Method for separating the conjugate

Abstract

The present invention aims to provide a bonded object separation method whereby an adhesive including a hydrophilic agent can be peeled off even if the adhesive is adhered firmly to a member. Provided is a method for separating a bonded object that includes two members bonded by an adhesive. The adhesive includes a hydrophilic agent. The method includes a step in which the bonded object is immersed in a solvent and the adhesive is peeled away from the members.

Description

[Technical Field]

[0001] The present invention relates to a method for separating zygotes. This application claims priority based on Japanese Patent Application No. 2020-137978, filed on August 18, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Generally, pressure-sensitive adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state at temperatures around room temperature, and have the property of easily adhering to an adherend when pressure is applied. Utilizing these properties, pressure-sensitive adhesives are widely used in a variety of fields in the form of supported pressure-sensitive adhesive sheets having a pressure-sensitive adhesive layer on a support, or in the form of support-less pressure-sensitive adhesive sheets having no support. After use, the above-mentioned pressure-sensitive adhesives are peeled from the adherend by appropriate means, if necessary. Patent Document 1 is an example of a technical document relating to pressure-sensitive adhesive sheets. Patent Document 2 is an example of a technical document relating to peeling pressure-sensitive adhesives from adherends. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-23656 [Patent Document 2] Japanese Patent Application Publication No. 2005-148638 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, from the perspective of reducing environmental impact and saving resources, it has become common to separate components bonded with adhesives from products after use and reuse them (recycle, reuse, etc.). For example, display devices built into products with display functions, such as smartphones, personal computers (desktop, notebook, tablet, etc.), and televisions, have a multi-layer structure containing multiple and heterogeneous functional components, such as liquid crystal display devices, organic electroluminescence (EL) display devices, and plasma display panels (PDPs), and each component contains different materials, so there are great advantages to reusing them through recycling, reuse, etc.

[0005] A pressure-sensitive adhesive bonded to an adherend such as a member is typically peeled from the adherend by utilizing the removability of the pressure-sensitive adhesive itself. However, pressure-sensitive adhesives that require high bonding reliability generally have high adhesive strength to the adherend, and tend to have poor removability (removability) from the adherend. Furthermore, the adherend may include a hard, brittle material such as glass or a thin material, and such an adherend may be damaged by the force applied when the pressure-sensitive adhesive is peeled off. Under these circumstances, the present inventors have proposed in Patent Document 1 a pressure-sensitive adhesive sheet (water-peelable pressure-sensitive adhesive sheet) that can be easily peeled off using an aqueous liquid such as water and has improved water resistance reliability during bonding, as a technology that achieves both adhesive strength to the adherend and removability.

[0006] However, even with such pressure-sensitive adhesives that have excellent removability, when used over a long period of time, the adhesive strength may increase due to factors such as the history of the usage environment, making it difficult to re-release as intended. Such pressure-sensitive adhesives adhere firmly to the adherend, and may not be removable even by immersion in warm water or using ultrasonic vibration, which is an obstacle to reuse. There is a demand for a method that can peel the pressure-sensitive adhesive from the adherend and separate the components joined by the pressure-sensitive adhesive, even when the pressure-sensitive adhesive has adhered firmly to the components, for example, by bonding the components together over a long period of time.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for separating joined bodies that enables peeling of a pressure-sensitive adhesive containing a hydrophilic agent even when the pressure-sensitive adhesive is firmly adhered to members. [Means for solving the problem]

[0008] This specification provides a method for separating an assembly including two components bonded with a pressure-sensitive adhesive. The pressure-sensitive adhesive includes a hydrophilic agent. The method also includes the step of immersing the assembly in a solvent to peel the pressure-sensitive adhesive from the components. This method allows the pressure-sensitive adhesive to be peeled from the components, even in an assembly in which the pressure-sensitive adhesive is firmly adhered to the components, thereby enabling separation of the assembly. For example, when a water-releasable pressure-sensitive adhesive containing a hydrophilic agent cannot be peeled from the components by water peeling using an aqueous liquid due to long-term bonding, etc. (i.e., when the water-releasability has been lost), the method can be applied to peel the pressure-sensitive adhesive. Furthermore, peeling by solvent immersion (solvent immersion peeling) does not require the application of external force to the adherend components, and therefore the components are less likely to be damaged when the pressure-sensitive adhesive is peeled.

[0009] In this specification, "two components bonded together with an adhesive" means that an adhesive is used in at least part of the bonding between the two components, and is not limited to bonding using only a specific adhesive containing a hydrophilic agent. For example, in an embodiment in which two components are bonded together with a double-sided adhesive sheet with a substrate, if at least one of the adhesives provided on each side of the double-sided adhesive sheet is an adhesive containing a hydrophilic agent, the two components are considered to be "bonded together with an adhesive."

[0010] In some preferred embodiments, the HSP (Hansen Solubility Parameters) distance between the pressure-sensitive adhesive and the solvent is 4.0 or less. When the pressure-sensitive adhesive to be peeled and the solvent used have the above-mentioned relationship (HSP distance), peeling by solvent immersion proceeds smoothly. The solvent preferably contains ethyl acetate. Ethyl acetate is not particularly limited, but is suitable for solvent immersion peeling of acrylic pressure-sensitive adhesives, for example.

[0011] In another preferred embodiment, the solvent has a hydrogen bond parameter (ΔH) of 15.0 or more in the HSP (Hansen Solubility Parameters). A solvent having the above hydrogen bond parameter value acts well on a pressure-sensitive adhesive containing a hydrophilic agent, and peeling by immersion in the solvent proceeds well.

[0012] In some embodiments, the adhesive is a solvent-based adhesive or an active energy ray-curable adhesive. The solvent immersion peeling method disclosed herein is suitable for peeling solvent-based adhesives and active energy ray-curable adhesives that contain a water compatibility agent.

[0013] In some embodiments, the two components are bonded together with a double-sided adhesive sheet containing the pressure-sensitive adhesive. The width of the adhesive sheet is 20 mm or more. The solvent immersion peeling method disclosed herein can effectively peel and separate an assembly bonded together with an adhesive sheet having a width of 20 mm or more.

[0014] In some preferred embodiments, the method for separating the bonded body involves immersing the bonded body in a solvent for 24 hours or more. By immersing the bonded body in the solvent for 24 hours or more, the adhesive is effectively peeled from the components. For example, after 24 hours have passed since the bonded body was immersed in the solvent, the adhesive may peel off from one of the two components by a distance of 20 mm or more.

[0015] Some preferred embodiments of the method include a step of determining whether the pressure-sensitive adhesive is water-releasable from at least one of the two components before immersing the bonded body in a solvent. Here, the water-releasability is achieved in the presence of an aqueous liquid at the location where the pressure-sensitive adhesive is to be peeled from the surface of the component. In this method, after confirming that water-releasability is not possible, the bonded body is immersed in a solvent. The method disclosed herein is particularly suitable for removing water-releasable deactivated pressure-sensitive adhesives that were originally water-releasable from an adherend but whose water-releasability has been impaired. [Brief explanation of the drawings]

[0016] [Figure 1] 5A to 5C are schematic cross-sectional views illustrating a method for separating a bonded body according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention are described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings for carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic for the purpose of clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the actual product provided.

[0018] <Method for separating the conjugate> The technology disclosed herein relates to a method for separating two members from a bonded structure including the members bonded with an adhesive. Hereinafter, an embodiment of the method disclosed herein will be described with reference to Fig. 1, but the method disclosed herein is not intended to be limited to this embodiment.

[0019] (zygote) A bonded structure to be separated by the technology disclosed herein includes two components bonded together with an adhesive. For example, a bonded structure 100 according to one embodiment shown in FIG. 1 has a structure in which a first component 120 and a second component 140 are bonded together with an adhesive 1. The bonded structure 100 is not particularly limited as long as it includes at least two components to be separated, and may include two or more components. For example, as shown in FIG. 1, the bonded structure 100 may be a multilayer structure in which two or more layered bodies are stacked. In an embodiment in which the bonded structure 100 is a multilayer structure, the first component 120 and the second component 140 may be sheet-shaped or plate-shaped. Furthermore, the two components may be continuous apart from the portion bonded together with the adhesive. In this embodiment, a metal component is used as the first component 120 and a glass component is used as the second component 140. However, the present invention is not limited thereto, and the bonded structure 100 may have various forms, such as an embodiment in which both the first component 120 and the second component 140 are transparent components (for example, at least one of them is a glass component).

[0020] The adhesive 1 is an adhesive containing a hydrophilic agent. In this embodiment, the adhesive 1 has a sheet-like form (adhesive sheet), specifically, a double-sided adhesive sheet without a substrate. The adhesive 1 can also be said to be layered (i.e., an adhesive layer). One surface (first adhesive surface) 1A of the adhesive 1 is adhered to the first member 120, and the other surface (second adhesive surface) 1B is adhered to the second member 140. In this manner, the first member 120 and the second member 140 are joined by the adhesive 1, which can be said to be sheet-like or layer-like. The adhesive sheet 1 of this embodiment has a width of 20 mm or more and a thickness of 100 μm or more.

[0021] As described above, the adhesive 1 contains a hydrophilic agent and is originally a water-releasable adhesive that can be peeled from an adherend by water peeling. However, due to its usage history, the water peeling property has been impaired, and the adhesive has become a water-releasable deactivated adhesive. As a result, the adhesive 1 firmly adheres to the first member 120 and the second member 140, making it difficult to peel the adhesive 1 from the first member 120 and the second member 140 not only by normal peeling but also by water peeling. Furthermore, the adhesive 1 has adhered so firmly to the first member 120 and the second member 140 that peeling is difficult even using warm water immersion, ultrasonic vibration, or the like. This type of phenomenon can occur, for example, when adhesive 1 is used to bond members over a long period of time, causing the adhesive strength to increase excessively.

[0022] In this specification, water peeling and water peelability refer to peeling using an aqueous liquid such as water and the ease of peeling (water peeling) (water peelability), and water peeling refers to peeling a pressure-sensitive adhesive from an adherend in a state where an aqueous liquid is present at the peel front (the point where peeling (separation) begins from the adhesive interface between the adhesive surface of the pressure-sensitive adhesive (which may be in the form of a pressure-sensitive adhesive layer or a pressure-sensitive adhesive sheet) and the surface of the adherend.

[0023] (Solvent immersion peeling) As described above, the bonded structure 100 containing the pressure-sensitive adhesive 1 that has become difficult to separate by conventional or water-based separation is immersed in a solvent 200 as shown in FIG. 1 . Specifically, the bonded structure 100 is placed in a suitable container 250 containing the solvent 200 and immersed in the solvent 200. This allows the pressure-sensitive adhesive 1 to be separated from the first member 120 and / or the second member 140. Specifically, the pressure-sensitive adhesive 1 immersed in the solvent 200 swells, and natural separation proceeds. Note that the solvent immersion separation may be supplemented with a separation method that uses external force, such as manual separation, or the pressure-sensitive adhesive may be separated by solvent immersion separation alone. The supplemental separation may be performed while the bonded structure is immersed in the solvent, or after the bonded structure is removed from the solvent.

