HIPE foam

Abstract

HIPE foam (1) is made of a polymer of an acrylic monomer and / or a styrene-based monomer. The HIPE foam (1) has a density of 30 kg / m3 to 350 kg / m3. The HIPE foam (1) contains expandable graphite. The amount of the expandable graphite (12) contained in the HIPE foam (1) is 3-25 mass%. The expandable graphite (12) may have a 1% weight loss temperature, as determined by thermogravimetric analysis, of 150-230°C.

Description

HIPE Form

[0001] This invention relates to HIPE foam.

[0002] Conventionally, porous materials known as HIPE foam are known, which have a cellular structure in which numerous air bubbles exist within a polymer of vinyl monomers, as well as a continuous cellular structure in which numerous pores are formed that connect the air bubbles.

[0003] In manufacturing HIPE foam, first, an aqueous phase consisting of an aqueous liquid such as water is encapsulated in a high proportion within an organic phase containing vinyl monomers, crosslinking agents, emulsifiers, polymerization initiators, etc., to form a water-in-oil type high-internal-phase emulsion (i.e., HIPE). By polymerizing the organic phase within this emulsion, HIPE foam can be obtained. HIPE foam is a polymer that reflects the dispersion form of the organic phase and aqueous phase in the high-internal-phase emulsion during polymerization, as well as the shape of the aqueous phase within the emulsion.

[0004] For example, Patent Document 1 describes a flame-retardant open-cell polymer foam formed by polymerizing a high internal phase water-in-oil droplet emulsion containing a continuous oil phase and a discontinuous water phase, characterized in that it has a limiting oxygen index (LOI) value of at least about 18%.

[0005] Japanese Patent Publication No. 2002-520465

[0006] In Patent Document 1, brominated aliphatic compounds are used to impart flame retardancy. However, even with the addition of such compounds, it was sometimes not possible to sufficiently improve the flame retardancy of HIPE foam.

[0007] This invention was made in view of the above background, and aims to provide a HIPE foam with high flame retardancy.

[0008] One aspect of the present invention relates to the following HIPE forms [1] to [6].

[0009] [1] A HIPE foam composed of a polymer of an acrylic monomer and / or a styrene monomer, wherein the density of the HIPE foam is 30 kg / m³ 3More than 350kg / m 3 The following is a HIPE foam, wherein the HIPE foam contains expandable graphite, and the amount of expandable graphite in the HIPE foam is 3% by mass or more and 25% by mass or less.

[0010] [2] The HIPE foam according to [1], wherein the temperature at which the expandable graphite loses 1% of its weight as measured by thermogravimetric analysis is 150°C or higher and 230°C or lower. [3] The HIPE foam according to [1] or [2], wherein the expansion ratio of the expandable graphite when heated at 400°C for 5 minutes is 25 cc / g or higher. [4] The HIPE foam according to any one of [1] to [3], wherein the 50% particle size D50 in the volume-based particle size distribution of the expandable graphite is 50 μm or higher and 1000 μm or lower.

[0011] [5] The HIPE foam according to [4], wherein the ratio (D90-D10) / D50 of the difference between the 90% particle size D90 and the 10% particle size D10 relative to the 50% particle size D50 in the volume-based particle size distribution of the expandable graphite is 0.85 or more and 1.4 or less. [6] The HIPE foam according to any one of [1] to [5], wherein the average bubble diameter of the HIPE foam is 20 μm or more and 200 μm or less.

[0012] According to the above embodiment, it is possible to provide a HIPE foam having high flame retardancy.

[0013] Figure 1 is an explanatory diagram showing an example of a low-vacuum scanning electron microscope image of HIPE foam. Figure 2 is an explanatory diagram showing an example of a temperature-storage modulus curve that shows the relationship between the temperature T and the storage modulus E' of HIPE foam.

[0014] (HIPE Foam) Preferred embodiments of HIPE foam are described below. HIPE foam as used herein is a porous polymer also known as polyHIPE foam, polyHIPE material, HIPE-derived foam material, high-internal-phase emulsion porous body, high-internal-phase emulsion foam, etc. HIPE foam is obtained, for example, by polymerizing monomers in an oil-in-water type high-internal-phase emulsion (i.e., HIPE) in which the aqueous phase is encapsulated in a high proportion within the organic phase. Furthermore, HIPE foam has a continuous cell structure in which numerous bubbles exist within the structure, and numerous through-pores are formed that connect adjacent bubbles.

[0015] HIPE foam is a porous polymer obtained, for example, by polymerizing vinyl monomers (specifically, acrylic monomers and / or styrene monomers) in a water-in-oil type high-internal-phase emulsion in which the aqueous phase is encapsulated in a high proportion in the organic phase. The term "polymerization" in this invention also includes copolymerization. HIPE foam is composed of 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 type high-internal-phase emulsion. Specifically, HIPE foam contains components derived from acrylic monomers and / or styrene monomers in the polymer backbone of the polymer. Furthermore, as will be described later, the polymer constituting HIPE foam may be crosslinked. HIPE foam composed of crosslinked polymers is produced, for example, by polymerizing acrylic monomers and / or styrene monomers in a high-internal-phase emulsion in the presence of a crosslinking agent.

[0016] Furthermore, HIPE foam is a porous cured product obtained by curing a high-internal-phase emulsion, and it can be said that its cell walls are composed of polymers (for example, vinyl polymers). These cells can also be called pores. The shape of the cell walls and cells in HIPE foam reflects the dispersion form of the organic phase and aqueous phase in the high-internal-phase emulsion during polymerization, as well as the shape of the aqueous phase (i.e., the dispersed phase) within the emulsion.

[0017] In the manufacturing process of the HIPE foam, the polymer is difficult to be stretched. Therefore, the HIPE foam generally has little molecular orientation and is a polymer with little anisotropy. The HIPE foam can be easily distinguished from foams in which the polymer is stretched during the manufacturing process, such as foams obtained by the extrusion foaming method using an extruder and foam particle molded bodies obtained by molding foam particles in a mold.

[0018] [Density] The density of the HIPE foam is 30 kg / m ３ or more and 350 kg / m ３ or less. By setting the density of the HIPE foam to 30 kg / m ３ or more, the strength of the HIPE foam can be easily improved. Also, in this case, the handleability of the HIPE foam can be improved. From the viewpoint of further enhancing such effects, the density of the HIPE foam is preferably 35 kg / m ３ or more, more preferably 40 kg / m ３ or more, and even more preferably 50 kg / m ３ or more.

[0019] Also, by setting the density of the HIPE foam to 350 kg / m ３ or less, the light weight of the HIPE foam can be improved. From the viewpoint of further enhancing such effects, the density of the HIPE foam is preferably 330 kg / m ３ or less, more preferably 300 kg / m ３ or less, and even more preferably 250 kg / m ３ or less.

[0020] In forming the preferable range of the density of the HIPE foam, the above-mentioned upper limit and lower limit of the density of the HIPE foam can be arbitrarily combined. For example, the preferable range of the density of the HIPE foam may be 35 kg / m ３ or more and 330 kg / m ３ or less, or 40 kg / m ３ or more and 300 kg / m ３ or less, or 50 kg / m ３ or more and <250 kg / m３ It may be as follows.

[0021] The density of the HIP foam described above is calculated by dividing the mass of the HIP foam by its volume. The volume of the HIP foam can be calculated based on its outer dimensions.

[0022] In the method for producing a HIP foam described later, the density of the HIP foam is adjusted to the above range by adjusting the ratio of the total amount of the vinyl monomer, crosslinking agent, emulsifier, and polymerization initiator to the amount of the aqueous phase (specifically, an aqueous liquid).

