HIPE foam and cutting materials

Abstract

To provide a HIPE foam having small local fluctuations in physical properties even when formed into a large size and a cutting processing material made of the HIPE foam.SOLUTION: A HIPE foam 1 uses a polymer of styrene monomer and / or acrylic monomer as a base resin, and has a size that allows a cube having a side length of 60 mm to be cut out. The density of the HIPE foam 1 is 35 kg / m3 or more and 350 kg / m 3 or less. In the HIPE foam 1, the density ratio ρmax / ρmin of the density ρmax of the highest density part 111, which has the highest density, to the density ρmin of the lowest density part 112, which has the lowest density, is 1.30 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to HIPE foams and machining materials. [Background technology]

[0002] Conventionally, porous materials called HIPE foams and the like have been known, which have a cellular structure in which a large number of bubbles exist in a polymer of a vinyl monomer, and also have an open-cell structure in which a large number of pores are formed that connect the bubbles (for example, Patent Document 1).

[0003] To produce HIPE foam, a water-in-oil high internal phase emulsion (HIPE) is first formed by incorporating a high proportion of an aqueous phase (water or other aqueous liquid) into an organic phase containing vinyl monomers, crosslinkers, emulsifiers, polymerization initiators, etc. The organic phase is then polymerized in this emulsion to produce HIPE foam. The HIPE foam is a polymer that reflects the dispersion morphology of the organic and aqueous phases and the dispersion shape of the aqueous phase in the high internal phase emulsion during polymerization.

[0004] The HIPE foam thus obtained is processed by slicing or cutting depending on the intended use, and then used for various purposes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 11-507409 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for larger HIPE foams, due to the need to improve the productivity of HIPE foam products and to increase the size of the products. However, conventional HIPE foams have a problem in that the local variations in their physical properties tend to increase as they are made larger.

[0007] The present invention has been made in consideration of the above background, and aims to provide a HIPE foam that has little local variation in physical properties even when enlarged, and a cutting processing material made from this HIPE foam. [Means for solving the problem]

[0008] One aspect of the present invention is a HIPE foam described in the following [1] to [5]. [1] A HIPE foam having a base resin of a polymer of a styrene-based monomer and / or an acrylic-based monomer, and having a size that allows cutting out a cube with a side length of 60 mm, The density of the HIPE foam is 35 kg / m 3 More than 350kg / m 3 is as follows: The density ρ of the minimum density portion, which is the portion with the lowest density in the HIPE foam min The density of the maximum density part, ρ, max density ratio ρ max / ρ min is 1.30 or less, HIPE form.

[0009] [2] The HIPE foam according to [1], wherein the HIPE foam has a columnar shape and a vertical length of 70 mm or more. [3] The HIPE foam according to [1] or [2], wherein the average cell diameter of the HIPE foam is 10 μm or more and 150 μm or less.

[0010] [4] The number of holes with a circular equivalent diameter of 3 mm or more in the cross section of the HIPE foam is 2 The HIPE form according to any one of [1] to [3], wherein the number of pieces is one or less (including zero pieces) per piece. [5] The number of holes with a circular equivalent diameter of 1 mm or more and less than 3 mm in the cross section of the HIPE foam is 2A HIPE form according to any one of [1] to [4], which has 30 or less pieces (including 0 pieces) per piece.

[0011] Another aspect of the present invention is a cutting material made from the HIPE foam according to any one of [1] to [5]. [Effects of the Invention]

[0012] According to the above-described embodiment, it is possible to provide a HIPE foam having small local variations in physical properties even when enlarged, and a cutting material made of this HIPE foam. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an illustration of a method for determining the maximum and minimum density portions of a HIPE foam. [Figure 2] Figure 2 is a low vacuum scanning electron micrograph of the HIPE foam. DETAILED DESCRIPTION OF THE INVENTION

[0014] (HIPE form) A preferred embodiment of a HIPE foam is described below. The HIPE foam in this specification is a porous polymer also known as a polyHIPE foam, a polyHIPE material, a HIPE-derived foam substance, a high internal phase emulsion porous body, or a high internal phase emulsion foam. HIPE foam can be obtained, for example, by polymerizing monomers in a water-in-oil high internal phase emulsion (i.e., a HIPE) in which a high ratio of aqueous phase is encapsulated in an organic phase. Furthermore, HIPE foam has an open-cell structure in which numerous cells exist within the structure and numerous through-holes are formed that connect adjacent cells.

[0015] HIPE foams are porous polymers obtained, for example, by polymerizing (or copolymerizing) vinyl monomers (specifically, acrylic monomers and / or styrene monomers) in a water-in-oil high internal phase emulsion, in which a high proportion of aqueous phase is encapsulated in an organic phase. HIPE foams use, as their base resin, a polymer containing components derived from acrylic monomers and / or styrene monomers, obtained, for example, by polymerizing acrylic monomers and / or styrene monomers in a water-in-oil high internal phase emulsion. Specifically, HIPE foams contain components derived from acrylic monomers and / or styrene monomers in the polymer backbone of the polymer. HIPE foams may also be produced by polymerizing acrylic monomers and / or styrene monomers in a high internal phase emulsion in the presence of a crosslinking agent. In this case, the HIPE foam uses, as its base resin, a polymer obtained by crosslinking a polymer of acrylic monomers and / or styrene monomers.

[0016] HIPE foam is a porous cured product obtained by curing a high internal phase emulsion, and its cell walls can be said to be composed of a polymer (e.g., a vinyl 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 aqueous phase in the high internal phase emulsion and the dispersion form of the aqueous phase (i.e., the dispersed phase) during polymerization.

[0017] During the manufacturing process of HIPE foam, the polymer is not easily stretched. Therefore, HIPE foam generally does not easily exhibit 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 expanded beads in a mold.

[0018] [density] The density of the HIPE foam is 35 kg / m 3 More than 350kg / m 3The density ρ of the minimum density portion of the HIPE foam is the lowest density portion. min The density of the maximum density part, ρ, max density ratio ρ max / ρ min The HIPE foam has a density in the above-mentioned specific range and further has a density ρ of the maximum density portion of 1.30 or less. max and the density of the minimum density part ρ min Density ratio ρ max / ρ min By setting the density ratio ρ within the above-mentioned specific range, it is possible to reduce local variations in physical properties even when the size is increased. max / ρ min The lower limit of is 1 by definition.

[0019] The density of HIPE foam is 40 kg / m 3 It is preferable that the saturation is 45 kg / m or more. 3 More preferably, it is 50 kg / m or more. 3 It is more preferable that the above conditions are satisfied. In this case, the strength, recovery, and ductility of the HIPE foam can be more easily improved. In addition, the handleability of the HIPE foam can be further improved.

[0020] The density of HIPE foam is 330 kg / m 3 It is preferable that the saturation is 300 kg / m or less. 3 More preferably, it is 280 kg / m or less. 3 It is more preferable that the HIPE foam has a thickness of 1000 MPa or less. In this case, the lightness and ductility of the HIPE foam can be further improved.

[0021] density ratio ρ max / ρ min From the viewpoint of more easily setting the density within the above-mentioned specific range, the density of the HIPE foam is 40 kg / m 3 More than 330kg / m 3 It is preferable that the saturation is 45 kg / m or less. 3 More than 300kg / m 3More preferably, it is 50 kg / m or less. 3 More than 280kg / m 3 It is even more preferable that:

[0022] Furthermore, the density ratio ρ max / ρ min In a HIPE foam having a density ratio ρ of 1.30 or less, the distribution of bubbles within the HIPE foam is relatively small, and bubbles are present relatively uniformly throughout the HIPE foam. Therefore, the HIPE foam can reduce local variations in physical properties. From the viewpoint of further reducing local variations in physical properties of the HIPE foam, the density ratio ρ max / ρ min is preferably 1.25 or less, and more preferably 1.20 or less.

[0023] The density of the HIPE foam described above is calculated by dividing the mass of the HIPE foam by the volume of the HIPE foam, which can be calculated based on the outer dimensions of the HIPE foam.

[0024] In addition, the density of the maximum density part of the HIPE foam is ρ max and the density of the minimum density part ρ minThe calculation method for is as follows. First, the HIPE foam is cut into five equal parts in each of the vertical, horizontal, and vertical directions to produce 125 rectangular parallelepiped pieces. For example, if the HIPE foam has a relatively simple shape, such as a rectangular parallelepiped or cubic shape, as in the HIPE foam 1 shown in Figure 1, the HIPE foam 1 can be divided into five equal parts in each of the vertical, horizontal, and vertical directions to produce the small pieces 11. On the other hand, although not shown in the figure, if the HIPE foam has a shape that cannot be used to obtain cubic pieces simply by dividing it into equal parts, such as a cylindrical or spherical shape, a rectangular parallelepiped with a side length of 60 mm or more can be cut from the HIPE foam, and then the rectangular parallelepiped can be divided into five equal parts in each of the vertical, horizontal, and vertical directions to produce the small pieces. Note that when dividing the HIPE foam using the above-mentioned method, if the HIPE foam before division has a skin surface, i.e., the surface that was in contact with the container during polymerization, the layer including the skin surface is removed before dividing the HIPE foam. Furthermore, when cutting out a rectangular parallelepiped with a side length of 60 mm or more from the HIPE foam before division, the largest possible rectangular parallelepiped is cut out from the HIPE foam before dividing the HIPE foam.