[0024] The solvent immersion time is an appropriate time for peeling the PSA 1 from either the first member 120 or the second member 140. Since this time varies depending on the type of PSA and adherend, the adhesion state, and the adhesion area, it is not limited to a specific range. The solvent immersion time is, for example, 12 hours or more, preferably 24 hours or more, but may be 48 hours or more, 72 hours or more, 100 hours or more, or 150 hours or more. By extending the solvent immersion time, the PSA peeling from the above-mentioned members progresses. From the viewpoint of peeling efficiency, the solvent immersion time is preferably within one week, and is preferably 120 hours or less, more preferably 90 hours or less, even more preferably 60 hours or less, and particularly preferably 30 hours or less.

[0025] The temperature of the solvent is not particularly limited and is usually in the room temperature range (for example, about 0°C to 40°C, typically about 10°C to 30°C), but the solvent may be heated to an appropriate temperature before use.

[0026] (solvent) The solvent to be used is not limited to a specific type, and one or more appropriate solvents are selected based on the type of adhesive, the solvent resistance of the adherend, etc. In this specification, the term "solvent" refers to an organic compound (also referred to as an organic solvent) that is liquid at 23°C and can be used as a solvent or dispersion medium.

[0027] In some embodiments, one or more solvents are preferably used that have a predetermined value or less of HSP (Hansen Solubility Parameters) distance to the adhesive to be peeled off by the solvent. The HSP distance between the adhesive and the solvent is, for example, 20 or less, or may be 15 or less, or 10 or less. Solvents that have a predetermined value or less of HSP distance to the adhesive tend to facilitate solvent immersion peeling. The HSP distance is suitably 8.0 or less (e.g., 5.0 or less), and preferably 4.0 or less (e.g., 3.0 or less). The lower limit of the HSP distance is usually greater than 0, and may be, for example, approximately 1 or more. The unit of HSP distance is MPa. 1 / 2 is.

[0028] In this specification, the HSP distance (Ra) between a pressure-sensitive adhesive and a solvent is determined by the following method. That is, the HSP values ​​(dispersion term (δD), polar term (δP), hydrogen bond term (δH)) of the pressure-sensitive adhesive and the solvent are determined, and the HSP value of the pressure-sensitive adhesive (δD PSA ,δP PSA ,δH PSA ) and the HSP value of the solvent (δD SOL ,δP SOL ,δH SOL ) vector distance is calculated. This is called the HSP distance. Specifically, the formula is: Ra = [4 × (δD PSA -δD SOL ) 2 +(δP PSA -δP SOL ) 2 +(δH PSA -δH SOL ) 2 ] 1 / 2 In the above formula, δD PSA , δP PSA and δH PSA represent the dispersion term (δD), polar term (δP), and hydrogen bond term (δH) of the adhesive, respectively, and δD SOL , δP SOL and δH SOL represent the dispersion term (δD), polar term (δP), and hydrogen bond term (δH) of the solvent, respectively. The HSP values ​​of adhesives and solvents, more specifically the dispersion term (δD), polar term (δP), and hydrogen bond term (δH), can be calculated using the software "HSPiP, Hansen Solubility Parameters in Practice ver4." If the adhesive and solvent are composed of multiple components, they can be calculated using the molecular group contribution method using the above software. Specifically, each constituent unit of the target substance is entered in SMILES notation, and the HSP value (δd, δp, δh) for each unit is calculated. For adhesives, the HSP values ​​(δd, δp, δh) of each constituent component of the adhesive are calculated based on the above method, and the HSP value of the entire adhesive (δD PSA ,δP PSA ,δH PSA ) is calculated. More specifically, the formula: (δD PSA ,δP PSA ,δH PSA )=[(δd a × mole fraction of a) + (δd b × b mole fraction) + …,(δp a × mole fraction of a) + (δp b × b mole fraction) + …,(δh a × mole fraction of a) + (δh b × mole fraction of b) + ...) In the above formula, a and b represent the respective components of the adhesive.

[0029] In some other embodiments, one or more solvents having a hydrogen bond parameter (ΔH) in HSP of a predetermined value or more are preferably used as the solvent. A solvent having a large hydrogen bond parameter value acts well on a pressure-sensitive adhesive containing a hydrophilic agent, and peeling by immersion in the solvent proceeds well. The ΔH of the solvent is, for example, 10.0 or more, suitably 12.0 or more, preferably 15.0 or more, more preferably 17.0 or more, and may be 20.0 or more. A solvent satisfying the above ΔH may have an HSP distance with the pressure-sensitive adhesive of, for example, more than 5 or more than 10, or even more than 15. The unit of the above ΔH is MPa. 1 / 2 The above ΔH can be determined by the above-mentioned HSP value calculation method.

[0030] Examples of the solvent include alcohols such as methanol, ethanol, and isopropyl alcohol (e.g., monohydric alcohols having 1 to 4 carbon atoms); aliphatic or alicyclic hydrocarbons such as hexane, heptane, cyclohexane, and cycloheptane; aromatic compounds (specifically, aromatic hydrocarbons) such as toluene and xylene; esters such as methyl acetate, ethyl acetate, and butyl acetate; ketones such as acetone and methyl ethyl ketone; ethers such as butyl methyl ether (dimethyl ether, diethyl ether), and halogenated alkanes such as 1,2-dichloroethane. These solvents can be used alone or in combination. Among these, alcohols, esters, and aromatic hydrocarbons are preferred, with methanol, ethanol, and ethyl acetate being more preferred, and ethyl acetate being particularly preferred. Suitable examples of these solvents (especially ethyl acetate) are suitable for solvent immersion stripping of acrylic pressure-sensitive adhesives, for example.

[0031] By carrying out the above-mentioned solvent immersion, it is possible to peel the adhesive from the members, even in the case of a bonded structure that is firmly adhered to the adhesive as described above and is difficult to peel by normal peeling or water peeling, and to separate (dismantle) the bonded structure. The above-mentioned method makes it possible to peel the adhesive from the members without damaging the adherend. Furthermore, since the adhesive can be peeled in a single solvent immersion step, and by simply leaving it while immersed in the solvent without requiring any additional operations, this method is highly practical.

[0032] In some embodiments, solvent immersion peeling is not only applicable to PSA that are difficult to peel by normal peeling or water peeling, but also to PSA containing a hydrophilic agent that is bonded to members in various states. The solvent immersion peeling disclosed herein makes it possible to peel the PSA from members without having to check whether it can be peeled by normal peeling or the like.

[0033] (Determining whether water peeling is possible) Although not particularly limited, the above-mentioned solvent immersion peeling is effective and suitable for peeling a PSA that has become difficult to peel by water peeling (in other words, a water-removable deactivated PSA) from a member, as described above. For this reason, a preferred embodiment of the bonded body separation method includes a step of determining whether the PSA can be water-removed from two members (the first and second members) bonded by the PSA before immersing the bonded body in a solvent (a water-removability determination step). After confirming that water-removability is not possible, the bonded body can be immersed in a solvent. It is usually difficult to determine from appearance whether a PSA can be water-removed from a member. Therefore, the determination of water-removability can typically be a step of actually attempting to peel the PSA by water peeling. Water peeling is defined as above and will be described in detail below, so a detailed explanation is omitted here. The bonded body separation method disclosed herein is preferably carried out in an embodiment including a water-removability determination step. According to the above method, it is possible to efficiently and effectively release from a member a water-removable deactivated pressure-sensitive adhesive whose water-removability has been impaired due to long-term bonding or the like.

[0034] (Adhesive adhesion state) It should be noted that a PSA (typically a PSA sheet) firmly adhered to a member prior to the solvent immersion peeling is difficult to peel from the member by conventional peeling. For example, the PSA may be bonded to the member with an adhesive strength such that the normal peel force is 10 N / 20 mm or greater when the PSA is manually peeled at a peel angle of 90 to 150 degrees and a peel speed of 10 to 100 mm / min under an environment of 23°C and 50% RH, with the force gauge fixed to the edge of the member. The force gauge is held by hand. The normal peel force may be, for example, 15 N / 20 mm or greater, 20 N / 20 mm or greater, or even 25 N / 20 mm or greater (typically 28 N / 20 mm or greater). A PSA adhered to a member with the above adhesive strength is difficult to peel from the adherend by conventional peeling methods, or the adherend is easily damaged, making smooth peeling difficult. The method disclosed herein is preferably applied to such PSA. In measuring the normal peeling force, a force gauge such as the "Digital Force Gauge FG-5100" manufactured by Satotec Co., Ltd. or an equivalent can be used. The same applies to the water peeling force described below.

[0035] Furthermore, a PSA (typically a PSA sheet) firmly adhered to a member prior to the solvent immersion peeling is difficult to peel from the member by water peeling. For example, the PSA may be bonded to the member with an adhesive strength such that the water peeling force is 10 N / 20 mm or greater when the PSA is manually peeled at a peel angle of 90 to 150 degrees and a peel speed of 10 to 100 mm / min in an environment of 23°C and 50% RH. The water peeling force may be, for example, 15 N / 20 mm or greater, 20 N / 20 mm or greater, or even 25 N / 20 mm or greater (typically 28 N / 20 mm or greater). PSA adhered to a member with such adhesive strength is difficult to peel from the member by water peeling, or smooth peeling is difficult because the adherend is easily damaged. The method disclosed herein is particularly suitable for such adhesives.

[0036] <Water peeling> Water peeling is defined as above, and specifically refers to a water peeling process in which, in a state where an aqueous liquid is present at the interface between the component and the pressure-sensitive adhesive at the peel front of the pressure-sensitive adhesive from the component, the aqueous liquid is allowed to penetrate into the interface in accordance with the movement of the peel front, thereby peeling the pressure-sensitive adhesive from the component.

[0037] The aqueous liquid can be water or a mixed solvent mainly composed of water, optionally containing a small amount of additives. Examples of solvents other than water that may be used in the mixed solvent include lower alcohols (e.g., ethyl alcohol) and lower ketones (e.g., acetone) that are uniformly miscible with water. Examples of additives that can be used include known surfactants. In some embodiments, an aqueous liquid that is substantially free of additives may be used. From the viewpoint of environmental hygiene, water is preferably used as the aqueous liquid. The water is not particularly limited, and may be, for example, distilled water, ion-exchanged water, or tap water, taking into consideration the purity required for the application and ease of availability. The temperature of the aqueous liquid is usually in the range of room temperature (10°C to 35°C), but warm water of 35°C or higher but lower than 90°C (e.g., 40°C to 60°C) may also be used.

[0038] In some embodiments, the water peeling can be performed by supplying an aqueous liquid near the outer edge of the adhesive (layer) attached to a member, allowing the aqueous liquid to penetrate from the outer edge of the adhesive to the interface between the adhesive and the member, and then proceeding with peeling of the adhesive without supplying new water (i.e., using only the aqueous liquid supplied to the member before peeling begins).If the water that penetrates the interface between the adhesive and the member in accordance with the movement of the peel front runs out during the water peeling process, additional water may be supplied intermittently or continuously after the start of the water peeling process.

