Resin sheet having uneven shape

Abstract

Provided is a novel means for reducing the wind noise generated by rotation of a propeller.　This resin sheet has an uneven shape on at least one surface thereof, and the average height of protruding parts is 20 μm or greater, while the total of a protruding-part area at 95% of the average height of the protruding parts is 0.1-55% relative to a projected area in the thickness direction of the resin sheet.

Description

Resin sheet with an uneven surface

[0001] This disclosure relates to a resin sheet having an uneven surface.

[0002] One known technique for reducing noise such as wind noise caused by the rotation of a propeller is to arrange a cylindrical duct around the propeller. In this technique, the noise generated by the rotation of the propeller is attenuated within the duct, and the noise is also reflected off the inner wall of the duct, generating noise of the opposite phase and thus canceling out the noise.

[0003] Furthermore, as described in Patent Document 1, there is a known active noise control (ANC) technology that reduces noise by outputting a control sound with the opposite phase to the noise using a speaker, and updates the control sound so that the residual noise collected by the error microphone is minimized.

[0004] Japanese Unexamined Patent Publication No. 7-160273

[0005] However, the above-mentioned technology requires the provision of a cylindrical duct surrounding the propeller or the placement of speakers around the propeller, leaving room for improvement in terms of simplifying the configuration. The object of this disclosure is to provide a novel means for reducing wind noise generated by the rotation of a propeller.

[0006] The disclosure includes the following embodiments: [1] A resin sheet having an uneven shape on at least one surface, wherein the average height of the protrusions is 20 μm or more, and the sum of the areas of the protrusions at 95% of the average height of the protrusions relative to the projected area of ​​the resin sheet in the thickness direction is 0.1% or more and 55% or less.

[0007] This disclosure provides a novel means for reducing wind noise generated by the rotation of a propeller.

[0008] This is a perspective view showing a resin sheet according to one embodiment of the present disclosure. This is a perspective view showing a resin sheet according to one embodiment of the present disclosure. This is a perspective view showing a resin sheet according to one embodiment of the present disclosure. This is a perspective view showing a resin sheet according to one embodiment of the present disclosure.

[0009] One embodiment of this disclosure will be described in detail below, but the scope of this disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of this disclosure. Each embodiment disclosed herein can be combined with any other features disclosed herein. Furthermore, if multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be made to create a suitable numerical range. Also, the lower and / or upper limits of the numerical range described herein may be replaced with numerical values ​​within that range, as shown in the examples. The expression "X to Y" indicating a numerical range means "X or more and Y or less". If multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be made to create a suitable numerical range. Also, the lower and / or upper limits of the numerical range described herein may be replaced with numerical values ​​within that range, as shown in the examples. If a specific description given for one embodiment also applies to other embodiments, that description may be omitted in the other embodiments.

[0010] [First Embodiment] A resin sheet according to one embodiment of the present disclosure is a resin sheet having an uneven shape on at least one surface, wherein the average height of the protrusions is 20 μm or more, and the sum of the protrusion areas at 95% of the average height of the protrusions relative to the projected area of ​​the resin sheet in the thickness direction is 0.1% or more and 55% or less. That is, the layer structure of the laminated resin sheet according to the first embodiment is, from top to bottom, an uneven shape (2) and a base layer (3). In this embodiment, the sum of the protrusion areas at 95% of the average height of the protrusions relative to the projected area of ​​the resin sheet in the thickness direction (hereinafter also referred to as the "protrusion area ratio at 95% height") is 0.1% or more and 55% or less. In one embodiment, the protrusion area ratio at 95% height is preferably 0.5% or more and 50% or less, more preferably 0.5% or more and 45% or less, and even more preferably 0.5% or more and 40% or less. By setting it within the above range, it becomes easier to obtain the effect of reducing wind noise generated by the rotation of the propeller. The resin sheet of this embodiment has the effect of reducing wind noise generated by the rotation of a propeller, and can particularly reduce sounds in the 1000-3000 Hz range. Here, wind noise generally refers to the unpleasant sound that occurs when the wind speed exceeds 4 m / s. Here, "projected area in the thickness direction" refers to the area when viewed from the side facing the surface of the resin sheet. Therefore, it is not affected by the shape of the surface (e.g., uneven shape). Furthermore, the convex area ratio at 95% height is a value related to the area of ​​the convex parts at 95% height of the average height of the convex parts, and even if there are low convex parts in the uneven shape that do not reach 95% height of the average height of the convex parts, such low convex parts do not affect the total area of ​​the convex parts. The convex area ratio at 95% height of the resin sheet can be measured by measuring the uneven shape of the resin sheet using a laser microscope and image processing software, and the arithmetic mean of the values ​​at any number of locations (e.g., 10 locations) can be used. The mechanism by which the resin sheet of this embodiment reduces wind noise generated by the rotation of the propeller is not well understood, but it is possible that the uneven shape affects the airflow and water flow on the surface of the resin sheet, or that the uneven shape scatters sound.

