Pressure-sensitive adhesive label

Abstract

To provide a pressure-sensitive adhesive label such that, even when a polyester container is recycled without removing the pressure-sensitive adhesive label, the appearance of the resulting recycled resin changes little.SOLUTION: A pressure-sensitive adhesive label comprises a polyester resin base material and a polyester-based pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition. The pressure-sensitive adhesive composition contains a polyester-based pressure-sensitive adhesive having a glass transition temperature of -40°C or higher.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive label. [Background technology]

[0002] In recent years, there has been a strong demand for the recycling of polyester-based containers due to issues such as environmental pollution and the depletion of petroleum resources. Among polyester-based containers, there is a particular demand for the recycling of polyethylene terephthalate (PET) bottles.

[0003] In material recycling of polyester containers, after collecting used containers, they are crushed, washed and dried into flakes, which are then heated and melted to form pellets, and the resulting recycled resin is molded into new products.

[0004] Typically, polyester containers such as PET bottles have adhesive labels (also referred to as labels) affixed to their surfaces, carrying various pieces of information. When such labeled polyester containers, such as PET bottles, are recycled, if the resin substrate of the label is not compatible with the resin constituting the polyester container, the resin substrate and adhesive constituting the label act as foreign matter, resulting in a problem of reduced mechanical properties of the recycled resin. Therefore, when discarding labeled polyester containers, consumers are required to remove the labels from the polyester containers. If consumers have not removed the labels from the polyester containers, recycling companies remove the labels, then crush the polyester containers into flakes, heat-melt them, and recycle them. However, the process of removing labels from polyester containers is extremely cumbersome and time-consuming, and increases recycling processing costs, resulting in problems of both operational and economic disadvantages.

[0005] In this regard, for example, Patent Document 1 below discloses an adhesive label having a polyester resin substrate that is compatible with the polyester container to be adhered, and a polyester adhesive disposed on one side of the polyester resin substrate. With a label configured in this manner, the resin substrate and adhesive are made of the same materials as the polyester container, making it possible to recycle the label without removing it from the polyester container. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-10489 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, if the adhesive label is recycled without being removed, the adhesive label will be mixed into the resin derived from the polyester-based container. The resulting recycled resin is pelletized and recycled into other products. For this reason, it is desirable that the recycled resin have minimal changes in appearance even if the adhesive label is mixed in.

[0008] Therefore, an object of the present invention is to provide an adhesive label that causes little change in the appearance of the resulting recycled resin when recycled resin is produced by recycling polyester containers without removing the adhesive label. [Means for solving the problem]

[0009] In order to achieve the above object, an adhesive label according to the present invention is an adhesive label having a polyester-based resin substrate and a polyester-based adhesive layer formed from an adhesive composition, wherein the adhesive composition contains a polyester-based adhesive having a glass transition temperature of −40° C. or higher. [Effects of the Invention]

[0010] According to the adhesive label of the present invention, even if a polyester-based container is recycled without removing the adhesive label, the appearance of the resulting recycled resin changes little. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating a pressure-sensitive adhesive label according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention is an adhesive label having a polyester-based resin substrate and a polyester-based adhesive layer (hereinafter also simply referred to as adhesive layer) formed from an adhesive composition, wherein the adhesive composition contains a polyester-based adhesive having a glass transition temperature of −40° C. or higher.

[0013] According to the adhesive label of the present invention, even if a polyester-based container is recycled as resin without peeling off the adhesive label, there is little change in appearance compared to resin recycled from a container that does not contain an adhesive label.

[0014] The present inventors have discovered that recycling PET containers and the like without removing the adhesive can sometimes result in changes in the appearance of molded products made from recycled resin. One possible cause of this change in appearance is the pelletization process involved in producing recycled resin. This pelletization process requires the resin to be heated and melted, typically at temperatures above 250°C. Furthermore, the resulting pellets are also exposed to temperatures above 250°C when molded into products. The present inventors hypothesized that the change in appearance of recycled resins is due to the decomposition of the adhesive caused by exposure to temperatures above 250°C during pelletization and molding. Based on this hypothesis, extensive research led to the completion of the present invention.

