Adhesive sheet, method for manufacturing same, and method for peeling object from adhesive sheet

Abstract

The present invention protects the rear surface of an object to be held by an adhesive sheet including an adhesive layer that has protrusions and recesses on the surface thereof.　This adhesive sheet includes a base material and an adhesive layer that has protrusions and recesses on the surface thereof. The adhesive layer contains a urethane prepolymer crosslinked with a polyfunctional isocyanate.

Description

Adhesive sheet, method for manufacturing the same, and method for peeling an object from the adhesive sheet

[0001] This invention relates to an adhesive sheet, a method for manufacturing the same, and a method for peeling an object from an adhesive sheet, and more particularly to the manufacturing of a semiconductor chip.

[0002] Adhesive sheets can be used to temporarily hold objects. For example, such adhesive sheets can be used to transfer an object to a desired position. They can also be used to support an object when performing processing such as cutting.

[0003] For example, Patent Document 1 discloses an adhesive sheet having an adhesive layer with an uneven surface. When the adhesive layer has an uneven surface in this way, the pressure generated between the object and the adhesive layer when holding an object is relieved through the recesses, making it easier to hold the object in a desired position on the adhesive sheet. It also prevents air bubbles from getting trapped between the object and the adhesive layer.

[0004] International Publication No. 2024 / 063124

[0005] On the other hand, there are times when it is necessary to protect the back surface (the side facing the adhesive sheet) of an object held by the adhesive sheet. For example, when dicing or backgrinding a semiconductor wafer, the back surface of the semiconductor wafer is generally protected by an adhesive sheet such as dicing tape or die bonding tape to prevent contamination. However, if the adhesive sheet described in Patent Document 1 is used for this purpose, there is a possibility that substances such as water that penetrate through the uneven surface may reach the back surface of the semiconductor wafer.

[0006] One embodiment of the present invention aims to protect the back surface of an object being held by an adhesive sheet having an adhesive layer with an uneven surface.

[0007] The inventors of this invention, after diligent research, discovered that the above problem could be solved by selecting a material for the adhesive layer such that the unevenness would be flattened when the object was held. After further research, they completed the present invention.

[0008] In other words, embodiments of the present invention relate to the following [1] to

[15] . [1] An adhesive sheet comprising a base material and an adhesive layer having irregularities on its surface, wherein the adhesive layer contains a urethane prepolymer crosslinked with a polyfunctional isocyanate. [2] The adhesive sheet according to [1], wherein the urethane prepolymer is crosslinked with 1.0 part by mass or more of the polyfunctional isocyanate per 100 parts by mass of the urethane prepolymer. [3] The adhesive sheet according to any one of [1] to [2], wherein the weight-average molecular weight of the urethane prepolymer is 10,000 or more and 1,000,000 or less. [4] The adhesive sheet according to any one of [1] to [3], wherein the hydroxyl value of the urethane prepolymer is 3.0 mg KOH / g or more and 15 mg KOH / g or less. [5] The adhesive sheet according to any one of [1] to [4], wherein the polyfunctional isocyanate is an aliphatic isocyanate. [6] The adhesive sheet according to any one of [1] to [5], wherein the polyfunctional isocyanate has a polymerizable double bond. [7] The adhesive sheet according to any one of [1] to [6], wherein the polyfunctional isocyanate has (meth)acryloyl groups. [8] The adhesive sheet according to any one of [1] to [7], wherein the mass average molecular weight of the polyfunctional isocyanate is 400 or more and 2000 or less. [9] The adhesive sheet according to any one of [1] to [8], wherein the surface of the adhesive layer has a plurality of protrusions, and the height of the plurality of protrusions is uniform.

[10] The adhesive sheet according to any one of [1] to [9], wherein the surface of the adhesive layer has a plurality of protrusions, and the height of each of the plurality of protrusions is 1 μm or more.

[11] The adhesive sheet according to any one of [1] to

[10] , wherein the surface of the adhesive layer has a plurality of protrusions, and the pitch of the plurality of protrusions is 1 μm or more and 100 μm or less. A method for peeling an object attached to an adhesive sheet according to any one of [1] to

[11] , comprising: an expansion step of expanding the adhesive sheet in the planar direction; and a peeling step of peeling the object from the adhesive layer of the adhesive sheet.

[13] The peeling method according to

[12] , wherein, prior to the expansion step, the irregularities of the adhesive layer to which the object is attached are flattened, and in the expansion step, the adhesive sheet is expanded so that the irregularities of the adhesive layer are restored.

[14] The peeling method according to any one of

[12] to

[13] , wherein the polyfunctional isocyanate has polymerizable double bonds, and further comprises an irradiation step of irradiating the adhesive layer with energy rays after the expansion step and before the peeling step.

[15] A method for manufacturing an adhesive sheet having an adhesive layer, comprising a forming step of forming a layer of a composition comprising a urethane prepolymer and a polyfunctional isocyanate, and a curing step of curing the layer of the composition so that it has irregularities on its surface.

[0009] One embodiment of the present invention provides an adhesive sheet having an adhesive layer with an uneven surface that can protect the back surface of an object being held.

[0010] Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings.

[0011] The attached drawings are included in the specification and constitute part thereof, illustrating embodiments of the present invention and are used together with the description to explain the principles of the present invention.

[0012] Cross-sectional view of an adhesive sheet according to one embodiment. Cross-sectional view of an adhesive sheet according to one embodiment. Top view of an adhesive sheet according to one embodiment. Top view of an adhesive sheet according to one embodiment. Diagram illustrating how to use the adhesive sheet according to one embodiment. Diagram illustrating how to use the adhesive sheet according to one embodiment. Diagram illustrating how to use the adhesive sheet according to one embodiment. Diagram illustrating how to use the adhesive sheet according to one embodiment. Flowchart of the manufacturing method of the adhesive sheet according to one embodiment. Flowchart of how to use the adhesive sheet according to one embodiment. Photograph showing the contact state between the expanded adhesive layer and each element in Example 1. Photograph showing the contact state between the expanded adhesive layer and each element in Example 2. Photograph showing the contact state between the expanded adhesive layer and each element in Example 5. Photograph showing the contact state between the expanded adhesive layer and each element in Example 6. Photograph showing the contact state between the expanded adhesive layer and each element in Example 7.

[0013] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0014] (Definitions) In this specification, mass-average molecular weight (Mw) and number-average molecular weight (Mn) are values ​​on a standard polystyrene basis measured by size exclusion chromatography, specifically values ​​measured according to JIS K7252-1:2016. Also in this specification, "(meth)acrylic acid" is a term that refers to both "acrylic acid" and "methacrylic acid," and the same applies to other similar terms.

[0015] In this specification, when a numerical range (e.g., a range of content, etc.) is described with one or more lower limits and one or more upper limits, it can be understood that any combination of lower and upper limits within that range is described. For example, the statement "preferably 1 to 9, more preferably 2 to 8, and even more preferably 3 to 7" clearly means that the numerical range may be any of the following: 1 to 9, 1 to 8, 1 to 7, 2 to 9, 2 to 8, 2 to 7, 3 to 9, 3 to 8, and 3 to 7. As another example, the statement "preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, preferably 9 or less, more preferably 8 or less, and even more preferably 7 or less" has the same meaning. Also, in this specification, parts by mass and mass percent indicate a proportion based on the mass of solids unless otherwise specified.

[0016] (Adhesive Sheet) An adhesive sheet according to one embodiment of the present invention comprises a base material and an adhesive layer having irregularities on its surface. This adhesive layer contains a urethane prepolymer crosslinked with a polyfunctional isocyanate. The irregularities of such an adhesive layer make it easy to crush when an object is attached, making it suitable for protecting the back surface of the object being held.

[0017] Furthermore, in one embodiment, when the pressure-sensitive adhesive sheet is stretched after an object is adhered thereto, the crushed uneven shape is restored. In such a pressure-sensitive adhesive sheet, stretching can reduce the holding force for the object. Such a pressure-sensitive adhesive sheet is particularly suitable when processing is performed on the adhered object.

[0018] FIG. 1A is a cross-sectional view schematically showing a pressure-sensitive adhesive sheet 100 according to one embodiment. Further, FIG. 2A is a top view schematically showing the pressure-sensitive adhesive sheet 100. The pressure-sensitive adhesive sheet 100 includes a pressure-sensitive adhesive layer 110 and a base material 120. The pressure-sensitive adhesive layer 110 has unevenness on the surface thereof.

[0019] (Pressure-sensitive adhesive layer) The pressure-sensitive adhesive layer 110 is a layer having adhesiveness. The pressure-sensitive adhesive layer 110 may contain a resin. The resin contained in the pressure-sensitive adhesive layer 110 is preferably an adhesive resin that has adhesiveness when used alone. On the other hand, it is not necessary for the resin contained in the pressure-sensitive adhesive layer 110 to be an adhesive resin. When the resin contained in the pressure-sensitive adhesive layer 110 is not an adhesive resin, a tackifier can be added to the pressure-sensitive adhesive layer 110.

[0020] In one embodiment, the resin is a polymer having a weight average molecular weight (Mw) of 10,000 or more. From the viewpoint of improving holding power, the weight average molecular weight (Mw) of the resin is preferably 10,000 or more, more preferably 70,000 or more, and still more preferably 140,000 or more. Further, from the viewpoint of keeping the storage modulus below a predetermined value, it is preferably 2,000,000 or less, more preferably 1,200,000 or less. In addition, from the viewpoint of improving holding power, the number average molecular weight (Mn) of the resin is preferably 10,000 or more, more preferably 50,000 or more, and still more preferably 100,000 or more. Further, from the viewpoint of keeping the storage modulus below a predetermined value, it is preferably 2,000,000 or less, more preferably 1,500,000 or less, and still more preferably 1,200,000 or less.

[0021] The pressure-sensitive adhesive layer 110 may contain one type of resin, or may contain two or more types of resins. Note that the pressure-sensitive adhesive layer 110 may be a laminate of two or more pressure-sensitive adhesive layers. In this case, the materials of the respective pressure-sensitive adhesive layers may be the same or different.

[0022] (Urethane prepolymer crosslinked with polyfunctional isocyanate) The pressure-sensitive adhesive layer 110 according to one embodiment contains a urethane prepolymer crosslinked with polyfunctional isocyanate. That is, the pressure-sensitive adhesive layer 110 contains a urethane-based pressure-sensitive adhesive. Further, the urethane-based pressure-sensitive adhesive contains a urethane resin.

