Adhesive tape

Abstract

Provided is an adhesive tape having excellent vapor release property, holding property, and container deformation suppressing property.　This adhesive tape is for use in sealing a vapor discharge port by being pressure-bonded to a container having the vapor discharge port, and comprises: a film-like base material; and a pressure-sensitive adhesive layer laminated on at least one surface of the base material. The surface of the pressure-sensitive adhesive layer has an uneven structure.

Description

adhesive tape

[0001] The present invention relates to an adhesive tape used for sealing a steam outlet by being pressed onto a container having the steam outlet.

[0002] When a sealed container is heated, the contents are heated and steam is generated, which can cause the container to expand and burst. To address this issue, many technologies have been proposed that incorporate steam release functions into the container lid or adhesive tape.

[0003] For example, Patent Document 1 discloses a tape for sealing a gas release gap in a container, which completely covers the gas release gap before heating to prevent the intrusion of foreign matter, peels off during heating to release gas, and can be resealed after heating as necessary.

[0004] Patent No. 6771281

[0005] The sealing tape proposed in Patent Document 1 requires an operation (external force) such as peeling off by a person to release the gas. Therefore, from the viewpoint of convenience, there is a demand for an adhesive tape that has the property of automatically releasing steam when heated (steam release property).

[0006] Furthermore, to prevent scattering, the adhesive tape is required to have the property (retention) of not peeling off completely and falling off from the container when steam is released, but rather maintaining at least a portion of the tape attached to the container.

[0007] Furthermore, if the container is resealed before the steam has been sufficiently released, the remaining steam in the container may condense, causing the container to undergo compression deformation. Therefore, there is a need for an adhesive tape that has the property of suppressing such deformation of the container (container deformation suppression property).

[0008] The present invention has been made in view of the above problems, and has an object to provide a pressure-sensitive adhesive tape that is excellent in vapor escape properties, vapor retention properties, and container deformation suppression properties.

[0009] The adhesive tape of the present invention is an adhesive tape used to seal a container having a steam outlet by being pressed against the container to seal the steam outlet, and comprises a film-like substrate and a pressure-sensitive adhesive layer laminated on at least one side of the substrate, and the surface of the pressure-sensitive adhesive layer has an uneven structure.

[0010] According to the present invention, it is possible to provide a pressure-sensitive adhesive tape that is excellent in vapor escape properties, retention properties, and suppression of container deformation.

[0011] FIG. 1 is a cross-sectional view showing an adhesive tape and a container according to one embodiment of the present invention, illustrating a state before steam is released. FIG. 2 is a cross-sectional view showing an adhesive tape and a container according to one embodiment of the present invention, illustrating a state in which pressure is rising due to the generation of steam. FIG. 3 is a cross-sectional view showing an adhesive tape and a container according to one embodiment of the present invention, illustrating a state in which steam is being released. FIG. 4 is a cross-sectional view showing an adhesive tape and a container according to one embodiment of the present invention, illustrating a state in which the adhesive tape is pressed against the container. FIG. 5 is a cross-sectional view showing an adhesive tape and a container according to one embodiment of the present invention, illustrating a state in which the concavo-convex structure of the pressure-sensitive adhesive layer appears in a portion of the peeled adhesive tape. FIG. 6 is a view showing an example of the concavo-convex structure of the pressure-sensitive adhesive layer in an adhesive tape according to one embodiment of the present invention. FIG. 7 is a view showing an example of the concavo-convex structure of the pressure-sensitive adhesive layer in an adhesive tape according to one embodiment of the present invention.

[0012] Hereinafter, a pressure-sensitive adhesive tape according to one embodiment of the present invention will be described in detail with reference to the drawings.

[0013] <<Adhesive Tape>> As shown in Fig. 1 , the adhesive tape 1 of this embodiment includes a film-like substrate 2 and a pressure-sensitive adhesive layer 3 laminated on one side of the substrate 2. The surface of the pressure-sensitive adhesive layer 3 has an uneven structure.

[0014] The adhesive tape 1 of this embodiment is used to seal the steam release port 101 by being pressure-bonded to a container 100 having the steam release port 101 .

