Resin recovery method

Abstract

A resin recovery method according to the present invention is a method for recovering a resin from a composite including a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1), wherein the resin recovery method includes a step (1) in which the composite and a subcritical fluid are brought into contact, the layer (A) and the layer (B) are decomposed and / or separated, and a solid resin (A) comprising a non-hydrolyzable resin (a2) and a solid resin (B) comprising a hydrolyzable resin (b2) are obtained. The non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are the same or differ only in molecular weight distribution, and the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or differ only in molecular weight distribution.

Description

Resin recovery method

[0001] The present invention relates to a method for recovering a resin from a composite containing multiple resins.

[0002] Due to growing interest in environmental issues and the efficient use of resources, there is a demand for the reuse of resin products. Films used in packaging, which are resin products, are generally composites of multiple resins, such as multi-layer films. In order to reuse these composites, it is necessary to separate and recover the resins from the composites according to their type.

[0003] In Patent Document 1, a laminate of a polyolefin layer and a layer of a foreign substance other than polyolefin selected from water-soluble foreign substances or hydrolyzable foreign substances is heated to 200 to 400°C under a specific pressure and treated with water, thereby dissolving only the foreign substances in water and recovering the polyolefin.

[0004] In Patent Document 2, a polyolefin resin film containing organic matter other than polyolefin resin is treated with water under conditions of heating at 200 to 350°C under a specific pressure, thereby hydrolyzing the organic matter other than polyolefin resin and recovering the polyolefin resin.

[0005] In Patent Document 3, a solid composite material consisting of two or more organic polymer compounds is hydrolyzed using supercritical water as a solvent, and the organic liquid and organic solid are separated. After that, the organic solid is recovered, and the separated organic liquid is separated and recovered by material by boiling point separation.

[0006] In Patent Document 4, a resin layer of a hydrolyzable polymer and a resin layer of a non-hydrolyzable polymer are decomposed and separated by a hydrothermal reaction under specific conditions, the hydrolyzable polymer is hydrolyzed and separated and recovered as a monomer, and the non-hydrolyzable polymer is separated and recovered while maintaining its molecular weight.

[0007] Japanese Patent Laid-Open No. 8-92411 Japanese Patent Laid-Open No. 11-35734 Japanese Patent Laid-Open No. 2001-316518 Japanese Patent Laid-Open No. 2023-1085

[0008] In Patent Documents 1 to 4, non-hydrolyzable resins such as polyolefin resins were recovered as resins and could be recycled as materials as they were, but hydrolyzable resins such as polyamide resins are decomposed down to the monomers and dissolved in water, making material recycling impossible. Instead, to recover the monomers, boiling point separation had to be carried out, which made the process difficult due to bumping and the like.

[0009] A first aspect of the present invention aims to separate and recover a hydrolyzable resin and a non-hydrolyzable resin in a resinous state from a composite containing the hydrolyzable resin and the non-hydrolyzable resin. A second aspect of the present invention aims to separate and recover a hydrolyzable resin in a resinous state from a molded product containing the hydrolyzable resin. A third aspect of the present invention aims to separate and recover a non-hydrolyzable resin in a resinous state from a molded product containing the non-hydrolyzable resin.

[0010] The present invention relates to the following, for example, to [1] to

[14] . [1] A method for recovering a resin from a composite comprising a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1), comprising: step (1) of contacting the composite with a subcritical fluid to decompose and / or separate layer (A) and layer (B) to obtain a solid resin (A) consisting of a non-hydrolyzable resin (a2) and a solid resin (B) consisting of a hydrolyzable resin (b2), wherein the non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are the same or differ only in molecular weight distribution, and the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or differ only in molecular weight distribution. [2] The resin recovery method of [1], further comprising: a recovery step (2) of separating and recovering the solid resin (A) and the solid resin (B) obtained in step (1) through a filter. [3] The resin recovery method of [1], further comprising a recovery step (2) of separating and recovering the solid resin (A) and the solid resin (B) obtained in the step (1) based on the difference in specific gravity between the solid resin (A) and the solid resin (B). [4] The resin recovery method of any of [1] to [3], wherein, when the number average molecular weight of the hydrolyzable resin (b1) is Mn1 and the number average molecular weight of the hydrolyzable resin (b2) is Mn2, the ratio of Mn2 to Mn1 (Mn2 / Mn1) is 0.15 or more and Mn2 is 2,300 or more. [5] The resin recovery method of any of [1] to [4], wherein, in the step (1), the time for contacting the composite with the subcritical fluid is 1 to 60 minutes. [6] The resin recovery method of any of [1] to [5], wherein the non-hydrolyzable resins (a1) and (a2) are polyolefin resins. [7] The resin recovery method according to any one of [1] to [6], wherein the hydrolyzable resins (b1) and (b2) are polyamide resins or polyester resins. [8] The resin recovery method according to [1] to [7], wherein the composite is waste plastic. [9] A method for recovering resin from a molded body containing a hydrolyzable resin (b1), comprising a step of contacting the molded body with a subcritical fluid to obtain a solid resin (B) consisting of a hydrolyzable resin (b2), wherein the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or have different molecular weight distributions.

[10] A method for recovering resin from a molded body containing a non-hydrolyzable resin (a1), comprising a step of contacting the molded body with a subcritical fluid to obtain a solid resin (A) consisting of a non-hydrolyzable resin (a2), wherein the non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are the same or have different molecular weight distributions.

[11] A material recycled product containing, as a raw material, the non-hydrolyzable resin (a2) recovered by the resin recovery method of any of [1] to [8] and

[10] .

[12] A material recycled product containing, as a raw material, the hydrolyzable resin (b2) recovered by the resin recovery method of any of [1] to [9].

[13] A method for producing a material recycled product, in which material recycling is performed using, as a raw material, the non-hydrolyzable resin (a2) recovered by the resin recovery method of any of [1] to [8] and

[10] .

[14] A method for producing a material recycled product, comprising: recycling the hydrolyzable resin (b2) recovered by any one of the resin recovery methods according to [1] to [9] as a raw material.

