Scintillator unit and radiation detector

Abstract

The invention provides a scintillator unit and a radiation detector, the scintillator unit has little light leakage from a scintillator to an adhesive layer, and the radiation detector can improve the sensitivity of radiation and the resolution of an image to be formed. Specifically disclosed is a scintillator unit including an adhesive layer between a scintillator and a support member, and a low refractive index layer having a lower refractive index than the adhesive layer between the scintillator and the adhesive layer.

Description

[0001] This application is a divisional application of the invention patent application with the application date of July 30, 2020, application number 202080049484.2 (international application number PCT / JP2020 / 029187), and invention name “Scintillator unit and radiation detector”. Technical Field

[0002] The present invention relates to a scintillator unit and a radiation detector. Background Art

[0003] Radiation detectors are used in medical settings and other settings to image subjects using radiation. They primarily consist of a scintillator that generates light from radiation (e.g., X-rays) and a detection unit containing a two-dimensional array of light-receiving devices. When a subject is irradiated with X-rays, the X-rays that pass through the subject generate light from the scintillator. The detection unit detects this light and forms a two-dimensional image of the transmitted X-rays.

[0004] A columnar crystal group containing multiple columnar crystals is used as a scintillator to efficiently transmit the light generated by the scintillator to a light receiving device, and to improve the sensitivity of the radiation detector to radiation. A space containing air is formed between the columnar crystals in the columnar crystal group. When alkali metal halide crystals such as cesium iodide (CsI) are used as columnar crystals, light entering the space containing air with a low refractive index from the columnar crystals with a high refractive index does not pass through, but is reflected at the interface between the columnar crystals and the space. Therefore, even if the light generated by the scintillator is emitted in any direction, the light generated in the columnar crystals is guided to the detection unit by utilizing the physical phenomenon of "total reflection" caused by the refractive index difference between the two media.

[0005] Furthermore, in order to guide most of the light generated by the scintillator to the detection unit, a reflective layer may be provided on the surface of the scintillator opposite the detection unit via an adhesive layer. For example, Patent Document 1 describes a flat panel detector (FPD) that includes, in this order in the direction of incidence of radiation, an air layer, a dielectric multilayer reflective film, an adhesive layer, a phosphor layer, and a photodetector.

[0006] Reference List

[0007] Patent Literature

[0008] PTL 1: International Publication No. WO 2016 / 167334 Summary of the Invention

[0009] Technical issues

[0010] The inventors of the present application studied the FPD described in Patent Document 1, which uses a group of columnar crystals containing CsI (refractive index = 1.74) as the phosphor layer and a layer containing an acrylic resin (refractive index = 1.45) as the adhesive layer. They found that light generated by the columnar crystals contained in the phosphor layer is less likely to be reflected at the interface between the phosphor layer and the adjacent adhesive layer and leak into the adhesive layer.

[0011] It was also found that light incident on the adhesive layer is attenuated in the adhesive layer, leaving room for further improvement in sensitivity to radiation.

[0012] It was also found that light generated from the columnar crystals contained in the phosphor layer propagates and diffuses in the adhesive layer, and then enters other columnar crystals, leaving room for further improving the clarity (resolution) of an image to be formed.

[0013] Therefore, an object of the present invention is to provide a scintillator unit with less light leakage from the scintillator to the adhesive layer. Another object of the present invention is to provide a radiation detector in which the sensitivity to radiation and the resolution of an image to be formed can be improved using the scintillator unit.

[0014] Solution to the problem

[0015] The present invention relates to a scintillator unit including an adhesive layer between a scintillator and a support member, wherein a low-refractive-index layer having a lower refractive index than the adhesive layer is located between the scintillator and the adhesive layer.

[0016] The present invention also relates to a radiation detector comprising: a scintillator unit including an adhesive layer between a scintillator and a supporting member, and a detection unit for detecting light generated from the scintillator, wherein the scintillator unit includes a low refractive index layer having a lower refractive index than the adhesive layer, and the detection unit is opposite to the low refractive index layer via the scintillator.

[0017] Advantageous Effects of the Invention

[0018] The present invention can provide a scintillator unit with less light leakage from the scintillator to the adhesive layer and a radiation detector capable of improving sensitivity to radiation and the resolution of an image to be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1A is a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention.

[0020] Figure 1B is a schematic enlarged cross-sectional view of an embodiment of a scintillator unit according to the present invention.

[0021] Figure 2Ais a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention.

[0022] Figure 2B is a schematic enlarged cross-sectional view of an embodiment of a scintillator unit according to the present invention.

[0023] Figure 3 is a schematic cross-sectional view of an embodiment of a low refractive index layer.

[0024] Figure 4 is a schematic cross-sectional view of an embodiment of a radiation detector according to the present invention.

[0025] Figure 5A is a scanning electron microscope (SEM) image of a scintillator unit according to the present invention.

[0026] Figure 5B is an enlarged scanning electron microscope (SEM) image of a scintillator unit according to the present invention.

[0027] Figure 6 is a SEM image of a scintillator unit according to the present invention. DETAILED DESCRIPTION

[0028] The scintillator unit according to the present invention includes an adhesive layer between the scintillator and the supporting member. The scintillator unit according to the present invention also includes a low refractive index layer between the scintillator and the adhesive layer, the refractive index of which is lower than that of the adhesive layer. The inventors of the present application studied the FPD described in Patent Document 1, which uses a columnar crystal group containing CsI (refractive index = 1.74) as the phosphor layer and a layer containing acrylic resin (refractive index = 1.45) as the adhesive layer. It was found that the light generated by the columnar crystals contained in the phosphor layer is difficult to reflect at the interface between the phosphor layer and the adjacent adhesive layer, and easily leaks into the adhesive layer. The term "total reflection" used herein refers to a phenomenon that is more likely to occur as the refractive index difference between the two media increases. Since the refractive index difference between the phosphor layer and the adjacent adhesive layer is small, "total reflection" is less likely to occur at the interface between the phosphor layer and the adhesive layer. Therefore, the inventors of the present application set a low refractive index layer with a refractive index lower than that of the adhesive layer between the phosphor layer (the "scintillator" in the present invention) and the adhesive layer.

[0029] Because the refractive index difference between the scintillator and the low-refractive-index layer is greater than that between the scintillator and the adhesive layer, light from the scintillator is more likely to be reflected at the interface between the scintillator and the low-refractive-index layer. This reduces the likelihood of light leaking from the scintillator into the adhesive layer. Consequently, radiation detectors incorporating this scintillator unit have improved sensitivity to radiation. Furthermore, light generated by the scintillator is less likely to propagate and diffuse within the adhesive layer. This also improves the resolution of the resulting image.

[0030] The following describes the embodiments of the present invention in detail. Unless otherwise specified, physical properties were determined at 25°C.

[0031] Figure 1A is a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention, Figure 1B is an enlarged view of the schematic cross-sectional view. Figure 1A In FIG, the scintillator unit 100 includes a low refractive index layer 104, an adhesive layer 103, and a support member 101 in this order on a scintillator 105. The incident direction of radiation 106 on the scintillator unit 100 is indicated by an arrow. Components of the scintillator unit 100 are described in detail below.

[0032] [Scintillator 105]

[0033] Figure 1B yes Figure 1A Magnified view of the square area. Preferably, the scintillator 105 in the scintillator unit 100 according to the present invention contains a material that emits light through radiation (X-rays, gamma rays, charged particles, etc.), and is an aggregate of multiple crystals (columnar crystals) in a columnar (or needle-shaped) shape (hereinafter referred to as a columnar crystal group). The columnar crystal group can be used as the scintillator 105 to easily guide light and prevent light scattering. This can further prevent light from leaking into the adhesive layer, making it difficult for light generated from one columnar crystal to enter another columnar crystal, thereby improving the resolution of the image to be formed.

[0034] The scintillator unit 100 according to the present invention is particularly suitable for use in radiation detectors produced by directly forming a scintillator film on a sensor panel including a detection unit. In this case, the scintillator 105 may be referred to as a scintillator film.

[0035] like Figure 1B As shown, the central axis 107 of the columnar crystals 102 is preferably arranged parallel to the incident direction of the radiation 106. However, it does not need to be strictly parallel to the incident direction of the radiation 106, but the tilt angle is preferably within 10 degrees, more preferably within 5 degrees. Furthermore, the columnar crystals 102 do not necessarily need to be uniformly tilted. The lack of strict parallelism does not significantly affect the advantages of the present invention. The scintillation light 109 emitted from the scintillator 105 by the radiation 106 is repeatedly reflected and propagated in the columnar crystals 102.

