Optical sensor cover

Abstract

To provide an optical sensor cover having suitable pressure resistance and light-shielding properties as the rear cover of a photomultiplier protective case, and with which there is no possibility of a compound for emitting light upon radiation and / or absorbing ultraviolet rays eluting off.SOLUTION: An optical sensor cover (20) is designed to protect a portion of a photomultiplier (2) rearward of a light-receiving surface (2S) and composed of a resin structure that includes a resin molding (20X) including a transparent resin, the resin structure including an approximately conical body part (21), the thickness of which is 6-15 mm, the total light transmittance of the body part (21) being 20% or less, and having pressure resistance not to rupture when the entire outer surface of the body part (21) is pressed with a pressure of 3 MPa, the content of the compound that has the properties to emit light upon radiation and / or absorb ultraviolent rays being 300 ppm or less.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a photosensor cover that protects the rear of a light receiving surface of a photomultiplier tube. [Background technology]

[0002] Numerous particle experiments have been conducted to clarify the formation of the universe and the origin of matter. Most elementary particles do not exist stably on their own in the natural world, but are discovered or created through the observation of cosmic rays and production reactions in accelerators. An example of an elementary particle is a charged particle, which is an elementary particle that carries an electric charge. For example, alpha and beta rays produced by nuclear decay are radiation made up of charged particles. When a charged particle moves through a substance, the light emitted when the speed of the charged particle is faster than the speed of light in that substance is called Cherenkov light. By observing this light, the energy, direction of travel, position, and type of particle of the charged particle can be determined. A photomultiplier tube amplifies Cherenkov light, which is made up of this weak photon energy, and can be taken out as a signal current. The wavelength range of Cherenkov light is wide, from ultraviolet to infrared, with ultraviolet being relatively stronger than visible and infrared light. The spectral sensitivity of the photomultiplier tubes used to observe Cherenkov light is from ultraviolet to visible light, with the sensitivity in the ultraviolet range being particularly important.

[0003] An example of the use of such photomultiplier tubes is the Water-Cherenkov Astrophysical Particle Observatory, which observes Cherenkov light generated in a huge water tank. In this instrument, photomultiplier tubes with water pressure resistance are placed on the wall of a tank filled with pure water, with their light-receiving surfaces facing the inside of the tank, and the photomultiplier tubes capture Cherenkov light generated by charged particles that are knocked out when nucleons or electrons in the water collide with neutrino particles. The photomultiplier tubes used in this instrument have a structure in which a photocathode, dynode, anode, and other electrodes are sealed in a high-vacuum glass container.

[0004] In recent years, as research has become more extensive and water tanks have become larger, it has become necessary to increase the diameter and pressure resistance of photomultiplier tubes. If a high-vacuum glass container breaks for some reason at a depth underwater where high water pressure is applied, the impact may cause a chain reaction of implosion of the surrounding photomultiplier tubes. However, since it is not easy to increase the strength of a glass container for a large-diameter photomultiplier tube that meets the purpose of research, it is preferable to attach a protective case that can withstand high water pressure to the photomultiplier tube. In order to enable replacement of the photomultiplier tube, it is preferable that the protective case has a structure that can be opened and closed freely, and is composed of a substantially hemispherical front cover that protects the light-receiving surface of the photomultiplier tube, and a rear cover that is detachably attached to the front cover and protects the area behind the light-receiving surface.

[0005] The protective cover is required to house the photomultiplier tube and protect it from water pressure and shock waves such as implosion. Protecting the photomultiplier tube is important because it leads to the protection of important electronic components (e.g., the electron multiplier section and electrodes such as the anode) enclosed inside the photomultiplier tube. For the above reasons, the front cover and rear cover are required to have high pressure resistance and explosion resistance. The main material for the front cover and rear cover is preferably resin, which has excellent strength and processability and is easy to reduce in weight. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-060867 A Summary of the Invention [Problem to be solved by the invention]

[0007] The front cover must be made of a material that is transparent to ultraviolet light so as not to impede the transmission of Cherenkov light. Patent Document 1 discloses a substantially hemispherical photosensor cover made of a transparent resin molded body that is UV-transmitting, as a photosensor cover suitable as a front cover for a photomultiplier tube protective case (claim 1). As a transparent resin suitable for the front cover, methacrylic resins such as polymethyl methacrylate (PMMA) are cited because they can achieve high ultraviolet transmittance (Claim 4, paragraph 0017).

[0008] On the other hand, the rear cover needs to be made of a material that does not emit light, absorb light, or reflect light, and does not interfere with the observation of Cherenkov light. In order not to interfere with the observation of Cherenkov light, the rear cover is preferably made to have high light-blocking properties. The main material of the rear cover can be a transparent resin such as an acrylic resin, just like the front cover. In this case, however, some measure must be taken to block light and prevent light reflection. From the viewpoint of reducing the weight of the entire protective cover and thus simplifying the entire device, it is preferable to make the thickness of the rear cover as thin as possible. The rear cover must not elute compounds that interfere with the measurement of Cherenkov light. Specifically, the rear cover is required not to elute compounds that emit light in response to radiation such as α-rays, β-rays, and γ-rays, and / or that absorb ultraviolet light. It is preferable that the rear cover contains a negligible amount or no compounds that emit light in response to radiation and / or absorb ultraviolet light.

