Extruded foam sheet, foamed molded article, and method for manufacturing an extruded foam sheet

Abstract

To provide a foam sheet which is excellent in heat deformation resistance and moldability while containing an aliphatic polyester-based resin, and has low apparent density, and a foam molding which facilitates production and is excellent in a light weight property, cushioning property and dimension accuracy.SOLUTION: A foam sheet that is composed of a resin composition containing one or more kinds of aliphatic polyester-based resins has apparent density of 30 kg / m3 or more and 100 kg / m3 or less, a gel fraction of 25 mass% or less, and a calorific value observed in a first temperature rising process determined by heat flux differential scan calorimetry at a heating rate of 10°C / min of 5.0 J / g or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a foamed sheet, a foamed molded article, and a method for manufacturing a foamed sheet, and more specifically, to a foamed sheet composed of a resin composition containing an aliphatic polyester resin, a foamed molded article composed of such a foamed sheet, and a method for manufacturing such a foamed sheet. [Background technology]

[0002] Conventionally, foamed products composed of foamed resin compositions have been widely used. These foamed products are lightweight yet strong, and have excellent cushioning and heat insulation properties. Known types of foamed products include foamed sheets and foamed beads obtained by impregnating non-foamed resin sheets or resin beads with foaming agents such as acetone or butane, and then heating them to cause foaming, as well as foamed molded articles produced by processing these into three-dimensional shapes using molds. Regarding foamed sheets, extruded foamed sheets are known, which are obtained by melting and kneading a foaming resin composition and a foaming agent in an extruder, and then extruding the resulting molten mixture into a sheet shape and foaming it through a seating die (flat die or circular die) attached to the tip of the extruder (extrusion foaming method).

[0003] This type of extruded foam sheet is used as a cushioning sheet in its sheet form, or made into bags for use as packaging material. Furthermore, this type of extruded foam sheet is used as a raw material for producing foamed molded products by thermoforming, and is widely used as a component of foamed molded products such as food trays and cups. In addition to being used as described above, extruded foam sheets are also widely used in the form of laminated foam sheets, in which a film layer (non-foamed layer) is laminated on one or both sides.

[0004] Incidentally, in recent years, there has been a demand for biodegradable resin products that can be decomposed in the natural environment, and resin compositions based on aliphatic polyester resins have come to be used as foaming resin compositions that serve as raw materials for foamed sheets and foamed beads. Foamed products such as foamed sheets are required to have a low apparent density from the viewpoint of buffering properties, but aliphatic polyester resins generally have poor foaming properties. Therefore, when producing foamed products containing aliphatic polyester resins, it has been conventionally considered to impart foaming suitability by giving the aliphatic polyester resin crosslinked structures or long-chain branched structures in the molecular structure of the aliphatic polyester resin, or by increasing its molecular weight. For example, Patent Document 1 describes a foamed sheet having a foamed layer containing a biodegradable polyester resin with a mass-average molecular weight of 150,000 to 400,000. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-164686 [Overview of the project] [Problems that the invention aims to solve]

[0006] Regarding foamed sheets and molded articles containing aliphatic polyester resins, it is required to have a low density from the viewpoints of cushioning properties and the like. Also, it is desired that the foamed sheet containing an aliphatic polyester resin has excellent moldability. And, when manufacturing a foamed molded article by thermoforming or the like, the foamed sheet containing an aliphatic polyester resin is likely to cause thermal deformation, and thus the dimensional accuracy is likely to decrease, and even when used as a sheet, it is difficult to ensure dimensional stability. Therefore, it is required that the foamed sheet has heat resistance to thermal deformation. However, it is difficult to obtain a foamed sheet containing an aliphatic polyester resin that has excellent heat resistance to thermal deformation and moldability while having a low density, and the above-mentioned desires have not been fulfilled. Therefore, an object of the present invention is to provide a foamed sheet that contains an aliphatic polyester resin and is excellent in heat resistance to thermal deformation and moldability, and moreover has a low apparent density, and thus to provide a foamed molded article that is easy to manufacture and is excellent in light weight, cushioning properties, and dimensional accuracy.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention provides a foamed sheet composed of a resin composition containing one or more aliphatic polyester resins, having an apparent density of 30 kg / m

[0009] , , , or more and 100 kg / m 3 or less, having a gel fraction of 25 mass% or less, and a foamed sheet having a heat generation amount observed in the first heating process determined by differential scanning calorimetry of heat flux at a heating rate of 10 °C / min of 5.0 J / g or less.

[0008] In order to solve the above problems, the present invention provides a foamed molded article, which is a thermoformed article composed of the above-mentioned foamed sheet.

[0009] Furthermore, the present invention provides obtaining a modified aliphatic polyester resin by melt-kneading an aliphatic polyester resin and an organic peroxide, Manufacturing a foamed sheet by extruding a resin composition containing the modified aliphatic polyester resin into a sheet shape together with a foaming agent, The foamed sheet to be manufactured is, having an apparent density of 30 kg / m 3 or more and 100 kg / m 3 or less, having a gel fraction of 25 mass% or less, and having a heat generation amount observed in the first heating process determined by differential scanning calorimetry at a heating rate of 10 °C / min of 5.0 J / g or less. A method for manufacturing a foamed sheet is provided.

Advantages of the Invention

[0010] According to the present invention, there is provided a foamed sheet that contains an aliphatic polyester resin and is excellent in heat resistance to deformation and moldability, and moreover has a low apparent density. A foamed molded article that is easy to manufacture and excellent in lightness, cushioning properties, and dimensional accuracy can be provided.

Brief Description of the Drawings

[0011] [Figure 1] A schematic cross-sectional view showing the state of a cross-section when a foamed sheet of one embodiment is cut along a plane parallel to the thickness direction. [Figure 2] A schematic cross-sectional view showing a cross-section when a laminated foamed sheet is cut along a plane parallel to the thickness direction. [Figure 3] A diagram showing the result (DSC curve) of performing differential scanning calorimetry (DSC) on the foamed sheet of Comparative Example 1. [Figure 4] A diagram showing the result (DSC curve) of performing differential scanning calorimetry (DSC) on the foamed sheet of Example 1. [Figure 5] A diagram representing the relationship between the frequency and the storage elastic modulus (G') in the dynamic viscoelasticity measurement of the foaming resin composition used in Example 1 as a graph on a double logarithmic axis and linearly approximated in the range of frequencies from 0.01 Hz to 0.1 Hz. [Figure 6] A diagram showing the measurement results of the complex viscosity (η*) of the foaming resin composition used in Example 1. [Figure 7]This figure shows the relationship between frequency and storage modulus (G') in the dynamic viscoelasticity measurement of the foaming resin composition used in Comparative Example 1, represented on a log-log axis graph and approximated by a straight line in the frequency range of 0.01 Hz to 0.1 Hz. [Figure 8] This figure shows the measurement results of the complex viscosity (η*) of the foaming resin composition used in Comparative Example 1. [Modes for carrying out the invention]

[0012] An embodiment of the present invention will be described below. In the following description, the foamed sheet 1 of this embodiment will be described using the example of a single-layer structure having only a single foamed layer 10, as shown in Figure 1. However, the foamed sheet 1 of this embodiment may also constitute the foamed layer 10 in a laminated foamed sheet 2 in which a non-foamed layer 20 is laminated on one or both sides of the foamed layer 10, as shown in Figure 2. Furthermore, in the following description, embodiments of the present invention will be described using the example of an extruded foamed sheet obtained by an extrusion foaming method.

[0013] The foamed sheet 1 and laminated foamed sheet 2 of this embodiment are not particularly limited in their use, but for example, they can be used as raw material sheets when producing foamed molded bodies by thermoforming. Furthermore, the foamed sheet 1 and laminated foamed sheet 2 may be used in their flat sheet form and can be used as forming materials for folding boxes, cushioning sheets, packaging bags, seedling trays, and heat insulating materials. The foamed sheet 1 and laminated foamed sheet 2 of this embodiment can be used in a wide range of applications beyond those mentioned above. In this embodiment, the low density of the foamed sheet 1 (foam layer 10) not only provides excellent lightness and cushioning properties to the foamed sheet itself, but also allows foamed products such as foamed molded bodies to exhibit excellent lightness and cushioning properties. Also, in this embodiment, the foamed sheet 1 (foam layer 10) has heat-deformability, allowing it to exhibit heat-deformability to foamed products and provide high dimensional stability to foamed products. The foamed molded body can be used for packaging and cushioning trays for agricultural products such as fruits and vegetables, and industrial materials such as cosmetic containers, as well as seedling trays, food containers, and heat insulating materials.

[0014] The foamed sheet 1 of this embodiment is composed of a resin composition (aliphatic polyester resin composition) containing an aliphatic polyester resin such as polylactic acid (PLA) or polybutylene succinate (PBS). The thickness of the foamed sheet 1 of this embodiment is not particularly limited, but can be, for example, 0.5 mm or more. The thickness of the foamed sheet 1 may be 1 mm or more, or 1.5 mm or more. The thickness of the foamed sheet 1 can be, for example, 8 mm or less. The thickness of the foamed sheet 1 may be 6 mm or less, or 4 mm or less.

[0015] When the foamed sheet 1 of this embodiment constitutes the foamed layer 10 of the laminated foamed sheet 2, the thickness of the non-foamed layer 20 laminated on its surface can be, for example, 1 μm or more. The thickness of the non-foamed layer 20 may be 5 μm or more, or 10 μm or more. The thickness of the non-foamed layer 20 can be, for example, 500 μm or less. The thickness of the non-foamed layer 20 may be 400 μm or less, 300 μm or less, or 200 μm or less. When the laminated foamed sheet 2 has non-foamed layers 20 on both sides of the foamed layer 10, the first non-foamed layer 20 (first non-foamed layer 21) laminated on one side of the foamed layer 10 and the second non-foamed layer 20 (second non-foamed layer 22) laminated on the other side do not need to have the same thickness, and may have different thicknesses.

