阅读说明：本技术 用于汽车应用的低密度环氧复合结构粘合剂 (Low density epoxy composite structural adhesives for automotive applications ) 是由 W·邝 R·谢 J·特雷维诺三世 于 2019-02-14 设计创作，主要内容包括：本公开内容提供一种复合结构粘合剂,其包含环氧树脂、低密度颗粒填料和硬化剂,复合结构粘合剂在固化时表现出至少以下良好平衡的性能：(i)密度小于1g/cm<Sup>3</Sup>；(ii)压缩模量大于500MPa；和(iii)搭接剪切强度大于750psi。该复合结构粘合剂可以用于多种应用,例如用于汽车应用以用来粘结和/或密封金属、塑料和复合材料部件。(The present disclosure provides a composite structural adhesive comprising an epoxy resin, a low density particulate filler and a hardener, the composite structural adhesive exhibiting, when cured, a good balance of at least the following properties: (i) density less than 1g/cm 3 (ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi. The composite structural adhesives may be used in a variety of applications, such as in automotive applications for bonding and/or sealing metal, plastic, and composite parts.)

1. A composite structural adhesive comprising:

(a) an epoxy resin;

(b) a low density particulate filler; and

(c) hardening agent

Wherein the composite structural adhesive exhibits at least the following properties when cured: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi.

2. The composite structural adhesive according to claim 1, wherein the epoxy resin comprises at least one multifunctional epoxy resin.

3. The composite structural adhesive according to claim 2, wherein the multifunctional epoxy resin is a trifunctional epoxy resin.

4. The composite structural adhesive according to claim 1, wherein the hardener comprises a polyfunctional amine or anhydride.

5. The composite structural adhesive according to claim 1, wherein the low density particulate filler comprises inorganic microspheres.

6. The composite structural adhesive of claim 1, further comprising a multifunctional acrylate.

7. The composite structural adhesive according to claim 1, further comprising a flame retardant consisting of a mixture of a compound selected from alkaline earth metal hydroxides or aluminum group hydroxides and at least one phosphorus-containing material.

8. A method of forming a bonded joint between two substrates comprising providing the composite structural adhesive according to claim 1, applying the composite structural adhesive to a surface of at least one of the two substrates, joining the two substrates such that the composite structural adhesive is sandwiched between the two substrates, and curing the composite structural adhesive to form a bonded joint between the two substrates.

9. The method of claim 8, wherein at least one of the two substrates is a metal.

10. A method according to claim 9, wherein the further substrate is a metal.

11. The method of claim 9, wherein the other substrate is not a metal.

12. The method of claim 8, wherein the two substrates are not metals.

13. A one-part composite structural adhesive comprising from about 10 wt% to about 70 wt% of an epoxy resin, from about 2 wt% to about 50 wt% of a low density particulate filler, and up to about 45 wt% of a hardener, wherein the wt% is based on the total weight of the composite structural adhesive, and wherein the one-part composite structural adhesive exhibits at least the following properties when cured: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi.

14. The one-part composite structural adhesive of claim 13, further comprising up to about 40 wt% of a flame retardant, wherein the wt% is based on the total weight of the composite structural adhesive.

15. A two-part composite structural adhesive comprising:

(a) part a comprising from about 10 wt% to about 90 wt% of an epoxy resin, from about 5 wt% to about 80 wt% of a low density particulate filler, and from about 5 wt% to about 60 wt% of a flame retardant, wherein the wt% is based on the total weight of part a; and

(b) part B comprising from about 10 wt% to about 90 wt% of a hardener, from about 5 wt% to about 80 wt% of a low density particulate filler, and from about 5 wt% to about 60 wt% of a flame retardant, wherein the wt% is based on the total weight of part B;

wherein a cured material is provided by mixing part a and part B together to form a composite structural adhesive and curing the composite structural adhesive, the material exhibiting at least the following properties: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi.

16. The two-part composite structural adhesive according to claim 15, wherein part a further comprises from about 0.5 wt% to about 25 wt% of a multifunctional acrylate, wherein the wt% is based on the total weight of part a.

17. The two-part composite structural adhesive according to claim 15, wherein part a and part B are mixed in a weight ratio of about 0.2:1 to about 2: 1.

Technical Field

The present disclosure generally relates to a composite structural adhesive comprising an epoxy resin, a low density particulate filler, and a hardener. The composite structural adhesives are particularly useful in automotive applications for bonding and/or sealing metal, plastic and composite parts.

Background

In the design of next generation automobiles, fuel efficiency has become important. To improve fuel economy, automobile manufacturers have begun replacing the heavier weight metals used in car and truck production with lighter weight metal, plastic and composite parts. The use of structural adhesives during assembly has become increasingly popular because the mechanical fasteners (nuts, bolts, screws, rivets, etc.) typically used to assemble heavier weight metals are not always feasible for assembling these lower weight components. Not only can structural adhesives reduce vehicle weight (it is estimated that these adhesives can provide up to 20 weight percent savings over metal fasteners), but the parts no longer need to be drilled or punched and the assembler does not need to measure torque or re-check the fastening operation to ensure proper bonding.