[0036] The columnar crystal group does not need to have the same columnar crystal diameter, and can also be a collection of columnar crystals of different diameters. The columnar crystal diameter refers to the equivalent circular diameter in the cross section perpendicular to the central axis of the columnar crystal. The term "equivalent circular diameter" used in this article refers to the "projected area equivalent circular diameter" usually mentioned in a microscope, which refers to the diameter of a perfect circle with the same area as the projected area. The columnar crystal diameter is preferably in the range of 0.01 to 50 μm, more preferably in the range of 0.1 to 15 μm. From one end to the other, the diameter of the columnar crystal can vary in the range of 0.01 to 50 μm.

[0037] Columnar crystals with diameters smaller than 0.01 μm are much smaller than the wavelength of light, suppressing geometrical diffraction and optical scattering. Consequently, light passes through the boundaries of the side surfaces of each columnar crystal and spreads widely throughout the columnar crystal group, potentially contributing to reduced resolution. Columnar crystals with diameters exceeding 50 μm increase the amount of light that is not fully reflected by the side surfaces of the columnar crystals, potentially causing significant light leakage into adjacent columnar crystals.

[0038] The columnar crystals 102 preferably have the same length in the direction of the central axis 107. A more uniform length of the columnar crystal group tends to result in higher resolution. However, the columnar crystal group does not necessarily have to be of the same length; the scintillator 105 may include both long and short columnar crystals. For example, scintillation light leaking from a short columnar crystal can enter an adjacent columnar crystal and propagate through the columnar crystal scintillator to a light receiving device directly below the adjacent columnar crystal. Therefore, the scintillator 105 can have any columnar crystal structure that achieves the desired resolution.

[0039] The scintillator 105 may include spaces or light scatterers in the columnar crystals 102. Although such spaces or light scatterers scatter the scintillation light, the scattered light can enter adjacent columnar crystals and can be guided in the columnar crystals to a light receiving device directly below the adjacent columnar crystals.

[0040] Examples of materials suitable for the scintillator 105 include halides of alkali metals, alkaline earth metals, transition metals, typical elements, and rare earth metals. Other examples include oxides, nitrides, chalcogenides, and Group 13 and Group 14 compounds. Specific examples include NaI(Tl), CsI(Tl), CsI(Na), Lu2SiO5(Ce), Lu2Y2SiO5, Gd2SiO5, Bi4Ge3O 12 , ZnWO4, CdWO4, PbWO4, LuAlO3, Y3Al5O 12 (Ce), YAlO3(Ce), Lu3Al5O 12 (Ce), Lu3Al5O 12(Pr) and CeF 3. In particular, the scintillator 105 preferably contains CsI(Tl).

[0041] [Supporting member 101]

[0042] Approximately half of the light generated by the scintillator 105 is repeatedly reflected in the columnar crystals 102 and propagates toward a surface of the scintillator 105 (hereinafter referred to as the light extraction surface), which is the surface opposite to the surface of the scintillator 105 where the support member 101 and the adhesive layer 103 are located. Since the refractive index of the low-refractive-index layer 104 is lower than that of the adhesive layer 103 between the adhesive layer 103 and the scintillator 105, most of the light transmitted in the direction of the support member 101 is reflected at the interface between the columnar crystals 102 and the low-refractive-index layer 104 and guided to the light extraction surface.

[0043] At least a portion of the support member 101 preferably includes a reflective layer or a light-absorbing layer. When the support member 101 includes a reflective layer capable of reflecting light, light leaking into the adhesive layer can be reflected back into the scintillator and propagated toward the light extraction surface, thereby increasing the amount of light to be detected and improving sensitivity to radiation.

[0044] The reflective layer can be made of a metal material such as aluminum. It is preferably a dielectric multilayer reflective layer with a higher reflectivity than metal materials. This further enhances sensitivity to radiation. The low-refractive-index layer 104 and the reflective layer are positioned on the scintillator 105. The low-refractive-index layer 104 and the reflective layer are bonded together by an adhesive layer 103. The adhesive layer 103 can also be referred to as a space-filling layer.

[0045] When the support member 101 includes a light-absorbing layer capable of absorbing light, the light-absorbing layer can absorb light that leaks into the adhesive layer 103 and prevent scintillation light emitted from one columnar crystal from entering another columnar crystal. The light-absorbing layer can absorb some or all of the light. The use of a light-absorbing layer reduces sensitivity to radiation but improves the resolution of the image being formed. The light-absorbing layer can be a sheet containing carbon particles.

[0046] The scintillator unit preferably includes a low-refractive index layer between the end of the columnar crystals in the extending direction and the adhesive layer. The low-refractive index layer 104 on one side of the scintillator 105 (columnar crystal group) improves the total internal reflection efficiency of light at the interface between the columnar crystals 102 and the low-refractive index layer 104, preventing light from leaking from the scintillator into the adhesive layer 103.

[0047] exist Figure 1A and Figure 1BIn the structure of the present invention shown, the scintillator 105, the low-refractive index layer 104, and the adhesive layer 103 are arranged in this order. It is important to form the low-refractive index layer 104 between the scintillator 105 and the adhesive layer 103 so as to be in contact with the scintillator 105. This can significantly reduce the amount of light leaking from the columnar crystals 102 into the adhesive layer 103.

[0048] The following describes a scintillator unit including a CsI (n=1.74) columnar film as the scintillator 105. The low refractive index layer (n=1.15) on the upper surface of the CsI can improve the total reflection efficiency at the interface between the low refractive index layer and the CsI, and can keep a large amount of light within the CsI. Therefore, the radiation detector including the scintillator unit can improve the sensitivity to radiation and the resolution of the image to be formed. That is, it is assumed that the radiation 106 enters the scintillator 105 and is converted into visible light at the light-emitting point 108. Among the generated light, the scintillation light 109 that reaches the interface between the scintillator 105 and the low refractive index layer 104 is more likely to stay in the scintillator 105 due to total reflection.

[0049] The total reflection efficiency at the interface with CsI (n=1.74) was compared between a known structure in which an adhesive layer (n=1.45) containing an acrylic resin is in contact with CsI and a structure of the present invention in which a low refractive index layer 104 is in contact with CsI. The total reflection efficiency was calculated using Snell's law for the solid angle of light emitted from the upper surface of CsI. S=1-cos[arcsin(n / 1.74)] represents the proportion S of light entering the medium on the upper surface of CsI from a point on the upper surface, where there is no total reflection of the light entering the medium from that point. When the refractive index of the upper surface medium is 1.74, since there is no refractive index difference, all light is transmitted, and S=1. If the refractive index n of the upper surface medium is 1.45, 1.20, 1.15, or 1.10, S is 0.45, 0.28, 0.25, or 0.23, respectively. Therefore, when the adhesive layer (n=1.45) is a low-refractive index layer, the ratio of light leakage from CsI is reduced by 38% for a low-refractive index layer with a refractive index n of 1.20, 44% when n=1.15, and 49% when n=1.10.

[0050] [Adhesive layer 103]

[0051] The adhesive layer 103 may be formed of any material having the function of bonding the support member 101 and the low refractive index layer 104. The adhesive layer 103 may be formed of a general-purpose thermoplastic resin. From the perspective of transparency, an acrylic resin is preferred.

[0052] Or, as Figure 2A and Figure 2BAs shown, an adhesive layer 110 having both adhesive and reflective functions may also be used. The adhesive layer 110 may include a scattering layer containing light scattering particles and a binder resin. In this structure, the adhesive layer 110 not only serves to bond the support member and the low refractive index layer together, but also serves to reflect light leaking from the low refractive index layer. For example, the adhesive layer 110 preferably contains titanium oxide as light scattering particles and epoxy resin as a binder. In such a structure, the low refractive index layer 104, the adhesive layer 110 having both adhesive and reflective functions, and the support member 101 are disposed on the scintillator 105. When the adhesive layer 110 is used, the support member preferably includes a light absorbing layer.

[0053] [Low refractive index layer 104]

[0054] exist Figure 1A 、 Figure 1B 、 Figure 2A and Figure 2B In the structure of the present invention shown, the low refractive index layer 104 preferably has a thickness T1 in the range of 300 nm to 5 μm. In the present invention, the thickness T1 of the low refractive index layer is defined as the average distance from the end of the columnar crystal to the interface between the low refractive index layer and the adhesive layer. To fully improve the total reflection efficiency, it is preferably a thickness equal to or greater than the emission wavelength of the scintillator. This determines the lower limit of T1. When using a scintillator that emits light in the visible light region, T1 is preferably greater than 300 nm. A T1 that is too large may result in a long optical path to the interface with the adhesive layer, more prone to lateral diffusion, and reduced resolution. Therefore, T1 is preferably 5 μm or less. The penetration depth T2 in the gaps between the columnar crystals of the low refractive index layer is preferably 25 μm or less. The penetration depth T2 in the gaps between the columnar crystals of the low refractive index layer is the length obtained by subtracting T1 from the average distance T3 from the interface between the low refractive index layer and the non-low refractive index layer portion located between the columnar crystals to the interface between the low refractive index layer and the adhesive layer. Excessive penetration depth may increase the proportion of light propagating between the columnar crystals and reduce resolution.

