Method for producing HIPE foam and HIPE foam

Abstract

To provide a HIPE foam and a method for producing the HIPE foam, the HIPE foam having excellent toughness and high sound absorption performance over a broad frequency band.SOLUTION: The present invention provides a method for producing a HIPE foam with an acrylic crosslinked polymer as its base resin, and a HIPE foam obtainable by the production method. The HIPE foam is produced by polymerizing an acrylic monomer in a water-in-oil high internal phase emulsion in which an organic phase encloses an aqueous phase. The organic phase contains an acrylic monomer, an acrylate compound with a functional group equivalent of 300 g / eq or more, and an organic solvent. The organic solvent is free of hydroxyl groups and has a solubility in water of 300 g / L or less (including 0) at 20°C. The quantities of the acrylate compound and organic solvent to be added are adjusted within a predetermined ratio.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a HIPE foam having an acrylic crosslinked polymer as a base resin, and a method for producing the same. [Background technology]

[0002] Conventionally, a method has been known in which a water-in-oil type high internal phase emulsion (i.e., HIPE) is formed by encapsulating a high ratio of an aqueous phase consisting of an aqueous liquid such as water in an organic phase containing a vinyl monomer, a crosslinking agent, an emulsifier, a polymerization initiator, etc., and the organic phase is polymerized in the emulsion to obtain a HIPE foam having a crosslinked polymer as a base resin. HIPE foams are expected to be used in various applications such as liquid absorbents, separation materials, and sound absorbers.

[0003] For example, Patent Document 1 proposes using HIPE foam as a sound absorbing material, taking advantage of the sound absorbing properties of the HIPE foam. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-50728 A Summary of the Invention [Problem to be solved by the invention]

[0005] In HIPE foam, the toughness can be increased by using a certain amount of a crosslinking agent with a relatively high functional group equivalent. On the other hand, when such a crosslinking agent is used to increase toughness, the sound absorption of the HIPE foam for high-frequency sound waves tends to deteriorate. Therefore, the development of a HIPE foam that combines excellent toughness with high sound absorption over a wide frequency range from low to high frequencies is desired.

[0006] The present invention has been made in view of the above background, and aims to provide a HIPE foam having excellent toughness and high sound absorption properties over a wide frequency range, and a method for producing the same. [Means for solving the problem]

[0007] One aspect of the present invention resides in a method for producing a HIPE foam according to the following [1] to [6]. [1] A method for producing a HIPE foam having an acrylic crosslinked polymer as a base resin by forming a water-in-oil type high internal phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and an acrylate compound as a crosslinking agent, and polymerizing the acrylic monomer in the emulsion, comprising: The functional group equivalent of the acrylate compound is 300 g / eq or more, The amount of the acrylate compound added relative to 100 parts by mass of the acrylic monomer is 10 parts by mass or more and 180 parts by mass or less, the organic phase further contains an organic solvent that does not have a hydroxyl group and has a solubility in water of 300 g / L or less (including 0) at a temperature of 20° C.; A method for producing a HIPE foam, wherein the amount of the organic solvent added is 10 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the total of the acrylic monomer and the acrylate compound.

[0008] [2] The method for producing a HIPE foam described in [1], wherein the viscosity of the organic phase at a temperature of 23°C, as measured by a B-type viscometer, is 1 mPa·s or more and 15 mPa·s or less. [3] The method for producing a HIPE foam described in [1] or [2], wherein the amount of the organic solvent added per 100 parts by mass of the acrylate compound is 50 parts by mass or more and 400 parts by mass or less. [4] The method for producing a HIPE foam according to any one of [1] to [3], wherein the boiling point of the organic solvent is 130° C. or lower.

[0009] [5] The method for producing a HIPE foam according to any one of [1] to [4], wherein the organic solvent is at least one selected from the group consisting of carboxylates, ketones, and aromatic compounds. [6] The method for producing a HIPE foam according to any one of [1] to [5], wherein the acrylate compound is an epoxy (meth)acrylate having a bisphenol structure.

[0010] Another aspect of the present invention is a HIPE foam according to the following items [7] to [9]. [7] A HIPE foam having an acrylic crosslinked polymer as a base resin, The HIPE foam has an elongation of 100% or more, and a breaking energy per unit weight of 0.03 J / g or more when broken, as measured by a tensile test based on JIS K6400-5:2012; The average sound absorption coefficient of the HIPE foam at frequencies of 1000 Hz, 2000 Hz and 3000 Hz measured by the normal incidence method of JIS A1405-2:2007 is 0.6 or more; A HIPE foam having a ratio of sound absorption coefficient at a frequency of 2000 Hz to sound absorption coefficient at a frequency of 1000 Hz of 0.80 or more.

[0011] [8] The density of the HIPE foam is 20 kg / m 3 More than 80kg / m 3 The HIPE form described in [7] is as follows: [9] The HIPE foam described in [7] or [8], wherein the average bubble diameter of the HIPE foam is 65 μm or more and 200 μm or less. Effect of the Invention

[0012] In the manufacturing method of the above aspect, the predetermined acrylate compound is added as a crosslinking agent in a predetermined ratio, and the predetermined organic solvent is added in a predetermined ratio, as described above. According to the manufacturing method, it is possible to manufacture a HIPE foam having excellent toughness and high sound absorption properties in a wide frequency range.

[0013] In addition, HIPE foam whose density, elongation, breaking energy per unit weight, and average sound absorption coefficient at a specified frequency and the ratio of sound absorption coefficient between specified frequencies are adjusted to be within the specified ranges as described above has excellent toughness and high sound absorption properties over a wide frequency range. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is an explanatory diagram showing an example of a low vacuum scanning electron microscope photograph of a cross section of the HIPE foam in Example 1. [Diagram 2] FIG. 2 is an explanatory diagram showing an example of a low vacuum scanning electron microscope photograph of a cross section of the HIPE foam in Comparative Example 1. [Diagram 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 PREFERRED EMBODIMENTS

[0015] In this specification, when the symbol "~" is used to express a numerical range, it is intended to include the numerical values ​​written before and after it. Furthermore, when a numerical value or physical value is expressed as a lower limit, it means that it is equal to or greater than that numerical value or physical value, and when a numerical value or physical value is expressed as an upper limit, it means that it is equal to or less than that numerical value or physical value. Furthermore, "parts by weight" and "% by weight" are essentially synonymous with "parts by mass" and "% by mass", respectively.

[0016] [HIPE Form] HIPE foam is a porous cross-linked polymer also called PolyHIPE foam, polyHIPE material, HIPE-derived foam material, high internal phase emulsion porous body, high internal phase emulsion foam body, etc., and is obtained by polymerizing monomers in a water-in-oil type high internal phase emulsion in which a high ratio of aqueous phase is contained in an organic phase. High internal phase emulsion is commonly called HIPE. HIPE foam has an open-cell structure in which many bubbles exist in the structure and many through holes are formed to connect adjacent bubbles.

[0017] HIPE foams are obtained, for example, by polymerizing acrylic monomers in a water-in-oil type high internal phase emulsion in which a high ratio of aqueous phase is contained in an organic phase. HIPE foams use, as a base resin, a crosslinked polymer containing a component derived from an acrylic monomer, which is obtained, for example, by polymerizing an acrylic monomer in a water-in-oil type high internal phase emulsion. Specifically, the crosslinked polymer contains a component derived from an acrylic monomer in the polymer skeleton. In other words, HIPE foams use, as a base resin, a crosslinked polymer (hereinafter referred to as an "acrylic crosslinked polymer" or simply referred to as a "crosslinked polymer") in which a polymer of a vinyl monomer containing an acrylic monomer is crosslinked.

[0018] In addition, HIPE foam is a porous cured material obtained by curing a high internal phase emulsion, and the cell walls can be said to be composed of an acrylic crosslinked polymer. The cells can also be said to be pores. The shapes of the cell walls and cells in HIPE foam reflect the dispersion form of the organic phase and the aqueous phase in the high internal phase emulsion and the dispersion form of the aqueous phase (i.e., the dispersed phase) during polymerization.

[0019] In the manufacturing process of HIPE foam, since the crosslinked polymer is difficult to stretch, HIPE foam generally has a polymer that is difficult to cause molecular orientation 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 foamed beads in a mold.

[0020] [HIPE foam manufacturing method] HIPE foam is produced by forming a water-in-oil type high internal phase emulsion in which an aqueous phase is encapsulated in an organic phase, and polymerizing an acrylic monomer in the emulsion. The organic phase of the water-in-oil type high internal phase emulsion is a continuous phase containing an acrylic monomer, a crosslinking agent, an organic solvent, etc., and the aqueous phase is a dispersed phase containing water such as deionized water. Specifically, the HIPE foam can be produced by carrying out an emulsification process, a polymerization process, and a drying process as follows.

[0021] First, an aqueous liquid (aqueous phase) containing water is dropped into an oily liquid (organic phase) containing organic substances such as acrylic monomers, crosslinking agents, and organic solvents while stirring the oily liquid (organic phase) to prepare a water-in-oil type high internal phase emulsion (emulsification process). Next, the high internal phase emulsion is heated to polymerize the acrylic monomers, crosslinking agents, etc. in the organic phase to obtain a polymerization product (specifically, a crosslinked polymer containing water) (polymerization process). After that, the polymerization product is dried to obtain a HIPE foam composed of the crosslinked polymer (drying process).

