Laminated sheet and container

Abstract

To provide: a laminate sheet making it possible to facilitate opening and closing of the container by delamination while reducing influence of heat treatment; and a container.SOLUTION: A laminate sheet 10 includes at least a surface layer 11 formed by a resin composition whose main component is homopolypropylene and whose tensile elasticity is 1500 MPa or more, and a subsurface layer 12 which is adjacent to the surface layer 11 and is formed by a resin composition whose main component is polyethylene.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laminated sheet and a container.

Background Art

[0002] Conventionally, laminated sheets have been used for containers such as pharmaceuticals, medical products, cosmetics, foods, beverages, industrial members, and electronic components. In such laminated sheets, polyolefin resins are often used as materials having excellent impact resistance. Particularly for containers such as foods and beverages, laminated sheets that are less affected by heat treatment in the heat sterilization process are preferably used. For example, in Patent Document 1, a technique is described in which, in a sheet composed of a base material layer and a seal layer, a polymer component derived from propylene is used in the seal layer, thereby providing excellent blocking resistance, heat seal strength, and impact resistance, and reducing appearance defects caused by heat treatment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the laminated sheet described in Patent Document 1 has low peelability between layers, it is not used, for example, for containers that are easily opened by utilizing delamination between layers.

[0005] Therefore, an object of the present invention is to provide a laminated sheet and a container that can easily open the container by delamination between layers while reducing the influence of heat treatment.

Means for Solving the Problems

[0006] [1] A laminated sheet comprising at least a surface layer formed of a resin composition mainly composed of homopolypropylene and having a tensile modulus of 1500 MPa or more, and a subsurface layer adjacent to the surface layer and formed of a resin composition mainly composed of polyethylene. [2] The laminated sheet according to [1], wherein the subsurface layer contains 70% by mass or more of high-density polyethylene. [3] The laminated sheet according to [2], wherein the subsurface layer further contains 30% by mass or less of homopolypropylene. [4] The laminated sheet according to any one of [1] to [3], wherein the thickness of the surface layer is 10 μm or more and 30 μm or less. [5] The laminated sheet according to any one of [1] to [4], further comprising first and second base material layers laminated on the side opposite to the surface layer with respect to the subsurface layer, and an oxygen barrier layer laminated between the first and second base material layers. [6] The laminated sheet according to [5], wherein the oxygen barrier layer contains an ethylene vinyl alcohol resin. [7] The laminated sheet according to any one of [1] to [6], having a thickness of 0.3 mm or more and 1.2 mm or less. [8] A container formed by molding the laminated sheet according to any one of [1] to [7] such that the surface layer is on the side of the contents. [9] A laminated sheet comprising at least a surface layer formed of a resin composition mainly composed of homopolypropylene and having a tensile modulus of 1500 MPa or more and a thickness of 10 μm or more and 30 μm or less, and a subsurface layer adjacent to the surface layer and containing more than 55% by mass of high-density polyethylene and less than 45% by mass of homopolypropylene.

[10] The laminated sheet according to any one of [1] to [3] or [9], wherein the thickness of the surface layer is 5 μm or more and 40 μm or less.

[11] The laminated sheet according to [1] to [6], [9] or

[10] , having a thickness of 0.2 mm or more and 1.5 mm or less.

[12] A container formed by molding the laminated sheet according to any one of [9] to

[11] such that the surface layer is on the side of the contents. [Effects of the Invention]

[0007] According to the above configuration, by using homopolypropylene as the main component of the surface layer, deformation and appearance defects during heat treatment can be prevented. In addition, since the main component of the surface layer is polypropylene and the main component of the subsurface layer is polyethylene, and the tensile elastic modulus of the surface layer is 1500 MPa or more, it is easy for the surface layer and the subsurface layer to peel off, and the surface layer is likely to break at the edge of the bonding region. Therefore, it is possible to facilitate the opening of the container due to delamination.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0010] In this specification, the main component of the resin composition forming each layer of the laminated sheet means the resin component having the highest content rate in the resin composition forming that layer. Therefore, the resin composition may contain other components in addition to the main component. The main component can be confirmed, for example, by the IR method. In this specification, the content rate of the components of the resin composition forming each layer of the laminated sheet is expressed as mass% with respect to the entire resin composition forming that layer unless otherwise specified. Also, in this specification, the tensile elastic modulus is measured according to JIS K7161 "Plastics - Test Method for Tensile Properties" for a single-layer film formed from the resin composition forming each layer of the laminated sheet. However, it is also possible to convert the tensile elastic modulus measured by other test methods into the measured value by JIS K7161.

