Polyolefin resin containers

Abstract

The present invention provides a polyolefin resin container that is recyclable without removing the adhesive label and has an excellent appearance for recycled products. [Solution] A polyolefin resin container having an adhesive label attached to it, wherein the adhesive label has a polyolefin resin base material and an adhesive layer, and the adhesive layer comprises a styrene block copolymer and a tackifying resin.

Description

[Technical Field]

[0001] This invention relates to a polyolefin resin container. [Background technology]

[0002] Polyolefin resins are used in many hollow molded products due to their excellent rigidity and moldability (for example, Patent Document 1).

[0003] In recent years, due to environmental pollution and the depletion of petroleum resources, there has been a strong demand for the recycling of containers. In material recycling of containers, the container is usually crushed into flakes, then heated and melted to homogenize the whole, and the resulting recycled resin is used as the material for new containers.

[0004] Typically, containers have adhesive labels (also called labels) attached to their surface, which have an information section on which various information is recorded. When recycling such labeled containers, if the resin base material of the label and the resin that makes up the container are not compatible, the resin base material of the label acts as a foreign substance, resulting in a problem where the mechanical properties of the recycled resin deteriorate. Therefore, in such cases, it is necessary to physically remove the label attached to the polyolefin resin container using equipment, then crush it into flakes, and heat melt it. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-179015 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the process of physically removing labels from containers using equipment is extremely complicated and time-consuming, and also results in high recycling costs, making it disadvantageous both operationally and economically.

[0007] Therefore, it is required that polyolefin resin containers be recycled without removing the labels attached to them. During such recycling, it is also required that the appearance of the recycled resin remains unchanged.

[0008] The present invention aims to provide a polyolefin resin container that is recyclable without removing the adhesive label and has an excellent appearance as a recycled product. [Means for solving the problem]

[0009] One embodiment of the present invention for achieving the above objective is a polyolefin resin container to which an adhesive label is attached, wherein the adhesive label has a polyolefin resin base material and an adhesive layer, and the adhesive layer comprises a styrene block copolymer and a tackifying resin. [Effects of the Invention]

[0010] According to the polyolefin resin container of the present invention, the adhesive label can be recycled without being removed from the container, and the recycled product has an excellent appearance. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the external appearance of a polyolefin resin container according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing a polyolefin resin container according to one embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view showing a polyolefin resin container according to another embodiment of the present invention. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of description, and may differ from the actual ratios.

[0013] In the present specification, "X to Y" indicating a range means "from X to Y inclusive". Unless otherwise specified, operations, measurements of physical properties and the like are performed under the conditions of room temperature (20 to 25°C) / relative humidity of 45 to 55% RH. In addition, "(meth)acrylate" refers to "acrylate" and "methacrylate", and "(meth)acrylic acid" refers to "acrylic acid" and "methacrylic acid". Further, the pressure-sensitive adhesive label for polyolefin resin containers of the present invention may also be simply referred to as a pressure-sensitive adhesive label.

[0014] Hereinafter, the configurations of a polyolefin resin container and a pressure-sensitive adhesive label attached thereto will be described with reference to the drawings.

[0015] Fig. 1 is a schematic external view of a polyolefin resin container according to an embodiment of the present invention. The container in Fig. 1 is a dispenser bottle 100 made of polyolefin resin. A pressure-sensitive adhesive label 10 is attached to the dispenser bottle 100.

[0016] Fig. 2 is a schematic cross-sectional view of the pressure-sensitive adhesive label 10. As shown in Fig. 2, the pressure-sensitive adhesive label 10 according to an embodiment of the present invention comprises, in order from the top, a display layer 11, a release coating layer 12, a polyolefin resin base material (hereinafter also simply referred to as a resin base material) 13, and a pressure-sensitive adhesive layer 14. When the release coating layer 12 comes into contact with an alkaline aqueous solution, it decomposes, dissolves or swells, thereby detaching (peeling) the display layer 11 from the pressure-sensitive adhesive label 10. That is, the release coating layer 12 can be detached from the resin base material 13 by an alkaline aqueous solution. Here, the alkaline aqueous solution is, for example, a 1.5 mass% sodium hydroxide aqueous solution at 70°C (pH 13.6). As a result, the detached display layer 11 floats on the liquid surface, facilitating recovery. The pressure-sensitive adhesive label 10 may also have other functional layers such as a primer layer between respective layers or on the surface.

[0017] Further, a form in which no release coat layer is provided between the resin base material 13 and the pressure-sensitive adhesive layer 14 is preferable. In one preferred embodiment, the resin base material 13 and the pressure-sensitive adhesive layer 14 are adjacent to each other. In another preferred embodiment, the lower layer of the release coat layer 12 consists only of the resin base material 13 and the pressure-sensitive adhesive layer 14.

[0018] In a preferred embodiment, the resin base material and the pressure-sensitive adhesive layer remain on the polyolefin resin container even after a treatment with alkaline water (alkali treatment) for peeling off the display portion. Specifically, it is preferable that the resin base material does not detach from the polyolefin resin container after being immersed in an aqueous sodium hydroxide solution having a pH of 13.6 at 70°C for 15 minutes. Since the resin base material remains on the polyolefin resin container even after the alkaline water treatment, recycling of the resin base material can be performed collectively with recycling of the polyolefin resin container. From the perspective of environmental impact, recycling of the resin base material without discarding it is also required. If the resin base material peels off from the container after the alkali treatment, it is necessary to collect and recycle the resin base material separately from the container in order to recycle the resin base material. According to the present embodiment, recycling of the resin base material can be performed collectively with recycling of the polyolefin resin container, so that work efficiency is significantly improved. In addition, since the pressure-sensitive adhesive layer does not dissolve or peel off in alkaline water, the pressure-sensitive adhesive layer can also be recycled together, further reducing environmental impact. Further, according to the resin base material and the pressure-sensitive adhesive layer of the present embodiment, even when processed into pellets or the like for recycling together with the resin container, coloration is suppressed, and an increase in haze is also suppressed.

[0019] Figure 3 is a schematic cross-sectional view of an adhesive label 20 according to another embodiment. In the adhesive label 20, there is an alkali-insoluble coating layer 15 between the display portion 11 and the detachable coating layer 12. That is, the alkali-insoluble coating layer 15 is located on the detachable coating layer 12 opposite the polyolefin resin substrate 13. When peeled off with alkali, the alkali-insoluble coating layer 15 does not dissolve or swell and remains as resin, so it is detached as a film together with the display portion 11 above. In other words, the display portion does not break into small pieces and maintains a certain size, making it easy to recover. Here, "on the detachable coating layer" does not only mean that the detachable coating layer and the alkali-insoluble coating layer are adjacent to each other, but there may also be other layers between the detachable coating layer and the alkali-insoluble coating layer. The preferred configuration is that the detachable coating layer and the alkali-insoluble coating layer are adjacent to each other.

[0020] Polyolefin resin containers are containers made from polyolefin resins such as polyethylene and polypropylene. Specifically, examples include resin containers for body soap, shampoo bottles, and dish soap. Resin containers can be manufactured by injection molding, vacuum molding, compression molding, etc., of polyolefin resins. A container is an outer casing containing contents, and is not limited to molded bodies; it also includes packaging materials.

