Method for cleaning thermal transfer sheet and method for producing recycled raw material

Abstract

To provide a method for cleaning a thermal transfer sheet that achieves both good cleaning properties and good low foaming properties.SOLUTION: A method for cleaning a thermal transfer sheet includes: a preparation step for preparing crushed pieces of a thermal transfer sheet; and a cleaning step in which the crushed pieces are cleaned using a neutral aqueous cleaning solution. A thickness of the thermal transfer sheet is 3.5 μm or more and 12 μm or less, the aqueous cleaning solution contains a cleaning agent containing at least a surfactant and water, a mass of the water being 160 times or more relative to a total mass of the crushed pieces, and a mass of the cleaning agent being 1 time or more and 85 times or less relative to a total mass of the crushed pieces.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for cleaning a thermal transfer sheet and a method for producing recycled raw materials. [Background technology]

[0002] One approach to environmental issues is resource recycling. For example, Patent Document 1 discloses a method for separating and recovering a laminate, which includes the steps of immersing a laminate having at least a plastic substrate layer and a printed layer in a release liquid, releasing the printed layer to a predetermined size, and recovering the plastic substrate. Furthermore, Patent Document 2 discloses an apparatus for deinking plastic pieces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7168814 [Patent Document 2] Patent No. 7368036 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, when a used thermal transfer sheet is reused as a resource, a cleaning process is required to clean the thermal transfer sheet so that recycling destinations are not limited. In the cleaning process, a cleaning solution is typically added to the crushed pieces of the thermal transfer sheet to bleach the coloring material contained in the crushed pieces and remove dirt from the crushed pieces. Because the crushed pieces of the thermal transfer sheet are thin and have little stiffness, they tend to clump together. Therefore, it is difficult to achieve good cleanability compared to cleaning targets such as thick resin sheets.

[0005] The present inventors have discovered that adding a surfactant to a cleaning solution can suppress the aggregation of fragments. However, adding a surfactant to a cleaning solution makes the cleaning solution more likely to foam during the cleaning process. When foam is generated in the cleaning solution, it is more likely to overflow from a tank, and overflow reduces work efficiency. Therefore, good low-foaming properties (low foaming) are required during the cleaning process. However, attempts to achieve good low-foaming properties may not result in good cleaning performance.

[0006] The present disclosure has been made in view of the above-mentioned circumstances, and has as its main object to provide a method for cleaning a thermal transfer sheet that achieves both good cleaning properties and good low foaming properties. [Means for solving the problem]

[0007] The present disclosure provides a method for cleaning a thermal transfer sheet, the method comprising a preparation step of preparing crushed pieces of the thermal transfer sheet, and a cleaning step of cleaning the crushed pieces using a neutral aqueous cleaning solution, wherein the thickness of the thermal transfer sheet is 3.5 μm or more and 12 μm or less, the aqueous cleaning solution contains a cleaning agent including at least a surfactant and water, the mass of the water relative to the total mass of the crushed pieces is 160 times or more, and the mass of the cleaning agent relative to the total mass of the crushed pieces is 1 time or more and 85 times or less.

[0008] The present disclosure provides a method for producing recycled raw materials, which includes a cleaning step of cleaning a thermal transfer sheet using the above-described method for cleaning a thermal transfer sheet. [Effects of the Invention]

[0009] The present disclosure has the effect of providing a method for cleaning a thermal transfer sheet that achieves both good cleaning properties and good low foaming properties. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a flow diagram illustrating a method for cleaning a thermal transfer sheet according to the present disclosure. [Figure 2] 1 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure. [Figure 3] FIG. 2 is a schematic plan view illustrating a fragment according to the present disclosure. [Figure 4] 1 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure. [Figure 5] 1 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure. [Figure 6] 1 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure. [Figure 7] FIG. 2 is a schematic plan view illustrating a fragment according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] Below, embodiments will be described with reference to the drawings. However, the present disclosure can be implemented in many different forms and is not limited to the description of the embodiments exemplified below. Furthermore, to clarify the description, the drawings may show the width, thickness, and shape of each part schematically compared to the actual form, but this is merely an example and should not be interpreted as limiting.

[0012] In this specification, when describing a mode in which another component is placed on a certain component, the term "above" or "below" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below the certain component so as to be in contact with the component, and a case in which another component is placed above or below the certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the term "on the surface" or "on the surface side" is used, unless otherwise specified, to include both a case in which another component is placed directly above or below the certain component so as to be in contact with the component, and a case in which another component is placed above or below the certain component with another component interposed therebetween.

[0013] The method for cleaning a thermal transfer sheet and the method for producing recycled raw materials according to the present disclosure will be described in detail below.

[0014] A. How to clean the thermal transfer sheet Fig. 1 is a flow diagram illustrating a method for cleaning a thermal transfer sheet according to the present disclosure. As shown in Fig. 1, in the method for cleaning a thermal transfer sheet according to the present disclosure, first, crushed pieces of the thermal transfer sheet are prepared (preparation step). Next, the crushed pieces are washed using a neutral aqueous cleaning solution (washing step).

[0015] 2A and 2B are schematic cross-sectional views illustrating a thermal transfer sheet according to the present disclosure, specifically illustrating a thermal transfer sheet before being crushed. As shown in FIG. 2A, the thermal transfer sheet 10 has, for example, a base layer 1 and a color material layer 2. The base layer 1 and the color material layer 2 are arranged in a thickness direction D. T The thermal transfer sheet 10 is arranged along the line . The thickness of the thermal transfer sheet 10 is defined as T. In the present disclosure, the thickness T is typically 3.5 μm or more and 12 μm or less. As shown in FIG. 2(b), the thermal transfer sheet 10 may have a release layer 3 between the substrate layer 1 and the color material layer 2. As shown in FIG. 2(c), the thermal transfer sheet 10 may have a primer layer 4 between the substrate layer 1 and the color material layer 2. As shown in FIG. 2(d), the thermal transfer sheet 10 may have a substrate layer 1 and a protective layer 5.

