Adhesive compositions, coverlays, bonding sheets, and electronic substrates

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

Technical Field

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

Background Art

[0002] In recent years, with the spread of electric vehicles handling large power and the progress of high-density and high-integration of electronic substrate circuits, excellent heat resistance has been required for adhesive compositions for such applications.

[0003] For example, the environment in which an in-vehicle electronic circuit board is used is harsh, and high reliability is required from the viewpoint of safety. In addition to long-term heat resistance, it is necessary to conform to severe durability tests such as long-term moisture resistance and thermal cycling. Generally, adhesive compositions used for in-vehicle applications include acrylic, polyester, urethane, epoxy adhesive compositions, etc. Patent Document 1 discloses an adhesive composition for bonding in-vehicle parts containing a block copolymer (B) having a polymer block (a) containing a polymerizable monomer (A) and a structural unit derived from a styrene compound and a structural unit derived from a maleimide compound, and an acrylic polymer block (b). However, the above adhesive composition has been desired to be further improved in terms of high heat resistance. For example, at present, it has been difficult for the above adhesive composition to continuously maintain excellent adhesiveness even after being exposed to a high-temperature environment of 150°C for 3000 hours. This is because the long-term heat resistance of the resin itself constituting these adhesive compositions is insufficient.

[0004] An imide-based adhesive composition is known as an adhesive composition having relatively excellent heat resistance, but there is room for improvement in terms of long-term moisture resistance and flexibility of the bonded object using the imide-based adhesive composition. Thus, it has been difficult for conventional adhesive compositions to satisfy both the required characteristics and long-term heat resistance required for various applications.

[0005] Furthermore, fluoropolymers are materials with excellent heat resistance and moisture resistance, and fluoropolymer-based adhesive compositions using them also exist. Patent Document 2 discloses an adhesive for electronic components made of a fluoropolymer having a fluoropolymer-containing aliphatic ring structure and at least one coupling group in the molecule. Fluoropolymer-based adhesive compositions require special modification treatment of the fluoropolymer to improve the adhesion of the fluoropolymer. On the other hand, fluoropolymer-based adhesive compositions have excellent long-term heat resistance and maintain sufficient peel strength even after being exposed to an environment of 150°C for 3000 hours. However, when using fluoropolymer-based adhesive compositions, the adhesive effect cannot be expected unless the substrate, such as a glossy copper foil surface, is subjected to surface treatment (such as roughening treatment). The need for such surface treatment not only narrows the range of application of the fluoropolymer-based adhesive composition but also leads to higher material costs.

[0006] To achieve both long-term heat resistance and the various properties required of adhesive compositions, the application of adhesive compositions using a blend of multiple polymers is also being considered. For example, an example of an adhesive composition using a blend of multiple polymers is an adhesive composition consisting of a fluoropolymer with excellent heat resistance and a relatively inexpensive acrylic polymer with excellent adhesive properties. However, conventionally, blends of fluoropolymers and acrylic polymers have been incompatible, and even when forcibly mixed by methods such as roll kneading, dispersion problems or failure to achieve the expected performance have occurred.

[0007] Therefore, adhesive compositions containing a blend of fluoropolymers and acrylic polymers had room for further improvement in terms of coatability and handling. For example, adhesive compositions for electronic circuit boards are often used by uniformly depositing a cured film of the adhesive composition onto a substrate such as a polyimide film to a thickness of 15 μm to 100 μm. However, fluoropolymers and acrylic polymers, which are incompatible with each other, cause layer separation in solvent systems. For this reason, solvent-based adhesive compositions blended with these polymers are difficult to coat onto a substrate to a uniform thickness, making them impractical for use. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2018 / 199269 [Patent Document 2] Japanese Patent Application Publication No. 6-322336 [Overview of the project] [Problems that the invention aims to solve]

