Curable resin compositions, laminated structures, cured products, and electronic components

Abstract

To provide a curable resin composition having characteristics that a dried coating film obtained has good resolution and that, even when cured materials after thermal curing are stored stacked under a high temperature environment, little sticking occurs.SOLUTION: Provided is a curable resin composition which is alkali-developable and forms a cured film by light exposure and a heating treatment. When a dried film having a thickness of 2-100 μm is formed from this curable resin composition, an arithmetic average roughness Ra of the dried film is less than 0.1 μm, and an arithmetic average roughness Ra of a dried film after thermal curing of the dried film becomes 0.1 μm to 1 μm. The curable resin composition of the present invention has characteristics that a dried coating film obtained has good resolution and that, even when cured materials after thermal curing are stored stacked under a high temperature environment, little sticking occurs.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a curable resin composition, a laminated structure of resin layers formed from the curable resin composition, a cured product thereof, and an electronic component having an insulating film made of the cured product, and particularly to a curable resin composition that is alkali-developable and forms a cured film by exposure and heat treatment, a laminated structure of resin layers formed from the curable resin composition, and an electronic component having a cured product thereof and an insulating film made of the cured product.

Background Art

[0002] Conventionally, as a protective film for a flexible printed wiring board, a non-photosensitive resin structure obtained by applying a thermosetting adhesive to a film such as polyimide has been used. As a method of forming such a non-photosensitive resin structure into a pattern on a flexible printed wiring board, conventionally, a method of thermocompression bonding on the flexible printed wiring board after punching to form holes has been taken. Alternatively, a method of directly pattern printing a solvent-soluble thermosetting resin composition on a flexible printed wiring board and thermosetting it to form a pattern has also been taken. In particular, polyimide film has been used as a suitable material for flexible printed wiring boards because it has flexibility and excellent heat resistance, mechanical properties, and electrical properties (see, for example, Patent Document 1). However, in the above-described conventional methods, the shape of the pattern end portion is deformed due to the bleeding of the resin during coating or thermocompression bonding, so it has been difficult to form fine patterns required for miniaturization of wiring and chip components mounted on flexible printed wiring boards.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, it is also conceivable to apply photosensitive solder resist, known as a permanent circuit protective film that allows for microfabrication, as a coverlay for flexible printed circuit boards. In flexible printed circuit boards, photosensitive solder resist requires a low crosslinking density to provide flexibility. Flexible substrates are thin and easily bent, so they are often stacked and fixed together for storage and transportation. Depending on the storage and transportation environment, they may be exposed to high temperatures, and when photosensitive solder resist is applied as a coverlay, the area protecting the flexible printed circuit board becomes larger, and due to the low crosslinking density, the coatings formed on the substrate may stick together.

[0005] Furthermore, in recent years, there has been an increasing demand for thinner coatings even in fields using rigid substrates. The phenomenon of coatings sticking to each other can occur not only with flexible substrates, but also with thin substrates such as rigid substrates with a thickness of 0.1 mm.

[0006] To solve this problem, increasing the surface roughness of the coating reduces the contact surface area, preventing adhesion. However, attempting to pattern a coating with a high surface roughness using photolithography results in halation on the coating surface, preventing sufficient resolution from being achieved.

[0007] In view of the aforementioned problems, the object of the present invention is to provide a curable resin composition that has good resolution of the dried coating film, good flexibility of the resulting cured product, and low adhesion when stacked for storage. [Means for solving the problem]

[0008] The inventors diligently conducted studies to achieve the above objectives. As a result, they discovered that by using a curable resin composition that maintains low surface roughness (arithmetic mean roughness) in the dried coating film and increases surface roughness (arithmetic mean roughness) after heat curing, it is possible to achieve both high resolution in the dried coating film and flexibility and low adhesion in the heat-cured film, thus completing the present invention. In this specification, resolution refers to the ability to express fine details in an image obtained when a resin layer made of the curable resin composition of the present invention is exposed and alkaline developed.

[0009] In other words, the object of the present invention is A curable resin composition that is alkali-developable and forms a cured film by exposure and heat treatment, It was found that this can be achieved by a curable resin composition characterized in that, when a dry coating film with a thickness of 2 to 100 μm is formed from the curable resin composition, the arithmetic mean roughness Ra of the dry coating film is less than 0.1 μm, and the arithmetic mean roughness Ra of the cured film after heat curing of the dry coating film is 0.1 μm or more and 1 μm or less.

[0010] In this specification, resolution refers to the detail rendering ability of an image obtained when a resin layer made of the curable resin composition of the present invention is pattern-exposed and then alkaline-developed.

[0011] Furthermore, when a curable resin composition forms a dry coating film with a thickness of 2 to 100 μm from the curable resin composition, it is preferable that the arithmetic mean roughness Ra of the dry coating film is less than 0.05 μm, and the arithmetic mean roughness Ra of the cured film after heat curing of the dry coating film is 0.1 μm or more and 0.5 μm or less.

[0012] Furthermore, it is preferable to include (A) an alkali-soluble polyamide-imide resin, (B) a photobase generator, (C) a thermosetting compound, and (D) a cellulose derivative.

[0013] Furthermore, it is preferable that (C) the thermosetting compound is an epoxy resin.

[0014] Furthermore, the above object of the present invention is achieved by a laminated structure in which at least one side of a resin layer formed of the curable resin composition of the present invention is supported or protected by a film. It can also be achieved by an electronic component having a cured product of the resin layer of the curable resin composition or the laminated structure of the present invention, and an insulating film made of the cured product of the present invention.

Advantages of the Invention

[0015] According to the curable resin composition of the present invention, the resulting dry coating film has good resolution, and the cured product after heat curing also has good flexibility. Even when the cured products are stacked and stored in a high-temperature environment, they have the property of having a small adhesion.

Brief Description of the Drawings

[0016] [Figure 1] It is an explanatory diagram of the MIT test performed using the evaluation substrate produced in the example as a test piece.

Modes for Carrying Out the Invention

[0017] <Curable Resin Composition> The curable resin composition of the present invention is a curable resin composition that is alkali-developable and forms a cured film by exposure and heat treatment, when a dry coating film with a thickness of 2 to 100 μm is formed from the curable resin composition, the arithmetic mean roughness Ra of this dry coating film is less than 0.1 μm, and the arithmetic mean roughness Ra of the cured film after heat curing of the dry coating film is 0.1 μm or more and 1 μm or less.

[0018] For the curable resin composition of the present invention to be alkali-developable and form a cured film by exposure and heat treatment, its constituent components include a compound having an alkali-soluble functional group (hereinafter also referred to as an alkali-soluble group) (hereinafter also referred to as an alkali-soluble compound), a (B) photo-base generator described later, and a (C) thermosetting compound.

[0019] Among these, the (B) photoacid generator functions as a catalyst for the addition reaction between the alkali-soluble compound and the (C) thermosetting compound by changing its molecular structure or cleaving the molecule upon irradiation with light such as ultraviolet light or visible light.

[0020] Examples of the alkali-soluble compound include a compound having a phenolic hydroxyl group, a compound having a carboxyl group, and a compound having a phenolic hydroxyl group and a carboxyl group. Preferably, the alkali-soluble compound is the (A) alkali-soluble polyamide-imide resin described later. Among them, as the (A) alkali-soluble polyamide-imide resin, it is preferable to use a polyamide-imide resin having a structure represented by the general formula (1) described later and a structure represented by the following general formula (2).

[0021] When a dry coating film with a thickness of 2 to 100 μm, more preferably 3 to 80 μm from the viewpoint of improving resolution, is formed from the curable resin composition of the present invention, the arithmetic mean roughness Ra of this dry coating film is less than 0.1 μm, preferably less than 0.05 μm, and the arithmetic mean roughness Ra of the cured film after heat curing of the dry coating film is 0.1 μm or more and 1 μm or less, preferably 0.1 μm or more and 0.5 μm or less.

