WO2025258481A1 - Method for producing recycled polyolefin film, and pellet raw material for extrusion molding of recycled polyolefin film - Google Patents

Abstract

The present invention provides a method for producing a recycled polyolefin film, the method comprising producing a polyolefin film through extrusion molding from a pellet raw material containing virgin polyolefin pellets and non-melting recycled polyolefin pellets; the bulk density of the recycled polyolefin pellets according to JIS-K -7365 is 0.35 g/ml or less; the bulk density of the pellet raw material is 0.4 g/mL or more.

Description

Manufacturing method for recycled polyolefin film, and pellet raw material for extrusion molding of recycled polyolefin film

This disclosure relates to a method for producing recycled polyolefin film and pellet raw materials for extrusion molding of recycled polyolefin film.

When producing recycled pellets using waste plastics such as polyolefins as raw materials, a known method involves first heating and melting the waste plastic, then extruding it into water, etc., and cooling it to form pellets (see, for example, Patent Document 1).

Furthermore, when recycled pellets are produced using waste plastics as raw materials, a method is known in which an antioxidant is added to the raw materials and then heated and melted to obtain thermoplastic resin composition molded articles with the quality and remaining life required for the intended use (see, for example, Patent Document 2).

International Publication No. 2023/053757 Japanese Patent Application Laid-Open No. 2003-285328 International Publication No. 2022/176171

First, in the above-mentioned method, the deterioration of plastic progresses during the heat-melting process, and the final product obtained using recycled pellets that have undergone heat-melting may have a poor appearance. For example, if the final product is a plastic film, not only may the number of defects such as gels and fish eyes increase, but yellowing may also occur.

As a result, attempts are being made to use non-melt pelletizers, which are capable of pelletizing waste plastic without applying excessive heat. Non-melt pelletizers can produce recycled pellets, for example, by stretching, twisting, shredding, and other processes on waste plastic film. However, it has been found that when attempting to extrude film using recycled pellets obtained in this way as a raw material, film formation defects can occur.

The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for producing recycled polyolefin film that can produce a film with a good appearance and suppressed yellowing, and that has excellent film formation suitability during extrusion molding.
Another object of the present disclosure is to provide a pellet raw material for extrusion molding of recycled polyolefin film that can be used in the manufacturing method.

Second Problem The present inventors have investigated the production of recycled polyolefin films from recycled pellets made from polyolefins. From the viewpoint of production efficiency, it is desirable to produce recycled polyolefin films without adding any additional antioxidants.

This disclosure provides a method for producing recycled polyolefin film that can produce a film that is inhibited from oxidative degradation without the need to add additional antioxidants.

Third Problem The present inventors have investigated the production of recycled polyolefin films from recycled pellets made from polyolefins. However, antioxidants are added to polyolefin pellets to prevent them from turning yellow. When recycled pellets are produced from waste plastics, the antioxidants are consumed in the resulting recycled pellets. Therefore, recycled polyolefin films obtained from such recycled pellets turn yellowish. When recycled polyolefin films are used for applications such as transparent bags, a yellowish film is undesirable because it raises suspicions of deterioration of the contents.

This disclosure provides a method for producing recycled polyolefin film that can produce films with reduced yellowing even when using recycled pellets.

First Invention Group With regard to the first problem, one aspect of the present disclosure provides a method for producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
Provided is a method for producing a recycled polyolefin film in which the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365.

The inventors have conducted extensive research into the relationship between the properties of recycled pellets and their suitability for film formation during extrusion molding, and have found that the apparent density (bulk density) of the pellet raw material affects the suitability for film formation.
Generally, recycled pellets obtained using a non-melting pelletizer have a low apparent density. When pellet raw material consisting of recycled pellets with such a low apparent density is used, the amount of resin transported per unit time is very small when the pellets are fed from a hopper and transported through the extruder screw. As a result, it has been found that a sufficient film formation speed cannot be achieved, which tends to result in film formation defects. The inventors have achieved the above invention, which can effectively address the appearance and film formation defects by adding a predetermined amount of high-bulk-density virgin pellets to low-bulk-density recycled pellets to adjust the variation in bulk density as pellet raw material.

The manufacturing method disclosed herein can be said to be a method for manufacturing recycled polyolefin film that can produce films with a good appearance and reduced yellowing, and that also has excellent film-forming suitability during extrusion molding.

In one embodiment of the above manufacturing method, the content of recycled polyolefin pellets in the pellet raw material may be 5 to 50 mass%.

In one embodiment of the above manufacturing method, the recycled polyolefin pellets may include fine fragments of polyolefin twisted cord.

In one embodiment of the above manufacturing method, the average diameter of the recycled polyolefin pellets may be 4 to 10 mm.

In one embodiment of the above manufacturing method, the manufacturing method may include a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

In one aspect of the above manufacturing method, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction.

One aspect of the present disclosure is a pellet feedstock comprising virgin polyolefin pellets and non-melt recycled polyolefin pellets,
The present invention provides a pellet raw material for extrusion molding of recycled polyolefin film, in which the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365.

Such pellet raw materials can be used in the above-mentioned manufacturing method, making it possible to produce films with a good appearance and reduced yellowing, and they also have excellent suitability for film formation during extrusion molding.

In one embodiment of the above pellet raw material, the recycled polyolefin pellets may include fine fragments of polyolefin twisted cord.

Second Invention Group With regard to the first problem, one aspect of the present disclosure provides a method for producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
Provided is a method for producing a recycled polyolefin film, in which the angle of repose of the recycled polyolefin pellets exceeds 30° and the angle of repose of the pellet raw material is 30° or less.

The inventors have conducted extensive research into the relationship between the properties of recycled pellets and their suitability for film formation during extrusion molding, and have found that the angle of repose of the pellet raw material affects the suitability for film formation.
Generally, recycled pellets obtained using a non-melting pelletizer have a large angle of repose. When pellet raw material consisting of recycled pellets with such a large angle of repose is used, the amount of resin transported per unit time is very small when it is fed from the hopper and transported through the extruder screw. As a result, it has been found that a sufficient film formation rate cannot be achieved, which tends to result in poor film formation. The inventors have developed the above invention, which can effectively address the appearance and film formation problems by adding a predetermined amount of virgin pellets with a small angle of repose to recycled pellets with a large angle of repose to adjust the variation in the angle of repose of the pellet raw material.

The manufacturing method disclosed herein can be said to be a method for manufacturing recycled polyolefin film that can produce films with a good appearance and reduced yellowing, and that also has excellent film-forming suitability during extrusion molding.

In one embodiment of the above manufacturing method, the content of recycled polyolefin pellets in the pellet raw material may be 5 to 50 mass%.

In one embodiment of the above manufacturing method, the recycled polyolefin pellets may include fine fragments of polyolefin twisted cord.

