Method for evaluating quality of raw material for manufacturing recycled film and method for manufacturing recycled film

Abstract

To provide a method for evaluating the quality of a raw material for manufacturing a recycled film for grasping the quality of the recycled film.SOLUTION: A method for evaluating the quality of a raw material for producing a recycled film, the method including an alkali treatment step of bringing a printed film into contact with an alkaline aqueous solution to detach a printed layer from a resin substrate, thereby obtaining a deinked substrate to be used as a raw material for producing a recycled film, the printed film including the resin substrate that is insoluble in the alkaline aqueous solution and on which the printed layer that is soluble in the alkaline aqueous solution is formed, and a deinking rate calculation step of calculating a deinking rate H or T according to the following formula (1) or (2): Deinking ratio H = {(Hx-Hz) / (Hx-Hy)} * 100 (1) (Hx: haze of printed film, Hy: haze of resin base material, Hz: haze of deinked base material. ) Deinking ratio T = {(Tz-Tx) / (Ty-Tx)} * 100 (2) (Tx: total light transmittance of printed film, Ty: total light transmittance of resin substrate, Tz: total light transmittance of deinked substrate. ) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating the quality of raw materials for producing recycled films and a method for producing recycled films. [Background technology]

[0002] In recent years, environmental pollution has become a problem due to the disposal or dumping of plastic products, such as packaging materials and plastic bottles made from plastic film, into the ocean as litter. These plastic products decompose in seawater and become submicron-sized fragments (microplastics), which float in the seawater. Microplastics are ingested by marine organisms such as fish and become concentrated in their bodies, raising concerns that they may affect the health of seabirds and humans that consume these marine organisms as food.

[0003] Packaging materials made from plastic film are used to package food products, pharmaceuticals, and other items. Packaging materials have a multi-layer structure, with various plastic substrates used as film base materials, including polyester, nylon (NY), polypropylene (PP), and polyethylene (PE). Generally, film substrates are printed with printing ink and then bonded to other film substrates or heat-melting resin substrates via adhesives, before being cut and heat-sealed to form packaging. Such multi-layer packaging materials contain multiple different materials, which presents a problem in that they cannot be recycled as is.

[0004] Regarding material recycling of multi-layer packaging materials, for example, Patent Document 1 discloses a technology in which a shrink label (printed film) with an alkali-removable ink layer is immersed in an alkaline solution, then immersed in water, and agitated to obtain a shrink film piece from which the ink layer has been removed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2021 / 225070 Summary of the Invention [Problem to be solved by the invention]

[0006] However, recycled films manufactured using shrink film pieces obtained based on the technology of Patent Document 1 may vary in appearance and strength between production lots. This is due to variations in the quality of the raw materials (shrink film pieces) used to manufacture the recycled film. In order to consistently manufacture recycled films with the desired appearance and strength, it is necessary to understand the quality of the raw materials in advance, but currently there is no well-established method for evaluating the quality of raw materials.

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for evaluating the quality of raw materials for recycled film production, in order to understand the quality of the raw materials prior to the production of recycled film. Another object of the present disclosure is to provide a method for producing recycled film that includes the quality evaluation method. [Means for solving the problem]

[0008] The present disclosure relates to the following aspects, for example: [1] An alkali treatment step in which a printed film having a resin substrate insoluble in an alkaline aqueous solution and a printed layer soluble in an alkaline aqueous solution is contacted with an alkaline aqueous solution to remove the printed layer from the resin substrate, thereby obtaining a deinked substrate to be used as a raw material for producing recycled film; a deinking rate calculation step of calculating the deinking rate H or the deinking rate T according to the following formula (1) or (2); A method for evaluating the quality of raw materials used in the production of recycled film. Deinking rate H={(Hx-Hz) / (Hx-Hy)}×100...(1) Hx: Haze of the printed film. Hy: Haze of the resin substrate. Hz: Haze of deinked substrate. Deinking rate T={(Tz-Tx) / (Ty-Tx)}×100...(2) Tx: Total light transmittance of the printed film. Ty: Total light transmittance of the resin substrate. Tz: Total light transmittance of the deinked substrate. [2] The quality evaluation method according to [1], wherein the resin substrate has a total light transmittance of 70% or more. [3] The quality evaluation method according to [1] or [2], wherein the printed layer contains a urethane resin having an acidic group. [4] The quality evaluation method according to any one of [1] to [3], wherein the printed film further comprises another resin substrate, and the resin substrate and the other resin substrate are laminated via an adhesive layer. [5] The quality evaluation method according to any one of [1] to [4], wherein the alkaline aqueous solution contains sodium hydroxide or tetramethylammonium hydroxide. [6] A recycled resin preparation step of obtaining recycled resin from the deinked base material evaluated by the quality evaluation method according to any one of [1] to [5]; a recycled film manufacturing process for obtaining a recycled film from the recycled resin; A method for producing recycled film, comprising: [Effects of the Invention]