[0022] When the arithmetic mean roughness Ra of the dry coating film is less than 0.1 μm, diffuse reflection of the light irradiated on the coating film during exposure is suppressed, and the resolution becomes good. Further, after heat curing, small irregularities occur on the cured film because the arithmetic mean roughness Ra of the cured film is 0.1 μm or more and 1 μm or less. Due to the presence of these irregularities, the contact area between the cured films arranged in a stacked manner becomes small, contributing to a decrease in adhesion.

[0023] The phenomenon in which the surface of the dried coating film is smooth before heat curing, but becomes rougher after heat curing, is thought to be caused by the curable resin composition of the present invention containing polymer components that have different compatibility with the above-mentioned (C) thermosetting compounds and alkali-soluble compounds. In other words, it is presumed that this occurs when polymer components that were dispersed in the dried coating film before heat curing migrate to the film surface during the heat curing reaction.

[0024] It is preferable to include a (D) cellulose derivative as this polymer component.

[0025] The curable resin composition of the present invention preferably contains (A) an alkali-soluble polyamide-imide resin, (B) a photobase generator, (C) a thermosetting compound, and (D) a cellulose derivative.

[0026] [(A) Alkali-soluble polyamide-imide resin] (A) Alkali-soluble polyamide-imide resins are preferred examples of the above-mentioned alkali-soluble photocurable compounds. (A) Alkali-soluble polyamide-imide resins contain alkali-soluble groups (one or more of phenolic hydroxyl groups and carboxyl groups).

[0027] Examples of such alkali-soluble polyamide-imide resins include resins obtained by reacting a carboxylic acid anhydride component with an amine component to obtain an imidide, and then reacting the obtained imidide with an isocyanate component. Here, the alkali-soluble group is introduced by using an amine component having a carboxyl group or a phenolic hydroxyl group. Furthermore, imidation may be carried out by thermal imidation, chemical imidation, or a combination of both.

[0028] Examples of carboxylic acid anhydride components include tetracarboxylic acid anhydrides and tricarboxylic acid anhydrides, but the formula is not limited to these acid anhydrides. Any compound having an acid anhydride group and a carboxyl group that react with an amino group or an isocyanate group, including its derivatives, can be used. Furthermore, these carboxylic acid anhydride components may be used individually or in combination.

[0029] As amine components, diamines such as aliphatic diamines and aromatic diamines, polyhydric amines such as aliphatic polyetheramines, diamines having a carboxyl group, and diamines having a phenolic hydroxyl group can be used. While the amine component is not limited to these amines, it is necessary to use an amine that can incorporate at least one functional group from a phenolic hydroxyl group and a carboxyl group. Furthermore, these amine components may be used individually or in combination.

[0030] As the isocyanate component, diisocyanates such as aromatic diisocyanates and their isomers and polymers, aliphatic diisocyanates, alicyclic diisocyanates and their isomers, and other general-purpose diisocyanates can be used, but are not limited to these isocyanates. Furthermore, these isocyanate components may be used individually or in combination.

[0031] (A) When an alkali-soluble polyamide-imide resin is included in the curable resin composition of the present invention, from the viewpoint of achieving a good balance between the alkali solubility (developability) of the polyamide-imide resin and other properties such as the mechanical properties of the cured product of the resin composition containing the polyamide-imide resin, the acid value (solids acid value) is preferably 30 mg KOH / g or more, more preferably 30 mg KOH / g to 150 mg KOH / g, and particularly preferably 50 mg KOH / g to 120 mg KOH / g. Specifically, by setting this acid value to 30 mg KOH / g or more, alkali solubility, i.e., developability, is improved, and furthermore, the crosslinking density with the thermosetting component after light irradiation is increased, and sufficient development contrast can be obtained. In addition, by setting this acid value to 150 mg KOH / g or less, the so-called thermal fogging in the PEB (POST EXPOSURE BAKE) process after light irradiation, described later, can be suppressed, and the process margin is increased.

[0032] Furthermore, (A) the molecular weight of the alkali-soluble polyamide-imide resin is preferably 20,000 or less in mass average molecular weight, more preferably 1,000 to 17,000, and even more preferably 2,000 to 15,000, considering the developability and cured film properties. When the molecular weight is 20,000 or less, the alkali solubility of the unexposed areas increases, improving the developability. On the other hand, when the molecular weight is 1,000 or more, sufficient developability and cured properties can be obtained in the exposed areas after the exposure and PEB process.

[0033] (A) When an alkali-soluble polyamide-imide resin is included in the curable resin composition of the present invention, it is particularly preferable to use a polyamide-imide resin having the structure shown in the following general formula (1) and the structure shown in the following general formula (2) in order to further improve developability and also improve flexibility and adhesion. Note that the structure shown in general formula (1) and the structure shown in the following general formula (2) are not limited to being included in one molecule of the alkali-soluble polyamide-imide resin (A), but may be included in the alkali-soluble polyamide-imide resin (A).

[0034] [ka] TIFF0007881353000002.tif32101

[0035] (In general formula (1), X1 is a residue of an aliphatic diamine (a) derived from a dimer acid having 24 to 48 carbon atoms (hereinafter also referred to as "dimer amine (a)"), In general formula (2), X2 is a residue of an aromatic diamine (b) having a carboxyl group (hereinafter also referred to as "carboxyl group-containing diamine (b)"). In general formulas (1) and (2), Y is independently either cyclohexane or an aromatic ring.

[0036] By incorporating the structure represented by the above general formula (1) and the structure represented by the above general formula (2), it is possible to obtain a polyamide-imide resin with excellent alkali solubility that can dissolve even when a mild alkaline solution such as a 1.0% by mass aqueous solution of sodium carbonate is used. Furthermore, the cured product of a curable resin composition containing such polyamide-imide resin can have excellent dielectric properties.

[0037] Dimer amine (a) can be obtained by reductive amination of the carboxyl group in the dimer of an aliphatic unsaturated carboxylic acid having 12 to 24 carbon atoms. That is, dimer amine (a), which is an aliphatic diamine derived from a dimer acid, can be obtained by polymerizing an unsaturated fatty acid such as oleic acid or linoleic acid to form a dimer acid, reducing it, and then aminating it. As such an aliphatic diamine, commercially available products such as PRIAMINE 1073, 1074, and 1075 (product name, manufactured by Croda Japan Co., Ltd.), which are diamines having a 36-carbon skeleton, can be used. Dimer amine (a) may preferably be derived from a dimer acid having 28 to 44 carbon atoms, and may be more preferably derived from a dimer acid having 32 to 40 carbon atoms.

[0038] Specific examples of carboxyl group-containing diamine (b) include 3,5-diaminobenzoic acid, 3,4-diaminobenzoic acid, 5,5'-methylenebis(anthranilic acid), and benzidine-3,3'-dicarboxylic acid. Carboxyl group-containing diamine (b) may be composed of one type of compound or multiple types of compounds. From the viewpoint of raw material availability, it is preferable that carboxyl group-containing diamine (b) contains 3,5-diaminobenzoic acid and 5,5'-methylenebis(anthranilic acid).

[0039] The relationship between the content of the structure represented by general formula (1) and the content of the structure represented by general formula (2) in the above polyamide-imide resin is not limited. From the viewpoint of achieving a good balance between the alkali solubility of the polyamide-imide resin and other properties such as the mechanical properties of the cured product of the curable resin composition containing the polyamide-imide resin, the content of dimer amine (a) (unit: mass%) is preferably 20 to 60 mass%, and more preferably 30 to 50 mass%. In this specification, "content of dimer amine (a)" means the ratio of the amount of dimer amine (a), which is positioned as one of the raw materials when manufacturing the polyamide-imide resin, to the mass of the manufactured polyamide-imide resin. Here, "mass of the manufactured polyamide-imide resin" is the value obtained by subtracting the theoretical amounts of water (H2O) produced in imidation and carbon dioxide (CO2) produced in amidation from the total amount of raw materials used to manufacture the polyamide-imide resin.

[0040] From the viewpoint of improving the alkali solubility of the polyamide-imide resin, it is preferable that the portion represented by Y in the above general formulas (1) and (2) has a cyclohexane ring. From the viewpoint of balancing the alkali solubility of the polyamide-imide resin with other properties such as the mechanical properties of the cured resin composition containing the polyamide-imide resin, the quantitative relationship between the aromatic ring and the cyclohexane ring in the portion represented by Y is preferably such that the molar ratio of the cyclohexane ring content to the aromatic ring content is 85 / 15 to 100 / 0, more preferably 90 / 10 to 99 / 1, and even more preferably 90 / 10 to 98 / 2.

