Package, and laminate constituting package

Abstract

To provide a package for microwave cooking configured so that vapor can be properly extracted from a vapor extraction part, and a laminate constituting the package.SOLUTION: A package for microwave cooking is composed of a laminate in which a polyethylene terephthalate film and a sealant layer are provided. The sealant layer has a sea-island structure therein. A standard deviation, which is obtained by performing approximation and normalization by Gaussian function to strength distribution obtained by subjecting, to Fourier transformation, an image of a cross section parallel to a machine direction of the sealant layer, observed with a scanning-type probe microscope, which is an image which is 1024px transversely and 512px vertically in resolution in which a length 10 μm is expressed by 512px, is 600 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a package and a laminate that constitutes the package. [Background technology]

[0002] Patent Document 1 discloses a package for microwave cooking that is made of a laminate including a polyethylene terephthalate film and a sealant layer. The package is provided with a steam vent that opens as a steam port when the internal pressure reaches or exceeds a predetermined pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-130141 Summary of the Invention [Problem to be solved by the invention]

[0004] In a package for microwave cooking such as that described in Patent Document 1, depending on the structure of the laminate that constitutes the package, steam may not escape from the steam release section even when the internal pressure of the package reaches or exceeds a predetermined pressure. The present disclosure provides a package for microwave cooking that allows steam to escape appropriately from the steam release section, and a laminate that constitutes the package. [Means for solving the problem]

[0005] One aspect of the present disclosure is a package for microwave cooking that is composed of a laminate including a polyethylene terephthalate film and a sealant layer. The sealant layer has an internal sea-island structure, and an image of a cross section of the sealant layer parallel to the machine direction is observed with a scanning probe microscope. The image is 1024 pixels wide and 512 pixels high, and is Fourier transformed at a resolution where 10 μm in length is expressed as 512 pixels. The intensity distribution is obtained by approximating and normalizing the image with a Gaussian function, and the standard deviation of the Gaussian function obtained is 600 or less. When the sealant layer has an intensity distribution that is approximated by a curve with a standard deviation of 600 or less, steam can be properly released from the steam release portion of the package for microwave cooking.

[0006] Another aspect of the present disclosure is a laminate that constitutes the above-described package for microwave cooking, and that provides the same effects as the above-described package. [Effects of the Invention]

[0007] The present disclosure can provide a package for microwave cooking that allows steam to escape appropriately through a steam release section, and a laminate that constitutes the package. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing an example of a packaging body according to an embodiment. [Figure 2] FIG. 2 is a plan view showing an example of the packaging bag shown in FIG. [Figure 3] FIG. 3 is a partially enlarged view showing another example of the steam release section of the packaging bag shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing an example of the laminate shown in FIG. [Figure 5] Figure 5(A) is an example of an image opened in Image J. Figure 5(B) is an example of a power spectrum. Figure 5(C) is a diagram explaining the area where the intensity distribution is confirmed. [Figure 6]Figure 6(A) shows the intensity distribution of the sample using CPP film A. Figure 6(B) shows the intensity distribution of the sample using CPP film B. Figure 6(C) shows the intensity distribution of the sample using CPP film C. [Figure 7] Fig. 7A is a graph obtained by approximating the data shown in Fig. 6A with a Gaussian function. Fig. 7B is a graph obtained by approximating the data shown in Fig. 6B with a Gaussian function. Fig. 7C is a graph obtained by approximating the data shown in Fig. 6C with a Gaussian function. [Figure 8] (A) of Fig. 8 is a graph obtained by normalizing the graph shown in (A) of Fig. 7. (B) of Fig. 8 is a graph obtained by normalizing the graph shown in (B) of Fig. 7. (C) of Fig. 8 is a graph obtained by normalizing the graph shown in (C) of Fig. 7. [Figure 9] FIG. 9 is a graph plotting the standard deviation of the Gaussian function for each sample. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes embodiments of the present disclosure. The following embodiments are examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The upper or lower limit of a numerical range specified in this disclosure may be replaced with any value shown in the examples. The upper and lower limit values ​​individually described may be combined arbitrarily. Unless otherwise specified, the materials or components exemplified in this disclosure may be used alone or in combination of two or more. In the description, the same elements or elements having the same functions are denoted by the same reference numerals, and redundant explanations are omitted. Positional relationships such as up, down, left, and right used in the description are based on the positional relationships shown in the drawings, unless otherwise specified.

