Adhesive with pressure adjustment function

Abstract

An adhesive with a pressure adjustment function according to the present invention is bonded to a resin adherend that has a vapor discharge port for the purpose of sealing the vapor discharge port. The adhesive force of this adhesive is decreased by the heat of the vapor discharged from the vapor discharge port, and this adhesive loses adhesion by the pressure of the vapor, thereby having the vapor discharged. This adhesive is capable of sealing the vapor discharge port again after the discharge of vapor, and does not require an external force for the re-sealing. This adhesive may contain a pressure-sensitive adhesive and a side-chain crystalline polymer which contains, as a monomer component, a (meth)acrylate that has a linear alkyl group having 12 to 30 carbon atoms.

Description

Pressure-adjustable adhesive

[0001] The present invention relates to a pressure-adjustable adhesive.

[0002] When a sealed container is heated, steam generated by the heating can cause the container to expand and burst. To address this problem, many technologies have been proposed that incorporate a steam release function into the container lid or adhesive tape. For example, Patent Document 1 proposes a configuration in which a heat-shrinkable film is used, which shrinks when heated to release steam.

[0003] On the other hand, in the conventional configuration proposed in Patent Document 1, the steam release port remains open after the steam is released, which raises the risk of the contents leaking or burns caused by the release of remaining steam. There is also the concern that foreign matter may get inside the container.

[0004] To solve this problem, for example, Patent Document 2 proposes a configuration in which an adhesive label is peeled off by the internal pressure of steam, and resealing is supported by the rigidity of the base material.

[0005] However, the configuration proposed in Patent Document 2 requires manual operation (external force) such as application of adhesive when resealing, and therefore there remains a concern that a small amount of heat from the steam released after heating may cause burns when resealing.

[0006] JP 2016-60531 A Patent No. 6771281 A

[0007] An object of the present invention is to provide a pressure-adjusting adhesive that has excellent sealing properties and vapor escape properties.

[0008] The pressure-adjusting adhesive of the present invention is an adhesive that is attached to a resin substrate having a steam outlet to seal the steam outlet, and its adhesive strength is reduced by the heat of the steam released from the steam outlet, and it peels off due to the pressure of the steam, allowing the steam to be released.

[0009] According to the present invention, there is an effect that sealing properties and vapor escape properties are excellent.

[0010] FIG. 1 is a cross-sectional view showing a pressure-adjustable adhesive (pressure-adjustable adhesive tape) and an adherend according to one embodiment of the present invention, illustrating a state before steam is released. FIG. 2 is a cross-sectional view showing a pressure-adjustable adhesive (pressure-adjustable adhesive tape) and an adherend 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 a pressure-adjustable adhesive (pressure-adjustable adhesive tape) and an adherend 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 a pressure-adjustable adhesive (pressure-adjustable adhesive tape) and an adherend according to one embodiment of the present invention, illustrating a state after steam has been released. FIG. 5 is a graph showing a water vapor pressure curve versus temperature. FIG. 6 is a graph showing water vapor pressure curves and temperature changes in adhesive strength of the pressure-adjustable adhesives according to Example 5 and Comparative Example 1.

[0011] Hereinafter, a pressure-adjustable adhesive (hereinafter simply referred to as "adhesive") according to one embodiment of the present invention will be described in detail with reference to the drawings, taking as an example the case where it is used in the form of an adhesive tape.

[0012] As shown in FIG. 1 , the pressure-adjustable adhesive tape (hereinafter, sometimes simply referred to as “adhesive tape”) 1 of this embodiment comprises a film-like substrate 2 and an adhesive layer 3 laminated on at least one side of the substrate 2.

[0013] The pressure-sensitive adhesive layer 3 contains the pressure-adjustable pressure-sensitive adhesive 4 of this embodiment. The pressure-sensitive adhesive layer 3 contains the pressure-sensitive adhesive 4 as a main component. The "main component" refers to a component that is contained in the largest amount by weight compared to other components. The main component may be, for example, 80% by weight or more. The content of the pressure-sensitive adhesive 4 in the pressure-sensitive adhesive layer 3 may be 80 to 100% by weight.

[0014] The pressure-sensitive adhesive 4 of this embodiment is attached to a resin adherend 100 having a steam release port 101 to seal the steam release port 101. The concept of "sealing the steam release port 101" is not limited to sealing the steam release port 101 before steam is released, but also includes resealing the steam release port 101 after steam is released. The steam release port 101 functions as a portion that releases steam. The shape of the steam release port 101 can be, for example, a hole or a slit.