[0009] Conventional adhesive compositions described in Patent Documents 1 and 2, etc., have made it difficult to achieve both long-term heat resistance and the various properties required of adhesive compositions. Therefore, the present inventors conducted diligent research and discovered that by using an adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler, it is possible to achieve both long-term heat resistance and the various properties required of adhesive compositions, thus completing the present invention. [Means for solving the problem]

[0010] The gist of the present invention is as follows: [1] An adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. [2] The modified fluoropolymer contains an unsaturated bond within the molecule, the adhesive composition according to [1] above. [3] The adhesive composition according to [1] or [2] above, wherein the acrylic polymer comprises at least one group selected from the group consisting of carboxyl groups and hydroxyl groups. [4] The adhesive composition according to any one of [1] to [3] above, wherein the thermosetting resin includes 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 described in any one of [1] to [6] above. [8] A bonding sheet comprising an adhesive composition according to any one of [1] to [6] above, or a cured product of the adhesive composition. [9] An electronic substrate comprising a cured product of any one of the adhesive compositions described in [1] to [6] above. [Effects of the Invention]

[0011] This invention provides an adhesive composition that achieves both long-term heat resistance and various properties required for adhesive compositions. [Brief explanation of the drawing]

[0012] [Figure 1] This diagram illustrates the manufacturing process of an electronic circuit board according to one embodiment. [Modes for carrying out the invention]

[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 this invention, the thermosetting resin can improve the compatibility of the modified fluoropolymer and acrylic polymer, which are immiscible with each other, in a solvent system. Furthermore, by including an inorganic filler in the adhesive composition, the compatibility of the modified fluoropolymer and acrylic polymer can be further improved, as well as the dispersibility of the modified fluoropolymer and acrylic polymer. 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 through the synergistic effect of the modified fluoropolymer, acrylic polymer, thermosetting resin, and inorganic filler. In particular, because the adhesive composition of the present invention has excellent long-term heat resistance, it maintains excellent adhesive strength even after being exposed to an environment of 150°C for 3000 hours. In addition, when using conventional fluoropolymer-based adhesive compositions, roughening treatment of the adherend (such as a glossy copper foil surface) was required, but because the adhesive composition of the present invention has excellent adhesion, roughening treatment of the adherend is not required. The properties required of the 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. Examples of properties required of the adhesive composition include coating properties, flame retardancy, long-term moisture resistance, liquid storage stability, insulation reliability, peel strength, solvent resistance, and solder heat resistance. The adhesive composition of the present invention, or the cured product thereof, may possess some or all of these properties. Furthermore, although modified fluoropolymers are somewhat expensive, the overall cost of the adhesive composition can be reduced by blending them with inexpensive acrylic polymers.

[0014] The following describes each component that makes up the adhesive composition.

[0015] (Modified fluoropolymer) Modified fluoropolymers are fluoropolymers having specific groups introduced through modification, and one or more types can be used. Modified fluoropolymers are not particularly limited, but examples include modified vinylidene fluoride polymers, hexafluoropropene polymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, and vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkyloxyalkyl vinyl ether copolymers.

[0016] Examples of commercially available fluoropolymers that can be used for modification include the binary fluoropolymers Viton A500 (trade name) (manufactured by Chemours), Viton A700 (trade name) (manufactured by Chemours), Daiel G802 (trade name) (manufactured by Daikin), and Daiel G7800 (trade name) (manufactured by Daikin), and the ternary fluoropolymers Viton GBL600S (trade name), GF600S (trade name), GF200S (trade name) (manufactured by Chemours), Technoflon P457, P757 (trade name) (manufactured by Solvey), etc. Furthermore, examples of units that constitute modified fluoropolymers 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] Depending on the type and content of the group (modifying group) introduced into the fluoropolymer by the modification treatment, the modification method and conditions can be selected, and the modification method of the fluoropolymer is not particularly limited. The modified fluoropolymer preferably contains an unsaturated bond as a modifying group in the molecule constituting the modified fluoropolymer. When the modifying group is an unsaturated bond in this way, in the presence of a ketone solvent such as acetone or methyl ethyl ketone as needed for the fluoropolymer, it 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. Thereby, a dehydrofluorination reaction of the fluoropolymer can be carried out to form an unsaturated bond in the fluoropolymer to obtain a modified fluoropolymer.