In one embodiment of the above manufacturing method, the average diameter of the recycled polyolefin pellets may be 4 to 10 mm.

In one embodiment of the above manufacturing method, the manufacturing method may include a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

In one aspect of the above manufacturing method, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction.

One aspect of the present disclosure is a pellet feedstock comprising virgin polyolefin pellets and non-melt recycled polyolefin pellets,
Provided is a pellet raw material for extrusion molding of recycled polyolefin film, in which the angle of repose of the recycled polyolefin pellets exceeds 30° and the angle of repose of the pellet raw material is 30° or less.

Such pellet raw materials can be used in the above-mentioned manufacturing method, making it possible to produce films with a good appearance and reduced yellowing, and they also have excellent suitability for film formation during extrusion molding.

In one embodiment of the above pellet raw material, the recycled polyolefin pellets may include fine fragments of polyolefin twisted cord.

Third Invention Group With regard to the second problem, one aspect of the present disclosure relates to the following method for producing a recycled polyolefin film.
[1] A process for producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the ratio (T2/T1) represented by the following formula (1) is 0.8 or more.
T2/T1...(1)
[In formula (1), T1 represents the oxidation induction time of non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C before pelletization, and T2 represents the oxidation induction time of non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C.]
[2] The manufacturing method according to [1], wherein the content of non-melting recycled polyolefin pellets in the pellet raw material is 10 to 50% by mass.
[3] The manufacturing method according to [1] or [2], wherein the non-melting recycled polyolefin pellets include fine fragments of polyolefin twisted cord.
[4] The method according to any one of [1] to [3], wherein the average diameter of the non-melting recycled polyolefin pellets is 4 to 10 mm.
[5] The manufacturing method according to any one of [1] to [4], comprising a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.
[6] The manufacturing method according to [5], wherein the process for producing non-melt recycled polyolefin pellets comprises stretching a waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it around the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.

Fourth Invention Group With regard to the third problem, one aspect of the present disclosure relates to the following method for producing a recycled polyolefin film.
[1] A method for producing a recycled polyolefin film, comprising a step of producing a polyolefin film by extrusion molding from pellet raw materials containing virgin polyolefin pellets and non-melting recycled polyolefin pellets.
[2] The method for producing a recycled polyolefin film according to [1], wherein the non-melting recycled polyolefin pellets satisfy the following formula (2):
YI1-YI2≦0.6...(2)
[In formula (2), YI1 represents the yellow index of a first test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 80% by mass of virgin polyolefin pellets for testing and 20% by mass of the non-melting recycled polyolefin pellets, and YI2 represents the yellow index of a second test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 100% by mass of the virgin polyolefin pellets for testing.]
[3] The manufacturing method according to [1] or [2], wherein the content of the non-melting recycled polyolefin pellets in the pellet raw material is 5 to 50% by mass.
[4] The manufacturing method according to any one of [1] to [3], wherein the non-melting recycled polyolefin pellets include fine fragments of polyolefin twisted cord.
[5] The method according to any one of [1] to [4], wherein the average diameter of the non-melting recycled polyolefin pellets is 4 to 10 mm.
[6] The manufacturing method according to any one of [1] to [5], comprising a step of producing the non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.
[7] The manufacturing method according to [6], wherein the step of producing the non-melting recycled polyolefin pellets comprises stretching the waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it around the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.

According to the first and second invention groups, which are one aspect of the present disclosure, a method for producing a recycled polyolefin film is provided that can produce a film with a good appearance and suppressed yellowing, and that has excellent film formation suitability during extrusion molding.
The present disclosure also provides a pellet raw material for extrusion molding of recycled polyolefin film that can be used in the manufacturing method.

The third invention group, which is one aspect of the present disclosure, provides a method for producing recycled polyolefin film that can produce a film in which oxidative degradation is suppressed without the need to add an additional antioxidant.

The fourth invention group, which is one aspect of the present disclosure, provides a method for producing recycled polyolefin film that can produce a film with reduced yellowing even when using recycled pellets.

FIG. 1 is a schematic diagram showing a repose angle measuring device according to the second invention group of the present disclosure.

First Invention Group Preferred embodiments of the first invention group of the present disclosure will be described in detail below, although the present disclosure is not limited to the following embodiments.

<Pellet raw materials>
The pellet raw materials are pellet raw materials for extrusion molding of recycled polyolefin films, including virgin polyolefin pellets and non-melting recycled polyolefin pellets.
In the pellet raw material, the bulk density of the recycled polyolefin pellets according to JIS-K-7365 is 0.35 g/mL or less, and the bulk density of the pellet raw material is 0.4 g/mL or more.

Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins synthesized directly from petroleum or fossil fuels. Examples of polyolefins include polyethylene, polypropylene, and polybutylene.

Virgin polyolefin pellets may be granular, cylindrical, or have a circular, oval, or elliptical cross section.

The average diameter of the 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 than pellets less than 1 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the virgin polyolefin pellets may be 2 to 6 mm.

The bulk density of the virgin polyolefin pellets can be 0.5 to 0.8 g/mL. A bulk density of 0.5 g/mL or more means that they are less likely to scatter when handled than pellets with a bulk density of less than 0.5 g/mL. On the other hand, a bulk density of 0.8 g/mL or less means that they are less likely to clog the equipment during production than pellets with a bulk density of more than 0.8 g/mL. From these perspectives, the bulk density of the virgin polyolefin pellets may be 0.5 to 0.7 g/mL.

The recycled polyolefin pellets in the present disclosure are pellets produced by a non-melting pelletizer, specifically pellets produced from waste polyolefin films using a non-melting pelletizer. Such pellets can be called non-melting recycled polyolefin pellets.
In this disclosure, "non-melt type" refers to a method in which the raw materials are not melted in the pellet manufacturing process, while "melt type" refers to a method in which the raw materials are melted in the pellet manufacturing process. Therefore, "non-melt type" pellets and "melt type" pellets are different.

Waste polyolefin film includes waste materials (PIR: post-industrial recycled materials) generated during polyolefin film production, specifically films with poor film formation or damaged films, as well as so-called edge waste (shredded scraps on both ends of the film). Waste polyolefin film may also be obtained by slitting polyolefin film during the manufacturing process. Examples of polyolefins include polyethylene, polypropylene, polybutylene, etc., as mentioned above.

The thickness of the waste polyolefin film may be 5 to 200 μm. The width of the waste polyolefin film may be 5 to 500 mm, or from the perspective of ease of making twisted cords, 5 to 50 mm.

As mentioned above, recycled polyolefin pellets have a low bulk density and a roughly granular to columnar shape, and are different in appearance from recycled polyolefin pellets obtained by heat melting. Recycled polyolefin pellets can also contain fine fragments of twisted polyolefin string. Here, "twisted polyolefin string" refers to waste polyolefin film that has been stretched into a string shape and then twisted by rotating it around the axis of stretching the string. "Fine fragments" refer to the twisted polyolefin string that has been shredded in a direction perpendicular to the direction in which the string was stretched.

