Method of producing reclaimed polyolefin resin

Abstract

To provide a method of efficiently producing reclaimed polyolefin resin from a polyolefin base material which has a decorative layer and includes a volatile component.SOLUTION: A method of producing reclaimed polyolefin resin is provided, by which a decorative layer and a volatile component are removed from the decorative layer being a coating film layer or an ink layer and a polyolefin base material containing the volatile component. The method of producing reclaimed polyolefin resin, comprises following steps (1) and (2): (1) treatment with alkaline chemicals under a temperature condition in a range of 60-150°C; (2) any one of (A) treatment by at least one liquid selected from water, an organic solvent and a liquid containing an acid except for hydrochloric acid or (B) heating treatment, under a temperature condition in a following range: (A) 60-150°C, (B) 80-150°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled polyolefin resin, and more particularly to a method for producing recycled polyolefin resin from a polyolefin substrate having a decorative layer and containing volatile components. [Background technology]

[0002] In order to achieve carbon neutrality, there is a growing demand for chemical recycling and material recycling, rather than thermal recycling, which emits carbon dioxide, even in the case of polyolefin materials. There are already efforts underway to remanufacture polyethylene terephthalate (PET) beverage bottles from collected bottles.

[0003] However, the bottle caps that seal the openings of the above-mentioned plastic bottles are not made from a single component, but are usually made from different components, such as polypropylene (PP) or polyethylene (PE). Therefore, if these could be collected and reused to manufacture bottle caps, recycling would be possible in line with the idea of ​​"realizing a circular society."

[0004] Furthermore, the Act amending the Food Sanitation Act, etc., promulgated on June 13, 2018, introduced a positive list system that allows only materials whose safety has been evaluated to be used for food utensils, containers, and packaging, and requires that recycled materials used in food contact applications must be materials whose safety is guaranteed in accordance with the positive list system.

[0005] Patent Document 1 (JP 2023-96775 A) proposes producing recycled bottle cap material from bottle caps that have already been released on the market. Patent Document 1 discloses a method for producing recycled bottle cap material from recovered bottle cap material, in which cleaning and contaminant removal processes are performed as decontamination steps. The cleaning process in Patent Document 1 involves immersing crushed bottle caps in heated alkaline water or water to remove contaminants, and the contaminant removal process is a heat treatment.

[0006] Patent Document 2 (Patent No. 7401019) describes a method for removing a printing layer or adhesive layer from a polyolefin substrate, and discloses a method in which a laminate is immersed in a release liquid containing a basic compound and allowed to stand for a certain period of time, and then the laminate is stirred in another release liquid containing a basic compound to remove the release layer, and the laminate is then separated and recovered.

[0007] Furthermore, resin materials used in applications such as bottle caps for PET bottled beverages emit odors due to the penetration of volatile odorous components, such as the citrus odor of the beverage or the resin odor, as well as the odor of lower fatty acids caused by spoiled beverages. When such resin materials are regenerated and recycled, odorous components may remain in the recycled resin, hindering its use. For this reason, the majority of recovered bottle caps and other materials are currently incinerated and landfilled or dumped. Furthermore, even when recovered and used as recycled resin, they are not reused horizontally but are limited to cascade recycling, and are only used in applications where odor is not a problem, such as gardening supplies and civil engineering and construction supplies.

[0008] Even when plastic substrates from automobile parts collected on the market are recycled and used, there is a problem in that the odorous components that have adhered to them remain even when they are used for interior applications. Patent Document 3 (JP 2023-83898 A) describes a method for producing recycled resin in which the volatile components in recycled resin containing polyolefins are reduced by heating and drying the crushed material while circulating a gas through it. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2023-96775 [Patent Document 2] Patent No. 7401019 [Patent Document 3] Japanese Patent Application Publication No. 2023-83898 Summary of the Invention [Problem to be solved by the invention]

[0010] Among the polyolefin products that are eligible for recycling, there is currently little progress in recycling polyolefin products that have a decorative layer, such as a coating layer or ink layer, attached to the surface of the polyolefin base material, such as bottle caps. The decorative layer contains pigments and UV-curable acrylic resins. Some of these materials may not be listed on the positive list. Furthermore, if the decorative layer remains, it will affect the appearance of the molded product and its mechanical properties, such as impact resistance.

[0011] Patent Document 1 does not at all recognize the problem of removing such a decorative layer. Patent Document 2 is about recycling of film substrates and does not mention anything about odorous components, etc. Patent Document 3 only describes the removal of volatile components. In particular, when recycling polyolefin substrates, it is a major challenge to provide a manufacturing method that removes the decorative layer and reduces or eliminates odorous components. [Means for solving the problem]

[0012] Under these circumstances, the inventors have conducted further research and discovered that by combining specific treatments, it is possible to effectively remove the decorative layer and volatile components from polyolefin substrates, leading to the completion of the present invention.