[0016] The thickness of foam sheet 1 can be measured using a constant-pressure thickness measuring instrument, such as the "Peacock Digital Linear Gauge PDN25" manufactured by Ozaki Seisakusho Co., Ltd. Specifically, the thickness of foam sheet 1 can be determined by measuring the thickness using a constant-pressure thickness measuring instrument when a 100g load is applied to the foam sheet with a circular jig with a diameter of 35.7mm. Alternatively, the thickness of foam sheet 1 can be determined by taking measurements at 10 or more points every 5cm in the width direction (TD), excluding the 20mm at both ends of the width direction (TD) perpendicular to the extrusion direction (MD), and calculating the arithmetic mean of these measurements. Furthermore, if the width of foam sheet 1 is narrow and it is not possible to secure 10 measurement points, the thickness of foam sheet 1 can be determined by securing as many measurement points as possible and calculating the arithmetic mean of all measurements.

[0017] The thickness of the non-foamed layer 20 in the laminated foam sheet 2 can be obtained by taking a micrograph of the cross-section of the non-foamed layer 20 (the cross-section in a plane perpendicular to the plane direction of the foam sheet 1) and calculating the arithmetic mean value of the measured values obtained by measuring the thickness of the non-foamed layer 20 at a plurality of randomly selected locations (for example, 10 locations) in the micrograph. The thickness of the foamed layer 10 can be obtained by subtracting the thickness of the non-foamed layer 20 from the thickness of the foam sheet 1.

[0018] The apparent density of the foam sheet 1 (foamed layer 10) of the present embodiment is 30 kg / m 3 or more. In order for the foamed product to exhibit high strength, it is advantageous for the apparent density to be a certain value or more. The apparent density may be 40 kg / m 3 or more, or may be 50 kg / m 3 or more. On the other hand, in order to more surely exhibit lightness and cushioning properties, it is desirable for the apparent density to be a certain value or less. The apparent density of the foam sheet 1 (foamed layer 10) of the present embodiment is 100 kg / m 3 or less. The apparent density may be 90 kg / m 3 or less, or may be 80 kg / m 3 or less.

[0019] The apparent density (kg / m 3 ) can be obtained by dividing the mass of the foam sheet 1 (foamed layer 10) per unit area (basis weight: g / m 2 ) by the thickness (mm) of the foam sheet 1 (foamed layer 10). The basis weight can be obtained by arithmetically averaging the measured values for a plurality of samples cut out from the foam sheet. The basis weight of the foam sheet can be obtained by cutting out six 10 cm × 10 cm sections at equal intervals in the width direction, excluding 20 mm at both ends in the width direction (TD) of the foam sheet 1, and measuring the mass (g) of each section. The basis weight can be obtained by converting the average value of the mass (g) of each section to the mass per 1 m 2 . Apparent density (kg / m 3 ) = Basis weight (g / m 2 ) ÷ Thickness (mm) The apparent density of the foamed layer 10 in the laminated foamed sheet 2 can be calculated by measuring the overall apparent density and the density of the non-foamed layer 20. The density of the non-foamed layer 20 can be determined by methods such as the water displacement method (Archimedes method).

[0020] The foamed sheet 1 (foamed layer 10) of this embodiment has a gel fraction of 25% by mass or less. The resin composition constituting the foamed sheet 1 (foamed layer 10) exhibits good foaming and thermoformability during extrusion foaming due to its low gel fraction, making it easy to produce foamed sheets 1 (foamed layer 10) and foamed molded articles with the desirable apparent density described above. The gel fraction may be 20% by mass or less, or 15% by mass or less. For example, the gel fraction may be 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0021] The gel fraction can be determined by taking multiple samples (for example, 5 samples) of approximately 0.5 g each from the foam sheet 1 (foam layer 10) and taking the arithmetic mean of the gel fractions in each sample. The gel fraction of a sample can be measured, for example, by the following procedure. • Accurately weigh the initial mass (Mo) of the sample. Prepare an 80-mesh wire mesh (wire diameter φ0.12 mm) for filtering the solution containing the dissolved sample, and accurately weigh the initial mass (Ms) of this wire mesh. Place the sample, 50cc of chloroform, and a stirrer bar into a beaker (capacity: 100cc), cover with aluminum foil, and set in the stirrer. Stir for 2 hours, then allow the sample to dissolve at room temperature. After 2 hours, remove the lid, filter the dissolved material in the beaker through the wire mesh, and collect the resin-insoluble material on the wire mesh. The resin-insoluble material is filtered and then air-dried in a fume hood along with the wire mesh to allow the chloroform to evaporate. The resin-insoluble material, along with the wire mesh after filtration, is dried in a constant-temperature dryer at 120°C for 2 hours, and then allowed to cool in a desiccator. • Measure the total mass (Mx) of the resin-insoluble material and the wire mesh after cooling. The gel fraction (mass %) is calculated using the following formula. Gel fraction (mass%)=(Mx-Ms) / Mo×100

[0022] The foamed sheet 1 (foamed layer 10) of this embodiment exhibits a heat generation rate of 5.0 J / g or less during the first heating process, as determined by differential scanning calorimetry (DSC) at a heating rate of 10°C / min. The heat generation rate observed by differential scanning calorimetry is the amount of heat generated during the crystallization of the aliphatic polyester resin, and is typically observed as an exothermic peak with a peak between 65°C and 130°C in the DSC curve.

[0023] Polyester resins are known to have a relatively slow crystallization rate compared to polyolefin resins and other crystalline resins. If the foamed sheet 1 (foamed layer 10) is not sufficiently crystallized, it may undergo shape changes such as warping and undulation under high-temperature storage conditions, potentially impairing dimensional accuracy. Furthermore, if the foamed sheet 1 (foamed layer 10) contains an aliphatic polyester resin in a state where crystallization is possible, crystallization will occur at the aforementioned temperatures, leading to similar shape changes in the foamed sheet 1 and potentially impairing dimensional accuracy. In addition, during thermoforming, the foamed sheet is often held at both ends with a jig called a clamp, heated, and supplied to a mold. In such cases, deformation of the foamed sheet may cause it to detach from the clamps, leading to problems.

[0024] When manufacturing low-density foamed sheets by extrusion foaming, the foam layer is particularly thin, so cooling air is applied to the foamed sheet immediately after extrusion to suppress bubble bursting during foaming. As a result, especially with low-density foamed sheets, there is a possibility that foamed sheets with a large amount of heat generation (containing many components that have not yet crystallized) may be produced. Therefore, as will be described later, in this embodiment, it is desirable to adjust the temperature and airflow of the air cooling to mitigate the cooling conditions of the foamed sheet after extrusion and to allow the aliphatic polyester resin to crystallize sufficiently.

[0025] In polylactic acid, it is known that α-crystals are formed at temperatures above 120°C during the cooling process from the molten state, and α'-crystals are formed below 90°C, with α-crystals exhibiting superior heat resistance compared to α'-crystals. Furthermore, in polybutylene succinate, it is known that β-crystals change to α-crystals upon heating. Therefore, by slowing the cooling process during manufacturing, the foamed sheet 1 (foamed layer 10) can be made less susceptible to thermal deformation, resulting in α-crystals being present. The presence of α-crystals can be confirmed by wide-angle X-ray diffraction (WAXD). The fact that the crystals contained in foamed sheet 1 (foamed layer) are generally α-crystals can be confirmed by heating the foamed sheet under the temperature conditions under which α-crystals are formed, and comparing the intensity of peaks originating from α-crystals by performing wide-angle X-ray diffraction before and after heating. For example, if the foamed sheet 1 is composed of a resin composition containing polybutylene succinate, wide-angle X-ray diffraction will show a peak originating from the (020) plane of the α crystal near where 2θ is 13°. Therefore, if the foamed sheet 1 is heated under certain conditions (e.g., 100°C for 20 minutes), and the change in peak intensity near 13° before and after heating (intensity after heating / intensity before heating) is, for example, 1.2 times or less, it can be determined that the crystals of the foamed sheet 1 have been sufficiently α-crystallized. It is preferable that the foamed sheet 1 be manufactured such that the change in intensity is 1.1 times or less, and it is preferable that it be manufactured so that no change in intensity is observed (intensity after heating / intensity before heating ≈ 1.0).

[0026] The amount of heat generated during the first heating process, as determined by differential scanning calorimetry (DSC), may be 4 J / g or less, 3 J / g or less, 2 J / g or less, or 1 J / g or less.

[0027] In this embodiment, the foamed sheet 1 (foamed layer 10) preferably exhibits an endothermic peak during the heating process in differential scanning calorimetry, and the difference between the absolute value of the endothermic amount observed during the heating process and the exothermic amount is preferably 30 J / g or more and 90 J / g or less. The endothermic amount observed in differential scanning calorimetry is the amount of heat generated as a result of the melting of the crystals of the aliphatic polyester resin, and is observed as an endothermic peak in the DSC curve with its peak at a temperature several tens of degrees higher than the exothermic peak due to crystallization.

[0028] By including an appropriate amount of aliphatic polyester resin crystals in the foamed sheet 1 (foamed layer 10), a good balance of heat deformation resistance and moldability can be imparted to the foamed product. The difference between the absolute value of the heat absorbed and the heat released may be 40 J / g or more, or 50 J / g or more. The difference between the absolute value of the heat absorbed and the heat released may be 80 J / g or less, or 70 J / g or less.

[0029] The amount of heat absorbed and the amount of heat released can be measured, for example, in the following manner. The endothermic (a) (heat of fusion) and exothermic (b) (heat of crystallization) can be measured by the methods described in JIS K7122:1987 and JIS K7122:2012. However, the sampling method and temperature conditions shall be as follows. • After filling the bottom of the aluminum measuring container with 5.5 ± 0.5 mg of the sample cut from foam sheet 1 (foam layer 10), ensuring there are no gaps, the aluminum lid is placed over it. Differential scanning calorimetry will be performed using a differential scanning calorimeter (for example, Hitachi High-Tech Science Corporation's "DSC7000X, AS-3"). In differential scanning calorimetry, the sample is heated and cooled in the following steps 1-2 under a nitrogen gas flow rate of 20 mL / min to obtain a DSC curve. (Step 1) Cool the temperature from 30°C to -40°C at a rate of 10°C / min. (Step 2) Heat from -40°C to 200°C at a rate of 10°C / min (first heating process). Furthermore, alumina will be used as the reference material at this time. The heat absorption (a) and heat generation (b) can be calculated using the analysis software provided with the device. Specifically, as shown in Figure 3, the heat absorption (a) is calculated from the area enclosed by the straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve itself. The heat generation (b) is calculated from the area enclosed by the straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve itself. As shown in Figure 4, if no crystallization (exothermic) peak is observed during the first heating process, the exothermic amount (b) should be 0 J / g. The same applies to the endothermic amount (a). However, if multiple melting (endothermic) peaks or crystallization (exothermic) peaks are observed, the sum of the heat amounts of each peak should be used as the endothermic amount (a) and the exothermic amount (b).

