Low-rebound 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

[Technical Field]

[0001] This invention relates to low-rebound polyurethane foam. [Background technology]

[0002] Polyurethane refers to a polymer compound having a urethane bond (-NH-C(O)O-). Generally, polyurethane is obtained by reacting the hydroxyl group (-OH) of a polyol with the isocyanate group (-NCO) of a polyisocyanate. Polyurethane is known to exhibit diverse properties by optimizing the type of polyol and / or polyisocyanate used. Therefore, polyurethane is used in various applications such as automotive parts, synthetic leather, paints, and adhesives. Furthermore, polyurethane foam, obtained by foaming polyurethane, is used in applications such as thermal insulation and cushioning materials.

[0003] Polyurethane foam is (a) A flexible polyurethane foam having interconnected cells, low compression hardness, and flexibility. (b) A rigid polyurethane foam having closed cells, being highly crosslinked in its molecular structure, and not possessing high elasticity like a flexible polyurethane foam, and (c) Semi-rigid polyurethane foam with properties intermediate between rigid and flexible. They can be broadly categorized into these two groups.

[0004] Of these, soft polyurethane foam exhibits viscoelasticity. Soft polyurethane foam with reduced elasticity and increased viscosity is also specifically called "slow recovery (SR) polyurethane foam." Because slow recovery polyurethane foam has excellent shock absorption properties, it is used in shock absorbers, protective mats, cushioning materials, vibration absorbers, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, and bedding cushions.

[0005] Various proposals have been made regarding such low-rebound polyurethane foams. For example, Patent Document 1 discloses a low-rebound foamed polyurethane resin obtained by reacting a composition containing a polyol with an average number of functional groups of 2 to 3 and a hydroxyl value of 20 to 200 mgKOH / g, an isocyanate, a resin microballoon that does not contain chlorine atoms, and a catalyst.

[0006] The document states: (A) Low-hardness polyurethane is sticky and adheres to the hand, making it difficult to use. (B) Adding microballoons to low-hardness polyurethane makes it less likely to adhere to the hand, but because the microballoons float up during the curing of the urethane resin, a density difference occurs between the top and bottom of the molded product, 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 density difference between the top and bottom of the molded product due to the buoyancy of microballoons can be reduced. It is stated.

[0007] Patent Document 2 discloses a sheet that is not a low-rebound polyurethane foam, but comprises a surface layer made of a polyurethane film and a foamed layer made of polyurethane foam, wherein the average cell diameter of the polyurethane foam is 50 μm or more and 300 μm or less. The document states that sheets with a surface layer and a foam layer have excellent abrasion resistance and shock absorption.

[0008] Low-rebound polyurethane foam has come into use as a cushioning material for smartphones, game consoles, and other devices. This cushioning material is extremely thin, typically 0.2 to 1.0 mm thick, and requires properties such as low compression set and high tensile strength, in addition to resistance resistance (SR). However, there have been no previous examples of low-rebound polyurethane foams that meet all of these requirements. In particular, resistance to stress (SR) and tensile strength are mutually exclusive. That is, increasing SR reduces tensile strength, and increasing tensile strength prevents SR from being expressed. Therefore, it is generally difficult to achieve both SR and tensile strength simultaneously. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2016-113537 [Patent Document 2] Japanese Patent Publication No. 2022-100615 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The problem that this invention aims to solve is to provide a low-rebound polyurethane foam with excellent low-rebound properties. Another problem that the present invention aims to solve is to provide a low-rebound polyurethane foam that has high tensile strength in addition to excellent low rebound properties. Furthermore, another problem that the present invention aims to solve is to provide a low-rebound polyurethane foam that, in addition to excellent low rebound properties, also exhibits low compression residual set. [Means for solving the problem]

[0011] To solve the above problems, the low-rebound polyurethane foam according to the present invention is It 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 bifunctional isocyanate prepolymer. [Effects of the Invention]

[0012] When producing a low-rebound polyurethane foam, when a mixture containing an n-functional isocyanate and a bifunctional isocyanate prepolymer is used as the polyisocyanate component, excellent SR properties are exhibited. This is presumably because the rigidity of the chain structure of the polyurethane is reduced by using a bifunctional isocyanate prepolymer with a long molecular length as one of the polyisocyanate components.

