Low-resilience polyurethane foam

Abstract

This low-resilience polyurethane foam is obtained by causing a reaction of a starting material composition which contains a polyisocyanate component and a polyol component, wherein the polyisocyanate component contains an n-functional isocyanate (n ≥ 3) and a bifunctional isocyanate prepolymer. It is preferable that the polyisocyanate component has an average number of functional groups of 2.05 or more. It is also preferable that the polyol component contains one or more high molecular weight polyols and one or more low molecular weight polyols.

Description

Low-resilience polyurethane foam

[0001] The present invention relates to a low-resilience polyurethane foam.

[0002] Polyurethane refers to a polymeric compound having a urethane bond (-NH-C(O)O-). Polyurethane is generally obtained by reacting the hydroxyl group (-OH) of a polyol with the isocyanate group (-NCO) of a polyisocyanate. It is known that polyurethane exhibits a variety of properties by optimizing the type of polyol and / or polyisocyanate. For this reason, polyurethane is used in various automobile parts, synthetic leather, paints, adhesives, etc. Furthermore, polyurethane foam, which is made by foaming polyurethane, is used in insulation materials, cushioning materials, etc.

[0003] Polyurethane foams are broadly classified into: (a) flexible polyurethane foams with interconnected cells, low compression hardness, and flexibility; (b) rigid polyurethane foams with closed cells, highly cross-linked molecular structure, and lacking the high elasticity of flexible polyurethane foams; and (c) semi-rigid polyurethane foams with properties intermediate between rigid and flexible.

[0004] Among these, flexible polyurethane foams exhibit viscoelasticity. Flexible polyurethane foams with reduced elasticity and increased viscosity are also called "low resilience (SR: slow recovery) polyurethane foams." Low resilience polyurethane foams have excellent shock absorption properties and are therefore used in shock absorbers, protective mats, buffer materials, vibration absorbers, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, bedding cushions, etc.

[0005] Various proposals have been made regarding such low-resilience polyurethane foams. For example, Patent Document 1 discloses a low-resilience polyurethane foam resin obtained by reacting a composition containing a polyol having an average functionality of 2 to 3 and a hydroxyl value of 20 to 200 mgKOH / g, an isocyanate, resin microballoons containing no chlorine atoms, and a catalyst.

[0006] The document states that: (A) low-hardness polyurethanes are sticky and stick to the hands, making them difficult to use; (B) when microballoons are added to low-hardness polyurethanes, they do not stick to the hands as easily, but the microballoons float up during the curing of the urethane resin, causing a difference in density between the top and bottom of the molded article; and (C) when a mixture containing 10% by weight or more of an alkylene oxide adduct of a polyhydric phenol having 2 to 3 functional groups is used as the polyol, the difference in density between the top and bottom of the molded article caused by the floating of microballoons can be reduced.

[0007] Patent Document 2 discloses a sheet that is not made of low-resilience polyurethane foam but has a surface layer made of a polyurethane film and a foam layer made of polyurethane foam, the average cell diameter of the polyurethane foam being 50 μm or more and 300 μm or less. The document states that the sheet having a surface layer and a foam layer has excellent abrasion resistance and impact absorption properties.

[0008] Low-resilience polyurethane foams have come to be used as cushioning materials for smartphones, game consoles, and other devices. These cushioning materials are very thin, about 0.2 to 1.0 mm thick, and required physical properties include low compressive residual strain and high tensile strength in addition to SR properties. However, no low-resilience polyurethane foams that satisfy all of these requirements have been proposed to date. In particular, SR properties and tensile strength are in a trade-off relationship. That is, attempting to develop SR properties reduces tensile strength, while increasing tensile strength prevents SR properties from being developed. Therefore, it is generally difficult to achieve both SR properties and tensile strength.

[0009] JP 2016-113537 A JP 2022-100615 A

[0010] The problem to be solved by the present invention is to provide a low-resilience polyurethane foam having excellent low resilience. Another problem to be solved by the present invention is to provide a low-resilience polyurethane foam having high tensile strength in addition to excellent low resilience. A further problem to be solved by the present invention is to provide a low-resilience polyurethane foam having small compression set in addition to excellent low resilience.

[0011] In order to solve the above problems, the low-resilience polyurethane foam according to the present invention is obtained by reacting a raw material composition containing a polyisocyanate component and a polyol component, and the polyisocyanate component contains an n-functional isocyanate (n≧3) and a difunctional isocyanate prepolymer.

[0012] When producing low-resilience polyurethane foam, a mixture containing an n-functional isocyanate and a difunctional isocyanate prepolymer as a polyisocyanate component exhibits excellent SR properties. This is thought to be because the use of a long molecular bifunctional isocyanate prepolymer as one of the polyisocyanate components reduces the rigidity of the polyurethane chain structure.

