Interstitial adhesive

Abstract

The present invention provides a two-part gap-filling adhesive, which comprises a base part and a hardener part that can be cured upon mixing. The base part comprises a polyfunctional epoxy resin having at least three epoxy functionalities and a difunctional epoxy resin that is miscibly blended with the polyfunctional epoxy resin. The hardener part comprises a polyetheramine. The base part or the hardener part further comprises an inorganic filler present in an amount of 10% to 60% based on the total weight of the two-part curable gap-filling adhesive, and a phosphate ester. The gap-filling adhesive enables the assembly of joints in one step, thus providing significant advantages to the user.

Description

Technical Field

[0001] The present disclosure provides a curable adhesive for a gap-filling bonding structure, such as a primary structure and a secondary structure in industrial applications. Background Art

[0002] A gasket is a thin sheet of material used to fill small gaps or spaces between components to be joined together. The gasket assumes the shape of the gap and can support a compressive load to prevent excessive deformation and damage to the structural components when typically fastened together using mechanical fasteners. Gaskets are used in industrial applications, such as in automotive and aerospace manufacturing. Various forms of gaskets are also used in residential and commercial construction.

[0003] Various types of gaskets can be used. Solid gaskets can be made of the same material as the mating components. Peelable laminated gaskets can be made of layers of thin metal sheets that can be removed layer by layer until a good fit is achieved. Liquid gasket materials work well in filling irregular or tapered interfaces and are typically used to fill gaps less than 0.7 millimeters in width.

[0004] Determining the necessity, size, and shape of a given gasket is generally an iterative and laborious process. Generally, the components are temporarily assembled, and then the gap between the skin and the substructure is visually inspected and measured. The components can then be disassembled and test gaskets fabricated. The components can then be reassembled with the gasket temporarily held in place to check the fit. This is a second temporary assembly operation, and such operations may need to be repeated until a proper fit is achieved.

[0005] Liquid gaskets are not structural adhesives because the adhesive layer does not lie in the primary load path. In a mechanically fastened joint, the shear load is carried by the fasteners rather than the bonded material. In these assemblies, the only load carried by the liquid gasket is the compressive load. Summary of the Invention

[0006] The present disclosure provides a liquid gap-filling composition that can also be used as an adhesive. When cured, the gap-filling composition provides high peel strength, as well as excellent thermal / wet bonding properties, and can simplify the manufacturing process by eliminating the need to apply a separate adhesive.

[0007] In a first aspect, there is provided a two-part curable gap-filling adhesive. The adhesive comprises: a base part comprising: a polyfunctional epoxy resin having at least three epoxide functionalities; and a difunctional epoxy resin co-blended miscibly with the polyfunctional epoxy resin; and a hardener part comprising a polyetheramine; wherein the base part or the hardener part further comprises an inorganic filler present in an amount of 10% to 60% based on the total weight of the two-part curable gap-filling adhesive, and a phosphate ester.

[0008] Definition

[0009] As used herein:

[0010] "Alkyl" means straight-chain and branched-chain alkyl groups and cycloalkyl groups having from 1 to 40 carbon atoms, from 1 to 20 carbon atoms, from 1 to 12 carbon atoms, or in some embodiments from 1 to 8 carbon atoms.

[0011] "Ambient conditions" means at a temperature of 23°C and a pressure of 1 atmosphere (i.e., 101.3 kPa);

[0012] "Ambient temperature" means a temperature of 23°C;

[0013] Unless otherwise specified, "average" means the arithmetic mean;

[0014] "Curing" means chemical crosslinking such as by exposure to radiation in any form, heating, or subjecting it to a chemical reaction that results in hardening or an increase in viscosity (e.g., at ambient temperature or under heating conditions);

[0015] "Cycloalkyl" means a cyclic alkyl group such as, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups.

[0016] "Organic group" means any carbon-containing functional group.

[0017] "Polymer" means a molecule having multiple repeating units;

[0018] "Substantially" means most or the majority, such as at least 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least 99.999% or more, or 100%. And

[0019] "Substituted", as used herein in connection with a molecule or organic group, means a state in which one or more of the hydrogen atoms contained therein are replaced by one or more non-hydrogen atoms. Detailed Description

[0020] As used herein, the terms "preferred" and "preferably" refer to the embodiments described herein that may provide certain benefits in certain circumstances. However, in the same or other circumstances, other embodiments may also be preferred. In addition, the recitation of one or more preferred embodiments does not imply that other embodiments are not available and is not intended to exclude other embodiments from the scope of the invention.

[0021] As used in this specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a / an" and "the" include plural referents. Thus, for example, reference to "a" or "the" component can include one or more components or equivalents thereof known to those skilled in the art. Additionally, the term "and / or" means one or all of the listed elements or any combination of two or more of the listed elements.

