JP7381880B2 - HIPE form - Google Patents

Description

The present invention relates to HIPE foams used to form machined products.

Conventionally, water-in-oil type high internal phase emulsions have been developed, in which a high proportion of an aqueous phase consisting of an aqueous liquid such as water is encapsulated in an organic phase containing vinyl monomers, crosslinking agents, emulsifiers, polymerization initiators, etc. That is, a method is known in which a porous polymer called HIPE foam is obtained by forming HIPE and polymerizing an organic phase in the emulsion. This porous polymer is a polymer that reflects the dispersion form of the organic phase and aqueous phase in the high internal phase emulsion and the dispersion form of the aqueous phase during polymerization, and a large number of bubbles are homogeneously formed in the polymer. It has a cell structure that exists, and also has an open cell structure in which a large number of pores that communicate between the cells are formed. Therefore, HIPE foam is expected to be applied to applications such as absorbent materials and separation materials.

Patent Document 1 proposes a HIPE foam with adjusted density, glass transition temperature, and toughness index. According to Patent Document 1, such HIPE foam has excellent toughness and is said to be suitable for articles such as wiping products. Further, Patent Document 2 proposes an organic porous body (that is, HIPE foam) that is obtained by the so-called HIPE method and has a predetermined cell structure. According to Patent Document 2, such HIPE foam has high physical strength, an adsorbent with excellent adsorption amount and adsorption speed, an ion exchanger with excellent durability against swelling and shrinkage, and a chromatograph with excellent separation performance. It is said to be used as a filler for graphics.

Special Publication No. 2003-514052 Japanese Patent Application Publication No. 2003-246809

However, when using the HIPE foam as a machining material for forming a machined product by cutting, the technique of Patent Document 2 lacks the toughness of the HIPE foam, and there is a risk that cracks or chips may occur during the cutting process. In the technique of Patent Document 1, the rigidity of the HIPE foam was insufficient, and there was a risk that the cut surface would not be smooth. Therefore, with conventional techniques, it has not been possible to obtain a HIPE foam that has both toughness and rigidity, and it has not been possible to obtain a HIPE foam that is suitable as a cutting material for forming cut products by cutting.

The present invention has been made in view of this background, and aims to provide a HIPE foam that has excellent cutting surface smoothness, is less prone to cracking or chipping during cutting, and has excellent machinability. be.

One embodiment of the present invention is a HIPE foam that is composed of a vinyl crosslinked polymer containing a styrene monomer component and/or an acrylic monomer component , and is used to form a cut product by cutting. And,
The apparent density ρ is 50 to 500 kg/m ³ ,
The value S/ρ of Charpy impact strength S with respect to the above apparent density ρ is 4.5 J · m / kg or more,
The storage elastic modulus E' at 23°C and the above apparent density ρ are measured by performing dynamic viscoelasticity measurements on the HIPE foam at a frequency of 1 Hz, a load of 98 mN, and a deformation mode of compression. satisfies the relationship of formula (I) below,
The molecular weight between crosslinking points Mc measured by performing the above dynamic viscoelasticity measurement is 2 × 10 ⁴ or less ,
The HIPE foam has a glass transition temperature of 50° C. or higher .
E'/ρ≧50kN・m/kg...(I)

In the above HIPE foam, the apparent density ρ, the Charpy impact strength value S/ρ relative to the apparent density, and the molecular weight between crosslinking points Mc are within the above ranges, and E'/ρ satisfies the relationship of formula (I). Therefore, HIPE foam has excellent cutting surface smoothness, is less prone to cracking or chipping during cutting, and has excellent cutting workability.

FIG. 1 is a low vacuum scanning electron micrograph (magnification: 500x) of the HIPE foam of the example. FIG. 2 is a DMA curve obtained by dynamic viscoelasticity measurement (that is, DMA) of the HIPE foam of the example.

Next, preferred embodiments of the HIPE foam will be described. In this specification, when "~" is used to express a numerical value or physical property value before and after it, it is used to include the values before and after it. Furthermore, when expressing a numerical value or physical property value as a lower limit, it means that it is greater than or equal to that numerical value or physical property value, and when expressing a numerical value or physical property value as an upper limit, it means that it is less than or equal to that numerical value or physical property value.

[HIPE form]
HIPE foam is a porous polymer generally also called PolyHIPE foam, polyHIPE material, high internal phase emulsion porous body, high internal phase emulsion foam, etc. It is obtained by polymerizing monomers in a water-in-oil type high internal phase emulsion, which is encapsulated in a high proportion in an organic phase. High Internal Phase Emulsion is commonly called HIPE. HIPE foam is more specifically a porous vinyl-based crosslinked polymer, for example, a water-in-oil type high internal phase emulsion in which a high proportion of an aqueous phase is encapsulated in an organic phase, in which a crosslinking agent is used. It is a porous vinyl crosslinked polymer obtained by polymerizing vinyl monomers in the presence of. Furthermore, HIPE foam is a porous cured product obtained by curing a high internal phase emulsion, and it can be said that the cell walls thereof are composed of a vinyl crosslinked polymer. Air bubbles can also be called pores.

HIPE foam is a polymer that reflects the dispersion form of the organic phase and aqueous phase in a high internal phase emulsion and the dispersion form of the aqueous phase (that is, the dispersed phase) during polymerization (specifically, a porous polymer). crosslinked polymer). As illustrated in FIG. 1, the HIPE foam 1 has a cell structure in which a large number of cells 13 are uniformly present in a porous crosslinked polymer 11 constituting the foam, and a large number of fine cells that communicate between the cells. It has an open cell structure in which pores 14 are formed. Note that in FIG. 1, the bubble 13 is a portion surrounded by the bubble wall 12. The pores 14 can also be referred to as micropores, through windows, through holes, and connecting holes.

Since HIPE foam is a structure made of a crosslinked polymer, it tends to have low resistance to load and shear (specifically, shear stress and shear stress), making it a relatively brittle polymer. Furthermore, since the polymer of HIPE foam is difficult to stretch during the manufacturing process, it generally becomes a polymer that is difficult to cause molecular orientation and has little anisotropy. HIPE foams are produced by various methods, such as foams obtained by an extrusion foaming method using an extruder, and foamed particle molded products obtained by in-mold molding of foamed particles obtained by foaming expandable resin particles. It is distinguished from foams that are sometimes produced by stretching.

The size of cells and pores in the HIPE foam is not particularly limited, but for example, the cell diameter is approximately 5 to 100 μm and the pore diameter is approximately 1 to 30 μm. Note that since pores are through holes that are formed in the cell walls and communicate between the cells, the pore diameter is usually smaller than the cell diameter.

HIPE foam has high rigidity and excellent toughness, has a good balance between rigidity and toughness, and has excellent machinability. Therefore, the cut product is particularly suitable for a wooden mold for casting, which will be described later.

The cell size of the HIPE foam can be controlled by adjusting the water droplet size of the aqueous phase (that is, the dispersed phase) of the high internal phase emulsion in the production method described below, and the cell size can be made fine. In HIPE foam, the average cell diameter can be easily adjusted to 100 μm or less. Note that the average cell diameter of the HIPE foam is the average value of the cell diameters, and the method for measuring it will be explained in Examples.

