Primer-Initiated Thermal Debonding of Curable Structural Adhesive Films

Abstract

The present invention relates to a debonding method comprising: providing a bonded article comprising, in sequence, a first adherend, a first primer layer, an adhesive layer, an optional second primer layer, and a second adherend; heating the article to a release temperature; and separating the first adherend and the second adherend. At room temperature, the adhesive layer exhibits a high lap shear greater than 1.0 MPa (145 psi) or even greater than 5.0 MPa (725 psi), however, at the release temperature, the adhesive layer exhibits a lap shear of no more than 0.34 MPa (50 psi) or even no more than 0.21 MPa (30 psi). The release temperature can be a temperature between 100° C. and 150° C. The adhesive layer may comprise: a first film-forming polymer or oligomer; a cured polymer comprising a polymer of a first substance comprising a first unsaturated free radical polymerizable group; a first transition metal cation; and an optional quaternary ammonium salt.

Description

Technical Field

[0001] The present disclosure relates to a method of reversing a structural adhesive bond by applying heat, wherein the adhesive bond comprises a structural adhesive film cured by a primer-initiated cure mechanism. 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 these patents 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 a method, which includes: a) providing a combined article, which includes in turn: a first adherend; a first primer layer; an adhesive layer; an optional second primer layer; and a second adherend; b) the article is heated to a release temperature; and c) separating the first adherend and the second adherend so that they are no longer combined together by the adhesive layer. At room temperature, the adhesive layer exhibits a lap shear greater than 1.0 MPa (145 psi) or even greater than 3.0 MPa (435 psi), 4.5 MPa (653 psi) or 5.0 MPa (725 psi). However, at the release temperature, the adhesive layer exhibits a lap shear no greater than 0.34 MPa (50 psi) or even no greater than 0.28 MPa (40 psi) or 0.21 MPa (30 psi). The release temperature can be between 100 ° C and 150 ° C; between 105 ° C and 135 ° C; or at a temperature between 105 ° C and 120 ° C. In some embodiments, the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a curing polymer comprising a polymer of a first substance comprising a first unsaturated free radical polymerizable group; iii) a first transition metal cation; and optionally iv) a quaternary ammonium salt. The first film-forming polymer or oligomer can be a (meth)acrylate polymer or oligomer. The curing polymer can also be a (meth)acrylate polymer or oligomer. The first substance can comprise two or more, three or more, or four or more first unsaturated free radical polymerizable groups. In some embodiments, the first unsaturated free radical polymerizable group is a (meth)acryloyl group. In some embodiments, the curing polymer is a peroxide-cured polymer. Additional embodiments of the method of the present disclosure are described below according to "Selected Embodiments".

[0005] The foregoing summary of the present disclosure is not intended to describe every embodiment of the present invention. Details of one or more embodiments of the present invention are also listed in the following detailed description. Other features, objects and advantages of the present invention will be apparent from the detailed description and claims.

[0006] In this application:

[0007] "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;

[0008] "Directly bonded" means two materials that are in direct contact with each other and bonded together;

[0009] "Direct application" means applying one material directly into another without an intermediate material;

[0010] "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";

[0011] "Film-forming" means capable of forming a continuous and coherent film, which in some embodiments may be produced by one or more of solidifying, curing, drying, or solvent removal of a melt, solution, suspension, or the like;

[0012] "Self-supporting membrane" means a membrane that is solid at normal temperature and pressure (NTP) and has mechanical integrity that is independent of contact with any supporting material (specifically excluding liquid, drying or in-situ cured surface coatings such as paints or primers, and membranes that do not have independent mechanical integrity);

[0013] "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;

[0014] "(Meth)acrylate" includes, individually and collectively, methacrylate and acrylate;

[0015] A "monomeric unit" of a polymer or oligomer is a segment of the polymer or oligomer derived from a single monomer;

[0016] “Normal temperature and pressure” or “NTP” means a temperature of 20°C (293.15 K, 68°F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa);

[0017] 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;

[0018] "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 generally meet the Dahlquist criterion of having a storage modulus of less than 0.3 MPa at 1 Hz and room temperature;

[0019] “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

[0020] "Unitary" or "unitary article" means an article that is a single piece and, although the article may include separately nameable elements, 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.