Structural adhesives that replace or reinforce metal fasteners and/or welds during automotive assembly are typically based on epoxies, polyurethanes, and acrylics. For example:

WO2016/108958 discloses a one-component structural adhesive comprising an epoxy resin, a polyurethane-based toughener, at least one amphiphilic block copolymer and one or more curing agents. Such structural adhesives are taught to exhibit improved impact resistance at low temperatures;

U.S. patent No. 9534072 discloses a structural adhesive prepared by reacting an organic polyisocyanate with a compound containing isocyanate-reactive hydrogen atoms in the presence of a trimerization catalyst. It is taught that such structural adhesives exhibit good adhesion under more severe weather conditions, such as at elevated temperatures or under salt-containing conditions;

WO2015/164031 discloses a two-component structural adhesive comprising acrylate polyurethane, epoxy resin, polythiol and polyamine. It is taught that such structural adhesives exhibit reduced read-through;

US2014/0147677 discloses a structural adhesive comprising an epoxy resin and a hardener, wherein the hardener is present in an amount about equal to or less than stoichiometric with respect to the epoxy resin. Such structural adhesives are taught to have good moisture resistance, failure mode after cure, impact stability and corrosion resistance;

US2011/0024039 and US patent No. 8618204 disclose one-and two-component structural adhesives, which typically comprise an epoxy resin, a curing agent, and a reactive liquid modifier or oil substitute. These structural adhesives are taught to exhibit good adhesion to clean surfaces and to surfaces contaminated with hydrocarbon-containing materials;

WO2007/143646 discloses a structural adhesive comprising an epoxy resin, a polyester, a blowing agent and a curing agent. The structural adhesive is taught to exhibit good corrosion resistance due to the presence of polyester; and

US2007/0155879 discloses a two-component structural adhesive comprising a vinyl monomer, a soluble polymer and an acetylenic diol adhesion promoter. It is taught that such structural adhesives exhibit improvements in the ability to bond various metals.

Commercially available structural adhesives used by automotive manufacturers typically have a density of greater than 1.2g/cm³The density of (c). If this density could be reduced, the vehicle weight would also be reduced, which results in improved fuel economy or driving range of the vehicle. For example, electric vehicles manufactured today typically have a driving range of about 70-230 miles per charge, which is significantly smaller than that of conventional gasoline or diesel powered vehicles. Since the power of the battery/charge is limited, significant advantages are obtained by reducing the overall weight of the electric vehicle. However, attempts to reduce the density of structural adhesives used in automotive manufacturing have resulted in a corresponding reduction in their mechanical properties. Thus, if an automotive structural adhesive could be developed with reduced density without mechanical degradation, it would allow electric vehicles to reach a driving range of, for example, 400 miles or more per charge, similar to that of gasoline powered vehicles.

Disclosure of Invention

The present disclosure generally provides a composite structural adhesive comprising (a) an epoxy resin, (b) a low density particulate filler, and (c) a hardener, wherein the composite structural adhesive exhibits a good balance of at least the following properties when cured: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi.

The present disclosure also provides a method of forming a bonded joint between two substrates comprising providing the composite structural adhesive, applying the composite structural adhesive to a surface of at least one of the two substrates, joining the two substrates such that the composite structural adhesive is sandwiched between the two substrates, and curing the composite structural adhesive to form a bonded joint between the two substrates.

The composite structural adhesive may be used as a structural adhesive in a variety of applications, such as in vehicle components, including but not limited to the following: a marine vehicle; an aircraft vehicle; a railway vehicle; automotive vehicles such as cars and motorcycles; and bicycles.

Detailed description of the invention

The present disclosure generally provides a composite structural adhesive comprising (a) an epoxy resin, (b) a low density particulate filler, and (c) a hardener. It has been surprisingly found that when certain low density particulate fillers are combined with an epoxy resin and hardener and cured, the cured composite structural adhesives of the present disclosure exhibit a density that is 30% -60% less than conventional structural adhesives currently used in automotive bonding applications, while also exhibiting similar (if not improved) mechanical and chemical properties, such as compression modulus, lap shear strength, adhesion to many substrates, temperature resistance, and flame retardancy. Thus, the composite structural adhesives of the present disclosure unexpectedly exhibit an excellent balance of physical, mechanical, and thermal properties compared to those of prior art structural adhesives.

The following terms shall have the following meanings:

as used herein, the term "structural adhesive" refers to an adhesive that is capable of bonding substrates together by surface attachment (i.e., the adhesive in a cured state forms part of the load-bearing structure of the bonded substrates). The structural adhesives of the present disclosure encompass one-component adhesives and multi-component adhesives such as two-component adhesives.

The term "low density particulate filler" means an average bulk density of less than about 0.6g/cm³E.g. 0.01g/cm³-0.5g/cm³Or 0.1g/cm³-0.4g/cm³The particulate filler of (3).

The term "high density particulate filler" means that the average bulk density is at least 1.5g/cm³Or at least 2.0g/cm³Or even at least 2.5g/cm³The particulate filler of (3).

The terms "cure", "cured" or similar terms mean that at least a portion of the polymerizable and/or crosslinkable components forming the composite structural adhesive are polymerized and/or crosslinked. Additionally, "curing" refers to subjecting the composite structural adhesive to curing conditions, such as, but not limited to, thermal curing, which results in the reaction of the reactive functional groups of the adhesive and results in polymerization and formation of a polymer. When the composite structural adhesive is subjected to curing conditions, and after polymerization and after most of the reactive groups have reacted, the reaction rate of the remaining unreacted reactive groups will gradually slow. The composite structural adhesive may be subjected to curing conditions until it is at least partially cured. The term "at least partially cured" means subjecting the composite structural adhesive to curing conditions wherein at least a portion of the reactive groups of the adhesive react to form a polymer. The composite structural adhesive may also be subjected to curing conditions such that substantially complete curing is obtained and wherein further curing does not result in significant further improvement in polymer properties such as compressive strength.