[0023] In the present specification, the urethane prepolymer refers to a prepolymer of urethane resin having a urethane bond in the molecule. The urethane prepolymer is a precursor of urethane resin, and the urethane resin is obtained by crosslinking the urethane prepolymer. In the present embodiment, the urethane prepolymer has a hydroxy group. The urethane prepolymer is crosslinked by the polyfunctional isocyanate via a hydroxy group.

[0024] The pressure-sensitive adhesive layer 110 having a urethane prepolymer crosslinked with polyfunctional isocyanate tends to maintain an uneven shape before attaching an object, while the uneven shape is easily crushed when attaching the object. Further, in one embodiment, when the pressure-sensitive adhesive layer 110 is stretched after attaching the object, the uneven shape is easily restored. Therefore, stretching the pressure-sensitive adhesive layer 110 makes it easy to peel off the object. The inventors of the present application consider that aggregation of the molecular chains of the prepolymer in an entangled manner in the urethane prepolymer crosslinked with polyfunctional isocyanate brings about such characteristics.

[0025] Such a urethane prepolymer can be obtained by a reaction between a polyol and a polyfunctional isocyanate. That is, the urethane prepolymer can have a structure in which polyols are linked via urethane bonds. More specifically, the urethane prepolymer can have a structure in which polyols are linked via urethane bonds and the main chain of the polyfunctional isocyanate. In this reaction, a urethane prepolymer having a hydroxy group can be obtained by using an excess of polyol. As the polyfunctional isocyanate, the polyfunctional isocyanate used for crosslinking the urethane prepolymer, which will be described later, can be used.

[0026] Examples of polyols include polyether polyols, polycarbonate polyols, and polyester polyols.

[0027] Examples of polyether polyols include polyether diols and polyether polyols with three or more functionalities. Other examples of polyether polyols include those obtained by coupling one or more of these polyether polyols using a coupling agent such as methylenedichloride.

[0028] Specific examples of polyether diols include poly(oxyalkylene) glycols such as poly(oxyethylene) glycol, poly(oxypropylene) glycol, poly(oxytetramethylene) glycol, and poly(oxy-3-methyltetramethylene) glycol; copolymerized poly(oxyalkylene) diols such as ethylene oxide / propylene oxide copolymer diol, tetrahydrofuran / ethylene oxide copolymer diol, and tetrahydrofuran / 3-methyltetrahydrofuran copolymer diol (copolymerization ratio is, for example, 1 / 9 to 9 / 1); and alkylene oxide adducts of bisphenol compounds such as bisphenol A, bisphenol B, bisphenol E, or bisphenol F. Specific examples of polyether polyols with three or more functions include alkylene oxide adducts of trivalent or higher polyhydric alcohols, such as alkylene oxide adducts of glycerin and alkylene oxide adducts of trimethylolpropane.

[0029] Examples of polyester polyols include polyester diols, trifunctional or more functional polyester polyols, and polyols obtained by coupling one or more of these using a coupling agent. Specific examples of polyester polyols include low molecular weight polyols with a molecular weight of 1,000 or less, condensed polyester diols obtained by reacting the above-mentioned polyether polyols with dicarboxylic acids, and polylactone diols obtained by ring-opening polymerization of lactones having 4 to 12 carbon atoms. Examples of dicarboxylic acids include aliphatic dicarboxylic acids having 4 to 10 carbon atoms such as succinic acid, adipic acid, or sebacic acid, and aromatic dicarboxylic acids having 8 to 15 carbon atoms such as terephthalic acid or isophthalic acid. Examples of lactones include ε-caprolactone and γ-valerolactone.

[0030] Examples of polycarbonate diols include polyhexamethylene carbonate diol.

[0031] In another embodiment, the urethane prepolymer has urea bonds within its molecule. Such a urethane prepolymer can be obtained by reacting a mixture of a polyol and a polyamine with a polyfunctional isocyanate. That is, the urethane prepolymer can have a structure in which the polyol and polyamine are linked via urethane or urea bonds.

[0032] The weight-average molecular weight (Mw) of the urethane prepolymer is preferably 10,000 to 1,000,000, more preferably 30,000 to 800,000, even more preferably 50,000 to 600,000, and particularly preferably 150,000 to 400,000. Increasing the weight-average molecular weight makes it easier to improve the viscosity while maintaining the elastic modulus of the adhesive layer 110, thus making it easier to flatten and restore uneven shapes. Decreasing the weight-average molecular weight can improve the tackiness of the adhesive layer 110.

[0033] The hydroxyl value of the urethane prepolymer is preferably 3.0 mg KOH / g or more and 35 mg KOH / g or less, more preferably 6.0 mg KOH / g or more and 25 mg KOH / g or less, and even more preferably 9.0 mg KOH / g or more and 15 mg KOH / g or less. Increasing the hydroxyl value improves the crosslinking density, making it easier to maintain the uneven shape of the adhesive layer 110. Conversely, decreasing the hydroxyl value makes it easier to maintain the viscosity of the adhesive layer 110. This hydroxyl value represents the mass (mg) of potassium hydroxide (KOH) equivalent to the hydroxyl groups contained in 1 g of solid content of the urethane prepolymer. In this specification, the hydroxyl value is the value measured by Method A (acetylation method) as defined in JIS K1557-1:2007.

[0034] (Polyfunctional Isocyanate) The polyfunctional isocyanate used to crosslink the urethane prepolymer is not particularly limited. The polyfunctional isocyanate may also be a polymer of a polyfunctional isocyanate such as isocyanurate. Furthermore, the polyfunctional isocyanate may be an adduct of a polyol such as trimethylolpropane to the polyfunctional isocyanate.

[0035] Examples of polyfunctional isocyanates include aliphatic isocyanates, alicyclic isocyanates, aromatic aliphatic isocyanates, and aromatic isocyanates. Examples of aliphatic isocyanates include aliphatic diisocyanates having 2 to 18 carbon atoms, such as ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, heptamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, 2,6-diisocyanatomethyl caproate, 2,6-diisocyanatoethyl caproate, bis(2-isocyanatoethyl) fumarate, and bis(2-isocyanatoethyl) carbonate. Examples of alicyclic isocyanates include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, and cyclohexylene diisocyanate, which have 4 to 15 carbon atoms. Examples of aromatic aliphatic isocyanates include m- or p-xylylene diisocyanate, diethylbenzene diisocyanate, α,α,α',α'-tetramethylxylylene diisocyanate, and 4,4'-diphenylmethane diisocyanate, which have 8 to 15 carbon atoms. Examples of aromatic isocyanates include 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, and 4,4'- or 2,4'-diphenylmethane diisocyanate, which have 6 to 20 carbon atoms.

[0036] In one embodiment, the polyfunctional isocyanate has polymerizable double bonds. The polyfunctional isocyanate may have an alkenyl group such as a vinyl group or an allyl group, or an aliphatic carbon-carbon double bond-containing group such as a (meth)acryloyl group, as a substituent having polymerizable double bonds. The urethane prepolymer crosslinked with a polyfunctional isocyanate having polymerizable double bonds is energy-ray reactive. That is, because such an energy-ray reactive resin has polymerizable double bonds, irradiating the adhesive layer 110 with energy rays can promote crosslinking between the polymerizable double bonds, thereby reducing the object-holding force. Such a resin is suitable as a material for the adhesive layer 110 because it can achieve both a higher holding force when attaching objects and a lower holding force when peeling objects off.

[0037] A polyfunctional isocyanate can be a compound having one or more polymerizable double bonds and two or more isocyanate groups. In one embodiment, the polyfunctional isocyanate has two to three isocyanate groups per molecule. Also in one embodiment, the polyfunctional isocyanate has one to two polymerizable double bonds per molecule. The polyfunctional isocyanate may be, for example, a urethane acrylate having one or more polymerizable double bonds and two or more isocyanate groups. Examples of such polyfunctional isocyanates include EBECRYL 4141, 4396, 4397, 4510, 4950, and 4250 (manufactured by Daicel Ornex Co., Ltd.). By using a compound with a relatively large molecular weight, such as urethane acrylate, as the polyfunctional isocyanate, the degree of freedom of crosslinking via the polyfunctional isocyanate is increased, thereby improving the object-holding power of the adhesive layer 110. Furthermore, the decrease in the object-holding force of the adhesive layer 110 when irradiated with energy rays can be made even greater.

[0038] From the viewpoint of increasing the degree of freedom of crosslinking via the polyfunctional isocyanate and improving the object-holding force of the adhesive layer, while maintaining the shape of the adhesive layer, the mass-average molecular weight of the polyfunctional isocyanate is preferably 400 to 2000, more preferably 500 to 1800, and even more preferably 600 to 1500.

[0039] The amount of polyfunctional isocyanate relative to the urethane prepolymer can be selected according to the desired ease of crushing the unevenness of the adhesive layer 110. By using less polyfunctional isocyanate, the unevenness of the adhesive layer 110 can be made easier to crush, and the holding power of the adhesive layer 110 can be increased. Furthermore, by limiting the amount of polyfunctional isocyanate, it is possible to suppress the decrease in the restorability of the unevenness due to the deactivated polyfunctional isocyanate acting as a plasticizer. On the other hand, by using more polyfunctional isocyanate, the crosslinking of the urethane prepolymer increases, making it easier to restore the unevenness of the adhesive layer 110 when the adhesive sheet is expanded.

[0040] In one embodiment, the urethane prepolymer is crosslinked with 0.1 parts by mass or more of a polyfunctional isocyanate per 100 parts by mass of the urethane prepolymer. The amount of polyfunctional isocyanate is preferably 0.1 parts by mass or more and 20 parts by mass or less, more preferably 0.5 parts by mass or more and 16 parts by mass or less, even more preferably 1 part by mass or more and 14 parts by mass or less, even more preferably 2 parts by mass or more and 12 parts by mass or less, even more preferably 3 parts by mass or more and 10 parts by mass or less, and particularly preferably 3.9 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the urethane prepolymer. In another embodiment, the polyfunctional isocyanate is isocyanurate, and its amount is preferably 1.0 part by mass or more and 10 parts by mass or less, and more preferably 1.1 parts by mass or more and 2.0 parts by mass or less, per 100 parts by mass of the urethane prepolymer. In another embodiment, the polyfunctional isocyanate is a polyol adduct of the polyfunctional isocyanate, and its amount is preferably 1.0 part by mass or more and 10 parts by mass or less, and more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, per 100 parts by mass of the urethane prepolymer.