[0009] The present invention has been made in consideration of the above circumstances, and has an object to provide an optical sensor cover that has suitable pressure resistance and light-shielding properties as a rear cover for a photomultiplier tube protective case, and is not susceptible to the elution of compounds that emit light in response to radiation and / or absorb ultraviolet light. [Means for solving the problem]

[0010] The present invention provides the following optical sensor covers [1] to [9]. [1] A photosensor cover that protects the rear portion of the light receiving surface of a photomultiplier tube, a resin structure including a resin molded body including a transparent resin, The resin structure includes a substantially conical main body and has a thickness of 6 to 15 mm. The total light transmittance of the main body measured in accordance with JIS K7361-1 is 20% or less, The entire outer surface of the main body has a pressure resistance of 3 MPa so that it will not break. An optical sensor cover having a content of compounds that emit light when exposed to radiation and / or absorb ultraviolet light of 300 ppm or less, as measured in accordance with JIS K6904.

[0011] [2] The optical sensor cover of [1], wherein the resin structure further has a flat peripheral portion formed outside the main body portion and extending perpendicular to the central axis of the main body portion. [3] The optical sensor cover according to [1] or [2], wherein the resin molding contains an acrylic resin. [4] The optical sensor cover according to any one of [1] to [3], wherein the resin structure is a laminate including the resin molded body and a reinforcing layer laminated on an outer surface of the resin molded body. [5] The optical sensor cover according to [4], wherein the reinforcing layer includes a cured thermosetting resin and reinforcing fibers. [6] The optical sensor cover according to [5], wherein the thermosetting resin comprises an unsaturated polyester resin. [7] The optical sensor cover according to any one of [4] to [6], wherein the reinforcing layer is a light-shielding layer. [8] The optical sensor cover according to any one of [1] to [3], wherein the resin structure is a laminate including the resin molded body and a light-shielding layer laminated on an outer surface of the resin molded body and including one or more colorants. [9] The optical sensor cover according to any one of [1] to [8], wherein the compound is styrene. Effect of the Invention

[0012] According to the present invention, it is possible to provide an optical sensor cover that has suitable pressure resistance and light-shielding properties as a rear cover for a photomultiplier tube protective case and is not susceptible to the elution of compounds that emit light in response to radiation and / or absorb ultraviolet light. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic perspective view of an optical sensor cover according to an embodiment of the present invention; [Diagram 2] 1 is a schematic cross-sectional view of an optical sensor cover according to an embodiment of the present invention. [Diagram 3] 11A and 11B are schematic cross-sectional views showing a design modification example of the optical sensor cover. [Figure 4] 1 is a schematic cross-sectional view of a case-equipped photomultiplier tube according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described in detail below. In order to enable replacement of the photomultiplier tube, the photomultiplier tube protective case can have a freely openable and closable structure consisting of a substantially hemispherical front cover that protects the light receiving surface of the photomultiplier tube, and a rear cover that is detachably attached to the front cover and protects the portion behind the light receiving surface (also called the rear). The photosensor cover of the present invention is a rear cover that protects the rear portion (rear portion) of the photomultiplier tube from the light receiving surface.

[0015] The protective cover is required to house the photomultiplier tube and protect it from water pressure and shock waves such as implosion. Protecting the photomultiplier tube is important because it leads to the protection of important electronic components (e.g., the electron multiplier section and electrodes such as the anode) enclosed inside the photomultiplier tube. For the above reasons, the front cover and rear cover are required to have high pressure resistance and explosion resistance. The main material for the front cover and rear cover is preferably resin, which has excellent strength and processability and is easy to reduce in weight. The rear cover must be made of a material that does not emit light, absorb light, or reflect light, and does not interfere with the observation of Cherenkov light. In order not to interfere with the observation of Cherenkov light, the rear cover is preferably made to have light blocking and anti-reflection properties.

[0016] The optical sensor cover of the present invention comprises a resin structure including a resin molded body containing a transparent resin. The resin molded body may have a single-layer structure or a multi-layer structure. The resin structure includes a substantially conical main body having a thickness of 6 to 15 mm. In this specification, "approximately conical" means a perfect cone shape and a deformed cone shape that a person skilled in the art can think of. Examples of deformed shapes include a shape with a chamfered tip, a shape with at least a part of the side of the cone curved inward or outward, a shape with a part of the side of the cone standing upright in a direction parallel to the central axis, a shape with the tip of the cone cut off, and combinations of these. The main body may have an opening for passing wiring or the like. FIG. 3 is a schematic cross-sectional view showing an example of a deformed shape.

[0017] The optical sensor cover of the present invention has a total light transmittance of 20% or less for the main body, and has pressure resistance such that it will not break when the entire outer surface of the main body is pressurized from the outside with a pressure of 3 MPa. The optical sensor cover of the present invention contains 300 ppm or less of a compound that emits light when exposed to radiation and / or absorbs ultraviolet light. In this specification, unless otherwise specified, the "total light transmittance" is a value measured in accordance with JIS K7361-1, and the "content of a compound having the property of emitting light in response to radiation and / or absorbing ultraviolet light" is a value measured in accordance with JIS K6904.

[0018] The resin structure preferably further includes a flat peripheral edge portion formed on the outside of the body portion and extending perpendicularly to the central axis of the body portion.

[0019] As described above, the main body of the resin structure has a total light transmittance of 20% or less and is excellent in light blocking properties. The resin structure may contain one or more colorants and / or one or more reinforcing fibers so that the total light transmittance is 20% or less. The colorant is not particularly limited, and known pigments and / or known dyes can be used. The reinforcing fibers are not particularly limited, and examples thereof include inorganic fibers such as glass fibers, silica fibers, and carbon fibers, organic fibers such as aramid fibers and polyester fibers, and combinations thereof. Glass fibers and carbon fibers are preferred. The reinforcing fibers can be used in the form of fibrous substrates such as cloth, paper, and mats. The main body of the resin structure, in which the total light transmittance is adjusted to 20% or less by using one or more colorants and / or one or more reinforcing fibers, particularly one or more reinforcing fibers, is also excellent in anti-reflection properties. The total light transmittance of the main body of the resin structure is preferably 10% or less, more preferably 5% or less, and particularly preferably 3% or less.

