Method for manufacturing a single-layer sealant film, single-layer sealant film, and packaging film

Abstract

To provide a method for manufacturing a single-layer sealant film that is capable of producing a single-layer sealant film with good appearance and sealing properties despite using recycled resin, and that also exhibits good film formation suitability during extrusion. [Solution] A method for manufacturing a single-layer sealant film, comprising the step of manufacturing a resin film by extrusion molding from pellet raw materials including virgin resin pellets (PA), melt-type recycled resin pellets (PB), and non-melt-type recycled resin pellets (PC).

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a single-layer sealant film, a single-layer sealant film, and a packaging film. [Background technology]

[0002] A sealant film is known that is characterized by having an intermediate layer containing recycled polyethylene between two virgin polyethylene layers, a first virgin polyethylene layer and a second virgin polyethylene layer (for example, Patent Document 1). Although such a sealant film is suitable from the viewpoint of utilizing recycled resin, its multilayer structure may reduce the transparency of the film. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2022 / 124229 [Patent Document 2] International Publication No. 2022 / 176171 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Therefore, the inventors attempted to produce a single-layer sealant film using recycled resin. However, they found that when using pellets of recycled resin obtained through a melting process (melt-type recycled resin), the film was prone to appearance defects and sealing defects caused by gel, fisheye, yellowing, etc. Therefore, they reconsidered the recycled resin used as the raw material and attempted to produce the film again by extrusion molding using pellets of recycled resin obtained without a melting process (non-melt-type recycled resin: see, for example, Patent Document 2), but found that film formation defects were prone to occur.

[0005] This disclosure is made in view of the above circumstances and aims to provide a method for manufacturing a single-layer sealant film that is capable of producing a single-layer sealant film with good appearance and sealing properties despite using recycled resin, and that also has good film formation suitability during extrusion formation. This disclosure also aims to provide single-layer sealant films and packaging films. [Means for solving the problem]

[0006] The inventors diligently investigated the relationship between the physical properties of recycled pellets to be used in combination with virgin pellets and the properties of the resulting sealant film. They found that using molten recycled pellets, which have good film-forming properties but are prone to gel formation, fisheye formation, and yellowing due to thermal history, and non-molten recycled pellets, which are not affected by thermal history but generally have low bulk density and tend to have poor film-forming properties, in combination is important to achieve both good appearance, sealing properties and film-forming properties, leading to this disclosure.

[0007] The summary of this disclosure is as follows: [1] A method for manufacturing a single-layer sealant film, comprising a step of manufacturing a resin film by extrusion molding from pellet raw materials including virgin resin pellets (PA), melt-type recycled resin pellets (PB), and non-melt-type recycled resin pellets (PC). [2] The manufacturing method according to [1], wherein the mass ratio of PC to PB in the pellet raw material (PB:PC) is 20:80 to 80:20. [3] The manufacturing method according to [1] or [2], wherein the mass ratio of PC to PB in the pellet raw material (PB:PC) is 20:80 to 60:40. [4] The manufacturing method according to any one of [1] to [3], wherein the content of PA in the pellet raw material is 80% by mass or less. [5] The manufacturing method according to [4], wherein the content of PA in the pellet raw material is 50% by mass or more. [6] The manufacturing method according to any one of [1] to [5], wherein the temperature difference between the highest and lowest melting points of PA, PB, and PC is 40°C or less. (However, the melting point refers to the temperature defined by the endothermic peak above 80°C in the DSC curve obtained by differential scanning calorimetry.) [7] A manufacturing method according to any one of [1] to [6], wherein the PA, the PB, and the PC are polyethylene. [8] A single-layer sealant film comprising virgin resin (A), melt-type recycled resin (B), and non-melt-type recycled resin (C). [9] The single-layer sealant film according to [8], wherein the mass ratio of C to B (B:C) is 20:80 to 80:20.

[10] The single-layer sealant film according to [8] or [9], wherein the mass ratio of C to B (B:C) is 20:80 to 60:40.

[11] A single-layer sealant film according to any one of [8] to

[10] , wherein the content of A is 80% by mass or less.