[0018] Thereafter, hydrogen fluoride acid and the like are removed by salting out and washing the modified fluoropolymer. For example, when the adhesive composition of the present invention is used as an adhesive for an electronic substrate such as an FPC (Flexible Printed Circuits; flexible circuit board), this salting out and washing process will affect the insulation reliability and long-term heat resistance of the final electronic substrate. Therefore, when the adhesive composition of the present invention is used as an adhesive for an electronic substrate, it is preferable to wash the modified fluoropolymer 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 with the total amount of components other than the solvent (the total amount of the modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and optionally the curing agent and curing accelerator of the thermosetting resin, additives other than the solvent) being 100% by weight. By the content of the modified fluoropolymer in the adhesive composition being 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 from 0.01 to 15 mol%, more preferably from 0.05 to 10 mol%, and even more preferably from 0.1 to 5 mol% based on the total number of moles of the monomers constituting the modified fluoropolymer. When the content of the modifying group is 0.1 mol% or more, the effect of modification becomes sufficient, and in the cured product of an example of the adhesive composition, the crosslinking density with the thermosetting resin becomes sufficient. As a result, the solder heat resistance and solvent resistance can be made sufficient. Further, when the content of the modifying group is 5 mol% or less, the modified fluoropolymer is effectively dissolved in the solvent and can be sufficiently used as a varnish. Since the conventional adhesive composition containing a fluoropolymer has poor adhesiveness, roughening treatment of the base material (such as the shiny surface of a copper foil) was required in advance before adhesion. In contrast, the adhesive composition of the present invention contains a modified fluoropolymer and an acrylic polymer, and thus has excellent adhesiveness due to the synergistic effect of these polymers. Therefore, when using the adhesive composition of the present invention, roughening treatment of the base material is not required in advance before adhesion.

[0021] (Acrylic polymer) It 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 part of the constituent monomers, and one or more acrylic polymers can be used. At least a part of the acrylic polymer preferably has a reaction point with a thermosetting resin such as containing at least one group selected from the group consisting of a carboxyl group and a hydroxyl group, and is crosslinkable with the thermosetting resin. By the acrylic polymer containing reaction points such as a carboxyl group and a hydroxyl group, a crosslinking reaction with the thermosetting resin in the adhesive composition can increase the crosslinking density with the thermosetting resin in the cured product of the adhesive composition, and properties such as peel strength and solder heat resistance can be improved.

[0022] Acrylic polymers may contain acrylic acid ester monomers and methacrylic acid ester monomers in addition to acrylic acid monomers and methacrylic acid monomers. One example of an acrylic polymer is a copolymer composed of monomers that do not contain carboxyl groups, such as ethyl acrylate (EA), butyl acrylate (BA), and methyl methacrylate (MMA), and monomers that contain carboxyl groups, such as methacrylic acid (MAA) and monobutyl fumarate (MBF). The proportion of monomers containing carboxyl groups and hydroxyl groups among the monomers constituting the acrylic polymer is preferably 0.01 to 5.0% by weight, and more preferably 0.1 to 3.0% by weight. By having the proportion of monomers containing carboxyl groups and hydroxyl groups among the monomers constituting the acrylic polymer within the above range, the acrylic polymer can effectively crosslink with the thermosetting resin, increasing the crosslinking 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 carboxyl groups and hydroxyl groups in an 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%, relative to the total number of moles of monomers constituting the acrylic polymer.