[0015] The shape of the adhesive label is not particularly limited, but is generally rectangular when viewed from the stacking direction. The adhesive label may also have a triangular or circular shape. The polyester-based adhesive layer is disposed, for example, on the entire surface of the resin substrate.

[0016] Considering adhesion to substrates such as PET bottles, the adhesive strength of the adhesive label is preferably 3.5 N / 25 mm or more, more preferably 5 N / 25 mm or more, and even more preferably 6.5 N / 25 mm or more. There is no particular upper limit to the adhesive strength of the adhesive label, but it may be 30 N / 25 mm or less, or even 20 N / 25 mm or less. The adhesive strength to the substrate was measured by peeling the release liner from each adhesive label, attaching the adhesive layer to a polyethylene terephthalate plate in a 23°C, 50% RH environment (application conditions: one-way application with a 2 kg rubber roller), and peeling the sheet in a 180° direction at a test speed of 0.3 m / min using a tensile tester in accordance with JIS Z0237:2022. The numerical value is converted to the peel force per 25 mm of sheet width (N / 25 mm).

[0017] The configuration of the adhesive label will be described below with reference to Fig. 1. The dimensional proportions in the drawing are exaggerated for the sake of explanation and may differ from the actual proportions.

[0018] FIG. 1 is a schematic cross-sectional view of an adhesive label 10 according to the present invention. As shown in FIG. 1, the adhesive label 10 according to the embodiment of the present invention has, from top to bottom, a printed portion 13, a coating layer 14, a resin substrate 16, an adhesive layer 15, and a release liner 30. The release liner 30 is composed of a release agent layer 12 and a release substrate 11 arranged in this order. The coating layer 14 can be peeled from the resin substrate 16 by washing and immersing in an alkaline aqueous solution. This makes it possible to detach (peel) the printed portion 13 from the adhesive label 10. The detached printed portion 13 floats on the surface, making it easy to collect. The adhesive label 10 may have other functional layers, such as a primer layer, between the layers or on the surface.

[0019] The concept of "label" includes what are called films, sheets, tapes, etc.

[0020] Each component of the pressure-sensitive adhesive label will be described below. In the following description, a PET bottle will be used as an example of the adherend, but the adherend is not limited to this. In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and measurements of physical properties are carried out under conditions of room temperature (20 to 25°C) and a relative humidity of 45 to 55% RH.

[0021] <Resin substrate> It is necessary to use a polyester film, which is made of the same material as the PET bottle as the adherend and is compatible with it, as the resin substrate. That is, the resin substrate is a polyester-based resin substrate. In terms of the quality, such as the mechanical properties, of the recycled resin, it is particularly advantageous to use a resin substrate for the polyester film that has a composition similar to that of the resin used in the PET bottle. The polyester-based resin substrate is preferably a crystalline polyester film. Examples of resin substrates used in this polyester film include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. One or more of these may be appropriately selected and used depending on the type of resin used in the adherend PET bottle so as to obtain a resin substrate that is compatible with it.

[0022] Here, compatibility means that the material melts at the temperature at which the PET bottle is heated and melted, is well mixed with the resin base material of the melted PET bottle, and does not deteriorate the properties of the recycled product. If the resin base material of the PET bottle is a mixture of two or more compatible resins, one of the resins in the mixture that makes up the PET bottle can be used as the resin for the resin base material.

[0023] The thickness of the resin substrate is not particularly limited and can be appropriately selected depending on the application, but is generally preferably in the range of 25 to 100 μm. By making the resin substrate thicker than 25 μm, the adhesive label can be easily released from the release liner during the labeling process. Furthermore, by making the resin substrate thicker than 100 μm, the roll length installed in the labeling device can be sufficiently long, reducing the frequency of roll replacement and improving work efficiency. This resin substrate may be obtained by any of the conventionally known film-forming methods, such as extrusion, calendaring, solution coating, and casting.