[0023] [Bubble Structure] The HIP foam is a porous polymer having a closed-cell structure as described above. As illustrated in FIG. 1, the HIP foam 1 has bubble walls 11 made of a polymer, and expandable graphite 12 is held inside the HIP foam 1. More specifically, expandable graphite 12 is dispersed and contained inside the HIP foam 1, and at least a part of the expandable graphite 12 is fixed by the bubble walls 11. Further, the HIP foam 1 has a bubble structure in which a large number of bubbles 13 are homogeneously present, and a closed-cell structure in which a large number of through-holes 14 that penetrate the bubble walls 11 and communicate between adjacent bubbles 13 are formed. Here, the bubble 13 is a portion surrounded by the bubble walls 11 in FIG. 1. The through-hole 14 is a hole that penetrates the bubble walls 11 and communicates between adjacent bubbles 13 in FIG. 1. Specifically, the through-hole 14 is formed in the bubble walls 11 and is a hole that communicates between adjacent bubbles 13 with the bubble walls 11 interposed therebetween. The through-hole 14 can also be referred to as a through-window or a connecting hole.

[0024] The average bubble diameter of the HIP foam is preferably 20 μm or more and 200 μm or less. By setting the average bubble diameter of the HIP foam within the specific range, the distribution of bubbles in the HIP foam can be made more uniform. As a result, the variation in the physical properties of the HIP foam can be further reduced.

[0025] The average bubble diameter described above is the average value of the equivalent circle diameters of the bubbles. The equivalent circle diameter of a bubble is the diameter of a perfect circle having the same area as the area of the bubble in the cross-section of the HIPE foam. The method for measuring the average bubble diameter will be described later. For example, it is measured by image analysis of the continuous bubble structure of the HIPE foam.

[0026] The average bubble diameter can be controlled by adjusting the droplet diameter of the aqueous phase (i.e., the dispersed phase) of the high internal phase emulsion in the method for producing the HIPE foam described later. For example, by reducing the droplet diameter, the bubble diameter can be made smaller.

[0027] 〔Polymer〕The HIPE foam is composed of a polymer of an acrylic monomer and / or a styrene monomer. In other words, the HIPE foam is composed of a polymer of a monofunctional vinyl monomer and has components derived from the monofunctional vinyl monomer. In this specification, vinyl monomers include monomers such as acrylic monomers and styrene monomers. As the vinyl monomer, an acrylic monomer and / or a styrene monomer can be used. More specifically, the HIPE foam may be composed of a polymer consisting only of components derived from an acrylic monomer, or may be composed of a polymer consisting only of components derived from a styrene monomer. Further, the HIPE foam may be composed of a copolymer having components derived from an acrylic monomer and components derived from a styrene monomer, or may be composed of a copolymer having at least one of the components derived from an acrylic monomer and components derived from a styrene monomer and other components.

[0028] The total of the proportion of the acrylic monomer and the proportion of the styrene monomer in the vinyl monomer is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0029] When seeking to obtain a relatively rigid HIPE foam, it is preferable that the HIPE foam be composed of a polymer of vinyl monomers mainly composed of styrene monomers. Specifically, the proportion of styrene monomers in the monofunctional vinyl monomer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0030] On the other hand, when seeking to obtain a relatively soft HIPE foam, it is preferable that the HIPE foam be composed of a polymer of vinyl monomers mainly composed of acrylic monomers. Specifically, the proportion of acrylic monomers in the monofunctional vinyl monomer is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0031] Examples of acrylic monomers include acrylic acid 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 acid 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.

[0032] As the acrylic monomer, it is preferable to use a (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group. When using a (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group as the acrylic monomer, it is preferable that the content of the (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group in the acrylic monomer is 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0033] Furthermore, as the (meth)acrylic acid ester having 3 to 10 carbon atoms in the hydrocarbon group, 2-ethylhexyl acrylate and / or butyl acrylate are preferred, and butyl acrylate is more preferred.

[0034] Examples of styrene monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-n-butylstyrene, p-t-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, sodium styrenesulfonate, and other styrene compounds.

[0035] Furthermore, it is preferable to use styrene as the styrene monomer. When styrene is used as the styrene monomer, it is preferable that the styrene content in the styrene monomer be 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0036] The polymer constituting HIPE foam may have components derived from a crosslinking agent in addition to the components derived from the vinyl monomers described above. In this specification, the term "crosslinking agent component" means a constituent unit derived from a crosslinking agent in a polymer. Furthermore, the term "crosslinking agent" means a compound that crosslinks (bonds) the polymer chains constituting the polymer, thereby forming a crosslinked structure within the polymer.

[0037] The polymer constituting the HIPE foam is preferably crosslinked. That is, the HIPE foam is preferably composed of a polymer of one or more vinyl monomers selected from the group consisting of acrylic monomers and styrene monomers, and a crosslinking agent described later. In other words, the polymer constituting the HIPE foam preferably has components derived from acrylic monomers and / or styrene monomers and components derived from the crosslinking agent. In this case, the balance between toughness and rigidity of the HIPE foam is improved.

[0038] From the viewpoint of making it easier to obtain HIPE foam having the desired physical properties, the mass ratio of the content of components derived from vinyl monomers to the content of components derived from the crosslinking agent in the crosslinked polymer is preferably 50:50 to 95:5, and more preferably 55:45 to 90:10.

[0039] As a crosslinking agent, for example, a vinyl compound having at least two functional groups selected from vinyl groups and isopropenyl groups in its molecule is used. By including components derived from the crosslinking agent in the polymer, the rigidity and toughness of the polymer can be increased. The vinyl compounds mentioned above also include compounds that contain vinyl groups and / or isopropenyl groups in the structure of their functional groups, such as acryloyl groups and methacryloyl groups. From the viewpoint of stably polymerizing the crosslinking agent, the number of functional groups in the vinyl compound is preferably six or less, preferably five or less, and more preferably four or less. Furthermore, from the viewpoint of making it easier to increase 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.

[0040] The polymer may be prepared using, for example, one type of crosslinking agent and may contain components derived from one type of crosslinking agent. From the viewpoint of increasing the rigidity of the polymer while also easily increasing its toughness, it is preferable that the polymer contains a hard crosslinking agent component derived from a hard crosslinking agent with relatively short molecular chains and a soft crosslinking agent component derived from a soft crosslinking agent with relatively long molecular chains. In this case, excessive embrittlement of the HIPE foam can be suppressed. The hard crosslinking agent can also be called the first crosslinking agent, and the soft crosslinking agent can also be called the second crosslinking agent.

[0041] As a hard crosslinking agent, a vinyl compound having a functional group equivalent of 130 g / eq or less is preferably used. By using such a hard crosslinking agent, the rigidity of HIPE foam can be increased more easily. This is thought to be because copolymerizing the hard crosslinking agent with a vinyl monomer reduces the mobility of the polymer molecular chains. From the viewpoint of obtaining this effect more reliably, it is more preferable that the functional group equivalent of the vinyl compound constituting the hard crosslinking agent is 120 g / eq or less.

[0042] On the other hand, from the viewpoint of facilitating the manufacture of HIPE foam, the lower limit of the functional group equivalent of the hard crosslinking agent is preferably 30 g / eq, more preferably 40 g / eq, even more preferably 50 g / eq, and particularly preferably 60 g / eq. The functional group equivalent of the hard crosslinking agent is the molar mass of the hard crosslinking agent per polymerizable functional group (i.e., vinyl group and isopropenyl group), and is obtained by dividing the molecular weight of the hard crosslinking agent by the number of polymerizable functional groups. Therefore, the unit of functional group equivalent can also be expressed as g / mol.

[0043] Examples of hard crosslinking agents include vinyl compounds such as 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.

[0044] These hard crosslinking agents may be used alone or in combination of two or more hard crosslinking agents. In other words, the hard crosslinking agent component contained in HIPE foam may be one type or two or more types. From the viewpoint of making it easier to adjust the rigidity of HIPE foam, it is preferable to use a hard crosslinking agent mainly composed of divinylbenzene and / or butanediol diacrylate, and more preferable to use a hard crosslinking agent mainly composed of divinylbenzene. The main component of the hard crosslinking agent means a component whose proportion in the hard crosslinking agent is 50% by mass or more. When divinylbenzene is included in the hard crosslinking agent, the proportion of divinylbenzene 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.

