Laminate and packaging container

Abstract

To provide a laminate which can be produced with a reduced amount of plastic and has the heat sealability.SOLUTION: A laminate 1 comprises a resin-based substrate layer 10 formed without using paper, and a heat-seal varnish layer 20 formed to cover one entire side of the substrate layer 10 in the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminate, more particularly to a heat-sealable laminate, and also to a packaging container using the laminate. [Background technology]

[0002] Heat-sealable laminates are used in containers for a variety of items. When a container is sealed using a heat-sealable laminate, the container can be sealed by fusion simply by applying heat and pressure, eliminating the need to use adhesives containing solvents on the sealing portion each time. For this reason, such containers are also widely used for food and other items.

[0003] Generally, as described in Patent Document 1, the above-mentioned laminate is formed by bonding a heat-sealable resin film to a resin film serving as a base material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-183635 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, efforts to reduce the amount of plastic used have been progressing in all fields in order to reduce the environmental impact, and heat-sealable laminates are no exception.

[0006] In view of the above circumstances, an object of the present invention is to provide a laminate that can be produced using a small amount of plastic and has heat-sealability. [Means for solving the problem]

[0007] A first aspect of the present invention is a laminate comprising a resin base layer formed without using paper, and a heat seal varnish layer formed to cover the entire thickness of one side of the base layer.

[0008] A second aspect of the present invention is a packaging container formed using the laminate according to the first aspect. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a laminate that has good sealing performance and is easy to open when applied to a container while reducing the amount of plastic used. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a laminate according to one embodiment of the present invention. [Figure 2] FIG. 10 is a diagram showing an example of a packaging container using the same laminate. [Figure 3] FIG. 10 is a schematic diagram showing a laminate according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to FIGS. 1 is a schematic diagram showing the layer structure of a laminate 1 according to this embodiment. The laminate 1 includes a base layer 10 made of resin and a heat seal varnish layer 20 provided on one surface of the base layer 10. The base material layer 10 can be configured in various ways, the details of which will be described later, but in any of the ways, the constituent materials contain resin in the largest amount, and do not contain paper.

[0012] Examples of resins that can be used to form the base layer 10 include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyamide, and polypropylene, and films made of these resins can be used as the base layer 10. The base layer 10 can also be made up of multiple layers using two or more of these resins. There are no particular limitations on the means for forming the multiple layers, and examples include dry lamination and coextrusion. The thickness of each resin layer can be, for example, 5 μm to 100 μm.

[0013] The barrier properties can be improved by providing a barrier layer on the base layer 10. When the barrier layer is formed by vapor deposition, examples of the material include inorganic oxides such as silicon oxide and aluminum oxide, and aluminum. When a container using the laminate 1 is expected to be heated by microwaves in a microwave oven, the barrier layer is preferably a transparent inorganic oxide layer. When the base layer 10 has multiple resin layers, the barrier layer may be located between two resin layers. The total thickness of the base layer 10 can be, for example, 5 μm to 100 μm, and the thickness of each layer constituting the base layer can be set appropriately within that range.

[0014] The heat seal varnish layer 20 is formed by applying a heat seal varnish to one surface of the base layer 10. In the present invention, the heat seal varnish refers to a material that can form a layer with heat sealability by coating, and is also called a heat seal agent. If the base layer 10 has a barrier layer, the heat seal varnish layer 20 may be formed on the barrier layer. The heat seal varnish layer 20 of this embodiment is formed so as to cover the entirety of one side in the thickness direction of the base material layer 10.

[0015] Examples of resin components that form the solid content of the heat seal varnish for forming the heat seal varnish layer 20 include ethylene-vinyl acetate (EVA) copolymer, ionomer resin, and other polyolefins. Among polyolefins, linear low density polyethylene (LLDPE), very low density linear polyethylene (VLDPE), polypropylene (PP), etc. are preferred. Although an organic solvent can be used as the solvent or dispersion medium contained in the heat seal varnish, when the varnish is used to store food, etc., it is preferable to use a hydrophilic solvent from the viewpoint of odor, etc. Examples of hydrophilic solvents include water and alcohol, and an example is a mixture of water and isopropanol. The heat seal varnish is preferably an aqueous emulsion in which the resin component is dispersed in a hydrophilic solvent. From the viewpoints of dispersion stability, coatability, and heat sealability, it is preferable to use an aqueous emulsion of EVA or polyolefins. In particular, for packaging containers for frozen foods and chilled foods, EVA is preferred because it maintains its sealability even when stored at low temperatures and can withstand microwave heating. The heat seal varnish may contain components other than the resin component, solvent, and dispersion medium, such as a lubricant.

