JP2023008068A - Polyurethane foam and sheet cushion - Google Patents

Abstract

To provide a polyurethane foam having large cushion feeling even when it was thinned, and, a sheet cushion using the same.SOLUTION: Polyurethane foam has a resonance magnification of 2.3 or more. The polyurethane foam preferably has a logarithmic decrement of 3.5 or less. The polyurethane foam preferably has an air permeability (method A) of 10 cm3/cm2/s or more and/or an air permeability (method B) of 10 L/min or more. Further, the polyurethane foam preferably has a core density of 35 kg/m3 or more and 80 kg/m3 or less. A seat cushion is made with such a polyurethane foam as a seat pad.SELECTED DRAWING: Figure 5

Description

TECHNICAL FIELD The present invention relates to a polyurethane foam and a seat cushion, and more particularly to a polyurethane foam that provides a high cushioning feeling even when thinned, and a seat cushion using such a polyurethane foam as a seat pad.

There are two types of automobile seats: a type in which a seat cushion (seating surface portion) and a seat back (rear portion) are separated, and a type in which both are integrated.
In addition, automobile seats are generally
(a) a seat pad for receiving the load of an occupant when the occupant is seated;
(b) a frame for supporting the seat pad;
(c) a trim cover that covers the outer surface of the seat pad;
A flexible polyurethane foam is generally used for the seat pad.

When an occupant sits on an automobile seat provided with a seat pad, the seat pad is compressed in the load direction in proportion to the magnitude of the load applied to the seat pad. The magnitude of the load applied to the seat pad varies depending on the shape of the automobile seat, the inclination of the seat back, the part of the human body in contact with the automobile seat, the posture of the occupant, and the like. Therefore, if the hardness of the seat pad is constant regardless of location, the seat may be uncomfortable to sit on.

In order to solve this problem, various proposals have been conventionally made.
For example, Patent Literature 1 discloses a method for producing a flexible polyurethane foam molded product by foam-molding a foaming raw material containing two kinds of foam stabilizers (silicone-based surfactant or fatty acid ester compound).
In the same document,
(a) By such a method, a flexible polyurethane foam molded article can be obtained in which the cell diameter gradually increases from the surface (seating surface) toward the thickness direction, and
(b) It is described that the cell diameter can be changed by changing the amount of addition of two kinds of foam stabilizers.

Patent Document 2 discloses a method for producing a flexible polyurethane foam by foam-molding a foaming raw material containing a foam stabilizer and SiO ₂ (a foam breaker), although it is not intended to improve the seating comfort of the seat. ing.
In the same document,
(a) By such a method, a flexible polyurethane foam having a spongy cell structure (a double cell structure in which coarse cells and fine cells are mixed) and having a low density and softness like a sponge can be obtained. a point, and
(b) SiO ₂ is described as having the effect of roughening the cells formed during foaming.

Patent Document 3 discloses a trifunctional polyol for flexible foam, a hydrophilic polyol, and a polyoxyalkylene-modified polysiloxane (a foam-breaking silicone for hard foam), although it is not intended to improve the seating comfort of the seat. Disclosed is a method for producing a coarse-celled flexible urethane foam in which a foaming raw material containing is foam-molded.
The document describes that a coarse-celled flexible urethane foam having coarse cells of 5 to 10 mmφ can be obtained by such a method.

Patent Document 4 describes a sheet in which the average diameter of cells forming a polyurethane foam is 550 to 1,000 μm, the number of holes per cell is 10 or less, and the average thickness of ribs forming the cells is 90 to 200 μm. A polyurethane foam for padding is disclosed.
This document describes that the resonance frequency and the resonance magnification can be reduced at the same time by defining the cell structure of the polyurethane foam.

Patent Document 5 discloses a polyurethane foam obtained by reacting raw materials for polyurethane foam containing polyols, polyisocyanates, a foaming agent, a catalyst, a cross-linking agent, a foam stabilizer and a foam breaker, followed by foaming and curing. is disclosed.
In the same document, when the type and content of raw materials are optimized, the hardness is 216 to 245 N, the resonance frequency is 4.2 Hz or more and 4.9 Hz or less, and the resonance magnification at a frequency of 2.0 to 4.0 Hz is 4.1 or more and 4.9 or less.

Patent Document 6 discloses a seat body composed of a urethane pad, a mesh cushion body incorporated in a seating portion of the seat body, a vent communicating with the mesh cushion body formed in the seat body, and a seat cover. A breathable sheet comprising:
In the same document,
(a) Such a breathable sheet can sufficiently prevent stuffiness and provide sufficient cushioning properties, and
(b) Aligning the vents with the holes in the pan frame results in a lower logarithmic decrement than when they are not aligned.

