Foam, additive for producing foam, powder, and method for producing foam

Abstract

Provided is a foam that has a low density suitable for a cushioning material. This foam contains starch (A), a vinyl alcohol-based polymer (B), and an inorganic compound (C). When a scattering intensity measurement is performed in pure water by a dynamic light scattering method at 25°C for components that pass through 200 mesh among dimethyl sulfoxide-insoluble contents included in the foam, the scattering intensity area derived from particles having a particle size of 1.5 µm or less accounts for 60% or more of the areas of all peaks in a particle size range of 8.0 µm or less.

Description

Foam, additives for foam production, powder, and method for producing foam

[0001] The present invention relates to foams, additives for foam production, powders, and methods for producing foams.

[0002] Expanded polystyrene (expanded polystyrene) is widely used as a foam material for cushioning and other applications. Expanded polystyrene is lightweight, inexpensive, and possesses excellent impact resistance and insulation properties, making it highly convenient. On the other hand, expanded polystyrene is prone to beads detaching due to external impacts, and is a common cause of fine plastic waste floating in the ocean. There are concerns that the chemical substances contained in this fine plastic waste floating in the ocean can be incorporated into the food chain and affect ecosystems, so countermeasures are desired. Against this backdrop, the development of biodegradable foams is progressing, and one example is a cushioning material containing starch and vinyl alcohol polymers. Patent document 1 describes a biodegradable resin foam manufactured by mixing a starch polymer with a specific water content, a polyvinyl alcohol resin, a nonionic surfactant, a thickener, and an inorganic filler.

[0003] Japanese Patent Application Publication No. 6-271694

[0004] In foams, low density and the formation of dense pores are desirable for them to exhibit excellent functionality as cushioning materials. However, conventional foams using starch and vinyl alcohol polymers do not have sufficiently low density, and there is a need for the development of foams more suitable as cushioning materials.

[0005] The present invention was made to solve the above problems and aims to provide a foam having a low density suitable for use as a cushioning material, as well as an additive for foam production, a powder, and a method for producing such a foam.

[0006] The above problems are: [1] A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein, in a measurement of the scattering intensity in pure water at 25°C using dynamic light scattering of the dimethyl sulfoxide insoluble components of the foam that pass through a 200-mesh mesh, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less is 60% or more; [2] A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein, in a wet measurement using laser diffraction / scattering, the mode diameter of the inorganic compound (C) is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm³. ３The foams are as follows: [3] The foam of [1] or [2] in which the primary particles of the inorganic compound (C) have a plate-like crystalline structure; [4] The foam of any of [1] to [3] in which the inorganic compound (C) has a petal-like crystalline structure; [5] The foam of any of [1] to [4] in which the inorganic compound (C) contains at least one selected from the group consisting of calcium carbonate and magnesium carbonate; [6] The foam of [5] in which the inorganic compound (C) contains at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide and calcium hydroxide; [7] The foam of any of [1] to [6] in which the inorganic compound (C) contains the element magnesium; [8] The foam of any of [1] to [7] in which the inorganic compound (C) contains basic magnesium carbonate; [9] The foam of any of [1] to [8] in which the inorganic compound (C) contains light basic magnesium carbonate;

[10] Any foam from [1] to [9], wherein the degree of saponification of vinyl alcohol polymer (B) is 70 mol% or more and 99 mol% or less;

[11] Any foam from [1] to

[10] , wherein the viscosity-average degree of polymerization of vinyl alcohol polymer (B) is 1,000 or more and 5,000 or less;

[12] Any foam from [1] to

[11] , wherein the starch (A) content in the total components with a boiling point of 105°C or higher is 70% by mass or more and 95% by mass or less;

[13] Any foam from [1] to

[12] , wherein the vinyl alcohol polymer (B) content in the total components with a boiling point of 105°C or higher is 4% by mass or more and 30% by mass or less;

[14] Any foam from [1] to

[13] , wherein the inorganic compound (C) content in the total components with a boiling point of 105°C or higher is 0.1% by mass or more and 5% by mass or less;

[15] Density is 0.005 g / cm³ ３ 0.07g / cm or more ３The following foams are any of [1] to

[14] :

[16] A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate;

[17] The foam of

[16] , wherein the inorganic compound (C) contains light basic magnesium carbonate;

[18] A powdered foam manufacturing additive containing a vinyl alcohol polymer (B) and an inorganic compound (C), wherein, in a measurement of the scattering intensity in pure water at 25°C by dynamic light scattering of the dimethyl sulfoxide insoluble components contained in the foam manufacturing additive that pass through a 200 mesh, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less is 60% or more;

[19] A powdery foam manufacturing additive containing at least one resin (B') selected from the group consisting of vinyl alcohol polymers, polyolefins, and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the mode diameter of the inorganic compound (C) in wet measurement using laser diffraction / scattering method is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm³. ３The following are foam manufacturing additives:

[20] The foam manufacturing additive of

[18] or

[19] , wherein the solubility of inorganic compound (C) in 100 g of water at 20°C is 0.01 g or more and 0.50 g or less;

[21] The foam manufacturing additive of any of

[18] to

[20] , wherein the primary particles of inorganic compound (C) have a plate-like crystalline structure;

[22] The foam manufacturing additive of any of

[18] to

[21] , wherein the inorganic compound (C) has a petal-like crystalline structure;

[23] The foam manufacturing additive of any of

[18] to

[22] , wherein the inorganic compound (C) contains basic magnesium carbonate;

[24] The foam manufacturing additive of any of

[18] to

[23] , wherein the content of inorganic compound (C) per 100 parts by mass of vinyl alcohol polymer (B) or resin (B') is 0.1 parts by mass or more and 30 parts by mass or less;

[25] A foam manufacturing additive from any of

[18] to

[24] , wherein an inorganic compound (C) is present on at least the surface of a powder of a vinyl alcohol polymer (B) or resin (B');

[26] A powder foam manufacturing additive containing at least one resin (B') selected from the group consisting of vinyl alcohol polymers, polyolefins and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate;

[27] A powder containing a vinyl alcohol polymer (B) and an inorganic compound (C), wherein the inorganic compound (C) has a petal-shaped crystalline structure;

[28] A method for manufacturing a foam from any of [1] to

[17] , comprising the steps of kneading starch (A), a vinyl alcohol polymer (B), an inorganic compound (C), and water to obtain a kneaded product, and foaming the kneaded product; The problem is solved by providing one of the following:

[29] A method for producing a foam, comprising the steps of kneading starch with any of the foam production additives from

[18] to

[26] to obtain a kneaded product, and foaming the kneaded product.

[0007] According to the present invention, it is possible to provide a foam having a low density suitable for use as a cushioning material, as well as an additive for foam production, a powder, and a method for producing such a foam.