[0011] Figure 1 is a schematic cross-sectional view showing the structure of a laminated sheet according to an embodiment of the present invention. As shown in Figure 1, the laminated sheet 10 has a surface layer 11, subsurface layers 12, 15, and base material layers 13, 14. Hereinafter, the configuration of each layer will be described. Note that the laminated sheet 10 is formed with a thickness suitable for forming a container as described later, specifically, for example, a thickness of 0.2 mm or more and 1.5 mm or less, preferably a thickness of 0.3 mm or more and 1.2 mm or less, but is not limited to this example.

[0012] The surface layer 11 is a layer that is joined to the lid by heat sealing or the like when the laminated sheet 10 is formed into a container described later. Specifically, the surface layer 11 is formed of a resin composition mainly composed of homopolypropylene (HPP) and having a tensile elastic modulus of 1500 MPa or more. The resin composition forming the surface layer 11 may contain, in addition to the main component HPP, polypropylene-based resins such as random polypropylene (RPP) or block polypropylene, polyethylene-based resins such as high-density polyethylene (HDPE) or low-density polyethylene (LDPE), or linear ethylene-α-olefin copolymers. As a non-limiting example, when the surface layer 11 is broken 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.

[0013] Here, in this specification, HDPE means polyethylene having a density of 920 kg / m 3 or more and 990 kg / m 3 or less. The density of HDPE is preferably 935 kg / m 3 or more, and more preferably 945 kg / m 3 or more. Also, the density of HDPE is preferably 966 kg / m 3 or less, and more preferably 960 kg / m 3 or less.

[0014] The underlying surface layer 12 is formed of a resin composition mainly composed of polyethylene. Since the main component of the surface layer 11 is HPP, by using polyethylene as the main component of the underlying surface layer 12, it is possible to easily peel between the surface layer 11 and the underlying surface layer 12. Specifically, for example, the underlying surface layer 12 is formed of a resin composition mainly composed of HDPE. In this case, as shown in the examples described later, the content of HDPE is preferably more than 55% by mass, more preferably 58% by mass or more, still more preferably 65% by mass or more, and particularly preferably 70% by mass or more. The content of HDPE may be 100% by mass. Also, in this case, the underlying surface layer 12 may further contain HPP. The content of HPP is preferably less than the remainder of HDPE, that is, less than 45% by mass, more preferably 42% by mass or less, still more preferably 35% by mass or less, and particularly preferably 30% by mass or less. Since the content of HDPE may be 100% by mass as described above, the content of HPP may be 0%. The underlying surface layer 15 is located on the opposite side of the surface layer 11 and the underlying surface layer 12 with the base layers 13 and 14 interposed therebetween, and is formed of the same resin composition as the underlying surface layer 12.

[0015] In the above example, the underlying surface layer 12 preferably contains two or more types of HDPE having different melt flow rates (MFR). For example, even when the average MFR of HDPE is the same, the peelability is more improved when containing two or more types of HDPE than when containing one type of HDPE. The peel strength is preferably 2.0 kgf or less, more preferably 1.5 kgf or less, still more preferably 1.0 kgf or less, and particularly preferably 0.8 kgf or less. Also, the peel strength is preferably 0.1 kgf or more, more preferably 0.3 kgf or more, and still more preferably 0.4 kgf or more. Note that if the peel strength is less than 0.1 kgf, the possibility of unintentional opening increases, which is not preferable.

[0016] For example, when the surface lower layer 12 contains the first and second types of HDPE, the MFR of the first type of HDPE is, for example, 5 g / 10 min or more, preferably 8 g / 10 min or more, more preferably 10 g / 10 min or more. Also, the MFR of the first type of HDPE is, for example, 20 g / 10 min or less, preferably 18 g / 10 min or less, more preferably 15 g / 10 min or less. The MFR of the second type of HDPE is, for example, 0.1 g / 10 min or more, preferably 0.2 g / 10 min or more, more preferably 0.3 g / 10 min or more. Also, the MFR of the second type of HDPE is, for example, 5 g / 10 min or less, preferably 3 g / 10 min or less, more preferably 2 g / 10 min or less. The content of the first type of HDPE is, for example, 1% or more, preferably 3% or more, more preferably 5% or more. Also, the content of the first type of HDPE is, for example, 50% or less, preferably 30% or less, more preferably 15% or less. The content of the second type of HDPE is, for example, 50% or more, preferably 70% or more, more preferably 85% or more. Also, the content of the second type of HDPE is, for example, 99% or less, preferably 97% or less, more preferably 95% or less.

