Reflection sheet and liquid crystal display

Abstract

Provided is a reflection sheet which has voids, and which, when laminated, for example, in a state of being in contact with a member such as a light guide plate, can suppress damage to the member such as the light guide plate in contact with the reflection sheet even when subjected to an impact due to a drop, and can preferably suppress adhesion of debris to the member such as the light guide plate in contact with the reflection sheet, the debris being generated by the surface of the reflection sheet being scraped. The reflection sheet comprises a photocured layer (C) composed of a photocurable composition (c) on at least one side of a laminate [I] having a layer structure in which a resin layer (A) containing a thermoplastic resin (a1) as a main component resin, a resin layer (B) containing a thermoplastic resin (b1) as a main component resin and a fine powder filler (b2), and a resin layer (A) containing a thermoplastic resin (a1) as a main component resin are laminated in this order.

Description

Reflective sheets and liquid crystal displays

[0001] This invention relates to a reflective sheet and a liquid crystal display. More specifically, it relates to a reflective sheet that can be suitably used as a component of a liquid crystal display in a portable information processing terminal such as a smartphone or tablet, and to a liquid crystal display using the same.

[0002] Reflective sheets are used in many fields, including liquid crystal displays, lighting fixtures, and illuminated signs. Recently, with the increasing size and sophistication of display performance in the field of liquid crystal displays, there is a growing need to supply as much light as possible to the liquid crystal to improve the performance of the backlight unit. As a result, reflective sheets are required to have even better light reflectivity (also simply called "reflectivity").

[0003] Examples of this type of reflective sheet include reflective films for liquid crystal displays that use white polyester films mainly composed of aromatic polyester resins (see, for example, Patent Document 1). Also known are reflective sheets that produce light scattering reflection by creating fine voids within a film by stretching a film formed by adding a filler to polypropylene resin (see, for example, Patent Document 2), and polyolefin resin light reflectors with a laminated structure consisting of a layer containing polyolefin resin and a filler, and a layer containing polyolefin resin (see, for example, Patent Document 3). Reflective films using such polyolefin resins have the advantage of being less susceptible to deterioration and yellowing of the film due to ultraviolet light.

[0004] Furthermore, a biaxially oriented reflective sheet with reduced thermal shrinkage is known, comprising a polypropylene resin and at least one resin incompatible with the polypropylene resin (see, for example, Patent Document 4). This reflective sheet has the characteristic of exhibiting a higher reflectivity compared to conventional reflective sheets with similar basis weight and density, even without containing a large amount of inorganic powder.

[0005] In recent years, there has been a demand for further thinning of liquid crystal displays (LCDs), and this demand also applies to the backlights contained within them. When thinning the backlight, components such as the rear casing and light guide plate must also be thinned, similar to the reflective sheet mentioned above. However, thinning these components reduces the mechanical strength of the backlight, so if an external force is applied to the display body, for example, the light guide plate and reflective sheet may come into strong localized contact, causing uneven brightness and color (hereinafter collectively referred to as "brightness unevenness"). Therefore, backlights used in thinned liquid crystal displays require reflective sheets with additional brightness unevenness prevention functions.

[0006] To resolve this problem of uneven brightness, reflective sheets containing particles on the surface layer have been proposed (see, for example, Patent Documents 5 and 6). Furthermore, in the case of liquid crystal displays used in small portable information processing terminals such as smartphones and tablet devices, further thinning is required, and reflective sheets with a layer thickness of about 90 μm or less that can be mounted on such small portable information processing terminals are known (see, for example, Patent Document 7).

[0007] Japanese Patent Publication No. 04-239540, Japanese Patent Publication No. 11-174213, Japanese Patent Publication No. 2005-031653, Japanese Patent Publication No. 2008-158134, Japanese Patent Publication No. 2015-163986, Japanese Patent Publication No. 2015-001596, Japanese Patent Publication No. 2019-82550

[0008] In devices that are frequently carried around, such as smartphones and tablet computers, reflective sheets are often laminated in contact with a light guide plate. Impacts such as drops can cause friction between the reflective sheet and the light guide plate, potentially scratching the light guide plate or causing the surface of the reflective sheet to be scraped off and adhere to the light guide plate as debris. It has been confirmed that this can result in uneven brightness.

[0009] Therefore, the present invention aims to provide a reflective sheet that, for example, when laminated in contact with a member such as a light guide plate, can suppress damage to the member such as a light guide plate that is in contact with the reflective sheet even when subjected to impact such as dropping, and preferably further suppresses the surface of the reflective sheet from being scraped off and adhering to the member such as a light guide plate that is in contact with the reflective sheet as debris.

[0010] To solve these problems, the present invention proposes a reflective sheet and a liquid crystal display in the following embodiments.

[0011] [1] A first aspect of the present invention is a reflective sheet having voids, wherein at least one side of a laminate [I] having a layer structure in which a resin layer (A) containing a thermoplastic resin (a1) as the main component resin, a resin layer (B) containing a thermoplastic resin (b1) as the main component resin and a fine powder filler (b2) are laminated in this order, is provided with a photocured product layer (C) made of a photocurable composition (c).

[0012] [2] A second aspect of the present invention is a reflective sheet in which, in the first aspect, the photocurable composition (c) is a photocurable composition containing a (meth)acryloyl group-containing compound (c1). [3] A third aspect of the present invention is a reflective sheet in which, in the first or second aspect, the arithmetic mean roughness (Ra) of the reflective sheet surface on the photocured layer (C) side is 0.3 μm or less. [4] A fourth aspect of the present invention is a reflective sheet in which, in any one of the first to third aspects, the pencil hardness of the surface of the photocured layer (C) is B or higher. [5] A fifth aspect of the present invention is a reflective sheet in which, in any one of the first to fourth aspects, the pencil hardness of the surface of the photocured layer (C) is B or higher and F or lower. [6] A sixth aspect of the present invention is a reflective sheet in which, in any one of the first to fifth aspects, the thickness of the photocured layer (C) is 0.1 μm or more and 20 μm or less.

[0013] [7] A seventh aspect of the present invention is a reflective sheet in which the porosity of the entire reflective sheet is 10 to 80% in any one of the first to sixth aspects. [8] A eighth aspect of the present invention is a reflective sheet in which the fine powder filler (b2) is an inorganic fine powder in any one of the first to seventh aspects. [9] A ninth aspect of the present invention is a reflective sheet in which the fine powder filler (b2) is titanium oxide in any one of the first to eighth aspects.

[10] A tenth aspect of the present invention is a reflective sheet in which the content of the fine powder filler (b2) in the resin layer (B) is 30 to 80% by mass relative to the entire resin layer (B).

[0014]

[11] An eleventh aspect of the present invention is a reflective sheet in any one of the first to tenth aspects, wherein the resin layer (B) has voids and the resin layer (A) does not have voids.

[12] A twelfth aspect of the present invention is a reflective sheet in any one of the first to eleventh aspects, wherein the resin layer (B) of the laminate [I] has voids and the resin layer (A) does not have voids, and the photocured layer (C) is provided in contact with the resin layer (A) of the laminate [I].

[13] A thirteenth aspect of the present invention is a reflective sheet in any one of the first to twelfth aspects, wherein the thermoplastic resin (a1) is a polyolefin resin.

[14] A fourteenth aspect of the present invention is a reflective sheet in any one of the first to thirteenth aspects, wherein the thermoplastic resin (b1) is a polyolefin resin.

[15] A fifteenth aspect of the present invention is a reflective sheet having a thickness of 30 to 250 μm, in any one of the first to fourteenth aspects.

[16] A sixteenth aspect of the present invention is a reflective sheet having a thickness of 30 to 250 μm, in any one of the first to fifteenth aspects.

[0015]

[17] A seventeenth aspect of the present invention is a reflective sheet used as a component of a backlight unit in any one of the first to sixteenth aspects.

[18] A eighteenth aspect of the present invention is a reflective sheet used as a component of a liquid crystal display in any one of the first to sixteenth aspects.

[19] A ninth aspect of the present invention is a liquid crystal display having a reflective sheet according to any one of the first to eighteenth aspects as a component.

[0016] The reflective sheet proposed by the present invention can suppress damage to components such as light guide plates, even when subjected to impacts such as drops, when the reflective sheet is laminated in contact with such components. Furthermore, by specifying the composition of the photocured layer (C), it is possible to suppress the abrasion of the reflective sheet surface and the resulting residue adhering to components such as light guide plates that are in contact with the reflective sheet. In addition, the reflective sheet proposed by the present invention is compatible with thin backlights that can be mounted on small portable information processing terminals. Therefore, the reflective sheet proposed by the present invention can be suitably used as a reflective sheet for liquid crystal displays and the like in small portable information processing terminals.

[0017] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as appropriate without departing from the spirit of the invention.

[0018] <<Reflective Sheet of the Invention>> A reflective sheet according to an example of an embodiment of the present invention (referred to as "Reflective Sheet of the Invention") is a reflective sheet having voids, wherein at least one side of a laminate [I] has a layer structure in which a resin layer (A) containing a thermoplastic resin (a1) as the main component resin, a resin layer (B) containing a thermoplastic resin (b1) as the main component resin and a fine powder filler (b2), and a photocured product layer (C) made of a photocurable composition (c) is provided.

[0019] Here, we will explain the technical concept behind the design of the reflective sheet of the present invention. However, the present invention is not limited in any way to the scope of the following technical concept. Conventionally, as a measure to prevent brightness unevenness, a reflective sheet has been constructed in a laminated form and its surface layer has been made to contain particles (especially large-particle organic particles). This was done to form protrusions on the surface of the reflective sheet by containing particles on the surface layer. The presence of protrusions on the surface of the reflective sheet prevents strong localized contact between the reflective sheet and components such as light guide plates that come into contact with it, thereby suppressing brightness unevenness. However, although such reflective sheets are effective in resolving the problem of brightness unevenness, in the case of smartphones and tablet devices, friction between the reflective sheet and components such as light guide plates due to impact from drops during handling may cause scratches on the light guide plate, or powder and oil from the surface of the reflective sheet may adhere to components such as light guide plates that come into contact with the reflective sheet as residue, potentially causing brightness unevenness. It is believed that the abrasion of this powdery resin can occur due to vibrations during the transportation process of the backlight unit, during the assembly of the liquid crystal display, and during product handling after assembly. Therefore, the inventors have found that by providing a photocured layer (C) on at least one side of the laminate, preferably on at least one surface of the reflective sheet of the present invention, it is possible to suppress damage to components such as light guide plates that come into contact with the reflective sheet, even when subjected to impacts such as drops. Furthermore, they have found that by specifying the composition of the photocured layer (C) to a predetermined composition, it is possible to suppress the generation of abrasive debris from the surface of the reflective sheet.

[0020] <Layer structure of the reflective sheet of the present invention> The reflective sheet of the present invention only needs to have a photocured material layer (C) on at least one side of the laminate [I] having a layer structure in which resin layer (A), resin layer (B), and resin layer (A) are laminated in that order. Therefore, examples of the laminate structure of the reflective sheet of the present invention include resin layer (A) / resin layer (B) / resin layer (A) / photocured material layer (C), photocured material layer (C) / resin layer (A) / resin layer (B) / resin layer (A) / photocured material layer (C), etc. However, it is not limited to these.