[Application]
HIPE foam is used to produce cut products by cutting. HIPE foam is made of a vinyl crosslinked polymer and is porous, so it can be cut into lightweight cut products. In the following description, the vinyl crosslinked polymer will be appropriately referred to as a "crosslinked polymer."

The cut product is, for example, a model. Models include architectural models of buildings, mechanical models of mechanical devices, vehicle models of cars and trains, casting models for making sand molds called casting molds, works of art and exhibits, etc. Examples include various models such as art models and pre-product models. Note that such a model material is manufactured by cutting an object to be cut (that is, a cutting material). Therefore, cutting materials are required to be able to be machined at high cutting speeds, to have excellent smoothness on the cut surface, to avoid cracking or chipping during cutting, and to have dimensions that do not easily change over time. . Examples of cutting include processing using an NC cutting machine, processing using a band saw, processing using a cutter, and the like.

The casting model is, for example, a model used for forming a sand mold. Such a model is appropriately called a "wooden model." In this case, in forming the sand mold, first, a casting model is manufactured as a cut product from the crosslinked polymer by cutting. This casting model is immersed in a mixture of silica sand, furan resin, binder, etc., which is a material for forming a sand mold, and the furan resin mixture is hardened by carbon dioxide gas radiation or air contact. After curing, the wooden mold is released from the hardened furan resin mixture to obtain a sand mold used as a casting mold. A casting can be obtained by pouring molten metal or the like into a sand mold and cooling it. The particle size of the main grains of silica sand is generally 75 μm to 850 μm. In order to improve the transferability on the surface of the wooden mold, it is preferable that the grain size of the silica sand in the area in contact with the wooden mold is small. The particle size classification (number) of silica sand is measured in accordance with JIS G 5901:2016, and in the particle size distribution at this time, the sieve opening with the highest weight ratio is the main particle.

The HIPE foam is preferably used for a casting model, and the cut product is preferably a casting model. In this case, the casting surface of the casting can be made smooth. This is because the crosslinked polymer constituting the HIPE foam has excellent smoothness of the cut surface.

[Apparent density ρ]
If the apparent density ρ of the HIPE foam is too low, the HIPE foam becomes too brittle. Therefore, there is a risk of chipping or cracking occurring during cutting. From the viewpoint of preventing chipping and cracking during cutting, the apparent density ρ of the HIPE foam is 50 kg/m ³ or more, preferably 70 kg/m ³ or more, and preferably 90 kg/m ³ or more. More preferred. On the other hand, if the apparent density of the HIPE foam is too high, the HIPE foam becomes too hard, reducing the processing speed during cutting and reducing the productivity of the cut product. From the viewpoint of improving processing speed, the apparent density ρ of the HIPE foam is 500 kg/m ³ or less, preferably 400 kg/m ³ or less, and more preferably 300 kg/m ³ or less. Note that the HIPE foam obtained by curing a high internal phase emulsion in which a high proportion of an aqueous phase is encapsulated in an organic phase usually has an apparent density of 500 kg/m ³ or less.

The apparent density ρ of the HIPE foam is calculated by dividing the weight by the volume.

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

[Charpy impact strength]
Charpy impact strength S is an indicator of the toughness of HIPE foam. If the value S/ρ of the Charpy impact strength S with respect to the apparent density ρ is too low, the HIPE foam becomes brittle and there is a risk that chipping or cracking may occur during cutting. From the viewpoint of preventing chipping and cracking during cutting, S/ρ is 4.5 J·m/kg or more, preferably 5.0 J·m/kg or more, and 5.5 J·m/kg. More preferably, it is at least kg. In addition, S/ρ can be increased to 20 J・m/ It is preferable that it is less than kg. Note that the magnitude of the Charpy impact strength of HIPE foam is highly dependent on the apparent density. On the other hand, the apparent density of HIPE foam is adjusted within a predetermined range depending on its use and purpose, so by setting the value S/ρ of Charpy impact strength S to the apparent density ρ within the above range, HIPE foam has excellent machinability within a predetermined apparent density range.

Charpy impact strength is measured based on the method described in JIS K7111:2006 at a measurement temperature of 23° C. and without a notch.

The value S/ρ of Charpy impact strength relative to the apparent density of HIPE foam can be increased by blending a predetermined amount of a predetermined crosslinking agent in the HIPE foam manufacturing method described below, and the type of monomer described below, It is adjusted to the above range by adjusting the blending ratio, the type of crosslinking agent, the blending ratio, etc.

[Storage modulus E' at 23°C]
The storage modulus E' at 23°C is an index of the hardness of the HIPE foam, and the storage modulus E' at 23°C and the apparent density ρ of the HIPE foam satisfy the relationship of formula I. That is, the value E'/ρ of the storage elastic modulus E' at 23° C. of the HIPE foam with respect to the apparent density ρ is 50 kN·m/kg or more.
E'/ρ≧50kN・m/kg...(I)

If E'/ρ is too low, the HIPE foam becomes too soft, reducing machinability and reducing the smoothness of the cut surface. In addition, the HIPE foam becomes easily deformed, and when the cut product is used as a casting model, there is a risk that the dimensional accuracy of the casting may be reduced. This is because the casting model is deformed during sand mold formation, for example. From the viewpoint of forming a cut surface with excellent smoothness and improving the dimensional accuracy of the casting, the storage modulus E' at 23°C for the apparent density ρ is 50 kN・m/kg or more, and 100 kN・m It is preferably at least 150 kN·m/kg, more preferably at least 150 kN·m/kg. Furthermore, E'/ρ is preferably 250 kN·m/kg or less, since the processing speed of the HIPE foam can be increased and the occurrence of chips and cracks during processing can be further suppressed.

The storage modulus E' of the HIPE foam is measured by performing dynamic viscoelasticity measurement on the HIPE foam under the following conditions: frequency: 1 Hz, load: 98 mN, deformation mode: compression. Regarding the measurement conditions, the frequency is a parameter for adjusting the cycle of deforming the measurement sample, and the load is the force applied to the measurement sample. By using the above measurement conditions, it is possible to suppress the occurrence of a discrepancy between the deformation to be applied to the HIPE foam and its response, and it is also possible to restore the HIPE foam to its initial state without causing plastic deformation. Therefore, the storage modulus E' of the HIPE foam can be appropriately evaluated.

Note that the storage modulus E' of the HIPE foam is highly dependent on the apparent density ρ. On the other hand, since the apparent density ρ of HIPE foam is adjusted within a predetermined range depending on its use and purpose, the value E'/ρ of the storage elastic modulus E' with respect to the apparent density ρ is set within the above range. As a result, the HIPE foam has excellent machinability within a predetermined apparent density range.

The storage modulus E' relative to the apparent density ρ of the HIPE foam can be increased by adding a monomer that increases the storage modulus of the resulting polymer in the HIPE foam manufacturing method described below. It is adjusted to the above range by adjusting the type of polymer, its blending ratio, the type of crosslinking agent, its blending ratio, etc.

