Sheet and container

Abstract

A foam sheet has a foam layer containing a thermoplastic polyester resin. The weight average molecular weight Mw of the foam layer is 80,000 or more. The abundance ratio of molecules having a differential molecular weight of 10,000 or less in the foam layer is from 6.1 mass% to 15.0 mass% relative to the total mass of the foam layer. The abundance ratio of molecules having a differential molecular weight of 500,000 or less in the foam layer is from 1.0 mass% to 10.0 mass% relative to the total mass of the foam layer, and the number of bubbles in the thickness direction of the foam layer is from 20 to 50.

Description

Sheets and containers

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

[0002] Foamed sheets and foamed containers made from thermoplastic polyester resins have excellent heat resistance and cold resistance and are easy to mold, and are therefore widely used as containers for foods to be cooked or frozen.

[0003] For example, Patent Document 1 describes a thermoplastic polyester-based resin foam sheet and a container that are excellent in deep-draw formability, and Patent Document 2 describes a thermoplastic polyester-based resin foam sheet that can be formed into a sharp shape that is faithful to the shape of a molding die.

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

[0005] Patent No. 5933395 Japanese Patent Application Laid-Open No. 8-3358 Patent No. 6797594

[0006] In the case of the container disclosed in Patent Document 1, it is described that a thermoplastic polyester resin foam sheet having excellent deep-draw formability can be obtained by setting the Z-average molecular weight of the thermoplastic polyester resin to 250,000 to 800,000. Furthermore, in the case of the thermoplastic polyester resin foam sheet disclosed in Patent Document 2, it is described that a sharp shape faithful to the molding die can be obtained by setting the ratio of the length of the cells in the longitudinal direction to the transverse direction to 1 to 4. However, both Patent Documents 1 and 2 only describe simple shapes such as cylindrical cups, and it has been difficult to produce foam containers with accurate shapes such as food containers, such as lunch boxes, which have partitions in the container body, or complex container body shapes that can be fitted with a lid.

[0007] Therefore, the present invention is intended to solve the above-mentioned problems, and one of its objects is to improve the uniformity of bubbles in a foamed sheet and a foamed container, thereby enabling a specific shape to be formed with high precision.

[0008] Furthermore, in the case of the foamed resin container of 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, but no measures are taken to improve the heat resistance and cold resistance of the foamed sheet itself, and there is a limit to how much the heat resistance and low-temperature brittleness can be improved by simply adjusting the molding conditions of the foamed sheet.

[0009] Therefore, the present invention is intended to solve the above problems, and one of its objects is to improve the heat resistance and cold resistance of foaming containers.

[0010] According to one embodiment of the present invention, there is provided a foamed sheet having a foamed layer containing a thermoplastic polyester resin, wherein the foamed layer has a weight average molecular weight Mw of 80,000 or more, the abundance ratio of molecules having a differential molecular weight of 10,000 or less in the foamed layer is 6.1 mass % or more and 15.0 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 to 50.

[0011] According to one embodiment of the present invention, there is provided a foamed sheet having a foamed layer containing a thermoplastic polyester resin, wherein the foamed layer has a weight average molecular weight Mw of 80,000 or more, the abundance ratio of molecules having a differential molecular weight of 50,000 or more in the foamed layer is 1.0 mass% or more and 10.0 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 to 50.

[0012] According to one embodiment of the present invention, there is provided a foamed sheet having a foamed layer containing a thermoplastic polyester resin, wherein the foamed layer has a weight average molecular weight Mw of 80,000 or more, the abundance ratio of 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, relative to the total mass of the foamed layer, and the abundance ratio of 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, relative to the total mass of the foamed layer, and the number of bubbles per mm of thickness of the foamed layer is 10 to 30.

[0013] In the foamed sheet, the cells in the foamed layer may be uniform.

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

[0015] In the foam sheet, the foam layer may have a specific gravity of 0.05 or more and 0.30 or less.

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

[0017] In the foam sheet, the foam layer may further contain 0.1% by weight or more and 6.0% by weight or less of a polyolefin resin.

[0018] The foamed sheet may have a 50% breaking energy in a falling ball impact test of 1.0 J or more.