[0015] The adhesive strength of the pressure-sensitive adhesive layer 3 decreases due to the temperature rise inside the container and the heat of the steam released from the steam release port 101. Therefore, as shown in FIGS. 2 and 3 , the temperature rise inside the container due to heating and the resulting increase in steam pressure inside the container cause a portion of the adhesive tape 1 to peel off, automatically releasing the steam. Therefore, the adhesive tape 1 of this embodiment has excellent vapor escape and retention properties. Furthermore, the uneven structure on the surface of the pressure-sensitive adhesive layer 3 also contributes to the vapor escape and retention properties. As shown in FIG. 4 , when the adhesive tape 1 is pressed against the container 100 before heating, the convex portions of the uneven structure on the surface of the pressure-sensitive adhesive layer 3 are compressed, while the adhesive tape 1 is in close contact, maintaining the sealing performance before steam release. When the container is heated, the adhesive strength of the pressure-sensitive adhesive layer 3 gradually decreases due to the increase in the temperature of the pressure-sensitive adhesive caused by heating the container. In the portions where the elastic force of the pressure-sensitive adhesive layer 3 and the increase in vapor pressure inside the container 100 exceed the adhesive force of the pressure-sensitive adhesive layer 3, the original uneven structure is reproduced, and the pressure-sensitive adhesive layer 3 is peeled off. Next, when the reproduced uneven structure increases the area of ​​the surface of the pressure-sensitive adhesive layer 3 that comes into contact with the vapor generated inside the container 100, the rate of temperature rise of the entire pressure-sensitive adhesive layer 3 increases, and the adhesive force of the surface of the pressure-sensitive adhesive layer 3 is reduced overall. Finally, the portions of the pressure-sensitive adhesive layer 3 where the adhesive force has decreased peel off, and the vapor is released from the vapor release port 101.

[0016] Furthermore, the pressure-sensitive adhesive tape 1 of this embodiment has a pressure-sensitive adhesive layer 3 with an uneven structure, and therefore is also excellent in suppressing container deformation. The reason for this effect is believed to be as follows: After heating is completed, when the momentum of the steam released from the steam release port 101 weakens, the tackiness of the pressure-sensitive adhesive layer 3 causes it to temporarily adhere to the periphery of the steam release port 101 when it comes into contact with the periphery. Furthermore, when the temperature drops and the pressure inside the container 100 gradually decreases, the pressure-sensitive adhesive layer 3 may adhere to the periphery of the steam release port 101 from the temporarily adhered area, causing the steam release port 101 to be resealed. As shown in FIG. 5 , in the portion of the adhesive tape 1 peeled from the container 100, the uneven structure of the surface of the pressure-sensitive adhesive layer 3 is revealed, reducing the contact area with the periphery of the steam release port 101, which is believed to make it less likely for a temporary adhesive state to occur. As a result, it is believed that the container is not resealed or is not resealed before sufficient steam is released, which makes it less likely for the remaining steam in the container to condense and compressively deform the container.

[0017] <Pressure-Sensitive Adhesive Layer> The pressure-sensitive adhesive layer 3 is made of a pressure-sensitive adhesive and has an uneven surface. A pressure-sensitive adhesive (pressure-sensitive adhesive) is an adhesive that has stickiness (tackiness), the ability to strongly adhere to a surface (adhesion), and the property of the adhesive to harden (cohesion).

[0018] (Uneven Structure) The uneven structure is not particularly limited as long as it is a structure that reduces the contact area between the container 100 and the periphery of the steam release port 101 .

[0019] The pattern of the relief structure may be a regular pattern or an irregular pattern, but a regular pattern is preferred. Examples of regular patterns include linear and dotted patterns. Examples of linear patterns include straight lines; wavy lines such as sine waves and triangular waves; and lattice patterns such as square lattice, rectangular lattice, triangular lattice, hexagonal lattice, rhombic lattice, and parallelogram lattice. In dotted patterns, examples of dot arrangements include square lattice arrangements, rectangular lattice arrangements, triangular lattice arrangements, hexagonal lattice arrangements, rhombic lattice arrangements, and parallelogram lattice arrangements. The dot shapes may be cylindrical, such as a square prism, or triangular prism; cone-shaped, such as a square pyramid, or triangular pyramid; truncated cone-shaped, such as a square pyramid, or triangular pyramid; or hemispherical or approximately hemispherical. In the case of a regular pattern, the convex portions protruding from the surface (concave portions) of the flat portion may show a regular pattern, or the concave portions recessed from the surface (convex portions) of the flat portion may show a regular pattern, but it is preferable that the concave portions recessed from the surface (convex portions) of the flat portion show a regular pattern.

[0020] When the direction perpendicular to the surface direction of the main surface of the pressure-sensitive adhesive tape is the thickness direction, the height of the convex portions in the concave-convex structure in the thickness direction (depth of the concave portions in the thickness direction) is preferably 1 μm or more and 30 μm or less, more preferably 3 μm or more and 25 μm or less, and even more preferably 5 μm or more and 25 μm or less. When the pattern of the concave-convex structure is a linear pattern, the width of the concave portions in the surface direction in the concave-convex structure is preferably 3 μm or more and 500 μm or less, more preferably 5 μm or more and 450 μm or less, and even more preferably 10 μm or more and 400 μm or less. When the pattern of the concave-convex structure is a linear pattern, the aspect ratio of the concave-convex structure (height of the convex portions in the thickness direction / width of the concave portions in the surface direction) is preferably 0.002 or more and 10.0 or less, more preferably 0.006 or more and 5.0 or less, and even more preferably 0.01 or more and 2.5 or less. When the pattern of the concave-convex structure is a dot pattern, the area per dot is not particularly limited, but is, for example, 0.001 mm ２ More than 10 mm ２or less, or 0.01 mm ２ More than 1 mm ２ The dot pitch (the distance between the centers of adjacent dots) is not particularly limited, but is, for example, 10 μm to 10 mm, 50 μm to 5 mm, or 100 μm to 1 mm.

