Foam body and method for producing same

Abstract

The present invention is a foam body comprising a starch (A) and a vinyl alcohol polymer (B), the foam body being characterized by the vinyl alcohol polymer (B) comprising at least two vinyl alcohol polymers having different degrees of saponification. As a result, provided is a foam body having both the density and bending resistance appropriate for a buffer material.

Description

Foam and manufacturing method thereof

[0001] The present invention relates to a foam and a method for producing the same.

[0002] Styrofoam is widely used as a foam material for cushioning and other purposes. While Styrofoam is lightweight, inexpensive, and has excellent impact resistance and cold insulation properties, its beads are easily detached by external impact, making it a potential source of fine plastic debris floating in the ocean. Countermeasures are needed to address the concern that the chemicals contained in fine plastic debris floating in the ocean could be absorbed into the food chain and affect the ecosystem. Against this background, biodegradable foams have been developed, and one example is a cushioning material containing starch and a vinyl alcohol-based polymer. For example, Patent Document 1 describes a biodegradable resin foam manufactured by blending a starch-based polymer with a specific moisture content, a polyvinyl alcohol-based resin, a nonionic surfactant, a thickener, and an inorganic filler.

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

[0004] However, according to the investigations of the present inventors, the foam described in Patent Document 1 sometimes has too high a density or insufficient bending resistance.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to provide a foam that has both density and bending resistance suitable for a cushioning material.

[0006] The above problem can be solved by providing any one of the following [1] to

[13] .[1] A foam containing starch (A) and a vinyl alcohol polymer (B), wherein the vinyl alcohol polymer (B) contains two or more vinyl alcohol polymers having different degrees of saponification; [2] The foam according to [1], wherein the degree of saponification of the vinyl alcohol polymer (B) is 70 to 99 mol%; [3] The foam according to [1] or [2], wherein the vinyl alcohol polymer (B) contains a vinyl alcohol polymer (B-1) and a vinyl alcohol polymer (B-2), and wherein the difference H2 - H1 between the degree of saponification H1 (mol%) of the vinyl alcohol polymer (B-1) and the degree of saponification H2 (mol%) of the vinyl alcohol polymer (B-2) is 1 mol% or more; [4] The foam according to [3], wherein the degree of saponification H1 of the vinyl alcohol polymer (B-1) is 60 to 95 mol%, and the degree of saponification H2 of the vinyl alcohol polymer (B-2) is 80 to 100 mol%; [5] The foam according to [3] or [4], wherein the weight ratio (B-1 / B-2) of the vinyl alcohol polymer (B-1) to the vinyl alcohol polymer (B-2) is 5 / 95 to 95 / 5; [6] The foam according to any one of [1] to [5], wherein the viscosity average degree of polymerization of the vinyl alcohol polymer (B) is 1,000 to 5,000; [7] The foam according to any one of [1] to [6], wherein the content of the vinyl alcohol polymer (B) is 1 to 40 parts by weight per 100 parts by weight of the starch (A); [8] The foam according to any one of [1] to [7], wherein the content of the starch (A) in the components having a boiling point of 105°C or higher is 70 to 95% by weight; [9] The foam according to any one of [1] to [8], further comprising an inorganic substance;

[10] The foam according to [9], wherein the inorganic substance is at least one selected from the group consisting of calcium carbonate, talc, and silica;

[11] The foam according to any one of [1] to

[10] , which has a density of 0.005 to 0.07 g / mL;

[12] A method for producing a foam, comprising the steps of kneading a raw material containing starch and two or more vinyl alcohol polymers differing in degree of saponification and foaming the raw material;

[13] A method for producing a foam, comprising the steps of kneading a raw material containing starch, two or more vinyl alcohol polymers differing in degree of saponification and water in an extruder and extruding and foaming the raw material with water vapor.

[0007] According to the present invention, it is possible to provide a foam that has both density and bending resistance suitable for a cushioning material.

