Sheet and molded article

Abstract

This sheet comprises a crystallizable polyester resin containing a polyethylene terephthalate as the main component. The z-average molecular weight of the polyester resin is 300,000 or less. The content of molecule components having a molecular weight of 10,000 or less is 6.5 wt% or less with respect to the total weight of the polyester resin. The content of molecule components having a molecular weight of 30,000 or less may be 25.0 wt% or less with respect to the total weight of the polyester resin.

Description

Sheets and molded products

[0001] One embodiment of the present invention relates to a sheet made of a crystallizable polyester resin. Another embodiment of the present invention relates to a molded article containing crystalline polyethylene terephthalate, manufactured by thermoforming the above sheet.

[0002] Polyethylene terephthalate is classified into crystalline and amorphous states depending on its state. Polyester resins containing crystalline polyethylene terephthalate have high heat resistance and are widely used in containers for foods that require heating during cooking.

[0003] Japanese Patent Publication No. 2003-11947 Japanese Patent Publication No. 2022-132301

[0004] While molded articles containing crystalline polyethylene terephthalate exhibit excellent heat resistance, they suffer from a problem where brittleness increases with increasing crystallinity, leading to a decrease in impact resistance at low temperatures (hereinafter referred to as "cold resistance"). Therefore, Patent Documents 1 and 2 disclose molded articles manufactured using a sheet in which amorphous polyethylene terephthalate (hereinafter referred to as "amorphous PET") and crystalline polyethylene terephthalate (hereinafter referred to as "crystalline PET") are laminated, in order to improve cold resistance. Molded articles manufactured in this manner contain not only crystalline PET but also amorphous PET, thus improving cold resistance. However, molded articles containing amorphous PET soften above the glass transition temperature, resulting in a problem of significantly reduced heat resistance.

[0005] Therefore, one objective of one embodiment of the present invention is to provide a sheet used in molded products manufactured by thermoforming, which can improve the cold resistance of the molded product while maintaining its heat resistance. Another objective is to provide a molded product that has improved cold resistance while maintaining its heat resistance.

[0006] In both Patent Document 1 and Patent Document 2, amorphous PET is used for the outer layer of the sheet before thermoforming. In this case, there is a problem that the metal adhesion is high and it is difficult to release it from the heat-set mold.

[0007] Therefore, one of the objectives of one embodiment of the present invention is to provide a sheet that is easy to release during thermoforming.

[0008] A sheet according to one embodiment of the present invention is a sheet made of a crystallizable polyester resin mainly composed of polyethylene terephthalate, wherein the z-average molecular weight of the polyester resin is 300,000 or less, and the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin is 6.5% by weight or less.

[0009] The content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin may be 25.0% by weight or less.

[0010] The polyester resin may have one peak in the differential molecular weight distribution curve obtained by gel permeation chromatography, in the range of logarithmic molecular weight between 3.5 and 6.5.

[0011] A molded article according to one embodiment of the present invention is a molded article manufactured by thermoforming the above-mentioned sheet, wherein the polyester resin includes polyethylene terephthalate in a crystalline state.

[0012] A sheet according to one embodiment of the present invention comprises a first outer layer, a second outer layer, and an intermediate layer between the first outer layer and the second outer layer, wherein each of the first outer layer, the second outer layer, and the intermediate layer contains a crystallizable polyester resin mainly composed of polyethylene terephthalate, the z-average molecular weight of the polyester resin in the sheet is 300,000 or less, and the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin is 6.5% by weight or less.

[0013] The content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin in the sheet may be 25.0% by weight.

[0014] The polyester resin in the sheet may have one peak in the range of logarithmic molecular weight between 3.5 and 6.5 in the differential molecular weight distribution curve obtained by gel permeation chromatography.

[0015] The content of the intermediate layer relative to the total weight of the sheet may be 50% by weight or more.

[0016] A molded article according to one embodiment of the present invention is a molded article manufactured by thermoforming the above-mentioned sheet, wherein each of the first outer layer, the second outer layer, and the intermediate layer contains polyethylene terephthalate in a crystalline state.

[0017] The degree of crystallinity of the first outer layer and the second outer layer may be greater than the degree of crystallinity of the intermediate layer.

[0018] The 50% fracture energy in a DuPont impact test at -20°C may be 1.0 J or higher.

[0019] A sheet according to one embodiment of the present invention includes a first outer layer, a second outer layer, and an intermediate layer between the first outer layer and the second outer layer, each of which includes a crystallizable polyester resin mainly composed of polyethylene terephthalate, the first outer layer includes a first crystal nucleating agent, and the second outer layer includes a second crystal nucleating agent.

[0020] The intermediate layer does not need to contain a crystal nucleating agent.

[0021] The intermediate layer contains a third nucleating agent, and the first, second, and third nucleating agents may be the same.

[0022] The intermediate layer contains a third nucleating agent, the first nucleating agent is added in a first content relative to the total amount of the first outer layer, the second nucleating agent is added in a second content relative to the total amount of the second outer layer, and the third nucleating agent is added in a third content relative to the total amount of the intermediate layer, the third content of which may be less than each of the first and second contents.

[0023] A molded product according to one embodiment of the present invention is a molded product manufactured by thermoforming the sheet, wherein the degree of crystallinity of the first outer layer and the second outer layer is greater than the degree of crystallinity of the intermediate layer.

[0024] The ratio of the thickness of the intermediate layer to the sum of the thicknesses of the first outer layer, the second outer layer, and the intermediate layer may be 5% or more and 95% or less.