[0022] (emulsification process) 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 ratio of the aqueous phase is, for example, three times or more that of the organic phase. The ratio of the aqueous phase to be contained in the organic phase can be adjusted by the weight ratio of the organic phase to the aqueous phase. In the water-in-oil type high internal phase emulsion, the mass ratio of the organic phase to the aqueous phase is preferably organic phase:aqueous phase=100:500 to 100:3000, and more preferably organic phase:aqueous phase=100:600 to 100:2500.

[0023] As described above, the HIPE foam has an open cell structure, and in such a cell structure, a large number of through holes are formed that communicate between adjacent cells. As illustrated in FIG. 1, the HIPE foam has a cell structure in which a large number of cells 12 are uniformly present, and also has an open cell structure in which a large number of through holes 13 are formed that penetrate the cell wall 11 and communicate between adjacent cells. In FIG. 1, the cells 12 are the parts surrounded by the cell wall 11. The through holes 13 are holes that penetrate the cell wall 11 and communicate between adjacent cells 12. Specifically, the through holes 13 are formed in the cell wall 11 and communicate between adjacent cells 12 with the cell wall 11 in between. The through holes 13 can also be called through windows or connecting holes. Since the through holes are holes that are generated in the cell wall and communicate between the cells, the diameter of the through holes is usually smaller than the diameter of the cells. The through-holes are formed when the oil film breaks due to the volumetric shrinkage of the polymer during polymerization of the monomer in the water-in-oil type high internal phase emulsion. The oil film becomes the cell wall as polymerization and crosslinking proceed. The average diameter of the through holes (average through hole diameter) can be controlled by adjusting the polymerization rate, the type and amount of the organic solvent, the composition and viscosity of the organic phase, the stirring power density, etc. For example, in preparing a high internal phase emulsion (emulsification step), the through hole diameter can be reduced by lowering the ratio of the aqueous phase to the organic phase, increasing the stirring power density, etc.

[0024] In the emulsification process, the stirring power density when stirring the organic phase and emulsion is 0.01 kW / m 3 More than 3kW / m 3It is preferable that the value is less than 0.03 kW / m 3 More than 1kW / 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 easy 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 multiplying this power by the volume (unit: m 3 ) can be calculated by dividing it by

[0025] The viscosity of the organic phase at a temperature of 23°C measured by a B-type viscometer is preferably 1 mPa·s or more and 15 mPa·s or less. In this case, it is easy to stably polymerize a HIPE foam having a desired cell structure. From the viewpoint of more stably producing a HIPE foam having good sound absorption properties, the viscosity of the organic phase at a temperature of 23°C is more preferably 12 mPa·s or less, and even more preferably 10 mPa·s or less. In addition, from the viewpoint of stably producing a HIPE foam having better toughness, the viscosity of the organic phase at a temperature of 23°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, and even more preferably 4 mPa·s or more. The viscosity of the organic phase can be measured as the viscosity of the oily liquid before the emulsion is formed. As the B-type viscometer, for example, a B-type rotational viscometer equipped with a UL low viscosity adapter (specifically, LVDV-II+Pro manufactured by Eiko Seiki Co., Ltd., etc.) can be used. As the spindle used in the measurement, spindle No. 00 can be used. In addition, the stirring speed when measuring the viscosity of the organic phase can be 10 rpm. The viscosity of the organic phase can be adjusted, for example, by the type and amount of the crosslinking agent and the type and amount of the organic solvent. More specifically, the viscosity of the organic phase tends to increase when the amount of the acrylate compound described below is increased, and the viscosity of the organic phase tends to decrease when the amount of the organic solvent described below is increased.

[0026] The viscosity of the high internal phase emulsion at 23° C. is preferably from 800 mPa·s to 1600 mPa·s, more preferably from 900 mPa·s to 1500 mPa·s, and even more preferably from 1000 mPa·s to 1400 mPa·s. In this case, it becomes easier to stably polymerize a HIPE foam having a desired cell structure. The viscosity of the high internal phase emulsion was measured by dynamic viscoelasticity measurement of the high internal phase emulsion using a rheometer at a shear rate of 50 s ―1 The viscosity of the high internal phase emulsion can be calculated at

[0027] Examples of acrylic monomers used as vinyl 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. The vinyl monomers and acrylic monomers are monofunctional monomers. From the viewpoint of stably producing a HIPE foam having better toughness and sound absorption properties, the acrylic monomer preferably contains a (meth)acrylic acid ester as a main component. Specifically, the acrylic monomer preferably contains 50% by mass or more of a (meth)acrylic acid ester, more preferably contains 60% by mass or more, even more preferably contains 80% by mass or more, and particularly preferably contains 90% by mass or more. From the same viewpoint, the acrylic monomer more preferably contains an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms as a main component, even more preferably contains an ester of (meth)acrylic acid and an alcohol having 2 to 16 carbon atoms as a main component, even more preferably contains an ester of (meth)acrylic acid and an alcohol having 3 to 10 carbon atoms as a main component, and particularly preferably contains an ester of acrylic acid and an alcohol having 3 to 10 carbon atoms as a main component. Furthermore, the acrylic monomer preferably contains butyl acrylate and / or 2-ethylhexyl acrylate as a main component, and preferably contains butyl acrylate as a main component. Incidentally, (meth)acrylic acid means acrylic acid and / or methacrylic acid.

[0028] In addition, in the emulsification step, the organic phase can contain vinyl monomers other than acrylic monomers. When the organic phase contains vinyl monomers other than acrylic monomers, the content ratio of the other vinyl monomers to 100 parts by mass of acrylic monomers is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less. In this case, it is easier to stably obtain HIPE foam with better sound absorption properties. As the other vinyl monomer, for example, a styrene monomer can be used, and a styrene monomer containing styrene as a main component can be used. More specifically, a styrene monomer having a styrene content of 50% by weight or more can be used, a styrene monomer having a styrene content of 80% by weight or more can be used, and a styrene monomer having a styrene content of 90% by weight or more can be used.

[0029] The crosslinking agent and the acrylic monomer constitute a crosslinked polymer, that is, the crosslinked polymer contains an acrylic monomer component derived from the acrylic monomer and a crosslinking agent component derived from the crosslinking agent.

[0030] As the crosslinking agent, at least an acrylate-based compound having a functional group equivalent of 300 g / eq or more is used. The acrylate-based compound is a multifunctional compound having at least two polymerizable functional groups in the molecule. Since the acrylate-based compound having such a functional group equivalent has a relatively long molecular chain, it is considered that the polymer molecular chains can be crosslinked without significantly decreasing the mobility of the polymer molecular chains by being copolymerized with an acrylic monomer as a crosslinking agent. The acrylate-based compound having a functional group equivalent of 300 g / eq or more used as a crosslinking agent is appropriately referred to as "acrylate-based compound A". The use of the acrylate-based compound A makes it easy to increase the toughness of the HIPE foam. If the functional group equivalent of the acrylate-based compound is too small, the toughness of the HIPE foam may be insufficient. From the viewpoint of further improving the toughness of the HIPE foam, the functional group equivalent of the acrylate-based compound A is preferably 500 g / eq or more, more preferably 600 g / eq or more, and even more preferably 700 g / eq or more. From the viewpoint of easy handling, the upper limit of the functional group equivalent of the acrylate compound A is preferably 5000 g / eq, more preferably 4000 g / eq, and even more preferably 3000 g / eq. The acrylate compound includes a compound having an acryloyl group and / or a methacryloyl group in the structure. From the viewpoint of stable polymerization of the crosslinking agent, the number of polymerizable functional groups that the vinyl compound has in the molecule is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. From the viewpoint of stable production of the desired HIPE foam, the acrylate compound is preferably a diacrylate compound having two polymerizable functional groups in the molecule. In addition, from the viewpoint of easier improvement of the toughness of the crosslinked polymer, the crosslinking agent preferably has polymerizable functional groups at least at both ends of the molecule, and more preferably has polymerizable functional groups only at both ends of the molecule. The functional group equivalent A of the acrylate compound means the molar mass of the acrylate compound per polymerizable functional group (specifically, acryloyl group or methacryloyl group), and the unit of functional group equivalent can also be expressed as [g / mol].

[0031] The amount of the acrylate compound A added is 10 parts by mass or more and 180 parts by mass or less relative to 100 parts by mass of the acrylic monomer. When the amount of the acrylate compound A added is small, the toughness of the HIPE foam tends to decrease, and when the amount of the acrylate compound A added relative to 100 parts by mass of the acrylic monomer is too small, the toughness of the HIPE foam may be insufficient. From the viewpoint of further improving the toughness, the amount of the acrylate compound A added relative to 100 parts by mass of the acrylic monomer is preferably 20 parts by mass or more, more preferably 30 parts by mass or more. On the other hand, when the amount of the acrylate compound A added is too large, the emulsion may become unstable during emulsification, and the HIPE foam may not be obtained. From the viewpoint of further preventing the instability of the emulsion, the amount of the acrylate compound A added relative to 100 parts by mass of the acrylic monomer is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less.

