Method and system for producing recycled polypropylene pellet and recycled polypropylene band

Abstract

To provide a system capable of operating re-pellet production and PP band production from a simple flexible container in an almost unmanned state.SOLUTION: This system is equipped with a first single stage extruder 2 for pelletizing the crushed product of a used simple flexible container bag 1 and the single stage extruder 2 has a cylinder 21, a laser filter, a dual piston screen changer 3 and a die part 24. The crushed product supplied to the single-stage extruder 2 together with pellets as necessary is melted at a temperature of 190 °C or higher and 230 °C or lower, sewing threads contained in the melted crushed product are removed with a screen of 120 mesh or less using a laser filter, and foreign matter is removed with a screen of 120 mesh or less using a screen changer 3 or the like. The first recycled resin melt from which the sewing threads and foreign matter have been removed is pelletized in the die part 24.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and system for producing recycled polypropylene pellets and recycled polypropylene bands, and more specifically to a method and system for producing recycled polypropylene pellets and recycled polypropylene bands using used flexible container bags or a combination of these and used polypropylene bands, which allows for almost unmanned production. [Background technology]

[0002] Packaging cable ties used for packaging are primarily made from polypropylene (hereinafter referred to as "PP") or polyethylene terephthalate (hereinafter referred to as "PET"), and are manufactured by adding secondary ingredients such as pigments, forming them into strips 5mm to 25mm wide, and then applying a diamond-shaped embossed pattern to the surface. Various types are used depending on the application, but domestic consumption is estimated at around 36,000 tons per year.

[0003] Currently, horizontal recycling, in which used PP packaging ties (hereinafter also referred to as "PP bands") are collected, sorted using a color sorting device, and then recycled into bands of blue, yellow, green, etc., is being developed as a method for recycling packaging bands. Horizontal recycling refers to the recycling of discarded materials back into their original products, such as recycling used PP bands into PP bands again. For example, Patent Document 1 discloses a method for manufacturing stretch packaging bands using a synthetic resin material in which a thermoplastic synthetic resin made from recycled synthetic resin is blended with titanium oxide to conceal the color of the recycled synthetic resin. Patent Document 1 also discloses a method for manufacturing stretch packaging bands using a synthetic resin material in which a colored pigment having a desired color is further blended to give the stretch packaging band a desired color.

[0004] However, as packaging cable ties are not subject to the Container Recycling Law, this movement has not yet taken off. While there are exceptions, such as PET bottles, where recycling is widespread, the vast, diverse, and complex range of plastic containers, packaging materials, and parts is a veritable dark continent for recycling. Meanwhile, the development of sorting technology and equipment that underpin and enable recycling has been remarkable in recent years, and the possibilities for recycling of plastic products that were previously unimaginable are expanding.

[0005] For example, flexible container bags are known as packaging material products that are used in large quantities. Flexible container bags are sometimes abbreviated to FIBC (hereinafter also referred to as "FIBC"), and are also called container bags, ton bags, ton bags, jumbo sandbags, cross containers, and trans bags. In English-speaking countries, they are called Flexible Intermediate Bulk Containers, and are generally abbreviated to FIBC. In addition to FIBC, they are also called bulk bags, big bags, jumbo bags, etc.

[0006] Among these, simple flexible containers are made into a bag shape using foldable flexible material for the purpose of transporting large quantities of powder and granular materials, and are equipped with a fishing belt for hoisting and an opening for filling and discharging, and are used to transport industrial chemicals, synthetic resins, ceramic and stone products, feed, food, etc. The term refers to the cross single type defined in JIS Z1651:2008 "Flexible containers for non-hazardous materials" or the cross type defined in "Flexible containers in accordance with contamination-related guidelines" established by the Japan Flexible Container Industry Association.

[0007] In recent years, simple flexible containers have come to be used in large quantities to treat industrial waste such as construction debris, rubble, cinders, and soil surplus, but their disposal after use has become a social issue.In response to this, business initiatives have been launched aimed at reusing used simple flexible containers, and simple flexible containers made from outer bags containing mainly PP components, inner bags containing mainly polyethylene (hereinafter also referred to as "PE") components, and mainly PET fibers and nylon (nylon 6, 12, 66, etc.) fibers used in sewing, are crushed, washed several times with water, and subjected to specific gravity separation and centrifugation in water to remove as many impurities and dirt as possible, and the crushed product, which is mostly made up of PP and PE components, is extracted and pelletized.

[0008] On the other hand, PP straps have a certain level of demand in industrial society as individual packaging materials. However, packaging cable ties, i.e., PP straps, are materials used in logistics and have an extremely short lifespan. From the perspective of resource conservation and waste reduction, the use of recycled materials has long been advocated. Approximately 30% of PP strap demand is for specialty types with special specifications, while the remaining 70% is for general-purpose types with standardized specifications. As mentioned above, horizontal recycling of PP straps has begun, but its penetration rate is estimated to be around 10% of the general-purpose type demand. While general-purpose types have the potential to be replaced by horizontally recycled products, i.e., recycled straps, the reasons for their limited penetration are thought to be their poor appearance in terms of color tone and aesthetics, as well as the insufficient supply of recycled products, particularly in abundance.

[0009] The types and grades of PP resin, which are the main raw materials for PP bands and simple flexible containers, are the same or similar, and their respective manufacturing processes are also similar. From this perspective, cascade recycling of used simple flexible containers into PP bands has been proposed (see Patent Document 2). Cascade recycling refers to the recycling of discarded original products into other products, often with lower quality requirements. Cascade recycling of flexible containers or combinations of used flexible containers with used PP bands into PP bands, which use roughly the same resin grade and inorganic materials as raw materials, can significantly expand the recyclability of plastic products. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 5238708 [Patent Document 2] Japanese Patent Application Publication No. 2017-222425 Summary of the Invention [Problem to be solved by the invention]

[0011] However, to recycle simple flexible containers into PP bands, either alone or in combination with used PP bands, it is necessary to separate and remove foreign matter such as the remaining contents of the simple flexible container, waste related to storage, and the PET thread and / or nylon thread (nylon 6, nylon 12, nylon 66, etc.) used in sewing, which is part of the construction. However, because the separation and removal of PET thread and / or nylon thread (hereinafter also referred to as "PET thread, etc.") is particularly difficult, no industrial production system that solves this problem has been found to date, and this has prevented cascade recycling of simple flexible containers into PP bands.