2. Description of the Related Art In recent years, there has been a trend toward reducing the thickness of rear cushions for automotive seat cushions in order to improve fuel efficiency or to secure a space for installing a battery in a hybrid vehicle. However, when a thin seat pad is produced using a conventional polyurethane foam in which fine cells are uniformly dispersed,
(a) small feeling of deflection;
(b) A feeling of bottoming out is felt when the deflection increases;
(c) Problems peculiar to thinning arise, such as a small cushion feeling.

On the other hand, Japanese Patent Laid-Open No. 2004-100000 describes that a seat with good riding comfort can be obtained by gradually increasing the cell diameter from the surface (seating surface) in the thickness direction. However, the method described in Patent Literature 1 cannot solve the above-described problem specific to thinning.

JP 2019-205613 A Japanese Patent No. 4898322 Japanese Patent Publication No. 02-057808 Japanese Patent No. 5932255 Japanese Patent No. 4689428 Japanese Patent Application Laid-Open No. 2004-073429

The problem to be solved by the present invention is to provide a polyurethane foam that has a great cushioning feeling even when the thickness is reduced.
Another problem to be solved by the present invention is to provide a seat cushion using such polyurethane foam.

In order to solve the above problems, the polyurethane foam according to the present invention has a resonance magnification of 2.3 or more.

Furthermore, a seat cushion according to the present invention is formed by using the polyurethane foam according to the present invention as a seat pad.

In the production of polyurethane foam, if the raw material composition is optimized, it is possible to obtain a polyurethane foam with a large resonance magnification, that is, a polyurethane foam with a large cushioning feeling even when the thickness is reduced.

FIGS. 1(A) to 1(C) are optical microscope photographs of cross sections of the polyurethane foams obtained in Examples 3 to 5, respectively. 2(A) to 2(C) show the diameters of 100 randomly selected cells appearing in cross sections of the polyurethane foams obtained in Examples 3 to 5, respectively.

FS characteristics of polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. FIG. FS properties of polyurethane foams obtained in Example 1 and Comparative Examples 2-5. 1 shows vibration curves of polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. FIG. 1 shows vibration curves of polyurethane foams obtained in Example 1 and Comparative Examples 2 to 5. FIG. 1 shows the results of a free drop test of polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. FIG. 1 shows the results of a free drop test of polyurethane foams obtained in Example 1 and Comparative Examples 2 to 3 and 5. FIG.

An embodiment of the present invention will be described in detail below.
[1. polyurethane foam]
A polyurethane foam according to the present invention is obtained by the method described below. Therefore, the polyurethane foam according to the present invention has the following characteristics.

[1.1. cell structure]
Polyurethane foams are generally
(a) an interconnected cell structure in which most of the cells are interconnected cells;
(b) a closed cell structure in which most of the cells are closed cells, or
(c) It is roughly classified into a structure having intermediate properties between the open-cell structure and the closed-cell structure.
Using the method described below,
(a) a flexible polyurethane foam containing closed cells, or
(b) Polyurethane foams with few or no closed cells are obtained.

[1.2. Cell diameter distribution]
A “large-diameter cell” refers to a cell having a diameter of 1000 μm or more.
"Small cell" refers to a cell having a diameter of less than 1000 µm.
"Cell diameter" refers to the length in the direction in which the length of the cell is the minimum (for example, when the cell is distorted and elliptical, the minor axis of the ellipse).

Defoamers have the effect of increasing the diameter of the cells of polyurethane foam. In addition, when a raw material mixture containing no silicone-based foam stabilizer and containing an antifoaming agent is used, a structure in which large-diameter cells and small-diameter cells are mixed (hereinafter, this is also referred to as a "double cell structure") is obtained. A polyurethane foam is obtained. At this time, the cell diameter distribution can be changed by controlling the composition of the raw material mixture.
In the case of a polyurethane foam having a double-cell structure, the polyurethane skeleton itself between large-diameter cells is a foam containing small-diameter cells. In the case of the present invention, the small-diameter cells in the skeleton may be open cells or closed cells.

By optimizing the manufacturing conditions,
(a) the average diameter of the large-diameter cells is 1400 μm or more and 5000 μm or less, and
(a) A polyurethane foam is obtained in which the average diameter of small-diameter cells is 300 μm or more and 500 μm or less.

