Binder composition, coverlay, adhesive sheet, and electronic substrate

Abstract

The present invention relates to an adhesive composition comprising a modified fluoropolymer, an acrylic polymer, a thermoset resin and an inorganic filler material.

Description

Technical Field

[0001] This invention relates to an adhesive composition, a cover layer, an adhesive sheet, and an electronic substrate. Background Technology

[0002] In recent years, with the increasing popularity of electric vehicles that use large amounts of electricity and the continuous advancement of high-density and high-integration electronic circuit boards, excellent heat resistance is required for adhesive compositions used in such applications.

[0003] For example, the operating environment of electronic circuit boards used in automotive applications is extremely harsh, requiring high reliability from a safety perspective. Besides long-term heat resistance, they also need to withstand stringent durability tests such as long-term moisture resistance and thermal cycling. Common adhesive compositions used in automotive applications include acrylic, polyester, urethane, and epoxy adhesive compositions. Patent Document 1 discloses an adhesive composition for bonding automotive components containing a polymeric monomer (A) and a block copolymer (B), wherein the block copolymer (B) has polymer blocks (a) comprising styrene-derived units and maleimide-derived units, and acrylic polymer blocks (b). However, further improvements in high heat resistance have been desired for the aforementioned adhesive compositions. For example, it is currently difficult for these adhesive compositions to maintain excellent adhesion even after exposure to a high temperature of 150°C for 3000 hours. This is because the resins constituting these adhesive compositions themselves have insufficient long-term heat resistance.

[0004] While imide-based adhesive compositions are known to have excellent heat resistance, adhesives using these compositions have room for improvement in long-term moisture resistance and flexural strength. Thus, it has been difficult to combine the required properties for various applications with long-term heat resistance in conventional adhesive compositions.

[0005] Furthermore, fluoropolymers are materials with excellent heat and moisture resistance, and fluoropolymer-based adhesive compositions also exist. Patent Document 2 discloses an adhesive for electronic components comprising a fluoropolymer having a fluorinated aliphatic ring structure and at least one coupling group within the molecule. To improve the adhesion of the fluoropolymer, the fluoropolymer-based adhesive composition requires special modification treatment of the fluoropolymer. On the other hand, fluoropolymer-based adhesive compositions exhibit excellent long-term heat resistance, maintaining sufficient peel strength even after exposure to 150°C for 3000 hours. However, when using fluoropolymer-based adhesive compositions, there are situations where adhesion cannot be expected without surface treatment (roughening treatment, etc.) on the glossy surface of the copper foil, which serves as the substrate. The necessity of such surface treatment not only narrows the application range of this fluoropolymer-based adhesive composition but also involves high material costs.

[0006] With the aim of combining long-term heat resistance with the various properties required for adhesive compositions, the application of adhesive compositions that blend multiple polymers has also been studied. For example, an example of an adhesive composition that blends multiple polymers can be cited as an example, which includes a blend of a fluoropolymer with excellent heat resistance and a relatively inexpensive acrylic polymer with excellent adhesion. However, in the past, with blends of fluoropolymers and acrylic polymers, the polymers are immiscible with each other, and even with forced mixing by methods such as roller mixing, poor dispersion and failure to achieve the desired performance can occur.

[0007] Therefore, adhesive compositions containing blends of fluoropolymers and acrylic polymers have room for further improvement in terms of coatability and workability. For example, adhesive compositions for electronic circuit boards are mostly used in a manner that allows the cured adhesive composition to form a uniform film on a substrate such as a polyimide film with a thickness of 15 μm to 100 μm. However, the immiscible fluoropolymers and acrylic polymers cause layer separation in solvent systems. Therefore, adhesive compositions in solvent systems containing these polymer blends are difficult to coat onto a substrate with a uniform thickness, hindering practical application.

