Thermally conductive sheet

Abstract

The present invention provides a thermally conductive sheet with improved light transmittance. According to the present invention, a thermally conductive sheet is provided, comprising a resin layer containing a resin and a thermally conductive filler. The refractive index np of the resin and the refractive index nf of the thermally conductive filler satisfy the following relationship: -0.04 ≤ (np-nf) ≤ 0.04. According to a preferred embodiment, the content of the thermally conductive filler is 50 parts by weight or greater and 250 parts by weight or less per 100 parts by weight of the resin.

Description

Technical Field

[0001] The present invention relates to a thermally conductive sheet. Background Art

[0002] In recent years, with the progress of high functionality of electronic devices (such as semiconductor elements), the amount of heat generated by electronic devices has tended to increase. Therefore, the importance of designing electronic devices with heat dissipation is increasing. Against this background, thermally conductive sheets are used between electronic devices such as light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs) in electronic devices that can become heat-generating bodies and heat dissipating bodies such as housings and heat spreaders for the purpose of effectively transferring the heat generated by the heat-generating body to the heat dissipating body. As a representative structure of a thermally conductive sheet, a structure of a thermally conductive layer having a form in which a thermally conductive filler is dispersed in a resin can be cited. As a prior art document related to thermally conductive sheets, Patent Document 1 can be cited.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-176980 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] Conventional thermally conductive sheets have not been particularly sensitive to visible light. Improving the transparency (light transmittance) of a thermally conductive sheet would make it easier to identify the proper placement of the sheet through the thickness of the sheet when placing it between a heating element and a heat sink during device construction, for example. This would improve device construction accuracy and operational efficiency.

[0008] The present invention has been made in view of the above-mentioned situation, and an object of the present invention is to provide a thermally conductive sheet having improved light transmittance.

[0009] Solutions for solving problems

[0010] According to the present invention, a thermally conductive sheet is provided that includes a resin layer containing a resin and a thermally conductive filler. Here, the difference in refractive index between the resin and the thermally conductive filler is 0.04 or less. That is, the refractive index np of the resin and the refractive index nf of the thermally conductive filler satisfy the following relationship: -0.04 ≤ (np - nf) ≤ 0.04. This configuration can improve the transmittance (light transmittance) of the thermally conductive sheet.

[0011] According to a preferred embodiment of the thermally conductive sheet disclosed herein, the content of the thermally conductive filler is 50 parts by weight or more and 250 parts by weight or less per 100 parts by weight of the resin. A thermally conductive sheet comprising a resin layer containing 50 parts by weight or more and 250 parts by weight of the thermally conductive filler per 100 parts by weight of the resin, wherein the refractive index np of the resin and the refractive index nf of the thermally conductive filler satisfy the following relationship: -0.04 ≤ (np - nf) ≤ 0.04, can achieve a suitable balance between good transparency and high thermal conductivity.

[0012] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the resin includes an acrylic polymer as a base polymer. The configuration including the resin layer containing the resin facilitates realization of a thermally conductive sheet having excellent light transmittance.

[0013] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the acrylic polymer is a polymer comprising a monomer component, monomer A, wherein the homopolymer of monomer A is a high-refractive-index polymer having a refractive index of 1.50 or greater. This configuration facilitates the formation of a resin layer having a small difference in refractive index between the thermally conductive filler and the resin, thereby improving the light transmittance of the thermally conductive sheet.

[0014] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the monomer A comprises at least one member selected from the group consisting of fluorene (meth)acrylates, phenylphenol (meth)acrylates, and benzyl (meth)acrylates. The use of this monomer A facilitates the formation of a resin layer having a small difference in refractive index between the thermally conductive filler and the resin, thereby improving the light transmittance of the thermally conductive sheet.

[0015] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the proportion of the monomer A in the total monomer components is 50% by weight or greater. This configuration facilitates the formation of a resin layer having a small difference in refractive index between the thermally conductive filler and the resin, further improving the light transmission performance of the thermally conductive sheet.

[0016] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the thermally conductive filler includes a hydrated metal compound (eg, aluminum hydroxide). This configuration enables a thermally conductive sheet having high thermal conductivity and improved light transmittance.

[0017] According to another preferred embodiment of the thermally conductive sheet disclosed herein, the resin has a refractive index np of 1.49 to 1.65. Using a resin having this refractive index np makes it easier to create a resin layer with a small difference in refractive index between the thermally conductive filler (e.g., a hydrated metal compound such as aluminum hydroxide) and the resin, further improving the light transmittance of the thermally conductive sheet.

[0018] In a preferred embodiment of the thermally conductive sheet disclosed herein, the resin layer is an adhesive layer (adhesive layer). When the resin layer is directly attached to an adherend, the thermally conductive sheet with this configuration can be positioned with good adhesion to the adherend, thereby improving thermal conductivity from the adherend. Furthermore, with this configuration, the thermally conductive sheet can be used not only for heat dissipation and heat conduction from adherends, but also for fixing and joining adherends. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic cross-sectional view showing the structure of a thermally conductive sheet according to one embodiment.

[0020] Figure 2 It is a schematic cross-sectional view showing the structure of a thermally conductive sheet according to still another embodiment.

[0021] Figure 3 It is a schematic cross-sectional view showing the structure of a thermally conductive sheet according to another embodiment.

[0022] Figure 4 It is a schematic cross-sectional view showing the structure of a thermally conductive sheet according to another embodiment.

[0023] Figure 5 (a) is a front view of a thermal characteristic evaluation device used in the measurement of thermal resistance values ​​in the embodiment. Figure 5 (b) is Figure 5 (a) is a schematic side view of the device shown.

[0024] Description of Reference Numerals

[0025] 10 Thermal Conductivity Sheet

[0026] 12 Resin layer

[0027] 12A Page 1

[0028] 12B Side 2

[0029] 20 Thermally conductive adhesive sheet (double-sided adhesive sheet)

[0030] 22 resin layer (adhesive layer)

[0031] 22A First bonding surface

[0032] 22B Second adhesive surface

[0033] 24 Release liner

[0034] 26 Release liner

[0035] 30 Thermally conductive adhesive sheet (double-sided adhesive sheet)

[0036] 32 Support substrate

[0037] 32A Page 1

[0038] 32B Page 2

[0039] 34 First resin layer

[0040] 34A Surface of the first resin layer (first adhesive surface)

[0041] 36 Second resin layer

[0042] 36A Surface of the second resin layer (second adhesive surface)

[0043] 38 Release liner

[0044] 39 Release liner

[0045] 40 Thermally conductive adhesive sheet (double-sided adhesive sheet)

[0046] 42 resin layer

[0047] 42A Page 1

[0048] 42B Page 2

[0049] 44 first adhesive layer

[0050] 44A Surface of the first adhesive layer (first adhesive surface)

[0051] 46 second adhesive layer

[0052] 46A Surface of the second adhesive layer (second adhesive surface)

[0053] 48 Release liner

[0054] 49 Release liner

[0055] 200 Thermally Conductive Adhesive Sheet with Release Liner

[0056] 300 Thermally Conductive Adhesive Sheet with Release Liner

[0057] 400 Thermally Conductive Adhesive Sheet with Release Liner DETAILED DESCRIPTION

[0058] The following describes preferred embodiments of the present invention. It should be noted that matters necessary for implementing the present invention, other than those specifically mentioned in this specification, can be understood by those skilled in the art based on the teachings regarding the implementation of the invention described in this specification and common knowledge at the time of application. The present invention can be implemented based on the disclosures in this specification and common knowledge in the art.

[0059] It should be noted that in the following drawings, components and parts having the same function are sometimes labeled with the same reference numerals for explanation, and repeated explanations are sometimes omitted or simplified. In addition, the embodiments described in the drawings are schematic for the purpose of clearly explaining the present invention and do not necessarily accurately represent the dimensions or scale of the actual product provided.

[0060] <Structural Example of Thermally Conductive Sheet>

[0061] The thermally conductive sheet disclosed herein comprises a resin layer. The resin layer may be an adhesive layer (a layer having adhesive properties) or a non-adhesive layer. When the resin layer is an adhesive layer, a thermally conductive sheet in which one or both of the first and second surfaces are formed by the surface (adhesive surface) of the resin layer is also considered a thermally conductive adhesive sheet.

[0062] As used herein, an "adhesive layer" refers to a layer having a peel strength of 0.1 N / 20 mm or greater when peeled off in a 180° direction at a tensile rate of 300 mm / min after being pressed against a SUS304 stainless steel plate as an adherend by a 2 kg roller being moved back and forth once for 30 minutes at a measurement temperature of 23°C, in accordance with JIS Z0237 (2004). Furthermore, a "non-adhesive layer" as used herein refers to a layer that does not constitute the adhesive layer, and typically refers to a layer having a peel strength of less than 0.1 N / 20 mm. A layer that does not adhere to a SUS304 stainless steel plate when pressed against the plate by a 2 kg roller being moved back and forth once at a measurement temperature of 23°C (a layer that does not exhibit substantial adhesiveness) is a typical example of the concept of a non-adhesive layer herein.

[0063] The thermally conductive sheet disclosed herein may be composed of the above-mentioned resin layer. Specifically, the thermally conductive sheet disclosed herein may be in the form of a substrate-free resin sheet having a first surface formed by one surface of the above-mentioned resin layer and a second surface formed by the other surface of the above-mentioned resin layer.