[1.3. FS (Force-Strain) Characteristics]
[1.3.1. deflection coefficient]
"Flexibility coefficient" is a value measured in accordance with JIS K6400-2: 2012, and after 75% pre-compression, when compressed to 75% at a constant speed, at 65% compression It is the value obtained by dividing the force (F65%) by the force ( _F25% ) at ₂₅ % compression (= _F65% /F25 _% ).

Since the polyurethane foam according to the present invention has a double-cell structure, it has a smaller deflection coefficient than polyurethane foams that do not have a double-cell structure. In general, the smaller the deflection coefficient, the greater the deflection in the high load range, and the greater the cushioning feeling. In order to obtain such effects, the deflection coefficient is preferably 2.8 or less. The deflection coefficient is preferably 2.7 or less, more preferably 2.4 or less.
On the other hand, if the deflection coefficient is too small, the amount of deflection will be too large and the feeling of hitting the bottom will be increased. Therefore, the deflection coefficient is preferably 2.0 or more. The deflection coefficient is more preferably 2.1 or more, more preferably 2.2 or more.

[1.3.2. 400N static spring constant]
"400N static spring constant (N/mm)" refers to the slope of the tangent line of the FS (Force-Strain) curve when the load is 400N.

Since the polyurethane foam according to the present invention has a double-cell structure, it has a smaller static spring constant of 400N than a polyurethane foam that does not have a double-cell structure. In general, the smaller the 400N static spring constant, the softer and more cushioned the feel of the foam when seated. In order to obtain such an effect, the 400N static spring constant is preferably 9.0N/mm or less. The 400N static spring constant is preferably 8.0N/mm or less.
On the other hand, if the 400N static spring constant is too small, the repulsive force of the polyurethane foam will be too small. Therefore, the 400N static spring constant is preferably 5.0N/mm or more. The 400N static spring constant is preferably 6.0 N/mm or more, more preferably 7.0 N/mm or more.

[1.4. Vibration characteristics]
[1.4.1. Resonance Magnification]
"Resonance magnification" refers to a value measured according to JASO B407. Specifically, using a tekken-type pressure plate with a mass of 50 kgf, the absolute displacement of the pressure plate was measured when the vibration table was vertically vibrated with a total width of 5 mm, and the resonance magnification was calculated from the absolute displacement. bottom. The value of vibration frequency was from 1 Hz to 11 Hz.

Since the polyurethane foam according to the present invention has a double-cell structure, it has a higher resonance magnification than a polyurethane foam that does not have a double-cell structure. In general, the greater the resonance magnification, the greater the cushion feeling. In order to obtain such effects, the resonance magnification is preferably 2.3 or more. The resonance magnification is more preferably 2.8 or more, more preferably 3.0 or more.
On the other hand, if the resonance magnification becomes too large, the polyurethane foam will transmit the vibration and cause a large amplitude. As a result, the foam bounces too much when the user sits on the seat, and the comfort of the seat deteriorates. Therefore, the resonance magnification is preferably 6.0 or less. The resonance magnification is more preferably 5.5 or less, more preferably 5.0 or less.

[1.4.2. Resonance frequency]
The "resonance frequency" is a value calculated when measuring the resonance magnification, and refers to the frequency at which the polyurethane foam resonates.

In general, the smaller the resonance frequency, the higher the elastic modulus of the urethane foam, and the more the cushioning property is felt. In order to obtain such effects, the resonance frequency is preferably 3 Hz to 4 Hz.

[1.4.3. 6 Hz magnification]
The "6 Hz magnification" is a value calculated when measuring the resonance magnification _, and is the ratio of the amplitude A3 of the pressure plate to the amplitude A0 when the polyurethane foam is vibrated at ₆ Hz ( ₌ A3/ A ₀ ).

The resonance frequency of human internal organs is about 6 Hz. Therefore, in the case of manufacturing a seat cushion using the polyurethane foam according to the present invention, the smaller the 6 Hz magnification of the polyurethane foam, the smaller the vibration received by the occupant's internal organs. In order to obtain such effects, the 6 Hz magnification is preferably 1.0 or less. The 6 Hz magnification is preferably 0.9 or less, more preferably 0.8 or less. The smaller the 6 Hz magnification, the better.

[1.5. Attenuation characteristics: Logarithmic attenuation]
“Logarithmic attenuation (λ)” is a value measured according to JASO B408 and represented by the following formula (1).
λ=log _e ( ₁ / _n )·( _a0 /a1+a1/ _a2 +...+ _{an-1 /} an)...(1)
Here,
a: amplitude,
n: number of waves read, read until less than 10% of the amplitude (a ₀ ) of the first waveform.

