Sheets and containers

Abstract

To provide a foamed container with improved heat resistance and cold resistance. [Solution] A foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the absolute value of the heat of crystallization of the foamed layer is less than 1.0 mJ / mg, the number of bubbles in the thickness direction of the foamed layer is 20 to 50, and the proportion of molecules with a differential molecular weight of 500,000 or more in the foamed layer is 1.0% by mass to 10.0% by mass relative to the total mass of the foamed layer.

Description

Technical Field

[0001] The present invention relates to a sheet and a container.

Background Art

[0002] Foamed sheets and containers made of thermoplastic polyester resins have excellent heat resistance and cold resistance and are easy to mold, so they are widely used for containers for foods that are cooked by heating or stored frozen.

[0003] For example, Patent Document 1 describes a thermoplastic polyester resin foamed sheet and container having excellent deep drawing formability, and Patent Document 2 describes a thermoplastic polyester resin foamed sheet that can obtain a sharp shape faithful to the mold.

[0004] Furthermore, for example, Patent Document 3 describes a foamed resin container excellent in heat resistance and low-temperature brittleness by adjusting the heat of crystallization and the degree of crystallinity within a certain range according to the molding conditions of the foamed sheet.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the case of the container described in Patent Document 1, it is stated that a thermoplastic polyester resin foam sheet with excellent deep-draw moldability can be obtained by having a Z-average molecular weight of 250,000 to 800,000 of the thermoplastic polyester resin. In the case of the thermoplastic polyester resin foam sheet described in Patent Document 2, it is stated that if the ratio of the length in the long direction to the short direction of the bubbles is 1 to 4, a sharp shape that is faithful to the mold can be obtained. However, both Patent Documents 1 and 2 are simple shapes such as cylindrical cups, and it has been difficult to manufacture foam containers with accurate shapes such as those with partitions in the container body of a bento box or complex container body shapes that can be fitted with a lid.

[0007] Therefore, the present invention aims to solve the above problems and, in part, to accurately form specific shapes by improving the uniformity of the bubbles in foamed sheets and foamed containers.

[0008] Furthermore, in the case of the foamed resin container described in Patent Document 3, the heat resistance and low-temperature brittleness of the foamed resin container are improved by adjusting the molding conditions of the foamed sheet. However, no measures are taken to improve the heat resistance and cold resistance of the foamed sheet itself, and there are limitations to improving heat resistance and low-temperature brittleness by simply adjusting the molding conditions of the foamed sheet.

[0009] Therefore, the present invention aims to solve the above problems and, in part, to improve the heat resistance and cold resistance of foamed containers. [Means for solving the problem]

[0010] According to one embodiment of the present invention, a foamed sheet is provided having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

[0011] According to one embodiment of the present invention, a foamed sheet is provided having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

[0012] According to one embodiment of the present invention, a foamed sheet is provided having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, the proportion of molecules with a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles per 1 mm thickness of the foamed layer is 10 or more and 30 or less.

[0013] In the foamed sheet described above, the air bubbles in the foamed layer may be uniform.

[0014] In the foamed sheet described above, the degree of dispersion Mw / Mn of the thermoplastic polyester resin may be 5 or more and 20 or less.

[0015] In the foamed sheet described above, the specific gravity of the foamed layer may be 0.05 or more and 0.30 or less.

[0016] In the foamed sheet described above, the foamed layer may further contain a crosslinking agent and a nucleating agent.

[0017] In the foamed sheet described above, the foamed layer may further contain 0.1% to 6.0% by weight of polyolefin resin.

[0018] In the foamed sheet described above, the 50% fracture energy in terms of impact strength from a falling ball may be 1.0 J or more.

[0019] In one embodiment of the present invention, there is a foamed layer containing a thermoplastic polyester resin, the weight average molecular weight Mw of the foamed layer is 80,000 or more, and the ratio of the molecules having a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less with respect to the total mass of the foamed layer, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less, and a foamed container is provided.

[0020] In one embodiment of the present invention, there is a foamed layer containing a thermoplastic polyester resin, the weight average molecular weight Mw of the foamed layer is 80,000 or more, and the ratio of the molecules having a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less with respect to the total mass of the foamed layer, and the ratio of the molecules having a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less with respect to the total mass of the foamed layer, and the number of bubbles per 1 mm thickness of the foamed layer is 10 or more and 30 or less, and a foamed container is provided.

[0021] According to one embodiment of the present invention, there is a foamed layer containing a thermoplastic polyester resin, the absolute value of the heat of crystallization of the foamed layer is less than 1.0 mJ / mg, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less, and a foamed container is provided.

[0022] According to one embodiment of the present invention, there is a foamed layer containing a thermoplastic polyester resin, the absolute value of the heat of crystallization of the foamed layer is less than 1.0 mJ / mg, and the number of bubbles per 1 mm thickness of the foamed layer is 10 or more and 30 or less, and a foamed container is provided.

[0023] In the above foamed container, the bubbles in the foamed layer may be uniform.

[0024] In the above foamed container, the temperature drop crystallization temperature of the foamed layer may be 185°C or more and 200°C or less.

[0025] In the above foamed container, the ratio of the molecules having a differential molecular weight of 500,000 or less in the foamed layer may be 1.0% by mass or more and 10.0% by mass or less with respect to the total mass of the foamed layer.