[0021] In particular, a layer configuration of resin layer (A) / resin layer (B) / resin layer (A) / photocured material layer (C) is preferred. By laminating resin layer (A), resin layer (B), and resin layer (A) in this order, that is, by having a laminated configuration of resin layer (A) / resin layer (B) / resin layer (A), the functional separation of each layer becomes possible, and performance such as reflective performance, heat resistance, folding resistance, reduction of brightness unevenness, and reduction of particle detachment can be improved. For example, resin layer (B) can be mainly given the role of providing light reflectivity, and resin layer (A) can be given the role of reducing brightness unevenness in addition to heat resistance. Furthermore, photocured material layer (C) can be given the role of preventing scratches on the light guide plate due to friction with the light guide plate when the reflective sheet is incorporated into a backlight unit, or preventing the surface of the reflective sheet from being scraped off and adhering to the light guide plate as debris. In the reflective sheet of the present invention, it is preferable that the photocured material layer (C) is arranged as the outermost layer on at least one surface.

[0022] The reflective sheet of the present invention only needs to have a layer structure of resin layer (A) / resin layer (B) / resin layer (A) / photocured material layer (C), but may also have "other layers" other than these. For example, the "other layer" may be on the surface opposite to the photocured material layer (C), or an "other layer" such as an adhesive layer or a primer layer may be interposed between the resin layer (A) and the resin layer (B), or an "other layer" such as a back surface functional layer may be provided on the surface opposite to the photocured material layer (C). However, it is not limited to these.

[0023] <Form of Resin Layer (A) and Resin Layer (B)> There are no restrictions on the more specific shape or manufacturing method of both resin layer (A) and resin layer (B), as long as they are in the form of a film, i.e., a thin film. In particular, it is preferable that resin layer (A) and resin layer (B) are in the form of a film produced by an extrusion method. When each layer is in the form of a film, each layer may be an unstretched film, or a uniaxially or biaxially oriented film. In particular, it is preferable that the film is stretched by at least 1.1 times in the uniaxial direction, and especially that it is a biaxially oriented film. It is also possible to manufacture films corresponding to each layer in advance and then laminate them to form a laminated structure, but it is preferable to manufacture them by a co-extrusion method that allows the laminated structure to be formed in one step. It is even preferable to stretch the laminated structure after it has been formed by co-extrusion, as this will stretch all the layers.

[0024] <This Laminate> This laminate [I] has a layer structure in which resin layer (A), resin layer (B), and resin layer (A) are laminated together, and resin layer (A) and / or resin layer (B) have voids, preferably resin layer (B) has voids. However, it is preferable that resin layer (A) does not have voids from the viewpoint of providing rigidity and preventing oxidative degradation of resin layer (B).

[0025] <Resin Layer (A)> Resin layer (A) contains thermoplastic resin (a1) as the main component resin. In the present invention, "main component resin" means the resin with the largest mass percentage among the resins constituting each layer, and it is permissible to include other resins to the extent that they do not interfere with the function of the main component resin. In this case, the content of the main component resin accounts for 50% by mass or more, preferably 70% by mass or more, and particularly preferably 90% by mass or more (including 100% by mass) of the resins constituting each layer. Furthermore, in the present invention, "resin" means polymer, or polymer.

[0026] (Thermoplastic resin (a1)) The thermoplastic resin (a1), which is the main component resin of the resin layer (A), is not particularly limited. For example, polyolefin resins, polyester resins, polycarbonate resins, poly(meth)acrylic acid resins, polystyrene resins, polyamide resins, etc. can be used. Among these, it is preferable that it contains a polyolefin resin. That is, it is preferable that the polyolefin resin in the resin layer (A) is the main component resin of the resin layer (A). By having a polyolefin resin as the main component resin of the resin layer (A), it can have affinity with the resin layer (B) and provide good interlayer adhesion.

[0027] The polyolefin resin used as the thermoplastic resin (a1), which is the main component resin of the resin layer (A), is not limited to any particular type. For example, at least one polyolefin resin can be selected from polypropylene resins such as polypropylene, propylene-ethylene copolymer, and propylene-α-olefin copolymer; polyethylene resins such as high-density polyethylene, low-density polyethylene, and ethylene-α-olefin copolymer; α-olefin resins such as polybutene-1 and polymethylpentene; cycloolefin resins such as ethylene-cyclic olefin copolymer; and olefin elastomers such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene polymer (EPDM). Among these, polypropylene resin, cycloolefin resin, or a combination of both is preferred due to their mechanical properties and flexibility. In particular, cycloolefin resin is preferred as the main component resin. Cycloolefin resin is suitable as the main component resin of the resin layer (A) because it has low visible light absorption and heat resistance.

[0028] The lower limit of the polyolefin resin content in the resin layer (A) is not limited, but is usually 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. It is preferable that the polyolefin resin content is above the lower limit, as this makes it possible to impart good flexibility to the reflective sheet of the present invention. Furthermore, the upper limit of the polyolefin resin content in the resin layer (A) is also not limited. Here, the polyolefin resin content refers to the total amount of all polyolefin resins in the resin layer (A).

[0029] (Cycloolefin Resin) Next, we will describe a cycloolefin resin, which is particularly preferred among the polyolefin resins mentioned above, as the main component resin of the resin layer (A).

[0030] Cycloolefin resins are polymer compounds whose main chain consists of carbon-carbon bonds and which have a cyclic hydrocarbon structure in at least a portion of the main chain. This cyclic hydrocarbon structure is introduced by using a monomer such as norbornene or tetracyclododecene, which have at least one olefinic double bond in the cyclic hydrocarbon structure (cycloolefin).

[0031] Cycloolefin resins are classified into cycloolefin addition polymers or hydrogenated thereof, cycloolefin and α-olefin addition polymers or hydrogenated thereof, and cycloolefin ring-opening polymers or hydrogenated thereof, all of which can be used as cycloolefin resins. Furthermore, cycloolefin resins may be either cycloolefin homopolymers or cycloolefin copolymers.

[0032] Specific examples of cycloolefin resins include, for example, monocyclic cycloolefins such as cyclopentene, cyclohexene, cyclooctene, cyclopentadiene, and 1,3-cyclohexadiene; bicyclo[2.2.1]hepta-2-ene (common name: norbornene), 5-methyl-bicyclo[2.2.1]hepta-2-ene, 5,5-dimethyl-bicyclo[2.2.1]hepta-2-ene, 5-ethyl-bicyclo[2.2.1]hepta-2-ene, 5-butyl-bicyclo[2.2.1]hepta-2-ene, 5-ethylidene-bicyclo[2.2.1]hepta-2-ene, and 5-hexy Bicyclic cycloolefins such as rubicyclo[2.2.1]hepta-2-ene, 5-octyl-bicyclo[2.2.1]hepta-2-ene, 5-octadecyl-bicyclo[2.2.1]hepta-2-ene, 5-methylidene-bicyclo[2.2.1]hepta-2-ene, 5-vinyl-bicyclo[2.2.1]hepta-2-ene, and 5-propenyl-bicyclo[2.2.1]hepta-2-ene; Examples include tricyclic cycloolefins such as tricyclo[4.3.0.12,5]deca-3,7-diene (common name: dicyclopentadiene); tetracyclic cycloolefins such as tetracyclo[4.4.0.12,5.17,10]dodeca-3-ene (also simply called tetracyclododecene); 8-cyclopentyl-tetracyclo[4.4.0.12,5.17,10]dodeca-3-ene, tetracyclo[8.4.14,7.01,10.03,8]pentadeca-5,10,12,14-tetraene (also called 1,4-methano-1,4,4a,5,10,10a-hexahydroanthracene); and polycyclic cycloolefins such as tetramers of cyclopentadiene. These cycloolefin resins can be used individually or in combination of two or more to form copolymers.

[0033] Specific examples of α-olefins copolymerizable with cycloolefins include, for example, ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene, which have 2 to 20 carbon atoms, preferably 2 to 8 carbon atoms, or ethylene or α-olefins. These α-olefins can be used individually or in combination of two or more.

[0034] The cycloolefin resin is preferably a resin that contains cycloolefin components as its main component, and the content of cycloolefin components in the cycloolefin resin is preferably 50% by mass or more, more preferably 60% by mass or more. In this case, the "main component" refers to the component with the largest mass proportion among the components constituting the cycloolefin resin, and the inclusion of other components is permitted as long as it does not interfere with the function of the main component. The content of the main component accounts for 50% by mass or more, preferably 70% by mass or more (including 100% by mass) of the components constituting the cycloolefin resin. The same applies to the main components of other resins.

[0035] When the cycloolefin resin is a copolymer of a cycloolefin such as norbornene and an α-olefin, from the viewpoint of obtaining a good balance between the effect of improving processing performance such as stretching by using α-olefin as a copolymer component and the effect of heat resistance by using cycloolefin as the main component of the copolymer component, the content of the cycloolefin component in the cycloolefin resin is preferably 60 to 100% by mass, and more preferably 65% ​​by mass or more, or 95% by mass or less. There are no particular restrictions on the polymerization method of cycloolefin or cycloolefin and α-olefin and the hydrogenation method of the obtained polymer, and these can be carried out according to known methods.

[0036] The melt flow rate (MFR) of the cycloolefin resin is not limited. For example, it is preferably 0.1 to 20 g / 10 min as measured in accordance with JIS K7210 at 230°C under a load of 21.18 N, and more preferably 0.5 g / 10 min or more or 15 g / 10 min or less.

[0037] The cycloolefin resin may be crystalline or amorphous. Among them, from the viewpoint of easy availability of materials, it is preferably amorphous.

[0038] The glass transition temperature (Tg) of the cycloolefin resin is not limited. From the viewpoint of heat resistance, the lower limit is preferably 70°C or higher, more preferably 80°C or higher, and still more preferably 85°C or higher. From the viewpoint of extensibility, the upper limit is preferably 170°C or lower, more preferably 160°C or lower, and still more preferably 150°C or lower. When the glass transition temperature of the cycloolefin resin is within the above range, the heat resistance and stretchability tend to be good. Here, the "glass transition point (Tg)" is the value read when the temperature is raised from -50°C to 250°C at a rate of 10°C / min using a differential scanning calorimeter, maintained isothermally for 1 minute, cooled to -50°C at a rate of 10°C / min, maintained isothermally for 1 minute, and then the temperature is raised to 250°C again at a rate of 10°C / min. In addition, two or more types of cycloolefin resins may be combined and mixed to adjust the glass transition point (Tg) of the mixed resin to the above range.

[0039] The cycloolefin resin may be used alone or two or more resins having different compositions, physical properties, etc. may be mixed and used. For example, two or more types of cycloolefin resins may be combined and mixed to adjust the MFR and Tg of the mixed resin to the above range.

[0040] The content of cycloolefin resin in the resin layer (A) is not limited. Preferably, it is 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more. A cycloolefin resin content above the lower limit is preferable because it makes it possible to impart good heat resistance to the reflective sheet of the present invention. Furthermore, there is no upper limit to the content of cycloolefin resin in the resin layer (A). Preferably, it is 95% by mass or less, more preferably 92% by mass or less, and even more preferably 90% by mass or less. A cycloolefin resin content below the upper limit is preferable because it results in good break resistance, bend resistance, and brightness unevenness prevention function of the reflective sheet of the present invention.

[0041] Commercially available cycloolefin resins can be used. Examples include Zeon Corporation's "Zeonor®" (hydrogenated ring-opening polymer of cyclic olefin), Mitsui Chemicals' "Apel®" (addition copolymer of ethylene and tetracyclododecene), and Polyplastics' "TOPAS®" (addition copolymer of ethylene and norbornene). Among these, "Zeonor" and "TOPAS" are preferred because they have low light absorption properties, allowing for the production of reflective sheets with high reflectivity.

[0042] (Other Polyolefin Resins) When using cycloolefin resin as the main component resin of resin layer (A), the flexural resistance and heat resistance can be improved by incorporating polyolefin resins other than cycloolefin resin (hereinafter referred to as "other polyolefin resins") into the resin layer (A). Alternatively, cycloolefin resin may be omitted as the main component resin of resin layer (A), and only "other polyolefin resins" may be used as the main component resin.