[0011] The surface area of the side with the concavo-convex shape per 1 cm of the resin sheet ２ ,

[0012] , is preferably 1.3 cm ２ or more, more preferably 1.3 to 10 cm ２ and even more preferably 1.4 to 8 cm ２ and particularly preferably 1.5 to 4 cm ２ Here, "per 1 cm of the resin sheet" ２ means the area per 1 cm when viewed from the side opposite to the surface having the concavo-convex shape. ２

[0012] The surface area per 1 cm of the resin sheet ２ can be measured using a measuring device conforming to JIS B0601-1994. Specifically, it can be measured using a shape measurement laser microscope (for example, "VK-X100" (manufactured by Keyence Corporation)). More specifically, after starting the shape measurement laser microscope main body (control unit) and the observation application (for example, "VK-H1VX" (manufactured by Keyence Corporation)), place the sample to be measured on the x-y stage. Rotate the lens turret of the microscope unit (for example, "VK-X110" (manufactured by Keyence Corporation)) to select an objective lens with a magnification of 10 to 100 times, and roughly adjust the focus and brightness in the image observation mode of the observation application. Operate the x-y stage to adjust so that the approximate center of the sample surface comes to the center of the screen. Use the autofocus function in the image observation mode of the observation application to focus on the surface of the sample. Select the simple mode of the shape measurement tab of the observation application and press the measurement start button to measure the surface shape of the sample and obtain a surface image file (it can be performed at a magnification where at least 6 to 10 repeating shapes can be confirmed in the case of regular concavo-convex). Start the analysis application (for example, "VK-H1XA" (manufactured by Keyence Corporation)), display the obtained surface image file, and then perform tilt correction. In the measurement of the surface area, the observation measurement range (area) in the measurement of the surface shape of the sample is 3 mm ２Surface images are obtained from multiple random locations on the sheet sample to achieve the above result. The average of the surface area per unit area of ​​all images is taken as the surface area per unit area of ​​the resin sheet.

[0013] <Resin Composition> In this embodiment, the resin sheet is composed of a resin composition. The resin composition is a composition mainly composed of resin. Here, "main component" means that it contains 50% by mass or more. Preferably, it contains 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass. Examples of resins to be used include resins containing at least one of the following: styrene resin, polyolefin resin, polycarbonate resin, polyvinyl chloride resin, fluororesin, acrylic resin, urethane elastomer (TPU), and thermoplastic elastomer. The resin composition may be an alloy of the above resins in any proportion, as long as it does not hinder the effects of the present invention. In one embodiment, from the viewpoint of processability, the resin preferably contains one or more selected from styrene resin, polyolefin resin, polycarbonate resin, and acrylic resin, and more preferably contains one or more selected from homopolypropylene, cycloolefin polymer, and acrylic resin.

[0014] As styrene-based resins, styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, p-t-butylstyrene, and chlorostyrene, either alone or in copolymers thereof; copolymers of these styrene monomers with other monomers, such as styrene-acrylonitrile copolymer (AS resin); or graft copolymers obtained by graft polymerization of the styrene monomers in the presence of other polymers, such as polybutadiene, styrene-butadiene copolymer, polyisoprene, and polychloroprene diene-based rubber polymers, such as high-impact polystyrene (HIPS resin) and styrene-acrylonitrile graft copolymer (ABS resin). Styrene-based thermoplastic elastomers can also be used.

[0015] Polyolefin resins refer to resins made of polymers containing α-olefin as a monomer. Polyolefin resins include, for example, polyethylene resins, polypropylene resins, and cycloolefin polymers.

[0016] Polyethylene resins can include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, linear medium-density polyethylene, etc. Not only individual materials but also copolymers, grafts, and blends having these structures can be used. Examples of the latter resins include copolymers and blends of resins having polar groups in the polyethylene chain, such as ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-acrylic acid ester copolymers, ethylene-methacrylic acid ester copolymers, ethylene-vinyl acetate-vinyl chloride copolymers, and terpolymers with acid anhydrides.

[0017] As polypropylene resins, homopolypropylene, random polypropylene, block polypropylene, etc., can be used. When using homopolypropylene, the structure of the homopolypropylene may be isotactic, atactic, or syndiotactic. When using random polypropylene, the α-olefin copolymerized with propylene preferably has 2 to 20 carbon atoms, more preferably 4 to 12 carbon atoms, such as ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, or 1-decene. When using block polypropylene, block copolymers (block polypropylene), block copolymers containing rubber components, or graft copolymers can be used. In addition to using these olefin resins alone, other olefin resins can also be used in combination.

[0018] As the cycloolefin polymer, either a homopolymer (COP) made from only one cycloolefin monomer, or a copolymer (COC) composed of one or more cycloolefin monomers and comonomers can be used. Examples of the cycloolefin monomer include dicyclic monomers such as norbornene and norbornadiene, tricyclic monomers such as dicyclopentadiene and dihydroxypentadiene, tetracyclic monomers such as tetracyclododecene, pentacyclic monomers such as cyclopentadiene trimers, heptacyclic monomers such as tetracyclopentadiene, or alkyl (methyl, ethyl, propyl, butyl, etc.), alkenyl (vinyl, etc.), alkylidene (ethylidene, etc.), and aryl (phenyl, tolyl, naphthyl, etc.) substituted compounds of these polycyclic monomers. Among these, norbornene-based monomers selected from the group consisting of norbornene, tetracyclododecene, or alkyl substituted compounds thereof are particularly preferred. As the comonomer, any monomer copolymerizable with the above-mentioned cycloolefin monomer is acceptable, and for example, alkene monomers are preferred. Examples of alkene monomers include ethylene, propylene, α-olefins such as 1-butene and 1-hexene, and isobutene. Alkene monomers may be linear or branched.