[0024] In the present invention, the resin substrate may be subjected to a surface treatment on one or both sides as desired to improve adhesion to a coating layer formed thereon or to a polyester-based pressure-sensitive adhesive layer formed on the opposite side. Examples of such surface treatments include surface roughening treatments such as sandblasting or solvent treatment, or surface oxidation treatments such as corona discharge treatment, chromic acid treatment, flame treatment, hot air treatment, and ozone / ultraviolet irradiation treatment.

[0025] In the present invention, a coating layer (print-receiving layer) having printability may be provided on one side of the resin substrate. As a result, printability is imparted to one side of the resin substrate. This coating layer prevents the occurrence of voids during printing due to protrusions (fisheyes) caused by undissolved resin parts mixed into the resin substrate during film formation, and also has the effect of improving the adhesion of printing ink.

[0026] <Polyester-based adhesive layer> Next, the polyester-based pressure-sensitive adhesive layer will be described. The polyester-based pressure-sensitive adhesive layer is formed from a pressure-sensitive adhesive composition containing a polyester-based pressure-sensitive adhesive (polyester-based resin).

[0027] The polyester-based pressure-sensitive adhesive used in the present invention can be obtained by copolymerizing copolymerization components containing a polycarboxylic acid component (A1) and a polyol component (A2) as constituent raw materials.

[0028] [Polycarboxylic acid component (A1)] Examples of the polyvalent carboxylic acid component (A1) used in the present invention include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, benzylmalonic acid, diphenic acid, 4,4'-oxydibenzoic acid, and naphthalenedicarboxylic acid; aliphatic dicarboxylic acids such as malonic acid, dimethylmalonic acid, succinic acid, glutaric acid, adipic acid, trimethyladipic acid, pimelic acid, 2,2-dimethylglutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, thiodipropionic acid, and diglycolic acid; and alicyclic dicarboxylic acids such as 1,3-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2,5-norbornanedicarboxylic acid, and adamantanedicarboxylic acid. These may be used alone or in combination of two or more.

[0029] Among these, it is preferable to contain an aromatic dicarboxylic acid in order to impart cohesive strength.

[0030] The content of such aromatic dicarboxylic acid is preferably 5 to 100 mol% based on the entire polycarboxylic acid component (A1). The glass transition temperature of the polyester-based pressure-sensitive adhesive can be increased by increasing the content of aromatic dicarboxylic acid. In this regard, the content of aromatic dicarboxylic acid is preferably more than 30 mol%, more preferably more than 40 mol%, and may even be more than 50 mol% based on the entire polycarboxylic acid component (A1). The glass transition temperature can be controlled to a higher value by, for example, lengthening the alkylene moiety of the aliphatic diol or using a branched alcohol as the polyol.

[0031] In order to impart tackiness, it is preferable that the composition contains an aliphatic dicarboxylic acid, and it is particularly preferable that the composition contains an aliphatic dicarboxylic acid having 4 to 12 carbon atoms.

[0032] The content of such aliphatic dicarboxylic acid is preferably 5 mol % or more, and particularly preferably 5 mol % or more and less than 70 mol %, based on the entire polybasic carboxylic acid component (A1).

[0033] In the present invention, from the viewpoint of a balance of adhesive properties, it is preferable to use an aromatic dicarboxylic acid and an aliphatic dicarboxylic acid in combination as the polycarboxylic acid component (A1), and the content ratio (molar ratio) of aromatic dicarboxylic acid / aliphatic dicarboxylic acid is preferably from 1 / 99 to 90 / 10.

[0034] Furthermore, trivalent or higher polycarboxylic acids can be used to increase the number of branching points in the polyester-based pressure-sensitive adhesive. Examples of such trivalent or higher polycarboxylic acids include trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, and trimesic acid. Of these, trimellitic acid is preferred because it is relatively less likely to cause gelation. The content of such trivalent or higher polycarboxylic acids is preferably 10 mol % or less, particularly preferably 0.1 to 5 mol %, based on the total polycarboxylic acid component (A1), in order to increase the cohesive strength of the pressure-sensitive adhesive. If the content is too high, gelation tends to occur easily during the production of the polyester-based pressure-sensitive adhesive.

