as the organic solvent used in the polymerization reaction. For example, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), 2-butanone, dimethyl sulfoxide (DMSO), hexamethylphosphoramide, N-methylcaprolactam, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, cresol, etc. 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 content of organic solvents in the polyamic acid composition is not particularly limited, but it is preferable that the concentration of polyamic acid be about 5 to 30% by weight. 【0032】 (optional ingredient) The polyamic acid composition of this embodiment may contain, as an optional component, for example, organic fillers, inorganic fillers, cyclization agents, imidation catalysts, curing agents, plasticizers, elastomers, coupling agents, pigments, flame retardants, heat dissipation agents, etc. 【0033】 [Polyimide] The polyimide of this embodiment is obtained by imidizing a polyamic acid having the above-described structure, which is a precursor. The method for imidizing the polyamic acid is not particularly limited, and a heat treatment such as heating at a temperature in the range of 80 to 400°C for several minutes to 24 hours is preferably employed. In this invention, the term "polyimide" refers to resins made of polymers having imide groups in their molecular structure, including polyimide, polyamideimide, polyetherimide, polyesterimide, polysiloxaneimide, and polybenzimidazoleimide. 【0034】 The polyimide of this embodiment, like polyamic acid, is obtained by reacting a tetracarboxylic dianhydride component containing tetracarboxylic dianhydride with a diamine component containing a diamine compound, and contains acid dianhydride residues derived from tetracarboxylic dianhydride and diamine residues derived from the diamine compound. The molar ratio of the tetracarboxylic dianhydride component to the diamine component in the starting material (tetracarboxylic dianhydride component / diamine component) is the same as that of polyamic acid. 【0035】 Furthermore, the polyimide of this embodiment has an imine bond formed by a ketone group derived from a tetracarboxylic dianhydride and / or a diamine compound, and an amino group derived from a diamine compound. Due to this imine bond, a branched chain is formed relative to the main chain of the imide bond of the polyimide, resulting in a significantly increased Mw compared to polyamic acid. 【0036】 The polyimide in this embodiment may be either thermoplastic or non-thermoplastic. When flexibility and adhesion are important, such as when the polyimide in this embodiment is applied as an adhesive layer to metal foil or other resin layers, it is preferable to use thermoplastic polyimide. When applied as an adhesive layer, the high film strength makes cohesive failure less likely and excellent peel strength can be achieved. On the other hand, when the polyimide of this embodiment is applied as the main layer (base layer) of the insulating resin layer in a polyimide film or metal-clad laminate, and the function of ensuring mechanical strength is important, it is preferable to use a non-thermoplastic polyimide. When applied as a base layer, the high film strength allows for the expression of excellent mechanical properties such as self-supporting properties, bending resistance, and impact resistance. Whether the polyimide in this embodiment is thermoplastic or non-thermoplastic can be designed by the type, combination, and molar ratio of the raw materials, tetracarboxylic dianhydride and diamine compound. In general, "thermoplastic polyimide" refers to polyimide whose glass transition temperature (Tg) can be clearly determined. However, in this invention, the storage modulus at 30°C measured using a dynamic viscoelasticity analyzer (DMA) is 1.0 × 10⁻⁶. 9 The Pa is greater than or equal to 1.0 × 10⁻¹⁶, and the storage modulus at 300°C is 1.0 × 10⁻¹⁶. 8 This refers to polyimides with a storage modulus of less than Pa. Furthermore, "non-thermoplastic polyimides" generally refer to polyimides that do not soften or become adhesive when heated. However, in this invention, the storage modulus at 30°C measured using a dynamic viscoelasticity analyzer (DMA) is 1.0 × 10⁻⁶. 9 The Pa is greater than or equal to 1.0 × 10⁻¹⁶, and the storage modulus at 300°C is 1.0 × 10⁻¹⁶. 8 This refers to polyimides with a Pa rating of 1.5 or higher. 【0037】 [Effect] In this embodiment, it is presumed that imine bonds are formed between the ketone groups in the polyamic acid and the terminal amino groups during the heat treatment used to imidize the polyamic acid. In other words, in this embodiment, the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) is less than 0.985, meaning that amino groups are present at almost all terminals. Therefore, it is thought that a dehydration condensation reaction occurs between the ketone groups in the polyamic acid and the terminal amino groups upon heating, forming imine bonds in the polyimide. As a result, numerous branched chains are generated in the polyimide main chain due to imine bonds, and the Mw of the polyimide is significantly higher than that of the polyamic acid. A model of such branched chain formation by imine bonds is shown below. Note that in the following model, the case where all acid anhydride residues are BTDA residues derived from 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is illustrated, but other acid dianhydride residues may also be included. 