Foam, method for producing the same, container, and foam preform

Abstract

This disclosure aims to provide a foam suitable for products that are susceptible to quality degradation due to light, as well as a method for manufacturing the same, a container, and a foam preform. [Solution] The foam according to the present disclosure is a foam that is a molded product of a molding material containing a thermoplastic resin, wherein the foam has a first non-foamed layer and a foamed layer, the foamed layer includes a first foamed layer having a plurality of bubbles 2 arranged in three dimensions and a bubble wall skeleton 4 that separates adjacent bubbles, the first foamed layer has a mesh-like bubble structure 5 in which the bubble wall skeleton has a mesh-like cross-section, and the mesh-like bubble structure includes continuous bubbles in which adjacent bubbles communicate with each other through openings 6 provided in the bubble wall skeleton.

Description

Technical Field

[0001] The present disclosure relates to a foam, a method for manufacturing the same, a container, and a foam preform.

Background Art

[0002] The origin of resin foam molding is at the Massachusetts Institute of Technology (MIT) in the United States, and since the 1980s, its technical applications have been promoted in various fields. In Japan, it is currently widely applied to resin injection molded products such as automotive parts. Technologies for applying a foam to a container have been proposed (see, for example, Patent Document 1). In Patent Document 1, as a preferable form when applying a foam to a container, each foam cell in a foamed state is in an independent state, its foam cell dimensions, a foam density gradient on the container wall, and a light shielding performance region in an aggregate of independent cells are disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the container of Patent Document 1, the light shielding performance is imparted by multiple scattering and reflection of light by the aggregate of independent cells. On the other hand, for products that are likely to deteriorate in quality due to light such as ultraviolet rays in beer beverages or cosmetic emulsions, very high light shielding properties are required for packaging. However, according to the study by the present inventors, it has been found that only foaming with independent foam cells, like the container of Patent Document 1, cannot obtain the light shielding performance required for products that are likely to deteriorate in quality due to light as described above.

[0005] An object of the present disclosure is to provide a foam suitable for products that are likely to deteriorate in quality due to light, a method for manufacturing the same, a container, and a foam preform. [Means for solving the problem]

[0006] The foam according to the present invention is a foam that is a molded article of a molding material containing a thermoplastic resin, wherein the foam has a first non-foamed layer and a foamed layer, the foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall skeleton that separates adjacent bubbles, the first foamed layer has a mesh-like bubble structure in which the bubble wall skeleton has a mesh-like cross-section, and the mesh-like bubble structure includes open bubbles in which adjacent bubbles communicate with each other through openings provided in the bubble wall skeleton.

[0007] In the foam according to the present invention, the foam layer further includes a configuration in which a second foam layer having a sea-island structure in which air bubbles are dispersed in a matrix made of the molding material is located between the first non-foamed layer and the first foam layer.

[0008] The foam according to the present invention further comprises a second non-foamed layer, preferably the foamed layer being located between the first non-foamed layer and the second non-foamed layer. Smoothness can be ensured on both the front and back surfaces of the foam.

[0009] In the foam according to the present invention, it is preferable that the mesh-like cell structure further includes closed cells in which adjacent cells are not connected to each other. This allows for a foam with higher strength.

[0010] In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, the surface of the foam opposite to the first non-foamed layer side is treated in accordance with JIS Z 8781-4:2013 and CIE1976 L * a * b * When measuring the chromaticity coordinates in the color space, L * The value of is 70 or more and 100 or less, and a * The value of is -1.0 or greater and 0 or less, and b * It is preferable that the value of is between -2.0 and 0. When foam is used as the outer wall of the container, the light-shielding properties can be further enhanced.

[0011] In the foam according to the present invention, for the surface on the side of the first non-foamed layer of the foam and the surface on the side opposite to the first non-foamed layer side, CIE1976 L * a * b * When the chromaticity coordinates in the color space are measured, the L of the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of L on the surface on the side of the first non-foamed layer, or L on the surface on the side of the first non-foamed layer * The value of is larger than the value of, and the a on the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of a on the surface on the side of the first non-foamed layer, or a on the surface on the side of the first non-foamed layer * The value of is smaller than the value of, and the b on the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of b on the surface on the side of the first non-foamed layer, or b on the surface on the side of the first non-foamed layer * The value of is smaller than the value of, and the b on the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of b on the surface on the side of the first non-foamed layer, or b on the surface on the side of the first non-foamed layer * The value of is the same as the value of, or the value of b on the surface on the side opposite to the first non-foamed layer side * It includes a form smaller than the value of.

[0012] In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, the D65 whiteness measured in accordance with ISO2470-2:2008 on the surface on the side opposite to the first non-foamed layer side of the foam is preferably 70 or more. When the foam is used as the outer wall of the container, the light-shielding property can be further enhanced.

[0013] In the foam according to the present invention, for the surface on the side of the first non-foamed layer of the foam and the surface on the side opposite to the first non-foamed layer side, when the D65 whiteness is measured in accordance with ISO2470-2:2008, the value of the D65 whiteness on the surface on the side opposite to the first non-foamed layer side is the same as the value of the D65 whiteness on the surface on the side of the first non-foamed layer, or includes a form larger than the value of the D65 whiteness on the surface on the side of the first non-foamed layer.

[0014] The foam according to the present invention includes a form in which, when the reflectance is measured on the surface of the foam on the first non-foaming layer side and the surface opposite to the first non-foaming layer side in accordance with JIS R 3106:2019 "Test method for transmittance, reflectance, and emissivity of plate glass and method for calculating the solar heat gain coefficient of building plate glass", the reflectance value of the surface opposite to the first non-foaming layer side at wavelengths of 240 to 800 nm is the same as the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm, or greater than the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm, and is within the range of 0 to 20% of the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm.

[0015] In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, it is preferable that the transmittance of light in the wavelength range of 480 to 500 nm of the foam is 15% or less. When the foam is used as the outer wall of a container, the light-shielding properties can be further enhanced.

[0016] The foam according to the present invention preferably has a gas barrier film on at least one of the surfaces of the first non-foamed layer side and the surface opposite to the first non-foamed layer side. When the foam is used as the outer wall of a container, deterioration of the contents of the container can be prevented.

[0017] The foam according to the present invention includes a form in which the thermoplastic resin is polyethylene terephthalate resin, and the intrinsic viscosity of the polyethylene terephthalate resin is 0.63 to 0.86 dl / g.

[0018] The container according to the present invention is characterized by having the foam material according to the present invention as its outer wall.

[0019] The container according to the present invention includes a configuration in which the first non-foaming layer is arranged on the inner surface side of the container, and the foamed layer is arranged on the outer surface side of the container relative to the first non-foaming layer.

[0020] The foamed preform according to the present invention is a foamed preform which is a molded product of a molding material containing a thermoplastic resin, wherein the foamed preform comprises a first non-foamed layer and a pre-foamed layer, the pre-foamed layer having a plurality of spherical foam cells, the particle size distribution based on the number of spherical foam cells having a broad particle size distribution with a distribution width of 52 μm or more, and the mode diameter being 49 to 62 μm, and the distribution width is the width of the frequency distribution graph of the particle size distribution obtained under the following condition 1. Condition 1: The particle size distribution is determined by measuring the number of spherical foam cells and their individual diameters in an observation image obtained by observing the cross-section of the foamed preform at a magnification of 200x using a reflection microscope.

[0021] In the foamed preform according to the present invention, the particle size distribution based on the number of spherical foam cells includes shapes in which the mode diameter is larger than the average diameter.

