JP2024108555A - Thermoplastic polyester resin foam molding - Google Patents

Abstract

To provide a thermoplastic polyester resin foamed molded product that resists deformation even under stress in a heated state.SOLUTION: A thermoplastic polyester resin foamed molded product includes a foamed layer including a thermoplastic polyester resin foam. The thermoplastic polyester resin foam includes a thermoplastic polyester resin. In the foamed layer, the difference in crystallinity between either surface section and the intermediate part is 15% or less.SELECTED DRAWING: None

Description

The present invention relates to a thermoplastic polyester resin foam molded product.

Traditionally, food and beverage products such as prepared meals, frozen foods, and coffee have been sold in thermoplastic resin containers. Purchasers of food and beverage products often heat and eat the food and beverage products in a microwave oven while they are still in the thermoplastic resin container. In particular, in recent years, due to the impact of the COVID-19 pandemic, there have been many opportunities to heat food and beverage products purchased at supermarkets and convenience stores in a microwave oven and eat them at home.

In addition, thermoplastic polystyrene-based resins have traditionally been used as thermoplastic resin containers for storing food, but in recent years, there has been a shift to alternative materials in light of environmental conservation concerns.

As one alternative material, thermoplastic polyester resins are attracting attention because of their excellent recyclability and the growing popularity of biomass raw materials produced using natural materials.

Patent Document 1 proposes a thermoplastic polyester resin foam sheet that contains a thermoplastic polyester resin and one or more crystallization promoters selected from inorganic crystallization promoters and organic crystallization promoters, and has a crystallization time of 14 minutes or less as measured by a specified measurement method, and a food packaging container that uses this foam sheet.

Patent Document 2 proposes a foamed resin container that includes a foamed layer of a thermoplastic polyester resin, in which the absolute value of the heat of crystallization is 1 to 5 mJ/mg and the degree of crystallization calculated by a specific formula is 20% or more.

Patent Document 3 proposes a polyester resin foam sheet in which 90% or more of the cells are closed cells (DIN ISO 4590), and the polyester resin forming the foam sheet has a carboxyl end group (CEG) equivalent of less than 100 meq/g.

Patent Document 4 proposes a resin composition containing a polyester resin (A) mainly composed of terephthalic acid and ethylene glycol and a modified polyolefin resin (C), in which the content of the polyester resin (A) in the resin composition is 85 to 99.5% by mass, the content of the modified polyolefin resin (C) is 0.5 to 15% by mass, the intrinsic viscosity of the resin composition is 0.8 to 1.2, the melt flow rate at 290°C is 3.5 to 5.5 g/10 min, and the carboxyl end group concentration is 30 equivalents/t or less, and a foam-molded product molded using this polyester resin composition is also proposed.

JP 2018-90761 A JP 2004-323554 A Special Publication No. 2022-533926 JP 2018-111812 A

On the other hand, when food or beverages stored in a thermoplastic resin container are heated in a microwave oven, the thermoplastic resin container is grasped, removed from the microwave oven, and moved to the desired location. At this time, in order to move the heated food smoothly, it is required that the grasped thermoplastic resin container does not deform.

However, the thermoplastic polyester resin foam containers described in Patent Documents 1 to 4 have the problem that they easily deform due to the heat from heated food and the weight of the food itself, and there is a demand for foam containers with excellent heat resistance that are less likely to deform even when food is heated in a microwave oven.

The present invention provides a thermoplastic polyester resin foam molded product that is resistant to deformation (excellent heat resistance) even when stress is applied in a heated state.

The present invention provides a thermoplastic polyester resin foam container that is resistant to deformation, for example, when food or beverage is heated in a microwave oven, despite the heat from the heated food or beverage and the weight of the food or beverage itself.

The thermoplastic polyester resin foam molding of the present invention is
A foam layer containing a thermoplastic polyester-based resin foam is provided.
The thermoplastic polyester resin foam contains a thermoplastic polyester resin,
The thermoplastic polyester resin has a total amount of ester compounds and ether compounds generated by GC/MS at 285° C. of 1000 ppm or less based on the total amount of the thermoplastic polyester resin.

The thermoplastic polyester resin foam molded product of the present invention is resistant to deformation even when a load is applied in a heated state.

Therefore, the thermoplastic polyester resin foam molded product of the present invention can be suitably used as a container for storing food and beverages. When the food and beverages stored in this container are heated using a microwave oven or the like, the container is not easily deformed even when subjected to the heat and mass of the heated food, and can be smoothly moved to the desired location while stably storing the food.

In the present invention, deformation of a thermoplastic polyester resin foam molded product refers to a state in which the thermoplastic polyester resin foam molded product does not return to its original state even after a stress such as a load applied to the thermoplastic polyester resin foam molded product is removed.

The thermoplastic polyester resin foam molded product of the present invention (hereinafter, sometimes simply referred to as "foam molded product") has a foam layer containing a thermoplastic polyester resin foam. In the foam layer, the difference in crystallinity between one of the surface portions and the middle portion is 15% or less.

The surface portion of the foam layer in a foam molded product refers to the portion between the surface of the foam layer of the foam molded product and a portion 0.2 mm deep from this surface. For example, if the foam molded product is a container, the surface of the foam layer of the foam molded product refers to the inner surface (the surface forming the storage portion) and outer surface of the container. If the foam molded product is a thermoformed product of a foam sheet, the surface of the foam layer of the foam molded product refers to the surface corresponding to the main surface (the surface with the largest area and the surface opposite this surface) of the foam layer of the foam sheet that is the original fabric of the foam molded product. The depth from the surface refers to the depth in the direction perpendicular to the surface. The middle portion of the foam layer of a foam molded product refers to the remaining portion of the foam layer from the foam molded product excluding both surface portions of the foam layer.

When the difference in crystallinity between one or both of the surface portions and the middle portion of the foam layer of a foam molded product is 15% or less, the foam molded product is less likely to deform even when a load is applied in a heated state, and has excellent heat resistance.

In foam-molded products, the difference between the crystallinity of the surface and the crystallinity of the middle part is within 15%, so that the crystallinity in the thickness direction of the foam layer is the same, and the thermal shrinkage rate is the same in the thickness direction. By making the thermal shrinkage rate in the thickness direction of the foam-molded product the same, even when stress is applied in a heated state, it is possible to prevent the occurrence of interface parts where the thermal shrinkage rate changes significantly, which would cause shear stress and result in a partial decrease in mechanical strength. Therefore, the foam-molded product has the excellent effect of maintaining excellent mechanical strength and not suffering from damage such as deformation.

In a foam-molded product, the difference in crystallinity between one of the surface portions of the foam layer and the middle portion of the foam layer is 15% or less, preferably 14% or less, more preferably 13% or less, more preferably 12% or less, and more preferably 7% or less.