In the fine fragments, the strands (polyolefin strands) that make up the twisted strand may be partially crimped together, i.e., the recycled polyolefin pellets may contain fine fragments of polyolefin crimped twisted strands.

The strings that make up the twisted string may themselves be stretched; that is, the twisted string may be made by twisting stretched polyolefin strings. "Stretching" here refers to the uniaxial or biaxial stretching process typically performed on polyolefin films.

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

Such recycled polyolefin pellets can be produced, for example, based on the contents of WO 2022/176171.

The average diameter of the recycled polyolefin pellets can be 4 to 10 mm. An average diameter of 4 mm or more makes them less likely to scatter during handling than pellets less than 4 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the recycled polyolefin pellets may be 5 to 9 mm.

The bulk density of recycled polyolefin pellets is 0.35 g/mL or less, as they are produced using a non-melting pelletizer, and this value is lower than the bulk density of virgin polyolefin pellets. There are no particular restrictions on the lower limit of bulk density, but it can be set to 0.1 g/mL, as this makes it easier to maintain the shape of the pellets in the recycling process described below. From these perspectives, the bulk density of recycled polyolefin pellets can be 0.15 to 0.3 g/mL, or may be 0.2 to 0.3 g/mL.

The bulk density of recycled polyolefin pellets can be adjusted, for example, by adjusting the stretching ratio of the raw film or the pressure applied by the conveying rolls. For example, the bulk density of recycled polyolefin pellets can be increased by increasing the stretching ratio or the pressure applied. Because recycled polyolefin pellets are produced through a recycling process in which the raw film is stretched, twisted, and other processes, they tend to have a lower bulk density than virgin polyolefin pellets.

The pellet raw material may contain virgin polyolefin pellets and recycled polyolefin pellets, or may consist of virgin polyolefin pellets and recycled polyolefin pellets (the total amount of virgin polyolefin pellets and recycled polyolefin pellets is substantially 100% by mass). The content of recycled polyolefin pellets in the pellet raw material may be 5 to 50% by mass. A recycled polyolefin pellet content of 5% by mass or more improves recyclability compared to when it is less than 5% by mass. On the other hand, a recycled polyolefin pellet content of 50% by mass or less improves film-forming suitability during extrusion molding compared to when it is more than 50% by mass. From these perspectives, the recycled polyolefin pellet content may be 10 to 50% by mass, 10 to 30% by mass, 10 to 25% by mass, or 15 to 20% by mass.

The bulk density of the pellet raw material is 0.4 g/mL or more from the viewpoint of improving film-forming suitability. The upper limit of the bulk density is not particularly limited, but can be 0.6 g/mL. From these viewpoints, the bulk density of the pellet raw material can be 0.4 to 0.6 g/mL, or may be 0.4 to 0.5 g/mL.
The bulk density of the pellet material can be adjusted by varying the amount of recycled polyolefin pellets.

In this disclosure, the average diameter is the average value of the maximum and minimum diameters when the pellets are placed on a table and viewed from a direction perpendicular to the table. The maximum and minimum diameters can be measured, for example, using a vernier caliper. The measurement is performed with the pellets in a stable state. A stable state means, for example, allowing the pellets to fall freely from 2 cm above the table and allowing them to come to rest.

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

<Method of manufacturing recycled polyolefin film>
The method for producing a recycled polyolefin film includes a step of producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melt recycled polyolefin pellets.
In the above manufacturing method, the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less, and the bulk density of the pellet raw material is 0.4 g/mL or more, according to JIS-K-7365.

In the process of producing polyolefin film by extrusion molding from pellet raw material, a general screw extruder used in T-die molding, inflation molding, etc. can be used.

The method for producing recycled polyolefin film may include, prior to the above step, a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

Here, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction. This results in recycled polyolefin pellets containing fine fragments of twisted polyolefin strings.

In the above process, the twisted polyolefin strings may be heated and pressurized to at least partially crimp the contact surfaces of the strings (polyolefin strings) that make up the twisted string. This results in recycled polyolefin pellets containing fine fragments of crimped twisted polyolefin strings. Heating the polyolefin strings can be carried out by heating them to their softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film.

<Summary of the first invention group of the present disclosure>
The first invention group of the present disclosure can be summarized as follows, for example.
[1] A process for producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365.
[2] The manufacturing method according to [1], wherein the content of the recycled polyolefin pellets in the pellet raw material is 5 to 50 mass%.
[3] The manufacturing method according to [1] or [2], wherein the recycled polyolefin pellets include fine fragments of polyolefin twisted cord.
[4] The method according to any one of [1] to [3], wherein the average diameter of the recycled polyolefin pellets is 4 to 10 mm.
[5] The manufacturing method according to any one of [1] to [4], comprising a step of producing the non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.
[6] The manufacturing method according to [5], wherein the step of producing the non-melting recycled polyolefin pellets comprises stretching the waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it around the stretching direction as a rotation axis, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.
[7] A pellet raw material containing virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A pellet raw material for extrusion molding of recycled polyolefin film, wherein the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365.
[8] The pellet raw material according to [7], wherein the recycled polyolefin pellets include fine fragments of polyolefin twisted cords.

Second Invention Group Preferred embodiments of the second invention group of the present disclosure will be described in detail below, although the present disclosure is not limited to the following embodiments.

<Pellet raw materials>
The pellet raw materials are pellet raw materials for extrusion molding of recycled polyolefin films, including virgin polyolefin pellets and non-melting recycled polyolefin pellets.
In the pellet raw material, the angle of repose of the recycled polyolefin pellets is more than 30°, and the angle of repose of the pellet raw material is 30° or less.

Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins synthesized directly from petroleum or fossil fuels. Polyolefins include polyethylene, polypropylene, polybutylene, etc.

Virgin polyolefin pellets may be granular, cylindrical, or have a circular, oval, or elliptical cross section.

The average diameter of the 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 than pellets less than 1 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the virgin polyolefin pellets may be 2 to 6 mm.

The angle of repose of virgin polyolefin pellets can be 15 to 40°. An angle of repose of 15° or more ensures granular viscosity compared to when the angle is less than 15°, making them easier to transport. On the other hand, an angle of repose of 40° or less provides better fluidity compared to when the angle is greater than 40°, making them easier to supply from a hopper during production. From these perspectives, the angle of repose of virgin polyolefin pellets may be 18 to 25°.

The recycled polyolefin pellets in the present disclosure are pellets produced by a non-melting pelletizer, specifically pellets produced from waste polyolefin films using a non-melting pelletizer. Such pellets can be called non-melting recycled polyolefin pellets.
In this disclosure, "non-melt type" refers to a method in which the raw materials are not melted in the pellet manufacturing process, while "melt type" refers to a method in which the raw materials are melted in the pellet manufacturing process. Therefore, "non-melt type" pellets and "melt type" pellets are different.

