Method for manufacturing recycled polyolefin film

Abstract

To provide a method for producing recycled polyolefin film that can manufacture films in which oxidative degradation is suppressed without the addition of antioxidants. [Solution] The process includes manufacturing a polyolefin film by extrusion molding from pellet raw materials including virgin polyolefin pellets and non-melting recycled polyolefin pellets. A method for producing recycled polyolefin film, wherein the ratio (T2 / T1) shown in the following formula (1) is 0.8 or greater. T2 / T1···(1) [In formula (1), T1 represents the oxidation induction time measured under an oxygen atmosphere at 200°C in the state before pelletizing of non-melting recycled polyolefin pellets, and T2 represents the oxidation induction time measured under an oxygen atmosphere at 200°C for non-melting recycled polyolefin pellets.]

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a recycled polyolefin film.

Background Art

[0002] When manufacturing recycled pellets from waste plastics such as polyolefins, a method is known in which the waste plastics are once heated and melted and then extruded into water or the like and cooled to form pellets (see, for example, Patent Document 1).

[0003] Also, when manufacturing recycled pellets from waste plastics, a method is known in which an antioxidant is added to the raw materials and heated and melted in order to obtain a thermoplastic resin composition molded body having quality and remaining life according to the application (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventors have considered obtaining a recycled polyolefin film from recycled pellets made from polyolefin. From the viewpoint of production efficiency, it is desirable to obtain a recycled polyolefin film without additionally adding an antioxidant.

[0006] The present disclosure provides a method for manufacturing a recycled polyolefin film capable of manufacturing a film in which oxidative degradation is suppressed without additionally adding an antioxidant. [Means for solving the problem]

[0007] One aspect of this disclosure relates to a method for producing the following 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 recycled polyolefin film, wherein the ratio (T2 / T1) shown in the following formula (1) is 0.8 or greater. T2 / T1···(1) [In formula (1), T1 represents the oxidation induction time measured under an oxygen atmosphere at 200°C in the state before pelletizing of non-melting recycled polyolefin pellets, and T2 represents the oxidation induction time measured under an oxygen atmosphere at 200°C for non-melting recycled polyolefin pellets.] [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] A method for producing non-melting recycled polyolefin pellets comprising fine fragments of polyolefin strands, according to [1] or [2]. [4] A manufacturing 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] A 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], comprising the steps of producing non-melting recycled polyolefin pellets, stretching a waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it with the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction. [Effects of the Invention]

[0008] According to this disclosure, a method for producing recycled polyolefin film is provided, which enables the production of a film in which oxidative degradation is suppressed without the addition of antioxidants. [Modes for carrying out the invention]

[0009] Preferred embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below.

[0010] <Method for manufacturing recycled polyolefin film> The method for producing recycled polyolefin film according to this embodiment 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, wherein the ratio (T2 / T1) shown in the following formula (1) is 0.8 or more. [In formula (1), T1 represents the oxidation induction time measured under an oxygen atmosphere at 200°C in the state before pelletizing of non-melting recycled polyolefin pellets, and T2 represents the oxidation induction time measured under an oxygen atmosphere at 200°C for non-melting recycled polyolefin pellets.]

[0011] The method for producing recycled polyolefin film according to this embodiment has a ratio (T2 / T1) of 0.8 or higher. This makes it possible to produce a film in which oxidative degradation is suppressed without the addition of antioxidants. Antioxidants are generally added together with other resins (virgin products). Since the method for producing recycled polyolefin film according to this embodiment does not require the addition of antioxidants, the proportion of recycled polyolefin resin can be increased. Therefore, the method for producing recycled polyolefin film according to this embodiment has excellent recyclability.

[0012] The pellet raw material is a pellet raw material for extrusion molding of recycled polyolefin films, including virgin polyolefin pellets and non-melting recycled polyolefin pellets.

[0013] Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins directly synthesized from petroleum or fossil fuels. Examples of polyolefins include polyethylene, polypropylene, polybutylene, and the like.

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

[0015] The average diameter of virgin polyolefin 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 polyolefin pellets may be 2 to 6 mm.