[0025] The density of each of the small pieces 11 thus obtained is calculated by dividing the mass of the small piece 11 by the volume of the small piece 11. The small piece 11 having the highest density is then designated as the maximum density portion 111 of the HIPE foam, and the density of the small piece is designated as the density ρ of the maximum density portion of the HIPE foam. max The small piece 11 having the lowest density is defined as the minimum density portion 112 of the HIPE foam, and the density of the small piece is defined as the density ρ of the minimum density portion of the HIPE foam. min The maximum density portion 111 is usually one of the small pieces 11 located at the top in the height direction (i.e., the up-down direction) during manufacturing. The minimum density portion 112 is usually one of the small pieces 11 located at the bottom in the height direction during manufacturing.

[0026] The density ratio ρ per unit length in the vertical direction of the HIPE foam max / ρ minThe value of (unit: 1 / m) is preferably 8.0 or less, more preferably 7.5 or less, and even more preferably 7.0 or less. In this case, the HIPE foam can be more easily enlarged while suppressing an increase in the local variation in physical properties of the HIPE foam. Note that the density ratio ρ per unit length in the vertical direction of the HIPE foam max / ρ min The lower limit of (unit: 1 / m) may be 2 or 3, for example.

[0027] From the same viewpoint, the density of the maximum density part per unit length in the vertical direction of the HIPE foam, ρ max and the density of the minimum density part ρ min The density difference ρ max -ρ min Value (unit: kg / m 3 ) / m) is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less, even more preferably 120 or less, and particularly preferably 100 or less. The density ρ of the maximum density part per unit length in the vertical direction of the HIPE foam is max and the density of the minimum density part ρ min The density difference ρ max -ρ min Value (unit: kg / m 3 The lower limit of ) / m) may be, for example, 5 or 10.

[0028] The method for specifying the vertical direction of the HIPE foam is as follows. First, the density ρ of the maximum density part is determined. max and the density of the minimum density part ρ minSmall rectangular pieces are prepared in the same manner as in the measurement method of 1. From these small pieces, small pieces exposed on the six faces of the HIPE foam or a cube cut from the HIPE foam are taken, one piece per face, and the density of each small piece is calculated. Then, the difference in density between each small piece and a small piece taken from the back of the face from which the small piece was taken is calculated. The direction of the faces with the largest calculated density difference is defined as the vertical direction. Note that the vertical direction of the HIPE foam identified in this way usually corresponds to the vertical direction during the manufacture of the HIPE foam. The vertical direction of the HIPE foam is also sometimes referred to as the height direction.

[0029] The density of the HIPE foam is adjusted to the above range by adjusting the ratio of the total amount of vinyl monomer, crosslinking agent, emulsifier, and polymerization initiator to the amount of aqueous phase (specifically, aqueous liquid) in the HIPE foam manufacturing method described below.

[0030] [HIPE foam shape] The HIPE foam may have any shape as long as it is large enough to cut out a cube with a side length of 60 mm. For example, the HIPE foam may have a columnar shape such as a rectangular prism or a pentagonal prism, or a cylindrical shape. From the viewpoint of increasing the degree of freedom in molding the HIPE foam into a desired shape, the shape of the HIPE foam is preferably columnar, and more preferably square prism. Note that square prisms include rectangular parallelepipeds. The HIPE foam is preferably large enough to cut out a cube with a side length of 90 mm, and more preferably large enough to cut out a cube with a side length of 100 mm.

[0031] In the production process of the HIPE foam, for example, the high internal phase emulsion is filled into a polymerization vessel, and the vessel is heated to polymerize the organic phase in the high internal phase emulsion. Polymerization of the organic phase typically proceeds in the high internal phase emulsion while the vessel is left stationary. When a large HIPE foam is produced using a deep vessel, the time required for the polymerization reaction to proceed sufficiently tends to be longer, and the aqueous phase in the high internal phase emulsion tends to gradually settle during polymerization. Therefore, when producing a large HIPE foam, the distribution of the aqueous phase (water droplets) tends to differ between the high internal phase emulsion at the top and the high internal phase emulsion at the bottom of the vessel, resulting in a tendency for the density distribution of the resulting HIPE foam to be uneven. In contrast, by employing the production method described below, the density ratio of the HIPE foam can be easily controlled within the specified range, thereby easily suppressing unevenness in the density distribution of the HIPE foam. Furthermore, the HIPE foam can reduce local variations in physical properties even when it is enlarged.

[0032] To make these effects more beneficial, it is preferable that the HIPE foam has a columnar shape and that the vertical length of the HIPE foam (i.e., the height of the HIPE foam) is 70 mm or more, more preferably 90 mm or more, even more preferably 100 mm or more, and particularly preferably 120 mm or more.On the other hand, the vertical length of the HIPE foam may be, for example, 500 mm or less, or 400 mm or less.Furthermore, it is more preferable that the vertical direction (height direction) of the HIPE foam coincides with the column axis direction of the columnar HIPE foam.

[0033] From the same viewpoint, when the volume of the HIPE foam is 1×10 6 mm 3 It is preferable that the value is 3×10 or more. 6 mm 3 More preferably, it is 5×10 or more. 6 mm 3On the other hand, the volume of the HIPE foam is, for example, 50×10 6 mm 3 It may be 40 x 10 or less. 6 mm 3 It may be the following:

[0034] [Bubble structure] As described above, HIPE foam is a porous polymer having an open-cell structure. As illustrated in FIG. 2, HIPE foam 1 has cell walls 12 made of a polymer. The HIPE foam 1 has a cell structure in which numerous cells 13 are uniformly distributed, and also has an open-cell structure in which numerous through-holes 14 penetrate the cell walls 12 and connect adjacent cells. In FIG. 2, the cells 13 are the portions surrounded by the cell walls 12. The through-holes 14 penetrate the cell walls 12 and connect adjacent cells 13. Specifically, the through-holes 14 are formed in the cell walls 12 and connect adjacent cells 13 across the cell walls 12. The through-holes 14 can also be referred to as through-holes or connecting holes.

[0035] The average cell diameter of the HIPE foam is preferably 10 μm or more and 150 μm or less. By setting the average cell diameter of the HIPE foam within the above specific range, the distribution of the cells within the HIPE foam can be made more uniform. As a result, the variation in the physical properties of the HIPE foam can be further reduced.

[0036] The aforementioned average cell diameter is the average value of the circle-equivalent diameter of the cells. The circle-equivalent diameter of the cells is the diameter of a perfect circle having the same area as the area of ​​the cells in the cross section of the HIPE foam. The method for measuring the average cell diameter will be described later, but it can be measured, for example, by image analysis of the open-cell structure of the HIPE foam.

[0037] The average cell size can be controlled by adjusting the droplet size of the aqueous phase (i.e., dispersed phase) of the high internal phase emulsion in the HIPE foam manufacturing method described below. For example, by reducing the droplet size, the cell size can be made smaller.

[0038] As the size of the HIPE foam increases, defects such as holes are more likely to form in the HIPE foam. The presence of such defects tends to impair the homogeneity of the HIPE foam. Therefore, from the viewpoint of further improving the homogeneity of the HIPE foam, the number of holes with a circle equivalent diameter of 3 mm or more in the cross section of the HIPE foam is set to 1 / m2. 2 It is preferable that there is one or less (including zero) per unit.

[0039] In addition, the number of holes with a circle equivalent diameter of 1 mm or more and less than 3 mm in the cross section of the HIPE foam is 2 It is preferable that the number of holes having a circle equivalent diameter of 1 mm or more and less than 3 mm per 1 m of cross-sectional area is 30 or less (including 0). In this case, the homogeneity of the HIPE foam can be further improved. In addition, by improving the appearance of the cut surface when the HIPE foam is cut, the quality of the HIPE foam can be further improved. From the same viewpoint, the number of holes having a circle equivalent diameter of 1 mm or more and less than 3 mm per 1 m of cross-sectional area is preferably 30 or less. 2 It is more preferable that there are 20 or less particles (including 0 particles) per square meter. 2 It is more preferable that there are 10 or less particles (including 0 particles) per square meter. 2 It is even more preferable that there are 5 or less (including 0) per unit area.