[0013] Also, when producing a low-rebound polyurethane foam using a raw material mixture containing an n-functional isocyanate and a bifunctional 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 improvement in tensile strength is presumably because the number of crosslinking points is maintained at an appropriate value by optimizing the isocyanate index and / or the number of branches. The compression set is reduced because (a) The reactivity is improved by relatively increasing the isocyanate index, the residual polyol component is reduced, and the tackiness is decreased, and (b) By optimizing the number of branches, the minimum necessary elasticity is ensured. It is considered to be. [Embodiments for Carrying Out the Invention]

[0015] Hereinafter, an embodiment of the present invention will be described in detail. [1. Low-rebound polyurethane foam] The low-rebound polyurethane foam according to the present invention is 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] "Polyisocyanate component" refers to a mixture of two or more polyisocyanates, which is one of the main raw materials for producing the low-rebound polyurethane foam according to the present invention. In the present invention, the polyisocyanate component comprises 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 it may further contain a difunctional isocyanate in addition to these.

[0017] [A. n-Functional Isocyanate] An "n-functional isocyanate" refers to a polyisocyanate having three or more isocyanate groups. When an n-functional isocyanate is included in the raw material composition, the number of branches in the raw material composition becomes an appropriate value, and the polymer chains are crosslinked appropriately. As a result, it is thought that the tensile strength of the low-rebound polyurethane foam is improved, or the compressive residual strain is reduced.

[0018] Examples of n-functional isocyanates include, The polynuclear compound 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, Triphenylmethane-4,4',4”-triisocyanate These are some examples. The raw material composition may contain one of these n-functional isocyanates, or it may contain two or more of them.

[0019] [B. Bifunctional isocyanate prepolymer] An "isocyanate prepolymer" is a compound obtained by reacting a polyol with a polyisocyanate, and having an isocyanate group at its terminal end. A "bifunctional isocyanate prepolymer" refers to an isocyanate prepolymer that has two isocyanate groups. In other words, a "bifunctional isocyanate prepolymer" is a linear compound (OCN-R'-NH-C(O)ORO(O)C-NH-R'-NCO) obtained by reacting one molecule of diol (HO-R-OH) with two molecules of bifunctional isocyanate (OCN-R'-NCO). Because the bifunctional isocyanate prepolymer has a long molecular length, using it to manufacture low-rebound polyurethane foam reduces the rigidity of the polyurethane chain structure. As a result, it is thought that the SR (stress resistance) of the low-rebound polyurethane foam will be further improved.

[0020] In the present invention, the type of bifunctional isocyanate prepolymer is not particularly limited, and the most suitable 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, carbodiimide-modified MDI, (b) Urethane-modified TDI, allophanate-modified TDI, biuret-modified TDI, isocyanurate-modified TDI, urea-modified TDI, carbodiimide-modified TDI, These are some examples. The raw material composition may contain one of these bifunctional isocyanate prepolymers, or it may contain two or more of them.

[0021] [C. 2-functional isocyanates] A "bifunctional isocyanate" refers to a compound having two isocyanate groups, excluding bifunctional isocyanate prepolymers.

[0022] For example, commercially available polymeric MDI contains 4,4'-MDI in addition to the polynuclear 4,4'-MDI. Similarly, 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. In addition to the n-functional isocyanates and bifunctional isocyanate prepolymers described above, the raw material composition may also contain one or more such bifunctional isocyanates. Specifically, examples of bifunctional isocyanates include the following:

[0023] (a) Bifunctional aromatic isocyanates: 2,4-Tolylene diisocyanate, 2,6-Tolylene diisocyanate, m-phenylenediisocyanate, p-phenylenediisocyanate, 4,4'-Diphenylmethane diisocyanate (4,4'-MDI), 2,4'-Diphenylmethanediisocyanate, 2,2'-Diphenylmethane diisocyanate, xylylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylenediiso Shea Nate, Examples include 3,3'-dimethoxy-4,4'-biphenylenediisocyanate.

