Polyimide resin filler material for insulation member

Abstract

To provide a polyimide resin filler that does not impair dielectric characteristics of a polyimide resin, adds mechanical strength and thermal property required for FPC, and can uniformly develop those characteristics.SOLUTION: An insulating polyimide resin composition that can suppress the rise in dielectric constant and dielectric loss tangent, and that offers a reduction in thermal expansion coefficient and an increase in tensile modulus while maintaining insulation strength, contains alumina particles with fibrous or needle-like shapes that satisfy the following (a) to (c): (a) hydrated alumina or alumina is with a long diameter of primary particle size between 200 nm and 3000 nm, and a short diameter between 1 nm and 10 nm, (b) the composition contains organic or inorganic acid in an amount of 0.1 equivalent or more and 2.0 equivalents or less relative to aluminum atoms, (c) a dispersion medium is organic solvent, where the content of alumina particles is more than 5 pts. wt. and less than or equal to 40 pts. wt. in 100 pts. wt. of the insulating polyimide resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersion composition containing alumina particles or alumina hydrate particles that can be used as a filler to be mixed with polyimide used in flexible printed circuits (hereinafter referred to as FPC). [Background technology]

[0002] Polyimide resins have excellent mechanical strength, heat resistance, and electrical insulation properties, and are widely used as electronic circuit board materials. For example, flexible copper-clad laminates, which are made by laminating copper foil on polyimide film as the substrate material, and FPCs with additional circuits are used in various electronic devices.

[0003] In recent years, the performance of electronic devices has improved, leading to faster information communication. As a result, the resin materials used in electronic devices are also required to be able to handle high-speed transmission. Reducing the dielectric constant and dielectric loss tangent is effective in suppressing delays and losses in electrical signals.

[0004] Various polyimide resins are being offered to support high-speed communications. In Patent Document 1, a low dielectric constant and a low dielectric loss tangent are achieved by incorporating a fluororesin into the polyimide resin that forms the insulating resin layer. In Patent Document 2, a low dielectric constant and a low dielectric loss tangent are achieved by focusing on the chemical structure of polyimide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2014-526399 [Patent Document 2] Japanese Patent Publication No. 2023-2497 Summary of the Invention

[0006] In Patent Document 1, it is difficult to uniformly disperse the fluororesin in the polyimide resin, and there is a problem that the performance may vary depending on the position on the film.

[0007] Although the polyimide resin proposed in Patent Document 2 has excellent dielectric properties, when used as an FPC, there is a problem that peeling occurs due to differences in the strength of the polyimide film and the coefficient of thermal expansion between the polyimide film and the copper foil. [Problem to be solved by the invention]

[0008] To provide a polyimide resin filler that adds the mechanical strength and thermal properties required for FPCs without impairing the dielectric properties of polyimide resin, and that uniformly expresses these properties. [Means for solving the problem]

[0009] In view of the above-mentioned prior art, the present inventors have conducted extensive research with the goal of developing an alumina filler-containing polyimide resin composite that has the performance required for FPCs without impairing the dielectric properties. As a result, they have succeeded in developing an alumina sol in which alumina particles with a major axis of 200 to 3000 nm and a minor axis of 1 to 10 nm are dispersed in an organic solvent. Furthermore, by using this alumina sol, they have succeeded in developing a polyimide resin composite in which the alumina filler is uniformly dispersed. Based on this finding, the present invention has been completed.

[0010] The gist of the present invention is as follows. [1] An insulating polyimide resin composition, which is an alumina hydrate or an alumina dispersion composition having a fibrous or acicular shape and which satisfies all of the following (a) to (c): (a) Alumina hydrate or alumina having a primary particle diameter of 200 nm or more and 3000 nm or less, and a minor axis of 1 nm or more and 10 nm or less, (b) Contains 0.1 equivalents or more and 2.0 equivalents or less of an organic acid or an inorganic acid relative to aluminum atoms; (c) The dispersion medium is an organic solvent [2] The alumina hydrate according to [1], or the alumina hydrate or alumina dispersion composition, wherein the crystal system of the alumina is boehmite or pseudo-boehmite. [3] The dispersion composition according to [1] or [2], which is used as a filler to be mixed with a polyimide resin. [Effects of the Invention]