[0012] According to estimates of the material classification of simple FIBC, approximately 2% by weight is PET yarn, etc., but the PET yarn, etc., which is part of the composition, has unique characteristics in terms of recycling. In other words, even if the filter is removed and all the PET yarn fragments are deliberately mixed into the PP to form a PP band, the performance of the PP band is not affected, and no particular change in appearance occurs visually. It is speculated that the fragments of PET yarn, etc., are mixed into the PP in a semi-molten state, and their fibrous nature plays a role similar to a filler. In other words, the fragments of PET yarn, etc., are not foreign matter to the PP band, but are a harmless part of the FIBC composition. This fact has been confirmed in a large number of test samples.

[0013] On the other hand, it is essential to remove foreign matter such as leftover flexible containers and storage waste. This is because the biggest problem with unmanned PP band production is that these contaminants can cause breaks in the stretching process and lead to abnormal appearances. To remove these contaminants, at least three types of filters are required: a minimum of 40 mesh, a maximum of 60-80 mesh, and a maximum of 120 mesh.

[0014] However, the 60-80 mesh filter used to remove this foreign matter also ends up filtering out pieces of PET threads and other components, causing the filter to become clogged approximately every 10-15 minutes. This is because the melting point of PET threads is 260-280°C, while the melting point of PP, the main material, is 190-200°C, and the PET threads and other components retain their unmelted fibrous form within the PP melting point temperature range.

[0015] When crushing simple flexible containers alone or in combination with used PP bands, the crushed material is recycled into pellets and then molded into recycled PP bands, the cut pieces of PET yarn and the like end up being troublesome waste like other foreign matter. However, in terms of the performance (physical properties and appearance) of the recycled PP bands produced, they are not simply foreign matter.

[0016] From this point of view, there are two conflicting issues involved in recycling crushed simple FIBC or crushed FIBC together with used PP bands into recycled PP bands, i.e., crushing crushed simple FIBC or crushed FIBC together with used PP bands into recycled pellets and molding recycled PP bands from the recycled pellets, and it is desirable to optimize these two issues.

[0017] The first challenge is to prioritize improving production volume and yield per unit time, allowing the inclusion of foreign matter such as leftover flexible containers and storage waste to the extent that it does not affect product quality, and forcibly producing recycled PP bands without using 60-80 mesh filters. The second challenge is to prioritize providing high-quality products, allowing for clogging of the 60-80 mesh filters by removed fragments of PET yarn, etc., and producing recycled PP bands from which up to 120 mesh foreign matter has been reliably removed, even if this reduces production volume and yield per unit time.

[0018] The object of the present invention is to provide a labor-saving manufacturing system that can carry out the entire PP band production process, from the production of recycled PP pellets (re-pellets) made from simple flexible containers or a combination of these with used PP bands, almost entirely unmanned, except for the shredding of the simple flexible containers and used PP bands, by selecting the originally desirable direction of producing recycled PP bands and removing cut products such as PET threads, which are not dangerous in terms of physical properties, and by selecting the original ... safe in terms of physical properties, and by selecting the original direction of producing recycled PP bands and removing [Means for solving the problem]

[0019] As a result of extensive research into solving the above problems, the inventors discovered that the above object can be achieved by using a single-stage extruder in the recycled polypropylene pellet manufacturing process and / or the recycled polypropylene band manufacturing process, and by equipping this single-stage extruder with a cylinder, a laser filter, a dual-piston screen changer or a sliding screen changer (hereinafter referred to as a "dual-piston screen changer, etc."), and a die section. This led to the completion of the present invention. Specifically, the present invention provides the following:

[0020] The invention according to a first aspect includes a recycled polypropylene pellet manufacturing process for manufacturing recycled polypropylene pellets from used simple flexible container bags or a combination of used simple flexible container bags and used polypropylene bands, and the recycled polypropylene pellet manufacturing process includes a melting step of feeding crushed used simple flexible container bags or a mixture of crushed used simple flexible container bags and crushed used polypropylene bands into a first single-stage extruder, together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the crushed bags as needed, and melting the crushed bags at a temperature of 190°C to 230°C to obtain a first recycled resin molten material; a foreign resin separation step of separating and removing sewing threads, which are part of the components, from the first recycled resin molten material in the first single-stage extruder; and a foreign material removal step of removing foreign materials from the first recycled resin molten material from which the sewing threads have been removed. This is a method for producing recycled polypropylene pellets, comprising: a removal step; and a pelletizing step in which the first recycled resin melt, from which the sewing thread and the foreign matter have been removed, is pelletized in the single-stage extruder, wherein the first single-stage extruder is equipped with a cylinder, a laser filter, a dual piston screen changer and / or a slider-type screen changer, and a die section; in the different resin separation step, the sewing thread is removed using a screen of 120 mesh or less using the laser filter; in the foreign matter removal step, the foreign matter is removed using a screen of 120 mesh or less using the dual piston screen changer and / or the slider-type screen changer; and in the pelletizing step, pellets are produced in the die section according to a strand method, a hot cut method, or an underwater cut method.

[0021] The second aspect of the invention is a method for producing recycled polypropylene bands, which further includes a recycled polypropylene band production step of producing recycled polypropylene bands from the recycled polypropylene pellets obtained by the first aspect of the invention.

[0022] Two-stage extruders are generally used to repelletize recovered plastics under the Container Recycling Law. However, because two-stage extruders subject the repellets to two heat treatments, this ultimately results in an increase in the melt flow index (MFI).

[0023] In the present invention, a foreign matter removal device consisting of a sewing thread separator for different resins, which is part of a configuration that uses a laser filter and is not normally equipped in extruders, and a subsequent dual piston screen changer, etc., is incorporated into the single-stage extruder for repelletization. This allows for continuous and reliable removal of foreign matter, such as broken pieces of PET threads and the like, as well as extremely small amounts of fine flexible container residue and storage waste, without cutting the strands, almost unmanned.

