Encapsulant sheet for self-luminous display or direct backlight, self-luminous display, and direct backlight

Abstract

The objective of the present invention is to provide an "encapsulant sheet for a self-luminous display or a direct backlight" provided with a preferred degree of moldability as an "encapsulant sheet for a self-luminous display or a direct backlight" and furthermore provided with a high degree of heat resistance that can withstand use even in particularly high-temperature environments.　Provided is an encapsulant sheet 1 for a self-luminous display or a direct backlight, said sheet comprising an olefin resin as a base resin, having a melting point between 45 °C and 60 °C inclusive, and containing in the resin component a crosslinking agent in a proportion between 0.1 mass% and 1.2 mass% inclusive.

Description

Encapsulant sheet for self-luminous display or direct backlight, self-luminous display, and direct backlight

[0001] The present invention relates to an encapsulant sheet for a self-luminous display or a direct backlight, a self-luminous display, and a direct backlight.

[0002] Development of self-luminous display devices, typified by micro LED televisions, is progressing as next-generation display devices. In these self-luminous display devices, an encapsulant sheet for protecting the light-emitting elements is laminated on the light-emitting surface of a surface light source device, such as an LED module, in which light-emitting elements, such as LED elements, are mounted on a wiring board (see Patent Document 1). In parallel with the development of these self-luminous display devices, development of encapsulant sheets that are highly suitable for use in self-luminous display devices or direct backlights is also progressing (see Patent Document 2).

[0003] Here, the "encapsulant sheet for self-luminous displays or direct backlights" disclosed in Patent Document 2 specifies the Vicat softening point of the base resin to a higher temperature range than conventional encapsulant sheets for electronic devices, and maintains the MFR of the same resin in a low MFR range that is the same as or lower than conventional encapsulant sheets. As a result, this encapsulant sheet is considered to be at a preferred level for self-luminous displays or direct backlights in terms of performance such as molding ability during heat press processing (ability to conform to unevenness on the mounting surface) and film thickness uniformity after heat press processing.

[0004] Here, the encapsulant sheet disclosed in Patent Document 2 uses a thermoplastic resin having excellent molding properties as a base resin, and therefore, in order to ensure the necessary heat resistance, a high-melting-point resin having a melting point of about 90°C is used as the base resin.

[0005] However, in some cases, a display device configured with a self-luminous display or a direct backlight is expected to reach a temperature of approximately 90°C inside the housing, for example, when used in a vehicle where the display is exposed to direct sunlight. This may be due to an increase in ambient temperature during use, as well as an increase in the amount of heat generated by the display itself due to increased brightness. In such cases, the "encapsulant sheet for a self-luminous display or a direct backlight" is required to have even higher heat resistance. However, a new problem has been recognized: encapsulant sheets using the above-mentioned thermoplastic resin as a base resin may have insufficient heat resistance, even if the base resin has a high melting point (approximately 90°C) as described above. Furthermore, when using a thermoplastic resin, it has been difficult to use a resin with a high melting point exceeding 90°C in order to maintain molding properties during hot press processing.

[0006] Therefore, in order to impart heat resistance to the "sealant sheet for a self-luminous display or a direct backlight" that can withstand the above-mentioned particularly high temperature environment, it is conceivable to make a so-called thermally crosslinked encapsulant sheet by incorporating a crosslinking agent into the encapsulant composition as a base resin in advance, and allowing crosslinking to proceed when the sheet is integrated into a self-luminous display or the like.

[0007] In this way, in the newly developed "thermally crosslinked encapsulant sheet for self-luminous displays or direct backlights," the progress of crosslinking during the modularization stage can impart high heat resistance to the final product, enabling it to withstand use in the above-mentioned harsh high-temperature environments. Furthermore, in such a "thermally crosslinked encapsulant sheet," a resin with a low melting point of about 50°C can be used as the base resin. This allows the encapsulant sheet to be formed while reliably suppressing the progress of crosslinking during the film formation stage, and also allows for an encapsulant sheet with excellent molding properties.

[0008] However, during the development of an encapsulant sheet for a self-luminous display or a direct backlight using a thermally crosslinkable resin with a low melting point (a melting point of about 50°C) as described above, the present inventors have come to recognize a new problem: among a group of encapsulant sheets manufactured using resins of the same type (e.g., low-density polyethylene resin) and melting point (e.g., 50°C) as base resins, some have heat resistance sufficient to withstand use in particularly high-temperature environments as described above, while others have insufficient heat resistance.

[0009] Furthermore, an encapsulant sheet for a self-luminous display or a direct backlight is required to have extremely high transparency in order to maintain a high level of image quality of the self-luminous display or the like.

[0010] On the other hand, in the case of a display device configured with a self-luminous display or a direct backlight, for example, when used in a vehicle exposed to direct sunlight, the ambient temperature rises during use, and the amount of heat generated by the display itself increases as the brightness increases, so that the temperature inside the housing is expected to reach approximately 90° C. In order to use the encapsulant sheet made of a thermoplastic resin disclosed in Patent Document 3 in such an environment, it may be possible to use a resin with an even higher melting point as the base resin.

[0011] However, such thermoplastic encapsulant sheets using a high-melting-point resin as a base resin have been recognized as having a new problem in terms of molding properties, such as the generation of fine bubbles at the interface between the encapsulant sheet and the electronic device when integrated into a self-luminous display or the like.

[0012] JP 2022-155737 A JP 2019-179913 A Japanese Patent No. 6760542 A

[0013] A first object of the present invention is to provide an encapsulant sheet for a self-luminous display or a direct backlight, which has a preferable level of molding property as an encapsulant sheet for a self-luminous display or a direct backlight, and which also has high heat resistance that can withstand use in a particularly high-temperature environment. A second object of the present invention is to provide an "encapsulant sheet for a self-luminous display or a direct backlight" which has high transparency and which also has high heat resistance that can withstand use in a particularly high-temperature environment and excellent molding property.

[0014] As a result of extensive research, the present inventors have discovered that the above-mentioned problem (first object) can be solved by using a low-melting-point thermocrosslinkable resin as the base resin for an "encapsulant sheet for a self-luminous display or direct backlight," and by limiting the base resin to one having a temperature difference between its extrapolated melting onset temperature and its melting point equal to or less than a predetermined value, thereby completing the present invention. The present inventors have discovered that the above-mentioned problem (second object) can be solved by using a thermocrosslinkable resin as the base resin for an "encapsulant sheet for a self-luminous display or direct backlight," and by limiting the α-olefin content of the base resin to within a specific range specific to the use of a "self-luminous display or direct backlight," thereby completing the present invention. Specifically, the present invention provides the following.

[0015] (1) An encapsulant sheet for a self-luminous display or a direct backlight, the encapsulant sheet having an olefin resin as a base resin, a melting point of 45°C or higher and 60°C or lower, and containing a crosslinking agent in an amount of 0.1% by mass or higher and 1.2% by mass or lower in the resin component.

[0016] (2) The encapsulant sheet according to (1), wherein the temperature difference between the extrapolated melting initiation temperature and the melting point is 17° C. or less. According to the encapsulant sheet of (2), it is possible to obtain an “encapsulant sheet for a self-luminous display or a direct backlight” that has molding properties and the like at a preferred level as an encapsulant sheet for a self-luminous display or a direct backlight, and also has high heat resistance that can withstand use in particularly high-temperature environments.

[0017] (3) The sealing material sheet according to (1), wherein the olefin-based resin has an α-olefin content of 9 mol % or more and 14 mol % or less.

[0018] According to the encapsulant sheet of (3), it is possible to obtain an “encapsulant sheet for a self-luminous display or a direct backlight” that has high transparency and also has high heat resistance and excellent molding properties that can withstand use in particularly high-temperature environments.

[0019] (4) Shear rate of 2.43 × 10 sec in all layers of the resin sheet measured at a temperature of 120 ° C. －１ The melt viscosity at ３ Pa・s or more 9.0×10 ３ The sealing material sheet according to (3), having a viscosity of Pa·s or less.

[0020] According to the encapsulant sheet of (4), it is possible to more reliably achieve both heat resistance and excellent molding properties at a higher level than in the encapsulant sheet of (3).

[0021] (5) A self-luminous display comprising the encapsulant sheet according to (2) or (3), a display surface panel, and a light-emitting module in which a plurality of light-emitting elements are mounted on a wiring board, wherein the encapsulant sheet covers the light-emitting elements and the wiring board and is laminated on the light-emitting module, and the display surface panel is laminated on the encapsulant sheet.

[0022] The self-luminous display element (5) can enjoy the advantageous effects of the "sealant sheet" (2) or (3) described above, maintaining a high level of image quality. Furthermore, by providing a high level of heat resistance that can withstand use in particularly high-temperature environments, it is possible to obtain a self-luminous display element that exhibits excellent durability in high-temperature environments.