Since the polyurethane foam according to the present invention has a double-cell structure, it has a smaller logarithmic decrement (λ) than a polyurethane foam that does not have a double-cell structure. In general, the smaller λ is, the greater the cushioning feeling is obtained. In order to obtain such effects, λ is preferably 3.5 or less. λ is more preferably 2.5 or less, more preferably 1.5 or less.

[1.6. core density]
When a raw material mixture containing polyol and isocyanate is poured into a mold and foamed, the vicinity of the contact surface with the mold becomes a layer with a low expansion ratio (skin layer), and the central portion becomes a layer with a high expansion ratio (core layer).
"Core density" is a value measured in accordance with JASO B408 and refers to the apparent density of the core layer.

In general, too much core density increases the weight of the polyurethane foam. Therefore, the core density is preferably 80 kg/m ³ or less. The core density is more preferably 75 kg/m ³ or less, more preferably 70 kg/m ³ or less.
On the other hand, if the core density is too low, the cushioning property will rather deteriorate, and the riding comfort will deteriorate when applied to a seat. In addition, when used for a long period of time, settling is likely to occur. Therefore, the core density is preferably 35 kg/m ³ or more. The core density is more preferably 40 kg/m ³ or more, more preferably 45 kg/m ³ or more.

[1.7. Breathability]
"Permeability (A method)" refers to a value measured according to JIS K6400-7 A method (sample size: 51 x 51 x 25 mm).
"Permeability (B method)" refers to a value measured according to JIS K6400-7 B method (sample thickness: 10 mm).

The air permeability (method A) of polyurethane foam affects resonance magnification, resilience, cushion feeling, and the like. In general, the higher the air permeability (A method), the better the resilience. In order to obtain such an effect, the air permeability (method A) is preferably 10 L/min or more. The air permeability (method A) is more preferably 20 L/min or more, more preferably 30 L/min or more.
However, if the air permeability (method A) is too high, the production may become difficult. Therefore, the air permeability (method A) is preferably 100 L/min or less. The air permeability (A method) is more preferably 80 L/min or less.

Similarly, the air permeability (B method) of polyurethane foam affects resonance magnification, resilience, cushion feeling, and the like. In general, the higher the air permeability (B method), the better the resilience. In order to obtain such effects, the air permeability (B method) is preferably 10 cm ³ /cm ² /s or more. The air permeability (B method) is more preferably 15 cm ³ /cm ² /s or more, more preferably 20 cm ³ /cm ² /s or more.
However, if the air permeability (method B) is too high, the production may become difficult. Therefore, the permeability (B method) is preferably 150 cm ³ /cm ² /s or less. The air permeability (B method) is more preferably 100 cm ³ /cm ² /s or less.
The polyurethane foam according to the present invention may satisfy either one of the above-described conditions regarding air permeability (method A) or air permeability (method B), or may satisfy both.

[2. Application]
The polyurethane foam according to the invention can be used for various purposes. Applications of the polyurethane foam according to the present invention include, for example,
(a) a seat pad for a seat cushion of an automobile seat;
(b) a seat pad for a seat back of an automobile seat;
(c) Mattresses, legless chairs, sofas, car wash sponges, washing sponges, bundles,
and so on.

Since the polyurethane foam according to the present invention has a large deflection in a high load range, it is possible to secure a necessary amount of deflection even if the thickness is reduced. Therefore, when this is used as a seat pad for a seat cushion, a seat cushion with a large cushion feeling can be obtained in spite of its relatively thin thickness.

[3. Method for producing polyurethane foam]
The method for producing a polyurethane foam according to the present invention comprises:
a first step of obtaining a raw material mixture containing an isocyanate, a polyol, a blowing agent, a catalyst, and optionally an antifoaming agent and/or a silicone foam stabilizer;
and a second step of reacting the raw material mixture.

[3.1. First step]
First, a raw material mixture containing an isocyanate, a polyol, a foaming agent, a catalyst and an antifoaming agent, and further containing or not containing a silicone foam stabilizer is obtained (first step).

[3.1.1. material]
[A. isocyanate]
In the present invention, the type of isocyanate is not particularly limited. Isocyanates may be aromatic, alicyclic or aliphatic. The isocyanate may be a bifunctional isocyanate having two isocyanates in one molecule, or a trifunctional or higher isocyanate having three or more isocyanate groups in one molecule. Furthermore, any one of these isocyanates may be used as the starting material, or two or more of them may be used in combination.

Examples of bifunctional aromatic isocyanates include
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 (2,4′-MDI),
2,2′-diphenylmethane diisocyanate (2,2′-MDI),
xylylene diisocyanate,
3,3′-dimethyl-4,4′-biphenylene diisonate,
3,3'-dimethoxy-4,4'-biphenylene diisocyanate and the like, and mixtures thereof may also be used.