[0022] In the methods described herein, various steps may be performed in any order without departing from the principles of the invention, except where a specific order of time or operations is explicitly recited. Additionally, the recited acts may be performed concurrently unless the explicit claim language implies that they be performed separately. For example, the claimed act of performing X and the claimed act of performing Y may be performed concurrently in a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0023] It should be noted that the term "comprising" and its variants do not have a limiting meaning when they appear in the appended specification. Additionally, "a", "an", "the", "at least one", and "one or more" may be used interchangeably herein. Relative terms such as left, right, forward, backward, top, bottom, side, upper, lower, horizontal, and vertical may be used herein, and if so, they are from the perspective observed in the specific figures. However, these terms are used only for the purpose of simplifying the description and do not limit the scope of the invention in any way.

[0024] References throughout this specification to "one embodiment", "certain embodiments", "one or more embodiments", or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as "in one or more embodiments", "in certain embodiments", "in one embodiment", or "in an embodiment" throughout this specification are not necessarily referring to the same embodiment of the invention.

[0025] Provided herein is a curable two - part composition for manufacturing gaskets for bonding components. In some cases, the bonding components can be used in automotive, aerospace, marine, residential, construction, or other commercial or industrial applications.

[0026] In some embodiments, the spacer member is an aircraft component. The aircraft component includes the skin and sub - structure of the aircraft. The aircraft sub - structure is not particularly limited and can include, for example, stringers, spars, ribs, and other frame elements in the aircraft wings and fuselage.

[0027] The structural shims are flight components of an aircraft and are made of a rigid load-bearing material. These shims are used to fill the gaps between assembled components that would otherwise cause indentation or buckling of the components and associated stress concentrations. These stress concentrations, if severe, can lead to fastener failure and ultimately significant damage to the aircraft. Accordingly, it is desirable to provide a composition (i.e., a liquid or paste) that can flow or spread easily before curing, allowing it to form a custom shim that precisely fits the gap into which it is installed.

[0028] The curable gap-filling adhesive provided is preferably a two-part composition comprising a base part and a curing agent part. The curable adhesive can be cured by mixing the base part and the curing agent part together. For ease of use, curing is typically carried out at ambient temperature.

[0029] Base material part

[0030] The base part of the curable two-part gap-filling adhesive comprises a blend of epoxy resins. More specifically, the blend comprises a difunctional epoxy resin and a polyfunctional epoxy resin having at least two and preferably three or more epoxide functionalities.

[0031] The difunctional epoxy resin has exactly two epoxide functionalities and can be blended miscibly with the polyfunctional epoxy resin. The polyfunctional epoxy resin can have an epoxide functionality of at least 2.1, at least 2.2, at least 2.3, at least 2.4, at least 2.5, at least 2.6, at least 2.7, at least 2.8, at least 2.9, or at least 3. The polyfunctional epoxy resin can also comprise two or more resins having an epoxide functionality greater than two.

[0032] Epoxy resins include glycidol, alicyclic resins, and epoxidized oils. The glycidylated resins can be reaction products of glycidyl ethers (such as epichlorohydrin) and bisphenol compounds (such as bisphenol A). Various examples of epoxy resins include C4-C28 alkyl glycidyl ethers; C2-C28 alkyl-glycidyl esters and alkenyl-glycidyl esters; C1-C28 alkylphenol glycidyl ethers, monophenol glycidyl ethers, and polyphenol glycidyl ethers; polyglycidyl ethers of pyrocatechol, resorcinol, hydroquinone, 4,4′-dihydroxydiphenylmethane (or bisphenol F), 4,4′-dihydroxy-3,3′-dimethyldiphenylmethane, 4,4′-dihydroxydiphenyldimethylmethane (or bisphenol A), 4,4′-dihydroxydiphenylmethylmethane, 4,4′-dihydroxydiphenylcyclohexane, 4,4′-dihydroxy-3,3′-dimethyldiphenylpropane, 4,4′-dihydroxydiphenyl sulfoxide, and tris(4-hydroxyphenyl)methane; polyglycidyl ethers of the chlorinated and brominated products of the above-mentioned diphenols; polyglycidyl ethers of phenolic resins; polyglycidyl ethers of diphenols obtained by etherifying the diphenols, the ethers of the diphenols being obtained by esterifying salts of aromatic hydroxycarboxylic acids with dihaloalkanes or dihalogen dialkyl ethers. Polyglycidyl ethers of polyphenols obtained by condensing phenols with long-chain halogenated alkanes containing at least two halogen atoms; N,N′-diglycidylaniline; N,N′-dimethyl-N,N′-diglycidyl-4,4′-diaminodiphenylmethane; N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane; N,N′-diglycidyl-4-aminophenyl glycidyl ether; N,N,N′,N′-tetraglycidyl-1,3-propylene bis-4-aminobenzoate; phenol novolac epoxy resins, cresol novolac epoxy resins, and combinations thereof.

[0033] Representative non-limiting examples of suitable epoxy resins include bis-4,4′-(1-methylethylidene)phenol diglycidyl ether and (chloromethyl)epoxide bisphenol A diglycidyl ether. Commercially available epoxy resins that can be used to practice the present invention include those sold under the trade name ARALDITE by Huntsman Corporation, The Woodlands, TX and those sold under the trade name EPON by Hexion Inc., Columbus, OH. Suitable epoxy resins also include glycidyl ethers of terphenols such as tris(hydroxyphenyl)methane. Such resins are commercially available under the trade name TACTIX from Huntsman Corporation, The Woodlands, TX.

