Tunable composite PSA / structural adhesive bonding via patterned surface-initiated curing

Abstract

The invention provides articles, these articles comprise successively: first adherend, first primer layer, adhesive layer and second adherend, wherein this adhesive layer comprises pressure-sensitive adhesive zone and structural adhesive zone.Usually, this first primer layer covers the first part adjacent to the structural adhesive zone of this first adherend, and does not cover the second part adjacent to the pressure-sensitive adhesive zone of this first adherend.The method for preparing this type of articles is provided, these methods comprise that curing initiation primer is applied to the first part of this first adherend to form the first primer layer, keep the second part of this first adherend simultaneously without this first primer layer, then curable adhesive film is applied on this first primer layer, make the part of this curable adhesive film solidify to form the structural adhesive zone, and other parts remain as uncured pressure-sensitive adhesive zone.

Description

Technical Field

[0001] The present disclosure relates to the bonding of adherends to adhesive layers having both pressure sensitive adhesive regions and structural adhesive regions and methods of making such bonds using patterned application of a cure initiating primer. Background Art

[0002] Applicants have previously studied the curing of adhesive films to form structural adhesive bonds, as disclosed in the following references: WO 2019 / 157262 "Film-Initiated Cure of Structural Adhesive Film", WO 2019 / 157264 "Primer-Initiated Cure of Structural Adhesive Film", WO 2019 / 157265 "Primer-Initiated Cure of Structural Adhesive Film" and WO 2019 / 164678 "Core-Sheath Filaments and Methods of Printing an Adhesive", the disclosures of which are incorporated herein by reference. (Docket Nos. 81407US002, 78901US002, 81371US002 and 82231US002).

[0003] The following references may be relevant to the general technical field of the present disclosure: US 2005 / 0214497, JPS6026079, CA 1,301,616, DE 10259457, EP 0140006, EP 0232936, EP 0889105, EP 1800865, GB 1,448,257, JP 09 / 111193, US 2004 / 0228998, US 2005 / 0230960, US 2008 / 0242764, US 2010 / 0061823, US 2010 / 0255239, US 2013 / 0052460, US 2016 / 0289513, US 3,625,875, US 3,639,500, US 3,994,764, US 3,996,308, US 4,170,612, US 4,316,000, US 4,373,077, US 4,452,955, US 4,472,231, US 4,569,976, US 4,945,006, US 4,946,529, US 5,003,016, US 5,106,808, US 6,734,249 and WO 2014 / 078115. Summary of the invention

[0004] In short, the present disclosure provides articles, which sequentially include: a) the first adherend; b) the first primer layer; c) adhesive layer; d) the optional second primer layer; and e) the second adherend; wherein the adhesive layer includes a pressure-sensitive adhesive region in an uncured state, these pressure-sensitive adhesive regions include a first substance, the first substance includes a first unsaturated free-radical polymerizable group, and wherein the adhesive layer includes a structural adhesive region, these structural adhesive regions include a polymer obtained by the local curing of the first substance, and the local curing of the first substance is achieved by the polymerization of the first unsaturated free-radical polymerizable group. Typically, the first primer layer covers the first part of the first adherend without covering the second part of the first adherend, wherein the pressure-sensitive adhesive region of the adhesive layer is bonded to the second part of the first adherend, and the structural adhesive region of the adhesive layer is bonded to the first part of the first adherend by the first primer layer. Typically, the structural adhesive region and the pressure-sensitive adhesive region are continuous from one side of the adhesive layer to the other side, thereby combining two adherends together. The contrast region can be patterned. In some embodiments, the discontinuous structural adhesive region is surrounded by a continuous pressure-sensitive adhesive region. In some embodiments, the discontinuous pressure-sensitive adhesive region is surrounded by a continuous structural adhesive region. In some embodiments, the pressure-sensitive adhesive region of the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a first substance comprising a first unsaturated free-radically polymerizable group, which first substance can be the first film-forming polymer or oligomer or a substance different from the first film-forming polymer or oligomer; iii) a first transition metal cation; and optionally iv) a quaternary ammonium salt. In some embodiments, the structural adhesive region of the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a polymer obtained by curing a first substance comprising a first unsaturated free-radically polymerizable group, the curing of the first substance being achieved by polymerization of the first unsaturated free-radically polymerizable group; iii) a first transition metal cation; and optionally iv) a quaternary ammonium salt. Additional embodiments of the articles of the present disclosure are described below.

[0005] On the other hand, the present disclosure provides methods, which include: a) providing a first adherend; b) applying a first primer to a first portion of the first adherend to form a first primer layer, while keeping the second portion of the first adherend free of the first primer layer; c) applying a curable adhesive film to the first primer layer and the second portion of the first adherend; and d) optionally applying the second adherend to the adhesive layer. The first primer is generally a curing initiating primer, which may include an oxidant such as a peroxide. The curable adhesive film is generally a pressure-sensitive adhesive. The curable adhesive film may include: i) a first film-forming polymer or oligomer; ii) a first substance comprising a first unsaturated free radical polymerizable group, which may be a first film-forming polymer or oligomer or a substance different from the first film-forming polymer or oligomer; iii) a first transition metal cation; and optionally iv) a quaternary ammonium salt. Typically, the curable adhesive film is an integral article. The curable adhesive film may be a self-supporting film. The curable adhesive film may be a hot-melt processable adhesive. Additional embodiments of the method of the present disclosure are described below.

[0006] The above summary of the present disclosure is not intended to describe every embodiment of the present invention. The details of one or more embodiments of the present invention are also listed in the following specific embodiments. Other features, objects and advantages of the present invention will be apparent from the specific embodiments and claims.

