JP7751972B2 - Laminate and container - Google Patents

Description

The present invention relates to a laminate and a container.

Laminates have traditionally been used in containers for pharmaceuticals, medical supplies, cosmetics, food, beverages, industrial materials, electronic components, and more. Polyolefin resins are often used in such laminates as they offer excellent impact resistance. For containers for food and beverages in particular, laminates that are less susceptible to the effects of heat treatment during the heat sterilization process are ideally suited. For example, Patent Document 1 describes a technology in which a sheet consisting of a base layer and a sealing layer uses a propylene-derived polymer component in the sealing layer, resulting in excellent blocking resistance, heat seal strength, and impact resistance, while also reducing appearance defects caused by heat treatment.

JP 2013-71409 A

However, the laminate described in Patent Document 1 above has poor interlayer peelability and poor edge cutting properties after peeling, and therefore cannot be used for, for example, containers that utilize interlayer peeling to make them easier to open. Furthermore, there is no mention of peelability when containers are stacked on top of each other after molding.

The present invention therefore aims to provide a laminate and a container that can be easily opened by peeling the layers of the container after molding, and that can easily separate stacked containers after molding.

[1] A laminate comprising at least a surface layer formed of a first resin composition containing polypropylene and polyethylene, and an undersurface layer adjacent to the surface layer and formed of a second resin composition containing polypropylene and polyethylene, wherein the arithmetic mean roughness Ra of the surface of the surface layer opposite the undersurface layer is 0.5 μm or more.
[2] The laminate described in [1], wherein the first resin composition contains 80% by mass or more and 99% by mass or less of polypropylene and 1% by mass or more and 20% by mass or less of polyethylene.
[3] The laminate according to [1] or [2], wherein the melting point of the polyethylene contained in the first resin composition is 115°C or higher and 140°C or lower.
[4] The laminate according to any one of [1] to [3], wherein the density of the polyethylene contained in the first resin composition is 930 kg/ ^m3 or more.
[5] The laminate according to any one of [1] to [4], wherein the polypropylene contained in the first resin composition is a homopolypropylene.
[6] The laminate according to any one of [1] to [5], wherein the first resin composition further contains a nucleating agent.
[7] The laminate according to any one of [1] to [6], wherein the thickness of the surface layer is 5 μm or more and 40 μm or less.
[8] The laminate according to any one of [1] to [7], wherein the second resin composition contains 15% by mass or more and 58% by mass or less of polypropylene.
[9] The laminate according to any one of [1] to [8], wherein the second resin composition contains at least two types of polyethylene having different melting points.
[10] The laminate according to any one of [1] to [9], wherein the second resin composition contains at least two types of polyethylene having different densities.
[11] The laminate according to any one of [1] to [10], wherein the density of the second resin composition is 900 kg/m ³ or more and 970 kg/m ³ or less.
[12] The laminate according to any one of [1] to [11], further comprising first and second base material layers laminated on the opposite side of the surface layer with respect to the subsurface layer, and an oxygen barrier layer laminated between the first and second base material layers.
[13] The laminate according to [12], wherein the oxygen barrier layer contains an ethylene vinyl alcohol resin.
[14] The laminate according to any one of [1] to [13], having a thickness of 0.2 mm or more and 1.5 mm or less.
[15] A container formed by molding the laminate according to any one of [1] to [14] so that the surface layer faces inward.
[16] The laminate according to any one of [1] to [14], wherein the second resin composition contains an elastomer.
[17] The laminate according to [16], wherein the content of the elastomer in the second resin composition is 0.5% by mass or more and 16% by mass or less.
[18] The laminate according to [16] or [17], wherein the melt flow rate of the elastomer contained in the second resin composition is 0.5 g/10 min or more and 5 g/10 min or less.
[19] The laminate according to any one of [16] to [18], wherein the elastomer contained in the second resin composition includes an ethylene-α-olefin copolymer.
[20] A container formed by molding the laminate according to any one of [16] to [19] so that the surface layer faces inward.

In this configuration, the resin composition forming the surface layer contains polypropylene, and the resin composition forming the undersurface layer contains polypropylene and polyethylene, which makes it easy for the surface layer and undersurface layer to peel apart, and the surface layer to easily break at the edge of the bonded area. Furthermore, the arithmetic mean roughness Ra of the surface of the surface layer opposite the undersurface layer is 0.5 μm or more, making it easy to peel stacked containers apart after molding.