[0008] <Foam> A foam according to an embodiment of the present invention is a foam containing starch (A), a vinyl alcohol polymer (hereinafter also referred to as "PVOH") (B), and an inorganic compound (C), and dimethyl sulfoxide (hereinafter also referred to as "DMSO") insoluble matter contained in the foam In the measurement of the scattering intensity in pure water by the dynamic light scattering method at 25°C of the components passing through 200 mesh, the ratio of the scattering intensity area of the region with a particle size of 1.5 μm or less to the total scattering intensity area of the region with a particle size of 8.0 μm or less is 60% or more. The foam has a low density suitable for a cushioning material. The reason for such an effect is presumed to be as follows. In the foam, in the measurement of the scattering intensity in pure water by the dynamic light scattering method at 25°C of the components passing through 200 mesh of the DMSO insoluble matter contained in the foam, the ratio of the scattering intensity area of the region with a particle size of 1.5 μm or less to the total scattering intensity area of the region with a particle size of 8.0 μm or less is 60% or more. This typically means that many of the components passing through 200 mesh of the DMSO insoluble matter such as the inorganic compound (C) are present in the foam in the form of fine particles with a particle size of 1.5 μm or less. In the production of the foam, usually, a nucleating agent which is a fine particle serves as a nucleus and bubbles are formed. In the foam according to an embodiment of the present invention, the particles functioning as a nucleating agent are particularly fine, so that they can exhibit an excellent function as a nucleating agent, and it is presumed that a low-density foam with good foaming is obtained.

[0009] A foam according to another embodiment of the present invention is a foam containing starch (A), PVOH (B), and an inorganic compound (C), and the mode diameter of the inorganic compound (C) in wet measurement using the laser diffraction / scattering method is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm ３ or less. The foam has small pore diameters of the formed bubbles and a low density suitable for a cushioning material. The reason for such an effect is presumed to be that the fine inorganic compound (C) functions as a good nucleating agent.

[0010] The foam according to another embodiment of the present invention is a foam containing starch (A), PVOH (B), and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate. The foam also has small pore diameters of the formed bubbles and a low density suitable for a cushioning material. The reason for such an effect is presumably that the inorganic compound (C) containing basic magnesium carbonate functions as a good nucleating agent.

[0011] Hereinafter, each component and the like of the foam according to the embodiment of the present invention will be described in detail.

[0012] (Starch (A)) Starch (A) is usually a component that becomes the main component of the foam according to the embodiment of the present invention. The main component means the component having the largest content on a mass basis. Starch (A) is not particularly limited, and examples include natural starches such as corn starch, potato starch, sweet potato starch, wheat starch, rice starch, tapioca starch, sago starch; processed starches such as etherified, esterified, and oxidized starches. One kind or two or more kinds of starch (A) can be used.

[0013] The lower limit of the content of starch (A) in all components having a boiling point of 105 ° C. or higher in the foam according to the embodiment of the present invention is preferably 70% by mass, more preferably 75% by mass, and further preferably 78% by mass, 80% by mass, 82% by mass or 85% by mass. The upper limit of the content of the starch (A) is preferably 95% by mass, more preferably 92% by mass, and further preferably 90% by mass. When the content of the starch (A) is within the above range, the foaming state of the foam tends to be good.

[0014] (PVOH (B)) PVOH (B) is a component that improves the moldability, physical properties, etc. of the foam. By containing PVOH (B), the stretchability during foaming, the curability after foaming, etc. can be enhanced, and the brittleness of the obtained foam can be improved. In addition, since both starch (A) and PVOH (B) are biodegradable resins, a foam with high biodegradability can be obtained by using these resins.

[0015] PVOH (B) is a vinyl alcohol unit (-CH ２It is a polymer having -CHOH-). Vinyl alcohol polymers are usually obtained by saponification of vinyl ester polymers. Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerianate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versaticate. Vinyl acetate is preferred as the vinyl ester monomer. When polymerizing vinyl esters, the vinyl ester may be copolymerized with other monomers.

[0016] The lower limit of the viscosity-average degree of polymerization of PVOH(B) is preferably 1,000, more preferably 1,200, even more preferably 1,400, and even more preferably 1,500. The upper limit of the viscosity-average degree of polymerization is preferably 5,000, more preferably 4,000, even more preferably 3,000, and even more preferably 2,000. When the viscosity-average degree of polymerization of PVOH(B) is within the above range, the foam tends to have density, strength, etc., that are more suitable for use as a buffer material.

[0017] The viscosity-average degree of polymerization of PVOH(B) is measured in accordance with JIS K 6726:1994. Specifically, the intrinsic viscosity [η] (liters / g) of PVOH is measured in water at 30°C, and the viscosity-average degree of polymerization P is calculated using the following formula based on this intrinsic viscosity [η] value. If the degree of saponification of PVOH is less than 99.5 mol%, the intrinsic viscosity [η] is measured after saponification until the degree of saponification reaches 99.5 mol% or more. P = ([η] × 10⁻¹⁰ ４ (8.29) （１／０．６２）

[0018] The lower limit of the degree of saponification of PVOH(B) is preferably 70 mol%, more preferably 80 mol%, more preferably 90 mol%, even more preferably 95 mol%, and may also be 96 mol%, 97 mol%, or 98 mol%. On the other hand, the upper limit of the degree of saponification is preferably 99 mol%, and more preferably 98 mol%. When the degree of saponification of PVOH(B) is within the above range, the density, strength, etc. of the foam tend to be more suitable for cushioning material. The degree of saponification of PVOH(B) is measured in accordance with JIS K 6726:1994.

[0019] PVOH(B) may have monomer units derived from monomers other than vinyl esters. Other monomers include α-olefins such as ethylene, propylene, n-butene, and isobutylene; (meth)acrylic acid and its salts; (meth)acrylic acid esters; (meth)acrylamide; (meth)acrylamide derivatives such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone(meth)acrylamide, (meth)acrylamidepropanesulfonic acid and its salts, (meth)acrylamidepropyldimethylamine and its salts or quaternary salts, N-methylol(meth)acrylamide and its derivatives; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether Examples include vinyl ethers such as tel, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, and fumaric acid, and their salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; 1,4-diacetoxybutene; 3,4-diacetoxy-1-butene; vinylformamide; and vinylpyrrolidone.

[0020] Other monomers include α-olefins, and more preferably ethylene. That is, the vinyl alcohol polymer may be an α-olefin-vinyl alcohol copolymer or an ethylene-vinyl alcohol copolymer (ethylene-modified polyvinyl alcohol).