[0013] That is, the present invention includes the following [1] to [7]. [1] A method for producing recycled polyolefin resin by removing a decorative layer, which is a coating layer or ink layer, and a volatile component from a polyolefin substrate, the decorative layer and the volatile component, the method comprising the following steps (1) and (2): (1) Treatment with alkaline chemicals, with temperature conditions in the range of 60°C to 150°C. (2) The treatment method is either (A) treatment with at least one liquid selected from water, organic solvents, and liquids containing acids other than hydrochloric acid, or (B) heat treatment, and the temperature conditions are within the following ranges. (A) 60℃~150℃ (B) 80℃~150℃

[0014] [2] The method for producing recycled polyolefin resin according to [1], wherein (1) is a process for removing the decorative layer. [3] A method for producing recycled polyolefin resin according to [1] or [2], wherein (2) is a process for mainly removing volatile components. [4] A method for producing recycled polyolefin resin according to [1], wherein the volatile components are derived from citrus fruits. [5] A method for producing recycled polyolefin resin according to [4], wherein the component derived from citrus fruits is terpene. [6] The method for producing a recycled polyolefin resin according to any one of [1] to [5], wherein the polyolefin base material is a bottle cap. [7] The method for producing a recycled polyolefin resin according to any one of [1] to [6], wherein the polyolefin substrate is a film or a bottle container. [Effects of the Invention]

[0015] According to the method for producing recycled polyolefin resin of the present invention, the decorative layer and volatile components of the polyolefin substrate can be effectively removed. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described. The present invention is a method for producing recycled polyolefin resin by removing the decorative layer and volatile components from a polyolefin substrate containing the decorative layer and volatile components through treatments in steps (1) and (2).

[0017] The decorative layer attached to the surface of the polyolefin substrate is a coating layer or an ink layer. The coating layer is generally a layer formed from a paint containing a pigment, a resin, a solvent, etc. Typical examples of the resin contained in the paint include acrylic resins, melamine resins, urethane resins, etc. The coating layer is formed on the surface of the polyolefin substrate by applying the paint to the polyolefin substrate and drying it.

[0018] The ink layer is generally a layer formed from an ink containing a dye or pigment, a resin, a solvent, etc. Typical examples of resins contained in the ink include acrylic resins (polyester acrylate, urethane acrylate, epoxy acrylate, etc.), epoxy resins, silicone resins, rosin resins, alkyd resins, soluble nitrocellulose, vinyl chloride-vinyl acetate copolymer resins, chlorinated PP resins, urethane resins, and polyamide resins. The ink layer is formed by printing the ink onto the surface of a polyolefin substrate. The coating layer or ink layer may be formed on the polyolefin surface via a primer layer, which is usually made of a resin, such as chlorinated polyethylene, chlorinated polypropylene resin, or acrylic-modified chlorinated polypropylene resin.

[0019] The polyolefin substrate is a polyolefin molded article. This polyolefin is a polymer having structural units derived from olefin. Examples of polyolefins that can be used include ethylene polymers, propylene polymers, ethylene-α-olefin copolymers, and propylene-α-olefin copolymers. These may be mixtures or may contain inorganic fillers.

[0020] The ethylene-based polymer has structural units derived from ethylene and may have structural units derived from an α-olefin having 3 to 20 carbon atoms. Examples of the α-olefin having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. The ethylene-based polymer preferably contains 0 to 1 mol% of structural units derived from an α-olefin having 3 to 20 carbon atoms, and is an ethylene homopolymer. Examples of the ethylene homopolymer include low-density polyethylene (LDPE) and high-density polyethylene (HDPE).

[0021] The ethylene-α-olefin copolymer is a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms. The ethylene-α-olefin copolymer contains 50 to 99 mol %, preferably 90 to 99 mol %, of structural units derived from ethylene, and 1 to 50 mol %, preferably 1 to 10 mol %, of structural units derived from the α-olefin. The α-olefin is as described above.

[0022] Such ethylene polymers and ethylene-α-olefin copolymers can be produced by polymerizing ethylene and α-olefins in the presence of a stereoregular polymerization catalyst, such as a Ziegler-Natta catalyst or a metallocene catalyst.

[0023] The propylene polymer has structural units derived from propylene, and may have structural units derived from ethylene or an α-olefin having 4 to 20 carbon atoms. The propylene polymer preferably has a content of structural units derived from ethylene or an α-olefin having 4 to 20 carbon atoms of 0 to 2 mass%, and is more preferably a propylene homopolymer. The α-olefin having 4 to 20 carbon atoms is as described above. The propylene-α-olefin copolymer may be a random copolymer or a block copolymer.

[0024] There are no particular limitations on the random copolymer, so long as it is a polymer obtained by random copolymerization of propylene and ethylene or an α-olefin. Among these, the propylene-α-olefin copolymer is preferably a binary random copolymerization of propylene and ethylene, or a terpolymerization of propylene, ethylene, and 1-butene. Such a polymer can be produced using a stereoregular polymerization catalyst similar to a stereoregular polymerization catalyst, under polymerization conditions and by a polymerization method similar to known polymerization conditions and methods.