[0010] [Packaging composition] FIG. 1 is a plan view showing an example of a packaging body according to one embodiment. The packaging body 1 is a packaging body for microwave cooking. Microwave cooking means cooking the contents inside the packaging body by heating in a microwave oven. The packaging body 1 includes a packaging bag 2 and a content 21 accommodated in an accommodation section 20 of the packaging bag 2. The packaging bag 2 is composed of two laminates 10a and 10b that form the side surfaces and a laminate 10c that forms the bottom surface. The laminates 10a, 10b, and 10c have the same structure. The laminate 10a is a laminate that includes a polyethylene terephthalate film and a sealant layer. Details of the laminates will be described later.

[0011] The packaging bag 2 has a top seal portion 22 at the top end, side seal portions 23, 24 at both side ends, and bottom seal portions 25, 26 at the bottom end. The top seal portion 22 and the side seal portions 23, 24 are formed by heat-sealing the sealant layers at the respective ends of the laminates 10a, 10b in an overlapping state. The bottom seal portion 25 is formed by heat-sealing the sealant layers at the respective ends of the laminates 10a, 10c in an overlapping state. The bottom seal portion 26 is formed by heat-sealing the sealant layers at the respective ends of the laminates 10b, 10c in an overlapping state. The dotted portions in FIG. 1 indicate the seal portions formed by heat sealing. The portions other than the sealed portions are non-sealed portions where the laminates 10a, 10b, 10c are not heat-sealed. The laminates 10a, 10b, and 10c that make up the packaging bag 2 form an internal space (storage section 20) that stores an item 21 by sealing the respective seal sections. In this way, the storage section 20 is surrounded by the laminates 10a, 10b, and 10c.

[0012] FIG. 2 is a plan view showing an example of the packaging bag shown in FIG. 1. The packaging body 1 may be manufactured using the packaging bag 2A shown in FIG. 2. In the packaging bag 2A, the upper end 22a of the laminate 10a (10b) is not heat-sealed. Before the upper end 22a is heat-sealed, the contents 21 are filled through the opening formed at the upper end 22a, and then the upper end 22a of the laminate 10a (10b) is heat-sealed. After the contents 21 are filled, the upper end seal portion 22 is formed, thereby obtaining the packaging body 1 shown in FIG. 1, in which the contents 21 are sealed in the storage portion 20 of the packaging bag 2. The position where the opening for filling the contents 21 is formed is not limited to the upper end 22a, and may be a side portion or a bottom portion.

[0013] A pair of notches 27, 27 may be provided in the side edge seal portions 23, 24 of the packaging bag 2. A planned tear line (not shown) may be provided connecting the pair of notches 27, 27. After heating the packaging body 1 in a microwave oven, the end user can open the packaging body 1 from one of the notches 27 along the planned tear line and remove the heated contents 21. The contents 21 are not particularly limited. The contents 21 may contain not only water but also oils and fats. Examples of the contents 21 include foods such as curry, stew, soup, simmered dishes, and grilled dishes.

[0014] The side edge seal portions 24 include steam release portions 28 configured to form steam vents that communicate between the storage portion 20 and the outside of the packaging bag 2 when the pressure in the storage portion 20 of the packaging bag 2 increases. The steam release portions 28 protrude toward the center CE of the packaging bag 2. When the contents 21 in the storage portion 20 are heated in a microwave oven and steam is generated, the storage portion 20 expands. As the storage portion 20 expands, the forces applied to the top end seal portion 22, the side edge seal portions 23, 24, and the bottom end seal portions 25, 26 increase the shorter the distance from the center CE. Therefore, large tensile stress is applied to the steam release portions 28 protruding toward the center CE as the contents 21 are heated.