[0055] <Composition and structure>

[0056] exist Figure 3 In the embodiment, by using a solid material having a refractive index of 1.65 or less as a skeleton and appropriately setting porosity for lowering the refractive index, the strength of the low refractive index layer 104 can be improved.

[0057] The solid material may be crystalline or amorphous. The solid material may be particles. The particles may be, but are not limited to, spherical particles, irregular particles, spherical particles or irregular particles connected in a beaded or branched manner, hollow particles having a cavity, or hollow particles connected in a beaded or branched manner.

[0058] Examples of the solid material include resins such as fluorinated polymers and acrylic resins, fluorides such as magnesium fluoride and calcium fluoride, carbonates such as calcium carbonate and potassium carbonate, sulfates such as barium sulfate, and oxides such as silicon dioxide and aluminum oxide.

[0059] Examples of low-refractive-index solid materials include organic materials such as fluorinated polymers and inorganic materials such as magnesium fluoride and silicon dioxide.

[0060] However, even low-index fluorinated polymers have a refractive index of about 1.30, while magnesium fluoride and silicon dioxide (quartz) have refractive indices of 1.38 and 1.46, respectively. Single materials with refractive indices well below 1.30 are primarily gases such as nitrogen or oxygen.

[0061] In terms of refractive index, cost, and chemical stability, the solid material preferably contains silicon dioxide. More specifically, the solid material preferably consists primarily of silicon dioxide. As used herein, the phrase "the solid material consists primarily of silicon dioxide" means that the solid material contains silicon dioxide at a content of 50% by mass or greater. The solid material typically contains silicon dioxide at a content of 90% by mass or greater.

[0062] Specific examples of the silica particles include Snowtex series manufactured by Nissan Chemical Industries, Ltd., organosilicone sol, Thrulya series manufactured by JGC Catalysts & Chemicals, Ltd., and Aerosil series manufactured by Evonik Industries AG and sold by AEROSIL GmbH.

[0063] The refractive index n a Material A and refractive index n b The composite material C composed of material B generally has a refractive index n approximately represented by formula (1) c :

[0064] Formula (1)

[0065] n c = [n a xv a / 100] + [n b xv b / 100] (1)

[0066] where v a and v b represent the volume fractions of material A and material B constituting the composite material (v a +v b =100).

[0067] According to formula (1), the composite material of solid material and air, i.e., the porous membrane with solid material skeleton as low refractive index layer 104, can have a refractive index lower than the original solid material. In such a structure, the lower the refractive index of the solid material skeleton or the higher the porosity of low refractive index layer 104, the lower the refractive index of low refractive index layer 104. In order to improve the porosity of low refractive index layer 104, low refractive index layer 104 can have a porous structure. In this respect, low refractive index layer 104 can be referred to as a porous membrane.

[0068] In formula (1), when material A is air and material B is silicon dioxide, the refractive index of air n is a is 1.00, the refractive index of silicon dioxide n b is 1.46, the volume fraction of silicon dioxide v b 100-V a Therefore, v a The refractive index n of the low refractive index layer 104 is determined to be c Function of v a Refers to porosity.

[0069] The porosity of the low refractive index layer 104 is preferably 60.0% to 95.0%, more preferably 65.0% to 90.0%.

[0070] For example, according to formula (1), when the porosity of the low refractive index layer 104 having a silica (refractive index 1.46) skeleton is less than 60.0%, the refractive index may exceed 1.15.

[0071] On the other hand, a porosity exceeding 95.0% may result in the refractive index of the low refractive index layer 104 being less than 1.05 and being too low, and the strength being low due to a small amount of the skeleton constituting the low refractive index layer 104 .

[0072] Silica preferably has at least one of an organic group and a hydroxyl group on its surface. Silica having hydroxyl groups on its surface has high hydrophilicity. Therefore, the low refractive index layer 104 having such a silica particle skeleton can have high hydrophilicity.

[0073] For example, the surface of silica can be modified with a silane coupling agent to impart functionality to the low refractive index layer 104. For silica having hydroxyl groups on the surface, a dehydration condensation reaction between the hydroxyl groups and the hydrolysis product of the silane coupling agent can be utilized.

[0074] Examples of the organic group include alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, propyl and butyl groups, hydrocarbon groups having a polymerizable moiety such as vinyl, acryloyl and methacryloyl groups, and aromatic hydrocarbon groups such as phenyl groups.

[0075] Silica having an organic group on its surface can impart various functions to the low refractive index layer 104 , such as water repellency, oil repellency, biocompatibility, electron transport properties, and polymerizability.

[0076] Not all functional groups on the silica surface are substituted by organic groups, and organic groups and hydroxyl groups may exist in any proportion.

[0077] [Hollow particles]

[0078] The low refractive index layer 104 including hollow particles is further described. However, the present invention is not limited thereto. The hollow particles have a shell formed of a solid material and have a cavity (space) inside the shell.

[0079] The low refractive index layer 104 preferably includes a plurality of hollow particles. The low refractive index layer 104 including a plurality of hollow particles may further include solid particles or a binder in addition to the hollow particles.

[0080] Figure 3 An example of the structure of the low refractive index layer 104 including hollow particles as primary particles composed of a solid material is shown.

[0081] The low refractive index layer 104 includes a plurality of hollow particles 301 and spaces 302 between the hollow particles 301. The hollow particles also include spaces 304. Figure 3 In FIG. 1 , reference numeral 303 denotes a housing, and reference numeral 305 denotes a substrate. The substrate 305 is a material on which the low refractive index layer 104 is to be formed. Figure 1A 、 Figure 1B 、 Figure 2A 、 Figure 2B and Figure 4 In the structure of the present invention shown, the substrate 305 corresponds to the scintillator 105 .

[0082] The porosity X (%) and the porosity Y (%) preferably satisfy the relationship X < Y, where the porosity X (%) is the ratio of the total volume of the spaces within the hollow particles to the unit volume of the low refractive index layer 104, and Y (%) is the ratio of the total volume of the spaces between the hollow particles to the unit volume of the low refractive index layer 104. (X + Y) represents the porosity of the low refractive index layer 104.

[0083] The refractive index n of the low refractive index layer 104 is expressed by the following formula (2):

[0084] Formula (2)

[0085] n=[n a x(X + Y) / 100] + [n s x(100 - X - Y) / 100] (2)

[0086] where na represents the refractive index of air (n a =1), n s represents the refractive index of the hollow particle shell (n s >1). According to formula (2), n increases with the increase of X+Y or n s decrease due to the decrease of .

[0087] The refractive index n of the low refractive index layer 104 is also expressed by the following formula (3):

[0088] Formula (3)

[0089] n=[n a x Y / 100] + [n p x (100 - Y) / 100] (3)

[0090] where n p represents the refractive index of a hollow particle (n p >1). Refractive index n p is an apparent refractive index calculated from the ratio of the volume and refractive index of the shell of a hollow particle to the volume and refractive index of the space between them. a =1,n b =n s , where v a represents the volume of the hollow particle space, v b represents the volume of the shell, then n c =n p According to formula (3), n increases with the increase of Y or n p decreases with the decrease of .

[0091] The refractive index n of the low refractive index layer 104 can also be measured by optical measurement and the known n a 、n s and n p Substitute into formulas (2) and (3) to estimate X and Y.

[0092] The dense arrangement of hollow particles reduces the volume fraction of the spaces between the hollow particles and increases the volume fraction of the shell formed by components with a higher refractive index than air, thereby increasing the refractive index of low-refractive-index layer 104. In contrast, the sparse arrangement of hollow particles increases the volume fraction of the spaces between the hollow particles and reduces the volume fraction of the shell, thereby reducing the refractive index of low-refractive-index layer 104. Therefore, in order to further reduce the refractive index of low-refractive-index layer 104, it is preferable to increase Y / X. More specifically, it is preferable to satisfy the relationship Y / X>1, that is, X<Y.