[0041] The method for producing the alkali-soluble polyamide-imide resin described above (A) is not limited and can be produced by known and conventional methods via an imidation step and an amide-imide step.

[0042] In the imidation step, one or two substances selected from the group consisting of dimer amine (a), carboxyl group-containing diamine (b), and cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride (c) and trimellitic anhydride (d) are reacted to obtain an imidide.

[0043] The amount of dimeramine (a) added is preferably such that the dimeramine (a) content is 20 to 60% by mass, and more preferably such that the dimeramine (a) content is 30 to 50% by mass. The definition of the dimeramine (a) content is as described above.

[0044] If necessary, other diamines may be used in conjunction with dimer amine (a) and carboxyl group-containing diamine (b). Other specific examples of diamines include 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, bis[4-(4-aminophenoxy)phenyl]methane, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ketone, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-bis(trifluoromethyl)biphenyl-4,4'-diamine, and 2,6,2',6'-tetramethyl-4 Aromatic diamines include ,4'-diamine, 5,5'-dimethyl-2,2'-sulfonyl-biphenyl-4,4'-diamine, 3,3'-dihydroxybiphenyl-4,4'-diamine, (4,4'-diamino)diphenyl ether, (4,4'-diamino)diphenyl sulfone, (4,4'-diamino)benzophenone, (3,3'-diamino)benzophenone, (4,4'-diamino)diphenylmethane, (4,4'-diamino)diphenyl ether, and (3,3'-diamino)diphenyl ether, while aliphatic diamines include hexamethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, octadecamethylenediamine, 4,4'-methylenebis(cyclohexylamine), isophoronediamine, 1,4-cyclohexanediamine, and norbornenediamine.

[0045] From the viewpoint of improving the alkali solubility of the polyamide-imide resin, it is preferable to use cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride (c) in the imidation process. The molar ratio of the amount of cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride (c) used to the amount of trimellitic anhydride (d) used is preferably 85 / 15 to 100 / 0, more preferably 90 / 10 to 99 / 1, and even more preferably 90 / 10 to 98 / 2.

[0046] The relationship between the amount of diamine compound used to obtain the imidide (specifically, dimer amine (a) and carboxyl group-containing diamine (b), and other diamines used as needed) and the amount of acid anhydride (specifically, one or two selected from the group consisting of cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride (c) and trimellitic anhydride (d)) is not limited. The amount of acid anhydride used is preferably such that its molar ratio to the amount of diamine compound used is 2.0 or more and 2.4 or less, and more preferably such that the molar ratio is 2.0 or more and 2.2 or less.

[0047] In the amide-imidation step, a diisocyanate compound is reacted with the imidide obtained in the above imidation step to obtain a polyamide-imide resin containing a substance having the structure shown in general formula (3) described later.

[0048] The specific type of diisocyanate compound is not limited. The diisocyanate compound may consist of one type of compound or multiple types of compounds.

[0049] Specific examples of diisocyanate compounds include aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, naphthalene-1,5-diisocyanate, o-xylylene diisocyanate, m-xylylene diisocyanate, and 2,4-tolylene dimer; and aliphatic diisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornene diisocyanate. (A) From the viewpoint of improving both the alkali solubility of the alkali-soluble polyamide-imide resin and the light transmittance of the polyamide-imide resin, it is preferable that the diisocyanate compound contains an aliphatic isocyanate, and it is more preferable that the diisocyanate compound is an aliphatic isocyanate.

[0050] The amount of diisocyanate compound used in the amide-imide process is not limited. From the viewpoint of imparting appropriate alkaline solubility to the polyamide-imide resin, the amount of diisocyanate compound used is preferably 0.3 to 1.0, more preferably 0.4 to 0.95, and particularly preferably 0.50 to 0.90, as a molar ratio to the amount of diamine compound used to obtain the imide compound.

[0051] The polyamide-imide resin produced in this manner is given by the following general formula (3) [ka] This includes substances having the structure shown by (in the above general formula (3), X is independently a diamine residue (a residue of a diamine compound), Y is independently an aromatic ring or a cyclohexane ring, and Z is a residue of a diisocyanate compound. n is a natural number.)

[0052] The combined amount of (A) an alkali-soluble polyamide-imide resin and (E) an optional component described later, which is an alkali-soluble polyimide resin, is, for example, 10 parts by mass or more and 85 parts by mass or less, preferably 15 parts by mass or more and 80 parts by mass or less, and particularly preferably 20 parts by mass or more and 75 parts by mass or less, per 100 parts by mass of the curable resin composition of the present invention.

[0053] [(B) Photobase Generator] The curable resin composition of the present invention preferably contains (A) an alkali-soluble polyamide-imide resin (and (E) an alkali-soluble polyimide resin of an optional component described later) and (C) a thermosetting compound, and (B) a photobase generator that can function as a catalyst for the addition reaction. (D) The photobase generator is a compound that generates one or more basic substances that can function as a catalyst for the addition reaction between a polyimide resin having a carboxyl group and a thermosetting component by changing its molecular structure or by cleaving the molecule upon irradiation with light such as ultraviolet light or visible light.

[0054] Examples of basic substances include secondary amines and tertiary amines.

[0055] Examples of photobase generators include α-aminoacetophenone compounds, oxime ester compounds, and compounds having substituents such as acyloxyimino groups, N-formylated aromatic amino groups, N-acylated aromatic amino groups, nitrobenzylcarbamate groups, and alcooxybenzylcarbamate groups. Among these, oxime ester compounds and α-aminoacetophenone compounds are preferred. As for α-aminoacetophenone compounds, those having two or more nitrogen atoms are particularly preferred.

[0056] Other photobase generators that can be used include WPBG-018 (trade name: 9-anthrylmethylN,N'-diethylcarbamate), WPBG-027 (trade name: (E)-1-[3-(2-hydroxyphenyl)-2-propenoyl]piperidine), WPBG-082 (trade name: guanidinium2-(3-benzoylphenyl)propionate), WPBG-140 (trade name: 1-(anthraquinon-2-yl)ethyl imidazolecarboxylate), etc. (all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). α-aminoacetophenone compounds have a benzoin ether bond in their molecule, and upon light irradiation, intramolecular cleavage occurs, generating a basic substance (amine) that exhibits curing catalytic activity.

[0057] Specific examples of α-aminoacetophenone compounds include commercially available compounds or solutions thereof such as (4-morpholinobenzoyl)-1-benzyl-1-dimethylaminopropane (Omnirad 369, trade name, manufactured by IGM Resins), 4-(methylthiobenzoyl)-1-methyl-1-morpholinoethane (Omnirad 907, trade name, manufactured by IGM Resins), and 2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone (Omnirad 379, trade name, manufactured by IGM Resins).

[0058] Any oxime ester compound that generates a basic substance upon light irradiation can be used. Among such oxime ester compounds, oxime ester-based photobase generators having a group represented by the following general formula (4) are preferred.

[0059] [ka]

[0060] (In the formula, R1 represents a hydrogen atom, an unsubstituted or C1-C6 alkyl group, a phenyl group substituted with a phenyl group or a halogen atom, an unsubstituted or C1-C6 alkyl group substituted with one or more hydroxyl groups, an alkyl group interrupted by one or more oxygen atoms, an unsubstituted or C1-C6 alkyl group or C5-C8 cycloalkyl group substituted with a phenyl group, an unsubstituted or C1-C6 alkyl group or a phenyl group, an alkanoyl group or benzoyl group of C2-C20, and R2 represents an unsubstituted or C1-C6 alkyl group, a phenyl group substituted with a phenyl group or a halogen atom, an unsubstituted or C1-C20 alkyl group substituted with one or more hydroxyl groups, an alkyl group interrupted by one or more oxygen atoms, an unsubstituted or C1-C6 alkyl group or C5-C8 cycloalkyl group substituted with a phenyl group, an alkanoyl group or benzoyl group of C2-C20, and an alkanoyl group or benzoyl group of C1-C6.) Commercially available oxime ester-based photobase generators include IRGACURE OXE01 and IRGACURE OXE02 from BASF Japan, and N-1919 and NCI-831 from ADEKA. Compounds having two oxime ester groups in the molecule, as described in Japanese Patent Publication No. 4344400, can also be suitably used.