[0021] While there are no particular limitations on the shape of the adhesive label, it is generally rectangular when viewed from the stacking direction. However, the adhesive label may also be triangular or circular in shape.

[0022] The mass of the adhesive label is preferably 10% by mass or less of the mass obtained by subtracting the adhesive label from the polyolefin resin container, and more preferably 5% by mass or less. By keeping the mass of the adhesive label below the above upper limit, discoloration and haze increase are suppressed even when processed into recycled products such as pellets for recycling together with the resin container. The mass of the adhesive label may be 0.05% by mass or more and 10% by mass or less, 0.1% by mass or more and 8% by mass or less, 0.1% by mass or more and 5% by mass or less, or 1% by mass or more and 5% by mass or less of the mass obtained by subtracting the adhesive label from the polyolefin resin container. Since the purpose of the adhesive label is to provide information, it has to be of a certain size or larger. In order to ensure that the polyolefin resin container is recycled well while maintaining a certain size or larger for the label, it is preferable that the mass of the adhesive label be within the above range.

[0023] The adhesive strength of the adhesive label is preferably 1.5 N / 25 mm or more, more preferably 3 N / 25 mm or more, and even more preferably 6.5 N / 25 mm or more, considering its adhesion to polyolefin resin containers. Furthermore, while there is no particular upper limit for the adhesive strength of the adhesive label, it may be 30 N / 25 mm or less, or 20 N / 25 mm or less. The adhesive strength to the substrate is measured by attaching the adhesive layer surface of the adhesive label to a polypropylene board and, after 24 hours, using a tensile testing machine in the 180° direction at a test speed of 0.3 m / min, according to JIS Z0237:2009. More specifically, the adhesive strength to the substrate is the value measured by the following method: an adhesive label with a release liner is left to stand for 24 hours in a standard environment (23°C, 50% RH), the release liner is peeled off, and the adhesive layer surface is attached to a polypropylene board. After standing in a standard environment for 24 hours, the adhesive strength is measured according to JIS Z0237:2009. Specifically, the adhesive label is peeled off in a 180° direction at a test speed of 0.3 m / min using a tensile testing machine, and the adhesive strength is measured. The value is converted to the peeling force per 25 mm of film width (N / 25 mm).

[0024] The surface area of ​​the adhesive label is 1 cm². 2Preferably, the surface area of ​​the adhesive label is 1 cm². 2 As a result, the adhesive label can be labeled with the minimum necessary information that should be conveyed to consumers, such as product information and recycling information. Furthermore, the surface area of ​​the adhesive label varies depending on the size of the container, but for example, 100 cm² 2 Preferably, the surface area of ​​the adhesive label is 100 cm². 2 The following conditions can suppress the increase in discoloration and haze.

[0025] The concept of "label" encompasses things like film, sheets, and tape.

[0026] The following describes each component that makes up an adhesive label.

[0027] <Display> The display section is a layer for displaying information, and in this invention, it is any layer. How the display section is formed is not particularly limited, and it can be formed by printing methods such as letterpress, flexographic printing, offset printing, relief printing, gravure printing, and screen printing.

[0028] The information displayed on the display unit may include, for example, letters, numbers, symbols, illustrations, photographs, graphs, barcodes, two-dimensional codes such as QR codes (registered trademarks), or combinations thereof.

[0029] <Alkali-insoluble coating layer> The alkali-insoluble coating layer is positioned beneath the display area. During alkali peeling, it remains as resin without dissolving or swelling, allowing the display area to detach as a film and be easily recovered. For this reason, it is preferable to position the alkali-insoluble coating layer on the display area surface (printed surface).

[0030] The alkali-insoluble coating layer is mainly composed of resin. Here, "main component" means that it is present in the alkali-insoluble coating layer at a concentration of 60% by mass or more (up to 100% by mass). The resin is alkali-insoluble. Here, alkali-insoluble means, for example, that its solubility in a 1.5% by mass aqueous sodium hydroxide solution at 70°C (pH 13.6) is 20% by mass or less (lower limit 0% by mass), preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably 1% by mass or less. Furthermore, it is preferable that the resin is alkali-non-swelling. Alkali-non-swelling means, for example, that the rate of weight change when immersed in a 1.5% by mass aqueous sodium hydroxide solution at 70°C (pH 13.6) for 15 minutes is less than 200%.

[0031] Examples of resins that form the alkali-insoluble coating layer include urethane-modified polyester resins, acrylic ester (co)polymers, epoxy resins, and polyamide resins. Among these, urethane-modified polyester resin is preferred as the resin that forms the alkali-insoluble coating layer because it provides high print adhesion. Furthermore, since the resin that forms the alkali-insoluble coating layer has reduced solubility in alkaline water, it is preferable that its acid value be 3 mg KOH / g or less, and more preferably 2 mg KOH / g or less.

[0032] Specific examples of urethane-modified polyester resins include polymers (polyester urethanes) obtained by reacting various polyisocyanate compounds with a polyester polyol having a hydroxyl group at the end of a polymer obtained by condensation polymerization of a polyol and a carboxylic acid component.

[0033] Examples of polyisocyanate compounds include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate.

[0034] The number-average molecular weight (Mn) of the urethane-modified polyester resin is preferably 2,000 to 100,000, and more preferably 5,000 to 50,000. Here, the number-average molecular weight (Mn) is the number-average molecular weight on a polystyrene basis, measured by gel permeation chromatography (GPC).

[0035] The glass transition temperature (Tg) of the urethane-modified polyester resin is preferably 100°C or lower, and more preferably -40 to 100°C.

[0036] Commercially available urethane-modified polyester resins may be used. Examples of commercially available products include the Byron series (product name): manufactured by Toyobo MC Co., Ltd., and preferably Byron UR-1400 (hydroxyl value 2-3, acid value less than 1, number average molecular weight 40,000, Tg 83℃), Byron UR-8300 (hydroxyl value 3-4, acid value less than 1, number average molecular weight 30,000, Tg 23℃), and Byron UR-6100 (hydroxyl value 4-6, acid value less than 1, number average molecular weight 25,000, Tg -30℃).

[0037] In the alkali-insoluble coating layer, the resin content is preferably 80 to 100% by mass, and more preferably 90 to 99% by mass.

[0038] The resin contained in the alkali-insoluble coating layer is preferably a crosslinked resin. This is preferable because the solubility in alkaline aqueous solutions is further reduced. To make the resin a crosslinked resin, a crosslinking agent can be included in the alkali-insoluble coating layer forming composition for forming the alkali-insoluble coating layer. In this case, a crosslinking agent that reacts with the crosslinkable reactive groups in the resin is appropriately selected. In particular, selecting a crosslinking agent that reacts with hydroxyl groups and / or carboxyl groups, which are crosslinkable reactive groups, is preferable because it allows the resin to be crosslinked, further reducing its solubility in alkaline aqueous solutions.

[0039] Crosslinking agents that can react with crosslinkable reactive groups (preferably hydroxyl groups and / or carboxyl groups) include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, and metal chelate-based crosslinking agents.