[0025] The propylene-α-olefin random copolymer preferably has a composition in which the amount of propylene-derived structural units (propylene content) is 94 to 98 mass%, and particularly preferably 95 to 97 mass%, based on 100 mass%, and the amount of ethylene or α-olefin-derived structural units (collectively referred to as the α-olefin content) is preferably 2 to 6 mass%, and particularly preferably 3 to 5 mass%.

[0026] The block copolymer consists of a propylene homopolymer portion and a propylene-α-olefin copolymer portion. For example, the propylene-based block copolymer preferably contains, as the propylene homopolymer portion, 60 to 99% by mass of the propylene homopolymer, and, as the propylene-α-olefin copolymer portion, 1 to 40% by mass of a propylene-α-olefin copolymer containing 40 to 90% by mole of structural units derived from propylene and 10 to 60% by mole of structural units derived from an α-olefin having 2 to 20 carbon atoms other than propylene (the total amount of polymers being 100 moles).

[0027] The above polymers may contain biomass-derived monomers (ethylene, propylene, α-olefins) and / or chemically recycled monomers (ethylene, propylene, α-olefins). The monomers constituting the polymer may be only biomass-derived monomers, only chemically recycled monomers, or may further contain both biomass-derived monomers and / or chemically recycled monomers and fossil fuel-derived monomers.

[0028] Biomass-derived monomers are monomers derived from any renewable natural raw materials and their residues, including fungi, yeast, algae, and bacteria, and contain 14C isotopes as carbon. -12 The biomass carbon concentration (pMC) measured in accordance with ASTM D 6866 is about 100 (pMC). The biomass-derived monomer can be obtained by a conventionally known method.

[0029] Chemically recycled monomers are monomers obtained by depolymerizing polymers such as waste plastics and returning them to monomer units such as ethylene through depolymerization, thermal decomposition, etc. Chemically recycled monomers can be obtained by conventionally known methods.

[0030] The inclusion of biomass-derived monomers in the above polymers is desirable from the perspective of reducing environmental impact (mainly greenhouse gas emissions). Furthermore, the inclusion of chemically recycled monomers in the above polymers is desirable from the perspective of reducing environmental impact (mainly waste reduction). Even when these monomers are used, if the polymer production conditions, such as the polymerization catalyst, polymerization process, and polymerization temperature, are the same, the molecular structure will be the same as that of ethylene-α-olefin copolymers made from fossil fuel-derived monomers.

[0031] The polyolefin substrate may also contain additives such as antioxidants (phenolic, phosphorus-based, sulfur-based), ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antifogging agents, antiblocking agents, processing aids, coloring pigments, crosslinking agents, foaming agents, inorganic or organic fillers, flame retardants, and nucleating agents that accelerate the crystallization rate.

[0032] Examples of polyolefin substrates include films, bottle containers, and bottle caps. For example, examples of polyolefin substrates with decorative layers include bottle caps for PET bottles. Typical PET bottle caps are manufactured by known manufacturing methods, such as compression molding and injection molding. Examples of bottle containers with decorative layers include cosmetic bottles and beverage bottles, and examples of film substrates with decorative layers include food packaging materials and bottle labels.

[0033] The polyolefin substrate can be recycled material (hereinafter referred to as PCR) collected from the market, or recycled material (hereinafter referred to as PIR) collected from the product manufacturing stage. In this case, the polyolefin substrate may contain recycled material that is not printed with a decorative layer or the like. An embodiment in which unprinted recycled material is not included can also be cited as an embodiment of the present invention. In the case of PCR, various odors permeate the product, so the method of the present invention can reduce odors. In the case of PIR, although substances that cause food odors or rotten odors are not attached, the present invention is also effective in reducing odors emitted from various odorous components that are attached during processing.

[0034] Examples of polyolefin substrates having a coating layer formed thereon include automobile interior materials, and packaging materials and bottles made of polyolefin substrates having an ink layer formed thereon. Furthermore, the decorative layer of the polyolefin substrate with a decorative layer may be removed while it is still in the state in which it has been used as an article, but if necessary, the decorative layer may be removed after the article has been crushed. Furthermore, known methods can be used for pulverization, and the particle size of the pulverized product is not particularly limited, but the average particle size is usually 500 to 5000 μm. In the present invention, it is not necessary to pulverize the polyolefin substrate in step (1). However, it is preferable to use a pulverized polyolefin substrate in step (2), since this increases the surface area of ​​the polyolefin substrate and is presumed to enhance the effect of the treatment with at least one liquid selected from water, organic solvents, and liquids containing acids other than hydrochloric acid (hereinafter sometimes referred to as "liquid treatment") or the heat treatment.

[0035] Process (1) The polyolefin substrate is treated with an alkaline chemical at a temperature in the range of 60° C. to 150° C. By carrying out step (1), it is possible to remove the decorative layer formed on the surface of the polyolefin layer, including the primer layer. The alkaline chemical is at least one selected from NaOH, KOH, LiOH, Mg(OH)2, Ba(OH)2, Ca(OH)2, Na2B4O7, K2B4O7, NaAlO2, Na2CO3, K2CO3, etc. An alkaline electrolyte can also be used. The alkaline chemical is used as an aqueous solution in which one or more alkaline substances exhibiting a desired pH value are dissolved in water. Among these, NaOH, KOH, and alkaline electrolytic water are preferred, and NaOH is more preferred. The pH of these treatment solutions is preferably 7.5 to 14, and more preferably 12 to 14.