[0009] According to the present disclosure, a method for evaluating the quality of raw materials for recycled film production is provided, for determining the quality of the raw materials prior to the production of recycled film. The present disclosure also provides a method for producing recycled film that includes the quality evaluation method. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing a printing substrate (printing film) comprising a resin substrate and a printing layer. [Figure 2] FIG. 2 is a schematic diagram showing a deinked substrate comprising a resin substrate and a printed layer. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0012] <Printed film> The printed film comprises at least a resin substrate insoluble in an alkaline aqueous solution on which a printed layer soluble in an alkaline aqueous solution is formed. The resin substrate on which the printed layer is formed is called a printing substrate, and the printed film may be the printing substrate itself. The printed film may also be called a waste film.

[0013] Examples of the configuration of the printed film are shown below, but are not limited to these. In the following examples, the first substrate is a substrate used as a raw material for producing recycled film, and the second and third substrates may be soluble or insoluble in alkaline aqueous solutions. Even if the second and third substrates are insoluble in alkaline aqueous solutions, the adhesive layer interposed between the layers will dissolve in the alkaline aqueous solution, causing the second and third substrates to detach from the first substrate. Resin substrate (first substrate) / printed layer (first release layer) Resin substrate (first substrate) / Printing layer (first detachable layer) / Adhesive layer (second detachable layer) / Another resin substrate (second substrate) Resin substrate (first substrate) / Printing layer (first detachment layer) / Adhesive layer (second detachment layer) / Other resin substrate (second substrate) / Adhesive layer (third detachment layer) / Other resin substrate (third substrate)

[0014] (Resin substrate) The resin substrate is insoluble in an alkaline aqueous solution. This allows the alkaline aqueous solution to be used to remove the printed layer, which is soluble in the alkaline aqueous solution, from a printed film comprising the resin substrate and the printed layer. Examples of such resin substrates include polyolefin resins, polyamide resins, polystyrene resins, vinyl chloride resins, vinyl acetate resins, ABS resins, acetal resins, polyvinyl alcohol resins, and cellulose-based plastics.

[0015] As the resin substrate, a substrate containing a polyolefin resin or a polyamide resin is preferred from the viewpoint of reuse as a recycled substrate. Examples of substrates containing a polyolefin resin include plastic substrates containing polyethylene (PE), biaxially oriented polypropylene (OPP), etc., as well as sealant substrates containing low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), acid-modified polyethylene, unoriented polypropylene (CPP), acid-modified polypropylene, copolymer polypropylene, etc. The substrate containing a polyolefin resin may be a substrate made of a polyolefin resin. Examples of substrates containing polyamide resins include polycaprolactam (nylon 6), poly-ω-aminoheptanoic acid (nylon 7), poly-ω-aminononanoic acid (nylon 9), polyundecaneamide (nylon 11), polylaurinlactam (nylon 12), polyethylenediamineadipamide (nylon 2,6), polytetramethyleneadipamide (nylon 4,6), and polyhexamethylenediadipamide (nylon 6). Examples of the substrate include a substrate containing polyamide resin such as polyhexamethylene sebacamide (nylon 6,10), polyhexamethylene decamide (nylon 6,12), polyoctamethylene adipamide (nylon 8,6), polydecamethylene adipamide (nylon 10,6), polydecamethylene sebacamide (nylon 10,10), polydecamethylene dodecamide (nylon 12,12), or metaxylenediamine-6 ​​nylon (MXD6). The substrate containing a polyamide resin may be a substrate made of a polyamide resin.

