JP7791824B2 - container - Google Patents

Description

This invention relates to containers, and more particularly to containers used as paper cups or cases for storing beverages, food, etc.

Conventionally, containers for storing beverages, food, etc. have used composite substrates in which synthetic resin is laminated on one or both sides of a paper substrate.

Japanese Patent No. 4750909 discloses a container that uses homopolyethylene terephthalate (PET) as the resin.

Furthermore, Japanese Patent Publication No. 5680917 discloses a container that uses copolymerized PET resin (copolymerization component ratio of 10 mol% to 40 mol%) as the resin.

Japanese Patent No. 4750909 Japanese Patent No. 5680917

Homo-PET, such as that used in Japanese Patent No. 4750909, generally has a relatively high melting point of around 255°C. Therefore, in order to form a uniform film on the surface of a paper substrate by extrusion lamination, the resin must be extruded at a high temperature exceeding 310°C. However, PET resin is prone to hydrolysis under high temperature conditions. Therefore, while it is often assumed that homo-PET resin, which has a naturally high melting point, will have higher heat resistance, if the extrusion temperature is too high, hydrolysis occurs in part of the PET resin on the surface of the container formed after extrusion lamination, resulting in a decrease in the heat resistance of that part and the entire container. On the other hand, lowering the extrusion temperature to reduce the effects of hydrolysis increases heat resistance, but the melt viscosity during extrusion lamination increases, making it difficult to form a uniform film on the paper surface. Even if a film could be successfully formed, the high melt viscosity of the resin would result in poor adhesion to the paper when extruded onto the paper surface, and when such a composite substrate was used to form a container, poor molding of the container due to the reduced adhesion would easily occur, or delamination would occur between the paper and the PET resin.

Furthermore, the copolymerized PET resin disclosed in Japanese Patent No. 5,680,917 has a relatively low melting point of 230°C or below, allowing for low resin extrusion temperatures, reducing hydrolysis at high temperatures and reducing the loss of adhesion to the paper during extrusion onto the paper surface. However, the low melting point of 230°C or below results in poor heat resistance for the resulting container after molding. In particular, when filling a container with a food that requires cooking, such as a gratin, a baking process under high temperatures is required to brown the surface after filling the container. This requires high heat resistance due to the high localized temperatures. Furthermore, when the food is baked, packaged, and distributed to the market as a food product, the container also becomes hot when heated in a microwave oven and consumed, requiring similar high heat resistance. However, the container disclosed in Japanese Patent No. 5,680,917, due to its poor heat resistance, fails to fully meet these requirements.

This invention was made to solve the above-mentioned problems, and aims to provide a container that has high adhesion between the substrate layer and the resin layer and is highly heat-resistant.

In order to achieve the above-mentioned object, a container in a first aspect of this invention is a container composed of a composite substrate having a base layer made of paper and a resin layer made of copolymerized polyethylene terephthalate resin laminated on at least one side of the base layer, wherein the copolymerized polyethylene terephthalate resin is a copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid, the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 1 mol% or more and less than 10 mol%, and the copolymerized polyethylene terephthalate resin has a melting point of 234°C or more and 250°C or less.

This configuration results in a container with high adhesion between the base layer and the resin layer and high heat resistance.

A container in a second aspect of this invention has the same configuration as the invention in the first aspect, but in which the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 4.0 mol% or less.

This configuration ensures good adhesion between the substrate layer and the resin layer and favorable heat resistance of the container.

A container in a third aspect of the present invention has the configuration of the invention in the first or second aspect, in which the adhesion of the resin layer to the substrate layer is 4 N/50 mm or more.

This configuration provides excellent adhesion.

A container in a fourth aspect of the present invention has the configuration of any one of the first to third aspects of the invention, wherein the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 1.5 mol% or more and 2.2 mol% or less.

This configuration improves adhesion between the substrate layer and the resin layer and the heat resistance of the container.

A container in a fifth aspect of the present invention is one in which, in the configuration of the invention in any one of the first to fourth aspects, the copolymerized polyethylene terephthalate resin is a biologically derived biomass polyethylene terephthalate resin with a bio-based carbon content of 5% or more.

By configuring it in this way, the amount of fossil fuels used can be reduced, improving carbon neutrality.