[0026] In the foamed container described above, the degree of crystallinity of the foamed layer, as measured by wide-angle X-ray diffraction, may be 25% or more. [Effects of the Invention]

[0027] By using one embodiment of the present invention, the uniformity of the bubbles in the foamed sheet and foamed container can be improved, thereby enabling the precise shaping of a specific form. Furthermore, by using one embodiment of the present invention, the heat resistance and cold resistance of the foamed container can be improved. [Brief explanation of the drawing]

[0028] [Figure 1] This is a perspective view of a foamed container according to one embodiment of the present invention. [Figure 2] This is a perspective view of a foamed container according to one embodiment of the present invention. [Figure 3] This is an SEM image of a cross-section of the foamed sheet of the present invention. [Figure 4] This is an SEM image of a cross-section of the foamed sheet of the present invention. [Figure 5] This is a flowchart showing a method for manufacturing a foamed sheet according to one embodiment of the present invention. [Figure 6] This is a flowchart showing a method for manufacturing a foamed container according to one embodiment of the present invention. [Modes for carrying out the invention]

[0029] The embodiments of the invention disclosed in this application will be described below with reference to the drawings. However, the present invention can be implemented in various forms without departing from its essence, and is not to be construed as being limited to the embodiments described below.

[0030] <First Embodiment> The foamed sheet according to the present invention will now be described.

[0031] (Foam sheet) The foamed sheet of the present invention has a foamed layer containing a thermoplastic polyester resin. In addition to the foamed layer, the foamed sheet may also have a film layer on top of it. The thickness of the foamed sheet is preferably 1.0 mm or more and 4.0 mm or less.

[0032] (Foam layer) The foamed layer contains a thermoplastic polyester resin and has multiple air bubbles. The thickness of the foamed layer is preferably between 1.0 mm and 4.0 mm.

[0033] The number of bubbles in the thickness direction of the foamed layer is between 20 and 50. Foamed layers with a bubble count within this range have high heat and cold resistance due to the large number of bubbles. Here, the number of bubbles in the thickness direction refers to the number of bubbles that at least partially overlap a straight line drawn in the thickness direction in a cross-sectional image obtained by cutting a foamed sheet in the thickness direction and observing the cross-section of the cut foamed sheet with a scanning electron microscope or the like.

[0034] The number of bubbles per 1 mm thickness of the foam layer is between 10 and 30. Foam layers with a bubble count within this range have high heat and cold resistance due to the large number of bubbles. Here, the number of bubbles per 1 mm thickness of the foam layer is the value obtained by dividing the number of bubbles that at least partially overlap a straight line drawn in the thickness direction in a cross-sectional image of a cross-section of a foam sheet cut in the thickness direction, observed with a scanning electron microscope, by the length (thickness) of the straight line in millimeters.

[0035] A uniform foam layer is defined as a cross-sectional image obtained by cutting a foam sheet in the thickness direction and observing the cross-section of the sheet with a scanning electron microscope, similar to measuring the number of bubbles. This image shows that at least a portion of the bubbles overlap a straight line drawn in the thickness direction, indicating uniformity. The diameter size of the bubbles in the long and short directions is measured, and the closer the maximum diameter size / minimum diameter size value is to 1, the more uniform the layer is, with 3.5 or less being preferable. The more uniform the size of the bubbles, the stronger the impact strength, and the better the cold resistance and shape retention.

[0036] Thermoplastic polyester resin refers to a thermoplastic resin having ester bonds, obtained by polycondensation of a polybasic acid and a polyhydric alcohol, and examples include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. The thermoplastic polyester resin is present in an amount of 90% by mass or more, preferably 95% by mass or more, relative to the foam layer.

[0037] The weight-average molecular weight Mw of the thermoplastic polyester resin is 80,000 or more. Preferably, the weight-average molecular weight Mw of the thermoplastic polyester resin is 90,000 to 250,000, and more preferably 100,000 to 200,000. A foamed layer containing a thermoplastic polyester resin with a weight-average molecular weight Mw in the above range or greater has high viscosity and can generate and maintain many bubbles when heated.

[0038] The proportion of molecules with a differential molecular weight of 10,000 or less in the thermoplastic polyester resin is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the thermoplastic polyester resin, preferably 7.0% by mass or more and 10.0% by mass or less. The proportion of molecules with a differential molecular weight of 500,000 or less in the thermoplastic polyester resin is 1% by mass or more and 10% by mass or less relative to the total mass of the thermoplastic polyester resin, preferably 4.0% by mass or more and 8.0% by mass or less. When the proportion of molecules with differential molecular weights in the thermoplastic polyester resin relative to the total mass of the thermoplastic polyester resin is within the above range, the foamed layer containing the thermoplastic polyester resin has high viscosity and can generate and maintain many bubbles when heated.

[0039] The dispersion degree Mw / Mn of the thermoplastic polyester resin is preferably 5.0 to 20.0, and more preferably 7.0 to 15.0. A foamed layer containing a thermoplastic polyester resin with a dispersion degree Mw / Mn within the above range has high viscosity, generates many bubbles when heated, and can maintain those bubbles.

