Recycling method for composite resin materials containing polyamide resin and polyolefin resin

Abstract

To provide a recycling method for composite resin materials containing polyamide and polyolefin resins, which enables recovery of high-quality polyamide resin from composite resin materials containing polyamide and polyolefin resins.SOLUTION: The recycling method for composite resin materials containing polyamide and polyolefin resins, comprises: a heating dissolving process for heating a composite resin material containing a polyamide resin and a polyolefin resin with a solvent containing polyol to obtain a mixture of a polyamide resin solution in which the polyamide resin is dissolved in the solvent containing polyol and a polyolefin resin melt in which the polyolefin resin is melted without being dissolved in the solvent containing polyol; a separation process for separating the mixture obtained by the heating dissolving process into the polyamide resin solution in which the polyamide resin is dissolved in the solvent containing the polyol and the polyolefin resin melt by using the viscosity difference between the polyamide resin solution in which the polyamide resin is dissolved in the solvent containing the polyol and the polyolefin resin melt; and a cooling distillation process for cooling quickly the polyamide resin solution in which the polyamide resin is dissolved in the solvent containing the polyol obtained in the separation process by using the latent heat of evaporation, and at the same time, distilling off the solvent containing the polyol to recover the polyamide resin.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for recycling a composite resin material containing a polyamide resin and a polyolefin resin. [Background technology]

[0002] In the past, businesses have been established to collect used thermoplastic plastic products such as PET bottles, sort them, remelt them, and further mold them for reuse.

[0003] In 2015, the 2030 Agenda for Sustainable Development, centered on the Sustainable Development Goals (SDGs), was adopted at the United Nations Summit. The SDGs are made up of 17 goals and 169 targets, ranging from poverty, hunger, health, education, water safety, and other issues such as development support for developing countries, to job satisfaction, economic growth, energy, and even climate change and biodiversity. They are international goals that aim to create a sustainable and better world by 2030. In 2020, Japan declared that it would aim to achieve zero greenhouse gas emissions overall by 2050, in other words, to achieve a carbon-neutral, decarbonized society. In response to this, in recent years, the promotion of the 3Rs, reduce, reuse, and recycle, has been further accelerated in order to protect the global environment.

[0004] In order to ensure various functionalities for plastic products, not only one type of plastic resin material is used, but composite resin materials containing two or more types of plastic resin materials are used for various purposes.

[0005] For example, in recent years, with the spread of frozen foods, composite resin materials containing polyamide-based resins and polyolefin-based resins have been used to protect foods and maintain their freshness, in which polyamide-based resins such as nylon film, which has excellent heat resistance, low temperature resistance, and puncture resistance, are laminated with polyolefin-based resins such as polyvinylidene chloride (hereinafter sometimes referred to as "PVDC") and polyolefin, which are resistant to the permeation of water vapor, oxygen, etc. If these composite resin materials are used as is without separating them into the individual resins, the products will have degraded physical properties.

[0006] Known methods for recycling polyamide resins to date include, for example, (i) a thermal recycling method in which polyamide resins are incinerated and recovered as thermal energy, (ii) a material recycling method in which polyamide resins are melted and then remolded for reuse, and (iii) a chemical recycling method in which polyamide resins are chemically depolymerized to return them to their raw nylon material and reused in nylon production, etc. Of these conventional recycling methods, the only way to separate and purify only polyamide resins from composite resin materials containing polyamide resins and polyolefin resins is to apply the chemical recycling method. However, chemical recycling is practically impossible because it requires a depolymerization step and a polymerization step. In particular, when a composite resin material contains a polyamide resin and an olefin resin containing chlorine, it is difficult to incinerate the material and recycle it, and in many cases the material is disposed of in landfills. Therefore, there is an urgent need to develop technology that will enable recycling by separating each resin material from various plastic products that use these composite resin materials.

[0007] For example, Patent Document 1 describes a method for recovering nylon from airbag scraps that contain silicone-coated nylon. The method described in Patent Document 1 involves dissolving nylon resin in ethylene glycol to separate silicone resin. Nylon resin dissolves when the temperature is raised to the boiling point of ethylene glycol (197°C). On the other hand, silicone resin does not dissolve or melt at this temperature (197°C), so the silicone resin can be easily separated. Here, the melting point of a general olefin resin is lower than the boiling point of ethylene glycol, and therefore, when the polyamide resin is in a dissolved state, the olefin resin is also molten and in a liquid state, making it difficult to separate the resin by filtration.

[0008] Patent Document 2 describes a method for removing a polyvinylidene chloride coating layer from a polyvinylidene chloride coating film and recovering a thermoplastic resin. The method described in Patent Document 2 is a method for recovering a thermoplastic resin such as a polyamide resin by continuously passing a thermoplastic resin film coated with polyvinylidene chloride through an organic solvent to dissolve the polyvinylidene chloride. However, organic solvents that dissolve polyvinylidene chloride (e.g., dimethylformamide, dimethylacetamide, tetrahydrofuran, etc.) are harmful to the human body. In addition, when the thermoplastic resin film is a polyamide-based resin, these solvents have a strong affinity with the polyamide resin and are difficult to completely remove, so that the polyamide-based resin cannot be reused.

[0009] Patent Document 3 describes a method of dissolving an aliphatic polyamide in a substantially anhydrous polyol (glycol) when recovering the aliphatic polyamide from a mixture of foreign matter and the aliphatic polyamide. When the glycol is heated to dissolve the aliphatic polyamide, the molecular weight of the aliphatic polyamide decreases, and the quality of the recycled polyamide decreases, making it unusable. To prevent this, the method described in Patent Document 3 is characterized in that a decrease in the degree of polymerization of the aliphatic polyamide is prevented by adding low-temperature glycol and cooling it. However, adding glycol for cooling requires a large amount of solvent, and the recovery of the solvent requires a lot of energy and time. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2018-172618 A [Patent Document 2] JP 2021-146682 A [Patent Document 3] Special Publication No. 10-512909 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in consideration of the above problems, and has an object to provide a method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin, which is capable of recovering high-quality polyamide-based resin from a composite resin material containing a polyamide-based resin and a polyolefin-based resin. [Means for solving the problem]

[0012] As a result of intensive research into solving the above problems, the present inventors have found that (1) When a composite material made of polyamide resin and polyolefin resin is heated together with a solvent containing polyol, the polyamide resin is hardly soluble, but dissolves when boiled. On the other hand, the polyolefin resin does not dissolve in the solvent containing polyol, and because of its low melting point, it melts at the boiling point of the solvent containing polyol and floats as a molten liquid. (2) The mixture of the polyamide resin solution and the polyolefin resin melt has a large difference in viscosity, so when the mixture is passed through a fine pore, the solution passes through a fine pore with a small pore diameter, but the melt does not pass through easily. Using this fact, we have considered separating the polyamide resin solution and the polyolefin resin melt. If the pore diameter is made small, the polyolefin resin melt hinders the polyamide resin solution from passing through, resulting in poor passability. On the other hand, if the pore diameter is large, both will pass through. Therefore, we have found that by selecting an appropriate pore diameter or by passing through the pore multiple times, it is possible to efficiently separate the solution in which the polyamide resin is dissolved in a solvent containing polyol from the polyolefin resin melt. (3) The polyamide resin dissolved at the boiling point of the polyol-containing solvent is reactive and undergoes a decrease in molecular weight, making it impossible to obtain a high-quality recycled polyamide resin. Possible methods for preventing the molecular weight reduction include: rapidly cooling to lower the temperature and slow down the reaction rate; rapidly cooling to precipitate the polyamide resin; and rapidly distilling off the solvent to precipitate the polyamide resin. Therefore, a method was investigated in which a polyamide-based resin solution in which the boiled polyamide-based resin, which has been separated from the polyolefin-based resin by a filter, is dissolved in a solvent containing a polyol, is transferred to a cooling distillation tank, and the solvent is immediately evaporated in a vacuum to lower the liquid temperature using the resulting latent heat. As the liquid temperature drops, the vacuum pressure is further reduced to evaporate the solvent. The resulting heat is used to further lower the liquid temperature. This process is repeated continuously to precipitate the polyamide-based resin by a method in which cooling and solvent distillation are performed simultaneously (hereinafter referred to as the "cooling distillation method"). As a result of carrying out this method, it was confirmed that the molecular weight reduction of the recycled polyamide-based resin was suppressed, and that the polyamide-based resin could be recycled, which led to the completion of the present invention.