[0030] If the foamed sheet 1 (foamed layer 10) of this embodiment has excessive secondary foaming properties, it may exhibit thermal deformation during thermoforming for reasons other than crystallization, potentially impairing its moldability. The secondary foaming ratio of the foamed sheet 1 (foamed layer 10) of this embodiment is preferably 0.9 times or more and 1.5 times or less. The secondary foaming ratio may also be 1.4 times or less, 1.3 times or less, or 1.2 times or less.

[0031] The secondary foaming ratio of the foamed sheet 1 (foamed layer 10) is preferably such that the above ratio is achieved when the following measurements are taken on the foamed sheet 1 or laminated foamed sheet 2 immediately after extrusion (for example, within 24 hours).

[0032] The secondary foaming ratio of foam sheet 1 (foam layer 10) can be determined as follows. Cut out three test pieces measuring 100mm x 100mm from the foam sheet. The test specimens were conditioned for 168 hours under a standard atmosphere of Class 2, symbol "23 / 50" (temperature 23±2℃, relative humidity 50±5%), as specified in JIS K 7100:1999, and the thickness (T1) (mm) of the center of each test specimen before heating was measured. The thickness (T1) of the center of each test specimen before heating can be measured in the same manner as when determining the thickness of foam sheet 1. The test specimens are placed on a flat surface in an oven set to 70°C without humidity control and heated for 150 seconds. After heating, they are removed from the oven and allowed to cool at room temperature for 30 minutes. The thickness (T2) (mm) of the center of each test specimen after heating is then measured. The thickness (T2) of the center of each test specimen after heating can be measured in the same manner as when determining the thickness of foam sheet 1. The secondary foaming ratio (times) of the three test specimens is calculated using the following formula, and the arithmetic mean value is taken as the secondary foaming ratio (times) of the foamed sheet. Secondary foaming ratio (times) = T2 / T1 • When determining the secondary foaming ratio of the foamed layer 10 in the state of the laminated foamed sheet 2, the thickness of the laminated foamed sheet before and after heating is measured in the same manner as above, and the thickness of the non-foamed layer 20 is subtracted from each to determine the thickness of the foamed layer before heating (T1) and the thickness of the foamed layer after heating (T2), thereby allowing the secondary foaming ratio to be calculated.

[0033] In this embodiment, the foamed sheet 1 (foamed layer 10) preferably has a heat loss of 0.1% by mass or more and 1.5% by mass or less. The heat loss may be 1.3% by mass or less, 1.1% by mass or less, 0.9% by mass or less, or 0.7% by mass or less.

[0034] The heat loss of the foamed sheet 1 (foamed layer 10) is preferably as described above when the following measurements are performed on the foamed sheet 1 or laminated foamed sheet 2 immediately after extrusion (for example, within 24 hours).

[0035] The heat loss of the foam sheet 1 (foam layer 10) can be determined as follows. From the foam sheet 1 (foam layer 10), cut out three samples so that each sample has a mass of approximately 10g. Each sample is conditioned for 168 hours under a standard atmosphere of Class 2, with the symbol "23 / 50" (temperature 23±2℃, relative humidity 50±5%) as specified in JIS K 7100:1999. Each sample, after conditioning, is wrapped in aluminum foil, and the mass (W1) (g) of each sample before heating is measured. Place each sample on a flat surface in an oven set to 180°C with no humidity control and heat for 30 minutes. After heating, remove each sample from the oven and allow it to cool for 30 minutes under a standard atmosphere of Class 2, designated as "23 / 50" in JIS K 7100:1999 (temperature 23±2℃, relative humidity 50±5%). Then, measure the mass (W2) (g) of each sample after heating. The heating loss (mass%) of each of the three samples is calculated using the following formula, and the arithmetic mean is taken as the heating loss (mass%) of the foamed sheet. Heating loss (mass%) = (W1-W2) / W1×100 If the heated sample adheres to the aluminum foil, making accurate measurement difficult, the mass of the aluminum foil may be weighed beforehand, the mass of the aluminum foil together with the sample before and after heating may be measured, and the mass of the aluminum foil may be subtracted from each measurement to determine the mass of each sample before heating (W1) and the mass of each sample after heating (W2).

[0036] In this embodiment, it may be advantageous for the foamed sheet 1 to exhibit superior moldability if the open-cell ratio of the foamed layer 10 is below a certain level. In this embodiment, it is preferable that the open-cell ratio of the foamed sheet 1 (foamed layer 10) is 60% or less. The open-cell ratio may be 50% or less, or 40% or less. In this embodiment, it may be advantageous for the foamed sheet 1 to exhibit superior cushioning and superior dimensional stability by suppressing excessive secondary foaming if the open-cell ratio of the foamed layer 10 is above a certain level. The open-cell ratio may be 10% or more, 15% or more, or 20% or more.

[0037] The open-cell ratio of the foamed sheet 1 (foamed layer 10) can be determined as follows. Cut out two or more sheet-like samples measuring 25mm x 25mm from the foam sheet, and stack the cut-out samples so that there are no gaps to create five test pieces with a thickness of approximately 25mm. The length and width dimensions of the obtained test specimen are measured using a caliper (e.g., Mitutoyo Corporation's "Digimatic Caliper"). The thickness dimension can be measured in the same manner as when determining the thickness of foam sheet 1 using a constant-pressure thickness measuring instrument (e.g., Ozaki Seisakusho Co., Ltd.'s "Peacock Digital Linear Gauge PDN25"). From the measured dimensions, the apparent volume (V1: cm) is calculated. 3 ) Using an air-comparison hydrometer (for example, Tokyo Science Co., Ltd. "Model 1000"), the volume of the test specimen (V2: cm³) was measured using the 1-1 / 2-1 atmosphere method. 3 ) The percentage of open cells (%) is calculated using the following formula, and the arithmetic mean of the percentages of open cells for the five test specimens is determined. The test specimens are pre-conditioned for at least 24 hours under a standard atmosphere of Class 2, symbol "23 / 50" (temperature 23±2℃, relative humidity 50±5%), as specified in JIS K 7100:1999. Measurements are also performed under the same standard atmosphere. Furthermore, the air-comparative hydrometer uses a standard sphere (large 28.96cm). 3 , small 8.58cm 3 It is used after correction using ). Open cell percentage (%) = (V1 - V2) / V1 × 100 (V1: Apparent volume, V2: Volume measured by an air-comparative hydrometer)

[0038] In order for the foamed sheet 1 of this embodiment to exhibit the above-described properties, it is preferable that the resin composition used to form the foamed layer 10 (foaming resin composition) has predetermined melting properties. The resin composition constituting the foamed layer 10 will be described below.

[0039] The resin composition in this embodiment may contain one or more types of aliphatic polyester resins. The foaming resin composition is preferably prepared so that it exhibits good foaming properties when manufacturing foamed products such as foamed sheets, and so that its characteristic values ​​are within a certain range in order to provide the resulting foamed product with properties such as cushioning.

[0040] The foaming resin composition preferably exhibits moderate fluidity when heated in order to exhibit good foaming properties. Specifically, in this embodiment, the melt mass flow rate (MFR) of the foaming resin composition at 190°C before being used to form the foamed sheet 1 (foamed layer 10) can be, for example, 0.3 g / 10 min or more and 5.0 g / 10 min or less. The MFR of the resin composition may be, for example, 0.4 g / 10 min or more, 0.6 g / 10 min or more, 0.8 g / 10 min or more, or 0.9 g / 10 min or more. The MFR of the resin composition may be, for example, 4.5 g / 10 min or less, 4.0 g / 10 min or less, 3.5 g / 10 min or less, or 3.0 g / 10 min or less.

[0041] In this embodiment, it is preferable that the MFR of the resin composition in the state in which it constitutes the foamed sheet 1 (foamed layer 10) (hereinafter also referred to as the "post-foamed resin composition") is the value described above.

[0042] The melt mass flow rate (MFR) of the foaming resin composition before forming the foamed sheet 1 (foamed layer 10) and the post-foamed resin composition in the state in which the foamed sheet 1 (foamed layer 10) is formed can be measured as follows. The melt mass flow rate (MFR) of a resin composition can be measured using a commercially available measuring instrument (for example, the "Melt Flow Index Tester (Automatic) 120-SAS" manufactured by Yasuda Seiki Seisakusho Co., Ltd.). MFR can be measured in accordance with JIS K 7210:1999 under the following measurement conditions. The sample for measurement should be vacuum-dried at 70°C for 5 hours or more. After drying, it should be vacuum-packed in a nylon poly bag for vacuum sealing and stored in a desiccator until immediately before measurement.

[0043] (Measurement conditions) Sample: 3-8g Preheat 1:200 seconds Preheat for 2 minutes and 30 seconds Test temperature: 190℃ Test load: 21.18N Piston travel distance (interval): 25mm Number of attempts: 3 The arithmetic mean of the measured values ​​obtained in each test is defined as the MFR (g / 10min) value.

[0044] The foaming resin composition preferably exhibits a moderate melt tension when heated in order to exhibit good foaming properties. The melt tension of the resin composition used in this embodiment at 190°C can be, for example, 30 cN or more and 60 cN or less. The melt tension may also be 35 cN or more, or 40 cN or more. The melt tension may also be 55 cN or less, or 50 cN or less. It is also preferable that the foamed resin composition has the above-mentioned melt tension.

