JP2015168733A - Ink composition, protective film, and flexible printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition capable of forming a cured film excellent in heat resistance, for example a protective film of a flexible printed wiring board, the protective film of the flexible printed wiring board formed by the ink composition, and the flexible printed wiring board having the protective film.SOLUTION: There is provided an ink composition containing siloxane modified polyimide, an epoxy resin, and an inorganic filler and having a weight average molecular weight (Mw) of the siloxane modified polyimide of 25,000 to 300,000. The ink composition contains further a phenol resin. The content of the epoxy resin is preferably 20 pts.mass or less based on 100 pts.mass of the siloxane modified polyimide. it is preferable that the siloxane modified polyimide is a condensate of a diamine component containing diaminosiloxane and aromatic tetracarboxylic dianhydride.

Description

  The present invention relates to an ink composition, a protective film, and a flexible printed wiring board.

  In recent years, the number of engine control units mounted on automobiles has increased as automobile systems have become electronic. On the other hand, as the needs for energy saving and weight reduction of automobiles increase, miniaturization of automobiles is demanded, and accordingly, expectations for printed wiring boards are increasing. For example, a printed wiring board is formed by attaching a copper foil to the surface side of a base film made of polyimide resin, etching the copper foil to form a conductive pattern, and then laminating a protective film so as to cover the surface of the conductive pattern. Is formed. This protective film is made of polyimide resin or the like, and plays a role of preventing oxidation, insulation and protection of the conductive pattern (see JP 2009-275076 A).

  However, when it is assumed that a conventional printed wiring board is used for an engine control unit around the engine of an automobile, heat resistance higher than that of other parts is required. For example, heat resistance of 150 ° C. is required around the engine. On the other hand, in the conventional printed wiring board, since the heat resistance of the protective film is insufficient, the present situation is that the application around the engine has not progressed. In view of this, an ink composition for a protective film has been studied in order to improve the heat resistance of the printed wiring board (see International Publication No. 2005/116152).

JP 2009-275076 A International Publication No. 2005/116152

  However, when the ink composition described in the above publication is used, it is difficult to say that heat resistance at 150 ° C. and 1,000 hours, which is said to be a minimum requirement for an engine control unit around an automobile engine, can be secured. .

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an ink composition capable of forming a cured film having excellent heat resistance, such as a protective film for a flexible printed wiring board. Another object of the present invention is to provide a protective film for a flexible printed wiring board formed from the ink composition, and a flexible printed wiring board provided with the protective film.

  The invention made in order to solve the above-described problems includes an ink composition containing a siloxane-modified polyimide, an epoxy resin, and an inorganic filler, wherein the siloxane-modified polyimide has a weight average molecular weight (Mw) of 25,000 or more and 300,000 or less. It is a thing.

  Another invention made to solve the above-described problems is a protective film that covers the conductive pattern of the flexible printed wiring board, and includes a cured film of the ink composition.

  Yet another invention made to solve the above-described problems is a flexible printed wiring board having the protective film.

  The ink composition of the present invention can form a cured film excellent in heat resistance, for example, a protective film for a flexible printed wiring board. Therefore, the ink composition can be suitably used for a protective film of a flexible printed wiring board and a flexible printed wiring board that require heat resistance, and can be suitably used for a flexible printed wiring board used in a high temperature environment.

It is typical sectional drawing which shows the principal part of one Embodiment of the flexible printed wiring board of this invention. It is typical sectional drawing for demonstrating the manufacturing method of the flexible printed wiring board of FIG. It is typical sectional drawing for demonstrating the manufacturing method of the flexible printed wiring board of FIG. It is typical sectional drawing for demonstrating the manufacturing method of the flexible printed wiring board of FIG. It is typical sectional drawing for demonstrating the manufacturing method of the flexible printed wiring board of FIG. It is typical sectional drawing for demonstrating the evaluation sample 1 of an Example.

[Description of Embodiment of the Present Invention]
The present invention is an ink composition containing a siloxane-modified polyimide, an epoxy resin, and an inorganic filler, wherein the siloxane-modified polyimide has a weight average molecular weight (Mw) of 25,000 or more and 300,000 or less.

  According to the ink composition, the heat resistance of the cured film formed from the ink composition is improved by containing the epoxy resin. The reason why the heat resistance is improved by containing an epoxy resin is not clear, but it is considered that the siloxane-modified polyimide is cross-linked by the epoxy resin. Moreover, it is thought that moisture resistance and mechanical strength are improved by crosslinking with such an epoxy resin.

  Moreover, the said ink composition can suppress aggregation of a siloxane modified polyimide by containing the siloxane modified polyimide whose weight average molecular weight (Mw) is a specific range. Therefore, the cured film of the ink composition can suppress a decrease in peel strength due to aggregation of the siloxane-modified polyimide. Furthermore, the cured film of the ink composition is further improved in mechanical strength and peel strength by blending an inorganic filler.

  In addition, the cured film of the ink composition has improved plating resistance by crosslinking with an epoxy resin, preventing aggregation of the modified polyimide, and the like. That is, the cured film of the ink composition suppresses, for example, plating solution soaking and surface roughness due to the plating solution when a circuit exposed portion exposed through the opening is plated in the manufacturing process of the flexible printed wiring board. be able to.

  The ink composition may further contain a phenol resin. Thus, an epoxy resin is bridge | crosslinked by a phenol resin by containing a phenol resin. Therefore, combined with the improvement effect of heat resistance, peel strength, mechanical strength, etc. obtained by crosslinking the siloxane-modified polyimide with the epoxy resin, the heat resistance of the cured film obtained from the ink composition by crosslinking with the phenol resin Properties, peel strength, moisture resistance, mechanical strength and the like are further improved.

  The content of the epoxy resin is preferably 20 parts by mass or less with respect to 100 parts by mass of the siloxane-modified polyimide. Thus, by making content of an epoxy resin 20 mass parts or less, an epoxy resin bridge | crosslinks a siloxane modified polyimide suitably, and further improves characteristics, such as the heat resistance of a cured film, adhesiveness, and mechanical strength. it is conceivable that.

（式（１）及び式（２）中、Ａｒは、４価の芳香族テトラカルボン酸残基である。
式（１）中、Ｒ^１は、２価のジアミンシロキサン残基である。
式（２）中、Ｒ^２は、２価の芳香族ジアミン残基である。
上記式（１）中、ｍは、上記シロキサン変性ポリイミドの全構造単位における上記第１構造単位のモル比率を表し、０．３５以上０．６５以下である。
上記式（２）中、ｎは、上記シロキサン変性ポリイミドの全構造単位における上記第２構造単位のモル比率を表し、０．３５以上０．６５以下である。
ただし、ｍとｎとの合計が１を超える場合はない。） The siloxane-modified polyimide may include a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2).

(In Formula (1) and Formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue.
In formula (1), R ¹ is a divalent diamine siloxane residue.
In formula (2), R ² is a divalent aromatic diamine residue.
In said formula (1), m represents the molar ratio of the said 1st structural unit in all the structural units of the said siloxane modified polyimide, and is 0.35-0.65.
In said formula (2), n represents the molar ratio of the said 2nd structural unit in all the structural units of the said siloxane modified polyimide, and is 0.35-0.65.
However, the sum of m and n does not exceed 1. )

  In the siloxane-modified polyimide, the ratio of the structural units represented by the above formulas (1) and (2) is 0.35 or more and 0.65 or less, that is, the number of siloxane residues in the molecule is an aromatic diamine residue. It is about the same as the group. As described above, the siloxane-modified polyimide in the cured film obtained from the ink composition does not contain an excessive amount of siloxane residues capable of degrading characteristics such as heat resistance. As a result, the ink composition can suppress a decrease in the heat resistance and the like of the cured film due to the siloxane residue.

  The siloxane-modified polyimide is preferably a condensate of a diamine component containing diaminosiloxane and an aromatic tetracarboxylic dianhydride. The composition ratio of the diaminosiloxane in the diamine component is preferably 66% by mass or more and 80% by mass or less. By containing a siloxane-modified polyimide having such a composition, a cured film having flame retardancy suitable for UL-94V-0, for example, a flexible print, without blending an inorganic flame retardant such as magnesium hydroxide. A cured film used for a protective film of a wiring board is obtained. And by not mix | blending an inorganic flame retardant, cured films, such as a protective film, can be made into a lower elastic modulus (softening) more, can suppress curvature, and the outstanding plating resistance is obtained. When the cured film is excellent in plating resistance, it is possible to prevent problems such as penetration by a plating solution when gold plating is applied to the exposed circuit portion after the cured film is formed.

  The side chain of the siloxane-modified polyimide may not contain an unsaturated double bond. Since the heat resistance of the siloxane-modified polyimide of the ink composition is improved by blending an epoxy resin, a siloxane-modified polyimide that does not contain an unsaturated double bond in the side chain can be used. Therefore, since there are few restrictions on the compounds that can be used as the diamine component and aromatic tetracarboxylic dianhydride and the degree of freedom of selection is high, it is easy to give various properties to the cured film and to reduce costs.