In foam-molded products, the difference in crystallinity between both surface portions of the foam layer and the crystallinity of the middle portion of the foam layer is preferably 15% or less, more preferably 14% or less, more preferably 13% or less, more preferably 12% or less, and more preferably 7% or less.

The crystallinity of the surface of the foam layer in the foam molded product is preferably 10% or more, more preferably 12% or more, and even more preferably 14% or more. The crystallinity of the surface of the foam layer in the foam molded product is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. By setting the crystallinity of the surface within the above range, it is possible to impart excellent heat resistance to the foam molded product and improve brittleness.

The crystallinity of the middle part of the foam layer in the foam molded product is preferably 10% or more, more preferably 12% or more, and even more preferably 14% or more. The crystallinity of the middle part of the foam layer in the foam molded product is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. By keeping the crystallinity of the surface part within the above range, it is possible to impart excellent heat resistance to the foam molded product and improve brittleness.

The crystallinity of the entire foam-molded product is preferably 10% or more, more preferably 12% or more, and even more preferably 14% or more. The crystallinity of the entire foam-molded product is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less. By keeping the crystallinity of the surface portion within the above range, it is possible to impart excellent heat resistance to the foam-molded product and improve brittleness.

For foam-molded products, the crystallinity of the surface, middle, and entire foam-molded product is measured as follows:

Prepare a sample of 5 to 6 mg according to the area for which crystallinity is to be measured, as follows:

When measuring the crystallinity of the surface of the foam layer, prepare a sample by slicing the part of the foam molded product between the surface of the foam layer and a part 0.2 mm deep from the surface using a 0.2 mm slicer or razor.

When measuring the crystallinity of the middle part, remove the entire surface from the foam layer of the foam-molded product as described above, and cut out a sample from the remaining part of the foam layer.

When measuring the crystallinity of the entire foam molded product, cut out a sample so that it includes the entire thickness of the foam molded product.

The obtained sample is subjected to DSC measurement using the following measuring device under the following measuring conditions in accordance with JIS K7122 to determine the heat of crystallization.
(Measuring device)
DSC device: Differential scanning calorimeter DSC7000X type (manufactured by Hitachi High-Tech Science Corporation) (measurement conditions)
Sample amount: 5.5±0.5 mg
Reference (alumina) amount: 5 mg
Nitrogen gas flow rate: 20 mL/min
Number of tests: 2

Using the heat of fusion and the heat of crystallization of the DSC curve obtained above, the degree of crystallinity is calculated based on the following formula.
Crystallinity (%)
= [{absolute value of heat of fusion (J/g)-absolute value of heat of crystallization (J/g)}
/Complete crystallization heat amount (J/g)]×100

Examples of foam-molded products include, but are not limited to, packaging containers for food and beverages, packaging containers for seasonings, lunch boxes, fruit containers, vegetable containers and other packaging containers for food and beverages, packaging materials for precision instruments, cushioning packaging materials for electrical appliances, and daily necessities.

The thickness of the foam layer of the foam molded product is preferably 0.2 to 8.0 mm, and more preferably 0.3 to 7.0 mm. If the thickness of the foam sheet is 0.2 mm or more, the strength of the foam molded product can be improved. If the thickness of the foam layer is 8.0 mm or less, the crystallinity of the foam molded product in the thickness direction can be easily adjusted to the same degree, and the foam molded product has excellent mechanical strength even under heated conditions and excellent heat resistance.

The expansion ratio of the foam layer of the foam molded product is preferably 1.5 to 6.0 times, and more preferably 2.0 to 5.0 times. If the expansion ratio of the foam sheet is 1.5 times or more, the heat insulating properties of the foam molded product are improved. If the expansion ratio of the foam sheet is 6.0 times or less, the mechanical strength of the foam molded product is improved. The expansion ratio of the foam layer is the reciprocal of the apparent density of the entire synthetic resin that constitutes the foam layer.

The foam molded product may have a non-foamed thermoplastic resin sheet laminated to one or both sides of the foam layer. When a non-foamed thermoplastic resin sheet is laminated to one side, heat applied to the foam molded product can be transferred to the foam layer in a diffused state via the non-foamed thermoplastic resin sheet. As a result, the foam molded product is prevented from partially forming areas with a high degree of crystallinity, and the foam molded product has excellent mechanical strength and excellent heat resistance even under heated conditions.

The thermoplastic non-foamed sheet may be any sheet that can be laminated and integrated onto the surface of the foamed layer. Examples of the thermoplastic resin that constitutes the thermoplastic non-foamed sheet include the above-mentioned thermoplastic polyester resins, polyolefin resins such as polyethylene resins and polypropylene resins, and polystyrene resins.

The foamed molded product may contain additives. Examples of such additives include surfactants, colorants, shrinkage inhibitors, flame retardants, lubricants, and deterioration inhibitors.

Foam molded products can be manufactured using general-purpose methods. For example, foam molded products can be manufactured by thermoforming a thermoplastic polyester resin foam sheet (hereinafter sometimes simply referred to as a "foam sheet") into various shapes using general-purpose methods.

As the thermoforming method, known forming methods can be used, such as vacuum forming and compressed air forming, or applications of these, such as free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming, and plug assist reverse load forming. Before thermoforming the foam sheet, the foam sheet may be heated to any temperature to soften the foam sheet (preheating step). In the preheating step, the surface temperature of the foam sheet is preferably 120 to 130°C.

If necessary, the foamed sheet may be heated during or after thermoforming to undergo a crystallization treatment. By subjecting the foamed sheet to a crystallization treatment, a portion of the thermoplastic polyester-based resin is crystallized. The crystallization treatment may be performed in a known manner, for example by heating the mold used for thermoforming to a temperature equal to or higher than the crystallization temperature of the thermoplastic polyester-based resin.

When producing a foam-molded product by thermoforming a foam sheet, the foam sheet used as the base material is not particularly limited. When subjecting the foam sheet to a crystallization treatment, the difference in crystallinity between the surface portion and the middle portion can be reduced to 15% or less by gently heating the foam sheet. As the foam sheet, it is preferable to use a foam sheet as described below, since this allows the thermoforming time to be shortened and the crystallinity to be easily controlled.

The foamed sheet described below can be easily crystallized in a general manner so that the crystallinity in the thickness direction is the same and at an appropriate crystallinity. Therefore, the foamed molded product obtained has excellent heat resistance and is resistant to deformation even when stress is applied under heating, and brittleness is improved, reducing the occurrence of cracks.

The foam sheet that serves as the raw material for thermoforming the foam-molded product has a foam layer that contains a thermoplastic polyester-based resin foam, and the thermoplastic polyester-based resin foam preferably contains a thermoplastic polyester-based resin.

The thermoplastic polyester resin constituting the thermoplastic polyester resin foam preferably has a total amount of ester compounds and ether compounds (hereinafter simply referred to as "ester compounds and ether compounds") generated by GC/MS at 285°C of 1000 ppm or less relative to the total amount of the thermoplastic polyester resin.