[0045] The melt tension of a resin composition (foaming resin composition, post-foaming resin composition) can be measured as follows. The melt tension can be measured using a commercially available rheometer and extensional viscometer (for example, the "Capillograph 1D" (special specifications for heating furnaces) capillary rheometer manufactured by Toyo Seiki Seisakusho Co., Ltd., and the "Rheotens 71.97" manufactured by Goettfert). The melt tension can be measured under the following conditions. • The sample is pre-dried under vacuum at 70°C for at least 5 hours. After drying, it is vacuum-packed in a nylon poly bag for vacuum sealing and stored in a desiccator until immediately before measurement. • Install the "Rheotens71.97" so that the distance from the die exit of the "Capillograph 1D" to the measuring section is 80 mm. (Note: If interference prevents the rheotens from being brought within 80 mm, take measures to avoid interference and set the rheotens in the designated location.) First, fill the barrel, which has been heated to a test temperature of 190°C, with the sample and preheat it for 5 minutes. The measurement time, including the preheating time, should not exceed 10 minutes from the time the sample is filled into the barrel. Next, a piston is inserted from the top of the barrel to extrude the molten resin in a string-like form. At this time, the piston descent speed (20 mm / min) is kept constant, and the extruded string-like material is passed through a rheotense wheel and taken up. Then, the take-up speed is gradually increased to measure the melt tension of the sample.

[0046] For the measurement results, the melt tension of the sample is defined as the average of the maximum and minimum tension values ​​immediately before the point where the string-like material breaks. If there is only one maximum point on the tension chart, that maximum value is defined as the melt tension. Furthermore, if the string-like material becomes thinner and the winding becomes free-spinning, that point is considered the break point, and the average of the maximum and minimum tension values ​​immediately before that point is defined as the melt tension of the sample.

[0047] (Measurement conditions for Capillograph 1D) Die: Diameter 2.095mm, length 8mm, inlet angle 90 degrees (conical) Barrel diameter: 9.55mm Piston speed: 20 mm / min Measurement temperature: 190℃

[0048] (Measurement conditions for rheotens) Wheel spacing: Top 0.6mm, Bottom 1.0mm Acceleration: 10mm / s 2 Retrieval speed: Initial velocity 6.92mm / s

[0049] In this embodiment, the foamed sheet 1 (foamed layer 10) has a gel fraction of 25% by mass or less, as described above. When manufacturing the foamed sheet 1 using the resin composition, shear force is applied to the resin composition. Therefore, even if the foaming resin composition contains more than 25% by mass of gel before being used in the manufacture of the foamed sheet 1, the gel fraction in the foamed sheet 1 (foamed layer 10) (gel fraction of the foamed resin composition) can be 25% by mass or less. In order to make the gel fraction of the foamed resin composition 25% by mass or less, it is preferable that the gel fraction of the foaming resin composition be below a certain level.

[0050] In this embodiment, the gel fraction of the foaming resin composition can be, for example, 40% by mass or less in order to obtain a foamed sheet with good elongation during extrusion sheet production and a low basis weight. The gel fraction of the foaming resin composition may be, for example, 30% by mass or less, 20% by mass or less, or 15% by mass or less. The gel fraction of the foaming resin composition can be measured in the same way as the gel fraction of the foamed sheet 1 (foamed layer 10) (gel fraction of the resin composition after foaming).

[0051] The foaming resin composition exhibits good foaming properties and yields a low-density foamed sheet, and the complex viscosity (η) observed at a frequency of 0.01 Hz in dynamic viscoelasticity measurements is important. * The foaming resin composition may be prepared such that, for example, it is between 10,000 Pa·s and 150,000 Pa·s. Furthermore, the foaming resin composition may be prepared such that the slope of the storage modulus (G') in the frequency range of 0.01 Hz to 0.1 Hz in dynamic viscoelasticity measurements is between 0.35 and 1.5.

[0052] The complex viscosity (η * The complex viscosity (η) may be 15,000 Pa·s or more, 20,000 Pa·s or more, or 25,000 Pa·s or more. * ) may be 120,000 Pa·s or less, 100,000 Pa·s or less, 80,000 Pa·s or less, or 60,000 Pa·s or less.

[0053] The foaming resin composition exhibits good foaming properties, and in order to obtain a low-density foamed sheet, the slope of the storage modulus (G') at frequencies of 0.01 Hz to 0.1 Hz in dynamic viscoelasticity measurements may be 0.37 or higher, 0.40 or higher, or 0.45 or higher. The slope of the storage modulus (G') may be 1.4 or lower, 1.3 or lower, 1.2 or lower, or 1.1 or lower. In this embodiment, "slope of storage modulus (G')" refers to the slope of the straight line when the measurement results of the storage modulus (G') at each frequency are represented on a log-log graph with frequency (Hz) on the horizontal axis and storage modulus (G') (Pa) on the vertical axis, and the graph is linearly approximated in the frequency range of 0.01 Hz to 0.1 Hz.

[0054] The slope of the storage modulus (G') of the foaming resin composition and the complex viscosity (η) * ) can be determined by dynamic viscoelasticity measurement as described above. More specifically, dynamic viscoelasticity measurement can be performed using a commercially available viscoelasticity measuring device (e.g., Anton Paar product name "PHYSICA MCR301") and a temperature control system (e.g., Anton Paar product name "CTD450") in the following procedure. • The sample is pre-dried under vacuum at 70°C for at least 5 hours. After drying, it is vacuum-packed in a nylon poly bag for vacuum sealing and stored in a desiccator until immediately before measurement. The sample is placed on a 50 mm diameter parallel plate (lower side) of a viscoelasticity measuring device heated to 190°C, and heated and melted in a nitrogen atmosphere for 5 minutes. The molten sample is compressed on a 25mm diameter parallel plate (upper side) until the gap between the parallel plates is 2mm, the excess resin is removed, and after heating for 5 minutes after reaching the measurement temperature ±1°C, dynamic viscoelasticity measurement is performed. The measurement conditions are as follows: (Measurement conditions) Distortion: 5% Frequency: 0.01~100 (Hz) (Measurement starts from the lowest frequency (0.01 Hz)) Number of measurement points: 21 (5 points / digit) Measurement temperature: 190℃ Atmosphere gas: Nitrogen

[0055] The slope of the storage modulus (G') is determined from the results of dynamic viscoelasticity measurements and from the curve of change of the storage modulus (G') with respect to frequency. Specifically, as shown in Figures 5 and 7, for each measurement point of the storage modulus (G'), the value of the storage modulus (G') (y-axis) against frequency (x-axis) is plotted as a log-log graph, and for the measurement points at frequencies from 0.01 Hz to 0.1 Hz, the power approximation formula (y = bx) is used. a A straight line is drawn using η. Here, a is the slope of the straight line, and b is a constant. That is, the value of the exponent (a) in the power approximation formula is the slope of the storage modulus (G'). Also, the complex viscosity (η * The value of ) can be determined by reading the numerical value at a frequency of 0.01 Hz from the results of dynamic viscoelasticity measurement.

[0056] The various properties of the foaming resin composition described above can be adjusted by selecting the type of aliphatic polyester resin to be used or by modifying the aliphatic polyester resin to impart a desired molecular structure. In particular, the melting properties and gel fraction of the foaming resin composition can be easily adjusted by using a modified aliphatic polyester resin (hereinafter also referred to as "modified aliphatic polyester resin").

[0057] The foaming resin composition may consist only of one or more aliphatic polyester resins, or it may also contain resins other than aliphatic polyester resins. Preferably, the content of resins other than aliphatic polyester resins is less than 20% by mass of all resins in the foaming resin composition. That is, the proportion of aliphatic polyester resins in the total resins in the foaming resin composition is preferably 80% by mass or more. The proportion of aliphatic polyester resins may be 90% by mass or more, or 95% by mass or more.

[0058] Resins other than aliphatic polyester resins can be introduced into foaming resin compositions, for example, as tackifiers or polymeric antistatic agents.

[0059] The aliphatic polyester resin contained in the foaming resin composition may be a hydroxy acid polycondensate, a ring-opening polymer of a lactone, or a polycondensate of a polyhydric alcohol component and a polyhydric carboxylic acid component. Examples of hydroxy acid polycondensates include polylactic acid and polycondensates of hydroxybutyric acid. Examples of ring-opening polymers of lactones include polycaprolactone and polypropiolactone. Examples of polycondensates of a polyhydric alcohol component and a polyhydric carboxylic acid component include polyethylene succinate, polybutylene succinate, polybutylene adipate, polybutylene succinate adipate, and polybutylene adipate terephthalate. Among these, the aliphatic polyester resin contained in the foaming resin composition is preferably either polybutylene succinate (PBS) or polybutylene succinate adipate (PBSA). The foaming resin composition preferably contains modified polybutylene succinate (hereinafter also referred to as "modified polybutylene succinate") or modified polybutylene succinate adipate (hereinafter also referred to as "modified polybutylene succinate adipate").

[0060] The unmodified aliphatic polyester resin (hereinafter also referred to as "unmodified aliphatic polyester resin") that serves as the starting material for modified aliphatic polyester resins preferably has plant-derived diols and dicarbons as its constituent units. That is, it is preferable that at least a portion of unmodified aliphatic polyester resins such as polylactic acid (PLA), polybutylene succinate (PBS), and polybutylene succinate adipate (PBSA) is plant-derived.

[0061] The unmodified aliphatic polyester resin preferably has a biomass content of 20% or more, as measured by ASTM D 6866 (2004). The biomass content of the unmodified aliphatic polyester resin may be 30% or more, or even 40% or more.

[0062] The unmodified aliphatic polyester resin preferably has a melt mass flow rate (MFR) of 8 g / 10 min or more and 40 g / 10 min or less at 190°C. The MFR of the unmodified aliphatic polyester resin may be 10 g / 10 min or more, 12 g / 10 min or more, 15 g / 10 min or more, or 20 g / 10 min or more. The MFR of the unmodified aliphatic polyester resin may be 35 g / 10 min or less, or 30 g / 10 min or less.

[0063] The MFR of unmodified aliphatic polyester resins can be measured by the same method as the MFR of resin compositions.

[0064] The unmodified aliphatic polyester resin preferably has a number-average molecular weight (Mn) of 20,000 or more and 60,000 or less. The number-average molecular weight (Mn) of the unmodified aliphatic polyester resin may be 25,000 or more, 30,000 or more, or 35,000 or more. The number-average molecular weight (Mn) of the unmodified aliphatic polyester resin may be 55,000 or less, 50,000 or less, 45,000 or less, or 40,000 or less.