[0043] The melt flow rate (MFR) of "other polyolefin resins" is not limited. In particular, it is preferable that the value measured in accordance with JIS K7210 at 230°C and a load of 21.18 N is 0.1 to 20 g / 10 min, and more preferably 0.5 g / 10 min or more, or 15 g / 10 min or less. Furthermore, when cycloolefin resin and "other polyolefin resins" are used in combination, it is preferable to adjust the MFR of the cycloolefin resin to the above range as well. Adjusting the MFR of both in this way tends to result in good mechanical properties as a reflective sheet.

[0044] As for "other polyolefin resins," one or more of the polyolefin resins exemplified above as the main component resin of the resin layer (A) can be used in combination. Among these, polyethylene resins and polypropylene resins are preferred, and among them, polypropylene resins are preferred from the viewpoint of having a high melting point, excellent heat resistance, and high mechanical properties such as elastic modulus. However, the use is not limited to these.

[0045] When "other polyolefin resins" refer to polypropylene resins, from the viewpoint of extrusion moldability, the melt flow rate (MFR) is preferably 0.1 to 20 g / 10 min, measured in accordance with JIS K7210 at 230°C and a load of 21.18 N, and more preferably 0.2 g / 10 min or more or 15 g / 10 min or less, and more preferably 0.5 g / 10 min or more or 12 g / 10 min or less.

[0046] When a cycloolefin resin and "other polyolefin resins" are used in combination as resin components constituting the resin layer (A), the relationship between the MFR of the cycloolefin resin ("MFR(CO)") and the MFR of the "other polyolefin resin" ("MFR(PO)") is preferably MFR(CO):MFR(PO) = 1:0.05 to 1:20, and more preferably 1:0.1 to 1:10. When the relationship between the MFRs of the two is within the above range, the other polyolefin resin tends to disperse in the cycloolefin resin, which is preferable because it tends to improve the mechanical properties as a reflective sheet.

[0047] The content of "other polyolefin resins" in resin layer (A) is not limited. When used in combination with cycloolefin resin, it is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more (relative to 100% by mass of resin layer (A)). The upper limit is also not limited. Preferably it is 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. If the content of "other polyolefin resins" is above the lower limit, it is preferable because it can more effectively suppress the breakage of resin layer (A) during stretching, and the interlayer adhesion between resin layer (A) and resin layer (B), or between resin layer (A) and resin layer (B), can be maintained at an even higher level. On the other hand, if the content of "other polyolefin resins" is below the upper limit, it tends to be possible to further improve heat resistance and brightness unevenness prevention function.

[0048] Furthermore, it is preferable that the polyolefin resin, which is the main component resin of resin layer (A), and the polyolefin resin, which is the main component resin of resin layer (B), are the same, as this improves the adhesion between resin layer (A) and resin layer (B). However, it is not limited to them being the same.

[0049] (Fine powder filler (a2)) The resin layer (A) may contain a fine powder filler (a2) as needed. By including a fine powder filler (a2) in the resin layer (A), the reflective properties of the reflective sheet of the present invention tend to be further improved due to light scattering caused by the refractive index difference between the main component resin of the resin layer (A), such as a polyolefin resin, and the fine powder filler (a2), as well as light scattering caused by the refractive index difference between the cavities formed around the fine powder filler (a2) during the manufacturing process of the reflective sheet of the present invention and the main component resin of the resin layer (A), such as a polyolefin resin, and further light scattering caused by the refractive index difference between the cavities formed around the fine powder filler (a2) and the fine powder filler (a2). If sufficient light reflectivity can be ensured by the resin layer (B), the resin layer (A) does not need to contain a fine powder filler (a2).

[0050] Regarding the type of fine powder filler (a2) that can be used in the resin layer (A) and the surface treatment method, the same as those described later as fine powder filler (b2) that can be used in the resin layer (B) can be used, and the preferred examples are also the same. Here, in the items described later as fine powder filler (b2) used in the resin layer (B), "resin layer (B)" shall be read as "resin layer (A)".

[0051] The fine powder filler (a2) contained in the resin layer (A) preferably has an average particle size of 0.05 μm or more and 5 μm or less, more preferably 0.1 μm or more or 2 μm or less. If the average particle size of the fine powder filler (a2) is above the lower limit, the dispersibility in the main component resin of the resin layer (A), such as a polyolefin resin, will not decrease, and a more homogeneous reflective sheet can be obtained. If the average particle size is below the upper limit, a dense interface is formed between the main component resin of the resin layer (A), such as a polyolefin resin, and the fine powder filler (a2), and a highly reflective reflective sheet can be obtained.

[0052] The average particle size of the fine powder filler can be measured as follows. The average particle size of the fine powder filler as a raw material can be measured as the average particle size (D50) obtained from the volume-based particle size distribution measured by dynamic light scattering or the like, or as the average particle size (D50) of 50% of the cumulative (mass-based) particle size in the equivalent spherical distribution measured using a centrifugal sedimentation particle size distribution analyzer. The average particle size of the fine powder filler (a2) contained in the resin layer (A) can be determined by observing the surface of the resin layer (A) or the cross-section of the reflective sheet of the present invention using an optical microscope or scanning electron microscope (SEM), measuring the diameters of 10 or more particles, and taking the average value. In this case, if the cross-sectional shape is not circular, the average of the longest and shortest diameters can be measured as the diameter of each particle. The same applies to the fine powder filler (b2) contained in the resin layer (B) described later, but in that case, the method of observing the cross-section of the reflective sheet of the present invention is preferable. Furthermore, if the shape of the fine powder filler (a2) contained in the resin layer (A) does not show any significant deformation from the shape of the raw material fine powder filler, the average particle size of the raw material fine powder filler can be considered as the average particle size of the fine powder filler contained in the resin layer (A).

[0053] When the resin layer (A) contains a fine powder filler (a2), the content of the fine powder filler (a2) in the resin layer (A) is not limited. Considering the light reflectivity, mechanical strength, productivity, etc., of the reflective sheet of the present invention, the content of the fine powder filler (a2) in the resin layer (A) is preferably 10 to 80% by mass relative to the entire resin layer (A) (i.e., relative to 100% by mass of the resin layer (A)), and more preferably 20% by mass or more, or 70% by mass or less. If the content of the fine powder filler (a2) is above the lower limit, the interface area between the resin constituting the resin layer (A) and the fine powder filler (a2) can be sufficiently secured, and the reflective sheet of the present invention can be given even higher reflectivity. If the content of the fine powder filler (a2) is below the upper limit, it is preferable because the mechanical strength required for the reflective sheet of the present invention can be secured more effectively.

[0054] (Other components) The resin layer (A) may further contain components other than the polyolefin resin (a1) and the fine powder filler (a2) as "other components". Examples of "other components" include resin components other than those mentioned above (including thermoplastic elastomers), antioxidants, light stabilizers, heat stabilizers, dispersants, ultraviolet absorbers, fluorescent whitening agents, compatibilizers, lubricants, and fillers other than the fine powder filler.

[0055] Furthermore, recycled raw materials generated during the manufacturing process of the reflective sheet of the present invention may be included in the resin layer (A) to the extent that they do not impair the performance of the reflective sheet of the present invention. The content ratio of recycled raw materials is not limited, but is preferably 1 to 60% by mass relative to the total mass of the resin layer (A) (relative to 100% by mass of the resin layer (A)), and more preferably 10% by mass or more or 50% by mass or less. If the content is above the lower limit, a cost benefit will be obtained by using recycled raw materials, and if it is below the upper limit, the light reflectivity and mechanical strength required for the reflective sheet of the present invention tend not to be impaired. However, if recycled raw materials are included in the resin layer (A), the surface roughness or reflectivity of the reflective sheet of the present invention may become unstable, so in such cases, it is preferable to include them in the resin layer (B) as described later.

[0056] <Resin layer (B)> The resin layer (B) contains a thermoplastic resin (b1), which is the main component resin, and a fine powder filler (b2).

[0057] (Thermoplastic resin (b1)) The thermoplastic resin (b1), which is the main component resin of the resin layer (B), is not particularly limited. For example, polyolefin resins, polyester resins, polycarbonate resins, poly(meth)acrylic acid resins, polystyrene resins, polyamide resins, etc. can be used. Among these, it is preferable to include a polyolefin resin. By having a polyolefin resin as the main component resin of the resin layer (B), adhesion to the resin layer (A) can be improved. However, the resin layer (B) may also contain resins other than polyolefin resins.

[0058] The polyolefin resin used as the thermoplastic resin (b1), which is the main component resin of the resin layer (B), is not particularly limited and can be selected from among those exemplified as the polyolefin resin (a1) of the resin layer (A). For example, at least one polyolefin resin selected from polypropylene resins such as polypropylene and propylene-ethylene copolymer, polyethylene resins such as high-density polyethylene, low-density polyethylene, and ethylene-α-olefin copolymer, cycloolefin resins such as ethylene-cyclic olefin copolymer, and olefin elastomers such as ethylene-propylene rubber (EPR) and ethylene-propylene-diene copolymer (EPDM) can be mentioned. Among these, polypropylene resin, cycloolefin resin, and polyethylene resin are preferred due to their mechanical properties and flexibility.

[0059] The polyolefin resin of resin layer (B) may be a different polyolefin resin from the polyolefin resin that is the main component of resin layer (A). However, from the viewpoint of improving the adhesion between resin layers (A) and (B), it is preferable to use a polyolefin resin that contains monomer units common to the polyolefin resin that is the main component of resin layer (A).

[0060] From the viewpoint of extrusion moldability, the polyolefin resin used in the resin layer (B) preferably has a melt flow rate (MFR) of 0.1 to 20 g / 10 min, measured in accordance with JIS K7210 at 230°C and a load of 21.18 N, more preferably 0.2 g / 10 min or more or 10 g / 10 min or less, and even more preferably 0.5 g / 10 min or more or 5 g / 10 min or less.

[0061] The content of polyolefin resin in the resin layer (B) is not limited, but is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more (relative to 100% by mass of the resin layer (B)). It is preferable that the polyolefin resin content is above the lower limit, as this further maintains the strength of the resin layer (B). There is also no upper limit to the polyolefin resin content in the resin layer (B), but from the standpoint of including the fine powder filler (b2), it is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. It is preferable that the polyolefin resin content is below the upper limit, as this maintains strength without reducing reflectivity.

[0062] (Fine powder filler (b2)) The resin layer (B) contains a fine powder filler (b2). The presence of the fine powder filler (b2) in the resin layer (B) improves the reflection characteristics by causing incident light to be diffusely reflected by the fine powder filler (b2), and also facilitates the formation of voids when the resin layer (B) is a stretched material.

[0063] The fine powder filler (b2) contained in the resin layer (B) is not limited, and examples include inorganic fine powders, organic fine powders, etc. Among these, it is preferable that the resin layer (B) contains the inorganic fine powder as the fine powder filler. In addition, inorganic fine powders and organic fine powders may be used in combination.

[0064] Examples of organic fine powders that can be contained in the resin layer (B) include polymer beads and polymer hollow particles, and these can be used individually or in combination of two or more types. Furthermore, as described later, the reflective sheet of the present invention may use scraps generated during the manufacturing process of the reflective sheet as recycled raw materials to be part of the raw materials for the resin layer (B). In that case, the materials contained in the resin layer (A) will also be contained in the resin layer (B).

