LAMINATE AND PACKAGING BAG

Abstract

A laminate including, a base material layer; a first polyethylene resin layer containing a first polyethylene resin and having a melt flow rate of less than 5 g/10 minutes, and a second polyethylene resin layer containing a second polyethylene resin and having a melt flow rate of 5 to 12 g/10 minutes, in this order, in which a ratio R.sub.2 (Mw/Mn) of a weight-average molecular weight Mw to a number average molecular weight Mn of the second polyethylene resin is 7 or less.

Claims

1. A laminate comprising: a base material layer; a first polyethylene resin layer comprising a first polyethylene resin and having a melt flow rate of less than 5 g/10 minutes, and a second polyethylene resin layer comprising a second polyethylene resin and having a melt flow rate of 5 to 12 g/10 minutes, wherein the base material layer, the first polyethylene resin layer, and the second polyethylene resin laver are laminated in stated order, and wherein a ratio R.sub.2 (Mw/Mn) of a weight-average molecular weight Mw to a number average molecular weight Mn of the second polyethylene resin is 7 or less.

2. The laminate according to claim 1, wherein a molecular weight distribution of the first polyethylene resin is sharper than a molecular weight distribution of the second polyethylene resin.

3. The laminate according to claim 1, wherein a thickness Ta of the first polyethylene resin layer and a thickness Tb of the second polyethylene resin layer satisfy conditions below.
2?Tb/(Ta+Tb)?100?30

4. The laminate according to claim 1, wherein the base material layer comprises at least a high-density polyethylene resin layer.

5. The laminate according to claim 1, wherein a polyethylene resin content is 90 mass % or more.

6. A packaging bag comprising: the laminate according to claim 1.

7. The laminate according to claim 1 further comprising an adhesive layer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0017] FIG. 1 is a front view schematically showing one embodiment of a standing pouch according to the present disclosure.

[0018] FIG. 2 is a cross-sectional view schematically showing a configuration of the standing pouch shown in FIG. 1.

[0019] FIG. 3 is a perspective view schematically showing bottom tape and a pair of side body portions constituting the standing pouch shown in FIG. 1.

[0020] FIG. 4 is a cross-sectional view schematically showing one embodiment of a laminate according to the present disclosure.

[0021] FIG. 5 is a graph showing a relationship between sealing temperatures and sealing strengths.

DESCRIPTION OF EMBODIMENT

[0022] Hereinafter, an embodiment of the present disclosure will be described in detail. Here, a standing pouch will be described as an example of a packaging bag in which mono-materialization is achieved. Standing pouches are used as refill pouches for shampoo, hand soap, detergent, and the like, and pouches for soup, seasonings, and the like. The present disclosure is not limited to the following embodiment.

[0023] <Standing Pouch>

[0024] FIG. 1 is a front view schematically showing a standing pouch according to the present embodiment. FIG. 2 is a cross-sectional view schematically showing a configuration of the standing pouch according to the present embodiment. A standing pouch 10 shown in these drawings is formed through heat-sealing a pair of side body portions 1 and 2 a bottom tape 3. Each of the pair of side body portions 1 and 2 and the bottom tape 3 is composed of a laminate containing at least a base material layer L1 and a sealant layer L2 (refer to FIG. 2). The formation of the standing pouch through heat-sealing can be carried out in the same manner as in a method in the related art.

[0025] The bottom tape 3 has one mountain fold part 3a. That is, when the standing pouch 10 stands on its own, the bottom tape 3 is placed in an inverted V-shape (refer to FIGS. 2 and 3). The bottom portion of the standing pouch 10 is composed of a heat-sealed portion 5 and a heat-sealed portion 6 as shown in FIG. 2. The heat-sealed portion 5 is a portion obtained by heat-sealing a bottom portion 1a of the side body portion 1 and one bottom portion 3b of the bottom tape 3. The heat-sealed portion 6 is a portion obtained by heat-sealing a bottom portion 2a of the side body portion 2 and the other bottom portion 3c of the bottom tape 3. The side body portions 1 and 2 and the bottom tape 3 are heat-sealed so that a bottom portion of the region for containing contents is curved and an upper side forms a circular arc shape as shown in FIG. 1.