[0065] The unmodified aliphatic polyester resin preferably has a mass-average molecular weight (Mw) of 100,000 or more and 200,000 or less. The mass-average molecular weight (Mw) of the unmodified aliphatic polyester resin may be 110,000 or more, or 120,000 or more. The mass-average molecular weight (Mw) of the unmodified aliphatic polyester resin may be 190,000 or less, 180,000 or less, 170,000 or less, or 160,000 or less.

[0066] The unmodified aliphatic polyester resin preferably has a dispersion degree (Mw / Mn), which is the ratio of the mass-average molecular weight (Mw) to the number-average molecular weight (Mn), of 2.2 or more and 5 or less. The dispersion degree (Mw / Mn) may be 2.5 or more, 2.8 or more, 3.1 or more, or 3.4 or more. The dispersion degree (Mw / Mn) may be 4.8 or less, 4.5 or less, 4.2 or less, or 3.9 or less.

[0067] The unmodified aliphatic polyester resin preferably has a Z-average molecular weight (Mz) of 100,000 to 500,000. The Z-average molecular weight (Mz) of the unmodified aliphatic polyester resin may be 140,000 or more, 180,000 or more, or 220,000 or more. The Z-average molecular weight (Mz) of the unmodified aliphatic polyester resin may be 450,000 or less, 400,000 or less, 350,000 or less, or 300,000 or less. In particular, the Z-average weight molecular weight (Mz) is preferably 100,000 to 300,000.

[0068] The average molecular weight of unmodified aliphatic polyester resins can be measured as the average molecular weight converted to standard polystyrene (PS) using gel permeation chromatography (GPC) by the following method. Dissolve 15 mg of unmodified aliphatic polyester resin in 6 mL of chloroform (immersion time: 6.0 ± 1.0 hours (complete dissolution)). • The chloroform solution is filtered through a filter (non-aqueous 0.45 μm syringe filter, manufactured by Shimadzu GLC Co., Ltd.) to obtain the measurement sample. • Analyze standard polystyrene under the following measurement conditions and create a standard polystyrene calibration curve. The unmodified aliphatic polyester resin is measured under the following conditions, and the average molecular weight is calculated using a pre-prepared standard polystyrene calibration curve.

[0069] (Measurement conditions) Measurement device: Gel permeation chromatograph (with built-in RI detector and UV detector) (HLC-8320GPC EcoSEC, manufactured by Tosoh Corporation) Column configuration: Sample side: Guard column TSKgel guardcolumn HXL-H (manufactured by Tosoh Corporation; 6.0mm I.D. x 4cm) x 1, Measurement column TSKgelGMHXL (7.8mm I.D. x 30cm) x 2 in series. Reference side: Resistance tube (inner diameter 0.1mm x 2m) x 2 in series. Column temperature: 40℃ Mobile phase: Chloroform Mobile phase flow rate: Sample side 1.0 mL / min, Reference side 0.5 mL / min Detector: Differential refractive index (RI) detector Standard sample: Standard polystyrene for calibration curve Sample injection volume: 50 μL Measurement time: 26 minutes Sampling pitch: 500ms

[0070] The standard polystyrene samples used for the calibration curve are STANDARD SM-105 (manufactured by Showa Denko Co., Ltd.) and STANDARD SH-75 (manufactured by Showa Denko Co., Ltd.), and polystyrene (PS) with mass-average molecular weights (Mw) of 5,620,000, 3,120,000, 1,250,000, 442,000, 151,000, 53,500, 17,000, 7,660, 2,900, and 1,320.

[0071] A calibration curve is created using the following method. The standard polystyrene samples for the calibration curve are divided into two groups: Group A (PS with Mw=5,620,000, PS with Mw=1,250,000, PS with Mw=151,000, PS with Mw=17,000, and PS with Mw=2,900) and Group B (PS with Mw=3,120,000, PS with Mw=442,000, PS with Mw=53,500, PS with Mw=7,660, and PS with Mw=1,320). From Group A, weigh out 2 mg of PS with Mw=5,620,000, 3 mg of PS with Mw=1,250,000, 4 mg of PS with Mw=151,000, 4 mg of PS with Mw=17,000, and 4 mg of PS with Mw=2,900, and dissolve the entire amount in 30 mL of chloroform. From Group B, weigh out 3 mg of PS with Mw=3,120,000, 4 mg of PS with Mw=442,000, 4 mg of PS with Mw=53,500, 4 mg of PS with Mw=7,660, and 4 mg of PS with Mw=1,320, and dissolve the entire amount in 30 mL of chloroform. The standard polystyrene calibration curve is obtained by creating a calibration curve (cubic equation) from the retention times obtained after injecting 50 μL of the dissolution solutions of Group A and Group B and measuring them.

[0072] One method for modifying such unmodified polyester resins is to perform crosslinking (partial crosslinking) using organic peroxides.

[0073] Examples of the aforementioned organic peroxides include peroxyesters, hydroperoxides, dialkylperoxides, diacylperoxides, peroxydicarbonates, peroxyketals, and ketoneperoxides.

[0074] Examples of the peroxyesters include t-butyl peroxy 2-ethylhexyl carbonate, t-hexyl peroxyisopropyl monocarbonate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyacetate, 2,5-dimethyl 2,5-di(benzoyl peroxy)hexane, and t-butyl peroxyisopropyl monocarbonate.

[0075] Examples of the aforementioned hydroperoxides include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0076] Examples of the dialkyl peroxides include dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

[0077] Examples of the aforementioned diacyl peroxides include dibenzoyl peroxide, di(4-methylbenzoyl) peroxide, and di(3-methylbenzoyl) peroxide.

[0078] Examples of the peroxydicarbonate include di(2-ethylhexyl)peroxydicarbonate and diisopropylperoxydicarbonate.

[0079] Examples of the peroxyketal include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, 2,2-di(t-butylperoxy)-butane, n-butyl4,4-di-(t-butylperoxy)valerate, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane.

[0080] Examples of the ketone peroxide include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0081] In this embodiment, it is preferable to use an organic peroxide with a slow reaction rate, and it is preferable to use an organic peroxide with a high half-life temperature. The 1-minute half-life temperature of the organic peroxide is preferably 150°C or higher and 200°C or lower.

[0082] The aforementioned 1-minute half-life temperature can be measured using a 0.1 mol / L solution with benzene as the solvent. Since the decomposition reaction of organic peroxides in dilute solutions can be considered a first-order reaction, if the initial concentration of the organic peroxide is C, the amount of decomposition is ΔC, the decomposition rate constant is k, and the time is t, the decomposition reaction can be expressed as shown in the following equations (1) and (2). Equation (1): dx / dt=k(C-ΔC) Equation (2): ln C / (C-ΔC)=kt Half-life time t 1 / 2 Then (C-ΔC) becomes C / 2, so the above equation becomes as follows. Equation (3): k·t 1 / 2 =ln2 Therefore, if we thermally decompose an organic peroxide at a certain temperature (T) and plot the relationship between time (t) and "ln C / (C-ΔC)" on a graph, we can determine the decomposition rate constant (k) from the slope of the approximate straight line, and the half-life time (t) at that temperature. 1 / 2 ) can be found. The decomposition rate constant k is then expressed by the Arrhenius equation as follows: Equation (4): k=Aexp(-ΔE / RT) Equation (5): lnk = lnA - ΔE / RT (A: frequency factor, ΔE: activation energy, R: gas constant, T: absolute temperature) The decomposition rate constant k at several temperatures is calculated, and the activation energy ΔE can be determined from the slope of the line obtained by plotting "lnk" and "1 / T". Using the calculated activation energy ΔE, "lnt" can be used instead of "lnk". 1 / 2 The 1-minute half-life temperature can be determined from the approximate straight line obtained by plotting the relationship between " and "1 / T".

[0083] As an organic peroxide having the above-mentioned half-life temperature, t-butyl peroxyisopropyl carbonate (half-life temperature at 1 minute: 158.8°C) is preferred.

[0084] The amount of organic peroxide is preferably 0.02 parts by mass or more and 0.45 parts by mass or less when the amount of unmodified aliphatic polyester resin to be modified is 100 parts by mass. The amount of organic peroxide may be 0.05 parts by mass or more, or 0.08 parts by mass or more. The amount of organic peroxide may be 0.4 parts by mass or less, or 0.3 parts by mass or less.

[0085] The foaming resin composition of this embodiment may contain one or more modified aliphatic polyester resins that have been modified as described above. For example, the foaming resin composition of this embodiment may contain modified polybutylene succinate and modified polybutylene succinate adipate. Alternatively, the foaming resin composition of this embodiment may contain one or more modified aliphatic polyester resins and one or more unmodified aliphatic polyester resins.

[0086] The foaming resin composition of this embodiment exhibits good foaming properties when melt-kneaded together with foaming components in an extruder and then extruded. Examples of foaming components supplied to the extruder along with the foaming resin composition include foam regulators and foaming agents. In addition to these, various additives may be added to the foaming resin composition during extrusion foaming. Examples of such additives include fillers, colorants, flame retardants, antibacterial agents, weather-resistant agents, and surfactants. The proportion of additives other than the resin in the foaming resin composition of this embodiment is usually 10% by mass or less. The proportion of additives may be 8% by mass or less, or 6% by mass or less.

[0087] The foamed sheet 1 in this embodiment can be produced by performing a modification step of melt-kneading an aliphatic polyester resin and an organic peroxide to obtain a modified aliphatic polyester resin, and a sheet production step of extruding a resin composition containing the modified aliphatic polyester resin into a sheet together with a foaming agent to produce a foamed sheet. The foaming resin composition may be prepared using only the modified aliphatic polyester resin obtained in the modification step, or it may be prepared by blending two or more modified aliphatic polyester resins, or by blending one or more modified aliphatic polyester resins with one or more unmodified aliphatic polyester resins.

[0088] In this embodiment, the modification step, the resin composition preparation step for preparing a foaming resin composition containing a modified aliphatic polyester resin, and the sheet production step using the foaming resin composition obtained in the resin composition preparation step may each be carried out in a batch or continuously. In addition, in this embodiment, a lamination step of laminating a non-foamed layer on one or both sides of the foamed sheet can be carried out after the sheet production step to produce a laminated foamed sheet. This lamination step may also be carried out in a batch or continuously.

