sound-absorbing material

Abstract

To provide a sound absorption material which is composed of an HIPE foam having high sound absorbency in a wide frequency region.SOLUTION: A sound absorption material 1 is composed of an HIPE foam containing a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and / or a styrenic monomer as a base material resin. A temperature obtained by subtracting a peak temperature of a loss tangent tanδ in a loss tangent tanδ curve from a temperature obtained by measuring the HIPE foam under the conditions of a frequency of 1 Hz, a load of 10 mN, and a deformation mode: compression by dynamic viscoelasticity measurement is 50°C or lower. A flow resistance per unit thickness of the HIPE foam at a flow rate of 0.5 mm / s measured based on ISO 9053-1:2018 is 7×104 N s / m4 or more and 1×106 N s / m4 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sound absorbing material. [Background technology]

[0002] Conventionally, sound-absorbing materials made of porous materials have been used in various fields such as automobiles and buildings. As this type of sound-absorbing material, for example, a sound-absorbing material made of polyurethane foam is known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2013-515837 Summary of the Invention [Problem to be solved by the invention]

[0004] However, sound-absorbing materials made of polyurethane foam have a problem in that they have low absorption of sound waves with relatively low frequencies of about 500 to 1000 Hz, such as road noise from automobiles.

[0005] On the other hand, an aqueous phase consisting of an aqueous liquid such as water is mixed with a vinyl monomer, a crosslinking agent, an emulsifier, a polymerization initiator, etc. A method is known in which a porous body made of a crosslinked polymer, called a HIPE foam, is obtained by forming a water-in-oil high internal phase emulsion (a so-called HIPE) in which a high proportion of a polyisoprene is encapsulated in an organic phase containing, for example, a polyisoprene, and polymerizing the organic phase in the emulsion. While such HIPE foams are expected to be used in a variety of applications, their use as sound-absorbing materials has not been explored to date, and there has been concern that they may not achieve the desired sound-absorbing performance.

[0006] The present invention has been made in view of the above background, and aims to provide a sound-absorbing material made of HIPE foam that has high sound absorption properties over a wide frequency range. [Means for solving the problem]

[0007] One aspect of the present invention is a sound-absorbing material made of a HIPE foam having a base resin that is a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and / or a styrene monomer, The HIPE foam is subjected to dynamic viscoelasticity measurement under the conditions of a frequency of 1 Hz, a load of 10 mN, and a deformation mode of compression, and the peak temperature of the loss tangent tanδ in the temperature-loss tangent tanδ curve is 50°C or less; The flow resistance per unit thickness of the HIPE foam at a flow velocity of 0.5 mm / s measured according to ISO 9053-1:2018 is 7 x 10 4 N·s / m 4 More than 1×10 6 N·s / m 4 The following are sound-absorbing materials. [Effects of the Invention]

[0008] The peak temperature of the loss tangent tanδ and the flow resistance per unit thickness in the temperature-loss tangent tanδ curve of the HIPE foam constituting the sound-absorbing material are each within the above-mentioned specific ranges. HIPE foam with these characteristics can effectively attenuate both structure-borne sound that propagates through the cell walls of the HIPE foam and air-borne sound that propagates through the air within the HIPE foam. Therefore, the sound-absorbing material composed of the HIPE foam has excellent sound absorption properties over a wide frequency range. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram showing an example of a low-vacuum scanning electron microscope photograph of a HIPE foam constituting a sound-absorbing material. [Figure 2] FIG. 2 is an explanatory diagram showing an example of a temperature-loss tangent tan δ curve showing the relationship between the temperature T and the loss tangent tan δ of the HIPE foam. [Figure 3]FIG. 3 is an explanatory diagram showing an example of a temperature-storage modulus curve showing the relationship between the temperature T and the storage modulus E′ of a HIPE foam. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, preferred embodiments of the sound-absorbing material will be described. In this specification, when a numerical value or a physical property value is enclosed before and after the symbol "to", the values ​​before and after the symbol are included. Furthermore, when a numerical value or a physical property value is expressed as a lower limit, it means that the value is equal to or greater than that numerical value or physical property value, and when a numerical value or a physical property value is expressed as an upper limit, it means that the value is equal to or less than that numerical value or physical property value. Furthermore, "parts by weight" and "% by weight" are essentially synonymous with "parts by mass" and "% by mass", respectively.

[0011] [HIPE Form] The sound-absorbing material in this specification is composed of HIPE foam. HIPE foam is a porous cross-linked polymer also known as polyHIPE foam, polyHIPE material, HIPE-derived foam material, high internal phase emulsion porous body, or high internal phase emulsion foam. It is obtained, for example, by polymerizing monomers in a water-in-oil high internal phase emulsion in which a high ratio of aqueous phase is encapsulated in an organic phase. High internal phase emulsion is commonly known as HIPE. HIPE foam has an open-cell structure with numerous bubbles present in its structure and numerous through-holes that connect adjacent bubbles.

[0012] HIPE foams are obtained, for example, by polymerizing vinyl monomers (specifically, acrylic monomers and / or styrene monomers) in the presence of a crosslinking agent in a water-in-oil high internal phase emulsion, in which a high proportion of aqueous phase is encapsulated in an organic phase. HIPE foams use, as their base resin, a crosslinked polymer containing components derived from acrylic monomers and / or styrene monomers, obtained, for example, by polymerizing acrylic monomers and / or styrene monomers in a water-in-oil high internal phase emulsion. Specifically, the crosslinked polymer contains components derived from acrylic monomers and / or styrene monomers in the polymer skeleton. In other words, HIPE foams use, as their base resin, a crosslinked polymer obtained by crosslinking a polymer of acrylic monomers and / or styrene monomers.

[0013] HIPE foam is a porous cured product obtained by curing a high internal phase emulsion, and its cell walls can be said to be composed of a crosslinked polymer (e.g., a vinyl-based crosslinked polymer). The cells can also be said to be pores. The shape of the cell walls and cells in HIPE foam reflects the dispersion form of the organic phase and aqueous phase in the high internal phase emulsion and the dispersion form of the aqueous phase (i.e., the dispersed phase) during polymerization.

[0014] Since the crosslinked polymer is difficult to stretch during the manufacturing process of HIPE foam, HIPE foam generally has a polymer that is difficult to align and has little anisotropy. HIPE foam can be easily distinguished from foams that are stretched during manufacturing, such as foams obtained by extrusion foaming using an extruder, and foamed bead moldings obtained by foaming expandable resin beads and molding the expanded beads in a mold.

[0015] [Bubble structure] As illustrated in FIG. 1 , the HIPE foam constituting the sound-absorbing material 1 has a cell structure in which numerous cells 12 are uniformly present, and an open-cell structure in which numerous through-holes 13 are formed that penetrate the cell walls 11 and connect adjacent cells. In FIG. 1 , the cells 12 are the portions surrounded by the cell walls 11. The through-holes 13 are holes that penetrate the cell walls 11 and connect adjacent cells 12. Specifically, the through-holes 13 are holes that are formed in the cell walls 11 and connect adjacent cells 12 across the cell walls 11. The through-holes 13 can also be referred to as through-windows or connecting holes. Because the through-holes are holes that are formed in the cell walls and connect cells, the diameter of the through-holes is usually smaller than the diameter of the cells.

[0016] The average diameter of the cells of the HIPE foam constituting the sound-absorbing material is preferably 20 μm or more and 160 μm or less. In this case, the sound absorption properties of the sound-absorbing material can be more easily improved. From the viewpoint of increasing the penetration of sound waves into the HIPE foam and facilitating the absorption of relatively high-frequency sounds, the average diameter of the cells of the HIPE foam is preferably 30 μm or more, more preferably 40 μm or more, and even more preferably 50 μm or more. Furthermore, from the viewpoint of facilitating the collision of sound waves that have penetrated into the HIPE foam with the cell walls and facilitating the absorption of relatively low-frequency sounds, the average diameter of the cells of the HIPE foam is preferably 150 μm or less, more preferably 140 μm or less, and even more preferably 120 μm or less.

[0017] The ratio of the average diameter of the through holes in the HIPE foam to the average diameter of the cells in the HIPE foam is preferably 0.05 or more and 0.5 or less. In this case, the sound absorption of the sound-absorbing material can be further improved over a wide frequency range. From the viewpoint of further improving the penetration of sound waves into the HIPE foam, the ratio of the average diameter of the through holes in the HIPE foam to the average diameter of the cells in the HIPE foam is more preferably 0.08 or more, and even more preferably 0.1 or more. Furthermore, from the viewpoint of making it easier for sound waves that have penetrated into the HIPE foam to collide with the cell walls, the ratio of the average diameter of the through holes in the HIPE foam to the average diameter of the cells in the HIPE foam is more preferably 0.4 or less, and even more preferably 0.3 or less. Furthermore, the average diameter of the through holes in the HIPE foam is preferably 5 μm or more and 30 μm or less, more preferably 6 μm or more and 25 μm or less, and even more preferably 8 μm or more and 20 μm or less.

[0018] The aforementioned average bubble diameter is the average value of the circle-equivalent diameters of the bubbles, which is the diameter of a perfect circle having the same area as the bubble area in the cross section of the HIPE foam. The average diameter of the through holes is the average value of the circle-equivalent diameters of the through holes, which is the diameter of a perfect circle having the same area as the through holes in the cross section of the HIPE foam. The method for measuring the average bubble diameter and the average diameter of the through holes will be described later, but they can be measured, for example, by image analysis of the open-cell structure of the HIPE foam.

[0019] The average bubble size can be controlled by adjusting the droplet size of the aqueous phase (i.e., the dispersed phase) of the high internal phase emulsion in the HIPE foam manufacturing method described below. For example, the droplet size in the high internal phase emulsion can be reduced by increasing the amount of emulsifier added or increasing the stirring power density during preparation of the high internal phase emulsion (emulsification step). Reducing the droplet size in the high internal phase emulsion can reduce the bubble size.