[0019] Examples of polycarbonate resins include those derived from aliphatic dihydroxy compounds and those derived from aromatic dihydroxy compounds. For example, those derived from aromatic dihydroxy compounds can be suitably used, and those derived from aromatic dihydroxy compounds (bisphenol) in which two aromatic dihydroxy compounds are linked via a certain type of bonding group are particularly preferred. These can be produced by known methods involving the polycondensation of dihydroxy compounds with phosgene or carbonate esters, but are not limited to such methods, and commercially available resins can also be used.

[0020] As the polyvinyl chloride resin, a polyvinyl chloride homopolymer or a copolymer of polyvinyl chloride and another copolymer can be used. When the polyvinyl chloride is a copolymer, it may be a random copolymer or a graft copolymer. As an example of a graft copolymer, for example, an ethylene-vinyl acetate copolymer or a thermoplastic urethane polymer can be used as the core polymer, and polyvinyl chloride can be graft polymerized to it. The polyvinyl chloride in this embodiment is an extrudeable flexible polyvinyl chloride and is a composition containing additives such as a polymeric plasticizer. As the polymeric plasticizer, known polymeric plasticizers can be used, but preferred examples include ethylene copolymer polymeric plasticizers such as ethylene-vinyl acetate-carbon monoxide copolymer, ethylene-(meth)acrylic acid ester-carbon monoxide copolymer, and ethylene-vinyl acetate copolymer with a high vinyl acetate content.

[0021] As fluorine-based resins, a homopolymer of vinylidene fluoride and a vinylidene fluoride copolymer mainly composed of vinylidene fluoride can be used. Polyvinylidene fluoride (PVDF) resin is a crystalline resin that exhibits various crystal structures such as α-type, β-type, γ-type, and αp-type. Examples of vinylidene fluoride copolymers include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene terpolymer, and mixtures of two or more of these.

[0022] Acrylic resins are obtained by polymerization of acrylic monomers. The type of acrylic monomer is not particularly limited as long as it does not impair the effects of the present invention. For example, acrylate monomers such as methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, benzyl acrylate, cyclohexyl acrylate, phenyl acrylate, and chloroethyl acrylate, or homopolymers of methacrylate monomers such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, and chloroethyl methacrylate, or copolymers obtained by copolymerizing two or more of these monomers can be used. The main component of the acrylic resin is methyl methacrylate units, and its content is preferably 60% by mass or more, and more preferably 70% by mass or more. Examples of polymerization methods for acrylic resins include known polymerization methods such as emulsion polymerization, soap-free emulsion polymerization, fine suspension polymerization, suspension polymerization, bulk polymerization, and solution polymerization. Among these polymerization methods, emulsion polymerization is preferred because it facilitates the production of high molecular weight products. When producing acrylic resins by emulsion polymerization, known emulsifiers can be used. Examples include anionic emulsifiers, nonionic emulsifiers, polymer emulsifiers, and reactive emulsifiers having unsaturated double bonds that can be radically polymerized within the molecule.

[0023] Urethane elastomers are resins that use diisocyanate and polyol as reaction raw materials, and in combination, the diisocyanate is diphenylmethane diisocyanate (MDI), H １２ Any combination of MDI-based, hexamethylene diisocyanate (HDI)-based, and polyols of polyether, polyester, or polycarbonate types may be selected, or a combination of several may be used. In one embodiment of this disclosure, a combination of an MDI-based or HDI-based diisocyanate and a carbonate-based polyol can be suitably used.

[0024] Thermoplastic elastomers include those having a structure that combines soft polymer materials and hard polymer materials. Specifically, these include styrene-based elastomers, olefin-based elastomers, vinyl chloride-based elastomers, polyester-based elastomers, and polyamide-based elastomers. These elastomers can generally be selected and used from those commercially available.

[0025] Examples of polycarbonate resins include those derived from aliphatic dihydroxy compounds and those derived from aromatic dihydroxy compounds. For example, those derived from aromatic dihydroxy compounds can be suitably used, and those derived from aromatic dihydroxy compounds (bisphenol) in which two aromatic dihydroxy compounds are linked via a certain type of bonding group are particularly preferred. These can be produced by known methods involving the polycondensation of dihydroxy compounds with phosgene or carbonate esters, but are not limited to such methods, and commercially available resins can also be used.

[0026] The melt mass flow rate of the resin composition at 190°C to 300°C is preferably 1 g / 10 min or higher. A melt mass flow rate of 1 g / 10 min or higher improves the ability to form uneven surfaces. The melt mass flow rate is measured according to JIS K 7210, under conditions of a load (2.16 kg to 10.0 kg) within a test temperature range of 190°C to 300°C.

[0027] The resin composition may contain other additives as long as they do not impair the effects of the present invention. Other additives that do not impair the effects of the present invention include water-repellent and oil-repellent agents; colorants such as pigments and dyes; lubricants and release agents such as silicone oils and alkyl esters; fibrous reinforcing agents such as glass fibers; fillers such as granular fine particles such as talc, clay, and silica, or flake-like fine particles such as mica; flame retardants; antibacterial agents; antiviral agents; heat stabilizers; low molecular weight antistatic agents such as salt compounds of sulfonic acid and alkali metals; and high molecular weight antistatic agents such as polyether ester amides. In one embodiment, it is preferable that the resin composition does not contain an antistatic agent.