[12] The single-layer sealant film according to

[11] , wherein the content of A is 50% by mass or more.

[13] A single-layer sealant film according to any one of [8] to

[12] , wherein the temperature difference between the highest and lowest melting points of A, B, and C is 40°C or less. (However, the melting point refers to the temperature defined by the endothermic peak above 80°C in the DSC curve obtained by differential scanning calorimetry.)

[14] A single-layer sealant film according to any one of [8] to

[13] , wherein A, B, and C are polyethylene.

[15] The single-layer sealant film and substrate layer described in any one of [8] to

[14] , A packaging film in which the aforementioned A, B, and C, and the base layer, contain polyethylene. [Effects of the Invention]

[0008] According to the present disclosure, there is provided a method for manufacturing a single-layer sealant film that can produce a single-layer sealant film with good appearance and sealing properties despite using recycled resin, and that also has good film-forming suitability during extrusion molding. Also, according to the present disclosure, a single-layer sealant film and a packaging film are provided.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, preferred embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments.

[0010] <Method for Manufacturing a Single-Layer Sealant Film> The method for manufacturing a single-layer sealant film includes a step of manufacturing a resin film by extrusion molding from pellet raw materials including virgin resin pellets (PA), melt-type recycled resin pellets (PB), and non-melt-type recycled resin pellets (PC).

[0011] In the step of manufacturing a resin film by extrusion molding from pellet raw materials, a general screw extruder used in a T-die molding method, an inflation molding method, or the like can be used.

[0012] Examples of the resin included in the virgin resin pellets (PA), melt-type recycled resin pellets (PB), and non-melt-type recycled resin pellets (PC) include polyolefins used for soft packaging sealant films, such as polyethylene, polypropylene, polybutylene, and ethylene vinyl acetate. In particular, from the viewpoint of excellent recyclability, each pellet may contain the same resin and may contain polyethylene. Examples of polyethylene include HDPE (high-density polyethylene), LDPE (low-density polyethylene), and LLDPE (linear low-density polyethylene).

[0013] The virgin resin pellets (PA) are pellets manufactured from virgin resin. Virgin resin is a resin directly synthesized from petroleum or fossil fuel.

[0014] Examples of the shape of virgin resin pellets include granular, columnar, etc. having a circular, oval or elliptical cross section.

[0015] The average diameter of virgin resin pellets can be 1 to 10 mm. When the average diameter is 1 mm or more, it is less likely to scatter during handling compared to the case where it is less than 1 mm. On the other hand, when the average diameter is 10 mm or less, the transportability during production is good compared to the case where it exceeds 10 mm. From these viewpoints, the average diameter of virgin resin pellets may be 2 to 6 mm.

[0016] The bulk density of virgin resin pellets can be 0.5 to 0.8 g / mL. When the bulk density is 0.5 g / mL or more, it is less likely to scatter during handling compared to the case where it is less than 0.5 g / mL. On the other hand, when the bulk density is 0.8 g / mL or less, clogging in the apparatus during production is less likely to occur compared to the case where it exceeds 0.8 g / mL. From these viewpoints, the bulk density of virgin resin pellets may be 0.5 to 0.7 g / mL.

[0017] The melt-type recycled resin pellets (PB) are pellets produced by a pellet manufacturing process that melts waste resin films, and specifically, are roughly granular pellets produced by a melt-type pelletizer. The melt-type recycled resin pellets are produced by heating and melting waste resin films and then cooling and solidifying them.

[0018] Examples of waste resin films include loss materials (PIR: post-industrial recycling materials) generated during resin film production, and specifically, defective film, damaged film, and so-called ear loss (fine cuttings at both ends of the film). The waste resin film may be obtained by slitting the resin film during the manufacturing process. The waste resin film may also be a material after consumer use (PCR: post-consumer recycling material).

[0019] Examples of the shape of melt-type recycled resin pellets include granular, columnar, etc. having a circular, oval or elliptical cross section.

[0020] The average diameter of melt-process recycled resin 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 resin pellets may also be 2 to 6 mm.