  The content of the inorganic filler is preferably 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the siloxane-modified polyimide. Thus, by making content of an inorganic filler into the said range, it is excellent by the effect by mix | blending an inorganic filler, ie, the improvement effect of mechanical strength and peeling strength.

  The average particle size of the inorganic filler is preferably 2 μm or more and 20 μm or less. Thus, characteristics, such as heat resistance of a cured film, improve further by making the average particle diameter of an inorganic filler into the said range.

  The inorganic filler is preferably plate-shaped, and the aspect ratio of the inorganic filler is preferably 5 or more and 100 or less. Thus, characteristics, such as heat resistance of a cured film, improve further because the aspect-ratio of an inorganic filler is the said range.

  The ink composition may further contain a melamine compound. By containing the melamine compound in this manner, the siloxane-modified polyimide molecules can be cross-linked by the melamine compound by heating after application of the ink composition. Therefore, the solvent resistance, mechanical strength, heat resistance, etc. of the cured film obtained from the ink composition can be improved.

  The present invention is a protective film for covering a conductive pattern of a flexible printed wiring board, and includes a protective film made of a cured film of the ink composition. Since the protective film is made of a cured film of the ink composition, the protective film is excellent in characteristics such as heat resistance, peel strength, mechanical strength, and plating resistance.

  The present invention further includes a flexible printed wiring board having the protective film. Since the flexible printed wiring board has the protective film, the protective film improves properties such as heat resistance, peel strength, and mechanical strength.

  The conductive pattern has a base conductor and a surface treatment layer formed on at least a part of the outer surface of the base conductor, and the main component of the surface treatment layer is gold (Au), nickel (Ni), tin It may be (Sn) or aluminum (Al). Thus, when a conductive pattern has a surface treatment layer containing the said main component, the spreading | diffusion to the reactive component with respect to the conductive component to a conductive pattern and the leakage of the conductive component from a conductive pattern can be suppressed. Thus, the weakening of a conductive pattern can be suppressed by suppressing the leakage of the conductive component from a conductive pattern by a surface treatment layer. Further, by suppressing the diffusion of the reactive component to the conductive pattern by the surface treatment layer, the reaction between the reactive component and the conductive component of the conductive pattern is suppressed, and the weakening of the conductive pattern can be suppressed. . As a result, the heat resistance is improved by improving the adhesion between the conductive pattern and the protective film. In particular, the flexible printed wiring board has a protective film excellent in plating resistance, and therefore, even when a surface treatment layer is formed by plating or the like, it is caused by surface roughness of the base conductor caused by a plating solution or the like. Generation | occurrence | production of color transfer, such as a fall of the peeling strength of a protective film, weakening, and whitening, can be suppressed.

  Here, the “weight average molecular weight (Mw)” is a weight average molecular weight in terms of polystyrene by gel permeation chromatography (GPC). The weight average molecular weight (Mw) of the present invention is a value measured under the following measurement conditions.

Measuring device: “HLC-8220GPC” manufactured by Tosoh Corporation
Column: GMH-HR-H
Mobile phase: N-methyl-2-pyrrolidone Column temperature: 40 ° C
Flow rate: 0.5 mL / min Sample concentration: 1.0% by mass
Sample injection volume: 10 μL
Detector: Differential refractometer Standard material: Monodisperse polystyrene

[Details of the embodiment of the present invention]
Hereinafter, an embodiment of the ink composition, protective film and flexible printed wiring board of the present invention will be described.

[Ink composition]
The ink composition contains a siloxane-modified polyimide, an epoxy resin, and an inorganic filler. The ink composition generally contains a solvent, and may further contain a phenol resin and a melamine compound, and may contain other optional components as long as the effects of the present invention are not impaired.

<Siloxane modified polyimide>
Siloxane-modified polyimide is the main adhesive component in the ink composition. This siloxane-modified polyimide is a polyimide containing a structural unit having a siloxane skeleton. In the siloxane-modified polyimide, it is preferable that the side chain does not contain an unsaturated double bond, that is, the side chain of the structural unit of the siloxane-modified polyimide does not contain an unsaturated double bond. Examples of the siloxane-modified polyimide include those containing a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2).

In formula (1) and formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue.
In formula (1), R ¹ is a divalent diamine siloxane residue.
In formula (2), R ² is a divalent aromatic diamine residue.

  Examples of the tetravalent aromatic tetracarboxylic acid residue represented by Ar include a tetravalent group represented by the following formula (3) or formula (4).

In formula (4), W represents a single bond, a divalent hydrocarbon group having 1 to 15 carbon atoms, —O—, —S—, —CO—, —SO ₂ —, —NH—, or —CONH—. It is. Among these, as W, a C1-C15 bivalent hydrocarbon group, a single bond, -CO-, or -O- is preferable.

  Examples of the divalent hydrocarbon group having 1 to 15 carbon atoms represented by W include, for example, a linear or branched divalent chain hydrocarbon group having 1 to 15 carbon atoms, and 3 to 15 carbon atoms. Examples thereof include a divalent alicyclic hydrocarbon group, a divalent aromatic hydrocarbon group having 6 to 10 carbon atoms, or a divalent group obtained by combining these groups.

The divalent diamine siloxane residue represented by R ¹ is a group having a siloxane bond (—Si—O—Si—). By increasing the ratio of the siloxane bond, sufficient flexibility can be imparted to the cured film formed from the ink composition even if the plasticizer content is reduced. As said bivalent diamine siloxane residue, the bivalent group represented, for example by following formula (5) is mentioned.

In Formula (5), R ³ and R ⁴ are each independently a divalent organic group that may contain a single bond or an oxygen atom. R ^{5 to} R ⁸ are each independently a hydrocarbon group having 1 to 6 carbon atoms. a represents the average number of repeating siloxane units (—SiR ⁵ R ⁶ —O—) in the diamine siloxane residue, and is an integer of 1-20. If a is less than 1, the flexibility of the cured film formed from the ink composition may be reduced. On the other hand, when a exceeds 20, the adhesiveness of the cured film may be reduced. From this point, as a, an integer of 5 to 15 is preferable.

Examples of the divalent aromatic diamine residue represented by R ² include divalent groups represented by the following formulas (6) to (8).

In Formula (6) to Formula (8), R ⁹ is each independently a monovalent hydrocarbon group or alkoxy group having 1 to 6 carbon atoms. Z represents a single bond, a divalent hydrocarbon group having 1 to 15 carbon atoms, -O -, - S -, - CO -, - SO 2 -, - NH- or -CONH-. b is an integer of 0-4.

  M in the above formula (1) represents the molar ratio of the first structural unit in all structural units of the siloxane-modified polyimide. N in the above formula (2) represents the molar ratio of the second structural unit in all structural units of the siloxane-modified polyimide. m and n are each independently 0.35 or more and 0.65 or less. However, the sum of m and n does not exceed 1. When m exceeds 0.65 (when n is less than 0.35), the heat resistance of the cured film obtained from the ink composition may be reduced. In addition, since the moisture permeability of the cured film is increased, there is a risk that the peel strength is likely to decrease under high temperature and high humidity, and the ink composition has a high fluidity at about 150 ° C. There is a possibility that oil at about 150 ° C. easily penetrates into a cured film obtained from the composition. On the other hand, when m is less than 0.35 (when n exceeds 0.65), the ratio of the siloxane bond in the siloxane-modified polyimide is reduced, and the cured film formed from the ink composition has sufficient flexibility. There is a possibility that it cannot be granted. Moreover, when m is less than 0.35 (when n exceeds 0.65), the coefficient of thermal expansion of the cured film increases, for example, when the cured film is applied to a protective film of a flexible printed wiring board. In addition, since the difference in coefficient of thermal expansion from the base film becomes large, the base film is likely to warp due to the difference in coefficient of thermal expansion during coating and drying of the ink composition, and workability may be reduced.

  The weight average molecular weight (Mw) of the siloxane-modified polyimide is 25,000 or more and 300,000 or less. The lower limit of the weight average molecular weight (Mw) is more preferably 40,000 and even more preferably 50,000. The upper limit of the weight average molecular weight (Mw) is more preferably 125,000 and even more preferably 90,000. If the weight average molecular weight (Mw) of the siloxane-modified polyimide is less than the above lower limit, the cohesive force is lowered, and thus sufficient peel strength may not be ensured. In addition, the cohesive strength of the ink composition at about 150 ° C. and the low peel strength may cause the oil at about 150 ° C. to easily penetrate into the cured film. Furthermore, the solvent remaining in the cured film may swell due to the low elastic modulus of the cured film formed from the ink composition at a reflow temperature of about 260 ° C. On the other hand, when the weight average molecular weight (Mw) of the siloxane-modified polyimide exceeds the above upper limit, aggregation of molecular chains of the siloxane-modified polyimide tends to occur, and the peel strength may be reduced.