[0065] Examples of the above-mentioned inorganic fine powders include calcium carbonate, magnesium carbonate, barium carbonate, magnesium sulfate, barium sulfate, calcium sulfate, zinc oxide, magnesium oxide, calcium oxide, titanium oxide, aluminum oxide, aluminum hydroxide, hydroxyapatite, silica, magnesium silicate, mica, talc, kaolin, clay, glass powder, asbestos powder, zeolite, and silicate clay. These can be used individually or in mixtures of two or more. Among these, considering the refractive index difference with the resin constituting the resin layer (B), those with a high refractive index are preferred, and it is particularly preferable to use calcium carbonate, barium sulfate, titanium oxide, or zinc oxide, which have a refractive index of 1.6 or higher.

[0066] In particular, titanium dioxide has a significantly higher refractive index compared to other inorganic fine powders, and can significantly increase the refractive index difference with the resin constituting the resin layer (B). Therefore, excellent light reflectivity can be obtained with a smaller amount of formulation than when other fillers are used. Furthermore, by using titanium dioxide, high light reflectivity can be obtained even when the thickness of the reflective sheet of the present invention is reduced. The content of titanium dioxide is not limited, but it is preferably 30% or more of the total mass of inorganic fine powders. When using a combination of organic fine powders and inorganic fine powders as a fine powder filler, it is preferable that 30% or more of the total mass be titanium dioxide. As titanium dioxide, commercially available products such as those manufactured by Ishihara Sangyo Co., Ltd., Chemours Co., Ltd., and Kronos Co., Ltd. can be used.

[0067] To improve the weather resistance and dispersibility of these inorganic fine powders in resins, inorganic fine powders that have been surface-treated with polyhydric alcohol compounds, siloxanes, alumina (aluminum oxide), silica, silicone compounds, amine compounds, fatty acids, fatty acid esters, metal soaps, etc., may be used.

[0068] The fine powder filler (b2) preferably has an average particle size of 0.05 to 15 μm, and more preferably 0.1 μm or more or 10 μm or less. If the average particle size of the fine powder filler (b2) is above the lower limit, it disperses well into the resin constituting the resin layer (B), so a more homogeneous reflective sheet can be obtained. If the average particle size of the fine powder filler is below the upper limit, a dense interface is formed between the resin constituting the resin layer (B) and the fine powder filler (b2), so a reflective sheet with higher reflectivity can be obtained. Here, the "average particle size" can be measured by the method described above.

[0069] The content of the fine powder filler (b2) in the resin layer (B) is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 45% by mass or more, relative to the total mass of the resin layer (B) (i.e., relative to 100% by mass of the resin layer (B)), considering the light reflectivity, mechanical strength, productivity, etc. of the reflective sheet of the present invention. If the content of the fine powder filler is above the lower limit, a sufficient surface area of ​​the interface between the thermoplastic resin (b1) constituting the resin layer (B) and the fine powder filler (b2) can be secured, and the reflective sheet of the present invention can be given high reflectivity. Furthermore, there is no upper limit to the content of the fine powder filler (b2), but it is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. If the content of the fine powder filler (b2) is below the upper limit, the mechanical strength required for the reflective sheet can be secured more effectively.

[0070] (Other components) The resin layer (B) may further contain components other than the thermoplastic resin (b1) and the fine powder filler (b2) as "other components". Examples of "other components" include crystal nucleating agents, antioxidants, light stabilizers, heat stabilizers, dispersants, ultraviolet absorbers, fluorescent whitening agents, compatibilizers, lubricants, and other additives.

[0071] Furthermore, recycled raw materials generated during the manufacturing process of the reflective sheet of the present invention may be included, provided that they do not impair the performance of the resin layer (B). The proportion of recycled raw materials is not limited, but is preferably 1 to 60% by mass relative to the total mass of the resin layer (B) (i.e., 100% by mass of the resin layer (B)), and more preferably 10% by mass or more, or 50% by mass or less. It is preferable if the content is above the lower limit because it provides a cost advantage from using recycled raw materials. On the other hand, it is preferable if the content is below the upper limit because it does not impair the light reflectivity and mechanical strength required for the reflective sheet. Typically, the thickness of the resin layer (B) accounts for a large proportion of the total thickness of the reflective sheet of the present invention, so it is preferable to include recycled raw materials in the resin layer (B) because it can reduce variations in the various properties of the reflective sheet of the present invention.

[0072] <Photocured Layer (C)> The photocured layer (C) is a layer made of a photocured product of the photocurable composition (c). The photocured layer (C) can be formed by applying the photocurable composition (c) to form a coating film, drying it as needed, and then irradiating the coating film with active energy rays.

[0073] Herein, in this specification, "(meth)acrylic" is a general term for "acrylic" and "methacrylic," and "(meth)acrylate" is a general term for "acrylate" and "methacrylate." "(meth)acryloyl group" is a general term for "acryloyl group" and "methacryloyl group," CH ２ =C(R1)-C(=O)- (where R1 is a hydrogen atom or a methyl group) is a group represented by this expression. Furthermore, "monofunctional" means having one radically polymerizable double bond. "Polyfunctional" means having two or more radically polymerizable double bonds; for example, "difunctional" means having two radically polymerizable double bonds.

[0074] (Photocurable composition (c)) The photocurable composition (c) preferably contains a compound having an ethylenically unsaturated group. Examples of compounds having an ethylenically unsaturated group include vinyl group-containing compounds and (meth)acryloyl group-containing compounds. Among these, (meth)acryloyl group-containing compound (c1) is more preferred from the viewpoint of excellent curability.

[0075] ((meth)acryloyl group-containing compound (c1)) The compound (c1) containing a (meth)acryloyl group may be a polymer (meth)acrylate compound or a monomer (meth)acrylate compound, and either may be used. These may also be used in combination. Here, the polymer (meth)acrylate compound includes macromonomers.

[0076] Examples of (meth)acrylate compounds include urethane (meth)acrylate compounds, epoxy (meth)acrylate compounds, polyester (meth)acrylate compounds, polyalkylene (meth)acrylate compounds, and other (meth)acrylate compounds. In this specification, "(meth)acrylate compound containing an acryloyl group," "(meth)acrylate compound," and "(meth)acrylate" are all concepts that encompass both compounds containing an acryloyl group and compounds having a methacryloyl group, and it is sufficient to contain either an acryloyl group, a methacryloyl group, or both.

[0077] The urethane (meth)acrylate compound can be any conventionally known compound and is not particularly limited. Examples include compounds obtained by the reaction of a hydroxyl-containing (meth)acrylate compound with an isocyanate compound, and compounds obtained by the reaction of a hydroxyl-containing (meth)acrylate compound with a polyol and an isocyanate compound. The urethane (meth)acrylate compound may be a polymer or a monomer.

[0078] Examples of the hydroxyl group-containing (meth)acrylate compounds include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerin mono (meth)acrylate, glycerin di (meth)acrylate, diglycerin mono (meth)acrylate, diglycerin tri (meth)acrylate, trimethylolpropane di (meth)acrylate, pentaerythritol mono (meth)acrylate, pentaerythritol di (meth)acrylate, pentaerythritol tri (meth)acrylate, dipentaerythritol di (meth)acrylate, dipentaerythritol tri (meth)acrylate, dipentaerythritol tetra (meth)acrylate, dipentaerythritol penta (meth)acrylate, sorbitol di (meth)acrylate, sorbitol tri (meth)acrylate, sorbitol tetra (meth)acrylate, sorbitol penta ( Examples of reaction products between (meth)acrylic acid and polyol diglycidyl include meth)acrylate, sorbitol mono(meth)acrylate, diglycerin di(meth)acrylate, adducts of glycidyl(meth)acrylate and (meth)acrylic acid, reaction products of two molecules of (meth)acrylic acid and one molecule of 1,6-hexanediol diglycidyl, reaction products of two molecules of epoxy(meth)acrylic acid and one molecule of neopentyl glycol diglycidyl, reaction products of two molecules of (meth)acrylic acid and one molecule of bisphenol A diglycidyl, reaction products of two molecules of (meth)acrylic acid and the diglycidyl derivative of the propylene oxide adduct of bisphenol A, reaction products of two molecules of (meth)acrylic acid and one molecule of phthalate diglycidyl, reaction products of two molecules of (meth)acrylic acid and one molecule of polyethylene glycol diglycidyl, and reaction products of two molecules of (meth)acrylic acid and one molecule of polypropylene glycol diglycidyl. These can be used individually or in combination.

[0079] The aforementioned isocyanate compounds refer to compounds having an isocyanate derivative structure, such as isocyanates or blocked isocyanates. Examples of the isocyanates include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylenediphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, ethylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, hydrogenated xylylene diisocyanate, methylenebis(4-cyclohexyl isocyanate), and isopropylidene dicyclohexyl diisocyanate. These isocyanates may also be reaction products with various polymers and compounds. Furthermore, polymers and derivatives of these isocyanates, such as biuretized, isocyanurateized, uretdioneized, and carbodiimide-modified forms, can also be used. These may be used individually or in combination.

[0080] The epoxy (meth)acrylate compound can be any conventionally known compound and is not particularly limited, but examples include compounds obtained by the reaction of an epoxy resin with (meth)acrylic acid or a carboxyl group-containing (meth)acrylate.

[0081] Examples of epoxy resins include compounds containing epoxy groups in their molecules, such as condensates of epichlorohydrin with hydroxyl or amino groups of ethylene glycol, polyethylene glycol, glycerin, polyglycerin, bisphenol A, polyepoxy compounds such as polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether, novolac-type epoxy resins such as cresol novolac-type and phenol novolac-type, and bisphenol-type epoxy resins such as bisphenol A-type, bisphenol F-type, and bisphenol S-type.

[0082] Examples of (meth)acrylic acid include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid.

[0083] Examples of the (meth)acrylate compounds include monofunctional (meth)acrylates and polyfunctional (meth)acrylates. Here, a polyfunctional (meth)acrylate refers to a compound having two or more (meth)acrylate groups in one molecule. The (meth)acrylate compound may be a polymer or a monomer.

[0084] The monofunctional (meth)acrylates mentioned above are not particularly limited. For example, alkyl (meth)acrylates such as methyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc., hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, etc., methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, ethoxypropyl (meth)acrylate, etc. Examples include aromatic (meth)acrylates such as lucoxyalkyl (meth)acrylate, benzyl (meth)acrylate, and phenoxyethyl (meth)acrylate; amino group-containing (meth)acrylates such as diaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; ethylene oxide-modified (meth)acrylates such as methoxyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, and phenylphenol ethylene oxide-modified (meth)acrylate; glycidyl (meth)acrylate; tetrahydrofurfuryl (meth)acrylate; and (meth)acrylic acid.

[0085] Among the polyfunctional (meth)acrylates mentioned above, the difunctional (meth)acrylates are not particularly limited, but examples include alkane diol di(meth)acrylates such as 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, tricyclodecanedimethylol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, Examples include bisphenol-modified di(meth)acrylates such as bisphenol F ethylene oxide-modified di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, urethane di(meth)acrylate, epoxy di(meth)acrylate, and the like.

[0086] Among the polyfunctional (meth)acrylates mentioned above, the (meth)acrylates with three or more functions are not particularly limited, but examples include alkylene hydrate-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, propylene oxide-modified trimethylolpropane tri(meth)acrylate, isocyanurate-modified tri(meth)acrylate, ε-caprolactone-modified tris(acrooxyethyl) isocyanurate, and other isocyanurate-modified tri(meth)acrylates. Examples include methylates, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, tetramethylolmethane ethylene oxide-modified tetra(meth)acrylate, ethylene oxide-modified pentaerythritol tetra(meth)acrylate, alkylenoxide-modified pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and others.