[0011] According to a first aspect of the present invention, it is possible to separate and recover a hydrolyzable resin and a non-hydrolyzable resin in a resin state from a composite containing the hydrolyzable resin and the non-hydrolyzable resin. According to a second aspect of the present invention, it is possible to separate and recover a hydrolyzable resin in a resin state from a molded product containing the hydrolyzable resin. According to a third aspect of the present invention, it is possible to separate and recover a non-hydrolyzable resin in a resin state from a molded product containing the non-hydrolyzable resin.

[0012] 1 is an example of an apparatus for carrying out the resin recovery method of the present invention.

[0013] A first aspect of the present invention is a method for recovering resin from a composite comprising a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1), comprising step (1) of contacting the composite with a subcritical fluid to decompose and / or separate the layers (A) and (B) to obtain a solid resin (A) consisting of a non-hydrolyzable resin (a2) and a solid resin (B) consisting of a hydrolyzable resin (b2), wherein the non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are either identical to each other or differ only in molecular weight distribution, and the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are either identical to each other or differ only in molecular weight distribution. In this specification, a solid resin refers to a resin that is solid at 25°C and 1 atm.

[0014] <Step (1)> In step (1), a composite including a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1) is contacted with a subcritical fluid. In step (1), the layer (A) and the layer (B) are decomposed and / or separated to obtain a solid resin (A) consisting of a non-hydrolyzable resin (a2) and a solid resin (B) consisting of a hydrolyzable resin (b2). Here, "consisting of" means that no components not contained in the composite are included. Preferably, it means that only trace amounts of impurities are included, and more preferably it means that "consisting only of."

[0015] A composite refers to a structure in which layers made of two or more resins or resin compositions are bonded together directly or via an adhesive or the like, and examples thereof include laminates and bonded bodies. The composite includes a layer (A) and a layer (B). The layers (A) and (B) may be adjacent to each other or may be bonded together, or may not be adjacent to each other. The composite may also include layers other than the layers (A) and (B) or other components. For example, the composite may optionally include an inorganic layer in addition to the layers (A) and (B).

[0016] In Layer (A), the non-hydrolyzable resin (a1) is preferably the main component, and in Layer (B), the hydrolyzable resin (b1) is preferably the main component. "In Layer (A), the non-hydrolyzable resin (a1) is the main component" means that the non-hydrolyzable resin (a1) is contained in the largest amount by mass of all the components of the composition constituting Layer (A), and means that the non-hydrolyzable resin (a1) accounts for 50 mass% or more, preferably 70 mass% or more, and more preferably 95 mass% or more of the 100 mass% composition constituting Layer (A). This also includes an embodiment in which 100 mass%, i.e., Layer (A) is composed solely of the non-hydrolyzable resin (a1). The same applies to "In Layer (B), the hydrolyzable resin (b1) is the main component."

[0017] A non-hydrolyzable resin is a resin in which the bonds in the resin are not hydrolyzed or are difficult to hydrolyze. Non-hydrolyzable thermoplastic resins are preferred, and examples thereof include polyethylene resins such as low-density polyethylene (LDPE) resin, linear low-density polyethylene (LLDPE) resin, and high-density polyethylene (HDPE) resin, polyolefin resins such as polypropylene resin, tetrafluoroethylene, ethylene / tetrafluoroethylene copolymer, halogenated polyolefins such as polyvinyl chloride, ethylene-vinyl acetate copolymer, acrylic resin, polystyrene resin, acrylonitrile-butadiene-styrene copolymer, and acrylonitrile-styrene copolymer. These may be used alone or in combination of two or more. Of these, polyolefin resins are preferred.

[0018] A hydrolyzable resin is a resin in which at least a portion of the bonds in the resin are hydrolyzed. Examples include ester bonds, amide bonds, imide bonds, ether bonds, urethane bonds, carbonate bonds, acetal bonds, hemiacetal bonds, ketal bonds, hemiketal bonds, and resins having bonds in which some or all of these oxygen atoms are sulfur atoms. Generally, a resin in which at least a portion of the bonds in the main chain in the resin are hydrolyzed is preferred, and a hydrolyzable thermoplastic resin is preferred. Specific examples include polyamide resins, polyester resins, polyurethane resins, polycarbonate resins, polyacetal resins, polyether resins, and phenolic resins. These may be used alone or in combination of two or more. Among these, polyamide resins and polyester resins are preferred, and polyamide resins are more preferred.

[0019] Examples of polyamide resins include aliphatic homopolyamide resins, aliphatic copolymer polyamide resins, semi-aromatic homopolyamide resins, semi-aromatic copolymer polyamide resins, aromatic homopolyamide resins, and aromatic copolymer polyamide resins. Examples of raw material monomers for polyamide resins include lactam compounds, aminocarboxylic acids, and combinations of diamines and dicarboxylic acids. Here, semi-aromatic polyamide resins refer to polyamide resins whose constituent units are combinations of diamines and dicarboxylic acids, in which one of the diamines and dicarboxylic acids is aliphatic and the other is aromatic.

[0020] Specific examples of polyamide resins include, but are not limited to, polyamide 410, polyamide 6, polyamide 56, polyamide 66, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide 56 / 6, polyamide 6 / 66, polyamide 6 / 12, polyamide 6 / 66 / 12, polyamide 9T, polyamide 6T, polyamide 6I, polyamide MXD6, polyamide 66 / 6T, polyamide 6T / 6, polyamide 66 / 6I, polyamide 6I / 6, polyamide 12 / 6T, polyamide 66 / 6T / 6I, polyamide 66 / 6 / 6I, polyamide 6T / 6I, and polyamide 6T / M5T.

[0021] Examples of the combination of the non-hydrolyzable resin (a1) and the hydrolyzable resin (b1) include the above-mentioned combinations of resins, and preferred examples include a combination of a polyolefin resin and a polyamide resin, and a combination of a polyolefin resin and a polyester resin.