[0040] Examples of isocyanate crosslinking agents include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, 2,6-diisocyanate methyl capeate, lysine diisocyanate, lysine ester triisocyanate, and 1,6,11-undecane triisocyanate. Examples include polyisocyanate compounds such as aliphatic diisocyanates like 1,3,6-hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and decamethylene diisocyanate; aromatic diisocyanates like tolylene diisocyanate and xylylene diisocyanate; and alicyclic diisocyanates like isophorone diisocyanate; as well as isocyanate derivatives such as adducts of polyisocyanate compounds with polyol compounds like trimethylolpropane, biuret and isocyanurate forms of polyisocyanate compounds, and difunctional forms of polyisocyanate compounds.

[0041] Examples of epoxy crosslinking agents include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, ethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, and diglycidylamine.

[0042] Examples of aziridine crosslinking agents include diphenylmethane-4,4'-bis(1-aziridine). Examples include lysine carboxamide, trimethylolpropane tri-β-aziridinyl propionate, tetramethylolmethane tri-β-aziridinyl propionate, toluene-2,4-bis(1-aziridine carboxamide), triethylene melamine, bisisophthaloyl-1-(2-methylaziridine), tris-1-(2-methylaziridine)phosphine, and trimethylolpropane tri-β-(2-methylaziridine)propionate.

[0043] Metal chelating crosslinking agents include chelating compounds of metal atoms such as aluminum, zirconium, titanium, zinc, iron, and tin, but aluminum chelating compounds are preferred in terms of performance. Examples of aluminum chelating compounds include diisopropoxyaluminum monooleyl acetate, monoisopropoxyaluminum bisoleyl acetate, monoisopropoxyaluminum monooleate monoethyl acetate, diisopropoxyaluminum monolauryl acetate, diisopropoxyaluminum monostearyl acetate, and diisopropoxyaluminum monoisostearyl acetate.

[0044] In particular, it is preferable that the crosslinking agent be an isocyanate-based crosslinking agent because it provides high print adhesion in the coated layer after crosslinking.

[0045] The above crosslinking agents may be used individually or in combination of two or more.

[0046] The amount of crosslinking agent added is set appropriately considering the amount of crosslinkable reactive groups in the resin, but it is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of resin.

[0047] The thickness of the alkali-insoluble coating layer is preferably 0.05 to 1 μm, and more preferably 0.05 to 0.5 μm, considering the ease of retrieval of the display portion and its thin film properties.

[0048] The alkali-insoluble coating layer may contain additives such as catalysts, UV absorbers, pigments, and fillers.

[0049] <Detachable coating layer> The detachable coating layer allows the display area (and the alkali-insoluble coating layer) to be peeled off from the resin substrate by washing and immersion in an alkaline aqueous solution (alkaline immersion). In other words, the detachable coating layer is alkali-peelable.

[0050] The desorbed coating layer is preferably alkali-soluble or alkali-swellable. Here, alkali solubility refers to, for example, a dissolution rate of 50% by mass or more in a 1.5% by mass aqueous solution of sodium hydroxide (pH 13.6) at 70°C. Alkaline swelling refers to, for example, a weight change rate of 200% or more when immersed in a 1.5% by mass aqueous solution of sodium hydroxide (pH 13.6) at 70°C for 15 minutes.

[0051] The thickness of the deleasable coating layer is preferably 0.01 to 5 μm, and more preferably 0.03 to 3 μm, from the viewpoint of deinking properties (removability of printing ink) when immersed in alkali.

[0052] In one embodiment, the desorbed coating layer contains an olefin copolymer. By including an olefin copolymer in the desorbed coating layer, the adhesion of the substrate to the polyolefin resin substrate can be improved. Examples of olefin polymers include polyolefins such as ethylene, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, and 1-octene, which are homopolymers or copolymers of α-olefins [high-pressure low-density polyethylene, linear low-density polyethylene (LLDPE), high-density polyethylene, ethylene-propylene random copolymer, ethylene-1-butene random copolymer, etc., or ethylene-α-olefin copolymers, etc.; propylene homopolymer (polypropylene), propylene-ethylene Examples include propylene-based polymers such as propylene random copolymer, propylene-ethylene-1-butene random copolymer (random polypropylene), propylene block copolymer, and propylene-1-butene random copolymer; 1-butene-based polymers such as 1-butene homopolymer, 1-butene-ethylene copolymer, and 1-butene-propylene copolymer; and 4-methyl-1-pentene-based polymers such as poly4-methyl-1-pentene homopolymer, 4-methyl-1-pentene-propylene copolymer, or 4-methyl-1-pentene-α-olefin copolymer.

[0053] In one embodiment, the decolorizing coating layer comprises a propylene polymer and an acid-modified ethylene copolymer. By using a combination of a propylene polymer and an acid-modified ethylene copolymer, it is possible to achieve both improved deinking properties (detachability from the label of the display area) and improved adhesion to the polyolefin resin substrate.

[0054] (Acid-modified ethylene copolymer) Acid-modified ethylene copolymers refer to polymers obtained by acid modification of polymers in which ethylene is a monomer component. In acid-modified ethylene copolymers, ethylene is the main component of the monomers constituting the polymer, and the main component is preferably 50% by mass or more (up to 100% by mass) of the total monomers, and more preferably 60% by mass or more.

[0055] 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 acrylic acid and / or maleic anhydride, and even more preferably acrylic acid. 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., can be used.

[0056] The acid-modified ethylene copolymer may also be a copolymer of ethylene with another monomer copolymerizable with ethylene, and (meth)acrylic acid ester may be used as the monomer. Examples of (meth)acrylic acid esters include esters 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, octyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate. Mixtures of these may also be used. Other copolymerizable components besides (meth)acrylic acid esters include 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 versatate; vinyl alcohol obtained by saponifying vinyl esters with basic compounds, etc.; 2-hydroxyethyl acrylate; glycidyl (meth)acrylate; (meth)acrylonitrile; styrene; substituted styrene; carbon monoxide; and sulfur dioxide.

[0057] 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. Here, (meth)acrylic acid(salt) refers to (meth)acrylic acid and / or (meth)acrylic acid salts, and maleic anhydride(salt) refers to maleic anhydride and / or maleic anhydride salts.

[0058] In the ethylene-acrylic acid (salt) copolymer, it is preferable that the content of ethylene (derived structural units) is 70 to 95% by mass, and the content of acrylic acid (salt) (derived structural units) is 5 to 30% by mass.

[0059] The weight-average molecular weight of an ethylene-acrylic acid (salt) copolymer is, for example, 5,000 to 10,000.

[0060] The melting point of the ethylene-acrylic acid (salt) copolymer is preferably, for example, 60 to 160°C, and more preferably 60 to 120°C.

[0061] In the present invention, as the acid-modified ethylene resin, it is preferable to use an aqueous dispersion of an ethylene-acrylic acid (salt) copolymer, which is obtained by neutralizing the ethylene-acrylic acid copolymer, from the viewpoint of adhesion to the polyolefin resin substrate. That is, a preferred embodiment of the present invention is an aqueous dispersion of an ethylene-acrylic acid (salt) copolymer as the acid-modified ethylene resin. The aqueous dispersion is in a form dissolved in an aqueous solvent or dispersed as an emulsion. Being an aqueous solvent makes it possible to reduce the amount of volatile organic compounds emitted during coating. Here, the aqueous solvent is at least one selected from water and a water-soluble organic solvent. Examples of water-soluble organic solvents include methanol, ethanol, isopropanol, butanol, acetone, methyl ethyl ketone, dimethylformamide, methyl cellulose, tetrahydrofuran, and ethylene glycol mono-t-butyl ether (ETB). To obtain the aqueous dispersion, a small amount of emulsifier or surfactant may be used, as long as it does not impair the effects of the present invention.