[0089] When the above processes are carried out continuously, all processes may be carried out on a single extrusion line. For example, the above processes can be carried out continuously using a tandem line comprising a first extruder located upstream in the direction of material movement and a second extruder connected downstream of the first extruder, with a seating die (flat die, circular die) attached to the tip of the second extruder. In this case, for example, the modification process can be carried out by supplying an unmodified aliphatic polyester resin and an organic peroxide to the first extruder and melt-kneading the unmodified aliphatic polyester resin and the organic peroxide in the first extruder. At this time, by setting the ratio of the unmodified aliphatic polyester resin and the organic peroxide to the aforementioned ratio (for example, 100 parts unmodified aliphatic polyester resin to 0.02 to 0.45 parts organic peroxide (mass ratio)), it is possible to obtain a modified aliphatic polyester resin suitable for foaming with a low gel content (gel fraction of 40% by mass or less), and it becomes easier to obtain a foaming resin composition suitable for producing foamed products with a good foamed state.

[0090] As mentioned above, this foaming resin composition can be suitable for obtaining foamed sheets with good foaming properties, low density, and low basis weight by being prepared so that the gel fraction is 40% by mass or less. Furthermore, the foaming resin composition can be even more suitable for obtaining foamed sheets with good foaming properties, low density, and low basis weight by being prepared so that the melt mass flow rate (MFR) and melt tension at 190°C are at predetermined values. Moreover, in dynamic viscoelasticity measurements, the storage modulus (G') of the foaming resin composition has a predetermined slope in the frequency range of 0.01 Hz to 0.1 Hz, and the complex viscosity (η) at a frequency of 0.01 Hz is also determined. * When this value reaches a predetermined level, it can be particularly suitable for obtaining a foamed sheet with good foaming properties, low density, and low basis weight.

[0091] The resin composition preparation step for obtaining such a foaming resin composition may be carried out in a first extruder or a second extruder. The resin composition preparation step may be carried out in parallel with the modification step by supplying other components, such as a foam regulator, together with an unmodified aliphatic polyester resin, from the middle of the first extruder. The foaming agent can also be supplied from the middle of the first extruder or in the second extruder. The lamination step can be carried out by extruding a resin composition for forming a non-foamed layer (hereinafter also referred to as the "non-foamed layer resin composition") from the seating die by co-extrusion, and can be carried out in parallel with the sheet manufacturing step. The lamination step may be carried out by extruding or dry laminating the non-foamed layer resin composition onto a foamed sheet that has been manufactured. Furthermore, foamed sheets and laminated foamed sheets can be manufactured by conventionally known methods, not limited to these methods.

[0092] When considering the material recyclability and biodegradability of the foamed product, it is preferable that the non-foamed layer is also composed of an aliphatic polyester resin composition. In this case, the aliphatic polyester resin contained in the non-foamed layer and the aliphatic polyester resin contained in the foamed layer may be the same or different.

[0093] To obtain a foamed sheet that is resistant to thermal deformation, it is preferable to use a blowing agent that does not easily remain on the foamed sheet and does not easily cause secondary foaming. Carbon dioxide is preferred as the blowing agent used in this embodiment. In this embodiment, in addition to carbon dioxide, or in place of carbon dioxide, hydrocarbons or nitrogen gas may be used as blowing agents. These blowing agents may be used individually or in combination of two or more. As the foam regulator, a general-purpose one such as talc can be used.

[0094] In the aforementioned sheet manufacturing process, as mentioned above, it is desirable to cool the foamed sheet immediately after extrusion more slowly than in conventional methods to allow the foamed sheet to crystallize sufficiently. In terms of slowing down the cooling of the foamed sheet (foamed layer), it can be said that adopting the co-extrusion method is advantageous when manufacturing laminated foamed sheets.

[0095] The foamed sheet produced in this way has an apparent density of 30 kg / m³. 3 More than 100kg / m 3 The foamed sheet is manufactured such that the gel fraction is 25% by mass or less, and the amount of heat generated during the first heating process, as determined by differential scanning calorimetry at a heating rate of 10°C / min, is 5.0 J / g or less, thereby achieving excellent lightness, cushioning properties, and dimensional accuracy. Furthermore, this foamed sheet can be suitable as a base sheet for producing foamed molded bodies (thermoformed bodies) by thermoforming or other methods. Conventional known methods such as vacuum forming, pressure forming, and vacuum pressure forming can be used as thermoforming methods to obtain thermoformed bodies. Foamed molded bodies with excellent lightness, cushioning properties, and dimensional accuracy can be easily produced by using the foamed sheet of this embodiment.

[0096] Although the above-mentioned examples are provided in this embodiment, the present invention is not limited in any way to the above examples. As described above, this embodiment discloses the following invention.

[0097] (1) A foamed sheet composed of a resin composition containing one or more types of aliphatic polyester resins, Apparent density is 30 kg / m³ 3 More than 100kg / m 3 Below, The gel fraction is 25% by mass or less. A foamed sheet in which the heat generation observed during the first heating process, as determined by differential scanning calorimetry of heat flux at a heating rate of 10°C / min, is 5.0 J / g or less.

[0098] (2) During the heating process in the differential scanning calorimetry of the heat flux, an amount of heat absorption was observed. The foamed sheet according to (1), wherein the difference between the absolute value of the heat absorbed and the heat released is 30 J / g or more and 90 J / g or less.

[0099] (3) The foamed sheet according to (1) and / or (2), wherein the aliphatic polyester resin is polybutylene succinate or polybutylene succinate adipate.

[0100] (4) The foamed sheet according to any one of (1) to (3), wherein the aliphatic polyester resin is at least partly plant-derived polybutylene succinate and / or at least partly plant-derived polybutylene succinate adipate.

[0101] (5) A foamed sheet as described in any one of (1) to (4), wherein the weight loss upon heating is 0.1% by mass or more and 1.5% by mass or less.

[0102] (6) A foamed sheet described in any one of (1) to (5), having a secondary foaming ratio of 0.9 times or more and 1.5 times or less.

[0103] (7) A foamed sheet as described in any one of (1) to (6), having an open-cell ratio of 60% or less.

[0104] (8) A foamed molded body which is a thermoformed body composed of any one of the foamed sheets described in (1) to (7).

[0105] (9) The process involves melt-kneading an aliphatic polyester resin with an organic peroxide to obtain a modified aliphatic polyester resin, The process includes extruding the resin composition containing the modified aliphatic polyester resin together with a foaming agent to produce a foamed sheet, The foam sheets we manufacture are Apparent density is 30 kg / m³ 3 More than 100kg / m 3 Below, The gel fraction is 25% by mass or less. A method for manufacturing a foamed sheet, wherein the amount of heat generated during the first heating process, as determined by differential scanning calorimetry at a heating rate of 10°C / min, is 5.0 J / g or less.

[0106] (10) The method for producing a foamed sheet according to (9), wherein the foaming agent is carbon dioxide. [Examples]

[0107] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the following examples.

[0108] The following aliphatic polyester resins were prepared to produce the foamed sheets of the examples and comparative examples. <Aliphatic polyester resin> • Aliphatic polyester resin (A): Manufactured by PTT MCC BIOCHEM, product name "BioPBS FZ71PM", a portion of the resin is plant-derived PBS. • Aliphatic polyester resin (B): Manufactured by PTT MCC BIOCHEM, product name "BioPBS FZ91PM", a portion of the resin is plant-derived PBS. • Aliphatic polyester resin (C): Manufactured by PTT MCC BIOCHEM, product name "BioPBS FD92PM", a portion of which is plant-derived PBSA. • Aliphatic polyester resin (D): Manufactured by Nature Works, product name "Biopolymer Ingeo6202D", the resin is entirely plant-derived PLA. The physical properties of the above aliphatic polyester resins are shown in Table 1.

[0109] [Table 1]

[0110] The following organic peroxides were used to modify the above-mentioned aliphatic polyester resin. Furthermore, the following foam modifiers and foaming agents were used when producing the foamed sheet. <Organic peroxide> • Organic peroxide (a): Manufactured by Nuurion Pharmaceuticals, trade name "Trigonox BPIC-C75", t-butyl peroxyisopropyl monocarbonate, half-life at 1 minute, temperature 156°C • Organic peroxide (b): Manufactured by NOF Corporation, trade name "Perbutyl P", α,α'-di-t-butylperoxydiisopropylbenzene, half-life at 1 minute, temperature 175℃ <Bubble adjusting agent> • Talc: Manufactured by Matsumura Sangyo Co., Ltd., product name "Crown Talc PP" <Foaming agent> ·carbon dioxide Butane: A mixture of isobutane and n-butane. Isobutane:n-butane = 35:65 (mass ratio)

[0111] The properties of the foaming resin composition and foamed sheet were evaluated as follows:

[0112] (Method for evaluating the physical properties of foaming resin compositions and foamed sheets) <Basic weight> Excluding the 20 mm at both ends of the width (TD) of each example of foam sheet, six 10 cm x 10 cm sections were cut at equal intervals in the width direction, and the mass (g) of each section was measured. The average mass (g) of each section was calculated as 1 m 2 The value converted to mass per unit, is the basis weight (g / m²) of the foamed sheet. 2 )

[0113] <thickness> The thickness of the foam sheet in each example was measured using a constant-pressure thickness measuring instrument (Peacock Digital Linear Gauge PDN25, manufactured by Ozaki Seisakusho Co., Ltd.). Specifically, the thickness was determined by applying a 100g load to the foam sheet using a circular jig with a diameter of 35.7mm and measuring the thickness with the constant-pressure thickness measuring instrument. The thickness of the foam sheet was measured at least 10 points every 5cm in the width direction (TD), excluding the 20mm at both ends of the width direction (TD) perpendicular to the extrusion direction (MD), and the arithmetic mean of these measurements was taken. If the width of the foam sheet was narrow and it was not possible to secure 10 measurement points, the arithmetic mean of all measurements was taken after securing as many measurement points as possible.