[0021] The bulk density of melt-process recycled resin 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 bulk 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 bulk density greater than 0.8 g / mL. From these perspectives, the bulk density of melt-process recycled resin pellets may also be 0.5 to 0.7 g / mL.

[0022] Non-melting recycled resin pellets (PC) are pellets manufactured using a pellet manufacturing process that does not melt waste resin film. Specifically, they are roughly granular pellets produced by a non-melting pelletizer. Therefore, "non-melting" pellets are different from the aforementioned "melting" pellets.

[0023] Examples of waste resin films include those listed in the section on melt-recycled resin pellets.

[0024] In particular, in non-melting recycled resin pellets, selvage loss is suitably used as waste resin film. The thickness of the waste resin film may be 5 to 200 μm. The width of the waste resin film may be 5 to 500 mm, or 5 to 50 mm from the viewpoint of ease of making the twisted cord described later.

[0025] Non-melting recycled resin pellets have a low bulk density and a generally granular to columnar shape, differing in form from recycled resin pellets obtained through heating and melting. Non-melting recycled resin pellets may contain fine fragments of resin twisted cord. Here, "resin twisted cord" refers to a cord made by stretching waste resin film and twisting it while rotating it with the stretching direction of the cord as the axis of rotation. "Fine fragments" refer to the resin twisted cord that has been cut in a direction perpendicular to the stretching direction of the cord.

[0026] In the fine fragments, the cords (resin cords) that make up the twisted cord may be partially crimped together, that is, the non-melting recycled resin pellets may contain fine fragments of resin-crimped twisted cords.

[0027] The cords that make up the twisted cord may themselves be stretched; in other words, the twisted cord may be made by twisting stretched resin cords together. "Stretching" here refers to stretching processes such as uniaxial stretching or biaxial stretching that are performed on ordinary resin films.

[0028] 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.

[0029] Such recycled resin pellets can be manufactured, for example, based on the contents of International Publication No. 2022 / 176171.

[0030] The average diameter of non-melt recycled resin pellets can be 4 to 10 mm. An average diameter of 4 mm or more makes them less likely to scatter 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 resin pellets may also be 5 to 9 mm.

[0031] The bulk density of non-melt recycled resin 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 resin pellets and melt-type recycled resin 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 resin pellets can be 0.15 to 0.3 g / mL, and may also be 0.2 to 0.3 g / mL.

[0032] The bulk density of non-melt recycled resin 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 resin pellets. Because non-melt recycled resin 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 resin pellets and melt-process recycled resin pellets.

[0033] The mass ratio (PB:PC) of non-melt recycled resin pellets (PC) to molten recycled resin pellets (PB) in the pellet raw material may be 20:80 to 80:20. When the proportion of molten recycled resin pellets (PB) is above the lower limit, film formation suitability tends to be good, and when it is below the upper limit, appearance and sealing performance tend to be good. From this viewpoint, the above mass ratio (PB:PC) may be 20:80 to 60:40, or 40:60 to 60:40.

[0034] The content of virgin resin pellets (PA) in the pellet raw material may be 80% by mass or less. This makes it easier to recycle. From this viewpoint, the above content may be 75% by mass or less. The content of virgin resin pellets (PA) in the pellet raw material may be 50% by mass or more. This makes it easier to achieve both a good appearance, sealing properties, and film-forming suitability. From this viewpoint, the above content may be 60% by mass or more, or even 70% by mass or more.

[0035] Melting point T of virgin resin pellets (PA) A , the melting point T of melt-type recycled resin pellets (PB) B , and the melting point T of non-melting recycled resin pellets (PC) C The temperature difference between the highest and lowest melting points may be within 40°C. This tends to result in good sealing properties. From this viewpoint, the above temperature difference may be within 30°C or even within 25°C. There is no particular limit to the lower limit of the temperature difference, but it can be, for example, 0°C. However, the melting point is defined as the temperature at which the endothermic peak peaks above 80°C appear on the DSC curve obtained by differential scanning calorimetry (heating rate of 10°C / min, heating from 0°C to 200°C). Each pellet may have multiple endothermic peaks; in this case, the highest and lowest melting points can be determined by comparing the endothermic peaks of each pellet. The same pellet may have both the highest and lowest melting points.