[0034] In some embodiments, an epoxy novolac resin can be used. In some embodiments, the polyfunctional epoxy resin includes a tetrafunctional epoxy resin based on m-xylenediamine, such as those sold under the trade name ERISYS by Emerald Performance Materials LLC, Vancouver, WA.

[0035] It may be advantageous to use a mixture of epoxy resins, the components of which are selected to provide desired viscosity characteristics prior to curing. In some embodiments, the polyfunctional epoxy resin includes a trifunctional epoxy resin, such as triphenylmethane triglycidyl ether or other glycidyl ethers having three or more epoxide groups per molecule. In some cases, the trifunctional epoxy resin is a solid epoxy resin at ambient temperature. Optionally, the trifunctional epoxy resin is blended with a tetrafunctional epoxy resin such as 4,4′-methylenebis(N,N-diglycidylaniline). The bifunctional epoxy resin can be a bisphenol A / epichlorohydrin-derived liquid epoxy resin or other glycidyl ethers having two epoxide groups per molecule.

[0036] The relative amounts of the polyfunctional epoxy resin and the bifunctional epoxy resin can be adjusted to obtain a suitable crosslink density, which in turn affects important adhesive properties such as glass transition temperature, tensile strength, and shear strength. A suitable amount of the low-viscosity bifunctional epoxy resin can also help the uncured adhesive flow and wet the bonding surface of the substrate to improve the bond strength. In the provided gap-filling adhesive, the polyfunctional epoxy resin and the bifunctional epoxy resin can be present in a relative weight ratio of 1:1 to 6:1, 1:1 to 4:1, 1:1 to 2:1, or in some embodiments less than, equal to, or greater than 1:1, 2:1, 3:1, 4:1, 5:1, or 6:1 relative to each other.

[0037] In a preferred embodiment, the polyfunctional epoxy resin includes a relative amount of trifunctional and tetrafunctional epoxy resins that balance the competing properties of stiffness and adhesiveness in the cured gap-filling adhesive. Certain epoxy resins (such as solid or semi-solid triphenylmethane triglycidyl ether) have been found to increase adhesive stiffness, while other epoxy resins (such as liquid tetrafunctional 4,4′-methylenebis(N,N-diglycidylaniline)) have been found to enhance adhesive strength.

[0038] Consistent with these considerations, the trifunctional epoxy resin and the tetrafunctional epoxy resin can be present in a relative weight ratio of 1:1 to 8:1, 1:1 to 6:1, 1:1 to 4:1, or in some embodiments less than, equal to, or greater than 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1 relative to each other.

[0039] One or more epoxy resins in the base portion can have any suitable molecular weight. The weight-average molecular weight can be from 100 g / mol to 50,000 g / mol, from 175 g / mol to 20,000 g / mol, from 250 g / mol to 10,000 g / mol, or in some embodiments less than, equal to, or greater than 100 g / mol; 125 g / mol; 150 g / mol; 175 g / mol; 200 g / mol; 250 g / mol; 300 g / mol; 350 g / mol; 400 g / mol; 450 g / mol; 500 g / mol; 550 g / mol; 600 g / mol; 650 g / mol; 700 g / mol; 750 g / mol; 800 g / mol; 850 g / mol; 900 g / mol; 950 g / mol; 1000 g / mol; 2000 g / mol; 5000 g / mol; 7,000 g / mol; 10,000 g / mol; 20,000 g / mol; 30,000 g / mol; 40,000 g / mol; or 50,000 g / mol.

[0040] Based on the total weight of the base portion and the hardener portion (i.e., based on the total weight of the gap-filling adhesive composition), the total mixture of the base portion and the curing agent portion typically contains at least 20 wt% epoxy resin. For example, the gap-filling adhesive can contain at least 25 wt%, at least 30 wt%, at least 40 wt%, or at least 50 wt% epoxy resin. The gap-filling adhesive can contain up to 90 wt% epoxy resin.

[0041] In some embodiments, the base portion further contains an inorganic filler to enhance the compressive strength of the cured gap-filling adhesive. Many useful inorganic fillers are possible. Examples include naturally occurring or synthetic materials such as silica; nitrides (e.g., silicon nitride); glass and fillers derived from, for example, Zr, Sr, Ce, Sb, Sn, Ba, Zn, and Al; feldspar; borosilicate glass; zirconia; titanium dioxide; and micron and submicron fumed silica particles (e.g., fumed silica such as those available under the trade name AEROSIL from Degussa Corp., Akron, Ohio, including "OX 50", "130", "150", and "200" silica, and CAB-O-OSIL M5 silica available from Cabot Corp., Tuscola, IL). In a preferred embodiment, the inorganic filler includes fumed silica. The fumed silica optionally has a median particle size in the range of 1 to 10 microns.