[0114] <Apparent Density> The basis weight and thickness of the foamed sheets in each example were used to calculate the basis weight using the following formula (s1). Apparent density (kg / m³) 3 ) = basis weight (g / m 2 ) ÷ Thickness (mm) ... (s1)

[0115] <Open cell ratio> From each example of foam sheet, two or more sheet-like samples measuring 25 mm x 25 mm were cut out, and the cut samples were stacked without any gaps to obtain a test specimen with a thickness of 25 mm. The length and width dimensions of the obtained test specimen were measured using a caliper (Mitutoyo Corporation's "Digimatic Caliper"). The thickness dimension was measured to 1 / 100 mm using a constant-pressure thickness measuring instrument (Ozaki Seisakusho Co., Ltd.'s "Peacock Digital Linear Gauge PDN25") in the same manner as when determining the thickness of foam sheet 1, and the apparent volume (V1: cm) was determined. 3 Next, the volume (V2: cm³) of the test specimen was determined using the 1-1 / 2-1 atmosphere method with a Tokyo Science Co., Ltd. "1000" air-comparison hydrometer. 3The open-cell ratio (%) was calculated using the following formula (s2), and the arithmetic mean of the open-cell ratios of the five test specimens was determined. The test specimens were pre-conditioned for more than 24 hours under a standard atmosphere of Class 2, symbol "23 / 50" (temperature 23±2℃, relative humidity 50±5%) as specified in JIS K 7100:1999, and then measured under the same standard atmosphere. The air-comparative hydrometer used a standard sphere (large 28.96cm). 3 , small 8.58cm 3 The correction was made using ). Open cell percentage (%) = (V1 - V2) / V1 × 100 ... (s2) (V1: Apparent volume, V2: Volume measured by an air-comparative hydrometer)

[0116] <Melting point, crystallization temperature> The melting point and crystallization temperature were measured using the methods described in JIS K7121:1987 and JIS K7121:2012. However, the sampling method and temperature conditions were as follows. Samples cut from the foaming resin composition and foaming sheets of each example were packed tightly into the bottom of an aluminum measuring container at a concentration of 5.5 ± 0.5 mg, and then the aluminum lid was placed over them. Differential scanning calorimetry was then performed using a Hitachi High-Tech Science Corporation "DSC7000X, AS-3" differential scanning calorimetry meter. Under a nitrogen gas flow rate of 20 mL / min, the samples were heated and cooled in the following steps 1 to 4 to obtain DSC curves. (Step 1) Cool the temperature from 30°C to -40°C at a rate of 10°C / min. (Step 2) Increase the temperature from -40°C to 200°C at a rate of 10°C / min (first heating process), and hold for 10 minutes. (Step 3) Cool the temperature from 200°C to -40°C at a rate of 10°C / min (cooling process) and hold for 10 minutes. (Step 4) Heat from -40°C to 200°C at a rate of 10°C / min (second heating process). Alumina was used as the reference material in this experiment. Using the analysis software provided with the apparatus, the temperature at the top of the melting peak observed during the second heating process was read as the melting point, as shown in Figures 3 and 4, and the temperature at the top of the crystallization peak during the cooling process was read as the crystallization temperature. However, if multiple melting peaks or crystallization peaks were observed, the one with the higher temperature was used as the melting point and crystallization temperature.

[0117] <Heat absorption (a), heat generation (b)> The endothermic (a) (heat of fusion) and exothermic (b) (heat of crystallization) were measured using the methods described in JIS K7122:1987 and JIS K7122:2012. However, the sampling method and temperature conditions were as follows. Samples cut from the foam sheets for each example were packed tightly into the bottom of an aluminum measuring container at a concentration of 5.5 ± 0.5 mg, and then the aluminum lid was placed over them. Differential scanning calorimetry was then performed using a Hitachi High-Tech Science Corporation "DSC7000X, AS-3" differential scanning calorimetry meter. Under a nitrogen gas flow rate of 20 mL / min, the samples were heated and cooled in the following steps 1-2 to obtain DSC curves. (Step 1) Cool the temperature from 30°C to -40°C at a rate of 10°C / min. (Step 2) Heat from -40°C to 200°C at a rate of 10°C / min (first heating process). Alumina was used as the reference material in this experiment. The endothermic (a) and exothermic (b) values ​​were calculated using the analysis software provided with the apparatus. Specifically, as shown in Figure 3, the endothermic (a) value was calculated from the area enclosed by the straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve itself. The exothermic (b) value was calculated from the area enclosed by the straight line connecting the point where the DSC curve deviates from the low-temperature baseline and the point where the DSC curve returns to the high-temperature baseline, and the DSC curve itself. In addition, as shown in Figure 4, if no crystallization (exothermic) peak was observed during the first heating process, the exothermic (b) value was set to 0 J / g. However, if multiple melting (endothermic) peaks or crystallization (exothermic) peaks were observed, the sum of the heat values ​​of each peak was used as the endothermic (a) and exothermic (b) values.

[0118] <Heating loss> From each example, three samples were cut from the foamed sheet immediately after extrusion, with each sample having a mass of approximately 10 g. Each sample was conditioned for 168 hours under a standard atmosphere of Class 2, with the symbol "23 / 50" (temperature 23±2°C, relative humidity 50±5%), according to JIS K 7100:1999. After that, each sample was wrapped in aluminum foil, and the mass (W1) (g) of each sample before heating was measured. Then, each sample was placed on a platform in an oven set to 180°C without humidity control and heated for 30 minutes. Each sample was removed from the oven and allowed to cool for 30 minutes under a standard atmosphere of Class 2, with the symbol "23 / 50" (temperature 23±2°C, relative humidity 50±5%), according to JIS K 7100:1999. After that, the mass (W2) (g) of each sample after heating was measured. The heat loss (mass%) of the three samples was calculated using the following formula (s3), and the arithmetic mean was taken as the heat loss (mass%) of the foamed sheet. Heating loss (mass%)=(W1-W2) / W1×100...(s3)

[0119] <Secondary foaming ratio> Three 100mm x 100mm test specimens were cut from the foamed sheet immediately after extrusion for each example. The test specimens were conditioned for 168 hours under a standard atmosphere of Class 2, symbol "23 / 50" (temperature 23±2℃, relative humidity 50±5%) as specified in JIS K 7100:1999, and the thickness (T1) (mm) of the center of each test specimen before heating was measured. Subsequently, the test specimens were placed on a flat surface in an oven set to 70℃ without humidity control and heated for 150 seconds. After removing them from the oven, they were cooled at room temperature for 30 minutes, and the thickness (T2) (mm) of the center of each test specimen after heating was measured. The thickness (T1 and T2) of the center of the test specimens was measured using a constant-pressure thickness measuring instrument (Peacock Digital Linear Gauge PDN25, manufactured by Ozaki Seisakusho Co., Ltd.) in the same manner as when the thickness of the foamed sheet for each example was determined. The secondary foaming ratio (times) of the three test specimens was calculated using the following formula (s4), and the arithmetic mean was taken as the secondary foaming ratio (times) of the foamed sheet. Secondary foaming ratio (times) = T2 / T1···(s4)

[0120] <Gel fraction> Approximately 0.5 g of sample was prepared from each example of modified aliphatic polyester resin and foamed sheet, and the initial mass (Mo) of the sample was accurately weighed. An 80-mesh wire mesh (wire diameter φ0.12 mm) was prepared for filtering the dissolved solution, and the initial mass (Ms) of this mesh was also accurately weighed. The sample, 50 cc of chloroform, and a stirrer bar were placed in a 100 cc beaker, covered with aluminum foil, and placed in a stirrer. The mixture was stirred for 2 hours at room temperature to dissolve the sample. After 2 hours, the lid was removed, and the dissolved material in the beaker was filtered through the aforementioned wire mesh, collecting the resin-insoluble material on the mesh. The resin-insoluble material, along with the filtered wire mesh, was air-dried in a fume hood to evaporate the chloroform. Next, the resin-insoluble material, along with the filtered wire mesh, was dried in a constant-temperature drying oven at 120°C for 2 hours, and then allowed to cool in a desiccator. The total mass (Mx) of the resin-insoluble material and the wire mesh after cooling was measured. The gel fraction (mass%) was calculated using the following formula (s5) and was used as the gel fraction of the foamed sheet. Gel fraction (mass%)=(Mx-Ms) / Mo×100...(s5)

[0121] (Method for evaluating the performance of foamed sheets) <Cushioning properties of foamed sheet (25% compressive stress)> The 25% compressive stress was measured in accordance with JIS K6767:1999. The 25% compressive stress was measured using the Shimadzu Corporation "Autograph AG-X plus 100kN" universal testing machine and the Shimadzu Corporation "TRAPEZIUM X" universal testing machine data processing. A 50mm x 50mm section was cut from each example's foam sheet and stacked to create a test specimen with a thickness of 10-13mm. The thickness of the test specimen was measured using a Peacock digital linear gauge with a circular jig with a diameter of 35.7mm, under a load of 100g. At least three test specimens were used. The test specimens were conditioned for 16 hours under a standard atmosphere of Class 2, symbol "23 / 50" according to JIS K 7100:1999, before being used for measurement. Measurements were performed under the same conditions, using a φ100mm compression plate with an initial load of approximately 3.0N and a compression speed of 5mm / min. The point where the initial load was applied was defined as the displacement origin. From the graphs obtained for each test specimen, the stress at which the initial load was applied was calculated from the thickness at which it was compressed by 25%, and the arithmetic mean of these stresses was used as the 25% compressive stress (kPa) of the foamed sheet as the evaluation criterion for cushioning performance.

[0122] Criteria for evaluating cushioning performance ◎: 25% compressive stress is less than 40 kPa. ○: The 25% compressive stress is between 40 kPa and 80 kPa. △: The 25% compressive stress is between 80 kPa and 200 kPa. ×: The 25% compressive stress is 200 kPa or higher.

[0123] <Thermoformability of foamed sheets (draw ratio)> From each example's foam sheet, a flat rectangular test piece measuring 700mm in length and 1050mm in width was cut out. A single-stage molding machine (manufactured by Tosei Sangyo Co., Ltd., product name "Unic Automatic Molding Machine FM-3A") was prepared, and the average temperature of the upper heater of this single-stage molding machine was set to 250°C, the average temperature of the lower heater to 222°C, the upper ambient temperature to 190°C, and the lower ambient temperature to 185°C. Next, the above test specimen was introduced into a single-shot molding machine and heated for a predetermined time. Then, molding was performed using a mold (mold surface temperature 50°C) with 22 frustums of different heights arranged in a shape with a diameter of 10 mm (top) and a diameter of 35 mm (bottom). The heights and drawing ratios of the 22 frustums of cones are shown in Table 2. The heating time was varied from 4 to 30 seconds at 2-second intervals, and molding was performed for each. The molded body obtained at each heating time was visually observed, and the maximum drawing ratio in which the molded body was free of cracks and holes and the shape was molded according to the mold was defined as the drawing ratio of the foamed sheet and used as the evaluation criterion for thermoformability.

