Gradient modulus embossed adhesive and method of making same

Abstract

This application discloses a gradient modulus imprinting adhesive and its preparation method, relating to the field of nanoimprinting materials technology. The gradient modulus imprinting adhesive comprises: a first network structural unit and a second network structural unit; the first network structural unit comprises an acrylate-based UV-curable component and a photoinitiator; the second network structural unit comprises an alkoxysilane-terminated oligomer, a bridging monomer containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst. This application, through the design of the first and second network structures, provides a gradient modulus imprinting adhesive that can solve the problem of existing nanoimprinting adhesives easily cracking and peeling during demolding.

Description

Technical Field

[0001] This application relates to the field of nanoimprint materials technology, and in particular to an imprint adhesive with gradient modulus and its preparation method. Background Technology

[0002] Nanoimprint lithography is one of the key processes for manufacturing high-precision micro and nanostructures. For structures with linewidths in the nanometer to micrometer range, high aspect ratios, or stringent requirements for surface accuracy, the imprinting adhesive must have sufficiently high modulus and hardness after curing to prevent collapse at the top of the microstructure, rounding at the edges, collapse of the sidewalls, or crosstalk between arrays, thereby ensuring pattern fidelity and device performance.

[0003] However, existing nanoimprint adhesives typically rely on increasing the overall modulus to suppress the stretching and springback of microstructures during demolding; but a high overall modulus can lead to overall material embrittlement, making it more prone to fracture, delamination and template damage under complex interfacial stress. Summary of the Invention

[0004] The main objective of this application is to provide a gradient modulus imprinting adhesive and its preparation method, aiming to solve the technical problem that existing nanoimprinting adhesives are prone to cracking and peeling during the demolding process.

[0005] To achieve the above objectives, this application proposes a gradient modulus imprinting adhesive, wherein the gradient modulus imprinting adhesive comprises: a first network structure unit and a second network structure unit; The first network structural unit includes an acrylate UV-curable component and a photoinitiator; The second network structural unit includes an alkoxysilane-terminated oligomer, a bridging monomer containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst.

[0006] In one feasible embodiment, the acrylate-based UV-curable component comprises a polyurethane acrylate oligomer, a multifunctional acrylate monomer, and a rigid difunctional acrylate monomer, and the gradient modulus imprinting adhesive comprises, by weight parts: The polyurethane acrylate oligomer: 25-60 parts; The rigid difunctional acrylate monomer: 10-35 parts; The multifunctional acrylate monomer: 2-15 parts; The alkoxysilane-terminated oligomer / polyether oligomer: 5-30 parts; The bridging monomer containing acrylate reactive groups and silane reactive groups: 0.5 to 10 parts; The photoinitiator: 0.5-5 parts; The catalyst for moisture curing: 0.01~1 part; Flexible diluent: 3 to 15 parts.

[0007] In one feasible embodiment, the polyurethane acrylate oligomer includes at least one of aliphatic polyester-based polyurethane diacrylate oligomer, hexafunctional aliphatic polyurethane acrylate oligomer, aliphatic polyurethane acrylate oligomer, aliphatic polyester-based polyurethane diacrylate oligomer, hydrophobic aliphatic polyurethane acrylate oligomer, and aliphatic polyester / polyether-based polyurethane acrylate oligomer. And / or, the rigid difunctional acrylate monomer includes at least one of ethoxylated bisphenol A diacrylate, tricyclodecanediethanol diacrylate, and 1,6-hexanediol diacrylate; And / or, the multifunctional acrylate monomer includes at least one of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate. And / or, the photoinitiator comprises at least one of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; And / or, the flexible diluent includes at least one of polyethylene glycol diacrylate, tripropylene glycol diacrylate, isoborneol acrylate, and hydroxyethyl acrylate.

[0008] In one feasible embodiment, the alkoxysilane-terminated oligomer includes at least one of trimethoxysilane-terminated polyurethane oligomer, triethoxysilane-terminated polyurethane oligomer, and methyldimethoxysilane-terminated polyurethane oligomer. And / or, the bridging monomer containing acrylate reactive groups and silane reactive groups includes at least one of γ-methacryloyloxypropyltrimethoxysilane, γ-acryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropylmethyldimethoxysilane; And / or, the moisture-curing catalyst includes at least one of dibutyltin dilaurate, stannous octoate, bismuth neodecanoate, bismuth isooctanoate, and tetrabutyl titanate.

[0009] In one feasible embodiment, the gradient modulus imprinting adhesive further comprises, by weight parts: Silane crosslinking accelerator: 0-8 parts; Coupling agent: 0.1~3 parts; Release agent: 0.05~1.5 parts; Leveling agent / defoamer: 0.05~1 part; Dehydrating agent: 0.1~3 parts; Stabilizer: 0.001~0.1 parts.

[0010] In one feasible embodiment, the silane crosslinking accelerator includes at least one of tetraethyl orthosilicate, methyltrimethoxysilane, and propyl orthosilicate; And / or, the coupling agent comprises at least one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane; And / or, the release agent includes at least one of perfluorooctyl acrylate, hexafluoroisopropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, and polyether-modified acrylated silicone. And / or, the leveling agent / defoamer includes at least one of polyester-modified polydimethylsiloxane containing acrylic functional groups, polyether-modified polydimethylsiloxane containing acrylic functional groups, fluorinated acrylate leveling agents, and silicone defoamers. And / or, the dehydrating agent includes at least one of trimethyl orthoformate, triethyl orthoformate, and vinyltrimethoxysilane; And / or, the stabilizer includes at least one of p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, hydroquinone, and phenothiazine.