[0011] According to the present invention, by mixing and stirring an alumina sol in which alumina nanofibers are uniformly dispersed in an organic solvent with a solution in which a polyimide resin is dissolved in an organic solvent, and then removing only the solvent from the mixture, it is possible to provide a resin composite in which alumina nanofibers are uniformly dispersed in a polyimide resin. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention is described in more detail below. The present invention is a resin composite characterized by using an alumina sol in which alumina nanofibers having a minor axis of 1 to 10 nm and a major axis of 100 to 3000 nm, which are produced by a sol-gel method, are surface-coated with either an organic acid or an inorganic acid compound, thereby uniformly dispersing the alumina in an organic solvent.

[0013] First, we will explain the alumina nanofibers of the present invention. The alumina nanofibers of the present invention are crystalline alumina hydrates represented by the composition formula Al2O3·nH2O (n = 1 to 1.5), consisting of fibrous or acicular particles synthesized by a sol-gel method using aluminum alkoxide as a raw material, and their crystalline system is boehmite or pseudo-boehmite.

[0014] The alumina nanofibers of the present invention are fibrous or acicular alumina particles having an average aspect ratio (major axis / minor axis) of 10 to 3,000, an average minor axis of 1 to 10 nm, and an average major axis of 100 to 3,000 nm, and preferably have an aspect ratio of 40 to 1,500, an average minor axis of 2 to 5 nm, and an average major axis of 200 to 3,000 nm.

[0015] Next, the surface coating of the alumina nanofibers of the present invention will be described. In the present invention, the surface of the alumina nanofibers is coated with one of a phosphoric acid compound, a sulfonic acid compound, and an organic acid, thereby changing the particle surface from hydrophilic to lipophilic, and enabling dispersion in an organic solvent.

[0016] The organic solvent in which the lipophilic alumina nanofibers of the present invention are dispersed is not particularly limited as long as it can produce an alumina organosol and has the ability to dissolve the target resin, and any general-purpose organic solvent can be used.

[0017] Next, a method for producing an alumina sol of the present invention will be described. The present invention comprises the steps of: preparing an aqueous alumina sol in which alumina nanofibers are dispersed, the alumina nanofibers having an average aspect ratio (major axis / minor axis) of 10 to 3,000, an average minor axis of 1 to 10 nm, and an average major axis of 100 to 3,000 nm; and coating the surfaces of the alumina nanofibers in the obtained aqueous alumina sol with a surface coating agent of either an organic acid or an inorganic acid, thereby preparing an alumina sol dispersed in an organic solvent.

[0018] The aqueous alumina sol in which alumina nanofibers are dispersed, used in the present invention, is prepared by hydrolyzing aluminum alkoxide as a raw material in an acid aqueous solution to form alumina hydrate, distilling off the produced alcohol, and then peptizing the resulting alumina sol under the specific conditions described below for the hydrolysis reaction conditions and the peptization treatment conditions.

[0019] The acid used for hydrolysis is preferably a monovalent acid such as hydrochloric acid, nitric acid, formic acid, acetic acid, propionic acid, or butyric acid, while inorganic acids are undesirable because they remain in the alumina even after calcination. As an organic acid, acetic acid is particularly preferable from the viewpoints of operability and economy. The amount of acid used is 0.2 to 2.0 moles, preferably 0.3 to 1.8 moles, relative to the amount of aluminum alkoxide. An amount of less than 0.2 moles is undesirable because the aspect ratio of the resulting particles is small. An amount of 2.0 moles or more reduces stability over time and is undesirable from the viewpoint of economy.

[0020] The hydrolysis conditions are preferably a temperature of 100°C or less for 0.1 to 3 hours. Temperatures above 100°C are not preferred because of the risk of bumping. Hydrolysis times of less than 0.1 hours are difficult to control the temperature, while those exceeding 3 hours are not preferred because the process time becomes too long.

[0021] The solids concentration of the aqueous acid solution of aluminum alkoxide to be hydrolyzed is preferably 2 to 15 wt%, and more preferably 3 to 10 wt%. If the solids concentration is 2 wt% or less, the aspect ratio of the resulting particles will be small, which is undesirable, while if it is 15 wt% or more, the stirrability of the reaction solution will decrease during peptization, which is undesirable.