A container in a sixth aspect of the present invention has the configuration of any one of the first to fifth aspects of the invention, and comprises a bottom and a side wall rising from the periphery of the bottom, the bottom and the side wall being connected by thermal bonding.

This configuration ensures that the bottom and side walls are firmly bonded together.

The container in the seventh aspect of the present invention is formed by press molding or folding a single sheet of base paper obtained from a composite substrate, in the configuration of the invention in any one of the first to fifth aspects.

When configured in this manner, the container becomes a press-molded or folded product.

As described above, the container in the first aspect of this invention has high adhesion between the base layer and the resin layer and is highly heat-resistant, which prevents defective molding of the container and makes it suitable for use when the contents become hot or when they undergo a baking process.

The container in the second aspect of this invention, in addition to the effects of the invention in the first aspect, is convenient to use because it has good adhesion between the substrate layer and the resin layer and good heat resistance of the container.

In addition to the effects of the first or second aspect of the invention, the container in the third aspect of the invention has good adhesion, which effectively prevents defective molding of the container.

The container in the fourth aspect of this invention, in addition to the effects of the invention in any of the first to third aspects, is more convenient to use because the adhesion between the substrate layer and the resin layer and the heat resistance of the container are more favorable.

In addition to the effects of the invention in any of the first to fourth aspects, the container in the fifth aspect of this invention can reduce the amount of fossil fuels used and improve carbon neutrality, thereby improving sustainability and contributing to environmental conservation.

In the sixth aspect of the present invention, in addition to the effects of any of the first to fifth aspects of the invention, the container has a bottom and side wall that are firmly bonded together, resulting in a stably molded container.

The container in the seventh aspect of this invention has the same effects as any of the first to fifth aspects of the invention, and in addition, since the container is a press-molded product or a molded product formed by bending, it is a stably molded container.

1 is a cross-sectional view showing the overall structure of a container according to a first embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of the "X" portion shown in FIG. 1; FIG. 10 is a cross-sectional view showing the overall structure of a container according to a second embodiment of the present invention. FIG. 10 is a perspective view showing a container according to a third embodiment of the present invention used in the examples.

Figure 1 is a cross-sectional view showing the overall structure of a container according to a first embodiment of the present invention, and Figure 2 is an enlarged cross-sectional view of the "X" portion shown in Figure 1.

Referring to these figures, the container 1 is mainly composed of a bottom 2 and a side wall 3 rising from the periphery of the bottom 2.

Referring to Figure 2, the side wall portion 3 is composed of a composite substrate 7 having a base layer 10 made of paper and a resin layer 11 made of copolymer polyethylene terephthalate resin laminated on the inner surface of the base layer 10 (the surface in the direction in which the contents are stored).

The bottom 2 is also made of a composite substrate 7 with the same configuration as the side wall 3, and the bottom 2 and side wall 3 are connected by thermal bonding. Specifically, the container shape is formed by punching out a side wall member (the expanded shape of the side wall 3) and a bottom member (the expanded shape of the bottom 2) of a predetermined shape from the composite substrate 7, and then bonding the ends of both members together using a known method such as thermal bonding.

The copolymerized polyethylene terephthalate resin in the present invention is a copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid (IPA), and the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 1 mol% or more and less than 10 mol%.

By configuring it in this way, the base material layer 10 and the resin layer 11 have high adhesion and the container has high heat resistance, which prevents molding defects in the container 1 and makes it suitable for use when the contents become hot or when they undergo a baking process.

