Curable precursors for structural adhesive compositions

Abstract

The present disclosure relates to a curable precursor of a structural adhesive composition, the curable precursor comprising: a heat-curable resin; a heat-curing initiator for the heat-curable resin; a radiation-self-polymerizable multifunctional compound comprising a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone; and a free radical polymerization initiator for the radiation-self-polymerizable multifunctional compound.

Description

Technical Field

[0001] The present disclosure relates generally to the field of adhesives, and more particularly to the field of structural adhesive compositions and films, particularly for bonding metal parts. More particularly, the present disclosure relates to a curable precursor of a structural adhesive composition and a partially cured precursor composition. The present disclosure also relates to a method of bonding two parts and a composite article. The present disclosure also relates to the use of a curable precursor of a structural adhesive composition for construction applications and automotive applications, particularly for body-in-white bonding applications in the automotive industry. Background Art

[0002] Adhesives have been used for multiple fixing, sealing, protection, marking and masking purposes. One type of adhesive particularly preferably used for many applications is represented by structural adhesives. Structural adhesives are generally thermosetting resin compositions, which can be used to replace or enhance conventional joining techniques, such as screws, bolts, nails, staples, rivets and metal fusion processes (e.g. welding, brazing and soldering). Structural adhesives are used for multiple applications, including general purpose industrial applications and high performance applications in automotive and aerospace industries. As suitable structural adhesives, adhesives should show high mechanical strength and durable mechanical strength, as well as high impact resistance.

[0003] In particular, structural adhesives can be used for metal joints in vehicles. For example, adhesives can be used to bond metal panels such as vehicle roofs to the supporting structure or chassis of the vehicle. In addition, adhesives can be used to bond two metal panels of a vehicle closure panel. A vehicle closure panel typically includes an assembly of an outer metal panel and an inner metal panel, whereby an edge of the outer panel is folded onto the edge of the inner panel to form an edge-wrapped structure. Typically, an adhesive is provided between the inner and outer panels to bond the panels together. In addition, a sealant is typically required to be applied to the joint of the metal panels to provide sufficient corrosion resistance. For example, U.S. Pat. No. 6,000,118 (Biernat et al.) discloses the use of a flowable sealant bead between the facing surfaces of two panels, and a film of an uncured lacquer-like resin is used between the flange on the outer panel and the exposed surface of the inner panel. The paint film is cured to a solid, impermeable state by performing a baking operation on the complete door panel. U.S. Pat. No. 6,368,008 (Biernat et al.) discloses the use of an adhesive to fix two metal panels together. The edge of the joint is also sealed by a metal coating. WO 2009 / 071269 (Morral et al.) discloses an expandable paste epoxy resin adhesive as a sealant for hemming flanges. Additional hemming structures are disclosed in U.S. Patent 6,528,176 (Asai et al.). Further efforts have been made to develop adhesive compositions whereby an adhesive can be used to join two metal panels (particularly the outer and inner panels of a vehicle closure panel) without the need for additional materials to seal the joint. Therefore, it is desirable to develop an adhesive system that seals the joint and provides corrosion resistance while providing adequate bonding. Partial solutions have been described, for example, in WO2007 / 014039 (Lamon), which discloses a heat expandable and curable epoxy-based precursor of an expanded thermosetting film toughened foaming film, the foaming film comprising a mixture of a solid epoxy resin and a liquid epoxy resin, and is claimed to provide both favorable energy absorption properties and gap filling properties when cured. Other partial solutions have been described in EP-A1-2700 683 (Elgimiabi et al.) and WO 2017 / 197087 (Aizawa), which disclose structural adhesive films suitable for forming hemmed flange structures. Structural adhesive films or tapes generally lack elasticity and have insufficient adhesion, which makes them only partially suitable for hemmed flange bonding. Other partial solutions have been described in US-A1-2018 / 0127625 (Shafer et al.), which discloses so-called structural bonding tapes. Structural bonding tapes are generally suboptimal in terms of performance attributes such as bond strength, stability and corrosion resistance.

[0004] Without questioning the technical advantages associated with the solutions known in the art, there remains a need for structural adhesive compositions that overcome the above-mentioned drawbacks. Summary of the invention

[0005] According to one aspect, the present disclosure is directed to a curable precursor of a structural adhesive composition, the curable precursor comprising:

[0006] a) heat curable resin;

[0007] b) heat curing initiators for heat curable resins;

[0008] c) a radiation self-polymerizable multifunctional compound comprising a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone; and

[0009] d) Free radical polymerization initiators for radiation self-polymerizable polyfunctional compounds.

[0010] According to another aspect, the present disclosure is directed to a partially cured precursor of a structural adhesive composition, the partially cured precursor comprising:

[0011] a) a polymeric material comprising a self-polymerization reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound;

[0012] b) optionally, some residual free radical polymerization initiator for the radiation self-polymerizable multifunctional compound;

[0013] c) a heat curable resin; and

[0014] d) a thermal curing initiator for the thermally curable resin; and

[0015] The heat-curable resin is (substantially) uncured.

[0016] In another aspect of the present disclosure, a method for bonding two components is provided, the method comprising the following steps:

[0017] a) applying a curable precursor or partially cured precursor as described above to a surface of at least one of the two components;

[0018] b) joining the two components such that the curable precursor or the partially cured precursor (mixed) structural adhesive composition is positioned between the two components; and

[0019] c) optionally, partially curing the curable precursor according to step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; and / or

[0020] d) substantially completely curing the partially cured precursor of step a) or c) by initiating a thermal curing initiator for the thermally curable resin to obtain a substantially completely cured (mixed)

[0021] Structural adhesive compositions bond two components.

[0022] According to yet another aspect, the present disclosure relates to the use of a curable precursor or a partially cured precursor as described above for industrial applications, in particular for construction and automotive applications. DETAILED DESCRIPTION

[0023] According to a first aspect, the present disclosure relates to a (mixed) curable precursor of a structural adhesive composition, the curable precursor comprising:

[0024] a) heat curable resin;

[0025] b) heat curing initiators for heat curable resins;

[0026] c) a radiation self-polymerizable multifunctional compound comprising a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone; and

[0027] d) Free radical polymerization initiators for radiation self-polymerizable polyfunctional compounds.

[0028] In the context of the present disclosure, it has been surprisingly found that the curable precursors as described above are particularly suitable for making structural adhesive compositions having excellent characteristics and properties with respect to elasticity, tack, cold flow, flexibility, handling characteristics and surface wetting in their uncured (or precured) state, and bond strength, aging stability and corrosion resistance in their fully cured state. It has been surprisingly found that the curable precursors of the structural adhesive compositions as described above combine most of the advantageous features of both structural adhesive films and structural bonding tapes known in the art without exhibiting their known drawbacks.

[0029] It has further been discovered that, in some embodiments, the curable precursors described above are provided with advantageous thixotropic properties, which make them particularly suitable for the manufacture of multi-dimensional structural adhesive articles and objects, particularly via suitable printing techniques.

[0030] Still surprisingly, it has been found that the curable precursors described above are particularly suitable for making one-part curable precursors for structural adhesive compositions due to their excellent chemical stability, and despite the different chemistry of the hybrid curing system employed. One-part curable precursors are superior to two-part curable precursor compositions because they do not require any specific delayed mixing steps or associated equipment, and generally offer more processing flexibility.

[0031] It has also been surprisingly discovered that, in some embodiments, the curable precursors described above are suitable for making structural adhesive compositions having excellent characteristics and performance in terms of adhesion to oil-contaminated substrates such as stainless steel and aluminum.

[0032] Without wishing to be bound by theory, it is believed that these excellent properties are due in particular to the presence of a specific hybrid curing system in the curable precursor, which involves: a) heat-induced curing of the heat-curable resin, and b) radiation-induced self-polymerization of the polyfunctional compound as specified above. Still without being bound by theory, it is believed that this dual-cure system / hybrid curing system involves two independent reaction systems, which have different chemical natures and which co-exist in the curable precursor without interfering with each other, which is able to form an interpenetrating network when fully cured, which interpenetrating network involves a polymer material comprising a self-polymerization reaction product of a polymerizable material and a polymerization product resulting from thermal curing of the heat-curable resin, the polymerizable material comprising a self-polymerizable polyfunctional compound.

[0033] More specifically, the above-described hybrid cure system is particularly suitable for implementing an overall cure mechanism involving a two-stage reaction, whereby two polymer networks are formed sequentially.

[0034] In the first stage reaction (stage B), the radiation self-polymerizable multifunctional compound self-polymerizes when initiated by a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a polymeric material containing a self-polymerization reaction product of a polymerizable material, the polymerizable material containing the self-polymerizable multifunctional compound. Typically, the temperature T1 at which the free radical polymerization initiator for the radiation self-polymerizable multifunctional compound is initiated is not sufficient to cause the initiation of the thermal curing initiator of the heat-curable resin. Therefore, the first stage reaction typically produces a partially cured precursor, in which the heat-curable resin is substantially uncured and is particularly embedded in a polymeric material containing a self-polymerization reaction product of a polymerizable material, the polymerizable material containing the self-polymerizable multifunctional compound.

[0035] The first stage reaction is generally referred to as a film-forming reaction, which generally results in a phase change in the initial curable precursor, particularly because the polymer material comprising the self-polymerization reaction product of the self-polymerizable multifunctional compound provides structural integrity to the initial curable precursor. Advantageously, the first stage reaction generally does not require any significant energy input.