[0011] In a feasible embodiment, the modulus ratio of the first region to the second region of the gradient modulus imprinting adhesive is 1.2 to 5.0, wherein the first region is a region with a depth of 0 nm to 200 nm from the outer surface of the imprinting adhesive, and the second region is a region with a depth of 5 μm to 10 μm from the outer surface of the imprinting adhesive.

[0012] This application embodiment also provides a method for preparing a gradient modulus imprinting adhesive as described above, the method comprising: The first network structure unit and the second network structure unit are mixed and stirred to obtain the imprinted collagen solution; The impression collagen solution is coated onto the substrate surface, and the impression template is brought into contact with the impression collagen solution and pressure is applied. The imprinted collagen solution is cured by ultraviolet light to form a first network structure; The UV-cured imprint adhesive solution is placed in a humid environment for moisture curing to form a second network structure with gradient modulus, thus obtaining an imprint adhesive with gradient modulus.

[0013] In one feasible embodiment, the water content of the imprinting collagen solution is less than or equal to 500 ppm; And / or, the viscosity of the imprinting collagen solution at 25°C is 50 mPa·s to 3000 mPa·s; And / or, the energy density of the ultraviolet light used for UV curing is 50 mJ / cm².2 ~3000mJ / cm 2 ; And / or, the double bond conversion rate of the first network structural unit is 30%~95%.

[0014] In one feasible embodiment, the temperature of the humid environment is 20°C to 80°C, and the relative humidity is 40% to 95%. And / or, the moisture curing time is 5 min to 48 h.

[0015] The present application proposes one or more technical solutions, which have at least the following technical effects: The gradient modulus imprinting adhesive includes a first network structural unit and a second network structural unit. The first network structural unit includes an acrylate UV-curable component and a photoinitiator. Upon UV irradiation in the presence of the photoinitiator, the first network structural unit rapidly undergoes free radical polymerization to form a rigid, permanent network with high cross-linking density. This first network structure provides immediate anti-collapse capability and dimensional stability for the micro / nano structure during the imprinting process. The second network structural unit includes alkoxysilane-terminated oligomers, bridging monomers containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst. After UV pre-curing, the second network structural unit utilizes the concentration gradient of ambient moisture diffusing from the surface of the imprinting adhesive inwards to induce a hydrolytic condensation reaction of the alkoxysilane groups, with the degree of reaction gradually decreasing from the surface to the interior. This results in the in-situ construction of a second network structure with a cross-linking density decreasing from the surface to the interior within the already formed first network structure, ultimately forming a spatially non-uniform interpenetrating network structure with a high surface modulus and high internal toughness. During the demolding process after the imprinting adhesive has cured, the surface high-modulus structure is subjected to stress first, which improves the surface's resistance to indentation, friction, and localized plastic deformation. Meanwhile, the internal high-toughness structure absorbs energy released from the substrate, reducing the probability of crack initiation and propagation leading to peeling. Therefore, this application embodiment provides a gradient modulus imprinting adhesive that solves the problem of existing nanoimprinting adhesives easily cracking and peeling during demolding by designing a first network structure and a second network structure. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1A flowchart illustrating the preparation method of the gradient modulus imprinting adhesive provided in the embodiments of this application. Figure 1 ; Figure 2 A flowchart illustrating the preparation method of the gradient modulus imprinting adhesive provided in the embodiments of this application. Figure 2 .

[0019] The purpose, features, and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0021] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the gradient modulus imprinting adhesive and its preparation method thereof. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0027] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0028] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the technical solution of this application is further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims made in this application.

[0029] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] To better understand the technical solution of this application, a detailed description will be provided below in conjunction with the accompanying drawings and specific implementation methods.

[0031] During repeated imprinting, demolding, subsequent bonding, and actual service, nanoimprint adhesives are prone to microcracks, edge chipping, whitening, and even localized peeling in areas such as the tips, edges, roots, and substrate interfaces of microstructures due to localized stress concentration. Existing nanoimprint adhesives typically rely on increasing the overall modulus to suppress the stretching and springback of microstructures during demolding; however, a high overall modulus can lead to overall material embrittlement, making it more susceptible to fracture, delamination, and template damage under complex interfacial stresses.

[0032] The gradient modulus imprinting adhesive provided in this application includes: a first network structural unit and a second network structural unit; the first network structural unit includes an acrylate UV-curable component and a photoinitiator; the first network structural unit rapidly undergoes free radical polymerization after UV irradiation in the presence of the photoinitiator, forming a rigid permanent network with high crosslinking density. The first network structure can provide immediate anti-collapse capability and dimensional stability for micro / nano structures during the imprinting process. The second network structural unit includes alkoxysilane-terminated oligomers, bridging monomers containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst. After UV pre-curing, the second network structural unit utilizes the concentration gradient of ambient moisture diffusing from the surface of the imprinting adhesive inward to induce hydrolysis and condensation reactions of alkoxysilane groups, with the degree gradually decreasing from the surface to the interior. This results in the in-situ construction of a second network structure with a crosslinking density decreasing from the surface to the interior within the already formed first network structure, ultimately forming a spatially non-uniform interpenetrating network structure with a high surface modulus and high internal toughness. During the demolding process after the imprinting adhesive has cured, the surface high-modulus structure is subjected to stress first, which improves the surface's resistance to indentation, friction, and localized plastic deformation. Meanwhile, the internal high-toughness structure absorbs energy released from the substrate, reducing the probability of crack initiation and propagation leading to peeling. Therefore, this application embodiment provides a gradient modulus imprinting adhesive that solves the problem of existing nanoimprinting adhesives easily cracking and peeling during demolding by designing a first network structure and a second network structure.