[0023] (6) The self-luminous display according to (5), wherein the encapsulant sheet has a gel fraction of 50% or more and 90% or less.

[0024] According to the self-luminous display element (6), the above-mentioned advantageous effects of the self-luminous display element (5) can be enjoyed, and the high heat resistance that can withstand use in particularly high temperature environments can be more stably exhibited, thereby making it possible to obtain a self-luminous display element that exhibits excellent durability in high temperature environments.

[0025] (7) The self-luminous display body according to (5), wherein the light-emitting elements are LED elements, each of which has a width and depth of 300 μm or less, a height of 200 μm or less, and an arrangement interval between the LED elements of 0.03 mm or more and 100 mm or less.

[0026] The self-luminous display body of (7) is an embodiment in which the self-luminous display body of (5) is applied to various high-definition LED display devices, such as a "dot matrix display device" in which a large number of LED elements (LED chips) are directly mounted on a substrate using a chip-on-board method. This makes it possible to obtain a high-definition LED display device that enjoys the above-mentioned advantageous effects of the self-luminous display body of (5) and has high heat resistance that can withstand use in particularly high-temperature environments, thereby demonstrating excellent durability in high-temperature environments.

[0027] (8) The self-luminous display body according to (5), wherein the light-emitting elements are LED elements, the width and depth of each of the LED elements are 50 μm or less, the height is 10 μm or less, and the spacing between the LED elements is 0.005 mm or more and 5 mm or less.

[0028] The self-luminous display body of (8) is an embodiment in which the self-luminous display body of (5) is applied to various ultra-high definition LED display devices, such as "micro LED televisions," which are expected to be next-generation video display devices. This makes it possible to obtain an ultra-high definition LED display device that enjoys the above-mentioned advantageous effects of the self-luminous display body of (5) and has high heat resistance that can withstand use in particularly high-temperature environments, thereby demonstrating excellent durability in high-temperature environments.

[0029] (9) A direct backlight comprising: the encapsulant sheet according to (2) or (3); and a light-emitting module in which a plurality of light-emitting elements are mounted on a wiring board, wherein the encapsulant sheet covers the light-emitting elements and the wiring board and is laminated on the light-emitting module.

[0030] According to the direct-type backlight (9), the above-mentioned advantageous effects of the "sealant sheet" (2) or (3) can be enjoyed, and the image quality can be maintained at a high level. Furthermore, by providing a high level of heat resistance that can withstand use in particularly high-temperature environments, a direct-type backlight that exhibits excellent durability in high-temperature environments can be obtained.

[0031] (10) A liquid crystal display comprising the direct-type backlight according to (9), a diffusion plate, and a display surface panel, wherein the diffusion plate is laminated on the sealing material sheet constituting the direct-type backlight.

[0032] The liquid crystal display (10) is an embodiment of the present invention as a liquid crystal display using the direct-type backlight (9) as a surface light source device, which provides the above-mentioned effects of the direct-type backlight (9), maintains high image quality, and provides excellent durability in high-temperature environments.

[0033] According to the present invention, it is possible to obtain an "encapsulant sheet for a self-luminous display or direct-type backlight," a "self-luminous display," a "direct-type backlight," and a "liquid crystal display" that has a preferable level of molding property as an encapsulant sheet for a self-luminous display or direct-type backlight, and also has high heat resistance that can withstand use in particularly high-temperature environments. Furthermore, according to the present invention, it is possible to obtain an "encapsulant sheet for a self-luminous display or direct-type backlight," a "self-luminous display," a "direct-type backlight," and a "liquid crystal display" that has high transparency and combines high heat resistance that can withstand use in particularly high-temperature environments with excellent molding property.

[0034] 1 is a plan view and a partially enlarged plan view of an image display surface of a self-luminous display (micro LED display device) configured using the "encapsulant sheet for a self-luminous display or a direct-type backlight" of the present invention. FIG. 2 is a cross-sectional view showing a cross section of the A-A portion of FIG. 1. FIG. 3 is a perspective view of an LED element constituting the self-luminous display (micro LED display device) of FIG. 1. FIG. 4 is a perspective view schematically showing an example of the configuration of a display device (liquid crystal display) using a direct-type backlight configured using the "encapsulant sheet for a self-luminous display or a direct-type backlight" of the present invention. FIG. 5 is a partially enlarged cross-sectional view of the periphery of a mounting region of one LED element in a display device (liquid crystal display) using a direct-type backlight of the present invention. FIG. 6 is a graph showing the melting point and extrapolated melting onset temperature of the "encapsulant sheet for a self-luminous display or a direct-type backlight (Example 1)" of the present invention. FIG. 7 is a graph showing the melting point and extrapolated melting onset temperature of an encapsulant sheet (Comparative Example 2) that does not satisfy the requirements of the present invention.

[0035] <Self-luminous display body> In this specification, the term "self-luminous display body" refers to an information display device that includes a display surface panel and a surface light source device made of a light-emitting module in which a large number of tiny light-emitting elements (LED elements, etc.) are mounted on a wiring board, and that displays visual information such as characters, images, and videos, and that can display the various types of visual information on the display surface panel by selectively blinking the light-emitting elements (LED elements, etc.) using a light-emission control means. Specific examples of "self-luminous display bodies" include "dot matrix display devices" in which a large number of LED elements (LED chips) are directly mounted on a board using a chip-on-board method, and the above-mentioned "micro LED television."

[0036] Furthermore, in this specification, the term "micro LED display device" collectively refers to a self-luminous display device, such as a "dot matrix display device" or a "micro LED television," in which "micro-sized LED elements" or "ultra-small-sized LED elements" are arranged in a matrix of approximately 1000 x 1000 or more with a pitch of approximately 0.005 mm to 5 mm. In this specification, a "micro-sized LED element" refers to an LED element having a width (W) and depth (D) of more than 50 μm and less than 300 μm, and a height (H) of more than 10 μm and less than 200 μm. Similarly, a "ultra-small-sized LED element" refers to an LED element having the same size but a width (W) and depth (D) of less than 50 μm and a height (H) of less than 10 μm (see FIG. 3 ). Note that when an LED element includes an LED chip and a resin cover covering it, the size of the LED element refers to the overall size of the light-emitting element, including the resin cover.

[0037] Hereinafter, the present invention will be described in detail, taking as an example a preferred embodiment of the present invention an embodiment in which the "self-luminous display body" of the present invention is implemented as a "micro LED display device." However, the technical scope of the present invention is not limited to the embodiment as a "micro LED display device." The present invention is not limited to only "micro LED display devices," but is a technology that can be applied to all "self-luminous displays" as defined above.

[0038] Fig. 1 is a front view of a micro LED display device 100, which is an example of an embodiment of a self-luminous display of the present invention, and a partially enlarged view (100A) thereof. Fig. 2 is a cross-sectional view showing a cross section of part A-A in Fig. 1, and is a drawing provided for explaining the layer structure of the micro LED display device 100 shown in Fig. 1. As shown in Figs. 1 and 2, this micro LED display device 100 includes an LED module 30 that functions as a surface light source device by mounting a large number of LED elements 10 on a wiring substrate 20, and a display surface panel 2.

[0039] [LED Module] The LED module 30 is a light-emitting module in the micro LED display device 100. As shown in Fig. 2, in the LED module 30, the LED elements 10 are mounted on the wiring portion 22 of the wiring substrate 20 via a solder layer 23 in a conductive manner. In the LED module 30, the light emission of each LED element 10 is individually controlled by a light-emission control means (not shown) such as an IC chip substrate that is separately joined.

[0040] In the LED module 30, an encapsulant sheet 1 is laminated on the mounting surface of the LED elements 10 in a manner that covers the LED elements 10. In the micro LED display device 100, the "encapsulant sheet for a self-luminous display or a direct backlight" of the present invention is used as this encapsulant sheet 1. Details of the "encapsulant sheet for a self-luminous display or a direct backlight" of the present invention will be described separately later.

[0041] Furthermore, in the micro LED display device 100, a display surface panel 2 such as various optical films and transparent protective glass is further laminated on the outer surface side of the encapsulant sheet 1 (the display surface side of the micro LED display device 100).

[0042] (Wiring Board) The support substrate 21 constituting the wiring board 20 in the LED module 30 can be a hard glass epoxy substrate conventionally known as a substrate for electronic circuits. Alternatively, the wiring board 20 can be made flexible by using a flexible resin film such as polyethylene terephthalate, polyimide, or polyethylene naphthalate as the support substrate 21. In either case, the wiring portion 22 can be formed from a metal such as copper or any other conductive material.

