Sealant film and packaging film

Abstract

To provide a sealant film that utilizes recycled resin and offers an excellent balance of cost and heat-sealability. [Solution] A sealant film comprising a first layer containing a melt-type recycled polyolefin and a heat-seal layer containing a non-melt-type recycled polyolefin.

Description

Technical Field

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[0001] The present disclosure relates to a sealant film and a packaging film.

Background Art

[0002] There is known a sealant film characterized in that an intermediate layer containing recycled polyethylene is provided between two virgin polyethylene layers, namely, a first virgin polyethylene layer and a second virgin polyethylene layer (for example, Patent Document 1). Although recycled resin is used in such a sealant film, the use of virgin resin is also essential, and there is room for improvement from the viewpoints of recycled resin utilization and cost.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, the inventors attempted to produce a new sealant film using recycled resin in order to further reduce the amount of virgin resin used. However, it was found that it is difficult to exhibit sufficient heat sealability when actually producing a sealant film using common recycled resin as described in Patent Document 1, that is, pellets of inexpensive recycled resin (melted recycled resin) obtained through a melting process.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a sealant film that utilizes recycled resin and has an excellent balance between cost and heat sealability. This disclosure also aims to provide a packaging film comprising the sealant film. [Means for solving the problem]

[0006] The inventors diligently investigated the relationship between the physical properties of recycled resin pellets and the properties of the resulting sealant film. They found that while melt-processed recycled resin pellets are cost-effective from the perspective of distribution volume, the thermal history they undergo during pellet production makes them prone to gel formation during film formation, and the resulting irregularities hinder good heat-sealability. Therefore, in order to improve heat-sealability while maintaining the amount of recycled resin used, they found it useful to have recycled resin obtained without a melting process (non-melting recycled resin: see, for example, Patent Document 2) play a role similar to that of the virgin resin that constitutes the heat-seal layer in Patent Document 1, leading to this disclosure.

[0007] The summary of this disclosure is as follows: [1] A sealant film comprising a first layer containing a melt-type recycled polyolefin and a heat-seal layer containing a non-melt-type recycled polyolefin. [2] The sealant film according to [1], wherein the content of the non-meltable recycled polyolefin is 80% by mass or more, based on the total amount of the heat seal layer. [3] The sealant film according to [1] or [2], wherein the heat seal layer does not contain the molten recycled polyolefin. [4] A sealant film according to any one of [1] to [3], wherein the content of the melt-type recycled polyolefin is 80% by mass or more, based on the total amount of the first layer. [5] The sealant film according to any one of [1] to [4], further comprising a second layer containing recycled polyolefin on the side of the first layer opposite to the heat seal layer side. [6] The sealant film according to any one of [1] to [5], wherein the melt-type recycled polyolefin and the non-melt-type recycled polyolefin are polyethylene. [7] A packaging film comprising a sealant film and a base layer as described in any one of [1] to [6]. [Effects of the Invention]

[0008] According to this disclosure, a sealant film is provided that utilizes recycled resin and offers an excellent balance between cost and heat-sealability. Furthermore, this disclosure provides a packaging film comprising the sealant film. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic cross-sectional view of a sealant film according to an embodiment of the present disclosure. [Modes for carrying out the invention]

[0010] Preferred embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below.

[0011] <Method for manufacturing sealant film> A method for manufacturing a sealant film comprises the steps of preparing a first layer-forming pellet raw material containing molten recycled polyolefin pellets, a heat-seal layer-forming pellet raw material containing non-molten recycled polyolefin pellets, and a second layer-forming pellet raw material containing recycled polyolefin pellets as needed, and then manufacturing a resin film (sealant film) by multilayer extrusion molding using these materials. Melt-process recycled polyolefin pellets and non-melt-process recycled polyolefin pellets are collectively referred to as recycled polyolefin pellets.

[0012] In the process of manufacturing resin films from pellet raw materials by extrusion molding, a general screw extruder used in methods such as T-die molding and inflation molding can be used. The conveyance of the pellets can be adjusted by changing the screw shape.