[0036] The alkaline chemical may also contain other compounding ingredients as needed. For example, it may contain small amounts of surfactants (anionic surfactants, cationic surfactants, nonionic surfactants), organic solvents, fatty acids, etc. Examples of surfactants include alkylbenzenesulfonates, dialkylsulfosuccinates, polyoxyethylene alkyl ethers, alkylamines such as triethylamine, and alkanolamines such as monoethanolamine. Examples of organic solvents include those that are highly compatible with water, such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, and t-butyl alcohol.

[0037] In the treatment of step (1), the polyolefin substrate with the decorative layer is immersed in the alkaline chemical, which hydrolyzes the resin components contained in the coating layer or ink layer, such as acrylic resin, and it is presumed that further treatment at a specific temperature accelerates the hydrolysis, and treatment at the specific temperature also causes the polyolefin substrate to expand, reducing the adhesion between the printing components and the substrate interface, allowing the decorative layer to be removed (peeled off).

[0038] The conditions for immersion in the alkaline chemical are not particularly limited as long as they are conditions that allow the decorative layer to be removed from the surface of the polyolefin substrate. In order to improve the efficiency of removing the decorative layer, it is preferable to immerse the polyolefin substrate in the decorative layer remover under heating. The temperature conditions for immersion are not particularly limited, but in order to efficiently regenerate, it is desirable that the polyolefin substrate does not melt. A temperature that does not melt the resin is preferable, and is also desirable from the viewpoint of energy saving.

[0039] When the polyolefin constituting the polyolefin substrate is polyethylene, the temperature condition is 60 to 120°C, preferably 80 to 120°C. When the polyolefin is polypropylene, the temperature condition is 60 to 150°C, preferably 80 to 150°C. The heating method may be steam heating, heating medium heating, or electric heating of the treatment vessel itself, or microwave dielectric heating of the water used for treatment, or a combination of both heating methods. Temperatures higher than the above range may cause the substrate to melt, resulting in poor handling and increased energy consumption. Temperatures lower than the above range may prevent the substrate from expanding, but the adhesive layer at the interface between the decorative layer and the substrate is maintained, resulting in reduced decorative layer removal efficiency. The pressure in step (1) is not particularly limited, and is usually carried out under normal pressure in consideration of work efficiency.

[0040] If agitation is performed in addition to immersion, the polyolefin substrates come into contact with each other, creating frictional forces, facilitating the removal of the decorative layer. Furthermore, adding glass beads to the container and vibrating the container brings the polyolefin substrates into contact with the glass beads, facilitating the removal of the decorative layer. Furthermore, stirring and vibration even out the temperature of the alkaline chemical, facilitating the removal of the decorative layer. The immersion time required to remove the decorative layer is affected by the thickness and size of the polyolefin substrate, so it is preferable to adjust the immersion time appropriately for each case. The immersion time is preferably 0.1 to 6 hours, and more preferably 0.5 to 2 hours.

[0041] After immersion treatment sufficient to remove the decorative layer, the polyolefin substrate is preferably removed from the removal solution and placed in a cleaning solution for approximately 0.1 to 1 hour for cleaning treatment. If cleaning is performed, the substrate is then removed from the cleaning solution and dried. Furthermore, stirring during the cleaning process can shorten the cleaning time. Examples of cleaning solutions include tap water, pure water, distilled water, purified water, and ion-exchanged water.

[0042] Process (2) In step (2), either (A) treatment with at least one liquid selected from water, organic solvents, and solutions containing acids other than hydrochloric acid, or (B) heat treatment is carried out. When the molded product is used as it is in step (1), it may be crushed as necessary.

[0043] In step (2), volatile components are primarily removed. Examples of volatile components in the present invention include components derived from the raw materials contained in the contents and components resulting from decomposition and decay. While the volatile components are not particularly limited, examples include components derived from citrus fruits, such as terpenes (e.g., limonene and A-terpineol), and lower fatty acids (e.g., acetic acid, butyric acid, valeric acid, and 3-methyl-2-hexenoic acid). Among these, terpenes typically remain highly persistent and are difficult to remove, making the method of the present invention effective. Terpenes such as limonene, in particular, have a high boiling point, but can be removed even at relatively low temperatures (e.g., at the present invention), making them extremely valuable in practical use. Furthermore, volatile components also include plasticizers, viscosity modifiers, ultraviolet absorbers, antioxidants, compatibilizers, gas barrier agents, antistatic agents, etc. contained in the resin molded body, as well as surfactants, fragrances, etc. contained in the contents of the packaging container.