Examples of bifunctional alicyclic isocyanates include
cyclohexane-1,4-diisocyanate, isophorone diisocyanate,
dicyclohexylmethane-4,4'-diisocyanate,
and methylcyclohexane diisocyanate.

Examples of bifunctional aliphatic isocyanates include
butane-1,4-diisocyanate, hexamethylene diisocyanate,
Examples include isopropylene diisocyanate, methylene diisocyanate, and lysine isocyanate. Di- or higher functional isocyanates include polymeric MDI and tri- or higher functional isocyanates.

Examples of tri- or higher functional isocyanates include:
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,
and so on.

[B. Polyol]
In the present invention, the type of polyol is not particularly limited. The polyol may be an ether-based polyol or an ester-based polyol. Furthermore, any one of these polyols may be used as the starting material, or two or more of them may be used in combination.

Examples of ether-based polyols include
(a) ethylene glycol, diethylene glycol, propylene glycol,
dipropylene glycol, butylene glycol, neopentyl glycol, glycerin,
Polyhydric alcohols such as pentaerythritol, trimethylolpropane, sorbitol and sucrose,
(b) There are polyether polyols obtained by adding alkylene oxides such as ethylene oxide and propylene oxide to polyhydric alcohols.

Examples of ester-based polyols include
(a) obtained by polycondensation of aliphatic carboxylic acids such as malonic acid, succinic acid and adipic acid, aromatic carboxylic acids such as phthalic acid, and aliphatic glycols such as ethylene glycol, diethylene glycol and propylene glycol; polyester polyol,
(b) phthalate ester polyols;

[C. Foaming agent]
The blowing agent is for generating air bubbles in the polyurethane. The blowing agent is
(a) chemical blowing agents that generate gas by thermal decomposition or chemical reaction (e.g. water that reacts with isocyanate groups to generate _CO2 );
(b) physical blowing agents that generate gas upon pressure reduction or heating (e.g., pentane, cyclopentane, methylene chloride, carbon dioxide gas, etc. dissolved in a resin under high pressure);
and so on.
Among these, the foaming agent is preferably water. This is because the carbon dioxide generated by the reaction between water and isocyanate promotes foaming, while the heat generated by the reaction between water and isocyanate promotes curing of the resin.

[D. catalyst]
In order to synthesize polyurethane, it is preferable to add a catalyst (resinizing catalyst) to the raw materials to promote the reaction between isocyanate and polyol.
When a chemical foaming agent, especially water, is used as the foaming agent, it is preferable to add a catalyst (foaming catalyst) to the raw material to accelerate the reaction between water and isocyanate to generate gas.
In the present invention, the type of catalyst is not particularly limited.

Examples of the resinification 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,
amine-based catalysts such as N-methyl-N'-(2dimethylamino)ethylpiperazine;
When the foaming agent is water, examples of foaming catalysts include triethylamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, triethylenediamine, diethanolamine, bis(2-dimethylaminoethyl) ether, Amine catalysts such as dimethylaminomorpholine, N-ethylmorpholine, tetramethylguanidine, and the like.

[E. Defoamer]
When the silicone-based foam stabilizer and antifoaming agent are added to the raw material mixture at the same time, optimizing the composition of the raw material mixture makes it possible to obtain a polyurethane foam containing closed cells and having a double-cell structure.
On the other hand, when the silicone-based foam stabilizer is not added to the raw material mixture and the antifoaming agent is added, a polyurethane foam having few or no closed cells and a double cell structure can be obtained. The antifoaming agent is not particularly limited as long as it has such a function.

Examples of antifoaming agents include fatty acid esters and vaseline. Any one of these antifoaming agents may be used, or two or more thereof may be used in combination.
Among these, the antifoaming agent is preferably a fatty acid ester. This is because the cells are likely to coalesce, forming a foam with a large cell diameter and easily forming a double cell structure.

[F. Foam stabilizer]
In general, foam stabilizers are said to have the effect of increasing the compatibility of each raw material for producing polyurethane, the effect of adjusting the surface tension of the mixed raw material, and the effect of stabilizing the bubbles generated by the foaming agent. . Examples of foam stabilizers include:
(a) nonionic surfactants such as polyethylene glycol alkyl ethers and sorbitan fatty acid esters;
(b) silicone surfactants such as polyether siloxane;
and so on.

