Polylactic acid resin foam molded products and display panels

Abstract

The present invention provides a polylactic acid resin foam molded article with excellent surface smoothness and good printability on its surface. It also provides display panels and containers with excellent surface smoothness and good printability on their surfaces. [Solution] The polylactic acid resin foam molded article according to an embodiment of the present invention is a polylactic acid resin foam molded article formed by molding a polylactic acid resin foam sheet, wherein the polylactic acid resin foam molded article has a first main surface and a second main surface facing the first main surface, and the minimum autocorrelation length Sal in at least one selected from the group consisting of the first main surface and the second main surface is 500 μm or less.

Description

Technical Field

[0001] The present invention relates to a polylactic acid resin foamed molded body and a display panel.

Background Art

[0002] Resin foams are lightweight and have excellent cushioning properties, and are easy to be processed into various shapes. Therefore, they are used as raw materials for various molded products, such as foamed plates and containers for plate-like base materials (display panels) printed on the surface for display.

[0003] For example, as for display panels, polystyrene resin plate-like foamed sheets that can be clearly printed with various inks on the surface of resin foam sheets have been proposed (Patent Documents 1-2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Since resin foams and resin foamed molded bodies formed therefrom are discarded in large quantities after being used in large quantities, they impose a great burden on the environment and are factors of various social problems, such as global warming problems, resource depletion problems, and waste treatment problems. Polystyrene resin plate-like foamed sheets are no exception. Thus, there is a demand for resin foamed molded bodies with a small environmental load and capable of good printing.

[0006] In view of the above problems, the present invention aims to provide a polylactic acid resin foam molded article that is biodegradable, has a low environmental impact, and can be manufactured relatively inexpensively, and that has excellent surface smoothness and is printable on its surface. Furthermore, the invention aims to provide display panels and containers that have excellent surface smoothness and are printable on their surfaces. [Means for solving the problem]

[0007] [1] The polylactic acid resin foam molded body according to the embodiment of the present invention is A polylactic acid resin foam molded article made by molding a polylactic acid resin foam sheet, The polylactic acid resin foam molded article has a first main surface and a second main surface facing the first main surface, The minimum autocorrelation length Sal in at least one selected from the group consisting of the first principal surface and the second principal surface is 500.0 μm or less. [2] The polylactic acid resin foamed molded article described in [1] above may have an average bubble diameter of 1000 μm or less. [3] The polylactic acid resin foam molded article described in [1] or [2] above may have a total light transmittance of 60% or less measured in the thickness direction. [4] The polylactic acid resin foam molded article described in any of [1] to [3] above may also be a polylactic acid resin foam sheet. [5] An exhibit panel according to an embodiment of the present invention is provided with printing applied to at least one selected from the group consisting of the first main surface and the second main surface of the polylactic acid resin foam molded body described in [4] above. [6] The polylactic acid resin foam molded product described in any of [1] to [4] above may be a foam container. [7] In the polylactic acid resin foam molded article described in any of [1] to [4] or [6] above, the polylactic acid resin foam sheet may have a heating dimensional change rate in the MD direction of less than 100% when heated at 125°C for 150 seconds. [Effects of the Invention]

[0008] According to embodiments of the present invention, it is possible to provide a polylactic acid resin foam molded article having excellent surface smoothness and being printable on its surface. Furthermore, it is possible to provide display panels and containers having excellent surface smoothness and being printable on their surfaces. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view of a polylactic acid resin foam board according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing the configuration of an annealing apparatus used in the manufacture of polylactic acid resin foam boards. [Figure 3] This is a schematic cross-sectional view of a container according to one embodiment of the present invention, where the container is a molded product produced by deep drawing. [Figure 4] This is a schematic diagram showing one preferred configuration of an extruder used in a method for producing modified polylactic acid resin. [Figure 5] This is a schematic diagram showing one preferred configuration of a manufacturing apparatus suitable for producing polylactic acid resin foam sheets according to an embodiment of the present invention. [Figure 6] This is a schematic diagram showing one preferred configuration of a manufacturing apparatus suitable for producing polylactic acid resin foam sheets according to an embodiment of the present invention. [Figure 7] This is a photograph of the surface of an evaluation sample used in the print evaluation of a polylactic acid resin foam molded product of Example 1. [Figure 8] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 2. [Figure 9] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 3. [Figure 10] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 4. [Figure 11] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 5. [Figure 12] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 6. [Figure 13] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Comparative Example 1. [Figure 14] This is a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded product of Example 10. [Modes for carrying out the invention]

[0010] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments.

[0011] <<<Polylactic acid resin foam molded product>>> The polylactic acid resin foam molded article of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet.

[0012] The polylactic acid resin foam molded article of the present invention has a first main surface and a second main surface facing the first main surface. The minimum autocorrelation length Sal in at least one selected from the group consisting of the first main surface and the second main surface facing the first main surface is 500.0 μm or less.

[0013] Sal is a surface roughness parameter defined in ISO 25178-2:2012. The polylactic acid resin foam molded article of the present invention has a low Sal value on its surface as described above, and possesses excellent surface smoothness. This reduces ink repulsion when printing on the surface, enabling good printing.

[0014] In order to better exhibit the effects of the present invention, the polylactic acid resin foam molded article of the present invention preferably has a Sal content of 480.0 μm or less, more preferably 450.0 μm or less, even more preferably 430.0 μm or less, particularly preferably 400.0 μm or less, and most preferably 370.0 μm or less on at least one selected from the group consisting of a first main surface and a second main surface. If the Sal content of the main surface of the polylactic acid resin foam molded article deviates significantly from the above range, the ink may be repelled during printing, and printing defects such as uneven coloring may easily occur. The smaller the Sal content of the polylactic acid resin foam molded article of the present invention, the better, and its lower limit is preferably 0.0 μm or more, and may be, for example, 100.0 μm or more.

[0015] In the polylactic acid resin foam molded article of the present invention, it is preferable that the Sal content of the first main surface and the second main surface is 500.0 μm or less, respectively.

[0016] The polylactic acid resin foam molded article of the present invention preferably has an average bubble diameter of 1000 μm or less, more preferably 100 μm to 900 μm, even more preferably 100 μm to 800 μm, particularly preferably 100 μm to 700 μm, and most preferably 100 μm to 620 μm, in order to better exhibit the effects of the present invention. When the average bubble diameter of the polylactic acid resin foam molded article of the present invention is within the above range, surface irregularities can be reduced and surface smoothness can be further improved. Therefore, better printing may be possible.

[0017] The polylactic acid resin foam molded article of the present invention exhibits the effects of the present invention more effectively when the total light transmittance measured in the thickness direction is preferably 60% or less, more preferably 55% or less, even more preferably 50% or less, particularly preferably 45% or less, and most preferably 42% or less. When the total light transmittance of the polylactic acid resin foam molded article of the present invention is within the above range, it can be made more aesthetically pleasing when printed on the surface. The lower limit of the above total light transmittance is not particularly limited, but for example, it is 10% or more. The total light transmittance of the polylactic acid resin foam molded article can be measured by a method in accordance with the provisions of JIS K7361-1:1997.

[0018] In this specification, the thickness of the polylactic acid resin foam molded article means the distance between the first main surface and the second main surface. The total light transmittance measured in the thickness direction of the polylactic acid resin foam molded article preferably satisfies the above range in at least one of the group consisting of measurements taken by irradiating light from the first main surface side and measurements taken by irradiating light from the second main surface side, and more preferably satisfies the above range in both cases.

[0019] The polylactic acid resin foam molded article of the present invention preferably has a glossiness of 3.0 or higher, more preferably 4.5 or higher, even more preferably 5.0 or higher, and particularly preferably 6.0 or higher, selected from the group consisting of a first main surface and a second main surface, in order to better exhibit the effects of the present invention. The upper limit of the glossiness is not particularly limited, but may be, for example, 40.0 or lower, 30.0 or lower, or even 25.0 or lower. The glossiness of the polylactic acid resin foam molded article can be measured by a method conforming to the 60-degree specular gloss method described in JIS Z8741:1997.

[0020] A preferred embodiment of the polylactic acid resin foam molded article of the present invention is a polylactic acid resin foam sheet. That is, the polylactic acid resin foam molded article of the present invention is preferably in the form of a sheet.

[0021] Another preferred embodiment of the polylactic acid resin foam molded article of the present invention is a foamed container. That is, the polylactic acid resin foam molded article of the present invention is preferably in various container shapes such as bowl shape, plate shape, cup shape, box shape, tray shape, etc.

[0022] Hereinafter, preferred embodiments of the present invention, namely polylactic acid resin foam boards and foam containers, will be described with reference to the drawings.

[0023] <<Embodiment 1 (Polylactic Acid Resin Foam Board)>> A polylactic acid resin foam board according to one embodiment of the present invention is made by molding (flattening) a polylactic acid resin foam sheet into a board shape, preferably by molding the polylactic acid resin foam sheet into a board shape and then cutting it to the desired dimensions as needed.

[0024] Figure 1 is a schematic cross-sectional view of a polylactic acid resin foam board according to one embodiment of the present invention. The polylactic acid resin foam board 1000 has a first main surface S11 and a second main surface S12 facing the first main surface S11.

[0025] As described above, the minimum autocorrelation length Sal in at least one selected from the group consisting of the first main surface S11 and the second main surface S12 is 500.0 μm or less. The polylactic acid resin foam board 1000 has a small Sal value on its surface (main surface) as described above, and has excellent surface smoothness. This reduces ink repulsion when printing on the surface, enabling good printing on the surface (first main surface S11 or second main surface S12).

[0026] In order to better exhibit the effects of the present invention, the amount of Sal in at least one selected from the group consisting of the first main surface S11 and the second main surface S12 is preferably 0.0 μm to 480.0 μm, more preferably 100.0 μm to 450.0 μm, even more preferably 100.0 μm to 400.0 μm, particularly preferably 100.0 μm to 350.0 μm, and most preferably 100.0 μm to 320.0 μm.

[0027] In order to better demonstrate the effects of the present invention, it is preferable that both the Sal on the first main surface S11 and the Sal on the second main surface S12 are independently 0.0 μm to 500.0 μm, 0.0 μm to 480.0 μm, 100.0 μm to 450.0 μm, 100.0 μm to 400.0 μm, and even 100.0 μm to 320.0 μm.

[0028] As described above, the average bubble diameter of the polylactic acid resin foam board 1000 is preferably 1000 μm or less, more preferably 100 μm to 900 μm, even more preferably 100 μm to 800 μm, particularly preferably 100 μm to 700 μm, and most preferably 100 μm to 620 μm. When the average bubble diameter of the polylactic acid resin foam board 1000 is within the above range, surface irregularities can be reduced and surface smoothness can be further improved. Therefore, better printing may be possible.

[0029] The polylactic acid resin foam board 1000 has an average bubble diameter dM in the MD direction (longitudinal direction of the polylactic acid resin foam sheet, extrusion flow direction) preferably of 200 μm to 1000 μm, more preferably of 250 μm to 950 μm, even more preferably of 300 μm to 900 μm, and particularly preferably of 350 μm to 800 μm. When the average bubble diameter dM of the polylactic acid resin foam board 1000 is within the above range, better printing may be possible.

[0030] The polylactic acid resin foam board 1000 has an average bubble diameter dT in the TD direction (the lateral (width) direction of the polylactic acid resin foam sheet, perpendicular to the extrusion flow direction) that is preferably 200 μm to 1100 μm, more preferably 250 μm to 1000 μm, even more preferably 300 μm to 900 μm, and particularly preferably 350 μm to 800 μm. When the average bubble diameter dT of the polylactic acid resin foam board 1000 is within the above range, better printing may be possible.

