Urethane foam and electronic devices

Abstract

To provide a novel urethane foam which is thin and has excellent performance. The urethane foam according to the embodiment has a thickness of 0.5 mm or less and an inorganic filler content of 0.1 to 12.0 mass %.

Description

[Technical Field]

[0001] The present invention relates to a urethane foam and an electronic device. [Background technology]

[0002] A known molding technique for high-density polyurethane foam sheets is the mechanical froth method, which involves foaming and curing polyurethane. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 566095 [Patent Document 2] Patent Publication No. 2021-66846 [Patent Document 3] Patent No. 4316757 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional techniques, when molding high-density polyurethane foam sheets using the mechanical froth method, the compound viscosity must be high to retain the entrained gas. Therefore, when molding thin foam sheets, for example, 0.5 mm or less in thickness, the coated surface is insufficiently leveled after the froth material is applied and passed through a coater. If thermal curing is performed in this state, the sheet surface becomes uneven (orange peel). This problem becomes more pronounced as the foam density decreases. Therefore, in conventional techniques, a process of smoothing the surface by pressing the substrate against the sheet after or during coating is required to smooth the unevenness of the sheet surface.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a novel urethane foam that is thin yet has excellent performance, and an electronic device equipped with the urethane foam. [Means for solving the problem]

[0006] One embodiment of the present invention is a urethane foam having a thickness of 0.5 mm or less and an inorganic filler content of 0.1 to 12.0 mass %. The urethane foam of the above embodiment may be obtained by curing a foam-forming composition obtained by foaming a foam-forming composition containing a polyol, a polyisocyanate, a foam stabilizer, and a filler by a mechanical froth method. In the urethane foam of the above embodiment, the inorganic filler may have an average particle size of 10 μm or less.

[0007] Another aspect of the present invention is an electronic device comprising the urethane foam according to any one of the above aspects. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a novel urethane foam that is thin yet has excellent performance, and a technique relating to the urethane foam. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an outline of a drop-type impact absorption tester used in a point impact absorption test. [Figure 2] FIG. 1 is a diagram showing an outline of a drop-type impact absorption tester used in a surface impact absorption test. [Figure 3] FIG. 1 is a diagram showing an outline of a compression set tester used to measure compression set. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expression "a to b" in the description of a range of numerical values ​​means that the range is from a to b, unless otherwise specified.

[0011] (urethane foam) The urethane foam according to the embodiment preferably has a thickness of 0.50 mm or less. The thickness of the urethane foam according to the embodiment may be 0.40 mm or less, or 0.30 mm or less. There is no particular lower limit to the thickness of the urethane foam according to the embodiment, but it may be, for example, 0.03 mm or more, 0.04 mm or more, 0.05 mm or more, 0.06 mm or more, 0.07 mm or more, 0.08 mm or more, 0.09 mm or more, or 0.10 mm or more.

[0012] The urethane foam according to the present embodiment preferably contains an inorganic filler. The content of the inorganic filler based on the total urethane foam is preferably 0.1 to 12.0% by mass. The upper limit of the inorganic filler content may be 11.0% by mass or less, 10.0% by mass or less, 9.0% by mass or less, or 8.0% by mass or less. The lower limit of the inorganic filler content may be 0.2% by mass or more, 0.4% by mass or more, or 0.6% by mass or more.

[0013] Examples of inorganic fillers include calcium carbonate, aluminum hydroxide, magnesium hydroxide, natural silica, synthetic silica, kaolin, clay, titanium oxide, barium sulfate, zinc carbonate, zinc oxide, glass beads, alumina beads, carbon, etc. Of these, calcium carbonate is preferably used as the inorganic filler from the viewpoint of improving the surface smoothness of the urethane foam. When calcium carbonate is used as the inorganic filler, the content of calcium carbonate is preferably 0.5 to 10.0 mass %, more preferably 1.0 to 9.0 mass %, and even more preferably 2.0 to 8.0 mass %, based on the total mass of the urethane foam.