[0039] The amount of aqueous liquid supplied before the start of peeling is not particularly limited, as long as it is an amount that allows the aqueous liquid to be introduced from outside the adhesive area of ​​the pressure-sensitive adhesive (layer) to the interface between the pressure-sensitive adhesive and the member. The amount of the aqueous liquid may be, for example, 5 μL or more, suitably 10 μL or more, or even 20 μL or more. There is no particular upper limit to the amount of the aqueous liquid. In some embodiments, from the viewpoint of improving workability, the amount of the aqueous liquid may be, for example, 10 mL or less, 5 mL or less, 1 mL or less, 0.5 mL or less, 0.1 mL or less, or 0.05 mL or less.

[0040] The operation of injecting the aqueous liquid into the interface between the adhesive (layer) and the member from the outer edge of the adhesive at the start of peeling can be carried out, for example, by inserting the tip of a tool such as a cutter knife or needle into the interface at the outer edge of the adhesive, by scratching and lifting the outer edge of the adhesive with a hook or nail, or by attaching a highly adhesive adhesive tape or suction cup to the back surface near the outer edge of the bonded body and lifting the edge of the adhesive.

[0041] Furthermore, the water peeling step can be preferably carried out in an embodiment in which the peel front is moved at a speed of 10 mm / min or more. Moving the peel front at a speed of 10 mm / min or more corresponds to peeling the PSA (layer) at a pulling speed of 20 mm / min or more, for example, under the condition of a peel angle of 180 degrees. The speed at which the peel front is moved may be, for example, 50 mm / min or more, 150 mm / min or more, 300 mm / min or more, or 500 mm / min or more. There is no particular upper limit to the speed at which the peel front is moved. The speed at which the peel front is moved may be, for example, 1000 mm / min or less.

[0042] The water peeling method disclosed herein is, for example, a method in which the peeling area of ​​the adhesive (layer) per 10 μL of aqueous liquid (e.g., water) volume used in the method is, for example, 50 cm 2 More than 100cm, preferably 2 The present invention can be implemented in the above-described manner.

[0043] <Joints and components> The bonded structure disclosed herein is not particularly limited as long as it includes two components bonded by a pressure-sensitive adhesive (typically a pressure-sensitive adhesive layer), and may be composed of two or more components. For example, it may be a multilayer structure in which two or more layered bodies are stacked. Such a bonded structure (typically a multilayer structure) may include a display component, an optical component such as a transparent component, or other functional component. By applying the bonded structure separation method disclosed herein to such a multilayered bonded structure containing multiple different components, the components contained in the product after use can be effectively reused.

[0044] The bonded structure disclosed herein may be a structure used in various applications and products. The bonded structure may be a structure for various applications that may require recycling or repair. For example, the bonded structure may include two or more components bonded together with an adhesive in structures constituting various mobile devices (portable devices), automobiles, home appliances, etc. Such bonding may be intended not only for fixing or joining, but also for molding, decoration, protection, support, etc. The materials of the bonded structure components bonded together with the adhesive, or the materials constituting at least the surfaces of the components, may be, for example, glass, metal, ceramic material, resin material, etc.

[0045] An optical member is a suitable example of a member constituting the bonded structure. In this specification, the term "optical member" refers to a member having optical properties (e.g., polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). Examples of optical members include polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, hard coat (HC) films, impact absorbing films, antifouling films, photochromic films, light control films, transparent conductive films (ITO films), decorative films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and even members formed by laminating these (these may be collectively referred to as "functional films"). The terms "plate" and "film" mentioned above are intended to encompass plate-like, film-like, sheet-like, and other forms. For example, "polarizing film" encompasses "polarizing plate" and "polarizing sheet," etc. The optical member may be, for example, a member (typically a component of a display device) used in a display device (typically an image display device).

[0046] The optical member is not particularly limited, and examples thereof include members (e.g., sheet-shaped, film-shaped, or plate-shaped members) made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin film, etc. In this specification, the term "optical member" also includes members (such as design films, decorative films, and surface protection films) that play a role in decorating or protecting the display device while maintaining its visibility.

[0047] Furthermore, the material constituting at least the surface of the optical member may be, for example, glass such as an alkali glass plate or alkali-free glass; metal materials such as stainless steel (SUS) and aluminum; ceramic materials such as alumina and silica; and resin materials such as acrylic resin, ABS resin, polycarbonate resin, polystyrene resin, and transparent polyimide resin. Suitable examples of the member include members containing inorganic materials such as the above-mentioned glass, ceramic materials, and metal materials. The member may be an optical member in which at least a portion of the surface to which the pressure-sensitive adhesive is attached is made of such a material.

[0048] The members constituting the bonded body may have a painted surface made of acrylic, polyester, alkyd, melamine, urethane, acid-epoxy crosslinked, or composites thereof (e.g., acrylic melamine, alkyd melamine), or a plated surface such as a galvanized steel sheet.

[0049] In some preferred embodiments, the members constituting the bonded structure are glass members containing a brittle material (typically a hard and brittle material) such as glass. For example, the bonded structure separation method disclosed herein is preferably applied to a bonded structure in which at least one of two members bonded with an adhesive is made of a brittle material such as glass. Hard and brittle materials such as glass may be unable to withstand the force applied when peeling off the adhesive attached thereto and may break. However, by employing the method disclosed herein, the adhesive can be peeled off from the member without causing breakage of the adherend such as glass. A typical example of a glass member is a glass plate having a plate shape.

[0050] The size of the glass member is not limited to a specific range, and the thickness of the glass member (e.g., a glass plate) can be, for example, 0.1 to 5 mm (e.g., 0.5 to 2 mm). The length of the glass member is, for example, 5 mm to 1 m (e.g., 50 mm or more, or even 100 mm or more and 500 mm or less). The method disclosed herein is preferably used when peeling off an adhesive from a glass member of such a size. The length of the glass member (e.g., a glass plate) refers to the length of the portion having the maximum length in the surface direction of the glass member.

[0051] The surface of the member may be hydrophilically treated. For example, the surface of the optical member described above may be treated to improve hydrophilicity, such as by corona treatment, plasma treatment, or hydrophilic coating treatment such as providing a hydrophilic coating layer. Members having such hydrophilically treated surfaces have improved hydrophilicity and a water contact angle limited to a predetermined value or less, making them suitable for peeling pressure-sensitive adhesives containing hydrophilic agents.

[0052] In embodiments in which the members constituting the bonded structure have a plate or sheet shape, the maximum thickness may be about 5 mm or less (e.g., 2 mm or less, preferably 1 mm or less). Members having such a maximum thickness are usually prone to deformation or breakage due to external forces, but by applying the method disclosed herein, the pressure-sensitive adhesive can be smoothly peeled off from the member without damaging it. The thickness of the plate or sheet-shaped member may usually be, for example, 0.1 to 5 mm (e.g., 0.5 to 2 mm).

[0053] The bonded structure according to some embodiments is a bonded structure for a display device. Examples of the display device include a liquid crystal display device, an organic EL display device, a PDP, and electronic paper. The technology disclosed herein is particularly suitable for use in a display device that includes expensive components, such as a foldable display device or an in-vehicle display device. The display device also includes a display device that allows input, such as a touch panel. Since there is a strong demand for recycling and reuse of the display device, it is particularly useful to apply the technology disclosed herein.

[0054] In the above-described display device, the display member bonded by the adhesive is a member that performs the display function of the display device, and is not otherwise particularly limited, and may be composed of, for example, various materials (including optical materials and light-emitting elements). The display member may be, for example, a liquid crystal display panel, an organic EL display panel, a PDP, a touch panel, or a display portion (display unit) thereof. Note that the term "panel" may also be referred to as a sheet or film. The shape of the display member is not particularly limited, and may be, for example, a sheet or plate shape. The display member may have a curved shape, or may be deformable or flexible. Such a display member is suitable as a display member for, for example, a foldable display device or a flexible display device.

[0055] In some preferred embodiments, one of the two components constituting the bonded structure is a glass component and the other is a display component. According to the method disclosed herein, even when the components bonded with an adhesive include a hard and brittle glass component and a display component (for example, a thin component having a thickness of 2 mm or less), the two components can be separated by solvent immersion peeling without damaging (typically cracking or splitting) the glass component and the display component.

[0056] The thickness of the display member is not limited to a specific range and can be, for example, 0.1 to 5 mm (e.g., 0.5 to 2 mm). For example, when peeling a pressure-sensitive adhesive from a display member having a thickness of 2 mm or less (e.g., 1 mm or less, or even 300 μm or less, typically 100 μm or less), it is effective to apply the technology disclosed herein to separate the display member, which is thin and therefore has low strength, without damaging it. The thickness of the display member may be approximately 50 μm or less, or may be 30 μm or less.

[0057] A bonded structure in which components are bonded with a pressure-sensitive adhesive may be one in which a certain period of time has passed since the bonding with the pressure-sensitive adhesive. For example, a product containing the bonded structure may have been bonded with the pressure-sensitive adhesive for a period of time that has continued until the product is collected for recycling or other purposes after use, or even until the end of its product life (for example, six months or more, one year or more, three years or more, or five years or more). Such a pressure-sensitive adhesive may have excessively high adhesive strength due to the usage environment, making intended re-removal difficult. For example, even a water-removable pressure-sensitive adhesive containing a hydrophilic agent that allows water removability using an aqueous liquid may lose its desired water removability after a long period of time, making re-removal difficult. By applying the technology disclosed herein to a bonded structure containing a pressure-sensitive adhesive in such a state, separation of the bonded structure can be preferably achieved.

[0058] Products, devices, and structures including the above-mentioned joined bodies can be components of electronic devices (preferably portable electronic devices) that require high adhesive reliability when joining components, while also requiring smooth removal for repair, replacement, inspection, recycling, etc. Examples of such components include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like wristwatches, modular-type devices worn on parts of the body with clips or straps, eyewear-type devices including eyeglasses (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, and earwear-type devices attached to the ears like earphones), digital cameras, digital video cameras, audio devices (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic organizers, e-books, in-vehicle information devices, portable radios, portable televisions, portable printers, portable scanners, and portable modems. The display device may be a component of electronic devices such as a desktop computer, a display, a television (liquid crystal, plasma, organic electroluminescence, etc.), etc. In this specification, "portable" does not simply mean being portable, but means having a level of portability that allows an individual (average adult) to carry it relatively easily.

[0059] <Adhesive> In the above-mentioned bonded structure, the form of the adhesive that bonds the components is not particularly limited and may bond the components in a regular or random pattern such as dots or stripes, but is typically in the form of a continuously formed layer of adhesive layer or adhesive sheet. For example, the adhesive may be configured as a support-less double-sided adhesive sheet consisting of an adhesive layer, or as a double-sided adhesive sheet (double-sided adhesive sheet) having an intermediate layer such as a substrate layer. This adhesive sheet has a configuration in which a first adhesive layer and a second adhesive layer are provided on each side of the intermediate layer (both of which are non-releasable).

[0060] The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is not limited to a single layer structure, and may further comprise one or more pressure-sensitive adhesive layers of the same or different composition. For example, in a pressure-sensitive adhesive sheet comprising an intermediate layer, the intermediate layer may be a pressure-sensitive adhesive layer, and in that case, the pressure-sensitive adhesive sheet may have at least three pressure-sensitive adhesive layers, including first and second pressure-sensitive adhesive layers constituting the surface of the pressure-sensitive adhesive sheet, and a pressure-sensitive adhesive layer serving as the intermediate layer.