[0016] The resin substrate may be a single layer or a multi-layer (laminate).

[0017] The thickness of the resin substrate is not particularly limited as it varies depending on the printed film to be recovered, but is preferably 5 to 200 μm, more preferably 10 to 150 μm.

[0018] The total light transmittance of the resin substrate is preferably 70% or more, more preferably 80% or more, from the viewpoint of calculating the deinking rate and satisfying the physical properties in appearance required for a packaging material. The above range is also suitable in that the printed layer printed on the back surface of the resin substrate can be visually recognized.

[0019] The haze of the resin substrate is preferably 20% or less, more preferably 10% or less, for the purpose of calculating the deinking rate and for satisfying the physical properties required for the appearance of a packaging material. Incidentally, by setting the haze within the above range, there is also the advantage that the printed layer printed on the back surface of the resin substrate can be visually recognized.

[0020] (Other resin substrates) When the printed film includes another resin substrate, the other resin substrate may be soluble or insoluble in an alkaline aqueous solution. Other resin substrates that are insoluble in alkaline aqueous solutions include those containing the resins exemplified in the resin substrate section. Other resin substrates that are soluble in alkaline aqueous solutions include polyester resins, polyurethane resins, polycarbonate resins, and (meth)acrylic resins.

[0021] The thickness of the other resin substrate is not particularly limited as it varies depending on the printed film to be recovered, but is preferably 5 to 200 μm, more preferably 10 to 150 μm.

[0022] (Printing layer) The printed layer is a layer on which any printed pattern is formed for the purpose of decoration, aesthetics, displaying the contents, expiration date, manufacturer or seller, etc., and includes a solid printed layer. The printed layer can also be called a release layer, and is formed on a resin substrate. The printing layer contains a water-soluble resin or a compound having an acidic group, and is detached from the resin substrate by dissolution in an alkaline aqueous solution, peeling, or the like. The printing layer preferably contains a water-soluble resin or a compound having an acidic group, and a colorant. The method for forming the printing layer is not limited, and the printing layer can be formed using a known method. From the viewpoint of recoatability, the printing layer preferably contains a compound having an acidic group. Furthermore, from the viewpoint of printability, the printing layer preferably contains a urethane resin having an acidic group, an acrylic resin having an acidic group, or a rosin-modified resin. Among these, it is more preferable to contain a urethane resin having an acidic group because of the ease of detachment in an alkaline aqueous solution. The printing layer may contain one of these resins alone, or two or more of them in combination.

[0023] The printed layer may be colored or colorless and may contain a known colorant used in printing inks and paints. Such colorants are not particularly limited, and examples include inorganic pigments, organic pigments, dyes, metal powders that impart metallic luster, near-infrared absorbing materials, and ultraviolet absorbing materials. Examples of inorganic pigments include colored pigments such as titanium oxide, red iron oxide, Prussian blue, ultramarine, carbon black, and graphite; and extender pigments such as calcium carbonate, kaolin, clay, barium sulfate, aluminum hydroxide, and talc. Suitable organic pigments include soluble azo pigments, insoluble azo pigments, azo lake pigments, condensed azo pigments, copper phthalocyanine pigments, condensed polycyclic pigments, etc. However, the pigments are not limited to these, and any pigment listed by its generic name in the Color Index can be used as appropriate. When the pigment is titanium oxide, the content of titanium oxide in the printed layer is preferably 20 to 80% by mass, more preferably 30 to 75% by mass. When the pigment is an inorganic pigment other than titanium oxide, an extender pigment, or an organic pigment, the content of each of these pigments in the printed layer is preferably 0.5 to 60% by mass, more preferably 10 to 50% by mass.