[0022] Examples of the optional inorganic layer include a metal layer that imparts gas barrier properties, aroma retention, light reflectivity, etc., and a hard coat layer that imparts scratch resistance. The metal layer is not particularly limited, and examples thereof include layers of aluminum, silicon, a combination of copper-nickel-chromium, gold, palladium, tin, ruthenium, black trivalent chromium, and tin-cobalt alloy. The hard coat layer is not particularly limited, and examples thereof include layers of ceramics mainly composed of metal oxides such as alumina, silica, zirconia, and titania.

[0023] Layer (A), Layer (B), and other components in the composite may contain, as optional components, appropriate functionality-imparting agents such as dyes, pigments, fibrous reinforcements, particulate reinforcements, plasticizers, antioxidants, heat resistance agents, foaming agents, weather resistance agents, crystal nucleating agents, crystallization accelerators, mold release agents, lubricants, antistatic agents, flame retardants, flame retardant assistants, and colorants. These are preferably components that are blended in small amounts as additives, and are not particularly limited, but are preferably contained in an amount of 5% by mass or less, more preferably 1% by mass or less, in each layer or in each composition that constitutes a layer.

[0024] In step (1), a composite including a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1) is contacted with a subcritical fluid. A subcritical fluid is a fluid that exists in a liquid state near its critical point and in a region where the temperature and / or pressure are lower than the critical point. The subcritical fluid is obtained by pressurizing the fluid at a temperature range above its boiling point. Examples of the fluid include water, alcohol, carbon dioxide, and nitrogen, and water is preferred from the viewpoint of having a high ionic product.

[0025] Contact refers to maintaining the composite in the subcritical fluid for a certain period of time. The method for contacting the composite with the subcritical fluid is not particularly limited, but is usually carried out in a sealed state, and can be carried out batchwise or continuously, with the continuous method being preferred. Preferably, the composite is placed in a pressure-resistant reaction vessel, heated, the autogenous pressure or pressure is adjusted, and the fluid is circulated at a predetermined temperature. Examples of the reaction vessel include sealed reaction vessels, such as autoclaves and reaction tubes. The heating method is not particularly limited, and examples include methods using a heater, a molten salt bath, etc.

[0026] The temperature and pressure of the subcritical fluid during contact are not particularly limited as long as a subcritical fluid is produced, but when the subcritical fluid is water, the temperature is preferably 120 to 374°C and 0.2 to 22 MPa. When the subcritical fluid is methanol, the temperature is preferably 85 to 240°C and 0.2 to 8 MPa. When the subcritical fluid is ethanol, the temperature is preferably 95 to 240°C and 0.2 to 6 MPa. When the temperature and pressure of the subcritical fluid are within the above ranges, the non-hydrolyzable resin (a2) can be easily recovered while maintaining the molecular weight of the non-hydrolyzable resin (a1), and the recovery rate of the hydrolyzable resin (b2), which is a resin of the hydrolyzable resin (b1), can also be increased.

[0027] The contact time (treatment time) is preferably 1 to 60 minutes, more preferably 1 to 30 minutes. When the time is within the above range, the non-hydrolyzable resin (a2) can be easily recovered while maintaining the molecular weight of the non-hydrolyzable resin (a1), and the recovery rate of the hydrolyzable resin (b2), which is a resin of the hydrolyzable resin (b1), can also be increased.

[0028] The temperature, pressure, treatment time, and other associated contact conditions of the subcritical fluid can be appropriately set with reference to this specification depending on the type of non-hydrolyzable resin (a1) and / or hydrolyzable resin (b1). Preferably, the conditions can also be set in accordance with the desired molecular weight of the hydrolyzable resin (b2).

[0029] The contact of the complex with the subcritical fluid can be carried out by adding an acid or a base. However, from the viewpoint of maintaining the molecular weight of the non-hydrolyzable resin (a1) and increasing the recovery rate of the hydrolyzable resin (b1) as a resin, it is preferable not to add an acid or a base in order to moderate the decomposition, and it is more preferable to carry out the contact under neutral conditions, and even more preferably under conditions of pH 6 to 8.

[0030] When the composite is brought into contact with the subcritical fluid, the amount of the subcritical fluid used (the amount of the subcritical fluid raw material charged into the reaction vessel) is such that the mass ratio of the subcritical fluid to the composite (subcritical fluid / composite) is preferably 0.5 to 500, more preferably 1 to 100, and even more preferably 5 to 20. When the mass ratio is within the above range, decomposition of the non-hydrolyzable resin can be suppressed, and layer peeling can be carried out smoothly.

[0031] Step (1) decomposes and / or separates layers (A) and (B). The composite is preferably delaminated. For example, layers (A), (B), and any other layers are delaminated. The treatment solution that has undergone step (1) contains a non-hydrolyzable resin (a2) and a hydrolyzable resin (b2). The non-hydrolyzable resin (a1) is separated and / or decomposed without being hydrolyzed by the subcritical fluid, and at least a portion, preferably all, of the non-hydrolyzable resin (a1) becomes a solid resin (A) composed of the non-hydrolyzable resin (a2). The non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are either identical or differ only in molecular weight distribution. That is, the two resins are the same type. In this specification, "the resins are the same or differ only in molecular weight distribution" means that the resins are the same type, have the same basic structure, and have the same or different molecular weight distributions. "The resins have the same basic structure" means that the resins are identical even if they are partially crosslinked, modified, or substituted, as long as the basic properties of the resins remain unchanged. The phrase "the molecular weight distribution is different (only the molecular weight distribution is different)" means that the molecular weight distribution is changed as a result of the change in molecular weight caused by step (1). The same applies to the hydrolyzable resin (b2) hereinafter. In other words, it is understood by those skilled in the art that various physical properties correlated with molecular weight are naturally changed with the change in molecular weight.

[0032] Since the non-hydrolyzable resin (a1) is not hydrolyzed, the non-hydrolyzable resin (a2) has a high retention rate of the molecular weight of the non-hydrolyzable resin (a1), and the retention rate of the number average molecular weight of the non-hydrolyzable resin (a2) to the number average molecular weight of the non-hydrolyzable resin (a1) ((number average molecular weight Mn4 of non-hydrolyzable resin (a2) / number average molecular weight Mn3 of non-hydrolyzable resin (a1))*100) is preferably 80% or more, more preferably 85% or more.

