JP7625399B2 - Sound-absorbing urethane foam - Google Patents

Description

The present invention relates to sound-absorbing urethane foam.

Conventionally, shock absorbing materials have been installed inside the doors, around the ceiling, and inside the pillars of automobiles to protect passengers from external shocks while in the automobile. Known shock absorbing materials include, for example, rigid polyurethane foam and foamed thermoplastic resin beads.

In addition, in today's automobiles, there is a demand to control noise such as engine noise and tire noise, and to increase the quietness inside the vehicle. However, the above-mentioned rigid polyurethane foam and thermoplastic resin bead foams generally have a closed cell structure, which causes the problem of poor sound absorption performance. Although there is known technology for imparting an open cell structure to rigid polyurethane foam and thermoplastic resin bead foams, it has been difficult to impart excellent sound absorption performance over a wide frequency range when the wall thickness is thin.

JP 2013-047338 A JP 2005-272806 A Patent No. 4461453

The present invention was made in consideration of the above circumstances, and aims to provide a sound-absorbing urethane foam with excellent sound-absorbing performance.

According to one aspect of the present invention, there is provided a sound-absorbing urethane foam. The sound-absorbing urethane foam has a normal incidence sound absorption rate of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz when the diameter is 29 mm and the thickness is 10 mm. The sound-absorbing urethane foam is obtained by foaming in a reaction system including a polyol, a polyisocyanate, a blowing agent, a catalyst, and an additive. The polyol includes polyol A having a weight average molecular weight in the range of 2000 to 12000 and an ethylene oxide content of 50% by weight or more, and polyol B having a weight average molecular weight in the range of 4000 to 12000 and an ethylene oxide content in the range of 5% by weight or more and less than 50% by weight. The weight ratio of polyol A to the weight of the polyol is in the range of 35% by weight to 80% by weight. The catalyst includes diethanolamine. The sound-absorbing urethane foam has an isocyanate index in the range of 130 to 250.

The present invention provides a sound-absorbing urethane foam with excellent sound-absorbing properties.

FIG. 2 is a plan view showing an example of a sound-absorbing urethane foam. A cross-sectional view showing a cross section along line II-II of the sound-absorbing urethane foam shown in Figure 1. 3 is a cross-sectional view showing a cross section of the sound-absorbing urethane foam shown in FIG. 1 taken along line III-III. FIG. 2 is a schematic diagram showing how sound waves propagate through a porous elastic material. FIG. 2 is a schematic diagram showing how an incident wave entering the skeleton of a porous elastic material is attenuated. 1 is a sound absorption coefficient graph showing the measurement results of the normal incidence sound absorption coefficient of a sound-absorbing urethane foam according to an embodiment. 4 is a sound absorption coefficient graph showing the measurement results of the normal incidence sound absorption coefficient of the sound-absorbing urethane foam according to the embodiment. 4 is a sound absorption coefficient graph showing the measurement results of the normal incidence sound absorption coefficient of the sound-absorbing urethane foam according to the embodiment. 4 is a sound absorption coefficient graph showing the measurement results of the normal incidence sound absorption coefficient of the sound-absorbing urethane foam according to the embodiment. 4 is a sound absorption coefficient graph showing the measurement results of the normal incidence sound absorption coefficient of the sound-absorbing urethane foam according to the embodiment.

The floor of a typical automobile is equipped with lower leg impact absorbing materials. Traditionally, foamed polypropylene and foamed polyethylene, which have excellent impact absorbing properties, have been the mainstream materials for lower leg impact absorbing materials, but rigid urethane foam, which has not only impact absorbing properties but also sound absorbing properties, is also used. Rigid urethane foam is characterized by being lighter and stronger than foamed polypropylene, for example.

Noise perceived by vehicle occupants inside the vehicle has a high sound pressure level in the low frequency band. Therefore, shock absorbing materials installed in vehicles are required to have not only a certain shock absorbing performance (buckling ability), but also, for example, excellent sound absorbing performance in the low frequency band. Recently, there has been an increasing demand to reduce the thickness of shock absorbing materials in order to realize a large interior space and to reduce the vehicle weight. In other words, there is a demand to achieve excellent sound absorbing performance and practical shock absorbing performance with shock absorbing materials that are as thin as possible.

The sound-absorbing urethane foam according to the embodiment has a diameter of 29 mm and a normal incidence sound absorption coefficient of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz when the diameter is 29 mm and the thickness is 10 mm. For example, a normal incidence sound absorption coefficient measurement performed on a block of 29 mm diameter and 10 mm thickness shows that the normal incidence sound absorption coefficient is 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. This block can be at least a part of the sound-absorbing urethane foam according to the embodiment. That is, the block is the sound-absorbing urethane foam itself, or a urethane foam cut into a cylindrical shape having the above dimensions from a sound-absorbing urethane foam having a size that allows cutting out a cylindrical shape of 10 mm thickness and 29 mm diameter. Note that in this specification, "normal incidence sound absorption coefficient" may be abbreviated to "sound absorption coefficient".

A sound-absorbing urethane foam that is as thin as 10 mm and has a normal incidence sound absorption rate of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz can be said to have excellent sound-absorbing performance. It is preferable that the sound-absorbing urethane foam has a designed surface. When the urethane foam is obtained by molding, for example, the designed surface refers to the surface that was in contact with the upper part of the metal mold during molding. The designed surface is also called the skin or skin surface. Whether or not the sound-absorbing urethane foam has a designed surface can be determined by observing the surface and/or cross section of the sound-absorbing urethane foam with a scanning electron microscope (SEM).