[0043] (LED Element) The LED element 10 is a light-emitting element that utilizes light emission at a PN junction where a P-type semiconductor and an N-type semiconductor are joined. Proposed structures include a structure in which a P-type electrode and an N-type electrode are provided on the top and bottom surfaces of the element, and a structure in which both a P-type and an N-type electrode are provided on one side of the element. LED elements of either structure can be used as the light-emitting element of the micro LED display device 100. As an example, the LED element disclosed as a "chip-type electronic component" in Japanese Patent Application Laid-Open No. 2006-339551 can be preferably used in the "self-luminous display" of the present invention. The LED element disclosed in this document is said to have dimensions of approximately 25 μm x 15 μm x 2.5 μm (width x depth x height) (corresponding to the "ultra-small LED element" of the present invention).

[0044] The LED element 10 used in the LED module 30 includes at least an LED light-emitting chip 11. It may also include a resin cover 12 covering the LED chip 11. When the LED element 10 includes the resin cover 12, the resin cover 12 is made of an organic insulating material such as epoxy resin, silicone resin, or polyimide resin. Among these, epoxy resin is particularly preferred. The resin cover 12 formed from epoxy resin not only protects the LED chip 11 from physical impact but also suppresses total reflection of light into the semiconductor that constitutes the LED chip 11 due to the difference in refractive index between the semiconductor and air, thereby enhancing the luminous efficiency of the LED element 10. The "encapsulant sheet for a self-luminous display or direct backlight" (encapsulant sheet 1) of the present invention is formed from an olefin-based resin that has excellent adhesion to epoxy resin, as described below. Therefore, it can be particularly preferably used as an encapsulant sheet laminated to cover the light-emitting surface of the LED element 10 in a micro LED display device 100 configured using LED elements 10 that include resin covers 12 formed from epoxy resin.

[0045] In the LED module 30, "micro-sized LED elements" can be preferably used. In this case, the spacing between the "micro-sized LED elements" is preferably 0.03 mm or more and 100 mm or less. This mounting mode of the "micro-sized LED elements" is also the standard mounting mode of LED elements in "dot matrix display devices."

[0046] Furthermore, when "ultra-small LED elements" are used in the LED module 30, the spacing between the "ultra-small LED elements" is preferably 0.005 mm or more and 5 mm or less. This mounting mode of the "ultra-small LED elements" is also the standard mounting mode of LED elements in "micro LED televisions."

[0047] There are no particular limitations on the overall size of the LED module 30. However, a diagonal length of 50 inches to 200 inches is preferred from the standpoint of cost performance. However, a light-emitting surface of a micro LED display device (self-luminous display body) can also be configured by tiling a plurality of LED modules 30 in a matrix on the same plane. Such a display body formed by combining a plurality of LED modules by tiling is also naturally included in the technical scope of the present invention. For example, a large micro LED display device with a large screen diagonal length of 600 inches can be configured by joining 100 x 100 LED modules 30, each with a diagonal length of 6 inches, vertically and horizontally.

[0048] [Method for manufacturing self-luminous display] The micro LED display device 100, which is an example of an embodiment of the self-luminous display of the present invention, can be obtained by laminating an LED module 30 for the self-luminous display, an encapsulant sheet 1, and other optical components arranged as needed into a laminate, and then integrating this laminate by heat pressing, and then further laminating and integrating the display surface panel 2 onto this laminate by adhesive bonding or the like. Note that the "step of integrating the laminate by heat pressing" can be performed by various known methods, such as roll lamination or vacuum lamination.

[0049] In the above manufacturing method, the encapsulant sheet 1 is laminated in a manner that exhibits sufficient molding properties in the "step of integrating the laminated body by heat pressing" to adequately cover the LED elements, and at the same time, crosslinking of the uncrosslinked encapsulant sheet 1 is also sufficiently progressed in parallel with the heat pressing, thereby making the micro LED display device 100 a self-luminous display body with extremely high heat resistance. Note that a self-luminous display body can also be manufactured by a manufacturing method in which a "heating step (curing step) for sufficiently progressing crosslinking of the encapsulant sheet" is performed after the above heat pressing, as a separate step from the "step of integrating the laminated body by heat pressing".

[0050] In the method for manufacturing a self-luminous display body of the present invention, the heating conditions (heating time, heating temperature, etc.) in the above-mentioned heat pressing process or the above-mentioned heating step (curing step) are appropriately optimized so that the gel fraction of the encapsulant sheet 1 is 50% or more and 90% or less, preferably 60% or more and 80% or less.

[0051] <Direct-type backlight> In this specification, a "direct-type backlight" is a light source unit that can be used as a light source for a direct-type backlight type liquid crystal display, and is a surface light source device that illuminates a display surface panel such as a liquid crystal display panel from the back side of the liquid crystal display. A direct-type backlight type "liquid crystal display" includes a display surface panel such as a liquid crystal display panel and a backlight that illuminates the display surface panel from the back side (see Figure 4).

[0052] An example of the "direct type backlight" of the present invention is a direct type backlight 200 shown in Fig. 5. The direct type backlight 200 is a light-emitting module in which a plurality of LED elements 10 are mounted on a wiring board 20, and the "sealant sheet for a self-luminous display or a direct type backlight (sealant sheet 1)" of the present invention is laminated in a manner that covers the LED elements 10 and the wiring board 20. Furthermore, in the direct type backlight 200, an optical member such as a diffusion plate 3 may be further laminated on the LED elements 10 via the sealant sheet 1.

[0053] 5, in a wiring board 20 constituting a direct-type backlight 200, a wiring section 22 is typically formed on a support substrate 21 via an adhesive layer 24. An insulating protective film 25 is formed on the support substrate 21 and the wiring section 22, and a reflective layer 26 made of a white resin or the like is further laminated on the insulating protective film 25. Furthermore, the LED element 10, which is composed of the LED light-emitting chip 11 and the light-diffusing lens 13, is mounted on the wiring section 22 via a solder layer 23 in a conductive manner.

[0054] [Method for Manufacturing Direct-Type Backlight] The direct-type backlight 200, which is one embodiment of the direct-type backlight of the present invention, can also be manufactured by laminating each component, including the encapsulant sheet 1, into a laminate and integrating this laminate by hot pressing. If necessary, it is preferable to previously bond some of the laminated members with an adhesive before the above-mentioned hot pressing. By sufficiently promoting crosslinking of the encapsulant sheet 1 (uncrosslinked encapsulant sheet 1) during hot pressing, a direct-type backlight 200 having extremely high heat resistance can be obtained. The direct-type backlight 200 can also be manufactured by further providing a separate heating step (curing step) for crosslinking after hot pressing, thereby sufficiently promoting crosslinking of the encapsulant sheet 1.

[0055] [Liquid Crystal Display] An example of the "liquid crystal display" of the present invention is a liquid crystal display 300 shown in Fig. 4. The liquid crystal display 300 includes a display surface panel 2 such as a liquid crystal display panel, and a direct-type backlight 200 as a surface light source device that illuminates the display surface panel 2 from the back side, with a diffuser plate 3 disposed between the direct-type backlight 200 and the display surface panel 2. In the direct-type backlight 200, the "encapsulant sheet for a self-luminous display or a direct-type backlight (encapsulant sheet 1)" of the present invention is laminated in a manner that covers the LED elements 10 and the wiring board 20, and the diffuser plate 3 is laminated on the encapsulant sheet 1.

[0056] <First embodiment of encapsulant sheet for self-luminous display body or direct-type backlight> The "encapsulant sheet for self-luminous display body or direct-type backlight (hereinafter also simply referred to as "encapsulant sheet")" of the first embodiment of the present invention is a resin sheet that can be preferably used as an encapsulant sheet that covers and laminates a large number of tiny LED elements mounted as light-emitting elements in various "self-luminous display bodies" or "direct-type backlights" on a wiring board of a surface light source device such as an LED module or a direct-type backlight, in order to protect the LED elements from mainly physical impact.

[0057] The "encapsulant sheet" of the present invention can be particularly preferably used for a "micro LED display device" that uses "micro-sized LED elements" as light-emitting elements, among various "self-luminous display bodies" or "direct backlights." A high-definition "dot matrix display device" can be constructed by directly mounting "micro-sized LED elements" on a wiring board using a chip-on-board method, and the "encapsulant sheet" of the present invention can be particularly preferably used as an encapsulant sheet for this "dot matrix display device," among various "self-luminous display bodies."