[Molecular weight between crosslinking points Mc]
The molecular weight between crosslinking points Mc is an index of the degree of crosslinking of the HIPE foam. If the molecular weight Mc between crosslinking points of the crosslinked polymer constituting the HIPE foam is too large (that is, the crosslinking density is too low), the fluidity of the resin in the micro region of the HIPE foam during cutting is high, so the resin It becomes easy to be ripped off by processing blades such as mills, and the smoothness of the cutting surface decreases. From the viewpoint of forming a cut surface with excellent smoothness, the molecular weight between crosslinking points Mc is 2 × 10 ⁴ or less, preferably 1 × 10 ⁴ or less, and more preferably 5 × 10 ³ or less. preferable. Further, from the viewpoint of suppressing a decrease in toughness and further suppressing chipping and cracking during cutting, the molecular weight between crosslinking points Mc is preferably 2×10 ³ or more.

The inter-crosslinking molecular weight Mc of the HIPE foam is measured as follows. Dynamic mechanical analysis (DMA) is performed on the HIPE foam under the conditions of frequency: 1 Hz, load: 98 mN, and deformation mode: compression. At this time, as the temperature rises, the crosslinked polymer that makes up the HIPE foam transitions from a glass state to a rubber state, so in the DMA curve obtained by plotting temperature on the horizontal axis and storage modulus E' on the vertical axis, The storage modulus E' rapidly decreases after reaching the glass transition temperature Tg (see FIG. 2). Thereafter, the DMA curve shows a plateau region (rubber-like plateau). Since E' is proportional to temperature in this plateau region, the molecular weight between crosslinking points Mc can be calculated from the following formula (II).
Mc=2(1+μ)ρRT/E'...(II)

In formula (II), μ is Poisson's ratio, and μ=0.5. ρ is the apparent density of the HIPE foam in kg/m ³ and R is the gas constant: 8.314 J/K/mol. T and E' are the temperature (unit: K) and storage modulus at an arbitrary point in the rubbery flat part, respectively. Note that T and E' are values measured at the rubber-like flat part. From the viewpoint of being able to appropriately calculate the molecular weight between crosslinking points Mc, the above E' is preferably measured in a temperature range of Tg + 50°C to Tg + 80°C (where Tg is the glass transition temperature of the HIPE foam). Note that Poisson's ratio is a value unique to a material, and is the value obtained by dividing the strain occurring in the vertical direction by the strain occurring in the parallel direction when stress is applied to an object, and multiplying this by -1. Theoretically, Poisson's ratio takes a value in the range of -1 to 0.5, and if it is a negative value, it means that if it collapses in the vertical direction, it will also collapse in the horizontal direction. Conversely, if it is a positive value, it means that if you collapse it vertically, it will expand horizontally. Under the above measurement conditions for dynamic viscoelasticity analysis, the strain that occurs in the crosslinked polymer constituting the HIPE foam is extremely small, and it can be assumed that no volume change occurs. .5, the storage elastic modulus E' and the molecular weight between crosslinking points Mc are calculated.

The molecular weight Mc between crosslinking points of HIPE foam can be reduced by adding a crosslinking agent in the HIPE foam manufacturing method described below, and the type of crosslinking agent and its blending ratio, the type of monomer and its It is adjusted to the above range by adjusting the blending ratio and the like.

[Average bubble diameter]
The average cell diameter of the HIPE foam is preferably 100 μm or less. In this case, the cut product of HIPE foam becomes more suitable as a model for casting using a sand mold (that is, a casting model). This is because it is possible to prevent molding sand such as silica sand from entering the bubbles of the HIPE foam constituting the cut product. In other words, it is possible to prevent the casting model from getting caught in the foundry sand. Further, since it is possible to suppress the biting of molding sand without applying a coating treatment to the surface of the casting model, it is possible to suppress manufacturing costs and simplify the manufacturing process.

Note that a typical example of a conventionally used cutting material is hard polyurethane foam. From the perspective of increasing cutting speed, hard polyurethane foam with a relatively low apparent density is usually used, but since the average cell diameter of such hard polyurethane foam is about 150 to 300 μm, it is difficult to use hard sand such as silica sand. It easily gets into the bubbles of polyurethane foam. As a result, when a casting model made of rigid polyurethane foam is embedded in a sand mold, sand gets into the air bubbles of the rigid polyurethane foam, causing sand entrainment, which may make it difficult to release the casting model. Therefore, a coating layer is generally formed on the surface of a casting model made of rigid polyurethane foam to prevent sand from chewing.

In addition, in rigid polyurethane foam, in order to reduce the average cell diameter, it is necessary to lower the expansion ratio (ie, increase the density). In this case, due to the increased hardness of the rigid polyurethane foam, there was a risk that the cutting speed would decrease and productivity would deteriorate. Therefore, in hard polyurethane foams, it is difficult to increase the cutting speed while suppressing sand encroachment.

From the viewpoint of easier mold release of the casting model and the elimination of the need to form a coating layer, the average cell diameter of the HIPE foam is preferably 80 μm or less, and more preferably 70 μm or less. The thickness is preferably 50 μm or less, particularly preferably 50 μm or less. In addition, the average cell diameter of the HIPE foam is preferably 5 μm or more, and preferably 10 μm or more, since this makes it easier to shorten the time required for dehydration and drying steps in the manufacturing process and improve productivity. More preferably, it is 15 μm or more.

The average cell size of HIPE foam is measured by image analysis. The measurement method will be explained in Examples.

The average cell diameter of the HIPE foam is adjusted within the above range by adjusting the stirring speed, stirring time, type of emulsifier, amount added, viscosity of the emulsion, etc. in the emulsification step in the manufacturing method described below.

[Glass-transition temperature]
The glass transition temperature of the HIPE foam is preferably 40-120°C. In this case, a HIPE foam with excellent machinability can be stably obtained. In order to ensure sufficient hardness at the environmental temperature during cutting and to prevent dimensional changes in the cut products in high-temperature environments, the glass transition temperature of the HIPE foam is preferably 50°C or higher, and preferably 60°C. It is more preferable that it is above. Further, the glass transition temperature of the HIPE foam is preferably 100° C. or lower, since this can further suppress a decrease in the toughness of the HIPE foam and further suppress the occurrence of chips and cracks during cutting.

The glass transition temperature of HIPE foam is measured by differential scanning calorimetry (DSC) analysis based on JIS K7121:1987. The glass transition temperature is the midpoint glass transition temperature of the DSC curve. ``(3) When measuring the glass transition temperature after a certain heat treatment'' is adopted as the condition adjustment of the test piece.

The glass transition temperature of the HIPE foam is adjusted within the above range by adjusting the type of vinyl monomer, its blending ratio, the type of crosslinking agent, its blending ratio, etc. in the HIPE foam manufacturing method described below. .

[Structural component]
Specifically, the crosslinked polymer constituting the HIPE foam is a polymer of a monofunctional vinyl monomer and a crosslinking agent, and contains components derived from the monofunctional vinyl monomer. In this specification, vinyl monomers include styrene monomers, acrylic monomers, and the like. As the vinyl monomer, a styrene monomer and/or an acrylic monomer can be used.