[0033] Based on this, embodiments of this application provide a gradient modulus imprinting adhesive, which includes: a first network structure unit and a second network structure unit; The first network structural unit includes an acrylate UV-curable component and a photoinitiator; In one feasible embodiment, the first network structure is an irreversible network structure that provides instant shaping capability, high energy storage modulus and anti-collapse capability for the micro-nano structure formed by the imprinting adhesive with gradient modulus during the imprinting process, ensuring the height retention rate and dimensional accuracy of the imprinted pattern.

[0034] Acrylic ester UV-curable components are a general term for compounds containing acryloyloxy or methacryloyloxy functional groups. In the presence of a photoinitiator, they can undergo rapid free radical polymerization under UV irradiation, crosslinking from liquid small molecules into a solid three-dimensional network, which is connected by irreversible covalent bonds to form a permanent network or rigid skeleton.

[0035] The role of photoinitiators is to absorb ultraviolet light energy and decompose to generate free radicals. These free radicals then initiate a chain polymerization reaction of carbon-carbon double bonds in acrylate components.

[0036] The second network structural unit includes alkoxysilane-terminated oligomers, bridging monomers containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst.

[0037] In a feasible embodiment, in the second network structural unit, the alkoxysilane-terminated oligomer refers to an oligomer with one or more hydrolyzable alkoxysilane functional groups bonded to the end of its molecular chain. The main chain of the oligomer is a polyurethane segment, a polyether segment, or a polyurethane-polyether copolymer segment. In the presence of a moisture-curing catalyst, the alkoxysilane functional groups undergo a hydrolysis reaction with water molecules in the environment to generate silanol groups. Subsequently, a condensation reaction occurs between the silanol groups to form a siloxane crosslinking network. This siloxane network interpenetrates and nests with the acrylate rigid network formed by the first network structural unit, thereby constituting an interpenetrating polymer network structure.

[0038] Bridged monomers containing acrylate reactive groups and silane reactive groups refer to organosilane compounds that simultaneously contain one or more acrylate groups that can participate in ultraviolet light free radical polymerization and one or more alkoxysilane groups that can participate in moisture condensation polymerization in the same molecular structure. During the ultraviolet light irradiation stage, the bridging monomer undergoes a copolymerization reaction with the acrylate component of the first network structural unit through its acrylate groups, thereby chemically bonding with the first network. In the subsequent moisture curing stage, it undergoes a hydrolysis condensation reaction through its alkoxysilane groups, thereby chemically bonding with the second network. This forms a chemical bridge between the first and second networks, significantly improving the compatibility and interfacial bonding strength of the two networks and preventing microscopic phase separation or relative slippage of the two networks during repeated stress.

[0039] Moisture-curing catalysts refer to organometallic compounds or metal salts that can catalyze the hydrolysis of alkoxysilane groups and the condensation of silanol groups. The addition of moisture-curing catalysts enables the second network structural unit to complete gradient cross-linking from the surface to the interior under normal temperature and humidity conditions, without the need for additional heating or special atmosphere equipment, thereby forming a gradient distribution feature where the cross-linking density gradually decreases and the modulus gradually decreases from the surface of the material to the interior.

[0040] In this embodiment, the first network structural unit undergoes rapid free radical polymerization upon UV irradiation in the presence of a photoinitiator, forming a rigid permanent network with high crosslinking density. This first network structure provides immediate anti-collapse capability and dimensional stability for the micro / nano structure during the imprinting process. The alkoxysilane functional groups in the second network structural unit undergo hydrolysis with water molecules in the environment in the presence of a moisture-curing catalyst to generate silanol groups. Subsequently, condensation reactions occur between these silanol groups, forming a gradient second network structure with gradually decreasing crosslinking density and modulus from the surface to the interior. This gradient second network structure interpenetrates and nests with the first network structure, thus forming an interpenetrating polymer network structure. The high-modulus surface region maintains the shape retention of edges, sidewalls, and tips, and improves abrasion resistance; the lower-modulus interior region absorbs peeling and shear stress, inhibiting crack propagation and interfacial delamination, thereby significantly reducing the demolding damage rate and delamination risk of the imprinting adhesive.

[0041] In one feasible embodiment, the acrylate-based UV-curable component includes polyurethane acrylate oligomers, multifunctional acrylate monomers, and rigid difunctional acrylate monomers, and the gradient modulus imprinting adhesive comprises, by weight fraction: Acrylic ester prepolymer: 25-60 parts; Rigid difunctional acrylate monomer: 10-35 parts; Multifunctional acrylate monomers: 2-15 parts; Alkoxysilane-terminated oligomers: 5–30 parts; Bridged monomers containing acrylate reactive groups and silane reactive groups: 0.5–10 parts; Photoinitiator: 0.5–5 parts; Moisture-curing catalyst: 0.01~1 part; Flexible diluent: 3 to 15 parts.

[0042] In one feasible embodiment, a polyurethane acrylate oligomer serves as the host resin, providing the main mechanical properties and the framework for UV curing of the imprinting adhesive.

[0043] Optionally, the weight parts of the polyurethane acrylate oligomer can be 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, etc.