[0031] As described above, the polylactic acid resin foam board 1000 has a total light transmittance measured in the thickness direction that is preferably 10% to 60%, more preferably 10% to 55%, even more preferably 10% to 50%, particularly preferably 10% to 45%, and most preferably 10% to 42%. When the total light transmittance of the polylactic acid resin foam board 1000 of the present invention is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more beautiful.

[0032] In order to better exhibit the effects of the present invention, the gloss of at least one selected from the group consisting of the first main surface S11 and the second main surface S12 of the polylactic acid resin foam board 1000 is preferably 3.0 to 60.0, more preferably 4.5 to 50.0, even more preferably 5.0 to 40.0, and particularly preferably 6.0 to 30.0. When the gloss of the polylactic acid resin foam board 1000 of the present invention is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more beautiful.

[0033] In order to better demonstrate the effects of the present invention, at least one selected from the group consisting of the first main surface S11 and the second main surface S12 of the polylactic acid resin foam board 1000 preferably has an average reflectance in the wavelength range of 350 nm to 900 nm of 35% to 85%, more preferably 40% to 80%, and even more preferably 45% to 75%. When the average reflectance of the polylactic acid resin foam board 1000 of the present invention is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more beautiful.

[0034] In terms of being able to better demonstrate the effects of the present invention, at least one selected from the group consisting of the first main surface S11 and the second main surface S12 of the polylactic acid resin foam board 1000 is CIE1976L * a * b * The whiteness based on the color space is preferably 75.0% to 100.0%, and more preferably is 80.0% to 100.0%, more preferably 85.0% to 100.0%, and particularly preferably 87.0% to 100.0%. When the whiteness of the polylactic acid resin foam board 1000 of the present invention is within the above range, the printing suitability is improved, and it can be made more beautiful when printed on the surface.

[0035] The polylactic acid resin foam board 1000 preferably has a thickness of 1.00 mm or more, more preferably 1.50 mm to 20.00 mm, still more preferably 2.00 mm to 15.00 mm, and particularly preferably 2.50 mm to 10.0 mm.

[0036] The polylactic acid resin foam board 1000 preferably has a basis weight of 100 g / m 2 ~500 g / m 2 and more preferably 150 g / m 2 ~450 g / m 2 and still more preferably 200 g / m 2 ~450 g / m 2 and particularly preferably 300 g / m 2 ~450 g / m 2 If the basis weight of the polylactic acid resin foam board 1000 is within the above range, the effects of the present invention can be further manifested. The method for measuring the basis weight will be described later.

[0037] For the polylactic acid resin foam board 1000, the maximum flexural strength in the MD direction of a measurement piece of 25 mm in the TD direction × 40 mm in the MD direction is preferably 10 N or more, more preferably 12 N to 50 N, still more preferably 13 N to 50 N, and even more preferably 14 N to �0 N.

[0038] For the polylactic acid resin foam board 1000, the maximum flexural strength in the TD direction of a measurement piece of 25 mm in the MD direction × 40 mm in the TD direction is preferably 7 N or more, more preferably 10 N to 50 N, and still more preferably 12 N to 50 N.

[0039] When the flexural strength of the polylactic acid resin foam board 1000 satisfies the above, cracking is less likely to occur.

[0040] Polylactic acid resin foam board 1000 can be suitably used for display panels (display panels) with printing applied to the surface.

[0041] An exhibit panel according to one embodiment of the present invention is made by printing on at least one selected from the group consisting of a first main surface S11 and a second main surface S12 of a polylactic acid resin foam board 1000. More specifically, an exhibit panel according to one embodiment of the present invention is made by printing on at least one selected from the group consisting of a first main surface S11 and a second main surface S12 of a polylactic acid resin foam sheet that has been formed into a board shape and cut to desired dimensions as needed (for example, a polylactic acid resin foam board 1000). Due to the excellent surface smoothness and printability of the polylactic acid resin foam board 1000, the exhibit panel according to one embodiment of the present invention has an excellent appearance, with reduced ink repelling and the like.

[0042] An exhibit panel according to one embodiment of the present invention may have the desired printing directly applied to the first main surface S11 or the second main surface S12 of the polylactic acid resin foam board 1000, but it is preferable that a base layer is provided and the printing is applied on top of the base layer. That is, the exhibit panel according to this embodiment preferably has a base layer that covers at least one selected from the group consisting of the first main surface S11 and the second main surface S12 of the polylactic acid resin foam board 1000, more specifically, a base layer that covers at least a portion of the main surface having a Sal content of 500.0 μm or less.

[0043] The base layer is preferably composed of a white ink composition and is typically a white painted layer. By having such a base layer, the display panel according to this embodiment can have improved adhesion and color development of the printing ink, resulting in a more aesthetically pleasing product. As mentioned above, the polylactic acid resin foam board 1000 has excellent surface smoothness, so the base layer can also be coated well.

[0044] Manufacturing of polylactic acid resin foam boards Polylactic acid resin foam board 1000 can be manufactured, for example, by annealing a polylactic acid resin foam sheet using the apparatus shown in Figure 2, and then cutting it into a predetermined shape. By performing a process including heating (annealing) using the apparatus shown in Figure 2, residual stress in the polylactic acid resin foam sheet can be removed, and it can be formed into a flat plate shape.

[0045] The annealing apparatus in Figure 2 consists of endless belt pairs, each consisting of endless belts 1a-4a and 1b-4b, arranged facing each other in the vertical direction with a gap slightly wider than the thickness of the polylactic acid resin foam sheet A supplied to the apparatus. Four sets of endless belt pairs B1-B4 are arranged at predetermined intervals in the conveying direction of the polylactic acid resin foam sheet A. The two sets of endless belt pairs B1 and B2 at the conveying start point form a heating zone C, while the two sets of endless belt pairs B3 and B4 at the conveying end point form a cooling zone D.

[0046] The annealing apparatus shown in Figure 2 is configured to sequentially and continuously supply polylactic acid resin foam sheet A between the opposing surfaces of the upper and lower endless belts 1a, 1b, 2a, and 2b of the two upstream endless belt pairs B1 and B2 that form a heating zone, and heat the polylactic acid resin foam sheet A while pressing it from both sides at a temperature of preferably 105°C to 165°C to remove any remaining strain in the polylactic acid resin foam sheet A and perform secondary foaming. Then, the polylactic acid resin foam sheet A, from which the strain has been removed, is sequentially and continuously supplied between the opposing surfaces of the upper and lower endless belts 3a, 3b, 4a, and 4b of the downstream endless belt pair B3 and B4, and cools the polylactic acid resin foam sheet A while pressing it from both sides at a temperature of preferably 4°C to 30°C, thereby performing the annealing process on the polylactic acid resin foam sheet A.

[0047] The conveying speed of the polylactic acid resin foam sheet A in the endless belt pairs B3 and B4 forming the cooling zone D is preferably adjusted appropriately so that the polylactic acid resin foam sheet A, which has been heated and expanded in the heating zone C, does not sag. For example, the conveying speed of the polylactic acid resin foam sheet A in the endless belt pairs B3 and B4 forming the cooling zone D may be the same as, or up to 1.03 times faster than, the conveying speed of the polylactic acid resin foam sheet A in the endless belt pairs B1 and B2 forming the heating zone C. By performing the annealing treatment on the polylactic acid resin foam sheet in this manner, residual internal strain can be reliably removed, improving the shape stability of the resulting polylactic acid resin foam board 1000.

[0048] <<Embodiment 2 (Foam Container)>> The foamed container according to the embodiment of the present invention is formed by molding a polylactic acid resin foam sheet into a container shape.

[0049] The foamed container according to the embodiment of the present invention can take any suitable shape. Such shapes can include various container shapes such as bowl-shaped, cup-shaped, box-shaped, and tray-shaped containers. The foamed container according to the embodiment of the present invention can be used publicly as a food packaging container. That is, the foamed container according to the embodiment of the present invention is preferably a food packaging container.

[0050] An example of a foamed container according to one embodiment of the present invention is a molded body formed by deep drawing, which may be a shallow-drawn molded body with a deep-drawn shape where the drawing depth is smaller than the diameter of the foamed container, or a deep-drawn molded body with a deep-drawn shape where the drawing depth is larger than the diameter of the foamed container.

[0051] Figure 3 is a schematic cross-sectional view of a foamed container according to one embodiment of the present invention, where the foamed container is a molded product formed by deep drawing. The foamed container 2000 has a first main surface S21 and a second main surface S22.

[0052] In Figure 3, the foam container 2000 comprises a main body including a bottom portion 310 and a side wall portion 320. As shown in Figure 3, the foam container 2000 may also have a flange portion 400 or a protruding portion 500 that extends outward at the upper end of the side wall portion 320. The cross-sectional shape of the foam container 2000 is not limited to the shape shown in Figure 3; for example, the bottom portion 310 and the side wall portion 320 may have a bent structure. The shape of the flange portion 400 and the protruding portion 500 are not limited to the shapes shown in Figure 3, nor are their positions limited to those shown in Figure 3. The thickness L of the foam container 2000 refers to the minimum thickness of the portion of the foam container 2000's cross-section that excludes the flange portion 400 and the protruding portion 500. The foam container 2000 does not need to have a flange portion 400 or a protruding portion 500.

[0053] As described above, the minimum autocorrelation length Sal in at least one selected from the group consisting of the first main surface S21 and the second main surface S22 is 500.0 μm or less. The foamed container 2000 has a small Sal value on its surface (main surface) as described above, and has excellent surface smoothness. This reduces ink repulsion when printing on the surface, and enables good printing on the surface (especially the first main surface S21). In the foamed container 2000, it is preferable that the Sal of the first main surface S21 is 500.0 μm or less.

[0054] In order to better exhibit the effects of the present invention, it is preferable that the Sal content of the first main surface S21 and the second main surface S22 be 0.0 μm to 500.0 μm, and more preferably 0 μm to 480.0 μm. In order to better exhibit the effects of the present invention, it is preferable that the Sal content of the first main surface S21 be 0 μm to 450.0 μm, 100 μm to 400.0 μm, and even more preferably 100 μm to 360.0 μm.

[0055] The average bubble diameter of the foamed container 2000 is preferably 1000 μm or less, more preferably 100 μm to 900 μm, even more preferably 100 μm to 800 μm, and particularly preferably 100 μm to 700 μm. When the average bubble diameter of the foamed container 2000 is within the above range, surface irregularities can be reduced and surface smoothness can be further improved. Therefore, better printing may be possible.

[0056] The foamed container 2000 has a total light transmittance measured in the thickness direction, preferably 10% to 60%, more preferably 10% to 55%, and even more preferably 10% to 50%. When the total light transmittance of the foamed container 2000 according to one embodiment of the present invention falls within the above range, the printability is improved, and when printing is applied to the surface, it can be made more aesthetically pleasing.

[0057] In order to better demonstrate the effects of the present invention, the gloss of at least one surface selected from the group consisting of the first main surface S21 and the second main surface S22 of the foamed container 2000 is preferably 3.0 to 40.0, more preferably 4.5 to 40.0, even more preferably 5.0 to 30.0, and particularly preferably 6.0 to 25.0. When the gloss of the foamed container 2000 according to one embodiment of the present invention is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more beautiful. The gloss of the first main surface S21 is preferably 3.0 to 40.0, 4.5 to 40.0, 5.0 to 30.0, and even more preferably 6.0 to 25.0.

[0058] In order to better demonstrate the effects of the present invention, at least one selected from the group consisting of the first main surface S21 and the second main surface S22 of the foamed container 2000 preferably has an average reflectance in the wavelength range of 350 nm to 900 nm of 30% to 85%, more preferably 35% to 80%, and even more preferably 40% to 75%. When the average reflectance is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more aesthetically pleasing.