[0024] (b) Bifunctional alicyclic isocyanates: Cyclohexane-1,4-diisocyanate, isophorone diisocyanate, Dicyclohexylmethane-4,4'-diisocyanate, Methylcyclohexanediisocyanate, etc.

[0025] (c)2 functional aliphatic isocyanates: Butane-1,4-diisocyanate, hexamethylene diisocyanate, Examples include isopropyl diisocyanate, methylene diisocyanate, and lysine isocyanate.

[0026] [D. Average number of functional groups in polyisocyanate components] "Average number of functional groups in polyisocyanate components" refers to the average number of functional groups per polyisocyanate molecule. The average number of functional groups in the polyisocyanate component affects the SR property, tensile strength, and / or compressive residual strain. Therefore, it is preferable to select an optimal value for the average number of functional groups in the polyisocyanate component depending on the purpose.

[0027] Generally, the higher the average number of functional groups in the polyisocyanate component, the higher the tensile strength and / or the lower the compressive residual strain. To obtain such effects, the average number of functional groups in the polyisocyanate component is preferably 2.05 or higher. More preferably, the average number of functional groups is 2.07 or higher, and even more preferably, 2.10 or higher. On the other hand, if the average number of functional groups of the polyisocyanate component becomes too large, the SR (sensory resistance) may decrease. Therefore, the average number of functional groups of the polyisocyanate component is preferably 3.00 or less. More preferably, the average number of functional groups is 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 "isocyanate index" is the value obtained by multiplying the ratio of the equivalent amount of isocyanate groups in the polyisocyanate in the raw material composition to the equivalent amount of active hydrogen groups in the raw material composition by 100.

[0029] Generally, a higher isocyanate index leads to higher tensile strength, but lower compressive resistance (SR). However, the low-rebound polyurethane foam according to the present invention uses polyisocyanates with different numbers of functional groups and optimizes the molecular structure of the polyisocyanates, resulting in superior SR despite having a higher isocyanate index than conventional materials. In particular, optimizing the average number of functional groups of the polyisocyanate components makes it possible to achieve a high level of balance between excellent SR, high tensile strength, and low compressive residual strain.

[0030] To obtain high tensile strength, an isocyanate index of 80 or higher is preferable. More preferably, the isocyanate index is 85 or higher, 90 or higher, or 95 or higher. On the other hand, if the isocyanate index becomes too high, the number of crosslinking sites may become excessive, which can reduce the SR (synthesis resistance). Therefore, an isocyanate index of 130 or less is preferable. More preferably, the isocyanate index is 125 or less, 120 or less, or 115 or less.

[0031] [1.1.2. Polyol components] "Polyol component" refers to one of the other main raw materials for manufacturing the low-rebound polyurethane foam according to the present invention. The raw material composition may contain one type of polyol, or it may contain two or more types.

[0032] [A. Materials] The type of polyol included in the polyol component is not particularly limited, and the most suitable material can be selected according to the purpose. The polyol may be an ether-based polyol, an ester-based polyol, an ether-ester-based polyol, or a polymer polyol. Specifically, polyols include the following:

[0033] Examples of ether-based 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. (b) Polyether polyols obtained by adding alkylene oxides such as ethylene oxide and propylene oxide to a polyhydric alcohol. These are some examples.

[0034] Examples of ester polyols include, (a) Polyester polyols obtained by polycondensation of aliphatic carboxylic acids such as malonic acid, succinic acid, and adipic acid, or aromatic carboxylic acids such as phthalic acid, and aliphatic glycols such as ethylene glycol, diethylene glycol, and propylene glycol, (b) Phthalate ester polyol These are some examples.