[0008] Existing technical documents Invention Patent Documents Invention Patent Document 1: International Publication No. 2018 / 199269 Invention Patent Document 2: Japanese Patent Application Publication No. 6-322336 Summary of the Invention

[0009] The problem that the invention aims to solve It is difficult for conventional adhesive compositions described in Patent Documents 1 and 2 to possess both long-term heat resistance and the various properties required for an adhesive composition. Therefore, the inventors conducted in-depth research and discovered that by forming an adhesive composition containing a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler, it is possible to possess both long-term heat resistance and the various properties required for an adhesive composition, thus completing the present invention.

[0010] Methods for solving problems The main structure of this invention is as follows.

[0011] An adhesive composition comprising a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler.

[0012] [2] According to the adhesive composition described in [1] above, wherein the modified fluoropolymer contains unsaturated bonds within the molecule.

[0013] [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 carboxyl and hydroxyl groups.

[0014] [4] The adhesive composition according to any one of [1] to [3] above, wherein the thermosetting resin comprises an epoxy resin.

[0015] [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 silicon dioxide, aluminum hydroxide, calcium carbonate and aluminum oxide.

[0016] [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 (modified fluoropolymer): (acrylic polymer) = 8:2 to 3:7.

[0017] [7] A covering layer comprising the adhesive composition described in any one of [1] to [6] above.

[0018] [8] An adhesive sheet comprising the adhesive composition described in any one of [1] to [6] above, or a cured product of the adhesive composition.

[0019] [9] An electronic substrate comprising a cured product of the adhesive composition described in any one of [1] to [6] above.

[0020] The effects of the invention It is possible to provide an adhesive composition that combines long-term heat resistance with all the properties required for an adhesive composition. Attached Figure Description

[0021] Figure 1 This is a diagram illustrating the manufacturing process of an electronic substrate according to one embodiment.

[0022] Symbol Explanation 1. Base membrane 2 Copper foil layer 2a Opening 3 Photoresist layer 4a Adhesive Composition 4b Polyimide film 5 Adhesive Sheets 6 Reinforcing plates Detailed Implementation

[0023] (Adhesive composition) The adhesive composition of the present invention comprises a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. In the present invention, the thermosetting resin improves the compatibility of the immiscible modified fluoropolymer and acrylic polymer in a solvent system. Furthermore, the inclusion of the inorganic filler further enhances the compatibility and dispersibility of the modified fluoropolymer and acrylic polymer. As a result, the adhesive composition of the present invention, through the synergistic effect of the modified fluoropolymer, acrylic polymer, thermosetting resin, and inorganic filler, combines long-term heat resistance with all the properties required for an adhesive composition. In particular, the adhesive composition of the present invention maintains excellent bond strength even after exposure to 150°C for 3000 hours due to its excellent long-term heat resistance. Furthermore, while conventional fluoropolymer-based adhesive compositions require roughening treatment of the bonded materials (such as the glossy surface of copper foil), the adhesive composition of the present invention eliminates the need for roughening treatment of the bonded materials due to its excellent adhesion. The desired properties 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 their respective proportions. Examples of desired properties for the adhesive composition include coatability, 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 its cured form, can possess some or all of these properties. Furthermore, although modified fluoropolymers are slightly expensive, the overall cost of the adhesive composition can be reduced by blending them with inexpensive acrylic polymers.

[0024] The components constituting the adhesive composition are described below.

[0025] (Modified fluoropolymer) Modified fluoropolymers are fluoropolymers having specific groups introduced through modification, and one or more groups can be used. There are no particular limitations on the modified fluoropolymer; examples include modified fluoropolymers obtained by modifying vinylidene fluoride polymers, hexafluoropropylene polymers, vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, and vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkoxyalkyl vinyl ether copolymers.

[0026] Commercially available fluoropolymers that can be used for modification include: Viton A500 (trade name) (manufactured by Chemours), Viton A700 (trade name) (manufactured by Chemours), DAI-EL G802 (trade name) (manufactured by Daikin), and DAI-EL G7800 (trade name) (manufactured by Daikin) as binary fluoropolymers; and Viton GBL600S (trade name), GF600S (trade name), GF200S (trade name) (manufactured by Chemours), and Technoflon P457 and P757 (trade name) (manufactured by Solvey) as ternary fluoropolymers. In addition, examples of units constituting modified fluoropolymers include: vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether, vinylidene fluoride-tetrafluoroethylene-perfluoroalkyl vinyl ether-perfluoroalkoxyalkyl vinyl ether, etc.