[0040] The weight-average molecular weight (Mw) and differential molecular weight of thermoplastic polyester resins can be measured according to the GPC (Gel Permeation Chromatography) method. Specifically, a sample of foamed sheet or foamed container was weighed into a 30 ml vial, dissolved in 1.0 ml of HFIP / chloroform mixed solvent (mixing ratio 1 / 1) per 5.0 mg, and then diluted with 9.0 ml of chloroform. This solution was filtered through a 0.50 μm PTFE disposable membrane filter unit, and the filtrate was used for measurement. (Measurement conditions) Column / Temperature: 3×PLgel10μ MIXED-B, 7.5×300mm (Agilent Technologies) / 40℃ Mobile phase: Chloroform for HPLC (Fujifilm Wako Pure Chemical Industries) Flow rate: 1.0mL / min Injection volume: 15μL Detector: 254nm (UV-Vis detector) Column calibration: Monodisperse PS (EasiCal Type PS-1 Polystyrene: Agilent Technologies) Molecular weight calibration: Relative calibration method (PS equivalent) Equipment: KP-22-13S Dual Pump (FROM), 717plus Automatic Injector, 2487 UV-Vis Detector (Waters Japan)

[0041] The foamed layer may contain any additives in addition to the thermoplastic polyester resin. For example, the foamed layer may contain a crosslinking agent and a nucleating agent. The foamed layer may contain polyolefins. The foamed layer may contain a blowing agent.

[0042] Examples of crosslinking agents include dianhydrides such as pyromellitic anhydride, polyfunctional epoxy compounds, oxazoline compounds, and oxazine compounds. The crosslinking agent content is 0.1% to 5.0% by mass, preferably 0.2% to 2.0% by mass, relative to the foamed layer. By including a crosslinking agent in the foamed layer, the molecular weight of the thermoplastic polyester resin can be increased, and the viscosity of the foamed layer can be improved.

[0043] Organic crystalline nucleating agents and inorganic crystalline nucleating agents can be used as nucleating agents. It is preferable to use organic crystalline nucleating agents. Examples of organic crystalline nucleating agents include polyether ether ketone. Examples of inorganic crystalline nucleating agents include talc. The nucleating agent content is 0.1% by mass or more and 2.0% by mass or less, preferably 0.2% by mass or more and 1.0% by mass or less, relative to the foamed layer. By incorporating the nucleating agent within the above range into the foamed layer, the number and size of bubbles can be easily controlled.

[0044] Examples of polyolefins include polyethylene and polypropylene. The polyolefin content is 0.1% by mass or more and 6.0% by mass or less, preferably 0.5% by mass or more and 2.5% by mass or less, relative to the foamed layer. By including polyolefin in the foamed layer within the above range, the viscosity of the thermoplastic polyester resin can be brought within the above preferred range, and the number of bubbles can be improved.

[0045] Examples of blowing agents include hydrocarbons such as carbon dioxide, propane, butane, and pentane. Two or more blowing agents may be used in mixture form. For example, carbon dioxide and butane can be mixed in any proportion, and the resulting mixture of blowing agents can be injected into a thermoplastic polyester resin.

[0046] (Method of manufacturing foamed sheets) A method for manufacturing a foamed sheet according to the present invention will be explained with reference to Figure 5. Figure 5 is a flowchart showing a method for manufacturing a foamed sheet according to one embodiment of the present invention.

[0047] The method for producing a foamed sheet according to the present invention is a method of extruding and foaming a molten mixture obtained by melt-kneading a thermoplastic polyester resin and an optional additive. The following production methods can be used as the method for producing a foamed sheet containing a thermoplastic polyester resin.

[0048] In step 100 (S100), a mixture of thermoplastic polyester resin and an optional additive is supplied to an extruder and melt-kneaded. In step 102 (S102), the melt-kneaded mixture is extruded and foamed through a die attached to the tip of the extruder. In step 104 (S104), the extruded foam is taken up by a take-up machine and expanded and molded on a mandrel attached to the die. At this time, the foam is molded while being cooled by surface cooling. In step 106 (S106), the molded foam is divided into two and wound into a sheet by a winding machine to become a foamed sheet. Dividing the foam into two includes cutting a part of the foam and opening the cut part, or cutting the foam into two or more pieces.

[0049] The extruder can be a single extruder or a tandem extruder consisting of multiple extruders connected in series. The extruder can be a single-screw or twin-screw extruder. When using a tandem extruder, single-screw or twin-screw extruders can be used for the first and second stages. Alternatively, when using a tandem extruder, a twin-screw extruder can be used for the first stage and a single-screw extruder for the second stage. Alternatively, the reverse combination may be used for a tandem extruder.

[0050] Large-diameter screws can be used in the extruder. When using a tandem extruder, the first and second stage extruders can use screws of the same diameter or different diameters. When using screws of different diameters, for example, a small-diameter screw can be used in the first stage extruder, and a larger-diameter screw than that of the first stage extruder can be used in the second stage extruder. Alternatively, the reverse combination may be used in a tandem extruder.

[0051] Extruders can use screws with long shafts. When using a tandem extruder, the first and second stage extruders can use screws with shafts of the same length or screws with shafts of different lengths. When using screws with shafts of different lengths, for example, the first stage extruder can use a screw with a long shaft, and the second stage extruder can use a screw with a shaft even longer than the screw of the first stage extruder. Alternatively, the reverse combination may be used in a tandem extruder.

[0052] In an extruder, the screw rotation speed can be set to a low speed. Specifically, the screw rotation speed can be set to 10 to 200 rpm. When using a tandem extruder, the screw rotation speed of the first stage extruder can be set to a high speed, and the screw rotation speed of the first stage extruder of the second stage can be set to a lower speed than that of the first stage extruder. In the case of a twin-screw extruder, the direction of screw rotation can be the same or different. For example, when extruding foam at low shear, the screws can be rotated in the same direction in a meshing type configuration, and when extruding foam at high shear, the screws can be rotated in different directions in a non-meshing type configuration.