1 is a schematic cross-sectional view showing the structure of a laminate according to a first embodiment of the present invention. 2 is a cross-sectional view showing an example of a container formed from the laminate shown in FIG. 1. FIG.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components that have substantially the same functional configuration will be assigned the same reference numerals, and redundant explanations will be omitted.

In this specification, the main component of the resin composition forming each layer of the laminate refers to the resin component with the highest content among the resin compositions forming that layer. Therefore, the resin composition may contain other components in addition to the main component. The main component can be identified, for example, by IR spectroscopy. In this specification, the content of the components of the resin composition forming each layer of the laminate is expressed as mass % relative to the total resin composition forming that layer, unless otherwise specified.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the structure of a laminate according to a first embodiment of the present invention. As shown in FIG. 1, the laminate 10 includes a surface layer 11, subsurface layers 12 and 15, and base layers 13 and 14. The configuration of each layer will be described below. The laminate 10 is formed to a thickness suitable for forming a container as described below, specifically, for example, a thickness of 0.01 mm or more and 1.8 mm or less, preferably 0.1 mm or more and 1.6 mm or less, more preferably 0.2 mm or more and 1.5 mm or less, even more preferably 0.25 mm or more and 1.4 mm or less, and particularly preferably 0.3 mm or more and 1.2 mm or less, but is not limited to this example.

The surface layer 11 is a layer that is bonded to the lid by heat sealing or the like when the laminate 10 is molded into a container, as described below. Specifically, the surface layer 11 is formed from a resin composition primarily composed of polypropylene. The resin composition that forms the surface layer 11 (hereinafter also referred to as the "first resin composition") preferably contains homopolypropylene (HPP) from the perspective of improving the appearance after heating. However, other than HPP, it may also contain polypropylene such as random polypropylene (RPP) or block polypropylene (BPP), polyethylene such as high-density polyethylene (HDPE) or medium-density polyethylene (MDPE), or linear ethylene-α-olefin copolymer. The first resin composition may also contain a nucleating agent. Specific examples of nucleating agents include organic carboxylic acids or metal salts thereof, aromatic sulfonates or metal salts thereof, organic phosphate compounds or metal salts thereof, dibenzylidene sorbitol or derivatives thereof, partial metal salts of rosin acid, inorganic fine particles, imides, amides, quinacridones, quinones, or mixtures thereof.

Examples of metal salts of organic carboxylic acids include aluminum benzoate, aluminum pt-butylbenzoate, sodium adipate, sodium thiophenecarboxylate, and sodium pyrrolecarboxylate.
Examples of dibenzylidene sorbitol or derivatives thereof include dibenzylidene sorbitol, 1,3:2,4-bis(o-3,4-dimethylbenzylidene)sorbitol, 1,3:2,4-bis(o-2,4-dimethylbenzylidene)sorbitol, 1,3:2,4-bis(o-4-ethylbenzylidene)sorbitol, 1,3:2,4-bis(o-4-chlorobenzylidene)sorbitol, 1,3:2,4-dibenzylidene sorbitol, etc. Specific examples include "Gelall MD" and "Gelall MD-R" (trade names) manufactured by New Japan Chemical Co., Ltd.
Examples of rosin acid partial metal salts include "Pine Crystal KM1600,""Pine Crystal KM1500," and "Pine Crystal KM1300" (trade names) manufactured by Arakawa Chemical Industries, Ltd.

Examples of inorganic fine particles include talc, clay, mica, asbestos, glass fiber, glass flakes, glass beads, calcium silicate, montmorillonite, bentonite, graphite, aluminum powder, alumina, silica, diatomaceous earth, titanium oxide, magnesium oxide, pumice powder, pumice balloons, aluminum hydroxide, magnesium hydroxide, basic magnesium carbonate, dolomite, calcium sulfate, potassium titanate, barium sulfate, calcium sulfite, and molybdenum sulfide.
Examples of the amide compound include adipic acid dianilide and suberic acid dianilide.
Among the above nucleating agents, it is preferable to use an organic metal phosphate (metal phosphate ester salt) represented by the following general formula, in view of its high effect of increasing the crystallization rate.
Specific examples of organic metal phosphates include "ADK STAB NA-11", "ADK STAB NA-21", "ADK STAB NA-71", "ADK STAB M701" and "ADK STAB M801" (all manufactured by Asahi Denka Co., Ltd.).