[0035] Examples of polymer polyols include, (a) A polyol such as a polyether polyol in which polymer particles obtained by polymerizing ethylenically unsaturated monomers such as acrylonitrile or styrene are dispersed. (b) Core-shell rubber (CSR) dispersed polyol These are some examples. CSR-dispersed polyol refers to a polyol in which core-shell rubber (CSR) particles are dispersed. Core-shell rubber particles specifically refer to rubber particles in which a particulate core component, mainly composed of a cross-linked rubber-like polymer, is graft-polymerized with a polymer different from the core component, thereby coating part or all of the surface of the particulate core component with a shell component. Examples of core components include cross-linked rubber particles. The type of rubber used for the cross-linked rubber particles is not limited to butadiene rubber, acrylic rubber, silicone rubber, butyl rubber, nitrile rubber, styrene rubber, synthetic natural rubber, ethylene propylene rubber, etc. 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. Furthermore, it is preferable that the shell component is graft polymerized onto the core component and chemically bonded to the polymer constituting the core component. Also, considering dispersibility with polyols, MBS (methyl methacrylate butadiene) is preferred as the core-shell rubber particle. styrene It is preferable that the polymer contains a copolymer-based polymer.

[0036] [B. Number average molecular weight, molecular weight] The low-rebound polyurethane foam may be manufactured using one type of polyol, or it may be manufactured using two or more types of polyol. If the low-rebound polyurethane foam is manufactured using two or more polyols, the polyol components are: (a) A mixture of two or more polyols having equivalent number average molecular weights or molecular weights, or (b) A mixture of two or more polyols with different number-average molecular weights or molecular weights may also be used.

[0037] To obtain a low-rebound polyurethane foam with excellent SR properties, the polyol component is necessary. One or more high molecular weight polyols, One or more low molecular weight polyols and It is preferable that it contains [the specified ingredient]. Here, "High molecular weight polyols" refer to polyols with a number-average molecular weight of 1000 or more. "Low molecular weight polyols" refer to polyols whose number-average molecular weight or molecular weight is less than 1000. "Molecular weight" refers to the formula weight based on a chemical formula.

[0038] The number-average molecular weight (Mni) of the i-th (i≧1) high molecular weight polyol is preferably 1500 or more, and more preferably 2000 or more. The number-average molecular weight or molecular weight (Mnj) of the j-th (j≧1) low molecular weight polyol is preferably 800 or less, and more preferably 600 or less.

[0039] [C. Number average molecular weight ratio] The "number-average molecular weight ratio of polyol components" refers to the case where the polyol component is a mixture of high molecular weight polyols and low molecular weight polyols. Total number average molecular weight (Mn) of low molecular weight polyols Ltotal The total number average molecular weight (Mn) of high molecular weight polyols relative to ) Htotal The ratio of (=Mn Htotal / Mn Ltotal ) refers to.

[0040] If Mni is the number-average molecular weight of the i-th (i≧1) high molecular weight polyol, and ni is the number ratio of the i-th high molecular weight polyol to the total number of high molecular weight polyols, then Mn Htotal =Σni×Mni It can be expressed as follows. Similarly, if Mnj is the number-average molecular weight or molecular weight of the j-th (j≧1) low molecular weight polyol, and nj is the number ratio of the j-th low molecular weight polyol to the total low molecular weight polyols, Mn Ltotal =Σnj×Mnj It can be expressed as follows.

[0041] The number-average molecular weight ratio of the polyol components primarily affects the SR (stress resistance) properties of low-rebound polyurethane foam. When manufacturing low-rebound polyurethane foam using two or more polyols with different molecular weights, generally, the higher the number-average molecular weight ratio, the better the SR properties. To obtain this effect, the number-average molecular weight ratio of the polyol components is preferably 2.0 or higher. More preferably, the number-average molecular weight ratio is 2.5 or higher, 3.0 or higher, 3.5 or higher, or 4.0 or higher.

[0042] On the other hand, if the number-average molecular weight ratio of the polyol components becomes too large, (a) Due to the difference in the glass transition points of each polyol, the temperature dependence becomes large, (b) the hard segments and soft segments of the resin skeleton are separated, and the SR property is impaired, (c) the compression residual strain deteriorates and problems such as these 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 case where the polyol component is a mixture of a high molecular weight polyol and a low molecular weight polyol. The ratio of the total weight (W T ) of the low molecular weight polyol to the total weight (W L ) of the polyol component (=W L ×100 / W T ).