[0019] In one embodiment of the present invention, there is provided a foamed container having a foamed layer containing a thermoplastic polyester resin, wherein the foamed layer has a weight average molecular weight Mw of 80,000 or more, the proportion of molecules having a differential molecular weight of 10,000 or less in the foamed layer is 6.1 mass% or more and 15.0 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 to 50.

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

[0021] According to one embodiment of the present invention, there is provided 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.

[0022] According to one embodiment of the present invention, there is provided 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 of thickness of the foamed layer is 10 to 30.

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

[0024] In the foamed container, the foamed layer may have a crystallization temperature upon cooling of 185°C or higher and 200°C or lower.

[0025] In the foamed container, the abundance ratio of 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, the foamed layer may have a crystallinity of 25% or more as measured by wide-angle X-ray diffraction.

[0027] By using one embodiment of the present invention, the uniformity of the bubbles in the foamed sheet and the foamed container can be improved, thereby enabling the foamed sheet and the foamed container to be precisely shaped into a specific shape. Also, by using one embodiment of the present invention, the heat resistance and cold resistance of the foamed container can be improved.

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

[0029] Hereinafter, each embodiment of the invention disclosed in this application will be described with reference to the drawings. However, the present invention can be embodied in various forms without departing from the spirit of the invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0030] First Embodiment A foamed sheet according to the present invention will be described.

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

[0032] (Foam Layer) The foam layer contains a thermoplastic polyester resin and has a plurality of bubbles. The thickness of the foam layer is preferably 1.0 mm or more and 4.0 mm or less.

[0033] The number of bubbles in the thickness direction of the foamed layer is from 20 to 50. A foamed layer having a number of bubbles in the above range has high heat resistance 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 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 mm of thickness of the foamed layer is 10 to 30. A foamed layer having a number of bubbles in the above range has high heat resistance and cold resistance due to the large number of bubbles. Here, the number of bubbles per mm of thickness of the foamed layer refers to the number of bubbles that at least partially overlap a 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, divided by the length (thickness) in mm of the line.

[0035] A uniform foam layer means that, as in the case of measuring the number of bubbles, a foam sheet is cut in the thickness direction, and in a cross-sectional image of the cut-out foam sheet observed with a scanning electron microscope or the like, the size of bubbles that at least partially overlap a line drawn in the thickness direction is uniform. The diameter sizes of the bubbles in the longitudinal and transverse directions are measured, and the closer the ratio of the maximum diameter size to the minimum diameter size is to 1, the more uniform the foam layer is, with 3.5 or less being preferred. The more uniform the bubble size, the stronger the impact strength and the improved cold resistance and formability.

[0036] The thermoplastic polyester resin is a thermoplastic resin having an ester bond obtained by polycondensation of a polybasic acid and a polyhydric alcohol, such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate. The thermoplastic polyester resin accounts for 90% by mass or more, preferably 95% by mass or more, of the foam layer.

[0037] The weight average molecular weight Mw of the thermoplastic polyester resin is at least 80,000. The weight average molecular weight Mw of the thermoplastic polyester resin is preferably at least 90,000 and not more than 250,000, and more preferably at least 100,000 and not more than 200,000. A foam layer containing a thermoplastic polyester resin having a weight average molecular weight Mw within the above range or equal to or greater than the above weight average molecular weight Mw has high viscosity and can generate and maintain many bubbles when heated.

[0038] The ratio of molecules having 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, and preferably 7.0% by mass or more and 10.0% by mass or less, relative to the total mass of the thermoplastic polyester resin. The ratio of molecules having 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, and preferably 4.0% by mass or more and 8.0% by mass or less, relative to the total mass of the thermoplastic polyester resin. When the ratio of molecules having a differential molecular weight of the thermoplastic polyester resin relative to the total mass of the thermoplastic polyester resin is within the above range, the foam layer containing the thermoplastic polyester resin has a high viscosity and can generate and maintain many bubbles when heated.

[0039] The polydispersity Mw / Mn of the thermoplastic polyester resin is preferably from 5.0 to 20.0, more preferably from 7.0 to 15.0. A foamed layer containing a thermoplastic polyester resin having a polydispersity Mw / Mn in the above range has high viscosity, and generates and maintains many bubbles upon heating.

