Adhesive composition, coverlay, bonding sheet, and electronic substrate

Abstract

The present invention relates to an adhesive composition containing a modified fluorine polymer, an acrylic polymer, a thermosetting resin, and an inorganic filler.

Description

Adhesive composition, coverlay, bonding sheet, and electronic substrate

[0001] The present invention relates to an adhesive composition, a coverlay, a bonding sheet, and an electronic substrate.

[0002] In recent years, with the spread of electric vehicles that use large amounts of power and the increasing density and integration of electronic substrate circuits, adhesive compositions for these applications and others are being required to have excellent heat resistance.

[0003] For example, electronic circuit boards for automotive applications are used in harsh environments, requiring high reliability from a safety perspective. They must meet stringent durability tests, including long-term heat resistance, long-term humidity resistance, and thermal cycling, in addition to long-term heat resistance. Adhesive compositions commonly used for automotive applications include acrylic, polyester, urethane, and epoxy adhesive compositions. Patent Document 1 discloses an adhesive composition for bonding automotive components, containing a polymerizable monomer (A) and a block copolymer (B) having a polymer block (a) containing a structural unit derived from a styrene compound and a structural unit derived from a maleimide compound, and an acrylic polymer block (b). However, further improvement in the high heat resistance of the adhesive composition has been desired. For example, the adhesive composition has difficulty maintaining excellent adhesion even after 3,000 hours of exposure to a high-temperature environment of 150°C. This is due to the lack of long-term heat resistance of the resins themselves that constitute these adhesive compositions.

[0004] Imide-based adhesive compositions are known as adhesive compositions with relatively excellent heat resistance, but there is still room for improvement in the long-term moisture resistance and flexibility of bonded articles using these imide-based adhesive compositions. As such, it has been difficult for conventional adhesive compositions to achieve both the required properties for various applications and long-term heat resistance.

[0005] Furthermore, fluoropolymers are materials with excellent heat resistance and moisture resistance, and fluoropolymer-based adhesive compositions using such materials also exist. Patent Document 2 discloses an adhesive for electronic components made of a fluoropolymer having a fluorinated alicyclic structure and at least one coupling group in the molecule. The fluoropolymer-based adhesive composition requires a special modification treatment of the fluoropolymer to improve the adhesive properties of the fluoropolymer. On the other hand, fluoropolymer-based adhesive compositions have excellent long-term heat resistance and maintain sufficient peel strength even after exposure to an environment of 150°C for 3,000 hours. However, when using a fluoropolymer-based adhesive composition, adhesive effectiveness cannot be expected unless a surface treatment (e.g., roughening treatment) is applied to the glossy surface of copper foil, which serves as the substrate. The need for such surface treatment not only narrows the application range of the fluoropolymer-based adhesive composition but also leads to increased material costs.

[0006] In order to achieve both long-term heat resistance and the various properties required of an adhesive composition, the use of adhesive compositions that use a blend of multiple polymers has also been considered. For example, an adhesive composition that uses a blend of multiple polymers is an adhesive composition that is a blend of a fluoropolymer, which has excellent heat resistance, and an acrylic polymer, which is relatively inexpensive and has excellent adhesive properties. However, in the past, blends of fluoropolymers and acrylic polymers were incompatible with each other, and even when forcibly mixed by methods such as roll kneading, the blends often resulted in poor dispersion or did not exhibit the expected performance.

[0007] For this reason, adhesive compositions containing a blend of a fluoropolymer and an acrylic polymer have room for further improvement in terms of coatability and handleability. For example, adhesive compositions for electronic circuit boards are often used by forming a cured product of the adhesive composition into a uniform film with a thickness of 15 μm to 100 μm on a substrate such as a polyimide film. However, fluoropolymers and acrylic polymers, which are incompatible with each other, cause layer separation in solvent-based systems. For this reason, it is difficult to coat solvent-based adhesive compositions containing a blend of these polymers to a uniform thickness on a substrate, making them difficult to use in practice.

[0008] International Publication No. 2018 / 199269 JP 6-322336

[0009] It was difficult to achieve both long-term heat resistance and the various properties required of an adhesive composition with the conventional adhesive compositions described in Patent Documents 1 and 2. As a result of extensive research, the present inventors discovered that an adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler can achieve both long-term heat resistance and the various properties required of an adhesive composition, and thus completed the present invention.