[0013] Furthermore, in the case of producing a low-resilience polyurethane foam using a raw material mixture containing an n-functional isocyanate and a difunctional isocyanate prepolymer, if the isocyanate index is relatively increased and / or the number of branches of the raw material composition is optimized, the tensile strength is improved and / or the compression set is reduced while maintaining excellent SR properties.

[0014] The reason for the improvement in tensile strength is thought to be that the number of crosslinking points is maintained at an appropriate value by optimizing the isocyanate index and / or the number of branches, and the reason for the reduction in compression set is thought to be that (a) the reactivity is improved by relatively increasing the isocyanate index, which reduces the residual polyol component and tackiness, and (b) the necessary minimum elasticity is ensured by optimizing the number of branches.

[0015] An embodiment of the present invention will be described in detail below. [1. Low-resilience polyurethane foam] The low-resilience polyurethane foam according to the present invention can be obtained by reacting a raw material composition containing a polyisocyanate component and a polyol component that satisfy predetermined conditions.

[0016] [1.1. Raw Material Composition] [1.1.1. Polyisocyanate Component] The "polyisocyanate component" is one of the main raw materials for producing the low-resilience polyurethane foam according to the present invention, and refers to a mixture of two or more polyisocyanates. In the present invention, the polyisocyanate component contains an n-functional isocyanate (n≧3) and a difunctional isocyanate prepolymer. The polyisocyanate component may consist only of an n-functional isocyanate and a difunctional isocyanate prepolymer, or may further contain a difunctional isocyanate in addition to these.

[0017] [A. n-functional isocyanate] "n-functional isocyanate" refers to a polyisocyanate having three or more isocyanate groups. When the raw material composition contains an n-functional isocyanate, the raw material composition has an appropriate number of branches, and the polymer chains are appropriately crosslinked. As a result, it is believed that the tensile strength of the low-resilience polyurethane foam is improved or the compression set is reduced.

[0018] Examples of n-functional isocyanates include polynuclear compounds of 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 1-methylbenzol-2,4,6-triisocyanate, 1,3,5-trimethylbenzol-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, and triphenylmethane-4,4',4"-triisocyanate. The raw material composition may contain any one of these n-functional isocyanates, or may contain two or more of them.

[0019] [B. Bifunctional Isocyanate Prepolymer] An "isocyanate prepolymer" refers to a compound obtained by reacting a polyol with a polyisocyanate and having an isocyanate group at its terminal. A "bifunctional isocyanate prepolymer" refers to a compound among isocyanate prepolymers that has two isocyanate groups. In other words, a "bifunctional isocyanate prepolymer" refers to a linear compound (OCN-R'-NH-C(O)O-R-O(O)C-NH-R'-NCO) obtained by reacting one molecule of a diol (HO-R-OH) with two molecules of a bifunctional isocyanate (OCN-R'-NCO). Because bifunctional isocyanate prepolymers have a long molecular length, when they are used to produce low-resilience polyurethane foams, the rigidity of the polyurethane chain structure decreases. As a result, it is believed that the SR properties of the low-resilience polyurethane foams are further improved.

[0020] In the present invention, the type of bifunctional isocyanate prepolymer is not particularly limited, and an optimum one can be selected depending on the purpose. Examples of bifunctional isocyanate prepolymers include: (a) urethane-modified MDI, allophanate-modified MDI, biuret-modified MDI, isocyanurate-modified MDI, urea-modified MDI, and carbodiimide-modified MDI; and (b) urethane-modified TDI, allophanate-modified TDI, biuret-modified TDI, isocyanurate-modified TDI, urea-modified TDI, and carbodiimide-modified TDI. The raw material composition may contain any one type of these bifunctional isocyanate prepolymers, or may contain two or more types.

[0021] [C. Bifunctional Isocyanate] The term "bifunctional isocyanate" refers to a compound having two isocyanate groups, other than a bifunctional isocyanate prepolymer.

[0022] For example, commercially available polymeric MDI contains 4,4'-MDI in addition to a polynuclear form of 4,4'-MDI. Furthermore, commercially available MDI prepolymers contain unreacted 4,4'-MDI in addition to a linear compound (urethane-modified MDI) obtained by reacting 4,4'-MDI with a low-molecular-weight diol. The raw material composition may contain one or more types of such difunctional isocyanates in addition to the n-functional isocyanate and difunctional isocyanate prepolymer described above. Specific examples of difunctional isocyanates include the following:

[0023] (a) Difunctional aromatic isocyanates: 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate (4,4'-MDI), 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, xylylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, and the like.