[0026] A side portion of the standing pouch 10 is composed of a heat-sealed portion 7. The width of the heat-sealed portion 7 is, for example, 5 to 18 mm, and may be 7 to 15 mm. When the width of the heat-sealed portion 7 is 5 mm or more, sufficient sealing strength is likely to be achieved. On the other hand, when the width thereof is 18 mm or less, a sufficient amount of contents of the standing pouch 10 is likely to be ensured.

[0027] As shown in FIG. 1, the standing pouch 10 has fused portions 9 on both sides of a bottom portion 10b. In the present embodiment, two fused portions 9 are formed and arranged vertically on one side of the standing pouch 10, and two fused portions 9 are formed and arranged vertically on the other side. The fused portions 9 join the side body portion 1 to the side body portion 2. The fused portions 9 are portions where sealant layers L2 of the side body portions 1 and 2 are locally fused through cut-out portions 8a and 8b provided in the bottom tape 3. As shown in FIG. 3, the cut-out portions 8a and 8b of the bottom tape 3 are regions between the mountain fold part 3a and bottom sides 3d and 3d and provided in side portions of the bottom tape 3. By providing the fused portions 9 on both sides of the bottom portion 10b, the self-supportability and drop resistance of the standing pouch 10 can be further improved. Here, although a case where two pairs of cut-out portions 8a and 8b are provided on one side of the bottom tape 3 to form two fused portions 9 is exemplified, a pair of cut-out portions may be provided on one side of the bottom tape 3 to form one fused portion 9.

[0028] From the viewpoint of recyclability, the polyethylene resin content in the standing pouch 10 is preferably 90 mass % or more. From the viewpoint of achieving a higher degree of mono-materialization, the polyethylene resin content in the standing pouch 10 is more preferably 92 mass % or more and still more preferably 95 mass % or more.

[0029] <Laminate>

[0030] Both the pair of side body portions 1 and 2 and the bottom tape 3 of the standing pouch 10 are substantially made of a polyethylene resin. FIG. 4 is a cross-sectional view schematically showing a laminate according to the present embodiment. A laminate 20 shown in this drawing contains the base material layer L1 and the sealant layer L2. The sealant layer L2 is constituted by a first polyethylene resin layer L2a and a second polyethylene resin layer L2b. The second polyethylene resin layer L2b constitutes the innermost surface of the laminate 20.

[0031] The polyethylene resin content in the laminate 20 is preferably 90 mass % or more. If the polyethylene resin content in the laminate 20 is 90 mass % or more, mono-materialization is likely to be achieved, which is preferable. From such a viewpoint, the polyethylene resin content in the laminate 20 is more preferably 92 to 100 mass % and still more preferably 95 to 100 mass %. If mono-materialization can be achieved, resins are likely to be regenerated, which is preferable. The laminate 20 has an excellent impact resistance due to its soft and stretchable firmness.

[0032] [Base Material Layer]

[0033] The base material layer L1 is preferably made of an unstretched polyethylene resin film. Since the base material layer L1 is unstretched, the resin has almost no orientation, and is easily stretched against external stresses such as pulling or shearing and difficult to break. The thickness of the base material layer L1 is, for example, 5 to 800 ?m, and may be 5 to 500 ?m or 10 to 50 ?m. The base material layer L1 has a melting point at least 20? C. higher than the second polyethylene resin layer L2b and preferably has a melting point at least 25? C. higher than that. The difference in melting points between the two can suppress melting of the base material layer L1 during the heat-sealing process. The difference in seal rising temperature between the base material layer L1 and the sealant layer L2 is preferably 25? C. or more and more preferably 30? C. or more. The seal rising temperature means the temperature at which sealing strength develops, as shown in FIG. 5. The melting point of a polyethylene resin can be measured using a differential scanning calorimeter (DSC).