[0008] The foam of the present invention is a foam containing starch (A) and a vinyl alcohol polymer (B), characterized in that the vinyl alcohol polymer (B) contains two or more vinyl alcohol polymers with different degrees of saponification. The inventors' studies have revealed that, in a foam containing starch (A) and a vinyl alcohol polymer (B), when the vinyl alcohol polymer (B) contains two or more vinyl alcohol polymers with different degrees of saponification, a foam having both density and bending resistance suitable for a cushioning material can be obtained. As can be seen from a comparison between the Examples and Comparative Examples described below, when the vinyl alcohol polymer (B) contains only one vinyl alcohol polymer with a low degree of saponification, as in Comparative Example 1, the resulting foam had a high density and a low bending break angle. When the vinyl alcohol polymer (B) contains only one vinyl alcohol polymer with a high degree of saponification, as in Comparative Example 2, the resulting foam had a low density, but a low bending break angle, and poor underwater disintegration properties. Furthermore, when comparing Comparative Example 3 and Example 3, both of which have the same degree of saponification of the vinyl alcohol polymer (B), the foam of Comparative Example 3 had a significantly lower bending fracture angle and a slightly higher density. The foam of Comparative Example 3 also tended to be less prone to collapse in water than Example 3. In contrast, in Examples 1 to 4, which contained two types of vinyl alcohol polymers with different degrees of saponification, the density of the resulting foams was controlled to a certain level or less, and the folding resistance was also good. Furthermore, the foams also had good water-borne collapse properties. This demonstrates the great significance of the present invention, which employs a vinyl alcohol polymer (B) containing two or more types of vinyl alcohol polymers with different degrees of saponification.

[0009] Examples of the starch (A) used in the present invention include natural starches such as corn starch, potato starch, sweet potato starch, wheat starch, rice starch, tapioca starch, and sago starch; and processed starches that have been subjected to etherification, esterification, oxidation, or the like. One or more of these may be appropriately selected and used.

[0010] The vinyl alcohol polymer (B) used in the present invention contains two or more vinyl alcohol polymers having different degrees of saponification. The vinyl alcohol polymer (PVOH) contains a vinyl alcohol unit (—CH ２ The vinyl alcohol polymer used in the present invention may be a polymer produced by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer. Examples of vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among the above, vinyl acetate is preferred as the vinyl ester monomer. When polymerizing the vinyl ester, the vinyl ester may be copolymerized with other monomers as long as the spirit of the present invention is not impaired. The total content of vinyl alcohol units and vinyl ester units in the vinyl alcohol polymer is preferably 80 mol% or more, more preferably 90 mol% or more, and in some cases 95 mol% or more or 98 mol% or more, based on the total monomer units of the vinyl alcohol polymer.

[0011] The saponification degree of the vinyl alcohol polymer (B) is preferably 70 to 99 mol%. The saponification degree is more preferably 75 mol% or more, even more preferably 80 mol% or more, particularly preferably 85 mol% or more, and most preferably 90 mol% or more. From the viewpoint of better bending resistance, a saponification degree of 92 mol% or more may be preferred. On the other hand, the saponification degree is more preferably 98 mol% or less, even more preferably 97 mol% or less. When the saponification degree is within the above range, the density of the resulting foam is controlled to a certain level or less, and the foam tends to have good bending resistance and excellent disintegration properties in water. From the viewpoint of better bending resistance and disintegration properties in water, a saponification degree of 94 mol% or less may be preferred. The saponification degree is measured in accordance with JIS K6726:1994.