[0040] The method for measuring the number of holes is as follows. First, the density ρ of the maximum density part is calculated. max and the density of the minimum density part ρ min Using the same method as in the calculation of (1), 125 small pieces are prepared from the HIPE foam. At least 20 observation targets are randomly selected from these small pieces, and the circle-equivalent diameter of the pores present on the surface of the observation target is calculated. The number of pores with a circle-equivalent diameter of 3 mm or more and the number of pores with a circle-equivalent diameter of 1 mm or more but less than 3 mm present on the surface of the observation target are then calculated based on the cross-sectional area of ​​1 m. 2 By converting this into the number of hits, the number of holes mentioned above can be calculated.

[0041] [Components] The base resin of a HIPE foam is a polymer of a styrene-based monomer and / or an acrylic monomer. That is, the base resin of a HIPE foam is a polymer of a monofunctional vinyl-based monomer and contains a component derived from the monofunctional vinyl-based monomer. In this specification, the vinyl-based monomer is a styrene-based monomer, an acrylic monomer, or the like. As the vinyl-based monomer, a styrene-based monomer and / or an acrylic monomer can be used. More specifically, the base resin of a HIPE foam may be a polymer consisting solely of a component derived from a styrene-based monomer, or a polymer consisting solely of a component derived from an acrylic monomer. Furthermore, the base resin of a HIPE foam may be a copolymer having a component derived from a styrene-based monomer and a component derived from an acrylic monomer, or a copolymer having at least one component derived from a styrene-based monomer and a component derived from an acrylic monomer, and another component.

[0042] Examples of the styrene-based monomer include styrene compounds such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene, pt-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, and sodium styrenesulfonate. Examples of acrylic monomers include acrylic esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, and adamantyl acrylate; and methacrylic esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, benzyl methacrylate, isobornyl methacrylate, dicyclopentanyl methacrylate, and adamantyl methacrylate. Other examples of acrylic monomers include acrylamide, methacrylamide, and acrylonitrile.

[0043] When the vinyl monomer contains a styrene monomer, the content of the styrene monomer in the vinyl monomer is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. In this case, a HIPE foam that is relatively hard and has excellent mechanical properties can be more easily obtained. When the vinyl monomer contains a styrene monomer and an acrylic monomer, the mass ratio of the styrene monomer to the acrylic monomer is preferably 40:60 to 90:10, more preferably 50:50 to 80:20, and this can reduce production costs and make it easier to adjust the physical properties to the desired level. Note that (meth)acrylic acid refers to acrylic acid and / or methacrylic acid.

[0044] The polymer constituting the HIPE foam may contain a component derived from a crosslinking agent in addition to the component derived from the vinyl monomer described above. The crosslinking agent component is a structural unit derived from the crosslinking agent in the polymer. The crosslinking agent is a compound that crosslinks (bonds) between the polymer chains constituting the polymer, forming a crosslinked structure within the polymer.

[0045] As the crosslinking agent, for example, a vinyl-based compound having at least two functional groups selected from vinyl groups and isopropenyl groups in the molecule is used. When a polymer contains a predetermined amount of a crosslinking agent component, the rigidity and toughness of the polymer can be increased. The vinyl-based compound also includes compounds containing a vinyl group and / or an isopropenyl group in the functional group structure, such as an acryloyl group or a methacryloyl group. From the viewpoint of stable polymerization of the crosslinking agent, the number of functional groups in the vinyl-based compound is preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. Furthermore, from the viewpoint of more easily increasing the toughness of the polymer, the crosslinking agent preferably has functional groups at at least both ends of the molecule, and more preferably has functional groups only at both ends of the molecule.

[0046] The polymer may contain one type of crosslinker component, for example, prepared using one type of crosslinker. However, it is preferable to use a polymer containing both a hard crosslinker component derived from a hard crosslinker with a relatively short molecular chain and a soft crosslinker component derived from a soft crosslinker with a relatively long molecular chain, since this increases the polymer's rigidity and toughness. In this case, excessive embrittlement of the HIPE foam can be suppressed. The hard crosslinker can also be referred to as the first crosslinker, and the soft crosslinker can also be referred to as the second crosslinker.

[0047] Examples of vinyl compounds used as hard crosslinking agents include divinylbenzene, triallyl isocyanurate, and esters of polyhydric alcohols and (meth)acrylic acid. Examples of esters of polyhydric alcohols and (meth)acrylic acid include vinyl compounds such as butanediol (meth)acrylates such as butanediol diacrylate; trimethylolpropane (meth)acrylates such as trimethylolpropane triacrylate; hexanediol (meth)acrylates such as hexanediol diacrylate; and pentaerythritol (meth)acrylates such as pentaerythritol tetraacrylate. However, the number of functional groups in the hard crosslinking agent is two or more. The functional groups are preferably vinyl groups and / or isopropenyl groups. These hard crosslinking agents may be used alone, or two or more types may be used in combination. In other words, the hard crosslinking agent component contained in the HIPE foam may be one type or two or more types. From the viewpoint of making it easier to adjust the rigidity of the HIPE foam, it is preferable to use a hard crosslinking agent whose main component is divinylbenzene and / or butanediol diacrylate, and it is more preferable to use a hard crosslinking agent whose main component is divinylbenzene. Note that the main component of the hard crosslinking agent means a component whose proportion in the hard crosslinking agent is 50% by mass or more. Furthermore, the proportion of the vinyl compound that is the main component in the hard crosslinking agent is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0048] Examples of vinyl compounds used as soft crosslinking agents include esters of polyhydric alcohols and (meth)acrylic acid, esters of polyether glycols and (meth)acrylic acid, esters of urethane oligomers and (meth)acrylic acid, esters of epoxy oligomers and (meth)acrylic acid, and (meth)acrylic-modified silicones. More specifically, examples of the vinyl compounds include nonanediol (meth)acrylates such as nonanediol diacrylate; decanediol (meth)acrylates such as decanediol diacrylate; polyethylene glycol (meth)acrylates such as polyethylene glycol diacrylate; polypropylene (meth)acrylates such as polypropylene glycol diacrylate; polytetramethylene glycol (meth)acrylates such as polytetramethylene glycol diacrylate; polyglycerin (meth)acrylates such as polyglycerin diacrylate; urethane (meth)acrylates such as urethane diacrylate; epoxy (meth)acrylates such as epoxy diacrylate; polyester (meth)acrylates such as polyester diacrylate; (meth)acrylic-modified silicones such as silicones modified with both ends (meth)acrylic; caprolactone-modified isocyanurates such as caprolactone-modified tris isocyanurates; ethoxylated bisphenol A (meth)acrylates such as ethoxylated bisphenol A dimethacrylate, etc. However, the number of functional groups in the soft crosslinking agent is two or more. The functional group is preferably a vinyl group and / or an isopropenyl group. These soft crosslinking agents may be used alone, or two or more types of soft crosslinking agents may be used in combination. That is, the soft crosslinking agent component contained in the HIPE foam may be one type or two or more types. Among these, from the viewpoint of easily increasing the toughness of the HIPE foam, it is preferable to use at least one compound selected from the group consisting of polyethylene glycol (meth)acrylate, urethane (meth)acrylate, epoxy (meth)acrylate, and (meth)acrylic-modified silicone as the soft crosslinking agent.

[0049] Furthermore, from the viewpoint of making it easier to adjust the toughness of the HIPE foam, it is preferable to use a soft crosslinking agent whose main component is polyethylene glycol di(meth)acrylate. The number of repeating structural units derived from ethylene glycol in the polyethylene glycol di(meth)acrylate is preferably 3 to 23. The main component of the soft crosslinking agent means a component that accounts for 50% by mass or more of the soft crosslinking agent. Furthermore, the proportion of the vinyl compound that is the main component of the soft crosslinking agent is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0050] Table 1 shows the molecular weights of representative crosslinking agents and the molecular weight per functional group (i.e., functional group equivalent weight).

[0051] [Table 1]

[0052] When the polymer constituting the HIPE foam is a copolymer of at least a styrene-based monomer, an acrylic-based monomer, and a crosslinker, the content of the styrene-based monomer component in the polymer is preferably 30 to 85 parts by mass, more preferably 40 to 75 parts by mass, and even more preferably 45 to 65 parts by mass, per 100 parts by mass of the vinyl-based monomer component and the crosslinker component constituting the polymer, from the viewpoint of achieving a better balance between toughness and rigidity of the HIPE foam. From the same viewpoint, the content of the acrylic-based monomer component in the polymer constituting the HIPE foam is preferably 10 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 20 to 40 parts by mass, per 100 parts by mass of the vinyl-based monomer component and the crosslinker component constituting the polymer.

