Scintillator unit and radiation detector

Abstract

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

Description

Technical Field

[0001] The present invention relates to a scintillator unit and a radiation detector. Background Art

[0002] A radiation detector is used to photograph a subject by radiation in a medical site or the like, and mainly includes a scintillator that generates light by radiation (e.g., X-ray) and a detection unit including a two-dimensionally arranged light receiving device. When the subject is irradiated with X-ray, the X-ray passing through the subject generates light from the scintillator, and the detection unit detects the light and forms a two-dimensional image of the transmitted X-ray.

[0003] A columnar crystal group including a plurality of columnar crystals is used as the scintillator, for effectively transmitting the light generated by the scintillator to the light receiving device, and for improving the sensitivity of the radiation detector to radiation. A space containing air is formed between the columnar crystals in the columnar crystal group. When an alkali metal halide crystal such as cesium iodide (CsI) is used as the columnar crystal, the light entering the space containing low refractive index air from the columnar crystal with a high refractive index does not pass through, but is reflected at the interface between the columnar crystal and the space. Therefore, even if the light generated by the scintillator is emitted in any direction, the light generated in the columnar crystal is guided to the detection unit by the physical phenomenon "total reflection" caused by the refractive index difference between the two media.

[0004] In addition, in order to guide most of the light generated by the scintillator to the detection unit, a reflective layer may be provided via an adhesive layer on the surface of the scintillator opposite to the detection unit. For example, Patent Document 1 describes a flat panel detector (FPD) including, in the incident direction of radiation, an air layer, a dielectric multilayer reflective film, an adhesive layer, a phosphor layer, and a photodetector in sequence.

[0005] Citation List

[0006] Patent Document

[0007] PTL 1: International Publication WO 2016 / 167334 Summary of the Invention

[0008] Technical Problem

[0009] The inventors of the present application studied the FPD described in Patent Document 1, which uses a columnar crystal group including CsI (refractive index = 1.74) as the phosphor layer and a layer including an acrylic resin (refractive index = 1.45) as the adhesive layer. As a result, it was found that the light generated by the columnar crystals included in the phosphor layer is difficult to be reflected at the interface between the phosphor layer and the adjacent adhesive layer and leaks into the adhesive layer.

[0010] It has also been found that light incident on the adhesive layer is attenuated in the adhesive layer, leaving room for further improvement in sensitivity to radiation.

[0011] It has also been found that light generated from columnar crystals included in the phosphor layer travels and diffuses in the adhesive layer and then enters other columnar crystals, leaving room for further improvement in the sharpness (resolution) of the image to be formed.

[0012] Accordingly, 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 scintillator unit can be used to improve sensitivity to radiation and the resolution of the image to be formed.

[0013] Solution to the problem

[0014] 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 refractive index lower than that of the adhesive layer is located between the scintillator and the adhesive layer.

[0015] The present invention also relates to a radiation detector including: a scintillator unit including an adhesive layer between a scintillator and a support member, and a detection unit configured to detect light generated from the scintillator, wherein the scintillator unit includes a low refractive index layer having a refractive index lower than that of the adhesive layer, and the detection unit faces the low refractive index layer via the scintillator.

[0016] Advantageous effects of the invention

[0017] 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 the image to be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A is a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention.

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

[0020] Figure 2A is a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention.

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

[0022] Figure 3 is a schematic cross-sectional view of an embodiment of the low refractive index layer.

[0023] Figure 4 It is a schematic cross-sectional view of an embodiment of a radiation detector according to the present invention.

[0024] Figure 5A It is a scanning electron microscope (SEM) image of a scintillator unit according to the present invention.

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

[0026] Figure 6 It is an SEM image of a scintillator unit according to the present invention. Detailed Description of the Invention

[0027] The scintillator unit according to the present invention includes an adhesive layer between the scintillator and the support member. The scintillator unit according to the present invention further includes a low refractive index layer having a refractive index lower than that of the adhesive layer between the scintillator and 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 a phosphor layer and a layer containing an acrylic resin (refractive index = 1.45) as an adhesive layer. As a result, it was found that the light generated by the columnar crystals contained in the phosphor layer is difficult to be reflected at the interface between the phosphor layer and the adjacent adhesive layer and is likely to leak 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 two media increases. Since the refractive index difference between the phosphor layer and the adjacent adhesive layer is small, "total reflection" is unlikely to occur at the interface between the phosphor layer and the adhesive layer. Therefore, the inventors of the present application provided a low refractive index layer having a refractive index lower than that of the adhesive layer between the phosphor layer ("scintillator" in the present invention) and the adhesive layer.

[0028] Since the refractive index difference between the scintillator and the low refractive index layer is greater than the refractive index difference 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 makes it difficult for light to leak from the scintillator into the adhesive layer. Therefore, a radiation detector including such a scintillator unit improves the sensitivity to radiation. In addition, the light generated from the scintillator is difficult to propagate and diffuse in the adhesive layer. This also improves the resolution of the image to be formed.

[0029] Embodiments of the present invention will be described in detail below. Physical properties are determined at 25 °C unless otherwise specified.

[0030] Figure 1A It is a schematic cross-sectional view of an embodiment of a scintillator unit according to the present invention, Figure 1B It is an enlarged view of the schematic cross-sectional view. In Figure 1AIn this case, the scintillator unit 100 includes a low refractive index layer 104, an adhesive layer 103, and a support member 101 in sequence on the scintillator 105. The incident direction of the radiation 106 on the scintillator unit 100 is indicated by the arrow. The components of the scintillator unit 100 will be described in detail below.

[0031] [Scintillator 105]

[0032] Figure 1B is Figure 1A an enlarged view of a square region of. Preferably, the scintillator 105 in the scintillator unit 100 according to the present invention contains a material that emits light through radiation (X-rays, γ-rays, charged particles, etc.), and is an aggregate of a plurality of columnar (or needle-like) crystals (hereinafter referred to as 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 leakage 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.

[0033] The scintillator unit 100 according to the present invention is particularly suitable for a radiation detector produced by a method of directly forming a scintillator film on a sensor panel including a detection unit. In this case, the scintillator 105 can be referred to as a scintillator film.

[0034] As Figure 1B shown, the central axis 107 of the columnar crystal 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. In addition, the columnar crystal 102 does not necessarily have a uniform tilt. 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 crystal 102.

[0035] The columnar crystal group does not need to have the same columnar crystal diameter, and can also be an aggregate of columnar crystals with different diameters. The columnar crystal diameter refers to the equivalent circle diameter in the cross-section perpendicular to the central axis of the columnar crystal. The term "equivalent circle diameter" used herein refers to the "projected area equivalent circle diameter" commonly mentioned in a microscope, which refers to the diameter of a perfect circle having 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. The diameter of the columnar crystal can vary in the range of 0.01 to 50 μm from one end to the other end.

[0036] The diameter of columnar crystals less than 0.01 μm is much smaller than the wavelength of light, thus suppressing geometric optical diffraction and optical scattering. Therefore, light passes through the boundaries of the side surfaces of each columnar crystal and spreads widely into the group of columnar crystals, which may be the cause of reduced resolution. Columnar crystals with a diameter exceeding 50 μm result in an increased amount of light that is not completely reflected by the side surfaces of the columnar crystals and may cause a large amount of light leakage into the columnar crystals adjacent to the original columnar crystal.