[0025] A sheet according to one embodiment of the present invention can improve the cold resistance of a molded product manufactured by thermoforming while maintaining its heat resistance. Furthermore, a molded product according to one embodiment of the present invention improves cold resistance while maintaining its heat resistance. In addition, when a crystal nucleating agent is added to the outer layer of the sheet, the crystallization of the outer layer is promoted, increasing the degree of crystallinity and reducing metal adhesion, thus making demolding easier.

[0026] This is a schematic diagram showing the structure of a sheet according to one embodiment of the present invention. This is a flowchart explaining the manufacturing method of a sheet according to one embodiment of the present invention. This is a schematic diagram showing the structure of a sheet according to one embodiment of the present invention. This is a schematic diagram showing the structure of a molded product according to one embodiment of the present invention. This is a flowchart explaining the manufacturing method of a molded product according to one embodiment of the present invention. This is a graph of the differential molecular weight distribution curve obtained by gel permeation chromatography in the example.

[0027] 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.

[0028] In order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc., of each part compared to the actual embodiment, but this does not limit the interpretation of the present invention. Furthermore, in the specification and drawings, components having the same function as those described with respect to previously shown figures may be denoted by the same reference numerals, and redundant explanations may be omitted.

[0029] <First Embodiment> A sheet 10 according to one embodiment of the present invention will be described with reference to Figures 1 and 2.

[0030] [1. Structure of Sheet 10] Figure 1 is a schematic diagram showing the structure of sheet 10 according to one embodiment of the present invention.

[0031] As shown in Figure 1, the sheet 10 is a sheet-like member that extends in the xy plane and includes a first surface 11 and a second surface 12 corresponding to the opposite surface of the first surface 11. As will be described in detail later, a molded product is manufactured by thermoforming the sheet 10. The thickness of the sheet 10 in the z-axis direction can be any thickness that allows for the manufacture of a molded product by thermoforming. For example, the thickness of the sheet 10 is 0.1 mm or more and 2.0 mm or less, but is not limited to this.

[0032] Sheet 10 is made of a crystallizable polyester resin. Here, a crystallizable polyester resin is a polyester resin that has a melting point and can be changed to either a crystalline or amorphous state by thermoforming. The crystallizable polyester resin in sheet 10 can be in a crystalline or amorphous state, for example, depending on the cooling conditions during thermoforming. Therefore, sheet 10 before thermoforming may be in a crystalline state or an amorphous state.

[0033] For example, examples of crystallizable polyester resins include polyethylene terephthalate resin (PET), polylactic acid resin (PLA), polybutylene terephthalate resin (PBT), and polyhydroxyalkanoate resin (PHA). Among these, PET has excellent heat resistance, so it is preferable that the sheet 10 be made of a crystallizable polyester resin mainly composed of PET. After thermoforming, PET in a crystalline state may be called C-PET, and PET in an amorphous state may be called A-PET.

[0034] On the other hand, polyester resins that do not have a melting point, maintain an amorphous state even when thermoformed, and do not change to a crystalline state are not included in the above-mentioned crystalline polyester resins. For example, polyethylene terephthalate resin (PETG) to which cyclohexanedimethanol has been added maintains an amorphous state even when thermoformed. Therefore, PETG is not included in the crystalline polyester resins.

[0035] As described above, whether a polyester resin is a crystallizable polyester resin can be clearly distinguished based on the materials contained in the polyester resin. Although details will be described later, although the sheet 10 is made of a crystallizable polyester resin, the polyester resin is crystallized in a molded product produced by thermoforming the sheet 10. That is, the molded product is made of, for example, C-PET.

[0036] Other components may be copolymerized into the crystallizable polyester resin as long as the object of the present invention is not impaired. Specifically, examples of copolymerization components for dicarboxylic acid components include isophthalic acid, naphthalenedicarboxylic acid, 4,4-diphenyldicarboxylic acid, adipic acid, sebacic acid, and ester-forming derivatives thereof. Examples of diol components include diethylene glycol, hexamethylene glycol, neopentyl glycol, and cyclohexanedimethanol. Furthermore, polyoxyalkylene glycols such as polyethylene glycol and polypropylene glycol may also be cited as copolymerization components. One or more of the above materials may be used as the copolymerization component.

[0037] In addition, the sheet 10 may contain a pigment as a coloring component, an impact modifier as a shock absorbing component, a crosslinking agent that links polymer chains, or the like.

[0038] [2. Method for Producing Sheet 10] Figure 2 is a flowchart illustrating a method for producing sheet 10 according to an embodiment of the present invention.

[0039] Figure 2 shows a flowchart of a method for producing sheet 10 using extrusion molding. Hereinafter, the method for producing the sheet 10 will be described according to the order of steps in the flowchart shown in Figure 2, but the method for producing the sheet 10 is not limited to extrusion molding.

[0040] In step S100, the polyester resin containing polyethylene terephthalate as a main component and other components are weighed.

[0041] In step S110, the weighed polyester resin and other components obtained in step S100 are supplied from a feed port of an extruder, melt-kneaded, formed into a sheet shape by a die of the extruder, and then the sheet 10 is extruded from a discharge port of the die. The extruded sheet 10 is wound up by a winder while being formed by rolls. The sheet 10 is made of a crystallizable polyester resin, and may be in either a crystalline state or an amorphous state. After the sheet 10 is extruded from the discharge port of the die, the crystalline state or amorphous state of the polyester resin in the sheet 10 can be controlled by adjusting the temperature of the rolls.

[0042] The sheet 10 produced by the above production method can be cut according to the size of a molded product for use.