[0042] One or more inorganic fillers may be present in any suitable amount. Relative to the total weight of the two-part curable gap-filling adhesive, the filler may be from 10 wt% to 60 wt%, from 12 wt% to 45 wt%, from 15 wt% to 30 wt%, or in some embodiments less than, equal to, or greater than 10 wt%, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt% or 60 wt%.

[0043] To facilitate the dispersion of the inorganic filler in the matrix resin, the base part may further comprise a phosphate ester. In some cases, the phosphate ester may be a phosphoric acid polyester copolymer containing acid groups. A useful phosphate ester may be purchased under the trade name BYK W9010 from Altana AG, Wesel, Germany.

[0044] The inorganic filler and the phosphate ester may be present in a relative weight ratio of 100:3 to 1000:3, 100:3 to 500:3, 100:3 to 300:3, or in some embodiments less than, equal to, or greater than 100:3, 150:3, 200:3, 250:3, 300:3, 350:3, 400:3, 450:3, 500:3, 600:3, 700:3, 800:3, 900:3 or 1000:3.

[0045] In some embodiments, the base part may comprise other toughening components. Exemplary toughening components may include, for example, core-shell rubber particles.

[0046] Core-shell particles are filler particles having two or more different concentric parts: a core and one or more shell layers surrounding the core. In some embodiments, the core is a core-shell rubber (CSR) particle with an elastomeric core made of physically crosslinked or microphase-separated polymer, and the shell layer is made of a non-elastomeric glassy polymer. Advantageously, the rubbery elastomeric core can enhance the toughness in the cured gap-filling adhesive, while the glassy polymer shell can provide compatibility between the filler particles and the matrix.

[0047] In an exemplary composite application, the core-shell particles may have a particle size in the range of 10 nm to 800 nm, 50 nm to 500 nm, or 80 nm to 300 nm, or in some embodiments less than, equal to, or greater than 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 70 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm or 1000 nm.

[0048] The core-shell particles can be uniformly dispersed in the composition or at least partially aggregated. The aggregated core-shell particles can be in physical contact with one or more other core-shell particles. In some embodiments, the core-shell particles form long-chain aggregated particles that extend throughout the body of the curable resin. Such chains of aggregated core-shell particles can be straight or branched. The chains of core-shell particles themselves can be uniformly distributed throughout the body of the curable resin. When the gap-filling adhesive cures, the configuration of such aggregates can be substantially maintained.

[0049] The core-shell rubber toughener can be present in an amount of 1 to 20 volume %, 1 to 15 volume %, 1 to 10 volume % of the total weight of the base part of the two-part curable gap-filling adhesive, or in some embodiments less than, equal to, or greater than 1 volume %, 2 volume %, 3 volume %, 4 volume %, 5 volume %, 6 volume %, 7 volume %, 8 volume %, 9 volume %, 10 volume %, 11 volume %, 12 volume %, 13 volume %, 14 volume %, 15 volume %, 16 volume %, 17 volume %, 18 volume %, 19 volume % or 20 volume %.

[0050] Further technical aspects of the core-shell particles are described elsewhere, such as in co-pending International Publication No. WO2019 / 005800 (Chen et al.).

[0051] The base part optionally contains one or more reactive diluents. Reactive diluents that reduce the viscosity of the epoxy resin mixture are typically epoxy resins having a saturated branched aliphatic or cyclic backbone. Examples of reactive diluents include, but are not limited to, diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol, and triglycidyl ether of trimethylolpropane. Diglycidyl ether of cyclohexane dimethanol can be commercially obtained under the trade name HELOXY MODIFIER 107 from Hexion Specialty Chemicals (Columbus, OH) and under the trade name EPODIL 757 from Evonik Industries AG, Essen, Germany.

[0052] The reactive diluent can be added in a suitable amount to obtain the desired viscosity profile of the uncured gap-filling adhesive. A typical amount, based on the total weight of the epoxy component, can be 1 to 12 weight %. Other details of the reactive diluent can be found, for example, in International Publication No. WO 2014 / 210298 (Elgimiabi et al.).

[0053] Hardener part

[0054] The hardener part contains at least one curing agent which, when mixed with the epoxy resin in the base part, undergoes a chemical reaction through which the two-part gap-filling adhesive cures.

[0055] Useful curing agents include cyclic compounds containing at least one cyclic moiety which can be aliphatic or aromatic. The cyclic moiety can be substituted by primary amino groups, i.e., the primary amino groups can be directly bonded to the ring. Preferably, the cyclic moiety is substituted by one or more residues carrying primary amino groups, optionally substituted at the terminal position. The residue can be, for example, a straight-chain or branched aminoalkyl group, preferably having a primary amino group at the terminal position.

[0056] The curing agent can contain at least one, preferably at least two primary amino groups (-NH 2 2) at the terminal position. The most preferred embodiments contain two primary amino groups and both primary amino groups are at the terminal positions of the molecule. At least one cyclic moiety is usually a five-membered or six-membered ring, which can be a hydrocarbon or heterohydrocarbon ring. The heterohydrocarbon ring usually contains one or more heteroatoms selected from nitrogen and oxygen atoms.

