Curable adhesive sheet, and method for producing cured product

Abstract

Provided is a curable adhesive sheet having a curable adhesive layer capable of forming a cured product having a loss tangent of 0.01 or less at 23°C and 1 GHz, and a first release film and a second release film enclosing the two surfaces of the curable adhesive layer, wherein the first release film has a colored resin film (i) and a release agent layer that is laminated on one surface of the colored resin film (i) and is in contact with the surface of the curable adhesive layer, the second release film has a resin film (ii) that is visually distinguishable from the colored resin film (i) and a release agent layer that is laminated on one surface of the resin film (ii) and is in contact with the surface of the curable adhesive layer, and the curable adhesive sheet satisfies requirement (Ia). Requirement (Ia): the thickness ratio [(T2) / (T1)] of the thickness (T2) of the second release film and the thickness (T1) of the first release film is 1.05 or greater.

Description

Curable adhesive sheet and method for producing cured product

[0001] The present invention relates to a curable adhesive sheet and a method for producing a cured product using the curable adhesive sheet.

[0002] In recent years, flexible printed circuit boards (FPCs) have been used as wiring components in response to the trend toward smaller and lighter electronic devices. FPCs can be manufactured by, for example, forming electrical circuits by etching the copper foil of a copper-clad laminate, in which copper foil is laminated to an insulating resin film such as polyimide. For such FPCs, a coverlay sheet having an insulating resin base material and an adhesive layer is laminated to the copper foil on which the electrical circuit is formed to protect the electrical circuit.

[0003] As an example of such a coverlay sheet, Patent Document 1 discloses an invention relating to a thermosetting adhesive sheet in which a thermosetting adhesive layer is formed on a substrate, the thermosetting adhesive layer being made of an adhesive composition containing a predetermined amount of a styrene-based elastomer, a modified polyphenylene ether resin having a polymerizable group at the end, an epoxy resin, and an epoxy resin curing agent.

[0004] JP 2019-135280 A

[0005] Incidentally, as described in Patent Document 1, a release sheet that has been subjected to a release treatment is provided on the surface of the thermosetting adhesive layer of a thermosetting adhesive sheet for the purpose of protecting the surface. Release sheets having a release layer on a paper substrate are widely used as release sheets. However, the paper substrate is prone to generating foreign matter such as dust and dirt, which can become trapped between the adherend and the thermosetting adhesive layer when the thermosetting adhesive layer is attached to the adherend. In particular, in the case of FPCs, the inclusion of foreign matter can cause malfunctions of electronic devices. Furthermore, when a release sheet other than a paper substrate is used, there is also a handling issue in that it is difficult to peel the release sheet from the thermosetting adhesive layer. Therefore, there is a need for a curable adhesive sheet that can suppress the inclusion of foreign matter when attached to an adherend and has excellent handleability.

[0006] The present invention provides a curable adhesive sheet having a curable adhesive layer capable of forming a cured product having a dielectric tangent of a predetermined value or less, and a first release film and a second release film sandwiching the curable adhesive layer on both sides, wherein the first release film has a colored resin film and the second release film has a resin film that is visually distinguishable from the colored resin film, and the ratio of the thickness of the second release film to the thickness of the first release film is a predetermined value or more.

[0007] Specifically, one aspect of the present invention is as follows: [1] A curable adhesive sheet having a curable adhesive layer capable of forming a cured product having a dielectric loss tangent of 0.01 or less at 23°C and 1 GHz, and first and second release films sandwiching both sides of the curable adhesive layer, wherein the first release film has a colored resin film (i) and a release agent layer laminated on one surface of the colored resin film (i) and in contact with the surface of the curable adhesive layer, and the second release film has a resin film (ii) that is visually distinguishable from the colored resin film (i) and a release agent layer laminated on one surface of the resin film (ii) and in contact with the surface of the curable adhesive layer, and the curable adhesive sheet satisfies the following requirement (Ia): Requirement (Ia): The thickness ratio [(T2) / (T1)] of the thickness (T2) of the second release film to the thickness (T1) of the first release film is 1.05 or greater. [2] The curable adhesive sheet according to [1] above, further satisfying the following requirement (Ib): Requirement (Ib): The thickness ratio [(T2) / (T1)] of the thickness of the second release film (T2) to the thickness of the first release film (T1) is 10.0 or less. [3] The curable adhesive sheet according to [1] or [2] above, further satisfying the following requirement (IIa): Requirement (IIa): The thickness difference [(T2) - (T1)] between the thickness of the second release film (T2) and the thickness of the first release film (T1) is 5.0 μm or more. [4] The curable adhesive sheet according to any one of [1] to [3] above, further satisfying the following requirement (IIb): Requirement (IIb): The thickness difference [(T2) - (T1)] between the thickness of the second release film (T2) and the thickness of the first release film (T1) is 165.0 μm or less. [5] The curable adhesive sheet according to any one of [1] to [4] above, further satisfying the following requirement (III): Requirement (III): The ratio [(R1) / (R2)] of the peel force (R1) when the first release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min to the peel force (R2) when the second release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min is 0.97 or less. [6] The curable adhesive sheet according to any one of [1] to [5] above, further satisfying the following requirement (IV).Requirement (IV): The peel force (R2) when the second release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min is greater than the peel force (R1) when the first release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min, and is 600 mN / 50 mm or less. [7] The curable adhesive sheet according to any one of [1] to [6] above, wherein the resin film (ii) is a transparent resin film. [8] The curable adhesive sheet according to any one of [1] to [7] above, wherein the curable adhesive layer is a layer formed from a curable adhesive composition containing a polyphenylene ether resin. [9] The curable adhesive sheet according to any one of [1] to [8] above, wherein, when the curable adhesive layer exposed by peeling off a first release film is attached to an adherend, the presence or absence of foreign matter at the interface between the curable adhesive layer and the adherend can be confirmed from the second release film side by optical inspection means.

[10] A method for producing a cured product using the curable adhesive sheet according to any one of [1] to [9] above, the method comprising the following steps (1) to (3): - Step (1): A step of peeling off the first release film to attach the exposed curable adhesive layer to an adherend; - Step (2): A step of confirming, from the second release film side by optical inspection means, the absence of foreign matter at the interface between the curable adhesive layer and the adherend; - Step (3): A step of curing the curable adhesive layer to form a cured product after step (2).

[0008] A curable adhesive sheet according to a preferred embodiment of the present invention can prevent the inclusion of foreign matter when applied to an adherend, and has excellent handleability, as the release film is easily removable.

[0009] 1 is a schematic cross-sectional view in the thickness direction of a curable adhesive sheet, showing an example of the configuration of the adhesive sheet of the present invention.

[0010] The numerical ranges described herein can be arbitrarily combined with upper and lower limit values. For example, when a numerical range is described as "preferably 20 to 120, more preferably 40 to 90," the ranges "20 to 90" and "40 to 120" are also included in the numerical ranges described herein. Furthermore, when a numerical range is described as "preferably 20 or more, more preferably 40 or more, and preferably 120 or less, more preferably 90 or less," the ranges "20 to 90" and "40 to 120" are also included in the numerical ranges described herein. In addition, for example, a numerical range described herein as "60 to 100" means a range of "60 or more and 100 or less." Furthermore, when specifying the upper and lower limit values ​​described herein, the numerical range from the lower limit value to the upper limit value can be specified by appropriately selecting from the respective options and combining them arbitrarily. In addition, multiple combinations of the various requirements described as preferred aspects of the present specification can be used.

[0011] In this specification, for example, "(meth)acrylate" is used as a term that refers to both "acrylate" and "methacrylate," and the same applies to other similar terms. In this specification, the "active ingredient" of a curable adhesive composition refers to the components contained in the curable adhesive composition excluding water and organic solvent diluents.

[0012] In this specification, the number average molecular weight (Mn) is a value calculated as a standard polystyrene as measured by gel permeation chromatography (GPC), and specifically, is a value measured based on the method described in the examples.

[0013] In this specification, the thickness of each layer constituting the curable adhesive sheet is a value measured in accordance with JIS K7130 (1999), and can be measured, for example, using a constant pressure thickness measuring device (manufactured by Teclock Corporation, product name "PG-02J").

[0014] [Configuration of Curable Adhesive Sheet] Figure 1 is a schematic cross-sectional view in the thickness direction of the adhesive sheet, showing an example of the configuration of the curable adhesive sheet of the present invention. As shown in Figure 1, the curable adhesive sheet 1 of the present invention has a curable adhesive layer 10, and a first release film 21 and a second release film 22 that sandwich both sides of the curable adhesive layer 10. When cured, the curable adhesive layer 10 can form a cured product having a dielectric loss tangent of 0.01 or less at 23°C and 1 GHz.

[0015] The first release film 21 has a colored resin film (i) 212 and a release layer 211 laminated on one surface of the colored resin film (i) 212 and in contact with the surface 10a of the curable adhesive layer 10. The colored resin film includes a white resin film. The second release film 22 has a resin film (ii) 222 and a release layer 221 laminated on one surface of the resin film (ii) 222 and in contact with the surface 10b of the curable adhesive layer 10. In the curable adhesive sheet of one embodiment of the present invention, the resin film (ii) of the second release film is visually distinguishable from the colored resin film (i) of the first release film.

[0016] In one embodiment of the curable adhesive sheet of the present invention, it is envisioned that, during use, the first release film 21 is peeled off, the exposed surface 10a of the curable adhesive layer 10 is attached to an adherend, and then the second release film 22 is peeled off. As described above, the first release film has a colored resin film (i) and the second release film has a resin film (ii) that is visually distinguishable from the colored resin film (i), thereby clearly distinguishing the first release film from the second release film. Therefore, in the curable adhesive sheet of one embodiment of the present invention, it is easy to identify the first release film to be peeled off first during use, preventing the mistake of accidentally peeling off the second release film. Furthermore, as described below, when the second release film is a colorless and transparent resin film, peeling off the first release film (i) first gives the entire curable adhesive sheet a nearly colorless and transparent appearance, which has the advantage of making it easy to visually recognize that the colored resin film (i) has been peeled off.

[0017] Furthermore, because both the first release film and the second release film use resin films as the base material, dust and other foreign matter caused by the release films is less likely to be generated. Therefore, the curable adhesive sheet of one embodiment of the present invention can effectively prevent the inclusion of foreign matter when attached to an adherend, and can therefore prevent malfunctions of electronic devices caused by the inclusion of foreign matter, even when used in, for example, an FPC.

[0018] In addition, the curable adhesive sheet of one embodiment of the present invention is preferably configured such that, when the curable adhesive layer exposed by peeling off the first release film is attached to an adherend, the presence or absence of foreign matter at the interface between the curable adhesive layer and the adherend can be confirmed from the second release film side using an optical inspection means. With this configuration, when the curable adhesive layer is attached to an adherend, it is possible to check from the second release film side whether foreign matter has been mixed in between the adherend and the curable adhesive layer. Therefore, measures such as re-attaching the curable adhesive sheet can be taken, thereby improving product yield. The above configuration can be used when the resin film of the second release film is, for example, a transparent resin film.

[0019]

[0003] In an adhesive sheet having a configuration in which an adhesive layer is sandwiched between two release films, when the release film uses a resin film as the substrate, it is more likely to cause a handling problem in that it is difficult to peel one of the release films from the adhesive layer compared to a release film using a general paper substrate. In particular, a curable adhesive layer having a low dielectric tangent, such as the curable adhesive sheet of the present invention, is often composed of a component that does not have a polar group or a component that has low polarity, and the surface polarity of the curable adhesive layer is low. Therefore, when a curable adhesive layer with a low surface polarity is sandwiched between two release films having resin films, it becomes increasingly difficult to peel one of the release films from the surface with low polarity of the curable adhesive layer during use, resulting in a handling problem.