[0044] Optionally, the polyurethane acrylate oligomer includes at least one of aliphatic polyester-based polyurethane diacrylate oligomer, hexafunctional aliphatic polyurethane acrylate oligomer, aliphatic polyurethane acrylate oligomer, aliphatic polyester-based polyurethane diacrylate oligomer, hydrophobic aliphatic polyurethane acrylate oligomer, and aliphatic polyester / polyether-based polyurethane acrylate oligomer. In one feasible embodiment, the rigid difunctional acrylate monomer contains a rigid molecular backbone and two acrylate double bonds that can participate in free radical polymerization. Its difunctional characteristics enable it to act as a crosslinking point to connect two polymer chains, significantly shortening the chain segment length between crosslinking points, thereby increasing the crosslinking density and glass transition temperature of the network, so that the cured imprinting adhesive has a high storage modulus and resistance to imprinting collapse.

[0045] Optionally, the weight parts of the rigid difunctional acrylate monomer can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, etc.

[0046] Optionally, the rigid difunctional acrylate monomer includes at least one of ethoxylated bisphenol A diacrylate, tricyclodecanediethanol diacrylate, and 1,6-hexanediol diacrylate.

[0047] In one feasible implementation, the flexible diluent is typically a low-viscosity monofunctional or difunctional acrylate containing flexible segments or having a low glass transition temperature. This reduces the overall viscosity of the system, improving its filling performance for the template's micro / nanostructures. Furthermore, introducing flexible segments into the high-rigidity network prevents the imprinting adhesive from becoming too brittle due to excessive cross-linking, thus providing toughening and reducing internal stress.

[0048] Optionally, the weight parts of the flexible diluent can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, etc.

[0049] Optionally, the flexible diluent includes at least one of polyethylene glycol diacrylate, tripropylene glycol diacrylate, isoborneol acrylate, and hydroxyethyl acrylate.

[0050] In one feasible embodiment, the multifunctional acrylate monomer contains three or more acrylate double bonds, and each molecule can participate in multiple crosslinking sites. Adding small amounts can significantly improve the curing rate and network density, enhance the microstructure's resistance to collapse and solvent resistance, and the decision to add and the amount should be made based on specific modulus requirements.

[0051] Optionally, the weight composition of the multifunctional acrylate monomer can be 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, etc.

[0052] Optionally, the multifunctional acrylate monomer includes at least one of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

[0053] Optionally, the photoinitiator can be 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, etc.

[0054] Optionally, the photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0055] Optionally, the weight parts of the alkoxysilane-terminated oligomer can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30 parts, etc.

[0056] Optionally, the alkoxysilane-terminated oligomers include at least one of trimethoxysilane-terminated polyurethane oligomers, triethoxysilane-terminated polyurethane oligomers, and methyldimethoxysilane-terminated polyurethane oligomers.

[0057] Optionally, the weight parts of the bridging monomer containing acrylate reactive groups and silane reactive groups can be 0.5 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.

[0058] Optionally, the bridging monomer containing acrylate reactive groups and silane reactive groups includes at least one of γ-methacryloyloxypropyltrimethoxysilane, γ-acryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropylmethyldimethoxysilane.

[0059] Optionally, the weight parts of the moisture-curing catalyst can be 0.01 parts, 0.02 parts, 0.04 parts, 0.06 parts, 0.08 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, etc.

[0060] Optionally, the catalyst for moisture curing includes at least one of dibutyltin dilaurate, stannous octoate, bismuth neodecanoate, bismuth isooctanoate, and tetrabutyl titanate.

[0061] In one feasible embodiment, the gradient modulus imprinting adhesive further includes, by weight parts: Silane crosslinking accelerator: 0-8 parts; Coupling agent: 0.1~3 parts; Release agent: 0.05~1.5 parts; Leveling agent / defoamer: 0.05~1 part; Dehydrating agent: 0.1~3 parts; Stabilizer: 0.001~0.1 parts.

[0062] Silane crosslinking accelerators are used to adjust the crosslinking density and curing speed of the second network. Adding an appropriate amount can enhance the modulus of the surface hard shell, while adding too much will cause the imprinting adhesive to become brittle and the gradient to weaken.

[0063] Optionally, the silane crosslinking promoter includes at least one of tetraethyl orthosilicate, methyltrimethoxysilane, and propyl orthosilicate.

[0064] Coupling agents significantly improve adhesion by forming chemical bonds between the printing adhesive and the substrate interface, preventing substrate delamination during demolding, while having no negative impact on the integrity of the gradient structure itself.

[0065] Optionally, the coupling agent includes at least one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0066] Release agents utilize their low surface energy properties to migrate to the material surface during the curing process, effectively reducing the adhesion and friction coefficient between the template and the printing adhesive, improving release smoothness and reducing microstructural damage.

[0067] Optionally, the release agent includes at least one of perfluorooctyl acrylate, hexafluoroisopropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, and polyether-modified acrylated silicone. Leveling agents and defoamers are used to reduce the surface tension of the composition, improve the uniformity of filling the microcavities of the template during coating, and suppress the generation of bubbles during mixing and coating, ensuring that the embossed pattern is complete and defect-free.

[0068] Optionally, the leveling agent / defoamer includes at least one of the following: polyester-modified polydimethylsiloxane containing acrylic functional groups, polyether-modified polydimethylsiloxane containing acrylic functional groups, fluorinated acrylate leveling agents, and silicone defoamers.

[0069] The dehydrating agent consumes trace amounts of moisture in the system through chemical means, inhibiting the premature hydrolysis of alkoxysilane groups during storage, thereby extending the shelf life of the printing adhesive and ensuring batch-to-batch process stability.