Examples of thermoplastic polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), polybutylene naphthalate (PBN), polytrimethylene terephthalate (PTT), and copolymers of terephthalic acid, ethylene glycol, and cyclohexane dimethanol. The thermoplastic polyester resin is preferably an aromatic thermoplastic polyester resin such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), or polytrimethylene terephthalate resin (PTT), and more preferably polyethylene terephthalate (PET). The thermoplastic polyester resins may be used alone or in combination of two or more.

The thermoplastic polyester resin may be a plant-derived polyester resin such as biopolyethylene terephthalate (bioPET) or biopolyethylene furanoate (bioPEF). The thermoplastic polyester resin may also be a so-called recycled raw material. Examples of the recycled raw material include skeletons generated during the manufacturing process of foam-molded products and recycled products after use. The skeleton is a residue generated after punching out a foam-molded product from a thermoformed foam sheet when the foam sheet is thermoformed to form a foam-molded product. The recycled raw material is preferably one having the same resin composition as the foam sheet.

Plant-derived polyester resins are polymers derived from plant materials (e.g., sugar cane, corn, etc.). "Polymers derived from plant materials" include polymers synthesized or extracted from plant materials. For example, "polymers derived from plant materials" include polymers obtained by polymerizing monomers synthesized or extracted from plant materials. "Monomers synthesized or extracted from plant materials" include monomers synthesized using compounds synthesized or extracted from plant materials. Plant-derived thermoplastic polyester resins include thermoplastic polyester resins in which some of the monomer units are "monomer units derived from plant materials."

The content of the thermoplastic polyester resin in the synthetic resin constituting the thermoplastic polyester resin foam is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, more preferably 95% by mass or more, more preferably 99% by mass or more, and more preferably 100% by mass.

It is preferable that the total amount of ester compounds and ether compounds generated by GC/MS at 285°C in the thermoplastic polyester resin contained in the thermoplastic polyester resin foam is 1000 ppm or less relative to the total amount of the thermoplastic polyester resin.

As a result of intensive research by the inventors, although it has not been clearly elucidated, it is believed that during the crystallization process of the thermoplastic polyester resin contained in the thermoplastic polyester resin foam, the low molecular weight ester compounds and ether compounds act as crystal nucleating agents and promote the crystallization of the thermoplastic polyester resin.

Low molecular weight ester compounds and ether compounds are more likely to move and aggregate than thermoplastic polyester resins, and it is believed that these aggregates act as crystal nucleating agents to promote the crystallization of thermoplastic polyester resins.

In addition, heat applied to the foam sheet is absorbed and is not easily transferred to the inside. Therefore, in the foam sheet and the thermoplastic polyester resin foam molded product obtained by thermoforming this foam sheet (hereinafter sometimes simply referred to as "foam molded product"), crystallization of the surface proceeds more rapidly than that of the interior, with low molecular weight ester compounds and ether compounds acting as crystal nucleating agents, and the degree of crystallization of the surface tends to be higher than that of the interior.

In foam sheets and foam molded products, if the crystallinity is non-uniform in the thickness direction, the thermal shrinkage rate will also be non-uniform in the thickness direction due to the non-uniformity of the crystallinity. If the thermal shrinkage rate is non-uniform in the thickness direction of foam sheets and foam molded products, when stress is applied in a heated state, shear stress will be generated at the interface where the thermal shrinkage rate changes significantly. As a result, the mechanical strength of the foam sheets and foam molded products will decrease, causing deformation and other damage.

Therefore, for the thermoplastic polyester resin of the thermoplastic polyester resin foam of the foam sheet and foam molded product, the total amount of ester compounds and ether compounds generated by GC/MS at 285°C is preferably 1000 ppm or less relative to the total amount of thermoplastic polyester resin. When configured in this way, the foam sheet and foam molded product are prevented from undergoing excessive crystallization at the surface compared to the inside when heated, and the degree of crystallization in the thickness direction is roughly the same or maintained in that state, and they have excellent heat resistance that is unlikely to deform even when stress is applied in a heated state.

In foam sheets and foam-molded products, excessive crystallization of the surface due to heating can be prevented, improving the brittleness of the foam sheets and foam-molded products.

The ester and ether compounds generated by GC/MS of thermoplastic polyester resin at 285°C are decomposition products that arise when the thermoplastic polyester resin is heated to 285°C, and are low molecular weight components. The ester and ether compounds do not contain polymers, but are monomer and oligomer components generated by the decomposition of the thermoplastic polyester resin. The molecular weight of the ester and ether compounds is preferably 400 or less, more preferably 200 or less.

The ester compounds include compounds produced by the thermal decomposition of thermoplastic polyester resins, compounds produced by the ester reaction of components produced by the thermal decomposition of thermoplastic polyester resins, and compounds produced by the ester reaction of components produced by the thermal decomposition of a crosslinking agent that crosslinks thermoplastic polyester resins, and contain ester bonds (-COO-) in the molecule. Examples of ester compounds include pyromellitic acid tetramethyl ester.

The ether-based compounds include compounds produced by the thermal decomposition of thermoplastic polyester-based resins, compounds produced by the reaction of components produced by the thermal decomposition of thermoplastic polyester-based resins, and compounds produced by the reaction of components produced by the thermal decomposition of a crosslinking agent that crosslinks thermoplastic polyester-based resins, and contain ester bonds (-O-) in the molecule. Examples of ether-based compounds include 2,2-dimethoxypropane.

In the foam sheet, the total amount of ester compounds and ether compounds generated by GC/MS at 285°C in the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 1000 ppm or less, more preferably 900 ppm or less, more preferably 800 ppm or less, more preferably 750 ppm or less, more preferably 400 ppm or less, more preferably 300 ppm or less, and more preferably 190 ppm or less, based on the total amount of the thermoplastic polyester resin.

In the foam-molded product, the total amount of ester compounds and ether compounds generated by GC/MS at 285°C in the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 1000 ppm or less, more preferably 900 ppm or less, more preferably 800 ppm or less, more preferably 750 ppm or less, more preferably 400 ppm or less, more preferably 300 ppm or less, and more preferably 190 ppm or less, based on the total amount of the thermoplastic polyester resin.

In the thermoplastic polyester resin, the total amount of the ester compounds and ether compounds can be reduced by, for example, (1) using a crosslinking agent with a low content of ester compounds and ether compounds, (2) reducing the water content of the crosslinking agent described below in advance and melt-kneading it in an extruder to cause a crosslinking reaction of the thermoplastic polyester resin, (3) lowering the surface temperature of the thermoplastic polyester resin foam immediately after extrusion foaming from the outlet at the tip of the extruder (e.g., the outlet of a die), or (4) lowering the shear rate of the foamable composition when extrusion foaming from the outlet at the tip of the extruder (e.g., the outlet of a die).