[0020] A first embodiment of the resin structure having a total light transmittance of 20% or less is a resin molded article containing a transparent resin and one or more colorants. In the first embodiment, the type and amount of one or more colorants are designed so that the total light transmittance of the main body of the resin structure is 20% or less. The total light transmittance of the main body of the resin structure can also be adjusted by the thickness of the main body.

[0021] A second embodiment of the resin structure having a total light transmittance of 20% or less is a laminate including a resin molded body containing a transparent resin and a light-shielding layer containing one or more colorants laminated on the outer surface of the resin molded body. The light-shielding layer can include one or more cured products of thermosetting resins and one or more colorants. In the second embodiment, the type and amount of one or more colorants are designed so that the total light transmittance of the main body of the resin structure is 20% or less. The total light transmittance of the main body of the resin structure can also be adjusted by the thickness of the light-shielding layer.

[0022] A third embodiment of the resin structure having a total light transmittance of 20% or less is a laminate including a resin molded body containing a transparent resin, and a reinforcing layer laminated on the outer surface of the resin molded body. In the third embodiment, the reinforcing layer contains one or more reinforcing fibers, and preferably contains one or more cured products of thermosetting resins and one or more reinforcing fibers. In this embodiment, the resin molded body and / or the reinforcing layer may contain one or more colorants as necessary. In the third embodiment, the types and amounts of one or more reinforcing fibers and one or more colorants used as necessary are designed so that the total light transmittance of the main body of the resin structure is 20% or less. The total light transmittance of the main body of the resin structure can also be adjusted by the thickness of the reinforcing layer.

[0023] In the third aspect, the reinforcing layer increases the strength of the resin molded body compared to that of the resin molded body alone. Therefore, even if the thickness of the resin structure is made relatively thin, sufficient strength can be ensured, and the weight of the resin structure can be reduced. By making the thickness of the resin structure relatively thin, the weight of the entire protective cover can be reduced, and thus the device including the photomultiplier tube can be simplified and the cost reduced. An example of a device including a photomultiplier tube is a water-Cherenkov cosmic particle observation device.

[0024] In the second and third embodiments, the thermosetting resin is not particularly limited, and examples thereof include unsaturated polyester resin, epoxy resin, phenol resin, melamine resin, and combinations thereof. Among them, unsaturated polyester resin is preferable.

[0025] The thickness of the optical sensor cover (resin structure) of the present invention is 6 to 15 mm, preferably 7 to 15 mm, and more preferably 7 to 12 mm. In the present invention, by using a transparent resin such as a methacrylic resin, which has excellent strength, as the main material, it is possible to provide an optical sensor cover that has pressure resistance that will not break when the entire outer surface is pressurized with a pressure of 3 MPa, even if the resin structure is designed to be relatively thin as described above. By forming a reinforcing layer containing reinforcing fibers on the outer surface of the resin molded body, the pressure resistance of the optical sensor cover can be further improved even if the resin structure is designed to be relatively thin as described above.

[0026] In the resin molded body, the approximately conical portion constituting the main body may vary in thickness from the front (front cover side) to the rear, and may be designed, for example, so that the thickness gradually decreases from the front (front cover side) to the rear. In the light-shielding layer and the reinforcing layer, the approximately conical portion constituting the main body may vary in thickness from the front (front cover side) to the rear, and may be designed, for example, so that the thickness gradually increases from the front (front cover side) to the rear.

[0027] The transparent resin for the resin molded body may be a known one, and examples of the transparent resin include acrylic resin, polycarbonate resin (PC), polyethylene terephthalate (PET), polystyrene (PS), cycloolefin polymer, polymethylpentene, and combinations thereof. The transparent resin preferably contains an acrylic resin. The acrylic resin is a homopolymer or copolymer of one or more monomers including (meth)acrylic acid and / or a (meth)acrylic acid ester. In this specification, "(meth)acrylic" is a general term for acrylic and methacrylic, and "(meth)acrylonitrile" is a general term for acrylonitrile and methacrylonitrile.

[0028] Among acrylic resins, methacrylic resins, which have a proven track record in existing water-Cherenkov-type cosmic particle observation devices, are preferred. Examples of methacrylic resins include homopolymers of methyl methacrylate (MMA) (polymethyl methacrylate, PMMA), copolymers of MMA and one or more other monomers, and combinations of these. As the methacrylic resin, either a non-crosslinked methacrylic resin or a crosslinked methacrylic resin may be used.

[0029] Generally, methacrylic resins are added with ultraviolet absorbers and / or light stabilizers to improve light resistance. The transparent resin used in the optical sensor cover of the present invention preferably contains a small amount of ultraviolet absorbers and light stabilizers, and more preferably does not contain ultraviolet absorbers and light stabilizers. Generally, there is no light source in the environment in which photomultiplier tubes are used, so there is no risk of ultraviolet degradation of the transparent resin. If the transparent resin contains ultraviolet absorbers and / or light stabilizers, these components may leak out of the protective cover due to leaching or volatilization for some reason, which may interfere with Cherenkov light observation.

[0030] In the second embodiment in which the resin structure is a laminate including a resin molded body containing a transparent resin and a light-shielding layer, the light-shielding layer can include one or more cured products of thermosetting resins and one or more colorants. In this case, the light-shielding layer can be formed using a coating agent including one or more thermosetting resins, one or more colorants, and one or more solvents (monomers, organic solvents, etc.). In this case, the resin molded body preferably includes a crosslinked resin (preferably a crosslinked methacrylic resin) so that the solvent component included in the coating agent does not cause crazes, cracks, etc. in the resin molded body.