[0040] The weight average molecular weight Mw and differential molecular weight of the thermoplastic polyester resin can be measured by Gel Permeation Chromatography (GPC). Specifically, a sample of a foam sheet or foam container is weighed into a 30 ml vial, and 1.0 ml of a HFIP / chloroform mixed solvent (mixing ratio 1 / 1) is added per 5.0 mg to dissolve, and then 9.0 ml of chloroform is added to dilute. This solution is filtered through a 0.50 μm PTFE disposable membrane filter unit, and the filtrate is used for measurement. (Measurement conditions) Column / temperature: 3 x PLgel 10μ MIXED-B, 7.5 x 300 mm (Agilent Technologies) / 40°C Mobile phase: HPLC-grade chloroform (Fujifilm Wako Pure Chemical Industries) Flow rate: 1.0 mL / min Injection volume: 15 μL Detector: 254 nm (UV-visible detector) Column calibration: Monodisperse PS (EasiCal Type PS-1 polystyrene: Agilent Technologies) Molecular weight calibration: Relative calibration method (PS conversion) Equipment: KP-22-13S dual pump (Flom), 717plus automatic injection device, 2487 UV-visible detector (Nihon Waters)

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

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

[0043] As the nucleating agent, an organic crystal nucleating agent or an inorganic crystal nucleating agent can be used. As the nucleating agent, it is preferable to use an organic crystal nucleating agent. As an organic crystal nucleating agent, for example, polyether ether ketone can be mentioned. As an inorganic crystal nucleating agent, for example, talc can be mentioned. The content of the nucleating agent 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 foam layer. By including the nucleating agent in the foam layer within the above range, the number and size of bubbles can be easily controlled.

[0044] Examples of polyolefins include polyethylene and polypropylene. The content of the polyolefin 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, based on the foam layer. By incorporating the polyolefin in the foam layer within the above range, the viscosity of the thermoplastic polyester resin falls within the above preferred range, and the number of bubbles can be increased.

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

[0046] (Method for Producing Foamed Sheet) The method for producing a foamed sheet according to the present invention will be described with reference to Fig. 5. Fig. 5 is a flowchart showing the method for producing 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 for extruding and foaming a molten mixture of a thermoplastic polyester resin and optional additives. The following production methods can be used to produce a foamed sheet containing a thermoplastic polyester resin.

[0048] In step 100 (S100), a mixture of thermoplastic polyester resin and optional additives is fed into 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 expanded and molded on a mandrel attached to the die while being taken up by a take-up machine. At this time, the foam is molded while being cooled by surface cooling. In step 106 (S106), the molded foam is divided into two pieces and wound into a sheet by a winder to form a foam sheet. Note that dividing the foam into two pieces includes cutting a portion of the foam and opening the cut portion, or cutting the foam into two or more pieces.

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

[0050] The extruder can be equipped with a large-diameter screw. When a tandem extruder is used, the first and second extruders can be equipped with screws of the same diameter or screws of different diameters. When screws of different diameters are used, for example, the first extruder can be equipped with a small-diameter screw, and the second extruder can be equipped with a screw of a larger diameter than the screw of the first extruder. Alternatively, the reverse combination can be used in a tandem extruder.

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

[0052] In the extruder, the screw rotation speed can be set to a low rotation speed. Specifically, the screw rotation speed can be set to 10 to 200 rpm. When a tandem extruder is used, the screw rotation speed of the first-stage extruder can be set to a high rotation speed, and the screw rotation speed of the first-stage extruder of the second-stage extruder can be set to a lower rotation speed than the screw rotation speed of the first-stage extruder. When a twin-screw extruder is used, the screw rotation directions may be the same or different directions. For example, when extrusion foaming is performed at low shear, the screws may be rotated in the same intermeshing direction, and when extrusion foaming is performed at high shear, the screws may be rotated in different non-intermeshing directions.

[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 a tandem extruder is used, the cylinders of the first and second extruders can be set to the same high temperature or different temperatures. When different temperatures are set, for example, the cylinder of the first extruder can be set to a high temperature, and the cylinder of the second extruder can be set to a high temperature but lower than the cylinder of the first extruder. Specifically, the cylinder of the first extruder can be set to 280°C to 290°C, and the cylinder of the second extruder can be set to 240°C to 260°C. The cylinders of a tandem extruder may also be set to the opposite combination of temperatures.