[0035] [Polyol component (A2)] Examples of the polyol component (A2) used in the present invention include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2,2 and dihydric alcohols such as aliphatic diols such as 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; and aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and their ethylene oxide and propylene oxide adducts. These may be used alone or in combination of two or more.

[0036] Among these, aliphatic diols and alicyclic diols are preferred because of their excellent reactivity. Particularly preferred aliphatic diols include ethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, and particularly preferred alicyclic diols include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol.

[0037] Furthermore, trihydric or higher polyhydric alcohols can be used to increase the number of branching points in the polyester-based pressure-sensitive adhesive, and examples of trihydric or higher polyhydric alcohols include pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, adamantanetriol, etc. The content of such trihydric or higher polyhydric alcohols is preferably 10 mol % or less, particularly preferably 0.1 to 5 mol %, based on the total polyol component (A2); if the content is too high, production of the polyester-based pressure-sensitive adhesive tends to be difficult.

[0038] The blending ratio of the polycarboxylic acid component (A1) and the polyol component (A2) is preferably 1 to 2 equivalents, particularly preferably 1.1 to 1.7 equivalents, of the polyol component (A2) per equivalent of the polycarboxylic acid component (A1).

[0039] The polyester-based adhesive used in the present invention is produced by arbitrarily selecting the polycarboxylic acid component (A1) and the polyol component (A2) and subjecting them to a polycondensation reaction in the presence of a catalyst by a known method.

[0040] The number average molecular weight of the polyester adhesive used in the present invention is preferably 5,000 to 150,000, particularly preferably 10,000 to 100,000, and further preferably 15,000 to 100,000, from the viewpoints of cohesive strength, heat resistance, mechanical strength, adhesiveness, and the like.

[0041] The number-average molecular weight is the number-average molecular weight converted into the molecular weight of standard polystyrene, and is measured using a high-performance liquid chromatograph (manufactured by Tosoh Corporation, "HLC-8320GPC") with one "TSK guard column super HH" column, two "TSK gel super HM-H" columns in series, and one "TSK gel super H2000" column.

[0042] The glass transition temperature (Tg) of the polyester-based pressure-sensitive adhesive is -40°C or higher. When the glass transition temperature of the polyester-based pressure-sensitive adhesive is -40°C or higher, increases in haze and yellowness caused by the pressure-sensitive adhesive can be suppressed. From the viewpoint of adhesive properties, the glass transition temperature of the polyester-based pressure-sensitive adhesive is preferably 10°C or lower. The glass transition temperature (Tg) is preferably -30 to 10°C, and more preferably -25 to 10°C. The glass transition temperature (Tg) is a value measured using a differential scanning calorimeter (DSC) in a measurement temperature range of -90 to 100°C and at a temperature rise rate of 10°C / min.

[0043] The mass loss rate of the polyester-based pressure-sensitive adhesive at 290°C is preferably 3.0% or less, more preferably 2.5% or less, even more preferably 2.0% or less, and even more preferably 1.5% or less. Such a polyester-based pressure-sensitive adhesive is less likely to decompose and has little change in appearance even when exposed to high temperatures of 250°C or more during pelletization or molding. The mass loss rate at 290°C is a value measured by the method described below.

[0044] The thermal decomposition starting temperature of the polyester-based pressure-sensitive adhesive is preferably 250° C. or higher, and more preferably 275° C. or higher. The thermal decomposition starting temperature is a value measured by the method described below.

[0045] The mass loss rate and thermal decomposition onset temperature were measured as follows. A differential thermal and thermogravimetric simultaneous analyzer (Shimadzu Corporation, product name "DTG-60") was used, and measurements were performed in accordance with JIS K7120:1987. Specifically, using nitrogen as the inlet gas, thermogravimetric measurements were performed by raising the temperature from 40°C to 500°C at a heating rate of 10°C / min. From the resulting thermogravimetric curve, the temperature at which the mass decreases by 1% relative to the mass at 40°C was determined as the thermal decomposition onset temperature. Furthermore, the mass loss rate at 290°C was calculated, with the mass at 40°C being taken as 100%.