[0021] The ratio of the height of the protrusions in the thickness direction to the thickness of the pressure-sensitive adhesive layer 3 (height of the protrusions in the thickness direction / thickness of the pressure-sensitive adhesive layer 3) is preferably 0.1 or more and 0.9 or less, and more preferably 0.2 or more and 0.8 or less. When the ratio is 0.1 or more, excellent container deformation suppression properties are likely to be obtained.

[0022] The pressure-sensitive adhesive layer 3 preferably contains a base resin (A) and a side-chain crystalline polymer (B). Such an adhesive for the pressure-sensitive adhesive layer 3 is also called a temperature-sensitive adhesive.

[0023] (Base Resin (A)) The base resin (A) may be acrylic. Examples of monomer components constituting the acrylic base resin include (meth)acrylates having an alkyl group with 1 to 12 carbon atoms. Examples of (meth)acrylates having an alkyl group with 1 to 12 carbon atoms include 2-ethylhexyl (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and butyl (meth)acrylate. The exemplified (meth)acrylates may be used alone or in combination of two or more. Note that (meth)acrylate means acrylate or methacrylate.

[0024] The monomer components constituting the base resin (A) may contain a polar monomer. Examples of the polar monomer include ethylenically unsaturated monomers having a carboxyl group, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; and ethylenically unsaturated monomers having a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 2-hydroxyhexyl (meth)acrylate. The exemplified polar monomers may be used alone or in combination of two or more.

[0025] Furthermore, the monomer components constituting the base resin (A) may contain, as a (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms, a (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms and / or a (meth)acrylate having an alkyl group having from 7 to 12 carbon atoms. Examples of (meth)acrylates having an alkyl group having from 1 to 6 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and hexyl (meth)acrylate. Examples of (meth)acrylates having an alkyl group having from 7 to 12 carbon atoms include 2-ethylhexyl (meth)acrylate. The exemplified (meth)acrylates may be used alone or in combination of two or more.

[0026] Specific compositions of the base resin (A) include the following compositions A and B. Composition A: Contains, as monomer components, a (meth)acrylate having an alkyl group with 1 to 12 carbon atoms and a polar monomer. Composition B: Contains, as monomer components, a (meth)acrylate having an alkyl group with 7 to 12 carbon atoms, a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, and a polar monomer.

[0027] In composition A, the (meth)acrylate having an alkyl group having from 1 to 12 carbon atoms may be from 85% by mass to 99% by mass, and the polar monomer may be from 1% by mass to 15% by mass. In composition B, the (meth)acrylate having an alkyl group having from 7 to 12 carbon atoms may be from 40% by mass to 65% by mass, the (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms may be from 30% by mass to 50% by mass, and the polar monomer may be from 5% by mass to 10% by mass.

[0028] The weight average molecular weight of the base resin (A) is preferably from 200,000 to 700,000, more preferably from 300,000 to 600,000. The weight average molecular weight is measured by gel permeation chromatography (GPC) and converted into polystyrene equivalent values.

[0029] (Side Chain Crystalline Polymer (B)) The side chain crystalline polymer (B) preferably has a structural unit derived from a (meth)acrylate monomer having a linear alkyl group having from 12 to 30 carbon atoms. In a (meth)acrylate having a linear alkyl group having from 12 to 30 carbon atoms, the linear alkyl group having from 12 to 30 carbon atoms functions as a side chain crystalline moiety in the side chain crystalline polymer. In other words, the side chain crystalline polymer is a comb-shaped polymer having a linear alkyl group having from 12 to 30 carbon atoms in its side chain, and crystallizes when this side chain is aligned into an orderly arrangement by intermolecular forces or the like.

[0030] The side-chain crystalline polymer is a polymer having a melting point, which is the temperature at which a specific portion of a polymer that was initially aligned in an ordered arrangement becomes disordered through an equilibrium process, and is a value obtained by measuring using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min.

[0031] The side-chain crystalline polymer crystallizes at temperatures below the melting point and undergoes a phase transition at temperatures above the melting point, exhibiting fluidity. That is, the side-chain crystalline polymer has temperature sensitivity, reversibly switching between a crystalline state and a fluid state in response to temperature changes. As a result, the side-chain crystalline polymer is in a crystalline state at temperatures below the melting point, and the pressure-sensitive adhesive layer 3 has sufficient adhesive strength to the container. Therefore, when the adhesive of the pressure-sensitive adhesive layer 3 is a temperature-sensitive adhesive, it exhibits excellent sealing properties (sealing ability or fixing strength) at temperatures below the melting point.

