Polyurethane foam and shoe sole materials

Abstract

The present invention provides: a polyurethane foam which has an adequately low hardness and excellent mechanical strength, while maintaining good rebound resilience; and a shoe sole member which is obtained using this polyurethane foam.　This polyurethane foam is configured from a polyurethane starting material that contains a polyol component, a polyisocyanate component, a foaming agent, a catalyst and a foam stabilizer, while being configured such that: the polyol component contains a polytetramethylene ether glycol that has a number average molecular weight of from 600 to 3,000; the proportion of the polytetramethylene ether glycol in the polyol component is 90% by mass or more; the polyisocyanate component contains (i) an isocyanate group-terminated prepolymer that has a number average molecular weight of from 500 to 2,000, an average number of functional groups of 2 and an isocyanate group content of from 3% by mass to 10% by mass and (ii) a modified MDI that has an isocyanate group content of from 25% by mass to 33% by mass; and the isocyanate group content in the polyisocyanate component is from 11% by mass to 27% by mass. A shoe sole member is configured using this polyurethane foam.

Description

[Technical Field]

[0001] The present invention relates to a polyurethane foam and a shoe sole member. [Background technology]

[0002] Foams such as polyurethane foam and ethylene-vinyl acetate copolymer foam have been used as structural components for a variety of applications. For example, shoe sole members made of polyurethane foam have excellent shock absorption properties and are used as structural components for the soles of not only general-use shoes but also athletic shoes such as walking shoes, running shoes, and trekking shoes. In addition to their use as shoe sole members, the polyurethane foams can also be used as matting materials, such as floor mats in workplaces and mats used as underlays when installing precision machinery.

[0003] When used for the soles of athletic shoes, polyurethane foam is required to have good resilience in addition to shock absorption. Athletic shoes with soles that have excellent resilience support the kick-off and facilitate foot movement, and are therefore expected to be effective in reducing the accumulation of fatigue during long periods of running or walking. In the present invention, the term "sole" refers to the bottom part of the shoe, and the term "sole material" refers to the constituent material (material) that makes up the sole.

[0004] For example, the invention described in Patent Document 1 aims to provide a polyurethane integral skin foam that has a high impact resilience over a wide temperature range and is excellent in mechanical strength and productivity. Specifically, Patent Document 1 discloses an invention of a polyurethane integral skin foam made from an organic polyisocyanate composition (A), a polyol component (B), a catalyst (C), and a blowing agent (D) as raw materials, in which the organic polyisocyanate composition (A) is a urethane-modified product of diphenylmethane diisocyanate and polytetramethylene ether glycol having a number average molecular weight of 1000 to 3500, and the organic polyisocyanate (a1) has an isocyanate group content of 7 to 25 mass%.

[0005] The invention described in Patent Document 2 aims to provide a polyurethane foam that is durable, has impact absorption and resilience, and is also flex-resistant. Specifically, Patent Document 2 discloses a polyurethane foam made from polyurethane raw materials containing a polyol component, a polyisocyanate component, a blowing agent, a catalyst, and a foam stabilizer, in which the polyol component is polytetramethylene ether glycol having a number-average molecular weight of 300 to 3,000, an average functionality of 2 to 3, and an average hydroxyl value of 50 to 200 mgKOH / g, and the polyisocyanate component contains a specified isocyanate-terminated prepolymer and a specified modified MDI, and the content ratio of the prepolymer to the modified MDI, the isocyanate index, and the compression set are specified within specified ranges. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2016-204635 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-105913 Summary of the Invention [Problem to be solved by the invention]

[0007] Generally, when the resilience of a polyurethane foam is improved, the hardness of the polyurethane foam also tends to increase. When a shoe sole is made using a high-hardness polyurethane foam, a relatively high hardness of the shoe sole is suitable for advanced runners, who have developed muscle strength. Therefore, advanced runners can take advantage of the high resilience to run comfortably. However, beginner runners do not have sufficient muscle strength, so if they use running shoes with hard soles, the impact on their knees will be greater, potentially increasing the risk of injury.

[0008] In addition, attempts have been made to provide polyurethane foams that increase resilience while keeping hardness within a moderate range. However, these have had the problem of difficulty in maintaining high mechanical strength. The soles of athletic shoes require sufficient mechanical strength to withstand repeated use. Therefore, polyurethane foams that have high resilience and low hardness but lack sufficient mechanical strength have been problematic as shoe sole components.