<Synthesis method of siloxane-modified polyimide>
The siloxane-modified polyimide can be synthesized as a condensate of an acid dianhydride component containing an aromatic tetracarboxylic acid and a diamine component containing a diaminosiloxane. Specifically, the siloxane-modified polyimide is a polymer solution obtained by forming a polyamic acid solution using a reaction solution in which an acid dianhydride component and a diamine component are added to an organic solvent, and then ring-closing (imidizing) by heating. Can be prepared.

  Examples of the acid dianhydride component include aromatic tetracarboxylic dianhydrides.

  Examples of the aromatic tetracarboxylic dianhydride include oxydiphthalic dianhydride. Examples of oxydiphthalic dianhydride include 4,4′-oxydiphthalic anhydride (also known as 5,5′-oxybis (isobenzofuran-1,3-dione)) (ODPA), 3,3′-oxydiphthalic anhydride. Products, 3,4'-oxydiphthalic anhydride and the like. The exemplified aromatic tetracarboxylic dianhydride may be used alone or in combination of two or more.

  Among the exemplified aromatic tetracarboxylic dianhydrides, 4,4'-oxydiphthalic anhydride (ODPA) is preferable. The ink composition contains a mixture containing 4,4′-oxydiphthalic anhydride (ODPA) as an aromatic tetracarboxylic dianhydride, whereby a flexible cured film is formed by the aromatic tetracarboxylic dianhydride. Obtained and warpage can be suppressed. When using an acid dianhydride component containing 4,4′-oxydiphthalic anhydride (ODPA), the molar ratio of 4,4′-oxydiphthalic anhydride (ODPA) in the acid dianhydride is as follows: It is preferably 40% or more, more preferably 60% or more, and may be 100%.

  As aromatic tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), pyromellitic dianhydride (PMDA) and the like. These may be used alone or in combination of two or more. Among them, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) is inexpensive and has some flexibility It is preferable because of its properties.

  Considering the material cost, aromatic tetracarboxylic dianhydrides include 4,4′-oxydiphthalic anhydride (ODPA) and 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride ( BTDA) or 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) is preferred, and those having a molar ratio of 4: 6 to 6: 4 are more preferred. In addition, since the cured film can be made flexible (low elastic modulus) and hardly warped by setting the composition ratio of diaminosiloxane in a specific range as described above, in aromatic tetracarboxylic dianhydride Even if the ratio of 4,4′-oxydiphthalic dianhydride is reduced, a cured film that is flexible (low elastic modulus) and hardly warps can be obtained. Therefore, the amount of expensive OPDA used can be reduced, and the cost can be reduced.

  Examples of the diamine component include diaminosiloxane and aromatic diamine.

  Examples of the diaminosiloxane include those in which an amino group is bonded to two ends of the diaminosiloxane residue represented by the above formula (5). By using diaminosiloxane as the diamine component, a siloxane skeleton can be introduced into the polyimide. Thereby, solubility is provided to the polyimide by the diaminosiloxane residue. As a result, the adhesion between the cured film formed from the ink composition and the substrate is improved. Furthermore, by using a specific amount of diaminosiloxane as a diamine component, it has flame retardancy suitable for UL-94V-0, VTM-0, etc., even without blending an inorganic flame retardant such as magnesium hydroxide. In addition, an ink composition that can form a protective film that is flexible (low elastic modulus) and hardly warps is obtained.

  As the diaminosiloxane, those represented by the following formulas (9) to (13) are preferable, and among these, the diaminosiloxane represented by the formula (9) is more preferable. The diaminosiloxanes represented by the following formulas (9) to (13) may be used alone or in combination of two or more.

  In the formulas (9) to (13), a has the same meaning as the above formula (5).

  Examples of the aromatic diamine include 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP), 1,3-bis (4-aminophenoxy) benzene, and 1,3-bis (3- Aminophenoxy) benzene (hereinafter also referred to as “APB”), 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoro Propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone (hereinafter also referred to as “BAPSM”), 2,2′-dimethyl-4,4 ′ -Diaminobiphenyl (m-TB), 2,2'-diethyl-4,4'-diaminobiphenyl, 2,2 ', 6,6'-tetramethyl-4,4'-dia Bruno biphenyl, 2,2'-diphenyl-4,4'-diamino biphenyl, 9,9-bis (4-aminophenyl) fluorene, and the like. Among these, 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP), 1,3-bis (3-aminophenoxy) benzene (APB), bis [4- (3-aminophenoxy) ) Phenyl] sulfone (BAPSM) is preferred. The exemplified aromatic diamines may be used alone or in combination of two or more.

  The lower limit of the mass-based composition ratio of diaminosiloxane in the diamine component is preferably 66% by mass, and more preferably 70% by mass. As an upper limit of the said composition ratio, 80 mass% is preferable and 77 mass% is more preferable. When the composition ratio of diaminosiloxane is less than the above lower limit, the elastic modulus of the protective film formed from the ink composition increases and warpage tends to occur. On the other hand, when the composition ratio of diaminosiloxane exceeds the above upper limit, the flame retardancy of the protective film is lowered, and when an inorganic flame retardant such as magnesium hydroxide is not blended, it conforms to UL-94V-0, VTM-0, etc. The flame retardance is not obtained. Moreover, when the composition ratio of diaminosiloxane increases, the glass transition temperature of the protective film tends to decrease and the problem of heat resistance tends to occur.

  The compounding ratio of the aromatic tetracarboxylic dianhydride and the diamine component (diaminosiloxane and aromatic diamine) in the reaction solution is approximately equimolar, for example, 45:55 to 55:45. The compounding ratio (molar ratio) of diaminosiloxane and aromatic diamine is 35:65 or more and 65:35 or less. By setting the blending ratio (molar ratio) of diaminosiloxane and aromatic diamine within the above range, the number of siloxane residues in the siloxane-modified polyimide is set to be about the same as the aromatic diamine residue. Therefore, the siloxane-modified polyimide is suppressed from having too many siloxane residues that can reduce short-term heat resistance. As a result, the ink composition can improve the short-term heat resistance of the cured film.

  The organic solvent used for the synthesis of the siloxane-modified polyimide is preferably a polar solvent, such as N-methyl-2-pyrrolidone, N, N′-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, acetonitrile, diglyme, γ-butyrolactone, Examples thereof include methyl benzoate, ethyl benzoate, γ-valerolactone, toluene, dioxane, tetrahydrofuran, sulfolane, hexamethylphosphoramide and the like. Among these, N-methyl-2-pyrrolidone, methyl benzoate, and γ-butyrolactone are preferable from the viewpoints of solubility, volatility, water absorption, odor, and the like. The amount of the organic solvent used is preferably equal to or greater than the amount that completely dissolves the soluble polyimide resin. These solvents may be used alone or in combination of two or more.

  The content of the organic solvent in the reaction solution is such that the content of the polyamic acid in the polyamic acid solution produced from this reaction solution is 5% by mass to 50% by mass, preferably 10% by mass to 40% by mass. The

  The conditions for the polyamic acid production reaction are such that the temperature of the reaction solution is 0 ° C. to 100 ° C. and the reaction time is 30 minutes to 24 hours.

  The polyamic acid solution can usually be used as it is, but may be used by concentrating, diluting or substituting with another organic solvent as necessary.

  The imidization of the polyamic acid is performed, for example, by heating the polyamic acid solution at a temperature of 80 ° C. to 250 ° C. for 1 hour to 24 hours. If necessary, a small amount of pyridine is added as a dehydration cyclization catalyst, and when the generated water is removed, imidization can be carried out efficiently at a low temperature.

<Epoxy resin>
The epoxy resin improves the heat resistance, mechanical strength, etc. of the cured film formed from the ink composition. It is estimated that this epoxy resin can act as a crosslinking agent for siloxane-modified polyimide. By crosslinking siloxane-modified polyimide with this epoxy resin, the cohesive force of the ink composition is increased, and it is presumed that the heat resistance, mechanical strength, etc. of the cured film formed from the ink composition are improved. Similarly, the retention strength of peel strength under high temperature and high humidity is also improved, but this is presumed to be due to the suppression of moisture permeation due to the improvement of cohesion and the low water absorption compared to polyimide. . Such an epoxy resin is not particularly limited as long as it is an epoxy resin having two or more epoxy groups in one molecule. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, alicyclic epoxy resin, glycidyl ester type epoxy resin, glycidyl amine type epoxy resin, hydantoin type Examples thereof include epoxy resins, isocyanurate type epoxy resins, acrylic acid-modified epoxy resins (epoxy acrylates), phosphorus-containing epoxy resins, halides thereof (brominated epoxy resins and the like), hydrogenated products, and the like. Among these, novolak type epoxy resins such as phenol novolak type epoxy resin and cresol novolak type epoxy resin are preferable from the viewpoint of heat resistance and low moisture absorption. The illustrated epoxy resins may be used alone or in combination of two or more.