[0032] Furthermore, at temperatures above the melting point, the fluidity of the side-chain crystalline polymer inhibits the adhesiveness of the base resin (A). As a result, the adhesive strength of the pressure-sensitive adhesive layer 3 to the container decreases. That is, when the adhesive of the pressure-sensitive adhesive layer 3 is a temperature-sensitive adhesive, the adhesive strength to the container decreases at temperatures above the melting point of the side-chain crystalline polymer. Therefore, the pressure-sensitive adhesive layer 3 exhibits excellent vapor release properties (easy peelability) at temperatures above the melting point.

[0033] Furthermore, when the pressure-sensitive adhesive layer 3 is a temperature-sensitive adhesive, it has high tack at high temperatures (e.g., 100°C), resulting in excellent resealability after vapor release (heating). Furthermore, if the pressure-sensitive adhesive layer 3 is cooled to a temperature below the melting point of the side-chain crystalline polymer, the side-chain crystalline polymer crystallizes, restoring adhesive strength, resulting in even better resealability.

[0034] Examples of (meth)acrylates having a linear alkyl group having 12 to 30 carbon atoms, which are monomer components constituting the side-chain crystalline polymer, include cetyl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate, and behenyl (meth)acrylate. The exemplified (meth)acrylates may be used alone or in combination of two or more. The number of carbon atoms in the linear alkyl group is preferably 14 to 30, more preferably 16 to 30.

[0035] The monomer components constituting the side-chain crystalline polymer may include other monomers copolymerizable with (meth)acrylates having a linear alkyl group having from 12 to 30 carbon atoms. Examples of other monomers include (meth)acrylates having an alkyl group having from 1 to 6 carbon atoms, polar monomers, etc. These monomers may include the same monomers as those exemplified for the base resin (A).

[0036] When the side-chain crystalline polymer contains a (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms as a monomer component, the preferred composition is 35 to 95% by mass of the (meth)acrylate having a linear alkyl group having from 12 to 30 carbon atoms and 5 to 65% by mass of the (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms, and a more preferred composition is 35 to 80% by mass of the (meth)acrylate having a linear alkyl group having from 12 to 30 carbon atoms and 20 to 65% by mass of the (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms.

[0037] A preferred composition of the side-chain crystalline polymer when it contains a (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms and a polar monomer as monomer components is 30 to 95 mass% of a (meth)acrylate having a linear alkyl group having from 12 to 30 carbon atoms, 0 to 60 mass% of a (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms, and 5 to 10 mass% of the polar monomer; a more preferred composition is 60 to 89 mass% of a (meth)acrylate having a linear alkyl group having from 12 to 30 carbon atoms, 10 to 30 mass% of a (meth)acrylate having an alkyl group having from 1 to 6 carbon atoms, and 1 to 10 mass% of the polar monomer.

[0038] The melting point of the side-chain crystalline polymer is preferably 100° C. or lower, more preferably 30° C. or higher and 80° C. or lower, and even more preferably 30° C. or higher and 60° C. or lower. In this case, excellent sealing properties (fixing power) can be exhibited at room temperature (e.g., 23° C.). The melting point can be adjusted, for example, by changing the composition of the monomer components constituting the side-chain crystalline polymer.

[0039] The weight-average molecular weight of the side-chain crystalline polymer is preferably 3,000 or more and 20,000 or less, more preferably 5,000 or more and 15,000 or less. In this case, when the side-chain crystalline polymer exhibits fluidity, the adhesive strength can be sufficiently reduced. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC) and converted into polystyrene equivalent.

[0040] The content of the side-chain crystalline polymer is preferably 30 parts by mass or less, more preferably 3 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the base resin (A). In this case, when the side-chain crystalline polymer exhibits fluidity at a temperature equal to or higher than its melting point, the adhesive strength of the pressure-sensitive adhesive layer 3 to the container can be sufficiently reduced.

[0041] (Crosslinking Agent) The pressure-sensitive adhesive layer 3 may further contain a crosslinking agent. Examples of crosslinking agents include aziridine compounds, epoxy compounds, metal chelate compounds, and isocyanate compounds. The crosslinking conditions include a heating temperature of about 80°C to 120°C and a heating time of about 1 minute to 20 minutes. The content of the crosslinking agent is preferably 0.1 parts by mass to 10 parts by mass per 100 parts by mass of the base resin (A).

[0042] (Characteristics of Pressure-Sensitive Adhesive Layer) Adhesion strength T of pressure-sensitive adhesive layer 3 at 23°C ２３ is preferably 1 N / 25 mm or more, more preferably 2 N / 25 mm or more. ２３ When the tension is 1 N / 25 mm or more, excellent sealing property before heating is likely to be obtained. ２３ The upper limit of the adhesive strength is not particularly limited, but is, for example, 20 N / 25 mm or less, or 15 N / 25 mm or less. In this specification, the adhesive strength of the pressure-sensitive adhesive layer 3 is the 180° peel strength measured by the method described in the Examples below.