In foam sheets and foam molded products, the total amount of ester compounds and ether compounds generated by GC/MS at 285°C in the thermoplastic polyester resin constituting the thermoplastic polyester resin foam refers to the value measured as follows.

Cut 0.5 g of sample from the center of the foam layer of the foam sheet or foam molded product, place in a 10 mL centrifuge tube, add 5 mL of acetone and mix. After shaking the centrifuge tube, inject 1 μL of the supernatant liquid of the solution sample in the centrifuge tube directly into the GC/MS and measure under the following measurement conditions. Calculate from the area value ratio of each component when the total area value of the detected peaks is taken as 100%.

Equipment: JEOL gas chromatograph mass spectrometer JMS-Q1000GC
Column: Agilent Technologies DB-1 (1.0 μm × 0.25 mm φ × 60 m)
Column temperature: 40℃ (3min) Heating rate: 15℃/min → 200℃ Heating rate: 25℃/min → 285℃ (17.93min)
Injection temperature: 285°C
Injection volume: 1 μL
Flow He=1.0mL/min
Run time 35 min
Split ratio 1:10
Detector voltage -1400V
Interface temperature: 250℃
Ion source temperature: 250℃
Ionization current 300μA
Ionization energy 70eV
Monitoring mass SCAN (M/Z=20-500)

In the foam sheet, the amount of carboxy end groups of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 100 equivalents/ton or less, more preferably 80 equivalents/ton or less, more preferably 70 equivalents/ton or less, more preferably 60 equivalents/ton or less, more preferably 57 equivalents/ton or less, and more preferably 50 equivalents/ton or less.

In the foam-molded product, the amount of carboxy end groups of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 100 equivalents/ton or less, more preferably 80 equivalents/ton or less, more preferably 70 equivalents/ton or less, more preferably 60 equivalents/ton or less, more preferably 57 equivalents/ton or less, and more preferably 50 equivalents/ton or less.

The carboxyl end groups in the thermoplastic polyester resin inhibit the crosslinking of the thermoplastic polyester resin by the crosslinking agent described below. When the crosslinking of the thermoplastic polyester resin by the crosslinking agent is inhibited, the thermoplastic polyester resin becomes more likely to crystallize. In addition, since heat applied to the foam sheet and foam-molded product is not easily transmitted to the inside, the crystallization of the foam sheet and foam-molded product is promoted more on the surface than inside, resulting in non-uniform crystallization and thermal shrinkage in the thickness direction, which reduces the mechanical strength of the foam sheet and foam-molded product and causes deformation and other damage.

By setting the amount of carboxy end groups in the thermoplastic polyester resin to 100 equivalents/ton or less, the inhibition of crosslinking of the thermoplastic polyester resin by the crosslinking agent described below is reduced, and excessive promotion of crystallization of the surface compared to internal crystallization during heating such as crystallization treatment of the thermoplastic polyester resin is suppressed. In the foam sheet and foam molded product, the degree of crystallization in the thickness direction is made to be the same or maintained in that state, damage such as deformation is reduced despite the addition of stress under heating, and excellent heat resistance can be imparted to the foam sheet and foam molded product.

In foam sheets and foam-molded products, heating can prevent the surface from crystallizing excessively, improving the brittleness of the foam sheets and foam-molded products.

The amount of carboxy end groups in the thermoplastic polyester resin can be reduced, for example, by using methods such as (1) reducing the water content of the crosslinking agent described below in advance and melt-kneading the crosslinking agent in an extruder to cause a crosslinking reaction of the thermoplastic polyester resin, (2) lowering the surface temperature of the thermoplastic polyester resin foam immediately after extrusion foaming from the outlet at the tip of the extruder (e.g., the outlet of a die), and (3) lowering the shear rate of the foamable composition when extrusion foaming from the outlet at the tip of the extruder (e.g., the outlet of a die).

In addition, the amount of carboxyl end groups in the thermoplastic polyester resin constituting the thermoplastic polyester resin foam in the foam sheet and foam molded product is the value measured as follows.

Take a 0.4g test piece from the center of the foam layer of the foam sheet or foam molded product and cut it into small pieces with scissors. Next, put the test piece into 10mL of benzyl alcohol, heat the benzyl alcohol at 180°C for 10 minutes using an aluminum block heater to dissolve the test piece in the benzyl alcohol, and after cooling, add 10mL of chloroform to the benzyl alcohol to prepare a sample solution. Add phenol red reagent to the sample solution and titrate with 0.1N sodium hydroxide solution using a titration device. The amount of carboxyl end groups in the thermoplastic polyester resin is determined from the amount of titration required to reach the endpoint.

In the foamed sheet, the content of acetic acid in the thermoplastic polyester resin is preferably 100 ppm or less, more preferably 80 ppm or less, more preferably 55 ppm or less, more preferably 40 ppm or less, and more preferably 30 ppm or less, based on the total amount of the thermoplastic polyester resin.

In the foam-molded product, the content of acetic acid in the thermoplastic polyester resin is preferably 100 ppm or less, more preferably 80 ppm or less, more preferably 55 ppm or less, more preferably 40 ppm or less, and more preferably 30 ppm or less, based on the total amount of the thermoplastic polyester resin.

The acetic acid in the thermoplastic polyester resin reacts with the hydroxyl groups of the thermoplastic polyester resin, inhibiting the crosslinking of the thermoplastic polyester resin by the crosslinking agent. If the crosslinking of the thermoplastic polyester resin by the crosslinking agent is inhibited, as described above, the crystallinity and thermal shrinkage rate in the thickness direction of the foam sheet and foam molded product become non-uniform, reducing the mechanical strength and causing damage such as deformation.

By keeping the content of acetic acid in the thermoplastic polyester resin to 100 ppm or less relative to the total amount of the thermoplastic polyester resin, the degree of crystallinity in the thickness direction of the foamed sheet and foam-molded product can be made to be the same or can be maintained in that state, and damage such as deformation can be reduced even when stress is applied under heating conditions, thereby imparting excellent heat resistance to the foamed sheet and foam-molded product.

In foam sheets and foam-molded products, heating can prevent the surface from crystallizing excessively, improving the brittleness of the foam sheets and foam-molded products.

In addition, the acetic acid content in the thermoplastic polyester resin constituting the thermoplastic polyester resin foam in the foam sheet and foam molded product is the value measured as follows.

A 2g sample is taken from the center of the foam layer of the foam sheet or foam molded product. Next, 2g of the sample is placed in a dedicated container and freeze-pulverized into powder form using a freeze-pulverizing device (Japan Analytical Industry Co., Ltd., freeze-pulverizing device, product name "JFC-300") to prepare a freeze-pulverized sample. The freeze-pulverizing conditions are a liquid nitrogen immersion pre-cooling time of 10 minutes and a shaking grinding time of 30 minutes.