[0020] To address this handling issue of difficulty in peeling the release film from the low-polarity surface of the curable adhesive layer, the curable adhesive sheet of the present invention is adjusted to satisfy the following requirement (Ia): Requirement (Ia): The thickness ratio [(T2) / (T1)] of the second release film (T2) to the first release film (T1) is 1.05 or greater. By adjusting the thickness ratio of the first release film to the second release film so as to satisfy the above requirement (I), the first release film can be easily peeled from a configuration in which the curable adhesive layer is sandwiched between the first release film and the second release film, resulting in a curable adhesive sheet with excellent handleability. This effect is thought to be due to the second release film acting as a support to fix the shape of the curable adhesive layer, making it easier to peel the first release film from the curable adhesive layer.

[0021] In one embodiment of the curable adhesive sheet of the present invention, from the viewpoint of facilitating peeling of the first release film from the curable adhesive layer in a state in which the curable adhesive layer is sandwiched between the first release film and the second release film, the thickness ratio [(T2) / (T1)] specified in the above requirement (I) is 1.05 or more, preferably 1.25 or more, more preferably 1.50 or more, and even more preferably 1.70 or more.

[0022] In one embodiment of the curable adhesive sheet of the present invention, in which the curable adhesive layer is sandwiched between the first release film and the second release film, it is preferable to further satisfy the following requirement (Ib) from the viewpoint of making it easier to peel the first release film from the curable adhesive layer and from the viewpoint of making it easier to wind a long curable adhesive sheet onto a small-diameter winding core. Requirement (Ib): The thickness ratio [(T2) / (T1)] of the thickness (T2) of the second release film to the thickness (T1) of the first release film is 10.0 or less. From the above viewpoint, the thickness ratio [(T2) / (T1)] specified in requirement (Ib) is 10.0 or less, preferably 7.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less.

[0023] In a curable adhesive sheet according to one embodiment of the present invention, in which the curable adhesive layer is sandwiched between a first release film and a second release film, it is preferable that the following requirement (IIa) be further satisfied, from the viewpoint of facilitating peeling of the first release film from the curable adhesive layer. Requirement (IIa): The thickness difference [(T2) - (T1)] between the thickness (T2) of the second release film and the thickness (T1) of the first release film is 5.0 μm or more. From this viewpoint, the thickness difference [(T2) - (T1)] specified in requirement (IIa) is 5.0 μm or more, preferably 10.0 μm or more, more preferably 20.0 μm or more, and even more preferably 30.0 μm or more.

[0024] In a curable adhesive sheet according to one embodiment of the present invention, in which the curable adhesive layer is sandwiched between a first release film and a second release film, it is preferable that the following requirement (IIb) be further satisfied, from the viewpoint of facilitating peeling of the first release film from the curable adhesive layer. Requirement (IIb): The thickness difference [(T2) - (T1)] between the thickness (T2) of the second release film and the thickness (T1) of the first release film is 165.0 μm or less. From this viewpoint, the thickness difference [(T2) - (T1)] specified in requirement (IIb) is 165.0 μm or less, preferably 100.0 μm or less, more preferably 70.0 μm or less, and even more preferably 50.0 μm or less.

[0025] In one embodiment of the curable adhesive sheet of the present invention, the curable adhesive layer is sandwiched between a first release film and a second release film. From the viewpoint of facilitating peeling of the first release film from the curable adhesive layer, it is preferable that the curable adhesive sheet further satisfy the following requirement (III). Requirement (III): The ratio [(R1) / (R2)] of the peel force (R1) when the first release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel speed of 300 mm / min to the peel force (R2) when the second release film is peeled from the curable adhesive layer at a peel angle of 180° and a peel speed of 300 mm / min is 0.97 or less. From this viewpoint, the ratio [(R1) / (R2)] specified in requirement (III) is 0.97 or less, preferably 0.95 or less, more preferably 0.88 or less, and even more preferably 0.80 or less. The ratio of the peel strength (R1) to the peel strength (R2) [(R1) / (R2)] specified in the above requirement (IIa) has no particular lower limit, but is preferably 0.2 or more, more preferably 0.35 or more.

[0026] In one embodiment of the curable adhesive sheet of the present invention, the curable adhesive layer is sandwiched between a first release film and a second release film. From the viewpoint of facilitating peeling of the first release film from the curable adhesive layer, it is preferable that the curable adhesive sheet further satisfy the following requirement (IV): Requirement (IV): The peel force (R2) when peeling the second release film from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min is greater than the peel force (R1) when peeling the first release film from the curable adhesive layer at a peel angle of 180° and a peel rate of 300 mm / min, and is 600 mN / 50 mm or less. From the above viewpoint, the peel force (R2) is 600 mN / 50 mm or less, preferably 450 mN / 50 mm or less, more preferably 250 mN / 50 mm or less, and even more preferably 150 mN / 50 mm or less.

[0027] In the curable adhesive sheet of one embodiment of the present invention, in which the curable adhesive layer is sandwiched between the first release film and the second release film, from the viewpoint of facilitating peeling of the first release film from the curable adhesive layer, the peel force (R1) is preferably smaller than the peel force (R2) and is 5 mN / 50 mm or more, more preferably 10 mN / 50 mm or more, and even more preferably 20 mN / 50 mm or more.

[0028] From the above, in a curable adhesive sheet according to one embodiment of the present invention, in a configuration in which the curable adhesive layer is sandwiched between a first release film and a second release film, it is preferable to further satisfy the following requirement (Va), and more preferably the following requirement (Vb), from the viewpoint of making it easier to peel the first release film from the curable adhesive layer. Requirement (Va): 5 mN / 50 mm≦peel force (R1)<peel force (R2)≦600 mN / 50 mm Requirement (Vb): 5 mN / 50 mm≦peel force (R1)<peel force (R2)≦250 mN / 50 mm

[0029] The peel strength (R1) and the peel strength (R2) can be adjusted by appropriately selecting the resin film constituting the first release film and the second release film, the type of the release agent forming the release agent layer, and the type and content of each component contained in the curable adhesive composition forming the curable adhesive layer. Specific adjustment methods are described in detail in the sections describing each component. In this specification, the peel strengths (R1) and (R2) refer to values ​​measured according to the method described in the Examples below.

[0030] Hereinafter, each layer constituting the curable adhesive sheet of one embodiment of the present invention and the materials forming the layers will be described.

[0031] [First Release Film, Second Release Film] The first release film used in one embodiment of the present invention may be configured to include a colored resin film (i) and a release layer formed from a release agent. Examples of resin components contained in the colored resin film (i) include polyester-based resins such as polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin; polyolefin-based resins such as polypropylene resin and polyethylene resin; polycarbonate resin; and mixed resins containing two or more of these. The colored resin film (i) may also contain additives such as ultraviolet absorbers, antistatic agents, light stabilizers, antioxidants, resin stabilizers, fillers, and colorants (pigments, dyes, etc.) in addition to the resin components. The colored resin film (i) may be a colored resin film colored by containing a colorant such as a pigment or dye together with the resin components, or may be a foamed resin film that has been foamed during film formation from a resin composition containing at least the resin components. The foamed resin film is typically a white, opaque colored resin film. Furthermore, a resin film formed from a resin composition containing a filler together with a resin component also becomes a colored resin film due to reduced transparency due to light scattering. A colorant may be further added to a foamed resin film or a colored resin film containing a filler. Alternatively, a colored resin film may be obtained by coloring a colorless resin film by providing a printed layer on the surface of the resin film by means of printing or the like. The front and back surfaces of the colored resin film (i) used in one embodiment of the present invention may have different colors.

[0032] The second release film used in one embodiment of the present invention may have a resin film (ii) that is visually distinguishable from the colored resin film (i) and a release agent layer. Examples of the resin film (ii) that is visually distinguishable from the colored resin film (i) include the following embodiments (a) to (h): (a) an embodiment in which the colored resin film (i) is opaque and the resin film (ii) is a colorless and transparent resin film; (b) an embodiment in which the colored resin film (i) is opaque and the resin film (ii) is a transparent colored resin film of a different color from the colored resin film (i); (c) an embodiment in which the colored resin film (i) is transparent and the resin film (ii) is an opaque colored resin film of a different color from the colored resin film (i); (d) an embodiment in which a visually visible mark is provided on the surface of the resin film (ii); (e) an embodiment in which the colored resin film (i) is opaque and the resin film (ii) is a transparent colored resin film of the same color as the colored resin film (i). (f) When the colored resin film (i) is transparent, the resin film (ii) is a colored resin film of the same color as the colored resin film (i), but is an opaque resin film. (g) When the colored resin film (i) is transparent, the resin film (ii) is a colored resin film of a different color from the colored resin film (i), but is a transparent resin film. (h) When the colored resin film (i) is transparent, the resin film (ii) is a colorless, transparent resin film. Among these embodiments, from the viewpoint of being more visually distinguishable from the colored resin film (i), the resin film (ii) is preferably any one of the above embodiments (a) to (d).

[0033] Furthermore, the resin film (ii) is preferably a transparent resin film that can be visually distinguished from the colored resin film (i), and more preferably a colorless transparent resin film. For a curable adhesive sheet using a second release film having a transparent resin film, after peeling off the first release film and attaching the curable adhesive layer to an adherend, the state of the interface between the adherend and the curable adhesive layer, such as whether or not foreign matter has been mixed in between the adherend and the curable adhesive layer, can be confirmed from the transparent resin film side of the second release film. If foreign matter is found to have been mixed in, the product yield can be improved by re-attaching the curable adhesive sheet. When the resin film (ii) is a transparent resin film, it is preferable that the colored resin film (i) be opaque so that the resin film (ii) can be easily visually distinguished from the colored resin film (i).

[0034] The haze of the transparent resin film (i) used in one embodiment of the present invention is sufficient as long as it is transparent enough to allow confirmation of any foreign matter that may be mixed in between the adherend and the curable adhesive layer after the curable adhesive layer is attached to the adherend, and is preferably 10.0% or less, more preferably 3.0% or less, even more preferably 1.0% or less, and even more preferably 0.6% or less. Furthermore, when the colored resin film (i) is opaque and the resin film (ii) is transparent, in order to clearly distinguish between the two resin films, the haze of the colored resin film (i) is preferably 30.0% or more, more preferably 45.0% or more, even more preferably 60.0% or more, and even more preferably 80% or more. The haze of the resin film can be measured using a commercially available haze meter.

[0035] Examples of the resin component contained in the resin film (ii) include the same resins as those exemplified as the resin component contained in the colored resin film (i) described above. In addition, examples of additives other than the resin component contained in the resin film (ii) include the same additives as those contained in the colored resin film (i) described above.

[0036] The release layers of the first and second release films can be formed from various release agents. Examples of such release agents include silicone-based release agents, rubber-based elastomer-based release agents such as olefin-based release agents, isoprene-based release agents, and butadiene-based release agents, and non-silicone-based release agents such as long-chain alkyl-based release agents, alkyd-based release agents, and fluorine-based release agents. Among these, non-silicone-based release agents are preferred as the release agents used to form the release layers, in order to prevent the silicon component from migrating to the adherend and causing malfunctions of electronic devices due to silicon contamination. Furthermore, in order to adjust the release strengths (R1) and (R2), it is preferred that at least one of the release layers of the first and second release films be formed from an alkyd-based release agent, and it is more preferred that both the release layers of the first and second release films be formed from an alkyd-based release agent.