[0013] That is, the present invention is as follows. Section 1. a heating and dissolving step of heating a composite resin material containing a polyamide-based resin and a polyolefin-based resin and a solvent containing a polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol; a separation step of separating the mixture obtained by the heat dissolution step into a polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt by utilizing a viscosity difference between the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt; and The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin includes a cooling distillation step of rapidly cooling the polyamide-based resin solution obtained in the separation step, in which the polyamide-based resin is dissolved in a solvent containing the polyol, by utilizing latent heat of vaporization, and at the same time, distilling off the solvent containing the polyol, thereby recovering the polyamide resin. Section 2. Item 2. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 1, wherein the polyol is at least one selected from the group consisting of ethylene glycol and propylene glycol. Section 3. 2. The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin according to claim 1, wherein the polyamide-based resin is at least one nylon selected from the group consisting of nylon 6, nylon 66, and copolymer resins thereof. Section 4. Item 2. A method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 1, wherein the polyolefin resin is at least one polyolefin resin selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, and polyvinylidene chloride. Section 5. Item 2. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 1, wherein the separation step is carried out using at least one filter having fine holes. Section 6. Item 6. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 5, wherein the filter has an opening rate of 19% or more and a mesh size of 0.5 to 2 mm. Section 7. The separation step is carried out using two filters having fine pores, Item 6. A method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 5, wherein the first filter has an opening rate of 19% or more and a mesh size of 0.5 to 2 mm, and the second filter has an opening rate of 19% or more and a mesh size of 0.2 to 0.5 mm. Section 8. Item 2. A method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to item 1, wherein the cooling distillation step is a cooling distillation step in which the solvent containing the polyol is removed by quenching using latent heat of vaporization, lowering the vacuum pressure in conjunction with the decrease in temperature, and lowering the final vacuum pressure to 24 hP or less. Section 9. a heating and dissolving step of heating a composite resin material containing a polyamide-based resin and a polyolefin-based resin and a solvent containing a polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol; a separation step of separating the mixture obtained by the heat dissolution step into a polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt by utilizing a viscosity difference between the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt; and The method for producing a recycled polyamide-based resin includes a cooling distillation step of rapidly cooling the polyamide-based resin solution obtained in the separation step, in which the polyamide-based resin is dissolved in a solvent containing the polyol, by utilizing latent heat of evaporation, and at the same time, distilling off the solvent containing the polyol, thereby recovering the polyamide resin. Section 10. Item 10. A recycled polyamide resin obtained by the production method according to item 9. Effect of the Invention

[0014] According to the present invention, it is possible to provide a method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin, which is capable of recovering a high-quality polyamide-based resin from a composite resin material containing a polyamide-based resin and a polyolefin-based resin.

[0015] [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a conceptual diagram showing a heating, dissolving and separating device for recovering polyamide resin according to the present invention. [Diagram 2] FIG. 2 is a conceptual diagram showing a cooling distillation device of the polyamide resin recovery apparatus of the present invention. [Diagram 3] FIG. 3 is another conceptual diagram showing the heating, dissolving and separating device of the polyamide resin recovery apparatus according to the present invention. [Figure 4] FIG. 4 is a conceptual diagram showing a separation filter. [Diagram 5] FIG. 5 is a conceptual diagram showing a two-stage separation method. [Figure 6] FIG. 6 is a conceptual diagram showing a two-stage separation method (an example in which mesh and punching are combined). [Figure 7] FIG. 7 is a photograph of the composite resin material placed in the polyamide resin recovery device of the present invention. [Figure 8] FIG. 8 is a photograph of the separated polyamide resin solution. [Figure 9]FIG. 9 is a photograph of the separation filter after the separation step. [Figure 10] FIG. 10 is a graph showing the chart results after measuring the raw composite resin material by FT-IR. [Figure 11] FIG. 11 is a graph showing the chart results after measuring the polyamide-based resin recycled according to the present invention by FT-IR. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Recycling method for composite resin material containing polyamide-based resin and polyolefin-based resin> The present invention will be described below. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin (hereinafter, also referred to as a "method for recycling a composite resin material") of the present invention includes the following steps (1) to (3). Step (1): A heating and dissolving step of heating a composite resin material containing a polyamide-based resin and a polyolefin-based resin and a solvent containing a polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol (hereinafter, this may be referred to as the "first step" or the "heating and dissolving step"); Step (2): A separation step of separating the mixture obtained by the heating and dissolving step into a polyamide-based resin solution in which the polyamide-based resin is dissolved in a solvent containing the polyol and the polyolefin resin melt by utilizing the viscosity difference between the polyamide-based resin solution in which the polyamide-based resin is dissolved in a solvent containing the polyol and the polyolefin resin melt (hereinafter, also referred to as the "second step" or "separation step"); Step (3): A cooling distillation step in which the polyamide resin solution obtained in the separation step, in which the polyamide resin is dissolved in a solvent containing the polyol, is rapidly cooled by utilizing latent heat of evaporation, and at the same time, the solvent containing the polyol is distilled off to recover the polyamide resin (hereinafter, this may be referred to as the "third step," the "cooling distillation step," or the "cooling solvent removal step"). By including the above steps (1) to (3), it is possible to recover a polyamide-based resin from a composite resin material containing a polyamide-based resin and a polyolefin-based resin without causing a decrease in the molecular weight of the polyamide-based resin.

[0018] Composite resin material containing polyamide resin and polyolefin resin The composite resin material in the present invention contains at least a polyamide resin and a polyolefin resin.

[0019] Polyamide Resin Polyamide resin is a general term for polymers linked by amide bonds, and the aliphatic polyamides nylon 6 and nylon 66 in particular are used as various engineering plastics in industrial products, carpets, automobile parts, etc., due to their excellent properties. As such, polyamide resins are used in a similar manner to polycarbonate (PC) as an engineering plastic. Polyamide resins are also an excellent material for fibers, with a market size second only to polyester.

[0020] The polyamide resin is not particularly limited as long as it can be dissolved in a solvent containing polyol. As the polyamide resin, a known aliphatic polyamide can be used. Aliphatic polyamide is also called "nylon". The polyamide resin may be a homopolymer or a copolymer. The aliphatic polyamide may contain an aromatic group in a part thereof. The aromatic ring may be a benzene ring; a condensed aromatic ring such as a naphthalene ring, an anthracene ring, or a pyrene ring; or a heteroaromatic ring such as a pyridine ring or a pyrrole ring. Specific examples of polyamide resins include ring-opening or aminocarboxylic acid condensates such as polycapramide (nylon 6), poly-α-pyrrolidone, poly-α-piperidone, and poly-ω-aminoheptanoic acid (nylon 7); Condensates of diamines and dibasic acids, such as polyethylene diamine adipamide (nylon 26), polytetramethylene adipamide (nylon 46), and polyhexamethylene adipamide (nylon 66); Aliphatic copolymer polyamides such as caprolactam / lauryl lactam copolymer (nylon 6 / 12), caprolactam / ω-aminononanoic acid copolymer (nylon 6 / 9), caprolactam / hexamethylene diammonium adipate copolymer (nylon 6 / 66), lauryl lactam / hexamethylene diammonium adipate copolymer (nylon 12 / 66), ethylenediamine adipamide / hexamethylene diammonium adipate copolymer (nylon 26 / 66), caprolactam / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon 66 / 610), and ethyleneammonium adipate / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymer (nylon 6 / 66 / 610); and the like.

[0021] These aliphatic polyamides may be copolymerized with aromatic polyamides. Examples of aromatic dibasic acids to be copolymerized include terephthalic acid, isophthalic acid, and 4,4'-diphenyl ether dicarboxylic acid. The aromatic diamine to be copolymerized may, for example, be metaxylylenediamine. As the polyamide resin, one or a combination of two or more of the above specific examples can be used.