Waste polyolefin film includes waste materials (PIR: post-industrial recycled materials) generated during polyolefin film production, specifically films with poor film formation or damaged films, as well as so-called edge waste (shredded scraps on both ends of the film). Waste polyolefin film may also be obtained by slitting polyolefin film during the manufacturing process. Examples of polyolefins include polyethylene, polypropylene, polybutylene, etc., as mentioned above.

The thickness of the waste polyolefin film may be 5 to 200 μm. The width of the waste polyolefin film may be 5 to 500 mm, or from the perspective of ease of making twisted cords, 5 to 50 mm.

As mentioned above, recycled polyolefin pellets have a roughly granular to columnar shape with a large angle of repose, and are different in appearance from recycled polyolefin pellets obtained by heat melting. Recycled polyolefin pellets can contain fine fragments of twisted polyolefin string. Here, "twisted polyolefin string" refers to waste polyolefin film that has been stretched into a string shape and then twisted by rotating it around the axis of stretching the string. "Fine fragments" refer to the twisted polyolefin string that has been shredded in a direction perpendicular to the direction in which the string was stretched.

In the fine fragments, the strands (polyolefin strands) that make up the twisted strand may be partially crimped together, i.e., the recycled polyolefin pellets may contain fine fragments of polyolefin crimped twisted strands.

The strings that make up the twisted string may themselves be stretched; that is, the twisted string may be made by twisting stretched polyolefin strings. "Stretching" here refers to the uniaxial or biaxial stretching process typically performed on polyolefin films.

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

Such recycled polyolefin pellets can be produced, for example, based on the contents of WO 2022/176171.

The average diameter of the recycled polyolefin pellets can be 4 to 10 mm. An average diameter of 4 mm or more makes them less likely to scatter during handling than pellets less than 4 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the recycled polyolefin pellets may be 5 to 9 mm.

The angle of repose of recycled polyolefin pellets is greater than 30° because they are produced using a non-melting pelletizer, and this value is greater than the angle of repose of virgin polyolefin pellets. There is no particular upper limit to the angle of repose, but it can be set to 50° because it makes it easier to maintain the shape of the pellets in the recycling process described below. From these perspectives, the angle of repose of recycled polyolefin pellets can be greater than 30° and not greater than 50°, or may be greater than 30° and not greater than 35°.

The angle of repose of recycled polyolefin pellets can be adjusted, for example, by adjusting the stretching ratio of the raw film or the pressure applied by the conveying rolls. For example, the angle of repose of recycled polyolefin pellets can be reduced by increasing the stretching ratio or the pressure applied. Because recycled polyolefin pellets are produced through a recycling process in which the raw film is stretched, twisted, and other processes, they tend to have a larger angle of repose than virgin polyolefin pellets.

The pellet raw material may contain virgin polyolefin pellets and recycled polyolefin pellets, or may consist of virgin polyolefin pellets and recycled polyolefin pellets (the total amount of virgin polyolefin pellets and recycled polyolefin pellets is substantially 100% by mass). The content of recycled polyolefin pellets in the pellet raw material may be 5 to 50% by mass. A recycled polyolefin pellet content of 5% by mass or more improves recyclability compared to when it is less than 5% by mass. On the other hand, a recycled polyolefin pellet content of 50% by mass or less improves film-forming suitability during extrusion molding compared to when it is more than 50% by mass. From these perspectives, the recycled polyolefin pellet content may be 10 to 50% by mass, 10 to 30% by mass, 10 to 25% by mass, or 15 to 20% by mass.

The angle of repose of the pellet raw material is 30° or less from the viewpoint of improving film-forming suitability. The lower limit of the angle of repose is not particularly limited, but can be 20°. From these viewpoints, the angle of repose of the pellet raw material can be 20 to 30°, or may be 25 to 28°.
The angle of repose of the pellet raw material can be adjusted by changing the amount of recycled polyolefin pellets.

In this disclosure, the average diameter is the average value of the maximum and minimum diameters when the pellets are placed on a table and viewed from a direction perpendicular to the table. The maximum and minimum diameters can be measured, for example, using a vernier caliper. The measurement is performed with the pellets in a stable state. A stable state means, for example, allowing the pellets to fall freely from 2 cm above the table and allowing them to come to rest.

In this disclosure, the angle of repose is the angle between the horizontal plane and the generatrix of the cone when pellets are dropped onto a horizontal plane from a certain height and deposited in a cone shape. The angle of repose (25°C, 40% RH) is measured as follows.
- Prepare a colorless, transparent acrylic resin box (with a protractor attached to the box).
- A jig is prepared that has side walls and a top plate surrounding the manhole, with a hopper attached to the top plate, and the manhole is placed inside the jig. A shutter is attached to the bottom end of the hopper. The hopper is shaped like a funnel, with two cylinders, one large and one small, connected by a constriction. The diameter of the cylinder at the bottom of the hopper is 33 mm, and the length is 30 mm. The height from the bottom end of the hopper to the bottom of the manhole is 89 mm.
-Put 50g of pellets into the hopper.
- Open the shutter at the bottom of the hopper and let the pellets fall towards the bottom of the manhole.
- Use a protractor to read the angle φ between the bottom of the box and the generatrix of the pellets piled up in a cone shape.

Figure 1 is a schematic diagram showing an apparatus for measuring the angle of repose. The diagram shows the manhole 1, hopper 2, jig 3, and cone-shaped pile of pellets 4 described above.

<Method of manufacturing recycled polyolefin film>
The method for producing a recycled polyolefin film includes a step of producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melt recycled polyolefin pellets.
In the above-mentioned production method, the angle of repose of the recycled polyolefin pellets exceeds 30°, and the angle of repose of the pellet raw material is 30° or less.

In the process of producing polyolefin film by extrusion molding from pellet raw material, a general screw extruder used in T-die molding, inflation molding, etc. can be used.

The method for producing recycled polyolefin film may include, prior to the above step, a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

Here, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction. This results in recycled polyolefin pellets containing fine fragments of twisted polyolefin strings.

In the above process, the twisted polyolefin strings may be heated and pressurized to at least partially crimp the contact surfaces of the strings (polyolefin strings) that make up the twisted string. This results in recycled polyolefin pellets containing fine fragments of crimped twisted polyolefin strings. Heating the polyolefin strings can be carried out by heating them to their softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film.