[0062] Examples of neutralizing agents for ethylene-acrylic acid copolymers include sodium hydroxide, ammonia, alkylamines, and alkanolamines, but sodium salts neutralized with sodium hydroxide are preferably used.

[0063] The solid content concentration of the aqueous dispersion of the ethylene-acrylic acid (salt) copolymer is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. The viscosity of the aqueous dispersion of the ethylene-acrylic acid (salt) copolymer at 25°C is, for example, 1 to 5000 mPa·s, and may be 10 to 5000 mPa·s. In this specification, viscosity is a value measured using a B-type rotational viscometer.

[0064] The aqueous dispersion of the ethylene-acrylic acid (salt) copolymer preferably has an emulsion shape (particle shape) in which the polymer is dispersed. In this case, the average particle size of the emulsion polymer is, for example, 500 nm or less, 300 nm or less, or 200 nm or less. Here, the average particle size of the ethylene-acrylic acid (salt) copolymer is the volume-based median diameter measured by laser diffraction dispersion method.

[0065] The aqueous dispersion of ethylene-acrylic acid copolymer may be a commercially available product, such as Zyxene AC (neutralized by ammonia), Zyxene L (neutralized by dimethylethanolamine), and Zyxene N (neutralized by sodium hydroxide) (all manufactured by Sumitomo Seika Co., Ltd.).

[0066] From the viewpoint of desorption properties, the content of the acid-modified ethylene copolymer is preferably 10% by mass or more, 15% by mass or more, 20% by mass or more, or 30% by mass or more in the desorbed coat layer. From the viewpoint of substrate adhesion and desorption properties, the content of the acid-modified ethylene copolymer may be 10-80% by mass, 10-70% by mass, 15-65% by mass or 20-65% by mass in the desorbed coat layer, more preferably 30-65% by mass, even more preferably 40-65% by mass, even more preferably 45-65% by mass, and particularly preferably 45-55% by mass.

[0067] (Propylene polymer) Examples of propylene polymers include polypropylene such as propylene homopolymers and propylene-α-olefin copolymers, and acid-modified propylene polymers. Among these, acid-modified propylene polymers are preferred due to their compatibility with acid-modified ethylene copolymers and their deinking properties. In propylene polymers, propylene is the main component of the monomers constituting the polymer, and the main component is preferably 50% by mass or more, and more preferably 60% by mass or more, of the total monomers.

[0068] 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.

[0069] 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 contrary.

[0070] The copolymerization amount of the unsaturated carboxylic acid or its acid anhydride relative to the propylene main chain is preferably, for example, 0.5 to 5% by mass relative to the solid content weight of the propylene main chain.

[0071] Furthermore, the acid-modified propylene polymer may be a copolymer with other α-olefins such as ethylene and butene.

[0072] 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 norbornenese; 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. These other monomers may be used individually or in combination of two or more.

[0073] Furthermore, some or all of the acidic groups may be neutralized (the acid-modified propylene polymer may be a (partially) neutralized product of the acid-modified propylene polymer). Examples of neutralizing agents include at least one compound selected from the group consisting of alkali metal salts, organic ammonium compounds, organic amine compounds, and ammonia. The degree of neutralization is, for example, 30 to 100 mol%.

[0074] Furthermore, an aqueous dispersion of an acid-modified ethylene copolymer is preferred, and from the viewpoint of compatibility with the aqueous dispersion, an aqueous dispersion of the propylene polymer is also preferred. In this case, the solid content concentration of the aqueous dispersion of the propylene polymer is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. The viscosity of the aqueous dispersion of the propylene polymer at 25°C is, for example, 0.1 to 1000 mPa·s, and may be 0.5 to 500 mPa·s.

[0075] The melting point of the propylene polymer is preferably, for example, 60 to 160°C, and more preferably 60 to 100°C.

[0076] From the viewpoint of substrate adhesion, the content of the propylene polymer is preferably 20% by mass or more, 25% by mass or more, 30% by mass or more, or 35% by mass or more in the desorbed coat layer. From the viewpoint of substrate adhesion and desorbability, the content of the propylene copolymer is preferably 20 to 80% by mass in the desorbed coat layer, and may also be 25 to 75% by mass, 30 to 75% by mass, or 35 to 75% by mass, and preferably 40 to 70% by mass, 40 to 65% by mass, 40 to 65% by mass, 45 to 65% by mass, 45 to 60% by mass, or 45 to 55% by mass.

[0077] From the viewpoint of substrate adhesion and delamination, the mass ratio of propylene polymer to acid-modified ethylene copolymer in the delamination coat layer is preferably 20:80 to 80:20, more preferably 30:70 to 70:30, even more preferably 40:60 to 60:40, and even more preferably 45:55 to 55:45.

[0078] (particle) The desorbing coating layer may contain particles for purposes such as improving the blocking resistance between films when they are formed into a roll shape.

[0079] The particles may be either inorganic or organic. 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. These particles may be used individually or in combination of two or more. Among these, silica is preferred as the particle material.

[0080] The particle content in the desorbed coating layer is set appropriately to achieve the desired objective (e.g., improved blocking resistance), but is, for example, 0.1 to 10 parts by mass per 100 parts by mass of the total of the propylene polymer and the acid-modified ethylene copolymer.

[0081] The average particle size is set appropriately considering the desired purpose, but for example, if the purpose is to improve blocking resistance, it is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.3 μm or more and 0.6 μm or less. In this specification, unless otherwise specified, the average particle size refers to the average particle size on a volume basis, and can be determined, for example, by measuring the particle dispersion using a Coulter counter particle size distribution analyzer with a 50 μm aperture.

[0082] (General-purpose additives, other resin components) The desorbed coating layer used in one aspect of the present invention may contain, in addition to the resins and particles described above, general-purpose additives such as surfactants and crosslinking agents, to the extent that it does not impair the effects of the present invention.

[0083] <Resin substrate> As the resin substrate, a polyolefin resin substrate made of the same material as the polyolefin resin container to be adhered is used, which is compatible with the polyolefin resin container. Examples of polyolefin resins that are preferably used as materials for the polyolefin resin substrate include homopolymers or copolymers of α-olefins such as ethylene and propylene, or cyclic olefins such as norbornene. Specifically, examples 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 materials may be appropriately selected and used. From these, one or more may be appropriately selected and used so as to obtain a resin substrate compatible with the type of resin used in the polyolefin resin container to be adhered. Here, compatibility means that the polyolefin resin container melts at the temperature at which it is heated and melted, and that the molten polyolefin resin container and the resin base material mix well, without degrading the properties of the recycled product. Furthermore, if the resin constituting the polyolefin resin container is a mixture of two or more compatible resins, one of the resins from the resin mixture constituting the polyolefin resin container can be used as the resin of the resin base material.

[0084] There are no particular restrictions on the thickness of the resin substrate, but it is generally preferable to be in the range of 20 to 100 μm.

[0085] In the present invention, the resin substrate can be surface-treated on one or both sides, if desired, in order to improve adhesion with a coating layer provided thereon or an adhesive layer provided on the opposite side. Examples of such surface treatment methods 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.