[0021] The lower limit of the content of α-olefin units relative to the total monomer units in the α-olefin-vinyl alcohol copolymer is preferably 0.1 mol%, more preferably 0.5 mol%, even more preferably 1 mol%, and may also be 2 mol%, 3 mol%, 4 mol%, or 5 mol%. On the other hand, the upper limit of this content is preferably 20 mol%, more preferably 15 mol%, even more preferably 13 mol%, and may also be 10 mol% or 8 mol%. The lower limit of the content of ethylene units relative to the total monomer units in the ethylene-modified polyvinyl alcohol (hereinafter sometimes referred to as the ethylene modification amount) is preferably 0.1 mol%, more preferably 0.5 mol%, even more preferably 1 mol%, and may also be 2 mol%, 3 mol%, 4 mol%, or 5 mol%. On the other hand, the upper limit of this content is preferably 20 mol%, more preferably 15 mol%, even more preferably 13 mol%, and may also be 10 mol% or 8 mol%.

[0022] The lower limit of the total content of vinyl alcohol units, vinyl ester units, and any α-olefin units relative to the total monomer units of PVOH(B) is preferably 80 mol%, more preferably 90 mol%, and may be 95 mol%, 97%, 99 mol%, or 99.5 mol%. The upper limit of the above total content may be 100 mol%.

[0023] For PVOH(B), only one type of PVOH may be used, or two or more types of PVOH with different degrees of polymerization, saponification, monomer unit composition, etc., may be used.

[0024] The lower limit of the PVOH(B) content in the foam according to the embodiment of the present invention, in relation to all components with a boiling point of 105°C or higher, is preferably 4% by mass, more preferably 7% by mass, and even more preferably 10% by mass, 12% by mass, or 15% by mass. The upper limit of the PVOH(B) content is preferably 30% by mass, more preferably 25% by mass, and even more preferably 22% by mass, 20% by mass, or 18% by mass. When the PVOH(B) content is within the above range, the foaming state of the foam tends to be better.

[0025] The lower limit of the PVOH(B) content in the foam according to the embodiment of the present invention is preferably 1 part by mass, more preferably 3 parts by mass, and even more preferably 5 parts by mass, 10 parts by mass, 12 parts by mass, or 15 parts by mass per 100 parts by mass of starch (A). The upper limit of the PVOH(B) content is preferably 40 parts by mass, more preferably 35 parts by mass, and even more preferably 30 parts by mass or 25 parts by mass. When the PVOH(B) content relative to starch (A) is within the above range, the foaming state of the foam tends to be better. Note that "100 parts by mass of starch (A)", which is the standard for the content of substances other than starch (A), means the mass of starch excluding the water originally contained in the starch.

[0026] (Inorganic Compound (C)) Inorganic compound (C) is a component that acts as a nucleating agent when manufacturing foam. Typically, inorganic compound (C) exists dispersed in the foam in the form of particles. Inorganic compound (C) is preferably a solid component with a melting point or decomposition temperature of 180°C or higher, 200°C or higher, 220°C or higher, 240°C or higher, 260°C or higher, or 300°C or higher. Inorganic compound (C) is usually a component with low solubility in water and can exist in particulate form in a mixture containing water. In addition, inorganic compound (C) is usually a component that is substantially insoluble in DMSO.

[0027] In a measurement of the scattering intensity in pure water at 25°C using dynamic light scattering at an embodiment of the present invention, the scattering intensity area of ​​the region with a particle size of 1.5 μm or less relative to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less is 60% or more. Hereinafter, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less relative to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less in the above scattering intensity measurement is also referred to as the "percentage of particles with a particle size of 1.5 μm or less". The lower limit of the percentage of particles with a particle size of 1.5 μm or less is preferably 70%, more preferably 75%, and even more preferably 80%. By having a percentage of particles with a particle size of 1.5 μm or less that is above the above lower limit, many of the components of the DMSO-insoluble matter that pass through the 200 mesh, such as inorganic compounds (C), function as good nucleating agents, and a low-density foam with good foaming can be obtained. The upper limit for the proportion of particles with a particle size of 1.5 μm or less may be 100%, 99%, 97%, or 95%.

[0028] The measurement of the scattering intensity in pure water at 25°C using dynamic light scattering for components of the DMSO-insoluble material contained in the foam that pass through a 200-mesh net is performed by the method described in the examples.

[0029] The "components that pass through the 200-mesh densitometer among the DMSO-insoluble components contained in the foam" typically include at least a portion of inorganic compound (C). The "components that pass through the 200-mesh densitometer among the DMSO-insoluble components contained in the foam" may also include components other than inorganic compound (C). The lower limit of the proportion of inorganic compound (C) among the "components that pass through the 200-mesh densitometer among the DMSO-insoluble components contained in the foam" is, for example, 30% by mass, and may be 40% by mass, 50% by mass, 60% by mass, 70% by mass, 80% by mass, or 90% by mass. The upper limit of the proportion of inorganic compound (C) among the "components that pass through the 200-mesh densitometer among the DMSO-insoluble components contained in the foam" may be 100% by mass.

[0030] Also, usually, the inorganic compound (C) is included in the "component passing through 200 mesh among the DMSO-insoluble components contained in the foam". As the lower limit of the ratio of the "component passing through 200 mesh among the DMSO-insoluble components contained in the foam" in the inorganic compound (C), 90% by mass is preferable, 95% by mass is more preferable, and 99% by mass is even more preferable. The upper limit of the ratio of the "component passing through 200 mesh among the DMSO-insoluble components contained in the foam" in the inorganic compound (C) may be 100% by mass.

[0031] In the above scattering intensity measurement, the scattering in the region with a particle size of 1.5 μm or less is derived not only from the inorganic compound (C), but also from the insoluble components of starch (A) and PVAH (B) and the insoluble components of other optional components. The same applies to the scattering in the region with a particle size exceeding 1.5 μm in the above scattering intensity measurement. In other words, the proportion of particles with a particle size of 1.5 μm or less is also affected by components other than the inorganic compound (C). Also, the type and shape of the inorganic compound (C) may affect the generation of insoluble components of starch (A) and PVAH (B). The manufacturing conditions (kneading conditions, foaming conditions, etc.) during the production of the foam may also affect the generation of insoluble components of starch (A) and PVAH (B) and the proportion of particles with a particle size of 1.5 μm or less.

[0032] In one embodiment of the present invention, the upper limit of the mode diameter of the inorganic compound (C) in the wet measurement using the laser diffraction / scattering method is 3.0 μm, preferably 2.6 μm, more preferably 2.2 μm, even more preferably 1.8 μm, and even more preferably 1.5 μm. Since the inorganic compound (C) is such fine particles, it functions as a good nucleating agent, and a foam with a low density can be obtained. The lower limit of the above mode diameter may be, for example, 0.3 μm, or may be 0.5 μm, 0.7 μm or 1.0 μm. The above mode diameter of the inorganic compound (C) is measured by the method described in the examples.