[0010] The present invention provides an adhesive composition comprising a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. [2] The adhesive composition according to [1] above, wherein the modified fluoropolymer contains an unsaturated bond in the molecule. [3] The adhesive composition according to [1] or [2] above, wherein the acrylic polymer contains at least one group selected from the group consisting of a carboxyl group and a hydroxyl group. [4] The adhesive composition according to any one of [1] to [3] above, wherein the thermosetting resin contains an epoxy resin. [5] The adhesive composition according to any one of [1] to [4] above, wherein the inorganic filler is at least one material selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum oxide. [6] The adhesive composition according to any one of [1] to [5] above, wherein the weight ratio of the modified fluoropolymer to the acrylic polymer contained in the adhesive composition is (modified fluoropolymer):(acrylic polymer) = 8:2 to 3:7. [7] A coverlay comprising the adhesive composition according to any one of [1] to [6] above. [8] A bonding sheet comprising the adhesive composition according to any one of [1] to [6] above or a cured product of the adhesive composition. [9] An electronic substrate comprising the cured product of the adhesive composition according to any one of [1] to [6] above.

[0011] It is possible to provide an adhesive composition that combines long-term heat resistance with the various properties required of an adhesive composition.

[0012] 1A to 1C are diagrams illustrating a manufacturing process of an electronic substrate according to an embodiment.

[0013] (Adhesive Composition) The adhesive composition of the present invention contains a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. In the present invention, the thermosetting resin can improve the compatibility of the modified fluoropolymer and the acrylic polymer, which are incompatible with each other, in a solvent system. Furthermore, by including an inorganic filler in the adhesive composition, the compatibility of the modified fluoropolymer and the acrylic polymer can be further improved, and the dispersibility of the modified fluoropolymer and the acrylic polymer can be improved. As a result, the adhesive composition of the present invention can achieve both long-term heat resistance and various properties required of an adhesive composition due to the synergistic effect of the modified fluoropolymer, the acrylic polymer, the thermosetting resin, and the inorganic filler. In particular, the adhesive composition of the present invention has excellent long-term heat resistance and maintains excellent adhesive strength even after exposure to an environment at 150°C for 3,000 hours. Furthermore, while conventional fluoropolymer-based adhesive compositions require roughening treatment or the like for the adherend (such as the glossy surface of copper foil), the adhesive composition of the present invention has excellent adhesion and therefore does not require roughening treatment or the like for the adherend. The properties required for an adhesive composition can be controlled by adjusting the weight-average molecular weight, Mooney viscosity, and glass transition temperature of the modified fluoropolymer and acrylic polymer, as well as the content ratio of the modified fluoropolymer and acrylic polymer. The properties required for an adhesive composition include coatability, flame retardancy, long-term moisture resistance, liquid storage stability, insulation reliability, peel strength, solvent resistance, solder heat resistance, etc., and the adhesive composition of the present invention or a cured product of the adhesive composition can have some or all of these properties. Furthermore, although modified fluoropolymers are somewhat expensive, blending the modified fluoropolymer with an inexpensive acrylic polymer can reduce the overall cost of the adhesive composition.

[0014] Each component constituting the adhesive composition will be described below.

[0015] (Modified Fluoropolymer) The modified fluoropolymer is a fluoropolymer having specific groups introduced by modification, and one or more types can be used. The modified fluoropolymer is not particularly limited, but examples thereof include modified fluoropolymers obtained by modifying vinylidene fluoride polymer, hexafluoropropene polymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkyloxyalkyl vinyl ether copolymer, etc.

[0016] Examples of commercially available fluoropolymers that can be used for modification include binary fluoropolymers such as Viton A500 (trade name) (manufactured by Chemours), Viton A700 (trade name) (manufactured by Chemours), Dai-el G802 (trade name) (manufactured by Daikin Industries, Ltd.), and Dai-el G7800 (trade name) (manufactured by Daikin Industries, Ltd.), and ternary fluoropolymers such as Viton GBL600S (trade name), GF600S (trade name), and GF200S (trade name) (manufactured by Chemours), and Technoflon P457 and P757 (trade names) (manufactured by Solvey). In addition, examples of units constituting the modified fluoropolymer include vinylidene fluoride, hexafluoropropene, tetrafluoroethylene, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether, and vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkyloxyalkyl vinyl ether.

[0017] The modification method and conditions may be selected depending on the type and content of the group (modifying group) to be introduced into the fluoropolymer by the modification treatment, and the method for modifying the fluoropolymer is not particularly limited. The modified fluoropolymer preferably contains an unsaturated bond as the modifying group within the molecule constituting the modified fluoropolymer. When the modifying group is an unsaturated bond, the fluoropolymer is treated with an alkaline substance such as potassium hydroxide, sodium hydroxide, cesium hydroxide, calcium hydroxide, calcium carbonate, or triethylamine, preferably at a temperature of about 20 to 70°C, in the presence of a ketone solvent such as acetone or methyl ethyl ketone, as needed. This causes a dehydrofluorination reaction of the fluoropolymer, forming an unsaturated bond in the fluoropolymer, thereby producing a modified fluoropolymer.