[0059] In order to better demonstrate the effects of the present invention, at least one selected from the group consisting of the first main surface S21 and the second main surface S22 of the foamed container 2000 preferably has a whiteness of 75.0% to 100.0%, more preferably 80.0% to 100.0%, even more preferably 83.0% to 100.0%, and particularly preferably 85.0% to 100.0%. When the whiteness is within the above range, the printability is improved, and when printing is applied to the surface, it can be made more beautiful.

[0060] The foamed container 2000 has a thickness of preferably 1.0 mm or more, more preferably 1.1 mm to 7.0 mm, even more preferably 1.2 mm to 5.0 mm, particularly preferably 1.3 mm to 3.0 mm, and most preferably 1.4 mm to 2.5 mm. If the thickness of the foamed container 2000 is too large outside the above range, the appearance of the foamed container 2000 may be poor. If the thickness of the foamed container 2000 is too small outside the above range, for example, the container strength and heat insulation of the foamed container 2000 may decrease, and it may not be possible to guarantee physical properties suitable for a food packaging container.

[0061] Manufacturing of foamed containers The foamed container 2000 according to the embodiment of the present invention can be manufactured by any suitable method, provided that the effects of the present invention are not impaired. Typically, the foamed container according to the embodiment of the present invention can be manufactured by preheating a polylactic acid resin foam sheet and then thermoforming it using a mold.

[0062] Any suitable method can be used for preheating. For example, one such method is to heat the polylactic acid resin foam sheet using any suitable heating means. Examples of such heating means include electric heaters, infrared heaters, and other heaters.

[0063] Preheating can be performed so that the surface temperature of the polylactic acid resin foam sheet is preferably in the range of 100°C to 140°C, more preferably in the range of 105°C to 135°C, even more preferably in the range of 110°C to 130°C, and particularly preferably in the range of 115°C to 125°C.

[0064] Preheating can be performed by heating for a suitable time using a heating means set to any suitable heating temperature. The heating temperature (set temperature of the heating means) is preferably 200°C to 800°C, more preferably 300°C to 700°C. The heating time is preferably 0.1 seconds to 60 seconds, more preferably 1 second to 30 seconds.

[0065] As a method for preheating to produce a foamed container 2000, which is an example of a foamed molded polylactic acid resin product according to an embodiment of the present invention, methods include heating at a higher temperature for a short time or heating at a lower temperature for a long time. In terms of providing a suitable foamed container 2000, the method of heating at a lower temperature for a long time is preferred. For example, a method of heating at a temperature of less than 500°C for more than 5 seconds is preferred, a method of heating at a temperature of 300°C to 470°C for a heating time of more than 5 seconds but 30 seconds or less is more preferred, a method of heating at a temperature of 350°C to 450°C for a heating time of more than 5 seconds but 20 seconds or less is even more preferred, and a method of heating at a temperature of 370°C to 430°C for a heating time of more than 5 seconds but 15 seconds or less is particularly preferred.

[0066] After preheating, any suitable thermoforming method can be used for thermoforming using a mold. Examples of such thermoforming methods include vacuum forming, pressure forming, vacuum pressure forming, plug-assisted forming, and match-mold forming, with match-mold forming being preferred.

[0067] The mold temperature in thermoforming is preferably 15°C to 160°C, more preferably 20°C to 150°C, even more preferably 25°C to 140°C, even more preferably 30°C to 130°C, particularly preferably 35°C to 120°C, and most preferably 40°C to 120°C, in order to properly produce the foamed container 2000. If the above temperature is too low or too high, shrinkage and foaming of the polylactic acid resin foamed molded body (foamed container 2000) are likely to occur after demolding, resulting in loss of surface smoothness, a dirty appearance, and impaired printability.

[0068] The mold holding time in thermoforming (the time the mold is held during molding) is preferably 0.1 seconds to 60 seconds, more preferably 1 second to 30 seconds, even more preferably 3 seconds to 30 seconds, and particularly preferably 5 seconds to 20 seconds, in order to adequately provide the foamed container 2000.

[0069] To obtain the foamed container 2000 according to the embodiment of the present invention, any appropriate steps may be taken in addition to the preheating and thermoforming described above, such as a step of releasing the polylactic acid resin foamed molded body from the mold.

[0070] <<<Polylactic acid resin foam sheet>>> The polylactic acid resin foam molded article according to an embodiment of the present invention is a polylactic acid resin foam molded article obtained by molding a polylactic acid resin foam sheet.

[0071] As the polylactic acid resin foam sheet that can be used to obtain the polylactic acid resin foam molded article according to the embodiment of the present invention, any suitable polylactic acid resin foam sheet can be used as long as it does not impair the effects of the present invention. Such a polylactic acid resin foam sheet may be one that has been manufactured by a preferred embodiment of the method for manufacturing a polylactic acid resin foam sheet, which will be described later, as it can better exhibit the effects of the present invention.

[0072] When a polylactic acid foamed resin sheet is heated at 125°C for 150 seconds, the dimensional change rate in the MD direction of the polylactic acid foamed resin sheet is, for example, 100.0% or less, preferably less than 100.0%, more preferably 95.0% or more and less than 100.0%, even more preferably 96.0% or more and less than 99.5%, and particularly preferably 97% or more and less than 99%. If the dimensional change rate in the MD direction of the polylactic acid foamed resin sheet is less than 95.0%, the warping of the polylactic acid foamed molded body (polylactic acid foamed board) tends to increase, and if it is 100.0% or more, uneven surface irregularities tend to occur during the production of the polylactic acid foamed board. For example, in the production of polylactic acid resin foam boards, when a polylactic acid resin foam sheet is continuously supplied over a length of 50m in the MD direction, uneven surface irregularities may occur on the surface of the discharged polylactic acid resin foam board. However, if the heating dimensional change rate of the polylactic acid resin foam sheet in the MD direction is less than 100.0%, the occurrence of surface irregularities can be reduced. Therefore, if the heating dimensional change rate of the polylactic acid resin foam sheet in the MD direction is within the above range, better printing may be possible.

[0073] When a polylactic acid foamed resin sheet is heated at 125°C for 150 seconds, the heating dimensional change rate of the polylactic acid foamed resin sheet in the TD direction is, for example, 100.0% or less, preferably less than 100%, more preferably 95.0% or more and less than 100.0%, even more preferably 96.0% or more and less than 99.0%, and particularly preferably 97.0% or more and less than 98.0%. If the heating dimensional change rate of the polylactic acid foamed resin sheet in the TD direction is within the above range, better printing may be possible.

[0074] The methods for measuring the heating dimensional change rate in the MD direction and the heating dimensional change rate in the TD direction will be described later. For the MD direction and the TD direction, the average values ​​of the heating dimensional change rate on the plug surface and the heating dimensional change rate on the air cooling surface will be defined as the "heating dimensional change rate in the MD direction" and the "heating dimensional change rate in the TD direction," respectively.

[0075] Manufacturing of polylactic acid resin foam sheets Polylactic acid resin foam sheets that can be used for molding polylactic acid resin foam molded articles according to embodiments of the present invention can be manufactured by any suitable method without impairing the effects of the present invention. Such polylactic acid resin foam sheets can preferably be manufactured by melt-kneading polylactic acid resin (P) with a foaming agent in an extruder and then extruding foaming.

[0076] Preferred embodiments of the polylactic acid resin (P) include embodiments that mainly contain modified polylactic acid resin, or embodiments that mainly contain unmodified polylactic acid resin.

[0077] "Modified polylactic acid resin" refers to a polylactic acid resin that has undergone a modification treatment, typically the polylactic acid resin that has undergone the modification treatment described in the first step of Embodiment A described later. "Unmodified polylactic acid resin" refers to a polylactic acid resin that has not undergone a modification treatment, typically the polylactic acid resin that is generally available and has not undergone the modification treatment described in the first step of Embodiment A described later.

[0078] Herein, in this specification, "contained as a main component" means that its content is preferably more than 50% by mass, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably substantially 100% by mass.In this specification, "substantially 100% by mass" means that the presence of trace amounts of impurities (e.g., less than 1% by mass) that have been unintentionally mixed in may be ignored.

[0079] The following describes two embodiments: Embodiment A (sometimes referred to as the two-stage method), in which a polylactic acid resin (P) containing modified polylactic acid resin as the main component is melt-kneaded with a foaming agent in an extruder and then extruded to produce a polylactic acid resin foam sheet; and Embodiment B (sometimes referred to as the one-stage method), in which an unmodified polylactic acid resin (P) containing unmodified polylactic acid resin as the main component is melt-kneaded with a foaming agent in an extruder and then extruded to produce a polylactic acid resin foam sheet.

[0080] ≪Embodiment A (Two-stage method)≫ In Embodiment A, a polylactic acid resin (P) containing a modified polylactic acid resin as the main component is melt-kneaded with a foaming agent in an extruder, and then extruded to produce a polylactic acid resin foam sheet.

[0081] The modified polylactic acid resin is preferably obtained by melt-kneading a polylactic acid resin composition containing polylactic acid resin and a modifier in an extruder.

[0082] Therefore, Embodiment A preferably includes a first step of melt-kneading a polylactic acid resin composition containing polylactic acid resin and a modifier in an extruder to produce a polylactic acid resin mainly composed of the modified polylactic acid resin, and a second step of melt-kneading the polylactic acid resin mainly composed of the modified polylactic acid resin with a foaming agent in an extruder and extruding it to produce a polylactic acid resin foam sheet.

[0083] For convenience, the following description assumes that the content of modified polylactic acid resin in polylactic acid resin (P), which contains modified polylactic acid resin as a main component, is substantially 100% by mass. That is, in the following description, Embodiment A includes a first step of producing modified polylactic acid resin by melt-kneading a polylactic acid resin composition containing polylactic acid resin and a modifier in an extruder, and a second step of producing a polylactic acid resin foam sheet by melt-kneading the modified polylactic acid resin with a foaming agent in an extruder and extruding foam. However, of course, the content of modified polylactic acid resin in polylactic acid resin (P), which contains modified polylactic acid resin as a main component, may actually be the percentage of the main component, as described above.

[0084] <1st process> In the first step, a polylactic acid resin composition containing polylactic acid resin and a modifier is melt-kneaded in an extruder to produce a modified polylactic acid resin. The polylactic acid resin used as a raw material in the first step here preferably means an unmodified polylactic acid resin.

[0085] Polylactic acid resin may be a homopolymer of lactic acid or a copolymer of lactic acid and other monomers. Examples of other monomers include aliphatic hydroxycarboxylic acids other than lactic acid, aliphatic polyhydric alcohols, aliphatic polyhydric acids, and polyfunctional polysaccharides.

[0086] The lactic acid constituting the polylactic acid resin may be either the L-form or the D-form, or both. In other words, the polylactic acid resin, which is a homopolymer of lactic acid, may be poly(L-lactic acid) resin, poly(D-lactic acid) resin, or poly(DL-lactic acid) resin.

[0087] Examples of hydroxycarboxylic acids other than lactic acid include glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 4-hydroxyvaleric acid, 5-hydroxyvaleric acid, and 6-hydroxycaproic acid.

[0088] Examples of aliphatic polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, tetramethylene glycol, and 1,4-cyclohexanedimethanol.

[0089] Examples of aliphatic polycarboxylic acids include oxalic acid, succinic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, undecanediic acid, and dodecanediic acid. Furthermore, the aliphatic polycarboxylic acid may also be an acid anhydride.

[0090] Examples of polyfunctional polysaccharides include cellulose, cellulose nitrate, methylcellulose, ethylcellulose, celluloid, viscose rayon, regenerated cellulose, cellophane, cuprazole, copper ammonia rayon, cuprophane, Bemberg, hemicellol, starch, acropectin, dextrin, dextran, glycogen, pectin, chitin, chitosan, gum arabic, guar gum, locust bean gum, and acacia gum.