[0037] The thickness (T1) of the first release film of the curable adhesive sheet of one embodiment of the present invention is, from the viewpoint of adjusting the peel strength (R1), preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 70 μm or less, and even more preferably 45 μm or less.

[0038] From the viewpoint of adjusting the peel strength (R2), the thickness (T2) of the second release film of the curable adhesive sheet of one embodiment of the present invention is preferably 33 μm or more, more preferably 47 μm or more, even more preferably 55 μm or more, and even more preferably 65 μm or more, and is preferably 270 μm or less, more preferably 210 μm or less, and even more preferably 140 μm or less.

[0039] [Curable Adhesive Layer] The curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention can form a cured product having a dielectric dissipation factor of 0.01 or less at 23°C and 1 GHz. The dielectric dissipation factor of the cured product that can be formed at 23°C and 1 GHz is 0.01 or less, preferably 0.005 or less, and more preferably 0.002 or less. There is no particular lower limit for the dielectric dissipation factor of the cured product at 23°C and 1 GHz, but it is preferably 0.00005 or more, more preferably 0.0001 or more. In this specification, the dielectric dissipation factor of the cured product refers to a value measured according to the method described in the Examples below.

[0040] The method for curing the curable adhesive layer may be a heat curing method or a photocuring method, and can be selected appropriately depending on the application. For example, when the curable adhesive sheet of one embodiment of the present invention is used as a coverlay sheet to form a cured product for protecting a circuit board, a heat curing method is preferred.

[0041] In the curable adhesive sheet of one embodiment of the present invention, the thickness of the curable adhesive layer is, from the viewpoint of forming a cured product having a thickness sufficient to protect the circuit board, preferably 3.0 μm or more, more preferably 5.0 μm or more, even more preferably 10 μm or more, and still more preferably 15 μm or more, and is preferably 60 μm or less, more preferably 45 μm or less.

[0042] The curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention can be formed from a curable adhesive composition containing a binder resin (A) (hereinafter also referred to as "component (A)"). From the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of forming a composition capable of forming a cured product with improved adhesive strength and low dielectric properties, the curable adhesive composition used in one embodiment of the present invention preferably further contains a polyphenylene ether resin (B) (hereinafter also referred to as "component (B)"). More preferably, the curable adhesive composition further contains a polyfunctional compound (C) (hereinafter also referred to as "component (C)") having two or more unsaturated hydrocarbon groups with terminal double bonds, in addition to components (A) and (B). Furthermore, the curable adhesive composition used in one embodiment of the present invention preferably further contains one or more selected from a cationic polymerization initiator (D) (hereinafter also referred to as "component (D)"), a crosslinking agent (E) (hereinafter also referred to as "component (E)") capable of reacting with the reactive functional group of component (A), and a silane coupling agent (F) (hereinafter also referred to as "component (F)"). In addition, the curable adhesive composition used in one embodiment of the present invention may contain additives other than these components (A) to (F) as long as the effects of the present invention are not impaired.

[0043] In the curable adhesive composition used in one embodiment of the present invention, from the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a curable adhesive layer or a cured product thereof with improved adhesive strength and low dielectric properties, the total content of component (A) and component (B) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and still more preferably 75% by mass or more, relative to the total amount (100% by mass) of the active ingredients of the curable adhesive composition, and is usually 100% by mass or less, preferably 99.90% by mass or less, more preferably 99.00% by mass or less, and even more preferably 95.00% by mass or less.

[0044] From the above viewpoints, in the curable adhesive composition used in one embodiment of the present invention, the total content of component (A), component (B), component (C), and component (D) is preferably 60% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more, relative to the total amount (100% by mass) of the active ingredients of the curable adhesive composition, and may typically be 100% by mass or less, 99.70% by mass or less, or 90% by mass or less.

[0045]

[0033] From the above viewpoints, in the curable adhesive composition used in one embodiment of the present invention, the total content of components (A), (B), (C), (D), (E), and (F) is preferably 60% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more, relative to the total amount (100% by mass) of the active ingredients of the curable adhesive composition. It is also typically 100% by mass or less, and may be 99.70% by mass or less, or 90% by mass or less. Details of each component contained in the curable adhesive composition used in one embodiment of the present invention are described below.

[0046] <Component (A): Binder Resin> The curable adhesive composition used in one embodiment of the present invention preferably contains a binder resin (A). By containing the binder resin (A), the composition can form a curable adhesive layer that has excellent adhesive strength and good shape stability when cured. The binder resin (A) may be used alone or in combination of two or more types.

[0047] In the curable adhesive composition used in one embodiment of the present invention, the content of component (A) is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, relative to the total amount (100% by mass) of active ingredients in the curable adhesive composition, and is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.

[0048] The number average molecular weight (Mn) of the binder resin (A) used in one embodiment of the present invention is preferably 10,000 or more, more preferably 25,000 or more, and even more preferably 35,000 or more, from the viewpoint of improving film-forming properties and forming a curable adhesive layer with good shape stability, and is preferably 150,000 or less, more preferably 100,000 or less, and even more preferably 70,000 or less, from the viewpoint of improving the solubility of component (A) in a diluent solvent and providing a composition with excellent coatability when the composition is in the form of a solution.

[0049] Examples of the binder resin (A) include polyolefin-based resins, phenoxy-based resins, polyimide-based resins, polyamideimide-based resins, polyvinyl butyral-based resins, polycarbonate-based resins, styrene-based resins, etc. Among these, the binder resin (A) used in one embodiment of the present invention preferably contains a polyolefin-based resin, from the viewpoint of providing a composition capable of forming a cured product having excellent dielectric properties in the high-frequency region (e.g., 1 GHz or higher).

[0050] The polyolefin resin may be any polymer having structural units derived from an olefin monomer, and may be a polymer consisting only of structural units derived from an olefin monomer, or may be a copolymer having structural units derived from an olefin monomer and structural units derived from a monomer copolymerizable with the olefin monomer.

[0051] The olefin monomer constituting the polyolefin resin may be an α-olefin having 2 or more carbon atoms, preferably an α-olefin having 2 to 8 carbon atoms, more preferably at least one selected from ethylene, propylene, 1-butene, isobutylene, and 1-hexene, and even more preferably at least one selected from ethylene and propylene. These olefin monomers may be used alone or in combination of two or more.

[0052] Furthermore, examples of monomers copolymerizable with olefin monomers constituting polyolefin resins include vinyl acetate, (meth)acrylic acid esters, styrene, etc. These monomers may be used alone or in combination of two or more. Specific examples of polyolefin resins used in one embodiment of the present invention include very low density polyethylene (VLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene, polypropylene (PP), ethylene-propylene copolymer, olefin elastomer (TPO), ethylene-vinyl acetate copolymer (EVA), ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylic acid ester copolymer, etc.

[0053] The binder resin (A) used in one embodiment of the present invention is a composition that can improve film-forming properties and form a curable adhesive layer with good shape stability, and can form a cured product with further improved low dielectric properties. From the viewpoint of reducing the peel force when peeling the first release film or the second release film from the curable adhesive layer, the binder resin (A) preferably contains a binder resin having a reactive functional group, more preferably contains one or more resins selected from polyolefin resins having reactive functional groups and styrene resins having reactive functional groups, and even more preferably contains at least a polyolefin resin (A1) having a reactive functional group.

[0054] In the curable adhesive composition used in one embodiment of the present invention, the content of the polyolefin resin (A1) is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, and even more preferably 85 to 100 mass%, relative to the total amount (100 mass%) of component (A) contained in the curable adhesive composition, from the viewpoint of obtaining a composition that can form a cured product with excellent low dielectric properties.

[0055] Examples of the reactive functional group contained in the binder resin (A) include a carboxy group, a group having a carboxylic anhydride structure, a group having a carboxylic ester structure, a hydroxyl group, an epoxy group, an amide group, an ammonium group, a nitrile group, an amino group, an imide group, an isocyanate group, an acetyl group, a thiol group, a sulfone group, a phosphone group, a nitro group, a halogen atom, an alkoxysilyl group, etc. The reactive functional group contained in the binder resin (A) may be composed of one type alone or two or more types in combination. Among these, the reactive functional group of the binder resin (A) is preferably a group selected from a carboxy group, a group having a carboxylic acid anhydride structure, an epoxy group, an amide group, an ammonium group, a nitrile group, an amino group, an imide group, an isocyanate group, an acetyl group, a thiol group, an ether group, a thioether group, a sulfone group, a phosphone group, a nitro group, a urethane group, a halogen atom, and an alkoxysilyl group. From the viewpoint of obtaining a composition that can form a cured product having superior adhesive strength and from the viewpoint of reducing the peel force when peeling the first release film or the second release film from the curable adhesive layer, a group selected from a carboxy group and a group having a carboxylic acid anhydride structure is more preferred. From the viewpoint of obtaining a composition that can form a cured product that is superior in both adhesive strength and low dielectric properties, a group having a carboxylic acid anhydride structure is even more preferred.

[0056] The binder resin (A) used in one embodiment of the present invention may be a modified resin in which a main chain resin is modified with a modifying agent to introduce the above-mentioned reactive functional group. Specific modified resins include, for example, acid-modified resins in which an acid group is introduced, and resins in which a hydroxyl group is introduced. From the viewpoint of obtaining a composition capable of forming a cured product having superior adhesive strength and reducing the peeling force when peeling the first release film or the second release film from the curable adhesive layer, acid-modified resins in which an acid group is introduced are preferred, and from the viewpoint of obtaining a composition capable of forming a cured product having superior adhesive strength and low dielectric properties, acid anhydride-modified resins in which an acid anhydride structure is introduced are more preferred.

[0057] Acid-modified resins or acid anhydride-modified resins (hereinafter also referred to as "unsaturated carboxylic acids, etc.") can be obtained, for example, by reacting an unsaturated carboxylic acid, etc. with a resin that serves as a main chain, thereby introducing a carboxy group or a carboxylic acid anhydride structure and graft-modifying it. The method for introducing the unsaturated carboxylic acid, etc. into the resin is not particularly limited, and examples include a method in which the resin and the unsaturated carboxylic acid, etc. are heated to a temperature equal to or higher than the melting point of the resin in the presence of a radical generator such as an organic peroxide or an azonitrile, thereby melting and reacting them, or a method in which the resin and the unsaturated carboxylic acid, etc. are dissolved in an organic solvent, and then heated and stirred in the presence of a radical generator, thereby reacting them.

[0058] Examples of unsaturated carboxylic acids include maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic acid, tetrahydrophthalic acid, and aconitic acid. Examples of unsaturated carboxylic acid anhydrides include maleic anhydride, itaconic anhydride, glutaconic anhydride, citraconic anhydride, aconitic anhydride, norbornene dicarboxylic anhydride, and tetrahydrophthalic anhydride. These may be used alone or in combination of two or more. Among these, maleic anhydride is preferred from the viewpoint of forming a composition capable of forming a cured product having excellent adhesive strength and low dielectric properties.

[0059] The amount of the unsaturated carboxylic acid or the like to be reacted with the resin is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and even more preferably 0.2 to 1 part by mass, relative to 100 parts by mass of the resin, from the viewpoint of obtaining a composition that can form a cured product that is superior in adhesive strength and low dielectric properties.