[0018] The modified fluoropolymer is then salted out and washed with water to remove hydrofluoric acid and the like. For example, when the adhesive composition of the present invention is used as an adhesive for electronic substrates such as FPCs (Flexible Printed Circuits), this salting out and washing process will affect the insulation reliability and long-term heat resistance of the final electronic substrate. For this reason, when the adhesive composition of the present invention is used as an adhesive for electronic substrates, it is preferable to wash the modified fluoropolymer with water until no impurities are detected.

[0019] The content of the modified fluoropolymer in the adhesive composition is preferably 15 to 80% by weight, more preferably 20 to 70% by weight, and even more preferably 25 to 60% by weight, based on 100% by weight of the total amount of components other than the solvent (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and optionally included curing agent and curing accelerator for the thermosetting resin, and additives other than the solvent). By keeping the content of the modified fluoropolymer in the adhesive composition within these ranges, the adhesive composition can maintain excellent long-term heat resistance.

[0020] The content of the modifying group in the modified fluoropolymer is not particularly limited, but is preferably 0.01 to 15 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol%, based on the total moles of the monomers constituting the modified fluoropolymer. When the modifying group content is 0.1 mol% or more, the modification effect is sufficient, and the cured product of an example adhesive composition exhibits sufficient crosslink density with the thermosetting resin. As a result, sufficient solder heat resistance and solvent resistance can be achieved. Furthermore, when the modifying group content is 5 mol% or less, the modified fluoropolymer effectively dissolves in solvents and can be fully utilized as a varnish. Conventional adhesive compositions containing fluoropolymers have poor adhesion, requiring prior roughening treatment of the substrate (e.g., the glossy surface of copper foil) before bonding. In contrast, the adhesive composition of the present invention contains a modified fluoropolymer and an acrylic polymer, and therefore exhibits excellent adhesion due to the synergistic effect of these polymers. Therefore, when using the adhesive composition of the present invention, prior roughening treatment of the substrate before bonding is not required.

[0021] (Acrylic Polymer) The acrylic polymer is not particularly limited as long as it contains at least one monomer selected from the group consisting of acrylic acid monomers and methacrylic acid monomers as at least a portion of its constituent monomers, and one or more acrylic polymers can be used. At least a portion of the acrylic polymer preferably has reactive sites with a thermosetting resin, such as at least one group selected from the group consisting of carboxyl groups and hydroxyl groups, and is capable of crosslinking with the thermosetting resin. When the acrylic polymer contains reactive sites such as carboxyl groups and hydroxyl groups, it undergoes a crosslinking reaction with the thermosetting resin in the adhesive composition, thereby increasing the crosslink density with the thermosetting resin in the cured product of the adhesive composition and improving properties such as peel strength and solder heat resistance.

[0022] In addition to acrylic acid monomers and methacrylic acid monomers, the acrylic polymer may contain acrylic acid ester monomers and methacrylic acid ester monomers. An example of an acrylic polymer is a copolymer of a monomer that does not contain a carboxyl group, such as ethyl acrylate (EA), butyl acrylate (BA), or methyl methacrylate (MMA), and a monomer that contains a carboxyl group, such as methacrylic acid (MAA) or monobutyl fumarate (MBF). The proportion of the monomer containing a carboxyl group or a hydroxyl group among the monomers that make up the acrylic polymer is preferably 0.01 to 5.0 wt %, and more preferably 0.1 to 3.0 wt %. By ensuring that the proportion of the monomer containing a carboxyl group or a hydroxyl group among the monomers that make up the acrylic polymer is within the above range, the acrylic polymer can effectively undergo a crosslinking reaction with the thermosetting resin, increasing the crosslink density with the thermosetting resin in the cured product of the adhesive composition and improving properties such as peel strength and solder heat resistance. The content of the carboxyl groups and hydroxyl groups in the acrylic polymer containing carboxyl groups and hydroxyl groups is preferably 0.01 to 5.0 mol %, more preferably 0.05 to 4.0 mol %, and even more preferably 0.1 to 3.0 mol %, based on the total number of moles of the monomers constituting the acrylic polymer.

[0023] Commercially available acrylic polymers can be used, for example, PA522HF (trade name) (manufactured by Unimatec Corporation). The weight-average molecular weight of the acrylic polymer is not particularly limited, but is preferably 150,000 to 1,500,000, and more preferably 300,000 to 1,300,000. The acrylic polymer may further contain a monomer other than acrylic acid monomers, methacrylic acid monomers, acrylic acid ester monomers, and methacrylic acid ester monomers, and ethylene can be used as such a monomer. Such an acrylic polymer can be an ethylene-acrylic copolymer, and a commercially available one such as Vamac Ultra IP (trade name) (manufactured by Celanese Corporation) can be used.