[0022] As the polyamide resin, nylon 6 and nylon 66 are preferably used. There are no particular limitations on the physical properties of nylon 6 and nylon 66. For example, nylon 6 can be used in a wide range of polymerization degrees, from low polymerization degrees (relative viscosity of about 2.4) used for clothing or fibers, to medium polymerization degrees (relative viscosity of about 2.7) used for films or carpets, to high polymerization degrees (relative viscosity of about 3.1) used for threads or molded products requiring high strength. Also, nylon 6 with a polymerization degree lower or higher than the above range can be used. The relative viscosity is measured in a 1.00% solution of concentrated sulfuric acid at 25° C. using an Ubbelohde viscometer (No. 2) in accordance with the measurement method described in JIS K 6920-2.

[0023] Polyolefin resin (B) Since polyolefin resins are non-polar compounds and polyols are polar compounds, normal polyolefin resins do not dissolve in polyols. The method for recycling composite resin materials of the present invention involves dissolving a polyamide resin in a polyol and separating it from a polyolefin resin that is not soluble in the polyol, and therefore all polyolefin resins that are not soluble in the polyol can be used, including polyolefin resins that contain chlorine.

[0024] Polyalkylene Resin The polyalkylene resin is not particularly limited, and examples thereof include polyethylene (PE), polypropylene (PP), polybutene, polystyrene (PS), and the like.

[0025] Polyethylene (PE) The polyethylene (PE) is not particularly limited, and may be, for example, a polyethylene having a density of 0.910 to 0.930 g / cm 3 and low density polyethylene with a density of 0.942 g / cm 3 The melting point of polyethylene is about 98 to 137° C., which is lower than the boiling point of the solvent containing polyol.

[0026] Polypropylene (PP) The polypropylene (PP) is not particularly limited, and may be a stereoregular homopolymer having a melting point of about 165° C., which is commonly used, or an atactic polymer. It may also be a low polymer for meltblown (MI value of 50 or more) or a high polymer for molding (MI value of 10 or less). Even in the case of polypropylene with a low degree of polymerization, the melt viscosity is much higher than the viscosity of a polyamide resin solution in which a polyamide resin is dissolved in a solvent containing a polyol, so it is possible to separate the polyamide resin solution in which a polyamide resin is dissolved in a solvent containing a polyol from the polypropylene.

[0027] Polybutene (PB) The polybutene (PB) is not particularly limited, and examples thereof include 1-polybutene, 2-polybutene, etc. Among them, 1-polybutene can be preferably used. The melting point of polybutene is about 128 to 142°C.

[0028] Polystyrene (PS) There is no particular limitation on polystyrene (PS). Polystyrene does not have a melting point, but flows at about 100°C.

[0029] Chlorine-containing resin The chlorine-containing resin is not particularly limited, and examples thereof include polyvinylidene chloride resins (e.g., sometimes written as "PVDC") and polyvinyl chloride (e.g., sometimes written as "vinyl chloride" or "PVC").

[0030] Polyvinylidene chloride resin (PVDC) There is no particular limitation on the polyvinylidene chloride resin (Polyvinylidene Chloride: PVDC). The polyvinylidene chloride resin is usually not a homopolymer but a copolymer of vinylidene chloride and another monomer copolymerizable therewith, and a copolymer is preferred. The copolymer may be a graft copolymer, a block copolymer, or a random copolymer. These resins may be used alone or in combination of two or more kinds.

[0031] Examples of other monomers copolymerizable with vinylidene chloride include vinyl chloride; acrylic acid alkyl esters (alkyl group has 1 to 18 carbon atoms) such as methyl acrylate, ethyl acrylate, butyl acrylate, and lauryl acrylate; methacrylic acid alkyl esters (alkyl group has 1 to 18 carbon atoms) such as methyl methacrylate, butyl methacrylate, and lauryl methacrylate; acrylonitrile; aromatic vinyl such as styrene; vinyl esters of aliphatic carboxylic acids having 1 to 18 carbon atoms such as vinyl acetate; alkyl vinyl ethers having 1 to 18 carbon atoms; vinyl polymerizable unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid; alkyl esters of vinyl polymerizable unsaturated carboxylic acids (including partial esters, alkyl group has 1 to 18 carbon atoms) such as maleic acid, fumaric acid, and itaconic acid. Among them, at least one selected from the group consisting of vinyl chloride, methyl acrylate, and lauryl acrylate is preferable. These monomers can be used alone or in combination of two or more. Since polyvinylidene chloride resins are used as copolymers, their melting point is low and they usually soften and flow at about 170° C. Therefore, they melt and become a molten liquid at the boiling point of the solvent containing the polyol.

[0032] There is no limit to the content of copolymerization components other than vinylidene chloride in polyvinylidene chloride resin copolymers, but those containing up to 50 mol% are usually called polyvinylidene chloride resins. For normal food packaging, those copolymerized with 10 to 30 mol% vinyl chloride are used.

[0033] Polyvinyl chloride resin (PVC) There is no particular limitation on the polyvinyl chloride resin (PVC), and it can be either a soft one containing a large amount of plasticizer or a hard one without plasticizer. Examples of the plasticizer include ester compounds such as phthalic acid, adipic acid, phosphoric acid, and trimellitic acid. There is no limitation on the amount of plasticizer, and it is usually used in an amount of less than 50% by mass based on the total amount of the resin, but there is no problem even if it is contained in an amount of more than that. The polyvinyl chloride resin may be a homopolymer or a copolymer of vinyl chloride and other monomers copolymerizable therewith. The copolymer may be a graft copolymer, a block copolymer, or a random copolymer. These resins may be used alone or in combination of two or more kinds. The melting point of a polyvinyl chloride resin that is usually used is about 85 to 170° C., which is lower than the boiling point of the polyol-containing solvent that is used.

[0034] Examples of other monomers constituting the copolymer include olefins such as ethylene, propylene, butene, etc.; vinyl esters of saturated acids such as vinyl acetate, vinyl laurate, etc.; alkyl esters of unsaturated acids such as methyl acrylate, methyl methacrylate, etc.; alkyl vinyl ethers such as lauryl vinyl ether; maleic acid, acrylonitrile, styrene, methylstyrene, vinylidene fluoride, etc. These monomers can be used alone or in combination of two or more kinds.

[0035] When the polyvinyl chloride resin is a copolymer, there is no limitation on the content of other monomer units in the copolymer.

[0036] Examples of the composite resin material containing the above-mentioned polyamide-based resin and polyolefin-based resin (hereinafter, also referred to as "composite resin material") include a composite resin material containing nylon 6 (a1) and polyvinylidene chloride (b1-1); A composite resin material containing nylon 66 (a2) and polyvinylidene chloride (b1-1); A composite resin material containing nylon 6 (a1) and polyvinyl chloride (b1-2); A composite resin material containing nylon 66 (a2) and polyvinyl chloride (b1-2); A composite resin material containing nylon 6 (a1) and polyethylene (b2-1); A composite resin material containing nylon 66 (a2) and polyethylene (b2-1); A composite resin material containing nylon 6 (a1) and polypropylene (b3-1); and composite resin materials containing nylon 66 (a2) and polypropylene (b3-1). Among them, composite resin materials containing nylon 6 (a1) and polyvinylidene chloride (b1-1) and composite resin materials containing nylon 6 (a1) and polyethylene (b2-1) are preferred.

[0037] The content of the polyolefin resin is 1 to 90 parts by mass, preferably 1 to 20 parts by mass, and more preferably 1 to 10 parts by mass, relative to 100 parts by mass in total of the polyamide resin and the polyolefin resin.

[0038] The form of the composite resin material is not particularly limited, and examples thereof include granular forms such as powder, beads, pellets, or fragments or crushed materials such as films, or layered forms such as coating layers, films, sheets, nonwoven fabrics, fibers, textiles, or constituent layers of packaging materials.