[0007] In this application:

[0008] "Common solvents" refers to low molecular weight organic liquids commonly used as solvents by those skilled in the art, which may include aliphatic and alicyclic hydrocarbons (e.g., hexane, heptane, and cyclohexane), aromatic solvents (e.g., benzene, toluene, and xylene), ethers (e.g., diethyl ether, glyme, diglyme, diisopropyl ether, and tetrahydrofuran), esters (e.g., ethyl acetate and butyl acetate), alcohols (e.g., ethanol and isopropanol), ketones (e.g., acetone, methyl ethyl ketone, and methyl isobutyl ketone), sulfoxides (e.g., dimethyl sulfoxide), amides (e.g., N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone), halogenated solvents (e.g., methyl chloroform, 1,1,2-trichloro-1,2,2-trifluoroethane, trichloroethylene, and trifluorotoluene), and mixtures thereof; provided that "common solvents" exclude substances that are monomers or otherwise reactants in a given composition;

[0009] "Directly bonded" means two materials that are in direct contact with each other and bonded together;

[0010] "Direct application" means applying one material directly into another material without an intermediate material;

[0011] "Substantially no" amount of a material in the composition may be replaced by "less than 5% by weight," "less than 4% by weight," "less than 3% by weight," "less than 2% by weight," "less than 1% by weight," "less than 0.5% by weight," "less than 0.1% by weight," or "none";

[0012] "Film-forming" means capable of forming a continuous and coherent film, which in some embodiments may be produced by one or more operations of solidifying, curing, drying or solvent removal of a melt, solution, suspension, etc.;

[0013] "Self-supporting film" means a film that is solid at normal temperature and pressure (NTP) and has mechanical integrity that is independent of contact with any supporting material (particularly excluding liquid, dry or in-situ cured surface coatings such as paints or primers, and films that do not have independent mechanical integrity);

[0014] "Hot melt processable adhesive" means an adhesive that contains substantially no conventional solvents and that can be hot melt processed under conventional conditions, wherein hot melt processing includes hot melt blending and extrusion;

[0015] "(Meth)acrylate" includes, individually and collectively, methacrylate and acrylate;

[0016] A "monomeric unit" of a polymer or oligomer is a segment of the polymer or oligomer derived from a single monomer;

[0017] “Normal temperature and pressure” or “NTP” means a temperature of 20°C (293.15K, 68°F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa);

[0018] A "side-chain" functional group of a polymer or oligomer is a functional group that does not form part of the backbone of the polymer or oligomer and is not a terminal group of the polymer;

[0019] "Pressure sensitive adhesive" or "PSA" means a material having the following properties: a) a tacky surface, b) the ability to adhere without exceeding finger pressure, c) the ability to adhere without being activated by any energy source, d) sufficient ability to hold onto the intended adherend, and preferably e) sufficient cohesive strength to be cleanly removed from the adherend; these materials typically meet the Dahlquist criterion of having a storage modulus of less than 0.3 MPa at 1 Hz and room temperature;

[0020] "Structural adhesive" means an adhesive that bonds by irreversible cure and, when bonded to its intended substrate, typically has a strength of at least 689 kPa (100 psi), in some embodiments at least 1379 kPa (200 psi), and in some embodiments at least 2067 kPa (300 psi), as measured as stress at break (peak stress) using the Lap Shear Test described in the Examples herein; and

[0021] "Unitary" or "unitary article" refers to an article that is a single piece and, although the article may include separately nameable elements, the article is formed from a single piece or aliquots of material without separating the single piece or aliquots (such as by extrusion, casting, stamping, molding, forging, machining, carving, etc.) and has no seams or joins between the elements.

[0022] Unless otherwise defined, all scientific and technical terms used herein have the meanings commonly used in the art.

[0023] Unless otherwise indicated, as used in this specification and the appended claims, past tense verbs such as "coated" and "embossed" are intended to indicate a structure and are not intended to limit the process used to obtain the structure.

[0024] As used in this specification and the appended claims, the singular forms "a," "an," and "the" encompass embodiments having plural referents unless the content clearly dictates otherwise.

[0025] As used in this specification and the appended claims, the term "or" is generally employed in its sense including "and / or" unless the content clearly dictates otherwise.

[0026] As used herein, "having", "including", "comprising", and the like are used in their open sense and generally mean "including but not limited to". It should be understood that the terms "consisting of" and "consisting essentially of" are included in the terms "comprising" and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a graph of shear strength as a function of percent cure (by area) for Examples 1 and 2 (Comparative Examples) and Examples 3-5, as described below.

[0028] Figure 2 The design of the mask used in Example 6 is shown as follows.

[0029] Figure 3 is a graph of load versus extension obtained during the peel strength testing in Example 6, as described below. DETAILED DESCRIPTION

[0030] The present disclosure provides articles, which include a first adherend and a second adherend that are combined together by an adhesive layer and at least one partial primer layer; wherein the adhesive layer includes a pressure-sensitive adhesive region and a structural adhesive region. The pressure-sensitive adhesive region is an uncured portion of the adhesive layer, and the structural adhesive region is a cured portion of the adhesive layer. The adhesive layer is typically an integral article as defined herein, that is, the contrasting region is not mechanically assembled together, but is produced by different treatments of different parts of a single sheet of adhesive layer material. The present disclosure also provides methods, which include applying a curing initiating primer to a first portion of the first adherend before applying a curable adhesive film and a second adherend, while keeping the second portion of the first adherend free of a curing initiating primer. The curing initiating primer of the present invention is a type that initiates the curing of a curable adhesive film to form a structural adhesive region in the adhesive layer; however, the present invention researchers have found that this curing exhibits limited propagation in the plane of the adhesive layer. Therefore, the cured structural adhesive region is formed on the primer, and the uncured pressure-sensitive adhesive region is maintained on the unprimed portion of the first adherend. The resulting bond may exhibit bonding properties intermediate between those of a fully cured (structural) adhesive layer or a fully uncured (pressure sensitive) adhesive layer, and may exhibit bonding properties superior to both.

[0031] Adhesive systems including curable adhesive films and cure-initiating primers are disclosed in WO 2019 / 157264 "Primer-Initiated Cure of Structural Adhesive Film"; and WO 2019 / 157265 "Primer-Initiated Cure of Structural Adhesive Film", the disclosures of which are incorporated herein by reference. (Docket Nos. 78901US002 and 81371US002). Any suitable adhesive layer and cure-initiating primer disclosed therein may be used in the practice of the present invention.