[0015] When the pressure in the storage section 20 reaches or exceeds a predetermined value, the side edge seal section 24 peels away from the inner edge in the steam release section 28, connecting the storage section 20 to the outside of the packaging bag 2 (packaging body 1). Steam then escapes to the outside through a steam vent hole (steam release hole) formed in the steam release section 28. The steam release section 28 has the function of forming a steam vent hole when the pressure in the storage section 20 rises, thereby preventing the packaging bag 2 (packaging body 1) from rupturing.

[0016] In the steam release section 28, a non-sealed section 29 is provided on the outside of the side edge sealed section 24. The seal width of the side edge sealed section 24 in the steam release section 28 is smaller than the seal width of the side edge sealed section 24 other than the steam release section 28. Therefore, when the pressure inside the accommodating section 20 increases, a steam vent port that connects the accommodating section 20 to the outside is appropriately formed in the steam release section 28. In order to appropriately release (exhaust) steam from the accommodating section 20 to the outside, the non-sealed section 29 may be provided with a through-hole that penetrates in the stacking direction of the stacks 10a, 10b.

[0017] The minimum seal width of the side edge seal portion 24 in the steam release portion 28 may be 1 to 5 mm, or may be 2 to 4 mm. In this case, steam can be appropriately released during heating in a microwave oven while maintaining hermetic sealing. The shape and position of the steam release portion 28 are not particularly limited. FIG. 3 is a partially enlarged view showing another example of the steam release portion of the packaging bag shown in FIG. 1. As shown in FIG. 3, the steam release portion 28 may protrude toward the center CE of the packaging bag 2. In a modified example, the steam release portion 28 may be provided in the upper end seal portion 22. Regardless of the shape and position, the minimum seal width of the steam release portion 28 may be within the above-mentioned numerical range. The steam release portion 28 may be provided in multiple locations.

[0018] The packaging bag 2 (packaging body 1) is subjected to a retort treatment in which it is heated for several minutes or more in a hot water spray at over 100° C. The packaging body 1 is sterilized by the retort treatment and can be stored at room temperature for a long period of time.

[0019] The packaging bag 2 does not need to include the laminate 10c that forms the bottom surface. In this case, the packaging bag 2 is formed by heat-sealing the sealant layers at the ends of the two laminates 10a and 10b in a state where they are overlapped.

[0020] [Laminate structure] Fig. 4 is a cross-sectional view showing an example of the laminate shown in Fig. 1. As shown in Fig. 4, the laminate 10 has a sealant layer 16 on one side of a polyethylene terephthalate (PET) film 11. A nylon 6 film 14 is interposed between the PET film 11 and the sealant layer 16. A first adhesive layer 13 is interposed between the PET film 11 and the nylon 6 film 14. A second adhesive layer 15 is interposed between the nylon 6 film 14 and the sealant layer 16. A printed layer 12 is interposed between the PET film 11 and the first adhesive layer 13. The laminate 10 only needs to include the PET film 11 and the sealant layer 16, and the printed layer 12, the first adhesive layer 13, the nylon 6 film 14, and / or the second adhesive layer 15 may be included as needed.

[0021] The thickness of the PET film 11 is not particularly limited and may be 9 to 25 μm, 10 to 20 μm, or 10 to 15 μm. The thickness of the PET film 11 may be adjusted depending on the application or desired properties.

[0022] The PET content in the PET film 11 may be 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more of the total amount of the PET film 11.

[0023] A commercially available PET film 11 can be used. The PET film 11 may be a stretched film or an unstretched film. It is believed that the degree of crystal orientation in a polymer film is improved by stretching the film. When a stretched film is used, the number of oriented crystals in the film increases, improving puncture strength. The stretching direction may be the MD direction or the TD direction. The stretching method may be any method that can provide a dimensionally stable film, such as uniaxial stretching, biaxial stretching, or a tubular method. From the viewpoint of further improving puncture strength, a biaxially stretched film may be used as the PET film 11. The biaxially stretched film may be a biaxially stretched film obtained by a simultaneous biaxial stretching method or a sequential biaxial stretching method.

[0024] The thickness of the nylon 6 film 14 is not particularly limited and may be 10 to 25 μm, 10 to 20 μm, or 12 to 17 μm. The thickness of the nylon 6 film 14 may be adjusted depending on the application or desired properties.