[0016] FIG. 3 is a schematic plan view illustrating fragments according to the present disclosure. As shown in FIG. 3, fragments 11 of a thermal transfer sheet are prepared in the present disclosure. Next, a cleaning process is performed in which the fragments 11 are cleaned using a neutral aqueous cleaning solution. The aqueous cleaning solution according to the present disclosure contains water and a cleaning agent containing at least a surfactant. Furthermore, according to the present disclosure, the ratio of the mass of water to the total mass of the fragments is within a predetermined range, and the mass of the cleaning agent to the total mass of the fragments is also within a predetermined range.

[0017] According to the present disclosure, by setting the mass of water and the mass of the cleaning agent relative to the total mass of the crushed pieces within a predetermined range, it is possible to achieve both good cleaning properties and good low-foaming properties. Conventionally, used thermal transfer sheets, or unused but unnecessary thermal transfer sheets, have been discarded as industrial waste without being recycled. When thermal transfer sheets are reused as resources, a cleaning process is required to clean the thermal transfer sheets so that recycling destinations are not limited.

[0018] In the cleaning process, a cleaning solution is typically applied to the thermal transfer sheet fragments to bleach the coloring material contained in the fragments and to remove dirt from the fragments. The thermal transfer sheet fragments are thin and have little stiffness. Therefore, as shown in Figure 3, multiple fragments 11 tend to clump together. Because the cleaning solution does not easily penetrate into the areas where multiple fragments 11 clump together, it is difficult to achieve good cleanability compared to cleaning objects such as thick resin sheets.

[0019] The present inventors have discovered that adding a surfactant to a cleaning solution can suppress the aggregation of fragments. However, adding a surfactant to a cleaning solution makes the cleaning solution more likely to foam during the cleaning process. Foaming in the cleaning solution can, for example, cause the solution to overflow from a tank, which reduces work efficiency. Therefore, good low-foaming properties are required during the cleaning process. However, attempts to achieve good low-foaming properties may not always result in good cleaning performance. For example, reducing the amount of detergent can easily achieve good low-foaming properties, but good cleaning performance may not be achieved. Furthermore, adding an anti-foaming agent to a cleaning solution can easily achieve good low-foaming properties, but the anti-foaming agent may inhibit the effectiveness of the detergent, resulting in poor cleaning performance.

[0020] In contrast, in the present disclosure, by setting the mass of water and the mass of cleaning agent relative to the total mass of the crushed fragments within a predetermined range, it is possible to achieve both good cleaning performance and good low-foaming properties. Specifically, by setting the mass of water within a predetermined range relative to the total mass of the crushed fragments, it is possible to allow the aqueous cleaning solution containing the cleaning agent to penetrate into the interior of the aggregated crushed fragments. Furthermore, by setting the mass of cleaning agent within a predetermined range relative to the total mass of the crushed fragments, it is possible to maintain good cleaning performance while suppressing the generation of bubbles in the cleaning solution during the cleaning process and maintaining good low-foaming properties.

[0021] Furthermore, by using a neutral aqueous cleaning solution, post-treatment such as neutralization is either unnecessary or easy compared to when an alkaline or acidic cleaning solution is used, thereby reducing the environmental impact. Furthermore, by using an aqueous cleaning solution, post-treatment is either unnecessary or easy compared to when a solvent-based cleaning solution is used, thereby reducing the environmental impact.

[0022] 1. Preparation process The preparation step in the present disclosure is a step of preparing crushed pieces of a thermal transfer sheet. The crushed pieces are obtained by crushing the thermal transfer sheet. The crushed pieces may be prepared by crushing the thermal transfer sheet yourself, or by collecting crushed pieces obtained by someone else crushing the thermal transfer sheet. Furthermore, as described below, the preparation step and the cleaning treatment step may be performed simultaneously. That is, the crushed pieces may be washed while the thermal transfer sheet is being crushed.

[0023] (1) Thermal transfer sheet As shown in FIG. 2(a), the thickness of the thermal transfer sheet 10 is designated as T. The thickness T is typically 12 μm or less, and may be 11 μm or less, 10 μm or less, or 9.0 μm or less. On the other hand, the thickness T is typically 3.5 μm or more, and may be 4.0 μm or more, or 5.0 μm or more. If the thickness T is within the above range, the fragments are likely to aggregate together. Furthermore, if the thermal transfer sheet is too thick or too thin, the thermal transferability may be reduced.

[0024] As shown in Figure 2(a), the thermal transfer sheet 10 may have a base material layer 1 and a colorant layer 2. Alternatively, as shown in Figure 2(d), the thermal transfer sheet 10 may have a base material layer 1 and a protective layer 5. Each layer constituting the thermal transfer sheet will be described below.

[0025] (i) Base material layer The substrate layer is preferably a resin film. The resin used for the resin film is not particularly limited, but examples thereof include polyester, polyamide, polyolefin, vinyl resin, vinyl acetal resin, (meth)acrylic resin, imide resin, cellulose resin, styrene resin, polycarbonate, and ionomer.

[0026] Examples of the polyester include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), 1,4-polycyclohexylene dimethylene terephthalate, and terephthalic acid-cyclohexanedimethanol-ethylene glycol copolymer. Examples of the polyamide include nylon 6 and nylon 6,6. Examples of the polyolefin include polyethylene (PE), polypropylene (PP), and polymethylpentene. Examples of the vinyl resin include polyvinyl chloride, polyvinyl alcohol (PVA), polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, and polyvinylpyrrolidone (PVP).

[0027] Examples of the vinyl acetal resin include polyvinyl acetoacetal and polyvinyl butyral. Examples of the (meth)acrylic resin include poly(meth)acrylate. "(Meth)acrylic" includes both "acrylic" and "methacrylic," and "(meth)acrylate" includes both "acrylate" and "methacrylate." Examples of the imide resin include polyimide and polyetherimide. Examples of the cellulose resin include cellophane, cellulose acetate, nitrocellulose, cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB). Examples of the styrene resin include polystyrene (PS).

[0028] The resin used for the resin film is preferably polyester, more preferably PET or PEN, and even more preferably PET. This is because it has excellent heat resistance and mechanical strength. The substrate layer may be a laminate of resin films. The resin film may be a stretched film or an unstretched film. From the viewpoint of mechanical strength, the resin film is preferably a stretched film stretched uniaxially or biaxially. The thickness of the substrate layer is not particularly limited as long as a thermal transfer sheet having a predetermined thickness is obtained, but may be, for example, 10 μm or less, 8.0 μm or less, 6.0 μm or less, less than 5.0 μm, or 4.5 μm or less. On the other hand, the thickness of the substrate layer is, for example, 2.5 μm or more, 3.0 μm or more, or 3.5 μm or more.