The content of the nucleating agent is, for example, 500 ppm or more, preferably 800 ppm or more, more preferably 1250 ppm or more, and particularly preferably 1400 ppm or more. The content of the nucleating agent is preferably 10000 ppm or less, more preferably 5000 ppm or less, and even more preferably 3000 ppm or less. The inclusion of a nucleating agent improves the edge-cutting properties of the surface layer 11, i.e., the ease with which it breaks when opened. As a non-limiting example, if the surface layer 11 breaks when the container is opened, the thickness of the surface layer 11 is preferably 5 μm or more and 40 μm or less, and more preferably 10 μm or more and 30 μm or less.

In addition, in this embodiment, the arithmetic mean roughness Ra of the surface of the surface layer 11 opposite the subsurface layer 12 is 0.5 μm or more. This provides the surface of the molded container with appropriate roughness, improving the peelability when stacking containers. Here, the arithmetic mean roughness Ra is specified in JIS B0601. The arithmetic mean roughness Ra is preferably 0.6 μm or more, more preferably 0.7 μm or more, even more preferably 0.8 μm or more, and particularly preferably 1.0 μm or more. There is no particular upper limit for the arithmetic mean roughness Ra, but it is usually 3.0 μm or less.

To achieve the above-described arithmetic mean roughness Ra, for example, the first resin composition forming the surface layer 11 may contain polyethylene. In this case, the first resin composition may contain 80% by mass or more and 99% by mass or less of polypropylene and 1% by mass or more and 20% by mass or less of polyethylene. The melting point of the polyethylene contained in the first resin composition is, for example, 115°C or higher, preferably 120°C or higher, and more preferably 125°C or higher. The melting point of the polyethylene contained in the first resin composition is, for example, 135°C or lower, preferably 140°C or lower. When multiple types of polyethylene are contained, it is sufficient that any one of the polyethylenes falls within this range. By setting the melting point of the polyethylene contained in the first resin composition within this range, the above-described arithmetic mean roughness Ra can be achieved.

In the present invention, the melting point of polyethylene is measured using a differential scanning calorimeter (DSC) ("Diamond DSC" manufactured by PerkinElmer Japan Co., Ltd.) in the temperature range of 50°C to 220°C at a heating rate of 10°C/min, and the temperature at which the endothermic peak reaches its peak is taken as the melting point.

In order to achieve the above-described arithmetic mean roughness Ra, the density of the polyethylene contained in the first resin composition forming the surface layer 11 is, for example, 900 kg/m ^{or more} , preferably 925 kg/m or ^more , and more preferably 945 kg/m or ^more . The density of the polyethylene contained in the first resin composition forming the surface layer 11 is, for example, 990 kg/m or ^less , preferably 970 kg/m ^or less, and more preferably 966 kg/m or ^less .

The undersurface layer 12 is adjacent to the surface layer 11 and is formed from a resin composition containing polypropylene and polyethylene. When the main component of the surface layer 11 is polypropylene, the undersurface layer 12 contains polypropylene and polyethylene, which makes it easier to peel the surface layer 11 from the undersurface layer 12. For example, the resin composition forming the undersurface layer 12 (hereinafter also referred to as the second resin composition) may contain 15% by mass or more and 58% by mass or less of polypropylene.

The second resin composition may contain at least two types of polyethylene having different melting points. The melting point of the first type of polyethylene contained in the second resin composition is, for example, 115°C or higher, preferably 120°C or higher, and more preferably 125°C or higher. The melting point of the polyethylene contained in the first type of second resin composition is, for example, 140°C or lower, and preferably 135°C or lower. The melting point of the second type of polyethylene contained in the second resin composition is, for example, 80°C or higher, preferably 90°C or higher, and more preferably 100°C or higher. The melting point of the polyethylene contained in the second type of second resin composition is, for example, 130°C or lower, preferably 120°C or lower, and more preferably 115°C or lower. By setting the polypropylene content and the type and melting point of the polyethylene, appropriate interlayer bonding strength can be obtained between the surface layer 11 and the undersurface layer 12, facilitating peeling of the surface layer 11 while improving the edge cutting properties of the surface layer 11. The undersurface layer 15 is located on the opposite side of the substrate layers 13 and 14 from the surface layer 11 and the undersurface layer 12, and is formed from the same resin composition as the undersurface layer 12.

