Adhesive sheet, adhesive body, and recovery method

Abstract

To provide an adhesive sheet that can be suitably peeled off and separated from a substrate when it is to be recycled after being attached to the substrate, and is suitable for recycling the substrate; to provide an adhesive body having an adhesive sheet and a substrate to which the adhesive sheet is attached, wherein the adhesive sheet can be suitably peeled off and separated from the substrate, and is suitable for recycling the substrate; and to provide a method for recovering a substrate that can suitably peel off and separate the adhesive sheet from the substrate. [Solution] The adhesive sheet of the present invention is an adhesive sheet that is attached to an adherend having a specific gravity greater than 1.0, and comprises a sheet base material and an adhesive layer, wherein the specific gravity of the sheet base material is less than 1.0, and the adhesive layer is made of a material containing a wash-off type adhesive.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, an adherend, and a recovery method.

Background Art

[0002] As a container for storing daily-use disinfectants, shampoos, hand soaps, body soaps, etc., plastic molded containers (plastic molded containers) are widely used. And, against the background of environmental problems and reduction of plastic resource usage, material recycling is practiced on used plastic molded containers to obtain resin materials (recycled resin materials). Furthermore, horizontal recycling for forming similar plastic molded containers using this resin material is also practiced (for example, Patent Document 1).

[0003] Normally, such plastic molded containers have adhesive labels (hereinafter, also simply referred to as "labels") with various information recorded on their surfaces.

[0004] Since the label (adhesive sheet) usually contains components different from the adherend, such as those with information recorded using ink, when recycled in a state where the label is attached to the container body which is the adherend, there is a problem that the quality of the recycled material deteriorates.

[0005] Also, it is conceivable to peel the label (adhesive sheet) from the container body which is the adherend in a treatment liquid. However, in such a case, the container body and the label (adhesive sheet) are dispersed in the treatment liquid, and it is difficult to separate them.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

[0007] The object of the present invention is to provide an adhesive sheet that can be suitably peeled off and separated from a substrate when it is subjected to recycling after being attached to the substrate, and is suitable for recycling the substrate; to provide an adhesive having an adhesive sheet and a substrate to which the adhesive sheet is attached, wherein the adhesive sheet can be suitably peeled off and separated from the substrate, and is suitable for recycling the substrate; and to provide a method for recovering a substrate that can suitably peel off and separate the adhesive sheet from the substrate. [Means for solving the problem]

[0008] These objectives are achieved by the present invention as described in (1) to (11) below. (1) An adhesive sheet that is attached to a substrate having a specific gravity greater than 1.0, It comprises a sheet base material and an adhesive layer, The specific gravity of the aforementioned sheet substrate is less than 1.0. An adhesive sheet characterized in that the adhesive layer is made of a material containing a wash-off type adhesive.

[0009] (2) The specific gravity of the adherend is 1.1 or greater, The adhesive sheet according to (1) above, wherein the specific gravity of the sheet substrate is 0.97 or less.

[0010] (3) The adhesive sheet according to (1) or (2) above, wherein the adherend is made of a material containing polyethylene terephthalate.

[0011] (4) The adhesive sheet according to any one of (1) to (3) above, wherein the sheet substrate is made of a material containing polypropylene.

[0012] (5) The adhesive sheet according to (4) above, wherein the sheet substrate further contains an inorganic filler.

[0013] (6) The adhesive sheet according to any one of (1) to (5) above, wherein the thickness of the adhesive layer is 5 μm or more and 100 μm or less.

[0014] (7) The adhesive sheet according to any one of (1) to (6) above, wherein the adhesive layer is made of a material containing an acrylic adhesive.

[0015] (8) The adhesive sheet according to any one of (1) to (7) above, wherein the adhesive sheet further has a coating layer on the side of the sheet substrate opposite to the side facing the adhesive layer.

[0016] (9) An adhesive comprising a substrate having a specific gravity greater than 1.0 and an adhesive sheet according to any one of (1) to (8) above attached to the substrate.

[0017] (10) A recovery method characterized by applying a liquid to the adhesive described in (9) above, separating the adherend and the sheet substrate in the liquid, and recovering at least the adherend.

[0018] (11) The recovery method according to (10) above, wherein the liquid is an alkaline liquid. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide an adhesive sheet that can be suitably peeled off and separated from a substrate when it is subjected to recycling after being attached to the substrate, and is suitable for recycling the substrate; an adhesive having an adhesive sheet and a substrate to which the adhesive sheet is attached, wherein the adhesive sheet can be suitably peeled off and separated from the substrate, and is suitable for recycling the substrate; and a method for recovering a substrate that can suitably peel off and separate the adhesive sheet from the substrate. [Brief explanation of the drawing]

[0020] [Figure 1] This is a cross-sectional view showing one example of the structure of an adhesive sheet. [Figure 2]It is a cross-sectional view showing a configuration example of an adhesive label. [Figure 3] It is a cross-sectional view showing a configuration example of an adherend. [Figure 4] It is a cross-sectional view showing an example of a state in which an alkaline liquid is applied to the adherend described in FIG. 3.

Mode for Carrying Out the Invention

[0021] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0022] [1] Adhesive Sheet First, the adhesive sheet of the present invention will be described.

[0023] FIG. 1 is a cross-sectional view showing a configuration example of an adhesive sheet. The adhesive sheet 1 shown in FIG. 1 has a sheet base material 2 and an adhesive layer 3. And the adhesive sheet 1 is to be adhered to an adherend 50 having a specific gravity of more than 1.0, the specific gravity of the sheet base material 2 is less than 1.0, and the adhesive layer 3 is composed of a material containing a wash-off type adhesive.

[0024] With such a configuration, when it is subjected to a recycling process after being adhered to the adherend 50, it can be suitably peeled off and separated from the adherend 50, and an adhesive sheet 1 suitable for recycling of the adherend 50 can be provided.