[0064] Figure 1 The structure of a thermally conductive sheet according to one embodiment is schematically shown. This thermally conductive sheet 10 is constructed as a substrate-free thermally conductive sheet 10 composed of a resin layer 12 serving as a non-adhesive layer. The thermally conductive sheet 10 includes a first surface 12A, which is a non-adhesive surface formed from one surface of the resin layer 12, and a second surface 12B, which is a non-adhesive surface formed from the other surface of the resin layer 12. The thermally conductive sheet 10 is used by placing the first surface 12A and the second surface 12B in close contact with each other at different locations on another component. The locations where the first surface 12A and the second surface 12B are in close contact can be separate locations on different components or different locations within a single component.

[0065] Figure 2The structure of a thermally conductive sheet according to another embodiment is schematically shown. The thermally conductive sheet is constituted in the form of a substrate-free thermally conductive adhesive sheet (double-sided adhesive sheet) 20 composed of an adhesive resin layer (adhesive layer) 22. The thermally conductive adhesive sheet 20 comprises: a first adhesive surface 22A constituted by one surface of the resin layer 22, and a second adhesive surface 22B constituted by the other surface of the resin layer 22. The thermally conductive adhesive sheet 20 is used by attaching the adhesive surfaces 22A and 22B to different parts of an adherend. The parts to which the adhesive surfaces 22A and 22B are attached may be respective parts of different components or different parts within a single component. The thermally conductive adhesive sheet 20 before use (i.e., before attachment to the adherend) is as follows: Figure 2 The components of a release-lined thermally conductive adhesive sheet 200 are shown, in which the first adhesive surface 22A and the second adhesive surface 22B are protected by release liners 24 and 26, respectively, with at least one side opposite the resin layer 22 serving as the release surface. Release liners 24 and 26 are preferably constructed, for example, by providing a release layer with a release treatment agent on one side of a sheet-like substrate (liner substrate), with that single side serving as the release surface. Alternatively, release liner 26 can be omitted, and a release liner 24 with both sides serving as release surfaces can be used. This is then overlapped with the thermally conductive adhesive sheet 20 and rolled into a spiral shape, thereby forming a release-lined thermally conductive adhesive sheet in a roll form, with the second adhesive surface 22B abutting against the back surface of the release liner 24 and protected.

[0066] Alternatively, the thermally conductive sheet disclosed herein may be in the form of a thermally conductive sheet with a substrate, in which a resin layer is laminated on one or both sides of a supporting substrate. Hereinafter, the supporting substrate may also be simply referred to as the "substrate." In the thermally conductive sheet of this embodiment, the resin layer may be an adhesive layer having adhesive properties or a non-adhesive layer having no adhesive properties (non-adhesive). However, from the perspective of improving adhesion to the substrate, the resin layer is preferably an adhesive layer.

[0067] Figure 3 The structure of a thermally conductive sheet according to one embodiment is schematically shown. The thermally conductive sheet is configured as a thermally conductive adhesive sheet with a substrate (double-sided adhesive sheet) 30, which includes: a sheet-shaped supporting substrate (e.g., a resin film) 32 having a first surface 32A and a second surface 32B; a first adhesive resin layer 34 fixedly provided on the first surface 32A; and a second adhesive resin layer 36 fixedly provided on the second surface 32B. The thermally conductive adhesive sheet 30 before use is as shown in FIG. Figure 3The components of a release-lined thermally conductive adhesive sheet 300 are shown in a configuration in which the surface (first adhesive surface) 34A of the first resin layer 34 and the surface (second adhesive surface) 36A of the second resin layer 36 are protected by release liners 38 and 39. Alternatively, the release liner 39 may be omitted, and a release liner 38 having both sides as release surfaces may be used. This may be overlapped with the thermally conductive adhesive sheet 30 and wound into a spiral shape, thereby forming a release-lined thermally conductive adhesive sheet in a configuration (roll form) in which the second adhesive surface 36A is protected by contacting the back surface of the release liner 38.

[0068] In the thermally conductive sheet 30 described above, the material constituting the support substrate 32 is not particularly limited. To achieve a thermally conductive sheet 30 with good light transmittance, a transparent resin film is preferably used as the support substrate 32. Non-limiting examples of resin films include polyolefin films primarily composed of polyolefins such as polypropylene and ethylene-propylene copolymers; polyester films primarily composed of polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate; and polyvinyl chloride films primarily composed of polyvinyl chloride. As a preferred example, PET film is preferably used for its transparency.

[0069] Alternatively, the thermally conductive sheet disclosed herein may be a thermally conductive adhesive sheet comprising an adhesive layer laminated on one or both sides of a resin layer. In such a thermally conductive sheet (thermally conductive adhesive sheet), the resin layer may be an adhesive layer or a non-adhesive layer. With this configuration, even a thermally conductive sheet comprising a resin layer as a non-adhesive layer can still form an adhesive surface on one or both sides of the thermally conductive sheet using the adhesive layer laminated on one or both sides of the resin layer.

[0070] Figure 4 The structure of a thermally conductive sheet according to one embodiment is schematically shown. The thermally conductive sheet is formed as a thermally conductive adhesive sheet (double-sided adhesive sheet) 40, which includes a resin layer 42 having a first surface 42A and a second surface 42B, a first adhesive layer 44 fixedly provided on the first surface 42A, and a second adhesive layer 46 fixedly provided on the second surface 42B. The thermally conductive adhesive sheet 40 before use is as shown in FIG. Figure 4 The components of a release-lined thermally conductive adhesive sheet 400 are shown in a configuration in which the surface (first adhesive surface) 44A of the first adhesive layer 44 and the surface (second adhesive surface) 46A of the second adhesive layer 46 are protected by release liners 48 and 49. Alternatively, the release liner 49 may be omitted, and a release liner 48 having both sides as release surfaces may be used. This release liner 48 may be superimposed on the thermally conductive adhesive sheet 40 and wound into a spiral shape, thereby forming a release-lined thermally conductive adhesive sheet in a configuration (roll form) in which the second adhesive surface 46A is protected by contact with the back surface of the release liner 48.

[0071] It should be noted that the adhesive contained in the first adhesive layer 44 and the second adhesive layer 46 is not particularly limited. For example, the adhesive may include one or more of various polymers such as acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers as a base polymer (i.e., a component that accounts for 50% by weight or more of the polymer components).

[0072] It should be noted that the concept of adhesive sheet herein encompasses objects referred to as adhesive tapes, adhesive films, and adhesive labels. The adhesive sheet may be in roll form, single sheet form, or may be cut, punched, or otherwise formed into a suitable shape depending on the intended use and manner of use. In the case of a thermally conductive adhesive sheet comprising an adhesive layer laminated on one or both sides of a resin layer, the adhesive layer is typically formed continuously, but this is not limiting. For example, the adhesive layer may be formed in a regular or random pattern, such as dots or stripes.

[0073] <Characteristics of Thermally Conductive Sheet>

[0074] The thermal conductivity of the thermally conductive sheet disclosed herein (based on the steady-state heat flow method. The same applies hereinafter.) is not particularly limited, and is typically 0.15 W / m·K or more. The higher the thermal conductivity, the easier it is to arrange between components that are desired to dissipate heat or conduct heat, making it suitable for the purpose of heat dissipation, heat conduction, etc. of the components. The above-mentioned thermal conductivity is preferably 0.2 W / m·K or more, more preferably 0.25 W / m·K or more, and further preferably 0.28 W / m·K or more, for example, it can be 0.3 W / m·K or more, 0.35 W / m·K or more, 0.4 W / m·K or more, or 0.48 W / m·K or more. There is no particular upper limit on the thermal conductivity of the thermally conductive sheet. Taking into account the balance with other properties such as transparency, in some embodiments, the thermal conductivity of the thermally conductive sheet may be, for example, 2.0 W / m·K or less, 1.5 W / m·K or less, 1.0 W / m·K or less, 0.8 W / m·K or less, 0.5 W / m·K or less, or less than 0.5 W / m·K. In some embodiments, the thermal conductivity of the thermally conductive sheet may be 0.45 W / m·K or less, 0.40 W / m·K or less, 0.35 W / m·K or less, or 0.32 W / m·K or less.

[0075] In this specification, the thermal conductivity of a thermally conductive sheet refers to a value measured by a steady-state heat flow method. More specifically, the thermal conductivity of a thermally conductive sheet can be measured by the method described in the Examples below.

[0076] The thermally conductive sheet having appropriate thermal conductivity as described above is arranged between components (typically, between a heating element and a heat sink) in electronic devices and products in a manner that closely fits the component, thereby effectively conducting heat. As a thermally conductive sheet used in this manner, by following and closely fitting the convex and concave portions of the component, the thermal resistance of the interface between the component and the thermally conductive sheet can be reduced. Therefore, a structure in which the thermally conductive material that mainly contributes to thermal conductivity is contained in (typically dispersed in) a medium such as a resin having a specified softness can be appropriately adopted. However, for the thermally conductive sheet having the above structure, the light transmittance (transparency) of the thermally conductive sheet itself is often reduced due to the refraction, dispersion, reflection, diffraction, and other effects of light at the interface between the medium and the thermally conductive material contained in the medium.

[0077] According to the technology disclosed herein, by setting the refractive index difference between the resin contained in the resin layer and the thermally conductive filler to 0.04 or less, a thermally conductive sheet having appropriately improved transmittance can be realized.

[0078] The transmittance of the thermally conductive sheet disclosed herein is not particularly limited. For example, the transmittance of the thermally conductive sheet is preferably 60% or greater, more preferably 70% or greater, and even more preferably 80% or greater (e.g., 85% or greater). The upper limit of the transmittance of the thermally conductive sheet is not particularly limited; however, from the perspective of achieving a balance with other properties such as thermal conductivity and adhesiveness, a transmittance of 99% or less is generally appropriate, and may be 95% or less, or even 90% or less.