[0032] Any suitable primer that initiates the curing of the selected curable adhesive film can be used in the practice of the present disclosure. Typically, the primer comprises an oxidant, an optional film-forming oligomer, and an optional transition metal cation. In some embodiments, the primer comprises a reactive oligomer comprising an unsaturated free radical polymerizable group; an oxidant; and an optional transition metal cation. In some embodiments, the primer comprises a reactive oligomer comprising a side chain unsaturated free radical polymerizable group; an oxidant; and an optional transition metal cation. In some embodiments, the primer comprises a blend of the following substances: a film-forming oligomer, a reactive substance comprising an unsaturated free radical polymerizable group, an oxidant; and an optional reducible transition metal cation. In some embodiments, the primer comprises a blend of the following substances: a film-forming oligomer; an oxidant; and an optional reducible transition metal cation. In some embodiments, the unsaturated free radical polymerizable group is selected from a vinyl-containing group, such as a (meth)acrylate group. In some embodiments, the oxidant comprises a peroxide group, such as a hydroperoxide group. In some embodiments, the transition metal cation is a cation of molybdenum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper or zinc. In some embodiments, the transition metal cation is a copper cation, such as Cu (II). In some embodiments, the transition metal cation is an iron cation, such as Fe (II) or Fe (III), such as those that may be present in Pigment Black 11 (Fe3O4 or FeO·Fe2O3), Pigment Red 102 (Fe2O3) or Pigment Yellow 42 (FeO (OH) ·H2O). In some embodiments, the primer also includes a crosslinking agent, which includes two or more or three or more unsaturated free radical polymerizable groups, such as a vinyl-containing group, such as a (meth) acrylate group, which may be the same or different from any crosslinking agent in the curable adhesive film. In some embodiments, the crosslinking agent is a crosslinking monomer. In some embodiments, the crosslinking agent is an oligomer. In some embodiments, the primer may also include an excipient to facilitate the transport of the oxidant. In some embodiments, a conventional plasticizer may be used as an excipient. In some embodiments, plasticizers may be used, such as low vapor pressure (at room temperature) plasticizers and / or high boiling point plasticizers. In some embodiments, the primer may also include fillers, such as solid or hollow particles, which include polymers, glass, ceramics, metals or metal oxide materials. The primer is typically applied as a solvent-based liquid by any suitable method, which may include brushing, spraying, dipping, etc. Additional embodiments of the primer of the present disclosure and their uses are provided in the accompanying drawings and the attached description, selected embodiments and examples.

[0033] Any suitable oxidant may be used in the primer. Suitable oxidants may include organic peroxides, inorganic peroxides or persulfates. Suitable organic peroxides may include hydroperoxides, ketone peroxides, diacyl peroxides, dialkyl peroxides, peroxyketals, peroxyesters and peroxydicarbonates. Suitable organic peroxides may include diperoxides, which may include diperoxides comprising a portion R1-OO-R2-OO-R3, wherein R1 and R3 are independently selected from H, alkyl (e.g., C1 to C6), branched alkyl (e.g., C1 to C6), cycloalkyl (e.g., C5 to C10), alkylaryl (e.g., C7 to C12) or aryl (e.g., C6 to C10), and R2 is selected from alkyl (e.g., (C1 to C6) or branched alkyl (e.g., C1 to C6). Suitable ketone peroxides may include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, methyl cyclohexanone peroxide and cyclohexanone peroxide. Suitable Peroxyesters may include α-cumyl peroxyneodecanoate, tert-butyl peroxypivalate, tert-butyl peroxyneodecanoate, 2,2,4-trimethylpentyl peroxy-2-ethylhexanoate, tert-pentyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxyisophthalate, di-tert-butyl peroxyhexahydroterephthalate, tert-butyl peroxy-3,3,5-trimethylhexanoate, tert-butyl peroxyacetate, tert-butyl peroxybenzoate, and tert-butyl peroxymaleate. Suitable peroxydicarbonates may include di-3-methoxy peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, di-tert-butyl peroxydicarbonate Diisopropyl peroxide-1-ester, di-n-propyl peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate and diallyl peroxydicarbonate. Suitable diacyl peroxides may include acetyl peroxide, benzoyl peroxide, decanoyl peroxide, 3,3,5-trimethylhexanoyl peroxide, 2,4-dichlorobenzoyl peroxide and lauroyl peroxide. Suitable dialkyl peroxides may include di-tert-butyl peroxide, dicumyl peroxide, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 1,3-bis(tert-butylperoxyisopropyl)benzene and 2,5-dimethyl-2,5-di(tert-butylperoxy)- 3-hexane. Suitable peroxyketals may include 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane, 2,2-bis(tert-butylperoxy)octane and 4,4-bis(tert-butylperoxy)pentanoic acid n-butyl ester. In some embodiments, the organic peroxide is a hydroperoxide, particularly a hydroperoxide comprising the moiety ROOH, wherein R is (e.g., C1 to C20)alkyl, (e.g., C3 to C20)branched alkyl, (e.g., C6 to C12)cycloalkyl, (e.g., C7 to C20)alkylaryl or (e.g., C6 to C12)aryl.Suitable organic hydroperoxides may include tert-butyl hydroperoxide, tert-amyl hydroperoxide, p-diisopropylbenzene hydroperoxide, cumene hydroperoxide, pinane hydroperoxide, p-methane hydroperoxide and 1,1,3,3-tetramethylbutyl hydroperoxide. Suitable oxidants may include peroxodisulfate components and / or peroxodiphosphate components. Suitable examples may include ammonium peroxodisulfate, sodium peroxodisulfate and potassium peroxodisulfate components and / or ammonium peroxodiphosphate, sodium peroxodiphosphate and potassium peroxodiphosphate components. Suitable organic peroxides may also include tert-butyl peroxyethylhexyl carbonate, tert-butyl peroxytrimethylhexanoate, tert-butyl peroxyethylhexanoate, tert-amyl peroxyethylhexanoate, tert-octyl peroxyethylhexanoate, tert-amyl peroxyethylhexyl carbonate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxyisobutyrate or tert-butyl hydroperoxide.