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

[0024] The acrylic polymer content in the adhesive composition is preferably 5 to 50% by weight, more preferably 10 to 40% by weight, and even more preferably 15 to 30% 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 curing agent and curing accelerator for the thermosetting resin, and 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 the cured product of the adhesive composition can maintain excellent long-term heat resistance while possessing some or all of the properties required of the adhesive composition (coating properties, 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 modified fluoropolymer to acrylic polymer contained in the adhesive composition, (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 having (modified fluoropolymer):(acrylic polymer) = 8 or less:2 or more, the adhesive composition can maintain excellent long-term heat resistance while also having excellent adhesion to smooth substrates, thereby reducing costs. Furthermore, by having (modified fluoropolymer):(acrylic polymer) = 3 or more:7 or less, the adhesive composition can maintain excellent long-term heat resistance. More specifically, conventional adhesive compositions containing acrylic polymers have difficulty having excellent long-term heat resistance, but the adhesive composition of the present invention, by containing a modified fluoropolymer, can maintain excellent long-term heat resistance (for example, maintaining adhesive strength even after being exposed to an environment of 150°C for 3000 hours).

[0026] (Inorganic filler) The type of inorganic filler is not particularly limited, but one or more of the following can be used: 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. As will be described later, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide also function as flame retardants, but in this specification they are included in "inorganic filler". 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 greatly improved even with a small amount.

[0027] The inorganic filler may be a hydrophobized inorganic filler, and examples of such hydrophobic treatments include silicone oil treatment and silane coupling agent treatment. By containing an inorganic filler, the adhesive composition of the present invention can further enhance the compatibility of the modified fluoropolymer and the acrylic polymer, as well as improve the dispersibility of the modified fluoropolymer and the acrylic polymer.

[0028] The amount of inorganic filler in the adhesive composition is not particularly limited, but it 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 acrylic polymer. Having an inorganic filler content of 3 parts by weight or more per 100 parts by weight of the total weight of the modified fluoropolymer and acrylic polymer further enhances the compatibility and dispersibility of the modified fluoropolymer and acrylic polymer. Furthermore, having an inorganic filler content of 120 parts by weight or less per 100 parts by weight of the total weight of the modified fluoropolymer and acrylic polymer prevents coating defects due to increased viscosity of the adhesive composition, air inclusion during lamination, and a decrease in adhesive strength.

[0029] (thermosetting resin) The thermosetting resin is not particularly limited as long as it is a resin that hardens by heat treatment, and one or more types 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 resin is preferable in terms of reactivity, heat resistance, and adhesion to the substrate. In addition to improving adhesion to the substrate, epoxy resin can crosslink with both modified fluoropolymers and acrylic polymers, and therefore can contribute to improving the crosslinking density with 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 types of epoxy resins can be cited, 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 naphthalenediols; diglycidyl ethers of phenols; diglycidyl ethers of alcohols; and alkyl-substituted and hydrogenated versions thereof.

[0031] The content of 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 the total amount of components other than solvents (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and optionally curing agent and curing accelerator for the thermosetting resin, and total amount of additives other than solvents) as 100% by weight. By having the content of thermosetting resin in the adhesive composition within these ranges, the compatibility of the modified fluoropolymer and acrylic polymer can be made excellent.

[0032] (Curing agents and curing accelerators for thermosetting resins) The adhesive composition may contain an amine compound as a curing agent for the thermosetting resin. From the viewpoint of curability, the amine compound is preferably an aromatic diamine compound. The amount of curing agent used for the thermosetting resin 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 curing accelerators to promote 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)]-ethyls-triazine, and 2,4,6-tris(dimethylaminomethyl)phenol. The amount of curing accelerator used for thermosetting resins 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, n-hexane, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, N-methylpyrrolidone (NMP), etc. One or more of these solvents can be used in combination. By containing a solvent, the adhesive composition can dissolve other components and improve the coatability of the adhesive composition. For example, by using two or more solvents with different volatility, such as methyl ethyl ketone (MEK), toluene, ethyl acetate, and isobutyl acetate, foaming of the adhesive film can be suppressed when the adhesive composition is dried after application.