[0061] Other examples include carbazole oxime ester compounds described in Japanese Patent Publication No. 2004-359639, Japanese Patent Publication No. 2005-097141, Japanese Patent Publication No. 2005-220097, Japanese Patent Publication No. 2006-160634, Japanese Patent Publication No. 2008-094770, Japanese Patent Publication No. 2008-509967, Japanese Patent Publication No. 2009-040762, and Japanese Patent Publication No. 2011-80036.

[0062] Such photobase generators may be used individually or in combination of two or more. The amount of (B) photobase generator in the curable resin composition of the present invention is, for example, 0.1 parts by mass or more and 40 parts by mass or less, preferably 0.2 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of (A) alkali-soluble polyamide-imide resin, or, if (E) alkali-soluble polyimide resin is included, per 100 parts by mass of the total amount of (A) alkali-soluble polyamide-imide resin and alkali-soluble polyimide resin.

[0063] When the amount is 0.1 parts by mass or more, a good contrast in the development resistance between the light-irradiated and unirradiated areas can be obtained. Furthermore, when the amount is 40 parts by mass or less, the properties of the cured product are improved.

[0064] [(C) Thermosetting compound] From the viewpoint of imparting heat resistance and chemical resistance to the cured product after heat curing, the curable resin composition of the present invention preferably contains (C) a thermosetting compound.

[0065] (C) The thermosetting compound can be a known and commonly used thermosetting resin such as epoxy resin, urethane resin, polyester resin, polyurethane containing hydroxyl, amino, or carboxyl groups, polyester, polycarbonates, polyols, phenoxy resin, acrylic copolymer resin, vinyl resin, oxazine resin, or cyanate resin.

[0066] In particular, from the viewpoint of heat resistance and chemical resistance, it is preferable that (C) the thermosetting compound is an epoxy resin.

[0067] Specific examples of epoxy resins include bisphenol A type epoxy resins such as jER828 from Mitsubishi Chemical Corporation, EHPE3150 from Daicel Corporation, EPICLON840 from DIC Corporation, Epotote YD-011 from Nippon Steel Chemical & Material Corporation, DER317 from Dow Chemical Corporation, and Sumi-Epoxy ESA-011 from Sumitomo Chemical Corporation (all are product names); brominated epoxy resins such as jERYL903 from Mitsubishi Chemical Corporation, EPICLON152 from DIC Corporation, Epotote YDB-400 from Nippon Steel Chemical & Material Corporation, DER542 from Dow Chemical Corporation, and Sumi-Epoxy ESB-400 from Sumitomo Chemical Corporation (all are product names); and jER152 from Mitsubishi Chemical Corporation and DEN from Dow Chemical Corporation.431, Novolac-type epoxy resins such as EPICLON N-730 from DIC Corporation, Epotote YDCN-701 from Nippon Steel Chemical & Material Co., Ltd., EPPN-201 from Nippon Kayaku Co., Ltd., and Sumiepoxy ESCN-195X from Sumitomo Chemical Co., Ltd. (all are product names); Bisphenol F-type epoxy resins such as EPICLON 830 from DIC Corporation, jER807 from Mitsubishi Chemical Corporation, and Epotote YDF-170, YDF-175, YDF-2004 from Nippon Steel Chemical & Material Co., Ltd. (all are product names) Xylionic resin; hydrogenated bisphenol A type epoxy resins such as Epotote ST-2004 (product name) manufactured by Nippon Steel Chemical & Material; glycidylamine type epoxy resins such as jER604 manufactured by Mitsubishi Chemical Corporation, Epotote YH-434 manufactured by Nippon Steel Chemical & Material Corporation, and Sumiepoxy ELM-120 manufactured by Sumitomo Chemical Corporation (all product names); hydantoin type epoxy resins; alicyclic epoxy resins such as Celoxide 2021 manufactured by Daicel Corporation (all product names) Examples include: trihydroxyphenylmethane-type epoxy resins such as EPPN-501 (all trade names) manufactured by Nippon Kayaku Co., Ltd.; bixylenol-type or biphenol-type epoxy resins or mixtures thereof such as YL-6056, YX-4000, and YL-6121 (all trade names) manufactured by Mitsubishi Chemical Corporation; bisphenol S-type epoxy resins such as EBPS-200 manufactured by Nippon Kayaku Co., Ltd., EPX-30 manufactured by ADEKA Corporation, and EXA-1514 (trade name) manufactured by DIC Corporation; bisphenol A novolac-type epoxy resins such as jER157S (trade name) manufactured by Mitsubishi Chemical Corporation; heterocyclic epoxy resins such as TEPIC (all trade names) manufactured by Nissan Chemical Corporation; biphenyl novolac-type epoxy resins; naphthalene group-containing epoxy resins such as ESN-190 manufactured by Nippon Steel Chemical & Material Co., Ltd. and HP-4032 manufactured by DIC Corporation; and epoxy resins having a dicyclopentadiene skeleton such as HP-7200 manufactured by DIC Corporation.

[0068] (C) The thermosetting compound may be added in any amount, but it is preferable to add it in a ratio such that the equivalent ratio (alkali-soluble group: thermosetting group such as epoxy group) of (A) the alkali-soluble polyamide-imide resin and (E) the alkali-soluble polyimide resin, if present, is 1:0.1 to 1:10.

[0069] [(D) Cellulose derivatives] The curable resin composition of the present invention preferably contains (D) a cellulose derivative as a polymer component having different compatibility with the above-mentioned (C) thermosetting compound and alkali-soluble photocurable compound. When (D) a cellulose derivative is included in the curable resin composition of the present invention, it is preferable that (D) a cellulose derivative is soluble in organic solvents and has a high glass transition temperature (Tg). Examples of (D) cellulose derivatives include cellulose ethers, carboxymethylcellulose, and cellulose esters, as described later.

[0070] Examples of cellulose ethers include ethylcellulose and hydroxyalkylcellulose. Commercially available ethylcellulose products include Etocell® 4, Etocell 7, Etocell 10, Etocell 14, Etocell 20, Etocell 45, Etocell 70, Etocell 100, Etocell 200, and Etocell 300 (all product names of Dow Chemical Company). Commercially available hydroxyalkylcellulose products include Metroz SM, Metroz 60SH, Metroz 65SH, Metroz 90SH, Metroz SEB, and Metroz SNB (all product names of Shin-Etsu Chemical Co., Ltd.).

[0071] Other commercially available carboxymethylcellulose products include CMCAB-641-0.2 (a product name manufactured by Eastman Chemical Company), Sunrose F, Sunrose A, Sunrose P, Sunrose S, and Sunrose B (all product names manufactured by Nippon Paper Industries Co., Ltd.).

[0072] A more preferred cellulose derivative is a cellulose ester obtained by esterifying the hydroxyl group of cellulose with an organic acid, specifically, the following formula (5) [ka] Examples of compounds represented by formula (5) are shown below. (In formula (5), R3, R4, and R5 each independently represent hydrogen or an acyl group, at least one of R3, R4, and R5 is hydrogen, and n is an integer of 1 or more, the upper limit of which is restricted by the molecular weight as described later.)

[0073] In the cellulose ester represented by formula (5) above, the content of acyl groups relative to the cellulose resin is in the range of more than 0 and 60 wt%, preferably in the range of 5 to 55 wt%.

[0074] In the cellulose ester represented by formula (5) above, the hydroxyl group content relative to the cellulose resin is preferably 0 to 6 wt%, and as acyl groups, the acetyl group content is preferably 0 to 40 wt%, and the propionyl group and / or butyryl group content is preferably in the range of 0 to 55 wt%. Here, "wt%" refers to the weight percentage of hydrogen or acyl groups relative to the weight of cellulose.