Approximately 1 g of the frozen and pulverized sample is accurately weighed into a cleaned 50 mL eye-boy flask. Next, 50 mL of ion-exchanged water is added to the frozen and pulverized sample and mixed well to produce mixed water. This mixed water is subjected to ultrasonic cleaning and extraction for approximately 10 minutes. After filtering the mixed water through an aqueous 0.20 μm chromatographic disk, IC is measured to measure the amount of acetate ions, and this amount of acetate ions is taken as the acetic acid content.

[Measurement of amount of dissolved ions (IC)]
Equipment: Tosoh IC IC-2001
Measured element: CH ₃ COO, NO ₃ Column TSKGEL superIC-AZ
Column temp. 40℃
Pump Injec.temp. RT Solven 3.2mM Na ₂ CO ₃ + 1.9mM NaHCO ₃
Flow Rate 0.8mL/min
Run time 17min
Injection Volume 30μL Detector Electrical conductivity detector

In the foam sheet, the number average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 5,000 or more, more preferably 6,000 or more, more preferably 7,000 or more, more preferably 8,000 or more, and more preferably 9,000 or more.

In the foam sheet, the number average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 20,000 or less, more preferably 18,000 or less, more preferably 15,000 or less, more preferably 12,000 or less, and more preferably 10,000 or less.

In the foam-molded product, the number average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 5,000 or more, more preferably 6,000 or more, more preferably 7,000 or more, more preferably 8,000 or more, and more preferably 9,000 or more.

In the foam-molded product, the number average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 20,000 or less, more preferably 18,000 or less, more preferably 15,000 or less, more preferably 12,000 or less, and more preferably 10,000 or less.

By making the number average molecular weight of the thermoplastic polyester resin 5,000 or more, the amount of carboxyl end groups in the thermoplastic polyester resin can be reduced, and as described above, the degree of crystallinity in the thickness direction of the foamed sheet and foam-molded product can be made to be the same or can be maintained in that state, and damage such as deformation can be reduced even when stress is applied under heating.

Furthermore, by making the number average molecular weight of the thermoplastic polyester resin 5000 or more, it is possible to reduce the decomposition of the thermoplastic polyester resin during the manufacturing process of the foam sheet, thereby reducing the production of the above-mentioned ester compounds and ether compounds as well as acetic acid. As a result, as described above, it is possible to impart excellent heat resistance to the foam sheet and foam-molded product.

In addition, by setting the number average molecular weight of the thermoplastic polyester resin to 20,000 or less, the thermoformability of the foam sheet is improved, the shear stress applied to the thermoplastic polyester resin during the thermoforming of the foam sheet is alleviated, and the decomposition of the thermoplastic polyester resin is reduced, thereby reducing the production of acetic acid in addition to the above-mentioned ester compounds and ether compounds. As a result, as described above, excellent heat resistance can be imparted to the foam sheet and foam-molded product.

In the foam sheet, the Z-average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 150,000 or more, more preferably 170,000 or more, more preferably 190,000 or more, and more preferably 200,000 or more.

In the foam sheet, the Z-average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 1,000,000 or less, more preferably 800,000 or less, more preferably 700,000 or less, and more preferably 500,000 or less.

In the foam-molded product, the Z-average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 150,000 or more, more preferably 170,000 or more, more preferably 190,000 or more, and more preferably 200,000 or more.

In the foam-molded product, the Z-average molecular weight of the thermoplastic polyester resin constituting the thermoplastic polyester resin foam is preferably 1,000,000 or less, more preferably 800,000 or less, more preferably 700,000 or less, and more preferably 500,000 or less.

By making the Z-average molecular weight of the thermoplastic polyester resin 150,000 or more, the amount of carboxyl end groups in the thermoplastic polyester resin can be reduced, and as described above, the degree of crystallinity in the thickness direction of the foamed sheet and foam-molded product can be made to be the same or maintained in that state, reducing damage such as deformation even when stress is applied under heating.

Furthermore, by making the Z-average molecular weight of the thermoplastic polyester resin 150,000 or more, it is possible to reduce the decomposition of the thermoplastic polyester resin during the manufacturing process of the foam sheet, thereby reducing the production of the above-mentioned ester compounds and ether compounds as well as acetic acid. As a result, as described above, it is possible to impart excellent heat resistance to the foam sheet and foam-molded product.

In addition, by setting the Z-average molecular weight of the thermoplastic polyester resin to 500,000 or less, the thermoformability of the foam sheet is improved, the shear stress applied to the thermoplastic polyester resin during thermoforming of the foam sheet is alleviated, and the decomposition of the thermoplastic polyester resin is reduced, thereby reducing the production of acetic acid in addition to the above-mentioned ester compounds and ether compounds. As a result, as described above, excellent heat resistance can be imparted to the foam sheet and foam-molded product.

The number average molecular weight and Z average molecular weight content of the thermoplastic polyester resin are values measured as follows:

Take a 5 g sample from the center of a foam sheet or foam molded product. Add 0.5 mL of HFIP and 0.5 mL of chloroform to the sample, shake gently, and leave for 5 hours. After confirming dissolution, dilute with chloroform to 10 mL, shake gently, and filter with a non-aqueous 0.45 μm syringe filter (Shimadzu GLC) for measurement.
Soaking time: 24.0±2.0hr (completely dissolved)
Comparative samples: SRM706a, MS-311, and TR-8580
(Measuring device)
GPC device: Tosoh Corporation, HLC-8320GPC (with built-in RI detector and UV detector)
Guard column: TOSOH TSK guard column Hxl-H (6.0 mm I.D. x 4 cm) x 1 Column (reference): TOSOH TSKgel Super H-RC (6.0 mm I.D. x 15 cm) x 2 Column (sample): TOSOH TSKgel GMHxl (7.8 mm I.D. x 30 cm) x 2 (measurement conditions)
Column temperature: 40°C
Detector temperature: 40°C
Pump inlet temperature: 40°C
Solvent: Chloroform Flow rate (reference): 0.5 mL/min
Flow rate (sample): 1.0 mL/min
Run time: 26 min
Data collection time: 10 to 25 minutes
Data interval: 500 msec
Injection volume: 15 μL (sample and TR-8580) / 50 μL (Shodex A/B, SRM706a, MS-311)
Detector: UV=254 nm

The content of inorganic substances in the foamed sheet is preferably 7% by mass or less, more preferably 5% by mass or less. The content of inorganic substances in the foamed molded product is preferably 7% by mass or less, more preferably 5% by mass or less. The inorganic substances are not particularly limited, but examples thereof include talc, tin oxide, smectite, bentonite, dolomite, sericite, feldspar powder, kaolin, mica, and montmorillonite.

When the content of inorganic matter in the foam sheet is 7% by mass or less, the shear stress applied to the thermoplastic polyester resin during the production of the foam sheet is alleviated, and the decomposition of the thermoplastic polyester resin is reduced, thereby reducing the production of the above-mentioned ester compounds and ether compounds as well as acetic acid. As a result, as described above, excellent heat resistance can be imparted to the foam sheet and foam-molded product.