[0027] The modification method and conditions can be selected based on the type and content of the groups (modified groups) introduced into the fluoropolymer through modification treatment; there are no particular limitations on the modification method for fluoropolymers. Preferably, the modified fluoropolymer contains unsaturated bonds as modifying groups within its molecule. When the modifying groups are unsaturated bonds, the fluoropolymer can be treated, as needed, in the presence of ketone solvents such as acetone or methyl ethyl ketone, using alkaline substances such as potassium hydroxide, sodium hydroxide, cesium hydroxide, calcium hydroxide, calcium carbonate, or triethylamine, preferably at a temperature of 20–70°C. This process involves the dehydrofluorination reaction of the fluoropolymer, which forms unsaturated bonds within the fluoropolymer, thus obtaining the modified fluoropolymer.

[0028] Then, hydrofluoric 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 electronic substrates such as FPCs (Flexible Printed Circuits), this salting out and washing process can 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 electronic substrates, it is preferable to wash the modified fluoropolymer until impurities are no longer detectable.

[0029] The total amount of components other than solvents (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and, where applicable, curing agent and curing accelerator of the thermosetting resin, and the total amount of additives other than solvents) is taken as 100% by weight. The content of 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. The content of modified fluoropolymer in the adhesive composition is within these ranges, thereby enabling the adhesive composition to maintain excellent long-term heat resistance.

[0030] The content of the modifying groups in the modified fluoropolymer is not particularly limited, but based on the total molar number of monomers constituting the modified fluoropolymer, it is preferably 0.01 to 15 mol%, more preferably 0.05 to 10 mol%, and even more preferably 0.1 to 5 mol%. When the content of the modifying groups is 0.1 mol% or more, the modification effect becomes sufficient, and in the cured product of an example adhesive composition, the crosslinking density with the thermosetting resin becomes sufficient. As a result, a product with sufficient resistance to solder heat and solvent resistance can be obtained. In addition, when the content of the modifying groups is 5 mol% or less, the modified fluoropolymer dissolves effectively in solvents and can be fully utilized as a varnish. Since the adhesive composition containing conventional fluoropolymers has poor adhesion, it is necessary to roughen the substrate (such as the glossy surface of copper foil) before bonding. In this regard, the adhesive composition of the present invention contains a modified fluoropolymer and an acrylic polymer, and therefore has excellent adhesion through the synergistic effect of these polymers. Therefore, when using the adhesive composition of the present invention, it is not necessary to roughen the substrate before bonding.

[0031] (Acrylic polymer) There is no particular limitation on the type of polymer that contains at least one monomer selected from the group consisting of acrylic monomers and methacrylic monomers as a constituent monomer; one or more acrylic polymers can be used. Preferably, at least a portion of the acrylic polymer has reaction sites with thermosetting resins, including at least one group selected from the group consisting of carboxyl groups and hydroxyl groups, and is a polymer capable of crosslinking with the thermosetting resin. Because the acrylic polymer contains reaction sites such as carboxyl and hydroxyl groups, it can increase the crosslinking density with the thermosetting resin in the cured adhesive composition by undergoing a crosslinking reaction with the thermosetting resin in the adhesive composition, thereby optimizing properties such as peel strength and solder heat resistance.