【0038】 [ka] 【0039】 In the formula, R represents the same or different types of diamine residues, and m and n represent integers indicating the number of repetitions. Also, (a) represents a polyamic acid that forms a branched chain via imine bonds, and (b) represents a polyamic acid that forms the main chain of a polyimide chain. 【0040】 Due to this phenomenon, in the polyamic acid / polyimide of this embodiment, it is possible to keep the Mw at the polyamic acid stage low when forming a polyimide with a certain Mw. As a result, compared to conventional polyamic acid / polyimide, the range of adjustability is expanded in the direction of suppressing the viscosity of the polyamic acid solution and in the direction of increasing the solid content concentration. 【0041】 While a method is known to form an imine crosslinked structure by reacting a polyimide containing a ketone group with a diamino compound such as a dihydrazide, the polyimide film obtained by this method may suffer from plasticization due to unreacted crosslinking agents or weakening due to excessively high crosslinking density, whereas the present invention does not suffer from such drawbacks. 【0042】 Next, Figure 1 shows the relationship between Mw (horizontal axis) of a typical aromatic polyamic acid and the tear propagation resistance (vertical axis) of the polyimide film obtained by imidizing it. Figure 1 shows two types of polyamic acid and polyimide film, but as a general trend, it can be seen that as the Mw of the polyamic acid increases, the tear propagation resistance of the polyimide film also gradually increases. Generally, a molar ratio of the raw material tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) close to 1 is advantageous for increasing the Mw of the polyamic acid. 【0043】 In contrast, in the polyamic acid / polyimide of this embodiment, the molar ratio of the raw material tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) is intentionally set to less than 0.985. Therefore, even if the molecular weight of the polyamic acid is designed to be relatively small, numerous branched chains are formed by imine bonds generated during the imidation reaction, allowing the molecular weight of the polyimide to be significantly increased compared to that of the polyamic acid. As a result, as shown in the examples below, the molecular weight of the polyamic acid can be designed to be lower than conventional methods in order to obtain a polyimide film with the target tear propagation resistance. In other words, it is possible to expand the adjustment range in the direction of reducing the Mw of the polyamic acid compared to conventional technology in order to obtain a polyimide film with the target strength. Therefore, the following applications become possible. 【0044】 In the polyamic acid / polyimide of this embodiment, the increase in viscosity of the polyamic acid composition (Mw of polyamic acid) can be suppressed even when the solid content concentration is increased. For example, when producing a relatively thick polyimide film with a thickness of about 50 to 200 μm, even if a high solid content concentration of about 15 to 20% by weight, which is advantageous for coating, is selected, the viscosity of the polyamic acid composition can be controlled to about 2,000 to 50,000 cP. On the other hand, since the Mw after imidization can be made sufficiently larger than the Mw of polyamic acid, a high-strength polyimide film can be produced. Such a thick, high-strength polyimide film is extremely useful for, for example, circuit boards, striplines, microstrip lines, RF cables, insulating materials, coating materials, heat insulating materials, and polyimide heaters that transmit high-frequency signals of 5G and beyond. 【0045】 Furthermore, the viscosity of the polyamic acid composition can be reduced (the Mw of the polyamic acid can be reduced) without lowering the solid content concentration. For example, when producing a relatively thin polyimide film with a thickness of about 3 to 15 μm, even if a low viscosity of about 500 to 10,000 cP, which is advantageous for coating, is selected, the high solid content concentration of the polyamic acid composition can be controlled to about 10 to 18% by weight. On the other hand, since the Mw after imidization can be made sufficiently larger than the Mw of the polyamic acid, a high-strength polyimide film can be produced without degrading film-forming properties. Such thin, high-strength polyimide films are extremely useful, for example, for space saving and miniaturization of circuit boards such as FPCs, as well as for heat dissipation materials and polyimide tubes. 