[0043] [3. Physical Properties of Sheet 10] The physical properties of the polyester resin contained in the sheet 10 can be measured by gel permeation chromatography (GPC). Specifically, the z-average molecular weight (Mz), the integral molecular weight distribution curve, and the differential molecular weight distribution curve of the polyester resin can be obtained by GPC. Unless otherwise specified, the molecular weights in the z-average molecular weight, the integral molecular weight distribution curve, and the differential molecular weight distribution curve are values converted in terms of polystyrene.

[0044] In the sheet 10, the z-average molecular weight of the polyester resin is 300,000 or less, preferably 275,000 or less, and more preferably 250,000 or less. When the z-average molecular weight is large, although the impact resistance of the molded product is improved, the fluidity of the polyester resin decreases. In this case, it is difficult to mold the polyester resin into a sheet, and problems such as decreased flatness of the sheet surface may occur. In addition, when thermoforming the sheet, it becomes difficult for the molded product to reproduce the shape of the mold. Therefore, by setting the z-average molecular weight of the polyester resin within the above range, the impact resistance of the molded product can be improved. Furthermore, the sheet 10 can be molded more easily, and the mold reproducibility of a molded product produced by thermoforming the sheet 10 can be improved.

[0045] The integral molecular weight distribution curve allows for the calculation of the content of molecular components with specific molecular weights. Specifically, the integral molecular weight distribution curve can be used to calculate the content of molecular components with a molecular weight of 10,000 or less, and the content of molecular components with a molecular weight of 30,000 or less.

[0046] In sheet 10, the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin is 6.5% by weight, preferably 6.0% by weight or less, and preferably 5.5% by weight or less. If the content of molecular components with a molecular weight of 10,000 or less is high, the impact resistance (cold resistance) of the molded product at low temperatures decreases. Therefore, by keeping the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin within the above range, the cold resistance of the molded product manufactured by thermoforming sheet 10 can be improved.

[0047] In sheet 10, the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin is 25.0% by weight or less, preferably 22.5% by weight or less, and more preferably 20.0% by weight or less. If the content of molecular components with a molecular weight of 30,000 or less is greater than 25.0% by weight, the drawdown will be large when the sheet is thermoformed, and the shapeability of the molded product will be poor. Therefore, by keeping the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin within the above range, the shapeability of the molded product produced by thermoforming sheet 10 can be improved.

[0048] Even if the z-average molecular weight of the polyester resin and the content of molecular components of a specific molecular weight relative to the total weight of the polyester resin are within the above-mentioned range, the polyester resin may contain molecular components with large molecular weights in order to improve the impact resistance of the molded product. In this case, two or more peaks will appear in the differential molecular weight distribution curve. However, polyester resins having two or more peaks in the differential molecular weight distribution curve are prone to crystalline non-uniformity when forming or thermoforming sheets. Therefore, it is preferable that the polyester resin has one peak in the differential molecular weight distribution curve in the range of logarithmic molecular weight between 3.5 and 6.5. Furthermore, it is even more preferable that the polyester resin does not have a peak exceeding the z-average molecular weight in the differential molecular weight distribution curve.

[0049] As described above, in the sheet 10 according to this embodiment, the z-average molecular weight of the polyester resin is adjusted, and even molded products made of polyester resin crystallized by thermoforming can have improved impact resistance. Furthermore, by adjusting the content of molecular components of specific molecular weights in the polyester resin of the sheet 10, the shapeability and cold resistance of the molded product can be improved.

[0050] <Second Embodiment> Referring to Figure 3, a sheet 20 according to one embodiment of the present invention will be described. In the following, if the configuration of sheet 20 is the same as that of sheet 10, the description of the configuration of sheet 20 may be omitted.

[0051] [1. Configuration of Sheet 20] Figure 3 is a schematic diagram showing the configuration of sheet 20 according to one embodiment of the present invention.

[0052] As shown in Figure 3, the sheet 20 is a sheet-like member that extends in the xy plane and includes a first surface 21 and a second surface 22 corresponding to the opposite surface of the first surface 21. As will be described in detail later, a molded product is manufactured by thermoforming the sheet 20. The thickness of the sheet 20 in the z-axis direction can be any thickness that is thermoplastic. For example, the thickness of the sheet 20 is 0.1 mm or more and 2.0 mm or less, but is not limited to this.

[0053] The sheet 20 includes a first outer layer 20-1, a second outer layer 20-2, and an intermediate layer 20-3 between the first outer layer 20-1 and the second outer layer 20-2. In other words, the sheet 20 has a laminated structure in which the first outer layer 20-1, the intermediate layer 20-3, and the second outer layer 20-2 are stacked in order. The first outer layer 20-1 and the second outer layer 20-2 form a first surface 21 and a second surface 22, respectively.

[0054] Each of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 contains a crystallizable polyester resin. The crystallizable polyester resin may be copolymerized with other components, as long as the objectives of the present invention are not impaired. Furthermore, at least one of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 may contain a pigment as a coloring component.

[0055] The first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 will be described in more detail below.

[0056] A nucleating agent may be added to each of the first outer layer 20-1 and the second outer layer 20-2. The nucleating agent can improve the crystallization rate and promote crystallization during thermoforming. Examples of nucleating agents include aliphatic polymers, organometallic salts, inorganic compounds, natural mineral particles, metal hydrates, or metal hydroxides. One or more of the above materials can be used as nucleating agents. The nucleating agents contained in the first outer layer 20-1 and the second outer layer 20-2 may be the same or different.