[0039] There are no limitations on the individual forms of the polyamide resin and the polyolefin resin. For example, various combinations are included, such as a film-like multilayer film containing a polyamide-based resin film and a polyolefin-based resin film, a core-sheath fiber with a polyamide-based resin core, a blended yarn of polyamide-based resin fiber and polyolefin-based resin fiber, a yarn in which a polyamide-based resin fiber is coated with a polyolefin-based resin, and a cloth in which a polyamide-based resin fabric is laminated with a polyolefin-based resin. Preferred forms of the composite resin material include a multilayer film in which a polyamide-based resin film and a polyolefin-based resin film are laminated, a nylon filament whose surface is coated with a polyolefin-based resin, and a waterproof sheet in which a nylon sheet is laminated with a polyolefin-based resin. The composite resin material of the present invention may be waste or may be virgin.

[0040] Optional ingredients The composite resin material may contain optional components, such as additives and resins other than the polyamide-based resin and polyolefin-based resin, as long as they do not adversely affect the effects of the present invention.

[0041] The content of the optional components is usually 0 to 30 parts by mass, preferably 0 to 20 parts by mass, and more preferably 0 to 10 parts by mass, relative to 100 parts by mass in total of the polyamide-based resin, the polyolefin-based resin, and the optional components.

[0042] Examples of the additives include various additives such as heat stabilizers, plasticizers, processing aids, colorants (e.g., pigments, dyes, etc.), UV absorbers, pH adjusters, and dispersion aids. These can be used alone or in combination of two or more. When an additive is included, the amount of the additive is not particularly limited, and is, for example, about 0.001% by mass to 10% by mass in 100% by mass of the composite resin material.

[0043] Polyol-containing solvent The polyol used in the present invention is an aliphatic compound having 2 to 6 carbon atoms and having two or more hydroxyl groups (-OH). The number of hydroxyl groups is preferably 2 to 4, more preferably 2 to 3, and even more preferably 2. Examples of polyols include ethylene glycol (EG), propylene glycol (PG), and glycerin, and ethylene glycol (EG), propylene glycol (PG), and the like are preferably used. The solution containing polyol may contain one type of polyol alone or two types of polyols (ethylene glycol and propylene glycol) in combination. Furthermore, a solvent other than polyol may be added. As the polyol-containing solvent, it is preferable to use ethylene glycol alone from the viewpoints of the solubility of the polyamide resin, the thermal stability of the solvent, and the recoverability of the solvent.

[0044] Polyols are characterized by a high boiling point due to intermolecular forces caused by hydroxyl groups. The boiling points of ethylene glycol and propylene glycol are 197°C and 188°C, respectively. The boiling points of other polyols are higher than these. Therefore, at the boiling points of polyols, general polyolefin resins melt. Well-known solvents for polyamide resins include concentrated sulfuric acid, formic acid, and phenols. These are good solvents that dissolve polyamide resins even at room temperature. However, these solvents are difficult to handle and toxic, and if they remain in recycled polyamide resins, they are dangerous to the human body. In contrast, the solvent used in the present invention is a solvent containing polyol (hereinafter, sometimes referred to as a "polyol solvent"). While a solvent containing polyol is less dangerous to the human body, it has poor solubility for polyamide-based resins and cannot dissolve the polyamide-based resin unless the temperature is raised to the boiling point. In addition, since it is a poor solvent, when a solution containing a polyamide-based resin is cooled, the dissolved polyamide-based resin becomes powdery and precipitates, which is a characteristic of the solvent. When polyamide resin is dissolved in a solvent containing polyol by raising the temperature to the boiling point, the degree of polymerization of the polyamide resin decreases. As described above, the relative viscosity decreases with the heating time, which leads to a decrease in the quality and a loss of market value of the recycled polyamide resin. In the present invention, by carrying out the heating and dissolving step, the separation step, and the cooling and distillation step, it is possible to recover a high-quality polyamide-based resin without causing a decrease in the degree of polymerization of the polyamide-based resin even when the polyamide-based resin is dissolved in a solvent containing a polyol.

[0045] Process (1) (heating melting process) The heating and dissolving step of step (1) is a step of heating a composite resin material containing the above-mentioned polyamide-based resin and polyolefin-based resin and a solvent containing the above-mentioned polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol.

[0046] Material size The composite resin material is cut and heated in a solvent containing polyol. The size of the composite resin material when heated is preferably small because the polyamide resin is easily dissolved. However, if the size of the composite resin material is smaller than the pore size of the filter of the net-like container used in step (2) for separating the polyamide resin from the polyolefin resin, the composite resin material will leak out of the net-like container. Therefore, the size of the composite resin material is preferably larger than the pore size of the net-like container. That is, there is no particular limitation on the cutting size of the composite resin material as long as it is larger than the pore size of the net-like container 2 .

[0047] Solvent volume The amount of the solvent is not particularly limited, and is, for example, 250 to 1000 parts by mass, and preferably 300 to 500 parts by mass, relative to 100 parts by mass of the composite resin material. By using an amount within this range, the composite resin material is sufficiently immersed in the solvent and easily dissolved, and it is possible to prevent the solvent from requiring a lot of energy and time to be recovered.

[0048] Heating temperature and time Polyamide-based resins are difficult to dissolve in polyol-containing solvents and do not dissolve until the boiling point of the polyol-containing solvent is reached. However, once the polyol-containing solvent reaches its boiling point, the polyamide-based resin instantly dissolves. When the polyamide resin dissolves, the molecular weight of the polyamide resin decreases, so it is preferable to proceed to the next step (2) (separation step) immediately after the polyamide resin dissolves. The upper limit of the heating time after the polyamide resin is dissolved is a maximum of about 10 minutes. In a composite resin material (multilayer film) containing a polyamide resin and a polyolefin resin, in a boiled solvent containing a polyol, the polyamide resin dissolves in the solvent containing a polyol, but the polyolefin resin does not dissolve in the solvent containing a polyol. That is, since the boiling point of the solvent containing a polyol is higher than that of the polyolefin resin, the polyolefin resin melts. When the polyolefin resin melts, the individual melts gather together and float as a large aggregate. When the melting point of the polyolefin resin is higher than the boiling point of the solvent containing a polyol, the polyolefin resin remains solid, so that it is easy to separate the polyamide resin from the polyolefin resin. However, since the melting point of a general polyolefin resin is lower than the boiling point of the solvent containing a polyol, the polyolefin resin melts and becomes liquid at the boiling point of the solvent containing a polyol, so that it is difficult to separate the two. In the case of polyvinylidene chloride, which has a high melting point, the polyolefin resin is usually used as a copolymer, so that the melting point is lowered. Therefore, the polyvinylidene chloride copolymer melts at the boiling point of the solvent containing polyol, and a mixture of a polyamide resin solution in which the polyamide resin is dissolved in the solvent containing polyol and a melt of the polyolefin resin is obtained.

[0049] Process (2) (separation process) The separation step of step (2) is a step of separating a solution containing a polyamide resin and a molten polyolefin resin from the mixture obtained in the heat dissolution step. In other words, the separation step in the present invention is a step of separating the mixture obtained by the heating and dissolving step into a polyamide-based resin solution in which the polyamide-based resin is dissolved in a solvent containing the polyol, and the polyolefin resin melt, by utilizing the viscosity difference between the polyamide-based resin solution in which the polyamide-based resin is dissolved in a solvent containing the polyol, and the polyolefin resin melt. The polyamide resin solution and the polyolefin resin melt contained in the mixture obtained in step (1) are both liquid. If solid and liquid are to be separated, they can be easily separated by filtering through a wire mesh. However, since both the polyamide resin and the polyolefin resin contained in the mixture are liquid, they cannot be easily separated. Therefore, when the mixture was separated using various wire meshes, it was found that when the mesh size was too small, neither the polyamide resin nor the polyolefin resin passed through. When the mesh size was made a little larger, the polyamide resin solution started to pass through the mesh, but only a small amount was able to pass through due to the high viscosity of the polyolefin resin melt. In this case, the purity of the polyamide resin recovered from the passed polyamide resin solution was high, but the recovery rate was low. When the mesh size was further increased, the polyamide resin solution passed through the mesh while the polyolefin resin melt did not, and it was found that there exists a mesh size that allows the two to be separated. When the mesh size was further increased, the polyamide resin solution and the molten polyolefin resin passed through together. The larger the mesh, the more the polyolefin resin melt passed through, and eventually the two passed through as a whole, together. As a result, by passing the mixture through a filter having an appropriate pore size, it became possible to separate a polyamide resin solution in which a polyamide resin is dissolved in a solvent containing a polyol from a polyolefin resin melt.