[0015] Examples of resins that may constitute the adherend 100 include synthetic resins such as polyethylene, polyethylene terephthalate (hereinafter sometimes referred to as "PET"), polypropylene, polyester, polystyrene, polyamide (hereinafter sometimes referred to as "nylon"), polyimide, polycarbonate, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-polypropylene copolymer, and polyvinyl chloride.

[0016] The adherend 100 does not have to be made entirely of resin. It is sufficient that the adherend 100 has a portion around the steam release port 101 that is attached to the adhesive 4 that is made of resin. Therefore, the adherend 100 may have a portion that is made of a material other than resin in an area that is not attached to the adhesive 4.

[0017] The adherend 100 may be, for example, a container used for packaging purposes. In FIG. 1, a container is shown as an example of the adherend 100. When the adherend 100 is a container, the contents contained therein may be those that generate water vapor when heated. The adherend 100 may be subjected to a surface treatment such as printing.

[0018] The adhesive 4 of this embodiment has a pressure adjusting function. In other words, the adhesive 4 of this embodiment can exert a pressure adjusting function. In addition, the adhesive 4 has excellent sealing properties and vapor escape properties.

[0019] Figures 5 and 6 show saturated water vapor pressure curves, and will be explained using water vapor pressure as an example. Figure 5 shows a water vapor pressure curve versus temperature. From this figure, it can be seen that water vapor pressure rises sharply around 60°C. Figure 6 shows a water vapor pressure curve and a graph showing the temperature change in adhesive strength of adhesives according to Example 5 and Comparative Example 1, which will be described later. The adhesive 4 of this embodiment (Example 5) shown in Figure 6 has low adhesive strength at 60°C, where water vapor pressure rises sharply, and maintains this low adhesive strength even at 100°C. On the other hand, the adhesive strength of Comparative Example 1 decreases almost linearly at room temperature (e.g., 23°C), 60°C, and 100°C.

[0020] These characteristics will be explained by applying them to the heating process in this embodiment. As shown in Fig. 2, when the adherend 100 is heated, the internal temperature of the adherend 100 increases and the internal pressure of the adherend 100, i.e., the water vapor pressure, also increases. When the temperature of the adherend 100 reaches approximately 60°C, the adhesive strength of the pressure-adjustable adhesive 4 suddenly decreases, as shown in Fig. 3, and the pressure applied to the vapor release port 101 causes the pressure-regulating pressure-adjustable adhesive tape 1 to peel off from the surface of the adherend 100, opening the vapor release port 101 and releasing the vapor inside the adherend 100 to the outside.

[0021] In such a case, the adhesive 4 must have high adhesive strength at room temperature and low adhesive strength at 60°C. At room temperature, it is necessary to isolate the inside from the outside, and sufficient adhesive strength is required to seal the steam release port 101. At 60°C, it is necessary to reliably and efficiently release the suddenly increased water vapor pressure to the outside in order to prevent damage to the adherend, so the adhesive strength of the adhesive 4 at 60°C must be sufficiently low. The adhesive strength at 60°C is preferably 2 N / 25 mm or less, and more preferably 1 N / 25 mm or less. A method for measuring adhesive strength will be described later.

[0022] If the adhesive strength at 60°C is greater than 2 N / 25 mm, water vapor may not be able to escape sufficiently, or the adherend 100 may be destroyed due to pressure concentration. When the adherend 100 is heated and the internal water vapor pressure increases around 60°C, the adhesive tape covering the steam release port 101 is pressurized from within the adherend 100 by the water vapor. If the adhesive strength at 60°C is greater than 2 N / 25 mm, the adhesive tape covering the steam release port 101 may not peel off, causing the adherend 100 to be destroyed. Alternatively, the adhesive tape covering the steam release port 101 may not peel off uniformly, increasing the possibility that only the portion with the weakest adhesive strength, i.e., only a portion of the adhesive tape, may peel off. In such cases, water vapor inside the adherend 100 will be concentrated and released from the peeled portion of the steam release port 101, resulting in insufficient water vapor escape or the adherend 100 being destroyed due to pressure concentration.

