Patent Description:
Adhesives have been used for a variety of holding, sealing, protecting, marking and masking purposes. One type of adhesive which is particularly preferred for many applications is represented by structural adhesives. Structural adhesives are typically thermosetting resin compositions that may be used to replace or augment conventional joining techniques such as screws, bolts, nails, staples, rivets and metal fusion processes (e.g. welding, brazing and soldering). Structural adhesives are used in a variety of applications that include general-use industrial applications, as well as high-performance applications in the automotive and aerospace industries. To be suitable as structural adhesives, the adhesives shall exhibit high and durable mechanical strength as well as high impact resistance.

Structural adhesives may, in particular, be used for metal joints in vehicles. For example, an adhesive may be used to bond a metal panel, for example a roof panel to the support structure or chassis of the vehicle. Further, an adhesive may be used in joining two metal panels of a vehicle closure panel. Vehicle closure panels typically comprise an assembly of an outer and an inner metal panel whereby a hem structure is formed by folding an edge of an outer panel over an edge of the inner panel. Typically, an adhesive is provided there between to bond the panels together. Further, a sealant typically needs to be applied at the joint of the metal panels to provide for sufficient corrosion resistance. For example, <CIT>) discloses the use of a flowable sealant bead between the facing surfaces of the two panels, and a thin film of uncured paint-like resin between a flange on the outer panel and the exposed surface of the inner panel. The paint film is cured to a solid impervious condition by a baking operation performed on the completed door panel. <CIT>) discloses the use of an adhesive for securing two metal panels together. The edge of the joint is further sealed by a metal coating. <CIT>) discloses an expandable epoxy paste adhesive as a sealant for a hem flange. A further hemmed structure is disclosed in <CIT>). Further efforts have been undertaken to develop adhesive compositions whereby two metal panels, in particular an outer and an inner panel of a vehicle closure panel, could be joined with an adhesive without the need for a further material for sealing the joint. Thus, it became desirable to develop adhesive systems that provide adequate bonding while also sealing the joint and providing corrosion resistance. A partial solution has been described in e.g. <CIT>), which discloses a thermally expandable and curable epoxy-based precursor of an expanded thermoset film toughened foamed film comprising a mixture of solid and liquid epoxy resins, and which is claimed to provide both favorable energy absorbing properties and gap filling properties upon curing. Other partial solutions have been described in <CIT>) and in <CIT>) which disclose structural adhesive films suitable for forming a hem flange structure. Structural adhesive films or tapes typically suffer from lack of elasticity and insufficient tackiness which makes them only partially suitable for hem flange bonding. Further partial solutions have been described in <CIT>) which discloses a so-called structural bonding tape. Structural bonding tapes are generally insufficient in terms of adhesive strength and corrosion resistance.

In some specific bonding applications, structural adhesives may be required to adhesively bond assemblies provided with challenging configurations or critical topologies. This is particularly the case in those situations where the parts to be bonded are provided with an uneven or irregular gap. A partial solution has been described in <CIT>) which discloses a structural adhesive film provided with different thicknesses along its extension. The described films are typically not fully satisfactory for providing acceptable bonding performance in assemblies provided with more complex three-dimensional configurations or topologies.

<CIT>, <CIT>, <CIT>, <CIT> and <CIT> relate to curable compositions based on cationically polymerizable monomers and initiators, wherein the compositions are used for a range of applications such as adhesives, dental impression or rapid prototyping.

Without contesting the technical advantages associated with the solutions known in the art, there is still a need for a structural adhesive composition which would overcome the above-mentioned deficiencies.

According to one aspect, the present disclosure is directed to a partially cured precursor of a structural adhesive composition as defined in the appended claims <NUM> to <NUM>.

In still another aspect of the present disclosure, it is provided a method of bonding two parts, which comprises the steps of:.

According to yet another aspect, the present disclosure relates to the use a partially cured precursor as described above, for industrial applications, in particular for construction and transportation applications, more in particular for body-in-white bonding applications for the automotive industry.

According to a first aspect, the present disclosure relates to a partially cured precursor of a structural adhesive as defined in appended claims <NUM> to <NUM>.

It has been surprisingly found that a curable precursor as described below is particularly suitable for manufacturing structural adhesive compositions provided with excellent characteristics and performance as to elasticity, tackiness, cold-flow, flexibility, handling properties and surface wetting in their uncured (or pre-cured) state, as well as to adhesive strength, ageing stability and corrosion resistance in their fully cured state. The curable precursor of a structural adhesive composition as described below have been surprisingly found to combine most of the advantageous characteristics of both the structural adhesive films and the structural bonding tapes known in the art, without exhibiting their known deficiencies.

It has further been discovered that a curable precursor as described below may be appropriately shaped in the form of a three-dimensional object, in particular a complex three-dimensional object, which makes it advantageously suitable to provide excellent bonding performance in assemblies provided with complex three-dimensional configurations or topologies. The curable precursor as described below is suitable for manufacturing structural adhesive compositions provided with excellent characteristics and performance as to adhesion to oily contaminated substrates, such as stainless steel and aluminum.

Without wishing to be bound by theory, it is believed that these excellent characteristics are due in particular to the combined presence of a thixotropic agent and a specific dual curing system in the curable precursor, wherein the curing system comprises: a) a polymerization initiator of a cationically self-polymerizable monomer which is initiated at a temperature T1, and b) a curing initiator of a curable monomer which is initiated at a temperature T2 and which is different from the polymerization initiator of the cationically self-polymerizable monomer. The thixotropic agent is believed to mainly provide the advantageous shapeability characteristics of the curable precursor. The curable precursor may be advantageously applied in a geometrically controlled way directly on a particular substrate.