<Method for measuring normal incidence sound absorption coefficient>
First, a cylindrical urethane foam block with a diameter of 29 mm (29φ) and a thickness of 10 mm is prepared as the object for measuring the sound absorption coefficient. The block is produced by molding using a metal mold that gives the block a thickness of 10 mm. The block can be prepared using a punching machine equipped with a 29φ punching die. Five of these blocks are prepared to calculate the average value of the sound absorption coefficient measurement results.

The sound absorption coefficient measurement device used is the Acoustic Duct/Transfer Function Method Normal Incidence Acoustic Measurement System Model 9301 manufactured by Rion Co., Ltd., or a device with equivalent functions. The normal incidence acoustic measurement system allows sound to be incident perpendicularly on a sound absorbing or insulating material inside an acoustic tube (acoustic duct), capturing the reflected or transmitted sound and measuring the sound absorption coefficient, acoustic impedance-related items, and transmission loss of the material. The normal incidence acoustic measurement system is started, the microphone is calibrated, and preparation for the sound absorption coefficient measurement is completed.

The sound absorption coefficient is measured by setting the block at a specified position inside the duct so that sound is incident in a direction parallel to the thickness direction of the block. Sound absorption coefficient measurements are performed in accordance with JIS A 1405:1994. If the block has a decorative surface, the block is set so that sound is incident on this decorative surface.

Then, the normal incidence sound absorption coefficients are measured for frequencies of 500 Hz, 630 Hz, 800 Hz, 1000 Hz, 1250 Hz, 1600 Hz, 2000 Hz, 2500 Hz, 3150 Hz, 4000 Hz, 5000 Hz, and 6300 Hz. This measurement is performed for each of the five blocks, and the normal incidence sound absorption coefficients at each frequency are calculated to determine the normal incidence sound absorption coefficient at each frequency. Based on the measurement results, a line graph can be created in which the horizontal axis indicates frequency (Hz) and the vertical axis indicates sound absorption coefficient (%). In this specification, the line graph is called a "sound absorption coefficient graph." The sound absorption coefficient graphs in Figs. 6 to 10 described later are logarithmic graphs.

When the sound absorption coefficient of the object being measured is 40% or more at all frequencies of 1000Hz, 1250Hz, 1600Hz, 2000Hz, 2500Hz, and 3150Hz, it can be considered that the normal incidence sound absorption coefficient is 40% or more over the entire frequency range of 1000Hz to 3150Hz.

As a result of normal incidence sound absorption measurements, sound-absorbing urethane foam preferably has a normal incidence sound absorption rate of 45% or more over the entire frequency range of 1000 Hz to 3150 Hz, and even more preferably has a normal incidence sound absorption rate of 50% or more. When sound-absorbing urethane foam is used as a lower limb impact absorbing material for automobiles, etc., the higher the sound absorption rate over the entire frequency range of 1000 Hz to 3150 Hz, the less likely the passengers in the automobile, etc. will perceive low-frequency noise. Therefore, the passengers can enjoy a comfortable ride. The low-frequency range refers to, for example, the frequency range of 1000 Hz to 3150 Hz.

From the viewpoint of effectively absorbing noise in the low frequency band, it is preferable that the sound-absorbing urethane foam has a peak sound absorption coefficient at frequencies between 1000 Hz and 2000 Hz in the sound absorption coefficient graph obtained as a result of normal incidence sound absorption coefficient measurement. In this case, the sound absorption coefficient at, for example, 500 Hz to 2000 Hz is excellent. For example, as shown in the sound absorption coefficient graph in Figure 6, Example 8 as an embodiment shows the best sound absorption coefficient at a frequency of 1600 Hz. In other words, Example 8 has a peak sound absorption coefficient at a frequency of 1600 Hz. Therefore, the sound-absorbing urethane foam of Example 8 can effectively absorb noise in the frequency band between 500 Hz and 2000 Hz.

The shape and dimensions of the sound-absorbing urethane foam are not particularly limited. The sound-absorbing urethane foam has a portion with a thickness of, for example, 15 mm or less. The normal incidence sound absorption coefficient measurement is performed, for example, on a block extracted from a portion with a thickness of 15 mm or less. Even in a portion with a thickness of 15 mm or less, the sound-absorbing urethane foam preferably has a diameter of 29 mm and a normal incidence sound absorption coefficient at a thickness of 10 mm of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. The block has, for example, a cylindrical shape with a diameter of 29 mm and a thickness of 10 mm.

In one example, the sound-absorbing urethane foam has a portion with a thickness of 10 mm or more, but it does not have to have a portion with a thickness of 10 mm or more. In such a case, when preparing a block for measuring the normal incidence sound absorption coefficient of the sound-absorbing urethane foam, a urethane foam with a thickness of 10 mm or more is manufactured using the same composition as the sound-absorbing urethane foam, and a block with a diameter of 29 mm and a thickness of 10 mm is prepared from the manufactured urethane foam, and the normal incidence sound absorption coefficient measurement is performed on this block.

Figure 4 shows a model diagram of sound propagation in a porous elastic material such as urethane foam. The sound-absorbing urethane foam according to the embodiment has, for example, the porous elastic structure shown in Figure 4. The porous elastic body 100 is made of a skeleton 101 having a three-dimensional lattice structure. The skeleton 101 includes an isocyanurate structure including urea bonds and urethane bonds. The isocyanurate structure is a cyclic structure formed by a trimerization reaction of isocyanate. The porous elastic body 100 includes voids 102 between the lattices formed by the skeleton 101. The voids 102 may be openings. The sizes of the multiple lattices formed by the skeleton 101 are not uniform.