[0022] The present invention relates to a method for producing a foam, comprising the steps of: preparing a bottomed cylindrical non-foaming preform which is a molded article of a molding material containing a thermoplastic resin, impregnated with an inert gas, and in a non-foaming state; a foaming step which converts the non-foaming preform into a foaming preform; and a blow molding step which blow-moldes the foaming preform into a foam, wherein the foaming step comprises a heating step which heats the non-foaming preform from the outer surface side to obtain an intermediate, and after the heating step which heats the heat unevenly distributed on the outer surface side of the intermediate to conduct heat to the inner surface side. The blow molding process includes a waiting step to reduce the temperature difference between the outer surface and the inner surface, and the blow molding process is a process of forming a foam having a first non-foamed layer and a foamed layer as the foam, wherein the foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall skeleton that separates adjacent bubbles, and the first foamed layer has a mesh-like bubble structure in which the bubble wall skeleton has a mesh-like cross-section, and the mesh-like bubble structure includes open bubbles in which adjacent bubbles communicate with each other through openings provided in the bubble wall skeleton.

[0023] In the foaming method according to the present invention, it is preferable that the foaming step is a process in which the heating step and the waiting step constitute one cycle, and this cycle is performed two or more times. By performing the heating step and the waiting step in multiple steps, bubbles can be grown throughout the entire thickness direction of the intermediate, and the difference in bubble size between the side closer to the outer surface and the side closer to the inner surface of the intermediate can be made smaller.

[0024] In the foaming method according to the present invention, the foaming step comprises a foaming preform having a first non-foaming layer and a pre-foaming layer, wherein the pre-foaming layer is a step of forming a foaming preform having a plurality of spherical foam cells, and the particle size distribution based on the number of spherical foam cells has a broad particle size distribution with a distribution width of 52 μm or more, and a mode diameter of 49 to 62 μm, and preferably the distribution width is the width of the frequency distribution graph of the particle size distribution obtained under the following condition 1. This makes it easier to form open bubbles in the first foam layer in the resulting foam. Condition 1: The particle size distribution is determined by measuring the number of spherical foam cells and their individual diameters in an observation image obtained by observing the cross-section of the foamed preform at a magnification of 200x using a reflection microscope. [Effects of the Invention]

[0025] According to this disclosure, it is possible to provide a foam suitable for products that are susceptible to quality degradation due to light, as well as a method for manufacturing the same, a container, and a foam preform. [Brief explanation of the drawing]

[0026] [Figure 1] This is a schematic partial cross-sectional view showing an example of a foam according to this embodiment. [Figure 2] This is a schematic diagram illustrating the first foamed layer. [Figure 3] This image shows an example of a mesh-like cellular structure. [Figure 4] This image shows an example of a sea-island structure. [Figure 5] This is a schematic partial cross-sectional view showing an example of a foamed preform according to this embodiment. [Figure 6] This is a schematic diagram illustrating the pre-foamed layer. [Figure 7] This image shows a cross-section of the foamed bottle in the thickness direction of Example 1. [Figure 8] This image shows a cross-section of the foamed bottle of Example 1 perpendicular to the thickness direction, where (a) shows the second non-foamed layer, (b) shows the first foamed layer, (c) shows the second foamed layer, and (d) shows the first non-foamed layer. [Modes for carrying out the invention]

[0027] Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these descriptions. Various modifications of the embodiments are possible as long as they achieve the effects of the present invention.

[0028] As shown in Figure 1, the foam 1 according to this embodiment is a foam that is a molded product of a molding material containing a thermoplastic resin, and the foam 1 has a first non-foamed layer 11 and a foamed layer 20, and as shown in Figure 2, the foamed layer 20 includes a first foamed layer 21 having a plurality of bubbles 2 arranged in three dimensions and a bubble wall skeleton 4 that separates adjacent bubbles 2 from each other, and as shown in Figure 3, the first foamed layer 21 has a mesh-like bubble structure 5 in which the bubble wall skeleton 4 has a mesh-like cross-section, and the mesh-like bubble structure 5 includes continuous bubbles in which adjacent bubbles 2 communicate with each other through openings 6 provided in the bubble wall skeleton 4.

[0029] The molding material is a material mainly composed of a thermoplastic resin. The thermoplastic resin is not particularly limited, but examples include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile butadiene styrene resin (ABS), acrylonitrile styrene resin (AS), acrylic resin (PMMA), or polyacetal (POM). Of these, PET is preferred as the thermoplastic resin. The molding material may consist only of a thermoplastic resin, or it may contain a thermoplastic resin plus various known additives or colorants, as long as they do not impair the effects of the present invention.

[0030] The foam 1 is not particularly limited, but it is preferably in a shape with a front and back surface, such as a plate, wall, or sheet, and is more preferably a blow-molded product.

[0031] The first non-foaming layer 11 is a layer that is substantially free of air bubbles 2 and is generally called a skin layer. Preferably, the surface of the first non-foaming layer 11 is the surface of either the front or back surface of the foam 1. The thickness of the first non-foaming layer 11 is not particularly limited, but is preferably 3 to 15% and more preferably 5 to 13% of the total thickness of the foam 1.

[0032] The foamed layer 20 is a layer containing air bubbles 2. The thickness of the foamed layer 20 is not particularly limited, but is preferably 65-97% of the total thickness of the foam 1, and more preferably 67-95%.

[0033] The first foam layer 21 is a layer in the foam layer 20 where the expansion of bubbles 2 has occurred excessively. Due to the large growth of bubbles 2, the solid parts around bubbles 2 are compressed, resulting in thin wall-like or thin columnar shapes. In the first foam layer 21, bubbles 2 are randomly arranged in the XYZ axis directions of the foam, as shown in Figure 2. Here, the X axis direction is horizontal to the surface of the foam 1, the Y axis direction is horizontal to the surface of the foam 1 and perpendicular to the X axis direction, and the Z axis direction is perpendicular to the surface of the foam 1, i.e., the thickness direction of the foam 1. In the first foam layer 21, most of the bubbles 2 have a flattened shape with their maximum width in the X axis direction and the Y axis direction, respectively, and these are distributed partially overlapping in the Z axis direction.

[0034] Figure 3 is a slice image of the foam 1 in the thickness direction, observed using an X-ray transmission inspection device (μnRay7600F, manufactured by Matsusada Precision Co., Ltd.). The scale in the lower right of Figure 3 represents 0.25 mm. In Figure 3, the white areas are bubble walls 3, and the black areas are bubbles 2. As shown in Figure 3, the outer circumference of each bubble 2 is surrounded by a bubble wall 3 made of the molding material. Adjacent bubbles 2 share a portion of the bubble wall 3. The bubble wall skeleton 4 is a three-dimensional structure that constitutes the first foam layer 21, where the bubble walls 3 surrounding each bubble 2 are connected in three dimensions. Preferably, the bubble wall skeleton 4 has a three-dimensional mesh structure that is connected in a mesh-like manner in various directions in three-dimensional space, including the XYZ axis direction.

[0035] Figure 3 shows an example of a cross-section in the XY axis direction. The mesh-like cellular structure, as shown in Figure 3, refers to a structure in which, when a cross-section is observed in any direction in the three-dimensional space of the first foam layer 21, the cross-sections of the cellular wall framework 4 are spread out like a mesh. It can also be described as a structure in which multiple pores (spaces consisting of bubbles 2) separated by the cross-sections of the cellular wall framework 4 are connected.

[0036] The network-like cellular structure includes open bubbles 2a. Open bubbles 2a refer to a state in which a bubble 2a1 is in communication with an adjacent bubble 2a2, as shown in Figure 3, because the bubble wall 3 separating the bubbles 2 has an opening 6. This state is sometimes called a ruptured bubble. The opening 6 is the part where the bubble wall 3 is interrupted, which appears white in Figure 3. Bubbles 2a1 and 2a2, shown as an example in Figure 3, are both open bubbles and are ruptured.

[0037] In the foam 1 according to this embodiment, it is preferable that the mesh-like cell structure further includes closed cells 2b in which adjacent cells are not connected to each other. Including closed cells 2b makes it possible to obtain a foam with higher strength. Closed cells 2b refer to a state in which the cell walls 3 separating the cells 2 do not have openings 6, and the cells 2 are in a space independent of the surrounding cells 2.