[0044] (A) Liquid treatment (A) The treatment with a liquid is a treatment using at least one liquid selected from water, an organic solvent, and a liquid containing an acid other than hydrochloric acid. The liquid may be in a liquid state at the processing temperature, but is preferably in a liquid state at 23°C. Examples of water include tap water, pure water, distilled water, purified water, and ion-exchanged water. Examples of organic solvents include hydrocarbons such as heptane and hexane, methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, t-butyl alcohol, etc. Preferred examples of hydrocarbons include those having 5 to 17 carbon atoms, and more preferably those having 5 to 10 carbon atoms. Furthermore, preferred hydrocarbons are aliphatic hydrocarbons, and more preferred are hydrocarbons without a cyclic structure. The alcohol preferably has 1 to 5 carbon atoms, and more preferably has 2 to 3 carbon atoms. Specific examples of acids other than hydrochloric acid include sulfuric acid, phosphoric acid, nitric acid, perchloric acid, and hypochlorous acid. Each of these is preferably in the form of a solution, more preferably an aqueous solution. The pH of these solutions is preferably 1 to 6.5, and more preferably 1 to 3.

[0045] Furthermore, at least one liquid selected from the group consisting of water, organic solvents, and liquids containing acids other than hydrochloric acid may contain other compounding ingredients in addition to alkali, if necessary, such as a small amount of a surfactant.

[0046] The surfactant may be at least one selected from the group consisting of anionic surfactants, cationic surfactants, nonionic surfactants, and amphoteric surfactants, without particular limitation. From the viewpoint of the ability to remove volatile components, at least one selected from the group consisting of anionic surfactants and nonionic surfactants is preferred.

[0047] When the surfactant has an alkyl group, the number of carbon atoms in the alkyl group is preferably 3 or more, more preferably 6 or more, and even more preferably 8 or more from the viewpoint of the ability to remove volatile components, and from the same viewpoint, is preferably 20 or less, more preferably 18 or less, and even more preferably 16 or less. Here, the number of carbon atoms in the alkyl group refers to the carbon number of the alkyl group with the largest number of carbon atoms when the surfactant has multiple alkyl groups in one molecule. From the viewpoint of the ability to remove volatile components, the number of alkyl groups in the surfactant is preferably 1 or more and 2 or less.

[0048] Examples of surfactants include alkylbenzenesulfonates, dialkylsulfosuccinates, polyoxyethylene alkyl ethers, alkylamines such as triethylamine, and alkanolamines such as monoethanolamine.

[0049] Of the liquids mentioned above, organic solvents are preferred.

[0050] The conditions for immersion in the liquid are not particularly limited as long as they allow volatile components to be removed from the surface of the polyolefin. To improve the decorative layer removal efficiency, immersion under heated conditions is preferred. The temperature condition for the liquid treatment is 60°C to 150°C. Conditions that do not melt the polyolefin substrate are desirable from the viewpoint of energy conservation, and are also preferred for ease of handling, such as not requiring a crushing process when the treated material is further supplied to a recycling process such as pelletization.

[0051] When the polyolefin constituting the polyolefin substrate is polyethylene, the temperature condition is 60 to 120°C, preferably 80 to 120°C. When the polyolefin is polypropylene, the temperature condition is 60 to 150°C, preferably 80 to 150°C. The heating method may be steam heating, heating medium heating, or electric heating of the treatment vessel itself, or a method of dielectrically heating the water used for treatment with microwaves, or a combination of both heating methods. High temperatures result in melting of the substrate, making it difficult to handle. Energy consumption also increases. Low temperatures result in less volatilization of volatile components. The immersion time required to remove volatile components is affected by the thickness and size of the polyolefin substrate, so it is preferable to adjust the immersion time appropriately for each case. The immersion time is preferably 0.1 to 8 hours, more preferably 0.5 to 6 hours.

[0052] Stirring in addition to immersion will make the liquid temperature uniform and promote the removal of volatile components. The immersion time required to remove the volatile components is affected by the thickness and size of the polyolefin substrate, so it is preferable to adjust the immersion time appropriately for each case. The immersion time is preferably 0.1 to 6 hours, and more preferably 0.5 to 2 hours.

[0053] After immersion treatment sufficient to remove volatile components, the polyolefin substrate is removed from the removal solution and placed in a cleaning solution for approximately 0.1 to 1 hour. It is then removed from the cleaning solution and dried. Furthermore, stirring during the cleaning process can shorten the cleaning time. Examples of cleaning solutions include tap water, pure water, distilled water, purified water, and ion-exchanged water. (A) The pressure in the treatment with the liquid is not particularly limited, and in consideration of work efficiency, the treatment is usually carried out under normal pressure, but at 100°C or higher, it is preferable to carry out the treatment under pressurized conditions.

[0054] (B) Heat treatment The heat treatment (B) is not particularly limited as long as it involves heating the polyolefin substrate that has been subjected to the step (1). The temperature condition is 80° C. to 150° C. Conditions under which the polyolefin substrate does not melt are desirable from the viewpoint of energy saving, and are also preferred from the viewpoint of ease of handling, such as not requiring a pulverization process when the treated material is further supplied to a recycling process such as pelletization.

[0055] When the polyolefin constituting the polyolefin substrate is polyethylene, the temperature condition is 60 to 120°C, preferably 80 to 120°C, and when the polyolefin is polypropylene, the temperature condition is 60 to 150°C, preferably 80 to 150°C.