If inorganic matter is present in the foam sheet, the heat applied to the foam sheet may be absorbed by the inorganic matter, causing the thermoplastic polyester resin around the inorganic matter to crystallize excessively. Therefore, by reducing the content of inorganic matter in the foam sheet, the thermoplastic polyester resin can be crystallized uniformly throughout, imparting excellent heat resistance to the foam sheet and foam-molded products.

When a foam-molded product is heated, the heat applied to the foam-molded product is absorbed by the inorganic material, and the degree of heating differs between the area around the inorganic material and the other thermoplastic polyester resin, leading to a difference in the degree of expansion. This can result in a decrease in mechanical strength at the interface where the degrees of expansion differ greatly, causing deformation of the foam-molded product. Therefore, the heat resistance of the foam-molded product can be improved by reducing the content of inorganic material in the foam-molded product.

The inorganic content in foam sheets and foam-molded products is measured as follows:

A 1.0 g sample is taken from the foam sheet or foam-molded product, and the ash content is determined under the measurement conditions described below using the measurement device described below, thereby measuring the inorganic matter content in the foam sheet or foam-molded product.
(Measuring device)
・Microwave muffle furnace Phoenixix (manufactured by CEM)
・Analytical balance GR-200 (manufactured by A&D)
(Ashing method)
A container containing 1.0 g of sample is placed in the above apparatus and ashed for 30 minutes under the following conditions.
Ashing conditions: DWELL TIME=30min, OPERATING TEMP=800℃
(Calculation method)
Amount of inorganic matter (mass%) = 100 x {(weight of container after incineration) - (weight of container only)}
/ {Sample (mass of foam sheet or foam-molded product = 1.0 g)}

[Method of manufacturing thermoplastic polyester resin foam sheet]
Next, a method for producing a thermoplastic polyester resin foam sheet will be described. The foam sheet can be produced by a known method.

The method for producing a foamed sheet includes, for example, a melt-kneading step in which a foamable composition containing a thermoplastic polyester resin, a crosslinking agent, and a foaming agent is melt-kneaded in an extruder, and a foaming step in which the foamable composition is extruded and foamed from a discharge port at the tip of the extruder. The extruder may be a single-screw extruder or a twin-screw extruder. The extruder may be a tandem extruder in which multiple extruders are connected.

The intrinsic viscosity (IV value) of the thermoplastic polyester resin used as the raw material is preferably 0.50 to 2.00, more preferably 0.80 to 1.50. When the intrinsic viscosity of the thermoplastic polyester resin is within the above range, decomposition of the thermoplastic polyester resin can be reduced during the foam sheet manufacturing process, and the foam sheet can be crystallized uniformly in the thickness direction.

The intrinsic viscosity of thermoplastic polyester resin is calculated based on a resin solution prepared by dissolving 1.0 g of thermoplastic polyester resin in 100 cc of a mixed solvent of tetrachloroethane and phenol in a 1:1 volume ratio, measuring the viscosity of the resin solution at 20°C, and then calculating the intrinsic viscosity.

The thermoplastic polyester resin in the foamable composition is crosslinked by a crosslinking agent in the extruder. The crosslinking agent is not particularly limited as long as it can crosslink the thermoplastic polyester resin. Examples of the crosslinking agent include compounds having multiple carboxylic anhydride groups (-CO-O-CO-) in the molecule (e.g., carboxylic dianhydrides such as pyromellitic anhydride), polyfunctional epoxy compounds, oxazoline compounds, etc., and compounds having multiple carboxylic anhydride groups in the molecule are preferred. Since crystallization can be achieved so that the crystallization degree in the thickness direction of the foamed sheet is roughly the same, carboxylic dianhydrides are more preferred, and pyromellitic anhydride is more preferred.

The amount of water contained in the crosslinking agent is preferably 0.1% by mass or less, more preferably 0.07% by mass or less, more preferably 0.05% by mass or less, and even more preferably 0.01% by mass or less.

When the moisture content in the crosslinking agent is 0.1% by mass or less, the thermal decomposition of the thermoplastic polyester resin can be reduced, and the amount of carboxyl end groups in the thermoplastic polyester resin can be reduced. In addition, when the crosslinking agent contains a compound having multiple carboxylic anhydride groups in the molecule, the self-ring opening of this compound can be reduced, and the amount of carboxyl end groups in the thermoplastic polyester resin can be reduced. By reducing the amount of carboxyl end groups in the thermoplastic polyester resin, as described above, the foamed sheet and the foamed molded product obtained by thermoforming this foamed sheet have excellent mechanical strength even under heated conditions and excellent heat resistance.

The moisture content in the crosslinking agent is a value measured as follows: 1-2 g of the raw material crosslinking agent is placed in a vial (Shimadzu GLC 10 mL screw vial) and capped (Shimadzu GLC silver screw cap with septum). In order to measure the moisture content of the crosslinking agent only, air before the blender is collected in a vial and similarly capped, which serves as the blank.

The moisture content is measured by placing the sample in a Mitsubishi Chemical Analytech "CA-200" Karl Fischer moisture analyzer and "VA-236S" moisture vaporizer. Mitsubishi Chemical Aquamicron AX and Aquamicron CXU are used as the anolyte and catholyte during the measurement, respectively. The measurement temperature is 128°C. _N2 is used as the carrier gas. The flow rate of the carrier gas is 250 mL/min. The number of times the sample is tested is three times. The moisture content of only the air at the sample collection location is measured twice, and the average value is used as the blank value. The blank value is subtracted from each measurement result and divided by the sample mass to calculate the moisture content (mass%) of the sample. The moisture content (mass%) of the sample was calculated using the following formula. As a final result, the arithmetic average of the three measurement results is used as the moisture content (mass%) of the sample.
Water content in crosslinker (mass%)
= [measured moisture content (μg) - blank moisture content (μg)]
÷ 1,000,000 ÷ sample weight (g) × 100

The content of acetic acid in the crosslinking agent is preferably 1000 ppm or less, more preferably 700 ppm or less, and even more preferably 500 ppm or less, based on the total amount of the crosslinking agent. The content of acetic acid in the crosslinking agent is measured in the same manner as the measurement method for the content of acetic acid in thermoplastic polyester resin, except that 2 g of the crosslinking agent is used as the sample.

The acetic acid in the crosslinking agent reacts with the hydroxyl groups of the thermoplastic polyester resin, inhibiting the crosslinking of the thermoplastic polyester resin by the crosslinking agent. If the crosslinking of the thermoplastic polyester resin by the crosslinking agent is inhibited, as mentioned above, the crystallinity and thermal shrinkage rate in the thickness direction of the foam sheet and foam molded product become non-uniform, reducing the mechanical strength and causing damage such as deformation.

