Steam outlet sealing label

Abstract

To provide a steam passing port sealing label in which peeling from a container and the like occurs easily by the heating of microwaves.SOLUTION: A steam passing port sealing label includes a heat-shrinkable base material and an adhesive layer. In the steam passing port sealing label, the adhesive layer includes a microwave heat generating material. The microwave heat generating material is at least one type selected from the group consisting of zinc oxide and acrylic polymer formed by copolymerizing cyano group-containing unsaturated compound. The steam passing port sealing label and a packaging body on which the steam passing port sealing label is attached are provided.SELECTED DRAWING: Figure 3A

Description

[Technical Field]

[0001] The present invention relates to a steam-passing opening sealing label. [Background technology]

[0002] When food such as a lunch box is heated using microwaves such as in a microwave oven, steam is generated from the heated food. The steam is discharged to the outside of the container through a steam vent (steam vent) in the lid of the lunch box, for example, allowing the food to be heated evenly. For hygiene reasons, such steam vents are sometimes sealed with a steam vent sealing label. To discharge steam, the label must partially open the steam vent, which requires the steam vent sealing label to be partially peeled off from the container. For example, Patent Document 1 discloses a steam vent sealing label whose label base is heat-shrinkable and deforms when heated by microwaves, allowing it to be peeled off from the steam vent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 10-123956 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because heat-shrinkable label substrates shrink due to steam generated by food, if the amount of water vapor from the food is small or if the food is heated for a short period of time, the label may not be destroyed (peel off) and the steam may not be released.

[0005] Therefore, an object of the present invention is to provide a steam-passing opening sealing label that is easily peeled off from a container or the like when heated by microwaves. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a steam-passing opening sealing label having a heat-shrinkable substrate and an adhesive layer, wherein the adhesive layer contains a microwave heat-generating material. [Effects of the Invention]

[0007] According to the steam-passing opening sealing label of the present invention, the label can be easily peeled off from the container or the like by heating with microwaves. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional schematic diagram showing a steam-passing opening sealing label according to one embodiment of the present invention. FIG. [Figure 2] FIG. 4 is a cross-sectional view showing a steam-passing opening sealing label according to another embodiment of the present invention. [Figure 3A] 1 is a schematic diagram of a top view of a steam passage opening sealing label of the first embodiment attached to a container lid which is a package. FIG. [Figure 3B] FIG. 3B is a schematic cross-sectional view of the embodiment of FIG. 3A from the side. [Figure 3C] FIG. 10 is a schematic diagram illustrating peeling of the steam-passing opening sealing label from the package when microwaves are irradiated. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0010] In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and physical properties are measured under conditions of room temperature (20 to 25°C) and relative humidity of 45 to 55% RH. In this specification, "(meth)acrylic" refers to "acrylic or methacrylic."

[0011] A sealing label according to one embodiment of the present invention is a steam-passing opening sealing label having a heat-shrinkable substrate and an adhesive layer, wherein the adhesive layer contains a microwave-generating material.

[0012] In the steam passage opening sealing label of this embodiment, the adhesive layer contains a microwave heat generating material. The microwave heat generating material is a material that generates heat when exposed to microwaves. When irradiated with microwaves by heating in a microwave oven or the like, the microwave heat generating material generates heat, causing the adhesive layer to become heated. The generated heat is transferred to the heat shrinkable substrate, causing the heat shrinkable substrate to shrink. This applies stress to the adhesive layer, causing the steam passage opening sealing label to peel off from the adherend, such as a container. This exposes and opens the steam passage opening, allowing steam generated within the package to be discharged to the outside. In this embodiment, the heat generated by the microwave heat generating material is utilized, and peeling of the steam passage opening sealing label can be stably achieved without relying on the amount of steam generated from the contents (e.g., food) inside the packaging container.

[0013] In the following description, the steam port sealing label may be simply referred to as a "sealing label" or a "label." The concept of a "label" includes films, sheets, tapes, and the like.

[0014] 1 is a schematic cross-sectional view of a sealable label 10a according to this embodiment. The sealable label 10 has a heat-shrinkable substrate 11, an adhesive layer 12, and a release liner 13 in this order.

[0015] The release liner 13 prevents dust and other foreign matter from adhering to the adhesive layer 12 until the adhesive layer 12 is attached to the adherend. Therefore, the release liner 13 is peeled off when the seal label 10a is attached to the adherend. For this reason, the seal label 10a may not have a release liner 13.