[0036] 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 is performed with approximately 50 pellets in a stable state. A stable state is, for example, when the pellet is allowed to free-fall from 2 cm above the stand and remains stationary.

[0037] In this disclosure, bulk density (25°C) is a value measured and calculated in accordance with JIS-K-7365.

[0038] <Single-layer sealant film> The single-layer sealant film comprises virgin resin (A), melt-type recycled resin (B), and non-melt-type recycled resin (C).

[0039] Virgin resin (A) is derived from the virgin resin pellets (PA), molten recycled resin (B) from the molten recycled resin pellets (PB), and non-molten recycled resin (C) from the non-molten recycled resin pellets (PC). Therefore, a single-layer sealant film can be described as a film extruded from pellet raw materials containing virgin resin pellets (PA), molten recycled resin pellets (PB), and non-molten recycled resin pellets (PC).

[0040] The preferred types and amounts of each resin in a single-layer sealant film are the same as the preferred types and amounts of each resin pellet in the pellet raw material, as follows.

[0041] Examples of virgin resins (A), melt-recycled resins (B), and non-melt-recycled resins (C) include polyolefins used in flexible packaging sealant films, such as polyethylene, polypropylene, polybutylene, and ethylene vinyl acetate. Each resin may be the same resin, and may also be polyethylene. Examples of polyethylene include HDPE (high-density polyethylene), LDPE (low-density polyethylene), and LLDPE (linear low-density polyethylene).

[0042] In a single-layer sealant film, the mass ratio (B:C) of non-melt recycled resin (C) to melt recycled resin (B) may be 20:80 to 80:20, 20:80 to 60:40, or 40:60 to 60:40.

[0043] In a single-layer sealant film, the content of virgin resin (A) may be 80% by mass or less, 75% by mass or less, 50% by mass or more, 60% by mass or more, or 70% by mass or more.

[0044] The melting point T of virgin resin (A) A , melting point T of melt-type recycled resin (B) B , and the melting point T of non-melting recycled resin (C) CThe temperature difference between the highest and lowest melting points may be 40°C or less, 30°C or less, or 25°C or less. There is no particular lower limit to the temperature difference, but it can be, for example, 0°C. Here, the melting point and temperature difference are as described in the section on pellet raw materials.

[0045] The thickness of the single-layer 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 to 200 μm.

[0046] <Packaging film> The packaging film comprises the above-mentioned single-layer sealant film and base layer. In particular, packaging films in which virgin resin (A), melt-recycled resin (B), non-melt-recycled resin (C), and base layer are polyethylene can be said to be single-material packaging films and have excellent recyclability.

[0047] A single-layer sealant film and a 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, treatment may be applied to the bonding surface of the two 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.

[0048] 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 single-layer sealant film side of the base layer.

[0049] A single-layer sealant film may have a layer containing virgin resin (A) on at least one side. This tends to improve sealing performance.

[0050] 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]

[0051] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0052] (Preparation of Pellets) Virgin polyethylene pellets (PA): Pellets of LLDPE (density 0.916, MFR 2.3). Melt recycled polyethylene pellets (PB): Recycled resin pellets produced by a melt pelletizer from a film manufactured using the above PA as raw material pellets. Non-melt recycled polyethylene pellets (PC): Recycled resin pellets produced by a non-melt pelletizer from a film manufactured using the above PA as raw material pellets.