[0041] In one embodiment, the molar ratio (isocyanate groups / hydroxyl groups) of isocyanate groups in the polyfunctional isocyanate to hydroxyl groups in the urethane prepolymer is 0.75 or more and 1.7 or less, preferably 0.85 or more and 1.5 or less, and more preferably 0.95 or more and 1.35 or less. This molar ratio is also called the R value.

[0042] The amount of polyfunctional isocyanate-crosslinked urethane prepolymer contained in the adhesive layer 110 relative to the total amount of components constituting the adhesive layer 110 can be appropriately set according to the desired adhesive strength of the adhesive layer 110. In one embodiment, the amount of polyfunctional isocyanate-crosslinked urethane prepolymer contained in the adhesive layer 110 relative to the total amount of components constituting the adhesive layer 110 is preferably 30% by mass or more and 99.99% by mass or less, more preferably 50% by mass or more and 99.95% by mass or less, even more preferably 70% by mass or more and 99.90% by mass or less, even more preferably 80% by mass or more and 99.80% by mass or less, and even more preferably 90% by mass or more and 99.50% by mass or less.

[0043] (Other resins) Examples of other resins that can be included in the adhesive layer 110, in addition to the urethane prepolymer crosslinked with polyfunctional isocyanate, include synthetic rubbers such as polyisobutylene resins, polybutadiene resins, and styrene-butadiene resins. Specific examples of synthetic rubbers include butadiene rubber, chloroprene rubber, isoprene rubber, styrene-butadiene copolymer (SBR), styrene-isoprene copolymer, acrylonitrile-butadiene copolymer (nitrile rubber), methyl methacrylate-butadiene copolymer, styrene-1,3-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-unconjugated diene terpolymer.

[0044] Further examples of resins included in the adhesive layer 110, in addition to the urethane prepolymer crosslinked with polyfunctional isocyanate, include acrylic resins; urethane resins other than the urethane prepolymer crosslinked with polyfunctional isocyanate; polyester resins; olefin resins; silicone resins; and polyvinyl ether resins. The adhesive layer 110 may also contain copolymers having two or more constituent units. The form of such copolymers is not particularly limited and may be block copolymers, random copolymers, alternating copolymers, or graft copolymers.

[0045] Generally, lowering the molecular weight of the resin contained in the adhesive layer 110, or reducing the crosslinking of the resin, makes the irregularities of the adhesive layer 110 more easily flattened when an object is attached. On the other hand, lowering the molecular weight of the resin contained in the adhesive layer 110, or reducing the crosslinking of the resin, further reduces the restorability of the irregularities of the adhesive layer 110 when the adhesive sheet 100 is expanded. When a urethane prepolymer crosslinked with a polyfunctional isocyanate is used as the material for the adhesive layer 110, even if the material for the adhesive layer 110 is formulated so that the irregularities flatten when an object is attached, the irregularities of the adhesive layer 110 are easily restored when the adhesive sheet 100 is expanded. For this reason, a urethane prepolymer crosslinked with a polyfunctional isocyanate is particularly suitable as the material for the adhesive layer 110 according to this embodiment.

[0046] The adhesive layer 110 may contain a tackifier in combination with these resins. Examples of tackifiers include alicyclic petroleum resins, aliphatic petroleum resins, terpene resins, ester resins, coumarone-indene resins, rosin resins, epoxy resins, phenolic resins, acrylic resins, butyral resins, olefin resins, chlorinated olefin resins, vinyl acetate resins, and modified or hydrogenated resins thereof.

[0047] The adhesive layer 110 may contain a thermoplastic resin. When a thermoplastic resin is used, it becomes easier to form irregularities on the adhesive layer 110 by heating and softening the resin. Furthermore, it becomes easier to maintain the formed irregular shape by cooling. Examples of thermoplastic resins include rubber-based resins, acrylic-based resins, urethane-based resins, and olefin-based resins.

[0048] The glass transition temperature (Tg) of the resin contained in the adhesive layer 110 is preferably -75°C or higher, more preferably -70°C or higher, preferably 5°C or lower, and more preferably -20°C or lower, from the viewpoint of improving the holding power of the adhesive layer 110. If the resin has two or more constituent units, the glass transition temperature (Tg) of the resin can be calculated using Fox's formula. The Tg of the monomers that derive the constituent units used in this case can be the value described in the Polymer Data Handbook or the Adhesion Handbook.

[0049] The amount of resin contained in the adhesive layer 110 relative to the total amount of components constituting the adhesive layer 110 can be appropriately set according to the desired adhesive strength of the adhesive layer 110. In one embodiment, the amount of resin contained in the adhesive layer 110 relative to the total amount of components constituting the adhesive layer 110 is preferably 30% by mass or more and 99.99% by mass or less, more preferably 50% by mass or more and 99.95% by mass or less, even more preferably 70% by mass or more and 99.90% by mass or less, even more preferably 80% by mass or more and 99.80% by mass or less, and even more preferably 90% by mass or more and 99.50% by mass or less.

[0050] (Other components of the adhesive layer) The adhesive layer 110 may contain components other than resin. For example, the adhesive layer 110 may contain one or more of the following: a catalyst, a curing retarder, a crosslinking agent, a photopolymerization initiator, an antioxidant, and other additives.

[0051] Examples of catalysts include catalysts for crosslinking urethane prepolymers with polyfunctional isocyanates. Such catalysts may remain in the adhesive layer 110. Examples of such catalysts include tertiary amine compounds and organometallic compounds. Examples of tertiary amine compounds include triethylamine, triethylenediamine, N,N-dimethylbenzylamine, N-methylmorpholine, and 1,8-diazabicyclo[5.4.0]undecene-7 (DBU). Examples of organometallic compounds include tin compounds and non-tin compounds. Examples of tin-based compounds include dibutyltin dichloride, dibutyltin oxide, dibutyltin dibromide, dibutyltin dimaleate, dibutyltin dilaurate, dibutyltin diacetate, dioctyltin dilaurate, dibutyltin sulfide, tributyltin sulfide, tributyltin oxide, tributyltin acetate, triethyltin ethoxide, tributyltin ethoxide, dioctyltin oxide, tributyltin chloride, tributyltin trichloroacetate, and tin 2-ethylhexanoate. Examples of non-tin compounds include titanium compounds such as dibutyltitanium dichloride, tetrabutyltitanate, and butoxytitanium trichloride; lead compounds such as lead oleate, lead 2-ethylhexanoate, lead benzoate, and lead naphthenate; iron compounds such as iron 2-ethylhexanoate and iron acetylacetonate; cobalt compounds such as cobalt benzoate and cobalt 2-ethylhexanoate; zinc compounds such as zinc naphthenate and zinc 2-ethylhexanoate; and zirconium naphthenate.

[0052] The adhesive layer 110 may contain one type of catalyst, or it may contain two or more types of catalysts. From the viewpoint of properly performing the crosslinking reaction, the catalyst content in the adhesive layer 110 is preferably 0.001 parts by mass or more and 5 parts by mass or less, more preferably 0.005 parts by mass or more and 1 part by mass or less, and even more preferably 0.01 parts by mass or more and 0.1 parts by mass or less, per 100 parts by mass of urethane prepolymer.

[0053] A curing retarder can be used to stabilize the adhesive layer composition before application. The type of curing retarder is not particularly limited. For example, a curing retarder can be selected depending on the catalyst. Examples of curing retarders include acetylacetone.

[0054] The adhesive layer 110 may contain one type of curing retarder, or it may contain two or more types of curing retarders. From the viewpoint of appropriately controlling the crosslinking reaction, the content of the curing retarder in the adhesive layer 110 is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of urethane prepolymer.

[0055] The crosslinking agent improves the storage modulus of the adhesive layer 110 in response to the application of energy. The type of energy is not particularly limited. The energy can be, for example, energy rays such as ultraviolet rays, electron beams, or ionizing radiation, or thermal energy. The crosslinking agent can be a compound into which polymerizable functional groups such as multiple bond-containing groups, oxetanyl groups, or epoxy groups have been introduced. The crosslinking agent can be selected in accordance with the resin contained in the adhesive layer 110. Note that the crosslinking agent referred to here is the unreacted crosslinking agent contained in the adhesive layer 110. Alternatively, the adhesive layer 110 may contain an energy-reactive resin into which polymerizable functional groups have been introduced instead of the crosslinking agent. When the adhesive layer 110 contains a crosslinking agent or an energy-reactive resin, applying energy to the adhesive layer 110 to which an object is attached reduces the holding power of the object by the adhesive layer 110.

[0056] The adhesive layer 110 may contain one type of crosslinking agent, or it may contain two or more types of crosslinking agents. From the viewpoint of properly performing the crosslinking reaction, the content of the crosslinking agent in the adhesive layer 110 is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0057] The photopolymerization initiator initiates a crosslinking reaction in response to irradiation with energy rays. If the adhesive layer 110 contains an energy-reactive resin, the addition of a photopolymerization initiator to the adhesive layer 110 allows the crosslinking reaction to proceed even with the application of relatively low energy.

[0058] Examples of photopolymerization initiators include 1-hydroxycyclohexylphenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzylphenyl sulfide, tetramethylthiuram monosulfide, azobisisobutyronitrile, dibenzyl, diacetyl, 8-chloroanthraquinone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0059] The adhesive layer 110 may contain one type of polymerization initiator or two or more types of polymerization initiators. The content of the photopolymerization initiator in the adhesive layer 110 is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less.

[0060] Examples of antioxidants include phenolic compounds such as hindered phenol compounds, aromatic amine compounds, sulfur compounds, and phosphorus compounds such as phosphate ester compounds.

[0061] Other additives that the adhesive layer 110 may contain are not particularly limited, but include, for example, ultraviolet absorbers such as benzotriazole compounds, oxazolic acidamide compounds, or benzophenone compounds; light stabilizers such as hindered amine, benzophenone, or benzotriazole compounds; resin stabilizers such as imidazole resin stabilizers, dithiocarbamate resin stabilizers, phosphorus resin stabilizers, or sulfur ester resin stabilizers; fillers, pigments, bulking agents, and softeners.

[0062] If the adhesive layer 110 contains these additives, the content of the additives in the adhesive layer 110 is preferably 0.0001% by mass or more, more preferably 0.01% by mass or more, particularly preferably 0.1% by mass or more, even more preferably 1% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0063] (Shape of the adhesive layer) The surface of the adhesive layer 110 according to this embodiment has an uneven surface. In one embodiment, the adhesive layer 110 has a plurality of convex portions on its surface that are separated from each other and whose boundaries are defined by recesses. Each of the plurality of convex portions may be separated by recesses that are continuous throughout the entire adhesive layer 110. For example, the adhesive layer 110 may have flat recesses and convex portions 111 that protrude from the flat recesses.