[0016] The pressure-sensitive adhesive layer 12 contains a microwave heat generating material. The microwave heat generating material generates heat when irradiated with microwaves from a microwave oven or the like, and the heat is transferred to the heat-shrinkable substrate 11. This causes the heat-shrinkable substrate to shrink, exposing part of the steam vent.

[0017] Fig. 2 is a cross-sectional schematic diagram of a sealable label 10b according to another embodiment. The sealable label 10b of Fig. 2 has a heat-shrinkable substrate 11, an adhesive layer 12, and a release liner 13, in this order. The adhesive layer 12 includes an adhesive layer a containing a heat-generating material and an adhesive layer b containing no heat-generating material. By arranging the heat-generating material in this manner, the amount of heat-generating material used can be reduced. In consideration of heat transfer to the heat-shrinkable substrate, the adhesive layer containing the heat-generating material is preferably arranged adjacent to the heat-shrinkable substrate. The adhesive layer may have multiple layers as in this embodiment, or may have two to four layers, or may have two layers.

[0018] The sealing label 10 is composed of a heat-shrinkable substrate 11, an adhesive layer 12, and a release liner 13. The steam-passing opening sealing label may have other functional layers on the heat-shrinkable substrate or between the layers. Examples of other functional layers include a printing layer and a primer layer.

[0019] In the embodiment of FIG. 1, the pressure-sensitive adhesive layer is disposed over the entire surface of the heat-shrinkable substrate, but the present invention is not limited to this embodiment, and the pressure-sensitive adhesive layer may be disposed, for example, only on the outer periphery of the heat-shrinkable substrate.

[0020] The shape of the label is not particularly limited, and may be any shape, such as square, rectangular, or oval, when viewed from above. The label may also have a tab to make it easier to remove from the container or package.

[0021] The adhesive strength of the steam-passing opening sealing label is preferably 1 N / 25 mm or more, more preferably 2 N / 25 mm or more, taking into account adhesion to containers, etc. Furthermore, the adhesive strength of the steam-passing opening sealing label is preferably 15 N / 25 mm or less, more preferably 10 N / 25 mm or less, taking into account peeling from containers, etc. The adhesive strength to the adherend is measured by attaching the adhesive layer side of the steam-passing opening sealing label to a polypropylene plate and measuring it after 24 hours in a 180° direction at a test speed of 300 mm / min according to JIS Z0237:2009 using a tensile tester. More specifically, the adhesive strength to the adherend is measured by the following method: the steam-passing opening sealing label is left to stand for one day under standard conditions (23°C, 50% RH), the release liner is peeled off, and the adhesive layer side is attached to a polypropylene plate. After leaving the film under standard conditions for 24 hours, the adhesive strength is measured according to JIS Z0237:2009. Specifically, the film is peeled off in a 180° direction at a test speed of 300 mm / min using a tensile tester, and the adhesive strength is measured. The numerical value is converted to the peel force per 25 mm of film width (N / 25 mm).

[0022] The method of forming each layer of the label seal 10, the materials, etc. will be described below.

[0023] <Heat-shrinkable substrate> The heat-shrinkable substrate 11 is not particularly limited, but a resin film that can shrink in a heated environment is preferably used.

[0024] The shrinkage percentage of the heat-shrinkable substrate 11 is preferably 10 to 90%, and more preferably 20 to 80%. The shrinkage percentage is calculated from the dimensions of the film before shrinkage and the dimensions after shrinkage when the film is heated to 70°C, based on the following formula:

[0025]

number

[0026] The heat-shrinkable substrate 11 as described above is not particularly limited, but specific examples include polyester films such as polyethylene terephthalate; polyolefin films such as polyethylene and polypropylene; uniaxially oriented films and biaxially oriented films such as polystyrene; polyamide; polyurethane; polyvinylidene chloride; and polyvinyl chloride. These heat-shrinkable substrates can also be used in combination of two or more types. Among these, it is preferable to use polyester films such as polyethylene terephthalate; or polyolefin films as the heat-shrinkable substrate 11.

[0027] Considering the heat shrinkability and peeling due to heating, the thickness of the heat-shrinkable substrate 11 is preferably 20 to 100 μm, and more preferably 30 to 100 μm.

[0028] <Adhesive layer 12> The pressure-sensitive adhesive layer 12 contains a microwave heat-generating material. Specific examples include a mode in which the pressure-sensitive adhesive layer contains a (non-heat-generating) pressure-sensitive adhesive and a (non-adhesive) microwave heat-generating material, a mode in which the pressure-sensitive adhesive layer contains a microwave heat-generating pressure-sensitive adhesive (a mode in which the pressure-sensitive adhesive is a microwave heat-generating material), and a mode in which the pressure-sensitive adhesive layer contains a microwave heat-generating pressure-sensitive adhesive and a (non-adhesive) microwave heat-generating material.