[0037] The columnar crystals 102 preferably have the same length in the direction of the central axis 107. A group of columnar crystals with more uniform length is more likely to have a higher resolution. However, the group of columnar crystals does not necessarily have the same length, and the scintillator 105 can include long columnar crystals and short columnar crystals. For example, the scintillation light leaking from the short columnar crystals can enter the adjacent columnar crystals and propagate in the columnar crystal scintillator to the light receiving device directly below the adjacent columnar crystals. Therefore, the scintillator 105 can have any columnar crystal structure capable of achieving the required resolution.

[0038] The scintillator 105 can include a space or a light scatterer in the columnar crystals 102. Although such a space or light scatterer scatters the scintillation light, the scattered light can enter the adjacent columnar crystals and can be directed in the columnar crystals to the light receiving device directly below the adjacent columnar crystals.

[0039] Examples of materials applicable to 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 14 compounds. Specific examples include NaI(Tl), CsI(Tl), CsI(Na), Lu 2 SiO 5 (Ce), Lu 2 Y 2 SiO 5 , Gd 2 SiO 5 , Bi 4 Ge 3 O 12 , ZnWO 4 , CdWO 4 , PbWO 4 , LuAlO 3 , Y 3 Al 5 O 12 (Ce), YAlO 3 (Ce), Lu 3 Al 5 O 12 (Ce), Lu 3 Al 5 O 12(Pr) and CeF 3 . In particular, the scintillator 105 preferably contains CsI(Tl).

[0040] [Support member 101]

[0041] Approximately half of the light generated by the scintillator 105 is repeatedly reflected in the columnar crystal 102 and propagates toward one surface of the scintillator 105 (hereinafter referred to as the light extraction surface), which is the opposite surface of 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 crystal 102 and the low refractive index layer 104 and is guided to the light extraction surface.

[0042] At least a part 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, the light leaking into the adhesive layer can be reflected back into the scintillator and propagate toward the light extraction surface, thereby increasing the amount of light to be detected and improving the sensitivity to radiation.

[0043] The reflective layer can be formed of a metal material such as aluminum. The reflective layer is preferably a dielectric multi-layer reflective layer with a higher reflectivity than the metal material. This further improves the sensitivity to radiation. The low refractive index layer 104 and the reflective layer are located on the scintillator 105. The low refractive index layer 104 and the reflective layer are bonded together by the adhesive layer 103. The adhesive layer 103 can also be referred to as a space filling layer.

[0044] When the support member 101 includes a light absorbing layer capable of absorbing light, the light absorbing layer can absorb the light leaking into the adhesive layer 103 and can prevent the scintillation light emitted from one columnar crystal from entering another columnar crystal. The light absorbing layer can absorb part or all of the light. The use of the light absorbing layer reduces the sensitivity to radiation but improves the resolution of the image to be formed. The light absorbing layer can be a sheet containing carbon particles.

[0045] The scintillator unit preferably includes a low refractive index layer between the end portion in the extending direction of the columnar crystal and the bonding layer. The low refractive index layer 104 on one surface of the scintillator 105 (columnar crystal group) improves the total reflection efficiency of the light at the interface between the columnar crystal 102 and the low refractive index layer 104 and prevents the light from leaking out of the scintillator into the adhesive layer 103.

[0046] In Figure 1A and Figure 1BIn the structure of the present invention shown, a scintillator 105, a low refractive index layer 104, and an adhesive layer 103 are arranged in sequence. It is important to form a low refractive index layer 104 in contact with the scintillator 105 between the scintillator 105 and the adhesive layer 103. This can greatly reduce the amount of light leaking from the columnar crystal 102 into the adhesive layer 103.

[0047] A scintillator unit including a CsI (n = 1.74) columnar film as the scintillator 105 is described below. The low refractive index layer (n = 1.15) on the upper surface of CsI can improve the total reflection efficiency at the interface between the low refractive index layer and CsI, and can keep a large amount of light within CsI. Therefore, a 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 radiation 106 enters the scintillator 105 and is converted into visible light at the light emission point 108. Among the generated light, the scintillation light 109 reaching 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.

[0048] The total reflection efficiency at the interface with CsI (n = 1.74) is compared between a known structure in which an adhesive layer (n = 1.45) containing an acrylic resin is in contact with CsI and the structure of the present invention in which the low refractive index layer 104 is in contact with CsI. For the solid angle of the light emitted from the upper surface of CsI, the total reflection efficiency is calculated using Snell's law. S = 1 - cos[arcsin(n / 1.74)] represents the proportion S of the light entering the medium on the upper surface of CsI from a point on the upper surface, where the light that does not undergo total reflection enters 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 the 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, then S is 0.45, 0.28, 0.25, or 0.23, respectively. Therefore, when the adhesive layer (n = 1.45) is the low refractive index layer, for a low refractive index layer with a refractive index n of 1.20, the proportion of light leaking from CsI is reduced by 38%, 44% when n = 1.15, and 49% when n = 1.10.

[0049] [Adhesive layer 103]

[0050] The adhesive layer 103 can be formed of any material having the function of bonding the support member 101 and the low refractive index layer 104 together. The adhesive layer 103 can be formed of a general thermoplastic resin. From the perspective of transparency, an acrylic resin is preferred.

[0051] Or, as Figure 2A and Figure 2BAs shown, an adhesive layer 110 having an adhesive and reflective function can also be used. The adhesive layer 110 may include a scattering layer containing light-scattering particles and a binder resin. In such a structure, the adhesive layer 110 not only serves to bond the support member and the low-refractive-index layer together, but also has the function of reflecting the light leaking from the low-refractive-index layer. For example, the adhesive layer 110 preferably contains titanium oxide as the light-scattering particles and epoxy resin as the binder. In such a structure, the low-refractive-index layer 104, the adhesive layer 110 having an adhesion and reflection function, 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 absorption layer.

[0052] [Low-refractive-index layer 104]

[0053] In 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 sufficiently improve the total reflection efficiency, it is preferably to have 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 300 nm or more. If T1 is too large, it may result in a long optical path to the interface with the adhesive layer, making it easier to diffuse in the lateral direction and reducing the resolution. Therefore, T1 is preferably 5 μm or less. The penetration depth T2 in the gap between the columnar crystals of the low-refractive-index layer is preferably 25 μm or less. The penetration depth T2 in the gap 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. If the penetration depth is too large, it may result in an increase in the proportion of light propagating between the columnar crystals and a reduction in the resolution.

[0054] <Composition and structure>

[0055] In Figure 3 , by appropriately setting the porosity for reducing the refractive index by using a solid material having a refractive index of 1.65 or less as the skeleton, the strength of the low-refractive-index layer 104 can be improved.

[0056] The solid material may be crystalline or non-crystalline. The solid material may be particles. The particles may be, but are not limited to, spherical particles, irregular-shaped particles, spherical particles or irregular-shaped particles connected in a bead-like or branched chain, hollow particles having a cavity, or hollow particles connected in a bead-like or branched chain.

[0057] Examples of solid materials 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 silica and alumina.

[0058] Examples of solid materials with a low refractive index include organic materials such as fluorinated polymers and inorganic materials such as magnesium fluoride and silica.