The term "reactive" refers to a functional group that is capable of chemically reacting with other functional groups either spontaneously or by the application of heat or by any other means known to those skilled in the art.

As used herein, the terms "on … …", "onto … …", "applied on … …", "applied on … …", "formed on … …", "deposited on … …", "deposited on … …" mean formed, covered, deposited or provided on a surface, but not necessarily in contact with the surface. For example, a composite structural adhesive that is "applied to a substrate" does not preclude the presence of one or more other intervening coating layers of the same or different composition located between the composite structural adhesive and the substrate.

When used in reference to the substantial absence of materials in an adhesive formulation, the term "substantially free" means that such materials are absent, or if present, are incidental impurities or by-products. In other words, the material does not affect the performance of the adhesive formulation.

The term "comprises (comprising)" and its derivatives are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is disclosed herein. For the avoidance of any doubt, all compositions claimed herein through use of the term "comprising" may include any additional additive or compound, unless indicated to the contrary. Conversely, the term "consisting essentially of … …", if present herein, excludes any other components, steps, or procedures from any subsequently recited range, except those that are not essential to operability, and the term "consisting of … …", if used, excludes any components, steps, or procedures not expressly described or recited. Unless otherwise indicated, the term "or" refers to the listed elements, individually as well as in any combination.

The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an epoxy resin" means one epoxy resin or more than one epoxy resin.

The terms "in an aspect," "according to an aspect," and the like generally mean that a particular feature, structure, or characteristic following the term is included in at least one aspect of the present disclosure, and may be included in more than one aspect of the present disclosure. Importantly, such phrases are not necessarily referring to the same aspect.

If the specification states that a component or feature is "may", "can", "result" or "may" include or have a property, that is, a particular component or feature is not required to include or have that property.

According to one aspect, the present disclosure provides a composite structural adhesive comprising (a) an epoxy resin (b) a low density particulate filler and (c) a hardener, wherein the resulting cured product formed by curing the composite structural adhesive comprises at least the following well-balanced properties: (1) density less than 1.0g/cm³(ii) a (2) Lap shear strength greater than 1000 psi; and (3) a compressive modulus greater than 750 MPa.

Generally, any epoxy-containing compound is suitable for use as the epoxy resin of the present disclosure, for example, U.S. patent nos. 5476748; 6506494, respectively; 6632893, respectively; 6376564, respectively; 6348513, respectively; 8742018, respectively; and 8440746, which are incorporated herein by reference. The epoxy resin may be solid or liquid and has at least one oxirane ring that is polymerizable by ring opening, i.e., an average epoxy functionality greater than 1, and in some aspects at least 2. The epoxy resin may be monomeric or polymeric, as well as aliphatic, cycloaliphatic, heterocyclic, aromatic, hydrogenated, or mixtures thereof. In some aspects, the epoxy resin contains greater than 1.5 epoxy groups per molecule and preferably at least 2 epoxy groups per molecule.

According to one aspect, the epoxy resin has a weight average molecular weight of about 150 to about 10000 or about 180 to about 1000. The molecular weight of the epoxy resin may also be selected to provide the desired properties of the cured adhesive.

In one aspect, the epoxy resin can be a polyglycidyl epoxy compound. The polyglycidyl epoxy compound may be polyglycidyl ether, poly (. beta. -methylglycidyl) ether, polyglycidyl ester or poly (. beta. -methylglycidyl) ester. The synthesis and examples of polyglycidyl ethers, poly (. beta. -methylglycidyl) ethers, polyglycidyl esters, and poly (. beta. -methylglycidyl) esters are disclosed in U.S. Pat. No. 5972563, which is incorporated herein by reference. For example, ethers may be obtained by reacting a compound having at least one free alcoholic hydroxyl group and/or phenolic hydroxyl group with a suitable substituted epichlorohydrin under alkaline conditions or in the presence of an acidic catalyst, followed by alkaline treatment. The alcohol may be, for example, acyclic alcohols such as ethylene glycol, diethylene glycol and higher poly (oxyethylene) glycols, propane-1, 2-diol, or poly (oxypropylene) glycols, propane-1, 3-diol, butane-1, 4-diol, poly (oxytetramethylene) glycols, pentane-1, 5-diol, hexane-1, 6-diol, hexane-2, 4, 6-triol, glycerol, 1,1, 1-trimethylolpropane, ditrimethylolpropane, pentaerythritol and sorbitol. However, suitable glycidyl ethers can also be obtained from cycloaliphatic alcohols, for example 1, 3-or 1, 4-dihydroxycyclohexane, bis (4-hydroxycyclohexyl) methane, 2, 2-bis (4-hydroxycyclohexyl) propane or 1, 1-bis (hydroxymethyl) cyclohex-3-ene, or they can have aromatic rings such as N, N-bis (2-hydroxyethyl) aniline or p, p' -bis (2-hydroxyethylamino) diphenylmethane.