[0012] In a preferred embodiment, the vinyl alcohol polymer (B) contains a vinyl alcohol polymer (B-1) and a vinyl alcohol polymer (B-2), and the difference H2-H1 between the degree of saponification H1 (mol%) of the vinyl alcohol polymer (B-1) and the degree of saponification H2 (mol%) of the vinyl alcohol polymer (B-2) is 1 mol% or more. The difference H2-H1 is more preferably 2 mol% or more, even more preferably 3 mol% or more, particularly preferably 5 mol% or more, and most preferably 8 mol% or more. On the other hand, the difference H2-H1 is preferably 25 mol% or less, more preferably 20 mol% or less, and even more preferably 15 mol% or less. When the difference H2-H1 is within the above range, the density of the resulting foam is controlled to a certain level or less, and the foam tends to have good bending resistance and excellent disintegration in water. When the vinyl alcohol polymer (B) contains three or more vinyl alcohol polymers with different degrees of saponification, it is sufficient that at least the vinyl alcohol polymer (B-1) and the vinyl alcohol polymer (B-2) satisfy the above-mentioned preferable ranges of H2-H1 are contained. For example, when the vinyl alcohol polymer (B) contains three vinyl alcohol polymers with degrees of saponification of 90 mol%, 90.5 mol%, and 91 mol%, respectively, H2 is 91 mol%, H1 is 90 mol%, and H2-H1 is 1 mol%.

[0013] In a preferred embodiment, the saponification degree H1 of the vinyl alcohol polymer (B-1) is 60 to 95 mol%, and the saponification degree H2 of the vinyl alcohol polymer (B-2) is 80 to 100 mol%. The saponification degree H1 is more preferably 65 mol% or more, even more preferably 70 mol% or more, particularly preferably 75 mol% or more, and most preferably 80 mol% or more. Meanwhile, the saponification degree H1 is more preferably 93 mol% or less, even more preferably 90 mol% or less. When the saponification degree H1 is within the above range, disintegration in water tends to be improved. Furthermore, the saponification degree H2 is more preferably 82 mol% or more, even more preferably 85 mol% or more, particularly preferably 90 mol% or more, and most preferably 95 mol% or more. Meanwhile, the saponification degree H1 is more preferably 99.9 mol% or less, even more preferably 99.8 mol% or less, and particularly preferably 99 mol% or less. If the saponification degree H2 is within the above range, the density of the resulting foam tends to be low.

[0014] In a preferred embodiment, the weight ratio (B-1 / B-2) of the vinyl alcohol polymer (B-1) to the vinyl alcohol polymer (B-2) is 5 / 95 to 95 / 5. The weight ratio (B-1 / B-2) is more preferably 10 / 90 or more, even more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more. Meanwhile, the weight ratio (B-1 / B-2) is more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and particularly preferably 80 / 20 or less. When the weight ratio (B-1 / B-2) is within the above range, the resulting foam tends to have good bending resistance. Furthermore, the density of the resulting foam is controlled to a certain level or less, and the foam tends to have excellent disintegrability in water.

[0015] The viscosity-average degree of polymerization of the vinyl alcohol polymer (B) is preferably 1,000 to 5,000. The viscosity-average degree of polymerization is more preferably 1,200 to 4,500, even more preferably 1,300 to 4,200, and particularly preferably 1,500 to 4,000. When the viscosity-average degree of polymerization is within the above range, the mechanical strength of the resulting foam tends to be excellent. The viscosity-average degree of polymerization is measured in accordance with JIS K6726:1994. That is, the vinyl alcohol polymer is resaponified to a saponification degree of 99.5 mol% or more, purified, and then the intrinsic viscosity [η] (liters / g) measured in water at 30°C can be calculated using the following formula: P = ([η] x 10,000 / 8.29) （１／０．６２）

[0016] In the foam of the present invention, the content of the vinyl alcohol polymer (B) is preferably 1 to 40 parts by weight per 100 parts by weight of the starch (A). Since the vinyl alcohol polymer (B) used in the present invention contains two or more vinyl alcohol polymers with different degrees of saponification, the content of the vinyl alcohol polymer (B) is the total content of the two or more vinyl alcohol polymers with different degrees of saponification. The content of the vinyl alcohol polymer (B) is more preferably 4 parts by weight or more, even more preferably 8 parts by weight or more, particularly preferably 10 parts by weight or more, and most preferably 12 parts by weight or more. If the content of the vinyl alcohol polymer (B) is above the above-mentioned lower limit, the density of the resulting foam tends to be low and the pore size of the foam tends to be small. On the other hand, the content of the vinyl alcohol polymer (B) is more preferably 35 parts by weight or less, even more preferably 30 parts by weight or less, particularly preferably 25 parts by weight or less, and most preferably 24 parts by weight or less. If the content of the vinyl alcohol polymer (B) is equal to or less than the upper limit, the production cost will be lower and the usage rate of petroleum-derived raw materials will be lower. Note that "100 parts by weight of starch (A)", which is the basis for the content of the vinyl alcohol polymer (B), means the weight excluding the water originally contained in the starch.