[0093] X and Y preferably satisfy the relationship X<(100-XY) <Y。

[0094] The low refractive index layer 104 may include particles composed of a solid material and a binder for bonding the particles together to increase strength. When a binder is used, the solids in the low refractive index layer 104 are the hollow particles and the outer shell of the binder, and the volume fraction of the solids relative to the unit volume of the low refractive index layer 104 is represented by (100-XY)(%).

[0095] Satisfying the relationship X<(100-XY) further increases the strength of the low-refractive-index layer 104. Satisfying the relationship (100-XY)<Y further decreases the refractive index of the low-refractive-index layer 104.

[0096] The sum of X and Y (X+Y) is preferably in the range of 60.0% to 95.0%, more preferably 65.0% to 90.0%. (X+Y) in these ranges makes it easy to adjust the strength of the low refractive index layer 104 and the refractive index of the low refractive index layer 104 within the desired range.

[0097] In the low refractive index layer 104 , X preferably ranges from 8.0% to 32.0%, more preferably from 10.0% to 28.0%, and still more preferably from 12.0% to 24.0%.

[0098] On the other hand, the range of Y is preferably 30.0% to 80.0%, more preferably 35.0% to 75.0%, and still more preferably 40.0% to 70.0%.

[0099] X and Y within these ranges make it easy to adjust the strength of low refractive index layer 104 and the refractive index of low refractive index layer 104 within a desired range.

[0100] Despite Figure 3 In the example shown, the hollow particles are substantially spherical, but the hollow particles can have any shape. The hollow particles have an outer shell 303 and a space 304 formed inside the hollow particle and surrounded by the outer shell. In this case, the hollow particles can be considered as core-shell particles containing air as a core.

[0101] The refractive index n of a hollow particle p It is expressed by formula (4):

[0102] Formula (4)

[0103] n p = [n s x(100 - V a ) / 100] + [n a x V a / 100] (4)

[0104] Where V aIt represents the volume fraction of the internal space relative to the total volume of the hollow particle. Therefore, the refractive index n of a hollow particle is p The refractive index n of the shell material s and the porosity V of the hollow particles a Decide.

[0105] The porosity V of a hollow particle a The range is preferably 30.0% to 70.0%, more preferably 35.0% to 65.0%.

[0106] The porosity V in these ranges a The refractive index of the low-refractive-index layer 104 can be easily lowered, the shell strength of the hollow particles can be kept constant, and the strength of the low-refractive-index layer 104 can be kept constant.

[0107] Like the refractive index of solid materials, the refractive index of the shell of the hollow particle is n s It is preferably 1.10 or more, 1.20 or more, 1.25 or more, 1.30 or more, or 1.35 or more, and is preferably 1.65 or less or 1.60 or less. These ranges can be freely combined.

[0108] In these ranges, the refractive index n of the hollow particle shell is s The following results can be produced: an easy-to-manufacture low-refractive-index layer 104 , high-strength hollow particles, a high-strength low-refractive-index layer 104 , and a low-refractive-index layer 104 with a low refractive index.

[0109] The outer shell of the hollow particle may be formed of the same material as the solid material.

[0110] The shell of the hollow particle may have micropores. The micropores in the shell can further reduce the refractive index of the shell.

[0111] The number-average particle size of the primary particles of the hollow particles is preferably in the range of 1 to 200 nm, more preferably 5 to 100 nm, further preferably 10 to 100 nm, and particularly preferably 20 to 100 nm.

[0112] The number average particle diameter within these ranges can result in easy production of hollow particles, easy prevention of light scattering, and further improvement in the transmittance of the low refractive index layer 104 .

[0113] [Fumed silica particles and chain silica particles]

[0114] The low refractive index layer 104 preferably includes at least one type of particle selected from the group consisting of secondary particles, chain-like secondary particles, and branched secondary particles, wherein the primary particles composed of solid materials in the secondary particles form a three-dimensional structure, the primary particles composed of solid materials are connected in a chain-like manner in the chain-like secondary particles, and the primary particles composed of solid materials are connected in a branched form in the branched secondary particles. When particles composed of solid materials form aggregates, the aggregates are also included in the secondary particles, and the primary particles composed of solid materials in the secondary particles form a three-dimensional structure.

[0115] The primary particles composed of solid materials form secondary particles with a three-dimensional structure, the chain-like secondary particles in which the primary particles composed of solid materials are connected in a chain-like manner, and the branched secondary particles in which the primary particles composed of solid materials are connected in a branched form reduce the volume fraction of the solid material in the low refractive index layer 104. This can increase the volume fraction of the space. As a result, the refractive index of the low refractive index layer 104 can be reduced.

[0116] The number average particle size of the primary particles composed of solid materials is preferably in the range of 1 to 200 nm, more preferably 5 to 100 nm, even more preferably 10 to 100 nm, particularly preferably 20 to 100 nm.

[0117] When the number average particle diameter of primary particle is within these scopes, can suitably control the aggregation of particle, and improve the dispersibility in the coating fluid.In addition, can prevent that primary particle from becoming light scatterer in the wavelength range of 400 to 700nm, and further improve the transmitance of low-index layer 104.

[0118] The following describes fumed silica particles as an example of secondary particles in which primary particles composed of a solid material form a three-dimensional structure. However, the present invention is not limited thereto.

[0119] Fumed silica particles can be produced by hydrolyzing silicon tetrachloride at high temperatures in an oxygen and hydrogen flame. In these fumed silica particles, primary particles measuring tens of nanometers fuse to form secondary particles with a three-dimensional structure. These secondary particles can aggregate and develop complex, high-order structures.

[0120] Due to its characteristic structure, fumed silica particles are very large particles with an apparent specific gravity of 0.01 to 0.1 g / cm 3 Therefore, the low refractive index layer 104 including the fumed silica particles has a high porosity and can significantly reduce the refractive index.

[0121] The number average particle size of the secondary particles is preferably in the range of 10 to 1000 nm, more preferably 50 to 500 nm.

[0122] When the number average particle diameter of the secondary particles is within these ranges, for example, primary particles of silica form a three-dimensional structure, and the secondary particles are not a single structure of aggregated primary particles.

[0123] The secondary particles having the above structure make it easy to control the porosity and refractive index of the low refractive index layer 104 within the above ranges. In addition, this makes it difficult to form large spaces between the secondary particles, which may be scatterers of light in the wavelength range of 400 to 700 nm, and makes it easy to control the transmittance of the low refractive index layer 104.

[0124] The number average particle size of the primary particles and the secondary particles can be measured using a transmission electron microscope (TEM) (both calculated from the arithmetic mean of the maximum diameters). As described above, the number average particle size of the primary particles and the secondary particles can be controlled, for example, by adjusting the conditions for the high-temperature hydrolysis of silicon tetrachloride in an oxygen and hydrogen flame.

[0125] <Film Formation Method>

[0126] [Method for preparing coating solution]

[0127] The following describes a method for preparing a coating liquid for forming the low refractive index layer 104. Although the following describes fumed silica particles in which primary particles of silica form a three-dimensional structure, the present invention is not limited thereto.

[0128] The fumed silica particles are dispersed in a solvent. The solvent for dispersing the silica particles is preferably a solvent with a high affinity for the fumed silica particles. A single solvent or a mixed solvent of two or more solvents can be used depending on the type of functional groups on the surface of the fumed silica particles.

[0129] The solvent is preferably an organic solvent and can be an alcohol solvent such as methanol, ethanol, propanol or isopropanol, a glycol solvent such as ethylene glycol or propylene glycol, an ether solvent such as dimethyl ether, ethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether, an acetate solvent such as ethyl acetate, propyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, or a ketone solvent such as acetone or methyl ethyl ketone.

[0130] Although water can be used as the solvent, water has a large surface tension and generates a strong capillary force when drying, which sometimes shrinks the space between the fumed silica particles, which may reduce the porosity of the low refractive index layer 104 and increase the refractive index.

[0131] When an alkali metal, particularly CsI, is used as the material of the scintillator 105, water is not suitable as a solvent due to its strong deliquescent property. Particles composed of a solid material may be used alone or in combination of two or more types thereof.

[0132] The mass content of particles composed of a solid material in the coating liquid is preferably 1.0% or greater, more preferably 2.0% or greater, even more preferably 3.0% or greater, and particularly preferably 7.0% or greater. The mass content of silica particles in the coating liquid is preferably 50.0% or less, more preferably 30.0% or less, and even more preferably 20.0% or less. These ranges can be freely combined.

[0133] For example, the concentration (solid content) of the fumed silica particles in the coating liquid is preferably in the range of 1.0 to 30.0% by mass, and more preferably in the range of 2.0 to 20.0% by mass.

