Method for separating and recovering polyamide, and method for producing film

Abstract

To provide a method for separating and recovering a polyamide by which the polyamide can be separated and recovered from a composite material containing an ethylene-vinyl alcohol copolymer and the polyamide in a relatively short time, and to provide a method for producing a film.SOLUTION: A method for separating and recovering a polyamide includes: preparing a composite material containing an ethylene-vinyl alcohol copolymer and a polyamide; adding the composite material to a mixed liquid containing an alcohol-based solvent and water; dissolving the ethylene-vinyl alcohol copolymer contained in the composite material in the mixed liquid to produce a solution; and filtering the solution to separate the solution into a filter product and a filtrate. The mixing ratio of the alcohol-based solvent and water in the mixed liquid is larger than 0.25 and smaller than 6.00. The mixing ratio is calculated by dividing the weight of water contained in the mixed liquid by the weight of the alcohol-based solvent contained in the mixed liquid.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for separating and recovering polyamide and a method for producing a film. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2021-146507 (Patent Document 1) discloses a method for separating substances using a specific gravity difference. In this separation method, the specific gravity difference between an ethylene-vinyl alcohol copolymer or polyamide and a polyester or chlorine-based resin is used to perform specific gravity separation between the ethylene-vinyl alcohol copolymer or polyamide and the polyester or chlorine-based resin (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-146507 A Summary of the Invention [Problem to be solved by the invention]

[0004] Depending on the ethylene content of the ethylene-vinyl alcohol copolymer and the type of polyamide, the specific gravity of the ethylene-vinyl alcohol copolymer and the specific gravity of the polyamide may be approximately the same. Therefore, the separation method disclosed in the above Patent Document 1 may not be able to separate and recover polyamide from a composite material containing an ethylene-vinyl alcohol copolymer and a polyamide. In addition, it is preferable that the time required to separate and recover polyamide from the composite material is short.

[0005] The present invention has been made to solve such problems, and an object of the present invention is to provide a method for separating and recovering polyamide, which is capable of separating and recovering polyamide from a composite material containing an ethylene-vinyl alcohol copolymer and a polyamide in a relatively short period of time, and a method for producing a film. [Means for solving the problem]

[0006] A method for separating and recovering polyamide according to an aspect of the present invention includes preparing a composite material containing an ethylene-vinyl alcohol copolymer and a polyamide, adding the composite material to a mixed liquid containing an alcohol-based solvent and water, dissolving the ethylene-vinyl alcohol copolymer contained in the composite material in the mixed liquid to produce a solution, and filtering the solution to separate the solution into a residue and a filtrate. The mixture ratio of the alcohol-based solvent to water in the mixture is greater than 0.25 and less than 6.00. The mixture ratio is calculated by dividing the weight of water contained in the mixture by the weight of the alcohol-based solvent contained in the mixture.

[0007] The present inventor(s) found that when the mixture ratio of the alcohol solvent to water in the mixed liquid is greater than 0.25 and less than 6.00, the dissolution of the ethylene-vinyl alcohol copolymer proceeds relatively quickly. According to the method for separating and recovering polyamide of the present invention, since the mixture ratio of the alcohol solvent to water in the mixed liquid is greater than 0.25 and less than 6.00, the ethylene-vinyl alcohol copolymer contained in the composite material can be dissolved in a relatively short time. As a result, according to this method for separating and recovering polyamide, the polyamide contained in the composite material can be recovered in a relatively short time.

[0008] In the above-mentioned method for separating and recovering a polyamide, the temperature of the mixed liquid when the ethylene-vinyl alcohol copolymer contained in the composite material is dissolved in the mixed liquid may be lower than 100°C.

[0009] Polyamide deteriorates significantly when immersed in a mixed liquid at 100° C. or higher. According to this method for separating and recovering polyamide, the temperature of the mixed liquid when the ethylene-vinyl alcohol copolymer contained in the composite material is dissolved in the mixed liquid is less than 100° C., so that deterioration of the polyamide during dissolution of the ethylene-vinyl alcohol copolymer can be relatively suppressed.

[0010] In the method for separating and recovering a polyamide, the difference between the boiling point of the alcohol solvent and the boiling point of water may be 30° C. or less.

[0011] When the ethylene-vinyl alcohol copolymer is recovered from the filtrate by evaporating the mixed liquid, if the difference between the boiling points of the alcohol solvent and water is large, the time required to recover the ethylene-vinyl alcohol copolymer becomes long. According to this method for separating and recovering polyamide, the difference between the boiling points of the alcohol solvent and water is 30° C. or less, so that the time required to recover the ethylene-vinyl alcohol copolymer can be relatively short.

[0012] In the above-mentioned method for separating and recovering a polyamide, the alcohol solvent may be n-propyl alcohol.

[0013] A method for producing a film according to another aspect of the present invention includes recovering a composition containing a polyamide through use of the above-described method for separating and recovering a polyamide, and producing a film by using the recovered composition.