Still without wishing to be bound by theory, it is believed that this dual/hybrid curing system involving two independent reactive systems, which have a different chemical nature and which co-exist in the curable precursor without interfering with each other, has the ability to form - upon complete curing - an interpenetrating network involving a polymeric material comprising the self-polymerization reaction product of a polymerizable material comprising the cationically self-polymerizable monomer and a polymeric product resulting from the curing of the curable monomer.

More specifically, the above described hybrid curing system is particularly suitable to perform an overall curing mechanism involving a two-stage reaction whereby two polymer networks are formed sequentially.

In a first stage reaction (stage-B), the cationically self-polymerizable monomers polymerize upon initiation by the polymerization initiator of the cationically self-polymerizable monomer at a temperature T1, thereby forming a polymeric material comprising the self-polymerization reaction product of a polymerizable material comprising the cationically self-polymerizable monomers. Typically, the temperature T1 at which the polymerization initiator of the cationically self-polymerizable monomer is initiated is insufficient to cause initiation of the curing initiator of the curable monomer. As a consequence, the first stage reaction typically results in a partially cured precursor, wherein the curable monomers are substantially uncured and are in particular embedded into the polymeric material comprising the self-polymerization reaction product of the polymerizable material comprising the cationically self-polymerizable monomers.

The first stage reaction which typically leads to a phase change of the initial curable precursor due in particular to the polymeric material comprising the self-polymerization reaction product of the cationically self-polymerizable monomers providing structural integrity to the initial curable precursor, is typically referred to as a film-forming reaction. Advantageously, the first stage reaction does typically not require any substantial energy input.

In the context of the present disclosure, it has been surprisingly found that the first stage reaction (stage-B) and the accompanying phase change does not, or only moderately affect, the three-dimensional shape of the initial curable precursor. As such, the partially cured precursor resulting for the first stage reaction is provided with excellent shape retention characteristics, when compared to the initial shape of the curable precursor. This is a particularly surprising and counterintuitive finding as the skilled person would have logically expected the three-dimensional polymeric network resulting from the self-polymerization reaction of the cationically self-polymerizable monomers (i.e. comprised in the partially cured precursor resulting from the first stage reaction) to substantially affect the three-dimensional shape of the initial curable precursor, due in particular to a modification of the viscosity, thixotropic and wettability characteristics of the initial curable precursor. In the context of the present disclosure, it has been no less surprisingly found that the thixotropic agent does not detrimentally affect the formation of the polymeric material resulting from the self-polymerization reaction of the cationically self-polymerizable monomers. This is a further unexpected finding as the thixotropic agent could have detrimentally affected not only the formation of the polymeric material per se (in particular the kinetic of the self-polymerization reaction of the cationically self-polymerizable monomers), but also the nature of three-dimensional polymeric network of the polymeric material resulting from the self-polymerization reaction of the cationically self-polymerizable monomers.

As such, the curable precursor enables near net shape application of the structural adhesive, whereby the initial shape of the curable precursor is retained and fixed by the formation of the polymeric material resulting from the self-polymerization reaction of the cationically self-polymerizable monomers occurring during the first stage reaction. The near net shape application enabled by the curable precursor considerably reduces, or even eliminates, the need for further reshaping, finishing, readjusting, and remodelling of the initially applied precursor after partial curing.

In a typical aspect, the partially cured precursor takes the form of a film-like self-supporting composition having a dimensional stability, which makes it possible for it to be pre-applied on a selected substrate, in particular a liner, until further processing. The partially cured precursor is typically provided with excellent characteristics and performance as to elasticity, tackiness, cold-flow and surface wetting. Advantageously, the partially cured precursor may be appropriately shaped to fulfil the requirements of any specific applications.

The second stage reaction (stage-A) occurs after the first stage reaction and typically involves curing the curable monomers upon initiation (typically thermal initiation) by the appropriate curing initiators at a temperature T2. This reaction step typically results in forming a polymeric product resulting from the curing of the curable monomer, in particular from the (co)polymerization of the curable monomers and the curing initiators (or curatives) of the curable monomers.

The curable precursor typically relies on the above-described dual/hybrid curing system involving two independent reactive systems activated at distinct temperatures (T1 and T2) to ensure performing the above-described two-stage reaction in a sequential manner. Advantageously, the curable precursor may be partially cured (or pre-cured) and pre-applied on a selected substrate before being finally cured in-place to produce a structural adhesive provided with excellent characteristics directly on the desired substrate or article.

As such, the curable precursor may be suitable for bonding metal parts, in particular for hem flange bonding of metal parts in the automotive industry. Advantageously still, the curable precursor is suitable for automated handling and application, in particular by fast robotic equipment.

In the context of the present disclosure, the expression "cationically self-polymerizable monomer" is meant to refer to a monomer able to form a polymeric product (homopolymer) resulting from the polymerization of the monomer almost exclusively with itself and involving the formation of a cationic intermediate moiety, thereby forming a homopolymer. The term "homopolymer" is herein meant to designate polymer(s) resulting from the polymerization of a single type of monomers.

In the context of the present disclosure still, the expression "curable monomer" is mean to refer to a monomer able to form a polymeric product (heteropolymer) resulting from the (co)polymerization of the curable monomers and the curing initiators (or curatives) of the curable monomers. The term "heteropolymer" is herewith meant to designate a polymer resulting from the (co)polymerization of more than one type of monomers.