[0029] The adhesive layer 12 is formed from an adhesive composition containing an adhesive.

[0030] The method for forming the pressure-sensitive adhesive layer is not particularly limited, and the pressure-sensitive adhesive layer may be formed by directly applying the pressure-sensitive adhesive composition to a heat-shrinkable substrate, or the pressure-sensitive adhesive layer may be formed on a release liner, which is then attached to the heat-shrinkable substrate. Specifically, a method may be mentioned in which the pressure-sensitive adhesive composition is applied to a release liner, and the pressure-sensitive adhesive layer made of the pressure-sensitive adhesive composition is transferred to the heat-shrinkable substrate.

[0031] The method for applying the pressure-sensitive adhesive composition to the heat-shrinkable substrate or release liner is not particularly limited, and the composition can be applied using a known application device such as a roll coater, a knife coater, an air knife coater, a bar coater, a blade coater, a slot die coater, a lip coater, or a gravure coater.

[0032] Considering heat generation and peelability, the thickness of the pressure-sensitive adhesive layer is preferably 10 to 150 μm, more preferably 20 to 120 μm, and even more preferably 30 to 100 μm.

[0033] [Adhesive] Examples of the pressure-sensitive adhesive include acrylic pressure-sensitive adhesives, rubber pressure-sensitive adhesives, silicone pressure-sensitive adhesives, urethane pressure-sensitive adhesives, polyester pressure-sensitive adhesives, styrene-diene block copolymer pressure-sensitive adhesives, vinyl alkyl ether pressure-sensitive adhesives, polyamide pressure-sensitive adhesives, fluorine-based pressure-sensitive adhesives, etc. Among these, acrylic pressure-sensitive adhesives are particularly preferred from the viewpoint of adhesive reliability.

[0034] The acrylic polymer constituting the acrylic pressure-sensitive adhesive is formed by using a monomer mixture containing an adhesive (meth)acrylic acid alkyl ester as the main monomer component, and optionally a monomer (copolymerizable monomer) that can be copolymerized with the (meth)acrylic acid alkyl ester.

[0035] Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, and stearyl (meth)acrylate. These may be used alone or in combination of two or more. Among these, butyl (meth)acrylate and / or 2-ethylhexyl (meth)acrylate are preferred from the viewpoint of adhesive performance.

[0036] From the viewpoint of exhibiting adhesive performance, the content of the (meth)acrylic acid alkyl ester is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the total amount of monomers in the monomer mixture. Also, from the viewpoint of peeling from the adherend, the content of the (meth)acrylic acid alkyl ester is preferably 99.5% by mass or less, more preferably 99% by mass or less, based on the total amount of monomers in the monomer mixture.

[0037] Examples of copolymerizable monomers copolymerizable with (meth)acrylic acid alkyl esters include carboxyl group-containing vinyl monomers such as (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, myristoleic acid, palmitoleic acid, and oleic acid; carboxylic acid anhydride group-containing vinyl monomers such as maleic anhydride and itaconic anhydride; hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates (2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and glycerin dimethacrylate; amide group-containing monomers such as acrylamide, methacrylamide, N-vinylpyrrolidone, and N,N-dimethylacrylamide; amino group-containing monomers such as aminoethyl (meth)acrylate and (meth)acryloylmorpholine; aromatic vinyl compounds such as styrene and substituted styrenes; cyano group-containing monomers such as acrylonitrile; and vinyl esters such as vinyl acetate. These may be used alone or in combination of two or more.

[0038] The content of the copolymerizable monomer in all the monomers is preferably 20% by mass or less, and more preferably 10% by mass or less (lower limit: 0% by mass).

[0039] The adhesive may be of any of a water-dispersion type, a solvent type, and a solventless type.

[0040] In addition, a configuration in which the pressure-sensitive adhesive itself is a microwave heat-generating material (a configuration in which the pressure-sensitive adhesive is a microwave heat-generating pressure-sensitive adhesive) is also suitable. Examples of such microwave heat-generating pressure-sensitive adhesives include pressure-sensitive adhesives composed of acrylic polymers obtained by copolymerizing a cyano group-containing unsaturated compound.