[0058] Furthermore, the "encapsulant sheet" of the present invention can be preferably used in "micro LED display devices" that use, as light-emitting elements, "ultra-small LED elements" that are even smaller in size than the above-mentioned "micro-sized LED elements" among various "self-luminous display bodies" or "direct backlights." By mounting "ultra-small LED elements" on a wiring board, it is possible to configure "micro LED televisions," which are expected to become the mainstream of next-generation televisions, and the "encapsulant sheet" of the present invention can be preferably used as an encapsulant sheet for these "micro LED televisions" among various "self-luminous display bodies."

[0059] The "encapsulant sheet" of the present invention can be preferably used as an encapsulant sheet for covering and laminating a large number of minute (or extremely small) LED elements in various "micro LED display devices" or various "liquid crystal display devices" equipped with "direct backlights." Furthermore, the "encapsulant sheet" of the present invention can adequately protect the LED elements, while imparting to these "micro LED display devices" or "liquid crystal display devices" exceptional heat resistance that enables them to withstand usage conditions in which they are placed in harsh high-temperature environments of around 90°C, depending on the situation, such as when installed inside an automobile.

[0060] The "encapsulant sheet" of the present invention, which has the above-described advantages over conventional "encapsulant sheets for self-luminous displays or direct backlights," is a sheet-like member obtained by forming a film from an encapsulant composition (details of this "encapsulant composition" will be described separately below) containing an olefin-based resin as a base resin. This "encapsulant sheet" is a resin sheet in an uncrosslinked state having a gel fraction of 0% or more and 10% or less, more preferably 0%, after film formation and before integration (modularization) into a "self-luminous display" or the like, and before the sheet is a standalone product. In this specification, unless otherwise specified, the "encapsulant sheet" of the present invention refers to a resin sheet in an uncrosslinked state after film formation and before integration (modularization) into a self-luminous display.

[0061] However, the "encapsulant sheet" of the present invention is a thermally crosslinkable resin sheet that is expected to undergo crosslinking during any process performed after film formation until the sheet is integrated with other components such as an LED module to complete a self-luminous display or a direct-type backlight. For this reason, as will be described in detail later, the "encapsulant sheet" contains a predetermined amount of crosslinking agent, specifically, a ratio of 0.1% by mass to 1.2% by mass in the resin component. Details of the type and content of the crosslinking agent will be described separately later in the explanation of the encapsulant composition.

[0062] Furthermore, after crosslinking has progressed in the "encapsulant sheet" of the present invention at the stage of a finished product such as a self-luminous display device or a direct-type backlight, the gel fraction is preferably 50% or more and 90% or less, and more preferably 60% or more and 80% or less.

[0063] Here, the term "gel fraction (%)" in this specification refers to a value obtained by placing 1.0 g of an encapsulant sheet in a resin mesh, extracting it with xylene at 110°C for 12 hours, removing the sheet together with the resin mesh, drying it, and weighing it. The masses before and after extraction were compared to measure the proportion (mass %) of residual insoluble matter. A gel fraction of 0% means that the residual insoluble matter is essentially zero, and the crosslinking reaction has not substantially started. More specifically, a "gel fraction of 0%" means that the residual insoluble matter is completely absent, or that the mass % of the residual insoluble matter measured using a precision balance is less than 0.05 mass %. The residual insoluble matter does not include pigment components other than the resin component. If the residual insoluble matter is found to be mixed in the above test with other contaminants, for example, the content of these contaminants in the resin component can be separately measured in advance to calculate the "gel fraction (%)" that should be obtained for the residual insoluble matter derived from the resin component excluding these contaminants.

[0064] The "encapsulant sheet" of the present invention has a melting point of 45° C. or higher and 60° C. or lower, more preferably a melting point of 50° C. or higher and 55° C. or lower, and the temperature difference between the extrapolated melting onset temperature and the melting point is 11° C. or lower, more preferably 10° C. or lower. By optimizing the melting point range for the thermal properties of the encapsulant sheet and limiting the temperature difference of the encapsulant sheet to within the above-mentioned specific range, it is possible to stably impart to the encapsulant sheet both favorable properties such as molding properties required for a self-luminous display device and exceptional heat resistance at the stage of the finished product, which is a self-luminous display device or a direct-type backlight. Furthermore, as will be shown later in the Examples, the inventors' research has revealed that, for example, even if a thermally crosslinkable encapsulant sheet has a melting point of 45°C or higher, if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds 11°C, sufficient heat resistance may not necessarily be exhibited after crosslinking has progressed in the finished product, and that even if the melting points are about the same, if the temperature difference between the extrapolated melting onset temperature and the melting point exceeds a certain value, adverse effects will also be exerted on the molding properties.

[0065] Here, the melting point of the encapsulant sheet in this specification refers to the melting peak temperature measured by differential scanning calorimetry (DSC) after the completion of sheeting of the encapsulant sheet, which is obtained by forming an encapsulant composition containing a resin component and other additives into a sheet by a molding method such as extrusion melt molding, i.e., at a stage after film formation but before crosslinking. The extrapolated melting onset temperature of the encapsulant sheet refers to a value determined in accordance with the method described in JIS K 7121-1987 "Method for measuring transition temperatures of plastics." Specifically, the melting peak temperature of the encapsulant sheet at a stage after film formation but before crosslinking is determined by DSC, and the extrapolated melting onset temperature is the temperature at the intersection of a straight line extending the low-temperature baseline toward the high-temperature side and a tangent drawn at the point where the gradient is greatest on the curve on the low-temperature side of the melting peak (when two or more overlapping melting peaks appear, the melting peak with the lower melting peak temperature is used).

[0066] For example, the graph in Figure 6 shows the melting point and extrapolated melting onset temperature of the "sealant sheet for self-luminous display or direct backlight (Example 1)" of the present invention, and the melting point of this "sealant sheet" is 51.0°C, the extrapolated melting onset temperature is 41.7°C, and therefore the temperature difference between the extrapolated melting onset temperature and the melting point is 9.3°C.

[0067] The melt mass flow rate (MFR) of the "encapsulant sheet" is preferably 10.0 g / 10 min or more and 40.0 g / 10 min or less, more preferably 10.0 g / 10 min or more and 30.0 g / 10 min or less, and most preferably 10.0 g / 10 min or more and 25.0 g / 10 min or less. By setting the MFR of the "encapsulant sheet" to 10.0 g / 10 min or more, an encapsulant sheet with excellent molding properties can be obtained. Furthermore, by setting the MFR to 40.0 g / 10 min or less, the encapsulant sheet after crosslinking can maintain a high level of film thickness uniformity after hot press processing for integration into a self-luminous display device or the like.

[0068] In this specification, the "MFR" of an encapsulant sheet refers to a value measured at a stage after completion of sheet formation of an encapsulant sheet obtained by forming an encapsulant composition containing a resin component and other additives into a sheet by a molding method such as extrusion melt molding, i.e., an MFR in an uncrosslinked state after film formation, in accordance with JIS K 7210, under conditions of 190°C and a load of 2.16 kg. In addition, when the encapsulant sheet is a multilayer film, the MFR is measured by performing the above-mentioned measurement while the multilayer state in which all layers remain integrally laminated is taken as the MFR value of the multilayer encapsulant sheet.

[0069] When the "encapsulant sheet" is made into a multilayer film, it is more preferable that each layer has a different MFR within a range that satisfies the essential constituent requirements of the present invention, and in this case, it is preferable that the layer with the higher MFR is disposed on the outermost layer side as a skin layer. Even when the encapsulant sheet of the present invention is a single-layer encapsulant sheet, it has sufficiently preferable transparency and heat resistance, and appropriate flexibility. However, by disposing a layer with a relatively high MFR as the outermost layer in this manner, it is possible to further improve adhesion and molding properties as a thermally crosslinkable encapsulant sheet while maintaining the above-mentioned preferable transparency and heat resistance.

[0070] The thickness of the "encapsulant sheet" of the present invention may be 3 μm or more and 1000 μm or less, and preferably 3 μm or more and 600 μm or less. A thickness of 1000 μm or less allows the "encapsulant sheet" of the present invention to exhibit sufficient molding properties. Specifically, during hot press processing with the LED elements covered, the resin constituting the encapsulant sheet can sufficiently fit into the irregularities on the LED module surface, achieving good gap-free lamination. Therefore, for example, in the case where the LED elements are arranged so as to occupy half of the area of ​​the surface covered by the encapsulant sheet, the "encapsulant sheet" of the present invention can adequately protect the LED elements from impact after integration into a self-luminous display or a direct backlight by using an "encapsulant sheet" having a thickness of about half the height of the LED elements. On the other hand, the lower limit of the thickness of the "encapsulant sheet" is usually considered to be at least 3 μm or more in order to maintain the homogeneity of the film, but for example, if the LED element to be covered is a "very small-sized LED element" with a height of 6 μm or less, an extremely thin "encapsulant sheet" with a thickness of 3 μm can be used to cover it. However, if the LED element to be covered is a "micro-sized LED element" with a height of 10 μm or more, the thickness of the "encapsulant sheet" is preferably 5 μm or more.