[0054] In this embodiment, the foamed sheet has a foamed layer containing a thermoplastic polyester resin having a weight-average molecular weight Mw of 80,000 or more, and the foamed layer contains molecules having a differential molecular weight of 10,000 or less and molecules having a differential molecular weight of 500,000 or less in the above-mentioned ratio. The foamed layer contains 20 to 50 bubbles in the thickness direction, which improves the uniformity of the bubbles in the foamed sheet.

[0055] Second Embodiment A foaming container according to the present invention will be described. Descriptions of configurations that are the same as or similar to the configurations described in the first embodiment may be omitted.

[0056] (Foaming container 100) The foaming container 100 can be used to heat-cook or freeze food. The foaming container 100 can have a partitioned shape. Fig. 1 is a schematic perspective view of the foaming container 100 according to this embodiment.

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

[0058] As shown in FIG. 1 , the foaming container 100 of the present invention includes a flange portion 110, a side portion 120, and a bottom portion 130. The flange portion 110 is provided on the upper peripheral edge of the foaming container 100. The side portion 120 is provided continuous with the inner side of the flange portion 110. The side portion 120 is provided at an incline in a cross-sectional view. The bottom portion 130 is provided on the inner side of the side portion 120. The bottom portion 130 is provided in an area surrounded by the flange portion 110 and the side portion 120 in a top view. The bottom portion 130 is provided with a partition 140 for storing multiple contents. The partition 140 shown in FIG. 1 is merely an example, and the partition 140 may be changed depending on the type of contents and the size of the container.

[0059] (Foaming container 200) The foaming container 200 of the present invention can have an internal fitting shape. Fig. 2 is a schematic perspective view of the foaming container 200 according to this embodiment.

[0060] As shown in Fig. 2, the foaming container 200 of the present invention includes a flange portion 110, a side portion 120, and a bottom portion 130. The flange portion 110 is provided on the upper peripheral edge of the foaming container. The side portion 120 is provided continuous with the inner side of the flange portion 110. The side portion 120 is provided at an incline in cross-sectional view, and a step 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 an area surrounded by the flange portion 110 and the side portion 120 in top view.

[0061] (Method for manufacturing a foaming container) A method for manufacturing a foaming container according to the present invention will be described with reference to Fig. 6. Fig. 6 is a flowchart showing a method for manufacturing a foaming container according to one embodiment of the present invention.

[0062] The foam container of the present invention includes a step of heating a foam sheet, sandwiching it between a mold, and thermoforming it. In step 200 (S200), the foam sheet is heated to 130°C to 210°C. In step 202 (S202), the mold is heated to 15°C to 70°C. In step 204 (S204), the foam sheet is sandwiched between the molds and cooled for 10 to 60 seconds. In step 206 (S206), the thermoformed foam sheet is released from the mold. Note that the mold can be, for example, a foam container mold as shown in FIG. 1.

[0063] This embodiment can also achieve the same effects as those of the first embodiment, that is, it is possible to provide a foaming container with uniform bubbles.

[0064] Third Embodiment A foaming container according to the present invention will be described. Descriptions of configurations that are the same as or similar to those described in the first and second embodiments may be omitted.

[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 in the foam layer within the above range and making 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 crystallization temperature of the thermoplastic polyester resin upon cooling is preferably 185° C. to 200° C. By including the number of cells in the foam layer within the above range and by setting the crystallization temperature of the thermoplastic polyester resin upon cooling 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 a thermoplastic polyester resin can be determined based on the DSC curve obtained by measuring the heat of crystallization according to differential scanning calorimetry (DSC). Specifically, a test piece of the foamed layer is cut out from a foaming container, heated at a rate of 10°C / min in a temperature range of 30 to 290°C, and cooled at a 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 more, more preferably 30% or more and 45% or less, as measured by wide-angle X-ray diffraction. By setting the degree of crystallinity of the foamed layer in 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 by wide-angle X-ray diffraction (XRD). Specifically, a 10 mm x 10 mm test piece of the foam layer was cut out from the foaming container shown in Figure 2 using an X-ray diffraction measurement device. The test piece was fixed to a sample holder, and an XRD profile was measured by the transmission method while rotating the holder. The device and conditions used for the measurement were as follows: Device: Empyrean manufactured by Spectris; X-ray source: CuKα; Output: 45 kV 40 mA; Scanning range: 2θ = 5° to 35°; Scanning speed: 0.5° / min; Step width: 0.026°; Detector: PIXcel ３ＤThe crystallinity can be calculated from the obtained profile using the following formula: Crystallinity % = crystal-derived peak area / (crystal-derived peak area + amorphous-derived halo area) × 100

[0071] The foam container 100 of the present invention has the foam layer of the present invention, and thus can form a partition 140 that can separate the contents.

