Method for producing recycled polyolefin film, and pellet raw material for extrusion molding of recycled polyolefin film

Abstract

To provide a method for producing a recycled polyolefin film which allows a film having favorable appearance with yellowing suppressed to be produced and which further achieves excellent suitability for film formation at the time of extrusion molding.SOLUTION: A method for producing a recycled polyolefin film comprises a step of producing a polyolefin film by extrusion molding from a pellet raw material containing virgin polyolefin pellets and non-melt-type recycled polyolefin pellets, wherein, according to JIS-K-7365, a bulk density of the recycled polyolefin pellets is 0.35 g / mL or less, and a bulk density of the pellet raw material is 0.4 g / mL or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a recycled polyolefin film and a pellet raw material for extrusion molding of the recycled polyolefin film. [Background technology]

[0002] When recycled pellets are produced using waste plastics such as polyolefins as raw materials, a method is known in which the waste plastics are first heated and melted, then extruded into water or the like, cooled, and pelletized (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 053757 [Patent Document 2] International Publication No. 2022 / 176171 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above method, the plastic deteriorates during the heat-melting process, so the final product made from recycled pellets that have been heat-melted may have poor appearance. For example, if the final product is a plastic film, there is a risk of yellowing as well as an increase in the number of defects such as gels and fish eyes.

[0005] Therefore, attempts have been made to use non-melt pelletizers, which can pelletize waste plastics 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.

[0006] 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. [Means for solving the problem]

[0007] One aspect of the present disclosure includes a process for producing a polyolefin film by extrusion from a pellet feedstock including virgin polyolefin pellets and non-melting recycled polyolefin pellets, The present invention provides 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.

[0008] 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.

[0009] The manufacturing method of the present disclosure can be said to be a method of manufacturing recycled polyolefin film that can produce films with a good appearance and suppressed yellowing, and that also has excellent film-forming suitability during extrusion molding.

[0010] In one embodiment of the above production method, the content of recycled polyolefin pellets in the pellet raw material may be 5 to 50% by mass.

[0011] In one embodiment of the above manufacturing method, the recycled polyolefin pellets may include shredded polyolefin twisted cords.

[0012] In one embodiment of the above production method, the recycled polyolefin pellets may have an average diameter of 4 to 10 mm.

[0013] In one embodiment of the above-mentioned manufacturing method, the manufacturing method may include a step of manufacturing non-melting recycled polyolefin pellets from waste polyolefin films using a non-melting pelletizer.

[0014] In one aspect of the above manufacturing method, 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 around the stretching direction as the axis of rotation, and shredding the twisted polyolefin string in a direction perpendicular to the stretching direction.

[0015] 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.

[0016] Such pellet raw material can be used in the above-mentioned production method, and can produce a film having a good appearance with suppressed yellowing, and also has excellent suitability for film formation during extrusion molding.

[0017] In one embodiment of the pellet raw material, the recycled polyolefin pellets may include shredded polyolefin twisted cords. [Effects of the Invention]

[0018] According to the present disclosure, a method for producing recycled polyolefin film is provided that can produce a film with a good appearance and suppressed yellowing, and that has excellent film-forming 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. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0020] <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.

[0021] Virgin polyolefin pellets are pellets made from virgin polyolefins. Virgin polyolefins are polyolefins synthesized directly from petroleum or fossil fuels. Polyolefins include polyethylene, polypropylene, and polybutylene.

[0022] The shape of the virgin polyolefin pellets may be granular, columnar, or the like having a circular, oval, or elliptical cross section.

[0023] The average diameter of the virgin polyolefin pellets can be 1 to 10 mm. When the average diameter is 1 mm or more, the pellets are less likely to scatter during handling than when they are less than 1 mm, while when the average diameter is 10 mm or less, the pellets are easier to transport during production than when they are more than 10 mm. From these viewpoints, the average diameter of the virgin polyolefin pellets may be 2 to 6 mm.

[0024] 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 makes them less likely to scatter during handling than pellets with a bulk density of less than 0.5 g / mL, while a bulk density of 0.8 g / mL or less makes them 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.

[0025] 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.

[0026] Examples of waste polyolefin films include waste materials (PIR: post-industrial recycled materials) generated during the production of polyolefin films, such as defectively formed films, damaged films, and so-called edge waste (shredded scraps at both ends of the film). Furthermore, waste polyolefin films may be obtained by slitting polyolefin films during the production process. Examples of polyolefins include polyethylene, polypropylene, polybutylene, etc., as described above.

[0027] The thickness of the waste polyolefin film may be 5 to 200 μm, and the width of the waste polyolefin film may be 5 to 500 mm, or from the viewpoint of ease of production of twisted cords, may be 5 to 50 mm.

[0028] As described above, recycled polyolefin pellets have a generally granular to columnar shape with low bulk density, 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 a waste polyolefin film that has been stretched into a string shape and then twisted by rotating it around the stretching direction of the string as the axis of rotation. "Fine fragments" refer to the twisted polyolefin string that has been shredded in a direction perpendicular to the stretching direction of the string.

