Method for recycling release sheet

Abstract

This method for recycling a release sheet comprises: step S1 for supplying, to a user, a resin sheet laminate including an adhesive sheet and a release sheet having a base made of a resin material; step S3 for collecting used release sheets by using a collection container; and step S5 for sorting and inspecting contents of the collection container. Step S5 includes an analysis test for analyzing the make-up of the contents by using visible light, infrared light, or ultrasound.

Description

How to recycle release sheets

[0001] The technology disclosed in this specification relates to a method for recycling release sheets.

[0002] In recent years, with the rise in environmental awareness, the reuse and recycling of various products, from industrial products to everyday items, has been proposed. The Plastic Resource Recycling Promotion Act has been enacted, and the collection and recycling of resin products has attracted particular attention. For example, the reuse of resin substrates used in the manufacturing process of laminates including polarizing plates has been considered (see, for example, Patent Document 1).

[0003] In recycling, it is important to efficiently collect and separate materials. The creation of a recycling system for printing materials is also being considered (see, for example, Patent Document 2).

[0004] JP 2015-118388 A JP 2017-139008 A

[0005] In recent years, efforts have been made not only to simply recycle resin materials, but also to "horizontal recycling," in which resin materials recovered from used products are regenerated and used as materials for the same products. In the case of horizontal recycling, the regenerated resin materials must maintain a quality close to that of virgin materials, so the contamination of foreign matter when recovering used materials becomes a bigger problem.

[0006] One example of horizontal recycling is the recovery of labels with adhesive layers and release sheets after use, which are then recycled into resin materials and reused in the manufacture of release sheets. While there are many different types and materials for labels, one type of release sheet can be used for many labels, so recovering the release sheets allows for effective recycling. However, because horizontal recycling of release sheets is a new initiative, the methods for achieving this have not yet been fully established.

[0007] An object of the present invention is to provide a method for recycling release sheets that can efficiently recycle release sheets while accurately removing foreign matter, and a release sheet suitable for this method.

[0008] The method for recycling release sheets disclosed in this specification includes the steps of: supplying a resin sheet laminate to a user; the resin sheet laminate including: an adhesive sheet having an adhesive layer; and a release sheet laminate bonded to the adhesive sheet, the release sheet having a first side on which a release agent layer is formed and a second side opposite the first side, and having a substrate made of a resin material; collecting used release sheets peeled from the resin sheet laminate from the user in the form of either a roll sheet or a single sheet using a collection container; storing the configuration of the release sheets in a memory unit of an analysis system having a memory unit, an irradiation unit, a detection unit, and a judgment unit; performing a sorting inspection of the contents of the collection container collected from the user; removing foreign matter determined by the sorting inspection not to be the used release sheets from the contents of the collection container; and recycling the used release sheets into resin raw material. The step of sorting and inspecting the contents of the collection container includes a step in which the detection unit detects visible light, infrared light, or ultrasonic waves that are irradiated from the irradiation unit onto the contents and reflected from or transmitted through the contents; a step in which the detection unit detects the composition of the contents based on the visible light, infrared light, or ultrasonic waves detected by the detection unit; a step in which the analyzed composition is compared with the composition of the release sheet stored in the memory unit; and a step in which roll sheets or single sheets among the contents that have a composition that does not match the composition of the stored release sheet are not the used release sheet.

[0009] According to the recycling method disclosed in this specification, the composition of the release sheet can be inspected using visible light, infrared light, or ultrasound for sorting, thereby enabling efficient recycling of used release sheets.

[0010] Fig. 1 is a cross-sectional view showing a resin sheet laminate including an example of a release sheet applied to the release sheet recycling method according to the first embodiment of the present disclosure. Fig. 2 is a plan view of the release sheet shown in Fig. 1, viewed from the side that contacts the pressure-sensitive adhesive layer. Fig. 3 is a cross-sectional view showing a resin sheet laminate including another example of a release sheet applied to the release sheet recycling method according to the first embodiment. Fig. 4 is a flow chart showing the release sheet recycling method according to the first embodiment. Fig. 5 is a block diagram showing an inspection system used in the recycling method according to the first embodiment. Fig. 6 is a flow chart showing details of the steps for performing a content sorting inspection.

[0011] (First embodiment) Fig. 1 is a cross-sectional view showing a resin sheet laminate provided with a release sheet, and Fig. 2 is a plan view of the release sheet as seen from the side that contacts the pressure-sensitive adhesive layer. Fig. 3 is a cross-sectional view showing another example of the release sheet. These release sheets 10 and 10A are applied to the recycling method according to the first embodiment.