[0134] When the amount of particles composed of a solid material in the coating liquid, for example, the amount (concentration) of fumed silica particles, is within the above range, the thickness of the low refractive index layer 104 can be easily adjusted to 500 nm or more. This also improves the uniform dispersibility of the fumed silica particles in the solvent, making it easier to adjust the transmittance of the low refractive index layer 104 within the above range.

[0135] Fumed silica particles are added to a solvent and dispersed. When a coating liquid containing the dispersed fumed silica particles while maintaining a complex, high-order structure is formed into a film, the size of the fumed silica particles and the spaces between them scatter visible light, thereby reducing the transmittance of the low refractive index layer 104. When the fumed silica particles are dispersed, the transparency of the coating liquid increases as the dispersion treatment time increases.

[0136] When a coating liquid containing appropriately dispersed fumed silica particles is formed into a film, the size of the fumed silica particle skeleton and the spaces between the fumed silica particles prevents them from scattering visible light. Therefore, the low refractive index layer 104 has a high transmittance.

[0137] Further dispersion treatment may destroy the ultra-high-order structure of the fumed silica particles into primary particles, may reduce the porosity, and tend to increase the refractive index of the low-refractive-index layer 104 .

[0138] Furthermore, excessive dispersion treatment may lead to so-called over-dispersion, and may easily cause the fumed silica particles to re-aggregate, and may reduce the transmittance of the low refractive index layer 104 after film formation.

[0139] Therefore, an appropriate dispersion state is preferred. The dispersion treatment can be performed using a stirrer, ultrasonic wave, planetary mixer, ball mill, bead mill, homogenizer, or the like.

[0140] Although hollow particles having a silica shell are used as the solid material in the following examples, the present invention is not limited thereto.

[0141] A dispersion of hollow particles can be used. The dispersion of hollow particles can be any dispersion of hollow particles that satisfies the requirements of the porosity of the hollow particles, the refractive index of the outer shell of the hollow particles, the number average particle size of the primary particles of the hollow particles, and the like.

[0142] For example, the Thrulya series manufactured by JGC Catalysts and Chemicals Ltd., which is an isopropyl alcohol (hereinafter referred to as IPA) dispersion of hollow particles having a silica shell (hereinafter referred to as hollow silica particles), is preferably used. In addition to commercially available products such as the Thrulya series, hollow silica particles dispersed in a solvent using the same method as for dispersing fumed silica particles in a solvent can also be used.

[0143] The concentration of the hollow particles in the solvent may be within the same range as the concentration (solid content) of the fumed silica particles in the coating liquid.

[0144] Hollow silica particles have hydroxyl groups on their surface and are hydrophilic. Therefore, highly hydrophobic solvents are not suitable. More specifically, it is preferred to use an octanol / water partition coefficient log P ow The organic solvent may be an alcohol solvent such as methanol, ethanol, propanol or isopropanol, a glycol solvent such as ethylene glycol or propylene glycol, an ether solvent such as dimethyl ether, ethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether or propylene glycol monoethyl ether, an acetate solvent such as ethyl acetate, propyl acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, or a ketone solvent such as acetone, methyl ethyl ketone, or the like.

[0145] As mentioned above, in order to reduce the refractive index of the film, it is necessary to increase Y and X + Y. One method is to randomly arrange hollow silica particles.

[0146] The following describes a method for randomly arranging hollow silica particles: the hollow silica particles are randomly arranged by forming loose aggregates of the hollow silica particles in a dispersion.

[0147] Aggregates are also included in secondary particles in which primary particles composed of a solid material form a three-dimensional structure.

[0148] One method of aggregating the well-dispersed hollow silica particles in the dispersion can be to add a solvent having a higher log P than the dispersion medium. ow The aggregation method is not limited thereto, and is preferably a method capable of controlling the aggregation state of the hollow silica particles.

[0149] Hollow silica particles have hydroxyl groups on their surface and are hydrophilic. Therefore, they have a higher logP than the dispersion medium. ow The addition of an aggregating agent, that is, an aggregating agent that is more hydrophobic than the dispersion medium, causes the aggregation of the hollow silica particles.

[0150] The logP of the aggregating agent used to aggregate the well-dispersed hollow silica particles in the dispersion is described below. ow and the amount of addition. The log P between the dispersion medium and the aggregating agent ow Too small a difference will result in the hollow silica particles not aggregating. ow If the difference is too large, even a small amount of aggregating agent will lead to strong aggregation of hollow silica particles. When hollow silica particles form large aggregates, the aggregates themselves may become light scatterers.

[0151] On the other hand, the large spaces formed between the large aggregates of the hollow silica particles also tend to act as light scatterers, which may make the low refractive index layer 104 after coating turbid, thereby possibly reducing the transmittance.

[0152] In addition, significant aggregation tends to reduce the storage stability of the coating solution. Therefore, in order to form a low-refractive-index, high-transmittance low-refractive-index layer 104, it is preferred to control the aggregation state of the hollow silica particles by the type and amount of the aggregating agent. By utilizing this characteristic and controlling the aggregation state of the hollow silica particles by the type and amount of the aggregating agent, the refractive index of the low-refractive-index layer 104 can be controlled.

[0153] In addition, filling the spaces between the hollow silica particles with some material can reduce Y and X+Y and increase the refractive index of the low refractive index layer 104. Therefore, in downstream processing, the aggregating agent can be preferably removed, more preferably by volatilizing the aggregating agent by heating.

[0154] The aggregating agent may be silicone oil such as X-22-164 (manufactured by Shin-Etsu Chemical Co., Ltd.), but is not limited thereto.

[0155] Next, a method of forming the low-refractive-index layer 104 will be described.

[0156] The film is formed using a coating liquid. The film can be formed by rod coating, doctor blade coating, brushing, spraying, spin coating, dip coating, or screen printing. Spin coating is preferred to ensure a uniform thickness of the low refractive index layer 104. Spray coating is preferred for forming a film on a large-area sensor panel with a scintillator.

[0157] Furthermore, in order to form the low refractive index layer 104 having a desired thickness and a flat upper surface, the rotation speed in the spin coating method may be appropriately adjusted.

[0158] The film formed by this method is preferably dried at a temperature in the range of 20°C to 100°C.

[0159] The film may be further heat treated. The heat treatment is preferably performed at a temperature in the range of 100°C to 200°C, more preferably 120°C to 180°C.

[0160] For example, when the heating temperature reaches 100° C. or higher, the solvent is less likely to remain in the spaces of the hollow particles. At a heating temperature of 200° C. or lower, the performance of the sensor panel corresponding to the light detection unit 113 is less likely to deteriorate.

[0161] When the film contains a binder and a polymerization initiator, it is preferably included in a heat curing or photocuring step. For heat curing, the solvent can be evaporated simultaneously with the heat curing of the binder in a drying or heating step.

[0162] Films formed from microparticles typically maintain their shape through intermolecular forces. Furthermore, hydrophobic interactions occur on the hydrophobic surfaces of the particles, while liquid crosslinking occurs on the hydrophilic surfaces of the particles. These are physical interactions. For example, when the film is heat-treated, the hydroxyl groups on the surfaces of the fumed silica particles chemically bond to each other through a dehydration reaction, potentially enhancing the strength of the film.

[0163] When a film including particles composed of a solid material is formed to lower the refractive index, van der Waals forces acting between the particles and liquid cross-linking maintain the structure and film shape.

[0164] In order to improve the strength of the film having such a structure, a binder for binding the particles together may be used. From the perspective of improving the film strength, the low refractive index layer 104 may further contain a binder.

[0165] The low-refractive-index layer 104 preferably comprises a binding material formed by binding a solid material with a binder. More specifically, the low-refractive-index layer 104 preferably comprises a binding material formed by binding particles composed of a solid material with a binder. The binding of a solid material and a binder is any binding concept including between primary particles composed of a solid material, between secondary particles formed from primary particles composed of a solid material, between primary particles and secondary particles, etc. The binding may be a chemical binding such as an ionic binding or a covalent binding, or may be a mechanical binding.

[0166] The binder may be a resin such as an acrylic resin, a fluororesin, a styrene resin, an imide resin, a polyurethane resin, or a phenolic resin.

[0167] The binder may also be an organic silicon compound prepared by polymerizing silicone oil having a polymerizable group or by hydrolysis and polycondensation of silicon alkoxide.

[0168] In addition to these binders, any transparent colorless binder having a low refractive index and capable of binding particles can be used.

[0169] An exemplary method for preparing a film containing a binder includes the steps of preparing a liquid mixture containing a solid material, a solvent and a binder, preparing a coating liquid by dispersing the liquid mixture, and forming a film by applying and drying the coating liquid and, if necessary, heating the coating liquid or irradiating the coating liquid with high-energy radiation.