[0087] Among these, polyfunctional (meth)acrylates are preferred from the viewpoint of forming crosslinks more efficiently, and trifunctional or more (meth)acrylates are more preferred. Specifically, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are preferred, and trimethylolpropane tri(meth)acrylate and dipentaerythritol hexaacrylate are more preferred.

[0088] The content of the (meth)acryloyl group-containing compound (c1) in the photocurable composition (c) varies depending on the application and the required properties of the photocurable layer (C), so it cannot be stated definitively. However, it is preferably in the range of 1% to 90% by mass, more preferably 3% to 80% by mass, even more preferably 5% to 70% by mass, particularly preferably 10% to 60% by mass, and most preferably 15% to 50% by mass, relative to the nonvolatile components (100% by mass) contained in the photocurable composition (c). By using it within this range, the effect of the present invention, namely the scratch resistance of the light guide plate, can be improved.

[0089] For the photocurable composition (c), in order to increase the molecular weight after curing and prevent the generation of shavings, it is preferable that the molecular weight (M) of the (meth)acryloyl group-containing compound (c1) be high. On the other hand, in order to increase the number of crosslinking sites from the viewpoint of similarly increasing the molecular weight after curing, it is preferable that the double bond equivalent (N) of the (meth)acryloyl group-containing compound (c1) exhibiting (meth)acryloyl groups per unit weight be large. From this viewpoint, the (meth)acryloyl group-containing compound (c1) is M × N ３ The value of is preferably 200,000 or more, and more preferably 250,000 or more, 500,000 or more, or 650,000 or more. The photocurable composition (c) is such an M×N ３ It is preferable that the compound contains a (meth)acryloyl group-containing compound (c1) having a value of M×N. ３ The upper limit of this value is usually preferably 3 million or less, more preferably 2.5 million or less, and especially preferably 2 million or less.

[0090] (Leveling Agent) To improve the appearance of the cured product, a leveling agent can be added to the photocurable composition (c). Examples of leveling agents include acrylic leveling agents, silicone leveling agents, and fluorine leveling agents. Among these, silicone leveling agents are more preferred from the viewpoint of improving wear resistance, and furthermore, silicone leveling agents having radical polymerizable functional groups are particularly preferred from the viewpoint of preventing the bleed-out of the leveling agent after the formation of the photocured product layer (C) during molding and other processes. Silicone leveling agents impart slip properties to the cured product and can achieve high wear resistance. Silicone leveling agents having radical polymerizable functional groups are incorporated into the cured product by reacting with the photocurable composition, and are very useful because they can achieve slip properties, wear resistance, and chemical resistance over a long period of time.

[0091] The leveling agent content in the photocurable composition (c) is preferably 20% by mass or less, more preferably 0.01% by mass or more or 10% by mass or less, even more preferably 0.1% by mass or more or 5% by mass or less, particularly preferably 0.2% by mass or more or 4% by mass or less, and most preferably 0.3% by mass or more or 3% by mass or less, relative to the non-volatile content in the photocurable composition (c). By using this range, not only is it possible to improve the appearance of the photocured layer (C), but also to improve its abrasion resistance.

[0092] (UV absorber) To improve the weather resistance of the cured product, a UV absorber can be added to the photocurable composition (c). From the viewpoint of heat resistance, a UV absorber with a molecular weight of 500 or more is preferred. From the viewpoint of good solubility in the composition and improvement of weather resistance, a UV absorber derived from triazine, benzophenone, benzotriazole, cyclic iminoester, salicylic acid ester, or cyanoacrylate compounds is preferred, and a UV absorber with a maximum absorption wavelength in the range of 240 to 380 nm is preferred. Among these, triazine and benzotriazole types are more preferred from the viewpoint of good UV absorption or excellent appearance when used as a photocured product layer (C), and triazine types are even more preferred.

[0093] The amount of ultraviolet absorber in the photocurable composition (c) is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, relative to the non-volatile content in the photocurable composition (c). Using this range allows for the effective formation of the photocurable layer (C) and improves the weather resistance of the photocurable layer (C).

[0094] When used in applications requiring photostability, good UV absorption is preferable. The transmittance of the laminate after curing at a wavelength of 360 nm is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and particularly preferably 50% or less. The lower limit depends on the application, but for applications where high photostability is required, a lower limit is preferable, so it is 0%. By using within this range, excellent photostability can be achieved.

[0095] (Light stabilizer) To further improve the light stability of the cured product, a light stabilizer can be added to the photocurable composition (c). A hindered amine-based light stabilizer is preferred. Among these, amino ether group-containing compounds are preferred from the viewpoint of weather resistance of the cured product, and bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-[[3,5-bis(1,1,dimethylethyl)-4-hydroxyphenyl]methyl] is particularly preferred. These compounds may be used individually or in combination of two or more.

[0096] The content of the light stabilizer in the photocurable composition (c) is preferably 20% by mass or less, more preferably 0.01% by mass or 15% by mass or less, even more preferably 0.1% by mass or 10% by mass or less, particularly preferably 0.5% by mass or 8% by mass or less, and most preferably 1% by mass or 5% by mass or less, relative to the nonvolatile components contained in the photocurable composition (c). By using within this range, the photocurable layer (C) can be effectively formed and the weather resistance of the photocurable layer (C) is improved.

[0097] (Photopolymerization Initiator) It is preferable to incorporate a photopolymerization initiator to accelerate the curing of the photocurable composition (c). The molecular weight of the photopolymerization initiator is preferably 1000 or less. Specific examples of photopolymerization initiators include, for example, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin-n-butyl ether, benzoin phenyl ether, benzyl diphenyl disulfide, dibenzyl, diacetyl, anthraquinone, naphthoquinone, 3,3'-dimethyl-4-methoxybenzophenone, benzophenone, p,p'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, pivaloin ethyl ether, benzyl dimethyl ketal, 1,1-dichloroacetophenone, p-t-butyldichloroacetophenone, 1 Examples include hydroxycyclohexylphenyl ketone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-dichloro-4-phenoxyacetophenone, phenylglyoxylate, α-hydroxyisobutylphenone, dibenzosparone, 1-(4-isopropylphenyl)-2-hydroxy-2-methyl-1-propanone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, tribromophenylsulfone, and tribromomethylphenylsulfone.

[0098] These photopolymerization initiators may be used individually or in combination of two or more. The content of the photopolymerization initiator in the photocurable composition (c) is preferably 20% by mass or less, more preferably 0.1% by mass or 15% by mass or less, even more preferably 0.3% by mass or 10% by mass or less, particularly preferably 0.5% by mass or 8% by mass or less, and most preferably 1% by mass or 7% by mass or less, relative to the nonvolatile components contained in the photocurable composition (c). Using within this range effectively promotes the formation of the photocured layer (C).

[0099] (Other components) The photocurable composition (c) may further contain, as needed, various additives such as organic solvents, antioxidants, anti-yellowing agents, bluing agents, pigments, dyes, defoamers, thickeners, anti-settling agents, antistatic agents, and anti-fogging agents.

[0100] Furthermore, when forming a photocurable layer (C), organic solvents may be used as needed to improve the workability when applying the photocurable composition (c). Examples of organic solvents include aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as diethyl ether, isopropyl ether, tetrahydrofuran, dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol monomethyl ether, anisole, and phenetol; ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, and ethylene glycol diacetate; amide solvents such as dimethylformamide, diethylformamide, and N-methylpyrrolidone; cellosolve solvents such as methyl cellosolve, ethyl cellosolve, and butyl cellosolve; alcohol solvents such as methanol, ethanol, propanol, isopropanol, and butanol; and halogen solvents such as dichloromethane and chloroform. These organic solvents may be used individually or in combination of two or more. Among these organic solvents, ester-based solvents, ether-based solvents, alcohol-based solvents, and ketone-based solvents are preferred because they easily improve workability during application.

[0101] (Method for forming the photocurable layer (C)) The photocurable layer (C) can be formed, for example, by applying a photocurable composition (c) to at least one side surface of the laminate [I] to form a coating film, drying it as necessary, and then irradiating the coating film with active energy rays.

[0102] The coating method of the photocurable composition (c) is not particularly limited. For example, it can be coated by known methods such as the die coating method, dip coating method, air knife coating method, curtain coating method, spin coating method, roller coating method, bar coating method, wire bar coating method, gravure coating method, reverse gravure coating method, spray coating, etc.

[0103] When the photocurable composition (c) contains an organic solvent, it is preferably pre-heated and dried before irradiation with active energy rays. By pre-heating and drying, the organic solvent in the coating film can be effectively removed. The drying temperature for heating and drying is preferably 30 to 200 °C, more preferably 40 to 150 °C, and even more preferably 50 to 120 °C. The drying time is preferably 0.01 to 30 minutes, and more preferably 0.1 to 10 minutes.

[0104] Examples of the active energy rays include ultraviolet rays, electron beams, visible light rays, infrared rays, X-rays, etc. Among them, ultraviolet rays and electron beams are preferable from the viewpoints of curability and prevention of resin deterioration, and ultraviolet rays are more preferable. The irradiation amount of the active energy rays can be appropriately selected according to the active energy rays to be irradiated. For example, when using ultraviolet rays, the integrated light amount of irradiation is preferably 20 to 5000 mJ / cm ２ is preferable, 100 to 3000 mJ / cm ２ is more preferable, and 200 to 2000 mJ / cm ２ is even more preferable. Also, as the illuminance, 50 to 600 mW / cm ２ is preferable, 75 to 450 mW / cm ２ is more preferable, and 100 to 300 mW / cm ２ is even more preferable. As the light source, for example, a medium-pressure mercury lamp, high-pressure mercury lamp, ultra-high-pressure mercury lamp, electrodeless lamp, metal halide lamp, LED lamp, or an electron beam such as an electron beam acceleration path of a scanning type or curtain type, high-pressure mercury lamp, ultra-high-pressure mercury lamp, low-pressure mercury lamp, etc. can be used.

[0105] (Thickness) The thickness of the photocured material layer (C) is preferably in the range of 0.1 to 20 μm, more preferably 0.2 μm or more or 10 μm or less, and even more preferably 0.3 μm or more or 7 μm or less. It is preferable that the thickness of the photocured material layer (C) is within the above range in that it can suppress scratches on components such as light guide plates. The thickness of the cured material can be determined by cross-sectional observation using an electron microscope or the like. Furthermore, regarding the thickness of the photocured material layer (C), generally, the thicker the layer, the higher the material cost and the greater the ratio of the thickness of the photocured material layer (C) to the reflective sheet, which tends to lead to a decrease in reflectivity. On the other hand, the thinner the photocured material layer (C), the more likely it is that coating defects will occur. From this viewpoint, the thickness of the photocured material layer (C) is particularly preferably 1 μm or more and 5 μm or less, and more preferably 2 μm or more or 4 μm or less.

[0106] <Voids> The reflective sheet of the present invention preferably has voids in order to enhance its reflective performance, and it is preferable that at least one of the layers has voids. That is, it is sufficient if one or more of the resin layer (A), resin layer (B), and photocured layer (C) have voids. In particular, in order to further enhance the reflective performance, it is preferable that one or more of the resin layer (A), resin layer (B), and resin layer (A) have voids, and among these, it is preferable that resin layer (B) has voids and resin layer (A) does not. If providing voids in resin layer (A) reduces mechanical properties such as heat resistance and elastic modulus, it is preferable to provide the above-mentioned voids only in resin layer (B). By providing such voids only in resin layer (B), the heat resistance of the entire film can be increased. In the present invention, whether or not the reflective sheet or each layer has voids can be determined by observing the cross-section of the reflective sheet or each layer with an electron microscope at a magnification of 2,000 to 5,000 times to see if voids are present.