[0072] The foamed container 200 of the present invention has the foamed layer of the present invention, and thus can form the step portion 150 for internal fitting.

[0073] (Method for Manufacturing Foamed Container) The method for manufacturing a foamed container according to the present invention will be described with reference to FIG. 6 again.

[0074] The foam container manufacturing method of the present invention includes a step of heating a foam sheet and sandwiching it between molds to perform thermoforming. In step 200 (S200), the foam 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 foam sheet is sandwiched between the molds and heated and maintained for 10 to 60 seconds. The heating and maintenance time for the foam sheet is preferably 30 to 45 seconds. Heating the foam sheet in the mold heated to 130°C to 210°C promotes crystallization of the thermoplastic polyester resin, 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 thermoformed foam sheet is released from the mold. The mold can be, for example, a foam container mold as shown in FIG. 1.

[0075] This embodiment can also achieve the same effects as those of the first and second embodiments, that is, it can provide a foaming container with uniform bubbles.

[0076] A foamed container manufactured according to one embodiment of the present invention will be described below. However, this example does not limit the scope of the present invention. The raw materials used in this example are listed below.

[0077] (Foam Sheet 1) A copolymerized polyethylene terephthalate with an IV of 0.80 was mixed as a thermoplastic polyester resin, pyromellitic anhydride as a crosslinking agent, talc as a nucleating agent, and low-density polyethylene as a polyolefin in a weight ratio of 96.5:1.0:0.5:2. The resulting mixture was fed to a first-stage extruder with a cylinder temperature set to 280°C to 290°C at 220 kg / h and melt-kneaded. The melt-kneaded mixture was then fed to a second-stage extruder with a cylinder temperature set to 240°C to 260°C, where it was melt-kneaded while injecting a mixed gas of butane and carbon dioxide as a blowing agent. The mixture melt-kneaded in 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 using a mandrel attached to the die. The foam was then air-cooled by surface cooling. The expanded foam was divided into two parts, which were then wound into a sheet using a winder to obtain a foam sheet having a thickness of 2.0 mm.

[0078] (Foamed Container 1) (Example 1) The obtained foamed sheet was heated to 130°C to 210°C and clamped in a mold for 10 seconds to obtain foamed containers having a partition shape for the container body for a lunch container shown in Figure 1 and an inner-fitting shape for the container body for a snack container shown in Figure 2.

[0079] (Example 2) A foamed container was obtained in the same manner as in Example 1, except that the thermoplastic polyester resin of the foamed sheet, the pyromellitic anhydride as the crosslinking agent, the talc as the nucleating agent, and the low-density polyethylene as the 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 copolymerized polyethylene terephthalate having an IV of 0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as the crosslinking agent, talc was used as the nucleating agent, and low-density polyethylene was used as the polyolefin 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 copolymerized polyethylene terephthalate having an IV of 0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as the crosslinking agent, talc was used as the nucleating agent, and low-density polyethylene was used as the polyolefin 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 copolymerized polyethylene terephthalate having an IV of 0.88 was used as the thermoplastic polyester resin for the foamed sheet, pyromellitic anhydride was used as the crosslinking agent, talc was used as the nucleating agent, and low-density polyethylene was used as the polyolefin 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 the thermoplastic polyester resin of the foamed sheet, the pyromellitic anhydride as the crosslinking agent, the talc as the nucleating agent, and the low-density polyethylene as the 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 copolymerized polyethylene terephthalate having an IV of 0.88 was used as the thermoplastic polyester resin for the foamed sheet.

[0085] (Evaluation of formability) The foamed containers shown in FIGS. 1 and 2 obtained in the examples were evaluated using a 3D scanner VL-700 manufactured by Keyence. The evaluation was performed based on the difference from the mold shape, and if there was no difference, it was marked "◯", and if there was a difference, it was marked "×". The results are shown in Table 2.