[0086] The materials constituting the resin substrate may contain various additives as needed. Examples of additives include stabilizers, colorants, and fillers.

[0087] <Adhesive layer> The thickness of the adhesive layer (or the film thickness after drying, if an adhesive composition containing a solvent such as an organic solvent or water is used) is typically 1 to 100 μm, preferably 5 to 50 μm.

[0088] The adhesive layer is formed from the adhesive.

[0089] The adhesive may be a solvent-based type containing a solvent or a solvent-free type (so-called hot melt type), but due to considerations for the environment, a solvent-free type is preferred, and also because it eliminates the need for solvent removal steps, and from the viewpoint of the effects of the present invention, the adhesive is preferably a hot melt type (hot melt adhesive).

[0090] The adhesive layer contains a styrene-based block copolymer, and preferably contains a tackifying resin for tackiness, and preferably contains a plasticizer for ease of handling and coating properties. Furthermore, it is preferable that the adhesive layer does not contain fatty acids so that it does not peel off when treated with an alkaline aqueous solution.

[0091] (Styrene-based block copolymer) The content of the styrene-based block copolymer in the adhesive layer is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and even more preferably 25% by mass or more and 45% by mass or less.

[0092] When the adhesive layer contains a tackifying resin and a plasticizer, the amount of styrene-based block copolymer is preferably 10 to 60 parts by mass, and more preferably 20 to 50 parts by mass, based on 100 parts by mass of the total of the styrene-based block copolymer, tackifying resin, and plasticizer.

[0093] The styrene copolymer content being within the above range results in excellent adhesive performance.

[0094] Styrene-based block copolymers generally consist of a polystyrene block and a rubber block, with the polystyrene portion constituting the hard segment and the rubber block the soft segment. Examples of soft segments include polybutadiene (B), polyisoprene (I), polyisobutylene (IB), and polyolefin elastomers (ethylene-propylene (EP), ethylene-butylene (EB), and butylene-butadiene (BB)).

[0095] Examples of styrene-based block copolymers include styrene-isoprene block copolymers such as styrene-isoprene block copolymer (SI) and styrene-isoprene-styrene block copolymer (SIS); styrene-butadiene block copolymers such as styrene-butadiene-styrene copolymer (SBS), styrene-butadiene-styrene-butadiene copolymer (SBSB), and styrene-butadiene-butylene-styrene copolymer (partially hydrogenated styrene-butadiene-styrene copolymer; SBBS); styrene-isobutylene-styrene block copolymer (SIBS); styrene-ethylene / butylene-styrene copolymer (SEBS); styrene-ethylene / propylene-styrene (SEPS) copolymer; and styrene-ethylene-ethylene / propylene-styrene (SEEPS) copolymer. Styrene-based block copolymers may be used individually or in combination of two or more types. Among these, the styrene-based block copolymer is preferably a styrene-isoprene block copolymer and / or a styrene-butadiene block copolymer, and more preferably a styrene-isoprene-styrene copolymer (SIS) and / or a styrene-butadiene-styrene copolymer (SBS), because it is easy to impart tackiness to the material.

[0096] The styrene monomer content in the styrene-based block copolymer is preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 45% by mass or less, among the monomers constituting the styrene-based block copolymer. A styrene content above the lower limit is preferable because it provides sufficient mechanical strength, and a styrene content below the upper limit is preferable because it exhibits high adhesive strength.

[0097] The styrene-based block copolymer may be a single structure, such as a linear structure, a branched structure, or a highly branched structure, or it may be a mixture of different structures. When a styrene-based resin rich in linear structures is used in the adhesive layer, excellent adhesive performance can be provided. For this reason, styrene-based resins may be mixed and used according to the required properties. In one preferred embodiment, the styrene-based copolymer has a linear structure.

[0098] The mass-average molecular weight (Mw) of the styrene-based block copolymer is preferably 50,000 to 500,000, and more preferably 100,000 to 400,000.

[0099] In this specification, "mass-average molecular weight (Mw)" is a value calculated on a standard polystyrene basis by gel permeation chromatography (GPC).

[0100] The mass-average molecular weight (Mw) is measured, for example, using a gel permeation chromatograph (manufactured by Tosoh Corporation, product name "HLC-8020") under the following conditions, and is expressed in terms of standard polystyrene equivalent. (Measurement conditions) • Column: A series of "TSK guard column HXL-H", "TSK gel GMHXL" (2 pieces), and "TSK gel G2000HXL" (all manufactured by Tosoh Corporation) linked together. Column temperature: 40°C • Developing solvent: tetrahydrofuran ·Flow rate: 1.0mL / min.

[0101] (Adhesive-forming resin) The tackifying resin is not particularly limited, and examples include alicyclic petroleum resins, rosin resins, terpene resins, and styrene resins. From the viewpoint of the effects of the present invention, the tackifying resin is preferably at least one selected from the group consisting of rosin resins and alicyclic petroleum resins, and more preferably alicyclic petroleum resins. Furthermore, since the adhesive layer tends to remain on the polyolefin resin container even after alkaline cleaning, the acid value of the tackifying resin is preferably less than 100 mg / KOH (lower limit 0 mg KOH / g), more preferably 50 mg KOH / g or less, and even more preferably 30 mg KOH / g or less. It is also preferable that the tackifying resin consists only of tackifying resins with an acid value of less than 100 mg KOH / g (it is preferable that tackifying resins with an acid value of 100 mg KOH / g or more are not included). Here, if multiple types of tackifying resins are used, it is preferable that the acid value of each tackifying resin is less than 100 mg KOH / g. The acid value can be measured, for example, by the titration method described in JIS K5601-2-1:1999 (ISO 3682:1993).

[0102] The tackifying resin may be used alone or in combination of two or more types.

[0103] Furthermore, tackifying resins are components that supplementarily improve the adhesive strength of the adhesive layer, and are oligomers with a mass-average molecular weight (Mw) of typically less than 10,000, and are distinct from the styrene-based block copolymers mentioned above.

[0104] The content of the tackifying resin in the adhesive layer is preferably 25% by mass or more and 60% by mass or less, and more preferably 30% by mass or more and 55% by mass or less. By having the tackifying resin content within the above range, suitable adhesive strength can be achieved.

[0105] Furthermore, if the adhesive layer contains a plasticizer, the amount of tackifying resin is preferably 25 parts by mass or more and 60 parts by mass or less, and more preferably 30 parts by mass or more and 55 parts by mass or less, based on 100 parts by mass of the total of the styrene-based block copolymer, tackifying resin, and plasticizer.

[0106] Furthermore, from the viewpoint of exhibiting adhesive strength over a wide temperature range, the mass ratio of styrene-based block copolymer to tackifying resin is preferably styrene-based block copolymer:tackifying resin = 1:0.5 to 2.5, and more preferably styrene-based copolymer:tackifying resin = 1:0.75 to 2.

[0107] The softening point of the tackifying resin is preferably 140°C or lower, more preferably 110°C or lower, and even more preferably 70 to 110°C. Having a softening point within this range results in superior adhesive strength. The softening point is measured by the ring-and-ball method described in JIS K5902-1969 or JIS K2207-1996. When using multiple types of tackifying resins, the softening point is calculated by multiplying the softening point of each resin by its blending mass ratio. For example, if 50% by mass of tackifying resin A with a softening point a°C and 50% by mass of tackifying resin B with a softening point b°C are used, the softening point (°C) of the tackifying resin is calculated as (a × 50 / 100 + b × 50 / 100).