[0124] ≪Evaluation Criteria for Thermoformability≫ ◎: Aperture ratio of 2.00 or higher. ○: Aperture ratio is between 1.60 and less than 2.00. △: Aperture ratio is between 1.30 and 1.60. ×: Diameter ratio is less than 1.30 or molding is not possible. Here, "unfit for molding" refers to the case of the frustum of cone No. 1 in Table 2, where the shape deviates significantly from the shape of the mold, or where cracks or holes are observed in the molded product.

[0125] [Table 2]

[0126] <Evaluation of heat deformation resistance of foamed sheets (heat deformation rate)> Three square-shaped test specimens, each approximately 10 cm on each side, were cut from each example of foam sheet so that each side was parallel to the extrusion direction (MD) or width direction (TD) of the foam sheet. Next, two straight lines were drawn in a cross shape on the foam sheet of each test specimen, connecting the centers of opposite sides. At this time, the length of the straight line in the extrusion direction (MD1) and the length of the straight line in the width direction (TD1) and the thickness of the foam sheet at the intersection of the cross (VD1) were measured before heating. Next, each test specimen was placed on a flat surface in an oven set to 70°C without humidity control and heated for 150 seconds. After that, it was removed from the oven and cooled at room temperature for 30 minutes. After that, the length of the straight lines in each direction (MD2, TD2) and the thickness (VD2) of each test specimen after heating were measured. Furthermore, the lengths of the straight lines (MD1 and MD2, TD1 and TD2) were measured using a caliper (Mitutoyo Corporation's "Digimatic Caliper"), and the thicknesses (VD1 and VD2) were measured using a constant-pressure thickness measuring instrument (Ozaki Seisakusho Co., Ltd.'s "Peacock Digital Linear Gauge PDN25") in the same manner as when determining the thickness of the foamed sheets in each example. The heat deformation rate (%) of each test specimen was calculated using the following formula (s6), and the arithmetic mean was taken as the heat deformation rate (%) of the foamed sheet, which was used as the evaluation criterion for heat deformation resistance. Heating deformation rate (%)=(MDr+TDr+VDr) / 3...(s6) MD deformation rate (MDr) (%) = (|MD2 - MD1| / MD1) × 100 TD deformation ratio (TDr) (%) = (|TD2 - TD1| / TD1) × 100 VD deformation ratio (VDr) (%) = (|VD2 - VD1| / VD1) × 100

[0127] ≪Evaluation Criteria for Heat Deformation Resistance≫ ◎: The heat deformation rate is less than 3%. ○: The heat deformation rate is 3% or more but less than 10%. △: The heat deformation rate is 10% or more but less than 15%. ×: The heat deformation rate is 15% or more.

[0128] ≪Overall evaluation of foam sheets≫ A comprehensive evaluation was conducted based on the following evaluation criteria for each example of foamed sheet, considering each characteristic item. ◎: All items received a "◎" rating. ○: All items were rated either "◎" or "○", with at least one item being rated "○". △: No "×" marks were given for any of the items, and at least one "△" mark was given for any of the items. ×: The evaluation for any of the items was "×".

[0129] <Preparation of modified aliphatic polyester resins> (Manufacturing Example 1) First, according to the formulation shown in Table 3, aliphatic polyester resin and organic peroxide, which had been pre-dried at 80°C for 4 hours, were dry-blended to obtain mixed pellets. Next, the mixed pellets were supplied to the hopper of a twin-screw extruder (57 mm diameter, L / D = 32), melted and kneaded under the extrusion conditions shown in Table 3, and strands of modified aliphatic polyester resin were extruded from the strand die attached to the tip of the twin-screw extruder. The mixture was then cooled in a water bath and cut into pellets using a pelletizer to obtain pellets of the foaming resin composition. The physical properties of the obtained foaming resin composition are shown in Table 3.

[0130] (Manufacturing Examples 2-9) Foaming resin composition pellets were obtained in the same manner as in Production Example 1, using the formulation and extrusion conditions shown in Table 3. The physical properties of the obtained foaming resin composition are shown in Table 3.

[0131] [Table 3]

[0132] <Production of foam sheets> (Example 1) The modified aliphatic polyester resin and a foam regulator were dry-blended according to the formulations shown in Table 4 to obtain the compound. The mixture was supplied to the hopper of the first extruder of a tandem extruder (the upstream first extruder is a single-screw extruder (55 mm diameter), and the downstream second extruder is a single-screw extruder (65 mm diameter)), and while the mixture was melted and kneaded in the first extruder, a foaming agent was injected under pressure midway through the first extruder to obtain a molten and kneaded product. The molten mixture was transferred to a second extruder to cool, and then extruded and foamed through a circular die (60 mm diameter) attached to the tip of the second extruder to form a cylindrical body composed of foamed sheets. The resin temperature and discharge volume at this time were as shown in Table 4. Cooling air was blown onto the inner and outer sides of a cylindrical foam sheet, and then the inner surface of the cylinder was brought into sliding contact with the outer surface of a predetermined mandrel to cool the cylinder from the inside. After that, the cylinder was cut continuously at one point along the extrusion direction to obtain a long strip of foam sheet, which was then wound into a roll. The physical properties and evaluation of the obtained foamed sheets are shown in Table 4.

[0133] (Examples 2-9) Foamed sheets were prepared in the same manner as in Example 1, except that the extrusion conditions and the take-up speed of the take-up machine were adjusted according to the formulation shown in Table 4. The physical properties and evaluation of the obtained foamed sheets are shown in Table 4.

[0134] (Comparative Example 1) Foamed sheets were prepared in the same manner as in Example 1, except that an unmodified aliphatic polyester resin (B) (unmodified aliphatic polyester resin) was used instead of a modified aliphatic polyester resin, and the extrusion conditions and take-up speed of the take-up machine were adjusted according to the formulation in Table 5. The physical properties and evaluation of the obtained foamed sheets are shown in Table 5.

[0135] (Comparative Examples 2-5) Foamed sheets were prepared in the same manner as in Example 1, except that the extrusion conditions and the take-up speed of the take-up machine were adjusted according to the formulation shown in Table 5. The physical properties and evaluation of the obtained foamed sheets are shown in Table 5.

[0136] Figure 3 shows the differential scanning calorimetry results for the foamed sheet of Comparative Example 1, and Figure 4 shows the differential scanning calorimetry results for the foamed sheet of Example 1. Figure 5 shows the relationship between the frequency and storage modulus (G') in the dynamic viscoelasticity measurement of the foaming resin composition used in Example 1, represented on a log-log graph, and linearly approximated in the frequency range of 0.01 Hz to 0.1 Hz, along with its complex viscosity (η * The measurement results of ) are shown in Figure 6. Furthermore, Figure 7 shows the relationship between frequency and storage modulus (G') in the dynamic viscoelasticity measurement of the foaming resin composition used in Comparative Example 1, represented on a log-log graph, and linearly approximated in the frequency range of 0.01 Hz to 0.1 Hz, and its complex viscosity (η * The measurement results are shown in Figure 8.

[0137] [Table 4]

[0138] [Table 5]

[0139] The overall evaluation of the foamed sheets in Examples 1 to 9, to which the present invention was applied, ranged from "△" to "◎". On the other hand, the foamed sheets in Comparative Examples 1 to 5 were evaluated as "×" in either cushioning, thermoformability, or heat deformation resistance, and the overall evaluation for all of them was "×". From the above results, it was confirmed that the foamed sheet to which the present invention is applied exhibits excellent cushioning properties, thermoformability, and heat deformation resistance. [Explanation of Symbols]

[0140] 1: Foam sheet, 10: Foam layer 2: Laminated foam sheet, 20: Non-foamed layer

Claims

1. An extruded foam sheet comprising a resin composition containing polybutylene succinate, Apparent density is 30 kg / m³ ３ More than 100kg / m ３ Below, The gel fraction is 0.3% by mass or more and 25% by mass or less. The amount of heat generated during the first heating process, as determined by differential scanning calorimetry at a heating rate of 10°C / min, is 5.0 J / g or less. An extruded foam sheet with a secondary foaming ratio of 0.9 times or more and 1.2 times or less.

2. During the heating process in the differential scanning calorimetry of the heat flux, an amount of heat absorption was observed. The extruded foam sheet according to claim 1, wherein the difference between the absolute value of the heat absorbed and the heat generated is 30 J / g or more and 90 J / g or less.

3. The extruded foam sheet according to claim 1, wherein the polybutylene succinate is a plant-derived polybutylene succinate.

4. The extruded foamed sheet according to claim 1, wherein the weight loss upon heating is 0.1% by mass or more and 1.5% by mass or less.

5. The extruded foamed sheet according to claim 1, wherein the open-cell ratio is 60% or less.

6. The extruded foamed sheet according to claim 5, wherein the open-cell ratio is 20% or more and 40% or less.

7. A foamed molded body, which is a thermoformed body composed of an extruded foamed sheet as described in any one of claims 1 to 6.

8. To obtain pellets made from a resin composition containing a modified aliphatic polyester resin by melt-kneading an aliphatic polyester resin and an organic peroxide, The process includes supplying the pellets and foaming agent to an extruder and extruding them into a sheet shape from a die provided at the tip of the extruder while foaming to produce an extruded foamed sheet. The extruded foam sheets that we manufacture are Apparent density is 30 kg / m³ ３ More than 100kg / m ３ Below, The gel fraction is 0.3% by mass or more and 25% by mass or less. A method for manufacturing an extruded foam sheet, wherein the amount of heat generated during the first heating process, as determined by differential scanning calorimetry at a heating rate of 10°C / min, is 5.0 J / g or less.

9. The method for producing an extruded foamed sheet according to claim 8, wherein the foaming agent is carbon dioxide.

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