[0016] There are no particular limitations on the method for applying the heat seal varnish, and examples include various coating methods such as gravure coating, die coating, blade coating, knife coating, and bar coating. The coating amount is, for example, 0.5 g / m2 as dry weight (roughly equal to the amount of solids). 2 More than 10g / m 2 It can be made with less than 3g / m 2 More than 6g / m 2 When the resin component of the heat seal varnish is one of those mentioned above, the thickness of the heat seal varnish layer 20 is roughly the numerical value of the coating amount expressed in the above units, with the unit of μm added. The drying conditions for the coating film can be, for example, 100°C to 120°C and about 15 to 60 seconds.

[0017] The laminate 1 according to this embodiment configured as described above can be applied to packaging containers of various types, but the following two aspects are the main aspects. First, a bag-shaped packaging container can be formed using only the laminate 1. In this case, when the heat seal varnish layers 20 are brought into contact with each other and heated, the heated portions are joined together by heat fusion. Therefore, a bag-shaped packaging container can be formed by folding one laminate 1 with the heat seal varnish layer 20 facing inward, or by stacking two laminates with the heat seal varnish layers 20 facing each other, and then heat-fusing the edges at a certain width. An example of the configuration of the laminate 1 suitable for a bag shape is one that includes a base layer 10 made of a polyamide such as nylon (Ny) and a heat seal varnish layer 20 whose main resin component is EVA.

[0018] In another embodiment, the laminate 1 is used as a lid material, and a container body obtained by resin molding is sealed with the laminate 1. For example, as shown in Fig. 2, the laminate 1 is placed on a container body 50 having a flange 51 around the periphery of an opening Op, with the heat seal varnish layer 20 facing the container body 50, so as to cover the opening Op including the flange 51. In this state, by heating the overlapping portion of the flange 51 and the laminate 1, the laminate 1 can be bonded to the flange 51 to seal the container body 50, thereby forming a packaging container 100. A suitable example of the resin constituting the container body 50 is PP. The container body 50 may further contain a component such as ethylene-vinyl alcohol copolymer (EVOH) to improve the gas barrier properties of the container body 50. The container body 50 may also further contain additives, for example, additives for improving processability, designability, and chemical durability.

[0019] In either of the above two embodiments, the packaging container using the laminate 1 has sufficient bonding strength, i.e., airtightness, and does not easily peel off, thereby suitably protecting the contents, even during frozen storage, transportation, etc. Furthermore, when the barrier layer is made of an inorganic oxide or when no barrier layer is provided, the laminate 1 is transparent, allowing the contents to be seen.

[0020] In the laminate 1 of this embodiment, the 180° peel strength when the heat seal varnish layer 20 is bonded to a surface made of polypropylene is 7 N / 15 mm or more in both the MD (Machine Direction) direction and TD (Transverse Direction) direction of the laminate 1. The 180° peel strength can be measured using a tensile tester on test pieces prepared by bonding the heat seal varnish layer 20 of the laminate 1 to a sheet having a PP layer on its surface under heat and pressure. The peel speed is 300 mm / min, and the maximum tensile load applied to each test piece before breakage is defined as the 180° peel strength. Because bonding conditions may vary slightly depending on the heat fusion conditions, the 180° peel strength in this invention is defined as the value measured using test pieces bonded at 210°C, 0.1 MPa, and 2 seconds. This measurement method is based on JIS Z0238:1998 with some conditions changed, and complies with JIS Z0238:1998. The MD and TD directions are two mutually perpendicular directions present in industrially produced laminates. Generally, in a resin film distributed in a roll state, the longitudinal direction is the MD direction and the width direction is the TD direction. In a resin film distributed in a rectangular or square shape, the direction in which one side extends is the MD direction, and the direction in which the other side perpendicular to the one side extends is the TD direction. Depending on the manufacturing process of the laminate, the molecular orientation may differ between the MD and TD directions, which may affect the 180° peel strength value in the present invention. In the laminate according to this embodiment, the above-mentioned value is satisfied whether the test piece is pulled in the MD or TD direction in the measurement of the 180° peel strength.