[0075] Commercially available cellulose esters include cellulose acetates such as CA-398-3, CA-398-6, CA-398-10, CA-398-30, CA-394-60S, and cellulose acetate butyrates such as CAB-551-0.01, CAB-551-0.2, CAB-553-0.4, CAB-531-1, CAB-500-5, CAB-381- Examples of cellulose acetate propionates include 0.1, CAB-381-0.5, CAB-381-2, CAB-381-20, CAB-381-20BP, CAB-321-0.1, CAB-171-15, and CAP-504-0.2, CAP-482-0.5, CAP-482-20 (all of the above cellulose derivatives are trade names of Eastman Chemical Company). Among these, cellulose acetate butyrate and cellulose acetate propionate are preferred from the viewpoint of solubility in solvents.

[0076] (D) The number-average molecular weight of the cellulose derivative is not particularly limited, but is preferably 5,000 to 500,000, more preferably 10,000 to 100,000. More preferably, the molecular weight is 10,000 to 30,000. When the molecular weight is within the above range, adhesion is small, that is, the evaluation result of adhesion is good, and the viscosity of the curable resin composition is within an appropriate range.

[0077] In this specification, the glass transition temperature Tg refers to the glass transition temperature measured by thermomechanical analysis (DSC) in accordance with the method described in "5.17.5 DSC method" of JIS C 6481:1996.

[0078] The cellulose derivative used in this invention is preferably derived from natural sources, which is preferable from the perspective of fossil fuel depletion. Furthermore, the starting material used for the cellulose derivative in this invention can be manufactured from recycled materials such as recycled pulp, providing a composition that is also preferable from an environmental perspective of CO2 reduction.

[0079] (D) Cellulose derivatives can be used alone or in a mixture of two or more. The amount of (D) cellulose derivative is, for example, 0.5 parts by mass to 20 parts by mass, preferably 1 part by mass to 15 parts by mass, and more preferably 1 part by mass to 10 parts by mass, per 100 parts by mass of (A) alkali-soluble polyamide-imide resin (and (E) alkali-soluble polyimide resin of optional components described later). When within this range, the surface roughness (arithmetic mean roughness Ra) of the dried coating can be less than 0.1 μm, adhesion is small, that is, the adhesion evaluation result is good, and the viscosity of the curable resin composition is within an appropriate range. This is thought to be because, before heat curing, (A) the alkali-soluble polyamide-imide resin, (C) the thermosetting compound, and (D) the cellulose derivative have good compatibility, and the polymer components are dispersed in the dried coating film. Furthermore, after thermal curing, the polymer components that were dispersed in the dried coating film migrate to the film surface during the thermal curing reaction, which is thought to increase the surface roughness (arithmetic mean roughness Ra) of the cured film after thermal curing compared to the dried coating film before thermal curing. By setting the number-average molecular weight and blending amount of (D) cellulose derivative within the above range, the surface roughness (arithmetic mean roughness Ra) after curing can also be set to 0.1 μm or more and 1 μm or less.

[0080] [(E) Alkali-soluble polyimide resin] From the viewpoint of heat resistance, the curable resin composition of the present invention preferably contains (E) an alkali-soluble polyimide resin.

[0081] (E) The alkali-soluble polyimide resin has an alkali-soluble functional group (hereinafter also referred to as an alkali-soluble group). An alkali-soluble functional group is a functional group that enables development of the curable resin composition of the present invention in an alkaline solution, and examples include a carboxyl group and a phenolic hydroxyl group.

[0082] Such (E) alkali-soluble polyimide resins include, for example, resins obtained by reacting a carboxylic acid anhydride component with an amine component and / or an isocyanate component. Here, the alkali-soluble group is introduced by using an amine component having a carboxyl group or a phenolic hydroxyl group. Furthermore, imidation may be carried out by thermal imidation, chemical imidation, or a combination of both.

[0083] Examples of carboxylic acid anhydride components include tetracarboxylic acid anhydrides and tricarboxylic acid anhydrides, but the formula is not limited to these acid anhydrides. Any compound having an acid anhydride group and a carboxyl group that react with an amino group or an isocyanate group, including its derivatives, can be used. Furthermore, these carboxylic acid anhydride components may be used individually or in combination.

[0084] As amine components, diamines such as aliphatic diamines and aromatic diamines, polyhydric amines such as aliphatic polyetheramines, diamines having a carboxyl group, and diamines having a phenolic hydroxyl group can be used. While the amine component is not limited to these amines, it is necessary to use an amine that can incorporate at least one functional group from a phenolic hydroxyl group and a carboxyl group. Furthermore, these amine components may be used individually or in combination.

[0085] As the isocyanate component, diisocyanates such as aromatic diisocyanates and their isomers and polymers, aliphatic diisocyanates, alicyclic diisocyanates and their isomers, and other general-purpose diisocyanates can be used, but are not limited to these isocyanates. Furthermore, these isocyanate components may be used individually or in combination.

[0086] In the synthesis of such (E) alkali-soluble polyimide resins, known and conventional organic solvents can be used. Such organic solvents are not limited in structure, as long as they do not react with the raw materials (carboxylic acid anhydrides, amines, isocyanates) and dissolve these raw materials. In particular, aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and γ-butyrolactone are preferred due to their high solubility of the raw materials.

[0087] (E) The alkali-soluble polyimide resin preferably has a carboxyl group as an alkali-soluble group, and is particularly preferably has both a carboxyl group and a phenolic hydroxyl group as an alkali-soluble group.

[0088] (E) From the viewpoint of achieving a good balance between the alkali solubility (developability) of the polyimide resin and other properties such as the mechanical properties of the cured product of the curable resin composition containing the polyimide resin, the acid value (solid content acid value) is preferably 20 to 200 mg KOH / g, and particularly preferably 60 to 150 mg KOH / g.

[0089] Furthermore, regarding (E) the molecular weight of the alkali-soluble polyimide resin, considering the developability and cured coating film characteristics, the mass-average molecular weight Mw is preferably 100,000 or less, more preferably 1,000 to 100,000, and even more preferably 2,000 to 50,000.

[0090] (E) When an alkali-soluble polyimide resin is incorporated, from the viewpoint of improving heat resistance and developability, the mixing ratio of (A) alkali-soluble polyamide-imide resin and (E) alkali-soluble polyimide resin can be 98:2 to 50:50 by mass ratio, preferably 95:5 to 50:50, and more preferably 95:5 to 70:30.

[0091] The curable resin composition of the present invention may further contain the following components as needed.

[0092] [Polymer resin] The curable resin composition of the present invention may be blended with known and conventional polymer resins to improve the flexibility and touch-dry properties of the resulting cured product. Examples of such polymer resins include polyester-based, phenoxy resin-based polymers, polyvinyl acetal-based, polyvinyl butyral-based, polyamide-based polymers, and elastomers. Such polymer resins may be used individually or in combination of two or more types.

[0093] [Inorganic fillers] The curable resin composition of the present invention may be blended with inorganic fillers to suppress curing shrinkage of the cured product and improve properties such as adhesion and hardness. Examples of such inorganic fillers include barium sulfate, amorphous silica, fused silica, spherical silica, talc, clay, magnesium carbonate, calcium carbonate, aluminum oxide, aluminum hydroxide, silicon nitride, aluminum nitride, boron nitride, Neuburg Silica Earth, and the like.

[0094] [Coloring agent] The curable resin composition of the present invention may contain known and conventional colorants such as red, orange, blue, green, yellow, white, and black. Such colorants may be pigments, dyes, or colorants.

[0095] [Organic solvents] The curable resin composition of the present invention may contain organic solvents for the preparation of the resin composition or for viscosity adjustment for application to a substrate or carrier film. Examples of such organic solvents include ketones, aromatic hydrocarbons, glycol ethers, glycol ether acetates, esters, alcohols, aliphatic hydrocarbons, and petroleum-based solvents. Such organic solvents may be used individually or as a mixture of two or more.

[0096] [Other ingredients] The curable resin composition of the present invention may further contain, if necessary, components such as mercapto compounds, adhesion promoters, antioxidants, and ultraviolet absorbers. These can be those that are known and commonly used.