[0060] <Component (B): Polyphenylene Ether Resin> The curable adhesive composition used in one embodiment of the present invention preferably contains a polyphenylene ether resin (B) from the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of providing a composition capable of forming a cured product having improved adhesive strength and low dielectric properties. The polyphenylene ether resin (B) may be used alone or in combination of two or more types.

[0061] In the curable adhesive composition used in one embodiment of the present invention, the content of component (B) is preferably 5 parts by mass or more, more preferably 12 parts by mass or more, and even more preferably 17 parts by mass or more, relative to 100 parts by mass of the total amount of component (A), and is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0062] From the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a cured product having improved adhesive strength and low dielectric properties, the number average molecular weight (Mn) of the polyphenylene ether resin (B) used in one aspect of the present invention is preferably 1,500 or more, more preferably 1,700 or more, and even more preferably 1,900 or more. Furthermore, from the viewpoint of improving the solubility of component (B) in a diluting solvent and obtaining a composition with excellent coatability when the composition is in the form of a solution, the number average molecular weight (Mn) is preferably 7,000 or less, more preferably 5,500 or less, and even more preferably 4,000 or less.

[0063] The polyphenylene ether resin (B) used in one embodiment of the present invention may be a resin having a structural unit represented by at least one of the following general formula (bi) and formula (b-ii) in the main chain.

[0064] In the above general formula (bi) or (b-ii), R ａ１ and R ａ２ are each independently a halogen atom (a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom), an alkyl group having 1 to 6 carbon atoms, or a phenyl group, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, even more preferably a methyl group or an ethyl group, and particularly preferably a methyl group. ａ１ and R ａ２Examples of the alkyl group having 1 to 6 carbon atoms that can be selected as m1 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group, an s-butyl group, an isobutyl group, an n-pentyl group, an n-hexyl group, etc. m1 and m2 each independently represent an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, and even more preferably 2.

[0065] From the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a cured product having improved adhesive strength while maintaining good low dielectric properties, the polyphenylene ether resin (B) used in one aspect of the present invention is preferably a resin having, as a main chain, a skeleton represented by the following formula (b-1):

[0066] In the above general formula (b-1), R ａ１ and R ａ２ , and m1 and m2 are the same as defined in the above general formula (bi) or formula (b-ii), and the types and numerical ranges of preferred groups are also the same. X is a divalent organic group, and at least one hydrogen atom of the organic group may be substituted with a substituent. p1 and p2 are each independently an integer of 0 or more, and p1 + p2 is an integer of 1 or more. * indicates the bonding position with the terminal group.

[0067] Examples of divalent hydrocarbon groups that can be selected as X include alkylene groups having 1 to 20 carbon atoms, oxyalkylene groups having 1 to 20 carbon atoms, alkenylene groups having 1 to 20 carbon atoms, cycloalkylene groups having 3 to 10 ring carbon atoms, cycloalkenylene groups having 3 to 10 ring carbon atoms, phenylene groups, biphenylene groups, terphenylene groups, naphthylene groups, and groups formed by combining two or more of these groups. The alkylene groups, oxyalkylene groups, and alkenylene groups may be linear or branched. The alkylene groups, oxyalkylene groups, and alkenylene groups may have a substituent selected from a halogen atom, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, and a cycloalkyl group having 3 to 10 carbon atoms. In addition, the above cycloalkylene group, cycloalkenylene group, phenylene group, biphenylene group, terphenylene group, and naphthylene group may have a substituent selected from a halogen atom, an alkyl group having 1 to 6 carbon atoms, an oxyalkyl group having 1 to 6 carbon atoms, and an alkenyl group having 1 to 6 carbon atoms.

[0068] Among these, from the viewpoint of adjusting the peel strength (R1) or (R2) and obtaining a composition that can form a cured product with further improved adhesive strength, X is preferably a group represented by the following formula (b-2):

[0069] In the above general formula (b-2), R ｂ１ and R ｂ２ are each independently a halogen atom (fluorine atom, chlorine atom, bromine atom, or iodine atom), an alkyl group having 1 to 6 carbon atoms, an oxyalkyl group having 1 to 6 carbon atoms, or an alkenyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, even more preferably a methyl group or an ethyl group, and particularly preferably a methyl group. ｂ１ and R ｂ２Examples of the alkyl group having 1 to 6 carbon atoms that can be selected as n1 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group, an s-butyl group, an isobutyl group, an n-pentyl group, an n-hexyl group, etc. n1 and n2 each independently represent an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 1 to 3, and even more preferably 3.

[0070] In the above general formula (b-2), A represents a single bond or a divalent hydrocarbon group. Examples of divalent hydrocarbon groups that can be selected as A include alkylene groups having 1 to 20 carbon atoms, oxyalkylene groups having 1 to 20 carbon atoms, alkenylene groups having 1 to 20 carbon atoms, cycloalkylene groups having 3 to 10 ring carbon atoms, and cycloalkenylene groups having 3 to 10 ring carbon atoms. The alkylene groups, oxyalkylene groups, and alkenylene groups may be linear or branched. The hydrocarbon groups that can be selected as A may have a substituent selected from a halogen atom, an alkyl group having 1 to 6 carbon atoms, an oxyalkyl group having 1 to 6 carbon atoms, and an alkenyl group having 1 to 6 carbon atoms. Among these, from the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition that can form a cured product with improved adhesive strength, A is preferably a single bond or an alkylene group having 1 to 20 carbon atoms, and more preferably a single bond.

[0071] From the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a cured product having improved adhesive strength, the polyphenylene ether resin (B) used in one embodiment of the present invention is more preferably a resin having, as the main chain, a skeleton represented by the following formula (b-3):

[0072] In the above general formula (b-3), R ａ１ and R ａ２ is the same as defined in the above general formula (bi) or (b-ii), and the types and ranges of preferred groups are also the same. ｂ１ and R ｂ２is the same as defined in the general formula (b-2) above, and the types and numerical ranges of the preferred groups are also the same. p1 and p2 are each independently an integer of 0 or more, and p1 + p2 is an integer of 1 or more. * indicates the bonding position with the terminal group. Note that, in the general formula (b-3) above, ａ１ , R ａ２ , R ｂ１ , and R ｂ２ are each independently preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 4 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, still more preferably a methyl group or an ethyl group, and particularly preferably a methyl group.

[0073] The polyphenylene ether resin (B) used in one embodiment of the present invention is preferably a polyphenylene ether resin having a vinyl group, from the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a cured product with improved low dielectric properties, crosslinkability, and heat resistance. The vinyl group contained in the polyphenylene ether resin (B) may be one that constitutes a part of a hydrocarbon-based substituent, such as a vinylbenzyl group or a vinylnaphthyl group. In other words, the polyphenylene ether resin (B) is formed by bonding a vinyl group or a vinyl-group-containing hydrocarbon group to a polyphenylene ether skeleton.

[0074] From the viewpoint of adjusting the peel strength (R1) or (R2) and from the viewpoint of obtaining a composition capable of forming a cured product having low dielectric properties, excellent crosslinkability, and excellent heat resistance, the polyphenylene ether resin (B) used in one embodiment of the present invention is preferably a resin having vinyl groups or vinyl group-containing hydrocarbon groups at both terminals of the main chain. The polyphenylene ether resin (B) having vinyl groups or vinyl group-containing hydrocarbon groups at both terminals of the main chain can be obtained by forming a polyphenylene ether skeleton as the main chain and then introducing vinyl groups or vinyl group-containing hydrocarbon groups to both terminals. Specifically, a difunctional phenol compound and a monofunctional phenol compound are reacted to obtain a polymer having phenolic hydroxyl groups at both terminals, and then the terminal phenolic hydroxyl groups are vinylbenzyl-etherified using 4-(chloromethyl)styrene, thereby obtaining the polyphenylene ether resin (B) having vinylbenzyl groups at both terminals of the polyphenylene ether skeleton.

[0075] The polyphenylene ether resin (B) used in one embodiment of the present invention is preferably a compound represented by the following general formula (b-4). p1 and p2 are each independently an integer of 0 or greater, and p1+p2 is an integer of 1 or greater.

[0076] The polyphenylene ether resin (B) used in one embodiment of the present invention may be a commercially available product, such as OPE-2St (a compound represented by the above general formula (b-4)) manufactured by Mitsubishi Gas Chemical Company, Inc.

[0077] <Component (C): Polyfunctional Compound> The curable adhesive composition used in one embodiment of the present invention preferably contains a polyfunctional compound (C) having two or more unsaturated hydrocarbon groups with a terminal double bond. The polyfunctional compound (C) in the present invention excludes compounds corresponding to components (A) and (B). By forming a composition containing the polyfunctional compound (C) together with the polyphenylene ether resin (B), a cured product can be formed that has a well-balanced improvement in low dielectric properties and adhesive strength. In particular, since the polyfunctional compound (C) has two or more unsaturated hydrocarbon groups, a crosslinked structure is formed in the resulting cured product, thereby forming a cured product with further improved adhesive strength. The polyfunctional compound (C) may be used alone or in combination of two or more types.

[0078] In the curable adhesive composition used in one embodiment of the present invention, the content of component (C) is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the total amount of component (A), from the viewpoint of obtaining a curable adhesive sheet that is capable of forming a cured product with excellent low dielectric properties while also improving application properties; and since an increase in the content of component (C) tends to increase the peel strength (R1) and the peel strength (R2), from the viewpoint of obtaining a curable adhesive sheet in which the peel strength (R1) or the peel strength (R2) is adjusted to be small, the content of component (C) is preferably 80 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0079] In the curable adhesive composition used in one embodiment of the present invention, from the viewpoint of forming a composition capable of forming a cured product having a good balance of low dielectric properties, adhesive strength, and heat resistance, the content ratio of component (B) to component (C) [(B) / (C)], in mass ratio, is preferably 15 / 85 or more, more preferably 30 / 70 or more, and is also preferably 85 / 15 or less, more preferably 70 / 30 or less.

[0080] In the curable adhesive composition used in one embodiment of the present invention, the total content of component (B) and component (C) is preferably 85 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 65 parts by mass or less, relative to 100 parts by mass of the total amount of component (A), from the viewpoint of producing a curable adhesive sheet that is adjusted to have a small peel force (R1) or (R2) while also having excellent application properties, and from the viewpoint of producing a composition that can form a cured product with excellent adhesive strength. Also, the total content of component (B) and component (C) is preferably 15 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 35 parts by mass or more.

[0081] The number of carbon atoms in each of the unsaturated hydrocarbon groups contained in the polyfunctional compound (C) used in one embodiment of the present invention is preferably 2 to 7, more preferably 2 to 4, and even more preferably 2 to 3. Examples of the unsaturated hydrocarbon group include a vinyl group, an allyl group, a 3-butenyl group, a 4-pentenyl group, a 5-hexenyl group, an isopropenyl group, a 1-methyl-2-propenyl group, a vinylbenzyl group, and a vinylnaphthyl group. Among these, the unsaturated hydrocarbon group contained in the polyfunctional compound (C) is preferably an allyl group.

[0082] The number of unsaturated hydrocarbon groups possessed by the polyfunctional compound (C) used in one embodiment of the present invention is 2 or more, but is preferably 2 to 4, more preferably 2 to 3, and even more preferably 2, from the viewpoint of making the crosslinked structure appropriately sparse and providing a composition that can form a cured product in which the generation of cracks is suppressed, and from the viewpoint of making a composition that can suppress cure shrinkage in the bonding step in which the curable adhesive layer is converted into a cured product and reduce warpage of the plate-like member that is the adherend, such as a circuit board.