[0032] In addition, as the crosslinking agent, a vinyl-based compound other than the acrylate-based compound A may be used in combination. Specifically, a vinyl-based compound having at least two functional groups selected from a vinyl group and an isopropenyl group in the molecule may be used. The vinyl-based compound also includes compounds containing a vinyl group and / or an isopropenyl group in the structure of the functional group, such as an acryloyl group or a methacryloyl group. From the viewpoint of stably polymerizing the crosslinking agent, the number of functional groups that the vinyl-based compound has in the molecule is preferably 6 or less, more preferably 5 or less, and more preferably 4 or less. In addition, from the viewpoint of making it easier to increase the toughness of the crosslinked polymer, the crosslinking agent preferably has functional groups at least at both ends of the molecule, and more preferably has functional groups only at both ends of the molecule.

[0033] It is preferable to use a vinyl-based compound having a functional group equivalent of less than 300 g / eq together with an acrylate-based compound having a functional group equivalent of 300 g / eq as a crosslinking agent, since this makes it easier to increase the toughness of the crosslinked polymer while increasing its rigidity. In this case, excessive embrittlement of the HIPE foam is easily suppressed, and even when a HIPE foam having a complex shape, such as having a thin portion, is produced, the occurrence of chipping in the HIPE foam can be suppressed, making the HIPE foam easier to handle. The vinyl-based compound having a functional group equivalent of less than 300 g / eq used as a crosslinking agent is appropriately referred to as "vinyl-based compound B".

[0034] Since the vinyl compound B has a relatively short molecular chain, it is believed that the mobility of the polymer molecular chain in the crosslinked polymer can be reduced by copolymerizing it with an acrylic monomer. By using the vinyl compound B in combination with the acrylate compound A, the toughness of the HIPE foam can be increased while the rigidity of the HIPE foam can be increased. This improves, for example, the processability and handleability of the HIPE foam. The lower limit of the functional group equivalent of the vinyl compound B 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 vinyl compound B is preferably 130 g / eq, more preferably 100 g / eq, and even more preferably 80 g / eq. The functional group equivalent of the vinyl compound means the molar mass of the vinyl compound per polymerizable functional group (specifically, an alkenyl group such as a vinyl group or an isopropenyl group), and the unit of the functional group equivalent can also be expressed as [g / mol]. When two or more types of vinyl compounds B are used, the weight average value of the functional group equivalents of all the vinyl compounds B is calculated, and this value is regarded as the functional group equivalent of the vinyl compound B. Similarly, when two or more types of acrylate compounds A are used, the weight average value of the functional group equivalents of all the acrylate compounds A is calculated, and this value is regarded as the functional group equivalent of the acrylate compound A.

[0035] From the viewpoint of improving toughness while maintaining rigidity, it is preferable to use a vinyl-based compound B and an acrylate-based compound A as crosslinking agents, and the functional group equivalent of the acrylate-based compound A is preferably 100 g / eq or more larger than the functional group equivalent of the vinyl-based compound B, preferably 300 g / eq or more larger, and more preferably 500 g / eq or more larger.

[0036] Examples of the acrylate-based compound A include esters of epoxy oligomers and (meth)acrylic acid, (meth)acrylic-modified silicones, and the like. Specifically, examples include 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 at both ends with (meth)acrylic; caprolactone-modified isocyanurates such as caprolactone-modified tris isocyanurates; and ethoxylated bisphenol A (meth)acrylates such as ethoxylated bisphenol A dimethacrylate. However, the number of functional groups in the crosslinking agent is two or more per molecule. The acrylate-based compound used as the acrylate-based compound A may be one type or two or more types.

[0037] From the viewpoint of further improving the toughness and sound absorption of the HIPE foam, it is preferable to use an epoxy (meth)acrylate having a functional group equivalent of 500 g / eq or more and 3000 g / eq or less as the acrylate-based compound A. From the same viewpoint, it is preferable that the acrylate-based compound A is an epoxy (meth)acrylate having a bisphenol structure, and more preferably an epoxy (meth)acrylate having a bisphenol A structure. Incidentally, having a bisphenol structure means that the molecular structure of the ester compound contains a chemical structure derived from bisphenol.

[0038] Examples of the vinyl-based compound used as the vinyl-based compound B include vinyl-based compounds such as divinylbenzene, triallyl isocyanurate, and esters of polyhydric alcohols and (meth)acrylic acid. Examples of the esters of polyhydric alcohols and (meth)acrylic acid include vinyl-based 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 vinyl-based compound B is two or more per molecule. The functional groups are preferably vinyl groups and / or isopropenyl groups. The vinyl-based compound B may be one type or two or more types. That is, the component derived from the vinyl-based compound B constituting the crosslinked polymer may be one type or two or more types. When vinyl compound B is used, the amount added is preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the total of the amount of acrylic monomer added and the amount of acrylate compound A added. The ratio of the amount of the vinyl compound B added to the amount of the acrylate compound A added is preferably 0.01 to 0.4, and more preferably 0.02 to 0.3.

[0039] From the viewpoint of making it easier to adjust the rigidity of the HIPE foam, it is preferable to use divinylbenzene and / or butanediol diacrylate as the vinyl-based compound B, and it is more preferable to use divinylbenzene.

[0040] Table 1 shows the molecular weights of representative crosslinking agents and the molecular weights per functional group (i.e., functional group equivalents).

[0041] [Table 1]

[0042] In addition, the total content of the components derived from the acrylic monomer and the components derived from the acrylate compound having a functional group equivalent of 300 g / eq or more in the crosslinked polymer is preferably 80 mass% or more, and more preferably 90 mass% or more.

[0043] In the emulsification step, an organic solvent that does not have a hydroxyl group and has a solubility in water of 300 g / L or less (including 0) at 20° C. is added to the organic phase. The organic solvent can be added to, for example, an oily liquid. The organic solvent can be said to be an organic compound that does not have a hydroxyl group and has a solubility in water of 300 g / L or less (including 0) at 20° C. and is liquid at 20° C. Preferably, the organic solvent is at least one organic solvent selected from the group consisting of carboxylate esters, ketones, and aromatic compounds. Examples of such organic solvents include xylene (solubility in water: 0.2 g / L), butyl acetate (solubility in water: 4.3 g / L), cyclohexanenone (solubility in water: 23 g / L), ethyl acetate (solubility in water: 81 g / L), and methyl ethyl ketone (solubility in water: 240 g / L). From the viewpoint of preventing shrinkage of the HIPE foam after drying and making it easier to adjust the density to the desired level, the solubility of the organic solvent in water at 20°C is preferably 2 g / L or more, more preferably 3 g / L or more, even more preferably 10 g / L or more, and particularly preferably 20 g / L or more. The solubility of an organic solvent in water at 20° C. means the amount (g) of the organic solvent that can be dissolved in 1 L of water at a temperature of 20° C. The solubility can be determined, for example, by the following method. First, the target organic solvent and water are mixed in a volume ratio of 1:1, and the organic solvent is saturated in the water at 20° C. Next, the water saturated with the organic solvent is collected as a sample, and the sample is analyzed by gas chromatography or the like, whereby the amount (g) of the organic solvent contained in 1 L of water can be determined.

[0044] The amount of the organic solvent added is 10 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the total of the acrylic monomer and the acrylate compound A. By setting the amount of the organic solvent added within this range, it is easy to obtain a HIPE foam with a desired density, and the cell structure of the HIPE foam is improved, and a HIPE foam that exhibits excellent sound absorption not only in the low frequency range (e.g., 1000 Hz or less) but also in the high frequency range (e.g., 1500 Hz or more) while maintaining high toughness can be stably obtained. When two or more organic solvents are used as the organic solvent, the total amount of organic solvents that do not have a hydroxyl group and have a solubility in water at 20°C of a specific value or less is defined as the amount of the organic solvent added. From the viewpoint of facilitating stable production of a HIPE foam exhibiting excellent sound absorbing properties, the amount of organic solvent added is preferably 15 parts by mass or more, and more preferably 20 parts by mass or more, per 100 parts by mass of the total of the acrylic monomer and the acrylate compound A. On the other hand, from the viewpoint of preventing shrinkage of the HIPE foam after drying and facilitating adjustment to a desired density, the amount of organic solvent added is preferably 140 parts by mass or less, more preferably 100 parts by mass or less, and even more preferably 80 parts by mass or less, per 100 parts by mass of the total of the acrylic monomer and the acrylate compound A. If an organic solvent with an excessively high solubility in water at 20° C. is added in excess, the emulsion may become unstable during emulsification, with the result that a HIPE foam may not be obtained. Even if the solubility of the organic solvent in water at 20° C. is not excessively high, if an organic solvent having a hydroxyl group, such as alcohol, is added in excess, the emulsion may become unstable.