[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 becomes too small, 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 becomes excessive, the SR property may conversely 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. Branching Number] The "branching number" refers to the number of branches per mole of molecules contained in the raw material composition, and is represented by the following formula. Branching number (per mol) = Σ (functional group number - 2) × (number of addition parts / molecular weight)

[0046] The number of branches in the raw material composition affects the SR properties, tensile strength, and compressive residual strain. Generally, the smaller the number of branches, the easier it is for SR properties to be exhibited. However, if the number of branches becomes too small, the tensile strength may decrease or the compressive residual strain may decrease. Therefore, a branching number of 0.010 or more is preferable. More preferably, the branching number is 0.012 or more, 0.014 or more, or 0.016 or more. On the other hand, if the number of branches becomes excessively large, the SR (Stress Retention) may decrease. Therefore, the number of branches is preferably 0.050 or less. More preferably, the number of branches is 0.048. below It is 0.046 or less, or 0.044 or less.

[0047] [1.1.4. Other ingredients] In addition to the polyisocyanate and polyol components mentioned above, the raw material composition for manufacturing low-rebound polyurethane foam may also contain the following components. The amount of each component added is not particularly limited, and it is preferable to select the optimal amount depending on the purpose.

[0048] [A. Resin-based 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 this invention, the type of resinification catalyst is not particularly limited. Examples of resinification catalysts include: a Examples include mine-based catalysts and metal catalysts.

[0049] Examples of amine-based catalysts include, 1,2-dimethylimidazole, 1-methylimidazole, N - (N',N'-dimethylaminoethyl)-morpholine, tetramethylguanidine, Dimethylaminoethanol, triethylenediamine, N-methyl-N'-(2-hydroxyethyl)-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 These are some examples.

[0050] Examples of metal catalysts include, (a) Tin catalysts such as stanus octoate and dibutylthin dilaurate, (b) Phenylmercury propionate, (c) Lead octenate These are some examples.

[0051] [B. Foam stabilizers] The raw material composition may contain a foam stabilizer. The foam stabilizer facilitates the dispersion of entrained gases during mechanical foaming of polyurethane, stabilizes bubbles, and adjusts the bubble structure. In this 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, (d) Phenolic compounds, These are some examples.

[0052] [C. Filler] The raw material composition may contain fillers. Fillers are used to increase the volume of the polyurethane foam, reduce the amount of polyurethane raw material used per unit volume, and lower the cost of the polyurethane foam. In this invention, the type of filler is not particularly limited. Examples of fillers include aluminum hydroxide, calcium carbonate, talc, and clay.

[0053] [D. Moisture absorbent material] The raw material composition may contain a moisture absorbent. The moisture absorbent is intended to remove moisture contained in the composition and suppress the reaction of polyisocyanate with moisture. When polyisocyanate reacts with moisture, CO2 gas is generated, which can make it difficult to control bubbles. In this 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. Antioxidants] The raw material composition may contain an antioxidant. The antioxidant is intended to suppress the deterioration of polyurethane due to oxidation. In this invention, the type of antioxidant is not particularly limited. Examples of antioxidants include hindered phenol antioxidants, amine antioxidants, sulfur antioxidants, and phosphorus antioxidants.

[0055] [1.2. Reactions of the raw material composition] The low-rebound polyurethane foam according to the present invention is manufactured using the mechanical flossing method. The "mechanical flossing method" refers to: (a) By mixing the raw material composition using a high-shear mixer while blowing in an inert gas, a foamed raw material composition containing fine bubbles is obtained. (b) Apply the foaming raw material composition to the surface of a substrate (e.g., PET film), (c) Heat the coating to a predetermined temperature and cure it. It refers to a method. In the present invention, the reaction conditions for the raw material composition are not particularly limited, and optimal conditions can be selected according to the purpose.