[0070] Optionally, the dehydrating agent includes at least one of trimethyl orthoformate, triethyl orthoformate, and vinyltrimethoxysilane.

[0071] Stabilizers prevent acrylate components from undergoing thermal or photopolymerization during storage by capturing free radicals or inhibiting self-polymerization reactions, while not affecting the normal crosslinking reaction during the moisture curing stage, thus ensuring the long-term stability and usability of the imprinting adhesive.

[0072] Optionally, the stabilizer includes at least one of p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, hydroquinone, and phenothiazine.

[0073] In one feasible embodiment, the modulus ratio of the first region to the second region of the gradient modulus imprinting adhesive is 1.2 to 5.0, wherein the first region is a region with a depth of 0 nm to 200 nm from the outer surface of the imprinting adhesive, and the second region is a region with a depth of 5 μm to 10 μm from the outer surface of the imprinting adhesive.

[0074] The first region refers to the thin surface layer on the outer surface of the printing adhesive. During the moisture curing stage, the first region is directly exposed to the ambient moisture and has the highest moisture concentration. This allows the hydrolysis and condensation reaction of the alkoxysilane-terminated oligomers to be most complete and efficient under the action of the catalyst. At the same time, the bridging monomers also form high-density chemical bridges in the first region, thereby obtaining a crosslinking density and storage modulus that are much higher than those in the interior. This results in a hard outer shell layer. The high-modulus surface layer can effectively resist the normal peel stress, tangential friction force, and transient concentrated stress generated at the interface between the template and the resin during the demolding process, maintaining the angular accuracy, sidewall perpendicularity, and overall shape retention of the microstructure.

[0075] The second region refers to the internal region from the outer surface of the imprinting adhesive. As the moisture diffuses from the surface inward, the concentration in the second region gradually decreases, the degree of moisture cross-linking reaction is significantly weakened, and the second network becomes sparse. The material modulus mainly comes from the first network structure formed by UV curing, so the modulus is relatively low but the toughness is better, forming a soft and tough core. During the demolding process, it acts as a mechanical buffer layer to absorb and dissipate the peeling energy, shear energy and impact energy from the interface and the root of the structure, inhibiting the initiation and propagation of cracks.

[0076] The modulus ratio between the first region and the second region can be 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, etc.

[0077] When the ratio is too low, the difference in modulus between the surface and the interior is too small, resulting in insufficient buffering and a high risk of fracture and delamination. When the ratio is too high, the excessively high surface modulus leads to increased brittleness and makes the stress concentration points at the interface prone to cracking. At the same time, an excessively soft interior layer may cause overall deformation of the microstructure. The above-mentioned ratio range ensures an optimal match between the high-modulus hard shell on the surface and the high-toughness core inside, thereby achieving both high shape retention and low demolding damage.

[0078] Optionally, the modulus ratio of the first region to the second region can be 1.5 to 3.0.

[0079] In one feasible embodiment, the modulus of the first region is higher than that of the second region.

[0080] In one feasible embodiment, the thickness of the identifiable high-modulus region of the cured imprinting adhesive is 50 nm to 10 μm.

[0081] Optionally, in a feasible embodiment, the thickness of the identifiable high-modulus region of the cured imprinting adhesive is 0.2–3 μm.

[0082] The second aspect of this application provides a method for preparing an imprinting adhesive with a gradient modulus as described above, referring to... Figure 1 and Figure 2 The methods include: Step S10: Mix and stir the first network structure unit and the second network structure unit to obtain the imprinted collagen solution; In one feasible embodiment, the first network structure unit, the second network structure unit, and other additives are mixed; if necessary, the moisture-sensitive component is premixed with the dehydrating agent, and the operation is carried out under nitrogen protection.

[0083] In one feasible embodiment, the relative humidity of the environment is ≤30% during the mixing process.

[0084] Step S20: Apply the impression collagen solution to the substrate surface, so that the impression template comes into contact with the impression collagen solution and pressure is applied; In one feasible embodiment, a uniform transparent or semi-transparent imprinting collagen solution is obtained by means of mechanical stirring, planetary stirring, vacuum degassing, etc.

[0085] In one feasible embodiment, the water content of the imprinting collagen solution is less than or equal to 500 ppm.

[0086] Imprinting adhesive contains moisture-sensitive components such as alkoxysilane-terminated oligomers. If the initial water content in the original solution is too high, the alkoxysilane groups will undergo premature hydrolysis and condensation reactions during storage, resulting in increased viscosity, gelation, or even complete failure of the adhesive. It will also disrupt the gradient formation mechanism from the surface to the interior during the subsequent moisture curing stage. Therefore, by adding a dehydrating agent or preparing the solution under dry conditions to control the water content to within 500 ppm, the pre-crosslinking reaction during storage can be effectively suppressed.

[0087] Alternatively, the embossing collagen solution can be sealed and stored by being placed in moisture-proof packaging (such as aluminum-plastic composite tubes, aluminum foil bags, or dry nitrogen filling containers).

[0088] In one feasible embodiment, the viscosity of the imprinting collagen solution at 25°C is 50 mPa·s to 3000 mPa·s.

[0089] When the viscosity is too low, the adhesive is too fluid and easily overflows from the template microcavities during the imprinting process, resulting in incomplete filling or uneven film thickness. It is also difficult to control the consistency of film thickness during coating. When the viscosity is too high, the adhesive cannot fully fill the submicron or even nanoscale template microstructures by capillary action, which can easily lead to air bubble residue or filling defects. At the same time, excessively high viscosity will increase the adhesion resistance between the template and the imprinting adhesive during demolding, thereby increasing the risk of demolding damage.