In the context of the present disclosure, the expression "the curable monomers are substantially uncured" is meant to designate that less than 10wt. %, less than 5wt. %, less than 2wt. %, or even less than <NUM> wt. % of the initial curable monomers are cured.

The terms "glass transition temperature" and "Tg" are used interchangeably and refer to the glass transition temperature of a (co)polymeric material or a mixture of monomers and polymers. Unless otherwise indicated, glass transition temperature values are determined by Differential Scanning Calorimetry (DSC).

According to one typical aspect of the curable precursor of the disclosure, the temperature T2 for use herein is greater than temperature T1. In a typical aspect, the temperature T1 at which the polymerization initiator of the cationically self-polymerizable monomer is initiated is insufficient to cause initiation of the curing initiator of the curable monomer which therefore remain substantially unreacted.

According to another typical aspect of the curable precursor, the cationically self-polymerizable monomer and the curable monomer for use herein are unable to chemically react with each other, in particular by covalent bonding, even when subjected to their respective polymerization or curing initiation. In an exemplary aspect, the cationically self-polymerizable monomer and the curable monomer are unable to chemically react with each other, when subjected to polymerization or curing initiation at a temperature of <NUM>.

In one exemplary aspect the temperature T1 for use herein is no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, no greater than <NUM>, or even no greater than <NUM>. In some exemplary aspects the polymerization initiator of the cationically self-polymerizable monomer is already initiated at room temperature (about <NUM>).

In another exemplary aspect the temperature T1 is in a range from -<NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>.

In still another exemplary aspect the temperature T2 for use herein is greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, greater than <NUM>, or even greater than <NUM>.

According to another typical aspect the temperature T2 is in a range from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, from <NUM> to <NUM>, or even from <NUM> to <NUM>.

In some exemplary aspects the curing initiator of the curable monomer for use herein which is initiated at a temperature T2 may be qualified as a thermally-initiated curing initiator or thermal initiator which is activated at substantially high temperatures.

Cationically self-polymerizable monomers for use herein are not particularly limited. Suitable cationically self-polymerizable monomers for use herein may be easily identified by those skilled in the art in the light of the present disclosure.

According to one advantageous aspect of the present invention, the cationically self-polymerizable monomer is an aziridino-functional polyether oligomer.

In a beneficial aspect of the disclosure, the cationically self-polymerizable monomer for use herein is an oligomer having, in particular a number average molecular weight no greater than <NUM>/mol, no greater than <NUM>/mol, no greater than <NUM>/mol, no greater than <NUM>/mol, or even no greater than <NUM>/mol. Unless otherwise indicated, the number average molecular weight is determined by GPC using appropriate techniques well known to those skilled in the art.

In an exemplary aspect, the aziridino-functional oligomer for use herein has a number average molecular weight no greater than <NUM>/mol, no greater than <NUM>/mol, no greater than <NUM>/mol, no greater than <NUM>/mol, or even no greater than <NUM>/mol.

According to an advantageous aspect, the cationically self-polymerizable monomer is an aziridino-functional (linear) polyether oligomer, in particular an N-alkyl aziridino-functional (linear) polyether oligomer.

Suitable polyether oligomers may be produced in a manner known to those skilled in the art by the reaction of the starting compound having a reactive hydrogen atom with alkylene oxides, for example ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrine or mixtures of two or more thereof. Especially suitable polyether oligomers for use herein are obtainable by polyaddition of ethylene oxide, <NUM>,<NUM>-propylene oxide, <NUM>,<NUM>-butylene oxide or tetrahydrofuran or of mixtures of two or more of the mentioned compounds with the aid of a suitable starting compound and a suitable catalyst.

In a particularly beneficial aspect, suitable polyether oligomers for use herein are polyetherdiols obtainable by cationic copolymerization of ethylene oxide and tetrahydrofuran under catalytic action of boron trifluoride etherate. Suitable cationically self-polymerizable monomers for use herein and possible production methods thereof are described e.g. in <CIT>).

The cationically self-polymerizable monomer for use herein may have the following formula:
<CHM>
wherein:.

The cationically self-polymerizable monomer for use herein may have the following formula:
<CHM>.

In an advantageous aspect, radical R<NUM> is an alkylene group having two carbon atoms. In another advantageous aspect, radical R<NUM> is independently selected from the group consisting of linear alkylene groups having <NUM> to <NUM> carbon atoms.

The cationically self-polymerizable monomer for use herein may have the following formula:
<CHM>
wherein a and b are integers greater than or equal to <NUM>, and the sum of a and b is equal to n.

According to an exemplary aspect n is selected such that the calculated number average molecular weight of the cationically self-polymerizable monomer is no greater than <NUM> grams/mole.

Curable monomers for use herein are not particularly limited, as long as they are different from the cationically self-polymerizable monomers.

According to an advantageous aspect of the present disclosure, the curable monomer for use herein comprises at least one functional group selected from the group consisting of epoxy groups.

The curable monomer may be an epoxy resin. Exemplary epoxy resins for use herein may be advantageously selected from the group consisting of phenolic epoxy resins, bisphenol epoxy resins, hydrogenated epoxy resins, aliphatic epoxy resins, halogenated bisphenol epoxy resins, novolac epoxy resins, and any mixtures thereof.