[0032] In addition to acrylic monomers and methacrylate monomers, acrylic polymers can also contain acrylate monomers and methacrylate monomers. An example acrylic polymer is a copolymer comprising carboxyl-free monomers such as ethyl acrylate (EA), butyl acrylate (BA), and methyl methacrylate (MMA) with carboxyl-containing monomers such as methacrylic acid (MAA) and monobutyl fumarate (MBF). The proportion of monomers containing carboxyl and hydroxyl groups in the monomers constituting the acrylic polymer is preferably 0.01 to 5.0% by weight, more preferably 0.1 to 3.0% by weight. When the proportion of carboxyl and hydroxyl groups in the monomers constituting the acrylic polymer is within the above range, the acrylic polymer can effectively undergo crosslinking reactions with thermosetting resins, increasing the crosslinking density with thermosetting resins in the cured adhesive composition and optimizing properties such as peel strength and solder heat resistance. The content of carboxyl and hydroxyl groups in the acrylic polymer containing carboxyl and hydroxyl groups relative to the total molar number of monomers constituting the acrylic polymer 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%.

[0033] Commercially available polymers can be used as acrylic polymers, such as PA522HF (trade name) (manufactured by Unimatec). The weight-average molecular weight of the acrylic polymer is not particularly limited, but is preferably 150,000 to 1,500,000, more preferably 300,000 to 1,300,000. The acrylic polymer may further contain monomers other than acrylic monomers, methacrylic monomers, acrylate monomers, and methacrylate monomers; ethylene is an example of such a monomer. Ethylene-acrylic copolymers can be used as examples of such acrylic polymers; commercially available polymers, such as Vamac ultra IP (trade name) (manufactured by Celanese).

[0034] The total amount of components other than solvents (modified fluoropolymers, acrylic polymers, thermosetting resins, inorganic fillers, and, where appropriate, curing agents and curing accelerators for thermosetting resins, and the total amount of additives other than solvents) is taken as 100% by weight. The content of acrylic polymers 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. With the content of acrylic polymers 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 and possess some or all of the properties required for the adhesive composition (coating properties, flame retardancy, long-term moisture resistance, liquid storage stability, insulation reliability, peel strength, solvent resistance, and solder heat resistance).

[0035] (Mixing ratio of modified fluoropolymer to acrylic polymer) The preferred weight ratio of the modified fluoropolymer to the acrylic polymer in the adhesive composition is (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. A (modified fluoropolymer):(acrylic polymer) ratio of 8 or less:2 or more allows the adhesive composition to maintain excellent long-term heat resistance and provides products with excellent adhesion to smooth substrates, thus achieving cost reduction. Furthermore, a (modified fluoropolymer):(acrylic polymer) ratio of 3 or more:7 or less allows the adhesive composition to maintain excellent long-term heat resistance. More specifically, adhesive compositions containing conventional acrylic polymers often lack excellent long-term heat resistance, but the adhesive composition of the present invention, by containing a modified fluoropolymer, maintains excellent long-term heat resistance (e.g., maintaining bond strength even after exposure to 150°C for 3000 hours).

[0036] (Inorganic filler material) The type of inorganic filler is not particularly limited, and 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. It should be noted that, as described later, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide also function as flame retardants, but are included in this specification as substances within the category of "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 more preferably, silica. The inclusion of silica in the inorganic filler allows for a significant improvement in the coating stability of the binder composition, even in small amounts.

[0037] The inorganic filler material can be a hydrophobically treated inorganic filler material, such as silicone oil treatment or silane coupling agent treatment. The adhesive composition of the present invention contains an inorganic filler material, thereby further improving the compatibility of the modified fluoropolymer and the acrylic polymer, and improving the dispersibility of the modified fluoropolymer and the acrylic polymer.

[0038] The content 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, relative to 100 parts by weight of the total weight of the modified fluoropolymer and acrylic polymer. When the content of inorganic filler is 3 parts by weight or more relative to 100 parts by weight of the total weight of the modified fluoropolymer and acrylic polymer, the compatibility and dispersibility of the modified fluoropolymer and acrylic polymer can be further improved. Furthermore, when the content of inorganic filler is 120 parts by weight or less relative to 100 parts by weight of the total weight of the modified fluoropolymer and acrylic polymer, it is possible to prevent poor coating, air ingress during lamination, and reduced bond strength caused by an increase in the viscosity of the adhesive composition.