[0031] In a third embodiment in which the resin structure is a laminate including a resin molded body containing a transparent resin and a reinforcing layer, the reinforcing layer can include one or more cured products of thermosetting resins and one or more reinforcing fibers. In this case, the reinforcing layer can be formed using a fiber base material and a coating agent including one or more thermosetting resins and one or more solvents (monomers, organic solvents, etc.). In this case, the resin molded body preferably includes a crosslinked resin (preferably a crosslinked methacrylic resin) so that the solvent component included in the coating agent does not cause crazes, cracks, etc. in the resin molded body.

[0032] The resin molded article can be produced by a known method. A first method for producing a resin molded body includes a method in which a mold having a space of a desired shape is prepared, and a resin molded body of the desired shape is directly molded by a known method such as cast polymerization, injection molding, etc. In this method, it is preferable to use a polymerizable raw material that has a small content of ultraviolet absorbent and light stabilizer, preferably does not contain ultraviolet absorbent and light stabilizer.

[0033] A second method for producing a resin molded body includes a method in which a flat resin plate, which is a primary molded product produced in advance by a publicly known method, is secondarily molded into a desired shape including an approximately conical main body and, if necessary, a peripheral portion. In this method, it is preferable to use, as the flat resin plate, a resin plate containing a small amount of ultraviolet absorbent and light stabilizer, preferably containing no ultraviolet absorbent or light stabilizer. The flat resin plate which is the primary molded product may be a commercially available product or may be manufactured. An example of a commercially available cross-linked resin sheet that does not contain ultraviolet absorbents or light stabilizers and has excellent moldability is the cross-linked methacrylic resin sheet "Paraglass SG" manufactured by Kuraray.

[0034] One method for producing methacrylic resin sheets such as PMMA sheets is to use a casting polymerization method in which a mold consisting of a gasket and a pair of template plates arranged facing each other at a specified distance with the gasket in between, is prepared, and a polymerizable raw material is injected into the internal space of the mold and polymerized and hardened by heating.

[0035] The polymerizable raw material can include one or more monomers (M) containing MMA, and optionally one or more non-crosslinked linear alkyl methacrylate polymers (P) containing MMA units, and a polymerization initiator. In the first embodiment in which the resin structure is a resin molded body, one or more colorants are added to the polymerizable raw material so that the total light transmittance of the resulting resin plate is 20% or less. In the second embodiment in which the resin structure is a laminate including a resin molded body and a light-shielding layer, and in the third embodiment in which the resin structure is a laminate including a resin molded body and a reinforcing layer, one or more colorants may be added to the polymerizable raw material.

[0036] Preferably, the polymerizable raw material can be prepared by mixing a syrup (S) containing a non-crosslinked linear alkyl methacrylate polymer (P) containing MMA units and one or more monomers (M1), one or more monomers (M2) containing MMA, and, if necessary, one or more crosslinking agents (M3), one or more polymerization initiators (A), and, if necessary, one or more optional additives. The monomer (M) includes one or more monomers (M1) contained in the syrup (S), one or more monomers (M2) including MMA, and one or more crosslinking agents (M3) used as necessary. The monomer (M2) is a monofunctional monomer that does not act as a crosslinking agent. The polymerizable raw material preferably contains a small amount of ultraviolet absorber and light stabilizer, and preferably does not contain any ultraviolet absorber or light stabilizer.

[0037] The polymerizable raw material may contain one or more other additives as necessary, which may include, without limitation, other resins of different types, antioxidants, dispersants, fillers, patterning materials such as resin granules and natural stone granules, plasticizers, and release agents.

[0038] The blending ratio of the raw materials is not particularly limited. The total amount of the raw materials other than the polymerization initiator (A), the chain transfer agent (B), and other additives is taken as 100 parts by mass. The amount of the syrup (S) is preferably 30 to 98 parts by mass, more preferably 50 to 95 parts by mass. The amount of the monomer (M2) (the total amount when a plurality of types are used) is preferably 2 to 70 parts by mass, more preferably 5 to 50 parts by mass. The amount of the crosslinking agent (M3) (the total amount when multiple types are used) is preferably 0.01 to 1.5 parts by mass, more preferably 0.3 to 0.8 parts by mass. If the amount of the crosslinking agent (M3) exceeds 1.5 parts by mass, the dimensional accuracy of the secondary molding may decrease. The amount of the chain transfer agent (B) (the total amount when multiple types are used) is preferably 0 to 2.0 g, more preferably 0 to 0.5 g, per 1 kg of the total amount of the raw materials other than the polymerization initiator (A), the chain transfer agent (B), and other additives. If the amount of the chain transfer agent (B) exceeds 2.0 g, the properties such as chemical resistance of the methacrylic resin plate obtained by primary molding may be deteriorated. The amount of the polymerization initiator (A) (total amount when multiple types are used) is preferably 0.05 to 3.0 g per 1 kg of the total amount of the raw materials other than the polymerization initiator (A), the chain transfer agent (B), and other additives. It is more preferable to adjust within this range according to the blending ratio of the raw materials.

[0039] The polymerizable raw material is preferably polymerized and cured in two or more stages by changing the temperature. Two-stage polymerization can be performed as follows. First, the mold in which the polymerizable raw material is injected into the internal space is immersed in a water bath whose temperature is controlled preferably at about 55 to 85°C, and held for about 1 to 20 hours to perform the first stage of polymerization and curing. Next, the mold is placed in a hot air drying furnace, and heated preferably at a temperature of about 80°C for about 2 to 15 hours, and then heated preferably at a temperature of about 120 to 130°C for about 3 to 15 hours to drive the reaction, to perform the second stage of polymerization and curing.