Epoxy resins are well known to those skilled in the art of structural adhesive compositions. Suitable epoxy resins for use herein and their methods of manufacturing are amply described e.g. in <CIT>) and in <CIT>).

The curable may be an epoxy resin selected from the group consisting of novolac epoxy resins, bisphenol epoxy resins, in particular those derived from the reaction of bisphenol-A with epichlorhydrin (DGEBA resins), and any mixtures thereof.

Polymerization initiators of the cationically self-polymerizable monomer for use herein are not particularly limited. Any polymerization initiators of cationically self-polymerizable monomers commonly known in the art of structural adhesives may be used in the context of the present disclosure. Suitable polymerization initiators of the cationically self-polymerizable monomer for use herein may be easily identified by those skilled in the art in the light of the present disclosure.

Exemplary polymerization initiators of the cationically self-polymerizable monomer for use herein are amply described in <NPL>), and in particular in <CIT>).

The polymerization initiator of the cationically self-polymerizable monomer for use herein may be selected from the group consisting of protonating agents, alkylating agents, and any combinations or mixtures thereof.

The polymerization initiator of the cationically self-polymerizable monomer may be selected from the group consisting of alkylating agents, in particular from the group consisting of arylsulphonic acid esters, sulfonium salts, in particular alkyl sulfonium salts, and any combinations or mixtures thereof.

More advantageously, the polymerization initiator of the cationically self-polymerizable monomer for use herein is selected from the group of arylsulphonic acid esters, in particular from the group consisting of p-toluene sulphonic acid esters, and preferably methyl-p-toluene sulfonate.

In an alternatively advantageous aspect of the disclosure, the polymerization initiator of the cationically self-polymerizable monomer is selected from the group consisting of protonating agents, in particular from the group consisting of Lewis acids, Broensted acids or precursor of Broensted acids, and any combinations or mixtures thereof.

In another advantageous aspect, the polymerization initiator of the cationically self-polymerizable monomer may be selected from the group consisting of Broensted acids, in particular from the group consisting of sulfonic acids, sulfonium acids, phosphonic acids, phosphoric acids, carboxylic acids, antimonic acids, boric acids, and any combinations, mixtures or salts thereof.

In still another advantageous aspect, the polymerization initiator of the cationically self-polymerizable monomer may be selected from the group consisting of Broensted acids, in combination with antacid-acting components, in particular selected from the group consisting of oxides, hydroxides, carbonates and carboxylates of the elements aluminium, chromium, copper, germanium, manganese, lead, antimony, tin, tellurium, titanium and zinc. The antacid-acting component may beneficially be selected to comprise zinc, and wherein the polymerization initiator of the cationically self-polymerizable monomer is in particular selected to be zinc tosylate.

Curing initiators of the curable monomer for use herein are not particularly limited, as long as they are different from the polymerization initiators of the cationically self-polymerizable monomers.

According to an advantageous aspect of the present disclosure, the curing initiator of the curable monomer is selected from the group consisting of primary amines, secondary amines, and any combinations or mixtures thereof.

The amines for use as curing initiator of the curable monomer may be selected from the group consisting of aliphatic amines, cycloaliphatic amines, aromatic amines, aromatic structures having one or more amino moiety, polyamines, polyamine adducts, dicyandiamides, and any combinations or mixtures thereof.

According to still another advantageous aspect the curing initiator of the curable monomer for use herein may be selected from the group consisting of dicyandiamide, polyamines, polyamine adducts, and any combinations or mixtures thereof.

In a preferred aspect, the curing initiator of the curable monomer may be selected to be dicyandiamide. Further it may be comprised a curing accelerator of the curable monomer, which is in particular selected from the group consisting of polyamines, polyamine adducts, ureas, substituted urea adducts, imidazoles, imidazole salts, imidazolines, aromatic tertiary amines, and any combinations or mixtures thereof.

Curing initiators and curing accelerators are well known to those skilled in the art of structural adhesive compositions. Suitable curing initiators and curing accelerators for use herein and their methods of manufacturing are amply described e.g. in <CIT>) and in <CIT>).

In one preferred execution, the curing accelerator of the curable monomer is selected from the group of polyamine adducts, substituted ureas, in particular N-substituted urea adducts.

The curing accelerator of the curable monomer may be selected from the group of substituted urea adducts, in particular N-substituted urea adducts. It has been indeed surprisingly discovered that the use of a curing accelerator of the curable monomer selected from the group of substituted urea adducts, in particular N-substituted urea adducts, substantially improve the adhesion properties, in particular the peel adhesion properties of the resulting structural adhesive composition.

Thixotropic agents for use herein are not particularly limited. Any thixotropic agents commonly known in the art of structural adhesives may be used in the context of the present disclosure. Suitable thixotropic agents for use herein may be easily identified by those skilled in the art in the light of the present disclosure.

According to one typical aspect of the disclosure, the thixotropic agent for use herein is selected from the group of inorganic and organic thixotropic agents.

According to another typical aspect, the thixotropic agent for use in the present disclosure is selected from the group of particulate thixotropic agents.

In an advantageous aspect of the present disclosure, the thixotropic agent for use herein is selected from the group of inorganic thixotropic agents, in particular silicon-based thixotropic agents and aluminum-based thixotropic agents.

In a more advantageous aspect, the thixotropic agent for use herein is selected from the group consisting of silica-based and silicate-based thixotropic agents.

According to a particularly advantageous aspect the thixotropic agent for use herein may be selected from the group consisting of fumed silica particles, in particular hydrophilic fumed silica and hydrophobic fumed silica; silicates particles, in particular phyllosilicates, and any mixtures thereof.