[0028] Examples of water-repellent and oil-repellent agents include silicone-based water repellents, carnauba wax, and fluorine-based water-repellent and oil-repellent agents. Examples of silicones include organopolysiloxane, dimethylpolysiloxane, methylphenylpolysiloxane, and methylhydrogenpolysiloxane, among which dimethylpolysiloxane is preferably used. Examples of commercially available products include "Cleanbell CB50-PP," "Cleanbell CB-30PE," "Cleanbell CB-1," and "Cleanbell CB-50AB" (manufactured by Fuji Chemical Co., Ltd.), which are silicone alloys with resin. Examples of commercially available carnauba wax include "Carnauba No. 1" (manufactured by Nikko Rica Co., Ltd.), and examples of fluorine-based water-repellent and oil-repellent agents include surfactants having perfluoroalkyl groups, with an example of a commercially available product being "Surflon KT-PA" (manufactured by AGC Seimi Chemical Co., Ltd.). The amount of water-repellent and oil-repellent agent added is preferably 0.5% to 25% by mass. If the concentration is less than 0.5% by mass, sufficient water-repellent and oil-repellent effects may not be obtained, and if it exceeds 25% by mass, moldability may deteriorate.

[0029] Either inorganic or organic antibacterial agents may be added. Inorganic agents are preferred considering dispersibility. Specifically, examples include inorganic antibacterial agents containing metal ions (Ag, Zn, Cu) and antibacterial agents derived from calcined seashells. Commercially available inorganic antibacterial agents containing metal ions include "Bactekiller BM102VT" (manufactured by Fuji Chemical Co., Ltd.), "Novaron VZF200", "Novaron (AG300)" (manufactured by Toagosei Co., Ltd.), "KM-10D-G", and "IM-10D-L" (manufactured by Sinanen Zeomic Co., Ltd.). An example of a calcined seashell-derived calcium antibacterial agent is "Scalo" (manufactured by FID Co., Ltd.). The amount of antibacterial agent to be added is preferably between 0.5% by mass and 5% by mass. Below 0.5% by mass, sufficient antibacterial activity may not be obtained, and above 5% by mass, production costs will increase.

[0030] Alkyl lubricants and release agents such as aliphatic hydrocarbon compounds, higher fatty acid compounds, higher aliphatic alcohol compounds, and fatty acid amide compounds, as well as silicone lubricants and release agents and fluorine lubricants and release agents can be used as lubricants and release agents. When using a lubricant and release agent, the amount added is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 to 2 parts by mass, out of 100 parts by mass of the total amount with the resin composition. Adding an amount of 0.01 parts by mass or more reduces the risk of a reduced release effect, and adding an amount of 5 parts by mass or less reduces the risk of bleed-out to the sheet surface.

[0031] Masterbatches in which lubricants and release agents are pre-alloyed to thermoplastic resins can also be used. For example, "Wax Master V" (manufactured by BASF) is a commercially available masterbatch based on urethane-based thermoplastic elastomers, and it is preferable to use a masterbatch when considering production efficiency. The amount of masterbatch added is preferably 1 to 8 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 3 to 6 parts by mass, out of 100 parts by mass of the total resin composition.

[0032] Examples of antistatic agents include polyether ester amide polymer antistatic agents and ionomer polymer antistatic agents. Commercially available polyether ester amide polymer antistatic agents include "Perestat 230," "Perestat 6500," "Perectron AS," and "Perectron HS" (manufactured by Sanyo Chemical Industries). Commercially available ionomer polymer antistatic agents include "Entera SD100" and "Entera MK400" (manufactured by Mitsui DuPont Polychemicals).

[0033] <Uneven Shape> The uneven shape constitutes the surface of the resin sheet. The uneven shape may have multiple independent protrusions, or it may form a continuous, integrated protrusion and have multiple independent recesses. Here, a protrusion refers to a part that protrudes from the surface of the base material layer (3) that forms the uneven shape (2), as shown in Figure 1, etc. Having multiple independent protrusions means that the protrusions are not connected to each other, and the uneven shape is formed by multiple protrusions via the base material layer, as shown in Figures 1 to 3. Forming a continuous, integrated protrusion and having multiple independent recesses means that the protrusions are connected to each other, and multiple recesses are formed between the protrusions, as shown in Figure 4. When the resin sheet has multiple independent protrusions, examples of the types of protrusions include columnar shapes such as rectangular columns and roughly circular columns (for example, Figure 3); conical shapes such as rectangular cones and roughly circular cones (for example, Figure 2); frustum shapes such as rectangular frustums and circular frustums; and rectangular ridge shapes such as square ridges and triangular ridges extending in one direction (for example, Figure 1). When a continuous series of concave and concave shapes forms a single convex portion and has multiple independent concave portions, examples of concave shapes include columnar shapes such as rectangular columns and roughly circular columns (for example, Figure 4); conical shapes such as rectangular cones and roughly circular cones; and frustum shapes such as rectangular frustums and circular frustums.

[0034] In this embodiment, the average height of the protrusions is 20 μm or more. In one embodiment, the average height of the protrusions is preferably 20 to 1000 μm, more preferably 20 to 800 μm, and even more preferably 25 to 600 μm. By setting the average height of the protrusions to 20 μm or more, the influence on the airflow and waterflow on the surface of the resin sheet is increased, making it easier to obtain the effect of reducing wind noise generated by the rotation of the propeller. The height of the protrusions (H) refers to the distance from the surface of the substrate layer at the point where the protrusions of the uneven shape are furthest from the surface of the substrate layer. For example, when the protrusions of the uneven shape are almost vertical to the substrate layer, the length from the base to the tip of the protrusions of the uneven shape represents the height of the uneven shape. The average height of the protrusions can be measured by measuring the uneven shape of the resin sheet using a laser microscope and image processing software, and the arithmetic mean of 30 measurements at any number of locations (e.g., 10 locations) can be used.