[0045] The reason why the above effect is obtained by adding the predetermined organic solvent is considered as follows. When the HIPE foam is produced, the toughness of the HIPE foam can be increased by using an acrylate-based compound A having a large functional group equivalent as a crosslinking agent and adding a predetermined amount of acrylate A. On the other hand, when the acrylate-based compound A is added, the viscosity of the organic phase is likely to increase, and when the aqueous phase and the organic phase are emulsified by stirring or the like, the water droplet diameter of the aqueous phase in the emulsion is likely to become small. Therefore, the bubbles 92 of the obtained HIPE foam 9 are likely to become small, and the average bubble diameter of the HIPE foam is also likely to become small (see FIG. 2). When the average bubble diameter of the HIPE foam becomes small, it becomes difficult for sound waves in the high frequency range to penetrate into the HIPE foam, and the sound absorption of the HIPE foam tends to decrease. In contrast, it is considered that by adding the predetermined organic solvent at the predetermined ratio as in the present disclosure, the viscosity of the organic phase can be prevented from becoming excessively high while using the acrylate-based compound A. This prevents the water droplet diameter in the emulsion from becoming excessively small, and prevents the bubbles 12 of the HIPE foam 1 from becoming small (see FIG. 1). As a result, it is believed that the average bubble diameter of the HIPE foam can be made relatively large, and an interconnected cell structure suitable for sound absorption is formed. For this reason, it is believed that the present disclosure can obtain a HIPE foam that can achieve both excellent toughness and sound absorption. By using the predetermined organic solvent at the predetermined ratio, a HIPE foam with excellent sound absorption properties in the low to high frequency range can be obtained, and the HIPE foam becomes suitable as a sound absorbing material. Such a HIPE foam is suitable as a sound absorbing material in the automotive field, including electric vehicles, because it has excellent sound absorption properties in a wide range of frequencies, such as road noise and brake noise, and also has excellent sound absorption properties in the high frequency range, such as abnormal noise called brake squeal generated by contact vibration between the disc rotor and the brake pad, and inverter noise. In addition, it is suitable as a sound absorbing material in the architectural field, etc., because it has excellent sound absorption properties in a wide range of frequencies. The HIPE foam of the present disclosure can also be used for applications such as vibration damping materials, shock absorbing materials, cleaning supplies, etc., and can be used for a variety of applications regardless of the requirements related to sound absorption.

[0046] The amount of organic solvent added to 100 parts by mass of acrylate compound A is preferably 50 parts by mass or more and 400 parts by mass or less, more preferably 60 parts by mass or more and 350 parts by mass or less, even more preferably 65 parts by mass or more and 250 parts by mass or less, and particularly preferably 70 parts by mass or more and 150 parts by mass or less. In this case, shrinkage of the HIPE foam after drying is suppressed, and a HIPE foam having a desired density can be easily obtained, and a HIPE foam exhibiting excellent sound absorption not only in the low frequency range but also in the high frequency range while maintaining high toughness can be stably obtained.

[0047] The boiling point of the organic solvent is not particularly limited as long as it is within a range in which the intended object of the present invention can be achieved. From the viewpoint of making it easier to remove the organic solvent from the HIPE foam after polymerization by heating or the like, the boiling point is preferably 160°C or less, more preferably 150°C or less, and even more preferably 130°C or less.

[0048] As a method of adding an aqueous liquid to an oily liquid in an emulsification step, for example, a method of starting stirring while an oily liquid and an aqueous liquid are supplied into a stirring vessel to perform emulsification can be adopted. From the viewpoint of easily obtaining a HIPE foam having a desired cell structure, it is preferable to adopt a method of supplying an oily liquid into a stirring vessel, starting stirring, and supplying an aqueous liquid into the vessel under stirring using a pump or the like to perform emulsification. When preparing a water-in-oil type high internal phase emulsion by dropping an aqueous liquid containing water into the oily liquid while stirring the oily liquid, the addition rate of the aqueous liquid is, for example, preferably 10% by weight / min or more and 1000% by weight / min or less, more preferably 100% by weight / min or more and 800% by weight / min or less, and even more preferably 200% by weight / min or more and 600% by weight / min or less, relative to 100% by weight 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.

[0049] As described above, the oil phase can contain a monomer such as an acrylic monomer, a crosslinking agent, etc., and the aqueous phase can contain water such as deionized water, an electrolyte, etc. In the emulsification step, for example, a monomer, a crosslinking agent, etc. are mixed to prepare an oily liquid, and an aqueous liquid such as water and an electrolyte is prepared, and then the aqueous liquid is added to the oily liquid under stirring to prepare a high internal phase emulsion. A polymerization initiator and an emulsifier can be added to the oily liquid and / or the aqueous liquid. This allows the organic phase and / or the aqueous phase to contain a polymerization initiator and an emulsifier, which can promote the polymerization of the monomer and the formation of the emulsion. In addition, additives such as a flame retardant, a flame retardant auxiliary, a light resistance agent, a colorant, and a radiation suppressant can be added to the oily liquid and / or the aqueous liquid. This allows the organic phase and / or the aqueous phase to contain the additives, and the effects of the additives can be obtained by imparting them to the HIPE foam.

[0050] The polymerization initiator is used to start the polymerization of the acrylic monomer. 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 peroxy piperate, t-hexyl peroxy piperate, t-butyl peroxy neoheptanoate, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, etc. 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), 2,2'azobis(2-methylbutyronitrile) and the like are used. From the viewpoint that polymerization can be performed without excessively increasing the temperature during polymerization and that adverse effects on the HIPE foam due to boiling water can be suppressed, the one-hour half-life temperature of the polymerization initiator is preferably 95°C or lower, more preferably 90°C or lower. In addition, from the viewpoint of safety, in order to suppress decomposition of the polymerization initiator at room temperature, the one-hour half-life temperature of the polymerization initiator is preferably 50°C or higher, more preferably 55°C or higher.

[0051] As the polymerization initiator, one or more substances can be used. From the viewpoint of shortening the polymerization time without decreasing 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 more and less than 70° C. and an organic peroxide having a one-hour half-life temperature of 70° C. or more and 90° C. or less. The polymerization initiator can be added to the organic phase and / or the aqueous phase as described above. 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 to be 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 acrylic monomer and the crosslinking agent.

[0052] The emulsifier is used for forming and stabilizing a high internal phase emulsion. For example, a surfactant can be used as the emulsifier. 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; copolymers of polyethylene glycol and polypropylene glycol, and the like, can be used. The amount of the emulsifier to be added can be, for example, in the range of 1 to 30 parts by weight per 100 parts by weight of the total of the acrylic monomer, the crosslinking agent, and the emulsifier.

[0053] The electrolyte is used to impart ionic strength to the aqueous phase and to increase the stability of the emulsion. As the electrolyte, a water-soluble electrolyte can be used. Specifically, calcium chloride, sodium chloride, magnesium chloride, sodium acetate, sodium citrate, sodium sulfate, calcium sulfate, magnesium sulfate, sodium dihydrogen phosphate, disodium hydrogen phosphate, etc. can be used. The amount of the electrolyte added can be, for example, in the range of 0.01 to 10 parts by weight with respect to 100 parts by weight of the aqueous liquid.

[0054] The flame retardant is used to improve the flame retardancy of the HIPE foam. Examples of the flame retardant include organic compounds containing halogen, phosphorus, nitrogen, silicone, etc.; inorganic compounds containing metal hydroxide, phosphorus, nitrogen, etc., and the flame retardant can be used within a range that does not impair the effects of the present invention. When the flame retardant is blended, the blending amount is preferably 5 to 20 parts by weight per 100 parts by weight of the total of the acrylic monomer component and the crosslinking agent component constituting the crosslinked polymer. From the viewpoint of easily imparting excellent flame retardancy even with a small amount of addition, it is preferable to use a brominated bisphenol flame retardant as the flame retardant, and it is more preferable to use 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 it is even more preferable to use 2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane.

[0055] In addition, the flame retardant synergist is used to improve the flame retardant efficiency. For example, when a halogen-based flame retardant is used, by using a radical generator such as dicumyl peroxide as the flame retardant synergist, the decomposition of the radical generator promotes the detachment of halogen from the flame retardant, and the flame retardant efficiency can be improved. In addition, when a halogen-based flame retardant is used, by using an antimony compound such as antimony trioxide as the flame retardant synergistically combining the radical trapping effect of the halogen-based flame retardant and the air blocking effect of antimony oxide, the flame retardant efficiency can be improved. The flame retardant may be used alone, or two or more flame retardants with different flame retardant mechanisms may be used in combination.

[0056] (polymerization process) In the polymerization step, a monomer such as an acrylic monomer is polymerized and the polymer is crosslinked to obtain a product (specifically, a crosslinked polymer containing moisture) (polymerization step). The polymerization temperature in the polymerization step is adjusted depending on, for example, the type of monomer such as an acrylic monomer, the type of polymerization initiator, the type of crosslinking agent, etc. From the viewpoint of increasing the productivity of the HIPE foam and making it easier to obtain a 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. In addition, 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.