[0013] Melt-type recycled polyolefin pellets are pellets produced by a pellet manufacturing process that involves melting waste polyolefin film. Specifically, they are roughly granular pellets produced by a melt-type pelletizer. Melt-type recycled polyolefin pellets are produced by heating and melting waste polyolefin film, followed by cooling and solidifying it.

[0014] Examples of waste polyolefin film include waste materials (PIR material: post-industrial recycled material) generated during the manufacture of polyolefin film, specifically including defective films, damaged films, and so-called edge loss (shredded scraps at both ends of the film). Waste polyolefin film may also be obtained by slitting polyolefin film during the manufacturing process. Furthermore, waste polyolefin film may be post-consumer recycled material (PCR material).

[0015] Examples of shapes for melt-process recycled polyolefin pellets include granular, columnar, and other shapes with circular, oval, or elliptical cross-sections.

[0016] The average diameter of melt-process recycled polyolefin pellets can be 1 to 10 mm. An average diameter of 1 mm or more reduces scattering during handling compared to pellets with a diameter of less than 1 mm, while an average diameter of 10 mm or less improves transportability during manufacturing compared to pellets with a diameter greater than 10 mm. From these perspectives, the average diameter of melt-process recycled polyolefin pellets may also be 2 to 6 mm.

[0017] The bulk density of molten recycled polyolefin pellets can be 0.5 to 0.8 g / mL. A bulk density of 0.5 g / mL or higher makes them less likely to scatter during handling compared to those with a density of less than 0.5 g / mL, while a bulk density of 0.8 g / mL or lower makes them less likely to clog the equipment during manufacturing compared to those with a density greater than 0.8 g / mL. From these perspectives, the bulk density of molten recycled polyolefin pellets may also be 0.5 to 0.7 g / mL.

[0018] The non-melting type recycled polyolefin pellet is a pellet produced by a pellet manufacturing process that does not melt the waste polyolefin film, specifically, a roughly granular pellet produced by a non-melting type pelletizer. Therefore, the "non-melting type" pellet is different from the aforementioned "melting type" pellet.

[0019] Examples of the waste polyolefin film include those described in the column of the melting type recycled polyolefin pellet.

[0020] Particularly in the case of non-melting type recycled polyolefin pellets, ear loss is preferably used as the waste polyolefin film. The thickness of the waste polyolefin film may be 5 to 200 μm. Also, the width of the waste polyolefin film may be 5 to 500 mm, and may be 5 to 50 mm from the viewpoint of ease of making the twisted cord described later.

[0021] The non-melting type recycled polyolefin pellet has a roughly granular to columnar shape with a low bulk density, and has a different aspect from the recycled polyolefin pellet with a high bulk density obtained through heat melting. The non-melting type recycled polyolefin pellet can contain fragments of resin (polyolefin) twisted cords. Here, the "resin twisted cord" is obtained by stretching a waste polyolefin film into a cord shape and twisting it with the stretching direction of the cord as the rotation axis. The "fragment" is obtained by cutting the resin twisted cord in a direction perpendicular to the stretching direction of the cord.

[0022] In the fragment, the cords (resin cords) constituting the twisted cord may be partially crimped, that is, the non-melting type recycled polyolefin pellet may contain fragments of resin crimped twisted cords.

[0023] The cord itself constituting the twisted cord may be stretched, that is, the twisted cord may be formed by twisting stretched resin cords. The "stretching" here refers to stretching processes such as uniaxial stretching and biaxial stretching performed on a normal resin film.

[0024] The fine fragments may be cylindrical in shape, and if the fine fragments are roughly granular, they may be cylindrical with an aspect ratio (ratio of diameter to height of cylinder) of approximately 1.

[0025] Such recycled polyolefin pellets can be manufactured, for example, in accordance with the contents of International Publication No. 2022 / 176171.