[0079] In this specification, the transmittance of a thermally conductive sheet can be measured using a commercially available transmittance meter (e.g., a high-speed integrating sphere spectrophotometer, model "DOT-3," manufactured by Murakami Color Research Laboratory Co., Ltd.) at a temperature of 23°C and a measurement wavelength of 400 nm. More specifically, the transmittance of a thermally conductive sheet can be measured using the method described in the Examples below.

[0080] <Resin Layer>

[0081] The thermally conductive sheet disclosed herein includes a resin layer. The refractive index np of the resin contained in the resin layer is not particularly limited. The refractive index nf of the thermally conductive filler contained in the resin layer along with the resin tends to be relatively higher than the refractive index of resins commonly used in the adhesive sheet field. Therefore, using a resin with a higher refractive index makes it easier to appropriately reduce the refractive index difference with the thermally conductive filler.

[0082] The refractive index np of the resin contained in the resin layer also depends on the type of thermally conductive filler used with the resin. In some embodiments, it is preferably 1.49 or more, more preferably 1.51 or more, and even more preferably 1.53 or more. In some embodiments, the refractive index np of the resin can be 1.55 or more, 1.56 or more, or 1.57 or more. The upper limit of the refractive index np of the resin also depends on the type of thermally conductive filler used. In some embodiments, it is preferably 1.65 or less, more preferably 1.63 or less, and even more preferably 1.61 or less. From the perspective of achieving a balance with other properties, in some embodiments, the refractive index np of the resin can be 1.59 or less, 1.57 or less, 1.55 or less, or 1.54 or less.

[0083] In this specification, the refractive index np of a resin can be measured using a commercially available Abbe refractometer (e.g., Model "DR-M2" manufactured by ATAGO Corporation). More specifically, the refractive index np of a resin can be measured using the method described in the Examples below. The same applies to the refractive index nf of the thermally conductive filler described below.

[0084] In the technology disclosed herein, the resin contained in the above-mentioned resin layer is not particularly limited. The above-mentioned resin can be, for example, a resin containing one or more of various polymers such as acrylic polymers, rubber polymers, polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, fluorine polymers as a base polymer (i.e., a component accounting for more than 50% by weight of the polymer component). The resin layer in the technology disclosed herein can be formed by a resin composition containing such a base polymer. The form of the resin composition is not particularly limited, for example, it can be a resin composition in various forms such as water-dispersible, solvent-based, hot-melt, active energy ray-curable (e.g., photocurable) and the like.

[0085] As used herein, "active energy rays" refer to energy rays having energy capable of initiating chemical reactions such as polymerization, crosslinking, and decomposition of initiators. Examples of active energy rays include ultraviolet (UV) light, visible light, infrared light, α-rays, β-rays, γ-rays, electron beams, neutron rays, and X-rays.

[0086] Although not particularly limited, the weight average molecular weight (Mw) of the base polymer may be, for example, approximately 5×10 4 According to the base polymer of Mw, it is easy to obtain a resin showing good cohesion. In some embodiments, the base polymer Mw can be, for example, 10×10 4 Above, can be 20×10 4 Above, it can also be 30×104 In addition, the Mw of the base polymer is usually about 500×10 4 The following are suitable: The base polymer having the above Mw is suitable for forming a resin layer having good unevenness conformability.

[0087] The Mw of the base polymer can be determined as a polystyrene-equivalent value by gel permeation chromatography (GPC). GPC measurement can be performed using, for example, a GPC apparatus, HLC-8220GPC, manufactured by Tosoh Corporation, under the following conditions.

[0088] [GPC measurement]

[0089] Sample concentration: 0.2 wt% (tetrahydrofuran (THF) solution)

[0090] Sample injection volume: 10μl

[0091] Eluent: THF

[0092] Flow rate: 0.6 ml / min

[0093] ·Measurement temperature: 40℃

[0094] Chromatographic column:

[0095] Sample column: TSK guard column SuperHZ-H (1 column) + TSK gel Super HZM-H (2 columns)

[0096] Reference column: TSK gel SuperH-RC (1 column)

[0097] Detector: Differential Refractometer (RI)

[0098] (High refractive index monomer A)

[0099] The base polymer preferably includes a monomer unit consisting of a monomer whose homopolymer is a high refractive index polymer of 1.50 or more (hereinafter also referred to as "high refractive index monomer A"). That is, the base polymer is preferably a polymer comprising a monomer component of a high refractive index monomer A whose homopolymer is a high refractive index polymer. By making the monomer component of the base polymer include the high refractive index monomer A, it becomes easy to adjust the refractive index of the base polymer to an appropriate range. Adjustment of the refractive index of the base polymer contributes to adjustment of the refractive index np of the resin containing the base polymer as the main component. Therefore, by using the high refractive index monomer A, a resin layer containing a resin having a small refractive index difference with the thermally conductive filler can be appropriately achieved.

[0100] In the technology disclosed herein, for the high refractive index monomer A that can be appropriately used, the refractive index of its homopolymer (high refractive index polymer) is preferably 1.51 or more, more preferably 1.52 or more, further preferably 1.53 or more (for example, 1.54 or more), can be 1.55 or more, can be 1.56 or more, or can be 1.57 or more. When using a high refractive index monomer A with a high refractive index of a homopolymer (high refractive index polymer), it becomes easy to adjust the refractive index np of the resin over a wide range. The upper limit of the refractive index of the homopolymer (high refractive index polymer) of the high refractive index monomer A is not particularly limited. From the viewpoint of obtaining a balance with other characteristics, the refractive index of the homopolymer (high refractive index polymer) of the high refractive index monomer A is appropriate to be about 1.7 or less, preferably 1.65 or less, more preferably 1.63 or less, further preferably 1.61 or less, can be 1.60 or less, can be less than 1.60, can be 1.59 or less, or can be 1.58 or less.

[0101] In the technology disclosed herein, examples of suitably usable high-refractive-index monomers A include monomers containing at least one selected from a sulfur atom, a halogen atom (preferably a halogen atom other than fluorine, such as bromine or iodine), a phosphorus atom, and an aromatic ring. Using such high-refractive-index monomers A facilitates obtaining a base polymer having a relatively high refractive index. Among these, monomers containing aromatic rings are preferred.

[0102] Examples of monomers having an aromatic ring include styrene, styrene derivatives such as α-methylstyrene, benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenylphenol (meth)acrylate which may be ethoxylated, fluorene (meth)acrylates and other (meth)acrylates having an aromatic ring, and toluene derivatives such as vinyltoluene and α-vinyltoluene. Examples of monomers having an aromatic ring and containing a sulfur atom include phenyl vinyl sulfide. These monomers may be used alone or in combination of two or more.

[0103] From the viewpoint of being able to appropriately adjust the refractive index of base polymer, the ratio of high refractive index monomer A in the total monomer composition of the base polymer is preferably 50 wt % or more. The content of high refractive index monomer A in the monomer composition is more preferably 55 wt % or more, and may also be 60 wt % or more. In some embodiments, the ratio of high refractive index monomer A in the total monomer composition is preferably 70 wt % or more, and may be 80 wt % or more, may be 90 wt % or more, and may also be 99 wt % or more. From the aspect of easily obtaining a balance of other characteristics such as adhesion, the ratio of high refractive index monomer A in the total monomer composition may be 80 wt % or less, may be 75 wt % or less, may be 70 wt % or less, and may also be 65 wt % or less in some embodiments.

[0104] When the monomer component of the base polymer contains two or more high-refractive index monomers A, the content of the high-refractive index monomer A in the monomer component refers to the total amount of the two or more high-refractive index monomers A.

[0105] In the technology disclosed herein, the base polymer is preferably an acrylic polymer.

[0106] It should be noted that, in this specification, "acrylic polymer" refers to a polymer containing monomer units derived from (meth)acrylic monomers in the polymer structure, typically, it refers to a polymer containing monomer units derived from (meth)acrylic monomers in a ratio of more than 50% by weight. In addition, a (meth)acrylic monomer refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl" means a meaning including acryloyl and methacryloyl. Therefore, the concept of (meth)acrylic monomers mentioned here can include both monomers having acryloyl groups (acrylic monomers) and monomers having methacryloyl groups (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" means a meaning including acrylic acid and methacrylic acid, and "(meth)acrylate" means a meaning including acrylate and methacrylate.

[0107] The acrylic polymer may be a polymer containing monomer units composed of an acrylic monomer (hereinafter also referred to as an acrylic high-refractive-index monomer Aa) as the high-refractive-index monomer A. Examples of the acrylic high-refractive-index monomer Aa include (meth)acrylates having an aromatic ring, sulfur-containing (meth)acrylates, and halogenated (meth)acrylates. These may be used alone or in combination of two or more.

[0108] Among these, (meth)acrylates having an aromatic ring can be preferably used.

[0109] Non-limiting examples of (meth)acrylates having an aromatic ring include benzyl (meth)acrylate, naphthyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxybutyl (meth)acrylate, phenylphenol (meth)acrylate which may be ethoxylated, and fluorene (meth)acrylates. Among these, fluorene (meth)acrylates, phenylphenol (meth)acrylates, and benzyl (meth)acrylate are preferred, and fluorene acrylates, phenylphenol acrylate which may be ethoxylated (e.g., ethoxylated o-phenylphenol acrylate), and benzyl acrylate are more preferred.

[0110] Here, the fluorene-based (meth)acrylate is a compound (monomer) having a fluorene skeleton and a (meth)acryloyl group in the molecule. Suitable compounds include compounds having a structure in which a (meth)acryloyl group is bonded to the fluorene skeleton directly or via an oxyalkylene chain (monooxyalkylene chain or polyoxyalkylene chain). Among such fluorene-based (meth)acrylates, preferred are so-called multifunctional fluorene-based (meth)acrylates in which the number of (meth)acryloyl groups bonded to the fluorene skeleton (including via an oxyalkylene chain) is two or more. Specific examples of the fluorene-based (meth)acrylate include products such as "OGSOL EA-0200," "EA-0500," and "EA-1000" manufactured by Osaka Gas Chemicals Co., Ltd.