[0057] Examples of aliphatic polymers include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, polybutene, polypentene, and polymethylpentene. Examples of organometallic salts include sodium benzoate, potassium benzoate, calcium benzoate, p-butyl sodium benzoate, p-butyl potassium benzoate, p-butyl calcium benzoate, sodium stearate, potassium stearate, calcium stearate, sodium montana, potassium montana, calcium montana, sodium palmitate, potassium palmitate, calcium palmitate, sodium salt of ethylene-methacrylic acid copolymer, potassium salt of ethylene-methacrylic acid copolymer, calcium salt of ethylene-methacrylic acid copolymer, alkali metal or alkaline earth metal salts of organic carboxylic acids such as sodium terephthalate and lithium terephthalate. Examples of inorganic compounds include graphite, carbon black, magnesium oxide, calcium silicate, magnesium silicate, calcium carbonate, or magnesium carbonate. Examples of mineral particles include talc or kaolin. Examples of metal hydrates include Mg ４ Al ２ (OH) １２ CO ３ 3H ２ Examples include O. Examples of metal hydroxides include Mg ３ Si ４ (OH) ２ These are some examples.

[0058] The content of the crystal nucleating agent in the first outer layer 20-1 is 0.05% by weight or more, preferably 0.1% by weight, and more preferably 0.2% by weight or more, relative to the total weight of the first outer layer 20-1. The upper limit of the crystal nucleating agent content is 10% by weight or less, preferably 8.0% by weight or less, and more preferably 6.0% by weight or less. By changing the content of the crystal nucleating agent, the degree of crystallinity of the first outer layer 20-1 after thermoforming can be adjusted.

[0059] The content of the nucleating agent in the second outer layer 20-2 is also within the above range. The content of the nucleating agent in the second outer layer 20-2 may be the same as or different from the content of the nucleating agent in the first outer layer 20-1. If the first outer layer 20-1 and the second outer layer 20-2 have the same nucleating agent and the same content, the raw materials prepared to form the first outer layer 20-1 and the second outer layer 20-2 can be standardized, thereby reducing raw material costs.

[0060] The intermediate layer 20-3 does not necessarily need to contain a crystal nucleating agent. Even if the intermediate layer 20-3 does not contain a crystal nucleating agent, it is possible to crystallize the polyester resin by thermoforming because the intermediate layer 20-3 contains a crystallizable polyester resin. However, the intermediate layer 20-3 may contain a crystal nucleating agent. In this case, the type and content of the crystal nucleating agent in the intermediate layer 20-3 are adjusted so that the crystallization rate in the intermediate layer 20-3 is slower than the crystallization rate in the first outer layer 20-1 and the second outer layer 20-2, respectively. For example, the content of the crystal nucleating agent in the intermediate layer 20-3 is smaller than the content of the crystal nucleating agent in the first outer layer 20-1 and the second outer layer 20-2, respectively. For example, the content of the crystal nucleating agent in the intermediate layer 20-3 is 0.005% by weight or more, preferably 0.01% by weight or more, and more preferably 0.05% by weight or more, based on the total weight of the intermediate layer 20-3. The upper limit of the content of the crystal nucleating agent in the intermediate layer 20-3 is 5.0% by weight or less, preferably 3.0% by weight or less, and more preferably 2.0% by weight or less. The crystal nucleating agent in the intermediate layer 20-3 may be the same as or different from the crystal nucleating agents in the first outer layer 20-1 and the second outer layer 20-2, respectively.

[0061] The crystallizable polyester in each of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 may be copolymerized with other components. Furthermore, at least a portion of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 may contain pigments as coloring components, impact modifiers as impact absorbing components, or crosslinking agents that link polymer chains.

[0062] In this embodiment, a sheet 20 having a three-layer laminated structure has been described, but the laminated structure of the sheet 20 is not limited to three layers.

[0063] [2. Method for Manufacturing Sheet 20] Sheet 20 can be manufactured using extrusion molding, similar to sheet 10. Therefore, the method for manufacturing sheet 20 will be explained in correspondence with the steps in the flowchart shown in Figure 2.

[0064] In step S100, a polyester resin mainly composed of polyethylene terephthalate and other components are weighed out as raw materials for the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3, respectively. A nucleating agent may be added to the polyester resin to adjust the degree of crystallinity of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3, respectively. For example, a first nucleating agent, a second nucleating agent, and a third nucleating agent may be added to the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3, respectively. Here, if the first, second, and third nucleating agents are the same, the content of the third nucleating agent is less than the content of the first and second nucleating agents.

[0065] In step S110, the three metered polyester resins and other components from step S100 are supplied from separate feed ports of the extruder, melt-mixed, and formed into a sheet shape by the extruder's die. The sheet 20, in which the first outer layer 20-1, intermediate layer 20-3, and second outer layer 20-2 are sequentially laminated, is then extruded from the die's discharge port. The extruded sheet 20 is formed on a roll and wound up by a winding machine. The sheet 20 is made of a crystallizable polyester resin and may be in a crystalline or amorphous state. After the sheet 20 is extruded from the die's discharge port, the crystalline or amorphous state of the polyester resin in the sheet 20 can be controlled by adjusting the temperature of the roll.

[0066] In an extruder, if the content of the intermediate layer 20-3 relative to the total weight of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 is less than 5% by weight, a sheet 20 with a good appearance cannot be obtained. On the other hand, if the content of the intermediate layer 20-3 relative to the total weight of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 exceeds 95% by weight, the first outer layer 20-1 and the second outer layer 20-2 will not be uniformly laminated. Therefore, the content of the intermediate layer 20-3 relative to the total weight of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 is 5% by weight or more and 95% by weight or less, preferably 30% by weight or more and 95% by weight or less, and more preferably 50% by weight or more and 95% by weight or less. The thickness of the intermediate layer 20-3 may be greater than the sum of the thicknesses of the first outer layer 20-1 and the second outer layer 20-2.

