Foam sheet, foam molding, and method for producing foam sheet

Abstract

To provide a foam sheet having a foam layer composed of a resin composition containing an aliphatic polyester-based resin which achieves both suppression of contraction and good appearance.SOLUTION: A foam sheet includes a foam layer composed of a resin composition containing a polyester-based resin, wherein the resin composition contains an aliphatic polyester-based resin as the polyester-based resin, and the foam layer has apparent density of 30 kg / m3 or more and 130 kg / m3 or less, thickness of 0.5 mm or more and 4.0 mm or less, and the number of air bubbles in a thickness direction of 2 pieces or more and 10 pieces or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a foam sheet, a foam molded article, and a method for producing a foam sheet. [Background technology]

[0002] Conventionally, products made of foamed resin compositions have been widely used. These types of products are lightweight yet strong, and have excellent cushioning and heat insulation properties. Examples of these types of products include foam sheets, foam beads, and foam molded articles made by processing these. As foam molded articles, in addition to two-dimensional products such as sheet-like products made by simply cutting foam sheets into a predetermined shape or foam sheets bonded together to form a flat bag, three-dimensional molded articles made by molding foam sheets or foam beads into a three-dimensional shape using a molding die are also known.

[0003] Among foam sheets, extruded foam sheets are widely used. These foam sheets are obtained by melt-kneading a resin composition and a foaming agent in an extruder, extruding the resulting molten mixture into a sheet through a sheeting die (such as a flat die or a circular die) attached to the tip of the extruder, and foaming the mixture simultaneously. Foam sheets can also be produced by impregnating a non-foamable resin sheet with a hydrocarbon or inorganic gas as a foaming agent under pressure and then releasing the pressure. However, extruded foam sheets are easily manufactured by foaming a resin composition and extruding it into a sheet. Therefore, the thickness and expansion ratio of the foamed layer formed can be easily adjusted. Therefore, extruded foam sheets are widely used as cushioning sheets in sheet form, as packaging materials in bag form, or as raw sheets for thermoforming food trays, cups, and other products. In addition to the above-mentioned uses of extruded foam sheets as a single foam layer, they 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] 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 the raw material for foam sheets. Foam sheets are required to have low apparent densities from the viewpoint of cushioning properties, but aliphatic polyester resins generally have poor foamability. Therefore, when producing foam products containing aliphatic polyester resins, attempts have been made to impart foamability by incorporating crosslinked structures or long-chain branched structures into the molecular structure of the aliphatic polyester resin or by increasing the molecular weight.

[0005] Immediately after production, a foam sheet typically contains a certain amount of blowing agent within the cells and cell membranes. This blowing agent dissipates from the foam sheet over time. Because the permeation rate of the blowing agent through the resin is generally faster than that of air, the dissipation of the blowing agent from the cells is faster than the inflow of air into the cells, which can cause the foam sheet to shrink after production, resulting in a decrease in thickness and width. This type of shrinkage is generally more pronounced in foam sheets with lower apparent densities, due to the thinner cell membranes and weaker cell strength. Foam sheet shrinkage gradually eases as air invades the cells. Therefore, the shrunken foam sheet gradually returns to its original state immediately after production within a few days to a few weeks. This period is referred to as the curing period, and a long curing period is undesirable from the perspective of the foam sheet production cycle, so it is desirable to shorten it.

[0006] Regarding this issue, for example, Patent Documents 1 and 2 listed below attempt to suppress shrinkage of foamed sheets by extrusion foaming a resin composition containing stearic acid monoglyceride as a shrinkage inhibitor together with an aliphatic polyester resin using butane. Non-Patent Documents 1 and 2 listed below also report that the use of carbon dioxide and nitrogen in combination as blowing agents in batch foaming can reduce the rate at which the blowing agent dissipates from within the cells, thereby making it possible to suppress shrinkage in aliphatic polyester resin foams compared to when carbon dioxide alone is used. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-211294 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-211295 [Non-patent literature]

[0008] [Non-Patent Document 1] Journal of CO2Utilization, Volume 64, October 2022, 102149: "Lightweight, low-shrinkage and high elastic poly(butylene adipate-co-terephthalate) foams achieved by microcellular foaming using N2 & CO2 as co-blowing agents" (DOI: https: / / doi.org / 10.1016 / j.jcou.2022.102149) [Non-patent document 2] Polymer Degradation and Stability, Volume 206, December 2022, 110182: "Low-shrinkage biodegradable PBST / PBS foams fabricated by microcellular foaming using CO2& N2 as co-blowing agents" (https: / / doi.org / 10.1016 / j.polymdegradstab.2022.110182) Summary of the Invention [Problem to be solved by the invention]

[0009] Although fatty acid compounds such as stearic acid monoglyceride function effectively as shrinkage inhibitors, their compatibility with resins is not sufficiently good, and they can migrate (bleed out) to the surface of the foam sheet, causing deposits on the foam molding production line that handles the foam sheet, or they may adhere to the packaged object after the foam sheet is made into a finished product such as packaging material.In addition, it is difficult to obtain low-density foams using methods that use nitrogen together with carbon dioxide as a blowing agent.

[0010] Although it would be possible to prevent the above-mentioned problems from becoming apparent if special materials such as shrinkage inhibitors or nitrogen were not used at all, or if used, only small amounts would suffice, no such method has been found, and therefore a new method for making foamed sheets containing aliphatic polyester resins less susceptible to shrinkage is desired.

[0011] To prevent shrinkage, it is believed that forming numerous fine bubbles in the foam layer to create a dense foam layer structure is effective. Increasing the amount of a cell control agent that promotes bubble generation in an attempt to create a dense foam layer can sometimes make it difficult to impart a good appearance to the foam sheet. For example, extruded foam sheets tend to exhibit pronounced corrugation marks (ridge-and-valley folds that form when the foam sheet emerges from the annular discharge port of a circular die, rippling to absorb the circumferential linear expansion caused by volume expansion). Furthermore, increasing the amount of a blowing agent that promotes bubble growth to achieve a low apparent density of the foam layer also tends to result in pronounced corrugation marks. In other words, it is particularly difficult to simultaneously suppress shrinkage and maintain a good appearance in a foam sheet with a low apparent density. Therefore, the present invention aims to achieve both suppression of shrinkage and a good appearance in a foam sheet having a foam layer composed of a resin composition containing an aliphatic polyester resin. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides: A foamed sheet including a foamed layer made of a resin composition including a polyester-based resin, the resin composition contains an aliphatic polyester resin as the polyester resin, The foam layer is Apparent density 30kg / m 3 More than 130kg / m 3 Below, The thickness is between 0.5mm and 4.0mm. To provide a foamed sheet having 2 or more and 10 or less bubbles in the thickness direction.

[0013] In order to solve the above problems, the present invention provides: The present invention provides a foamed molded article, which is a molded article made of the foamed sheet described above.