In another advantageous aspect the thixotropic agent for use herein may be selected from the group of organic thixotropic agents, in particular polyamide waxes, hydrolysed castor waxes and urea derivatives-based thixotropic agents.

In a particularly advantageous aspect, the thixotropic agent for use herein may be selected from the group consisting of fumed silica particles, in particular hydrophobic fumed silica particles; silicate-based particles, in particular phyllosilicate particles; polyamide waxes, and any mixtures thereof.

According to an exemplary aspect, the curable precursor of the disclosure comprises no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, or even no greater than <NUM> wt. %, of the thixotropic agent, based on the overall weight of curable precursor.

According to another exemplary aspect, the curable precursor comprises from <NUM> to <NUM> wt. %, from <NUM> to <NUM> wt. %, from <NUM> to <NUM> wt. %, from <NUM> to <NUM> wt. %, from <NUM> to <NUM> wt. %, or even from <NUM> to <NUM> wt. %, of the thixotropic agent, based on the overall weight of curable precursor.

According to a typical aspect the curable precursor further may comprise a second curable monomer which is also different from the cationically self-polymerizable monomer.

In an advantageous aspect, the second curable monomer may comprise at least one functional group selected from the group consisting of epoxy groups, in particular glycidyl groups. Advantageously still, the second curable monomer may be an epoxy resin, in particular selected from the group consisting of phenolic epoxy resins, bisphenol epoxy resins, hydrogenated epoxy resins, aliphatic epoxy resins, halogenated bisphenol epoxy resins, novolac epoxy resins, and any mixtures thereof.

The second curable monomer for use herein may be an epoxy resin selected from the group consisting of hydrogenated bisphenol epoxy resins, in particular those derived from the reaction of hydrogenated bisphenol-A with epichlorhydrin (hydrogenated DGEBA resins), and any mixtures thereof. In the context it has been indeed surprisingly discovered that the use of a second curable monomer selected in particular from the group of hydrogenated bisphenol epoxy resins, substantially maintains or even improve the adhesion properties, in particular the peel adhesion properties of the resulting structural adhesive composition towards oily contaminated substrates. These specific curable precursors are particularly suitable to result into structural adhesive compositions having outstanding excellent oil-contamination tolerance towards, in particular oily contaminated metal substrates.

Exemplary oily contamination is for example mineral oils, and synthetic oils. Typical mineral oils include paraffinic mineral oils, intermediate mineral oils and naphthenic mineral oils.

In an advantageous aspect, the adhering step(s) of the surfaces to be bonded may be performed without using a pre-cleaning step of the substrates, parts and, and/or without using an adhesion promoter, in particular a priming composition or a tie layer.

According to another advantageous aspect, the curable precursor may comprise a thermoplastic resin. Thermoplastic resins for use herein are not particularly limited. Any thermoplastic resins commonly known in the art of structural adhesives may be used in the context of the present disclosure. Suitable thermoplastic resins for use herein may be easily identified by those skilled in the art in the light of the present disclosure.

Thermoplastic resins are known to those skilled in the art of structural adhesive compositions. Suitable exemplary thermoplastic resins for use herein are described e.g. in <CIT>).

The the thermoplastic resins for use herein may have a glass transition temperature (Tg) in a range from <NUM> and <NUM>, when measured by Differential Scanning Calorimetry (DSC).

In a more advantageous aspect, the thermoplastic resins for use herein may have a softening point comprised between <NUM> and <NUM>, preferably between <NUM> and <NUM>, more preferably between <NUM> and <NUM>.

The thermoplastic resin for use herein may be selected from the group consisting of polyether thermoplastic resins, polypropylene thermoplastic resins, polyvinyl chloride thermoplastic resins, polyester thermoplastic resins, polycaprolactone thermoplastic resins, polystyrene thermoplastic resins, polycarbonate thermoplastic resins, polyamide thermoplastic resins, polyurethane thermoplastic resins, and any combinations of mixtures thereof.

The thermoplastic resin for use herein may be selected from the group of polyether thermoplastic resins, and in particular polyhydroxyether thermoplastic resins.

In a more advantageous aspect, the polyhydroxyether thermoplastic resins for use herein may be selected from the group consisting of phenoxy resins, polyether diamine resins, polyvinylacetal resins, in particular polyvinyl butyral resins, and any combinations or mixtures thereof.

The thermoplastic resin for use herein may be selected from the group of phenoxy resins.

It has been indeed surprisingly discovered that the use of a thermoplastic resin, in particular a thermoplastic resin selected from the group of phenoxy resins, substantially improve the adhesion properties, in particular the peel adhesion properties, as well as the toughening characteristics of the resulting structural adhesive composition. This is particularly surprising and counterintuitive as thermoplastic resins are generally recognized and used as film-forming additives.

The curable precursor may be substantially free of acrylic-based monomers or acrylic resins. By "substantially free of acrylic-based monomers or acrylic resins", it is herewith meant to express that the curable precursor comprises less than 10wt. %, less than 5wt. %, less than 2wt. %, less than <NUM> wt. %, or even less than <NUM>. % of acrylic-based monomers or acrylic resins.

The curable precursor of the disclosure may be substantially free of free radical-polymerizable monomers or compounds, in particular irradiation-initiated free radical initiators. By "substantially free of free radical-polymerizable monomers or compounds", it is herewith meant to express that the curable precursor comprises less than 10wt. %, less than 5wt. %, less than 2wt. %, less than <NUM> wt. %, or even less than <NUM>. % of free radical-polymerizable monomers or compounds.