[0053] Furthermore, it is preferable to use styrene as the styrene-based monomer. When styrene is used as the styrene-based monomer, the content of styrene in the styrene-based monomer is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Furthermore, it is preferable to use a (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group as the acrylic monomer. When a (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group is used as the acrylic monomer, the content of the (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group in the acrylic monomer is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0054] Moreover, the (meth)acrylic acid ester having a hydrocarbon group with 3 to 10 carbon atoms is preferably 2-ethylhexyl acrylate and / or butyl acrylate, and more preferably butyl acrylate.

[0055] When the polymer constituting the HIPE foam contains a hard crosslinking agent component and a soft crosslinking agent component, the content of the hard crosslinking agent component in the polymer is preferably 1 to 10 parts by mass, more preferably 2 to 6 parts by mass, and even more preferably 2 to 5 parts by mass, per 100 parts by mass of the total vinyl monomer component and crosslinking agent component constituting the polymer, from the viewpoint of easily increasing the rigidity of the HIPE foam. Furthermore, from the viewpoint of preventing the HIPE foam from becoming excessively embrittled, the content of the soft crosslinking agent component in the polymer is preferably 3 to 50 parts by mass, more preferably 5 to 40 parts by mass, and even more preferably 8 to 30 parts by mass, per 100 parts by mass of the total vinyl monomer component and crosslinking agent component constituting the polymer.

[0056] [Application] The HIPE foam can be used for various purposes depending on its physical properties. For example, the HIPE foam may be used as a sound-absorbing material, cleaning material, wiping material, etc. As described above, the HIPE foam has the characteristic of having little local variation in physical properties even when it is made large. Therefore, by producing a large HIPE foam and then slicing it to the desired dimensions, sound-absorbing materials and the like having the desired properties can be efficiently produced.

[0057] The HIPE foam may also be used as a cutting material for producing a cut product by cutting. As described above, the HIPE foam has the property of having small local variations in physical properties even when it is made large, so that by using the HIPE foam as a cutting material, larger cut products can be easily obtained.

[0058] Examples of machined products include various models such as architectural models of buildings and the like, machine models of machinery and the like, vehicle models of cars, trains and the like, casting models for making sand molds for casting called wooden casting patterns, artistic models of artworks and exhibits and the like, pre-product models, etc. Note that such model materials are produced by subjecting the object to be cut (i.e., the cutting material) to cutting processing.

[0059] The HIPE foam is preferably used to prepare a casting pattern. A casting pattern is, for example, a pattern used to form a sand mold. Such a pattern is sometimes referred to as a "wooden pattern." Because the HIPE foam has excellent smoothness on the cut surface, a casting pattern prepared from the HIPE foam has a smooth surface. Furthermore, since the surface shape of the casting pattern is reflected in the surface shape of the casting, a casting having a smooth casting surface can be easily obtained by casting using a casting pattern having a smooth surface.

[0060] (HIPE foam manufacturing method) HIPE foams are obtained by polymerizing water-in-oil high internal phase emulsions, in which the organic phase is a continuous phase containing vinyl monomers, crosslinkers, emulsifiers, polymerization initiators, etc., and the aqueous phase is a dispersed phase containing water, such as deionized water.

[0061] The method for producing a HIPE foam includes, for example, an emulsification step of 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 / or a styrene monomer, an emulsifier, and a polymerization initiator; and a polymerization step of polymerizing an acrylic monomer and / or a styrene monomer in the water-in-oil high internal phase emulsion filled in a reaction vessel.

[0062] [Emulsification process] In the emulsification step, a water-in-oil type high internal phase emulsion is prepared by adding dropwise an aqueous liquid (aqueous phase) containing water into an oily liquid while stirring an oily liquid (organic phase) containing organic substances such as a vinyl monomer, an emulsifier, and a polymerization initiator. In the emulsification step, a high internal phase emulsion can be prepared by adding an aqueous liquid to an oily liquid so that the volume of the aqueous phase is, for example, three times or more the volume of the organic phase. The proportion of the aqueous phase contained in the organic phase can be adjusted by adjusting the mass ratio of the organic phase to the aqueous phase. The content of the aqueous phase in the high internal phase emulsion is preferably 250 to 3000 parts by mass, more preferably 400 to 2500 parts by mass, and even more preferably 500 to 2000 parts by mass, per 100 parts by mass of the organic phase.

[0063] The viscosity of the water-in-oil type high internal phase emulsion formed in the emulsification step is preferably 1 Pa·s or more and 250 Pa·s or less. By setting the viscosity of the high internal phase emulsion within the above-mentioned specific range, the aqueous phase can be uniformly dispersed in the high internal phase emulsion, and the dispersion state of the aqueous phase can be stabilized. As a result, cells can be more uniformly formed in the finally obtained HIPE foam, and the density ρ of the maximum density part can be reduced. max and the density of the minimum density part ρ minThis reduces the difference between the viscosity and the local variation in physical properties. If the viscosity of the high internal phase emulsion is too low, the aqueous phase in the high internal phase emulsion will tend to settle due to gravity. As a result, the air bubbles will tend to be unevenly distributed in the part of the HIPE foam that was at the bottom during production, and the density ρ of the maximum density part will be lower. max and the density of the minimum density part ρ min On the other hand, if the viscosity of the high internal phase emulsion is too high, air bubbles are likely to be mixed in during stirring of the high internal phase emulsion, and defects such as pores are likely to form in the final HIPE foam. From the viewpoint of more easily avoiding these problems, the viscosity of the water-in-oil high internal phase emulsion formed in the emulsification step is more preferably 3 Pa·s or more and 200 Pa·s or less, even more preferably 5 Pa·s or more and 150 Pa·s or less, and particularly preferably 10 Pa·s or more and 100 Pa·s or less.

[0064] The viscosity of the water-in-oil type high internal phase emulsion is a value measured using a Brookfield viscometer. A specific method for measuring the viscosity of the high internal phase emulsion will be described in detail in the Examples.

[0065] The stirring speed in the emulsification step is not particularly limited. For example, the stirring power density is 0.01 kW / m 3 More than 10kW / m 3 The stirring power density in the emulsification step can be set appropriately within the following range: From the viewpoint of making it easier to obtain a HIPE foam having a desired cell structure, the stirring power density in the emulsification step is set to 0.03 kW / m 3 More than 7kW / m 3 It is more preferable that the stirring power density (unit: kW / m 3 ) is calculated by calculating the power (unit: kW) during stirring from the torque (unit: N m) and rotation speed (unit: rpm) of the stirring device used in the emulsification process, and then multiplying this power by the volume (unit: m 3 ) can be calculated by dividing by

[0066] The method of adding the aqueous liquid to the oily liquid in the emulsification step is not particularly limited, but may include a method in which the oily liquid and the aqueous liquid are placed in a stirring vessel and stirring is initiated to carry out emulsification, or a method in which only the oily liquid is placed in a stirring vessel and stirring is initiated, and the aqueous liquid is then added to the vessel using a pump or the like while stirring to carry out emulsification. When the aqueous liquid is added using a pump or the like, the addition rate of the aqueous liquid is not particularly limited, but may be adjusted, for example, within a range of 10% by mass / min to 1000% by mass / min relative to 100% by mass of the oily liquid. The addition rate of the aqueous liquid is more preferably 100% by mass / min to 800% by mass / min, and even more preferably 200% by mass / min to 600% by mass / min, relative to 100% by mass of the oily liquid (organic phase). Furthermore, the specific embodiment of the emulsification step is not particularly limited, and various embodiments can be employed, such as a batch-type emulsification step in which emulsification is performed using a stirring vessel equipped with a stirring device or a centrifugal shaker, or a continuous emulsification step in which an oily liquid and an aqueous liquid are continuously supplied and mixed into a line equipped with a static mixer, a mesh, or the like.

[0067] The aqueous phase may contain water such as deionized water, a polymerization initiator, an electrolyte, etc. In the emulsification step, for example, an oily liquid and an aqueous liquid are prepared, and the aqueous liquid is added to the oily liquid under stirring to prepare a high internal phase emulsion. In addition, in the emulsification step, additives such as a flame retardant, a flame retardant auxiliary, a light stabilizer, and a colorant may be appropriately blended into the aqueous phase and / or organic phase.

[0068] Flame retardants are used to improve the flame retardancy of HIPE foams. Examples of flame retardants include organic compounds containing halogen, phosphorus, nitrogen, silicone, etc.; and inorganic compounds containing metal hydroxides, phosphorus, nitrogen, etc. Flame retardants can be used within a range that does not impair the effects of the present invention. When a flame retardant is added, the amount is preferably 5 to 20 parts by mass per 100 parts by mass of the total of the vinyl monomer component and crosslinker component that constitute the polymer. From the viewpoint of easily imparting excellent flame retardancy even with a small amount of addition, a brominated bisphenol-based flame retardant is preferably used as the flame retardant, more preferably a brominated bisphenol-based flame retardant having a 2,3-dibromo-2-methylpropyl group and / or a brominated bisphenol-based flame retardant having a 2,3-dibromopropyl group, and even more preferably 2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane.