The crosslinked polymer is preferably composed of a polymer of a vinyl monomer containing a styrene monomer and/or an acrylic monomer, and a crosslinking agent. That is, it is preferable that the crosslinked polymer has a styrene monomer component and/or an acrylic monomer component. In this case, the HIPE foam has a better balance of toughness and rigidity. The styrenic monomer component means a structural unit derived from a styrene monomer in a crosslinked polymer, and the acrylic monomer component means a structural unit derived from an acrylic monomer in a crosslinked polymer. do. The content of the styrene monomer component and/or acrylic monomer component in the crosslinked polymer is preferably 50% by weight or more, more preferably 60% by weight or more, and 70% by weight or more. It is more preferable that the amount is 80% by weight or more, and particularly preferably 80% by weight or more.

Styrene monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, p-n - Styrenes such as butylstyrene, pt-butylstyrene, divinylbenzene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, styrenesulfonic acid, sodium styrenesulfonate Examples include compounds. Acrylic monomers include acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and hydroxyethyl acrylate; methyl methacrylate, ethyl methacrylate, and methacrylate. Examples include alkyl methacrylates such as propyl acid, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate. Further, examples of the acrylic monomer include acrylamide, methacrylamide, acrylonitrile, and the like.

The crosslinked polymer may be composed of a copolymer of a vinyl monomer containing styrene and/or methyl methacrylate and an alkyl (meth)acrylate other than methyl methacrylate, and a crosslinking agent. preferable. In this case, it is easy to obtain a HIPE foam composed of a crosslinked polymer having desired physical properties. Note that the (meth)acrylic acid alkyl ester is an ester of (meth)acrylic acid and an alcohol, and is preferably an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms.

When the vinyl monomer contains styrene and/or methyl methacrylate, the content of styrene and/or methyl methacrylate in the vinyl monomer is preferably 40% by weight or more, and 50% by weight. It is more preferably at least 60% by weight, and even more preferably at least 60% by weight. Further, the weight ratio of styrene and/or methyl methacrylate to (meth)acrylic acid alkyl ester other than methyl methacrylate is preferably 40:60 to 90:10, and preferably 50:50 to 80:20. It is more preferable that there be. In this case, the effects of reducing manufacturing costs and making it easier to adjust the desired physical properties can be obtained. Note that (meth)acrylic acid means acrylic acid and/or methacrylic acid.

In addition, from the viewpoint of being able to stably obtain a HIPE foam having excellent physical properties and a desired glass transition temperature, the number of carbon atoms in the alkyl group constituting the (meth)acrylic acid alkyl ester other than methyl methacrylate is as follows: It is preferably from 1 to 20, more preferably from 2 to 18, even more preferably from 3 to 16, even more preferably from 4 to 12. Among these, it is particularly preferable to use butyl acrylate.

The crosslinked polymer has a crosslinked structure and contains a crosslinking agent component. The crosslinking agent component is a structural unit derived from a crosslinking agent in a crosslinked polymer. As the crosslinking agent, for example, a vinyl compound having at least two functional groups selected from a vinyl group and an isopropenyl group in the molecule is used. When the crosslinked polymer contains a predetermined amount of the crosslinking agent component, the value of the Charpy impact strength of the crosslinked polymer can be increased and the value of the molecular weight between crosslinking points of the crosslinked polymer can be decreased. Note that the vinyl compounds include compounds containing a vinyl group and/or isopropenyl group in the structure of the functional group, such as an acryloyl group or a methacryloyl group. From the viewpoint of stably polymerizing the crosslinking agent, the number of functional groups in the vinyl compound is preferably 6 or less, preferably 5 or less, and more preferably 4 or less. Further, from the viewpoint of making it easier to improve the cutting workability of the crosslinked polymer, the crosslinking agent preferably has a functional group at least at both ends of the molecule, and more preferably only at both ends of the molecule.

The crosslinked polymer may be prepared using one type of crosslinking agent and may contain one type of crosslinking agent component, but it is possible to increase the toughness of the crosslinked polymer while increasing the rigidity of the crosslinked polymer. It is preferable to contain a hard crosslinking agent component derived from a hard crosslinking agent with a relatively short molecular chain and a soft crosslinking agent component derived from a soft crosslinking agent with a relatively long molecular chain because it is easy to increase the . In this case, it becomes easy to adjust the molecular weight Mc between crosslinking points of the HIPE foam, the Charpy impact strength value S/ρ relative to the apparent density, and the value E'/ρ the storage elastic modulus at 23°C relative to the apparent density to the above ranges. . Note that the hard crosslinking agent can also be referred to as a first crosslinking agent, and the soft crosslinking agent can also be referred to as a second crosslinking agent.

The hard crosslinking agent (that is, the first crosslinking agent) is preferably a vinyl compound having a functional group equivalent of 130 g/mol or less. Since such hard crosslinking agents have relatively short molecular chains, they are thought to reduce the mobility of polymer molecular chains by being copolymerized with vinyl monomers. By using a hard crosslinking agent, it becomes easier to increase the rigidity of the HIPE foam. In addition, from the viewpoint of facilitating the production of HIPE foam, the lower limit of the functional group equivalent of the hard crosslinking agent is preferably approximately 30 g/mol, more preferably 40 g/mol, and 50 g/mol. is more preferable, and even more preferably 60 g/mol. Moreover, it is preferable that the upper limit of the functional group equivalent of the hard crosslinking agent is 120 g/mol. Note that the functional group equivalent of the hard crosslinking agent means the molar mass of the hard crosslinking agent per functional group.

The soft crosslinking agent (that is, the second crosslinking agent) is preferably a vinyl compound having a functional group equivalent of more than 130 g/mol and less than 5000 g/mol. Such soft crosslinking agents have relatively long molecular chains, so when copolymerized with vinyl monomers, they can link between polymer molecular chains without significantly reducing the mobility of polymer molecular chains. It is thought that it can be crosslinked. By using a soft crosslinking agent, it is easy to increase the toughness of HIPE foam. In addition, from the viewpoint of handleability, the upper limit of the functional group equivalent of the soft crosslinking agent is preferably 3000 g/mol, more preferably 2000 g/mol, and even more preferably 1000 g/mol. Further, the lower limit of the functional group equivalent of the soft crosslinking agent is preferably 150 g/mol, more preferably 180 g/mol, and even more preferably 200 g/mol. Note that the functional group equivalent of the soft crosslinking agent means the molar mass of the soft crosslinking agent per functional group.

From the viewpoint of further improving the above effects, specifically, from the viewpoint of making it easier to increase the toughness and rigidity of the HIPE foam, the functional group equivalent of the soft crosslinking agent is more than the functional group equivalent of the hard crosslinking agent. It is preferably 60 g/mol or more, more preferably 80 g/mol or more, even more preferably 100 g/mol or more, and even more preferably 120 g/mol or more. In other words, the difference between the functional group equivalent of the soft crosslinking agent and the functional group equivalent of the hard crosslinking agent is 60 g/mol or more, more preferably 80 g/mol or more, and 100 g/mol or more. is more preferable, and even more preferably 120 g/mol or more. In addition, when two or more types of hard crosslinking agents are used, the weight average value of the functional group equivalents of all the hard crosslinking agents is calculated, and this value is taken as the functional group equivalent of the hard crosslinking agents. Similarly, when two or more types of soft crosslinking agents are used, the weight average value of the functional group equivalents of all the soft crosslinking agents is calculated, and this value is taken as the functional group equivalent of the soft crosslinking agents.