[0022] After distilling off the alcohol produced by hydrolysis, a peptization treatment is carried out. The peptization treatment is carried out by heating at 100°C to 200°C for 0.1 to 10 hours, and more preferably at 110 to 180°C for 0.5 to 5 hours. A heating temperature of less than 100°C requires a long reaction time, while a heating temperature of more than 200°C requires a high-pressure vessel or the like, which is economically disadvantageous and therefore undesirable. A heating time of less than 0.1 hour results in small particle size and poor storage stability, while a heating time of more than 10 hours simply lengthens the process time, which is undesirable.

[0023] Next, an organic solvent and a surface coating agent are added to the aqueous alumina sol obtained in the above step, and the mixture is mixed, followed by solvent substitution. Examples of the solvent substitution method include a method using an ultrafiltration membrane and a dehydration method utilizing the boiling point difference between water and the organic solvent.

[0024] In the present invention, by satisfying these conditions, it is possible to produce and provide an alumina sol in which alumina nanofibers having a minor axis of 1 to 10 nm, a major axis of 100 to 3,000 nm, and an aspect ratio (major axis / minor axis) of 10 to 3,000 are surface-coated with a compound of either an inorganic acid or an organic acid, and dispersed in an organic solvent.

[0025] Next, the method for producing the polyimide resin composite of the present invention will be described.

[0026] The method for incorporating the alumina filler into the polyimide can be any known method and is not particularly limited. For example, the alumina nanofibers may be dispersed in a solvent before synthesizing a polyamic acid solution, which is a precursor of the polyimide, and then the polyamic acid may be synthesized. Alternatively, the synthesized polyamic acid solution may be mixed with a dispersion of the alumina filler that has been dispersed in a solvent beforehand. Alternatively, the alumina filler dispersion may be mixed with a solution in which polyimide powder is dispersed.

[0027] The method for producing the alumina filler-containing polyimide film can be a known method and is not particularly limited. For example, the resin composition is cast onto any supporting substrate to form a coating film. The coating film is then partially imidized or the solvent is dried to remove a certain amount at any temperature. When the resin composition is a polyamic acid, it is completely imidized to obtain a polyimide film. The heating conditions may be appropriately set depending on the thickness of the final film to be obtained and the production speed.

[0028] The organic solvent for dissolving the resin of the present invention is not particularly limited, and any organic solvent can be used as long as it has the ability to dissolve the target resin.

[0029] The amount of alumina filler added to polyimide is preferably 5 to 40 wt%, and more preferably 20 to 40 wt%. If the amount added exceeds 40 wt%, the physical properties of the resin composite, such as flexibility and bending strength, will be significantly reduced, making it impractical. If the amount added is less than 1 wt%, the expected effects, specifically, the improvement in strength, heat resistance, and thermal expansion suppression effects, will hardly be achieved.

[0030] The polyimide film of the present invention preferably has a relative dielectric constant of 3.2 or less at 1 GHz, a dielectric loss tangent of 0.0250 or less, a dielectric breakdown strength of 0.20 or more when a direct current is applied at 30°C, and a linear thermal expansion coefficient of 10 to 25 ppm at 50 to 250°C. [Example]

[0031] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0032] <Dielectric constant and dielectric loss tangent measurement> The dielectric constant and dielectric loss tangent were measured using a KEYSIGHT E4991A RF Impedance / Material Analyzer. The polyimide film was cut into a 10 mm x 10 mm piece and measured at 1 GHz.

[0033] <Measurement of dielectric breakdown strength> The dielectric breakdown strength was measured using a Glassman DC power supply WR100N / P2.5, a North Star High Voltage high voltage probe VD-100, an Agilent Technologies oscilloscope DSO1102B, and an NF Corporation function generator WF1974. The polyimide film was sandwiched between spherical electrodes and heated to 30°C. The film was immersed in silicone oil and a DC current was applied to measure the dielectric breakdown voltage.