【0046】 As described above, the polyamic acid composition of the present invention allows for a wide range of mutual adjustments of the molecular weight, viscosity, and solid content concentration of the polyamic acid. Therefore, various polyimide films with different Mw, film thickness, etc., can be formed according to the purpose without sacrificing coating properties or film-forming properties. In particular, when forming high molecular weight and high strength polyimide films, the wide range of adjustment for the viscosity and solid content concentration of the polyamic acid composition is advantageous in the industrial-scale production of polyimide films. 【0047】 [Polyimide film] The polyimide film of this embodiment contains the polyimide having the above configuration as the main component of the resin. Here, "main component of the resin" means a component that is present in more than 50% by weight of the total resin components. The polyimide film preferably contains 70% by weight or more of the polyimide having the above configuration, more preferably 80% by weight or more of the polyimide having the above configuration, and most preferably all of the resin components consist of the polyimide having the above configuration. The polyimide film of this embodiment may also have a structure in which it is laminated with any polyimide layer. 【0048】 The polyimide film of this embodiment can be manufactured by carrying out a method including the following steps I and II. 【0049】 I) A step of forming a polyamic acid coating film by applying the above polyamic acid composition onto a substrate and drying it. In step I, there are no particular restrictions on the substrate, and for example, metal foils such as copper foil, glass plates, resin films such as polyimide films, polyamide films, and polyester films, and laminates thereof can be used. Furthermore, there are no particular restrictions on the method of applying the polyamic acid composition, and it can be applied using coaters such as commas, dies, knives, and lips. 【0050】 II) A step of forming a polyimide film by heat-treating the coated film and imidizing the polyamic acid. In step II, the heat treatment conditions can be the same as those for the synthesis of polyimide described above. In step II, the coated film may be peeled from the substrate before heat treatment and the heat treatment may be performed on the polyamic acid gel film; however, it is preferable to perform the heat treatment on the substrate to complete the imidization of the polyamic acid. In this case, since the polyamic acid resin layer is imidized while fixed to the supporting substrate, changes in expansion and contraction of the polyimide layer during the imidization process can be suppressed, and the thickness and dimensional accuracy of the polyimide film can be maintained. When heat treatment is performed on the substrate, the process may further include a step of peeling the polyimide film from the substrate. 【0051】 [Metal-clad laminate] The metal-clad laminate of this embodiment comprises an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, wherein the insulating resin layer includes a polyimide layer made of the polyimide film. The insulating resin layer may also include any resin layer other than the polyimide layer made of the polyimide film. 【0052】 As the metal layer, metal foil can be preferably used. There are no particular restrictions on the material of the metal foil, 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 or copper alloys are particularly preferred. As the copper foil, rolled copper foil or electrolytic copper foil may be used, and commercially available copper foil can be preferably used. 【0053】 In this embodiment, for example, when used in the manufacture of FPCs, the preferred thickness of the metal layer is in the range of 3 to 50 μm, and more preferably in the range of 5 to 30 μm. 【0054】 The metal foil used as the metal layer may have surface treatments such as rust prevention, siding, aluminum alkoxide, aluminum chelate, or silane coupling agent applied to its surface. The metal foil can be in the form of cut sheets, rolls, or endless belts, but to achieve productivity, it is more efficient to use rolls or endless belts that allow for continuous production. Furthermore, from the viewpoint of maximizing the improvement in wiring pattern accuracy on the circuit board, the metal foil is preferably formed into long rolls. 【0055】 Metal-clad laminates can be manufactured by carrying out a method that includes the following steps i and ii. i) A step of forming a polyamic acid coating film by applying the above polyamic acid composition onto a substrate containing metal foil and drying it. ii) A step of forming a polyimide layer by heat-treating the coating film on a substrate containing metal foil and imidizing the polyamic acid. 【0056】 Steps i and ii can be carried out in the same manner as steps I and II of the above-described method for manufacturing a polyimide film, except that a substrate containing metal foil is used and the imidation is completed on the substrate. Here, "substrate containing metal foil" means metal foil alone, a laminate of metal foil and a resin film, a laminate of metal foil and a polyamic acid coated film, etc. 