[0014] In order to solve the above problems, the present invention provides: A method for producing a foamed sheet having a foam layer, comprising: modifying the aliphatic polyester resin by melt-kneading the aliphatic polyester resin and an organic peroxide; and extruding a resin composition containing the modified aliphatic polyester resin together with a foaming agent into a sheet to form the foam layer from the resin composition, The foam layer Apparent density 30kg / m 3 More than 130kg / m 3 below, Thickness is 0.5mm or more and 4.0mm or less, The present invention provides a method for producing a foamed sheet such that the foamed sheet has 2 to 10 cells in the thickness direction. [Effects of the Invention]

[0015] In the present invention, when a foam layer is formed from a resin composition containing an aliphatic polyester resin, the foam layer is provided with a predetermined apparent density and thickness, and the number of cells in the thickness direction of the foam layer is set to a predetermined number. This can suppress shrinkage of the foam sheet and also improve the appearance of the foam sheet. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the cross section of a foamed sheet cut along a plane parallel to the thickness direction. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a cross section of the laminated foam sheet cut along a plane parallel to the thickness direction. [Figure 3a] FIG. 3a is a schematic diagram showing a packaging bag (three-sided bag) which is one form of foam molded article. [Figure 3b] FIG. 3b is a schematic diagram showing a packaging bag (a two-sided bag) which is one form of the foam molded article. [Figure 4] FIG. 4 is an SEM image of the MD plane of the foamed sheet of Example 1. [Figure 5] FIG. 5 is an SEM image of the MD plane of the foamed sheet of Example 4. [Figure 6] FIG. 6 is an SEM image of the MD plane of the foamed sheet of Example 5. [Figure 7] FIG. 7 is a photograph of the surface of the foamed sheet of Example 1 (showing the state of corrugated marks). [Figure 8] FIG. 8 is a photograph of the surface of the foamed sheet of Example 4 (showing the state of corrugated marks). [Figure 9] FIG. 9 is a photograph of the surface of the foamed sheet of Example 5 (showing the state of corrugated marks). DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described below. The following description will be focused on a case where the foamed sheet 1 has a single-layer structure including only a single foamed layer 10, as shown in Fig. 1. The foamed sheet 1 of this embodiment may also constitute the foamed layer 10 of 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 Fig. 2.

[0018] In this embodiment, the foam sheet 1 is an extruded foam sheet obtained by an extrusion foaming method. Detailed description will be given of an example in which the foam sheet 1 and the laminated foam sheet 2 are molded into foamed products such as packaging bags. The foam sheet 1 and the laminated foam sheet 2 of this embodiment are not particularly limited in their applications. They may be used as flat sheets or as materials for folding boxes, buffer sheets, seedling raising sheets, insulation materials, interleaf paper, and the like. The foam sheet 1 and the laminated foam sheet 2 of this embodiment can also be used as base sheets for thermoforming containers such as trays and bowls, and can be used for a wide range of applications other than these. An example of a foamed product is a packaging bag 3 having a rectangular shape in plan view, as shown in FIGS. 3a and 3b. The foam sheet 1 can be used, for example, as a base sheet for producing the packaging bag 3 by overlapping sheet bodies 30 of a predetermined size and heat-sealing the peripheral edges.

[0019] The foam sheet 1 of this embodiment not only exhibits reduced shrinkage after production, requiring a short curing period until the foaming agent is sufficiently replaced with air and the thickness is restored, but also exhibits a good appearance. In foam products produced using a molding die for thermoforming or other processes, even if the surface of the raw sheet is not sufficiently smooth and attractive, the molding surface of the die is brought into contact with the sheet surface during molding, thereby smoothing the surface. For example, in extruded foam sheets, variations in surface gloss may alternate across the width and persist for a long period in the extrusion direction, resulting in the appearance problem known as corrugation marks. These corrugation marks are less noticeable in the molded product after thermoforming than in the original foam sheet.

[0020] Since the packaging bag 3 or the buffer sheet is not pressed against a forming mold during production, the surface condition of the foamed sheet 1 before molding is directly reflected in the surface condition of the molded product. Therefore, the foamed sheet 1 of the present embodiment, which can achieve both shrinkage suppression and good appearance, can be said to be particularly effective in such applications. In particular, bleed-out is more likely to be a practical problem for the packaging bag 3 than for buffer sheets, etc. Therefore, the foamed sheet 1 of the present embodiment, which can be used without using a shrinkage inhibitor or, if used, can reduce the amount used, is suitable for use as a base roll (a foamed sheet for bag making) used to form the packaging bag 3, and is particularly suitable as a foamed sheet for bag making for the packaging bag 3 in which the surface condition of the base roll before molding is maintained as the surface condition of the product, as described above.

[0021] 3a and 3b, a packaging bag 3 will be described as an example of a foamed molded article made up of a foam sheet 1. The packaging bag 3 illustrated in the figures is rectangular in plan view, as described above, with a first sheet portion 3a constituting one side and a second sheet portion 3b constituting the opposite side of the first sheet portion 3a overlapping each other, and the first sheet portion 3a and the second sheet portion 3b are connected along three of the four sides, while the first sheet portion 3a and the second sheet portion 3b can be separated along the remaining side to form an opening 3c. The packaging bag 3 illustrated in the figures is configured so that the packaged item can be inserted and removed through the opening 3c.

[0022] The packaging bag 3 may be a three-sided bag as shown in Fig. 3a, in which two rectangular sheet bodies 30 are overlapped and three sides are joined with an adhesive or heat sealing to form a bonded section 3d along the three sides excluding the opening 3c, or a so-called two-sided bag, in which a single horizontally elongated sheet body 30 is divided into approximately four equal parts in the left-right direction, a vertical fold 30a is made at one-quarter of the length from each end, and the two end portions are folded inward along the fold 30a to form a bonded section 3d in an inverted T shape by heat sealing along the side opposite the opening 3c, and the first sheet portion 3a and the second sheet portion 3b are connected along the remaining two sides via a fold 3e. The packaging bag 3 may also be one in which a gusset (gusset) is formed on one of the three joined sides to increase the capacity.

[0023] The foamed bag sheet used to produce this type of packaging bag 3 is provided for the production of the packaging bag 3 in the form of a sheet roll in which a long strip of foamed sheet is wound into a roll to enable continuous production of the packaging bag 3.

[0024] If a foamed sheet used to manufacture this type of packaging bag 3 shrinks, the sheet roll will loosen, causing the tension of the foamed sheet running along the manufacturing line for packaging bags to fluctuate significantly or causing the foamed sheet to meander along the line, thereby reducing the productivity of the packaging bags 3. On the other hand, the foamed sheet 1 of this embodiment is less likely to cause such problems. Therefore, the foamed sheet of this embodiment is suitable as a foamed sheet for bag making, not only because it is easy to avoid the problem of bleed-out, but also from the viewpoint of production efficiency.

[0025] In this embodiment, the low density of the foamed sheet 1 (foamed layer 10) not only makes the foamed sheet 1 lightweight and excellent in shock-absorbing properties, but also allows it to exhibit excellent lightness and shock-absorbing properties to foamed molded articles such as packaging bags.

[0026] The foamed sheet 1 of this embodiment is made 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 may be, for example, 0.5 mm or more. The thickness of the foamed sheet 1 may be 1.0 mm or more, or 1.5 mm or more. The thickness of the foamed sheet 1 may be, for example, 4.0 mm or less. The thickness of the foamed sheet 1 may be 3.5 mm or less, or 3.0 mm or less.

[0027] When the foamed sheet 1 of this embodiment constitutes the foamed layer 10 of the laminated foam sheet 2, the thickness of the non-foamed layer 20 laminated on the surface thereof 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 foam 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.

[0028] The thickness of the foam sheet 1 can be measured using a constant-pressure thickness gauge, such as the "Peacock Digital Linear Gauge PDN25" manufactured by Ozaki Seisakusho Co., Ltd. Specifically, the thickness of the foam sheet 1 can be determined by measuring the thickness of the foam sheet when a 100 g load is applied to the foam sheet using a circular jig with a diameter of 35.7 mm. The thickness of the foam sheet 1 can be determined, for example, by measuring at least 10 points every 5 cm in the transverse direction (TD) perpendicular to the extrusion direction (MD), excluding 20 mm intervals at both ends of the transverse direction (TD). The thickness of the foam sheet 1 can be determined as the arithmetic mean of the measurements. If the width of the foam sheet 1 is too narrow to ensure 10 measurement points, the arithmetic mean of all measurements taken can be determined as the thickness of the foam sheet 1.