[0038] In the foam 1 according to this embodiment, the foam layer 20 further includes a configuration in which a second foam layer 22 having a sea-island structure 7 in which bubbles 2 are dispersed in a matrix 8 made of molding material is located between the first non-foamed layer 11 and the first foam layer 21. Figure 4 is a slice image of the foam 1 in the thickness direction observed using an X-ray transmission inspection device (μnRay7600F, manufactured by Matsusada Precision Co., Ltd.). The scale in the lower right of Figure 4 represents 0.25 mm. In Figure 4, the white areas are the matrix 8, and the black areas are the bubbles 2. The second foam layer 22 is a layer in the foam layer 20 in which the degree of expansion of bubbles 2 is small, and due to the small growth of bubbles 2, the solid parts around the bubbles 2 remain in clumps, and islands of bubbles 2 are mixed in the sea of ​​matrix 8 made of molding material.

[0039] In this embodiment, it is preferable that the thickness of the first foam layer 21 is large, and the ratio of the thickness of the first foam layer 21 to the total thickness of the foam layer 20 is preferably 80% or more, more preferably 90% or more, even more preferably 95% or more, and particularly preferably 100%. The larger the ratio of the thickness of the first foam layer 21 to the total thickness of the foam layer 20, the more the difference in whiteness, chromaticity, and reflectance between the front and back surfaces can be almost eliminated, and the light-shielding performance of the foam 1 can be further improved.

[0040] The foam body 1 according to this embodiment further has a second non-foamed layer 12, as shown in Figure 1, and the foamed layer 20 is preferably located between the first non-foamed layer 11 and the second non-foamed layer 12. Smoothness can be ensured on both the front and back surfaces of the foam body 1. The second non-foamed layer 12 is a layer that is substantially free of air bubbles 2 and is generally called a skin layer. The surface of the second non-foamed layer 12 is preferably the surface of the foam body 1 opposite to the side facing the first non-foamed layer 11. The thickness of the second non-foamed layer 12 is not particularly limited, but is preferably 3 to 15% of the total thickness of the foam body 1, and more preferably 5 to 13%. The thickness of the second non-foamed layer 12 is preferably equal to or greater than the thickness of the first non-foamed layer 11.

[0041] The first non-foamed layer 11, the foamed layer 20, and the second non-foamed layer 12 are layers made of the same molding material. The first non-foamed layer 11, the foamed layer 20, and the second non-foamed layer 12 are stacked in the thickness direction (Z-axis direction) of the foam 1.

[0042] Figure 1 shows a configuration in which the foam 1 consists of a first non-foaming layer 11, a second foaming layer 22, a first foaming layer 21, and a second non-foaming layer 12. However, the present invention is not limited to the configuration shown in Figure 1, and only requires the inclusion of at least the first non-foaming layer 11 and the first foaming layer 21. For example, the foam 1 may consist only of the first non-foaming layer 11 and the first foaming layer 21, only of the first non-foaming layer 11, the second foaming layer 22, and the first foaming layer 21, or only of the first non-foaming layer 11, the first foaming layer 21, and the second non-foaming layer 12.

[0043] There are no clear boundaries between the layers of the foam, and the structure may change continuously. In Figure 1, the boundaries between the first non-foamed layer 11 and the second foamed layer 22, the boundary between the second foamed layer 22 and the first foamed layer 21, and the boundary between the first foamed layer 21 and the second non-foamed layer 12 are represented by dashed lines, but these are not lines that indicate clear boundaries, but merely schematic representations of the approximate boundary locations. To explain with specific examples, near the boundary between the first non-foamed layer 11 and the second foamed layer 22, there may be a mixture of areas without bubbles and areas with a sea-island structure. Near the boundary between the second foamed layer 22 and the first foamed layer 21, there may be a mixture of areas with a sea-island structure and areas with a network-like bubble structure. Near the boundary between the first foamed layer 21 and the second non-foamed layer 12, there may be a mixture of areas with a network-like bubble structure and areas without bubbles.

[0044] In the foam 1 according to this embodiment, when the thickness of the foam 1 is 250 μm or more and 450 μm or less, the surface of the foam 1 opposite to the first non-foamed layer 11 is treated in accordance with JIS Z 8781-4:2013 and CIE1976 L * a * b * When measuring the chromaticity coordinates in the color space, L * The value of is 70 or more and 100 or less, and a * The value of is -1.0 or greater and 0 or less, and b * It is preferable that the value of is between -2.0 and 0. By setting it within this range, the foam 1 is perceived as substantially white to the naked eye. When the foam 1 is used as the outer wall of the container, the contents of the container can be protected from harmful light such as ultraviolet rays. In this embodiment, when the foam 1 is used as the outer wall of the container, it is preferable that the surface of the foam 1 opposite to the first non-foamed layer 11 side be the outer surface of the container, and the surface of the foam 1 on the first non-foamed layer 11 side be the inner surface of the container. L of the surface of the foam 1 opposite to the first non-foamed layer 11 side * The value of is more preferably 80 or more and 90 or less. The surface of the foam 1 opposite to the first non-foaming layer 11 side a * The value of is more preferably -0.5 or greater and 0 or less. b on the surface of the foam 1 opposite to the first non-foamed layer 11 side *The value of is more preferably -0.9 or greater and 0 or less. In this embodiment, when the foam 1 is in bottle shape, L * a * b * This is the average value of measurements taken at any three locations in the vertical center of the bottle. Also, if foam 1 is tray-shaped, L * a * b * This is the average of the values ​​measured at any three locations in the center of the tray along its longitudinal direction.

[0045] When the thickness of foam 1 is 250 μm or more and 450 μm or less, the surface of the first non-foamed layer 11 of foam 1 is treated according to JIS Z 8781-4:2013 and CIE1976 L * a * b * When measuring the chromaticity coordinates in the color space, L * The value of is 45 or greater and 100 or less, and a * The value of is -1.0 or greater and 0 or less, and b * The value of is preferably -1.0 or greater and 0 or less. L on the surface of the first non-foamed layer 11 side of the foam 1 * The value of is more preferably 70 or more and 80 or less. * The value of is more preferably -0.3 or greater and 0 or less. * The value of is more preferably between -0.35 and 0.

[0046] In the foam 1 according to this embodiment, the surface of the foam 1 on the non-foamed layer 11 side and the surface on the opposite side from the first non-foamed layer 11 side are treated according to JIS Z 8781-4:2013 and CIE1976 L * a * b * When measuring the chromaticity coordinates in the color space, the L on the surface opposite to the first non-foamed layer 11 side * The value of is L on the surface of the first non-foaming layer 11. * The same value as the value of, or the L of the surface on the first non-foaming layer 11 side. * The value is greater than the a on the surface opposite to the first non-foaming layer 11 side.* The value of is a on the surface of the first non-foaming layer 11. * The same value as the value of, or the surface of the first non-foaming layer 11 side a * The value is smaller than the value of b on the surface opposite to the first non-foaming layer 11 side. * The value of is the b of the surface on the first non-foaming layer 11 side. * The value is the same as the value of, or the value of the surface on the first non-foaming layer 11 side of b * It includes forms smaller than the value of . The thicker the first foamed layer 21, the greater the L of the surface on the opposite side from the first non-foamed layer 11. * Ō, a * The value and b * The value of and the L of the surface on the first non-foaming layer 11 side * Ō, a * The value and b * The difference with the value tends to become smaller. And when the entire foamed layer 20 is the first foamed layer 21, the L of the surface opposite to the first non-foamed layer 11 side * Ō, a * The value and b * The value of and the L of the surface on the first non-foaming layer 11 side * Ō, a * The value and b * The value becomes substantially the same. Here, substantially the same means that the difference is within the margin of error.