[0040] As a material for gaskets used in the cast polymerization method, soft polyvinyl chloride resins are widely used. Soft polyvinyl chloride resins usually contain phthalates such as dioctyl phthalate (DOP) and dibutyl phthalate (DBP) as plasticizers to soften the resin. Such phthalates contain aromatic rings and are ultraviolet absorbing compounds. In the cast polymerization method, there is a risk that the content of ultraviolet absorbing compounds in the resulting methacrylic resin plate will increase due to the plasticizer eluted from the gasket during polymerization and curing.

[0041] In the cast polymerization method, the orientation of the mold during polymerization and hardening can be either vertical or horizontal. In the vertical arrangement, the polymerizable raw material is convected in the mold by heating, and the low-density plasticizer gathers at the upper end of the mold (this part is eventually cut out), and almost no plasticizer remains in the part that will actually become the product. Therefore, with this method, the content of the ultraviolet absorbing compound in the obtained methacrylic resin board can be reduced, and the content of the ultraviolet absorbing compound can be reduced to 300 ppm or less.

[0042] In the horizontal arrangement, the plasticizer eluted from the gasket may diffuse from the vicinity of the gasket to the surface direction of the mold plate due to convection of the polymerizable raw material caused by heating, and the content of the ultraviolet absorbing compound in the obtained methacrylic resin plate may increase. Therefore, in the horizontal arrangement, the viscosity of the polymerizable raw material at 25°C is preferably set to a range of 0.1 to 10 Pa·s, more preferably 0.7 to 3 Pa·s. By specifying it in this way, the diffusion range of the plasticizer eluted from the gasket can be limited to a narrow range, for example, within a range of about 5 mm from the gasket. In this case, if the outer periphery of the methacrylic resin plate taken out of the mold is cut off, a methacrylic resin plate containing almost no plasticizer can be obtained as a product. Therefore, in this method, the content of the ultraviolet absorbing compound in the obtained methacrylic resin plate can be reduced, and the content of the ultraviolet absorbing compound can be reduced to 300 ppm or less.

[0043] The concentration of the crosslinked alkyl methacrylate polymer in the methacrylic resin plate obtained by cast polymerization is not particularly limited, and is preferably 60 to 95% by mass, more preferably 75 to 95% by mass. The concentration of the non-crosslinked linear alkyl methacrylate polymer (P) in the methacrylic resin plate is not particularly limited, and is preferably 40 to 5 mass %, more preferably 25 to 5 mass %.

[0044] The secondary molding method is not particularly limited, and examples thereof include vacuum molding and compressed air molding. After the resin plate is heated and softened to an appropriate temperature in advance using a heating furnace or the like, the peripheral portion is fixed horizontally, and the plate can be processed into a desired shape by aligning it with a mold or by bending it with pressure without using a mold using vacuum, compression, air, mechanical pressure, or a combination of these. The secondary molding temperature is preferably 150°C or higher, more preferably 180°C or higher.

[0045] In the second embodiment, in which the resin structure is a laminate including a resin molded body containing a transparent resin and a light-shielding layer, after obtaining a resin molded body by the above-mentioned first or second manufacturing method, a light-shielding layer is formed on the outer surface of the resin molded body. The light-shielding layer can include one or more cured products of thermosetting resins and one or more colorants. In this case, the light-shielding layer can be formed, for example, by applying a coating agent containing one or more thermosetting resins, one or more colorants, and one or more solvents (monomers, organic solvents, etc.) to the outer surface of the resin molded body and curing it.

[0046] In a third embodiment in which the resin structure is a laminate including a resin molded body containing a transparent resin and a reinforcing layer, after obtaining the resin molded body by the above-mentioned first or second manufacturing method, a reinforcing layer is formed on the outer surface of the resin molded body. The reinforcing layer can include one or more cured products of thermosetting resins and one or more reinforcing fibers. In this case, the reinforcing layer can be formed using a coating agent including a fiber base material, one or more thermosetting resins, one or more colorants as necessary, and one or more solvents (monomers, organic solvents, etc.).

[0047] The reinforcing layer can be formed by a known method, and a hand lay-up method or the like is preferable. An example of a method for forming the reinforcing layer will be described below. <Process (S1)> First, a coating agent containing one or more thermosetting resins, and optionally one or more colorants, and one or more solvents (monomers, organic solvents, etc.) is applied onto the outer surface of a resin molded body to form a primer layer.

[0048] <Process (S2)> Next, one or more fiber substrates such as glass mats impregnated with a coating agent containing one or more thermosetting resins, one or more colorants as necessary, and one or more solvents (monomers, organic solvents, etc.) are laminated on the outer surface of the resin molded body with the primer layer formed on the surface in a thickness corresponding to the desired thickness of the reinforcing layer. A brush, a dedicated roller, etc. are pressed from above to remove air bubbles and to bring the one or more fiber substrates containing the coating agent into close contact with the resin molded body.

[0049] Instead of carrying out the above process, a process may be carried out in which one or more preforms of a fiber substrate such as a glass mat are laminated on the outer surface of the resin molding on which the primer layer has been formed, the above coating agent is sprayed or applied onto the laminate, and then a brush, a special roller, or the like is pressed onto the laminate to remove air bubbles while adhering the one or more fiber substrates containing the coating agent to the resin molding.

[0050] <Process (S3)> Next, the coating agent used in the primer layer and the coating agent impregnated in the fiber substrate are cured. For example, after being cured to some extent at room temperature of 20 to 25°C, it can be thermally cured using a hot air drying oven or the like. The thermal curing conditions can be designed according to the composition of the coating agent, and for example, 60 to 80°C for 3 to 5 hours is preferable. The thermal curing is performed so that the polymerization of the residual monomer remaining after the room temperature curing is completed. Aromatic ring-containing monomers, such as styrene, are ultraviolet absorbing compounds. In the present invention, the heat curing is completed so that the amount of residual monomer remaining after heat curing is negligible or zero, thereby making it possible to make the content of the ultraviolet absorbing compound in the obtained resin structure 300 ppm or less. In this manner, the reinforcing layer can be formed.