[0036] The partially cured precursor can usually take the form of a film-like self-supporting composition or multidimensional object with dimensional stability, which makes it possible to pre-apply it to a selected substrate, particularly a liner, until further processing. The partially cured precursor usually has excellent characteristics and performances about elasticity, tackiness, cold flow and surface wettability. It is believed that the radiation self-polymerizable polyfunctional compound comprising a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone plays a key role in obtaining the favorable characteristics of the partially cured precursor as described above. Advantageously, the partially cured precursor can be appropriately shaped to meet the requirements of any specific application.

[0037] The second stage reaction (A stage) occurs after the first stage reaction and involves thermally curing the heat-curable resin when thermally initiated by a suitable heat-curing initiator at a temperature T2 that is generally greater than temperature T1. This reaction step generally results in the formation of a polymer product resulting from the heat curing of the heat-curable resin, in particular from the (co)polymerization of the heat-curable resin and a heat-curing initiator (or curing agent) for the heat-curable resin.

[0038] The curable precursors of the present disclosure generally rely on the above-mentioned dual-cure system / hybrid-cure system, which involves two independent reaction systems activated with different triggering steps to ensure that the above-mentioned two-stage reaction is carried out in a sequential manner. Advantageously, the curable precursors of the present disclosure can be partially cured (or pre-cured) and pre-applied on a selected substrate, and then finally cured in situ to produce a structural adhesive with excellent characteristics directly on the desired substrate or article.

[0039] Therefore, the curable precursors of the present disclosure are particularly suitable for bonding metal parts, especially for hemming flange bonding of metal parts in the automotive industry. The curable precursors of the structural adhesive compositions as described herein are also extremely suitable for making multi-dimensional structural adhesive articles and objects. Still advantageously, the curable precursors are suitable for automated processing and application, especially automated processing and application by fast robotic equipment.

[0040] In the context of the present disclosure, the expression "radiation self-polymerizable compound" means a compound capable of forming a polymer product (homopolymer) produced by almost complete radiation-induced polymerization of the compound with itself, thereby forming a homopolymer. The term "homopolymer" refers herein to one or more polymers produced entirely by the polymerization of a single type of monomer.

[0041] Still in the context of the present disclosure, the expression "thermally curable resin" means a resin / monomer capable of forming a polymer product (heteropolymer) resulting from the thermally induced (co)polymerization of a curable resin and a thermal curing initiator (or curing agent) of the thermally curable resin. The term "heteropolymer" herein means a polymer resulting from the (co)polymerization of more than one type of monomer.

[0042] In the context of the present disclosure, the expression "the heat-curable resin is substantially uncured" means that less than 10 wt%, less than 5 wt%, less than 2 wt% or even less than 1 wt% of the initial curable resin is unreacted.

[0043] The terms "glass transition temperature" and "Tg" are used interchangeably and refer to the glass transition temperature of a (co)polymer material or mixture of monomers and polymers. Unless otherwise indicated, glass transition temperature values ​​are determined by differential scanning calorimetry (DSC).

[0044] According to one typical aspect of the curable precursor of the present disclosure, a free radical polymerization initiator is initiated at a temperature T1, wherein a thermal curing initiator is initiated at a temperature T2, wherein the temperature T2 is greater than the temperature T1, and wherein the temperature T1 is insufficient to cause initiation of the thermal curing initiator, which thus remains substantially unreacted.

[0045] According to another typical aspect of the curable precursor of the present disclosure, the temperature T1 is no greater than 90°C, no greater than 80°C, no greater than 60°C, no greater than 50°C, no greater than 40°C, no greater than 30°C, no greater than 25°C, no greater than 20°C or even no greater than 15°C.

[0046] According to yet another typical aspect of the curable precursor of the present disclosure, the temperature T1 ranges from -10°C to 85°C, 0°C to 80°C, 5°C to 60°C, 5°C to 50°C, 10°C to 40°C or even 15°C to 35°C.

[0047] According to yet another typical aspect of the present disclosure, temperature T2 is greater than 90°C, greater than 100°C, greater than 120°C, greater than 140°C, greater than 150°C, greater than 160°C, greater than 180°C or even greater than 200°C.

[0048] According to yet another typical aspect of the present disclosure, temperature T2 is in the range of 95-250°C, 100-220°C, 120-200°C, 140-200°C, 140-180°C or even 160-180°C.

[0049] In another typical aspect of the curable precursor of the present disclosure, the heat-curable resin and the radiation-self-polymerizable multifunctional compound are (substantially) incapable of chemically reacting with each other, especially chemically reacting with each other through covalent bonds, even when subjected to polymerization or curing initiation. In an exemplary aspect, when subjected to polymerization or curing initiation at a temperature of 23° C., the heat-curable resin and the radiation-self-polymerizable multifunctional compound are (substantially) incapable of chemically reacting with each other.

[0050] The heat curable resin used in this article is not particularly limited. Any heat curable resin commonly known in the field of structural adhesives can be used in the context of this disclosure. According to this disclosure, those skilled in the art can easily identify suitable heat curable resins for use in this article.

[0051] According to an advantageous aspect of the present disclosure, the heat-curable resin used herein comprises at least one functional group selected from epoxy groups, in particular glycidyl groups.

[0052] According to another advantageous aspect, the heat-curable resin used herein comprises at least one epoxy resin. Exemplary epoxy resins used herein can be advantageously selected from epoxy novolac resins, bisphenol epoxy resins, hydrogenated epoxy resins, aliphatic epoxy resins, halogenated bisphenol epoxy resins, novolac epoxy resins, and any mixtures thereof.

[0053] Epoxy resins are well known to those skilled in the art of structural adhesive compositions. Suitable epoxy resins for use herein and methods for making them are fully described in, for example, EP-A1-2 700 683 (Elgimiabi et al.) and WO 2017 / 197087 (Aizawa).

[0054] In one particularly advantageous aspect of the present disclosure, the heat-curable resin for use herein is an epoxy resin selected from novolac epoxy resins, bisphenol epoxy resins, particularly those derived from the reaction of bisphenol-A with epichlorohydrin (DGEBA resins), and any mixtures thereof.

[0055] The heat curing initiator for the heat curable resin used herein is not particularly limited. Any heat curing initiator for the heat curable resin commonly known in the field of structural adhesives can be used in the context of the present disclosure. According to the present disclosure, those skilled in the art can easily identify suitable heat curing initiators for use herein.

[0056] According to a typical aspect of the present disclosure, the thermal curing initiator used herein is selected from a fast-reacting curing initiator, a latent curing initiator, and any combination or mixture thereof. More typically, the thermal curing initiator used herein is selected from a fast-reacting thermal initiation curing initiator, a latent thermal initiation curing initiator, and any combination or mixture thereof.

[0057] According to an advantageous aspect of the present disclosure, the thermal curing initiator is selected from primary amines, secondary amines, and any combination or mixture thereof.

[0058] According to another advantageous aspect, the amine used as thermal curing initiator for the thermally curable resin is selected from aliphatic amines, cycloaliphatic amines, aromatic amines, aromatic structures having one or more amino moieties, polyamines, polyamine adducts, dicyandiamide and any combination or mixture thereof.

[0059] According to yet another advantageous aspect of the present disclosure, the heat curing initiator used herein is selected from dicyandiamide, polyamine, polyamine adduct, and any combination or mixture thereof.

[0060] In a preferred aspect, the curing initiator for the heat-curable resin of the present disclosure is selected to be dicyandiamide.

[0061] In an advantageous embodiment, the curable precursor of the present disclosure also includes a thermal curing accelerator for the thermally curable resin. Any thermal curing accelerator for the thermally curable resin commonly known in the field of structural adhesives can be used in the context of the present disclosure in a formal manner. According to the present disclosure, those skilled in the art can easily identify suitable thermal curing initiators for use herein.

[0062] Thermal curing initiators and thermal curing accelerators are well known to those skilled in the art of structural adhesive compositions. Suitable thermal curing initiators and thermal curing accelerators for use herein and methods for making the same are fully described in, for example, EP-A1-2 700683 (Elgimiabi et al.) and WO 2017 / 197087 (Aizawa).

[0063] In an advantageous embodiment, the thermal curing accelerator used herein is selected from polyamines, polyamine adducts, urea, substituted urea adducts, imidazoles, imidazole salts, imidazolines, aromatic tertiary amines, and any combination or mixture thereof.

[0064] In a preferred embodiment, the heat curing accelerator for the heat curable resin is selected from polyamine adducts, substituted ureas, and in particular N-substituted urea adducts.

[0065] In a particularly preferred embodiment of the present disclosure, the thermal curing accelerator for the thermally curable resin is selected from substituted urea adducts, in particular N-substituted urea adducts. In the context of the present disclosure, it has surprisingly been found that the use of a thermal curing accelerator for the thermally curable resin selected from substituted urea adducts, in particular N-substituted urea adducts, significantly improves the adhesion properties, in particular the peel adhesion properties, of the resulting structural adhesive composition. Without wishing to be bound by theory, it is believed that the use of a thermal curing accelerator selected from substituted urea adducts, in particular N-substituted urea adducts, favorably affects the overall curing profile of the curable precursor according to the present disclosure, which in turn translates into improved adhesion properties.

[0066] According to an advantageous aspect of the present disclosure, the curable precursor may further comprise a second heat-curable resin, which is typically different from the (first) heat-curable resin, as described above.