[0024] (b) Difunctional alicyclic isocyanates: cyclohexane-1,4-diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, methylcyclohexane diisocyanate, and the like.

[0025] (c) Difunctional aliphatic isocyanates: butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropylene diisocyanate, methylene diisocyanate, lysine isocyanate, and the like.

[0026] [D. Average Number of Functional Groups of Polyisocyanate Component] "Average number of functional groups of the polyisocyanate component" refers to the average number of functional groups per polyisocyanate molecule. The average number of functional groups of the polyisocyanate component affects the SR property, tensile strength, and / or compression set. Therefore, it is preferable to select an optimal value for the average number of functional groups of the polyisocyanate component depending on the purpose.

[0027] Generally, the greater the average number of functional groups in the polyisocyanate component, the higher the tensile strength and / or the smaller the compression set. To achieve these effects, the average number of functional groups in the polyisocyanate component is preferably 2.05 or more. The average number of functional groups is more preferably 2.07 or more, and even more preferably 2.10 or more. On the other hand, if the average number of functional groups in the polyisocyanate component is too large, the SR properties may decrease. Therefore, the average number of functional groups in the polyisocyanate component is preferably 3.00 or less. The average number of functional groups is more preferably 2.90 or less, 2.80 or less, 2.70 or less, 2.60 or less, 2.50 or less, or 2.40 or less.

[0028] [E. Isocyanate Index] The term "isocyanate index" refers to the value obtained by multiplying the ratio of the equivalent weight of isocyanate groups of the polyisocyanate in the raw material composition to the equivalent weight of active hydrogen groups in the raw material composition by 100.

[0029] Generally, the higher the isocyanate index, the higher the tensile strength but the lower the SR property. However, the low-resilience polyurethane foam of the present invention uses polyisocyanates with different numbers of functional groups and optimizes the molecular structure of the polyisocyanates, so it exhibits excellent SR property despite having a higher isocyanate index than conventional foams. In particular, optimizing the average number of functional groups of the polyisocyanate component makes it possible to achieve a high level of compatibility between excellent SR property, high tensile strength, and low compression set.

[0030] To obtain high tensile strength, the isocyanate index is preferably 80 or more. The isocyanate index is more preferably 85 or more, 90 or more, or 95 or more. On the other hand, if the isocyanate index is too high, the number of crosslinking points becomes excessive, which may result in a decrease in SR properties. Therefore, the isocyanate index is preferably 130 or less. The isocyanate index is more preferably 125 or less, 120 or less, or 115 or less.

[0031] [1.1.2. Polyol Component] The "polyol component" refers to another main raw material for producing the low-resilience polyurethane foam according to the present invention. The raw material composition may contain one type of polyol, or two or more types.

[0032] [A. Materials] The type of polyol contained in the polyol component is not particularly limited, and an optimum material can be selected depending on the purpose. The polyol may be any of ether-based polyol, ester-based polyol, ether ester-based polyol, and polymer polyol. Specific examples of polyols include the following:

[0033] Examples of ether polyols include: (a) polyhydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, glycerin, pentaerythritol, trimethylolpropane, sorbitol, and sucrose; and (b) polyether polyols in which alkylene oxides such as ethylene oxide and propylene oxide are added to polyhydric alcohols.

[0034] Examples of ester polyols include: (a) polyester polyols obtained by polycondensation of an aliphatic carboxylic acid such as malonic acid, succinic acid, or adipic acid, or an aromatic carboxylic acid such as phthalic acid, with an aliphatic glycol such as ethylene glycol, diethylene glycol, or propylene glycol; and (b) phthalate ester polyols.

[0035] Examples of polymer polyols include: (a) a dispersion of polymer particles obtained by polymerizing ethylenically unsaturated monomers such as acrylonitrile and styrene in a polyol such as polyether polyol; and (b) a core-shell rubber (CSR)-dispersed polyol. A CSR-dispersed polyol refers to a dispersion of core-shell rubber (CSR) particles in a polyol. Specifically, core-shell rubber particles refer to rubber particles in which a particulate core component, primarily composed of a crosslinked rubber-like polymer, is partially or entirely coated with a shell component by graft polymerizing a polymer different from the core component onto the surface of the particulate core component. Examples of core components include crosslinked rubber particles. The type of rubber used for the crosslinked rubber particles is not limited, and examples include butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, nitrile rubber, styrene rubber, synthetic natural rubber, and ethylene propylene rubber. Examples of shell components include polymers polymerized from one or more monomers selected from the group consisting of acrylic acid esters, methacrylic acid esters, and aromatic vinyl compounds. The shell component is preferably graft-polymerized onto the core component and chemically bonded to the polymer constituting the core component. In consideration of dispersibility in polyol, the core-shell rubber particles preferably contain an MBS (methyl methacrylate-butadiene-ethylene copolymer) polymer.