[0021] In the laminate 1 of this embodiment, the 135° peel strength when the heat seal varnish layer 20 is bonded to a surface made of polypropylene is 5 N / 15 mm or more and 11 N / 15 mm or less in both the MD and TD directions of the laminate 1. In the laminate according to this embodiment, when the 135° peel strength of the laminate 1, in which the joining surface of the laminate is joined to a container body made of PP, is measured, the 135° peel strength is 5 N / 15 mm or more whether the laminate is pulled in the MD or TD, providing sufficient joining strength. On the other hand, the 135° peel strength value is 11 N / 15 mm or less, allowing the user to open the package smoothly without applying excessive force. The 135° peel strength can be measured using a tensile tester using a test piece prepared by bonding the heat seal varnish layer 20 of the laminate 1 to a sheet having a PP layer on its surface under heat and pressure. The test piece is fixed to a stainless steel plate and held at a 45° angle relative to the vertical. While holding the lower end of the 45°-inclined sheet with the tester's grip, the lower end of the laminate, held by another grip, is moved vertically upward at a peel speed of 500 mm / min. The 135° peel strength is defined as the maximum tensile load applied to each test piece until breakage occurs. As with the 180° peel strength, the value measured using a test piece bonded at 210°C, 0.1 MPa, and 2 seconds is defined as the 135° peel strength in this invention. This measurement method is based on JIS Z0238:1998 with some conditions changed, and complies with JIS Z0238:1998.

[0022] In a laminate in which the layer exhibiting heat fusion bonding is made of a resin film having heat fusion bonding properties, the layer exhibiting heat fusion bonding properties is often several tens of μm or more thick, and is often thicker than the base layer. In the laminate 1 according to this embodiment, the layer that exhibits heat-sealability is the heat-seal varnish layer 20, so the layer that exhibits heat-sealability can be formed thin to a degree that would be difficult to achieve if a film were used. As a result, the amount of plastic used can be significantly reduced compared to the general heat-sealable laminates described above, and the environmental load can be significantly reduced. On the other hand, when applied to packaging containers, in either of the two aspects described above, it exhibits sufficient bonding strength while also being easy to open. Furthermore, since it has a resin base layer 10 formed without using paper, it has the advantage of being easy to construct lightweight. Furthermore, it has good thermal efficiency during sealing, is soft, and has no stiffness, making it easy to open. Because it is thin, during production, the drying efficiency of the heat seal varnish is good, and the volume of the roll is reduced, resulting in good productivity.

[0023] The laminate and packaging container according to the present embodiment will be further described using examples and comparative examples. The technical scope of the present invention is not limited solely by the specific contents of the examples and comparative examples.

[0024] The materials used in the examples and comparative examples are shown below. (base material layer) Base layer A: A 12 μm thick PET film with a barrier layer made of aluminum oxide on one side Base layer B: Polyamide film (thickness 15 μm) (heat seal varnish layer) Heat seal varnish: A water-based emulsion containing EVA as the main component and water and isopropanol as the solvent or dispersion medium.

[0025] (Examples 1, 3, and 5) A heat seal varnish was applied to the entire surface of the substrate layer A on the barrier layer side and dried to form a heat seal varnish layer 20. The amount of the heat seal varnish applied was 3 g / m2 in terms of dry weight.2 It was decided. In this manner, laminates according to Examples 1, 3 and 5 were produced. (Examples 2, 4, and 6) Heat seal varnish coating amount: 5g / m2 (dry weight) 2 Laminates according to Examples 2, 4, and 6 were produced in the same manner as in Examples 1, 3, and 5, except for the above.

[0026] (Examples 7, 9, 10, and 12) A heat seal varnish was applied to the entire surface of one side of the base layer B and dried to form a heat seal varnish layer 20. The amount of heat seal varnish applied was 5.2 g / m2 in terms of dry weight. 2 It was decided. In this manner, laminates according to Examples 7, 9, 10 and 12 were produced. (Examples 8 and 11) The amount of heat seal varnish applied is 3.5g / m2 in dry weight. 2 Except for the above, laminates according to Examples 8 and 11 were produced in the same manner as in Examples 7, 9, 10 and 12.

[0027] (Comparative Examples 1 and 2) The amount of heat seal varnish applied is 2g / m2 in dry weight. 2 Laminates according to Comparative Examples 1 and 2 were produced in the same manner as in Examples 1, 3 and 5, except for the above. (Comparative Example 3) The amount of heat seal varnish applied is 2.1g / m2 in dry weight. 2 A laminate according to Comparative Example 3 was produced in the same manner as in Examples 7, 9, 10, and 12, except for the above.