[0067] In an advantageous aspect, the heat-curable resin used in the present disclosure comprises at least one functional group selected from epoxy groups, in particular glycidyl groups. Still advantageously, the heat-curable resin used herein is an epoxy resin, in particular selected from epoxy novolac resins, bisphenol epoxy resins, hydrogenated epoxy resins, aliphatic epoxy resins, halogenated bisphenol epoxy resins, novolac epoxy resins and any mixtures thereof.

[0068] In a particularly preferred embodiment of the present disclosure, the second heat-curable resin used herein is an epoxy resin selected from halogenated bisphenol epoxy resins, particularly those derived from the reaction of halogenated bisphenol-A with epichlorohydrin (halogenated DGEBA resins), and any mixtures thereof. In the context of the present disclosure, it has surprisingly been found that the use of a second heat-curable resin particularly selected from hydrogenated bisphenol epoxy resins substantially maintains or even improves the adhesion properties, particularly the peel adhesion properties, of the resulting structural adhesive composition to oil-contaminated substrates. These particular curable precursors are particularly suitable for forming structural adhesive compositions having excellent oil resistance, particularly to oil-contaminated metal substrates.

[0069] Exemplary oily contaminants are, for example, mineral oils and synthetic oils. Typical mineral oils include paraffinic mineral oils, intermediate mineral oils, and naphthenic mineral oils.

[0070] According to typical aspects, the curable precursor according to the present disclosure comprises 2 wt % to 50 wt %, 2 wt % to 40 wt %, 3 wt % to 40 wt %, 5 wt % to 30 wt %, 10 wt % to 30 wt %, or even 15 wt % to 30 wt % of the thermally curable resin, wherein the weight percentages are based on the total weight of the curable precursor.

[0071] The radiation self-polymerizable multifunctional compounds used herein are not particularly limited, as long as they contain a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone. According to the present disclosure, those skilled in the art can easily identify suitable radiation self-polymerizable multifunctional compounds used herein.

[0072] The polyether oligomer backbones used herein are not particularly limited as long as they meet the above detailed requirements. Based on this disclosure, those skilled in the art can easily identify suitable polyether oligomer backbones for use herein.

[0073] Without wishing to be bound by theory, it is believed that the radiation self-polymerizable multifunctional compound as described above not only participates in the formation of a polymer material comprising the self-polymerization reaction product of the self-polymerizing multifunctional compound under the stage B reaction described above and resulting in the phase change of the initial curable precursor, but also formally acts as a reactive diluent, rheology modifier and compatibilizer for the curable precursor, which in turn helps to provide a curable precursor with excellent flexibility properties and a stage B reaction product with favorable elastic properties. It is also believed that the radiation self-polymerizable multifunctional compound as described above beneficially affects the adhesion properties of the curable precursor, particularly due to the beneficial surface wetting properties provided by the oligomeric polyether backbone, in particular.

[0074] In one advantageous aspect of the present disclosure, the radiation self-polymerizable multifunctional compound used herein comprises a polyether oligomer backbone having a number average molecular weight of at least 2000 g / mol.

[0075] Unless otherwise indicated, the number average molecular weight of the radiatable self-polymerizable multifunctional compounds is determined by conventional gel permeation chromatography (GPC) using appropriate techniques well known to those skilled in the art.

[0076] In beneficial aspects of the present disclosure, the polyether oligomer backbone used herein has a number average molecular weight greater than 2000 g / mol, greater than 2500 g / mol, greater than 3000 g / mol, greater than 3500 g / mol, or even greater than 4000 g / mol.

[0077] In another beneficial aspect of the present disclosure, the polyether oligomer backbone has a number average molecular weight of no greater than 10.000 g / mol, no greater than 9500 g / mol, no greater than 9000 g / mol, no greater than 8500 g / mol, or even no greater than 8000 g / mol.

[0078] In yet another beneficial aspect, the polyether oligomer backbone used in the present disclosure has a number average molecular weight in the range of 2000 g / mol to 20.000 g / mol, 2000 g / mol to 15.000 g / mol, 2000 g / mol to 12.000 g / mol, 2500 g / mol to 10.000 g / mol, 2500 g / mol to 9.000 g / mol, 3000 g / mol to 8500 g / mol, 3500 g / mol to 8000 g / mol, or even 4000 g / mol to 8000 g / mol.

[0079] In yet another advantageous aspect of the present disclosure, the polyether oligomer backbone comprises (or consists of) a linear polyether oligomer backbone.

[0080] According to an advantageous aspect, the (linear) polyether oligomer backbone used herein is obtained by copolymerization of tetrahydrofuran units, ethylene oxide units and optionally propylene oxide units.

[0081] In an advantageous aspect, at least one free radical (co)polymerizable reactive group located at each terminal position of the polyether oligomer backbone is selected from ethylenically unsaturated groups.

[0082] According to another advantageous aspect, the ethylenically unsaturated groups are selected from (meth)acrylic groups, vinyl groups, styryl groups, and any combination or mixture thereof.

[0083] In a more advantageous aspect of the present disclosure, the ethylenically unsaturated groups used herein are selected from methacrylic groups, acrylic groups, and any combination or mixture thereof.

[0084] In particularly preferred aspects of the present disclosure, the ethylenically unsaturated groups for use herein are selected from methacrylic acid groups.

[0085] Advantageously, the radiation self-polymerizable multifunctional compounds used herein are ethylenically unsaturated compounds.

[0086] According to one advantageous aspect of the curable precursor of the present disclosure, the radiation self-polymerizable multifunctional compound used herein has the following formula:

[0087]

[0088] in:

[0089] Y is a free radical (co)polymerizable reactive group, especially an ethylenically unsaturated group;

[0090] Each R 2 independently selected from alkylene groups, in particular having 2 to 6 carbon atoms;

[0091] and n is an integer which is specifically selected such that the calculated number average molecular weight of the radiation self-polymerizable multifunctional compound is at least 2000 g / mol.

[0092] According to another advantageous aspect of the present disclosure, the radiation self-polymerizable multifunctional compound has the following formula:

[0093]

[0094] in:

[0095] Each R 2 are independently selected from alkylene groups, in particular having 2 to 6 carbon atoms; and

[0096] n is an integer which is chosen in particular such that the calculated number average molecular weight of the radiation self-polymerizable multifunctional compound is in the range from 2000 g / mol to 20.000 g / mol.

[0097] In a particular aspect, n is selected so that the calculated number average molecular weight is at least 2000g / mol, at least 3000g / mol or even at least 4000g / mol. In another particular aspect, n is selected so that the calculated number average molecular weight is not more than 20.000g / mol, not more than 15.000g / mol or even not more than 10.000g / mol. In another specific aspect, n is selected so that the calculated number average molecular weight is between 2000g / mol and 20.000g / mol, between 3000g / mol and 15.000g / mol or even between 3000g / mol and 10.000g / mol, wherein all ranges include endpoints.

[0098] According to yet another advantageous aspect of the present disclosure, the radiation self-polymerizable multifunctional compound has the following formula:

[0099]

[0100] in:

[0101] n is an integer which is chosen in particular such that the calculated number average molecular weight of the radiation self-polymerizable polyfunctional compound is in the range from 2000 g / mol to 20.000 g / mol.

[0102] According to yet another advantageous aspect of the present disclosure, the radiation self-polymerizable multifunctional compound has the following formula:

[0103]

[0104] in:

[0105] a and b are integers greater than or equal to 1, the sum of a and b equals n, and wherein n is particularly selected such that the calculated number average molecular weight of the polyether oligomer is in the range of 2000 g / mol to 20.000 g / mol.

[0106] In a particular aspect, n is selected so that the calculated number average molecular weight is at least 2000g / mol, at least 3000g / mol or even at least 4000g / mol. In another particular aspect, n is selected so that the calculated number average molecular weight is not more than 20.000g / mol, not more than 15.000g / mol or even not more than 10.000g / mol. In another specific aspect, n is selected so that the calculated number average molecular weight is between 2000g / mol and 20.000g / mol, between 3000g / mol and 15.000g / mol or even between 3000g / mol and 10.000g / mol, wherein all ranges include endpoints.

[0107] According to yet another advantageous aspect of the present disclosure, the linear polyether oligomer backbone is obtained by copolymerization of tetrahydrofuran units and ethylene oxide units, wherein the molar ratio of these monomer units ranges from 1:2.5 to 1:5 or even from 1:3 to 1:4.

[0108] According to yet another advantageous aspect, the radiation self-polymerizable multifunctional compound used in the present disclosure has a glass transition temperature (Tg) of no greater than 20°C, no greater than 15°C, or even no greater than 10°C, when measured by differential scanning calorimetry (DSC).

[0109] Without wishing to be bound by theory, it is believed that radiation self-polymerizable multifunctional compounds having a glass transition temperature (Tg) of no greater than 20°C, no greater than 15°C, or even no greater than 10°C are provided with favorable viscoelastic properties, which in turn are believed to beneficially contribute to providing the favorable properties described above with respect to the overall radiation self-polymerizable multifunctional compound.

[0110] In one advantageous aspect, the curable precursor of the present disclosure contains no more than 25 weight percent, no more than 20 weight percent, no more than 15 weight percent, no more than 10 weight percent, or even no more than 8 weight percent of a radiation self-polymerizable multifunctional compound, wherein the weight percentages are based on the total weight of the curable precursor.