[0023] This point can be more specifically shown by the adhesive strength reduction coefficient shown in Equation 1. Equation 1: Adhesive strength reduction coefficient = "Adhesive strength at 23°C" / "Adhesive strength at 60°C"

[0024] The adhesive strength reduction coefficient is preferably 4 or greater, and more preferably 10 or greater. When the adhesive strength reduction coefficient is 4 or greater, adhesive strength at room temperature (e.g., 23°C) can be ensured, i.e., steam release port 101 can be sealed, and steam release port 101 can be reliably opened at 60°C. When the adhesive strength reduction coefficient is less than 4, the adhesive strength at room temperature is too low to seal steam release port 101, or the adhesive strength at 60°C is too high, making it impossible to reliably open steam release port 101.

[0025] Furthermore, the change in adhesive strength of the adhesive 4 can be set in more detail by the degree of change in adhesive strength shown in Equation 2. Equation 2: Degree of change in adhesive strength = "adhesive strength at 23°C / adhesive strength at 60°C" / "ratio of adhesive strength at 60°C / adhesive strength at 100°C"

[0026] The degree of change in adhesive strength is preferably 1 or more, and more preferably 4 or more. Figure 6 shows the change in adhesive strength relative to the change in water vapor pressure. When the degree of change in adhesive strength is 1 or more, i.e., when the change from 60°C to 100°C is smaller than the change from 23°C to 60°C, the adhesive strength of the adhesive 4 decreases significantly in the temperature range where water vapor pressure increases rapidly, and the reduced adhesive strength of the adhesive 4 can be maintained thereafter, and the steam release port 101 that opened at 60°C remains open even at 100°C.

[0027] On the other hand, if the degree of change in adhesive strength is less than 1, i.e., if the change from 60°C to 100°C is greater than the change from 23°C to 60°C, the adhesive strength will not decrease sufficiently in the temperature range where the water vapor pressure inside the adherend 100 rises sharply, and there is a possibility that the adherend 100 will be destroyed. Furthermore, if the temperature of the adherend 100 continues to rise, the extremely increased water vapor pressure inside the adherend 100 will be suddenly released around 100°C, which may cause the steam release port 101 to break down or the adherend 100 to break down.

[0028] 4, the adhesive 4 of this embodiment can reseal the steam release port 101 after steam is released, and may not require an external force for resealing. The adhesive 4 may be able to reseal the steam release port 101 without human contact. In this case, the adhesive 4 has the advantage of having excellent resealability.

[0029] Resealing is thought to be possible due to the tack strength in the high temperature range, i.e., the temperature range of 60°C or higher. When steam is released from the steam release port 101, the steam continues to be released from the inside of the adherend 100 to the outside through the steam release port 101. Even when the temperature stops rising and gradually decreases, steam continues to be released at temperatures up to around 60°C. In conventional technology, even if the adhesive tape touches the steam release port 101, it cannot remain in place, making resealing difficult without an external force. In the pressure-adjustable adhesive tape 1 of this embodiment, the tack strength is strong at the high temperature range of 60°C and 100°C, and the force of the release from the steam release port 101 weakens, so that when the adhesive 4 comes into contact with the periphery of the steam release port 101, it temporarily adheres due to the high tack strength. Next, when the temperature falls below 60°C and the pressure inside the adherend 100 is gradually reduced, the adhesive 4 adheres to the periphery of the steam release port 101, starting from the area that was temporarily adhered by the tack force, and the steam release port 101 can be sealed again. The tack force of the adhesive 4 at 60°C is 3 N / 19.6 mm. 2 More than 6N / 19.6mm is preferable. 2 The above is more preferable. The method for measuring the tackiness will be described later.

[0030] The pressure-sensitive adhesive 4 of this embodiment has excellent sealing properties (fixing strength) at room temperature (e.g., 23°C). The pressure-sensitive adhesive 4 of this embodiment also has excellent peelability when heated and resealability after heating.

[0031] The pressure-sensitive adhesive 4 of this embodiment may contain a pressure-sensitive adhesive and a side-chain crystalline polymer. Such a pressure-sensitive adhesive 4 is also called a temperature-sensitive adhesive. A temperature-sensitive adhesive is an adhesive whose adhesive strength changes in response to temperature changes. Below, a specific description will be given of the case where the pressure-sensitive adhesive 4 is a temperature-sensitive adhesive.

[0032] Pressure sensitive adhesives are polymers that have tacky properties.