[0014] The average particle size (volume-based D50) of the inorganic filler is preferably 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, or 5 μm or less. The lower limit of the average particle size of the inorganic filler is, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, or 0.5 μm. The average particle size of the inorganic filler can be measured using a laser diffraction scattering method.

[0015] The shape of the inorganic filler is not particularly limited, and may be spherical, prism-like, scaly, or needle-like.

[0016] The urethane foam according to the present embodiment preferably contains an organic filler. The content of the organic filler based on the entire urethane foam is preferably 2.0% by mass or less, and may be 1.5% by mass or less, or 1.0% by mass or less. The lower limit of the organic filler content is not particularly limited, but is, for example, 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more based on the entire urethane foam.

[0017] Examples of organic fillers include fibrous fillers such as polymer polyol (POP), microcellulose, and aramid fiber, and particulate fillers such as polyester fine particles, polyurethane fine particles, vinyl polymer fine particles, and acrylic polymer fine particles.

[0018] The urethane foam described above has excellent properties such as surface smoothness, point impact absorption, surface impact absorption, and compression set, despite its thin wall.

[0019] (Foam composition) The foam composition according to the embodiment can be used to produce a urethane foam having a thickness of 0.5 mm or less. The foamable composition according to the embodiment includes a polyol, a polyisocyanate, a filler, and a foam stabilizer. The foamable composition is foamed by a mechanical froth method to obtain a foam-molding composition, which is then cured to obtain the urethane foam. Each of the raw materials used in the foamable composition according to the embodiment is described below.

[0020] The (blended) viscosity (25°C) of the foamable composition is preferably 100 mPa·s or more, 200 mPa·s or more, or 300 mPa·s or more, and preferably 800 mPa·s or less, 700 mPa·s or less, or 600 mPa·s or less. By using a foamable composition with the above-mentioned viscosity range, it is possible to form a thin-walled urethane foam with a smooth surface.

[0021] (Polyol) The polyol used in the foam composition according to the embodiment is not particularly limited as long as it does not impair the effects of the present invention. Examples of polyols include polyester polyols, polycarbonate polyols, polyether polyols, and polyester ether polyols. These may be used alone or in combination. Since the polyisocyanate compound forms a urethane skeleton, it can be freely selected in consideration of the desired properties of the urethane foam.

[0022] Examples of polyester polyols include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid; and esters or acid anhydrides thereof, with ethylene glycol, 1,3-propylene glycol, 1,2-propylene ... Examples include polyester polyols such as polypropylene glycol obtained by dehydration condensation reaction with 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, etc., or mixtures thereof; and polylactone diols obtained by ring-opening polymerization of lactone monomers such as ε-caprolactone and methylvalerolactone.

[0023] Examples of polycarbonate polyols include those obtained by reacting at least one polyhydric alcohol such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, 1,8-octanediol, 1,9-nonanediol, or diethylene glycol with diethylene carbonate, dimethyl carbonate, diethyl carbonate, or the like.

[0024] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc., which are obtained by polymerizing cyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, etc., and copolyethers thereof. Polyether polyols can also be obtained by polymerizing the above-mentioned cyclic ethers using polyhydric alcohols such as glycerin and trimethylolethane.

[0025] Examples of polyester ether polyols include those obtained by a dehydration condensation reaction of aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and azelaic acid; aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as hexahydrophthalic acid, hexahydroterephthalic acid, and hexahydroisophthalic acid; or acid esters or acid anhydrides thereof with glycols such as diethylene glycol or propylene oxide adducts, or mixtures thereof.