[0090] Step S30: The imprinted collagen solution is cured by ultraviolet light to form a first network structure.

[0091] In one feasible embodiment, a uniform thickness adhesive film is formed on the substrate by spin coating, scraping, or other methods. Then, a template with a micro-nano structure pattern is pressed into the adhesive layer and appropriate pressure is applied to completely fill the micro-cavity structure of the template with adhesive, eliminating air bubbles and excess adhesive.

[0092] Under ultraviolet light irradiation, the photoinitiator decomposes to generate free radicals, which initiate a chain polymerization reaction of the carbon-carbon double bonds in the acrylate components. This process typically takes from a few seconds to tens of seconds, rapidly transforming the material from a liquid to a solid state while precisely replicating the micro-nano structure on the template onto the cured adhesive layer. The resulting primary network structure, primarily composed of acrylate, is responsible for fixing the shape of the microstructure and providing initial modulus and resistance to collapse.

[0093] In one feasible embodiment, the energy density of the ultraviolet radiation used for ultraviolet curing is 50 mJ / cm². 2 ~3000mJ / cm 2 .

[0094] When the energy density is too low, the free radical initiation efficiency is insufficient, and the first network structural unit cannot form a sufficient crosslinking density, resulting in low strength of the imprinted adhesive during demolding, easy microstructure collapse or high loss. When the energy density is too high, the first network will be over-crosslinked and the double bond conversion rate will be close to complete, making the polymer network too rigid and losing sufficient molecular mobility. At the same time, over-crosslinking will hinder the diffusion channels of subsequent environmental moisture into the material interior and inhibit the formation of the second network structural unit from the surface to the inside, thus failing to obtain the expected gradient distribution structure of high surface modulus and high internal toughness.

[0095] In one feasible embodiment, the double bond conversion rate of the first network structural unit is 30% to 95%.

[0096] When the double bond conversion rate is too low, the first network structure has not yet formed an effective mechanical skeleton. The imprinting adhesive lacks sufficient shape retention during demolding, and the microstructure is prone to permanent deformation or springback, resulting in a decrease in replication accuracy. When the double bond conversion rate is too high, the first network is over-cured, and the polymer network becomes dense and rigid. This not only increases the overall brittleness of the material and makes it prone to breakage during demolding, but also severely restricts the diffusion and penetration rate of water molecules. This prevents the second network structural units from forming an effective crosslinking density gradient inside the material, ultimately resulting in an insignificant difference in modulus between the surface hard shell and the internal tough core, and a loss of stress buffering function.

[0097] In one feasible embodiment, the thickness of the imprinted collagen solution with gradient modulus coated on the substrate surface is 0.1 μm to 200 μm.

[0098] Optionally, the thickness of the imprinted collagen solution with gradient modulus coated on the substrate surface is 0.2 μm to 50 μm.

[0099] In one feasible embodiment, the pressure applied after the imprinting template comes into contact with the imprinting collagen liquid of gradient modulus is 0.01MPa to 2.0MPa, and is maintained for 1s to 300s.

[0100] In one feasible embodiment, the wavelength of the ultraviolet light used in ultraviolet curing is 250 nm to 450 nm.

[0101] Step S40: Place the UV-cured imprinting adhesive stock solution in a humid environment for moisture curing to form a second network structure with gradient modulus, thereby obtaining an imprinting adhesive with gradient modulus.

[0102] In one feasible embodiment, water molecules in a humid environment first contact the surface area of ​​the imprinting adhesive. Under the promotion of a moisture-curing catalyst, the alkoxysilane-terminated oligomers and alkoxysilane groups in the bridging monomers undergo hydrolysis to generate silanol groups. Subsequently, silanol groups undergo condensation polymerization to form a siloxane crosslinking network. Since water molecules diffuse gradually from the material surface inwards, the water concentration exhibits a gradient distribution from high to low during diffusion. Therefore, the surface area experiences the most complete hydrolysis and condensation polymerization reaction, resulting in the highest crosslinking density of the second network. In contrast, the internal area experiences a gradual decrease in the number of water molecules reaching the surface, leading to a slower crosslinking reaction. The density gradually decreases, eventually forming a spatially non-uniform distribution of the second network crosslinking density that gradually decreases from the surface to the interior. This gradient distribution of crosslinking density interpenetrates and nests with the existing UV-curable network of the first network structural unit, thereby constructing a gradient modulus structure with high surface modulus and low internal modulus within a single material. The high-modulus surface region endows the imprinting adhesive with excellent anti-friction, anti-scratch, and shape retention capabilities, while the low-modulus, high-toughness internal region acts as a stress buffer layer to effectively absorb peel stress and impact energy during the demolding process, inhibiting crack initiation and propagation, and achieving a synergistic unity of high shape retention and low demolding damage.

[0103] In one feasible embodiment, the temperature of the humid environment is 20°C to 80°C, and the relative humidity is 40% to 95%.

[0104] Optionally, the temperature of the humid environment can be 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, etc.

[0105] Optionally, the relative humidity of the humid environment can be 40%, 45%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.

[0106] In one feasible embodiment, the moisture curing time is 5 min to 48 h.

[0107] In one feasible embodiment, the cured gradient modulus imprinting adhesive can be kept at 40°C to 80°C for 10 min to 120 min for post-treatment of the imprinting adhesive, which can stabilize the internal stress of the imprinting adhesive and improve batch consistency.