[0097] Furthermore, known and conventional additives such as fine silica powder, hydrotalcite, organic bentonite, and montmorillonite, as well as silicone-based, fluorine-based, and polymer-based defoamers and / or leveling agents, silane coupling agents, and rust inhibitors can be incorporated.

[0098] <Laminated structure> The laminated structure of the present invention is characterized in that at least one side of a resin layer formed with the curable resin composition of the present invention is supported or protected by a film.

[0099] The resin layer may be a single layer or may have a laminated structure of two or more resin layers. In the case of a laminated structure of two or more resin layers, for example, resin layers formed with the curable resin composition of the present invention may be laminated, or the structure may be a laminate of a resin layer formed with the curable resin composition of the present invention and a resin layer formed with a curable resin composition not according to the present invention.

[0100] In the latter case, the laminated structure is such that at least one side of the resin layers is supported or protected by a film, and the resin layers have a laminated structure of, for example, a resin layer (A) provided on a substrate such as a flexible printed circuit board, and a resin layer (B) provided on resin layer (A). Resin layer (A) is made of, for example, an alkali-developable resin composition containing an alkali-soluble resin and a heat-reactive compound.

[0101] The above-mentioned laminated structure can be manufactured, for example, as follows:

[0102] Specifically, first, the curable resin composition of the present invention, which constitutes the resin layer, is diluted with an organic solvent to an appropriate viscosity and applied to a carrier film (support film) using a known method such as a comma coater, according to a conventional method. If the resin layer has a laminated structure, the application operation is repeated with or without changing the resin composition being applied. Then, by drying at a temperature of 50 to 130°C for 1 to 30 minutes, a dried coating film of the resin layer in a B-stage state (semi-cured state) can be formed on the carrier film, thereby producing the laminated structure of the present invention. The resin layer of this laminated structure is a so-called dry film. A peelable cover film (protective film) can be further laminated on this dry film for purposes such as preventing dust from adhering to the surface of the dried coating film. Conventional plastic films can be used as the carrier film and cover film, and for the cover film, it is preferable that the adhesive force when peeling off the cover film is less than the adhesive force between the resin layer and the carrier film. There are no particular restrictions on the thickness of the carrier film and cover film, but they are generally appropriately selected in the range of 10 to 150 μm.

[0103] <Cured product> The cured product of the present invention is obtained by curing the curable resin composition of the present invention or the resin layer of the laminated structure of the present invention.

[0104] <Electronic Components> The curable resin composition and the resin layer of the laminated structure of the present invention can be effectively used in electronic components such as flexible printed circuit boards. Specifically, examples include flexible printed circuit boards having a cured insulating film formed by creating a layer of the curable resin composition or the resin layer of the laminated structure of the present invention on a flexible printed circuit board substrate, patterning it by light irradiation, and forming a pattern with a developing solution.

[0105] The manufacturing method for flexible printed circuit boards will be described in detail below.

[0106] <Manufacturing method for flexible printed circuit boards> An example of manufacturing a flexible printed circuit board using the curable resin composition of the present invention or the resin layer of the laminated structure of the present invention is shown below. Specifically, the manufacturing method includes the steps of: applying the curable resin composition of the present invention or attaching the resin layer of the laminated structure of the present invention to a flexible printed circuit board substrate on which a conductive circuit has been formed to form a resin layer (layer formation step); irradiating this resin layer with active energy rays in a patterned manner (exposure step); and alkaline developing the exposed resin layer to form a patterned resin layer image (development step). Furthermore, if necessary, after alkaline development, further photocuring or thermal curing (post-cure step) can be performed to completely cure the resin layer and form a cured film, thereby obtaining a highly reliable flexible printed circuit board.

[0107] Furthermore, the manufacture of a flexible printed circuit board using the curable resin composition of the present invention or the resin layer of the laminated structure of the present invention can also be carried out according to other procedures. Specifically, the manufacturing method includes the steps of: applying the curable resin composition of the present invention or attaching the resin layer of the laminated structure of the present invention to a flexible printed circuit board substrate on which a conductive circuit has been formed to form a resin layer (layer formation step); irradiating this resin layer with active energy rays in a patterned manner (exposure step); heating the exposed resin layer (heating (PEB) step); and alkaline developing the heated resin layer to form a patterned resin layer image (development step). In addition, if necessary, further photocuring or thermal curing (post-cure step) can be performed after alkaline development to completely cure the resin layer, form a cured film, and obtain a highly reliable flexible printed circuit board. [Examples]

[0108] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified below, "parts" refers to parts by mass of solids.

[0109] ((A) Synthesis of alkali-soluble polyamide-imide resins) [Synthesis Example 1] In a 300 mL four-necked flask equipped with a nitrogen gas inlet tube, thermometer, and stirrer, 28.61 g (0.052 mol) of an aliphatic diamine derived from a 36-C16 dimer acid (Croda Japan, product name PRIAMINE1075) as dimer amine (a), 4.26 g (0.028 mol) of 3,5-diaminobenzoic acid as carboxyl group-containing diamine (b), and 85.8 g of γ-butyrolactone were charged and dissolved at room temperature.

[0110] Next, 30.12 g (0.152 mol) of cyclohexane-1,2,4-tricarboxylic acid anhydride (c) and 3.07 g (0.016 mol) of trimellitic anhydride (d) were charged and held at room temperature for 30 minutes. Then, 30 g of toluene was charged, the temperature was raised to 160°C, and after removing the water produced with the toluene, the mixture was held for 3 hours and cooled to room temperature to obtain a solution containing the imidide.

[0111] To the solution containing the obtained imidide, 14.30 g (0.068 mol) of trimethylhexamethylene diisocyanate as a diisocyanate compound was charged and held at 160°C for 32 hours. Dilution with 21.4 g of cyclohexanone yielded (A) a solution (A-1) containing an alkali-soluble polyamide-imide resin. The obtained polyamide-imide resin had a mass-average molecular weight Mw of 5250, a solid content of 41.5% by mass, an acid value of 63 mg KOH / g, and a dimer amine (a) content of 40.0% by mass.

[0112] [Synthesis Example 2] In a 300 mL four-necked flask equipped with a nitrogen gas inlet tube, thermometer, and stirrer, 29.49 g (0.054 mol) of an aliphatic diamine derived from a C36 dimer acid (Croda Japan, product name PRIAMINE1075) as dimer amine (a), 4.02 g (0.026 mol) of 3,5-diaminobenzoic acid as carboxyl group-containing diamine (b), and 73.5 g of γ-butyrolactone were charged and dissolved at room temperature.

[0113] Next, 31.71 g (0.160 mol) of cyclohexane-1,2,4-tricarboxylic acid anhydride (c) and 1.54 g (0.008 mol) of trimellitic anhydride (d) were charged and held at room temperature for 30 minutes. Then, 30 g of toluene was charged, the temperature was raised to 160°C, and after removing the water produced with the toluene, the mixture was held for 3 hours and cooled to room temperature to obtain a solution containing the imidide.

[0114] To the solution containing the obtained imidide, 6.90 g (0.033 mol) of trimethylhexamethylene diisocyanate and 8.61 g (0.033 mol) of dicyclohexylmethane diisocyanate were charged as diisocyanate compounds, and the mixture was held at 160°C for 32 hours. Dilution with 36.8 g of cyclohexanone yielded (A) a solution (A-2) containing an alkali-soluble polyamide-imide resin. The obtained polyamide-imide resin had a mass-average molecular weight Mw of 5840, a solid content of 40.4% by mass, an acid value of 62 mg KOH / g, and a dimer amine (a) content of 40.1% by mass.

[0115] [Synthesis Example 3] In a 300 mL four-necked flask equipped with a nitrogen gas inlet tube, thermometer, and stirrer, 6.98 g of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 3.80 g of 3,5-diaminobenzoic acid, 8.21 g of polyetherdiamine (Huntsman, product name elastamine RT1000, molecular weight 1025.64), and 86.49 g of γ-butyrolactone were charged and dissolved at room temperature.