[0024] The print layer may contain a pigment derivative or a resin-type dispersant as a dispersant for the colorant. A pigment derivative is a compound in which a substituent has been introduced into the pigment skeleton. The content of the pigment derivative is preferably 0.01 to 10 mass %, more preferably 0.05 to 6 mass %, and even more preferably 0.1 to 4 mass %, based on the mass of the colorant. A content of 0.01 mass % or more ensures excellent releasability from the resin substrate, while a content of 10 mass % or less can suppress reattachment of the printed layer. The resin-type dispersant functions to adsorb to the colorant and stabilize its dispersion in printing ink, etc. The content of the resin-type dispersant is preferably 0.01 to 30 mass %, more preferably 0.05 to 20 mass %, and even more preferably 0.1 to 10 mass %, based on the mass of the colorant. When the content is 0.01 mass % or more, the colorant is easily released from the resin substrate, and when it is 30 mass % or less, the printed layer is easily water-resistant.

[0025] The thickness of the printed layer is preferably 0.1 to 100 μm, more preferably 0.1 to 10 μm, and even more preferably 1 to 5 μm.

[0026] (adhesive layer) When the printed film includes another resin substrate, the resin substrate can be bonded to the other resin substrate or to the other resin substrate via an adhesive layer. The adhesive layer can also be called a release layer and is disposed in contact with the resin substrate or the printed layer. The adhesive layer contains a compound having an acidic group and is detached from the resin substrate or the printing layer by dissolution in an alkaline aqueous solution, peeling, or the like. By containing a compound having an acidic group in the adhesive layer, the adhesive layer can be detached using the alkaline aqueous solution described above. In other words, the adhesive layer can be said to be an adhesive layer that is soluble in an alkaline aqueous solution. The method for forming the adhesive layer is not limited, and the adhesive layer can be formed using a known method.

[0027] From the viewpoint of releasability, the adhesive layer preferably contains, as a main component, polyurethane obtained by curing an adhesive containing a polyester polyol having an acidic group and at least one polyisocyanate selected from the group consisting of aliphatic polyisocyanates and araliphatic polyisocyanates. The polyester polyol may be any known polyester polyol as long as it has an acidic group. By including such a polyester polyol, an ester bond having a high affinity with an alkaline aqueous solution is formed, and the elimination property is improved, which is preferable. The polyester polyol may be used alone or in combination of two or more kinds. The polyisocyanate to be combined with the polyester polyol is preferably at least one selected from the group consisting of known aliphatic polyisocyanates and araliphatic polyisocyanates.

[0028] (Other layers) In addition to the above layers, the printed film may further include a barrier layer such as an aluminum foil, a metal vapor deposition layer of aluminum, or the like, or a metal oxide vapor deposition layer of silica, alumina, or the like. The metal vapor deposition layer and metal oxide vapor deposition layer may be formed on a resin substrate, and such a resin substrate can be referred to as a gas barrier substrate. The aluminum foil, aluminum vapor deposition layer, and alumina vapor deposition layer dissolve in an alkaline aqueous solution and are detached from the adjacent resin substrate, and therefore can also be referred to as a detachment layer. The thickness of the aluminum foil can be set in the range of 3 to 50 μm from an economical point of view.

[0029] <Quality evaluation method for raw materials used in recycled film manufacturing> The method for evaluating the quality of raw materials for recycled film production includes an alkali treatment step of contacting a printed film having a resin substrate insoluble in alkaline aqueous solutions, on which a printed layer soluble in alkaline aqueous solutions has been formed, with an alkaline aqueous solution to remove the printed layer from the resin substrate, thereby obtaining a deinked substrate to be used as a raw material for recycled film production; a deinking rate calculation step of calculating the deinking rate H or the deinking rate T according to the following formula (1) or (2); Equipped with. Deinking rate H={(Hx-Hz) / (Hx-Hy)}×100...(1) Hx: Haze of the printed film. Hy: Haze of the resin substrate. Hz: Haze of deinked substrate. Deinking rate T={(Tz-Tx) / (Ty-Tx)}×100...(2) Tx: Total light transmittance of the printed film. Ty: Total light transmittance of the resin substrate. Tz: Total light transmittance of the deinked substrate.