[0012] FIG. 4 is a flow chart showing the release sheet recycling method according to the first embodiment, and FIG. 5 is a block diagram showing an analysis system used in the recycling method of this embodiment.

[0013] In the recycling method of the present embodiment, the release sheet 10 peeled from the resin sheet laminate 20 shown in Fig. 1 or the release sheet 10A peeled from the resin sheet laminate 20A is collected. The resin sheet laminate 20 includes a base sheet 7, an adhesive sheet 15 having an adhesive layer 5 provided on one surface of the base sheet 7, and the release sheet 10 bonded to the adhesive layer 5.

[0014] The release sheet 10 has a first surface 6 on which a release agent layer 3 is formed and a second surface 8 opposite the first surface 6, and a substrate 1 made of a resin material on which a three-dimensional shape 4 is formed on at least one of the first surface 6 and the second surface 8. Here, "three-dimensional shape" refers to a three-dimensional shape, such as a recess, a protrusion, or an uneven portion, that is three-dimensional relative to a plane. The shape is not particularly limited as long as it is three-dimensional. The substrate 1 is sheet-like, and in Figures 1 and 2, the three-dimensional shape 4 is an example of a truncated cone-shaped recess. The first surface 6 is formed with a recess pattern in which recesses are repeatedly arranged at regular intervals in a two-dimensional direction. The pressure-sensitive adhesive layer 5 is formed with an inverse recess pattern corresponding to this recess pattern, in which multiple protrusions 13 are separated by lattice-shaped grooves 11. The recess pattern formed on the first surface 6 can also be said to be formed by lattice-shaped protrusions 9.

[0015] With this configuration, air escapes from the grooves 11 when the adhesive sheet 15 is attached to the adherend, so that the adhesive sheet can be attached to the adherend without trapping air.

[0016] Even a release sheet that does not have a three-dimensional shape and has a flat release surface, such as the release sheet 10A used in the resin sheet laminate 20A shown in FIG. 3, can be recycled by this recycling method.

[0017] The substrate sheet 7 may be formed of one or more materials selected from a resin sheet, paper, and synthetic paper, or may be a laminate of these materials. When the adhesive sheet 15 is a label or the like, an easy-adhesion layer that improves adhesion to ink may be formed on at least one of the surface of the substrate sheet 7 that contacts the adhesive layer 5 and the surface opposite to this surface.

[0018] The size of the uneven pattern formed on the release sheet 10 is not particularly limited, but it is preferable if the height of the three-dimensional shape 4 is, for example, 5 μm or more and 100 μm or less, the length and width are 20 μm or more and 1000 μm or less, and the spacing between adjacent three-dimensional shapes 4 is approximately 20 μm or more and 1000 μm or less, and the pattern allows the formation of grooves 11 in the adhesive layer 5 that serve as air passages, as this can effectively reduce air entrapment when the adhesive sheet 15 is applied.

[0019] The adhesive layer 5 may be formed using one or more adhesives selected from urethane-based, acrylic-based, silicone-based, polyester-based, and rubber-based adhesives. As the adhesive, a plant-derived adhesive may be used, or a plant-derived tackifier or the like may be added.

[0020] The substrate 1 of the release sheets 10 and 10A may be made of a recyclable resin material. While the resin material is not particularly limited, polyester resin, especially polyethylene terephthalate (PET), is preferred due to its versatility and established recycling technology. The substrate 1 may be transparent or white, but may not be colored with ink or the like from the perspective of reuse. If the substrate 1 is made of a porous resin material, it will be white. Because the substrate 1 is porous, the amount of resin material used can be reduced compared to when using a typical transparent resin film. For example, Kamishine (registered trademark) from Toyobo Co., Ltd. can be used as the substrate 1. From an environmental perspective, the substrate 1 may also contain biomass polyester containing plant-derived materials.

[0021] The release agent layer 3 contains a release agent such as a silicone resin or a fluororesin, and in the example shown in Fig. 1, is formed so as to conform to the shape of the three-dimensional shape 4. The thickness of the release agent layer 3 is generally about 5 µm or less. An antistatic layer may be provided on the second surface 8 and / or the first surface 6 of the substrate 1.