[0016] The oxidation induction time of virgin polyolefin pellets may be, for example, 2.2 to 3.5 hours.

[0017] In the present disclosure, the oxidation induction time indicates a value measured using a chemiluminescence analyzer at 200 °C in an oxygen atmosphere. The oxidation induction time may be measured, for example, under the following measurement conditions. (Measurement conditions) Measuring device: Chemiluminescence analyzer CLA-FS4 manufactured by Tohoku Electronic Industry Co., Ltd. Measuring temperature: 200 °C Sample amount: 0.2 g Measurement interval: 10 seconds Measurement time: within 8 hours Atmosphere: 100% oxygen

[0018] The non-melting type 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 referred to as non-melting type recycled polyolefin pellets. In the present disclosure, "non-melting type" means a method in which raw materials are not melted in the pellet manufacturing process, while "melting type" means a method in which raw materials are melted in the pellet manufacturing process. Therefore, "non-melting type" pellets and "melting type" pellets are different.

[0019] In the present disclosure, "the state before pelletization of non-melting type recycled polyolefin pellets" refers to the state of waste polyolefin films as raw materials.

[0020] Examples of waste polyolefin films include loss materials (PIR: post-industrial recycle materials) generated during the production of polyolefin films. Specifically, in addition to films with poor film formation and damaged films, so-called ear losses (fine chips at both ends of the film) and the like can be mentioned.

[0021] Non-melting type recycled polyolefin pellets have a generally granular to columnar shape as described above, and are different in form from the recycled polyolefin pellets obtained through heat melting. Non-melting type recycled polyolefin pellets can contain fine fragments of polyolefin twisted cords. Here, "polyolefin twisted cord" refers to a cord formed by stretching a waste polyolefin film into a cord shape and then twisting it with the stretching direction of the cord as the axis of rotation. "Fine fragment" refers to the polyolefin twisted cord cut into pieces in a direction perpendicular to the stretching direction of the cord.

[0022] In the fine fragments, the cords (polyolefin cords) constituting the twisted cord may be partially crimped. That is, non-melting type recycled polyolefin pellets may contain fine fragments of polyolefin crimped twisted cords.

[0023] The cords themselves constituting the twisted cord may be stretched. That is, the twisted cord may be formed by twisting stretched polyolefin cords. The "stretching" mentioned here refers to stretching processes such as uniaxial stretching and biaxial stretching performed on ordinary polyolefin films.

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

[0025] Such non-melting recycled polyolefin pellets can be manufactured, for example, according to the contents of International Publication No. 2022 / 176171.

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

[0027] The ratio (T2 / T1) shown in formula (1) above is 0.8 or greater, preferably 0.85 or greater, more preferably 0.9 or greater, and even more preferably 0.95 or greater. Oxidative degradation is suppressed when (T2 / T1) is within this range. 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.

[0028] 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.

[0029] 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.

[0030] The pellet raw material includes 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 may be substantially 100% by mass). The content of non-melting recycled polyolefin pellets in the pellet raw material can be 5 to 50% by mass. A content of 5% by mass or more of non-melting recycled polyolefin pellets improves recyclability compared to a content of less than 5% by mass, while a content of 50% by mass or less of non-melting recycled polyolefin pellets improves film formation suitability during extrusion molding compared to a content of more than 50% by mass. From these viewpoints, 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.

[0031] In this disclosure, the average diameter is the average of the maximum and minimum diameters when the pellet is placed on a stand and viewed from a direction perpendicular to the stand. The maximum and minimum diameters can be measured, for example, with calipers. The measurement should be performed with the pellet 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.

[0032] In the process of manufacturing polyolefin film from pellet raw materials by extrusion molding, a general screw extruder used in methods such as T-die molding and inflation molding can be used.

[0033] A method for producing recycled polyolefin film may include, prior to the above-mentioned steps, a step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

[0034] Here, the process for producing non-melting recycled polyolefin pellets may include stretching a waste polyolefin film to form a polyolefin string, twisting the polyolefin string by rotating it with the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction. This yields non-melting recycled polyolefin pellets containing fine fragments of the polyolefin string.