[0025] More specifically, when an adhesive body 100, which has an adhesive sheet 1 (for example, an adhesive label 10 as an adhesive sheet with a printed section 5 as described later) attached to an adherend 50, is to be recycled, by applying a liquid to the adhesive body 100, the adherend 50 and the sheet substrate 2 can be suitably separated in the liquid, and by utilizing the difference in specific gravity between the adherend 50 and the sheet substrate 2, the adherend 50 can be unevenly distributed in the liquid, with the adherend 50 unevenly distributed in the liquid, and the sheet substrate 2 unevenly distributed in the liquid, with the adherend 50 unevenly distributed in the liquid, with the sheet substrate 2 unevenly distributed in the liquid, even when the liquid containing the adhesive body 100 is stirred, the adherend 50 can be unevenly distributed in the liquid, with the adherend 50 unevenly distributed in the liquid, with the sheet substrate 2 unevenly distributed in the liquid, with the adherend 50

[0026] In this specification, "specific gravity" refers to the ratio of the density of a substance at 20°C to the density of water at the same temperature.

[0027] Furthermore, in this specification, "wash-off adhesive" refers to an adhesive that is soluble in liquid, or an adhesive that is not soluble but peels off from the adherend when immersed in liquid. The liquid may be, for example, an alkaline liquid.

[0028] Furthermore, in this specification, the concept of "sheet" includes things referred to as film, tape, etc.

[0029] [1-1] Sheet base material The sheet substrate 2 is a sheet-like component that has the function of supporting the adhesive layer 3 and the coating layer 4.

[0030] The specific gravity of the sheet substrate 2 should be less than 1.0, but is preferably 0.97 or less, more preferably 0.95 or less, and even more preferably 0.93 or less.

[0031] This makes it easier to increase the specific gravity difference between the adherend 50 and the sheet substrate 2, allowing for a more favorable recovery of the adherend 50 from which the sheet substrate 2 has peeled off.

[0032] In particular, when the specific gravity of the adherend 50 is 1.1 or higher, and the specific gravity of the sheet substrate 2 is 0.97 or lower, the adherend 50 that has peeled off the sheet substrate 2 can be recovered even more effectively.

[0033] The difference between the specific gravity of the adherend 50 and the specific gravity of the sheet substrate 2 is preferably 0.13 or more, more preferably 0.25 or more, and even more preferably 0.37 or more.

[0034] This allows for even more favorable recovery of the adherend 50 from which the sheet substrate 2 has peeled off.

[0035] The sheet substrate 2 is typically made of a resin material. Examples of resin materials constituting the sheet substrate 2 include polyolefin resins and their foams, expanded polystyrene, expanded polyvinyl chloride, expanded polyester, and expanded polyethylene terephthalate, all of which have a specific gravity of less than 1.0. Among these, polyolefin resins are preferred.

[0036] This makes it easier to ensure that the sheet substrate 2 meets the specific gravity requirements mentioned above. Furthermore, it improves the adhesion between the sheet substrate 2 and the adhesive layer 3, which is composed of a wash-off type adhesive, thereby improving the reliability of the adhesive sheet 1. It also offers cost advantages.

[0037] Polyolefin resins are polymer compounds having a chemical structure obtained by polymerizing olefins containing carbon-carbon double bonds as monomers.

[0038] Such polyolefin resins generally have low specific gravity and excellent flexibility. Therefore, by having the sheet substrate 2 composed of a material containing a polyolefin resin, the specific gravity conditions described above can be suitably met, and the conformability of the adhesive sheet 1 to curved surfaces can be improved. As a result, it can be more suitably adhered to the adherend 50 having a curved surface.

[0039] Examples of polyolefin resins constituting the sheet substrate 2 include polyethylene (PE), polypropylene (PP), polybutene (PB), ethylene-propylene copolymer, olefin elastomer (TPO), ethylene-vinyl acetate copolymer (EVA), ethylene-methyl methacrylate copolymer (EMMA), and olefin ternary copolymers such as ethylene-propylene-(5-ethylidene-2-norbornene). One or more of these can be selected and used in combination, but it is preferable that at least one of polypropylene and polyethylene be used, and more preferably polypropylene. Polypropylene may be, for example, stretched polypropylene (OPP).

[0040] When the sheet substrate 2 is made of a material containing a polyolefin resin (particularly polypropylene), the content of the polyolefin resin in the sheet substrate 2 is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more. This makes the aforementioned effects even more pronounced.

[0041] The sheet substrate 2 may contain resin materials other than those mentioned above, i.e., resin materials with a specific gravity of 1.0 or higher. Hereinafter, such resin materials will also be referred to as "high-specific-gravity resin materials" in this section.

[0042] When the sheet substrate 2 contains a high-density resin material, the proportion of the high-density resin material to the total resin material constituting the sheet substrate 2 is preferably sufficiently low, specifically, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0043] Examples of high-density resin materials include polyester resins such as polyethylene terephthalate (PET), polybutylene succinate, and polylactic acid, as well as acrylic resins, acetate resins, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polystyrene, polyvinyl chloride (PVC), polyamide, polyimide, polycarbonate, and cellulose acetate.

[0044] If the sheet substrate 2 is made of a material containing polypropylene, it is preferable that the sheet substrate 2 further contains an inorganic filler.

[0045] This allows for the formation of numerous fine pores with inorganic fillers as nuclei within the sheet substrate 2 when the film is stretched, making it easier to whiten, opaqueize, and lighten the sheet substrate 2.

[0046] Examples of inorganic fillers include calcium carbonate, calcined clay, talc, diatomaceous earth, titanium dioxide, zinc oxide, silicon dioxide, magnesium oxide, and barium sulfate, but calcium carbonate, calcined clay, and talc are preferred. This makes the aforementioned effects even more pronounced.

[0047] When the sheet substrate 2 contains the inorganic filler described above, the content of the inorganic filler in the sheet substrate 2 is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less. This makes the aforementioned effects even more pronounced.