[0025] The nylon 6 film 14 is a polymer film containing nylon 6, which is a synthetic polymer containing polyamide. The polyamide content in the nylon 6 film 14 may be 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more of the total amount of the nylon 6 film 14. Since the nylon 6 film 14 has excellent puncture strength and flexibility, the inclusion of the nylon 6 film 14 can further improve the puncture strength and flexibility of the laminate 10.

[0026] A commercially available nylon 6 film 14 can be used. The nylon 6 film 14 may be a stretched film or an unstretched film. When a stretched film is used, the amount of oriented crystals in the film increases, improving puncture strength. The stretching direction may be either the MD direction or the TD direction. The stretching method may be any method that can provide a dimensionally stable film, such as uniaxial stretching, biaxial stretching, or a tubular method. The biaxially stretched film obtained by biaxial stretching may be obtained by a simultaneous biaxial stretching method, or may be obtained by a sequential biaxial stretching method from the viewpoint of orienting the internal molecules and improving puncture strength. A nylon 6 film 14 obtained by a tubular method may be used from the viewpoint of sufficiently orienting the internal molecules of the nylon 6 film 14 and further improving puncture strength.

[0027] The sealant layer 16 is a layer that provides heat-sealing properties to the laminate 10. The sealant layer 16 may be made of, for example, a thermoplastic resin. Examples of the thermoplastic resin include polyolefin-based resins such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), and ethylene-α-olefin copolymer; ethylene-based resins such as ethylene-(meth)acrylic acid copolymer; blends of polyethylene and polybutene; homopolypropylene resin (PP); propylene-ethylene random copolymers, propylene-ethylene block copolymers, and propylene-α-olefin copolymers; and polypropylene-based resins. The sealant layer 16 may also be made of a mixture of two or more of these thermoplastic resins. The thermoplastic resin can be appropriately selected depending on the intended use.

[0028] The resin constituting the sealant layer 16 may contain various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier.

[0029] A commercially available sealant layer can be used as the sealant layer 16. The sealant layer 16 may be an unstretched film (for example, an unstretched polypropylene film) from the viewpoint of improving the sealing property by heat sealing. The thickness of the sealant layer 16 can be adjusted depending on the mass of the contents or the shape of the packaging bag, and may be approximately 10 to 100 μm.

[0030] The first adhesive layer 13 is interposed between the PET film 11 and the nylon 6 film 14. The second adhesive layer 15 is interposed between the nylon 6 film 14 and the sealant layer 16. The materials for the first adhesive layer 13 and the second adhesive layer 15 are, for example, polyester-isocyanate resin, urethane resin, polyether resin, etc. The first adhesive layer 13 firmly bonds the PET film 11 and the nylon 6 film 14. The second adhesive layer 15 firmly bonds the nylon 6 film 14 and the sealant layer 16. The materials for the first adhesive layer 13 and the second adhesive layer 15 may be the same or different from each other.

[0031] The thicknesses of the first adhesive layer 13 and the second adhesive layer 15 are not particularly limited and may be, for example, 0.5 to 5.0 μm, or 2 to 3 μm. When the thickness of the first adhesive layer 13 is 0.5 μm or more, the adhesion between the PET film 11 and the nylon 6 film 14 can be improved. When the thickness of the second adhesive layer 15 is 0.5 μm or more, the adhesion between the nylon 6 film 14 and the sealant layer 16 can be improved. When the thickness of the first adhesive layer 13 and the second adhesive layer 15 is 5.0 μm or less, the recyclability of the laminate 10 can be improved. The thickness of the first adhesive layer 13 and the second adhesive layer 15 may be the same as or different from each other.

[0032] The first adhesive layer 13 and the second adhesive layer 15 are layers that bond two adjacent layers together when forming the laminate 10. The laminate 10 can be formed by laminating a nylon 6 film 14 onto a PET film 11 and then laminating a sealant layer 16 to the nylon 6 film 14. Methods for forming the laminate 10 include dry lamination, which uses an adhesive such as a one-component or two-component curing urethane adhesive, non-solder dry lamination, and extrusion lamination, which uses a thermoplastic resin as described above that is heated and melted and extruded into a curtain shape for lamination. The adhesive used to laminate the nylon 6 film 14 to the PET film 11 forms the first adhesive layer 13 as shown in FIG. 4. The adhesive used to laminate the sealant layer 16 to the nylon 6 film 14 forms the second adhesive layer 15 as shown in FIG. 4.