Examples of the vinyl compound used as a hard crosslinking agent include divinylbenzene, butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, hexanediol di(meth)acrylate, and the like. However, the number of functional groups in the hard crosslinking agent is two or more. Preferably, the functional group is a vinyl group and/or an isopropenyl group. The number of hard crosslinking agents may be one type, or two or more types may be used. That is, the number of hard crosslinking agent components constituting the crosslinked polymer may be one, or two or more. Note that from the viewpoint of making it easier to adjust the rigidity of the HIPE foam, it is preferable to use divinylbenzene and/or butanediol di(meth)acrylate as the hard crosslinking agent.

Vinyl compounds used as soft crosslinking agents include nonanediol di(meth)acrylate, decanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. Examples include meth)acrylate, polyglycerin di(meth)acrylate, urethane di(meth)acrylate, epoxy di(meth)acrylate, polyester di(meth)acrylate, silicone modified with (meth)acrylic at both ends, and the like. However, the number of functional groups in the soft crosslinking agent is two or more. Preferably, the functional group is a vinyl group and/or an isopropenyl group. The number of soft crosslinking agents may be one type, or two or more types may be used. In other words, the number of soft crosslinking agent components constituting the crosslinked polymer may be one, or two or more. In addition, from the viewpoint of making it easier to adjust the toughness of the HIPE foam, it is preferable to use polyethylene glycol di(meth)acrylate as the soft crosslinking agent. In this case, the number of repeating structural units derived from ethylene glycol in the polyethylene glycol di(meth)acrylate is preferably 3 to 23.

Table 1 shows the molecular weights and molecular weights per functional group (that is, functional group equivalents) of typical crosslinking agents.

When the crosslinked polymer is composed of at least a copolymer of a styrene monomer, an acrylic acid alkyl ester other than methyl methacrylate, and a crosslinking agent, the molecular weight Mc between the crosslinking points of the HIPE foam and the apparent density The Charpy impact strength value S/ρ and the storage modulus value E'/ρ at 23°C relative to the apparent density can be easily adjusted to the above ranges, and the HIPE foam has a better balance between toughness and rigidity. From this point of view, the content of the styrene monomer component in the crosslinked polymer is 30 parts by weight or more, and 90 parts by weight, based on the total of 100 parts by weight of the vinyl monomer component and the crosslinking agent component that constitute the crosslinked polymer. It is preferably at most 40 parts by weight and at most 80 parts by weight, even more preferably at least 50 parts by weight and at most 70 parts by weight. From the same point of view, the content of (meth)acrylic acid alkyl ester components other than methyl methacrylate in the crosslinked polymer should be 100 parts by weight in total of the vinyl monomer component and crosslinking agent component that constitute the crosslinked polymer. On the other hand, it is preferably 5 parts by weight or more and 50 parts by weight or less, more preferably 10 parts by weight or more and 40 parts by weight or less, and even more preferably 15 parts by weight or more and 30 parts by weight or less. Furthermore, it is preferable to use styrene as the styrene monomer, and the content of styrene in the styrene monomer is preferably 50% by weight or more, more preferably 80% by weight or more, and 90% by weight or more. More preferably, it is at least % by weight.

In addition, when the crosslinked polymer is composed of a copolymer of at least methyl methacrylate, styrene, an alkyl (meth)acrylate other than methyl methacrylate, and a crosslinking agent, the methacrylic acid in the crosslinked polymer The total content of the methyl component and the styrene component is 30 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the vinyl monomer component and crosslinking agent component that constitute the crosslinked polymer. The content is preferably 40 parts by weight or more and 70 parts by weight or less. In this case, the content of the (meth)acrylic acid alkyl ester other than methyl methacrylate in the crosslinked polymer is based on the total of 100 parts by weight of the vinyl monomer component and the crosslinking agent component that constitute the crosslinked polymer. The amount is preferably 5 parts by weight or more and 50 parts by weight or less, more preferably 10 parts by weight or more and 40 parts by weight or less, and even more preferably 15 parts by weight or more and 30 parts by weight or less. Further, in this case, the content of the methyl methacrylate component is preferably 50% by weight or more, more preferably 60% by weight or more, with the total of the methyl methacrylate component and styrene component being 100% by weight. , more preferably 70% by weight or more.

From the viewpoint of easily adjusting the molecular weight between crosslinking points Mc of HIPE foam, the Charpy impact strength value S/ρ relative to the apparent density, and the value E'/ρ the storage elastic modulus at 23°C relative to the apparent density to the above ranges, the crosslinking weight The content of the crosslinking agent component during coalescence (specifically, the total content of the soft crosslinking agent component and the hard crosslinking agent component) is the content of the vinyl monomer component and the crosslinking agent component that make up the crosslinked polymer. It is preferably 7 parts by weight or more and 27 parts by weight or less, and more preferably 8 parts by weight or more and 26 parts by weight or less, based on a total of 100 parts by weight.

From the viewpoint of easily adjusting the molecular weight between crosslinking points Mc of HIPE foam, the Charpy impact strength value S/ρ relative to the apparent density, and the value E'/ρ the storage elastic modulus at 23°C relative to the apparent density to the above ranges, the crosslinking weight The content of the hard crosslinking agent component in the combination shall be 3 parts by weight or more and 17 parts by weight or less based on the total of 100 parts by weight of the vinyl monomer component and the crosslinking agent component that constitute the crosslinked polymer. The amount is preferably 4 parts by weight or more and 16 parts by weight or less. From the same viewpoint, the content of the soft crosslinking agent component in the crosslinked polymer is 2 parts by weight or more with respect to the total of 100 parts by weight of the vinyl monomer component and the crosslinking agent component that constitute the crosslinked polymer. It is preferably 18 parts by weight or less, more preferably 3 parts by weight or more and 16 parts by weight or less. From the same viewpoint, the weight ratio of the hard crosslinking agent component to the soft crosslinking agent component is preferably 0.3 to 5, more preferably 0.4 to 4.

[Production method]
HIPE foam is produced by polymerizing a high internal phase emulsion, specifically, by polymerizing a water-in-oil type high internal phase emulsion. The organic phase of the water-in-oil high internal phase emulsion is a continuous phase containing vinyl monomers, crosslinking agents, emulsifiers, polymerization initiators, etc., and the aqueous phase is a dispersed phase containing water such as deionized water. be. Specifically, a high internal phase emulsion porous body can be produced by performing an emulsification step, a polymerization step, and a drying step as described below.