The upper limit of the copolymerization ratio of isophthalic acid is preferably 8 mol% or less, more preferably 4.0 mol% or less, and even more preferably 2.2 mol% or less. The lower limit is preferably 1.5 mol% or more. Therefore, the range of the upper and lower limits is preferably 1.5 mol% or more and 2.2 mol% or less. In this way, the effects of improving adhesion and heat resistance can be more suitably achieved. Generally, polyethylene terephthalate resins are obtained by polycondensation of an acid component mainly composed of terephthalic acid and a glycol component mainly composed of ethylene glycol. However, the copolymerized polyethylene terephthalate resin used in the present invention contains isophthalic acid in addition to terephthalic acid as an acid component, and the copolymerized polyethylene terephthalate resin is obtained by copolymerizing this isophthalic acid in a predetermined ratio. Note that other acid components may be contained within a range that does not impair the effects of the present invention, and the glycol component may include components such as diethylene glycol in addition to ethylene glycol. Furthermore, the copolymerized polyethylene terephthalate resin used in the present invention may be a mixture of multiple polyethylene terephthalate resins with different copolymerization ratios, adjusted to a predetermined copolymerization ratio suitable for the present invention. For example, a homopolyethylene terephthalate resin and a copolymerized polyethylene terephthalate resin may be mixed in a predetermined ratio to adjust to a predetermined copolymerization ratio suitable for the present invention, or a mixture of polyethylene terephthalate resins with different copolymerization ratios may be mixed in a predetermined ratio to adjust to a predetermined copolymerization ratio suitable for the present invention. The copolymerization ratio of isophthalic acid can be calculated by subjecting the copolymerized polyethylene terephthalate resin to qualitative and quantitative analysis by ^1H -NMR spectrum measurement. Specifically, the monomer units composed of terephthalic acid and the monomer units composed of isophthalic acid in the copolymerized polyethylene terephthalate resin are estimated from the spectrum obtained by ^1H -NMR spectrum measurement, and the composition ratio (molar ratio) of each monomer unit in the copolymerized polyethylene terephthalate resin is calculated from the peak area ratio of the spectrum, and the ratio (%) of the "molar ratio of isophthalic acid monomer unit" to the "total molar ratio of terephthalic acid monomer unit and molar ratio of isophthalic acid monomer unit" is calculated.

Furthermore, the copolymerized polyethylene terephthalate resin of the present invention has a melting point of 234°C or higher and 250°C or lower. Furthermore, the melting point is preferably 240°C or higher and 250°C or lower, and even more preferably 243°C or higher and 250°C or lower. This configuration ensures that the melting point falls within a suitable range, allowing the extrusion temperature during extrusion lamination to be kept relatively low while the melting point itself is sufficiently high, resulting in favorable adhesion between the base layer 10 and the resin layer 11 and favorable heat resistance of the container 1. The melting point can be measured by differential scanning calorimetry (DSC).

Furthermore, the crystalline portion (%) of the copolymerized polyethylene terephthalate resin in the present invention is preferably 2% or more and 15% or less, and more preferably 3% or more and 10% or less. This configuration improves adhesion between the substrate layer 10 and the resin layer 11, and reduces molding defects of the container 1. In particular, when the container of the present invention is manufactured by press-molding a single sheet of base paper obtained from the composite substrate 7, the shape retention of the container may decrease over time due to springback of the paper after press-molding. However, if the crystalline portion (%) of the copolymerized polyethylene terephthalate resin constituting the composite substrate 7 is within the above range, the adhesion between the substrate layer 10 and the resin layer 11 and the adhesion between the resin layers 11 themselves are improved, thereby suppressing the decrease in shape retention after press-molding. The crystalline portion (%) of the copolymerized polyethylene terephthalate resin can be determined, for example, by removing only the resin layer 11 from the composite substrate 7, measuring its dissolution behavior by differential scanning calorimetry (DSC), and calculating the crystalline portion percentage (%) based on the following formula 1. The portion other than the crystalline portion is assumed to be an amorphous portion, and the amorphous portion can be calculated by the formula: amorphous portion (%)=100-crystalline portion (%).
Formula 1:

Furthermore, in the present invention, the adhesion of the resin layer 11 to the base layer 10 is preferably 4 N/50 mm or more. This configuration provides favorable adhesion, thereby favorably preventing molding defects in the container 1. From the viewpoint of molding defects, the higher the adhesion value, the better, so there is no particular upper limit for the adhesion, but considering the ease of disassembling and dismantling the container to reduce the volume of waste after use, a value of approximately 20 N/50 mm or less is sufficient. The adhesion can be measured using the measurement method described in the Examples below.

Furthermore, the polyethylene terephthalate resin in the present invention is preferably a biomass polyethylene terephthalate resin derived from living organisms (biomass resources) with a bio-based carbon content of 5% or more. Polyethylene terephthalate resin is a resin obtained by polycondensation of ethylene glycol and terephthalic acid, the main components of which are derived from ethylene glycol and terephthalic acid. However, most polyethylene terephthalate resins (including those disclosed in the aforementioned Japanese Patents No. 4,750,909 and No. 5,680,917) are derived from fossil resources. By converting this into a biomass polyethylene terephthalate resin derived from living organisms such as sugarcane, the amount of fossil resources used can be reduced, and carbon neutrality is improved, thereby improving sustainability and contributing to environmental conservation.