[0041] Examples of (meth)acrylic acid alkyl esters constituting the acrylic polymer obtained by copolymerizing a cyano group-containing unsaturated compound include those listed above. Among them, from the viewpoint of adhesive performance, butyl (meth)acrylate and / or 2-ethylhexyl (meth)acrylate are preferred. Butyl (meth)acrylate is even more preferred because of its high dielectric constant.

[0042] From the viewpoint of exhibiting adhesive properties, the content of the (meth)acrylic acid ester constituting the acrylic polymer obtained by copolymerizing a cyano group-containing unsaturated compound is preferably 70 mass% or more, more preferably 75 mass% or more, based on the total amount of monomers in the monomer mixture. Also, from the viewpoint of peeling from the adherend, the content of the (meth)acrylic acid ester is preferably 99 mass% or less, more preferably 97 mass% or less, based on the total amount of monomers in the monomer mixture.

[0043] Examples of cyano group-containing unsaturated compounds copolymerizable with (meth)acrylic acid alkyl esters include acrylonitrile, methyl-2-cyanoacrylate, ethyl-2-cyanoacrylate, n-butyl cyanoacrylate, and 2-octyl cyanoacrylate. Among these, cyano group-containing unsaturated compounds are preferably cyanoacrylates such as methyl-2-cyanoacrylate, ethyl-2-cyanoacrylate, n-butyl cyanoacrylate, and 2-octyl cyanoacrylate. The content of the cyano group-containing unsaturated compound in all monomers constituting the acrylic polymer is preferably 1 to 30% by mass, and more preferably 3 to 20% by mass.

[0044] In addition, other copolymerizable monomers (hereinafter also simply referred to as other monomers) copolymerizable with (meth)acrylic acid alkyl esters may be used as monomers constituting the acrylic polymer obtained by copolymerizing a cyano group-containing unsaturated compound. Examples of such monomers include carboxyl group-containing vinyl monomers such as (meth)acrylic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid, myristoleic acid, palmitoleic acid, and oleic acid; carboxylic acid anhydride group-containing vinyl monomers such as maleic anhydride and itaconic anhydride; hydroxyl group-containing monomers such as hydroxyalkyl (meth)acrylates (2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, and glycerin dimethacrylate; amide group-containing monomers such as acrylamide, methacrylamide, N-vinylpyrrolidone, and N,N-dimethylacrylamide; amino group-containing monomers such as aminoethyl (meth)acrylate and (meth)acryloylmorpholine; aromatic vinyl compounds such as styrene and substituted styrene; and vinyl esters such as vinyl acetate. These may be used alone or in combination. Among these, (meth)acrylic acid and hydroxyalkyl (meth)acrylate are preferred as other monomers. Acrylic acid is more preferred due to its high dielectric constant. The content of other monomers in all monomers is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less (lower limit: 0% by mass).

[0045] [Crosslinking agent] The pressure-sensitive adhesive composition may contain a crosslinking agent in addition to the acrylic polymer. Known crosslinking agents can be used as the crosslinking agent. Examples of crosslinking agents include, but are not limited to, isocyanate-based crosslinking agents, epoxy-based crosslinking agents, metal chelate-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, and carbodiimide-based crosslinking agents.

[0046] When a crosslinking agent is added, the amount of the crosslinking agent added is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, relative to 100 parts by mass of the acrylic polymer.

[0047] [Microwave heating materials] A microwave heat generating material (hereinafter also simply referred to as a heat generating material) refers to a material that generates heat when irradiated with microwaves.

[0048] Examples of heat-generating materials include ferrites such as barium titanate, strontium titanate, spinel ferrite, hexagonal ferrite, and garnet ferrite; and inorganic materials containing water of crystallization, such as carbon black, silicon carbide (SiC), titanium carbide (TiC), zirconium carbide (ZrC), tungsten carbide (WC), aluminum oxide (Al2O3), zinc oxide (ZnO), calcium oxide (CaO), CaO·6Al2O3, zirconium boride (ZrB2), titanium boride (TiB2), molybdenum boride (MoB), calcium fluoride (CaF2), titanium oxide, potassium niobate, hydrated aluminum silicate, iron oxide, magnesium oxide, and hydrated aluminosilicates of alkali metals or alkaline earth metals. Among these, zinc oxide is preferred as the inorganic heat-generating material from the viewpoint of heat generation.

[0049] The microwave heat generating material may be the above-mentioned microwave heat generating adhesive.