[0111] Preferred examples of sulfur-containing (meth)acrylates include 1,2-bis(meth)acryloylthioethane, 1,3-bis(meth)acryloylthiopropane, 1,4-bis(meth)acryloylthiobutane, 1,2-bis(meth)acryloylmethylthiobenzene, and 1,3-bis(meth)acryloylmethylthiobenzene.

[0112] Preferred examples of the halogenated (meth)acrylate include 6-(4,6-dibromo-2-isopropylphenoxy)-1-hexyl acrylate, 6-(4,6-dibromo-2-sec-butylphenoxy)-1-hexyl acrylate, 2,6-dibromo-4-nonylphenyl acrylate, and 2,6-dibromo-4-dodecylphenyl acrylate.

[0113] From the viewpoint of being able to appropriately adjust the refractive index of the base polymer, the proportion of the acrylic high refractive index monomer Aa in the total monomer component of the base polymer is preferably 50% by weight or more. The content of the acrylic high refractive index monomer Aa in the monomer component is more preferably 55% by weight or more, and can be 60% by weight or more. In some embodiments, the proportion of the acrylic high refractive index monomer Aa in the total monomer component is preferably 70% by weight or more, can be 80% by weight or more, can be 90% by weight or more, or can be 99% by weight or more. From the viewpoint of easily obtaining a balance between other properties such as adhesion, the proportion of the acrylic high refractive index monomer Aa in the total monomer component can be 80% by weight or less, can be 75% by weight or less, can be 70% by weight or less, or can be 65% by weight or less in some embodiments.

[0114] When the monomer components of the base polymer include two or more acrylic high-refractive-index monomers Aa, the content of the acrylic high-refractive-index monomer Aa in the monomer components refers to the total amount of the two or more acrylic high-refractive-index monomers Aa.

[0115] In some embodiments, the acrylic polymer may be a polymer containing monomer units derived from an alkyl (meth)acrylate. As the alkyl (meth)acrylate, preferably used are those having 1 to 20 carbon atoms (i.e., C 1-20 (meth)acrylate esters containing a linear or branched alkyl group. 1-20 In some embodiments, the proportion of alkyl esters may be, for example, 10% by weight or more, 20% by weight or more, or 30% by weight or more. 1-20 The ratio of the alkyl ester may be, for example, 50% by weight or less, 45% by weight or less, or 40% by weight or less.

[0116] As (meth)acrylic acid C 1-20 Non-limiting specific examples of the alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, (meth)acrylate ) nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, etc.

[0117] Among these, it is preferred to use at least (meth)acrylic acid C 1-18 Alkyl esters, more preferably at least (meth) acrylic acid C 1-14 In some embodiments, the acrylic polymer may contain a (meth) acrylic acid C 4-12 Alkyl ester (preferably acrylic acid C 4-10 Alkyl esters, such as acrylic acid C 6-10 As a monomer unit, at least one of (meth)acrylic acid C is used. For example, an acrylic polymer containing one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) is preferred, and an acrylic polymer containing at least 2-EHA is particularly preferred. 1-18Examples of the alkyl ester include methyl acrylate, methyl methacrylate (MMA), n-butyl methacrylate (BMA), 2-ethylhexyl methacrylate (2EHMA), and isostearyl acrylate (ISTA).

[0118] The monomer units constituting the acrylic polymer may contain, as needed, other monomers (hereinafter referred to as comonomers) other than the high-refractive-index monomer Aa and the (meth)acrylic-acid alkyl ester that are copolymerizable with the high-refractive-index monomer Aa or the (meth)acrylic-acid alkyl ester. Suitable comonomers include monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, amide groups, etc.). Monomers having polar groups can help introduce crosslinking points into the acrylic polymer or increase the cohesive force of the acrylic polymer. Comonomers may be used alone or in combination of two or more.

[0119] Specific non-limiting examples of the copolymerizable monomer include the following.

[0120] Carboxyl group-containing monomers: for example, acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid, etc.

[0121] Monomers containing anhydride groups: for example, maleic anhydride and itaconic anhydride.

[0122] Hydroxyl-containing monomers: for example, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate.

[0123] Monomers containing sulfonic acid groups or phosphoric acid groups: for example, styrenesulfonic acid, allylsulfonic acid, sodium vinylsulfonate, 2-(meth)acrylamide-2-methylpropanesulfonic acid, (meth)acrylamidepropanesulfonic acid, sulfopropyl (meth)acrylate, (meth)acryloyloxynaphthalenesulfonic acid, 2-hydroxyethylacryloyl phosphate, etc.

[0124] Epoxy group-containing monomers: for example, epoxy group-containing acrylates such as glycidyl (meth)acrylate and 2-ethyl glycidyl (meth)acrylate, allyl glycidyl ether, and glycidyl (meth)acrylate.

[0125] Monomers containing cyano groups: such as acrylonitrile, methacrylonitrile, etc.

[0126] Isocyanate group-containing monomers: for example, 2-isocyanatoethyl (meth)acrylate, etc.

[0127] Amide group-containing monomers: for example, (meth)acrylamide; N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di(n-butyl) (meth)acrylamide, N,N-di(tert-butyl) (meth)acrylamide and other N,N-dialkyl (meth)acrylamide; N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N-n-butyl (meth)acrylamide and other N-alkyl (meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinyl acetamide; monomers having hydroxyl groups and amide groups, for example, N-(2-hydroxyethyl) (meth)acrylamide; N-hydroxyalkyl(meth)acrylamide, such as N-(2-hydroxypropyl)(meth)acrylamide, N-(1-hydroxypropyl)(meth)acrylamide, N-(3-hydroxypropyl)(meth)acrylamide, N-(2-hydroxybutyl)(meth)acrylamide, N-(3-hydroxybutyl)(meth)acrylamide, and N-(4-hydroxybutyl)(meth)acrylamide; monomers having an alkoxy group and an amide group, such as N-alkoxyalkyl(meth)acrylamide, such as N-methoxymethyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, and N-butoxymethyl(meth)acrylamide; and N,N-dimethylaminopropyl(meth)acrylamide, N-(meth)acryloylmorpholine, and the like.

[0128] Monomers having a nitrogen atom-containing ring: for example, N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, N-vinylpyridazine, etc. (for example, lactams such as N-vinyl-2-caprolactam).

[0129] Monomers having a succinimide skeleton include, for example, N-(meth)acryloyloxymethylenesuccinimide, N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, and N-(meth)acryloyl-8-oxyhexamethylenesuccinimide.

[0130] Maleimides: for example, N-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, N-phenylmaleimide, etc.

[0131] Itaconimides: for example, N-methyl itaconimide, N-ethyl itaconimide, N-butyl itaconimide, N-octyl itaconimide, N-2-ethylhexyl itaconimide, N-cyclohexyl itaconimide, N-lauryl itaconimide, etc.

[0132] Aminoalkyl (meth)acrylates: for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and tert-butylaminoethyl (meth)acrylate.

[0133] Alkoxy-containing monomers: for example, alkoxyalkyl (meth)acrylates such as 2-methoxyethyl (meth)acrylate, 3-methoxypropyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, butoxyethyl (meth)acrylate, and ethoxypropyl (meth)acrylate; and alkoxyalkylene (meth)acrylates such as methoxyethylene glycol (meth)acrylate and methoxypolypropylene glycol (meth)acrylate.

[0134] Vinyl esters: such as vinyl acetate, vinyl propionate, etc.

[0135] Vinyl ethers: vinyl alkyl ethers such as methyl vinyl ether and ethyl vinyl ether.

[0136] Aromatic vinyl compounds: for example, styrene, α-methylstyrene, vinyltoluene, etc.

[0137] Olefins: such as ethylene, butadiene, isoprene, isobutylene, etc.

[0138] (Meth)acrylates having an alicyclic hydrocarbon group: for example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, and the like.

[0139] (Meth)acrylates having an aromatic hydrocarbon group: for example, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, and the like.

[0140] In addition, (meth)acrylates containing heterocycles such as tetrahydrofurfuryl (meth)acrylate, (meth)acrylates containing halogen atoms such as (meth)acrylates containing vinyl chloride or fluorine atoms, (meth)acrylates containing silicon atoms such as silicone (meth)acrylates, and (meth)acrylates derived from terpene compound derivative alcohols.

[0141] In some embodiments, the copolymerizable monomer that can be preferably used includes at least one monomer selected from the group consisting of N-vinyl cyclic amide represented by the following general formula (M1) and hydroxyl-containing monomers (monomers having a hydroxyl group and other functional groups, for example, monomers containing a hydroxyl group and an amide group).

[0142]

[0143] Here, R in the above general formula (M1) 1 It is a divalent organic group.

[0144] Specific examples of N-vinyl cyclic amides include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, and N-vinyl-3,5-morpholinedione. N-vinyl-2-pyrrolidone and N-vinyl-2-caprolactam are particularly preferred.

[0145] Specific examples of hydroxyl-containing monomers include 2-hydroxyethyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and N-(2-hydroxyethyl) (meth)acrylamide. Preferred examples include 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4HBA), and N-(2-hydroxyethyl)acrylamide (HEAA).

[0146] When using the above-mentioned comonomer, its amount is not particularly limited, and is generally appropriate to be 0.01% by weight or more of the total monomer composition. From the perspective of better utilizing the effects brought about by the use of the comonomer, the amount of the comonomer can be set to 0.1% by weight or more of the total monomer composition, or it can be set to 1% by weight or more. In addition, the amount of the comonomer can be set to 50% by weight or less of the total monomer composition, preferably 40% by weight or less. This can improve the unevenness tracking performance.