Particularly important representatives of polyglycidyl ethers or poly (. beta. -methylglycidyl) ethers are based on monocyclic phenols, for example on resorcinol or hydroquinone, on polycyclic phenols, for example on bis (4-hydroxyphenyl) methane (bisphenol F), 2, 2-bis (4-hydroxyphenyl) propane (bisphenol A), bis (4-hydroxyphenyl) sulfone (bisphenol S), alkoxylated bisphenol A, F or S, triol-extended bisphenol A, F or S, brominated bisphenol A, F or S, hydrogenated bisphenol A, F or S, glycidyl ethers of phenols and phenols having side groups or side chains, on condensation products of phenols or cresols obtained under acidic conditions with formaldehyde, for example bisphenol A and cresol novolaks, or on siloxane diglycidyl bases.

Polyglycidyl esters and poly (. beta. -methylglycidyl) esters can be produced by reacting epichlorohydrin or glycerol dichloropropanol or beta-methyl epichlorohydrin with polycarboxylic acid compounds. The reaction is conveniently carried out in the presence of a base. The polycarboxylic acid compound may be, for example, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid or dimerized or trimerized linoleic acid. However, likewise, it is also possible to use cycloaliphatic polycarboxylic acids, such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid or 4-methylhexahydrophthalic acid. It is also possible to use aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, trimellitic acid or pyromellitic acid, or, for example, carboxyl-terminated adducts of trimellitic acid and polyols such as glycerol or 2, 2-bis (4-hydroxycyclohexyl) propane.

In another aspect, the epoxy resin may be a non-glycidyl epoxy compound. The non-glycidyl epoxy compounds may be linear, branched or cyclic in structure. For example, may include one or more epoxide compounds wherein the epoxide group forms part of an alicyclic or heterocyclic ring system. Other epoxy-containing compounds include those having at least one epoxycyclohexyl group bonded directly or indirectly to a group containing at least one silicon atom. Examples are disclosed in U.S. patent No. 5639413, which is incorporated herein by reference. Still others include epoxides containing one or more cyclohexene oxide groups and epoxides containing one or more cyclopentene oxide groups.

Specific examples of non-glycidyl epoxy compounds include the following: a difunctional non-glycidyl epoxide compound wherein the epoxide group forms part of a cycloaliphatic or heterocyclic ring system: bis (2, 3-epoxycyclopentyl) ether, 1, 2-bis (2, 3-epoxycyclopentyloxy) ethane, 3, 4-epoxycyclohexyl-methyl 3, 4-epoxycyclohexanecarboxylate, 3, 4-epoxy-6-methyl-cyclohexylmethyl 3, 4-epoxy-6-methylcyclohexanecarboxylate, bis (3, 4-epoxycyclohexylmethyl) adipate, bis (3, 4-epoxy-6-methylcyclohexylmethyl) adipate, ethylenebis (3, 4-epoxycyclohexanecarboxylate) and ethyleneglycol bis (3, 4-epoxycyclohexylmethyl).

In some particular aspects, the difunctional non-glycidyl epoxy compound comprises a cycloaliphatic difunctional non-glycidyl epoxy, such as 3, 4-epoxycyclohexyl-methyl 3 ', 4 ' -epoxycyclohexanecarboxylate and 2,2 ' -bis- (3, 4-epoxy-cyclohexyl) -propane, with the former being most preferred.

In yet another aspect, the epoxy resin may be a poly (N-glycidyl) compound or a poly (S-glycidyl) compound. The poly (N-glycidyl) compounds can be obtained, for example, by dehydrochlorination of the reaction product of epichlorohydrin with an amine containing at least two amine hydrogen atoms. These amines may be, for example, n-butylamine, aniline, toluidine, m-xylylenediamine, bis (4-aminophenyl) methane or bis (4-methylaminophenyl) methane. Other examples of poly (N-glycidyl) compounds include N, N '-diglycidyl derivatives of cycloalkyleneureas, such as ethyleneurea or 1, 3-propyleneurea, and N, N' -diglycidyl derivatives of hydantoins, such as 5, 5-dimethylhydantoin. Examples of poly (S-glycidyl) compounds are di-S-glycidyl derivatives derived from dithiols, such as ethane-1, 2-dithiol or bis (4-mercaptomethylphenyl) ether.

Epoxy resins in which the 1, 2-epoxide groups are attached to different heteroatoms or functional groups can also be used. Examples include the N, N, O-triglycidyl derivative of 4-aminophenol, the glycidyl ether/glycidyl ester of salicylic acid, N-glycidyl-N' - (2-glycidyloxypropyl) -5, 5-dimethylhydantoin or 2-glycidyloxy-1, 3-bis (5, 5-dimethyl-1-glycidylhydantoin-3-yl) propane.

Other epoxide derivatives such as vinylcyclohexene dioxide, limonene monooxide, vinylcyclohexene monooxide, 3, 4-epoxycyclohexylmethacrylate, 3, 4-epoxy-6-methylcyclohexylmethyl 9, 10-epoxystearate, and 1, 2-bis (2, 3-epoxy-2-methylpropoxy) ethane may also be used.

Further, the epoxy resin may be a pre-reaction adduct of an epoxy resin such as those described above, with a compound having free hydrogen reactive with the epoxy group. Typically, such reactive hydrogens are present in carboxylic acid groups, aromatic hydroxyl groups, amino groups, and mercapto groups.