[0020] The through-holes are formed by the rupture of an oil film due to volumetric shrinkage of the polymer during polymerization of monomers in a water-in-oil high internal phase emulsion during the manufacturing method of HIPE foam described below. The oil film becomes the cell wall as polymerization and crosslinking progress. The average diameter of the through-holes can be controlled by adjusting the polymerization rate, the composition and viscosity of the organic phase, the stirring power density, and other factors during the manufacturing method of HIPE foam described below. For example, the through-hole diameter can be reduced by lowering the ratio of the aqueous phase to the organic phase or increasing the stirring power density during the preparation of the high internal phase emulsion (emulsification step).

[0021] [Flow Resistance] The flow resistance per unit thickness of the HIPE foam at a flow velocity of 0.5 mm / s measured according to ISO 9053-1:2018 is 7 x 10 4 N·s / m 4 More than 1×10 6 N·s / m 4 The flow resistance described above is a value that indicates how difficult it is for air to flow inside a porous body when air is circulated through the porous body, and the higher the flow resistance, the more difficult it is for air to flow inside the porous body.

[0022] The resistance of air to flow through a porous material at a gentle breeze correlates with the resistance of sound waves to propagate through the material. Therefore, the flow resistance per unit thickness of a HIPE foam is considered an index that can adequately represent the sound-absorbing properties of the foam. The flow resistance per unit thickness at a flow velocity of 0.5 mm / s can be calculated based on the flow resistance measured when air is passed through the HIPE foam at a flow velocity of 0.5 mm / s. However, to improve measurement accuracy, the flow resistance per unit thickness at a flow velocity of 0.5 mm / s can also be measured when air is passed through the HIPE foam at a flow velocity of, for example, 1 to 3 mm / s, and calculated based on the relationship between each flow velocity and flow resistance.

[0023] If the flow resistance per unit thickness of HIPE foam becomes too low, sound waves that penetrate into the HIPE foam will have difficulty colliding with the cell walls, and the cell walls will not attenuate structure-borne sound sufficiently. This may result in a deterioration of sound absorption in the relatively low frequency range.

[0024] On the other hand, if the flow resistance per unit thickness of HIPE foam is excessively high, it is thought that sound waves will have difficulty penetrating into the HIPE foam, and the attenuation of airborne sound due to viscous resistance etc. that occurs between the sound waves and the cell walls will be insufficient. Therefore, in this case, the sound absorption in the relatively high frequency range will decrease, which may lead to a deterioration in sound absorption.

[0025] By setting the flow resistance per unit thickness of the HIPE foam within the above-mentioned range, it is possible to attenuate both airborne sound, which has a relatively high frequency, and structure-borne sound, which has a relatively low frequency, in a balanced manner among the sound waves propagating through the HIPE foam. As a result, it is possible to improve the sound absorption properties in the relatively low frequency range and also improve the sound absorption properties of the sound-absorbing material over a wide frequency range.

[0026] The flow resistance per unit thickness of a HIPE foam is mainly related to the density, cell diameter, and ratio of cell diameter to through-hole diameter of the HIPE foam. Therefore, by controlling the cell wall and cell structure in the HIPE foam, the flow resistance per unit thickness of the HIPE foam can be adjusted to the above-mentioned specific range. For example, as the density of the HIPE foam decreases, the proportion of cells in the volume of the HIPE foam increases, and the flow resistance per unit thickness decreases. Also, for example, as the cell diameter of the HIPE foam increases, air can more easily flow through the cells of the HIPE foam, and the flow resistance per unit thickness decreases.

[0027] [Tanδ peak temperature] The peak temperature of the loss tangent tanδ in the temperature-loss tangent tanδ curve (hereinafter referred to as the "T-tanδ curve") of the HIPE foam obtained by dynamic viscoelasticity measurement (DMA: Dynamic Mechanical Analysis) is 50°C or less. The T-tanδ curve is measured by subjecting the HIPE foam to dynamic viscoelasticity measurement under the conditions of frequency: 1 Hz, load: 10 mN, and deformation mode: compression. In the dynamic viscoelasticity measurement, the heating rate is preferably 10°C / min and the temperature range is preferably -100 to 120°C.

[0028] Figure 2 shows an example of a T-tanδ curve for a HIPE foam. The vertical axis in Figure 2 represents the loss tangent tanδ, and the horizontal axis represents temperature. The T-tanδ curve has a tanδ peak where the tanδ value reaches a maximum near the glass transition temperature Tg of the crosslinked polymer that constitutes the HIPE foam. The loss tangent tanδ obtained by dynamic viscoelasticity measurement is the ratio E" / E' of the loss modulus E" to the storage modulus E' of the crosslinked polymer. Furthermore, at the peak temperature of the loss tangent tanδ for HIPE foam and in the temperature range around it, the value of the loss modulus E" is relatively large compared to the storage modulus E'. Furthermore, as the ratio E" / E' of the loss modulus E" to the storage modulus E' increases, vibrations applied to the crosslinked polymer are more easily converted into thermal energy, which facilitates vibration damping.

[0029] On the other hand, as mentioned above, among the sound waves propagating within the HIPE foam, components having relatively low frequencies propagate mainly through the cell walls of the HIPE foam. Therefore, by setting the peak temperature of the loss tangent tanδ of the HIPE foam within the above-mentioned specific range, it is possible to efficiently attenuate structure-borne sound in a typical usage environment when using the HIPE foam as a sound-absorbing material (e.g., under room temperature conditions of 1 to 30°C). As a result, it is possible to improve the sound absorption properties of the sound-absorbing material in the relatively low frequency range.

[0030] From the viewpoint of further enhancing this effect, the peak temperature of tan δ of the HIPE foam is preferably 40° C. or less, more preferably 30° C. or less, and even more preferably 20° C. or less. If the peak temperature of tan δ of the HIPE foam is excessively high, the attenuation of solid-borne sound in the typical usage environment when the HIPE foam is used as a sound-absorbing material may be insufficient, which may lead to a deterioration in the sound absorption properties of the sound-absorbing material in the relatively low frequency range.

[0031] From the viewpoint of increasing the mechanical strength of the HIPE foam, the peak temperature of tan δ is preferably −60°C or higher, more preferably −50°C or higher, even more preferably −40°C or higher, and particularly preferably −30°C or higher.

[0032] [Maximum value of tanδ] The maximum value of the loss tangent tanδ in the temperature-loss tangent tanδ curve is preferably 0.4 or more. By setting the peak temperature of tanδ of the HIPE foam within the above-mentioned specific range and further setting the maximum value of tanδ, i.e., the value of tanδ at the peak top of the T-tanδ curve, within the above-mentioned specific range, the sound absorption properties of the sound-absorbing material in the relatively low frequency range can be further improved. From the same viewpoint, the maximum value of the loss tangent tanδ in the temperature-loss tangent tanδ curve is more preferably 0.5 or more, even more preferably 0.6 or more, particularly preferably 0.7 or more, and most preferably 0.8 or more.

[0033] Furthermore, the maximum value of the loss tangent tanδ of the HIPE foam is preferably 1.6 or less, more preferably 1.5 or less, and even more preferably 1.4 or less. In this case, a more uniform crosslinked structure can be formed in the crosslinked polymer constituting the HIPE foam. As a result, the ductility and recovery of the HIPE foam can be improved, and the handling properties as a sound-absorbing material can be further improved.

[0034] [tanδ half width] The half-value width of the tan δ peak, which indicates the maximum value of the loss tangent tan δ in the temperature-loss tangent tan δ curve, is preferably 10°C or more and 80°C or less. In this case, the ductility and flexibility of the HIPE foam can be further improved, and the handleability as a sound-absorbing material can be further enhanced. From the viewpoint of forming a more uniform crosslinked structure in the crosslinked polymer and further improving the ductility of the HIPE foam, the half-value width of the tan δ peak is more preferably 70°C or less, even more preferably 50°C or less, and particularly preferably 40°C or less. Furthermore, from the viewpoint of easily increasing the ductility of the HIPE foam while maintaining the recovery properties of the HIPE foam, the half-value width of the tan δ peak is more preferably 15°C or more, even more preferably 20°C or more.

[0035] The half width H of the tan δ peak means the temperature width of the tan δ peak at the position where the value of the loss tangent tan δ is half (1 / 2) of the maximum value in the tan δ peak (that is, the full width at half maximum) (see FIG. 2).

[0036] The peak temperature, maximum value, and half-value width of the loss tangent tanδ peak can be adjusted to desired values ​​by controlling the type and content of the crosslinking agent, the type and content of the monomer, etc., in the HIPE foam manufacturing method described below. For example, the peak temperature of the loss tangent tanδ can be lowered by increasing the content of a component derived from a monomer that lowers the glass transition temperature, such as butyl acrylate, in the crosslinked polymer. Furthermore, for example, by not excessively increasing the content of the crosslinking agent component in the crosslinked polymer and appropriately incorporating a soft crosslinking agent component (described below) as the crosslinking agent component, the increase in the peak temperature of the loss tangent tanδ can be suppressed and the peak temperature of the loss tangent tanδ can be maintained low. Furthermore, for example, by not excessively increasing the content of the hard crosslinking agent component (described below) in the crosslinked polymer and appropriately incorporating a soft crosslinking agent component in the crosslinked polymer, the maximum value of the loss tangent tanδ can be increased and the half-value width of the tanδ peak can be reduced.