[0083] From the viewpoint of obtaining a composition capable of forming a cured product having improved low dielectric properties and adhesive strength in a more balanced manner, the polyfunctional compound (C) used in one aspect of the present invention is preferably a polyfunctional compound having two or more of the unsaturated hydrocarbon groups and further having a saturated hydrocarbon group. From the above viewpoint, the number of saturated hydrocarbon groups possessed by the polyfunctional compound (C) used in one aspect of the present invention is preferably 1 to 4, more preferably 1 to 2, and even more preferably 1.

[0084] Examples of the saturated hydrocarbon group include an alkyl group and an alkyl group substituted with an alkoxy group. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a t-butyl group, an s-butyl group, an isobutyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, and an n-pentadecyl group. The number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 4 to 18, even more preferably 6 to 16, and still more preferably 8 to 15.

[0085] Examples of the alkyl group substituted with an alkoxy group include a methoxymethyl group, an ethoxymethyl group, a 2-methoxyethoxymethyl group, a benzyloxymethyl group, etc. The number of carbon atoms in the alkyl group substituted with an alkoxy group is preferably 2 to 15, more preferably 2 to 12, and even more preferably 3 to 10.

[0086] The polyfunctional compound (C) used in one embodiment of the present invention preferably includes a polyfunctional compound (C1) having two unsaturated hydrocarbon groups. As described above, a composition containing such a polyfunctional compound (C1) having two unsaturated hydrocarbon groups can be a composition that can form a cured product in which cracking is suppressed and warping of the adherend, such as a plate-like member such as a circuit board, is reduced, and can also be a composition that can form a cured product with further improved low dielectric properties and adhesive strength. From the above perspective, it is more preferable that the polyfunctional compound (C1) is a polyfunctional compound having two unsaturated hydrocarbon groups and at least one saturated hydrocarbon group.

[0087] From the above viewpoints, in the curable adhesive composition used in one embodiment of the present invention, the content of the polyfunctional compound (C1) is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, and still more preferably 90 to 100 mass%, relative to the total amount (100 mass%) of component (C) contained in the curable adhesive composition.

[0088] The polyfunctional compound (C) used in one embodiment of the present invention is preferably a polyfunctional compound having a heterocyclic skeleton. By including a polyfunctional compound having a heterocyclic skeleton, a composition can be obtained that can form a cured product with improved low dielectric properties and adhesive strength. Specific examples of the heterocyclic skeleton include an isocyanurate skeleton and a glycoluril skeleton.

[0089] Examples of the polyfunctional compound (C) used in one embodiment of the present invention include a compound having an isocyanurate skeleton represented by the following general formula (c-1) and a compound having a glycoluril skeleton represented by the following general formula (c-2).

[0090] In the general formula (c-1), R １１ ~R １３ are each independently an unsaturated hydrocarbon group having a double bond at a terminal, or a saturated hydrocarbon group, and R １１ ~R １３ At least two of the above are unsaturated hydrocarbon groups. ２１ ~R ２６ are each independently a hydrogen atom, an unsaturated hydrocarbon group having a double bond at the terminal, or a saturated hydrocarbon group, and R ２１ ~R ２６ At least two of R are the unsaturated hydrocarbon groups. １１ ~R １３ and R ２１ ~R ２６ Specific examples of the unsaturated hydrocarbon group and saturated hydrocarbon group that can be selected as are as described above, and the preferred range of the number of carbon atoms is also as described above.

[0091] From the viewpoint of being a composition capable of forming a cured product in which cracking is suppressed and warpage of the adherend, such as a plate-like member such as a circuit board, is reduced, and also capable of forming a cured product having further improved low dielectric properties and adhesive strength, the polyfunctional compound (C) used in one aspect of the present invention preferably includes a compound having an isocyanurate skeleton represented by the general formula (c-1) above, and more preferably includes a compound (C11) having an isocyanurate skeleton represented by the following general formula (c-11):

[0092] In the above general formula (c-11), R ａ is a saturated hydrocarbon group, and specific examples are as described above. ａ is preferably an alkyl group. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 4 to 18 carbon atoms, even more preferably 6 to 16 carbon atoms, and even more preferably 8 to 15 carbon atoms.

[0093] From the above viewpoints, in the curable adhesive composition used in one embodiment of the present invention, the content of compound (C11) is preferably 50 to 100 mass%, more preferably 70 to 100 mass%, even more preferably 80 to 100 mass%, and still more preferably 90 to 100 mass%, relative to the total amount (100 mass%) of component (C) contained in the curable adhesive composition.

[0094] The polyfunctional compound (C) used in one embodiment of the present invention may be a commercially available product. Specific examples of commercially available products include L-DAIC (product name, manufactured by Shikoku Chemical Industry Co., Ltd., a compound represented by the general formula (c-11) above), TAIC (registered trademark) (product name, manufactured by Mitsubishi Chemical Corporation, a compound represented by the R １１ ~R １３ is an allyl group), TA-G (product name, manufactured by Shikoku Chemicals Corporation, compound represented by the above general formula (c-2)), and the like.

[0095] The molecular weight (formula weight) of the polyfunctional compound (C) used in one aspect of the present invention is preferably 200 or more, more preferably 230 or more, and even more preferably 270 or more, from the viewpoint of providing a composition that easily forms a cured product having the desired physical properties, and from the viewpoint of providing a curable adhesive sheet in which the peel strength (R1) or the peel strength (R2) is adjusted to be small, since the smaller the molecular weight of component (C), the higher the peel strength (R1) and the peel strength (R2) tend to be.Furthermore, from the viewpoint of providing a composition that easily forms a curable adhesive layer that is easy to apply at room temperature, the molecular weight (formula weight) is preferably 1000 or less, more preferably 800 or less, and even more preferably 500 or less.

[0096] The boiling point of the polyfunctional compound (C) used in one embodiment of the present invention is preferably 175 to 350° C., more preferably 200 to 300° C. The 5% weight loss temperature of the polyfunctional compound (C) used in one embodiment of the present invention is preferably 175 to 350° C., more preferably 200 to 300° C.

[0097] Furthermore, from the viewpoint of obtaining a composition that can form a cured product with excellent low dielectric properties and that can easily form a curable adhesive layer that is easy to apply at room temperature, the polyfunctional compound (C) used in one embodiment of the present invention is preferably a compound that is liquid at 25° C. In this specification, the term "compound that is liquid at 25° C." refers to a compound that has fluidity at 25° C., and specifically refers to a compound that has a viscosity of 2 to 10,000 mPa s as measured at 25° C. and 1.0 rpm using an E-type viscometer.

[0098] <Component (D): Cationic Polymerization Initiator> The curable adhesive composition used in one embodiment of the present invention preferably further contains a cationic polymerization initiator (D). By forming a curable adhesive composition containing the cationic polymerization initiator (D), the polymerization reaction of components (B) and (C) can be sufficiently progressed, and the storage stability of the formed curable adhesive layer can be improved. The cationic polymerization initiator (D) may be used alone or in combination of two or more types.

[0099] In the curable adhesive composition used in one embodiment of the present invention, the content of component (D) is, from the viewpoint of allowing the polymerization reaction of components (B) and (C) to sufficiently proceed and forming a curable adhesive layer with improved storage stability, preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, more preferably 0.10 parts by mass or more, even more preferably 0.15 parts by mass or more, even more preferably 0.20 parts by mass or more, still more preferably 0.25 parts by mass or more, and particularly preferably 0.30 parts by mass or more, relative to 100 parts by mass of the total amount of components (B) and (C). Also, the content of component (D) is preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.0 parts by mass or less, even more preferably 1.5 parts by mass or less, still more preferably 1.0 part by mass or less, and particularly preferably 0.70 parts by mass or less.

[0100] The cationic polymerization initiator (D) used in one embodiment of the present invention may be a thermal cationic polymerization initiator or a photo-induced cationic polymerization initiator. However, from the viewpoint of enabling polymerization to be carried out in a simple process, a thermal cationic polymerization initiator is preferred.

[0101] The thermal cationic polymerization initiator used in one embodiment of the present invention is a compound capable of generating a cationic species that initiates polymerization upon heating, and examples thereof include sulfonium salts, quaternary ammonium salts, phosphonium salts, diazonium salts, iodonium salts, etc. These thermal cationic polymerization initiators may be used alone or in combination of two or more.

[0102] Examples of sulfonium salts include triphenylsulfonium tetrafluoroborate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium hexafluoroarsinate, tris(4-methoxyphenyl)sulfonium hexafluoroarsinate, diphenyl(4-phenylthiophenyl)sulfonium hexafluoroarsinate, etc. Commercially available sulfonium salts can also be used, such as ADEKAOPTON SP-150, ADEKAOPTON SP-170, ADEKAOPTON CP-66, ADEKAOPTON CP-77 (all manufactured by ADEKA Corporation), SAN-AID SI-60L, SAN-AID SI-80L, SAN-AID SI-100L, SAN-AID SI-B2A, SAN-AID SI-B3 (all manufactured by Sanshin Chemical Industry Co., Ltd.), CYRACURE UVI-6974, ... Examples of suitable grease include UVI-6990 (manufactured by Union Carbide), UVI-508, UVI-509 (manufactured by General Electric Company), FC-508, FC-509 (manufactured by Minnesota Mining and Manufacturing Company), CD-1010, CD-1011 (manufactured by Thurstomer Corporation), and CI series products (manufactured by Nippon Soda Co., Ltd.).

[0103] Examples of quaternary ammonium salts include tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, tetrabutylammonium hydrogen sulfate, tetraethylammonium tetrafluoroborate, tetraethylammonium p-toluenesulfonate, N,N-dimethyl-N-benzylanilinium hexafluoroantimonate, N,N-dimethyl-N-benzylanilinium tetrafluoroborate, N,N-dimethyl-N-benzylpyridinium hexafluoroantimonate, N,N-diethyl-N-benzyltrifluoromethanesulfonate, N,N-dimethyl-N-(4-methoxybenzyl)pyridinium hexafluoroantimonate, and N,N-diethyl-N-(4-methoxybenzyl)toluidinium hexafluoroantimonate.

[0104] Examples of phosphonium salts include ethyltriphenylphosphonium hexafluoroantimonate and tetrabutylphosphonium hexafluoroantimonate.

[0105] Examples of diazonium salts include AMERICURE (manufactured by American Can Co.), ULTRASET (manufactured by Adeka Corporation), and the like.

[0106] Examples of iodonium salts include diphenyliodonium hexafluoroarsinate, bis(4-chlorophenyl)iodonium hexafluoroarsinate, bis(4-bromophenyl)iodonium hexafluoroarsinate, phenyl(4-methoxyphenyl)iodonium hexafluoroarsinate, etc. Commercially available iodonium salts can also be used, such as UV-9310C (manufactured by Toshiba Silicones Co., Ltd.), Photoinitiator 2074 (manufactured by Rhone-Poulenc), UVE series products (manufactured by General Electric Co.), and FC series products (manufactured by Minnesota Mining and Manufacturing Co.).

[0107] When the curable adhesive composition of one embodiment of the present invention contains a cationic polymerization initiator (D), at least a portion of the cationic polymerization initiator (D) may be a high-temperature reactive thermal cationic polymerization initiator that exhibits an exothermic peak top temperature of more than 120°C when differential scanning calorimetry is performed under the following conditions: (Differential Scanning Calorimetry Conditions) A measurement sample is a mixture containing 0.1 part by mass of the cationic polymerization initiator to be measured, 100 parts by mass of bisphenol A diglycidyl ether, and 0.1 part by mass of γ-butyrolactone, and differential scanning calorimetry is performed from 30°C to 300°C at a heating rate of 10°C / min to measure the peak temperature of the exothermic peak.