[0033] A printed layer 12 can be provided on the surface of the PET film 11 facing the nylon 6 film 14. The printed layer 12 is provided in a position visible from the outside of the laminate for the purpose of displaying information about the contents, identifying the contents, or improving the design of the packaging bag. The printing method and printing ink are not particularly limited, and are appropriately selected from known printing methods and printing inks taking into consideration printability on the film, design such as color tone, adhesion, and safety as a food container. Examples of printing methods that can be used include gravure printing, offset printing, gravure-offset printing, flexographic printing, and inkjet printing. From the viewpoints of productivity and high-resolution images, gravure printing may be used.

[0034] To improve the adhesion of the printed layer 12, the surface of the PET film 11 on the side of the printed layer 12 may be subjected to various pretreatments such as corona treatment, plasma treatment, and flame treatment, or a coating layer such as an easy-adhesion layer may be provided.

[0035] [Sealant layer details] When the pressure in the storage section 20 reaches or exceeds a predetermined value, the side edge seal section 24 peels away from the inner edge at the vapor release section 28, connecting the storage section 20 to the outside of the packaging bag 2 (packaging body 1). For vapor to escape properly, the side edge seal section 24 needs to peel away appropriately in response to the pressure in the storage section 20. In other words, the structure of the sealant layer 16, which seals the side edge seal section 24, affects the ability of vapor to escape properly (vapor permeability). The structure of the sealant layer 16 that particularly affects vapor permeability is the sea-island structure present inside the sealant layer 16. The sea-island structure is a two-phase structure in which a main first phase (resin phase) exists continuously like a sea, and a second phase (rubber phase) exists discontinuously like islands within the first phase.

[0036] The sea-island structure of the sealant layer 16 can be evaluated by observing a cross section of the sealant layer 16 with a scanning probe microscope. Scanning probe microscopes include atomic force microscopes. In a scanning probe microscope, a cantilever, which acts as a measuring probe, is vibrated at a resonant frequency while scanning the sample surface to measure the surface shape. Of the images obtained, phase images are digitized by image analysis. A cross section parallel to the machine direction (MD) of the sealant layer 16 is the subject of evaluation.

[0037] In order to accurately observe the sea-island structure, feature analysis is performed on an image of the cross section of the sealant layer 16 observed with a scanning probe microscope. The feature analysis includes, in order, a Fourier transform process, an approximation process, and a normalization process.

[0038] Fourier transform processing considers an image signal as a superposition of sine waves with different frequencies and analyzes the dominant frequency components in the image. Analyzing the dominant sine waves in an image allows us to obtain the shape, size, and distribution of the dominant structures in the image. The Fourier transform processing utilizes the Fast Fourier Transform (FFT) algorithm. Because images are two-dimensional data, a one-dimensional FFT is performed horizontally, followed by a one-dimensional FFT vertically. This results in a spatial frequency spectrum. The power spectrum is obtained by taking the root mean square of the spatial frequency spectrum. Pre-installed software can be used for Fourier transform processing. For example, the FFT provided by the image analysis software ImageJ (https: / / imagej.nih.gov / ij / ) can be used. The power spectrum can be obtained by using ImageJ's FFT.

[0039] The approximation process is a process of approximating the intensity distribution of the power spectrum with a function. The approximation process approximates the intensity distribution of the power spectrum in a predetermined region with a function. One example of the function is a Gaussian function. The Gaussian function is expressed by the following formula:

number

[0040] Normalization is a process of scaling data from a minimum value of 0 to a maximum value of 1. For example, this can be achieved by dividing the data by the maximum value. The normalization may be performed using software prepared in advance.