[0111] In another advantageous aspect, the curable precursor of the present disclosure comprises 0.5 wt % to 20 wt %, 0.5 wt % to 15 wt %, 1 wt % to 15 wt %, 2 wt % to 15 wt %, 2 wt % to 12 wt %, 2 wt % to 10 wt %, 3 wt % to 10 wt %, or even 3 wt % to 8 wt % of the radiation self-polymerizable multifunctional compound, wherein the weight percentages are based on the total weight of the curable precursor.

[0112] The curable precursor according to the present disclosure also includes a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound. The free radical polymerization initiator for the radiation self-polymerizable multifunctional compound used herein is not particularly limited. According to the present disclosure, those skilled in the art can easily identify suitable free radical polymerization initiators for the radiation self-polymerizable multifunctional compound used herein.

[0113] According to typical aspects of the present disclosure, the free radical polymerization initiator of the radiation-polymerizable multifunctional compound is selected from the group consisting of a Norrish type (I) free radical polymerization initiator, a Norrish type (II) free radical polymerization initiator, and any combination or mixture thereof.

[0114] According to an advantageous aspect of the present disclosure, the free radical polymerization initiator of the radiation-polymerizable multifunctional compound is selected from the group consisting of Norrish type (I) free radical polymerization initiators and any combination or mixture thereof.

[0115] According to a more advantageous aspect of the present disclosure, the free radical polymerization initiator used herein is selected from benzyl ketal, hydroxyacetophenone, aminoacetophenone, aryl alkyl ketone, phosphine oxide, benzoin ether, substituted acetophenone, substituted α-ketol, photoactive oxime and any combination or mixture thereof.

[0116] According to an even more advantageous aspect of the present disclosure, the free radical polymerization initiator used herein is selected from benzyl ketal, hydroxyacetophenone, and any combination or mixture thereof.

[0117] In a typical aspect, the curable precursor of the present disclosure comprises no more than 10 wt%, no more than 8 wt%, no more than 6 wt%, no more than 5 wt%, no more than 4 wt%, no more than 2 wt%, no more than 1 wt%, no more than 0.8 wt%, no more than 0.6 wt%, no more than 0.5 wt%, no more than 0.4 wt%, no more than 0.2 wt%, or even no more than 0.1 wt% of a free radical polymerization initiator of a radiation self-polymerizable multifunctional compound, wherein the weight percentages are based on the total weight of the curable precursor.

[0118] In another typical aspect, the curable precursor of the present disclosure comprises 0.01 wt % to 10 wt %, 0.01 wt % to 8 wt %, 0.02 wt % to 6 wt %, 0.02 wt % to 5 wt %, 0.02 wt % to 4 wt %, 0.03 wt % to 3 wt %, 0.03 wt % to 2 wt %, 0.03 wt % to 1.8 wt %, 0.03 wt % to 1.6 wt %, 0.03 wt % to 1.5 wt %, 0.03 wt % to 1.4 wt %, or even 0.03 wt % to 1 wt % of a free radical polymerization initiator of a radiation self-polymerizable multifunctional compound, wherein the weight percentages are based on the total weight of the curable precursor.

[0119] In one specific aspect of the curable precursor according to the present disclosure, the weight ratio of the radiation self-polymerizable multifunctional compound to the free radical polymerization initiator of the radiation self-polymerizable multifunctional compound ranges from 200:1 to 5:1, 180:1 to 8:1, 150:1 to 8:1, 100:1 to 8:1, or even 100:1 to 10:1.

[0120] According to one advantageous aspect, the curable precursor of the present disclosure comprises:

[0121] a) 5 to 40 wt%, 5 to 35 wt%, 10 to 35 wt%, 15 to 35 wt%, 15 to 30 wt%, or even 15 to 25 wt% of a heat curable resin;

[0122] b) 0.1 wt % to 20 wt %, 0.2 wt % to 15 wt %, 0.2 wt % to 10 wt %, 0.5 wt % to 8 wt %, 1 wt % to 6 wt %, or even 2 wt % to 5 wt % of a thermal curing initiator for the thermally curable resin;

[0123] c) 0.5 to 20 wt%, 0.5 to 15 wt%, 1 to 15 wt%, 2 to 15 wt%, 2 to 12 wt%, 2 to 10 wt%, 3 to 10 wt%, or even 3 to 8 wt% of a radiation self-polymerizable multifunctional compound;

[0124] d) 0.01 to 10 wt. %, 0.02 to 6 wt. %, 0.02 to 5 wt. %, 0.02 to 4 wt. %, 0.03 to 2 wt. %, 0.03 to 1.8 wt. %, 0.03 to 1.5 wt. % or even 0.03 to 1 wt. % of a free radical polymerization initiator for the radiation self-polymerizable polyfunctional compound;

[0125] e) optionally, 0.05 to 10 wt %, 0.1 to 8 wt %, 0.1 to 5 wt %, 0.2 to 4 wt %, 0.5 to 3 wt %, or even 1 to 3 wt % of a thermal curing accelerator for the thermally curable resin;

[0126] f) optionally, a toughening agent; and

[0127] g) optionally, a thixotropic agent;

[0128] The weight percentages are based on the total weight of the curable precursor.

[0129] In an advantageous embodiment, the curable precursor of the present disclosure may also include a thixotropic agent. Any thixotropic agent commonly known in the field of structural adhesives may be used in the context of the present disclosure in a formal manner. According to the present disclosure, those skilled in the art can easily identify suitable thixotropic agents for use herein.

[0130] According to an advantageous aspect of the present disclosure, the curable precursor further comprises a thixotropic agent, which is generally selected from inorganic thixotropic agents and organic thixotropic agents.

[0131] According to another advantageous aspect of the present disclosure, the thixotropic agent used herein is selected from particulate thixotropic agents.

[0132] According to a more advantageous aspect of the present disclosure, the thixotropic agent used herein is selected from inorganic thixotropic agents, in particular silicon-based thixotropic agents and aluminum-based thixotropic agents.

[0133] According to an even more advantageous aspect of the present disclosure, the thixotropic agent used herein is selected from silica-based thixotropic agents and silicate-based thixotropic agents.

[0134] In a very advantageous aspect, the curable precursor of the present disclosure further comprises a thixotropic agent selected from fumed silica particles, in particular hydrophilic fumed silica and hydrophobic fumed silica; silicate particles, in particular phyllosilicate, and any mixtures thereof.

[0135] In a particularly advantageous aspect of the present disclosure, the thixotropic agent used herein is selected from organic thixotropic agents, in particular polyamide waxes, hydrolyzed castor waxes, and thixotropic agents based on urea derivatives.

[0136] In another particularly advantageous aspect of the present disclosure, the thixotropic agent used herein is selected from fumed silica particles, especially hydrophobic fumed silica particles; silicate-based particles, especially phyllosilicate particles; polyamide waxes, and any mixtures thereof.

[0137] According to exemplary aspects of the present disclosure, the curable precursor includes no greater than 20 wt%, no greater than 15 wt%, no greater than 10 wt%, no greater than 8 wt%, or even no greater than 5 wt% of the thixotropic agent based on the total weight of the curable precursor.

[0138] According to another exemplary aspect of the present disclosure, the curable precursor contains 0.05 wt % to 20 wt %, 0.1 wt % to 15 wt %, 0.5 wt % to 10 wt %, 0.5 wt % to 8 wt %, 1 wt % to 6 wt %, or even 1 wt % to 5 wt % of a thixotropic agent, based on the total weight of the curable precursor.

[0139] The curable precursors of the present disclosure may take any suitable form, as is well known to those skilled in the art of structural adhesives. The suitable form will depend on the target application and conditions of use.

[0140] In a favorable aspect of the present disclosure, curable precursor is in the form of a one-part (mixed) structural adhesive composition. One-part curable precursors are superior to two-part curable precursor compositions because they do not involve any specific delayed mixing step, which usually requires special precautions, additional method steps and special equipment. The feature of one-part curable precursors is generally to provide more processing and formulation flexibility than its two-part counterparts. However, the present disclosure is not limited thereto.

[0141] Thus, and in an alternative aspect, the curable precursor of the present disclosure is in the form of a two-part (mixed) structural adhesive composition having a first part and a second part, wherein:

[0142] a) The first part comprises:

[0143] i. radiation-polymerizable multifunctional compounds; and

[0144] ii. a heat curing initiator for heat curable resins;

[0145] b) The second part comprises:

[0146] i. a heat curable resin; and

[0147] ii. a free radical polymerization initiator for a radiation self-polymerizable multifunctional compound;

[0148] wherein the first part and the second part are kept separate before combining the two parts and forming the (mixed) structural adhesive composition.

[0149] According to another alternative aspect, the curable precursor of the present disclosure is in the form of a two-part (mixed) structural adhesive composition having a first part and a second part, wherein:

[0150] a) The first part comprises:

[0151] i. radiation-polymerizable multifunctional compounds; and

[0152] ii. a free radical polymerization initiator for a radiation self-polymerizable multifunctional compound;

[0153] b) The second part comprises:

[0154] i. a heat curable resin; and

[0155] ii. a heat curing initiator for heat curable resins;

[0156] wherein the first part and the second part are kept separate before combining the two parts and forming the (mixed) structural adhesive composition.

[0157] According to another aspect, the present disclosure is directed to a partially cured precursor of a structural adhesive composition, the partially cured precursor comprising:

[0158] a) a polymeric material comprising a self-polymerization reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound;

[0159] b) optionally, some residual free radical polymerization initiator for the radiation self-polymerizable multifunctional compound;

[0160] c) a heat curable resin; and

[0161] d) a thermal curing initiator for the thermally curable resin; and

[0162] The heat curable resin is (substantially) uncured and is particularly embedded in a polymeric material comprising a self-polymerizing reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound.