[0024] Laser filters are devices for separating and removing foreign resins, the level of which has rapidly improved in recent years. This device is a fully automatic device that places a pre-perforated (laser-machined) metal plate inside a cavity, moves this in a direction that compresses the molten resin filled in the cavity outward, filtering it, and then automatically scrapes off any foreign resins remaining on the surface of the metal plate after filtration. This means that there is no need to replace the metal perforated plate every time the device separates and removes a large amount of sewing thread that is part of the composition.

[0025] A dual piston screen changer or the like is a device that filters the extrusion material extruded from an extruder. In the present invention, crushed simple flexible containers or a combination of these and used PP bands are melted and kneaded in a single-stage extruder, and then filtered through the above-mentioned foreign matter removal device, thereby removing most impurities, dirt, etc.

[0026] The invention according to a third aspect includes a recycled polypropylene band manufacturing process for manufacturing recycled polypropylene bands from recycled polypropylene pellets recycled from used simple flexible container bags or a combination of used simple flexible container bags and used polypropylene bands, and the recycled polypropylene band manufacturing process includes a melting process for supplying the recycled polypropylene pellets, together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the recycled polypropylene pellets, to a second single-stage extruder as needed, and melting the recycled polypropylene pellets at a temperature of 190°C to 230°C to obtain a second recycled resin melt; a foreign resin separation and removal process for removing sewing threads, which are part of the constituents, from the second recycled resin melt in the second single-stage extruder; and a foreign matter removal process for removing foreign matter from the second recycled resin melt from which the sewing threads have been removed. the second single-stage extruder is equipped with a cylinder, a laser filter, a dual piston screen changer and / or a slider-type screen changer, and a die section, the foreign resin separation and removal step uses a laser filter to remove the sewing thread with a screen of 120 mesh or less, and the foreign matter removal step uses the dual piston screen changer and / or the slider-type screen changer to remove the foreign matter with a screen of 120 mesh or less, and after the foreign matter removal step, the second recycled resin melt from which the sewing thread and the foreign matter have been removed is sent to the die section, and recycled polypropylene bands are produced from the die section using a polypropylene band production apparatus subsequent to the second single-stage extruder.

[0027] In the present invention, a laser filter, which is a device for separating and removing foreign resins, and a subsequent foreign matter removal device such as a dual piston screen changer, which are not normally installed in extruders, are installed in the single-stage extruder for melting the pellets. This allows for the continuous, almost unmanned, reliable removal of foreign matter such as broken pieces of PET yarn and extremely small amounts of fine flexible container residue and storage waste, without cutting the strand.

[0028] The invention relating to the fourth feature is in a different category from the invention relating to the first feature. The invention relating to the fifth feature is in a different category from the invention relating to the second feature. The invention relating to the sixth feature is in a different category from the invention relating to the third feature.

[0029] The seventh aspect of the invention is recycled polypropylene pellets derived from used simple flexible container bags or a combination of such bags and used polypropylene bands, which contain 95% by weight or more polypropylene and thread-like material derived from polyethylene terephthalate and / or nylon, and have a melt flow index (MFI) of 4.0 g / 10 min to 5.5 g / 10 min at a temperature of 230°C and a load of 2.16 kg. The eighth aspect of the invention is recycled polypropylene bands derived from used simple flexible container bags or a combination of such bags and used polypropylene bands, which contain 95% by weight or more polypropylene and thread-like material derived from polyethylene terephthalate and / or nylon, and have a melt flow index (MFI) of 4.0 g / 10 min to 5.5 g / 10 min at a temperature of 230°C and a load of 2.16 kg.

[0030] According to the seventh and eighth aspects of the invention, recycled polypropylene pellets derived from used simple flexible container bags, which contain thread-like impurities derived from polyethylene terephthalate and the like, or a combination of these with used polypropylene bands, can be provided in a high-quality state with an MFI of 4.0 g / 10 min or more and 5.5 g / 10 min or less. [Effects of the Invention]

[0031] This invention makes it possible to manufacture flexible container re-pellets, the raw material for manufacturing flexible container bands, from used simplified flexible containers or combinations of these with used PP bands, and to produce and sell flexible container bands using these raw materials.The flexible container pellets and flexible container bands can be used as an alternative to virgin PP bands, contributing to CO2 reduction and plastic waste reduction. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 shows an example of a simple flexible container 1. [Figure 2] FIG. 2 is a schematic diagram of a single-stage extruder 2. [Figure 3] FIG. 3 is a schematic diagram of the screen changer 3. DETAILED DESCRIPTION OF THE INVENTION

[0033] First, although the following disclosure, diagrams, and / or claims may be described as being presented alone or in combination with one or more other aspects, the subject matter of the immediate disclosure is not intended to be so limited. That is, the immediate disclosure, diagrams, and claims are intended to encompass the various aspects described herein, each alone or in one or more combinations with each other. For example, even if the immediate disclosure describes and illustrates a first, second, and third embodiment in such a way that the first embodiment is described and illustrated specifically in conjunction with the second embodiment, or the second embodiment is described and illustrated only in conjunction with the third embodiment, the immediate disclosure and illustrations are not so limited and may include only the first embodiment, only the second embodiment, only the third embodiment, or one or more combinations of the first, second, and / or third embodiments, such as the first and second embodiments, the first and third embodiments, the second and third embodiments, or the first, second, and third embodiments.

[0034] The use of the phrase "or" in this text shall mean a "non-exclusive" arrangement unless expressly specified otherwise. For example, when we say "item X is A or B," we mean either: (1) item X is either A or B, or (2) item X is both A and B. In other words, the word "or" is not used to define an "exclusive" arrangement. For example, the "exclusive 'or'" arrangement for the statement "item X is A or B" requires that X be either A or B.

[0035] Additionally, the phrases "comprising at least one of" and "comprising at least one of the following," when used in conjunction with a system or element, mean that the system or element includes one or more of the elements listed after the phrase. For example, if there are three types of elements, element 1 through element 3, the phrases "comprising at least one of" and "comprising at least one of the following" are to be interpreted as any of the following structural arrangements: a device including the first element, a device including the second element, a device including the third element, a device including the first and second elements, a device including the first and third elements, a device including the second and third elements, or a device including the first, second, and third elements.