[0009] Furthermore, provision of a polyurethane foam that maintains the balance of impact resilience, hardness, and mechanical strength described above is expected to be useful not only as a shoe sole material but also as, for example, a mat material. From the above perspective, both of the polyurethane foams disclosed in Patent Documents 1 and 2 have room for improvement.

[0010] The present invention has been made in view of the above-mentioned problems, and aims to provide a polyurethane foam that exhibits a moderately low hardness and excellent mechanical strength while maintaining good impact resilience, and a shoe sole member made of the polyurethane foam. [Means for solving the problem]

[0011] The polyurethane foam of the present invention is a polyurethane foam made from polyurethane raw materials including a polyol component, a polyisocyanate component, a blowing agent, a catalyst, and a foam stabilizer, the polyol component contains polytetramethylene ether glycol having a number average molecular weight of 600 or more and 3000 or less, and the proportion of the polytetramethylene ether glycol in the polyol component is 90 mass% or more; The polyisocyanate component is i) an isocyanate group-terminated prepolymer having a number average molecular weight of 500 or more and 2000 or less and an isocyanate group content of 3% by mass or more and 10% by mass or less; ii) modified MDI having an isocyanate group content of 25% by mass or more and 33% by mass or less; Including, The isocyanate group content in the polyisocyanate component is 11% by mass or more and 27% by mass or less. the law of nature, The average cell diameter of the cells constituting the polyurethane foam is more than 100 μm and 150 μm or less, The hardness of the polyurethane foam measured using an Asker rubber hardness tester type C in accordance with JIS K 7312 is less than 50, The polyurethane foam has a rebound resilience of 60% or more as measured in accordance with JIS K 6255. The breaking strength of the polyurethane foam measured in accordance with JIS K 6251 is 1.0 MPa or more, The elongation at break of the polyurethane foam measured in accordance with JIS K 6251 is 400% or more. It is characterized by the following.

[0012] The shoe sole member of the present invention is characterized by being made using the polyurethane foam of the present invention. [Effects of the Invention]

[0013] According to the present invention having the above configuration, it is possible to provide a polyurethane foam that maintains good impact resilience, exhibits a moderately low hardness, and also has excellent mechanical strength. Therefore, the shoe sole member made of the polyurethane foam of the present invention can be preferably used as a shoe sole member for athletic shoes, particularly athletic shoes for beginners. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Polyurethane foam] The polyurethane foam of the present invention is produced using polyurethane raw materials including a polyol component, a polyisocyanate component, a blowing agent, a catalyst, and a foam stabilizer. The polyol component contains polytetramethylene ether glycol (hereinafter also referred to as PTMG) having a number average molecular weight of 600 to 3000. In the present invention, the ratio of PTMG in the polyol component is adjusted to be 90% by mass or more. The polyisocyanate component contains an isocyanate group-terminated prepolymer having predetermined characteristics and a modified MDI having predetermined characteristics, and is adjusted so that the isocyanate group content in the polyisocyanate component is 11% by mass or more and 27% by mass or less. Here, the isocyanate group-terminated prepolymer having predetermined characteristics is an isocyanate group-terminated prepolymer having a number average molecular weight of 500 or more and 2000 or less and an isocyanate group content of 3% by mass or more and 10% by mass or less. Furthermore, the modified MDI having the predetermined characteristics is a modified MDI having an isocyanate group content of 25% by mass or more and 33% by mass or less.

[0015] By satisfying the above-mentioned requirements, the present invention can provide a polyurethane foam having both high impact resilience and low hardness, and also excellent mechanical strength. The polyurethane foam of the present invention will be described in more detail below.

[0016] (Polyol component) The polyol component in the present invention contains 90% by mass or more of PTMG having a number average molecular weight of 600 to 3000. In the present invention, two or more types of PTMG having different number average molecular weights may be mixed and used. When two or more types of PTMG are mixed and used, the number average molecular weight of the PTMG mixture may be adjusted to be within the above range. If the number-average molecular weight of PTMG is less than 600, there is a risk that good impact resilience cannot be obtained. On the other hand, if the number-average molecular weight of PTMG exceeds 3000, the resulting polyurethane foam may have non-uniform cell sizes, making it difficult to exhibit low hardness or may not exhibit good mechanical strength. From the viewpoint of ensuring that the resulting polyurethane foam has low hardness, good flexibility, and is likely to exhibit good impact resilience, the number-average molecular weight of PTMG is preferably in the range of 1000 to 2500. The polyol component in the present invention contains 90% by mass or more of PTMG. Therefore, the number average molecular weight of the polyol component is significantly affected by the number average molecular weight of the contained PTMG. In the present invention, the number average molecular weight of the polyol component is preferably adjusted to be 600 or more and 3,000 or less. Examples of PTMG include ring-opening polymers obtained by cationic polymerization of tetrahydrofuran, and amorphous PTMG in which a dihydric alcohol is copolymerized with tetrahydrofuran polymerization units. The term "amorphous" refers to a liquid state at room temperature (25°C). Examples of amorphous PTMG include copolymers of tetrahydrofuran and alkyl-substituted tetrahydrofuran, and copolymers of tetrahydrofuran and branched glycols. Examples of the alkyl-substituted tetrahydrofuran include 3-methyltetrahydrofuran. Examples of the branched glycol include neopentyl glycol.