  Examples of commercially available phenol novolac epoxy resins include “jER152”, “jER154” (above, Japan Epoxy Resin Co., Ltd.), “EPPN-201-L” (Nippon Kayaku Co., Ltd.), “Epicron N-740”, “ Epicron N-770 "(above, DIC Corporation)," Epototo YDPN-638 "(Nippon Steel & Sumikin Chemical Co., Ltd.) and the like.

  Examples of commercially available products of the cresol novolac type epoxy resin include “EOCN-1020”, “EOCN-102S”, “EOCN-103S”, “EOCN-104S” (Nippon Kayaku Co., Ltd.), “Epiclon N-660”. , “Epicron N-670”, “Epicron N-680”, “Epicron N-695” (above, DIC) and the like.

  Among the novolak-type epoxy resins, an epoxy resin that is solid at normal temperature and has a softening point of 120 ° C. or less is preferable from the viewpoint of improving the heat resistance of the siloxane-modified polyimide.

  As a minimum of content of an epoxy resin, 1 mass part is preferable with respect to 100 mass parts of the said siloxane modified polyimide, 2 mass parts is more preferable, and 3 mass parts is further more preferable. As an upper limit of content of an epoxy resin, 20 mass parts is preferable with respect to 100 mass parts of the said siloxane modified polyimide, 15 mass parts is more preferable, and 10 mass parts is further more preferable. If the content of the epoxy resin is less than the lower limit, the siloxane-modified polyimide cannot be sufficiently crosslinked, and the heat resistance may not be sufficiently improved. On the other hand, when the content of the epoxy resin exceeds the above upper limit, the proportion of the uncrosslinked epoxy resin increases and the heat resistance may be lowered.

<Inorganic filler>
The inorganic filler improves the peel strength, mechanical strength, etc. of the cured film formed from the ink composition.

  Examples of inorganic fillers include talc, silica, alumina, silicon carbide, boron carbide, titanium carbide, tungsten carbide, silicon nitride, boron nitride, aluminum nitride, mica, potassium titanate, barium titanate, calcium carbonate, magnesium oxide, and oxidation. Zirconium etc. are mentioned.

  Examples of the form of the inorganic filler include a plate shape, a spherical shape, a needle shape, a fiber shape, and an indeterminate shape. Especially, as a form of an inorganic filler, plate shape is preferable.

  When the inorganic filler is plate-like, the lower limit of the aspect ratio of the inorganic filler is preferably 5, more preferably 8, and even more preferably 10. The upper limit of the aspect ratio of the inorganic filler is preferably 100, more preferably 75, and even more preferably 40. If the aspect ratio of the inorganic filler is less than the above lower limit, the peel strength may not be sufficiently improved. On the other hand, when the aspect ratio of the inorganic filler exceeds the above upper limit, it is estimated that the cured film becomes brittle, and the peel strength may be reduced.

As a minimum of the average particle diameter of an inorganic filler, 2 micrometers is preferred and 3 micrometers is more preferred.
The upper limit of the average particle size is preferably 20 μm, more preferably 15 μm, and even more preferably 10 μm. If the average particle size is less than the lower limit, the peel strength between the obtained cured film and the substrate may not be sufficiently improved. On the other hand, if the average particle size exceeds the upper limit, the resulting cured film may be brittle and the peel strength may be reduced.

  Here, the “average particle diameter” is a median diameter (d50) calculated from a cumulative distribution measured by a laser diffraction method or a manufacturer's nominal value.

  As a minimum of content of an inorganic filler, 5 mass parts is preferred to 100 mass parts of siloxane modification polyimide, 10 mass parts are more preferred, and 20 mass parts are still more preferred. As an upper limit of content of an inorganic filler, it is 100 mass parts, 70 mass parts is preferable, and 50 mass parts is more preferable. If the content is less than the lower limit, the peel strength between the obtained cured film and the substrate may not be sufficiently improved. On the other hand, when the said content exceeds the said upper limit, there exists a possibility that the cured film obtained may become weak and peeling strength may fall.

<Phenolic resin>
A phenol resin crosslinks an epoxy resin. In addition to phenol-formaldehyde resin, this phenol resin includes xylene resin, resorcin resin, resorcin-modified phenol resin, cresol-modified phenol resin, alkylphenol-modified resin and the like. This phenol resin can be synthesized from, for example, a phenol component and an aldehyde component.

  Examples of the phenol component include, in addition to phenol, alkylphenols such as cresol, xylenol, and isopropylphenol; divalent phenols such as resorcin; and vinylphenols such as p-vinylphenol. These phenol components may be used alone or in combination of two or more.

  Examples of the aldehyde component include formaldehyde and aldehyde group-containing compounds such as acetaldehyde and furfural. These aldehyde components may be used alone or in combination of two or more.

Examples of commercially available phenolic resins include:
“Sumikanol 610” (Taoka Chemical Co., Ltd.);
“Tamanol 1010R”, “Tamanol 100S”, “Tamanol 510”, “Tamanol 7509”, “Tamanol 7705” (above, Arakawa Chemical Industries);
"Shonol CKM-1634", "Shonol CKM-1636", "Shonol CKM-1737", "Shonol CKM-1282", "Shonol CKM-904", "Shonol CKM-907", "Show Nord CKM-908 "," Shonol CKM-983 "," Shonol CKM-2400 "," Shonol CKM-941 "," Shonol CKM-2103 "," Shonol CKM-2432 "," Shonol CKM -5254 "," BKM-2620 "," BRP-5904 "," RM-0909 "," BLS-2030 "," BLS-3574 "," BLS-3122 "," BLS-362 "," BLS-356 ”,“ BLS-3135 ”,“ CLS-3940 ”,“ CLS-3950 ” “BRS-324”, “BRS-621”, “BLL-3085”, “BRL-113”, “BRL-114”, “BRL-117”, “BRL-134”, “BRL-274”, “BRL” -2584 "," BRL-112A "," BRL-120Z "," CKS-3898 "(above, Showa Denko);
"SP-460B", "SP103H", "HRJ-1367" (above, Schenectady Chemical Company);
“Register Top PL2211” (Gunei Chemical Industry Co., Ltd.);
“PR-HF-3”, “PR-53194”, “PR-53195” (Sumitomo Bakelite);
“Nikanol PR1440”, “Nikanol L”, “Nikanol P100” (Fudo Corporation);
“Pryofen 5010”, “Pryofen 503”, “TD-447” (DIC Corporation) and the like can be mentioned.

<Melamine compound>
The melamine compound crosslinks between siloxane-modified polyimide molecules, and heats the cured film formed from the ink composition by applying the ink composition to a substrate or the like, and then heating it. Can be improved. Examples of the melamine compound include hexamethylmethoxymelamine.

  The lower limit of the melamine compound content in the ink composition is preferably 0.1% by mass, and more preferably 2.5% by mass. As an upper limit of content of a melamine compound, 10 mass% is preferable and 7.5 mass% is more preferable. The heating conditions for curing the coating film are preferably 180 ° C. to 200 ° C. and 10 to 60 minutes.

  One of the phenol resin and the melamine compound may be used alone, or both may be used in combination. Moreover, in addition to one or both of a phenol resin and a melamine compound, you may contain another hardening | curing agent instead of one or both.

  As other curing agents, known ones can be used, such as polyamine curing agents, acid dianhydride curing agents, imidazole curing agents, boron trifluoride amine complex salts, aromatic diamine curing agents, Carboxylic acid curing agents and the like can be mentioned. These curing agents may be used alone or in combination of two or more.

  Examples of polyamine curing agents include aliphatic amine curing agents such as diethylenetriamine and tetraethylenetetramine; alicyclic amine curing agents such as isophorone diamine; aromatic amine curing agents such as diaminodiphenylmethane and phenylenediamine. It is done.

  Examples of the acid dianhydride curing agent include phthalic anhydride, pyromellitic anhydride, trimellitic anhydride, hexahydrophthalic anhydride, and the like.

  Examples of the imidazole curing agent include methylimidazole, phenylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and the like.

  The content of the curing agent in the ink composition may be determined according to the target degree of curing. As a minimum of content of a hardening agent, although 0 mass part may be sufficient with respect to 100 mass parts of epoxy resins, 1 mass part is preferred, 5 mass parts is more preferred, and 10 mass parts is still more preferred. As an upper limit of content of a hardening | curing agent, 100 mass parts or less are preferable, and 90 mass parts or less are more preferable. If the content of the curing agent is less than the above lower limit, the heat resistance of the siloxane-modified polyimide may not be sufficiently improved. On the other hand, if the content of the curing agent exceeds the upper limit, the effect of improving the heat resistance is not expected as compared with the content of the curing agent, which may increase the cost.

<Optional component>
Examples of optional components include plasticizers, flame retardants, flame retardant aids, pigments, antioxidants, masking agents, lubricants, processing stabilizers, foaming agents, and coupling agents.