[0033] In one embodiment of the present invention, the upper limit of the bulk density of the inorganic compound (C) may be, for example, 0.80 g / cm ３ but 0.40 g / cm ３ is preferable, and 0.35 g / cm ３More preferably, 0.30 g / cm³ ３ A more preferable concentration is 0.27 g / cm³. ３ Even more preferable is 0.24 g / cm³. ３ This is particularly preferable. For example, when the loose bulk density is low for an inorganic compound (C) with a particle size (e.g., mode diameter, etc.) of similar size, it can be said that the bulkiness is due to the complex shape of the particles with many irregularities. When such an inorganic compound (C) with a low loose bulk density and a complex shape with many irregularities is used, the inorganic compound (C) functions as a good nucleating agent, making it possible to reduce the pore size of the bubbles in the resulting foam and lower the density. The lower limit of the above loose bulk density is, for example, 0.05 g / cm³. ３ It may also be 0.10 g / cm³. ３ , 0.13 g / cm³ ３ , 0.15 g / cm ３ Or 0.17 g / cm³ ３ That's fine.

[0034] "Loose bulk density" refers to the bulk density when the sample is allowed to fall naturally through a sieve and fill a container, and the value shall be measured in accordance with the Japan Powder Industry Technology Association standard SAP05-98:2013.

[0035] The inorganic compound (C) may be present in the foam in the form of primary particles or in the foam in the form of secondary particles.

[0036] The inorganic compound (C) may be amorphous or crystalline, but it is preferably crystalline. The crystalline structure of the primary particles of the inorganic compound (C) is preferably plate-like. By using an inorganic compound (C) whose primary particles have a plate-like crystalline structure, the inorganic compound (C) functions as a better nucleating agent, making it possible to reduce the pore size of the bubbles in the resulting foam, lower the density, and so on.

[0037] The inorganic compound (C) preferably has a petal-shaped crystalline structure as secondary particles. By using an inorganic compound (C) whose secondary particles have a petal-shaped crystalline structure, the inorganic compound (C) functions as a better nucleating agent, making it possible to reduce the pore size of the bubbles in the resulting foam and lower its density. This is because the petal-shaped form itself functions well as a nucleating agent, and secondary particles with a petal-shaped crystalline structure are more easily refined into finer particles during the kneading process in the manufacturing of the foam, and these refined particles function as particularly good nucleating agents. Even when an inorganic compound (C) with a petal-shaped crystalline structure is used and a foam is obtained through the kneading process, not all of the inorganic compound (C) is refined, and at least some of the inorganic compound (C) may remain in the foam while maintaining its petal-shaped crystalline structure. The crystalline structure of the primary or secondary particles of the inorganic compound (C) can be confirmed by an electron microscope or the like.

[0038] Examples of inorganic compounds (C) include carbonates such as calcium carbonate and magnesium carbonate, phosphates such as tricalcium phosphate, silicates such as calcium silicate and magnesium silicate, hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide, oxides such as titanium dioxide, aluminum oxide, and magnesium oxide, talc, silica, clay, kaolin, and white carbon. One or more inorganic compounds (C) can be used.

[0039] The inorganic compound (C) preferably contains a carbonate, more preferably contains at least one selected from the group consisting of calcium carbonate and magnesium carbonate, and even more preferably contains magnesium carbonate. The inorganic compound (C) containing a carbonate functions as a better nucleating agent, which can reduce the pore size of the bubbles in the resulting foam, lower the density, and so on.

[0040] The inorganic compound (C) may also preferably contain a hydroxide. The hydroxide is preferably at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide, more preferably at least one selected from the group consisting of magnesium hydroxide and calcium hydroxide, and even more preferably magnesium hydroxide. In particular, the inorganic compound (C) preferably contains a hydroxide together with a carbonate. In this case, it is preferable that the carbonate and the hydroxide contain the same metal element. Specific examples of such forms include the inorganic compound (C) containing magnesium carbonate and magnesium hydroxide, and the inorganic compound (C) containing calcium carbonate and calcium hydroxide.

[0041] When inorganic compound (C) contains hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide, and especially when inorganic compound (C) contains hydroxides together with carbonates such as calcium carbonate and magnesium carbonate, the following advantages are obtained. During the foam manufacturing process, when starch (A), PVOH (B), inorganic compound (C), and water are kneaded, the water solubility of hydroxides is relatively high, causing the hydroxides in inorganic compound (C) to dissolve and the inorganic compound (C) to become finer. The finely granulated inorganic compound (C) functions well as a nucleating agent, making it possible to reduce the pore size of the bubbles in the resulting foam and lower its density. However, even highly water-soluble components such as hydroxides do not completely dissolve, and hydroxides may remain in the inorganic compound (C) in the resulting foam.

[0042] The inorganic compound (C) preferably contains magnesium. Examples of inorganic compounds containing magnesium include magnesium carbonate, magnesium hydroxide, magnesium oxide, and magnesium silicate, with at least one selected from the group consisting of magnesium carbonate and magnesium hydroxide being preferred, and magnesium carbonate being more preferred. The inclusion of magnesium in inorganic compound (C) makes it possible to reduce the pore size of the bubbles in the resulting foam and lower its density.

[0043] In one embodiment of the present invention, the inorganic compound (C) may contain basic magnesium carbonate. Basic magnesium carbonate is mMgCO2. ３ Mg(OH) ２ nH ２ It is an inorganic compound represented by the compositional formula O (m = 3 to 5, n = 3 to 7). Basic magnesium carbonate generally has a plate-like crystalline structure in its primary particles and is slightly water-soluble, so it can function particularly well as a nucleating agent, making the pore size of the bubbles in the resulting foam smaller and lower in density. It is more preferable that the inorganic compound (C) is basic magnesium carbonate having a petal-like crystalline structure.

[0044] The basic magnesium carbonate contained in inorganic compound (C) is preferably light basic magnesium carbonate. When inorganic compound (C) containing light basic magnesium carbonate is used, inorganic compound (C) functions as a good nucleating agent, which can reduce the pore size of the bubbles in the resulting foam and lower its density. The particles of inorganic compound (C) containing light basic magnesium carbonate have a loose bulk density of 0.25 g / cm³. ３ The following particles may also be used, for example, 0.24 g / cm³ ３ The following or 0.22 g / cm³ ３ The following particles may also be used. The lower limit of the loose bulk density of particles of the inorganic compound (C) containing light basic magnesium carbonate is, for example, 0.10 g / cm³. ３ It may also be 0.13 g / cm³. ３ , 0.15 g / cm ３ Or 0.17 g / cm³ ３ It may also be the case that the basic magnesium carbonate contained in inorganic compound (C) is heavy basic magnesium carbonate. The particles of inorganic compound (C) containing heavy basic magnesium carbonate have a loose bulk density of 0.25 g / cm³. ３ Even ultrafine particles are acceptable, 0.27 g / cm³ ３ 0.30 g / cm³ or more ３ The particles may be larger than those specified above. The upper limit of the loose bulk density of the particles of the inorganic compound (C) containing heavy basic magnesium carbonate is, for example, 0.50 g / cm³.３ It may also be 0.40 g / cm³. ３ Or 0.35 g / cm³ ３ That's fine.