[0059] However, even for fluorinated polymers with a low refractive index, their refractive index is about 1.30, the refractive indices of magnesium fluoride and silica (quartz) are 1.38 and 1.46 respectively, and the single materials with a refractive index far lower than 1.30 are mainly gases such as nitrogen or oxygen.

[0060] In terms of refractive index, cost, and chemical stability, the solid material preferably contains silica. More specifically, the solid material preferably consists mainly of silica. The phrase "the solid material consists mainly of silica" used herein means that the silica content of the solid material is 50% or more by mass. The silica content of the solid material is usually 90% or more by mass.

[0061] Specific examples of silica particles include the Snowtex series manufactured by Nissan Chemical Industries, Ltd. of Japan, silicone sols, the Thrulya series manufactured by JGC Catalysts & Chemicals Ltd., and the Aerosil series manufactured by Evonik Industries AG and sold by AEROSIL Co., Ltd.

[0062] For a composite material C composed of a material A with a refractive index of n a and a material B with a refractive index of n b , it generally has a refractive index n approximately represented by Equation (1) c :

[0063] Formula (1)

[0064] n c = [n a x v a / 100] + [n b x v b / 100] (1)

[0065] where v a and v b respectively represent the volume fractions of material A and material B constituting the composite material (v a + v b = 100).

[0066] According to Equation (1), a composite material of a solid material and air, i.e., a porous film having a solid material skeleton, serves as the low refractive index layer 104 and can have a refractive index lower than that of the original solid material. In such a structure, the lower the refractive index of the solid material skeleton or the higher the porosity of the low refractive index layer 104, the lower the refractive index of the low refractive index layer 104. To increase the porosity of the low refractive index layer 104, the low refractive index layer 104 can have a porous structure. In this regard, the low refractive index layer 104 can be referred to as a porous film.

[0067] In Equation (1), when material A is air and material B is silica, the refractive index n of air a is 1.00, and the refractive index n of silica b is 1.46. The volume fraction v of silica b is 100 - v a . Therefore, v a can be determined as a function of the refractive index n of the low refractive index layer 104 c . v a refers to the porosity.

[0068] The porosity of the low refractive index layer 104 is preferably 60.0% to 95.0%, more preferably 65.0% to 90.0%.

[0069] For example, according to Equation (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.

[0070] On the other hand, a porosity exceeding 95.0% may cause the refractive index of the low refractive index layer 104 to be less than 1.05 and too low, and the strength is low due to the small amount of the skeleton constituting the low refractive index layer 104.

[0071] Silica preferably has at least one of an organic group and a hydroxyl group on its surface. Silica having a hydroxyl group on its surface has high hydrophilicity. Therefore, the low refractive index layer 104 having such a silica particle skeleton can have high hydrophilicity.

[0072] 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 a hydroxyl group on its surface, a dehydration condensation reaction between the hydroxyl group and the hydrolysis product of the silane coupling agent can be utilized.

[0073] Examples of the organic group include alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, propyl, and butyl, hydrocarbon groups having a polymerizable moiety such as vinyl, acryloyl, and methacryloyl, and aromatic hydrocarbon groups such as phenyl.

[0074] Silica with an organic group on its surface can endow the low refractive index layer 104 with various functions, such as water repellency, oil repellency, biocompatibility, electron transport properties, and polymerizability.

[0075] Not all functional groups on the silica surface are replaced by organic groups, and the organic groups and hydroxyl groups can exist in any proportion.

[0076] [Hollow particles]

[0077] The low refractive index layer 104 containing 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 a cavity (space) inside the shell.

[0078] The low refractive index layer 104 preferably contains a plurality of hollow particles. The low refractive index layer 104 containing a plurality of hollow particles may further contain solid particles or a binder in addition to the hollow particles.

[0079] Figure 3 An example of the structure of the low refractive index layer 104 containing hollow particles as primary particles composed of a solid material is shown.

[0080] The low refractive index layer 104 contains a plurality of hollow particles 301 and a space 302 between the hollow particles 301. The hollow particles also include a space 304. In Figure 3 In, reference numeral 303 denotes the shell, and reference numeral 305 denotes the substrate. The substrate 305 is the material on which the low refractive index layer 104 is to be formed. In 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.

[0081] 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 space in 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 space 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.

[0082] The refractive index n of the low refractive index layer 104 is represented by the following formula (2):

[0083] Formula (2)

[0084] n = [n a x (X + Y) / 100] + [n s x (100 - X - Y) / 100] (2)

[0085] where n arepresents the refractive index of air (n a = 1), and n s represents the refractive index of the outer shell of the hollow particles (n s > 1). According to formula (2), n decreases as X + Y increases or n s decreases.

[0086] The refractive index n of the low refractive index layer 104 is also represented by the following formula (3):

[0087] Formula (3)

[0088] n = [n a x Y / 100] + [n p x (100 - Y) / 100] (3)

[0089] where n p represents the refractive index of a hollow particle (n p > 1). The refractive index n p is an apparent refractive index, which is calculated from the ratio of the volume and refractive index of the outer shell in a hollow particle to the volume and refractive index of its space. Therefore, if n a = 1, n b = n s , in formula (1) v a represents the volume of the space of the hollow particle, v b represents the volume of the outer shell, then n c = n p . According to formula (3), n decreases as Y increases or n p decreases.

[0090] It is also possible to measure the refractive index n of the low refractive index layer 104 by optical measurement and substitute the known n a , n s and n p into formulas (2) and (3) to estimate X and Y.

[0091] The dense arrangement of the hollow particles reduces the volume fraction of the space between the hollow particles and increases the volume fraction of the outer shell formed by the component with a refractive index higher than that of air, thereby increasing the refractive index of the low refractive index layer 104. In contrast, the sparse arrangement of the hollow particles increases the volume fraction of the space between the hollow particles and reduces the volume fraction of the outer shell, thereby reducing the refractive index of the low refractive index layer 104. Therefore, in order to further reduce the refractive index of the 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.

[0092] X and Y preferably satisfy the relationship X < (100 - X - Y) < Y.

[0093] The low refractive index layer 104 may include particles made of a solid material and a binder that binds the particles together to improve strength. When a binder is used, the solid in the low refractive index layer 104 is the outer shell of the hollow particles and the binder, and the volume fraction of the solid relative to the unit volume of the low refractive index layer 104 is represented by (100-X-Y)(%).

[0094] Satisfying the relationship X < (100-X-Y) further improves the strength of the low refractive index layer 104. Satisfying the relationship (100-X-Y) < Y further reduces the refractive index of the low refractive index layer 104.

[0095] The range of the sum (X+Y) of X and Y is preferably from 60.0% to 95.0%, more preferably from 65.0% to 90.0%. (X+Y) within 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 ranges.

[0096] In the low refractive index layer 104, the range of X is preferably from 8.0% to 32.0%, more preferably from 10.0% to 28.0%, still more preferably from 12.0% to 24.0%.

[0097] On the other hand, the range of Y is preferably from 30.0% to 80.0%, more preferably from 35.0% to 75.0%, still more preferably from 40.0% to 70.0%.

[0098] X and Y within these ranges make 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 ranges.

[0099] Although in Figure 3 the example shown the hollow particles are substantially spherical, the hollow particles can have any shape. The hollow particles have an outer shell 303 and a space 304 formed inside the hollow particles and surrounded by the outer shell. In this case, the hollow particles can be considered as core-shell particles containing air as the core.