[0017] In the foam of the present invention, the content of starch (A) in the components having a boiling point of 105°C or higher is preferably 70 to 95% by weight. The content of the starch (A) is more preferably 75% by weight or higher, even more preferably 78% by weight or higher, particularly preferably 82% by weight or higher, and most preferably 85% by weight or higher. On the other hand, the content of the starch (A) is more preferably 92% by weight or lower, even more preferably 90% by weight or lower, and particularly preferably 88% by weight or lower. When the content of the starch (A) is within the above range, the foaming state of the starch tends to be good.

[0018] The foam of the present invention preferably further contains an inorganic substance. Examples of inorganic substances include calcium carbonate, magnesium carbonate, tricalcium phosphate, talc, silica, clay, kaolin, calcium silicate, titanium oxide, aluminum oxide, and white carbon. Among these, at least one inorganic substance selected from the group consisting of calcium carbonate, talc, and silica is preferably used. The content of the inorganic substance is preferably less than 5 parts by weight, more preferably less than 4 parts by weight, and even more preferably less than 3 parts by weight, per 100 parts by weight of starch (A). On the other hand, the content of the inorganic substance is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and particularly preferably 0.5 parts by weight or more, per 100 parts by weight of starch (A). Note that "100 parts by weight of starch (A)," which is the standard for the content of the inorganic substance, refers to the weight excluding the moisture originally contained in the starch.

[0019] The foam of the present invention may contain other components in addition to the starch (A), the vinyl alcohol polymer (B), and the inorganic substance. Examples of such other components include heat stabilizers, ultraviolet absorbers, antioxidants, colorants, plasticizers, photoinitiators, deodorizers, antistatic agents, lubricants, desiccants, fillers, pigments, dyes, processing aids, flame retardants, and antifogging agents. The content of such other components is preferably 0.001 to 1% by weight.

[0020] The density of the foam of the present invention is preferably 0.005 to 0.07 g / mL. The density of the foam is more preferably 0.04 g / mL or less, even more preferably 0.039 g / mL or less, particularly preferably 0.038 g / mL or less, and most preferably 0.037 g / mL or less. When the density of the foam is equal to or less than the above upper limit, the foam tends to have excellent heat insulating properties and shock absorbing properties. On the other hand, the density of the foam is more preferably 0.008 g / mL or more, even more preferably 0.01 g / mL or more. When the density of the foam is equal to or greater than the above lower limit, the foam tends to have excellent mechanical strength. The density of the foam can be measured by the method described in the Examples.

[0021] The flexural fracture angle of the foam of the present invention is preferably 25° or more. The flexural fracture angle of the foam is more preferably 28° or more, and even more preferably 29° or more. On the other hand, there is no particular upper limit to the flexural fracture angle of the foam, and it may be, for example, 90° or less. When the flexural fracture angle of the foam is within the above range, the foam tends to be less likely to crack and has excellent bending resistance.

[0022] The method for producing a foam of the present invention is not particularly limited. A method for producing a foam, comprising the steps of kneading and foaming raw materials containing starch and two or more vinyl alcohol-based polymers with different degrees of saponification, is also one aspect of the present invention. The starch (A) described above can be used as the starch, and the two or more vinyl alcohol-based polymers with different degrees of saponification can be the vinyl alcohol-based polymer (B-1) and the vinyl alcohol-based polymer (B-2) described above. As a method for kneading the raw materials, the starch and the two or more vinyl alcohol-based polymers with different degrees of saponification can be premixed and then fed into an extruder, injection foaming device, or the starch and the two or more vinyl alcohol-based polymers with different degrees of saponification can be fed separately. When fed separately, they can be fed through a single feed port or two or more feed ports. It is preferable that the raw materials further contain the inorganic substance described above. The inorganic substance content is preferably within the range described above.