As a plasticizer, for example,
Trimethyl phosphate, triethyl phosphate, tributyl phosphate, tri-2-ethylhexyl phosphate, tributoxyethyl phosphate, trioleyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl Phosphate ester plasticizers such as diphenyl phosphate, xylenyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate;
Polyester plasticizers such as 1,3-butylene glycol adipic acid;
Phthalate plastics such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, diisononyl phthalate, ethyl phthalyl ethyl glycolate Agent;
Dimethyl adipate, diisobutyl adipate, dibutyl adipate, di-2-ethylhexyl adipate, diisodecyl adipate, dibutyl diglycol adipate, di-2-ethylhexyl azelate, dimethyl sebacate, dibutyl sebacate, di-2-ethylhexyl sebacate, methyl- Examples include fatty acid ester plasticizers such as acetylricinoleate. These plasticizers may be used alone or in combination of two or more.

The flame retardant imparts flame retardancy to an adhesive or the like formed from the ink composition. Examples of flame retardants include:
Ethylenebispentabromobenzene, ethylenebispentabromodiphenyl, tetrabromoethane, tetrabromobisphenol A, hexabromobenzene, decabromobiphenyl ether, tetrabromophthalic anhydride, polydibromophenylene oxide, hexabromocyclodecane, ammonium bromide, etc. Brominated flame retardants;
Triallyl phosphate, alkyl allyl phosphate, alkyl phosphate, dimethyl phosphate, phosphorate, halogenated phosphorate ester, trimethyl phosphate, tributyl phosphate, trioctyl phosphate, tributoxyethyl phosphate, octyl diphenyl phosphate, tricresyl phosphate , Cresylphenyl phosphate, triphenyl phosphate, tris (chloroethyl) phosphate, tris (2-chloropropyl) phosphate, tris (2,3-dichloropropyl) phosphate, tris (2,3-dibromopropyl) phosphate, tris (bromo) Chloropropyl) phosphate, bis (2,3 dibromopropyl) 2,3 dichloropropyl phosphate, bis (chloro Propyl) monooctyl phosphate, polyphosphonate, polyphosphate, aromatic polyphosphates, dibromo neopentyl glycol, tris (diethyl phosphinate) phosphoric acid ester or phosphorous compounds such as aluminum;
Polyols such as phosphonate type polyols, phosphate type polyols, halogen elements;
Aluminum hydroxide, magnesium hydroxide, magnesium carbonate, antimony trioxide, antimony trichloride, zinc borate, antimony borate, boric acid, antimony molybdate, molybdenum oxide, phosphorus / nitrogen compound, calcium / aluminum silicate, zirconium compound, Metal powders or inorganic compounds such as tin compounds, dosonite, calcium aluminate hydrate, copper oxide, metallic copper powder, calcium carbonate, barium metaborate;
Nitrogen compounds such as melamine cyanurate, triazine, isocyanurate, urea, guanidine;
Other compounds such as silicone polymers, ferrocene, fumaric acid, maleic acid and the like can be mentioned. Among these, halogen-based flame retardants such as brominated flame retardants and chlorine-based flame retardants are preferable. Bromine-based flame retardants and chlorine-based flame retardants may be used alone or in combination of two or more.

  The flame retardant aid further improves the flame retardancy of a cured film formed from the ink composition. Examples of the flame retardant aid include antimony trioxide.

  The pigment is for coloring a cured film formed from the ink composition. Various known pigments can be used as the pigment, and examples thereof include titanium oxide.

  As an antioxidant, the oxidation of the cured film formed from the ink composition is prevented. Various known antioxidants can be used as the antioxidant, and examples thereof include phenolic antioxidants.

  When blending optional components in the ink composition of the present invention, the lower limit of the total content of the optional components is preferably 1 part by mass and more preferably 2 parts by mass with respect to 100 parts by mass of the polyimide resin. As an upper limit of the said total content, 10 mass parts is preferable and 7 mass parts is more preferable.

<Solvent>
The ink composition solvent dissolves the siloxane-modified polyimide. The solvent is not particularly limited as long as it can dissolve the siloxane-modified polyimide, but is preferably a polar solvent, for example, N-methyl-2-pyrrolidone, N, N′-dimethylacetamide, dimethylformamide, dimethylsulfoxide, acetonitrile , Diglyme, γ-butyrolactone, methyl benzoate, ethyl benzoate, γ-valerolactone, phenol, toluene, dioxane, tetrahydrofuran, sulfolane, hexamethylphosphoramide and the like. These solvents may be used alone or in combination of two or more. From the viewpoints of solubility, volatility, water absorption, odor, etc., methyl benzoate and γ-butyrolactone are used alone or in combination. It is preferable to do. Moreover, as a solvent, it is preferable to use the thing similar to the solvent used for the synthesis | combination of a siloxane modified polyimide. It is preferable to use such a solvent because a solvent replacement operation is not necessary in the production of the ink composition.

  The amount of the solvent used is preferably at least the amount that completely dissolves the siloxane-modified polyimide. The upper limit of the content of the solvent in the ink composition is, for example, 70% by mass, and preferably 60% by mass. As a minimum of content of a solvent, it is 30 mass%, for example, and 40 mass% is preferred.

<Preparation of ink composition>
The ink composition can be prepared by mixing a siloxane-modified polyimide, an epoxy resin, an inorganic filler, a curing agent such as a phenol resin or a melamine compound, and other optional components as necessary. The ink composition is preferably prepared in a state where the above components are dissolved or dispersed in a solvent.

  The solvent used for preparing the ink composition is as described above as the solvent for the ink composition.

[Protective film]
The protective film covers the conductive pattern of the flexible printed wiring board. This protective film is formed from the ink composition described above.

  The protective film can be formed by applying the ink composition to a substrate on which a conductive pattern is formed on a base film and then drying.

  The ink composition can be applied by a known method. Examples of the application method include a spray method, a roll coating method, a spin coating method, a slit die coating method, a bar coating method, and an ink jet method. Can be mentioned.

  The ink composition can be dried at a low temperature because the siloxane-modified polyimide contained in the ink composition is imidized and does not require heating for imidization. However, when a phenol resin, a melamine compound, or another curing agent is blended in the ink composition, the ink composition may be heated after drying, or may be dried together with heating for curing.

[Flexible printed wiring board]
A flexible printed wiring board 1 in FIG. 1 has flexibility, and includes a base film 2, a conductive pattern 3, and a protective film 4.

[Base film]
The base film 2 has insulating properties and preferably has flexibility. Examples of the main component of the base film 2 include polyimide, polyethylene terephthalate, fluororesin, and liquid crystal polymer, and polyimide is preferable from the viewpoints of flexibility and strength. The base film 2 may contain a resin other than polyimide, an antistatic agent, and the like.

  Although it does not specifically limit as a minimum of the average thickness of the base film 2, 3 micrometers is preferable, 5 micrometers is more preferable, and 10 micrometers is more preferable. Moreover, as an upper limit of the average thickness of the base film 2, although not specifically limited, 200 micrometers is preferable, 150 micrometers is more preferable, and 100 micrometers is more preferable. If the average thickness of the base film 2 is less than the above lower limit, the insulation and mechanical strength may be insufficient. On the other hand, if the average thickness of the base film 2 exceeds the above upper limit, the thickness of the flexible printed wiring board 1 may be too large, and the flexibility is insufficient when the base film 2 is required to be flexible. There is a risk of becoming.

[Conductive pattern]
The conductive pattern 3 is laminated on the surface side of the base film 2. The conductive pattern 3 has a base conductor 30. The conductive pattern 3 may further have a surface treatment layer 31.

<Base conductor>
The base conductor 30 is formed in a desired pattern by etching a metal foil such as copper or aluminum. The lower limit of the average thickness of the base conductor 30 is not particularly limited, but is preferably 2 μm and more preferably 5 μm. The upper limit of the average thickness of the base conductor 30 is not particularly limited, but is preferably 100 μm and more preferably 75 μm. If this average thickness is less than the above lower limit, the conductivity may be insufficient. On the other hand, if the average thickness exceeds the upper limit, flexibility may be lowered and the request for thinning may be violated.

<Surface treatment layer>
The surface treatment layer 31 prevents leakage of the conductive component from the base conductor 30 or diffusion of reactive components (oxygen, sulfur, etc.) to the conductive component into the base conductor 30. That is, the surface treatment layer 31 also plays a role of improving oil resistance. The surface treatment layer 31 covers the surface of the base conductor 30 and may cover the side surfaces of the base conductor 30 in series. The material of the surface treatment layer 31 is not particularly limited as long as it can prevent the leakage of the conductive component from the base conductor 30 or the diffusion of the reactive component to the base conductor 30. For example, metal, resin, ceramic, and the like And the like. Especially, as a material of the surface treatment layer 31, Au, Ni, Sn, and Al are preferable.