[0014] According to this method for producing a film, the film is produced using polyamide separated and recovered from a composite material, so that the polyamide contained in the composite material can be effectively reused. Effect of the Invention

[0015] According to the present invention, it is possible to provide a method for separating and recovering a polyamide, which is capable of separating and recovering a polyamide from a composite material containing an ethylene-vinyl alcohol copolymer and a polyamide in a relatively short time, and a method for producing a film. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating a cross section of a film that is a first example of a composite material. [Diagram 2] FIG. 2 is a schematic diagram showing a cross section of a film that is a second example of a composite material. [Diagram 3]1 is a flow chart showing an example of a procedure for separating and recovering polyamide from a film (three-layer structure). [Figure 4] 1 is a flow chart showing an example of a procedure for separating and recovering polyamide from a film (four-layer structure). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter also referred to as "the present embodiment") will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated. Also, each drawing is drawn in a schematic manner with objects appropriately omitted or exaggerated for ease of understanding.

[0018] The method for separating and recovering polyamide according to the present embodiment is a method for separating and recovering polyamide from a composite material (e.g., a laminated film) containing at least an ethylene-vinyl alcohol copolymer (hereinafter also referred to as "EVOH") and a polyamide. An example of a composite material, a procedure for separating and recovering polyamide, and an example of reusing the recovered polyamide will be described below in order.

[0019] [1. Examples of composite materials] There are various types of composite materials that are the subject of the present embodiment, and in addition to those that contain EVOH and polyamide, they may also contain materials that are separated separately from these (hereinafter also referred to as "different materials"). Furthermore, they may also contain materials that are separated together with any of EVOH, polyamide, and different materials (mixed resins and additives, which will be described later).

[0020] <1-1.EVOH> Examples of the target EVOH include the following: The ethylene content of the EVOH is preferably about 55 mol % or less, more preferably about 20 mol % to 50 mol %, and further preferably about 25 mol % to 44 mol %.

[0021] The degree of saponification of the vinyl acetate component of EVOH is preferably about 90 mol % or more, and more preferably about 95 mol % or more.

[0022] EVOH may further contain small amounts of comonomers such as α-olefins, such as propylene, isobutene, α-octene, α-dodecene, α-octadecene, etc.; unsaturated carboxylic acids or derivatives thereof (e.g., salts, partial alkyl esters, full alkyl esters, nitriles, amides, anhydrides); and unsaturated sulfonic acids or salts thereof.

[0023] <1-2. Polyamide> Polyamides of interest include, for example, aromatic polyamides, aliphatic polyamides, and polyamide elastomers.

[0024] Examples of aromatic polyamides include amorphous aromatic polyamides (amorphous nylons) obtained by polycondensation of aliphatic diamines such as hexamethylenediamine with dicarboxylic acids such as terephthalic acid and isophthalic acid or derivatives thereof. Examples of aromatic polyamides include, preferably, copolymers of hexamethylenediamine-terephthalic acid-hexamethylenediamine-isophthalic acid.

[0025] Examples of aromatic polyamides include crystalline aromatic polyamides obtained by polycondensation reaction of aromatic diamines such as metaxylylenediamine and paraxylylenediamine with dicarboxylic acids or derivatives thereof such as adipic acid, suberic acid, sebacic acid, cyclohexanedicarboxylic acid, terephthalic acid, and isophthalic acid. Examples of aromatic polyamides include crystalline aromatic polyamides such as polymetaxylyleneadipamide (MXD-nylon). Examples of polyamide elastomers include polyether ester amide elastomers.

[0026] As the aliphatic polyamide, aliphatic nylon and its copolymer can be preferably used.Specifically, as the aliphatic polyamide, polycapramide (nylon-6), poly-ω-aminoheptanoic acid (nylon-7), poly-ω-aminononanoic acid (nylon-9), polyundecane amide (nylon-11), polylauryllactam (nylon-12), polyethylenediamine adipamide (nylon-2,6), polytetramethylene adipamide (nylon-4,6), polyhexamethylene adipamide (nylon-6,6), polyhexamethylene sebacamide (nylon-6,10), polyhexamethylene dodecamide (nylon-6,12), polyoctamethylene adipamide (nylon-8,6), polydecamethylene adipamide (nylon-10,8) and the like can be preferably used.

[0027] Specific examples of aliphatic polyamides that can be preferably used include caprolactam / lauryl lactam copolymers (nylon-6 / 12), caprolactam / ω-aminononanoic acid copolymers (nylon-6 / 9), caprolactam / hexamethylene diammonium adipate copolymers (nylon-6 / 6,6), lauryl lactam / hexamethylene diammonium adipate copolymers (nylon-12 / 6,6), ethylenediamine adipamide / hexamethylene diammonium adipate copolymers (nylon-2,6 / 6,6), caprolactam / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymers (nylon-6,6 / 6,10), and ethyleneammonium adipate / hexamethylene diammonium adipate / hexamethylene diammonium sebacate copolymers (nylon-6 / 6,6 / 6,10). These aliphatic polyamides may be used alone or in combination of two or more.