[0036] [B. Number Average Molecular Weight, Molecular Weight] The low-resilience polyurethane foam may be produced using one type of polyol, or may be produced using two or more types of polyols. When the low-resilience polyurethane foam is produced using two or more types of polyols, the polyol component may be: (a) a mixture of two or more types of polyols having the same number average molecular weight or molecular weight, or (b) a mixture of two or more types of polyols having different number average molecular weights or molecular weights.

[0037] In order to obtain a low-resilience polyurethane foam with excellent SR properties, the polyol component preferably contains one or more high-molecular-weight polyols and one or more low-molecular-weight polyols. Here, "high-molecular-weight polyol" refers to a polyol having a number-average molecular weight of 1,000 or more, and "low-molecular-weight polyol" refers to a polyol having a number-average molecular weight or molecular weight of less than 1,000. "Molecular weight" refers to the formula weight based on the chemical formula.

[0038] The number average molecular weight (Mn) of each of the ith (i≧1) high molecular weight polyols is preferably 1500 or more, more preferably 2000 or more. The number average molecular weight or molecular weight (Mn) of each of the jth (j≧1) low molecular weight polyols is preferably 800 or less, more preferably 600 or less.

[0039] [C. Number average molecular weight ratio] The "number average molecular weight ratio of polyol components" refers to the ratio of the total number average molecular weight (Mn Ltotal ) to the total number average molecular weight (Mn Htotal ) ratio (= Mn Htotal / Mn Ltotal )

[0040] When the number average molecular weight of the ith (i≧1) high molecular weight polyol is Mn and the number ratio of the ith high molecular weight polyol to the total high molecular weight polyols is ni, Mn Htotal Similarly, if the number average molecular weight or molecular weight of the jth (j≧1) low molecular weight polyol is Mnj and the number ratio of the jth low molecular weight polyol to all low molecular weight polyols is nj, then Mn Ltotal =Σnj × Mnj.

[0041] The number-average molecular weight ratio of the polyol components mainly affects the SR properties of low-resilience polyurethane foams. When producing low-resilience polyurethane foams using two or more polyols with different molecular weights, the SR properties generally improve as the number-average molecular weight ratio increases. To achieve this effect, the number-average molecular weight ratio of the polyol components is preferably 2.0 or more. The number-average molecular weight ratio is more preferably 2.5 or more, 3.0 or more, 3.5 or more, or 4.0 or more.

[0042] On the other hand, if the number average molecular weight ratio of the polyol components becomes too large, problems such as: (a) temperature dependency increases due to differences in the glass transition points of the polyols, (b) SR properties are impaired due to separation of the hard and soft segments of the resin skeleton, and (c) compression set is deteriorated may occur. Therefore, the number average molecular weight ratio is preferably 10 or less.

[0043] [D. Content of low molecular weight polyol] The "content of low molecular weight polyol" refers to the total weight (W) of the polyol component when the polyol component is a mixture of a high molecular weight polyol and a low molecular weight polyol. T ) to the total weight of low molecular weight polyols (W L ) ratio (= W L ×100 / W H )

[0044] The content of the low molecular weight polyol mainly affects the SR property of the low resilience polyurethane foam. If the content of the low molecular weight polyol is too low, the SR property may decrease. Therefore, the content of the low molecular weight polyol is preferably 40.0 mass% or more. The content is more preferably 45.0 mass% or more, or 50 mass% or more. On the other hand, if the content of the low molecular weight polyol is excessive, the SR property may decrease. Therefore, the content of the low molecular weight polyol is preferably 75.0 mass% or less. The content is more preferably 70.0 mass% or less, or 65.0 mass% or less.

[0045] [1.1.3. Number of branches] The "number of branches" refers to the number of branches per 1 mol of molecules contained in the raw material composition, and is expressed by the following formula: Number of branches (number / mol) = Σ (number of functional groups - 2) × (number of parts added / molecular weight)

[0046] The number of branches in the raw material composition affects the SR property, tensile strength, and compressive set. Generally, the smaller the number of branches, the more easily the SR property is exhibited. However, if the number of branches is too small, the tensile strength may decrease or the compressive set may become small. Therefore, the number of branches is preferably 0.010 or more. The number of branches is more preferably 0.012 or more, 0.014 or more, or 0.016 or more. On the other hand, if the number of branches is excessively large, the SR property may decrease. Therefore, the number of branches is preferably 0.050 or less. The number of branches is more preferably 0.048, 0.046 or less, or 0.044 or less.

[0047] [1.1.4. Other Components] The raw material composition for producing a low-resilience polyurethane foam may contain the following components in addition to the polyisocyanate component and polyol component described above. The amount of each component added is not particularly limited, and it is preferable to select an optimal amount depending on the purpose.