The density of the second resin composition is, for example, 850 kg/m ^{or more} , preferably 880 kg/m or ^more , more preferably 900 kg/m or ^more , and even more preferably 915 kg/m or ^more . The density of the second resin composition is, for example, 970 kg/m ^or less, preferably 950 kg/m ^or less, and more preferably 932 kg/m ^{or less} . The density can be measured, for example, by an underwater displacement method.

Furthermore, the second resin composition may contain at least two types of polyethylene having different densities. The density of the first type of polyethylene contained in the second resin composition is, for example, 900 kg/m ³ or more, preferably 925 kg/m ³ or more, and more preferably 945 kg/m ³ or more. The density of the first type of polyethylene contained in the second resin composition is, for example, 990 kg/m ³ or less, preferably 970 kg/m ³ or less, and more preferably 966 kg/m ³ or less. The density of the second type of polyethylene contained in the second resin composition is, for example, 880 kg/m ³ or more, preferably 903 kg/m ³ or more, and even more preferably 910 kg/m ³ or more. The density of the second type of polyethylene contained in the second resin composition is, for example, 950 kg/m ³ or less, preferably 945 kg/m ³ or less, and more preferably 930 kg/m ³ or less.

In the above example, the content of the relatively high-density polyethylene contained in the second resin composition is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. It is also preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less. The content of the relatively low-density polyethylene contained in the second resin composition is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more. It is also preferably 45% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less.

By setting the polypropylene content and the polyethylene type density and content in this way, appropriate interlayer bond strength can be obtained between the surface layer 11 and the subsurface layer 12, making it easier to peel the surface layer 11 while improving the edge cutting properties of the surface layer 11.

By setting the melting points and densities of the at least two types of polyethylene contained in the second resin composition within the above ranges, more appropriate interlayer bond strength can be obtained between the surface layer 11 and the subsurface layer 12, making it easier to peel the surface layer 11 while also improving the edge cutting properties of the surface layer 11.

The base layers 13 and 14 are laminated on the subsurface layer 12 on the side opposite the surface layer 11, and are formed of a resin containing at least one of the group consisting of an olefin-based resin, a polystyrene-based resin, and a polyester-based resin. Examples of olefin-based resins include polypropylene and polyethylene. Examples of polyester-based resins include polyethylene terephthalate (PET). An inorganic filler such as talc may be added to the base layers 13 and 14 to improve rigidity. An oxygen barrier layer containing an ethylene-vinyl alcohol resin such as ethylene-vinyl alcohol copolymer (EVOH) may be added between the base layers 13 and 14.

In the laminate 10 described above, the layer configuration other than the surface layer 11 and subsurface layer 12 is optional; for example, additional layers may be included depending on the required rigidity and barrier properties, or any layer may be omitted.

Figure 2 is a cross-sectional view showing an example of a container formed from the laminate shown in Figure 1. The container 100 shown in Figure 2 includes a container body formed from the laminate 10, and a lid 20 joined to the container body. In the example shown, the container body is formed into a shape including a bottom portion 101, a side portion 102, and a flange portion 103, and the lid 20 is joined to the container body at a joining region 105 formed in the flange portion 103, for example by heat sealing. In this example, the container body is formed so that the surface layer 11 of the laminate 10 faces inward. As a result, the surface layer 11 of the laminate 10 forming the container body faces the storage space SP, and the lid 20 and the surface layer 11 of the laminate 10 are joined at the joining region 105.

When the containers 100 described above are stacked after molding, the stacked containers can be easily peeled apart because the surface of the surface layer 11 has been given a moderate degree of roughness as described above. However, if the surface of the surface layer 11 is excessively smooth, the breathability between the containers will be low and the adhesive force will be strong, making it difficult to peel them apart.