[0061] In the above-mentioned bonded structure, the adhesive used to bond the members (which may be in the form of an adhesive layer or an adhesive sheet; the same applies hereinafter unless otherwise specified) may be an adhesive comprising one or more adhesives selected from various known adhesives such as acrylic adhesives, rubber adhesives (natural rubber-based, synthetic rubber-based, and mixtures thereof), silicone adhesives, polyester adhesives, urethane adhesives, polyether adhesives, polyamide adhesives, and fluorine-based adhesives. Here, the term "acrylic adhesive" refers to an adhesive whose main component (base polymer) is an acrylic polymer. The same applies to rubber adhesives and other adhesives.

[0062] The "base polymer" of a PSA refers to the main component of the rubbery polymer contained in the PSA, and is not intended to be limiting in any other sense. The rubbery polymer is a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the "main component" refers to the component that is contained in the largest proportion by weight among the components. Therefore, for example, if a PSA is composed of three or more components, the content of the main component in the PSA may be 34% by weight or more.

[0063] In this specification, the term "acrylic polymer" refers to a polymer derived from a monomer component containing more than 50% by weight of an acrylic monomer, and is also referred to as an acrylic polymer. The acrylic monomer refers to a monomer derived from a monomer having at least one (meth)acryloyl group in one molecule. In this specification, the term "(meth)acryloyl" refers to acryloyl and methacryloyl in a comprehensive sense. Similarly, the term "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense, and the term "(meth)acrylic" refers to acrylic and methacrylic in a comprehensive sense.

[0064] (acrylic adhesive) In some embodiments, an acrylic pressure-sensitive adhesive may be preferably used as a constituent material of the pressure-sensitive adhesive. Specifically, the pressure-sensitive adhesive disclosed herein may be an acrylic pressure-sensitive adhesive containing an acrylic polymer. Acrylic pressure-sensitive adhesives tend to have excellent transparency, weather resistance, and design flexibility. Acrylic pressure-sensitive adhesives with high transparency are preferably used for optical applications, and ultimately for bonding applications in display devices.

[0065] The PSA disclosed herein preferably contains, as a base polymer, an acrylic polymer composed of a monomer component containing 33% by weight or more of a (meth)acrylic acid alkyl ester having a linear or branched alkyl group having 1 to 20 carbon atoms at the ester terminal. Hereinafter, a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 20 carbon atoms at the ester terminal will be referred to as "(meth)acrylic acid C X-Y Among all the monomer components of the acrylic polymer according to some embodiments, (meth)acrylic acid C is sometimes referred to as "alkyl ester" because it is easy to balance the properties. 1-20 The proportion of the alkyl ester is, for example, 35% by weight or more, suitably 50% by weight or more, and may be 55% by weight or more. 1-20The proportion of alkyl esters may be, for example, 99.9% by weight or less, 99% by weight or less, or 95% by weight or less. 1-20 The proportion of the (meth)acrylic acid alkyl ester may be, for example, 85% by weight or less, 75% by weight or less, or 65% by weight or less, from the viewpoint of the cohesiveness of the adhesive. 1-20 The alkyl esters can be used alone or in combination of two or more.

[0066] Among these, at least (meth)acrylic acid C 4-20 It is preferable to use alkyl esters, and at least (meth)acrylic acid C 4-18 It is more preferable to use alkyl esters. For example, it is preferable to include one or both of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (2EHA) as the monomer component, and an acrylic adhesive containing at least BA is particularly preferable. (Meth)acrylic acid C 4-18 The alkyl esters can be used alone or in combination of two or more.

[0067] The monomer components constituting the acrylic polymer may contain, in addition to the (meth)acrylic acid alkyl ester, other monomers (copolymerizable monomers) copolymerizable with the (meth)acrylic acid alkyl ester, as necessary. Suitable copolymerizable monomers include monomers having polar groups (e.g., carboxyl groups, hydroxyl groups, nitrogen atom-containing rings, etc.) and monomers whose homopolymers have relatively high glass transition temperatures (e.g., 10°C or higher). Monomers having polar groups can be useful for introducing crosslinking points into the acrylic polymer or for increasing the cohesive strength of the adhesive. The copolymerizable monomers may be used alone or in combination of two or more.

[0068] Non-limiting examples of copolymerizable monomers include carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, monomers containing sulfonic acid groups or phosphoric acid groups, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring, monomers having a succinimide skeleton, maleimides, aminoalkyl (meth)acrylates, alkoxy group-containing monomers, alkoxysilyl group-containing monomers, vinyl esters, vinyl ethers, aromatic vinyl compounds, olefins, (meth)acrylic acid esters having an alicyclic hydrocarbon group, (meth)acrylic acid esters having an aromatic hydrocarbon group, as well as heterocycle-containing (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate, halogen atom-containing (meth)acrylates such as vinyl chloride and fluorine atom-containing (meth)acrylates, silicon atom-containing (meth)acrylates such as silicone (meth)acrylate, and (meth)acrylic acid esters obtained from terpene compound derivative alcohols. Among these, carboxy group-containing monomers, hydroxy group-containing monomers, monomers having a nitrogen atom-containing ring, and (meth)acrylic acid esters having an alicyclic hydrocarbon group are preferred.

[0069] Suitable examples of copolymerizable monomers, such as carboxyl group-containing monomers, include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Examples of monomers having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine (e.g., lactams such as N-vinyl-2-caprolactam). Examples of the (meth)acrylic acid ester having an alicyclic hydrocarbon group include (meth)acrylates containing an alicyclic hydrocarbon group, such as cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, and adamantyl (meth)acrylate.

[0070] When such a copolymerizable monomer is used, its amount is not particularly limited, and is suitably, for example, 0.01% by weight or more of the total monomer components. From the viewpoint of better demonstrating the effect of using the copolymerizable monomer, the amount of the copolymerizable monomer may be 0.1% by weight or more, or even 0.5% by weight or more of the total monomer components. Furthermore, from the viewpoint of easily balancing the adhesive properties, the amount of the copolymerizable monomer used is suitably 60% by weight or less of the total monomer components, or may be 50% by weight or less, or may be 40% by weight or less.

[0071] In some embodiments, the monomer components constituting the acrylic polymer may contain a hydroxyl group-containing monomer. The use of a hydroxyl group-containing monomer can suitably adjust the cohesive strength and degree of crosslinking (e.g., crosslinking with an isocyanate crosslinking agent) of the PSA. Examples of the hydroxyl group-containing monomer include those exemplified above. For example, 2-hydroxyethyl acrylate (HEA) and 4-hydroxybutyl acrylate (4HBA) are preferred. The hydroxyl group-containing monomers may be used alone or in combination of two or more. When a hydroxyl group-containing monomer is used, there are no particular restrictions on its amount. In some preferred embodiments, the amount of the hydroxyl group-containing monomer used is 15% by weight or more, suitably 20% by weight or more, and preferably 25% by weight or more, of the total monomer components. Furthermore, from the viewpoint of suppressing the water absorption of the PSA, in some embodiments, the amount of the hydroxyl group-containing monomer used is suitably, for example, 50% by weight or less (e.g., 45% by weight or less) of the total monomer components, and may be 40% by weight or less, 30% by weight or less, or 20% by weight or less.

[0072] In some embodiments, the monomer component constituting the acrylic polymer may contain an alicyclic hydrocarbon group-containing (meth)acrylate. This can enhance the cohesive strength of the adhesive. Examples of the alicyclic hydrocarbon group-containing (meth)acrylate include those exemplified above. For example, cyclohexyl acrylate (CHA) and isobornyl acrylate are preferred. The alicyclic hydrocarbon group-containing (meth)acrylate may be used alone or in combination of two or more. When an alicyclic hydrocarbon group-containing (meth)acrylate is used, its amount is not particularly limited and can be, for example, 1% by weight or more, 5% by weight or more, or even 10% by weight or more of the total monomer components. The upper limit of the amount of the alicyclic hydrocarbon group-containing (meth)acrylate used is suitably approximately 40% by weight or less, and may be 25% by weight or less (e.g., 15% by weight or less).

[0073] In some embodiments, the monomer components constituting the acrylic polymer may contain a nitrogen atom-containing monomer. This can enhance the cohesive strength of the adhesive. Examples of the nitrogen atom-containing monomer include those exemplified above. Suitable examples of the nitrogen atom-containing monomer include a monomer having a nitrogen atom-containing ring. For example, N-vinyl cyclic amide is mentioned, and N-vinyl-2-pyrrolidone is particularly preferred. The nitrogen atom-containing monomer may be used alone or in combination of two or more. The amount of the nitrogen atom-containing monomer (preferably the nitrogen atom-containing ring-containing monomer) used is not particularly limited, and may be, for example, 1% by weight or more, 5% by weight or more, or even 10% by weight or more of the total monomer components. Furthermore, the amount of the nitrogen atom-containing monomer used is suitably, for example, 40% by weight or less, or may be 30% by weight or less, or may be 15% by weight or less of the total monomer components.

[0074] In some embodiments, the proportion of carboxyl group-containing monomers in the monomer components of the acrylic polymer may be, for example, less than 10 wt%, less than 3 wt%, or less than 1 wt% (e.g., less than 0.1 wt%). Substantially no carboxyl group-containing monomers may be used as monomer components of the acrylic polymer. Here, "substantially no carboxyl group-containing monomers" means that carboxyl group-containing monomers are not used at least intentionally. Acrylic polymers with such compositions may have metal corrosion inhibitory properties for adherends containing metals.

[0075] The composition of the monomer components constituting the acrylic polymer can be set so that the glass transition temperature Tg, calculated based on the composition of the monomer components using the Fox formula, is −75° C. or higher and 10° C. or lower. In some embodiments, from the viewpoint of adhesive strength and the like, the Tg is suitably 0° C. or lower, preferably −10° C. or lower, and may be −20° C. or lower or −30° C. or lower. Furthermore, from the viewpoint of cohesion and the like, the Tg may be, for example, −60° C. or higher, −50° C. or higher, −45° C. or higher, or −40° C. or higher.

[0076] Here, the Fox equation is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg=Σ(Wi / Tgi) In the Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature of a homopolymer of monomer i (unit: K). The glass transition temperature of the homopolymer used to calculate Tg is determined from known sources, specifically, from the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). When multiple values ​​are listed in this document, the highest value is used.

[0077] For polymerization, known or conventional thermal polymerization initiators or photopolymerization initiators can be used depending on the polymerization method and polymerization mode. Thermal polymerization initiators are not particularly limited, but examples include azo-based polymerization initiators, peroxide-based initiators, redox-based initiators formed by combining peroxides with reducing agents, and substituted ethane-based initiators. Photopolymerization initiators are not particularly limited, but examples include ketal-based photopolymerization initiators, acetophenone-based photopolymerization initiators, benzoin ether-based photopolymerization initiators, acylphosphine oxide-based photopolymerization initiators, α-ketol-based photopolymerization initiators, aromatic sulfonyl chloride-based photopolymerization initiators, photoactive oxime-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzyl-based photopolymerization initiators, benzophenone-based photopolymerization initiators, and thioxanthone-based photopolymerization initiators. The polymerization initiators can be used alone or in combination of two or more. The amount of such a thermal polymerization initiator or photopolymerization initiator used is not particularly limited and may be a normal amount depending on the polymerization method, polymerization mode, etc. For example, about 0.001 to 5 parts by weight (typically about 0.01 to 2 parts by weight, for example, about 0.01 to 1 part by weight) of the polymerization initiator can be used per 100 parts by weight of the monomer to be polymerized.