[0037] [Molecular weight between crosslinking points] The molecular weight Mc between crosslinking points is an index of the degree of crosslinking of the crosslinked polymer that constitutes the HIPE foam. The molecular weight between crosslinking points of the crosslinked polymer is 1.0 × 10 4 Over 30 x 10 4 In this case, the mechanical properties such as ductility and recovery of the HIPE foam are further improved, and the handling property as a sound absorbing material can be further improved. From the viewpoint of further improving the ductility of the HIPE foam, the molecular weight between crosslinking points of the crosslinked polymer is preferably 2.0 × 10 or less. 4 More preferably, it is 2.5×10 or more. 4 More preferably, it is 3.0×10 or more. 4 From the viewpoint of improving the restoring property of the HIPE foam, the molecular weight between crosslinking points of the crosslinked polymer is particularly preferably 25×10 or more. 4 More preferably, it is 20×10 4 It is even more preferable that:

[0038] The molecular weight Mc between crosslinks of the crosslinked polymer constituting the HIPE foam is measured as follows. Dynamic viscoelasticity measurements are performed on the HIPE foam under the conditions of a frequency of 1 Hz, a load of 10 mN, and a deformation mode of compression. During the temperature rise process of the dynamic viscoelasticity measurements, the temperature-storage modulus E' curve (hereinafter referred to as the "T-E' curve"), plotting temperature on the horizontal axis and storage modulus E' on the vertical axis, shows a relatively flat shape until the temperature of the HIPE foam exceeds the glass transition temperature Tg. When the temperature of the HIPE foam rises to near the glass transition temperature Tg, the crosslinked polymer constituting the HIPE foam transitions from a glassy to a rubbery state. Then, when the crosslinked polymer transitions from the glassy to rubbery state, the storage modulus E' in the T-E' curve drops sharply (see Figure 3). After the temperature of the HIPE foam exceeds the glass transition temperature Tg, the T-E' curve shows a plateau region (a flat rubber-like portion). In this plateau region, E' is proportional to the temperature, so the molecular weight between crosslink points, Mc, can be calculated from the following formula (I). Mc=2(1+μ)ρRT / E' (I)

[0039] In formula (I), μ is Poisson's ratio, μ = 0.5, ρ is the density of the HIPE foam (unit: kg / m 3 ), R is the gas constant (8.314 J / (K·mol)), T is the temperature (unit: K) at an arbitrary point on the rubber-like flat portion, and E' is the storage modulus (unit: kPa) at the temperature T. To accurately calculate the molecular weight Mc between crosslinks, the temperature T used to calculate the molecular weight Mc between crosslinks is preferably selected within the range of Tg + 50°C to Tg + 80°C (where Tg is the glass transition temperature of the crosslinked polymer that constitutes the HIPE foam). The Poisson's ratio is a material-specific value calculated by dividing the strain generated in the direction perpendicular to the applied stress by the strain generated in the direction parallel to the applied stress, and multiplying this value by -1. Theoretically, the Poisson's ratio ranges from -1 to 0.5. A negative value indicates that a material will be crushed horizontally when crushed vertically. Conversely, a positive value indicates that a material will be stretched horizontally when crushed vertically. Under the dynamic viscoelasticity measurement conditions described above, the strain generated in the cross-linked polymer constituting the HIPE foam is very small, and it can be assumed that no volume change occurs. Therefore, the storage modulus E' and the molecular weight between cross-linking points Mc are calculated under the condition of constant volume, i.e., a Poisson's ratio of 0.5.

[0040] The molecular weight Mc between crosslinks of the crosslinked polymer constituting the HIPE foam can be reduced by adding a crosslinking agent in the manufacturing method of the HIPE foam described below, and can be adjusted to a desired value by adjusting the type of crosslinking agent and its mixing ratio, the type of monomer and its mixing ratio, etc. For example, the molecular weight between crosslinks can be reduced by adding a large amount of a hard crosslinking agent component described below to the crosslinked polymer. Furthermore, the molecular weight between crosslinks can be made relatively high by increasing the ratio of a soft crosslinking agent component described below in the crosslinking agent component or by adding a soft crosslinking agent component with a large molecular weight per functional group as the crosslinking agent component.

[0041] [density] The density of HIPE foam is 10 kg / m3 More than 200kg / m 3 In this case, the sound absorption of the sound absorbing material can be further improved over a wide frequency range. From the viewpoint of further enhancing this effect and increasing the mechanical strength of the HIPE foam, the density of the HIPE foam is preferably 20 kg / m or less. 3 More preferably, it is 30 kg / m or more. 3 More preferably, it is 40 kg / m or more. 3 It is particularly preferable that the content is 45 kg / m or more. 3 It is most preferable that the density of the HIPE foam is 180 kg / m or more. In order to further increase the lightness of the sound absorbing material while ensuring excellent sound absorption, the density of the HIPE foam is 180 kg / m 3 More preferably, it is 150 kg / m or less. 3 More preferably, it is 120 kg / m or less. 3 It is particularly preferred that:

[0042] The density ρ of a HIPE foam is the mass of the HIPE foam divided by the volume of the HIPE foam, which can be calculated based on the outer dimensions of the HIPE foam.

[0043] The density ρ of the HIPE foam can be adjusted to a desired value by adjusting the ratio of the total amount of the vinyl monomer, crosslinking agent, emulsifier, and polymerization initiator to the amount of the aqueous phase (specifically, aqueous liquid) in the HIPE foam production method described below. For example, the density ρ can be reduced by increasing the ratio of the aqueous phase to the organic phase during preparation of the high internal phase emulsion (emulsification step).

[0044] [Glass transition temperature Tg] The glass transition temperature Tg of the crosslinked polymer constituting the HIPE foam is preferably -60°C or higher and 30°C or lower. In this case, the peak temperature of tan δ of the HIPE foam can be more easily adjusted to the specific range. As a result, the sound absorption properties of the sound absorbing material in the relatively low frequency range can be more reliably improved. From the viewpoint of increasing the strength of the HIPE foam, the glass transition temperature Tg of the crosslinked polymer is preferably -50°C or higher, more preferably -40°C or higher, and even more preferably -30°C or higher. Furthermore, from the viewpoint of more reliably improving the sound absorption properties of the sound absorbing material in the relatively low frequency range, the glass transition temperature Tg of the crosslinked polymer is preferably 20°C or lower, more preferably 10°C or lower, even more preferably 0°C or lower, and particularly preferably -10°C or lower.

[0045] The glass transition temperature Tg of the cross-linked polymer that constitutes the HIPE foam is measured by differential scanning calorimetry (DSC) based on JIS K7121:1987. The glass transition temperature is the midpoint glass transition temperature of the DSC curve. The test specimen is conditioned as follows: (3) Measurement of the glass transition temperature after a certain heat treatment.

[0046] The glass transition temperature Tg of the crosslinked polymer constituting the HIPE foam is adjusted to fall within the above range by adjusting the type and blending ratio of the vinyl monomer, the type and blending ratio of the crosslinking agent, etc. in the manufacturing method of the HIPE foam described below.

[0047] [Components] Specifically, the crosslinked polymer constituting the HIPE foam is a polymer of a monofunctional vinyl monomer and a crosslinking agent, and contains a component derived from the monofunctional vinyl monomer. In this specification, the vinyl monomer is a styrene monomer, an acrylic monomer, or the like. The vinyl monomer can be an acrylic monomer and / or a styrene monomer. More specifically, the crosslinked polymer constituting the HIPE foam may contain a component derived from the acrylic monomer and a component derived from the crosslinking agent, or may contain a component derived from the styrene monomer and a component derived from the crosslinking agent. Furthermore, the crosslinking agent constituting the HIPE foam may contain a component derived from the acrylic monomer, a component derived from the styrene monomer, and a component derived from the crosslinking agent.

[0048] The crosslinked polymer is preferably composed of a polymer of a vinyl monomer including an acrylic monomer and / or a styrene monomer and a crosslinking agent. Specifically, the crosslinked polymer preferably contains an acrylic monomer component and / or a styrene monomer component in the polymer skeleton, as well as a crosslinking agent component described below. In this case, the toughness and rigidity of the HIPE foam can be further increased, and the handleability of the sound-absorbing material can be further improved. The styrene monomer component refers to a structural unit derived from a styrene monomer in the crosslinked polymer, and the acrylic monomer component refers to a structural unit derived from an acrylic monomer in the crosslinked polymer.

[0049] From the viewpoint of facilitating the production of a HIPE foam having desired physical properties, the total content of the acrylic monomer component and the styrene monomer component in the crosslinked polymer is preferably 50% by weight or more, more preferably 60% by weight or more. From the same viewpoint, the total content of the acrylic monomer component and the styrene monomer component in the crosslinked polymer is preferably 98% by weight or less, more preferably 96% by weight or less.

[0050] Examples of the styrene-based monomer include styrene compounds such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene, pt-butylstyrene, divinylbenzene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, and sodium styrenesulfonate. Examples of acrylic monomers include acrylic esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, and adamantyl acrylate; and methacrylic esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, isobornyl methacrylate, dicyclopentanyl methacrylate, and adamantyl methacrylate. Other examples of acrylic monomers include acrylamide, methacrylamide, and acrylonitrile.

[0051] The crosslinked polymer may be composed of a copolymer of a (meth)acrylic acid ester and a crosslinking agent, but is preferably composed of a copolymer of a styrene-based monomer, a vinyl-based monomer including a (meth)acrylic acid ester, and a crosslinking agent. In other words, the crosslinked polymer preferably has a component derived from a styrene-based monomer and a component derived from a (meth)acrylic acid ester (i.e., structural unit) in the polymer skeleton. In this case, a HIPE foam having desired physical properties can be easily obtained.

[0052] Since the crosslinked polymer is a crosslinked polymer, it has components (i.e., structural units) derived from the crosslinking agent in the polymer skeleton. The (meth)acrylic acid ester is an ester of (meth)acrylic acid and an alcohol, and is preferably an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms.