[0047] In the foam 1 according to this embodiment, when the thickness of the foam 1 is 250 μm or more and 450 μm or less, the D65 whiteness measured in accordance with ISO 2470-2:2008 on the surface of the foam 1 opposite to the first non-foamed layer 11 is preferably 70 or more, and more preferably 80 or more. When the foam is used as the outer wall of a container, the contents of the container can be protected from harmful light such as ultraviolet rays. In this embodiment, when the foam 1 is in the shape of a bottle, the D65 whiteness is the average value of the values ​​measured at any three locations in the center of the bottle in the vertical direction. When the foam 1 is in the shape of a tray, the D65 whiteness is the average value of the values ​​measured at any three locations in the center of the tray in the longitudinal direction.

[0048] The D65 whiteness of the surface on the side of the first non-foamed layer 11 is preferably 35 or higher, and more preferably 45 or higher.

[0049] In the foam body 1 according to this embodiment, when the D65 whiteness is measured in accordance with ISO 2470-2:2008 on the surface on the side of the first non-foamed layer 11 and the surface on the opposite side of the first non-foamed layer 11, the D65 whiteness value of the surface on the opposite side of the first non-foamed layer 11 is either the same as the D65 whiteness value of the surface on the side of the first non-foamed layer 11, or greater than the D65 whiteness value of the surface on the side of the first non-foamed layer 11. Furthermore, the difference between the D65 whiteness of the surface on the side of the first non-foamed layer 11 and the D65 whiteness value of the surface on the side of the first non-foamed layer 11 is preferably 0 to 35, and more preferably 0 to 25. As the thickness of the first foam body 21 increases, the difference between the D65 whiteness value of the surface on the opposite side of the first non-foamed layer 11 and the D65 whiteness value of the surface on the side of the first non-foamed layer 11 tends to decrease. Furthermore, when the entire foamed layer 20 is the first foamed layer 21, the D65 whiteness value of the surface opposite to the first non-foamed layer 11 side and the D65 whiteness value of the surface on the first non-foamed layer 11 side are substantially the same. Here, substantially the same means that the difference is within the margin of error.

[0050] The foam according to the present invention, when the reflectance is measured on the surface opposite to the first non-foamed layer in accordance with JIS R 3106:2019 "Test method for transmittance, reflectance, and emissivity of plate glass and method for calculating the solar heat gain coefficient of building plate glass", preferably the reflectance value at a wavelength of 390 nm on the surface opposite to the first non-foamed layer is 70% or more, and more preferably 75% or more. When the foam 1 is used as the outer wall of a container, the contents of the container can be protected from harmful light such as ultraviolet rays. In this embodiment, when the foam 1 is in the shape of a bottle, the reflectance is the average value of the values ​​measured at any three locations in the center of the bottle in the vertical direction. When the foam 1 is in the shape of a tray, the reflectance is the average value of the values ​​measured at any three locations in the center of the tray in the longitudinal direction.

[0051] In this embodiment, when the reflectance of the foam is measured in accordance with JIS R 3106:2019 "Test method for transmittance, reflectance, and emissivity of plate glass and method for calculating solar heat gain coefficient of building plate glass", the reflectance value of the surface opposite to the first non-foaming layer at wavelengths of 240 to 800 nm is the same as, or greater than, the reflectance value of the surface opposite to the first non-foaming layer at wavelengths of 240 to 800 nm, and is preferably within the range of 0 to 20%, and more preferably within the range of 0 to 5%, relative to the reflectance value of the surface on the first non-foaming layer at wavelengths of 240 to 800 nm.

[0052] The reflectance value at wavelengths of 240 to 2600 nm on the surface opposite to the first non-foamed layer 11 is preferably within the range of 0 to 20%, and more preferably within the range of 0 to 5%, of the reflectance value at wavelengths of 240 to 2600 nm on the surface on the first non-foamed layer 11 side.

[0053] In the foam according to this embodiment, when the thickness of the foam 1 is 250 μm or more and 450 μm or less, the transmittance of light in the wavelength range of 480 to 500 nm of the foam 1 is preferably 15% or less, and more preferably 10 to 12%. When the foam 1 is used as the outer wall of a container, the contents of the container can be protected from harmful light such as ultraviolet rays. In this embodiment, when the foam 1 is in the shape of a bottle, the transmittance of light is measured at at least one arbitrary location at the center of the bottle in the vertical direction. When the foam 1 is in the shape of a tray, the transmittance of light is measured at at least one arbitrary location at the center of the tray in the longitudinal direction.

[0054] In this embodiment, it is preferable that the foam 1 has a gas barrier film on at least one of the surfaces, either the surface on the side of the first non-foaming layer 11 or the surface opposite to the side of the first non-foaming layer 11. When the foam 1 is used as the outer wall of a container, deterioration of the contents of the container can be prevented. The gas barrier film is not particularly limited and can be any known coating layer, such as a DLC (Diamond-Like Carbon) film or various vapor-deposited films. The gas barrier film may be provided only on the surface on the side of the first non-foaming layer 11, only on the surface opposite to the side of the first non-foaming layer 11, or on both the surface on the side of the first non-foaming layer 11 and the surface opposite to the side of the first non-foaming layer 11. It is preferable that the gas barrier film be provided on either the surface of the first non-foaming layer 11 or the surface of the second non-foaming layer 12, or both. When forming a vapor-deposited film as the gas barrier film, the thermal load can be reduced by vapor deposition on the surfaces of the non-foaming layers 11 and 12. Furthermore, because the non-foaming layers 11 and 12 have high smoothness, they can perform their gas barrier function without impairing the gas barrier performance of the gas barrier film.

[0055] In this embodiment, the intrinsic viscosity of the thermoplastic resin is not particularly limited as long as it is within a range suitable for molding. However, considering the ease of bubble breaking, it is preferable to select a resin with a relatively low intrinsic viscosity that is suitable for molding containers such as bottles and trays. In the foam according to this embodiment, the thermoplastic resin is polyethylene terephthalate resin, and the intrinsic viscosity of the polyethylene terephthalate resin includes forms with an intrinsic viscosity of 0.63 to 0.86 dl / g. It is more preferable that the intrinsic viscosity of the polyethylene terephthalate resin is 0.63 to 0.82 dl / g. When the foam is a container such as a bottle or tray, the intrinsic viscosity of the polyethylene terephthalate resin is the intrinsic viscosity measured on a piece cut from the container.

[0056] The container according to this embodiment has the foam 1 according to this embodiment as its outer wall. The foam 1 according to this embodiment is suitable for use as the outer wall of a container. The container is not particularly limited, but for example, it may be a bottle or a tray. If the container is a bottle, the volume of the bottle is preferably 50 to 3,000 ml, more preferably 50 to 500 ml, and even more preferably 60 to 150 ml. The contents are not particularly limited, but are preferably beer beverages or substances that are easily degraded by light such as ultraviolet rays, such as cosmetic lotions.

[0057] The container according to this embodiment includes a configuration in which the first non-foaming layer 11 is arranged on the inner surface side of the container and the foamed layer 20 is arranged on the outer surface side of the container than the first non-foaming layer 11. If the foamed body 1 further comprises a second non-foaming layer 12, it is preferable that the second non-foaming layer 12 is arranged on the outer surface side of the container.

[0058] The foamed preform 100 according to this embodiment is a foamed preform which is a molded product of a molding material containing a thermoplastic resin. As shown in Figure 5, the foamed preform 100 has a first non-foamed layer 111 and a pre-foamed layer 120. As shown in Figure 6, the pre-foamed layer 120 has a plurality of spherical foam cells 102. The particle size distribution based on the number of spherical foam cells 102 has a distribution width of 52 μm or more and a mode diameter of 49 to 62 μm. The particle size distribution based on the number of spherical foam cells has a broad particle size distribution with a distribution width of 52 μm or more and a mode diameter of 49 to 62 μm, and the distribution width is the width of the frequency distribution graph of the particle size distribution obtained under the following condition 1. Condition 1: The particle size distribution is determined by measuring the number of spherical foam cells and their individual diameters in an observation image obtained by observing the cross-section of the foamed preform at a magnification of 200x using a reflection microscope.

[0059] The foamed preform 100 is preferably, for example, a hot parison or cold parison for blow molding. The shape of the foamed preform 100 is not particularly limited, but for example, if the foam 1 is a bottle, it is a bottomed cylindrical shape, and if the foam 1 is a tray, it is a disc shape or a bowl shape.