[0026] The average diameter of non-melt recycled polyolefin pellets can be 4 to 10 mm. An average diameter of 4 mm or more reduces scattering during handling compared to pellets with a diameter of less than 4 mm, while an average diameter of 10 mm or less improves transportability during manufacturing compared to pellets with a diameter greater than 10 mm. From these perspectives, the average diameter of non-melt recycled polyolefin pellets may also be 5 to 9 mm.

[0027] The bulk density of non-melt recycled polyolefin pellets is 0.35 g / mL or less from the perspective of being manufactured by a non-melt pelletizer, and this value is smaller than that of virgin polyolefin pellets and melt recycled polyolefin pellets. The lower limit of the bulk density is not particularly limited, but it can be set to 0.1 g / mL from the perspective of easily maintaining the shape of the pellets in the recycling process described later. From these perspectives, the bulk density of non-melt recycled polyolefin pellets can be 0.15 to 0.3 g / mL, and may also be 0.2 to 0.3 g / mL.

[0028] The bulk density of non-melt recycled polyolefin pellets can be adjusted, for example, by adjusting the stretching ratio of the raw material film or the pressure applied by the conveyor rolls. For instance, increasing the stretching ratio or the pressure applied can increase the bulk density of non-melt recycled polyolefin pellets. Because non-melt recycled polyolefin pellets are manufactured through a recycling process that involves stretching and twisting the raw material film, their bulk density tends to be lower compared to virgin polyolefin pellets and melt-process recycled polyolefin pellets.

[0029] Each pellet raw material may contain virgin polyolefin pellets to adjust the physical properties of the pellets and the characteristics of the sealant film. Virgin polyolefin pellets are pellets manufactured from virgin polyolefins. Virgin polyolefins are resins synthesized directly from petroleum or fossil fuels.

[0030] Virgin polyolefin pellets can take various shapes, including granular, columnar, or oval cross-sections.

[0031] The average diameter of virgin polyolefin pellets can be 1 to 10 mm. An average diameter of 1 mm or more makes them less likely to scatter during handling compared to pellets with a diameter of less than 1 mm, while an average diameter of 10 mm or less improves transportability during manufacturing compared to pellets with a diameter greater than 10 mm. From these perspectives, the average diameter of virgin polyolefin pellets may also be 2 to 6 mm.

[0032] The bulk density of virgin polyolefin pellets can be 0.5 to 0.8 g / mL. A bulk density of 0.5 g / mL or higher makes them less likely to scatter during handling compared to those with a density of less than 0.5 g / mL, while a bulk density of 0.8 g / mL or lower makes them less likely to clog in the manufacturing equipment compared to those with a density greater than 0.8 g / mL. From these perspectives, the bulk density of virgin polyolefin pellets may also be 0.5 to 0.7 g / mL.

[0033] The polyolefins contained in melt-process recycled polyolefin pellets, non-melt-process recycled polyolefin pellets, and virgin polyolefin pellets include polyethylene, polypropylene, polybutylene, ethylene vinyl acetate, and other polyolefins used in flexible packaging sealant films. Particularly from the viewpoint of excellent recyclability, each pellet may contain the same polyolefin, or it may contain polyethylene. Examples of polyethylene include HDPE (high-density polyethylene), LDPE (low-density polyethylene), and LLDPE (linear low-density polyethylene).

[0034] The content of melt-type recycled polyolefin pellets in the first layer-forming pellet raw material may be 80% by mass or more, 90% by mass or more, or 100% by mass, from the viewpoint of cost, utilization of recycled resin, etc.

[0035] The content of non-melt-type recycled polyolefin pellets in the pellet raw material for heat-seal layer formation may be 80% by mass or more, 90% by mass or more, or 100% by mass, from the viewpoint of heat-sealability. Also, from the same viewpoint, the pellet raw material for heat-seal layer formation does not need to contain molten-type recycled polyolefin pellets.