In one particular aspect, the composite structural adhesive may contain only one epoxy resin, while in other aspects, the composite structural adhesive may contain a mixture of epoxy resins.

According to another aspect, the epoxy resin comprises at least one multifunctional epoxy resin. The multifunctional epoxy resin may be a difunctional epoxy resin, a trifunctional epoxy resin, a tetrafunctional epoxy resin, or a mixture thereof.

Examples of difunctional epoxy resins include, but are not limited to, diglycidyl ethers of bisphenol A-based materials (e.g., Epon)^TM828 epoxy resin, d.e.r.^TM331 and d.e.r.^TM661 epoxy resin,

123 epoxy resin, and

184 epoxy resin).

Examples of trifunctional epoxy resins include, but are not limited to, triglycidyl ethers of aminophenols (e.g., as inMY 0510, MY 0500, MY 0600, and MY 0610 epoxy).

Examples of tetrafunctional epoxy resins include, but are not limited to, tetraglycidyl ethers of methylenedianiline (e.g., toluene diamine)MY 9655 epoxy), tetraglycidyl diaminodiphenylmethane (e.g.MY-721, MY-720, 725, MY 9663, 9634, and 9655 epoxy resins) and sorbitol polyglycidyl ethers (e.g., EJ-190 epoxy resins and

GE-60 epoxy).

In yet another aspect, the epoxy resin may comprise at least one multifunctional epoxy resin and, together therewith, at least one monofunctional epoxy resin. Examples of such monofunctional epoxy resins include, but are not limited to, phenyl glycidyl ether, tolyl glycidyl ether, p-tert-butylphenyl glycidyl ether, C₆-C₂₈Alkyl glycidolAlkyl ether, C₆-C₂₈Fatty acid glycidyl esters and C₆-C₂₈An alkylphenol glycidyl ether.

The amount of epoxy resin used in the composite structural adhesive may depend on the target molecular weight and epoxy functionality. According to some aspects, the composite structural adhesive may include an epoxy resin in an amount of about 10 wt% to about 90 wt%, based on the total weight of the composite structural adhesive. In other aspects, the composite structural adhesive may include an epoxy resin in an amount of about 12.5 wt% to about 75 wt%, or about 15 wt% to about 60 wt%, or about 17.5 wt% to about 50 wt%, or even about 20 wt% to about 40 wt%, where the wt% is based on the total weight of the composite structural adhesive.

The composite structural adhesive also contains a low density particulate filler. In some aspects, the low-density particulate filler includes, but is not limited to, naturally occurring minerals, man-made materials, silica particles, lightweight waste products, and mixtures thereof. Examples of such fillers generally include, but are not limited to, perlite, vermiculite, hollow microspheres and microspheres or microbeads made of glass, ceramic, carbon, metal or synthetic resins, fumed silica, colloidal silica, precipitated silica, silica gels, ground tires, ground wood fibers, ground cellulose fibers, and ground polymeric foams made from a variety of different polymers including polyesters, polyamides, polystyrenes, polyurethanes, and polyisocyanurates.

In other aspects, the low-density particulate filler may comprise irregularly shaped particles or spherical particles or mixtures thereof.

Irregularly shaped particles include particles that lack a uniform spherical or platelet shape. Irregularly shaped particles are typically obtained by precipitation, milling or comminution or comprise fused or aggregated primary particles to produce particles having an irregular shape or surface texture. The irregularly shaped particles typically have a particle size of less than about 300 μm, and even less than about 100 μm.

The spherical particles have or substantially have a spherical shape and may be hollow or solid. Spherical particles typically have a particle size of less than about 300 μm, and even less than about 100 μm.

According to a particular aspect, the low-density particulate filler comprises spherical hollow particles, such as hollow inorganic particles or hollow organic particles, such as inorganic microspheres or organic microspheres, or a combination thereof. The hollow portion of the particles may be filled with a gas or a mixture of gases, a liquid or a mixture of liquids, or a mixture of one or more gases and one or more liquids, or may be evacuated.

The inorganic microspheres may be selected from a variety of materials including, by way of example, glass, silica, ceramic (including sol-gel derived), zirconia, and combinations thereof. The inorganic particles can comprise silica, soda lime borosilicate glass, silica-alumina ceramic, alkali aluminosilicate ceramic types, alumina, or combinations thereof in some aspects. The inorganic microspheres may be selected such that they allow the cured composite structural adhesive to exhibit low density without compromising compressive strength. Thus, in one particular aspect, the inorganic microspheres will have less than 0.5g/cm³And at least 85 wt% and even at least 90 wt% of the inorganic microspheres have a crush strength of at least 2500psi or at least 4000psi, wherein the wt% is based on the total weight of the inorganic microspheres. The inorganic microspheres may have an average particle size of from about 1 μm to about 300 μm, or from about 10 μm to about 100 μm.

In another aspect, the inorganic microspheres are glass microspheres or microbubbles such as those described in U.S. patent No. 3365315, the contents of which are incorporated herein by reference. The walls of these microspheres are made by expanding solid glass particles at a temperature above 1000 ℃ to form an apparent density of about 0.14 to about 0.38g/cm³Tiny hollow spheres having a wall thickness of about 0.5-2.0 microns and an average particle size of about 60 microns. Other glassy or inorganic microspheres that may be used to synthesize fused water-insoluble alkali metal silicate-based glasses are described in U.S. patent No. 3230184, and microspheres made from sodium silicate useful in the present disclosure are described in U.S. patent No. 3030215, the contents of which are incorporated herein by reference. Microspheres made from thermally expanded natural minerals such as perlite, pozzolan, fly ash and vermiculite can also be used. Commercially available phosphorOrganic microspheres are included under the trade name Scotchlite^TMA glass bubble,Inorganic microspheres andthose under ceramic microspheres.