[0034] The melting point of the base material layer L1 is preferably 120? C. or higher and more preferably 125? C. or higher. Examples of polyethylene resins constituting the base material layer L1 include a high-density polyethylene resin (HDPE) and a medium-density polyethylene resin (MDPE). Among these, HDPE and MDPE having a density of 0.925 g/cm.sup.3 or higher are preferably used from the viewpoint of heat resistance. In particular, a high-density polyethylene resin having a density in a range of 0.93 to 0.98 g/cm.sup.3 is preferably used.

[0035] The polyethylene resin constituting the base material layer L1 is not limited to those derived from petroleum, but may be partly or wholly a resin material of biological origin (for example, biomass polyethylene in which ethylene of biomass origin is used as a raw material). A method for producing a polyethylene resin of biomass origin is disclosed in, for example, Japanese Unexamined Patent Publication No. 2010-511634. The base material layer L1 may contain commercially available biomass polyethylene (such as Green PE manufactured by Braskem S. A.), or may contain mechanically recycled polyethylene made from used polyethylene products or resins (so-called burrs) produced in the manufacturing process of polyethylene products.

[0036] The base material layer L1 may contain components other than the polyethylene resin. Examples thereof include polyamide, polyethylene terephthalate, polypropylene, polyvinyl alcohols, and biodegradable resin materials (for example, polylactic acid, polycaprolactone, polyhydroxyalkanoate, polyglycolic acids, modified polyvinyl alcohols, casein, and modified starch). The base material layer L1 may contain additives such as an antistatic agent, an ultraviolet absorber, a plasticizer, a lubricant, and a colorant. The amount of component other than the polyethylene resin in the base material layer L1 is, based on a total amount of the base material layer L1, preferably 0 to 15 mass % and more preferably 0 to 10 mass %.

[0037] The base material layer L1 may be a single layer, or may be formed of a plurality of layers. From the viewpoint of heat resistance, the base material layer L1 preferably contains at least a high-density polyethylene resin layer (a layer containing a high-density polyethylene resin).

[0038] [Sealant Layer]

[0039] As described above, the sealant layer L2 is constituted by a first polyethylene resin layer L2a and a second polyethylene resin layer L2b. The thickness of the sealant layer L2 is, for example, 40 to 150 ?m, and may be 20 to 250 ?m.

[0040] (First Polyethylene Resin Layer) The first polyethylene resin layer L2a contains a first polyethylene resin and has a melt flow rate of less than 5 g/10 minutes. The melt flow rate of the first polyethylene resin layer L2a is preferably 0.5 g/10 minutes or more and less than 5 g/10 minutes, and more preferably 2 g/10 minutes or more and less than 5 g/10 minutes. A melt flow rate of less than 5 g/10 minutes results in higher melt tension, which facilitates suppressing of wrinkles during processing through an inflation method or the like. That is, it is inferred that, when the sealant layer L2 is heated to melt, the first polyethylene resin layer L2a is less likely to flow than the second polyethylene resin layer L2b, and the first polyethylene resin layer L2a serves as a support base material to maintain high film formation accuracy, resulting in a smooth and highly transparent film.

[0041] The ratio R.sub.1 (Mw/Mn) of the weight-average molecular weight Mw to the number average molecular weight Mn of the polyethylene resin constituting the first polyethylene resin layer L2a may be, for example, 1 to 12, 1 to 8, 1 to 6, 1 to 5, 1 to 4.5, or 1 to 4. The molecular weight distribution of the first polyethylene resin may be sharper than the molecular weight distribution of the second polyethylene resin. If the molecular weight distribution of the first polyethylene resin is sharp, there are few low-molecular-weight components and such components can be suppressed from appearing on the surface of the sealant layer L2 via the second polyethylene resin layer L2b. In a case where the first polyethylene resin layer L2a and the second polyethylene resin layer L2b are each composed of a single polyethylene resin, if the ratio R.sub.1 of the first polyethylene resin is smaller than the ratio R.sub.2 of the second polyethylene resin, it can be determined that the molecular weight distribution of the first polyethylene resin is sharper than that of the second polyethylene resin.