By keeping the content of acetic acid in the crosslinking agent at 1000 ppm or less relative to the total amount of crosslinking agent, the degree of crystallinity in the thickness direction of the foamed sheet and foam-molded product can be made to be the same or can be maintained in that state, reducing damage such as deformation even when stress is applied under heating conditions.

In the resulting foamed sheet and foam-molded product, excessive crystallization of the surface portion can be prevented, improving the brittleness of the foamed sheet and foam-molded product.

In the crosslinking agent, the total amount of the ester-based compound and the ether-based compound is preferably 1000 ppm or less, more preferably 800 ppm or less, based on the total amount of the crosslinking agent. When the total amount of the ester-based compound and the ether-based compound in the crosslinking agent is 1000 ppm or less, the foam sheet and the foam-molded product can have the same degree of crystallinity in the thickness direction or maintain the same degree of crystallinity by heating such as crystallization treatment, and are endowed with excellent heat resistance that is less likely to cause deformation even when stress is applied in a heated state. In the obtained foam sheet and foam-molded product, excessive crystallization of the surface portion can be prevented, and the brittleness of the foam sheet and the foam-molded product can be improved.

The total amount of ester-based compounds and ether-based compounds in the crosslinking agent is measured in the same manner as the method for measuring the total amount of ester-based compounds and ether-based compounds in the foamed sheet described above, except that 0.5 g of the crosslinking agent is used as the sample.

The content of the crosslinking agent in the foamable composition is preferably 0.05 parts by mass or more, more preferably 0.08 parts by mass or more, per 100 parts by mass of the thermoplastic polyester resin. The content of the crosslinking agent in the foamable composition is preferably 0.5 parts by mass or less, more preferably 0.3 parts by mass or less, per 100 parts by mass of the thermoplastic polyester resin. When the content of the crosslinking agent is 0.05 parts by mass or more, the crosslinking of the thermoplastic polyester resin can be performed uniformly throughout, and the foam sheet can be crystallized to the same extent in the thickness direction. Therefore, the foam sheet and the foam-molded product obtained by thermoforming this foam sheet have excellent mechanical strength even under heated conditions and have excellent heat resistance.

The foaming agent is not particularly limited as long as it can foam the thermoplastic polyester resin. Examples of the foaming agent include saturated aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, and hexane, ethers such as dimethyl ether, fluorocarbons such as methyl chloride, 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane, and monochlorodifluoromethane, carbon dioxide, and nitrogen, with dimethyl ether, propane, normal butane, isobutane, carbon dioxide, and nitrogen being preferred. The foaming agents may be used alone or in combination of two or more.

The amount of foaming agent supplied to the extruder may be adjusted appropriately depending on the expansion ratio of the foamed sheet to be produced.

A foamed sheet can be produced by extruding and foaming the molten foamable composition from the outlet at the tip of the extruder. The foamable composition may be extruded and foamed into a cylindrical shape from a circular die connected to the extruder, and then cut in the extrusion direction to form a sheet, or the foamable composition may be extruded and foamed into a sheet from the extruder.

The shear rate of the foamable composition when extrusion foamed from the discharge port (die) at the tip of the extruder is preferably 7500 s ^-1 or less. More preferably, it is 6500 s ^-1 or less, and more preferably, it is 6000 s ^-1 or less. More preferably, it is 5000 s ^-1 or less, and more preferably, it is 4000 s ^-1 or less. When the shear rate of the foamable composition is 7500 s ^-1 or less, the generation of acetic acid due to decomposition of the thermoplastic polyester resin is reduced, excellent heat resistance is imparted to the foam sheet and the foam-molded product, and damage such as deformation can be reduced despite the application of stress under heating conditions.

The shear rate of the foamable composition can be calculated based on the area of the outlet at the tip of the extruder and the amount of foamable composition discharged. The shear rate of the foamable composition can be controlled by adjusting the temperature of the foamable composition during extrusion foaming and the opening degree of the outlet at the tip of the extruder.

The surface temperature of the thermoplastic polyester resin foam immediately after extrusion foaming from the discharge port at the tip of the extruder is preferably 310°C or less, more preferably 305°C or less, and more preferably 300°C or less. The surface temperature of the thermoplastic polyester resin foam immediately after extrusion foaming from the discharge port at the tip of the extruder is preferably 275°C or more. When the surface temperature of the thermoplastic polyester resin foam is 310°C or less, the generation of acetic acid due to decomposition of the thermoplastic polyester resin is reduced, excellent heat resistance is imparted to the foam sheet and the foam molded product, and damage such as deformation of the foam sheet and the foam molded product can be reduced despite the addition of stress under heating conditions. When the surface temperature of the thermoplastic polyester resin foam is 275°C or more, the frictional resistance with the cooling device (e.g., mandrel, etc.) in the cooling process after extrusion foaming is reduced, and damage such as cutting of the foam sheet is prevented, thereby improving the surface properties of the foam sheet.

When a thermoplastic resin non-foamed sheet is laminated onto one or both sides of a foam sheet, a known method may be used. Examples of methods for laminating a thermoplastic resin non-foamed sheet onto the surface of a foam sheet include (1) a method of laminating a foam sheet and a thermoplastic resin non-foamed sheet by co-extrusion, and (2) a method of producing a foam sheet and a thermoplastic resin non-foamed sheet separately, and then laminating the thermoplastic resin non-foamed sheet onto the surface of the foam sheet by heat fusion or via an adhesive.

The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

In the examples and comparative examples, the following compounds were used.
(Thermoplastic polyester resin)
Polyethylene terephthalate (manufactured by Far East New Century Co., Ltd., product name "CH611", IV value: 1.06)

(Crosslinking Agent)
Pyromellitic anhydride 1 (PMDA1, manufactured by Puyang Shenghua De Processing Co., Ltd., total amount of ester compounds and ether compounds: 700 ppm, acetic acid content: 0 ppm)
Pyromellitic anhydride 2 (PMDA2, Daicel Corporation, total amount of ester compounds and ether compounds: 300 ppm, acetic acid content: 1200 ppm)

(Examples 1 to 9, Comparative Examples 1 to 4)
The polyethylene terephthalate was dried for 16 hours at 100° C. The talc (cell regulator) was dried for 16 hours at 130° C.

10 kg of the crosslinking agent and 10 bags of a desiccant (Toyota Chemical Industries, Ltd., N (white) 100G) were placed in an aluminum bag (manufactured by ADY, product name "MBY-92100"), the aluminum bag was sealed by heat sealing, and then it was left to dry at 25°C for the drying time shown in Table 1. The amount of moisture contained in the crosslinking agent after drying is shown in Table 1. When the drying time is "0 hours", it means that the above drying process was not performed. In Comparative Example 4, the crosslinking agent was dried by leaving it to stand in a dryer maintained at 100°C for 4 hours without using a desiccant. In addition, the total amount of ester compounds and ether compounds (total amount of esters and ethers) and the acetic acid content (amount of acetic acid) of the crosslinking agent before drying are shown in Table 1.