[0067] The sheet 20 manufactured by the above manufacturing method can be cut and used according to the size of the molded product.

[0068] [3. Physical Properties of Sheet 20] Sheet 20, which has a laminated structure, has the same physical properties as Sheet 10. The z-average molecular weight of the polyester resin in Sheet 20 is 300,000 or less, preferably 275,000 or less, and more preferably 250,000 or less. In addition, the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin in Sheet 20 is 25.0% by weight or less, preferably 22.5% by weight or less, and more preferably 20.0% by weight or less. In addition, the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin in Sheet 20 is 6.5% by weight, preferably 6.0% by weight or less, and more preferably 5.5% by weight or less. Furthermore, in the differential molecular weight distribution curve, it is preferable that the polyester resin in Sheet 20 has one peak in the range of logarithmic molecular weight of 3.5 to 6.5.

[0069] As described above, the sheet 20 according to this embodiment also has an adjusted z-average molecular weight of the polyester resin, and even if the molded product is made of polyester resin crystallized by thermoforming, its impact resistance can be improved. Furthermore, by adjusting the content of molecular components of specific molecular weights in the polyester resin of the sheet 20, the shapeability and cold resistance of the molded product can be improved. Moreover, in the sheet 20, the first outer layer 20-1 and the second outer layer 20-2 that come into contact with the heat-set mold can be sufficiently crystallized and solidified. As a result, the molded product is easy to release from the heat-set mold and has excellent processability.

[0070] Furthermore, in this embodiment, by adding a crystal nucleating agent to each of the first outer layer 20-1 and the second outer layer 20-2 of the sheet 20 that come into contact with the heat-setting mold, the first outer layer 20-1 and the second outer layer 20-2 can be sufficiently crystallized and solidified. In this case as well, the molded product is easy to release from the heat-setting mold and has excellent processability. As a result, the cycle time in thermoforming can be shortened. Therefore, the molded product can have its degree of crystallinity reduced while maintaining heat resistance, thereby improving impact resistance.

[0071] <Third Embodiment> A molded product 30 according to one embodiment of the present invention will be described with reference to Figures 4 and 5.

[0072] [1. Structure of the molded product 30] Figure 4 is a schematic diagram showing the structure of the molded product 30 according to one embodiment of the present invention.

[0073] The molded product 30 shown in Figure 4 is a so-called food container. The molded product 30 has an inner surface 31 and an outer surface 32, and food is contained on the inner surface 31 side. As will be described in detail later, the molded product 30 is manufactured by thermoforming a sheet 10 or a sheet 20. When the molded product 30 is manufactured from a sheet 10, the inner surface 31 and the outer surface 32 are formed by a first surface 11 and a second surface 12, respectively. When the molded product 30 is manufactured from a sheet 20, the inner surface 31 and the outer surface 32 are formed by a first surface 21 and a second surface 22, respectively.

[0074] The structure of the molded product 30 corresponds to the structure of the sheet 10 or sheet 20 before thermoforming, but the polyester resin crystallizes during thermoforming. When the molded product 30 is manufactured from the sheet 10, the polyester resin constituting the molded product 30 is crystallized regardless of whether the polyester resin of the sheet 10 is in a crystalline or amorphous state. That is, the molded product 30 contains, for example, crystalline PET. Also, when the molded product 30 is manufactured from the sheet 20, the polyester resin of the first outer layer 20-1, the second outer layer 20-2, and the intermediate layer 20-3 of the sheet 20 is in a crystalline or amorphous state, and the polyester resin of the first outer layer, the second outer layer, and the intermediate layer constituting the molded product 30 is crystallized. That is, each of the first outer layer, the second outer layer, and the intermediate layer of the molded product 30 contains crystalline polyester resin. Furthermore, the degree of crystallinity of the first outer layer and the second outer layer constituting the molded product 30 manufactured from the sheet 20 is greater than the degree of crystallinity of the intermediate layer. As will be described in detail later, the increased degree of crystallinity of the first and second outer layers makes it possible to easily release the molded product 30 from the heat-set mold.

[0075] [2. Method for Manufacturing Molded Product 30] Figure 5 is a flowchart illustrating a method for manufacturing a molded product 30 according to one embodiment of the present invention.

[0076] The molded product 30 is manufactured by thermoforming the sheet 10 or sheet 20, and Figure 5 shows a flowchart of the manufacturing method. The manufacturing method of the molded product 30 will be described below in the order of the steps in the flowchart shown in Figure 5, but the manufacturing method of the molded product 30 is not limited to this.

[0077] In step S300, sheet 10 or sheet 20 is heated. The heating temperature is, for example, 90°C to 240°C.

[0078] In step S310, the heat-set mold is heated. The heating temperature is, for example, between 90°C and 240°C.

[0079] In step S320, sheet 10 or sheet 20 is held in a heat-setting mold for a predetermined time and heated. The predetermined time is, for example, 1 second or more and 60 seconds or less. The heat-setting mold used is a mold corresponding to the molded product 30. In step S320, the polyester resin contained in sheet 10 or sheet 20 is crystallized.