[0100] The refractive index n p of a single hollow particle is represented by Equation (4):

[0101] Formula (4)

[0102] n p = [n s x (100-V a ) / 100] + [n a x V a / 100] (4)

[0103] where V a represents the volume fraction of the internal space relative to the total volume of the hollow particle. Therefore, the refractive index n of a single hollow particlep Determined by the refractive index n of the shell material s and the porosity V of the hollow particles a and.

[0104] The porosity V of a single hollow particle a is preferably in the range of 30.0% to 70.0%, more preferably in the range of 35.0% to 65.0%.

[0105] The porosity V within these ranges a can easily reduce the refractive index of the low refractive index layer 104, keep the shell strength of the hollow particles constant, and keep the strength of the low refractive index layer 104 constant.

[0106] Similar to the refractive index of solid materials, the refractive index n of the shell of the hollow particles s is preferably 1.10 or more, 1.20 or more, 1.25 or more, 1.30 or more, or 1.35 or more, and preferably 1.65 or less or 1.60 or less. These ranges can be freely combined.

[0107] The refractive index n of the shell of the hollow particles within these ranges s can produce the following results: an easily formed low refractive index layer 104, high-strength hollow particles, a high-strength low refractive index layer 104, and a low refractive index low refractive index layer 104.

[0108] The shell of the hollow particles can be formed of the same material as the solid material.

[0109] The shell of the hollow particles can have micropores. The micropores in the shell can further reduce the refractive index of the shell.

[0110] The range of the number-average particle size of the primary particles of the hollow particles is preferably 1 to 200 nm, more preferably 5 to 100 nm, further preferably 10 to 100 nm, and particularly preferably 20 to 100 nm.

[0111] The number-average particle size within these ranges can produce the following results: easy manufacture of hollow particles, easy prevention of light scattering, and further improvement of the transmittance of the low refractive index layer 104.

[0112] [Fumed silica particles and chain-like silica particles]

[0113] The low refractive index layer 104 preferably contains at least one type of particle selected from the group consisting of secondary particles, chain-like secondary particles, and branched-chain secondary particles. In the secondary particles, primary particles composed of a solid material form a three-dimensional structure. In the chain-like secondary particles, primary particles composed of a solid material are connected in a chain-like manner. In the branched-chain secondary particles, primary particles composed of a solid material are connected in a branched-chain form. When particles composed of a solid material form aggregates, the aggregates are also included in the secondary particles, and in the secondary particles, primary particles composed of a solid material form a three-dimensional structure.

[0114] In the secondary particles in which primary particles composed of a solid material form a three-dimensional structure, in the chain-like secondary particles in which primary particles composed of a solid material are connected in a chain-like manner, and in the branched-chain secondary particles in which primary particles composed of a solid material are connected in a branched-chain form, the volume fraction of the solid material in the low refractive index layer 104 is reduced. This can increase the volume fraction of the space. Thereby, the refractive index of the low refractive index layer 104 can be reduced.

[0115] The number average particle diameter of the primary particles composed of a solid material preferably ranges from 1 to 200 nm, more preferably from 5 to 100 nm. The number average particle diameter of the primary particles composed of a solid material is still more preferably from 10 to 100 nm, and particularly preferably from 20 to 100 nm.

[0116] When the number average particle diameter of the primary particles is within these ranges, the aggregation of the particles can be appropriately controlled, and the dispersibility in the coating liquid can be improved. In addition, it is possible to prevent the primary particles from becoming light scatterers in the wavelength range of 400 to 700 nm, and further improve the transmittance of the low refractive index layer 104.

[0117] Examples of the secondary particles in which primary particles composed of a solid material form a three-dimensional structure are described below for fumed silica particles. However, the present invention is not limited thereto.

[0118] Fumed silica particles can be manufactured by high-temperature hydrolysis of silicon tetrachloride in an oxygen and hydrogen flame. In the fumed silica particles manufactured by this manufacturing method, primary particles of several tens of nanometers fuse to form secondary particles having a three-dimensional structure. The secondary particles can aggregate and have a complex higher-order structure.

[0119] Due to its characteristic structure, the fumed silica particles are very large particles, and their apparent specific gravity is in the range of 0.01 to 0.1 g / cm 3 range. Therefore, the low refractive index layer 104 containing fumed silica particles has a high porosity and can significantly reduce the refractive index.

[0120] The number average particle size of the secondary particles preferably ranges from 10 to 1000 nm, more preferably from 50 to 500 nm.

[0121] When the number average particle diameter of the secondary particles is within these ranges, for example, the primary particles of silica form a three-dimensional structure, and the secondary particles are not a single structure of aggregated primary particles.

[0122] 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 a large space between the secondary particles that may be a light scatterer in the wavelength range of 400 to 700 nm, and makes it easy to control the light transmittance of the low refractive index layer 104.

[0123] The number average particle diameters of the primary particles and the secondary particles (both calculated from the arithmetic mean of the maximum diameters) can be measured by a transmission electron microscope (TEM). As described above, the number average particle diameters of the primary particles and the secondary particles can be controlled, for example, by adjusting the conditions for high-temperature hydrolysis of silicon tetrachloride in an oxygen and hydrogen flame.

[0124] <Film formation method>

[0125] [Method for preparing a coating solution]

[0126] The method for preparing a coating solution for forming the low refractive index layer 104 is described below. Although fumed silica particles in which the primary particles of silica form a three-dimensional structure are described below, the present invention is not limited thereto.

[0127] The fumed silica particles are dispersed in a solvent. The solvent for dispersing the silica particles is preferably a solvent having a high affinity for the fumed silica particles. One solvent or a mixed solvent of two or more solvents can be used according to the type of functional group on the surface of the fumed silica particles.

[0128] 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, diethyl 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 or propylene glycol monoethyl ether acetate, or a ketone solvent such as acetone or methyl ethyl ketone.

[0129] Although the solvent can be water, the surface tension of water is large, and a large capillary force is generated during drying, which sometimes causes the space between the fumed silica particles to contract. This may reduce the porosity of the low refractive index layer 104 and can increase the refractive index.

[0130] When an alkali metal, especially CsI, is used as the material of the scintillator 105, water is not suitable as a solvent due to its strong deliquescence. Particles composed of solid materials can be used alone or in combination of two or more of their types.

[0131] The content of the particles composed of solid materials in the coating liquid is preferably 1.0% or more, more preferably 2.0% or more, further preferably 3.0% or more, and particularly preferably 7.0% or more in terms of mass. The content of the silica particles in the coating liquid is preferably 50.0% or less, more preferably 30.0% or less, and further preferably 20.0% or less in terms of mass. These ranges can be freely combined.

[0132] For example, the concentration (solid component) of the fumed silica particles in the coating liquid preferably ranges from 1.0% to 30.0% in terms of mass, and more preferably from 2.0% to 20.0%.

[0133] When the amount of the particles composed of solid materials in the coating liquid, such as the amount (concentration) of the 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 can also improve the uniform dispersion of the fumed silica particles in the solvent and easily adjust the transmittance of the low refractive index layer 104 within the above range.