[0023] Another aspect of the present invention is a method for producing a foam, comprising the steps of kneading raw materials containing starch, two or more vinyl alcohol polymers with different degrees of saponification, and water in an extruder and extrusion-foaming them with steam. The starch can be the starch (A) described above, and the two or more vinyl alcohol polymers with different degrees of saponification can be the vinyl alcohol polymer (B-1) and the vinyl alcohol polymer (B-2) described above. The extruder is not particularly limited, but examples include a single-screw extruder, a twin-screw extruder, and a multi-screw extruder with two or more screws. In the case of a single-screw extruder, two or more extruders can be connected together and a valve placed in the resin flow path between them to increase the pressure. Similarly, two or more twin-screw extruders or two or more multi-screw extruders can be connected together to produce a foam. Of these, a twin-screw extruder is preferably used.

[0024] The extruder used in the present invention may be equipped with a strand die, a circular die, a T-die, or the like. That is, in a preferred embodiment, the material is discharged using a strand die, a circular die, or a T-die. In this manner, the raw material kneaded in the extruder is extrusion-foamed with steam through the strand die, circular die, or T-die, and a foam in the shape of a strand (rod), a cocoon ball, a sheet, a plate, or the like can be obtained. From this perspective, in a preferred embodiment, the shape of the foam obtained is a strand, a cocoon ball, a sheet, or a plate. A cutter may be provided at the discharge outlet of the extruder (at the outlet of the die if the extruder is equipped with a die) to cut the discharged foam.

[0025] The method for kneading raw materials containing starch, two or more vinyl alcohol polymers with different degrees of saponification, and water in an extruder is not particularly limited. The starch, two or more vinyl alcohol polymers with different degrees of saponification, and water may be mixed in advance and then fed into the extruder. Alternatively, the starch, two or more vinyl alcohol polymers with different degrees of saponification, and water may be fed separately. Alternatively, two of the starch, two or more vinyl alcohol polymers with different degrees of saponification, and water may be mixed in advance and then fed into the extruder, and the remaining one may be fed separately. When fed separately, they may be fed through a single feed port or through two or more feed ports. The order in which the starch, two or more vinyl alcohol polymers with different degrees of saponification, and water are fed is not particularly limited. However, the inventors' investigations have revealed that if the starch, two or more vinyl alcohol polymers with different degrees of saponification are fed first, the water volatilizes in the cylinder, causing the polymers to lose fluidity and solidify, which can lead to the screw clogging and the extrusion becoming unable to continue. From this viewpoint, it is a preferred embodiment to start the supply of water to the extruder and then supply at least one selected from the group consisting of the starch and the vinyl alcohol-based polymer, and it is a more preferred embodiment to start the supply of water to the extruder and then supply a raw material in which the starch and the vinyl alcohol-based polymer are premixed. It is preferable that the raw material further contains the inorganic substance described above. The content of the inorganic substance is preferably within the range described above.

[0026] The amount of water to be added is preferably 1 to 40 parts by weight, more preferably 3 to 35 parts by weight, and even more preferably 5 to 30 parts by weight, relative to 100 parts by weight of the raw materials. Note that the suitable amount of water to be added is the weight including the water originally contained in the starch and the vinyl alcohol polymer, and the reference "100 parts by weight of raw materials" means the weight excluding the water originally contained in each raw material.

[0027] According to the present invention, a foam can be obtained that has both density and bending resistance suitable for a cushioning material. The foam thus obtained can be suitably used as a cushioning material or a heat insulating material. Furthermore, since the foam has excellent disintegrability in water, it can be suitably used as a biodegradable cushioning material or a biodegradable heat insulating material.

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The bending fracture angle, density, and water disintegrability of the foams were evaluated by the following methods.