[0057] Examples of suitable curing agents include but are not limited to: cyclohexane containing one or more terminal primary amino groups and / or aminoalkyl residues having one or more terminal primary amino groups, piperazine containing one or more terminal primary amino groups and / or aminoalkyl residues having one or more terminal primary amino groups, and morpholine containing one or more terminal primary amino groups and / or aminoalkyl having a terminal primary amino group. Specific examples include but are not limited to bis- or tris-aminoalkyl piperazine or morpholine. Specific examples include but are not limited to 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane (also known as isophorone diamine) and N,N-bis(3-aminopropyl)piperazine.

[0058] The curing agent can be an aliphatic cyclic (poly)amine as described above or can be an adduct of such an aliphatic cyclic polyamine with one or more epoxy resins, provided that the aliphatic cyclic polyamine used is in molar excess to ensure that the adduct preferably contains at least two primary amino groups at the terminal position of the adduct. Preferably, the epoxy resin used to form the adduct is the same or similar to one of the epoxy resins used in the epoxy component. For example, the first curing agent is a diamine and reacts with an epoxy resin having two glycidyl groups to form an adduct, and the first major curing agent can be used at a molar ratio of diamine to epoxy resin greater than or equal to 2:1 to form an amine-containing adduct having two amino groups. Usually, a molar excess of amine is used such that the curing agent includes the amine-containing adduct and free (unreacted) amine curing agent. For example, the molar ratio of the amine curing agent to the epoxy resin having two glycidyl groups can be greater than 2.5:1, greater than 3:1, greater than 3.5:1 or greater than 4:1.

[0059] Useful aliphatic amines need not be cyclic and can include straight-chain and / or branched polyetheramines. In some embodiments, the curing agent composition comprises at least one adduct of an excess of a difunctional non-branched polyetheramine and an epoxy resin, typically in a molar excess of 200% to 800%, 300% to 600%, 400% to 500%, or in some embodiments less than, equal to, or greater than 200%, 250%, 300%, 350%, 400%, 450%, 500%, 550%, 600%, 650%, 700%, 750% or 800%.

[0060] The non-branched polyetheramine can have a molecular weight of 130 g / mol to 500 g / mol, 180 g / mol to 400 g / mol, 200 g / mol to 300 g / mol, or in some embodiments less than, equal to, or greater than 130 g / mol, 140 g / mol, 150 g / mol, 160 g / mol, 170 g / mol, 180 g / mol, 190 g / mol, 200 g / mol, 220 g / mol, 250 g / mol, 270 g / mol, 300 g / mol, 320 g / mol, 350 g / mol, 370 g / mol, 400 g / mol, 420 g / mol, 450 g / mol, 470 g / mol or 500 g / mol.

[0061] The non-branched polyetheramine can have between one and four ether oxygens and more typically two or three ether oxygens. In some embodiments, the non-branched polyetheramine can be a compound according to Formula I:

[0062] H 2 N-[(CH 2 ) x O] y -(CH 2 ) x -NH 2 [I],

[0063] wherein y is selected from 1, 2, 3 or 4, and wherein each x is independently selected from 2, 3 or 4.

[0064] In some embodiments, the non-branched polyetheramine can be 4,7,10-trioxa-1,13-tridecanediamine (TTD). In some embodiments, the non-branched polyether diamine can be 4,7-dioxadecane 1,10-diamine, which is commercially available under the trade name JEFFAMINE EDR 176.

[0065] Relative to the total weight of the gap-filling adhesive before curing, a suitable amount of polyetheramine can be 5% to 30%, 5% to 20%, 5% to 15%, or in some embodiments less than, equal to, or greater than 5%, 10%, 15%, 20%, 25%, or 30%.

[0066] In some cases, the hardener portion further comprises a co-curing agent. The co-curing agent can be imidazole or its salt, imidazoline or its salt, or a phenol substituted with a tertiary amino group. An exemplary co-curing agent is tris-2,4,6-(dimethylaminomethyl)phenol, which is commercially available under the trade name ANCAMINE K54 from Evonik Industries AG, Essen, Germany.

[0067] Any component that can be present in the base portion of the two-part curable gap-filling adhesive can also be present in the hardener portion. For example, the hardener portion can contain any inorganic filler described in the reference base portion in the amounts provided earlier, such as fumed silica. The hardener portion can also contain any phosphate ester used in combination with the inorganic filler, as described in the reference base portion in the amounts provided previously. The hardener portion can also contain any core-shell rubber toughening agent described in the reference base portion in the amounts provided earlier.

[0068] In any of the above cases, both the base portion and the hardener portion can contain the above components in similar or different proportions.

[0069] Either or both of the base portion and the hardener portion can additionally contain additives, including impact modifiers, other functional fillers, rheological modifiers, and / or pigments known to those skilled in the art.