[0034] <Measurement of coefficient of linear expansion (CTE)> The linear expansion coefficient was measured using a thermomechanical analyzer TMA8311 manufactured by Rigaku Corporation. The temperature was repeatedly increased from 30°C to 350°C at a rate of 10°C / min, and the measurement data from 50°C to 250°C during the second temperature increase was used. Sample shape: Load: 20mN Measurement temperature range: 30 to 350°C Atmosphere: Air atmosphere

[0035] <Measurement of tensile modulus> The tensile modulus was measured using a tabletop tensile tester MCT2150 manufactured by A&D Co., Ltd. The polyimide film was cut into a 10 mm x 80 mm piece, and the measurement was performed by clamping both 15 mm long ends with a chuck.

[0036] Preparation and Use of Water-Dispersed Alumina Sol 1. Preparation of water-dispersed alumina sol A (average minor axis: 4 nm, average major axis: 3,000 nm, average aspect ratio: 750) A 500 ml four-neck flask was charged with 130 g of ion-exchanged water and 8.8 g (0.146 mol) of acetic acid, and the liquid temperature was raised to 30°C while stirring. To this, 27.0 g (0.132 mol) of aluminum isopropoxide was added dropwise over 0.5 hours, and the liquid temperature was raised to 95°C while distilling off the generated isopropyl alcohol. The reaction solution was transferred to a magnetic stirring autoclave and reacted at 150°C for 6 hours while stirring. The reaction solution was cooled to below 40°C, and the reaction was terminated. Alumina nanofiber sol A was obtained with a solids concentration of 4.9 mass% in the reaction solution. Observation of the alumina particles in the resulting alumina sol using a transmission electron microscope (TEM) revealed that the alumina particles were alumina nanofibers with an average minor axis of 4 nm, an average major axis of 3,000 nm, and an average aspect ratio of 750. 2. Preparation of water-dispersed alumina sol B (average minor axis: 5 nm, average major axis: 200 nm, average aspect ratio: 40) A 500 ml four-neck flask was charged with 130 g of ion-exchanged water and 6.0 g (0.100 mol) of acetic acid, and the liquid temperature was raised to 30°C while stirring. 27.0 g (0.132 mol) of aluminum isopropoxide was added dropwise over 0.5 hours, and the liquid temperature was raised to 95°C while distilling off the generated isopropyl alcohol. The reaction liquid was transferred to a magnetic stirring autoclave and reacted at 160°C for 6 hours while stirring. The reaction liquid was cooled to below 40°C, and the reaction was terminated. Alumina nanofiber sol C was obtained with a solids concentration of 4.9 mass% in the reaction liquid. Observation of the alumina particles in the resulting alumina sol using a transmission electron microscope (TEM) revealed that the alumina particles had an average minor axis of 5 nm, an average major axis of 200 nm, and an average aspect ratio of 40. 3. Alumina sol C (Aluminum sol-A2: manufactured by Kawaken Fine Chemicals Co., Ltd.), an acetic acid peptized sol with a minor axis of 10 nm, a major axis of 50 nm, and an aspect ratio of 5, was used. 4. Alumina sol D (Aluminum sol-5S, manufactured by Kawaken Fine Chemicals Co., Ltd.), an acetic acid peptized sol with a minor axis of 20 nm, a major axis of 20 nm, and an aspect ratio of 1, was used.

[0037] Synthesis Example 1: DMAc-dispersed alumina sol A The above-mentioned water-dispersed alumina sol A (minor axis 4 nm, major axis 3000 nm) was prepared as a DMAc (dimethylacetamide)-dispersed alumina sol A by reference to a known method (JP 2016-44114 A).

[0038] (Synthesis Examples 2 to 4: DMAc-dispersed alumina sol) The following DMAc-dispersed alumina sols were obtained in the same manner as in Synthesis Example 1, except that the water-dispersed sol in Synthesis Example 1 was changed: DMAc-dispersed alumina sol B (minor axis 5 nm, major axis 200 nm), DMAc-dispersed alumina sol C (minor axis 10 nm, major axis 50 nm), and DMAc-dispersed alumina sol D (minor axis 20 nm, major axis 20 nm).

[0039] <Reference example 1> To prepare the polyimide film, soluble polyimide powder KPI-MX300F (Kawamura Industries) was added to DMAc, stirred, degassed, and then coated onto a glass plate using a bar coater. The mixture was dried in a fan dryer at 100°C for the primary drying and then at 200°C for the secondary drying. The polyimide film was then cut off from the glass plate.