[0045] As a soft crosslinking agent, a vinyl compound having a functional group equivalent of more than 130 g / eq and 5000 g / eq or less can be preferably used. By using such a soft crosslinking agent, the toughness of HIPE foam can be more easily increased. This is thought to be because copolymerizing the soft crosslinking agent with a vinyl monomer allows for crosslinking of the polymer molecular chains without significantly reducing the mobility of the polymer molecular chains.

[0046] From the viewpoint of more reliably obtaining such effects, the functional group equivalent of the vinyl compound constituting the soft crosslinking agent is more preferably 4000 g / eq or less, and even more preferably 3000 g / eq or less. On the other hand, the lower limit of the functional group equivalent of the soft crosslinking agent is preferably 150 g / eq, more preferably 180 g / eq, even more preferably 200 g / eq, and particularly preferably 600 g / eq. The functional group equivalent of the soft crosslinking agent is the molar mass of the soft crosslinking agent per polymerizable functional group (i.e., vinyl group and isopropenyl group), and is obtained by dividing the molecular weight of the soft crosslinking agent by the number of polymerizable functional groups.

[0047] As soft crosslinking agents, for example, vinyl compounds such as 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 can be used. Examples of esters of polyhydric alcohols and (meth)acrylic acid include nonanediol (meth)acrylates such as nonanediol diacrylate and decanediol (meth)acrylates such as decanediol diacrylate. Examples of esters of polyether glycols and (meth)acrylic acid include 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, and polyglycerin (meth)acrylates such as polyglycerin diacrylate.

[0048] Examples of esters of urethane oligomers and (meth)acrylic acid include urethane (meth)acrylates such as urethane diacrylate. Examples of esters of epoxy oligomers and (meth)acrylic acid include epoxy (meth)acrylates such as epoxy diacrylate. In addition, as soft crosslinking agents, for example, polyester (meth)acrylates such as polyester diacrylate; (meth)acrylic modified silicones such as (meth)acrylic modified silicones at both ends; caprolactone modified isocyanurates such as caprolactone modified trisisocyanurate; and ethoxylated bisphenol A (meth)acrylates such as ethoxylated bisphenol A dimethacrylate can also be used. However, the number of functional groups in the soft crosslinking agent is two or more. The functional groups are preferably vinyl groups and / or isopropenyl groups.

[0049] These soft crosslinking agents may be used individually or in combination of two or more soft crosslinking agents. In other words, the soft crosslinking agent component contained in HIPE foam may be one type or two or more types. Among these, from the viewpoint of easily increasing the toughness of 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.

[0050] When HIPE foam is composed of a polymer of vinyl monomers mainly composed of styrene monomers, it is preferable to use a soft crosslinking agent mainly composed of polyethylene glycol di(meth)acrylate. In this case, the toughness of the HIPE foam can be further increased while maintaining its rigidity. The number of repeating structural units derived from ethylene glycol in polyethylene glycol di(meth)acrylate is preferably 3 to 23. The main component of the soft crosslinking agent refers to a component whose proportion in the soft crosslinking agent is 50% by mass or more. When polyethylene glycol di(meth)acrylate is included in the soft crosslinking agent, the proportion of polyethylene glycol di(meth)acrylate in 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.

[0051] When HIPE foam is composed of a polymer of vinyl monomers mainly composed of acrylic monomers, it is preferable to use a soft crosslinking agent mainly composed of epoxy (meth)acrylate from the viewpoint of easily improving the toughness and ductility of the HIPE foam. In this case, it is preferable that the epoxy (meth)acrylate contains a structure derived from bisphenol in its molecular structure, and more preferably a structure derived from bisphenol A. Furthermore, when epoxy (meth)acrylate is included in the soft crosslinking agent, the proportion of epoxy (meth)acrylate in 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.

[0052] When the polymer constituting the HIPE foam contains components derived from a hard crosslinking agent, the content of the components derived from the hard crosslinking agent in the polymer is preferably 1 to 15 parts by mass, more preferably 2 to 12 parts by mass, and even more preferably 3 to 9 parts by mass, based on 100 parts by mass of the total of the components derived from the vinyl monomer and the components derived from the crosslinking agent. In this case, the rigidity of the HIPE foam can be increased more easily.

[0053] When HIPE foam is composed of a polymer of vinyl monomers mainly consisting of styrene monomers, and the polymer contains components derived from a soft crosslinking agent, the content of the components derived from the soft crosslinking agent in the polymer is preferably 2 parts by mass or more and 10 parts by mass or less, and more preferably 3 parts by mass or more and 8 parts by mass or less, based on 100 parts by mass of the total of the components derived from the vinyl monomers and the components derived from the crosslinking agent. In this case, it is easier to avoid excessive embrittlement of the HIPE foam while maintaining its rigidity.

[0054] When HIPE foam is composed of a polymer of vinyl monomers mainly composed of acrylic monomers, and the polymer contains components derived from a soft crosslinking agent, the content of the components derived from the soft crosslinking agent in the polymer is preferably 3 parts by mass or more and 60 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and even more preferably 10 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the total of the components derived from the vinyl monomers and the components derived from the crosslinking agent. In this case, the toughness and ductility of the HIPE foam can be more easily improved.

[0055] When the polymer constituting HIPE foam contains components derived from a crosslinking agent, the molecular weight between crosslinking points of the polymer is 0.1 × 10⁻⁶. 5 The above 3 x 10 5 Preferably, it is 0.2 × 10 5 The above 2 x 10 5 The following is more preferable. The molecular weight between crosslinking points serves as an indicator of the degree of crosslinking of the polymer constituting the HIPE foam. By keeping the molecular weight between crosslinking points within the aforementioned specific range, excessive embrittlement of the HIPE foam can be easily avoided, and the handling properties of the HIPE foam can be further improved. The molecular weight between crosslinking points is obtained by performing dynamic viscoelasticity measurements under the conditions of frequency: 1 Hz, load: 20 mN, and deformation mode: compression. A more detailed method for measuring the molecular weight between crosslinking points will be described later.

[0056] When the HIPE foam is composed of a polymer of vinyl monomers mainly composed of styrene monomers, the glass transition temperature Tg of the polymer constituting the HIPE foam is preferably 40°C to 150°C, more preferably 50°C to 140°C, and even more preferably 60°C to 130°C. In this case, a HIPE foam that is rigid and exhibits excellent rigidity even at relatively high temperatures can be obtained.

[0057] When the HIPE foam is composed of a polymer of vinyl monomers mainly composed of acrylic monomers, the glass transition temperature Tg of the polymer constituting the HIPE foam is preferably -30°C to 20°C, more preferably -25°C to 10°C, and even more preferably -20°C to 0°C. In this case, a HIPE foam that is both flexible and has good ductility can be obtained.

[0058] The glass transition temperature Tg of the polymer constituting HIPE foam is specifically the intermediate glass transition temperature obtained by differential scanning calorimetry (DSC) based on JIS K7121:1987. For conditioning the test specimen in measuring the glass transition temperature Tg, the conditions described in "(3) When measuring the glass transition temperature after performing a certain heat treatment" are adopted.

[0059] [Expandable Graphite] HIPE foam contains expandable graphite. Expandable graphite refers to graphite configured to expand in volume when heated. More specifically, expandable graphite has a structure in which intercalation compounds are inserted between layers of graphite, such as flake graphite, and can expand when heated by the volatilization of the intercalation compounds. Expandable graphite can be obtained, for example, by treating graphite with an inorganic acid such as concentrated sulfuric acid, nitric acid, or selenic acid, and a strong oxidizing agent such as concentrated nitric acid, perchloric acid, perchlorate, permanganate, dichromate, or hydrogen peroxide to generate intercalation compounds between the layers of graphite. Commercially available expandable graphite can be used as the expandable graphite used in this invention. Furthermore, the expandable graphite of this invention also includes those distributed as expandable graphite, expanded graphite, etc., and can be suitably used as expandable graphite if, for example, the 1% weight loss temperature measured by the method described later falls within the range described later.