[0042] The melting point of the first polyethylene resin layer L2a is preferably 120? C. or lower and more preferably 95? C. to 110? C. That is, the first polyethylene resin layer L2a is preferably composed of a polyethylene resin having a melting point of 120? C. or lower and more preferably composed of a polyethylene resin having a melting point of 95? C. to 110? C. The first polyethylene resin layer L2a is preferably composed of a polyethylene resin having a density of less than 0.925 g/cm.sup.3 (more preferably 0.900 to 0.920 g/cm.sup.3). Specific examples thereof include a linear low-density polyethylene resin (LLDPE) and a very low-density polyethylene resin (VLDPE). A blend of these polyethylene resins may be used.

[0043] The first polyethylene resin layer L2a may contain a plurality of polyethylene resins as first polyethylene resins. In the case where the first polyethylene resin layer L2a contains a plurality of polyethylene resins, the first polyethylene resin layer L2a preferably contains at least a polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.1, melting point, and density.

[0044] The content of the polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.1, melting point, and density may be, based on the total mass of the polyethylene resins constituting the first polyethylene resin layer L2a, 60 to 100 mass %, 80 to 100 mass %, 90 to 100 mass %, or 95 to 100 mass %. The content of the polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.1, melting point, and density may be substantially 100 mass % (a mode in which a first polyethylene resin layer L2a is made of a polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.1, melting point, and density) based on the total mass of the polyethylene resins constituting the first polyethylene resin layer L2a.

[0045] The first polyethylene resin layer L2a may contain additives such as an antioxidant, a slipping agent, a flame retardant, an anti-blocking agent, a light stabilizer, a dehydrating agent, a tackifier, a crystal nucleating agent, and a plasticizer. The amount of component other than the polyethylene resins in the first polyethylene resin layer L2a is, based on the total amount of the first polyethylene resin layer L2a, preferably 0 to 15 mass % and more preferably 0 to 10 mass %.

[0046] The first polyethylene resin layer L2a is preferably sufficiently thicker than the second polyethylene resin layer L2b. That is, the proportion of the thickness of the first polyethylene resin layer L2a is preferably 70% to 98% based on the total thickness of the sealant layer L2. When this proportion is 70% or higher, the stability of film formation can increase and a smooth film without wrinkles can be supplied. On the other hand, when this proportion is 98% or lower, the second polyethylene resin layer L2b can sufficiently play a role of preventing adhesion. This proportion is more preferably 75% to 95% and still more preferably 80% to 90%.

[0047] (Second Polyethylene Resin Layer)

[0048] The second polyethylene resin layer L2b contains a second polyethylene resin and has a melt flow rate of 5 to 12 g/10 minutes. The melt flow rate of the second polyethylene resin layer L2b is preferably 5 to 10 g/10 minutes, and more preferably 6 to 9 g/10 minutes. A melt flow rate of 5 g/10 minutes or more results in a low extrusion load during production, less heat generation inside an extruder, and less resin degradation. That is, it is inferred that, when the sealant layer L2 is heated to melt, the second polyethylene resin layer L2b is more likely to flow than the first polyethylene resin layer L2a, thereby providing low-temperature sealability and reducing low-molecular-weight components formed through resin decomposition due to thermal deterioration.

[0049] The ratio R.sub.2 (Mw/Mn) of the weight-average molecular weight Mw to the number average molecular weight Mn of the second polyethylene resin constituting the second polyethylene resin layer L2b is, 7 or less, and may be 1.5 to 7, 2 to 6, 3 to 6, 4 to 6, 4.5 to 6, or 5 to 6. By setting the ratio R.sub.2 of the second polyethylene resin to 7 or less, the second polyethylene resin layer L2b can sufficiently play a role of preventing adhesion. That is, a sharp molecular weight distribution means a low content of low-molecular-weight components. Few low-molecular-weight components reduce tackiness and the melting point rises steeply, which suppresses sticking even when, for example, a certain amount of heat is applied in a state where seal surfaces are brought into contact with each other. A polyethylene resin having a sharp molecular weight distribution can be obtained through, for example, a gas phase polymerization method in which a metallocene catalyst is used.