[0051] The main body of the optical sensor cover of the present invention contains 300 ppm or less of a compound that emits light when exposed to radiation and / or absorbs ultraviolet light. Examples of the radiation include α-rays, β-rays, and γ-rays. Examples of the compound that emits light when exposed to radiation and / or absorbs ultraviolet light include aromatic ring-containing compounds such as phthalates and styrene. In the present invention, by devising the production method as described above, the content of the compound that emits light when exposed to radiation and / or absorbs ultraviolet light in the obtained resin structure can be reduced to a negligible amount of 300 ppm or less, which is zero.

[0052] The structures of an optical sensor cover according to an embodiment of the present invention and a case-equipped photomultiplier tube according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 and Fig. 2 are a schematic perspective view and a schematic cross-sectional view, respectively, of an optical sensor cover (rear cover) of this embodiment. Fig. 3 is a schematic cross-sectional view showing a design modification example of the optical sensor cover (rear cover) of this embodiment. Fig. 4 is a schematic cross-sectional view of a case-equipped photomultiplier tube.

[0053] As shown in FIG. 4, the case-equipped photomultiplier tube 3 of this embodiment comprises a photomultiplier tube 2 housed in a protective case 1. The case-equipped photomultiplier tube 3 of this embodiment comprises a protective case 1 and a photomultiplier tube 2 housed in the protective case 1. The photosensor cover 20 of this embodiment can be used as a rear cover for the photomultiplier tube 2. The photosensor cover 20 can be combined with the front cover 10 to form a protective case 1 for the photomultiplier tube. The photomultiplier tube 2 can be fixed in the protective case 1 using a known fixing jig (not shown).

[0054] As shown in FIG. 4, the front cover 10 of one embodiment includes a substantially hemispherical main body portion 11 and a flat peripheral portion 13 formed on the outside of the main body portion 11 and extending perpendicular to the central axis of the main body portion 11. The front cover 10 is made of a resin molded body containing a transparent resin such as a methacrylic resin, and protects the light receiving surface 2S of the photomultiplier tube 2. The front cover 10 is preferably UV-transparent and transmits UV rays having a wavelength of 300 nm or more. The front cover 10 is preferably pressure-resistant so as not to break when the entire outer surface of the main body 11 is pressurized with a pressure of 3 MPa. The front cover 10 can be manufactured, for example, by the manufacturing method described in Patent Document 1 listed in the [Background Art] section.

[0055] 1, the optical sensor cover 20 of this embodiment is made of a resin structure including a substantially conical main body 21 and a flat peripheral edge 23 formed outside the main body 21 and extending in a direction perpendicular to the central axis of the main body 21. As shown in FIG. 4, the optical sensor cover 20 protects a portion (rear portion) behind the light receiving surface 2S of the photomultiplier tube 2.

[0056] It is preferable that the peripheral portion 13 of the front cover 10 and the peripheral portion 23 of the optical sensor cover (rear cover) 20 are both flat in shape, so that they can be closely attached by surface joining. It is preferable that the front cover 10 and the optical sensor cover (rear cover) 20 are detachably fixed together using bolts or the like, so that the photomultiplier tube 2 can be replaced.

[0057] As shown in FIG. 2, the optical sensor cover 20 of this embodiment is a laminate of a resin molded body 20X containing a transparent resin and a reinforcing layer 20Y laminated on the outer surface of the resin molded body 20X. The resin molded body 20X is preferably a transparent methacrylic resin molded body containing a cross-linked methacrylic resin. In this embodiment, in the resin molded body 20X, the thickness of the substantially conical portion constituting the main body 21 gradually decreases from the front (the front cover 10 side) to the rear.

[0058] In this embodiment, the reinforcing layer 20Y contains one or more types of cured thermosetting resin and one or more types of reinforcing fibers. The reinforcing layer 20Y may contain one or more types of colorants, if necessary. In this embodiment, the total light transmittance of the main body 21 of the resin structure is adjusted to 20% or less by the type and amount of one or more reinforcing fibers and one or more colorants used as necessary contained in the reinforcing layer 20Y, and the thickness of the reinforcing layer 20Y. That is, in this embodiment, the reinforcing layer 20Y can function as a light-shielding layer.

[0059] The main body of the optical sensor cover 20 may have a modified cone shape, for example, as shown in FIG. The optical sensor cover 20 shown in Figures 2 to 4 illustrates an example of an embodiment of the third aspect in which the resin structure is a laminate including a resin molded body and a reinforcing layer, the reinforcing layer also serving as a light-shielding layer.

[0060] As described above, according to the present invention, it is possible to provide an optical sensor cover that has suitable pressure resistance and light-shielding properties as a rear cover for a photomultiplier tube protective case, and is not susceptible to the elution of compounds that emit light in response to radiation and / or absorb ultraviolet light. The optical sensor cover of the present invention has excellent pressure resistance and can effectively protect the photomultiplier tube and the important electronic components enclosed therein (e.g., the electron multiplier section and electrodes such as the anode) from water pressure and shock waves such as implosion. The optical sensor cover of the present invention is made of a resin molded body that mainly contains transparent resin, and therefore has excellent strength and processability, and can also be made lightweight. The optical sensor cover of the present invention is made of a resin molded body mainly containing a transparent resin, so that light emission, light absorption, and light reflection do not occur. The optical sensor cover of the present invention has a total light transmittance of 20% or less and is excellent in light blocking properties. The optical sensor cover of the present invention also contains a compound that emits light in response to radiation and / or absorbs ultraviolet light at a content of 300 ppm or less. For these reasons, the optical sensor cover of the present invention does not interfere with the observation of Cherenkov light. EXAMPLES

[0061] Examples and comparative examples according to the present invention will be described. [Evaluation items and evaluation methods] (exterior) The resin structure having a laminated structure of the methacrylic resin layer and the reinforcing layer was visually observed, and the appearance was evaluated according to the following criteria. ◯ (Good): No defects in appearance such as crazes or cracks were observed. × (Poor): Appearance defects such as crazes and cracks are observed.