[0108] Commercially available high-temperature reactive thermal cationic polymerization initiators include, for example, San-Aid SI-B3, San-Aid SI-B4, San-Aid SI-B5, and San-Aid SI-150 (all manufactured by Sanshin Chemical Industry Co., Ltd.).

[0109] <Reactive Curing Agent Other Than Cationic Polymerization Initiator (D)> The curable adhesive composition used in one embodiment of the present invention may contain a reactive curing agent other than the cationic polymerization initiator (D) in place of or together with the cationic polymerization initiator (D), within a range that does not impair the effects of the present invention. In the curable adhesive composition used in one embodiment of the present invention, the content of the other reactive curing agent may be 0 to 90 parts by mass, 0 to 50 parts by mass, 0 to 40 parts by mass, 0 to 30 parts by mass, 0 to 20 parts by mass, 0 to 10 parts by mass, 0 to 5.0 parts by mass, 0 to 2.0 parts by mass, 0 to 1.0 parts by mass, 0 to 0.10 parts by mass, 0 to 0.010 parts by mass, or 0 to 0.0010 parts by mass, relative to 100 parts by mass of the total amount of component (D). On the other hand, when the curable adhesive composition of one embodiment of the present invention does not contain the cationic polymerization initiator (D), the content of the other reactive curing agent may be 0.01 parts by mass or more, 0.05 parts by mass or more, 0.10 parts by mass or more, 0.15 parts by mass or more, 0.20 parts by mass or more, 0.25 parts by mass or more, or 0.30 parts by mass or more, relative to 100 parts by mass of the total amount of component (B) and component (C), or may be 6.0 parts by mass or less, 5.0 parts by mass or less, 3.0 parts by mass or less, 2.0 parts by mass or less, 1.5 parts by mass or less, 1.0 part by mass or less, or 0.70 parts by mass or less.

[0110] Examples of the reactive curing agent (D) other than the cationic polymerization initiator include amine compounds such as benzylmethylamine and 2,4,6-trisdimethylaminomethylphenol; imidazole compounds such as 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-heptadecylimidazole; Lewis acids such as boron trifluoride-monoethylamine complex and boron trifluoride-piperazine complex; and peroxides such as di(t-butylperoxy)diisopropylbenzene.

[0111] <Component (E): Crosslinking Agent> When the curable adhesive composition used in one embodiment of the present invention contains a binder resin having a reactive functional group as component (A), it preferably further contains a crosslinking agent (E) capable of reacting with the reactive functional group. By using a composition containing a crosslinking agent (E) in addition to component (A), a curable adhesive layer with a high effect of suppressing the exudation of adhesive components can be formed. That is, during the process of forming a curable adhesive layer from a coating film formed from the curable adhesive composition, the crosslinking agent (E) reacts with the reactive functional group of the binder resin (A), forming a crosslinked structure within the coating film, thereby forming a curable adhesive layer that is resistant to fluidization even when heated. As a result, the formed curable adhesive layer is less likely to exude from the edges during the bonding process in which the curable adhesive layer is applied to an adherend such as a circuit board, cured, and bonded to the adherend. Furthermore, from the viewpoint of adjusting the peel strength (R1) or (R2), it is preferable to use a composition containing a crosslinking agent (E). The crosslinking agent (E) may be used alone or in combination of two or more types.

[0112] In the curable adhesive composition used in one embodiment of the present invention, the content of component (E) is, relative to 100 parts by mass of the total amount of component (A), preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, more preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, even more preferably 0.10 parts by mass or more, even more preferably 0.15 parts by mass or more, even more preferably 0.20 parts by mass or more, still more preferably 0.25 parts by mass or more, and particularly preferably 0.30 parts by mass or more; and is preferably 10.0 parts by mass or less, more preferably 8.0 parts by mass or less, more preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 4.0 parts by mass or less, even more preferably 3.0 parts by mass or less, even more preferably 2.5 parts by mass or less, still more preferably 2.0 parts by mass or less, and particularly preferably 1.5 parts by mass or less.

[0113] The molecular weight of the crosslinking agent (E) used in one embodiment of the present invention is preferably 1,000 or less, more preferably 800 or less, even more preferably 700 or less, still more preferably 600 or less, and particularly preferably 500 or less, from the viewpoint of increasing the probability of reaction with component (A), making it easier to form a crosslinked structure, and providing a composition that can form a curable adhesive layer that is more effective at suppressing the bleeding of adhesive components.Furthermore, from the viewpoint of adjusting the molecular weight so that the crosslinking agent (E) can be retained within the curable adhesive layer by heating in the drying step of forming the curable adhesive layer, and providing a composition that can exhibit the effects of adding the crosslinking agent (E), the molecular weight is preferably 100 or more, more preferably 150 or more, even more preferably 200 or more, still more preferably 250 or more, and particularly preferably 300 or more.

[0114] The crosslinking agent (E) used in one embodiment of the present invention is appropriately selected depending on the type of reactive functional group possessed by component (A), and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, and aziridine-based crosslinking agents. Among these, from the viewpoint of storage stability, the crosslinking agent (E) used in one embodiment of the present invention is preferably at least one selected from isocyanate-based crosslinking agents, epoxy-based crosslinking agents, and metal chelate-based crosslinking agents. Furthermore, from the viewpoint of obtaining a composition capable of forming a cured product with further improved low dielectric properties, the crosslinking agent (E) used in one embodiment of the present invention is preferably a crosslinking agent having an isocyanurate skeleton.

[0115] The isocyanate crosslinking agent is preferably a compound having two or more isocyanate groups in the molecule, and examples thereof include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, diphenylmethane-4,4-diisocyanate, isophorone diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, tetramethylxylylene diisocyanate, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, adducts of these polyisocyanate compounds with polyol compounds such as trimethylolpropane, and biuret and isocyanurate forms of these polyisocyanate compounds.

[0116] The epoxy crosslinking agent is preferably a compound having two or more epoxy groups in the molecule, and examples thereof include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, and diglycidylamine.

[0117] Examples of the metal chelate crosslinking agent include chelate compounds having metal ions that function as crosslinking points. Examples of the metal ions include aluminum ions, zirconium ions, titanium ions, zinc ions, iron ions, and tin ions. Among these, aluminum chelate compounds are preferred as the metal chelate crosslinking agent, including aluminum tris(acetylacetonate), acetylacetonate aluminum bis(ethylacetoacetate), diisopropoxyaluminum monooleylacetoacetate, and monoisopropoxyaluminum bisoleylacetoacetate.

[0118] Among these, from the viewpoint of obtaining a composition capable of forming a curable adhesive layer having a higher effect of suppressing bleeding of adhesive components and a composition capable of forming a cured product having further improved low dielectric properties, the crosslinking agent (E) used in one embodiment of the present invention is preferably an isocyanate-based crosslinking agent, more preferably an isocyanurate of a polyisocyanate compound, and even more preferably one or more selected from an isocyanurate of 1,5-pentamethylene diisocyanate [1,3,5-tris(5-isocyanatopentyl)-1,3,5-triazine-2,4,6-trione] and an isocyanurate of 1,6-hexamethylene diisocyanate [1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazine-2,4,6-trione].

[0119] <Component (F): Silane Coupling Agent> The curable adhesive composition used in one embodiment of the present invention preferably further contains a silane coupling agent (F). By using a composition containing a silane coupling agent, a cured product with improved adhesive strength can be formed. The silane coupling agent (F) may be used alone or in combination of two or more types.

[0120] In the curable adhesive composition used in one embodiment of the present invention, the content of component (F) is, relative to 100 parts by mass of the total amount of component (A), preferably 0.001 parts by mass or more, more preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, even more preferably 0.05 parts by mass or more, even more preferably 0.07 parts by mass or more, even more preferably 0.10 parts by mass or more, still more preferably 0.12 parts by mass or more, and particularly preferably 0.15 parts by mass or more, and is also preferably 6.0 parts by mass or less, more preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 2.0 parts by mass or less, even more preferably 1.5 parts by mass or less, even more preferably 1.0 part by mass or less, still more preferably 0.80 parts by mass or less, and particularly preferably 0.60 parts by mass or less.

[0121] The silane coupling agent (E) used in one embodiment of the present invention is preferably an organosilicon compound having at least one alkoxysilyl group in the molecule. Specific examples of the silane coupling agent include silane coupling agents having a (meth)acryloyl group, such as 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane; vinyltrimethoxysilane, vinyltriethoxysilane, dimethoxymethyl Silane coupling agents having a vinyl group such as vinyl silane, diethoxymethyl vinyl silane, trichlorovinyl silane, vinyl tris(2-methoxyethoxy) silane; silane coupling agents having an epoxy group such as 2-(3,4-epoxycyclohexyl) ethyl trimethoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-glycidoxypropyl methyl diethoxy silane, 3-glycidoxypropyl triethoxy silane, 8-glycidoxyoctyl trimethoxy silane; silane coupling agents having a styryl group such as p-styryl trimethoxy silane, p-styryl triethoxy silane; N-(2-aminoethyl)-3-aminopropyl methyl dimethoxy silane, N-(2-aminoethyl)-3-aminopropyl tri ... Silane coupling agents having an amino group, such as i-ethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride; silane coupling agents having a ureido group, such as 3-ureidopropyltrimethoxysilane and 3-ureidopropyltriethoxysilane; silane coupling agents having a halogen atom, such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane; silane coupling agents having a mercapto group, such as 3-mercaptopropylmethyldimethoxysilane and 3-mercaptopropyltrimethoxysilane;Examples of suitable silane coupling agents include silane coupling agents having a sulfide group, such as bis(trimethoxysilylpropyl)tetrasulfide and bis(triethoxysilylpropyl)tetrasulfide; silane coupling agents having an isocyanate group, such as 3-isocyanatepropyltrimethoxysilane and 3-isocyanatepropyltriethoxysilane; silane coupling agents having an allyl group, such as allyltrichlorosilane, allyltriethoxysilane and allyltrimethoxysilane; and silane coupling agents having a hydroxyl group, such as 3-hydroxypropyltrimethoxysilane and 3-hydroxypropyltriethoxysilane.

[0122] <Cyclic Ether Compound> The curable adhesive composition used in one embodiment of the present invention may further contain a cyclic ether compound. The cyclic ether compound may be any compound having a cyclic ether group. Examples of the cyclic ether group include an oxirane group (epoxy group), an oxetane group (oxetanyl group), a tetrahydrofuryl group, and a tetrahydropyranyl group. In this specification, the oxirane group includes groups having an oxirane structure, such as a glycidyl group, a glycidyl ether group, and an epoxycyclohexyl group. The cyclic ether compound may be used alone or in combination of two or more types.

[0123] Compositions containing a cyclic ether compound have the property of being able to form cured products with excellent adhesive strength. However, the cured products tend to have large values ​​of relative permittivity and dielectric loss tangent, and to have inferior low dielectric properties compared to compositions containing the above-mentioned component (B) or (C) but not containing a cyclic ether compound.