[0050] The melting point of the second polyethylene resin layer L2b is preferably 120? C. or lower and more preferably 95? C. to 110? C. That is, the second polyethylene resin layer L2b is preferably composed of a polyethylene resin having a melting point of 120? C. or lower and more preferably composed of a polyethylene resin having a melting point of 95? C. to 110? C. The second polyethylene resin layer L2b is preferably composed of a polyethylene resin having a density of less than 0.925 g/cm.sup.3 (more preferably 0.900 to 0.920 g/cm.sup.3). Specific examples thereof include a linear low-density polyethylene resin (LLDPE) and a very low-density polyethylene resin (VLDPE). A blend of these polyethylene resins may be used.

[0051] The second polyethylene resin layer L2b may contain a plurality of polyethylene resins as second polyethylene resins. In the case where the second polyethylene resin layer L2b contains a plurality of polyethylene resins, the second polyethylene resin layer L2b preferably contains at least a polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.2, melting point, and density.

[0052] The content of the polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.2, melting point, and density may be, based on the total mass of the polyethylene resins constituting the second polyethylene resin layer L2b, 60 to 100 mass %, 80 to 100 mass %, 90 to 100 mass %, or 95 to 100 mass %. The content of the polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.2, melting point, and density may be substantially 100 mass % (a mode in which a second polyethylene resin layer L2b is made of a polyethylene resin that satisfies at least one of the ranges of the above-described ratio R.sub.2, melting point, and density) based on the total mass of the polyethylene resins constituting the second polyethylene resin layer L2b.

[0053] In a case where the second polyethylene resin layer L2b contains a plurality of polyethylene resins, the content of a polyethylene resin having a ratio R.sub.2 exceeding 6 among the second polyethylene resins constituting the second polyethylene resin layer L2b is, based on the total mass of the polyethylene resins constituting the second polyethylene resin layer L2b, preferably 0 to 5 mass % and more preferably 0 to 1 mass %. The second polyethylene resin layer L2b may not contain a polyethylene resin having a ratio R.sub.2 exceeding 6.

[0054] In a case where the first polyethylene resin layer L2a and/or the second polyethylene resin layer L2b contain a plurality of polyethylene resins, the sharper molecular weight distribution of the first polyethylene resins than that of the second polyethylene resins can be confirmed by the fact that a weighted average value calculated by taking into account the content of each polyethylene resin to the total amount of the first polyethylene resins from the ratio R.sub.1 of each polyethylene resin in the first polyethylene resin layer L2a is smaller than a weighted average value calculated by taking into account the content of each polyethylene resin to the total amount of the second polyethylene resins from the ratio R.sub.2 of each polyethylene resin in the second polyethylene resin layer L2b.

[0055] The second polyethylene resin layer L2b may contain additives such as an antioxidant, a slipping agent, a flame retardant, an anti-blocking agent, a light stabilizer, a dehydrating agent, a tackifier, a crystal nucleating agent, and a plasticizer. The amount of component other than the polyethylene resins in the second polyethylene resin layer L2b is, based on the total amount of the second polyethylene resin layer L2b, preferably 0 to 15 mass % and more preferably 0 to 10 mass %.

[0056] The second polyethylene resin layer L2b is preferably sufficiently thinner than the first polyethylene resin layer L2a. That is, the proportion of the thickness of the second polyethylene resin layer L2b is preferably 2% to 30% based on the total thickness of the sealant layer L2. When this proportion is 2% or higher, the second polyethylene resin layer L2b can sufficiently play a role of preventing adhesion. On the other hand, when this proportion is 30% or lower, the sealant layer L2 is likely to be formed. This proportion is more preferably 5% to 25% and still more preferably 10% to 20%.