[0050] The shape of the filter is not particularly limited as long as it has pores, and examples thereof include a wire mesh, a punched plate, a lattice, etc. The filter may be in the form of a sheet or a container. There is also no limitation on the material thereof, and as long as it is not affected by a high-temperature polyol-containing solvent, it may be metal, glass, carbon, plastic, etc. The mesh size of a separable filter is, for example, usually 0.2 to 4 mm, preferably 0.3 to 3 mm, and more preferably 0.5 to 2 mm, in the case of a plain woven wire mesh. The shape of the pores is not particularly limited and may be any shape, such as a square, a rectangle, a trapezoid, a rhombus, a triangle, a hexagon, a circle, an ellipse, or the like. If the cross-sectional area of ​​the pores is the same, approximately the same effect can be obtained. There is no particular restriction on the wire diameter of the wire netting, but as the wire diameter increases, the opening rate decreases, which hinders the filter passing of the polyamide resin solution and reduces the recovery rate of the recycled polyamide resin. Therefore, in order to obtain a certain level of recovery rate or higher, a certain level of opening rate or higher is necessary. That is, the opening rate is usually 19% or higher, and preferably 22% or higher.

[0051] The separation step can be carried out not only once but also twice or more times. In order to efficiently obtain a recycled polyamide resin with high purity, it is preferable to pass the resin through a filter not only once but also twice or more times. When the separation step is carried out twice, the filters can be called a first filter and a second filter. If the mesh size of the first filter is made large, for example 3 to 4 mm, the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing polyol can easily pass through, and can be separated from the polyolefin resin melt in a short time. Moreover, the amount of polyamide resin remaining in the filter due to the obstruction of the polyolefin resin melt that does not pass through the filter is reduced, so the recovery rate of the polyamide resin is increased. However, since the mesh size is large, there is a drawback that a part of the polyolefin resin melt passes through the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing polyol. To compensate for this drawback, a second filter with a smaller mesh size is used, making it possible to remove the polyolefin resin melt that is accompanied by the polyamide resin. The mesh size of the second filter is, for example, usually 0.2 to 2 mm, and preferably 0.3 to 1 mm. Even if the mesh size of the second filter is small, there is little interfering olefin resin, so that the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing a polyol can smoothly pass through the mesh.

[0052] Step (3) (cooling distillation step) The cooling distillation step of step (3) is a step of rapidly cooling the polyamide resin solution obtained in the separation step, in which the polyamide resin is dissolved in a solvent containing the polyol, by utilizing latent heat of vaporization, and at the same time, distilling off the solvent containing the polyol, thereby recovering the polyamide resin. As described above, if the polyamide resin dissolved in the polyol-containing solvent is not immediately cooled to lower the temperature, the degree of polymerization will decrease, and the quality of the recovered polyamide resin will deteriorate. As a cooling method, in Patent Document 3 described in the Background Art, the same solvent as that used to dissolve the polyamide resin is added for cooling. However, this method requires a large amount of solvent to be recovered, and the recovery requires a lot of time and energy. In the present invention, therefore, a cooling distillation method is adopted in which a solution of a high-temperature polyamide resin dissolved in a solvent containing a polyol is evacuated to evaporate the solvent, and then the solvent is cooled using the latent heat of evaporation (for example, the latent heat of evaporation of ethylene glycol is 191 cal / g), and when the temperature drops due to cooling, the vacuum pressure is further lowered to evaporate the solvent and the temperature is lowered using the latent heat, and this process is repeated. This cooling distillation method allows cooling, precipitation of the polyamide resin, and removal of the solvent to be performed simultaneously. According to this method, the decrease in molecular weight of the recovered polyamide resin can be minimized. It is preferable that the vacuum pressure is gradually decreased along with the decrease in temperature so as not to cause bumping, and the solvent is distilled off in as short a time as possible. This is preferably accomplished by using a vacuum regulator that senses the solution temperature and automatically reduces the vacuum in a programmed manner. The solvent is distilled off simultaneously with cooling, so that granular polyamide resin rapidly precipitates and precipitates. By further reducing the vacuum pressure to distill off the solvent, recycled polyamide resin can be obtained.

[0053] The cooling time is not particularly limited, but it is preferable to lower the temperature to a temperature at which the polyamide resin precipitates in as short a time as possible, because if the polyamide resin precipitates, the degree of polymerization is less likely to decrease. When the polyol-containing solvent is ethylene glycol, the polyamide resin precipitates at about 130° C. In this case, the upper limit of the cooling time is preferably 80 minutes or less, and more preferably 40 minutes or less, for the time required to reach 130° C. The vacuum pressure at which the boiling point of ethylene glycol reaches 130°C is 33 hP. Therefore, it is preferable to quickly lower the pressure to that level.

[0054] When the amount of solvent is reduced by distillation, the polyamide resin melts, which inhibits the evaporation of the solvent and takes a long time to distill. Also, when the polyamide resin melts, it becomes difficult to discharge it from the cooling distillation tank. Therefore, in order to prevent melting, stirring or adding water is effective. When adding water, it is necessary that the temperature of the polyamide resin solution in which the polyamide resin is dissolved in the polyol-containing solvent is 100° C. or less. After lowering the temperature to 100° C. or less, it is preferable to return the pressure to atmospheric pressure and add water.

[0055] (First embodiment) A first embodiment of the method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to the present invention will be described. The polyamide resin recovery apparatus includes a heating and dissolving separation apparatus 1 and a cooling and distilling apparatus 10. FIG. 1 is a conceptual diagram showing a heating, dissolving and separating device of a polyamide resin recovery apparatus in a first embodiment of the present invention. FIG. 2 is a conceptual diagram showing a cooling distillation device of the polyamide resin recovery apparatus in the first embodiment of the present invention.

[0056] 1, the heating, dissolving and separation apparatus 1 has a net-shaped container 2, a dissolving pot lid 3, a dissolving pot 4, an on-off valve 5, a reflux condenser 6, and a temperature detector 7. The temperature detector 7 is linked to a vacuum pressure regulating valve 22.

[0057] The net-like container 2 is a container formed from a wire mesh with a wire diameter of 0.5 mm and 10 mesh (10 meshes per inch). A composite resin material containing cut polyamide-based resin and polyolefin-based resin is placed in this net-like container 2. Note that, although a net-like container is used as a filter in this embodiment, the present invention is not limited to this, and a punched plate, a lattice box having a lattice shape, or the like may also be used.

[0058] The dissolving pot 4 is a pot made of stainless steel (SAS316 or the like) and has a dissolving pot lid 3 at the top and an on-off valve 5 at the bottom. As shown in Fig. 1, the dissolving pot 4 can suspend a net-like container 2 inside. The mixture contained in the dissolving pot 4 is sent to a cooling distillation tank 11 of a cooling distillation apparatus by opening the on-off valve 5.

[0059] The reflux condenser 6 is formed integrally with the dissolving pot 4 via a pipe above the dissolving pot 4. The reflux condenser 6 is a device for condensing the boiled gaseous solvent into a liquid and returning the liquid solvent to the dissolving pot 4.

[0060] The heating and dissolving separation apparatus having the above-mentioned configuration can carry out step (1) (heating and dissolving step) and step (2) (separation step) of the method for recycling a composite resin material containing the above-mentioned polyamide-based resin and polyolefin-based resin.

[0061] As shown in FIG. 2, the cooling distillation apparatus 10 includes a cooling distillation tank 11, an agitator 12, an on-off valve 13, a polyamide recovery tank 14, a condenser 16, a solvent recovery tank 17, a vacuum pump 18, a temperature detector 20, a vacuum pressure detector 21, a vacuum pressure regulating valve 22, and the like.