[0033] Furthermore, since the non-hydrolyzable resin (a1) is not hydrolyzed, the non-hydrolyzable resin (a2) is not broken into fine particles such as powder. Due to the high molecular weight retention rate and shape characteristics, the solid resin (A) made of the non-hydrolyzable resin (a2) is useful as a raw material for material recycling. Furthermore, when the non-hydrolyzable resin (a1) melts upon contact with a subcritical fluid, the molecular weight difference between the non-hydrolyzable resin (a2) and the hydrolyzable resin (b2) increases due to the high molecular weight retention rate of the non-hydrolyzable resin (a1) as described above. As a result, the viscosity difference between the non-hydrolyzable resin (a2) and the hydrolyzable resin (b2) may increase. In this case, the viscosity difference can be utilized to separate the non-hydrolyzable resin (a2) and the hydrolyzable resin (b2).

[0034] In step (1), at least a portion of the hydrolyzable resin (b1) is hydrolyzed by contact with a subcritical fluid, resulting in a solid resin (B) at least a portion of which is composed of a hydrolyzable resin (b2). The hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or differ only in molecular weight distribution. That is, the types of the two resins are the same. It is preferable that the hydrolyzable resin (b1) and the hydrolyzable resin (b2) differ only in molecular weight distribution.

[0035] When the number average molecular weight of the hydrolyzable resin (b1) is Mn1 and the number average molecular weight of the hydrolyzable resin (b2) is Mn2, the ratio of Mn2 to Mn1 (Mn2 / Mn1) is preferably 0.15 or more, and Mn2 is preferably 2300 or more. Furthermore, it is particularly preferable that the hydrolyzable resin (b2) is obtained in the form of a fine powder.

[0036] Mn2 / Mn1 represents the retention rate of the molecular weight of the hydrolyzable resin (b1) in the hydrolyzable resin (b2). Thus, the hydrolyzable resin (b2) is a resin obtained by maintaining the molecular weight of at least a portion of the hydrolyzable resin (b1). The fact that Mn2 is the above value indicates that the hydrolyzable resin (b2) is obtained as a resin. Even after step (1), at least a portion of the hydrolyzable resin (b1) remains as a resin without being decomposed into monomers or oligomers.

[0037] Since Mn2 / Mn1 and Mn2 are within the above ranges, at least a portion of the hydrolyzable resin (b1) is recovered as a solid resin (B) having a certain molecular weight. The solid resin (B) can also be used as a raw material for material recycling.

[0038] The requirement that Mn2 / Mn1 and Mn2 fall within the above ranges can be met by carrying out step (1). Preferably, this requirement can be met by setting the temperature, pressure, and contact time as described above in step (1).

[0039] As described above, according to the present invention, by including step (1), both non-hydrolyzable resins and hydrolyzable resins can be recovered as solid resins, which is useful for material recycling. Compared to chemical recycling, which decomposes resins down to monomers during recovery, material recycling can simplify the process of manufacturing new products and is therefore a highly effective recycling method.

[0040] In the resin recovery method of the present invention, the recovery rate of the non-hydrolyzable resin (a1) ((mass of non-hydrolyzable resin (a2) / mass of non-hydrolyzable resin (a1))×100) is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. According to the resin recovery method of the present invention, the non-hydrolyzable resin (a1) can be recovered at a high recovery rate as the non-hydrolyzable resin (a2), which may differ only in molecular weight distribution.

[0041] The recovery rate of the hydrolyzable resin (b1) ((mass of the hydrolyzable resin (b2) / mass of the hydrolyzable resin (b1))×100) is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, and particularly preferably 80% or more. According to the resin recovery method of the present invention, the hydrolyzable resin (b1) can be recovered as the hydrolyzable resin (b2) which may differ only in molecular weight distribution.

[0042] As shown by the recovery rate, in step (1), components other than the non-hydrolyzable resin (a2) and the hydrolyzable resin (b2) may also be produced. For example, components such as monomers and dimers of units constituting the hydrolyzable resin may be produced. Furthermore, depending on the layer contained in the composite, components other than the non-hydrolyzable resin (a2) and the hydrolyzable resin (b2) may also be produced.

[0043] <Step (2)> The resin recovery method preferably includes a recovery step (2) following the step (1). The recovery step (2) may be in an embodiment 1 in which the solid resin (A) and the solid resin (B) obtained in the step (1) are separated and recovered through a filter, or in an embodiment 2 in which the solid resin (A) and the solid resin (B) obtained in the step (1) are separated and recovered based on the difference in specific gravity.

[0044] Aspect 1, in which the solid resin (A) and solid resin (B) obtained in step (1) are separated and recovered through a filter, is as follows. After step (1), the treatment liquid is cooled, and the non-hydrolyzable resin (a2) and hydrolyzable resin (b2) contained in the treatment liquid are preferably obtained as powdery solid resins. Therefore, for example, without a step such as boiling point separation, the non-hydrolyzable resin (a2) as solid resin (A) and the hydrolyzable resin (b2) as solid resin (B) can be easily separated and recovered. The filter is not particularly limited, and for example, a filter made of metal, thermoplastic resin, or thermosetting resin can be used.

[0045] The vertical and horizontal mesh sizes of the filter are not particularly limited, but from the viewpoint of facilitating separation of the resin, each is preferably 10 to 100 μm mesh, more preferably 20 to 70 μm mesh. The filter may be a single-stage filter or a multi-stage filter. Using a multi-stage filter with a different mesh for each stage is preferred, as this enables more effective separation.