[0029] The thickness of the non-foamed layer 20 in the laminated foam sheet 2 can be determined by taking a micrograph of the cross section of the non-foamed layer 20 (a cross section in a plane perpendicular to the planar direction of the foamed sheet 1), measuring the thickness of the non-foamed layer 20 at multiple randomly selected points (e.g., 10 points) in the photograph, and calculating the arithmetic mean of the measured values. The thickness of the foamed layer 10 can be determined by subtracting the thickness of the non-foamed layer 20 from the thickness of the laminated foam sheet 2.

[0030] The foamed sheet 1 (foamed layer 10) of this embodiment has an apparent density of 30 kg / m 3 That's all. In order to make the foamed product have high strength, it is advantageous for the apparent density to be above a certain level. The apparent density is 40 kg / m 3 It may be more than 50 kg / m 3 On the other hand, in order to ensure light weight and cushioning properties, it is desirable that the apparent density be a certain value or less. The apparent density of the foamed sheet 1 (foamed layer 10) of this embodiment is 130 kg / m 3 The apparent density is 110 kg / m 3 It may be less than 80 kg / m 3 It may be the following:

[0031] Apparent density (kg / m 3 ) is the mass (basis weight: g / m) of the foam sheet 1 (foam layer 10) per unit area. 2 ) by the thickness (mm) of the foam sheet 1 (foam layer 10). The basis weight can be determined by arithmetically averaging the values ​​measured for a plurality of samples cut out from the foam sheet. The basis weight of the foam sheet can be determined by cutting out ten 10 cm x 10 cm pieces at equal intervals in the width direction (TD) of the foam sheet 1, excluding 20 mm at both ends, and measuring the mass (g) of each piece. If the width of the foam sheet 1 is too narrow to secure 10 pieces, the arithmetic mean of the measurements of all the pieces can be obtained by securing as many pieces as possible and using this as the basis weight of the foam sheet 1. The basis weight is calculated by averaging the mass (g) of each piece per 1 m 2This can be calculated by converting it into mass per unit. 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 the underwater displacement method (Archimedes' method) or the like.

[0032] The foam sheet 1 (foam layer 10) has two or more and ten or less bubbles in its thickness direction. The foam sheet 1 is less likely to shrink when the number of bubbles in the thickness direction is greater. On the other hand, the foam sheet 1 is more likely to have a good appearance when the number of bubbles in the thickness direction is smaller. Therefore, in this embodiment, the number of bubbles in the foam sheet 1 is appropriately adjusted to allow the foam sheet to exhibit both shrinkage suppression and a good appearance. The number of bubbles in the thickness direction may be three or more, or may be four or more. The number of bubbles in the thickness direction may be nine or less, or may be eight or less.

[0033] The number of bubbles in the thickness direction can be confirmed by observing the cross section of the foamed sheet 1 after the curing period (change in thickness recovery) using a scanning electron microscope (SEM) and counting the number of bubbles in the thickness direction of the foamed sheet. Specifically, first, a surface along the extrusion direction (MD direction) of the foamed sheet 1 (MD surface) and a surface along the TD direction (transverse direction perpendicular to the extrusion direction) (TD surface) are cut from the center of the width direction of the foamed sheet 1 to a size that can be observed with a scanning electron microscope (SEM). Next, these MD and TD surfaces are photographed using an SEM (e.g., Hitachi High-Technologies Corporation, Model: SU1510). The magnification is adjusted (e.g., 15 to 50 times) so that the entire thickness of the foamed sheet 1 (from the upper surface layer to the lower surface layer) fits in the photograph. In each photograph of the MD and TD surfaces, five straight lines are drawn at equal intervals in the thickness direction (VD) of the foam sheet from the upper surface to the lower surface, and the number of bubbles that touch or intersect each line is counted. The number of bubbles obtained in the MD and TD surfaces is then averaged and rounded off to the nearest whole number to calculate the number of bubbles in the thickness direction.

[0034] The foamed sheet 1 has a better shrinkage suppression effect when the average cell diameter of the foamed layer 10 is smaller. On the other hand, the foamed sheet 1 has an advantage in that a good appearance is more easily achieved when the average cell diameter of the foamed layer 10 is larger. The average cell diameter of the foamed layer 10 is, for example, 200 μm or more and 1000 μm or less. The average cell diameter of the foamed layer 10 may be 300 μm or more, or 400 μm or more. The average cell diameter of the foamed layer 10 may be 900 μm or less, 800 μm or less, or 700 μm or less.

[0035] The average cell diameter can be measured based on cross-sectional photographs of the MD and TD surfaces of the foamed sheet 1 after the curing period (change in thickness recovery) using a scanning electron microscope (SEM (Hitachi High-Technologies Corporation, Model: SU1510)) at an observation magnification adjusted (for example, 15 to 50 times) so that the entire thickness of the foamed sheet 1 (from the upper surface layer to the lower surface layer) is included, in the same manner as in the method for measuring the number of bubbles in the thickness direction. Specifically, in measuring the average cell diameter, first, microscopic images are taken of two fields of view for each of the MD and TD surfaces, for a total of four fields of view. For each of the two MD images, ten bubbles are randomly selected and the longest bubble diameter is measured in the extrusion direction (MD) using the measurement function of the SEM control software. If there are fewer than ten bubbles in the two images, add more MD images so that the number of bubbles measured reaches ten. The measured bubble lengths for each image are arithmetically averaged to obtain the average bubble diameter D in the extrusion direction. MD Let's say. For each of the two images of the TD plane, ten bubbles are randomly selected and the longest bubble diameter in the transverse direction (TD) is measured using the measurement function of the SEM control software. If there are fewer than ten bubbles in the two images, add more images of the TD plane so that the number of bubbles measured reaches ten. The measured bubble lengths for each image are arithmetically averaged to obtain the average bubble diameter D in the transverse direction. TD Let's say. For each of one image of the MD plane and one image of the TD plane, ten bubbles are randomly selected and the measurement function of the SEM control software is used to measure the longest bubble diameter in the thickness direction (VD), which is perpendicular to the extrusion direction (MD) and the width direction (TD). If there are fewer than ten bubbles in the two images, additional images of the MD and TD planes are added so that the number of bubbles measured in each cross-sectional image is 10. The lengths of the bubbles measured for each image are arithmetically averaged to determine the average bubble diameter in the thickness direction, D VD Let's say. The average bubble diameter is calculated by the cube root of the product of the bubble diameters in each direction. That is, the average bubble diameter is calculated using the following formula: Average bubble diameter (μm)=(D MD ×D TD ×D VD ) 1 / 3 D MD : Bubble diameter in extrusion direction (MD) (μm) D TD : Bubble diameter in the transverse direction (TD) (μm) D VD : Bubble diameter in thickness direction (VD) (μm)

[0036] In the foamed sheet 1 of this embodiment, it is advantageous for shrinkage to be suppressed if the foamed layer 10 has an open cell ratio of at least a certain level. The open cell ratio may be 20% or more, 25% or more, or even 30% or more. In the foamed sheet 1 of this embodiment, it is advantageous for cushioning properties and strength to be exhibited if the foamed layer 10 has an open cell ratio of at most a certain level. The foamed sheet 1 (foamed layer 10) of this embodiment preferably has an open cell ratio of 60% or less. The open cell ratio may be 55% or less, or may be 50% or less.