[0147] The method for obtaining the acrylic polymer is not particularly limited, and various polymerization methods known as methods for synthesizing acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. Among several embodiments, solution polymerization or photopolymerization can be preferably employed.

[0148] The initiator used for polymerization can be appropriately selected from conventionally known thermal polymerization initiators, photopolymerization initiators, etc., depending on the polymerization method.

[0149] Examples of thermal polymerization initiators include azo-based polymerization initiators, persulfates, peroxide-based polymerization initiators, and redox-based polymerization initiators. The amount of the thermal polymerization initiator used is not particularly limited, but can be, for example, within a range of 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, relative to 100 parts by weight of the monomer components used to prepare the acrylic polymer.

[0150] The photopolymerization initiator is not particularly limited, and examples thereof include benzoin ether-based photopolymerization initiators, acetophenone-based photopolymerization initiators, α-ketal-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, ketal-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. The amount of the photopolymerization initiator used is not particularly limited, and for example, the amount can be within a range of 0.01 to 5 parts by weight, preferably 0.05 to 3 parts by weight, relative to 100 parts by weight of the monomer components used to prepare the acrylic polymer.

[0151] In some embodiments, the acrylic polymer can be included in the resin composition for forming the resin layer in the form of a partial polymer (acrylic polymer syrup) obtained by irradiating a mixture of the above-mentioned monomer components with a polymerization initiator with ultraviolet light to polymerize a portion of the monomer components. The resin composition containing the acrylic polymer syrup can be applied to a specific object to be coated and irradiated with ultraviolet light to complete the polymerization. In other words, the acrylic polymer syrup can be considered as a precursor of the acrylic polymer. The resin layer disclosed herein can, for example, contain an acrylic polymer as a base polymer in the form of the acrylic polymer syrup, and can be formed using a resin composition containing an appropriate amount of a polyfunctional monomer described below, as needed.

[0152] (cross-linking agent)

[0153] The resin layer may be used as needed for purposes such as adjusting cohesive force. As the cross-linking agent, any cross-linking agent known in the art of resins containing adhesives may be used, and examples thereof include epoxy cross-linking agents, isocyanate cross-linking agents, silicone cross-linking agents, oxazoline cross-linking agents, aziridine cross-linking agents, silane cross-linking agents, alkyl etherified melamine cross-linking agents, and metal chelate cross-linking agents. Isocyanate cross-linking agents, epoxy cross-linking agents, and metal chelate cross-linking agents may be particularly suitably used. One cross-linking agent may be used alone or in combination of two or more.

[0154] The amount used when using a cross-linking agent is not particularly limited. For example, it can be set to an amount exceeding 0 parts by weight relative to 100 parts by weight of the base polymer. In addition, the amount of the cross-linking agent can be set to, for example, 0.01 parts by weight or more relative to 100 parts by weight of the base polymer, and is preferably set to 0.05 parts by weight or more. By increasing the amount of the cross-linking agent, there is a tendency to obtain higher cohesion. In some embodiments, the amount of the cross-linking agent can be 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more relative to 100 parts by weight of the base polymer. On the other hand, from the viewpoint of avoiding the reduction of the concave-convex followability caused by excessive increase in cohesion, it is appropriate that the amount of the cross-linking agent is generally set to 15 parts by weight or less relative to 100 parts by weight of the base polymer, or it can be set to 10 parts by weight or less, or it can be set to 5 parts by weight or less. The technology disclosed herein can also be appropriately implemented without using a cross-linking agent.

[0155] In order to more effectively carry out any of the above-mentioned cross-linking reactions, a cross-linking catalyst may also be used. As the cross-linking catalyst, for example, a tin catalyst (particularly dioctyltin dilaurate) may be preferably used. The amount of the cross-linking catalyst used is not particularly limited, and for example, it may be approximately 0.0001 to 1 part by weight relative to 100 parts by weight of the base polymer.

[0156] The resin layer may contain a multifunctional monomer as needed. A multifunctional monomer may be used in place of or in combination with the crosslinking agent described above, thereby contributing to purposes such as adjusting cohesive strength. For example, a multifunctional monomer may be preferably used in a resin layer formed from a photocurable adhesive composition.

[0157] Examples of the polyfunctional monomer include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butanediol(meth)acrylate, and hexanediol di(meth)acrylate. Among them, trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate can be preferably used. The polyfunctional monomers can be used alone or in combination of two or more.

[0158] The amount of the multifunctional monomer used varies depending on its molecular weight, the number of functional groups, etc., but it is generally appropriate to set it in the range of about 0.01 to 3.0 parts by weight relative to 100 parts by weight of the base polymer. In some embodiments, the amount of the multifunctional monomer used can be, for example, 0.02 parts by weight or more, or 0.03 parts by weight or more relative to 100 parts by weight of the base polymer. By increasing the amount of the multifunctional monomer used, there is a tendency to obtain higher cohesion. On the other hand, from the viewpoint of avoiding the reduction of the concave-convex followability caused by excessive increase in cohesion, the amount of the multifunctional monomer used can be 2.0 parts by weight or less, or 1.0 parts by weight or less, or 0.5 parts by weight or less relative to 100 parts by weight of the base polymer.

[0159] (Tackifying resin)

[0160] The resin layer may contain a tackifying resin as needed. The tackifying resin is not particularly limited, and examples thereof include rosin-based tackifying resins, terpene-based tackifying resins, phenolic tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastic-based tackifying resins. The tackifying resins may be used alone or in combination of two or more.

[0161] As the tackifying resin, a tackifying resin having a softening point (softening temperature) of approximately 80°C or higher (preferably approximately 100°C or higher, for example, approximately 120°C or higher) can be preferably used. The upper limit of the softening point is not particularly limited, but can be, for example, approximately 200°C or lower (typically 180°C or lower). The softening point of the tackifying resin can be measured according to the softening point test method (ring and ball method) specified in JIS K2207.

[0162] When using tackifying resin, its content is not particularly limited, and can be set according to purpose, purposes in the mode of giving play to suitable adhesive properties.Tackifying resin can be, for example, more than 5 weight parts, or more than 10 weight parts relative to the content (comprising two or more tackifying resins) of base polymer 100 weight parts, or more than 10 weight parts.On the other hand, from the viewpoint improving concavo-convex followability, in some ways, it is appropriate that the content of tackifying resin is set to less than 100 weight parts relative to base polymer 100 weight parts, or less than 50 weight parts, or less than 25 weight parts.Or, it is also possible not to use tackifying resin.

[0163] (filler)

[0164] The resin layer disclosed herein contains a thermally conductive filler. Furthermore, the resin layer disclosed herein may contain fillers other than the thermally conductive filler, as long as the effects of the present invention are not significantly impaired. Below, fillers that can be used in the present invention are generally described, followed by a description of the thermally conductive fillers that can be used in the present invention.

[0165] The filler is not particularly limited, and for example, granular or fibrous fillers can be used. The filler can be used alone or in combination of two or more.

[0166] The constituent materials of the filler can be, for example, metals such as copper, silver, gold, platinum, nickel, aluminum, chromium, iron, stainless steel, etc.; metal oxides such as aluminum oxide, silicon oxide (typically silicon dioxide), titanium oxide, zirconium oxide, zinc oxide, tin oxide, tin oxide doped with antimonic acid, copper oxide, nickel oxide, etc.; aluminum hydroxide [Al2O3·3H2O or Al(OH)3], boehmite [Al2O3·H2O or AlOOH], magnesium hydroxide [MgO·H2O or Mg(OH)2], calcium hydroxide [CaO·H2O or Ca(OH)2], zinc hydroxide [Zn(OH)2], silicic acid [H4SiO4 or H2SiO3 or H2Si2O5], iron hydroxide [Fe2O3·H2O or 2FeO(OH)], copper hydroxide [Cu(OH)2], barium hydroxide [BaO·H2O or BaO·9H2O], zirconium oxide hydrate [ZrO·nH2O], tin oxide hydrate [ZrO·nH2O], Hydrated metal compounds such as SnO·H2O], basic magnesium carbonate [3MgCO3·Mg(OH)2·3H2O], hydrotalcite [6MgO·Al2O3·H2O], dawsonite [Na2CO3·Al2O3·nH2O], borax [Na2O·B2O5·5H2O], zinc borate [2ZnO·3B2O5·3.5H2O]; carbides such as silicon carbide, boron carbide, nitrogen carbide, and calcium carbide; aluminum nitride, nitride Nitrides such as silicon, boron nitride, and gallium nitride; carbonates such as calcium carbonate; titanates such as barium titanate and potassium titanate; carbon-based materials such as carbon black, carbon tubes (typically carbon nanotubes), carbon fibers, and diamonds; inorganic materials such as glass; polymers such as polystyrene, acrylic resins (e.g., polymethyl methacrylate), phenolic resins, benzoguanamine resins, urea resins, silicone resins, polyesters, polyurethanes, polyethylene, polypropylene, polyamides (e.g., nylon), polyimides, and polyvinylidene chloride. Alternatively, natural raw material particles such as volcanic white sand deposits, clay, and sand may be used. Furthermore, various synthetic fiber materials and natural fiber materials may be used as fibrous fillers.

[0167] From the perspective of not easily impairing the surface smoothness of the resin layer even when the content in the resin layer is relatively high, granular fillers are preferably used. The shape of the particles is not particularly limited and may be blocky, needle-shaped, plate-shaped, or layered. Blocky shapes may include, for example, spherical, rectangular, crushed, or irregular shapes thereof. The structure of the particles is not particularly limited and may, for example, be a dense structure, a porous structure, or a hollow structure.