[0022] The analysis system 30 shown in Figure 5 includes a memory unit 21 that can store configuration information of the release sheets 10, 10A, such as the thickness and material of each layer, an analysis device 25 that analyzes the configuration of the object to be inspected in the form of a roll sheet or a sheet, and a judgment unit 27.

[0023] The analysis device 25 has an irradiation unit 24 that irradiates the test object with visible light, infrared light, ultrasonic waves, or the like, and a detection unit 22 that detects light reflected from or transmitted through the test object to analyze the layer structure, thickness, and constituent materials of the test object. The type of analysis device 25 is not particularly limited, but it is desirable that the device be capable of detecting differences in the structure of the test object with sufficient accuracy. When the analysis device 25 uses infrared light, it may be a dispersive type or a Fourier transform type (FT-IR). Using a Fourier transform type analysis device 25 enables high-speed analysis with high accuracy. The determination unit 27 compares the configuration information of the release sheets 10, 10A read from the memory unit 21 with the configuration of the object to be inspected analyzed by the analyzer 25, and if the configuration of the object to be inspected matches the configuration of the release sheets 10, 10A, it determines that the roll sheet or single sheet is the release sheet 10, 10A, and if the configuration of the object to be inspected does not match the configuration of the release sheets 10, 10A, it determines that the roll sheet or single sheet is not the release sheet 10, 10A. In this step, the determination of whether or not it is a foreign object is made for each roll sheet and each single sheet.

[0024] At least one of the memory unit 21 and the determination unit 27 may be provided within the analysis device 25 or may be provided externally to the analysis device 25. The analysis device 25 may be a portable handheld type or a stationary type that is fixed in position. When a stationary analysis device 25 is used, it is possible to continuously inspect test objects transported by a conveying device such as a belt conveyor. For continuous inspection, it is preferable that the analysis by the analysis device 25 be completed within, for example, one second. When the analysis device 25 is a handheld type, it can be used even when the analysis takes several seconds to several tens of seconds. In addition, by using the analysis device 25 closer to the test object, reflected light or transmitted light can be detected more reliably, thereby improving the accuracy of the analysis.

[0025] The release sheets 10, 10A are recycled according to the procedure shown in Figure 4. First, in step S1, the resin sheet laminate 20, 20A is supplied and sold to a user, or sold to a processor, who processes it and then supplies it to the user. The processor prints on the surface of the adhesive sheet 15, or performs processes such as punching and half-cutting. In some cases, the user performs printing and other processes themselves.

[0026] Next, in step S2, the user who has been supplied with the resin sheet laminate 20, 20A or a processed product thereof uses the resin sheet laminate 20, 20A by peeling off the adhesive sheet 15 from the release sheet 10, 10A. The user stores and accumulates the used release sheets 10, 10A after peeling, rather than discarding them.

[0027] In step S3, the used release sheets 10, 10A that have reached a predetermined amount are collected from the user in a collection container in the form of either a roll sheet or a sheet. The length of the roll sheet, the size of the sheet, and whether or not it has a cut portion are not particularly limited.

[0028] In step S4, the memory unit 21 stores the configuration of the release sheets 10, 10A. Specifically, the layer configuration of the release sheets 10, 10A, the material and thickness of each layer, etc. This step may be performed at any time before the subsequent sorting inspection.

[0029] In step S5, the contents of the collection container are subjected to a separation inspection. The separation inspection S5 includes an analytical test in which the composition of the contents is analyzed using visible light, infrared light, or ultrasonic waves to determine whether the contents are the release sheets 10, 10A. Details of the analytical test are shown in FIG. 6.

[0030] First, in step S5A, the composition of the contents of the collection container is analyzed for each roll sheet or each sheet. The analysis results by the analyzer 25 are sent to the determination unit 27.

[0031] Next, in steps S5B and S5C, the determination unit 27 compares the configuration of the contents with the configuration of the release sheets 10, 10A stored in the memory unit 21. If the contents include a rolled sheet or a single sheet having a configuration that does not match the stored configuration of the release sheets 10, 10A, the determination unit 27 determines that the rolled sheet or single sheet has a configuration that matches the configuration of the release sheets 10, 10A and is a used release sheet 10, 10A.

[0032] If it is determined that the object to be inspected is not a used release sheet 10, 10A, the object to be inspected is determined to be a foreign object in step S5D. This method makes it possible to easily detect release sheets that have different shapes but the same sheet structure, such as release sheets 10 and 10A, so that even if there are multiple types of release sheets to be recycled, they can be reliably separated. On the other hand, if separation based on optical properties using visible light is difficult, such as when release sheets 10, 10A are white, accurate separation based on the sheet structure is possible using infrared light or ultrasound.