A sound wave SW is incident on the porous elastic body 100. The vibrations transmitted by the sound wave SW generate an air-propagating wave 103 that passes through the voids 102 and a solid-propagating wave 104 that propagates through the skeleton 101. The air-propagating wave 103 and the solid-propagating wave 104 interact with each other while they are propagating, and each of the propagating waves is attenuated (sound absorption). In addition, a part of the incident wave that is incident on the skeleton 101 as the solid-propagating wave 104 is attenuated by being converted to thermal energy as shown in FIG. 5. As shown in FIG. 5, a part of the incident wave I that is incident on the skeleton 101 collides with the skeleton 101 and is reflected as a reflected wave R. The other part of the incident wave I that is incident on the skeleton 101 is emitted from the skeleton 101 to the outside of the skeleton 101 as a transmitted wave T after propagating through the skeleton 101. The wave that is incident on the skeleton 101 can be converted to thermal energy r while propagating through the skeleton 101.

The sound absorption rate of sound-absorbing urethane foam varies depending on how the skeleton within the sound-absorbing urethane foam is constructed. From the viewpoint of sound absorption rate, it is undesirable for the proportion of cyclic structures in the skeleton 101 to be too small, and undesirable for it to be too large. In order to improve the sound absorption performance of sound-absorbing urethane foam, it is effective to mix not only closed cell structures but also open cell structures. When manufacturing sound-absorbing urethane foam by foaming, if the equivalent weight of polyol is increased, it tends to be difficult to form a membrane. In other words, there is a tendency for more open cell structures to be formed. In that case, the portion that exists as a lattice structure is relatively reduced, making it difficult for sound waves to propagate through the voids 102 and to be converted into thermal energy, which may result in a decrease in sound absorption performance.

Focusing on the breathability of sound-absorbing urethane foam, for example, reducing the breathability of the foam promotes the conversion of sound waves into thermal energy, which tends to improve sound absorption performance. However, if the breathability is reduced too much, the amount of sound waves emitted as reflected waves increases, and sound absorption performance tends to deteriorate.

The air permeability of a sound-absorbing urethane foam having a thickness of 10 mm is preferably, for example, 0.5 cc/ ^cm2 /sec to 40 cc/ ^cm2 /sec. By setting the air permeability within this range, a good sound absorption coefficient can be obtained in the low frequency band. The air permeability of a sound-absorbing urethane foam having a thickness of 10 mm is more preferably 10 cc/ ^cm2 /sec to 30 cc/ ^cm2 /sec. The air permeability can be measured in accordance with JIS K6400 7 B method: 2012.

The raw materials and blending for obtaining the sound-absorbing urethane foam according to the embodiment will be described. The sound-absorbing urethane foam can be obtained, for example, by foaming in a reaction system containing polyol, polyisocyanate, a foaming agent, a catalyst, and additives. From the viewpoint of making it easier to control the bubble structure, molding is the preferred manufacturing method.

When producing polyurethane foam by molding, a liquid obtained by mixing and stirring a polyol component and a polyisocyanate component is poured into a mold. When these components cure, the foaming reaction and the resinification reaction proceed simultaneously. Therefore, when molding a polyurethane foam having a thin portion, for example a portion having a thickness of 10 mm or less, it is desirable that the molding proceeds appropriately even in the part of the mold corresponding to that portion. In other words, it is desirable that the thin portion of the obtained polyurethane foam does not have defects such as skin peeling, underfill, air pockets, and cracks. Sound-absorbing polyurethane foams that have few defects and can be produced in the desired shape have excellent moldability. Moldability varies depending on various factors, but it is desirable that the sound-absorbing polyurethane foam according to the embodiment has excellent moldability in the thin portion.

In order to obtain a sound-absorbing urethane foam that has a normal incidence sound absorption rate of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz as a result of normal incidence sound absorption rate measurements, it is preferable that the polyol component (polyol) used as a raw material contains the following polyol B. Polyol B has a weight average molecular weight in the range of 4000 to 12000 and an ethylene oxide content of 5% by weight or more and less than 50% by weight. Polyol B is, for example, polypropylene glycol having a hydroxyl group at the end. If polyol B with a weight average molecular weight of 4000 or more is used, the number of crosslinking points during the reaction can be reduced, and a urethane foam with low breathability can be obtained. As described above, a urethane foam with low breathability has excellent sound absorption performance.

Note that a complex shape includes, for example, a shape that includes a portion that is 15 mm or less in thickness. When performing the normal incidence sound absorption coefficient measurement described above, it is desirable to extract the block to be measured so that it includes a portion that is 15 mm or less in thickness. This is because a urethane foam that has excellent sound absorption performance in such thin portions can be estimated to be a sound-absorbing urethane foam that has excellent sound absorption performance overall.

If the weight average molecular weight of polyol B exceeds 12,000, the viscosity of polyol B will be too high, and it may be impossible to mold a sound-absorbing urethane foam. Alternatively, since the molecular chains are long, the crosslink density after molding will be low and the foam will tend to be too soft, and it may be impossible to obtain a proper foam. Note that, at the time of filing this application, polyols with a weight average molecular weight of more than 12,000 are not commercially available and are difficult to obtain.

The weight average molecular weight of polyol B is preferably in the range of 5,000 to 8,000, and more preferably in the range of 6,500 to 7,500.