[0060] The amount of expandable graphite in the HIPE foam is 3% by mass or more and 25% by mass or less. By incorporating 3% by mass or more of expandable graphite into the HIPE foam, the flame retardancy of the HIPE foam can be improved. The reasons why expandable graphite improves the flame retardancy of the HIPE foam include, for example, that the expansion of the expandable graphite can suppress heat transfer within the HIPE foam, and that the vaporization of interlayer compounds when the expandable graphite is heated is an endothermic reaction, which can lower the temperature of the combustible material during expansion.

[0061] If the amount of expandable graphite in the HIPE foam is too low, it may lead to a decrease in the flame retardancy of the HIPE foam. From the viewpoint of further improving the flame retardancy of the HIPE foam, the amount of expandable graphite in the HIPE foam is preferably 4% by mass or more, more preferably 5% by mass or more, and even more preferably 6% by mass or more.

[0062] On the other hand, if the amount of expandable graphite in the HIPE foam is too high, the stability of the high internal phase emulsion (HIPE) may decrease during the manufacturing process of the HIPE foam described later, which may make it difficult to form the HIPE foam. This problem can be easily avoided by setting the amount of expandable graphite in the HIPE foam to 25% by mass or less, preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less.

[0063] In determining the preferred range for the amount of expandable graphite in the HIPE foam, the upper and lower limits of the amount of expandable graphite mentioned above can be arbitrarily combined. For example, the preferred range for the amount of expandable graphite in the HIPE foam may be 4% by mass or more and 20% by mass or less, 5% by mass or more and 18% by mass or less, or 6% by mass or more and 15% by mass or less.

[0064] The 1% weight loss temperature of expandable graphite, as measured by thermogravimetric analysis, is preferably between 130°C and 250°C, more preferably between 150°C and 230°C, even more preferably between 155°C and 220°C, particularly preferably between 158°C and 210°C, and most preferably between 160°C and 200°C. The 1% weight loss temperature of expandable graphite corresponds to the temperature at which expansion of the expandable graphite begins. Expandable graphite having a 1% weight loss temperature within the above-mentioned specific range can easily expand during the combustion of HIPE foam. Therefore, in this case, the flame retardancy of the HIPE foam can be further improved.

[0065] The method for measuring the 1% weight loss temperature of expandable graphite is as follows: First, approximately 10 mg of expandable graphite is placed in a sample pan, and the sample pan is placed in the furnace of a thermogravimetric analyzer (for example, Hitachi High-Tech Science Co., Ltd.'s "TG / DTA 7200"). The atmosphere inside the furnace is air. Then, the temperature inside the furnace is raised to 40°C and maintained at this temperature until the mass of the expandable graphite stabilizes. From the point when the mass of the expandable graphite stabilizes, the temperature inside the furnace is raised at a heating rate of 10°C / min to obtain the thermogravimetric curve of the expandable graphite. Then, using the weight of the expandable graphite at the start of the temperature rise inside the furnace as a reference, the temperature at which the weight of the expandable graphite decreases by 1% is defined as the 1% weight loss temperature of the expandable graphite.

[0066] The 1% weight loss temperature of expansive graphite can be adjusted by changing the type and content of intercalation compounds. For example, if the boiling point of the intercalation compounds contained in expansive graphite is high, the 1% weight loss temperature tends to be higher.

[0067] When expandable graphite is heated at 400°C for 5 minutes, the expansion ratio of the expandable graphite is preferably 20 cc / g or more, more preferably 25 cc / g or more, even more preferably 30 cc / g or more, particularly preferably 40 cc / g or more, and most preferably 50 cc / g or more. The expansion ratio of expandable graphite is an indicator of how much the expandable graphite expands upon heating. By setting the expansion ratio of the expandable graphite within the above-mentioned specific range, good flame retardancy can be more stably imparted to the HIPE foam. From the viewpoint of flame retardancy of the HIPE foam, there is no upper limit to the expansion ratio of the expandable graphite, but the upper limit of the expansion ratio of the expandable graphite may be, for example, 150 cc / g, 130 cc / g, 110 cc / g, or 100 cc / g.

[0068] In determining a preferred range for the expansion ratio of expandable graphite, the upper and lower limits of the expansion ratio of expandable graphite described above can be arbitrarily combined. For example, the preferred range for the expansion ratio of expandable graphite may be 20 cc / g or more and 150 cc / g or less, 25 cc / g or more and 150 cc / g or less, 30 cc / g or more and 150 cc / g or less, 40 cc / g or more and 130 cc / g or less, 50 cc / g or more and 110 cc / g or less, or 50 cc / g or more and 100 cc / g or less.

[0069] The method for measuring the expansion ratio of expandable graphite is as follows: First, a stainless steel container (internal volume 1 L) is heated in a furnace set to 400°C for 5 minutes. Next, approximately 1 g of expandable graphite is accurately weighed and placed in the container, then heated at 400°C for 5 minutes to expand the expandable graphite. The expanded graphite is placed in a graduated cylinder, and its bulk volume is measured based on the scale of the graduated cylinder. The expansion ratio of the expandable graphite is then obtained by dividing the bulk volume of the expanded graphite (unit: cc) by the mass of the expandable graphite (unit: g). The expansion ratio of expandable graphite can be adjusted by changing the content and type of intercalation compounds, the particle size of the expandable graphite, etc.

[0070] In the volume-based particle size distribution of expandable graphite, the 50% particle size D50 is preferably 50 μm to 1000 μm, more preferably 100 μm to 950 μm, even more preferably 150 μm to 900 μm, particularly preferably 200 μm to 850 μm, and most preferably 250 μm to 800 μm. In this case, during the manufacturing process of HIPE foam, poor dispersion of the aqueous phase is less likely to occur, and the stability of the high-internal-phase emulsion can be further enhanced. As a result, HIPE foam having the desired cellular structure and good flame retardancy can be obtained more easily.

[0071] Furthermore, in the volume-based particle size distribution of expandable graphite, the ratio (D90-D10) / D50, which is the difference between the 90% particle size D90 and the 10% particle size D10 relative to the 50% particle size D50, is preferably 0.85 or more and 1.4 or less, and more preferably 0.85 or more and 1.3 or less. (D90-D10) / D50 is an indicator of the particle size distribution of expandable graphite, and the smaller the value, the narrower the particle size distribution. Expandable graphite with (D90-D10) / D50 within the above range has an appropriate breadth in its particle size distribution. By using such expandable graphite, the deterioration of the mechanical properties of the HIPE foam due to the addition of expandable graphite becomes less likely. As a result, HIPE foam with good mechanical properties can be stably obtained.

[0072] The volume-based particle size distribution of expandable graphite is measured using a laser diffraction / scattering particle size distribution analyzer (for example, the "MT3000" manufactured by Microtrac-Bell Co., Ltd.). Furthermore, the 50% particle size D50 refers to the particle size at which the cumulative frequency of particles with smallest particle size accounts for 50% in the aforementioned volume-based particle size distribution. Similarly, the 10% particle size D10 refers to the particle size at which the cumulative frequency of particles with smallest particle size accounts for 10% in the aforementioned volume-based particle size distribution, and the 90% particle size D90 refers to the particle size at which the cumulative frequency of particles with smallest particle size accounts for 90% in the aforementioned volume-based particle size distribution.

[0073] [Applications] 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, or core material for vacuum insulation.

[0074] Furthermore, the HIPE foam may be used as a cutting material for manufacturing machined parts by machining. Examples of machined parts include architectural models of buildings, mechanical models of machinery and equipment, vehicle models of cars and trains, casting models for making casting sand molds called casting patterns, art models of works of art and exhibits, and various other models such as pre-made product models. Such model materials are manufactured by machining the workpiece (i.e., the material to be machined).

[0075] (Method for manufacturing HIPE foam) HIPE foam is obtained by polymerizing a water-in-oil high-internal-phase emulsion. The organic phase of the water-in-oil high-internal-phase emulsion is a continuous phase containing vinyl monomers such as acrylic monomers and / or styrene monomers, crosslinking agents, emulsifiers, polymerization initiators, etc., and the aqueous phase is a dispersed phase containing water such as deionized water. Expandable graphite is also dispersed in the high-internal-phase emulsion.