[0035] In the above process, the twisted polyolefin cord may be heated and pressurized to at least partially compress the contact surfaces of the cords (polyolefin cords) constituting the twisted cord. This yields non-melting recycled polyolefin pellets containing fine fragments of the polyolefin compressed twisted cord. The polyolefin cord can be heated to its softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film. [Examples]

[0036] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0037] [Manufacturing of recycled polyethylene film] (Example 1) Low-density polyethylene pellets (MFR: 2.3 g / 10 min, density: 0.916) were prepared as virgin polyethylene pellets. The average diameter of the virgin polyethylene pellets was 4.8 mm.

[0038] Selvedge loss from polyethylene film manufacturing was collected as waste polyolefin film. The selvedge loss had a thickness of 150 μm and a width of 10 to 30 mm. Recycled polyethylene pellets were then produced from the collected selvedge loss using a non-melting type pelletizer ecoPelle GP-3 manufactured by Maruyasu Co., Ltd. The recycled polyethylene pellets were fine fragments of polyethylene twisted cord, formed by partially crimping the cords that make up the twisted cord. The twisted cord itself was made by twisting stretched polyethylene cords together.

[0039] The average diameter of the recycled polyethylene pellets was 6.9 mm.

[0040] Virgin polyethylene pellets and recycled polyethylene pellets were mixed (virgin polyethylene pellets:recycled polyethylene pellets = 80:20 (mass ratio)) to prepare the pellet raw material. Recycled polyethylene film was manufactured using the pellet raw material in a single-layer inflation film deposition machine.

[0041] (Comparative Example 1) Recycled polyethylene film was manufactured in the same manner as in Example 1, except that a heated melting type pelletizer INTAREMA manufactured by EREMA Corporation was used instead of a non-melting type pelletizer ecoPelle GP-3 to produce recycled polyethylene pellets from the recovered edge loss.

[0042] (Reference example 1) In the same manner as in Example 1, selvage loss from polyethylene film production was recovered as waste polyolefin. Then, recycled polyethylene pellets were produced from the recovered selvage loss using an INTAREMA type heated melting pelletizer manufactured by EREMA. A masterbatch containing a phenolic antioxidant was added as an antioxidant during the production of the recycled polyethylene pellets (5%). The amount added was 1 part by weight of masterbatch per 100 parts by weight of selvage loss.

[0043] [Measurement of oxidation induction time] The oxidation induction time T1 of selvage loss during polyethylene film production, which is the raw material for recycled polyethylene pellets, and the oxidation induction time T2 of 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 its ratio (T2 / T1) are shown in Table 1.

[0044] (Measurement conditions) Measurement device: Chemiluminescence analyzer CLA-FS4 manufactured by Tohoku Electronics Industry Co., Ltd. Measurement temperature: 200℃ Sample amount: 0.2g Measurement interval: 10 seconds Measurement time: within 8 hours Atmosphere: 100% oxygen

[0045] [Table 1]

Claims

1. The process includes manufacturing a polyolefin film by extrusion molding from pellet raw materials, including virgin polyolefin pellets and non-melting recycled polyolefin pellets. A method for producing recycled polyolefin film, wherein the ratio (T2 / T1) shown in the following formula (1) is 0.8 or greater. T2 / T1...(1) [In formula (1), T1 represents the oxidation induction time measured under an oxygen atmosphere at 200°C in the state of the non-melting recycled polyolefin pellet before pelletization, and T2 represents the oxidation induction time measured under an oxygen atmosphere at 200°C in the non-melting recycled polyolefin pellet.]

2. The manufacturing method according to claim 1, wherein the content of the non-melting recycled polyolefin pellets in the pellet raw material is 5 to 50% by mass.

3. The manufacturing method according to claim 1 or 2, wherein the non-melting recycled polyolefin pellets include fine fragments of polyolefin twisted cord.

4. The manufacturing method according to claim 1 or 2, wherein the average diameter of the non-melting recycled polyolefin pellets is 4 to 10 mm.

5. The manufacturing method according to claim 1 or 2, comprising the step of producing non-melting recycled polyolefin pellets from waste polyolefin film using a non-melting pelletizer.

6. The manufacturing method according to claim 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 with the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.

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