Organic microspheres include polymeric microspheres made from organic polymers (i.e., materials comprising repeat units derived from monomers containing at least one unsaturated carbon-carbon bond). Typical examples of such polymers include, but are not limited to, acrylonitrile polymers or copolymers, acrylate polymers or copolymers, vinylidene polymers or copolymers, polyacetate polymers or copolymers, polyester polymers or copolymers, vinylidene chloride/acrylonitrile copolymers, acrylate/acrylonitrile copolymers, and combinations thereof.

In addition, the organic microspheres may be unexpanded or pre-expanded organic hollow microspheres. Unexpanded organic cenospheres (sometimes referred to as expandable organic microbeads) are for example under the trade name

And

obtainable under microspheres. Such microspheres comprise a thermoplastic shell that contains a volatile liquid such as hydrocarbons (e.g., ethane, ethylene, propane, propylene, butane, isobutane, neopentane, acetylene, hexane, heptane, and isopentane), chlorofluorocarbons, tetraalkylsilanes (e.g., tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyln-propylsilane), and perfluorocarbons. When subjected to heat or similar activation energy, the microspheres expand significantly to many times their original size and retain that size after the activation energy is removed. The thermoplastic shell may include, but is not limited to, polyvinylidenepolyacrylonitrile-polymethylmethacrylate, and polystyrene-polyacrylonitrile copolymers.

The pre-expanded organic microspheres are pre-expanded by using an organic blowing agent (e.g., a hydrocarbon as described above, including pentane, isopentane, butane, or mixtures thereof) or an inorganic blowing agent (e.g., air, carbon dioxide, nitrogen, argon, or mixtures thereof) to provide particles having a larger size but a lower density. For example, the pre-expanded organic microspheres may contain 1% to 99%, 25% to 95%, or 50% to 90% air by volume. The pre-expanded microspheres may be partially expanded (i.e. capable of further expansion) or fully expanded. For example, the microspheres may be more than 50% expanded, more than 60% expanded, more than 70% expanded, more than 80% expanded, more than 90% expanded, or 100% (i.e., fully) expanded, as determined based on the density of the microspheres.

The pre-expanded organic microspheres described herein may be derived from expandable polymers including, for example, thermoplastic polymers. Examples include polystyrene (e.g., radical polymerized glass-clear polystyrene (GPPS) or anion polymerized polystyrene (APS)), styrene-based copolymers (e.g., styrene-maleic anhydride copolymer, styrene-butadiene copolymer, styrene- α -methylstyrene copolymer, acrylonitrile-butadiene-styrene (ABS) copolymer, styrene-acrylonitrile (SAN) copolymer, styrene-methyl methacrylate copolymer, acrylonitrile-styrene-acrylate (ASA) copolymer, methacrylate-butadiene-styrene (MBS) copolymer, or methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymer), polyethylene (e.g., low density polyethylene, high density polyethylene, and linear low density polyethylene), polypropylene, polyesters, polyvinyl chloride, cellulose acetate, copolymers of vinyl chloride and vinylidene chloride, polyacrylates, polymethacrylates, thermoplastic polyurethanes and polyamides, and mixtures thereof. Additional examples of suitable pre-expanded microspheres include those derived from polyphenylene ether, polystyrene-polyphenylene ether blends, polyoxymethylene, poly (methyl methacrylate), methyl methacrylate copolymers, ethylene-propylene copolymers (e.g., random and block), ethylene-vinyl acetate copolymers, polycarbonates, polyethylene terephthalate, aromatic polyester/polyether glycol block copolymers, polyethylene, and polymerized vinyl aromatic resins. Examples of vinyl aromatic resins include solid homopolymers of styrene, vinyl toluene, vinyl xylene, ethyl vinyl benzene, isopropyl styrene, t-butyl styrene, chlorostyrene, dichlorostyrene, fluorostyrene, bromostyrene; solid copolymers of two or more monovinyl aromatic compounds, and solid copolymers of one or more monovinyl aromatic compounds and a copolymerizable olefinic compound (e.g., acrylonitrile, methyl methacrylate, or ethyl acrylate).

Such pre-expanded organic microspheres are for example under the trade name

Micro-spheres,Expandable graphite particles and

commercially available under microspheres.

In one aspect, only the above inorganic microspheres are included in the composite structural adhesive, while in another aspect, a combination of the above organic microspheres and inorganic microspheres are included in the composite structural adhesive.

The concentration and properties of the low density particulate filler for the composite structural adhesive may be selected such that the density of the composite structural adhesive is less than 1g/cm³Or less than 0.8g/cm³Or even about 0.5g/cm³-0.75g/cm³Or still even about 0.55g/cm³-0.65g/cm³。

Thus, in one aspect, the composite structural adhesives of the present disclosure may contain from about 1 wt% to about 80 wt%, or from about 2 wt% to about 60 wt%, or from about 5 wt% to about 50 wt%, or from about 7.5 wt% to about 45 wt%, or from about 10 wt% to about 40 wt%, or even from about 15 wt% to about 30 wt% of the low-density particulate filler, based on the total weight of the composite structural adhesive.