  The surface treatment layer 31 can be formed, for example, by plating for Au, Ni and Sn and by vapor deposition for Al. Further, the surface treatment layer 31 may be formed by a chemical vapor deposition method such as thermal CVD or plasma CVD, a physical vapor deposition method such as sputtering or ion plating, or a thermal spraying method such as gas spraying or electric spraying. In particular, the surface treatment layer 31 is preferably formed by plating. By forming the surface treatment layer 31 by plating in this way, it has an appropriate thickness at a low cost, and effectively prevents leakage of the conductive component from the base conductor 30 and diffusion of the reactive component of the base conductor 30. A surface treatment layer 31 that can be formed can be formed. From this point of view, the surface treatment layer 31 is more preferably Au, Ni, and Sn that can be easily formed by plating. In particular, the flexible printed wiring board 1 is generally subjected to a high-temperature process such as soldering in a reflow furnace at the time of manufacture, and is assumed to be used at a high temperature of 150 ° C. Ni which is excellent in the resistance is more preferable.

  The lower limit of the average thickness of the surface treatment layer 31 is not particularly limited, but is preferably 0.01 μm, more preferably 0.03 μm, and even more preferably 0.05 μm. The upper limit of the average thickness of the surface treatment layer 31 is not particularly limited, but is preferably 6.0 μm, more preferably 1.0 μm, and even more preferably 0.5 μm. If the average thickness of the surface treatment layer 31 is less than the above lower limit, leakage of conductive components such as copper and prevention of diffusion of reactive components to the base conductor 30 may not be sufficient. On the other hand, when the average thickness exceeds the upper limit, it is possible to prevent leakage of the conductive component from the base conductor 30 and diffusion of the reactive component to the base conductor 30 as compared with the cost increase due to the increase in thickness. There is a possibility that the effect cannot be expected.

  Instead of forming the surface treatment layer 31, the surface of the base conductor 30 may be rust-proofed with copper bright. Here, copper bright is obtained by dissolving a water-soluble polymer such as polyoxyethylene alkyl ether in isopropyl alcohol and hydroxybutyric acid. By performing such a rust prevention treatment, it is expected that a water-soluble polymer such as polyoxyethylene alkyl ether adheres to the surface of the base conductor 30. Metals such as copper to which polyoxyethylene alkyl ether or the like adheres deteriorates the adhesiveness with a protective film formed from a conventional ink composition, so a flexible printed wiring board in which such a base conductor is subjected to rust prevention treatment Tends to decrease the heat resistance. On the other hand, since the protective film 4 formed from the ink composition has excellent adhesion to the rust-proof base conductor 30 (conductive pattern 3), the flexible printed wiring board due to the reduced adhesion of the protective film 4 1 can be suppressed.

<Protective film>
The protective film 4 has a function of preventing, insulating and protecting the conductive pattern 3. The protective film 4 is formed from the ink composition described above.

  Although there is no restriction | limiting in particular as average thickness of the protective film 4, As a minimum, 5 micrometers is preferable and 10 micrometers is more preferable. The upper limit of the average thickness of the protective film 4 is preferably 100 μm, and more preferably 75 μm. When the average thickness of the protective film 4 is less than the upper limit or exceeds the upper limit, the formation of the protective film 4 may be difficult. In addition, as the average thickness of the protective film 4 is increased, the warp during coating and drying of the ink composition when the protective film 4 is formed tends to increase, and the amount of residual solvent in the protective film 4 increases, so that during reflowing. They are vaporized and become voids, which increases the possibility of a decrease in peel strength and appearance defects. Since the protective film 4 is required to have a thickness capable of embedding the conductive pattern 3, when the conductive pattern 3 is thick, the protective film 4 needs to be thick.

[Method for manufacturing flexible printed wiring board]
Next, a method for manufacturing the flexible printed wiring board 1 will be described with reference to FIGS. 2A to 2D. The manufacturing method of the flexible printed wiring board 1 uses a base film 2 having insulation and flexibility, and a step of forming a conductive pattern 3 made of metal such as copper laminated on the surface side of the base film 2. And a step of forming the protective film 4 on the surface side of the base film 2. In the present embodiment, a case where the base conductor 30 is made of copper and the surface treatment layer 31 is Ni plated will be described.

<Conductive pattern formation process>
The conductive pattern forming step uses a copper clad laminate 5 in which a copper foil (copper film) 3A is laminated on a base film 2 as shown in FIGS. 2A to 2C, and a predetermined planar shape is formed by patterning a copper foil 30 ′. After the base conductor 30 is formed, the surface treatment layer 31 is formed on the base conductor 30.

(Copper clad laminate)
As the copper-clad laminate 5 shown in FIG. 2A, a copper foil 30 ′ is laminated on the base film 2. As a method of laminating the copper foil 30 ′ on the base film 2, for example, an adhesive method in which the copper foil 30 ′ is bonded to the base film 2 using an adhesive, or a resin composition that is a material of the base film 2 on the copper foil 30 ′ Sputtering / plating in which a thin conductive layer (seed layer) having a thickness of several nanometers is formed on the base film 2 by sputtering or vapor deposition, and then a metal layer is formed on the seed layer by electrolytic plating. And a laminating method in which a metal foil is attached by hot pressing.

(Patterning)
As shown in FIG. 2B, the patterning of the copper foil 30 ′ can be performed by a known method, for example, photoetching. Photoetching is performed by forming a resist film having a predetermined pattern on the surface of the copper foil 30 ′, and then dissolving the conductor layer 6A exposed from the resist film with an etching solution and removing the resist film.

(Formation of surface treatment layer)
As shown in FIG. 2C, the surface treatment layer 31 is formed, for example, by plating the base conductor 30 with Ni. As this plating treatment, electrolytic plating and electroless plating can be used. If electroless plating is used, the thickness of the surface treatment layer 31 can be made uniform easily and reliably. On the other hand, by using electrolytic plating, the dense surface treatment layer 31 can be formed, and the surface treatment layer 31 can be easily provided on the side surface of the base conductor 30. In particular, it is preferable to use electroless plating capable of plating the surface treatment layer 31 having a thin and uniform thickness with inexpensive equipment.

<Protective film formation process>
As shown in FIG. 2D, the protective film forming step is performed by heating the coating film 4 ′ after applying the ink composition so as to selectively cover the conductive pattern 3 except for the terminal portion by screen printing. Is called.

  The ink composition can be applied by a known method. Examples of the application method include a spray method, a roll coating method, a spin coating method, a slit die coating method, a bar coating method, and an ink jet method. Can be mentioned.

  The heating temperature of the coating film is preferably 120 ° C. or higher and 200 ° C. or lower, and the heating time is preferably 1 minute or longer and 60 minutes or shorter. By making heating temperature and heating time into the said range, while being able to exhibit the adhesiveness of the protective film 4 effectively, alteration of the base film 2 grade | etc., Can be suppressed. The heating method is not particularly limited, and examples thereof include a method of heating using a heating means such as a hot press, oven, hot plate, etc., and pressure heating by hot press is preferred.

[advantage]
When the ink composition contains an epoxy resin, the heat resistance of a cured film (such as the protective film 4 of the flexible printed wiring board 1) formed from the ink is improved. The reason why the heat resistance is improved by containing an epoxy resin in the ink composition is not clear, but it is considered that the siloxane-modified polyimide is cross-linked by the epoxy resin when the ink composition is heated. . Further, it is considered that the cured film (protective film 4 or the like) of the ink composition is improved in moisture resistance, mechanical strength, and the like by being crosslinked with an epoxy resin.

  Further, the ink composition can suppress aggregation of the siloxane-modified polyimide having a weight average molecular weight (Mw) in a specific range. Therefore, the cured film (protective film 4 etc.) of the ink composition can suppress a decrease in peel strength due to aggregation of the siloxane-modified polyimide. In addition, the cured film (such as the protective film 4) of the ink composition is further improved in mechanical strength and peel strength by blending an inorganic filler.

  Therefore, the flexible printed wiring board 1 in which the protective film 4 is formed from the ink composition is excellent in these characteristics because the characteristics of the protective film 4 such as heat resistance and mechanical strength are improved.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  The flexible printed wiring board is not limited to a single-sided printed wiring board in which a conductive pattern is formed on one side, and may be a double-sided printed wiring board in which a conductive pattern is formed on both sides, and a plurality of conductive patterns are laminated. A multilayer printed wiring board may be used.

  The flexible printed wiring board may be obtained by omitting the surface treatment layer in the conductor pattern.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Synthesis of siloxane-modified polyimide]
The types and blending ratios of the acid dianhydride component and the diamine component were as shown in Table 1, and siloxane-modified polyimides (PI1) to (PI11) were synthesized by the method shown below. In Table 1, “-” means that the corresponding component is not blended.

<Synthesis Example 1> (Synthesis of Siloxane-Modified Polyimide (PI1))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.4: 0.6 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 25 mass%: 75 mass%) to obtain a reaction solution. The content of the organic solvent in the reaction solution was set such that the content of the polyamide resin in the siloxane-modified polyimide precursor solution was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 16 hours, and the polymer solution containing a siloxane modification polyimide (PI1) was obtained by imidating a siloxane modification polyimide precursor.