[0053] In an extruder, the temperature of the cylinder housing the screw can be set to a high temperature. Specifically, the temperature of the cylinder housing the screw can be set to 240°C to 290°C. When using a tandem extruder, the cylinders of the first and second stage extruders can be set to the same high temperature or to different temperatures. When setting different temperatures, for example, the cylinder of the first stage extruder can be set to a certain high temperature, and the cylinder of the second stage extruder can be set to a high temperature but lower than the cylinder of the first stage extruder. Specifically, the cylinder of the first stage extruder can be set to 280°C to 290°C, and the cylinder of the second stage extruder can be set to 240°C to 260°C. The reverse combination of temperatures may be set for the cylinders of a tandem extruder.

[0054] In this embodiment, the foamed sheet has a foamed layer containing a thermoplastic polyester resin with a weight-average molecular weight Mw of 80,000 or more, and the ratio of molecules with a differential molecular weight of 10,000 or less and molecules with a differential molecular weight of 500,000 or less in the foamed layer is as described above, and the number of bubbles in the thickness direction of the foamed layer is 20 to 50, thereby improving the uniformity of the bubbles in the foamed sheet.

[0055] <Second Embodiment> The foamed container according to the present invention will now be described. Descriptions of configurations similar to or identical to those described in the first embodiment may be omitted.

[0056] (Foam container 100) The foamed container 100 can be used to heat and cook or freeze food. The foamed container 100 may have a partitioned shape. Figure 1 is a schematic perspective view of the foamed container 100 according to this embodiment.

[0057] The foamed container of the present invention has a foamed layer containing a thermoplastic polyester resin.

[0058] The foamed container 100 of the present invention includes a flange portion 110, a side portion 120, and a bottom portion 130, as shown in Figure 1. The flange portion 110 is provided on the upper periphery of the foamed container 100. The side portion 120 is provided adjacent to the inside of the flange portion 110. The side portion 120 is provided at an angle in cross-sectional view. The bottom portion 130 is provided inside the side portion 120. The bottom portion 130 is provided in the area surrounded by the flange portion 110 and the side portion 120 in a top view. The bottom portion 130 is provided with dividers 140 for storing multiple contents. The dividers 140 shown in Figure 1 are merely examples, and these dividers 140 may be changed depending on the type of contents and the size of the container.

[0059] (Foam container 200) The foamed container 200 of the present invention may have an internal fitting shape. Figure 2 is a schematic perspective view of the foamed container 200 according to this embodiment.

[0060] The foamed container 200 of the present invention includes a flange portion 110, a side portion 120, and a bottom portion 130, as shown in Figure 2. The flange portion 110 is provided on the upper periphery of the foamed container. The side portion 120 is provided adjacent to the inside of the flange portion 110. The side portion 120 is provided at an inclination in cross-sectional view, and a stepped portion 150 is provided on the flange portion 110 side for fitting with a lid (not shown). The bottom portion 130 is provided inside the side portion 120. The bottom portion 130 is provided in the region surrounded by the flange portion 110 and the side portion 120 in a top view.

[0061] (Method of manufacturing foam containers) The method for manufacturing a foamed container according to the present invention will be explained with reference to Figure 6. Figure 6 is a flowchart showing the method for manufacturing a foamed container according to one embodiment of the present invention.

[0062] The foamed container of the present invention includes the steps of heating a foamed sheet and heat-molding it by sandwiching it in a mold. In step 200 (S200), the foamed sheet is heated to 130°C to 210°C. In step 202 (S202), the mold is heated to 15 to 70°C. In step 204 (S204), the foamed sheet is sandwiched in the mold and cooled for 10 to 60 seconds. In step 206 (S206), the heat-molded foamed sheet is released from the mold. For example, a mold for a foamed container as shown in Figure 1 can be used as the mold.

[0063] In this embodiment as well, the same effects as in the first embodiment can be achieved. That is, a foamed container with uniform bubbles can be provided.

[0064] <Third Embodiment> The foamed container according to the present invention will now be described. Configurations that are the same as or similar to those described in the first and second embodiments may be omitted from the description.

[0065] The foamed container of the present invention has a foamed layer containing a thermoplastic polyester resin.

[0066] (Foam layer) The absolute value of the heat of crystallization of the thermoplastic polyester resin is preferably less than 1.0 mJ / mg. By including the number of bubbles within the above range in the foamed layer and keeping the absolute value of the heat of crystallization of the thermoplastic polyester resin less than 1.0 mJ / mg, the heat resistance and cold resistance of the foamed container can be improved.

[0067] The cooling crystallization temperature of the thermoplastic polyester resin is preferably 185°C to 200°C. By including the number of bubbles in the foamed layer within the above range and setting the cooling crystallization temperature of the thermoplastic polyester resin within the above range, the heat resistance and cold resistance of the foamed container can be improved.

[0068] The absolute value of the heat of crystallization and the cooling crystallization temperature of thermoplastic polyester resin can be measured according to differential scanning calorimetry (DSC) and determined based on the obtained DSC curve. Specifically, a test piece of the foamed layer is cut from a foamed container and heated at a heating rate of 10°C / min in the temperature range of 30 to 290°C, and then cooled at a cooling rate of 10°C / min. The heat of crystallization can be determined from the exothermic peak during heating in the obtained DSC curve, and the cooling crystallization temperature can be determined from the exothermic peak during cooling.