[0045] In the foam according to the embodiment of the present invention, the content of inorganic compound (C) in the total components with a boiling point of 105°C or higher is preferably 0.1% by mass or more and 5% by mass or less. When the content of inorganic compound (C) is within the above range, the foaming state of the foam tends to be better. The lower limit of the content of inorganic compound (C) is more preferably 0.2% by mass, even more preferably 0.3% by mass, and may also be 0.4% by mass, 0.5% by mass, 0.8% by mass, 1.0% by mass, or 1.5% by mass. The upper limit of the content of inorganic compound (C) is more preferably 4% by mass, even more preferably 3% by mass, and may also be 2.5% by mass, 2.0% by mass, 1.5% by mass, 1.0% by mass, or 0.8% by mass. When the content of inorganic compound (C) is relatively high, the bubbles in the resulting foam tend to be smaller. On the other hand, when the content of inorganic compound (C) is relatively low, the density of the resulting foam tends to be lower.

[0046] The lower limit of the inorganic compound (C) content in the foam according to the embodiment of the present invention is preferably 0.1 parts by mass, more preferably 0.2 parts by mass, even more preferably 0.3 parts by mass, and may also be 0.4 parts by mass, 0.5 parts by mass, 0.8 parts by mass, 1.0 part by mass, or 1.5 parts by mass, per 100 parts by mass of starch (A). The upper limit of the inorganic compound (C) content is preferably 5 parts by mass, more preferably 4 parts by mass, even more preferably 3 parts by mass, and may also be 2.5 parts by mass, 2.0 parts by mass, 1.5 parts by mass, 1.0 part by mass, or 0.8 parts by mass.

[0047] The lower limit of the inorganic compound (C) content in the foam according to the embodiment of the present invention is preferably 0.1 parts by mass, more preferably 0.5 parts by mass, even more preferably 1.0 part by mass, and may also be 2, 3, 4, 5, or 7 parts by mass per 100 parts by mass of PVOH(B). The upper limit of the inorganic compound (C) content is preferably 30 parts by mass, more preferably 20 parts by mass, even more preferably 15 parts by mass, and may also be 12, 10, 7, 5, or 4 parts by mass.

[0048] The foam according to the embodiment of the present invention may contain water in addition to starch (A), PVOH (B), and inorganic compound (C). Water is used in the manufacturing process and may remain in the foam. The upper limit of the water content in the foam is preferably 30% by mass, more preferably 25% by mass, and may be 20%, 15%, or 10% by mass. The lower limit of the water content in the foam is preferably 0.1% by mass, more preferably 1% by mass, and may be 3% or 5% by mass.

[0049] The foam according to the embodiment of the present invention may contain other components besides starch (A), PVOH (B), an inorganic compound (C), and water. Examples of other components include heat stabilizers, ultraviolet absorbers, antioxidants, colorants, plasticizers, deodorizers, antistatic agents, lubricants, drying agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. Any of these other components may be organic compounds. The upper limit of the content of the above-mentioned other components in the foam may be, for example, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0050] The density of the foam according to the embodiment of the present invention is 0.005 g / cm³. ３ 0.07g / cm or more ３ The following is preferable. The upper limit of the above density is 0.04 g / cm³. ３ More preferably, 0.03 g / cm³ ３ More preferably, 0.026 g / cm³ ３ Even more preferable is 0.025 g / cm³. ３ ,0.024g / cm ３ Or 0.023 g / cm³ ３This is also acceptable. When the density of the foam is below the above upper limit, the cushioning, heat insulation, etc., tend to increase. The lower limit of the above density is 0.01 g / cm³. ３ More preferably, 0.02 g / cm³ ３ More preferably, 0.022 g / cm³ ３ Even more preferable is 0.023 g / cm³. ３ Or 0.024 g / cm³ ３ This is also acceptable. The mechanical strength of the foam tends to increase when the density of the foam is above the lower limit mentioned above. The density of the foam is the value measured by the method described in the examples.

[0051] The upper limit of the pore diameter of the bubbles formed in the foam according to the embodiment of the present invention may be, for example, 3 mm, but is preferably 2 mm, more preferably 1.5 mm, even more preferably 1.1 mm, even more preferably 1.0 mm, and may also be 0.9 mm or 0.8 mm. The lower limit of the pore diameter may be preferably 0.1 mm, more preferably 0.2 mm, and may also be 0.3 mm, 0.4 mm or 0.5 mm. By keeping the pore diameter of the bubbles formed in the foam below the above upper limit, the thermal insulation, cushioning, mechanical strength, etc. of the foam are exhibited in a well-balanced manner. In this specification, when simply referred to as the pore diameter of the foam, it means the pore diameter of the bubbles formed in the foam. Furthermore, the pore diameter of the foam is a value measured by the method described in the examples.

[0052] The foam according to the embodiment of the present invention has a low density. This foam can be suitably used as a cushioning material, heat insulating material, space filling material, etc. Furthermore, this foam is also useful as a biodegradable cushioning material, biodegradable heat insulating material, etc.

[0053] <Additive for Foam Production> An additive for foam production according to one embodiment of the present invention (hereinafter also simply referred to as "additive") is a powdered additive containing PVOH (B) and an inorganic compound (C), wherein, in a measurement of the scattering intensity in pure water at 25°C by dynamic light scattering of the DMSO-insoluble components that pass through a 200-mesh mesh at 25°C, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less (percentage of particles with a particle size of 1.5 μm or less) is 60% or more. The lower limit of the percentage of particles with a particle size of 1.5 μm or less is preferably 70%, more preferably 75%, and even more preferably 80%. The upper limit of the percentage of particles with a particle size of 1.5 μm or less may be 100%, 99%, 97%, or 95%.

[0054] Another embodiment of the present invention provides a powdered additive containing at least one resin (B') selected from the group consisting of PVOH, polyolefins, and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the mode diameter of the inorganic compound (C) in wet measurement using laser diffraction / scattering is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm³. ３ The following applies:

[0055] Another embodiment of the present invention provides a powdered additive containing at least one resin (B') selected from the group consisting of PVOH, polyolefins, and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate.

[0056] According to these embodiments of the present invention, by mixing with starch and foaming, a foam having a low density suitable for use as a buffer can be obtained.