[0040] Example 1 DMAc-dispersed alumina sol A (minor axis: 4 nm, major axis: 3000 nm) was added to the DMAc-dispersed polyimide solution, followed by stirring and degassing. The filler was 20 wt % when the polyimide was 100 wt %. The subsequent procedures were the same as in Reference Example 1 to obtain an alumina filler-containing polyimide film.

[0041] Examples 2 to 4 An alumina filler-containing polyimide film was obtained in the same manner as in Example 1, except that the filler content in Example 1 was changed. The amounts added are shown in Table 1. In addition, for Example 4, various measurements could not be performed because the film was brittle.

[0042] Comparative Example 1 An alumina filler-containing polyimide was obtained in the same manner as in Example 1, except that the alumina filler used was DMAc-dispersed alumina sol B (minor axis: 5 nm, major axis: 200 nm). The amounts added are shown in Table 1.

[0043] Comparative Example 2 An alumina filler-containing polyimide was obtained in the same manner as in Example 1, except that the alumina filler used was DMAc-dispersed alumina sol C (minor axis: 10 nm, major axis: 50 nm). The amounts added are shown in Table 1.

[0044] Comparative Example 3 An alumina filler-containing polyimide was obtained in the same manner as in Example 1, except that the alumina filler used was DMAc-dispersed alumina sol D (minor axis: 20 nm, major axis: 20 nm). The amounts added are shown in Table 1.

[0045] Comparative Example 4 A silica filler-containing polyimide was obtained in the same manner as in Example 1, except that the filler used was organosilica sol DMAc-ST (manufactured by Nissan Chemical Industries, Ltd., particle size 12 nm). The amounts added are shown in Table 1. [Table 1]

[0046] Comparing the results of Example 1 and Comparative Example 1, it was found that even if the length of the alumina filler particles was shortened, there was no difference in the electrical properties of dielectric constant, dielectric dissipation factor, and insulating strength, but heat resistance and mechanical strength such as CTE and tensile modulus were reduced. Comparing the results of Example 1 and Comparative Examples 2 and 3, particles with a shorter major axis had a lower CTE. In the case of the silica filler of Comparative Example 4, the insulating strength and CTE were reduced. Comparing Examples 1 to 4, when the alumina filler was 5 wt%, the tensile modulus was improved while maintaining the electrical properties, but a sufficient value was not obtained. Furthermore, when the alumina filler was 50 wt%, the composition became brittle. As is clear from Table 1, according to the method of the present invention, by preparing a composition by mixing an alumina filler having a major axis of 200 nm or more and 3000 nm or less and a minor axis of 1 nm or more and 10 nm or less with a polyimide resin containing more than 5 parts by weight and not more than 40 parts by weight, it is possible to suppress increases in the dielectric constant and dielectric tangent, while maintaining insulation strength, and to impart a high suppression effect on the coefficient of thermal expansion and an improvement effect on the tensile modulus of elasticity. [Industrial Applicability]

[0047] The insulating polyimide resin composition of the present invention can improve the mechanical strength and thermal stability of polyimide resins used for flexible printed circuit boards, for example, without impairing the electrical properties thereof.

Claims

1. An insulating polyimide resin composition comprising alumina particles having a fibrous or acicular shape that satisfy all of the following (a) to (c), which can suppress increases in dielectric constant and dielectric dissipation factor, and can impart an effect of reducing the coefficient of thermal expansion and an effect of improving the tensile modulus of elasticity while maintaining insulating strength, and the composition contains more than 5 parts by weight and not more than 40 parts by weight of the alumina particles per 100 parts by weight of the insulating polyimide resin: (a) Alumina hydrate or alumina having a primary particle diameter of 200 nm or more and 3000 nm or less and a minor axis of 1 nm or more and 10 nm or less; (b) containing an organic acid or an inorganic acid in an amount of 0.1 equivalent or more and 2.0 equivalents or less relative to aluminum atoms; (c) The dispersion medium is an organic solvent

2. 2. The alumina hydrate or alumina dispersion composition according to claim 1, wherein the crystalline form of the alumina is boehmite or pseudoboehmite.

3. The dispersion composition according to claim 1 or 2, which is used as a filler to be mixed with a polyimide resin.

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