[0071] The "encapsulant sheet" of the present invention may be a single-layer film, or may be a multilayer film composed of a core layer and skin layers disposed on both sides of the core layer. For example, in an encapsulant sheet that is a multilayer film composed of three or more layers, the thickness of the outermost layer is preferably 30 μm or more and 120 μm or less, and the thickness ratio of the intermediate layer composed of all layers other than the outermost layer to the outermost layer (outermost layer:intermediate layer:outermost layer) is preferably in the range of 1:3:1 to 1:8:1. This allows the encapsulant sheet as a whole to maintain favorable heat resistance while exhibiting favorable molding properties in the outermost layer.

[0072] Furthermore, the "encapsulant sheet" of the present invention can be formed into a "black encapsulant sheet" having a black color by using a resin composition containing a black colorant as the "encapsulant composition" and forming a film from it. For example, by using such a "black encapsulant sheet" in a self-luminous display body comprising a light-shielding layer, the "encapsulant sheet" of the present invention can enjoy the advantages brought about by the desirable qualities of high heat resistance and excellent molding properties, while improving contrast by reducing reflected light from the wiring board side and preventing the light of adjacent LED elements from mixing, thereby improving display quality. In addition, it can also simplify the layer structure of the self-luminous display body and contribute to improving productivity (see JP 2022-103204 A). Details of additives such as colorants used when the "encapsulant sheet" of the present invention is made into a "black encapsulant sheet" will be described separately below as an explanation of the encapsulant composition. In this specification, "black" refers to a color in which the CIE color coordinates measured in accordance with JIS Z8701-1999 using a C light source and a viewing angle of 2 degrees are -1.0≦a ＊ ≦2.5 and −1.0≦b ＊ ≦15.0, and L ＊ For the value, 0≦L ＊ This refers to a color tone in the range of ≦50.

[0073] Furthermore, the "encapsulant sheet" of the present invention can be formed into a "light-diffusing encapsulant sheet" that diffuses light emitted from an LED element by using a resin composition containing a light diffusing agent as the "encapsulant composition" and forming a film from the resin composition. When the "encapsulant sheet" has a multi-layer structure, the diffusing agent may be contained in only some of the layers. For example, by using such a "light-diffusing encapsulant sheet" in a direct backlight, the "encapsulant sheet" of the present invention can enjoy the advantages brought about by the desirable qualities of high heat resistance and excellent molding properties, while the distance between the wiring board and the LED element, which was previously ensured by a spacer, can be ensured by this "light-diffusing encapsulant sheet". This eliminates the need for a diffusion plate, making it possible to achieve a thinner direct backlight (see JP 2021-9807 A). Details of additives such as colorants used when the encapsulant sheet of the present invention is made into a "light-diffusing encapsulant sheet" will be described separately below in the description of the encapsulant composition.

[0074] [Encapsulant composition] The encapsulant composition (hereinafter also simply referred to as "encapsulant composition") used in producing the "encapsulant sheet" of the present invention is a thermally crosslinkable resin composition containing a low-density olefin-based resin (preferably a polyethylene-based resin) as a base resin and a crosslinking agent as an essential component. In this specification, the term "base resin" refers to the resin with the largest content ratio among the resin components of a resin composition containing the base resin. In addition, when a mixed resin is made of the same type of resin but with different densities (for example, multiple polyethylenes each with a different densities), the entire mixed resin is referred to as the base resin.

[0075] (Base Resin) The base resin of the "encapsulant composition" forming the "encapsulant sheet" of the present invention can be selected from a wide variety of olefin-based resins, as long as it has a melting point of 45° C. or higher and 60° C. or lower and the temperature difference between the extrapolated melting onset temperature and the melting point is in the range of 11° C. or lower. Among these, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various polyethylene-based resins can be preferably used.

[0076] Furthermore, among the various polyethylenes mentioned above, linear low-density polyethylene (LLDPE) has a narrow crystallinity distribution and uniform crystal size, so not only are there no large crystals, but the crystallinity itself is low, and when processed into a sheet shape as an encapsulant sheet, it has excellent transparency. Therefore, when an "encapsulant sheet" made from an "encapsulant composition" using this as a base resin is placed on the light-receiving surface side of a solar cell element in a self-luminous display, it can better prevent a decrease in power generation efficiency due to attenuation of light incident on the solar cell element.

[0077] The density of the olefin resin used as the base resin of the "encapsulant composition" is 0.875 g / cm ３ 0.900g / cm or more ３ Preferably, it is 0.880 g / cm or less. ３ 0.890g / cm or more ３ The density of the base resin of the encapsulant composition is more preferably 0.875 g / cm or less. ３ By setting the density to 0.900 g / cm or more, the heat resistance of the sealing material sheet can be stably improved to a sufficient level. ３ By setting the thickness to the following, the adhesion of the "encapsulant sheet" to the wiring board or the like can be maintained at a sufficiently preferable level.

[0078] Furthermore, the term "polyethylene resin" as used herein includes not only ordinary polyethylene obtained by polymerizing ethylene, but also resins obtained by polymerizing compounds having ethylenically unsaturated bonds such as α-olefins, resins obtained by copolymerizing a plurality of different compounds having ethylenically unsaturated bonds, and modified resins obtained by grafting other chemical species onto these resins.

[0079] Among these, a "silane copolymer obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer" can be preferably used as part of the base resin of the encapsulant composition. By using such a resin, sufficient adhesive strength can be obtained between the "encapsulant sheet" and other laminated members such as a glass protective substrate or a solar cell element.

[0080] The content of the ethylenically unsaturated silane compound in the copolymer of an α-olefin and an ethylenically unsaturated silane compound is, for example, preferably 0.001% by mass or more and 15% by mass or less, more preferably 0.01% by mass or more and 5% by mass or less, and most preferably 0.05% by mass or more and 2% by mass or less, based on the total mass of the copolymer.

[0081] (Crosslinking Agent) The crosslinking agent used in the "sealant composition" preferably has a one-hour half-life temperature of 120° C. or higher and 145° C. or lower. This allows the "sealant composition" according to the present invention to be a composition that can be melt-extruded at a temperature range of 110° C. or lower.

[0082] Specific examples of preferred crosslinking agents that satisfy the above conditions include peroxyketals such as n-butyl 4,4-di(t-butylperoxy)valerate, ethyl 3,3-di(t-butylperoxy)butyrate, and 2,2-di(t-butylperoxy)butane, and dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and 2,5-dimethyl-2,5-di(t-peroxy)hexyne-3, which can be preferably used as crosslinking agents to be added to the encapsulant composition.

[0083] The content of the crosslinking agent in the "encapsulant composition" may be from 0.2% by mass to 1.2% by mass, and more preferably from 0.4% by mass to 0.8% by mass, relative to the base resin in the "encapsulant composition." By setting the content of the crosslinking agent within the above range, the "encapsulant sheet" of the present invention can be provided with excellent heat resistance. As described above, the encapsulant sheet of the present invention is formed into a film without causing substantial crosslinking to proceed, and it is expected that the content of the crosslinking agent in the encapsulant sheet at the sheet stage after film formation will be in the range of from 0.1% by mass to 1.2% by mass.

[0084] (Crosslinking Aid) The "encapsulant composition" preferably contains a crosslinking aid that is a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group, more preferably a polyfunctional monomer in which the functional group is an allyl group, a (meth)acrylate group, or a vinyl group. This promotes an appropriate crosslinking reaction, thereby improving the heat resistance of the "encapsulant sheet" to a high level. In addition, this crosslinking aid reduces the crystallinity of the base resin, such as linear low-density polyethylene, that forms the encapsulant sheet, thereby maintaining transparency. This not only improves the heat resistance as described above, but also makes it possible to further improve the transparency of the "encapsulant sheet."

[0085] Specific examples of cross-linking aids that can be used in the "sealant composition" include polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, and diallyl maleate; poly(meth)acryloxy compounds such as trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA), ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and 1,9-nonanediol diacrylate; and epoxy compounds containing a double bond and an epoxy group, such as glycidyl methacrylate, 4-hydroxybutyl acrylate glycidyl ether, and 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and trimethylolpropane polyglycidyl ether, each of which contains two or more epoxy groups. These may be used alone or in combination of two or more. Among the above cross-linking aids, TAIC is particularly preferably used because it has good compatibility with linear low-density polyethylene, reduces crystallinity by cross-linking, maintains transparency, and is likely to exhibit a significant effect of imparting flexibility at low temperatures. The content of the cross-linking aid in the "encapsulant composition" is preferably 0.01% by mass or more and 3% by mass or less, and more preferably 0.05% by mass or more and 2.0% by mass or less, relative to the base resin in the "encapsulant composition".