  The weight average molecular weight (Mw) of the siloxane-modified polyimide in the obtained siloxane-modified polyimide solution was 92,000. The definition and measurement method of the weight average molecular weight (Mw) are as described above.

<Synthesis Example 2> (Synthesis of Siloxane Modified Polyimide (PI2))
A polymer solution containing a siloxane-modified polyimide (PI2) was prepared in the same manner as in Synthesis Example 1 except that the reaction solution was reacted at 180 ° C. for 14 hours to produce polyamic acid to obtain a siloxane-modified polyimide precursor solution. Obtained. In addition, the weight average molecular weight (Mw) of the siloxane modified polyimide (PI2) was 75,000.

<Synthesis Example 3> (Synthesis of Siloxane-Modified Polyimide (PI3))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.6: 0.4 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 42 mass%: 58 mass%) to obtain a reaction solution. In addition, the content of the organic solvent in the reaction solution was set to such an amount that the content of the siloxane-modified polyamide resin was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 10 hours, and the polymer solution containing a siloxane modification polyimide (PI3) was obtained by imidating a siloxane modification polyimide precursor. The weight average molecular weight (Mw) of the siloxane-modified polyimide (PI3) was 42,000.

<Synthesis Example 4> (Synthesis of Siloxane-Modified Polyimide (PI4))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.5: 0.5 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 33 mass%: 67 mass%) to obtain a reaction solution. The content of the organic solvent in the reaction solution was set such that the content of the polyamide resin in the siloxane-modified polyimide precursor solution was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 13 hours, and the polymer solution containing a siloxane modification polyimide (PI4) was obtained by imidating a siloxane modification polyimide precursor. The weight average molecular weight (Mw) of the siloxane-modified polyimide (PI4) was 64,000.

<Synthesis Example 5> (Synthesis of Siloxane-modified Polyimide (PI5))
As a mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), 4,4′-oxydiphthalic anhydride (ODPA) as an acid dianhydride, as an aromatic diamine 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine (“KF-” of Shin-Etsu Chemical Co., Ltd.) 8010 ", average molecular weight: about 1000) (PSA) molar ratio of 1.0: 0.5: 0.5 (mass ratio of aromatic diamine to siloxane diamine in the total diamine component is 33% by mass: 67% by mass) ) To obtain a reaction solution. In addition, the content of the organic solvent in the reaction solution was set to such an amount that the content of the siloxane-modified polyamide resin was 30% by mass.

  The polymer solution containing a siloxane-modified polyimide (PI5) was obtained by reacting the reaction solution at a temperature of 180 ° C. for 10 hours to imidize the siloxane-modified polyimide precursor. The weight average molecular weight (Mw) of the siloxane-modified polyimide (PI5) was 45,000.

<Synthesis Example 6> (Synthesis of Siloxane-modified Polyimide (PI6))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.4: 0.6 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 25 mass%: 75 mass%) to obtain a reaction solution. In addition, the content of the organic solvent in the reaction solution was set to such an amount that the siloxane-modified polyamide resin content was 30% by mass.

  The temperature of the reaction solution was set at 180 ° C. for 12 hours to obtain a polymer solution containing siloxane-modified polyimide. In addition, the weight average molecular weight (Mw) of the siloxane modified polyimide (PI6) was 56,000.

<Synthesis Example 7> (Synthesis of Siloxane-modified Polyimide (PI7))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.3: 0.7 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 17 mass%: 83 mass%) to obtain a reaction solution. In addition, content of the organic solvent in a reaction solution was set to the quantity from which content of polyamic acid in a siloxane modification polyimide precursor solution will be 30 mass%.

  The temperature of the reaction solution was 180 ° C. for 16 hours to obtain a polymer solution containing a siloxane-modified polyimide. The siloxane-modified polyimide (PI7) had a weight average molecular weight (Mw) of 77,000.

<Synthesis Example 8> (Synthesis of siloxane-modified polyimide (PI8))
A mixed solvent of N-methyl-2-pyrrolidone and xylene as an organic solvent (mass ratio is 1: 1), and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride as an acid dianhydride (BPDA), 2,2-bis [4- (4-aminophenoxy) siphenyl] propane (BAPP) as an aromatic diamine, and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as a siloxane diamine ("KF-8010" of Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 1.0: 0.4: 0.6 (mass ratio of aromatic diamine and siloxane diamine in all diamine components) Was added at 25 mass%: 75 mass%) to obtain a reaction solution. In addition, the content of the organic solvent in the reaction solution was set to such an amount that the content of the siloxane-modified polyimide was 30% by mass.

  The temperature of the reaction solution was set at 180 ° C. for 8 hours to obtain a polymer solution containing a siloxane-modified polyimide. The siloxane-modified polyimide (PI8) had a weight average molecular weight (Mw) of 29,000.

<Synthesis Example 9> (Synthesis of Siloxane-Modified Polyimide (PI9))
To a mixed solvent (mass ratio 6: 4) of γ-butyrolactone and methyl benzoate as an organic solvent, 4,4′-oxydiphthalic anhydride (ODPA) and 3,3 ′, 4 as acid dianhydrides , 4′-benzophenonetetracarboxylic dianhydride (BTDA), 1,3-bis (3-aminophenoxy) benzene (APB) as an aromatic diamine, and an amine represented by the above formula (9) as a siloxane diamine Compound having an equivalent weight of 420 g / eq (“KF-8010” manufactured by Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 0.5: 0.5: 0.5: 0.5 (total diamine components Were added at a mass ratio of aromatic diamine to siloxane diamine of 26 mass%: 74 mass%) to obtain a reaction solution. The content of the organic solvent in the reaction solution was set such that the content of the polyamide resin in the siloxane-modified polyimide precursor solution was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 16 hours, and the polymer solution containing a siloxane modification polyimide (PI9) was obtained by imidating a siloxane modification polyimide precursor.

  The weight average molecular weight (Mw) of the siloxane-modified polyimide in the obtained siloxane-modified polyimide solution was 55,000. The definition and measurement method of the weight average molecular weight (Mw) are as described above.

<Synthesis Example 10> (Synthesis of Siloxane-modified Polyimide (PI10))
In a mixed solvent (mass ratio 6: 4) of γ-butyrolactone and methyl benzoate as an organic solvent, 4,4′-oxydiphthalic anhydride (ODPA) as an acid dianhydride, 1 as an aromatic diamine , 3-bis (3-aminophenoxy) benzene (APB) and a compound having an amine equivalent of 420 g / eq represented by the above formula (9) as siloxane diamine (“KF-8010” from Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) is added at a molar ratio of 1.0: 0.5: 0.5 (mass ratio of aromatic diamine to siloxane diamine in all diamine components is 26% by mass: 74% by mass). Got. The content of the organic solvent in the reaction solution was set such that the content of the polyamide resin in the siloxane-modified polyimide precursor solution was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 16 hours, and the polymer solution containing a siloxane modification polyimide (PI10) was obtained by imidating a siloxane modification polyimide precursor.

  The weight average molecular weight (Mw) of the siloxane-modified polyimide in the obtained siloxane-modified polyimide solution was 60,000. The definition and measurement method of the weight average molecular weight (Mw) are as described above.

<Synthesis Example 11> (Synthesis of Siloxane-modified Polyimide (PI11))
To a mixed solvent (mass ratio 6: 4) of γ-butyrolactone and methyl benzoate as an organic solvent, 4,4′-oxydiphthalic anhydride (ODPA) and 3,3 ′, 4 as acid dianhydrides , 4′-benzophenonetetracarboxylic dianhydride (BTDA), 1,3-bis (3-aminophenoxy) benzene (APB) as an aromatic diamine, and an amine represented by the above formula (9) as a siloxane diamine Compound having an equivalent weight of 420 g / eq (“KF-8010” manufactured by Shin-Etsu Chemical Co., Ltd., average molecular weight: about 1000) (PSA) in a molar ratio of 0.5: 0.5: 0.4: 0.6 (all diamine components) Was added at a mass ratio of aromatic diamine to siloxane diamine of 19 mass%: 81 mass%) to obtain a reaction solution. The content of the organic solvent in the reaction solution was set such that the content of the polyamide resin in the siloxane-modified polyimide precursor solution was 30% by mass.

  The temperature of the said reaction solution was made into 180 degreeC, it was made to react for 16 hours, and the polymer solution containing a siloxane modification polyimide (PI11) was obtained by imidating a siloxane modification polyimide precursor.

  The weight average molecular weight (Mw) of the siloxane-modified polyimide in the obtained siloxane-modified polyimide solution was 48,000. The definition and measurement method of the weight average molecular weight (Mw) are as described above.