[0033] The side-chain crystalline polymer contains, as a monomer component, a (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms. In the (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms, the linear alkyl group having 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 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.

[0034] 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.

[0035] 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 4 has sufficient adhesive strength to resins. Therefore, when the pressure-sensitive adhesive 4 is a temperature-sensitive adhesive, it exhibits excellent sealing properties (sealing ability or fixing strength) at temperatures below the melting point.

[0036] Furthermore, at temperatures above the melting point, the side-chain crystalline polymer exhibits fluidity, which inhibits the adhesive properties of the pressure-sensitive adhesive described above. As a result, the adhesive strength of the pressure-sensitive adhesive 4 to the resin decreases. That is, when the pressure-sensitive adhesive 4 is a temperature-sensitive adhesive, the adhesive strength to the resin decreases at temperatures above the melting point of the side-chain crystalline polymer. Therefore, the pressure-sensitive adhesive 4 exhibits excellent vapor release properties (easy peelability) at temperatures above the melting point.

[0037] Furthermore, when the pressure-sensitive adhesive 4 is a temperature-sensitive adhesive, the adhesive has high tack at high temperatures (e.g., 100°C), resulting in excellent resealability after vapor release (heating). Furthermore, when the pressure-sensitive adhesive 4 is cooled to a temperature below the melting point of the side-chain crystalline polymer, the side-chain crystalline polymer crystallizes, restoring the adhesive strength, resulting in even better resealability.

[0038] 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. Note that (meth)acrylate refers to acrylate or methacrylate. The linear alkyl group preferably has 16 to 30 carbon atoms.

[0039] The monomer components constituting the side-chain crystalline polymer may contain other monomers that can be copolymerized with a (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms. Examples of other monomers include a (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, a polar monomer, and the like.

[0040] Examples of (meth)acrylates having an alkyl group having 1 to 6 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, etc. The exemplified (meth)acrylates may be used alone or in combination of two or more.

[0041] Examples of polar monomers 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 hydroxyl 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.

[0042] When the side-chain crystalline polymer contains a (meth)acrylate having an alkyl group having 1 to 6 carbon atoms as a monomer component but does not contain a polar monomer as a monomer component, the preferred composition is 35 to 95 wt % of a (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms and 5 to 65 wt % of a (meth)acrylate having an alkyl group having 1 to 6 carbon atoms, and a more preferred composition is 35 to 80 wt % of a (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms and 20 to 65 wt % of a (meth)acrylate having an alkyl group having 1 to 6 carbon atoms.

[0043] A preferred composition of the side-chain crystalline polymer containing a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms and a polar monomer as monomer components is 30 to 95% by weight of a (meth)acrylate having a linear alkyl group with 12 to 30 carbon atoms, 0 to 60% by weight of a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, and 5 to 10% by weight of the polar monomer, and a more preferred composition is 60 to 89% by weight of a (meth)acrylate having a linear alkyl group with 12 to 30 carbon atoms, 10 to 30% by weight of a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, and 1 to 10% by weight of the polar monomer.

[0044] Examples of the method for polymerizing the monomer components include solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. When the solution polymerization method is employed, the monomer components and a solvent are mixed, and a polymerization initiator, a chain transfer agent, etc. are added as needed, followed by reaction at about 40 to 90°C for about 2 to 10 hours with stirring.

[0045] The melting point of the side-chain crystalline polymer is preferably 100° C. or lower, more preferably 30 to 80° C., and even more preferably 30 to 60° C. 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 that constitute the side-chain crystalline polymer.

[0046] The weight-average molecular weight of the side-chain crystalline polymer is preferably 3,000 to 20,000, more preferably 5,000 to 15,000. In this case, the adhesive strength can be sufficiently reduced when the side-chain crystalline polymer exhibits fluidity. The weight-average molecular weight is a value measured by gel permeation chromatography (GPC) and converted into polystyrene equivalent.

[0047] The content of the side-chain crystalline polymer is preferably 30 parts by weight or less, more preferably 3 to 20 parts by weight, relative to 100 parts by weight of the pressure-sensitive adhesive. In this case, when the side-chain crystalline polymer exhibits fluidity at a temperature equal to or higher than the melting point, the adhesive strength of the pressure-sensitive adhesive 4 to the resin can be sufficiently reduced.

[0048] The pressure-sensitive adhesive may be acrylic. Examples of monomer components constituting acrylic pressure-sensitive adhesives include (meth)acrylates having an alkyl group having 1 to 12 carbon atoms. Examples of (meth)acrylates having an alkyl group having 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.