Since the ethylene oxide content of polyol B is less than 50% by weight, it has a higher retention of bubbles generated during the foaming process compared to polyol A described later. In addition, when the ethylene oxide content is less than 50% by weight, a film tends to form in the obtained sound-absorbing urethane foam, resulting in low breathability and a tendency for the sound absorption rate in the low frequency range to be excellent. This is thought to be because incident waves in the low frequency range are input to the sound-absorbing urethane foam with low breathability, and the incident waves are converted into thermal energy and absorbed inside the sound-absorbing urethane foam. By using polyol B, it becomes easier to obtain a sound-absorbing urethane foam that is not only excellent in sound absorption performance but also excellent in moldability. The ethylene oxide content of polyol B is preferably in the range of 5% to 40% by weight, and more preferably in the range of 5% to 30% by weight.

It is preferable that polyol B has a terminal ethylene oxide cap structure.

The hydroxyl value of polyol B is preferably 14 mg KOH/g or more and 56 mg KOH/g or less.

The polyol component (polyol) preferably further contains polyol A described below. Polyol A has a weight average molecular weight in the range of 2000 to 12000 and an ethylene oxide content of 50% by weight or more. Polyol A is, for example, a polyether polyol. Polyol A has a higher polarity than polyol B. Therefore, by using polyol A in combination with polyol B, a polyurethane foam having a more interconnected cell structure can be obtained compared to the use of polyol B alone. In other words, a polyurethane foam having a moderately interconnected cell structure is obtained, and such a polyurethane foam has excellent sound absorbing performance. In addition, polyol A also has a relatively high weight average molecular weight, which contributes to obtaining a sound absorbing urethane foam with excellent moldability.

The weight average molecular weight of polyol A is preferably in the range of 6,500 to 10,000, and more preferably in the range of 7,000 to 9,000.

The hydroxyl value of polyol A is preferably 18 mg KOH/g or more and 52 mg KOH/g or less.

The polyol component may contain other polyols different from polyol A and polyol B. Examples of other polyols include polyether polyols having a weight average molecular weight of 1000 or more and less than 4000, an ethylene oxide content of less than 5%, and a hydroxyl value of 40 mgKOH/g or more. Blending a polyether polyol having a weight average molecular weight of less than 4000 as the other polyol has the effect of making it easier to impart impact absorption performance (buckling properties).

In one example, the blending ratios of polyol A, polyol B and other polyols in the polyol component (polyol) can be 35% to 80% by weight, 5% to 40% by weight and 5% to 30% by weight, respectively. However, they are blended so that the total is 100% by weight. The blending ratios can be adjusted as appropriate, so long as the normal incident sound absorption coefficient of the resulting sound-absorbing urethane foam is 40% or more over the entire frequency range of 1000 Hz to 3150 Hz.

The weight ratio of polyol B to the weight of the polyol component (polyol) can be in the range of 5% to 40% by weight. If the weight ratio of polyol B to the weight of the polyol component is too small, the sound-absorbing urethane foam will have high breathability, and the sound absorption rate in the frequency range of 1000 Hz to 3150 Hz may decrease. On the other hand, if the weight ratio of polyol B to the weight of the polyol component is too large, the breathability may decrease, and the sound absorption rate in the frequency range of 1000 Hz to 3150 Hz may decrease. The weight ratio of polyol B to the weight of the polyol component (polyol) is preferably in the range of 5% to 30% by weight.

The weight ratio of polyol B to the weight of the polyol component may be in the range of 5% by weight to 20% by weight, in the range of 5% by weight to 15% by weight, or in the range of 10% by weight to 20% by weight.

The weight ratio of polyol A to the weight of the polyol component is preferably in the range of 50% to 75% by weight. The weight ratio of polyol A to the weight of the polyol component may be in the range of 50% to 80% by weight, in the range of 55% to 75% by weight, in the range of 60% to 75% by weight, or in the range of 65% to 75% by weight.

The weight ratio of the other polyol to the weight of the polyol component may be in the range of 10% by weight to 30% by weight, or in the range of 15% by weight to 25% by weight.

The blending ratios of polyol A, polyol B and other polyols in the polyol component can be determined by appropriately combining the above-mentioned numerical ranges. For example, the weight ratio of polyol A can be in the range of 55% to 75% by weight, the weight ratio of polyol B can be in the range of 5% to 15% by weight, and the weight ratio of other polyols can be in the range of 15% to 25% by weight.

As the polyisocyanate, it is preferable to use diphenylmethane diisocyanate (MDI). Diphenylmethane diisocyanate may be monomeric MDI, polymeric MDI, or a mixture thereof. The polyisocyanate may contain only one type of MDI, or may contain two or more types. MDI has better curing properties than toluene diisocyanate (TDI), and is therefore superior in terms of molding.

The isocyanate index used in producing the sound-absorbing urethane foam is, for example, in the range of 100 to 250, and preferably in the range of 130 to 180. However, there is no limit to the isocyanate index used in producing the sound-absorbing urethane foam, so long as the normal incidence sound absorption rate of the resulting sound-absorbing urethane foam is 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. If the isocyanate index is too low, the molding (molding) of the urethane foam itself may be difficult, and it may become impossible to remove it from the mold. If the isocyanate index is too high, only the surface (skin) is present, and there are excessive voids or cavities inside. In other words, the foam has a coarse mesh structure, and if it is produced by molding, it is prone to tearing when removed from the mold.

Catalysts that can be used include resinification catalysts, isocyanurate catalysts (trimerization catalysts), surface modification catalysts, and foaming catalysts. For each catalyst, a known catalyst used for that application can be used.

The resinification catalyst is used, for example, in an amount of 1 to 3 parts by weight relative to the weight of the polyol component. The isocyanurate catalyst is used, for example, in an amount of 2 to 5 parts by weight relative to the weight of the polyol component. The surface modification catalyst can be used, for example, in an amount of 0.5 to 5 parts by weight relative to the weight of the polyol component, and is preferably used in an amount of 1 to 3 parts by weight. The foaming catalyst is used, for example, in an amount of 0.1 to 1 part by weight relative to the weight of the polyol component.