[0039] (Thermosetting resin) Thermosetting resins are not particularly limited to any resin that is cured by heat treatment, and can include one or more of the following: epoxy resin, phenolic resin, xylene resin, guanidine resin, diallyl phthalate resin, vinyl ester resin, unsaturated polyester resin, furan resin, polyimide resin, polyurethane resin, cyanate ester resin, maleimide resin, benzocyclobutene resin, etc. From the perspectives of reactivity, heat resistance, and adhesion to the substrate, epoxy resin is preferred as a thermosetting resin. In addition to improving adhesion to the substrate, epoxy resin can undergo crosslinking reactions with modified fluoropolymers and acrylic polymers, thus facilitating an increase in the crosslinking density with modified fluoropolymers and acrylic polymers in the cured adhesive composition. As a result, the long-term heat resistance and solder heat resistance of the cured adhesive composition can be improved.

[0040] Epoxy resins can be categorized into various types, including bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and other bisphenol-type epoxy resins; cresol phenolic varnish type epoxy resin, phenolic varnish type epoxy resin, bisphenol A phenolic varnish type epoxy resin, and other phenolic varnish type epoxy resins; alicyclic epoxy resins; aliphatic chain epoxy resins; diglycidyl ether compounds of biphenol; diglycidyl ether compounds of naphthalene glycol; diglycidyl ether compounds of phenols; diglycidyl ether compounds of alcohols; and their alkyl-substituted products and hydrogenated products.

[0041] The total amount of components other than the solvent (modified fluoropolymer, acrylic polymer, thermosetting resin, inorganic filler, and, where appropriate, curing agent and curing accelerator of the thermosetting resin, and the total amount of additives other than the solvent) is taken as 100% by weight. 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. With the content of thermosetting resin in the adhesive composition within these ranges, a product with excellent compatibility between the modified fluoropolymer and the acrylic polymer can be obtained.

[0042] (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 in the thermosetting resin is preferably 0 to 70 parts by weight relative to 100 parts by weight of the thermosetting resin, more preferably 1 to 50 parts by weight, and even more preferably 3 to 30 parts by weight.

[0043] The adhesive composition may include imidazoles as curing accelerators to promote curing. Imidazole compounds used as curing accelerators may 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, 2,4,6-tris(dimethylaminomethyl)phenol, etc. The amount of curing accelerator used in the thermosetting resin is preferably 0 to 10 parts by weight relative to 100 parts by weight of the thermosetting resin, more preferably 0.1 to 5.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight.

[0044] (Other additives) The adhesive composition may contain solvents 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., and one or more of these solvents can be used in combination. The presence of solvents in the adhesive composition allows for the dissolution of other components, thereby improving 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 during drying after coating can be suppressed.

[0045] Furthermore, the binder composition may contain additives other than modified fluoropolymers, acrylic polymers, thermosetting resins, and inorganic fillers, as needed. In one example, modified fluoropolymers exhibit excellent flame retardancy; therefore, when the content of modified fluoropolymers in the binder composition is high, the binder composition may not contain flame retardants. On the other hand, when the content of modified fluoropolymers in the binder composition is low, the binder 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. It should be noted that when the metal hydroxide used as a flame retardant is aluminum hydroxide, magnesium hydroxide, or calcium hydroxide, it also functions as an "inorganic filler." Therefore, in this specification, aluminum hydroxide, magnesium hydroxide, and calcium hydroxide belong to the "inorganic filler" of this invention. From the viewpoint of improving the operability of the binder composition, the binder composition may also contain known additives such as dispersants, defoamers, and rheology control agents, as needed.

[0046] (Method for manufacturing adhesive composition) The method for manufacturing the adhesive composition is not particularly limited. For example, the following method can be used: preparing a first solution containing a modified fluoropolymer and a second solution containing an acrylic polymer, and mixing the first solution, the second solution, a thermosetting resin, an inorganic filler, and, as needed, a curing agent, a curing accelerator, and additives of the thermosetting resin using a mixing apparatus such as a ball mill to obtain the adhesive composition. Heat can be applied during the mixing of the raw materials of the adhesive composition, or heat can be applied to the obtained adhesive composition. By applying heat during the mixing of the raw materials of the adhesive composition, the solubility of the raw materials of the adhesive composition can be improved. Furthermore, by heating the adhesive composition containing the solvent, the crosslinking reaction between the modified fluoropolymer and the acrylic polymer and the thermosetting resin is promoted, and adhesion is increased, thereby allowing for suitable control of coatability.