[0037] The open cell ratio of foamed sheet 1 (foamed layer 10) can be determined as follows. Cut out several sheet samples measuring 25mm long x 25mm wide from the foam sheet. Stack the cut samples together without leaving any gaps to create test pieces 21-23mm thick, with three pieces to be tested. The test piece is conditioned for 16 hours under the environment of JIS K7100:1999 symbol 23 / 50, grade 2, and the thickness (mm) is measured. The thickness dimension can be measured in the same manner as for determining the thickness of the foamed sheet 1 using a constant pressure thickness measuring device (for example, "Peacock Digital Linear Gauge PDN25" manufactured by Ozaki Seisakusho Co., Ltd.). From the measured dimensions, the apparent volume (V1: cm 3 ) is found. Using a Shimadzu Corporation "Accupyk II 1340-100cc" dry automatic density meter, the volume (cm 3 ) is measured. The measurement conditions are as follows: Gas used: Nitrogen Container used: 35cc Filling pressure: 0.005 psig Pressure equilibrium end rate: 0.005 psig / min Repeat count: 1 time The open cell rate (%) of each sample was calculated using the following formula, and the arithmetic mean value was taken as the open cell rate of foam sheet 1 (foam layer 10). Open cell rate (%) = {(apparent volume - volume measured with dry automatic density meter) / apparent volume} x 100

[0038] The foamed sheet 1 of this embodiment can be produced, for example, by melt-kneading a resin composition and a foaming agent in an extruder, extruding the resulting molten mixture through an annular outlet of an annular die at the tip of the extruder and foaming it (extrusion foaming) to form a tubular foam, expanding the tubular foam by placing it around the outer periphery of a cooling mandrel with a diameter larger than the outlet, cooling it from the inner periphery, and, if necessary, cooling it by blowing air from the inner and / or outer periphery between the annular die and the cooling mandrel, continuously cutting the expanded tubular foam on the cooling mandrel in the extrusion direction to form strips, and winding up the strip-shaped foam sheet into a roll. The laminated foam sheet 2 can be produced by co-extruding the non-foamed layer 20 with the foamed layer 10, or by first producing a single-layer foamed sheet 1 and then extrusion laminating or dry laminating the non-foamed layer 20 onto the foamed sheet 1.

[0039] In order for the foamed sheet 1 (foamed layer 10) produced in this manner to exhibit the above-mentioned properties, it is preferable that the resin composition before extrusion foaming used to form foamed layer 10 (hereinafter also referred to as the "foaming resin composition") and the resin composition in the state constituting foamed sheet 1 (hereinafter also referred to as the "foamed resin composition") have predetermined melting properties. The resin composition constituting foamed layer 10 will be described below.

[0040] In this embodiment, by appropriately adjusting the number of cells in the thickness direction of the foamed sheet 1, excellent properties are exhibited in both shrinkage suppression and appearance. Therefore, during extrusion foaming, it is preferable to prevent excessively small cells from forming, and it is preferable to set conditions that allow each cell to expand to a sufficient size. In extrusion foaming, by growing the cells while maintaining a good balance between the bubble expansion force of the foaming agent and the tension acting on the cell membrane, it is possible to form relatively large cells (or achieve a low apparent density) while suppressing cell breakage. Therefore, in order to form relatively large cells, it is advantageous for the resin composition in a molten state to have a melt viscosity and melt tension of a certain level or higher in order to suppress cell breakage during the cell growth process. On the other hand, if the melt viscosity and melt tension are too high, it may hinder cell growth.

[0041] In extrusion foaming, bubble growth can be controlled to some extent not only by the melting properties of the resin composition but also by the cooling conditions after extrusion of the molten mixture extruded into a sheet. For example, although the foaming agent dissipates rapidly from the tubular foam immediately after extrusion, rapid cooling of the tubular foam at this time can suppress the dissipation of the blowing agent and allow the blowing agent contained in the molten mixture to be effectively utilized for bubble growth. On the other hand, excessive cooling increases the melt viscosity and melt tension of the molten mixture, making bubble growth difficult. Furthermore, the foamable resin composition of this embodiment may contain one or more aliphatic polyester resins. Furthermore, if the aliphatic polyester resin begins to crystallize relatively early after the tubular foam is extruded, it can also reduce the extensibility of the bubble film. For this reason, when producing the foam sheet 1, it is advantageous to quickly cool only the surface layer of the tubular foam immediately after extrusion to suppress the dissipation of the blowing agent while maintaining the interior of the sheet at a temperature at which the resin composition remains flexible. In general, when producing a foamed sheet, cooling air is blown onto the extruded tubular foam from the inner or outer periphery. To bring the tubular foam into the state described above and promote cell growth, the temperature of the cooling air may be increased somewhat, but the air volume may be increased to quickly cool the surface layer while slowing the rate at which the cooling effect reaches the interior of the sheet. Alternatively, instead of blowing cooling air onto the tubular foam over the entire area between the annular die and the cooling mandrel, cooling air may be applied at a position close to the annular die to quickly cool only the surface layer of the tubular foam.

[0042] In this embodiment, it is preferable to prepare a foamed sheet 1 having cells in a predetermined state in consideration of both the extrusion conditions and the melting characteristics of the resin composition.

[0043] The foamable resin composition preferably exhibits appropriate fluidity upon heating in order to exhibit good foamability. Specifically, in this embodiment, the foamable resin composition before being used to form the foam sheet 1 (foam layer 10) may have a melt mass-flow rate (MFR) at 190°C of, for example, 0.1 g / 10 min or more and 5.0 g / 10 min or less. The MFR of the resin composition may be, for example, 0.2 g / 10 min or more, or 0.3 g / 10 min or more. The MFR of the resin composition may be, for example, 4.0 g / 10 min or less, 3.0 g / 10 min or less, 2.0 g / 10 min or less, or 1.0 g / 10 min or less.

[0044] In this embodiment, it is preferable that the resin composition in the state of constituting foamed sheet 1 (foamed layer 10) (hereinafter also referred to as "foamed resin composition") also has the above-mentioned MFR value.

[0045] The melt mass-flow rate (MFR) of the foaming resin composition before forming the foamed sheet 1 (foamed layer 10) and the foamed resin composition in the state of constituting the foamed sheet 1 (foamed layer 10) can be measured as follows. The melt mass flow rate (MFR) of the resin composition can be measured using a commercially available measuring device (for example, "Melt Flow Index Tester (Automatic) 120-SAS" manufactured by Yasuda Seiki Seisakusho Co., Ltd.). MFR can be measured under the following conditions in accordance with JIS K 7210:1999. The sample to be measured is vacuum dried at 70°C for at least 5 hours, and after drying, it is placed in a nylon plastic bag for vacuum packing, vacuum packed, and stored in a desiccator until just before measurement.

[0046] (Measurement conditions) Sample: 3 to 8 g Preheat 1:200 seconds Preheat 2:30 seconds Test temperature: 190℃ Test load: 21.18N Piston travel distance (interval): 25mm Number of tests: 3 The arithmetic mean value of the measured values ​​obtained in each test is taken as the MFR (g / 10 min).

[0047] The foamable resin composition preferably exhibits an appropriate melt tension upon heating in order to exhibit good foamability. The melt tension at 190°C of the resin composition used in this embodiment can be, for example, 30 cN or more and 100 cN or less. The melt tension may be 35 cN or more, or 40 cN or more. The melt tension may be 95 cN or less, or 90 cN or less. The melt tension may be 80 cN or less, 70 cN or less, or 60 cN or less. The melt tension may be 55 cN or less, or 50 cN or less. It is preferable that the foamed resin composition also has the melt tension as described above.