In this invention, the biobased carbon content, which is an indicator of the proportion of biologically derived materials in a polyethylene terephthalate copolymer resin, is preferably 5% or higher, and more preferably 15% or higher. The higher the biobased carbon content, the lower the proportion of fossil-derived materials, resulting in a container that is more environmentally friendly. On the other hand, a higher biobased carbon content also increases costs, so it is preferable to keep it within an appropriate range. The biobased carbon content can be expressed as the C14 content obtained using a radiocarbon (C14) measurement method in accordance with ISO-16620-2 (equivalent to the ASTM-D6866 standard). Fossil resources contain very little C14, while biological resources contain a certain proportion (105.5 pMC). Therefore, if the C14 content in the polyethylene terephthalate copolymer resin is designated as PC14, the biobased carbon content can be calculated using the following formula:

Bio-based carbon content (%) = PC14/105.5 x 100
Next, FIG. 3 is a cross-sectional view showing the overall structure of a container according to a second embodiment of the present invention.

Note that the container 21 according to the second embodiment of the present invention is basically similar in configuration to the container 1 according to the first embodiment described above, so the following explanation will focus on the differences.

Referring to the same figure, the container 21 is formed by press molding a sheet of base paper obtained from a composite substrate 27 (similar in configuration to the composite substrate 7 in the first embodiment described above). Specifically, the sheet of base paper obtained from the composite substrate 27 is punched out into a predetermined shape and then press molded to form the container 21, which has a bottom 22 and a side wall 23 rising from the periphery of the bottom 22.

Furthermore, although not shown, the container according to the third embodiment is formed by folding a sheet of base paper obtained from a composite substrate (with the same configuration as composite substrate 7 in the first embodiment described above) and forming it into a predetermined container shape. Specifically, a sheet of base paper obtained from the composite substrate is punched out into a predetermined shape, and then the base paper is folded or otherwise formed into a bottom and side walls rising from the periphery of the bottom, thereby forming a container with a bottom and side walls rising from the periphery of the bottom.

The containers according to each embodiment of the present invention can be used for a variety of purposes, including, but not limited to, storing food. They are particularly suitable for storing food that is heated under high-temperature conditions after being filled into the container. Specifically, they can be used under high-temperature heating conditions of 100°C or higher, and can also be called heat-resistant paper containers. They can also be used for cooking in ovens (including toasters, grills, etc.) at temperatures of 200°C or higher.

Furthermore, in the containers according to the embodiments of the present invention, the composition of the paper that constitutes the composite substrate is not particularly limited, and pure white roll paper, kraft paper, parchment paper, ivory paper, Manila paper, card paper, cup paper, etc. can be used depending on the desired application. Furthermore, the basis weight of the paper is preferably 150 g/m ² to 500 g/m ^2. By configuring it in this way, it becomes easier to form the container and the cost of the container can be reduced.

Furthermore, in the containers according to each embodiment of the present invention, the method of laminating polyethylene terephthalate resin onto paper is not particularly limited, and examples include extrusion lamination, thermal lamination, dry lamination, and wet lamination. In the present invention, extrusion lamination is preferred because it is suitable for mass production, is cost-effective, and allows direct lamination without an anchor coat or the like. However, this does not preclude the formation of an anchor coat layer on the paper beforehand during extrusion lamination.

Furthermore, in the containers according to each embodiment of the present invention, the thickness of the resin layer is not particularly limited, but is preferably between 6 μm and 50 μm. Within this range, the desired heat resistance can be imparted to the container. Furthermore, when the resin layers of the composite substrate are thermally bonded together during container molding, it becomes easier to raise the temperature of the resin uniformly, enabling uniform adhesion. Furthermore, the occurrence of tunneling and pinholes in the resin layer during thermal bonding can be suppressed.

Furthermore, in the containers according to each embodiment of the present invention, the resin layer is formed on the inner surface of the base material layer, but it is sufficient that it is formed on at least one surface, and it may also be formed on both surfaces.

Furthermore, in the containers according to each embodiment of the present invention, an anchor coat layer may be interposed between the base layer and the resin layer as described above, or a printed layer may be formed, as long as the object of the present invention is not impaired. Furthermore, the paper of the base layer may be subjected to corona treatment.