[0069] In addition, HIPE foam can be appropriately blended with a flame retardant synergist to improve flame retardancy. For example, when a halogen-based flame retardant is used, if a radical generator such as dicumyl peroxide is used as the flame retardant synergist, the decomposition of the radical generator promotes the elimination of halogen from the flame retardant, which is expected to improve flame retardancy. Furthermore, when a halogen-based flame retardant is used, if an antimony compound such as antimony trioxide is used as the flame retardant synergist, the radical trapping effect of the halogen-based flame retardant and the air blocking effect of the antimony oxide are combined synergistically, which is expected to improve flame retardancy. Note that a single flame retardant may be used, or two or more flame retardants with different flame retardancy mechanisms may be used in combination.

[0070] The polymerization initiator is used to initiate the polymerization of vinyl monomers. As the polymerization initiator, a radical polymerization initiator can be used. Specifically, dilauroyl peroxide (LPO), bis(4-t-butylcyclohexyl) peroxydicarbonate (LTCP), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(3,5,5-trimethylhexanoyl) peroxide, t-butyl peroxypivalerate, t-hexyl peroxypivalerate, t-butyl peroxyneoheptanoate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, etc. Examples of polymerization initiators that can be used include organic peroxides such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(4-dimethylvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate), and 2,2'-azobis(2-methylbutyronitrile). These polymerization initiators may be used alone or in combination of two or more.

[0071] The polymerization initiator added to the high internal phase emulsion preferably contains a polymerization initiator having a one-hour half-life temperature of 40°C or higher and 70°C or lower. By using a polymerization initiator having a one-hour half-life temperature of 40°C or higher and 70°C or lower, the polymerization initiation temperature of the vinyl monomer in the polymerization step can be lowered. Furthermore, by lowering the polymerization initiation temperature of the vinyl monomer, the vinyl monomer can be sufficiently advanced before the sedimentation of the aqueous phase in the water-in-oil high internal phase emulsion progresses. As a result, cells are more uniformly formed in the finally obtained HIPE foam, and the density ρ of the maximum density part is reduced. max and the density of the minimum density part ρ min The difference can be made smaller.

[0072] The polymerization initiator can be added to the organic phase and / or the aqueous phase. When the polymerization initiator is added to the aqueous phase, a water-soluble polymerization initiator such as 2,2'azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride, 2,2'azobis(2-methylpropionamidine dihydrochloride, potassium persulfate, ammonium persulfate, etc. may be used. The amount of the polymerization initiator added can be, for example, in the range of 0.1 to 5 parts by mass per 100 parts by mass of the total of the vinyl monomer and the crosslinking agent. In addition, when the density ρ of the maximum density part is max and the density of the minimum density part ρ min From the viewpoint of being able to reduce the difference between the above, the amount of polymerization initiator added is preferably 0.4 parts by mass or more and 4 parts by mass or less, and more preferably 0.6 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the total of the vinyl monomer and the crosslinking agent.

[0073] The emulsifier is used to form and stabilize a high internal phase emulsion. Examples of the emulsifier include surfactants. Specifically, glycerol esters such as polyglycerol condensed ricinoleate, polyglycerol stearate, polyglycerol oleate, polyglycerol laurate, and polyglycerol myristate are used; sorbitol esters such as sorbitan oleate, sorbitan stearate, sorbitan laurate, sorbitan laurate, and sorbitan palmitate; ethylene glycol sorbitan esters; ethylene glycol esters; and copolymers of polyethylene glycol and polypropylene glycol. The amount of emulsifier added can be, for example, from 1 to 30 parts by mass per 100 parts by mass of the total of the vinyl monomer, crosslinker, and emulsifier.

[0074] The electrolyte is used to impart ionic strength to the aqueous phase and increase the stability of the emulsion. A water-soluble electrolyte can be used. Specific examples include calcium chloride, sodium chloride, magnesium chloride, sodium acetate, sodium citrate, sodium sulfate, calcium sulfate, magnesium sulfate, sodium dihydrogen phosphate, and disodium hydrogen phosphate. The amount of electrolyte added can be, for example, in the range of 0.01 to 10 parts by mass per 100 parts by mass of the aqueous liquid.

[0075] [Polymerization process] In the polymerization step, the water-in-oil high internal phase emulsion is filled into a reaction vessel, and then a styrene-based monomer and / or an acrylic monomer is polymerized in the reaction vessel. In the polymerization step, for example, the high internal phase emulsion in the reaction vessel is heated to polymerize the vinyl-based monomer and obtain a polymerization product (specifically, a polymer containing water). Suitable methods for heating the high internal phase emulsion in the polymerization step include heating with a heat transfer liquid such as hot water, and heating with electromagnetic waves such as high frequency waves and microwaves. The use of these heating methods facilitates the rapid completion of the polymerization of the vinyl-based monomer, making it easier to produce a HIPE foam having a desired density ratio, etc.

[0076] The polymerization temperature in the polymerization step is adjusted depending on, for example, the type of vinyl polymer, the type of polymerization initiator, the type of crosslinking agent, etc. max and the density of the minimum density part ρ min From the viewpoint of further reducing the difference between the polymerization temperature and the polymerization time, the polymerization temperature is preferably 50° C. or higher and 90° C. or lower. When the polymerization temperature is within the above-mentioned range, the polymerization time is preferably 0.5 hours or higher and 15 hours or lower, more preferably 0.5 hours or higher and 12 hours or lower, and even more preferably 0.5 hours or higher and 10 hours or lower.

[0077] In the polymerization step, it is preferable to raise the temperature of the acrylic monomer and / or the styrene monomer to 50°C within 3 hours from the time when the water-in-oil type high internal phase emulsion is completely charged into the reaction vessel. In this way, by rapidly raising the temperature of the vinyl monomer in the polymerization step, the polymerization of the vinyl monomer can be sufficiently advanced before the sedimentation of the aqueous phase in the water-in-oil type high internal phase emulsion progresses. As a result, cells are more uniformly formed in the finally obtained HIPE foam, and the density of the maximum density part ρ max and the density of the minimum density part ρ min From this viewpoint, in the polymerization step, it is more preferable to make the temperature of the acrylic monomer and / or the styrenic monomer reach 50°C within 1 hour from the time when the charging of the water-in-oil type high internal phase emulsion into the reaction vessel is completed, and it is even more preferable to make the temperature of the acrylic monomer and / or the styrenic monomer reach 50°C within 0.5 hours.

[0078] In addition, in the polymerization step, it is preferable to set the time from the completion of filling the water-in-oil type high internal phase emulsion into the reaction vessel until the polymerization conversion rate of the acrylic monomer and / or the styrene type monomer reaches 90% within 7 hours. In this way, by polymerizing the vinyl type monomer in the polymerization step in a relatively short time, the polymerization of the vinyl type monomer can be sufficiently progressed before the sedimentation of the aqueous phase in the water-in-oil type high internal phase emulsion progresses. As a result, cells are more uniformly formed in the finally obtained HIPE foam, and the density ρ of the maximum density part is reduced. max and the density of the minimum density part ρ min From this viewpoint, in the polymerization step, the time from the completion of charging the water-in-oil type high internal phase emulsion into the reaction vessel until the polymerization conversion rate of the acrylic monomer and / or the styrene monomer reaches 90% is more preferably within 5 hours, and even more preferably within 4 hours.

[0079] In the polymerization process, the high internal phase emulsion filled in the reaction vessel is heated using a heat transfer medium such as hot water or electromagnetic waves such as high frequency waves or microwaves, and by increasing the heating efficiency of the monomer in the reaction vessel, the polymerization temperature can be raised to a predetermined temperature quickly and the time required for the polymerization conversion rate of the monomer to reach 90% can be shortened.

[0080] The polymerization conversion rate of the vinyl monomer in the polymerization step is calculated as follows. First, the polymerization step is carried out by the method described above until the polymerization conversion rate is measured. Next, the temperature of the contents of the reaction vessel is cooled to 30°C or less within 10 minutes from the time when the polymerization step has progressed to the time when the polymerization conversion rate is measured, thereby terminating the polymerization reaction.