[0035] In one embodiment, the number of protrusions on the surface having the concavo-convex shape is preferably 1 or more per 1 cm ２ and more preferably 1 or more and less than 50,000 per 1 cm, ２ still more preferably 1 or more and less than 10,000 per 1 cm, ２ and particularly preferably 1 or more and less than 2,500 per 1 cm. The measurement of the number of protrusions can be carried out by measuring the concavo-convex shape of the resin sheet using a laser microscope and image processing software, and using the arithmetic mean value of the values at any number of locations (for example, 10 locations). ２

[0036] In one embodiment, the average width of the protrusions is preferably 20 to 1000 μm, more preferably 20 to 800 μm, and still more preferably 25 to 600 μm. The width (W) of the protrusion means the width of the protrusion at the base (the surface of the base material layer), and means the minimum value of the diameter (the length of the straight line passing through the center) of the protrusion when viewed from the side facing the surface of the resin sheet. For example, when the shape of the protrusion when viewed from the side facing the surface of the resin sheet is a circle, the width of the protrusion means its diameter; when it is a rectangle, it means its short side; and when it is a mesh shape, it means its wire diameter. The measurement of the average width of the protrusions can be carried out by measuring the concavo-convex shape of the resin sheet using a laser microscope and image processing software, and using the arithmetic mean value of the 30 measured values at any number of locations (for example, 10 locations).

[0037] ​In one embodiment, the average spacing of the uneven surface is preferably 20 to 1000 μm, more preferably 20 to 800 μm, and even more preferably 25 to 600 μm. It may also be 20 to 120 μm or 20 to 100 μm. The spacing of the uneven surface (S) refers to the distance at the base of the protrusion (surface of the base material layer) between a protrusion and its nearest adjacent protrusion, as viewed from the side facing the surface of the resin sheet, when the resin sheet has a plurality of independent protrusions. When the uneven surface forms a continuous, integrated protrusion and has a plurality of independent recesses, it refers to the minimum diameter of the recess. For example, when the uneven surface has a plurality of independent cylinders, the spacing of the uneven surface refers to the distance between a cylinder and its nearest adjacent cylinder, and when the uneven surface has a mesh shape, it refers to the opening width (mesh size) of the mesh. The average spacing of the uneven surface can be measured by measuring the uneven surface of the resin sheet using a laser microscope and image processing software, and then using the arithmetic mean of 30 measurements taken at any number of locations (for example, 10 locations).

[0038] It is preferable that the uneven shapes are arranged regularly on the surface of the substrate layer. Here, "arranged regularly" means that the uneven shapes are not arranged randomly, that is, they are arranged in an orderly manner (for example, at regular intervals) in one or two directions. Whether or not the arrangement of the hair-like structures is regular is determined by the arrangement of the bases of the protrusions of the uneven shapes. In one embodiment, the uneven shapes are located on the substrate layer at predetermined intervals, and the positions of the bottom surfaces of the protrusions of the uneven shapes are arranged in an orderly manner in the longitudinal and / or short-length directions of the substrate layer. The arrangement of the protrusions of the uneven shapes is not particularly limited, and a grid arrangement or a staggered arrangement can be selected.

[0039] In one embodiment, the porosity of the concavo-convex shape is preferably more than 45% and less than 99.9%, more preferably more than 50% and less than 99.9%, and even more preferably more than 55% and less than 99.9%. Here, the porosity means the ratio of the volume of the space to the total volume of the layer constituting the concavo-convex shape. The porosity of the concavo-convex shape can be measured by measuring the concavo-convex shape of the resin sheet using a laser microscope and image processing software, and using the arithmetic mean value of the values at any number of locations (for example, 10 locations).

[0040] <Substrate layer> The substrate layer is a layer that constitutes the base portion of the concavo-convex shape. The thickness (t) of the substrate layer refers to the thickness from the root of the concavo-convex shape to the surface on the opposite side of the substrate layer. The average thickness of the substrate layer is preferably 200 to 1000 μm, more preferably 300 to 900 μm, and even more preferably 400 to 80 μm. The average thickness of the substrate layer can be measured by cutting out cross-sectional slices from any 3 locations using a microtome and measuring the thickness from the root of the concavo-convex shape to the other layer interface at 10 locations for the sample, and using the arithmetic mean value of the 30 measurement values.

[0041] There may be no structural boundary between the substrate layer and the concavo-convex shape, and a continuous phase may be formed. Having no structural boundary means that the substrate layer and the concavo-convex shape are integrally formed and there is no structurally distinct boundary portion between them. Forming a continuous phase means that there is no seam between the substrate layer and the concavo-convex shape and it is in a non-discontinuous (continuous phase) state. The substrate layer and the concavo-convex shape may be derived from the same solid resin sheet. Being derived from the same solid resin sheet means, for example, that the substrate layer and the concavo-convex shape are directly or indirectly obtained based on the same resin sheet. The substrate layer and the concavo-convex shape may be formed from the same solid resin sheet. Being formed from the same solid resin sheet means that the substrate layer and the concavo-convex shape are directly formed by processing a single resin sheet. By having no structural boundary between the substrate layer and the concavo-convex shape and forming a continuous phase, the separation of the hair-like bodies from the underlying layer due to external stimuli is suppressed. The substrate layer and the concavo-convex shape are preferably made of the same resin composition.