[0048] Furthermore, the sheet substrate 2 may contain components other than those listed above. Hereinafter, such components will also be referred to as "other components" in this section. Other components include, for example, plasticizers, stabilizers, colorants, and flame retardants.

[0049] The content of other components in the sheet substrate 2 is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0050] The thickness of the sheet substrate 2 is not particularly limited, but is preferably 10 μm or more and 250 μm or less, more preferably 15 μm or more and 200 μm or less, and even more preferably 20 μm or more and 150 μm or less.

[0051] This improves the mechanical strength of the adhesive sheet 1, the ease of handling when attaching the adhesive sheet 1 (adhesive label 10) to the substrate 50, and the ease of handling of the sheet substrate 2 after it is separated from the substrate 50 during recycling of the substrate 100.

[0052] Such a sheet substrate 2 can be manufactured by known methods, such as film formation methods including extrusion, calendering, solution coating, and casting.

[0053] [1-2] Adhesive layer The adhesive layer 3 has the function of attaching the adhesive sheet 1 (adhesive label 10) to the object 50. The adhesive layer 3 is composed of a material containing a wash-off type adhesive.

[0054] Such an adhesive layer 3 can be soluble in liquid, or it can be non-soluble but can be removed from the adherend by immersion in liquid. For materials that are soluble in liquids, it is preferable that the gel fraction when the adhesive layer 3 is immersed in a 1.5% by mass sodium hydroxide aqueous solution at 70°C for 30 minutes is 0% or more and 10% or less.

[0055] This allows for a more favorable separation of the adherend 50 and the sheet substrate 2 when recycling the adhesive body 100 after use.

[0056] The adhesive layer 3 is preferably composed of a material containing an acrylic adhesive, and more preferably contains an acrylic polymer as an adhesive, which contains a "specific hydrophilic monomer" as a constituent monomer in a predetermined proportion, as described later.

[0057] This makes it possible to increase the solubility of the adhesive layer 3 in alkaline liquids.

[0058] [1-2-1] Acrylic polymer containing a specific hydrophilic monomer as a constituent monomer in a predetermined proportion. The adhesive contained in the adhesive layer 3 may be an acrylic polymer containing a specific hydrophilic monomer, which is an acrylate having an ether bond, as a constituent monomer, and the proportion of the specific hydrophilic monomer to the total adhesive is 60% by mass or more and 90% by mass or less.

[0059] With this configuration, the hydrophilicity of the adhesive becomes more favorable, the adhesive layer 3 has more favorable solubility (alkali solubility), and the adhesive strength of the adhesive layer 3 to the adherend 50 becomes more favorable.

[0060] In the following description, an acrylic polymer that contains the specified hydrophilic monomer as a constituent monomer and in which the proportion of the specified hydrophilic monomer is 60% by mass or more and 90% by mass or less is also referred to as a "specified hydrophilic monomer-containing adhesive."

[0061] [1-2-1-1] Specific hydrophilic monomer The adhesive containing a specific hydrophilic monomer contains a specific hydrophilic monomer, which is an acrylate having an ether bond, as a constituent monomer.

[0062] Examples of specific hydrophilic monomers that constitute the adhesive containing specific hydrophilic monomers include 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate, and methoxypolyethylene glycol (meth)acrylate. One or more selected from these can be used in combination, but it is preferable that at least one selected from the group consisting of 2-methoxyethyl acrylate, methoxytriethylene glycol acrylate, and 2-ethoxyethyl acrylate is used, and it is more preferable that it is 2-methoxyethyl acrylate.

[0063] As a result, the adhesive layer 3 has even more suitable solubility (alkali solubility).

[0064] The proportion of the specific hydrophilic monomer in the total adhesive containing the specific hydrophilic monomer is 60% by mass or more and 90% by mass or less, but is preferably 65% ​​by mass or more and 88% by mass or less, and more preferably 70% by mass or more and 85% by mass or less. This makes the aforementioned effects even more pronounced.

[0065] In particular, when the adhesive containing a specific hydrophilic monomer contains 2-methoxyethyl acrylate as the specific hydrophilic monomer, the ratio of the content of 2-methoxyethyl acrylate to the total specific hydrophilic monomers constituting the adhesive is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 75% by mass or more. This makes the aforementioned effects even more pronounced.

[0066] [1-2-1-2] Constituent monomers other than specific hydrophilic monomers Adhesives containing specific hydrophilic monomers contain, in addition to the aforementioned specific hydrophilic monomers, other constituent monomers. Hereafter, in this section, constituent monomers other than the specific hydrophilic monomers will also be referred to as "other monomers."

[0067] Other monomers that constitute the adhesive containing a specific hydrophilic monomer include, for example, (meth)alkyl acrylates such as 2-ethylhexyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and n-butyl (meth)acrylate, (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, and (meth)acrylamide, but it is preferable to include at least one selected from the group consisting of 2-ethylhexyl acrylate, n-butyl acrylate, and acrylic acid.

[0068] This makes it possible to make the adhesive strength of the adhesive layer 3 to the adherend 50 more suitable, and to more reliably prevent unintended peeling of the adhesive sheet 1 (adhesive label 10) from the adherend 50.

[0069] In particular, the adhesive strength of the adhesive layer 3 becomes more suitable when the adhesive containing a specific hydrophilic monomer also contains 2-ethylhexyl acrylate or n-butyl acrylate as other monomers.

[0070] When a specific hydrophilic monomer-containing adhesive contains 2-ethylhexyl acrylate in addition to the specific hydrophilic monomer, the content of 2-ethylhexyl acrylate in the entire specific hydrophilic monomer-containing adhesive is preferably 1% by mass or more and 35% by mass or less, more preferably 2% by mass or more and 30% by mass or less, and even more preferably 3% by mass or more and 20% by mass or less.