[0028] <1-3. Different materials> The different material to be further separated from the composite material may be a material that is not dissolved in the mixture liquid (solvent) described below. Specifically, the different material may be a material having the following functions in the composite material:

[0029] (1-3-1. Barrier layer) Examples of the barrier layer include those having a barrier function. Specific examples include a resin layer such as a polyester resin having barrier properties such as an oxygen barrier and a water vapor barrier. In addition, the barrier layer may be a metal vapor deposition film having barrier properties such as an oxygen barrier, a water vapor barrier, an aroma retention property, or an oil barrier. Specific examples of the metal vapor deposition film include metal vapor deposition films of metals such as metal oxides, silicon, aluminum, titanium, zirconium, tin, chromium, zinc, gold, silver, platinum, and nickel. Alternatively, a barrier coat of such a material may be applied.

[0030] (1-3-2. Adhesive layer) Examples include adhesive layers that bond layers of composite materials. Specifically, examples include polyolefin resins such as PP, PE (LLDPE, HDPE, LDPE), modified polyolefins, and modified styrene-based elastomers.

[0031] (1-3-3. Sealant layer) The sealant layers are bonded together to form a bag shape, and examples of such resin materials include low-density, medium-density, high-density, linear low-density polyethylene, propylene homopolymer, propylene-ethylene copolymer, and polyvinyl acetate-based olefin resins.

[0032] (1-3-4.Others) Examples of resins include those that have mechanical strength and dimensional stability, as well as heat resistance. Specific examples include polystyrene resins, polycarbonate resins, and ABS resins.

[0033] <1-4. Additives that can be mixed with EVOH and polyamide> The EVOH and polyamide to be separated and recovered may be mixed with, for example, a resin (hereinafter also referred to as a "mixed resin") or an additive to the extent that it does not affect the physical properties (e.g., transparency, strength, etc.; the same applies below).

[0034] Examples of such resins include modified ethylene acetate, vinyl acetate copolymer, methacrylic acid copolymer ionomer, α-olefin, unsaturated carboxylic acid or its salt, partial alkyl ester, complete alkyl ester, nitrile, amide, anhydride, comonomer such as unsaturated sulfonic acid or its salt, polyester-based elastomer, polyamide-based elastomer, polyolefin-based elastomer, polystyrene-based elastomer, polyurethane-based elastomer, polyvinyl chloride-based elastomer, ionomer polymer, etc.

[0035] Examples of additives include modifiers, antioxidants, antiblocking agents, heat stabilizers, antifogging agents, antistatic agents, lubricants, UV inhibitors, light stabilizers, flame retardants, antibacterial agents, fluorescent brighteners, flex resistance agents, colorants, fillers, etc., and particularly include additives derived from organic compounds. These may be mixed with the separated EVOH or polyamide as long as they do not affect the physical properties of the EVOH or polyamide.

[0036] Specific materials are, for example, as follows: Modifiers include elastomers such as modified EVA, modified polyester, modified polyethylene, and amorphous nylon; Antiblocking agents include, for example, silica-based and acrylic-based agents; Heat stabilizers include phenol-based, phosphorus-based, and thioether-based agents; Antifogging agents include glycerin fatty acid esters, polyglycerin fatty acid esters, sorbitan fatty acid esters, and the like; Lubricants include fatty acid-based compounds such as fatty acids, fatty acid salts, and fatty acid amides.

[0037] Such resins or additives are dissolved in a solvent described later together with EVOH, and are separated and recovered as a mixture with EVOH. However, the above resins and additives may have different solubilities depending on the type of solvent selected for this technology, so they are not necessarily mixed with EVOH and separated. Therefore, some additives may be separated and recovered as a mixture with polyamide or a different material. Additives that are mixed with polyamide or a different material and separated include additives that are not soluble in the solvent described later, particularly pigments, inorganic additives, and additives derived from crosslinked resins.

[0038] <1-5. Form of composite material> An example of a composite material is a film that includes multiple layers.

[0039] Fig. 1 is a schematic diagram showing a cross section of a film 10, which is a first example of a composite material. As shown in Fig. 1, the film 10 includes a first layer 11, a second layer 12, and a third layer 13. Each of the first layer 11 and the third layer 13 is, for example, a layer containing polyamide. The second layer 12 is a layer containing EVOH. In this case, the EVOH is separated from the film 10 by a method described later, and a composition containing polyamide is recovered.

[0040] Fig. 2 is a schematic diagram showing a cross section of a film 10A, which is a second example of a composite material. As shown in Fig. 2, the film 10A includes a first layer 11, a second layer 12, a third layer 13, and a fourth layer 14. The fourth layer 14 is, for example, a layer containing linear low density polyethylene (LLDPE). In this case, the EVOH and LLDPE are separated from the film 10 by a method described later, and a composition containing polyamide is recovered.

[0041] The film used as the composite material may be composed of two layers or five or more layers. At least one layer may contain EVOH, and the other layers may contain polyamide. Alternatively, at least one layer may contain a mixture of EVOH and polyamide. The layer containing the above-mentioned different material may not be required. The mixed resin and the additives do not necessarily have to be mixed, but when they are mixed, they can be mixed with at least one of EVOH and polyamide. In addition, the composite material does not have to be formed in a film shape, and may be in various forms such as pellets.

[0042] [2. Polyamide separation and recovery procedure] <2-1. First example> As a first example of a method for separating and recovering polyamide from a composite material, a procedure for separating and recovering polyamide from a film 10 shown in FIG. 1 will be described.