[0048] The melt tension of the resin composition (the foamable resin composition, the foamed resin composition) can be measured as follows. The melt tension can be measured using a commercially available rheometer and extensional viscosity measuring device (for example, the "Capillograph 1D" (special furnace specification) capillary rheometer manufactured by Toyo Seiki Seisaku-sho, Ltd., and the "Rheotens 71.97" manufactured by Goettfert). The melt tension can be measured under the following conditions: The sample should be vacuum dried at 70°C for at least 5 hours in advance, and after drying, it should be placed in a nylon plastic bag for vacuum packing, vacuum packed, and stored in a desiccator until immediately before measurement. -Install the "Rheotens 71.97" so that the distance from the die exit of the "Capilograph 1D" to the measurement section is 80 mm (if interference occurs and the Rheotens cannot be brought close enough to 80 mm, take measures to avoid interference and set the Rheotens in the designated location). First, fill the barrel with the sample, which has been heated to a test temperature of 190°C, and preheat it for 5 minutes. The measurement time, including the preheating time after filling the barrel with the sample, should not exceed 10 minutes. Next, a piston is inserted from the top of the barrel and the molten resin is extruded into a string shape. At this time, the piston descending speed (20 mm / min) is kept constant, and the extruded string is passed through a Rheotens wheel and taken up. After that, the take-up speed is gradually increased and the melt tension of the sample is measured.

[0049] Regarding the measurement results, the melt tension of the sample is the average of the maximum and minimum tension values ​​just before the point at which the string-like material breaks. If there is only one maximum point on the tension chart, that maximum value is used as the melt tension. Also, if the string-like material becomes thinner and the winding becomes idling, that point is considered to be the break point, and the average of the maximum and minimum tension values ​​just before that point is used as the melt tension of the sample.

[0050] (Capillograph 1D measurement conditions) Die: diameter 2.095 mm, length 8 mm, inlet angle 90 degrees (conical) Barrel diameter: 9.55mm Piston speed: 20mm / min Measurement temperature: 190℃

[0051] (Rheotensile measurement conditions) Wheel spacing: top 0.6mm, bottom 1.0mm Acceleration: 10mm / s 2 Pulling speed: Initial speed 6.92mm / s

[0052] To ensure good extensibility of the foamed film during foaming, the foamed sheet 1 (foamed layer 10) of this embodiment preferably has a gel fraction of 25% by mass or less, as measured using chloroform. The gel fraction may be 20% by mass or less, or 15% by mass or less. The gel fraction may be, for example, 0.1% by mass or more, 0.2% by mass or more, or 0.3% by mass or more.

[0053] The gel fraction can be determined by taking multiple samples (e.g., five samples) of about 0.5 g each from the foam sheet 1 (foam layer 10) and calculating the arithmetic mean of the gel fractions of the individual samples. 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 stir bar in a beaker (volume: 100cc), cover with aluminum foil, set on a stirrer, and stir for 4 hours at room temperature to dissolve the sample. After 2 hours, remove the lid, filter the dissolved material in the beaker through the wire mesh, and collect the insoluble resin material on the wire mesh. After filtering the insoluble resin, let the wire mesh dry naturally in a draft chamber to evaporate the chloroform. After filtering the insoluble resin, dry the wire mesh in a thermostatic oven at 120°C for 2 hours, then leave to cool in a desiccator. After cooling, measure the total mass (Mx) of the insoluble resin and the wire mesh. Calculate the gel fraction (mass%) using the following formula: Gel fraction (mass%) = {(Mx - Ms) / Mo} × 100

[0054] The foamable resin composition preferably has a predetermined melting point and crystallization temperature. The same applies to the foamed resin composition. The melting point of the foamable resin composition and the foamed resin composition is preferably 100°C or higher. On the other hand, the crystallization temperature of the foamable resin composition and the foamed resin composition is preferably lower than 100°C. The melting point can be, for example, 100°C or higher and 150°C or lower. The melting point can be 105°C or higher, or 110°C or higher. The melting point can be 140°C or lower, or 130°C or lower. The crystallization temperature can be, for example, 90°C or higher and 99°C or lower. The crystallization temperature can be 98°C or lower, or 97°C or lower. The crystallization temperature can be 91°C or higher, or 92°C or higher.

[0055] The melting point and crystallization temperature of the foamable resin composition and the foamed resin composition can be measured by the methods described in JIS K7121: 1987 and JIS K7121: 2012. The sampling method and temperature conditions are as follows: Fill the bottom of an aluminum measurement container with 5.5±0.5 mg of samples cut out from the foaming resin composition and foam sheet (foamed resin composition) without leaving any gaps, then cover with an aluminum lid. Next, differential scanning calorimetry was performed using a Hitachi High-Tech Science DSC7000X, AS-3 differential scanning calorimeter. The sample was heated and cooled using the following steps 1 to 4 under a nitrogen gas flow rate of 20 mL / min to obtain a DSC curve. (Step 1) Decrease the temperature from 30°C to -40°C at a rate of 10°C / min. (Step 2) The temperature is increased from -40°C to 200°C at a rate of 10°C / min (first temperature increase process) and held for 10 minutes. (Step 3) The temperature is lowered from 200°C to -40°C at a rate of 10°C / min (cooling process) and held for 10 minutes. (Step 4) The temperature is increased from -40°C to 200°C at a rate of 10°C / min (second temperature increase process). Alumina is used as the reference material. Then, using the analytical software provided with the device, read the temperature at the top of the melting peak observed during the second heating process and use this as the melting point, and read the temperature at the top of the crystallization peak during the cooling process and use this as the crystallization temperature. However, if multiple melting peaks or crystallization peaks are observed, use the higher temperatures as the melting point and crystallization temperature.

[0056] In order to adjust the various characteristic values ​​as described above to desired values, the foamable resin composition may contain an aliphatic polyester resin that has been modified by partial crosslinking or the like (hereinafter also referred to as a "modified aliphatic polyester resin"). Examples of such a modification method by crosslinking (partial crosslinking) include a method using a radical reaction using an organic peroxide.

[0057] Examples of the organic peroxide include peroxyesters, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

[0058] The organic peroxide is preferably used in an amount of 0.02 to 0.6 parts by mass per 100 parts by mass of the aliphatic polyester resin before modification (hereinafter also referred to as "unmodified aliphatic polyester resin"). The amount of organic peroxide may be 0.05 parts by mass or more, or may be 0.08 parts by mass or more. The amount of organic peroxide may be 0.5 parts by mass or less, or may be 0.4 parts by mass or less.

[0059] The foamable resin composition may be composed of only one or more aliphatic polyester resins, or may contain a polyester resin other than an aliphatic polyester resin (for example, an aromatic polyester resin). The polyester resin other than an aliphatic polyester resin may be a modified polyester resin modified with an organic peroxide or the like, or may be an unmodified polyester resin. The foamable resin composition may also contain a resin other than a polyester resin. The content of the resin other than an aliphatic polyester resin is preferably less than 20% by mass relative to all resins contained in the foamable resin composition. That is, the proportion of the aliphatic polyester resin relative to all resins contained in the foamable resin composition is preferably 80% by mass or more. The proportion of the aliphatic polyester resin may be 90% by mass or more, or may be 95% by mass or more. The proportion of the modified aliphatic polyester resin relative to all resins contained in the foamable resin composition is preferably 80% by mass or more. The proportion of the modified aliphatic polyester resin relative to all resins contained in the foamable resin composition is preferably 80% by mass or more. The proportion of the modified aliphatic polyester resin may be 90% by mass or more, or may be 95% by mass or more.