[0062] (Thickness) For a resin molded body having a single-layer structure made of a methacrylic resin layer, and a resin structure having a laminated structure of a methacrylic resin layer and a reinforcing layer, the thicknesses of multiple locations including the periphery (thickest part) and the tip (thinnest part) were measured to within 0.1 mm using a micrometer. As a result, the thicknesses of each layer and the total thickness were obtained for multiple locations including the periphery (thickest part) and the tip (thinnest part) of the resin structure.

[0063] (Total light transmittance) A test piece 50 mm long and 50 mm wide was cut out from the center of the side of a resin structure consisting of a laminated structure of a methacrylic resin layer and a reinforcing layer, and the total light transmittance was measured using a spectrophotometer ("SE5000" manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS-K7361.

[0064] (Pressure resistance) The resin structure having a laminated structure of a methacrylic resin layer and a reinforcing layer was evaluated for pressure resistance as follows. A quarter-section sample was used as the analysis model, which was divided equally into four parts by two mutually perpendicular planes passing through the central axis of the resin structure. Using the "General-purpose nonlinear structural analysis solution MARC" made by MSC Software Corporation, an analysis was performed to see whether or not the structure would break when a pressure of 3 MPa was applied as an external force. The analysis used the thickness data measured by the above method and the physical properties (Young's modulus and Poisson's ratio) of each resin used. The constraint condition for the periphery was full constraint.

[0065] A flat plate having the same laminated structure as the thinnest part of the resin structure (for example, in Example 1, a laminated structure of a 0.7 mm thick methacrylic resin layer and a 6.3 mm thick reinforcing layer) was molded. Using this as a reference, the tensile breaking strength was measured in accordance with JIS K7113 using Shimadzu Corporation's "Autograph Precision Universal Tester AG-10TB." For example, in the case of the thinnest part of the resin structure in Example 1, which is a laminated structure of Kuraray's "Paraglass SG85" (0.7 mm thick) and a reinforcing layer (6.3 mm thick), the Young's modulus was 19.9 GPa, the Poisson's ratio was 0.22, and the tensile breaking strength of the flat plate was 150 MPa.

[0066] The tensile stress in the plate surface direction at each position was obtained when a pressure of 3 MPa was applied to the entire outer surface of the main body of the optical sensor cover of the above analysis model. The tensile stress at the part with the greatest strain was obtained and compared with the tensile breaking strength (actual measured value) of the above reference, and evaluated according to the following criteria. ◯ (Good): The tensile stress at the portion with the greatest strain is smaller than the reference tensile breaking strength, and the specimen does not break. × (bad): The tensile stress at the portion with the greatest strain is equal to or greater than the reference tensile breaking strength, and the specimen breaks.

[0067] (Residual styrene monomer amount) To quantify the ultraviolet absorbing compounds, the following measurements were carried out. A test piece was cut out from the peripheral part, which was the thickest part of the resin structure consisting of a laminated structure of a methacrylic resin layer and a reinforcing layer, and the amount of residual styrene monomer (mass%) relative to the entire test piece was determined in accordance with JIS-K6904 using a Shimadzu Corporation gas chromatography GC2014 (column: Agilent Technologies "DB-1", length 30 m, inner diameter 0.25 mm, liquid film 1 μm).

[0068] [Example 1] (Production of resin molded products) As the resin base plate, we prepared "Paraglass SG85" (8 mm thick) manufactured by Kuraray, a methacrylic resin casting plate suitable for deep drawing and molding of complex shapes in sanitary applications, etc. This resin base plate is a resin plate that contains cross-linked methacrylic resin and does not contain ultraviolet absorbers or light stabilizers. From the resin base plate, a resin plate for molding measuring 800 mm in length and 800 mm in width was cut out. The cut resin plate was placed on a fiber reinforced plastic (FRP) wrapped in flannel fabric, placed in a far infrared oven heated to 210°C, and heated for 30 minutes. The heated resin plate was placed on a mold and only the peripheral portion was fixed horizontally, after which a compressed air box was immediately placed on top of it and a pressure of 3 kg / cm was applied from above. 2 The mold was then curved and swelled downwards using compressed air, and then slowly cooled.

[0069] In this manner, a resin molded body (20X) having a single-layer structure made of a methacrylic resin layer having a shape as shown in Figures 1 and 2 was obtained. This resin molded body includes a substantially conical main body and a flat peripheral portion formed on the outside of this main body and extending in a direction perpendicular to the central axis of the main body, and the substantially conical main body was designed so that its thickness gradually decreases from the front (front cover side) to the rear. The outer diameter of the peripheral portion of the resin molded body was 680 mmφ, and the height in the central axis direction was 582 mm.

[0070] (Formation of reinforcing layer) A gel coat for fiber-reinforced plastics (FRP) (TOMATEC's "7S7259PT") containing an unsaturated polyester resin, which is a thermosetting resin, and one or more colorants was applied to the entire outer surface of the obtained resin molded body to a thickness of 0.4 mm to form a primer layer. Next, a glass mat ("MC380AS104SS" manufactured by Nitto Boseki) was placed on the primer layer. The thickness of the glass mat was designed so that the thickness of the thinnest part (specifically, the pointed end) of the finally obtained resin structure would be the value shown in Table 1.