[0081] After the contents have been cooled, the HIPE foam undergoing polymerization is removed from the reactor. A sample is then taken from the center of the HIPE foam. The amount of unreacted vinyl monomer remaining in this sample is measured using gas chromatography. The polymerization conversion rate of the vinyl monomer is calculated using the following formula (1). Polymerization conversion rate (unit: mass%) = 100 - amount of unreacted vinyl monomer (unit: mass%) (1)

[0082] [Drying process] The polymerization product obtained as described above, i.e., the water-containing polymer, can be dehydrated to obtain a HIPE foam (drying process). In the drying process, the polymerization product is dried using an oven, vacuum dryer, high-frequency / microwave dryer, or the like. Upon completion of drying, the water droplets in the emulsion before polymerization become bubbles in the dried polymer, resulting in a HIPE foam. Before drying, the polymerization product can be dehydrated by squeezing, for example, using a press. Squeezing can be performed at room temperature (e.g., 23°C), but it can also be performed at a temperature above the glass transition temperature of the polymer that constitutes the HIPE foam. In this case, dehydration by squeezing is facilitated and the drying time can be shortened. Alternatively, the polymer can be dehydrated by centrifugation. This also shortens the drying time. [Example]

[0083] Examples of the HIPE foam are described below. The acrylic monomers, styrene monomers, crosslinking agents, emulsifiers, and polymerization initiators used in the examples and comparative examples, along with their abbreviations, are as follows:

[0084] Acrylic monomers BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate Styrene monomers St: styrene

[0085] Crosslinking agent DVB: Divinylbenzene (Nippon Steel Chemical & Material Co., Ltd. "DVB-570", purity 57%) PEGDA: Polyethylene glycol diacrylate ("NK Ester A-400" manufactured by Shin-Nakamura Chemical Co., Ltd.) EpDA: epoxy diacrylate (specifically, both-end acrylic-modified epoxy prepolymer, "EBECRYL (registered trademark) 3708" manufactured by Daicel-Allnex Corporation) ·emulsifier PGPR: Polyglycerol condensed ricinoleate ("CRS-75" manufactured by Sakamoto Pharmaceutical Co., Ltd.) DGMO: Diglycerin monooleate

[0086] Polymerization initiator LPO: Dilauryl peroxide (NOF Corporation "Perloyl (registered trademark) L", 1-hour half-life temperature: 79.5°C) LTCP: bis(4-t-butylcyclohexyl) peroxydicarbonate (NOF Corporation, "Perloyl TCP"; 1-hour half-life temperature: 57.5°C) PPS: Potassium persulfate

[0087] Example 1 In this example, a HIPE foam was produced by the following method. First, 54 parts by mass of styrene as a styrene-based monomer, 24 parts by mass of butyl acrylate as an acrylic monomer, 12 parts by mass of divinylbenzene and 5 parts by mass of polyethylene glycol diacrylate as crosslinking agents, 5 parts by mass of polyglycerin condensed ricinoleate as an emulsifier, and 0.5 parts by mass of dilauroyl peroxide and 0.2 parts by mass of bis(4-t-butylcyclohexyl)peroxydicarbonate as polymerization initiators were added to a 3-L glass vessel equipped with a torque converter stirrer. These were mixed in the glass vessel to form an organic phase.

[0088] Next, the stirring power density is 1.6 kW / m 3 While stirring the organic phase at 400°C, 614 parts by mass of deionized water at 20°C was added to the glass vessel at a rate of approximately 450 g / min. After the addition of the deionized water was completed, stirring was continued for 10 minutes to prepare a water-in-oil (i.e., W / O) high internal phase emulsion. The stirring power density after emulsification was 1.4 kW / m 3 The stirring power density (unit: kW / m 3 ) is calculated by calculating the power (unit: kW) from the torque (unit: N m) and rotation speed (unit: rpm) of the agitator, and the volume of the contents (unit: m 3 ) can be calculated by dividing by

[0089] Next, the stirring power density was set to 0.1 kW / m 3 The pressure in the glass container was reduced to 0°C, and an aspirator was connected to the glass container to reduce the pressure inside the container, thereby removing the microbubbles contained in the emulsion. 10 minutes after the start of the pressure reduction, stirring was stopped and the pressure inside the container was returned to atmospheric pressure. From the start of stirring until the end of stirring, the temperature inside the glass container was maintained at 20°C using a chiller.

[0090] The high internal phase emulsion thus obtained was filled into a reaction vessel measuring approximately 160 mm in width, 220 mm in length, and 170 mm in depth. The high internal phase emulsion in the reaction vessel was then irradiated with microwaves at 1000 W for approximately 15 minutes using a microwave heating device, raising the temperature of the center of the high internal phase emulsion to 70°C. After microwave heating was completed, the reaction vessel was placed in a constant-temperature water bath at 70°C, and the contents of the reaction vessel were heated with hot water for 6 hours. As a result, the styrene-based monomer, acrylic monomer, and crosslinking agent in the high internal phase emulsion were polymerized, forming a HIPE foam containing water in the reaction vessel.

[0091] Next, the reaction vessel was removed from the constant-temperature water bath to cool the HIPE foam. The HIPE foam was then removed from the reaction vessel and washed with water. The washed HIPE foam was dried in a 90°C oven until it reached a constant weight, and then cut at a position 2 mm deep from the surface of the HIPE foam to remove the skin layer (the layer including the skin surface of the HIPE foam). In this way, a rectangular HIPE foam composed of a vinyl polymer was obtained. The dimensions of this HIPE foam were 160 mm long, 220 mm wide, and 170 mm high (vertical length). The vertical direction of the HIPE foam corresponds to the vertical direction during polymerization of the HIPE foam.

[0092] The charge composition of this example is shown in Table 2. The contents of various components (vinyl monomer and crosslinking agent) in the HIPE foam can be calculated from the blending amounts of each component (in the case of the crosslinking agent, the blending amount excluding impurities) and the total blending amount of the vinyl monomer component and the crosslinking agent component (excluding impurities) at the time of charging.

[0093] Example 2 In this example, a HIPE foam was obtained in the same manner as in Example 1, except that the dimensions of the reaction vessel used during polymerization were changed to approximately 500 mm in width, approximately 500 mm in length, and approximately 110 mm in depth, and that the high internal phase emulsion was heated for 12 hours using only hot water in a 70°C thermostatic water bath without using microwaves. The dimensions of the HIPE foam in this example were 500 mm in length, 500 mm in width, and 110 mm in height (vertical length).

[0094] Example 3 In this example, a HIPE foam was obtained in the same manner as in Example 2, except that the amount of the aqueous phase added relative to the organic phase was changed as shown in Table 2. In this example, the stirring power density at the completion of emulsification was 1.6 kW / m 3 It was.

[0095] Example 4 In this example, a HIPE foam was obtained in the same manner as in Example 1, except that the amount of the aqueous phase added relative to the organic phase was changed as shown in Table 3. The stirring power density at the completion of emulsification in Example 4 was 1.0 kW / m 3 It was.

[0096] (Examples 5, 8, and 9) In this example, a HIPE foam was obtained in the same manner as in Example 1, except that the compositions of the aqueous phase and the organic phase were changed as shown in Table 3 or Table 4. The stirring power density at the completion of emulsification in Example 5 was 2.0 kW / m 3 The stirring power density at the completion of emulsification in Example 8 was 2.1 kW / m 3 The stirring power density at the completion of emulsification in Example 9 was 1.7 kW / m 3 It was.

[0097] Example 6 In this example, the stirring rotation speed during emulsification was changed, and the stirring power density during degassing was set to 0.06 kW / m 3 A HIPE foam was obtained in the same manner as in Example 1, except that the stirring power density at the time of completion of emulsification in this example was 0.06 kW / m 3 It was.

[0098] Example 7 In this example, a HIPE foam was obtained in the same manner as in Example 1, except that the stirring rotation speed during emulsification was changed. Note that the stirring power density at the completion of emulsification in this example was 7.9 kW / m 3 It was.

[0099] Example 10 In this example, a HIPE foam was obtained in the same manner as in Example 2, except that the dimensions of the reaction vessel used during polymerization were changed to approximately 250 mm in width, approximately 250 mm in length, and approximately 300 mm in depth. The dimensions of the HIPE foam in this example were 250 mm in length, 250 mm in width, and 300 mm in height (vertical length).

[0100] (Comparative Example 1) In this example, the compositions of the aqueous phase and organic phase were changed as shown in Table 5, and the high internal phase emulsion was heated for 12 hours using only hot air in a 70°C oven without using microwaves, and a HIPE foam was obtained in the same manner as in Example 1. The stirring power density after the completion of emulsification in this example was 1.4 kW / m 3 It was.

[0101] (Comparative Example 2) In this example, a HIPE foam was obtained in the same manner as in Comparative Example 1, except that the compositions of the aqueous phase and organic phase were changed as shown in Table 5 and the polymerization temperature of the high internal phase emulsion was changed to 65°C. In this example, the stirring power density after completion of emulsification was 1.5 kW / m 3 It was.