[0124] In the curable adhesive composition used in one aspect of the present invention, the content of the cyclic ether compound may be less than 5.0 mass%, less than 3.0 mass%, less than 1.0 mass%, less than 0.50 mass%, less than 0.10 mass%, less than 0.010 mass%, less than 0.0010 mass%, less than 0.00010 mass%, or less than 0.000010 mass%, relative to the total amount (100 mass%) of the active ingredients of the curable adhesive composition. Furthermore, in the curable adhesive composition used in one aspect of the present invention, the content of the cyclic ether compound may be less than 5.0 parts by mass, less than 3.0 parts by mass, less than 1.0 part by mass, less than 0.50 parts by mass, less than 0.10 parts by mass, less than 0.010 parts by mass, less than 0.0010 parts by mass, less than 0.00010 parts by mass, or less than 0.000010 parts by mass, relative to 100 parts by mass of the total amount of components (A) to (C) included in the curable adhesive composition.

[0125] <Inorganic Filler> The curable adhesive composition used in one embodiment of the present invention may further contain an inorganic filler, or may be a composition that does not contain an inorganic filler. Examples of inorganic fillers include silica, alumina, talc, aluminum hydroxide, magnesium hydroxide, titanium oxide, mica, aluminum borate, barium sulfate, boron nitride, forsterite, zinc oxide, magnesium oxide, and calcium carbonate. These inorganic fillers may be used alone or in combination of two or more.

[0126] However, in the curable adhesive composition used in one aspect of the present invention, the content of the inorganic filler may be 0 to 30 mass%, 0 to 20 mass%, 0 to 10 mass%, 0 to 5.0 mass%, 0 to 2.0 mass%, 0 to 1.0 mass%, 0 to 0.1 mass%, 0 to 0.01 mass%, or 0 to 0.001 mass%, relative to the total amount (100 mass%) of the active ingredients of the curable adhesive composition. Furthermore, in the curable adhesive composition used in one aspect of the present invention, the content of the inorganic filler may be less than 50 parts by mass, less than 30 parts by mass, less than 10 parts by mass, less than 5.0 parts by mass, less than 1.0 part by mass, less than 0.1 part by mass, less than 0.01 part by mass, less than 0.001 part by mass, or less than 0.0001 part by mass, relative to 100 parts by mass of the total amount of components (A) to (C) contained in the curable adhesive composition.

[0127] <Other Additives> The curable adhesive composition used in one embodiment of the present invention may contain additives other than the above-mentioned components, as long as the effects of the present invention are not impaired. Examples of other additives include ultraviolet absorbers, antistatic agents, light stabilizers, antioxidants, resin stabilizers, pigments, extenders, softeners, etc. These additives may be used alone or in combination of two or more. The content of these additives can be appropriately set depending on the type of additive. For example, the content of each additive may be 0.001 to 30 parts by mass, 0.005 to 20 parts by mass, 0.01 to 10 parts by mass, or 0.03 to 5 parts by mass, relative to 100 parts by mass of the total amount of component (A) contained in the curable adhesive composition.

[0128] <Liquid Active Ingredient> The curable adhesive composition used in one embodiment of the present invention preferably contains an active ingredient that is liquid at 25° C. By using a composition that contains a liquid active ingredient, the application properties of the curable adhesive layer that is formed can be improved.

[0129] In the curable adhesive composition used in one embodiment of the present invention, the content of the active ingredient that is liquid at 25°C, relative to the total amount (100% by mass) of the active ingredients in the curable adhesive composition, is preferably 7.0% by mass or more, more preferably 10% by mass or more, and even more preferably 12% by mass or more, from the viewpoint of forming a composition that can form a curable adhesive layer with excellent adhesion. Furthermore, since the peel strength (R1) and peel strength (R2) tend to increase as the content of the active ingredient that is liquid at 25°C increases, from the viewpoint of forming a curable adhesive sheet in which the peel strength (R1) or the peel strength (R2) is adjusted to be small, the content is preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 25% by mass or less.

[0130] From the viewpoint of obtaining a composition capable of forming a curable adhesive layer with excellent adhesion and capable of forming a cured product with further improved low dielectric properties and adhesive strength, it is preferred that at least one of the active ingredients that are liquid at 25°C contained in the curable adhesive composition used in one embodiment of the present invention is a polyfunctional compound (C). In the curable adhesive composition used in one embodiment of the present invention, the content of the polyfunctional compound (C) relative to the total amount (100% by mass) of active ingredients that are liquid at 25°C is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, and may usually be 100% by mass or less, preferably 99.0% by mass or less, and more preferably 98.0% by mass or less.

[0131] <Dilution Solvent> The curable adhesive composition used in one embodiment of the present invention may be in the form of a solution by further adding a dilution solvent. Examples of the dilution solvent used in one embodiment of the present invention include aromatic hydrocarbon solvents such as benzene and toluene; ester solvents such as ethyl acetate and butyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as n-pentane, n-hexane, and n-heptane; and alicyclic hydrocarbon solvents such as cyclopentane, cyclohexane, and methylcyclohexane. These dilution solvents may be used alone or in combination of two or more. Note that these dilution solvents may be the solvents used in the synthesis of components (A) and (B), or one or more solvents other than the solvents used in the synthesis of components (A) and (B) may be added.

[0132] When the curable adhesive composition used in one embodiment of the present invention is in the form of a solution, the concentration of the active ingredient in the curable adhesive composition is appropriately set to achieve the desired viscosity, taking into consideration factors such as coatability. The active ingredient concentration may be preferably 3.0% by mass or more, more preferably 10% by mass or more, and may be preferably 70% by mass or less, more preferably 50% by mass or less, relative to the total amount (100% by mass) of the curable adhesive composition.

[0133] [Method for producing a curable adhesive sheet] A method for producing a curable adhesive sheet according to one embodiment of the present invention can be achieved by applying the above-described curable adhesive composition to the release layer of the first release film or the second release film by a known application method. From the viewpoint of improving the coatability to the release film, it is preferable to dilute the curable adhesive composition with a dilution solvent to form a solution.

[0134] Examples of methods for applying the curable adhesive composition include spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

[0135] After applying the curable adhesive composition to form a coating film, a drying treatment is preferably performed. Examples of drying methods include hot air drying, heated roll drying, and infrared irradiation. The formed coating film is preferably dried by heating at a temperature of 80°C to 150°C for 30 seconds to 5 minutes (preferably 40 seconds to 3 minutes, more preferably 45 seconds to 2 minutes). Through this drying process, a curable adhesive layer can be formed on the release layer of the first release film or the second release film. Furthermore, by laminating the other release film on the exposed surface of the formed curable adhesive layer, a curable adhesive sheet according to one embodiment of the present invention can be obtained. From the viewpoint of facilitating the production of a curable adhesive sheet satisfying the above-mentioned requirement (III) or requirement (IV), it is preferable to apply the curable adhesive composition to a second release film and then laminate a first release film on the exposed surface of the formed curable adhesive layer.

[0136] When the curable adhesive composition used to form the curable adhesive layer contains a crosslinking agent (E), it is preferable to carry out a seasoning step in which the composition is held for a certain period of time (for example, about 1 to 14 days) in order to complete the crosslinking reaction.

[0137] [Method for producing a cured product] The present invention also provides a method for producing a cured product using the curable adhesive sheet of one aspect of the present invention described above. The method for producing a cured product of the present invention preferably includes the following steps (1) to (3). Step (1): A step of peeling off a first release film to expose the curable adhesive layer and attaching it to an adherend. Step (2): A step of confirming, from the second release film side, using an optical inspection means, that no foreign matter is present at the interface between the curable adhesive layer and the adherend. Step (3): After step (2), a step of curing the curable adhesive layer to produce a cured product.

[0138] In step (1), the first release film is peeled off to expose the curable adhesive layer, which is then applied to an adherend. The curable adhesive sheet of one embodiment of the present invention has excellent handleability because the first release film is easily peeled off from the curable adhesive layer, even when the curable adhesive layer is sandwiched between the first release film and the second release film. The curable adhesive sheet also has excellent handleability because the first release film and the second release film are visually distinguishable from each other.

[0139] Step (2) is a step of confirming by optical inspection means from the second release film side that no foreign matter is present at the interface between the curable adhesive layer and the adherend, which contributes to improving product yield by confirming whether or not foreign matter has been mixed in.

[0140] Step (3) is a step of curing the curable adhesive layer after step (2) to form a cured product. The method for curing the adhesive layer may be a heat curing method or a photocuring method, and is selected depending on the types of components contained in the curable adhesive composition that forms the curable adhesive layer. However, from the viewpoint of productivity, a heat curing method is preferred. The heating temperature during heat curing is preferably 80 to 200°C, more preferably 90 to 190°C, and even more preferably 100 to 180°C, and the heating time is preferably 10 minutes to 12 hours, more preferably 30 minutes to 6 hours, and even more preferably 40 minutes to 3 hours. Furthermore, heat pressing is preferably performed during heat curing. The pressure during heat pressing is preferably 0.1 to 10 MPa, more preferably 0.5 to 8.0 MPa, and even more preferably 1.0 to 5.0 MPa. Furthermore, when curing the curable adhesive layer by a photocuring method, the curable adhesive layer can be cured by irradiating it with energy rays such as ultraviolet rays. The method for producing a cured product using the curable adhesive sheet of one embodiment of the present invention is not limited to one that includes step (2), and step (2) does not have to be performed between step (1) and step (3).

[0141] [Method of using the curable adhesive sheet, and method of manufacturing a circuit board with the cured product] The cured product obtained by curing the curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention has excellent low dielectric properties in the high frequency range. Therefore, the curable adhesive sheet of one embodiment of the present invention is preferably used when forming components in devices that require low dielectric properties, and is particularly preferably used as a coverlay sheet for protecting circuit boards. Examples of circuit boards include flexible printed circuit boards (FPCs).

[0142] Because the curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention has the above-mentioned properties, the present invention can also provide the following [1] and [2]. [1] A method for using a curable adhesive sheet, comprising an adhesion step of laminating the curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention described above to a circuit board, curing the curable adhesive layer to form a cured product, and adhering the cured product to the circuit board. [2] A method for producing a circuit board with a cured product, comprising an adhesion step of laminating the curable adhesive layer of the curable adhesive sheet of one embodiment of the present invention described above to a circuit board, curing the curable adhesive layer to form a cured product, and adhering the cured product to the circuit board.

[0143] In the above [1] and [2], it is preferable to confirm that no foreign matter is present at the interface between the curable adhesive layer and the circuit board by optically inspecting the curable adhesive layer from the second release film side after bonding the curable adhesive layer to the circuit board. In addition, in the above [1] and [2], the method for curing the curable adhesive layer to form a cured product can be adjusted depending on the type of reactive curing agent such as component (D), and may be a thermal curing method or a photocuring method. Specifically, the same method as in step (3) of the method for producing a cured product according to one embodiment of the present invention described above can be mentioned.

[0144] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. The physical properties were measured by the methods shown below.

[0145] [Number average molecular weight (Mn)] Measurement was performed using a gel permeation chromatograph (manufactured by Tosoh Corporation, product name "HLC-8320 GPC") under the following conditions, and the value measured in terms of standard polystyrene was used. (Measurement conditions) Column: "TSK gel guard column super H-H", "TSK gel super HM-H", "TSK gel super HM-H", and "TSK gel super H2000" connected in sequence (all manufactured by Tosoh Corporation) Column temperature: 40°C Developing solvent: tetrahydrofuran Flow rate: 1.0 mL / min

[0146] [Thickness of Each Layer] Measurements were made using a constant pressure thickness measuring instrument (manufactured by Teclock Corporation, product name "PG-02J") in accordance with JIS K6783, Z1702, and Z1709.