[0053] (Measurement of Melting Point) For each of the pellets PA, PB, and PC, differential scanning calorimetry (heating rate 10 °C / min, heating from 0 °C to 200 °C) was performed, and the temperature defined by the peak of the endothermic peak at 80 °C or higher from the obtained DSC curve was taken as the melting point of each pellet. It is presumed that the difference in melting point among the pellets is due to the change in the crystal structure of the resin by the recycling process. T A : Maximum 117 °C, minimum 97 °C T B : Maximum 115 °C, minimum 108 °C T C : Maximum 119 °C, minimum 102 °C

[0054] (Manufacture of Sealant Film) The above PA, PB, and PC were mixed to prepare a pellet raw material, and using this, a recycled polyethylene sealant film was manufactured with a single-layer inflation film forming machine. The mixing ratio and melting point information of each pellet are shown in Table 1. On the right side of the melting point, the symbols (A, B, and C) corresponding to the pellet raw materials (PA, PB, and PC) indicating the melting point are shown.

[0055] In Table 1, "A content ratio" refers to the amount of virgin polyethylene pellets (PA) based on the total amount of pellet raw materials (total amount of PA, PB, and PC), or the amount of virgin polyethylene (A) based on the total amount of sealant film. In Table 1, "B:C mixing ratio" refers to the mass ratio of non-melt-type recycled resin pellets (PC) to molten-type recycled resin pellets (PB) in the pellet raw material, or the mass ratio of non-melt-type recycled polyethylene (C) to molten-type recycled polyethylene (B) in the sealant film.

[0056] (Various evaluations) Table 1 shows the results of evaluating each film using the following evaluation criteria. For Comparative Example 3, which could not be formed into a film, no evaluation other than film formation suitability was performed.

[0057] -Appearance Evaluation- A... There were very few gels or fisheyes, and no yellowing was observed visually. B...There were few gels or fish eyes, and almost no yellowing was observed visually. C... Significant gel formation or fisheye was observed, or yellowing was visible to the naked eye. -Thermal weldability- A... No residual high-melting-point components or excessive melting of low-melting-point components occurred during sealing. C...During sealing, residual high-melting-point components or excessive melting of low-melting-point components occurred. -Recyclability- A...The amount of recycled resin used, based on the total amount of film, was 20% or more. C... The amount of recycled resin used, based on the total amount of film, was less than 20%. -Film-forming suitability- A...Film formation was possible with almost no fluctuation in resin pressure during the process. B...Although there were some fluctuations in resin pressure during film formation, film formation was possible. C…Film formation was impossible due to large fluctuations in resin pressure during film formation.

[0058] [Table 1]

Claims

1. A method for manufacturing a single-layer sealant film, comprising a step of manufacturing a resin film by extrusion molding from pellet raw materials including virgin resin pellets (PA), melt-type recycled resin pellets (PB), and non-melt-type recycled resin pellets (PC).

2. The manufacturing method according to claim 1, wherein the mass ratio of PC to PB in the pellet raw material (PB:PC) is 20:80 to 80:

20.

3. The manufacturing method according to claim 1 or 2, wherein the content of PA in the pellet raw material is 80% by mass or less.

4. The manufacturing method according to claim 1 or 2, wherein the temperature difference between the highest and lowest melting points of PA, PB, and PC is 40°C or less. (However, the melting point is defined as the temperature at which the endothermic peak of the DSC curve obtained by differential scanning calorimetry reaches 80°C or higher.)

5. The manufacturing method according to claim 1 or 2, wherein the PA, PB, and PC include polyethylene.

6. A single-layer sealant film comprising virgin resin (A), melt-type recycled resin (B), and non-melt-type recycled resin (C).

7. The single-layer sealant film according to claim 6, wherein the mass ratio of C to B (B:C) is 20:80 to 80:

20.

8. The single-layer sealant film according to claim 6 or 7, wherein the content of A is 80% by mass or less.

9. The single-layer sealant film according to claim 6 or 7, wherein the temperature difference between the highest and lowest melting points of A, B, and C is 40°C or less. (However, the melting point refers to the temperature defined by the endothermic peak apex of the DSC curve obtained by differential scanning calorimetry, which is 80°C or higher.)

10. The single-layer sealant film according to claim 6 or 7, wherein A, B, and C contain polyethylene.

11. The single-layer sealant film and substrate layer according to claim 6 or 7 are provided, A packaging film in which the aforementioned A, B, and C, and the base layer, contain polyethylene.

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