[0163] In a typical aspect of the partially cured precursor of the structural adhesive, the heat-curable resin is substantially uncured and is particularly embedded in a polymer material comprising a self-polymerization reaction product of a polymerizable material comprising a radiation-autopolymerizable multifunctional compound. In a typical aspect, the heat-curable resin is still a liquid compound embedded in a polymer material resulting from self-polymerization of the radiation-autopolymerizable multifunctional compound, wherein the polymer material represents a fully established three-dimensional network.

[0164] The partially cured precursor is usually stable and is a self-supporting composition with dimensional stability, which makes it possible to pre-apply it to a selected substrate, particularly a liner, until further processing. In particular, the pre-applied substrate can be suitably transferred to other production sites until final full curing is performed. Still advantageously, the partially cured precursor can be suitably shaped or printed to meet the requirements of any selected application. The partially cured precursor usually has excellent characteristics and performances about elasticity, tack, cold flow and surface wettability.

[0165] According to typical aspects of the partially cured precursor according to the present disclosure, the polymer material comprising the self-polymerization reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound is substantially fully polymerized and specifically has a degree of polymerization of greater than 90%, greater than 95%, greater than 98% or even greater than 99%.

[0166] Since the polymer material comprising the self-polymerization reaction product of the radiation-self-polymerizable multifunctional compound is substantially completely polymerized, the polymerization reaction advantageously has a fixed and irreversible end and does not trigger any shelf life shortening reaction in the remainder of the curable precursor. It is believed that this feature advantageously affects the overall shelf life of the curable precursor.

[0167] In a typical aspect of the present disclosure, the partially cured precursor has a shear storage modulus in the range of 1000 Pa to 250.000 Pa, 1000 Pa to 200.000 Pa, 2000 Pa to 150.000 Pa, 3000 Pa to 150.000 Pa, 3000 Pa to 100.000 Pa, or even 3000 Pa to 80.000 Pa, when measured according to the test method described in the experimental section.

[0168] In an advantageous aspect, the partially cured precursor according to the present disclosure has a glass transition temperature (Tg) of no greater than 0°C, no greater than -5°C, no greater than -10°C, no greater than -15°C, or even no greater than -20°C, when measured by DSC.

[0169] In another advantageous aspect of the present disclosure, the partially cured precursor has an elongation at break of at least 50%, at least 80%, at least 100%, at least 150%, or even at least 200%, when measured according to the tensile test DIN EN ISO 527. This particular property makes the partially cured precursor and the resulting structural adhesive suitable for automated processing and application, especially automated processing and application by high-speed robotic equipment. More particularly, the partially cured precursor and the resulting structural adhesive of the present disclosure enable efficient automation of the process of forming a metal joint between metal sheets.

[0170] According to another aspect, the present disclosure relates to a structural adhesive composition obtainable by substantially fully curing the curable precursor as described above, in particular at a temperature of T2 or higher.

[0171] In the context of the present disclosure, the expression "substantially fully cured curable precursor" is intended to express that as a result of the polymerization / curing step, greater than 90 weight percent, greater than 95 weight percent, greater than 98 weight percent, or even greater than 99 weight percent of the total amount of the thermally curable resin and the radiation self-polymerizable multifunctional compound is polymerized / cured.

[0172] In typical aspects, the structural adhesive composition comprises an interpenetrating network involving a polymeric material comprising a self-polymerizing reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound and a polymerization product resulting from the curing of a thermally curable resin.

[0173] Depending on the intended application and conditions of use, the curable precursor or partially or fully cured (hybrid) structural adhesive compositions of the present disclosure may take or be shaped in any suitable form.

[0174] According to an advantageous aspect, the curable precursor or partially or fully cured structural adhesive composition of the present disclosure is formed into an elongated film form. The elongated film shape is a conventional and convenient shape to pre-apply the structural adhesive to a selected substrate, particularly a liner, prior to further processing.

[0175] In a particular aspect of the present disclosure, the elongated films used herein have a thickness greater than 500 microns, greater than 600 microns, greater than 700 microns, greater than 800 microns, greater than 900 microns, or even greater than 1000 microns.

[0176] In another specific aspect of the present disclosure, the elongated films used herein have a thickness of no greater than 500 microns, no greater than 400 microns, no greater than 300 microns, no greater than 200 microns, no greater than 100 microns, or even greater than 50 microns.

[0177] While an elongated film shape may be convenient in many different applications, this particular shape is not always satisfactory for adhesively bonding components having complex three-dimensional configurations or topologies, particularly when there are challenging bonding areas or surfaces.

[0178] Therefore, on the other hand, the curable precursor of the present disclosure or the partially or completely cured (mixed) structural adhesive composition can be formed into the form of a three-dimensional object. Suitable three-dimensional object shapes for this article will vary widely according to the specific configuration of the target bonding application and the assembly to be bonded, particularly the bonding area. According to the present disclosure, those skilled in the art will easily identify the exemplary three-dimensional object shapes for this article.

[0179] According to an exemplary aspect of the present disclosure, the three-dimensional object has a shape selected from the following: circular, semicircular, elliptical, square, rectangular, triangular, trapezoidal, polygonal, or any combination thereof.

[0180] In the context of the present disclosure, the shape of a three-dimensional object is herein intended to refer to the shape of a portion of the three-dimensional object according to a direction substantially perpendicular to the largest dimension of the three-dimensional object.

[0181] In yet another aspect, the present disclosure is directed to a composite article comprising a curable precursor or a partially or fully cured (hybrid) structural adhesive composition as described above applied to at least a portion of a surface of the article.

[0182] Suitable surfaces and articles for use herein are not particularly limited.Any surfaces, articles, substrates, and materials generally known to be suitable for use in combination with structural adhesive compositions may be used in the context of the present disclosure.

[0183] In a typical aspect, an article for use herein includes at least one component, particularly a metal or composite component.

[0184] In one advantageous aspect, the composite articles according to the present disclosure are used in body-in-white bonding applications in the automotive industry, particularly for hemming flange bonding of components, more particularly metal or composite components; and in structural bonding operations in the aviation and aerospace industry.

[0185] According to yet another aspect of the present disclosure, there is provided a curing system suitable for a (mixed) structural adhesive composition, wherein the curing system comprises:

[0186] a) a heat curing initiator for the heat curable resin; and

[0187] b) a free radical polymerization initiator for a radiation self-polymerizable multifunctional compound, the free radical polymerization initiator comprising a polyether oligomer backbone and at least one free radical (co)polymerizable reactive group at each terminal position of the oligomer backbone.

[0188] In particular, all specific and preferred aspects relating to the structural adhesive composition, the thermally curable resin, the thermal curing initiator for the thermally curable resin, the radiation self-polymerizable multifunctional compound, the free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, the temperatures T1 and T2, and the curable precursor or partially cured precursor described above in the context of the curable precursor or partially cured precursor are fully applicable to the curing system of the structural adhesive composition.

[0189] According to another aspect, the present disclosure relates to a method of manufacturing a composite article, the method comprising the step of using a curable precursor as described above or a partially cured precursor as described above.

[0190] According to yet another aspect, the present disclosure provides a method for manufacturing (mixing) a structural adhesive composition, the method comprising the steps of:

[0191] a) providing a curable precursor as described above;

[0192] b) partially curing the curable precursor of step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; and

[0193] c) substantially fully curing the partially cured precursor of step b) by initiating a thermal cure initiator for the thermally curable resin to obtain a substantially fully cured (hybrid) structural adhesive composition.

[0194] In the context of the present disclosure, the expression "substantially fully cured partially cured precursor" is intended to express that as a result of the polymerization / curing step, greater than 90 weight percent, greater than 95 weight percent, greater than 98 weight percent, or even greater than 99 weight percent of the total amount of the thermally curable resin and the radiation self-polymerizable multifunctional compound is polymerized / cured.

[0195] In yet another aspect of the present disclosure, there is provided a method of bonding two components, the method comprising the step of using the curable precursor or partially cured precursor as described above.

[0196] According to a particular aspect of the present disclosure, a method of bonding two components comprises the following steps:

[0197] a) applying a curable precursor or partially cured precursor as described above to a surface of at least one of the two components;

[0198] b) joining the two components such that the curable precursor or the partially cured precursor (mixed) structural adhesive composition is positioned between the two components; and

[0199] c) optionally, partially curing the curable precursor according to step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; and / or

[0200] d) substantially fully curing the partially cured precursor of step a) or c) by initiating a thermal curing initiator for the thermally curable resin, thereby obtaining a substantially fully cured (mixed) structural adhesive composition and bonding the two components.

[0201] According to an advantageous aspect of the method for bonding two components, the two components are metal components.