[0043] Adhesion strength T of pressure-sensitive adhesive layer 3 at 60°C ６０ is preferably 2N / 25mm or less, more preferably 1N / 25mm or less. ６０ When the T is 2N / 25mm or less, excellent steam escape properties are likely to be obtained. ６０ The lower limit of is not particularly limited, but is, for example, 0.01 N / 25 mm or more, or 0.001 N / 25 mm or more.

[0044] Adhesion strength T of pressure-sensitive adhesive layer 3 at 100°C １００ is preferably 0.5 N / 25 mm or less, more preferably 0.3 N / 25 mm or less. １００ When the T is 0.5 N / 25 mm or less, excellent steam escape properties are likely to be obtained. １００ The lower limit of is not particularly limited, but is, for example, 0.01 N / 25 mm or more, or 0.001 N / 25 mm or more.

[0045] Regarding the pressure-sensitive adhesive layer 3, T ６０ But, T ２３It is preferably 20% or less, more preferably 10% or less, even more preferably 5% or less, and particularly preferably 1% or less. ６０ But, T ２３ When the thickness is 20% or less of the pressure-sensitive adhesive layer 3, excellent vapor escape properties are easily obtained. １００ But, T ２３ It is preferably 10% or less, more preferably 5% or less, even more preferably 1% or less, and particularly preferably 0.5% or less. １００ But, T ２３ When the content is 10% or less, excellent vapor escape properties are likely to be obtained.

[0046] The thickness of the pressure-sensitive adhesive layer 3 is preferably 5 μm or more and 100 μm or less, and more preferably 5 μm or more and 50 μm or less.

[0047] <Substrate> As described above, the pressure-sensitive adhesive tape 1 of the present embodiment includes the film-like substrate 2. The term "film-like" is not limited to only film-like, but also includes film-like and sheet-like forms as long as the effects of the present embodiment are not impaired.

[0048] Examples of materials constituting the substrate 2 include synthetic resins such as polyethylene, polyethylene terephthalate, polypropylene, polyester, polyamide, polyimide, polycarbonate, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-polypropylene copolymer, and polyvinyl chloride.

[0049] The substrate 2 may have either a single-layer structure or a multi-layer structure. The substrate 2 may be subjected to a surface treatment to enhance adhesion to the pressure-sensitive adhesive layer 3. Examples of surface treatments include corona discharge treatment, plasma treatment, blast treatment, chemical etching treatment, and primer treatment.

[0050] The thickness of the substrate 2 is preferably 25 μm or more and 188 μm or less, more preferably 25 μm or more and 125 μm or less. In particular, when the thickness of the substrate 2 is 25 μm or more and 60 μm or less, the vapor escape property tends to be improved. Furthermore, when the thickness of the substrate 2 is 38 μm or more and 125 μm or less, the resealability tends to be improved.

[0051] <Release Sheet> A release sheet may be laminated on the surface of the pressure-sensitive adhesive layer 3 side of the pressure-sensitive adhesive tape 1. Examples of the release sheet include a sheet made of paper, polyethylene terephthalate, or the like, to which a release agent such as silicone has been applied. The thickness of the release sheet is preferably 5 μm or more and 500 μm or less, more preferably 25 μm or more and 250 μm or less. The release sheet is peeled off when the pressure-sensitive adhesive tape 1 is used.

[0052] The surface of the release sheet may be embossed to form a concave-convex structure on the pressure-sensitive adhesive layer 3, as described below.

[0053] <Container> In order to easily achieve the objects and effects of the present invention, the material of the container 100 is preferably a material that is impermeable to water vapor, and is preferably a resin. Examples of resins that constitute the container 100 include synthetic resins such as polyethylene, polyethylene terephthalate (hereinafter sometimes referred to as "PET"), polypropylene, polyesters other than PET, polystyrene, polyamide (hereinafter sometimes referred to as "nylon"), polyimide, polycarbonate, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-polypropylene copolymer, and polyvinyl chloride. The above synthetic resins are also preferably used as resin compositions containing various fillers, reinforcing agents, and various known additives.

[0054] When the material of the container 100 is resin, the entire material of the container does not have to be resin. In the container 100, it is preferable that the material around the steam release port 101 that is attached to the adhesive tape 1 is made of resin. In this way, the container 100 may have a portion that is made of a material other than resin in an area that is not attached to the adhesive tape 1.

[0055] The container 100 may be composed of a container part that contains the contents and has an opening, and a lid part that closes the opening of the container part. In this case, the lid part made of a film or sheet may be heat-sealed to the container part.