[0134] The fumed silica particles are added to the solvent and dispersed. When the coating liquid in which the fumed silica particles are dispersed while maintaining a complex high-order structure forms a film, the size of the fumed silica particles and the spaces between the fumed silica particles causes visible light to be scattered, so the transmittance of the low refractive index layer 104 decreases. When the fumed silica particles are subjected to a dispersion treatment, the transparency of the coating liquid increases with the increase in the dispersion treatment time.

[0135] When the coating liquid containing properly dispersed fumed silica particles forms a film, the size of the framework of the fumed silica particles and the spaces between the fumed silica particles makes them not become scatterers of visible light. Therefore, the low refractive index layer 104 has a high transmittance.

[0136] Further dispersion treatment may destroy the ultra-high 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.

[0137] In addition, excessive dispersion treatment causes so-called over-dispersion, easily causes the fumed silica particles to re-aggregate, and may reduce the transmittance of the low refractive index layer 104 after film formation.

[0138] Therefore, an appropriate dispersion state is preferred. A dispersing treatment can be carried out using a stirrer, ultrasonic waves, a planetary mixer, a ball mill, a bead mill, a homogenizer, etc.

[0139] Although hollow particles having a silica shell are used as the solid material in the examples below, the present invention is not limited thereto.

[0140] A dispersion liquid of hollow particles can be used. The dispersion liquid of hollow particles can be any dispersion liquid of hollow particles that satisfies the porosity of the hollow particles, the refractive index of the shell of the hollow particles, the number average particle diameter of the primary particles of the hollow particles, etc.

[0141] For example, it is preferable to use the Thrulya series manufactured by JGC Catalysts and Chemicals Ltd., which is an isopropyl alcohol (hereinafter also referred to as IPA) dispersion liquid of hollow particles having a silica shell (hereinafter also referred to as hollow silica particles). In addition to commercially available products such as the Thrulya series, hollow silica particles dispersed in a solvent by the same method as the solvent dispersion of fumed silica particles can also be used.

[0142] The concentration of the hollow particles in the solvent can be in the same range as the concentration (solid component) of the fumed silica particles in the coating liquid.

[0143] The surface of the hollow silica particles has hydroxyl groups and is hydrophilic. Therefore, a highly hydrophobic solvent is not suitable. More specifically, it is preferable to use an organic solvent with an octanol / water partition coefficient log P ow of 2 or less. The organic solvent can be an alcohol solvent such as methanol, ethanol, propanol, or isopropyl alcohol, a glycol solvent such as ethylene glycol or propylene glycol, an ether solvent such as dimethyl ether, diethyl 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, or propylene glycol monoethyl ether acetate, or a ketone solvent such as acetone or methyl ethyl ketone.

[0144] As described 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 the hollow silica particles.

[0145] A method for randomly arranging the hollow silica particles is described below. The hollow silica particles are randomly arranged by forming loose aggregates of the hollow silica particles in the dispersion liquid.

[0146] The aggregates are also included in the secondary particles in which the primary particles composed of the solid material form a three-dimensional structure.

[0147] One method of aggregating hollow silica particles well dispersed in a dispersion can be to add a solvent (hereinafter referred to as an aggregating agent) having a higher log P than the dispersion medium. The aggregation method is not limited to this, and a method capable of controlling the aggregation state of the hollow silica particles is preferred. ow The surface of the hollow silica particles has hydroxyl groups and is hydrophilic. Therefore, the addition of an aggregating agent having a higher log P than the dispersion medium, that is, an aggregating agent more hydrophobic than the dispersion medium, causes aggregation of the hollow silica particles.

[0148] The surface of the hollow silica particles has hydroxyl groups and is hydrophilic. Therefore, the addition of an aggregating agent having a higher log P than the dispersion medium, that is, an aggregating agent more hydrophobic than the dispersion medium, causes aggregation of the hollow silica particles. ow The surface of the hollow silica particles has hydroxyl groups and is hydrophilic. Therefore, the addition of an aggregating agent having a higher log P than the dispersion medium, that is, an aggregating agent more hydrophobic than the dispersion medium, causes aggregation of the hollow silica particles.

[0149] The log P of the aggregating agent for aggregating the well-dispersed hollow silica particles in the dispersion and the addition amount are described below. If the difference in log P between the dispersion medium and the aggregating agent is too small, the hollow silica particles will not aggregate. If the difference in log P between the dispersion medium and the aggregating agent is too large, strong aggregation of the hollow silica particles will occur even when the addition amount of the aggregating agent is small. When the hollow silica particles form large aggregates, the aggregates themselves may become light scatterers. ow The log P between the dispersion medium and the aggregating agent ow If the difference is too small, the hollow silica particles will not aggregate. If the difference in log P between the dispersion medium and the aggregating agent is too large, strong aggregation of the hollow silica particles will occur even when the addition amount of the aggregating agent is small. When the hollow silica particles form large aggregates, the aggregates themselves may become light scatterers. ow If the difference is too small, the hollow silica particles will not aggregate. If the difference in log P between the dispersion medium and the aggregating agent is too large, strong aggregation of the hollow silica particles will occur even when the addition amount of the aggregating agent is small. When the hollow silica particles form large aggregates, the aggregates themselves may become light scatterers.

[0150] On the other hand, the large spaces formed between the large aggregates of the hollow silica particles also tend to become light scatterers, which may cause the low refractive index layer 104 after coating to be turbid, thereby possibly reducing the transmittance.

[0151] In addition, significant aggregation tends to reduce the storage stability of the coating solution. Therefore, in order to form the low refractive index layer 104 with a low refractive index and high transmittance, it is preferable to control the aggregation state of the hollow silica particles by the type and addition amount of the aggregating agent. The refractive index of the low refractive index layer 104 can be controlled by utilizing this property and controlling the aggregation state of the hollow silica particles by the type and addition amount of the aggregating agent.

[0152] In addition, filling the spaces between the hollow silica particles with some materials can reduce Y and X + Y and increase the refractive index of the low refractive index layer 104. Therefore, in the downstream process, it is preferable to remove the aggregating agent, and more preferably to volatilize the aggregating agent by heating.

[0153] The aggregating agent can be, for example, a silicone oil such as X-22-164 (manufactured by Shin-Etsu Chemical Co., Ltd.), but is not limited thereto.

[0154] The formation method of the low refractive index layer 104 is described below.

[0155] A coating liquid is used to form a film. The film can be formed by a bar coating method, a doctor blade method, a brush coating method, a spray coating method, a spin coating method, a dip coating method, or a screen printing method. Among them, in order to make the thickness of the low refractive index layer 104 uniform, the spin coating method is preferably used. When forming a film on a large-area sensor panel having a scintillator, the spray coating method is preferably used.

[0156] In addition, 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 can be appropriately adjusted.

[0157] The film formed by this method is preferably dried in a temperature range of 20 °C to 100 °C.

[0158] The film can be further heat-treated. The heat treatment is preferably carried out in a temperature range of 100 °C to 200 °C, more preferably in the range of 120 °C to 180 °C.

[0159] For example, when the heating temperature reaches 100 °C or higher, it is less likely that the solvent remains in the space of the hollow particles. At a heating temperature below 200 °C, the performance of the sensor panel corresponding to the light detection unit 113 is less likely to deteriorate.

[0160] When the film contains a binder and a polymerization initiator, a thermal curing or photocuring step is preferably included. For thermal curing, the evaporation of the solvent can be carried out simultaneously with the thermal curing of the binder in the drying or heating step.