[0043] FIG. 3 is a flow chart showing an example of a procedure for separating and recovering polyamide from a film 10 (three-layer structure). Referring to FIG. 3, in a preparation step, the film 10 is cut (step S100). Specifically, the film 10 is cut into a predetermined size. This increases the contact area between the cut film 10 and a mixed liquid (solvent) described below, making it easier for the EVOH to dissolve. The size after cutting is not particularly limited, but is, for example, 0.5 to 4 cm square, and preferably 1 to 2 cm square. However, this step is not necessarily required, and in the next step, the film 10 may be immersed directly in the solvent without being cut.

[0044] After the preparation process is completed, the EVOH is dissolved (step S110). Specifically, the film 10 cut in step S100 is added to the mixture, and the EVOH is dissolved in the mixture to generate a solution. The dissolving process is performed under an inert gas atmosphere such as nitrogen or argon. The mixture used as the solvent is a mixture containing an alcohol-based solvent and water.

[0045] Since it is preferable to reuse the mixture in the form of a mixture without changing the composition, this system does not require isolation of each component by distillation. When the boiling point difference between the solvent components is large, if the heating temperature is set according to the high boiling point component in order to shorten the recovery process, a separate cooling facility is required for the low boiling point component. As a result, the equipment cost increases. Therefore, the difference between the boiling point of the alcohol solvent contained in the mixture and the boiling point of water is 30°C or less, preferably 20°C or less, and more preferably 10°C or less. In addition, it is preferable to check the composition of the recovered mixture and, if the composition has changed, adjust it by adding the necessary solvent component.

[0046] Furthermore, EVOH dissolves in the mixed liquid when the temperature of the mixed liquid is greater than 50° C. and less than 100° C., preferably greater than 60° C. and less than 100° C., more preferably greater than 70° C. and less than 100° C., and even more preferably greater than 70° C. and less than 80° C. Since the dissolution of EVOH is carried out at a relatively low temperature, the polyamide contained in the film 10 is unlikely to deteriorate when the EVOH dissolves. The mixed liquid hardly dissolves polyamide.

[0047] Alcohol-based solvents have affinity and azeotropy with water. In addition, alcohol-based solvents do not undergo phase separation when mixed with water. This is because when an alcohol-based solvent that undergoes phase separation when mixed with water is used, EVOH does not dissolve, or EVOH that has dissolved once reprecipitates due to water acting as a poor solvent in an immiscible state. Whether or not an alcohol-based solvent undergoes phase separation when mixed with water can be confirmed by the following method. First, water and any organic solvent are added to a beaker in a volume ratio of 1:1. Next, after stirring with a stirrer for 30 seconds, the stirring is stopped and the mixture is left to stand for 5 minutes, and visually confirmed whether or not phase separation has occurred.

[0048] The SP value of alcohol-based solvents is, for example, 9 to 16 (cal / cm 3 ) 0.5 and preferably 10 to 15 (cal / cm 3 ) 0.5 and more preferably 11 to 14 (cal / cm3 ) 0.5 The SP value in the present invention is calculated by Fedor's calculation method. Fedor's calculation method for the SP value is described in RF Fedor; Polymer Engineering Science, 14(2)147-154(1974). Examples of alcohol-based solvents include methanol, ethanol, n-propyl alcohol, and isopropyl alcohol. As the alcohol-based solvent, one type of alcohol-based solvent may be used alone, or two or more types of alcohol-based solvents may be used in combination.

[0049] The mixing ratio of the alcohol solvent to water in the mixed liquid is greater than 0.25 and less than 6.00. Preferably, the mixing ratio of the alcohol solvent to water in the mixed liquid is greater than or equal to 0.33 and less than or equal to 5.00. The mixing ratio of the alcohol solvent to water in the mixed liquid is calculated by the following formula (1). That is, the mixing ratio of the alcohol solvent to water in the mixed liquid is calculated by dividing the weight of water contained in the mixed liquid by the weight of the alcohol solvent contained in the mixed liquid. Mixing ratio = (weight of water) / (weight of alcohol-based solvent) (1)

[0050] When the dissolving step is completed, the solution produced in the dissolving step is filtered (step S120). Specifically, the solution produced in the dissolving step is filtered by a filter. The filtering step is performed under an inert gas atmosphere such as nitrogen or argon. The filter is not particularly limited as long as it can separate the filtrate (film residue), and for example, a filter with an opening diameter of 100 μm or less can be used. In addition, reduced pressure filtration (suction filtration) may be adopted in which the filtrate is filtered while being sucked into a reduced pressure container. This can shorten the filtration time. In addition, the filtrate may be separated by centrifugation. This separates the filtrate containing polyamide from the filtrate in which EVOH is dissolved. In addition, since the filtrate containing polyamide may have undissolved EVOH attached thereto, the filtrate containing polyamide may be treated again in the dissolving step. By carrying out this treatment, polyamide with an even higher purity can be obtained.