[0060] The first non-foamed layer 111 is the layer that becomes the first non-foamed layer 11 in the foam 1, and substantially does not contain spherical foam cells 102. Preferably, the surface of the first non-foamed layer 111 forms the inner surface of the foam preform 100.

[0061] The pre-foamed layer 120 is the layer that becomes the foamed layer 20 in the foam 1, and spherical foam cells 102 are dispersed within it. The spherical foam cells 102 are substantially spherical and contain gas. A matrix 103 made of molding material surrounds the spherical foam cells 102. As shown in Figure 6, the pre-foamed layer 120 contains spherical foam cells 102 of various diameters.

[0062] In the pre-foamed layer 120, the particle size distribution based on the number of spherical foam cells 102 has a distribution width of 52 μm or more and a mode diameter of 49 to 62 μm. A distribution width of 60 μm or more is more preferable. The upper limit of the distribution width is not particularly limited, but for example, it is preferably 80 μm or less, and more preferably 75 μm or less. A mode diameter of 52 to 58 μm is more preferable. Having a so-called broad particle size distribution with a wide distribution width as described above makes it possible to form a first foamed layer 21 containing ruptured bubbles in the foam 1 obtained by blow molding the foamed preform 100. On the other hand, if there is a so-called sharp particle size distribution with a distribution width of less than 52 μm, as in Patent Document 1, the foamed layer will not contain ruptured bubbles, resulting in a grayish color with low whiteness and failing to achieve the desired light-shielding performance. The particle size distribution is measured as follows. A 10 mm square section is cut from a predetermined location on the foamed preform 100, frozen, and then cut with a diamond knife to obtain an observation cross-section. The observation cross-section is observed at a magnification of 200x using a reflecting microscope. The number of spherical foam cells present in this observation image and the diameter of each cell are measured to determine the particle size distribution. The observation position is not particularly limited, but for example, if the foam 1 is a bottle, it is preferably the position at the center of the body in the vertical direction after molding, and if the foam 1 is a tray, it is preferably the position at the center of the tray in the longitudinal direction after molding.

[0063] The foamed preform 100 preferably comprises a second non-foamed layer 112 in addition to the first non-foamed layer 111 and the pre-foamed layer 120, as shown in Figure 5. The second non-foamed layer 112 is the layer that becomes the second non-foamed layer 12 in the foam 1 and substantially does not contain spherical foam cells 102. The surface of the second non-foamed layer 112 preferably forms the outer surface of the foamed preform 100.

[0064] There are no clear boundaries between the layers of the foamed preform 100, and the structure may change continuously. In Figure 5, the boundary lines between the first non-foamed layer 111 and the pre-foamed layer 120, and the boundary lines between the pre-foamed layer 120 and the second non-foamed layer 112 are represented by dashed lines, but these are not lines that indicate clear boundaries, but merely schematic representations of the approximate boundary locations.

[0065] In the foamed preform according to this embodiment, the particle size distribution based on the number of spherical foam cells 102 includes morphs in which the mode diameter is larger than the average diameter. A mode diameter larger than the average diameter means that there are many spherical foam cells 102 that have grown to have a large particle size. The average diameter is the number-average particle diameter obtained in the measurement of the particle size distribution described above. The value of the mode diameter is preferably 5% to 35% of the value of the average diameter, and more preferably 7% to 34%.

[0066] In the particle size distribution of the spherical foam cells 102 based on the number of cells, the standard deviation is preferably 10 to 15 μm, and more preferably 11 to 12 μm.

[0067] The method for manufacturing the foam 1 according to this embodiment includes the steps of: preparing a bottomed cylindrical non-foaming preform which is a molded article of a molding material containing a thermoplastic resin, is impregnated with an inert gas, and is in a non-foaming state; a foaming step to convert the non-foaming preform into a foaming preform; and a blow molding step to blow mold the foaming preform into a foam, wherein the foaming step includes a heating step to obtain an intermediate by heating the non-foaming preform from the outer surface side; and conducting the heat that is unevenly distributed on the outer surface side of the intermediate after the heating step to the inner surface side. The blow molding process includes a waiting step to reduce the temperature difference, and the blow molding process is a process to form a foam 1 having a first non-foamed layer 11 and a foamed layer 20 as shown in Figures 1 to 3, wherein the foamed layer 20 includes a first foamed layer 21 having a plurality of bubbles 2 arranged in three dimensions and a bubble wall skeleton 4 that separates adjacent bubbles 2, and the first foamed layer 21 has a mesh-like bubble structure 5 in which the bubble wall skeleton 4 has a mesh-like cross-section, and the mesh-like bubble structure 5 includes continuous bubbles in which adjacent bubbles 2 communicate with each other through openings 6 provided in the bubble wall skeleton 4.

[0068] The preparation step is to prepare a non-foaming preform. The non-foaming preform is essentially in a non-foaming state. The method for manufacturing the non-foaming preform is not particularly limited, but preferably includes the steps of: heating the molding material to form a resin molten material; impregnating the resin molten material with an inert gas; filling the resin molten material impregnated with the inert gas into a molding die; and performing injection molding while applying pressure to the resin molten material in the molding die and maintaining the pressure. The inert gas is not particularly limited, and may be nitrogen gas or carbon dioxide gas. If a non-foaming preform has already been prepared as a preform impregnated with an inert gas, it may be obtained and used. The method for impregnating the resin molten material with an inert gas is not particularly limited, and may be a method of injecting an inert gas as a supercritical fluid into the resin molten material under high pressure to dissolve it, or a method of adjusting the filling rate of the resin molten material and supplying the inert gas into the cylinder at a low pressure below the cylinder pressure to dissolve it. In the latter method, the amount of gas dissolved can be brought close to the saturation concentration, and a foaming state similar to that of the former method can be obtained even at a low supply pressure.

[0069] The foaming process is a process of expanding an inert gas impregnated inside the non-foaming preform to form spherical foam cells 102. The foaming process includes a heating process to obtain an intermediate by heating the non-foaming preform from the outer surface side, and a waiting process to reduce the temperature difference between the outer and inner surfaces of the intermediate by conducting the heat that is unevenly distributed on the outer surface side of the intermediate to the inner surface side after the heating process.

[0070] The heating step preferably involves heating to a temperature above the glass transition point of the thermoplastic resin contained in the molding material. For example, if the thermoplastic resin is PET, the heating temperature is preferably 90 to 130°C, and more preferably 100 to 120°C. Here, the heating temperature is the temperature of the outer surface of the non-foamed preform or intermediate. The heating time is not particularly limited, but is preferably 5 to 20 seconds, and more preferably 10 to 15 seconds. The intermediate is a foamed preform precursor before the waiting step after the heating step.

[0071] The waiting step is a process in which heat that was unevenly distributed on the outer surface side of the intermediate during the heating step is transferred to the inner surface side by heat conduction. This allows spherical foam cells to grow sufficiently throughout the thickness direction of the foamed preform, resulting in a broad particle size distribution of spherical foam cells not only on the side closer to the outer surface of the foamed preform but also on the side closer to the inner surface. It is preferable not to apply heat during the waiting step, but the waiting step may be performed while residual heat from the heating step remains, or with some heat applied. Residual heat or some heat application slows down the rate at which the outer surface temperature of the preform decreases. By transferring heat to the inner surface of the preform through the waiting step, the stability of the stretch molding can be further enhanced. The waiting time in the waiting step is not particularly limited, but is preferably 5 to 20 seconds, and more preferably 10 to 15 seconds.