[0046] A second embodiment of recovering the solid resin (A) and solid resin (B) obtained in step (1) by separating them based on the difference in specific gravity is as follows. When the specific gravity is such that the hydrolyzable resin (b2) is greater than the subcritical fluid and greater than the non-hydrolyzable resin (a2), the solid resin (A) and the solid resin (B) can be separated based on their specific gravity. Specifically, by cooling in the subcritical fluid, the hydrolyzable resin (b2) dissolved in the subcritical fluid settles and precipitates, while the non-hydrolyzable resin (a2) is on the surface of the subcritical fluid. The two are then separated. It is preferable that no other steps other than the cooling operation are included between steps (1) and (2).

[0047] <Pretreatment Step> The resin recovery method may include an optional pretreatment step prior to step (1). Examples of the pretreatment step include a step of pulverizing the molded article composite. The pulverization step has the advantage of increasing the contact area with the subcritical fluid. The pulverization means is not particularly limited as long as it is a known pulverization means, and examples thereof include mills such as a joke crusher, a gyratory crusher, a cone crusher, an impact crusher, a roll crusher, an autogenous crusher, a stamp mill, a stone-type crusher, a crusher, a large shredder, a ring mill, a roll mill, a cutter mill, a hammer mill, a turbo mill, a jet mill, a pin mill, a centrifugal mill, and a chopper mill, a crusher, a rotoplex, a pulverizer, and an ultra rotor. Wet pulverization may also be used. The composite can also be pulverized in a frozen state. Pulverization also includes cutting.

[0048] Further, the pretreatment step may include a step of melting the composite of the molded article. By melting the composite at a melting temperature equal to or higher than the melting temperature of the resin to be recovered, components that do not melt at that temperature can be separated and removed before step (1). The melting temperature is preferably equal to or higher than the melting points of the non-hydrolyzable resin (a1) and the hydrolyzable resin (b1) and lower than a temperature at which these resins do not undergo thermal degradation. Examples of melting means include a melt kneader, a kneading extruder, a gear pump, etc.

[0049] The pretreatment step may include a washing step for washing the composite. When waste plastic is used as the composite, it is particularly preferable to have a washing step.

[0050] One or more of the above-mentioned pulverization step, melting step, and washing step can be performed. When multiple steps are performed from among these, the melting step is preferably performed immediately before step (1), and the washing step, pulverization step, and melting step are more preferably performed in this order.

[0051] <Post-treatment step> The resin recovery method may include an optional post-treatment step after step (1) or optional step (2). Examples of the post-treatment step include a drying step of the recovered solid resin (A) and solid resin (B). In addition, the method may include a purification step of the recovered solid resin (A) and solid resin (B) after step (1) or optional step (2).

[0052] <Material Recycling> Examples of composites used in the resin recovery method include molded articles containing two or more resins. From the viewpoint of effective resource utilization, waste plastics (waste such as used resin molded articles and defectively molded resin molded articles) are preferred. Examples of waste plastics include, but are not limited to, plastic automobile parts (chassis, interior, outer layer, window glass, lighting parts such as headlamp covers and reflectors, side mirrors, display parts, safety mechanisms such as safety belts, airbags, and airbag covers, fuel system mechanisms such as tanks, piping, and pumps, electrical wiring mechanisms such as connectors, and mechanical mechanisms such as gears), plastic parts (housings, display parts, electrical circuit boards, antennas, etc.) of electrical equipment (e.g., home appliances and personal computers) and mobile communication terminals, various optical disks, plastic parts for medical and health equipment (dialysis equipment, infusion bags, disposable syringes, physical training equipment, etc.), various molded articles such as containers, packaging trays, stationery, toys, furniture, daily necessities, and home appliance housings, as well as packaging films (including packaging for pharmaceuticals such as tablets, powders, and liquids), and plastic shopping bags. The solid resin recovered from such composites can be used as a raw material for material recycling, thereby contributing to the Sustainable Development Goals (SDGs).

[0053] Specifically, material recycling can be achieved by a method for producing a material recycled product, in which the non-hydrolyzable resin (a2) recovered by the resin recovery method described above is used as a raw material. In this method, the non-hydrolyzable resin (a2) is used as a raw material, and, if necessary, further polymerized with a monomer and / or mixed with other components to obtain a material recycled product. Since the non-hydrolyzable resin (a2) has a high molecular weight retention rate relative to the non-hydrolyzable resin (a1), it can also be recycled without polymerization. In this way, a material recycled product containing the non-hydrolyzable resin (a2) as a raw material can be obtained.

[0054] Furthermore, specific examples of material recycling include a method for producing a material recycled product, in which the hydrolyzable resin (b2) recovered by the resin recovery method is used as a raw material. In this production method, the hydrolyzable resin (b2) is used as a raw material, and, if necessary, monomers are additionally polymerized and / or mixed with other components to obtain a material recycled product. According to the resin recovery method, at least a portion of the hydrolyzable resin (b1) is recovered as the resin hydrolyzable resin (b2), which simplifies the process for producing a new product compared to chemical recycling, making this a highly effective recycling method. In this way, a material recycled product containing the hydrolyzable resin (b2) as a raw material can be obtained.

[0055] A second aspect of the present invention is a method for recovering a resin from a molded body containing a hydrolyzable resin (b1), comprising the step of contacting the molded body with a subcritical fluid to obtain a solid resin (B) consisting of a hydrolyzable resin (b2), wherein the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or have different molecular weight distributions.

[0056] Examples of the hydrolyzable resin (b1) include the resins exemplified in the first aspect of the present invention. The method for contacting the molded body with a subcritical fluid in the step of obtaining a solid resin (B) made of the hydrolyzable resin (b2) is not particularly limited, and includes the same method as in the first aspect of the present invention.

[0057] The temperature and pressure of the subcritical fluid during contact are not particularly limited as long as a subcritical fluid is produced, but when the subcritical fluid is water, the temperature is preferably 120 to 374°C and 0.2 to 22 MPa. When the subcritical fluid is methanol, the temperature is preferably 85 to 240°C and 0.2 to 8 MPa. When the subcritical fluid is ethanol, the temperature is preferably 95 to 240°C and 0.2 to 6 MPa. When the temperature and pressure of the subcritical fluid are within the above ranges, the recovery rate of the hydrolyzable resin (b2), which is a resin of the hydrolyzable resin (b1), can be increased.