[0170] The binder preferably comprises siloxane, more preferably comprises silsesquioxane.

[0171] Silsesquioxane is composed of the formula [R 1 (SiO 1.5 ) n ](R1 represents a reactive functional group, such as at least one selected from the group consisting of a polymerizable group, a hydroxyl group, a chlorine atom, an alkyl group having 1 to 6 carbon atoms and an alkoxy group having 1 to 6 carbon atoms), and is a hybrid material of silica and organic matter.

[0172] Silsesquioxane (hereinafter sometimes referred to as SQ) is a siloxane compound whose main chain skeleton is composed of Si-O bonds and has the composition formula [R 1 (SiO 1.5 ) n ] indicates. 1 Preferably, it represents at least one polymerizable group selected from the group consisting of an acryloyl group, a methacryloyl group, an oxetanyl group, and an epoxy group.

[0173] When the silsesquioxane acts to bind together a large number of particles composed of a solid material, the membrane can have higher strength while maintaining high porosity.

[0174] Silsesquioxane may have any polymeric form, for example, known linear polysiloxanes, cage polysiloxanes, or ladder polysiloxanes. The silsesquioxane structure is a structure in which each silicon atom is bonded to three oxygen atoms, and each oxygen atom is bonded to two silicon atoms (the number of oxygen atoms relative to the number of silicon atoms is 1.5). From a cost perspective, linear polysiloxanes, cage polysiloxanes, and ladder polysiloxanes may be used in combination.

[0175] Silsesquioxane preferably has a polymerizable group (R in the above formula) in the molecule. 1 ) and can be cured by free radical polymerization or cationic polymerization.

[0176] The silsesquioxane curable by radical polymerization may be one having an acryloyl group or a methacryloyl group as R. The silsesquioxane curable by cationic polymerization may be one having an oxetane group or an epoxy group as R.

[0177] Specific examples include the silsesquioxane derivative SQ series (AC-SQ, MAC-SQ, and OX-SQ) manufactured by Toagosei Co., Ltd.

[0178] Silsesquioxane is a high-viscosity liquid and is preferably added to the coating liquid. A polymerization initiator may be added as necessary.

[0179] The binder content of the functional film is preferably in the range of 3.0 to 60.0 parts by mass, more preferably 7.0 to 30.0 parts by mass, per 100 parts by mass of the particles composed of the solid material. The binder content of the functional film is more preferably in the range of 7.0 to 25.0 parts by mass, particularly preferably 10.0 to 25.0 parts by mass, per 100 parts by mass of the particles composed of the solid material.

[0180] The coating liquid can be applied on a substrate, and the silsesquioxane can be cured by heating or light irradiation.

[0181] By doing so, a film containing a binding material in which particles composed of a solid material and silsesquioxane are bound together is formed. The silsesquioxane can be cured to increase the strength of the film.

[0182] Examples of the polymerization initiator include free radical photopolymerization initiators, cationic photopolymerization initiators, thermal free radical polymerization initiators, and thermal cationic polymerization initiators. These polymerization initiators can be used alone or in combination.

[0183] Examples of free radical photopolymerization initiators include, but are not limited to, optionally substituted 2,4,5-triaryl imidazole dimers, such as 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, 2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer, 2-(o-fluorophenyl)-4,5-diphenylimidazole dimer, and 2-(o- or p-methoxyphenyl)-4,5-diphenylimidazole dimer; benzophenone derivatives, such as benzophenone, N,N'-tetramethyl-4,4'-diaminobenzophenone (Michler's ketone), N,N'-tetraethyl-4,4'-diaminobenzophenone, 4-methoxy-4'-dimethylaminobenzophenone, 4- Chlorobenzophenone, 4,4'-dimethoxybenzophenone and 4,4'-diaminobenzophenone; α-aminoaromatic ketone derivatives, such as 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one; quinones, such as 2-ethylanthraquinone, phenanthrenequinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 1,2-phenylanthraquinone, 2,3-phenylanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, 1-methylanthraquinone, 1,2-chloroanthraquinone, 4-naphthoquinone, 9,10-phenanthrenequinone, 2-methyl-1,4-naphthoquinone and 2,3-dimethylanthraquinone; benzoin ether derivatives, such as Such as benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether; benzoin derivatives such as benzoin, methyl benzoin, ethyl benzoin and propyl benzoin; benzyl derivatives such as benzyl dimethyl ketal; acridine derivatives such as 9-phenylacridine and 1,7-di(9,9'-acridinyl)heptane; N-phenylglycine derivatives such as N-phenylglycine; acetophenone derivatives such as acetophenone, 3-methylacetophenone, acetophenone ketal, 1-hydroxycyclohexylphenyl ketone and 2,2-dimethoxy-2-phenylacetophenone; thioxanthone derivatives such as thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone and 2-chlorothioxanthone; acylphosphine oxide derivatives such as 2,4-dimethylthioxanthone; ,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide; oxime ester derivatives, such as 1,2-octanedione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)] and ethyl ketone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetooxime); xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one and 2-hydroxy-2-methyl-1-phenylpropan-1-one.

[0184] Examples of commercially available products of free radical photopolymerization initiators include, but are not limited to, Irgacure 184, 369, 651, 500, 819, 907, 784, 2959, CGI-1700, -1750 and -1850, CG24-61, Daro 1173, Lucirin TPO, LR8893, LR8970 (manufactured by BASF, "Darocur" and "Lucirin" are registered trademarks), and Uvecryl P36 (manufactured by UCB).

[0185] The cationic photopolymerization initiator is preferably an onium salt, an aromatic onium salt, an arylsulfonium salt, an aryliodonium salt, etc. Specific examples of the anion include tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, perchlorate ion, trifluoromethanesulfonate ion, and fluorosulfonate ion.

[0186] Examples of commercially available products of the cationic photopolymerization initiator include CPI-210S (manufactured by San-Apro Co., Ltd.), UVI-6950 (manufactured by Union Carbide Corporation), and Adeka Optomer SP-150 (manufactured by San-Apro Co., Ltd.) and Adeka Optomer SP-150 (manufactured by Adeka Corporation).

[0187] The polymerization initiator content of the coating liquid is preferably in the range of 0.01 to 1.5 parts by mass, more preferably 0.03 to 1.0 part by mass, per 100 parts by mass of the silsesquioxane solid.

[0188] The coating solution can be prepared by mixing particles composed of a solid material, a solvent, a binder, and a polymerization initiator of choice. The solvent is preferably an organic solvent. The organic solvent can be, but is not limited to, an alcohol, a carboxylic acid, an aliphatic or alicyclic hydrocarbon, an aromatic hydrocarbon, an ester, a ketone, an ether, or a mixture of two or more thereof.

[0189] Examples of alcohols include methanol, ethanol, 2-propanol, butanol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, 4-methyl-2-pentanol, 2-ethylbutanol, 3-methoxy-3-methylbutanol, ethylene glycol, diethylene glycol, and glycerol.

[0190] Specific examples of carboxylic acids include n-butyric acid, α-methylbutyric acid, isovaleric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3-dimethylbutyric acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 2-ethylhexanoic acid, and 3-ethylhexanoic acid.

[0191] Specific examples of the aliphatic or alicyclic hydrocarbons include n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane.

[0192] The aromatic hydrocarbon is preferably toluene, xylene or ethylbenzene.

[0193] Examples of the esters include ethyl formate, ethyl acetate, n-butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and γ-butyrolactone.

[0194] Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

[0195] Examples of ethers include dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether.

[0196] In view of solution stability, it is preferred to use alcohol among the above-mentioned solvents to prepare the coating solution.

[0197] The coating liquid can be prepared by adding a predetermined amount of a binder and a self-selected polymerization initiator to a liquid containing particles composed of a solid material dispersed in a solvent. The liquid containing particles dispersed in an organic solvent can be prepared by dispersing a particle powder in a solvent using the same method as the above-mentioned dispersion treatment (e.g., using a ball mill, etc.), or can be a commercially available dispersion liquid.

[0198] When forming a film using the coating liquid, coating is performed in an inert gas atmosphere such as dry air or dry nitrogen. The relative humidity of the dry atmosphere is preferably 30% or less.

[0199] In addition, the solution coating method for film formation can be a known coating method, such as dipping, spin coating, spray coating, printing, flow coating, or a combination thereof. The film thickness can be controlled by changing the pulling speed in the dipping method or the substrate rotation speed in the spin coating method or by changing the concentration of the coating solution.