[0062] The cooling distillation tank 11 is a device that contains a polyamide resin solution in which a polyamide resin, sent from the dissolving tank 4 through an on-off valve 5, is dissolved in a solvent containing a polyol, and distills the polyol-containing solvent while cooling it. The cooling distillation tank 11 is equipped with a stirring device 12 and a water pipe 19 for washing with water. In addition, an on-off valve 13 is provided below the heating tank of the cooling distillation tank 11. In addition, the cooling distillation tank 11 can be equipped with a heating device, a cooling device, etc. The cooling distillation tank 11 is set to a predetermined degree of vacuum inside by a vacuum pump 18. That is, the cooling distillation tank 11 is equipped with a system that measures the temperature of the polyamide resin solution in the cooling distillation tank 11 and automatically reduces the vacuum pressure according to the temperature drop due to the latent heat of evaporation. The polyol-containing solvent vaporized by vacuum evaporation is sent to a condenser 16, liquefied, and recovered in a solvent recovery tank 17.

[0063] The polyamide recovery tank 14 is a container for storing the polyamide 15 transferred from the cooling distillation tank 11 via the on-off valve 13 and for allowing the solid to cool.

[0064] The condenser 16 is connected to the cooling distillation tank 11 via a pipe. The condenser 16 is a device for condensing the boiled gaseous solvent into a liquid and recovering the liquid solvent in a solvent recovery tank 17.

[0065] The solvent recovery tank 17 is a container for recovering the polyol-containing solvent liquefied in the condenser 16 . Here, the vacuum pump 18, the temperature detector 20, the vacuum pressure detector 21, and the vacuum pressure regulating valve 22 are devices for performing vacuum distillation.

[0066] In the cooling distillation apparatus 10 configured as above, the step (3) (cooling distillation step) of the above-mentioned method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin can be carried out. In the first embodiment of the apparatus, step (1) (heating and dissolving step) and step (2) (separation step) are performed in a dissolving vessel 4, and step 3 (cooling and distillation step) is performed in a cooling distillation tank 11. However, it is also possible to perform steps (1), (2), and (3) all in one vessel.

[0067] Next, the method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to the first embodiment of the present invention will be specifically described.

[0068] In this embodiment, first, a composite resin material containing a polyamide-based resin and a polyolefin-based resin is chopped into pieces of appropriate size (composite resin material chopping process). The chopping size may be larger than the pores of the filter used, and varies depending on the equipment used or the processing amount. The polyolefin resin melted by heating does not split into small particles, but rather merges with each other to form a large molten mass. Therefore, there is no problem with the cut size of the composite resin material as long as it is larger than the pore size of the filter.

[0069] Next, the dissolving vessel 3 of the dissolving vessel 4 is opened, the on-off valve 5 at the bottom of the dissolving vessel 4 is closed, and a predetermined amount of a solvent containing polyol (for example, ethylene glycol) is injected (solvent injection step). Next, the dissolving vessel 3 of the dissolving vessel 4 is closed, and the dissolving vessel 4 is heated to a boiling temperature by a heating burner (not shown). The generated solvent vapor containing polyol is liquefied in the reflux condenser 6 and refluxed to the dissolving vessel 2.

[0070] A predetermined amount of a composite resin material containing a polyamide resin and a polyolefin resin is measured and placed in the net-like container 2 . When the temperature of the polyol-containing solvent in the dissolving pot 4 reaches a temperature 10 to 20°C lower than the boiling point, the dissolving pot lid 3 of the dissolving pot 4 is opened, and the net-like container 2 containing a predetermined amount of composite resin material is suspended from the top of the dissolving pot 4 and immersed in the polyol-containing solvent. When heating is continued and the temperature of the solvent reaches the boiling point, the polyamide resin instantly dissolves. Since the polyolefin resin has a low melting point, it melts and liquefies before the boiling point is reached. Therefore, as soon as the temperature of the solvent reaches the boiling point, the net container 2 is slightly lifted up and kept afloat, and the on-off valve 5 at the bottom of the dissolving tank 4 is opened, and the polyamide-based resin solution dissolved in the polyol-containing solvent is transferred to the cooling distillation device 10. If this is not done, the degree of polymerization of the polyamide-based resin will decrease.

[0071] When the mixture of the polyamide resin solution dissolved in the polyol-containing solvent and the molten polyolefin resin flows down into the cooling distillation apparatus 10, the mixture passes through the pores of the net-like container 2. At that time, the polyamide resin solution dissolved in the polyol-containing solvent passes through the pores, but the molten polyolefin resin does not pass through due to its high viscosity. In this manner, the polyamide resin solution in which the polyamide resin is dissolved in the polyol-containing solvent can be separated from the polyolefin resin melt. In order to efficiently recover a high-quality polyamide resin, it is preferable to pass the resin through a plurality of filters. That is, a polyamide-based resin solution in which a polyamide-based resin is dissolved in a solvent containing a polyol is passed through the first filter at high speed using a filter with large pores. Because the first filter has large pores, some of the polyolefin-based resin melt also passes through. The partially passed polyolefin-based resin melt is removed with a second filter with small pores, allowing high-quality polyamide-based resin to be recovered in a short time. As a method for this, as shown in Figure 4, a method consisting of a net-like container 2 having a first filter 2a and a second filter 2b installed at the bottom of a dissolving pot 4 may be used. Also, as shown in Figure 5, a net-like container 2 having a second filter 2b may be placed below the net-like container 2 having the first filter 2a, so that separation may be performed in two stages. Alternatively, as shown in FIG. 6, a net container having a first filter 2a may be hung by a hook, and a net container 2 having a second filter 2b may be placed on the outside of the net container.

[0072] By passing the mixture through the filter twice in this manner, the polyamide-based resin solution in which the polyolefin-based resin melt has been completely removed and the polyamide-based resin is dissolved in a solvent containing polyol can be efficiently introduced into the cooling distillation tank 11. The polyamide resin adhering to the polyolefin resin residue can be recovered by adding it to the next batch, or the like. In this embodiment, the dissolving pot 4 is heated using a heating burner (not shown), but this is not limited to this, and heating may be performed using a heat medium, or a solvent heated in a separate container may be sent to the dissolving pot 4. Alternatively, the net container 2 containing the composite resin material may be placed in the dissolving vessel 4 in advance, and the polyol-containing solvent may be poured into the net container 2, followed by heating together with the solvent.

[0073] The amount of the solvent containing the polyol is determined by the capacity of the dissolving vessel 4 . The amount of the composite resin material containing the polyamide resin and the polyolefin resin to be treated with the solvent will be described below. As described above, in order to improve productivity, it is preferable to have a smaller amount of solvent relative to the composite resin material. Conversely, in order to increase solubility, it is preferable to have a larger amount of solvent. In particular, when there is little solvent and many parts of the composite resin material are not immersed in the solvent, it takes time to dissolve, which is not preferable because it causes deterioration of the polyamide resin. In order to satisfy both requirements, the amount of solvent is appropriately 250 to 1000 parts by mass, and preferably 350 to 500 parts by mass, relative to 100 parts by mass of the composite resin material. In principle, the amount of composite resin material to be processed should be determined based on the concentration of polyamide resin dissolved in a solvent containing polyol, but the success of this invention is due to the fact that the melt viscosity of the polyolefin resin melt is significantly higher than the viscosity of the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing polyol, and the separation of the two is successfully achieved. Since the difference in viscosity between the two is particularly large, the difference in concentration between the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing polyol and the polyolefin resin melt does not affect the separation. In other words, the amount of composite resin material and solvent to be processed can be determined taking into account the solubility or productivity rather than the concentration of the polyamide resin.

[0074] If polyamide resin dissolves in a solvent containing polyol, the degree of polymerization of the polyamide resin decreases, so the solution must be rapidly cooled to minimize this. Therefore, as soon as the composite resin material containing polyamide resin and polyolefin resin dissolves or melts in the solvent, the net-shaped container 2 is lifted slightly upward with the melting pot lid 3 closed, and the opening / closing valve 5 at the bottom of the melting pot 4 is opened to lift the net-shaped container 2 even further upward. The polyamide resin solution in which the polyamide resin is dissolved in the solvent containing polyol flows down into the cooling distillation tank 11. It is desirable to cool the cooling distillation tank 11 in advance with a refrigerant in the jacket.