[0056] The heating method is not particularly limited. Furthermore, the heating method may be either steam heating, heating medium heating, heating of the treatment vessel itself by electric heating, or a method of dielectrically heating the water mixed with the pulverized recovered material by microwaves, or a method combining both heating methods.

[0057] The heating time required to remove odorous components is affected by the thickness and size of the polyolefin substrate, so it is preferable to adjust the immersion time appropriately for each case. The heating time is preferably 0.5 to 24 hours, more preferably 2 to 12 hours.

[0058] Specifically, the polyolefin substrate may be placed in a heating device such as a heating dryer or an infrared heating device. In addition to the drying treatment using a normal pressure heating device, examples of the drying treatment include vacuum drying treatment in which heating is performed in a vacuum dryer, hot air treatment in which hot air is applied to the polyolefin substrate, hot inert gas treatment in which the polyolefin substrate is heated through a hot inert gas, hot water treatment in which the polyolefin substrate is immersed in a hot water bath, and hot steam treatment in which heated steam is passed through the polyolefin substrate.Furthermore, a method in which both heated steam and an inert gas are passed through may also be used.Among these, hot inert gas treatment, heated steam treatment, or a combination thereof is preferred, and hot inert gas treatment is more preferred from an economical point of view. As the heat treatment, it is particularly preferable to pass an inert gas or heated steam through the mixture.

[0059] The inert gas used is not particularly limited, and air, nitrogen gas, helium gas, argon gas, etc. may be used. Regarding temperature conditions, when using a heating device, the atmospheric temperature is adjusted. In the case of vacuum heat treatment, the atmospheric temperature of the dryer or drying device is adjusted. The atmospheric temperature is also adjusted in the case of hot air treatment, hot inert gas treatment, heated steam treatment, etc.

[0060] In the case of hot water treatment, the temperature is the hot water temperature. In the case of hot inert gas treatment, the temperature of the inert gas is adjusted to a predetermined temperature by heating the introduction means, etc. In the case of heated steam treatment, the temperature of the heated steam is adjusted to a predetermined temperature.

[0061] (2) After the end of the process, the recovered material may be washed, dehydrated, or dried as needed, and may further be pulverized or granulated. Granulation can be performed using a variety of kneading extruders, including single-screw extruders, twin-screw extruders, Banbury mixers, and roll mills, and is not particularly limited. Depending on the desired product specifications, the recycled material may be mixed with other resins, fillers, and additives to adjust the quality. The preferred treatment procedure is step (1) followed by step (2). This is because the treatment in step (1) may cause odors from alkaline chemicals to permeate the polyolefin substrate, and the odors that permeate in step (1) can be removed in step (2). The manufacturing method for recycled polyolefin resin of the present invention described above can be combined with the removal or reduction of printing components and odorous components, making it possible to expand into applications such as food contact, and is expected to enable horizontal recycling, which has previously been difficult. That is, according to the method for producing recycled polyolefin resin of the present invention, the decorative layer is removed, making the material highly safe for use as a food contact material. Furthermore, odorous components are reduced or eliminated, so the odor remaining in molded products made from recovered materials is also reduced. Therefore, collected PET bottle caps can be expanded into horizontal recycling of food contact materials, etc. Similarly, collected automobile parts can be expanded into interior applications. Furthermore, according to the method for producing recycled polyolefin resin of the present invention, it may be possible to provide a recycled polyolefin resin having excellent appearance and high impact resistance in the resulting molded article.Furthermore, it is possible to provide a recycled polyolefin resin having excellent appearance and high impact resistance in the resulting molded article. [Example]

[0062] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0063] The samples used were polyethylene PET bottle caps collected from the market.

[0064] [Example 1] <Step (1): Alkaline chemical treatment> A SUS test container was placed with 12g of a high-density polyethylene PET bottle cap and 300ml of a 5% by weight sodium hydroxide aqueous solution as a decorative layer remover, and immersed at 80°C for 0.5 hours. The temperature is the actual measured temperature of the decorative layer remover. After immersion in the decorative layer remover, the test liquid adhering to the removed sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The moisture on the sample was wiped off, and the remaining state of the printed portion was visually observed.

[0065] <Step (2): Treatment with Liquid> 12 g of PET bottle caps treated with the above removal method and 300 ml of isopropyl alcohol were placed in a stainless steel test container and immersed for 6 hours at 80°C. The temperature mentioned above refers to the actual measured temperature of the liquid. After immersion, the isopropyl alcohol adhering to the removed sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes.

[0066] How to evaluate remaining print After step (1) was completed, the sample was visually observed before step (2) to evaluate whether there was any residual printing. Furthermore, even when step (1) was not performed, the sample was visually observed and evaluated before step (2). Furthermore, the presence or absence of residual printing was also evaluated after step (2).