First, an aqueous liquid containing water (aqueous phase) is added dropwise to an oily liquid (organic phase) containing organic substances such as vinyl monomers, crosslinking agents, emulsifiers, and polymerization initiators while stirring. A water type high internal phase emulsion is prepared (emulsification process). In the emulsification step, a high internal phase emulsion can be prepared by adding an aqueous liquid to an oily liquid such that the volume of the aqueous phase is, for example, three times or more that of the organic phase. Note that the ratio of the aqueous phase included in the organic phase can be adjusted by adjusting the weight ratio of the organic phase and the aqueous phase. The content of the aqueous phase in the high internal phase emulsion is preferably 300 to 1,600 parts by weight, more preferably 350 to 1,400 parts by weight, even more preferably 400 parts by weight, based on 100 parts by weight of the organic phase. ~1200 parts by weight. Next, the high internal phase emulsion is heated to polymerize the vinyl monomer, crosslinking agent, etc. of the organic phase to obtain a polymerization product (specifically, a crosslinked polymer containing water) (polymerization step ). Thereafter, a HIPE foam composed of a crosslinked polymer is obtained by drying the polymerization product (drying step).

The stirring speed in the emulsification step is not particularly limited, but can be adjusted within the range of stirring power density of 0.1 kW/m ³ to 5 kW/m ³ , for example. In addition, the method of adding the aqueous liquid to the oily liquid in the emulsification process is not particularly limited, but stirring may be started with the oily liquid and the aqueous liquid placed in the stirring container in advance. Alternatively, only the oil-based liquid may be introduced and stirred, and then the aqueous liquid may be added using a pump or the like. The rate of addition of the aqueous liquid in this case is not particularly limited, but can be adjusted, for example, in the range of 10 wt%/min to 1000 wt%/min relative to the oily liquid. In addition, emulsification methods include a batch-type emulsification process that emulsifies using a stirring container equipped with a stirring device or a centrifugal shaker, and a continuous emulsification process in which oil-based liquids and aqueous liquids are mixed in a line equipped with a static mixer, mesh, etc. The emulsification method is not particularly limited, such as a continuous emulsification process in which the components are supplied and mixed simultaneously.

The aqueous phase can include water, such as deionized water, a polymerization initiator, an electrolyte, and the like. 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 while stirring to prepare a high internal phase emulsion. Further, in the emulsification step, additives such as flame retardants, light stabilizers, colorants, etc. can be appropriately blended.

A polymerization initiator is used to initiate polymerization of vinyl monomers. As the polymerization initiator, a radical polymerization initiator can be used. Specifically, dilauroyl peroxide (LPO), 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, di(3,5,5-trimethylhexanoyl)peroxide, t -Butyl peroxy pivalate, t-hexyl peroxy pivalate, t-butyl peroxy neoheptanoate, t-butyl peroxy neodecanoate, t-hexyl peroxy neodecanoate, di(2 - Organic peroxides such as ethylhexyl) peroxydicarbonate, di(4-t-butylcyclohexyl)peroxydicarbonate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, benzoyl peroxide; 2,2'-azobisisobutyronitrile, 2,2'azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'azobis(4-dimethylvaleronitrile), dimethyl 2,2'azobis (2-methylpropionate), 2,2'azobis(2-methylbutyronitrile), and other azo compounds are used. One or more types of substances can be used as the polymerization initiator. Polymerization initiators can be added to the organic phase and/or the aqueous phase. In addition, when adding a polymerization initiator to the aqueous phase, 2,2'azobis(2-(2-imidazolin-2-yl)propane) dihydrochloride, 2,2'azobis(2-methylpropionamidine dihydrochloride) A water-soluble polymerization initiator such as potassium persulfate, ammonium persulfate, etc. may be used.The amount of the polymerization initiator added is, for example, 0 to 100 parts by weight in total of the vinyl monomer and the crosslinking agent. .1 to 5 parts by weight.

Emulsifiers are used to form and stabilize high internal phase emulsions. As the emulsifier, for example, a surfactant can be used. Specifically, glycerol esters such as polyglycerin condensed ricinoleate, polyglycerin stearate, polyglycerin oleate, polyglycerin laurate, and polyglycerin myristate; sorbitan oleate, sorbitan stearate, sorbitan laurate, and sorbitan laurate. , sorbitol esters such as sorbitan palmitate; ethylene glycol sorbitan esters; ethylene glycol esters; copolymers of polyethylene glycol and polypropylene glycol, etc. are used. The amount of the emulsifier added can be, for example, in the range of 1 to 30 parts by weight, based on 100 parts by weight of the vinyl monomer, crosslinking agent, and emulsifier.

Electrolytes are used to impart ionic strength to the aqueous phase and increase emulsion stability. As the electrolyte, a water-soluble electrolyte can be used. Specifically, calcium chloride, sodium chloride, magnesium chloride, sodium acetate, sodium citrate, sodium sulfate, calcium sulfate, magnesium sulfate, etc. are used. The amount of electrolyte added can be, for example, in the range of 0.1 to 10 parts by weight per 100 parts by weight of the aqueous liquid.

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, and the like. The polymerization temperature is, for example, 50°C to 90°C.

In the drying step, the water-containing crosslinked polymer is dried using an oven, vacuum dryer, high frequency/microwave dryer, or the like. When the drying is completed, the locations where there were water droplets in the emulsion before polymerization become bubbles in the polymer after drying, and a porous body can be obtained. Before drying, the crosslinked polymer can be dehydrated by compression using, for example, a press. Squeezing may be performed at room temperature (for example, 23° C.), but it can also be performed, for example, at a temperature equal to or higher than the glass transition temperature of the crosslinked polymer constituting the HIPE foam. In this case, dehydration by squeezing becomes easy and drying time can be shortened. Further, the crosslinked polymer can also be dehydrated by centrifugation. In this case too, the drying time is shortened.

Examples and comparative examples of HIPE foam will be described below. In this example, HIPE foams shown in Examples in Table 2 and Comparative Examples in Table 3 were manufactured by the following method. Note that the specific aspects of the HIPE foam according to the present invention are not limited to the aspects of the examples shown below, and the configuration can be changed as appropriate within the scope of the gist of the present invention. In addition, "%" in Examples means weight %. Example 5 is a reference example in this application.

[Example 1]
First, in a glass container with an internal volume of 3 L equipped with a stirring device, 54 g of styrene as a vinyl monomer and 24 g of butyl acrylate were placed in a glass container with a purity of 57% as a hard crosslinking agent (hereinafter referred to as the first crosslinking agent). Divinylbenzene: 12g (6.84g as divinylbenzene), polyethylene glycol diacrylate as a soft crosslinking agent (hereinafter referred to as the second crosslinking agent) (specifically, NK ester A- manufactured by Shin Nakamura Chemical Co., Ltd.) 400/purity 95%): 5 g (4.75 g as polyethylene glycol diacrylate), polyglycerin condensed ricinoleate as an emulsifier (specifically, CRS-75 manufactured by Sakamoto Pharmaceutical Co., Ltd.): 5 g, as a polymerization initiator 0.5 g of lauroyl peroxide was added. An organic phase was formed by mixing these in a glass container.

While stirring the organic phase at a stirring power density of 1.6 kW/m ³ , 614 g of pure water was added at a rate of about 450 g/min. After the addition of water was finished, stirring was continued for 10 min, and the mixture was stirred in the oil. A water type (that is, W/O type) high internal phase emulsion was prepared. The stirring power density after completion of emulsification was 1.4 kW/m ³ .