[0056] The container 100 has a steam release port 101. Examples of the shape of the steam release port 101 include a hole and a slit. The steam release port 101 may consist of a single opening or multiple openings. The position of the steam release port 101 is not particularly limited, but when the container 100 consists of the above-mentioned container portion and lid portion, the steam release port 101 may be located in the center or approximately the center of the surface of the lid portion. When the container 100 containing food is heated, the center or approximately the center of the surface of the lid portion is likely to expand from the inside to the outside of the container due to pressure inside the container. This makes it easier for the adhesive tape 1 to be partially peeled off from the lid portion when the container 100 is heated.

[0057] The contents contained in the container 100 include contents that generate steam or the like when heated. The container 100 may be subjected to a surface treatment such as printing.

[0058] <Method for manufacturing adhesive tape> Examples of a method for manufacturing the adhesive tape 1 of the present embodiment include a manufacturing method including a step of laminating a pressure-sensitive adhesive layer 3 on at least one surface of a substrate 2 and a step of forming a concave-convex structure on the surface of the pressure-sensitive adhesive layer 3, and a manufacturing method including a step of laminating a pressure-sensitive adhesive layer 3 having a concave-convex structure on its surface on at least one surface of a substrate 2.

[0059] To laminate the pressure-sensitive adhesive layer 3 on at least one surface of the substrate 2, for example, a coating liquid may be prepared by adding a solvent to the adhesive of the pressure-sensitive adhesive layer 3, and the resulting coating liquid may be applied to one or both surfaces of the substrate 2 using a coater or the like, followed by drying. Examples of coaters include a knife coater, a roll coater, a calendar coater, a comma coater, a gravure coater, and a rod coater.

[0060] A method for forming a concave-convex structure on the surface of the pressure-sensitive adhesive layer 3 includes, for example, laminating an embossed release sheet onto the pressure-sensitive adhesive layer 3 and transferring the concave-convex structure.

[0061] Examples of a method for laminating the pressure-sensitive adhesive layer 3 having an uneven structure on at least one surface of the substrate 2 include a method of laminating the layer by printing such as gravure printing.

[0062] It is also preferable to color the surface of the base material 2 or provide it with a pattern or lettering, taking into consideration the coloring, pattern, lettering, etc. on the surface of the container 100 so as not to impair the aesthetic appeal of the container 100. Furthermore, a portion of the base material 2 may be colored with a thermosensitive dye that irreversibly changes color when heated, so that it can be visually confirmed that the container 100 has been heated once.

[0063] The present invention will be explained in more detail below by showing examples, but the scope of the present invention is not limited to these examples.

[0064] (Synthesis Examples A, B, D: Base Resin) First, the monomers shown in Table 1 were added to a reaction vessel in the ratios shown in Table 1 to obtain a monomer mixture. The monomers shown in Table 1 are as follows: EHA: 2-ethylhexyl acrylate AA: acrylic acid C1A: methyl acrylate HEA: 2-hydroxyethyl acrylate HBA: 4-hydroxybutyl acrylate

[0065] Next, the solvents shown in Table 1 were added to the reaction vessel so as to obtain a mixed solution with a solid content as shown in Table 1. The solvents shown in Table 1 are as follows: EtAc: ethyl acetate, hep: heptane, tol: toluene.

[0066] The resulting mixture was degassed with nitrogen gas for 30 minutes or more. The mixture was then heated to 55°C, and 0.3 parts by mass (solids equivalent) of NOF Corporation's peroxide "Perbutyl ND" was added to 100 parts by mass of the monomer mixture, followed by a reaction for 4 hours.

[0067] The mixture was then heated to 80°C, and NOF Corporation's peroxide "Perhexyl PV" was added in a ratio of 0.5 parts by mass (solid content equivalent) per 100 parts by mass of the monomer mixture, followed by a reaction for 2 hours to obtain a base resin.

[0068] (Synthesis Examples C and E: Side Chain Crystalline Polymer) First, the monomers shown in Table 1 were added to a reaction vessel in the ratios shown in Table 1 to obtain a monomer mixture. The monomers shown in Table 1 are as follows: C18A: stearyl acrylate C1A: methyl acrylate AA: acrylic acid

[0069] Next, dodecyl mercaptan was added as a chain transfer agent in a proportion of 5 parts by mass (solid content equivalent) per 100 parts by mass of the monomer mixture, and a solvent shown in Table 1 was further added to the reaction vessel so that the solid content concentration became the proportion shown in Table 1, thereby obtaining a mixed liquid. The obtained mixed liquid was then degassed with nitrogen gas for 30 minutes or more.

[0070] The mixture was then heated to 70°C, and 0.5 parts by mass (solid content equivalent) of a peroxide "Perhexyl PV" manufactured by NOF Corporation was added to 100 parts by mass of the monomer mixture, followed by a reaction for 1 hour. The mixture was then heated to 80°C and reacted for 4 hours to obtain a side-chain crystalline polymer.

[0071] The weight-average molecular weight of the obtained base resin is shown in Table 1. The weight-average molecular weight and melting point of the obtained side-chain crystalline polymer are also shown in Table 1. The weight-average molecular weight is a value measured by GPC and converted into polystyrene equivalent. The melting point is a value measured using DSC at a heating rate of 10°C / min.