[0021] Unless defined otherwise, all scientific and technical terms used herein have the meanings commonly used in the art.

[0022] Unless otherwise indicated, as used in this specification and the appended claims, past tense verbs such as "coated" and "embossed" are intended to refer to the structure and are not intended to limit the method used to obtain the structure.

[0023] 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.

[0024] 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.

[0025] As used herein, "having," "including," "comprising," and the like are used in their open-ended sense and generally mean "including but not limited to." It should be understood that the terms "consisting of" and "consisting essentially of" are encompassed by the terms "comprising," and the like. DETAILED DESCRIPTION

[0026] The present disclosure provides the method for reversing structural strength adhesive bonding by applying heat, wherein adhesive bonding comprises the adhesive film solidified by the curing mechanism caused by primer.The method comprises: a) providing combined article, this combined article comprises successively: the first adherend; the first primer layer; the adhesive layer; the optional second primer layer; and the second adherend; b) the article is heated to the release temperature; and c) separating the first adherend and the second adherend so that they are no longer combined together by the adhesive layer.At room temperature, the adhesive layer shows a lap shear greater than 1.0MPa (145psi) or even greater than 4.5MPa (653psi).However, at the release temperature, the adhesive layer shows a lap shear not greater than 0.34MPa (50psi) or even not greater than 0.21MPa (30psi).

[0027] The release temperature is between 100°C and 150°C; or in various embodiments between 100°C and 145°C; between 100°C and 140°C; between 100°C and 135°C; between 100°C and 130°C; between 100°C and 125°C; between 100°C and 120°C; between 105°C and 150°C; between 105°C and 145°C; between 105°C and 140°C; between 105°C and 135°C; between 105°C and 130°C; between 105°C and 125°C; between 105°C and 12 between 0°C; between 110°C and 150°C; between 110°C and 145°C; between 110°C and 140°C; between 110°C and 135°C; between 110°C and 130°C; between 110°C and 125°C; between 110°C and 120°C; between 115°C and 150°C; between 115°C and 145°C; between 115°C and 140°C; between 115°C and 135°C; between 115°C and 130°C; between 115°C and 125°C; or a temperature between 115°C and 120°C.

[0028] Suitable adhesive / primer systems may include those disclosed in 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. 78901US002, 81371US002, and 82231US002). Any suitable adhesive layer and cure-initiating primer disclosed therein may be used in the practice of the present invention.

[0029] Suitable adhesive / primer systems can provide structural strength bonds, however, these structural strength bonds can be weakened to the point where they can be manually removed for purposes such as reworking or recycling the bonded substrate.

[0030] 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 oxidizing agent, 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 oxidizing agent; 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 oxidizing agent; 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 oxidizing agent; and an optional reducible transition metal cation. In some embodiments, the primer comprises a blend of the following substances: a film-forming oligomer; an oxidizing agent; 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 oxidizing agent 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 further comprises a crosslinking agent comprising two or more or three or more unsaturated free radical polymerizable groups, such as a vinyl 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 further comprise 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 such as low vapor pressure (at room temperature) plasticizers and / or high boiling point plasticizers may be used. In some embodiments, the primer may further comprise fillers such as solid or hollow particles comprising 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 primers disclosed herein and their uses are provided in selected embodiments and examples.

[0031] Any suitable oxidizing agent can be used in the primer. Suitable oxidizing agents can include organic peroxides, inorganic peroxides or persulfates. Suitable organic peroxides can include hydroperoxides, ketone peroxides, diacyl peroxides, dialkyl peroxides, peroxyketals, peroxyesters and peroxydicarbonates. Suitable organic peroxides can include diperoxides, which can include diperoxides comprising the moiety 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 can include methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide, methylcyclohexanone peroxide and cyclohexanone peroxide. Suitable The 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 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)- 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 n-butyl 4,4-bis(tert-butylperoxy)valerate. 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 peroxyethylhexylcarbonate, tert-butyl peroxytrimethylhexanoate, tert-butyl peroxyethylhexanoate, tert-amyl peroxyethylhexanoate, tert-octyl peroxyethylhexanoate, tert-amyl peroxyethylhexylcarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxyneodecanoate, tert-butyl peroxyisobutyrate, or tert-butyl hydroperoxide.