[0058] The contact time (treatment time) is preferably 1 to 60 minutes, more preferably 1 to 30 minutes, and even more preferably 1 to 10 minutes. When the time is within the above range, the recovery rate of the hydrolyzable resin (b1) as the hydrolyzable resin (b2) can be increased. The pH and the amount of the subcritical fluid used are also the same as in the first aspect of the present invention.

[0059] At least a portion of the hydrolyzable resin (b1) is hydrolyzed by a subcritical fluid to form a solid resin (B) at least a portion of which is composed of a hydrolyzable resin (b2). The hydrolyzable resin (b1) and the hydrolyzable resin (b2) may be the same or may have different molecular weight distributions. That is, the types of the two resins are the same. It is preferable that the hydrolyzable resin (b1) and the hydrolyzable resin (b2) have different molecular weight distributions.

[0060] When the number average molecular weight of the hydrolyzable resin (b1) is Mn1 and the number average molecular weight of the hydrolyzable resin (b2) is Mn2, the ratio of Mn2 to Mn1 (Mn2 / Mn1) is preferably 0.15 or more, and Mn2 is preferably 2,300 or more.

[0061] The recovery rate of the hydrolyzable resin (b1) ((mass of the hydrolyzable resin (b2) / mass of the hydrolyzable resin (b1))×100) is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, and particularly preferably 80% or more. According to the resin recovery method of the present invention, the hydrolyzable resin (b1) can be recovered as the hydrolyzable resin (b2) which may differ only in molecular weight distribution.

[0062] A third aspect of the present invention is a method for recovering a resin from a molded body containing a non-hydrolyzable resin (a1), comprising the step of contacting the molded body with a subcritical fluid to obtain a solid resin (A) comprising a non-hydrolyzable resin (a2), wherein the non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are the same or have different molecular weight distributions.

[0063] Examples of the non-hydrolyzable resin (a1) include the resins exemplified in the first aspect of the present invention. The method for contacting the molded body with a subcritical fluid in the step of obtaining a solid resin (A) made of the non-hydrolyzable resin (a2) is not particularly limited, and includes the same method as in the first aspect of the present invention.

[0064] The non-hydrolyzable resin (a1) is separated and / or decomposed by the subcritical fluid without being hydrolyzed, and at least a part of it, preferably all of it, becomes a solid resin (A) consisting of the non-hydrolyzable resin (a2). The non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) may be the same or may have different molecular weight distributions. That is, the types of the two resins are the same.

[0065] Since the non-hydrolyzable resin (a1) is not hydrolyzed, the non-hydrolyzable resin (a2) has a high retention rate of the molecular weight of the non-hydrolyzable resin (a1), and the retention rate of the number average molecular weight of the non-hydrolyzable resin (a2) to the number average molecular weight of the non-hydrolyzable resin (a1) ((number average molecular weight Mn4 of non-hydrolyzable resin (a2) / number average molecular weight Mn3 of non-hydrolyzable resin (a1))*100) is preferably 80% or more, more preferably 85% or more.

[0066] The recovery rate of the non-hydrolyzable resin (a1) ((mass of the non-hydrolyzable resin (a2) / mass of the non-hydrolyzable resin (a1))×100) is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. According to the resin recovery method of the present invention, the non-hydrolyzable resin (a1) can be recovered at a high recovery rate as the non-hydrolyzable resin (a2), which may differ only in molecular weight distribution.

[0067] The second and third aspects of the present invention may have the same pretreatment and posttreatment steps as the first aspect of the present invention. The hydrolyzable resin (b2) obtained in the second aspect of the present invention and the non-hydrolyzable resin (a2) obtained in the third aspect of the present invention are suitable for material recycling similar to the first aspect of the present invention.

[0068] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0069] [Example 1] The following operation was carried out using the manufacturing apparatus shown in Figure 1. ３ Reactor 4 was filled with 10 g of crushed material of a "multilayer film (polyamide content 25% by mass) composed of a laminate of a polyamide 6 resin layer, a polyethylene (LDPE) resin layer, and an adhesive layer" (number average molecular weight of the polyamide 6 resin: 15,016, number average molecular weight of the polyethylene (LDPE) resin: 37,970). Stainless steel mesh filters (mesh size 55 μm) were installed at the inlet and outlet of reactor 4. Degassed purified water was passed through reactor 4 to remove the air, and then the flow path was changed by valve operation to one in which the purified water did not pass through reactor 4. In other words, in this flow path, the purified water passed through pump 1, heating furnace 2, cooling means 5', and back pressure valve 6. To maintain a constant temperature of the heated purified water, the flow rate was set so that the mass ratio of the total flow rate to the sample from the start to the end of the treatment was 10. Heating of the heaters built into reactor 3 and heating furnace 2 was started, and when the temperatures of reactor 3 and heating furnace 2 reached 325°C, reactor 4 was installed in reactor 3, and the valve was operated to switch the flow path of the purified water so that the purified water leaving heating furnace 2 passed through reactor 4. That is, in this flow path, the purified water passed through pump 1, heating furnace 2, reactor 4, cooling means 5, and back pressure valve 6. The valve was also operated to adjust the pressure so that the purified water became subcritical water. The treatment started when the temperature inside reactor 4 reached 325°C, and purified water was allowed to continue flowing for 30 minutes. The purified water that flowed through reactor 4 passed through cooling means 5 and was discharged outside the system. This purified water discharged outside the system was continuously collected for 30 minutes. The purified water discharged outside the system was cloudy. After stopping pump 1, reactor 4 was removed from reactor 3 and immersed in cold water for rapid cooling to complete the treatment. The cloudy purified water was filtered, the solids were recovered, and the recovery rate was calculated. The solids in reactor 4 were recovered, and the recovery rate was calculated. The recovered solids were identified by infrared spectroscopy (ATR method). As a result, the solids recovered from the cloudy purified water were polyamide 6 resin, and the solids recovered from reactor 4 were polyethylene resin. The number average molecular weight of the recovered polyamide 6 resin was 2,399.