[0116] Next, 17.84 g of cyclohexane-1,2,4-tricarboxylic acid-1,2-anhydride and 2.88 g of trimellitic anhydride were charged and held at room temperature for 30 minutes. Then, 30 g of toluene was charged, the temperature was raised to 160°C, and after removing the water produced with the toluene, the mixture was held for 3 hours and cooled to room temperature to obtain the imidide solution.

[0117] To the obtained imidide solution, 9.61 g of trimellitic anhydride and 17.45 g of trimethylhexamethylene diisocyanate were charged and the mixture was held at 160°C for 32 hours. Thus, (A) an alkali-soluble polyamide-imide resin solution (A-3) containing carboxyl groups was obtained. The solid content was 40.1% by mass, and the acid value was 83 mgKOH / g.

[0118] (E) Synthesis of alkali-soluble polyimide resins [Synthesis Example 4] In a separable three-necked flask equipped with a stirrer, nitrogen inlet tube, fractionation ring, and condenser, 22.4 g of 3,3'-diamino-4,4'-dihydroxydiphenylsulfone, 8.2 g of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 30 g of NMP, 30 g of γ-butyrolactone, 27.9 g of 4,4'-oxydiphthalic anhydride, and 3.8 g of trimellitic anhydride were added, and the mixture was stirred at 100 rpm at room temperature under a nitrogen atmosphere for 4 hours. Then, 20 g of toluene was added, and the mixture was stirred for 4 hours at 150 rpm in a silicone bath at 180°C while distilling off the toluene and water to obtain a polyimide resin solution (PI-1) having phenolic hydroxyl groups and carboxyl groups.

[0119] The resulting resin (solid content) had an acid value of 18 mg KOH, a Mw of 10,000, and a hydroxyl group equivalent of 390.

[0120] <1. Preparation of curable resin compositions for Examples 1-12 and Comparative Examples 1-3> According to the component compositions shown in Table 1 below, the materials for the curable resin compositions of Examples 1 to 12 and Comparative Examples 1 to 3 were blended, pre-mixed in a stirrer, and then kneaded in a three-roll mill to prepare each curable resin composition for forming a resin layer. Unless otherwise specified, the values ​​in Table 1 represent parts by mass of solids.

[0121] For each of the curable resin compositions described above, a resin layer (dried coating) in the B-stage state (semi-cured state) was formed, as shown below, and its resolution was evaluated. Furthermore, as described later, the surface roughness of the coating films in the B-stage state (semi-cured state) and after heat curing was evaluated for both the flexible wiring board having this B-stage state (semi-cured state) resin layer and the flexible wiring board having the cured product of this resin layer. In addition, for the flexible wiring board having the cured product of the resin layer, heat resistance (solder heat resistance), gold plating resistance (chemical resistance), flexibility, and adhesion were also evaluated. The results are shown in Table 1.

[0122] <2. Formation of the resin layer> Flexible printed circuit boards with 18 μm thick copper circuits were prepared and pre-treated using MEC CZ-8100. Then, each curable resin composition obtained in Examples 1-12 and Comparative Examples 1-3 was applied to the pre-treated flexible printed circuit board so that the dried film thickness was as shown in Table 1. Finally, the boards were dried in a hot air circulating drying oven at 90°C for 30 minutes to form a B-stage (semi-cured) resin layer (dried coating).

[0123] <3. Fabrication of evaluation board> As described above, the uncured resin layer on each flexible printed circuit board substrate, which has a resin layer formed on it, is first exposed to 300 mJ / cm² via a negative mask using an exposure device equipped with a metal halide lamp (HMW-680-GW20: manufactured by Oak Manufacturing Co., Ltd.). 2 Pattern exposure was performed to form an aperture with a diameter of 200 μm. Subsequently, a PEB process was carried out at 90°C for 30 minutes, followed by development (30°C, 0.2 MPa, 1 mass% Na2CO3 aqueous solution) for 60 seconds, and then heat curing at 150°C for 60 minutes to form a cured resin layer (cured coating film) on a flexible printed circuit board (evaluation board).

[0124] <4. Evaluation of surface roughness> The arithmetic mean surface roughness Ra was measured for the resin layer (dried coating) in the B-stage state (semi-cured state) formed on the flexible printed circuit board as described in <2. Formation of Resin Layer>, or for the resin layer on the thermo-cured evaluation board prepared as described in <3. Preparation of Evaluation Board>. The measured value was the average of 5 arbitrary points within an observation range of 100 × 100 μm. A shape measuring laser microscope (VK-X100, manufactured by Keyence Corporation) was used to measure the arithmetic mean surface roughness Ra. After starting the shape measuring laser microscope (VK-X100) main unit (control unit) and the VK observation application (VK-H1VX, manufactured by Keyence Corporation), a support film with an intermediate layer to be measured (with the side containing the intermediate layer facing upwards) was placed on the xy stage. The lens revolving nosepiece of the microscope unit (VK-X110, manufactured by Keyence Corporation) was rotated to select a 10x magnification objective lens, and the focus and brightness were roughly adjusted in the image observation mode of the VK observation application (VK-H1VX, manufactured by Keyence Corporation). The xy stage was operated to adjust the part of the sample surface to be measured so that it was in the center of the screen. The 10x magnification objective lens was changed to a 100x magnification lens, and the autofocus function of the image observation mode of the VK observation application (VK-H1VX, manufactured by Keyence Corporation) was used to focus on the surface of the sample. The easy mode was selected in the shape measurement tab of the VK observation application (VK-H1VX, manufactured by Keyence Corporation), and the measurement start button was pressed to measure the surface shape of the sample and obtain a surface image file. The VK analysis application (VK-H1XA, manufactured by Keyence Corporation) was launched, the obtained surface image file was displayed, and tilt correction was performed.

[0125] The observation measurement range (horizontal) for measuring the surface shape of the sample was set to 100 μm × 100 μm. The line roughness window was displayed, JIS B 0601-1994 was selected in the parameter setting area, then the horizontal line was selected from the measurement line button, and the horizontal line was displayed at an arbitrary location in the surface image. By pressing the OK button, the arithmetic mean surface roughness Ra value was obtained. Furthermore, the horizontal line was displayed at four different locations in the surface image, and the arithmetic mean surface roughness Ra value for each was obtained. The average of the five obtained values ​​was calculated and used as the arithmetic mean surface roughness Ra value for each resin layer surface.

[0126] <5. Evaluation of Resolution> As described in <2. Formation of Resin Layer>, the B-stage (semi-cured) resin layer (dried coating) formed on the flexible printed circuit board was subjected to measurement of the arithmetic mean roughness Ra of each dried coating as described in <4. Evaluation of Surface Roughness>. The dried coatings of each example, Comparative Example 1, and Comparative Example 3 were less than 0.1 μm. The arithmetic mean roughness Ra of the dried coating of Comparative Example 2 was 0.1 or greater. For each of these dried coatings, exposure was first performed using an exposure apparatus equipped with a metal halide lamp (HMW-680-GW20: manufactured by Oak Seisakusho) via a negative mask at 300 mJ / cm². 2 Pattern exposure was performed to form apertures with diameters of 150 μm and 200 μm. The substrate with the exposed resin layer was then heat-treated at 90°C for 30 minutes.

[0127] Subsequently, the substrate was immersed in a 1% by mass sodium carbonate aqueous solution at 30°C for 1 minute of development, and the pattern formation state was observed to evaluate the resolution. The evaluation criteria are as follows.

[0128] ◎: Good formation of a 150 μm aperture pattern. ○: The 200 μm aperture pattern is formed well, but the 150 μm aperture pattern is slightly defective. ×: The unexposed areas show developability, but there is a defect in the formation of the 200 μm aperture pattern (insufficient resolution).

[0129] <6. Evaluation of heat resistance (solder heat resistance)> As described in <3. Preparation of Evaluation Boards>, rosin-based flux was applied to the evaluation boards, and they were immersed in a solder bath pre-set to 260°C for 20 seconds (10 seconds x 2). The blistering and peeling of the cured coating were observed, and the heat resistance (solder heat resistance) was evaluated. The evaluation criteria are as follows.

[0130] ◎: No swelling or peeling occurred even after immersion for 10 seconds twice. ○: There was no swelling or peeling after immersion for 10 seconds once, but peeling occurred after the second immersion. ×: Swelling and peeling occurred after immersion for 10 seconds once.