[0064] As shown in Figure 2A, the surface of the adhesive layer 110 may have protrusions 111 arranged regularly. Regular arrangement of protrusions means that the protrusions are aligned in a straight line at regular intervals. On the other hand, the protrusions 111 may be arranged so that the intervals between them vary regularly. For example, the intervals between the protrusions 111 may be shorter in the center of the adhesive sheet 100 and longer in the peripheral area of ​​the adhesive sheet 100. Furthermore, the protrusions 111 may be arranged irregularly.

[0065] Figure 2B is a top view showing another shape of the adhesive layer 110. As shown in Figure 2B, the surface of the adhesive layer 110 may be provided with stripe-shaped protrusions 111. In Figure 2B, line-shaped protrusions 111 having a certain width are arranged at regular intervals. The width or spacing of these line-shaped protrusions 111 may vary regularly, or the line-shaped protrusions 111 may be arranged irregularly.

[0066] The pitch P of the protrusions 111 is preferably 1 μm to 100 μm, more preferably 5 μm to 50 μm, even more preferably 10 μm to 35 μm, and even more preferably 15 μm to 25 μm. The holding force can be limited by increasing the pitch P. Conversely, the holding force can be increased by shortening the pitch P to increase the contact area between the adhesive layer 110 and the object. Here, the pitch P of the protrusions 111 refers to the distance between the center point of one arbitrarily selected protrusion 111 and the center point of the nearest other protrusion 111. For example, in Figure 2A, the pitch P of the protrusions 111 represents the distance between the center point of a protrusion 111 and the center point of the nearest other protrusion 111 on a straight line in which the protrusions 111 are aligned at regular intervals. When the protrusions 111 are aligned on multiple straight lines, the pitch P represents the distance between the center points of the protrusions 111 on the straight line in which the protrusions 111 are aligned at the shortest pitch. In the case of Figure 2B, the pitch P of the protrusions 111 represents the distance between adjacent protrusions 111. In this specification, the distance between protrusions 111 means the distance between the centers of the protrusions 111.

[0067] The specific shape of the protrusion 111 is not particularly limited. For example, the protrusion 111 may have a pillar shape. Specifically, the protrusion 111 may have a cylindrical shape, a prismatic shape, a cone shape, a pyramidal shape, a spherical shape, or a hemispherical shape. Also, as described above, the protrusion 111 may extend in a linear shape or in a curved shape such as a wave shape. Furthermore, these protrusions 111 may be provided with a taper or reverse taper. For example, as shown in Figure 1B, the protrusion 111 may be tapered. Also, as shown in Figure 1B, the tip of the protrusion 111 may be curved. With such a configuration, the impact when attaching an object to the adhesive layer 110 is further mitigated, making it easier for the adhesive layer 110 to hold the object without it shifting. On the other hand, the tip of the protrusion 111 may be flat. As another example, the protrusion 111 may be hemispherical or part of a sphere. Also, the protrusion 111 may be T-shaped. As yet another example, the protrusions 111 may be in the shape of a collection of granules, mushroom-shaped, lotus leaf-shaped, or needle-shaped. As yet another example, the surface of the adhesive layer 110 may be rough or fibrous, and such a surface can also be said to have irregularities.

[0068] The width or diameter of each protrusion 111 is preferably 1 μm to 100 μm, more preferably 2 μm to 500 μm, even more preferably 5 μm to 30 μm, and even more preferably 10 μm to 20 μm. By increasing the width or diameter of the protrusion 111, the holding force of the object can be maintained. Conversely, by decreasing the width or diameter of the protrusion 111, the ease of peeling the object can be increased. Here, the width and diameter of the protrusion 111 refer to the minimum and maximum distances (represented as W in Figure 1B) between two parallel lines tangent to the protrusion 111 on both sides of the surface of the recess.

[0069] Furthermore, the area of ​​each protrusion 111 is preferably 10 μm ２ 2000 μm or more ２ More preferably, 20 μm ２ 1000 μm or more ２ More preferably 30 μm ２ 500 μm or more ２The following applies: By increasing the area of ​​the protrusion 111, the holding force of the object can be maintained. Conversely, by decreasing the area of ​​the protrusion 111, the ease of removing the object can be increased. Here, the area of ​​the protrusion 111 refers to the area of ​​the part that protrudes from the surface of the recess (in the case of Figure 1B, the area of ​​a circle with diameter W).

[0070] In one embodiment, the height of each protrusion 111 is preferably 1 μm to 20 μm, more preferably 3 μm to 15 μm, and even more preferably 5 μm to 10 μm. By increasing the height of the protrusion 111, the ease of peeling the object can be improved. Conversely, by decreasing the height of the protrusion 111, the holding force of the object can be improved. Here, the height of the protrusion 111 is represented by H in Figure 1B. Also in one embodiment, the heights of the multiple protrusions 111 on the adhesive layer 110 are uniform. In another embodiment, the adhesive layer 110 may have a first plurality of protrusions having a first uniform height and a second plurality of protrusions having different heights. Here, the second plurality of protrusions may have a second uniform height. For example, the protrusion 111 may consist of such first and second protrusions. In a further embodiment, the adhesive layer 110 may have a plurality of protrusions 111 of random heights.

[0071] Furthermore, the total area of ​​the protrusions 111 relative to the area of ​​the adhesive layer 110 is preferably 1% to 95%, more preferably 5% to 75%, even more preferably 10% to 70%, even more preferably 18% to 65%, and even more preferably 40% to 60%. By increasing the total area of ​​the protrusions 111, the holding power of the object can be maintained. Conversely, by decreasing the total area of ​​the protrusions 111, the ease of peeling the object can be improved.

[0072] The thickness of the pressure-sensitive adhesive layer 110 is preferably 1 µm or more and 100 µm or less, more preferably 2 µm or more and 75 µm or less, still more preferably 5 µm or more and 50 µm or less, and particularly preferably 10 µm or more and 30 µm or less. Increasing the thickness of the pressure-sensitive adhesive layer 110 improves the adhesive strength. Further, reducing the thickness of the pressure-sensitive adhesive layer 110 can reduce the volume of the pressure-sensitive adhesive sheet 100. Note that the thickness of the pressure-sensitive adhesive layer 110 refers to the thickness including the convex portions 111.

[0073] (Characteristics of Pressure-Sensitive Adhesive Layer) In one embodiment, the relaxation modulus G of the pressure-sensitive adhesive layer 110 measured 1000 seconds after application of stress Ｔ and the relaxation modulus G measured immediately after application of stress Ｉ the residual stress ratio, which is the ratio of (G Ｔ / G Ｉ ) is 56% or more and 100% or less. G Ｔ / G Ｉ By setting G1000 / G0 to 56% or more and 100% or less, when the pressure-sensitive adhesive sheet 100 with an object adhered thereto is stretched in the planar direction, the irregularities on the surface of the pressure-sensitive adhesive layer 110 can be restored. G Ｔ / G Ｉ Increasing the value of G1000 / G0 makes it easier for the irregularities on the surface of the pressure-sensitive adhesive layer 110 to recover. From this viewpoint, the value of G Ｔ / G Ｉ is preferably 58% or more, and more preferably 60% or more. G Ｔ / G Ｉ can be increased by increasing the crosslinking of the resin contained in the pressure-sensitive adhesive layer 110. For example, by increasing the amount of polyfunctional isocyanate used for crosslinking urethane prepolymer, G Ｔ / G Ｉ can be increased.

[0074] In the present specification, the relaxation modulus is measured in accordance with JIS K7244-1:1998. More specifically, a sample for relaxation modulus measurement is produced by laminating the pressure-sensitive adhesive layer 110 to a thickness of 0.8 mm and punching the laminate into a cylindrical body having a diameter of 8 mm. Further, the relaxation modulus is measured by straining the sample by 5% at 25°C. G Ｉ is measured 0.1 seconds after the stress is applied.

[0075] In one embodiment, the permanent shear strain of the adhesive layer 110 is 0.1% or less. By setting the permanent shear strain to 0.1% or less, the surface irregularities of the adhesive layer 110 can be restored when the adhesive sheet 100 to which an object is attached is expanded in the planar direction. By further reducing the permanent shear strain, the surface irregularities of the adhesive layer 110 become easier to restore. From this viewpoint, the permanent shear strain of the adhesive layer 110 is preferably 0.07% or less, and more preferably 0.05% or less. The permanent shear strain can be reduced by increasing the crosslinking of the resin contained in the adhesive layer 110. For example, the permanent shear strain can be reduced by increasing the amount of polyfunctional isocyanate used to crosslink the urethane prepolymer.

[0076] In this specification, permanent shear strain is measured in accordance with JIS K6767:1999. More specifically, a sample for measuring permanent shear strain is prepared by laminating adhesive layers 110 to a thickness of 0.8 mm and punching it out into a cylindrical shape with a diameter of 8 mm. A stress of 8000 Pa is then applied to the sample, and after 1800 seconds the applied stress is removed (set to 0 Pa), and this state is maintained for a while. The shear strain is measured 1800 seconds after removal (3600 seconds after the start of application), and this is defined as the permanent shear strain.

[0077] As described above, in one embodiment, the polyfunctional isocyanate has polymerizable double bonds, and the adhesive layer 110 is energy ray reactive. In this case, the gel fraction of the adhesive layer 110 before energy ray irradiation is preferably 80% to 92%, more preferably 85% to 91%, from the viewpoint of increasing object retention. Furthermore, the gel fraction of the adhesive layer 110 after energy ray irradiation is preferably 85% to 95%, more preferably 88% to 93%, from the viewpoint of increasing ease of peeling. Furthermore, the difference in gel fraction of the adhesive layer 110 before and after energy ray irradiation is preferably 0.5% to 10%, more preferably 1% to 5%, from the viewpoint of increasing ease of peeling. In this specification, the gel fraction is measured as shown in the examples.

[0078] Furthermore, the adhesive strength of the adhesive layer 110 before energy ray irradiation is preferably 0.5 N / 25 mm to 10 N / 25 mm, and more preferably 1 N / 25 mm to 5 N / 25 mm, from the viewpoint of increasing the object holding force. Furthermore, the adhesive strength of the adhesive layer 110 after energy ray irradiation is preferably 0.1 N / 25 mm to 1.5 N / 25 mm, and more preferably 0.2 N / 25 mm to 1 N / 25 mm, from the viewpoint of increasing ease of peeling. Furthermore, the difference in adhesive strength of the adhesive layer 110 before and after energy ray irradiation is preferably 0.2 N / 25 mm to 10 N / 25 mm, and more preferably 1 N / 25 mm to 5 N / 25 mm, from the viewpoint of increasing ease of peeling. These adhesive strengths are measured as shown in the examples.