[0033] If the wettability of the first surface 6 of the release sheet 10, 10A is lower than that of the second surface 8 and the wettability of both surfaces is known, a wettability test can be performed in the classification test S5. The wettability test can be performed, for example, using a dyne pen with a wettability greater than that of the first surface 6 but equal to or less than that of the second surface 8. As a specific example, if the wettability of the first surface of the release sheet 10, 10A is less than 30 dyn / cm (=30 mN / m) and the wettability of the second surface is 40 dyn / cm (=40 mN / m), ink from a 40 dyn / cm dyne pen can be applied to both surfaces of the contents (rolled sheet or individual sheets). If the ink is repelled on both surfaces after 5 seconds, or if the ink is not repelled on both surfaces, the contents can be easily determined not to be release sheets 10, 10A. Whether or not the ink is repelled can be confirmed visually or by connecting a camera or the like to an analytical device.

[0034] In the wettability test, both the wettability test and the analytical test in substep 5A, in which the contents are analyzed using light or ultrasound, can be performed, or only one of them can be performed. It is possible to select whether the wettability test results or the analytical test results are to be prioritized in the judgment. For example, if the results of both the analytical test and the wettability test match, that result can be used; if they do not match, the predetermined results of the analytical test or the wettability test can be prioritized in the judgment. Furthermore, if the results do not match, it can be determined that the release sheet 10, 10A is not the release sheet 10, 10A. The judgment using the results of the analytical test and the wettability test can also be performed by the judgment unit of the analysis device.

[0035] Since the wettability test can be applied regardless of the color or transparency of the release sheets 10, 10A, it is preferable to use the results of the wettability test when the release sheets 10, 10A are opaque and separation based on optical properties is difficult. Furthermore, while analytical tests using visible light, infrared light, or ultrasound make it difficult to determine whether or not a release agent layer 3 is present, a wettability test makes it easy to determine whether or not a release agent layer 3 is present. Therefore, by using the wettability test in combination, even when the contents of a collection container contain a resin sheet that has the same resin composition as the substrate 1 of the release sheets 10, 10A but does not have a release agent layer 3, the possibility of determining that the resin sheet does not have a release agent layer 3 is a used release sheet 10, 10A can be reduced, and the reliability of the separation test can be significantly improved without incurring significant costs.

[0036] The wettability test may be performed after or before the analytical test using visible light, infrared light, or ultrasound. If the wettability test is performed first, it is preferable to perform the analytical test using visible light, infrared light, or ultrasound even if the result indicates that the contents are not the used release sheet 10, 10A. Performing both tests makes it easier to identify the type of foreign matter detected in step S5. Recording the inspection result history in a storage device or the like makes it easier to take measures to prevent foreign matter contamination. However, if the wettability test indicates that the contents are not the used release sheet 10, 10A, the analytical test may not be performed. Furthermore, if the wettability test is performed after the analytical test, the wettability test may be performed regardless of the analytical test results, or the decision to perform the wettability test may be made depending on the analytical test results.

[0037] The resin sheet laminate 20, 20A may have a configuration in which multiple release sheets 10, 10A are connected by connection tape. In this case, the connection tape can be easily separated based on the difference in material between the connection tape and the release sheets 10, 10A. If the object to be inspected is a roll sheet, only a portion may be inspected.

[0038] Next, in step S6 shown in FIG. 4, foreign matter that is determined not to be the used release sheets 10, 10A in the sorting inspection is removed from the contents of the collection container.

[0039] In step S7, the contents may be pretreated as needed. For example, the used release sheets 10, 10A may be washed with warm water or alkaline water to remove the release agent layer 3 and antistatic layer, and then cut into an appropriate size and heated and melted to form pellets. If there are no particular problems, the used release sheets 10, 10A may be formed into pellets without removing the release agent layer 3. As a pretreatment, the surface of the used release sheets 10, 10A may be polished. There are methods for polishing both sides of the used release sheets 10, 10A simultaneously, and methods for polishing only one side. When polishing only one side, the wettability test described above using ink can be performed to identify which side is the first side 6 on which the release agent layer 3 is formed, making it easier to remove the release agent layer 3.