[0168] When a photocurable (eg, ultraviolet curable) resin composition is used, it is preferred to use a filler composed of an inorganic material from the viewpoint of the photocurability (polymerization reactivity) of the resin composition.

[0169] In the technology disclosed herein, fillers composed of inorganic materials can be preferably used as thermally conductive fillers. Suitable examples of thermally conductive fillers include densely structured fillers composed of hydrated metal compounds, metal oxides, and metals. Resin layers containing thermally conductive fillers tend to have improved thermal conductivity.

[0170] In some embodiments, a thermally conductive filler composed of a hydrated metal compound may be preferably used. The above-mentioned hydrated metal compound generally has a decomposition starting temperature in the range of approximately 150 to 500°C and is of the general formula M x O y A compound represented by nH2O (M is a metal atom, x and y are integers greater than 1 determined by the valence of the metal, and n is the number of waters of crystallization contained) or a complex salt containing the above compound. A suitable example of a hydrated metal compound is aluminum hydroxide.

[0171] Hydrated metal compounds are commercially available. Examples of commercially available aluminum hydroxide include the trade name "Hydilite H-100-ME" (primary average particle size 75 μm) (manufactured by Showa Denko K.K.), the trade name "Hydilite H-10" (primary average particle size 55 μm) (manufactured by Showa Denko K.K.), the trade name "Hydilite H-32" (primary average particle size 8 μm) (manufactured by Showa Denko K.K.), the trade name "Hydilite H-31" (primary average particle size 20 μm) (manufactured by Showa Denko K.K.), the trade name "Hydilite H-42" (primary average particle size 1 μm) (manufactured by Showa Denko K.K.), and the trade name "B103ST" (primary average particle size 7 μm) (manufactured by Nippon Light Metal Co., Ltd.). Examples of commercially available magnesium hydroxide include "KISUMA 5A" (primary average particle size 1 μm) (manufactured by Kyowa Chemical Industry Co., Ltd.).

[0172] Examples of commercially available thermally conductive fillers other than hydrated metal compounds include boron nitrides such as "HP-40" (manufactured by Mizushima Iron & Steel Co., Ltd.) and "PT620" (manufactured by Momentive Corporation); aluminum oxides such as "AS-50" (manufactured by Showa Denko K.K.) and "AS-10" (manufactured by Showa Denko K.K.); and tin doped with antimonate such as "SN-100S" (manufactured by Ishihara Sangyo Co., Ltd.). For example, the product name is "SN-100P" (manufactured by Ishihara Sangyo Co., Ltd.), the product name is "SN-100D (water dispersion)" (manufactured by Ishihara Sangyo Co., Ltd.), etc.; for example, as titanium oxide, the product name is "TTO series" (manufactured by Ishihara Sangyo Co., Ltd.), etc. can be listed; for example, as zinc oxide, the product name is "ZnO-310" (manufactured by Sumitomo Osaka Cement Co., Ltd.), the product name is "ZnO-350" (manufactured by Sumitomo Osaka Cement Co., Ltd.), the product name is "ZnO-410" (manufactured by Sumitomo Osaka Cement Co., Ltd.), etc. can be listed.

[0173] In the technology disclosed herein, the difference between the refractive index nf of the thermally conductive filler contained in the resin layer and the refractive index np of the resin contained in the resin layer is 0.04 or less. By combining a resin layer containing a resin with such a small refractive index difference and a thermally conductive filler, a highly translucent thermally conductive sheet can be easily realized.

[0174] As long as the refractive index difference between the refractive index np of the resin and the refractive index nf of the thermally conductive filler satisfies the above relationship, there is no restriction on the size relationship. That is, in the technology disclosed herein, the value obtained by subtracting the refractive index nf of the thermally conductive filler from the refractive index np of the resin (np-nf) is within ±0.04. In some embodiments, np-nf is preferably greater than or equal to -0.02 and less than or equal to 0.04, can be greater than or equal to 0 and less than or equal to 0.03, or can be greater than or equal to 0 and less than or equal to 0.02. In addition, in other embodiments, np-nf can be greater than or equal to -0.04 and less than or equal to 0, can be greater than or equal to -0.04 and less than or equal to -0.01, or can be greater than or equal to -0.04 and less than or equal to -0.02. When the value obtained by subtracting the refractive index nf of the thermally conductive filler from the refractive index np of the resin is within the above range, it is easy to achieve a thermally conductive sheet with high light transmittance.

[0175] The refractive index nf of the thermally conductive filler is not particularly limited as long as it satisfies the aforementioned relationship with the refractive index np of the resin. In some embodiments, the refractive index nf of the thermally conductive filler is preferably 1.70 or less, more preferably 1.65 or less, and even more preferably 1.60 or less. The lower limit of the refractive index nf of the thermally conductive filler is not particularly limited; however, a value of 1.45 or greater is generally appropriate, preferably 1.50 or greater, and even more preferably 1.55 or greater.

[0176] The content of the thermally conductive filler in the resin layer is not particularly limited and can be set according to the desired thermal conductivity of the thermally conductive sheet, etc. The content of the thermally conductive filler can be 5 parts by weight or more, 10 parts by weight or more, or 33 parts by weight or more relative to 100 parts by weight of the resin contained in the resin layer. The content of the thermally conductive filler is preferably 50 parts by weight or more, more preferably 66 parts by weight or more, and even more preferably 100 parts by weight or more relative to 100 parts by weight of the resin. By increasing the content of the thermally conductive filler, there is a tendency for the thermal conductivity of the resin layer to be improved. In some embodiments, the content of the thermally conductive filler can be 120 parts by weight or more, 150 parts by weight or more, or 185 parts by weight or more relative to 100 parts by weight of the resin contained in the resin layer. In addition, from the perspective of suppressing the reduction in the light transmittance of the resin layer or preventing the reduction in the surface smoothness of the resin layer so as to easily obtain a good close adhesion with the component (such as an adherend), the content of the thermally conductive filler is generally appropriate to be 900 parts by weight or less relative to 100 parts by weight of the resin contained in the resin layer, preferably 400 parts by weight or less, more preferably 300 parts by weight or less or 250 parts by weight or less, and can be 200 parts by weight or less.

[0177] The average particle size of the thermally conductive filler is not particularly limited. It is appropriate that the above-mentioned average particle size is generally 100 μm or less, preferably 50 μm or less, and can be 20 μm or less. When the average particle size is small, there is a tendency for the surface smoothness of the resin layer to be improved and the adhesion to the component (such as the adherend) to be improved. In some embodiments, the average particle size of the thermally conductive filler can be 10 μm or less, 5 μm or less, or 3 μm or less. In addition, the average particle size of the filler can be, for example, 0.1 μm or more, 0.2 μm or more, or 0.5 μm or more. It is advantageous from the viewpoint of the handleability and dispersibility of the thermally conductive filler that the average particle size is not too small.

[0178] In some embodiments, the average particle size of the thermally conductive filler is preferably less than 0.5Ta relative to the thickness Ta of the resin layer. Here, the average particle size of the thermally conductive filler in this specification refers to the particle size (50% median particle size) at which the cumulative particle size on a weight basis is 50% in the particle size distribution obtained by measurement based on a sieving method unless otherwise specified. When the average particle size of the thermally conductive filler is less than 50% of the thickness Ta of the resin layer, it can be said that more than 50% by weight of the thermally conductive filler contained in the resin layer has a particle size smaller than the thickness Ta of the resin layer. By making more than 50% by weight of the filler contained in the resin layer have a particle size smaller than the thickness Ta of the resin layer, the surface of the resin layer (the adhesive surface when the resin is an adhesive) tends to maintain a good surface state (such as smoothness) more. This is preferred from the viewpoint of improved thermal conductivity due to improved adhesion to the contact body (for example, adherend).

[0179] The thermally conductive sheet disclosed herein can be preferably implemented in a manner such that, in the particle size distribution obtained by measurement based on the above-mentioned sieving method, 60% or more by weight of the thermally conductive filler contained in the resin layer has a particle size smaller than the thickness Ta of the resin layer (more preferably 0.7Ta, further preferably 0.5Ta). The proportion of particles in the thermally conductive filler having a particle size smaller than the thickness Ta of the resin layer (more preferably 0.7Ta, further preferably 0.5Ta) can be, for example, 70% or more by weight, 80% or more by weight, or 90% or more by weight. More preferably, substantially the entire amount of the thermally conductive filler contained in the resin layer has a particle size smaller than the thickness Ta of the resin layer (more preferably 0.7Ta, further preferably 0.5Ta). Here, substantially the entire amount typically refers to 99% or more by weight and 100% or less, for example, 99.5% or more by weight and 100% or less by weight.

[0180] (Dispersant)

[0181] The resin composition used to form the resin layer may contain a dispersant as needed to disperse the filler well in the resin composition. A resin composition in which the filler is well dispersed can form a resin layer having improved uniformity of thermal conductivity.

[0182] As the dispersant, a known surfactant can be used. The surfactant includes nonionic, anionic, cationic and amphoteric surfactants. The dispersant can be used alone or in combination of two or more.

[0183] As an example of a preferred dispersant, a phosphoric acid ester can be cited. For example, phosphoric acid monoesters, phosphoric acid diesters, phosphoric acid triesters, and mixtures thereof can be used. Specific examples of phosphoric acid esters include phosphoric acid monoesters of polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, or polyoxyethylene aryl ethers, phosphoric acid diesters of polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, or polyoxyethylene aryl ethers, phosphoric acid triesters of polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, or polyoxyethylene aryl ethers, and derivatives thereof. Suitable examples include phosphoric acid monoesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers, and phosphoric acid diesters of polyoxyethylene alkyl ethers or polyoxyethylene alkyl aryl ethers. The number of carbon atoms in the alkyl group of such a phosphoric acid ester is, for example, 6 to 20, preferably 8 to 20, more preferably 10 to 18, and typically 12 to 16.