[0060] The aliphatic polyester resin contained in the foamable resin composition may be a hydroxy acid polycondensate, a ring-opening polymerization product of lactone, or a polycondensate of a polyhydric alcohol component and a polycarboxylic acid component. Examples of hydroxy acid polycondensates include polylactic acid and polycondensates of hydroxybutyric acid. Examples of ring-opening polymerization products of lactone include polycaprolactone and polypropiolactone. Examples of polycondensates of a polyhydric alcohol component and a polycarboxylic 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 foamable resin composition is preferably polybutylene succinate (PBS) from the viewpoint of imparting excellent cushioning properties to the foamed sheet 1. As described above, the foamable resin composition preferably contains polybutylene succinate modified with an organic peroxide or the like.

[0061] Resins other than aliphatic polyester-based resins, such as tackifiers and polymeric antistatic agents, may be incorporated into the foamable resin composition. Examples of foaming components supplied to the extruder together with the foamable resin composition include cell regulators and foaming agents. During extrusion foaming, various additives may be added to the foamable resin composition. Examples of such additives include fillers, colorants, flame retardants, antibacterial agents, weather resistance agents, and surfactants. The proportion of additives other than resins in the foamable resin composition of this embodiment is typically 10% by mass or less. The proportion of additives may be 8% by mass or less, or may be 6% by mass or less. The component configuration of the foamed resin composition is the same as that of the foamable resin composition, and therefore, the preferred proportions of resins in the foamed resin composition will not be repeated here.

[0062] The modified aliphatic polyester resin can be produced by reacting an organic peroxide with an unmodified aliphatic polyester resin in an extruder, and by melt-kneading them in the extruder. Therefore, the foamable resin composition as described above may be produced by mixing the components to prepare resin pellets, and then supplying the resin pellets to the extruder to perform extrusion foaming, or may be produced by melt-kneading the unmodified aliphatic polyester resin and the organic peroxide in the extruder immediately before extrusion foaming, thereby modifying the composition by a radical reaction.

[0063] As described above, in producing the foamed sheet 1 of the present embodiment, the aliphatic polyester resin and the organic peroxide are melt-kneaded to modify the aliphatic polyester resin, and a resin composition containing the modified aliphatic polyester resin is extruded together with a foaming agent into a sheet to form the foamed layer 10 from the resin composition. The apparent density of the foamed layer 10 is 30 kg / m 3 More than 130kg / m 3 Hereinafter, foamed sheet 1 is produced so as to have a thickness of 0.5 mm or more and 4.0 mm or less and to have 2 or more and 10 or less cells in the thickness direction.

[0064] Carbon dioxide is preferred as the blowing agent used in extrusion foaming of the foamable resin composition. In this embodiment, a hydrocarbon or the like may be used as a blowing agent in addition to or instead of carbon dioxide. A small amount of nitrogen gas may also be used in combination with carbon dioxide or a hydrocarbon. These blowing agents may be used alone or in combination of two or more.

[0065] To suppress shrinkage of the foamed sheet 1 and provide a good appearance, the foamable resin composition preferably contains the cell regulator. Examples of the cell regulator include inorganic compound particles such as talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, magnesium carbonate, potassium sulfate, barium sulfate, and glass beads, as well as organic compound particles such as polytetrafluoroethylene. Furthermore, azodicarbonamide, sodium bicarbonate, or a mixture of sodium bicarbonate and citric acid, which also function as a thermal decomposition type foaming agent, can also be used as a cell regulator. The cell regulator may be added to the foamable resin composition in the form of a masterbatch or by dry blending. To achieve an appropriate number of bubbles in the thickness direction of the foamed sheet 1, for example, the ratio of the cell regulator to 100 parts by weight of the resin contained in the foamable resin composition is preferably 0.01 parts by weight or more, more preferably 0.05 parts by weight or more, and particularly preferably 0.5 parts by weight or more. In order to provide foam sheet 1 with a good appearance, the foaming resin composition preferably contains no more than 3 parts by mass of the cell control agent, more preferably no more than 2 parts by mass, and particularly preferably no more than 1.5 parts by mass.

[0066] To suppress shrinkage of the foamed sheet 1 after production, the foaming resin composition may contain a shrinkage inhibitor. Examples of shrinkage inhibitors that can be used include fatty acid esters, aliphatic amines, and fatty acid amides. Examples of the fatty acid esters include esters of fatty acids having 8 to 30 carbon atoms and polyhydric alcohols having 3 to 7 hydroxyl groups. Examples of fatty acids having 8 to 30 carbon atoms include lauric acid, oleic acid, stearic acid, behenic acid, lignoceric acid, cerotic acid, heptacoic acid, montanic acid, melissic acid, and lacteric acid. Examples of polyhydric alcohols having 3 to 7 hydroxyl groups include glycerin, diglycerin, triglycerin, erythritol arabidopsis, xylamydium tetanylate, mannitol, sorbitol, and sorbitan.

[0067] Although the shrinkage inhibitor is expected to effectively suppress shrinkage of the foamed sheet 1, fatty acid compounds do not have a sufficiently good affinity with aliphatic polyester resins, which can cause problems due to bleed-out. Therefore, for example, the foamable resin composition preferably contains 10,000 ppm or less of the shrinkage inhibitor, more preferably 5,000 ppm or less, and particularly preferably 1,000 ppm or less, and it is particularly preferred that the foamed resin composition does not contain any shrinkage inhibitor.

[0068] The content of the shrinkage inhibitor can be determined by measuring the total amount of fatty acid ester, aliphatic amine, and fatty acid amide extracted from the foamed sheet 1 using an organic solvent by liquid chromatography.

[0069] Specifically, the quantitative determination of fatty acid esters, fatty amines, and fatty acid amides can be carried out using a liquid chromatography-tandem mass spectrometer (LC-MS / MS) (for example, "ACCELA" manufactured by Termo Scientific).

[0070] The calibration curves used to quantify these fatty acid compounds are prepared using four different concentrations of standard solutions (10 ppm, 5 ppm, 2.5 ppm, 1 ppm) prepared by diluting a 1000 ppm standard solution (methanol solution) of the fatty acid compound (fatty acid ester, fatty amine, fatty acid amide) to be quantified with methanol. The sample to be measured by LC-MS / MS is prepared as follows. -Cut the foam sheet into pieces approximately 2 mm square to obtain an extraction sample of approximately 0.15 g. The extracted sample is accurately weighed, and placed in a PTFE (polytetrafluoroethylene) pressure-resistant container together with 10 ml of methanol, and the pressure-resistant container is sealed. Heat the sealed pressure-resistant container in an oven at 120°C for 2 hours, then remove it from the oven and allow it to cool naturally at room temperature. Open the pressure vessel that has been cooled to room temperature and filter the extract through filter paper (No. 5A). The filtrate obtained by the above filtration is used as the measurement sample for LC-MS / MS. From the measurement results, calculate the amount of fatty acid compounds in the filtrate using the calibration curve obtained earlier. The amount of anti-shrinkage agent in foam sheet 1 is calculated from the amount of fatty acid compounds contained in the filtrate.

[0071] The absence of a shrinkage inhibitor in the foamed sheet 1 can be confirmed by checking that the content of fatty acid compounds determined by the above measurement is at the impurity level (for example, 100 ppm or less).

[0072] The above-described bleed-out problem can also occur in a laminated foam sheet 2. For example, in a laminated foam sheet 2 in which the non-foamed layer 20 is formed by coextrusion, bleed-out occurs similarly to a foam sheet 1 having a single foam layer 10. Furthermore, in a laminated foam sheet in which the non-foamed layer 20 is formed by dry lamination, good adhesion between the non-foamed layer 20 and the foam layer 10 is difficult to achieve, which can cause the non-foamed layer 20 to partially peel off from the foam layer 10, resulting in blisters. Therefore, although the above detailed description is primarily focused on a foam sheet 1 having a single foam layer 10, the effects achieved in the foam sheet 1 are also achieved in a laminated foam sheet 2. Furthermore, the above detailed description is directed to specific examples of the present invention, and the present invention is not limited to these examples.