According to another aspect, the hardening of the composite structural adhesive may be achieved by the addition of any one or more chemical materials known in the art for curing such adhesives. Such materials are compounds having reactive moieties that can react with the epoxy groups of the epoxy resin and are referred to herein as "hardeners" and also include materials known to those skilled in the art as curing agents, activators, catalysts or accelerators. While some hardeners promote curing by catalysis, other hardeners participate directly in the reaction of the resin and are incorporated into the thermoplastic polymer network formed by condensation, extension and/or crosslinking of the resin. Depending on the hardener, heat may or may not be required for significant reaction to occur. Oxidizing agents for epoxy resins include, but are not limited to, aromatic amines, cyclic amines, aliphatic amines, alkyl amines, polyether amines, including those which can be derived from polypropylene oxide and/or polyethylene oxide, anhydrides, carboxylic acid amides, polyamides, polyphenols, cresol and phenol novolac resins, imidazoles, guanidines, substituted ureas, melamine resins, guanamine derivatives, tertiary amines, lewis acid complexes such as boron trifluoride and boron trichloride, and polythiols. Any of the epoxy-modified amine products, Mannich-modified products, and Michael-modified addition products of the above hardeners may also be used. All of the above curing agents may be used alone or in any combination.

In a particular aspect, the hardener is a polyfunctional amine. As used herein, the term "polyfunctional amine" refers to an amine having at least two primary and/or secondary amino groups in one molecule. For example, the polyfunctional amine may be an aromatic polyfunctional amine having two amino groups bonded to benzene in any of the ortho, meta and para positional relationships, such as phenylenediamine, xylylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene and 3, 5-diaminobenzoic acid, aliphatic polyfunctional amines such as ethylenediamine and propylenediamine, alicyclic polyfunctional amines such as 1, 2-diaminocyclohexane, 1, 4-diaminocyclohexane, piperazine, 1, 3-bispiperidylpropane and 4-aminomethylpiperazine, and the like. These polyfunctional amines may be used alone or as a mixture thereof.

Exemplary aromatic amines include, but are not limited to, 1,8 diaminonaphthalene, m-phenylenediamine, diethylenetoluenediamine, diaminodiphenylsulfone, diaminodiphenylmethane, diaminodiethyldimethyldiphenylmethane, 4 ' -methylenebis (2, 6-diethylaniline), 4 ' -methylenebis (2-isopropyl-6-methylaniline), 4 ' -methylenebis (2, 6-diisopropylaniline), 4 ' - [1, 4-phenylenebis (1-methyl-ethylene) ] dianiline, 4 ' - [1, 3-phenylenebis (1-methyl-ethylene) ] dianiline, 1, 3-bis (3-aminophenoxy) benzene, bis- [4- (3-aminophenoxy) phenyl ] sulfone, bis- (3-aminophenoxy) phenyl ] sulfone, Bis- [4- (4-aminophenoxy) phenyl ] sulfone, 2' -bis [4- (4-aminophenoxy) phenyl ] propane. In addition, the aromatic amines may include heterocyclic polyfunctional amine adducts, as disclosed in U.S. patent nos. 4427802 and 4599413, both of which are incorporated herein by reference in their entirety.

Examples of cyclic amines include, but are not limited to, bis (4-amino-3-methyldicyclohexyl) methane, diaminodicyclohexylmethane, bis (aminomethyl) cyclohexane, N-aminoethylpyrazine, 3, 9-bis (3-aminopropyl) -2,4,8, 10-tetraoxaspiro (5,5) undecane, m-xylylenediamine, isophoronediamine, menthenediamine, 1, 4-bis (2-amino-2-methylpropyl) piperazine, N, n' -dimethylpiperazine, pyridine, picoline, 1, 8-diazabicyclo [5,4,0] -7-undecene, benzylmethylamine, 2- (dimethylaminomethyl) -phenol, 2-methylimidazole, 2-phenylimidazole and 2-ethyl-4-methylimidazole.

Exemplary aliphatic amines include, but are not limited to, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 3- (dimethylamino) propylamine, 3- (diethylamino) -propylamine, 3- (methylamino) propylamine, tris (2-aminoethyl) amine; 3- (2-ethylhexyloxy) propylamine, 3-ethoxypropylamine, 3-methoxypropylamine, 3- (dibutylamino) propylamine, and tetramethyl-ethylenediamine, 3 '-iminobis (propylamine), N-methyl-3, 3' -iminobis (propylamine), allylamine, diallylamine, triallylamine, polyoxypropylene diamine and polyoxypropylene triamine.

Exemplary alkylamines include, but are not limited to, methylamine, ethylamine, propylamine, isopropylamine, butylamine, sec-butylamine, tert-butylamine, n-octylamine, 2-ethylhexylamine, dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, di-sec-butylamine, di-tert-butylamine, di-n-octylamine, and di-2-ethylhexylamine.