[0032] A primer is applied to the surface of the first adherend to be covered with the adhesive layer.

[0033] Optionally, before applying solidification initiation primer, one or more secondary primers are applied to the surface of the first adherend. Optionally, before applying solidification initiation primer, one or more secondary primers are applied to the surface of the second adherend. Secondary primer is not solidified and initiated usually.

[0034] In the practice of the present disclosure, any suitable curable adhesive film can be used. Curable adhesive films are generally pressure-sensitive adhesives (PSAs). Curable adhesive films are generally self-supporting films. Curable adhesive films are solid under NTP. In some embodiments, these films comprise a blend of the following substances: a reactive oligomer comprising an unsaturated free radical polymerizable group; an optional reducing agent; and an optional transition metal cation. In some embodiments, these films comprise a blend of the following substances: a reactive oligomer comprising a side chain unsaturated free radical polymerizable group; an optional reducing agent; and an optional transition metal cation. In some embodiments, these films comprise a blend of the following substances: a film-forming oligomer, a reactive substance comprising 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, curable adhesive film also includes a cross-linking 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 cross-linking agent is a cross-linking monomer. In some embodiments, the cross-linking agent is an oligomer. In some embodiments, 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, 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 curable adhesive film of the present disclosure, the strips comprising the curable adhesive film and their purposes are provided in selected embodiments and examples.

[0035] When present, any suitable transition metal cation may be used, including those listed above with respect to the cure initiating primer.

[0036] When present, any suitable reducing agent can be used, including organic 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 acid (particularly C2-C30 carboxylic acid or C12-C22 carboxylic acid). 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, linolenic 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, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, methyldiphenylamine, and isoamyl 4-dimethylaminobenzoate. In other embodiments, the reducing agent may be a sodium sulfinate derivative or an organometallic compound.

[0037] 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 their production method can be as taught in EP 1800865. Such channels achieve unique purposes in the use of the article of the present disclosure. By allowing trapped bubbles to escape, the degassing channels can help improve contact with the primer. Alternatively, when the adhesive film or tape 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 adapts to uneven surfaces, although these substrates are non-flexible.

[0038] Upon contact with the cure-initiating primer, the curable adhesive film begins to cure, forming a bond having the strength of a structural adhesive.

[0039] In some embodiments of method as herein described, the loss of adhesiveness is uncommon at the temperature that rises, because this is carried out by reversible mechanism.If substrate does not separate, when returning NTP, tackiness agent can get back to 70%, 80% or even 90% of its intensity.This can make an adherend can debond from many adherends that are attached on the substrate and can not adversely affect other adherends, such as being bonded to the 3rd adherend, the 4th adherend or the 5th adherend of the first adherend or the second adherend by identical adhesive system (primer and adhesive layer).In addition, this can make adherend reposition relative to each other by being heated to release temperature, and cooling (or allowing cooling) realizes the repositioning in conjunction with adherend in conjunction with goods.

[0040] Additional embodiments of the disclosure are described in the following selected embodiments and examples.

[0041] Selected implementation plans

[0042] 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.

[0043] M1. A method comprising:

[0044] a) providing a bonded product, said bonded product comprising, in order:

[0045] i) a first adherend;

[0046] ii) a first primer layer;

[0047] iii) an adhesive layer;

[0048] iv) an optional second primer layer; and

[0049] v) a second adherend;

[0050] b) heating the article to a release temperature; and

[0051] c) separating the first adherend and the second adherend so that they are no longer bonded together by the adhesive layer;

[0052] wherein the release temperature is a temperature between 100° C. and 150° C.;

[0053] wherein the adhesive layer exhibits a lap shear greater than 1.0 MPa (145 psi) at room temperature as determined by the Lap Shear Test Method described herein; and

[0054] wherein the adhesive layer exhibits a lap shear of no more than 0.34 MPa (50 psi) at the release temperature as determined by the Lap Shear Test Method described herein.