[0057] In the drying process, the crosslinked polymer containing water is dried using an oven, a vacuum dryer, a high-frequency / microwave dryer, or the like. When the drying is completed, the places where water droplets were present in the emulsion before polymerization become air bubbles in the polymer after drying, and a HIPE foam can be obtained. Before drying, the crosslinked polymer can be dehydrated by squeezing it using, for example, a press. The squeezing can be performed at room temperature (for example, 23°C), but 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 becomes easier, and the drying time can be shortened. The crosslinked polymer can also be dehydrated by centrifugation. In this case, the drying time is also shortened.

[0058] The organic solvent may be dissolved in the water present in the crosslinked polymer or the bubbles of the HIPE foam after the polymerization step. Such organic solvent can be removed in the drying step. In addition, by using an organic solvent with low solubility in water, the amount of organic solvent remaining in the HIPE foam can be reduced.

[0059] The HIPE foam obtained by the above method has a specific elongation and a specific breaking energy, as described below, and has an average sound absorption coefficient at a specific frequency that is equal to or greater than a specific value, and the ratio of the sound absorption coefficient between the specific frequencies satisfies a specific relationship. Such a HIPE foam has excellent toughness and can exhibit high sound absorption properties over a wide wave number range, so it can be suitably used, for example, as a sound absorbing material. The obtained HIPE foam also has excellent toughness, so it can be used not only as a sound absorbing material, but also as a packaging material, a shock absorbing material, etc. The HIPE foam can be used for various purposes as it is after production, or can be cut or otherwise processed to a desired shape to produce a sound absorbing material or the like.

[0060] [HIPE Form] From the viewpoint of improving ductility and stably obtaining HIPE foam with a desired cell structure, the HIPE foam uses a crosslinked polymer obtained by crosslinking a polymer of an acrylic monomer as the base resin. The density of the HIPE foam is 20 kg / m 3 More than 80kg / m 3 It is preferable that the thickness is less than 30 kg / m 3 More than 70kg / m 3 The density is adjusted to within the above range by, for example, adjusting the charge composition of the monomer, crosslinking agent, water, and the like.

[0061] The crosslinked polymer, which is the base resin of the HIPE foam, contains a component derived from an acrylic monomer and a component derived from an acrylate compound. The crosslinked polymer has a mass ratio of the component derived from the acrylic monomer to the component derived from the acrylate compound of preferably 90:10 to 35:65, more preferably 85:15 to 35:65, and even more preferably 80:20 to 40:60. In addition, the component derived from the acrylic monomer preferably contains a component derived from a (meth)acrylic acid ester as a main component. Specifically, the component derived from the acrylic monomer preferably contains 50% by mass or more of the component derived from the (meth)acrylic acid ester, more preferably contains 60% by mass or more, even more preferably contains 80% by mass or more, and particularly preferably contains 90% by mass or more. In addition, the component derived from the acrylic monomer more preferably contains an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms as a main component, even more preferably contains an ester of (meth)acrylic acid and an alcohol having 2 to 16 carbon atoms as a main component, even more preferably contains an ester of (meth)acrylic acid and an alcohol having 3 to 10 carbon atoms as a main component, and particularly preferably contains an ester of acrylic acid and an alcohol having 3 to 10 carbon atoms as a main component. In addition, the acrylic monomer preferably contains butyl acrylate and / or 2-ethylhexyl acrylate as a main component, and preferably contains butyl acrylate as a main component.

[0062] The elongation of the HIPE foam is 100% or more, and the breaking energy per unit weight when the HIPE foam breaks is 0.03 J / g or more. Such a HIPE foam has excellent toughness and can prevent breakage in various applications, for example, during installation or use. The elongation of the HIPE foam is preferably 130% or more, and more preferably 150% or more. The breaking energy per unit weight of the HIPE foam is preferably 0.05 J / g or more, and more preferably 0.1 J / g or more. The upper limit of the elongation of the HIPE foam is not limited as long as it is within a range that can achieve the intended object of the present disclosure, but is approximately 500%, may be 400%, or may be 300%. Similarly, the upper limit of the breaking energy of the HIPE foam is approximately 1 J / g, and may be 0.8 J / g. The elongation and breaking energy of the HIPE foam are measured by a tensile test based on JIS K6400-5:2012. The elongation and breaking energy per unit of the HIPE foam are adjusted to the above ranges by, for example, adjusting the type of monomer, the type and addition of the crosslinking agent, and the cell diameter of the HIPE foam. For example, the elongation and breaking energy per unit of the HIPE foam can be increased by adding a relatively large amount of the acrylate compound A used as a crosslinking agent. In addition, the elongation and breaking energy per unit of the HIPE foam can be easily increased by relatively increasing the cell diameter of the HIPE foam.

[0063] The HIPE foam has an average sound absorption coefficient of 0.60 or more at frequencies of 1000Hz, 2000Hz, and 3000Hz, and a ratio of the sound absorption coefficient at 2000Hz to the sound absorption coefficient at 1000Hz is 0.80 or more. In this way, the average sound absorption coefficient at the specified frequency is a specific value or more, and the ratio of the sound absorption coefficient between the specified frequencies satisfies a specific relationship, resulting in a HIPE foam that exhibits sound absorption characteristics that show a high sound absorption coefficient over a wide wave number range in the relationship between frequency and sound absorption coefficient. This results in a HIPE foam that has excellent sound absorption properties over a wide frequency range. In addition, such a HIPE foam with excellent sound absorption properties is more suitable as a sound absorbing material.

[0064] From this viewpoint, the average sound absorption coefficient of the HIPE foam at frequencies of 1000 Hz, 2000 Hz, and 3000 Hz is preferably 0.65 or more, more preferably 0.70 or more. The upper limit of the average value is usually 1, and may be 0.9. From the same viewpoint as above, the ratio of the sound absorption coefficient of the HIPE foam at a frequency of 2000 Hz to the sound absorption coefficient of the HIPE foam at a frequency of 1000 Hz is preferably 0.85 or more, more preferably 0.90 or more. The upper limit of the ratio of the sound absorption coefficient of the HIPE foam at a frequency of 2000 Hz to the sound absorption coefficient of the HIPE foam at a frequency of 1000 Hz is approximately 1.4, and may be 1.3. From the same viewpoint as above, the ratio of the sound absorption coefficient of the HIPE foam at a frequency of 3000 Hz to the sound absorption coefficient of the HIPE foam at a frequency of 1000 Hz is preferably 0.80 or more, more preferably 0.85 or more, and more preferably 0.90 or more. On the other hand, the upper limit of the ratio of the sound absorption coefficient of the HIPE foam at a frequency of 3000 Hz to the sound absorption coefficient of the HIPE foam at a frequency of 1000 Hz is approximately 1.4, and may be 1.3. From the viewpoint of further improving sound absorption, the sound absorption coefficient of the HIPE foam at frequencies of 1000 Hz, 2000 Hz, and 3000 Hz is preferably 0.6 or more, and more preferably 0.7 or more. The upper limit of the sound absorption coefficient at each of the aforementioned frequencies is usually 1, and may be 0.9.

[0065] The sound absorption coefficient of the HIPE foam at each frequency is measured by the normal incidence method of JIS A1405-2:2007. A HIPE foam having a predetermined range of elongation and breaking energy, and having a predetermined range of the average frequency and the ratio of the sound absorption coefficient between the frequencies, can be produced by adding a predetermined amount of the specific organic solvent while adjusting the type of monomer and the type and amount of the acrylate-based compound A when forming the organic phase. In particular, adding a predetermined amount of the specific organic solvent makes it easier to make the bubble diameter of the HIPE foam relatively large, and makes it easier to obtain a HIPE foam having a predetermined range of the average frequency and the ratio of the sound absorption coefficient between the frequencies, even when the acrylate-based compound A is used as a crosslinking agent.

[0066] As described above, a HIPE foam having a specific elongation and a specific breaking energy, an average sound absorption coefficient at a specific frequency being equal to or greater than a specific value, and a ratio of sound absorption coefficients between specific frequencies satisfying a specific relationship can be produced by the above-mentioned production method. Specifically, the HIPE foam is obtained by polymerizing an acrylic monomer in a water-in-oil type high internal phase emulsion containing an organic phase containing an acrylic monomer, an acrylate compound having a functional group equivalent of 300 g / eq or more, and an organic solvent having no hydroxyl group and a solubility in water of 300 g / L or less (including 0) at 20°C in a specific relationship, and an aqueous phase containing water.

[0067] The storage modulus of the HIPE foam at 23°C is preferably 5 kPa or more and 2000 kPa or less. In this case, the HIPE foam has a suitable flexibility. The storage modulus of the HIPE foam can be adjusted within the above range according to various uses of the HIPE foam. From the viewpoint of further increasing the flexibility of the HIPE foam, the storage modulus of the HIPE foam at 23°C is preferably 300 kPa or less, more preferably 200 kPa or less, even more preferably 100 kPa or less, and particularly preferably 50 kPa or less. In addition, from the viewpoint of increasing the rigidity of the HIPE foam while maintaining the flexibility of the HIPE foam, the storage modulus of the HIPE foam at 23°C is preferably 1 kPa or more, more preferably 3 kPa or more, even more preferably 5 kPa or more, and particularly preferably 10 kPa or more. The storage modulus is measured by performing dynamic viscoelasticity measurement on the HIPE foam under the conditions of frequency: 1 Hz, load: 10 mN, and deformation mode: compression. The storage modulus can be adjusted to fall within the above range by controlling the type and amount of crosslinking agent, the type and amount of monomer, the ratio of organic phase to aqueous phase, and the like.