[0017] Polyurethane foams molded using PTMG in combination with other polyol components may lack sufficient breaking strength and elongation at break, resulting in insufficient mechanical strength. Shoe sole members made using polyurethane foams with such weak mechanical strength may be susceptible to repeated use and may deteriorate quickly, or the ease of running and fatigue resistance provided by their high rebound resilience and low hardness may not last long.

[0018] As described above, in the present invention, the content of PTMG in the polyol component is 90% by mass or more. From the viewpoint of more sufficiently maintaining high mechanical strength, the content of PTMG in the polyol component is preferably 95% by mass or more, and more preferably 100% by mass.

[0019] Generally, when the PTMG content in the polyol component is high, the molded polyurethane foam tends to be hard, and it is difficult to reduce the hardness. In contrast, the present invention makes it possible to provide a polyurethane foam that has a moderately low hardness, high impact resilience, and excellent mechanical strength by adjusting the isocyanate group content in the polyisocyanate component to 11% by mass or more and 27% by mass or less. The polyurethane foam of the present invention having a high PTMG content can exhibit even better impact resilience, hardness, and mechanical strength by specifying the isocyanate group content within the preferred range described above and adjusting the average cell diameter of the cells constituting the polyurethane foam, as described below, to the range of 100 μm or more and 150 μm or less.

[0020] If necessary, any component such as a crosslinking agent may be added to the polyol component described above. Examples of crosslinking agents that can be used include alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, tetramethylene ether glycol, glycerin, pentaerythritol, trimethylolpropane, monoethanolamine, diethanolamine, isopropanolamine, aminoethylethanolamine, sucrose, sorbitol, glucose, etc. Of these, those with three or more functional groups are particularly preferred.

[0021] (Polyisocyanate component) The polyisocyanate component includes i) an isocyanate-terminated prepolymer having a number average molecular weight of 500 to 2000 and an isocyanate group content of 3 to 10% by mass, and ii) a modified MDI having an isocyanate group content of 25 to 33% by mass. The modified MDI refers to modified diphenylmethane diisocyanate. The ratio of the isocyanate group-terminated prepolymer to the modified MDI (isocyanate group-terminated prepolymer / modified MDI) is not particularly limited, but is preferably 97 / 3 to 3 / 97 by mass, more preferably 85 / 15 to 15 / 85, and even more preferably 80 / 20 to 20 / 80.

[0022] From the perspective of applications of polyurethane foam, when the polyurethane foam is used as a shoe sole member, the mass ratio of isocyanate-terminated prepolymer / modified MDI is preferably 90 / 10 to 50 / 50, more preferably 85 / 15 to 55 / 45, and even more preferably 80 / 20 to 60 / 40, within the above-mentioned range. Thus, when the polyisocyanate component contains the same amount of modified MDI relative to the isocyanate-terminated prepolymer or a smaller amount within a specified range, the polyurethane foam tends to exhibit high breaking strength and elongation at break. This makes it possible to provide a polyurethane foam that is more suitable for shoe sole members that are subjected to repeated impacts.

[0023] i) Isocyanate-terminated prepolymer: The above-mentioned i) isocyanate group-terminated prepolymer (hereinafter also simply referred to as prepolymer) has a number average molecular weight of 500 or more and 2000 or less, and an isocyanate group content of 3% by mass or more and 10% by mass or less. If a prepolymer with a number-average molecular weight exceeding 2000 or an isocyanate group content of less than 3% by mass is used, the foaming properties of the resulting polyurethane foam may be insufficient, resulting in high hardness. Furthermore, such prepolymers have a high viscosity and tend to be difficult to mix with other materials, which may result in poor productivity of the polyurethane foam. On the other hand, if a prepolymer having a number average molecular weight of less than 500 or an isocyanate group content of more than 10% by mass is used, the polyurethane foam produced may foam too much and not exhibit good impact resilience.