[0050] The heat-generating material may be used alone or in combination of two or more. From the viewpoint of heat generation, a combination of an inorganic heat-generating material and an acrylic polymer obtained by copolymerizing a cyano group-containing unsaturated compound is particularly preferred.

[0051] From the viewpoint of heat generation, the heat generating material that generates heat when exposed to microwaves is preferably at least one selected from the group consisting of zinc oxide and acrylic polymers obtained by copolymerizing a cyano group-containing unsaturated compound.

[0052] From the viewpoint of heat generation and adhesiveness, the heat-generating material is preferably contained in the adhesive layer at 5 to 80 mass %, more preferably 10 to 75 mass %, even more preferably 30 to 70 mass %, and particularly preferably 50 to 65 mass %.

[0053] [Other additives] The pressure-sensitive adhesive composition may further contain other additives known in the art, such as tackifiers, fillers, pigments, UV absorbers, wetting agents, and preservatives.

[0054] <Release liner> The sealable label of this embodiment may have a release liner 13. The release liner is a member that has the function of protecting the pressure-sensitive adhesive layer 12 and preventing a decrease in adhesiveness. The release liner 13 is peeled off from the pressure-sensitive adhesive film when the label is attached to an adherend.

[0055] The release liner 13 is not particularly limited, but examples thereof include plastic films such as polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyolefin films such as polypropylene and polyethylene; and papers such as fine paper, glassine paper, and kraft paper.

[0056] The thickness of release liner 13 is usually about 10 to 400 μm. A layer made of a release agent such as silicone may be provided on the surface of release liner 13 to improve the releasability of pressure-sensitive adhesive layer 12. When such a layer is provided, the thickness of the layer is usually about 0.01 to 5 μm.

[0057] <Package, how to use> A second embodiment of the present invention is a package to which the steam passage opening sealing label of the first embodiment is attached.

[0058] FIG. 3A is a schematic diagram of the top view of a sealing label of the first embodiment attached to a container lid. In FIG. 3A, the sealing label 10 is attached so as to cover the steam vent hole 21 provided in the container lid 20. Here, the sealing label 10 in this figure is the sealing label 10a of FIG. 1 with the release liner 13 removed. FIG. 3B is a schematic cross-sectional view of the embodiment of FIG. 3A from the side. The sealing label 10 (heat-shrinkable base material 11, adhesive layer 12) is attached so as to cover the steam vent hole 21 provided in the container lid 20 arranged on the upper surface of the container body 30. When microwaves from a microwave oven or the like are irradiated, the adhesive layer 12 generates heat and the heat-shrinkable base material 11 shrinks, causing a portion of the sealing label 10 to peel off from the container lid 20 and opening the steam vent hole 21 (FIG. 3C). This allows steam to be discharged through the steam vent hole 21. The shape of the steam vent 21 is not particularly limited, and may be any shape such as a square, rectangle, or oval when projected from above. Furthermore, the steam vent may not be a hole, but may be a notch.

[0059] Examples of packaging materials include bags and containers. Examples of materials for bags and containers include resins. Examples of resins include, but are not limited to, polyethylene resins, polypropylene resins, polystyrene resins, methacrylic resins, polyvinyl chloride resins, polyamide resins, polycarbonate resins, polyethylene terephthalate resins, polybutylene terephthalate resins, cellulose acetate resins, and ethylene-vinyl alcohol copolymer resins (EVOH, etc.).

[0060] Specific examples of packaging include lunch boxes, etc. Lunch boxes usually contain food. [Example]

[0061] The effects of the present invention will be explained using the following examples and comparative examples. In the examples, the units "parts" and "%" are sometimes used, but unless otherwise specified, they represent "parts by mass" or "% by mass." Unless otherwise specified, each operation is carried out at room temperature (25°C).

[0062] [Example 1] An acrylic adhesive was obtained by adding 1 part by mass (solid content) of an isocyanate crosslinking agent, Coronate L (manufactured by Tosoh Corporation), to 100 parts by mass of a toluene solution (solid content 40% by mass) of an acrylic polymer (weight average molecular weight 350,000) formed from monomers with a monomer composition of butyl acrylate (BA) / 2-ethylhexyl acrylate (2-EHA) / acrylic acid (AA) = 60 / 30 / 10 (mass ratio).

[0063] A pressure-sensitive adhesive composition was prepared by adding 50 parts by mass of zinc oxide to 50 parts by mass of the acrylic polymer.