[0057] As some or all of the polyethylene resins constituting the sealant layer L2, biomass polyethylene using ethylene of biomass origin as a raw material may be used. Such a sealant film is disclosed in, for example, Japanese Unexamined Patent Publication No. 2013-177531. The sealant layer L2 may contain mechanically recycled polyethylene made from used polyethylene products or resins (so-called burrs) produced in the manufacturing process of polyethylene products.

[0058] (Other Layers)

[0059] A laminate may include an adhesive layer (not shown in the drawing) between a base material layer L1 and a sealant layer L2. An adhesive forming the adhesive layer can be selected according to a bonding method, and a urethane adhesive, a polyester adhesive, and the like can be used. By providing such an adhesive layer, the interlayer adhesion between the base material layer L1 and the sealant layer L2 is increased and delamination is less likely to occur, whereby pressure resistance or impact resistance of a pouch can be maintained.

[0060] The adhesive layer preferably does not contain chlorine. Since the adhesive layer does not contain chlorine, it is possible to prevent an adhesive or a regenerated resin after recycling from being colored or smelling bad due to heat treatment. A biomass material is preferably used for the adhesive layer from the viewpoint of environmental consideration. In addition, biomass polyethylene can be used for a polyethylene resin. From the viewpoint of environmental consideration, the adhesive preferably does not contain a solvent.

[0061] The laminate may further include, for example, a gas barrier layer from the viewpoint of improving gas barrier properties against water vapor or oxygen. The gas barrier layer may be provided between the base material layer L1 and the sealant layer L2, or may be provided on the surface of the base material layer L1 opposite to the sealant layer L2. The amount of water vapor permeation of the laminate may be, for example, 5 g/m.sup.2.Math.day or less, 1 g/m.sup.2.Math.day or less, or 0.5 g/m.sup.2.Math.day or less. The amount of oxygen permeation of the laminate may be, for example, 1 cc/m.sup.2.Math.day.Math.atm or less, 0.5 cc/m.sup.2.Math.day.Math.atm or less, or 0.2 cc/m.sup.2.Math.day.Math.atm or less. The inclusion of a gas barrier layer in the laminate protects contents from deteriorating due to water vapor or oxygen, and the long-term quality is likely to be maintained.

[0062] Examples of gas barrier layers include a vapor deposition layer of an inorganic oxide. By using a vapor deposition layer of an inorganic oxide, it is possible to obtain high barrier properties with a very thin layer that does not affect the recyclability of the laminate. Examples of inorganic oxides include aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the viewpoints of transparency and barrier properties, an inorganic oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. The thickness of a vapor deposition layer of an inorganic oxide can be set to, for example, 5 nm to 100 nm, and may be 10 nm to 50 nm. When the thickness thereof is 5 nm or thicker, the barrier properties are likely to be exhibited favorably, and when the thickness thereof is 100 nm or thinner, the flexibility of the laminate is easily maintained. A vapor deposition layer can be formed through, for example, a physical vapor phase growth method and a chemical vapor phase growth method.

[0063] The laminate may include a metal layer (metal foil) instead of or in addition to the vapor deposition layer of the inorganic oxide. Various metal foils made of aluminum, stainless steel, and the like can be used as metal layers, and among these, aluminum foil is preferable from the viewpoints of moisture-proof properties, workability such as spreadability, costs, and the like. General soft aluminum foil can be used as aluminum foil. Among these, aluminum foil containing iron is preferable from the viewpoints of excellent pinhole resistance and spreadability during molding. In a case where a metal layer is provided, the thickness thereof may be 7 to 50 ?m and 9 to 15 ?m from the viewpoints of barrier properties, pinhole resistance, and workability.