Next, the stirring power density was lowered to 0.1 kW/m ³ and an aspirator was connected to the glass container to reduce the pressure inside the container to remove microbubbles contained in the emulsion. Ten minutes after the start of pressure reduction, stirring was stopped and the inside of the container was returned to atmospheric pressure.

The contents were filled into a stainless steel container with a length of about 140 mm, a width of about 110 mm, and a depth of about 60 mm, and polymerized in an oven at 70° C. for about 18 hours to obtain a water-containing HIPE foam. The HIPE foam was removed from the oven and cooled to room temperature.

After cooling, the HIPE foam was taken out from the stainless steel container, washed with water, dehydrated, and dried in an oven at 85° C. until it reached a constant weight. In this way, a rectangular parallelepiped-shaped HIPE foam made of a vinyl crosslinked polymer was obtained. The apparent density of this HIPE foam was 147 g/L.

Table 2 shows the charging composition of this example. In addition, in the table, compound names are abbreviated as follows.
St: Styrene BA: Butyl acrylate MMA: Methyl methacrylate DVB: Divinylbenzene TMPTA: Trimethylolpropane triacrylate BDODA: Butanediol diacrylate PEGDA: Polyethylene glycol diacrylate UDA: Urethane diacrylate LPO: Lauroyl peroxide

[Examples 2 to 13, Comparative Examples 1 to 6]
Example 1 except that the types and blending ratios of the vinyl monomer, the first crosslinking agent, and the second crosslinking agent, the blending ratio of the emulsifier, and the amount of water added were changed as shown in Tables 2 and 3. HIPE foam was produced in the same manner. In Example 10, emulsification was started while stirring the organic phase at a stirring power density of 3.1 kW/m ³ to prepare a W/O type high internal phase emulsion. The stirring power density after emulsification was completed was 2.0 kW/m ³ . In Example 11, emulsification was started while stirring the organic phase at a stirring power density of 1.0 kW/m ³ to prepare a W/O type high internal phase emulsion. The stirring power density after emulsification was completed was 0.9 kW/m ³ . In Example 12, emulsification was started while stirring the organic phase at a stirring power density of 0.5 kW/m ³ to prepare a W/O type high internal phase emulsion. The stirring power density after emulsification was completed was 0.4 kW/m ³ .

[evaluation]
The following measurements and evaluations were performed for Examples 1 to 13 and Comparative Examples 1 to 6. The results for Examples 1 to 13 are shown in Table 2, and the results for Comparative Examples 1 to 6 are shown in Table 3.

(apparent density: ρ)
A test without a skin layer of a specified size (specifically, thickness: 20 mm, width: 25 mm, length: 120 mm) from the HIPE foam, including the center of the HIPE foam manufactured as described above. I cut out three pieces. Next, the weight and actual size (specifically, volume) of the test piece were measured. The apparent density of the test piece was calculated by dividing the weight of the test piece by the volume, and the arithmetic mean value of the apparent densities of the three test pieces was taken as the apparent density ρ of the HIPE foam.

(Glass transition temperature: Tg)
Tg was calculated by differential scanning calorimetry (ie, DSC) analysis based on JIS K7121:1987. As a measuring device, DSC250 manufactured by T.A. Instruments was used. Specifically, first, about 2 mg of a test piece was taken from near the center of the HIPE foam. As for the condition adjustment of the test piece, "(3) When measuring the glass transition temperature after performing a certain heat treatment" was adopted. Next, a DSC curve was obtained by performing DSC measurement on the test piece at a heating rate of 10° C./min. The midpoint glass transition temperature was determined from this DSC curve, and this value was defined as the glass transition temperature Tg.

(Storage modulus at 23°C: E')
Three 5 mm x 5 mm x 5 mm cube-shaped test pieces without a skin layer were cut out from near the center of the HIPE foam. These three test pieces were subjected to dynamic viscoelastic analysis (DMA) to measure the storage modulus E' at 23°C. As a measuring device, DMA7100 manufactured by Hitachi High-Tech Science Co., Ltd. was used. The arithmetic mean value of the measured values was defined as the storage modulus E' at 23°C. The details of the measurement conditions are as follows.
・Deformation mode: Compression ・Temperature: 0-200℃
・Temperature increase rate: 5℃/min
・Frequency: 1Hz
・Load: 98mN

(Molecular weight between crosslinking points: Mc)
The molecular weight between crosslinking points Mc was calculated from the above formula (II) using the storage elastic modulus E' and temperature T in the rubbery flat part measured by dynamic viscoelastic analysis of the three test pieces. Note that FIG. 2 shows a typical example of the DMA curve of the HIPE foam of the example. The DMA curve is obtained by plotting temperature on the horizontal axis and storage modulus E' on the vertical axis. In the examples, each crosslinking point is determined from the storage modulus E' at three temperatures randomly selected from within the temperature range of Tg + 50°C to Tg + 80°C, which is the rubbery flat part of the crosslinked polymer constituting the HIPE foam. The arithmetic mean value of the nine calculated molecular weights between crosslinking points was employed as the molecular weight between crosslinking points Mc. Note that Tg is the glass transition temperature of the HIPE foam.

(Smoothness of cutting surface)
First, cutting was performed on the HIPE foam as follows. Specifically, a straight groove was cut into the HIPE foam using an NCN8200 manufactured by SHODA Co., Ltd. as a cutting machine and a square end mill (4 blades, diameter 20 mm) manufactured by Fukuda Seiko Co., Ltd. as a cutting tool. was formed. The cutting conditions are as follows.
・Mill rotation speed: 3000rpm
・Mill feed speed: 5000mm/min
・Cutting depth: 10mm
Next, the surface roughness of the cut surface (specifically, the bottom surface of the groove) was measured using a 3D shape measuring machine VR-3200 manufactured by Keyence Corporation. The observation magnification was 12 times, and the measurement area was approximately 18 mm x 24 mm in actual size. This range corresponds to the entire area of the observation surface. As for surface roughness, arithmetic mean surface roughness Sa and maximum surface roughness Sz were measured. Note that the arithmetic mean surface roughness Sa is the average value of the unevenness from the reference surface, and the maximum surface roughness is the difference between the highest point and the lowest point.
Smoothness is evaluated as "○" when the arithmetic mean surface roughness Sa is 20 μm or less and the maximum surface roughness Sz is 500 μm or less, and when the arithmetic mean surface roughness Sa exceeds 20 μm or the maximum surface roughness A case where Sz exceeded 500 μm was evaluated as “×”.

(Hard to chip)
In order to evaluate the resistance to chipping, a visual evaluation was performed on a straight groove machined using the same cutting machine and cutting conditions as used for the above-mentioned evaluation of the smoothness of the cut surface. If there is no chipping or cracking in the right-angled part formed by the groove and groove, the chipping resistance is evaluated as "〇", and if chipping or cracking occurs, the chipping resistance is evaluated as "x". did.

(Charpy impact strength: S)
A test piece with a thickness of 4 mm, width: 10 mm, and length: 80 mm without a skin layer was cut from near the center of the HIPE foam, and a Charpy impact test was conducted in accordance with JIS K7111:2006 to determine the Charpy impact strength of the test piece. was measured. The measurement was carried out using a Charpy impact tester manufactured by Toyo Seiki Seisakusho Co., Ltd., at a measurement temperature of 23° C. and without a notch. Further, by dividing the Charpy impact strength by the apparent density, the value S/ρ of the Charpy impact strength with respect to the apparent density was calculated.