<Summary of the second invention group of the present disclosure>
The second invention group of the present disclosure can be summarized as follows, for example.
[1] A process for producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the angle of repose of the recycled polyolefin pellets is greater than 30° and the angle of repose of the pellet raw material is 30° or less.
[2] The manufacturing method according to [1], wherein the content of the recycled polyolefin pellets in the pellet raw material is 5 to 50 mass%.
[3] The manufacturing method according to [1] or [2], wherein the recycled polyolefin pellets include fine fragments of polyolefin twisted cord.
[4] The method according to any one of [1] to [3], wherein the average diameter of the recycled polyolefin pellets is 4 to 10 mm.
[5] The manufacturing method according to any one of [1] to [4], comprising a step of producing the non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.
[6] The manufacturing method according to [5], wherein the step of producing the non-melting recycled polyolefin pellets comprises stretching the waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it around the stretching direction as a rotation axis, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.
[7] A pellet raw material containing virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A pellet raw material for extrusion molding of a recycled polyolefin film, wherein the angle of repose of the recycled polyolefin pellets is more than 30° and the angle of repose of the pellet raw material is 30° or less.
[8] The pellet raw material according to [7], wherein the recycled polyolefin pellets include fine fragments of polyolefin twisted cords.

Third Invention Group Preferred embodiments of the third invention group of the present disclosure will now be described in detail, although the present disclosure is not limited to the following embodiments.

<Method of manufacturing recycled polyolefin film>
The method for producing a recycled polyolefin film according to this embodiment includes a step of producing a polyolefin film by extrusion molding from pellet raw materials containing virgin polyolefin pellets and non-melting recycled polyolefin pellets, and the ratio (T2/T1) shown in the following formula (1) is 0.8 or more.
[In formula (1), T1 represents the oxidation induction time of non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C before pelletization, and T2 represents the oxidation induction time of non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C.]

The recycled polyolefin film manufacturing method according to this embodiment has a ratio (T2/T1) of 0.8 or higher. This makes it possible to manufacture a film in which oxidative degradation is suppressed without the need to add additional antioxidants. Furthermore, antioxidants are generally added together with other resins (virgin products). The recycled polyolefin film manufacturing method according to this embodiment does not require the addition of additional antioxidants, so the proportion of recycled polyolefin resin can be increased. Therefore, the recycled polyolefin film manufacturing method according to this embodiment has excellent recyclability.

The pellet raw materials are pellet raw materials for extrusion molding of recycled polyolefin film, including virgin polyolefin pellets and non-melting recycled polyolefin pellets.

Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins synthesized directly from petroleum or fossil fuels. Examples of polyolefins include polyethylene, polypropylene, and polybutylene.

Virgin polyolefin pellets may be granular, cylindrical, or have a circular, oval, or elliptical cross section.

The average diameter of the 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 than pellets less than 1 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the virgin polyolefin pellets may be 2 to 6 mm.

The oxidation induction time for virgin polyolefin pellets may be, for example, 2.2 to 3.5 hours.

In the present disclosure, the oxidation induction time refers to a value measured using a chemiluminescence analyzer under an oxygen atmosphere at 200° C. The oxidation induction time may be measured, for example, under the following measurement conditions.
(Measurement conditions)
Measurement device: Chemiluminescence analyzer CLA-FS4 manufactured by Tohoku Electronics Industry Co., Ltd.
Measurement temperature: 200℃
Sample amount: 0.2 g
Measurement interval: 10 seconds Measurement time: within 8 hours Atmosphere: 100% oxygen

The non-melting recycled polyolefin pellets in the present disclosure are pellets produced by a non-melting pelletizer, specifically pellets produced from waste polyolefin films using a non-melting pelletizer. Such pellets can be called non-melting recycled polyolefin pellets.
In this disclosure, "non-melt type" refers to a method in which the raw materials are not melted in the pellet manufacturing process, while "melt type" refers to a method in which the raw materials are melted in the pellet manufacturing process. Therefore, "non-melt type" pellets and "melt type" pellets are different.

In this disclosure, "non-melt recycled polyolefin pellets in a state before pelletization" refers to the state of the waste polyolefin film that is the raw material.

Waste polyolefin film includes waste materials (PIR: post-industrial recycled materials) generated during the production of polyolefin film, such as poorly formed film, damaged film, and so-called edge waste (shredded scraps from both ends of the film).

As mentioned above, non-melt recycled polyolefin pellets have a roughly granular to columnar shape, and are different in appearance from recycled polyolefin pellets obtained by heat melting. Non-melt recycled polyolefin pellets can contain fine fragments of twisted polyolefin string. Here, "twisted polyolefin string" refers to waste polyolefin film that has been stretched into a string shape and then twisted by rotating it around the axis of stretching the string. "Fine fragments" refer to the twisted polyolefin string that has been shredded in a direction perpendicular to the direction in which the string was stretched.

In the fine fragments, the strands (polyolefin strands) that make up the twisted strand may be partially crimped together, i.e., the non-melting recycled polyolefin pellets may contain fine fragments of polyolefin crimped twisted strands.

The strings that make up the twisted string may themselves be stretched; that is, the twisted string may be made by twisting stretched polyolefin strings. "Stretching" here refers to the uniaxial or biaxial stretching process typically performed on polyolefin films.

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

Such non-melting recycled polyolefin pellets can be produced, for example, based on the contents of WO 2022/176171.

The average diameter of non-melt type recycled polyolefin pellets can be 4 to 10 mm. An average diameter of 4 mm or more makes them less likely to scatter during handling than pellets less than 4 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of non-melt type recycled polyolefin pellets may be 5 to 9 mm.

The above-mentioned non-melt recycled polyolefin pellets, which are obtained by stretching waste polyolefin film into a string-like shape and then twisting it around the axis of rotation in the stretching direction of the string, do not have an oxidation induction time that is too short compared to the non-melt recycled polyolefin pellets in their pre-pelletization state.

The ratio (T2/T1) represented by the above formula (1) is 0.8 or greater, preferably 0.85 or greater, more preferably 0.9 or greater, and even more preferably 0.95 or greater. When (T2/T1) is within this range, oxidative degradation is suppressed. The ratio (T2/T1) may be, for example, 1.4 or less, 1.3 or less, 1.25 or less, 1.2 or less, 1.15 or less, 1.1 or less, 1.05 or less, or 1.0 or less. The ratio (T2/T1) can be adjusted by adjusting the heating temperature or heating time in the recycling process.

In the above formula (1), T1 is preferably 1.25 hours or more, more preferably 1.4 hours or more, and even more preferably 1.5 hours or more. T1 may be, for example, 2.3 hours or less, 2.1 hours or less, or 1.9 hours or less.

In the above formula (1), T2 is preferably 1.2 hours or more, more preferably 1.4 hours or more, and even more preferably 1.6 hours or more. T2 may be, for example, 2.3 hours or less, 2.1 hours or less, or 2.0 hours or less.