[0041] The Gaussian function approximation curve obtained by feature analysis reflects the characteristics of the island portions. In the power spectrum intensity distribution, the position corresponding to the center of the image is a low-frequency component, and the further away from the center of the image, the higher the frequency component becomes. If the intensity at the position corresponding to the center of the image is stronger than at other positions, this means that there tends to be more large island portions. If the intensity at the position corresponding to the center of the image is weaker than at other positions, or if there is no change in intensity regardless of image position, this means that there tends to be more small island portions. This is presumably a reflection of the characteristics of the island portions that stand out when viewed from a distance.

[0042] In the case of an image with a horizontal dimension of 1024 px and a vertical dimension of 512 px at a resolution where 10 μm in length is expressed as 512 px, the standard deviation of the Gaussian function approximation curve obtained by feature analysis is 600 or less. The standard deviation of the Gaussian function may be 550 or less, or may be 500 or less. In these cases, steam properly passes through the steam vent portion 28. If the standard deviation of the Gaussian function exceeds 600 (or exceeds 500, or exceeds 550), steam does not properly pass through the steam vent portion 28. Although the cause of this is not certain, it is believed that peeling of the side edge seal portion 24 occurs by propagating between islands in the sea-island structure. If there is a tendency for there to be many small islands, the propagation paths become excessive, and proper peeling does not occur. In the case of the Gaussian function approximation curve obtained by feature analysis, the standard deviation of the Gaussian function may be 100 or more. If the standard deviation of the Gaussian function is less than 100, steam may not properly pass through the steam release portion 28. This is because the sealant layer 16 softens, making it difficult to maintain the designed strength. Also, if the area of ​​the island portion is large, there is no propagation path, which is presumably why proper peeling does not occur. Note that if the image size is doubled in both length and width, the standard deviation also doubles.

[0043] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. A predetermined intermediate layer may be provided between each layer of the laminate 10 to improve the functionality of the laminate 10. The configuration of the intermediate layer can be appropriately referenced from the description of the configuration of the sealant layer 16 described above. Providing an intermediate layer in the laminate 10 can further reduce deformation of the laminate during the production of packaging bags. Multiple intermediate layers may be used depending on the application of the laminate 10.

[0044] The laminate 10 may include a vapor-deposited layer that has been previously deposited on any of the layers that make up the laminate. Vapor deposition materials used for the vapor-deposited layer include metals such as Si, Al, Sn, In, Zn, Fe, and Mn, and inorganic compounds containing one or more of these metals. Examples of such inorganic compounds include silicon oxides (SiO ), such as silicon monoxide and silicon dioxide. x ), aluminum oxide, magnesium oxide, tin oxide, indium oxide, etc. In addition to these inorganic compounds, the inorganic oxide may contain at least one metal selected from the group consisting of Si, Al, Sn, In, Zn, Fe, and Mn, or an oxide thereof.

[0045] The laminate 10 may include, for example, an anchor coat layer adjacent to at least one selected from the printed layers 12. By including the anchor coat layer, the adhesion of the printed layer 12 can be increased, further improving the puncture strength of the laminate 10. The anchor coat layer can be formed by applying an anchor coat agent onto a predetermined layer and drying it. Examples of anchor coat agents include polyester-based polyurethane resins and polyether-based polyurethane resins. The thickness of the anchor coat layer is not particularly limited and may be 0.1 to 1.0 μm or 0.3 to 0.5 μm.

[0046] The PET film 11 and the nylon 6 film 14 may be bonded directly to each other without the first adhesive layer 13. Also, the nylon 6 film 14 and the sealant layer 16 may be bonded directly to each other without the second adhesive layer 15. [Example]

[0047] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0048] [Packaging preparation] A commercially available polyethylene terephthalate (PET) film with a thickness of 12 μm, a commercially available nylon 6 film with a thickness of 15 μm, and a commercially available unoriented polypropylene (CPP) film with a thickness of 60 μm were prepared. The CPP film functions as a sealant layer. CPP film A, CPP film B, and CPP film C, each with a different sea-island structure, were prepared.