[0202] According to another advantageous aspect, the method for bonding two parts is used for flange bonding of metal parts, wherein:

[0203] - the partially cured precursor is formed into the form of an elongated film;

[0204] - the partially cured precursor film has a first portion proximate a first end of the precursor film and a second portion proximate a second end opposite the first end of the thermally curable resin of the precursor film;

[0205] - the first metal portion comprises a first metal panel having a first body portion and a first flange portion along an edge of the first body portion adjacent to a first end of the first body portion;

[0206] - the second metal portion comprises a second metal panel having a second body portion and a second flange portion along an edge of the second body portion adjacent to a second end of the second body portion;

[0207] The method comprises the following steps:

[0208] a) adhering the partially cured precursor film to the first metal panel or the second metal panel, whereby after adhering and folding, a metal joint is obtained, wherein the partially cured precursor film is folded such that:

[0209] i. a first portion of the partially cured precursor film is disposed between the second flange of the second metal panel and the first body portion of the first metal panel, and

[0210] ii. a second portion of the partially cured precursor film is disposed between the first flange of the first metal panel and the second body portion of the second metal panel; and

[0211] b) substantially fully curing the partially cured precursor by initiating a thermal cure initiator for the thermally curable resin to obtain a substantially fully cured (hybrid) structural adhesive composition and bond the metal joint.

[0212] According to still another advantageous aspect of the method of bonding two components, one side of the first edge portion of the first metal component is folded back and a hemming flange structure is formed so as to sandwich the second metal component, and a curable precursor or a partially cured precursor as described above is provided so as to adhere at least the first edge portion of the first metal component and the first surface side of the second metal component to each other.

[0213] Methods for bonding two parts, in particular for hemming flange bonding of metal parts, are well known to those skilled in the art of structural adhesive compositions. Suitable methods for bonding two parts herein are fully described in, for example, EP-A1-2 700 683 (Elgimiabi et al.) and WO 2017 / 197087 (Aizawa).

[0214] In particular aspects of the present disclosure, the substrates, parts and surfaces used in these methods comprise a metal selected from aluminum, steel, iron and any mixture, combination or alloy thereof. More advantageously, the substrates, parts and surfaces used herein comprise a metal selected from aluminum, steel, stainless steel and any mixture, combination or alloy thereof. In a particularly advantageous embodiment of the present disclosure, the substrates, parts and surfaces used herein comprise aluminum.

[0215] According to another aspect, the present disclosure relates to a metal part assembly obtainable by a method as described above.

[0216] In yet another aspect of the present disclosure, there is provided a (continuous) method of manufacturing a (mixed) (shaped) curable precursor of a structural adhesive composition, the method comprising the following steps:

[0217] a) providing a mixing device including a reaction chamber and an extrusion die;

[0218] b) providing a curable precursor of a (hybrid) structural adhesive composition as described above:

[0219] c) introducing and mixing (mixing) a curable precursor of the structural adhesive composition in a reaction chamber of a mixing device to form an extrudable composition;

[0220] d) extruding the extrudable composition of step c) through said extrusion die, thereby forming an extrudate of said curable precursor of said (mixed) structural adhesive composition;

[0221] e) optionally, shaping the extrudate;

[0222] f) optionally, cooling the extrudate of step d) or e); and

[0223] g) causing the radiation self-polymerizable multifunctional compound to self-polymerize in the extrudate or allowing the radiation self-polymerizable multifunctional compound to self-polymerize.

[0224] According to an advantageous aspect of the method of making a curable precursor for a structural adhesive composition, a free radical polymerization initiator is initiated at temperature T1, wherein a thermal curing initiator is initiated at temperature T2, wherein temperature T2 is greater than temperature T1, and wherein temperature T1 is insufficient to cause initiation of the thermal curing initiator.

[0225] According to another advantageous aspect of the method, the step of introducing and mixing (mixing) the curable precursors of the structural adhesive composition in the reaction chamber of the mixing device to form the extrudable composition is performed at a temperature not greater than temperature T2 and in particular not greater than temperature T1.

[0226] According to yet another advantageous aspect of the method, the temperature T1 is not greater than 90°C, not greater than 80°C, not greater than 60°C, not greater than 50°C, not greater than 40°C, not greater than 30°C, not greater than 25°C, not greater than 20°C or even not greater than 15°C.

[0227] According to yet another advantageous aspect of the method, the temperature T1 is in the range of -10 to 85°C, 0 to 80°C, 5 to 60°C, 5 to 50°C, 10 to 40°C or even 15 to 35°C.

[0228] According to yet another advantageous aspect of the method, the temperature T2 is greater than 90°C, greater than 100°C, greater than 120°C, greater than 140°C, greater than 150°C, greater than 160°C, greater than 180°C or even greater than 200°C.

[0229] According to yet another advantageous aspect of the method, the temperature T2 is in the range of 95-250°C, 100-220°C, 120-200°C, 140-200°C, 140-180°C or even 160-180°C.

[0230] In a further beneficial aspect of the method for making a curable precursor of a structural adhesive composition, the step of causing the radiation self-polymerizable multifunctional compound to self-polymerize or allowing the radiation self-polymerizable multifunctional compound to self-polymerize in the extrudate is performed by providing (high-energy actinic) radiation, more particularly UV radiation, electron beam radiation or gamma radiation.

[0231] In yet another advantageous aspect of the method, the step of self-polymerizing or allowing self-polymerization of the radiation self-polymerizable multifunctional compound in the extrudate is performed by providing UV radiation, particularly UV-C radiation or UV-A radiation, more particularly UV-A radiation.

[0232] In yet another beneficial aspect of the present disclosure, the step of forming an extrudate of a curable precursor of a (mixed) structural adhesive composition involves a calendering process step, in particular a calendering process step whereby the extrudable composition is directed into the nip of two counter-rotating rollers.

[0233] In yet another beneficial aspect of the present disclosure, the method for making a curable precursor of a structural adhesive composition further comprises the step of shaping the extrudate of step c) into the form of a three-dimensional object, and wherein the step of shaping the extrudate is particularly carried out simultaneously with the step of extruding the extrudable composition through an extrusion die.

[0234] In yet another advantageous aspect of the method, the three-dimensional object used herein has a shape selected from the group consisting of circular, semicircular, oval, square, rectangular, triangular, trapezoidal, polygonal shapes, or any combination thereof.

[0235] In another alternative aspect of the method, the three-dimensional object used herein is formed in the form of an elongated film.

[0236] According to a particularly advantageous aspect of the process, the mixing device used herein is selected from a single screw extruder and a multi-screw extruder and any combination thereof.

[0237] In the context of the present disclosure, it has surprisingly been found that the use of single screw extruders and multi-screw extruders in the method of making a (mixed) curable precursor of a structural adhesive composition as described above is particularly beneficial. It has been found that single screw extruders and multi-screw extruders provide excellent mixing performance and properties for the initial ingredients and raw materials of the curable precursor as described above, which in turn provide excellent extrudability properties of the extrudable composition, especially when used in combination with an extrusion die.

[0238] According to another advantageous aspect of the process, the mixing device used herein is selected from a single screw extruder, a twin screw extruder, a planetary roller extruder and a ring extruder.

[0239] According to a more advantageous aspect of the process, the mixing device used herein is selected from a co-rotating multi-screw extruder and a counter-rotating multi-screw extruder.

[0240] According to an even more advantageous aspect of the process, the mixing device used herein is a twin-screw extruder, in particular a co-rotating twin-screw extruder.

[0241] According to an alternative advantageous aspect of the method, the mixing device used herein is a planetary roll extruder, which specifically comprises a central main shaft and a plurality of planetary gear main shafts, and the central main shaft and the planetary gear main shafts are characterized by a screw-like geometry.

[0242] According to yet another aspect, the present disclosure relates to a method of manufacturing a (hybrid) structural adhesive article, the method comprising the following steps:

[0243] a) applying a curable precursor as described above to a substrate using a printing technique;

[0244] b) partially curing the curable precursor of step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor of the (hybrid) structural adhesive article, the partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound;

[0245] c) optionally, substantially completely curing the partially cured precursor of the (hybrid) structural adhesive article obtained in step b) by initiating a thermal curing initiator for the thermally curable resin, thereby obtaining a substantially completely cured (hybrid) structural adhesive article; and

[0246] d) optionally, removing the partially cured precursor of the (hybrid) structural adhesive article obtained in step b) or the substantially fully cured (hybrid) structural adhesive article obtained in step c) from the substrate.

[0247] In the context of the present disclosure, it has been surprisingly found that the curable precursors as described above are particularly suitable for application to various substrates by various printing techniques (including conventional and less conventional printing techniques). Without wishing to be bound by theory, it is believed that this excellent compatibility for printing techniques is due to the favorable viscosity and rheological properties of the curable precursors as described above.

[0248] In advantageous aspects of the method of making a structural adhesive article, the structural adhesive article for use herein is in the form of a two-dimensional object or a three-dimensional object.

[0249] In a more advantageous aspect of the method, the three-dimensional object used herein has a shape selected from the group consisting of circular, semicircular, oval, square, rectangular, triangular, trapezoidal, polygonal shapes, or any combination thereof.

[0250] In another more advantageous aspect of the method, the three-dimensional object used herein is shaped in the form of elongated films, continuous or discontinuous beads, designed shapes or figures, readable text or logos, and any combination thereof.

[0251] According to another aspect of the present disclosure, there is provided a method for printing (mixing) a structural adhesive composition, the method comprising the following steps:

[0252] a) applying a curable precursor as described above to a substrate using a printing technique;

[0253] b) partially curing the curable precursor of step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; and

[0254] c) Optionally, substantially fully curing the partially cured precursor of step b) by initiating a thermal cure initiator for the thermally curable resin.

[0255] In a typical aspect of these methods, the printing technology used in this article is selected from inkjet printing, screen printing, gravure printing, flexographic printing, offset printing, thermally driven printing, piezoelectric driven printing, pressure driven printing, automatic injection molding, direct writing molding, 3D printing pen, xyz robot dispensing, micro-dispensing printing, displacement driven dispensing printing, pneumatic driven dispensing printing and any combination thereof.