[0068] The glass transition temperature of the crosslinked polymer constituting the HIPE foam is preferably -50°C or higher and 30°C or lower, more preferably -40°C or higher and 20°C or lower, and even more preferably -30°C or higher and 10°C or lower. In this case, it is easy to obtain a HIPE foam having good ductility and good flexibility. The glass transition temperature of the crosslinked polymer can be measured based on JIS K7121:1987. The glass transition temperature is determined as the midpoint glass transition temperature.

[0069] The molecular weight Mc between crosslinking points of the crosslinked polymer is an index of the degree of crosslinking of the crosslinked polymer constituting the HIPE foam. 4 More than 20×10 4 In this case, the mechanical properties such as ductility and recovery of the HIPE foam are further improved. From the viewpoint of stably 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 3.0×10 or more. 4 From the viewpoint of easily improving the restoring property of the HIPE foam, the molecular weight between crosslinking points of the crosslinked polymer is more preferably 15×10 4 More preferably, it is 10×10 4 It is even more preferable that:

[0070] The molecular weight Mc between crosslinking points of the crosslinked polymer constituting the HIPE foam is measured as follows. The HIPE foam is subjected to dynamic viscoelasticity measurement under the conditions of frequency: 1 Hz, load: 10 mN, and deformation mode: compression. During the temperature rise process of the dynamic viscoelasticity measurement, the temperature-storage modulus E' curve (hereinafter referred to as the "T-E' curve") obtained by plotting the temperature on the horizontal axis and the 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 the vicinity of the glass transition temperature Tg, the crosslinked polymer constituting the HIPE foam transitions from a glassy state to a rubbery state. Then, when the crosslinked polymer transitions from the glassy state to a rubbery state, the storage modulus E' in the T-E' curve drops sharply (see FIG. 3). After the temperature of the HIPE foam exceeds the glass transition temperature Tg, the T-E' curve shows a plateau region (rubber-like flat portion). In this plateau region, E' is proportional to the temperature, so the molecular weight between crosslinking points, Mc, can be calculated from the following formula (I). Mc = 2(1 + μ)ρRT / E' (I)

[0071] In formula (I), μ is the 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. From the viewpoint of appropriately calculating the molecular weight Mc between crosslinking points, it is preferable that the temperature T used for calculating the molecular weight Mc between crosslinking points is selected within the range of Tg+50°C to Tg+80°C (where Tg is the glass transition temperature of the crosslinked polymer constituting the HIPE foam).

[0072] From the viewpoint of obtaining a HIPE foam having good toughness and excellent sound absorbing properties, the average cell diameter of the HIPE foam is preferably 65 μm or more and 200 μm or less. From the viewpoint of easily improving sound absorbing properties in a lower frequency range, the average cell diameter of the HIPE foam is preferably 180 μm or less, more preferably 150 μm or less, and even more preferably 120 μm or less.

[0073] The average cell size of the HIPE foam 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 manufacturing process of the HIPE foam. For example, the average cell size can be reduced by reducing the droplet size.

[0074] From the viewpoint of obtaining a HIPE foam having good toughness and excellent sound absorbing properties, the average through-pore diameter of the HIPE foam is more preferably 10 μm or more and 30 μm or less. In addition, from the viewpoint of making it easier to improve the sound absorption properties of the HIPE foam over a wide frequency range, the ratio of the average through hole diameter of the HIPE foam to the average cell diameter of the HIPE foam is preferably 0.10 or more and 0.50 or less, and more preferably 0.20 or more and 0.40 or more.

[0075] The average cell diameter of HIPE foam is the average value of the circle-equivalent diameters of the cells in the HIPE foam. The circle-equivalent diameter of a cell is the diameter of a perfect circle with the same area as the cell in the cross section of the HIPE foam. The average through-hole diameter of HIPE foam is the average value of the circle-equivalent diameters of the through-holes in the HIPE foam. The circle-equivalent diameter of a through-hole is the diameter of a perfect circle with the same area as the through-hole in the cross section of the HIPE foam. The average cell diameter and average through-hole diameter are measured by performing image analysis of the open cell structure of the HIPE foam.

[0076] HIPE foam is particularly suitable as a sound absorbing material. In addition, HIPE foam, which is a sound absorbing material, can also be used for various purposes such as liquid absorbing material, separating material, and shock absorbing material. EXAMPLES

[0077] Examples and comparative examples of HIPE foams are described below. In these examples, the HIPE foams shown in Tables 2 to 7 were produced by the following method. Note that the specific aspects of the HIPE foams according to the present invention are not limited to the aspects of the examples shown below, and the configurations can be appropriately changed without departing from the gist of the present invention.

[0078] [Example 1] First, 60.5 g of butyl acrylate as an acrylic monomer, 4.31 g of divinylbenzene (functional group equivalent: 65 g / eq) as a vinyl compound B, 32.7 g of epoxy prepolymer modified with acrylic at both ends (functional group equivalent: 750 g / eq) as an acrylate compound A, 27.5 g of ethyl acetate as an organic solvent, 8.1 g of polyglycerin condensed ricinoleate as an emulsifier, 0.55 g of dilauroyl peroxide as a polymerization initiator, and 0.55 g of bis(4-t-butylcyclohexyl) peroxydicarbonate were added to a glass container with an internal volume of 3 L and equipped with a stirrer with a torque converter. These were mixed in the glass container to form an organic phase. The epoxy prepolymer modified with acrylic at both ends was "EBECRYL (registered trademark) 3708" manufactured by Daicel-Allnex Corporation, and is an epoxy diacrylate having a bisphenol A structure.

[0079] Stirring power density: 0.03kW / m 3 While stirring the organic phase at 1000 W, 2063 g of deionized water was added at a rate of about 450 g / min (addition rate of about 450 wt% / min for 100 wt% organic phase), and stirring was continued for 10 minutes after the addition of deionized water was completed to prepare a water-in-oil type (i.e., W / O type) high internal phase emulsion. Note that 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 mixing device, and the volume of the contents (unit: m 3 ) to find the answer.

[0080] Next, an aspirator was connected to the glass container to reduce the pressure inside the container and remove the microbubbles contained in the emulsion. 10 minutes after the start of the reduction in pressure, the stirring was stopped and the pressure inside the container was returned to atmospheric pressure.

[0081] The contents of the glass container were filled into a container with a length of about 250 mm, a width of about 180 mm, and a depth of about 90 mm, and polymerized in a hot water bath at 70° C. for about 10 hours to obtain a water-containing HIPE foam. The HIPE foam was removed from the hot water bath and cooled to room temperature.

[0082] After cooling, the HIPE foam was taken out of the container, washed with water, dehydrated, and dried in an oven at 85°C until it reached a constant weight. In this way, a rectangular HIPE foam made of a crosslinked polymer was obtained. The density (actual apparent density) of the HIPE foam was 49 kg / m 3 It was.

[0083] The composition of the crosslinked polymer is shown in Table 2. The content of each component (monomer and crosslinking agent) in the crosslinked polymer can be calculated from the amount of each component and the total amount of the vinyl monomer component and the crosslinking agent component added at the time of charging. The amount of organic solvent and deionized water added in the table is the amount added when the organic phase (excluding the polymerization initiator) is 100 parts by mass. In the table, the compound names are abbreviated as follows: The solubility of organic solvents in water at a temperature of 20° C. is shown as the value given on the pages (pages 112, 168, 243, 244, 246, 280, and 285) corresponding to each compound in Techniques of Chemistry Vol. II, Organic Solvents (3rd Ed.). St: styrene BA: Butyl acrylate 2-EHA: 2-ethylhexyl acrylate DVB: Divinylbenzene PEGDA: Polyethylene glycol diacrylate (NK Ester A-400, manufactured by Shin-Nakamura Chemical Co., Ltd.) EpDA: epoxy diacrylate (specifically, a bisphenol structure-containing epoxy prepolymer modified with acrylic at both ends, "EBECRYL (registered trademark) 3708" manufactured by Daicel-Allnex Corporation) PGPR: Polyglycerol condensed ricinoleate (CRS-75, manufactured by Sakamoto Pharmaceutical Co., Ltd.) LPO: Dilauryl peroxide (Perloyl L, manufactured by NOF Corporation) LTCP: Bis(4-t-butylcyclohexyl) peroxydicarbonate (Peroyl TCP manufactured by NOF Corporation) EtAc: ethyl acetate Xy: Xylene BuAc: butyl acetate MEK: Methyl ethyl ketone CHO: Cyclohexanone ACE: Acetone HeOH: 1-Hexanol

[0084] [Examples 2 to 11, Comparative Examples 1 to 9] The feed composition was changed as shown in Tables 3 and 6. In Examples 5, 7, and 8, the stirring power density in the emulsification process was changed to 0.20 kW / m 3 A HIPE foam was produced in the same manner as in Example 1, except for the above change.