[0036] The second layer-forming pellet material includes at least one of molten recycled polyolefin pellets and non-molten recycled polyolefin pellets. From the viewpoint of suppressing film curling, the second layer-forming pellet material may be the same as the pellet material for heat-seal layer formation. The second layer-forming pellet raw material may include melt-processed recycled polyolefin pellets from the viewpoint of cost, utilization of recycled resin, etc., and the content of melt-processed recycled polyolefin pellets may be 80% by mass or more, 90% by mass or more, or 100% by mass. The pellet raw material for forming the second layer may contain non-meltable recycled polyolefin pellets, from the viewpoint of utilizing recycled resin and heat-sealability (when the second layer is also used as a heat-sealable layer), and the content of non-meltable recycled polyolefin pellets may be 80% by mass or more, 90% by mass or more, or 100% by mass.

[0037] When each of the above pellet raw materials contains virgin polyolefin pellets, there are no particular restrictions on the amount contained in each layer, but from the viewpoint of ensuring sufficient use of recycled resin, it may be 20% by mass or less, 10% by mass or less, or 5% by mass or less.

[0038] In this disclosure, the average diameter is the average of the maximum and minimum diameters when the pellet is placed on a stand and viewed from a direction perpendicular to the stand. The maximum and minimum diameters can be measured, for example, with calipers. The measurement should be performed with approximately 20 pellets in a stable state. A stable state is, for example, when the pellets are allowed to free-fall from 2 cm above the stand and remain stationary.

[0039] In this disclosure, bulk density (25°C) is a value measured and calculated in accordance with JIS-K-7365.

[0040] <Sealant film> The sealant film comprises a heat-seal layer containing a non-melt-type recycled polyolefin, a first layer containing a melt-type recycled polyolefin, and a second layer containing recycled polyolefin as needed. Each layer may contain virgin polyolefin to adjust the properties of the sealant film. Melt-process recycled polyolefins and non-melt-process recycled polyolefins are collectively referred to as recycled polyolefins.

[0041] Figure 1 is a schematic cross-sectional view of a sealant film according to an embodiment of the present disclosure. As shown in the figure, the sealant film 10 comprises a heat seal layer 1, a first layer 2, and optionally a second layer 3 in this order. That is, the sealant film 10 further comprises, optionally, a second layer 3 on the side of the first layer 2 opposite to the heat seal layer 1.

[0042] The heat seal layer 1 can also be described as a heat-sealable layer, and is the layer that is heat-sealed when the sealant film 10 is heated by a heat sealer or the like. Because the heat seal layer 1 is a layer containing non-melt-type recycled polyolefin, it is possible to achieve excellent heat sealability while ensuring the amount of recycled resin used in the sealant film 10 as a whole.

[0043] The first layer 2 is a layer that maintains the strength of the sealant film 10, and is also a layer that is laminated with the base layer when it is used as a packaging film. By including melt-process recycled polyolefin in the first layer 2, it is possible to ensure the amount of recycled resin used in the sealant film 10 as a whole while keeping costs down.

[0044] The second layer 3 may be a layer having the same function as the first layer 2, or a layer having the same function as the heat seal layer 1. By including a melt-type recycled polyolefin in the second layer 3, it is possible to ensure the amount of recycled resin used in the sealant film 10 as a whole while keeping costs down. On the other hand, by including a non-melt-type recycled polyolefin in the second layer 3, it is possible to achieve excellent heat sealability while ensuring the amount of recycled resin used in the sealant film 10 as a whole. In the latter case, the sealant film will have layers with heat sealability on both the front and back surfaces, and can therefore be used, for example, as a sealant film for tube containers.

[0045] The components of melt-process recycled polyolefins are derived from melt-process recycled polyolefin pellets, the components of non-melt-process recycled polyolefins are derived from non-melt-process recycled polyolefin pellets, and the components of virgin polyolefins are derived from virgin polyolefin pellets. Therefore, sealant film can be described as a film formed by extrusion molding from the aforementioned pellet raw materials.