[0200] The film can be cured by irradiation with high-energy radiation such as light irradiation or radiation irradiation, or by heating. Curing can be performed by combining irradiation with high-energy radiation and heating.

[0201] For curing using high-energy radiation, the high-energy beam may be, but is not limited to, an electron beam, X-rays, ultraviolet radiation, or the like. When the high-energy beam is ultraviolet radiation, the wavelength of the radiation is preferably in the range of 160 to 400 nm, and the output is preferably in the range of 0.1 to 2000 mW / cm 2 From the perspective of preventing oxidation of silsesquioxane, the curing atmosphere is preferably an inert atmosphere such as nitrogen. Curing by heating is performed at a temperature range of 50°C to 250°C, preferably 80°C to 200°C, for 1 to 20 minutes.

[0202] <Evaluation Method of Film Porosity and Refractive Index>

[0203] The porosity X (%) and porosity Y (%) of the membrane can be calculated as follows.

[0204] First, a carbon film was applied to the film formed on the substrate using a 681-type ion beam coater IBC (manufactured by Gatan), and then ion beam sectioning (30 kV-0.1 nA) was performed using a focused ion beam scanner (FIB-SEM, manufactured by FEI Corporation, Nova 600). SEM images were then acquired using a scanning electron microscope (hereinafter referred to as SEM) at an accelerating voltage of 2 kV.

[0205] The observation magnification of the SEM image is such that the entire film can be observed at least in the thickness direction and, for example, the shape of each hollow particle can be discerned. More specifically, the observation magnification is approximately 50,000 to 200,000.

[0206] The unit volume of the membrane is 1000 nm × 1000 nm × 100 nm (thickness direction). To calculate the porosity in the cross-sectional SEM images, the hollow particles and the spaces between them were identified by binarization of the grayscale images, and the area of each region was calculated. Image processing was performed using the image analysis software Image J (NIH Image, available at https: / / imagej.nih.gov / ij / ).

[0207] More specifically, the area A (%) of the hollow particle is multiplied by the volume fraction V of the internal space relative to the total volume of the hollow particle. a To calculate the porosity X (%): X = Ax V a The porosity Y (%) is Y=100-A.

[0208] The refractive index n of the low-refractive-index layer 104 can be calculated from X and Y thus calculated using Formula (2).

[0209] [Radiation Detector]

[0210] like Figure 4 As shown, the scintillator unit 100 and the detection unit 113 for detecting light from the scintillator unit 100 can constitute a radiation detector 115. The detection unit 113 includes a substrate 111 and light receiving devices 112 arranged in two directions on the substrate 111. The detection unit 113 is adjacent to the surface facing the low refractive index layer via the scintillator 105. A polymer protective layer can be located at the boundary between the detection unit 113 and the scintillator 105 to protect the detection unit 113. A fiber optic plate (FOP) or the like can also be used.

[0211] Exemplary embodiments

[0212] Although the scintillator unit according to the present invention is described in detail in the following exemplary embodiments, the present invention is not limited to these exemplary embodiments.

[0213] (Exemplary embodiment 1)

[0214] <Preparation of Scintillator>

[0215] As described below, a scintillator was prepared on a substrate by a heating evaporation method. A heating boat in a vacuum chamber was filled with CsI raw material powder. The substrate placed opposite the boat was a glass substrate and was mounted on a turntable. The vacuum chamber was evacuated to 1×10 -3 A high vacuum of less than Pa was set at a boat temperature of 670°C. Another boat was placed in the vacuum chamber, filled with thallium iodide (TlI) raw material powder, which serves as the luminescence center, and heated to form a film. The raw material was deposited onto a 50 mm square glass substrate while rotating at 60 rpm.

[0216] Hollow silica particles with a silica shell were selected as the particles for forming the low-refractive index layer. The coating liquid for film formation was prepared using Thrulya 4110 manufactured by JGC Catalysts & Chemicals Co., Ltd. (dispersion medium: IPA, silica solids content: 20.5% by mass, number average particle size per hollow particle: 60 nm, porosity per hollow particle: 45%, refractive index per hollow particle: 1.25). The dispersion prepared in this manner is referred to as a hollow silica particle dispersion.

[0217] A film of the hollow silica particle dispersion was formed on the prepared scintillator by spin coating to form a low refractive index layer. The film was formed by rotating the substrate at a rotation speed of 1500 rpm for 15 seconds.

[0218] <Formation of Support Member (Reflective Layer)>

[0219] The support member is formed by coating the scintillator with aluminum (Al), which is applied to a polyethylene terephthalate (PET) film to a thickness of approximately 30 microns. The aluminum serves as a reflective layer. To improve adhesion to the scintillator with the low-refractive index layer, a thermoplastic resin film approximately 30 microns thick is pre-formed before forming the support member. Adhesion between the scintillator, reflective layer, and support member is enhanced by heating them in a vacuum laminator at a temperature range of 80°C to 100°C.

[0220] <Structural Assessment>

[0221] The prepared scintillator unit was sliced (8 kV - 3 mA, 2 hours) using a triple ion milling device (Leica EM-TIC-3X). Subsequently, in order to remove deposits, fine ion beam slicing (30 kV - 0.1 nA) was performed in a focused ion beam processing device (FIB-SEM, manufactured by FEI Company, Nova 600). Then, SEM images were acquired at an acceleration voltage of 2 kV using a scanning electron microscope (hereinafter referred to as SEM). Figure 5A The low magnification SEM image is shown, Figure 5B and the high magnification SEM image near the interface of the low refractive index layer is shown. The adhesive layer, the low refractive index layer, and the CsI columnar crystals are tightly bonded. The low refractive index layer is flat and fills the gap at the end of the CsI columnar crystals. The average distance from the top of each columnar crystal to the interface between the low refractive index layer and the adhesive layer is defined as the thickness (T1) of the low refractive index layer. In Exemplary Embodiment 1, T1 calculated by measuring the distances of 30 CsI columnar crystals was 2.0 μm. In addition, by measuring the distance from the interface between the low refractive index layer and the non-low refractive index layer part between the 30 CsI columnar crystals for which T1 was calculated to the interface between the low refractive index layer and the adhesive layer, the average distance T3 was calculated to be 17 μm. The penetration depth T2 in the gap between the columnar crystals of the low refractive index layer was obtained by subtracting T1 from T3, and was 15 μm.

[0222] Cross-sectional SEM images were obtained at a high magnification where individual hollow particles could be observed. The hollow particles and the space between the hollow particles were discriminated by binarization of the grayscale image, and the area of each region was calculated. Given the calculated area of the hollow particles and the volume fraction of the internal space with respect to the total volume of the hollow particles, the porosity of the low refractive index layer was calculated to be 67%. The refractive index of the low refractive index layer was calculated to be 1.15 using formula (2), where n s is 1.46.

[0223] <MTF Evaluation and Sensitivity Evaluation>

[0224] The prepared scintillator unit was irradiated with X-rays for modulation transfer function (MTF) evaluation and sensitivity evaluation. The MTF evaluation was performed using a general edge method. The scintillator was irradiated with X-rays having a tube voltage of 80 kV, and the MTF at 2 LP / mm was evaluated using an image formed on a light receiving device by an optical system focused on the surface of the scintillator on the light extraction surface side.

[0225] <Fabrication of Radiation Detector>

[0226] A polyimide layer is formed as a polymer protective layer by spin coating on the sensor panel including the detection unit. A scintillator is formed on the polyimide layer. A low-refractive-index layer is then formed on the scintillator and bonded to the Al reflective layer via an adhesive layer (a layer containing a thermoplastic resin) using a vacuum laminator to form a radiation detector.

[0227] (Exemplary embodiment 2)

[0228] Exemplary Embodiment 2 was the same as Exemplary Embodiment 1 except that the rotation speed of the spin-coated substrate was changed to 1000 rpm for 15 seconds to form the low refractive index layer.

[0229] (Exemplary embodiment 3)

[0230] Exemplary Embodiment 3 is the same as Exemplary Embodiment 1 except that the low refractive index layer is formed by spraying five times.

[0231] (Exemplary embodiment 4)

[0232] Exemplary Embodiment 4 was the same as Exemplary Embodiment 1 except that a coating liquid prepared by diluting a hollow silica particle dispersion with IPA to a silica solid content of 10.0% by mass was used and sprayed 20 times to form a film to form a low refractive index layer.

[0233] (Exemplary embodiment 5)

[0234] Exemplary Embodiment 5 is the same as Exemplary Embodiment 1 except that the reflective layer is formed of an epoxy resin containing titanium oxide, and the epoxy resin serves as an adhesive layer and also as a reflective layer. Exemplary Embodiment 5 corresponds to Figure 2A and Figure 2B The structure according to the present invention is shown.