[0086] (Fitability of lid) Using the container body of the foamed container shown in Fig. 2 obtained in the examples and comparative examples, the fitability of the lid was evaluated by closing the container body with the lid. The fitability was evaluated as "Good" if there was resistance to climbing over the step in the container body using the lid, and as "Poor" if there was no resistance to the container body using the lid. The results are shown in Table 2.

[0087] (Evaluation 1 of Foam Sheet) The number average molecular weight Mn and weight average molecular weight Mw of the thermoplastic polyester resin of the obtained foam sheet test piece were measured using GPC. The number average molecular weight Mn and weight average molecular weight Mw were defined as weight molecular weights converted into polystyrene. The measurement results are shown in Table 1. The weight average molecular weight Mw was 80,000 or more. The dispersity (Mw / Mn) was 5 to 20.

[0088] From the chromatograph obtained by GPC, a molecular weight (logarithmic value) was plotted on the horizontal axis against the cumulative concentration fraction on the vertical axis to create an integrated molecular weight curve. The slope (differential value) of the curve at each molecular weight was determined, and a differential molecular weight curve was created by plotting the molecular weight (logarithmic value) on the horizontal axis against the differential value on the vertical axis. The ratio of the peak area for molecular weights of 10,000 or less to the peak area for molecular weights of 1,000,000 to 4,000,000 was 6.1 to 15.0% by mass. The ratio of the peak area for molecular weights of 500,000 or less to the peak area for molecular weights of 1,000,000 to 4,000,000 was 1.0 to 10.0% by mass. This suggests that a high molecular weight thermoplastic polyester resin was obtained, and that the foamed sheet had high viscosity.

[0089] (Number and Size of Bubbles) A ​​test specimen was cut out from the foam sheet so that the cross section was exposed, and the cross section was observed using a scanning electron microscope (FlexSEM1000I, Hitachi High-Tech Corporation). FIG. 3 is an SEM image of the cross section of the foam sheet of the present invention. In the SEM image, a line was drawn in the thickness direction of the foam layer, and the number of bubbles that at least partially overlapped the line was counted. Furthermore, in the SEM image, the diameters of the bubbles in the longitudinal and transverse directions were measured, and the maximum diameter size / minimum diameter size was calculated. FIG. 4 is an SEM image showing an example of the number and size of bubbles counted in a portion (framed with a white dashed line) of the SEM image shown in FIG. 3. The results of the number and size of bubbles are shown in Table 1. Specifically, as shown in FIG. 4, a line was drawn as indicated by a double-headed arrow, and bubbles 1 to 7 that at least partially overlapped the line were counted. Furthermore, the diameters of the bubbles in the longitudinal and transverse directions indicated by the dashed arrows in FIG. 4 were measured. The results are shown in Table 1.

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

[0091] (Specific Gravity) Test pieces measuring 20 mm x 20 mm were cut out from the foam sheet or foam container, and the specific gravity was measured using a specific gravity measuring device AUW220D manufactured by Shimadzu Corporation. The measurement results are shown in Table 1. In Examples 1 to 4, the specific gravity of the foam layer was 0.30 or less, and the larger the number of cells in the foam layer, the smaller the specific gravity of the foam layer.

[0092] (Falling Ball Impact Strength) Foamed sheet test pieces with thicknesses of 1.0 mm to 4.0 mm were subjected to a falling weight impact test in accordance with JIS K7211 to calculate the 50% fracture energy. The equipment and conditions used for the measurement were as follows: Specifications: Newton Drop Ball Tester, Toyo Seiki Seisakusho Co., Ltd. Test Method: (1) Prepare 20 test pieces and set them in the tester so that the steel ball would fall on the center of the test piece. (2) Drop the steel ball onto a spare 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 piece, observe whether it broke or not. If the test piece did not break, enter "O" in the test results table; if the test piece broke, enter "X." (4) If the first test piece broke, lower the drop position by d cm; if not, raise it by d cm. (d = 5 cm). (5) Continue testing all test pieces.