[0036] A similar interpretation is intended when the phrase "used in at least one of" is used herein. Additionally, "and / or" is used herein as a verbal conjunction to indicate that one or more of the listed elements or conditions are included or occur. For example, a device including a first element, a second element, and / or a third element is to be interpreted as any of the following structural arrangements: a device including the first element, a device including the second element, a device including the third element, a device including the first and second elements, a device including the first and third elements, a device including the second and third elements, or a device including the first, second, and third elements.

[0037] In addition, the use of the phrase "and / or" in the text means a "non-exclusive" agreement, as stipulated in the Japanese Industrial Standards (JIS) "Format and preparation method of standard sheets JIS Z 8301."

[0038] An example of a preferred embodiment of the present invention will be described below with reference to the drawings. Note that this is merely an example, and the technical scope of the present invention is not limited to this example.

[0039] <Manufacturing method of recycled polypropylene bands> This method is roughly divided into two steps: (1st step) a recycled PP pellet manufacturing process in which recycled PP pellets are manufactured from simple flexible containers or a combination of simple flexible containers and used PP bands, and (2nd step) a recycled PP band manufacturing process in which recycled PP bands are manufactured from the recycled PP pellets. During this process, it is necessary to remove foreign matter contained in the simple flexible containers, and this removal is carried out in either or both of the 1st and 2nd steps.

[0040] [First embodiment] When foreign matter is removed at least in the first step [Step 1: Recycled PP pellet manufacturing process] The first step may be located in the same factory as the second step, the recycled PP band manufacturing process, or may be located separately in different factories.

[0041] The equipment and devices that make up the first step are first a crusher for simple flexible containers or used PP bands, then a water washing device for the crushed products, then a centrifugal dehydrator, and finally an extruder.

[0042] First, used simple flexible containers are collected. Figure 1 shows an example of a simple flexible container 1. Simple flexible container 1 is composed of multiple components, such as a flexible container body 11 made of an outer bag containing a PP component as its main component and an inner bag containing a PE component as its main component, hanging belts 12, an inlet fastening tape 13, an outlet fastening tape 14, and an attachment part 15. PET fiber, nylon fiber, etc. are used for hanging belts 12, inlet fastening tape 13, outlet fastening tape 14, and attachment part 15. Furthermore, since the simple flexible container has been used, other impurities and dirt are attached to it.

[0043] Next, the collected used simple flexible containers 1 are crushed in a crusher, and the crushed products are washed with water and dehydrated and dried.

[0044] Next, the crushed simple FIBC 1 is fed into the single-stage extruder 2. The raw material fed into the single-stage extruder 2 may be the crushed simple FIBC 1 alone, or a combination of the crushed simple FIBC 1 and crushed used PP bands (not shown). Among these, it is preferable that the raw material fed into the single-stage extruder 2 be a combination of the crushed simple FIBC 1 and crushed used PP bands (not shown) because (1) an improvement in the tensile strength of the recycled product is expected, (2) an increase in the amount of material recovered is expected, (3) variation in physical properties is reduced, and (4) deterioration of physical properties during recycling is reduced.

[0045] The advantages of using both are explained below. First, we will explain the difference between recycled pellets made from used simple flexible containers alone and recycled pellets made from used PP bands alone.

[0046] With the exception of special-order products, the type and grade of PP resin used as the main raw material for both is the same or very similar, and they can be considered to be made from almost the same raw material. Both also contain calcium carbonate (CaCO3) as a major additive to prevent cracking during stretching. Furthermore, the flat yarn and PP bands that form the base material for simple flexible containers are both manufactured using a warp stretching process to achieve high tensile strength.

[0047] However, there are differences in the amount of calcium carbonate and the specific gravity of the two. PP bands are almost the same standard for general-purpose products made by Japanese manufacturers, with the calcium carbonate content being 1.2% on a volume basis and the specific gravity of recycled pellets being 0.920 g / cm. 3 On the other hand, there is no standardized product standard for the amount of calcium carbonate mixed and the specific gravity of simple flexible containers alone, as there is for PP bands, and the amount of calcium carbonate mixed varies from company to company, ranging from 3.0% to 4.2%. The specific gravity also varies from company to company, ranging from 0.935 g / cm 3 (Shinyo Co., Ltd.), 0.946 g / cm 3 (Yuzawa Clean Center Co., Ltd.), 0.975g / cm 3 (FUKURO, Fu Shun Yu Industrial Co., Ltd. (Taiwan)) and others.

[0048] Important parameters for the physical properties of PP bands are tensile strength and the fusion strength specified therein (70% or more of the tensile strength of the base material), but as long as PP bands are recycled using only used PP bands as raw materials, there is uniformity in the standards of each company for used PP bands as raw materials, so even if used PP bands from different companies are mixed, there will be no major problems in terms of quality for either the recycled pellets obtained from used PP bands or the recycled bands.

[0049] However, when recycling PP straps using only simple FIBC as raw material, the calcium carbonate content varies from manufacturer to manufacturer, ranging from 3.0% to 4.2%. Therefore, when recycled pellets and recycled straps are obtained from a mixture of used PP straps from different manufacturers, variations in quality can occur. Table 1 compares the physical properties of pellets recycled from PP straps and pellets recycled from simple FIBC, which contain a relatively high calcium carbonate content. High calcium carbonate content in the raw material reduces the tensile strength of the recycled pellets. Because the calcium carbonate content of PP straps is lower than that of simple FIBC, using a blend of crushed simple FIBC and crushed PP straps as raw material is expected to not only improve the tensile strength of the recycled product, but also reduce the variation in physical properties, even when used PP straps from different manufacturers are mixed together. [Table 1]

[0050] When a blend of crushed simple flexible containers and crushed PP bands is used as the raw material, from the viewpoint of improving the quality of the recycled product and preventing variations in physical properties, the weight of used PP bands per 1.0 simple flexible container weight is preferably 0.1 or more, more preferably 0.3 or more, and even more preferably 0.5 or more. On the other hand, taking into consideration the original purpose of recycling simple flexible containers, the weight of used PP bands per 1.0 simple flexible container weight is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less.