The pellet raw material may contain virgin polyolefin pellets and non-melting recycled polyolefin pellets, and may consist of virgin polyolefin pellets and non-melting recycled polyolefin pellets (the total amount of virgin polyolefin pellets and non-melting recycled polyolefin pellets is substantially 100% by mass). The content of non-melting recycled polyolefin pellets in the pellet raw material may be 5 to 50% by mass. A non-melting recycled polyolefin pellet content of 5% by mass or more improves recyclability compared to when it is less than 5% by mass. On the other hand, a non-melting recycled polyolefin pellet content of 50% by mass or less improves film-forming suitability during extrusion molding compared to when it is more than 50% by mass. From these perspectives, the content of non-melting recycled polyolefin pellets may be 10 to 50% by mass, 10 to 30% by mass, 10 to 25% by mass, or 15 to 20% by mass.

In this disclosure, the average diameter is the average value of the maximum and minimum diameters when the pellets are placed on a table and viewed from a direction perpendicular to the table. The maximum and minimum diameters can be measured, for example, using a vernier caliper. The measurement is performed with the pellets in a stable state. A stable state means, for example, allowing the pellets to fall freely from 2 cm above the table and allowing them to come to rest.

In the process of producing polyolefin film by extrusion molding from pellet raw material, a general screw extruder used in T-die molding, inflation molding, etc. can be used.

The method for producing recycled polyolefin film may include, prior to the above step, a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

Here, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction. This results in non-melting recycled polyolefin pellets containing fine fragments of twisted polyolefin strings.

In the above process, the twisted polyolefin strings may be heated and pressurized to at least partially crimp the contact surfaces of the strings (polyolefin strings) that make up the twisted string. This results in non-melting recycled polyolefin pellets containing fine fragments of crimped twisted polyolefin strings. Heating the polyolefin strings can be carried out by heating them to their softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film.

Fourth Invention Group Preferred embodiments of the fourth invention group of the present disclosure will now be described in detail, although the present disclosure is not limited to the following embodiments.

<Method of manufacturing recycled polyolefin film>
The method for producing a recycled polyolefin film according to this embodiment includes a step of producing a polyolefin film by extrusion molding from pellet raw materials containing virgin polyolefin pellets and non-melting recycled polyolefin pellets. By using non-melting recycled polyolefin pellets as the recycled pellets, it is possible to produce a film with reduced yellowing.

The pellet raw materials are pellet raw materials for extrusion molding of recycled polyolefin film, including virgin polyolefin pellets and non-melting recycled polyolefin pellets.

Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins synthesized directly from petroleum or fossil fuels. Polyolefins include polyethylene, polypropylene, polybutylene, etc.

Virgin polyolefin pellets may be granular, cylindrical, or have a circular, oval, or elliptical cross section.

The average diameter of the 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 than pellets less than 1 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of the virgin polyolefin pellets may be 2 to 6 mm.

The non-melting recycled polyolefin pellets in the present disclosure are pellets produced by a non-melting pelletizer, specifically pellets produced from waste polyolefin films using a non-melting pelletizer. Such pellets can be called non-melting recycled polyolefin pellets.
In this disclosure, "non-melt type" refers to a method in which the raw materials are not melted in the pellet manufacturing process, while "melt type" refers to a method in which the raw materials are melted in the pellet manufacturing process. Therefore, "non-melt type" pellets and "melt type" pellets are different.

Waste polyolefin film includes waste materials (PIR: post-industrial recycled materials) generated during the production of polyolefin film, such as poorly formed film, damaged film, and so-called edge waste (shredded scraps from both ends of the film).

As mentioned above, non-melt recycled polyolefin pellets have a roughly granular to columnar shape, and are different in appearance from recycled polyolefin pellets obtained by heat melting. Non-melt recycled polyolefin pellets can contain fine fragments of twisted polyolefin string. Here, "twisted polyolefin string" refers to waste polyolefin film that has been stretched into a string shape and then twisted by rotating it around the axis of stretching the string. "Fine fragments" refer to the twisted polyolefin string that has been shredded in a direction perpendicular to the direction in which the string was stretched.

In the fine fragments, the strands (polyolefin strands) that make up the twisted strand may be partially crimped together, i.e., the non-melting recycled polyolefin pellets may contain fine fragments of polyolefin crimped twisted strands.

The strings that make up the twisted string may themselves be stretched; that is, the twisted string may be made by twisting stretched polyolefin strings. "Stretching" here refers to the uniaxial or biaxial stretching process typically performed on polyolefin films.

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

Such non-melting recycled polyolefin pellets can be produced, for example, based on the contents of WO 2022/176171.

The average diameter of non-melt type recycled polyolefin pellets can be 4 to 10 mm. An average diameter of 4 mm or more makes them less likely to scatter during handling than pellets less than 4 mm, while an average diameter of 10 mm or less makes them easier to transport during production than pellets greater than 10 mm. From these perspectives, the average diameter of non-melt type recycled polyolefin pellets may be 5 to 9 mm.

Polyolefin film obtained from pellet raw material containing the above-mentioned non-melting recycled polyolefin pellets, which are obtained by stretching waste polyolefin film into a string-like shape and then twisting it around the axis of rotation in the stretching direction, is not too yellowish compared to polyolefin film obtained from pellet raw material containing only virgin pellets.

Non-melt recycled polyolefin pellets preferably satisfy the following formula (2). When recycled pellets are produced using waste plastics as the raw material, an antioxidant may be added to the raw material and heated to melt it in order to obtain a thermoplastic resin composition molded product with the quality and remaining life appropriate for the application. From the perspective of production efficiency, it is preferable to obtain recycled polyolefin film without adding any additional antioxidant. When non-melt recycled polyolefin pellets satisfy the following formula (2), it tends to be possible to produce a film in which oxidative degradation is further suppressed without adding any additional antioxidant.

YI1-YI2≦0.6...(2)
[In formula (2), YI1 represents the yellow index of a first test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 80% by mass of virgin test polyolefin pellets and 20% by mass of non-melting recycled polyolefin pellets, and YI2 represents the yellow index of a second test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 100% by mass of virgin test polyolefin pellets.]

In the above formula (2), the left side (YI1-YI2) is preferably 0.55 or less, and even more preferably 0.5 or less, as this tends to further suppress oxidative degradation.

In the above formula (2), YI1 may be 4.7 or more, 4.75 or more, or 4.8 or more, and may be 5.2 or less, 5.15 or less, or 5.1 or less.

In the above formula (2), YI2 may be 4.3 or more, 4.35 or more, or 4.4 or more, and may be 4.7 or less, 4.65 or less, or 4.6 or less.

The test virgin polyolefin pellets used in the first test piece and the test virgin polyolefin pellets used in the second test piece are the same.

The yellow index of the first test piece and the second test piece may be a value measured using a spectrophotometer in accordance with JIS K7373:2006. The first test piece and the second test piece may each be a single-layer film, or a laminate of two or more films stacked together to a total thickness of 750 μm.