[0042] In one embodiment of this disclosure, the thickness (T) of the resin sheet refers to the sum of the average height of the uneven surface and the average thickness of the base material layer. The thickness of the resin sheet is preferably 220 to 2000 μm, more preferably 220 to 1800 μm, and even more preferably 225 to 1600 μm. By setting the thickness to 220 μm or more, curling of the sheet can be suppressed, and by setting it to 2000 μm or less, manufacturing costs can be reduced. The thickness of the resin sheet can be measured according to Method A of JIS L 1913:2010.

[0043] In one embodiment, the resin sheet is a laminate. For example, the resin sheet may be a laminate in which a second layer is formed on the side opposite to the side of the base layer that has an uneven shape. That is, the layer structure of the laminated resin sheet according to this embodiment is, from top to bottom, an uneven shape, a base layer, and a second layer.

[0044] <Second Layer> The average thickness of the second layer is preferably 10 to 400 μm, more preferably 20 to 300 μm, and even more preferably 30 to 200 μm. By setting the average thickness of the second layer to 200 μm or less, production costs can be reduced. Here, the uneven shape and the base layer are the same as those described above, so the explanation is omitted. The sum of the average thicknesses of the uneven shape, the base layer, and the second layer is preferably 220 to 1490 μm, more preferably 260 to 1400 μm, and even more preferably 310 to 1300 μm. As the second layer in the resin sheet according to this embodiment, it is preferable to use a thermoplastic resin that can be adhered to the base layer. For example, the same resin composition as the base layer, polycarbonate resins, polyester resins, and polymer alloy resins thereof can be suitably used. The mass ratio of polycarbonate resin to polyester resin in the polymer alloy resin is preferably 50:50 to 90:10, more preferably 60:40 to 80:20, and even more preferably 65:35 to 75:25. Here, the polymer alloy resin refers to a high-molecular-weight multi-component system, and may be a polymer blend having a certain degree of compatibility through mixing, a block copolymer or graft copolymer formed by copolymerization, or a mixture of incompatible resins. As the polyester resin, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, polymethylene terephthalate, and polyester resins copolymerized with diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, or dicarboxylic acid components such as adipic acid, sebatic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid can be used. The second layer may contain other additives as needed.Other additives that do not impair the effects of the present invention include water repellents, oil repellents, colorants such as pigments and dyes, lubricants and release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fibers, fillers such as granular fine particles of talc, clay, and silica, or flake-like fine particles such as mica, low molecular weight antistatic agents such as salt compounds of sulfonic acid and alkali metals, high molecular weight antistatic agents such as polyether ester amides, flame retardants, antibacterial agents, antiviral agents, and heat stabilizers. The second layer may also have a partially crosslinked structure, as long as it does not impair the effects of the present invention.

[0045] [Manufacturing of the Resin Sheet Body] The method for manufacturing the resin sheet body according to this disclosure is not limited to any method, but typically includes a step of melt-extruding the raw resin and imparting an uneven shape to one side of the obtained sheet. For example, a feed block or a multi-manifold die can be used in the manufacturing process.

[0046] There are no particular limitations on the method for creating the uneven shape, and any method known to those skilled in the art can be used. For example, methods such as manufacturing using an extrusion molding method, a roll-to-roll method, a photolithography method, a hot press method, a method using a pattern roll and UV-curing resin, or a method using a 3D printer can be used.

[0047] For example, when using an extrusion molding method, a resin sheet can be manufactured by extruding a sheet using a T-die method and casting it with a transfer roll that has been processed to create an uneven surface, and a touch roll. As the transfer roll with the uneven surface, a roll can be used in which fine irregularities ranging from several micrometers to several hundred micrometers in size are regularly applied to the surface of the roll by methods such as laser engraving, electroforming, etching, or mill engraving. This method makes it possible to create regularly arranged uneven surfaces. Here, "regular" means that the irregularities are not arranged randomly, that is, they are arranged in an orderly manner in one or two directions. As the arrangement of the irregularities in one embodiment, a grid arrangement or a staggered arrangement can be selected. In terms of size, the opening diameter of the recesses, the depth of the recesses, and the spacing between the recesses range from several micrometers to several hundred micrometers. As the material of the transfer roll, for example, metal or ceramic can be used. The spacing of the uneven surfaces can be adjusted by adjusting the spacing of the recesses on the transfer roll, and the height of the uneven surfaces can be adjusted by adjusting the depth of the recesses on the transfer roll. To create a textured surface on the transfer roll, laser engraving or electroforming is particularly suitable for precise processing in the depth direction compared to etching, blasting, mill engraving, etc., and is therefore especially preferred. The transfer roll can be made of materials such as metal or ceramic. On the other hand, the touch roll can be made of various materials, such as silicone rubber, NBR rubber, EPT rubber, butyl rubber, chloroprene rubber, or fluororubber. In one embodiment, a touch roll with a rubber hardness (JIS K 6253) of 40 to 100 can be used. A Teflon® layer may be formed on the surface of the touch roll.