[0057] The resin (B') contained in the additive according to the embodiment of the present invention is at least one selected from the group consisting of PVOH, polyolefins, and aliphatic aromatic polyesters. The specific form and preferred form of PVOH as resin (B') are the same as the specific form and preferred form of PVOH (B) contained in the foam according to the embodiment of the present invention described above. Examples of polyolefins as resin (B') include polyethylene and polypropylene, with polypropylene being preferred. Examples of aliphatic aromatic polyesters as resin (B') include poly(butylene adipate-co-terephthalate) (PBAT), poly(ethylene adipate-co-terephthalate) (PEAT), and poly(propylene adipate-co-terephthalate) (PPAT), with PBAT being preferred. PVOH is preferred as resin (B') because of its excellent water solubility and biodegradability.

[0058] The specific forms and preferred forms of PVOH(B) and inorganic compound(C) contained in the additive according to the embodiment of the present invention are the same as the specific forms and preferred forms of PVOH(B) and inorganic compound(C) contained in the foam according to the embodiment of the present invention described above.

[0059] The specific form and preferred form of the "component that passes through 200 mesh of DMSO-insoluble matter" contained in the additive according to the embodiment of the present invention are the same as the specific form and preferred form of the "component that passes through 200 mesh of DMSO-insoluble matter" contained in the foam according to the embodiment of the present invention. Furthermore, the "measurement of scattering intensity in pure water at 25°C by dynamic light scattering method of the component that passes through 200 mesh of DMSO-insoluble matter contained in the additive" is performed in accordance with the "measurement of scattering intensity in pure water at 25°C by dynamic light scattering method of the component that passes through 200 mesh of DMSO-insoluble matter contained in the foam".

[0060] The lower limit of the solubility of the inorganic compound (C) contained in the additive according to the embodiment of the present invention in 100 g of water at 20°C is preferably 0.01 g, more preferably 0.02 g, even more preferably 0.03 g, and still more preferably 0.04 g. In this way, when the inorganic compound (C) contained in the additive has a solubility of above the lower limit, when the additive is kneaded with starch and water during the foam manufacturing process, the inorganic compound (C) dissolves slightly and becomes finer. The finely granulated inorganic compound (C) functions well as a nucleating agent, making it possible to make the pore size of the bubbles in the resulting foam smaller and lower the density. The upper limit of the solubility of the inorganic compound (C) in 100 g of water at 20°C is preferably 0.50 g, more preferably 0.40 g, even more preferably 0.30 g, and still more preferably 0.20 g or 0.10 g. By keeping the solubility of the inorganic compound contained in the additive below the above upper limit, the excessive dissolution of the inorganic compound (C) during the above-mentioned kneading is suppressed, allowing it to fully exhibit its function as a nucleating agent.

[0061] In the additive according to the embodiment of the present invention, it is preferable that an inorganic compound (C) is present on at least the surface of the PVOH (B) or resin (B') powder. The additive may be a mixture of the PVOH (B) or resin (B') powder and the inorganic compound (C) powder.

[0062] The lower limit of the inorganic compound (C) content in the additive according to the embodiment of the present invention is preferably 0.1 parts by mass, more preferably 0.5 parts by mass, even more preferably 1.0 part by mass, and may also be 2, 3, 4, 5, or 7 parts by mass per 100 parts by mass of PVOH (B) or resin (B'). The upper limit of the inorganic compound (C) content is preferably 30 parts by mass, more preferably 20 parts by mass, even more preferably 15 parts by mass, and may also be 12, 10, 7, 5, or 4 parts by mass. When the inorganic compound (C) content is within the above range, the foamed state of the resulting foam tends to be better. Also, when the inorganic compound (C) content is relatively high, the bubbles in the resulting foam tend to be smaller. On the other hand, when the inorganic compound (C) content is relatively low, the density of the resulting foam tends to be lower.

[0063] The additive according to the embodiment of the present invention may contain water in addition to PVOH (B) or resin (B') and inorganic compound (C). The water may be contained in the PVOH or resin used as a raw material. The upper limit of the water content in the additive may be 10% by mass or 5% by mass. The lower limit of the water content in the foam may be 0.01% by mass or 0.1% by mass.

[0064] The additive according to the embodiment of the present invention may contain other components besides PVOH (B) or resin (B'), inorganic compound (C), and water. Examples of other components include heat stabilizers, ultraviolet absorbers, antioxidants, colorants, plasticizers, deodorizers, antistatic agents, lubricants, drying agents, pigments, dyes, processing aids, flame retardants, and antifogging agents. The upper limit of the content of the above-mentioned other components in the additive may be, for example, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0065] <Powder> The powder according to one embodiment of the present invention contains PVOH (B) and an inorganic compound (C), wherein the inorganic compound (C) has a petal-shaped crystalline structure. The specific form and preferred form of the powder are the same as the specific form and preferred form of the additive according to one embodiment of the present invention, which contains PVOH (B) and an inorganic compound (C), wherein the inorganic compound (C) has a petal-shaped crystalline structure.

[0066] <Method for producing foam> The method for producing foam according to the embodiments of the present invention is not particularly limited. A method for producing foam according to one embodiment of the present invention comprises the steps of obtaining a kneaded product by kneading starch (A), PVOH (B), an inorganic compound (C), and water, and foaming the kneaded product. A method for producing foam according to another embodiment of the present invention comprises the steps of obtaining a kneaded product by kneading starch and an additive according to the embodiments of the present invention, and foaming the kneaded product.

[0067] The method of kneading starch (A), PVOH (B), inorganic compound (C), and water in the process of obtaining the kneaded product is not particularly limited, nor is it limited to the method of kneading starch and additives. For example, each raw material component may be mixed in advance and then supplied into the equipment such as an extruder or injection foaming device, or each raw material component may be supplied separately. If supplied separately, they may be supplied from one supply port or from two or more supply ports.

[0068] In the process of obtaining the kneaded product, the amount of water added is preferably 1 to 40 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 20 parts by mass, per 100 parts by mass of the total raw material components (each component contained in the target foam). Note that the standard "100 parts by mass of total raw material components" refers to the mass of each raw material component excluding the water originally contained in it.

[0069] Mixing can be effectively carried out, for example, by an extruder. The extruder is not particularly limited, but examples include single-screw extruders, twin-screw extruders, and multi-screw extruders with two or more screwdrivers. In a single-screw extruder, the pressure can be increased by connecting two or more extruders and placing valves in the resin flow path between them. Similarly, two or more twin-screw extruders or multi-screw extruders with two or more screwdrivers may be connected for production. A twin-screw extruder is preferably used as the extruder.

[0070] In the foaming process, there are no particular restrictions on the method of foaming the kneaded material, but one example is to extrude the kneaded material, which has been kneaded in an extruder, with steam. In this case, it is preferable that the extruder is equipped with dies such as strand dies, circular dies, T-dies, and slit dies. By using such an extruder, the kneaded material, which has been kneaded in the extruder, is extruded and foamed with steam through the dies (strand dies, circular dies, T-dies, slit dies, etc.) to obtain foam in the form of strands (rods), cocoons, sheets, plates, etc. From this viewpoint, it is preferable that the shape of the obtained foam is in the form of strands, cocoons, sheets, or plates. A cutter may be installed at the discharge port of the extruder (or the die outlet if the extruder is equipped with dies) to cut the discharged foam.