[0072]

[0073] <Preparation of Pressure-Sensitive Adhesive Tapes> [Examples 1 to 9] First, a crosslinking agent (Tetrad X manufactured by Mitsubishi Gas Chemical Company, Inc.) and, if necessary, the side-chain crystalline polymer obtained in Synthesis Example C were added to the base resin obtained in Synthesis Example A in the amounts shown in Table 2 to obtain a coating solution. The amounts shown in Table 2 are values ​​calculated as solids content per 100 parts by mass of the base resin.

[0074] Next, the obtained coating liquid was applied to one side of a substrate. After removing the solvent in the coating film by heating, an embossed release sheet was laminated on the coating film. Thereafter, a crosslinking reaction was carried out under conditions of 110°C x 5 minutes to obtain an adhesive tape in which a pressure-sensitive adhesive layer was laminated on one side of the substrate. The substrate was a 50 mm thick PET film that had been corona-treated on both sides. The release sheet was a paper separator that had been coated with silicone on its surface and had been embossed.

[0075] In Examples 1 to 5, paper separators with the same embossing were used, while in the other Examples, paper separators with different embossing processes were used. In Examples 1 to 5, the pressure-sensitive adhesive layer of the adhesive tape from which the release sheet was peeled had a concave-convex structure in a triangular lattice pattern of equilateral triangles with sides of 0.6 mm, as shown in FIG. 6 , and the sides of the equilateral triangles were formed with grooves (concave portions) with a depth of 9 μm and a width of 35 μm. The thickness of the pressure-sensitive adhesive layer in the flat portions (convex portions) other than the sides of the equilateral triangles was 30 μm. In Example 6, the pressure-sensitive adhesive layer of the adhesive tape from which the release sheet was peeled had a concave-convex structure in a pattern in which dots were arranged in a rectangular lattice pattern, as shown in FIG. 7 . The dots were formed as concave portions with approximately square bases with sides of 320 μm and approximately quadrangular prisms with a height of 20 μm. The shorter side a of the dot spacing was 60 μm, and the longer side b of the dot spacing was 125 μm. The thickness of the pressure-sensitive adhesive layer in the flat portions (convex portions) other than the dots was 30 μm. In Example 7, the pressure-sensitive adhesive layer of the adhesive tape from which the release sheet was peeled off had a concave-convex structure in a pattern in which dots were arranged in a square lattice pattern, as shown in FIG. 8. The dots were formed as approximately square prism-shaped depressions with bases measuring 350 μm on a side and a height of 20 μm. The dot spacing c was 180 μm. The thickness of the pressure-sensitive adhesive layer in the flat portions (convex portions) other than the dots was 30 μm. In Example 8, the pressure-sensitive adhesive layer of the adhesive tape from which the release sheet was peeled off had a concave-convex structure in a pattern in which dots were arranged in a rectangular lattice pattern, as shown in FIG. 7. The dots were formed as approximately square prism-shaped depressions with bases measuring 300 μm on a side and a height of 15 μm. The dot spacing was 65 μm on the shorter side a and 130 μm on the longer side b. The thickness of the pressure-sensitive adhesive layer in flat portions (convex portions) other than the dots was 30 μm. In Example 9, an adhesive tape was obtained in the same manner as in Example 4, except that the thickness of the pressure-sensitive adhesive layer was changed to 20 μm. [Example 10] First, a crosslinking agent (Takenate D-101E manufactured by Mitsui Chemicals, Inc.) and the side-chain crystalline polymer obtained in Synthesis Example E were added to the base resin obtained in Synthesis Example D in the amounts shown in Table 2, to obtain a coating liquid. An adhesive tape was obtained in the same manner as in Example 1, except that the thickness of the pressure-sensitive adhesive layer was changed to 20 μm.

[0076] [Comparative Examples 1 to 5] Coating solutions were obtained in the same manner as in Examples 1 to 8. Next, the obtained coating solutions were applied to one side of a substrate, and a crosslinking reaction was carried out under conditions of 110°C x 5 minutes, thereby obtaining adhesive tapes in which a 30 μm thick pressure-sensitive adhesive layer was laminated on one side of the substrate. Furthermore, a release sheet was laminated on the surface of the obtained adhesive tape. The same film as in Examples 1 to 8 was used as the substrate. The release sheet was a PET film whose surface was coated with silicone and which was not embossed.

[0077] Comparative Example 6 First, a crosslinking agent (Takenate D-101E manufactured by Mitsui Chemicals, Inc.) and thermally expandable microcapsules (DU40 manufactured by Nippon Phillite Co., Ltd.) were added to the base resin obtained in Synthesis Example B in the amounts shown in Table 2 to obtain a coating liquid. The amounts shown in Table 2 are values ​​calculated as solid content per 100 parts by mass of the base resin. Next, in the same manner as in Comparative Examples 1 to 5, pressure-sensitive adhesive tapes laminated with a release sheet were obtained.