[0055] M2. The method of embodiment M1, wherein the release temperature is a temperature between 105°C and 135°C.

[0056] M3. The method of embodiment M1, wherein the release temperature is a temperature between 105°C and 120°C.

[0057] M4. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 1.5 MPa (218 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0058] M5. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 2.0 MPa (290 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0059] M6. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 2.5 MPa (363 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0060] M7. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 3.0 MPa (435 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0061] M8. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 3.5 MPa (508 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0062] M9. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 4.0 MPa (580 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0063] M10. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 4.5 MPa (653 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0064] M11. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 5.0 MPa (725 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0065] M12. The method of any one of embodiments M1 to M3, wherein the adhesive layer exhibits a lap shear greater than 5.5 MPa (798 psi) at room temperature as determined by the Lap Shear Test Method described herein.

[0066] M13. The method of any one of embodiments M1 to M12, wherein the adhesive layer exhibits a lap shear of no more than 0.31 MPa (45 psi) at the release temperature as determined by the Lap Shear Test Method described herein.

[0067] M14. The method of any one of embodiments M1 to M12, wherein the adhesive layer exhibits a lap shear of no more than 0.28 MPa (40 psi) at the release temperature as determined by the Lap Shear Test Method described herein.

[0068] M15. The method of any one of embodiments M1 to M12, wherein the adhesive layer exhibits a lap shear of no more than 0.24 MPa (35 psi) at the release temperature as determined by the Lap Shear Test Method described herein.

[0069] M16. The method of any one of embodiments M1 to M12, wherein the adhesive layer exhibits a lap shear of no more than 0.21 MPa (30 psi) at the release temperature as determined by the Lap Shear Test Method described herein.

[0070] MC1. The method of any one of embodiments M1 to M16, wherein the adhesive layer comprises:

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

[0072] ii) a cured polymer comprising a polymer of a first species, the first species comprising a first unsaturated free-radically polymerizable group;

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

[0074] iv) quaternary ammonium salts.

[0075] MC2. The method of embodiment MC1, wherein the first film-forming polymer or oligomer is a (meth)acrylate polymer or oligomer.

[0076] MC3. The method of any one of embodiments MC1 to MC2, wherein the cured polymer is a (meth)acrylate polymer or oligomer.

[0077] MC4. The method of any one of embodiments MC1 to MC3, wherein the first substance comprises two or more first unsaturated free-radically polymerizable groups.

[0078] MC5. The method of any one of embodiments MC1 to MC3, wherein the first substance comprises three or more first unsaturated free-radically polymerizable groups.

[0079] MC6. The method of any one of embodiments MC1 to MC3, wherein the first substance comprises four or more first unsaturated free-radically polymerizable groups.

[0080] MC7. The method of any one of embodiments MC1 to MC6, wherein the first unsaturated free-radically polymerizable group is a (meth)acryloyl group.

[0081] MC8. The method of any one of embodiments MC1 to MC7, wherein the cured polymer is a peroxide-cured polymer.

[0082] MC9. The method of any one of embodiments MC1 to MC8, wherein the adhesive layer comprises a quaternary ammonium salt.

[0083] 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.

[0084] Example

[0085] Unless otherwise noted, all reagents were obtained or purchased from Aldrich Chemical Co., Milwaukee, WI, or could be synthesized by known methods.

[0086] 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 %" are used interchangeably.

[0087] Material

[0088]

[0089]

[0090] Synthesis of copolymer 1

[0091] 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.