[0091] In polylactic acid resin, the content of structural parts derived from lactic acid (L- and D-forms) in the molecule is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more.

[0092] The polylactic acid resin used as a raw material may be recycled in some respects.

[0093] In the first step, a modified polylactic acid resin is produced by using a modifier to increase the molecular weight of the polylactic acid resin or to give the polylactic acid resin crosslinked structures or long-chain branched structures in its molecular structure.

[0094] The modifier may be one type or two or more types. The amount of modifier used is preferably 0.1 to 2.0 parts by mass, more preferably 0.2 to 1.5 parts by mass, and even more preferably 0.3 to 1.0 parts by mass, per 100 parts by mass of polylactic acid resin, in order to better exhibit the effects of the present invention.

[0095] Radical initiators can be used as modifiers. By using radical initiators as modifiers, crosslinked structures and long-chain branched structures can be introduced into the molecular structure of the polylactic acid resin. In this case, the radical initiator is used to react the polylactic acid resins with each other. When polylactic acid resins are reacted with a radical initiator having appropriate reactivity, for example, the decomposition starting point of the polylactic acid resin in the extruder can be attacked by free radicals generated by the radical initiator, and that site can become a crosslinking point (branching point) and be stabilized. With such modification, the thermal stability of the polylactic acid resin increases and it becomes less likely to be reduced in molecular weight when passing through the extruder.

[0096] Examples of radical initiators include organic peroxides, azo compounds, and halogen molecules, with organic peroxides being preferred.

[0097] Examples of organic peroxides include peroxyesters, hydroperoxides, dialkylperoxides, diacylperoxides, peroxydicarbonates, peroxyketals, and ketoneperoxides.

[0098] Examples of peroxyesters include t-butyl peroxyisopropyl carbonate, t-butyl peroxy-2-ethylhexyl carbonate, t-hexyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, t-hexyl peroxybenzoate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate, t-butyl peroxyacetate, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane.

[0099] Examples of hydroperoxides include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0100] Examples of dialkyl peroxides include α,α-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

[0101] Examples of diacyl peroxides include dibenzoyl peroxide, di(4-methylbenzoyl) peroxide, and di(3-methylbenzoyl) peroxide.

[0102] Examples of peroxydicarbonates include di(2-ethylhexyl)peroxydicarbonate and diisopropylperoxydicarbonate.

[0103] Examples of peroxyketals include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, 2,2-di(t-butylperoxy)-butane, n-butyl-4,4-di-(t-butylperoxy)valerate, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane.

[0104] Examples of ketone peroxides include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0105] Modification with organic peroxides may result in undesirable problems. For example, it may cause the modified polylactic acid resin to contain components with excessively high molecular weights that form a gel when heated and melted, or it may cause odor problems due to the decomposition residue of the organic peroxides. These issues may adversely affect the effectiveness of the present invention.

[0106] In order to suppress the occurrence of problems associated with modification by organic peroxides as described above, to easily modify the polylactic acid resin to a state suitable for foaming, and to provide a polylactic acid resin foam molded article that can better exhibit the effects of the present invention, one preferred embodiment of the organic peroxide is at least one selected from the group consisting of peroxyesters and dialkyl peroxides. In order to provide a polylactic acid resin foam molded article that can further exhibit the effects of the present invention, the peroxyester is more preferably a peroxycarbonate-based organic peroxide such as t-butyl peroxyisopropyl carbonate, t-butyl peroxy-2-ethylhexyl carbonate, or t-hexyl peroxyisopropyl carbonate, and even more preferably t-butyl peroxyisopropyl carbonate. The dialkyl peroxide is more preferably α,α-bis(t-butylperoxy)diisopropylbenzene.

[0107] The above-mentioned organic peroxides can provide a polylactic acid resin foam molded article that can further exhibit the effects of the present invention, and the 1-minute half-life temperature is preferably 140°C to 190°C, more preferably 145°C to 185°C, even more preferably 150°C to 180°C, and particularly preferably 152°C to 178°C. In one preferred embodiment, the above 1-minute half-life temperature is preferably 140°C to 180°C, more preferably 145°C to 170°C, even more preferably 150°C to 160°C, and particularly preferably 150°C to 158°C.

[0108] The organic peroxides described above may be in liquid or solid (powder) form. However, from the viewpoint of uniform reactivity in the extruder and ease of handling, a liquid form is preferred.

[0109] The amount of organic peroxide used depends on its molecular weight and other factors, but in order to better exhibit the effects of the present invention, it is preferably 0.1 to 2.0 parts by mass, more preferably 0.2 to 1.5 parts by mass, and even more preferably 0.3 to 1.0 parts by mass, per 100 parts by mass of polylactic acid resin.

[0110] Chain extenders may be used as modifiers. In modification using chain extenders, compounds having one or more functional groups that can react with hydroxyl groups and carboxyl groups present in the molecular structure of polylactic acid resin, such as acrylic organic compounds, epoxy organic compounds, and isocyanate organic compounds, can be used.

[0111] Examples of chain elongators include Joncryl® ADR 4368 (manufactured by BASF), Joncryl® ADR 4468 (manufactured by BASF), Cardura® E10 (manufactured by Shell), and long-chain acrylates described in EP application No. 08166596.0.

[0112] When a chain extender is used as a modifier, the amount of chain extender used is preferably 0.1 to 2.0 parts by mass, more preferably 0.2 to 1.5 parts by mass, and even more preferably 0.3 to 1.0 parts by mass, per 100 parts by mass of polylactic acid resin, in order to better exhibit the effects of the present invention.

[0113] In the first step, the polylactic acid resin composition containing the polylactic acid resin and the modifier may contain any suitable other components besides the polylactic acid resin and the modifier, as long as they do not impair the effects of the present invention. The total amount of polylactic acid resin and modifier in the polylactic acid resin composition containing the polylactic acid resin and the modifier is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass.

[0114] In the first step, the polylactic acid resin composition containing the polylactic acid resin and the modifier may be pre-mixed with the polylactic acid resin, the modifier, and other components as needed. Examples of such mixing methods include using a mixer such as a tumbler, ribbon blender, V-blender, Henschel mixer, or Readygay mixer.

[0115] In the first step, a polylactic acid resin composition containing polylactic acid resin and a modifier is melt-kneaded in an extruder.

[0116] Any suitable extruder can be used as the extruder, as long as it does not impair the effects of the present invention. A twin-screw extruder is preferred as the extruder in terms of being able to better express the effects of the present invention.

[0117] Twin-screw extruders may be equipped with strand dies or T-dies. In this case, the extruded strand-like or sheet-like mixture may be cooled and cut with a pelletizer or the like to form pellets.

[0118] A twin-screw extruder may be equipped with a granulation die (hot-cut die). In this case, the mixture is pelletized immediately after being extruded.

[0119] The temperature conditions for melt mixing can vary depending on the size and discharge rate of the extrusion, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, the temperature of the raw material feed section is preferably set to 100°C to 200°C.

[0120] The rotational speed of the extruder can vary depending on the size of the extrusion and the discharge volume, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, a preferred rotational speed is 20 rpm to 800 rpm.

[0121] The modified polylactic acid resin obtained in the first step may be dried by, for example, subjecting it to a drying process. Typically, the modified polylactic acid resin obtained in the first step may be obtained by cooling a strand-shaped mixture extruded from a twin-screw extruder equipped with a strand die, cutting the resulting pellets with a pelletizer, and then subjecting them to a drying process.

[0122] In the drying process, drying can be carried out using a dryer such as a dehumidifying dryer, a vacuum dryer, or a hot air dryer. The modified polylactic acid resin, which has been thoroughly dried using such a dryer, may be directly fed into the extruder in the subsequent second step (without being exposed to a moisture-containing environment), or the modified polylactic acid resin, which has been thoroughly dried using such a dryer, may be immediately sealed in an aluminum bag or the like after drying, and then opened just before being fed into the extruder in the subsequent second step.

[0123] The first step can be carried out using any suitable apparatus, provided that it does not impair the effects of the present invention. In order to better demonstrate the effects of the present invention, the first step can be carried out using, for example, a manufacturing apparatus as shown in Figure 4.

[0124] As shown in Figure 4, in the first step, typically, the polylactic acid resin used as raw material, which is fed into the hopper 11, is melted and kneaded by the twin-screw extruder 30, the strand-shaped kneaded material extruded from the strand die 3 is cooled by the cooling device 6, then pelletized by the pelletizer 4, and finally dried by the drying device 5, and the resulting modified polylactic acid resin is supplied to the second step.

[0125] The modified polylactic acid resin obtained in the first step has a moisture content of preferably 0.30% by mass or less, more preferably 0.25% by mass or less, even more preferably 0.20% by mass or less, particularly preferably 0.17% by mass or less, and most preferably 0.15% by mass or less. The lower limit of the above moisture content is better the less it is, and ideally it is 0% by mass.

[0126] The MFR (melt mass flow rate) of the modified polylactic acid resin obtained in the first step is preferably 0.2 g / 10 min to 20 g / 10 min, more preferably 0.5 g / 10 min to 10 g / 10 min, even more preferably 1.0 g / 10 min to 5.0 g / 10 min, particularly preferably 1.1 g / 10 min to 4.0 g / 10 min, and most preferably 1.2 g / 10 min to 3.0 g / 10 min.

[0127] The melt tension of the modified polylactic acid resin obtained in the first step is preferably 5 cN to 100 cN, more preferably 10 cN to 80 cN, even more preferably 20 cN to 70 cN, and particularly preferably 25 cN to 60 cN.

[0128] <Second process> In the second step, the modified polylactic acid resin obtained in the first step is melt-kneaded with a foaming agent in an extruder, and then extruded to produce a polylactic acid resin foam sheet.

[0129] The foaming agent may be one type or two or more types.

[0130] As a blowing agent, any suitable blowing agent can be used as long as it does not impair the effects of the present invention. Examples of blowing agents include volatile blowing agents that become a gas at room temperature (23°C) and atmospheric pressure (1 atm), and decomposition-type blowing agents that generate gas by thermal decomposition, and preferably, volatile blowing agents.

[0131] Preferably, the volatile blowing agent is an organic compound whose boiling point is below the softening point of the polylactic acid resin and which is gaseous or liquid at atmospheric pressure. Specific examples include aliphatic hydrocarbons such as propane, n-butane, isobutane, pentane (n-pentane, isopentane, neopentane), and n-hexane; alicyclic hydrocarbons such as cyclopentane and cyclopentadiene; ketones such as acetone and methyl ethyl ketone; alcohols such as methanol, ethanol, and isopropyl alcohol; low-boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether; and halogen-containing hydrocarbons such as trichloromonofluoromethane and dichlorodifluoromethane. Inorganic gases such as carbon dioxide, nitrogen, and ammonia may also be used as volatile blowing agents. Among these, the volatile foaming agent is preferably at least one selected from n-butane, isobutane, n-pentane, isopentane, neopentane, cyclopentane, and cyclopentadiene, and more preferably at least one selected from n-butane, isobutane, n-pentane, and isopentane, in terms of being able to better express the effects of the present invention.

[0132] Examples of decomposition-type foaming agents include azodicarbonamide, dinitrosopentamethylenetetramine, sodium bicarbonate, or a mixture of an organic acid such as citric acid or its salt with a bicarbonate.

[0133] The amount of foaming agent used can be appropriately set depending on the purpose. The amount of foaming agent used is preferably 0.1 to 10.0 parts by mass, more preferably 0.3 to 7.0 parts by mass, even more preferably 0.5 to 5.0 parts by mass, and particularly preferably 0.8 to 3.0 parts by mass, when the amount of modified polylactic acid resin is 100 parts by mass.