[0024] The above-mentioned i) prepolymer is a prepolymer having an isocyanate group at its terminal, obtained by reacting a polyol with a polyisocyanate so that the isocyanate group (NCO group) is in excess. Here, the term "excessive isocyanate group" means that the NCO group content in the prepolymer is in the range of 3% by mass to 10% by mass.

[0025] The polyol may be one material selected from the following α, β, and γ, or a mixture of two or more materials. Among these, polyether polyol is preferred, and polytetramethylene ether glycol is more preferred. α) Polyether polyol or polyester polyol β) Polymer polyols (for example, polyether polyols graft-copolymerized with polyacrylonitrile, acrylonitrile-styrene copolymers, etc.) γ) Among the alcohols listed above as examples of crosslinking agents, those with two functional groups

[0026] Examples of the polyisocyanate include aromatic isocyanates such as diphenylmethane diisocyanate (4,4'-MDI), polymeric MDI (crude MDI), 2,4-tolylene diisocyanate (2,4-TDI), and 2,6-tolylene diisocyanate (2,6-TDI); aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate (HDI); and alicyclic diisocyanates such as isophorone diisocyanate, hydrogenated TDI, and hydrogenated MDI. These can be used alone or in combination of two or more types, with 4,4'-MDI being preferred.

[0027] That is, i) the prepolymer is preferably one obtained by using polytetramethylene ether glycol as the polyol and 4,4'-MDI as the polyisocyanate and reacting them. The prepolymer obtained by reacting polytetramethylene ether glycol with 4,4'-MDI has high crystallinity in the polytetramethylene ether glycol portion. Therefore, the use of such a prepolymer facilitates the production of urethane foam with high impact resilience, and the prepolymer exhibits good compatibility with ii) modified MDI, which is used in combination as a polyisocyanate component. Furthermore, the use of such a prepolymer also facilitates the mixing of the prepolymer obtained by reacting polytetramethylene ether glycol with 4,4'-MDI and the isocyanate component containing modified MDI with the polyol component, polytetramethylene ether glycol, with good compatibility. This facilitates the creation of a uniform molecular structure in the resulting urethane foam, stabilizing its quality.

[0028] ii) Modified MDI: In the present invention, the modified MDI used has an isocyanate group content of 25% by mass or more and 33% by mass or less. If the content is within this range, the modified MDI can be handled as a liquid at room temperature. i) Prepolymer has a high viscosity due to its large molecular weight. However, by mixing i) prepolymer with ii) modified MDI, which is liquid at room temperature, the viscosity of the polyisocyanate component can be appropriately reduced. This allows for good mixability between the polyisocyanate component and the polyol component. If the NCO group content in the modified MDI is less than 25% by mass, the foamability of the polyurethane foam produced may be insufficient. On the other hand, if the NCO group content exceeds 33% by mass, the amount of modified MDI contained in the polyisocyanate component will be small in order to adjust the NCO group content. If the amount of modified MDI is small in this way, it becomes difficult to adjust the viscosity of the polyisocyanate component containing the high-molecular-weight i) prepolymer to an adequately low level, and there is a risk that the mixing ability of the polyisocyanate component and the polyol component when reacted may be poor.

[0029] Specific examples of modified MDI that is liquid at room temperature include polymeric (crude MDI), urethane-modified, urea-modified, allophanate-modified, biuret-modified, carbodiimide-modified, uretonimine-modified, uretdione-modified, isocyanurate-modified, etc. Among these, it is preferable to select polymeric (crude MDI) and / or carbodiimide-modified as the modified MDI because of the excellent molecular (crosslinked) structure after reaction with the polyol component.

[0030] (Isocyanate group content in polyisocyanate component) In the present invention, the polyisocyanate component containing the above-described i) prepolymer and ii) modified MDI has an isocyanate group content of 11% by mass or more and 27% by mass or less. If the isocyanate group content is less than 11% by mass, the resulting polyurethane foam will have a small cell size and high hardness. On the other hand, if the isocyanate group content exceeds 27% by mass, the resulting polyurethane foam will not exhibit good impact resilience. From the above viewpoints, the isocyanate group content is preferably 12% by mass or more and 25% by mass or less, more preferably 12% by mass or more and 21% by mass or less, even more preferably 12% by mass or more and 17% by mass or less, and particularly preferably 12% by mass or more and 15% by mass or less. The polyisocyanate component in the present invention may further contain an isocyanate (third isocyanate) in addition to the above-mentioned i) prepolymer and ii) modified MDI.