[0108] This embodiment first forms a first network framework through UV curing, and then induces a second network gradient crosslinking from the surface to the interior through moisture induction. This achieves a gradient modulus structure in the imprinting adhesive that is strong on the outside and tough on the inside, effectively solving the problem that existing homogeneous imprinting adhesives cannot simultaneously achieve high shape retention and low demolding damage. The UV pre-curing is controlled at a moderate conversion rate to reserve channels for subsequent moisture diffusion. Moisture curing utilizes the natural moisture concentration gradient to drive a decrease in crosslinking density, requiring no additional heating or special equipment. It perfectly adapts to the process window of existing production lines, while significantly reducing template wear, extending template life, and improving batch production stability and overall yield.

[0109] To enable those skilled in the art to clearly understand the details and operations of the above embodiments of this application, and to demonstrate the significant improvement in the performance of the method for preparing gradient modulus imprinting adhesive in the embodiments of this application, the above technical solutions are illustrated below through multiple embodiments and comparative examples.

[0110] The composition of the imprinting adhesive in the examples is shown in Table 1.

[0111] Table 1. Imprinting adhesive components of the examples (parts by weight)

[0112] The components of Comparative Examples 1 to 3 are the same as those of Example 1.

[0113] The preparation methods of the imprinting adhesives in the examples and comparative examples include the following steps: In a dry environment with relative humidity ≤20%, the substances of the first network structure unit are mixed first, and then the substances of the second network structure unit are added. After stirring evenly, functional additives such as coupling agent, release agent, leveling agent, dehydrating agent and polymerization inhibitor are added.

[0114] Degas under vacuum or planetary degassing conditions for 10–30 min to obtain a uniformly imprinted collagen solution.

[0115] The printing adhesive is coated onto the substrate surface and bonded to the template, with the pressure controlled between 0.05 and 0.30 MPa.

[0116] UV curing is performed to bring the imprinting adhesive to a demoldable or near-demoldable state. For flexible, breathable templates, controlled moisture can be introduced while the template is in place to pre-form a shell on the surface before demolding. For rigid templates, demolding can be performed after UV curing, followed by secondary moisture curing in a constant temperature and humidity chamber. Moisture curing under constant temperature and humidity conditions allows the second network to gradually form from the surface inwards, thereby obtaining an imprinting adhesive with a gradient modulus structure.

[0117] The preparation conditions for the examples and comparative examples are different, as shown in Table 2: Table 2 Preparation conditions of the examples and comparative examples

[0118] The performance tests of the imprinting adhesives in the examples and comparative examples are as follows, and the performance test results are shown in Table 3: 1. Modulus test: The storage modulus or equivalent modulus of the first and second regions of the imprinted adhesive sample at 25°C, as well as the thickness of the high modulus region, are tested using DMA or nanoindentation method.

[0119] 2. Nanoimprint conformance test: A standard grid template with a depth of 300 nm, a linewidth of 500 nm, and a period of 1000 nm was used for imprinting. The ratio of the structure height H1 to the template height H0 after curing was measured by AFM or SEM, and the height retention rate was calculated, where the height retention rate = H1 / H0 × 100%.

[0120] 3. Demolding force test: Using a standard wire grid template of the same size and material (depth 300 nm, line width 500 nm, period 1000 nm), after the imprinting adhesive has cured, the same model of demolding equipment is used to vertically peel the template from the imprinting adhesive interface at a constant rate. The peak peeling force during the demolding process is recorded in real time by a tension sensor, and the average value of three parallel tests is taken as the final demolding force (unit: N).

[0121] Table 3 Performance results of the imprinting adhesives in the examples and comparative examples

[0122] According to the performance test results in Table 3, Comparative Example 1, which is a UV-curing-only solution, shows that the imprinting adhesive does not have a significant difference in modulus between the surface and interior in the thickness direction, belonging to a homogeneous high-modulus network structure. Although its height retention rate reaches 94.3%, indicating a certain shape retention capability, the lack of a modulus gradient distribution from the surface to the interior means that the interfacial peeling stress cannot be effectively dissipated and buffered within the material during demolding. This easily leads to stress concentration at the root or edge of the microstructure, resulting in fracture, chipping, and substrate delamination. Comparative Example 2, which is a moisture-curing-only solution, lacks a UV pre-curing and rapid shaping step, resulting in severely insufficient early structural support and a height retention rate of only 82.5%. The replication accuracy of micro-nano structures cannot be guaranteed, and structural collapse and dimensional shrinkage are prone to occur during demolding because the material has not yet formed sufficient mechanical strength. Comparative Example 3 is an excessive UV pre-curing scheme. The excessive cross-linking of the first network structure hinders the diffusion of moisture and the formation of the gradient of the second network structure. The imprinting adhesive is generally brittle and the gradient is not obvious, which increases the demolding force and the risk of structural damage. In contrast, the imprinting adhesives with gradient modulus in Examples 1 to 3 form a tough skeleton through UV pre-curing and then undergo moisture-induced gradient cross-linking from the surface to the inside to form a significant "hard on the outside and tough on the inside" gradient modulus structure, which can effectively avoid cracking and peeling during the demolding process of the imprinting adhesive.

Claims

1. A gradient modulus imprintable glue, characterized in that, The gradient modulus imprinting adhesive includes: a first network structure unit and a second network structure unit; The first network structural unit includes an acrylate UV-curable component and a photoinitiator; The second network structural unit includes an alkoxysilane-terminated oligomer, a bridging monomer containing acrylate reactive groups and silane reactive groups, and a moisture-curing catalyst.