[0030] 1 is a schematic diagram showing a printing substrate 10 (printing film) comprising a resin substrate 1 and a printing layer 2. By subjecting this printing substrate to an alkali treatment, a deinked substrate can be obtained. Figure 2 is a schematic diagram showing a deinked substrate 20 comprising a resin substrate 1 and a printed layer 2. The figure shows that part of the printed layer 2 has been removed by alkali treatment. However, regardless of the figure, the printed layer 2 may be substantially completely removed with no remaining layer remaining.

[0031] In this way, the quality evaluation method of the present disclosure can be applied to printed films that can be treated with alkali to obtain deinked substrates that are raw materials for producing recycled films. For example, films that have a resin substrate that is soluble in an alkaline aqueous solution, or films that have a printed layer or adhesive layer that is insoluble in an alkaline aqueous solution, are not subject to the quality evaluation method of the present disclosure.

[0032] (alkaline aqueous solution) The alkaline aqueous solution contains a basic compound. The inclusion of the basic compound can cause the release layer of the printed layer or the like to swell, thereby allowing the release. The alkaline aqueous solution preferably contains 50% by mass or more of water, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The alkaline aqueous solution can also be referred to as a release liquid.

[0033] The alkaline aqueous solution penetrates through the surface or edge portion of the printed film, which is a laminate, and comes into contact with at least the printed layer, dissolving or swelling the printed layer, thereby causing the printed layer to detach from the resin substrate.

[0034] Suitable examples of basic compounds contained in the alkaline aqueous solution include sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)), barium hydroxide (Ba(OH)), sodium carbonate (NaCO), and tetramethylammonium hydroxide. More preferred are sodium hydroxide and tetramethylammonium hydroxide.

[0035] The content of the basic compound in the alkaline aqueous solution is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and even more preferably 2 to 15% by mass, based on the total amount of the alkaline aqueous solution. When the content is within the above range, the alkaline aqueous solution can retain sufficient basicity to detach the detachment layer and recover the deinked base material.

[0036] The alkaline aqueous solution may contain a surfactant. The surfactant primarily serves to improve the releasability of the printed layer and adhesive layer. This is because the surfactant acts to facilitate penetration of the alkaline aqueous solution into the printed layer and adhesive layer, accelerating the detachment of these layers. In addition, the surfactant adsorbs to the detached components (the various detached layers) and the surface of the deinked substrate, thereby preventing the detached components from reattaching to the deinked substrate.

[0037] To efficiently proceed with the removal step, it is preferable that the printed film is cut or crushed in advance so that the removal layer, such as the printed layer, is exposed on the cross section when it is brought into contact with the alkaline aqueous solution. In such a case, the printed layer, etc. can be removed in a shorter time. That is, the method for evaluating the quality of raw materials for recycled film production may include a step of shredding or pulverizing the printed film to obtain shredded or pulverized printed film before the alkali treatment step.

[0038] The method of contacting the printed film with the alkaline aqueous solution includes immersing the printed film in the alkaline aqueous solution or stirring the printed film in the alkaline aqueous solution, which causes the printed layer and other components to be detached from the resin substrate, and the deinked substrate is recovered. In this case, if the printed film has a second or third substrate that is insoluble in an alkaline aqueous solution, a known method that utilizes the differences in the physical properties of each substrate can be used to recover the target deinked substrate. Such methods include, for example, a method of floating and sinking by utilizing the difference in specific gravity, and a method of centrifuging.

[0039] The temperature of the alkaline aqueous solution is preferably in the range of 30 to 100°C, more preferably 40 to 90°C, and particularly preferably 50 to 80°C. The mass ratio of the printed film to the total amount of the alkaline aqueous solution is preferably 2 to 50 mass %, more preferably 3 to 40 mass %, and even more preferably 5 to 30 mass %. The contact time between the printed film and the alkaline aqueous solution (immersion time or stirring time) is preferably 3 minutes to 5 hours, more preferably 10 minutes to 4 hours, and even more preferably 15 minutes to 3 hours. When stirring is performed, the stirring speed is preferably 20 to 5000 rpm, more preferably 50 to 4000 rpm, and even more preferably 100 to 3000 rpm.