[0046] The acid value of the polyester-based pressure-sensitive adhesive is preferably 10 mgKOH / g or less, more preferably 3 mgKOH / g or less, and even more preferably 1.5 mgKOH / g or less. When the acid value is within the above range, hydrolysis is suppressed and cohesive strength is easily maintained.

[0047] The hydroxyl value of the polyester-based pressure-sensitive adhesive is preferably 1 to 50 mgKOH / g, more preferably 1 to 30 mgKOH / g, even more preferably 1 to 20 mgKOH / g, and particularly preferably 2 to 15 mgKOH / g. When the hydroxyl value is within this range, the effects of the present invention are more easily achieved.

[0048] The acid value and hydroxyl value of the polyester-based pressure-sensitive adhesive are determined by neutralization titration in accordance with JIS K 0070:1992.

[0049] The polyester-based pressure-sensitive adhesive may be any of an emulsion type, a solvent type, and a solventless type.

[0050] From the viewpoint of adhesiveness, the content of the polyester-based pressure-sensitive adhesive is preferably 80% by mass or more, more preferably 90% by mass or more, in terms of solid content in the pressure-sensitive adhesive composition. The content of the polyester-based pressure-sensitive adhesive is appropriately adjusted by the amount of crosslinking agent added, and is, for example, 99% by mass or less, in terms of solid content in the pressure-sensitive adhesive composition.

[0051] The pressure-sensitive adhesive composition may contain a crosslinking agent. Typically, a crosslinking agent is used to crosslink the polyester resin, resulting in excellent cohesive strength and excellent performance as a pressure-sensitive adhesive. Examples of such crosslinking agents include polyisocyanate compounds (isocyanate-based crosslinking agents) and polyepoxy compounds, which are compounds having functional groups that react with the hydroxyl and / or carboxyl groups contained in the polyester resin. Among these, polyisocyanate compounds are particularly preferred because they can achieve a good balance between initial adhesion, mechanical strength, and heat resistance.

[0052] Examples of such polyisocyanate compounds include polyisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, and hydrogenated xylylene diisocyanate, as well as isocyanate adducts such as a tolylene diisocyanate adduct of trimethylolpropane, a hexamethylene diisocyanate adduct, and an isophorone diisocyanate adduct. The above polyisocyanate compounds may also be used in which the isocyanate moiety is blocked with phenol, lactam, or the like. These crosslinking agents may be used alone or in combination of two or more.

[0053] The amount of the crosslinking agent to be added can be appropriately selected depending on the molecular weight of the polyester resin and the intended use, but in general, taking into consideration adhesiveness and the like, it is preferably 0.5 to 5 parts by mass per 100 parts by mass of the polyester resin.

[0054] The polyester-based pressure-sensitive adhesive composition may contain conventionally known additives such as hydrolysis inhibitors, softeners, ultraviolet absorbers, stabilizers, antistatic agents, and tackifiers, as well as other powdery or particulate additives such as inorganic or organic fillers, metal powders, and pigments, within the range that does not impair the effects of the present invention.

[0055] The polyester-based pressure-sensitive adhesive composition may be prepared by dissolving or suspending the above-mentioned materials constituting the pressure-sensitive adhesive layer in a suitable solvent, such as esters such as ethyl acetate and butyl acetate; ketones such as methyl isobutyl ketone, methyl ethyl ketone and cyclohexanone; and aromatic hydrocarbons such as toluene and xylene.

[0056] The method for forming the polyester-based pressure-sensitive adhesive layer is not particularly limited, but the polyester-based pressure-sensitive adhesive layer may be formed by directly coating the pressure-sensitive adhesive composition on a resin substrate, or the polyester-based pressure-sensitive adhesive layer may be formed on a release liner and then laminated to the resin substrate. Specifically, a method may be used in which the pressure-sensitive adhesive composition is coated on a release liner and dried, and the polyester-based pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition is transferred onto the resin substrate.