[0108] Petroleum resins are obtained by polymerizing diolefins and monoolefins in the fractions of cracked oil, which are by-products of the production of ethylenes by steam cracking of petroleum products, using known methods. C5 petroleum resins are those made from C5 fractions such as isoprene, 1,3-pentadiene, cyclopentene, and cyclopentadiene, while C9 petroleum resins are those made from C9 fractions such as styrene, vinyltoluene, α-methylstyrene, indene, alkylindene, and dicyclopentadiene.

[0109] Examples of alicyclic petroleum resins include alicyclic hydrocarbon resins obtained by cyclizing and then polymerizing C5 petroleum resins, polymers of cyclic diene compounds (such as cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dipentene, ethylidenebicycloheptene, vinylcycloheptene, tetrahydroindene, vinylcyclohexene, and limonene) or their hydrogenated products, and alicyclic hydrocarbon resins obtained by hydrogenating the aromatic rings of C9 petroleum resins or C5 / C9 petroleum resins. Among these, alicyclic petroleum resins obtained by hydrogenating C5 petroleum resins / C9 petroleum resins are preferred. Alicyclic petroleum resins may be used alone or in combination of two or more types.

[0110] Alicyclic petroleum resins may be commercially available products, such as the Alcon® series (Alcon® P-90, P-100, P-115, P-125, P-140, M-90, M-100, M-115, M-135 (all manufactured by Arakawa Chemical Industries, Ltd.)) and the Quintone® series (Quintone® 1105, 1325, 1340, TD-401, 1500, 1525L, 1920, 2940, etc.) (all manufactured by Nippon Zeon Co., Ltd.).

[0111] Examples of rosin resins that can be used include gum rosin, wood rosin, tall oil rosin, and rosin derivatives such as polymerized rosin, disproportionated rosin, hydrogenated rosin, reinforced rosin, rosin esters, polymerized rosin esters, rosin phenol, disproportionated rosin esters, and hydrogenated rosin esters. Polyhydric alcohols that can be used for esterification include ethylene glycol, diethylene glycol, glycerin, and pentaerythritol. In addition, one or more of these can be used in combination.

[0112] Examples of terpene resins include terpene resins, terpene phenol resins, aromatically modified terpene resins, and hydrogenated terpene resins obtained by hydrogenating these, with aromatically modified terpene resins being preferred. Terpene resins may be used individually or in combination of two or more types.

[0113] Examples of styrene-based resins include monopolymers of α-methylstyrene, monopolymers of styrene monomers, copolymers of α-methylstyrene and styrene monomers, and copolymers of α-methylstyrene, styrene monomers, and other monomers. Styrene-based resins may be used individually or in combination of two or more types.

[0114] (Plasticizer) From the standpoint of the applicability of the adhesive when forming the adhesive layer, it is preferable to include a plasticizer.

[0115] The plasticizer is not particularly limited, and conventionally known plasticizers can be used. Examples include petroleum-based plasticizers; natural oils such as tall oil; dialkyl dibasic acids such as dibutyl phthalate, dioctyl phthalate, or dibutyl adipate; and low molecular weight liquid polymers such as liquid polybutene or liquid polyisoprene.

[0116] Among these, it is preferable that the plasticizer be a petroleum-based plasticizer, as this further enhances the effects of the present invention, is particularly stable against heat and ultraviolet light, and allows for the production of an adhesive with excellent hue. Furthermore, an embodiment in which the plasticizer is solely a petroleum-based plasticizer is also a preferred embodiment.

[0117] Furthermore, petroleum-based plasticizers can be used in combination with other plasticizers. In this case, it is preferable to use petroleum-based plasticizers at a concentration of 60% or more, 70% or more, 80% or more, or 90% or more (up to a maximum of 100% by mass) of the total amount of plasticizers (100% by mass).

[0118] Examples of petroleum-based plasticizers include paraffinic process oils, naphthenic process oils, and aromatic process oils. Petroleum-based plasticizers may be used alone or in combination of two or more. In particular, naphthenic process oils are preferred as petroleum-based plasticizers because they have excellent compatibility with other components and good adhesive properties.

[0119] The plasticizer content in the adhesive layer is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 50% by mass or less. A plasticizer content above the lower limit ensures good applicability of the adhesive, while an adhesive content below the upper limit ensures adhesive strength.

[0120] Furthermore, if the adhesive layer contains a plasticizer, the amount of plasticizer is preferably 5 to 50 parts by mass, more preferably 10 to 60 parts by mass, and even more preferably 20 to 50 parts by mass, based on 100 parts by mass of the total of the styrene-based block copolymer, tackifying resin, and plasticizer.

[0121] <Manufacturing method> The method for manufacturing adhesive labels is not particularly limited, but as an example when the adhesive is a hot-melt type adhesive, a heated hot-melt type adhesive is applied to a release liner, and a resin substrate is laminated onto the resulting adhesive layer. Alternatively, an adhesive layer may be formed on the resin substrate beforehand, and then the release liner may be laminated on top of it.

[0122] A release liner typically comprises a release substrate and a release agent layer, and is laminated onto the adhesive layer to ensure the adhesiveness of the adhesive until the adhesive label is attached to a polyolefin resin container. Examples of release substrates include paper, laminated paper (paper substrate laminated with a thermoplastic resin such as polyethylene), or polyester films. The thickness of the release liner is preferably 25 to 250 μm. Examples of release agents constituting the release agent layer 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.

[0123] If the adhesive is of the hot-melt type, it is preferable that it is heated to melt when applied to the release liner or resin substrate, and the melting temperature (coating temperature) is, for example, 120 to 210°C or 130 to 190°C.

[0124] The method of applying the adhesive is not particularly limited, and can be applied using known coating equipment such as a roll coater, knife coater, air knife coater, bar coater, blade coater, slot die coater, lip coater, or gravure coater.

[0125] Furthermore, a desorption coating layer and an alkali-insoluble coating layer can be pre-formed on the resin substrate.

[0126] Each coating layer is prepared by mixing a resin, additives as needed, and a solvent to create a coating layer-forming composition (a desorbing coating layer-forming composition or an alkali-insoluble coating layer-forming composition; hereinafter collectively referred to simply as the coating layer-forming composition). The solvent is appropriately selected depending on the form of the resin, and examples include water, alcohols (e.g., ethanol, isopropanol, etc.), toluene, methyl ethyl ketone, and ethyl acetate. One solvent may be used alone, or two or more may be used in combination.

[0127] Subsequently, the coating layer-forming composition is applied to the resin substrate or coating layer to form a coating layer (a desorbable coating layer or an alkali-insoluble coating layer). There are no particular limitations on the application method, and conventionally known methods, such as applying the coating layer-forming composition onto the resin substrate and drying it to form each coating layer, can be employed. There are no particular limitations on the application method, but various coating devices such as blade coaters, air knife coaters, rod blade coaters, bar blade coaters, gravure coaters, bar coaters, multi-stage roll coaters, roll coaters, reverse roll coaters, curtain coaters, and spray coaters can be appropriately selected and used for application.