Furthermore, in the containers according to each embodiment of the present invention, the copolymerized polyethylene terephthalate resin may contain appropriate amounts of various additives such as chain extenders, ultraviolet absorbers, lubricants, antistatic agents, heat stabilizers, antioxidants, pigments, dyes, hydrolysis inhibitors, light stabilizers, and plasticizers, within the scope that does not impair the objectives of the present invention.

Furthermore, in the containers according to each embodiment of the present invention, the method for producing the copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid is not particularly limited, and copolymerization may be carried out using known methods and conditions, and multiple polyethylene terephthalate resins may be mixed to adjust the copolymerization ratio, as described above.

The present invention will be specifically explained below based on examples. However, the embodiments of the present invention are not limited to the examples.

(Example Preparation 1)
First, several types of copolymerized polyethylene terephthalate resins were prepared, each obtained by copolymerizing with isophthalic acid at different ratios, or by mixing multiple polyethylene terephthalate resins with different copolymerization ratios to adjust to a predetermined copolymerization ratio. Biomass polyethylene terephthalate resins were prepared as the resin used in Examples 1 and 3, and homopolyethylene terephthalate resins were prepared as the resin used in Comparative Example 1. The ratios ( ^% ) of the "isophthalic acid monomer unit molar ratio" to the "total of the terephthalic acid monomer unit molar ratio and the isophthalic acid monomer unit molar ratio" were calculated by qualitative and quantitative analysis using 1H-NMR. The copolymerization ratios of isophthalic acid in each copolymerized polyethylene terephthalate resin were 2.0% (Example 1), 1.6% (Example 2), 5.0% (Example 3), 7.5% (Example 4), 9.2% (Example 5), 3.0% (Example 6), 3.9% (Example 7), 14.1% (Comparative Example 2), and 10.5% (Comparative Example 3), respectively. The copolymerization ratio of isophthalic acid in the homopolyethylene terephthalate resin was 0% (Comparative Example 1). The melting points of each resin were measured using a commercially available differential scanning calorimeter. Furthermore, the biobased carbon content was measured using a radiocarbon (C14) measurement method in accordance with ISO-16620-2 (equivalent to the ASTM-D6866 standard), and calculated using the biobased carbon content calculation formula described above.

Paper having a basis weight of 230 g/ ^m2 was used as a substrate layer, and one side of the substrate was coated by extrusion lamination with each of the above-mentioned types of polyethylene terephthalate resin to a thickness of 30 μm in Examples 1, 2, 4, 6, 7, and Comparative Examples 1 to 3, 40 μm in Example 3, and 20 μm in Example 5. Each composite substrate was produced by extrusion lamination. The thickness of the polyethylene terephthalate resin was measured by observing the cross section of the composite substrate using a commercially available microscope.

Side wall members and bottom members of a predetermined shape were punched out from each type of composite substrate to create containers large enough to hold 300g of the white sauce described below, and these were then combined and thermally bonded to produce the containers of Examples 1 to 7 and Comparative Examples 1 to 3.

(Adhesion test)
Test pieces measuring 50 mm × 150 mm were cut out from each of the types of composite substrates prepared above, and a peel test was performed at a 180° peel angle and a speed of 100 mm/min to test the adhesion between the substrate layer and the resin layer of the composite substrate.

The measuring device used was a MAX-R2KN-B model manufactured by Japan Measurement Systems Co., Ltd. Ideal adhesion is complete delamination between the paper layers, but it was determined that there was no problem if there was enough strength to cause partial delamination between the paper layers. Adhesion was evaluated as follows: less than 4N/50mm was x (unsuitable), 4N/50mm to 7N/50mm was △ (acceptable), and 7N/50mm or more was ○ (suitable).