[0069] The degree of crystallinity of the foamed layer is preferably 25% or higher, and more preferably 30% to 45%, as measured by wide-angle X-ray diffraction. By setting the degree of crystallinity of the foamed layer within the above range, the heat resistance and cold resistance of the foamed container can be improved.

[0070] The crystallinity of the foam layer was measured according to wide-angle X-ray diffraction (XRD). Specifically, using an X-ray diffraction analyzer, a 10 mm x 10 mm test specimen of the foam layer was cut from the foam container shown in Figure 2. The test specimen was fixed in a sample holder, and the XRD profile was measured by transmission while rotating the holder. The equipment and conditions used for the measurement are as follows. Equipment: Spectris Empyrean X-ray source:CuKα Output: 45kV 40mA Scanning range: 2θ = 5° to 35° Scanning speed: 0.5° / min Step width: 0.026° Detector: PIXcel 3D The degree of crystallinity can be calculated from the obtained profile using the following formula. Crystallinity % = Crystalline peak area / (Crystalline peak area + Amorphous halo area) × 100

[0071] The foamed container 100 of the present invention, by having the foamed layer of the present invention, can form a partition 140 that can separate the contents.

[0072] The foamed container 200 of the present invention, by having the foamed layer of the present invention, can form a stepped portion 150 for internal fitting.

[0073] (Method of manufacturing foam containers) The method for manufacturing a foamed container according to the present invention will be explained again with reference to Figure 6.

[0074] The foamed container of the present invention includes the steps of heating a foamed sheet and heat-molding it by sandwiching it in a mold. In step 200 (S200), the foamed sheet is heated to 130°C to 210°C. In step 202 (S202), the mold is heated to 130°C to 210°C. In step 204 (S204), the foamed sheet is sandwiched in the mold and heated and held for 10 to 60 seconds. The heating and holding time for the foamed sheet is preferably 30 to 45 seconds. By heating the foamed sheet in a mold heated to 130 to 210°C, the crystallization of the thermoplastic polyester resin progresses, and the thermoplastic polyester resin reaches the absolute value of the heat of crystallization and the cooling crystallization temperature described above. In step 206 (S206), the heat-molded foamed sheet is released from the mold. For example, a mold for a foamed container as shown in Figure 1 can be used as the mold.

[0075] In this embodiment as well, the same effects as in the first and second embodiments can be achieved. In other words, a foamed container with uniform bubbles can be provided. [Examples]

[0076] The following describes a foamed container manufactured based on one embodiment of the present invention. This embodiment is not limited to the present invention. The raw materials used in this embodiment are shown below.

[0077] (Foam sheet 1) Copolymerized polyethylene terephthalate with an IV of 0.80 was used as the thermoplastic polyester resin, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as the polyolefin, all mixed in a weight ratio of 96.5:1.0:0.5:2. The resulting mixture was supplied at a rate of 220 kg / h to a first-stage extruder set to a cylinder temperature of 280°C to 290°C and melt-kneaded. Next, the melt-kneaded mixture was supplied to a second-stage extruder set to a cylinder temperature of 240°C to 260°C and melt-kneaded while injecting a mixed gas of butane and carbon dioxide, which was used as a blowing agent, into the mixture. The melt-kneaded mixture from the second-stage extruder was extruded and foamed at low shear through a die attached to the tip of the second-stage extruder. The extruded foam was taken up by a take-up machine and expanded and molded on a mandrel attached to the die. At this time, the foam was air-cooled by surface cooling. The expanded and molded foam was divided into two parts and wound into a sheet using a winding machine to obtain a foam sheet with a thickness of 2.0 mm.

[0078] (Foam container 1) (Example 1) The obtained foamed sheet was heated to 130°C to 210°C and placed in a mold for 10 seconds to obtain foamed containers with the partition shape for the container body of a bento box shown in Figure 1 and the internal fitting shape for the container body of a snack food container shown in Figure 2.

[0079] (Example 2) A foamed container was obtained in the same manner as in Example 1, except that a thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 93.5:2.0:0.5:4.

[0080] (Example 3) A foamed container was obtained in the same manner as in Example 1, except that copolymer polyethylene terephthalate with IV=0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as a crosslinking agent, talc was used as a nucleating agent, and low-density polyethylene was used as a polyolefin, all mixed in a weight ratio of 98:0.5:0.5:1.

[0081] (Example 4) A foamed container was obtained in the same manner as in Example 1, except that copolymer polyethylene terephthalate with IV=0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as a crosslinking agent, talc was used as a nucleating agent, and low-density polyethylene was used as the polyolefin, all mixed in a weight ratio of 98:1.0:0.5:2.

[0082] (Example 5) A foamed container was obtained in the same manner as in Example 1, except that copolymer polyethylene terephthalate with IV=0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as a crosslinking agent, talc was used as a nucleating agent, and low-density polyethylene was used as a polyolefin, all mixed in a weight ratio of 93.5:2:0.5:4.

[0083] (Comparative Example 1) A foamed container was obtained in the same manner as in Example 1, except that a thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 99:0.5:0.5:0.

[0084] (Comparative Example 2) A foamed container was obtained in the same manner as in Comparative Example 1, except that copolymer polyethylene terephthalate with IV=0.88 was used as the thermoplastic polyester resin for the foamed sheet.