The pellet raw material may contain virgin polyolefin pellets and non-melting recycled polyolefin pellets, and may consist of virgin polyolefin pellets and non-melting recycled polyolefin pellets (the total amount of virgin polyolefin pellets and non-melting recycled polyolefin pellets is substantially 100% by mass). The content of non-melting recycled polyolefin pellets in the pellet raw material may be 5 to 50% by mass. A non-melting recycled polyolefin pellet content of 5% by mass or more improves recyclability compared to when it is less than 5% by mass. On the other hand, a non-melting recycled polyolefin pellet content of 50% by mass or less improves film-forming suitability during extrusion molding compared to when it is more than 50% by mass. From these perspectives, the content of non-melting recycled polyolefin pellets may be 10 to 50% by mass, 10 to 30% by mass, 10 to 25% by mass, or 15 to 20% by mass.

In this disclosure, the average diameter is the average value of the maximum and minimum diameters when the pellets are placed on a table and viewed from a direction perpendicular to the table. The maximum and minimum diameters can be measured, for example, using a vernier caliper. The measurement is performed with the pellets in a stable state. A stable state means, for example, allowing the pellets to fall freely from 2 cm above the table and allowing them to come to rest.

In the process of producing polyolefin film by extrusion molding from pellet raw material, a general screw extruder used in T-die molding, inflation molding, etc. can be used.

The method for producing recycled polyolefin film may include, prior to the above step, a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

Here, the process for producing non-melting recycled polyolefin pellets may include stretching waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as the axis of rotation, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction. This results in non-melting recycled polyolefin pellets containing fine fragments of twisted polyolefin strings.

In the above process, the twisted polyolefin strings may be heated and pressurized to at least partially crimp the contact surfaces of the strings (polyolefin strings) that make up the twisted string. This results in non-melting recycled polyolefin pellets containing fine fragments of crimped twisted polyolefin strings. Heating the polyolefin strings can be carried out by heating them to their softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film.

First Consideration The first invention group of the present disclosure will be explained in more detail by the following examples, but the present invention is not limited to these examples.

As virgin polyethylene pellets, low-density polyethylene pellets (MFR: 2.3 g/10 min, density: 0.916) were prepared.
The virgin polyethylene pellets had an average diameter of 4.8 mm and a bulk density of 0.52 g/mL.

The waste polyolefin film was scrapped from polyethylene film manufacturing. The scrap was 150 μm thick and 10 to 30 mm wide. Recycled polyethylene pellets were then produced from the scrap using a non-melting pelletizer, Ecopelle GP-3, manufactured by Maruyasu Co., Ltd. The recycled polyethylene pellets were fine fragments of twisted polyethylene string, consisting of strings that had been partially crimped together. The twisted strings were also made by twisting stretched polyethylene strings.

The average diameter of the recycled polyethylene pellets was 6.9 mm and the bulk density was 0.24 g/mL.

A pellet raw material was prepared by mixing the virgin polyethylene pellets and recycled polyethylene pellets in the ratios shown in Table 1. The bulk density of the mixed polyethylene pellets in this example was 0.44 g/mL.
Using the pellet raw material of each example, a recycled polyethylene film or a polyethylene film was produced in a single layer inflation film forming machine. When the obtained films of each example were visually observed, no yellowing was observed in any of them.

The film-forming suitability and recyclability of each pellet material during extrusion molding were evaluated according to the following criteria. The results are shown in Table 1.
(Film forming suitability)
A: A film could be formed without film breakage.
B: Film breakage occurred, and the film could not be formed properly.
(Recyclability)
A: Recycled materials were included.
B: No recycled material was included.

Second Consideration The second invention group of the present disclosure will be explained in more detail by the following examples, but the present invention is not limited to these examples.

As virgin polyethylene pellets, low-density polyethylene pellets (MFR: 2.3 g/10 min, density: 0.916) were prepared.
The virgin polyethylene pellets had an average diameter of 4.8 mm and an angle of repose of 21°.

The waste polyolefin film was scrapped from polyethylene film manufacturing. The scrap was 150 μm thick and 10 to 30 mm wide. Recycled polyethylene pellets were then produced from the scrap using a non-melting pelletizer, Ecopelle GP-3, manufactured by Maruyasu Co., Ltd. The recycled polyethylene pellets were fine fragments of twisted polyethylene string, consisting of strings that had been partially crimped together. The twisted strings were also made by twisting stretched polyethylene strings.

The average diameter of the recycled polyethylene pellets was 6.9 mm and the angle of repose was 31°.

A pellet raw material was prepared by mixing the virgin polyethylene pellets and recycled polyethylene pellets in the ratio shown in Table 2. The angle of repose of the mixed polyethylene pellets in this example was 27°.
Using the pellet raw material of each example, a recycled polyethylene film or a polyethylene film was produced in a single layer inflation film forming machine. When the obtained films of each example were visually observed, no yellowing was observed in any of them.

The film-forming suitability and recyclability of each pellet material during extrusion molding were evaluated according to the following criteria. The results are shown in Table 2.
(Film forming suitability)
A: A film could be formed without film breakage.
B: Film breakage occurred, and the film could not be formed properly.
(Recyclability)
A: Recycled materials were included.
B: No recycled material was included.

Third Consideration The third invention group of the present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples.

[Production of recycled polyethylene film]
(Example 3-1)
Low-density polyethylene pellets (MFR: 2.3 g/10 min, density: 0.916) were prepared as virgin polyethylene pellets. The virgin polyethylene pellets had an average diameter of 4.8 mm.

Waste polyolefin film was collected from waste edge waste during polyethylene film production. The thickness of the edge waste was 150 μm, and its width was 10 to 30 mm. Recycled polyethylene pellets were then produced from the collected edge waste using a non-melting pelletizer, Ecopelle GP-3, manufactured by Maruyasu Co., Ltd. The recycled polyethylene pellets were fine fragments of twisted polyethylene string, consisting of strings that had been partially crimped together. The twisted strings were also made by twisting stretched polyethylene strings.

The average diameter of the recycled polyethylene pellets was 6.9 mm.

Virgin polyethylene pellets and recycled polyethylene pellets were mixed (virgin polyethylene pellets: recycled polyethylene pellets = 80:20 (mass ratio)) to prepare pellet raw material. Recycled polyethylene film was produced using the pellet raw material in a single-layer inflation film extrusion machine.

(Comparative Example 3-1)
A recycled polyethylene film was produced in the same manner as in Example 3-1, except that recycled polyethylene pellets were produced from the recovered edge waste using a heat-melt pelletizer INTEREMA type manufactured by EREMA instead of the non-melt pelletizer ecopelle GP-3.