[0128] After applying the coating layer-forming composition, a drying process may be performed. Drying conditions are set as appropriate, but for example, 80 to 160°C for 10 to 60 seconds.

[0129] The application of adhesive labels to polyolefin resin containers (labeling) is carried out using a labeling device such as the one disclosed in Japanese Patent No. 5956220.

[0130] During labeling, the adhesive label attached to the release liner is transported, and when the adhesive label is peeled off the release liner, the release liner is folded back. At this time, the adhesive layer is exposed, and the exposed adhesive layer is attached to the polyolefin resin container. The transport speed of the adhesive label in the labeling device (labeling speed) is not particularly limited, but for example, it is 20 to 150 m / min.

[0131] <Recycled resin compositions and recycling methods> The polyolefin resin container described above exhibits suppressed discoloration and reduced haze buildup, even without removing the adhesive label.

[0132] Polyolefin resin containers to which adhesive labels are attached can be recycled into resin compositions, for example, as follows.

[0133] (1) Treatment process with alkaline aqueous solution This process involves contacting a polyolefin resin container with an alkaline aqueous solution to detach and remove the display portion from the resin substrate using the detachable coating layer. To detach the display portion placed on the resin substrate, the resin container can be treated by immersing it in the alkaline aqueous solution or by contacting it with the alkaline aqueous solution. The alkaline aqueous solution can be prepared by dissolving various alkalis in water. Examples of alkalis include ammonia, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate. From the viewpoint of versatility, it is preferable to use an alkaline aqueous solution of sodium hydroxide. The concentration of the alkaline aqueous solution is, for example, 1 to 7.5% by mass. The treatment time for the alkaline aqueous solution is, for example, 5 to 60 minutes. The temperature of the alkaline aqueous solution, such as a sodium hydroxide aqueous solution, into which the laminate is immersed should be room temperature (25°C) to 90°C. The aqueous solution may be stirred during the treatment of the alkaline aqueous solution. In addition, washing with water may be performed after the alkaline treatment.

[0134] (2) Pelletization / Flakeization Next, the polyolefin resin container can be crushed into flakes, or the flakes can be heated and melted to form pellets. The pellets can then be further molded into molded products or fibrous materials through various molding processes. Examples of molding methods using pellets include extrusion molding, including inflation molding and extruded sheet molding, blow molding, and injection molding. In this way, recycled resin (resin composition) can be obtained from polyolefin resin containers to which adhesive labels have been attached.

[0135] The present invention also encompasses the following aspects.

[0136] (1) A polyolefin resin container having an adhesive label attached to it, wherein the adhesive label has a polyolefin resin base material and an adhesive layer, and the adhesive layer comprises a styrene block copolymer and a tackifying resin.

[0137] (2) The polyolefin resin container according to (1), wherein the mass of the adhesive label is 10% by mass or less of the mass obtained by subtracting the adhesive label from the polyolefin resin container.

[0138] (3) The polyolefin resin container according to (1) or (2), wherein the adhesive label has a desorption coating layer on the polyolefin resin substrate opposite to the adhesive layer.

[0139] (4) The polyolefin resin container according to (3), wherein the detachable coating layer contains an olefin polymer.

[0140] (5) The polyolefin resin container according to either (3) or (4), wherein the desorbed coating layer comprises a propylene polymer and an acid-modified ethylene copolymer.

[0141] (6) A polyolefin resin container according to any one of (1) to (5), wherein the resin substrate does not detach from the polyolefin resin container after being immersed in sodium hydroxide solution at pH 13.6 and 70°C for 15 minutes.

[0142] (7) The polyolefin resin container according to any one of (1) to (6), wherein the tackifying resin is at least one selected from the group consisting of rosin resins and alicyclic petroleum resins.

[0143] (8) The polyolefin resin container according to any one of (1) to (7), wherein the tackifying resin is an alicyclic petroleum resin.

[0144] (9) A polyolefin resin container according to any one of (1) to (8), wherein the tackifying resin consists only of a tackifying resin with an acid value of less than 100 mg KOH / g.

[0145] (10) The polyolefin resin container according to any one of (1) to (9), wherein the adhesive layer further contains a plasticizer.

[0146] A method for recycling a polyolefin resin container according to any of (1) to (10), comprising treating the polyolefin resin container with an alkaline aqueous solution to alkalinely peel off the detachable coating layer, and regenerating the polyolefin resin container from which the detachable coating layer has been removed.

[0147] (12) Having a detachable coating layer, a polyolefin resin substrate and an adhesive layer, The adhesive layer comprises a styrene-based block copolymer and a tackifying resin, wherein the adhesive label is for polyolefin-based resin containers.

[0148] (13) The adhesive label according to (12), wherein the detachable coating layer comprises a propylene polymer and an acid-modified ethylene copolymer.

[0149] (14) The adhesive label according to (12) or (13), wherein the tackifying resin is at least one selected from the group consisting of rosin resins and alicyclic petroleum resins.

[0150] (15) The adhesive label according to any one of (12) to (14), wherein the tackifying resin is an alicyclic petroleum resin.

[0151] (16) The adhesive label according to any one of (12) to (15), wherein the tackifying resin consists only of tackifying resins with an acid value of less than 100 mg KOH / g.

[0152] (17) The adhesive label according to any one of (12) to (16), wherein the adhesive layer further comprises a plasticizer. [Examples]

[0153] Next, we will describe the examples. In the examples, the units "parts" or "%" may be used, but unless otherwise specified, they represent "parts by mass" or "mass%". Also, unless otherwise specified, each operation is carried out at room temperature (25°C).

[0154] (Manufacturing of adhesive label 1) Thirty parts by mass of a styrene-based elastomer (styrene-butadiene-styrene block copolymer, Asaprene T-436 manufactured by Asahi Kasei Corporation) as a base polymer, forty parts by mass of a fully hydrogenated petroleum resin (Alcon P-100 manufactured by Arakawa Chemical Industries, Ltd., acid value 0 mg KOH / g) as a tackifying resin, and thirty parts by mass of naphthenic process oil (Diana Fresia manufactured by Idemitsu Kosan Co., Ltd.) as a plasticizer were melt-kneaded at 160°C to obtain a styrene-based hot melt adhesive 1.

[0155] The styrene-based hot melt adhesive 1 obtained above was melt-coated onto a glassine paper release liner to a thickness of 20 μm at 160°C, and a transparent biaxially oriented polypropylene film (thickness 50 μm) as a base material was laminated to the side of the adhesive layer opposite the release liner to obtain an adhesive label 1.

[0156] (Manufacturing of adhesive label 2) Adhesive label 2 was obtained in the same manner as adhesive label 1, except that 20 parts by mass of rosin resin (Ester Gum HP, manufactured by Arakawa Chemical Industries, Ltd., acid value 20 mg KOH / g or less) and 20 parts by mass of C5-C9 petroleum resin (Petrotac® 100V, manufactured by Tosoh Corporation, acid value 0 mg KOH / g) were used as tackifying resins.

[0157] (Manufacturing of adhesive label 3) 100 parts by mass of acrylic emulsion (HV-C9500, manufactured by Toagosei Co., Ltd.) was applied to a glassine paper release liner to a dry thickness of 20 μm and dried at 90°C for 1 minute. A transparent biaxially oriented polypropylene film (thickness 50 μm) was laminated to the side of the adhesive layer opposite the release liner to obtain an adhesive label 3.