[0017] The base material layers 13, 14 are formed of a resin containing at least any one of the group consisting of, for example, an olefin resin, a polystyrene resin, and a polyester resin. Examples of the olefin resin include polypropylene and polyethylene. Examples of the polyester resin include polyethylene terephthalate (PET). An inorganic filler such as talc may be added to the base material layers 13, 14 in order 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 material layers 13, 14.

[0018] In addition, in the laminated sheet 10 described above, the layer configuration other than the surface layer 11 and the surface lower layer 12 is arbitrary, and for example, additional layers may be included according to the required rigidity and barrier properties, and any layer may be omitted.

[0019] Figure 2 is a cross-sectional view showing an example of a container formed from the laminated sheet shown in Figure 1. The container 100 shown in Figure 2 includes a container body formed by shaping the laminated sheet 10 and a lid body 20 joined to the container body. In the illustrated example, the container body is shaped into a shape including a bottom surface portion 101, a side surface portion 102, and a flange portion 103, and the lid body 20 is joined to the container body by, for example, heat sealing at a joining region 105 formed in the flange portion 103. In this example, the laminated sheet 10 is arranged such that the surface layer 11 faces the lid body 20 and the storage space SP in which the contents are stored. That is, the container body is formed using the laminated sheet 10 such that the surface layer 11 faces the contents side. Therefore, at the joining region 105, the lid body 20 and the surface layer 11 of the laminated sheet 10 are joined.

[0020] When the container 100 as described above is heat-treated for sterilization of the contents or the like, since the surface layer 11 in contact with the high-temperature contents or the internal atmosphere of the storage space SP is formed of a resin composition mainly containing HPP, it is possible to prevent deformation of the container body during heat treatment and appearance defects on the inner surface of the container body after heat treatment.

[0021] Also, as described above, since the main component of the surface layer 11 of the laminated sheet 10 is polypropylene and the main component of the surface lower layer 12 is polyethylene, it is easy to peel between the surface layer 11 and the surface lower layer 12. Utilizing this, in the container 100, the interlayer bonding strength between the surface layer 11 and the surface lower layer 12 of the laminated sheet 10 constituting the container body can be made weaker than the bonding strength between the lid body 20 and the surface layer 11 in the bonding region 105 and the interlayer bonding strength between the surface lower layer 12 and the base material layer 13. As a result, when the user picks up and peels off the end of the lid body 20, in the bonding region 105, the surface layer 11 is peeled off together with the lid body 20, and delamination occurs between the surface layer 11 and the surface lower layer 12. When the lid body 20 and the surface layer 11 are peeled off to the inner edge of the bonding region 105, the surface layer 11 breaks there (edge breakage), and thereafter only the lid body 20 is peeled off from the container body. Since the tensile elastic modulus of the surface layer 11 is 1500 MPa or more, the surface layer 11 is likely to break in the above situation, and the container 100 can be opened with a smaller force.

Example

[0022] Next, examples of the present invention will be described.

[0023] First, the test results using a container formed with a laminated sheet will be described. In the examples and comparative examples described below, a container formed with a laminated sheet adjusted so that the total layer thickness is 300 μm, the thickness of the surface layer is 10 μm to 20 μm, and the thickness of the surface lower layer on the surface layer side is 50 μm was filled with a food rich in oil as the content, and the appearance on the surface layer side of the container after a heat sterilization process (heat treatment) at 120°C for 30 minutes was evaluated. Also, a film was heat-sealed to the surface layer side of the container, the opening strength indicating the peelability of the surface layer at the time of opening was measured, and the breakability (ease of edge breakage) was qualitatively evaluated. The results are shown in Table 1. The peelability was evaluated by the numerical value (kgf) of the opening strength and A (good) to C (bad), and the breakability was evaluated by A (good) to D (bad). If none of them were bad (C or D), it was determined to be suitable for practical use. The tensile elastic modulus was measured in accordance with JIS K7161 by forming a single-layer film of the resin composition forming the surface layer in each example.