[0107] The voids in the reflective sheet of the present invention can be formed by incorporating a fine powder filler into the composition constituting each layer and stretching, preferably biaxially stretching. Alternatively, they can be formed by incorporating an immiscible resin into the thermoplastic resin constituting each layer and stretching, preferably biaxially stretching.

[0108] The porosity of the entire reflective sheet of the present invention (including the photocured layer (C)) is not particularly limited, but is preferably 10% or more, more preferably 20% or more, while the upper limit is preferably 80% or less, more preferably 70% or less. If the porosity of the reflective sheet of the present invention is above the lower limit, the whitening of the reflective sheet of the present invention progresses sufficiently, and it tends to have high light reflectivity. Furthermore, if the porosity of the reflective sheet of the present invention is below the upper limit, the mechanical strength of the reflective sheet of the present invention tends to be favorable.

[0109] As mentioned above, from the viewpoint of improving light reflection performance, it is preferable that the resin layer (B) has voids. In this case, the porosity of the resin layer (B) is not particularly limited, but is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. On the other hand, the upper limit is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. If the porosity of the resin layer (B) is above the lower limit, the whitening of the reflective sheet of the present invention will proceed sufficiently, and it will tend to have higher light reflectivity. Furthermore, if the porosity of the resin layer (B) is below the upper limit, the mechanical strength of the reflective sheet of the present invention will be more favorable.

[0110] The porosity of a reflective sheet (including the photocured layer (C)) can be determined by the following method. For a reflective sheet, using a fixed-point thickness gauge with a flat tip and a diameter of 5 mm (for example, FFA-1 manufactured by Ozaki Seisakusho Co., Ltd.), if the thickness measured with an additional load of 25 kgf applied on top of the weight used to apply the measuring force is x, and the thickness measured without the additional load is y, then the porosity can be calculated using the following formula: Porosity (%) = {(y - x) / y} × 100

[0111] As mentioned above, it is preferable that the resin layer (A) does not have voids, from the viewpoint of providing rigidity and preventing oxidative degradation of the resin layer (B). Furthermore, in the reflective sheet of the present invention, it is preferable that the resin layer (B) of the laminate [I] has voids and the resin layer (A) does not have voids, and it is also preferable that the photocurable layer (C) is provided in contact with the resin layer (A) of the laminate [I], in order to prevent the photocurable composition (c) from penetrating into the voids and impairing the reflective performance.

[0112] <Thickness> The thickness of the reflective sheet of the present invention is preferably 30 to 250 μm. In particular, considering ease of handling in practical terms, the thickness of the reflective sheet of the present invention is more preferably 40 μm or more or 200 μm or less, and more preferably 50 μm or more or 150 μm or less.

[0113] The thickness of the resin layer (A) (or the thickness of each layer if there are two or more resin layers (A)) is not particularly limited, but is preferably 0.1 to 20 μm, more preferably 0.5 μm or more or 15 μm or less, and even more preferably 1 μm or more or 10 μm or less. When the thickness of the resin layer (A) is within the above range, it is easy to achieve both heat resistance and high brightness. Here, the thickness of the resin layer (A) refers to the average thickness. Also, if there are multiple resin layers (A) in the reflective sheet of the present invention, it refers to the thickness of each layer.

[0114] The thickness of the resin layer (B) (or the total thickness if there are two or more resin layers (B)) is not particularly limited, but is preferably 20 to 240 μm, more preferably 30 μm or more or 190 μm or less, and even more preferably 40 μm or more or 140 μm or less. When the thickness of the resin layer (B) is within the above range, the reflective properties tend to be good. Here, the thickness of the resin layer (B) refers to the average thickness.

[0115] Furthermore, even when the thermoplastic resin that is the main component resin in resin layer (A) and the thermoplastic resin contained as the main component resin in resin layer (B) are the same or have high affinity, there may be cases in the reflective sheet of the present invention where there is no boundary between resin layer (A) and resin layer (B), or where it cannot be confirmed. In such cases, the thickness of each layer as described above, and the thickness ratio of each layer as described below, can be determined from the ratio of raw materials used and extrusion amounts for each layer when manufacturing the reflective sheet of the present invention.

[0116] In the reflective sheet of the present invention, the ratio of the thickness of resin layer (B) to the thickness of resin layer (A) ((B) / (A)) is preferably 1 to 40, more preferably 2 or more or 30 or less, and particularly preferably 3 or more or 15 or less. If the thickness ratio of resin layer (B) to resin layer (A) is 1 or more, the reflective properties tend to be good, and the flexibility is also good, which tends to improve the bendability. Furthermore, if the thickness ratio of resin layer (B) to resin layer (A) is below the upper limit, the heat resistance tends to be good. Note that if the above thickness ratio has two or more layers of resin layer (A) or resin layer (B), it means the thickness ratio of the total thickness of each layer.

[0117] (Arithmetic mean roughness Ra) The arithmetic mean roughness (Ra) of the sheet surface on the side with the photocured material layer (C) of the reflective sheet of the present invention is preferably 0.3 μm or less, more preferably 0.25 μm or less, and particularly preferably 0.2 μm or less, from the viewpoint of suppressing the decrease in brightness due to the provision of the photocured material layer (C).

[0118] Furthermore, the arithmetic mean roughness Ra of the photocured material layer (C) side surface of the laminate [I] (a laminate [I] consisting of resin layer (A) / resin layer (B) / resin layer (A)) constituting the reflective sheet of the present invention is not particularly limited, but is preferably 0.05 μm or more, more preferably 0.1 μm or more. If the arithmetic mean roughness Ra of the photocured material layer (C) side surface of the laminate [I] is above the lower limit, the reflective characteristics are good and brightness unevenness tends to be further suppressed, which is preferable. On the other hand, the upper limit of the arithmetic mean roughness Ra of the surface opposite to the photocured material layer (C) of the laminate [I] constituting the reflective sheet of the present invention is not particularly limited, but is preferably 0.7 μm or less, more preferably 0.5 μm or less, even more preferably 0.4 μm or less, and particularly preferably 0.2 μm or less. If the arithmetic mean roughness Ra of the surface of the laminate [I] opposite to the photocured layer (C) is less than or equal to the upper limit, it is preferable because it tends to have good reflection characteristics and suppress particle detachment.

[0119] The arithmetic mean roughness Ra of the surface on the opposite side of the photocured layer (C) of the laminate [I] can be optimized by adjusting the thickness ratio of the resin layer (A) and the resin layer (B), the type and blending ratio of the thermoplastic resin which is the main component resin of the resin layer (A), and the stretching conditions when manufacturing the reflective sheet. Furthermore, the arithmetic mean roughness Ra of the surface of the photocured layer (C) can be optimized by adding a leveling agent, changing the solid content concentration, or changing the drying rate after coating. The measurement of the arithmetic mean roughness Ra shall be in accordance with JIS B0601, and more specifically, it shall be based on the method of the examples described below.

[0120] (Pencil Hardness) The pencil hardness of the surface of the photocured layer (C) is preferably B or higher, more preferably HB or higher, and even more preferably F or higher. Methods for adjusting the pencil hardness of the surface of the photocured layer (C) include, for example, when preparing the photocurable composition (c), using polyfunctional monomers, polyfunctional oligomers, or polyfunctional polymers with a large number of radically polymerizable double bonds per molecular weight to increase the crosslinking density, increasing the blending ratio of these, or increasing the blending ratio of the photopolymerization initiator. However, the method is not limited to these methods. The measurement of the pencil hardness of the surface of the photocured layer (C) shall be in accordance with JIS K 5600-5-4 (1999), and more specifically, based on the method of the examples described below.

[0121] (Reflectance) The reflective sheet of the present invention can have high reflective performance. There are no limitations on the reflective performance of the reflective sheet of the present invention, and the average reflectance of at least one side can be 95% or more, more preferably 96% or more, and especially 97% or more. With a reflective sheet having such reflective performance, a liquid crystal display or the like incorporating this reflective sheet of the present invention can achieve sufficient brightness on its screen. Here, "reflectance" refers to the average reflectance for light with a wavelength of 420 to 700 nm, and a more detailed measurement method will be described in the examples below.

[0122] <Method for Manufacturing the Reflective Sheet of the Present Invention> Below, as an example of a method for manufacturing the reflective sheet of the present invention, a method for manufacturing a reflective sheet with a four-layer structure of "resin layer (A) / resin layer (B) / resin layer (A) / photocured material layer (C)" will be described. However, the manufacturing method is not limited to the method described below.

[0123] (Resin Composition A) A resin composition A is prepared by blending a thermoplastic resin (a1) and, if necessary, other additives as raw materials for the resin layer (A). Specifically, these raw materials are mixed in a ribbon blender, tumbler, Henschel mixer, etc., and then kneaded at a temperature above the resin flow start temperature (for example, 220°C to 270°C) using a Banbury mixer, single-screw or twin-screw extruder, etc. to obtain resin composition A. Alternatively, resin composition A can be obtained by adding a predetermined amount of each raw material using separate feeders, etc. Alternatively, a portion of the raw materials can be prepared as a masterbatch and used as a raw material. Alternatively, a resin composition can be prepared in advance using a portion of the raw materials, and this resin composition can be kneaded with the other raw materials to obtain resin composition A.

[0124] (Resin Composition B) As raw materials for the resin layer (B), resin composition B is prepared by blending a thermoplastic resin (b1), a fine powder filler (b2), and other additives as needed. Specifically, after mixing these raw materials in a ribbon blender, tumbler, Henschel mixer, etc., resin composition B can be obtained by kneading them at a temperature above the melting point of the resin (for example, 190°C to 270°C) using a Banbury mixer, a single-screw or twin-screw extruder, etc. Also, similar to resin composition A, it is possible to manufacture it using a feeder, etc., use a portion of the raw materials as a masterbatch, or prepare a resin composition in advance using a portion of the raw materials.

[0125] Next, the resin compositions A and B obtained in this manner are dried as necessary, and then supplied to separate extruders, where they are heated to a predetermined temperature or higher to melt them. The conditions such as the extrusion temperature are arbitrary. For example, the extrusion temperature of resin composition A and resin composition B is preferably 220°C to 270°C.

[0126] Subsequently, the molten resin compositions A and B are combined in a T-die designed for two types and three layers, extruded in a layered manner from the slit-shaped discharge port of the T-die, and solidified in close contact with a cooling roll to form a cast sheet.

[0127] It is preferable to stretch the obtained cast sheet in at least one axial direction. By stretching, the interface between the thermoplastic resin (b1) and the fine powder filler (b2) inside the resin layer (B) peels off, forming voids, which promotes whitening of the sheet and can increase the light reflectivity of the film. Furthermore, it is even more preferable to stretch the cast sheet in two axial directions. With uniaxial stretching alone, the voids formed only take the form of fibrous structures that are stretched in one direction, but with biaxial stretching, these voids are stretched in both longitudinal and transverse directions, resulting in a disc-shaped structure. In other words, by biaxial stretching, the peeling area at the interface between the thermoplastic resin (b1) and the fine powder filler (b2) inside the resin layer (B) increases, further promoting whitening of the sheet, and as a result, the light reflectivity of the film can be further increased. In addition, biaxial stretching reduces the anisotropy of the film's shrinkage direction, which can improve the heat resistance of the film and increase its mechanical strength.