[0235] (Exemplary Embodiment 6)

[0236] AEROSIL R812 (manufactured by Nippon Aerosil Co., Ltd.) is a fumed silica particle having a methyl group on its surface and is used in a hollow silica particle dispersion to form a low refractive index layer. Fumed silica particles dispersed in propylene glycol monomethyl ether (PGME) and a solvent with a solid content of 6.88% by mass are sealed in a glass container together with zirconium oxide (ZrO2) balls with a diameter of 0.5 mm. The glass container is rotated at a speed of 30 rpm on a ball mill turntable for 48 hours to disperse the fumed silica particles. The fumed silica particle dispersion prepared by a dispersion treatment using a ball mill is used as a coating liquid. The coating liquid is sprayed five times by a spraying method to form a film to form a low refractive index layer. Except for this, exemplary embodiment 6 is the same as exemplary embodiment 1.

[0237] Figure 6 : shows a cross-sectional SEM image obtained by the same method as in Example 1. The low refractive index layer is formed along the concavo-convex at the end of the CsI columnar crystal. The low refractive index layer in the spin coating method ( Figure 5A and Figure 5B ) is formed to fill the gaps between the columnar crystals, thereby having a flat surface, which becomes an interface with the adhesive layer in a subsequent step, however, the low refractive index layer ( Figure 6 ) is formed along the concave and convex parts of the columnar crystals.

[0238] (Comparative Example 1)

[0239] Comparative Example 1 is the same as Exemplary Example 1 except that the low refractive index layer is not formed.

[0240] (Comparative Example 2)

[0241] A thick low-refractive-index layer was formed. The fumed silica particle dispersion in Exemplary Embodiment 6 was used as a coating liquid, and a film was formed in the same manner as in Exemplary Embodiment 1 by spin coating.

[0242] Table 1 summarizes the MTF and sensitivity evaluation results for Example Examples 1 to 6 and Comparative Examples 1 and 2. The film thickness is the average thickness (T1) from the top of each CsI columnar crystal. The MTF and sensitivity evaluation values are compared to the known structure without a low refractive index layer according to Comparative Example 1.

[0243] (Discussion)

[0244] In Example 1, the low-refractive-index layer increased the MTF by 15% and the sensitivity by 10%. This is because the low-refractive-index layer on the CsI improves the total reflection efficiency at the interface between the CsI and the low-refractive-index layer and increases the amount of light remaining in the CsI. The light leaking into the adhesive layer propagates parallel to the surface of the light receiving part and is repeatedly reflected and attenuated in the adhesive layer, resulting in reduced sensitivity (equivalent to light attenuation) and reduced MTF. The low-refractive-index layer can reduce the amount of light leaking into the adhesive layer and improve sensitivity and MTF.

[0245] [Film Formation Method]

[0246] Comparing exemplary embodiments 1 to 4 shows the differences caused by the film forming method. The spin coating method in exemplary embodiments 1 and 2 has higher sensitivity than the spray coating method in exemplary embodiments 3 and 4. In the spray coating method, droplets of the sprayed coating liquid are deposited on the ends of the columnar crystals, and areas without a low refractive index layer are scattered on the scintillator. In contrast, in the spin coating method, a low refractive index layer is formed on the entire surface of the scintillator. Therefore, the scintillator unit formed by the spin coating method is less likely to leak light into the adhesive layer. Compared with exemplary embodiment 3, exemplary embodiment 4 has a higher spraying frequency, a larger area with a low refractive index layer, and higher sensitivity.

[0247] [Type of silica particles]

[0248] Comparing exemplary embodiments 3, 4, and 6 shows the differences caused by the type of silica particles. When the film forming method is a spray coating method, the fumed silica in exemplary embodiment 6 has a higher MTF improvement rate than the hollow silica in exemplary embodiments 3 and 4. This may be because the low refractive index layer formed by fumed silica has a lower refractive index than the low refractive index layer formed by hollow silica, and has a higher total reflection efficiency at the interface between the CsI scintillator and the low refractive index layer. However, the low refractive index layer formed by hollow silica generally has a higher strength. This is because in the bonding material of the hollow particles and the binder, the binder located at the contact points between the hollow particles has a strong contribution to the bonding between the hollow particles and improves the strength of the film.

[0249] [Thickness of low refractive index layer]

[0250] Exemplary embodiments 1 to 4 and 6 and Comparative Example 2 are compared to illustrate the differences due to the thickness (film thickness) of the low refractive index layer. When the thickness of the low refractive index layer was varied using hollow silica (Exemplary embodiments 1 to 4), MTF improved by 11% in Exemplary embodiment 3 with a film thickness of 0.6 μm, and by 15% in Exemplary embodiments 1, 2, and 4 with a film thickness of 1.0 μm or greater.

[0251] When the thickness of the low-refractive-index layer was varied using fumed silica (Example 6 and Comparative Example 2), the MTF improved by 22% in Example 6, which had a film thickness of 0.5 μm, compared to Comparative Example 1, which did not have a low-refractive-index layer. However, it decreased in Comparative Example 2, which had a film thickness of 16 μm. Therefore, a low-refractive-index layer with a thickness of at least 0.5 μm significantly contributes to improving the MTF. On the other hand, in Comparative Example 2, where the film thickness was too great, the optical path length of light reflected by the reflective layer was long, light diffused laterally, and the MTF decreased.

[0252] [Reflection layer]

[0253] Comparing Example 1 and Example 5 illustrates the differences caused by the reflective layer. In Example 5, the adhesive layer, which has both reflective and adhesive functions, also functions as a reflective layer, preventing light from leaking through the adhesive layer. This reduces light attenuation, increases the amount of light reaching the light detection unit, and significantly improves sensitivity. Half of the light generated by the scintillator travels toward the light detection unit, while the other half travels in the opposite direction. Compared to the former, the latter has a longer optical path to the light detection unit and, due to the use of an adhesive layer that also functions as a reflective layer, also exhibits light scattering, resulting in a lower MTF than the other example embodiments using an Al reflective layer.

[0254] Table 1

[0255]

[0256]

[0257] Therefore, the present invention can provide a radiation detector with improved sensitivity and resolution.

[0258] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to disclose the scope of the present invention, the following claims are made.

[0259] This application claims the benefit of Japanese Patent Application No. 2019-141821, filed on Jul. 31, 2019, which is hereby incorporated by reference herein in its entirety.

Claims

1. A scintillator unit, comprising: In the incident direction of radiation, the support member, the adhesive layer, the low refractive index layer and the scintillator are arranged in this order, wherein: The low refractive index layer has a refractive index lower than that of the adhesive layer, and At least a portion of the support member includes a reflective layer that reflects light generated by the scintillator and transmits the light toward a light extraction surface.

2. The scintillator unit according to claim 1, wherein The scintillator comprises a plurality of columnar crystals, and The low refractive index layer is located between the end portion of each columnar crystal in the extending direction and the adhesive layer.

3. The scintillator unit according to claim 1 or 2, wherein: At least a portion of the support member includes a light absorbing layer. The scintillator unit according to claim 1 , wherein: The adhesive layer includes a scattering layer containing light scattering particles and a binder resin. The scintillator unit according to claim 1 , wherein: The adhesive layer includes a thermoplastic resin. The scintillator unit according to claim 1 , wherein: The adhesive layer includes an acrylic resin.

7. The scintillator unit according to claim 1 or 2, wherein: The low refractive index layer includes silicon dioxide. The scintillator unit according to claim 1 , wherein: The low refractive index layer includes hollow particles.

9. The scintillator unit according to claim 8, wherein The hollow particles have an outer shell with a refractive index of 1.60 or less.

10. The scintillator unit according to claim 8, wherein The hollow particles have an outer shell having a refractive index of 1.35 or greater. The scintillator unit according to claim 1 or 2, wherein: The low refractive index layer has a porosity in the range of 60.0% to 95.0%.

12. The scintillator unit according to claim 1 or 2, wherein: The low refractive index layer has a thickness in the range of 300 nm to 5 μm.

13. The scintillator unit according to claim 1 or 2, wherein: The low refractive index layer contains fumed silica particles.

14. A radiation detector, comprising: In order of incidence of radiation are a support member, an adhesive layer, a low refractive index layer, a scintillator, and a detection unit for detecting light generated from the scintillator, wherein The low-refractive-index layer has a refractive index lower than that of the adhesive layer, The detection unit is opposite to the low refractive index layer via the scintillator, and At least a portion of the support member includes a reflective layer that reflects light generated by the scintillator and transmits the light toward a light extraction surface.

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