As described above, when the silicone-based foam stabilizer and antifoaming agent are added to the raw material mixture at the same time, optimizing the composition of the raw material mixture results in obtaining a polyurethane foam containing closed cells and having a double-cell structure. can be done.
On the other hand, if the composition of the raw material mixture is optimized without adding a silicone-based foam stabilizer and adding an antifoaming agent to the raw material mixture, it is possible to A structured polyurethane foam can be obtained.

[3.1.2. Addition amount]
[A. isocyanate index]
The term "isocyanate index" refers to the ratio of the number of moles of isocyanate groups in a raw material to the number of moles of active hydrogen groups in a raw material (polyol, blowing agent, etc.) (=(NCO equivalent/active hydrogen equivalent)×100). .

If the isocyanate index is too small, the formation of the resin will not be promoted, and hardness and strength will decrease, or foaming will become difficult. Therefore, the isocyanate index is preferably 70 or more. The isocyanate index is preferably 80 or higher, more preferably 90 or higher.
On the other hand, if the isocyanate index is too large, the urethane foam will be too hard. Therefore, the isocyanate index is preferably 120 or less. The isocyanate index is preferably 115 or less, more preferably 110 or less.

[B. Foaming agent]
It is preferable to select an optimum amount of the foaming agent to be added according to the type of the foaming agent.
For example, when the foaming agent is water, if the amount of the foaming agent added is too small, the amount of air bubbles generated will be insufficient and the desired foam structure will not be obtained. Therefore, the addition amount of the foaming agent is preferably 1.0 parts by mass or more with respect to 100 parts by mass of the polyol. The amount of foaming agent added is preferably 2.0 parts by mass or more, more preferably 3.0 parts by mass or more.
On the other hand, if the amount of blowing agent added becomes excessive, the amount of isocyanate added must be increased in order to maintain the isocyanate index. As a result, the reaction between the blowing agent and the isocyanate proceeds excessively, and the exothermic temperature may become excessively high. Therefore, the amount of foaming agent to be added is preferably 10 parts by mass or less with respect to 100 parts by mass of polyol. The amount of foaming agent added is preferably 6 parts by mass or less, more preferably 5 parts by mass or less.

[C. catalyst]
One or more catalysts are used. The total amount of catalyst used is preferably 0.1 to 5.0 parts by mass, more preferably 0.3 to 3.0 parts by mass, based on 100 parts by mass of polyol.

[D. Defoamer]
If the amount of the antifoaming agent added is too small, the cells become small and the difference between the large-diameter cells and the small-diameter cells disappears, making it impossible to satisfy the characteristics of the double-cell structure. Therefore, the amount of the antifoaming agent to be added is preferably 0.5 parts by mass or more with respect to 100 parts by mass of the polyol. The amount of the antifoaming agent to be added is preferably 1.0 parts by mass or more, more preferably 2.0 parts by mass or more.
On the other hand, if the antifoaming agent is added in an excessive amount, the cells become too large and the hardness decreases. Therefore, the amount of the antifoaming agent to be added is preferably 15 parts by mass or less with respect to 100 parts by mass of the polyol. The additive amount of the antifoaming agent is preferably 12 parts by mass or less, more preferably 10 parts by mass or less.

[F. Foam stabilizer]
When adding a foam stabilizer, if the amount of the foam stabilizer added is too small, the cells in the foam may become non-uniform. Therefore, the amount of the foam stabilizer added is preferably 0.01 parts by mass or more with respect to 100 parts by mass of the polyol. The amount of the foam stabilizer added is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more.
On the other hand, when the amount of the foam stabilizer added is excessive, the cells may become closed cells and the foam may shrink. Therefore, the amount of the foam stabilizer added is preferably 2.0 parts by mass or less with respect to 100 parts by mass of the polyol. The additive amount of the foam stabilizer is preferably 1.8 parts by mass or less, more preferably 1.5 parts by mass or less.

[3.2. Second step]
Next, the obtained raw material mixture is poured into a suitable mold to react the raw material mixture (second step). Thereby, the polyurethane foam according to the present invention is obtained.

[4. action]
The silicone-based foam stabilizer has the effect of stabilizing the bubbles generated by foaming. Therefore, by adding a silicone-based foam stabilizer to a raw material mixture for producing a polyurethane foam, a polyurethane foam in which fine cells are uniformly dispersed can be obtained. However, the polyurethane foam obtained in this way has little deflection in a high-load region, so that when the thickness is reduced, the cushioning feeling is also small.

On the other hand, in the case of producing a polyurethane foam using a raw material mixture containing or not containing a silicone foam stabilizer and containing an antifoaming agent, if the raw material composition is optimized, a polyurethane foam with a large resonance magnification, i.e. , a polyurethane foam having a large cushioning feeling can be obtained even when the thickness is reduced.