[0075] Next, in order to remove the solvent from the solution in which the polyamide resin has been dissolved in the polyol-containing solvent, which has been introduced into the cooling distillation tank 11, the on-off valve 5 is closed and vacuum distillation is started. When a vacuum is applied, evaporation occurs and the temperature drops due to the latent heat. If the vacuum pressure is further lowered, the temperature drops further. Note that if the vacuum pressure is lowered too much, the solvent will suddenly vaporize and bump, and the solution will pass through the condenser 16 and reach the solvent recovery tank 17. To prevent this trouble, it is desirable to prepare a temperature-vapor pressure curve for the solvent in advance, and to equip a system that automatically controls the vacuum pressure by automatically opening and closing the vacuum pressure regulating valve 22 while detecting the temperature of the solution with a temperature detector 20. In this case, it is desirable to carry out distillation while stirring in order to make the temperature of the solvent uniform. Also, the cooling distillation tank 11 may be cooled with a refrigerant in a jacket in order to increase the cooling rate.

[0076] When a solution in which a polyamide resin is dissolved in a solvent containing a polyol is introduced into a cooling distillation tank 11, the temperature of the solution drops and the polyamide resin precipitates. The solution is stirred by a stirrer 12 to prevent the precipitated polyamide resin from making it difficult for the solvent to precipitate and to make the temperature in the tank uniform. By stirring, the remaining solvent adhering to the precipitated polyamide resin can be easily removed. When the vacuum pressure reaches its limit, the amount of remaining solvent can be reduced by heating. In addition, fusion between the precipitated polyamide resins may occur. In order to prevent fusion, it is preferable to inject a small amount of water. When injecting water, it is necessary for safety reasons to keep the temperature of the solution in which the polyamide resin is dissolved in the polyol-containing solvent at 100°C or less in order to prevent hydrolysis. To achieve this, for example, when the polyol-containing solvent is ethylene glycol, it is preferable to finally lower the vacuum pressure in the cooling distillation tank 11 to 24 hP or less, preferably 15 hP or less.

[0077] Since the polyol-containing solvent is a poor solvent for polyamide-based resin, even if the polyol-containing solvent evaporates in the cooling distillation tank 11, the polyamide-based resin does not become an integrated lump, but falls in the form of particles. The polyamide-based resin that falls can be deposited on the bottom of the cooling distillation tank 11. The fallen material deposited on the bottom of the cooling distillation tank 11 is brittle and easily breaks apart even if it is slightly fused, and can be recovered in the polyamide recovery tank 14 as small pieces of polyamide-based resin by opening the opening / closing valve 13 at the bottom of the cooling distillation tank 11. The regenerated polyamide obtained from the small pieces of polyamide-based resin thus recovered is a polyamide-based resin with an undegraded degree of polymerization, and can be used as it is, or can be melted and pelletized for use.

[0078] The polyol-containing solvent vaporized in the cooling distillation tank 11 is condensed and liquefied in the condenser 16 and stored in the solvent recovery tank 17. The polyol-containing solvent stored in the solvent recovery tank 17 is then sent to the heating dissolution separation device 2 and can be reused as a solvent for polyamide-based resins when carrying out the method for recycling a composite resin material. EXAMPLES

[0079] The present invention will be described in more detail below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0080] <Test Example 1> Measurement by IR (infrared spectroscopy) To confirm the amount of PVDC contained in the following samples A to E (whether chlorine atoms were contained), measurements were made using an IR device (manufactured by Shimadzu Corporation, model: IR-408). Measurement conditions: Diamond ATR method (Det. TDS, Scan: 16 times, Res. 4 cm-1)

[0081] <Test Example 2> Determination of chlorine by combustion ion chromatography. In order to confirm the amount of PVDC contained in the following samples A to E (whether chlorine atoms are contained), measurements were performed using an apparatus (manufactured by Mitsubishi Chemical Analytech Thermofish Scientific, model: AQF-2100 + ICS-1600).

[0082] <Test Example 3> Relative Viscosity Measurement The relative viscosity of the following samples A to E was measured in accordance with JIS K-6920-2. Measurement conditions: Solvent: 96% concentrated sulfuric acid, temperature: 25°C, concentration: 0.01 g / ml, Ubbelohde viscometer used.

[0083] <Example 1> A composite resin material film containing a polyamide resin composition (nylon 6) and a polyolefin resin composition (PVDC), which is a recycled raw material, was cut into desired sizes (approximately 1 cm x 2 cm), and 10 g of the film was placed in a net-like container 2 with a filter 1 (mesh size 1.0 mm, wire diameter 0.29 mm, 20 mesh). This container was placed in a melting pot 4 containing 50 ml of ethylene glycol preheated to 190°C, and further heated to boil the ethylene glycol. The polyamide resin dissolved at the same time as the mixture boiled. The polyolefin resin melted, and the individual melts combined to form a single melt mass, which appeared to sink due to its high specific gravity, but was kept floating due to the boiling bubbles. The net-shaped container 2 was immediately removed from the dissolving vessel 4, and the nylon 6 ethylene glycol solution was put into the cooling distillation tank 11 equipped with the stirring device 12. The cooling distillation tank 11 was cooled in a water bath, and the vacuum pump 18 was operated. The vacuum pressure control valve 22 installed on the suction side of the vacuum pump 18 was opened slightly to start suction with the vacuum pump 18, and then the opening of the vacuum pressure control valve 22 was gradually increased to reduce the vacuum pressure so as not to cause bumping. As the temperature decreased due to the latent heat of evaporation, the vacuum pressure was reduced accordingly. Stirring was continued during this time, and the vacuum pressure decreased to 14 hPa and the temperature to 85°C in 35 minutes. After breaking the vacuum and returning to atmospheric pressure, the distillation residue was washed with water and dried to obtain polyamide powder sample A (7.5 g). Thus, in Example 1, the heating and dissolving step, the separation step, and the cooling and distillation step were carried out.

[0084] result Sample E, the recycled raw material, has a chlorine peak as shown in Figure 9, whereas the chlorine peak disappeared as shown in Figure 10 in the IR measurement of Sample A obtained in Example 1, proving that the polyamide-based resin could be recycled. Furthermore, it was found by combustion ion chromatography that the total chlorine content of Sample A was less than 0.35 wt%. On the other hand, Sample E, the recycled raw material, had a total chlorine content of 3.85 wt%, proving that the polyamide-based resin could be recycled by the method of Example 1. The polyamide resin (nylon 6) obtained in Example 1 had a relative viscosity indicating the degree of polymerization of 2.671.

[0085] <Comparative Example 1> The procedure was the same as in Example 1 up to the point where the nylon 6 ethylene glycol solution was charged into the cooling distillation apparatus 10. After charging the nylon 6 ethylene glycol solution into the cooling distillation apparatus 10, the solution was heated and distilled at normal pressure, and 60 ml of ethylene glycol was distilled off over 30 minutes. The precipitated residue was allowed to cool, washed with water, and dried. The resulting recycled nylon 6 granules were colored brown, and their relative viscosity had decreased to 1.913.

[0086] <Reference example 1> The composite resin material used in Example 1 was dissolved in formic acid at room temperature, and after removing the insoluble PVDC, sodium carbonate was added to precipitate nylon 6. The relative viscosity of this precipitated nylon was 2.716. That is, the relative viscosity of the raw material composite resin material sample E was 2.713, and in Reference Example 1 in which the solvent was removed at normal pressure, it was found that the relative viscosity was reduced to 1.913.

[0087] <Example 2> Polyamide powder sample B (5.4 g) was obtained from the solution that passed through the filter in the same manner as in Example 1, except that the net container was replaced with Filter 2 (mesh size 0.5 mm, wire diameter 0.14 mm, 40 mesh).

[0088] result As a result of IR measurement, the chlorine peak disappeared (not shown) in Example 2 as well, and it was found that the polyamide resin could be recycled. Furthermore, by combustion ion chromatography, it was found that the total chlorine content of Sample A was less than 0.33 wt%. On the other hand, the total chlorine content of Sample E, which is the recycled raw material, was 3.85 wt%, and it was found that the polyamide resin could be recycled by the method of Example 2. The relative viscosity of Sample B was 2.684.