[0026] (Polyisocyanate) The polyisocyanate used in the foam composition according to the embodiment is not particularly limited as long as it does not impair the effects of the present invention. For example, bifunctional polyisocyanate compounds include 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI), m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI), hydrogenated MDI, xylylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, and polyisocyanates. Examples of suitable isocyanates include aromatic isocyanates such as dimethylmethylene polyphenyl polyisocyanate, 1,5-naphthalene diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, and tetramethylxylene diisocyanate (TMXDI); alicyclic isocyanates such as cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and methylcyclohexane diisocyanate; and alkylene isocyanates such as butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, and lysine diisocyanate. Examples of tri- or higher functional polyisocyanates include 1-methylbenzene-2,4,6-triisocyanate, 1,3,5-trimethylbenzene-2,4,6-triisocyanate, biphenyl-2,4,4'-triisocyanate, diphenylmethane-2,4,4'-triisocyanate, methyldiphenylmethane-4,6,4'-triisocyanate, 4,4'-dimethyldiphenylmethane-2,2',5,5'tetraisocyanate, triphenylmethane-4,4',4"-triisocyanate, polymeric MDI, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, bicycloheptane triisocyanate, and 1,8-diisocyanatomethyloctane. The polyisocyanate may be a modified product or derivative thereof. These polyisocyanates may be used alone or in combination. Since the polyisocyanate forms a urethane skeleton, it can be freely selected in consideration of the desired properties of the urethane foam.

[0027] The NCO index of the polyisocyanate is preferably 70 to 110, and more preferably 80 to 105. The NCO index is defined as the value obtained by dividing the total number of isocyanate groups in the polyisocyanate by the total number of active hydrogens that react with the isocyanate groups, and multiplying this value by 100. In other words, the NCO index is 100 when the number of active hydrogens that react with the isocyanate groups is stoichiometrically equal to the number of isocyanate groups in the polyisocyanate.

[0028] (filler) Examples of the filler used in the foam composition according to the embodiment include inorganic fillers and organic fillers. (inorganic filler) The inorganic filler (filling agent) used in the foam composition according to the embodiment is the same as that described for urethane foam, and the content (blending amount) of the inorganic filler in the foam composition is preferably 12.0% by mass or less, and may be 11.0% by mass or less, 10.0% by mass or less, 9.0% by mass or less, or 8.0% by mass or less. The lower limit of the inorganic filler content is not particularly limited, but is, for example, 0.1% by mass or more, 0.2% by mass or more, 0.4% by mass or more, or 0.6% by mass or more based on the entire foam composition.

[0029] (organic filler) The organic filler (filling agent) may be prepared as a single raw material, or may be prepared in a state blended with a polyol or a pigment described below. Therefore, in the present disclosure, the amount of the organic filler may also include the amount of the organic filler blended with the polyol or pigment. The content of the organic filler based on the entire foamable composition is preferably 2.0% by mass or less, and may be 1.5% by mass or less, or 1.0% by mass or less. The lower limit of the content of the organic filler is not particularly limited, but is, for example, 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more based on the entire foamable composition.

[0030] (catalyst) The foamable composition according to the embodiment may contain a catalyst. As the catalyst, an amine catalyst for urethane foam, a metal catalyst, or the like may be used alone or in combination. Examples of the amine catalyst include monoamine compounds, diamine compounds, triamine compounds, polyamine compounds, cyclic amine compounds, alcohol amine compounds, and ether amine compounds, and these may be used alone or in combination of two or more. Examples of the metal catalyst include organotin compounds, organoiron compounds, organobismuth compounds, organolead compounds, organozinc compounds, etc., and these may be used alone or in combination of two or more. The amount of catalyst to be added is determined appropriately, but is, for example, 0.1 to 50 parts by mass per 100 parts by mass of polyol.

[0031] (Foam stabilizer) Examples of foam stabilizers used in the foam composition according to the embodiment include silicone-based foam stabilizers and cardanol-based surfactants, and a plurality of types of these foam stabilizers may be used. Of these, silicone-based foam stabilizers are preferably used as the foam stabilizer. The amount of the foam stabilizer to be added is preferably 0.5 to 12 parts by mass, more preferably 1 to 11 parts by mass, and even more preferably 2 to 10 parts by mass, per 100 parts by mass of the polyol.

[0032] (pigment) The foamable composition according to the embodiment may contain a pigment, such as a mixture of a carbon pigment (black pigment) and a polymer polyol dispersed in the polymer polyol. The blending amount of the pigment is preferably 0.5 to 12 parts by mass, more preferably 1 to 11 parts by mass, and even more preferably 2 to 10 parts by mass, per 100 parts by mass of the polyol.