[0071] When a specific hydrophilic monomer-containing adhesive contains n-butyl acrylate in addition to the specific hydrophilic monomer, the content of n-butyl acrylate in the entire specific hydrophilic monomer-containing adhesive is preferably 2% by mass or more and 25% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less.

[0072] This makes it possible to achieve a more favorable balance between sufficient adhesive strength to the adherend 50 and excellent separation of the adhesive layer 3 from the sheet substrate 2 and adherend 50 when treated with an alkaline liquid (alkaline solution).

[0073] Furthermore, by including acrylic acid as another monomer in the specific hydrophilic monomer-containing adhesive, the excellent separation properties of the adhesive layer 3 from the sheet substrate 2 and adherend 50 when treated with an alkaline solution can be further improved. In addition, it can form crosslinks with the crosslinking agent described later, thereby improving the cohesive force of the adhesive layer 3.

[0074] When a specific hydrophilic monomer-containing adhesive contains acrylic acid in addition to the specific hydrophilic monomer, the acrylic acid content in the entire specific hydrophilic monomer-containing adhesive is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less, and even more preferably 3% by mass or more and 7% by mass or less.

[0075] This makes it possible to achieve a more favorable balance between sufficient adhesive strength to the adherend 50 and excellent separation of the adhesive layer 3 from the sheet substrate 2 and adherend 50 when treated with an alkaline solution.

[0076] Adhesives containing specific hydrophilic monomers may be crosslinked with a crosslinking agent. This is advantageous in increasing the adhesive strength of the adhesive layer 3 to the adherend 50 and the cohesive force of the adhesive layer 3.

[0077] The crosslinking agent is not particularly limited, and known crosslinking agents can be appropriately selected and used. Specifically, examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, and carbodiimide-based crosslinking agents, and one or more selected from these can be used in combination. Among these, epoxy-based crosslinking agents are preferred.

[0078] The amount of crosslinking agent added is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.25 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the adhesive containing the specific hydrophilic monomer. This makes the aforementioned effects even more pronounced.

[0079] If the adhesive layer 3 contains an adhesive containing a specific hydrophilic monomer, the content of the adhesive containing the specific hydrophilic monomer in the adhesive layer 3 is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. This makes the aforementioned effects even more pronounced.

[0080] [1-2-2] Other ingredients The adhesive layer 3 may contain components other than those mentioned above (hereinafter referred to as "other components" in this section). Examples of other components include colorants, fillers, softeners, heat and light stabilizers, antioxidants, etc., and one or more of these can be selected and used in combination.

[0081] For example, various dyes and pigments can be used as coloring agents. Examples of fillers include zinc oxide, titanium dioxide, silica, calcium carbonate, and barium sulfate.

[0082] Examples of softening agents include process oils, liquid rubber, and plasticizers. Examples of heat and light stabilizers include benzophenone-based stabilizers, benzotriazole-based stabilizers, and hindered amine-based stabilizers.

[0083] Examples of antioxidants include anilide-based antioxidants, phenol-based antioxidants, phosphite-based antioxidants, and thioester-based antioxidants.

[0084] However, the content of other components in the adhesive layer 3 is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0085] [1-2-3] Other conditions The adhesive layer 3 preferably satisfies the condition that the gel fraction when immersed in ethyl acetate at 23°C for 72 hours is 50% or more, more preferably 50% to 95%, and even more preferably 50% to 85%.

[0086] As a result, the adhesive layer 3 can achieve both appropriate cohesive force and adhesive force, allowing for efficient processing of the adhesive sheet 1. Furthermore, unintended peeling of the adhesive sheet 1 (adhesive label 10) from the adherend 50 can be more effectively suppressed.

[0087] Furthermore, the gel fraction value when immersed in ethyl acetate at 23°C for 72 hours can be adjusted, for example, by the amount of crosslinking agent and the ratio of each monomer (especially the ratio of acrylic acid) in the components of the adhesive layer 3.

[0088] In the measurement of the gel fraction described above, 20,000 parts by mass or more of ethyl acetate can be used per 100 parts by mass of adhesive layer 3. Furthermore, it is preferable to use 100 mg or more of adhesive layer 3 in the measurement of the gel fraction described above. Therefore, for example, when using 100 mg of adhesive layer 3 in the measurement of the gel fraction described above, 20 g of ethyl acetate can be used.

[0089] The thickness of the adhesive layer 3 is preferably 5 μm or more and 100 μm or less, more preferably 10 μm or more and 50 μm or less, and even more preferably 15 μm or more and 50 μm or less.

[0090] This allows for more suitable adhesive strength to be achieved with respect to the adherend 50, and also improves the handling of the adhesive sheet 1 (adhesive label 10) when attaching it to the adherend 50. Furthermore, it improves the peelability when peeling the sheet substrate 2 from the adherend 50.

[0091] Examples of adhesives that are not soluble in liquid but can be removed from an adherend by immersion in a liquid include adhesives containing an acrylic copolymer and a compound with an acid value of 30 mgKOH / g or more, wherein the acrylic copolymer is obtained by copolymerizing a monomer mixture containing more than 0.5% by mass of acid group-containing vinyl monomers.

[0092] [1-3] Coat layer In the configuration shown in Figure 1, a coating layer 4 is further provided on the side of the sheet substrate 2 opposite to the side facing the adhesive layer 3.

[0093] With such a coating layer 4 provided, for example, when a printed portion 5 is provided on an adhesive sheet 1 to form an adhesive label 10 (as an adhesive sheet), the printed portion 5 can be formed more favorably, and the visibility of the printed portion 5, the durability and reliability of the adhesive label 10 can be improved.

[0094] Furthermore, for example, since the coating layer 4 is made of a material that dissolves when immersed in alkaline hot water, as will be described later, when the adhesive 100 is recycled, not only can the sheet substrate 2 and the adherend 50 be separated, but the sheet substrate 2 and the coating layer 4 (especially the coating layer 4 on which the printed portion 5 is provided) can also be separated. As a result, not only the adherend 50 but also the sheet substrate 2 can be suitably used as recycled material.