The curable precursor may comprise a cationically self-polymerizable monomer and a curable monomer in a weight ratio ranging from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or even from <NUM>:<NUM> to <NUM>:<NUM>.

The curable precursor may be in the form of a one-part structural adhesive composition.

The curable precursor may be in the form of a two-part structural adhesive composition having a first part and a second part, wherein:.

wherein the two-part (hybrid) structural adhesive composition further comprises the thixotropic in either the first part, the second part or in both parts; wherein the first part and the second part are kept separated prior to combining the two parts and forming the structural adhesive composition.

According the appended claims, the present disclosure is directed to a partially cured precursor of a structural adhesive composition, comprising:.

and wherein the shape is selected from the group consisting of circular, semi-circular, ellipsoidal, square, rectangular, triangular, trapezoidal, polygonal shape, or any combinations thereof.

In a typical aspect of the partially cured precursor of a structural adhesive, the curable monomers are substantially uncured and are, in particular, embedded into the polymeric material comprising the self-polymerization reaction product of a polymerizable material comprising a cationically self-polymerizable monomer. In a typical aspect, the curable monomers are still liquid monomers embedded into the polymeric material resulting from the self-polymerization of the cationically self-polymerizable monomers, wherein this polymeric material represents a fully-established three-dimensional network.

The partially cured precursor typically is a stable and self-supporting composition having a dimensional stability, which makes it possible for it to be pre-applied on a selected substrate, in particular a liner, until further processing. In particular, the pre-applied substrate may be suitably transferred to other production sites until final full curing is performed. Advantageously still, the partially cured precursor may be appropriately shaped to fulfil the specific requirements of any selected applications. The partially cured precursor is typically provided with excellent characteristics and performance as to elasticity, tackiness, cold-flow and surface wetting.

According to a typical aspect of the partially cured precursor according to the disclosure, the polymeric material comprising the self-polymerization reaction product of the polymerizable material comprising the cationically self-polymerizable monomer is substantially fully polymerized and has in particular a degree of polymerization of more than <NUM>%, more than <NUM>%, more than <NUM>%, or even more than <NUM>%. As the polymeric material comprising the self-polymerization reaction product of the cationically self-polymerizable monomer is substantially fully polymerized, this polymerization reaction has advantageously a fixed and irreversible end and will not trigger any shelf-life reducing reactions in the remaining of the curable precursor. This characteristic will beneficially impact the overall shelf-life of the curable precursor.

According to a particularly advantageous aspect of the partially cured precursor, the polymeric material comprises or consists of a polyetherimine, in particular a linear or branched polyethylenimine (PEI). The polyetherimine typically results from the self-polymerization of bis-aziridino compounds, in particular N-alkyl aziridino-functional polyether oligomers, acting as cationically self-polymerizable monomers.

In one typical aspect the partially cured precursor may have a shear storage modulus in a range from <NUM> to <NUM> Pa, from <NUM> to <NUM> Pa, from <NUM> to <NUM> Pa, from <NUM> to <NUM> Pa, from <NUM> to <NUM> Pa, or even from <NUM> to <NUM> Pa, when measured according to the test method described in the experimental section.

According to an exemplary aspect, the partially cured precursor may have a shear storage modulus deviation no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, no greater than <NUM>%, or even no greater than <NUM>%, when compared to the shear storage modulus of the corresponding curable precursor prior to partial curing, when the shear storage modulus deviation is measured according to the test method described in the experimental section.

According to another exemplary aspect, the partially cured may have a shape retention factor greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, greater than <NUM>%, or even greater than <NUM>%, when compared to the shape of the corresponding curable precursor prior to partial curing, when the shape retention factor is measured according to the test method described in the experimental section.

In one advantageous aspect, the partially cured may have a glass transition temperature (Tg) no greater than <NUM>, no greater than -<NUM>, no greater than -<NUM>, no greater than -<NUM>, or even no greater than -<NUM>, when measured by DSC.

In another advantageous aspect the partially cured precursor may have an elongation at break of at least <NUM>%, at least <NUM>%, at least <NUM>%, at least <NUM>%, or even at least <NUM>%, when measured according to tensile test DIN EN ISO <NUM>. This particular property makes the partially cured precursor and the resulting structural adhesive suitable for automated handling and application, in particular by high-speed robotic equipment. More particularly, the partially cured precursor and the resulting structural adhesive of the present disclosure enables efficient automation of the process of forming a metal or composite material joint between metal or composite material plates.

According to one advantageous aspect, the curable precursor or the partially or fully cured structural adhesive composition may be shaped in the form of an elongated film. The elongated film shape is one conventional and convenient shape for the structural adhesive to be pre-applied on a selected substrate, in particular a liner, until further processing. However, this specific shape is not always satisfactory for adhesively bond assemblies provided with complex three-dimensional configurations or topologies, in particular provided with challenging bonding areas.

Accordingly, the curable precursor or the partially or fully cured (hybrid) structural adhesive composition may - in another aspect - be shaped in the form of a three-dimensional object. Suitable three-dimensional object shapes for use herein will broadly vary depending on the targeted bonding application and the specific configuration of the assembly to bond, in particular the bonding area. Exemplary three-dimensional object shapes for use herein will be easily identified by those skilled in the art in the light of the present disclosure.