[0076] HIPE foam comprises, for example, an emulsification step of forming a water-in-oil high-internal-phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and / or a styrene monomer, expandable graphite, an emulsifier, and a polymerization initiator; a polymerization step of polymerizing the acrylic monomer and / or styrene monomer in the water-in-oil high-internal-phase emulsion filled in a reaction vessel; and a drying step of drying the water in the polymerization product obtained in the polymerization step.

[0077] [Emulsification Process] The specific form of the emulsification process is not particularly limited, and various forms can be adopted. For example, in the emulsification process, an oily liquid (organic phase) containing organic substances such as acrylic monomers and / or styrene monomers, expandable graphite, emulsifiers, and polymerization initiators may be stirred while an aqueous liquid (aqueous phase) containing water is dropped into the oily liquid to disperse the aqueous phase in the organic phase and produce the water-in-oil high-internal-phase emulsion. When a crosslinking agent is used, it is preferable to blend the crosslinking agent into the organic phase. According to the above emulsification method, expandable graphite can be dispersed more easily in the high-internal-phase emulsion. As a result, it becomes easier to produce HIPE foam with the desired physical properties.

[0078] In the emulsification process, a high-internal-phase emulsion can be prepared by adding an aqueous liquid to an oily liquid such 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 encapsulated in the organic phase can be adjusted by 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 300 parts by mass or more and 3000 parts by mass or less, more preferably 400 parts by mass or more and 2500 parts by mass or less, and even more preferably 500 parts by mass or more and 2000 parts by mass or less, per 100 parts by mass of the organic phase.

[0079] In the emulsification process, expandable graphite is added to the HIPE foam so that its amount falls within the range described above. The amount of expandable graphite in the high internal phase emulsion is preferably 3% to 25% by mass, more preferably 4% to 20% by mass, even more preferably 5% to 18% by mass, and particularly preferably 6% to 15% by mass, when the total amount of acrylic monomers and / or styrene monomers, crosslinking agents, and expandable graphite is taken as 100% by mass.

[0080] For detailed information regarding the composition of the expandable graphite used in the emulsification process, please refer to the description of the expandable graphite contained in HIPE foam mentioned above. Furthermore, for detailed information regarding the composition of the acrylic monomer, styrene monomer, and crosslinking agent used in the emulsification process, please refer to the descriptions of the corresponding components in the polymers constituting HIPE foam mentioned above.

[0081] The stirring speed in the emulsification process is not particularly limited, but for example, if the stirring power density is 0.01 kW / m 3 10kW / m or more 3 The following range can be appropriately set: Stirring power density in the emulsification process (unit: kW / m³) 3 The power (in kW) during stirring is calculated from the torque (in N·m) and rotational speed (in rpm) of the stirring device used in the emulsification process, and this power is used to calculate the volume (in m³) of the contents of the container in the emulsification process. 3 It can be found by dividing by ).

[0082] The method of adding aqueous liquid to oily liquid in the emulsification process is not particularly limited, but methods such as starting stirring with both oily and aqueous liquids in a stirring container and performing emulsification, or starting stirring with only oily liquid in a stirring container and then adding aqueous liquid to the container using a pump or the like while stirring is performed to perform emulsification, can be employed. When adding aqueous liquid using a pump or the like, the rate of addition of aqueous liquid is not particularly limited, but can be adjusted, for example, in the range of 10% by mass / min to 1000% by mass / min relative to 100% by mass of oily liquid. Furthermore, the specific form of the emulsification process is not particularly limited, and various forms can be employed, such as a batch-type emulsification process using a stirring container equipped with a stirring device or a centrifugal shaker, or a continuous-type emulsification process in which oily and aqueous liquids are continuously supplied and mixed in a line equipped with a static mixer or mesh, etc.

[0083] The aqueous phase may contain water such as deionized water, polymerization initiators, electrolytes, etc. In the emulsification process, for example, an oily liquid and an aqueous liquid are prepared separately, and the aqueous liquid is added to the oily liquid under stirring to produce a high-internal-phase emulsion. In addition, in the emulsification process, additives such as flame retardants, flame retardant aids, lightfasteners, and colorants may be appropriately added to the aqueous phase and / or organic phase, as long as they do not impair the effects described above.

[0084] Polymerization initiators are used to initiate the polymerization of vinyl monomers. Radical polymerization initiators can be used as polymerization initiators. 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 peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneoheptanoate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecano Organic peroxides such as eth, di(2-ethylhexyl)peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, and benzoyl peroxide; azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'azobis(4-dimethylvaleronitrile), dimethyl2,2'azobis(2-methylpropionate), and 2,2'azobis(2-methylbutyronitrile) can be used. These polymerization initiators may be used alone or in combination of two or more polymerization initiators.

[0085] From the viewpoint of shortening the polymerization time without reducing the density uniformity of the HIPE foam, it is preferable that the polymerization initiator added to the high internal phase emulsion contains a polymerization initiator with a 1-hour half-life temperature of 50°C or higher and less than 70°C, and an organic peroxide with a 1-hour half-life temperature of 70°C or higher and 90°C or lower.

[0086] Polymerization initiators can be added to the organic phase and / or the aqueous phase. When a polymerization initiator is added to the aqueous phase, water-soluble polymerization initiators 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 polymerization initiator added can be, for example, in the range of 0.1 parts by mass to 5 parts by mass per 100 parts by mass of the total of the vinyl monomer and the crosslinking agent.

[0087] Emulsifiers are used for the formation and stabilization of high-internal-phase emulsions. Examples of emulsifiers include surfactants. Specifically, glycerol esters such as polyglycerol condensed ricinolate, polyglycerol stearate, polyglycerol oleate, polyglycerol laurate, and polyglycerol myristate; sorbitol esters such as sorbitan oleate, sorbitan stearate, sorbitan laurate, 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, between 1 and 30 parts by mass per 100 parts by mass of the total of the vinyl monomer, crosslinking agent, and emulsifier.

[0088] Electrolytes are used to impart ionic strength to the aqueous phase and enhance the stability of the emulsion. Water-soluble electrolytes 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 electrolyte added can be, for example, in the range of 0.01 parts by mass to 10 parts by mass per 100 parts by mass of aqueous liquid.

[0089] [Polymerization Process] In the polymerization process, the water-in-oil high-internal-phase emulsion is filled into a reaction vessel, and then the acrylic monomer and / or styrene monomer are polymerized in the reaction vessel. In the polymerization process, for example, the acrylic monomer and / or styrene monomer as vinyl monomers can be polymerized by heating the high-internal-phase emulsion in the reaction vessel to obtain a polymerization product (specifically, a polymer containing water). If a crosslinking agent is added to the organic phase in the polymerization process, the polymer chains constituting the polymer are crosslinked (bonded) by the crosslinking agent. As a result, a crosslinked structure is formed in the polymer. Suitable heating methods for the high-internal-phase emulsion in the polymerization process include heating with a heat transfer fluid such as hot water, or heating with electromagnetic waves such as high frequency and microwaves. By adopting these heating methods, the polymerization of vinyl monomers can be completed earlier, making it easier to produce HIPE foam with the desired density ratio.

[0090] The polymerization temperature in the polymerization process is adjusted, for example, by the type of vinyl polymer, the type of polymerization initiator, the type of crosslinking agent, etc. The polymerization temperature may be in the range of, for example, 50°C to 90°C.

[0091] [Drying Process] HIPE foam can be obtained by removing water from the polymerization product obtained as described above, that is, from the water-containing polymer. In the drying process, the polymerization product is dried using an oven, vacuum dryer, high-frequency / microwave dryer, etc. Once drying is complete, the areas where there were water droplets in the emulsion before polymerization become bubbles in the polymer after drying, and HIPE foam can be obtained. Before drying, the polymerization product can be dehydrated by pressing, for example, using a press. Pressing may 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 constituting the HIPE foam, for example. In this case, dehydration by pressing becomes easier, and the drying time can be shortened. Dehydration of the polymer can also be performed by centrifugal separation. In this case as well, the drying time can be shortened.