[0085] [evaluation] The following measurements and evaluations were carried out for Examples 1 to 11 and Comparative Examples 1 to 9. The results are shown in Tables 4, 5, and 7. In Comparative Examples 3 and 4, the emulsion became unstable during emulsification, and a stable emulsion could not be formed, so that a HIPE foam could not be obtained by polymerization. In Comparative Example 6, the aqueous phase and the organic phase could not be emulsified, and it was difficult to form an emulsion, so that a HIPE foam could not be obtained by polymerization. Therefore, evaluation of the HIPE foam was omitted in these Comparative Examples.

[0086] (viscosity of organic phase, viscosity of high internal phase emulsion) An organic phase corresponding to each Example and Comparative Example was prepared so as to have the same composition as the organic phase in each Example and Comparative Example. 14 mL of the prepared organic phase was added to a 16 ml container, and the container was placed in a B-type viscometer (B-type rotational viscometer: LVDV-II+Pro, manufactured by Eiko Seiki Co., Ltd.) equipped with a UL low viscosity adapter. Spindle No. 00 was used as the spindle, and the organic phase was stirred at a temperature of 23°C and a stirring speed of 10 rpm. After confirming that the torque range of the B-type viscometer was in the range of 10 to 100%, the viscosity of the organic phase was measured. The results are shown in Table 2. In addition, high internal phase emulsions corresponding to Example 1 and Comparative Example 1 were prepared using the same feed composition and emulsification conditions as those of the high internal phase emulsions (HIPEs) in Example 1 and Comparative Example 1. The following measurements were performed on the prepared high internal phase emulsions, and the shear rate was 50 s ―1 The viscosity of the high internal phase emulsions was measured at 23°C. First, a rotational rheometer ("Discovery HR-2" manufactured by TA Instruments) was prepared as a measuring device. As a measuring geometry, a coaxial double cylinder geometry ("HA Aluminum Recessed End Rotor" and "Stainless Steel Standard Concentric Cylinder Cup with Cap" manufactured by TA Instruments) equipped with a Peltier coaxial cylinder temperature system ("DHR Smart Swap Concentric Cylinder Peltier Jacket" manufactured by TA Instruments) was used. The temperature of the measurement device geometry was set to 23°C, and 9 mL of high internal phase emulsion was placed in the geometry as a sample. After that, it was waited for 60 seconds until the temperature of the sample reached 20°C. After the temperature of the sample was stabilized at 20°C, the shear rate was reduced to 0.1 s ―1 From 100s over 180 seconds ―1 The viscosity of the sample was measured while increasing the shear rate to 10. The data acquisition interval was set so that 50 or more data points were acquired during an increase in shear rate of one order of magnitude. The data thus obtained was input into an analysis software ("TRIOS" manufactured by TA Instruments) and a straight line analysis was performed to determine a linear regression equation. Then, the linear regression equation was used to determine the linear regression equation. ―1 The viscosity of the sample at this point was taken as the viscosity of the high internal phase emulsion. As a result, the viscosity of the high internal phase emulsion of Example 1 was 1210 mPa·s, and the viscosity of the high internal phase emulsion of Comparative Example 1 was 1726 mPa·s.

[0087] (density ρ) Three rectangular parallelepiped test pieces, each having a thickness of 25 mm, width of 50 mm, and length of 50 mm, were cut out from the HIPE foam, 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 pieces was calculated by dividing the weight of the test pieces by the volume calculated based on the outer dimensions. The arithmetic average value of the densities of the three test pieces was then calculated as the density ρ (specifically, the actual apparent density) ρ (unit: kg / m) of the HIPE foam. 3 ). The target density was taken as 100%, and the actual apparent density was divided by the target density and expressed as a percentage, and the density change rate (%) relative to the target density was calculated by subtracting the target density (100%) from this value. The target density is the density of the HIPE foam estimated from the composition charged during polymerization, such as the blending ratio of the organic phase and the aqueous phase in the high internal phase emulsion, and the types and amounts of monomers and crosslinking agents in the organic phase. The density change rate is a positive value, and the larger the value, the greater the shrinkage of the HIPE foam.

[0088] (glass transition temperature Tg) Based on JIS K7121:1987, Tg was calculated by differential scanning calorimetry (i.e., DSC) analysis. As a measuring device, DSC250 manufactured by TA Instruments Japan Co., Ltd. was used. Specifically, first, a test piece of about 2 mg was taken from near the center of the HIPE foam. As a condition adjustment of the test piece, "(3) A case where the glass transition temperature is measured after a certain heat treatment" was adopted. Specifically, the taken test piece was left to stand for 24 hours or more in a constant temperature and humidity room at a temperature of 23°C and a humidity of 50%. Next, the test piece was heated at a heating rate of 10°C / min to a temperature about 30°C higher than the temperature at the end of the glass transition, and was kept at this temperature for 10 minutes, and then cooled at a cooling rate of 10°C / min to a temperature about 50°C lower than the glass transition temperature. For example, in the measurement of Tg of the HIPE foam of Example 1, it was heated to 20°C and then cooled to -65°C. After cooling, the temperature was kept for 10 minutes to stabilize the apparatus, and DSC measurement was performed at a heating rate of 10°C / min up to a temperature about 30°C higher than the temperature at the end of the glass transition, to obtain a DSC curve. The flow rate of nitrogen gas in the measurement environment was 30 mL per minute. The midpoint glass transition temperature was determined from this DSC curve, and this value was taken as the glass transition temperature Tg. The measurement temperature range in the DSC measurement was -90°C to 70°C.

[0089] (Molecular weight between crosslinking points Mc) Three cubic test pieces with no skin surface, each measuring 10 mm x 10 mm x 10 mm, were cut out from near the center of the HIPE foam. Dynamic mechanical analysis (DMA) was performed on these three test pieces to obtain T-E' curves in the temperature range of -100 to 120°C. Figure 3 shows an example of a T-E' curve for a 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

[0090] Three temperatures T were randomly selected from the rubber-like flat portion (specifically, the temperature range of Tg+50°C to Tg+80°C) in each of the T-E' curves of the three test pieces, and the storage modulus E' at the temperature T was determined. Then, using these storage modulus E' and temperature T, the molecular weight Mc between crosslinking points at each temperature was calculated from the following formula (I). The arithmetic average value of the nine molecular weights between crosslinking points calculated from the T-E' curves of the three test pieces was adopted as the molecular weight Mc between crosslinking points. Note that Tg is the glass transition temperature of the crosslinked polymer constituting the HIPE foam. Mc = 2(1 + μ)ρRT / E' (I)

[0091] In addition, under the measurement conditions for the dynamic viscoelasticity measurement described above, the distortion 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 were calculated under a constant volume condition, i.e., a Poisson's ratio of 0.5.

[0092] (Storage modulus E' at 23°C) The storage modulus at 23° C. was calculated from the storage modulus E' in the temperature range of -100 to 120° C. measured by the dynamic mechanical analysis (DMA). As a representative example, an example of the T-E' curve of the HIPE foam according to the example is shown in FIG.

[0093] (average bubble diameter) The method for measuring the average cell diameter is as follows. Using a feather blade, samples for observation were cut out from the center of the lateral direction and thickness direction of the rectangular parallelepiped HIPE foam, and from the center of the thickness direction at both ends of the lateral direction. Next, the samples were 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 (magnification: 500 times) of the HIPE foam according to the embodiment is shown in FIG. 1. Also, an example of a cross-sectional photograph (magnification: 500 times) of the HIPE foam according to the comparative example produced without using an organic solvent is shown in FIG. 3. The detailed observation conditions were as follows.

[0094] - Sample pretreatment: The sample was treated for electrical conductivity 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)

[0095] 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 photographs of each sample. 2 The measurement area was set so that the above was the case. Next, the bubble diameters of the bubbles present in the measurement area were calculated, and the arithmetic average of these was taken as the bubble diameter of each sample. The average bubble diameter of the HIPE foam was calculated by arithmetic averaging the bubble diameters of the three samples obtained. The detailed analysis procedure and conditions were as follows.

[0096] (1) Monochrome conversion (2) Smoothing filter (3x3, 8 neighborhoods, number of processes = 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 based on feature (area) (50~∞μm 2 (Only select 8 neighbors) (7) Dilation without connections to neighbors (8 neighbors, number of processes = 3) (8) Measurement of circle equivalent diameter (calculated from area, 8 neighbors)

[0097] (Average through hole diameter) Cross-sectional photographs of the HIPE foam were taken in the same manner as the method for calculating the average bubble diameter, except that the observation magnification was changed to 500 times and the observation mode was changed to the backscattered electron method (standard). Next, the cross-sectional photographs were analyzed using image processing software (WinROOF2013, manufactured by Mitani Shoji Co., Ltd.), and a number of areas with a total area of ​​1 mm were plotted on the cross-sectional photographs 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 in the measurement area were calculated, and the arithmetic average of these was taken as the through-hole diameter of each sample. The average through-hole diameter of the HIPE foam was obtained by arithmetic averaging the through-hole diameters of the three samples obtained. The detailed analysis procedure and conditions were as follows.