[0047] (Instructions for use of the adhesive composition) The adhesive composition contains a modified fluoropolymer, an acrylic polymer, a thermosetting resin, and an inorganic filler. In one example, the modified fluoropolymer and the acrylic polymer in the adhesive composition before curing do not crosslink with the thermosetting resin, and the thermosetting resin does not cure. In another example, in the adhesive composition cured by heat treatment, the modified fluoropolymer crosslinks with the thermosetting resin through the modifying groups introduced into it during the modification treatment, and the acrylic polymer crosslinks with the thermosetting resin through carboxyl groups, hydroxyl groups, etc. Therefore, the compatibility of the modified fluoropolymer and the acrylic polymer can be improved through the thermosetting resin. The heat treatment conditions are not particularly limited, but the temperature is preferably 140–200°C, more preferably 150–190°C, and even more preferably 160–180°C; the time is preferably 1–24 hours, more preferably 2–18 hours, and even more preferably 3–12 hours.

[0048] (Use of the adhesive composition) The adhesive composition can be used in a variety of applications, including as an adhesive composition for cover layers, adhesive sheets, electronic substrates (e.g., FPCs), etc. More specifically, it can be used as a cover layer for an electronic substrate containing the adhesive composition, an adhesive 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.

[0049] Figure 1 This is a diagram illustrating the manufacturing process of an electronic substrate 10 comprising a cured product of the adhesive composition of the present invention. (See diagram for details.) Figure 1 As shown in (a), after forming a copper foil layer 2 on a base film 1 such as polyimide, a photoresist layer 3 is further formed on the copper foil layer 2.

[0050] Next, as Figure 1 As shown in (b), a predetermined pattern is formed within the photoresist layer 3 by exposing it. Then, the photoresist layer 3 with the predetermined pattern is used as a mask to etch the copper foil layer 2, thereby forming an opening 2a within the copper foil layer 2. Next, the adhesive composition 4a of the present invention is pre-coated onto the polyimide film 4b using a coating machine such as a coating machine, and the adhesive composition 4a is dried directly in an uncured state to obtain a cover layer composed of the polyimide film 4b and the adhesive composition 4a on the polyimide film 4b.

[0051] Then, as Figure 1 As shown in (c), after the cover layer is disposed to cover the opening 2a, heat treatment is performed under pressure. Through this heat treatment, the adhesive composition 4a becomes a cured product, which can effectively bond the cover layer. At this time, an electronic substrate 10 containing the cured product of the adhesive composition 4a is obtained.

[0052] Next, as Figure 1 As shown in (d), after attaching the adhesive sheet 5 containing the adhesive composition of the present invention to the reinforcing plate 6, the electronic substrate 10 is disposed on the adhesive sheet 5 and subjected to heat treatment under pressure. Through this heat treatment, the adhesive composition contained in the adhesive sheet 5 becomes a cured product, enabling effective bonding between the reinforcing plate 6 and the electronic substrate 10. Next, the electronic substrate 10, which is fixed to the reinforcing plate 6 by the adhesive sheet 5, undergoes shaping and other processing. An FPC can be used as an example of the electronic substrate 10. Figure 1 The adhesive composition 4a and the adhesive sheet 5 contain an adhesive composition or a cured product of the adhesive composition that is superior 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.

[0053] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, but includes all the concepts of the present invention and all the ways contained in the claims, and various changes can be made within the scope of the present invention.

[0054] Example Next, in order to further clarify the effects of the present invention, embodiments will be described, but the present invention is not limited to these embodiments.