[0029] (ii) Color material layer The coloring material layer is a layer containing at least a coloring material, and examples of the coloring material include magenta, yellow, cyan, and black.

[0030] The coloring material may be a pigment or a dye. Examples of the coloring material include carbon black, acetylene black, lamp black, black smoke, iron black, aniline black, silica, calcium carbonate, titanium oxide, cadmium red, cadmium phosphate red, chrome red, vermilion, red iron oxide, azo pigments, alizarin lake, quinacridone, cochineal lake perylene, yellow ochre, aureolin, cadmium yellow, cadmium orange, chrome yellow, zinc yellow, Naples yellow, nickel yellow, greenish yellow, ultramarine, rock ultramarine, cobalt, phthalocyanine, anthraquinone, indicoid, cinnabar green, cadmium green, chrome green, phthalocyanine, azomethine, perylene, and aluminum pigments.

[0031] The colorant may be a sublimable dye, such as a diarylmethane dye, a triarylmethane dye, a thiazole dye, a merocyanine dye, a pyrazolone dye, a methine dye, an indoaniline dye, an acetophenone azomethine dye, a pyrazoloazomethine dye, a xanthene dye, an oxazine dye, a thiazine dye, an azine dye, an acridine dye, an azo dye, a spiropyran dye, an indolinospiropyran dye, a fluoran dye, a naphthoquinone dye, an anthraquinone dye, or a quinophthalone dye.

[0032] The content of the color material in the color material layer is not particularly limited, but may be, for example, 5% by mass or more and 75% by mass or less, or 10% by mass or more and 50% by mass or less.

[0033] The colorant layer may be a melt-transfer type colorant layer in which a colorant such as a pigment or dye is dispersed in a heat-melting binder, or a sublimation transfer type colorant layer in which a sublimation dye is dissolved or dispersed in a binder. Examples of the binder include resins. Examples of the resins include polyester, polyurethane, polyamide, polyimide, polycarbonate, polyolefin, (meth)acrylic resin, vinyl resin, styrene resin, cellulose resin, phenoxy resin, epoxy resin, and ionomer.

[0034] The melt-transfer colorant layer may contain a wax as a binder. Examples of the wax include microcrystalline wax, carnauba wax, paraffin wax, Fischer-Tropsch wax, polyethylene wax, Japan wax, beeswax, whale wax, libota wax, wool wax, shellac wax, candelilla wax, petrolactam, polyester wax, partially modified wax, fatty acid ester, and fatty acid amide. The melt-transfer colorant layer may contain both a resin and a wax as a binder.

[0035] The melt-transfer colorant layer may contain a cured product (crosslinked structure) of the binder. Examples of curing agents for curing the binder include isocyanate and carbodiimide. The melt-transfer colorant layer may contain, as the binder, a cured product (crosslinked structure) of at least one of an actinic radiation-curable monomer and an actinic radiation-curable oligomer. The actinic radiation-curable monomer and actinic radiation-curable oligomer refer to monomers and oligomers that polymerize (cure) when irradiated with actinic radiation. "Actinic radiation" refers to radiation that chemically reacts with the actinic radiation-curable monomer and actinic radiation-curable oligomer to promote polymerization. Examples of actinic radiation include visible light, ultraviolet light, X-rays, electron beams, α-rays, β-rays, and γ-rays.

[0036] Examples of actinic radiation-curable monomers include urethane acrylate, epoxy acrylate, polyester acrylate, polyether acrylate, polyethylene acrylate, silicone acrylate, and polyol acrylate. The number of functional groups in the actinic radiation-curable monomer is not particularly limited, but may be, for example, 2 or more, or may be 3 or more. On the other hand, examples of actinic radiation-curable oligomers include polymers or copolymers of the actinic radiation-curable monomers. The number of functional groups in the actinic radiation-curable oligomer is not particularly limited, but may be, for example, 2 or more, or may be 3 or more.

[0037] The thickness of the colorant layer is not particularly limited as long as a thermal transfer sheet having a predetermined thickness is obtained, but may be, for example, 0.3 μm or more and 7 μm or less, or 1 μm or more and 6 μm or less. The colorant layer and the substrate layer may be arranged so as to be in direct contact with each other, or may be arranged via another layer. Examples of the other layer include a release layer and a primer layer.

[0038] (iii) Protective layer The protective layer (OP layer) is a transparent layer containing a resin. The resin used for the protective layer is not particularly limited, but examples thereof include polyester, polystyrene, polyurethane, (meth)acrylic resin, (meth)acrylic urethane resin, and vinyl chloride-vinyl acetate copolymer. The resin may be, for example, a silicone-modified resin. The protective layer may contain a colorant such as a fluorescent whitening agent, or may not contain a colorant. The thickness of the protective layer is not particularly limited, as long as a thermal transfer sheet having a predetermined thickness is obtained, but is, for example, 0.1 μm to 2.0 μm. The thermal transfer sheet may have both one or more colorant layers and a protective layer on one side of the base layer. Examples of the one or more colorant layers include a red colorant layer (Mg layer), a yellow colorant layer (Ye layer), a blue colorant layer (Cy layer), and a black colorant layer (Bk layer).

[0039] (iv) Other layers As shown in FIG. 2(b), the thermal transfer sheet 10 may have a release layer 3 between the substrate layer 1 and the colorant layer 2. The provision of the release layer 3 can improve transferability. The release layer is preferably made of a material that is easily cleaned with an aqueous cleaning solution and preferably contains a resin. Examples of the resin include (meth)acrylic resin, vinyl resin, styrene resin, cellulose resin, polyester, polyurethane, polyamide, polyimide, and polycarbonate. The release layer may contain a cured product (crosslinked structure) of a binder. Examples of curing agents that cure the binder include isocyanate and carbodiimide. The release layer may contain a cured product (crosslinked structure) of at least one of an actinic radiation-curable monomer and an actinic radiation-curable oligomer as a binder. The release layer may also contain additives such as a lubricant, an ultraviolet absorber, a light stabilizer, and an antioxidant.