[0064] A laminate may include an anchor coat layer between the base material layer L1 and the sealant layer L2. The anchor coat layer may be a very thin layer that does not affect the recyclability of the laminate, and can be formed using an anchor coat agent. Examples of anchor coat agents include an acrylic resin, an epoxy resin, an acrylic urethane resin, a polyester-polyurethane resin, a polyether-polyurethane resin, and a polyvinyl alcohol resin. As the anchor coat agents, an acrylic urethane resin and a polyester-polyurethane resin are preferable from the viewpoints of heat resistance and interlayer adhesive strength.

[0065] The laminate may further include, for example, a printed layer. The printed layer may be provided between the base material layer L1 and the sealant layer L2, or may be provided on the surface of the base material layer L1 opposite to the sealant layer L2. In a case where a printed layer is provided, printing ink that does not contain chlorine is preferably used from the viewpoint of preventing the printed layer from being colored or smelling bad during remelting. In addition, a biomass material is preferably used for a compound contained in a printing ink from the viewpoint of environmental consideration.

[0066] The embodiment of the present disclosure has been described above in detail, but the present disclosure is not limited to the above-described embodiment. For example, in the above-described embodiment, a standing pouch has been exemplified as an application target of a laminate, but the laminate according to the embodiment may be applied to manufacture of other packaging bags. For example, one laminate may be folded into two so that sealant layers face each other and then sealed on three sides to form a bag, or two laminates may be stacked so that sealant layers face each other and then heat-sealed on four sides to form a bag. Packaging bags can accommodate contents such as foods and medicaments as contents. Packaging bags can be subjected to heat sterilization treatment such as boiling treatment.

EXAMPLES

[0067] Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the present disclosure is not limited by the following examples.

Example 1

[0068] The following materials were used to produce laminates. [0069] Base material layer: Unstretched HDPE film (thickness: 35 ?m, density: 0.948 g/cm.sup.3, melting point: 135? C.) [0070] Adhesive layer: Urethane adhesive [0071] First seal layer: LLDPE with low-temperature sealability (density: 0.916 g/cm.sup.3, MFR: 4.0 g/10 minutes, melting point: 102? C., Mw/Mn: 4.0) [0072] Second seal layer: anti-adhesion VLDPE (density: 0.913 g/cm.sup.3, MFR: 10.0 g/10 minutes, melting point: 104? C., Mw/Mn: 5.5)

[0073] The first seal layer (thickness: 80 ?m) was provided on the surface of a support film. A sealant layer having a two-layer structure was obtained by providing the second seal layer (thickness: 20 ?m) on the surface of this first seal layer. Each laminate according to Example 1 was obtained by adhering the sealant layer to the base material layer via the adhesive layer (thickness: 1 to 2 ?m). After adhering the base material layer to the sealant layer, the above-described support film was peeled off. As a resin constituting the first seal layer, a resin having a sharper molecular weight distribution than that of a resin constituting the second seal layer was used.

Example 2

[0074] Each laminate according to Example 2 was obtained in the same manner as in Example 1 except that the second seal layer was formed using a blend of the following two types of polyethylene resins (density: 0.912 g/cm.sup.3, MFR: 5.0 g/10 minutes, melting point: 103? C.). [0075] LLDPE (density: 0.915 g/cm.sup.3, MFR: 7 g/10 minutes, melting point: 102? C., Mw/Mn: 4.0) [0076] VLDPE (density: 0.913 g/cm.sup.3, MFR: 8 g/10 minutes, melting point: 104? C., Mw/Mn: 5.5)

[0077] 5 parts by mass of LLDPE and 5 parts by mass of VLDPE were blended. As a resin constituting the first seal layer, a resin having a sharper molecular weight distribution than that of the resins constituting the second seal layer was used.