(Examples 1 to 6, Comparative Examples 1 to 5)
[1. Preparation of sample]
For polyols,
(a) main polyol 1 (manufactured by Sanyo Chemical Industries, Ltd., KC737),
(b) main polyol 2 (manufactured by Sanyo Chemical Industries, Ltd., No. 38), and
(c) polymer polyol (manufactured by Sanyo Chemical Industries, Ltd., FM5704)
was used.

As the isocyanate, K645 (modified MDI) manufactured by Covestro with an isocyanate content (NCO%) of 28% was used.
An amine-based catalyst (33LSI) manufactured by EVONIK was used as a resinification catalyst.
Water was used as the foaming agent, and an amine catalyst (BL-19) manufactured by EVONIK was used as the foaming catalyst.
Fatty acid ester manufactured by EVONIK was used as an antifoaming agent.
S240 manufactured by Covestro was used as a foam breaker.
Further, a silicone-based foam stabilizer (B8738LF2) manufactured by EVONIK was used as a foam stabilizer.

Table 1 shows the mixing ratio (parts by mass) of the raw materials. Raw materials were blended at the blending ratio shown in Table 1 to obtain a raw material mixture for producing flexible polyurethane foam. This raw material mixture was poured into a mold of 40 cm×40 cm×t10 cm and foamed at a mold temperature of about 60.degree.

[2. Test method]
[2.1. Cell diameter distribution]
A molded polyurethane foam having a thickness of 100 mm was horizontally sliced at a position of 45 mm and a position of 60 mm from the surface side to obtain a flat plate having a thickness of 15 mm. Further, a cut sample of 100×100×15 mm was produced from approximately the center of the flat plate, and this was used as the core layer.
An optical micrograph of the horizontal plane (100×100 mm plane) of the core layer was taken. 100 cells were randomly selected from the cells appearing on the horizontal plane, and the diameter of each cell was measured. When each cell was distorted and elliptical, the minor axis of the cell was measured and defined as the "diameter".

[2.2. Hardness]
The hardness (25% ILD) of the polyurethane foam was measured according to JIS K6400-2:2012 (Method D).
[2.3. FS characteristics]
An FS curve was obtained for the obtained polyurethane foam in a load range of 0N to 980N. Further, the hysteresis loss, 400N static spring constant, and deflection coefficient were calculated from the FS curve according to JIS K6400-2.

[2.4. Vibration characteristics]
The vibration characteristics of the polyurethane foam were measured according to JASO B407. The frequency was 1-10 Hz. A resonance magnification, a resonance frequency, a 10 Hz magnification, and a 6 Hz magnification were obtained from the obtained vibration curve.
[2.5. Attenuation characteristics]
A free drop test was performed on the polyurethane foam according to JJASO B408. A logarithmic decay rate and a decay time were calculated from the obtained decay curve.

[2.6. core density]
The core density of the flexible polyurethane foam was measured according to JASO B408.
[2.7. Breathability]
Air permeability (A method) was measured according to JIS K6400-7 A method (sample size: 51 x 51 x 25 mm). In addition, air permeability (B method) was measured according to JIS K6400-7 B method (sample thickness: 10 mm).

[3. result]
[3.1. Cell diameter distribution]
1(A) to 1(C) show optical micrographs of cross sections of the polyurethane foams obtained in Examples 3 to 5, respectively. 2(A) to 2(C) show the diameters of 100 randomly selected cells appearing in the cross section of the polyurethane foams obtained in Examples 3 to 5, respectively. From FIGS. 1 and 2, it can be seen that the larger the amount of antifoaming agent added, the larger the ratio of the large-diameter cells and the larger the diameter of the large-diameter cells.

Table 2 shows the cell size distribution, deflection coefficient, and 400 N static spring constant of large-diameter cells and small-diameter cells contained in the polyurethane foams obtained in Examples 1-6 and Comparative Examples 1-5. Table 2 shows the following.
In addition, "M _small " means that when 100 or more cells are randomly selected from all the cells contained in the polyurethane foam and the cumulative distribution of the diameter of the cells is determined based on the number, the cumulative distribution in the cumulative distribution Refers to the arithmetic mean of the cell diameters with values ranging from 0% to 10%.
“M _large ” means the arithmetic mean of the diameters of cells whose integrated value in the integrated distribution is in the range of 90% to 100%.
"CV _total " refers to the coefficient of variation of the diameter of all cells contained in the polyurethane foam.
"CV _small " refers to the coefficient of variation of the diameter of the small cells contained in the polyurethane foam.
"CV _large " refers to the coefficient of variation of the diameter of the large cells contained in the polyurethane foam.
“ΔCV” refers to CVlarge−CVsmall.
"m _large " refers to the average diameter of large cells.
“m _small ” refers to the average diameter of small cells.