[0071] The glass mat was impregnated with a viscous liquid ("Rigolac NS159BQTN" manufactured by Showa Denko) in which an unsaturated polyester resin, which is a thermosetting resin, and one or more colorants were dissolved in a polymerizable monomer by a hand lay-up method. Specifically, the viscous liquid was sprayed onto the glass mat, and then the surface was smoothed with a roller to remove bubbles. Next, the composition was left at room temperature of 20 to 25° C. for 4 hours to harden to a certain extent, and then heat-treated at 80° C. for 3 hours to harden the composition.

[0072] In the manner described above, a reinforcing layer (also called an FRP layer) containing a thermosetting resin, reinforcing fibers, and one or more colorants was formed to obtain a resin structure consisting of a laminated structure of a methacrylic resin layer and an FRP layer. The main manufacturing conditions and evaluation results are shown in Table 1. In the examples shown in Table 1, conditions not listed in the table were common conditions.

[0073] [Examples 2 and 3] In Example 2, a resin molded body and a resin structure were obtained in the same manner as in Example 1, except that the resin base plate was changed to "Paraglass SG95" (thickness 10 mm) manufactured by Kuraray and the thickness conditions of each layer were changed. In Example 3, a resin molded body and a resin structure were obtained in the same manner as in Example 1, except that the resin base plate was changed to "Paraglass SG85" (6 mm thick) manufactured by Kuraray and the thickness conditions of each layer were changed. The resin base plates used in Examples 2 and 3 were both resin plates containing a crosslinked methacrylic resin and no ultraviolet absorbing agent or light stabilizer. The main manufacturing conditions and evaluation results are shown in Table 1.

[0074] [Comparative Example 1] A resin molded body and a resin structure were obtained in the same manner as in Example 1, except that the resin base plate was changed to "Paraglass P" (8 mm thick) manufactured by Kuraray and the thickness conditions of each layer were changed. The resin base plate used in Comparative Example 1 is a resin plate that does not contain a crosslinked methacrylic resin, an ultraviolet absorbing agent, and a light stabilizer. The main manufacturing conditions and evaluation results are shown in Table 1.

[0075] [Comparative Examples 2 and 3] In Comparative Example 2, a resin molded body and a resin structure were obtained in the same manner as in Example 1, except that the heat curing step was not performed and the thickness conditions of each layer were changed. In Comparative Example 3, a resin molded article and a resin structure were obtained in the same manner as in Example 1, except that the heat curing conditions were changed to 60° C. for 3 hours and the thickness conditions of each layer were changed. The main manufacturing conditions and evaluation results are shown in Table 1.

[0076] [Table 1]

[0077] [Summary of results] The resin structures obtained in Examples 1 to 3 all had good appearances with no crazes or cracks, high light shielding properties with a total light transmittance of 5% or less, and good pressure resistance. In addition, the amount of residual styrene monomer in each of the resin structures obtained in these Examples was negligibly small at 300 ppm or less, and there was no risk of the residual styrene monomer, which is an ultraviolet absorbing compound, leaking out and interfering with the measurement of Cherenkov light. All of the resin structures obtained in these Examples were suitable for use as rear covers for photomultiplier tubes.

[0078] The resin structure obtained in Comparative Example 1 had crazes and a poor appearance. In this comparative example, a resin base plate not containing a crosslinked methacrylic resin was used, and it is believed that crazes (also called solvent crazes) occurred in the resin molded body due to a solvent such as a styrene monomer in the reinforcing layer formation process. The resin structure obtained in this comparative example had poor pressure resistance due to the formation of crazes, and was unsuitable as a rear cover for a photomultiplier tube.

[0079] In Comparative Examples 2 and 3, the curing in the reinforcing layer formation step was insufficient, so the resin structures obtained had a very large content of residual styrene monomer, which is an ultraviolet absorbing compound, and were poor in quality. The resin structures obtained in these Comparative Examples were unsuitable for use as rear covers for photomultiplier tubes because there was a risk that the residual styrene monomer would leak out and interfere with the measurement of Cherenkov light.

[0080] The present invention is not limited to the above-described embodiment and examples, and appropriate design changes are possible without departing from the spirit of the present invention. [Explanation of symbols]

[0081] 1 Protective case 2 Photomultiplier tube 2S light receiving surface 3 Photomultiplier tube with case 10 Front cover 11 Main body 13 Periphery 20 Optical sensor cover (rear cover) 20X Resin Molded Body 20Y Reinforcement layer 21 Main body 23 Periphery

Claims

1. A photosensor cover for protecting a rear portion of a light receiving surface of a photomultiplier tube, The present invention comprises a resin structure including a resin molded body containing a crosslinked methacrylic resin and not containing an ultraviolet absorber or a light stabilizer, and a light-shielding layer containing reinforcing fibers laminated on an outer surface of the resin molded body, the resin structure includes a substantially conical body portion and has a thickness of 6 to 15 mm; The main body has a total light transmittance of 5% or less as measured in accordance with JIS K7361-1, The main body has a pressure resistance such that it will not break when the entire outer surface of the main body is pressurized at a pressure of 3 MPa, An optical sensor cover, in which the content of a compound having the property of emitting light in response to radiation and / or absorbing ultraviolet light is 300 ppm or less as measured in accordance with JIS K6904.

2. The optical sensor cover of claim 1 , wherein the resin structure further includes a flat peripheral edge portion formed outside the body portion and extending perpendicularly to a central axis of the body portion.

3. The optical sensor cover according to claim 1 or 2, wherein the content of the crosslinked methacrylic resin in the resin molded body is 60 to 95 mass%.

4. The optical sensor cover according to any one of claims 1 to 3, wherein the light-shielding layer further contains a cured product of a thermosetting resin and a colorant.

5. The optical sensor cover of claim 4 , wherein the thermosetting resin comprises an unsaturated polyester resin.

6. The optical sensor cover of any one of claims 1 to 5, wherein the compound is styrene.

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