[0095] Below, as an example of a coating layer 4, we will describe in detail a coating layer 4 composed of a material that dissolves when immersed in alkaline hot water.

[0096] The coating layer 4, which dissolves when immersed in alkaline hot water, is preferably composed of a material containing a propylene polymer and an acid-modified ethylene copolymer.

[0097] This allows for, for example, the efficient and suitable separation of the coating layer 4 from the sheet substrate 2 when recycling the adhesive 100, using a relatively low-temperature alkaline solution and a relatively short processing time.

[0098] (Propylene polymer) Examples of propylene polymers include polypropylene such as propylene homopolymers and propylene-α-olefin copolymers, and acid-modified propylene polymers.

[0099] Such propylene polymers exhibit superior compatibility with acid-modified ethylene copolymers. As a result, unintended phase separation in the coating layer 4 can be more effectively prevented, leading to improved reliability of the adhesive sheet 1.

[0100] In propylene polymers, propylene is the main component of the monomers that make up the polymer. The propylene content in the total monomers constituting the propylene polymer is preferably 50% by mass or more, and more preferably 60% by mass or more. This makes the aforementioned effects even more pronounced.

[0101] Acid modification can be introduced using unsaturated carboxylic acids or their acid anhydrides. Examples of unsaturated carboxylic acids and their acid anhydrides (hereinafter also referred to as unsaturated carboxylic acid components) include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid, as well as half-esters and half-amides of unsaturated dicarboxylic acids. Among these, it is preferable to use at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, and maleic anhydride for acid modification.

[0102] Unsaturated carboxylic acid or acid anhydride-modified polyolefins are usually preferably obtained by copolymerizing a polyolefin with an unsaturated carboxylic acid or acid anhydride using methods known to the extent of the unsaturated carboxylic acid or acid anhydride.

[0103] The copolymerization amount of the propylene main chain with an unsaturated carboxylic acid or its acid anhydride is preferably, for example, 0.5% by mass or more and 5% by mass or less, relative to the solid content mass of the propylene main chain.

[0104] Furthermore, the acid-modified propylene polymer may be a copolymer with other α-olefins such as ethylene and butene.

[0105] The propylene polymer may further contain other monomeric components that can copolymerize with propylene. Examples of other monomers include (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, and octyl (meth)acrylate; alkenes and dienes having more than 6 carbon atoms such as 1-octene and norbornenes; maleic acid esters such as dimethyl maleate, diethyl maleate, and dibutyl maleate; (meth)acrylamide; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versaticate, and vinyl alcohols obtained by saponifying these vinyl esters with a basic compound; (meth)acrylic acid derivatives such as 2-hydroxyethyl acrylate, glycidyl (meth)acrylate, and (meth)acrylonitrile; and substituted or unsubstituted styrene. One or more of these can be selected and used in combination.

[0106] The melting point of the propylene polymer is preferably, for example, 60°C to 160°C, and more preferably 60°C to 100°C.

[0107] This ensures that the adhesive sheet 1 has excellent durability while also providing more favorable adhesion of the coating layer 4 to the sheet substrate 2.

[0108] The content of the propylene polymer in the coating layer 4 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 75% by mass or less, and even more preferably 30% by mass or more and 75% by mass or less. This results in more favorable adhesion of the coating layer 4 to the sheet substrate 2.

[0109] The content of the acid-modified propylene polymer in the coating layer 4 is preferably 20% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 75% by mass or less, and even more preferably 30% by mass or more and 75% by mass or less. This results in more favorable adhesion of the coating layer 4 to the sheet substrate 2.

[0110] (Acid-modified ethylene copolymer) Acid-modified ethylene copolymers are polymers formed by acid modification of polymers in which ethylene is the monomer component.

[0111] By using such an acid-modified ethylene copolymer, the adhesion between the sheet substrate 2 and the coating layer 4 can be improved, and the adhesive sheet 1 can be more effectively peeled off at the interface between the sheet substrate 2 and the coating layer 4 when recycling it after use.

[0112] The proportion of ethylene monomer components in the total monomers of the acid-modified ethylene copolymer is preferably 50% by mass or more, and more preferably 60% by mass or more. This makes the aforementioned effects even more pronounced.

[0113] Acid modification can be introduced using unsaturated carboxylic acids or their acid anhydrides. Examples of unsaturated carboxylic acids and their acid anhydrides (hereinafter also referred to as unsaturated carboxylic acid components) include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, crotonic acid, as well as half-esters and half-amides of unsaturated dicarboxylic acids. In particular, it is preferable to use at least one selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, and maleic anhydride for acid modification, more preferably at least one of acrylic acid and maleic anhydride, and even more preferably acrylic acid. This makes the aforementioned effects even more pronounced.

[0114] Furthermore, the unsaturated carboxylic acid component only needs to be copolymerized in the polyolefin, and its form is not limited; for example, random copolymerization, block copolymerization, graft copolymerization, etc.

[0115] The acid-modified ethylene copolymer may further be a copolymer with another monomer copolymerizable with ethylene, and (meth)acrylic acid ester may be used as the monomer. Examples of (meth)acrylic acid esters include esterified products of (meth)acrylic acid with an alcohol having 1 to 30 carbon atoms (preferably 1 to 20 carbon atoms). Specific examples of such compounds include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, lauryl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate.

[0116] Other copolymerizable components besides (meth)acrylic acid esters include, for example, alkenes and dienes with more than 6 carbon atoms such as 1-octene and norbornene, maleic acid esters such as dimethyl maleate, diethyl maleate, and dibutyl maleate, (meth)acrylamides, alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether, vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versaticate, as well as vinyl alcohol obtained by saponifying vinyl esters with basic compounds, etc., 2-hydroxyethyl acrylate, glycidyl (meth)acrylate, (meth)acrylonitrile, styrene, substituted styrene, carbon monoxide, sulfur dioxide, and the like.