[0034] Primer is applied to not all surfaces of the first adherend to be covered by the adhesive layer. Primer can be applied to 1% to 99% of the surface of the first adherend to be covered by the curable adhesive film, 1% to 95%, 1% to 90%, 1% to 85%, 1% to 80%, 1% to 75%, 1% to 70%, 1% to 65%, 1% to 60%, 1% to 55%, 1% to 50%, 1% to 45%, 1% to 40%, 1% to 35%, 1% to 30%, 1% to 25% of the first adherend to be covered by the curable adhesive film. , 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, 5% to 95%, 5% to 90%, 5% to 85%, 5% to 80%, 5% to 75%, 5% to 70%, 5% to 65%, 5% to 60%, 5% to 55%, 5% to 50%, 5% to 45%, 5% to 40%, 5% to 35%, 5% to 30%, 5% to 25%, 5% to 20%, 5% to 15% or 5% to 10% of the surface. Partial coverage can be achieved by any suitable method, such as by selective application using a mask or stencil or using a brush or spray nozzle, which can be mechanically or digitally controlled. Any suitable application pattern can be used, such as straight, curved, oblique or dashed lines; square, rectangular, triangular, hexagonal or other polygonal grids; or can be random or ordered dots of circular, elliptical, polygonal or other shapes. The pattern features may have a width and / or spacing dimension of 1 micron to 1000 microns, 1 micron to 500 microns, 1 micron to 250 microns, 1 micron to 125 microns, 1 micron to 50 microns, 1 micron to 25 microns, 1 micron to 10 microns, 1 micron to 5 microns, 5 microns to 1000 microns, 5 microns to 500 microns, 5 microns to 250 microns, 5 microns to 125 microns, 5 microns to 50 microns, 5 microns to 25 microns, or 5 microns to 10 microns. Additional embodiments of the application pattern of the primer of the present disclosure are provided in the drawings and accompanying descriptions, selected embodiments and examples.

[0035] Optionally, before applying the curing initiation primer, one or more secondary primers are applied to part or all of the surface of the first adherend. Optionally, before applying the curing initiation primer, one or more secondary primers are applied to part or all of the surface of the second adherend. Secondary primer is not usually cured and initiated.

[0036] Any suitable curable adhesive film can be used in the practice of the present disclosure. The curable adhesive film is generally a pressure sensitive adhesive (PSA). The curable adhesive film is generally a self-supporting film. The curable adhesive film is solid under NTP. In some embodiments, these films include a blend of the following substances: a reactive oligomer, the reactive oligomer includes an unsaturated free radical polymerizable group; an optional reducing agent; and an optional transition metal cation. In some embodiments, these films include a blend of the following substances: a reactive oligomer, the reactive oligomer includes a side chain unsaturated free radical polymerizable group; an optional reducing agent; and an optional transition metal cation. In some embodiments, these films include a blend of the following substances: a film-forming oligomer, a reactive substance including an unsaturated free radical polymerizable group; an optional reducing agent; and an optional transition metal cation and an optional quaternary ammonium salt. In some embodiments, the unsaturated free radical polymerizable group is selected from a vinyl-containing group, such as a (meth) acrylate group. In some embodiments, the oligomer is a poly (meth) acrylate oligomer. In some embodiments, the curable adhesive film also includes a crosslinking agent, which includes two or more or three or more unsaturated free radical polymerizable groups, such as vinyl-containing groups, such as (methyl) acrylate groups. In some embodiments, the crosslinking agent is a crosslinking monomer. In some embodiments, the crosslinking agent is an oligomer. In some embodiments, the curable adhesive film also includes a redox accelerator, such as a quaternary amine. In other embodiments, the redox accelerator can be selected from compounds containing organic or inorganic chloride ions, such as amine hydrochloride or sodium chloride. In some embodiments, the curable adhesive film may also include fillers, such as solid or hollow particles, which include polymers, glass, ceramics, metals or metal oxide materials. Additional embodiments of the curable adhesive film of the present disclosure, strips including the curable adhesive film and their uses are provided in the accompanying drawings and the attached description, selected embodiments and examples.

[0037] When present, any suitable transition metal cation may be used, including those listed above with respect to the cure initiating primer.

[0038] When present, any suitable reducing agent can be used, including organic components and inorganic components and their mixtures. Suitable reducing agents can include ascorbic acid components, tertiary amine components, sulfinate components, sulfite components, borane components, (thio) urea components, (thio) barbituric acid components, saccharin, reducing sugars (such as dextrose, glucose and fructose), and metal salts of any of the aforementioned substances. In some embodiments, the reducing agent comprises an ascorbic acid moiety. Such reducing agents can include ascorbic acid salts or esters, or can be connected to the ascorbic acid moiety by an ether bond. Ketals or acetals can also be useful. Suitable salts can include alkali metal salts and alkaline earth metal salts, such as Na, K, Ca and their mixtures. Ascorbic esters can include those formed by reacting one or more hydroxyl functional groups of ascorbic acid with carboxylic acids (particularly C2-C30 carboxylic acids or C12-C22 carboxylic acids). Suitable examples of C2 to C30 carboxylic acids include fatty acids, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, myristoleic acid, palmitoleic acid, hexadecenoic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, trans-linoleic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid and docosahexaenoic acid. In some embodiments, the reducing agent comprises an ascorbic acid moiety and can be easily dissolved in or mixed with other components of the film, such as a reducing agent containing a hydrophobic moiety. In other embodiments, the reducing agent can be a tertiary amine, such as N, N-dimethyl-p-toluidine, N, N-dimethyl-aminoethyl methacrylate, triethanolamine, 4-dimethylaminobenzoic acid methyl ester, 4-dimethylaminobenzoic acid ethyl ester, methyl diphenylamine and 4-dimethylaminobenzoic acid isopentyl ester. In other embodiments, the reducing agent may be a sodium sulfinate derivative or an organometallic compound.

[0039] In some embodiments, the curable adhesive film has an outer surface, i.e., a surface facing the substrate, which includes embossed degassing channels that can help air escape during the outer surface is applied to the substrate. These channels and production methods thereof can be as taught in EP 1800865. Such channels achieve unique purposes in the use of the disclosed article. By allowing trapped bubbles to escape, the degassing channels can help to improve contact with primer. Alternatively, when the adhesive film or strip has an embossed face and an unembossed face, the unembossed face can be placed on the first substrate, and then the second substrate can be contacted with the embossed face. This method may be particularly useful when two rigid substrates are to be joined, because it allows degassing and is adapted to uneven surfaces, although these substrates are non-flexible.