As the surface modification catalyst, it is preferable to use diethanolamine (DEA). DEA has OH groups at both ends. These OH groups crosslink with the NCO groups of the isocyanate, which increases the strength of the skeleton of the resulting polyurethane foam, improving or stabilizing moldability and suppressing skin peeling. As a result, it is possible to mold complex shapes. For example, even if the shape has a thin portion, cracking during demolding can be suppressed. In other words, polyurethane foam containing DEA can achieve excellent moldability even in mold molding with complex shapes.

As other additives, for example, a foam stabilizer and/or a plasticizer can be added. The foam stabilizer and plasticizer can improve the moldability of the polyurethane foam. The other additives are used in an amount of, for example, 5 to 30 parts by weight based on the weight of the polyol component.

Any known blowing agent used in the manufacture of general polyurethane foams can be used. An example of the blowing agent is water. As for other additives, including foam stabilizers, any known additives used in the manufacture of general polyurethane foams can be used.

The density of the sound-absorbing urethane foam is, for example, within the range of 70 kg/m ³ to 120 kg/m ³ , and preferably within the range of 80 kg/m ³ to 100 kg/m ^3. If the density is within this range, even a urethane foam having a portion with a thickness of 15 mm or less can exhibit practical shock absorbing performance.

The compressive strength of the sound-absorbing urethane foam is, for example, in the range of 0.05 MPa to 0.5 MPa.

An example of a sound-absorbing urethane foam according to the embodiment will be described with reference to Figures 1 to 3.

Figure 1 is a plan view that shows an example of a sound-absorbing urethane foam. Figure 1 shows an example in which the sound-absorbing urethane foam is a lower limb impact absorbing material (foot panel). Figure 2 is a cross-sectional view that shows an outline of the cross section of the sound-absorbing urethane foam shown in Figure 1 taken along line II-II. Figure 3 is a cross-sectional view that shows an outline of the cross section of the sound-absorbing urethane foam shown in Figure 1 taken along line III-III.

The lower leg impact absorbing material 10 comprises a first portion 1, a second portion 2, and a thick portion 3. The first portion 1, the second portion 2, and the thick portion 3 are integrally molded by molding using a single die to form the lower leg impact absorbing material 10. The lower leg impact absorbing material 10 can be mounted, for example, on the floor of an automobile. For example, a floor mat is laid on the lower leg impact absorbing material 10 mounted on the floor of the automobile, and both feet of the occupant are placed on the lower leg impact absorbing material via the floor mat.

The first portion 1 and the second portion 2 are thinner than the thick portion 3. The second portion 2 is generally rectangular and has an end face defined by a boundary portion 4. The first portion 1 and the thick portion 3 extend from the end face of the second portion 2. The lower limb impact absorbing material 10 is curved so that the boundary portion 4 between the second portion 2 and the first portion 1 and the thick portion 3 forms a valley. The boundary portion 4 forms a valley on one side of the lower limb impact absorbing material 10, but forms a peak on the other side.

The lower limb impact absorbing material 10 has a surface 5 where the second portion 2, the first portion 1, and the thick portion 3 form a valley. The lower limb impact absorbing material 10 has a back surface 6 where the second portion 2, the first portion 1, and the thick portion 3 form a mountain. The thick portion 3 has a convex shape on the surface 5. In other words, the thick portion 3 has a structure on the surface 5 that protrudes beyond the surface of the first portion 1, using the surface of the first portion 1 as a reference.

When the lower leg impact absorbing material 10 is mounted on the floor of an automobile, for example, the right foot of the occupant is placed on the surface 5 of the first portion 1 and the second portion 2, and the left foot of the occupant is placed on the surface 5 of the second portion 2 and the thick portion 3.

The thickness of the first portion 1 and the second portion 2 is, for example, 30 mm or less. The first portion 1 and the second portion 2 can each have a portion with a thickness of 15 mm or less. The thickness of this portion may be 10 mm or less. The thickness of the thick portion 3 is, for example, 70 mm to 110 mm.

In Figures 1 to 3, the sound-absorbing urethane foam is used as an example of a lower limb impact absorbing material, but the uses of the sound-absorbing urethane foam are not particularly limited, and it is suitable for use in applications that require sound absorption and impact absorption performance. Sound-absorbing urethane foam can be used, for example, as door interior cushioning material, head protection material, floor raising material, tool boxes, luggage boxes, ceiling material, seat core material, sun visor core material, pillar core material, etc. It is also possible to obtain sound-absorbing urethane foam in the desired shape by cutting the foam.

[Example]
Examples will be described below, but the embodiments are not limited to the examples described below.

According to the formulation shown in Table 1 below, sound-absorbing urethane foams according to Examples 1 to 17, 6A, and 7A were produced by molding. The raw materials listed in Table 1 are as follows. In Table 1, the blending ratio of each raw material is shown in parts by weight. However, "index" indicates the isocyanate group equivalent (concentration) in the polyisocyanate relative to the total of the active hydroxyl group equivalent (concentration) in the polyol, the hydroxyl group equivalent (concentration) of other materials containing an active hydroxyl group equivalent (concentration), and the hydroxyl group equivalent (concentration) of water.

The sound-absorbing urethane foams of Examples 18 to 23 were produced by molding according to the formulation shown in Table 2 below. The raw materials listed in Table 2 are as follows. In Table 2, the blending ratio of each raw material is shown in parts by weight.