[0070] Interstitial filling method

[0071] Before use, the base portion and the hardener portion are kept separate from each other to avoid premature curing. In use, these portions are mixed to provide a homogeneous reactive mixture. The amounts of each portion contained in the mixture can be selected to provide the desired molar ratio of epoxy groups from the base portion to amine hydrogen atoms from the hardener portion. The ratio of the amine hydrogen equivalent weight of the curing agent to the epoxy equivalent can be selected such that there are sufficient amine groups to react completely with the epoxy groups in the epoxy resin, as well as any other reactive diluents or additives (if present).

[0072] The now mixed gap-filling adhesive can then be disposed between the bonding surfaces of two or more corresponding substrates and then allowed to cure, thereby providing a bonded assembly. In a preferred bonding method, two substrates cooperate with a reactive mixture disposed therebetween, and the two substrates are further fixed to each other using mechanical fasteners that extend through the substrates and the reactive mixture during curing. The provided composition can be particularly suitable as a gasket material, especially for filling residual gaps between components of an assembly while acting as an adhesive capable of supporting tensile, shear, and peel loads.

[0073] In many embodiments, the gap-filling adhesive composition will have a low viscosity at ambient temperature, enabling it to be syringe injected or otherwise applied. Generally, the composition exhibits a low degree of relaxation or creep upon application.

[0074] In many embodiments, the gap-filling adhesive composition provided herein will be fully cured after 24 to 48 hours at ambient temperature and can be sanded or drilled 4 hours after application. In many embodiments, the gap-filling adhesive composition will have a pot life (time for positioning and adjustment) of about 3 hours and cure can be accelerated by gentle heating, typically curing at 70 °C in less than 30 minutes.

[0075] The cured composition exhibits good mechanical properties required for gap-filling applications (and especially gap-filling applications for the automotive and aircraft industries). For example, the cured gasket composition may have a cohesive strength of at least 2500 psi (17.2 MPa), as measured by lap shear strength. For example, the lap shear strength can be at least 3000 psi (20.7 MPa) or at least 3200 psi (22.1 MPa).

[0076] Substrate materials can include metals (e.g., steel, iron, copper, aluminum, or alloys thereof) and composite materials. Composites typically contain one or more types of fibers embedded in a resin. Typical fibers include carbon fibers, glass fibers, and combinations thereof. The resin can be an epoxy resin, a phenolic resin, a polyamide resin, or combinations or other resins thereof. Preferably, the composition is applied to fill residual gaps between composite materials, most preferably fiber-reinforced resins, including carbon fiber and glass fiber-reinforced epoxy composites.

[0077] In many embodiments, the gap-filling adhesive composition will exhibit high compressive strength characteristics at ambient and elevated temperatures, as well as high peel resistance at non-elevated temperatures, such as at ambient temperature. For example, the gap-filling adhesive can have a compressive modulus of 500 MPa to 2500 MPa, 700 MPa to 2000 MPa, or 700 MPa to 1500 MPa at 90 °C when cured. The same gap-filling adhesive can have an average floating roller peel strength of 50 N / 25 mm to 250 N / 25 mm, 100 N / 25 mm to 250 N / 25 mm, or 120 N / 25 mm to 250 N / 25 mm at ambient temperature when cured.

[0078] The gap-filling adhesives provided are not limited to applications in aircraft and automotive components. The gaps to be filled can also be located between assembled parts or components of residential or commercial buildings. For example, the provided gap-filling adhesives can be used to fill gaps in components of a wind power plant or a power station, such as the rotor blades or towers of a wind turbine.

[0079] Additional exemplary embodiments are provided below, which are not intended to be exhaustive:

[0080] 1. A two-part curable gap-filling adhesive, the two-part curable gap-filling adhesive comprising: a base part, the base part comprising: a polyfunctional epoxy resin having at least three epoxy functionalities; and a difunctional epoxy resin blended miscibly with the polyfunctional epoxy resin; and a hardener part, the hardener part comprising a polyetheramine; wherein the base part or the hardener part further comprises an inorganic filler present in an amount of 10% to 60% based on the total weight of the two-part curable gap-filling adhesive, and a phosphate ester.

[0081] 2. The two-part curable gap-filling adhesive according to embodiment 1, wherein the polyfunctional epoxy resin and the difunctional epoxy resin are present in a weight ratio of 1:1 to 6:1.

[0082] 3. The two-part curable gap-filling adhesive according to embodiment 1 or 2, wherein the base part and / or the hardener part further comprises core-shell rubber particles present in an amount of 1% to 20% based on the total weight of the two-part curable gap-filling adhesive.

[0083] 4. The two-part curable gap-filling adhesive according to any one of embodiments 1-3, wherein the polyfunctional epoxy resin comprises a trifunctional epoxy resin.

[0084] 5. The two-part curable gap-filling adhesive according to embodiment 4, wherein the trifunctional epoxy resin comprises triphenylmethane triglycidyl ether.

[0085] 6. The two-part curable gap-filling adhesive according to any one of embodiments 1-5, wherein the polyfunctional epoxy resin comprises a tetrafunctional epoxy resin.

[0086] 7. The two-part curable gap-filling adhesive according to embodiment 6, wherein the tetrafunctional epoxy resin comprises 4,4'-methylenebis(N,N-diglycidylaniline).