[0073] As mentioned above, this specification includes the following disclosures. (1) A foamed sheet including a foamed layer made of a resin composition including a polyester-based resin, the resin composition contains an aliphatic polyester resin as the polyester resin, The foam layer is Apparent density 30kg / m 3 More than 130kg / m 3 Below, The thickness is between 0.5mm and 4.0mm. A foamed sheet with 2 to 10 bubbles in the thickness direction.

[0074] (2) The foamed sheet according to (1), wherein the foamed layer has an average cell diameter of 200 μm or more and 1000 μm or less.

[0075] (3) The foam sheet according to (1) or (2), wherein the foam layer has an open cell rate of 20% or more and 60% or less.

[0076] (4) The foamed sheet according to any one of (1) to (3), wherein the aliphatic polyester resin is polybutylene succinate.

[0077] (5) A foamed molded article which is a molded article made of the foamed sheet according to any one of (1) to (4).

[0078] (6) A method for producing a foamed sheet having a foam layer, comprising: modifying the aliphatic polyester resin by melt-kneading the aliphatic polyester resin and an organic peroxide; and extruding a resin composition containing the modified aliphatic polyester resin together with a foaming agent into a sheet to form the foam layer from the resin composition, The foam layer Apparent density 30kg / m 3 More than 130kg / m 3 below, Thickness is 0.5mm or more and 4.0mm or less, The method for producing a foamed sheet comprises producing the foamed sheet so that the number of cells in the thickness direction is 2 to 10.

[0079] (7) (6) The method for producing a foamed sheet according to (6), wherein the foaming agent is carbon dioxide.

[0080] (8) The method for producing a foamed sheet according to (6) or (7), wherein the resin composition contains a cell control agent.

[0081] (9) The method for producing a foamed sheet according to any one of (6) to (8), wherein the resin composition does not contain a shrinkage inhibitor. [Example]

[0082] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

[0083] The following aliphatic polyester resins were prepared to produce the foamed sheets of the Examples and Comparative Examples. <Aliphatic polyester resin> Manufactured by PTT MCC BIOCHEM, product name "BioPBS FZ71PM", a PBS in which part of the resin is plant-derived.

[0084] [Table 1]

[0085] The following organic peroxides were used to modify the aliphatic polyester resin: The following cell regulators, foaming agents, and additives (shrinkage inhibitors) were used to prepare foamed sheets. <Organic peroxide> Nouryon Chemical Company, trade name "Trigonox BPIC-C75", t-butylperoxyisopropyl monocarbonate, 1-minute half-life temperature 156°C <Foam adjuster> Talc masterbatch: A masterbatch made by mixing talc (manufactured by Matsumura Sangyo Co., Ltd., product name "Crown Talc PP") and aliphatic polyester resin (manufactured by PTT MCC BIOCHEM, product name "BioPBS FZ91PM") in a 50:50 (mass ratio) talc:aliphatic polyester resin ratio. Chemical foaming agent masterbatch: Manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., product name "Fine Cell Master PO410K". <Foaming agent> ·carbon dioxide Butane: A mixture of isobutane and normal butane. Isobutane: normal butane = 35:65 (mass ratio). <Additives (shrinkage prevention agents)> Stearic acid monoglyceride (Kao Corporation, product name "Electrostripper TS-5")

[0086] (Methods for evaluating physical properties of foamable resin compositions and foam sheets) The foamed sheet's "basis weight," "thickness," "number of cells in the thickness direction," "apparent density," "open cell ratio," "average cell diameter," "MFR," "melt tension," "melting point," "crystallization temperature," and "gel fraction" were measured by the methods described above.

[0087] (Method for evaluating the performance of foam sheets) The performance of the foamed sheet was evaluated as follows.

[0088] <Evaluation of the lightweight properties of foam sheets> The lightness of the foamed sheet was evaluated based on the apparent density of the foamed sheet in each example according to the following criteria.

[0089] <Lightweightness evaluation criteria> ◎: Apparent density is 60 kg / m 3 is less than. ○: Apparent density is 60 kg / m 3 More than 80kg / m 3 is less than. △: Apparent density is 80 kg / m 3 More than 130kg / m 3 is less than. ×: Apparent density is 130 kg / m 3 That's all.

[0090] <Evaluation of thickness shrinkage of foam sheets> Immediately after being wound on the winder, a sheet slice (50 cm long, full width) was taken from the outermost surface of the sheet roll, and the initial thickness T0 (mm) was immediately measured. The sheet slice was then stored in an atmosphere at a temperature of 20±10°C, and the thickness of the foam sheet was measured every 15 minutes for 180 minutes after the sheet slice was taken, and the smallest thickness of the foam sheet was designated T1 (mm). The thickness at each measurement time was measured using a constant pressure thickness gauge in the same manner as the method for measuring foam sheet thickness. The thickness shrinkage rate (%) of the foamed sheet was calculated from the ratio of the initial thickness T0 (mm) of the foamed sheet to the smallest thickness T1 (mm) of the foamed sheet using the following formula. Thickness shrinkage rate (%) = {(T0-T1) / T0} x 100

[0091] <Evaluation criteria for thickness shrinkage> The thickness shrinkage of the foamed sheet was evaluated based on the thickness shrinkage rate of the foamed sheet according to the following criteria. ◎: Thickness shrinkage rate is less than 30%. ○: Thickness shrinkage rate is 30% or more and less than 40%. △: Thickness shrinkage rate is 40% or more and less than 50%. ×: Thickness shrinkage rate is 50% or more.

[0092] <Evaluation of foam sheet thickness recovery> Immediately after being wound on the winder, a sheet slice (50 cm long, full width) was taken from the outermost surface of the roll, and the initial thickness T0 (mm) was immediately measured. The sheet slice was then stored in an atmosphere at a temperature of 20±10°C, and the thickness of the foam sheet was measured every 15 minutes for 180 minutes after the sheet slice was taken, and the smallest thickness of the foam sheet was designated as T1 (mm). The thickness at each measurement time was measured using a constant pressure thickness gauge in the same manner as in the method for measuring foam sheet thickness. The sheet slices were then stored in an atmosphere at a temperature of 23±2°C, and the thickness of the foamed sheet was measured every day (24 hours). The thickness was measured to 1 / 100 mm using a constant pressure thickness gauge in the same manner as in the method for measuring the thickness of a foamed sheet. The day when the thickness measurement was the same as the previous day's measurement was determined to be the day when the thickness recovery was complete. The day when the thickness T1 (mm) of the foamed sheet was measured was designated as day 0, and the number of days elapsed until the day when thickness recovery was completed was designated as the number of days for thickness recovery.

[0093] <Evaluation criteria for thickness recovery> The thickness recovery of the foamed sheet was evaluated based on the number of days until the thickness of each foamed sheet was recovered, according to the following criteria. ◎: Thickness recovery time is less than 7 days. ○: Thickness recovery time was 7 days or more but less than 14 days. △: Thickness recovery time was 14 days or more but less than 21 days. ×: Thickness recovery time is 21 days or more.

[0094] <Evaluation of the appearance of foam sheets> The state of the corrugated marks on the foamed sheet of each example was visually inspected and evaluated according to the following criteria.

[0095] <Appearance evaluation criteria> ⊚: No corrugation marks were observed and the surface smoothness was extremely excellent. ◯: Slight corrugation marks occurred, and the surface smoothness was excellent. △: Corrugated marks were observed and the surface smoothness was poor. ×: Corrugated marks are significantly observed and the surface smoothness is extremely poor.