[0046] The preferred types and quantities of each polyolefin in the sealant film are the same as the preferred types and quantities of each polyolefin pellet in the pellet raw material, as follows.

[0047] Examples of melt-process recycled polyolefins, non-melt-process recycled polyolefins, and virgin polyolefins include polyethylene, polypropylene, polybutylene, ethylene vinyl acetate, and other polyolefins used in flexible packaging sealant films. Each polyolefin may be the same polyolefin, or it may be polyethylene. Examples of polyethylene include HDPE (high-density polyethylene), LDPE (low-density polyethylene), and LLDPE (linear low-density polyethylene).

[0048] The content of the melt-recycled polyolefin in the first layer may be 80% by mass or more, 90% by mass or more, or 100% by mass, as described above.

[0049] The content of non-melt-type recycled polyolefin in the heat seal layer may be 80% by mass or more, 90% by mass or more, or 100% by mass. Furthermore, the heat seal layer does not need to contain melt-type recycled polyolefin.

[0050] The second layer comprises at least one of melt-process recycled polyolefin and non-melt-process recycled polyolefin. The second layer may be made of the same raw materials as the heat-seal layer. The second layer may contain a melt-process recycled polyolefin, in which case the content of the melt-process recycled polyolefin may be 80% by mass or more, 90% by mass or more, or 100% by mass. The second layer may contain a non-meltable recycled polyolefin, in which case the content of the non-meltable recycled polyolefin may be 80% by mass or more, 90% by mass or more, or 100% by mass.

[0051] If each of the above layers contains virgin polyolefin, there are no particular restrictions on the amount contained in each layer, but it may be 20% by mass or less, 10% by mass or less, or 5% by mass or less.

[0052] Based on the total amount of sealant film, the recycled polyolefin content may be 80% by mass or more, 90% by mass or more, or 100% by mass, from the viewpoint of utilizing recycled resins, etc.

[0053] The thickness of the first layer can be 15 to 150 μm. A thickness of 15 μm or more makes it easier to ensure film strength compared to a thickness of less than 15 μm, while a thickness of 150 μm or less makes it easier to control costs compared to a thickness greater than 150 μm. From these perspectives, the thickness of the first layer may also be 20 to 100 μm.

[0054] The thickness of the heat seal layer can be 5 to 100 μm. A heat seal layer thickness of 5 μm or more makes it easier to obtain heat-seal strength compared to a thickness of less than 5 μm, while a heat seal layer thickness of 100 μm or less makes heat sealing easier compared to a thickness greater than 100 μm. From these perspectives, the thickness of the heat seal layer may also be 20 to 100 μm.

[0055] The ratio of the thickness of the heat seal layer to the thickness of the first layer (thickness of the heat seal layer / thickness of the first layer) can be between 0.2 and 1. A thickness ratio of 0.2 or more tends to improve film formation compared to a ratio of less than 0.2, while a thickness ratio of 1 or less tends to reduce costs compared to a ratio greater than 1. From these perspectives, the thickness ratio may be between 0.2 and 0.5, or between 0.25 and 0.4.

[0056] The thickness of the second layer can be 5 to 70 μm. A second layer thickness of 5 μm or more tends to improve film formation compared to a thickness of less than 5 μm, while a second layer thickness of 70 μm or less tends to reduce costs compared to a thickness greater than 70 μm. From these viewpoints, the thickness of the second layer may also be 10 to 50 μm. From the viewpoint of suppressing film curling, the thickness of the second layer may be the same as the thickness of the heat seal layer.

[0057] The thickness of the sealant film is adjusted according to the size of the packaging film, so there are no particular restrictions, but it may be, for example, 30-300 μm or 30-200 μm.

[0058] <Packaging film> The packaging film comprises the sealant film and the base layer described above. In particular, packaging films in which the melt-process recycled polyolefin, non-melt-process recycled polyolefin, and virgin polyolefin, as well as the base layer, all contain polyethylene, can be said to be single-material packaging films and have excellent recyclability.