[0048] [A. Resinification Catalyst] The raw material composition may contain a resinification catalyst. The resinification catalyst is a catalyst for promoting the reaction between the OH group of the polyol and the NCO group of the polyisocyanate. In the present invention, the type of the resinification catalyst is not particularly limited. Examples of the resinification catalyst include an amine catalyst and a metal catalyst.

[0049] Examples of the amine catalyst include 1,2-dimethylimidazole, 1-methylimidazole, N,(N',N'-dimethylaminoethyl)-morpholine, tetramethylguanidine, dimethylaminoethanol, triethylenediamine, N-methyl-N'-(2hydroxyethyl)-piperazine, N,N,N',N'-tetramethylpropane-1,3-diamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N",N"-pentamethyl-(3-aminopropyl)ethylenediamine, N,N'-dimethylpiperazine, N,N,N',N'-tetramethylhexane-1,6-diamine, N,N,N',N",N"-pentamethyldipropylene-triamine, N-(2-hydroxyethyl)morpholine, ethylene glycol bis(3-dimethyl)-aminopropyl ether, N,N-dimethylcyclohexylamine, N-methyl-N'-(2-dimethylamino)ethylpiperazine, etc.

[0050] Examples of metal catalysts include: (a) tin catalysts such as stannous octoate and dibutyltin dilaurate; (b) phenylmercury propionate; and (c) lead octenate.

[0051] [B. Foam Stabilizer] The raw material composition may contain a foam stabilizer. The foam stabilizer facilitates the dispersion of entrained gas during mechanical foaming of polyurethane, stabilizes bubbles, and adjusts the bubble structure. In the present invention, the type of foam stabilizer is not particularly limited. Examples of foam stabilizers include: (a) silicone-based foam stabilizers; (b) fluorine-containing compound-based foam stabilizers; (c) anionic surfactants such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate; and (d) phenol-based compounds.

[0052] [C. Filler] The raw material composition may contain a filler. The filler increases the volume of the polyurethane foam, reduces the amount of polyurethane raw material used per unit volume, and reduces the cost of the polyurethane foam. In the present invention, the type of filler is not particularly limited. Examples of fillers include aluminum hydroxide, calcium carbonate, talc, and clay.

[0053] [D. Moisture Absorbent] The raw material composition may contain a moisture absorbent. The moisture absorbent is intended to remove moisture contained in the composition and inhibit the polyisocyanate from reacting with moisture. When the polyisocyanate reacts with moisture, CO2 gas is generated, which may make it difficult to control bubbles. In the present invention, the type of moisture absorbent is not particularly limited. Examples of moisture absorbents include molecular sieves, synthetic zeolites, silica powder, alumina powder, lithium hydroxide powder, and barium hydroxide powder.

[0054] [E. Antioxidant] The raw material composition may contain an antioxidant. The antioxidant is used to suppress deterioration of the polyurethane due to oxidation. In the present invention, the type of antioxidant is not particularly limited. Examples of antioxidants include hindered phenol-based antioxidants, amine-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants.

[0055] [1.2. Reaction of Raw Material Composition] The low-resilience polyurethane foam according to the present invention is produced using a mechanical froth method. The "mechanical froth method" refers to a method comprising the steps of: (a) using a high-shear mixer to mix a raw material composition while blowing in an inert gas to produce a foaming raw material composition containing fine bubbles; (b) applying the foaming raw material composition to the surface of a substrate (e.g., a PET film); and (c) heating the coating to a predetermined temperature to cure it. In the present invention, the reaction conditions for the raw material composition are not particularly limited, and optimal conditions can be selected depending on the purpose.

[0056] [1.3. Properties] [1.3.1. Thickness] In the present invention, the thickness of the low-resilience polyurethane foam is not particularly limited, and an optimal thickness can be selected depending on the purpose. When the low-resilience polyurethane foam is used as a cushioning material for electronic or electrical equipment, the thinner the thickness, the better. By using the low-resilience polyurethane foam of the present invention, it is possible to produce a sheet that not only has excellent SR properties but also has a thickness of 2.0 mm or less. When the production conditions are optimized, the thickness can be 1.5 mm or less, or even 1.0 mm or less.

[0057] [1.3.2. Return Speed] "Return speed" refers to the time it takes for a sample to return to its original shape when a 1 kg load is applied for 5 seconds to a compression surface with a diameter of 15 mm using a constant pressure loader and then the load is released. A high return speed (long recovery time) indicates excellent SR properties. In the low-resilience polyurethane foam according to the present invention, the return speed can be increased by optimizing the molecular structure of the polyisocyanate used as a raw material, the average number of functional groups of the polyisocyanate, the isocyanate index, the number of branches, etc. When the production conditions are optimized, the return speed becomes 1.5 seconds or more. When the production conditions are further optimized, the return speed becomes 3.0 seconds or more, 6.0 seconds or more, or 10 seconds or more.