[0147] [Peel Force (R1)] The curable adhesive sheet to be measured was cut into a size of 150 mm length x 50 mm width to prepare a test sample. Then, one adhesive surface of double-sided tape was attached to the surface of the test sample opposite to the surface that contacts the curable adhesive layer of the second release film, and the other adhesive surface of the double-sided tape was placed on the surface of the metal plate and pressure-bonded. Next, under an environment of 23 ° C. and 50% relative humidity, a precision universal testing machine (manufactured by Shimadzu Corporation, product name "Autograph AG-IS") was used to peel the first release film to be measured for peel force from the test sample fixed to the metal plate under conditions of a peel angle of 180 ° and a peel speed of 300 mm / min, and the value measured when this was taken as "peel force (R1)".

[0148] [Peel Force (R2)] The first release film was removed from the curable adhesive sheet to be measured, and the exposed adhesive surface was placed on a 25 μm thick polyimide film (Kapton 100H, manufactured by DuPont Toray Co., Ltd.) on the surface of alkali-free glass, and then pressed at 100 ° C. using a thermal laminator. Next, the curable adhesive sheet and the polyimide film were cut into a size of 150 mm length x 50 mm width to prepare a test sample. One adhesive surface of double-sided tape was attached to the side of the polyimide film of the test sample opposite to the side on which the curable adhesive layer was laminated, and the other adhesive surface of the double-sided tape was placed on the surface of the metal plate and pressed. A peel test was performed on this test sample in the same manner as in the measurement of the peel force (R1) described above. That is, the second release film to be measured for peel force was peeled from a test sample fixed to a metal plate using the precision universal testing machine under conditions of a temperature of 23°C and a relative humidity of 50%, at a peel angle of 180° and a peel speed of 300 mm / min, and the value measured was taken as the "peeling force (R2)."

[0149] Production Examples 1 and 2 (1) Preparation of Curable Adhesive Compositions The components shown in Table 1 were blended in the amounts (active ingredient ratios) shown in Table 1 and dissolved in toluene to prepare curable adhesive compositions (1) and (2) so as to achieve the desired active ingredient concentrations. Details of the components used in preparing curable adhesive compositions (1) and (2) are as follows. <Component (A): Binder Resin> - "Modified Polyolefin": A solution containing a maleic anhydride-modified α-olefin polymer (solid at 25°C) with Mn = 47,000 (manufactured by Mitsui Chemicals, Inc., product name "UNISTOR H-200"). <Component (B): Polyphenylene Ether Resin> - "Polyphenylene Ether Resin (b1)": A solution containing a vinylbenzyl-modified polyphenylene ether (compound represented by the general formula (b-4) above, solid at 25°C) with Mn = 2,200 (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "OPE-2St 2200"). "Polyphenylene ether resin (b2)": a solution containing vinylbenzyl-modified polyphenylene ether having Mn=1,200 (a compound represented by the general formula (b-4) above, solid at 25°C) (manufactured by Mitsubishi Gas Chemical Company, Inc., product name "OPE-2St 1200"). <Component (C): Polyfunctional compound> "Polyfunctional compound": a polyphenylene ether resin having Mn=1,200 (a compound represented by the general formula (b-4) above, solid at 25°C). ａ is an alkyl group having 8 to 15 carbon atoms. Manufactured by Shikoku Chemical Industry Co., Ltd., product name "L-DAIC", molecular weight = 377.27, liquid at 25°C. <Component (D): Cationic polymerization initiator> - "Thermal cationic polymerization initiator": thermal cationic polymerization initiator (manufactured by Sanshin Chemical Industry Co., Ltd., product name "Sanaid SI-B3"), solid at 25°C. <Component (E): Crosslinking agent> - "Isocyanate crosslinking agent": 1,3,5-tris(5-isocyanatopentyl)-1,3,5-triazine-2,4,6-trione (manufactured by Mitsui Chemicals, Inc., product name "Stabio D-370N"), molecular weight = 462, liquid at 25°C. <Component (F): Silane Coupling Agent> - "Silane coupling agent": 8-glycidoxyoctyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., product name "KBM4803"), liquid at 25°C.

[0150]

[0151] Examples 1 to 4, Comparative Example 1 The release films and curable adhesive compositions used to form the curable adhesive layers used in the following examples and comparative examples are as follows. <First Release Film> Non-silicone Release Film (1): Product name "PC38 AL-5", manufactured by Lintec Corporation, a non-silicone release film having a release layer formed from an alkyd-based release agent on a foamed white polyethylene terephthalate (PET) film, thickness: 38 μm. <Second Release Film> Non-silicone Release Film (2): Product name "SP-PET50 AL-5", manufactured by Lintec Corporation, a non-silicone release film having a release layer formed from an alkyd-based release agent on a colorless PET film, thickness: 50 μm. Non-silicone Release Film (3): Product name "SP-PET75 AL-5", manufactured by Lintec Corporation, a non-silicone release film having a release layer formed from an alkyd-based release agent on a colorless PET film, thickness: 75 μm. Non-silicone release film (4): Product name "SP-PET38 AL-5", manufactured by Lintec Corporation, a non-silicone release film having a release layer formed from an alkyd-based release agent on a colorless PET film, thickness: 38 μm. <Materials for forming the curable adhesive layer> Curable adhesive composition (1): Curable adhesive composition (1) prepared in Production Example 1 with the composition shown in Table 1. Curable adhesive composition (2): Curable adhesive composition (2) prepared in Production Example 2 with the composition shown in Table 1.

[0152] A curable adhesive composition described in Table 1 was applied to the release layer of a second release film described in Table 2 to form a coating, and the coating was dried to form a curable adhesive layer 25 μm thick. The exposed surface of the formed curable adhesive layer was then bonded to the release layer of a first release film described in Table 2 to produce a curable adhesive sheet.

[0153] The peel strengths (R1) and (R2) of the prepared curable adhesive sheets were measured using the method described above. The results are shown in Table 2. Furthermore, the dielectric loss tangent of the cured product obtained by curing the curable adhesive layer and the releasability of the first release film were evaluated using the following evaluation methods. These results are also shown in Table 2.

[0154] [Dielectric Loss Tangent of Cured Product] A plurality of the prepared curable adhesive sheets were prepared, and multiple curable adhesive layers were stacked to form a curable adhesive layer approximately 1 mm thick. A laminate was obtained by laminating a second release film, a curable adhesive layer approximately 1 mm thick, and a first release film in this order. This laminate was then heated at 160°C for 1 hour to cure the curable adhesive layer, forming a cured product. The first and second release films were then removed to obtain a measurement sample. The dielectric loss tangent of the cured product at 23°C and 1 GHz was measured for the obtained measurement sample using an RF impedance material analyzer (Keysight Technologies, product name "E4991A"). In this specification, 1 GHz is used as an example of a high-frequency range.

[0155] [Evaluation of releasability of first release film] When an attempt was made to peel off only the first release film while the curable adhesive layer of the prepared curable adhesive sheet was sandwiched between the first release film and the second release film, the ease of peeling was evaluated on a 5-point scale from 5 (maximum) to 1 (minimum), based on the ease of peeling of the curable adhesive sheet of Comparative Example 1. The guidelines for ease of peeling for each standard are as follows: - "5": Compared to Comparative Example 1, the ease of peeling was felt to be extremely great, with a dramatic difference. - "4": Compared to Comparative Example 1, the ease of peeling was felt to be sufficient, with a clear difference. - "3": Compared to Comparative Example 1, the ease of peeling was felt to be greater. - "2": Compared to Comparative Example 1, the ease of peeling was felt to be somewhat greater. - "1": The ease of peeling was the same as that of Comparative Example 1, or worse than that of Comparative Example 1.

[0156]

[0157] As can be seen from Table 2, the curable adhesive sheets produced in Examples 1 to 4 have easier peeling of the first release film and are easier to handle than Comparative Example 1. Furthermore, because the curable adhesive sheets produced in Examples 1 to 4 use a non-silicone release agent, there is no migration of silicone components to the adherend, and contamination of the adherend can be suppressed.

[0158] REFERENCE SIGNS LIST 1 Curable adhesive sheet 10 Curable adhesive layer 10a, 10b Surface 21 First release film 211 Release layer 212 Resin film 22 Second release film 221 Release layer 222 Resin film

Claims

1. A curable adhesive sheet having a curable adhesive layer capable of forming a cured product having a dielectric tangent of 0.01 or less at 23°C and 1 GHz, and a first release film and a second release film sandwiching both surfaces of the curable adhesive layer, wherein the first release film has a colored resin film (i) and a release agent layer laminated on one surface of the colored resin film (i) and contacting the surface of the curable adhesive layer, the second release film has a resin film (ii) distinguishable from the colored resin film (i) and a release agent layer laminated on one surface of the resin film (ii) and contacting the surface of the curable adhesive layer, and satisfies the following requirement (Ia). - Requirement (Ia): The thickness ratio [(T2) / (T1)] of the thickness (T2) of the second release film to the thickness (T1) of the first release film is 1.05 or more.

2. Furthermore, the curable adhesive sheet according to claim 1, which satisfies the following requirement (Ib). - Requirement (Ib): The thickness ratio [(T2) / (T1)] of the thickness (T2) of the second release film to the thickness (T1) of the first release film is 10.0 or less.

3. Furthermore, the curable adhesive sheet according to claim 1 or 2, which satisfies the following requirement (IIa). - Requirement (IIa): The thickness difference [(T2)-(T1)] between the thickness (T2) of the second release film and the thickness (T1) of the first release film is 5.0 μm or more.

4. Furthermore, the curable adhesive sheet according to claim 1 or 2, which satisfies the following requirement (IIb). - Requirement (IIb): The thickness difference [(T2)-(T1)] between the thickness (T2) of the second release film and the thickness (T1) of the first release film is 165.0 μm or less.

5. Furthermore, the curable adhesive sheet according to claim 1 or 2, which satisfies the following requirement (III). - Requirement (III): The ratio [(R1) / (R2)] of the peeling force (R1) when peeling the first release film from the curable adhesive layer at a peeling angle of 180° and a peeling speed of 300 mm / min to the peeling force (R2) when peeling the second release film from the curable adhesive layer at a peeling angle of 180° and a peeling speed of 300 mm / min is 0.97 or less.

6. Furthermore, the curable adhesive sheet according to claim 1 or 2, which satisfies the following requirement (IV). - Requirement (IV): The peeling force (R2) when peeling the second peeling film from the curable adhesive layer at a peeling angle of 180° and a peeling speed of 300 mm / min is greater than the peeling force (R1) when peeling the first peeling film from the curable adhesive layer at a peeling angle of 180° and a peeling speed of 300 mm / min, and is 600 mN / 50 mm or less.

7. The curable adhesive sheet according to claim 1 or 2, wherein the resin film (ii) is a transparent resin film.

8. The curable adhesive sheet according to claim 1 or 2, wherein the curable adhesive layer is a layer formed from a curable adhesive composition containing a polyphenylene ether resin.

9. When the curable adhesive layer exposed by peeling the first peeling film is attached to an adherend, the presence or absence of foreign matter at the interface between the curable adhesive layer and the adherend can be confirmed by optical inspection means from the side of the second peeling film. The curable adhesive sheet according to claim 1 or 2.

10. A method for manufacturing a cured product using the curable adhesive sheet according to claim 1 or 2, the method for manufacturing a cured product having the following steps (1) to (3). - Step (1): A step of attaching the curable adhesive layer exposed by peeling the first peeling film to an adherend. - Step (2): A step of confirming, by optical inspection means from the side of the second peeling film, that there is no foreign matter at the interface between the curable adhesive layer and the adherend. - Step (3): After step (2), a step of curing the curable adhesive layer to obtain a cured product.