[0093] H ５０ : 50% breaking height [cm] Ha: Test height when height level i is 0 [cm] d: Height interval when raising or lowering the height [cm] i: Height level that increases or decreases by one (0 to ±5) n ｉ : Number of test pieces broken at each level N: Total number of test pieces broken E ５０: 50% breaking energy [J] m: weight of steel ball [kg] g: acceleration of gravity [9.807 m / s ２ ]

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

[0095] (Foaming container) A 5 mg test piece from the bottom of the foaming container was subjected to DSC measurement using a differential scanning calorimeter (DSC7000X model, manufactured by Hitachi High-Tech Science Corporation) in accordance with JIS K7122. The measurement conditions were a nitrogen gas flow rate of 20 mL / min, a temperature increase rate of 10°C / min, and a temperature decrease rate of 10°C / min. The heat of crystallization was less than 1 mJ / mg, and the crystallization temperature upon heat decrease was 185 to 200°C.

[0096]

[0097]

[0098] (Foam Sheet 2) 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 fed to a first-stage extruder set at a cylinder temperature of 280°C to 290°C at 220 kg / h and melt-kneaded. The melt-kneaded mixture was then fed to a second-stage extruder set at a cylinder temperature of 240°C to 260°C, and melt-kneaded while injecting a mixed gas of butane and carbon dioxide as a blowing agent. The mixture melt-kneaded in 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 using a mandrel attached to the die. The foam was then air-cooled by surface cooling. The expanded foam was divided into two and wound into a sheet using a winder to obtain a foam sheet with a thickness of 2.0 mm.

[0099] (Foamed Container 2) (Example 6) The obtained foamed sheet was sandwiched between a mold heated to 150°C for 10 seconds to obtain a foamed container having a bottom thickness of 2.5 mm as shown in Fig. 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 the thermoplastic polyester resin of the foamed sheet, the pyromellitic anhydride as the crosslinking agent, the talc as the nucleating agent, and the low-density polyethylene as the polyolefin were mixed in a weight ratio of 93.5:2.0:0.5:4.

[0102] (Example 9) A thermoplastic polyester resin for a 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 a foamed container was obtained in the same manner as in Example 6, except that the temperature of the mold 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 a 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 Fig. 2 obtained in the example was left to stand in a thermostatic chamber set at 100°C for 30 minutes, then taken out to room temperature, and the external appearance was checked. The container was evaluated as ◯ if there was no deformation, and x if there was deformation.

[0106] (Evaluation of microwave oven suitability) The microwave oven suitability was evaluated by filling 180 g of commercially available retort curry into the foam container obtained in the example shown in Figure 2, heating it at 600 W for 60 seconds, removing the contents, washing the container, and observing the external shape and inner surface. The evaluation was performed by rating ◯ if there was no deformation or broken bubbles, and × if there was deformation or broken bubbles.

[0107] (Evaluation of Cold Resistance) To evaluate cold resistance, the foam containers obtained in the examples shown in Figure 2 were subjected to a drop weight impact test in accordance with JIS K7211 to check for damage. The equipment and conditions used for the measurement are as follows. Specifications: Newton ball drop tester, manufactured by Toyo Seiki Seisakusho Co., Ltd. Test method: (1) Ten containers were prepared and set so that the ball would fall into the center of the bottom of the container. (2) At a temperature of -20°C, a 535g (2.0 inch) steel ball was dropped from a height of 30cm. (3) Evaluation criteria: ◯: 1 or less broken containers; △: 2-5 broken containers; ×: 5 or more broken containers.

[0108] (Evaluation of Foam Sheet 2) The number average molecular weight Mn and weight average molecular weight Mw of the thermoplastic polyester resin of the obtained foam sheet test piece were measured using GPC. The number average molecular weight Mn and weight average molecular weight Mw were defined as weight average molecular weights in terms of polystyrene. The weight average molecular weight Mw was 80,000 or more.

[0109] From the chromatograph obtained by GPC, a molecular weight (logarithmic value) was plotted on the horizontal axis against the cumulative concentration fraction on the vertical axis to create an integrated molecular weight curve. The slope (differential value) of the curve at each molecular weight was determined, and a differential molecular weight curve was created by plotting the molecular weight (logarithmic value) on the horizontal axis against the differential value on the vertical axis. The ratio of the peak area for molecular weights of 10,000 or less to the peak area for molecular weights of 1,000,000 to 4,000,000 was 6.1 to 15.0% by mass. The ratio of the peak area for molecular weights of 500,000 or less to the peak area for molecular weights of 1,000,000 to 4,000,000 was 1.0 to 10.0% by mass. This suggests that a high molecular weight thermoplastic polyester resin was obtained, and that the foamed sheet had high viscosity.