[0024] The content of the acrylic polymer in the adhesive composition is preferably 5 to 50 wt%, more preferably 10 to 40 wt%, and even more preferably 15 to 30 wt%, based on 100 wt% of the total amount of components other than the solvent (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and optionally the curing agent and curing accelerator for the thermosetting resin, and the total amount of additives other than the solvent). By having the acrylic polymer content in the adhesive composition within these ranges, the adhesive composition or a cured product of the adhesive composition can maintain excellent long-term heat resistance while possessing some or all of the properties required of an adhesive composition (coatability, flame retardancy, long-term moisture resistance, liquid storage stability, insulation reliability, peel strength, solvent resistance, solder heat resistance).

[0025] (Mixing Ratio of Modified Fluoropolymer and Acrylic Polymer) The weight ratio of the modified fluoropolymer to the acrylic polymer contained in the adhesive composition is preferably (modified fluoropolymer):(acrylic polymer) = 8:2 to 3:7, more preferably 7:3 to 4:6, and even more preferably 7:3 to 5:5. By satisfying a (modified fluoropolymer):(acrylic polymer) ratio of 8 or less:2 or more, the adhesive composition maintains excellent long-term heat resistance while also providing excellent adhesion to smooth substrates, thereby enabling cost reduction. Furthermore, by satisfying a (modified fluoropolymer):(acrylic polymer) ratio of 3 or more:7 or less, the adhesive composition can maintain excellent long-term heat resistance. More specifically, while conventional adhesive compositions containing acrylic polymers have had difficulty in achieving excellent long-term heat resistance, the adhesive composition of the present invention, by containing a modified fluoropolymer, can maintain excellent long-term heat resistance (e.g., maintain adhesive strength even after exposure to an environment of 150°C for 3,000 hours).

[0026] (Inorganic Filler) The type of inorganic filler is not particularly limited, and one or more of silica, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, calcium silicate, aluminum silicate, calcium carbonate, aluminum oxide, magnesium oxide, tin oxide, titanium oxide, manganese oxide, zirconium oxide, silicon nitride, aluminum nitride, boron nitride, talc, mica, kaolin, etc. can be used. As described below, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide also function as flame retardants, but are considered to be included in the "inorganic filler" in this specification. Among these inorganic fillers, it is preferable to include at least one material selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum oxide, and it is more preferable to include silica. By including silica in the inorganic filler, the coating stability of the adhesive composition can be significantly improved even with a small amount.

[0027] The inorganic filler may be an inorganic filler that has been hydrophobized, and examples of this hydrophobization treatment include silicone oil treatment, silane coupling agent treatment, etc. By including an inorganic filler in the adhesive composition of the present invention, the compatibility of the modified fluoropolymer and the acrylic polymer can be further enhanced, and the dispersibility of the modified fluoropolymer and the acrylic polymer can be improved.

[0028] The content of the inorganic filler in the adhesive composition is not particularly limited, but is preferably 3.0 to 120 parts by weight, more preferably 10 to 100 parts by weight, and even more preferably 15 to 90 parts by weight, per 100 parts by weight of the total weight of the modified fluoropolymer and the acrylic polymer. By having the inorganic filler content be 3 parts by weight or more per 100 parts by weight of the total weight of the modified fluoropolymer and the acrylic polymer, the compatibility and dispersibility of the modified fluoropolymer and the acrylic polymer can be further improved. Furthermore, by having the inorganic filler content be 120 parts by weight or less per 100 parts by weight of the total weight of the modified fluoropolymer and the acrylic polymer, problems such as poor coating due to increased viscosity of the adhesive composition, air inclusion during lamination, and reduced adhesive strength can be prevented.

[0029] (Thermosetting Resin) The thermosetting resin is not particularly limited as long as it is a resin that cures upon heat treatment. One or more of epoxy resins, phenolic resins, xylene resins, guanamine resins, diallyl phthalate resins, vinyl ester resins, unsaturated polyester resins, furan resins, polyimide resins, polyurethane resins, cyanate resins, maleimide resins, benzocyclobutene resins, etc. can be used. As the thermosetting resin, epoxy resins are preferably used in terms of reactivity, heat resistance, and adhesion to substrates. In addition to improving adhesion to substrates, epoxy resins are capable of crosslinking with both modified fluoropolymers and acrylic polymers, which can contribute to improving the crosslink density with the modified fluoropolymers and acrylic polymers in the cured product of the adhesive composition. As a result, the long-term heat resistance and solder heat resistance of the cured product of the adhesive composition can be improved.