[0035] Furthermore, the adhesive composition may contain additives other than modified fluoropolymers, acrylic polymers, thermosetting resins, and inorganic fillers, as needed. For example, since modified fluoropolymers have excellent flame retardancy, if the content of modified fluoropolymers in the adhesive composition is large, the adhesive composition may not contain a flame retardant. On the other hand, if the content of modified fluoropolymers in the adhesive composition is small, 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. Note that if the metal hydroxide used as a flame retardant is aluminum hydroxide, magnesium hydroxide, or calcium hydroxide, then aluminum hydroxide, magnesium hydroxide, and calcium hydroxide also function as "inorganic fillers." For this reason, in this specification, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide are considered to be "inorganic fillers" of the present invention. From the viewpoint of improving the handling of the adhesive composition, the adhesive composition may contain known additives such as dispersants, defoamers, and rheology control agents, as needed.

[0036] (Method for manufacturing adhesive compositions) The method for producing the adhesive composition is not particularly limited, but for example, one method involves preparing a first solution containing a modified fluoropolymer and a second solution containing an acrylic polymer, and then mixing the first solution, the second solution, a thermosetting resin, an inorganic filler, and optionally a curing agent, a curing accelerator, and additives for the thermosetting resin using a mixing device such as a ball mill to obtain the adhesive composition. Heat may be applied during the mixing of the raw materials of this adhesive composition, or heat may be applied to the obtained adhesive composition. Applying heat during the mixing of the raw materials of the adhesive composition can improve the solubility of the raw materials of the adhesive composition. Furthermore, by heating the adhesive composition containing a solvent, the crosslinking reaction between the modified fluoropolymer and the acrylic polymer and the thermosetting resin is promoted, and the viscosity is increased, allowing for favorable control of the coating properties.

[0037] (How to use adhesive compositions) 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 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 modified groups introduced to the modified fluoropolymer by the modification treatment, and the acrylic polymer is crosslinked to the thermosetting resin via carboxyl groups, hydroxyl groups, etc. Therefore, the compatibility of the modified fluoropolymer and acrylic polymer can be improved via the thermosetting resin. The conditions for the heat treatment are not particularly limited, but the temperature is preferably 140 to 200°C, more preferably 150 to 190°C, 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 compositions) The adhesive composition can be used in a variety of applications, including as an adhesive composition for coverlays, bonding sheets, and electronic substrates (e.g., FPCs). 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, or an electronic substrate containing a cured product of the adhesive composition.

[0039] Figure 1 is a diagram illustrating the manufacturing process of an electronic substrate 10 according to one embodiment, which includes a cured product of the adhesive composition of the present invention. As shown in Figure 1(a), a copper foil layer 2 is formed on a base film 1 such as polyimide, and then a photoresist layer 3 is further formed on the copper foil layer 2.

[0040] Next, as shown in Figure 1(b), a predetermined pattern is formed within the photoresist layer 3 by exposure. After this, an opening 2a is created within the copper foil layer 2 by etching the copper foil layer 2 using the photoresist layer 3 on which the predetermined pattern has been formed as a mask. Next, the adhesive composition 4a of the present invention is applied to the polyimide film 4b in advance using a coating machine such as a coater, and then 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] Next, as shown in Figure 1(c), the coverlay is positioned to cover the opening 2a, and then heat treatment is performed under pressure. This heat treatment causes the adhesive composition 4a to harden, allowing the coverlay to be effectively bonded. At this point, an electronic substrate 10 containing the hardened adhesive composition 4a is obtained.