[0040] 4 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure, specifically showing a melt transfer type thermal transfer sheet. The peel layer 3 shown in FIG. 4 is usually transferred to the transferee side as part of the transfer layer α during thermal transfer. The thermal transfer sheet 10 is oriented in the thickness direction D T In the thermal transfer sheet 10, a back layer 6 may be provided on the opposite side of the color material layer 2 with respect to the base layer 1. By providing the back layer 6, it is possible to suppress the occurrence of sticking caused by a thermal head. T In the above, an adhesive layer 7 may be provided on the side opposite to the base layer 1 with respect to the colorant layer 2. By providing the adhesive layer 7, it is possible to improve adhesion to the transfer target. Known structures can be adopted for the release layer 3, back layer 6, and adhesive layer 7.

[0041] As shown in FIG. 2(c), the thermal transfer sheet 10 may have a primer layer 4 between the substrate layer 1 and the colorant layer 2. By providing the primer layer 4, the adhesion between the substrate layer 1 and the colorant layer 2 can be improved. The primer layer is preferably made of a material that is easy to wash off with a cleaning solution, and preferably contains a resin. Examples of such resins include polyester, vinyl resin, (meth)acrylic resin, styrene resin, polyamide, polyether, urethane resin, and cellulose resin.

[0042] FIG. 5 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure, specifically showing a sublimation transfer type thermal transfer sheet. The primer layer 4 shown in FIG. 5 improves the adhesion between the substrate layer 1 and the colorant layer 2. The thermal transfer sheet 10 is formed in the thickness direction D T In the thermal transfer sheet 10, a back layer 6 may be provided on the opposite side of the color material layer 2 with respect to the base layer 1. By providing the back layer 6, it is possible to suppress the occurrence of sticking caused by a thermal head. Furthermore, the thermal transfer sheet 10 has a thickness D T In the above, a second primer layer 8 may be provided between the base layer 1 and the back layer 6. By providing the second primer layer 8, the adhesion between the base layer 1 and the back layer 6 is improved. Known configurations can be adopted for the primer layer 4, the back layer 6, and the second primer layer 8.

[0043] FIG. 6 is a schematic cross-sectional view illustrating a thermal transfer sheet according to the present disclosure, specifically showing a thermal transfer sheet having a protective layer (OP layer). The primer layer 4 shown in FIG. 6 improves the adhesion between the protective layer 5 and the adhesive layer 7. The adhesive layer 7 according to the present disclosure may be a heat seal layer. The thermal transfer sheet 10 has a thickness in the thickness direction D T In the thermal transfer sheet 10, a back layer 6 may be provided on the opposite side of the color material layer 2 with respect to the base layer 1. By providing the back layer 6, it is possible to suppress the occurrence of sticking caused by a thermal head. Furthermore, the thermal transfer sheet 10 has a thickness D TIn the thermal transfer sheet of the present disclosure, a second primer layer 8 may be provided between the base layer 1 and the back layer 6. By providing the second primer layer 8, the adhesion between the base layer 1 and the back layer 6 is improved. Known configurations can be adopted for the primer layer 4, the back layer 6, and the second primer layer 8. Note that the thermal transfer sheet of the present disclosure may further have known layers not shown in FIGS. 4 to 6.

[0044] (2) Shattered fragments The crushed pieces in the present disclosure are obtained by crushing a thermal transfer sheet. Therefore, the layer structure of the crushed pieces is usually the same as the layer structure of the thermal transfer sheet before crushing. For example, the crushed pieces may have at least a substrate layer and a colorant layer. The crushed pieces may have a release layer or a primer layer between the substrate layer and the colorant layer. The crushed pieces may also have at least a substrate layer and a protective layer. Furthermore, the crushed pieces may have each of the layers described above in "(1) Thermal Transfer Sheet." The thickness of the crushed pieces is also usually the same as the thickness of the thermal transfer sheet before crushing. The thickness of the thermal transfer sheet is as described above.

[0045] The planar shape of the fragments is not particularly limited. The planar shape of the fragments refers to the outer edge shape of the fragments when observed from the thickness direction. Here, the fragments are classified into fragments X and fragments Y according to their planar shape. Fragments X have a planar shape that is quadrangular or a shape that can be approximated to a quadrangle. On the other hand, fragments Y are fragments that do not fall under the category of fragments X.

[0046] As shown in Figure 7(a), the shape of the fragments 11 in plan view may be rectangular (quadrilateral). On the other hand, as shown in Figures 7(b) and (d), the fragments 11 may have a cutout 12 in part. Even in such a case, if the cutout 12 is small, the shape of the fragments 11 in plan view will be a shape that can approximate a quadrangle. The "shape that can approximate a quadrangle" is defined as follows: As shown in Figures 7(c) and (e), imagine a virtual quadrangle 13 (rectangle or square) that is inscribed in the fragments 11. Let the area of ​​the virtual quadrangle 13 be S.A The area of ​​the fragment 11 is S B Let's say S A S against B The ratio (S B / S A ) is 0.8 or more, it corresponds to a "shape that can be approximated as a rectangle."

[0047] As shown in Figures 7(a) and 7(c), the length of the short side of the crushed fragment X is L1, and the length of the long side of the crushed fragment X is L2. The aspect ratio (L2 / L1) is not particularly limited, but may be, for example, 1.5 to 10.0, 2.0 to 9.0, or 2.0 to 5.0. Although not specifically shown, the planar shape of the crushed fragment X may be a square (rectangle). A square includes a rectangle with an aspect ratio (L2 / L1) of 1.0 to less than 1.5. L1 may be, for example, 1 mm to 5 cm, or 3 mm to 3.5 cm. On the other hand, L2 may be, for example, 1 mm to 10 cm, or 3 mm to 9 cm. Furthermore, as shown in Figure 7(c), when the planar shape of the crushed fragment X is a shape that can be approximated to a rectangle, L1 and L2 are set based on a virtual rectangle 13.

[0048] On the other hand, as shown in Figure 7(f), the fragments 11 may have a complex shape. In this case, too, as shown in Figure 7(g), a virtual quadrangle 13 (rectangle or square) is assumed to be inscribed in the fragments 11. B / S A If the ratio is less than 0.8, it does not fall under the category of "a shape that can be approximated as a rectangle." If multiple imaginary rectangles 13 can be assumed, S B / S A The largest one is adopted. The planar shape of the fragment 11 shown in Figure 7(f) is neither a "rectangle" nor a "shape that can be approximated to a rectangle," so it does not fall under fragment X, but rather fragment Y. The proportion of fragment X to the total of fragment X and fragment Y, based on the number, may be, for example, 10% or more and 90% or less, or 20% or more and 80% or less.