<Preparation of ink composition>
Example 1
100 parts by mass (solid content equivalent) of siloxane-modified polyimide (A1) dissolved in a mixed solvent of N-methyl-2-pyrrolidone and xylene (mass ratio is 1: 1) as a solvent, talc as an inorganic filler (Japan) 45 parts by mass of “MICRO ACE K1” of talc: average particle size 8 μm, epoxy resin (“EPICLON N695” of DIC (softening point 90 ° C. to 100 ° C., epoxy equivalent 209 g / eq to 219 g / eq)) An ink composition was obtained by mixing 3 parts by mass of a phenol resin (“GPH-65” manufactured by Nippon Kayaku Co., Ltd.) as a curing agent.

(Examples 2-7 and Comparative Examples 1-8)
An ink composition was prepared in the same manner as in Example 1 except that the components having the types and contents shown in Table 2 were used. In addition, “-” in Table 2 indicates that the corresponding component was not blended.

<Production of evaluation sample>
As an evaluation sample, according to the following method, a copper clad laminate with a protective film (evaluation sample 1) shown in FIG. 3 and a copper clad laminate with a protective film obtained by subjecting the copper foil of this evaluation sample 1 to nickel plating (evaluation) Sample 2) was prepared.

(Preparation of evaluation sample 1)
First, a copper foil (thickness 35 μm) coated with an ink composition so as to have a thickness of 45 μm to 55 m in order to form an adhesive layer is coated with a polyimide film (“Kapton 100H” from Toray DuPont; thickness 25 μm). Further, thermocompression bonding was performed at a pressure of 3 MPa, a heating temperature of 180 ° C., and a pressing time of 45 minutes. The copper foil used was rust-proofed with copper bright. This rust prevention treatment was performed using a rust prevention solution in which polyoxyethylene alkyl ether, which is a water-soluble polymer, was dissolved in isopropyl alcohol and hydroxybutyric acid. Subsequently, after coating the ink composition so that thickness might be set to 45 micrometers-55m on the surface of copper foil, it heated at 180 degreeC for 45 minutes, and formed the protective film.

(Preparation of evaluation sample 2)
Evaluation sample 2 is an evaluation sample, except that in the preparation of evaluation sample 1 of FIG. 3, a copper-clad laminate was subjected to electroless nickel plating to form a surface treatment layer having a thickness of 0.1 μm on the copper foil surface. 1 was prepared.

<Evaluation>
About the evaluation samples 1 and 2 which used the adhesive fat composition of Examples 1-7 and Comparative Examples 1-8, peeling strength and reflow heat resistance were evaluated according to the following method. The evaluation results are shown in Table 3. In addition, "-" of the evaluation item in Table 3 means that it has not been evaluated (cannot be evaluated).

(Peel strength)
The peel strength was measured as peel strength according to JIS-K-6854-2: 1999 “Adhesive—Peeling peel strength test method—Part 2: 180 degree peel” under the following four conditions. The peel strength was measured using a tensile tester “Autograph AG-IS” manufactured by Shimadzu Corporation. In the measurement of peel strength, the entire end of the copper clad laminate of evaluation sample 1 or evaluation sample 2 was sandwiched, and the polyimide film was fixed and a peeling force was applied.

Peel strength 1: Initial peel strength at which the evaluation sample 1 was produced Peel strength 2: Peel strength at normal temperature after leaving the evaluation sample 1 at 150 ° C. for 1,000 hours Peel strength 3: Perform nickel plating treatment Peel strength at normal temperature after leaving the evaluation sample 2 left at 150 ° C. for 1,000 hours Peel strength 4: Peel strength at normal temperature after leaving the evaluation sample 1 at 85 ° C. and 85% for 1,000 hours

(Reflow heat resistance)
The reflow heat resistance was evaluated by checking the presence or absence of deformation after leaving the evaluation sample 1 or the evaluation sample 2 in a constant temperature bath at 260 ° C. for 1 minute. The evaluation criteria are as follows. In Table 3, the reflow heat resistance 1 is the result using the evaluation sample 1, and the reflow heat resistance 2 is the result using the evaluation sample 2.

A: Deformation is not recognized B: Deformation is recognized

  As is apparent from Table 3, the evaluation samples using the ink compositions of Examples 1 to 7 have higher peel strength and reflow heat resistance than the evaluation samples using the ink compositions of Comparative Examples 1 to 8. It was excellent. The evaluation samples using the ink compositions of Examples 1 to 7 had no particular problems with respect to the evaluation of the peel strength 1 corresponding to the initial peel strength and the evaluation of the peel strength 2 to 4 corresponding to the long-term peel strength.

  Moreover, the evaluation samples 1 and 2 using the ink compositions of Examples 1 to 7 tend to be excellent in the evaluation of the reflow heat resistance 1.

(Reference Examples 1-4)
The ink compositions of Reference Examples 1 to 4 were prepared in the same manner as in Comparative Example 3 except that the inorganic fillers having the average particle diameter and aspect ratio shown in Table 4 were used. Moreover, inorganic filler B1-B5 shown in Table 4 is as follows.

B1: “MICRO ACE K1” by Nippon Talc
B2: “MICRO ACE P8” by Nippon Talc
B3: “GAT-40” by Nippon Talc
B4: “MICRO ACE P2” by Nippon Talc
B5: “Mistrone Vapor Talc” by Nippon Mytron

  Evaluation samples 1 and 2 were prepared using this ink composition, and the above-described peel strength and reflow heat resistance were evaluated. The evaluation results are shown in Table 4. Table 4 shows the evaluation results of Comparative Example 3 at the same time.

  As is apparent from Table 4, the evaluation samples 1 and 2 using the ink compositions of Reference Examples 1 to 4 had the peel strengths 1 and 2 and the reflow heat resistance 2 that were the same as or higher than those of Comparative Example 3. . Therefore, when an inorganic filler whose average particle diameter and aspect ratio are in the range of Reference Examples 1 to 4 is blended with the ink compositions of Examples 1 to 4, the evaluation sample using the ink compositions of Examples 1 to 4 It is presumed that peel strength and heat resistance equivalent to or higher than 1 and 2 can be obtained.

  The ink composition of the present invention can form a cured film excellent in heat resistance, for example, a protective film for a flexible printed wiring board. Therefore, the ink composition can be suitably used for a protective film for a flexible printed wiring board and a flexible printed wiring board that are required to have heat resistance, and can be suitably used for a flexible printed wiring board used in a high temperature environment.

DESCRIPTION OF SYMBOLS 1 Flexible printed wiring board 2 Base film 3 Conductive pattern 30 Base conductor 30 'Copper foil 31 Surface treatment layer 4 Protective film 4' Coating film 5 Copper clad laminated board

Claims (13)

Containing siloxane-modified polyimide, epoxy resin, and inorganic filler,
The ink composition wherein the siloxane-modified polyimide has a weight average molecular weight (Mw) of 25,000 or more and 300,000 or less.   The ink composition according to claim 1, further comprising a phenol resin.   The ink composition according to claim 1 or 2, wherein the content of the epoxy resin is 20 parts by mass or less with respect to 100 parts by mass of the siloxane-modified polyimide. The ink according to claim 1, 2 or 3, wherein the siloxane-modified polyimide includes a first structural unit represented by the following formula (1) and a second structural unit represented by the following formula (2). Composition.

(In Formula (1) and Formula (2), Ar is a tetravalent aromatic tetracarboxylic acid residue.
In formula (1), R ¹ is a divalent diamine siloxane residue.
In formula (2), R ² is a divalent aromatic diamine residue.
In said formula (1), m represents the molar ratio of the said 1st structural unit in all the structural units of the said siloxane modified polyimide, and is 0.35-0.65.
In said formula (2), n represents the molar ratio of the said 2nd structural unit in all the structural units of the said siloxane modified polyimide, and is 0.35-0.65.
However, the sum of m and n does not exceed 1. ) The siloxane-modified polyimide is a condensate of a diamine component containing diaminosiloxane and an aromatic tetracarboxylic dianhydride,
The ink composition according to claim 1, wherein the composition ratio of the diaminosiloxane in the diamine component is 66% by mass or more and 80% by mass or less.   The ink composition according to any one of claims 1 to 5, wherein a side chain of the siloxane-modified polyimide does not contain an unsaturated double bond.   The ink composition according to any one of claims 1 to 6, wherein the content of the inorganic filler is 5 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the siloxane-modified polyimide.   The ink composition according to any one of claims 1 to 7, wherein the inorganic filler has an average particle size of 2 µm or more and 20 µm or less. The inorganic filler is plate-shaped,
The ink composition according to any one of claims 1 to 8, wherein an aspect ratio of the inorganic filler is 5 or more and 100 or less.   The ink composition according to any one of claims 1 to 9, further comprising a melamine compound. A protective film covering the conductive pattern of the flexible printed wiring board,
A protective film comprising a cured film of the ink composition according to claim 1.   The flexible printed wiring board which has a protective film of Claim 11. The conductive pattern has a base conductor and a surface treatment layer formed on at least a part of the outer surface of the base conductor,
The flexible printed wiring board according to claim 12, wherein a main component of the surface treatment layer is gold (Au), nickel (Ni), tin (Sn), or aluminum (Al).

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