[0070] [Example 2] The same operation as in Example 1 was carried out, except that the start of treatment was considered to be when the temperature inside reactor 4 reached 280°C. The recovered solid was identified by infrared spectroscopy (ATR method). As a result, the solid recovered from the cloudy purified water was polyamide 6 resin, and the solid recovered from reactor 4 was polyethylene resin. The number average molecular weight of the recovered polyamide 6 resin was 2625.

[0071] Reference Example 1 The same procedure as in Example 1 was carried out, except that 10 g of polyamide 6 resin pellets (number average molecular weight 14,644) was used as a sample instead of 10 g of a pulverized product (10 g) of a "multilayer film (polyamide content 25% by mass) composed of a polyamide 6 resin layer, a polyethylene (LDPE) resin layer, and an adhesive layer laminated together." The cloudy purified water was filtered, the solid was recovered, and the recovery rate was calculated. The recovered solid was identified by infrared spectroscopy (ATR method). As a result, the solid recovered from the cloudy purified water was found to be polyamide 6 resin. The number average molecular weight of the recovered polyamide 6 resin was 2,420. The results are shown in Table 1.

[0072] [Reference examples 2 and 3] Internal volume 10cm ３ In a stainless steel reaction tube, 0.3 g of polyamide 6 resin pellets (product name: UBE Nylon 1030B) as a sample and 3 cm of water were added. ３ was introduced and sealed. The reaction tube was placed in a molten salt bath, and subcritical water was prepared at the treatment temperature shown in Table 1. The pellets were brought into contact with the subcritical water at the temperature and for the treatment time shown in Table 1. After the contact treatment with subcritical water, the reaction tube was cooled with water, and the treated product was recovered. The treated water was filtered, and the solid was recovered, and the recovery rate was calculated. The recovered solid was identified by infrared spectroscopy (ATR method). As a result, the recovered solid was found to be polyamide 6 resin. The results are shown in Table 1.

[0073] Reference Example 4 The same procedures as in Reference Examples 2 and 3 were carried out, except that 0.3 g of polyethylene terephthalate pellets (product name: Velpet PBK1) were used as the sample instead of 0.3 g of "polyamide 6 resin pellets," and the pellets were brought into contact with subcritical water at the treatment temperature and for the treatment time shown in Table 2. The recovered solid was identified by infrared spectroscopy (ATR method). As a result, the recovered solid was found to be polyethylene terephthalate. The results are shown in Table 2.

[0074] [Reference Examples 5 and 6] The same procedures as in Reference Examples 2 and 3 were carried out, except that 0.3 g of polyethylene pellets (LDPE) (product name: UBE Polyethylene F222NH, number average molecular weight: 35238) was used as the sample instead of 0.3 g of "polyamide 6 resin layer pellets," and the pellets were contacted with subcritical water at the treatment temperature and for the treatment time shown in Table 3. The recovered solid was identified by infrared spectroscopy (ATR method). As a result, the recovered solid was a polyethylene resin. The results are shown in Table 3.

[0075] <Calculation of recovery rate of recovered hydrolyzable resin or non-hydrolyzable resin> The recovery rate of the resin was calculated using the following formula. The unit of resin amount is mass. Recovery rate (%) = amount of recovered hydrolyzable resin / amount of hydrolyzable resin in the sample before treatment Recovery rate (%) = amount of recovered non-hydrolyzable resin / amount of non-hydrolyzable resin in the sample before treatment

[0076] <Measurement of average molecular weight of hydrolyzable resin polyamide 6> The number average molecular weight Mn2 of the recovered solid hydrolyzable resin polyamide 6 was measured by GPC using the following method and conditions. Similarly, the number average molecular weight Mn1 of the hydrolyzable resin before treatment was measured.

[0077] (Measurement of number average molecular weight (GPC)) GPC apparatus: HLC-8220GPC (manufactured by Tosoh Corporation, detector: RI) Column: Shodex HFIP-LG + HFIP-806M × 2 Eluent: HFIP + 10 mM CF ３ COONa Flow rate: 0.8 mL / min Column temperature: 40°C Sample concentration: 0.05 wt / vol%

[0078] <Measurement of average molecular weight of hydrolyzable resin polyethylene terephthalate> The recovered solid hydrolyzable resin was subjected to NMR measurement by the following method and conditions to measure the number average molecular weight Mn2. Similarly, the number average molecular weight Mn1 before treatment was measured.

[0079] (Measurement of number average molecular weight (NMR)) NMR apparatus: AL400 manufactured by JEOL Ltd. (1) Quantitative determination of hydroxyl group terminals 30 mg of a sample was weighed and dissolved in 1.0 ml of CDCl3 / HFIP = 1 / 1 (v / v), 1 (2) Quantitative Determination of Acid Terminals 30 mg of a sample was weighed and dissolved in 4 mg of triethylamine and 1.0 ml of CDCl / HFIP = 1 / 1 (v / v). 1 H-NMR was measured. The number average molecular weight was calculated according to the following formula: Although isophthalic acid and diethylene glycol were also present, they were not included in the calculation due to their trace amounts.

[0080] <Measurement of Average Molecular Weight of Non-hydrolyzable Resin> The recovered solid non-hydrolyzable resin was subjected to GPC measurement using the following method and conditions to measure the number average molecular weight Mn4. Similarly, the number average molecular weight Mn3 of the non-hydrolyzable resin before treatment was measured.

[0081] (Measurement of number average molecular weight (GPC)) High temperature GPC apparatus: HLC-8321GPC / HT (manufactured by Tosoh Corporation, detector: RI) Column: TSKgel guard column HHR(S) + TSKgel GMHHR-H(S)HT x 2 Eluent: o-dichlorobenzene Flow rate: 1.0 mL / min Column temperature: 145°C Sample concentration: 0.1 wt / vol%

[0082] <Calculation of Molecular Weight Retention Rate of Recovered Hydrolyzable Resin> The ratio of the number average molecular weight Mn2 of the recovered hydrolyzable resin to the number average molecular weight Mn1 of the hydrolyzable resin before treatment ([Mn2 / Mn1]×100(%)) was calculated and is shown in Tables 1 and 2.