[0040] Upon contact with the cure initiating primer, the curable adhesive film begins to cure, thereby forming a structural adhesive region in the adhesive layer; however, the present researchers have found that this cure exhibits limited propagation within the plane of the adhesive layer. Thus, a cured structural adhesive region is formed adjacent to the primer, while an uncured pressure-sensitive adhesive region remains above the unprimed portion of the first adherend. The structural adhesive region may account for 1% to 99% of the adhesive layer, 1% to 95%, 1% to 90%, 1% to 85%, 1% to 80%, 1% to 75%, 1% to 70%, 1% to 65%, 1% to 60%, 1% to 55%, 1% to 50%, 1% to 45%, 1% to 40%, 1% to 35%, 1% to 30%, 1% to 25%, 1% to 20%, 1% to 15%, 1% to 10% of the adhesive layer. , 1% to 5%, 5% to 95%, 5% to 90%, 5% to 85%, 5% to 80%, 5% to 75%, 5% to 70%, 5% to 65%, 5% to 60%, 5% to 55%, 5% to 50%, 5% to 45%, 5% to 40%, 5% to 35%, 5% to 30%, 5% to 25%, 5% to 20%, 5% to 15% or 5% to 10%, with the remainder of the adhesive layer being pressure sensitive adhesive area. Any suitable structural adhesive area pattern may be used, such as straight, curved, oblique or dashed lines; square, rectangular, triangular, hexagonal or other polygonal grids; or random or ordered dots that may be circular, elliptical, polygonal or other shapes. Pattern features can have 1 micron to 1000 micron, 1 micron to 500 micron, 1 micron to 250 micron, 1 micron to 125 micron, 1 micron to 50 micron, 1 micron to 25 micron, 1 micron to 10 micron, 1 micron to 5 micron, 5 microns to 1000 micron, 5 microns to 500 micron, 5 microns to 250 microns, 5 microns to 125 microns, 5 microns to 50 microns, 5 microns to 25 microns or 5 microns to 10 micron width and / or the spacing size.In various embodiments, the structural adhesive region can be continuous or discontinuous, and the pressure-sensitive adhesive region can be continuous or discontinuous.In some embodiments, the structural adhesive region is discontinuous and surrounded by continuous pressure-sensitive adhesive region, for example, the different posts in domain are separated by continuous pressure-sensitive adhesive region arrangement.In some embodiments, the discontinuous pressure-sensitive adhesive region is surrounded by continuous structural adhesive region.

[0041] Additional embodiments of patterns of adhesive layer domains for use in the present disclosure are provided in the Figures and accompanying Description, Selected Embodiments and Examples.

[0042] Additional embodiments of the disclosure are described in the following selected embodiments and examples.

[0043] Selected Implementation

[0044] The following embodiments, represented by letters and numbers, are intended to further illustrate the present disclosure but should not be construed as unduly limiting the present disclosure.

[0045] A1. A product comprising, in order:

[0046] a) a first adherend;

[0047] b) a first primer layer;

[0048] c) an adhesive layer;

[0049] d) an optional second primer layer;

[0050] e) a second adherend;

[0051] The adhesive layer comprises pressure-sensitive adhesive regions in an uncured state, the pressure-sensitive adhesive regions comprising a first substance comprising first unsaturated free-radically polymerizable groups, and the adhesive layer comprises structural adhesive regions comprising polymers obtained by curing the first substance, the curing of the first substance being achieved by polymerization of the first unsaturated free-radically polymerizable groups.

[0052] A2. The article of embodiment A1, wherein the adhesive layer is a one-piece article.

[0053] A3. The article according to any one of embodiments A1 to A2, wherein the adhesive layer is derived from a self-supporting film.

[0054] A4. The article of any one of embodiments A1 to A3, wherein the first primer layer covers a first portion of the first adherend, wherein the first primer layer does not cover a second portion of the first adherend, and wherein the second portion of the first adherend is directly bonded to the adhesive layer.

[0055] A5. An article according to embodiment A4, wherein the pressure sensitive adhesive region of the adhesive layer is directly bonded to the second portion of the first adherend; and wherein the structural adhesive region of the adhesive layer is bonded to the first portion of the first adherend through the first primer layer.

[0056] A6. The article of any one of embodiments A4 to A5, wherein the first portion of the first adherend accounts for 1% to 99% of the surface of the adherend covered by the adhesive layer, and the second portion of the first adherend accounts for 99% to 1% of the surface of the adherend covered by the adhesive layer.

[0057] A7. The article of any one of embodiments A1 to A6, wherein the adhesive layer has a first side adjacent to the first primer layer and an opposite side, wherein the structural adhesive region is continuous from the first side to the opposite side.

[0058] A8. The article of any one of embodiments A1 to A7, wherein the adhesive layer has a first side adjacent to the first primer layer and an opposite side, and wherein the pressure-sensitive adhesive region is continuous from the first side to the opposite side.

[0059] A9. The article of any one of embodiments A1 to A8, wherein the first primer layer is directly bonded to the first adherend and the adhesive layer.

[0060] A10. The article of any one of embodiments A1 to A9, wherein the adhesive layer is directly bonded to the second adherend.

[0061] A11. The article of any one of embodiments A1 to A10, comprising a second primer layer.

[0062] A12. The article of embodiment A11, wherein the second primer layer is directly bonded to the adhesive layer and the second adherend.

[0063] A13. The article of any one of embodiments A1 to A12, wherein in the plane of the adhesive layer, one or more structural adhesive regions are surrounded by a continuous pressure-sensitive adhesive region.

[0064] A14. The article of any one of embodiments A1 to A13, wherein two or more structural adhesive regions are discontinuous with each other in the plane of the adhesive layer and are each surrounded by a continuous pressure-sensitive adhesive region.

[0065] A15. The article of any one of embodiments A1 to A14, wherein the pressure-sensitive adhesive region of the adhesive layer comprises:

[0066] i) a first film-forming polymer or oligomer;

[0067] ii) a first material comprising a first unsaturated free-radically polymerizable group, the first material being a first film-forming polymer or oligomer or a material different from the first film-forming polymer or oligomer; and

[0068] iii) a first transition metal cation; and optionally

[0069] iv) Quaternary ammonium salts.