[0051] After the filtration process is completed, the filtered material (film residue) is dried (step S130). The filtered material is naturally dried or heated for a predetermined time, for example, about 1 to 3 days. In order to shorten the drying time, the drying may be performed under reduced pressure conditions. As a result, the polyamide is recovered as a dried solid. The recovered polyamide may contain the above-mentioned mixed resins and additives.

[0052] Furthermore, EVOH may be recovered from the filtrate in which EVOH is dissolved. Temperature and time conditions are not particularly limited since they depend on the type of solvent. For example, the filtrate (EVOH solution) may be cooled to 40°C or less and allowed to stand for 0.5 to 2 hours to precipitate EVOH. EVOH may be precipitated by cooling using a cooling device or the like. The precipitated EVOH is separated by filtration, and the EVOH is recovered as a residue. As another method, the solution may be heated to evaporate the solvent, and the EVOH may be recovered as a dried product. In this case, the solvent may be removed while stirring.

[0053] <2-2. Second example> As a second example of the method for separating and recovering polyamide from a composite material, a procedure for separating and recovering polyamide from a film 10A shown in FIG. 2 will be described.

[0054] Fig. 4 is a flow chart showing an example of a procedure for separating and recovering polyamide from film 10A (four-layer structure). With reference to Fig. 4, steps S200 to S230 are the same as steps S100 to S130 in Fig. 3, respectively, except that the target film is different. Therefore, description of steps S200 to S230 will not be repeated.

[0055] When the first drying step is completed in step S230, the LLDPE contained in the first filtrate produced in step S230 is dissolved (step S240). Specifically, the first filtrate produced in step S230 is added to limonene, and the LLDPE is dissolved in the limonene to produce a solution.

[0056] When the second dissolution step is completed, the solution produced in the second dissolution step is filtered (step S250). Specifically, the solution produced in the second dissolution step is filtered by a filter. The filter is not particularly limited as long as it can separate the filtrate (film residue), but for example, a filter with an opening diameter of 100 μm or less can be used. In addition, reduced pressure filtration (suction filtration) may be adopted in which the filtrate is filtered while being sucked into a reduced pressure container. This can shorten the filtration time. Alternatively, the filtrate may be separated by centrifugation. This separates the filtrate containing polyamide from the filtrate in which LLDPE is dissolved.

[0057] When the second filtration step is completed, the second filtrate (film residue) is dried (step S260). The second filtrate is naturally dried or heated for a predetermined time, for example, about 1 to 3 days. In order to shorten the drying time, drying may be performed under reduced pressure conditions. As a result, polyamide is recovered as a dried solid. The recovered polyamide may contain the above-mentioned mixed resins and additives.

[0058] [3. Examples of reuse of recovered polyamide, etc.] The polyamide thus recovered can be pelletized, or the powder or pelletized polyamide can be melt-formed into a film to form a single-layer or multi-layer recycled film.

[0059] The recycled film may be a single layer of polyamide resin, or may be a multi-layer including other resin layers. The other resin layers may be, for example, virgin raw materials derived from petroleum or virgin raw materials derived from biomass. They may also be recycled raw materials. In this case, it does not matter whether they are chemically recycled or mechanically recycled.

[0060] The recovered polyamide resin can be contained in a single layer or in multiple layers (e.g., surface layer, core layer), but for example, the recovered polyamide resin is preferably 1 to 10% by weight or more of the recycled film. Each layer of the recycled film may contain an antiblocking agent and additives. Examples of additives include heat stabilizers, antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, flame retardants, antibacterial agents, and fluorescent whitening agents. Each recovered resin may be reused as a raw material for the original film.

[0061] Such recycled films can be molded by sequential biaxial stretching. In this case, the longitudinal stretching ratio is preferably 1 or more, and the transverse stretching ratio is preferably 2.5 or more. The extrusion temperature is preferably 150°C or more and 300°C or less. The transverse stretching can be set to 50°C or more and 220°C or less in the tenter stretching machine in the preheating zone, stretching zone, and heat setting zone during molding.

[0062] The polyamide-based resin contained in the recycled film can be 0.1 to 100% by weight, more preferably 0.1 to 80% by weight, and even more preferably 0.1 to 60% by weight of the recovered polyamide-based resin. The present inventors have confirmed that a recycled film having such a content of recovered polyamide-based resin can have physical properties equivalent to those of a film using a virgin material as the polyamide-based resin.

[0063] [4. Features] As described above, in the polyamide separation and recovery method according to the present embodiment, the mixture ratio of the alcohol solvent and water in the mixed liquid used as a solvent is greater than 0.25 and less than 6.00. The inventor(s) found that when the mixture ratio of the alcohol solvent and water in the mixed liquid is greater than 0.25 and less than 6.00, the dissolution of the ethylene-vinyl alcohol copolymer proceeds relatively quickly. According to the polyamide separation and recovery method according to the present embodiment, since the mixture ratio of the alcohol solvent and water in the mixed liquid is greater than 0.25 and less than 6.00, the ethylene-vinyl alcohol copolymer contained in the composite material can be dissolved in a relatively short time. As a result, according to this polyamide separation and recovery method, the polyamide contained in the composite material can be recovered in a relatively short time.