[0161] The film formed of fine particles generally maintains its film shape by intermolecular forces. In addition, hydrophobic interaction acts on the hydrophobic surface of the fine particles, and liquid crosslinking acts on the hydrophilic surface of the fine particles. These are physical interactions. For example, when the film is heat-treated, the hydroxyl groups on the surface of the fumed silica particles are chemically bonded to each other through a dehydration reaction, and it is expected to improve the strength of the film.

[0162] When forming a film containing particles composed of a solid material to reduce the refractive index, the van der Waals force and liquid crosslinking acting between the particles maintain the structure and film shape.

[0163] A binder for bonding the particles together can be used in the method of improving the strength of the film having such a structure. From the perspective of improving the film strength, the low refractive index layer 104 can also contain a binder.

[0164] The low refractive index layer 104 preferably contains a binding material formed by binding solid materials with a binder. More specifically, the low refractive index layer 104 preferably contains a binding material formed by binding particles composed of solid materials with a binder. The binding of the solid material and the binder encompasses any binding concept such as between primary particles composed of solid materials, between secondary particles formed by primary particles composed of solid materials, between primary particles and secondary particles, etc. The binding can be, for example, a chemical binding such as ionic binding or covalent binding, or it can be a mechanical binding.

[0165] The binder can be a resin, such as an acrylic resin, a fluororesin, a styrene resin, an imide resin, a polyurethane resin, or a phenolic resin.

[0166] The binder can also be an organosilicon compound prepared by polymerizing a silicone oil having a polymerizable group or by hydrolysis and polycondensation of a silanolate.

[0167] In addition to these binders, any transparent and colorless binder having a low refractive index and capable of binding particles can be used.

[0168] Exemplary preparation methods of the film containing a binder include the following steps: preparing a liquid mixture containing a solid material, a solvent, and a binder, preparing a coating liquid by subjecting the liquid mixture to a dispersion treatment, and forming a film by coating and drying the coating liquid and, if necessary, heating the coating liquid or irradiating the coating liquid with high-energy radiation.

[0169] The binder preferably contains siloxane, and more preferably contains silsesquioxane.

[0170] Silsesquioxane is a compound having a T3 unit structure represented by the compositional formula [R 1 (SiO 1.5 ) n (R 1 (wherein R 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 an organic substance.

[0171] Silsesquioxane (hereinafter sometimes simply referred to as SQ) is a siloxane compound whose main chain skeleton is composed of Si-O bonds, and is represented by the compositional formula [R 1 (SiO 1.5 ) n . R 1 preferably 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.

[0172] When the function of the silsesquioxane is to bind together a large number of particles composed of solid materials, the film can have higher strength while maintaining high porosity.

[0173] The silsesquioxane can have any polymer 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 is 1.5 relative to the number of silicon atoms). In terms of cost, linear polysiloxanes, cage polysiloxanes, and ladder polysiloxanes can be used in combination.

[0174] The silsesquioxane is preferably a compound having a polymerizable group (R in the above formula) in the molecule and curable by free radical polymerization or cationic polymerization. 1 ) and curable by free radical polymerization or cationic polymerization.

[0175] The silsesquioxane curable by free radical polymerization can be a silsesquioxane having an acryloyl group or a methacryloyl group as R. The silsesquioxane curable by cationic polymerization can be a silsesquioxane having an oxetanyl group or an epoxy group as R.

[0176] Specific examples include the silsesquioxane derivatives SQ series (AC-SQ, MAC-SQ, and OX-SQ) manufactured by Toagosei Co., Ltd.

[0177] The silsesquioxane is a high-viscosity liquid and is preferably added to the coating solution. A polymerization initiator can be added if necessary.

[0178] For every 100 parts by mass of the particles composed of solid materials, the content of the binder in 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. For every 100 parts by mass of the particles composed of solid materials, the content of the binder in 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.

[0179] The coating solution can be coated on a substrate, and the silsesquioxane can be cured by heating or light irradiation.

[0180] Through such an operation, a film containing a binding material in which particles composed of solid materials are bound together with the silsesquioxane is formed. The silsesquioxane can be cured to increase the strength of the film.

[0181] Examples of the polymerization initiator include free radical photoinitiators, cationic photoinitiators, thermal free radical polymerization initiators, and thermal cationic polymerization initiators. These polymerization initiators can be used alone or in combination.

[0182] Examples of free radical photoinitiators include, but are not limited to, optionally substituted 2,4,5-triaryl imidazole dimers, such as 2-(o-chlorophenyl)-4,5-diphenyl imidazole dimer, 2-(o-chlorophenyl)-4,5-di(methoxyphenyl) imidazole dimer, 2-(o-fluorophenyl)-4,5-diphenyl imidazole dimer, and 2-(o- or p-methoxyphenyl)-4,5-diphenyl imidazole 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-amino aromatic 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, phenanthraquinone, 2-tert-butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, 1-methylanthraquinone, 1,2-chloroanthraquinone 4-naphthoquinone, 9,10-phenanthraquinone, 2-methyl-1,4-naphthoquinone, and 2,3-dimethylanthraquinone; benzoin ether derivatives, 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-bis(9,9'-acridinyl)heptane; N-phenylglycine derivatives, such as N-phenylglycine; acetophenone derivatives, such as acetophenone, 3-methylacetophenone, acetophenone ketal, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone; thioxanthone derivatives, such as thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, and 2-chlorothioxanthone; acylphosphine oxide derivatives, such as 2,4,6-trimethylbenzoyl diphenylphosphine 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-benzoyl oxime)] and acetone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyl oxime); 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.

[0183] Examples of commercially available products of free radical photoinitiators 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 Corporation, "Darocur" and "Lucirin" are registered trademarks), Uvecryl P36 (manufactured by UCB).

[0184] The cationic photoinitiators are preferably onium salts, aromatic onium salts, arylsulfonium salts, aryliodonium salts, etc. Specific examples of the anions include tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroantimonate ion, perchlorate ion, trifluoromethanesulfonate ion and fluorosulfonate ion.

[0185] Examples of commercially available products of cationic photoinitiators include CPI-210S (manufactured by San-Apro Limited), UVI-6950 (manufactured by Union Carbide Corporation) and Adeka Optomer SP-150 (manufactured by San-Apro Limited) and Adeka Optomer SP-150 (manufactured by Adeka Corporation).

[0186] In terms of quality, for every 100 parts of silsesquioxane solid, the content of the polymerization initiator in the coating liquid preferably ranges from 0.01 to 1.5 parts by mass, more preferably from 0.03 to 1.0 parts by mass.

[0187] The coating liquid can be prepared by mixing particles composed of solid materials, solvents, binders and optionally polymerization initiators. The solvent is preferably an organic solvent. The organic solvent can be an alcohol, carboxylic acid, aliphatic or alicyclic hydrocarbon, aromatic hydrocarbon, ester, ketone, ether, or a mixed solvent of two or more of them, but is not limited thereto.

[0188] Examples of the alcohol 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.

[0189] Specific examples of the carboxylic acid 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-methylvaleric acid, 4-methylvaleric acid, 2-ethylvaleric acid, 3-ethylvaleric acid, 2,2-dimethylvaleric acid, 3,3-dimethylvaleric acid, 2,3-dimethylvaleric acid, 2-ethylhexanoic acid and 3-ethylhexanoic acid.