[0070] A16. The article of any one of embodiments A1 to A15, wherein the structural adhesive region of the adhesive layer comprises:

[0071] i) a first film-forming polymer or oligomer;

[0072] ii) a polymer obtained by curing a first substance comprising a first unsaturated free-radically polymerizable group, the curing of the first substance being achieved by polymerizing the first unsaturated free-radically polymerizable group;

[0073] iii) a first transition metal cation; and optionally

[0074] iv) Quaternary ammonium salts.

[0075] M1. A method comprising:

[0076] a) providing a first adherend;

[0077] b) applying a first primer to a first portion of a first adherend to form a first primer layer, while keeping a second portion of the first adherend free of the first primer layer;

[0078] c) applying a curable adhesive film to the first primer layer and the second portion of the first adherend; and

[0079] d) optionally applying a second adherend to the adhesive layer.

[0080] M2. The method of embodiment M1, wherein the first portion of the first adherend accounts for 1% to 99% of the surface of the adherend covered by the adhesive layer, and the second portion of the first adherend accounts for 99% to 1% of the surface of the adherend covered by the adhesive layer.

[0081] M3. The method of any one of embodiments M1 to M2, wherein the curable adhesive film is a unitary article.

[0082] M4. The method of any one of embodiments M1 to M3, wherein the curable adhesive film is a self-supporting film.

[0083] M5. The method of any one of embodiments M1 to M4, wherein the curable adhesive film is applied directly to the first primer layer and the second portion of the first adherend.

[0084] M6. The method of any one of embodiments M1 to M5, wherein the first primer is applied directly to the first portion of the first adherend.

[0085] M7. The method of any one of embodiments M1 to M6, comprising applying a second adherend to the curable adhesive film.

[0086] M8. The method of any one of embodiments M1 to M6, comprising applying the second adherend directly to the curable adhesive film.

[0087] M9. The method of any one of embodiments M1 to M6, comprising applying a second primer to the second adherend before applying the second adherend to the adhesive layer. M10. The method of any one of embodiments M1 to M9, wherein in the plane of the first adherend, one or more first portions of the first adherend are surrounded by a continuous second portion of the first adherend.

[0088] M11. The method of any one of embodiments M1 to M10, wherein in the plane of the first adherend, two or more first portions of the first adherend are discontinuous with each other and are each surrounded by a continuous second portion of the first adherend.

[0089] M12. The method of any one of embodiments M1 to M11, wherein the curable adhesive film is a hot melt processable adhesive.

[0090] M13. The method of any one of embodiments M1 to M12, wherein the curable adhesive film is a pressure sensitive adhesive.

[0091] M14. The method of any one of embodiments M1 to M13, wherein the curable adhesive film comprises:

[0092] i) a first film-forming polymer or oligomer;

[0093] ii) a first substance comprising a first unsaturated free-radically polymerizable group, the first substance being a first film-forming polymer or oligomer or a substance different from the first film-forming polymer or oligomer;

[0094] iii) a first transition metal cation; and optionally

[0095] iv) Quaternary ammonium salts.

[0096] M15. The method of any one of embodiments M1 to M14, wherein the first primer is a cure initiating primer.

[0097] M16. The method of any one of embodiments M1 to M15, wherein the first primer comprises an oxidizing agent.

[0098] M17. A method according to embodiment M16, wherein the oxidizing agent is a peroxide.

[0099] While objects and advantages of this disclosure are further illustrated by the following examples, the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this disclosure.

[0100] Example

[0101] Unless otherwise noted, all reagents were obtained or purchased from Aldrich Chemical Co., Milwaukee, WI, or could be synthesized by known methods.

[0102] Unless otherwise indicated, all parts, percentages, ratios, etc. in the examples and the remainder of the specification are by weight. The following abbreviations may be used: m = meter; cm = centimeter; mm = millimeter; um = micrometer; ft = foot; in = inch; RPM = revolutions per minute; kg = kilogram; oz = ounce; lb = pound; Pa = Pascal; sec = second; min = minute; hr = hour; and RH = relative humidity. The terms "weight %", "% weight" and "wt %" may be used interchangeably.

[0103] Material

[0104]

[0105]

[0106] Synthesis of copolymer 1

[0107] The material was prepared as described in Synthesis Example S1 of US 2013 / 0184394 A1, except that the pre-binder composition was as follows: 90 parts M1, 10 parts AA, 0.15 parts photoinitiator-1, 0.12 parts Cu2EHA, 0.4 parts antioxidant-1, and 0.001 parts HDDA branching monomer / crosslinker.

[0108] Compounding of BTEAC dispersions

[0109] A masterbatch premix was prepared by mixing 2640 g of BTEAC and 9360 g of M410 for 30 minutes using a Cowles blade Cowles mixer (DISPERMAT CN-10, BYK-Gardner, Columbia, MD, USA) until homogeneous. The mixed materials were transferred to a HCPS-1 / 4 immersion mill (Hockmeyer Equipment Corporation, Elizabeth City, NC, USA) equipped with a 0.50 mm wedge screen loaded with approximately 550 grams of 1.0 mm yttrium-stabilized zirconia grinding media (Torayceram, Toray Industries, Inc.). The mill was operated at approximately 40 Hz; and the slurry temperature was maintained at approximately 80° C.-85° C. during grinding using a thermostatic bath / immersion circulator (HAAKE P1-C41P with Phoenix II controller, Thermo Fisher Scientific, NH, USA). The material was ground for 2 hours to a D90 of 15.74 microns PSD. Particle size was measured as described in the test methods below.