[0134] In the second step, the extruder may contain any other suitable components other than the modified polylactic acid resin and the blowing agent, to the extent that they do not impair the effects of the present invention. In the second step, the total content of the modified polylactic acid resin and the blowing agent in the total of the modified polylactic acid resin, the blowing agent and any other components contained in the extruder is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass.

[0135] In the second step, the extruder may contain foaming aids as other components. There may be only one type of foaming aid, or two or more types. Examples of foaming aids include diisobutyl adipate, toluene, cyclohexane, ethylbenzene, liquid paraffin, and coconut oil.

[0136] In the second step, the extruder may contain a foam regulator as another component. There may be only one type of foam regulator or two or more types. Examples of foam regulators include higher fatty acid amides, partial esters of higher fatty acids and alcohols, talc, calcium carbonate, mica, citric acid, sodium bicarbonate, polytetrafluoroethylene, aluminum hydroxide, and silica. Examples of higher fatty acid amides include fatty acid monoamides such as oleamide, stearamide, and hydroxystearamide; and fatty acid bisamides such as methylenebisstearamide and ethylenebisstearamide. Examples of higher fatty acids in partial esters of higher fatty acids and alcohols include fatty acids with 15 or more carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, and behenic acid. Examples of partial esters of higher fatty acids and alcohols include monoglyceride stearate and diglyceride stearate.

[0137] The amount of foam regulator used can be appropriately set depending on the purpose. The amount of foam regulator used is preferably 10.0 parts by mass or less, more preferably 0.1 to 10.0 parts by mass, 0.3 to 9.0 parts by mass, 0.5 to 8.0 parts by mass, 0.8 to 7.0 parts by mass, even more preferably 1.0 to 6.0 parts by mass, particularly preferably 1.5 to 5.0 parts by mass, and most preferably 2.0 to 4.0 parts by mass, when the amount of modified polylactic acid resin is 100 parts by mass.

[0138] Other components not listed above include, for example, other resins, pigments, radiant heat transfer inhibitors, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antioxidants, antistatic agents, spreading agents, weathering agents, flame retardants, UV absorbers, light stabilizers, anti-aging agents, anti-fogging agents, fragrances, and antibacterial agents.

[0139] In the second step, the modified polylactic acid resin, a foam regulator, and other components may be pre-mixed as needed. Examples of such mixing methods include using a mixer such as a tumbler, ribbon blender, V-blender, Henschel mixer, or Readygay mixer.

[0140] In the second step, the modified polylactic acid resin obtained in the first step is melt-kneaded with a foaming agent in an extruder and then extruded and foamed.

[0141] Any suitable extruder can be used as the extruder, as long as it does not impair the effects of the present invention. In terms of being able to better express the effects of the present invention, a tandem extruder is preferably used as the extruder.

[0142] The tip of the tandem extruder is equipped with any suitable die, within the limits that do not impair the effects of the present invention, so that a polylactic acid resin foam sheet is ultimately obtained. Preferably, it may also be equipped with a cooling mandrel, a winding roller for winding the polylactic acid resin foam sheet as a raw material roll, and so on.

[0143] The second step can be carried out using any suitable apparatus, provided that it does not impair the effects of the present invention. In terms of enabling the effects of the present invention to be more fully realized, the second step can be carried out using, for example, a manufacturing apparatus such as the one shown in Figure 5.

[0144] The manufacturing apparatus illustrated in Figure 5 includes a tandem extruder 10 and a circular die CD that extrudes the polylactic acid resin composition melted and kneaded in the tandem extruder 10 in a cylindrical shape. Furthermore, this manufacturing apparatus includes a cooling device CL for air-cooling the foamed sheet extruded in a cylindrical shape from the circular die CD, a mandrel MD for expanding the diameter of the cylindrical foamed sheet into a cylinder of a predetermined size, a slitting device for slitting the foamed sheet after it has passed through the mandrel MD to divide it into two sheets, and a winding roller 22 for winding up the slit foamed sheet 1 after it has passed through a plurality of rollers 21. The extruder upstream of the tandem extruder 10 (hereinafter also referred to as "first extruder 10a") is provided with a hopper 11 for feeding in the modified polylactic acid resin that will be the raw material for the foamed sheet, and a gas introduction section 12 for supplying a foaming agent into the cylinder. Downstream of the first extruder 10a, there is an extruder (hereinafter also referred to as "second extruder 10b") for melt-kneading a polylactic acid resin composition containing modified polylactic acid resin and a foaming agent.

[0145] The temperature conditions for melt mixing can vary depending on the size of the extrusion and the discharge rate, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, the temperature of the raw material feed section of the upstream extruder 10a is preferably set to 100°C to 200°C, more preferably to 140°C to 200°C, the temperature of the upstream extruder 10a thereafter is preferably set to 120°C to 300°C, more preferably to 140°C to 270°C, and the temperature of the downstream extruder 10b is preferably set to 100°C to 250°C, more preferably to 120°C to 220°C.

[0146] The rotational speed of the extruder can vary depending on the size of the extrusion and the discharge volume, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, such rotational speeds are preferably 10 rpm to 300 rpm for the upstream extruder 10a and preferably 5 rpm to 200 rpm for the downstream extruder 10b.

[0147] In air cooling using the CL cooling device, cooling air at, for example, 15°C to 40°C, preferably 20°C to 40°C, is blown onto the inner and outer surfaces of the conventional foam sheet. The amount of air blown onto each surface is, for example, 0.05 m³. 3 / m 2 ~0.3m 3 / m 2 Preferably 0.07m 3 / m 2 ~0.3m 3 / m 2 , comfortable 0.1m 3 / m 2 ~0.3m 3 / m 2 More preferably 0.1m 3 / m 2 ~0.2m 3 / m 2 And, or 0.05m 3 / m 2 ~0.20m 3 / m 2 That's fine.

[0148] Through the above second step, a polylactic acid resin foam sheet is obtained.

[0149] ≪Embodiment B (One-Step Method)≫ In Embodiment B, a polylactic acid resin (P) containing unmodified polylactic acid resin as the main component is melt-kneaded with a foaming agent in an extruder, and then extruded to produce a polylactic acid resin foam sheet.

[0150] For convenience, the following explanation assumes that the content of unmodified polylactic acid resin in the polylactic acid resin (P), which contains unmodified polylactic acid resin as the main component, is substantially 100% by mass. That is, in the following explanation, Embodiment B produces a polylactic acid resin foam sheet by melt-kneading polylactic acid resin (i.e., unmodified polylactic acid resin) with a foaming agent in an extruder and extruding foam. However, of course, the content of unmodified polylactic acid resin in the polylactic acid resin (P), which contains unmodified polylactic acid resin as the main component, may actually be the percentage of the main component, as mentioned above.

[0151] With regard to the polylactic acid resin, the explanation in the first step of Embodiment A described above can be directly applied.

[0152] The polylactic acid resin used as a raw material may be recycled in some respects.

[0153] In Embodiment B, the moisture content of the polylactic acid resin used as raw material fed into the extruder is preferably 0.30% by mass or less, more preferably 0.25% by mass or less, even more preferably 0.20% by mass or less, particularly preferably 0.17% by mass or less, and most preferably 0.15% by mass or less. The lower limit of the above moisture content is better the less it is, and ideally it is 0% by mass.

[0154] In Embodiment B, the polylactic acid resin used as a raw material to be fed into the extruder may be dried using a dryer such as a dehumidifying dryer, vacuum dryer, or hot air dryer before being fed into the extruder. Alternatively, the polylactic acid resin that has been thoroughly dried using such a dryer may be fed directly into the extruder (without being exposed to a moisture-containing environment), or the polylactic acid resin that has been thoroughly dried using such a dryer may be sealed in an aluminum bag or the like immediately after drying, and then opened and fed into the extruder just before being fed in.

[0155] Regarding the type of foaming agent, the explanation in the second step of Embodiment A described above can be directly applied.

[0156] The amount of foaming agent used can be appropriately set depending on the purpose. The amount of foaming agent used is preferably 0.1 to 10.0 parts by mass, more preferably 0.3 to 7.0 parts by mass, even more preferably 0.5 to 5.0 parts by mass, and particularly preferably 0.8 to 3.0 parts by mass, when the amount of polylactic acid resin is 100 parts by mass.

[0157] In Embodiment B, the extruder may contain any other suitable components besides the polylactic acid resin and the blowing agent, as long as they do not impair the effects of the present invention. In Embodiment B, the total content of the polylactic acid resin and the blowing agent in the total of the polylactic acid resin, the blowing agent and any other components contained in the extruder is preferably 50% to 100% by mass, more preferably 70% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass.

[0158] In Embodiment B, the extruder preferably contains a modifier as another component. By including a modifier, the polylactic acid resin can be made to have a high molecular weight, or a crosslinked structure or a long-chain branched structure can be given to the molecular structure of the polylactic acid resin.

[0159] Regarding the modifier, the explanation in the first step of Embodiment A described above can be directly applied.

[0160] In Embodiment B, the extruder may contain a foaming aid as another component. The explanation of the foaming aid in the second step of Embodiment A described above can be directly applied.

[0161] In Embodiment B, the extruder may contain a foam regulator as another component. The explanation of the foam regulator in the second step of Embodiment A described above can be directly applied.

[0162] Other components not listed above include, for example, other resins, pigments, radiant heat transfer inhibitors, crosslinking agents, plasticizers, stabilizers, fillers, lubricants, colorants, antioxidants, antistatic agents, spreading agents, weathering agents, flame retardants, UV absorbers, light stabilizers, anti-aging agents, anti-fogging agents, fragrances, and antibacterial agents.

[0163] In Embodiment B, the polylactic acid resin, modifier, foam regulator, and other components as needed may be pre-mixed. Examples of such mixing methods include using a mixer such as a tumbler, ribbon blender, V-blender, Henschel mixer, or Readygay mixer.

[0164] In Embodiment B, the polylactic acid resin is melt-kneaded with a foaming agent in an extruder.

[0165] Any suitable extruder can be used as the extruder, as long as it does not impair the effects of the present invention. A twin-screw extruder is preferred as the extruder in terms of being able to better express the effects of the present invention.

[0166] In Embodiment B, the tip of the twin-screw extruder is equipped with any suitable die, within the limits that do not impair the effects of the present invention, so that a polylactic acid resin foam sheet is ultimately obtained. Preferably, it may also be equipped with a cooling mandrel, a winding roller for winding the polylactic acid resin foam sheet as a raw material roll, and so on.

[0167] Embodiment B can be carried out using any suitable apparatus as long as it does not impair the effects of the present invention. In terms of more effectively exhibiting the effects of the present invention, Embodiment B can be carried out using, for example, a manufacturing apparatus as shown in Figure 6.

[0168] The manufacturing apparatus illustrated in Figure 6 includes a twin-screw extruder 30 and a circular die CD that extrudes the polylactic acid resin composition, which has been melt-kneaded in the twin-screw extruder 30, in a cylindrical shape. Furthermore, this manufacturing apparatus includes a cooling device CL for air-cooling the foamed sheet extruded in a cylindrical shape from the circular die CD, a mandrel MD for expanding the diameter of the cylindrical foamed sheet to form a cylinder of a predetermined size, a slitting device for slitting the foamed sheet after it has passed through the mandrel MD to divide it into two sheets, and a winding roller 22 for winding up the slit foamed sheet 1 after it has passed through a plurality of rollers 21. Upstream of the twin-screw extruder 30, there is a hopper 11 for feeding in the polylactic acid resin, which is the raw material for the foamed sheet. Downstream of the twin-screw extruder 30, there is a gas introduction section 12 for supplying a foaming agent into the cylinder. When the extrusion foaming process is carried out using such equipment, the polylactic acid resin is modified and foaming agents are mixed in the twin-screw extruder 30 to prepare a polylactic acid resin composition that will be the raw material for the foamed sheet, and then extrusion foaming is performed from the circular die CD.