[0117] Examples of acid-modified ethylene copolymers include ethylene-(meth)acrylic acid (salt) copolymers, ethylene-(meth)acrylic acid (salt)-maleic anhydride (salt) copolymers, acid-modified polyethylene, or ethylene-(meth)acrylic acid ester-unsaturated carboxylic acid copolymers obtained by further acrylic modification of these acid-modified resins with (meth)acrylic acid esters, etc. Among these, ethylene-(meth)acrylic acid (salt) copolymers are preferred as the acid-modified ethylene resin. This makes the aforementioned effects even more pronounced.

[0118] Furthermore, (meth)acrylic acid (salt) refers to at least one of (meth)acrylic acid or (meth)acrylic acid salt, and maleic anhydride (salt) refers to at least one of maleic anhydride or maleic anhydride salt.

[0119] In the ethylene-(meth)acrylic acid (salt) copolymer, the content of ethylene (derived constituent units) is preferably 70% by mass or more and 95% by mass or less. This makes the aforementioned effects even more pronounced.

[0120] In the ethylene-(meth)acrylic acid (salt) copolymer, the content of (meth)acrylic acid (salt) (derived constituent units) is preferably 5% by mass or more and 30% by mass or less. This makes the aforementioned effects even more pronounced.

[0121] The weight-average molecular weight of the ethylene-(meth)acrylic acid (salt) copolymer is preferably 5,000 or more and 10,000 or less. This makes the aforementioned effects even more pronounced.

[0122] In this specification, the mass-average molecular weight (Mw) value is a value calculated on a standard polystyrene basis by gel permeation chromatography (GPC).

[0123] The melting point of the ethylene-(meth)acrylic acid (salt) copolymer is preferably, for example, 60°C to 160°C, and more preferably 60°C to 120°C.

[0124] This ensures that the adhesive sheet 1 has excellent durability while also providing more favorable adhesion of the coating layer 4 to the sheet substrate 2.

[0125] The content of the acid-modified ethylene copolymer in the entire coating layer 4 is preferably 10% by mass or more and 80% by mass or less, more preferably 12% by mass or more and 70% by mass or less, and even more preferably 15% by mass or more and 65% by mass or less. This makes the aforementioned effects even more pronounced.

[0126] When the content of propylene polymer in the coating layer 4 is XP [mass%] and the content of acid-modified ethylene copolymer is XE [mass%], it is preferable that the relationship 0.25 ≤ XP / XE ≤ 4.0 is satisfied, more preferably that 0.40 ≤ XP / XE ≤ 2.3 is satisfied, and even more preferably that 0.80 ≤ XP / XE ≤ 1.5 is satisfied.

[0127] This results in improved adhesion of the coating layer 4 to the sheet substrate 2 and better detachability from the sheet substrate 2.

[0128] Even if the coating layer 4 is composed of a material containing a propylene polymer and an acid-modified ethylene copolymer, it may also contain other components (hereinafter referred to as "other components" in this section) in addition to the propylene polymer and the acid-modified ethylene copolymer.

[0129] However, the sum of the content of propylene polymers and acid-modified ethylene copolymers in the coating layer 4 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0130] Other components include, for example, particles that have functions such as improving the slipperiness of the coating layer 4, colorants, fillers, softeners, heat and light stabilizers, and antioxidants.

[0131] The aforementioned particles may be either inorganic or organic particles. Examples of inorganic particles include zirconia, silica, titanium dioxide, kaolin, alumina, titania, zeolite, calcium carbonate, barium sulfate, magnesium hydroxide, calcium phosphate, glass, mica, and talc. Examples of organic particles include acrylic resin particles such as polymethyl methacrylate, polystyrene particles, styrene-acrylic resin particles, and polycarbonate particles. One or more of these can be selected and used in combination.

[0132] The content of the aforementioned particles is not particularly limited, but it can be 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total amount of the propylene polymer and the acid-modified ethylene copolymer.

[0133] The average particle diameter of the aforementioned particles is not particularly limited, but is preferably 0.1 μm or more and 1.0 μm or less, and more preferably 0.3 μm or more and 0.6 μm or less. This allows for improved resistance to blocking.

[0134] In this specification, unless otherwise specified, the average particle diameter refers to the average particle diameter based on volume, which can be determined, for example, by measuring the particle dispersion using a Coulter counter particle size distribution analyzer (Beckman Coulter, TA-II model) with a 50 μm aperture.

[0135] The coating layer 4 may be, for example, a laminate having multiple layers, or it may be composed of a gradient material whose composition changes in a gradual manner in the thickness direction.

[0136] The thickness of the coating layer 4 is not particularly limited, but is preferably 0.01 μm or more and 5.0 μm or less, and more preferably 0.03 μm or more and 3.0 μm or less.

[0137] As a result, when recycling the adhesive 100, the coating layer 4 can be separated from the sheet substrate 2 more efficiently by using a relatively low-temperature alkaline solution and a relatively short processing time.

[0138] The specific gravity of the coating layer 4 is usually less than 1.0. Therefore, even if the coating layer 4 does not separate from the sheet substrate 2, the specific gravity of the laminate of the coating layer 4 and the sheet substrate 2 can be made sufficiently small, and the adherend 50 separated from the sheet substrate 2 can be more preferably recovered when the adhesive body 100 is recycled.

[0139] The specific gravity of the coating layer 4 is preferably 0.97 or less, more preferably 0.95 or less, and even more preferably 0.93 or less. This makes the aforementioned effects even more pronounced.

[0140] The specific gravity of the laminate of the sheet substrate 2 and the coating layer 4 is usually less than 1.0. Therefore, even if the coating layer 4 does not separate from the sheet substrate 2, the adherend 50 that has separated from the sheet substrate 2 can be more preferably recovered during the recycling of the adhesive 100.