[0051] The raw material fed into the single-stage extruder 2 may further contain virgin pellets. Virgin pellets are new pellets that are not recycled. Because virgin pellets have no thermal history and do not contain calcium carbonate, they are expected to have the effect of suppressing the MFR, improving the tensile strength of the recycled product, and suppressing variations in physical properties even when used PP bands from various companies are mixed together.

[0052] When virgin pellets are added to the raw materials, from the viewpoint of improving the quality of the recycled product and preventing variations in physical properties, the weight of virgin pellets per 1.0 weight of the recycled product (simple flexible containers and used PP bands combined) is preferably 0.1 or more, and more preferably 0.2 or more. On the other hand, taking into consideration the original purpose of recycling simple flexible containers, the weight of virgin pellets per 1.0 weight of the recycled product (simple flexible containers and used PP bands combined) is preferably 0.5 or less, and more preferably 0.4 or less.

[0053] 2 is a schematic diagram of a single-stage extruder 2. The single-stage extruder 2 has a cylinder 21, a rotatable screw 22 inserted in the cylinder 21, an inlet 23 connected to the cylinder 21, and a die section 24 connected to the cylinder 21.

[0054] This embodiment is characterized in that the extruder for producing recycled PP pellets has a single-stage structure.

[0055] Two-stage extruders are more commonly used for repelletizing recovered plastics under the Container Recycling Law. For example, paragraph

[0054] of Patent No. 6442002, "Method for Regenerating Waste Synthetic Resin," also presumes two-stage extrusion and describes the removal of thermoplastic and thermosetting resins, metals, and other foreign matter using a laser screen. However, because two-stage extruders subject the repellets to two heat histories, this ultimately results in an increase in the melt flow index (MFI).

[0056] In this embodiment, a foreign matter removal device consisting of a laser filter and two types of dual piston type screen changers and / or a sliding type screen changer, which are not usually installed in extruders, is installed at the cylinder tip 25 of the single-stage extruder 2 for re-pelletization. This makes it possible to continuously and reliably remove foreign matter such as broken pieces of PET yarn and extremely small amounts of fine residual flexible containers and storage waste almost unmanned (with extremely low replacement frequency) without cutting the strand.

[0057] Sewing threads such as PET and nylon (NY) are part of the simple flexible container construction, and therefore account for a very large amount, approximately 2% of the weight, and cannot be removed in the water washing process. Therefore, with conventional screen meshes, the large amount of threads causes clogging in approximately 10 to 15 minutes on a 60-80 mesh screen, making it impossible to automate the removal of PET sewing threads. This means that replacing the mesh requires manual labor, significantly reducing extrusion volume.

[0058] Laser filters are devices for separating different resins and removing foreign matter, and the level of technology has rapidly improved in recent years. Laser filters can use metal perforated plates with large surface areas, and because of their large surface area, the filtration pressure can be significantly reduced compared to conventional screen meshes. This means that large amounts of unwanted material can be separated.

[0059] In addition, since filtering is performed by moving a metal perforated plate perpendicular to the resin flow path inside the cavity, non-filtered material can be automatically cleaned after filtration using a scraper built into the mechanism, and by repeating this process continuously, production can be continued without the need for manual labor.

[0060] By using a laser filter, it is possible to filter out the large amount of PET shredded yarn at the PP melting temperature range, without having to melt it at high temperatures to pass through the screen mesh. In other words, it is possible to find a way to avoid the biggest problem in pelletizing crushed flexible container products.

[0061] In the classic wire mesh method, the wire mesh is fixed and the molten resin moves through it to be filtered. The laser filter method is the reverse of the conventional method, where a perforated metal plate moves through the molten resin to filter it, and after filtering, foreign matter is automatically scraped off with a scraper (wiper). This is the greatest feature and benefit of the laser filter.

[0062] The laser filter is suitable for removing about 2% of impurities such as PET thread fragments, and can handle up to 5% of impurities. The metal perforated plate is replaced once a month, and the scraper is replaced about once a week.

[0063] The filter size is not particularly limited, but is preferably 120 mesh (opening 0.132 mm) or less, more preferably 20 mesh (opening 0.98 mm) to 100 mesh (opening 0.154 mm), and even more preferably 40 mesh (opening 0.455 mm) to 60 mesh (opening 0.233 mm). Laser filters may have elliptical holes rather than square holes. In this case, the filter size is determined from the length of one side of a square with the same area as the elliptical holes.

[0064] The screen changer is a device that filters the extrusion material extruded from the extruder. As shown in Fig. 3, the screen changer 3 includes a case body 31 fixed to the front end 25 of the extruder 2, and a screen unit 32 supported by the case body 31 and capable of sliding in the X-axis direction perpendicular to the extrusion direction. The screen unit 32 includes a slide plate 34 that passes through a guide hole 33 provided in the case body 31, and multiple (e.g., two) filtering screens 35 attached to the slide plate 34.

[0065] Generally, the amount of residual materials, dirt, garbage, and other added materials mixed in is small to begin with, and most of them can usually be removed in the washing process after crushing, so there is very little foreign matter that needs to be removed with a screen mesh. Therefore, continuous production without stopping can be achieved using methods such as dual piston or sliding screen types.

[0066] According to the present invention, in the process of producing high-quality pellets from crushed FIBC material, a composite mechanism that combines a device for separating different resins that are part of the composition (laser filter) with a device for removing foreign matter that is subsequently mixed in (screen changer) is introduced between the cylinder 21 and the die section 24 of the extruder 2, thereby establishing an unmanned continuous production system.

[0067] As a safety measure, it is preferable to add an antioxidant when processing the recycled PP pellets.

[0068] When PP is attacked by heat and oxygen, peroxy radicals (POO·), which are generated when free radicals react with oxygen, act as the main chain-carrying radical. These peroxy radicals are highly reactive and accelerate degradation. Alkoxy radicals, which are generated by peroxy radicals through hydrogen abstraction reactions, beta-cleavage reactions, radical-radical reactions, and double bond addition reactions, also contribute to degradation through similar reaction mechanisms.