[0079] (Base material) The base material 120 functions as a support for the adhesive layer 110. The base material 120 is located on the side opposite to the side of the adhesive layer 110 that has irregularities.

[0080] In one embodiment, the adhesive sheet 100 is expandable in the planar direction. From this viewpoint, a flexible substrate can be used as the base material 120. Furthermore, by using a flexible substrate as the base material 120, the cushioning when holding an object can be improved, the lamination of adhesive sheets can be facilitated, or the adhesive sheets can be made into a roll form. As the base material 120, for example, a resin film can be used. The resin film is a film in which a resin-based material is used as the main material, and may consist of a resin material or may contain additives in addition to the resin material. The resin film may have laser light transmittance.

[0081] Specific examples of resin films include polyethylene films such as low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, and high-density polyethylene (HDPE) film; polyolefin films such as polypropylene film, polybutene film, polybutadiene film, poly(4-methyl-1-pentene) film, ethylene-norbornene copolymer film, and norbornene resin film; ethylene copolymer films such as ethylene-vinyl acetate copolymer film, ethylene-(meth)acrylic acid copolymer film, and ethylene-(meth)acrylic acid ester copolymer film; polyvinyl chloride films such as polyvinyl chloride film and vinyl chloride copolymer film; polyester films such as polyethylene terephthalate film and polybutylene terephthalate film; polyurethane film; polyimide film; polystyrene film; polycarbonate film; and fluororesin film. In addition, films containing a mixture of two or more materials, crosslinked films in which the resin forming these films is crosslinked, and modified films such as ionomer films may also be used. Furthermore, the base material 120 may be a laminated film in which two or more resin films are laminated.

[0082] From the viewpoint of facilitating the expansion of the adhesive sheet, the base material 120 is preferably a polyolefin film or a vinyl chloride copolymer film. Examples of polyolefin films include polyethylene films, polypropylene films, and copolymers containing unsubstituted olefins such as ethylene or propylene as constituent units, such as ethylene copolymers containing ethylene-methacrylic acid copolymer (EMAA). Examples of vinyl chloride copolymer films include vinyl chloride-vinylidene chloride copolymer films, vinyl chloride-vinyl acetate copolymer films, and vinyl chloride-ethylene copolymer films. The form of such copolymers is not particularly limited and may be block copolymers, random copolymers, alternating copolymers, or graft copolymers. These films may also contain other resin components or additives.

[0083] The thickness of the base material 120 is not particularly limited, but from the viewpoint of achieving both support and roll winding properties, it is preferably 10 μm or more, more preferably 25 μm or more, even more preferably 40 μm or more, on the other hand, it is preferably 500 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, even more preferably 120 μm or less, and particularly preferably 90 μm or less.

[0084] To facilitate the uniform expansion of the adhesive sheet, the tensile modulus of the base material 120 is preferably 50 MPa or more, more preferably 80 MPa or more, even more preferably 120 MPa or more, preferably 2500 MPa or less, more preferably 1000 MPa or less, and even more preferably 500 MPa or less. In this specification, the tensile modulus is measured in accordance with JIS K7161-1:2014.

[0085] Similarly, to facilitate the expansion of the adhesive sheet, the elongation at break of the base material 120 is preferably 110% or more, more preferably 120% or more, even more preferably 130% or more, and particularly preferably 150% or more. In this specification, the elongation at break is measured in accordance with JIS K 7127:1999.

[0086] (Release Sheet) The adhesive sheet 100 according to this embodiment may also have a release sheet 150 in contact with the adhesive layer 110, as shown in Figure 1A. For illustrative purposes, Figure 1A shows the adhesive layer 110 and the release sheet 150 separated. As shown in Figure 1A, the release sheet 150 has an uneven surface that is complementary to the uneven surface of the adhesive layer 110. However, it is not essential that the release sheet 150 has a shape complementary to the uneven surface of the adhesive layer 110. For example, the surface of the release sheet 150 may be flat.

[0087] The release sheet 150 has a release layer 160. The release layer 160 is a layer that is easily peeled off from the adhesive layer 110. The release layer 160 may have an uneven surface that is complementary to the uneven surface of the adhesive layer 110. That is, the release layer 160 has a recess 161, and the recess 161 has a shape that is complementary to the protrusion 111.

[0088] The release sheet 150 may have a base material 170 on the side that does not come into contact with the adhesive layer 110. This base material 170 can be designed in the same way as the base material 120, but it does not need to have the same composition or structure as the base material 120. The release sheet 150 may also have an undercoat layer (not shown) between the release layer 160 and the base material 170.

[0089] (Other layers) The adhesive sheet 100 may have layers other than the base material 120 and the adhesive layer 110. Such additional layers may be provided between these layers or on the outside of these layers. For example, an additional adhesive layer may be provided on the surface of the base material 120 opposite to the adhesive layer 110. The adhesive sheet 100 can be attached to another object via such an adhesive layer. The type of the additional adhesive layer is not particularly limited, and for example, an additional adhesive layer can be formed using a general adhesive.

[0090] (Characteristics of the adhesive sheet) The planar shape of the adhesive sheet 100 is not particularly limited. In the example shown in Figure 2A, the adhesive sheet 100 is circular. However, the adhesive sheet 100 may be a circular shape with a portion missing. For example, the adhesive sheet 100 may have a shape obtained by cutting off each end of a circle with a straight line. The adhesive sheet 100 may have another shape such as an ellipse or a rectangle. The planar shapes of the adhesive layer 110 and the base material 120 may correspond to the planar shape of the adhesive sheet 100.

[0091] In one embodiment, the adhesive sheet 100 is expandable in the planar direction. As will be described later, the adhesive layer 110 shown in Figure 3C deforms as shown in Figure 3D when the adhesive sheet 100 is expanded. When the adhesive sheet 100 is expanded, shear stress acts between the protrusions 111 and the object. Also, when the adhesive sheet 100 is expanded, the pitch P of the protrusions 111 increases, and the number of protrusions 111 that can hold one object decreases. For these reasons, the inventors of the present invention consider that the holding force of the object by the protrusions 111 decreases. In one embodiment, the adhesive sheet 100 is expandable by preferably 5% or more, more preferably 10% or more, even more preferably 25% or more, and particularly preferably 50% or more in the planar direction (for example, one direction or two orthogonal directions) from the viewpoint of sufficiently reducing the holding force of the object.

[0092] (Method for manufacturing adhesive sheet) There are no particular restrictions on the method for manufacturing the adhesive sheet 100. Below, an example of a method for manufacturing the adhesive sheet 100 will be described with reference to Figure 4.

[0093] In S410, an adhesive composition that will be the material for the adhesive layer 110 is prepared. The adhesive composition can be prepared by adding an organic solvent to a raw material composition containing each component of the adhesive layer 110. For example, in one embodiment, a composition containing a urethane prepolymer and a polyfunctional isocyanate is prepared. This composition may contain a solvent. This composition may also contain the catalyst described above for crosslinking the urethane prepolymer with the polyfunctional isocyanate. This composition may also contain the curing retarder described above. The amounts of each component are as described above. For example, the R value in the adhesive composition may be 0.75 or more and 1.7 or less. Examples of solvents include toluene, ethyl acetate, and methyl ethyl ketone.

[0094] In one embodiment, a urethane prepolymer solution composition is used as the material for the raw material composition. The urethane prepolymer solution composition may contain a solvent in addition to the urethane prepolymer. Here, the hydroxyl value of the urethane prepolymer solution composition is preferably 1.0 mg KOH / g or more and 9.5 mg KOH / g or less, more preferably 2.0 mg KOH / g or more and 7.0 mg KOH / g or less, and even more preferably 3.0 mg KOH / g or more and 5.0 mg KOH / g or less. This hydroxyl value represents the mass (mg) of potassium hydroxide (KOH) equivalent to the hydroxyl groups contained in 1 g of the urethane prepolymer solution composition. By increasing the hydroxyl value, the crosslinking density can be improved, making it easier to maintain the uneven shape of the adhesive layer 110. Also, by decreasing the hydroxyl value, it becomes easier to maintain the viscosity of the adhesive layer 110.

[0095] In S420, a layer of the adhesive composition prepared in S410 is formed. For example, a layer of the adhesive composition can be provided on the substrate 120 by forming a coating film by applying the adhesive composition onto the substrate 120 and then drying it. Methods for applying the solution include spin coating, spray coating, bar coating, knife coating, roll coating, roll knife coating, blade coating, die coating, gravure coating, and printing methods (e.g., screen printing and inkjet printing).

[0096] In step S430, the layer of the adhesive composition is cured to have an uneven surface. That is, the urethane prepolymer is crosslinked with a polyfunctional isocyanate. In one embodiment, the layer of the adhesive composition is cured while a mold is in contact with the layer of the adhesive composition. This mold has an uneven surface that is complementary to the unevenness provided on the surface of the adhesive layer 110. Specifically, the layer of the adhesive composition can be pressed with the mold, the layer can be heated and maintained for a predetermined time, and then the mold can be removed. In this way, an adhesive layer 110 having an uneven surface is formed on the substrate 120, and an adhesive sheet 100 is obtained. A specific method for heating the layer of the adhesive composition while pressing with a mold is to vacuum hot laminate the layer of the adhesive composition provided on the substrate 120 and the mold.

[0097] The heating temperature can be selected according to the material of the adhesive layer 110. For example, from the viewpoint of performing a sufficient reaction with low energy, the reaction temperature is preferably 70°C to 120°C, and more preferably 80°C to 110°C. The heating time can also be selected according to the material of the adhesive layer 110. For example, from the viewpoint of performing a sufficient reaction with low energy, the reaction time is preferably 10 seconds to 10 minutes, and more preferably 30 seconds to 5 minutes.

[0098] In one embodiment in which a urethane prepolymer is crosslinked with a polyfunctional isocyanate having polymerizable double bonds, the polymerizable double bonds are not crosslinked in the step of curing the layer of the adhesive composition. For example, by performing heating but not energy ray irradiation, the polymerizable double bonds can be left unreacted.

[0099] Alternatively, a release sheet 150 having an uneven surface may be used as a mold. In this case, in S420, a layer of adhesive composition is formed on the uneven surface of the release sheet 150. Then, in S430, by heating the layer of adhesive composition, an adhesive layer 110 having an uneven surface is formed. In this case, an adhesive sheet 100 can be produced by further attaching a base material 120 to the side of the adhesive layer 110 opposite to the uneven surface.