[0040] In step S8, the used release sheets 10, 10A are recycled into resin raw materials. The recycling method into resin raw materials is not particularly limited, and various methods can be used depending on the resin composition of the release sheet 10. The recycled resin raw materials can be reused to produce release sheets. When producing release sheets, recycled raw materials can be used alone, or they can be mixed with virgin raw materials. In consideration of the environmental impact, it is preferable that the base material of a newly produced release sheet contains at least 10% by mass of recycled resin raw materials. The release sheets 10, 10A may contain so-called horizontally recycled resin raw materials recycled from used release sheets. The use of horizontally recycled materials is preferable because it directly leads to savings in petroleum resources.

[0041] In the method of the present embodiment, the PSA sheet 15 included in the resin sheet laminate 20, 20A does not necessarily have to have the base sheet 7, and may have a configuration in which the PSA sheet 15 does not have a base sheet and is sandwiched between two release sheets 10, 10A. Alternatively, a resin sheet laminate 20 in which the release agent layer 3 is provided on both sides of the base 1 and the release sheet 10 is provided on only one side of a so-called substrate-less PSA sheet 15 may be sold in step S1. In this case, the resin sheet laminate 20 may be provided in a roll state in which the back surface (second surface) of the release sheet 10 is in contact with the surface of the PSA layer 5 opposite to the release sheet 10.

[0042] 4 may be performed consecutively after the release sheets collected from the user in step S3 are received. Alternatively, steps S4 and S5 may be performed as part of an acceptance inspection of the release sheets collected from the user. In this case, the release sheets may be rejected if it is determined that the release sheets contain more than the allowable amount of foreign matter.

[0043] According to the recycling method of this embodiment, foreign matter can be detected and removed accurately and efficiently.

[0044] The release sheet recycling method of the present disclosure is useful in the field of environmentally friendly pressure-sensitive adhesive sheets such as labels.

[0045] REFERENCE SIGNS LIST 1 substrate 3 release agent layer 4 three-dimensional shape 5 adhesive layer 7 substrate sheet 9 protrusion 10, 10A release sheet 11 groove 13 recess 15 adhesive sheet 20, 20A resin sheet laminate 21 memory section 22 detection section 24 irradiation section 25 analysis device 27 determination section 30 analysis system

Claims

1. A method for producing a resin sheet laminate comprising: a step of supplying to a user a resin sheet laminate comprising an adhesive sheet having an adhesive layer, and a release sheet laminated to the adhesive sheet, the release sheet having a first side on which a release agent layer is formed and a second side opposite to the first side, the release sheet having a base material made of a resin material; a step of collecting from the user the used release sheet peeled off from the resin sheet laminate in a form selected from a roll sheet and a single sheet using a collection container; a determination step of conducting a sorting inspection of the contents of the collection container collected from the user to determine whether or not the contents are the used release sheet; a step of removing foreign matter determined in the determination step to be not the used release sheet from the contents of the collection container; and a step of recycling the used release sheet into a resin raw material, the determination step including an analytical test using visible light, infrared light or ultrasonic waves to determine whether or not the contents are the used release sheet using an analysis system having a memory unit, an irradiation unit, a detection unit and a determination unit, The analytical test includes a sub-step of detecting visible light, infrared light or ultrasonic waves irradiated from the irradiation unit to the contents and reflected from or transmitted through the contents by the detection unit, and a sub-step of checking in the judgment unit whether or not the detection result of the detection unit matches the configuration of the release sheet pre-stored in the memory unit to judge whether or not the contents are the used release sheet.

2. The method for recycling release sheets according to claim 1, wherein the release sheets include those having a flat shape and those having projections and recesses formed on the first surface.

3. The recycling method according to claim 1, wherein the analysis system has a handheld analysis device including the irradiation unit and the detection unit.

4. The recycling method of claim 1, wherein the first side of the release sheet has a lower wettability than the second side, and the determination step includes a wettability test, the wettability test including an application step of applying ink to both sides of the contents having a wettability greater than the first side and less than or equal to the second side, a detection step of detecting whether the applied ink is repelled, and a determination step of determining whether the contents are the used release sheet based on the detection result of the detection step, and wherein if the wettability test determines that the contents are not the used release sheet, regardless of the determination in the analytical test.

5. The recycling method according to claim 1, wherein the base material of the release sheet is made of polyester resin.

6. The recycling method according to any one of claims 1 to 5, wherein the base material of the release sheet contains 10% by mass or more of recycled resin raw material.

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