[0169] The temperature conditions for melt mixing can vary depending on the size of the extrusion and the discharge rate, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, the temperature of the raw material feed section of the twin-screw extruder 30 is preferably set to 100°C to 200°C, more preferably to 120°C to 200°C, and the temperature of the twin-screw extruder 30 thereafter is preferably set to 120°C to 300°C, more preferably to 120°C to 250°C.

[0170] The rotational speed of the extruder can vary depending on the size of the extrusion and the discharge volume, so any appropriate conditions can be adopted within a range that does not impair the effects of the present invention. For example, for a twin-screw extruder 30, such a rotational speed is preferably 20 rpm to 800 rpm.

[0171] In air cooling using the CL cooling device, cooling air at, for example, 15°C to 40°C, preferably 20°C to 40°C, is blown onto the inner and outer surfaces of the conventional foam sheet. The amount of air blown onto each surface is, for example, 0.05 m³. 3 / m2 ~0.3m 3 / m 2 Preferably 0.07m 3 / m 2 ~0.3m 3 / m 2 , comfortable 0.1m 3 / m 2 ~0.3m 3 / m 2 More preferably 0.1m 3 / m 2 ~0.2m 3 / m 2 And, or 0.05m 3 / m 2 ~0.20m 3 / m 2 That's fine.

[0172] According to Embodiment B described above, a polylactic acid resin foam sheet can be obtained. [Examples]

[0173] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement and evaluation methods for each characteristic are as follows.

[0174] <Measurement of the minimum autocorrelation length (Sal) on the surface of a polylactic acid foam molded product> The minimum autocorrelation length Sal was measured for each of the two main surfaces of the polylactic acid resin foam molded body as follows. In this example, of the main surfaces of the polylactic acid resin foam molded body, the surface corresponding to the mandrel contact surface during the production of the polylactic acid resin foam sheet before molding (main surface) is described as the "plug surface," and the other main surface (non-mandrel contact surface) is described as the "air cooling surface." For measuring Sal, we use the Evident DSX1000 digital microscope. Three 50mm x 50mm test pieces were cut from the polylactic acid resin foam molded bodies obtained in the examples and comparative examples. Each test piece was cut from three arbitrarily selected locations in the width direction (TD direction) of the polylactic acid resin foam molded body. For the container shape example, three test pieces of the above size were cut from the side wall of the foam container. Each test piece was fixed to the sample stage using double-sided tape to prevent the back of the sample from lifting. Using the automatic bonding function, a 3D image of the outermost surface in a 0.5cm square area was acquired. The objective lens of the DSX10-XLOB20X was used for image acquisition. Using the instrument's accompanying software "Analysis Application," the fitting area was set to the entire area, shape removal was performed in 2D, and then Sal was calculated using the above software. The above operation was performed on both the plug surface and the air cooling surface. Measurements were taken for all test pieces, i.e., the number of tests was 3 for each example, and the arithmetic mean of these measurements was taken as the minimum autocorrelation length Sal for each example.

[0175] <Measurement of average bubble diameter in polylactic acid foam board> The average bubble diameter of a plate-shaped polylactic acid resin foam molded product (polylactic acid resin foam sheet) was measured as follows. The average bubble diameter was measured in accordance with the test method of ASTM D2842-69. Specifically, the polylactic acid resin foam boards obtained in the examples and comparative examples were cut perpendicular to the surface of the polylactic acid resin foam board along the extrusion flow direction (MD direction) and the width direction (TD direction) perpendicular to the extrusion direction in the production of polylactic acid resin foam sheets. The central part of each cross section parallel to the MD direction (hereinafter referred to as the "MD cross section") and the cross section parallel to the TD direction (hereinafter referred to as the "TD cross section") were magnified and photographed using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies Corporation) at different locations (i.e., two fields of view for each cross section, for a total of four fields of view). Next, the captured images were printed on A4 paper in a 2x2 arrangement (4 images in total). Three arbitrary lines (60mm in length) parallel to the MD direction were drawn on each of the two MD cross-section images, and three arbitrary lines (60mm in length) parallel to the TD direction were drawn on each of the two TD cross-section images. In addition, three lines (60mm in length) parallel to the direction perpendicular to the MD and TD directions (thickness direction, hereinafter referred to as "VD direction") were drawn on one of the MD cross-section images and one of the TD cross-section images. As a result, six arbitrary lines of 60mm in length, parallel to the MD, TD, and VD directions, were drawn on the image on the paper. At this time, the magnification of the electron microscope image was adjusted so that each line was contained within the foam. When drawing the lines, care was taken to ensure that the lines penetrated the bubbles without making point contact as much as possible. The number of bubbles present on six arbitrary straight lines in the MD, TD, and VD directions was counted. If a bubble was point-contacting a straight line, it was included in the count. Furthermore, if both ends of a straight line were located within the bubble without penetrating it, the bubbles containing both ends of the line were also included. The arithmetic mean of the counted bubbles was used to determine the number of bubbles in each direction. The average chord length t of the bubbles in each direction was calculated using the following formula, based on the magnification of the image used for bubble counting and this number of bubbles. Average chord length t (μm) = 60000 / (number of bubbles x imaging magnification) (Average chord length tM in the MD direction (μm) = 60000 / (Number of bubbles in the MD direction × Magnification)) (Average chord length tT in the TD direction (μm) = 60000 / (Number of bubbles in the TD direction × Magnification)) (Average chord length tV in the VD direction (μm) = 60000 / (Number of bubbles in the VD direction × Magnification)) Here, the magnification was calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (manufactured by Mitutoyo Corporation) and using the following formula. Magnification = Measured value on scale bar (mm) / Displayed value on scale bar (mm) The bubble diameter in each direction was calculated using the following formula. Bubble diameter d(μm)=t(μm) / 0.616 (Average bubble diameter dM(μm) in the MD direction = tM(μm) / 0.616) (Average bubble diameter dT(μm) in the TD direction = tT(μm) / 0.616) (Average bubble diameter dV(μm) in the VD direction = tV(μm) / 0.616) The average bubble diameter of the polylactic acid resin foam board was defined as the geometric mean of the average bubble diameter dM in the MD direction, the average bubble diameter dT in the TD direction, and the average bubble diameter dV in the VD direction. In other words, the average bubble diameter (average of the three directions) of the polylactic acid resin foam board was calculated using the following formula. Average bubble diameter (μm) = (dM (μm) × dT (μm) × dV (μm)) 1 / 3

[0176] <Measurement of average bubble diameter in foamed containers> The average bubble diameter of the polylactic acid resin foam molded body in the shape of a container was measured as follows. In the foamed container, which is a foamed polylactic acid resin molded body obtained in the example, the side wall was cut perpendicular to the side wall along an arbitrary direction A and direction B perpendicular to direction A. The central part of each cross section parallel to direction A (hereinafter referred to as "cross section A") and cross section parallel to direction B (hereinafter referred to as "cross section B") was magnified and photographed in two images at different locations using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies Corporation) (i.e., two fields of view for each cross section, for a total of four fields of view). In the following, the average bubble diameter was calculated in the same manner, replacing "MD direction" and "MD cross-section" with "A direction" and "A cross-section," respectively, as in the explanation in <Measurement of Average Bubble Diameter of Polylactic Acid Resin Foam Board> above, and replacing "TD direction" and "TD cross-section" with "B direction" and "B cross-section," respectively. Specifically, the captured images were printed on A4 paper in a 2x2 arrangement (4 images in total). Three arbitrary lines of 60mm length parallel to the A direction were drawn on each of the two A section images, and three arbitrary lines of 60mm length parallel to the B direction were drawn on each of the two B section images. Furthermore, three arbitrary lines of 60mm length were drawn in the thickness direction (direction perpendicular to the sidewall, VD direction) perpendicular to the A and B directions, respectively. At this time, the magnification of the electron microscope images was adjusted so that each line was contained within the foam. When drawing the lines, care was taken to ensure that the lines penetrated the bubbles without making point contact as much as possible. The number of bubbles present on six arbitrary straight lines in directions A, B, and VD was counted. When a bubble was point-contacting a straight line, it was included in the count. Furthermore, when both ends of a straight line were located within a bubble without penetrating it, the bubbles containing both ends of the line were also included. The arithmetic mean of the counted bubbles was calculated to determine the number of bubbles in each direction. The average chord length t of the bubbles in each direction was calculated using the following formula, based on the magnification of the image used for counting the bubbles and this number of bubbles. Average chord length t (μm) = 60000 / (number of bubbles x imaging magnification) (Average chord length tA in direction A (μm) = 60000 / (Number of bubbles in direction A × Magnification)) (Average chord length tB in direction B (μm) = 60000 / (Number of bubbles in direction B × Magnification)) (Average chord length tV in the VD direction (μm) = 60000 / (Number of bubbles in the VD direction × Magnification)) Here, the magnification was calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (manufactured by Mitutoyo Corporation) and using the following formula. Magnification = Measured value on scale bar (mm) / Displayed value on scale bar (mm) The bubble diameter in each direction was calculated using the following formula. Bubble diameter d(μm)=t(μm) / 0.616 (Average bubble diameter dA(μm) in direction A = tA(μm) / 0.616) (Average bubble diameter in direction B dB(μm) = tB(μm) / 0.616) (Average bubble diameter dV(μm) in the VD direction = tV(μm) / 0.616) The average bubble diameter of the foamed container was calculated using the geometric mean of the average bubble diameters dA in direction A, dB in direction B, and dV in direction VD. Specifically, the average bubble diameter (average of the three directions) of the foamed container was calculated using the following formula. Average bubble diameter (μm) = (dA (μm) × dB (μm) × dV (μm)) 1 / 3

[0177] <Measurement of the thickness of polylactic acid foam board> For the polylactic acid resin foam boards obtained in the examples and comparative examples, the thickness was measured at nine equally spaced points in the width direction (TD direction), excluding the 20 mm at both ends, using a dial thickness gauge SM-112 (manufactured by Teclock). The arithmetic mean of the measured values ​​was taken as the thickness of the polylactic acid resin foam board.

[0178] <Measuring the thickness of foam containers> For the foam containers obtained in the examples, if the container was point-symmetric when viewed from the planar direction, the thickness from end to end of the cross-section obtained by cutting it with a plane passing through its center point and a central axis that makes a 90-degree angle with the planar direction was measured. If the container was not point-symmetric when viewed from the planar direction, the thickness from end to end of the cross-section obtained by cutting it with a plane passing through its centroid point and a centroid axis that makes a 90-degree angle with the planar direction was measured with a dial thickness gauge SM-112 (manufactured by Teclock). The minimum measured thickness was taken as the thickness of the foam container. If there were flanges or protrusions, those parts were excluded.

[0179] <Measurement of basis weight of polylactic acid foam board> Excluding the 25 mm at both ends of the polylactic acid resin foam board obtained in the examples and comparative examples, six 10 cm x 10 cm sections were cut at equal intervals in the width direction (TD direction), and the mass (g) of each section was measured to the nearest 0.001 g. The average mass (g) of each section was measured at 1 m 2 The value converted to mass per unit is the basis weight (g / m²) of the polylactic acid resin foam board. 2 ) Basis weight (g / m 2 ) = (Average mass of the intercept (g) / (10 (cm) × 10 (cm))) × 10000 (cm2 / m 2 )

[0180] <Measurement of total light transmittance> The total light transmittance τt in the thickness direction (VD direction) of the polylactic acid resin foam molded articles obtained in the examples and comparative examples is given by JIS K7361-1:1997 "Plastics - Total light transmittance of transparent materials". The rate was measured according to the method described in "Test Method for Rate - Part 1: Single Beam Method". In other words, a haze meter (manufactured by Murakami Color Technology Research Institute Co., Ltd., model: HM-150) Using the device, after the light source stabilized, the test specimens were measured using the light source (D65) and the double-beam method. The measurement was performed 30 minutes after the device was started up to confirm that the light source was stable. For the polylactic acid foam board, three 50mm squares were cut out from three arbitrarily selected locations in the width direction (TD direction). For the foam container, one 50mm square was cut out from three arbitrarily selected locations on the side wall. Measurements were performed on all test specimens, i.e., three tests were conducted for each example, and the arithmetic mean of these measurements was taken as the value of total light transmittance (τt). Here, the test specimens were conditioned for more than 24 hours at a temperature of 20±2°C and a humidity of 65±5%, and then measured in a test environment of 20±2°C and 65±5% humidity. The thickness of the test specimens was equivalent to the thickness of the polylactic acid resin foam molded articles of each example and comparative example. The total light transmittance was measured as described above for both cases: when light was irradiated from the plug side of the polylactic acid resin foam molded body and when light was irradiated from the air-cooled side.