[0069] Peroxy radicals abstract hydrogen from other organic substances to become hydroperoxides, which then generate new free radicals and cause a chain reaction. The requirements for antioxidants that suppress this autoxidation reaction are as follows: Taking these into consideration, the optimal antioxidant is selected based on its chemical structure and molecular weight. (1) Preventing radical generation and chain reactions caused by radicals (2) Prevention of chain reactions caused by peroxy radicals (3) Prevention of autoxidation by transition metals (4) Good compatibility with resins (5) Does not volatilize at processing temperatures (6) Long oxygen absorption induction time (7) Neither the additive nor the reactant is colored. (8) Insoluble in water and oil (9) Non-toxic

[0070] The performance of an antioxidant depends on its diffusion rate, reaction rate, and number of radicals trapped within the plastic. A high diffusion rate facilitates mobility within the plastic, favoring reaction with radicals. However, a high diffusion rate also promotes bleeding, so antioxidants must be selected based on both factors. The diffusion rate varies depending on (1) the antioxidant's molecular weight, (2) steric hindrance, (3) resin structure, and (4) ambient temperature. Therefore, the appropriate antioxidant varies depending on the type of plastic and the environment in which it is used. Therefore, these factors must be taken into consideration when selecting an antioxidant. Phenols or amines are preferred as radical chain inhibitors, phosphites or sulfur-based compounds are preferred as peroxide decomposers, and hydrazines or amides are preferred as metal deactivators. Antioxidants suitable for each application inhibit reactions occurring on the surface of recycled PP pellets and recycled PP bands. Some antioxidants trap radicals and prevent autoxidation, while others decompose hydroperoxides into harmless compounds. The former are called primary antioxidants, and the latter are called secondary antioxidants. Furthermore, transition metals react with hydroperoxides to generate harmful peroxy radicals, so the metal deactivator also has an antioxidant effect.

[0071] The purpose of using an antioxidant in the present invention is to prevent the thermoplastic resin from being decomposed into smaller molecules due to thermal degradation, which can occur when producing recycled raw materials by kneading simple flexible containers at high temperatures in extruder 302. There are no particular limitations on the type of antioxidant, but examples include phenol-based radical chain inhibitors and phosphite-based peroxide decomposers.

[0072] In particular, a combination of a primary antioxidant that scavenges radicals and a secondary antioxidant that has the ability to decompose hydrocarbons exhibits a high synergistic effect. Because the phenolic antioxidant has the effect of suppressing the autoxidation of the phosphite antioxidant, and the phosphite antioxidant has the effect of suppressing the discoloration of the phenolic antioxidant, the combination of a phenolic and a phosphite antioxidant exhibits a synergistic effect in terms of oxidation prevention.

[0073] The content of the antioxidant is not particularly limited, but it is preferable to use, for example, a phenol-based antioxidant and a phosphite-based antioxidant in a combined amount of 0.05% each.

[0074] Furthermore, in order to prevent the propagation of cracks in extruded and stretched products such as stretched packaging bands, it is preferable to add calcium carbonate or talc in an extruder in a ratio of 0 to 10 parts by weight per 100 parts by weight of crushed used simple flexible container 201, melt the mixture with the recycled raw material, knead it, and filter it to produce recycled PP pellets. Note that 0 part by weight means that there are cases where it is not necessary to add calcium carbonate or talc.

[0075] Alternatively, a colorant with a complementary hue (i.e., an organic or inorganic colorant, or both organic and inorganic colorants) can be added to an extruder in powder, granule, or masterbatch form, melted, mixed, and filtered with the recycled raw material to produce recycled PP pellets. According to the color circle, each hue has a complementary color that is the exact opposite (e.g., blue-green for red, yellow-green for purple, blue-purple for yellow, etc.). Because recycled raw materials are produced from a collection of simple flexible containers, they have hues that include pigments and dyes originating from the simple flexible containers. Adding a colorant with a complementary hue (i.e., a powder, granule, or masterbatch) to an extruder in powder, granule, or masterbatch form to the recycled raw material or the dominant hue in the mixed color can neutralize the recycled raw material. If necessary, a white coloring material such as barium sulfate may be added in the form of powder, granules, or masterbatch to increase the brightness of the achromatized recycled raw material.

[0076] To ensure that extrusion-stretched products such as stretched packaging bands made from recycled PP pellets have a desired hue, a colorant having the hue that the composite recycled resin composition is intended to produce, i.e., an organic colorant, an inorganic colorant, or both an organic colorant and an inorganic colorant, is introduced into an extruder in the form of powder, granules, or masterbatch, and then melted, kneaded, and filtered with the recycled raw material to produce recycled PP pellets. Therefore, in the present invention, in order to ensure that the composite recycled resin composition has a desired hue, it is preferable that the composite recycled resin composition contains at least two colorants, i.e., a colorant having a hue intended to neutralize the recycled raw material, and a colorant having the hue that the composite recycled resin composition is intended to produce. In this way, by adding a colored colorant whose hue is complementary to the hue of the recycled raw material to make the recycled raw material achromatic, the composite recycled resin composition can produce the desired hue using the colored colorant whose hue is intended to be produced by the composite recycled resin composition, more vividly than when titanium oxide is added to conceal the color of the recovered synthetic resin.

[0077] To suppress the formation and growth of resinous deposits (commonly known as "pitting gunk") in the die 307 of the extruder used in the recycled PP pellet production process, it is preferable to add at least one selected from the group including calcium stearate, magnesium stearate, zinc stearate, calcium carbonate, and talc to the extruder, or to add at least one selected from the group including calcium stearate, magnesium stearate, zinc stearate, calcium carbonate, and talc and a compatibilizer that has affinity for both the at least one selected from the group including calcium stearate, magnesium stearate, zinc stearate, calcium carbonate, and talc to the extruder, and then melt, knead, and filter the recycled raw material to produce recycled PP pellets. Addition of these substances is effective when the temperature of the thermoplastic resin component in the extruder 302 is in the range of 190 to 230°C.