[0028] For each example and comparative example, a three-layer sheet was molded having a layer of a mixture of PP and EVOH (EVOH content of 4% by mass) between a pair of PP layers, and the opening of the resulting container body was sealed with a laminate to produce a container for evaluation according to each example. Examples 1, 3, and 5 use the same laminate, but the heat-sealing conditions (temperature, pressure, and time) used to produce the packaging containers are different. The same applies to other groups such as Examples 2, 4, and 6. The heat-sealing conditions for each example are listed in Table 1 below.

[0029] In parallel, the 180° peel strength and 135° peel strength were measured using test pieces that simulated the bond between the container body and the laminate, generally in the same manner as described above. The details of each are given below. (180° peel strength) The laminate was bonded to a flat sheet having the three-layer structure described above. The laminate and sheet were bonded using a TP-701-B heat seal tester manufactured by Tester Sangyo Co., Ltd. The heat seal tester used had a seal bar width of 5 mm. The length direction of the seal bar was perpendicular to the MD direction. Heat fusion between the laminate and sheet was performed at each heat seal position at the bonded portion between the laminate and sheet under the conditions shown in Table 1. Three test pieces were cut out from the partially heat-sealed assembly, each having a width of 15 mm, a length parallel to the MD, one end unsealed, and the other end heat-sealed over a length of 30 to 50 mm. Separately, a laminate and a sheet were heat-sealed in the same manner as above, except that the length of the seal bar was perpendicular to the TD. Three test pieces were cut out from the partially heat-sealed assembly, each having a width of 15 mm, a length parallel to the TD, one end unsealed, and the other end heat-sealed over a length of 30 to 50 mm. The 180° peel strength of each specimen was then measured using a Tensilon universal testing machine. The unheat-sealed laminate and sheet of each specimen were gripped by the grips of the testing machine and moved away from each other. The relative movement speed of the grips, i.e., the peel speed, was 300 mm / min. The maximum tensile load applied to each specimen until it broke was recorded. For each example, the 180° peel strength in the MD direction was calculated by arithmetically averaging the maximum tensile loads obtained for the three specimens whose length directions were parallel to the MD direction, and the 180° peel strength in the TD direction was calculated by arithmetically averaging the maximum tensile loads obtained for the three specimens whose length directions were parallel to the TD direction.

[0030] (135° peel strength) For each example, three specimens parallel to the MD direction and three specimens parallel to the TD direction were prepared. The test piece was fixed on a stainless steel plate and held at a 45° angle to the vertical. While the sheet tilted downward at 45° was held by a gripper of the testing machine, the laminate chucked by another gripper was moved vertically upward. The peel speed was 500 mm / min. Then, the 135° peel strength in the MD direction was measured using the same procedure as for the 180° peel strength.

[0031] Furthermore, the sealing property and the ease of opening of the evaluation containers were evaluated according to the following procedures. (Sealability) 200 ml of water was poured into the container body, and then the container body was sealed with the laminate to produce five evaluation packaging containers B (hereinafter simply referred to as "evaluation containers") for each example. The container body was 30 mm high, and the opening in plan view was a rectangle with long sides of 120 mm and short sides of 90 mm. The evaluation containers according to each example were subjected to a drop strength test according to JIS Z0238:1998, "Test Methods for Heat-Sealed Flexible Packaging Bags and Semi-Rigid Containers." Specifically, each evaluation container was dropped eight times from a height of 50 cm onto a solid surface. In the first drop, the evaluation container was dropped so that its bottom struck the surface. In the second drop, the evaluation container was dropped so that one of its long sides struck the surface. In the third drop, the evaluation container was dropped so that the other of its long sides struck the surface. In the fourth drop, the evaluation container was dropped so that one of its short sides struck the surface. In the fifth drop, the evaluation container was dropped so that the other of its short sides struck the surface. In the sixth drop, the evaluation container was dropped so that one corner struck the surface. In the seventh drop, the evaluation container was dropped so that the other corner struck the surface. In the eighth drop, the evaluation container was dropped so that yet another corner struck the surface. The evaluation was conducted in two stages as follows: A: None of the five evaluation containers leaked after eight drops. B: After eight drops, the lid of one or more of the evaluation containers broke or partially peeled off, causing leakage of the contents.

[0032] (openability) For each example, an evaluation container prepared separately from the one for evaluating the sealing property was used, and the laminate was peeled off by hand from a corner of the container body in a plan view, and evaluated according to the following criteria. A: I was able to open it smoothly without spilling any water. B: The container could be opened without spilling water, but opening was not smooth due to zipping, etc. Alternatively, almost the entire laminate peeled off from the container body immediately after starting the opening operation, and this peeling could not be stopped at the desired position. C: It was difficult to open due to a tear in part of the laminate, or zipping occurred, causing the contents to spill out. Although C was set as the standard in this study, no applicable cases were found. Table 1 shows the heat fusion conditions for each example, as well as the measurement and evaluation results for each item.