[0092] As described above, the HIPE foam of the present invention can be manufactured, for example, by the following method: an emulsification step of forming a water-in-oil high-internal-phase emulsion in which an aqueous phase containing water is encapsulated in an organic phase containing an acrylic monomer and / or a styrene monomer, expandable graphite, and a polymerization initiator; and a polymerization step of polymerizing the acrylic monomer and / or a styrene monomer in the water-in-oil high-internal-phase emulsion, wherein the content of the aqueous phase in the high-internal-phase emulsion is 300 parts by mass or more and 3000 parts by mass or less per 100 parts by mass of the organic phase, and the amount of expandable graphite in the high-internal-phase emulsion is 3% by mass or more and 25% by mass or less when the sum of the amount of acrylic monomer and / or styrene monomer, the amount of crosslinking agent, and the amount of expandable graphite is 100% by mass.

[0093] Examples of the HIPE foam described above are explained below. The acrylic monomers, styrene monomers, crosslinking agents, emulsifiers, and polymerization initiators used in the examples and comparative examples, and their abbreviations, are as follows.

[0094] (Vinyl monomers) St: Styrene BA: Butyl acrylate

[0095] (Crosslinking agent) DVB: Divinylbenzene (DVB-570 manufactured by Nippon Steel Chemical & Material Co., Ltd., functional group equivalent 65 g / eq) PEGDA: Polyethylene glycol diacrylate (NK Ester A-400 manufactured by Shin Nakamura Chemical Industry Co., Ltd., functional group equivalent 254 g / eq) EpDA: Epoxy diacrylate (specifically, acrylic-modified epoxy prepolymer at both ends, EBECRYL® 3708 manufactured by Daicel Ornex Co., Ltd., 750 g / eq)

[0096] (Emulsifier) ​​PGPR: Polyglycerin condensed ricinolate (CRS-75, manufactured by Sakamoto Pharmaceutical Co., Ltd.)

[0097] (Polymerization initiators) LPO: Dilauroyl peroxide ("Perloyl® L" manufactured by NOF Corporation, 1.5-hour half-life temperature: 79.5°C) LTCP: Bis(4-t-butylcyclohexyl) peroxydicarbonate ("Perloyl TCP" manufactured by NOF Corporation, 1.5-hour half-life temperature: 57.5°C)

[0098] (Expandable Graphite) EG1: "953240L" manufactured by Ito Graphite Industry Co., Ltd. EG2: "EXP-80S220" manufactured by Fuji Graphite Industry Co., Ltd. EG3: "EXP-32S160" manufactured by Fuji Graphite Industry Co., Ltd. EG4: "EXP-50HO" manufactured by Fuji Graphite Industry Co., Ltd. EG5: "EXP-50SL" manufactured by Fuji Graphite Industry Co., Ltd. EG6: "EXP-200S" manufactured by Fuji Graphite Industry Co., Ltd. EG7: "EXP-50S120K" manufactured by Fuji Graphite Industry Co., Ltd.

[0099] Table 1 shows the physical properties of the expandable graphite used in the examples and comparative examples.

[0100]

[0101] The 10% particle size D10, 50% particle size D50, and 90% particle size D90 in Table 1 are values ​​calculated based on the volume-based particle size distribution of expandable graphite. The detailed measurement conditions for the particle size distribution are as follows.

[0102] • Measurement device: Laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell Co., Ltd. "MT3000") • Measurement method: Wet method • Measurement mode: Transmission • Solvent: Pure water • Refractive index of measurement sample: 1.81 • Flow rate: 50% • Ultrasonic treatment: 20W, 1 second • Degassing: 2 times

[0103] The 1% weight loss temperature of expandable graphite in Table 1 was measured as follows. First, approximately 10 mg of expandable graphite was placed in a sample pan, and the sample pan was placed in the furnace of a thermogravimetric analyzer (Hitachi High-Tech Science Co., Ltd. "TG / DTA 7200"). The atmosphere inside the furnace was air. Then, the temperature inside the furnace was raised to 40°C and maintained at this temperature until the mass of the expandable graphite stabilized. From the point when the mass of the expandable graphite stabilized, the temperature inside the furnace was increased at a heating rate of 10°C / min, and the thermogravimetric curve of the expandable graphite was obtained. Then, using the weight of the expandable graphite at the start of the temperature increase inside the furnace as the baseline, the temperature at which the weight of the expandable graphite decreased by 1% was defined as the 1% weight loss temperature of the expandable graphite.

[0104] Furthermore, the expansion ratio of the expandable graphite in Table 1 was measured as follows. First, a stainless steel container (internal volume 1 L) was heated for 5 minutes in a heating furnace (Yamato Scientific FO610) set to 400°C. Next, approximately 1 g of expandable graphite was accurately weighed and placed in the container, and heated at 400°C for 5 minutes to expand the expandable graphite. The expanded graphite was placed in a graduated cylinder, and the bulk volume of the expanded graphite was measured based on the scale of the graduated cylinder. Then, the expansion ratio of the expandable graphite was obtained by dividing the bulk volume of the expanded graphite (unit: cc) by the mass of the expandable graphite (unit: g).

[0105] (Example 1) In this example, HIPE foam was manufactured by the following method. First, 55.5 parts by mass of butyl acrylate as an acrylic monomer, 4 parts by mass of divinylbenzene and 30 parts by mass of epoxy diacrylate as crosslinking agents, 7.5 parts by mass of polyglycerin condensed ricinolate as an emulsifier, 0.5 parts by mass of dilauroyl peroxide and 0.5 parts by mass of bis(4-t-butylcyclohexyl) peroxydicarbonate as polymerization initiators, and EG1 as expandable graphite were placed in a glass container with a volume of 3 L equipped with a torque converter stirrer. The amount of expandable graphite was as shown in Table 2. By mixing these in the glass container, an organic phase containing expandable graphite was formed.

[0106] Next, the stirring power density is 0.03 kW / m². 3While stirring the organic phase, 1900 parts by mass of pure water at 20°C was added to the glass container at a rate of approximately 450 g / min. By continuing stirring for 10 minutes after the addition of pure water was completed, a water-in-oil (W / O) high-internal-phase emulsion was prepared. The stirring power density (unit: kW / m) was also measured. 3 The power (in kW) is calculated from the torque (in N·m) and rotational speed (in rpm) of the stirring device, and this power is then used to determine the volume (in m³) of the contents of the container. 3 It can be found by dividing by ).

[0107] Next, an aspirator was connected to the glass container to reduce the pressure inside the container, thereby removing microbubbles from the emulsion. Ten minutes after the start of reduced pressure, stirring was stopped and the pressure inside the container was returned to atmospheric pressure. During the entire process, from the start to the end of stirring, the temperature inside the glass container was maintained at 20°C using a chiller.

[0108] The resulting high-internal-phase emulsion was filled into a polymerization mold approximately 250 mm long, 400 mm wide, and 60 mm deep. The polymerization mold was then placed in a constant-temperature water bath set to 70°C and heated in the bath for approximately 10 hours to polymerize the vinyl monomers and crosslinking agent in the high-internal-phase emulsion, forming a HIPE foam containing water in the reaction vessel.

[0109] Next, the polymerization mold was removed from the constant-temperature water bath and the HIPE foam was cooled. Then, the HIPE foam was removed from the polymerization mold and washed with water. The washed HIPE foam was dried in an oven set to 90°C until a constant weight was reached. In this way, a rectangular parallelepiped HIPE foam was obtained, composed of a polymer of an acrylic monomer (butyl acrylate) as a vinyl monomer.

[0110] Table 2 shows the composition of the mixture used in this example. The content of various components (vinyl monomers and crosslinking agents) in the HIPE foam can be determined from the amount of each component blended at the time of mixing (for crosslinking agents, the amount excluding impurities) and the total amount of vinyl monomer components and crosslinking agent components (excluding impurities).