[0067] Evaluation method for odor components After step (2), approximately 2 g of the PET bottle cap was shredded and placed in a vial, which was then sealed. The vial was heated to 150°C, and an SPME (solid-phase microextraction) fiber was inserted into the vial to capture the generated gas for 15 minutes. The SPME fiber was then subjected to GC / MS. The amount of odorous component (limonene) was determined from the peak area value of the chromatogram obtained by GC / MS, and the reduction effect was confirmed. Residual amount of limonene (%)=(chromatogram peak area value of limonene after treatment in step (2)) / (chromatogram peak area value of limonene before treatment in step (1))×100

[0068] ●SPME-GC / MS conditions SPME fiber: Carboxen / PDMS Heating collection temperature: 150℃(15min) Desorption temperature: 300℃(3min) GC-MS device: 7890B-5977B (manufactured by Agilent) Column: HP-5MS (30m x 0.25mm ID x 0.5μm) Column flow rate: 1.5 mL / min (constant flow rate control) Injection mode: Splitless CTS: -150℃ (4 min) Heating conditions: 50°C (2 min) → Heating rate 10°C / min → 320°C (1 min)

[0069] [Example 2] Treatment and evaluation were carried out in the same manner as in Example 1, except that in step (2) in Example 1, hexane was used instead of isopropyl alcohol and the immersion temperature was set to 60°C.

[0070] [Example 3] The treatment in step (1) was carried out in the same manner as in Example 1, and then the following heat treatment (thermal inert gas treatment) was carried out as step (2). The PET bottle caps were placed in a ventilated dryer, which was then heated and heated nitrogen was passed through the device and released to the outside. The temperature of the ventilated dryer and the heated nitrogen were adjusted so that the temperature inside the ventilated dryer reached the specified temperature. The specified temperature was the actual temperature measured inside the ventilated dryer. After 8 hours, the heater was turned off and the temperature had dropped, after which the samples were removed and evaluated. Temperature inside the ventilation dryer: 110℃ Heated nitrogen flow rate: 50 L / min

[0071] [Example 4] The treatment in step (1) was carried out in the same manner as in Example 1, and then the following heat treatment (inert gas treatment + heated steam treatment) was carried out as step (2). The PET bottle caps are placed inside the ventilated dryer, the temperature of the ventilated dryer is increased, and heated nitrogen and heated steam are passed through the device and released to the outside. The temperature of the ventilated dryer, heated nitrogen, and heated steam is adjusted so that the temperature inside the ventilated dryer reaches the specified temperature. The specified temperature is the actual measured temperature inside the ventilated dryer. After 8 hours, the heater is turned off and the temperature drops, and then the samples are removed and evaluated. Temperature inside the ventilation dryer: 110℃ Heated nitrogen flow rate: 50 L / min Heating steam temperature: 95℃ Heating steam flow rate: 13.3g / min

[0072] [Example 5] The treatment in step (1) was carried out in the same manner as in Example 1, and then the following heat treatment (infrared heat treatment + hot air treatment) was carried out as step (2). The temperature inside the infrared heating device is raised to the specified temperature, and then the plastic bottle cap is placed inside the device. The specified temperature is the actual temperature measured inside the infrared heating device. After 0.5 hours, the sample was removed and placed in a hot air dryer that had been heated to a predetermined temperature. After 6 hours, the sample was removed and evaluated. Temperature inside infrared heating device: 110℃ Hot air dryer temperature: 110℃

[0073] [Example 6] In Example 3, step (1) was carried out using an alkaline electrolyte (electrolyte: K2CO3) instead of the 5 mass% sodium hydroxide aqueous solution, and the thermal inert gas treatment was similarly carried out to obtain a sample. The obtained sample was similarly evaluated.

[0074] [Comparative Example 1] <Step (1): Non-alkaline chemical treatment> 12 g of a plastic bottle cap and 300 ml of a 5% by mass aqueous solution of hydrochloric acid were placed in a stainless steel test container and immersed for 6 hours at 80° C. The test liquid adhering to the removed sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The moisture on the sample was wiped off, and the remaining state of the printed portion was visually observed.

[0075] <Step (2): Treatment with Liquid> 12 g of the treated PET bottle cap and 300 ml of water were placed in a test container made of SUS and immersed at 30° C. for 1 hour. The odor components of the obtained samples were evaluated in the same manner as in Example 1.

[0076] Comparative Example 2 In Example 1, instead of the liquid treatment (treatment with isopropyl alcohol) in step (2), a similar treatment was carried out using a 5 mass % aqueous sodium hydroxide solution, and the obtained sample was evaluated in the same manner.

[0077] Comparative Example 3 The following thermal inert gas treatment was carried out. The alkaline chemical treatment in step (1) above was not carried out. Thermal inert gas treatment The same PET bottle caps as in Example 1 were placed in the ventilated dryer, the ventilated dryer was heated, heated nitrogen was passed through the device, and the heated nitrogen was released to the outside. The temperature of the ventilated dryer and the heated nitrogen were adjusted so that the temperature inside the ventilated dryer reached a predetermined temperature. The predetermined temperature was the actual measured temperature inside the ventilated dryer. After 8 hours, the heater was turned off and the temperature had dropped, and then the sample was removed and evaluated. Temperature inside the ventilation dryer: 110℃ Heated nitrogen flow rate: 50 L / min The odor components of the obtained samples were evaluated in the same manner as in Example 1.