[0031] (foaming agent) Water can be used as the blowing agent. The amount added is preferably 0.5 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the polyol component. Examples of the water include ion-exchanged water and distilled water, with ion-exchanged water being preferred. If the amount of blowing agent is less than 0.5 parts by mass, foaming may be insufficient. On the other hand, if the amount of blowing agent is more than 3 parts by mass, foaming may proceed too far, causing the cells of the resulting polyurethane foam to become rough. In this case, problems such as the interior of the resulting polyurethane foam becoming prone to cracking may occur, resulting in poor foam condition and poor resilience.

[0032] (catalyst) The catalyst may be any catalyst that has been conventionally used in the production of polyurethane foams, and examples thereof include amine catalysts such as triethylenediamine and diethanolamine, and metal catalysts such as bismuth catalysts, but are not particularly limited thereto. The amount added is preferably 0.1 parts by mass or more and 5 parts by mass or less relative to 100 parts by mass of the polyol component.

[0033] (Foam stabilizer) In the present invention, the polyol component containing 90% by mass or more of PTMG is reacted with the polyisocyanate component containing an isocyanate group-terminated prepolymer and modified MDI, and the resulting mixture is foamed and cured in a mold (forming die), thereby causing a urethane reaction and foaming, thereby forming a polyurethane foam. A foam stabilizer is contained to improve the cell size of the polyurethane foam obtained by such urethane foaming. There are no particular limitations on the foam stabilizer as long as it is usable in the production of urethane foam. From the viewpoint of easily obtaining good impact resilience, the viscosity of the foam stabilizer is preferably 300 mPa·s (25°C) to 2000 mPa·s (25°C), and more preferably 800 mPa·s (25°C) to 1000 mPa·s (25°C). Silicone-based foam stabilizers with such a suitable viscosity range are particularly preferred. If the viscosity of the foam stabilizer is less than 300 mPa·s (25°C), the foam stabilization effect will be weak, causing the cells to become coarse, and there is a risk that high impact resilience will not be achieved. On the other hand, if the viscosity exceeds 2000 mPa·s (25°C), it will be difficult for the foam stabilizer to be uniformly dispersed in the polyurethane raw materials. As a result, it will be difficult to achieve a uniform cell size in the resulting foam, and there is a risk that the physical properties will change locally.

[0034] When a silicone-based compound having a viscosity within the above-described suitable range is used as a foam stabilizer, the silicone-based compound is preferably added in an amount of 0.5 parts by mass or more and 9 parts by mass or less, and more preferably 0.5 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the polyol component. If the amount is less than 0.5 parts by mass, the foam-stabilizing effect is weak, the cells become coarse, and there is a risk that high impact resilience cannot be obtained. On the other hand, if the amount exceeds 9 parts by mass, the impact resilience of the resulting polyurethane foam may be poor. Furthermore, if the amount exceeds 9 parts by mass, the foam stabilizer may bleed out from the surface of the resulting polyurethane foam, which may result in poor handling, such as impaired adhesion between the polyurethane foam and other components. By adding an amount of the silicone-based compound within the above-mentioned suitable viscosity range of 5 parts by mass or less per 100 parts by mass of the polyol component, the surface of the polyurethane foam will not become sticky, and a high-quality polyurethane foam can be provided.

[0035] In addition to the polyol component, isocyanate component, blowing agent, catalyst, and foam stabilizer, the raw materials for the polyurethane foam of the present invention may also contain additives commonly used in the production of polyurethane foams, such as plasticizers, fillers, antioxidants, defoamers, compatibilizers, colorants, stabilizers, and ultraviolet absorbers, as needed, within the range in which the effects of the present invention can be obtained.

[0036] (Polyurethane foam) Average cell bubble diameter: The polyurethane foam of the present invention preferably has an average cell diameter of 100 μm to 150 μm. By intentionally adjusting the cell diameter to a slightly larger value, it is easy to provide a polyurethane foam having high resilience, low hardness, and excellent mechanical properties such as breaking strength and elongation at break. If the average cell diameter is less than 100 μm, mechanical properties will be impaired, and if the average cell diameter is more than 150 μm, high impact resilience will be difficult to achieve. The average cell diameter is more preferably more than 100 μm and not more than 150 μm, even more preferably more than 100 μm and not more than 135 μm, even more preferably more than 100 μm and not more than 130 μm, and particularly preferably more than 100 μm and not more than 120 μm.