[0078] <Evaluation> The adhesive strength to the PET film, vapor escape property, retention property, and container deformation suppression property of the obtained pressure-sensitive adhesive tape were evaluated. The evaluation methods are shown below, and the results are shown in Table 2.

[0079] (Adhesive Strength) The 180° peel strength against a PET film at 23°C, 60°C, and 100°C was measured in accordance with JIS Z0237. Specifically, an adhesive tape was pressure-bonded to a PET film as an adherend under the following conditions, and then the adhesive tape was peeled at 180° from the PET film as an adherend at a rate of 300 mm / min using a load cell. The PET film as an adherend was a film having a thickness of 25 μm and an untreated surface.

[0080] [23° C.] The adhesive tape was pressure-bonded to a PET film as an adherend at an ambient temperature of 23° C., allowed to stand at this ambient temperature for 20 minutes, and then peeled off at an angle of 180°.

[0081] [60°C] The pressure-sensitive adhesive tape was pressure-bonded to a PET film as an adherend at an ambient temperature of 23°C, allowed to stand at this ambient temperature for 20 minutes, and then the ambient temperature was raised to 60°C. The tape was allowed to stand at this ambient temperature for 5 minutes, and then peeled off at an angle of 180°.

[0082] [100°C] The pressure-sensitive adhesive tape was pressure-bonded to a PET film as an adherend at an ambient temperature of 23°C, allowed to stand at this ambient temperature for 20 minutes, and then the ambient temperature was raised to 100°C. The tape was allowed to stand at this ambient temperature for 5 minutes, and then peeled off at an angle of 180°.

[0083] (Vapor Escape Property) First, a test container was prepared. Specifically, a semicircular slit with a diameter of 10 mm was provided in the center of a PET film measuring 110 mm x 110 mm and having a heat seal layer on one side. A 30 mm x 30 mm adhesive tape was pressed around the slit to obtain a lid. 100 mL of water was placed in a polypropylene cup container having a diameter of 100 mm and a 5 mm wide flange, and the lid obtained above was pressed with a heat seal to prepare a test container.

[0084] The test container was heated in a microwave oven at 500W for 90 seconds, and the steam release property was evaluated by visually checking whether steam was released from the slit in the center without breaking the heat seal. The evaluation criteria were set as follows: ◯: Steam was automatically released ×: Steam was not automatically released or the heat seal broke

[0085] (Retention) When heat treatment was carried out in the steam release test, the peeling state of the adhesive tape when steam was released was visually confirmed and the retention was evaluated. The evaluation criteria were set as follows: ◯: Only a part of the adhesive tape peeled off and did not fall off from the central slit part. ×: The adhesive tape peeled off entirely and fell off from the central slit part.

[0086] (Container Deformation Inhibition) After the heat treatment in the steam escape test, the water and the test container were left to cool. Then, the container was visually inspected for deformation, and the container deformation inhibition was evaluated. The evaluation criteria were set as follows: ◯: The container was not deformed by compression; ×: The container was deformed by compression.

[0087]

[0088] As is clear from Table 2, the pressure-sensitive adhesive tapes of Examples 1 to 10, which have a pressure-sensitive adhesive layer with an uneven structure, are excellent in vapor escape properties, retention properties, and container deformation suppression properties. On the other hand, the pressure-sensitive adhesive tapes of Comparative Examples 1 to 6, which have a pressure-sensitive adhesive layer without an uneven structure, are inferior in any of vapor escape properties, retention properties, and container deformation suppression properties.

[0089] REFERENCE SIGNS LIST 1 adhesive tape 2 substrate 3 pressure-sensitive adhesive layer 100 container 101 steam outlet

Claims

1. An adhesive tape used to seal a steam release port by being pressed against a container having the steam release port, the adhesive tape comprising a film-like substrate and a pressure-sensitive adhesive layer laminated on at least one side of the substrate, the surface of the pressure-sensitive adhesive layer having an uneven structure.

2. The adhesive tape according to claim 1, wherein the pressure-sensitive adhesive layer comprises a base resin (A) and a side-chain crystalline polymer (B), and the side-chain crystalline polymer (B) comprises a structural unit derived from a (meth)acrylate monomer having a linear alkyl group having from 12 to 30 carbon atoms.

3. The adhesive strength T of the pressure-sensitive adhesive layer at 60°C ６０ is the adhesive strength T at 23°C ２３ The adhesive strength at 100°C is 20% or less of the １００ is the T ２３ The pressure-sensitive adhesive tape according to claim 1 or 2, wherein the thickness is 10% or less of the thickness of the adhesive tape.

4. Said T １００ The pressure-sensitive adhesive tape according to claim 3, wherein the tension strength is 0.3 N / 25 mm or less.

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