[0184] As the phosphate ester, commercially available products can be used. Examples include "PLYSURF A212E," "PLYSURF A210G," "PLYSURF A212C," and "PLYSURF A215C" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; and "PHOSPHANOL RE610," "PHOSPHANOL RS710," and "PHOSPHANOL RS610" manufactured by Toho Chemical Co., Ltd.

[0185] The amount of the dispersant used can be set to, for example, 0.01 to 25 parts by weight relative to 100 parts by weight of the filler, and it is usually appropriate to set it to 0.1 to 25 parts by weight. From the viewpoint of preventing the coating property of the resin composition from being reduced and the smoothness of the surface from being reduced due to poor dispersion of the filler, the amount of the dispersant used relative to 100 parts by weight of the filler is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, further preferably 2 parts by weight or more, and can be set to 5 parts by weight or more. In addition, from the viewpoint of avoiding the reduction of performance such as adhesion caused by excessive use of the dispersant, the amount of the dispersant used relative to 100 parts by weight of the filler is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and can be set to 12 parts by weight or less or 10 parts by weight or less.

[0186] The amount of the dispersant used can be set to, for example, 0.01 to 25 parts by weight relative to 100 parts by weight of the thermally conductive filler, and it is usually appropriate to set it to 0.1 to 25 parts by weight. From the viewpoint of preventing the reduction in the coating properties of the resin composition and the reduction in the smoothness of the surface caused by poor dispersion of the thermally conductive filler, the amount of the dispersant used relative to 100 parts by weight of the thermally conductive filler is preferably 0.15 parts by weight or more, more preferably 0.3 parts by weight or more, further preferably 0.5 parts by weight or more, and can be set to 1 part by weight or more. In addition, from the viewpoint of avoiding the reduction in properties such as the adhesion of the resin caused by excessive use of the dispersant, the amount of the dispersant used relative to 100 parts by weight of the thermally conductive filler is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and can be set to 12 parts by weight or less or 10 parts by weight.

[0187] In addition, the resin layer in the technology disclosed herein may contain known additives that can be used in resins such as adhesives, such as leveling agents, plasticizers, softeners, colorants (dyes, pigments, etc.), antistatic agents, antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, as needed, within a range that does not significantly hinder the effects of the present invention.

[0188] (Formation of Resin Layer)

[0189] The resin layer contained in the thermally conductive sheet disclosed herein can be a cured layer of a resin composition. That is, the resin layer can be formed by imparting (e.g., applying) the resin composition to an appropriate surface and then appropriately performing a curing treatment. When two or more curing treatments (drying, crosslinking, polymerization, etc.) are performed, they can be performed simultaneously or in multiple stages. For a resin composition using a partial polymer of a monomer component (e.g., an acrylic polymer slurry), typically, as the above-mentioned curing treatment, a final copolymerization reaction is performed. That is, the partial polymer is provided for a further copolymerization reaction to form a complete polymer. For example, in the case of a photocurable resin composition, light irradiation is implemented. Curing treatments such as crosslinking and drying can be implemented as needed. For example, when it is necessary to dry the photocurable resin composition, light curing can be performed after drying. For a resin composition using a complete polymer, typically, as the above-mentioned curing treatment, drying (heat drying), crosslinking, etc. are implemented as needed.

[0190] The resin composition can be applied using a conventional coater such as a gravure coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, or a spray coater.

[0191] The thickness of the resin layer of the thermally conductive sheet disclosed herein is not particularly limited. From the perspective of improving thermal conductivity and light transmittance, the thickness of the resin layer is generally 600 μm or less, preferably 300 μm or less, more preferably 100 μm or less, and can be less than 100 μm, 80 μm or less, 70 μm or less, 60 μm or less, or 55 μm or less. From the perspective of improving the unevenness tracking property of the thermally conductive sheet (which can also be understood as unevenness absorption), in some embodiments, the thickness of the resin layer can be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more.

[0192] In some embodiments, the resin layer may be a resin layer formed from a solvent-free resin composition. Solvent-free herein refers to a resin composition having a solvent content of 5% by weight or less, typically 1% by weight or less. It should be noted that the solvent refers to a component that is not contained in the resin layer finally formed. Therefore, for example, unreacted monomers that may be contained in an acrylic polymer slurry are not included in the concept of the solvent. As a solvent-free resin composition, for example, a photocurable or hot-melt resin composition may be used. Among them, a resin layer formed from a photocurable (e.g., UV-curable) resin composition is preferred. The formation of a resin layer using a photocurable resin composition is mostly carried out by sandwiching the resin composition between two sheets and curing it by irradiating light in a state where the air is blocked.

[0193] <Purpose>

[0194] The thermally conductive sheet disclosed herein can be used to dissipate heat from components (e.g., adherends) that contact the sheet, or to transfer heat through the sheet. The excellent transparency of the thermally conductive sheet disclosed herein facilitates improved device construction precision. Therefore, the thermally conductive sheet disclosed herein is suitable for dissipating heat from components in precision equipment and small precision devices requiring high precision, or for transferring heat through the sheet.

[0195] Furthermore, when the thermally conductive sheet disclosed herein is configured as a thermally conductive adhesive sheet, the thermally conductive adhesive sheet has high transparency and adhesiveness, and is therefore suitable not only for heat dissipation from adherends and heat transfer via the thermally conductive sheet, but also for fixing, joining, and supporting components of precision equipment, etc.

[0196] Hereinafter, some examples related to the present invention will be described, but the present invention is not limited to the contents shown in the examples. It should be noted that "parts" and "%" in the following description are based on weight unless otherwise specified.

[0197] <Example 1>

[0198] (Preparation of resin composition)

[0199] 58 parts of fluorene acrylate (manufactured by Osaka Gas Chemicals Co., Ltd., trade name "OGSOL EA-0300") and 42 parts of phenylphenol acrylate (manufactured by Shin-Nakamura Chemical Industry, ethoxylated o-phenylphenol acrylate, trade name "A-LEN-10") as monomer components, 200 parts of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., trade name "Aluminum Hydroxide B103", average particle size 7 μm) as a thermally conductive filler, 1.25 parts of a filler dispersant, trade name "Plysurf A212E" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), 0.05 parts of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, trade name "Irgacure 184") as a photopolymerization initiator, and 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by BASF, trade name "Irgacure 651") 0.05 parts was added, and the mixture was stirred at 1000 rpm for 5 minutes to prepare resin composition C1.

[0200] (Formation of Resin Layer)

[0201] Two release liners, R1 and R2, were prepared, each having a polyester film with one side treated with a silicone release agent. Release liner R1 used "Diafoil MRF" (38 μm thick), manufactured by Mitsubishi Plastics Corporation. Release liner R2 used "Diafoil MRE" (38 μm thick), manufactured by Mitsubishi Plastics Corporation.

[0202] The resin composition C1 prepared above was applied to the release surface of the release liner R1 to form a coating layer with a thickness of 50 μm. Next, the surface of the coating layer was covered with a release liner R2 in such a manner that its release surface was the side of the coating layer, thereby isolating the coating layer from oxygen. The laminated sheet (having a laminated structure of release liner R1 / coating layer / release liner R2) was irradiated with an illumination of 3 mW / cm for 360 seconds using a chemical lamp manufactured by Toshiba Corporation. 2 The coating layer is cured by applying ultraviolet light to form a resin layer. A thermally conductive sheet comprising the resin layer is thus produced. The illuminance values ​​described above are measured using an industrial UV detector (manufactured by TOPCON CORPORATION, trade name "UVR-T1," light receiving unit model UD-T36) with a peak sensitivity wavelength of approximately 350 nm.

[0203] <Example 2>

[0204] A thermally conductive sheet of this example was produced in the same manner as in Example 1 except that the amount of aluminum hydroxide added was changed to 100 parts relative to 100 parts in total of the monomer components.

[0205] <Example 3>

[0206] A thermally conductive sheet of this example was prepared in the same manner as in Example 2 except that the blending amount of fluorene acrylate was changed to 17 parts and the blending amount of phenylphenol acrylate was changed to 83 parts.

[0207] <Example 4>

[0208] A thermally conductive sheet of this example was prepared in the same manner as in Example 2 except that the blending amount of fluorene acrylate was changed to 83 parts and the blending amount of phenylphenol acrylate was changed to 17 parts.

[0209] <Example 5>

[0210] As monomer components, 50 parts of 2-ethylhexyl acrylate (2EHA), 50 parts of benzyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #160"), 5 parts of N-vinyl-2-pyrrolidone (NVP), 2 parts of acrylic acid (AA), and 1 part of 4-hydroxybutyl acrylate (4HBA) were mixed. As photopolymerization initiators, 0.05 parts of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, trade name "Irgacure 184") and 0.05 parts of 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by BASF, trade name "Irgacure 651") were added, and the mixture was irradiated with ultraviolet light in a nitrogen atmosphere and polymerized until the viscosity (BH viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 10 Pa·s, thereby producing a partial polymer having a polymerization rate of 5%. To 70 parts of the prepared partial polymer, 30 parts of benzyl acrylate (trade name "Viscoat #160" manufactured by Osaka Organic Chemical Industry Co., Ltd.) was added as a diluting monomer to prepare acrylic polymer A5 in the form of acrylic polymer syrup.