[0033] (Other ingredients) The foamable composition according to the embodiment may contain other components as needed, such as additives such as a crosslinking agent, a weathering agent, a plasticizer, a foaming agent, a foaming assistant, and a flame retardant. The plasticizer may be any plasticizer that is used in polyurethane foams. Weathering agents include bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate. The foaming agent may be any agent capable of generating bubbles in the polyurethane, and examples thereof include chemical foaming agents that generate gas through thermal decomposition or chemical reaction (e.g., water that reacts with isocyanate groups to generate CO2), and physical foaming agents that generate gas through pressure reduction or heating (e.g., pentane, cyclopentane, methylene chloride, carbon dioxide, etc. dissolved in resin under high pressure). As the foaming aid, alternatives to chlorofluorocarbons such as hydrofluoroolefins (HFOs) or hydrocarbons such as pentane can be used alone or in combination.

[0034] When the foam composition described above is foamed and cured to form a thin-walled urethane foam (for example, 0.5 mm or less), the foam surface is less likely to become uneven. Therefore, a thin-walled urethane foam with a smooth surface can be formed without the need for a surface smoothing treatment using a separate material.

[0035] (urethane foam manufacturing) The method for producing a urethane foam according to the embodiment includes a raw material preparation step and a foaming and curing step. Each step will be described in detail below.

[0036] <Raw material preparation process> In the raw material preparation step, the raw materials described above are mixed to prepare a foam composition, which is a raw material mixture for a urethane foam. The mixing method is not particularly limited, but may be, for example, mixing while stirring in a container such as a mixing tank for mixing the components.

[0037] <Foaming and curing process> In the foaming and curing step, a predetermined foaming gas is added to the foam composition obtained in the raw material preparation step, and they are thoroughly mixed to form a state in which a large number of bubbles exist in the foam composition. This foaming and curing step is usually carried out by thoroughly mixing the liquid foam composition obtained in the raw material preparation step with the foaming gas using a mixing device such as a mixing head. The foaming gas mixed into the foam composition during the foaming and curing process forms the cells in the foam sheet. The amount of foaming gas determines the expansion ratio and density of the resulting foam sheet. This contributes to the point impact absorption rate, surface impact absorption rate, and compression set of the urethane foam. To adjust the density of the urethane foam, the mass of the required urethane foam raw materials is calculated based on the desired density and the volume of the urethane foam raw materials, and the amount of foaming gas is determined to achieve the desired volume for this mass. While air is typically used as the foaming gas, other inert gases such as nitrogen, carbon dioxide, helium, and argon can also be used.

[0038] <Foaming method and conditions> The foaming method according to the present disclosure is preferably a mechanical frothing method, in which the foam composition is stirred with a stirring blade or the like to mix air from the atmosphere into the foam composition, thereby causing foaming. The stirring device can be any stirring device commonly used in the mechanical froth method, and examples thereof include a homogenizer, a dissolver, and a mechanical froth foaming machine. According to the mechanical froth method, urethane foams with densities suitable for various applications can be obtained by adjusting the mixing ratio of the foam composition and air. By adjusting the density, the point impact absorption rate, surface impact absorption rate, and compression set of the urethane foam can be adjusted. The mixing time for mixing the foam-forming composition with air is not particularly limited, but is usually 1 to 10 minutes, preferably 2 to 6 minutes. The mixing temperature is also not particularly limited, but is usually room temperature. The stirring speed during the mixing is preferably 200 rpm or higher (more preferably 500 rpm or higher) to make the bubbles finer, and is preferably 2000 rpm or lower (more preferably 800 rpm or lower) to ensure smooth discharge of the foam-forming composition from the foaming machine.

[0039] <Formation of urethane foam> The foamable composition thus foamed can be formed into a sheet-like urethane foam having a desired thickness by known means such as a casting method using a doctor knife or doctor roll.