[0111] (Examples 2-4) The HIPE foams of these examples have the same configuration as the HIPE foam of Example 1, except that the amount of expandable graphite is changed as shown in Table 2. The manufacturing method of the HIPE foams of Examples 2-4 is generally the same as the manufacturing method of the HIPE foam of Example 1, except that the amount of expandable graphite is changed as shown in Table 2.

[0112] (Examples 5-10) The HIPE foams of these examples have the same configuration as the HIPE foam of Example 1, except that they contain the expandable graphite shown in Table 2 or Table 3 instead of EG1. The manufacturing method of the HIPE foams of Examples 5-10 is the same as the manufacturing method of the HIPE foam of Example 1, except that the expandable graphite shown in Table 2 or Table 3 is used.

[0113] (Example 11) The HIPE foam of Example 11 has the same structure as the HIPE foam of Example 1, except that it is composed of a polymer of a styrene monomer (specifically styrene), uses only divinylbenzene as a crosslinking agent, and the amounts of the crosslinking agent and the amount of expandable graphite are changed as shown in Table 3. The method for producing the HIPE foam of Example 11 is generally the same as the method for producing the HIPE foam of Example 1, except that the composition of the organic phase and the amount of expandable graphite are changed as shown in Table 3.

[0114] (Example 12) The HIPE foam of Example 12 has the same structure as the HIPE foam of Example 1, except that it is composed of a polymer of a styrene monomer (styrene) and an acrylic monomer (butyl acrylate), that divinylbenzene and polyethylene glycol diacrylate are used as crosslinking agents, and that the amount of crosslinking agent is changed as shown in Table 3. The method for producing the HIPE foam of Example 12 is the same as the method for producing the HIPE foam of Example 1, except that the composition of the organic phase is changed as shown in Table 3.

[0115] (Comparative Example 1) The HIPE foam of Comparative Example 1 has the same composition as the HIPE foam of Example 1, except that it does not contain expandable graphite. The method for manufacturing the HIPE foam of Comparative Example 1 is the same as the method for manufacturing the HIPE foam of Example 1, except that expandable graphite was not incorporated.

[0116] (Comparative Example 2) The HIPE foam of Comparative Example 2 has the same configuration as the HIPE foam of Example 1, except that the amount of expandable graphite is changed as shown in Table 3. The method for manufacturing the HIPE foam of Comparative Example 2 is the same as the method for manufacturing the HIPE foam of Example 1, except that the amount of expandable graphite is changed as shown in Table 3.

[0117] (Comparative Example 3) The HIPE foam of Comparative Example 3 has the same composition as the HIPE foam of Example 2, except that it contains a brominated flame retardant (2,2-bis(4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl)propane ("SR-130" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.)) instead of expandable graphite. The method for manufacturing the HIPE foam of Comparative Example 3 is generally the same as the method for manufacturing the HIPE foam of Example 2, except that it does not contain expandable graphite and the brominated flame retardant is added in the ratios shown in Table 3.

[0118] Next, we will explain the evaluation methods for each physical property shown in Tables 2 and 3.

[0119] (Target density and density of HIPE foam) Three test specimens were cut from the center of the HIPE foam, excluding the skin surface, i.e., the surface that was in contact with the polymerization type during the polymerization of the high-internal-phase emulsion. The length of each test specimen was 50 mm, the width was 50 mm, and the thickness was 25 mm. The mass (in kg) of these test specimens was calculated from the volume (in m) calculated from the external dimensions. ３ By dividing by ), the density of each test specimen (unit: kg / m³) can be calculated. ３ The density of the HIPE foam was calculated. The arithmetic mean of the densities of these three test specimens was then taken as the density of the HIPE foam. In addition, the "Target Density" column in Tables 2 and 3 shows the density of the HIPE foam expected from the filling ratio of the high internal phase emulsion.

[0120] (Average bubble diameter) Three observation samples were cut from the HIPE foam using a feather blade, ensuring that the skin surface was not included. One of the three samples contained a portion of the rectangular hiPE foam that was located 1 cm inward from one end in the longitudinal direction toward the longitudinal center, and was central in both the short-side and thickness directions. The remaining two samples contained portions that were located 1 cm inward from one end in the longitudinal direction toward the longitudinal center, and were 1 cm inward from both ends in the short-side direction toward the short-side center, and were central in the thickness direction. These three samples were observed using a low-vacuum scanning electron microscope ("Miniscope™ TM3030Plus" manufactured by Hitachi High-Tech Science Corporation), and cross-sectional images were taken. Figure 1 shows an example of a cross-sectional image of the HIPE foam. The detailed observation conditions were as follows.

[0121] • Sample pretreatment: The sample was treated for conductivity using a metal coating apparatus (MSP-1S, manufactured by Vacuum Device Co., Ltd.). Au-Pd was used as the target electrode. • Observation magnification: 100x • Acceleration voltage: 5kV • Observation conditions: Surface (low magnification) • Observation mode: Secondary electrons (standard)

[0122] Next, the captured cross-sectional images were imported into image processing software ("NanoHunter NS2K-Pro" manufactured by NanoSystem Co., Ltd.), and the following analysis was performed. First, the total area of ​​each sample was placed on the cross-sectional image. 2 The measurement area was set as described above. When setting the measurement area, care was taken to minimize the inclusion of expansive graphite appearing in the cross-sectional photographs. Next, the bubble diameters (equivalent circular diameters) of the bubbles within the measurement area were calculated. The arithmetic mean of these values ​​was then used as the bubble diameter for each sample. Furthermore, the arithmetic mean of the bubble diameters of the three samples was calculated, and this value was used as the average bubble diameter of the HIPE foam. The detailed analysis procedure and conditions are as follows.

[0123] (1) Monochrome conversion (2) Smoothing filter (3x3, 8 neighbors, processing count = 1) (3) Density unevenness correction (brighter than background, size = 5) (4) NS method binarization (darker than background, sharpness = 9, sensitivity = 1, noise reduction, density range = 0 to 255) (5) Shrinkage (8 neighbors, processing count = 1) (6) Image selection by feature quantity (area) (50 to ∞ μm) 2 (7) Only selected, 8 neighbors) (8) Expansion that is not connected to neighbors (8 neighbors, number of processing steps = 3) (8) Circular diameter measurement (calculated from area, 8 neighbors)

[0124] (Glass Transition Temperature) The glass transition temperature was calculated by differential scanning calorimetry (i.e., DSC) analysis based on JIS K7121:1987. A DSC250 manufactured by T.A. Instrument Japan Co., Ltd. was used as the measuring device. Specifically, first, a test specimen of approximately 2 mg was taken from near the center of the HIPE foam. This test specimen was conditioned according to "(3) When measuring the glass transition temperature after performing a certain heat treatment". Specifically, the collected test specimen was left standing for more than 24 hours in a constant temperature and humidity chamber at a temperature of 23°C and a humidity of 50%. Next, the test specimen was heated at a heating rate of 10°C / min to a temperature approximately 30°C higher than the temperature at which the glass transition was completed, held at this temperature for 10 minutes, and then cooled at a cooling rate of 10°C / min to a temperature approximately 50°C lower than the glass transition temperature. After cooling, the device was stabilized by holding it at this temperature for 10 minutes. Then, a DSC curve was obtained by performing DSC measurements at a heating rate of 20°C / min up to a temperature approximately 30°C higher than the temperature at which the glass transition was completed. The midpoint glass transition temperature was determined from this DSC curve and this value was defined as the glass transition temperature.