[0024] In Examples 1 to 4, the surface layer was formed of a resin composition containing 100% by mass of HPP (in Example 1, product name Y-2000GV (manufactured by Prime Polymer Co., Ltd.), in Example 2, product name MA2 (manufactured by Nippon Polypro Co., Ltd.), in Example 3, product name EA9HD (manufactured by Nippon Polypro Co., Ltd.), in Example 4, product name F-133A (manufactured by Prime Polymer Co., Ltd.)). Each of the above-mentioned HPPs has a tensile elastic modulus of 1500 MPa or more when formed into a single-layer film. On the other hand, in Comparative Examples 1 and 2, the surface layer was formed of a resin composition containing 100% by mass of HPP (in Comparative Example 1, product name F-127D (manufactured by Prime Polymer Co., Ltd.), in Comparative Example 2, product name E-111G (manufactured by Prime Polymer Co., Ltd.)). Each of these HPPs has a tensile elastic modulus of less than 1500 Mpa when formed into a single-layer film. Also, throughout Examples 1 to 4 and Comparative Examples 1 and 2, the subsurface layer was formed of a resin composition containing 70% by mass of HDPE (product name 6203B (manufactured by Prime Polymer Co., Ltd.; density 956 kg / m 3 )) and 30% by mass of HPP (product name Y-2000GV (manufactured by Prime Polymer Co., Ltd.)).

[0025] On the other hand, Comparative Example 3 is a conventional example in which the surface layer does not contain HPP as a main component (HDPE is the main component). Specifically, in Comparative Example 3, the surface layer was formed of a resin composition containing 100% of HDPE (product name HE481 (manufactured by Nippon Polyethylene Co., Ltd.; density 956 kg / m 3 )) and the subsurface layer was formed of a resin composition containing 80% of HPP (product name E-111G (manufactured by Prime Polymer Co., Ltd.)), 10% of LDPE (product name R300 (manufactured by Ube Maruzen Polyethylene Co., Ltd.)), and 10% of HDPE (product name 6203B (manufactured by Prime Polymer Co., Ltd.; MFR 0.35 g / 10 min)).

[0026] In Example 5, the surface layer was formed of a resin composition containing 100% by mass of HPP (trade name MA2, manufactured by Japan Polypropylene Corporation), and the subsurface layer was formed of a resin composition containing a total of 70% by mass of two types of HDPE (specifically, 10% by mass of trade name HE481 (manufactured by Japan Polyethylene Corporation; MFR 13 g / 10 min) and 60% by mass of trade name 6203B (manufactured by Prime Polymer Co., Ltd.; MFR 0.35 g / 10 min)) and 30% by mass of HPP (trade name E-111G, manufactured by Prime Polymer Co., Ltd.).

[0027] In Example 6, the surface layer was formed of a resin composition containing 95% by mass of HPP (trade name MA2, manufactured by Japan Polypropylene Corporation) and 5% by mass of HDPE (trade name 6203B, manufactured by Prime Polymer Co., Ltd.), and the subsurface layer was formed of a resin composition containing a total of 60% by mass of two types of HDPE (specifically, 10% by mass of trade name HE481 (manufactured by Japan Polyethylene Corporation; MFR 13 g / 10 min) and 50% by mass of trade name 6203B (manufactured by Prime Polymer Co., Ltd.; MFR 0.35 g / 10 min)) and 40% by mass of HPP (trade name E-111G, manufactured by Prime Polymer Co., Ltd.).

[0028]

Table 1

[0029] As shown in Table 1 above, in Examples 1 to 4 where the surface layer was mainly composed of HPP and the tensile elastic modulus of the surface layer was 1500 MPa or more, in addition to no appearance defects occurring after heat treatment (OK), evaluations were obtained that the peelability and breakability were also suitable for practical use (peelability was A or B, breakability was A to C). On the other hand, in Comparative Examples 1 and 2 where the surface layer was mainly composed of HPP but the tensile elastic modulus of the surface layer was less than 1500 MPa, no appearance defects occurred after heat treatment, but evaluations were obtained that the peelability and breakability were not suitable for practical use (peelability was C, breakability was D). Also, in Comparative Example 3 which is a conventional example, although the peelability and breakability were good, appearance defects occurred after heat treatment (NG).