[0072] In the foam manufacturing method according to this embodiment, the foaming process is preferably a process in which one cycle consists of a heating process and a waiting process, and one cycle is performed two or more times. By dividing the heating process and the waiting process into multiple steps, bubbles can be grown throughout the entire thickness direction of the intermediate, and the difference in bubble size between the side closer to the outer surface and the side closer to the inner surface of the intermediate can be made smaller. By dividing one cycle of the heating process and the waiting process into two or more steps, deformation due to softening of the foamed preform can be prevented, the temperature difference between the outer and inner surfaces of the foamed preform can be reduced in a short time, foaming can be promoted, and the particle size distribution of spherical foam cells can be made broad over a wide area in the thickness direction of the preform. In addition, by conducting the heat applied to the outer surface of the preform to the inner surface, the stability of the stretch moldability can be increased and whitening can be suppressed. When one cycle is performed two or more times, the heating temperature and heating time of each heating process may be the same or different from each other, and the temperature and waiting time of each waiting process may be the same or different from each other. When performing one cycle more than once, it is preferable to shorten the waiting time with each subsequent cycle. This promotes foaming while further improving the stability of the stretch molding process.

[0073] When performing a heating and waiting cycle only once, it is preferable to heat the intermediate while cooling its outer surface with air. This prevents whitening and allows heat to be transferred from the outer surface to the inner surface, resulting in more uniform heating of both the outer and inner surfaces.

[0074] In the foam manufacturing method according to this embodiment, the foaming step includes a foam preform 100 having a first non-foamed layer 111 and a pre-foamed layer 120, as shown in Figure 5. The pre-foamed layer 120 is a step in which a foam preform having a plurality of spherical foam cells 102 is formed, as shown in Figure 6. Preferably, the particle size distribution based on the number of spherical foam cells 102 has a distribution width of 52 μm or more and a mode diameter of 49 to 62 μm. This facilitates the formation of open cells 2a in the first foam layer 21 in the resulting foam 1. Furthermore, the resulting foam preform may further have a second non-foamed layer 112, as shown in Figure 5.

[0075] The blow molding process can be carried out by known methods. The foam obtained by blow molding the foamed preform that has undergone the foaming process described above comprises a first foamed layer having a mesh-like cellular structure as shown in Figure 3.

[0076] Conventionally, after heating in the foaming process, blow molding is performed without a waiting period. When blow molding is performed without a waiting period after heating, the spherical foam cells of the preform do not grow sufficiently, and the blow-molded preform has multiple spherical cells with substantially uniform particle sizes, i.e., a sharp particle size distribution. As a result, the resulting foam has a foam layer without air bubbles, and the desired light-shielding performance cannot be obtained. In contrast, in the manufacturing method of foam 1 according to this embodiment, a waiting period is provided after heating in the foaming process, allowing the spherical foam cells to grow throughout the entire thickness direction of the preform. More specifically, in the waiting period, as shown in Figure 6, it is presumed that while the previously generated spherical foam cells grow significantly, new spherical foam cells are generated and grow from the gaps between these grown spherical foam cells, and a preform with a broad particle size distribution is produced by this mechanism. When such a preform is blow-molded, a foam layer with air bubbles is formed, and the light-shielding performance of foam 1 can be made very high. [Examples]

[0077] Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified. Note that the number of added parts is the value on a solid content basis.

[0078] (Example 1) A closed-bottom cylindrical non-foaming preform was prepared using PET resin (intrinsic viscosity: 0.76 dl / g) and impregnated with nitrogen gas in a nearly saturated state, but without foaming. The non-foaming preform was heated using an infrared heater at 100-120°C for 18 seconds (first heating step), and then left unheated for 10 seconds to obtain an intermediate (first waiting step). Next, the obtained intermediate was heated using an infrared heater at 100-120°C for 18 seconds (second heating step), and then left unheated for 3 seconds to obtain a foamed preform (second waiting step). Finally, the obtained foamed preform was blow-molded to obtain a foamed bottle with a capacity of 500 ml.

[0079] (Comparative Example 1) A non-foaming preform similar to that in Example 1 was heated to 100-120°C for 18 seconds using an infrared heater to create a foamed preform, which was then immediately blow-molded to obtain a foamed bottle with a capacity of 500 ml.

[0080] (Cross-sectional observation of foamed preform) For the foamed preforms of Example 1 and Comparative Example 1, the position at the vertical center of the molded bottle was observed in cross-section at 200x magnification using an optical microscope (model: Eclipse LV100ND, Nikon Corporation) to measure the particle size distribution of the spherical foam cells. In Example 1, the distribution width was 75 μm, the mode diameter was 55 μm, and the average diameter was 46 μm. In Comparative Example 1, the distribution width was 40 μm, the mode diameter was 40 μm, and the average diameter was 40 μm.

[0081] (Observation of the appearance of the foam bottle) The appearance of the foam bottles from Example 1 and Comparative Example 1 was compared. As a result, the foam bottle from Example 1 was white, while the foam bottle from Comparative Example 1 was grayish in color. Furthermore, when a region including the center in the vertical direction of the foam bottle was cut out and held up to the light, Example 1 transmitted less light than Comparative Example 1.

[0082] (L * a * b * (Measurement of chromaticity coordinates in color space) For the foamed bottle of Example 1, a spectrophotometer / colorimeter (PF-7000, manufactured by Nippon Denshoku Industries Co., Ltd.) was used to measure L * a * b * The chromaticity coordinates and D65 whiteness in the color space were measured. The measurement position was the vertical center of the bottle, and measurements were taken at three locations. As a result, on the outer surface of the bottle, L * The values ​​were 87.14, 86.83, and 87.05 respectively, and the mean was 87.00. * The values ​​were -0.23, -0.25, and -0.25 respectively, and the mean was -0.24, b * The values ​​were -1.09, -1.19, and -1.17 respectively, with an average of -1.15. The D65 whiteness values ​​were 71.55, 71.03, and 71.45 respectively, with an average of 71.34. On the inner surface of the bottle, L * The values ​​were 73.17, 72.92, and 73.44 respectively, and the mean was 73.18. * The values ​​were -0.18, -0.18, and -0.17 respectively, and the mean was -0.18, b * The values ​​were -0.34, -0.34, and -0.39 respectively, with an average of -0.36. The D65 whiteness values ​​were 45.76, 45.38, and 46.21 respectively, with an average of 45.78.

[0083] (reflectance) The reflectance of the foamed bottle of Example 1 was measured using an ultraviolet-visible-near-infrared spectrophotometer (UH4150, Hitachi High-Tech Corporation). Measurements were taken at three locations, at the vertical center of the bottle. As a result, throughout the entire measurement area, the reflectance of the outer surface of the bottle was the same as or greater than the reflectance of the inner surface of the bottle, and was within 20% of the reflectance of the inner surface of the bottle. The measurement conditions were as follows: Measurement range: 240~2600nm Measurement method: Reflection method Reference: Standard whiteboard made of aluminum oxide Detectors: Integrating sphere / photomultiplier tube (240-850 nm), Integrating sphere / PbS (850-2600 nm) Detector switching wavelength: 850nm Light source switching wavelength: 340nm Sampling interval: 1.00 nm Scan speed: 300nm / min Slit width: 6.00 nm (fixed)

[0084] (Light transmittance) The light transmittance of the foamed bottle from Example 1 was measured using a spectrophotometer (U-3900, Hitachi High-Tech Corporation). The measurement was taken at one location, in the center of the bottle in the vertical direction. As a result, the light transmittance at a wavelength of 500 nm was 12.9%.

[0085] (Cross-section observation of a foam bottle) For the foamed bottle of Example 1, the cross-section in the thickness direction and the cross-section perpendicular to the thickness direction were observed at a magnification of 22x using an X-ray transmission inspection device (μnRay7600F, manufactured by Matsusada Precision Co., Ltd.). The cross-sectional image in the thickness direction is shown in Figure 7, and the cross-section perpendicular to the thickness direction is shown in Figure 8. In Figure 7, the right side of the paper is the outer surface side of the bottle, and the left side of the paper is the inner surface side of the bottle. As shown in Figure 7, the foamed bottle had a second non-foamed layer on the outer surface side of the bottle and a first non-foamed layer on the inner surface side of the bottle, with a foamed layer between the first non-foamed layer and the second non-foamed layer. The second non-foamed layer was thicker than the first non-foamed layer. As shown in Figures 8(a) and 8(d), the second non-foamed layer and the first non-foamed layer were bubble-free, as shown in Figure 8(b), the first foamed layer had a mesh-like bubble structure, and as shown in Figure 8(c), the second non-foamed layer had a sea-island structure. Furthermore, when a foamed bottle with a capacity of 100 ml was produced as a foamed material using the same method as in Example 1, the cross-sectional state of the foamed bottle with a capacity of 100 ml had the same structure as the foamed bottle in Example 1.