[0056] [1.3. Characteristics] [1.3.1. Thickness] In this invention, the thickness of the low-rebound polyurethane foam is not particularly limited, and the optimal thickness can be selected according to the purpose. sex When using polyurethane foam as cushioning material for electronic and electrical equipment, the thinner the foam, the better. Using the low-rebound polyurethane foam according to the present invention, it is possible to manufacture sheets that not only have excellent SR (stress resistance) but also have a thickness of 2.0 mm or less. By optimizing the manufacturing conditions, the thickness can be reduced to 1.5 mm or less, or even 1.0 mm or less.

[0057] [1.3.2. Return Speed] "Recovery speed" refers to the time it takes for a sample to return to its original shape after a 1kg load is applied to a 15mm diameter compression surface using a constant pressure loader for 5 seconds, and then the load is released. A high recovery speed (long recovery time) indicates superior SR (stress resistance). In the low-rebound 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. Optimizing the manufacturing conditions results in a return speed of 1.5 seconds or more. Further optimization of the manufacturing conditions results in a return speed of 3.0 seconds or more, 6.0 seconds or more, or 10 seconds or more.

[0058] [1.3.3. Compression Residual Strain] "Compression residual strain" refers to the value measured according to JIS K6401:2011. In the low-rebound 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, etc. Optimizing the manufacturing conditions reduces the compression set to 20% or less. Further optimization of the manufacturing conditions reduces the compression set to 10% or less, or even 5% or less.

[0059] [1.3.4. Tensile Strength] "Tensile strength" refers to the value measured according to JIS K 6251:2010. In the low-rebound 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, etc. Optimizing the manufacturing conditions results in a tensile strength of 0.3 MPa or higher. Further optimization of the manufacturing conditions results in a tensile strength of 0.4 MPa or higher, or even 0.5 MPa or higher.

[0060] [1.3.5. Growth] "Elongation" refers to the value measured according to JIS K 6251:2010. In the low-rebound 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, etc. Optimizing the manufacturing conditions results in an elongation of 200% or more. Further optimization of the manufacturing conditions results in an elongation of 250% or more, or even 300% or more.

[0061] [1.3.6. Density] "Density" refers to the value measured according to JIS K 6401:2011. The low-rebound polyurethane foam according to the present invention is manufactured by the mechanical flossing method, and therefore has a relatively low density. By optimizing the manufacturing conditions, the density can be increased to 600 kg / m³. 3 The following results are obtained. Further optimization of the manufacturing conditions results in a density of 550 kg / m³.3 Below 450kg / m 3 Below 250kg / cm 3 Below 200kg / m 3 Below, or 150 kg / m 3 The following applies.

[0062] [1.3.7. Average Cell Diameter] "Average cell diameter" refers to the average value of the equivalent circular diameter of the cells appearing in the cross-section of polyurethane foam. The low-rebound polyurethane foam according to the present invention is manufactured using a mechanical flossing method, resulting in a uniform dispersion of fine cells within the polyurethane foam. Optimizing the manufacturing conditions, the average cell diameter is 50 μm to 300 μm. Further optimization of the manufacturing conditions results in an average cell diameter of preferably 50 μm to 250 μm, and more preferably 50 μm to 200 μm.

[0063] [1.4. Purpose] The low-rebound polyurethane foam according to the present invention can be used for various applications. sex Applications of polyurethane foam include, for example, shock absorbers, protective mats, cushioning materials, vibration absorbers, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, and bedding cushions.

[0064] Low rebound according to the present invention sex Polyurethane foam is not only excellent in low resilience but also has high tensile strength despite being thin, making it particularly suitable as a cushioning material for electronic and electrical equipment. Examples of cushioning materials for electronic and electrical equipment include: (a) A cushioning material placed on the back side of various image display devices such as liquid crystal displays to absorb shocks received by the display device. (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. These are some examples. Furthermore, in addition to its use as a cushioning material, the low-rebound polyurethane foam according to the present invention can also be used as a base material for adhesive tapes, gaskets, and sealing materials.