[0100] (Method of using the adhesive sheet) The adhesive sheet 100 according to one embodiment can be used to handle objects. For example, the adhesive sheet 100 according to one embodiment can be used to temporarily hold an object. For example, the adhesive sheet 100 can be used to receive an object held on another holding substrate, temporarily hold the object, and transfer the object to a desired position on a transfer destination. As a specific example, the adhesive sheet according to one embodiment can be used to transfer a semiconductor chip obtained by dicing to a desired position.

[0101] On the other hand, the adhesive sheet 100 according to one embodiment can protect the back surface of the object to which it is attached. For this reason, the adhesive sheet 100 is suitable for applications that involve processing the object to which it is attached. The method of handling an object using the adhesive sheet according to one embodiment will be described below with reference to the flowchart in Figure 5.

[0102] (S510: Attachment of object) In S510, an object is attached to the adhesive layer 110 of the adhesive sheet 100. The type of object is not particularly limited. The object may be, for example, an element. Examples of elements include semiconductor chips such as LED chips, semiconductor chips with protective films, and semiconductor chips with die attach films (DAF). The element may also be a micro light-emitting diode, a mini light-emitting diode, a power device, a MEMS (Micro Electro Mechanical Systems), or a controller chip, or a component thereof. The element may also be a pieced material such as a wafer, panel, or substrate. The element may have a circuit surface on which an integrated circuit having circuit objects such as transistors, resistors, and capacitors is formed. Furthermore, the element is not necessarily limited to a pieced material, and may be various wafers or various substrates that have not been pieced.

[0103] Furthermore, the size of the object is not particularly limited. The size of the object is, for example, preferably 100 μm. ２ More preferably 10,000 μm ２ More preferably 1,000,000 μm ２ (1 mm) ２ (and above), more preferably 25 mm ２ The above is particularly preferably 50 mm ２ That is all. On the other hand, the size of the object is preferably 5000 mm. ２ More preferably 2000 mm ２ More preferably, 1000 mm ２ More preferably, 500 mm ２ The following is particularly preferred: 200 mm ２The following applies. The thickness of the object is not particularly limited. For example, the thickness of the object is preferably 1 μm or more, more preferably 5 μm or more. On the other hand, the thickness of the object is preferably 1 cm or less, more preferably 1 mm or less, and even more preferably 100 μm or less.

[0104] Examples of wafers include silicon wafers, silicon carbide (SiC) wafers, and compound semiconductor wafers (e.g., gallium phosphide (GaP) wafers, gallium arsenide (GaAs) wafers, indium phosphide (InP) wafers, gallium nitride (GaN) wafers). The size of the wafer is not particularly limited, but is preferably 6 inches (approximately 150 mm in diameter) or larger, and more preferably 12 inches (approximately 300 mm in diameter) or larger. The shape of the wafer is not limited to circular, and may be square or rectangular, for example.

[0105] Examples of panels include fan-out type semiconductor packages (e.g., FOWLP or FOPLP). That is, the workpiece may be a semiconductor package before or after individualization in fan-out type semiconductor package manufacturing technology. The size of the panel is not particularly limited, but may be, for example, a rectangular substrate of about 300 to 700 mm.

[0106] Examples of substrates include glass substrates, sapphire substrates, or compound semiconductor substrates.

[0107] When an object approaches the adhesive layer 110 in order to adhere it to the adhesive layer 110, pressure is generated between the object and the adhesive layer 110. However, because the surface of the adhesive layer 110 has irregularities, the pressure generated between the object and the adhesive layer 110 is relieved, making it easier to capture the object at the desired position on the adhesive sheet. In addition, the irregularities on the surface of the adhesive layer 110 also suppress the formation of air bubbles between the object and the adhesive layer 110. On the other hand, once the object is adhered to the adhesive layer 110, the irregularities on the surface of the adhesive layer 110 are flattened. At this time, the object comes into surface contact with the adhesive layer 110. Therefore, the side of the object facing the adhesive layer 110 (the back side) can be protected by the adhesive layer 110. Furthermore, because the object comes into surface contact with the adhesive layer 110, the holding power of the object by the adhesive layer 110 is improved.

[0108] In one embodiment, an object is transferred from a holding substrate to an adhesive sheet 100, and the adhesive sheet 100 holds the transferred object. For example, a semiconductor wafer can be attached to a wafer substrate, and then the semiconductor wafer can be diced. The element on the wafer substrate obtained by dicing can then be brought into close contact with the adhesive layer 110 of the adhesive sheet 100. Subsequently, the adhesion between the wafer substrate and the element can be reduced by applying an external stimulus such as laser light. In another embodiment, the element attached to the holding substrate may be separated from the holding substrate by an external stimulus. Specifically, the element moves away from the holding substrate relative to the holding substrate. Also, the element moves closer to the adhesive sheet relative to the adhesive sheet. Then, the element is separated from the holding substrate and captured by the adhesive sheet when it comes into contact with the adhesive layer 110 of the adhesive sheet. Through such a process, the element can be transferred from the wafer substrate to the adhesive sheet 100.

[0109] (S520: Processing of the object) In S520, processing is performed on the object attached to the adhesive layer 110 of the adhesive sheet 100. The processing method is not particularly limited. For example, processes such as wiring formation, back metal formation, cleaning, plating, dicing, back grinding, and sealing can be performed. For example, if a semiconductor wafer is attached to the adhesive layer 110 of the adhesive sheet 100, the semiconductor wafer on the adhesive layer 110 can be diced. In this embodiment, since the semiconductor wafer is in surface contact with the adhesive layer 110, the water used during dicing is prevented from reaching the back surface of the semiconductor wafer.

[0110] (S530: Expansion of the adhesive sheet) In S530, the adhesive sheet 100 is expanded in the planar direction. By expanding the adhesive sheet 100 in the planar direction, the spacing between objects attached to the adhesive sheet 100 widens. For example, when a semiconductor wafer is diced in S520, the expansion of the adhesive sheet 100 in the planar direction widens the spacing between elements. This makes it easier to selectively pick up objects in S540.

[0111] In one embodiment, before S530, the irregularities of the adhesive layer 110 to which the object is attached are flattened. Then, in S530, the adhesive sheet 100 is expanded so that the irregularities of the adhesive layer 110 are restored. That is, by expanding the adhesive sheet 100 in the planar direction, shear stress acts between the adhesive layer 110 and the object, resulting in the restoration of the irregularities of the adhesive layer 110. As a result, the holding force of the object by the adhesive layer 110 decreases as described above. Therefore, it becomes easier to peel off the object in S540. Further processing to reduce the adhesive strength of the adhesive layer 110 may be performed in S530. For example, if the adhesive layer 110 contains an energy ray reactive resin, the adhesive layer 110 can be irradiated with energy rays such as ultraviolet light.

[0112] In one embodiment, after expanding the adhesive sheet 100 in the planar direction, the adhesive layer 110 can be irradiated with energy rays before peeling off the object in S540. In this embodiment, the adhesive layer 110 contains an energy ray-reactive resin. For example, the adhesive layer 110 may contain a urethane prepolymer crosslinked with a polyfunctional isocyanate having polymerizable double bonds. By irradiating the adhesive sheet 100 with energy rays after expanding it in the planar direction, the storage modulus of the adhesive layer 110 is improved while the contact area between the adhesive layer 110 and the object is reduced. As a result, the object-holding force of the adhesive layer 110 after the unevenness is restored is further reduced. Note that when irradiating the adhesive sheet 100 with energy rays after expanding it in the planar direction, the contact area between the adhesive layer 110 and the object is reduced, compared to when irradiating the adhesive sheet 100 and the object while they are in surface contact before expanding it in the planar direction, thus further reducing the holding force of the adhesive layer 110.

[0113] The type of energy ray is not particularly limited and examples include ultraviolet light, electron beams, or ionizing radiation. Preferably, the energy ray is ultraviolet light, meaning the adhesive layer 110 is preferably ultraviolet reactive. The amount of energy ray irradiated can be set according to the type of adhesive layer 110 and the desired holding force. For example, when irradiating with ultraviolet light, the amount of ultraviolet light is set to 20 mJ / cm² from the viewpoint of sufficiently reducing the holding force. ２ Preferably, it is 100 mJ / cm² or higher. ２ It is more preferable that the above conditions are met. Furthermore, the amount of ultraviolet light should be 1000 mJ / cm² from the viewpoint of shortening the processing time. ２ Preferably, it is 500 mJ / cm². ２ The following is more preferable:

[0114] The method of expanding the adhesive sheet 100 is not particularly limited. For example, the expansion of the adhesive sheet 100 may be carried out in one direction, two directions, or multiple directions. The expansion rate of the adhesive sheet 100 is also not particularly limited. For example, the expansion rate of the adhesive sheet in one direction is preferably 5% to 300%, more preferably 10% to 200%, even more preferably 20% to 150%, and particularly preferably 50% to 100%. By increasing the expansion rate, the holding force of the object can be sufficiently reduced. By decreasing the expansion rate, the breakage of the adhesive sheet can be suppressed. From a similar viewpoint, the expansion rate of the adhesive sheet in two mutually orthogonal directions is preferably 5% to 300%, more preferably 10% to 200%, even more preferably 20% to 150%, and particularly preferably 50% to 100%.

[0115] (S540: Detachment of object) In S540, the object is detached from the adhesive layer 110 of the adhesive sheet 100. The method of detaching the object is not particularly limited. For example, the method described above can be used to transfer an object attached to the holding substrate to the adhesive sheet 100. As an example, an adsorption member such as a vacuum collet can be used to detach the object from the adhesive layer 110. The adsorbed object can then be moved to a desired position on the transfer destination.

[0116] In one embodiment, by reducing the holding force of the adhesive layer 110 in S530, the object can be peeled off the adhesive layer 110 without applying physical stimulation such as pressing with a pin from the opposite side of the adhesive layer 110. However, the object may be peeled off the adhesive layer 110 while applying physical stimulation from the opposite side of the adhesive layer 110.

[0117] Furthermore, according to the inventors' studies, when attempting to peel an object from the adhesive layer 110, increasing the suction force in accordance with the holding force of the adhesive layer 110 makes the object, such as an element, more susceptible to damage. In particular, when peeling thin objects such as elements, increasing the suction force makes the object even more susceptible to damage. On the other hand, reducing the adhesive force of the adhesive layer 110 reduces the holding force of the object on the adhesive layer 110. As a result, the object may shift position when processing it. However, in this embodiment, the holding force of the object changes by expanding the adhesive sheet 100. Therefore, it is possible to achieve both a high holding force of the adhesive layer 110 when attaching an object to the adhesive sheet 100 and when processing an object on the adhesive sheet 100, and a low holding force of the adhesive layer 110 when peeling an object from the adhesive sheet 100. From this viewpoint, the adhesive sheet of this embodiment is suitable for handling thin objects. For example, the thickness of the object held by the adhesive sheet is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less.