[0029] In the fine pieces, the strings (polyolefin strings) that make up the twisted string may be partially crimped together, that is, the recycled polyolefin pellets may contain fine pieces of crimped twisted polyolefin strings.

[0030] The strands that make up the twisted strand may themselves be stretched, i.e., the twisted strand may be formed by twisting stretched polyolefin strands. The "stretching" referred to here refers to the stretching process such as uniaxial stretching or biaxial stretching that is performed on ordinary polyolefin films.

[0031] The shreds may be cylindrical, and if the shreds are roughly granular, may be cylindrical with an aspect ratio (ratio of cylinder diameter to height) of about 1.

[0032] Such recycled polyolefin pellets can be produced, for example, based on the contents of WO 2022 / 176171.

[0033] The average diameter of the recycled polyolefin pellets can be 4 to 10 mm. When the average diameter is 4 mm or more, they are less likely to scatter during handling than when they are less than 4 mm, while when the average diameter is 10 mm or less, they are easier to transport during production than when they are more than 10 mm. From these perspectives, the average diameter of the recycled polyolefin pellets may be 5 to 9 mm.

[0034] The bulk density of recycled polyolefin pellets is 0.35 g / mL or less because they are produced using a non-melting pelletizer, and this value is lower than the bulk density of virgin polyolefin pellets. The lower limit of the bulk density is not particularly limited, but can be set to 0.1 g / mL because the pellet shape can be easily maintained in the recycling process described below. From these perspectives, the bulk density of recycled polyolefin pellets can be set to 0.15 to 0.3 g / mL, or may be 0.2 to 0.3 g / mL.

[0035] The bulk density of recycled polyolefin pellets can be adjusted, for example, by adjusting the stretching ratio of the raw material 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 by the conveying rolls. Recycled polyolefin pellets are produced through a recycling process in which the raw material film is stretched, twisted, or otherwise processed, and therefore tend to have a lower bulk density than virgin polyolefin pellets.

[0036] The pellet raw material contains virgin polyolefin pellets and recycled polyolefin pellets, and 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 can improve recyclability compared to when the recycled polyolefin pellet content is less than 5% by mass. On the other hand, a recycled polyolefin pellet content of 50% by mass or less can improve film-forming suitability during extrusion molding compared to when the recycled polyolefin pellet content 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.

[0037] 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.

[0038] 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 perpendicularly 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. The stable state means, for example, allowing the pellets to fall freely from 2 cm above the table and allowing them to stand still.

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

[0040] <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 production 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.

[0041] In the process of producing a polyolefin film by extrusion molding from pellet raw materials, a general screw extruder used in a T-die molding method, inflation molding method, etc. can be used.

[0042] 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.

[0043] Here, the process for producing non-melting recycled polyolefin pellets may include stretching a waste polyolefin film to form polyolefin strings, twisting the polyolefin strings by rotating them around the stretching direction as a rotation axis, and shredding the twisted polyolefin strings in a direction perpendicular to the stretching direction, thereby obtaining recycled polyolefin pellets containing fine fragments of twisted polyolefin strings.

[0044] In the above process, the twisted polyolefin strings may be heated and pressurized to at least partially pressurize the contact surfaces of the strings (polyolefin strings) that make up the twisted string. This results in recycled polyolefin pellets containing fine fragments of the compressed twisted polyolefin strings. Heating the polyolefin strings can be performed by heating them to their softening temperature using hot air or the like, taking into account the softening temperature of the waste polyolefin film.

[0045] <Summary of this disclosure> The outline of the present disclosure is 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 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 recycled polyolefin pellets have an average diameter of 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 described in [5], 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. [7] A pellet 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. [Example]

[0046] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0047] 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.

[0048] Edge waste from polyethylene film production was collected as waste polyolefin film. The thickness of the edge waste was 150 μm and its width was 10 to 30 mm. Recycled polyethylene pellets were 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 polyethylene twisted strings, which were made by partially crimping the strings that made up the twisted strings together. The twisted strings were also made by twisting stretched polyethylene strings.

[0049] The average diameter of the recycled polyethylene pellets was 6.9 mm and the bulk density was 0.24 g / mL.

[0050] A pellet raw material was prepared by mixing the virgin polyethylene pellets and recycled polyethylene pellets in the ratio 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.

[0051] 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 film was formed without film breakage. ×: The film could not be properly formed due to film breakage. (Recyclability) ○: Recycled materials were included. ×: No recycled material was included.

[0052] [Table 1]

Claims

1. 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.

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

3. The method of claim 1 or 2, wherein the recycled polyolefin pellets comprise shredded polyolefin twisted cord.

4. The method according to claim 1 or 2, wherein the recycled polyolefin pellets have an average diameter of 4 to 10 mm.

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

6. 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 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 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.

8. 8. The pellet feedstock of claim 7, wherein the recycled polyolefin pellets comprise shredded polyolefin strands.

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