[0058] [1.3.3. Compression Set] "Compression set" refers to a value measured based on JIS K6401:2011. In the low-resilience polyurethane foam according to the present invention, the compression set can be reduced by optimizing the molecular structure of the polyisocyanate used as a raw material, the average number of functional groups of the polyisocyanate, the isocyanate index, the number of branches, and the like. When the production conditions are optimized, the compression set becomes 20% or less. When the production conditions are further optimized, the compression set becomes 10% or less, or even 5% or less.

[0059] [1.3.4. Tensile Strength] "Tensile strength" refers to a value measured based on JIS K 6251:2010. In the low-resilience polyurethane foam according to the present invention, the tensile strength can be increased by optimizing the molecular structure of the polyisocyanate used as a raw material, the average number of functional groups of the polyisocyanate, the isocyanate index, the number of branches, and the like. When the production conditions are optimized, the tensile strength becomes 0.3 MPa or more. When the production conditions are further optimized, the tensile strength becomes 0.4 MPa or more, or 0.5 MPa or more.

[0060] [1.3.5. Elongation] "Elongation" refers to a value measured based on JIS K 6251:2010. In the low-resilience polyurethane foam according to the present invention, the elongation can be increased by optimizing the molecular structure of the polyisocyanate used as a raw material, the average number of functional groups of the polyisocyanate, the isocyanate index, the number of branches, and the like. When the production conditions are optimized, the elongation becomes 200% or more. When the production conditions are further optimized, the elongation becomes 250% or more, or even 300% or more.

[0061] [1.3.6. Density] "Density" refers to a value measured based on JIS K 6401:2011. The low-resilience polyurethane foam according to the present invention has a relatively low density because it is produced by a mechanical froth method. When the production conditions are optimized, the density is 600 kg / m 3 Further optimization of the manufacturing conditions results in a density of 550 kg / m 3 Below, 450kg / m 3 Below, 250kg / cm 3 Below, 200kg / m 3 or less, or 150 kg / m 3 The following is the result.

[0062] [1.3.7. Average Cell Diameter] "Average cell diameter" refers to the average value of the equivalent circle diameter of cells appearing in the cross section of a polyurethane foam. Since the low-resilience polyurethane foam according to the present invention is produced using a mechanical froth method, fine cells are uniformly dispersed inside the polyurethane foam. When the production conditions are optimized, the average cell diameter is 50 μm or more and 300 μm or less. When the production conditions are further optimized, the average cell diameter is preferably 50 μm or more and 250 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0063] [1.4. Uses] The low resilience polyurethane foam according to the present invention can be used in a variety of applications, including shock absorbing materials, protective mats, buffer materials, vibration absorbing materials, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, and bedding cushions.

[0064] The low-resilience polyurethane foam of the present invention not only has excellent low resilience but also high tensile strength despite its thinness, making it particularly suitable as a cushioning material for electronic and electrical equipment. Examples of cushioning materials for electronic and electrical equipment include: (a) cushioning materials placed on the backside of various image display devices such as liquid crystal displays to absorb impacts received by the display devices; and (b) cushioning materials for display components such as touch panels, cameras, and lenses used in mobile communications such as mobile phones, smartphones, and personal digital assistants. In addition to its use as a cushioning material, the low-resilience polyurethane foam of the present invention can also be used as a substrate for adhesive tapes, gaskets, and sealing materials.

[0065] [2. Function] Conventional low-resilience polyurethane foams are generally produced using raw material compositions containing an excess amount of polyol (raw material compositions having an isocyanate index of less than 80). Low-resilience polyurethane foams obtained in this manner have a high SR property but low tensile strength and a large compression set due to the presence of a large amount of unreacted OH groups. On the other hand, simply increasing the isocyanate index increases the tensile strength and reduces the compression set, but decreases the SR property.

[0066] In contrast, when producing low-resilience polyurethane foam, a mixture containing an n-functional isocyanate and a difunctional isocyanate prepolymer as a polyisocyanate component exhibits excellent SR properties. This is thought to be because the use of a long molecular bifunctional isocyanate prepolymer as one of the polyisocyanate components reduces the rigidity of the polyurethane chain structure.

[0067] Furthermore, in the case of producing a low-resilience polyurethane foam using a raw material mixture containing an n-functional isocyanate and a difunctional isocyanate prepolymer, if the isocyanate index is relatively increased and / or the number of branches of the raw material composition is optimized, the tensile strength is improved and / or the compression set is reduced while maintaining excellent SR properties.