[0040] (hardening) The urethane foam can be cured by any known method, including, for example, a heating step (thermal crosslinking). In the heating step, for example, hot air drying can be used. The heating temperature and heating time are not particularly limited, but may be, for example, about 80° C. for about 1 to 3 minutes. To further promote the curing of the urethane foam, a heating step may be performed after the urethane foam is formed. The heating method can be a known method, such as using a thermostatic bath maintained at a predetermined temperature. The heating temperature and heating time are not particularly limited as long as they can provide the desired properties of the urethane foam. For example, the heating temperature can be 50 to 150°C, and the heating time can be 1 to 48 hours. These can be freely set depending on the type of raw material. For example, heating for 20 hours or more in an environment of 50°C or higher (e.g., 50 to 100°C) is preferred, heating for 20 hours or more in an environment of 70°C or higher (e.g., 70 to 100°C) is more preferred, and heating for 20 hours or more in an environment of 80°C or higher (e.g., 80 to 100°C) is even more preferred.

[0041] (buffer material) The cushioning material according to the embodiment includes the urethane foam of the above-described aspect. Specifically, the cushioning material according to the embodiment is thin yet has excellent surface smoothness, impact absorption properties, and compression set, and therefore can be used as an impact absorbing sheet for protecting precision electronic and electrical components inside electronic and electrical devices.

[0042] (electronic equipment) The electronic device according to the embodiment includes the cushioning material of the above-described aspect. Specifically, the electronic device according to the embodiment has a structure in which the cushioning material is attached to the electronic device, such as an electronic or electrical component to be protected. This improves workability when assembling the electronic device.

[0043] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. [Example]

[0044] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0045] The raw materials shown in Table 1 were blended to obtain foam compositions for each of the Examples and Comparative Examples. Nitrogen was added as an inert gas to the obtained foam composition, and it was foamed by the mechanical froth method (foaming conditions: 100 to 1000 rpm). The resulting urethane foam was cast onto a PET film using a doctor knife so that the thickness of the resulting urethane foam would be as shown in Table 1, and the resulting urethane foam was heat-treated in an oven at 120°C for 5 minutes to obtain a sheet-like urethane foam.

[0046] [Table 1]

[0047] Polyol A: Sanyo Chemical Industries, Ltd., GA-3000, hydroxyl value: 56.1 mg KOH / g, number of functional groups = 3 Polyol B: Mitsui Chemicals, Inc., AN-230, 28.6 mg KOH / g, number of functional groups = 2, polymer (POP) particle (organic filler) content = 22 mass% Polyol C: Sanyo Chemical Industries, Ltd., PP-2000, 56.1 mg KOH / g, number of functional groups = 2 Polyol D: Sanyo Chemical Industries, Ltd., PP-400, hydroxyl value: 280.5 mg KOH / g, number of functional groups = 2 Polyol E: Daicel Corporation, PLC205U, hydroxyl value: 212.0 mg KOH / g, number of functional groups = 2 Polyol F: ADEKA Corporation, DPG, hydroxyl value: 837.0 mg KOH / g, number of functional groups = 2 Polyol G: Sanyo Chemical Industries, Ltd., GP-3000, hydroxyl value: 56.1 mg KOH / g, number of functional groups = 3 Polyol H: Mitsubishi Chemical Corporation, 1,4-butanediol, hydroxyl value: 56.1 mg KOH / g, number of functional groups = 2 Catalyst: Organic acid salt system, manufactured by Nippon Chemical Industry Co., Ltd., FIN-P1, Hydroxyl value: 56.1 mg KOH / g Silicone foaming agent 1: Dow Toray, SZ-1952, hydroxyl value: 40.0 mg KOH / g Silicone foaming agent 2: Momentive L-5614 Pigment: Sanyo Pigment Co., Ltd., UT Black J112, hydroxyl value: 41.9 mg KOH / g, POP blend, polymer (POP) particle (organic filler) content = 20% by mass Filler (inorganic filler) 1: Calcium carbonate, manufactured by Shiraishi Calcium Co., Ltd., Silver W, average particle size (volume basis D50) = 1.5 μm Filler (inorganic filler) 2: aluminum hydroxide, manufactured by ICA, H-10, average particle size (volume basis D50) = 25 μm Isocyanate: Polymeric MDI (crude MDI), manufactured by BASF, M5S, NCO%: 31.5%, average functionality = 2.4

[0048] <Evaluation test> The urethane foams or foam compositions of each Example and Comparative Example were subjected to the following measurements and evaluations. The results are shown in Table 1.