[0049] The pressure-sensitive adhesive may contain a polar monomer as a monomer component. The pressure-sensitive adhesive may also contain a (meth)acrylate having an alkyl group having 1 to 6 carbon atoms as a monomer component. Examples of the (meth)acrylate having an alkyl group having 1 to 6 carbon atoms and the polar monomer include the same ones as those exemplified for the side-chain crystalline polymer.

[0050] Specific compositions of the pressure-sensitive adhesive include the following compositions A and B. Composition A: Contains a (meth)acrylate having an alkyl group with 1 to 12 carbon atoms and a polar monomer as monomer components. Composition B: Contains a (meth)acrylate having an alkyl group with 1 to 12 carbon atoms, a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, and a polar monomer as monomer components.

[0051] Composition A may contain 90 to 99% by weight of a (meth)acrylate having an alkyl group with 1 to 12 carbon atoms and 1 to 10% by weight of a polar monomer, while composition B may contain 40 to 65% by weight of a (meth)acrylate having an alkyl group with 1 to 12 carbon atoms, 30 to 50% by weight of a (meth)acrylate having an alkyl group with 1 to 6 carbon atoms, and 5 to 10% by weight of a polar monomer.

[0052] Examples of the method for polymerizing the monomer components include solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. When the solution polymerization method is employed, the monomer components and a solvent are mixed, and a polymerization initiator, a chain transfer agent, etc. are added as needed, followed by reaction at about 40 to 90°C for about 2 to 10 hours with stirring.

[0053] The weight-average molecular weight of the pressure-sensitive adhesive, which is a polymer of the above-mentioned monomer components, is preferably 200,000 to 600,000, and more preferably 300,000 to 500,000. The weight-average molecular weight is measured by gel permeation chromatography (GPC) and converted into a polystyrene equivalent value.

[0054] When the 180° peel strength of the PSA 4 from the polyethylene terephthalate film at 100°C is low, the vapor escape property tends to be improved. Also, when the tack strength of the PSA 4 at 100°C is high, the resealability tends to be improved.

[0055] The 180° peel strength of the pressure-sensitive adhesive 4 against a polyethylene terephthalate film at 100°C is preferably 0.3 N / 25 mm or less, more preferably 0.2 N / 25 mm or less. The tack strength of the pressure-sensitive adhesive 4 at 100°C is preferably 2.0 N / 19.6 mm or less. 2 More preferably, 3.0N / 19.6mm 2 In these cases, stable vapor release properties and resealability can be exhibited for the resin adherend 100 that is widely used in packaging applications.

[0056] The 180° peel strength is a value measured in accordance with JIS Z 0237. The tack strength is a probe tack value measured in accordance with ASTM D 2979, except that the contact load was changed to 300 gf.

[0057] The pressure-sensitive adhesive 4 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 approximately 90 to 120°C and a heating time of approximately 1 to 20 minutes. The content of the crosslinking agent is preferably 0.1 to 10 parts by weight per 100 parts by weight of the pressure-sensitive adhesive.

[0058] As described above, the pressure-sensitive adhesive tape 1 of this 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 this embodiment are not impaired.

[0059] 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.

[0060] 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.

[0061] The thickness of the substrate 2 is preferably 25 to 188 μm, more preferably 25 to 125 μm. When the thickness of the substrate 2 is 25 to 60 μm, the vapor escape property tends to be improved. When the thickness of the substrate 2 is 38 to 125 μm, the resealability tends to be improved.

[0062] 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 pressure-sensitive adhesive 4, 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.

[0063] The thickness of the pressure-sensitive adhesive layer 3 is preferably 5 to 100 μm, more preferably 5 to 50 μm.

[0064] When pressure-sensitive adhesive layers are laminated on both sides of the substrate 2, the pressure-sensitive adhesive layer 3 on one side and the pressure-sensitive adhesive layer on the other side may be the same as or different from each other in thickness, composition, etc. Furthermore, as long as the pressure-sensitive adhesive layer 3 on one side contains the pressure-adjustable pressure-sensitive adhesive 4 described above, the pressure-sensitive adhesive layer on the other side is not particularly limited.