[0086] [Other Additives] The "encapsulant composition" may further contain other components. For example, hindered amine light stabilizers (HALS), ultraviolet absorbers, heat stabilizers, adhesion improvers, nucleating agents, dispersants, leveling agents, plasticizers, antifoaming agents, flame retardants, and various other fillers may be added as appropriate. The content ratio of these additives varies depending on the particle shape, density, etc., but is preferably within the range of 0.001% by mass to 60% by mass of each additive in the "encapsulant composition." The inclusion of these additives can impart stable mechanical strength over a long period of time, as well as preventive effects against yellowing, cracking, and the like, to the "encapsulant composition."

[0087] (Black Colorant) When the "encapsulant sheet" of the present invention is a "black encapsulant sheet," the black colorant used to impart an appropriate color to the resin sheet is preferably a pigment-based material. For example, carbon black, which is commonly used as a black pigment, is one example of a preferred pigment. When coloring for display applications, black is often achieved by combining multiple dyes. In this case, however, uneven pressure during adhesive lamination can easily cause color unevenness. Furthermore, since dye-based materials are prone to dye degradation (fading), it is preferable to use a pigment-based material from the viewpoint of heat resistance. However, if it is necessary to reduce the transmittance of a specific wavelength in order to expand the color tone range, an appropriate amount of dye can also be used.

[0088] When carbon black is used as the black pigment, the content of carbon black in the resin component of the "black encapsulant sheet" may be adjusted appropriately within a range of 0.0001% by mass or more and 50% by mass or less depending on the thickness of the "black encapsulant sheet" and the required color. When the thickness of the "black encapsulant sheet" exceeds 500 μm, the required black color can be expressed by setting the content of carbon black to 0.0001% by mass or more. When the thickness of the "black encapsulant sheet" is 10 μm or less, the content of carbon black may be adjusted within a range of 10% by mass or more and 50% by mass or less. By setting the content of carbon black within the above range, stable coloring with sufficiently little unevenness can be achieved.

[0089] When the "encapsulant sheet" of the present invention is to be a "black encapsulant sheet," it is more preferable to add a dispersant to the "encapsulant composition." Various metal soaps can be used as the dispersant. Furthermore, in addition to metal soaps, a low content of polyethylene wax or the like can also be used as the dispersant. Specific examples of preferred dispersants include lithium stearate, magnesium stearate, calcium stearate, barium stearate, zinc stearate, calcium laurate, barium laurate, zinc laurate, calcium ricinoleate, barium ricinoleate, zinc ricinoleate, and zinc octoate. Among these, calcium stearate, zinc stearate, zinc laurate, and the like are preferred from the viewpoint of the melting point of the resin. In particular, calcium stearate, which is often contained in ordinary polyethylene-based resins, can be preferably used as the dispersant because it does not deteriorate compatibility.

[0090] Furthermore, when the "sealant sheet" of the present invention is intended to be a "black encapsulant sheet," the combination with an antioxidant is also important in order to promote good dispersion of the black pigment, and it is preferable to add a phenolic or phosphorus-based antioxidant to the resin component of the encapsulant composition in a proportion of 200 ppm or more and 800 ppm or less.

[0091] (Light Diffuser) The light diffuser used when the "encapsulant sheet" of the present invention is made into a "light-diffusing encapsulant sheet" is not particularly limited as long as it can diffuse light from an LED element, but it is preferable that the light diffuser has a refractive index of 1.4 or more and 2.2 or less. Such a refractive index can be measured by the Becke method, minimum deviation method, deviation analysis, mode line method, ellipsometry, Abbe method, etc. Furthermore, it is preferable that the refractive index of the light diffuser has a predetermined refractive index difference from the base resin constituting the "encapsulant sheet". Specifically, this refractive index difference is preferably 0.03 or more, more preferably 0.05 or more.

[0092] The light diffusing agent may be an organic material or an inorganic material. Specific examples of organic light diffusing agents include polymethyl methacrylate (PMMA) resin particles, melamine resin particles, silicone resin particles, styrene resin, polyurethane resin, polyester resin, fluorine-based resin, and synthetic resins such as copolymers thereof. These may be used alone or in combination of two or more. On the other hand, specific examples of inorganic light diffusing agents include TiO ２ , SiO ２ , Al ２ O ３ Examples of the inorganic fillers include silicon, zirconia, glass, smectite, kaolinite, etc. These may also be used alone or in combination of two or more.

[0093] From the viewpoint of dispersibility in the resin, the shape of the light diffusing agent is preferably particulate, and in this case, the average primary particle size (D50) of the light diffusing agent is preferably 0.1 μm or more and 50 μm or less, and more preferably 1 μm or more and 20 μm or less.

[0094] Furthermore, the content of the light diffusing agent in the "encapsulant composition" is preferably 0.1% by mass or more and 50% by mass or less. By setting the content of the light diffusing agent within this range, it is possible to reliably diffuse the light emitted from the LED element and also to prevent the light diffusing agent from becoming difficult to disperse and forming clumps. When the "encapsulant sheet" has a multilayer structure, the content of the light diffusing agent refers to the proportion of the light diffusing agent in the layer containing the light diffusing agent.

[0095] <Method for producing encapsulant sheet> The "encapsulant sheet" of the present invention can be produced by a method of melt-molding the "encapsulant composition" described in detail above. The melt-molding of the encapsulant composition can be carried out by known molding methods, specifically, various molding methods such as injection molding, extrusion molding, blow molding, compression molding, and rotational molding. The lower limit of the molding temperature during molding may be a temperature exceeding the melting point of the encapsulant composition. The upper limit of the molding temperature may be a temperature at which crosslinking does not start during film formation, depending on the one-minute half-life temperature of the crosslinking agent used, that is, a temperature at which the gel fraction of the encapsulant composition can be maintained at 10% or less, preferably 0%. Examples of the sealing material sheet according to the first embodiment

[0096] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0097] <Production of encapsulant sheet of first embodiment for self-luminous display> Each example and comparative example was produced using an encapsulant composition having the composition shown in Table 1 below. A linear low-density polyethylene resin (LLDPE) was used as the base resin, and Luperox TBEC (manufactured by Arkema Yoshitomi Co., Ltd.) was used as the crosslinking agent. The one-hour half-life temperature of this crosslinking agent is 121°C. Film formation was performed using a film forming machine equipped with a φ30 mm extruder and a 200 mm wide T-die, with an extrusion temperature of 90°C, a take-up speed of 1.1 m / min, and a film thickness of 450 μm in each case, to produce the encapsulant sheets of each example and comparative example.

[0098]

[0099] Evaluation Example 1: Heat Resistance A "heat creep test" was conducted to evaluate heat resistance using the method described below. In the "heat creep test," a 5 cm x 7.5 cm piece of the encapsulant sheet of each of the Examples and Comparative Examples was placed on a glass plate. A 5 cm x 7.5 cm glass plate was then placed on top of the sheet. A vacuum lamination process was then performed using a vacuum laminator for solar cell module manufacturing under conditions of a temperature of 150°C, a vacuuming time of 5 minutes, a press holding time of 10 minutes, and an upper chamber pressure of 50 KPa to prepare a "heat resistance evaluation sample." The large-sized glass was then placed vertically and left at 100°C for 168 hours. The distance (mm) traveled by the 5 cm x 7.5 cm glass plate after leaving the sheet was measured, and the heat resistance of the "encapsulant sheet" of the present invention was evaluated based on the following "evaluation criteria." The evaluation results are shown in Table 2. (Evaluation criteria) A: 0 mm or more and less than 0.5 mm B: 0.5 mm or more and less than 5 mm C: 5 mm or more

[0100] Evaluation Example 2: Molding Property As a test for evaluating heat resistance, a "molding test" was performed by the following method. In the "molding test," an LED module was first prepared in which micro-sized LED elements measuring 25 μm wide x 15 μm deep x 2.5 μm high were arranged at 2 mm pitches on the surface of a 200 × 300 mm glass epoxy wiring substrate. A 300 μm-thick encapsulant sheet of any of the Examples and Comparative Examples was laminated on the LED element-arranged surface of the module. A 50 μm-thick ethylene tetrafluoroethylene (ETFE) film that had been corona-treated on one side was then laminated on the encapsulant sheet as a surface protection film. A vacuum lamination process was then performed using a vacuum laminator for producing solar cell modules under conditions of a temperature of 150°C, a vacuuming time of 5 minutes, a press holding time of 10 minutes, and an upper chamber pressure of 50 KPa to produce a "molding property test module." Thereafter, each of the test modules was visually observed, and the molding properties of the "encapsulant sheet" of the present invention were evaluated based on the following "evaluation criteria." The evaluation results are shown in Table 2. (Evaluation criteria) A: The encapsulant sheet completely conformed to the irregularities of the LED element arrangement surface. No void formation was observed. B: 2 mm２ C: 2 mm or less. ２ More than three bubbles within the range were observed, or a part of the encapsulant sheet did not completely conform to the unevenness of the opposing LED element placement surface, resulting in the formation of a defective lamination part (void) near the LED element.