[0181] <Measurement of glossiness> The surface gloss of the plug surface and air-cooled surface of the polylactic acid resin foam molded articles obtained in the examples and comparative examples was measured in accordance with the 60-degree specular gloss method described in JIS Z8741:1997 "Specular gloss - Measurement method". Measurements were performed using a gloss checker IG320 (manufactured by Horiba, Ltd.). For polylactic acid foam boards, five arbitrary points were measured on each surface, and the arithmetic mean was taken as the gloss value for each surface. For foam containers, five arbitrary points were measured on the side wall of each surface, and the arithmetic mean was taken as the gloss value for each surface.

[0182] <Measurement of average reflectance> The reflectivity (%) of the plug surface and air-cooling surface of the polylactic acid resin foam molded bodies obtained in the examples and comparative examples was measured as the average reflectance (%) from ultraviolet to near-infrared light (wavelength 350 nm to 900 nm). A Shimadzu UV-3600Plus ultraviolet-visible-near-infrared spectrophotometer was used as the measuring device. A 60mm diameter integrating sphere and barium sulfate were used as standard whiteboards for the measurements. For polylactic acid resin foam boards, measurements were taken at three arbitrarily selected locations in the width direction (TD direction) on each surface (i.e., three tests were performed), and the arithmetic mean was taken as the average reflectance value for each surface. For foam containers, measurements were taken at three arbitrarily selected locations on the side walls of each surface, and the arithmetic mean was taken as the average reflectance value for each surface.

[0183] <Measuring Whiteness> The whiteness of the plug surface of the polylactic acid resin foam molded articles obtained in the examples and comparative examples was measured as follows. Colorimetric measurements were performed in accordance with the method described in JIS Z8722:2009. Specifically, colorimetric measurements were performed using the "SE-7700" spectrophotometer manufactured by Nippon Denshoku Industries Co., Ltd., and the "Colormate Pro" data processing software. The diameter of the test specimens was a square with sides of 100 mm, and the thickness of the test specimens was the thickness of the polylactic acid resin foam molded body for each example and comparative example. At this time, each test specimen was cut from three arbitrarily selected locations in the width direction (TD direction) of the polylactic acid resin foam molded body. For the container shape example, three test specimens of the above size were cut from the side wall of the foam container. The measurement conditions were as follows: Measurement method: Reflection method Lighting diameter: φ28mm Light source: D65 Viewing angle: 10° Standard plate: X=91.7, Y=96.8, Z=103.7 The test specimens were conditioned for at least 24 hours under a standard atmosphere of Class 2, symbol "23 / 50" according to JIS K 7100:1999, before being measured. Measurements were performed in an environment of 20±2°C and 65±5% humidity. For permeable test specimens, the tristimulus value (D65 / 10°) X was applied to the back surface. Measurements were taken using a dedicated whiteboard with Y=77.0 and Z=77.1. JIS Z8781-4:2013 "Colorimetry - CIE1976L" * a * b * According to the "color space", the above The device is CIE1976 L * a * b * The whiteness W was calculated based on the color space. Measurements were taken for all test specimens, meaning three tests were performed for each example. The arithmetic mean of these measurements was taken as the whiteness value for each example.

[0184] <Bending strength of polylactic acid foam board> The bending strength of the polylactic acid resin foam boards obtained in the examples and comparative examples was evaluated by measuring the maximum bending strength in the MD direction and TD direction, respectively, in accordance with JIS K7221-1:2006. In detail, the maximum bending strength was measured using a Shimadzu Autograph AG-X plus 100kN universal testing machine and Shimadzu Trapezium X universal testing machine data processing. Five test pieces measuring 25 mm wide x 40 mm long were cut from the polylactic acid foam board in the MD direction, and five test pieces measuring 25 mm wide x 40 mm long were cut in the TD direction. In other words, five test pieces measuring 25 mm in the TD direction x 40 mm in the MD direction were cut from the polylactic acid foam board for measuring bending strength in the MD direction, and five test pieces measuring 25 mm in the MD direction x 40 mm in the TD direction were cut from the polylactic acid foam board for measuring bending strength in the TD direction. 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 measurement. The measurements were also performed under the same conditions as above, with a test speed of 1 mm / min. The pressure wedge was set to 5R, the support base to 2R, and the distance between supports to 32 mm. From the obtained graph, the maximum point load at which the load is greatest was automatically calculated, and the maximum bending strength was determined.

[0185] <Print Evaluation> The print evaluation of the polylactic acid resin foam molded articles obtained in the examples and comparative examples was carried out as follows. (Polylactic acid foam board) A 20cm square was cut from the polylactic acid resin foam board obtained in the Examples and Comparative Examples to be used as the substrate. A coating machine (Imoto Seisakusho, IMC-7370) with the baker applicator set to 5 so that the coating film thickness would be approximately 125μm was set on the plug side surface of the substrate. Then, 1.5g of black ink (Mimaki Engineering Co., Ltd., LUS-120 Black) was dropped onto the substrate in front of the baker applicator using a dropper. After that, the coating machine was set to a coating speed of 15 and the device was started. A coating film was formed on the surface (plug side) of the substrate in this way to obtain an evaluation sample. (Foam container) Except for cutting a 50mm x 50mm section from a foam container to use as the base material and using 0.1g of black ink, the coating film was formed on the surface of the base material in the same manner as described above (for polylactic acid foam board) to obtain an evaluation sample. As mentioned above, the ratio of ink volume to substrate area was the same for both the print evaluation of polylactic acid resin foam boards and the print evaluation of foam containers. (evaluation) The surface condition of each evaluation sample, after the coating film was formed as described above, was visually observed and evaluated according to the following criteria. ◎: The ink has almost no color unevenness and the ink is applied uniformly. ○: There are some inconsistencies in the ink color, but the entire surface is coated with ink. ×: The ink was repelled, and the entire surface was not coated. Furthermore, "whether the entire surface is coated with ink / not coated" means that the entire area of ​​the substrate that should be coated by the coating machine is coated with ink / not coated.

[0186] <Temperature change rate of polylactic acid resin foam sheet when heated> The dimensional change rate of the polylactic acid resin foam sheet used in the manufacture of the polylactic acid resin foam molded product was measured by heating as follows. Excluding the 50 mm at both ends of the obtained polylactic acid resin foam sheet, five 100 mm square sections were cut at equal intervals to form a planar square. Then, a cross was drawn on each of the two main surfaces of the five obtained test pieces: the air cooling surface and the plug surface. The cross was formed by two straight lines connecting the centers of two pairs of opposing sides on the outer shape of each main surface. Next, each test piece was heated in a heating oven (ESPEC, PH-102) at 125°C for 150 seconds, and then the test pieces were left to cool at room temperature for 5 minutes. The lengths of the straight lines drawn on the air-cooled surface and the plug surface of the test specimen before and after heating were measured, and the heating dimensional change rates in the MD direction and the heating dimensional change rates in the TD direction were calculated for the plug surface and the air-cooled surface side of the polylactic acid resin foam molded body using the following formulas. Here, the heating change rate in the MD direction is the rate of change in the length of the straight line extending in the MD direction (the longitudinal direction of the polylactic acid resin foam sheet, i.e., the extrusion flow direction), and the heating change rate in the TD direction is the rate of change in the length of the straight line extending in the TD direction (the width direction of the polylactic acid resin foam sheet, i.e., the direction perpendicular to the extrusion flow direction). Percentage change in dimensions due to heating (%) = Length after heating (mm) / Length before heating (mm) × 100 Measurements were taken for all test specimens, and the arithmetic mean of these measurements is listed in Table 1 as the heating dimensional change rate of the air-cooled surface and the heating dimensional change rate of the plug surface in the MD or TD direction for each example. Furthermore, the arithmetic mean of the heating dimensional change rate of the air-cooled surface and the heating dimensional change rate of the plug surface were used as the heating dimensional change rate in the MD direction and the heating dimensional change rate in the TD direction.

[0187] <Surface condition of polylactic acid foam board> The surface condition of the polylactic acid resin foam boards obtained in Examples 1 to 9 and Comparative Example 1 was evaluated as follows. (measurement) In the polylactic acid resin foam boards of Examples 1 to 9 and Comparative Example 1, if surface irregularities occurred, the affected area was selected. If no surface irregularities occurred, an arbitrary area was selected, and sections measuring 500 mm in the MD direction and 50 mm in the TD direction were cut out to be used as measurement samples. The thickness of the obtained samples was continuously measured along the MD direction using a benchtop thickness gauge "TOF-4R" (manufactured by Yamabun Electric Co., Ltd.) under the following conditions. Standard thickness: 3.0 mm Measurement length: 300mm Measurement pitch: 1mm Noise reduction: None (evaluation) ○: Within the measurement range, there is no region with a length of 50 mm where the difference between the maximum thickness and the minimum thickness is 0.1 mm or more. ×: Within the measurement range, there exists a region with a length of 50 mm where the difference between the maximum thickness and the minimum thickness is 0.1 mm or more. Specifically, samples in which the difference between the maximum and minimum thickness in a 50mm range of any length selected from the 300mm measurement length was less than 0.1mm were given a ○ rating, while samples with one or more 50mm ranges where the difference between the maximum and minimum thickness was 0.1mm or more, regardless of whether there was a 50mm range where the difference between the maximum and minimum thickness was less than 0.1mm, were given a × rating.