[0128] When stretching the cast sheet, the stretching temperature is preferably above the glass transition temperature (Tg) of the thermoplastic resin contained in resin layer (A) or resin layer (B). If the stretching temperature is above the glass transition temperature (Tg), the film can be stretched stably without breaking. When stretching the cast sheet, the stretching temperature is preferably below the higher of (Tg + 50)°C or the melting point (Tm) of the thermoplastic resin. If the stretching temperature is below the higher of (Tg + 50)°C or the melting point (Tm) of the thermoplastic resin, the stretch orientation will increase, resulting in a larger porosity, making it easier to obtain a film with high reflectivity.

[0129] The stretching sequence in biaxial stretching is not particularly limited; for example, simultaneous biaxial stretching or sequential stretching is permitted. After forming a molten cast sheet, it may be stretched in the flow direction (MD) by roll stretching, then stretched in the transverse direction (TD) by tenter stretching, or biaxial stretching may be performed by tubular stretching, etc. The stretching ratio in the case of biaxial stretching is not limited. The area ratio is usually 4 times or more, preferably 5 times or more, and the upper limit is usually 25 times or less, preferably 20 times or less. It is preferable to keep the area ratio within the above range so that the porosity of the reflective sheet can be controlled to an appropriate range and excellent reflective performance can be achieved. When sequential biaxial stretching is performed, the stretching ratio of the first axis is preferably 1.1 to 5.0 times, more preferably 1.5 to 3.5 times, and the stretching ratio of the second axis is preferably 1.1 to 5.0 times, more preferably 2.5 to 4.5 times.

[0130] After stretching, it is preferable to perform heat fixing to impart dimensional stability (shape stability of voids) to the reflective sheet. The processing temperature for heat fixing the film is preferably 130 to 165°C. The processing time required for heat fixing is preferably 1 second to 3 minutes. There are no particular limitations on the heat fixing equipment, but it is preferable to perform the heat fixing process using a tenter that can perform heat fixing after stretching.

[0131] Thus, the laminate [I] (a laminate of resin layer (A) / resin layer (B) / resin layer (A) [I]) constituting the reflective sheet of the present invention can be obtained. Although the co-extrusion method of two types and three layers has been described above, it is also possible to create a laminate structure by coating, extrusion lamination, heat fusion, adhesive, etc. instead of the co-extrusion method.

[0132] The reflective sheet of the present invention can be obtained by providing a photocured material layer (C) on at least one side of the laminate [I] constituting the reflective sheet of the present invention obtained as described above, using the method described above.

[0133] <Applications> The reflective sheet of the present invention can be used as is, as a reflective sheet having the layer structure described above. Furthermore, it can be used in a configuration laminated on a metal plate or resin plate (collectively referred to as "metal plate, etc."), and is useful as a reflector as a component of the above-mentioned applications, namely liquid crystal display devices such as liquid crystal displays. Therefore, a liquid crystal display device can be provided using the reflective sheet of the present invention as a component. In addition, since the reflective sheet of the present invention is also useful as a reflector as a component of lighting fixtures or illuminated signs, lighting fixtures or illuminated signs can also be provided using the reflective sheet of the present invention as a component.

[0134] Examples of metal plates on which the reflective sheet of the present invention is laminated include aluminum plates, stainless steel plates, and galvanized steel plates. The method of laminating the reflective sheet of the present invention onto the metal plate is not particularly limited. Examples include using an adhesive, heat bonding, bonding via an adhesive sheet, and extrusion coating. More specifically, an adhesive such as polyester, polyurethane, or epoxy is applied to the surface of the metal plate to which the reflective sheet is to be bonded, and the reflective sheet is then bonded. Next, the coated surface is dried and heated using an infrared heater and a hot air heating furnace, and while maintaining the surface of the metal plate at a predetermined temperature, the reflective sheet is immediately coated and cooled using a roll laminator to obtain a reflector.

[0135] The applications of the reflective sheet of the present invention are not limited. Due to its excellent reflective performance, the reflective sheet of the present invention is useful as a component used in liquid crystal display devices such as liquid crystal displays, for example, as a reflective member. In particular, it is useful for liquid crystal displays in thin portable information processing terminals such as smartphones and tablet devices. For example, it is suitable as a component of the backlight unit of a liquid crystal display, that is, as a reflective sheet provided in the backlight unit of a liquid crystal display. Furthermore, the reflective sheet of the present invention is useful as a component of a backlight unit. When the reflective sheet of the present invention is used as a component of a backlight unit, the occurrence of brightness unevenness and particle detachment can be reduced. Incidentally, a liquid crystal display is generally composed of a liquid crystal panel, a polarizing reflective sheet, a diffusion sheet, a light guide plate, a reflective sheet, a light source, a light source reflector, etc.

[0136] In particular, the reflective sheet of the present invention is preferably used with the photocured material layer (C) side surface in contact with a component such as a light guide plate. When the reflective sheet of the present invention is laminated in contact with a component such as a light guide plate, it is possible to suppress damage to the component such as a light guide plate that is in contact with the reflective sheet, even if it is subjected to impact such as dropping. Furthermore, by specifying the composition of the photocured material layer (C), it is possible to suppress the abrasion of the reflective sheet surface and the adhesion of debris to the component such as a light guide plate that is in contact with the reflective sheet. Therefore, the reflective sheet of the present invention is preferably used with the photocured material layer (C) side surface in contact with a component such as a light guide plate as a reflective sheet that plays a role in efficiently directing light from a light source to a liquid crystal panel or light guide plate. It is also preferable to use the reflective sheet of the present invention as a light source reflector that plays a role in concentrating irradiated light from a light source placed at the edge and directing it to the light guide plate, with the photocured material layer (C) side surface in contact with a component such as a light guide plate.

[0137] Furthermore, there are no restrictions on the material of the light guide plate, and it can be suitably used in backlight units equipped with various light guide plates, such as those made of polycarbonate resin, polymethyl methacrylate (PMMA) resin, methyl methacrylate-styrene copolymer (MS resin), and cycloolefin resin, and is particularly suitable for backlight units equipped with a light guide plate made of polycarbonate resin. Therefore, it is possible to provide a backlight unit equipped with the reflective sheet of the present invention and a light guide plate made of polycarbonate resin, polymethyl methacrylate (PMMA) resin, methyl methacrylate-styrene copolymer (MS resin), cycloolefin resin, etc.

[0138] The reflective sheet of the present invention can be used in a variety of applications other than those mentioned above, such as various industrial materials, packaging materials, optical materials, and electrical materials.

[0139] <Explanation of Terms> In this invention, the term "film" includes "sheet," and the term "sheet" also includes "film." In this invention, "reflection" means the reflection of light unless otherwise specified, and more specifically, the reflection of visible light. In this invention, when expressed as "X to Y" (where X and Y are any numbers), unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as "preferably greater than X" and "preferably less than Y." Also, when expressed as "greater than or equal to X" (where X is any number), unless otherwise specified, it includes the meaning of "preferably greater than X," and when expressed as "less than or equal to Y" (where Y is any number), unless otherwise specified, it includes the meaning of "preferably less than Y."

[0140] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to mass.

[0141] <Measurement and Evaluation Methods> The measurement and evaluation methods for the samples obtained in the examples and comparative examples are described below.

[0142] (Thickness of the reflective sheet and each layer) The thickness of the reflective sheet (all layers) was measured in μm at 9 points using a fixed-point thickness gauge (FFA-1, manufactured by Ozaki Seisakusho Co., Ltd.), and the average value was rounded to the nearest whole number. The thickness of each layer of resin layer (A) and resin layer (B) was determined by multiplying the total thickness of resin layer (A) and resin layer (B) by the extrusion ratio during sheet molding, and rounding to the nearest whole number. The thickness of the photocured layer (C) was determined by subtracting the total thickness of resin layer (A) and resin layer (B) measured before the photocured layer (C) was laminated from the total thickness of the reflective sheet after the photocured layer (C) was laminated, and rounding the average value of the result to the nearest whole number.

[0143] (Void Ratio) The porosity was calculated using the following formula when measuring a reflective sheet with a fixed-point thickness gauge (FFA-1, manufactured by Ozaki Seisakusho Co., Ltd.) with a flat tip and a diameter of 5 mm, applying an additional load of 25 kgf on top of the weight used to apply the measuring force, and when measuring without the additional load, the thickness was x. Void Ratio (%) = {(y - x) / y} × 100

[0144] (Tape Peeling Evaluation) After applying adhesive tape (manufactured by 3M Japan Ltd., product name "Scotch Ultra Clear Tape S BK-18") to the photocured layer (C) side surface and the opposite side (resin layer (A) side) surface of a reflective sheet (sample), the adhesive tape was peeled off, and the surface of the reflective sheet after peeling was visually inspected and judged according to the following criteria. ◎ (excellent): No peeling of the reflective sheet surface was visually confirmed. ○ (better): Slight peeling of the reflective sheet surface was visually confirmed. △ (good): Partial peeling of the reflective sheet surface was confirmed. × (poor): Large peeling or a large amount of partial peeling of the reflective sheet surface was confirmed.

[0145] (Pencil Hardness) To evaluate the hardness of the surface of the photocured layer (C), a surrogate evaluation was performed as described below. In the case of polyolefin resins described herein, measurement is difficult because the laminate (a laminate formed from resin layer (A) and resin layer (B)) deforms due to its porous nature. Therefore, a sample for pencil hardness measurement was prepared by coating, drying, and UV curing in the same manner as in the examples described later, except that a transparent biaxially oriented polyester film (thickness 100 μm) was used instead of the laminate. Pencil hardness was measured with a load of 750 gf, referring to JIS K5600-5-4 (1999).

[0146] (Arithmetic Mean Roughness) A reflective sheet (sample) is fixed on a flat glass plate, and in accordance with JIS B0601, the arithmetic mean roughness Ra of the photocured layer (C) side sheet surface is measured in both the MD and TD directions using a surface roughness meter (Mitutoyo Corporation, Surftest SJ-210 standard drive type). ＭＤ Ra ＴＤ The following measurements were taken: The measurement speed was 0.5 mm / second, the measurement length was 4.0 mm, and the load was 0.75 mN. The measured values ​​in each direction (MD and TD) were measured (Ra ＭＤ Ra ＴＤ The arithmetic mean roughness Ra was calculated as the average value of the following: For Comparative Example 1, the laminate was used as the measurement sample instead of the reflective sheet (sample).

[0147] (Brightness) A 6.5-inch edge-lit backlight unit was used. The backlight unit was constructed by stacking the following layers on the back chassis from bottom to top: a reflective sheet (sample), a polycarbonate resin light guide plate with LEDs on the edge, a diffusion sheet, two prisms, and a diffusion sheet (topmost). The backlight was lit at a voltage of 27V and a current of 30mA, and the frontal brightness was measured twice for each reflective sheet using a luminance meter (Konica Minolta, CA2500-s) in a darkroom. The relative brightness was determined with the brightness of a reflective sheet without a photocured layer (C) set to 100. For Comparative Example 1, a laminate was used instead of a reflective sheet (sample) for the measurement.

[0148] (Ball Drop Test) When a reflective sheet (sample) is incorporated into the backlight of a liquid crystal display, the following ball drop test was conducted as a substitute test to evaluate the scratches and adhesion of debris to the light guide plate due to impact and friction when a device such as a smartphone is dropped. A drop test sample was prepared by layering a polyvinyl chloride mat (manufactured by Echo Metal Co., Ltd., cutting mat 1149-189, 3 mm thick), an aluminum plate (100 μm thick, GM55 material), a reflective sheet (sample), a polycarbonate resin light guide plate, and a polyester film (80 μm thick) on a 5 cm thick SUS plate, from bottom to top. At this time, the reflective sheet (sample) was positioned so that the photocured material layer (C) of the reflective sheet (sample) was on the upper side, in other words, so that the photocured material layer (C) was in contact with the polycarbonate resin light guide plate. For Comparative Example 1, a laminate was used instead of a reflective sheet (sample) to prepare the drop test sample.