【0057】 [Circuit board] The metal-clad laminate of the present invention is useful as a circuit board material for FPCs and the like, and a circuit board made by processing the metal-clad laminate of the present invention is also an embodiment of the present invention. This circuit board can be manufactured by forming a wiring layer by processing the metal layer of the metal-clad laminate obtained by the manufacturing method of the metal-clad laminate into a pattern using a conventional method. The patterning of the metal layer can be carried out by any method, such as using photolithography and etching. When manufacturing a circuit board, the usual processes, such as through-hole processing in the preceding process and terminal plating and outline processing in the subsequent process, can be carried out according to conventional methods. [Examples] 【0058】 The features of the present invention will be explained in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. In the following examples, unless otherwise specified, various measurements and evaluations are performed as described below. 【0059】 [Viscosity measurement] Viscosity was measured at 25°C using an E-type viscometer (Brookfield, product name: DV-II+Pro). The rotation speed was set so that the torque was between 10% and 90%, and the value was read after 2 minutes had elapsed since the start of measurement, when the viscosity had stabilized. 【0060】 [Measurement of weight-average molecular weight] The measurements were performed using gel permeation chromatography (Tosoh Corporation, product name: HLC-8420GPC). Polystyrene was used as the standard substance, and N,N-dimethylacetamide was used as the eluent. 【0061】 [Measurement of the coefficient of thermal expansion (CTE)] Using a thermomechanical analyzer (manufactured by Hitachi High-Tech Science Corporation, product name: TMA6100), the temperature was raised from 30°C to 270°C at a constant heating rate, held at that temperature for 10 minutes, and then cooled at a rate of 5°C / minute to determine the average thermal expansion coefficient from 250°C to 100°C. 【0062】 [Measurement of glass transition temperature (Tg) and storage modulus] A dynamic viscoelasticity analyzer (DMA: TA Instruments, product name; RSA-G2) was used to measure the heating rate from 30°C to 400°C at a rate of 5°C / min and a frequency of 1 Hz. The glass transition temperature was determined from the temperature at which the loss modulus was maximized based on the main dispersion. 【0063】 [Measurement of Tensile Modulus] The measurements were taken using a tensile and compression testing machine (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name: Strograph R-1). The material was stretched at a chuck distance of 101.6 mm and a sweep speed of 10 mm / min, and the tensile modulus was calculated from the slope of the resulting stress-displacement curve. 【0064】 [Measurement of tear propagation resistance] A test specimen measuring 63.5 mm in length and 50 mm in width was prepared, a 12.7 mm long cut was made in the specimen, and the test was performed using a light-load tear tester manufactured by Toyo Seiki Co., Ltd. 【0065】 [Measurement of peel strength] Samples were prepared by processing copper foil from a flexible copper-clad laminate to a width of 1.0 mm. The surface of the polyimide layer was fixed to an aluminum plate with double-sided tape, and measurements were taken using a Tensilon tester (manufactured by Toyo Seiki Seisakusho Co., Ltd., product name: Strograph VE-1D). The median strength was determined when the copper foil was pulled at a speed of 50 mm / min in a 180-degree direction and peeled off by 10 mm. 【0066】 The abbreviations used in the examples and comparative examples refer to the following compounds. PMDA: Pyromellitic dianhydride BTDA:3,3',4,4'-benzophenonetetracarboxylic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene DMAc: N,N-dimethylacetamide 【0067】 (Synthesis Example 1) 255.0 parts by weight of DMAc was mixed with 21.43 parts by weight of m-TB (100.92 moles) and stirred at room temperature for at least 30 minutes until completely dissolved. Next, 16.26 parts by weight of PMDA (74.56 moles) and 7.31 parts by weight of BPDA (24.85 moles) were added and stirred at room temperature for 4 hours to obtain polyamic acid solution A with a viscosity of 27,400 cP and a weight-average molecular weight of 117,000. 【0068】 [Example 1] 264.0 parts by weight of DMAc was mixed with 10.62 parts by weight of TPE-R (36.33 moles) and 7.71 parts by weight of m-TB (36.33 moles) and stirred at room temperature until completely dissolved. Next, 6.85 parts by weight of BTDA (21.25 moles) and 10.82 parts by weight of PMDA (49.59 moles) were added and stirred at room temperature for 4 hours to obtain polyamic acid solution 1 with a viscosity of 700 cP and a weight-average molecular weight of 101,000. Polyamic acid solution 1 was uniformly applied to a copper foil so that the cured thickness was approximately 25 μm. The solution was then heated and dried at a temperature of 140°C or lower to remove the solvent. Furthermore, the temperature was gradually increased from 140°C to 360°C to complete the imidation process. After that, the copper foil was etched off to obtain polyimide film 1. The physical properties of the obtained polyimide film 1 are shown in Table 1. Polyamic acid solution 1 was applied to a copper foil (electrolytic copper foil, thickness: 12 μm, ten-point average roughness Rz: 1 μm) to a thickness of 2 μm after curing, and then heated and dried at a temperature of 140°C or lower to remove the solvent. Polyamic acid solution A was then applied to a thickness of 21 μm after curing, and then heated and dried at a temperature of 140°C or lower to remove the solvent. Furthermore, polyamic acid solution 1 was applied to a thickness of 2 μm after curing, and then heated and dried at a temperature of 140°C or lower to remove the solvent. Subsequently, imidization was performed by gradually increasing the temperature from 140°C to 360°C to obtain a single-sided copper-clad laminate 1. The obtained single-sided copper-clad laminate 1 was processed into a circuit and the measured peel strength was 0.9 kN / m. 