[0085] (Excipient properties evaluation) The foam containers shown in Figures 1 and 2 obtained in the examples were evaluated using a Keyence VL-700 3D scanner. The evaluation was based on the difference from the mold shape, with "○" indicating no difference and "×" indicating a difference. The results are shown in Table 2.

[0086] (Lid fit) The fit of the lids was evaluated using the foamed container bodies shown in Figure 2, obtained in the examples and comparative examples, by closing the container body with the lids. The fit was evaluated as follows: if the lid could overcome the step in the container body using the lid, it was marked as "○"; if there was no resistance when closing the container body using the lid, it was marked as "×". The results are shown in Table 2.

[0087] (Evaluation of foam sheet 1) The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the thermoplastic polyester resin were measured using GPC (Gravity Propagation). The number-average molecular weight (Mn) and weight-average molecular weight (Mw) were defined as weight molecular weights in polystyrene equivalents. The measurement results are shown in Table 1. The weight-average molecular weight (Mw) was 80,000 or higher. The degree of dispersion (Mw / Mn) ranged from 5 to 20.

[0088] From the chromatographs obtained by GPC, a cumulative molecular weight curve was created by plotting molecular weight (logarithmic value) on the x-axis and the cumulative concentration fraction on the y-axis. The slope (derivative value) of the curve at each molecular weight was determined, and a differential molecular weight curve was created by plotting molecular weight (logarithmic value) on the x-axis and the differential value on the y-axis. The ratio of the peak area for molecular weights below 10,000 to the peak area for molecular weights between 1 million and 4 million was 6.1% by mass to 15.0% by mass. The ratio of the peak area for molecular weights below 500,000 to the peak area for molecular weights between 1 million and 4 million was 1.0% by mass to 10.0% by mass. From this, it was suggested that a high molecular weight thermoplastic polyester resin was obtained, resulting in a foamed sheet with high viscosity.

[0089] (Number and size of bubbles) A test specimen was cut out so that the cross-section of the foamed sheet was exposed, and the cross-section was observed using a scanning electron microscope (Hitachi High-Tech Corporation: FlexSEM1000I). Figure 3 is an SEM image of the cross-section of the foamed sheet of the present invention. In the SEM image, a straight line was drawn in the thickness direction of the foamed layer, and the number of bubbles that overlapped at least partially with the straight line was counted. In addition, the diameter size in the long and short directions of the bubbles was measured in the SEM image, and the maximum diameter size / minimum diameter size was calculated. Figure 4 is an SEM image showing an example of the number of bubbles and bubble sizes counted for a portion of the SEM image shown in Figure 3 (white dashed frame). The results for the number of bubbles and bubble sizes are shown in Table 1. Specifically, as shown in Figure 4, a straight line was drawn as a double-headed arrow, and bubbles 1 to 7 that overlapped at least partially with the straight line were counted. In addition, as shown in Figure 4, the diameter size in the long and short directions of the double-headed arrows shown by the dashed lines was measured. The obtained results are shown in Table 1.

[0090] In Examples 1 to 4, the number of bubbles in the thickness direction of the foamed layer was 20 or more. The number of bubbles per 1 mm thickness of the foamed layer was 10 or more. The average size of the bubbles was between 200 and 400 μm, and the uniformity of the bubble size was 3.4 or less. In Comparative Examples 1 and 2, the number of bubbles in the thickness direction of the foamed layer and the number of bubbles per 1 mm thickness of the foamed layer were less than 10. In Comparative Examples 1 and 2, the uniformity of the bubble size was 3.5 or more, and the average size of the bubbles varied.

[0091] (specific gravity) A 20mm x 20mm test piece was cut from a foam sheet or foam container, and its specific gravity was measured using a Shimadzu AUW220D specific gravity measuring device. The results obtained are shown in Table 1. In Examples 1 to 4, the specific gravity of the foam layer was 0.30 or less, and the results showed that a larger number of bubbles in the foam layer resulted in a lower specific gravity.

[0092] (Impact strength of falling ball) The 50% fracture energy was calculated for test specimens of foamed sheets with thicknesses ranging from 1.0 mm to 4.0 mm using the drop weight impact test method in accordance with JIS K7211. The equipment and conditions used for the measurement are as follows. Equipment used: Fall ball testing machine "Newton" (Toyo Seiki Seisakusho Co., Ltd.) Test method: (1) Prepare 20 test specimens and set them in the testing machine so that the steel ball falls into the center of each specimen. (2) Drop the steel ball onto a preliminary sample to determine the starting height (0 level) and the weight of the steel ball. (3) After the steel ball falls onto the first test specimen, observe whether it breaks or not. If the specimen does not break, write "○" on the test result sheet; if the specimen breaks, write "×". (4) If the first test specimen breaks, lower the drop position by d [cm]; if it does not break, raise it by d [cm]. (d = 5 [cm]) (5) Continue testing all test specimens.

[0093]

number

[0094] The results obtained are shown in Table 2. In the example, the impact strength of the falling ball was 1.0 J or higher. In the comparative example, the impact strength of the falling ball was 0.6 J or lower, which was about half the strength of the example.

[0095] (Foam container) A 5 mg specimen from the bottom of a foamed container was subjected to differential scanning calorimeter (DSC7000X model) measurement in accordance with JIS K7122. The measurement conditions were a nitrogen gas flow rate of 20 mL / min, a heating rate of 10 °C / min, and a cooling rate of 10 °C / min. The heat of crystallization was less than 1 mJ / mg, and the crystallization temperature was between 185 and 200 °C.