[0029] [Viscosity Average Degree of Polymerization of Vinyl Alcohol-Based Polymer] The viscosity average degree of polymerization of the vinyl alcohol-based polymer was measured in accordance with JIS K6726:1994. Specifically, when the degree of saponification was less than 99.5 mol%, the polymer was saponified until the degree of saponification reached 99.5 mol% or more, and the viscosity average degree of polymerization of the obtained vinyl alcohol-based polymer was calculated by the following formula using the intrinsic viscosity [η] (liters / g) measured in water at 30°C. In Examples 1 to 4, the vinyl alcohol-based polymer (B-1) and the vinyl alcohol-based polymer (B-2) were mixed in the content ratio shown in Table 1, and then the viscosity average degree of polymerization was calculated in the same manner as above. Viscosity average degree of polymerization = ([η] x 10 ４ / 8.29) （１／０．６２）

[0030] [Saponification Degree of Vinyl Alcohol Polymer] The saponification degree (mol %) of the vinyl alcohol polymer was measured in accordance with JIS K 6726: 1994. The saponification degree of the vinyl alcohol polymer (B) (PVOH (B)) in Examples 1 to 4 was measured in accordance with JIS K 6726: 1994 after mixing the vinyl alcohol polymer (B-1) and the vinyl alcohol polymer (B-2) in the content ratio shown in Table 1.

[0031] [Bending Failure Angle of Foam] The strand-shaped foams obtained in the Examples and Comparative Examples were cut into 10 cm lengths using a utility knife. The foams were then stored at 20°C and 33% relative humidity for at least 3 days and used as samples. The left half (5 cm) of each sample was sandwiched between two 20 cm x 2.5 cm x 1.0 cm hemlock timbers and held in place with one hand. Specifically, the sample was placed on one hemlock timber with the long side oriented horizontally, with the left half (5 cm) resting on the hemlock timber. Another hemlock timber was then placed on top of the sample and fixed so that the two hemlock timbers were horizontal. The end of the sample not sandwiched between the hemlock timbers was then held by hand, and the sample was bent using the end of the timber as a fulcrum until it broke. The bending angle at which the break occurred was measured using a protractor. If the sample did not break even after being bent 90° or more, the bending failure strength was recorded as 90°. The same measurement was carried out five times, and the average value was taken as the bending breaking angle.

[0032] [Foam Density] Standard sand (Toyoura Standard Sand, manufactured by Toyoura Silica Industry Co., Ltd.) was weighed out using a 100 mL graduated cylinder, and the weight A [g] of 100 mL of standard sand was measured. The density X [g / mL] of the standard sand was calculated using the following formula: Density X [g / mL] = A [g] / 100 [mL] Next, the strand-shaped foams obtained in the Examples and Comparative Examples were cut into lengths of 5 cm using a utility knife. An amount of cut foam with a volume of 100 mL or less was separated using a 100 mL graduated cylinder. The weight B [g] of this foam was measured, and the entire amount was placed in a 100 mL graduated cylinder, and standard sand was poured up to the 100 mL mark. The weight C [g] of the poured standard sand was measured, and the volume Y [mL] and density Z [g / mL] of the foam were calculated using the following formula: Foam Volume Y [mL] = (A - C) / X Foam Density Z [g / mL] = B / Y

[0033] [Foam Disintegrability in Water] The strand-shaped foams obtained in the Examples and Comparative Examples were cut into 1 cm lengths using a utility knife. 0.3 g of the cut foam and 60 mL of ion-exchanged water were placed in a 300 mL Erlenmeyer flask and stirred at 20°C for 3 hours at 400 rpm using a magnetic stirrer. The stirred solution was filtered through a 200-mesh (74 μm opening) nylon mesh, and the filtered nylon mesh was dried at 105°C until no volatile matter remained. The difference between the weight of the nylon mesh after drying and the weight of the nylon mesh before filtration was taken as the total amount of filtrate, and the amount of water-insoluble matter of the foam was calculated using the following formula to evaluate the foam's disintegrability in water. The nonvolatile content of the foam was determined by drying the cut foam at 105°C for 4 hours and then calculating the weights before and after drying using the following formula. Note that a smaller value for disintegrability in water indicates a foam that is more easily disintegrated in water. Water disintegration rate of foam (%) = [total amount of filtrate (g) × 10,000] / [0.3 (g) × non-volatile content rate of foam (wt%)] Non-volatile content rate of foam (wt%) = [weight after drying (g) × 100] / [weight before drying (g)]