[0256] In particularly advantageous aspects of these methods, the printing technology used herein is selected from microdispensing printing technology, in particular inkjet printing, more in particular piezoelectrically driven (multi-dimensional) inkjet printing.

[0257] In the context of the present disclosure, it has indeed surprisingly been found that the curable precursors as described above are particularly suitable for application by micro-dispensing printing techniques, in particular using a piezoelectric inkjet printing device controlled by a piezoelectric actuator.

[0258] According to yet another aspect, the present disclosure relates to the use of a curable precursor or a partially or fully cured (hybrid) structural adhesive composition as described above for industrial applications, in particular for construction and automotive applications, more particularly for body-in-white bonding applications in the automotive industry and for structural bonding operations in the aviation and aerospace industry.

[0259] In a preferred aspect of the present disclosure, the curable precursor or partially or fully cured (hybrid) structural adhesive composition as described above is used for bonding metal or composite parts, in particular for hemming flange bonding of metal or composite parts in the automotive industry.

[0260] According to another aspect, the present disclosure relates to the use of a curable precursor or a partially cured precursor as described above for bonding metal or composite parts, in particular for hemming flange bonding of metal or composite parts in the automotive industry.

[0261] In yet another aspect, the present disclosure relates to the use of a curable precursor or a partially or fully cured (hybrid) structural adhesive composition as described above for forming a curable precursor or a partially or fully cured (hybrid) structural adhesive composition shaped in the form of an article as described above.

[0262] In yet another aspect, the present disclosure relates to the use of a curable precursor of a (hybrid) structural adhesive composition as described above for (hybrid) structural adhesive printing.

[0263] In yet another aspect, the present disclosure relates to the use of a curing system as described above for the manufacture of a (hybrid) structural adhesive composition as described above.

[0264] Example

[0265] The present disclosure is further illustrated by the following examples. These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims.

[0266] Test Method :

[0267] Preparation of formulations for testing :

[0268] The curable precursor composition is prepared by extrusion mixture of one-component or two-component (part B and part A) preparation. The preparation of various components is described below. After achieving a uniform mixture, the preparation is extruded between two pads using a scraper coater to produce a film with a thickness of 0.3 mm. The sample is then placed under a UV-A lamp and the adhesive film is irradiated for 4 minutes, which triggers the first reaction step (B stage reaction step) to obtain a partially cured precursor. The resulting band is then cut into a certain shape and applied to the surface of the test plate in the manner specified below for further testing.

[0269] Preparation of test samples for OLS test and T-peel test :

[0270] The surfaces of the OLS and T peel samples (steel, grade DX54+ZMB-RL1615) were cleaned with n-heptane and, in the case of oil-contaminated samples, with 3 g / m 2 The test samples were coated with a test oil (PL 3802-39S, commercially available from Fuchs Petrolub AG, Germany). Prior to testing, the test samples were placed at ambient room temperature (23°C + / - 2°C, 50% relative humidity + / - 5%) for 24 hours, and the OLS and T peel strengths were measured as described below.

[0271] 1) Lap shear strength (OLS) according to DIN EN 1465 .

[0272] Lap shear strength is determined according to DIN EN 1465 using a Zwick Z050 tensile tester (commercially available from Zwick GmbH & Co. KG, Ulm, Germany) running at a chuck speed of 10 mm / min. In order to prepare a lap shear strength test assembly, a shaped B-stage tape is placed on one surface of the prepared test plate. Afterwards, the sample is covered with a second steel strip to form a 13 mm lap joint. The lap joint is then clamped together using two binder clips, and the test assembly is further stored at room temperature for 4 hours after bonding, and then placed in an air circulation oven at 180 ° C for 30 minutes. The next day, the sample is tested directly. For each of the embodiments, five samples are measured, and the results are averaged and reported in MPa.

[0273] 2) T-peel strength according to DIN EN ISO 11339 .

[0274] According to DIN EN ISO 11339, the T-peel strength is determined using a Zwick Z050 tensile tester (commercially available from Zwick GmbH & Co. KG, Ulm, Germany) operating at a crosshead speed of 100 mm / min. In order to prepare the T-peel strength test assembly, the formed B-stage tape is placed directly in the middle of the T-peel test plate. The second test plate surface is then immediately bonded to the 100 mm overlap joint formed first. The samples are then fixed together with a clamp and first stored at room temperature for 12 hours and then placed in an air circulation oven at 180°C for 30 minutes. The next day, the samples are tested directly. Three samples are measured for each of the embodiments, and the results are averaged and reported in Newtons (N).

[0275] 3) Shear storage modulus (G') .

[0276] Shear storage modulus was measured on a plate-plate rheometer (ARES, Rheometric Scientific) at constant temperature (35°C).

[0277] raw material :

[0278] In the examples, the following raw materials were used:

[0279] Eponex 1510 is a hydrogenated bisphenol epoxy resin commercially available from Hexion Specialty Chemicals GmbH, Iserlohn, Germany.

[0280] DEN 431 is an epoxy resin commercially available from DOW Chemical Pacific, The Heeren, Singapore.

[0281] Epikote 828 is an epoxy resin commercially available from Hexion Specialty Chemicals GmbH, Iserlohn, Germany.

[0282] Epikote 1004 is an epoxy resin commercially available from Hexion Specialty Chemicals GmbH, Iserlohn, Germany.

[0283] 1K EBSA is a one-component epoxy-based structural adhesive comprising: a) 55 to 65 wt % of bisphenol-A-(epichlorohydrin) epoxy resin (number average molecular weight Mn not greater than 700 g / mol; b) 1.0 to 5.0 wt % of bisphenol A; and c) 1.0 to 2.5 wt % of glycidyl neodecanoate, and is available from 3M Deutschland GmbH, Neuss, Germany.

[0284] Amicure CG1200 is a dicyandiamide-based latent cure initiator for epoxides, commercially available from Evonik, Allentown, PA, USA.

[0285] Dyhard UR500 is a urea-based curing accelerator for epoxides, commercially available from AlzChem Trostberg, Germany.

[0286] Amicure UR2T is a urea-based curing accelerator for epoxides, commercially available from Evonik, Allentown, PA, USA.

[0287] Ancamine 2441 is a polyamine-based cure accelerator for epoxides commercially available from Evonik, Allentown, PA, USA.

[0288] D-6000-DMA is a dimethacrylate polyether oligomer having a number average molecular weight of about 6000 g / mol and is available from 3M Espe GmbH, Germany.

[0289] KaneAce MX 257 is a toughening agent commercially available from Kaneka Belgium NV, Westerlo, Belgium.

[0290] KaneAce MX 153 is a toughening agent commercially available from Kaneka Belgium NV, Westerlo, Belgium.

[0291] Paraloid EXL 2650J is a toughening agent commercially available from IMCDBenelux NV, Mechelen, Belgium.

[0292] Omnirad BDK 2,2-dimethoxy-2-phenylacetophenone is a free radical polymerization initiator commercially available from iGm resins, Waalwijk Netherlands.

[0293] Irgacure 1173 2-hydroxy 2-methyl-1-phenyl-propan-1-one, a free radical polymerization initiator, is commercially available from BASF, Germany.

[0294] Shieldex AC-5 is a silica-based corrosion inhibitor commercially available from Grace GmbH, Germany.

[0295] MinSil SF20 is a fused silica filler obtained from 3M Company, USA.

[0296] Aerosil R202 is a fumed silica surface treated with polydimethylsiloxane, commercially available from Evonik GmbH, Germany.

[0297] Dynasylan GLYEO is a silane-based adhesion promoter commercially available from Evonik GmbH, Germany.

[0298] Example :

[0299] Preparation of Example 1

[0300] An exemplary one-component curable composition according to Example 1 was prepared by combining the ingredients from the material list of Table 1. KaneAce MX 257, KanAce MX 153, Eponex 1510, and DEN 431 were first placed in a small beaker and mixed together at 3500 rpm for 1 minute using a planetary high-speed mixer (DAC 150FVZ Speedmixer, commercially available from Hauschild Engineering, Germany). Aerosil R202 was added and mixed into the resin at 1500 rpm under vacuum for 2 minutes using a high-speed vacuum mixer "ARV-130 Thinky Mixer" (purchased from Thinky Corporation, USA). Then, Omnirad BDK was added and mixed until a uniform mixture was achieved. Thereafter, Sil Cell 32, Shieldex AC-5, and MinSil SF20 were added in sequence and blended into the mixture by mixing at 3500 rpm for 1 minute. Then, Dynasylan GLYEO was added, followed by Amicure CG 1200, Dyhard UR500 and D-6000-DMA. In Table 1, all concentrations are given in weight %.

[0301] Preparation of Examples 2 to 4

[0302] The exemplary one-component curable compositions of Examples 2 to 4 were prepared by mixing the ingredients from the material list of Table 1 at a screw speed of 1200 rpm in an 18 mm twin screw extruder (obtained from Coperion GmbH, Stuttgart, Germany) with an L / D ratio of 48. The extruder was operated at 300 rpm and all barrels were set at a temperature of 30° C. The formulations described utilized a masterbatch containing 37.5 wt % Paraloid EXL and 62.5 wt % Epikote 828 (hereinafter referred to as MB EXL / 828).

[0303] Preparation of Example 5

[0304] The exemplary 2-component (Part A and Part B) curable composition of Example 5 was prepared by combining the ingredients from the materials list of Table 1 .