[0110] Hot Melt Compounding of Curable Pressure Sensitive Adhesive (PSA) Films

[0111] A co-rotating twin-screw extruder with a diameter of 30 mm (available as "ZSK-30" from Werner & Pfleiderer, Ramsey, NJ) was used to prepare a curable pressure-sensitive adhesive film. The twin-screw extruder had 12 zones, each zone being equivalent to one-twelfth of the screw length, and an aspect ratio of 36:1. The twin-screw extruder operated at 300 rpm, and the temperature in zones 1-7 was 250 °F (121.1 °C), and the temperature in zones 8-12 was 220 °F (104.4 °C). Copolymer 1 in a small bag was fed into a 2-inch (51 mm) single-filler extruder (commercially available from Bonnot, Uniontown, OH) in Uniontown, Ohio. The single-filler extruder masticated the polymer and fed it into zone 2 of the twin-screw extruder at a rate of 52.1 g / min. The BTEAC dispersion was fed in a split stream into zone 4 of the extruder at a rate of 3.05 g / min, into zone 7 at a rate of 9.88 g / min, and into zone 9 at a rate of 11.29 g / min, from a peristaltic pump (505DU, purchased from Watson Marlow Ltd., Cornwall, England) into zones 4 and 9, and from a second peristaltic pump (956-0000 head on an IP56 pump, purchased from Thermo Scientific, Barrington, IL) into zones 7 and 9. The molten mixture passed from the extruder to a polymer melt pump (available as "PEP-II 3CC / REV" from Zenith Pumps, Monroe, NC) set at 280°F (137.8°C) and pumped at 84 cm / s. 3 / minute rate was pumped into a rotating rod die set at 280°F (137.8°C). The molten mixture was coated as a continuous sheet of pressure-sensitive adhesive about 5 mils (0.13 mm) thick onto a silicone-coated multi-coated kraft paper release liner. The curable PSA film thus formed was used in each of the following examples.

[0112] Test Method

[0113] Laser Cutting

[0114] The patterned mask was cut using a CO2 laser plotter system (VLS 6.60 Universal Laser System, Scottsdale, AZ). The laser was set at 3M with variable power. TMCutting is performed on a polyester strip 8402 which has been placed on a silicone coated polyester release liner which is oriented with the green polyester strip facing the laser so that the laser first passes through the green polyester strip and then through the polyester release liner.

[0115] Patterned Primer Application

[0116] A laser patterned green polyester tape was adhered to a clean stainless steel substrate and then a primer was applied to the sample as described below. After the primer dried, the green polyester tape patterned mask was removed from the sample to reveal the patterned primer.

[0117] Particle size measurement

[0118] The particle size of the BTEAC dispersion was measured by laser diffraction using a Horiba LA-950V (Horiba, Kyoto, Japan). The following refractive index values ​​were used for calculation: MEK (1.3791) and BTEAC (1.4790). The second differential method was used for smoothing based on 150 iterations. The dispersion was diluted to approximately 1% by weight of solids with MEK. The diluted sample was then added to a measurement chamber equipped with MEK until the transmittance was between the recommended levels of 85% and 95%. D90 is the maximum particle size below which 90% of the sample volume is present.

[0119] 90° peel adhesion test

[0120] A 2 inch x 5 inch (5 cm x 12.5 cm) stainless steel panel was washed with MEK, a 50 / 50 water / IPA solution, and acetone and then air dried. Depending on the embodiment, the primer was applied to the entire contact area of ​​the substrate, which was not primed, or the primer was applied in a pattern as described above under "Patterned Primer Coating". A 1 inch (2.5 cm) wide strip of curable adhesive film was laminated between a patterned primed panel and a 2.8 cm wide strip of 0.003 inch (0.008 cm) thick anodized aluminum foil using a 4.5 lb (2.0 kg) roller, laminated 3 times at 24 inches / minute. After standing at room temperature for 72 hours, a 90° peel test was performed at 12 inches / minute (30 cm / min) using an Insight tensile tester (MTS, Eden Prairie, MN), and data was collected to indicate the change in peel adhesion as a result of the cured area from the patterned primer.

[0121] ASTM Designation: D3330. Data reported in pounds per inch.

[0122] Lap shear test

[0123] A 1 inch x 4 inch x 0.064 inch (2.5 cm x 10 cm x 1.6 mm) aluminum substrate was washed with MEK, 50 / 50 water / IPA solution and acetone and then air dried. Depending on the embodiment, the primer was applied to the entire contact area of ​​the substrate, which was not primed, or the primer was applied in a pattern as described above under "Patterned Primer Coating". A 1 inch x 1 inch (2.5 cm x 2.5 cm) portion of the strip sample (curable adhesive film on the release liner) was applied to the end above the top of the patterned primer. The release liner was removed and a second primer-free aluminum substrate was applied to the sample adhesive, thereby closing the bond (the total bond area was 1 inch x 1 inch (2.5 cm x 2.5 cm) and the cured portion was variable with the applied pattern) and forming a test assembly. The test assembly was saturated by rolling across the bond 3 times with a 15 lb (6.8 kg) automatic roller at 24 inches / minute. The bonded test assembly was placed at room temperature for 24 hours before testing.

[0124] Dynamic lap shear testing was performed at ambient temperature using a Sintech 5 tensile tester (MTS, Eden Prairie, MN). The test specimens were loaded into the grips and the crosshead was operated at 0.1 inches per minute to load the specimens to failure. The stress at break was recorded in pounds per square inch (PSI).

[0125] ASTM Designation: D 1002. Data reported in pounds per square inch.

[0126] Example

[0127] Example 1

[0128] A cure initiating primer was prepared by mixing 0.80 g TBEC into 20.0 g UPUV in a 40 mL glass vial. The primer was applied to the entire contact area of ​​one substrate each for shear (T2024 aluminum) and peel (stainless steel) testing. Test specimens were assembled using curable PSA films as described above and shear and peel testing was performed.

[0129] Example 2

[0130] No primer was applied to the substrate for the peel and shear tests. The test specimens were assembled for the shear and peel tests and no primer was applied to any substrate, ie, the curable PSA film was applied directly to the substrate for the shear and peel tests as described above.

[0131] Example 3

[0132] During assembly of the test specimens for shear and peel testing, a cure initiating primer as prepared in Example 1 was applied in a pattern of vertical lines (parallel to the long sides of the sample substrates). The primer was applied so that the 0.125 inch (0.318 cm) wide lines were parallel to the long sides of the sample substrates. This resulted in two lines of cured material in the peel test that were 0.125 inches (0.318 cm) wide (25% of the peel front width) and two cured lines that were 0.125 inches by 1 inch (0.318 cm by 2.5 cm), with a total bond area of ​​the shear specimens of 1 inch by 1 inch (2.5 cm by 2.5 cm) each (25.0% of the total cured area).