[0092] Compounding of BTEAC dispersions

[0093] A masterbatch premix was prepared by mixing 2640 g of BTEAC and 9360 g of M410 for 30 minutes using a Cowles blade blender (DISPERMAT CN-10, BYK-Gardner, Columbia, MD, USA) until homogeneous. The mixed materials were transferred to an HCPS-1 / 4 immersion mill (Hockmeyer Equipment Corporation, Elizabeth City, NC, USA) equipped with a 0.50 mm wedge screen loaded with approximately 550 g 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. to 85° C. during milling using a thermostatic bath / immersion circulator (HAAKE P1-C41P with Phoenix II controller, Thermo Fisher Scientific, NH, USA). The material was milled for 2 hours to a D90 of 15.74 μm PSD. Particle size was measured as described in the test methods below.

[0094] Hot Melt Compounding of PSA Adhesive Tapes

[0095] The pressure-sensitive adhesive coated tape was prepared using a 30 mm diameter co-rotating twin-screw extruder (available as "ZSK-30" from Werner & Pfleiderer, Ramsey, NJ). The twin-screw extruder had 12 zones, each corresponding to one-twelfth of the screw length, and a length-to-diameter ratio of 36:1. The twin-screw extruder was operated at 300 rpm, with temperatures of 250°F (121.1°C) in zones 1-7 and 220°F (104.4°C) in zones 8-12. The pouches of Copolymer 1 were fed into a 2-inch (51 mm) single-filler extruder available from Bonnot, 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 3 The mixture was pumped at a rate of 100 psi / min 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 approximately 5 mils (0.13 mm) thick onto a silicone-coated, multi-coated kraft paper release liner. The coated PSA transfer tape thus formed was used as described in Examples 1-3 below.

[0096] Test methods

[0097] Particle size measurement

[0098] 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 with MEK to approximately 1% solids by weight. The diluted sample was then added to a measurement chamber containing 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.

[0099] Lap shear test

[0100] An aluminum substrate measuring 1 inch by 4 inches by 0.064 inches (2.5 cm by 10 cm by 1.6 mm) was washed with MEK, a 50 / 50 solution of water / IPA, and acetone, then air-dried. The primer was applied as described. A 1 inch by 1 inch (2.5 cm by 2.5 cm) section of PSA transfer tape was applied to the end above the top of the primer. The release liner was removed, and a second primed aluminum substrate was applied to the sample adhesive, closing the bond (total bond area was 1 inch by 1 inch (2.5 cm by 2.5 cm)) 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 per minute. The bonded test assembly was allowed to rest as described before testing.

[0101] Dynamic lap shear testing was performed at the indicated temperatures using a Sintech 5 tensile tester (MTS, Eden Prairie, MN) equipped with a variable temperature oven. The test specimens were loaded into the holders inside the oven and the crosshead was operated at 0.1 inches per minute, thereby loading the specimens to failure. Peak stress was recorded in pounds per square inch (PSI).

[0102] ASTM designation: D 1002. Data are reported in pounds per square inch.

[0103] Example

[0104] Example 1

[0105] A cure-initiating primer was prepared by mixing 0.80 g of TBEC into 20.0 g of UPUV in a 40 mL glass vial. The primer was applied to both substrates by gently wiping the surface three times with a small Kim Wipe that had been dipped in the primer mixture. Test specimens for lap shear testing were assembled as described above and allowed to stand at 71°F (22°C) for 24 hours prior to testing.

[0106] Example 2

[0107] Test specimens for lap shear testing were prepared as in Example 1, except that the testing was performed after 24 hours at 120°F (48.9°C).

[0108] Example 3

[0109] Test specimens for lap shear testing were prepared as in Example 1, except that the testing was performed after 7 days at 71°F (22°C).

[0110] Comparative Example 1

[0111] Test specimens for lap shear testing were prepared as in Example 1, except that 468MP was used as the adhesive layer and applied to a clean substrate without any primer. Testing was performed after 24 hours at 71°F (22°C).

[0112] Comparative Example 2

[0113] Test specimens for lap shear testing were prepared as in Example 1, except that 4941 was used as the adhesive layer and applied to a clean substrate without any primer applied. Testing was performed after 24 hours at 71°F (22°C).