[0080] In sheet 20, if a crystal nucleating agent is included in each of the first outer layer 20-1 and the second outer layer 20-2, crystallization can be promoted. In this case, the polyester resin contained in each of the first outer layer 20-1 and the second outer layer 20-2 has a high degree of crystallinity. On the other hand, the intermediate layer 20-3 does not contain a crystal nucleating agent, or if it does, the amount is small. Therefore, the crystallization rate of the intermediate layer 20-3 is slower than that of the first outer layer 20-1 and the second outer layer 20-2. Consequently, the polyester resin contained in the intermediate layer 20-3 also crystallizes, but at a slower rate, and as a result, the intermediate layer 20-3 has a lower degree of crystallinity than the first outer layer 20-1 and the second outer layer 20-2.

[0081] In step S330, the thermoformed sheet 10 or sheet 20 is released from the heat-setting mold. In particular, the thermoformed sheet 20 has good release properties and can be easily released from the heat-setting mold.

[0082] Through the above steps, the molded product 30 is manufactured.

[0083] [3. Physical Properties of Molded Article 30] The physical properties of the polyester resin contained in the molded article 30 can also be measured by GPC. Since the molded article 30 is manufactured using sheet 10 or sheet 20, the molded article 30 has the same physical properties as sheet 10 or sheet 20. The z-average molecular weight of the polyester resin in the molded article 30 is 300,000 or less, preferably 275,000 or less, and more preferably 250,000 or less. In addition, the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin in the molded article 30 is 25.0% by weight or less, preferably 22.5% by weight or less, and more preferably 20.0% by weight or less. In addition, the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin in the molded article 30 is 6.5% by weight, preferably 6.0% by weight or less, and more preferably 5.5% by weight or less. Furthermore, in the differential molecular weight distribution curve, it is preferable that the polyester resin in the molded product 30 has one peak in the range of logarithmic molecular weight of 3.5 to 6.5.

[0084] Furthermore, the impact resistance of the molded product 30 can be evaluated by a DuPont impact test. For example, the impact resistance (cold resistance) of the molded product 30 at low temperatures can be evaluated by performing a DuPont impact test at -20°C. The molded product 30 has improved cold resistance, and its 50% fracture energy at -20°C is 0.6 J or more, preferably 0.7 J or more, and more preferably 1.0 J or more.

[0085] A nucleating agent may be added to the molded product 30, and the amount of nucleating agent contained in the molded product 30 can be determined, for example, based on the amount of nucleating agent contained in each layer constituting the sheet 20. In addition, in a molded product 30 manufactured by thermoforming the sheet 20, the degree of crystallinity of the intermediate layer 20-3 is lower than the degree of crystallinity of the first outer layer 20-1 and the second outer layer 20-2, respectively, but the degree of crystallinity of the molded product 30 may be determined based on the degree of crystallinity of each layer constituting the sheet 20.

[0086] As described above, the molded product 30 according to this embodiment is manufactured by thermoforming sheet 10 or sheet 20. Both sheet 10 and sheet 20 are made of a crystallizable polyester resin, and the molded product 30 thermoformed using sheet 10 or sheet 20 is composed of crystallized polyester resin, for example, C-PET. Therefore, the molded product 30 has high heat resistance. Furthermore, by adjusting the content of molecular components of a specific molecular weight contained in sheet 10 or sheet 20, or by adjusting the amount of crystal nucleating agent added, the molded product 30 can have excellent processability and improved cold resistance. In particular, the molded product 30 using sheet 20 has excellent release properties from heat-set molds. Therefore, the molded product 30 can have improved cold resistance while maintaining heat resistance.

[0087] In the following sections, the sheet 20 according to the second embodiment and the molded product 30 according to the third embodiment will be described in more detail based on the manufactured examples.

[0088] <First Embodiment> As samples for Examples 1 to 3, sheets 20 were prepared using the manufacturing method described in the second embodiment. In all of the sheets 20 according to Examples 1 to 3, the first outer layer and the second outer layer each contain a crystallizable polyester resin to which a crystal nucleating agent has been added. On the other hand, as a sample for Comparative Example 1, a single-layer sheet made of a crystallizable polyester resin without a crystal nucleating agent was prepared. Also, as a sample for Comparative Example 2, a single-layer sheet made of a crystallizable polyester resin with a crystal nucleating agent added was prepared. As the crystallizable polyester resin, PET with an IV value of 1.0 copolymer manufactured by Indorama was used. In addition, a masterbatch manufactured by Sukano was commonly used as the crystal nucleating agent. That is, the materials of the first outer layer and the second outer layer are the same. Therefore, in the following, the first outer layer and the second outer layer may be described as the outer layer. The thickness of the sheet 20 and the single-layer sheet is 0.55 mm. The detailed conditions for the samples in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0089]

[0090] The thickness of each layer constituting the samples of Examples 1 to 3 and Comparative Examples 1 to 2 was calculated. The ratio of each layer to the sheet thickness (0.55 mm) of each sample is shown in Table 2.

[0091]

[0092] [3. Evaluation of Crystallization of Sheet 20 and its Molded Products] Differential scanning calorimetry (DSC) was performed to evaluate the crystallization of the samples from Example 2 and Comparative Example 2 and the molded products manufactured using them. The crystallization energies calculated from DSC are shown in Table 3.

[0093]

[0094] The molded product after thermoforming has a significantly lower crystallization energy compared to the sheet 20 before thermoforming. This means that the degree of crystallization is increased by thermoforming, and by using sheet 20, it is possible to manufacture molded products with a high degree of crystallization. Furthermore, the molded products using not only the sample in Example 2 but also the sample in Comparative Example 2 also show a high degree of crystallization.