[0037] The average cell diameter can be determined by the following method. First, a polyurethane foam is cut at a randomly selected position to expose the cut surface. An area of ​​predetermined dimensions is randomly selected from the cut surface to define the selected area. The area of ​​predetermined dimensions is, for example, a rectangular area 4 mm long and 3 mm wide. The number of cells (cells) present in the selected area (total number of cells) and the diameter of each cell (diameter of each cell) are measured using a microscope. The arithmetic mean value of the cell diameters measured as described above is calculated, and this is defined as the average cell diameter in the present invention.

[0038] There are no particular limitations on the method for adjusting the average cell diameter of a polyurethane foam. For example, by adjusting the amount of catalyst or blowing agent added, a polyurethane foam exhibiting an average cell diameter within the desired range can be molded.

[0039] hardness: The hardness of the polyurethane foam of the present invention is preferably less than 50, more preferably less than 47, from the viewpoint of exhibiting appropriate flexibility. Shoe sole members made using polyurethane foams with a hardness of less than 50 are suitable as components for the soles of athletic shoes for beginners. Use of such shoe sole members reduces the burden on the knees and other parts of the body when the shoe touches the ground. From the viewpoint of maintaining good shock absorption, the hardness is preferably 35 or more, and more preferably 40 or more. A polyurethane foam with too low a hardness cannot fully absorb shock, and when used as a shoe sole member, there is a risk of causing a malfunction. When the polyurethane foam of the present invention is used as a mat member, the hardness is also preferably in the above-mentioned range. The hardness of the polyurethane foam of the present invention is measured in accordance with JIS K 7312 under a temperature condition of 23±2° C. using an Asker rubber hardness tester, type C.

[0040] Apparent density: The apparent density of the polyurethane foam of the present invention is not particularly limited, but is preferably 0.30 g / cm 3 More than 0.35g / cm 3 It is preferable that the apparent density is in the range below. Furthermore, in the present invention, it is more preferable that the apparent density is in the above range and the average cell diameter is 100 μm or more and 150 μm or less. The apparent density of the polyurethane foam of the present invention is measured in accordance with JIS K 7222.

[0041] Rebound elasticity: The rebound resilience of the polyurethane foam of the present invention is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more, from the viewpoint of achieving good kick-off and smooth foot movement when the polyurethane foam is used in shoe soles or mats. On the other hand, in the present invention, there is no particular limitation on the upper limit of the rebound resilience, but from the viewpoint of easily achieving a good balance between hardness and mechanical properties, it is preferably less than 80%, more preferably less than 75%, and even more preferably less than 70%.

[0042] The impact resilience of the polyurethane foam of the present invention is measured in accordance with JIS K 6255.

[0043] It is particularly preferable that the polyurethane foam of the present invention has a hardness of less than 50 and a rebound resilience of 50% or more. Such a polyurethane foam can provide an excellent shoe sole that is easy for even beginners to run in and that effectively absorbs impact upon landing and reduces strain on the knees and other parts of the body.

[0044] Breaking Strength: From the viewpoint of improving the durability of articles made using the polyurethane foam, the breaking strength of the polyurethane foam of the present invention is preferably 1.0 MPa or more, more preferably 1.5 MPa or more, and even more preferably 2.0 MPa or more. In particular, when a polyurethane foam having a breaking strength of 1.5 MPa or more is used as a sole material for athletic shoes, the sole can be prevented from deteriorating in a short period of time even when used under severe conditions such as repeated impact loads or bending.

[0045] The breaking strength of the polyurethane foam of the present invention is measured in accordance with JIS K 6251.

[0046] Elongation at break: The elongation at break of the polyurethane foam of the present invention is not particularly limited, but when used in applications where repeated flexing is expected, such as shoe soles, it is preferably 300% or more, more preferably 350% or more, and even more preferably 400% or more.

[0047] The elongation at break of the polyurethane foam of the present invention is measured in accordance with JIS K 6251.

[0048] Maximum shock load: From the viewpoint of ensuring good impact absorption of articles made using the polyurethane foam, the maximum impact load of the polyurethane foam of the present invention is preferably 1.5 kN or less as measured as follows: The maximum impact load can be measured using a drop impact test on a test piece cut to a thickness of 12.5 mm, in which a bullet-shaped weight w (made of iron, 5.1 kg) is struck from a height of 50 mm using an Instron product called "dynatup GRC8200."