[0030] In addition, in Example 5, in addition to the evaluation that there was no appearance defect after heat treatment and the peelability and breakability were suitable for practical use, the opening strength decreased and the openability improved. The opening strength of Example 5 (0.6 kgf) was lower than the opening strengths of Examples 1 to 4. On the other hand, in Example 6, even when the HDPE content in the surface lower layer was 60%, the evaluation that there was no appearance defect after heat treatment and the peelability and breakability were suitable for practical use was obtained.

[0031] From the above results, it can be seen that by setting the main component of the surface layer in the laminated sheet to HPP and setting the tensile elastic modulus of the surface layer to 1500 MPa or more, it is possible to easily open the container due to delamination while maintaining the peelability and breakability while preventing appearance defects during heat treatment.

[0032] Next, the experimental results regarding the composition of the surface lower layer when the surface layer of the laminated sheet is configured as described above will be explained. Table 2 shows examples in which the composition of the surface lower layer was changed when the surface layer was formed of a resin composition having HPP as the main component in the same manner as in Examples 1 to 4 and Comparative Examples 1 and 2 shown in Table 1 above.

[0033]

Table 2

[0034] Table 3 shows examples in which, when forming a surface layer with a resin composition containing 100% by mass of HPP as in Examples 1 to 4 and Comparative Examples 1 and 2 shown above, the blending ratio of HDPE and HPP in the composition of the surface lower layer was changed. Specifically, while the content of HDPE in the resin composition forming the surface lower layer decreases to 55% by mass or 40% by mass, the content of HPP increases to 45% by mass or 60% by mass. In these examples, evaluations were obtained that the peelability and breakability were not suitable for practical use (peelability was C and breakability was D). From this result, when forming a surface layer with a resin composition having HPP as the main component, it is understood that the content of HDPE in the surface lower layer is preferably more than 55% by mass, more preferably 58% by mass or more, still more preferably 65% by mass or more, and particularly preferably 70% by mass or more. The content of HPP is preferably less than the balance of HDPE, that is, less than 45% by mass, more preferably 42% by mass or less, still more preferably 35% by mass or less, and particularly preferably 30% by mass or less. Also, in the examples shown as Comparative Examples 1 and 2 above, where the main component of the surface layer was HPP and the tensile modulus was less than 1500 MPa, it can be seen that the evaluation does not improve even if the blending ratio of HDPE and HPP in the surface lower layer is changed.

[0035]

Table 3

[0036] As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to these examples. It is obvious that those skilled in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

Explanation of Reference Signs

[0037] 10... laminated sheet, 11... surface layer, 12... sub-surface layer, 13... base material layer, 14... base material layer, 15... sub-surface layer, 20... lid, 100... container, 101... bottom part, 102... side part, 103... flange part, SP... storage space.

Claims

1. A surface layer formed of a resin composition mainly composed of homopolypropylene and having a tensile modulus of 1500 MPa or more, and a subsurface layer adjacent to the surface layer and formed of a resin composition mainly composed of polyethylene are included at least, wherein the subsurface layer is a laminated sheet containing 58% by mass or more of high-density polyethylene and 42% by mass or less of homopolypropylene.

2. A surface layer formed of a resin composition mainly composed of homopolypropylene and having a tensile modulus of 1500 MPa or more, and a subsurface layer adjacent to the surface layer and formed of a resin composition mainly composed of polyethylene are included at least, wherein the subsurface layer contains 70% by mass or more of high-density polyethylene, and the thickness of the surface layer is 5 μm or more and 40 μm or less in a laminated sheet.

3. The laminated sheet according to Claim 2, wherein the subsurface layer further contains 30% by mass or less of homopolypropylene.

4. The laminated sheet according to Claim 1, wherein the thickness of the surface layer is 5 μm or more and 40 μm or less.

5. The laminated sheet according to any one of Claims 1 to 3, wherein the thickness of the surface layer is 10 μm or more and 30 μm or less.

6. The laminated sheet according to any one of Claims 1 to 5, further including first and second base material layers laminated on the side opposite to the surface layer with respect to the subsurface layer, and an oxygen barrier layer laminated between the first and second base material layers.

7. The laminated sheet according to Claim 6, wherein the oxygen barrier layer contains an ethylene vinyl alcohol resin.

8. The laminated sheet according to any one of Claims 1 to 7, having a thickness of 0.3 mm or more and 1.2 mm or less.

9. A container formed by molding the laminated sheet according to any one of Claims 1 to 8 such that the surface layer faces the content side.

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