A short-screw extruder (screw diameter: φ90 mm) was prepared, and a circular die (bore: 35 mm) was attached to the tip of the short-screw extruder. The maximum set temperature of the extruder was 285° C. The polyethylene terephthalate, talc, and crosslinking agent in the predetermined amounts shown in Table 1 were mixed and fed to the short-screw extruder (screw diameter: φ90 mm) for melt-kneading. Furthermore, butane gas was injected into the extruder from a zone set at 265° C. at a flow rate shown in Table 1. The foamable composition containing polyethylene terephthalate, a crosslinking agent, and butane, which was melt-kneaded in the extruder, was extruded and foamed from the discharge port of the circular die to produce a cylindrical polyethylene terephthalate foam, and this polyethylene terephthalate foam was continuously fed to a mandrel and cooled. The cooled polyethylene terephthalate foam was cut open to obtain a polyethylene terephthalate foam sheet (thickness: 1.2 mm, basis weight: 330 g/m ² , width 665 mm).
obtained.

The amount of foamable composition discharged from the extruder is shown in Table 1. The shear rate of the foamable composition when extruded and foamed from the outlet of the circular die of the extruder is shown in Table 1. The surface temperature of the polyethylene terephthalate foam (surface temperature of the PET foam) immediately after extrusion and foaming from the outlet of the circular die is shown in Table 1.

The total amount of ester compounds and ether compounds (total amount of esters and ethers), the amount of carboxyl end groups (amount of carboxyl end groups), the amount of acetic acid (amount of acetic acid), and the amount of inorganic substances (amount of inorganic substances) contained in the polyethylene terephthalate constituting the foam layer of the obtained polyethylene terephthalate foam sheet were measured as described above, and the results are shown in Table 1.

The number average molecular weight and Z average molecular weight of the polyethylene terephthalate constituting the foam layer of the obtained polyethylene terephthalate foam sheet were measured as described above, and the results are shown in Table 1.

The resulting polyethylene terephthalate foam sheet was fed into a heater tank at 150°C and preheated for 90 seconds. The surface temperature of the polyethylene terephthalate foam sheet was 125°C.

A preheated polyethylene terephthalate foam sheet was fed between the male and female molds heated to 180°C, and compressed air was fed from the male mold side to bring the polyethylene terephthalate foam sheet into close contact with the female mold. The male and female molds were then clamped for six seconds to form the foam sheet into a vacuum-pressure molded product in the shape of a container. The foam molded product was formed in a cylindrical shape with an open top and a bottom, and a flange was formed around the entire periphery of the edge of the top opening facing outward.

The crystallinity of the foam layer of the obtained foam molded product was measured in the surface, middle, and entire foam molded product as described above, and the results are shown in Table 1. The crystallinity of both surface parts of the foam layer was the same. The difference in crystallinity between the surface and middle parts of the foam layer of the foam molded product (difference in crystallinity) is shown in Table 1.

The obtained foam molded products were subjected to a freezing drop test and a range-up test as described below, and the results are shown in Table 1.

The total amount of ester compounds and ether compounds (total amount of esters and ethers), the amount of carboxyl end groups (amount of carboxyl end groups), the amount of acetic acid (amount of acetic acid), and the amount of inorganic substances (amount of inorganic substances) contained in the polyethylene terephthalate constituting the foam layer of the obtained foam-molded product were measured as described above, and the results are shown in Table 1.

The number average molecular weight and Z average molecular weight of the polyethylene terephthalate constituting the foam layer of the obtained foam-molded product were measured as described above, and the results are shown in Table 1.

(Frozen drop test)
After adding 250 cc of water to the obtained foam-molded product, the foam-molded product was left to stand in a freezer at -25°C for 24 hours. After that, the upper end opening of the foam-molded product was held with both hands and the foam-molded product was dropped from a height of 1 m. The condition of the foam-molded product after the drop was visually confirmed and evaluated as follows.

A: No cracks were observed in the foamed product.
B: A crack occurred in the foam molded product, but the crack penetrated the foam molded product in the thickness direction.
There was no one there.
C: The foam-molded product had a crack penetrating in the thickness direction.
D: The foam-molded article was broken into a number of pieces, and the ice inside the foam-molded article was scattered.

(Range up test)
100 cc of vegetable oil was added to the obtained foam-molded product, and the upper opening of the foam-molded product was sealed with a polyethylene film. The foam-molded product containing the vegetable oil was heated in a microwave oven at 1500 W output for 1 minute. After that, the flange of the foam-molded product was lifted with one hand and evaluated based on the following criteria.

A: The foam-molded product could be lifted without deformation.
B: The foam molded product warps, but can be lifted without deformation.
When all the vegetable oil was removed from the foamed product, the foamed product returned to its original state.
It has been restored.
C: Warping occurs in the foam molded product, but the vegetable oil in the foam molded product does not spill out.
The foam molded product could be lifted without any deformation. All the plants were removed from the foam molded product.
When the oil was removed, the foam returned to its original state.
D: The container of the foam molded product is deformed and inverted inwards and outwards, causing the vegetable oil in the container to spill out.
Even if all the vegetable oil was removed from the foamed molded product, the foamed molded product returned to its original state.
I didn't.

The present invention has excellent thermoformability and can be easily thermoformed into a thermoplastic polyester resin foam molded product. The resulting foam molded product is resistant to deformation even when a load is applied in a heated state, and can be suitably used as a foam container for storing food.

Claims (9)

A foam layer containing a thermoplastic polyester-based resin foam is provided.
The thermoplastic polyester resin foam contains a thermoplastic polyester resin,
A thermoplastic polyester resin foam molded article, characterized in that in the foam layer, the difference in crystallinity between one of the surface portions and the central portion is 15% or less. The thermoplastic polyester resin foam molded product according to claim 1, characterized in that in the foam layer, the difference in crystallinity between both surface portions and the middle portion is 15% or less. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that a non-foamed thermoplastic resin sheet is laminated and integrated on one or both sides. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that the total amount of ester compounds and ether compounds generated by GC/MS at 285°C is 1000 ppm or less based on the total amount of the thermoplastic polyester resin. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that the amount of carboxyl end groups of the thermoplastic polyester resin is 100 equivalents/ton or less. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that the content of acetic acid in the thermoplastic polyester resin is 100 ppm or less based on the total amount of the thermoplastic polyester resin. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that the number average molecular weight of the thermoplastic polyester resin is 5,000 or more. The thermoplastic polyester resin foam molded product according to claim 1 or 2, characterized in that the content of inorganic matter is 7% by mass or less. The thermoplastic polyester resin foam molded product according to claim 1 or 2, which is a container.