[0030] Various epoxy resins can be used, including bisphenol type epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin; novolac type epoxy resins such as cresol novolac type epoxy resin, phenol novolac type epoxy resin, and bisphenol A novolac type epoxy resin; alicyclic epoxy resins; aliphatic chain epoxy resins; diglycidyl ether compounds of biphenols, diglycidyl ethers of naphthalenediol, diglycidyl ethers of phenols, diglycidyl ethers of alcohols, and alkyl-substituted and hydrogenated versions of these.

[0031] The content of the thermosetting resin in the adhesive composition is preferably 1.0 to 30% by weight, more preferably 2.0 to 20% by weight, and even more preferably 3.0 to 15% by weight, based on 100% by weight of the total amount of components other than the solvent (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and optionally the curing agent and curing accelerator for the thermosetting resin, and the total amount of additives other than the solvent). By having the content of the thermosetting resin in the adhesive composition within these ranges, excellent compatibility between the modified fluoropolymer and the acrylic polymer can be achieved.

[0032] (Curing agent and curing accelerator for thermosetting resin) The adhesive composition may contain an amine compound as a curing agent for the thermosetting resin. From the viewpoint of curing properties, the amine compound is preferably an aromatic diamine compound. The amount of the curing agent for the thermosetting resin used is preferably 0 to 70 parts by weight, more preferably 1 to 50 parts by weight, and even more preferably 3 to 30 parts by weight, per 100 parts by weight of the thermosetting resin.

[0033] The adhesive composition may contain imidazoles as a curing accelerator to accelerate curing. Examples of imidazole compounds used as curing accelerators include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1-(2-cyanoethyl)2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-methylimidazole, 2,4-diamino-6-[2-methylimidazoline-(1)]-ethyl s-triazine, and 2,4,6-tris(dimethylaminomethyl)phenol. The amount of the curing accelerator for the thermosetting resin used is preferably 0 to 10 parts by weight, more preferably 0.1 to 5.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight, per 100 parts by weight of the thermosetting resin.

[0034] (Other Additives) The adhesive composition may contain a solvent as needed. Examples of solvents include acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), toluene, xylene, methanol, ethanol, 1-propanol, 2-propanol (IPA), 1-butanol, 2-butanol, cyclohexane, cyclohexanone, cyclohexanol, normal hexane, ethyl acetate, normal propyl acetate, isopropyl acetate, normal butyl acetate, isobutyl acetate, and N-methylpyrrolidone (NMP). These solvents may be used alone or in combination of two or more. By containing a solvent in the adhesive composition, other components can be dissolved, improving the coatability of the adhesive composition. For example, by using a combination of two or more solvents with different volatility, such as methyl ethyl ketone (MEK), toluene, ethyl acetate, and isobutyl acetate, foaming of the coating film of the adhesive composition can be suppressed when the adhesive composition is applied and then dried.

[0035] The adhesive composition may contain additives other than the modified fluoropolymer, acrylic polymer, thermosetting resin, and inorganic filler, as needed. For example, since the modified fluoropolymer has excellent flame retardancy, when the content of the modified fluoropolymer in the adhesive composition is high, the adhesive composition may not contain a flame retardant. On the other hand, when the content of the modified fluoropolymer in the adhesive composition is low, the adhesive composition may contain a certain amount of flame retardant to meet the flame retardancy requirements. Examples of flame retardants include phosphorus-based flame retardants, nitrogen-based flame retardants, and metal hydroxides. When the metal hydroxide flame retardant is aluminum hydroxide, magnesium hydroxide, or calcium hydroxide, the aluminum hydroxide, magnesium hydroxide, or calcium hydroxide also functions as an "inorganic filler." Therefore, in this specification, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide are considered to be "inorganic fillers" in the present invention. To improve the handleability of the adhesive composition, the adhesive composition may contain known additives, such as dispersants, antifoaming agents, and rheology control agents, as needed.

[0036] (Method for Producing Adhesive Composition) The method for producing the adhesive composition is not particularly limited, but examples include a method in which a first solution containing a modified fluoropolymer and a second solution containing an acrylic polymer are prepared, and the first solution, the second solution, a thermosetting resin, an inorganic filler, and, if necessary, a curing agent for the thermosetting resin, a curing accelerator, and additives are mixed in a mixing device such as a ball mill to produce an adhesive composition. Heat may be applied when mixing the raw materials for the adhesive composition, or heat may be applied to the resulting adhesive composition. By applying heat when mixing the raw materials for the adhesive composition, the solubility of the raw materials for the adhesive composition can be improved. Furthermore, by heating the solvent-containing adhesive composition, the crosslinking reaction between the modified fluoropolymer and the acrylic polymer and the thermosetting resin is promoted, resulting in increased viscosity, and thus the coatability can be favorably controlled.