[0059] The sealant film and the substrate layer may be laminated together via an adhesive such as a urethane-based adhesive, epoxy-based adhesive, or silicone-based adhesive (these may also be barrier adhesives). In this case, the bonding surface of the two may be treated to improve the coating performance (wettability) of the adhesive. Examples of such treatments include corona discharge treatment, ozone treatment, and application of an anchor coating agent.

[0060] The base layer may have a printed layer for purposes such as displaying information about the contents, improving the identifiability and concealment of the contents, and enhancing the design of the packaging bag. The printed layer may be formed, for example, on the sealant film side of the base layer.

[0061] The packaging film may further include layers that are commonly found in packaging films, such as a barrier layer (e.g., a vapor-deposited layer, a barrier coating), a surface protection layer, and a surface functional layer (e.g., a matte layer). [Examples]

[0062] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0063] (Preparing the pellets) Virgin polyethylene pellets: LLDPE (density 0.916, MFR 2.3) pellets. The average diameter is 4.8 mm and the bulk density is 0.52 g / mL. Melt-type recycled polyethylene pellets: Recycled resin pellets produced by a melt-type pelletizer from films manufactured using the above-mentioned virgin polyethylene pellets as raw material pellets. The average diameter is 4.5 mm and the bulk density is 0.50 g / mL. Non-melt recycled polyethylene pellets: Recycled resin pellets produced by a non-melt pelletizer from a film manufactured using the above-mentioned virgin polyethylene pellets as raw material pellets. The average diameter is 6.9 mm and the bulk density is 0.24 g / mL.

[0064] (Manufacturing of sealant film) The virgin polyethylene pellets, molten recycled polyethylene pellets, and non-molten recycled polyethylene pellets were mixed in the mixing ratios shown in Table 1 to prepare pellet raw materials. Using these, polyethylene sealant films having a predetermined thickness for each layer were manufactured in a multilayer inflation film deposition machine.

[0065] In Table 1, "P content" refers to the amount of each pellet relative to the total amount of pellet raw materials, or the amount of resin derived from each pellet relative to the total amount of sealant film.

[0066] (Various evaluations) Table 1 shows the results of evaluating each film according to the following evaluation criteria. The sealant film in the example can be said to be a film that makes full use of recycled resin while maintaining an excellent balance between cost and heat sealability.

[0067] - Heat sealable (Heat seal temperature: 130℃) - ○...The heat sealability was good. ×...The heat sealability was poor. -Recyclability (amount of recycled resin used)- ○...The amount of recycled resin used, based on the total amount of film, was 80% by mass or more. ×...The amount of recycled resin used, based on the total amount of film, was less than 80% by mass. -cost- ○...Among those with a ○ rating for recyclability, the amount of melt-process recycled resin used, based on the total amount of film, was 40% by mass or more.

[0068] [Table 1] [Explanation of Symbols]

[0069] 1...Heat seal layer, 2...First layer, 3...Second layer, 10...Sealant film.

Claims

1. A sealant film comprising a first layer containing a melt-type recycled polyolefin and a heat-seal layer containing a non-melt-type recycled polyolefin.

2. The sealant film according to claim 1, wherein the content of the non-meltable recycled polyolefin is 80% by mass or more based on the total amount of the heat seal layer.

3. The sealant film according to claim 1, wherein the heat seal layer does not contain the molten recycled polyolefin.

4. The sealant film according to claim 1, wherein the content of the melt-type recycled polyolefin is 80% by mass or more, based on the total amount of the first layer.

5. The sealant film according to claim 1, further comprising a second layer containing recycled polyolefin on the side of the first layer opposite to the heat-seal layer side.

6. The sealant film according to claim 1, wherein the melt-type recycled polyolefin and the non-melt-type recycled polyolefin are polyethylene.

7. A packaging film comprising a sealant film and a base layer according to any one of claims 1 to 6.

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