[0211] To 100 parts of the acrylic polymer A5 (acrylic polymer syrup) prepared above, 0.08 parts of dipentaerythritol hexaacrylate (trade name "KAYARAD DPHA-40H", manufactured by Nippon Kayaku Co., Ltd.) as a multifunctional monomer, 1.25 parts of "Plysurf A212E" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a filler dispersant, and 200 parts of aluminum hydroxide (trade name "Aluminum Hydroxide B103", manufactured by Nippon Light Metal Co., Ltd., average particle size 7 μm) as a thermally conductive filler were added and uniformly mixed to prepare a resin composition C5.

[0212] A thermally conductive sheet of this example was prepared in the same manner as in Example 1, except that the resin composition C5 prepared above was used instead of the resin composition C1. It should be noted that the resin layer contained in the thermally conductive sheet of this example has adhesive properties; in other words, the thermally conductive sheet of this example is a double-sided adhesive sheet.

[0213] <Example 6>

[0214] A thermally conductive sheet of this example was produced in the same manner as in Example 1 except that aluminum hydroxide and a filler dispersant were not added.

[0215] <Example 7>

[0216] A thermally conductive sheet of this example was prepared in the same manner as in Example 5 except that 30 parts of 2-ethylhexyl acrylate (2EHA) was used as a diluting monomer instead of benzyl acrylate.

[0217] <Example 8>

[0218] 80 parts of 2-ethylhexyl acrylate (2EHA), 12 parts of 2-methoxyethyl acrylate (MEA), 7 parts of N-vinyl-2-pyrrolidone (NVP), and 1 part of N-(2-hydroxyethyl)acrylamide (HEAA) as monomer components, and 0.05 parts of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, trade name "Irgacure 184") and 0.05 parts of 2,2-dimethoxy-1,2-diphenylethane-1-one (manufactured by BASF, trade name "Irgacure 651") as photopolymerization initiators were blended, and the mixture was irradiated with ultraviolet light under a nitrogen atmosphere and polymerized until the viscosity (BH viscometer, No. 5 rotor, 10 rpm, measurement temperature 30°C) reached approximately 20 Pa·s. Acrylic polymer A8 was prepared in the form of a partially polymerized acrylic polymer syrup in which part of the above monomer components was polymerized.

[0219] To 100 parts of the acrylic polymer A8 (acrylic polymer syrup) prepared above, 0.05 parts of dipentaerythritol hexaacrylate (trade name "KAYARAD DPHA-40H", manufactured by Nippon Kayaku Co., Ltd.) as a multifunctional monomer, 0.9 parts of "Plysurf A212E" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a filler dispersant, and 100 parts of aluminum hydroxide (trade name "Aluminum Hydroxide B103", manufactured by Nippon Light Metal Co., Ltd., average particle size 7 μm) as a thermally conductive filler were added and uniformly mixed to prepare a resin composition C8.

[0220] A thermally conductive sheet of this example was produced in the same manner as in Example 1 except that the resin composition C8 prepared above was used instead of the resin composition C1.

[0221] <Example 9>

[0222] A thermally conductive sheet of this example was prepared in the same manner as in Example 8 except that the amount of aluminum hydroxide added was changed to 250 parts relative to 100 parts of the acrylic polymer.

[0223] <Refractive Index>

[0224] The refractive index of a resin obtained by curing a resin composition obtained by removing aluminum hydroxide as a thermally conductive filler from the resin composition used to prepare the thermally conductive sheet for each example, in the same manner as described above, was measured using a multi-wavelength Abbe refractometer (manufactured by ATAGO, model "DR-M2") at a wavelength of 589 nm and 23°C (the same conditions were used for the refractive index measurement of the thermally conductive filler below). The obtained values ​​are shown in the "Refractive Index np" column of Table 1. Furthermore, the refractive index of aluminum hydroxide as a thermally conductive filler used to prepare the thermally conductive sheet for each example was measured, and the obtained values ​​are shown in the "Refractive Index nf" column of Table 1. Furthermore, for each thermally conductive sheet for each example, the value obtained by subtracting the filler refractive index nf from the measured resin refractive index np was calculated, and the obtained value is shown in the "Refractive Index Difference np-nf" column of Table 1.

[0225] <Measurement of Transmittance>

[0226] The transmittance of the thermally conductive sheet for each example was determined using a high-speed integrating sphere spectroscopic transmittance meter (model "DOT-3") manufactured by Murakami Color Research Laboratory Co., Ltd. At a temperature of 23°C, light with a wavelength of 400 nm was perpendicularly irradiated onto one surface of the thermally conductive sheet and the intensity of the light transmitted through the other surface was measured. The obtained values ​​are shown in the "Transmittance" column in Table 1.

[0227] <Measurement of Thermal Conductivity>

[0228] For each thermally conductive sheet, Figure 5 The thermal conductivity in the thickness direction is measured using the thermal characteristic evaluation apparatus shown in (a) and (b). Figure 5 (a) is a front view of the thermal characteristics evaluation device. Figure 5 (b) is a schematic side view of the thermal characteristics evaluation device. It should be noted that the release liners R1 and R2 were removed during the measurement.

[0229] Specifically, a thermally conductive sheet S (20 mm long, 20 mm wide) is sandwiched between a pair of blocks (sometimes also referred to as "rods") L made of aluminum (A5052, thermal conductivity: 140 W / m·K) in the form of 20 mm cubes. The blocks L are then placed in close contact with the thermally conductive sheet S. The blocks L are then positioned one above the other between a heating element (heater block) H and a heat sink (a cooling substrate with cooling water circulating inside) C. Specifically, the heating element H is positioned above the upper block L, and the heat sink C is positioned below the lower block L.

[0230] At this time, a pair of blocks L that are in close contact with the thermally conductive sheet S are located between a pair of pressure adjustment screws J that pass through the heating element H and the heat sink C. It should be noted that the structure is as follows: a load sensor R is arranged between the pressure adjustment screws J and the heating element H, and the pressure when the pressure adjustment screws J are tightened can be measured. This pressure is used as the pressure applied to the thermally conductive sheet S. Specifically, in this test, the pressure applied to the thermally conductive sheet S is set to 25N / cm 2 (250kPa) to tighten the pressure adjustment screw J.

[0231] Furthermore, three probes P (1 mm in diameter) of a contact displacement meter were installed from the heat sink C side, penetrating the lower block L and the thermally conductive sheet S. The upper ends of the probes P were in contact with the lower surface of the upper block L, enabling the measurement of the gap between the upper and lower blocks L (the thickness of the thermally conductive sheet S).

[0232] Temperature sensors D were attached to the heating element H and the upper and lower blocks L. Specifically, a temperature sensor D was attached to one location on the heating element H. In addition, temperature sensors D were attached to five locations on each block L at intervals of 5 mm in the vertical direction.

[0233] During measurement, the pressure adjusting screw J was first tightened to apply pressure to the thermally conductive sheet S, the temperature of the heating element H was set to 80° C., and cooling water at 20° C. was circulated through the radiator C.

[0234] After the temperatures of the heating element H and the upper and lower blocks L stabilize, the temperatures of the upper and lower blocks L are measured using temperature sensors D. The heat flux through the thermally conductive sheet S is calculated from the thermal conductivity (W / m·K) and temperature gradient of the upper and lower blocks L. Furthermore, the interface temperature between the upper and lower blocks L and the thermally conductive sheet S is calculated. This temperature is then used to calculate the thermal conductivity (W / m·K) under the aforementioned pressure using the following thermal conductivity equation (Fourier's law). The resulting values ​​are shown in the "Thermal Conductivity" column of Table 1.

[0235] Q=-λgradT

[0236] Among them, in the above formula,

[0237] Q: heat flux per unit area

[0238] gradT: temperature gradient

[0239] λ: thermal conductivity

[0240] [Table 1]

[0241] Table 1

[0242]

[0243] It was confirmed that the thermally conductive sheets of Examples 1 to 5, which contained aluminum hydroxide as a thermally conductive filler and had a value (np - nf) obtained by subtracting the refractive index nf of aluminum hydroxide from the refractive index np of the resin within ±0.04, had significantly higher thermal conductivity than the thermally conductive sheet of Example 6 and exhibited higher transmittance than the thermally conductive sheets of Examples 7 to 9.

[0244] While specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The claims encompass various modifications and variations of the specific examples described above.

Claims

1. A thermally conductive sheet comprising a resin layer containing a resin and a thermally conductive filler, The resin comprises an acrylic polymer as a base polymer, The acrylic polymer contains monomer units derived from an alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms. The ratio of the monomer unit derived from the alkyl (meth)acrylate having a linear or branched alkyl group having 1 to 20 carbon atoms in the total amount of the monomer components is 10% by weight or more and 50% by weight or less, The acrylic polymer is a polymer containing monomer components of monomer A. The monomer A is a monomer whose homopolymer is a high refractive index polymer of 1.50 or higher. The monomer A comprises at least one selected from the group consisting of fluorene (meth)acrylate, phenylphenol (meth)acrylate and benzyl (meth)acrylate, The proportion of the monomer A in the total amount of the monomer components is 50% by weight or more, The thermally conductive filler comprises a hydrated metal compound, The refractive index np of the resin and the refractive index nf of the thermally conductive filler satisfy the following relationship: -0.04≤(np-nf)≤0.

04.

2. The thermally conductive sheet according to claim 1, wherein The content of the thermally conductive filler is 50 parts by weight or more and 250 parts by weight or less based on 100 parts by weight of the resin.

3. The thermally conductive sheet according to claim 1 or 2, wherein The refractive index np of the resin is 1.49 or more and 1.65 or less.

4. The thermally conductive sheet according to claim 1 or 2, wherein The resin layer is a layer having adhesiveness.

5. The thermally conductive sheet according to claim 3, wherein The resin layer is a layer having adhesiveness.

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