[0190] Specific examples of aliphatic or alicyclic hydrocarbons include n - hexane, n - octane, cyclohexane, cyclopentane, and cyclooctane.

[0191] The aromatic hydrocarbon is preferably toluene, xylene, or ethylbenzene.

[0192] Examples of 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.

[0193] Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

[0194] Examples of ethers include dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether.

[0195] Considering the solution stability, it is preferable to use an alcohol in the above solvents to prepare the coating solution.

[0196] The coating solution can be prepared by adding a predetermined amount of binder and a self - selected polymerization initiator to a liquid containing particles composed of solid materials dispersed in a solvent. The liquid containing particles dispersed in an organic solvent can be prepared by dispersing particle powder in a solvent by the same method as the above - mentioned dispersion treatment (for example, using a ball mill, etc.), or it can be a commercially available dispersion.

[0197] When forming a film using the coating solution, the coating is carried out in an inert gas atmosphere such as dry air or dry nitrogen. The relative humidity of the drying atmosphere is preferably 30% or less.

[0198] In addition, the solution coating method for film formation can be a known coating method, such as dip coating, spin coating, spray coating, printing, flow coating, or a combination thereof. The film thickness can be controlled by changing the pulling speed in dip coating or the substrate rotation speed in spin coating or by changing the concentration of the coating solution.

[0199] The film can be cured by high - energy radiation irradiation such as light irradiation or radiation irradiation or by heating. Curing can be carried out by combining high - energy radiation irradiation and heating.

[0200] For curing by high - energy radiation irradiation, the high - energy beam can be an electron beam, X - ray, ultraviolet radiation, etc., but is not limited thereto. When the high - energy beam is ultraviolet radiation, the range of the radiation wavelength is preferably 160 to 400 nm, and the output range is preferably 0.1 to 2000 mW / cm 2 . Considering the prevention of the oxidation of silsesquioxane, the curing atmosphere is preferably an inert atmosphere such as nitrogen. Curing by heating is carried out in the temperature range of 50°C to 250°C, preferably 80°C to 200°C, for 1 to 20 minutes.

[0201] <Method for Evaluating Membrane Porosity and Refractive Index>

[0202] The porosity X (%) and porosity Y (%) of the membrane can be calculated as follows.

[0203] First, a carbon film is coated on the membrane formed on the substrate using an ion beam coater IBC type 681 (manufactured by Gatan), and then ion beam slicing (30 kV - 0.1 nA) is performed in a focused ion beam processing device (FIB-SEM, manufactured by FEI Company, Nova 600). Then, a SEM image is obtained at an acceleration voltage of 2 kV using a scanning electron microscope (hereinafter referred to as SEM).

[0204] The observation magnification of the SEM image is such that at least the entire membrane can be observed in the thickness direction, and for example, the shape of each hollow particle can be distinguished. More specifically, the observation magnification is about 50,000 to 200,000.

[0205] The unit volume of the membrane is 1000 nm × 1000 nm × 100 nm (in the thickness direction). To calculate the porosity in the cross-sectional SEM image, the hollow particles and the space between the hollow particles are distinguished by binarization of the grayscale image, and the area of each region is calculated. Image processing is performed using image analysis software Image J (NIH Image, available from https: / / imagej.nih.gov / ij / ).

[0206] More specifically, the porosity X (%) is calculated by multiplying the area A (%) of the hollow particles by the volume fraction V of the internal space relative to the total volume of the hollow particles a : X = A x V a . The porosity Y (%) is Y = 100 - A.

[0207] The refractive index n of the low refractive index layer 104 can be calculated using formula (2) from the X and Y calculated thereby.

[0208] [Radiation Detector]

[0209] As Figure 4 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. An optical fiber plate (FOP), etc. can also be used.

[0210] Exemplary Embodiment

[0211] 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.

[0212] (Exemplary Embodiment 1)

[0213] (Preparation of Scintillator)

[0214] As described below, a scintillator is prepared on a substrate by a thermal evaporation method. A heating boat in a vacuum chamber is filled with CsI raw material powder. The substrate placed opposite the boat is a glass substrate and is mounted on a turntable. The vacuum chamber is evacuated to a high vacuum of 1×10 -3 Pa or less at one time with a vacuum pump, and the temperature of the boat is set to 670 °C. Another boat is placed in the vacuum chamber, filled with thallium iodide (TlI) raw material powder used as a luminescence center, and heated while forming a film. While rotating at a speed of 60 rpm, the raw materials are deposited on a 50-mm square glass substrate.

[0215] Hollow silica particles having a silica shell are selected as the particles for forming the low refractive index layer. A coating liquid for film formation is prepared using Thrulya 4110 (dispersion medium: IPA, silica solid content: 20.5% by mass, number average particle diameter of one hollow particle: 60 nm, porosity of one hollow particle: 45%, refractive index of one hollow particle: 1.25) manufactured by JGC Catalysts and Chemicals Ltd. The dispersion liquid thus prepared may be referred to as a hollow silica particle dispersion liquid.

[0216] A film of the hollow silica particle dispersion liquid is formed on the prepared scintillator by a spin coating method to form a low refractive index layer. The film is formed by rotating the substrate at a speed of 1500 rpm for 15 seconds.

[0217] (Formation of Support Member (Reflection Layer))

[0218] The support member is formed by covering the scintillator with aluminum (Al) held on a poly(ethylene terephthalate) (PET) film with a thickness of about 30 μm. The aluminum serves as a reflection layer. In order to improve the adhesion to the scintillator on which the low refractive index layer is formed, a thermoplastic resin film with a thickness of about 30 μm is pre-formed before forming the support member. The adhesion between the scintillator, the reflection layer, and the support member is improved by heating in the temperature range of 80 °C to 100 °C using a vacuum laminator.

[0219] (Structure Evaluation)

[0220] 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 obtained using a scanning electron microscope (hereinafter referred to as SEM) at an acceleration voltage of 2 kV. Figure 5A A low-magnification SEM image is shown, Figure 5B showing a high-magnification SEM image near the interface of the low refractive index layer. 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.

[0221] 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 Equation (2), where n s is 1.46.

[0222] <MTF Evaluation and Sensitivity Evaluation>

[0223] 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.

[0224] <Fabrication of Radiation Detector>

[0225] A polyimide layer is formed as a polymer protective layer by spin coating on a sensor panel including a detection unit. A scintillator is formed on the polyimide layer. Then, a low refractive index layer is formed on the scintillator, and it is bonded to an Al reflective layer via an adhesive layer (a layer containing a thermoplastic resin) by a vacuum laminator to form a radiation detector.

[0226] (Exemplary Embodiment 2)

[0227] The spin-coated substrate rotation speed is changed to 1000 rpm for 15 seconds to form a low refractive index layer. Except for this, Exemplary Embodiment 2 is the same as Exemplary Embodiment 1.

[0228] (Exemplary Embodiment 3)

[0229] The low refractive index layer is formed by film formation through spraying five times. Except for this, Exemplary Embodiment 3 is the same as Exemplary Embodiment 1.

[0230] (Exemplary Embodiment 4)

[0231] A coating solution prepared by diluting a hollow silica particle dispersion with IPA to a silica solid content of 10.0% by mass is used, and the low refractive index layer is formed by film formation through spraying 20 times. Except for this, Exemplary Embodiment 4 is the same as Exemplary Embodiment 1.