[0048] The uneven surface of a sheet can also be created by pressing the sheet together with a mold that has been processed to create the uneven surface. Similar to the case using a transfer roll, the dimensions of the uneven surface on the resin sheet can be adjusted by adjusting the dimensions of the uneven surface on the mold.

[0049] [Applications] The resin sheet of this disclosure can be used as a resin sheet to be attached to a surface that comes into contact with an airflow. It can also be used as a resin sheet to reduce wind noise generated by the airflow flowing over the surface of the resin sheet. Furthermore, by attaching the resin sheet according to the above embodiment to a surface that comes into contact with an airflow, wind noise generated by the airflow flowing over the surface of the resin sheet can be reduced. Therefore, it can be used in a method for reducing wind noise generated by the airflow flowing over the surface of a resin sheet, which includes attaching the resin sheet according to the above embodiment to a surface that comes into contact with an airflow. Here, airflow means a flow of air having a predetermined air pressure and a predetermined flow velocity relative to an object.

[0050] [Articles] An article according to one embodiment of the present disclosure is an article to which the resin sheet according to the above embodiment is attached. The resin sheet according to the above embodiment can be attached to the surface of a general article, and in addition to insert molding and in-mold molding, the attachment method can be general vacuum forming, pressure forming, or, as an application thereof, a method in which the resin sheet is heated and softened in a vacuum and then released to atmospheric pressure to overlay (form) it onto the surface of an existing article, but is not limited to these. Furthermore, as a method of heating and softening the sheet before molding, known sheet heating methods such as radiant heating using an infrared heater, which is a non-contact heating method, can be applied. Examples of articles to which the resin sheet is attached include propellers of drones, rotor blades of helicopters, wings and fuselage surfaces of aircraft, and the body surfaces of automobiles.

[0051] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure is disclosed below: [1] A resin sheet having an uneven surface on at least one surface, wherein the average height of the protrusions is 20 μm or more, and the sum of the areas of the protrusions at 95% of the average height of the protrusions relative to the projected area of ​​the resin sheet in the thickness direction is 0.1% or more and 55% or less. [2] The resin sheet according to [1] for application to a surface in contact with an airflow. [3] The number of protrusions on the surface having the uneven surface is 1 cm ２The resin sheet according to [1] or [2], wherein there is one or more per [4] side surface having the uneven shape, ２ A resin sheet according to any one of [1] to [3], having 1 or more but less than 50,000 pieces per unit. [5] The number of protrusions on the side having the uneven shape is 1 cm ２ [1] to [4] A resin sheet according to any one of [1] to [4], having one or more but less than 10,000 units per sheet. [6] A resin sheet according to any one of [1] to [5], comprising a thermoplastic resin. [7] A resin sheet according to [6], wherein the thermoplastic resin is a polyolefin resin. [8] A resin sheet according to any one of [1] to [7], which is a laminate. [9] A resin sheet according to any one of [1] to [8] for reducing wind noise generated by airflow over the surface of a resin sheet.

[10] An article to which a resin sheet according to any one of [1] to [9] is attached.

[11] A method for reducing wind noise generated by airflow over the surface of a resin sheet, comprising attaching a resin sheet according to any one of [1] to [9] to a surface in contact with airflow. Each configuration and combination thereof in each embodiment are examples, and additions, omissions, substitutions, and other changes to the configuration can be made as appropriate without departing from the spirit of this disclosure.

[0052] The present disclosure will be further illustrated by the following examples, but these examples will not limit the interpretation of the present disclosure.

[0053] The various raw materials used in the examples are as follows: [Resin composition] (1) Resin / Olefin resin (Homopolypropylene (PP); "F107DJ" manufactured by Prime Polymer Co., Ltd.)

[0054] [Example 1] A sheet with a thickness of 500 μm was formed using a resin composition. Next, the formed sheet was sandwiched between a mold that had been processed with embossing by chromium oxide spraying and laser engraving, and a release sheet made of polyimide resin. The sheet was then pressed for 120 seconds at a pressure of 4 MPa while being heated to 170°C using a press machine (Mini Test Press 10 manufactured by Toyo Seiki Co., Ltd.). This yielded a resin sheet with the composition and embossed shape shown in Table 1. The average thickness of the base layer was 220 μm.

[0055] [Example 2] A resin sheet was obtained in the same manner as in Example 1, except that the resin composition, mold dimensions, and press pressure were adjusted to obtain the composition and uneven shape shown in Table 1. The average thickness of the base layer was 250 μm.

[0056] [Examples 3-5, Comparative Example 2] Resin sheets were obtained in the same manner as in Example 1, except that the resin composition, mold dimensions, and press pressure were adjusted to obtain the compositions and uneven shapes shown in Tables 1 and 2. The average thickness of the base material layer was 220 μm, 160 μm, 220 μm, and 160 μm, respectively.

[0057] [Comparative Example 1] A resin sheet was obtained in the same manner as in Example 1, except that the resin composition was adjusted to match the composition shown in Table 2 and pressing was not performed using a press machine. The average thickness of the base layer was 250 μm. Since the resin sheet of Comparative Example 1 did not have an uneven surface, the 95% height area was not measured.

[0058] The methods for evaluating the various properties of the resin sheets prepared in the examples and comparative examples are as follows.