[0083] <Calculation of Molecular Weight Retention Rate of Recovered Non-hydrolyzable Resin> The ratio of the number average molecular weight Mn4 of the recovered non-hydrolyzable resin to the number average molecular weight Mn3 of the non-hydrolyzable resin before treatment ([Mn4 / Mn3] × 100 (%)) was calculated and is shown in Tables 1 and 3.

[0084]

[0085] Examples 1 and 2 demonstrated that non-hydrolyzable resins were recovered with a high molecular weight retention rate, while hydrolyzable resins were also recovered as recyclable resins. Example 2, with a treatment temperature of 280°C, demonstrated higher recovery rates and molecular weight retention rates for polyethylene resins and polyamide resins than Example 1, with a treatment temperature of 325°C. Reference Example 1 demonstrated that even when pellets consisting of only hydrolyzable resins were used, molecular weight retention rates and recovery rates similar to those achieved when composites were used. Reference Examples 2 and 3 demonstrated that in the case of polyamide resins, a treatment temperature of 280°C resulted in much higher recovery rates and molecular weight retention rates for hydrolyzable resins than Reference Example 1. In particular, Reference Example 3, with a treatment time of 5 minutes, demonstrated a recovery rate exceeding 90% and a high molecular weight retention rate. These results demonstrate that when the composite used in Example 2 was treated at 280°C for 5 minutes, the recovery rate was approximately 90% and the molecular weight retention rate was approximately 40%.

[0086]

[0087] It can be seen from Reference Example 4 that polyethylene terephthalate can be recovered at a high recovery rate even when polyethylene terephthalate is treated alone as a hydrolyzable resin with subcritical water. It can also be seen that polyethylene terephthalate can be recovered at a recovery rate as high as in Reference Example even when a composite containing polyethylene terephthalate and a non-hydrolyzable resin is treated.

[0088]

[0089] Reference Examples 5 and 6 revealed that even when a non-hydrolyzable resin was treated alone with subcritical water, extremely high recovery rates and molecular weight retention rates were achieved. From the results of Reference Example 5, it is expected that when the treatment temperature is 280°C, even when treating a composite containing a hydrolyzable resin and a polyethylene resin as in Example 2, if the treatment conditions are longer than those of Example 2, such as 60 minutes, the molecular weight retention rate of the polyethylene resin will be higher than that of Example 2. From the results of Reference Example 6, it is expected that when the treatment temperature is 325°C, even when treating a composite containing a hydrolyzable resin and a polyethylene resin as in Example 1, even if the treatment conditions are longer than those of Example 1, such as 60 minutes, the recovery rate and molecular weight retention rate of the polyethylene resin will not be higher than those of Example 1.

[0090] The resin recovery method of the present invention can recover both non-hydrolyzable resins and hydrolyzable resins as resins, and is therefore useful for recovering non-hydrolyzable resins and hydrolyzable resins contained in waste plastics as raw materials for material recycling.

[0091] REFERENCE SIGNS LIST 1 Pump 2 Heating furnace 3 Reactor 4 Reactor 5 Cooling means 5' Cooling means 6 Back pressure valve

Claims

1. A method for recovering a resin from a complex comprising a layer (A) containing a non-hydrolyzable resin (a1) and a layer (B) containing a hydrolyzable resin (b1), comprising step (1) of contacting the complex with a subcritical fluid to decompose and / or separate the layer (A) and the layer (B) to obtain a solid resin (A) consisting of a non-hydrolyzable resin (a2) and a solid resin (B) consisting of a hydrolyzable resin (b2); wherein the non-hydrolyzable resin (a1) and the non-hydrolyzable resin (a2) are the same or differ only in molecular weight distribution, and the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or differ only in molecular weight distribution.

2. The resin recovery method according to claim 1, further comprising a recovery step (2) of separating and recovering the solid resin (A) and the solid resin (B) obtained in the step (1) through a filter.

3. The resin recovery method according to claim 1, further comprising a recovery step (2) of separating and recovering the solid resin (A) and the solid resin (B) obtained in the step (1) based on the difference in specific gravity between the solid resin (A) and the solid resin (B).

4. A method for recovering resin according to claim 1, wherein the ratio of Mn2 to Mn1 (Mn2 / Mn1) is 0.15 or more, and Mn2 is 2,300 or more, where Mn1 is the number average molecular weight of the hydrolyzable resin (b1) and Mn2 is the number average molecular weight of the hydrolyzable resin (b2).

5. The method for recovering resin according to claim 1, wherein in the step (1), the time for which the complex is contacted with the subcritical fluid is 1 to 60 minutes.

6. The method for recovering resin according to claim 1, wherein the non-hydrolyzable resins (a1) and (a2) are polyolefin resins.

7. The method for recovering resin according to claim 1, wherein the hydrolyzable resins (b1) and (b2) are polyamide resins or polyester resins.

8. The resin recovery method according to claim 1, wherein the composite is waste plastic.

9. A method for recovering a resin from a molded body containing a hydrolyzable resin (b1), comprising the step of contacting the molded body with a subcritical fluid to obtain a solid resin (B) consisting of a hydrolyzable resin (b2), wherein the hydrolyzable resin (b1) and the hydrolyzable resin (b2) are the same or have different molecular weight distributions.

10. A material recycled product containing as a raw material the non-hydrolyzable resin (a2) recovered by the resin recovery method according to any one of claims 1 to 8.

11. A material recycled product containing as a raw material the hydrolyzable resin (b2) recovered by the resin recovery method according to any one of claims 1 to 9.

12. A method for producing a material recycled product, comprising the steps of: recycling the non-hydrolyzable resin (a2) recovered by the resin recovery method according to any one of claims 1 to 8 as a raw material.

13. A method for producing a material recycled product, comprising the steps of: recycling the hydrolyzable resin (b2) recovered by the resin recovery method according to any one of claims 1 to 9 as a raw material.

Images