[0131] <7. Evaluation of gold plating resistance (chemical resistance)> The evaluation was performed using the evaluation board prepared as described in <3. Preparation of Evaluation Board>, and the following method was used.

[0132] The evaluation substrate was plated with 5 μm of nickel and 0.05 μm of gold at 80-90°C using commercially available electroless nickel and electroless gold plating baths. The gold plating resistance (chemical resistance) was evaluated by observing the substrate and the cured coating. The evaluation criteria are as follows.

[0133] ○: No seepage between the substrate and the cured coating. △: Indicates that seepage has been observed between the substrate and the cured coating. ×: Part of the hardened coating has peeled off.

[0134] <8. Flexibility (MIT exam)> Each evaluation substrate prepared as described in <3. Preparation of Evaluation Substrates> was used as a test specimen, and the MIT test was performed using an MIT Fracture Tester Type D (manufactured by Toyo Seiki Seisakusho) in accordance with JIS P8115, treating the film as paper, to evaluate its flexibility. Specifically, as shown in Figure 1, test specimen 1 was mounted on the apparatus, and with a load F (0.5 kgf) applied, test specimen 1 was attached vertically to clamp 2, and bending was performed at a bending angle α of 135 degrees and a speed of 175 cpm, and the number of reciprocal folds until fracture was measured. The test environment was 25°C, and the radius of curvature was R = 0.38 mm. The evaluation criteria are as follows.

[0135] ◎: It was bent more than 200 times, and no cracks appeared in the hardened coating at the bent points. ○: It was bent 170-199 times and similarly did not crack. △: It was bent 150-169 times and similarly did not crack. ×: Cracks appeared after 149 or fewer folds.

[0136] <9. Adhesion> As described in <2. Formation of Resin Layer>, the resin layer was formed on each flexible printed circuit board substrate in the B-stage state (semi-cured state). The arithmetic mean roughness Ra of each dried coating was measured as described in <4. Evaluation of Surface Roughness>. The dried coatings of each example, Comparative Example 1, and Comparative Example 3 were less than 0.1 μm. The arithmetic mean roughness Ra of the dried coating of Comparative Example 2 was 0.1 or greater. For each of these dried coatings, exposure was first performed using a metal halide lamp-equipped exposure device (HMW-680-GW20: manufactured by Oak Seisakusho) via a negative mask at 300 mJ / cm². 2The substrates were exposed to solid light. Subsequently, a PEB process was performed at 90°C for 30 minutes, followed by development (30°C, 0.2 MPa, 1 mass% Na2CO3 aqueous solution) for 60 seconds, and then heat curing at 150°C for 60 minutes to form a cured coating film. Flexible printed circuit boards (evaluation boards) were then fabricated. For each cured coating film, the arithmetic mean roughness Ra of each dried coating film was measured as described in <4. Evaluation of Surface Roughness>. The dried coating films of each example, Comparative Example 2, and Comparative Example 3 had a roughness of 0.1 μm or more and 1 μm or less. The arithmetic mean roughness Ra of the dried coating film of Comparative Example 1 was less than 0.1.

[0137] The obtained evaluation boards were cut into 2cm squares, stacked in groups of 10, and left at 20, 30, 40, and 60°C for 72 hours each. The presence or absence of adhesion was then checked. The evaluation criteria were as follows:

[0138] ◎: No sticking at 60℃ ○: No sticking at temperatures below 40℃, but slight sticking at 60℃. △: No sticking below 30℃, but sticking occurs above 40℃. ×: Sticking is observed at all temperatures.

[0139] [Table 1] The details of the components in Table 1 are as follows:

[0140] A-1: A polyamide-imide resin-containing solution produced by [Synthesis Example 1] of ((A) Synthesis of alkali-soluble polyamide-imide resin) described above. A-2: A polyamide-imide resin-containing solution produced by [Synthesis Example 2] of ((A) Synthesis of alkali-soluble polyamide-imide resin) described above. A-3: A polyamide-imide resin-containing solution produced by [Synthesis Example 3] of ((A) Synthesis of alkali-soluble polyamide-imide resin) described above. PI-1: Alkali-soluble polyimide resin solution produced by [Synthesis Example 4] of (E) Synthesis of alkali-soluble polyimide resin described above. P7-532: Polyurethane acrylate, acid value 47 mg KOH / g (manufactured by Kyoeisha Chemical Co., Ltd.) IRGACURE OXE02: Oxime-based photopolymerization initiator (manufactured by BASF) CAB-553-0.4: Cellulose acetate derivative, number average molecular weight 20,000, 20 wt% DPM solution (manufactured by Eastman Chemical Corporation) (The quantities in Table 1 indicate the mass parts of solids in the 20 wt% DPM solution) CAB-504-0.2: Cellulose acetate derivative, number average molecular weight 15,000, 20 wt% DPM solution (manufactured by Eastman Chemical Corporation) (The quantities in Table 1 indicate the mass parts of solids in the 20 wt% DPM solution) JER828: Bisphenol A type epoxy resin, epoxy equivalent weight 190, mass-average molecular weight 380 (manufactured by Mitsubishi Chemical Corporation) B-30: Barium sulfate (manufactured by Sakai Chemical Industry Co., Ltd.)

[0141] As shown in Table 1, a comparison of the examples and comparative examples revealed that when a curable resin composition capable of alkali development and forming a cured film by exposure and heat treatment is used to form a dry coating film with a thickness of 2 to 100 μm, if the arithmetic mean roughness Ra of the dry coating film is less than 0.1 μm, and the arithmetic mean roughness Ra of the cured film after heat curing is between 0.1 μm and 1 μm, the formed resin layer (dry coating film) exhibits excellent resolution, and the cured coating film (cured product) after heat curing not only exhibits excellent heat resistance, gold plating resistance, and flexibility, but also exhibits minimal adhesion after high-temperature storage.

[0142] Furthermore, a comparison of Examples 1, 2, 4, 9-11 with Examples 3, 5-8, 12 revealed that when the thickness of the dried coating film is set to 3 μm or more and 80 μm or less, the arithmetic mean roughness Ra of the dried coating film is set to less than 0.05 μm, and the ratio of the arithmetic mean roughness Ra of the cured film after heat curing to the arithmetic mean roughness Ra of the dried coating film (arithmetic mean roughness Ra of the cured film after heat curing / arithmetic mean roughness Ra of the dried coating film) is set to 6 or more, the resolution of the formed resin layer (dried coating film) is greatly improved, and the adhesion of the cured coating film (cured product) after high-temperature storage is further reduced.

Claims

1. A curable resin composition that is alkali-developable and forms a cured film by exposure and heat treatment, It contains (A) an alkali-soluble polyamide-imide resin, (B) a photobase generator, (C) a thermosetting compound, and (D) a cellulose derivative. The number-average molecular weight of the (D) cellulose derivative is 5,000 to 500,000. The amount of the (D) cellulose derivative blended is 0.5 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the (A) alkali-soluble polyamide-imide resin. A curable resin composition characterized in that, when a dry coating film with a thickness of 2 to 100 μm is formed from the curable resin composition, the arithmetic mean roughness Ra of the dry coating film is less than 0.1 μm, and the arithmetic mean roughness Ra of the cured coating film after heat curing of the dry coating film is 0.1 μm or more and 1 μm or less.

2. The curable resin composition according to claim 1, characterized in that when a dry coating film with a thickness of 2 to 100 μm is formed from the curable resin composition, the arithmetic mean roughness Ra of the dry coating film is less than 0.05 μm, and the arithmetic mean roughness Ra of the cured coating film after heat curing of the dry coating film is 0.1 μm or more and 0.5 μm or less.

3. The curable resin composition according to claim 1, characterized in that the (C) thermosetting compound is an epoxy resin.

4. A laminated structure characterized in that at least one side of a resin layer formed from the curable resin composition described in claim 1 is supported or protected by a film.

5. A curable resin composition according to claim 1, or a cured product of a resin layer according to claim 4.

6. An electronic component characterized by having an insulating film made of the cured product described in claim 5.

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