(1) Polyol 1: trade name: QB8000 (weight average molecular weight 8000, polyoxyethylene content 80%) manufactured by Toho Chemical Industry Co., Ltd.
(2) Polyol 2: Trade name: EP-901P (weight average molecular weight 7000, polyoxyethylene content 15%) manufactured by Mitsui Chemicals SKC Polyurethanes Co., Ltd.
(3) Polyol 3; Trade name: NC630 (weight average molecular weight 7400, polyoxyethylene content 14% to 16%) manufactured by Dow Chemical
(4) Polyol 4: Trade name: KC745 (weight average molecular weight: 5000, polyoxyethylene content: 20% to 25%) manufactured by Sanyo Chemical Industries, Ltd.
(5) Polyol 5; trade name: EP330N (weight average molecular weight: 5000, polyoxyethylene content: 10% to 12%) manufactured by Mitsui Chemicals SKC Polyurethanes Co., Ltd.
(6) Polyol 6; trade name: T-5000D (weight average molecular weight 5000, polyoxyethylene content 0%) manufactured by Mitsui Chemicals SKC Polyurethanes, Inc.
(7) Polyol 7; Trade name: CP1421 (weight average molecular weight 5000, polyoxyethylene content 75%) manufactured by Dow Chemical
(8) Polyol 8; Trade name: V4053 manufactured by Dow Chemical (weight average molecular weight: 12,500, polyoxyethylene content: 69%)
(9) Polyol 9; trade name of Mitsui Chemicals SKC Polyurethanes Co., Ltd.: T-3000S (weight average molecular weight 3000, polyoxyethylene content 0%)
(10) Additive A: Trade name: EM ALEX DEG-di-O (diethyl glycol dioleate) manufactured by Nippon Nyukazai Co., Ltd.
(11) Additive B: Trade name: SF2962 manufactured by Dow Corning Toray Co., Ltd.
(12) Additive C: Trade name: VORASURF 1280 additive, manufactured by Dow Corning Toray Co., Ltd.
(13) Antioxidant: Trade name: Irganox 1135 manufactured by BASF Japan Ltd.
(14) Catalyst A: N-(dimethylpropyl)diisopropylamine (DPA: N-N, N'-diisopropanolamine) (resinification catalyst)
(15) Catalyst B: Trade name: TMR7 (trimerization catalyst) manufactured by Air Products Japan Co., Ltd.
(16) Catalyst C: Diethanolamine (DEA) (surface-modified catalyst)
(17) Catalyst D: Trade name: Niax catalyst A-1 (foam catalyst) manufactured by Momentive Performance Materials, Inc.
(18) Foaming agent: Water (19) Polyisocyanate: Trade name: Sumidur 44 V 20 L, manufactured by Sumika Covestro Urethane Co., Ltd.

(Example 1)
According to the formulation shown in Table 1 (by hand foaming), raw materials other than polyisocyanate, i.e., polyol component, additives, antioxidant, catalyst and foaming agent were blended to prepare a polyol-containing mixture in a disposable cup. The polyol component according to Example 1 includes polyol 1, polyol 2 and polyol 9. The obtained polyol-containing mixture is designated as Liquid A. The temperature of Liquid A was adjusted to 37°C ± 2°C. In addition, polyisocyanate was prepared as Liquid B, and the temperature of Liquid B was adjusted to 37°C ± 2°C.

A sample production mold with inner dimensions of 350 mm width, 350 mm depth, and 10 mm height was prepared, and the mold was heated to a temperature range of 65°C to 70°C and the temperature was maintained. The temperature was measured using a surface thermometer. The mold consisted of a cylindrical lower mold with a bottom, only the top surface of which was open, and an upper mold whose top surface could be closed.

Next, liquid B was added to liquid A prepared in a disposable cup, and the mixture was stirred and mixed for 5 seconds to obtain a mixed solution. Here, when the total weight parts of the polyol components were taken as 100, the weight parts of liquid A containing the polyol components were 160.4 weight parts, and the weight parts of liquid B were 235.5 weight parts. The resulting mixed solution was immediately poured into the lower die of a mold, and the upper surface of the lower die was closed using the upper die, and cured for 6 minutes. During this time, the surface temperature of the mold was maintained at 65°C to 70°C. After that, the mold was removed from the mold and left to stand at room temperature for 2 days to obtain a sound-absorbing urethane foam with dimensions of 350 mm x 350 mm x 10 mm.

(Example 2)
A sound-absorbing urethane foam was obtained in the same manner as in Example 1, except that the amount of polyisocyanate in the compounding recipe was changed to 376.8 parts by weight, thereby changing the index to 160.

(Example 3)
A sound-absorbing urethane foam was obtained in the same manner as in Example 1, except that the amount of catalyst C (DEA) was changed to 1.24 parts by weight.

(Example 4)
A sound-absorbing urethane foam was obtained in the same manner as in Example 3, except that the amount of polyisocyanate in the compounding recipe was changed to 288.3 parts by weight, thereby changing the index to 120.

(Example 5)
A sound-absorbing urethane foam was obtained in the same manner as in Example 3, except that the amount of polyisocyanate in the compounding recipe was changed to 336.4 parts by weight, thereby changing the index to 140.

(Example 6)
A sound-absorbing urethane foam was obtained in the same manner as in Example 3, except that the amount of polyisocyanate in the compounding recipe was changed to 384.4 parts by weight, thereby changing the index to 160.

(Example 7)
A sound-absorbing urethane foam was obtained in the same manner as in Example 3, except that the amount of polyisocyanate in the compounding recipe was changed to 600.7 parts by weight, thereby changing the index to 250.

(Example 8)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 3 was used instead of Polyol 2.