[0053] The HIPE foam has as its base resin a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and a styrene monomer, and it is preferable that the acrylic monomer contains an ester of (meth)acrylic acid and an alcohol having from 1 to 20 carbon atoms. In this case, the sound absorption properties of the sound-absorbing material can be more easily improved.

[0054] When the vinyl monomer contains an acrylic monomer, the content of the acrylic monomer in the vinyl monomer is preferably 50% by weight or more, more preferably 60% by weight or more, and even more preferably 70% by weight or more. When the vinyl monomer contains an acrylic monomer and a styrene monomer, the weight ratio of the acrylic monomer to the styrene monomer is preferably 50:50 to 95:5 (acrylic monomer:styrene monomer), and more preferably 60:40 to 90:10. This provides the effects of reducing production costs and facilitating adjustment to desired physical properties. From the same viewpoint, the styrene monomer preferably contains styrene. In this case, the content of styrene in the styrene monomer is preferably 50% by weight or more, more preferably 60% by weight or more, even more preferably 80% by weight or more, and particularly preferably 90% by weight or more. (Meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0055] Furthermore, from the viewpoint of stably obtaining a crosslinked polymer having desired physical properties, the number of carbon atoms in the hydrocarbon group constituting the (meth)acrylic acid ester is preferably 1 to 20, more preferably 2 to 18, even more preferably 3 to 16, and particularly preferably 3 to 12. The hydrocarbon group is more preferably an alkyl group. The hydrocarbon group may be cyclic or acyclic. Among these, it is preferable to use a (meth)acrylic acid ester having a hydrocarbon group with a carbon number of 3 to 10. In this case, the content of (meth)acrylic acid esters having a hydrocarbon group with a carbon number of 3 to 10 in the acrylic monomer is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0056] Furthermore, it is more preferable to use 2-ethylhexyl acrylate and / or butyl acrylate as the (meth)acrylic acid ester, and even more preferable to use butyl acrylate. In this case, the content of 2-ethylhexyl acrylate and / or butyl acrylate in the acrylic monomer is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. When 2-ethylhexyl acrylate or butyl acrylate is used as the (meth)acrylic acid ester, the glass transition temperature of the crosslinked polymer can be easily lowered.

[0057] A crosslinked polymer has a crosslinked structure and contains a crosslinker component. The crosslinker component is a structural unit derived from the crosslinker in the crosslinked polymer. The crosslinker is a compound that crosslinks (bonds) between the polymer chains that make up the polymer, forming a crosslinked structure within the polymer.

[0058] As the crosslinking agent, for example, a vinyl-based compound having at least two functional groups selected from vinyl groups and isopropenyl groups in the molecule is used. By including a predetermined amount of a crosslinking agent component in the crosslinked polymer, the rigidity and toughness of the crosslinked polymer can be increased and the molecular weight between crosslinking points of the crosslinked polymer can be reduced. The vinyl-based compound also includes compounds containing a vinyl group and / or an isopropenyl group in the functional group structure, such as an acryloyl group or a methacryloyl group. From the viewpoint of stable polymerization of the crosslinking agent, the number of functional groups contained in the vinyl-based compound molecule is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. Furthermore, from the viewpoint of more easily increasing the toughness of the crosslinked polymer, the crosslinking agent preferably has functional groups at at least both ends of the molecule, and more preferably has functional groups only at both ends of the molecule.

[0059] The crosslinked polymer may contain a single crosslinker component, for example, produced using a single crosslinking agent. However, it is preferable to use a crosslinker containing both a hard crosslinker component derived from a hard crosslinker with a relatively short molecular chain and a soft crosslinker component derived from a soft crosslinker with a relatively long molecular chain, since this increases the stiffness and toughness of the crosslinked polymer. In this case, it becomes easier to adjust the peak temperature of the loss tangent tanδ of the crosslinked polymer constituting the HIPE foam within the desired range. Furthermore, excessive embrittlement of the HIPE foam is suppressed, and even when producing a HIPE foam with a complex shape, such as one with thin sections, chipping can be suppressed, improving handling as a sound-absorbing material. The hard crosslinker may also be referred to as the first crosslinker, and the soft crosslinker may also be referred to as the second crosslinker.

[0060] The hard crosslinking agent (i.e., the first crosslinking agent) is preferably a vinyl compound having a functional group equivalent of 130 g / eq or less. Because such hard crosslinking agents have relatively short molecular chains, copolymerization with a vinyl monomer is thought to reduce the mobility of the polymer molecular chain. The use of a hard crosslinking agent facilitates the enhancement of the rigidity of HIPE foam. From the viewpoint of facilitating the production of HIPE foam, the lower limit of the functional group equivalent of the hard crosslinking agent is preferably 30 g / eq, more preferably 40 g / eq, even more preferably 50 g / eq, and even more preferably 60 g / eq. The upper limit of the functional group equivalent of the hard crosslinking agent is preferably 120 g / eq. The functional group equivalent of a hard crosslinking agent refers to the molar mass of the hard crosslinking agent per functional group (specifically, a vinyl group, an alkenyl group such as an isopropenyl group), and the functional group equivalent can also be expressed in units of [g / mol].

[0061] The soft crosslinking agent (i.e., the second crosslinking agent) is preferably a vinyl compound having a functional group equivalent weight of more than 130 g / eq and not more than 5000 g / eq. Because such soft crosslinking agents have relatively long molecular chains, copolymerization with a vinyl monomer is believed to enable crosslinking between polymer molecular chains without significantly reducing the mobility of the polymer molecular chains. The use of a soft crosslinking agent facilitates the enhancement of the toughness of HIPE foam. From the viewpoint of ease of handling, the upper limit of the functional group equivalent weight of the soft crosslinking agent is preferably 5000 g / eq, more preferably 4000 g / eq, and even more preferably 3000 g / eq. The lower limit of the functional group equivalent weight of the soft crosslinking agent is preferably 150 g / eq, more preferably 180 g / eq, and even more preferably 200 g / eq. The functional group equivalent of a soft crosslinking agent means the molar mass of the soft crosslinking agent per functional group (specifically, an alkenyl group such as a vinyl group or an isopropenyl group), and the unit of functional group equivalent can also be expressed as [g / mol].

[0062] From the viewpoint of facilitating further enhancement of the toughness and rigidity of the HIPE foam and facilitating adjustment of the peak temperature of the loss tangent tanδ within the above-mentioned range, the functional group equivalent of the soft crosslinking agent is preferably 100 g / eq or more, more preferably 120 g / eq or more, greater than the functional group equivalent of the hard crosslinking agent. In other words, the difference between the functional group equivalent of the soft crosslinking agent and the functional group equivalent of the hard crosslinking agent is preferably 100 g / eq or more, more preferably 120 g / eq or more. Furthermore, from the viewpoint of further enhancing polymerization stability and facilitating the stable production of a HIPE foam excellent in rigidity and toughness, the difference between the functional group equivalent of the soft crosslinking agent and the functional group equivalent of the hard crosslinking agent is preferably 3000 g / eq or less, more preferably 2000 g / eq or less, and even more preferably 1000 g / eq or less. When two or more hard crosslinking agents are used, the weight average of the functional group equivalents of all the hard crosslinking agents is calculated, and this value is the functional group equivalent of the hard crosslinking agent. Similarly, when two or more soft crosslinking agents are used, the weight average of the functional group equivalents of all the soft crosslinking agents is calculated, and this value is the functional group equivalent of the soft crosslinking agent.

[0063] From the viewpoint of more reliably obtaining the above-mentioned effects, it is preferable that the crosslinked polymer contains a component derived from a first crosslinking agent having a functional group equivalent of 130 g / mol or less and a component derived from a second crosslinking agent having a functional group equivalent of more than 130 g / mol and 5000 g / mol or less, and that the functional group equivalent of the second crosslinking agent is 100 g / mol or more greater than the functional group equivalent of the first crosslinking agent.

[0064] Examples of vinyl compounds used as hard crosslinking agents include divinylbenzene, triallyl isocyanurate, and esters of polyhydric alcohols and (meth)acrylic acid. Examples of esters of polyhydric alcohols and (meth)acrylic acid include vinyl compounds such as butanediol (meth)acrylates such as butanediol diacrylate; trimethylolpropane (meth)acrylates such as trimethylolpropane triacrylate; hexanediol (meth)acrylates such as hexanediol diacrylate; and pentaerythritol (meth)acrylates such as pentaerythritol tetraacrylate. However, the number of functional groups in the hard crosslinking agent is two or more per molecule. The functional groups are preferably vinyl groups and / or isopropenyl groups. The hard crosslinking agent may be one type or two or more types. In other words, the hard crosslinking agent component constituting the crosslinked polymer may be one type or two or more types.

[0065] From the viewpoint of making it easier to adjust the rigidity of the HIPE foam, it is preferable to use a hard crosslinking agent whose main component is divinylbenzene and / or butanediol diacrylate. The main component of the hard crosslinking agent means a component that accounts for 50% by weight or more of the hard crosslinking agent. The proportion of the vinyl compound that is the main component of the hard crosslinking agent is preferably 60% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0066] Examples of vinyl compounds used as soft crosslinking agents include esters of polyhydric alcohols and (meth)acrylic acid, esters of polyether glycols and (meth)acrylic acid, esters of urethane oligomers and (meth)acrylic acid, esters of epoxy oligomers and (meth)acrylic acid, and (meth)acrylic-modified silicones. More specifically, examples of the vinyl compounds include nonanediol (meth)acrylates such as nonanediol diacrylate; decanediol (meth)acrylates such as decanediol diacrylate; polyethylene glycol (meth)acrylates such as polyethylene glycol diacrylate; polypropylene (meth)acrylates such as polypropylene glycol diacrylate; polytetramethylene glycol (meth)acrylates such as polytetramethylene glycol diacrylate; polyglycerin (meth)acrylates such as polyglycerin diacrylate; urethane (meth)acrylates such as urethane diacrylate; epoxy (meth)acrylates such as epoxy diacrylate; polyester (meth)acrylates such as polyester diacrylate; (meth)acrylic-modified silicones such as silicones modified with both ends (meth)acrylic; caprolactone-modified isocyanurates such as caprolactone-modified tris isocyanurates; ethoxylated bisphenol A (meth)acrylates such as ethoxylated bisphenol A dimethacrylate, etc. However, the number of functional groups in the soft crosslinking agent is two or more per molecule. The functional group is preferably a vinyl group and / or an isopropenyl group. The soft crosslinking agent may be one type or two or more types. In other words, the soft crosslinking agent component constituting the crosslinked polymer may be one type or two or more types.