[0078] As described above, pelletized recycled raw material can be produced by the single-stage extruder 302. The melt flow index (MFI) of the recycled PP pellets is 4.0 g / 10 min or more and 5.5 g / 10 min or less (MFI measurement conditions: temperature 230°C, weight 2.16 kg).

[0079] [Second step: Recycled PP band manufacturing process] In this embodiment, the method for producing a recycled PP band using recycled PP pellets as a raw material is not particularly limited. The obtained recycled PP pellets are melt-stretched to produce a band made of a cured product of the recycled resin composition. The melt-stretching can be carried out according to a known method. The band is then subjected to the surface treatment described above, cut to the desired length, and wound up to produce a recycled packaging binding band.

[0080] [Second embodiment] When foreign matter is removed at least in the second step [Step 1: Recycled PP pellet manufacturing process] In the first embodiment, a foreign matter removal device composed of a laser filter and two types of dual piston type screen changers following the laser filter was installed in the cylinder tip 401 of the single-stage extruder 302, but this is not particularly limited in the second embodiment. The foreign matter removal device may or may not be installed in the cylinder tip 401 of the single-stage extruder 302.

[0081] [Second step: Recycled PP band manufacturing process] In the first embodiment, the obtained recycled PP pellets were simply melt-stretched, but in the second embodiment, there are limitations on the configuration of the extruder used to melt the recycled PP pellets. As explained in [First Step: Recycled PP Pellets Manufacturing Process] of the first embodiment, the extruder must be a single-stage extruder, and a foreign matter removal device consisting of a laser filter and two types of dual-piston screen changers following it must be installed at the cylinder tip 401 of the single-stage extruder 302. As in the first embodiment, it is possible to continuously and reliably remove foreign matter such as broken PET yarn fragments and extremely small amounts of fine flexible container residue and storage waste almost unmanned (with extremely low replacement frequency) without cutting the strand. [Example]

[0082] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples. There is no.

[0083] <Preparation of raw materials> The four types of raw materials shown in Table 2 were prepared as raw materials to be fed to the extruder. [Table 2] Crushed flexible container: specific gravity 0.975, calcium carbonate content 4.0% Recycled pellets: specific gravity 0.912, calcium carbonate content 1.2% Virgin pellets: specific gravity 0.900, calcium carbonate content 0.0%

[0084] <Test> Example 1 In the apparatus described in the first embodiment, raw material having the composition shown in #1 was supplied to the first single-stage extruder 2, and the crushed material was melted to obtain a first recycled resin melt. Then, sewing threads were removed using a 60-mesh screen with a laser filter, and foreign matter was removed using a 120-mesh screen with a dual-piston screen changer. The material was then pelletized in the die section 24 according to the strand method to obtain recycled pellets according to Example 1.

[0085] Example 2 Regenerated pellets according to Example 2 were obtained in the same manner as in Example 1, except that the raw material composition was the composition shown in #2.

[0086] [Reference example 1] Regenerated pellets according to Reference Example 1 were obtained in the same manner as in Example 1, except that the raw material composition was the composition shown in #3.

[0087] [Reference example 2] Regenerated pellets according to Reference Example 2 were obtained in the same manner as in Example 1, except that the raw material composition was the composition shown in #4.

[0088] Comparative Example 1 The recycled pellets according to Comparative Example 1 were obtained by the method described in JP 2017-014316 A. That is, the recycled pellets according to Comparative Example 1 were obtained by a method including the steps of: providing a plurality of extruders each having a cylinder, a rotatable screw inserted into the cylinder, an inlet connected to the cylinder, and a die lip connected to the cylinder; connecting the provided extruders in series in multiple stages so that the die lip of a first extruder is connected to the inlet of a second extruder; providing a mesh unit having a mesh size of 0.3 mm or less or 60 or more meshes in the die lip of the first extruder or the second extruder among the multiple stage extruders; introducing the shredded flexible containers into the inlet of the first extruder among the multiple stage extruders; and melting the introduced flexible containers in the multiple stage extruders and filtering them through the mesh unit. The composition of the raw material fed into the first extruder was the composition shown in #1, and the conditions for the first and second extruders were the same as in Example 1.

[0089] Comparative Example 2 Regenerated pellets according to Comparative Example 2 were obtained in the same manner as in Comparative Example 1, except that the raw material composition was the composition shown in #2.

[0090] <Evaluation> The MFR and tensile strength were measured, and the results are shown in Table 3. [Table 3]

[0091] In Examples 1 to 3, the production of recycled PP pellets (Repellets) using simple flexi-bags or a combination of simple flexi-bags and used PP bands as raw materials could be carried out almost unmanned, except for the crushing of the simple flexi-bags and used PP bands.

[0092] In Examples 1 to 3, a foreign matter removal device consisting of a sewing thread separator for different resins, which is part of a configuration using a laser filter and is not normally provided in extruders, and a subsequent dual piston screen changer, etc., was incorporated into the single-stage extruder for repelletization. This is thought to have made it possible to achieve continuous and reliable removal of foreign matter, such as broken pieces of PET threads and the like, as well as extremely small amounts of fine flexible container residue and storage waste, almost unmanned, without cutting the strands.

[0093] In contrast, in Comparative Examples 1 to 3, foreign matter such as residual flexible containers and storage waste could not be completely removed, and continuous unmanned production of recycled pellets could not be achieved. This is thought to be because the two-stage extruder subjects the recycled pellets to a double heat history, which ultimately resulted in an increase in the melt flow index (MFI).