[0049] A laminate was prepared by bonding a PET film, a nylon 6 film, and a CPP film A with an aliphatic ester adhesive. Two square laminates measuring 130 mm x 130 mm were cut from the prepared laminate, with two sides parallel to the MD of the CPP film A. The two cut-out laminates were overlapped with the CPP film A facing inward while aligning the MD of the CPP film A. One of the four sides of the square perpendicular to the MD of the CPP film A was heat-sealed to form a steam release hole. Two heat-sealing conditions were set. The first heat-sealing condition was a pressure of 0.2 MPa, a treatment time of 1.5 seconds, and a treatment temperature of 190 to 220°C. The second heat-sealing condition was a pressure of 0.1 to 0.3 MPa, a treatment time of 1.5 seconds, and a treatment temperature of 200°C.

[0050] Next, two of the remaining three sides of the square were heat-sealed, and 50 ml of water was filled into the remaining side and heat-sealed to form a filled product. The filled product was then subjected to a spray retort treatment. The conditions for the spray retort treatment were a treatment temperature of 121°C and a treatment time of 30 minutes. The filled product that had undergone the spray retort treatment was allowed to cool for 12 hours or more to form a package. As a result, six packaged products were prepared as samples: a packaged product made with CPP film A under the first heat-sealing conditions, a packaged product made with CPP film A under the second heat-sealing conditions, a packaged product made with CPP film B under the first heat-sealing conditions, a packaged product made with CPP film B under the second heat-sealing conditions, a packaged product made with CPP film C under the first heat-sealing conditions, and a packaged product made with CPP film C under the second heat-sealing conditions.

[0051] [Observation of sea-island structure] A cross section of the sealant layer 16 in the unsealed portion of the sample was prepared to observe the sea-island structure. The cross section of the sealant layer 16 was prepared as follows: First, the front and back surfaces of the sample were corona-treated, and then the sample was cut into 2 mm x 3 mm strips. The resulting strips were then embedded in a photocurable resin (Aronix LCR D-800, a visible light-curable resin manufactured by Toa Gosei Co., Ltd.) and cured by light irradiation to obtain a block consisting of the sample and the cured resin in which it was embedded. The resulting block was then fixed in an insert for an SPM sample holder (an insert for an AFM sample holder manufactured by Leica Microsystems). At room temperature (25°C), the block was trimmed with a glass knife and the sample cross section (perpendicular to the layer interface and parallel to the MD) was cut with a diamond knife until the cross section was mirror-finished under cooling at -40°C. The cross-section cutting device used was a Leica Microsystems ultramicrotome EMUC7 in combination with a cooling option EM FC7. The cutting speed was set to 1 mm / s, and the cutting film thickness was set to 200 nm. The cutting direction was parallel to the MD of the sealant layer 16.

[0052] The cross section of the sealant layer 16 is observed using the following method. After cutting the cross section, the block piece is fixed in place using an SPM sample holder insert. A phase image is measured at the center of the sample thickness using a scanning probe microscope (SPM). The measurement conditions are: the MD of the sample is the X direction, the thickness direction of the sample is the Y direction, the field of view is 20 μm in the X direction, 10 μm in the Y direction, and the resolution is 1024 in the X direction and 512 in the Y direction. The scanning speed is 0.5 Hz, the X direction is the FastScan scanning direction, and the shape is measured using the SPM's AC mode (tapping mode) to acquire phase, height, and amplitude images. The SPM used is a JupiterXR (trade name) manufactured by Oxford Instruments. The SPM's cantilever (measurement probe) is an AC160TS (trade name) manufactured by Olympus, with typical characteristics of a tip curvature radius of 7 nm and a spring constant of 26 N / m. Also, adjust the Setpoint, Drive Amplitude, and Integral Gain so that the sea-island structure can be clearly observed in the phase image. Specifically, in the phase image, the phase during measurement should be smaller than the phase before the cantilever and sample contact (engagement), in the height image, the trace and retrace signals should be the same, and in the amplitude image, the trace and retrace signals should be inverted.

[0053] The above measurements were performed at three locations for each sample. Because the phase value may gradually fluctuate due to changes in the state of the cantilever tip during measurement, the influence of fluctuations was reduced by performing a plane fit process on the phase image after measurement using JupiterXR analysis software. The obtained phase image was then quantified using JupiterXR analysis software.