[0040] In the deinking rate calculation process, the deinking rate H or deinking rate T is calculated for the deinked substrate obtained by removing the printed layer, etc. from the resin substrate according to formula (1) or (2) as described above. This is done to confirm to what extent the layers that should be removed from the printed film (removed layers such as printed layers) have been removed, as the purpose is to use the deinked substrate as a raw material for producing recycled film. This makes it possible to grasp the quality of the raw material prior to producing recycled film.

[0041] In the above formula (1), the denominator is the haze of the printed film minus the haze of the resin substrate, i.e., this represents the haze due to the layers that should be removed. The numerator is the haze of the printed film minus the haze of the deinked substrate, i.e., this represents the haze due to the layers that should be removed that actually removed. By taking the ratio of the two, the percentage of layers that should be removed that have been removed can be quantified.

[0042] In the above formula (2), the denominator is the total light transmittance of the printed film minus the total light transmittance of the resin substrate, i.e., this represents the decrease in total light transmittance due to the layers that should be removed. The numerator is the total light transmittance of the printed film minus the total light transmittance of the deinked substrate, i.e., this represents the decrease in total light transmittance due to the layers that should be removed actually being removed. By taking the ratio of the two, the percentage of layers that should be removed that have been removed can be quantified.

[0043] The haze and total light transmittance of the resin substrate can be measured by preparing a resin substrate equivalent to that of the printed film.

[0044] The haze and total light transmittance are measured using a haze meter in accordance with JIS K 7136 (haze) and JIS K 7361 (total light transmittance), respectively. Each value is the average value of 10 measurements.

[0045] The above quality evaluation method may further include a step of selecting a deinked base material with a deinking rate H of 80% or more or a deinking rate T of 80% or more. This makes it possible to stably produce recycled films with the desired appearance and strength. From this perspective, the values ​​of the deinking rate H and the deinking rate T are preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. There are no particular upper limits to the values ​​of the deinking rate H and the deinking rate T, but they can be set to substantially 100%.

[0046] <Recycled film manufacturing method> The method for producing recycled film includes a recycled resin preparation step of obtaining recycled resin from a deinked base material that has been evaluated by the above-mentioned method for evaluating the quality of raw materials for producing recycled film; and a recycled film manufacturing process for obtaining recycled film from recycled resin.

[0047] A recycled resin can be prepared by recovering the deinked base material and melt-kneading it. Melt-kneading can be carried out, for example, by adding various additives to the deinked base material as needed, mixing them in a Henschel mixer, tumbler, disper, or the like, and then using a batch mixer such as a kneader, roll mill, super mixer, Henschel mixer, Schuggi mixer, vertical granulator, high-speed mixer, Farmatrix, ball mill, steel mill, sand mill, vibration mill, attritor, or Banbury mixer, a twin-screw extruder, a single-screw extruder, or a rotor-type twin-screw kneader. Of these, it is preferable to use a twin-screw extruder for melt-kneading. Thereby, a recycled resin, which is a resin composition, is obtained. The shape of the recycled resin is not particularly limited, and it may be in the form of pellets, powder, granules, or beads.

[0048] Recycled resins can be thermoformed to obtain recycled films. The thermoforming method is not particularly limited, and examples include injection molding, extrusion molding, blow molding, and compression molding. The resulting recycled films can be used in a variety of fields, including packaging materials. [Example]

[0049] The present disclosure will be described in detail below based on examples, but the present disclosure is not limited to these examples.

[0050] Example 1 A printed film (printed substrate) was produced by forming a printed layer (2.0 μm thick) using urethane ink (Laminstar manufactured by Toyochem, containing a urethane resin with acidic groups) on a resin substrate (Ny Film, Harden Film N1100 manufactured by Toyobo, 15 μm thick, 4% haze, 80% total light transmittance) by gravure printing. Note that this is a resin substrate that is insoluble in alkaline aqueous solution and a printed layer that is soluble in alkaline aqueous solution. The printed film was placed in an alkaline aqueous solution (3 wt% sodium hydroxide, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; 10 w / v% sodium hydroxide solution was diluted with pure water) at 60°C, stirred at 300 rpm for 60 minutes, then washed with water and dried to obtain a deinked substrate. The deinked base material was kneaded in a molten state using a twin-screw extruder, and then pellets (recycled resin) were produced using a pelletizer. The pellets were fed into a T-die extruder, kneaded in a molten state, and extruded to produce a recycled film (recycled Ny film).