[0125] (Molecular weight between crosslinking points) The molecular weight between crosslinking points was measured using the HIPE foam obtained in Examples 3, 5, and 11 by the following method. Three test pieces were cut from near the center of the HIPE foam, excluding the skin surface. The test pieces had a rectangular parallelepiped shape with dimensions of 10 mm in length, 10 mm in width, and 7 mm in thickness. Dynamic viscoelasticity measurements (DMA) were performed by applying a load to a 10 mm x 10 mm surface of these three test pieces, and T-E' curves were obtained in the temperature range of -100 to 200°C. Figure 2 shows an example of the T-E' curve of the HIPE foam. The T-E' curve is obtained by plotting temperature on the horizontal axis and the storage modulus E' on the vertical axis. A DMA7100 manufactured by Hitachi High-Tech Science Corporation was used as the measuring device. The details of the measurement conditions are as follows: ・Deformation mode: Compression ・Temperature: -100 to 200°C ・Heating rate: 5°C / min ・Frequency: 1 Hz ・Load: 20 mN

[0126] Three temperatures T were randomly selected from the rubbery flat portion (specifically, the temperature range from Tg + 50°C to Tg + 80°C) in the T-E' curves of the three test specimens described above, and the storage modulus E' at these temperatures T was determined. Next, using these storage moduli E' and temperatures T, the molecular weight between crosslinking points at each temperature was calculated from the following equation (I). The arithmetic mean of the nine molecular weights between crosslinking points calculated from the T-E' curves of the three test specimens was then defined as the molecular weight 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)

[0127] Furthermore, under the dynamic viscoelasticity measurement conditions described above, the strain generated in the crosslinked polymer constituting the HIPE foam is very small, and it can be assumed that no volume change occurs. Therefore, the molecular weight Mc between crosslinking points was calculated under the condition of constant volume, i.e., a Poisson's ratio of 0.5. As a result of the measurement, the molecular weight between crosslinking points of the HIPE foam obtained in Example 3 was 0.8 × 10⁻⁶. 5 Therefore, the inter-crosslinking molecular weight of the HIPE foam obtained in Example 5 is 1.1 × 10⁻¹⁶. 5 Therefore, the inter-crosslinking molecular weight of the HIPE foam obtained in Example 11 is 0.15 × 10⁻¹⁵. 5 That was the case.

[0128] (Flame Retardancy) Flame retardancy was evaluated using a method in accordance with the flammability test method specified in FMVSS (Federal Motor Vehicle Safety Standard) No. 302. Specifically, a test specimen was prepared by cutting HIPE foam to create a plate-like shape with a length of 340 mm, a width of 102 mm, and a thickness of 12.7 mm, where one of the surfaces enclosed by the 340 mm side and the 102 mm side was the skin surface. A start line was drawn on this test specimen 38 mm away from the base end in the longitudinal direction, and an end line was drawn 254 mm away from the base end. Using this test specimen, a flammability test was performed in the same manner as in FMVSS No. 302, with the skin surface in contact with the flame of a burner.

[0129] In the "Flame Retardancy" column of Tables 2 and 3, the "Average Burning Rate" column shows the arithmetic mean of the burning rates of the three test specimens. The burning rate was recorded as "0" if the test specimen self-extinguished. Furthermore, in the "Evaluation" column of Tables 2 and 3, the symbol "A" was used if the average burning rate was 60 mm / min or less (including cases where all test specimens self-extinguished, i.e., 0); the symbol "B" was used if the average burning rate exceeded 60 mm / min but was 102 mm / min or less; the symbol "C" was used if the average burning rate exceeded 102 mm / min but was 230 mm / min or less; and the symbol "D" was used if the average burning rate exceeded 230 mm / min.

[0130] (Elongation at Fracture and Stress at Fracture) Elongation at fracture and stress at fracture were measured for the HIPE foam obtained in Examples 1 to 10 and Comparative Example 1. First, a 10 mm thick plate-like body was cut from the HIPE foam, excluding the skin surface. Next, five No. 1 shaped test specimens were made from the plate-like body using a No. 1 shaped dumbbell-shaped punching die specified in JIS K 6400-5:2012. Tensile tests were performed on these test specimens using an Autograph AGS-10kNX from Shimadzu Corporation, under the following conditions based on JIS K 6400-5:2012. The fracture point was determined from the load-displacement curve of each test specimen, and the elongation and stress at the fracture point were calculated. The median value of the elongation of the five test specimens obtained in this way was defined as the elongation at fracture. The stress at the fracture point of the test specimen showing the median elongation was defined as the stress at fracture. The detailed conditions for the tensile tests are as follows.

[0131] • Test equipment: Shimadzu Corporation "Autograph (registered trademark) AGS-10kNX" • Room temperature: 23°C • Humidity: 50% • Tensile speed: 500 mm / min

[0132] When the HIPE foam is composed of a polymer of vinyl monomers mainly consisting of acrylic monomers, from the viewpoint of obtaining a HIPE foam with excellent ductility, it is preferable that the elongation at the breaking point of the HIPE foam be 80% or more, more preferably 100% or more, and even more preferably 120% or more.

[0133] Furthermore, from the perspective of obtaining a HIPE foam with good tensile strength, the ratio of the fracture stress of the HIPE foam to the density of the HIPE foam should be 0.1 kPa / (kg / m). 3 Preferably, it is 0.2 kPa / (kg / m³) or higher, and 3 It is more preferable that the ratio of the fracture stress of the HIPE foam to the density of the HIPE foam is, for example, 3 kPa / (kg / m). 3 ) may be less than or equal to 2 kPa / (kg / m³). 3 ) The following are also acceptable.

[0134] (Emulsification) In the process of preparing the HIPE foam described above, after emulsifying the high internal phase emulsion, pure water that did not disperse in the organic phase was collected and its mass was measured. In the "Percentage of poorly dispersed water" column of Tables 2 and 3, the value (unit: mass %) is recorded as the ratio of the mass of pure water that did not disperse in the organic phase to the total mass of pure water added to the organic phase. A lower percentage of poorly dispersed water indicates that the aqueous phase is stably dispersed in the organic phase in the high internal phase emulsion.

[0135]

[0136]

[0137] As shown in Tables 2 and 3, the HIPE foams of Examples 1 to 12 are composed of polymers of acrylic monomers and / or styrene monomers, and the density of the HIPE foam is within the specified range. Furthermore, the HIPE foam contains expandable graphite, and its amount is within the specified range. Therefore, the HIPE foams of Examples 1 to 12 exhibited excellent flame retardancy.

[0138] On the other hand, as shown in Table 3, the HIPE foam of Comparative Example 1 did not contain expandable graphite and therefore had inferior flame retardancy.

[0139] In the manufacturing process of the HIPE foam in Comparative Example 2, a larger amount of expandable graphite than the specified range was added to the organic phase. As a result, in Comparative Example 2, it was not possible to form a stable high-internal-phase emulsion, making it difficult to produce HIPE foam.

[0140] The HIPE foam in Comparative Example 3 had inferior flame retardancy because it contained a brominated flame retardant instead of expandable graphite.

[0141] Although specific embodiments of the HIPE foam according to the present invention have been described above based on the examples, the embodiments of the HIPE foam according to the present invention are not limited to those of the examples, and the configuration can be modified as appropriate without impairing the spirit of the present invention.

Claims

1. A HIPE foam composed of polymers of acrylic monomers and / or styrene monomers, wherein the density of the HIPE foam is 30 kg / m³ 3 More than 350kg / m 3 The following is a HIPE foam, wherein the HIPE foam contains expandable graphite, and the amount of expandable graphite in the HIPE foam is 3% by mass or more and 25% by mass or less.

2. The HIPE foam according to claim 1, wherein the temperature at which the expandable graphite loses 1% of its weight as measured by thermogravimetric analysis is 150°C or higher and 230°C or lower.

3. The HIPE foam according to claim 1 or 2, wherein the expansion ratio of the expandable graphite when heated at 400°C for 5 minutes is 25 cc / g or more.

4. The HIPE foam according to any one of claims 1 to 3, wherein the 50% particle size D50 in the volume-based particle size distribution of the expandable graphite is 50 μm or more and 1000 μm or less.

5. The HIPE foam according to claim 4, wherein the ratio (D90-D10) / D50 of the difference between the 90% particle size D90 and the 10% particle size D10 relative to the 50% particle size D50 in the volume-based particle size distribution of the expandable graphite is 0.85 or more and 1.4 or less.

6. The HIPE foam according to any one of claims 1 to 5, wherein the average bubble diameter of the HIPE foam is 20 μm or more and 200 μm or less.

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