[0141] The specific gravity of the laminate of the sheet substrate 2 and the coating layer 4 is preferably 0.97 or less, more preferably 0.95 or less, and even more preferably 0.93 or less. This makes the aforementioned effects even more pronounced.

[0142] [1-4] Adhesive labels as adhesive sheets Next, the adhesive label according to the present invention will be described. Figure 2 is a cross-sectional view showing one example of the configuration of an adhesive label.

[0143] The adhesive label 10 has a printed section 5 on the side of the adhesive sheet 1 opposite to the adhesive layer 3. Having such a printing unit 5 allows for the display of, for example, predetermined information.

[0144] The printed section 5 may be any pattern, such as letters, symbols, figures, designs, barcodes, two-dimensional codes such as QR codes (registered trademarks), and one or more of these can be selected and used in combination.

[0145] Specific information displayed using characters and symbols may include, for example, information about the adherend 50, the contents of the adherend 50, the packaging of the adherend 50, etc. (hereinafter collectively referred to as "adherend 50, etc."). More specifically, this may include the product name, manufacturer name, usage instructions, product number, manufacturing number, price, components, net weight, expiration date, best-before date, name, address, telephone number, email address, and website URL of the manufacturer, distributor, shipper, shipping company, and delivery destination, as well as the shipping date and delivery date. Note that the printed section 5 may be printed using solid color printing.

[0146] Methods for forming the printed section 5 include, for example, flexographic printing, offset printing, letterpress printing, gravure printing, screen printing, inkjet printing, electrophotography (electrostatic) printing, and the like.

[0147] Such adhesive labels 10 can also be considered a form of the adhesive sheet of the present invention.

[0148] [2] Adhesive body Next, the adhesive body of the present invention will be described. Figure 3 is a cross-sectional view showing one example of the structure of an adhesive body.

[0149] The adhesive body of the present invention is characterized by comprising a substrate having a specific gravity greater than 1.0 and an adhesive sheet of the present invention attached to the substrate.

[0150] This configuration provides an adhesive body having an adhesive sheet and a substrate to which the adhesive sheet is attached, which allows for the adhesive label to be suitably peeled off and separated from the substrate, and is suitable for recycling the substrate.

[0151] In particular, the adhesive body 100 shown in Figure 3 has an adhesive sheet containing the adhesive label 10 described in [1-4] above. In other words, the adhesive body 100 shown in Figure 3 has a substrate 50 with a specific gravity greater than 1.0 and an adhesive label 10 attached to the substrate 50.

[0152] [2-1] Adhesive labels (adhesive sheets) The adhesive label 10 of the adhesive body 100 comprises a sheet base material 2, an adhesive layer 3 disposed on one side of the sheet base material 2, and a coating layer 4 disposed on the other side of the sheet base material 2, with a printed portion 5 provided on the surface of the coating layer 4. The adhesive layer 3 is made of a material containing a wash-off type adhesive.

[0153] The adhesive label 10 (adhesive sheet) provided on the adhesive body 100 preferably satisfies the conditions described in [1] above. This results in the effects described above.

[0154] In the configuration shown in Figure 3, an adhesive label 10 having a printed portion 5 is attached to the adherend 50 as an adhesive sheet, but an adhesive label without a printed portion 5 may also be provided. The adhesive sheet provided by the adherend of the present invention may be, for example, an adhesive sheet having a metal layer such as an aluminum vapor-deposited film, or an adhesive sheet without a printed portion as described above.

[0155] [2-2] Adherent The adherend 50 is to which the adhesive label 10, which is an adhesive sheet according to the present invention, is attached.

[0156] The specific gravity of the adherend 50 to which the adhesive sheet 1 is attached should be greater than 1.0, but is preferably 1.1 or higher, more preferably 1.2 or higher, and even more preferably 1.3 or higher.

[0157] This makes it easier to increase the specific gravity difference between the adherend 50 and the sheet substrate 2, allowing for a more favorable recovery of the adherend 50 from which the sheet substrate 2 has peeled off.

[0158] The adherend 50 may be made of any material that satisfies the specific gravity conditions described above, but it is preferable that it be mainly composed of plastic material.

[0159] This allows for more favorable recycling of the adherend 50 from which the sheet substrate 2 has peeled off.

[0160] In this specification, "main component" refers to the component with the highest concentration in the target area. If there are multiple components with the highest concentration in the target area, all of them shall be considered main materials.

[0161] Examples of plastic materials constituting the adherend 50 include polyester resins such as polyethylene terephthalate (PET), polybutylene succinate, and polylactic acid, acrylic resins, acetate resins, acrylonitrile-butadiene-styrene copolymer (ABS) resins, polystyrene, polyvinyl chloride (PVC), polyamide, polyimide, polycarbonate, and cellulose acetate. However, it is preferable that the adherend 50 is composed of a material containing polyethylene terephthalate.

[0162] This makes it easier to ensure that the adherend 50 meets the specific gravity requirements mentioned above. Furthermore, it improves the adhesion between the adherend 50 and the adhesive layer 3, which is composed of a wash-off type adhesive, thereby improving the reliability of the adherend 100, and also allows for convenient separation from the adhesive layer 3 during recycling.

[0163] If the adherend 50 is made of a material containing polyethylene terephthalate, the polyethylene terephthalate content in the adherend 50 is preferably 70% by mass or more, more preferably 75% by mass or more, and even more preferably 80% by mass or more. This makes the aforementioned effects even more pronounced.

[0164] The adherend 50 is not particularly limited, but examples include various containers for holding various liquids and solids (including powders), gel materials, etc. More specifically, various containers for holding food and beverages, cosmetics, disinfectants, shampoos (including foam types), hand soaps (including foam types), body soaps (including foam types), conditioners, cosmetics, hair styling products, waxes, cleaning solutions, solvents, etc.