[0064] The resulting adhesive composition was applied to a release liner using a knife coater to a film thickness of 25 μm after drying, and then dried to obtain an adhesive layer. The adhesive layer surface was transferred to a 50 μm thick shrink PET film (Mitsubishi Chemical Corporation, Hishipet LX-18S (model number), shrinkage rate 30% at 75°C) as a heat-shrinkable substrate to prepare a steam-passing opening sealing label.

[0065] [Example 2] A steam-passing opening sealing label was produced in the same manner as in Example 1, except that the thickness of the adhesive layer was 50 μm.

[0066] [Example 3] A steam-passing opening sealing label was produced in the same manner as in Example 1, except that the thickness of the adhesive layer was 100 μm.

[0067] [Example 4] A steam-passing opening sealing label was produced in the same manner as in Example 1, except that 40 parts by mass of zinc oxide was added to 60 parts by mass of the acrylic adhesive.

[0068] [Example 5] A steam-passing opening sealing label was produced in the same manner as in Example 1, except that 60 parts by mass of zinc oxide was added to 40 parts by mass of the acrylic adhesive.

[0069] [Example 6] An acrylic adhesive was obtained by adding 1 part by mass (solid content) of the isocyanate crosslinking agent Coronate L (manufactured by Tosoh Corporation) to 100 parts by mass of a toluene solution (solid content 40% by mass) of an acrylic polymer (weight average molecular weight 350,000) formed from monomers with a monomer composition of butyl acrylate (BA) / 2-ethylhexyl acrylate (2-EHA) / methyl-2-cyanoacrylate / acrylic acid (AA) = 50 / 30 / 10 / 10 (mass ratio).

[0070] A steam passage opening sealing label was produced in the same manner as in Example 5, except that the above adhesive was used.

[0071] [Example 7] An acrylic adhesive was obtained by adding 1 part by mass (solid content) of the isocyanate crosslinking agent Coronate L (manufactured by Tosoh Corporation) to 100 parts by mass of a toluene solution (solid content 40% by mass) of an acrylic polymer (weight average molecular weight 350,000) formed from monomers with a monomer composition of butyl acrylate (BA) / 2-ethylhexyl acrylate (2-EHA) / methyl-2-cyanoacrylate / acrylic acid (AA) = 60 / 20 / 10 / 10 (mass ratio).

[0072] A steam passage opening sealing label was produced in the same manner as in Example 5, except that the above adhesive was used.

[0073] [Example 8] A steam-passing opening sealing label was produced in the same manner as in Example 6, except that zinc oxide was not added to the adhesive.

[0074] [Comparative Example 1] A steam-passing opening sealing label was produced in the same manner as in Example 1, except that zinc oxide was not added.

[0075] <Evaluation method> A commercially available microwave-safe container (made of polystyrene foam) was used as the container. A roughly U-shaped cut in plan view (length of cut (length from the end of the cut to the curved part): approximately 10 mm) was formed in the center of the lid of this container.

[0076] The steam passage opening sealing labels prepared in the Examples and Comparative Examples were attached to cover the cuts (steam passage openings) in the container lids.

[0077] The label was then irradiated with microwaves at 750 W using a microwave oven. The time until peeling occurred is shown in Table 1. Peeling here refers to a state in which 50% or more of the label area has peeled off from the container lid.

[0078] [Table 1]

[0079] As can be seen from the above results, the steam-passing opening sealing label of the example was peeled off from the container lid in a short time by microwave irradiation even in the absence of water vapor from the contents. [Explanation of symbols]

[0080] 10a, 10b, 10 sealing label, 11 heat-shrinkable substrate; 12 adhesive layer, 13 release liner, 20 container lid, 21 Steam vent; 30 Container body.

Claims

1. A steam-passing opening sealing label having a heat-shrinkable substrate and an adhesive layer, the pressure-sensitive adhesive layer contains a microwave heat-generating material, The microwave heat generating material comprises an acrylic polymer obtained by copolymerizing a cyano group-containing unsaturated compound.

2. The steam-passing opening sealing label according to claim 1, wherein the microwave heat generating material further comprises an inorganic heat generating material.

3. 3. The steam-passing opening sealing label according to claim 1, wherein the adhesive contained in the adhesive layer is an acrylic adhesive.

4. The steam-passing opening sealing label according to any one of claims 1 to 3, wherein the shrinkage rate of the heat-shrinkable substrate is 10 to 90%.

5. The steam-passing opening sealing label according to any one of claims 1 to 4, having an adhesive strength of 1 N / 25 mm or more and 15 N / 25 mm or less.

6. A package having the steam-passing opening sealing label according to any one of claims 1 to 5 attached thereto.

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