[0188] <Overall Rating> Based on the print quality evaluation and surface condition evaluation results, an overall evaluation was conducted according to the following criteria. ◎: Print evaluation result is ◎, and surface condition evaluation result is ○ ○: The print evaluation result is ○, and the surface condition evaluation result is ○ △: Print evaluation result is ◎ or ○, and surface condition evaluation result is × ×: Print evaluation result is ×, AND surface condition evaluation result is ○ or ×

[0189] [Example 1] (Preparation of polylactic acid resin foam sheets) Polylactic acid resin (manufactured by Anhui Fengyuan Futai Lai Polylactic Acid Co., Ltd., product name "FY602", MFR = 16.0 g / 10 min, D-isomer ratio = 2.0 ± 0.5 ml%, melting point = 164.3 °C, density = 1240 kg / m³) 3 The moisture content of ) was adjusted to 0.04 mass%. A mixture was obtained by stirring and mixing 100 parts by mass of 4% by mass polylactic acid resin and 0.5 parts by mass of t-butyl peroxyisopropyl monocarbonate (manufactured by Kayaku Nurion Co., Ltd., "Triganox BPIC-75", half-life temperature T1 = 158.8°C) using a ribbon blender. The resulting mixture was fed into a twin-screw extruder with a bore diameter of 57 mm (L / D = 31.5). The feed section temperature was set to 170°C, and the temperature thereafter was set to 200°C. Under these conditions, the mixture was melted and kneaded in the twin-screw extruder at a rotation speed of 100 rpm. The kneaded material was then extruded in strand form from a die (diameter φ3 mm, 18 holes) attached to the tip of the extruder at a discharge rate of 50 kg / hour. Next, the extruded strand-shaped mixture was cooled by passing it through a 2-meter-long cooling water tank containing 30°C water. The cooled strands were cut in a pelletizer to form pellets, and then dried in a dehumidifying dryer at a drying temperature of 70°C. Modified polylactic acid resin was obtained in the manner described above. The moisture content of the obtained modified polylactic acid resin pellets was 0.03% by mass. A mixture was prepared by dry blending 100 parts by mass of the obtained modified polylactic acid resin with 2.5 parts by mass of a foam regulator ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.). In a tandem extruder equipped with a first extruder (upstream) with a diameter of φ50 mm and a second extruder (downstream) with a diameter of φ65 mm, the above mixture was supplied to the first extruder with a diameter of φ50 mm through a hopper and heated and melted at 220°C. In order to confirm whether the moisture content of the modified polylactic acid resin changes between the time the modified polylactic acid resin is prepared and supplied to the hopper, the moisture content of the modified polylactic acid resin collected in the hopper when only the modified polylactic acid resin was supplied to the first extruder through the hopper was checked separately, and it remained at 0.03% by mass. Subsequently, 1.2 parts by mass of butane (isobutane / n-butane = 35% by mass / 65% by mass) was injected into the first extruder under pressure as a blowing agent and melt-kneaded together with the above mixture to obtain a molten kneaded product. Next, the molten mixture was transferred to a second extruder with a diameter of φ65 mm and cooled to 170°C. Then, it was extruded and foamed through a circular die with a diameter of φ70 mm at a discharge rate of 30 kg / hour to obtain a cylindrical foam sheet. At this time, immediately after being extruded from the circular die, the cylindrical foam sheet was cooled by blowing cooling air (30°C) onto both the inner surface (plug surface) and the outer surface (air cooling surface) of the cylindrical foam sheet at the air volume shown in Table 1. The obtained cylindrical foam was placed along a φ206 mm mandrel whose interior was cooled with water at approximately 20°C, and its outer surface was cooled and molded by blowing air through an air ring larger than its diameter. The foam was then cut at one point on the circumference with a cutter and wound up with a winding machine at the winding speed (drawing speed) shown in Table 1 to produce a roll-shaped polylactic acid resin foam sheet.

[0190] (Fabrication of polylactic acid resin foam molded products (polylactic acid resin foam sheets)) Annealing of polylactic acid resin foam sheets wound into a roll was performed using an annealing apparatus as shown in Figure 2. Specifically, the annealing apparatus consists of four pairs of endless belts B1 to B4, each consisting of endless belts 1a to 4a and 1b to 4b facing each other in the vertical direction, arranged at predetermined intervals in the direction of transport of the polylactic acid resin foam sheet. The two pairs of endless belts B1 and B2 on the transport start side constitute the heating zone C, and the two pairs of endless belts B3 and B4 on the transport end side constitute the cooling zone D. The spacing between endless belts 1a and 1b, 2a and 2b, 3a and 3b, and 4a and 4b was set based on the thickness after secondary foaming so that the surface of the transported polylactic acid resin foam sheet would come into contact with each endless belt after secondary foaming, and so that it would be sufficiently heated and cooled from both sides without being excessively compressed. In detail, polylactic acid resin foam sheets were sequentially and continuously supplied to the endless belt pair B1 and B2 constituting the heating zone C and heated to remove any remaining strain in the polylactic acid resin foam sheets. The temperatures of the endless belts 1a, 1b, 2a, and 2b were maintained at 120°C. Subsequently, the polylactic acid resin foam sheet heated in heating zone C was sequentially and continuously supplied to the endless belt pair B3 and B4 constituting cooling zone D to cool it down, and then cut to a predetermined length. The temperature of the endless belts 3a, 3b, 4a, and 4b was maintained at 20°C. Furthermore, the conveying speed of the polylactic acid foam sheet by the endless belt pairs B3 and B4 that constitute the cooling zone D was adjusted to a speed at which the conveyed polylactic acid foam sheet did not sag. After annealing, the plate was cut to a predetermined length as described above to obtain a flat plate. The flat plate obtained in the manner described above was designated as the polylactic acid resin foam molded product (polylactic acid resin foam plate) of Example 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 1. Figure 7 shows a photograph of the surface of the evaluation sample in the print evaluation of the polylactic acid resin foam molded body of Example 1. The polylactic acid resin foam molded body of Example 1 had sufficient flexural strength.

[0191] [Example 2] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 2 was obtained in the same manner as in Example 1, except that the winding speed (drawing speed) of the winding machine was changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 2. Figure 8 shows a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded body of Example 2. The polylactic acid resin foam molded body of Example 2 had sufficient flexural strength.

[0192] [Example 3] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 3 was obtained in the same manner as in Example 1, except that the amount of foam regulator (Crown Talc, manufactured by Matsumura Sangyo Co., Ltd.) used was changed to 2.2 parts by mass, and the winding speed (drawing speed) on the winding machine was changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 3. Figure 9 shows a photograph of the surface of the evaluation sample used in the print evaluation of the polylactic acid resin foam molded body of Example 3. The polylactic acid resin foam molded body of Example 3 had sufficient flexural strength.

[0193] [Example 4] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 4 was obtained in the same manner as in Example 1, except that the amount of foam regulator ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.) used was changed to 2.0 parts by mass, and the winding speed (drawing speed) on the winding machine was changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 4. Figure 10 shows a photograph of the surface of the evaluation sample in the print evaluation of the polylactic acid resin foam molded body of Example 4. The polylactic acid resin foam molded body of Example 4 had sufficient flexural strength.

[0194] [Example 5] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 5 was obtained in the same manner as in Example 1, except that the amount of foam regulator ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.) used was changed to 1.0 part by mass, and the winding speed (drawing speed) on the winding machine was changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results of the polylactic acid resin foam molded body of Example 5. Figure 11 shows a photograph of the surface of the evaluation sample in the print evaluation of the polylactic acid resin foam molded body of Example 5. The polylactic acid resin foam molded body of Example 5 had sufficient flexural strength.

[0195] [Example 6] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 6 was obtained in the same manner as in Example 1, except that the amount of foam regulator (Crown Talc, manufactured by Matsumura Sangyo Co., Ltd.) used was changed to 0.8 parts by mass, and the winding speed (drawing speed) on the winding machine was changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 6. Figure 12 shows a photograph of the surface of the evaluation sample in the print evaluation of the polylactic acid resin foam molded body of Example 6. The polylactic acid resin foam molded body of Example 6 had sufficient flexural strength.

[0196] [Example 7] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 7 was obtained in the same manner as in Example 1, except that the winding speed (drawing speed) of the winding machine was changed as shown in Table 1. Table 1 shows the printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 7. The polylactic acid resin foam molded body of Example 7 had sufficient flexural strength.

[0197] [Example 8] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 8 was obtained in the same manner as in Example 1, except that the winding speed (drawing speed) of the winding machine and the airflow rate of the cooling air were changed as shown in Table 1. Table 1 shows the printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded article of Example 8. The polylactic acid resin foam molded article of Example 8 had sufficient flexural strength.

[0198] [Example 9] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Example 9 was obtained in the same manner as in Example 1, except that the amount of cooling air was changed as shown in Table 1. Table 1 shows the printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded body of Example 9. The polylactic acid resin foam molded body of Example 9 had sufficient flexural strength.

[0199] [Comparative Example 1] In the preparation of the polylactic acid resin foam sheet, the polylactic acid resin foam molded article (polylactic acid resin foam board) of Comparative Example 1 was obtained in the same manner as in Example 1, except that the amount of foam adjusting agent ("Crown Talc" manufactured by Matsumura Sangyo Co., Ltd.) used was changed to 0.5 parts by mass, and the winding speed (drawing speed) and the airflow rate of the cooling air on the winding machine were changed as shown in Table 1. Table 1 shows the various printability, print evaluation results, and surface condition evaluation results for the polylactic acid resin foam molded article of Comparative Example 1. Figure 13 shows a photograph of the surface of the evaluation sample in the print evaluation of the polylactic acid resin foam molded article of Comparative Example 1.

[0200] [Example 10] (Preparation of polylactic acid resin foam sheets) A roll-shaped polylactic acid resin foam sheet was prepared in the same manner as in Example 1.

[0201] (Fabrication of polylactic acid resin foam molded products (foamed containers)) A test piece with a planar square shape of 340 mm in length and 340 mm in width was cut out from the produced polylactic acid resin foamed sheet. Using a small single-shot molding machine (manufactured by Wakisaka Engineering Co., Ltd., product name "FVS-500 type"), the set temperature of the heater in the heating furnace was set to 400 °C. Next, the above test piece was introduced into the heating furnace of the small single-shot molding machine for preheating. At this time, the preheating time was 10 seconds, and the surface temperature of the foamed sheet after preheating was 115 °C. Immediately after the preheating of the foamed sheet, match mold molding was performed using a mold at 110 °C (opening diameter 220 mm, bottom diameter 170 mm, height 38 mm, draw ratio 0.17) to produce a circular dish-shaped polylactic acid resin foamed molded body (foamed container) having an opening at the top. At this time, the surface (plug surface) corresponding to the mandrel contact surface during the production of the polylactic acid resin foamed sheet was configured to form the outer surface (the first main surface S21 in FIG. 3) of the foamed container. The time during which the foamed sheet was sandwiched by the mold (mold holding time) was 10 seconds. In the above manner, the polylactic acid resin foamed molded body (foamed container) of Example 10 was obtained. A photograph of the surface of the evaluation sample in the printing evaluation of the polylactic acid resin foamed molded body of Example 10 is shown in FIG. 14.

[0202]

Table 1

Industrial Applicability

[0203] The polylactic acid resin foamed sheet of the present invention is easy to be formed into various shapes, and thus can be used as a raw material for various molded products including packaging materials.

Explanation of Reference Numerals

[0204] 1000 Polylactic acid resin foamed board S11 First main surface S12 Second main surface A Polylactic acid resin foamed sheet 1a, 2a, 3a, 4a, 1b, 2b, 3b, 4b endless belt B1, B2, B3, B4 Endless Belt C Heating Zone D Cooling Zone 2000 foamed containers S21 First Main Surface S22 Second Main Surface 310 Bottom part 320 Side wall section 400 flange section 500 Projection part L Thickness 1. Foam sheet 3 Strand Die 4 Pelletizer 5 Drying equipment 6 Cooling device 10 Tandem extruders 10a First extruder 10b Second extruder 11 Hopper 12 Gas inlet 21 Laura 22 Rewinding roller 30 Twin-screw extruder

Claims

1. A polylactic acid resin foam molded article made by molding a polylactic acid resin foam sheet, The polylactic acid resin foam molded body has a first main surface and a second main surface facing the first main surface. The minimum autocorrelation length Sal in at least one selected from the group consisting of the first principal surface and the second principal surface is 500.0 μm or less. Polylactic acid resin foam molded product.

2. The polylactic acid resin foamed molded article according to claim 1, wherein the average bubble diameter is 1000 μm or less.

3. The polylactic acid resin foam molded article according to claim 1, wherein the total light transmittance measured in the thickness direction is 60% or less.

4. The polylactic acid resin foamed molded article according to claim 1, wherein the polylactic acid resin foam board.

5. An exhibition panel comprising printing on at least one selected from the group consisting of the first main surface and the second main surface of the polylactic acid resin foam molded body described in claim 4.

6. A foamed container, a foamed polylactic acid resin foamed molded body according to claim 1.

7. The polylactic acid resin foam molded article according to claim 1, wherein the polylactic acid resin foam sheet has a heating dimensional change rate in the MD direction of less than 100% when heated at 125°C for 150 seconds.

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