[0042] Next, as shown in Figure 1(d), a bonding sheet 5 containing the adhesive composition of the present invention is attached to the reinforcing plate 6, and then the electronic substrate 10 is placed on the bonding sheet 5 and heat treatment is performed under pressure. This heat treatment causes the adhesive composition contained in the bonding sheet 5 to harden, effectively bonding 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 shaping. An FPC can be used as the electronic substrate 10. The adhesive composition 4a and the adhesive composition contained in the bonding sheet 5 in Figure 1, or the hardened product of the adhesive composition, are superior in some or all of the following properties: coating properties, liquid storage stability, initial peel strength, long-term heat resistance, long-term moisture resistance, insulation reliability, solvent resistance, and solder heat resistance.

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

[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 1-8) A modified fluoropolymer was obtained by alkaline modification treatment of a commercially available fluoropolymer (Viton A500 (trade name); manufactured by Chemours) to obtain a modified fluoropolymer having 0.8 mol% of unsaturated bonds relative to the total number of moles of monomers constituting the modified fluoropolymer within its molecule. The first solution was obtained by dissolving the modified fluoropolymer thus obtained in a solvent (MEK / toluene = 1 / 1 solvent) to a content of 25% by weight. A second solution was obtained by using a commercially available carboxyl group-containing acrylic polymer (PA522HF (trade name); manufactured by Unimatec) as the acrylic polymer and dissolving it in toluene solvent to a content of 15% by weight. The first and second solutions obtained as described above were mixed, and then uncured thermosetting resins A and B, and silica and aluminum hydroxide (flame retardant) as inorganic fillers were mixed and dispersed in a ball mill. Finally, a curing agent and curing accelerator for the thermosetting resin were added to obtain an adhesive composition with the composition shown in Table 1. Note that Table 1 does not list the content of "solvent (MEK / toluene = 1 / 1 solvent)" and "toluene solvent," but rather shows the composition of components other than solvents in the adhesive composition.

[0046] (Comparative Examples 1-5) Adhesive compositions were obtained in the same manner as in Examples 1-8, except for the compositions shown in Table 2. Note that the adhesive compositions of Comparative Examples 1-2 did not contain modified fluoropolymers, therefore the first solution preparation step in Examples 1-8 was omitted. The adhesive composition of Comparative Example 4 did not contain an acrylic polymer, therefore the second solution preparation step in Examples 1-8 was omitted. The adhesive composition of Comparative Example 3 did not contain silica or aluminum hydroxide, therefore silica and aluminum hydroxide were not added during 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 first solution preparation step in Examples 1-8. Note that Table 2 does not list the content of "solvent (MEK / toluene = 1 / 1 solvent)" and "toluene solvent," but shows the composition of components other than the solvent in the adhesive composition.

[0047] In the following examples, evaluation samples were prepared using the adhesive compositions to assess their properties as follows.

[0048] (Creation of evaluation samples A and B) Coverlays were prepared by coating polyimide film (Apical 25NPI (product name); manufactured by Kaneka Corporation) with the adhesive compositions of each example so that the thickness of the adhesive composition after drying was 25 μm or 40 μm, and then drying them. The adhesive surface of the coverlay, which was prepared so that the thickness of the adhesive composition after drying was 25 μm, was bonded to the glossy surface of copper material (PNS H1035RA (product name); manufactured by Arisawa Seisakusho Co., Ltd.) using a vacuum press at 170°C and 2 MPa, and post-curing (hardening treatment) was performed in an oven (PH-202 (product name); manufactured by ESPEC Corporation) at 160°C for 6 hours to obtain evaluation sample A.

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

[0050] (Measurement of the properties of adhesive compositions) 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 10 mm wide strips, and the polyimide film was peeled at a 90° angle at 50 mm / min using a tensile testing machine (manufactured by AandD) in an atmosphere of 23°C, and the initial peel strength [N / mm] was measured.

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

[0053] (3) Peel strength after 1000 hours of heat resistance testing at 85°C and 85% relative humidity. Evaluation sample A, prepared in the same manner as the initial peel strength, was left in a constant temperature and humidity chamber at 85°C and 85% relative humidity for 1000 hours. After cooling to room temperature, the peel strength [N / mm] was measured in the same manner as the initial peel strength.