According to one exemplary aspect of the present disclosure, the three-dimensional object has a shape selected from the group consisting of circular, semi-circular, ellipsoidal, square, rectangular, triangular, trapezoidal, polygonal shape, or any combinations thereof.

In the context of the present disclosure, the shape of the three-dimensional object is herein meant to refer to the shape of the section of the three-dimensional object according to a direction substantially perpendicular to the greatest dimension of the three-dimensional obj ect.

In yet another aspect of the present disclosure, it is a provided a method of bonding two parts comprising the step of using a partially cured precursor as described above.

According to a particular aspect of the disclosure, the method of bonding two parts comprises the steps of:.

According to an advantageous aspect of the method of bonding two parts, the two parts are metal or composite material parts.

According to another advantageous aspect, the method of bonding two parts is for hem flange bonding of metal or composite material parts as in the appended claims.

Methods of bonding two parts, in particular for hem flange bonding of metal parts, are well known to those skilled in the art of structural adhesive compositions. Suitable methods of bonding two parts for use herein are amply described e.g. in <CIT>) and in <CIT>).

In a particular aspect the substrates, parts and surfaces for use in these methods may comprise a metal selected from the group consisting of aluminum, steel, iron, and any mixtures, combinations or alloys thereof. More advantageously, the substrates, parts and surfaces may comprise a metal selected from the group consisting of aluminum, steel, stainless steel and any mixtures, combinations or alloys thereof. The substrates, parts and surfaces may comprise aluminum.

The substrates, parts and surfaces for use in these methods may comprise a composite material.

Any composite material commonly known in the art may be used in the context of the present disclosure. Suitable composite material for use herein may be easily identified by those skilled in the art in the light of the present disclosure.

In one particular aspect, the composite material may be selected from the group consisting of epoxy-based materials, phenolic-based materials, polyamide-based materials, polyethylene-based materials, polypropylene-based materials, polybutylene terephthalate-based materials, and any combinations or mixtures thereof.

In another aspect, the composite material may comprise a resin matrix and reinforcing fibers. Exemplary resin matrices may comprise a base material advantageously selected from the group consisting epoxy-based materials, phenolic-based materials, polyamide-based materials, polyethylene-based materials, polypropylene-based materials, polybutylene terephthalate-based materials, and any combinations or mixtures thereof. In another particular aspect, the reinforcing fibers are selected from the group consisting of carbon fibers, glass fibers, ceramic fibers, and any combinations or mixtures thereof.

According to still another aspect, the present disclosure relates to the use of a partially cured precursor as described above, for industrial applications, in particular for construction and automotive applications, in particular for body-in-white bonding applications for the automotive industry and for structural bonding operations for the aeronautic and aerospace industries.

According to yet another aspect, the present disclosure relates to the use of a partially cured precursor as described above, for bonding metal or composite material parts, in particular for hem flange bonding of metal or composite material parts in the automotive industry.

The present disclosure is further illustrated by the following examples. These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims.

The curable precursor compositions are prepared from an extruded mixture of two components (Part B and Part A). The preparation of both, part A and B, is described hereinafter. Parts A and Part B are weighed into a beaker in the appropriate mixing ratio and mixed at <NUM> rpm for <NUM> minutes until a homogeneous mixture is achieved. As soon as this step is completed the mixing initiates the first reaction step (stage-B reaction step) resulting in a partially cured precursor within a period ranging from <NUM> to <NUM> minutes. Within the open time, the obtained paste is applied to the surface of the test panel for further testing in the manner specified below.

The surface of OLS and T-peel samples (steel, grade DX54+ZMB-RL1615) are cleaned with n-heptane. The test samples are left at ambient room temperature (<NUM> +/- <NUM>, <NUM>% relative humidity +/-<NUM>%) for <NUM> hours prior to testing and the OLS and T-peel strengths are measured as described above.

Overlap shear strength is determined according to DIN EN <NUM> using a Zwick Z050 tensile tester (commercially available by Zwick GmbH & Co. KG, Ulm, Germany) operating at a cross head speed of <NUM>/min. For the preparation of an Overlap Shear Strength test assembly, the paste resulting from the mixing of Part A and Part B is spackled onto one surface of a test panel and removed with a squeegee to give a defined layer having a thickness of <NUM>. The sample is then stored at room temperature for <NUM> hours to ensure full transformation into a precured precursor. Afterwards, the sample is covered by a second steel strip forming an overlap joint of <NUM>. The overlap joints are then clamped together using two binder clips and the test assemblies are further stored at room temperature for <NUM> hours after bonding, and then placed into an air circulating oven for <NUM> minutes at <NUM>. The next day, the samples are either tested directly or undergo ageing and are tested thereafter. Five samples are measured for each of the examples and results averaged and reported in MPa.

T-Peel strength is determined according to DIN EN ISO <NUM> using a Zwick Z050 tensile tester (commercially available by Zwick GmbH & Co. KG, Ulm, Germany) operating at a cross head speed of <NUM>/min. For the preparation of a T-Peel Strength test assembly, the paste resulting from the mixing of Part A and Part B is placed in a syringe without needle cap and directly applied to the first surface via extruding a bead onto the middle of the T-peel test panel. The second test panel surface is then immediately bonded to the first forming an overlap j oint of <NUM>, without waiting for the transformation into a precured precursor state. The inclusion of glass beads into the formulation ensures that the right thickness of the layer (<NUM>,<NUM>) is reached by pressing the surfaces together. After removal of squeezed-out adhesive, the samples are fixed together with clamps and first stored at room temperature for <NUM> hours, and then placed into an air circulating oven for <NUM> minutes at <NUM>. The next day, the samples are either tested directly or undergo ageing and are tested thereafter. Three samples are measured for each of the examples and results averaged and reported in Newtons (N).