[0087] 8. The two-part curable gap-filling adhesive according to any one of embodiments 1-7, wherein the trifunctional epoxy resin and the tetrafunctional epoxy resin are present in a relative weight ratio of 1:1 to 8:1.

[0088] 9. The two-part curable gap-filling adhesive according to any one of embodiments 1-8, wherein the polyetheramine comprises trioxadecane diamine.

[0089] 10. The two-part curable gap-filling adhesive according to any one of embodiments 1-9, wherein the polyetheramine is present in an amount of 5% to 30% based on the total weight of the two-part curable gap-filling adhesive.

[0090] 11. The two-part curable gap-filling adhesive according to any one of embodiments 1-10, wherein the inorganic filler comprises pyrogenic silica.

[0091] 12. A bonding assembly, the bonding assembly comprising a reaction product of the two-part curable gap-filling adhesive according to any one of embodiments 1-11, the reaction product being disposed between the bonding surfaces of two or more corresponding substrates.

[0092] Examples

[0093] The objects and advantages of the present disclosure are further illustrated by the following non-limiting examples, but the specific materials and their amounts, as well as other conditions and details cited in these examples, should not be construed as undue limitations on the present disclosure. Unless otherwise specified, all parts, percentages, and ratios in the examples and the remainder of this specification are by weight.

[0094] Table 1: Materials

[0095]

[0096]

[0097]

[0098] Testing method :

[0099] The 2024-T3 bare aluminum panels are obtained from Erickson Metals of Minnesota, Inc., Coon Rapids, Minnesota. Prior to bonding with the structural adhesive, the panels are subjected to the following panel preparation process:

[0100] Panel preparation

[0101] Immerse the bare aluminum panels in an OAKITE 165 (BASF Corporation) caustic wash solution at 85 °C (185 °F) for 10 minutes. Then immerse the panels in tap water at 21 °C (69.8 °F) for 10 minutes, followed by continuous spray rinsing with tap water for approximately 3 minutes. Then immerse the panels in a Forest Products Laboratory (FPL) etch solution at 66 °C (151 °F) for 10 minutes, after which the panels are spray rinsed with water at 21 °C (69.8 °F) for approximately 3 minutes, allowed to drain for an additional 10 minutes, and then dried in an oven at 54 °C for 30 minutes. Prepare the etched panels for bonding with the adhesive and use them within 8 - 12 hours.

[0102] Floating roller peel (FRP) strength test

[0103] Follow the method of EN2243-2:2006. Prepare etched panels of 2024-T3 bare aluminum measuring 20.3 cm × 7.6 cm × 0.16 cm (8.0 inches × 3.0 inches × 0.063 inches) and 25.4 cm × 7.6 cm × 0.064 cm (10 inches × 3 inches × 0.025 inches) for testing as described above under "Panel Preparation". Apply the adhesive corresponding to the example or comparative example to the etched panel of 2024-T3 bare aluminum measuring 20.3 cm × 7.6 cm × 0.16 cm. Then apply the primed 25.4 cm X 7.6 cm X 0.064 aluminum panel to the 20.3 cm × 7.6 cm × 0.16 cm panel to which the adhesive has been applied. Then press the assembly between metal blocks at an approximate pressure of 2 - 5 psi (13.8 - 34.5 KPa). Cure the panel assembly at ambient temperature for 72 hours and then evaluate the floating roller peel strength according to ASTM D-3167-76 with the following modifications. For each example or comparative example, test three samples and report the average value (in N / 25 mm). Cut a test strip measuring 1.27 cm (0.5 inches) wide along the longitudinal direction of the bonded aluminum panels. Conduct the test at a rate of 30.5 cm / minute (6 inches / minute) at ambient temperature. In each test, peel the thinner substrate from the thicker substrate and normalize the results to a width of 25 mm (approx. 1 inch).

[0104] Compression modulus test

[0105] Cylindrical samples 2.54 cm (1 inch) in length and 1.27 cm (0.5 inch) in diameter were prepared by injecting the mixed product into a silicone mold. These samples were cured at room temperature for one week. The compression modulus of each compound was tested at a test speed of 0.127 cm / min (0.05 inch / min) according to the method of ISO604:2002. Five specimens were tested for each composition and the average value was recorded. For testing at an elevated temperature (i.e., 90 °C), the samples were pre-conditioned at this temperature for at least fifteen minutes before testing.

[0106] Examples 1 - 4 (EX1 - EX4) and Comparative Examples 1 - 2 (CE1 - CE2)

[0107] Preparation of Part A

[0108] Part A of the epoxy curable composition was prepared by combining the primary amine component (EC130 or 2422 or BAPP) with epoxy resin E828 in a glass container equipped with a laboratory stirrer in each case. The mixture was mixed at ambient temperature for about fifteen minutes and then heated to 80 °C (176 °F) by using an oil bath. The mixture was kept at 80 °C (176 °F) with stirring for sixty minutes. Then the mixture was cooled to ambient temperature and transferred to a DAC 150 SPEEDMIXER (obtained from Hauschild & Co. KG of Hamm Westphalia, Germany). ATBN and K54 were added to the mixture and mixed at 2000 rpm for one minute. Then SF20, A140, R202 and Blue were added and mixed at 3500 rpm for two minutes. Then the composition was degassed under vacuum for 2 minutes while mixing. In Table 2, all concentrations are given in weight percentages.