[0065] [2. Effect] Conventional low-rebound polyurethane foams are generally manufactured using raw material compositions with an excess of polyol (raw material compositions with an isocyanate index of less than 80). Low-rebound polyurethane foams obtained in this way have a large amount of unreacted OH groups remaining, resulting in high SR properties but low tensile strength and high compressive residual strain. On the other hand, simply increasing the isocyanate index increases tensile strength and decreases compressive residual strain, but reduces SR properties.

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

[0067] Furthermore, when producing a low-rebound polyurethane foam using a raw material mixture containing an n-functional isocyanate and a bifunctional isocyanate prepolymer, relatively increasing the isocyanate index and / or optimizing the number of branches in the raw material composition improves tensile strength and / or reduces compressive residual strain while maintaining excellent SR properties.

[0068] The improvement in tensile strength is thought to be due to the optimization of the isocyanate index and / or branching number, which maintained an appropriate number of crosslinking points. The reason why the compressive residual strain becomes smaller is, (a) By relatively increasing the isocyanate index, reactivity is improved, residual polyol components are reduced, and tackiness is decreased, and (b) By optimizing the number of branches, the minimum necessary elasticity was ensured, It is thought that... [Examples]

[0069] (Examples 1-29, Comparative Examples 1-7) [1. Sample Preparation] Table 1 shows a list of the raw materials used. The raw materials shown in Table 1 were blended in predetermined ratios. The raw material composition was placed in a mixing head and mixed while stirring until homogeneous with inert gas (nitrogen) to obtain a foamed raw material composition containing fine bubbles. The foamed 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 = (56100 × 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 dispersion medium, PPG. Similarly, the number-average molecular weight of the polymer polyol represents the number-average molecular weight of the dispersion medium, PPG. Furthermore, the CSR particles contained in the CSR-dispersed polyol are MBS (methyl methacrylate-butadiene-styrene copolymer) polymers.

[0070] [Table 1]

[0071] [2. Test Method] [2.1. Return Speed] A 1kg load (compression surface: φ15mm) was applied to each sample for 5 seconds using a constant pressure load device (ASKER CL-150). After that, the load was released and the return speed was measured. [2.2. Compression Residual Strain] Compression residual strain was measured according to JIS K6401:2011.

[0072] [2.3. Density] The density was measured according to JIS K 6401:2011. [2.4. Tensile Strength] Tensile strength was measured according to JIS K 6251:2010. [2.5. Growth] Elongation was measured according to JIS K 6251:2010. [2.6. 180° Detachment] A 30mm wide x 125mm long sample was attached to the surface of a reinforcing plate made of ABS resin using double-sided tape. The size of the double-sided tape was the same as the size of the sample. Next, a 24mm wide x 130mm long PET film was attached to the surface of the sample using double-sided tape. Furthermore, the PET film was pressed onto the surface of the sample. The pressing was performed by passing a 2kg roll back and forth twice over the surface of the PET film. After pressing, the sample was left for 24 hours. Next, the PET film was pulled at a 180° angle to the adhesive surface. The test speed was set to 300 mm / min. The force (N / 24 mm) required to peel the PET film in the central 50 mm section of the sample was measured. [2.7. Shear Strength] A SUS plate was attached to both sides of a 25mm x 25mm sample using double-sided tape. The size of the double-sided tape was the same as the size of the sample. The SUS plate was pulled vertically, and the force (N) at which the sample underwent shear failure was measured. [2.8. 25% CLD hardness] The 25% CLD hardness was measured according to 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 for each sample. From Tables 2 to 4, the following can be observed.

[0074] (1) In Comparative Examples 1 to 5, as the isocyanate index decreased, the return speed increased and the elongation 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 showed a higher return rate and higher tensile strength than Comparative Example 1. This is thought to be because the rigidity of the polyurethane chain structure was reduced by using a bifunctional isocyanate prepolymer.