The shear storage modulus is determined on a plate-plate rheometer (ARES, Rheometric Scientific) at a constant temperature (<NUM>).

The shape retention is determined according to the following procedure.

The curable compositions are shaped side-by-side into three-dimensional longitudinal beads having an equilateral triangle shape on a stainless-steel plate, using a customized squeegee provided with a suitable geometrically shaped recess. The steel plate is then placed at a <NUM>° angle for <NUM> hours at <NUM>. Afterwards, the steel plate is placed horizontally. The movement of the three-dimensional longitudinal bead is visually observed from a top view, and the shape retention factor is measured according to the following procedure.

The width of the base of the longitudinal bead is measured from a top view, wherein the base of the longitudinal bead is meant to refer to that portion of the bead which is direct contact with the stainless-steel plate. The middle of this width value is calculated and reported as value (A). This value corresponds to the distance between the lower extremity of the base of the longitudinal bead and the tip of the equilateral triangle which is opposed to the base, and which would be theoretically obtained for a three-dimensional longitudinal bead which remains unchanged through time (shape retention factor of <NUM>%). In order to calculate the actual shape retention factor of the three-dimensional longitudinal beads, the actual distance between the lower extremity of the base of the longitudinal bead and the tip of the equilateral triangle which is opposed to the base, is measured and reported as value (B). This value is then compared to the theoretical value (A) according to the following formula: <MAT>.

In the examples, the following raw materials and commercial adhesive tapes used are used:.

The exemplary <NUM>-component (Part A and Part B) curable compositions according to the present disclosure are prepared by combining the ingredients from the list of materials of Table <NUM> in a high-speed mixer (DAC <NUM> FVZ Speedmixer, available from Hauschild Engineering, Germany) stirring at <NUM> rpm for <NUM> minutes until a homogeneous mixture is achieved. In Table <NUM>, all concentrations are given as wt. Comparative example C1 does not comprise any thixotropic agent.

Part B is prepared as follows:
KaneAce MX <NUM>, KanAce MX <NUM>, PK-HA, Eponex <NUM>, Epikote <NUM> and DEN <NUM> are placed in a small beaker and mixed together using a planetary high-speed mixer (DAC150 FVZ) at <NUM> rpm for <NUM> minute. Then, the polymerization initiator of the cationically self-polymerizable monomer is added and mixed until a homogeneous mixture is obtained. Thereafter, the thixotropic agent, Sil Cell <NUM>, Shieldex AC-<NUM> and MinSil SF20 are subsequently added and blended into the mixture by mixing at <NUM> rpm for <NUM> minute. Then, Dynasylan GLYEO is added, followed by Glass Beads, resulting into Part B of the <NUM>-component curable compositions.

Part A is prepared as follows:
Amicure CG1200 and Dyhard UR500 are placed in a beaker. Subsequently, the bisaziridino polyether (BAPE) is added to the mixture which is then mixed using a planetary high-speed mixer (DAC150 FVZ) at <NUM> rpm for <NUM> minute until a homogeneous mixture is achieved, resulting into Part A of <NUM>-component curable compositions.

Part A and Part B are weighed into a beaker in the correct mixing ratio and mixed at <NUM> rpm for <NUM> minutes until a homogeneous mixture is achieved.

All the exemplary curable compositions (Ex. <NUM> to Ex. <NUM>) are stably shaped into three-dimensional longitudinal beads having the following shapes: triangle, semi-circular, rectangle, square, trapeze. The compositions are shaped using a customized squeegee provided with a suitable geometrically shaped recess. Upon visual observation, it appeared that the shape of the exemplary curable compositions remained substantially unchanged upon partial curing (stage B reaction).

The shape retention performance of the curable compositions according to Ex. <NUM> and Ex. C1 are tested according to the test method described hereinbefore.

As can be seen from the results shown in Table <NUM>, the partially cured curable precursors according to the present disclosure (Ex. <NUM> and Ex. <NUM>) are provided with excellent shape retention characteristics when compared to partially cured curable precursors not according to the disclosure (Ex.

Claim 1:
A partially cured precursor of a structural adhesive composition, comprising:
a) a polymeric material comprising the self-polymerization reaction product of a polymerizable material comprising a cationically self-polymerizable monomer, wherein the cationically self-polymerizable monomer is an aziridino-functional polyether oligomer;
b) optionally, some residual polymerization initiator of the cationically self-polymerizable monomer which is initiated at a temperature T1;
c) a curable monomer which is different from the cationically self-polymerizable monomer, wherein the curable monomer which is different from the cationically self-polymerizable monomer comprises at least one functional group selected from the group consisting of epoxy groups;
d) a curing initiator of the curable monomer which is initiated at a temperature T2 and which is different from the polymerization initiator of the cationically self-polymerizable monomer; and
e) a thixotropic agent; and
wherein the curable monomers are substantially uncured and are in particular embedded into the polymeric material comprising the self-polymerization reaction product of a polymerizable material comprising a cationically self-polymerizable monomer;
wherein the partially cured precursor of a structural adhesive composition is shaped in the form of a three-dimensional object; and
wherein the shape is selected from the group consisting of circular, semi-circular, ellipsoidal, square, rectangular, triangular, trapezoidal, polygonal shape, or any combinations thereof.