[0055] (Examples 1-8) A modified fluoropolymer (Viton A500, trade name; manufactured by Chemours) was obtained by alkali modification treatment, which has 0.8 mol% of unsaturated bonds in the molecule relative to the total molar number of monomers constituting the modified fluoropolymer. A first solution was obtained by dissolving the thus obtained modified fluoropolymer in a solvent (MEK / toluene = 1 / 1 solvent) to a concentration of 25 wt%. A second solution was obtained by dissolving a commercially available carboxyl-containing acrylic polymer (PA522HF, trade name; manufactured by Umart) in toluene to a concentration of 15 wt%. The first and second solutions were mixed, and then uncured thermosetting resins A and B, silica as inorganic filler, and aluminum hydroxide (flame retardant) were mixed and dispersed using a ball mill. A curing agent and a curing accelerator for the thermosetting resin were then added, thereby obtaining the final adhesive composition 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 adhesive composition other than the solvent.

[0056] (Comparative Examples 1-5) Except for the composition shown in Table 2, the binder compositions were obtained in the same manner as in Examples 1-8. It should be noted that since the binder compositions of Comparative Examples 1-2 did not contain modified fluoropolymers, the preparation step of the first solution in Examples 1-8 was omitted. Similarly, since the binder composition of Comparative Example 4 did not contain acrylic polymers, the preparation step of the second solution in Examples 1-8 was omitted. The binder composition of Comparative Example 3 did not contain silica or aluminum hydroxide, therefore, silica and aluminum hydroxide were not added during dispersion treatment by ball milling. In Comparative Example 5, an unmodified fluoropolymer (Viton A500 (trade name); manufactured by Chemours) was used instead of the modified fluoropolymer in the preparation step of the first solution in Examples 1-8. It should be noted that in Table 2, the contents of "solvent (MEK / toluene = 1 / 1 solvent)" and "toluene solvent" are not listed; the composition of the binder compositions excluding the solvent is shown.

[0057] In the following examples, adhesive compositions were used to prepare evaluation samples of their properties.

[0058] (Evaluate the preparation of samples A and B) The adhesive compositions of each example were coated onto a polyimide film (APICAL 25NPI (trade name); manufactured by Kaneka Corporation) to achieve a thickness of 25 μm or 40 μm after drying, and then dried to create a cover layer. The bonding surface of the cover layer, with a thickness of 25 μm after drying, was bonded to the glossy surface of a copper material (PNS H1035RA (trade name); manufactured by Arisawa Corporation) using a vacuum press at 170°C and 2 MPa. Post-curing was then performed in an oven (PH-202 (trade name); manufactured by ESPEC Corporation) at 160°C for 6 hours, thus obtaining evaluation sample A.

[0059] The coating layer, prepared in such a way that the thickness of the dried adhesive composition described above is 40 μm, was bonded to a polyimide film (APICAL 25NPI (trade name); manufactured by Kaneka Corporation) using a vacuum press at 170°C and 2 MPa, and then post-cured (curing treatment) in an oven (PH-202 (trade name); manufactured by Espec Corporation) at 160°C for 6 hours, thereby obtaining evaluation sample B.

[0060] (Determination of the properties of the adhesive composition) Using samples A and B obtained as described above, the properties of the adhesive composition were determined as follows.

[0061] Initial peel strength Evaluation sample A was cut to a width of 10 mm. The polyimide film was peeled at 90° and 50 mm / min using a tensile testing machine (manufactured by A&D) at 23°C. The initial peel strength [N / mm] was measured.

[0062] Peel strength after heat resistance tests at 150°C for 1000 hours and 3000 hours Evaluation sample A, prepared in the same manner as the initial peel strength, was placed in an atmospheric oven at 150°C for 1000 hours and 3000 hours, and then cooled at room temperature. The peel strength [N / mm] was measured in the same manner as the initial peel strength.

[0063] Peel strength after 1000 hours of heat resistance test at 85℃ and 85% relative humidity. Evaluation sample A, prepared in the same manner as the initial peel strength, was placed in a constant temperature and humidity bath at 85°C and 85% relative humidity for 1000 hours, and then cooled at room temperature. The peel strength [N / mm] was measured in the same manner as the initial peel strength.