(Heat resistance test)
Using each type of container prepared above, the following two types of heat resistance tests were carried out.
(1) Microwave Oven Heating Test 100 g of water was placed in each container, heated for 3 minutes at 500 W in a microwave oven (manufactured by SANYO Electric Co., Ltd., model number: EMO-FM23C, without turntable), and then removed. The containers were left with the water in them for 12 hours, after which the presence or absence of water leakage from the containers and the surface condition of the resin layer constituting the containers were visually confirmed. The test was conducted with five containers for each test. The water leakage evaluation was judged as ◯ (good) if no water leakage occurred in any of the five containers, and × (unsuitable) if water leakage occurred in even one of the five containers. Furthermore, the surface condition of the resin layer was evaluated as ◯ (good) if no abnormalities such as bubbles or tears were found on the surface of the resin layer constituting all five containers, and × (unsuitable) if abnormalities such as bubbles or tears were found on the surface of the resin layer constituting even one of the five containers.
(2) Baking test after filling containers with white sauce Each container was filled with 300 g of white sauce manufactured by Heinz Japan Co., Ltd., and then the filled containers were baked in an oven manufactured by Fujimac Co., Ltd. (model number: FSCC101) at a heating temperature of 200°C for 5 minutes and at 260°C for 5 and 10 minutes, respectively. The test was performed with n = 5 at each temperature. After the baking test, the white sauce was removed from the container, and the presence or absence of delamination (peeling at the interface between the paper substrate layer and the resin layer) between the base layer and the resin layer of the composite substrate constituting the container was visually confirmed. A case in which no delamination occurred anywhere on the container was judged as ◯ (suitable), and a case in which delamination occurred anywhere on the container was judged as × (unsuitable).

Table 1 below shows the composition of each type of container (resin, composite substrate) and the results of each test.

As shown in Table 1, Examples 1 to 7, in which the copolymerization ratio and melting point of isophthalic acid were within the preferred ranges, exhibited suitable adhesion and showed no problems with heat resistance in a baking test at a heating temperature of 200°C. In particular, Examples 1 to 4, 6, and 7, in which the copolymerization ratio of isophthalic acid was 1.5 mol% or more and 8 mol% or less, also showed suitable results in heat resistance in a baking test at a heating temperature of 260°C for a heating time of 5 minutes. Furthermore, Examples 1, 2, 6, and 7, in which the copolymerization ratio of isophthalic acid was 4.0 mol% or less, also showed suitable results in heat resistance in a baking test at a heating temperature of 260°C for a heating time of 10 minutes.

Furthermore, it was confirmed that Example 1, which had a bio-based carbon content of 17%, Example 3, which had a bio-based carbon content of 6.2%, Example 6, which had a bio-based carbon content of 21.1%, and Example 7, which had a bio-based carbon content of 18.7%, also had favorable adhesion and heat resistance, similar to the other examples with a bio-based carbon content of 0%.

(Example Preparation 2)
Similar to the above-mentioned "Example Preparation 1," multiple types of copolymerized polyethylene terephthalate resins and homopolyethylene terephthalate resins were prepared. Then, a paper with a basis weight of 230 g/ ^m2 was used as the substrate layer, and each of the above-mentioned types of polyethylene terephthalate resin was coated on both sides of the substrate to a thickness of 30 μm by extrusion lamination to prepare each composite substrate. The melting point, thickness, and bio-based carbon content of the polyethylene terephthalate resin were measured using the same method as in "Example Preparation 1." These values are shown in Table 2.

In Table 2, in Examples 1-1, 2-1, 6, 7, and Comparative Example 1, the resins used were the same as those used in Examples 1, 2, 6, 7, and Comparative Example 1 in Table 1, and extrusion lamination was performed under the same extrusion conditions. On the other hand, in Examples 1-2 and 2-2, the resins used were the same as those used in Examples 1 and 2, but the extrusion conditions were appropriately adjusted, such as by slowing the extrusion speed, so as to obtain a crystalline fraction (%) different from that of Examples 1 and 2. The crystalline fraction (%) of the copolymerized polyethylene terephthalate resin was determined by removing the resin layer from the composite substrate constituting the paper container after press molding, as described below, and measuring its dissolution behavior by differential scanning calorimetry (DSC), and then calculating it using the above-mentioned formula 1.

A sheet of base paper of the specified shape was then punched out from each type of composite substrate and press-molded to produce a container with a rolled edge around the perimeter, as shown in Figure 4.

Figure 4 is an oblique view showing a container of the third embodiment of the present invention used in the examples.