[0065] A release film may be laminated on the surface of the pressure-sensitive adhesive tape 1. An example of a release film is one in which a release agent such as silicone is applied to the surface of a film made of polyethylene terephthalate or the like. The thickness of the release film is preferably 5 to 500 μm, more preferably 25 to 250 μm. The release film is peeled off when the pressure-sensitive adhesive tape 1 is used.

[0066] The use form of the pressure-adjustable adhesive is not limited to the form of an adhesive tape. The adhesive may be used as is, or may be used in the form of an adhesive sheet, as described below.

[0067] The pressure-adjustable pressure-sensitive adhesive sheet of this embodiment (hereinafter sometimes simply referred to as "pressure-adjustable sheet") contains the pressure-adjustable pressure-sensitive adhesive described above and is in the form of a substrate-less sheet. The thickness of the pressure-adjustable pressure-sensitive adhesive sheet is preferably 5 to 100 μm, more preferably 5 to 50 μm.

[0068] The pressure-sensitive adhesive sheet contains a pressure-adjusting pressure-sensitive adhesive as a main component. The pressure-sensitive adhesive content in the pressure-sensitive adhesive sheet may be 80 to 100 wt %.

[0069] A release film may be laminated on the surface of the pressure-sensitive adhesive sheet. Examples of the release film include the same films as those exemplified for the pressure-sensitive adhesive tape 1. The release film is peeled off when the pressure-sensitive adhesive sheet is used.

[0070] The present invention will be described in detail below with reference to synthesis examples and examples, but the present invention is not limited to the following synthesis examples and examples.

[0071] (Synthesis Examples A, B, C: Pressure-Sensitive Adhesives) 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 HBA: 4-hydroxybutyl acrylate

[0072] Next, the solvents shown in Table 1 were added to the reaction vessel so as to give a solid content concentration shown in Table 1, thereby obtaining a mixed solution. The solvents shown in Table 1 are as follows: EtAc: ethyl acetate, tol: toluene, hep: heptane

[0073] 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 weight (solids equivalent) of NOF Corporation's peroxide "Perbutyl ND" was added to 100 parts by weight of the monomer mixture, followed by a reaction for 4 hours.

[0074] 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 weight (solids content) per 100 parts by weight of the monomer mixture, followed by a reaction for 2 hours to obtain a pressure-sensitive adhesive.

[0075] (Synthesis Examples D, E, F, G: 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 C22A: behenyl acrylate AA: acrylic acid

[0076] Next, dodecyl mercaptan was added as a chain transfer agent in a proportion of 5 parts by weight (solid content equivalent) per 100 parts by weight 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.

[0077] The mixture was then heated to 70°C, and 0.5 parts by weight (solid content equivalent) of NOF Corporation's peroxide "Perhexyl PV" was added to 100 parts by weight 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.

[0078] The weight-average molecular weight of the obtained pressure-sensitive adhesive 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 obtained by measuring with GPC and converting it into polystyrene. The melting point is a value measured using DSC at a heating rate of 10°C / min.

[0079]

[0080] (Adhesion strength to PET) [Examples 1 to 12] <Preparation of adhesive tape> First, a coating solution was obtained by adding to the pressure-sensitive adhesive obtained in the synthesis example the crosslinking agent shown in Table 2 and the side-chain crystalline polymer obtained in the synthesis example in the combination and amount shown in Table 2. The amounts added shown in Table 2 are values ​​calculated as solids content per 100 parts by weight of the pressure-sensitive adhesive.

[0081] The crosslinking agents shown in Table 2 are as follows: Aziridine-based: aziridine compound "ChemiTite PZ-33" manufactured by Nippon Shokubai Co., Ltd. Epoxy-based: epoxy compound "TETRAD-X" manufactured by Mitsubishi Gas Chemical Company, Inc. Aluminum chelate-based: metal chelate compound aluminum trisacetylacetonate manufactured by Kawaken Fine Chemicals Co., Ltd. Isocyanate-based: isocyanate compound "Coronate L-45E" manufactured by Nippon Polyurethane Industry Co., Ltd.

[0082] The resulting coating solution was then applied to one side of a substrate, and a crosslinking reaction was carried out at 110°C for 3 minutes to obtain a pressure-sensitive adhesive tape having a 30 µm thick pressure-sensitive adhesive layer laminated on one side of the substrate. The substrate was a PET film having a thickness shown in Table 2 and having been corona-treated on both sides.