[0095] [4. Evaluation of Heat Resistance of Molded Products] The heat resistance of molded products manufactured using the samples from Examples 1 to 3 and Comparative Examples 1 to 2 was evaluated. The heat resistance was evaluated in accordance with JIS S209 7.4 by placing the molded product in a constant temperature bath heated to a predetermined temperature for one hour and evaluating whether significant deformation occurred. The evaluation results are shown in Table 4. In Table 4, "○" indicates that no significant deformation occurred, and "×" indicates that significant deformation occurred.

[0096]

[0097] As can be seen from Table 4, the molded products made using the samples of Examples 1 to 3 did not show significant deformation even at a temperature of 160°C, and no decrease in heat resistance was observed. In particular, the molded products made using the samples of Examples 1 to 3 did not show significant deformation even at a temperature of 220°C, indicating excellent heat resistance. On the other hand, although the molded product made using the sample of Comparative Example 2 did not show significant deformation up to a temperature of 220°C, the molded product made using the sample of Comparative Example 1 showed significant deformation even at a temperature of 160°C.

[0098] [5. Evaluation of Cold Resistance of Molded Products] [5-1. Freezing Drop Test] To evaluate cold resistance, molded products with a 300g weight were stored in a -20°C freezer for 16 hours or more. After that, a freezing drop test was conducted in which the molded products were dropped from a height of 1m with the bottom of the molded product facing downwards. In the freezing drop test, three molded products were prepared for each of Examples 1 to 3 and Comparative Examples 1 to 2 (i.e., N=3), and each molded product was dropped three times, and the number of broken molded products was counted. If all three did not break, it was evaluated as "○", if one or two broke, it was evaluated as "△", and if all three broke, it was evaluated as "×". The evaluation results are shown in Table 5.

[0099]

[0100] As can be seen from Table 5, the molded products made using the samples of Examples 1 to 3 possess cold resistance, as evidenced by the presence of uncracked molded products. The molded product made using the sample of Comparative Example 1 also possesses cold resistance, but as mentioned above, it lacks heat resistance, indicating that it is not a molded product that maintains heat resistance while improving cold resistance.

[0101] [5-2. DuPont Impact Test] In order to quantify the above-mentioned freezing drop test, a DuPont impact test in accordance with JIS K7211-1 was performed as an evaluation of the impact resistance of molded products at low temperatures. Specifically, test pieces of 100 mm length × 50 mm width were prepared from each molded product of Example 1, Example 2, and Comparative Example 2, a DuPont impact test was performed on the prepared test pieces, and 50% fracture energy was calculated. The DuPont impact test was performed under the conditions of a temperature of -20°C and a drop load of 0.3 kg. Table 6 shows the 50% fracture energy (E at -20°C calculated from the DuPont impact test ５０ ).

[0102]

[0103] As can be seen from Table 6, in the molded products of Example 1 and Example 2, the 50% fracture energy at -20°C is 0.7 J or more. On the other hand, in the molded product of Comparative Example 2, the 50% fracture energy at -20°C is less than 0.7 J. This result is the same as the above-mentioned freezing drop test, and indicates that the molded products of Example 1 and Example 2 have improved impact resistance at low temperatures, that is, cold resistance, compared to the molded product of Comparative Example 2.

[0104] <Second Example> [1. Preparation of Samples] As samples of Examples 5 to 8, sheets 20 were prepared using the manufacturing method described in the second embodiment, and then molded products 30 were prepared using the manufacturing method described in the third embodiment. Table 7 shows the raw materials of the sheets 20 in each sample and their contents.

[0105]

[0106] The raw material PET, the crystal nucleating agent as a masterbatch, the pigment, the impact modifier, and the crosslinking agent were common to each sample, and commercially available products were used.

[0107] The polyester resin contained in each of the first outer layer, intermediate layer, and second outer layer of each sample is crystallized by thermoforming, and each of the first outer layer, intermediate layer, and second outer layer of each sample contains PET in a crystalline state.

[0108] Furthermore, a commercially available product (a gratin dish from a supermarket) was used as the sample for Comparative Example 3, which served as a comparison for the samples in Examples 5 to 8.

[0109] [2. Sample Evaluation] [2-1. GPC] The physical properties of the polyester resin of each sample were evaluated using GPC. Specifically, the z-average molecular weight (Mz), integral molecular weight distribution curve, and differential molecular weight distribution curve were calculated using GPC, and the content of molecular components with a molecular weight of 10,000 or less and the content of molecular components with a molecular weight of 30,000 or less were obtained from the integral molecular weight distribution curve. For GPC measurement, test pieces prepared from each sample were dissolved in a 30 ml vial at a ratio of 1 / 1:1 HFIP / chloroform mixed solvent per 5.0 mg, and 9.0 ml of chloroform was added to prepare the solution. The solution was filtered through a 0.50 μm PTFE disposable membrane filter unit, and the filtrate was measured. Table 8 shows the GPC measurement conditions, and Table 9 shows the z-average molecular weight, the content of molecular components with a molecular weight of 10,000 or less, and the content of molecular components with a molecular weight of 30,000 or less obtained from GPC. In Table 9, the content of molecular components with a molecular weight of 10,000 or less and the content of molecular components with a molecular weight of 30,000 or less are both expressed as a percentage of the total weight of the polyester resin.

[0110]

[0111]

[0112] As can be seen from Table 9, in Examples 5 to 8, the content of molecular components with a molecular weight of 10,000 or less is 6.5% by weight or less, and the content of molecular components with a molecular weight of 30,000 or less is 25.0% by weight or less. On the other hand, in Comparative Example 3, the content of molecular components with a molecular weight of 10,000 or less is more than 6.5% by weight, and the content of molecular components with a molecular weight of 30,000 or less is more than 25.0% by weight.