[0034] Example 1 (1) Preparation of Raw Materials Cornstarch (Oji Cornstarch Co., Ltd., moisture ratio 13.3 wt%), PVOH-1 (unmodified polyvinyl alcohol, degree of saponification 88 mol%, viscosity average degree of polymerization 1700, moisture ratio 4 wt%), PVOH-2 (unmodified polyvinyl alcohol, degree of saponification 98 mol%, viscosity average degree of polymerization 1700, moisture ratio 4 wt%), and calcium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed in a weight ratio of 100:7:7:1.25. A tumbler mixer was used for mixing. The above weight ratios exclude the moisture originally contained in each raw material.

[0035] (2) Production of Foam Using a twin-screw extruder (TEX30α-45.5BW-4V, manufactured by The Japan Steel Works, Ltd., motor output 18.5 kW, screw diameter 30 mm, L / D 45.5) equipped with a strand die having one hole with a diameter of 2 mm, foam was produced by extrusion foaming at a resin temperature of 210°C while injecting 7.9 parts by weight of water per 100 parts by weight of the raw material obtained in (1) above. The evaluation results of the obtained foam are shown in Table 1.

[0036] [Examples 2 to 4, Comparative Examples 1 to 3] Raw materials were prepared in the same manner as in Example 1, except that the content of the vinyl alcohol polymer was changed as shown in Table 1. Using the obtained raw materials, foams were produced in the same manner as in Example 1. The evaluation results of the obtained foams are shown in Table 1. PVOH-3 to PVOH-5 were all unmodified polyvinyl alcohols, and had a water content of 4% by weight.

[0037]

Claims

1. A foam containing starch (A) and a vinyl alcohol polymer (B), wherein the vinyl alcohol polymer (B) contains two or more vinyl alcohol polymers with different degrees of saponification.

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

3. The foam according to claim 1, wherein the vinyl alcohol polymer (B) contains a vinyl alcohol polymer (B-1) and a vinyl alcohol polymer (B-2), and the difference H2-H1 between the degree of saponification H1 (mol%) of the vinyl alcohol polymer (B-1) and the degree of saponification H2 (mol%) of the vinyl alcohol polymer (B-2) is 1 mol% or more.

4. The foam according to claim 3, wherein the degree of saponification H1 of the vinyl alcohol polymer (B-1) is 60 to 95 mol %, and the degree of saponification H2 of the vinyl alcohol polymer (B-2) is 80 to 100 mol %.

5. The foam according to claim 3 or 4, wherein the weight ratio (B-1 / B-2) of the vinyl alcohol polymer (B-1) to the vinyl alcohol polymer (B-2) is 5 / 95 to 95 / 5.

6. The foam according to any one of claims 1 to 4, wherein the vinyl alcohol polymer (B) has a viscosity-average degree of polymerization of 1,000 to 5,000.

7. The foam according to any one of claims 1 to 4, wherein the content of the vinyl alcohol polymer (B) is 1 to 40 parts by weight per 100 parts by weight of the starch (A).

8. The foam according to any one of claims 1 to 4, wherein the content of starch (A) in the component having a boiling point of 105°C or higher is 70 to 95% by weight.

9. The foam according to any one of claims 1 to 4, further comprising an inorganic substance.

10. The foam according to claim 9, wherein the inorganic substance is at least one selected from the group consisting of calcium carbonate, talc, and silica.

11. The foam according to any one of claims 1 to 4, having a density of 0.005 to 0.07 g / mL.

12. A method for producing a foam, comprising the steps of kneading and foaming raw materials containing starch and two or more vinyl alcohol polymers having different degrees of saponification.

13. A method for producing a foam, comprising the steps of kneading raw materials containing starch, two or more vinyl alcohol polymers with different degrees of saponification, and water in an extruder and extruding and foaming them with water vapor.

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