[0102] (Comparative Example 3) In this example, the stirring rotation speed during emulsification was changed and the stirring power density during degassing was set to 0.02 kW / m 3 A HIPE foam was obtained in the same manner as in Example 1, except that the stirring power density at the time of completion of emulsification in this example was 0.02 kW / m 3 It was.

[0103] Comparative Example 4 In this example, a HIPE foam was obtained in the same manner as in Example 9, except that the high internal phase emulsion was heated for 12 hours using only hot air at 70°C without using microwaves.

[0104] Next, the evaluation methods for each of the physical properties shown in Tables 2 to 5 will be explained.

[0105] [High internal phase emulsion viscosity] Using a Brookfield viscometer ("LVDV-II+Pro" manufactured by Eiko Seiki Co., Ltd.), the viscosity of the high internal phase emulsion was measured after the emulsification step was completed. Because the high internal phase emulsions obtained in the examples and comparative examples are pseudoplastic fluids, they have high viscosity when the shear rate is zero (i.e., when left stationary), and decrease as the shear rate increases. Therefore, even when measuring the same high internal phase emulsion, the measured viscosity value changes when the spindle rotation speed (i.e., shear rate) changes. To avoid the influence of such viscosity changes due to shear rate, the spindle rotation speed was set to 0.2 rpm, and measurements were performed using a spindle whose torque during measurement was in the range of 10% to 90% of the maximum allowable torque of the device. More specifically, the LV-1 spindle was used when the viscosity was approximately 10,000 mPa·s or less, the LV-2 spindle when it was approximately more than 10,000 mPa·s but less than 80,000 mPa·s, and the LV-3 spindle when it was approximately more than 80,000 mPa·s. The measurement temperature was 20°C, and the amount of high internal phase emulsion used for the measurement was 600 mL.

[0106] [Time to reach 50°C, 60°C, and 70°C at the center point] The temperature measurement at the center of the reaction vessel during polymerization was conducted as a separate experiment from the preparation of the HIPE foam described above. Specifically, a fluorescent fiber optic thermometer (FL-2000) manufactured by Anritsu Meter Co., Ltd. was used, with the tip of the probe fixed at the center of the reaction vessel. Polymerization was initiated using the same procedure as in the preparation of the HIPE foam described above, and the temperature change at the center of the reaction vessel was measured. The time required for the temperature at the center of the reaction vessel to reach 50°C, 60°C, and 70°C from the start of heating in the above measurement was then defined as the time required for the temperature at the center of the reaction vessel to reach 50°C, 60°C, and 70°C from the start of heating in the polymerization process.

[0107] [Time required to reach 90% polymerization conversion] The measurement of the time required for the polymerization conversion rate to reach 90% was carried out as an experiment separate from the preparation of the HIPE foam described above. First, the time required for the polymerization conversion rate to reach 90% was predicted by simulation. Next, a high internal phase emulsion was prepared using the same method as in the Examples and Comparative Examples, and the polymerization process was carried out up to the time when the polymerization conversion rate was to be measured, based on the prediction from the simulation. After the polymerization process was allowed to proceed up to the time when the polymerization conversion rate was to be measured, the temperature of the contents of the reaction vessel was cooled to 30°C or below within 10 minutes to terminate the polymerization reaction.

[0108] After the contents had cooled completely, the HIPE foam in the middle of polymerization was removed from the reactor. A sample was then taken from the center of the HIPE foam. The amount of unreacted vinyl monomer remaining in this sample was measured using gas chromatography. The amount of unreacted vinyl monomer thus obtained was used to calculate the polymerization conversion rate according to the following formula: Polymerization conversion rate (unit: mass%) = 100 - amount of unreacted vinyl monomer (unit: mass%)

[0109] The above operation was repeated multiple times while gradually changing the time elapsed from the start of polymerization at 0.5 hour intervals, and the time elapsed from the start of polymerization when the polymerization conversion rate reached 90% or more was defined as the time required to reach 90% polymerization conversion rate.

[0110] The detailed measurement conditions for gas chromatography are as follows:

[0111] First, approximately 5 g of cyclopentanol was placed in a 100 mL volumetric flask as an internal standard, and the mass of the cyclopentanol was weighed to three decimal places. Next, dimethylformamide (DMF) was added to the volumetric flask to bring the total volume to 100 mL. Further DMF was added to this cyclopentanol / DME solution, diluting the solution 100 times to prepare the internal standard solution.

[0112] Next, approximately 1 g of the sample to be measured was weighed out to three decimal places. The weighed sample was dissolved in approximately 18 mL of DMF, and exactly 2 mL of the internal standard solution was added using a volumetric pipette. 1 μL of the resulting solution was collected using a microsyringe and introduced into a gas chromatograph to obtain a chromatogram. The peak areas of the unreacted vinyl monomer and the internal standard were determined from the chromatogram, and the concentrations of each component were calculated using the following formula (2). Component concentration (mass%)=(Wi / 10000)×2×(An / Ai)×Fn÷Ws×100 (2)

[0113] The meanings of the symbols in the above formula (2) are as follows: Wi: Mass of cyclopentanol used to prepare the internal standard solution (unit: g) Ws: mass of sample dissolved in DMF (unit: g) An: Peak area of ​​each component measured by gas chromatography Ai: Peak area of ​​the internal standard during gas chromatographic measurement Fn: Correction coefficient for each component determined from a previously prepared calibration curve

[0114] The gas chromatographic analysis conditions were as follows: Equipment used: Gas chromatograph GC-6AM manufactured by Shimadzu Corporation Detector: FID (Flame Ionization Detector) Column material: Glass column with an inner diameter of 3 mm and a length of 5000 mm Column packing material: [Liquid phase name] FFAP (free fatty acids), [Liquid phase impregnation rate] 10% by mass, [Carrier name] Chomasorb W diatomaceous earth for gas chromatography, [Carrier particle size] 60 / 80 mesh, [Carrier treatment method] AW-DMCS (water washing, calcination, acid treatment, silane treatment), [Packaging volume] 90 mL Inlet temperature: 250℃ Column temperature: 120℃ Detector temperature: 250°C Carrier gas: N2, flow rate: 40 ml / min

[0115] [Density of the maximum density part ρ max , density of the minimum density part ρ min ] After removing the skin layer, the HIPE foam was divided into five equal parts in each of the vertical, horizontal, and vertical directions (height direction), to prepare 125 rectangular parallelepiped pieces. Next, the mass (unit: kg) of each piece was calculated based on the volume (unit: m) calculated from the external dimensions. 3 ) to obtain the density of each piece (unit: kg / m 3 ) was calculated. Then, the piece with the highest density among the 125 pieces was taken as the maximum density part, and its density was calculated as the density ρ of the maximum density part. max The small piece with the lowest density was defined as the minimum density part, and its density was defined as the density ρ of the minimum density part. min In both the examples and comparative examples, the maximum density portion was a small piece including the upper surface of the HIPE foam after the skin layer was removed, and the minimum density portion was a small piece including the lower surface of the HIPE foam after the skin layer was removed.

[0116] In addition, Tables 2 to 5 show the minimum density part ρ min Density of the maximum density part ρ max density ratio ρ max / ρ min The density ratio / height is the value obtained by dividing this density ratio by the height (vertical length) of the HIPE foam, and the density of the maximum density part ρ max and the density of the minimum density part ρ min The density difference ρ max -ρmin The density difference was divided by the height of the HIPE foam, and the density difference / height value was recorded.

[0117] [HIPE foam overall density] The mass of the HIPE foam (unit: kg) is calculated from the external dimensions and the volume (unit: m 3 ) to obtain the density of the entire HIPE foam (unit: kg / m 3 ) was calculated.

[0118] [Maximum bending stress at upper part, maximum bending stress at lower part] After removing the skin layer, the HIPE foam was cut along a plane 20 mm deep from the upper surface, with the upper surface being the upper surface in the height direction as manufactured. Five test pieces, each 25 mm wide, 120 mm long, and 20 mm thick, were prepared from the resulting 20 mm thick plate of HIPE foam, including the upper surface. Three-point bending tests were performed using these test pieces in accordance with JIS K7221-1:2006. The arithmetic mean value of the maximum bending stress of the five test pieces was taken as the maximum bending stress of the upper part.

[0119] The specific test conditions for the three-point bending test are as follows: Measuring device: Shimadzu Corporation "Autograph AGS-10kNG" ·Room temperature: 23℃ ·Humidity: 50% Test speed: 10mm / min Distance between supports: 100mm Support and indenter tip shape: cylindrical with a radius of 5 mm

[0120] Furthermore, after removing the skin layer, the HIPE foam was cut along a plane 20 mm deep from the bottom surface, with the lower surface being the surface in the height direction at the time of manufacture. Five test pieces, each 25 mm wide, 120 mm long, and 20 mm thick, were prepared from the resulting 20 mm thick plate of HIPE foam, including the bottom surface. Three-point bending tests were performed using these test pieces in accordance with JIS K7221-1:2006. The arithmetic mean value of the maximum bending stresses of the five test pieces was taken as the maximum bending stress of the lower part.