[0059] (1) Using a laser microscope ("VK-X100", manufactured by Keyence Corporation) to obtain the surface area ratio of the convex part at 95% height, images were taken of 10 arbitrary locations, and the surface area ratio was determined for each image using the following procedure, and the average value was taken as the surface area ratio of the convex part at 95% height. Procedure 1: Correct the image tilt. Procedure 2: Use the cross-sectional profile function to determine the bottom height of 20 locations per image. Also, detect the same number of convex height values ​​as the height difference from the bottom. Take the average values ​​of each as the bottom height and convex height. Procedure 3: Use the unevenness measurement function to detect convex parts in the same image, setting the reference height to 95% of the bottom height + convex height. Take the displayed surface area ratio value as the surface area ratio of that location.

[0060] (2) Measurement of the average width of the uneven surface, the average height of the uneven surface, the average spacing of the uneven surface, and the average thickness of the base layer The average width of the uneven surface, the average height of the uneven surface, the average spacing of the uneven surface, and the average thickness of the base layer of the resin sheet were measured using a laser microscope ("VK-X100", manufactured by Keyence Corporation). For the samples to be measured, cross-sectional sections were cut from three arbitrary locations on the resin sheet using a microtome. For the average height of the uneven surface, the height was measured at 10 locations for each sample, and the arithmetic mean of these 30 measurements was used. For the average width of the uneven surface, the width was measured at 10 locations for each sample, and the arithmetic mean of these 30 measurements was used. For the average spacing of the uneven surface, the spacing was measured at 10 locations for each sample, and the arithmetic mean of these 30 measurements was used. For the average thickness of the base layer, the thickness of the base layer was measured at 10 locations for each sample, and the arithmetic mean of these 30 measurements was used. The thickness of the base layer was defined as the distance from the base of the protrusion to the surface of the layer on the opposite side.

[0061] (3) Wind noise evaluation test A resin sheet was attached to the tip of the wing-shaped model over a width of 250 mm. Next, the wing-shaped model with the resin sheet attached was placed inside a wind tunnel. The wind noise was measured using a sound level meter when wind (20 m / s) was blown from a nozzle onto the area of ​​the wing-shaped model with the resin sheet attached, and compared with the case where the resin sheet was not attached. The measurement results were a comparison of the cumulative values ​​in the frequency range of 1000 to 3000 Hz. 0 dB was used when there was no change from the case where the resin sheet was not attached, and a negative value was used when the wind noise decreased. A value less than 0 was evaluated as having a wind noise suppression effect.

[0062] Evaluation tests were conducted on various properties using the resin sheets obtained in each example and comparative example, and the results are shown in Tables 1 and 2.

[0063]

[0064]

[0065] The following was revealed from the results shown in Tables 1 and 2. The resin sheets of Examples 1 to 5 had wind noise measurements of less than 0 dB compared to the case without a resin sheet, indicating a wind noise suppression effect. On the other hand, the resin sheets of Comparative Examples 1 and 2 did not have a wind noise suppression effect. It is presumed that the resin sheet of Comparative Example 1 did not have an uneven surface, and therefore had too little effect on the airflow over the surface of the resin sheet. It is presumed that the resin sheet of Comparative Example 2 had a certain level of convex area ratio at 95% height, and therefore had insufficient effect on the airflow over the surface of the resin sheet.

[0066] Although the present invention has been described above using various embodiments, it goes without saying that the technical scope of the present invention is not limited to the embodiments described above. It will be obvious to those skilled in the art that various modifications or improvements can be made to the above embodiments. Furthermore, it is clear from the claims that such modified or improved forms may also be included within the technical scope of the present invention.

[0067] The resin sheet of this embodiment can reduce wind noise generated by the rotation of a propeller, and therefore has industrial applicability as a resin sheet for reducing wind noise generated by the airflow over the surface of the resin sheet.

[0068] 1. Resin sheet 2. Uneven surface 3. Base layer W: Width of uneven surface H: Height of uneven surface S: Spacing between uneven surfaces t: Thickness of base layer

Claims

1. A resin sheet having an uneven surface on at least one surface, wherein the average height of the protrusions is 20 μm or more, and the sum of the areas of the protrusions at 95% of the average height of the protrusions relative to the projected area in the thickness direction of the resin sheet is 0.1% or more and 55% or less.

2. The resin sheet according to claim 1 for application to a surface in contact with an airflow.

3. The number of protrusions on the side surface having the uneven shape is 1 cm ２ The resin sheet according to claim 1 or 2, wherein there is one or more per sheet.

4. The number of protrusions on the side surface having the uneven shape is 1 cm ２ The resin sheet according to claim 1 or 2, wherein the number of pieces is between 1 and 50,000.

5. The number of protrusions on the side surface having the uneven shape is 1 cm ２ The resin sheet according to claim 1 or 2, wherein the number of pieces is between 1 and 10,000.

6. A resin sheet according to claim 1 or 2, comprising a thermoplastic resin.

7. The resin sheet according to claim 6, wherein the thermoplastic resin is a polyolefin resin.

8. A resin sheet according to claim 1 or 2, which is a laminate.

9. The resin sheet according to claim 1 or 2 for reducing wind noise generated by airflow over the surface of the resin sheet.

10. An article to which the resin sheet described in claim 1 or 2 is attached.

11. A method for reducing wind noise generated by airflow over the surface of a resin sheet, comprising attaching the resin sheet described in claim 1 or 2 to a surface that comes into contact with the airflow.

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