[0049] Flexibility: The flexibility of the polyurethane foam of the present invention is not particularly limited, but when it is used in applications where repeated flexing is expected, such as shoe soles, it is preferable that it can be flexed 10,000 times or more before cracks appear in the following test. The test is carried out by bonding a test piece cut to a thickness of 6 mm to a 2 mm thick Texon board (manufactured by Bontex, product name "#347"), and bending the test piece at an angle of 90° at a rate of 100 flexes per minute.

[0050] [Sole parts] The polyurethane foam of the present invention described above can be used in various applications, among which the polyurethane foam of the present invention is preferably used as a shoe sole material because it exhibits good impact resilience, low hardness, and excellent mechanical properties. A shoe sole constructed using a shoe sole member made of the polyurethane foam of the present invention supports the user's push-off, facilitates leg movement, and exhibits good flexibility, providing good comfort and reducing the occurrence of injuries. Therefore, shoes equipped with the above-mentioned shoe sole are excellent as shoes for a variety of exercises, and are particularly suitable for beginners and the elderly. The sole member of the present invention may be a component that forms part of the sole, or may form the entire sole. Here, the sole may be a single, integral part of the bottom of the shoe, or may be composed of multiple parts such as an insole and / or midsole and an outsole. For example, the entirety of one or more parts that form the sole, such as the insole, midsole, or outsole, may be composed of the sole member of the present invention, or any part of one part may be composed of the sole member of the present invention.

[0051] [mat] The polyurethane foam of the present invention can also be suitably used as a component of a mat, since the polyurethane foam of the present invention exhibits good impact resilience, low hardness, and excellent mechanical properties, and is therefore effective in mats, particularly floor mats. When a mat made from the polyurethane foam of the present invention is laid on a floor and the person works, walks, or stands on the floor for a long period of time, the accumulation of fatigue is reduced. [Example]

[0052] Liquid A was prepared by mixing the polyol component, catalyst, foam stabilizer, and blowing agent according to the formulation shown in Table 1. Liquid A and liquid B (polyisocyanate component) were mixed in the formulation shown in Table 1 and poured into a mold. The mixture was reacted at a mold temperature of 40°C, and then demolded to obtain a polyurethane foam. The numerical values ​​showing the composition of materials in Table 1 are in parts by mass.

[0053] <Polyol component> PTMG2000: Polytetramethylene ether glycol (number average molecular weight 2000, hydroxyl value 57.2 mg KOH / g, average functionality 2) <Catalyst> Amine catalyst: Triethylenediamine <Foam stabilizer> Silicone compounds: Viscosity: 900 mPa·s (25°C) <Foaming agent> Ion-exchanged water <Polyisocyanate component> Isocyanate-terminated prepolymer (PTMG2000) reacted with 4,4'-MDI Prepolymer: number average molecular weight 1000, average functionality 2, isocyanate group content 8.01% by mass Carbodiimide-modified MDI (carbodiimide-modified, average functionality 2, isocyanate group content 28.2%)

[0054] The polyurethane foams obtained in each of the Examples and Comparative Examples were appropriately cut to prepare test pieces, and the following measurements were carried out. The measurement results are shown in Table 1. <Average cell diameter (μm)> The resulting polyurethane foam was cut at randomly selected positions to expose the cut surface. A rectangular area of ​​4 mm x 3 mm was randomly selected from the cut surface to define the selected area. The number of cells (air bubbles) present within the selected area (total number of cells) and the diameter of each cell (diameter of each air bubble) were measured using a microscope. The arithmetic mean value of the measured cell diameters was calculated and used as the average air bubble diameter. Apparent density (g / cm 3 )> A test piece cut into a rectangular parallelepiped of 15 mm x 15 mm x 10 mm was used to measure the apparent density in accordance with JIS K 7222. <Hardness> Asker C hardness Using test pieces cut to a thickness of 12.5 mm, the hardness (Asker C hardness) of the polyurethane foam was measured using an Asker rubber hardness tester, type C, in accordance with JIS K 7312. <Rebound elasticity (%)> Using test pieces cut to a thickness of 12.5 mm, the impact resilience was measured in accordance with JIS K 6255. <Breaking strength (MPa)> Using test pieces cut into dumbbell shapes (type 2), the breaking strength of the polyurethane foam was measured in accordance with JIS K 6251. <Elongation at break (%)> Using test pieces cut into dumbbell shapes (type 2), the elongation at break of the polyurethane foam was measured in accordance with JIS K 6251. <Maximum impact load (kN)> In a drop impact test on a test piece cut to a thickness of 12.5 mm, a bullet-shaped weight w (made of iron, 5.1 kg) was hit from a height of 50 mm, and the maximum impact load measured using an Instron product called "dynatup GRC8200" was used as an index. A smaller maximum impact load indicates better impact absorption, and in the present invention, a maximum impact load of 1.5 kN or less was considered to indicate good impact absorption. <Flexibility test (10,000 times)> A test specimen was prepared by bonding a test piece cut to a thickness of 6 mm to a 2 mm thick Texon board (trade name "#347" manufactured by Bontex Corporation). The test specimen was bent at an angle of 90° at a rate of 100 times per minute, and the number of times until cracks appeared was counted. In the present invention, bending resistance was determined to be good if it could be bent 10,000 times or more.