[0089] <Example 3> Except for replacing the net-like container with filter 3 (a punched plate with a pore size of 0.5 mm in diameter and an opening rate of 19.0%), the same manufacturing method as in Example 1 was used to obtain sample C from the filter 2 side and polyamide powder sample D (8.8 g) from the solution side.

[0090] result As a result of IR measurement, the chlorine peak disappeared (not shown) in Example 3 as well, and it was found that the polyamide resin could be recycled. Furthermore, by combustion ion chromatography, it was found that the total chlorine content of Sample D was less than 0.01 wt%. On the other hand, the total chlorine content of Sample C remaining on the filter side was 20.27 wt%. It was found that the polyamide resin could be recycled by the method of Example 3. The relative viscosity of Sample D was 2.706.

[0091] <Reference example 2> The composite resin material film (sample E) containing a polyamide resin composition (nylon 6) and a polyolefin resin composition (PVDC), which are recycled raw materials, had a chlorine peak as shown in Figure 9. Furthermore, by combustion ion chromatography, the total chlorine content of sample E, which is a recycled raw material, was 3.85 wt%.

[0092] <Example 4> An experiment was carried out in the same manner as in Example 1 above, using 10 g of a composite resin film made of nylon 6 and polyvinylidene chloride, except that the amount of ethylene glycol and the size of the mesh were changed as shown in Table 1 below, and the amount (g) of resin that passed through the mesh of the filter was measured. This amount is the amount of recycled polyamide-based resin after removing ethylene glycol. The results are shown in Table 1.

[0093] [Table 1]

[0094] result As shown in Table 1, when the mesh size was 5 mm, all the material passed through. In other words, if the pore diameter was increased, the polyolefin resin melt flowed down through the pores together with the polyamide resin solution and was mixed into the recycled polyamide resin, resulting in a decrease in quality. If the pore diameter was decreased, the polyolefin resin melt did not pass through the filter and remained entirely in the net-like container 2, and only the polyamide resin solution flowed down, making separation possible. However, it was found that if the pore diameter was too small, the quality of the recycled polyamide resin improved, but the polyamide resin solution remained on the filter together with the polyolefin resin melt, resulting in a decrease in the yield of the recycled polyamide resin.

[0095] <Example 5> As shown in Fig. 5, a double net-like container was used and the filter was passed twice. The first filter 2a had a wire diameter of 0.47 mm and a mesh size of 3.2 mm, and the second filter 2b had a wire diameter of 0.12 mm and a mesh size of 0.30 mm. As in Example 4, 10 g of a composite film of nylon 6 and polyvinylidene chloride was used. The ratio of the solvent ethylene glycol was 5, that is, 50 ml of ethylene glycol was used, and nylon 6 was recycled in the same manner as in Example 1. In the first filter 2a, the nylon 6 ethylene glycol solution flowed down rapidly, accompanied by a small amount of polyvinylidene chloride melt. However, in the second filter 2b, there was almost no obstruction from the polyvinylidene chloride melt, so only the nylon 6 ethylene glycol solution was able to pass smoothly through the 0.3 mm pores. The mass of nylon 6 recovered from the passing solution was 9.1 g. In addition, in Example 4, the amount of nylon 6 that passed through the 0.3 mm pore was only 3.2 g (see Table 1). It was found that the recovery rate could be improved significantly by using the filter multiple times in this way. The relative viscosity of the nylon 6 obtained in Example 5 was 2.701, and there was no decrease in molecular weight, indicating that there was no problem with the quality.

[0096] <Example 6> An experiment was carried out in the same manner as in Example 3, except that ethylene glycol was used in an amount five times that of the raw material film, and the aperture and opening ratio were changed as shown in Table 2 below, and the amount (g) of the resin that passed through the filter was measured. This amount is the amount of recycled polyamide resin after removing ethylene glycol. The results are shown in Table 2.

[0097] [Table 2]

[0098] result As shown in Table 2, it was found that the yield of recovered polyamide-based resin increases when the opening diameter is increased. In addition, it was found that the yield of recovered polyamide-based resin decreases when the opening rate is small, so that an opening rate of 19% or more, preferably 22% or more, is necessary to increase the recovery rate.

[0099] <Example 7> A recycled nylon 6 sample B (7.5 g) and polyethylene (2.1 g) were obtained in the same manner as in Example 1, except that a composite resin material film containing nylon 6 and polyethylene was used instead. As a result, only nylon 6 was separated, and recycled nylon 6 was obtained, in the same manner as in Example 1. The relative viscosity of the recovered nylon 6 was 2.684. The polyethylene remaining in the filter can be used as recycled polyethylene. [Explanation of symbols]

[0100] 1 Heating dissolution separation device 2. Net-shaped container 2a First filter 2b Second Filter 3 Melting pot lid 4 Melting pot 5. Opening and closing valve 6 Reflux Condenser 7 Temperature detector 10 Cooling distillation apparatus 11 Cooling distillation tank 12 Stirring device 13. On-off valve 14 Polyamide recovery tank 15 Polyamide 16 Condenser 17 Solvent recovery tank 18 Vacuum Pump 19 Water Pipe 20 Temperature detector 21 Vacuum pressure detector 22 Vacuum pressure regulator

Claims

1. a heating and dissolving step of heating a composite resin material containing a polyamide-based resin and a polyolefin-based resin and a solvent containing a polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol; a separation step of separating the mixture obtained by the heat dissolution step into a polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt by utilizing a viscosity difference between the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt; and The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin includes a cooling distillation step of rapidly cooling the polyamide-based resin solution obtained in the separation step, in which the polyamide-based resin is dissolved in a solvent containing the polyol, by utilizing latent heat of vaporization, and at the same time, distilling off the solvent containing the polyol, thereby recovering the polyamide resin.

2. 2. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to claim 1, wherein the polyol is at least one selected from the group consisting of ethylene glycol and propylene glycol.

3. 2. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to claim 1, wherein the polyamide resin is at least one nylon selected from the group consisting of nylon 6, nylon 66, and copolymer resins thereof.

4. 2. The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin according to claim 1, wherein the polyolefin-based resin is at least one polyolefin-based resin selected from the group consisting of polyethylene, polypropylene, polyvinyl chloride, and polyvinylidene chloride.

5. 2. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to claim 1, wherein the separation step is carried out using at least one filter having fine holes.

6. 6. The method for recycling a composite resin material containing a polyamide resin and a polyolefin resin according to claim 5, wherein the filter has an opening rate of 19% or more and a mesh size of 0.5 to 2 mm.

7. The separation step is carried out using two filters having fine pores, 6. The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin according to claim 5, wherein the first filter has an opening rate of 19% or more and a mesh size of 0.5 to 2 mm, and the second filter has an opening rate of 19% or more and a mesh size of 0.2 to 0.5 mm.

8. 2. The method for recycling a composite resin material containing a polyamide-based resin and a polyolefin-based resin according to claim 1, wherein the cooling distillation step removes the polyol-containing solvent by cooling distillation, which involves quenching using latent heat of vaporization, lowering the vacuum pressure in conjunction with the decrease in temperature, and lowering the final vacuum pressure to 24 hP or less.

9. a heating and dissolving step of heating a composite resin material containing a polyamide-based resin and a polyolefin-based resin and a solvent containing a polyol to obtain a mixture of a polyamide-based resin solution in which the polyamide-based resin is dissolved in the solvent containing the polyol, and a polyolefin resin melt in which the polyolefin-based resin is melted without being dissolved in the solvent containing the polyol; a separation step of separating the mixture obtained by the heat dissolution step into a polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt by utilizing a viscosity difference between the polyamide resin solution in which the polyamide resin is dissolved in a solvent containing the polyol and the polyolefin resin melt; and The method for producing a recycled polyamide-based resin includes a cooling distillation step of rapidly cooling the polyamide-based resin solution obtained in the separation step, in which the polyamide-based resin is dissolved in a solvent containing the polyol, by utilizing latent heat of evaporation, and at the same time, distilling off the solvent containing the polyol, thereby recovering the polyamide resin.

10. A recycled polyamide resin obtained by the method according to claim 9.

Images