[0075] (3) In Examples 1 to 7, the return speed increased as the average number of functional groups of the polyisocyanate component decreased, but the tensile strength was maximized when the average number of functional groups of the polyisocyanate component was 2.132 (Example 6). This is thought to be because when the average number of functional groups becomes too small, the number of crosslinking points becomes excessively small. (4) Examples 8 to 14 showed higher tensile strength compared to Examples 1 to 7, which had the same average number of functional groups in the polyisocyanate component, but tended to have a slightly lower recovery speed. 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, compared to Examples 1 to 5, which had the same average number of functional groups in the polyisocyanate component, the return speed was higher but the tensile strength tended to decrease. This is thought to be because the isocyanate index of Examples 15 to 19 was lower than that of Examples 1 to 5. (6) Comparative Examples 6-7 showed a slightly lower 180° peel strength. On the other hand, Examples 20-29 showed high 180° peel strength and high shear strength while maintaining a high return rate. This is thought to be because a low molecular weight polyol containing core-shell rubber (CSR) particles and a low molecular weight polyol with 3.0 functional groups were further added to the raw material.

[0077] [Table 2]

[0078] [Table 3]

[0079] [Table 4]

[0080] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0081] The low-rebound polyurethane foam according to the present invention can be used as shock absorbers, protective mats, cushioning materials, vibration absorbers, shoe insoles, shoe sole cushions, pillow cushions, seat cushions, chair cushions, bedding cushions, and the like.

[0082] Furthermore, the low-rebound polyurethane foam according to the present invention is (a) A cushioning material placed on the back side of various image display devices such as liquid crystal displays to absorb shocks received by the display device. (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. It can be used as cushioning material for electronic and electrical equipment such as the following. Furthermore, the low-rebound polyurethane foam according to the present invention can also be used as a base material for adhesive tapes, gaskets, and sealing materials.

Claims

1. It is obtained by reacting a raw material composition containing a polyisocyanate component and a polyol component. The polyisocyanate component comprises an n-functional isocyanate (n≧3) and a bifunctional isocyanate prepolymer. The return speed is 1.5 seconds or more. Low-rebound polyurethane foam. However, the aforementioned "recovery speed" refers to the time it takes for the sample shape to recover after applying a 1 kg load to a 15 mm diameter compression surface using a constant pressure loader for 5 seconds, and then releasing the load.

2. The low-rebound polyurethane foam according to claim 1, wherein the polyisocyanate component has an average number of functional groups of 2.05 or more.

3. The aforementioned polyol component is One or more high molecular weight polyols, One or more low molecular weight polyols and A low-rebound polyurethane foam according to claim 1, comprising: however, The aforementioned "high molecular weight polyol" refers to a polyol having a number-average molecular weight of 1000 or more. The term "low molecular weight polyol" refers to a polyol whose number average molecular weight or molecular weight is less than 1000.

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

5. The low-rebound polyurethane foam according to claim 3, wherein the total content of the low molecular weight polyol 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) of the polyol components. T The total weight (W) of the low molecular weight polyol relative to ) L The ratio of (=W) L ×100 / W T ) refers to.

6. The low-rebound polyurethane foam according to claim 1, wherein the thickness is 2.0 mm or less.

7. A low-rebound polyurethane foam according to claim 1, used as a cushioning material for electronic and electrical equipment.

8. The low-rebound polyurethane foam according to claim 1, obtained by reacting the raw material composition using a mechanical flossing method.

9. The low-rebound polyurethane foam according to claim 1, comprising polycaprolactone polyol as the polyol component.

10. The low-rebound polyurethane foam according to claim 1, wherein the polyol component comprises rubber particles in which part or all of the surface of a particulate core component mainly composed of a rubbery polymer is coated with a shell component.

11. The low-rebound polyurethane foam according to claim 1, wherein the compression set is 5% or less. However, the aforementioned "compression residual strain" refers to the value measured according to JIS K6401:2011.

12. The raw material composition further comprises a moisture absorbent, according to claim 1, a low-rebound polyurethane foam.

13. The raw material composition further comprises a filler, as described in claim 1, for the low-rebound polyurethane foam.

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