[0121] Tables 2 to 5 also list the average value of the maximum bending stress, stress ratio, standard deviation of the maximum bending stress, coefficient of variation of the maximum bending stress, and specific strength, which were calculated based on the measurement results of these maximum bending stresses. Specifically, the average value of the maximum bending stress is the arithmetic mean value of the maximum bending stresses of five test specimens taken from the upper portion and five test specimens taken from the lower portion. The stress ratio is the ratio of the maximum bending stress of the upper portion to the maximum bending stress of the lower portion, expressed as a percentage (unit: %). The standard deviation of the maximum bending stress is a value calculated from the maximum bending stress of five test specimens taken from the upper portion and the maximum bending stress of five test specimens taken from the lower portion. The coefficient of variation of the maximum bending stress is the ratio of the standard deviation of the maximum bending stress to the average value, expressed as a percentage (unit: %). The specific strength is the ratio (unit: kN·m / kg) of the arithmetic mean value of the maximum bending stress at the upper part and the maximum bending stress at the lower part to the density of the entire HIPE foam.

[0122] [Average bubble diameter] First, the density of the maximum density part mentioned above, ρ max and the density of the minimum density part ρ min Of the 125 small pieces produced by the calculation method, one small piece was randomly taken from each of the vertical rows. These five samples were observed using a low-vacuum scanning electron microscope ("Miniscope (registered trademark) TM3030Plus" manufactured by Hitachi High-Tech Science Corporation), and cross-sectional photographs were taken. Figure 2 shows an example of a cross-sectional photograph of a HIPE foam. The detailed observation conditions were as follows:

[0123] Sample pretreatment: Conductive treatment of the sample was performed using a metal coating device ("MSP-1S" manufactured by 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)

[0124] Next, the cross-sectional photographs were analyzed using image processing software (NanoHunter NS2K-Pro from NanoSystems Co., Ltd.), and the bubble diameter (circle equivalent diameter) of the bubbles present on the cross-sectional photographs of each sample was calculated. The arithmetic mean value of these was then used as the bubble diameter of each sample. Furthermore, the bubble diameters of the five samples were arithmetically averaged, and this value was used as the average bubble diameter of the HIPE foam. The detailed analysis procedures and conditions were as follows:

[0125] (1) Monochrome conversion (2) Smoothing filter (3x3, 8 neighbors, processing count = 1) (3) Density unevenness correction (brighter than background, size = 5) (4) NS binarization (darker than background, clarity = 9, sensitivity = 1, noise removal, density range = 0 to 255) (5) Contraction (8 neighbors, number of processes = 1) (6) Image selection by feature (area) (50 to ∞ μm 2 (select only 8 neighbors) (7) Dilation without neighbor connections (8 neighbors, number of processes = 3) (8) Circle equivalent diameter measurement (calculated from area, 8 neighbors)

[0126] [1m 2 Number of holes with a circular equivalent diameter of 3 mm or more per unit area, and number of holes with a circular equivalent diameter of 1 to 3 mm per unit area The density of the maximum density part mentioned above, ρ max and the density of the minimum density part ρ minTwenty small pieces were randomly selected from the 125 small pieces prepared by the calculation method. The circle-equivalent diameters of the holes present in the cross sections of these 20 observation objects were calculated. Then, the number of holes present in the cross sections of the observation objects with a circle-equivalent diameter of 3 mm or more and the number of holes with a circle-equivalent diameter of 1 mm or more but less than 3 mm were counted. These values ​​were divided by the area of ​​the cross section where the observation was performed to calculate the area per 1 m of the cross section. 2 The number of holes present per square was calculated.

[0127] In addition, the "Maximum diameter of hole" column in Tables 2 to 5 lists the maximum circle-equivalent diameter of holes present in the cross section of the above-mentioned object of observation.

[0128] [Smoothness of cutting surface] Using the HIPE foams obtained in Examples 1, 2, 7, and 10 and Comparative Examples 1 and 3, the smoothness of the cut surface was evaluated by the following method.

[0129] First, a cutting sample including the underside of the HIPE foam was cut out from the HIPE foam after removing the skin layer. Next, a linear groove was formed on the underside of the HIPE foam in the cutting sample using a cutting machine. The detailed cutting conditions are as follows: Cutting equipment: NC router (SHODA Corporation "NCN8200") Cutting tool: Square end mill (Fukuda Iron Works, 4-flute, 20mm diameter) Cutting tool rotation speed: 3000 rpm Cutting tool feed rate: 5000mm / min Cutting depth: 10mm

[0130] Next, the arithmetic mean surface roughness Sa and maximum surface roughness Sz of the bottom surface of the groove formed by cutting were measured using a 3D shape measuring instrument VR-3200 manufactured by Keyence Corporation. The observation magnification was 12x, and the measurement area was a range of approximately 18mm x 24mm in actual dimensions. This measurement area corresponds to the entire area of ​​the observation surface when observed at 12x magnification. The arithmetic mean surface roughness Sa is the average value of the irregularities from the reference surface, and the maximum surface roughness Sz is the difference between the highest and lowest points.

[0131] In the above evaluation, the smoothness of the cut surface (i.e., the bottom surface of the groove) was judged to be good when the arithmetic mean roughness Sa of the bottom surface of the groove was 20 μm or less and the maximum surface roughness Sz was 500 μm or less.Furthermore, the smoothness of the cut surface (i.e., the bottom surface of the groove) was judged to be poor when the arithmetic mean roughness Sa of the bottom surface of the groove exceeded 20 μm or the maximum surface roughness Sz exceeded 500 μm.

[0132] [Table 2]

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

[0136] As shown in Tables 2 to 4, the density of the HIPE foam of the examples and the density ρ of the minimum density part min Density of the maximum density part ρ max density ratio ρ max / ρ min are each within the specified range. Therefore, the HIPE foam of the example has small local variations in physical properties even when enlarged. Furthermore, as a result of the evaluation of the "smoothness of the cut surface," the HIPE foam of the example had good smoothness on the cut surface and was excellent in machinability even when enlarged.

[0137] On the other hand, as shown in Table 5, the density ratio ρ max / ρ minwas larger than the specified range. This is because, during the polymerization process, the aqueous phase settled before the polymerization of the vinyl monomer had fully progressed due to reasons such as a long time until the polymerization reaction began or a low viscosity of the organic phase, resulting in more bubbles forming at the bottom of the HIPE foam than at the top. Furthermore, as a result of the evaluation of the "smoothness of the cut surface," the HIPE foam of the comparative example had poor smoothness on the cut surface, and its machinability deteriorated when it was made larger. It is believed that the local density variation in the HIPE foam of the comparative example made it more likely for the base resin to tear or break when the bottom surface of the HIPE foam was cut, resulting in a loss of smoothness.

[0138] The above describes specific embodiments of the HIPE foam of the present invention based on examples, but the embodiments of the HIPE foam of the present invention are not limited to the embodiments, and the configuration can be changed as appropriate within the scope that does not detract from the spirit of the present invention. [Explanation of symbols]

[0139] 1 HIPE Form 11 pieces 111 Maximum density part 112 Minimum density part

Claims

1. A HIPE foam having a base resin of a polymer of a styrene-based monomer and / or an acrylic-based monomer, and having a size that allows cutting out a cube with a side length of 60 mm, The density of the HIPE foam is 50 kg / m ３ More than 350kg / m ３ is as follows: The density ρ of the minimum density portion, which is the portion with the lowest density in the HIPE foam ｍｉｎ The density of the maximum density part, ρ, ｍａｘ density ratio ρ ｍａｘ / ρ ｍｉｎ is 1.30 or less, A HIPE foam, wherein the number of holes having a circular equivalent diameter of 3 mm or more in the cross section of the HIPE foam is 1 or less (including 0) per m 2 of cross-sectional area.

2. 2. The HIPE foam according to claim 1, wherein the HIPE foam has a columnar shape and a vertical length of 70 mm or more.

3. 2. The HIPE foam according to claim 1, wherein the average cell diameter of the HIPE foam is 10 μm or more and 150 μm or less.

4. The number of holes having a circle equivalent diameter of 1 mm or more and less than 3 mm in the cross section of the HIPE foam is ２ The HIPE foam according to claim 1, wherein the number of particles per particle is 30 or less (including 0).

5. A cutting processing material composed of the HIPE foam described in any one of claims 1 to 4.

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