[0078] In the polymerization, various conventionally known chain transfer agents (which may also be understood as molecular weight regulators or polymerization degree regulators) can be used as needed. Examples of the chain transfer agent include mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur chain transfer agent) may be used. The chain transfer agent may be used alone or in combination of two or more. When a chain transfer agent is used, the amount used may be, for example, about 0.01 to 1 part by weight per 100 parts by weight of the monomer components. The technology disclosed herein can also be preferably practiced in an embodiment in which a chain transfer agent is not used.

[0079] The molecular weight of the acrylic polymer obtained by appropriately employing the above-mentioned various polymerization methods is not particularly limited and can be set within an appropriate range depending on the required performance. The weight average molecular weight (Mw) of the acrylic polymer is, for example, about 10 × 10 4 From the viewpoint of achieving a good balance between cohesive strength and adhesive strength, 4 The acrylic polymer according to some embodiments preferably has a viscosity of about 50×10 4 The upper limit of the Mw of the acrylic polymer is approximately 500 × 10 4 Below (for example, approximately 150 x 10 4 The Mw can be approximately 75×10 4 Here, Mw refers to a value calculated in terms of standard polystyrene obtained by gel permeation chromatography (GPC). As a GPC device, for example, a model "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) may be used.

[0080] The pressure-sensitive adhesive disclosed herein can be formed using a pressure-sensitive adhesive composition containing the monomer components described above in the form of a polymer, an unpolymer (i.e., a form in which the polymerizable functional group is unreacted), or a mixture thereof. The pressure-sensitive adhesive composition can be in various forms, such as a water-dispersed pressure-sensitive adhesive composition in which the pressure-sensitive adhesive (adhesive component) is dispersed in water, a solvent-based pressure-sensitive adhesive composition in which the pressure-sensitive adhesive is contained in an organic solvent, an active energy ray-curable pressure-sensitive adhesive composition prepared to form a pressure-sensitive adhesive upon curing with active energy rays such as ultraviolet light or radiation, or a hot-melt pressure-sensitive adhesive composition that is applied in a heated, molten state and forms a pressure-sensitive adhesive upon cooling to around room temperature. The pressure-sensitive adhesive composition according to some embodiments is a solvent-based pressure-sensitive adhesive composition or a solventless pressure-sensitive adhesive composition. Solventless pressure-sensitive adhesive compositions include active energy ray-curable pressure-sensitive adhesive compositions and hot-melt pressure-sensitive adhesive compositions. The solvent immersion peeling method disclosed herein is effective for solvent-based pressure-sensitive adhesives formed from solvent-based pressure-sensitive adhesive compositions and active energy ray-curable pressure-sensitive adhesives (typically UV-curable pressure-sensitive adhesives) formed from active energy ray (typically UV-curable) pressure-sensitive adhesive compositions.

[0081] The pressure-sensitive adhesive composition according to some embodiments may be an active energy ray-curable pressure-sensitive adhesive composition. In this specification, "active energy rays" refers to energy rays having energy capable of inducing chemical reactions such as polymerization reactions, crosslinking reactions, and decomposition of initiators. Examples of active energy rays include light such as ultraviolet rays, visible light, and infrared rays, and radioactive rays such as α-rays, β-rays, γ-rays, electron beams, neutron beams, and X-rays. A suitable example of an active energy ray-curable pressure-sensitive adhesive composition is a photocurable pressure-sensitive adhesive composition. Photocurable pressure-sensitive adhesive compositions have the advantage that even thick pressure-sensitive adhesive layers can be easily formed. Among these, ultraviolet-curable pressure-sensitive adhesive compositions are preferred.

[0082] A photocurable pressure-sensitive adhesive composition typically contains at least a portion of the monomer components of the composition (which may be a portion of the type of monomer or a portion of the amount) in the form of a polymer. The polymerization method used to form the polymer is not particularly limited, and various conventionally known polymerization methods can be appropriately employed. For example, thermal polymerization such as solution polymerization, emulsion polymerization, and bulk polymerization (typically carried out in the presence of a thermal polymerization initiator); photopolymerization carried out by irradiation with light such as ultraviolet light (typically carried out in the presence of a photopolymerization initiator); and radiation polymerization carried out by irradiation with radiation such as beta rays and gamma rays can be appropriately employed. Among these, photopolymerization is preferred.

[0083] Photocurable pressure-sensitive adhesive compositions according to some preferred embodiments contain a partial polymer of a monomer component (e.g., an acrylic partial polymer). Such a partial polymer is typically a mixture of a polymer derived from the monomer component and an unreacted monomer, and is preferably in a syrup-like state (a viscous liquid). Hereinafter, a partial polymer of this nature may be referred to as a "monomer syrup" or simply as a "syrup." The polymerization method used to partially polymerize the monomer component is not particularly limited, and various polymerization methods such as those described above can be appropriately selected and used. From the viewpoints of efficiency and simplicity, a photopolymerization method can be preferably employed. Photopolymerization allows the polymerization conversion rate of the monomer component (monomer conversion) to be easily controlled by changing polymerization conditions such as the light irradiation dose (light amount).

[0084] The polymerization conversion rate of the monomer mixture in the partially polymerized product is not particularly limited. The polymerization conversion rate can be, for example, about 70% by weight or less, and from the viewpoint of ease of preparation and coatability of the pressure-sensitive adhesive composition containing the partially polymerized product, it is suitably about 50% by weight or less, and preferably about 40% by weight or less. The lower limit of the polymerization conversion rate is not particularly limited, but is typically about 1% by weight or more, and suitably about 5% by weight or more.

[0085] The pressure-sensitive adhesive composition containing the partial polymer may contain other components (e.g., a photopolymerization initiator, a hydrophilic agent as described below, a crosslinking agent, a polyfunctional monomer, an acrylic oligomer, a tackifying resin, a silane coupling agent, etc.) that are used as needed. The method for blending such other components is not particularly limited, and for example, the other components may be contained in the monomer mixture in advance, or may be added to the partial polymer.

[0086] A PSA according to some embodiments is a PSA formed from a water-dispersed PSA composition. A typical example of a water-dispersed PSA composition is an emulsion-type PSA composition. An emulsion-type PSA composition typically contains a polymer of a monomer component and additives used as needed. Emulsion polymerization of the monomer component is usually carried out in the presence of an emulsifier. Emulsion polymerization produces a polymerization reaction liquid in the form of an emulsion in which a polymer of the monomer component is dispersed in water. The water-dispersed PSA composition used to form the PSA can be preferably produced using the polymerization reaction liquid.

[0087] The emulsifier for emulsion polymerization is not particularly limited, and known anionic emulsifiers, nonionic emulsifiers, etc. can be used. The emulsifiers can be used alone or in combination of two or more. Non-limiting examples of anionic emulsifiers include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene lauryl sulfate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, and sodium polyoxyethylene alkyl sulfosuccinate. Non-limiting examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene polyoxypropylene block polymers. Emulsifiers having reactive functional groups (reactive emulsifiers) may also be used. Examples of reactive emulsifiers include radically polymerizable emulsifiers having a structure in which a radically polymerizable functional group such as a propenyl group or an allyl ether group is introduced into the above-mentioned anionic or nonionic emulsifiers.

[0088] The amount of emulsifier used in emulsion polymerization may be, for example, 0.2 parts by weight or more, 0.5 parts by weight or more, 1.0 parts by weight or more, or 1.5 parts by weight or more, relative to 100 parts by weight of the monomer components. Furthermore, from the viewpoint of improving water-resistant adhesive strength or improving the transparency of the adhesive, in some embodiments, the amount of emulsifier used is suitably 10 parts by weight or less, preferably 5 parts by weight or less, and may be 3 parts by weight or less, relative to 100 parts by weight of the monomer components. The emulsifier used in emulsion polymerization here may also function as a hydrophilic agent, as described below.

[0089] The PSA composition according to some embodiments may be a solvent-based PSA composition. A solvent-based PSA composition typically contains a solution polymer of a monomer component and an additive (e.g., a hydrophilic agent) used as needed. The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents (e.g., toluene, ethyl acetate, etc.). Solution polymerization produces a polymerization reaction liquid in which a polymer of a monomer component is dissolved in the polymerization solvent. The solvent-based PSA composition disclosed herein can be preferably produced using the polymerization reaction liquid.

[0090] (Water compatibility agent) The pressure-sensitive adhesive contains a hydrophilic agent. By incorporating a hydrophilic agent into the pressure-sensitive adhesive, the peel force can be effectively reduced using an aqueous liquid such as water, improving water releasability. The reason for this is not particularly limited, but it is believed that hydrophilic agents generally have hydrophilic regions and tend to be unevenly distributed on the surface of the pressure-sensitive adhesive, thereby efficiently increasing the water affinity of the pressure-sensitive adhesive surface. This effectively reduces the peel force when the pressure-sensitive adhesive comes into contact with water, improving water releasability. However, the pressure-sensitive adhesive used to bond components in the bonded structure may lose its inherent water releasability due to long-term use or other circumstances, resulting in a water-releasable deactivated pressure-sensitive adhesive that is difficult to remove with water releasability. Even with such a hydrophilic-agent-containing pressure-sensitive adhesive with deactivated water releasability, the pressure-sensitive adhesive can be released from the components to which it is bonded by applying the technology disclosed herein. The hydrophilic agent is typically contained in the pressure-sensitive adhesive composition (and thus the pressure-sensitive adhesive) in a free form. As the hydrophilic agent, one that is liquid at room temperature (about 25° C.) can be preferably used from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, etc. The hydrophilic agents can be used alone or in combination of two or more.

[0091] The HLB of the hydrophilic agent (typically a surfactant) is not particularly limited, but is, for example, 3.0 or more, suitably approximately 5.0 or more, preferably 8.0 or more, more preferably 10 or more, and even more preferably 13 or more (e.g., 15 or more). By incorporating a hydrophilic agent having an HLB within the above range into a pressure-sensitive adhesive (e.g., a pressure-sensitive adhesive containing an acrylic polymer), even if water releasability is impaired, it can be peeled from a substrate by solvent immersion peeling. The upper limit of the HLB is 20 or less, and may be, for example, 18 or less, or 16 or less (e.g., 15 or less).

[0092] In this specification, HLB stands for Hydrophile-Lipophile Balance according to Griffin, which is a value that indicates the degree of affinity of a surfactant for water or oil, and is a ratio of hydrophilicity to lipophilicity expressed as a number between 0 and 20. The definition of HLB is as described in W.C. Griffin: J. Soc. Cosmetic Chemists, 1, 311 (1949), and in "Surfactant Handbook," 3rd Edition, Kogaku Toshosha Publishing, November 25, 1972, pp. 179-182, co-authored by Takahashi Etsutami, Namba Yoshiro, Koike Motoo, and Kobayashi Masao. Hydrophilic agents having the above HLB can be selected based on the common technical knowledge of those skilled in the art, for example by referring to the above references as necessary.