[0057] The method for applying the pressure-sensitive adhesive composition to the substrate or release liner is not particularly limited, and the composition can be applied using a known coating device such as a roll coater, knife coater, air knife coater, bar coater, blade coater, slot die coater, lip coater, gravure coater, etc. Drying conditions are not particularly limited, and the drying is usually performed at 60 to 150°C for 10 to 90 seconds.

[0058] The thickness of the pressure-sensitive adhesive layer (film thickness after drying) is usually 5 to 100 μm, preferably 10 to 50 μm.

[0059] <Print section> The printed portion 13 is a layer for displaying information, and is an optional layer in the present invention. There are no particular limitations on how the printed portion 13 is formed, and it can be formed by, for example, flexographic printing, offset printing, relief printing, gravure printing, screen printing, thermal transfer, or the like.

[0060] The information displayed on the printed portion may be, for example, letters, numbers, illustrations, photographs, graphs, or a combination thereof.

[0061] <Coating layer> The coating layer 14 is a layer that can be peeled off from the resin substrate 16 by washing and immersion in an alkaline aqueous solution, and is an optional layer in the present invention. The material constituting the coating layer is not particularly limited, as long as it has good adhesion to the polyester film resin substrate and can be easily peeled off from the polyester film by washing and immersion in an alkaline aqueous solution. A preferred configuration is one in which a (water-based) polyester resin is used as the anchor layer and a (solvent-based) polyester urethane resin (print-receiving layer) is used on top of that layer. This configuration improves printability and allows the coating layer to be peeled off from the anchor layer by an alkaline aqueous solution. Examples of polyester resins for the anchor layer of the coating layer include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. The use of a water-based polyester resin is particularly desirable. "Water-based" here means aqueous, e.g., water-soluble, water-dispersible, or water-suspendable.

[0062] The thickness of the coating layer is, for example, 0.2 to 30 μm.

[0063] The method for coating the resin substrate with the above material is not particularly limited, and any conventionally known method such as bar coating, knife coating, roll coating, blade coating, die coating, or curtain coating can be used.

[0064] <Release liner> As shown in FIG. 1, the release liner 30 has a release substrate 11 and a release agent layer 12.

[0065] The material of the release substrate 11 is not particularly limited, and known materials can be used. Examples include resin materials and paper. Examples of resin materials include polyester and polyolefin. Examples of paper include kraft paper, high-quality paper, glassine paper, and laminated paper laminated with a thermoplastic resin such as polyethylene.

[0066] The thickness of the release liner 30 is preferably 25 μm or more and 100 μm or less. By making the thickness of the release liner 30 25 μm or more, the adhesive label 10 (20) has excellent suitability for punching. Furthermore, by making the thickness of the release liner 30 100 μm or less, the release liner 30 has excellent releasability from the adhesive layer 15 during the labeling process.

[0067] Examples of the release agent constituting the release agent layer 12 include silicone-based release agents, long-chain alkyl-based release agents, fluorine-based release agents, and rubber-based release agents. Among these, silicone-based release agents are preferred. The thickness of the release agent layer is usually about 0.01 to 5 μm.

[0068] <Polyester-based containers> The adhesive label is preferably affixed to a polyester-based container such as a polyethylene terephthalate (PET) bottle. The present invention also provides a polyester-based container having the above-mentioned adhesive label affixed thereto. The polyester-based container refers to a container made of a polyester-based resin. Examples of polyester-based resins include polyethylene terephthalate. The container can be manufactured by subjecting the polyester-based resin to injection molding, vacuum forming, pressure forming, or the like.

[0069] The present invention also includes the following aspects.

[0070] (1) An adhesive label having a polyester-based resin substrate and a polyester-based adhesive layer formed from an adhesive composition, the adhesive composition including a polyester-based adhesive having a glass transition temperature of −40° C. or higher.

[0071] (2) The adhesive label according to (1), wherein the glass transition temperature is 10°C or lower.