[0067] From the viewpoint of easily adjusting the toughness of the HIPE foam, it is preferable to use a soft crosslinking agent whose main component is polyethylene glycol di(meth)acrylate. The number of repeating structural units derived from ethylene glycol in the polyethylene glycol di(meth)acrylate is preferably 3 to 23. Furthermore, from the viewpoint of further improving the ductility and strength of the HIPE foam, it is preferable to use a soft crosslinking agent whose functional group equivalent is 500 g / eq or more and 3000 g / eq or less. It is more preferable to use a soft crosslinking agent whose main component is urethane (meth)acrylate and / or epoxy (meth)acrylate and whose functional group equivalent is 500 g / eq or more and 3000 g / eq or less. It is even more preferable to use a soft crosslinking agent whose main component is epoxy (meth)acrylate and whose functional group equivalent is 500 g / eq or more and 3000 g / eq or less. The main component of the soft crosslinking agent means a component whose proportion in the soft crosslinking agent is 50% by weight or more. The proportion of the vinyl compound that is the main component in the soft crosslinking agent is preferably 60% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more.

[0068] Table 1 shows the molecular weights of representative crosslinking agents and the molecular weight per functional group (i.e., functional group equivalent weight).

[0069] [Table 1]

[0070] When the crosslinked polymer is composed of at least an acrylic monomer, a styrene monomer, and a crosslinking agent, the content of the acrylic monomer component in the crosslinked polymer is preferably 50 to 95 parts by weight, more preferably 60 to 90 parts by weight, and even more preferably 70 to 85 parts by weight, per 100 parts by weight of the total vinyl monomer components and crosslinking agent components constituting the crosslinked polymer, from the viewpoints of easily adjusting the tan δ peak temperature within the above range and of obtaining a better balance between toughness and rigidity of the HIPE foam. From the same viewpoint, the content of the styrene monomer component in the crosslinked polymer is preferably 3 to 45 parts by weight, more preferably 5 to 30 parts by weight, and even more preferably 10 to 25 parts by weight, per 100 parts by weight of the total vinyl monomer components and crosslinking agent components constituting the crosslinked polymer. The acrylic monomer is preferably a (meth)acrylic acid ester having a hydrocarbon group with 3 to 10 carbon atoms, and the content of the (meth)acrylic acid ester having a hydrocarbon group with 3 to 10 carbon atoms in the acrylic monomer is preferably 50% by weight or more, more preferably 80% by weight or more, and even more preferably 90% by weight or more. The (meth)acrylic acid ester having a hydrocarbon group with 3 to 10 carbon atoms is preferably 2-ethylhexyl acrylate and / or butyl acrylate, and more preferably butyl acrylate.

[0071] From the viewpoint of facilitating adjustment of the peak temperature of tanδ of the crosslinked polymer within a desired range, the content of the crosslinking agent component in the crosslinked polymer (specifically, the total content of the soft crosslinking agent component and the hard crosslinking agent component in the crosslinked polymer) is preferably 3 parts by weight or more and 40 parts by weight or less, and more preferably 4 parts by weight or more and 35 parts by weight or less, relative to 100 parts by weight of the total of the vinyl monomer component and the crosslinking agent component constituting the crosslinked polymer.

[0072] Furthermore, when the crosslinked polymer contains a crosslinker component having a functional group equivalent of 500 g / eq or more and 3000 g / eq or less, the content of the crosslinker component having a functional group equivalent of 500 g / eq or more and 3000 g / eq or less in the crosslinked polymer is preferably 20 parts by weight or more and 40 parts by weight or less per 100 parts by weight of the total of the vinyl monomer component and the crosslinker component constituting the crosslinked polymer. The crosslinker component having a functional group equivalent of 500 g / eq or more and 3000 g / eq or less corresponds to a soft crosslinker.

[0073] When the crosslinked polymer contains a hard crosslinking agent component and a soft crosslinking agent component, the content of the hard crosslinking agent component in the crosslinked polymer is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and even more preferably 3 to 10 parts by weight, per 100 parts by weight of the total vinyl monomer component and crosslinking agent component constituting the crosslinked polymer, from the viewpoints of easily increasing the rigidity of the HIPE foam and easily adjusting the peak temperature of tan δ within a desired range. Furthermore, from the viewpoints of easily adjusting the peak temperature of tan δ within a desired range while suppressing excessive embrittlement of the HIPE foam, the content of the soft crosslinking agent component in the crosslinked polymer is preferably 2 to 40 parts by weight, more preferably 3 to 35 parts by weight, per 100 parts by weight of the total vinyl monomer component and crosslinking agent component constituting the crosslinked polymer. From the same viewpoint, the weight ratio of the hard crosslinking agent component to the soft crosslinking agent component is preferably 0.05 or more and 4 or less, more preferably 0.06 or more and 3 or less, and even more preferably 0.08 or more and 2 or less.

[0074] [Sound absorption] When the normal incident sound absorption coefficient is measured at 23°C using the HIPE foam with a thickness of 20 mm, the total normal incident sound absorption coefficient at frequencies of 125 to 5000 Hz is preferably 8 or more, and more preferably 9 or more. By using a HIPE foam with such sound absorption properties as a sound absorbing material, the sound absorbing properties of the sound absorbing material can be further improved over a wide frequency range.

[0075] Furthermore, when the normal incidence sound absorption coefficient is measured at 23°C using the 20mm thick HIPE foam, the sum of the normal incidence sound absorption coefficients at frequencies from 500 to 1000Hz is preferably 2.5 or more, more preferably 3.0 or more. By using a HIPE foam with such sound absorption properties as a sound absorbing material, the sound absorption properties of the sound absorbing material in the low frequency range can be further improved. The method for measuring the sum of the normal incidence sound absorption coefficients in each frequency range will be explained in the Examples.

[0076] [Thickness of sound-absorbing material] The minimum thickness of the sound-absorbing material is preferably 10 mm or more, more preferably 15 mm or more, and even more preferably 20 mm or more. By setting the minimum thickness of the sound-absorbing material within the above-mentioned specific range, it is possible to ensure excellent sound absorption in any part of the sound-absorbing material.

[0077] [Application] As described above, the HIPE foam has good sound absorption properties in a relatively low frequency range and excellent sound absorption properties over a wide frequency range, and therefore can be suitably used as a sound absorbing material. In particular, the HIPE foam can be suitably used as a sound absorbing material for absorbing sounds with frequencies of 100 to 5000 Hz. Sound absorbing materials made of such HIPE foam can be suitably used in, for example, automobiles and buildings.

[0078] [HIPE foam manufacturing method] HIPE foams are produced by polymerizing a high internal phase emulsion, specifically a water-in-oil type high internal phase emulsion, in which the organic phase is a continuous phase containing vinyl monomers, crosslinking agents, emulsifiers, polymerization initiators, etc., and the aqueous phase is a dispersed phase containing water, such as deionized water.

[0079] More preferred embodiments of the method for producing a HIPE foam (specifically, the first and second embodiments) are as follows. The first aspect is a method for producing a HIPE foam by forming a water-in-oil high internal phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and / or a styrene-based monomer, a crosslinking agent, an emulsifier, and a polymerization initiator, and polymerizing the acrylic monomer and / or the styrene-based monomer in the emulsion, the crosslinking agent is a vinyl-based compound having at least two functional groups selected from a vinyl group and an isopropenyl group in the molecule, and includes a first crosslinking agent having a functional group equivalent of 130 g / eq or less, and a second crosslinking agent having a functional group equivalent of more than 130 g / eq and 5000 g / eq or less; the functional group equivalent weight of the second crosslinking agent is at least 100 g / eq greater than the functional group equivalent weight of the first crosslinking agent; the amount of the crosslinking agent added is 3 parts by weight or more and 40 parts by weight or less relative to 100 parts by weight of the total of the acrylic monomer, the styrene monomer, and the crosslinking agent; The method for producing a HIPE foam includes a ratio of the weight of the first crosslinking agent to the weight of the second crosslinking agent of 0.05 or more and 4 or less.

[0080] A second aspect is a method for producing a HIPE foam by forming a water-in-oil high internal phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and / or a styrene-based monomer, a crosslinking agent, an emulsifier, and a polymerization initiator, and polymerizing the acrylic monomer and / or the styrene-based monomer in the emulsion, the crosslinking agent is a vinyl-based compound having at least two functional groups selected from a vinyl group and an isopropenyl group in the molecule, and the crosslinking agent has a functional group equivalent of 500 g / eq or more and 3000 g / eq or less; The method for producing a HIPE foam is characterized in that the amount of the crosslinking agent added is 20 parts by weight or more and 40 parts by weight or less relative to 100 parts by weight of the total of the acrylic monomer, the styrene monomer, and the crosslinking agent. The above-mentioned explanations of the type and content of the vinyl monomer, the type and content of the crosslinking agent, etc. are also referred to as appropriate in the method for producing HIPE foam.

[0081] Specifically, the HIPE foam can be produced by carrying out an emulsification step, a polymerization step, and a drying step as follows.