[0158] <Preparation of samples for recyclability evaluation> (Preparation of Sample 1) A transparent polypropylene container and adhesive label 1, from which the release liner had been removed, were crushed into flakes. The material was mixed in a ratio of transparent polypropylene container to adhesive label 1 of 95:5 (by mass), and pelletized using a twin-screw extruder at a molding temperature of 210°C. The resulting pellets were injection molded into a 1.5 mm thick plate to obtain sample 1.

[0159] (Preparation of Sample 2) Sample 2 was obtained in the same manner as in Example 1, except that adhesive label 2 was used as the adhesive label, and a mixture of transparent polypropylene container and adhesive label 2 in a mass ratio of 95:5 was used as the pellet material.

[0160] (Preparation of Sample 3) Sample 3 was obtained in the same manner as Sample 2, except that a mixture of transparent polypropylene container and adhesive label 2 (mass ratio) was used as the pellet material.

[0161] (Preparation of Sample 4) Comparative example sample 4 was obtained in the same manner as sample 1, except that adhesive label 3 was used as the adhesive label and a mixture of transparent polypropylene container and adhesive label 3 in a mass ratio of 95:5 was used as the pellet material.

[0162] (Preparation of sample 5) Only crushed transparent polypropylene containers were used as the pellet material, and the pellets were prepared in the same manner as in Sample 1. The resulting pellets were injection molded into a 1.5 mm thick plate to obtain Sample 5, a reference example.

[0163] <Evaluation of recyclability> 1. Rate of increase in haze value The haze values ​​(%) of samples 1-5 were measured using a haze meter (NDH5000, manufactured by Nippon Denshoku Industries Co., Ltd.), and the rate of increase in haze values ​​for samples 1-4 was calculated using the following formula. Rate of increase [%] = (Haze value of samples 1-4 - Haze value of sample 5) × 100 / Haze value of sample 5 The haze value is preferably 40% or less, more preferably 30% or less, and still more preferably less than 22%.

[0164] 2. Color difference The color values (L* value, a* value, b* value) of Samples 1 to 5 were measured with a spectrophotometer (SE6000, manufactured by Nippon Denshoku Industries Co., Ltd.), and the color difference was obtained using the following formula. Color difference ΔE*[-] = {(L x *-L0*) 2 +(a x *-a0*) 2 +(b x *-b0*) 2} 1 / 2 L x *, a x *, b x *: L* values, a* values, and b* values of each example and comparative example (Samples 1 to 4) L0*, a0*, b0*: L* value, a* value, and b* value of the reference example (Sample 5) The color difference is preferably 10 or less, more preferably 8 or less, and still more preferably 5.5 or less.

[0165] The results are shown in Table 1.

[0166]

Table 1

[0167] As shown above, compared with Sample 4 that uses an acrylic pressure-sensitive adhesive as the pressure-sensitive adhesive label, Samples 1 to 3 that use a styrene-based copolymer pressure-sensitive adhesive as the pressure-sensitive adhesive label exhibited a lower increase in haze and smaller color difference from the container of Sample 5 to which no label was attached. Therefore, it can be concluded that even when the container of the present invention is recycled into a recycled product, the change in appearance is small.

[0168] <Evaluation of Peeling Test Using Alkaline Water> A composition for forming a detachable coating layer was obtained by mixing 50 parts by mass (solids) of an aqueous dispersion of an acid-modified propylene polymer (product name: Arrowbase® DA-5010N, manufactured by Unitika Ltd.) and 50 parts by mass (solids) of an aqueous dispersion of sodium ion neutralized ethylene-acrylic acid copolymer (product name: Zyxen N, manufactured by Sumitomo Seika Co., Ltd.).

[0169] A deleasible coating layer was formed on the substrates of adhesive labels 1 and 2 by applying and drying a deleasible coating layer composition using a Meyer bar so that the film thickness after drying was 1 μm.

[0170] Solid color printing was performed on the delamination coating layer using a printing press (RI Tester) and UV161 J Sumi S ink (manufactured by T&K TOKA Corporation). The ink was then cured by UV irradiation with a high-pressure mercury lamp, and the material was cut into 10mm x 10mm pieces.

[0171] The cut adhesive labels were attached to a 25mm x 50mm polypropylene sheet serving as the substrate, and then placed in 1L of a 1.5% by mass sodium hydroxide aqueous solution (pH 13.6) at 70°C. The solution was stirred for 15 minutes, and the peeling of the print and adhesive labels was checked. It is preferable that the print peels off from the adhesive label while the adhesive label does not peel off from the substrate.

[0172] The results are shown in Table 2.

[0173] [Table 2]

[0174] As described above, with adhesive labels in which a detachable coating layer is placed on a polyolefin resin substrate, it was confirmed that the printing peels off well when immersed in alkali, while the resin substrate does not detach from the polypropylene adherend, thus demonstrating excellent recyclability. [Explanation of Symbols]

[0175] 10 adhesive labels, 11 Display section, 12 Detached coating layer, 13 Resin substrate, 14. Adhesive layer, 15. Alkali-insoluble coating layer, 100 Polyolefin resin containers.

Claims

1. A polyolefin resin container having an adhesive label attached, The adhesive label has a polyolefin resin substrate and an adhesive layer. The adhesive layer comprises a styrene-based block copolymer and a tackifying resin, in a polyolefin-based resin container.

2. The polyolefin resin container according to claim 1, wherein the mass of the adhesive label is 10% by mass or less of the mass obtained by subtracting the adhesive label from the polyolefin resin container.

3. The polyolefin resin container according to claim 1, wherein the adhesive label has a desorption coating layer on the polyolefin resin substrate opposite the adhesive layer.

4. The polyolefin resin container according to claim 3, wherein the desorbed coating layer contains an olefin polymer.

5. The polyolefin resin container according to claim 3, wherein the desorbed coating layer comprises a propylene polymer and an acid-modified ethylene copolymer.

6. The polyolefin resin container according to claim 1, wherein the resin substrate does not detach from the polyolefin resin container after being immersed in sodium hydroxide solution at pH 13.6 and 70°C for 15 minutes.

7. The polyolefin resin container according to claim 1, wherein the tackifying resin is at least one selected from the group consisting of rosin resins and alicyclic petroleum resins.

8. The polyolefin resin container according to claim 1, wherein the tackifying resin is an alicyclic petroleum resin.

9. The polyolefin resin container according to claim 1, wherein the tackifying resin consists solely of a tackifying resin with an acid value of less than 100 mg KOH / g.

10. The polyolefin resin container according to claim 1, wherein the adhesive layer further contains a plasticizer.

11. A method for recycling polyolefin resin containers according to claim 3, The polyolefin resin container is treated with an alkaline aqueous solution to remove the detached coating layer using alkali. A method for recycling polyolefin resin containers, comprising regenerating a polyolefin resin container from which the detached coating layer has been removed.

12. It has a detachable coating layer, a polyolefin resin substrate, and an adhesive layer. The adhesive layer comprises a styrene-based block copolymer and a tackifying resin, wherein the adhesive label is for polyolefin-based resin containers.

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