【0069】 [Example 2] Polyamic acid solution 2, polyimide film 2, and single-sided copper-clad laminate 2 were obtained in the same manner as in Example 1, except for the composition ratios shown in Table 1. The physical properties of each are shown in Table 1. 【0070】 [Reference Examples 1-3, Comparative Examples 1-3] Polyamic acid solutions 3-8, polyimide films 3-8, and single-sided copper-clad laminates 3-8 were obtained in the same manner as in Example 1, except for the composition ratios shown in Table 1. The physical properties of each are shown in Table 1. 【0071】 [Table 1] 【0072】 Table 1 shows that in Examples 1 and 2, despite having a lower Mw of polyamic acid compared to Reference Examples 1-3, they exhibited tear propagation resistance and peel strength equivalent to Reference Examples 1-3. This indicates that in Examples 1 and 2, cohesive failure is less likely to occur due to the high film strength. 【0073】 Figure 2 shows the relationship between the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) and the tear propagation resistance of the polyimide film in Examples 1 and 2, Reference Examples 1-3, and Comparative Examples 1-3 described above. Figure 3 shows the relationship between the Mw of the polyamic acid and the tear propagation resistance of the polyimide film. In Figures 2 and 3, "Example 1," "Reference Example 1," "Comparative Example 1," etc., refer to the corresponding "Example," "Reference Example," and "Comparative Example," and their respective numbers. 【0074】 As shown in Figure 2, in Comparative Examples 1 to 3, when the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) exceeds 1, the tear propagation resistance decreases with increasing molar ratio. In contrast, in Examples 1 and 2, even when the molar ratio is less than 0.985, the tear propagation resistance is comparable to that of Reference Examples 1 to 3, where the molar ratio is around 1. On the other hand, Figure 3 shows that in Examples 1 and 2, even though the Mw of the polyamic acid is lower than in Reference Examples 1 to 3, the same tear propagation resistance as in Reference Examples 1 to 3 is exhibited. From these results, it is considered that in Examples 1 and 2, the polyimide becomes more molecular weight due to the imination reaction during thermal imidation, resulting in the same tear propagation resistance as in Reference Examples 1 to 3. Furthermore, the results for Comparative Examples 1-3 in Figure 3 are consistent with those in Figure 1 above, indicating that when the molar ratio of the tetracarboxylic dianhydride component to the diamine component exceeds 1, the tear propagation resistance of the polyimide film gradually increases as the Mw of the polyamic acid increases. 【0075】 Although embodiments of the present invention have been described in detail above for illustrative purposes, the present invention is not limited to the above embodiments.

Claims

[Claim 1] A metal-clad laminate comprising an insulating resin layer and a metal layer laminated on one or both sides of the insulating resin layer, The insulating resin layer includes a polyimide film containing polyimide as the main component of the resin, The polyimide is a polyimide obtained by reacting a tetracarboxylic dianhydride component containing a tetracarboxylic dianhydride with a diamine component containing a diamine compound, A metal-clad laminate characterized in that the molar ratio of the tetracarboxylic dianhydride component to the diamine component (tetracarboxylic dianhydride component / diamine component) is less than 0.985, and it has an imine bond formed by a ketone group derived from the tetracarboxylic dianhydride and / or the diamine compound and an amino group derived from the diamine compound. [Claim 2] A method for manufacturing a metal-clad laminate according to Claim 1, The following steps i and ii; i) A step of forming a polyamic acid coating film by applying a polyamic acid composition onto a substrate containing metal foil and drying it, ii) A step of forming a polyimide layer made of the polyimide film by heat-treating the coating film on a substrate containing metal foil and imidizing the polyamic acid, A method for manufacturing a metal-clad laminate containing [a specific component]. [Claim 3] A circuit board in which the metal layer of the metal-clad laminate described in Claim 1 is processed into wiring.

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