[0133] Example 4

[0134] During assembly of the test specimens for shear and peel testing, a cure initiating primer as prepared in Example 1 was applied in a pattern of horizontal lines (parallel to the short edge of the sample substrate). The primer was applied so that the 0.125 inch (0.318 cm) wide lines were parallel to the short edge of the sample substrate. This resulted in several lines of cured material in the peel test that were 0.125 inches (0.318 cm) wide (alternating 0% / 100% of the peel front width) and three cured lines that were 0.125 inches by 1 inch (0.318 cm by 2.5 cm), with a total bond area of ​​the shear specimens of 1 inch by 1 inch (2.5 cm by 2.5 cm) each (37.5% of the total cured area).

[0135] Example 5

[0136] A cure initiating primer prepared as in Example 1 was applied to the area to be bonded in a pattern of 0.250 inch (0.635 cm) diameter dots. This resulted in two rows of cured dots in the peel test (50% of the peel front width at the largest diameter) and four cured dots of 0.05 square inches (0.32 square centimeters), with a total bond area of ​​1 inch x 1 inch (2.5 cm x 2.5 cm) each for the shear specimen (19.6% of the total cured area).

[0137] Table 1. Summary of data for Examples 1-5

[0138]

[0139] It can be seen that the dot pattern of Example 5 provides a peel adhesion equal to the maximum value, which is confirmed by the fact that the fully uncured Example 2 (Comparative Example) still has a shear strength 2.5 times that of Example 2 (Comparative Example). Example 4 represents a shear and peel strength between the fully cured Example 1 (Comparative Example) and the fully uncured Example 2 (Comparative Example), indicating that practitioners can trade off shear and peel to adjust the adhesive properties according to specific applications. Comparison of Examples 3 and 4 shows that the shear and peel strength properties of the bonded substrate can be directionally adjusted by using a directional pattern. Figure 1 is a graph of shear strength as a function of percent cure (by area) for Examples 1-5.

[0140] Example 6

[0141] The cure initiating primer prepared as in Example 1 was applied in a pattern of variable width lines parallel to the short edge of the sample substrate. This produced a pattern of several lines ranging from 0.5 inches (0.318 cm) down to 0.005 inches (0.013 cm) wide. The design of the mask used in this process is depicted in Figure 2 No shear samples were produced for this example. Figure 3 A graph of the load versus extension obtained during the peel strength test is shown, indicating that the uncured portion of the adhesive film provides greater peel strength. Figure 3 In the figure, "S" indicates the starting side of the peeling, and "P" indicates the ending side of the peeling.

[0142] Various modifications and alterations of this disclosure will become apparent to those skilled in the art without departing from the scope and principles of this disclosure, and it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth above.

Claims

1. A product, comprising in order: a) a first adherend; b) a first primer layer; c) an adhesive layer; d) an optional second primer layer; e) a second adherend; wherein the first primer layer covers a first portion of the first adherend, wherein the first primer layer does not cover a second portion of the first adherend, wherein the adhesive layer comprises a pressure-sensitive adhesive region in an uncured state, the pressure-sensitive adhesive region comprising a first substance, the first substance comprising a first unsaturated free-radically polymerizable group, wherein the second portion of the first adherend is directly bonded to the adhesive layer, wherein the adhesive layer comprises a structural adhesive region, the structural adhesive region comprising a polymer obtained by curing the first substance, the curing of the first substance being achieved by polymerization of the first unsaturated free-radically polymerizable group, and wherein the structural adhesive region of the adhesive layer is bonded to the first portion of the first adherend through the first primer layer.

2. The article of claim 1, wherein the adhesive layer has a first side adjacent to the first primer layer and an opposite side, wherein the structural adhesive region is continuous from the first side to the opposite side, and wherein the pressure sensitive adhesive region is continuous from the first side to the opposite side.

3. The article of claim 1 wherein, in the plane of the adhesive layer, one or more structural adhesive regions are surrounded by a continuous pressure sensitive adhesive region.

4. The article of claim 1 wherein, in the plane of the adhesive layer, one or more pressure sensitive adhesive regions are surrounded by a continuous structural adhesive region.

5. The article of any one of claims 1 to 4, wherein the pressure-sensitive adhesive region of the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a first substance comprising a first unsaturated free-radically polymerizable group, wherein the first substance may be the first film-forming polymer or oligomer or a substance different from the first film-forming polymer or oligomer; iii) a first transition metal cation; and optionally iv) Quaternary ammonium salts.

6. The article of any one of claims 1 to 4, wherein the structural adhesive region of the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a polymer obtained by curing a first substance comprising a first unsaturated free-radically polymerizable group, the curing of the first substance being achieved by polymerizing the first unsaturated free-radically polymerizable group; iii) a first transition metal cation; and optionally iv) Quaternary ammonium salts.

7. A method for forming a composite pressure sensitive adhesive / structural adhesive bond, the method comprising: a) providing a first adherend; b) applying a first primer to a first portion of the first adherend to form a first primer layer, while keeping a second portion of the first adherend free of the first primer layer; c) applying a curable adhesive film to the first primer layer and a second portion of the first adherend; as well as d) optionally applying a second adherend to the adhesive layer, wherein the first primer is a cure initiating primer, the curable adhesive film is a pressure sensitive adhesive, and the curable adhesive film cures upon contact with the first primer, the curing having limited propagation within the plane of the adhesive layer, thereby forming a cured structural adhesive area above the first primer, while an uncured pressure sensitive adhesive area remains on the unprimed second portion of the first adherend.

8. The method of claim 7, wherein the curable adhesive film is a unitary article.

9. The method of claim 7, wherein the curable adhesive film is a self-supporting film.

10. The method of claim 7, comprising applying the second adherend to the curable adhesive film.

11. The method of claim 7, wherein in the plane of the first adherend, one or more first portions of the first adherend are surrounded by a continuous second portion of the first adherend.

12. The method of claim 7, wherein the curable adhesive film is a hot melt processable adhesive.

13. The method according to any one of claims 7 to 12, wherein the curable adhesive film comprises: i) a first film-forming polymer or oligomer; ii) a first substance comprising a first unsaturated free-radically polymerizable group, wherein the first substance may be the first film-forming polymer or oligomer or a substance different from the first film-forming polymer or oligomer; iii) a first transition metal cation; and optionally iv) Quaternary ammonium salts.

14. The method of any one of claims 7 to 12, wherein the first primer comprises an oxidizing agent.

15. The method of claim 14, wherein the oxidizing agent is a peroxide.

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