[0082] First, a water-in-oil type high internal phase emulsion is prepared by dropping an aqueous liquid (aqueous phase) containing water into an oily liquid while stirring an oily liquid (organic phase) containing organic substances such as a vinyl monomer, a crosslinking agent, an emulsifier, and a polymerization initiator (emulsification step). In the emulsification step, a high internal phase emulsion can be prepared by adding an aqueous liquid to an oily liquid so that the volume of the aqueous phase is, for example, three times or more the volume of the organic phase. The proportion of the aqueous phase contained in the organic phase can be adjusted by adjusting the weight ratio of the organic phase to the aqueous phase. The content of the aqueous phase in the high internal phase emulsion is preferably 300 to 3,000 parts by weight, more preferably 400 to 2,500 parts by weight, and even more preferably 500 to 2,000 parts by weight, per 100 parts by weight of the organic phase. Next, the high internal phase emulsion is heated to polymerize the vinyl monomer, crosslinking agent, and other components in the organic phase, thereby obtaining a polymerization product (specifically, a water-containing crosslinked polymer) (polymerization step). Thereafter, the polymerization product is dried to obtain a HIPE foam composed of a crosslinked polymer (drying step).

[0083] In the emulsification process, the stirring power density when stirring the organic phase and emulsion is 0.01 kW / m 3 More than 10kW / m 3 It is preferable that the value is less than 0.03 kW / m 3 More than 7kW / m 3 It is more preferable that the mixing power density (unit: kW / m) in the emulsification step is less than 100%. In this case, it is easier to obtain a HIPE foam having a desired cell structure. 3 ) is calculated by calculating the power (unit: kW) required for stirring from the torque (unit: N m) and rotation speed (unit: rpm) of the stirring device used in the emulsification process, and then multiplying this power by the volume (unit: m 3 ) can be calculated by dividing by

[0084] Furthermore, as a method for adding an aqueous liquid to an oily liquid in the emulsification step, for example, a method can be used in which the oily liquid and the aqueous liquid are placed in a stirring vessel and stirring is initiated to carry out emulsification. From the viewpoint of easily obtaining a HIPE foam having a desired cell structure, it is preferable to adopt a method in which the oily liquid is placed in a stirring vessel and stirring is initiated, and then the aqueous liquid is added to the vessel using a pump or the like while stirring to carry out emulsification. When preparing a water-in-oil high internal phase emulsion by adding an aqueous liquid containing water into the oily liquid dropwise while stirring the oily liquid, the addition rate of the aqueous liquid is, for example, preferably 10 wt% / min to 1000 wt% / min, more preferably 100 wt% / min to 800 wt% / min, and even more preferably 200 wt% / min to 600 wt% / min, relative to 100 wt% of the oily liquid (organic phase). Examples of the emulsification method include a batch-type emulsification process in which emulsification is performed using a stirring vessel equipped with a stirring device or a centrifugal shaker, and a continuous emulsification process in which an oily liquid and an aqueous liquid are continuously supplied and mixed in a line equipped with a static mixer, a mesh, etc. The emulsification method is not particularly limited.

[0085] The aqueous phase may contain water such as deionized water, a polymerization initiator, an electrolyte, etc. In the emulsification step, for example, an oily liquid and an aqueous liquid are prepared, and the aqueous liquid is added to the oily liquid under stirring to prepare a high internal phase emulsion. In addition, in the emulsification step, additives such as a flame retardant, a flame retardant auxiliary, a light stabilizer, and a colorant may be appropriately blended into the aqueous phase and / or organic phase.

[0086] Flame retardants are used to improve the flame retardancy of HIPE foams. Examples of flame retardants include organic compounds containing halogens, phosphorus, nitrogen, silicone, etc.; and inorganic compounds containing metal hydroxides, phosphorus, nitrogen, etc. Flame retardants can be used within a range that does not impair the effects of the present invention. When a flame retardant is added, the amount is preferably 5 to 20 parts by weight per 100 parts by weight of the total of the vinyl monomer component and the crosslinker component that constitute the crosslinked polymer. From the viewpoint of easily imparting excellent flame retardancy even with a small amount of addition, a brominated bisphenol flame retardant is preferably used as the flame retardant, more preferably a brominated bisphenol flame retardant having a 2,3-dibromo-2-methylpropyl group and / or a brominated bisphenol flame retardant having a 2,3-dibromopropyl group, and even more preferably 2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane.

[0087] In addition, HIPE foam can be appropriately blended with a flame retardant synergist to improve flame retardancy. For example, when a halogen-based flame retardant is used, if a radical generator such as dicumyl peroxide is used as the flame retardant synergist, the decomposition of the radical generator promotes the elimination of halogen from the flame retardant, which is expected to improve flame retardancy. Furthermore, when a halogen-based flame retardant is used, if an antimony compound such as antimony trioxide is used as the flame retardant synergist, the radical trapping effect of the halogen-based flame retardant and the air blocking effect of the antimony oxide are combined synergistically, which is expected to improve flame retardancy. Note that a single flame retardant may be used, or two or more flame retardants with different flame retardancy mechanisms may be used in combination.

[0088] The polymerization initiator is used to initiate the polymerization of vinyl monomers. As the polymerization initiator, a radical polymerization initiator can be used. Specifically, dilauroyl peroxide (LPO), bis(4-t-butylcyclohexyl) peroxydicarbonate (LTCP), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(3,5,5-trimethylhexanoyl) peroxide, t-butyl peroxypivalerate, t-hexyl peroxypivalerate, t-butyl peroxyneoheptanoate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, etc. Examples of suitable polymerization initiators include organic peroxides such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(4-dimethylvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile). To prevent water from boiling during polymerization, the polymerization initiator preferably has a one-hour half-life temperature of 95°C or lower, more preferably 90°C or lower. From the standpoint of safety, the polymerization initiator's one-hour half-life temperature is preferably 50°C or higher, more preferably 55°C or higher, to prevent decomposition of the polymerization initiator at room temperature.

[0089] One or more substances can be used as the polymerization initiator. From the viewpoint of shortening the polymerization time without reducing the uniformity of the density of the HIPE foam, it is preferable to use a combination of an organic peroxide having a one-hour half-life temperature of 50°C or higher and lower than 70°C and an organic peroxide having a one-hour half-life temperature of 70°C or higher and 90°C or lower. The polymerization initiator can be added to the organic phase and / or the aqueous phase. When the polymerization initiator is added to the aqueous phase, a water-soluble polymerization initiator such as 2,2'azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride, 2,2'azobis(2-methylpropionamidine)dihydrochloride, potassium persulfate, or ammonium persulfate may be used. The amount of the polymerization initiator added can be, for example, in the range of 0.1 to 5 parts by weight per 100 parts by weight of the total of the vinyl monomer and the crosslinking agent.

[0090] Emulsifiers are used to form and stabilize high internal phase emulsions. Examples of emulsifiers that can be used include surfactants. Specifically, glycerol esters such as polyglycerol condensed ricinoleate, polyglycerol stearate, polyglycerol oleate, polyglycerol laurate, and polyglycerol myristate; sorbitol esters such as sorbitan oleate, sorbitan stearate, sorbitan laurate, sorbitan laurate, and sorbitan palmitate; ethylene glycol sorbitan esters; ethylene glycol esters; and copolymers of polyethylene glycol and polypropylene glycol. The amount of emulsifier added can be, for example, 1 to 30 parts by weight per 100 parts by weight of the total of the vinyl monomer, crosslinker, and emulsifier.

[0091] The electrolyte is used to impart ionic strength to the aqueous phase and increase the stability of the emulsion. A water-soluble electrolyte can be used. Specific examples include calcium chloride, sodium chloride, magnesium chloride, sodium acetate, sodium citrate, sodium sulfate, calcium sulfate, magnesium sulfate, sodium dihydrogen phosphate, and disodium hydrogen phosphate. The amount of electrolyte added can be, for example, in the range of 0.01 to 10 parts by weight per 100 parts by weight of the aqueous liquid.

[0092] The polymerization temperature in the polymerization step is adjusted depending on, for example, the type of vinyl monomer, the type of polymerization initiator, the type of crosslinking agent, etc. From the viewpoints of increasing the productivity of HIPE foam and making it easier to obtain HIPE foam having a desired cell structure, the polymerization temperature is preferably 50°C to 90°C, and more preferably 70°C to 85°C. Furthermore, when the polymerization temperature is within the above-mentioned range, the polymerization time is preferably 0.5 to 15 hours, more preferably 0.5 to 12 hours, and even more preferably 0.5 to 10 hours.

[0093] In the drying process, the water-containing crosslinked polymer is dried using an oven, vacuum dryer, high-frequency / microwave dryer, etc. Upon completion of drying, the areas where water droplets were present in the emulsion before polymerization become bubbles in the dried polymer, resulting in the production of a HIPE foam. Before drying, the crosslinked polymer can be dehydrated by squeezing using, for example, a press. Squeezing can be performed at room temperature (e.g., 23°C), but it can also be performed at a temperature above the glass transition temperature of the crosslinked polymer that constitutes the HIPE foam. In this case, dehydration by squeezing is facilitated, and the drying time can be shortened. The crosslinked polymer can also be dehydrated by centrifugation. This also shortens the drying time.

[0094] The HIPE foam obtained by the above method can be used as a sound absorbing material as it is. Alternatively, the HIPE foam can be machined to a desired shape to create a sound absorbing material. [Example]

[0095] Examples and comparative examples of sound-absorbing materials are described below. In these examples, sound-absorbing materials made of HIPE foam shown in the examples in Table 2 and the comparative examples in Table 3 were manufactured by the following method. Note that the specific aspects of the sound-absorbing material according to the present invention are not limited to the aspects of the examples shown below, and the configuration can be changed as appropriate within the scope of the gist of the present invention. Note that "%" in the examples means % by weight.