・Average bubble diameter (difficulty in chewing sand)
The average cell diameter of the HIPE foam was measured and the difficulty of sand chewing was determined. The difficulty of sand chewing was evaluated as "○" when the average bubble diameter was 100 μm or less, and as "x" when the average bubble diameter exceeded 100 μm. The method for measuring the average bubble diameter is as follows. Using a feather blade, samples for observation were cut out from the center of the rectangular parallelepiped-shaped HIPE foam in the transverse direction and the thickness direction, and from the center of the thickness direction at both ends of the transverse direction. Next, the sample was observed with a low vacuum scanning electron microscope (Miniscope (registered trademark) TM3030Plus, manufactured by Hitachi High-Tech Science Co., Ltd.), and a cross-sectional photograph was taken. A typical example of a cross-sectional photograph (magnification: 500 times) of the example is shown in FIG. The detailed observation conditions were as follows.
- Sample pretreatment: The sample was subjected to conductive treatment using a metal coating device (MSP-1S manufactured by Vacuum Device Co., Ltd.). Au--Pd was used for the target electrode.
・Observation magnification: 50x ・Acceleration voltage: 5kV
・Observation conditions: Surface ・Observation mode: Secondary electron (standard)
Next, the cross-sectional photographs taken were analyzed using image processing software (NanoHunter NS2K-Pro, manufactured by Nano System Co., Ltd.) to determine the average bubble diameter of each sample. The average cell diameter of the HIPE foam was determined by arithmetic averaging the three average cell diameters obtained. The detailed analysis procedure and conditions were as follows.
(1) Monochrome conversion (2) Smoothing filter (3 x 3, 8 neighborhoods, number of processing = 1)
(3) Density unevenness correction (brighter than background, size = 5)
(4) NS method binarization (darker than background, sharpness = 9, sensitivity = 1, noise removed, density range = 0 to 255)
(5) Shrinkage (near 8, number of processing = 1)
(6) Image selection based on feature quantity (area) (select only 50 to ∞μm ² , 8 neighborhoods)
(7) Expansion not connected to neighbors (8 neighbors, number of processing = 3)
(8) Circle equivalent diameter measurement (calculated from area, 8 neighborhood)

As understood from Table 2, the HIPE foam of the example can sufficiently increase the machining speed during cutting. In the evaluation of smoothness, cutting was actually performed at a sufficiently fast mill feed rate of 5000 mm/min, but in the example, the HIPE foam showed excellent smoothness without chipping or cracking. A cut surface was formed. This is because, in the example, the apparent density ρ, the Charpy impact strength value S/ρ relative to the apparent density, the storage elastic modulus value E'/ρ relative to the apparent density, and the molecular weight between crosslinking points Mc are within the above-described predetermined ranges. be.

The vinyl crosslinked polymer constituting the HIPE foam of the example has not only a crosslinked structure caused by a crosslinking agent but also an open cell structure as shown in the representative example of FIG. Therefore, shrinkage due to the pressure difference between the inside and outside of the cells, which tends to occur in a porous body with a closed cell structure, is less likely to occur, and the dimensions are less likely to change over time, resulting in excellent dimensional stability. Therefore, for example, when a cut product is used as a wooden mold, a highly accurate casting can be manufactured. Furthermore, since the cut product itself can be prevented from changing its shape and dimensions, the HIPE foam of the example is suitable for various uses that require prevention of dimensional changes.

Further, the HIPE foam of the example is a crosslinked polymer formed from a copolymer of at least a styrene monomer and an acrylic monomer. Therefore, it has a good balance of rigidity and toughness while having appropriate brittleness. Therefore, HIPE foam is suitable for cutting.

Moreover, the average cell diameter of the HIPE foam of the example is sufficiently smaller than the particle diameter of the silica sand used in the sand mold. Therefore, HIPE foam is suitable for casting models, and in particular for wooden molds used for forming sand molds. Moreover, when using the cut product of the HIPE foam of the example as a casting model, it is not necessarily necessary to provide a coating layer. Further, since the HIPE foam of the example has a small average cell diameter, a cut product with a clear appearance (that is, fine texture) and a high design quality can be obtained by cutting.

Comparative Example 1 was an example in which the molecular weight between crosslinking points was large, and the smoothness of the cut surface was insufficient.

Comparative Example 2, Comparative Example 3, and Comparative Example 5 are examples in which the Charpy impact strength value S/ρ relative to the apparent density is small, and they are likely to chip during cutting.

Comparative Examples 4 and 6 are examples in which the storage elastic modulus value E'/ρ at 23° C. relative to the apparent density is small, and the smoothness of the cut surface is insufficient.

1 HIPE foam 11 Crosslinked polymer 12 Cell wall 13 Cell 14 Pore

Claims (7)

HIPE foam is composed of a vinyl crosslinked polymer containing a styrene monomer component and/or an acrylic monomer component , and is used to form a cut product by cutting,
The apparent density ρ is 50 to 500 kg/m ³ ,
The value S/ρ of Charpy impact strength S with respect to the above apparent density ρ is 4.5 J · m / kg or more,
The storage elastic modulus E' at 23°C and the above apparent density ρ are measured by performing dynamic viscoelasticity measurements on the HIPE foam at a frequency of 1 Hz, a load of 98 mN, and a deformation mode of compression. satisfies the relationship of formula (I) below,
The molecular weight between crosslinking points Mc measured by performing the above dynamic viscoelasticity measurement is 2 × 10 ⁴ or less ,
The HIPE foam has a glass transition temperature of 50° C. or higher .
E'/ρ≧50kN・m/kg...(I) The HIPE foam according to claim 1, wherein the HIPE foam has an average cell diameter of 100 μm or less. The HIPE foam according to claim 1 or 2, wherein the HIPE foam has a glass transition temperature of 120°C or less . The vinyl crosslinked polymer is composed of a polymer of a vinyl monomer containing a styrene monomer and/or an acrylic monomer and a crosslinking agent,
The vinyl monomer contains styrene and/or methyl methacrylate,
The HIPE foam according to any one of claims 1 to 3 , wherein the total content of styrene and methyl methacrylate in the vinyl monomer is 40% by weight or more . The vinyl crosslinked polymer is composed of a copolymer of a crosslinking agent and a vinyl monomer containing styrene and/or methyl methacrylate and an alkyl (meth)acrylate other than methyl methacrylate. The HIPE foam according to any one of claims 1 to 4, wherein the (meth)acrylic acid alkyl ester is an ester of (meth)acrylic acid and an alcohol having 1 to 20 carbon atoms. The vinyl crosslinked polymer includes a vinyl monomer component, a first crosslinking agent component having a functional group equivalent of 130 g/mol or less, and a first crosslinking agent component having a functional group equivalent of more than 130 g/mol and 5000 g/mol or less. 2. HIPE foam according to any one of claims 1 to 5, comprising two crosslinker components. HIPE foam according to any one of claims 1 to 6, wherein the cut workpiece is a casting model.

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