[0093] In some embodiments, as the hydrophilic agent, at least one compound selected from surfactants and compounds having polyoxyalkylene skeletons can be used.As surfactants and compounds having polyoxyalkylene skeletons, one or more of known surfactants and compounds having polyoxyalkylene skeletons can be used without any particular limitation.It goes without saying that among the above surfactants, there are compounds having polyoxyalkylene skeletons, and vice versa.

[0094] As a surfactant that can be used as a hydrophilic agent, known nonionic surfactants, anionic surfactants, cationic surfactants, etc. can be used. Among them, nonionic surfactants are preferred. The surfactants can be used alone or in combination of two or more.

[0095] Examples of nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; polyoxyethylene alkylphenyl ethers such as polyoxyethylene octylphenyl ether and polyoxyethylene nonylphenyl ether; sorbitan fatty acid esters such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, and sorbitan monooleate; polyoxyethylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan triisostearate, polyoxyethylene sorbitan monooleate, and polyoxyethylene sorbitan trioleate; polyoxyethylene glyceryl ether fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; etc. These nonionic surfactants can be used alone or in combination of two or more.

[0096] Examples of anionic surfactants include alkyl sulfates such as lauryl sulfate and octadecyl sulfate; fatty acid salts; alkylbenzenesulfonates such as nonylbenzenesulfonate and dodecylbenzenesulfonate; naphthalenesulfonates such as dodecylnaphthalenesulfonate; alkyldiphenyletherdisulfonates such as dodecyldiphenyletherdisulfonates; polyoxyethylene alkylether sulfates such as polyoxyethyleneoctadecylethersulfonate and polyoxyethylenelaurylethersulfonate; polyoxyethylene alkylphenylether sulfates such as polyoxyethylenelaurylphenylethersulfonate; polyoxyethylene styrenated phenylether sulfate; sulfosuccinates such as laurylsulfosuccinate and polyoxyethylenelaurylsulfosuccinate; polyoxyethylene alkylether phosphates; polyoxyethylene alkylether acetates; etc. When the anionic surfactant forms a salt, the salt can be, for example, a metal salt (preferably a monovalent metal salt) such as sodium salt, potassium salt, calcium salt, magnesium salt, etc., an ammonium salt, an amine salt, etc. These anionic surfactants can be used alone or in combination of two or more.

[0097] Examples of compounds having a polyoxyalkylene skeleton that can be used as a hydrophilic agent include polyalkylene glycols such as polyethylene glycol (PEG) and polypropylene glycol (PPG); polyethers containing polyoxyethylene units, polyethers containing polyoxypropylene units, compounds containing oxyethylene units and oxypropylene units (these units may be arranged randomly or in blocks); and derivatives thereof. Furthermore, among the surfactants described above, compounds having a polyoxyalkylene skeleton can also be used. These can be used alone or in combination of two or more. Among these, it is preferable to use a compound having a polyoxyethylene skeleton (also called a polyoxyethylene segment), and PEG is more preferable.

[0098] The molecular weight (chemical formula weight) of the compound having a polyoxyalkylene skeleton (e.g., polyethylene glycol) is not particularly limited, and is suitably, for example, less than 1000. From the viewpoint of ease of preparation of the adhesive composition, it is preferably about 600 or less (e.g., 500 or less). The lower limit of the molecular weight of the compound having a polyoxyalkylene skeleton (e.g., polyethylene glycol) is not particularly limited, and those having a molecular weight of about 100 or more (e.g., about 200 or more, or even about 300 or more) are preferably used.

[0099] The content of the hydrophilic agent in the pressure-sensitive adhesive is not particularly limited and can be set so that the effect of the hydrophilic agent is appropriately exhibited. In some embodiments, the content of the hydrophilic agent can be, for example, 0.001 parts by weight or more, suitably 0.01 parts by weight or more, preferably 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more, per 100 parts by weight of the polymer (e.g., acrylic polymer) contained in the pressure-sensitive adhesive. In other embodiments, the content of the hydrophilic agent can be, for example, 1.0 parts by weight or more, or even 1.5 parts by weight or more, per 100 parts by weight of the polymer contained in the pressure-sensitive adhesive. In addition, in some embodiments, the amount of the hydrophilic agent used can be approximately 3 parts by weight or less, suitably approximately 2 parts by weight or less, preferably less than 1 part by weight, and more preferably less than 0.5 parts by weight, per 100 parts by weight of the polymer. Limiting the amount of the hydrophilic agent used tends to make it easier to maintain adhesive strength. In addition, in optical applications, the optical properties of the pressure-sensitive adhesive tend to be less likely to be impaired. A pressure-sensitive adhesive containing the above-mentioned limited amount of hydrophilic agent can preferably achieve both adhesive strength and solvent immersion releasability, and in optical applications, can also have optical properties.

[0100] (polyfunctional monomer) A polyfunctional monomer may be used in the pressure-sensitive adhesive composition (and thus the pressure-sensitive adhesive) as needed. The polyfunctional monomer may be useful for purposes such as adjusting cohesive strength. The polyfunctional monomer may form a crosslinked structure with appropriate flexibility by reacting the ethylenically unsaturated groups with light (e.g., ultraviolet) irradiation during the formation of the pressure-sensitive adhesive layer or after application to an adherend. Therefore, in this specification, the term "polyfunctional monomer" may be rephrased as a crosslinking agent. For example, a polyfunctional monomer may be preferably used in a pressure-sensitive adhesive formed from a photocurable pressure-sensitive adhesive composition. A compound having two or more ethylenically unsaturated groups may be used as the polyfunctional monomer. The polyfunctional monomer may be used alone or in combination of two or more.

[0101] Examples of the ethylenically unsaturated group contained in the polyfunctional monomer include, but are not limited to, an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group. From the viewpoint of photoreactivity, preferred ethylenically unsaturated groups include an acryloyl group and a methacryloyl group. Among them, an acryloyl group is preferred.

[0102] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, epoxy acrylate, polyester acrylate, urethane acrylate, butyl diol (meth)acrylate, and hexyl diol di(meth)acrylate. Of these, trimethylolpropane tri(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and dipentaerythritol hexa(meth)acrylate are preferred.

[0103] The amount of polyfunctional monomer used varies depending on its molecular weight, number of functional groups, etc., but it is appropriate to use, for example, a range of approximately 0.01 to 3.0 parts by weight per 100 parts by weight of the monomer component that forms the polymer contained in the adhesive (typically, an acrylic polymer or a monomer component of the polymer).

[0104] (Crosslinking agent) The adhesive composition disclosed herein may contain a crosslinking agent as needed, primarily for the purpose of crosslinking within the adhesive (layer) or between the adhesive and its adjacent surface. The type of crosslinking agent is not particularly limited, and it can be selected from conventionally known crosslinking agents, for example, depending on the composition of the adhesive composition, so that the crosslinking agent exerts an appropriate crosslinking function within the adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, carbodiimide-based crosslinking agents, melamine-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. These may be used alone or in combination of two or more.

[0105] The content of the crosslinking agent (the total amount when two or more crosslinking agents are included) is not particularly limited. From the viewpoint of realizing a pressure-sensitive adhesive that exhibits well-balanced adhesive properties such as adhesive strength and cohesive strength, the content of the crosslinking agent is suitably approximately 5 parts by weight or less, preferably approximately 0.001 to 5 parts by weight, more preferably approximately 0.001 to 4 parts by weight, and even more preferably approximately 0.001 to 3 parts by weight, per 100 parts by weight of the monomer components (e.g., acrylic polymers or monomer components of the polymers) that form the polymers contained in the pressure-sensitive adhesive. Alternatively, the pressure-sensitive adhesive composition may be a pressure-sensitive adhesive composition that does not contain the above-mentioned crosslinking agent. When a photocurable pressure-sensitive adhesive composition is used as the pressure-sensitive adhesive composition disclosed herein, the pressure-sensitive adhesive composition may be substantially free of a crosslinking agent such as an isocyanate-based crosslinking agent. Here, the pressure-sensitive adhesive composition being substantially free of a crosslinking agent (typically an isocyanate-based crosslinking agent) means that the amount of crosslinking agent per 100 parts by weight of the monomer components is less than 0.05 parts by weight (e.g., less than 0.01 part by weight).

[0106] A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Furthermore, the adhesive composition used to form the adhesive may contain a crosslinking retarder (e.g., a compound that generates keto-enol tautomerism) if desired. The amounts of the crosslinking catalyst and crosslinking retarder used are not limited to a specific range, and appropriate amounts are used depending on the purpose, etc.

[0107] (tackifying resin) The adhesive may contain a tackifying resin. Examples of tackifying resins include rosin-based tackifying resins, rosin derivative tackifying resins, petroleum-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, and ketone-based tackifying resins. These can be used alone or in combination of two or more. Of these, one or more selected from rosin-based tackifying resins, rosin derivative tackifying resins, and terpene phenolic resins can be preferably used. For example, a tackifying resin (preferably a rosin derivative tackifying resin) having a softening point of 80°C or higher (e.g., 120°C or higher and 180°C or lower) can be preferably used.

[0108] To optimally achieve the desired effects, the amount of tackifier resin used is preferably 1 part by weight or more per 100 parts by weight of the monomer components constituting the polymer contained in the PSA, and may be 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, or 25 parts by weight or more. Furthermore, to achieve a good balance between adhesion to the adherend and cohesion, the amount of tackifier resin used per 100 parts by weight of the monomer components may be, for example, 50 parts by weight or less, or 30 parts by weight or less. Alternatively, the content of the tackifier resin in the PSA may be, for example, less than 1 part by weight per 100 parts by weight of the monomer components, and the PSA may be substantially free of tackifier resin.

[0109] (acrylic oligomer) The pressure-sensitive adhesive disclosed herein may contain an acrylic oligomer from the viewpoint of improving cohesive strength and adhesiveness. As the acrylic oligomer, it is preferable to use a polymer having a Tg higher than that of the acrylic polymer. For example, in an embodiment in which ultraviolet irradiation is used during the preparation of the pressure-sensitive adhesive, an acrylic oligomer is preferable because it is less likely to cause polymerization inhibition.

[0110] Suitable examples of acrylic oligomers include homopolymers of dicyclopentanyl methacrylate (DCPMA), cyclohexyl methacrylate (CHMA), isobornyl methacrylate (IBXMA), isobornyl acrylate (IBXA), dicyclopentanyl acrylate (DCPA), 1-adamantyl methacrylate (ADMA), and 1-adamantyl acrylate (ADA), as well as copolymers of DCPMA and methyl methacrylate (MMA), copolymers of DCPMA and IBXMA, copolymers of ADA and MMA, copolymers of CHMA and isobutyl methacrylate (IBMA), copolymers of CHMA and IBXMA, copolymers of CHMA and acryloylmorpholine (ACMO), copolymers of CHMA and diethylacrylamide (DEAA), and copolymers of CHMA and AA. The acrylic oligomers can be used alone or in combination of two or more.