[0101] <Gel Fraction of Encapsulant Sheet> A 1.0 g test piece was taken as a sample from each of the encapsulant sheets constituting the above-mentioned "heat resistance evaluation sample," and the gel fraction of each encapsulant sheet was measured by the "gel fraction measurement method" described in detail above. The measurement results are shown in Table 2.

[0102] <Melting Point and Extrapolated Melting Onset Temperature of Encapsulant Sheet> The melting point and extrapolated melting onset temperature of each encapsulant sheet in an uncrosslinked state after film formation were measured by the measurement method described in detail above ("differential scanning calorimetry (DSC), measurement method based on JIS K 7121-1987"). The measurement results are shown in Table 2.

[0103]

[0104] From Table 2, it can be seen that the "encapsulant sheet" of the present invention is an "encapsulant sheet" that has sufficient molding properties for finely uneven surfaces and also has high heat resistance that can withstand use in particularly high-temperature environments.

[0105] <Second embodiment of encapsulant sheet for self-luminous display or direct backlight> The encapsulant sheet of the second embodiment is used in the same manner as the encapsulant sheet of the first embodiment described above, and the descriptions in paragraphs

[0056] to

[0063] of the encapsulant sheet of the first embodiment described above also apply to the encapsulant sheet of the second embodiment. The encapsulant sheet of the second embodiment differs from the encapsulant sheet of the first embodiment described above in the following respects. The "encapsulant sheet" of the second embodiment of the present invention has a melting point of 45°C or higher and 60°C or lower, more preferably a melting point of 50°C or higher and 55°C or lower. Since the "encapsulant sheet" of the present invention is made of a thermocrosslinkable resin, it can have sufficient heat resistance even when using such a low-melting-point resin with excellent molding properties. In this specification, the melting point of the encapsulant sheet refers to a melting peak temperature measured by differential scanning calorimetry (DSC) at a stage after the completion of sheet formation of the encapsulant sheet, which is obtained by forming an encapsulant composition containing a resin component and other additives into a sheet by a molding method such as extrusion melt molding, i.e., at a stage after film formation but before crosslinking.

[0106] Furthermore, the "encapsulant sheet" of the present invention has a shear rate of 2.43 × 10 sec in the entire resin sheet layer measured at a temperature of 120°C. －１ The melt viscosity at 2.0 × 10 ３ Pa・s or more 9.0×10 ３ It is preferable that the melt viscosity is 3.0×10 Pa s or less, and more preferably 3.0×10 ３ Pa・s or more 8.0×10 ３ Pa s or less, and even more preferably 3.0 × 10 ３ Pa・s or more 4.0×10 ３ Pa s or less, and most preferably 3.2 × 10 ３ Pa・s or more 3.4×10 ３ In this specification, the melt viscosity is measured by a method in accordance with JIS K7199.

[0107] The above "melt viscosity" is 2.0 x 10 ３By setting the viscosity at Pa·s or higher, in the production of an "encapsulant sheet" using a thermally crosslinkable resin, it is possible to effectively suppress resin extrusion due to excessive flow during heat pressing and the occurrence of poor light emission due to lateral stress on the LED elements, and furthermore, it is possible to effectively maintain the uniformity of the film thickness of the encapsulant sheet in which crosslinking has progressed after the heat pressing. In a self-luminous display such as the micro LED display device 100, the encapsulant sheet laminated on the light-emitting surface side of the LED elements requires particularly uniform film thickness. This is because even a slight difference in film thickness between the center and the edges of this encapsulant sheet will cause the encapsulant sheet to become lenticular, which will have an unintended and undesirable effect on the display quality of the micro LED display device.

[0108] On the other hand, assuming that a thermal crosslinkable resin is used as the base resin, the above "melt viscosity" is set to 9.0 × 10 ３ By making the viscosity of the encapsulating material sheet 4.0×10 Pa s or less, it is possible to achieve both high heat resistance and molding properties at a higher level during hot press processing of the encapsulating material sheet. ３ By limiting the viscosity to a low range of Pa·s or less, it is possible to further improve the molding properties while maintaining the heat resistance, and therefore it is possible to achieve both the heat resistance and molding properties at an extremely high level.

[0109] Measured at a temperature of 120°C, shear rate 2.43 x 10 sec －１The melt viscosity at a desired value can be obtained by, for example, selecting the polyolefin that is the base resin of the resin sheet or a material other than the base resin contained in the encapsulant composition. Considerations for selecting a polyolefin include, for example, the molecular structure, molecular weight, and density of the polyolefin. The "melt viscosity" value can be adjusted by, for example, the type and number of polymerizations of the olefin, the length of the linear chain portion, the number and length of branched portions, and the type, number, and length of side chain portions, as the molecular structure of the polyolefin. Specifically, increasing the length of the linear chain portion tends to decrease the "melt viscosity" value, while decreasing the length of the linear chain portion tends to increase the "melt viscosity" value. Increasing the number of branched portions tends to decrease the "melt viscosity" value, while decreasing the number of branched portions tends to increase the "melt viscosity" value. Introducing polar groups into the side chain portion tends to increase the "melt viscosity" value. Increasing the molecular weight of the polyolefin tends to increase the "melt viscosity" value, while decreasing the molecular weight of the polyolefin tends to decrease the "melt viscosity" value. Increasing the density of the polyolefin tends to increase the "melt viscosity" value, while decreasing the density of the polyolefin tends to decrease the "melt viscosity" value. Examples of adjustments using materials other than the base resin contained in the encapsulant composition include adding a resin with a "melt viscosity" different from that of the base resin, or adding an inorganic component such as a filler.

[0110] Conventionally, the MFR value, which has been widely adopted as an index of the fluidity of an encapsulant sheet, is measured at 190°C when measured in accordance with JIS K6922. However, this temperature is dissociated from the temperature at which an encapsulant sheet for a self-luminous display device actually melts during heat press processing. The reason for this is presumably that MFR is an evaluation of flowability under static load and is an index assuming a low viscosity liquid. As an index for controlling the fluidity of a resin during heat press processing, as described above, the shear modulus at a temperature of 120°C, i.e., a shear rate of 2.43 x 10 sec measured at a temperature of 120°C, is used. －１By using the melt viscosity at 1000 kJ / cm2 as an index for optimizing the physical properties of an encapsulant sheet for a self-luminous display, it is possible to obtain an index for more effective and precise resin selection that is more suited to the actual use of the encapsulant sheet.

[0111] The melt viscosity is a measurement of the viscosity when melted. The "encapsulant sheet" of the present invention is not subjected to heat-press processing at a temperature much higher than 120°C in order to avoid the progression of crosslinking during film formation, but is subjected to heat-press processing at a temperature close to 120°C. On the other hand, polyolefins have a certain viscosity at temperatures around 120°C. Since the "encapsulant sheet" of the present invention is required to fill the gaps between micro-sized LED elements, it is also important to pay attention to the viscosity of the encapsulant sheet.

[0112] Other than that, the MFR, thickness, layer structure, etc. of the sealing material sheet of the second embodiment are the same as those of the sealing material sheet of the above-mentioned first embodiment. That is, the matters described in paragraphs

[0067] to

[0073] of the sealing material sheet of the above-mentioned first embodiment also apply to the sealing material sheet of the second embodiment.

[0113] [Encapsulant composition] The encapsulant composition used in producing the encapsulant sheet of the second embodiment of the present invention (hereinafter also simply referred to as "encapsulant composition") is a thermally crosslinkable resin composition containing a low-density olefin-based resin (preferably a polyethylene-based resin) as a base resin and a crosslinking agent as an essential component. When the same type of resins but different densities (for example, multiple polyethylenes each having different densities) are used as a mixed resin, the entire mixed resin is used as the base resin. When the same type of resins but different densities (for example, multiple polyethylenes each having different densities) are used as a mixed resin, the entire mixed resin is used as the base resin.

[0114] (Base Resin) As the base resin of the encapsulant composition forming the encapsulant sheet of the present invention, various olefin-based resins having a melting point in the range of 45° C. to 60° C. can be preferably used. For example, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (M-LLDPE), and various other polyethylene-based resins can be selected.