(1) When the M _large /M _small ratio was 5.0 or more, except for Example 2, the deflection coefficient was 2.8 or less. Moreover, when the M _large /M _small ratio was 6.0 or more, the deflection coefficient was 2.7 or less except for Example 2. Furthermore, when the M _large /M _small ratio was 8.0 or more, the deflection coefficient was 2.4 or less.
(2) When both the silicone-based foam stabilizer and the antifoaming agent were added, the 400N static spring constant became 9N/mm or less when the added amount of the antifoaming agent was 6 parts by mass or more.
(3) When only the antifoaming agent was added, the 400N static spring constant was 9N/mm or less regardless of the amount of the antifoaming agent added.

(4) When the CV _total was 50% or more, the deflection coefficient was 2.8 or less except for Example 2 and Comparative Example 1. Moreover, when the CV _total was 60% or more, the deflection coefficient was 2.7 or less except for Example 2. Furthermore, when the CV _total was 90% or more, the deflection coefficient was 2.4 or less.
(5) When ΔCV was −30% to 60%, the 400N static spring constant became 10N/mm or less except for Example 2. Furthermore, when ΔCV was -5% to 40%, the 400N static spring constant was 9N/mm or less, except for Example 2.

[3.2. FS characteristics]
FIG. 3 shows the FS properties of the polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. FIG. 4 shows the FS characteristics of the polyurethane foams obtained in Example 1 and Comparative Examples 2-5. 3 and 4, regardless of the presence or absence of a silicone-based foam stabilizer, it can be seen that the greater the amount of antifoaming agent added, the greater the amount of deflection in the high-load region.

[3.3. Vibration characteristics]
5 shows vibration curves of the polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. FIG. When the silicone-based foam stabilizer was not added, the resonance frequency did not change significantly even when the amount of antifoaming agent added was increased. On the other hand, as the amount of antifoaming agent added increased, the resonance magnification decreased, but was 2.3 or more, which was good. The air permeability tends to decrease as the amount of the antifoaming agent added increases.

FIG. 6 shows vibration curves of the polyurethane foams obtained in Example 1 and Comparative Examples 2-5. When the silicone-based foam stabilizer was added and the amount of the antifoaming agent added was 4 to 8 parts by mass, the resonance frequency shifted to the high frequency side. This is probably because the polyurethane foam has a closed-cell structure and the air permeability of the polyurethane foam has decreased.

[3.4. Attenuation characteristics]
FIG. 7 shows the results of the free drop test of the polyurethane foams obtained in Examples 2 to 6 and Comparative Example 1. When no silicone foam stabilizer was added, the logarithmic decrement increased as the amount of antifoam added increased. This is considered to be due to the lower air permeability. In particular, Examples 3 and 4, in which the antifoaming agent was added in an amount of 2 parts or 4 parts, had a logarithmic decrement of 1.5 or less, which was very excellent, and a moderate cushioning feeling was obtained.

FIG. 8 shows the results of the free drop test of the polyurethane foams obtained in Example 1 and Comparative Examples 2-3 and 5. When the silicone foam stabilizer and the antifoaming agent were added at the same time, the resilience was lower than when only the antifoaming agent was added. This is probably because the polyurethane foam has a closed-cell structure and the air permeability of the polyurethane foam has decreased.

[3.5. comprehensive evaluation]
Table 3 shows a list of various test results.

Although the embodiments of the present invention have been described in detail above, the present invention is by no means limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

The polyurethane foam according to the present invention can be used as an interior material for automobiles and aircraft, and as a damping material and soundproofing material for OA equipment and electric appliances.

Claims (6)

A polyurethane foam having a resonance magnification of 2.3 or more. 2. The polyurethane foam according to claim 1, which has a logarithmic decrement of 3.5 or less. 3. The polyurethane foam according to claim 1, which has an air permeability (A method) of 10 cm ³ /cm ² /s or more and/or an air permeability (B method) of 10 L/min or more. 4. The polyurethane foam according to any one of claims 1 to ³ , having a core density of ³⁵ kg/m3 or more and 80 kg/m3 or less. 5. The polyurethane foam according to any one of Claims 1 to 4, which does not contain a silicone foam stabilizer. A seat cushion using the polyurethane foam according to any one of claims 1 to 5 as a seat pad.

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