[0232] (Exemplary Embodiment 5)

[0233] The reflective layer is formed of an epoxy resin containing titanium oxide, which serves as an adhesive layer and also as a reflective layer. Except for this, Exemplary Embodiment 5 is the same as Exemplary Embodiment 1. Exemplary Embodiment 5 corresponds to Figure 2A and Figure 2B the structure according to the present invention shown.

[0234] (Exemplary Embodiment 6)

[0235] AEROSIL R812 (manufactured by Nippon Aerosil Co., Ltd.) is fumed silica particles having methyl groups on their surfaces and is used for 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 at a solid content of 6.88% by mass are sealed in a glass container together with zirconia (ZrO2) balls with a diameter of 0.5 mm. The glass container is rotated on a ball mill turntable at a rotation speed of 30 rpm for 48 hours to disperse the fumed silica particles. The fumed silica particle dispersion prepared by dispersion treatment using a ball mill is used as a coating solution. The coating solution is sprayed five times by spraying to form a film to form a low refractive index layer. Except for this, Exemplary Embodiment 6 is the same as Exemplary Embodiment 1.

[0236] Figure 6 Shows a cross-sectional SEM image obtained by the same method as in Exemplary Embodiment 1. The low refractive index layer is formed along the unevenness at the ends of the CsI columnar crystals. 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, thus having a flat surface that becomes the interface with the adhesive layer in subsequent steps. However, the low refractive index layer ( Figure 6 ) in the spraying method is formed along the unevenness of the columnar crystals.

[0237] (Comparative Example 1)

[0238] No low refractive index layer was formed. Except for this, Comparative Example 1 is the same as Exemplary Embodiment 1.

[0239] (Comparative Example 2)

[0240] A thick low refractive index layer was formed. The silica particle dispersion liquid in Exemplary Embodiment 6 was used as the coating liquid, and a film was formed by the spin coating method in the same manner as in Exemplary Embodiment 1.

[0241] Table 1 summarizes the MTF and sensitivity evaluation results of Exemplary Embodiments 1 to 6 and Comparative Examples 1 and 2. The film thickness is the average thickness (T1) starting from the top of each CsI columnar crystal. The MTF and sensitivity evaluation values are the ratios to the known structure without a low refractive index layer according to Comparative Example 1.

[0242] (Discussion)

[0243] In Exemplary Embodiment 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 CsI improved the total reflection efficiency at the interface between CsI and the low refractive index layer and increased the amount of light remaining in CsI. The light leaking into the adhesive layer propagates parallel to the surface of the light receiving portion, while being repeatedly reflected and attenuated in the adhesive layer, resulting in a decrease in sensitivity (equivalent to light attenuation) and a decrease in MTF. The low refractive index layer can reduce the amount of light leaking into the adhesive layer and improve the sensitivity and MTF.

[0244] [Film Formation Method]

[0245] Comparative exemplary embodiments 1 to 4 show the differences caused by the film-forming method. The spin coating method in exemplary embodiments 1 and 2 has higher sensitivity than the spraying method in exemplary embodiments 3 and 4. In the spraying method, the droplets of the coated liquid sprayed are deposited at the ends of the columnar crystals, and regions without a low refractive index layer are dispersed 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 region with a low refractive index layer, and higher sensitivity.

[0246] [Type of silica particles]

[0247] Comparative exemplary embodiments 3, 4, and 6 are compared to show the differences caused by the type of silica particles. When the film-forming method is the spraying 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 higher strength. This is because in the binding material of the hollow particles and the binder, the binder at the contact points between the hollow particles contributes strongly to the binding between the hollow particles and improves the strength of the film.

[0248] [Thickness of the low refractive index layer]

[0249] Comparative exemplary embodiments 1 to 4 and 6 and comparative example 2 are compared to show the differences caused by the thickness (film thickness) of the low refractive index layer. When changing the thickness of the low refractive index layer using hollow silica (exemplary embodiments 1 to 4), in exemplary embodiment 3 with a film thickness of 0.6 μm, the MTF increased by 11%, and in exemplary embodiments 1, 2, and 4 with a thickness of 1.0 μm or more, it increased by 15%.

[0250] When changing the thickness of the low refractive index layer using fumed silica (exemplary embodiment 6 and comparative example 2), compared with comparative example 1 without a low refractive index layer, the MTF increased by 22% in exemplary embodiment 6 with a film thickness of 0.5 μm, but decreased in comparative example 2 with a film thickness of 16 μm. Therefore, a low refractive index layer with a thickness of at least 0.5 μm contributes sufficiently to improving the MTF. On the other hand, in comparative example 2 with an excessively large film thickness, the optical path length of the light reflected by the reflective layer is long, the light diffuses laterally, and the MTF decreases.

[0251] [Reflective layer]

[0252] Compare Exemplary Embodiment 1 and Exemplary Embodiment 5 to show the differences caused by the reflective layer. The adhesive layer having both reflective and adhesive functions in Exemplary Embodiment 5 also acts as a reflective layer, preventing light leakage from propagating through the adhesive layer, thereby reducing light attenuation, increasing the amount of light reaching the light detection unit, and greatly improving the sensitivity. Half of the light generated by the scintillator propagates towards the light detection unit, while the other half propagates in the opposite direction. Compared with the former, the latter has a longer optical path to reach the light detection unit, and also has light scattering when using an adhesive layer that also serves as a reflective layer, so it has a lower MTF than other exemplary embodiments using an Al reflective layer.

[0253] Table 1

[0254]

[0255] Therefore, the present invention can provide a radiation detector with improved sensitivity and resolution.

[0256] The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the gist and scope of the present invention. Therefore, the following claims are proposed to disclose the scope of the present invention.

[0257] This application claims the priority of Japanese Patent Application No. 2019-141821 filed on July 31, 2019, the entire content of which is incorporated herein by reference.

Claims

1. A scintillator unit, the scintillator unit comprising: a support member, an adhesive layer, a low refractive index layer, and a scintillator in order in the incident direction of radiation, wherein, the low refractive index layer has a refractive index lower than that of the adhesive layer.

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

3. The scintillator unit according to claim 1 or 2, wherein, at least a part of the support member includes a reflective layer or a light absorbing layer.

4. The scintillator unit according to claim 1 or 2, wherein, the adhesive layer includes a scattering layer containing light scattering particles and a binder resin.

5. The scintillator unit according to claim 1 or 2, wherein, the adhesive layer contains a thermoplastic resin.

6. The scintillator unit according to claim 1 or 2, wherein, the adhesive layer contains an acrylic resin.

7. The scintillator unit according to claim 1 or 2, wherein, the low refractive index layer contains silica.

8. The scintillator unit according to claim 1 or 2, wherein, the low refractive index layer contains hollow particles.

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

10. The scintillator unit according to claim 8, wherein, the hollow particles have a shell with a refractive index of 1.35 or more.

11. 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, the radiation detector comprising: a support member, an adhesive layer, a low refractive index layer, a scintillator, and a detection unit for detecting light generated from the scintillator in order in the incident direction of radiation, wherein, the low refractive index layer has a refractive index lower than that of the adhesive layer, and the detection unit is opposed to the low refractive index layer via the scintillator.

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