[0055] [Table 1] [Industrial Applicability]

[0056] The polyurethane foam of the present invention has excellent resilience while maintaining low hardness and excellent mechanical properties such as breaking strength and elongation at break. Furthermore, since the polyurethane foam of the present invention has excellent impact absorption and flexibility, it is suitable for use as a shoe sole material. In addition, the polyurethane foam of the present invention is widely used in applications requiring impact absorption, resilience, moderate flexibility, and good mechanical strength, such as matting, helmet interiors, protectors, vehicle shock absorbers, and flooring materials.

[0057] The present invention described above encompasses the following technical ideas. (1) A polyurethane foam made from polyurethane raw materials including a polyol component, a polyisocyanate component, a blowing agent, a catalyst, and a foam stabilizer, the polyol component contains polytetramethylene ether glycol having a number average molecular weight of 600 or more and 3000 or less, and the proportion of the polytetramethylene ether glycol in the polyol component is 90 mass% or more; The polyisocyanate component is i) an isocyanate group-terminated prepolymer having a number average molecular weight of 500 or more and 2000 or less and an isocyanate group content of 3% by mass or more and 10% by mass or less; ii) modified MDI having an isocyanate group content of 25% by mass or more and 33% by mass or less; Including, The polyurethane foam is characterized in that the polyisocyanate component has an isocyanate group content of 11% by mass or more and 27% by mass or less. (2) The polyurethane foam according to (1) above, wherein the average cell diameter of the cells constituting the polyurethane foam is 100 μm or more and 150 μm or less. (3) The polyurethane foam according to (1) or (2) above, wherein the proportion of polytetramethylene ether glycol in the polyol component is 95% by mass or more. (4) The hardness of the polyurethane foam measured using an Asker rubber hardness tester type C in accordance with JIS K 7312 is less than 50; The polyurethane foam according to any one of (1) to (3) above, wherein the polyurethane foam has a rebound resilience of 60% or more as measured in accordance with JIS K 6255. (5) The polyurethane foam according to any one of (1) to (4) above, wherein the breaking strength of the polyurethane foam measured in accordance with JIS K 6251 is 1.0 MPa or more. (6) The polyurethane foam according to any one of (1) to (5) above, wherein the elongation at break of the polyurethane foam measured in accordance with JIS K 6251 is 400% or more. (7) A shoe sole member made from the polyurethane foam according to any one of (1) to (6) above.

Claims

1. A polyurethane foam made from polyurethane raw materials including a polyol component, a polyisocyanate component, a blowing agent, a catalyst, and a foam stabilizer, the polyol component contains polytetramethylene ether glycol having a number average molecular weight of 600 or more and 3,000 or less, and the proportion of the polytetramethylene ether glycol in the polyol component is 90 mass% or more; The polyisocyanate component is i) an isocyanate group-terminated prepolymer having a number average molecular weight of 500 or more and 2000 or less and an isocyanate group content of 3% by mass or more and 10% by mass or less; ii) modified MDI having an isocyanate group content of 25% by mass or more and 33% by mass or less; Including, the isocyanate group content in the polyisocyanate component is 11% by mass or more and 27% by mass or less, The average cell diameter of the cells constituting the polyurethane foam is more than 100 μm and 150 μm or less, The hardness of the polyurethane foam measured using an Asker rubber hardness tester type C in accordance with JIS K 7312 is less than 50, The polyurethane foam has a rebound resilience of 60% or more as measured in accordance with JIS K 6255, The breaking strength of the polyurethane foam measured in accordance with JIS K 6251 is 1.0 MPa or more, A polyurethane foam characterized in that the elongation at break of the polyurethane foam measured in accordance with JIS K 6251 is 400% or more.

2. 2. The polyurethane foam according to claim 1, wherein the proportion of polytetramethylene ether glycol in the polyol component is 95% by mass or more.

3. A shoe sole member formed using the polyurethane foam according to claim 1 or 2.

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