[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 (FlexSEM1000I, Hitachi High-Tech Corporation). FIG. 3 is an SEM image of the cross section of a foamed sheet of the present invention. FIG. 4 is an SEM image showing an example of the number of bubbles counted in a portion (framed with a white dashed line) of the SEM image shown in FIG. 3. In the SEM image, a line was drawn in the thickness direction of the foamed layer, and the number of bubbles that at least partially overlapped the line was counted. In addition, in the SEM image, the diameter sizes of the bubbles in the longitudinal and transverse directions were measured, and the maximum diameter size / minimum diameter size was calculated. FIG. 4 is an SEM image showing an example of the number and size of bubbles counted in a portion (framed with a white dashed line) of the SEM image shown in FIG. 3. The results of the number and size of bubbles are shown in Table 3. Specifically, as shown in FIG. 4, a line was drawn as indicated by a double-headed arrow, and bubbles 1 to 7 that at least partially overlapped the line were counted. Furthermore, the diameters in the long and short directions indicated by the double-headed arrows shown in dashed lines were measured as shown in Figure 4. The results are shown in Table 3.

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

[0112] (Foamed Container) The test piece of the bottom surface of the obtained foamed container shown in FIG. 2 was analyzed by wide-angle X-ray diffraction using a horizontal sample X-ray diffractometer for thin film evaluation (Rigaku Corporation: Smart Lab). In Examples 6 to 9, the crystallinity of the foamed container was 26% or more. In Comparative Examples 3 and 4, the crystallinity of the foamed container was 23% or less. The measurement results are shown in Table 4.

[0113] A 5 mg test piece from the bottom of the foaming 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 temperature increase rate of 10°C / min, and a temperature decrease rate of 10°C / min. In Examples 6 to 9, the heat of crystallization was less than 1.0 mJ / mg, and the temperature-decreasing 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 temperature-decreasing crystallization temperature was higher than 200°C.

[0114]

[0115]

[0116] Within the scope of the concept of the present invention, a person skilled in the art may conceive of various modifications and alterations, and it is understood that these modifications and alterations also fall within the scope of the present invention. For example, to the above-described embodiment, a person skilled in the art may appropriately add or delete components, combine or change the design of the embodiments, or add or omit processing or change conditions, and these modifications and alterations are also included within the scope of the present invention as long as they maintain the gist of the present invention.

[0117] 100: Foaming container, 110: Flange portion, 120: Side portion, 130: Bottom portion, 140: Partition, 150: Step portion

Claims

1. It has a foamed layer containing 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 500,000 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.

2. It has a foamed layer containing 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 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 500,000 or more in the foam layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foam layer. A foamed sheet in which the number of air bubbles per 1 mm thickness of the foamed layer is between 10 and 30.

3. 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 foamed sheet according to claim 1.

4. The number of bubbles in the thickness direction of the foamed layer is between 20 and 50. The foamed sheet according to claim 2.

5. The bubbles in the foamed layer are uniform. The foamed sheet according to claim 1 or 2.

6. The dispersion degree Mw / Mn of the thermoplastic polyester resin is 5 or more and 20 or less. The foamed sheet according to claim 1 or 2.

7. The specific gravity of the foamed layer is 0.05 or more and 0.30 or less. The foamed sheet according to claim 1 or 2.

8. The foamed layer further comprises a crosslinking agent and a nucleating agent. The foamed sheet according to claim 1 or 2.

9. 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 claim 1 or 2.

10. The 50% fracture energy in the impact strength of a falling ball is 1.0 J or more. The foamed sheet according to claim 1 or 2.

11. It has a foamed layer containing thermoplastic polyester resin, 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 500,000 or more in the foam layer is 1.0% by mass or more and 10.0% by mass or less relative to the total mass of the foam layer. A foamed container in which the number of bubbles per 1 mm thickness of the foamed layer is between 10 and 30.