[0083] A release film was laminated on the surface of the obtained adhesive tape. The lamination of the release film was carried out at room temperature (23° C.). The release film used was a 38 μm thick PET film with a silicone coating on its surface.

[0084] Comparative Examples 1 and 2 Pressure-sensitive adhesive tapes were obtained in the same manner as in Examples 1 to 12, except that a coating solution was obtained by adding the crosslinking agents shown in Table 2 to the pressure-sensitive adhesive obtained in Synthesis Example in the combination and amount shown in Table 2. Then, each evaluation was carried out under the same conditions as in Examples 1 to 12, except that this pressure-sensitive adhesive tape was used.

[0085] <Evaluation> The adhesive strength to PET film, room temperature sealing property, and vapor escape property of the obtained pressure-sensitive adhesive tapes were evaluated. The evaluation methods are shown below, and the results are shown in Table 2.

[0086] (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, the adhesive tape was applied to a PET film as an adherend under the following conditions, and then the adhesive tape was peeled 180° from the PET film as an adherend at a rate of 300 mm / min using a load cell (n=3). The PET film as an adherend was a film-like film with a thickness of 0.025 mm and an untreated surface. In the adhesive strength column of Table 2, (1) indicates the adhesive strength reduction coefficient described above, and (1) / (2) indicates the degree of change in adhesive strength described above.

[0087] [23° C.] The adhesive tape was applied 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°.

[0088] [60°C] The adhesive tape was attached 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 adhesive tape was allowed to stand at this ambient temperature for 5 minutes, and then peeled off at an angle of 180°.

[0089] [100°C] The adhesive tape was attached 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 adhesive tape was allowed to stand at this ambient temperature for 5 minutes, and then peeled off at an angle of 180°.

[0090] (Room Temperature Sealing Property) The room temperature sealing property was evaluated from the results of measuring the adhesive strength at 23° C. The evaluation criteria were set as follows: ⊚: 7.0 N / 25 mm or more ◯: 5.0 N / 25 mm or more and less than 7.0 N / 25 mm ×: less than 5.0 N / 25 mm

[0091] (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 attached around the slit to obtain a lid. 100 ml of water was poured into a polypropylene cup container having a diameter of 100 mm and a 5 mm wide flange, and the lid obtained above was heat-sealed to prepare a test container.

[0092] The test containers were heated in a microwave oven at 500W for 90 seconds, and the steam escape property was evaluated by visually checking whether steam escaped from the slit in the center without breaking the heat seal (n=5). The evaluation criteria were set as follows: ◎: Steam escaped in all 5 times; ○: Steam escaped 3-4 times out of 5 times; ×: Steam escaped 2 or less times out of 5 times.

[0093]

[0094] As is clear from Table 2, Examples 1 to 12 are excellent in easy peelability when heated. It is understood that Examples 1 to 12 are excellent in room temperature sealing property and vapor escape property with respect to PET film.

[0095] (Adhesion to nylon) Examples 13 to 18 Preparation of adhesive tapes Adhesive tapes were obtained in the same manner as in Examples 1 to 12, except that a coating solution was obtained by adding the crosslinking agent shown in Table 3 and the side-chain crystalline polymer obtained in the synthesis example in the combination and amount shown in Table 3 to the pressure-sensitive adhesive obtained in the synthesis example. The addition amounts shown in Table 3 are values ​​calculated as solids content per 100 parts by weight of pressure-sensitive adhesive. The crosslinking agent shown in Table 3 is the same as the crosslinking agent shown in Table 2. A release film was laminated on the surface of the obtained adhesive tape in the same manner as in Examples 1 to 12.

[0096] Comparative Examples 3 to 4 Pressure-sensitive adhesive tapes were obtained in the same manner as in Examples 13 to 18, except that a coating solution was obtained by adding the crosslinking agents shown in Table 3 to the pressure-sensitive adhesive obtained in Synthesis Example in the combination and amount shown in Table 3. Then, each evaluation was carried out under the same conditions as in Examples 13 to 18, except that this pressure-sensitive adhesive tape was used.

[0097] <Evaluation> The adhesive strength to nylon, room temperature sealing property, and vapor escape property of the obtained pressure-sensitive adhesive tape were evaluated. The evaluation methods are shown below, and the results are shown in Table 3.

[0098] (Adhesive Strength) The 180° peel strength against a nylon film was measured at 23° C., 60° C. and 100° C. under the same conditions as for the adhesive strength against PET, except that a nylon film was used as the adherend instead of the PET film. The nylon film used was a film with a thickness of 0.015 mm and had an untreated surface.