[0064] (4) Flame retardancy Evaluation sample B was cut into strips measuring 13mm × 125mm, and a flame retardancy test was conducted according to the UL94 V-0 test. Specifically, the upper end of the long side of the sample was fixed with a clamp, and the strip was suspended perpendicular to the ground. Under atmospheric conditions, the lower end of evaluation sample B was ignited with a 20mm flame and followed for 10 seconds. After 10 seconds, the 20mm flame was removed, and after the flame extinguished, the 20mm flame was followed again for 10 seconds. According to the UL94 V-0 test evaluation criteria, compliance with V-0 was rated as "0", and non-compliance with V-0 was rated as "×".

[0065] (5) Resistance to solder heat after humidification Evaluation sample A was cut into 30mm square pieces. Then, it was placed in a constant temperature and humidity bath at 40°C and 80% relative humidity for 72 hours to allow it to absorb moisture. Immediately after removing it from the bath, the polyimide side of evaluation sample A was immersed in a solder bath at a pre-set constant temperature of 230–300°C for 10 seconds. Samples without bulging or peeling were designated "acceptable," while samples with bulging or peeling were designated "unacceptable." The highest temperature at which it was considered acceptable was recorded. It should be noted that in the solder heat resistance tests after humidification in Comparative Examples 5 and 6, bulging and peeling occurred at 230°C, therefore the evaluation was "<230".

[0066] (6) Coating properties To achieve a uniform thickness, the adhesive composition for evaluation was applied using a coater and dried in an oven set to 140°C, thereby creating a coating of the adhesive composition. Visual evaluation was performed, with "0" indicating no unevenness in the adhesive composition coating and "×" indicating unevenness.

[0067] The evaluation results of the above (1) to (6) for each example evaluated as described above are shown in Tables 1 to 2 below.

[0068] [Table 1] [Table 2] The materials used in Tables 1 and 2 are shown below.

[0069] Silica; R972V (trade name), manufactured by Aerogel Co., Ltd., Japan. Aluminum hydroxide; BE033 (trade name), manufactured by Nippon Light Metals 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. Hardener; MED-J (trade name), manufactured by Comia Chemical Industry Co., Ltd. Curing accelerator; Tetrad X (trade name), manufactured by Mitsubishi Gas Chemical Co., Ltd. As shown in Table 1, the adhesive compositions of Examples 1 to 8 contain modified fluoropolymers, acrylic polymers, thermosetting resins, and inorganic fillers (silica and aluminum hydroxide). Therefore, the cured adhesive compositions have excellent heat resistance (peel strength) of 0.4 [N / mm] or more over a long period of time, and also have excellent flame retardancy, solder heat resistance after humidification, and coatability.

[0070] As shown in Table 2, the adhesive compositions of Comparative Examples 1 and 2 do not contain modified fluoropolymers. Therefore, the peel strength of the cured adhesive composition after 3000 hours at 150°C is 0.2 [N / mm], indicating poor long-term heat resistance and a "×" rating for flame retardancy, thus being considered poor. The adhesive composition of Comparative Example 3 does not contain inorganic fillers (silica and aluminum hydroxide). Therefore, the dispersibility of the modified fluoropolymer and acrylic polymer is poor, making the adhesive composition difficult to coat, and other properties cannot be determined. The adhesive composition of Comparative Example 4 does not contain acrylic polymers. Therefore, the initial peel strength of the cured adhesive composition and the peel strength after a heat resistance test at 85°C and 85% relative humidity for 1000 hours are 0.2 [N / mm], indicating poor heat resistance. The solder heat resistance after humidification is also low, at "<230". The adhesive composition of Comparative Example 5 does not contain modified fluoropolymers. Therefore, the solder heat resistance after humidification is low, at "<230".

Claims

1. An adhesive composition comprising 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 unsaturated bonds within its 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 carboxyl and hydroxyl groups.

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

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

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

7.

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

8. An adhesive sheet comprising the adhesive composition of claim 1 or 2, or a cured product of the adhesive composition.

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

Images