[0049] <Thickness> The thickness of the urethane foam was measured with a thickness gauge.

[0050] <density> The density was obtained by calculating the mass per unit volume of the urethane foam.

[0051] <Arithmetic mean roughness> The arithmetic mean roughness (Sa) of the surface of the urethane foam of each example and comparative example was measured using a laser microscope (Keyence Corporation, VK-X3000) in accordance with ISO 25178. The obtained arithmetic mean roughness (Sa) values ​​are shown in Table 1. The obtained arithmetic mean roughness (Sa) values ​​were evaluated according to the following criteria. ◎(Excellent): 7.5μm or less ×(Not allowed): More than 7.5μm

[0052] <25%CLD> The 25% CLD (25% compressive stress at 25°C) of the urethane foam was determined using the method described in JIS K624-2:2016 "Vulcanized rubber and thermoplastic rubber - Determination of stress-strain characteristics."

[0053] <T - peel strength> The urethane foam was molded into a size of 24 mm in width and 150 mm in length to obtain test specimens. Double - sided tapes (manufactured by Nitto Denko Corporation, No5000NS, 24 mm in width and 150 mm in length) were respectively pasted on both sides of the test specimens. On each double - sided tape, a PET film with a width of 24 mm, a length of 200 mm, and a thickness of 25 μm was pasted, and a five - layer test body composed of PET film / double - sided tape / test specimen / double - sided tape / PET film was obtained. A pair of PET films protruding from the ends of the test specimens was pulled apart in the vertical direction (lamination direction) at a speed of 1000 mm / min using an autograph, and the strength at the time of material failure (interlayer delamination) was measured, and the average value of n = 3 was calculated.

[0054] <Point impact absorbency> Using a drop - type impact absorbency tester, a point impact absorption test was conducted, and the point impact absorption rate of the urethane foam was calculated according to the following formula (1). Point impact absorption rate (%) ={(f a0 - f a1 ) / f a0}×100 (1) In formula (1), f a0 is the impact load when the impact absorption test is conducted without installing the sample on the sample stage. f a0 is the impact load when the impact absorption test is conducted with the sample installed on the sample stage. The impact load was measured by a sensor installed on the sample stage. The measurement of the impact load in the point impact absorption test was carried out by dropping an impactor (steel ball) with a weight of 4.5 g from a height of 100 mm onto a test specimen obtained by processing the urethane foam into a size of φ50 mm in an environment with a temperature of 23℃. The following criteria were used for the evaluation of point impact absorbency. ○ (Good): 35% or more × (Poor): Less than 35%

[0055] <Surface impact absorbency> Using a drop - type impact absorbency tester, a surface impact absorption test was conducted, and the surface impact absorption rate of the urethane foam was calculated according to the following formula (2). Surface impact absorption rate (%) ={(fb0 -f b1 ) / f b0}×100 (2) In equation (2), f b0 is the impact load when the impact absorption test is performed without placing the sample on the sample stage, but with only a 5 mm thick acrylic plate. b0 is the impact load when an impact absorption test was conducted with the sample placed on the sample stage and a 5 mm thick acrylic plate placed on top of the sample. The impact load was measured by a sensor installed on the sample stage. The impact load in the surface impact absorption test was measured by dropping a 13.8g impactor (steel ball) from a height of 100mm onto a test piece made of urethane foam processed to a size of φ50mm in an environment with an ambient temperature of 23°C. The surface impact absorption was evaluated using the following criteria. ○ (Good): 15% or more × (defective): Less than 15%