[0071] In the foaming process, the temperature of the kneaded material when it is extruded is preferably 120°C to 300°C, more preferably 160°C to 260°C, and even more preferably 180°C to 240°C. By performing extrusion foaming at such temperatures, a foam with particularly sufficient foaming can be obtained.

[0072] <Other Embodiments, etc.> The foam, foam manufacturing additive, powder, and foam manufacturing method of the present invention are not limited to the embodiments described above. For example, the foam manufacturing additive of the present invention may be used in the manufacture of foams other than those mainly composed of starch. The powder of the present invention can be used for various applications other than the manufacture of foams.

[0073] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by such examples. The density, pore size, and proportion of particles with a particle size of 1.5 μm or less of the foam, as well as the loose bulk density and modal diameter of the inorganic compound, were evaluated or measured by the following methods.

[0074] [Foam density] 100 cm³ ３ Using a graduated cylinder, measure out 100 cm of standard sand (Toyoura Standard Sand, manufactured by Toyoura Silica Industry Co., Ltd.). ３ Measure the mass A [g] and calculate the density X [g / cm³] of the standard sand using the following formula. ３ The density X [g / cm³] was calculated. ３ ]=A[g] / 100[cm ３ Next, the strand-like foam obtained in the examples and comparative examples was cut to a length of 5 cm using a utility knife. ３ Using a graduated cylinder, the volume is 100 cm³. ３ The following amounts of cut foam were separated. After measuring the mass B [g] of this foam, the entire amount was divided into 100 cm³. ３ Place in a graduated cylinder and add 100 cm of standard sand. ３ The mixture was poured up to the mark. The mass C [g] of the poured standard sand was measured, and the volume Y [cm³] of the foam was calculated using the following formula. ３ ] and density Z [g / cm³] ３ The volume Y [cm³] of the foam was calculated. ３ ] = (A - C) / X Density of foam Z [g / cm³] ３ ] = B / Y

[0075] [Pore Diameter of Foam] The strand-shaped foam obtained in the examples and comparative examples was cut to a thickness of approximately 5 mm using a utility knife. The cross-section of the foam was colored red with vermilion ink, and then an image of the cross-section was taken using a digital microscope (Keyence Corporation, VHX-6000). The diameter of the pores in the foam was measured from the captured image using the accompanying software. The pore diameter was measured for 10 arbitrary pores observed, and the average value was taken as the pore diameter of the foam.

[0076] [Percentage of particles with a particle size of 1.5 μm or less in the foam] 3 g of the foam obtained was gradually added to 27 g of DMSO over 10 minutes while heating and stirring in an 85°C hot water bath, and then stirred for 30 minutes. After the resulting solution was cooled to 25°C, it was centrifuged at 10°C and 20,000 rpm for 15 minutes using a centrifuge. The entire precipitate obtained from the separated liquid was collected in 50 cm³. ３ The mixture was added to deionized water and stirred. The resulting suspension was filtered using a 200-mesh (74 μm mesh) nylon mesh. After stirring the obtained filtrate by pipetting, it was collected by pipette, and the scattering intensity distribution of the particles in the filtrate was measured by dynamic light scattering at 25°C using an optical measuring instrument ELSZ (Otsuka Electronics Co., Ltd.). From the obtained scattering intensity distribution, the ratio of the scattering intensity area of ​​particles with a particle size of 1.5 μm or less to the total scattering intensity area of ​​particles with a particle size of 8.0 μm or less was calculated. The same measurement was performed three times, and the average value was taken as the "percentage of particles with a particle size of 1.5 μm or less".

[0077] [Loose Bulk Density of Inorganic Compounds] The loose bulk density was measured in accordance with the Japan Powder Technology Association standard SAP05-98:2013. Specifically, the following procedure was followed: 50 cm ３ Using a funnel, add an inorganic compound to a graduated cylinder to a depth of 50 cm. ３ The mixture was filled. The mass A of the filled inorganic compound was measured using a precision balance. The loose bulk density was calculated using the following formula: Loose bulk density [g / cm³] ３ ]=A[g] / 50[cm ３ The same measurement was performed three times, and the average value was defined as the "loose bulk density."

[0078] [Mode Diameter of Inorganic Compounds] Wet particle size distribution measurements of inorganic compounds were performed using a laser diffraction particle size analyzer (SALD-2200, Shimadzu Corporation). During particle size distribution analysis, particle size distributions were obtained using multiple different refractive indices, and then the particle size distribution was obtained using the refractive index that resulted in the largest 10% particle size. The mode diameter was determined from the obtained particle size distribution. The same measurement was performed twice, and the average value was defined as the "mode diameter".

[0079] [Example 1] Corn starch (manufactured by Oji Corn Starch Co., Ltd., moisture content 13.3% by mass), PVOH (unmodified polyvinyl alcohol, saponification degree 98 mol%, viscosity-average degree of polymerization 1,700, moisture content 4% by mass), and light basic magnesium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries Ltd.) were mixed in a mass ratio of 100:20:0.35 to obtain a raw material mixture. A tumbler mixer was used for mixing. Note that the above mass ratio is the value excluding the moisture originally contained in each raw material component.

[0080] Using a twin-screw extruder (TEX30α-45.5BW-4V, manufactured by Japan Steel Works Ltd., motor output 18.5kW, screw diameter 30mm, L / D 45.5) equipped with a strand die having one hole with a diameter of 2 mm, 7.3 parts by mass of water were injected into 100 parts by mass of the above raw material mixture, and while kneading the mixture, the mixture was extruded and foamed at a temperature of 210°C to obtain the foam of Example 1. The obtained foam was evaluated as described above. The evaluation results are shown in Table 1.

[0081] [Examples 2-6, Comparative Examples 1-2] Foams for Examples 2-6 were obtained and evaluated in the same manner as in Example 1, except that the type and amount of inorganic compound added were changed as shown in Table 1. In Comparative Example 1, the mica contained KAl ２ (Si ３ Al)O １０ (OH, F) ２ Mica "C-4000" having the following composition was used. The evaluation results are shown in Table 1.

[0082] [Example 7] An additive was obtained by mixing PVOH and an inorganic compound in the ratios shown in Table 1, and a raw material mixture was obtained by mixing the obtained additive with corn starch. Using the obtained raw material mixture, the foam of Example 7 was obtained in the same manner as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0083] [Example 8] The foam of Example 8 was obtained in the same manner as in Example 1, except that PVOH was changed to ethylene-modified polyvinyl alcohol (ethylene modification amount 4 mol%, degree of saponification 98 mol%, viscosity-average degree of polymerization 1,700, water content 4% by mass) and the amount of inorganic compound added was changed as shown in Table 1, and the foam was evaluated.