[0109] Table 2: Composition of Part A (weight percentage)

[0110]

[0111]

[0112] Preparation of Part B :

[0113] Part B of the epoxy curable composition was prepared by combining the compounds listed in Table 3 in a DAC 150 SPEEDMIXER at ambient temperature. In the first step, the epoxy resin component and the wetting agent were mixed at 3000 rpm for two minutes. Then the solid components were added and mixed at 3500 rpm for two minutes. Then the mixture was degassed at 2000 rpm under vacuum for two minutes. In Table 3, all concentrations are given in weight percentages.

[0114] Table 3: Composition of Part B (weight percentage)

[0115] EX1 EX2 EX3 EX4 CE1 CE2 MX257 14.45 14.45 14.45 14.45 14.45 14.45 T742 30 30 30 0 30 30 MY721 17 17 17 0 17 17 D.E.N.431 9 9 9 56 9 9 E1510 3 3 3 3 3 3 E757 1.5 1.5 1.5 1.5 1.5 1.5 GLYEO 1.5 1.5 1.5 1.5 1.5 1.5 W9010 0.5 0.5 0.5 0.5 0.5 0.5 SF20 21 21 21 21 21 21 R202 2 2 2 2 2 2 C - Yellow 0.05 0.05 0.05 0.05 0.05 0.05

[0116] Mixing of Part A and Part B :

[0117] Using a static Quadro MFQ 10 - 24T mixer obtained from Sulzer Mixpac of Winterthur, Switzerland, Parts A and B of the composition were mixed together at a volume ratio of 2:1 (Part B: Part A) using a 200 ml column at ambient temperature.

[0118] Testing

[0119] Compressive modulus and FRP tests were conducted. The test conditions and results are presented in Table 4.

[0120] Comparative Example 3 (CE3)

[0121] Samples of LOCTITE EA 9394 AERO adhesive obtained from Henkel Corporation of Düsseldorf, Germany, were subjected to compressive modulus and FRP tests. The results are shown in Table 4.

[0122] Table 4: Test results

[0123] Examples Compression modulus, MPa (psi) FRP N / 25mm EX1 1000(1.43E5) 125 EX2 1100(1.57E5) 130 EX3 1200(1.71E5) 30 EX4 440(6.29E4) 175 CE1 1500(2.14E5) 0 CE2 1350(1.93E5) 0 CE3 1500(2.14E5) 0

[0124] All references, patents, and patent applications cited in the above - mentioned patent - certificated application are hereby incorporated by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between the incorporated reference section and this application, the information in the foregoing description shall prevail. The foregoing description given to enable a person of ordinary skill in the art to practice the present disclosure protected by the claims should not be construed as limiting the scope of the present disclosure, which is defined by the claims and all their equivalents.

Claims

1. A two-part curable gap-filling adhesive, the two-part curable gap-filling adhesive comprising: A base part, the base part comprising: A polyfunctional epoxy resin having an epoxy functionality of at least three, wherein the polyfunctional epoxy resin comprises a trifunctional epoxy resin and a tetrafunctional epoxy resin in a relative weight ratio of 1:1 to 8:1; and A difunctional epoxy resin blended miscibly with the polyfunctional epoxy resin; and A hardener part, the hardener part comprising a polyetheramine; Wherein the base part or the hardener part further comprises an inorganic filler present in an amount of 10% to 60% relative to the total weight of the two-part curable gap-filling adhesive, and a phosphate ester, Wherein the polyfunctional epoxy resin and the difunctional epoxy resin are present in a weight ratio of 1:1 to 6:1; Wherein the polyetheramine is present in an amount of 10% to 30% relative to the total weight of the two-part curable gap-filling adhesive; Wherein the base part and / or the hardener part comprises core-shell rubber particles; and Wherein the inorganic filler comprises fumed silica.

2. The two-part curable gap-filling adhesive according to claim 1, wherein the base part and / or the hardener part comprises core-shell rubber particles present in an amount of 1% to 20% relative to the total weight of the two-part curable gap-filling adhesive.

3. The two-part curable gap-filling adhesive according to claim 1, wherein the trifunctional epoxy resin comprises triphenylmethane triglycidyl ether.

4. The two-part curable gap-filling adhesive according to claim 1, wherein the tetrafunctional epoxy resin comprises 4,4'-methylenebis(N,N-diglycidylaniline).

5. The two-part curable gap-filling adhesive according to any one of claims 1-4, wherein the polyetheramine comprises trioxadecane diamine.

6. A bonding assembly, the bonding assembly comprising a reaction product of the two-part curable gap-filling adhesive according to any one of claims 1-5, the reaction product being disposed between the bonding surfaces of two or more corresponding substrates.

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