2. The embossed stamping adhesive of claim 1 wherein, The acrylate-based UV-curable component includes polyurethane acrylate oligomers, multifunctional acrylate monomers, and rigid difunctional acrylate monomers. By weight, the gradient modulus imprinting adhesive comprises: The polyurethane acrylate oligomer: 25-60 parts; The rigid difunctional acrylate monomer: 10-35 parts; The multifunctional acrylate monomer: 2-15 parts; The alkoxysilane-terminated oligomer: 5-30 parts; The bridging monomer containing acrylate reactive groups and silane reactive groups: 0.5 to 10 parts; The photoinitiator: 0.5-5 parts; The catalyst for moisture curing: 0.01~1 part; Flexible diluent: 3 to 15 parts.

3. The embossed stamping adhesive of claim 2 wherein, The polyurethane acrylate oligomers include at least one of the following: aliphatic polyester-based polyurethane diacrylate oligomers, hexafunctional aliphatic polyurethane acrylate oligomers, aliphatic polyurethane acrylate oligomers, aliphatic polyester-based polyurethane diacrylate oligomers, hydrophobic aliphatic polyurethane acrylate oligomers, and aliphatic polyester / polyether-based polyurethane acrylate oligomers. And / or, the rigid difunctional acrylate monomer includes at least one of ethoxylated bisphenol A diacrylate, tricyclodecanediethanol diacrylate, and 1,6-hexanediol diacrylate; And / or, the multifunctional acrylate monomer includes at least one of trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate. And / or, the photoinitiator comprises at least one of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; And / or, the flexible diluent includes at least one of polyethylene glycol diacrylate, tripropylene glycol diacrylate, isoborneol acrylate, and hydroxyethyl acrylate.

4. The embossed stamping adhesive of claim 2 wherein, The alkoxysilane-terminated oligomers include at least one of trimethoxysilane-terminated polyurethane oligomers, triethoxysilane-terminated polyurethane oligomers, and methyldimethoxysilane-terminated polyurethane oligomers. And / or, the bridging monomer containing acrylate reactive groups and silane reactive groups includes at least one of γ-methacryloyloxypropyltrimethoxysilane, γ-acryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropylmethyldimethoxysilane; And / or, the moisture-curing catalyst includes at least one of dibutyltin dilaurate, stannous octoate, bismuth neodecanoate, bismuth isooctanoate, and tetrabutyl titanate.

5. The embossed stamping adhesive of claim 2 wherein, By weight, the gradient modulus imprinting adhesive further includes: Silane crosslinking accelerator: 0-8 parts; Coupling agent: 0.1~3 parts; Release agent: 0.05~1.5 parts; Leveling agent / defoamer: 0.05~1 part; Dehydrating agent: 0.1~3 parts; Stabilizer: 0.001~0.1 parts.

6. The embossed stamping adhesive of claim 5 wherein, The silane crosslinking accelerator includes at least one of tetraethyl orthosilicate, methyltrimethoxysilane, and propyl orthosilicate. And / or, the coupling agent comprises at least one of γ-glycidoxypropyltrimethoxysilane and γ-aminopropyltriethoxysilane; And / or, the release agent includes at least one of perfluorooctyl acrylate, hexafluoroisopropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, and polyether-modified acrylated silicone. And / or, the leveling agent / defoamer includes at least one of polyester-modified polydimethylsiloxane containing acrylic functional groups, polyether-modified polydimethylsiloxane containing acrylic functional groups, fluorinated acrylate leveling agents, and silicone defoamers. And / or, the dehydrating agent includes at least one of trimethyl orthoformate, triethyl orthoformate, and vinyltrimethoxysilane; And / or, the stabilizer includes at least one of p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, hydroquinone, and phenothiazine.

7. The embossed stamping adhesive of claim 1 wherein, The modulus ratio of the first region to the second region of the gradient modulus imprinting adhesive is 1.2 to 5.0, wherein the first region is a region with a depth of 0 nm to 200 nm from the outer surface of the imprinting adhesive, and the second region is a region with a depth of 5 μm to 10 μm from the outer surface of the imprinting adhesive.

8. A method of preparing a gradient modulus embossing adhesive according to any one of claims 1 to 7, characterized in that, The method includes: The first network structure unit and the second network structure unit are mixed and stirred to obtain the imprinted collagen solution; The impression collagen solution is coated onto the substrate surface, and the impression template is brought into contact with the impression collagen solution and pressure is applied. The imprinted collagen solution is cured by ultraviolet light to form a first network structure; The UV-cured imprint adhesive solution is placed in a humid environment for moisture curing to form a second network structure with gradient modulus, thus obtaining an imprint adhesive with gradient modulus.

9. The method for preparing gradient modulus embossing adhesive as described in claim 8, characterized in that, The water content of the imprinting collagen solution is less than or equal to 500 ppm; And / or, the viscosity of the imprinting collagen solution at 25°C is 50 mPa·s to 3000 mPa·s; and / or the energy density of the ultraviolet light for the ultraviolet light curing is 50 mJ / cm 2 3000 mJ / cm 2 ; And / or, the double bond conversion rate of the first network structural unit is 30%~95%.

10. The method for preparing gradient modulus imprinting adhesive as described in claim 8, characterized in that, The temperature of the humid environment is 20℃~80℃, and the relative humidity is 40%~95%. And / or, the moisture curing time is 5 min to 48 h.

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