[0037] (Method of Using the Adhesive Composition) The adhesive composition contains a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. In one example, in the adhesive composition before curing, the modified fluoropolymer and the acrylic polymer are not crosslinked to the thermosetting resin, and the thermosetting resin is not cured. In another example, in the adhesive composition after curing by heat treatment, the modified fluoropolymer is crosslinked to the thermosetting resin via the modifying groups introduced into the modified fluoropolymer by the modification treatment, and the acrylic polymer is crosslinked to the thermosetting resin via carboxyl groups, hydroxyl groups, or the like. This improves the compatibility of the modified fluoropolymer and the acrylic polymer via the thermosetting resin. The heat treatment conditions are not particularly limited, but the temperature is preferably 140 to 200°C, more preferably 150 to 190°C, and even more preferably 160 to 180°C, and the time is preferably 1 to 24 hours, more preferably 2 to 18 hours, and even more preferably 3 to 12 hours.

[0038] (Uses of adhesive composition) The adhesive composition can be used for various purposes, and can be used as an adhesive composition for a coverlay, a bonding sheet, an electronic substrate (e.g., FPC), etc. More specifically, it can be used as a coverlay for an electronic substrate containing the adhesive composition, a bonding sheet containing the adhesive composition or a cured product of the adhesive composition, an electronic substrate containing a cured product of the adhesive composition, etc.

[0039] 1A and 1B are diagrams illustrating a manufacturing process for an electronic substrate 10 according to one embodiment, which includes a cured product of the adhesive composition of the present invention. As shown in Fig. 1A, a copper foil layer 2 is formed on a base film 1 made of polyimide or the like, and then a photoresist layer 3 is further formed on the copper foil layer 2.

[0040] 1(b), the photoresist layer 3 is exposed to light to form a predetermined pattern in the photoresist layer 3. Thereafter, the copper foil layer 2 is etched using the photoresist layer 3 with the predetermined pattern formed thereon as a mask, thereby forming openings 2a in the copper foil layer 2. Next, the adhesive composition 4a of the present invention is applied in advance to a polyimide film 4b using a coating machine such as a coater, and the adhesive composition 4a is dried in an uncured state to obtain a coverlay consisting of the polyimide film 4b and the adhesive composition 4a on the polyimide film 4b.

[0041] 1(c), a coverlay is placed to cover the inside of the opening 2a, and then heat treatment is performed under pressure. This heat treatment hardens the adhesive composition 4a, allowing the coverlay to be effectively bonded. At this time, an electronic substrate 10 containing the hardened adhesive composition 4a is obtained.

[0042] Next, as shown in FIG. 1( d ), a bonding sheet 5 containing the adhesive composition of the present invention is attached to a reinforcing plate 6, and then an electronic substrate 10 is placed on the bonding sheet 5 and heat-treated while being pressed. This heat treatment hardens the adhesive composition contained in the bonding sheet 5, enabling effective bonding between the reinforcing plate 6 and the electronic substrate 10. Next, the electronic substrate 10 fixed on the reinforcing plate 6 by the bonding sheet 5 is subjected to processing such as contouring. An example of the electronic substrate 10 is an FPC. The adhesive composition 4 a and the adhesive composition contained in the bonding sheet 5 in FIG. 1 or a cured product of the adhesive composition are excellent in some or all of the following properties: coatability, liquid storage stability, initial peel strength, long-term heat resistance, long-term moisture resistance, insulation reliability, solvent resistance, and solder heat resistance.

[0043] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention.

[0044] Next, examples will be described to further clarify the effects of the present invention, but the present invention is not limited to these examples.

[0045] Examples 1 to 8: A commercially available fluoropolymer (Viton A500 (trade name); manufactured by Chemours) was subjected to an alkali modification treatment to obtain a modified fluoropolymer having 0.8 mol% of unsaturated bonds in the molecule relative to the total moles of the monomers constituting the modified fluoropolymer. The modified fluoropolymer thus obtained was dissolved in a solvent (MEK / toluene = 1 / 1 solvent) so that the content was 25 wt% to obtain a first solution. A commercially available carboxyl group-containing acrylic polymer (PA522HF (trade name); manufactured by Unimatec Co., Ltd.) was used as the acrylic polymer, and the acrylic polymer was dissolved in a toluene solvent so that the content was 15 wt% to obtain a second solution. The first and second solutions obtained as described above were mixed, and then uncured thermosetting resins A and B and silica and aluminum hydroxide (a flame retardant) were added as inorganic fillers. The mixture was dispersed in a ball mill, and a curing agent and a curing accelerator for the thermosetting resin were added to obtain adhesive compositions having the compositions shown in Table 1. It should be noted that Table 1 does not list the contents of "solvent (MEK / toluene = 1 / 1 solvent)" and "toluene solvent," but shows the composition of the components other than the solvent in the adhesive composition.