[0098] (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, times = 3) (5) Measurement from shape characteristics (measurement items = circle equivalent diameter, number)

[0099] (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 based on JIS A 1405-2. Specifically, a disk-shaped test piece with a thickness of 20 mm and a diameter of 40 mm was cut out from near the center of the HIPE foam so as not to include 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.

[0100] FFT analysis conditions Sampling frequency: 32,000Hz FFT points: 8192 points Output signal: Random signal (both during measurement and calibration) Window function: Hanning (for both measurement and calibration) Overlap: 75% (both during measurement and calibration) -Average number of times measured: 400 Average number of calibrations: 800

[0101] 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 Length of the air gap behind: 0mm ·Temperature: 23℃

[0102] As a result, the normal incidence sound absorption coefficient of the HIPE foam was measured at frequencies of 125Hz, 500Hz, 600Hz, 700Hz, 800Hz, 900Hz, 1000Hz, 1500Hz, 2000Hz, 2500Hz, 3000Hz, 3500Hz, 4000Hz, 4500Hz and 5000Hz. The normal incidence sound absorption coefficient at 1000Hz, 2000Hz and 3000Hz is shown in the table.

[0103] The sum of the normal incidence sound absorption coefficients at each frequency measured by the above method is shown in the table as the sum of the sound absorption coefficients from 125 to 5000 Hz. 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 in the table as low frequency sound absorption (total of 500 to 1000 Hz), and the sum of the normal incidence sound absorption coefficients at 1500 to 5000 Hz is shown in the table as high frequency sound absorption (total of 1500 to 5000 Hz).

[0104] (Elongation at break) A plate of 10 mm thickness was cut out from the center of the HIPE foam. Five No. 1-shaped test pieces were prepared from the plate using a No. 1-shaped dumbbell punching die specified in JIS K 6400-5:2012. Tensile tests were performed on these test pieces under the following conditions based on JIS K 6400-5:2012 using an autograph AGS-10kNX made by Shimadzu Corporation. The gauge length at break was calculated from the obtained load-displacement curve, and the ratio (unit: %) of the difference between the gauge length at break and the gauge length before break was calculated to the gauge length before break, which was taken as the elongation at break for each test piece. The median value of the five measurement results was taken as the elongation at break. ·Room temperature: 23℃ ·Humidity: 50% Pulling speed: 500mm / min

[0105] (Breaking energy per unit weight) The energy in the region from 0% strain to the strain at break in the load-displacement curve measured by the tensile test was calculated. The breaking energy per unit weight of the HIPE foam was calculated using the value automatically calculated by the autograph AGS-10kNX. The median value of the five measurement results was then used as the breaking energy per unit weight.

[0106] (Folding test) A sample of 40 mm in thickness, 150 mm in length, and 150 mm in width was cut from near the center of the HIPE foam. The sample was folded so that it overlapped in the thickness direction and the vertical length was halved, and the presence or absence of breakage was visually observed. When no breakage was observed, it was evaluated as "Good", and when breakage was observed, it was evaluated as "Poor".

[0107] [Table 2]

[0108] [Table 3]

[0109] [Table 4]

[0110] [Table 5]

[0111] [Table 6]

[0112] [Table 7]

[0113] As shown in Tables 2 to 7, the HIPE foams of the examples use a crosslinked polymer in which a polymer of an acrylic monomer is crosslinked as a base resin, and the density, elongation, breaking energy per unit weight, and sound absorption coefficient are within the specific ranges. Therefore, these HIPE foams have excellent toughness and high sound absorption in a wide frequency range. The HIPE foams are produced by polymerizing an acrylic monomer in a water-in-oil high internal phase emulsion in which an aqueous phase is contained in an organic phase. The HIPE foams of the examples are produced by adjusting the amount of the acrylate compound and the organic solvent added to the specified ratio, in which the organic phase contains an acrylic monomer, the specified acrylate compound, and the specified organic solvent.

[0114] On the other hand, in Comparative Example 1, the HIPE foam was produced without using any organic solvent during production. Therefore, the HIPE foam of Comparative Example 1 had inferior high frequency sound absorption properties compared to the Examples. In Comparative Example 2, an excess of organic solvent was added during production to produce the HIPE foam. Therefore, the HIPE foam of Comparative Example 2 had poorer high-frequency sound absorption properties than the Examples. In addition, volume shrinkage occurred in Comparative Example 2, and the density was higher than the target density. Thus, it was difficult to adjust the density of the HIPE foam.

[0115] In Comparative Example 3, an organic solvent having a hydroxyl group was used during emulsification, and in Comparative Example 4, an organic solvent having excessive solubility in water was used during emulsification. Therefore, in Comparative Examples 3 and 4, the emulsion was not stabilized during emulsification, and a water-in-oil type high internal phase emulsion could not be formed. As a result, a HIPE foam could not be obtained.

[0116] In Comparative Example 5, a HIPE foam having a density as high as that of Example 11 was produced without using an organic solvent. Therefore, the HIPE foam of Comparative Example 5 had inferior high frequency sound absorption properties compared to the examples. In Comparative Example 6, the amount of acrylate compound A added was increased to the same level as in Example 4, but no organic solvent was used. Therefore, in Comparative Example 6, the emulsion was not stabilized during emulsification, and a water-in-oil type high internal phase emulsion could not be formed. As a result, a HIPE foam could not be obtained.

[0117] In Comparative Example 7, a HIPE foam was produced without using an organic solvent, using an acrylic monomer and a styrene monomer as monomers as in Example 9. In Comparative Example 8, a HIPE foam with a high density similar to that of Example 11 was produced without using an organic solvent, using an acrylic monomer and a styrene monomer as monomers as in Example 11. Therefore, the HIPE foams of Comparative Examples 7 and 8 had inferior high-frequency sound absorption properties compared to the examples.

[0118] In Comparative Example 9, a HIPE foam was produced without using an organic solvent, but using an acrylate compound having a functional group equivalent of less than 300 g / eq instead of the acrylate compound A. Therefore, the HIPE foam of Comparative Example 9 did not pass the folding test and had lower toughness than the examples.

[0119] The above describes specific embodiments of the HIPE foam of the present invention based on the examples, but the specific embodiments of the HIPE foam of the present invention are not limited to the embodiments shown in the examples, and the configuration can be changed as appropriate within the scope that does not depart from the spirit of the present invention. [Explanation of symbols]

[0120] 1 HIPE Form 11 Bubble Wall 12 Bubbles 13 Through hole

Claims

1. A method for producing a HIPE foam having an acrylic crosslinked polymer as a base resin, comprising forming a water-in-oil type high internal phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and an acrylate compound as a crosslinking agent, and polymerizing the acrylic monomer in the emulsion, comprising the steps of: The functional group equivalent of the acrylate compound is 300 g / eq or more, The amount of the acrylate compound added relative to 100 parts by mass of the acrylic monomer is 10 parts by mass or more and 180 parts by mass or less, the organic phase further contains an organic solvent that does not have a hydroxyl group and has a solubility in water of 300 g / L or less (including 0) at a temperature of 20° C.; A method for producing a HIPE foam, wherein the amount of the organic solvent added is 10 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the total of the acrylic monomer and the acrylate compound.

2. 2. The method for producing a HIPE foam according to claim 1, wherein the viscosity of the organic phase at a temperature of 23° C., as measured by a Brookfield viscometer, is 1 mPa·s or more and 15 mPa·s or less.

3. The method for producing a HIPE foam according to claim 1 or 2, wherein the amount of the organic solvent added is 50 parts by mass or more and 400 parts by mass or less per 100 parts by mass of the acrylate compound.

4. The method for producing a HIPE foam according to claim 1 or 2, wherein the boiling point of the organic solvent is 130°C or lower.

5. The method for producing a HIPE foam according to claim 1 or 2, wherein the organic solvent is at least one selected from the group consisting of carboxylic acid esters, ketones, and aromatic compounds.

6. The method for producing a HIPE foam according to claim 1 or 2, wherein the acrylate compound is an epoxy (meth)acrylate having a bisphenol structure.

7. A HIPE foam having an acrylic crosslinked polymer as a base resin, The HIPE foam has an elongation of 100% or more, and a breaking energy per unit weight of 0.03 J / g or more when broken, as measured by a tensile test based on JIS K6400-5:2012; The average sound absorption coefficient of the HIPE foam at frequencies of 1000 Hz, 2000 Hz and 3000 Hz measured by the normal incidence method of JIS A1405-2:2007 is 0.60 or more; A HIPE foam having a ratio of the sound absorption coefficient of the HIPE foam at a frequency of 2000 Hz to the sound absorption coefficient of the HIPE foam at a frequency of 1000 Hz of 0.80 or more.

8. The density of the HIPE foam is 20 kg / m ３ More than 80kg / m ３ 8. The HIPE foam of claim 7, wherein:

9. 9. The HIPE foam according to claim 7 or 8, wherein the average cell diameter of the HIPE foam is 65 μm or more and 200 μm or less.

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