As described above, the surface layer 11 of the laminate 10 is primarily composed of polypropylene, and the subsurface layer 12 contains polypropylene and polyethylene, which facilitates peeling between the surface layer 11 and the subsurface layer 12. Taking advantage of this, in the container 100, the interlayer bond strength between the surface layer 11 and the subsurface layer 12 of the laminate 10 constituting the container body can be made weaker than the bond strength between the lid 20 and the surface layer 11 in the bonding region 105 and the interlayer bond strength between the subsurface layer 12 and the base layer 13. As a result, when a user grasps an edge of the lid 20 and peels it off, the surface layer 11 is peeled off along with the lid 20 in the bonding region 105, resulting in interlayer delamination between the surface layer 11 and the subsurface layer 12. When the lid 20 and surface layer 11 are peeled down to the inner edge of the bonding region 105, the surface layer 11 breaks (edge tear), and only the lid 20 is subsequently peeled off from the container body.

Second Embodiment
Next, a second embodiment of the present invention will be described. In this embodiment, the resin composition (second resin composition) forming the undersurface layer 12 in the laminate 10 configured in the same manner as in the first embodiment contains polypropylene, one or more types of polyethylene, and an elastomer. Except for this, the configuration of this embodiment is the same as in the first embodiment, and therefore a detailed description thereof will be omitted.

In the second embodiment, the melting point of the polyethylene contained in the second resin composition is, for example, 115°C or higher, preferably 120°C or higher, and more preferably 125°C or higher. The melting point of the polyethylene contained in the second resin composition is, for example, 140°C or lower, preferably 135°C or lower. The elastomer contained in the second resin composition is not particularly limited, but is preferably an ethylene-α-olefin copolymer. The melt flow rate (MFR) of the elastomer is preferably 0.5 g/10 min or higher and preferably 5.0 g/10 min or lower. The MFR of the elastomer is more preferably 0.8 g/10 min or higher, and even more preferably 1.0 g/10 min or higher. The MFR of the elastomer is more preferably 4 g/10 min or lower, even more preferably 3.5 g/10 min or lower, and particularly preferably 2 g/10 min or lower.

By adjusting the polyethylene and polypropylene contents, the polyethylene melting point, and the inclusion of a predetermined amount of elastomer in the second resin composition forming the undersurface layer 12, appropriate interlayer bond strength can be achieved between the surface layer 11 and the undersurface layer 12, facilitating peeling of the surface layer 11 while improving the edge sharpness of the surface layer 11 and further improving the appearance. The undersurface layer 15 is also formed from the same second resin composition as the undersurface layer 12.

Furthermore, in the second embodiment, the density of the second resin composition is, for example, 850 kg/m or ^more , preferably 880 kg/m or ^more , more preferably 900 kg/m ^{or more} , and even more preferably 915 kg/m ^{or more} . Furthermore, the density of the second resin composition is, for example, 970 kg/m ^{or less} , preferably 950 kg/m ^or less, and more preferably 932 kg/m or ^less . The density can be measured, for example, by an underwater displacement method.

Furthermore, in the second embodiment, the density of the polyethylene contained in the second resin composition is, for example, 900 kg/m or ^more , preferably 925 kg/m or ^more , and more preferably 945 kg/m or ^more . The density of the polyethylene contained in the second resin composition is, for example, 990 kg/m ^{or less} , preferably 970 kg/m ^or less, and more preferably 966 kg/m or ^less .

In the second embodiment, the content of the elastomer in the second resin composition is preferably 16% by mass or less, more preferably 14% by mass or less, even more preferably 10% by mass or less, even more preferably 7% by mass or less, and particularly preferably 5% by mass or less. The lower limit is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more.

Next, examples of the present invention will be described. Table 1 shows the content in mass % of the resin compositions forming the surface layer and undersurface layer in the examples and reference examples. The various parameters of the HPP and HDPE in the surface layer and the HPP, HDPE, and LDPE in the undersurface layer are as follows. The nucleating agent used was ADK STAB M701 (manufactured by ADEKA Corporation, 5 wt% masterbatch (MB)). The elastomer used was TAFUMER DF710 (manufactured by Mitsui Chemicals, Inc.), an ethylene-α-olefin copolymer with an MFR of 1.2 g/10 min. The laminate consisted of the surface layer, undersurface layer, substrate layer, adhesive layer, oxygen barrier layer, adhesive layer, substrate layer, and undersurface layer stacked in this order, and the overall thickness of the laminate was 0.3 mm.