[0046] Comparative Examples 1 to 5 Adhesive compositions were obtained in the same manner as in Examples 1 to 8, except that the compositions shown in Table 2 were used. The adhesive compositions of Comparative Examples 1 and 2 did not contain a modified fluoropolymer, and therefore did not have the step of preparing the first solution of Examples 1 to 8. The adhesive composition of Comparative Example 4 did not contain an acrylic polymer, and therefore did not have the step of preparing the second solution of Examples 1 to 8. The adhesive composition of Comparative Example 3 did not contain silica or aluminum hydroxide, and therefore silica and aluminum hydroxide were not added when performing the dispersion treatment using a ball mill. In Comparative Example 5, an unmodified fluoropolymer (Viton A500 (trade name); manufactured by Chemours) was used instead of the modified fluoropolymer in the step of preparing the first solution of Examples 1 to 8. Table 2 does not list the contents of the "solvent (MEK / toluene = 1 / 1 solvent)" and the "toluene solvent," and instead shows the composition of the components in the adhesive composition other than the solvent.

[0047] In the following, samples for evaluating the properties were prepared using the adhesive compositions of each example as follows.

[0048] (Preparation of Evaluation Samples A and B) The adhesive composition of each example was applied to a polyimide film (Apical 25NPI (trade name); manufactured by Kaneka Corporation) so that the thickness of the adhesive composition after drying would be 25 μm or 40 μm, and then dried to prepare a coverlay. The adhesive surface of the coverlay, prepared so that the thickness of the adhesive composition after drying would be 25 μm, was bonded to the glossy surface of a copper material (PNS H1035RA (trade name); manufactured by Arisawa Manufacturing Co., Ltd.) using a vacuum press under conditions of 170 ° C. and 2 MPa, and post-cured (cured) in an oven (PH-202 (trade name); manufactured by ESPEC Corporation) under conditions of 160 ° C. and 6 hours, thereby obtaining evaluation sample A.

[0049] The coverlay prepared so that the thickness of the adhesive composition after drying would be 40 μm was bonded to a polyimide film (Apical 25NPI (trade name); manufactured by Kaneka Corporation) in a vacuum press at 170°C and 2 MPa, and post-cured (hardened) in an oven (PH-202 (trade name); manufactured by ESPEC Corporation) at 160°C for 6 hours to obtain evaluation sample B.

[0050] (Measurement of Properties of Adhesive Composition) Using the evaluation samples A and B obtained as described above, the properties of the adhesive composition were measured as follows.

[0051] (1) Initial Peel Strength Evaluation Sample A was cut into a width of 10 mm, and the polyimide film was peeled off in a 90° direction at 50 mm / min using a tensile tester (manufactured by AandD) in an atmosphere of 23°C, to measure the initial peel strength [N / mm].

[0052] (2) Peel strength after heat resistance test at 150°C for 1000 hours and 3000 hours Evaluation sample A prepared in the same manner as for the initial peel strength was left in an atmospheric oven at 150°C for 1000 hours and 3000 hours, and then allowed to cool to room temperature, and the peel strength [N / mm] was measured in the same manner as for the initial peel strength.

[0053] (3) Peel strength after heat resistance test at 85°C and 85% relative humidity for 1000 hours Evaluation sample A prepared in the same manner as for the initial peel strength was left in a thermo-hygrostat at 85°C and 85% relative humidity for 1000 hours, and then allowed to cool to room temperature, and the peel strength [N / mm] was measured in the same manner as for the initial peel strength.

[0054] (4) Flame Retardancy Evaluation Sample B was cut into strips measuring 13 mm x 125 mm, and a flame retardancy test was conducted with reference to the UL94 V-0 test. Specifically, the upper end of the long side of the sample was fixed with a clip, and the strip was hung perpendicular to the ground. In the atmosphere, the lower end of Evaluation Sample B was ignited with a 20 mm flame and allowed to follow for 10 seconds. After 10 seconds, the flame was removed 20 mm, and after the fire had gone out, the 20 mm flame was again allowed to follow the lower end of the sample for 10 seconds. In accordance with the evaluation criteria for the UL94 V-0 test, samples that met V-0 standards were evaluated as "Good", and samples that did not meet V-0 standards were evaluated as "Poor".