[0118] The method of using the adhesive sheet will be further explained with reference to Figures 3A, 3B, 3C, and 3D. Figure 3A shows the adhesive sheet before an object is attached to it. As shown in Figure 3A, the outer periphery of the adhesive sheet is fixed to the frame 320. For example, the adhesive layer 110 can be attached to the frame 320. The shape of the frame 320 is not particularly limited. For example, the frame 320 may be a circular or rectangular frame-shaped member having an opening. In one embodiment, a circular ring frame is used as the frame. By using a ring frame, the adhesive sheet 100 can be expanded in all directions. On the other hand, instead of a frame, two or more separate fixing members may be used. The adhesive sheet 100 can be expanded by attaching the adhesive layer 110 to each fixing member and pulling the fixing members away from each other.

[0119] Figure 3B shows the adhesive sheet to which object 140 is attached in S310. In Figure 3B, object 140 is a semiconductor wafer.

[0120] Figure 3C shows the adhesive sheet after object 140 has been processed in S320. In the example shown in Figure 3C, object 140 has been separated into individual pieces, objects 140a to 140d.

[0121] Figure 3D shows the adhesive sheet expanded in the planar direction in S330. As shown in Figure 3D, the adhesive sheet can be expanded by bringing the adhesive sheet fixed to the frame 320 into contact with the base 310, and then displacing (pulling down) the frame 320 toward the base 310. The configuration of the base 310 is not particularly limited and may, for example, be cylindrical or rectangular parallelepiped. The base 310 may also be mesh-like or ring-shaped. The speed of displacement of the frame 320 relative to the base 310 is preferably 0.1 mm / sec to 10 mm / sec, and more preferably 0.5 mm / sec to 5 mm / sec. Increased displacement improves productivity. Delayed displacement suppresses damage to the adhesive sheet. The amount of displacement of the frame 320 is preferably 1 mm to 150 mm, and more preferably 10 mm to 100 mm. Increased displacement sufficiently reduces the holding force of the object. Decreased displacement suppresses damage to the adhesive sheet. Subsequently, objects 140a to 140d are peeled off the adhesive sheet using the method described above.

[0122] By following the procedure described above, an object can be transferred to any destination using an adhesive sheet. Another embodiment of the present invention relates to a method for peeling an object from an adhesive sheet that holds the object in an adhesive layer. Such a peeling method may include a step of expanding the adhesive sheet, as in S530, and a step of peeling the object from the adhesive sheet, as in S540. Another embodiment of the present invention relates to a method for manufacturing an article. Such a manufacturing method may include a step of processing an object, as in S520, a step of expanding the adhesive sheet, as in S530, and a step of peeling the object from the adhesive sheet, as in S540. Furthermore, a method for manufacturing an article according to another embodiment of the present invention may include a step of performing post-treatment on the object peeled from the adhesive sheet. The type of post-treatment is not particularly limited. For example, treatments such as wiring formation, back metal formation, cleaning, plating, individualization, thinning, and sealing may be performed.

[0123] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way to the following examples.

[0124] The following compounds were used in the examples and comparative examples.

[0125] <(A) Component: Urethane Prepolymer> In Examples 1 to 8, the urethane prepolymer used was a urethane adhesive main material (manufactured by Sanyo Chemical Industries, Ltd., product name "Polysic UPK-2", weight-average molecular weight 240,000), which is a polyol component. The material used was a urethane prepolymer solution composition, containing 30 parts by mass of urethane prepolymer per 100 parts by mass of the solution composition. The hydroxyl value of the solution composition was 3.2 mgKOH / g, and the hydroxyl value of the urethane prepolymer itself was 11 mgKOH / g.

[0126] In Examples 9 to 17, the urethane prepolymer (A2) used was a polyol component, specifically a urethane adhesive main component (manufactured by artience Co., Ltd., product name "Ciabein SP-205", weight-average molecular weight 110,000). The material used was a urethane prepolymer solution composition, containing 50 parts by mass of urethane prepolymer per 100 parts by mass of the solution composition. The hydroxyl value of the solution composition was 5.0 mgKOH / g, and the hydroxyl value of the urethane prepolymer itself was 10 mgKOH / g.

[0127] <Component (B): Polyfunctional Isocyanate Compound> The following polyfunctional isocyanate compounds were used: (B1) Hexamethylene diisocyanate-based polyisocyanurate type composition (product name "Coronate HX", manufactured by Tosoh Corporation, NCO content 21.1% by mass) (B2) Hexamethylene diisocyanate-based trimethylolpropane adduct composition (product name "Coronate HL", manufactured by Tosoh Corporation, NCO content 12.8% by mass) (B3) Isocyanate group-containing urethane acrylate (manufactured by Daicel Ornex Corporation, product name "EBECRYL4141", number of acrylate groups per molecule: 1, number of isocyanate groups per molecule: 2.0, mass ratio of isocyanate groups in the solid content of the polyfunctional isocyanate compound: 12.8%, average molecular weight: 700, viscosity: 10000 mPa·s / 23℃) (B4) Isocyanate group-containing urethane acrylate (manufactured by Daicel Ornex Corporation, product name "EBECRYL4396", number of acrylate groups per molecule: 1, number of isocyanate groups per molecule: 2.1, mass ratio of isocyanate groups in the solid content of the polyfunctional isocyanate compound: 7.5%, average molecular weight: 1200, viscosity: 16000 mPa·s / 23℃) (B5) Isocyanate group-containing urethane acrylate (manufactured by Daicel Ornex Corporation, product name "EBECRYL4510", number of acrylate groups per molecule: 2, number of isocyanate groups per molecule: 2.0, mass ratio of isocyanate groups in the solid content of the polyfunctional isocyanate compound: 7.8%, average molecular weight: 1200, viscosity: 20000 mPa·s / 23℃, contains 10% butyl acetate)

[0128] (Examples 1-8) A coating solution for adhesive compositions was prepared by dissolving the amounts of urethane prepolymer (A) and polyfunctional isocyanate compound (B1 or B2) shown in Table 1, along with 0.02 parts by mass of tin-based catalyst (dioctyl tin dilaurate) and 0.5 parts by mass of curing retarder (acetylacetone) in toluene. Table 1 shows the parts by mass of solids of each component.

[0129] This adhesive composition coating liquid was applied to the release surface of a release sheet (fine embossed release sheet) with a concave shape, and the resulting coating film was dried at 100°C for 2 minutes to form an adhesive layer with a thickness of 20 μm. The uneven shape of the formed adhesive layer on its surface was a grid-like arrangement of pillars, similar to that shown in Figure 2A. The pitch (P) between pillars in the adhesive sheet was 20 μm. In addition, as shown in Figure 1B, the height (H) of each pillar was 8 μm, the diameter of the tip (T) was 8 μm, and the diameter of the base (W) was 16 μm. The release sheet had a concave shape on its surface that was complementary to this uneven shape.

[0130] An adhesive sheet was prepared by laminating the unembossed surface of a substrate (ethylene methacrylic acid copolymer (EMAA) film, acid content 9% by mass, with a textured surface on one side due to embossing, thickness 80 μm, tensile modulus 160 MPa) onto the adhesive layer thus obtained.

[0131] (Examples 9-17) Adhesive compositions were prepared by dissolving the amounts of urethane prepolymer (A2), polyfunctional isocyanate compound (B3, B4, or B5), and photopolymerization initiator (2,2-dimethoxy-2-phenylacetophenone) shown in Table 2, along with 0.02 parts by mass of tin-based catalyst (dioctyl tin dilaurate) and 0.5 parts by mass of curing retarder (acetylacetone) per 100 parts by mass of urethane prepolymer (A2), in toluene. Adhesive sheets were prepared using this adhesive composition coating solution in the same manner as in Example 1. Table 2 shows the parts by mass of solids of each component.

[0132] (Evaluation of Adhesive Sheets) The adhesive sheets obtained in each embodiment were attached to a ring frame (made of stainless steel, with an inner diameter of 194 mm), and the adhesive sheets were cut to match the outer diameter of the ring frame. Next, a wafer substrate (ground silicon wafer, 8 inches in diameter, 150 μm thick) was fixed to a separately prepared dicing tape. Then, by dicing the wafer substrate into 10 mm x 10 mm squares, multiple elements (silicon chips, with element sizes of 10 mm x 10 mm x 150 μm) were obtained. The obtained multiple elements were attached to the adhesive layer of the adhesive sheet in the central part of the inside of the ring frame, so that the ground surface was attached to the uneven surface of the adhesive layer. The attachment was performed by vacuum lamination under conditions of 40°C and 0.5 MPa. Then, by peeling off the dicing tape, the multiple elements were transferred from the dicing tape to the adhesive sheet. In this way, an adhesive sheet with multiple elements attached and supported by a ring frame was obtained as an evaluation sample. The contact state between the adhesive layer of the thus obtained adhesive sheet and the elements was evaluated. The evaluation results are shown in Tables 1 and 2. In Tables 1 and 2, a "crushing" value of Y indicates that the element and the adhesive layer were in surface contact, meaning that the irregularities of the adhesive layer were crushed and the element adhered not only to the convex parts of the adhesive layer but also to the concave parts.

[0133] Furthermore, the adhesive sheets of the obtained evaluation samples were expanded, and the contact state between the adhesive sheet and the element was observed. The expansion of the adhesive sheet was performed as shown in Figures 3C and 3D. That is, with the element supported by the base 310 through the adhesive sheet, the ring frame, frame 320, was pulled down 60 mm relative to the base 310 to expand the adhesive sheet. The pulling speed was 1 mm / second. After the adhesive sheet was expanded, the contact state between the adhesive layer of the adhesive sheet and the element was evaluated. The evaluation results are shown in Tables 1 and 2. In Tables 1 and 2, "Restored" Y indicates that at least a portion of the surface of each element was separated from the recesses of the adhesive layer, that is, at least a portion of the irregularities of the adhesive layer at the interface between the adhesive layer and the element was restored. Also, "Restored" N indicates that the entire surface of each element was in surface contact with the adhesive layer, that is, the irregularities of the adhesive layer at the interface between the adhesive layer and the element remained flattened.