(Reference example 3-1)
In the same manner as in Example 3-1, waste polyolefin was recovered from the waste edge of polyethylene film during production. Then, recycled polyethylene pellets were produced from the recovered waste edge using an INTEREMA-type heat-melting pelletizer manufactured by EREMA. When producing the recycled polyethylene pellets, a masterbatch containing a phenolic antioxidant was added as an antioxidant (5%). The amount of masterbatch added was 1 part by weight per 100 parts by weight of the waste edge.

[Measurement of oxidation induction time]
The oxidation induction time T1 of edge loss during the production of polyethylene film, which is the raw material for recycled polyethylene pellets, and the oxidation induction time T2 of the recycled polyethylene pellets were measured. The measurement conditions were as follows. The oxidation induction time T1 was 1.8 hours. The oxidation induction time T2 and the ratio (T2/T1) are shown in Table 3.

(Measurement conditions)
Measurement device: Chemiluminescence analyzer CLA-FS4 manufactured by Tohoku Electronics Industry Co., Ltd.
Measurement temperature: 200℃
Sample amount: 0.2 g
Measurement interval: 10 seconds Measurement time: within 8 hours Atmosphere: 100% oxygen

Fourth Consideration The fourth invention group of the present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples.

[Production of recycled polyethylene film]
(Example 4-1)
Low-density polyethylene pellets (MFR: 2.3 g/10 min, density: 0.916) were prepared as virgin polyethylene pellets. The virgin polyethylene pellets had an average diameter of 4.8 mm.

Waste polyolefin film was collected from waste edge waste during polyethylene film production. The thickness of the edge waste was 150 μm, and its width was 10 to 30 mm. Recycled polyethylene pellets were then produced from the collected edge waste using a non-melting pelletizer, Ecopelle GP-3, manufactured by Maruyasu Co., Ltd. The recycled polyethylene pellets were fine fragments of twisted polyethylene string, consisting of strings that had been partially crimped together. The twisted strings were also made by twisting stretched polyethylene strings.

The average diameter of the recycled polyethylene pellets was 6.9 mm.

Virgin polyethylene pellets and recycled polyethylene pellets were mixed (virgin polyethylene pellets: recycled polyethylene pellets = 80:20 (mass ratio)) to prepare pellet raw material. Recycled polyethylene film was produced using the pellet raw material in a single-layer inflation film extrusion machine.

(Example 4-2)
A recycled polyethylene film was produced in the same manner as in Example 4-1, except that the mixing ratio of the virgin polyethylene pellets and the recycled polyethylene pellets was changed to virgin polyethylene pellets: recycled polyethylene pellets = 50:50 (mass ratio).

(Comparative Example 4-1)
Instead of the non-melt pelletizer ecopellet GP-3, an INTEREMA-type heat-melt pelletizer manufactured by EREMA was used to produce melt-type recycled polyethylene pellets from recovered waste. Specifically, the same waste as in Example 4-1 was first recovered. The recovered waste was supplied to the supply section of the INTEREMA-type heat-melt pelletizer. The supplied waste was finely crushed in the crushing section. The crushed waste material was introduced into the extrusion section. Within the extrusion section, the waste material was transported by a screw and melted by heating at a temperature above the melting point of the waste material, resulting in a melted waste material. The melt was discharged from a hole provided at the outlet of the extrusion section and then cut with a cutter. The melt was cooled in water to solidify the melt, resulting in a solidified material. The solidified material was drained and further dried to obtain melt-type recycled polyethylene pellets. A recycled polyethylene film was produced in the same manner as in Example 4-2, except that the obtained melt-process recycled polyethylene pellets were used as the recycled polyethylene pellets.

(Reference example 4-1)
As the pellet raw material, the same virgin polyethylene pellets as in Example 4-1 were prepared. Using the pellet raw material, a polyethylene film was produced in a single-layer inflation film forming machine.

[Yellow index measurement]
For each example, 15 sheets of the obtained polyethylene film were stacked to obtain a laminate. The yellow index of the obtained laminate (total thickness: 750 μm) was measured using a spectrophotometer in accordance with JIS K7373:2006. The results are shown in Table 4.

1...mesh, 2...hopper, 3...jig, 4...pellets piled up in a cone shape.

Claims (13)

The process comprises a step of producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365. The process comprises a step of producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the angle of repose of the recycled polyolefin pellets is greater than 30° and the angle of repose of the pellet raw material is 30° or less. The process comprises a step of producing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A method for producing a recycled polyolefin film, wherein the ratio (T2/T1) represented by the following formula (1) is 0.8 or more.
T2/T1...(1)
[In formula (1), T1 represents the oxidation induction time of the non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C before pelletization, and T2 represents the oxidation induction time of the non-melt recycled polyolefin pellets measured in an oxygen atmosphere at 200°C.] A method for producing recycled polyolefin film, comprising a step of producing a polyolefin film by extrusion molding from pellet raw materials containing virgin polyolefin pellets and non-melting recycled polyolefin pellets. The method for producing a recycled polyolefin film according to claim 4, wherein the non-melting recycled polyolefin pellets satisfy the following formula (2):
YI1-YI2≦0.6...(2)
[In formula (2), YI1 represents the yellow index of a first test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 80 mass % of virgin polyolefin pellets for testing and 20 mass % of the non-melting recycled polyolefin pellets, and YI2 represents the yellow index of a second test piece having a thickness of 750 μm obtained by extrusion molding from a raw material containing 100 mass % of the virgin polyolefin pellets for testing.] The manufacturing method described in any one of claims 1 to 5, wherein the content of the recycled polyolefin pellets in the pellet raw material is 5 to 50 mass%. The manufacturing method described in any one of claims 1 to 6, wherein the recycled polyolefin pellets include fine fragments of polyolefin twisted cord. The manufacturing method described in any one of claims 1 to 7, wherein the recycled polyolefin pellets have an average diameter of 4 to 10 mm. The manufacturing method described in any one of claims 1 to 8, comprising a step of producing the non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer. The manufacturing method described in claim 9, wherein the process for producing the non-melt recycled polyolefin pellets comprises: stretching the waste polyolefin film to form a polyolefin string; twisting the polyolefin string by rotating it around the stretching direction as the axis of rotation; and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction. A pellet raw material comprising virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A pellet raw material for extrusion molding of recycled polyolefin film, wherein the bulk density of the recycled polyolefin pellets is 0.35 g/mL or less and the bulk density of the pellet raw material is 0.4 g/mL or more according to JIS-K-7365. A pellet raw material comprising virgin polyolefin pellets and non-melting recycled polyolefin pellets,
A pellet raw material for extrusion molding of a recycled polyolefin film, wherein the angle of repose of the recycled polyolefin pellets is more than 30° and the angle of repose of the pellet raw material is 30° or less. The pellet material described in claim 11 or 12, wherein the recycled polyolefin pellets comprise shredded polyolefin twisted cords.