[0049] The crushed pieces are obtained by crushing the thermal transfer sheet. Examples of crushing devices for crushing the thermal transfer sheet include jaw crushers, impact crushers, cutter mills, stamp mills, ring mills, roller mills, jet mills, and hammer mills. The crushing conditions for the thermal transfer sheet are not particularly limited and are appropriately adjusted so as to obtain the crushed pieces described above.

[0050] 2. Cleaning process The cleaning step in the present disclosure is a step of cleaning the crushed pieces with a neutral aqueous cleaning solution containing at least a surfactant-containing cleaning agent and water.

[0051] In the present disclosure, the mass of water relative to the total mass of the crushed fragments is typically 160 times or more, or may be 180 times or more, or may be 200 times or more. If the mass of water (water volume) is too small, the aqueous cleaning solution containing the detergent cannot penetrate into the interior of the aggregated crushed fragments, and good cleaning performance may not be achieved. On the other hand, the mass of water relative to the total mass of the crushed fragments is not particularly limited, but may be, for example, 600 times or less, 550 times or less, or 500 times or less. If the mass of water (water volume) is too large, a large amount of aqueous cleaning solution is required, which may reduce the efficiency of the cleaning process.

[0052] In the present disclosure, the mass of the detergent relative to the total mass of the crushed pieces is typically 1 to 85 times, or alternatively 1.2 to 40 times, or 1.5 to 15 times. If the mass (amount of detergent) of the detergent is too small, good cleaning performance may not be achieved. On the other hand, if the mass (amount of detergent) of the detergent is too large, it may be difficult to maintain good low-foaming properties during the cleaning process.

[0053] (1) Detergent The aqueous cleaning solution contains a cleaning agent containing at least a surfactant. In this disclosure, a cleaning agent refers to a component that contributes to improved cleaning performance and is soluble or compatible with water. The use of a surfactant suppresses aggregation of the fragments, improving cleaning performance. Another example of a cleaning agent is an antifoaming agent. By appropriately adjusting the amount of antifoaming agent, it is possible to prevent the contact area between the fragments and the aqueous cleaning solution from being reduced by bubbles, thereby improving cleaning performance. Another example of a cleaning agent is an amphipathic glycol-based solvent or glycol ether-based solvent. These solvents have both a portion with high affinity for water (hydrophilic group) and a portion with low affinity for water (hydrophobic group), allowing them to wet and penetrate not only hydrophilic materials but also hydrophobic materials, improving cleaning performance.

[0054] Examples of the surfactant include a nonionic surfactant, a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. The aqueous cleaning liquid may contain only one type of surfactant, or may contain two or more types of surfactants.

[0055] Examples of nonionic surfactants include ether-based surfactants such as polyoxyalkylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyalkylene lauryl ethers; epoxy-based surfactants such as ethylene oxide propylene oxide block copolymers; ester-based surfactants such as polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyglycerin fatty acid esters, and sucrose fatty acid esters; amine-based surfactants such as polyoxyethylene alkylamines; amide-based surfactants such as polyoxyethylene fatty acid amides, fatty acid alkylolamides, and alkylalkanolamides; and glycol-based surfactants such as acetylene glycol, oxyethylene adducts of acetylene glycol, and polyethylene glycol polypropylene glycol block copolymers.

[0056] Examples of cationic surfactants include ammonium salt surfactants such as didecyl dimethyl ammonium salt, distearyl dimethyl ammonium salt, dioctyl dimethyl ammonium salt, distearyl dihydroxyethyl ammonium salt, di-beef tallow alkyl dimethyl ammonium salt, di(stearoyloxyethyl) dimethyl ammonium salt, di(oleoyloxyethyl) dimethyl ammonium salt, di(stearoyloxyisopropyl) dimethyl ammonium salt, di(oleoyloxyisopropyl) dimethyl ammonium salt, and di(oleoyloxybutyl) dimethyl ammonium salt. The ammonium salt surfactant is preferably an ammonium halide surfactant such as an ammonium chloride surfactant or an ammonium bromide surfactant. Other examples of cationic surfactants include methosulfate surfactants such as didecyl dimethyl ammonium methosulfate, di(palmitoyloxyethyl) dimethyl ammonium methosulfate, di(stearoyloxyethyl) methyl hydroxyethyl ammonium methosulfate, and tri(stearoyloxyethyl) methyl methosulfate.

[0057] Examples of anionic surfactants include sulfonate-based surfactants such as alkylbenzenesulfonates, alkylphenylsulfonates, alkylnaphthalenesulfonates, sulfonates of higher fatty acid esters, and sulfonates of higher alcohol ethers; sulfate ester salt-based surfactants such as sulfate ester salts of higher fatty acid esters and sulfate ester salts of higher alcohol ethers; fatty acid salt-based surfactants such as higher fatty acid salts; sulfosuccinate-based surfactants such as higher alkyl sulfosuccinates; carboxylate-based surfactants such as polyoxyethylene alkyl ether carboxylates; sulfate-based surfactants such as polyoxyethylene alkyl ether sulfates; and phosphate-based surfactants such as alkyl phosphates and polyoxyethylene alkyl ether phosphates.

[0058] Examples of amphoteric surfactants include betaine surfactants and amine oxide surfactants. Examples of betaine surfactants include imidazoline betaines, alkyldimethylaminoacetic acid betaines, fatty acid amidopropyl betaines, and sulfobetaines. Examples of amine oxide surfactants include alkyldimethylamine oxides.

[0059] The main surfactant component in the aqueous cleaning liquid may be a nonionic surfactant, a cationic surfactant, an anionic surfactant, or an amphoteric surfactant. The main surfactant component refers to the surfactant that accounts for the largest mass proportion of all surfactants contained in the aqueous cleaning liquid.