[0054] The phase image digitized by Jupiter XR was opened in Image J, and a power spectrum was obtained using Image J's pre-defined FFT algorithm. Figure 5(A) is an example of an image opened in Image J. Figure 5(B) is an example of a power spectrum. A region AR was specified from the obtained power spectrum to check the intensity distribution. Figure 5(C) is a diagram explaining the region to check the intensity distribution. Region AR was set to the center of the image (X: 512, Y: 312-712). This was because a strong intensity distribution in the vertical direction was confirmed in the power spectrum. The intensity distribution of region AR was extracted. The results are shown in Figure 6(A) to (C).

[0055] Figure 6(A) shows the intensity distribution of the sample using CPP film A. Figure 6(B) shows the intensity distribution of the sample using CPP film B. Figure 6(C) shows the intensity distribution of the sample using CPP film B. The intensity distribution shown in Figure 6(C) is a superimposition of the intensity distributions obtained from three images measured at three locations.

[0056] Next, an approximation process using a Gaussian function was performed using Excel's Solver. The results are shown in Figure 7(A) to (C). Figure 7(A) is a graph obtained by approximating the data shown in Figure 6(A) with a Gaussian function. Figure 7(B) is a graph obtained by approximating the data shown in Figure 6(B) with a Gaussian function. Figure 7(C) is a graph obtained by approximating the data shown in Figure 6(C) with a Gaussian function. As shown in Figure 7(A) to (C), by approximating with a Gaussian function, the three overlapping graphs for each sample became distinguishable.

[0057] Next, normalization processing was performed. Figure 8(A) is a graph obtained by normalizing the graph shown in Figure 7(A). Figure 8(B) is a graph obtained by normalizing the graph shown in Figure 7(B). Figure 8(C) is a graph obtained by normalizing the graph shown in Figure 7(C). Normalization makes the characteristics of each sample clear and enables evaluation using standard deviation.

[0058] Here, samples with a standard deviation of the Gaussian function of 600 or less were designated Examples, and samples with a standard deviation of more than 600 were designated Comparative Examples. FIG. 9 is a graph plotting the standard deviation of the Gaussian function for each sample. As shown in FIG. 9, the sample in which CPP film A was used as the sealant layer 16 and subjected to heat sealing and spray retort treatment had an average standard deviation of 741 at three measured locations, exceeding 600, and was designated Comparative Example A. The sample in which CPP film B was used as the sealant layer 16 and subjected to heat sealing and spray retort treatment had an average standard deviation of 499 at three measured locations, less than 600, and was designated Example B. The sample in which CPP film C was used as the sealant layer 16 and subjected to heat sealing and spray retort treatment had an average standard deviation of 448 at three measured locations, less than 600, and was designated Example C.

[0059] [Confirmation of vapor permeability] The samples according to the examples and comparative examples were cooked in a microwave oven to check their steam permeability. Specifically, they were cooked at 600 W for two minutes to check whether they could be steamed. The results are shown in Table 1. [Table 1] The samples produced under the first heat sealing conditions are Examples B, C, and Comparative Example A, and the samples produced under the second heat sealing conditions are Examples B1, C1, and A1. In Examples B, B1, C, and C1, where the standard deviation of the Gaussian function obtained by analyzing an image of a cross section parallel to the MD of the sealant layer 16 is 600 or less, vapor permeability was confirmed, while in Comparative Example A, where the standard deviation was over 600, vapor permeability was not confirmed. Thus, it was demonstrated that a package having vapor permeability can be defined using a new parameter related to the sea-island structure. [Explanation of symbols]

[0060] 1...packaging body, 10, 10a, 10b, 10c...laminate body, 11...polyethylene terephthalate film, 16...sealant layer.

Claims

1. A package for microwave cooking made of a laminate including a polyethylene terephthalate film and a sealant layer, a package, wherein the sealant layer has an internal sea-island structure, and wherein an image of a cross section of the sealant layer parallel to the machine direction is observed with a scanning probe microscope, the image being 1024 px horizontal and 512 px vertical, at a resolution where 10 μm in length is expressed as 512 px, and the image is Fourier transformed to obtain an intensity distribution, and the image is approximated and normalized with a Gaussian function, and the standard deviation of the Gaussian function obtained is 600 or less.

2. A laminate constituting the packaging body according to claim 1.

Images