[0084] Table 1 shows the primary particle shape, secondary particle shape, loose bulk density, and mode diameter of the inorganic compounds used. Furthermore, the solubility of basic magnesium carbonate (light) used in Example 1, etc., in 100 g of water at 20°C was 0.05 g. The solubility of calcium carbonate used in Example 6, in 100 g of water at 20°C, was 0.00 g.

[0085] In the production of each foam in Examples 1 to 8, no shrinkage of the foam occurred after extrusion. On the other hand, in the production of each foam in Comparative Examples 1 and 2, shrinkage of the foam occurred after extrusion. The presence or absence of this shrinkage is also shown in Table 1. When using the inorganic compounds of Examples 1 to 8, water vapor is efficiently generated starting from the fine particles of the inorganic compound in the kneaded mixture, and more moisture evaporates. As a result, the moisture content in the kneaded mixture (foam) after extrusion decreases more rapidly than in Comparative Examples 1 and 2, and the solidification of the foamed starch is promoted, which is thought to have suppressed shrinkage of the foam after extrusion.

[0086]

[0087] As shown in Table 1, each of the foams in Examples 1 to 8, in which the proportion of particles with a particle size of 1.5 μm or less is 60% or more, has a density of 0.03 g / cm³. ３ The following characteristics were observed, and the material had a low density suitable for cushioning. Furthermore, the mode diameter was 3.0 μm or less, and the loose bulk density was 0.40 g / cm³. ３ The foams used in Examples 1-5, 7, and 8, which were based on the inorganic compounds described below, had low density and also sufficiently small pore sizes.

[0088] The foam of the present invention can be suitably used as a cushioning material, heat insulating material, space filling material, etc.

Claims

1. A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein, in a measurement of the scattering intensity in pure water at 25°C by dynamic light scattering of the dimethyl sulfoxide-insoluble components that pass through a 200-mesh mesh, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less is 60% or more.

2. A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein the mode diameter of the inorganic compound (C) in wet measurement using laser diffraction / scattering is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm³. ３ The following is a foam.

3. The foam according to claim 1 or claim 2, wherein the primary particles of the inorganic compound (C) have a plate-like crystalline structure.

4. The foam according to claim 1 or claim 2, wherein the inorganic compound (C) has a petal-shaped crystalline structure.

5. The foam according to claim 1 or claim 2, wherein the inorganic compound (C) contains at least one selected from the group consisting of calcium carbonate and magnesium carbonate.

6. The foam according to claim 5, wherein the inorganic compound (C) contains at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide.

7. The foam according to claim 1 or claim 2, wherein the inorganic compound (C) contains the element magnesium.

8. The foam according to claim 1 or claim 2, wherein the inorganic compound (C) contains basic magnesium carbonate.

9. The foam according to claim 1 or claim 2, wherein the inorganic compound (C) contains light basic magnesium carbonate.

10. The foam according to claim 1 or claim 2, wherein the degree of saponification of the vinyl alcohol polymer (B) is 70 mol% or more and 99 mol% or less.

11. The foam according to claim 1 or claim 2, wherein the viscosity-average degree of polymerization of the vinyl alcohol polymer (B) is 1,000 or more and 5,000 or less.

12. The foam according to claim 1 or claim 2, wherein the starch (A) content in the total components with a boiling point of 105°C or higher is 70% by mass or more and 95% by mass or less.

13. The foam according to claim 1 or claim 2, wherein the content of vinyl alcohol polymer (B) in the total components with a boiling point of 105°C or higher is 4% by mass or more and 30% by mass or less.

14. The foam according to claim 1 or claim 2, wherein the content of inorganic compounds (C) in the total components with a boiling point of 105°C or higher is 0.1% by mass or more and 5% by mass or less.

15. Density is 0.005 g / cm³ ３ 0.07g / cm or more ３ The foam according to claim 1 or claim 2, which is as follows:

16. A foam containing starch (A), a vinyl alcohol polymer (B), and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate.

17. The foam according to claim 16, wherein the inorganic compound (C) contains light basic magnesium carbonate.

18. A powdered foam manufacturing additive containing a vinyl alcohol polymer (B) and an inorganic compound (C), wherein, in a measurement of the scattering intensity in pure water at 25°C by dynamic light scattering of the dimethyl sulfoxide-insoluble components contained in the foam manufacturing additive that pass through a 200-mesh mesh, the ratio of the scattering intensity area of ​​the region with a particle size of 1.5 μm or less to the total scattering intensity area of ​​the region with a particle size of 8.0 μm or less is 60% or more.

19. A powdered foam manufacturing additive containing at least one resin (B') selected from the group consisting of vinyl alcohol polymers, polyolefins, and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the mode diameter of the inorganic compound (C) measured by wet measurement using laser diffraction / scattering is 3.0 μm or less, and the loose bulk density of the inorganic compound (C) is 0.40 g / cm³. ３ The following are additives for foam manufacturing.

20. The additive for producing foam according to claim 18 or claim 19, wherein the solubility of inorganic compound (C) in 100 g of water at 20°C is 0.01 g or more and 0.50 g or less.

21. The additive for producing foam according to claim 18 or claim 19, wherein the primary particles of the inorganic compound (C) have a plate-like crystalline structure.

22. The additive for producing foam according to claim 18 or claim 19, wherein the inorganic compound (C) has a petal-shaped crystalline structure.

23. The additive for producing foam according to claim 18 or claim 19, wherein the inorganic compound (C) contains basic magnesium carbonate.

24. The additive for producing foam according to claim 18 or claim 19, wherein the content of the inorganic compound (C) per 100 parts by mass of the vinyl alcohol polymer (B) or resin (B') is 0.1 parts by mass or more and 30 parts by mass or less.

25. The additive for producing foam according to claim 18 or claim 19, wherein an inorganic compound (C) is present on at least the surface of the powder of a vinyl alcohol-based polymer (B) or resin (B').

26. A powdered foam manufacturing additive comprising at least one resin (B') selected from the group consisting of vinyl alcohol polymers, polyolefins, and aliphatic aromatic polyesters, and an inorganic compound (C), wherein the inorganic compound (C) contains basic magnesium carbonate.

27. A powder containing a vinyl alcohol polymer (B) and an inorganic compound (C), wherein the inorganic compound (C) has a petal-shaped crystalline structure.

28. A method for producing a foam according to claim 1 or claim 2, comprising the steps of: kneading starch (A), a vinyl alcohol polymer (B), an inorganic compound (C), and water to obtain a kneaded product; and foaming the kneaded product.

29. A method for producing a foam, comprising the steps of: kneading starch with an additive for producing a foam according to claim 18 or claim 19 to obtain a kneaded product; and foaming the kneaded product.

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