[0060] The aqueous cleaning solution may not contain a nonionic surfactant, a cationic surfactant, an anionic surfactant, or an amphoteric surfactant. In the present disclosure, "the aqueous cleaning solution does not contain A" means both a case where the aqueous cleaning solution does not contain A (e.g., a nonionic surfactant) at all, and a case where the aqueous cleaning solution contains a trace amount of A (e.g., a nonionic surfactant) but the concentration is so low that A does not exhibit its function.

[0061] The aqueous cleaning liquid may or may not contain a defoaming agent as a cleaning agent. Examples of the defoaming agent include silicone-based defoaming agents, mineral oil-based defoaming agents, oil-based defoaming agents, fatty acid-based defoaming agents, fatty acid ester-based defoaming agents, alcohol-based defoaming agents, amide-based defoaming agents, phosphate ester-based defoaming agents, and metal soap-based defoaming agents.

[0062] Silicone-based antifoaming agents may be emulsion-type, self-emulsifying, oil-type, oil compound-type, or solvent-type. Examples of emulsion-type silicone-based antifoaming agents include Kao's "Antifoam E-20," Shin-Etsu Chemical's "KM-89" and "KM-98," Asahi Kasei Wacker Silicone's "FC2913" and "SILFOAM SE47," and BYK-Chemie Japan's "BYK-015" and "BYK-1640." Examples of self-emulsifying silicone-based antifoaming agents include Shin-Etsu Chemical's "KS-540" and "X-50-1176," and Asahi Kasei Wacker Silicone's "SILFOAM SD670" and "SILFOAM SD850."

[0063] Examples of oil-type silicone defoamers include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., "AK350" and "AK12500" manufactured by Asahi Kasei Wacker Silicone, and "BYK-1770" manufactured by BYK Japan. Examples of oil-compound silicone defoamers include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., "SILFOAM SC370" and "PULPSIL22274VP" manufactured by Asahi Kasei Wacker Silicone, and "BYK-017" and "BYK-018" manufactured by BYK Japan. Examples of solvent-type silicone defoamers include "KM-89" and "KM-98" manufactured by Shin-Etsu Chemical Co., Ltd., and "BYK-019" and "BYK-025" manufactured by BYK Japan.

[0064] The aqueous cleaning solution may contain at least one of an amphipathic glycol solvent and a glycol ether solvent as a cleaning agent. Alternatively, the aqueous cleaning solution may not contain at least one of an amphipathic glycol solvent and a glycol ether solvent as a cleaning agent. Examples of amphipathic glycol solvents or glycol ether solvents include propylene glycol, ethylene glycol, diethylene glycol, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.

[0065] The concentration of the cleaning agent in the aqueous cleaning liquid is not particularly limited, but may be, for example, 0.2% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, or 2.0% by mass or more. If the cleaning agent concentration is too low, good cleaning performance may not be achieved. On the other hand, the cleaning agent concentration in the aqueous cleaning liquid may be, for example, 15.0% by mass or less, 14.5% by mass or less, or 12% by mass or less. If the cleaning agent concentration is too high, it may be difficult to maintain good low-foaming properties.

[0066] When the aqueous cleaning liquid contains a surfactant and an antifoaming agent, the mass ratio of the antifoaming agent to the mass of the surfactant is not particularly limited, but may be, for example, 0.05 to 1.5 times, 0.08 to 1.0 times, or 0.1 to 0.5 times. The concentration of the surfactant in the aqueous cleaning liquid is not particularly limited, but may be, for example, 0.15 to less than 15.0 mass%, 0.25 to 10.0 mass%, or 0.25 to 7.5 mass%. The concentration of the antifoaming agent in the aqueous cleaning liquid is not particularly limited, but may be, for example, 0.01 to 9.0 mass%, 0.015 to 6.0 mass%, or 0.015 to 4.5 mass%.

[0067] (2) Water-based cleaning solution The aqueous cleaning solution contains a solvent whose main component is water. The solvent may contain only water, or may further contain a water-soluble organic solvent. The proportion of water in the total solvent is, for example, 50% by mass or more, or 70% by mass or more, or even 90% by mass or more.

[0068] The aqueous cleaning liquid is neutral. "Neutral" means that the pH of the aqueous cleaning liquid is 5.5 or more and 9.0 or less at 25°C. If the pH of the aqueous cleaning liquid is within the above range, neutralization treatment is unnecessary or the burden of the neutralization treatment is reduced. Furthermore, the surface tension of the aqueous cleaning liquid is not particularly limited, but is preferably 25 mN / m or more and 50 mN / m or less. This is because the colorant layer fused to the substrate layer by heating during thermal transfer can be effectively decolorized.

[0069] (3) Cleaning method The cleaning process in the present disclosure is a process of cleaning a plurality of crushed pieces. In the cleaning process, a large number of crushed pieces are cleaned. Because each crushed piece is thin and has little stiffness, the crushed pieces tend to aggregate together. In contrast, in the present disclosure, an aqueous cleaning solution containing a surfactant is used to prevent the crushed pieces from aggregating together.

[0070] The method for cleaning the crushed pieces using an aqueous cleaning solution is not particularly limited, but an example is a method in which the crushed pieces are immersed in the aqueous cleaning solution. The temperature of the aqueous cleaning solution during immersion is not particularly limited, but may be, for example, 25°C or higher and 100°C or lower, or 30°C or higher and 80°C or lower. The immersion time is, for example, 1 minute or longer and 24 hours or shorter.

[0071] It is preferable to agitate the aqueous cleaning solution in which the crushed pieces are immersed. Agitation improves the cleaning effect. When agitating the aqueous cleaning solution in which the crushed pieces are immersed, media such as beads may be used, or no media may be used. In the former case, the media dispersed in the aqueous cleaning solution come into contact with the crushed pieces, improving cleaning performance, but at the same time, making foam more likely to be generated. In the latter case, cleaning performance is lower than in the former case, but foam generation can be suppressed.

[0072] The preparation step and the cleaning step may be carried out simultaneously. For example, the preparation step and the cleaning step can be carried out simultaneously by using a wet crusher to crush the thermal transfer sheet while cleaning the crushed pieces.

[0073] The method for washing the thermal transfer sheet may include a separation step of separating the washed fragments from the aqueous washing solution containing the washed fragments after the washing treatment step. Examples of the separation method include a method using a filter or a method using a centrifuge.