Surface layer: HPP (melt flow rate: 16 g/10 min, density: 900 kg/m ³ , tensile modulus: 1,600 MPa)
HDPE (melt flow rate: 0.35 g/10 min, melting point: 130°C, density: 956 kg/m ³ )
Subsurface layer: HPP (melt flow rate: 0.5 g/10 min, density: 890 kg/m ³ to 920 kg/m ³ , isotactic pentad fraction: 93 mol%)
HDPE (melt flow rate: 0.5 g/10 min, melting point: 133°C, density: 956 kg/m ³ )
LDPE (in Examples 1 to 8 and 12, melt flow rate: 0.35 g/10 min, melting point: 109° C., density: 920 kg/m ³ )

Measurement of arithmetic mean roughness (Ra value) Using "Handysurf E-35B" manufactured by Tokyo Seimitsu Co., Ltd., the arithmetic mean roughness (Ra value) of the surface of the surface layer opposite to the subsurface layer was measured under the following measurement conditions in accordance with JIS B0601-1994.
<Measurement conditions>
Measurement distance: 4 mm
Cutoff: 0.8 mm
・Stylus: Tip diameter 5 μm, tip angle 90° cone, material diamond ・Measuring force: 4 mN or less

The seal strength shown in Table 1 above was measured using an Imada Digital Force Gauge at a tension speed of 300 mm/min and a 15 mm width at which a lid made of a film primarily composed of random polypropylene was bonded to a laminated container body at a sealing time of 1.2 seconds, a sealing pressure of 0.24 MPa, and a sealing temperature of 200°C. Because delamination occurs between the surface layer and subsurface layer of the container body, the measured seal strength indicates the interlayer bond strength between the surface layer and subsurface layer. Edge sharpness and opening feel were qualitatively evaluated using a sensory test. Specifically, for containers with lids bonded as described above, the edge sharpness of the surface layer and opening feel when the lid was peeled off were evaluated on a five-point scale from A (very good) to E (poor). In this evaluation, A to D are acceptable.

In the examples, the surface layer is formed from a resin composition primarily composed of polypropylene, and the subsurface layer is formed from a resin composition containing polypropylene and polyethylene. Specifically, in Examples 1 to 4 and 6, the resin composition of the surface layer contains 90% by mass of polypropylene (HPP), 7% by mass of polyethylene (HDPE), and 3% by mass of a nucleating agent. In Examples 5, 7, and 8, the resin composition of the surface layer contains 95% by mass of polypropylene (HPP), 5% by mass of polyethylene (HDPE), and no nucleating agent. In Examples 9 to 13, the resin composition of the surface layer also contains 95% by mass of polypropylene (HPP), 5% by mass of polyethylene (HDPE), and no nucleating agent.

On the other hand, in Examples 1 to 5, the resin composition of the undersurface layer contains 30% to 45% by mass of polypropylene (HPP) and two types of polyethylene with different densities and melting points, specifically HDPE and LDPE, in the proportions shown in the table. As a result, the density of the undersurface layer in Examples 1 to 5 is 920 kg/m ³ to 930 kg/m ^3. In contrast, in Examples 6 to 8, the undersurface layer is formed of a resin composition containing HPP and HDPE but no LDPE. As a result, the density of the undersurface layer in Examples 6 to 8 is 933 kg/m ³ to 940 kg/m ^3. In Examples 9 to 11 and 13, the undersurface layer is formed of a resin composition containing HPP and HDPE but no LDPE, and an elastomer is further added. The elastomer content of the resin composition forming the undersurface layer is 3% by mass in Examples 9 to 11 and 15% by mass in Example 13. In Example 12, the resin composition of the undersurface layer contains 30 mass % polypropylene (HPP) and two types of polyethylene with different densities and melting points, specifically HDPE and LDPE, in proportions different from those in Example 1. Comparative Example 1 is an example in which the surface layer is formed from 100% HPP, and the undersurface layer is formed from a resin composition containing HPP and HDPE but no LDPE.