[0305] Place Betamate 1480 in a small beaker as Part B.

[0306] D-6000-DMA was placed in a separate small beaker. Irgacure 1173 was then added and mixed using a planetary high speed mixer (DAC 150.1FVZ Speedmixer, commercially available from Hauschild Engineering, Germany) at 3500 rpm for 1 minute until a homogeneous mixture was achieved to form Part A. Prior to use, Parts A and B were mixed using a planetary high speed mixer at 3500 rpm for 1 minute until a homogeneous mixture was achieved.

[0307] Table 1: Exemplary Formulations

[0308]

[0309]

[0310] OLS performance on clean and oil-contaminated substrates

[0311] Clean steel samples and the tested oil (3 g / m 2 OLS strength properties were tested on steel samples contaminated with PL 3802-39S (commercially available from Fuchs Petrolub AG, Germany).

[0312] Table 2: Results of OLS test .

[0313] Example 1 Example 5 OLS on clean substrate (MPa) 13.0 - OLS on oil-contaminated substrate (MPa) 15.8 19.3

[0314] As can be seen from the results shown in Table 2, the structural adhesives according to the present disclosure provide excellent performance and characteristics with respect to lap shear strength on both clean and oil-contaminated substrates. The results further show (see Example 1) even improved OLS strength performance provided by the structural adhesives according to the present disclosure on oil-contaminated substrates when compared to clean substrates.

[0315] Strength properties of OLS on oil-contaminated substrates with various thermal curing conditions

[0316] The tested oil (3 g / m 2 The OLS strength properties were tested on steel samples contaminated with PL3802-39S (commercially available from Volkswagen Fuel Products AG, Germany).

[0317] C1: 20 minutes at 160°C (suboptimal curing conditions);

[0318] C2: 30 minutes at 180°C (optimal curing conditions);

[0319] C3: 40 minutes at 200°C (suboptimal curing conditions).

[0320] Table 3: Results of OLS testing with various thermal curing conditions .

[0321] Example 2 Example 3 Example 4 OLS for thermal condition C1 (MPa) - 18.0 9.1 OLS for thermal condition C2 (MPa) 14.4 18.4 17.0 OLS for thermal condition C3 (MPa) - 17.9 16.7

[0322] From the results shown in Table 3, it can be seen that improved OLS strength properties are obtained when using a curable composition comprising a substituted urea-based curing accelerator for epoxides (Example 3) when compared to a curable composition not comprising any curing accelerator for epoxides (Example 2), or even when compared to using a conventional polyamine-based curing accelerator for epoxides (Example 4), especially when sub-optimal thermal curing conditions are used.

[0323] T peeling performance

[0324] Also for the tested oil (3g / m 2 The T-peel performance was tested on steel samples contaminated with PL 3802-39S, commercially available from Volkswagen Fuel Products AG, Germany.

[0325] Table 4: T-peel test results .

[0326] Example 5 T-peeling on oil-contaminated substrates (N) 202

[0327] As can be seen from the results shown in Table 4, the structural adhesives according to the present disclosure provide excellent performance and characteristics with respect to T-peel strength.

Claims

1. A curable precursor for a structural adhesive composition, the curable precursor comprising: a heat-curable resin, the heat-curable resin comprising epoxy functional groups; a thermal curing initiator for the thermally curable resin, wherein the thermal curing initiator is selected from aliphatic amines, alicyclic amines, aromatic structures having one or more amino moieties, polyamines, polyamine adducts, dicyandiamide, and any combination thereof; 0.5 to 20 weight percent of a radiation self-polymerizable multifunctional compound comprising a polyether oligomer backbone and at least one free radical polymerizable reactive group at each terminal position of the oligomer backbone, wherein the weight percents are all based on the total weight of the curable precursor; and 0.01 wt % to 10 wt % of a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, wherein the free radical polymerization initiator is selected from a Norrish I type free radical polymerization initiator, a Norrish II type free radical polymerization initiator, and any combination thereof, wherein the free radical polymerization initiator initiates at a temperature T1, wherein the thermal curing initiator initiates at a temperature T2, wherein the temperature T2 is greater than the temperature T1, and wherein the temperature T1 is insufficient to cause initiation of the thermal curing initiator.

2. A curable precursor according to claim 1, wherein the epoxy functional groups are glycidyl groups.

3. The curable precursor according to claim 1, wherein the thermal curing initiator is selected from the group consisting of primary amines, secondary amines, and any combination or mixture thereof.

4. The curable precursor according to claim 1, further comprising a thermal curing accelerator for the heat-curable resin, the thermal curing accelerator being selected from the group consisting of polyamines, polyamine adducts, ureas, substituted urea adducts, imidazoles, imidazole salts, imidazolines, aromatic tertiary amines, and any combination thereof.

5. The curable precursor of claim 1, wherein the radiation self-polymerizable multifunctional compound comprises a polyether oligomer backbone having a number average molecular weight of at least 2000 g / mol.

6. The curable precursor of claim 1, wherein the at least one free radically polymerizable reactive group located at each terminal position of the polyether oligomer backbone is selected from ethylenically unsaturated groups.

7. The curable precursor according to claim 1, wherein the radiation self-polymerizable multifunctional compound has the following formula: in: Y is an ethylenically unsaturated group; Each R 2 independently selected from alkylene groups having 2 to 6 carbon atoms; and n is an integer selected so that the calculated number average molecular weight of the radiation self-polymerizable multifunctional compound is at least 2000 g / mol.

8. The curable precursor according to claim 1, wherein the free radical polymerization initiator of the radiation self-polymerizable multifunctional compound is selected from benzyl ketals, aryl alkyl ketones, phosphine oxides, benzoin ethers, substituted acetophenones, substituted α-keto alcohols, photoactive oximes, and any combination thereof.

9. The curable precursor according to claim 8, wherein the free radical polymerization initiator of the radiation self-polymerizable multifunctional compound is selected from hydroxyacetophenone, aminoacetophenone and any combination thereof.

10. The curable precursor according to claim 1, comprising: 5 to 40 wt % of said heat curable resin; 0.1 wt % to 20 wt % of the heat curing initiator for the heat curable resin; 0.5 wt % to 20 wt % of the radiation self-polymerizable multifunctional compound; 0.01 wt % to 10 wt % of the free radical polymerization initiator for the radiation self-polymerizable multifunctional compound; Optionally, 0.05 wt % to 10 wt % of a curing accelerator for the heat-curable resin; Optionally, a toughening agent; and Optionally, a thixotropic agent; The weight percentages are based on the total weight of the curable precursor.

11. A partially cured precursor of a structural adhesive composition formed by partially curing the curable precursor according to any one of claims 1 to 10, the partially cured precursor comprising: a polymeric material comprising a self-polymerized reaction product of a polymerizable material comprising a radiation self-polymerizable multifunctional compound comprising a polyether oligomer backbone and at least one free radical polymerizable reactive group at each terminal position of the oligomer backbone; Optionally, some residual free radical polymerization initiator for the radiation self-polymerizable multifunctional compound; The heat curable resin ； and said heat curing initiator for said heat curable resin; wherein the heat-curable resin is uncured and embedded in the polymer material comprising the self-polymerization reaction product of the polymerizable material, the polymerizable material comprising the radiation self-polymerizable multifunctional compound.

12. A method of making a curable precursor for a structural adhesive composition, the method include: providing a mixing apparatus including a reaction chamber and an extrusion die; Providing a curable precursor of the structural adhesive composition according to any one of claims 1 to 10; introducing and mixing said curable precursor of said structural adhesive composition in said reaction chamber of said mixing apparatus to form an extrudable composition; extruding the extrudable composition through the extrusion die to form an extrudate of the curable precursor of the structural adhesive composition; Optionally, shaping the extrudate; Optionally, cooling the extrudate; as well as The radiation self-polymerizable multifunctional compound is self-polymerized or allowed to self-polymerize in the extrudate.

13. A method of making a structural adhesive article, the method include: a) applying the curable precursor according to any one of claims 1 to 10 to a substrate using a printing technique; b) partially curing the curable precursor of step a) by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound, thereby forming a partially cured precursor of the structural adhesive article, the partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; c) optionally, substantially completely curing the partially cured precursor of the structural adhesive article obtained in step b) by initiating a thermal curing initiator for the thermally curable resin, thereby obtaining a substantially completely cured structural adhesive article; as well as d) optionally, removing the partially cured precursor of the structural adhesive article obtained in step b) or the substantially fully cured structural adhesive article obtained in step c) from the substrate.

14. A method for bonding two parts, the method include: applying a curable precursor or a partially cured precursor according to any one of claims 1 to 11 to a surface of at least one of the two components; joining the two components such that the curable precursor or the partially cured precursor is positioned between the two components; as well as Optionally, partially curing the curable precursor by initiating a free radical polymerization initiator for the radiation self-polymerizable multifunctional compound to form a partially cured precursor comprising a polymer material produced from a self-polymerization reaction product of the radiation self-polymerizable multifunctional compound; and / or The partially cured precursor is substantially fully cured by initiating a thermal cure initiator for the thermally curable resin to obtain a substantially fully cured structural adhesive composition and bond the two components.

15. Use of a curable precursor or partially cured precursor according to any one of claims 1 to 11 for industrial applications including construction and automotive applications.

16. The use according to claim 15, wherein the automotive application comprises a body-in-white bonding application for the automotive industry.

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