[0149] A metal object with a spherical tip (R=15mm, mass 200g, made of SUS) was dropped from a height of 3cm onto the polyester film of the drop test sample, and this process was repeated 30 times at each location. After repeating this process 30 times at five locations within the same drop test sample, the light guide plate was removed from the drop test sample, and the dot side that had been in contact with the reflective sheet was observed using a microscope (Keyence Corporation, VHX-6000, magnification 500). The number of locations on the light guide plate where scratches were observed, and the number of locations where debris from the reflective sheet was attached to the light guide plate were counted. Preferably, the number of locations with scratches and locations with attached debris should be one or less, and more preferably zero.

[0150] <Raw Materials> The raw materials used in the production of the laminate are described below.

[0151] (COP-A) Amorphous cycloolefin resin (MFR (230°C, 21.18N): 1.5g / 10min, Tg: 129°C) (COP-B) Amorphous cycloolefin resin (MFR (230°C, 21.18N): 15g / 10min, Tg: 105°C)

[0152] (PP-A) Homopolypropylene resin, MFR (230℃, 21.18N): 2.4g / 10min (PP-B) Homopolypropylene resin, MFR (230℃, 21.18N): 0.5g / 10min

[0153] (Titanium Oxide) Rutile-type titanium oxide, TiO2, manufactured by the chlorine process and surface-treated with alumina and silica. ２ Content 96.0%, average particle size (D50): 0.31 μm

[0154] (Preparation of resin composition A) As shown in Table 1 below, COP-A, COP-B, and PP-B were mixed in a mass ratio of COP-A:COP-B:PP-B = 50:25:25 to prepare resin composition A as the raw material for the resin layer (A).

[0155] (Preparation of resin composition B1) As shown in Table 1 below, PP-A and titanium oxide were melt-mixed in a mass ratio of 35:65 in a coaxial twin-screw extruder heated to 270°C and pelletized to produce resin composition B1 as a raw material for resin layer (B).

[0156] (Preparation of resin composition B2) As shown in Table 1 below, PP-A and titanium oxide were melt-mixed in a mass ratio of 45:55 in a coaxial twin-screw extruder heated to 270°C and pelletized to produce resin composition B2 as a raw material for resin layer (B).

[0157]

[0158] (Preparation of Laminates) <Manufacturing Example 1> The above resin compositions A and B1 were supplied to extruders A and B heated to 250°C, respectively. After melting in each extruder, they were co-extruded from a T-die to form a sheet with a three-layer structure of resin layer (A) / resin layer (B) / resin layer (A), and then cooled and solidified to form an unstretched laminate. The resin layers (A) / resin layer (B) / resin layer (A) were extruded in a mass ratio of 3 / 28 / 3, respectively. The resulting laminate was roll-stretched 2.3 times in the film flow direction (MD) at a temperature of 142°C, followed by biaxial stretching by tenter stretching 3 times in the orthogonal direction (TD) at 136°C. Finally, a heat-setting treatment was performed at 158-162°C for 2 minutes to obtain a laminate with a total thickness of 82 μm (resin layer (A) / resin layer (B) / resin layer (A) = 6 μm / 70 μm / 6 μm) and a porosity P1 of 48.8% (a laminate without a photocured layer (C)).

[0159] <Manufacturing Example 2> The above resin compositions A and B2 were supplied to extruders A and B heated to 250°C, respectively. After melting in each extruder, they were co-extruded from a T-die to form a sheet with a three-layer structure of resin layer (A) / resin layer (B) / resin layer (A), and then cooled and solidified to form an unstretched laminate. The resin layers (A) / resin layer (B) / resin layer (A) were extruded in a mass ratio of 3 / 28 / 3, respectively. The resulting laminate was roll-stretched 2.3 times in the film flow direction (MD) at a temperature of 142°C, followed by biaxial stretching by tenter stretching 3 times in the orthogonal direction (TD) at 136°C. Further heat-setting treatment was performed at 158-162°C for 2 minutes to obtain a laminate with a total thickness of 82 μm (resin layer (A) / resin layer (B) / resin layer (A) = 8 μm / 66 μm / 8 μm) and a porosity P1 of 48.8% (a laminate without a photocured layer (C)).

[0160] The laminates obtained in Manufacturing Example 1 and Manufacturing Example 2 were each milled using an ion beam milling method with argon gas, and the cross-sections were observed using an electron microscope (2000x magnification). It was confirmed that voids existed in the resin layer (B) of both laminates.

[0161] <Photo-cured layer (C)> The raw materials used to produce the photo-cured layer (C) will be explained below.

[0162] ((meth)acryloyl group-containing compound (c1)) (c1-1): (meth)acrylate polyfunctional monomer: dipentaerythritol hexaacrylate (hexafunctional) (Kayarad DPHA manufactured by Nippon Kayaku Co., Ltd., double bond equivalent = 10.4 mmol / g) (c1-2): (meth)acrylate polyfunctional polymer (double bond equivalent = 4.41 mmol / g, hydroxyl group equivalent = 4.41 mmol / g, mass average molecular weight Mw = 20,000) (c1-3): urethane acrylate oligomer (molecular weight 2,000, number of acryloyl groups 10, double bond equivalent = 5 mmol / g)

[0163] Here, the molecular weight (M), the double bond equivalents representing the (meth)acryloyl group (N) per unit weight, and M × N of the above (meth)acryloyl group-containing compound (c1) are given. ３ The values ​​are as shown in Table 2 below.

[0164]

[0165] In order to increase the molecular weight after curing and prevent the generation of shavings, it is preferable that the molecular weight (M) of the (meth)acryloyl group-containing compound be high. Similarly, in order to increase the crosslinking sites from the viewpoint of increasing the molecular weight after curing, it is preferable that the double bond equivalent (N) representing the (meth)acryloyl group per unit weight be large. ３ It is preferable that the value is 250,000 or more, and more preferably 650,000 or more.

[0166] (Leveling agent): Silicone-based leveling agent with radical polymerizable functional groups MEGAFACE RS-57 (manufactured by DIC Corporation) (Photopolymerization initiator): Hydroxycyclohexylphenyl ketone (molecular weight 204.27) (Antioxidant): Adekastab 3010 (manufactured by ADEKA Corporation) (Solvent PGM): Polypropylene glycol monomethyl ether (manufactured by Sankyo Chemical Co., Ltd.) (Solvent MEK): 2-Butanone (manufactured by Nacalai Tesque Co., Ltd.)

[0167] <Examples 1-5> (Preparation of coating solution) The above raw materials were blended to prepare the coating solution as shown in Table 1. The solid content concentration was adjusted to 20% by mass in all cases.

[0168] The laminate prepared in Manufacturing Example 1 or Manufacturing Example 2 was subjected to corona treatment on the surface to be coated, and wetting was confirmed by dropping Nacalai Tesque Co., Ltd.'s "Wetting Index Standard Solution No. 64" onto it. The coating solution was applied to the corona-treated laminate using a wire bar, dried in an 80°C oven for 1 minute to evaporate the solvent, and then irradiated with UV light using a high-pressure mercury lamp (cumulative light intensity: 200 mJ / cm²). ２ The following steps were taken: the material was photocured to form a photocured layer (C) and a reflective sheet (sample) was obtained. The laminate without the photocured layer (C), the composition of the coating liquid, the thickness of the photocured layer (C), the porosity (%) of the reflective sheet, the tape peel evaluation results, pencil hardness, scratches on the light guide plate and adhesion of debris to the light guide plate in the ball drop test, arithmetic mean roughness Ra [μm], and brightness are shown in Table 3. The laminate produced in Manufacturing Example 1 (a laminate without the photocured layer (C)) is also shown in Comparative Example 1 in Table 3.

[0169]

[0170] From the results in Table 3, Examples 1 to 5 are reflective sheets having a photocured layer (C) made of a (meth)acryloyl group-containing compound, exhibiting a surface pencil hardness of B or higher, good results in tape peel tests, and no scratches on the light guide plate in the ball drop test. In particular, Examples 1 to 3 and 5 showed even better reflective sheeting, with no residue adhering to the light guide plate in the ball drop test. This is presumed to be because the photocured layer (C) contains a (meth)acryloyl group-containing compound such as a polyfunctional monomer, polyfunctional oligomer, or polyfunctional polymer, resulting in the formation of a high molecular weight cured product and reducing the amount of low molecular weight components detached from the surface of the reflective sheet. Furthermore, regarding the effect of providing the photocured layer (C) on brightness, Example 1 showed a decrease of 0.5% or less, while Examples 2 to 5 showed an increase, demonstrating good brightness. These results are thought to be due to an arithmetic mean roughness Ra of 0.3 μm or less, which increases the amount of light with a larger emission angle of diffusely reflected light from the resin layer (B) within the reflective sheet, thus improving brightness or suppressing brightness reduction. Although the reflectance of the reflective sheets produced in the examples and comparative examples is not shown, it is clear from the composition of the reflective sheets that they have high reflective performance.

Claims

1. A reflective sheet having voids, wherein at least one side of a laminate [I] having a layer structure in which a resin layer (A) containing a thermoplastic resin (a1) as the main component resin, a resin layer (B) containing a thermoplastic resin (b1) as the main component resin and a fine powder filler (b2) are laminated in this order, is provided with a photocured product layer (C) made of a photocurable composition (c).

2. The reflective sheet according to claim 1, wherein the photocurable composition (c) is a photocurable composition containing a (meth)acryloyl group-containing compound (c1).

3. The reflective sheet according to claim 1, wherein the arithmetic mean roughness (Ra) of the reflective sheet surface on the side of the photocured material layer (C) is 0.3 μm or less.

4. The reflective sheet according to claim 1, wherein the pencil hardness of the surface of the photocured material layer (C) is B or higher.

5. The reflective sheet according to claim 1, wherein the pencil hardness of the surface of the photocured material layer (C) is between B and F.

6. The reflective sheet according to claim 1, wherein the thickness of the photocured layer (C) is 0.1 μm or more and 20 μm or less.

7. The reflective sheet according to claim 1, wherein the void ratio of the entire reflective sheet is 10 to 80%.

8. The reflective sheet according to claim 1, wherein the fine powder filler (b2) is an inorganic fine powder.

9. The reflective sheet according to claim 1, wherein the fine powder filler (b2) is titanium dioxide.

10. The reflective sheet according to claim 1, wherein the content of the fine powder filler (b2) in the resin layer (B) is 30 to 80% by mass relative to the entire resin layer (B).

11. The reflective sheet according to claim 1, wherein the resin layer (B) has voids and the resin layer (A) does not have voids.

12. The reflective sheet according to claim 1, wherein the resin layer (B) of the laminate [I] has voids, the resin layer (A) does not have voids, and the photocured layer (C) is provided in contact with the resin layer (A) of the laminate [I].

13. The reflective sheet according to claim 1, wherein the thermoplastic resin (a1) is a polyolefin resin.

14. The reflective sheet according to claim 1, wherein the thermoplastic resin (b1) is a polyolefin resin.

15. The reflective sheet according to claim 1, wherein the sheet thickness is 30 to 250 μm.

16. The reflective sheet according to claim 1, characterized in that the surface of the photocured material layer (C) of the reflective sheet is arranged to be in contact with the light guide plate.

17. The reflective sheet according to claim 1, used as a component of a backlight unit.

18. The reflective sheet according to claim 1, used as a component of a liquid crystal display.

19. A liquid crystal display comprising a reflective sheet as described in any one of claims 1 to 17 as a constituent element.

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