[0086] (Note) Some or all of the above embodiments may also be described as follows, but are not limited to the following. (Note 1) The foam according to the present invention is a foam that is a molded article of a molding material containing a thermoplastic resin, wherein the foam has a first non-foamed layer and a foamed layer, the foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall skeleton that separates adjacent bubbles, the first foamed layer has a mesh-like bubble structure in which the bubble wall skeleton has a mesh-like cross-section, and the mesh-like bubble structure includes open bubbles in which adjacent bubbles communicate with each other through openings provided in the bubble wall skeleton. (Note 2) In the foam according to the present invention, the foam layer further includes a configuration in which a second foam layer having a sea-island structure in which air bubbles are dispersed in a matrix made of the molding material is located between the first non-foamed layer and the first foam layer. (Note 3) The foam according to the present invention further comprises a second non-foamed layer, and it is preferable that the foamed layer is located between the first non-foamed layer and the second non-foamed layer. Smoothness can be ensured on both the front and back surfaces of the foam. (Appendix 4) In the foam according to the present invention, it is preferable that the reticulated bubble structure further includes independent bubbles in which the adjacent bubbles do not communicate with each other. A foam with higher strength can be obtained. (Appendix 5) In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, the surface of the foam on the side opposite to the first non-foamed layer side is CIE1976 L * a * b * When the chromaticity coordinates in the color space are measured, L * The value of is 70 or more and 100 or less, and a * The value of is -1.0 or more and 0 or less, and b * The value of is preferably -2.0 or more and 0 or less. When the foam is used as the outer wall of a container, the light shielding property can be further enhanced. (Appendix 6) In the foam according to the present invention, for the surface of the foam on the first non-foamed layer side and the surface on the side opposite to the first non-foamed layer side, CIE1976 L * a * b * When the chromaticity coordinates in the color space are measured, L of the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of L of the surface on the first non-foamed layer side, or L of the surface on the side opposite to the first non-foamed layer side * The value of is larger than the value of L of the surface on the first non-foamed layer side, and a of the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of a of the surface on the first non-foamed layer side, or a of the surface on the side opposite to the first non-foamed layer side * The value of is smaller than the value of a of the surface on the first non-foamed layer side, and b of the surface on the side opposite to the first non-foamed layer side * The value of is the same as the value of b of the surface on the first non-foamed layer side, or b of the surface on the side opposite to the first non-foamed layer side * The value of is smaller than the value of b of the surface on the first non-foamed layer side, including a form where * The value of is the same as the value of b of the surface on the first non-foamed layer side, or b of the surface on the side opposite to the first non-foamed layer side * The value of is smaller than the value of b of the surface on the first non-foamed layer side * The value of is smaller than the value of b of the surface on the first non-foamed layer side. (Note 7) In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, it is preferable that the D65 whiteness measured on the surface of the foam opposite to the first non-foamed layer side in accordance with ISO 2470-2:2008 is 70 or more. When the foam is used as the outer wall of a container, the light-shielding properties can be further enhanced. (Note 8) In the foam according to the present invention, when the D65 whiteness is measured in accordance with ISO 2470-2:2008 for the surface on the first non-foaming layer side and the surface on the opposite side of the foam, the D65 whiteness value of the surface on the opposite side of the first non-foaming layer is either the same as the D65 whiteness value of the surface on the first non-foaming layer side, or greater than the D65 whiteness value of the surface on the first non-foaming layer side. (Note 9) The foam according to the present invention includes a form in which, when the reflectance is measured in accordance with JIS R 3106:2019 "Test method for transmittance, reflectance, and emissivity of plate glass and method for calculating the solar heat gain coefficient of building plate glass" for the surface of the foam on the side of the first non-foaming layer and the surface on the opposite side of the first non-foaming layer, the reflectance value of the surface on the opposite side of the first non-foaming layer at wavelengths of 240 to 800 nm is the same as the reflectance value of the surface on the side of the first non-foaming layer at wavelengths of 240 to 800 nm, or greater than the reflectance value of the surface on the side of the first non-foaming layer at wavelengths of 240 to 800 nm, and is within the range of 0 to 20% of the reflectance value of the surface on the side of the first non-foaming layer at wavelengths of 240 to 800 nm. (Note 10) In the foam according to the present invention, when the thickness of the foam is 250 μm or more and 450 μm or less, it is preferable that the transmittance of light in the wavelength range of 480 to 500 nm of the foam is 15% or less. When the foam is used as the outer wall of a container, the light-shielding properties can be further enhanced. (Note 11) The foam according to the present invention preferably has a gas barrier film on at least one of the surfaces of the first non-foamed layer side and the surface opposite to the first non-foamed layer side. When the foam is used as the outer wall of a container, deterioration of the contents of the container can be prevented. (Note 12) The foam according to the present invention includes a form in which the thermoplastic resin is polyethylene terephthalate resin and the intrinsic viscosity of the polyethylene terephthalate resin is 0.63 to 0.86 dl / g. (Note 13) The container according to the present invention is characterized by having the foam material according to the present invention as its outer wall. (Note 14) The container according to the present invention includes a configuration in which the first non-foamed layer is arranged on the inner surface side of the container and the foamed layer is arranged on the outer surface side of the container than the first non-foamed layer. (Note 15) The foamed preform according to the present invention is a foamed preform which is a molded product of a molding material containing a thermoplastic resin, wherein the foamed preform has a first non-foamed layer and a pre-foamed layer, the pre-foamed layer has a plurality of spherical foam cells, and the particle size distribution based on the number of spherical foam cells is characterized in that the distribution width is 52 μm or more and the mode diameter is 49 to 62 μm. (Note 16) In the foamed preform according to the present invention, the particle size distribution based on the number of spherical foam cells includes forms in which the mode diameter is larger than the average diameter. (Note 17) The method for producing a foam according to the present invention includes the steps of: preparing a bottomed cylindrical non-foaming preform which is a molded article of a molding material containing a thermoplastic resin, is impregnated with an inert gas, and is in a non-foaming state; foaming the non-foaming preform into a foaming preform; and blow molding the foaming preform into a foam, wherein the foaming step includes a heating step of heating the non-foaming preform from the outer surface side to obtain an intermediate, and after the heating step, heat that is unevenly distributed on the outer surface side of the intermediate is conducted to the inner surface side. The blow molding process includes a waiting step to reduce the temperature difference between the outer surface and the inner surface of the intermediate, and the blow molding process is a process to form a foam having a first non-foamed layer and a foamed layer as the foam, wherein the foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall skeleton that separates adjacent bubbles, and the first foamed layer is characterized in that the bubble wall skeleton has a mesh-like bubble structure having a mesh-like cross-section, and the mesh-like bubble structure includes open bubbles in which adjacent bubbles communicate with each other through openings provided in the bubble wall skeleton. (Note 18) In the foaming method according to the present invention, it is preferable that the foaming step is a process in which the heating step and the waiting step constitute one cycle, and this cycle is performed two or more times. By performing the heating step and the waiting step in multiple steps, bubbles can be grown throughout the entire thickness direction of the intermediate, and the difference in bubble size between the side closer to the outer surface and the side closer to the inner surface of the intermediate can be made smaller. (Note 19) In the foaming method according to the present invention, the foaming step comprises a first non-foamed layer and a pre-foamed layer as the foamed preform, wherein the pre-foamed layer is a step of forming a foamed preform having a plurality of spherical foam cells, and the particle size distribution based on the number of spherical foam cells preferably has a distribution width of 52 μm or more and a mode diameter of 49 to 62 μm. This makes it easier to form open bubbles in the first foam layer in the resulting foam. [Explanation of Symbols]

[0087] 1. Foam 2,2a1,2a2 bubbles 2a Continuous bubbles 2b Closed cells 4. Cell wall skeleton 5. Mesh-like cellular structure 6 aperture 7 Sea-island structure 8 Matrix 11. First non-foaming layer 12. Second non-foaming layer 20 Foam layer 21 First foam layer 100 foam prefoam 102 Spherical foam cells 103 Matrix 111 First non-foaming layer 112 Second non-foaming layer 120 Pre-foamed layer

Claims

1. In a foam, which is a molded product of a molding material containing a thermoplastic resin, The foam has a first non-foamed layer and a foamed layer. The foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall framework that separates adjacent bubbles. The first foamed layer has a mesh-like cellular structure in which the cellular wall framework has a mesh-like cross-section, The foam is characterized in that the mesh-like cellular structure includes open cells through which adjacent cells communicate with each other via openings provided in the cell wall framework.