[0064] In the polyamide separation and recovery method according to the present embodiment, the temperature of the mixed liquid when the ethylene-vinyl alcohol copolymer contained in the composite material is dissolved in the mixed liquid is less than 100°C. When the polyamide is immersed in a mixed liquid of 100°C or higher, the deterioration of the polyamide becomes significant. More specifically, when the polyamide resin is exposed to a temperature higher than 100°C, the polyamide may turn yellow. This is because the polyamide resin is thermally deteriorated in the presence of oxygen. Therefore, the drying temperature specified by the resin manufacturer is generally 80°C to 100°C. According to the polyamide separation and recovery method according to the present embodiment, the temperature of the mixed liquid when the ethylene-vinyl alcohol copolymer contained in the composite material is dissolved in the mixed liquid is less than 100°C, so that the deterioration of the polyamide during the dissolution of the ethylene-vinyl alcohol copolymer can be relatively suppressed.

[0065] In the method for separating and recovering polyamide according to the present embodiment, the difference between the boiling point of the alcohol solvent and the boiling point of water is 30° C. or less. When the ethylene-vinyl alcohol copolymer is recovered from the filtrate by evaporating the mixed liquid, if the difference between the boiling point of the alcohol solvent and the boiling point of water is large, the time required to recover the ethylene-vinyl alcohol copolymer becomes long. According to this method for separating and recovering polyamide, since the difference between the boiling point of the alcohol solvent and the boiling point of water is 30° C. or less, the time required to recover the ethylene-vinyl alcohol copolymer can be relatively short.

[0066] 5. Other embodiments The concept of the above embodiment is not limited to the embodiment described above. Hereinafter, an example of another embodiment to which the concept of the above embodiment can be applied will be described.

[0067] In the above embodiment, each dissolving step may be performed under pressure. After the filtration step of step S120 in Fig. 3 and after the second filtration step of step S250 in Fig. 4, the filtered material may be washed with the mixed liquid (may be while being heated).

[0068] In addition, polyamide can be recovered by the above separation and recovery method from a composite material having a printed layer that has been collected from the market, for example, a film including a printed layer / polyamide layer / EVOH layer. In this case, a known step of removing the printed layer is provided prior to the above step. To remove the printed layer, for example, the printed layer can be removed by alkaline cleaning, the printed layer can be physically removed by scraping, or a release layer can be provided in advance between the printed layer and the substrate layer, and the printed layer can be peeled off.

[0069] The above describes the embodiments of the present invention by way of example. That is, the detailed description and the accompanying drawings are disclosed for the purpose of illustrative description. Therefore, some components described in the detailed description and the accompanying drawings may be non-essential components for solving the problem. Therefore, just because the non-essential components are described in the detailed description and the accompanying drawings, it should not be immediately determined that the non-essential components are essential.

[0070] Furthermore, the above-described embodiment is merely an example of the present invention in every respect. The above-described embodiment can be improved or modified in various ways within the scope of the present invention. In other words, in implementing the present invention, specific configurations can be appropriately adopted according to the embodiment. EXAMPLES

[0071] Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

[0072] [1. Experiment 1] <1-1. Experimental Procedure> Pellet-shaped EVOH resin (saponified ethylene-vinyl acetate copolymer, ethylene 32 mol%) was prepared as the dissolution target. The EVOH resin was added to a mixed liquid (solvent) with an arbitrary mixing ratio, and stirred while heating so that the solvent temperature was within a specified temperature range. After that, the time until the EVOH resin was visually dissolved was measured. The charging concentration of the EVOH resin was 5 wt%. The charging concentration was calculated using the following formula (2). Charge concentration = (EVOH weight) / (EVOH weight + mixed liquid weight) (2)

[0073] <1-2. Mixtures (solvents) used in each example and comparative example> The mixtures used in the examples are as shown in Table 1 below, and the mixtures used in the comparative examples are as shown in Table 2 below.

[0074] [Table 1] [Table 2]

[0075] In each of Examples 1-7, the solvent temperature during dissolution of the EVOH resin was maintained at 70°C to 80°C. In each of Examples 1-5, a mixture of water and n-propyl alcohol was used as the solvent. The difference between the boiling points of water and n-propyl alcohol was 2.8°C. The solvent mixing ratios in Examples 1-5 were 1.00, 0.33, 3.00, 4.00, and 5.00, respectively.

[0076] In Example 6, isopropyl alcohol was used as the solvent. The difference between the boiling point of water and the boiling point of isopropyl alcohol was 17.6°C. The solvent mixing ratio in Example 6 was 3.00. In Example 7, ethanol was used as the solvent. The difference between the boiling point of water and the boiling point of ethanol was 21.7°C. The solvent mixing ratio in Example 7 was 3.00.

[0077] In each of Comparative Examples 1-6, a mixture of water and n-propyl alcohol was used as the solvent. The solvent mixing ratios in Comparative Examples 1-6 were 0.25, 0.20, 6.00, 3.00, 4.00, and 3.00, respectively. The dissolution temperature in each of Comparative Examples 1-3 was maintained at 70°C to 80°C. The dissolution temperature in each of Comparative Examples 4 and 5 was maintained at 25°C. The dissolution temperature in Comparative Example 6 was maintained at 50°C.