[0111] The Mw of the acrylic oligomer is typically about 1,000 or more but less than about 30,000, preferably about 1,500 or more but less than about 10,000, and more preferably about 2,000 or more but less than about 5,000. When the Mw is within the above range, the effect of improving cohesion and adhesion to adjacent surfaces is easily achieved. The Mw of the acrylic oligomer can be measured by gel permeation chromatography (GPC) and calculated as a value equivalent to standard polystyrene. Specifically, the measurement is performed using a Tosoh HPLC 8020 with two TSKgel GMH-H (20) columns at a flow rate of about 0.5 mL / min in tetrahydrofuran solvent.

[0112] When an acrylic oligomer is contained in the PSA, the content thereof can be, for example, 0.01 parts by weight or more relative to 100 parts by weight of the base polymer (typically an acrylic polymer), and from the viewpoint of obtaining a higher effect, it may be 0.05 parts by weight or more, or even 0.1 parts by weight or more. Furthermore, from the viewpoint of compatibility with the base polymer, the content of the acrylic oligomer is preferably less than 30 parts by weight, and may be, for example, 10 parts by weight or less, or 1 part by weight or less.

[0113] (Silane coupling agent) The PSA disclosed herein may contain a silane coupling agent. In embodiments containing a silane coupling agent, the silane coupling agent is preferably contained in the PSA composition (and thus the PSA) in a free form. The inclusion of a silane coupling agent tends to increase the adhesive strength of the PSA to an adherend (e.g., a glass member), but the improved adhesive strength tends to reduce the releasability from the adherend during peeling. Even in such PSAs (adhesives firmly adhered to members), even if the water releasability is impaired due to the inclusion of a hydrophilic agent, the PSA can still be peeled from the member by solvent immersion peeling.

[0114] Examples of silane coupling agents include silicon compounds having an epoxy structure such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silicon compounds such as 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)3-aminopropyltrimethoxysilane, and N-(2-aminoethyl)3-aminopropylmethyldimethoxysilane; 3-chloropropyltrimethoxysilane; acetoacetyl group-containing trimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane. Among these, preferred examples include 3-glycidoxypropyltrimethoxysilane and acetoacetyl group-containing trimethoxysilane. The silane coupling agents can be used alone or in combination of two or more.

[0115] The amount of silane coupling agent used can be set so as to obtain the desired effect, and is not particularly limited. In some embodiments, the amount of silane coupling agent used may be, for example, 0.001 parts by weight or more relative to 100 parts by weight of the monomer components constituting the polymer contained in the PSA. To obtain a higher effect, the amount may be 0.005 parts by weight or more, 0.01 parts by weight or more, or even 0.015 parts by weight or more. In some embodiments, the amount of silane coupling agent used may be, for example, 3 parts by weight or less, 1 part by weight or less, or 0.5 parts by weight or less relative to 100 parts by weight of the monomer components constituting the PSA. The technology disclosed herein can also be implemented in an embodiment using a PSA that is substantially free of a silane coupling agent. Limiting the amount of silane coupling agent used or not using a silane coupling agent tends to improve releasability from the adherend.

[0116] (Other ingredients) The PSA disclosed herein may optionally contain various additives commonly used in the field of PSA, such as viscosity adjusters (e.g., thickeners), pH adjusters, leveling agents, plasticizers, fillers, colorants such as pigments and dyes, stabilizers, preservatives, antioxidants, etc. These various additives may be conventionally known and can be used in the usual manner, and are not particularly characteristic of the present invention, so detailed description thereof will be omitted.

[0117] In the technology disclosed herein, the amount of components other than the base polymer (preferably an acrylic polymer) in the PSA may be limited. In the technology disclosed herein, the amount of components other than the base polymer in the PSA is, for example, approximately 30% by weight or less, suitably approximately 15% by weight or less, and preferably approximately 12% by weight or less (e.g., approximately 10% by weight or less). PSA with such a composition is likely to satisfy predetermined optical properties (e.g., transparency) and may be preferably used for optical applications. In some embodiments, the amount of components other than the base polymer in the PSA may be approximately 5% by weight or less, approximately 3% by weight or less, or approximately 1.5% by weight or less (e.g., approximately 1% by weight or less). Compositions in which the amount of components other than the base polymer (e.g., an acrylic polymer) is limited in this way may be preferably used for photocurable PSA compositions.

[0118] (Formation of adhesive layer) When the PSA has the form of a PSA layer, the PSA layer may be a cured layer of the PSA composition. That is, the PSA layer can be formed by applying (e.g., coating) the PSA composition to a suitable surface and then appropriately performing a curing treatment. When two or more curing treatments (drying, crosslinking, polymerization, etc.) are performed, these can be performed simultaneously or in multiple stages. For PSA compositions using a partial polymer of a monomer component (acrylic polymer syrup), the curing treatment typically involves a final copolymerization reaction. That is, the partial polymer is subjected to a further copolymerization reaction to form a fully polymerized product. For example, in the case of a photocurable PSA composition, light irradiation is performed. Curing treatments such as crosslinking and drying may be performed as needed. For example, when a photocurable PSA composition requires drying (e.g., a photocurable PSA composition in the form of a partial polymer of a monomer component dissolved in an organic solvent), the composition may be dried and then photocured. For PSA compositions using a fully polymerized product, the curing treatment typically involves drying (heat drying), crosslinking, etc. as needed. A pressure-sensitive adhesive layer having a multi-layer structure of two or more layers can be prepared by laminating pre-formed pressure-sensitive adhesive layers together, or by applying a pressure-sensitive adhesive composition onto a pre-formed first pressure-sensitive adhesive layer and curing the pressure-sensitive adhesive composition to form a second pressure-sensitive adhesive layer.

[0119] The pressure-sensitive adhesive composition can be applied using a conventional coater such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater or spray coater.

[0120] (Adhesive layer thickness) The thickness of the pressure-sensitive adhesive layer is not particularly limited and may be, for example, approximately 3 μm to 2000 μm. From the viewpoint of adhesion to the adherend, such as conformability to unevenness, in some embodiments, the thickness of the pressure-sensitive adhesive layer is, for example, 10 μm or more, preferably 50 μm or more, and may be 70 μm or more, 100 μm or more, or 150 μm or more. A thick pressure-sensitive adhesive has high adhesive strength, which tends to increase over time, making it difficult to peel. On the other hand, if the adherend is solvent-impermeable, the solvent only comes into contact with the pressure-sensitive adhesive at the edge of the pressure-sensitive adhesive layer during solvent immersion. Therefore, the thicker the pressure-sensitive adhesive layer, the more easily the solvent acts on the pressure-sensitive adhesive. Applying the method disclosed herein to such a pressure-sensitive adhesive layer is effective. Furthermore, from the viewpoint of preventing adhesive residue due to cohesive failure of the pressure-sensitive adhesive layer, in some embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 1000 μm or less, 500 μm or less, 300 μm or less, or even 200 μm or less.

[0121] (Haze value) The pressure-sensitive adhesive is preferably an optical pressure-sensitive adhesive. The optical pressure-sensitive adhesive may be one that does not impair optical properties. The haze value of the pressure-sensitive adhesive (layer), and therefore the pressure-sensitive adhesive sheet, is not particularly limited, but in some embodiments, the haze value is suitably about 10% or less, and may be about 5% or less (e.g., about 3% or less). The haze value is preferably 1.0% or less. Such highly transparent pressure-sensitive adhesives are suitable for optical applications that require high light transmittance. The haze value may be less than 1.0%, less than 0.7%, or 0.5% or less (e.g., 0 to 0.5%). The haze value can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive.

[0122] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto the object to be measured. It is also called the cloudiness value. The haze value can be expressed by the following formula: Th[%]=Td / Tt×100 In the above formula, Th is the haze value [%], Td is the scattered light transmittance, and Tt is the total light transmittance. The haze value can be measured by attaching the adhesive surface of a pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet to one side of alkali glass with a haze value of 0.1% to form a laminate of the pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet and the alkali glass, and then using a haze meter (for example, product name "MR-100" manufactured by Murakami Color Research Laboratory). For measurement, the alkali glass with the pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet attached is positioned so that the pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet faces the light source. Since the haze value of alkali glass is 0.1%, the haze value [%] of the pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet is determined by subtracting 0.1% from the measured value.

[0123] (base material layer) In some embodiments, the pressure-sensitive adhesive sheet used to bond members in a bonded structure includes a substrate layer. The substrate layer is a support (support layer) that supports the pressure-sensitive adhesive layer. The substrate layer can be an intermediate layer disposed between the first and second pressure-sensitive adhesive layers that constitute the surfaces of the pressure-sensitive adhesive sheet.

[0124] Examples of the substrate layer disclosed herein include various resin films such as polyolefin film, polyester film, and polyvinyl chloride film; foam sheets made of foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials alone or in combination (e.g., natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate); papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil, copper foil, and stainless steel (SUS). Layered bodies made by combining these may also be used. Examples of substrate layers with such composite structures include laminated substrates (multilayer substrates) in which metal foil and the above-mentioned resin film are laminated, and resin sheets reinforced with inorganic fibers such as glass cloth.

[0125] As the material for the substrate layer, a material containing a resin film that can independently maintain its shape (self-supporting or independent) as a base film can be preferably used. Here, "resin film" refers to a resin film that has a non-porous structure and typically contains substantially no air bubbles (void-free). Therefore, the resin film is a concept that is distinguished from foam films and nonwoven fabrics. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure). The resin film may be a transparent film. Transparent resin films are suitable for optical applications.

[0126] Suitable examples of resin materials constituting the resin film include polyester resins, polyphenylene sulfide (PPS) resins, polyolefin resins, and polyimide resins. Specific examples of resin films that can be preferably used as the substrate layer include polyethylene terephthalate (PET) films, polyethylene naphthalate (PEN) films, PPS films, polyether ether ketone (PEEK) films, transparent polyimide (CPI) films, polypropylene (PP) films, and triacetyl cellulose (TAC) films. Preferred examples from the standpoint of strength include PET films, PEN films, PPS films, PEEK films, and CPI films. Preferred examples from the standpoints of availability, dimensional stability, optical properties, and the like include PET films, CPI films, and TAC films.

[0127] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc. The amount of additives to be added is not particularly limited and can be set appropriately depending on the application, etc.

[0128] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately used.

[0129] The substrate layer may be substantially composed of such a resin film. Alternatively, the substrate layer may include an auxiliary layer in addition to the resin film. Examples of the auxiliary layer include a surface treatment layer such as an undercoat layer or a release layer. Furthermore, the surface of the substrate layer facing the pressure-sensitive adhesive layer may be subjected to a conventionally known surface treatment, such as corona treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, application of a primer (primer), antistatic treatment, or release treatment, as needed.

[0130] The thickness of the substrate layer is not particularly limited and may be, for example, approximately 1000 μm or less, or approximately 500 μm or less. From the viewpoint of weight reduction and thinning, it is preferably approximately 100 μm or less, or even 70 μm or less. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate layer may be, for example, 1 μm or more, or preferably approximately 20 μm or more, and preferably approximately 30 μm or more.