[0165] [3] Collection method Next, the recovery method of the present invention will be described.

[0166] The recovery method of this embodiment involves applying a liquid to the adhesive body 100, separating the adherend 50 and the sheet substrate 2 that constitute the adhesive body 100 in the liquid, and recovering at least the adherend 50.

[0167] This provides a method for recovering an adherend that allows for the effective peeling and separation of the adhesive sheet from the adherend.

[0168] Prior to applying the liquid to the adhesive 100, the adhesive 100 may, for example, be crushed into flakes.

[0169] The separated parts (for example, the adherend 50 separated from the sheet substrate 2, or the sheet substrate 2 separated from the adherend 50 and the coating layer 4) are further subjected to sorting, washing, and other processes to produce recycled resin material (recycled material).

[0170] Figure 4 is a cross-sectional view showing an example of the adhesive described in Figure 3 after an alkaline liquid has been applied to it.

[0171] By using an alkaline liquid as the aforementioned liquid, the adhesive layer 3, which is composed of a material containing a wash-off type adhesive, can be more preferably dissolved, and the adherend 50 can be more preferably separated from the sheet substrate 2. Furthermore, if a liquid-soluble wash-off type adhesive is used, and the coating layer 4 also satisfies the aforementioned conditions, the adhesive layer 3 and the coating layer 4 (the coating layer 4 on which the printed portion 5 is provided) can also be separated from the sheet substrate 2. As a result, not only the adherend 50 but also the sheet substrate 2 can be preferably recovered as a recyclable material.

[0172] On the other hand, the portion including the printed section 5 is not recyclable and is, for example, discarded. In the illustrated configuration, the coating layer 4 is separated from the sheet substrate 2, so the sheet substrate 2 is also recyclable. However, if the coating layer 4 is not separated from the sheet substrate 2, the sheet substrate 2 is also not recyclable and is, for example, discarded.

[0173] One method for applying the alkaline solution to the adhesive body 100 is an immersion method, in which the adhesive body 100 is immersed in the alkaline solution.

[0174] By employing the immersion method, the adhesive body 100 can be easily separated into multiple parts. This allows for improved efficiency in the recycling process.

[0175] When using the immersion method, it is preferable to stir the adhesive body 100 while it is immersed in the alkaline solution. This allows for more efficient separation of the adhesive body 100.

[0176] The alkaline solution is not particularly limited, but for example, an alkaline aqueous solution can be used. Examples of alkaline aqueous solutions include sodium hydroxide solution.

[0177] When an aqueous solution of sodium hydroxide is used as the alkaline solution, the concentration of sodium hydroxide is not particularly limited, but is preferably 0.1% by mass or more and 4.4% by mass or less, more preferably 0.5% by mass or more and 3.0% by mass or less, and even more preferably 1.0% by mass or more and 2.0% by mass or less. This allows for more efficient separation of the adhesive body 100.

[0178] The temperature of the alkaline solution applied to the adhesive body 100 is not particularly limited, but is preferably 95°C or lower, more preferably 90°C or lower, and even more preferably 60°C to 85°C. This allows for more efficient separation of the adhesive body 100.

[0179] The immersion time of the adhesive body 100 in the alkaline solution is not particularly limited, but is preferably 5 minutes or more and 60 minutes or less, more preferably 10 minutes or more and 50 minutes or less, and even more preferably 15 minutes or more and 45 minutes or less. This allows for more reliable separation of the adhesive body 100 into multiple parts.

[0180] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto.

[0181] For example, the adhesive sheet of the present invention may have other components besides the layers described above, such as an undercoat layer, an intermediate layer, or a surface protective layer.

[0182] Furthermore, although the above-described embodiment described an adhesive sheet having a coating layer, the adhesive sheet of the present invention does not necessarily have a coating layer.

[0183] Furthermore, for example, the adhesive body of the present invention may have other components besides the layers described above, such as an undercoat layer, an intermediate layer, or a surface protective layer.

[0184] Furthermore, for example, the recovery method of the present invention may include steps other than those described above, such as a pre-treatment step, an intermediate treatment step, and a post-treatment step. [Explanation of symbols]

[0185] 1: Adhesive sheet 2: Sheet base material 3: Adhesive layer 4: Coat layer 5: Printing department 10: Adhesive Labels 50: Adherent 100: Adhesive body

Claims

1. An adhesive sheet that is attached to a substrate with a specific gravity greater than 1.0, It comprises a sheet base material and an adhesive layer, The specific gravity of the aforementioned sheet substrate is less than 1.

0. An adhesive sheet characterized in that the adhesive layer is made of a material containing a wash-off type adhesive.

2. The specific gravity of the adherend is 1.1 or higher. The adhesive sheet according to claim 1, wherein the specific gravity of the sheet substrate is 0.97 or less.

3. The adhesive sheet according to claim 1, wherein the adherend is made of a material containing polyethylene terephthalate.

4. The adhesive sheet according to claim 1, wherein the sheet substrate is made of a material containing polypropylene.

5. The adhesive sheet according to claim 4, wherein the sheet substrate further comprises an inorganic filler.

6. The adhesive sheet according to claim 1, wherein the thickness of the adhesive layer is 5 μm or more and 100 μm or less.

7. The adhesive sheet according to claim 1, wherein the adhesive layer is made of a material containing an acrylic adhesive.

8. The adhesive sheet according to claim 1, wherein the adhesive sheet further has a coating layer on the side of the sheet substrate opposite to the side facing the adhesive layer.

9. An adhesive comprising a substrate having a specific gravity greater than 1.0 and an adhesive sheet according to any one of claims 1 to 8 attached to the substrate.

10. A recovery method characterized by applying a liquid to the adhesive described in claim 9, separating the adherend and the sheet substrate in the liquid, and recovering at least the adherend.

11. The recovery method according to claim 10, wherein the liquid is an alkaline liquid.

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