[0072] (3) The adhesive label according to (1) or (2), which has an alkali-peelable coating layer on a resin substrate opposite the adhesive layer.

[0073] (4) The adhesive label according to any one of (1) to (3), which is an adhesive label to be attached to a polyester-based container.

[0074] (5) A polyester-based container having the adhesive label according to any one of (1) to (4) attached thereto. [Example]

[0075] Next, the examples will be described. In the examples, the units "parts" or "%" may be used, but unless otherwise specified, they represent "parts by mass" or "% by mass." Furthermore, unless otherwise specified, each operation is carried out at room temperature (25°C).

[0076] Example 1 A polyester-based adhesive composition was prepared by adding and mixing 2 parts by mass (solid content) of an isocyanate-based crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate HL") and 40 parts by mass of ethyl acetate to 100 parts by mass (solid content) of a polyester-based resin (polyester-based adhesive) (manufactured by Mitsubishi Chemical Corporation, trade name "Nichigo Polyester NP-120S45EO", glass transition temperature -25°C, solid content 45%).

[0077] The obtained polyester-based pressure-sensitive adhesive composition was applied using a knife coater onto a release liner (thickness: 88 μm) made of polyethylene-laminated glassine paper coated with a silicone-based release agent so that the film thickness after drying would be 20 μm, and then dried at 90°C for 1 minute to form a polyester-based pressure-sensitive adhesive layer.

[0078] A 50 μm thick crystalline polyethylene terephthalate film was attached onto the adhesive layer to obtain the adhesive label of Example 1.

[0079] Example 2 An adhesive label was obtained in the same manner as in Example 1, except that a polyester-based resin (manufactured by Mitsubishi Chemical Corporation, product name "Nichigo Polyester LP-050S50TO", glass transition temperature 10°C, solid content 50%) was used as the polyester-based resin.

[0080] (Comparative Example 1) An adhesive label was obtained in the same manner as in Example 1, except that a polyester-based resin (manufactured by Mitsubishi Chemical Corporation, product name "Nichigo Polyester NP-110S50EO", glass transition temperature -50°C, solid content 50%) was used as the polyester-based resin.

[0081] (Evaluation method) For adhesive labels, the release liner was removed from the small pieces of label, and 5% of the label was added to recycled PET resin derived from PET bottles and mixed. The mixture was heated to a temperature of 240-260°C in a twin-screw kneading extruder, melted, and then pelletized. The pellets were then molded into 1mm-thick plates at a temperature of 280-290°C in an air-pressure injection molding machine.

[0082] In addition, a plate was formed in the same manner using recycled PET resin without any adhesive labels mixed in (control).

[0083] The haze and yellowness of the resulting plate were measured according to the following measurement methods. (1) Haze measurement The haze value was measured using a haze meter (NDH-5000 manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7136:2000. (2) Measurement of b* value The b* value was determined using a color difference meter (SE6000 manufactured by Nippon Denshoku Industries Co., Ltd.) by the transmission method based on JIS Z8781-4:2013.

[0084] The difference compared to a control without the adhesive label mixed in is shown in the table below.

[0085] [Table 1]

[0086] From the above results, it can be seen that the adhesive labels of the examples, even when mixed with recycled PET resin, showed less change in haze and b* than when not mixed. [Explanation of symbols]

[0087] 10 adhesive labels, 11 Resin substrate, 12 release agent layer, 13 Printing Department, 14 coat layers, 15 adhesive layer, 16 peeling substrate, 30 release liners.

Claims

1. The film has a polyester resin substrate and a polyester pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive composition, The adhesive composition of the adhesive label contains a polyester-based adhesive having a glass transition temperature of −40° C. or higher.

2. The adhesive label according to claim 1 , wherein the glass transition temperature is 10° C. or lower.

3. 3. The adhesive label according to claim 1, further comprising an alkali-peelable coating layer on a resin substrate opposite the adhesive layer.

4. The adhesive label according to claim 1 or 2, which is an adhesive label to be attached to a polyester-based container.

5. A polyester-based container having the adhesive label according to claim 1 or 2 attached thereto.

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