[0056] <Compression Residual Set> The test specimens were prepared by molding urethane foam into a rectangular shape measuring 5 cm long and 5 cm wide. The test specimen was placed on the specimen stage of the compression set tester shown in Figure 3. Spacers, each adjusted to 50% of the urethane foam's pre-compression thickness (as listed in Table 1), were placed around the specimen. The spacers were positioned at a distance that prevented them from contacting the specimen, even during the compression test. A stainless steel compression plate, which compresses and deforms the specimen, was placed over the entire specimen and spacer. The height of the compression plate was adjusted using a ball screw and positioning nut until it was in close contact with the spacer, and the ball screw and positioning nut were tightened to secure the specimen in place. Each foam sheet in this state was heated to 70°C and heated for 22 hours. The compression plate was then removed and left at 22°C for 30 minutes. The thickness was measured and used as the post-compression thickness, and the compression set was calculated using Equation (3). Compression set (%) = (thickness before compression - thickness after compression release) / thickness before compression × 100 (3) In addition, the compression set was calculated in the same manner as the test method described above, except that a spacer adjusted to a thickness of 25% of the thickness of the urethane foam before compression (thickness listed in Table 1) was used. The compression set was evaluated using the following criteria. ○ (Good): Less than 10% × (defective): 10% or more

[0057] <Glass transition temperature (Tg)> The glass transition temperature (Tg) of the urethane foam was determined by measuring the peak value of tanδ using a dynamic viscoelasticity analyzer (DMA, model MCR302, manufactured by Anton Paar) at a temperature increase rate of 5°C / min from -80°C to 150°C at 1 Hz according to the procedure of JIS K7198.

[0058] <Loss tangent (tanδ)> The storage modulus and loss modulus were measured using a dynamic viscoelasticity apparatus (Anton Paar, model MCR302) according to the procedure of JIS-K7198, under conditions of -80°C to 150°C, temperature increase at 5°C / min, and frequency of 1 Hz. The loss modulus divided by the storage modulus was defined as the loss tangent (tanδ).

[0059] <Blend viscosity> 50 mL of the foam composition prepared in each Example and Comparative Example was weighed out and placed in a sample bottle, and after heating to 25°C in a thermostatic bath, the (blended) viscosity was measured using a B-type viscometer (manufactured by Brookfield, model: DV-I+).

[0060] <Foaming ability (froth density)> The froth density when foamed by the mechanical froth method was calculated using the following procedure. 100mL disposable cup (cup volume: 157cm 3 The foamed foam composition (foam-forming composition) is placed in the disposable cup and the mass is measured. The froth density is calculated by (measured mass - empty disposable cup mass) / disposable cup volume.

[0061] <Bubble stability> The bubble stability was calculated according to the following formula (4). Foam stability = froth density / density (4) The cell stability is preferably 0.85 to 1.15 or 0.90 to 1.10. When the cell stability is in this range, it indicates that the cells are not broken by heating. In other words, the urethane foam is not becoming densified. [Industrial Applicability]

[0062] The urethane foam of the present disclosure is thin but has a smooth surface, and is useful as a cushioning material and as a material for electronic devices that include such cushioning material. [Explanation of symbols]

[0063] One-point impact absorption tester Two-sided impact absorption tester 3. Compression set tester 10, 20 impactor (steel ball) Samples 11, 22, and 31 (foam sheets) 12, 23 Sample stage (SUS) 13, 24 sensors 21 Acrylic board 30 compression plate 32 spacer 33 Sample stage 34 Ball screw 35 Positioning nut

Claims

1. The thickness is 0.5 mm or less, A urethane foam having an inorganic filler content of 0.1 to 12.0 mass %.

2. 2. The urethane foam according to claim 1, obtained by curing a foam-forming composition obtained by foaming a foam-forming composition containing a polyol, a polyisocyanate, a foam stabilizer, and a filler by a mechanical froth method.

3. The urethane foam according to claim 1, wherein the inorganic filler has an average particle size of 10 μm or less.

4. An electronic device comprising the urethane foam according to any one of claims 1 to 3.

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