[0134]

[0135]

[0136] The residual stress ratios shown in Table 2 were evaluated as follows. First, the adhesive composition coating liquid used in each example was applied to the release surface of a smooth release sheet, and the resulting coating film was dried at 100°C for 2 minutes to form an adhesive layer. Multiple adhesive layers thus formed were laminated to a thickness of 0.8 mm. The resulting laminate was punched out into a cylindrical shape with a diameter of 8 mm and a height of 0.8 mm to create a sample for measurement.

[0137] For the above-mentioned measurement samples, the relaxation modulus G(t) (MPa) was measured in accordance with JIS K7244-1:1998 using a viscoelasticity measuring device (Anton Paar, product name "MCR301") at a temperature of 25°C while continuously straining the sample by 5%. The relaxation modulus G after 1000 seconds from the application of stress was measured for the samples corresponding to each example. Ｔ The relaxation modulus G 0.1 seconds after stress is applied. Ｉ The ratio of this to the residual stress ratio (G Ｔ / G Ｉ )

[0138] As shown in Tables 1 and 2, it was confirmed that when an object was attached to the adhesive sheets of Examples 1 to 17, the unevenness was flattened. Therefore, the adhesive sheets of each example can protect the back surface of the object while having advantageous effects such as improved positioning performance of the object due to the uneven surface and prevention of air bubble inclusion.

[0139] Furthermore, as shown in Table 1, it was confirmed that increasing the amount of the polyfunctional isocyanate compound made it easier for the unevenness of the adhesive layer to be restored when the adhesive sheet was expanded. On the other hand, it was confirmed that even when the amount of the polyfunctional isocyanate compound was increased, the unevenness was still flattened when an object was attached to it.

[0140] In Examples 1-4 and 9-17, immediately after expanding the adhesive sheet, some of the irregularities in the adhesive layer at the interface between each element and the adhesive layer were restored. However, after leaving it for a while, all of the irregularities in the adhesive layer at the interface between each element and the adhesive layer were restored. Furthermore, comparing Example 1 and Example 2, Example 2 showed a higher proportion of restored irregularities in the adhesive layer immediately after expanding the adhesive sheet. Furthermore, comparing Example 1 and Example 3, Example 3 showed a higher proportion of restored irregularities in the adhesive layer immediately after expanding the adhesive sheet. Finally, comparing Example 2 and Example 3, the proportion of restored irregularities in the adhesive layer immediately after expanding the adhesive sheet was about the same.

[0141] Furthermore, in Examples 5 to 8, immediately after the adhesive sheet was expanded, all the irregularities of the adhesive layer at the interface between each element and the adhesive layer remained flattened. Even after being left unattended, all the irregularities of the adhesive layer at the interface between each element and the adhesive layer remained flattened.

[0142] Furthermore, as in Examples 9 to 17, the residual stress ratio (G Ｔ / G Ｉ It was confirmed that by setting the ratio to between 56% and 100%, the unevenness of the adhesive layer is restored when the adhesive sheet is expanded.

[0143] Figures 6A, 6B, 6C, 6D, and 6E are photographs showing the contact state between the adhesive layer and each element immediately after the adhesive sheet is expanded, in Examples 1, 2, 5, 6, and 7, respectively. In each figure, the areas where each element is in surface contact with the adhesive layer are shown as dark areas.

[0144] In several examples, the gel fraction and adhesive strength of the adhesive layer were measured before and after energy ray irradiation to confirm that the object's retention ability decreased upon irradiation. The measurement results are shown in Table 2. The methods for measuring the gel fraction and adhesive strength are described below.

[0145] <Gel Fraction Evaluation> The gel fraction of the adhesive layer was evaluated as follows. First, in each example, a heavy release sheet (Lintec Corporation, product name "SP-PET382150") was used instead of a release sheet with a concave shape (fine embossed release sheet), and the adhesive composition of each example was applied to the release surface of the heavy release sheet to form an adhesive layer with a thickness of 25 μm. Next, the release surface of a light release sheet (Lintec Corporation, product name "SP-PET381031") was bonded to the obtained adhesive layer instead of a substrate (ethylene methacrylic acid copolymer (EMAA) film) to create a substrate-less adhesive sheet consisting of a heavy release sheet / adhesive layer / light release sheet. The obtained substrate-less adhesive sheet was cut to a size of 100 mm in length x 100 mm in width. Then, the light release sheet was peeled off from the adhesive sheet, and the adhesive layer was attached to a polyester mesh (mesh size 200) measuring 120 mm in length x 120 mm in width. Subsequently, the release liner was removed, and the adhesive layer was wrapped in a polyester mesh to prepare a test sample. Hereafter, the adhesive layer after the release liner has been removed will be referred to as the "object of measurement."

[0146] The test samples were left to stand for 24 hours in an environment with a temperature of 23°C and a relative humidity of 50%, and then their mass was weighed using a precision balance. The mass of the object to be measured before immersion (M1) was calculated by subtracting the mass of the polyester mesh from the measured mass.

[0147] Next, the test sample was immersed in toluene at room temperature (23°C) for 168 hours. After immersion, the test sample was removed and dried in an oven at 100°C for 2 hours. Furthermore, the test sample was left to stand for 24 hours in an environment of 23°C and 50% relative humidity, and then its mass was weighed using a precision balance. The mass of the object to be measured after immersion and drying (M2) was calculated by subtracting the mass of the polyester mesh from the measured mass.

[0148] The gel fraction was calculated using the following formula based on the mass M1 of the object to be measured before immersion and the mass M2 of the object to be measured after immersion and drying: Gel fraction (mass%) = (M2 / M1) × 100

[0149] Furthermore, before wrapping it in polyester mesh, an ultraviolet irradiation device (Heraeus) was used to achieve an illuminance of 230 mW / cm². ２ , light intensity 190mJ / cm ２ Aside from the irradiation with ultraviolet light, the procedure was the same as described above, and the gel fraction after ultraviolet irradiation was measured.

[0150] (Adhesion Measurement) The adhesive strength of the adhesive layer was measured as follows. An adhesive layer with a thickness of 25 μm was formed on a release sheet using the adhesive composition obtained in each example. The method for forming the adhesive layer, including heating conditions, was the same as in each example, and the same irregularities as in each example were formed on the adhesive layer.

[0151] From the obtained adhesive layer, a sample measuring 25 mm x 200 mm was cut out for adhesion strength measurement. The release sheet was peeled off the adhesive layer, and the surface of the exposed adhesive layer was pressed onto the mirror surface of a mirror silicon wafer using a laminator. After pressing, the sample was left to stand for 1 hour at 23°C and 50% RH (relative humidity) to prepare the adhesion strength measurement sample.

[0152] The adhesive strength of the prepared samples was measured at 23°C and 50% RH (relative humidity) using a tensile testing machine (manufactured by A&D Co., Ltd., product name "Tensilon®") at a tensile speed of 300 mm / min using the 180° peel method based on JIS Z0237:2000. Table 2 shows the measured adhesive strength as adhesive strength (180°).

[0153] Furthermore, after pressing and letting it stand for one hour, an ultraviolet irradiation device (Heraeus) was used to achieve an irradiance of 230 mW / cm². ２ , light intensity 190mJ / cm ２ The procedure was the same as described above, except that the samples were irradiated with ultraviolet light and then left to stand for one hour in an environment of 23°C and 50% RH (relative humidity). The adhesive strength after ultraviolet irradiation was then measured.

[0154] As shown in Table 2, irradiation of an adhesive layer containing a urethane prepolymer crosslinked with a polyfunctional isocyanate increased the gel fraction and decreased the adhesive strength.

[0155] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

[0156] This application claims priority based on Japanese Patent Application No. 2025-053675, No. 2025-053677, No. 2025-053678, and No. 2025-158143, filed on 27 March 2025, and all of the contents of those applications are incorporated herein by reference.

[0157] 100: Adhesive sheet, 110: Adhesive layer, 111: Protrusion, 120: Substrate

Claims

1. An adhesive sheet comprising a base material and an adhesive layer having an uneven surface, wherein the adhesive layer contains a urethane prepolymer crosslinked with a polyfunctional isocyanate.

2. The adhesive sheet according to claim 1, wherein the urethane prepolymer is crosslinked with 1.0 part by mass or more of the polyfunctional isocyanate per 100 parts by mass of the urethane prepolymer.

3. The adhesive sheet according to claim 1, wherein the weight-average molecular weight of the urethane prepolymer is 10,000 or more and 1,000,000 or less.

4. The adhesive sheet according to claim 1, wherein the hydroxyl value of the urethane prepolymer is 3.0 mg KOH / g or more and 15 mg KOH / g or less.

5. The adhesive sheet according to claim 1, wherein the polyfunctional isocyanate is an aliphatic isocyanate.

6. The adhesive sheet according to claim 1, wherein the polyfunctional isocyanate has polymerizable double bonds.

7. The adhesive sheet according to claim 1, wherein the polyfunctional isocyanate has a (meth)acryloyl group.

8. The adhesive sheet according to claim 1, wherein the mass-average molecular weight of the polyfunctional isocyanate is 400 or more and 2000 or less.

9. The adhesive sheet according to claim 1, wherein the surface of the adhesive layer has a plurality of protrusions, and the height of the plurality of protrusions is uniform.

10. The adhesive sheet according to claim 1, wherein the surface of the adhesive layer has a plurality of protrusions, and the height of each of the plurality of protrusions is 1 μm or more.

11. The adhesive sheet according to claim 1, wherein the surface of the adhesive layer has a plurality of protrusions, and the pitch of the plurality of protrusions is 1 μm or more and 100 μm or less.

12. A method for peeling an object attached to an adhesive sheet according to any one of claims 1 to 11, comprising: an expansion step of expanding the adhesive sheet in the planar direction; and a peeling step of peeling the object from the adhesive layer of the adhesive sheet.

13. The peeling method according to claim 12, wherein, prior to the expansion step, the irregularities of the adhesive layer to which the object is attached are flattened, and in the expansion step, the adhesive sheet is expanded so that the irregularities of the adhesive layer are restored.

14. The peeling method according to claim 12, wherein the polyfunctional isocyanate has polymerizable double bonds, and further comprises an irradiation step of irradiating the adhesive layer with energy rays after the expansion step and before the peeling step.

15. A method for manufacturing an adhesive sheet having an adhesive layer, comprising: a forming step of forming a layer of a composition comprising a urethane prepolymer and a polyfunctional isocyanate; and a curing step of curing the layer of the composition so that it has irregularities on its surface.

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