[0113] Figure 6 shows a graph of the differential molecular weight distribution curve obtained by GPC. In the graph, the horizontal axis represents the logarithmic molecular weight (logM), and the vertical axis represents the slope of the integral molecular weight distribution curve (dwt / d(logM)).

[0114] As can be seen from Figure 6, Examples 5 to 8 have one peak between logarithmic molecular weights of 4.9 and 5.0 (roughly corresponding to molecular weights between 79,000 and 100,000). Therefore, in all Examples 5 to 8, there is a peak at a molecular weight below the z-average molecular weight. On the other hand, Comparative Example 3 has a peak not only around logarithmic molecular weight of 4.8 (roughly corresponding to molecular weight of 63,000), but also at logarithmic molecular weight of 5.7 (roughly corresponding to molecular weight of 500,000). Therefore, Comparative Example 3 has two peaks, with peaks present at molecular weights exceeding the z-average molecular weight.

[0115] [2-2. DuPont Impact Test] To evaluate the impact resistance of molded products at low temperatures, the same DuPont impact test as described above was performed. Table 10 shows the 50% fracture energy at -20°C calculated from the DuPont impact test.

[0116]

[0117] As can be seen from Table 10, the 50% fracture energy at -20°C is 1.0 J or more in Examples 5 to 8. On the other hand, the 50% fracture energy at -20°C in Comparative Example 3 is less than 1.0 J. This result indicates that Examples 5 to 8 have improved impact resistance at low temperatures, i.e., cold resistance, compared to Comparative Example 3.

[0118] Any effects or benefits other than those brought about by the embodiments described above, if they are clear from the description herein or easily predictable to a person skilled in the art, are naturally considered to be brought about by the present invention.

[0119] 10, 20: Sheet, 11, 21: First surface, 12, 22: Second surface, 20-1: First outer layer, 20-2: Second outer layer, 20-3: Intermediate layer, 30: Molded product, 31: Inner surface, 32: Outer surface

Claims

1. A sheet made of a crystallizable polyester resin mainly composed of polyethylene terephthalate, wherein the z-average molecular weight of the polyester resin is 300,000 or less, and the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin is 6.5% by weight or less.

2. The sheet according to claim 1, wherein the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin is 25.0% by weight or less.

3. The sheet according to claim 1, wherein the polyester resin has one peak in the range of logarithmic molecular weight of 3.5 to 6.5 in the differential molecular weight distribution curve obtained by gel permeation chromatography.

4. A molded article manufactured by thermoforming a sheet according to any one of claims 1 to 3, wherein the polyester resin comprises polyethylene terephthalate in a crystalline state.

5. A sheet comprising a first outer layer, a second outer layer, and an intermediate layer between the first outer layer and the second outer layer, wherein each of the first outer layer, the second outer layer, and the intermediate layer contains a crystallizable polyester resin mainly composed of polyethylene terephthalate, the z-average molecular weight of the polyester resin in the sheet is 300,000 or less, and the content of molecular components with a molecular weight of 10,000 or less relative to the total weight of the polyester resin is 6.5% by weight or less.

6. The sheet according to claim 5, wherein the content of molecular components with a molecular weight of 30,000 or less relative to the total weight of the polyester resin in the sheet is 25.0% by weight.

7. The sheet according to claim 5, wherein the polyester resin in the sheet has one peak in the range of logarithmic molecular weight of 3.5 to 6.5 in the differential molecular weight distribution curve obtained by gel permeation chromatography.

8. The sheet according to claim 5, wherein the content of the intermediate layer relative to the total weight of the sheet is 50% by weight or more.

9. A molded article manufactured by thermoforming a sheet according to any one of claims 5 to 8, wherein each of the first outer layer, the second outer layer, and the intermediate layer comprises polyethylene terephthalate in a crystalline state.

10. The molded article according to claim 9, wherein the degree of crystallinity of the first outer layer and the second outer layer is greater than the degree of crystallinity of the intermediate layer.

11. The molded article according to claim 9, wherein the 50% fracture energy in a DuPont impact test at -20°C is 1.0 J or more.

12. A sheet comprising a first outer layer, a second outer layer, and an intermediate layer between the first outer layer and the second outer layer, wherein each of the first outer layer, the second outer layer, and the intermediate layer comprises a crystallizable polyester resin mainly composed of polyethylene terephthalate, the first outer layer comprises a first nucleating agent, and the second outer layer comprises a second nucleating agent.

13. The sheet according to claim 12, wherein the intermediate layer does not contain a crystal nucleating agent.

14. The sheet according to claim 12, wherein the intermediate layer comprises a third nucleating agent, and the first nucleating agent, the second nucleating agent, and the third nucleating agent are the same.

15. The sheet according to claim 12, wherein the intermediate layer contains a third nucleating agent, the first nucleating agent is added in a first content relative to the total amount of the first outer layer, the second nucleating agent is added in a second content relative to the total amount of the second outer layer, and the third nucleating agent is added in a third content relative to the total amount of the intermediate layer, the third content being smaller than each of the first and second contents.

16. A molded article manufactured by thermoforming a sheet according to any one of claims 12 to 15, wherein the degree of crystallinity of the first outer layer and the second outer layer is greater than the degree of crystallinity of the intermediate layer.

17. The molded article according to claim 16, wherein the ratio of the thickness of the intermediate layer to the sum of the thicknesses of the first outer layer, the second outer layer, and the intermediate layer is 5% or more and 95% or less.

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