[0096] [Table 1]

[0097] [Table 2]

[0098] (Foam sheet 2) A thermoplastic polyester resin, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 98:0.5:0.5:1. The resulting mixture was supplied at a rate of 220 kg / h to a first-stage extruder set to a cylinder temperature of 280°C to 290°C and melt-kneaded. Next, the melt-kneaded mixture was supplied to a second-stage extruder set to a cylinder temperature of 240°C to 260°C and melt-kneaded while injecting a mixed gas of butane and carbon dioxide, which is a blowing agent, into the mixture. The melt-kneaded mixture from the second-stage extruder was extruded and foamed at low shear through a die attached to the tip of the second-stage extruder. The extruded foam was taken up by a take-up machine and expanded and molded on a mandrel attached to the die. At this time, the foam was air-cooled by surface cooling. The expanded and molded foam was divided into two parts and wound into a sheet using a winding machine to obtain a foam sheet with a thickness of 2.0 mm.

[0099] (Foam container 2) (Example 6) The resulting foam sheet was placed in a mold heated to 150°C for 10 seconds to obtain a foam container with a bottom thickness of 2.5 mm as shown in Figure 2.

[0100] (Example 7) A foamed container was obtained in the same manner as in Example 6, except that the mold temperature was heated to 190°C.

[0101] (Example 8) A foamed container was obtained in the same manner as in Example 6, except that a thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 93.5:2.0:0.5:4.

[0102] (Example 9) A foamed container was obtained in the same manner as in Example 6, except that a thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 96.5:1.0:0.5:2, and the mold temperature was heated to 200°C.

[0103] (Comparative Example 3) A foamed container was obtained in the same manner as in Example 6, except that a thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin were mixed in a weight ratio of 99:0.5:0.5:0, and the mold temperature was heated to 120°C.

[0104] (Comparative Example 4) A foamed container was obtained in the same manner as in Example 6, except that the mold temperature was heated to 150°C.

[0105] (Heat resistance evaluation) For the heat resistance evaluation, the foamed container shown in Figure 2 obtained in the example was placed in a constant temperature bath set to 100°C for 30 minutes, then removed to room temperature and its external shape was checked. A circle (○) was used for containers that showed no deformation, and a cross (×) was used for containers that were deformed.

[0106] (Microwave oven suitability evaluation) Microwave compatibility was assessed by filling the foamed container shown in Figure 2, obtained in the example, with 180g of commercially available retort curry, heating it at 600W for 60 seconds, removing the contents, washing the container, and observing its external shape and inner surface. Containers without deformation or foam bursting were rated as ○, while those with deformation or foam bursting were rated as ×.

[0107] (Cold tolerance evaluation) For the cold resistance evaluation, the foamed container shown in Figure 2, obtained in the examples, was examined for damage using a drop weight impact test method adapted from JIS K7211. The equipment and conditions used for the measurement are as follows. Equipment used: Fall ball testing machine "Newton" (Toyo Seiki Seisakusho Co., Ltd.) Test method: (1) Prepare 10 containers and set the ball to fall into the center of the bottom of each container. (2) The temperature is -20℃, a 535g (2.0 inch) steel ball is dropped from a height of 30cm. (3) Judgment criteria: ○: 1 or fewer damaged balls, △: 2 to 5 damaged balls, ×: 5 or more damaged balls.

[0108] (Evaluation of foam sheets 2) The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the thermoplastic polyester resin were measured using GPC (Gravity Propagation). The number-average molecular weight (Mn) and weight-average molecular weight (Mw) were defined as weight molecular weights in terms of polystyrene. The weight-average molecular weight (Mw) was 80,000 or greater.

[0109] From the chromatographs obtained by GPC, a cumulative molecular weight curve was created by plotting molecular weight (logarithmic value) on the x-axis and the cumulative concentration fraction on the y-axis. The slope (derivative value) of the curve at each molecular weight was determined, and a differential molecular weight curve was created by plotting molecular weight (logarithmic value) on the x-axis and the differential value on the y-axis. The ratio of the peak area for molecular weights below 10,000 to the peak area for molecular weights between 1 million and 4 million was 6.1% by mass to 15.0% by mass. The ratio of the peak area for molecular weights below 500,000 to the peak area for molecular weights between 1 million and 4 million was 1.0% by mass to 10.0% by mass. From this, it was suggested that a high molecular weight thermoplastic polyester resin was obtained, resulting in high viscosity of the foamed sheet.

[0110] (Number and size of bubbles) A test specimen was cut out so that the cross-section of the foamed sheet was exposed, and the cross-section was observed using a scanning electron microscope (Hitachi High-Tech Corporation: FlexSEM1000I). Figure 3 is an SEM image of the cross-section of the foamed sheet of the present invention. Figure 4 is an SEM image showing an example of the number of bubbles counted in a portion of the SEM image shown in Figure 3 (white dashed frame). In the SEM image, a straight line was drawn in the thickness direction of the foamed layer, and the number of bubbles that overlapped at least partially with the straight line was counted. In addition, the diameter size in the long and short directions of the bubbles was measured in the SEM image, and the maximum diameter size / minimum diameter size was calculated. Figure 4 is an SEM image showing an example of the number of bubbles and bubble size counted in a portion of the SEM image shown in Figure 3 (white dashed frame). The results for the number of bubbles and bubble size are shown in Table 3. Specifically, as shown in Figure 4, a straight line was drawn as a double-headed arrow, and bubbles 1 to 7 that overlapped at least partially with the straight line were counted. In addition, as shown in Figure 4, the diameter size in the long and short directions of the double-headed arrows shown by the dashed lines was measured. The results obtained are shown in Table 3.