[0096] [Example 1] First, a 3 L glass vessel equipped with a torque converter-equipped stirrer was charged with 14.5 g of styrene and 66 g of butyl acrylate as vinyl monomers, 7 g of 57%-purity divinylbenzene as a hard crosslinking agent (hereinafter referred to as the first crosslinking agent) (4.0 g of divinylbenzene), 5 g of polyethylene glycol diacrylate (specifically, NK Ester A-400 manufactured by Shin-Nakamura Chemical Co., Ltd.) as a soft crosslinking agent (hereinafter referred to as the second crosslinking agent) (4.8 g of polyethylene glycol diacrylate), 7.5 g of polyglycerin condensed ricinoleate (specifically, CRS-75 manufactured by Sakamoto Pharmaceutical Co., Ltd.) as an emulsifier, and 0.5 g of dilauroyl peroxide and 0.5 g of bis(4-t-butylcyclohexyl)peroxydicarbonate as polymerization initiators. These were mixed in the glass vessel to form an organic phase.

[0097] Stirring power density: 0.03kW / m 3 While stirring the organic phase, 2090 g of deionized water was added at a rate of approximately 450 g / min (an addition rate of approximately 450 wt% / min relative to 100 wt% of the organic phase), and stirring was continued for 10 minutes after the addition of deionized water was completed to prepare a water-in-oil (i.e., W / O) high internal phase emulsion. The stirring power density (unit: kW / m 3 ) is calculated by calculating the power (unit: kW) from the torque (unit: N m) and rotation speed (unit: rpm) of the agitator, and the volume of the contents (unit: m 3 ) was calculated by dividing by

[0098] Next, the stirring power density was set to 0.03 kW / m 3 The pressure in the glass container was reduced by connecting an aspirator to the container to remove the microbubbles contained in the emulsion. After 10 minutes from the start of the pressure reduction, the stirring was stopped and the pressure in the container was returned to atmospheric pressure.

[0099] The contents of the glass container were poured into a container measuring approximately 250 mm in length, 180 mm in width, and 90 mm in depth, and polymerized in a hot water bath at 70°C for approximately 10 hours to obtain a water-containing HIPE foam. The HIPE foam was then removed from the hot water bath and cooled to room temperature.

[0100] After cooling, the HIPE foam was removed from the container, washed with water, dehydrated, and dried in an oven at 85°C until it reached a constant weight. In this way, a sound-absorbing material consisting of a rectangular parallelepiped HIPE foam made of a vinyl-based cross-linked polymer was obtained. The density of the HIPE foam that constituted the sound-absorbing material was 50 kg / m 3 It was.

[0101] The charge composition of this example is shown in Table 2. The contents of various components (vinyl monomer and crosslinking agent) in the crosslinked polymer can be calculated from the blending amounts of the various components (in the case of the crosslinking agent, the blending amount excluding impurities) at the time of charging and the total blending amount of the vinyl monomer component and the crosslinking agent component (excluding impurities). In the tables, the compound names are abbreviated as follows: St: styrene BA: butyl acrylate 2-EHA: 2-ethylhexyl acrylate DVB: Divinylbenzene PEGDA: Polyethylene glycol diacrylate PPGDA: Polypropylene glycol diacrylate ("APG-400" manufactured by Shin-Nakamura Chemical Co., Ltd.) EpDA: epoxy diacrylate (specifically, both-end acrylic-modified epoxy prepolymer, "EBECRYL (registered trademark) 3708" manufactured by Daicel-Allnex Corporation) LPO: Dilauryl peroxide LTCP: bis(4-t-butylcyclohexyl) peroxydicarbonate

[0102] [Examples 2 to 8, Comparative Examples 1 to 5] Sound absorbing materials made of HIPE foam were produced in the same manner as in Example 1, except that the charged compositions were changed as shown in Tables 2 and 3. In addition to the feed composition, changes were made in Examples 3 and 5 and Comparative Examples 2 and 5, such as changing the stirring power density in the emulsification step to 4.4 kW / m 3 In Examples 6 and 7, the stirring power density in the emulsification step was changed to 0.2 kW / m 3 In Example 8, the stirring power density in the emulsification step was changed to 0.6 kW / m 3 In Comparative Examples 1 and 3, the stirring power density in the emulsification step was changed to 7.8 kW / m 3 In Comparative Example 4, the stirring power density in the emulsification step was changed to 0.02 kW / m 3 was changed to.

[0103] [evaluation] The following measurements and evaluations were carried out for Examples 1 to 8 and Comparative Examples 1 to 5. The results are shown in Tables 2 and 3.

[0104] (density ρ) Three rectangular parallelepiped test pieces, each 25 mm thick, 50 mm wide, and 50 mm long, were cut out from the HIPE foam constituting the sound-absorbing material, including the center but excluding the skin surface, i.e., the surface that was in contact with the container during polymerization. The weight and outer dimensions of the test pieces were then measured. The density of the test piece was calculated by dividing the weight of the test piece by the volume calculated based on the outer dimensions. The arithmetic mean value of the densities of the three test pieces was then used to calculate the density ρ (unit: kg / m) of the HIPE foam. 3 ) was decided.

[0105] (glass transition temperature Tg) Tg was calculated by differential scanning calorimetry (DSC) analysis based on JIS K7121:1987. A DSC250 manufactured by TA Instruments Japan was used as the measurement device. Specifically, a test specimen weighing approximately 2 mg was first taken from near the center of the HIPE foam constituting the sound-absorbing material. The test specimen was conditioned as described in "(3) Measurement of the glass transition temperature after a certain heat treatment." Specifically, the sample was left standing in a constant temperature and humidity chamber at 23°C and 50% humidity for at least 24 hours. The test specimen was then heated at a rate of 10°C / min to a temperature approximately 30°C higher than the temperature at the end of the glass transition, held at this temperature for 10 minutes, and then cooled at a rate of 10°C / min to a temperature approximately 50°C lower than the glass transition temperature. For example, in measuring the Tg of the HIPE foam in Example 1, the specimen was heated to 40°C and then cooled to -45°C. After cooling, the temperature was maintained for 10 minutes to stabilize the apparatus, and DSC measurements were performed at a heating rate of 20°C / min up to a temperature approximately 30°C higher than the temperature at the end of the glass transition, to obtain a DSC curve. The midpoint glass transition temperature was determined from this DSC curve, and this value was taken as the glass transition temperature, Tg. The temperature range for the DSC measurements was -90°C to 70°C.

[0106] (Molecular weight between crosslinking points Mc) Three 10mm x 10mm x 10mm cubic test pieces without skin were cut from the center of the HIPE foam that constitutes the sound-absorbing material. Dynamic mechanical analysis (DMA) was performed on these three test pieces, and T-E' curves were obtained over a temperature range of -100 to 120°C. Figure 3 shows an example of a T-E' curve for HIPE foam. The T-E' curve is obtained by plotting temperature on the horizontal axis and storage modulus E' on the vertical axis. The measurement device used was a DMA7100 manufactured by Hitachi High-Tech Science Corporation. The measurement conditions were as follows: Deformation mode: Compression ·Temperature: -100~120℃ Heating rate: 10℃ / min Frequency: 1Hz Load: 10mN

[0107] Three temperatures T were randomly selected from the rubber-like plateau (specifically, the temperature range from Tg+50°C to Tg+80°C) in the T-E' curves of each of the three test pieces, and the storage modulus E' at each temperature T was determined. Using these storage moduli E' and temperatures T, the inter-crosslinking molecular weight Mc at each temperature was calculated according to the following formula (I). The arithmetic mean value of the nine inter-crosslinking molecular weights calculated from the T-E' curves of the three test pieces was used as the inter-crosslinking molecular weight Mc. Note that Tg is the glass transition temperature of the crosslinked polymer that constitutes the HIPE foam. Mc=2(1+μ)ρRT / E' (I)

[0108] Under the dynamic viscoelasticity measurement conditions described above, the strain generated in the cross-linked polymer constituting the HIPE foam is extremely small, and it can be assumed that no volume change occurs. Therefore, the molecular weight Mc between cross-linking points was calculated under the condition of constant volume, i.e., a Poisson's ratio of 0.5.

[0109] (average bubble diameter) The average diameter of the bubbles was measured as follows. Using a feather blade, samples for observation were cut out from the center of the lateral direction and thickness direction of a rectangular parallelepiped HIPE foam, and from the center of the thickness direction at both ends of the lateral direction. The samples were then observed with a low-vacuum scanning electron microscope (Miniscope (registered trademark) TM3030Plus manufactured by Hitachi High-Tech Science Corporation), and cross-sectional photographs were taken. An example of a cross-sectional photograph of the HIPE foam (magnification: 500x) is shown in Figure 1. The detailed observation conditions were as follows:

[0110] Sample pretreatment: Conductive treatment of the sample was performed using a metal coating device (MSP-1S from Vacuum Device Co., Ltd.). Au-Pd was used as the target electrode. Magnification: 50x Acceleration voltage: 5kV Observation conditions: Surface (low magnification) Observation mode: Secondary electrons (standard)

[0111] Next, the cross-sectional photographs were analyzed using image processing software (NanoHunter NS2K-Pro from NanoSystems Co., Ltd.), and a total area of ​​5 mm was plotted on the cross-sectional photograph of each sample. 2 The measurement area was set so that the above was the case. Next, the bubble diameters of the bubbles present within the measurement area were calculated, and the arithmetic mean value of these was used as the bubble diameter for each sample. The average bubble diameter of the HIPE foam was determined by arithmetically averaging the bubble diameters of the three samples obtained. The detailed analysis procedures and conditions were as follows:

[0112] (1) Monochrome conversion (2) Smoothing filter (3x3, 8 neighbors, processing count = 1) (3) Density unevenness correction (brighter than background, size = 5) (4) NS binarization (darker than background, clarity = 9, sensitivity = 1, noise removal, density range = 0 to 255) (5) Contraction (8 neighbors, number of processes = 1) (6) Image selection by feature (area) (50 to ∞ μm 2 (select only 8 neighbors) (7) Dilation without neighbors (8 neighbors, processing count = 3) (8) Measurement of circle equivalent diameter (calculated from area, 8 neighbors)

[0113] (average diameter of through holes) Cross-sectional photographs of the HIPE foam were taken using the same procedure as for calculating the average bubble diameter, except that the observation magnification was changed to 500x and the observation mode was changed to backscattered electron method (standard). Next, the cross-sectional photographs were analyzed using image processing software (WinROOF2013, manufactured by Mitani Shoji Co., Ltd.), and a line with a total area of ​​1 mm was drawn on the cross-sectional photograph of each sample. 2 The measurement area was set so that the above was the case. Next, the through-hole diameters of the through-holes present within the measurement area were calculated, and the arithmetic mean value of these was used as the through-hole diameter of each sample. The average diameter of the through-holes in the HIPE foam was determined by arithmetically averaging the through-hole diameters of the three samples obtained. The detailed analysis procedures and conditions were as follows:

[0114] (1) Monochrome imaging (2) Averaging filter (filter size = 3 × 3, number of times = 1) (3) Automatic binarization (discriminant analysis method, extraction area = dark area, target density range = 0 to 255) (4) Morphology adjustment (dilation, number of times = 3) (5) Measurement based on shape characteristics (measurement items = equivalent circle diameter, number)

[0115] (Tan δ peak temperature, maximum value, and half-width of tan δ peak) In the same manner as in the measurement of the molecular weight between crosslinks Mc, a T-tanδ curve was obtained in the temperature range of -100 to 120°C. The loss tangent tanδ is the value obtained by dividing the loss modulus E" by the storage modulus E', and in the dynamic viscoelasticity measurement, E', E" and tanδ can be measured simultaneously. Figure 2 shows an example of a T-tanδ curve for a HIPE foam. In Figure 2, the vertical axis represents the loss tangent tanδ, and the horizontal axis represents the temperature (unit: °C).

[0116] The value of tan δ at the peak top in the T-tan δ curve obtained in this way was taken as the maximum value of the loss tangent tan δ, and the temperature at which tan δ reached its maximum value was taken as the peak temperature of tan δ. In addition, two temperatures at which the value of tan δ reached half of the maximum value were determined for the tan δ peak appearing in the T-tan δ curve, and the half-width H was taken as the temperature difference.

[0117] (flow resistance per unit thickness) The flow resistance per unit thickness of the HIPE foam that constitutes the sound-absorbing material was measured in accordance with ISO 9053-1:2018. Specifically, a circular test piece with a diameter of 40 mm and a thickness of 20 mm was cut from near the center of the HIPE foam, excluding the skin surface. This test piece was attached to the sample holder of a measuring device (the "AirReSys" flow resistance measurement system manufactured by Nihon Onkyo Engineering Co., Ltd.), and air was passed from one end of the test piece to the other at a flow velocity of 1 to 3 mm / s. The differential pressure at a flow velocity of 0.5 mm / s was calculated from the relationship between the measured flow velocity and the difference in pressure between one end and the other end of the test piece (i.e., the differential pressure). The flow resistance per unit thickness (unit: N·s / m) was then calculated based on the differential pressure at a flow velocity of 0.5 mm / s and the shape of the test piece. 4 The results are shown in Tables 2 and 3.

[0118] (sound absorption) The sound absorption was evaluated based on the normal incidence sound absorption coefficient of the HIPE foam at 23°C at each frequency, measured according to JIS A 1405-2. Specifically, a disk-shaped test piece 20 mm thick and 40 mm in diameter was cut from near the center of the HIPE foam, excluding the skin surface. This test piece was placed in the sample holder of a measuring device (a normal incidence sound absorption coefficient measuring system "WinZacMTX" manufactured by Nihon Onkyo Engineering Co., Ltd.), and measurements were performed under the following conditions.

[0119] FFT analysis conditions Sampling frequency: 32,000Hz FFT score: 8192 points Output signal: Random signal (both during measurement and calibration) Window function: Hanning (for both actual measurement and calibration) Overlap: 75% (both during measurement and calibration) Average number of times measured: 400 Average number of calibrations: 800

[0120] Measurement conditions ·Measurement type: Sound absorption coefficient / reflectance (reflection method) Microphone type: 2-microphone method Distance between sample surface and MicA: 80mm Microphone distance: 30mm Sample diameter: 40mm Sample thickness: 20mm -Back air gap length: 0mm ·Temperature: 23℃

[0121] Using the above method, the normal incident sound absorption coefficient of the HIPE foam was measured at frequencies of 125 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz, 600 Hz, 700 Hz, 800 Hz, 900 Hz, 1000 Hz, 1500 Hz, 2000 Hz, 2500 Hz, 3000 Hz, 3500 Hz, 4000 Hz, 4500 Hz and 5000 Hz.

[0122] The sum of the normal incidence sound absorption coefficients at each frequency measured by the above method is shown as the total normal incidence sound absorption coefficient for frequencies from 125 to 5000 Hz in the "All Frequencies" column of Tables 2 and 3. Furthermore, of the normal incidence sound absorption coefficients at each frequency measured by the above method, the sum of the normal incidence sound absorption coefficients at 500 to 1000 Hz is shown as the total normal incidence sound absorption coefficient for frequencies from 500 to 1000 Hz in the "500 to 1000 Hz" column of Tables 2 and 3. [Table 2]

[0123] [Table 3]

[0124] As shown in Table 2, the sound-absorbing materials of Examples 1 to 8 have a base resin that is a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and / or a styrene monomer, and are composed of HIPE foams whose peak tan δ temperature and flow resistance per unit thickness are each within the specified ranges. Therefore, these sound-absorbing materials have improved sound absorption in the low frequency range and excellent sound absorption over a wide frequency range.

[0125] On the other hand, as shown in Table 3, the HIPE foam constituting the sound-absorbing material of Comparative Example 1 has too high a flow resistance per unit thickness. Therefore, the sound-absorbing material of Comparative Example 1 is inferior in sound absorption properties across all frequency ranges compared to the sound-absorbing materials of Examples 1 to 8.

[0126] The HIPE foam constituting the sound-absorbing material of Comparative Example 2 has a peak temperature of tan δ that is higher than the specific range, and the flow resistance per unit thickness is too low. Therefore, the sound-absorbing material of Comparative Example 2 is inferior to the sound-absorbing materials of Examples 1 to 8 in sound absorption properties in the relatively low frequency range. The HIPE foam constituting the sound-absorbing material of Comparative Example 3 has a lower flow resistance per unit thickness than that of Comparative Example 1, but a higher flow resistance than the specific range. Therefore, the sound-absorbing material of Comparative Example 3 has inferior sound absorption properties in all frequency ranges compared to the sound-absorbing materials of Examples 1 to 8.

[0127] The HIPE foam constituting the sound-absorbing material of Comparative Example 4 has too low a flow resistance per unit thickness, and therefore the sound-absorbing material of Comparative Example 4 is inferior to the sound-absorbing materials of Examples 1 to 8 in sound absorption properties in the relatively low frequency range. The HIPE foam constituting the sound-absorbing material of Comparative Example 5 has an excessively high peak temperature of tan δ. Therefore, the sound-absorbing material of Comparative Example 5 is inferior to the sound-absorbing materials of Examples 1 to 8 in sound absorption properties in a relatively low frequency range.

[0128] The above describes specific aspects of the sound-absorbing material according to the present invention based on examples, but the specific aspects of the sound-absorbing material according to the present invention are not limited to the aspects shown in the examples, and the configuration can be changed as appropriate within the scope that does not impair the intent of the present invention. [Explanation of symbols]

[0129] 1. Sound-absorbing material 11 Bubble Wall 12 Bubbles 13 Through hole

Claims

1. A sound-absorbing material made of a HIPE foam having a base resin that is a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer or a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and a styrene monomer, the peak temperature of loss tangent tanδ in a temperature-loss tangent tanδ curve measured by subjecting the HIPE foam to dynamic viscoelasticity measurement under the conditions of a frequency of 1 Hz, a load of 10 mN, and a deformation mode of compression is 50°C or less; The flow resistance per unit thickness of the HIPE foam at a flow rate of 0.5 mm / s measured based on ISO 9053-1:2018 is 7 x 10 ４ N·s / m ４ 1x10 or more ６ N·s / m ４ Below is the sound-absorbing material.

2. 2. The sound-absorbing material according to claim 1, wherein the maximum value of the loss tangent tanδ in the temperature-loss tangent tanδ curve is 0.4 or more.

3. The molecular weight between crosslinking points of the crosslinked polymer is 1.0 × 10 ４ 30 x 10 or more ４ 3. The sound-absorbing material according to claim 1 or 2, wherein:

4. The sound-absorbing material according to any one of claims 1 to 3, wherein the HIPE foam has a base resin that is a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer and a styrene monomer, and the acrylic monomer includes an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms.

5. The density of the HIPE foam is 10 kg / m 3 More than 200kg / m 3 The sound-absorbing material according to any one of claims 1 to 4, wherein:

6. The sound-absorbing material according to any one of claims 1 to 5, wherein the average diameter of the cells of the HIPE foam is 20 µm or more and 160 µm or less.

7. A sound-absorbing material described in any one of claims 1 to 6, wherein the ratio of the average diameter of the through holes that penetrate the cell walls of the HIPE foam and connect adjacent cells to the average diameter of the cells of the HIPE foam is 0.05 or more and 0.5 or less.

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