[0078] Comparative Example 4 The following hot air treatment was carried out. The alkaline chemical treatment in step (1) above was not carried out.

[0079] Hot air treatment The same PET bottle caps as in Example 1 were placed in a heated hot air dryer and heated at 80°C for 8 hours. Device name: Stec Co., Ltd. Model: SBD-50AS The odor components of the obtained samples were evaluated in the same manner as in Example 1.

[0080] Comparative Example 5 The following vacuum heat treatment was carried out. The alkaline chemical treatment in step (1) above was not carried out.

[0081] Vacuum heating and drying process The same PET bottle caps as in Example 1 were placed in a heating vacuum dryer, and the inside of the dryer was heated at 80°C for 8 hours while creating a vacuum. Device name: Yamato Scientific Co., Ltd. Model: DP300 The odor components of the obtained samples were evaluated in the same manner as in Example 1.

[0082] Comparative Example 6 The following hot water treatment (corresponding to liquid treatment) was carried out. The alkaline chemical treatment in step (1) above was not carried out.

[0083] Hot water treatment 12 g of a plastic bottle cap and 300 ml of water were placed in a stainless steel test container and immersed at 80°C for 6 hours. The odor components of the obtained samples were evaluated in the same manner as in Example 1.

[0084] Comparative Example 7 The following treatments were carried out: The alkaline chemical treatment in step (1) above was not carried out. Liquid treatment 12 g of a plastic bottle cap and 300 ml of a 0.04 mass % aqueous solution of hypochlorous acid were placed in a stainless steel test container and immersed at 30°C for 1 hour. The odor components of the obtained samples were evaluated in the same manner as in Example 1. Although step (1) was not carried out in Comparative Examples 3 to 7, the presence of unprinted print was checked. In all cases, the printed components remained intact, and unprinted print was present. The results of the above examples and comparative examples are shown in Table 1.

[0085] [Table 1]

[0086] [Comparative Example 8] 12 g of a plastic bottle cap and 300 ml of a 5% by mass aqueous solution of hydrochloric acid were placed in a stainless steel test container and immersed for 6 hours at 80° C. After immersion, the sample was removed, the hydrochloric acid adhering to the sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The test liquid adhering to the removed sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The moisture on the sample was wiped off, and the remaining state of the printed portion was visually observed. Furthermore, when the odor components were evaluated, the remaining amount of limonene was found to be 100%.

[0087] Comparative Example 9 12 g of plastic bottle caps and 300 ml of isopropyl alcohol were placed in a stainless steel test container and immersed for 6 hours at 80°C. After immersion, the sample was removed, the isopropyl alcohol adhering to the sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The moisture on the sample was wiped off and the remaining print was visually inspected. The results are shown in Table 2. Furthermore, an evaluation of odor components revealed that the remaining amount of limonene was 12%.

[0088] [Comparative Example 10] 12 g of plastic bottle caps and 300 ml of hexane were placed in a stainless steel test container and immersed for 6 hours at 60°C. After immersion, the sample was removed, the isopropyl alcohol adhering to the sample was rinsed with water, and the sample was placed in a beaker containing water (room temperature) and stirred with a stirrer for 10 minutes. The moisture on the sample was wiped off, and the remaining state of the printed portion was visually observed. Furthermore, an evaluation of odor components revealed that the remaining amount of limonene was 1%.

[0089] From the above results, it can be seen that by combining the predetermined steps (1) and (2) as in the examples, the decorative layer can be removed and odorous components can be efficiently removed. Furthermore, in the Examples, the decorative layer could be removed and the volatile components could be significantly removed, compared to the case where the alkali treatment in step (1) was omitted, as in Comparative Example 3-10. However, even when heating in the presence of alkali, which does not correspond to step (2), was performed, as in Comparative Example 2, the removal of the volatile components was insufficient.

Claims

1. A method for producing recycled polyolefin resin by removing a decorative layer, which is a coating layer or ink layer, and a volatile component from a polyolefin substrate, the decorative layer and the volatile component, the method comprising the following steps (1) and (2): (1) Treatment with alkaline chemicals, with temperature conditions in the range of 60°C to 150°C. (2) (A) Treatment with at least one liquid selected from water, organic solvents, and liquids containing acids other than hydrochloric acid or (B) heat treatment, wherein the temperature conditions are within the following ranges: (A) 60℃~150℃ (B) 80℃~150℃

2. The method for producing recycled polyolefin resin according to claim 1, wherein (1) is a step for mainly removing a decorative layer.

3. The method for producing recycled polyolefin resin according to claim 1 or 2, wherein (2) is a step for mainly removing volatile components.

4. The method for producing recycled polyolefin resin according to claim 1, wherein the volatile components are components derived from citrus fruits.

5. The method for producing recycled polyolefin resin according to claim 4, wherein the component derived from citrus fruits includes terpene.

6. The method for producing recycled polyolefin resin according to claim 1, wherein the polyolefin substrate is a bottle cap.

7. The method for producing recycled polyolefin resin according to claim 1, wherein the polyolefin substrate is a film or a bottle container.

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