[0068] The reason for the improvement in tensile strength is thought to be that the number of crosslinking points is maintained at an appropriate value by optimizing the isocyanate index and / or the number of branches, and the reason for the reduction in compression set is thought to be that (a) the reactivity is improved by relatively increasing the isocyanate index, which reduces the residual polyol component and tackiness, and (b) the necessary minimum elasticity is ensured by optimizing the number of branches.

[0069] (Examples 1 to 29, Comparative Examples 1 to 7) [1. Sample Preparation] Table 1 shows a list of the raw materials used. The raw materials shown in Table 1 were blended in a predetermined ratio. The raw material composition was charged into a mixing head and stirred and mixed to homogeneity while mixing in an inert gas (nitrogen), to obtain a foaming raw material composition containing fine bubbles. The foaming raw material composition was applied to a PET film, and the coating was heat-cured at 200°C. The number-average molecular weight was calculated using the following formula: Number-average molecular weight = (56,100 × number of functional groups) / hydroxyl value. In Table 1, the number-average molecular weight of the CSR-dispersed polyol represents the number-average molecular weight of the PPG dispersion medium. Similarly, the number-average molecular weight of the polymer polyol represents the number-average molecular weight of the PPG dispersion medium. Furthermore, the CSR particles contained in the CSR-dispersed polyol are MBS (methyl methacrylate-butadiene-styrene copolymer)-based polymers.

[0070]

[0071] [2. Test Method] [2.1. Return Speed] A load of 1 kg (compression surface: φ15 mm) was applied to each sample for 5 seconds using a constant pressure loader (manufactured by ASKER, CL-150). After that, the load was released and the return speed was measured. [2.2. Compression Set] Compression set was measured based on JIS K6401:2011.

[0072] [2.3. Density] The density was measured based on JIS K 6401:2011. [2.4. Tensile Strength] The tensile strength was measured based on JIS K 6251:2010. [2.5. Elongation] The elongation was measured based on JIS K 6251:2010. [2.6. 180° Peeling] A sample measuring 30 mm wide and 125 mm long was attached to the surface of an ABS resin reinforcing plate via double-sided tape. The size of the double-sided tape was the same as the size of the sample. Next, a 24 mm wide and 130 mm long PET film was attached to the surface of the sample via double-sided tape. The PET film was then pressure-bonded to the sample surface. Pressure-bonding was performed by rolling a 2 kg roll back and forth twice on the surface of the PET film. After pressure-bonding, the sample was left for 24 hours. Next, the PET film was pulled in a 180° direction relative to the adhesive surface. The test speed was 300 mm / min. The force (N / 24 mm) when the PET film peeled off was measured in a 50 mm section in the center of the sample. [2.7. Shear strength] SUS plates were attached to both sides of a 25 mm x 25 mm sample using double-sided tape. The size of the double-sided tape was the same as the size of the sample. The SUS plates were pulled vertically, and the force (N) when the sample broke due to shear was measured. [2.8. 25% CLD hardness] 25% CLD hardness was measured based on JIS K6254:2010.

[0073] [3. Results] The results are shown in Tables 2 to 4. Tables 2 to 4 also show the raw material composition of each sample. The following can be seen from Tables 2 to 4.

[0074] (1) In the case of Comparative Examples 1 to 5, as the isocyanate index decreased, the return speed increased and the elongation also increased, but the tensile strength tended to decrease. This is thought to be because the number of crosslinking points decreases as the isocyanate index decreases. (2) Although Examples 1 to 7 had the same isocyanate index as Comparative Example 1, they had a higher return speed and higher tensile strength than Comparative Example 1. This is thought to be because the use of a bifunctional isocyanate prepolymer reduced the rigidity of the polyurethane chain structure.

[0075] (3) In the case of Examples 1 to 7, the return speed increased as the average functionality of the polyisocyanate component decreased, but the tensile strength reached a maximum when the average functionality of the polyisocyanate component was 2.132 (Example 6). This is thought to be because when the average functionality becomes too small, the number of crosslinking points becomes excessively small. (4) In Examples 8 to 14, the tensile strength was higher than in Examples 1 to 7, which had the same average functionality of the polyisocyanate component, but the return speed tended to be slightly lower. This is thought to be because the isocyanate index of Examples 8 to 14 was higher than that of Examples 1 to 7.

[0076] (5) In Examples 15 to 19, the return speed was higher but the tensile strength tended to be lower compared to Examples 1 to 5, which had the same average functionality of the polyisocyanate component. This is thought to be because the isocyanate index of Examples 15 to 19 was lower than that of Examples 1 to 5. (6) In Comparative Examples 6 and 7, the 180° peel strength was slightly lower. On the other hand, Examples 20 to 29 exhibited high 180° peel strength and high shear strength while maintaining a high return speed. This is thought to be due to the addition of a low molecular weight polyol containing core-shell rubber (CSR) particles and a low molecular weight polyol with a functionality of 3.0 to the raw materials.