[0074] The method for washing a thermal transfer sheet may include a water washing step (rinsing step) in which the washed fragments are washed with water after the washing treatment step. By performing the water washing step, the aqueous cleaning solution remaining on the fragments can be removed. The water washing step may be performed simultaneously with the separation step or after the separation step. Alternatively, the separation step may be performed again after the water washing step. Furthermore, the water used in the water washing step may be heated. That is, the washed fragments may be washed with warm water. The temperature of the warm water is, for example, 35°C or higher and 60°C or lower.

[0075] The method for cleaning the thermal transfer sheet may include a drying step for drying the cleaned crushed pieces after the cleaning treatment step. The drying step may be performed after the separation step. The drying conditions are not particularly limited, and are preferably adjusted appropriately so as to obtain the desired recycled material.

[0076] The present disclosure also provides a method for cleaning a thermal transfer sheet, the method comprising: a preparation step of preparing crushed pieces of the thermal transfer sheet; and a cleaning step of cleaning the crushed pieces using a neutral aqueous cleaning solution, wherein the thickness of the thermal transfer sheet is 3.5 μm or more and 12 μm or less, and the aqueous cleaning solution contains a cleaning agent including at least a surfactant and water, and when 10 of the crushed pieces of the thermal transfer sheet after cleaning are stacked and the visual transmission density is measured with a black-and-white transmission densitometer, the visual transmission density is less than 0.50, and when the aqueous cleaning solution, adjusted to an amount of 50 g of water, is added to a 100 mL measuring cylinder with an inner diameter of φ28 mm and the cylinder is suctioned up and down 100 times, and the foam height is measured, the foam height is less than 30 mm.

[0077] B. Manufacturing methods for recycled materials The method for producing recycled materials according to the present disclosure includes a cleaning step for cleaning the thermal transfer sheet. In the cleaning step, the thermal transfer sheet is cleaned using the cleaning method described above in "A. Method for cleaning the thermal transfer sheet."

[0078] According to the present disclosure, by washing a thermal transfer sheet using the above-mentioned washing method, it is possible to obtain recycled raw materials while achieving both good washability and good low-foaming properties. The washing process is the same as that described above in "A. Method for washing a thermal transfer sheet," so a description thereof will be omitted here.

[0079] The method for producing recycled materials may optionally include a pelletizing step of pelletizing the washed crushed pieces, thereby obtaining recycled materials in the form of pellets.

[0080] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included within the technical scope of the present disclosure. [Example]

[0081] [Example 1] The thermal transfer sheet used was a thermal transfer sheet X (sublimation transfer type thermal transfer sheet, DS621, manufactured by Dai Nippon Printing Co., Ltd.). The thickness of the thermal transfer sheet X was 6.0 μm, and the thickness of the base layer constituting the thermal transfer sheet X was 4.5 μm. Next, the thermal transfer sheet was shredded using a ribbon shredder (device name: GRASYS BiT) to obtain shredded pieces. The cutting method was twisted micro-cutting, and the maximum shredding speed was 12 m / min.

[0082] An aqueous cleaning solution was then prepared containing surfactant N1 (an ether-based nonionic surfactant, Emulgen 106, manufactured by Kao Corporation) as a cleaning agent and antifoaming agent (a silicone-based antifoaming agent, Antifoam E-20, manufactured by Kao Corporation) and water as a solvent. The surfactant N1 and antifoaming agent were mixed in a mass ratio of surfactant N1:antifoaming agent of 87.5:12.5.

[0083] The resulting aqueous cleaning solution was then added to a container, and the container was heated in a hot water bath until the temperature of the aqueous cleaning solution reached 50°C to 55°C. Next, the crushed pieces were placed in a 100 mL beaker, and the heated aqueous cleaning solution was added. The mixture was stirred at room temperature at 300 rpm for 10 minutes. The amount of crushed pieces added was 0.1 g. After stirring, the washed crushed pieces were collected using a sieve with 2 mm openings. Next, the collected crushed pieces were placed in 50 g of hot water at 50°C to 55°C and stirred at room temperature at 300 rpm for 5 minutes (rinsing step). Next, after stirring, the washed crushed pieces were collected using a sieve with 2 mm openings, drained, and dried.

[0084] [Examples 2 to 17, Comparative Examples 1 to 4] Crushed pieces of thermal transfer sheet were washed in the same manner as in Example 1, except that the type and amount of thermal transfer sheet, the type and amount of surfactant, whether or not an antifoaming agent was added, and the amount of water in the aqueous cleaning solution were changed as shown in Table 1. In Table 1, thermal transfer sheet Y is a melt-transfer type thermal transfer sheet (V300, manufactured by Dai Nippon Printing Co., Ltd.). The thickness of thermal transfer sheet Y was 6.0 μm, and the thickness of the substrate layer constituting thermal transfer sheet Y was 4.5 μm. Also in Table 1, surfactant N2 is an epoxy-based nonionic surfactant (ADEKA Pluronic TR704, manufactured by ADEKA Corporation), and surfactant A1 is an anionic surfactant (polyoxyethylene alkyl ether sulfate, Hitenol NF-08, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0085] [evaluation] (cleanability) Ten pieces of the washed crushed pieces obtained in the Examples and Comparative Examples were stacked, and the visual transmission density was measured using a black-and-white transmission densitometer (X-Rite 341C). A visual transmission density of less than 0.3 was evaluated as A, a visual transmission density of 0.3 or more but less than 0.5 was evaluated as B, and a visual transmission density of 0.5 or more was evaluated as C. The results are shown in Table 1.

[0086] (low foaming) In the examples and comparative examples, the aqueous cleaning solution before cleaning was added to a 100 mL measuring cylinder (compliant with JIS R 3505:1994) with an inner diameter of 28 mm. After leaving it to stand for a while, it was vigorously shaken up and down 100 times (approximately 30 seconds). After shaking, the measuring cylinder was left to stand, and the foam height was read visually. A foam height of 10 mm or less was evaluated as A, a foam height of more than 10 mm but less than 30 mm was evaluated as B, and a foam height of 30 mm or more was evaluated as C. The results are shown in Table 1.