[0078] <1-3. Experimental results> The experimental results are shown in Tables 3 and 4 below.

[0079] [Table 3] [Table 4]

[0080] It was found that when the mixing ratio of the alcohol solvent to water was greater than 0.25 and less than 6.00, the EVOH resin dissolved in a short time.

[0081] [2. Experiment 2] <2-1. Films covered> First, two types of films were prepared as targets of the separation and recovery method of the present invention, as shown in Tables 5 and 6. Target film 1 is a three-layer film (composite material) and is shown in Table 5. On the other hand, target film 2 is a four-layer film (composite material) and is shown in Table 6.

[0082] [Table 5] [Table 6]

[0083] <2-2. Separation and collection procedure> The procedure shown in Figure 3 was carried out for the target film 1. That is, for the target film 1, first, in the preparation process, the film was cut into 1 cm 2 The film was pulverized to a size of about 100 mm. Next, in the dissolving process, the pulverized film was immersed in a mixed solution as a solvent and heated to a temperature of 70°C to 80°C. The mixed solution was a mixture of water and n-propyl alcohol, and the solvent mixing ratio in the mixed solution was 1.00. After heating and stirring for 60 minutes, the heating was stopped. In this way, a solution in which EVOH was dissolved was obtained.

[0084] Next, in the filtration step, the solution produced in the dissolving step was roughly filtered to separate the residue and the filtrate. Then, in the drying step, the residue was heated and dried to recover the polyamide. The filtrate obtained in the filtration step was cooled to 40°C to precipitate the EVOH. The precipitated EVOH was then recovered by suction filtration using a membrane filter (opening diameter 1 μm).

[0085] The procedure shown in Figure 4 was carried out for the target film 2. That is, for the target film 2, first, in the preparation process, the film was cut into 1 cm 2 The film was pulverized to a size of about 100 mm. Next, in the first dissolution step, the pulverized film was immersed in a mixed solution as a solvent and heated to a temperature of 70°C to 80°C. The mixed solution was a mixture of water and n-propyl alcohol, and the solvent mixing ratio in the mixed solution was 1.00. After heating and stirring for 60 minutes, the heating was stopped. In this way, a solution in which EVOH was dissolved was obtained.

[0086] Next, in the first filtration step, the solution produced in the first dissolution step was roughly filtered to separate into a first residue and a first filtrate. Then, in the first drying step, the first residue was heated and dried to recover a composition containing polyamide and LLDPE. The first filtrate obtained in the first filtration step was cooled to 40°C to precipitate EVOH. The precipitated EVOH was then recovered by suction filtration using a membrane filter (opening diameter 1 μm).

[0087] In the second dissolution step, the first residue was immersed in limonene, which was a solvent, and heated to a temperature of 90° C. After heating and stirring for 30 minutes, the heating was stopped. Thus, a second solution in which LLDPE was dissolved was obtained.

[0088] Subsequently, in the second filtration step, the second solution was roughly filtered to separate into a second filtrate and a second filtrate. Subsequently, in the second drying step, the filtrate was dried by heating to recover a polyamide.

[0089] <2-3. Recovery Results> For target film 1, the recovery rate of polyamide was 90%. For target film 2, the recovery rate of polyamide was 84%.

[0090] <2-4. Analysis of recovered materials 1 (FT-IR)> The recovered EVOH and polyamide were analyzed by FT-IR with virgin EVOH and polyamide. A Perkin Elmer Fourier transform infrared spectrophotometer (FT-IR) SPectrum 100 was used as the measuring device, and the characteristic peaks of EVOH and polyamide were compared between virgin and recovered EVOH and polyamide. The results are as follows.

[0091] Table 7 shows a comparison of the absorption spectra of the recovered polyamide and virgin polyamide. The "○" in Table 7 indicates the points where the peaks of the absorption spectra of both match (the same applies to Table 8 described below). As shown above, the peaks of the absorption spectra of both match at multiple points, which shows that almost pure polyamide was recovered. [Table 7]

[0092] Table 8 shows a comparison of the absorption spectra of the recovered EVOH and virgin EVOH. As shown, the absorption spectrum peaks of both coincide at multiple points, which indicates that almost pure EVOH was recovered. [Table 8]

[0093] <2-5. Analysis of recovered materials 2 (DSC)> The recovered EVOH and polyamide were compared with virgin EVOH and polyamide by DSC measurement. In this measurement, DSC (differential scanning calorimetry) was used in accordance with JIS K 7122 (transition heat measurement method). The measurement device used was DSC2910 [trade name, manufactured by TA Instruments Co., Ltd.]. Measurement was performed in the range of 40°C to 200°C at a heating rate of 10°C / min, and the endothermic peak top temperature (melting point) was calculated. The results are as follows. [Table 9]

[0094] According to Table 9, the endothermic peak top temperatures of the virgin material and the recovered material are almost the same, and no other endothermic peaks were observed, so the recovered polyamide and EVOH are considered to be almost pure substances.