[0111] In Examples 6 to 9, the number of bubbles (absolute number) in the thickness direction of the foamed layer was 20 or more. The number of bubbles per 1 mm thickness of the foamed layer was 10 or more. In Comparative Examples 3 and 4, the number of bubbles in the thickness direction of the foamed layer and the number of bubbles per 1 mm thickness of the foamed layer were less than 10. In the Examples, the average size of the bubbles was within 300-400 μm, and the uniformity of the bubble size was 3.2 or less. In the Comparative Examples, the uniformity of the bubble size was 3.5 or more, and the average size of the bubbles varied.

[0112] (Foam container) The test specimens from the bottom of the foamed containers shown in Figure 2 were analyzed by wide-angle X-ray diffraction using a horizontal X-ray diffractometer for thin film evaluation (Rigaku Corporation: Smart Lab). In Examples 6 to 9, the crystallinity of the foamed containers was 26% or higher. In Comparative Examples 3 and 4, the crystallinity of the foamed containers was 23% or lower. The measurement results are shown in Table 4.

[0113] A 5 mg test specimen from the bottom of a foamed container was subjected to DSC measurement in accordance with JIS K7122 using a differential scanning calorimeter (DSC7000X model) manufactured by Hitachi High-Tech Science Corporation. The measurement conditions were a nitrogen gas flow rate of 20 mL / min, a heating rate of 10 °C / min, and a cooling rate of 10 °C / min. In Examples 6 to 9, the heat of crystallization was less than 1.0 mJ / mg, and the cooling crystallization temperature was 185 to 200 °C. In Comparative Examples 3 and 4, the heat of crystallization was 1.0 mJ / mg or more, and the cooling crystallization temperature was higher than 200 °C.

[0114] [Table 3]

[0115] [Table 4]

[0116] Within the scope of the spirit of the present invention, a person skilled in the art can conceive of various modifications and alterations, and it is understood that such modifications and alterations also fall within the scope of the present invention. For example, any addition or deletion of components, combination or design changes of the embodiments, or addition, omission, or modification of processes, as performed by a person skilled in the art to the above-described embodiments, are also included within the scope of the present invention, as long as they retain the gist of the present invention. [Explanation of Symbols]

[0117] 100... Foam container, 110... Flange section, 120... Side section, 130... Bottom section, 140... Partition, 150... Step section

Claims

1. A foamed sheet having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

2. The foamed layer contains a thermoplastic polyester resin, the weight-average molecular weight Mw of the foamed layer is 80,000 or more, and the proportion of molecules with a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foamed layer. A foamed sheet in which the number of air bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

3. A foamed sheet having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, the proportion of molecules with a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles per 1 mm thickness of the foamed layer is 10 or more and 30 or less.

4. The bubbles in the foamed layer are uniform. The foamed sheet according to any one of claims 1 to 3.

5. The dispersion degree Mw / Mn of the thermoplastic polyester resin is 5 or more and 20 or less. The foamed sheet according to any one of claims 1 to 3.

6. The specific gravity of the foamed layer is 0.05 or more and 0.30 or less. The foamed sheet according to any one of claims 1 to 3.

7. The foamed layer further comprises a crosslinking agent and a nucleating agent. The foamed sheet according to any one of claims 1 to 3.

8. The foamed layer further comprises 0.1% by weight or more and 6.0% by weight or less of polyolefin resin. The foamed sheet according to any one of claims 1 to 3.

9. The 50% fracture energy in the impact strength of a falling ball is 1.0 J or more. The foamed sheet according to any one of claims 1 to 3.

10. A foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

11. A foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the weight-average molecular weight Mw of the foamed layer is 80,000 or more, the proportion of molecules with a differential molecular weight of 10,000 or less in the foamed layer is 6.1% by mass or more and 15.0% by mass or less relative to the total mass of the foamed layer, the proportion of molecules with a differential molecular weight of 50,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foamed layer, and the number of bubbles per 1 mm thickness of the foamed layer is 10 or more and 30 or less.

12. A foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the absolute value of the heat of crystallization of the foamed layer is less than 1.0 mJ / mg, and the number of bubbles in the thickness direction of the foamed layer is 20 or more and 50 or less.

13. A foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the absolute value of the heat of crystallization of the foamed layer is less than 1.0 mJ / mg, and the number of bubbles per 1 mm thickness of the foamed layer is 10 to 30.

14. The bubbles in the foamed layer are uniform. The foamed container according to claim 12 or 13.

15. The cooling crystallization temperature of the foamed layer is 185°C or higher and 200°C or lower. The foamed container according to claim 12 or 13.

16. The foamed container according to claim 12 or 13, wherein the proportion of molecules with a differential molecular weight of 500,000 or more in the foamed layer is 1.0% by mass or more and 10.0% by mass or less with respect to the total mass of the foamed layer.

17. The aforementioned foamed layer has a crystallinity of 25% or more, as measured by wide-angle X-ray diffraction. The foamed container according to claim 12 or 13.

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