[0096] <Evaluation of migration of foam sheets> Six sheet slices measuring 5 cm x 9 cm were cut from arbitrarily selected locations on the foam sheet. Three glass plates of the same size were prepared, and three sets of samples were prepared by sandwiching the glass plates between two of the sheet slices. A weight of 1 kg was placed on the samples, and the samples were kept in a thermo-hygrostat chamber set at 60°C and a relative humidity of 80% for 24 hours. After 24 hours, the cut-out sample sheets were removed from the thermo-hygrostat chamber, peeled from both sides of the glass plates, and the state of the glass plates was visually evaluated.

[0097] <Transferability evaluation criteria> The migration of the foamed sheet was evaluated based on the state of the glass plate in each example according to the following criteria. ◎: No migration was observed at all. ○: If you look closely, you can faintly see the migration. △: The migration can be clearly seen at a glance. ×: Sticky transfer material can be seen all over the surface.

[0098] <Overall evaluation of foam sheets> The foamed sheets of each example were comprehensively evaluated based on the various properties according to the following criteria. ◎: All items were rated as "◎" or "〇". ◯: All items were rated as "◎", "◯", or "△", with one or more "△" but less than three. △: All items were rated as "◎", "〇", or "△", with three or more "△"s. ×: The evaluation of any item was "×".

[0099] <Preparation of modified aliphatic polyester resin> First, according to the formulation in Table 2, an aliphatic polyester resin that had been previously dehumidified and dried at 70° C. for 5 hours and an organic peroxide were dry-blended to obtain mixed pellets. Next, the mixed pellets were fed into the hopper of a twin-screw extruder (diameter 51 mm, L / D=48) and melt-kneaded under the extrusion conditions shown in Table 3. Strands of the modified aliphatic polyester resin were extruded from a strand die attached to the tip of the twin-screw extruder, cooled in a water tank, and cut into pellets using a pelletizer to obtain pellets of the foamable resin composition. The physical properties of the obtained foamable resin composition are shown in Table 2.

[0100] [Table 2]

[0101] <Preparation of foam sheet> Example 1 According to the formulation in Table 3, a modified aliphatic polyester resin that had been dehumidified and dried at 70° C. for 5 hours in advance and a cell regulator were dry-blended to prepare a formulation. The compound was fed into the hopper of the first extruder of a tandem extruder connected to two extruders (the first extruder on the upstream side was a single-screw extruder (diameter 50 mm), and the second extruder on the downstream side was a single-screw extruder (diameter 65 mm)). The compound was melt-kneaded in the first extruder while a foaming agent was injected midway through the first extruder to obtain a melt-kneaded product. The molten mixture was transferred to a second extruder, cooled, and extruded through a circular die (diameter 70 mm) attached to the tip of the second extruder to form a cylindrical foamed sheet. The resin temperature was 135°C and the extrusion rate was 30 kg / h. Cooling air was blown onto the inner and outer sides of the cylindrical foamed sheet, and then the inner surface of the cylinder was brought into sliding contact with the outer peripheral surface of a predetermined mandrel to cool the cylinder from the inner surface. Thereafter, one portion of the cylinder was continuously cut along the extrusion direction to obtain a long strip-like foamed sheet, which was then wound into a roll by a winder. The physical properties and evaluation of the resulting foamed sheet are shown in Table 3.

[0102] [Table 3]

[0103] Examples 2 to 11 A foamed sheet was produced in the same manner as in Example 1 according to the formulation in Table 3. The physical properties and evaluation of the resulting foamed sheet are shown in Table 3.

[0104] (Comparative Examples 1 to 4) A foamed sheet was produced in the same manner as in Example 1 according to the formulation in Table 4. The physical properties and evaluation of the resulting foamed sheet are shown in Table 4.

[0105] [Table 4]

[0106] The foamed sheets of Examples 1 to 10 were overall evaluated as "good" to "good". On the other hand, Example 11, which contained a large amount of stearic acid monoglyceride (additive), was overall evaluated as "fair". The foamed sheets of Comparative Examples 1 to 4 were evaluated as "poor" in either the light weight evaluation, thickness shrinkage evaluation, or appearance evaluation, and all were overall evaluated as "poor".

[0107] Comparisons between Example 1 and Examples 10 and 11, and between Comparative Example 1 and Comparative Example 4, show that the thickness shrinkage and thickness recovery were roughly the same, and that when carbon dioxide was used as the foaming agent, shrinkage was not suppressed even by adding stearic acid monoglyceride. Examples 10 and 11 and Comparative Example 4, which used stearic acid monoglyceride, were evaluated for migration as "good" to "fair," and were inferior to the other Examples and Comparative Examples.

[0108] Figures 4-6 show microscopic images of the MD surface taken with a scanning electron microscope for Example 1 (Figure 4), which has three thickness-direction bubbles; Example 4 (Figure 5), which has five thickness-direction bubbles; and Example 5 (Figure 6), which has seven thickness-direction bubbles. Figures 7-9 show photographs of the foam sheet surface (state of corrugation marks) for Example 1 (Figure 7), which received an appearance rating of "Excellent," Example 4 (Figure 8), which received an appearance rating of "Good," and Example 5 (Figure 9), which received an appearance rating of "Poor." In Figures 7-9, the longitudinal direction is the extrusion direction (MD) of the foam sheet, and the transverse direction is the width direction (TD) of the foam sheet. These figures reveal that as the number of thickness-direction bubbles increases to 3, 5, and 7, the corrugation marks on the foam sheet surface become more noticeable, making it more difficult to maintain a good appearance.

[0109] From the above results, it was confirmed that the foamed sheet to which the present invention is applied has both a beautiful appearance and suppressed shrinkage after extrusion. [Explanation of symbols]

[0110] 1: Foam sheet, 2: Laminated foam sheet, 3: Packaging bag, 10: Foam layer, 20: Non-foam layer

Claims

1. A foamed sheet including a foamed layer made of a resin composition including a polyester-based resin, the resin composition contains an aliphatic polyester resin as the polyester resin, The foam layer is Apparent density 30 kg / m ３ More than 130kg / m ３ Below, The thickness is 0.5 mm or more and 4.0 mm or less, A foamed sheet having 2 or more and 10 or less bubbles in the thickness direction.

2. 2. The foamed sheet according to claim 1, wherein the foamed layer has an average cell diameter of 200 μm or more and 1000 μm or less.

3. 2. The foamed sheet according to claim 1, wherein the foamed layer has an open cell ratio of 20% to 60%.

4. 2. The foamed sheet according to claim 1, wherein the aliphatic polyester resin is polybutylene succinate.

5. A foamed molded article, which is a molded article formed from the foamed sheet according to any one of claims 1 to 4.

6. A method for producing a foamed sheet having a foam layer, comprising: modifying the aliphatic polyester resin by melt-kneading the aliphatic polyester resin and an organic peroxide; and extruding a resin composition containing the modified aliphatic polyester resin together with a foaming agent into a sheet to form the foam layer from the resin composition, The foam layer Apparent density 30 kg / m ３ More than 130kg / m ３ below, The thickness is 0.5 mm or more and 4.0 mm or less, The method for producing a foamed sheet, wherein the foamed sheet is produced so that the number of cells in the thickness direction is 2 to 10.

7. The method for producing a foamed sheet according to claim 6, wherein the foaming agent is carbon dioxide.

8. The method for producing a foamed sheet according to claim 6 , wherein the resin composition contains a cell control agent.

9. The method for producing a foamed sheet according to claim 6, wherein the resin composition does not contain a shrinkage inhibitor.

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