(Example 9)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 4 was used instead of Polyol 2.

(Example 10)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 5 was used instead of Polyol 2.

(Example 11)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 6 was used instead of Polyol 2.

(Example 12)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 7 was used instead of Polyol 2.

(Example 13)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that Polyol 8 was used instead of Polyol 2.

(Example 14)
A sound-absorbing urethane foam was obtained in the same manner as in Example 1, except that the amount of catalyst C (DEA) was changed to 2.48 parts by weight.

(Example 15)
A sound-absorbing urethane foam was obtained in the same manner as in Example 14, except that the amount of polyisocyanate in the formulation was changed to 392.0 parts by weight, thereby changing the index to 160.

(Example 16)
A sound-absorbing urethane foam was obtained in the same manner as in Example 1, except that the compounding ratio of each raw material was changed as shown in the column for Example 16 in Table 1.

(Example 17)
A sound-absorbing urethane foam was obtained in the same manner as in Example 16, except that the amount of polyisocyanate in the formulation was changed to 605.1 parts by weight, thereby changing the index to 250.

(Example 6A)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6, except that a sample preparation mold having inner dimensions of 350 mm width, 350 mm depth, and 30 mm height was used.

(Example 7A)
A sound-absorbing urethane foam was obtained in the same manner as in Example 6A, except that the amount of polyisocyanate in the compounding recipe was changed to 576.6 parts by weight, thereby changing the index to 240.

(Examples 18 to 23)
A sound-absorbing urethane foam was obtained in the same manner as in Example 1, except that the compounding ratio of each raw material was changed as shown in Table 2.

<Moldability evaluation>
The moldability (curability) of each of the sound-absorbing urethane foams obtained in Examples 1 to 23 and Examples 6A and 7A was evaluated by sensory evaluation. The urethane foam in a good condition when demolded was rated as "○", the foam in which finger marks remained when demolded by hand (insufficient curing) or the design surface peeled off was rated as "△", and the urethane foam collapsed or was in a severely insufficient curing state was rated as "×". Among Examples 1 to 23, Examples 6, 8-10, 12, 13, 15, and 18 to 23, which had a cure property of "○", had design surfaces on both sides of the 10 mm thick block. Examples of the evaluation "×" include, for example, that the foam was stringy when demolded, that the foam was ragged and brittle, or that the cells inside the foam collapsed and collapsed. In addition, if the design surface peels off when demolded, the sound absorbing performance and air permeability will change, so when multiple urethane foams are produced in continuous operation, it tends to be difficult to obtain urethane foams with stable sound absorbing performance. Therefore, it is preferable that the design surface is cured so that it does not peel off when demolded.

<Sound absorption performance evaluation>
The sound absorbing performance of the sound absorbing urethane foam according to each example was evaluated according to the method for measuring the normal incidence sound absorption coefficient described in the embodiment. In the entire frequency range of 1000 Hz to 3150 Hz, those having a normal incidence sound absorption coefficient of 40% or more were evaluated as "○", and those having a band in which the normal incidence sound absorption coefficient is less than 40% in the frequency range of 1000 Hz to 3150 Hz were evaluated as "×". However, for those evaluated as "×" in the above moldability evaluation, the sound absorbing performance could not be properly evaluated, so no evaluation was performed. In Table 1, in the row of "sound absorbing performance", examples that were not evaluated are indicated by diagonal lines.

As shown in Tables 1 and 2, the sound-absorbing urethane foams of Examples 5-13, 15-16, 18-23, 6A, and 7A had practical moldability. In other words, the moldability of these examples was rated as "Good" or "Good." Therefore, it was possible to evaluate the sound-absorbing performance.

Also, as shown in Table 1, for Examples 6A and 7A, the thickness of the urethane foam being evaluated is 30 mm.

Figures 6-10 show sound absorption coefficient graphs for Examples 5-13, 15-16, 18-23, 6A, and 7A, for which sound absorption coefficient measurements were possible. Figure 6 shows the results for Examples 6, 8-10. Figure 7 shows the results for Examples 6, 11-13, and 16. Figure 8 shows the results for Examples 5-7 and 15. Figure 9 shows the results for Examples 6A and 7A. Figure 10 shows the results for Examples 18-23. In each sound absorption coefficient graph, the horizontal axis shows frequency (Hz) and the vertical axis shows sound absorption coefficient (%).

<Density measurement>
The density of each of the sound-absorbing urethane foams according to the examples was measured and found to be 90 kg/ ^m3 .

Density was evaluated in accordance with the measurement method specified in JIS K 7222:2005.

Figure 6 shows the sound absorption coefficient measurement results for the sound-absorbing urethane foams of Examples 6 and 8-10, which have a common index of 160. These examples are examples in which the polyol corresponding to the above-mentioned polyol B was changed. The sound-absorbing urethane foams of Examples 6 and 8-10 contained polyol 2 (EP-901P), polyol 3 (NC630), polyol 4 (KC745), and polyol 5 (EP330N) as the polyol component. All of these polyols had a weight average molecular weight in the range of 4000 to 12000 and an ethylene oxide content in the range of 5% by weight or more and less than 50% by weight, so the obtained sound-absorbing urethane foams had a normal incidence sound absorption coefficient of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz.