[0131] (Adhesive sheet size) In embodiments in which two components are joined by a pressure-sensitive adhesive sheet, the length and width of the pressure-sensitive adhesive sheet (e.g., the length and width of a band-shaped pressure-sensitive adhesive sheet) are not particularly limited. Since the entire surface of a pressure-sensitive adhesive sheet is usually adhered to an adherend, if the adherend is solvent-impermeable, the solvent only comes into contact with the adhesive from the edge of the pressure-sensitive adhesive sheet during solvent immersion. Therefore, the larger the size (length and width) of the pressure-sensitive adhesive sheet, the longer the solvent immersion peeling process tends to take. The technology disclosed herein can achieve the desired effect even with relatively large pressure-sensitive adhesive sheets, for example, pressure-sensitive adhesive sheets with at least one of a length and width of 20 mm or more (or even 40 mm or more, e.g., 60 mm or more). Furthermore, the width of the widest portion of the pressure-sensitive adhesive sheet (specifically, the adhesive region of the pressure-sensitive adhesive sheet) peeled by the technology disclosed herein may be, for example, 200 mm or less, or even 100 mm or less, from the viewpoint of solvent immersion peeling efficiency. [Example]

[0132] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

[0133] <Preparation of adhesive sheet> (Example A) A monomer syrup containing a partial polymerization product of the monomer mixture was prepared by photopolymerization under a nitrogen atmosphere with ultraviolet light irradiation until the viscosity reached approximately 15 Pa·s (BH viscometer, No. 5 rotor, 10 rpm, 30°C). To 100 parts of this monomer syrup, 0.1 parts of dipentaerythritol hexaacrylate as a polyfunctional monomer, 0.3 parts of a nonionic surfactant (polyoxyethylene sorbitan monolaurate, HLB 16.7, product name "Rheodor TW-L120", manufactured by Kao Corporation) as a hydrophilic agent, and 0.4 parts of a silane coupling agent (product name "KBE403" manufactured by Shin-Etsu Silicones Co., Ltd.) were added and mixed uniformly to prepare an ultraviolet-curable pressure-sensitive adhesive composition.

[0134] The adhesive composition obtained above was applied to a 38 μm thick release film R1 (manufactured by Mitsubishi Plastics, product name "MRF#38"), one side of which is a polyester film with a release surface, and then covered with a 38 μm thick release film R2 (manufactured by Mitsubishi Plastics, product name "MRE#38"), one side of which is a polyester film with a release surface, to block out air. The adhesive composition was then cured by irradiating with ultraviolet light to form a 200 μm thick adhesive layer. The ultraviolet light was irradiated using a black light lamp at an illuminance of 4 mW / cm. 2The test was carried out under the condition that the adhesive was irradiated for 180 seconds with an industrial UV checker (manufactured by Topcon Corporation, product name "UVR-T1") with a peak sensitivity wavelength of approximately 350 nm. In this way, pressure-sensitive adhesive sheet A (a pressure-sensitive adhesive sheet consisting only of a pressure-sensitive adhesive layer) was obtained. The surface of pressure-sensitive adhesive sheet A to be attached to the adherend was protected by release films R1 and R2.

[0135] (Production Example B> A pressure-sensitive adhesive sheet B was obtained in the same manner as in Preparation Example A, except that no water affinity agent was used.

[0136] <Evaluation of peelability by solvent immersion immediately after lamination> The solvent immersion releasability of PSA sheets A and B was evaluated using the following method. The release liner covering one surface of the PSA layer (support-less double-sided PSA sheet) was peeled off from the PSA sheet, and an 11 μm-thick aluminum foil (manufactured by Toyo Aluminum Echo Products, product name "Sunfoil") was laminated to the exposed adhesive surface, which was then cut to a size of 80 mm × 200 mm. Next, the release liner covering the other surface of the PSA layer was peeled off, and the exposed adhesive surface was laminated to the entire surface (65 mm × 165 mm) of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., prepared by the float method, 1.35 mm thick, blue plate edge polished, contact angle with distilled water of the surface to be laminated with the PSA sheet: 8°). This aluminum foil / adhesive / alkali glass plate laminate was pressed into place by rolling a 2 kg rubber roller back and forth twice. The aluminum foil and adhesive protruding from the alkali glass plate were cut and removed, producing an aluminum foil / adhesive / alkali glass plate laminate to be evaluated. A number of the above laminates were prepared and each was immersed in each of the solvents shown in Table 1. The peel distance [mm] from the edge (one end) in the width direction of the pressure-sensitive adhesive sheet (65 mm wide) was measured 5 hours and 24 hours after the start of immersion. The solvent immersion was carried out at 23°C. The results are shown in Table 1. Note that "peeled" in the table indicates that the entire pressure-sensitive adhesive sheet peeled off from the adherend (specifically, the sheet was lifted and peeled off from the adherend due to swelling of the adhesive), which can be said to be a peel distance of 32.5 mm from the one end. Note that "-" in the table indicates that no measurement was performed.

[0137] The contact angle of the alkali glass plate is measured by the following method. Specifically, measurements are performed using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DMo-501 model," control box "DMC-2," and control and analysis software "FAMAS (version 5.0.30)") under an ambient temperature of 23°C and 50% RH using the sessile drop method. A 2 μL drop of distilled water is used, and the contact angle is calculated using the Θ / 2 method from an image taken 5 seconds after the drop (performed with N5).

[0138] <Evaluation of peelability after accelerated testing> (Solvent immersion peeling) For PSA sheets A and B, aluminum foil / adhesive / alkali glass plate laminates to be evaluated were prepared in the same manner as in the evaluation of solvent immersion peelability immediately after lamination. Multiple such laminates were prepared and heated and stored at 60°C for 4 days (an accelerated test equivalent to 25°C x 200 days using the Arrhenius method). The laminates were then immersed in each of the solvents listed in Table 1, and the peel distance [mm] in the width direction of the PSA sheet (65 mm wide) was measured 24 hours, 72 hours, 84 hours, and one week after the start of immersion. Solvent immersion was performed at 23°C. The results are shown in Table 2.

[0139] (Water peeling) For PSA Sheets A and B, aluminum foil / adhesive / alkali glass plate laminates were prepared and subjected to an accelerated test (storage at 60°C for 4 days) in the same manner as in the solvent immersion peelability evaluation after the accelerated test. Next, in an environment of 23°C and 50% RH, a peel trigger was created at the edge with a cutter or plastic spatula, and 20 μL of distilled water was added to the point where the adhesive began to separate from the alkali glass plate (the peel front). The aluminum foil / adhesive laminate was manually peeled from the alkali glass plate at a speed that ensured peeling within 3 minutes, taking care to avoid tearing or cracking. However, for both PSA Sheets A and B, the aluminum foil tore during peeling, and the adhesive could not be smoothly peeled without damaging the adherend.

[0140] (HSP value and HSP distance) In addition, the HSP values ​​(dispersion parameter (δD), polar parameter (δP), and hydrogen bond parameter (δH)) were calculated for the adhesive of adhesive sheet A and each solvent, and the HSP distance between the adhesive and each solvent was determined. The results are shown in Table 3.

[0141] [Table 1]

[0142] [Table 2]

[0143] [Table 3]

[0144] As shown in Table 1, when the PSA sheets were laminated to the adherends and then evaluated for releasability by solvent immersion, no significant difference in releasability was observed between PSA Sheet A containing a hydrophilic agent and PSA Sheet B containing no hydrophilic agent. However, after an accelerated test at 60°C for 4 days, PSA Sheet B containing no hydrophilic agent did not peel at all from the adherend, whereas PSA Sheet A containing a hydrophilic agent peeled more rapidly from the adherend with increasing immersion time. Specifically, the PSA swelled upon solvent immersion, leading to spontaneous peeling. Among these, solvent immersion using ethyl acetate enabled the PSA to be peeled with the shortest immersion time. Furthermore, after an accelerated test at 60°C for 4 days, it was confirmed that PSA Sheet A containing a hydrophilic agent, which originally had water releasability, lost its water releasability.

[0145] Based on the HSP of the adhesive and solvent, the solvent immersion releasability of the adhesive and solvent was examined. In several test examples (specifically, examples using non-alcoholic solvents), as shown in Table 3, it was confirmed that the HSP distance between the adhesive and solvent correlated with the solvent immersion releasability shown in Table 2. Specifically, hexane, which had an HSP distance of 9.3 to the adhesive, failed to remove the adhesive by solvent immersion. However, when toluene, which had an HSP distance of 4.2, was used, solvent immersion releasability was observed. Furthermore, ethyl acetate, which had an HSP distance of 4.0 or less, exhibited the best solvent immersion releasability for the adhesive evaluated. Furthermore, in several other test examples (specifically, examples using alcoholic solvents), the experimental results and HSP values ​​indicated a tendency for solvent immersion releasability to improve as the hydrogen bond parameter (δH) increased. It is believed that the hydrogen bond parameter contributed to the improved releasability because PSA Sheet A contained a hydrophilic agent. Alcohols such as methanol and ethanol, which had a δH of 15.0 or greater, exhibited good solvent immersion releasability.

[0146] The above results show that by performing solvent immersion peeling on a bonded structure containing two components bonded with an adhesive containing a hydrophilic agent, the adhesive can be peeled from the components and the two components can be separated.

[0147] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0148] 1 Adhesive (adhesive sheet) 1A One surface (first adhesive surface) 1B Other surface (second adhesive surface) 100 zygote 120 First member 140 Second member 200 solvent 250 containers

Claims

1. A method for separating a bonded structure including two members bonded with an adhesive, comprising: the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive containing an acrylic polymer as a base polymer, The adhesive contains a water-compatible agent, the content of the hydrophilic agent in the pressure-sensitive adhesive is 0.01 parts by weight or more and 2 parts by weight or less per 100 parts by weight of the acrylic polymer, a step of immersing the bonded body in an organic solvent to peel off the pressure-sensitive adhesive from the member; The method, wherein the HSP (Hansen Solubility Parameters) distance between the pressure-sensitive adhesive and the organic solvent is 4.0 or less.

2. A method for separating a bonded structure including two members bonded with an adhesive, comprising: the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive containing an acrylic polymer as a base polymer, The adhesive contains a water-compatible agent, the content of the hydrophilic agent in the pressure-sensitive adhesive is 0.01 parts by weight or more and 2 parts by weight or less per 100 parts by weight of the acrylic polymer, a step of immersing the bonded body in an organic solvent at 0°C to 40°C to peel off the pressure-sensitive adhesive from the member; The organic solvent has a hydrogen bond term (δH) in HSP of 15.0 or more.

3. The method according to claim 1 or 2, wherein the adhesive is a solvent-based adhesive or an active energy ray-curable adhesive.

4. The method according to any one of claims 1 to 3, wherein the two members are joined by a double-sided adhesive sheet containing the adhesive, and the width of the adhesive sheet is 20 mm or more.

5. The method according to any one of claims 1 to 4, wherein the bonded body is immersed in the organic solvent for 24 hours or more.

6. 6. The method according to claim 5, wherein the adhesive is peeled from one of the two members by a distance of 20 mm or more 24 hours after the bonded body is immersed in the organic solvent.

7. a step of determining whether the pressure-sensitive adhesive can be water-removed from at least one of the two members before immersing the bonded body in an organic solvent, The water peeling is performed in a state where an aqueous liquid is present at the location where the PSA is to be peeled from the surface of the member, The method according to any one of claims 1 to 6, wherein after it is confirmed that the bonded body is not peelable with water, the bonded body is immersed in an organic solvent.

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