[0115] Furthermore, among the above-mentioned olefin-based resins, a resin having an α-olefin content of 9 mol % or more and 14 mol % or less, more preferably 12 mol % or more and 13 mol % or less, can be preferably used as the base resin of the encapsulant composition that forms the encapsulant sheet of the present invention. The olefin-based resins containing an α-olefin include resins obtained by polymerizing an α-olefin, resins obtained by copolymerizing a plurality of different compounds having an α-olefin, and modified resins obtained by grafting another chemical species onto these resins. The content of the α-olefin can be measured, for example, by the following "method for measuring α-olefin content" ("method for measuring α-olefin content"). A sample (0.35 g) cut out from the encapsulant sheet to be measured is heated and dissolved in 2.0 ml of hexachlorobutadiene, and the resulting solution is filtered through a glass filter (G2). After adding 0.5 ml of deuterated benzene, the tube is charged with an NMR tube having an inner diameter of 10 mm, and 13C-NMR measurement (accumulation number of 8000 or more) is performed at 120°C using an NMR measurement device. From the obtained 13C-NMR spectrum, the content ratio of α-olefin units (α-olefin content (mol %)) in the base resin (polyethylene resin) of each of the encapsulant sheets is quantified.

[0116] The number of carbon atoms of the α-olefin contained in the olefin-based resin is preferably C4, C6, or C8. By optimizing the α-olefin content in the base resin of the encapsulant composition that forms the encapsulant sheet as described above, the transparency of the thermally crosslinkable encapsulant sheet can be maintained at a high level.

[0117] Furthermore, the various olefin-based resins used as the base resin of the encapsulant composition forming the encapsulant sheet of the present invention have a melting point range within the above range, and a shear rate of 2.43 × 10 sec measured at a temperature of 120°C. －１ The melt viscosity at 2.0 × 10 ３ Pa・s or more 9.0×10 ３ It is preferable to use a resin having a viscosity of Pa·s or less.

[0118] The matters described in paragraphs

[0076] to

[0080] regarding the base resin of the sealing material sheet of the first embodiment are also applicable to the base resin of the sealing material sheet of the second embodiment.

[0119] The crosslinking agent, crosslinking aid, and other additives used in the encapsulant composition of the encapsulant sheet of the second embodiment are the same as the crosslinking agent, crosslinking aid, and other additives used in the encapsulant composition of the encapsulant sheet of the first embodiment described above. The method for producing the encapsulant sheet of the second embodiment is also the same as the method for producing the encapsulant sheet of the first embodiment described above. That is, the matters described in paragraphs

[0081] to

[0095] of the encapsulant sheet of the first embodiment described above also apply to the encapsulant sheet of the second embodiment. Examples of the sealing material sheet according to the second embodiment

[0120] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0121] <Production of Second Embodiment of Encapsulant Sheet for Self-luminous Display> For each Example and Comparative Example, an encapsulant composition having the composition shown in Table 1 below was used for production. A linear low-density polyethylene resin (LLDPE) was used as the base resin (however, for each Example and Comparative Example, a resin with a different molecular weight was used as appropriate, as necessary), and "Luperox TBEC" (manufactured by Arkema Yoshitomi Co., Ltd.) was used as the crosslinking agent. The one-hour half-life temperature of this crosslinking agent is 121°C.

[0122] <α-olefin content of encapsulant sheet> For each of the encapsulant sheets of each Example and Comparative Example, the content of α-olefin units in the base resin (polyethylene resin) (α-olefin content (mol %)) was measured by the above-mentioned "method for measuring α-olefin content." The NMR measurement device used was a JNM GX-400 NMR measurement device manufactured by JEOL Ltd.

[0123]

[0124] <Evaluation Example 1: Heat Resistance> The test method and evaluation criteria for evaluating heat resistance were the same as those for the sealing material sheet of the first embodiment (paragraph

[0099] ). The evaluation results are shown in Table 4.

[0125] <Evaluation Example 2: Molding property> The test method and evaluation criteria for evaluating the molding property were the same as those of the sealing material sheet of the first embodiment (paragraph

[0100] ). The evaluation results are shown in Table 4.

[0126] <Evaluation Example 3: Transparency> Regarding transparency, the haze of the encapsulant sheets (formed to a thickness of 450 μm) of the examples and comparative examples was measured, and the transparency of the "encapsulant sheet" of the present invention was evaluated based on the following "evaluation criteria." In this evaluation example, the haze was measured in accordance with JIS K7136 using a haze meter HM150 manufactured by Murakami Color Research Laboratory Co., Ltd. The evaluation results are shown in Table 4. (Evaluation criteria) A: The haze of the encapsulant sheet is 4.5% or less. B: The haze of the encapsulant sheet is more than 4.5% and less than or equal to 10%. C: The haze of the encapsulant sheet is more than 10%.

[0127] <Gel Fraction of Sealant Sheet> The gel fraction of the sealant sheet was measured in the same manner as in the sealant sheet of the first embodiment (paragraph

[0101] ). The evaluation results are shown in Table 4.

[0128] <Melting Point of Encapsulant Sheet> The melting point of each encapsulant sheet in an uncrosslinked state after film formation was measured by “differential scanning calorimetry (DSC).” The measurement results are shown in Table 4.

[0129] <Melt viscosity of encapsulant sheet> The melt viscosity of each encapsulant sheet in an uncrosslinked state after film formation was measured at a shear rate of 2.43 × 10 sec. －１ The "melt viscosity at 120°C" was measured in accordance with JIS K7199 using a Capillograph 1-B manufactured by Toyo Seiki Seisakusho, with a set temperature of 120°C, D = 1 mm, and a capillary with L / D = 10. The measurement results are shown in Table 4.

[0130]

[0131] From Table 4, it can be seen that the "encapsulant sheet" of the present invention is an "encapsulant sheet" that has high transparency, sufficient molding properties for finely uneven surfaces, and high heat resistance that can withstand use in particularly high-temperature environments.

[0132] REFERENCE SIGNS LIST 1 Encapsulating material sheet 2 Display surface panel 3 Diffusion plate 10 LED element 11 LED light-emitting chip 12 Resin cover 13 Light diffusion lens 20 Wiring board 21 Support substrate 22 Wiring portion 23 Solder layer 24 Adhesive layer 25 Insulating protective film 26 Reflective layer 30 LED module 100, 100A, 100B Micro LED display device (self-luminous display) 200 Direct backlight 300 Liquid crystal display (direct backlight system)

Claims

1. An encapsulant sheet for a self-luminous display or a direct backlight, which uses an olefin resin as the base resin, has a melting point of 45°C or higher and 60°C or lower, and contains a crosslinking agent in an amount of 0.1% by mass or higher and 1.2% by mass or lower in the resin component.

2. The sealing material sheet according to claim 1, wherein the temperature difference between the extrapolated melting initiation temperature and the melting point is 17°C or less.

3. The sealing material sheet according to claim 1, wherein the olefin resin has an α-olefin content of 9 mol % or more and 14 mol % or less.

4. Shear rate of 2.43 x 10 sec in all layers of the resin sheet measured at a temperature of 120°C －１ The melt viscosity at ３ Pa・s or more 9.0×10 ３ The sealing material sheet according to claim 3 , having a viscosity of not more than Pa·s.

5. A self-luminous display comprising: an encapsulant sheet according to claim 2 or 3; a display surface panel; and a light-emitting module in which a plurality of light-emitting elements are mounted on a wiring board, wherein the encapsulant sheet covers the light-emitting elements and the wiring board and is laminated on the light-emitting module, and the display surface panel is laminated on the encapsulant sheet.

6. The self-luminous display according to claim 5, wherein the gel fraction of the sealing material sheet is 50% or more and 90% or less.

7. The self-luminous display body according to claim 5, wherein the light-emitting elements are LED elements, the width and depth of each of the LED elements are greater than 50 μm and not more than 300 μm, and the height is not more than 200 μm, and the arrangement interval between each of the LED elements is not less than 0.03 mm and not more than 100 mm.

8. The self-luminous display body according to claim 5, wherein the light-emitting elements are LED elements, the width and depth of each of the LED elements are 50 μm or less, and the height is 10 μm or less, and the arrangement interval between each of the LED elements is 0.005 mm or more and 5 mm or less.

9. A direct backlight comprising: the encapsulant sheet according to claim 2 or 3; and a light-emitting module in which a plurality of light-emitting elements are mounted on a wiring board, wherein the encapsulant sheet covers the light-emitting elements and the wiring board and is laminated on the light-emitting module.

10. A liquid crystal display comprising the direct-type backlight according to claim 9, a diffusion plate, and a display surface panel, wherein the diffusion plate is laminated on the sealing material sheet that constitutes the direct-type backlight.

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