[0087] [Table 1]

[0088] As shown in Table 1, in Examples 1 to 17, it was confirmed that good cleaning performance and good low-foaming properties were obtained by setting the ratio of the mass of water to the total mass of crushed pieces (c / a) and the ratio of the mass of cleaning agent to the total mass of crushed pieces (b / a) within the specified ranges. On the other hand, in Comparative Examples 1 and 2, the value of c / a was too small, so good cleaning performance was not obtained. In Comparative Example 3, the value of b / a was too small, so good cleaning performance was not obtained. In Comparative Example 4, the value of b / a was too large, so good low-foaming properties were not obtained.

[0089] Furthermore, comparing Examples 1 to 4 and 15, Examples 1, 2 and 15 were particularly excellent in cleaning performance and low foaming. Thus, when the aqueous cleaning liquid contains a nonionic surfactant as the surfactant and a silicone-based antifoaming agent as the antifoaming agent, it is preferable that b / a is 9 times or more. On the other hand, it is preferable that b / a is, for example, 20 times or less.

[0090] Furthermore, when Examples 6 to 11 are compared, Examples 9 and 10 are particularly excellent in cleaning performance and low foaming. Thus, when the aqueous cleaning liquid contains a nonionic surfactant as the surfactant but does not contain an antifoaming agent, b / a is preferably 20 times or more and 80 times or less, and more preferably 20 times or more and 70 times or less.

[0091] Furthermore, when Examples 12 and 13 are compared, Example 12 exhibits superior cleaning properties compared to Example 13. Thus, when the aqueous cleaning liquid contains a nonionic surfactant as the surfactant and no antifoaming agent, b / a is preferably 1.2 or more. On the other hand, b / a is preferably, for example, 20 or less. It was also confirmed that, when an anionic surfactant was used, as in Example 14, cleaning properties and low foaming were excellent. Furthermore, when Examples 15 to 17 were compared with Examples 1 to 14, when a sublimation transfer thermal transfer sheet was used, the cleaning properties and low foaming properties were similar to those when a melt-transfer thermal transfer sheet was used.

[0092] Thus, the present disclosure provides, for example, the following inventions.

[0093] [1] A method for cleaning a thermal transfer sheet, comprising: The method for cleaning the thermal transfer sheet includes a preparation step of preparing crushed pieces of the thermal transfer sheet, and a cleaning step of cleaning the crushed pieces with a neutral water-based cleaning solution, The thickness of the thermal transfer sheet is 3.5 μm or more and 12 μm or less, The aqueous cleaning liquid contains a cleaning agent containing at least a surfactant and water, The mass of the water relative to the total mass of the fragments is 160 times or more, A method for cleaning a thermal transfer sheet, wherein the mass of the cleaning agent is 1 to 85 times the total mass of the crushed pieces.

[0094] [2] The method for cleaning a thermal transfer sheet according to [1], wherein the mass of the water is 600 times or less the total mass of the crushed pieces.

[0095] [3] The method for cleaning a thermal transfer sheet according to [1] or [2], wherein the concentration of the cleaning agent in the aqueous cleaning liquid is 0.2% by mass or more and 15.0% by mass or less.

[0096] [4] The method for cleaning a thermal transfer sheet according to any one of [1] to [3], wherein the aqueous cleaning liquid contains an antifoaming agent as the cleaning agent.

[0097] [5] The method for cleaning a thermal transfer sheet according to any one of [1] to [3], wherein the aqueous cleaning liquid does not contain an antifoaming agent as the cleaning agent.

[0098] [6] The method for cleaning a thermal transfer sheet according to any one of [1] to [5], wherein the aqueous cleaning liquid contains at least one surfactant selected from the group consisting of a nonionic surfactant, an anionic surfactant, a cationic surfactant, and an amphoteric surfactant.

[0099] [7] The method for cleaning a thermal transfer sheet according to any one of [1] to [6], wherein the thermal transfer sheet has a base layer and at least one of a colorant layer and a protective layer.

[0100] [8] The method for cleaning a thermal transfer sheet according to [7], wherein the thickness of the substrate layer is less than 5.0 μm.

[0101] [9] A method for producing recycled raw materials, comprising a cleaning step of cleaning a thermal transfer sheet using the method for cleaning a thermal transfer sheet according to any one of [1] to [8]. [Explanation of symbols]

[0102] 1...Base material layer 2...color material layer 3...Release layer 4...Primer layer 5…Protective layer 6…Back layer 7...Adhesive layer 8...Second primer layer 10...Thermal transfer sheet 11...Debris

Claims

1. A method for cleaning a thermal transfer sheet, comprising: The method for cleaning the thermal transfer sheet includes a preparation step of preparing crushed pieces of the thermal transfer sheet, and a cleaning step of cleaning the crushed pieces with a neutral water-based cleaning solution, The thickness of the thermal transfer sheet is 3.5 μm or more and 12 μm or less, The aqueous cleaning liquid contains a cleaning agent containing at least a surfactant and water, The mass of the water relative to the total mass of the crushed fragments is 160 times or more, A method for cleaning a thermal transfer sheet, wherein the mass of the cleaning agent is 1 to 85 times the total mass of the crushed pieces.

2. 2. The method for cleaning a thermal transfer sheet according to claim 1, wherein the mass of the water is 600 times or less the total mass of the crushed pieces.

3. The method for cleaning a thermal transfer sheet according to claim 1 , wherein the concentration of the cleaning agent in the aqueous cleaning liquid is 0.2% by mass or more and 15.0% by mass or less.

4. The method for cleaning a thermal transfer sheet according to claim 1 , wherein the aqueous cleaning liquid contains an antifoaming agent as the cleaning agent.

5. The method for cleaning a thermal transfer sheet according to claim 1 , wherein the aqueous cleaning liquid does not contain an antifoaming agent as the cleaning agent.

6. The method for cleaning a thermal transfer sheet according to claim 1 , wherein the aqueous cleaning liquid contains at least one surfactant selected from the group consisting of a nonionic surfactant, an anionic surfactant, a cationic surfactant, and an amphoteric surfactant.

7. The method for cleaning a thermal transfer sheet according to claim 1 , wherein the thermal transfer sheet has a base layer and at least one of a colorant layer and a protective layer.

8. The method for cleaning a thermal transfer sheet according to claim 7, wherein the thickness of the substrate layer is less than 5.0 μm.

9. A method for producing recycled raw materials, comprising a cleaning step of cleaning a thermal transfer sheet using the method for cleaning a thermal transfer sheet according to any one of claims 1 to 8.

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