Referring to the figure, the dimensions of the container after press molding are as follows:
Length D in the longitudinal direction (including the flange): Approximately 177 mm
Width W in the short direction (including the flange): Approximately 123 mm
Height H: approx. 27 mm
Diameter of the rolled edge _X1 : approx. 3 mm
Flange width (including rolled edge) x ₂ : approx. 7 mm
(Shape retention test)
For the containers after press molding, (1) the width in the short side direction of the container immediately after molding (W in Figure 4), (2) the width in the short side direction of the container 30 minutes after molding, and (3) the width in the short side direction of the container 24 hours after molding were measured, and compared with the container immediately after molding, the change in the width in the short side direction of the container over time due to springback of the paper was confirmed after 30 minutes and 24 hours. Specifically, the rate of dimensional change was calculated using Equation 2.

Equation 2: Width (mm) in the shortest direction of the container after a predetermined time has elapsed since molding ÷ Width (mm) in the shortest direction of the paper container immediately after molding × 100 = % degree of opening of the paper container due to springback over time
The shape retention test was carried out using five samples for each paper container, and the arithmetic mean value of the five paper container samples was calculated.

As shown in Table 2 above, in all Examples, the dimensional change in the width of the container in the shortest direction 30 minutes and 24 hours after press molding was only 103%, indicating good shape retention. On the other hand, in the Comparative Examples, the change increased to 105% after 30 minutes and 110% after 24 hours, indicating poor shape retention. This is presumably because the crystalline portion (%) of the resin layer in the Examples was within the specified range, resulting in good adhesion of the resin layer to the wrinkled and rolled portions of the container formed by squeezing during press molding, and minimizing paper springback after press molding. On the other hand, in the Comparative Examples, the crystalline portion (%) of the resin layer was high, resulting in poor adhesion of the resin layer to the wrinkled and rolled portions of the container, presumably preventing paper springback from being suppressed after press molding, resulting in poor shape retention.

As described above, the container of the present invention is suitable, for example, as a paper cup or case for storing beverages, food, etc.

Claims (8)

A container (1) comprising a composite substrate (7) including a base layer (10) made of paper and a resin layer (11) made of copolymerized polyethylene terephthalate resin laminated on at least one surface of the base layer,
The copolymerized polyethylene terephthalate resin is a copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid,
a copolymerization ratio of the isophthalic acid in the copolymerized polyethylene terephthalate resin is 1 mol% or more and less than 10 mol%,
The copolymerized polyethylene terephthalate resin has a melting point of 234°C or higher and 250°C or lower,
A container in which 100 g of water is placed in the container, heated in a microwave oven at 500 W for 3 minutes, and then removed. The container is left with the water in it for 12 hours, after which there is no water leakage from the container and no abnormalities such as bubbles or tears on the surface of the resin layer. The container is filled with 300 g of white sauce, and then heated in an oven at a heating temperature of 200°C and 260°C for a heating time of 5 minutes in both cases, and in both cases no delamination occurs between the base material layer and the resin layer of the composite base material that constitutes the container . A container (1) comprising a composite substrate (7) including a base layer (10) made of paper and a resin layer (11) made of copolymerized polyethylene terephthalate resin laminated on at least one surface of the base layer,
The copolymerized polyethylene terephthalate resin is a copolymerized polyethylene terephthalate resin obtained by copolymerization with isophthalic acid,
a copolymerization ratio of the isophthalic acid in the copolymerized polyethylene terephthalate resin is 1 mol% or more and less than 10 mol%,
The copolymerized polyethylene terephthalate resin has a melting point of 234°C or higher and 250°C or lower,
The copolymerized polyethylene terephthalate resin has a crystalline portion (%) of 2% or more and 15% or less,
The resin layer has an adhesion to the base layer of 4 N/50 mm or more . The container according to claim 1 or claim 2, wherein the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 4.0 mol% or less. 2. The container according to claim 1 , wherein the resin layer has an adhesion to the base material layer of 4 N/50 mm or more. A container according to any one of claims 1 to 4, wherein the copolymerization ratio of isophthalic acid in the copolymerized polyethylene terephthalate resin is 1.5 mol% or more and 2.2 mol% or less. A container according to any one of claims 1 to 5, wherein the copolymerized polyethylene terephthalate resin is a biologically derived biomass polyethylene terephthalate resin with a bio-based carbon content of 5% or more. It comprises a bottom (2) and a side wall (3) rising from the periphery of the bottom,
7. The container according to claim 1, wherein the bottom and the side wall are connected by thermal bonding. The container according to any one of claims 1 to 6, wherein the container is a press-molded product or a folded-molded product.