[0094] Among them, Examples 2 and 3 have excellent tensile strength, and Example 3 has even better tensile strength. When recycling PP straps using only simple flexible containers as raw materials, the amount of calcium carbonate varies from company to company within a range of 3.0% to 4.2%, so if recycled pellets and recycled straps are obtained from a mixture of used PP straps from different companies, variations in quality may occur. Since the amount of calcium carbonate contained in PP straps is less than the amount of calcium carbonate contained in simple flexible containers, using a blend of crushed simple flexible containers and crushed PP straps as raw materials is thought to not only improve the tensile strength of the recycled product, but also suppress variations in physical properties even when used PP straps from different companies are mixed. [Explanation of symbols]

[0095] 1 Simple flexible container 11 Flexible container body 12 Lifting belt 13 Inlet fastening tape 14. Discharge outlet fastening tape 15 Mounting part 2 Single-stage extruder 21 cylinders 22 Screw 23 Inlet 24 Dice Section 25 Cylinder tip 3 Screen Changer 31 Case body 32 Screen Unit 33 Guide hole 34 Slide plate 35 screens

Claims

1. The process includes a recycled polypropylene pellet manufacturing process for manufacturing recycled polypropylene pellets from used simple flexible container bags or a combination of the same and used polypropylene bands, The recycled polypropylene pellet manufacturing process includes a melting step of supplying crushed used simple flexible container bags or a mixture of crushed used simple flexible container bags and crushed used polypropylene bands to a first single-stage extruder, together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the crushed products as needed, and melting the crushed products at a temperature of 190°C or more and 230°C or less to obtain a first recycled resin molten product; a foreign resin separation step of separating and removing sewing thread, which is a part of the constituent material, from the first recycled resin molten product in the first single-stage extruder; a foreign matter removal step of removing foreign matter from the first recycled resin molten product from which the sewing thread has been removed; and a pelletizing step of pelletizing the first recycled resin molten product from which the sewing thread and the foreign matter have been removed in the single-stage extruder. the first single-stage extruder includes a cylinder, a laser filter, a dual piston screen changer and / or a slider-type screen changer, and a die section, and in the different resin separation step, the sewing thread is removed using the laser filter with a screen of 120 mesh or less, and in the foreign matter removal step, the foreign matter is removed using the dual piston screen changer and / or the slider-type screen changer with a screen of 120 mesh or less; In the pelletizing step, the recycled polypropylene pellets are pelletized in the die section according to a strand method, a hot cut method, or an underwater cut method.

2. A method for producing a recycled polypropylene band, further comprising a recycled polypropylene band production step of producing a recycled polypropylene band from the recycled polypropylene pellets obtained by the production method according to claim 1.

3. The process includes a recycled polypropylene band manufacturing process for manufacturing recycled polypropylene bands from recycled polypropylene pellets recycled from used simple flexible container bags or a combination of used simple flexible container bags and used polypropylene bands, The recycled polypropylene band manufacturing process includes: A melting step in which the recycled polypropylene pellets are supplied to a second single-stage extruder, optionally together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the recycled polypropylene pellets, and the recycled polypropylene pellets are melted at a temperature of 190°C or higher and 230°C or lower to obtain a second recycled resin melt; a step of separating and removing a different resin from the second recycled resin melt in the second single-stage extruder, the step of removing sewing threads that are part of the components; a foreign matter removing step of removing foreign matter from the second recycled resin melt from which the sewing thread has been removed; Including, The second single-stage extruder includes a cylinder, a laser filter, a dual piston screen changer and / or a slider-type screen changer, and a die section; In the step of separating out different resins, the sewing thread is removed using a screen of 120 mesh or less using the laser filter, In the foreign matter removal step, the foreign matter is removed using the dual piston screen changer and / or the slide type screen changer with a screen of 120 mesh or less, After the foreign matter removal step, the second recycled resin melt from which the sewing thread and the foreign matter have been removed is sent to the die section, and recycled polypropylene bands are produced from the die section using a polypropylene band manufacturing device subsequent to the second single-stage extruder.

4. a first single-stage extruder for pelletizing crushed used simple flexible container bags or a mixture thereof in combination with crushed used polypropylene bands, together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the crushed materials, as required; The first single-stage extruder has a cylinder, a laser filter, a dual piston screen changer and / or a sliding screen changer, and a die section; The crushed product supplied to the first single-stage extruder is melted at a temperature of 190°C or higher and 230°C or lower, The sewing thread contained in the melted crushed product is removed using the laser filter with a screen of 120 mesh or less, Foreign matter contained in the melted crushed product is removed using a screen of 120 mesh or less using the dual piston screen changer and / or the slide type screen changer, A system for manufacturing recycled polypropylene pellets, wherein the first recycled resin melt from which the sewing thread and foreign matter have been removed is pelletized in the die section using a strand method, a hot cut method, or an underwater cut method.

5. A system for producing recycled polypropylene bands, further comprising a second single-stage extruder and a polypropylene band production device following the second single-stage extruder, downstream of the production system described in claim 4.

6. A second single-stage extruder into which recycled polypropylene pellets, which are recycled from crushed products obtained by crushing used simple flexible container bags or a mixture of crushed products and crushed products of used polypropylene bands, are supplied, if necessary, together with 50 parts by mass or less of virgin pellets per 100 parts by mass of the recycled polypropylene pellets; a polypropylene band manufacturing apparatus following the second single-stage extruder; Equipped with the second single-stage extruder has a cylinder, a laser filter, a dual piston screen changer and / or a sliding screen changer, and a die section; The recycled polypropylene pellets supplied to the second single-stage extruder are melted at a temperature of 190°C or higher and 230°C or lower, The sewing thread contained in the melted recycled polypropylene pellets is removed using the laser filter with a screen of 120 mesh or less, Foreign matter contained in the molten recycled polypropylene pellets is removed using a screen of 120 mesh or less using the dual piston screen changer and / or the sliding screen changer, A recycled polypropylene band manufacturing system in which the second recycled resin melt from which the sewing thread and foreign matter have been removed is sent to the die section, and recycled polypropylene bands are manufactured from the die section using a polypropylene band manufacturing device subsequent to the band extruder.

7. 95% by weight or more of polypropylene; and a thread derived from polyethylene terephthalate and / or nylon, The melt flow index (MFI) at a temperature of 230°C and a load of 2.16 kg is 4.0 g / 10 min or more and 5.5 g / 10 min or less. Recycled polypropylene pellets derived from used simple flexible container bags or a combination of these and used polypropylene bands.

8. 95% by weight or more of polypropylene; and a thread derived from polyethylene terephthalate and / or nylon, The melt flow index (MFI) at a temperature of 230°C and a load of 2.16 kg is 4.0 g / 10 min or more and 5.5 g / 10 min or less. Recycled polypropylene bands derived from used simple flexible container bags or a combination of these and used polypropylene bands.

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