[0095] <2-6. Reusing Recovered Resin Materials> (Film manufacturing) The polyamide-based multilayer film (three-layer film) shown in Table 10 was manufactured using the polyamide-based resin (nylon 6) and EVOH resin recovered as described above as raw materials. The film manufactured using all virgin raw materials was designated Reference Example A. Reference Example A was prepared by replacing part of the polyamide-based resin in the surface layer with recycled resin as Example A. Reference Example A was prepared by replacing part of the EVOH resin in the middle layer with recycled resin as Example B. Reference Example A was prepared by replacing part of the polyamide-based resin in the surface layer with recycled resin and part of the EVOH resin in the middle layer with recycled resin as Example C. The numerical values ​​of each composition in Table 10 below are in weight % of each layer.

[0096] The manufacturing method is as follows. First, the material is fed into an extruder with a barrel temperature of 180 to 260°C, and extruded from a multilayer die at 220 to 260°C into a three-layered sheet having a polyamide resin front and back layers and an EVOH resin middle layer, and then cooled and solidified by a take-up roll at 25 to 30°C. Next, the material is stretched at a stretch ratio of 4 in a tenter stretching machine with a preheating zone of 80 to 100°C, a stretching zone of 80 to 130°C, and a heat setting zone of 150 to 230°C, and then wound up by a winding machine to obtain a polyamide multilayer film. [Table 10]

[0097] The following physical properties were measured for each of the obtained polyamide-based multilayer films.

[0098] (Puncture resistance of each film) The puncture strength of polyamide films was measured using a method based on JIS Z-1707 (1997). A test piece was fixed and pierced with a semicircular needle with a diameter of 1.0 mm and a tip radius of 0.5 mm at a speed of 50 ± 5 mm per minute, and the maximum stress until the needle penetrated (puncture strength (N)) was measured. At least five test pieces were used, and the average value was calculated to obtain the measurement result. -Puncture strength (at 23°C): A strength of 8.0N or more is considered good. -Puncture strength (under -25℃ conditions): A strength of 13.0N or more is considered good.

[0099] (Impact resistance of each film) The impact strength (J) of the polyamide film was measured using an impact tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). Impact strength (at 23°C): A strength of 0.9 J or more is good, and 1.0 J or more is even better. Impact strength (at -25°C): A strength of 0.3 J or more is good, and 0.5 J or more is even better.

[0100] (Flexibility of each film) The pinhole resistance of the polyamide film due to bending was measured using a Gelbo Flex Tester manufactured by Rikagaku Kogyo Co., Ltd.

[0101] A polyamide film bag made into a cylindrical shape with a folded diameter of 150 mm and a length of 300 mm was attached to a Gelbo Flex Tester, and a 440° twist was applied in the first 88.9 mm, followed by a linear horizontal movement of 63.5 mm. This was repeated 1,000 times at a test speed of 40 times / min under conditions of 5°C, -5°C and -25°C, and the number of pinholes was then counted using a penetrant. The number of pinholes was measured at 300cm in the center of the sample. 2 The number of pinholes was measured for three samples, and the average value was used as the measurement result. Bend resistance (at 5°C): 5 or less pinholes is good, and 3 or less is even better. Bend resistance (under -5°C conditions): 7 or less pinholes is good, and 5 or less is even better. Bend resistance (under -25°C conditions): A pinhole count of 27 or less is considered good, and a pinhole count of 25 or less is even better.

[0102] (Oxygen permeability of each film) The oxygen permeability was measured under the measurement conditions (20° C.×65% RH) in accordance with JIS K7126-2 using an OX-TRAN MODEL2 / 21 (manufactured by MOCON) as the measuring device.

[0103] The measurement results of each physical property are shown in Table 11 below. [Table 11]

[0104] The results in Table 11 show that there is no significant difference in physical properties between the virgin material film of Reference Example A and the recycled material films of Examples A to C, and that the recycled material films can be used in the same manner as virgin material films. [Explanation of symbols]

[0105] 10,10A film, 11 first layer, 12 second layer, 13 third layer, 14 fourth layer.

Claims

1. Providing a composite material comprising an ethylene-vinyl alcohol copolymer and a polyamide; adding the composite material to a mixture containing an alcohol-based solvent and water; dissolving the ethylene-vinyl alcohol copolymer contained in the composite material in the mixed liquid to form a solution; filtering the solution to separate the solution into a filtrate and a filtrate; a mixing ratio of the alcohol-based solvent to the water in the mixed solution is greater than 0.25 and less than 6.00; The method for separating and recovering a polyamide, wherein the mixing ratio is calculated by dividing a weight of the water contained in the mixed liquid by a weight of the alcohol-based solvent contained in the mixed liquid.

2. 2. The method for separating and recovering a polyamide according to claim 1, wherein the temperature of the mixed liquid when the ethylene-vinyl alcohol copolymer contained in the composite material is dissolved in the mixed liquid is less than 100° C.

3. 3. The method for separating and recovering a polyamide according to claim 1 or 2, wherein the difference between the boiling point of the alcohol-based solvent and the boiling point of the water is 30° C. or less.

4. The method for separating and recovering a polyamide according to claim 1 or 2, wherein the alcohol-based solvent is n-propyl alcohol.

5. Recovering a composition containing the polyamide through the use of the method for separating and recovering the polyamide according to claim 1 or 2; and producing a film by using the recovered composition.

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