Comparative Example 1

[0078] Each laminate according to Comparative Example 1 was obtained in the same manner as in Example 1 except that a single-layer sealant layer (thickness: 100 ?m) was provided using the following polyethylene resin instead of providing the sealant layer having a two-layer structure. [0079] Sealant layer: LLDPE with low-temperature sealability (density: 0.916 g/cm.sup.3, MFR: 4.0 g/10 minutes, melting point: 105? C., Mw/Mn: 10.0)

Comparative Example 2

[0080] Each laminate according to Comparative Example 2 was obtained in the same manner as in Example 1 except that a single-layer sealant layer (thickness: 100 ?m) was provided using the following polyethylene resin instead of providing the sealant layer having a two-layer structure. [0081] Sealant layer: LLDPE with low-temperature sealability (density: 0.915 g/cm.sup.3, MFR: 2.0 g/10 minutes, melting point: 102? C., Mw/Mn: 11.0)

[0082] <Sealing Strength>

[0083] The sealing strengths of the laminates according to the examples and the comparative examples were measured as follows. That is, laminates were overlapped so that the sealant layers faced each other and sealed using a heat sealer having a width of 10 mm. The sealing conditions were pressure: 0.2 MPa and time: 1.0 second. The sealing was performed at a predetermined sealing temperature (from 80? C. to 200? C. at intervals of 10? C.). Each test piece was obtained by cutting the sealed packaging material into a width of 15 mm. A T-peel test was carried out using a tensile tester at a rate of 300 mm/min. FIG. 5 shows a relationship between the sealing temperature and the sealing strength (N/15 mm). Table 1 shows peeling modes of the test pieces (sealing temperature: 120? C. and 140? C.) after the T-peel test. The peeling modes were visually observed.

TABLE-US-00001 TABLE 1 Sealing temperature 120? C. 140? C. Example 1 Cohesive peeling Cohesive peeling Example 2 Cohesive peeling Cohesive peeling Comparative Interfacial peeling Interfacial peeling Example 1 Comparative Interfacial peeling Interfacial peeling Example 2

[0084] <Manufacture of Standing Pouch>

[0085] The laminates according to the examples and the comparative examples were used as main bodies and bottom materials, and standing pouches were manufactured using a bag-making machine manufactured by Totani Corporation. The pouch size was as follows. [0086] Top and bottom: 230 mm [0087] Width: 150 mm [0088] Folding width: 40 mm

[0089] In the laminates of Comparative Example 3, the base material layers were thermally fused to a seal bar of the bag-making machine, so it was impossible to make a bag.

[0090] (Evaluation of Opening Properties)

[0091] The standing pouches according to the examples and the comparative examples were each passed through nip rolls heated to 60? C. under a pressure of 0.5 MPa. Thereafter, a force required to open an opening portion of each standing pouch was measured. The results are shown in Table 2.

[0092] (Pressure-Resistance Test)

[0093] About 400 mL of normal-temperature water was sealed in each of the standing pouches according to the examples and the comparative examples. Breakage of each bag was confirmed when a static load of 80 kgf was applied to each sealed body for 1 minute. This test was performed 10 times to measure the number of bags broken. The results are shown in Table 2.

[0094] (Drop Test)

[0095] About 400 mL of normal-temperature water was sealed in each of the standing pouches. Breakage of each bag was confirmed when each sealed body was dropped 10 times from a height of 1 m in an upright position. This test was performed 5 times to measure the number of bags broken. The results are shown in Table 2.

TABLE-US-00002 TABLE 2 Pressure- resistance test Drop test Force (number of (number of required bags broken/ bags broken/ for opening number of number of (N) evaluations) evaluations) Example 1 0.00 0/10 0/5 Example 2 0.01 0/10 0/5 Comparative 0.10 1/10 3/5 Example 1 Comparative 0.25 1/10 1/5 Example 2

REFERENCE SIGNS LIST

[0096] 1,2 Side body portion [0097] 1a, 2a, 3b, 3c, 10b Bottom portion [0098] 3 Bottom tape [0099] 3a Mountain fold part [0100] 3d Bottom side [0101] 5, 6, 7 Heat-sealed portion [0102] 8a, 8b Cut-out portion [0103] 9 Fused portion [0104] 10 Standing pouch [0105] 20 Laminate [0106] L1 Base material layer [0107] L2 Sealant layer [0108] L2a First polyethylene resin layer [0109] L2b Second polyethylene resin layer