[0077]

[0078]

[0079]

[0080] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the present invention.

[0081] The low resilience polyurethane foam according to the present invention can be used for shock absorbing materials, protective mats, buffer materials, vibration absorbing materials, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, bedding cushions, etc.

[0082] The low-resilience polyurethane foam according to the present invention can be used as a cushioning material for electronic and electrical devices, such as: (a) a cushioning material arranged on the back side of various image display devices such as liquid crystal displays to absorb impacts received by the display devices, and (b) a cushioning material for display members such as touch panels, cameras, and lenses used in mobile communications such as mobile phones, smartphones, and personal digital assistants. The low-resilience polyurethane foam according to the present invention can also be used as a substrate for pressure-sensitive adhesive tapes, gaskets, and sealing materials.

Claims

1. The polyisocyanate polymer is obtained by reacting a raw material composition containing a polyisocyanate component and a polyol component, The polyisocyanate component includes an n-functional isocyanate (n≧3) and a difunctional isocyanate prepolymer, The return speed is 1.5 seconds or more. Low-resilience polyurethane foam. The "return speed" refers to the time it takes for the sample to return to its original shape when a load of 1 kg is applied to a compression surface of 15 mm diameter by a constant pressure loader for 5 seconds and then the load is released.

2. 2. The low-resilience polyurethane foam according to claim 1, wherein the polyisocyanate component has an average functionality of 2.05 or more.

3. The polyol component is one or more high molecular weight polyols; one or more low molecular weight polyols; The low resilience polyurethane foam of claim 1 , comprising: however, The "high molecular weight polyol" refers to a polyol having a number average molecular weight of 1,000 or more. The "low molecular weight polyol" refers to a polyol having a number average molecular weight or molecular weight of less than 1,000.

4. 4. The low-resilience polyurethane foam according to claim 3, wherein the number average molecular weight ratio of the polyol component is 2.0 or more. however, The "number average molecular weight ratio of the polyol component" refers to the total number average molecular weight (Mn Ltotal ) to the total number average molecular weight (Mn Htotal ) ratio (= Mn Htotal / Mn Ltotal )

5. 4. The low-resilience polyurethane foam according to claim 3, wherein the total content of the low-molecular-weight polyols is 40.0 mass % or more and 75.0 mass % or less. however, The "total content of low molecular weight polyols" refers to the total weight (W T ) to the total weight of the low molecular weight polyol (W L ) ratio (= W L ×100 / W T )

6. 2. The low-resilience polyurethane foam according to claim 1, which has a thickness of 2.0 mm or less.

7. 2. The low-resilience polyurethane foam according to claim 1, which is used as a cushioning material for electronic and electrical equipment.

8. The polyol component is one or more high molecular weight polyols; one or more low molecular weight polyols; Including, The total content of the low-molecular-weight polyol is 40.0 mass% or more and 70.0 mass% or less, The polyisocyanate component has a weight ratio of the bifunctional isocyanate prepolymer of 20 or more and 80 or less. The low-resilience polyurethane foam according to claim 1. however, The "high molecular weight polyol" refers to a polyol having a number average molecular weight of 1,000 or more. The "low molecular weight polyol" refers to a polyol having a number average molecular weight or molecular weight of less than 1,000. The "total content of low-molecular-weight polyols" refers to the ratio of the total weight (WL) of the low-molecular-weight polyols to the total weight (WT) of the polyol components (=WL×100 / WT); The "weight ratio of the bifunctional isocyanate prepolymer" refers to the weight of the bifunctional isocyanate prepolymer when the total weight of the polyisocyanate component is taken as 100.

9. A low-resilience polyurethane foam as described in claim 1, obtained by reacting the raw material composition using a mechanical froth method.

10. A low-resilience polyurethane foam as described in claim 1, which contains polycaprolactone polyol as the polyol component.

11. A low-resilience polyurethane foam as described in claim 1, wherein the polyol component contains rubber particles in which particulate core components, primarily composed of a rubbery polymer, have their surface partially or entirely coated with a shell component.

12. A low-resilience polyurethane foam as described in claim 1, having a compression residual set of 5% or less. The "compression residual strain" refers to a value measured based on JIS K6401:2011.

13. A low-resilience polyurethane foam as described in claim 1, wherein the raw material composition further contains a moisture absorbent.

14. A low-resilience polyurethane foam as described in claim 1, wherein the raw material composition further contains a filler.