[0054] (4) Flame retardant Evaluation sample B was cut into strips measuring 13 mm x 125 mm, and a flame retardancy test was conducted based on the UL94 V-0 test. Specifically, the upper end of the long side of the sample was secured with a clip, and the strip was suspended perpendicular to the ground. Under atmospheric conditions, the lower end of evaluation sample B was ignited with a 20 mm flame and followed for 10 seconds. After 10 seconds, the 20 mm flame was removed, and after the flame went out, the 20 mm flame was followed again on the lower end of the sample for another 10 seconds. In accordance with the evaluation criteria of the UL94 V-0 test, samples that were equivalent to V-0 were rated "○", and those that were not equivalent to V-0 were rated "×".

[0055] (5) Heat resistance of solder after humidification Evaluation sample A was cut into 30 mm squares. Then, evaluation sample A was left in a constant temperature and humidity chamber at 40°C and 80% relative humidity for 72 hours to allow it to absorb moisture. Immediately after removing evaluation sample A from the constant temperature and humidity chamber, it was immersed for 10 seconds with the polyimide side facing up in a solder bath that had been pre-set to a constant temperature of 230-300°C. Samples without blistering or peeling were judged as "pass," and those showing blistering or peeling were judged as "fail," and the highest temperature at which a pass was observed was recorded. In comparative examples 5 and 6, blistering and peeling occurred at 230°C in the heat resistance of the humidified solder, so they were evaluated as "<230."

[0056] (6) Coatability To ensure uniform thickness, the adhesive composition for evaluation was applied using an applicator, and the solvent was dried in an oven set to 140°C to create a coating of the adhesive composition. A coating without unevenness was marked with a "○" (○) and a coating with unevenness was marked with a "×" (×) (×) by visual inspection.

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

[0058] [Table 1]

[0059] [Table 2]

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

[0061] As shown in Table 1, the adhesive compositions of Examples 1 to 8 contain a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler (silica, aluminum hydroxide). As a result, the cured products of these adhesive compositions exhibit excellent heat resistance (peel strength) of 0.4 [N / mm] or more over a long period of time, as well as excellent flame retardancy, heat resistance after humidified soldering, and coating properties.

[0062] In contrast, as shown in Table 2, the adhesive compositions of Comparative Examples 1 and 2 did not contain modified fluoropolymers, resulting in poor long-term heat resistance, with a peel strength of 0.2 [N / mm] after 3000 hours at 150°C, and poor flame retardancy ("×"). The adhesive composition of Comparative Example 3 did not contain inorganic fillers (silica and aluminum hydroxide), resulting in poor dispersibility of the modified fluoropolymer and acrylic polymer, making coating of the adhesive composition difficult, and other properties could not be measured. The adhesive composition of Comparative Example 4 did not contain an acrylic polymer, resulting in poor heat resistance, with an initial peel strength and a peel strength of 0.2 [N / mm] after 1000 hours at 85°C and 85% relative humidity after the heat resistance test. The heat resistance of the solder after humidification was also low ("<230"). The adhesive composition of Comparative Example 5 did not contain modified fluoropolymers, resulting in low heat resistance of "<230" after humidification. [Explanation of symbols]

[0063] 1 Base film 2 Copper foil layer 2a opening 3. Photoresist layer 4a Adhesive composition 4b Polyimide film 5 Bonding Sheet 6. Reinforcement plate

Claims

1. An adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler, The modified fluoropolymer contains unsaturated bonds within its molecule. The thermosetting resin includes an epoxy resin. The acrylic polymer has reaction sites with the epoxy resin, An adhesive composition 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.

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

3. 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.

4. A coverlay comprising the adhesive composition according to claim 1 or 2.

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

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

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