2. The foam according to claim 1, wherein the foam layer further comprises a second foam layer having a sea-island structure in which air bubbles are dispersed in a matrix made of the molding material, between the first non-foamed layer and the first foam layer.

3. The aforementioned foam further comprises a second non-foaming layer, The foamed body according to claim 1, characterized in that the foamed layer is located between the first non-foamed layer and the second non-foamed layer.

4. The foam according to claim 1, characterized in that the mesh-like cellular structure further includes closed cells in which adjacent cells are not connected to each other.

5. When the thickness of the foam is 250 μm or more and 450 μm or less, the surface of the foam opposite to the first non-foamed layer is treated according to JIS Z 8781-4:2013 and CIE1976 L ＊ a ＊ b ＊ When measuring the chromaticity coordinates in the color space, L ＊ The value of is 70 or more and 100 or less, and a ＊ The value of is -1.0 or greater and 0 or less, and b ＊ The foam according to claim 1, characterized in that the value of is -2.0 or greater and 0 or less.

6. For the surface on the side of the first non-foamed layer of the foam and the surface on the side opposite to the first non-foamed layer side, CIE1976 L ＊ a ＊ b ＊ When measuring the chromaticity coordinates in the color space L on the surface opposite to the first non-foamed layer side ＊ The value of is L of the surface on the first non-foaming layer side. ＊ The same value as the value of the first non-foaming layer side L ＊ Greater than the value, a on the surface opposite to the first non-foamed layer side ＊ The value of is the a of the surface on the first non-foaming layer side. ＊ The same value as the value of the first non-foaming layer side a ＊ Smaller than the value, b on the surface opposite to the first non-foamed layer side ＊ The value of is the b of the surface on the first non-foaming layer side. ＊ The same value as the value of the first non-foaming layer side, or the b of the surface on the first non-foaming layer side. ＊ The foam according to claim 1, characterized in that the value is smaller than the value of .

7. The foam according to claim 1, characterized in that when the thickness of the foam is 250 μm or more and 450 μm or less, the D65 whiteness of the surface of the foam opposite to the first non-foamed layer side, measured in accordance with ISO 2470-2:2008, is 70 or more.

8. When the D65 whiteness was measured on the surface of the foam on the first non-foamed layer side and the surface on the opposite side of the first non-foamed layer side in accordance with ISO 2470-2:2008, The foam according to claim 1, characterized in that the D65 whiteness value of the surface opposite to the first non-foaming layer side is the same as the D65 whiteness value of the surface on the first non-foaming layer side, or is greater than the D65 whiteness value of the surface on the first non-foaming layer side.

9. When the reflectance is measured on the surface of the foam on the first non-foamed layer side and the surface on the opposite side of the first non-foamed layer side in accordance with JIS R 3106:2019 "Test method for transmittance, reflectance, and emissivity of flat glass and method for calculating the solar heat gain coefficient of building flat glass", The foam according to claim 1, characterized in that the reflectance value of the surface opposite to the first non-foaming layer side at wavelengths of 240 to 800 nm is the same as the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm, or greater than the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm, and within the range of 0 to 20% of the reflectance value of the surface on the first non-foaming layer side at wavelengths of 240 to 800 nm.

10. The foam according to claim 1, characterized in that when the thickness of the foam is 250 μm or more and 450 μm or less, the transmittance of light in the wavelength range of 480 to 500 nm of the foam is 15% or less.

11. The foam according to claim 1, characterized in that the foam has a gas barrier film on at least one of the surfaces of the first non-foamed layer side and the surface opposite to the first non-foamed layer side.

12. The thermoplastic resin is polyethylene terephthalate resin. The foam according to claim 1, characterized in that the intrinsic viscosity of the polyethylene terephthalate resin is 0.63 to 0.86 dl / g.

13. A container characterized by having the foam material described in any one of claims 1 to 12 as its outer wall.

14. The container according to claim 13, characterized in that the first non-foaming layer is arranged on the inner surface side of the container, and the foaming layer is arranged on the outer surface side of the container more than the first non-foaming layer.

15. In foamed preforms, which are molded products made from a thermoplastic resin, The foamed preform has a first non-foamed layer and a pre-foamed layer. The pre-foamed layer has a plurality of spherical foam cells, The particle size distribution of the spherical foam cells, based on the number of cells, has a broad particle size distribution with a distribution width of 52 μm or more, and a mode diameter of 49 to 62 μm. The foamed preform is characterized in that the distribution width is the width of the frequency distribution graph of the particle size distribution obtained under the following condition 1. Condition 1: The particle size distribution is determined by measuring the number of spherical foam cells and their individual diameters in an observation image obtained by observing the cross-section of the foamed preform at a magnification of 200x using a reflection microscope.

16. The foamed preform according to claim 15, characterized in that, in the particle size distribution based on the number of spherical foam cells, the mode diameter is larger than the average diameter.

17. A process for preparing a bottomed cylindrical non-foaming preform, which is a molded article of a molding material containing a thermoplastic resin, and is impregnated with an inert gas and in a non-foaming state. A foaming process to convert the aforementioned non-foaming preform into a foamed preform, A blow molding process in which the aforementioned foamed preform is blow-molded to form a foam, Includes, The foaming process includes a heating step of heating the non-foamed preform from the outer surface side to obtain an intermediate, and a waiting step of conducting the heat that is unevenly distributed on the outer surface side of the intermediate to the inner surface side after the heating step to reduce the temperature difference between the outer surface and the inner surface of the intermediate. The blow molding process is a process of forming a foam having a first non-foamed layer and a foamed layer, wherein the foamed layer includes a first foamed layer having a plurality of bubbles arranged in three dimensions and a bubble wall skeleton that separates adjacent bubbles. A method for manufacturing a foam, characterized in that the first foam layer has a mesh-like cell structure in which the cell wall framework has a mesh-like cross-section, and the mesh-like cell structure includes open cells in which adjacent cells communicate with each other through openings provided in the cell wall framework.

18. The method for producing a foam according to claim 17, characterized in that the foaming step is a step in which the heating step and the waiting step constitute one cycle, and the cycle is performed two or more times.

19. The foaming process comprises a foamed preform having a first non-foamed layer and a pre-foamed layer, wherein the pre-foamed layer forms a foamed preform having a plurality of spherical foam cells. The particle size distribution of the aforementioned spherical foam cells, based on the number of cells, has a broad particle size distribution with a distribution width of 52 μm or more, and a mode diameter of 49 to 62 μm. The method for producing foam according to claim 17 or 18, characterized in that the distribution width is the width of the frequency distribution graph of the particle size distribution obtained under the following condition 1. Condition 1: The particle size distribution is determined by measuring the number of spherical foam cells and their individual diameters in an observation image obtained by observing the cross-section of the foamed preform at a magnification of 200x using a reflection microscope.

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