[0055] (5) Solder Heat Resistance After Humidification Evaluation Sample A was cut into 30 mm squares. Evaluation Sample A was then left in a thermo-hygrostat chamber at 40°C and 80% relative humidity for 72 hours to absorb moisture. Evaluation Sample A was then removed from the thermo-hygrostat chamber and immediately immersed, polyimide side up, in a solder bath pre-set at a constant temperature of 230-300°C for 10 seconds. Samples showing no blistering or peeling were rated "pass," while samples showing blistering or peeling were rated "fail," and the highest temperature at which they passed was recorded. Note that Comparative Examples 5 and 6 were rated "<230" for solder heat resistance after humidification because they showed blistering and peeling at 230°C.

[0056] (6) Coatability To achieve a uniform thickness, the adhesive composition to be evaluated was applied using an applicator, and the solvent was dried in an oven set to 140° C. to form a coating film of the adhesive composition. When visually evaluated, adhesive composition coatings that were uniform were rated as "Good", and adhesive composition coatings that were uneven were rated as "Poor".

[0057] The results of the evaluations (1) to (6) for each example evaluated as described above are shown in Tables 1 and 2 below.

[0058]

[0059]

[0060] The materials used in Tables 1 and 2 are as follows: Silica: R972V (trade name), manufactured by Nippon Aerosil Co., Ltd. Aluminum hydroxide: BE033 (trade name), manufactured by Nippon Light Metal Co., Ltd. Thermosetting resin A: Epoxy resin, JER1001 (trade name), manufactured by Mitsubishi Chemical Corporation Thermosetting resin B: Epoxy resin, N-695 (trade name), manufactured by DIC Corporation Curing agent: MED-J (trade name), manufactured by Kumiai Chemical Industry Co., Ltd. Curing accelerator: Tetrad X (trade name), manufactured by Mitsubishi Gas Chemical Company, Inc.

[0061] As shown in Table 1, the adhesive compositions of Examples 1 to 8 contained a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler (silica, aluminum hydroxide), and therefore the cured products of these adhesive compositions had excellent heat resistance (peel strength) of 0.4 [N / mm] or more over an extended period of time, and also had excellent flame retardancy, solder heat resistance after humidification, and coatability.

[0062] In contrast, as shown in Table 2, the adhesive compositions of Comparative Examples 1 and 2 did not contain a modified fluoropolymer, and therefore the cured products of these adhesive compositions had a peel strength of 0.2 [N / mm] after 3000 hours at 150°C, indicating poor long-term heat resistance, and their flame retardancy was also poor, resulting in a rating of "X." The adhesive composition of Comparative Example 3 did not contain an inorganic filler (silica and aluminum hydroxide), resulting in poor dispersion of the modified fluoropolymer and acrylic polymer, making application of the adhesive composition difficult and preventing measurement of other properties. The adhesive composition of Comparative Example 4 did not contain an acrylic polymer, and therefore the cured products of this adhesive composition had poor initial peel strength and a peel strength of 0.2 [N / mm] after a 1000-hour heat resistance test at 85°C and 85% relative humidity, indicating poor heat resistance. The solder heat resistance after humidification was also low at "<230." The adhesive composition of Comparative Example 5 did not contain a modified fluoropolymer, and therefore its solder heat resistance after humidification was low at "<230."

[0063] REFERENCE SIGNS LIST 1 base film 2 copper foil layer 2a opening 3 photoresist layer 4a adhesive composition 4b polyimide film 5 bonding sheet 6 reinforcing plate

Claims

1. An adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler.

2. The adhesive composition according to claim 1, wherein the modified fluoropolymer contains an unsaturated bond in the molecule.

3. The adhesive composition according to claim 1 or 2, wherein the acrylic polymer contains at least one group selected from the group consisting of a carboxyl group and a hydroxyl group.

4. The adhesive composition according to claim 1 or 2, wherein the thermosetting resin comprises an epoxy resin.

5. The adhesive composition according to claim 1 or 2, wherein the inorganic filler is at least one material selected from the group consisting of silica, aluminum hydroxide, calcium carbonate, and aluminum oxide.

6. The adhesive composition according to claim 1 or 2, wherein the weight ratio of the modified fluoropolymer to the acrylic polymer contained in the adhesive composition is (modified fluoropolymer):(acrylic polymer)=8:2 to 3:

7.

7. A coverlay comprising the adhesive composition of claim 1 or 2.

8. A bonding sheet comprising the adhesive composition according to claim 1 or 2, or a cured product of said adhesive composition.

9. An electronic substrate comprising a cured product of the adhesive composition according to claim 1 or 2.

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