[0033] [Table 1]

[0034] As shown in Table 1, in Examples 3, 4, 8, and 9, sufficient bond strength to the PP surface was achieved by heat sealing at 210°C, 0.1 MPa, and 2 seconds, as defined in the present invention, and no significant difference in bond strength was observed between the MD and TD directions. Furthermore, the results of other Examples showed that sufficient bond strength could be achieved even under heat sealing conditions slightly different from the above definition. The results of Examples 11 and 12 showed that good sealability could be achieved by heating for a sufficient length of time, even at low heat sealing temperatures. The laminates according to each example can be bonded to a surface made of PP with sufficient peel strength, and are suitable for producing containers using a container body in which at least a portion of the surface is made of polypropylene. In fact, the evaluation of the sealing property and the ease of opening using the evaluation containers was also good.

[0035] Although the present invention has been described above, the specific configuration is not limited to this embodiment, and modifications and combinations of the configuration within the scope of the gist of the present invention are also included.

[0036] In the above-described embodiment, an example was shown in which a heat seal varnish layer was provided to cover the entire surface of one side of the base layer, but this is not necessarily required. For example, as in the modified laminate 1A shown in FIG. 3, the heat seal varnish layer 20 formed on one side of the base layer may be frame-shaped. In the example shown in FIG. 3, multiple window-shaped areas are formed on the surface on which the heat seal varnish layer 20 is provided, exposing the base layer 10. Therefore, by cutting out one or more window-shaped areas and the heat seal varnish layer 20 located around them, they can be used as a lid material to seal a container body having a corresponding opening. Two cut-out laminates can also be used to form a bag-shaped packaging container. In this way, by providing a heat seal varnish layer in a manner that does not cover the entire one side of the base layer, the amount of plastic used can be further reduced compared to the above-mentioned embodiment, and the environmental load can be reduced. Although it is extremely difficult to industrially produce a laminate having a heat seal layer of this type using a heat seal film, the difficulty can be significantly reduced by using a heat seal varnish, and industrial mass production becomes possible.

[0037] The laminate according to the present invention may have other layers, such as a printed layer or a functional layer, between the substrate layer and the heat seal varnish layer.

[0038] Packaging containers formed using the laminate of the present invention can withstand heating in a microwave oven, and are therefore suitable for use with foods that are displayed in a refrigerated or frozen state and are expected to be heated in a microwave oven when eaten. When heating in a microwave oven, the packaging container needs to be slightly opened before being placed in the microwave to prevent it from bursting during heating due to the generation of steam, but as an alternative method, a second heat seal varnish layer with a lower bonding strength than heat seal varnish layer 20 may be provided on a portion of the heat seal varnish layer 20. In this way, when the pressure inside the packaging container increases due to the generation of steam, the second heat seal varnish layer peels off, allowing the steam to escape appropriately and preventing bursting, thereby saving the user the trouble of opening the container beforehand. The method for forming the area with low bonding strength is not limited to the second heat seal varnish layer, and weakening processing using a laser or the like can also be used. [Explanation of symbols]

[0039] 1, 1A laminate 10 Base material layer 20 Heat seal varnish layer 50 Container body 51 flange 100 packaging containers Op Aperture

Claims

1. a resin base layer formed without using paper; a heat seal varnish layer formed so as to cover the entire one side of the base layer in the thickness direction; Equipped with Laminate.

2. When the heat seal varnish layer is bonded to a polypropylene surface under heat sealing conditions of 210°C, 0.1 MPa, and 2 seconds, the 135° peel strength measured in accordance with JIS Z0238:1998 is 5 N / 15 mm or more and 11 N / 15 mm or less in both the MD and TD directions of the laminate. The laminate according to claim 1 .

3. When the heat seal varnish layer is bonded to a polypropylene surface under heat sealing conditions of 210°C, 0.1 MPa, and 2 seconds, the 180° peel strength measured in accordance with JIS Z0238:1998 is 7 N / 15 mm or more in both the MD and TD directions of the laminate. The laminate according to claim 1 .

4. A packaging container formed using the laminate according to any one of claims 1 to 3.

5. At least a portion of the surface of the container body is made of polypropylene and has an opening. The heat seal varnish layer is bonded to the polypropylene surface by heat fusion, thereby sealing the opening with the laminate. The packaging container according to claim 4.

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