[0099] (Room Temperature Sealability) The room temperature sealability was evaluated under the same conditions as for adhesive strength to PET.

[0100] (Vapor escape property) A test container was prepared in the same manner as for the vapor escape property in adhesive strength to PET, except that a nylon film was used instead of a PET film to obtain a lid material. Then, except for using this test container, the vapor escape property in adhesive strength to PET was evaluated under the same conditions as for the vapor escape property in adhesive strength to PET.

[0101]

[0102] As is clear from Table 3, Examples 13 to 18 are excellent in easy peelability when heated. It is also clear that Examples 13 to 18 are excellent in room temperature sealing property and vapor escape property for nylon film.

[0103] (Tack strength) Examples 19 to 30 Preparation of adhesive tapes Adhesive tapes were obtained in the same manner as in Examples 1 to 12, except that a coating solution was obtained by adding the crosslinking agent shown in Table 4 and the side-chain crystalline polymer obtained in the synthesis example in the combination and amount shown in Table 4 to the pressure-sensitive adhesive obtained in the synthesis example. The addition amounts shown in Table 4 are values ​​calculated as solid content relative to 100 parts by weight of the pressure-sensitive adhesive. The crosslinking agent shown in Table 4 is the same as the crosslinking agent shown in Table 2. A release film was laminated on the surface of the obtained adhesive tape in the same manner as in Examples 1 to 12.

[0104] The adhesive tapes thus obtained were evaluated for tack and resealability. The evaluation methods are shown below, and the results are shown in Table 4.

[0105] (Tack Strength) The probe tack values ​​were measured at 23° C., 60° C. and 100° C. in accordance with ASTM D 2979, except that the contact load was changed to 300 gf.

[0106] (Resealability) After evaluating the "vapor escape property" in the adhesive strength to PET described above, whether the container resealed without applying an external force was evaluated. The evaluation criteria were set as follows: ◎: Resealed all 5 times; ○: Resealed 3 to 4 times out of 5 times; ×: Resealed 2 or less times out of 5 times

[0107] Comparative Example 5 A pressure-sensitive adhesive tape was obtained in the same manner as in Examples 19 to 30, except that a crosslinking agent shown in Table 4 and a foaming agent shown below were added to the pressure-sensitive adhesive obtained in Synthesis Example in the combinations and amounts shown in Table 4 to obtain a coating solution. Then, except that this pressure-sensitive adhesive tape was used, each evaluation was carried out under the same conditions as in Examples 19 to 30. The results are shown in Table 4. Foaming agent: thermally expandable microcapsules "551DU40" manufactured by EXPANCEL Co., Ltd., with an average particle size of 10 to 16 μm and a foaming temperature of 90° C. or higher

[0108]

[0109] As is clear from Table 4, Examples 19 to 30 were able to achieve resealability after heating without applying external force. It can be seen that Examples 19 to 30 have excellent resealability.

[0110] DESCRIPTION OF SYMBOLS 1... Pressure-adjustable adhesive tape 2... Substrate 3... Adhesive layer 4... Pressure-adjustable adhesive 100... Adherend 101... Steam release port

Claims

1. An adhesive with a pressure-regulating function that is attached to a resinous substrate having a steam release port to seal the steam release port, and whose adhesive strength is reduced by the heat of the steam released from the steam release port, and that peels off due to the pressure of the steam, allowing the steam to be released.

2. The pressure-regulating adhesive according to claim 1, wherein the vapor release port can be resealed after vapor release and no external force is required for resealing.

3. The pressure-adjustable adhesive according to claim 1 or 2, comprising: a pressure-sensitive adhesive; and a side-chain crystalline polymer containing, as a monomer component, a (meth)acrylate having a linear alkyl group having 12 to 30 carbon atoms.

4. The pressure-adjustable adhesive according to claim 3, wherein the adhesive strength to resin decreases at temperatures above the melting point of the side-chain crystalline polymer.

5. A pressure-adjustable adhesive sheet comprising the pressure-adjustable adhesive according to claim 1 or 2.

6. An adhesive tape with pressure-regulating function, comprising: a film-like substrate; and an adhesive layer laminated on at least one surface of the substrate and containing the adhesive with pressure-regulating function according to claim 1 or 2.