[0114] Comparative Example 3

[0115] Prepared as in Example 1, except that 4941 was used and the primer applied was UPUV. Test specimens for lap shear testing were prepared as in Example 1, except that 4941 was used as the adhesive layer and the primer was a non-curing initiating primer, UPUV. Testing was performed after 24 hours at 71°F (22°C).

[0116] Comparative Example 4

[0117] Prepared as in Example 1 except using 4941. For the purpose of creating a control experiment, a cure initiating primer was used but was not expected to initiate any cure in the 4941 tapes. Testing was performed after 24 hours at 71°F (22°C).

[0118] Comparative Example 5

[0119] Prepared as in Example 1 except using 4941. Used UPUV primer on one substrate and cure initiating primer on the other. Tested after 24 hours at 71°F (22°C).

[0120] Table 1a. Lap shear adhesion as measured by peak stress (lbf / in²) as a function of temperature (°F). number

[0121]

[0122] NT = Not Tested

[0123] Table 1b. Lap shear adhesion measured by peak stress (MPa) as a function of temperature (°C)

[0124]

[0125] NT = Not Tested

[0126] At elevated temperatures, adhesive separation or "popping" is observed. At low temperatures, a combination of adhesive and cohesive separation is observed.

[0127] It can be seen that adhesives according to the present disclosure can provide structural strength bonds, however, these structural strength bonds can be weakened to the point where they can be manually removed for purposes such as reworking or recycling the bonded substrate.

[0128] Various modifications and alterations to 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 method for reversing structural strength adhesive bonding, comprising: a) providing a bonded product, said bonded product comprising, in order: i) a first adherend; ii) a first primer layer; iii) an adhesive layer; iv) a second primer layer; and v) a second adherend; wherein the adhesive layer comprises: i) a first film-forming polymer or oligomer; ii) a peroxide-cured polymer comprising a polymer of a first substance comprising a first unsaturated free-radically polymerizable group; iii) a first transition metal cation; and optionally iv) a quaternary ammonium salt, wherein the adhesive layer has been cured by primer-initiated curing of an oxidizing agent containing peroxide groups included in the primers of the first and second primer layers, and wherein the adhesive layer exhibits a lap shear greater than 1.5 MPa (218 psi) at room temperature as measured by a lap shear test method according to ASTM D1002; b) debonding the adhesive layer by heating the bonded article to a release temperature between 100° C. and 150° C., wherein the adhesive layer exhibits a lap shear of no more than 0.34 MPa (50 psi) at the release temperature as measured by the lap shear test method according to ASTM D1002; and c) separating the first adherend and the second adherend so that they are no longer bonded together by the adhesive layer.

2. The method of claim 1, wherein the release temperature is a temperature between 105°C and 135°C.

3. The method of claim 1, wherein the release temperature is a temperature between 105°C and 120°C.

4. The method of claim 1, wherein the adhesive layer exhibits a lap shear greater than 3.0 MPa (435 psi) at room temperature as measured by the lap shear test method according to ASTM D1002.

5. The method of claim 1, wherein the adhesive layer exhibits a lap shear greater than 5.0 MPa (725 psi) at room temperature as measured by the lap shear test method according to ASTM D1002.

6. The method of claim 1, wherein the adhesive layer exhibits a lap shear of no greater than 0.28 MPa (40 psi) at the release temperature as measured by the lap shear test method according to ASTM D1002.

7. The method of claim 1, wherein the first film-forming polymer or oligomer is a (meth)acrylate polymer or oligomer.

8. The method of claim 1, wherein the cured polymer is a (meth)acrylate polymer or oligomer.

9. The method of claim 1, wherein the first substance comprises two or more first unsaturated free radical polymerizable groups.

10. The method of claim 1, wherein the first substance comprises three or more first unsaturated free radical polymerizable groups.

11. The method of claim 1, wherein the first substance comprises four or more first unsaturated free radical polymerizable groups.

12. The method of claim 1, wherein the first unsaturated free radical polymerizable group is a (meth)acryloyl group.

13. The method of claim 1, wherein the adhesive layer comprises a quaternary ammonium salt.

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