First, the Ra value of the surface layer was 1.2 μm in all of Examples 1 to 8, satisfying the condition of Ra≧0.5 μm, which is the range exemplified above. In the above examples, the surface layer was primarily composed of HPP, which not only improved the appearance after heating but also improved the peelability when molded containers were stacked on top of each other. Examples 9 to 13 had Ra values of 0.8 μm or 0.9 μm, which also satisfied the condition of Ra≧0.5 μm. Comparative Example 1, in which the surface layer was formed from 100% HPP, had an Ra value of 0.4 μm, which did not satisfy the condition of Ra≧0.5 μm, which is the range exemplified above.

Next, with regard to the seal strength between the surface layer and the subsurface layer and the edge-cutting performance, Examples 1 to 5 each had a seal strength of 1.5 kgf or less, showing very good values. Examples 6 to 8 had a seal strength of 4.0 kgf or less, showing good values, and edge-cutting performance was graded A to C, indicating good openability. Examples 9 to 12 also had a seal strength of 1.5 kgf or less and edge-cutting performance was graded A or B, indicating good openability. Example 13 had a relatively high seal strength of 5.0 kgf, but edge-cutting performance was graded A, indicating good openability. On the other hand, Comparative Example 1 had a seal strength of over 6.0 kgf and edge-cutting performance was graded D, indicating relatively poor openability, although within the acceptable range. Examples 9 to 12 had a grade of A or B, indicating the best results for openability. Examples 1 to 8 and 13 had an openability rating of C or D, which was an improvement over Comparative Example 1's openability rating of E, and was also within the acceptable range.

The above describes in detail preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to these examples. It is clear that a person skilled in the art of the technology to which the present invention pertains could conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

10...Laminate, 11...Surface layer, 12...Subsurface layer, 13...Base layer, 14...Base layer, 15...Subsurface layer, 20...Lid, 100...Container, 101...Bottom portion, 102...Side portion, 103...Flange portion, SP...Storage space.

Claims (15)

a surface layer formed of a first resin composition containing 80% by mass or more and 99% by mass or less of polypropylene and 1% by mass or more and 20% by mass or less of polyethylene;
an undersurface layer adjacent to the surface layer and formed of a second resin composition containing 15% by mass or more and 58% by mass or less of polypropylene , 42% by mass or more and 85 % by mass or less of polyethylene, and 0% by mass or more and 16% by mass or less of elastomer;
an arithmetic mean roughness Ra of the surface of the surface layer opposite to the subsurface layer is 0.5 μm or more and 3.0 μm or less;
A laminate in which the interlayer bond strength between the surface layer and the subsurface layer at a tensile speed of 300 mm/min per 15 mm width is 0.69 kgf or more and 5.0 kgf or less . The laminate described in claim 1, wherein the melting point of the polyethylene contained in the first resin composition is 115°C or higher and 140°C or lower. The laminate according to claim 1 or 2, wherein the polyethylene contained in the first resin composition has a density of 930 kg/m ³ or more. The laminate described in any one of claims 1 to 3, wherein the polypropylene contained in the first resin composition is homopolypropylene. The laminate described in any one of claims 1 to 4, wherein the first resin composition further contains a nucleating agent. A laminate according to any one of claims 1 to 5, wherein the thickness of the surface layer is 5 μm or more and 40 μm or less. The laminate described in any one of claims 1 to 6, wherein the second resin composition contains at least two types of polyethylene having different melting points. The laminate described in any one of claims 1 to 7, wherein the second resin composition contains at least two types of polyethylene having different densities. The laminate according to claim 1 , wherein the density of the second resin composition is 900 kg/m ³ or more and 970 kg/m ³ or less. The laminate described in any one of claims 1 to 9, further comprising first and second substrate layers laminated on the side of the subsurface layer opposite the surface layer, and an oxygen barrier layer laminated between the first and second substrate layers. The laminate described in claim 10, wherein the oxygen barrier layer contains an ethylene vinyl alcohol resin. The laminate described in any one of claims 1 to 11, wherein the thickness of the laminate is 0.2 mm or more and 1.5 mm or less. The laminate according to claim 1 , wherein the elastomer contained in the second resin composition has a melt flow rate of 0.5 g/10 min or more and 5 g/10 min or less. 14. The laminate according to claim 1 , wherein the elastomer contained in the second resin composition includes an ethylene-α-olefin copolymer. A container formed by molding the laminate according to any one of claims 1 to 14 so that the surface layer faces inward.