[0051] Example 7 A recycled film was produced in the same manner as in Example 1, except that the alkaline aqueous solution was changed to a tetramethylammonium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., 2.38 wt %).

[0052] (Other Examples) A recycled film was produced in the same manner as in Example 1 or 7, except that the alkali treatment conditions were changed as shown in Table 1.

[0053] <Various evaluations> (Deinking rate measurement) A haze meter was used to measure Hx: haze of the printed film, Hy: haze of the resin substrate, and Hz: haze of the deinked substrate, as well as Tx: total light transmittance of the printed film, Ty: total light transmittance of the resin substrate, and Tz: total light transmittance of the deinked substrate. The deinking rate H or T was then calculated according to the following formula (1) or (2). The results are shown in Table 1. Deinking rate H={(Hx-Hz) / (Hx-Hy)}×100...(1) Deinking rate T={(Tz-Tx) / (Ty-Tx)}×100...(2)

[0054] (Appearance evaluation) The deinked substrate was visually observed and its appearance was evaluated as follows. By using a deinked substrate with a good appearance, rated ○ or △, recycled film with good appearance can be stably produced. The results are shown in Table 1. ◯: Almost no residue of the printed layer was observed. △: A slight residue of the printed layer was observed. ×: Residue of the printed layer was clearly observed.

[0055] (Strength evaluation) The breaking elongation of the resin substrate and recycled film was measured using a tensile tester in accordance with JIS K7161-1:2014 (ISO 527-1:2012). The difference in breaking elongation between the resin substrate and recycled film was evaluated as follows. The results are shown in Table 1. ◯: The difference in breaking elongation was less than 5%. △: The difference in breaking elongation was 5% or more and less than 10%. ×: The difference in breaking elongation was 10% or more.

[0056] [Table 1]

[0057] Table 1 shows that by using a deinked substrate with a deinking rate of 80% or more as the raw material, recycled film with the desired appearance and strength can be stably produced. In other words, Table 1 shows that by calculating the deinking rate of the deinked substrate after alkali treatment, it is possible to grasp the quality of the raw material prior to producing recycled film. [Explanation of symbols]

[0058] 1...resin substrate, 2...printed layer, 10...printed substrate (printed film), 20...deinked substrate.

Claims

1. an alkali treatment step in which a printed film having a resin substrate insoluble in an alkaline aqueous solution and having a printed layer soluble in an alkaline aqueous solution formed thereon is brought into contact with an alkaline aqueous solution to remove the printed layer from the resin substrate, thereby obtaining a deinked substrate to be used as a raw material for producing recycled films; a deinking rate calculation step of calculating a deinking rate H or a deinking rate T according to the following formula (1) or (2); A method for evaluating the quality of raw materials used in the production of recycled film. Deinking rate H={(Hx-Hz) / (Hx-Hy)}×100...(1) Hx: Haze of the printed film. Hy: Haze of the resin substrate. Hz: Haze of deinked substrate. Deinking rate T={(Tz-Tx) / (Ty-Tx)}×100...(2) Tx: total light transmittance of the printed film. Ty: total light transmittance of the resin substrate. Tz: Total light transmittance of deinked substrate.

2. The quality evaluation method according to claim 1 , wherein the resin substrate has a total light transmittance of 70% or more.

3. The quality evaluation method according to claim 1 , wherein the printed layer contains a urethane resin having an acidic group.

4. The quality evaluation method according to claim 1 , wherein the printed film further comprises another resin substrate, and the resin substrate and the other resin substrate are laminated together via an adhesive layer.

5. The quality evaluation method according to claim 1 , wherein the alkaline aqueous solution contains sodium hydroxide or tetramethylammonium hydroxide.

6. A recycled resin preparation step of obtaining recycled resin from the deinked base material evaluated by the quality evaluation method according to any one of claims 1 to 5; a recycled film manufacturing process for obtaining a recycled film from the recycled resin; A method for producing recycled film, comprising:

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