Figure 7 also shows the sound absorption coefficient measurement results for the sound-absorbing urethane foams of Examples 6, 11-13, and 16, which all have the same index of 160. Unlike Examples 6 and 8-10, the sound-absorbing urethane foams of Examples 11-13 did not contain a polyol component equivalent to polyol B. Instead, they contained a polyol component with an ethylene oxide content of 50% by weight or more. As a result, the breathability of the resulting sound-absorbing urethane foam was high, the conversion of incident waves to thermal energy inside the urethane was reduced, and the incident waves were difficult to absorb, so the sound absorption coefficient of Examples 11-13 in the range of 1000 Hz to 3150 Hz was inferior to that of Example 6. In addition, the sound-absorbing urethane foam of Example 16 contained only polyol 1 (QB8000) and polyol 9, which have a weight average molecular weight of 4000 or more and an ethylene oxide content of 80%, as polyol components, so there were many open cells and it is possible that the sound absorption performance in the low frequency range was not excellent.

Figure 8 shows the sound absorption coefficient measurement results for the sound-absorbing urethane foams of Examples 5-7 and 15. Examples 5-7 and 15 are examples in which sound-absorbing urethane foams were manufactured with the same recipe, except for the content of catalyst C (DEA) and the index conditions. All of these examples had normal incidence sound absorption coefficients of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. Example 7, which has an index of 250, had a poorer sound absorption coefficient at 1000 Hz compared to Examples 5, 6, and 15. On the other hand, Example 7 had the best sound absorption coefficient at 3150 Hz among these examples. This shows that by increasing the index, the frequency band in which sound can be efficiently absorbed tends to change from a low frequency band to a high frequency band of about 2000 Hz to 6000 Hz.

The prescription for Example 6A is the same as that for Example 6. The prescription for Example 7A is almost the same as that for Example 7, except that the index is 240. As is clear from FIG. 9, when the thickness of the block is 30 mm when measuring the sound absorption coefficient, the sound absorption coefficient at frequencies below 2000 Hz is significantly improved. On the other hand, it can be seen that there is a problem in that the sound absorption coefficient in the low frequency band is significantly reduced when the thickness of the block is 10 mm. The sound-absorbing urethane foam according to the embodiment has excellent sound absorption performance because the normal incidence sound absorption coefficient is 40% or more over the entire frequency range of 1000 Hz to 3150 Hz, even when the thickness of the block is 10 mm.

In Examples 1 to 15 and Examples 6A and 7A shown in Table 1, the content of polyol 1 corresponding to polyol A in the polyol component was 57.85% by weight. In contrast, in Examples 18 to 23 shown in Table 2, the content of polyol 1 corresponding to polyol A in the polyol component was 70% to 75% by weight. Even when the content of polyol A in the polyol component was increased in this way, the moldability of the obtained sound-absorbing urethane foam was excellent, and the normal incidence sound absorption rate was 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. For example, when the weight ratio of polyol A in the weight of the polyol component is within the range of 35% to 80% by weight, a sound-absorbing urethane foam with excellent sound-absorbing performance can be obtained.

In Examples 1 to 15 and Examples 6A and 7A shown in Table 1, the content of polyols 2 to 8 corresponding to polyol B in the polyol component was 24.79% by weight. In contrast, in Examples 18 to 23 shown in Table 2, the content of polyol 2 corresponding to polyol B in the polyol component was 5% to 10% by weight. Even when the content of polyol B in the polyol component was reduced in this way, the moldability of the obtained sound-absorbing urethane foam was excellent, and the normal incidence sound absorption rate was 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. For example, when the weight ratio of polyol B in the weight of the polyol component is within the range of 5% to 40% by weight, a sound-absorbing urethane foam with excellent sound-absorbing performance can be obtained.

Figure 10 shows the sound absorption coefficient measurement results for the sound-absorbing urethane foams of Examples 18 to 23. As shown in the graph in Figure 10, the sound-absorbing urethane foams of Examples 18 to 23 all had normal incidence sound absorption coefficients of 40% or more over the entire frequency range of 1000 Hz to 3150 Hz.

The present invention is not limited to the above-described embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention. The embodiments may be implemented in appropriate combination, in which case the combined effects can be obtained. Furthermore, the above-described embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple constituent elements disclosed. For example, if the problem can be solved and an effect can be obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the configuration from which the constituent elements are deleted can be extracted as an invention.

1...first part, 2...second part, 3...thick part, 4...boundary part, 5...surface, 6...back side, 10...lower limb shock absorbing material, 100...porous elastic body, 101...skeleton, 102...void, 103...air-propagating wave, 104...solid-propagating wave, SW...sound wave, I...incident wave, R...reflected wave, T...transmitted wave, r...thermal energy.

Claims (3)

A sound-absorbing urethane foam obtained by foaming in a reaction system containing a polyol, a polyisocyanate, a foaming agent, a catalyst, and an additive,
The polyol includes polyol A having a weight average molecular weight in the range of 2,000 to 12,000 and an ethylene oxide content of 50% by weight or more, and polyol B having a weight average molecular weight in the range of 4,000 to 12,000 and an ethylene oxide content in the range of 5% by weight or more and less than 50% by weight,
the weight ratio of the polyol A to the weight of the polyol is within a range of 35% by weight to 80% by weight,
the catalyst comprises diethanolamine;
A sound-absorbing urethane foam having an isocyanate index in the range of 130 to 250, a diameter of 29 mm, and a normal incidence sound absorption coefficient of 40% or more when the foam has a thickness of 10 mm over the entire frequency range of 1000 Hz to 3150 Hz. The thickness of the portion is 15 mm or less,
2. The sound-absorbing urethane foam according to claim 1, wherein the normal incidence sound absorption coefficient at said portion when the diameter is 29 mm and the thickness is 10 mm is 40% or more over the entire frequency range of 1000 Hz to 3150 Hz. 3. The sound-absorbing urethane foam according to claim 1 , wherein the weight ratio of said polyol B to the weight of said polyol is within a range of 5% to 40%.