Exemplary anhydrides include, but are not limited to, cyclohexane-1, 2-dicarboxylic anhydride, 1-cyclohexene-1, 2-dicarboxylic anhydride, 2-cyclohexene-1, 2-dicarboxylic anhydride, 3-cyclohexene-1, 2-dicarboxylic anhydride, 4-cyclohexene-1, 2-dicarboxylic anhydride, 1-methyl-2-cyclohexene-1, 2-dicarboxylic anhydride, 1-methyl-4-cyclohexene-1, 2-dicarboxylic anhydride, 3-methyl-4-cyclohexene-1, 2-dicarboxylic anhydride, 4-methyl-4-cyclohexene-1, 2-dicarboxylic anhydride, dodecenyl succinic anhydride, 4-methyl-1-cyclohexene-1, 2-dicarboxylic anhydride, phthalic anhydride, hexahydrophthalic anhydride, nadic methyl anhydride, dodecenyl succinic anhydride, tetrahydrophthalic anhydride, maleic anhydride, pyromellitic dianhydride, trimellitic anhydride, benzophenone tetracarboxylic dianhydride, bicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic anhydride, methylbicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic anhydride, bicyclo [2.2.1] hept-5-ene-2, 3-dicarboxylic anhydride, dichloromaleic anhydride, chlorendic anhydride, tetrachlorophthalic anhydride and any derivative or adduct thereof.

Exemplary imidazoles include, but are not limited to, imidazole, 1-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-n-propylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1, 2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-isopropyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 2-isopropylimidazole, 2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 2-cyanoethyl-2, 1-cyanoethyl-2-phenylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenylimidazole, 2-phenyl-4, 5-dihydroxymethylimidazole, 1, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-dodecyl-2-methylimidazole and 1-cyanoethyl-2-phenyl-4, 5-bis (2-cyanoethoxy) methylimidazole.

Exemplary substituted guanidines are methylguanidine, dimethylguanidine, trimethylguanidine, tetramethylguanidine, methylisobiguanide, dimethylbiguanide, tetramethylbiguanide, hexamethylbiguanide, heptamethylisobiguanide, and cyanoguanidine (dicyandiamide). Representative guanamine derivatives that may be mentioned are alkylated benzoguanamine resins, benzoguanamine resins or methoxymethylethoxymethylbenzguanamine. Substituted ureas may include p-chlorophenyl-N, N-dimethylurea (meturon), 3-phenyl-1, 1-dimethylurea (fenuron), or 3, 4-dichlorophenyl-N, N-dimethylurea (diuron).

Exemplary tertiary amines include, but are not limited to, trimethylamine, tripropylamine, triisopropylamine, tributylamine, tri-tert-butylamine, tri-N-octylamine, N-dimethylaniline, N-dimethyl-benzylamine, pyridine, N-methylpiperidine, N-methylmorpholine, N-dimethylaminopyridine, morpholine derivatives such as bis (2- (2, 6-dimethyl-4-morpholinyl) ethyl) - (2- (4-morpholinyl) ethyl) amine, bis (2- (2, 6-dimethyl-4-morpholinyl) ethyl) - (2- (2, 6-diethyl-4-morpholinyl) ethyl) amine, tris (2- (4-morpholinyl) ethyl) amine and tris (2- (4-morpholinyl) propyl) amine, tri-butyl amine, tri-N-butyl amine, N-dimethyl-4-morpholinyl) ethyl) amine, bis (2- (2, 6-dimethyl, Diazabicyclooctane (DABCO), and heterocyclic compounds having an amidine bond such as diazabicyclo.

Amine-epoxy adducts are well known in the art and are described, for example, in U.S. patent nos. 3756984, 4066625, 4268656, 4360649, 4542202, 4546155, 5134239, 5407978, 5543486, 5548058, 5430112, 5464910, 5439977, 5717011, 5733954, 5789498, 5798399, and 5801218, each of which is incorporated herein by reference in its entirety. Such amine-epoxy adducts are the products of the reaction between one or more amine compounds and one or more epoxy compounds. Preferably, the adduct is a solid, which is insoluble in epoxy resins at room temperature, but which becomes soluble upon heating and acts as an accelerator to increase the cure rate. While any type of amine can be used (with heterocyclic amines and/or amines containing at least one secondary nitrogen atom being preferred), imidazole compounds are particularly preferred. Exemplary imidazoles include 2-methylimidazole, 2, 4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, and the like. Other suitable amines include, but are not limited to, piperazine, piperidine, pyrazole, purine, and triazole. Any kind of epoxy compound may be used as the other starting material for the adduct, including monofunctional and multifunctional epoxy compounds such as those previously described with respect to the epoxy resin component.

In one aspect, the composite structural adhesive of the present disclosure may contain up to about 90 wt% of a hardener, based on the total weight of the composite structural adhesive. In other aspects, the composite structural adhesive may contain up to about 80 wt%, or up to about 70 wt%, or up to about 60 wt%, or up to about 50 wt%, or up to about 40 wt%, or up to about 30 wt%, or up to about 20 wt%, or even up to about 10 wt% hardener, based on the total weight of the composite structural adhesive.

In another aspect, the composite structural adhesive may optionally contain a flame retardant. The composite structural adhesives of the present disclosure may include from about 5 wt% to about 60 wt% of a flame retardant consisting of a mixture of (i) a compound selected from alkaline earth metal hydroxides and aluminum group hydroxides and (ii) at least one phosphorus-containing material.

The family of compounds selected from alkaline earth metal hydroxides and aluminum group hydroxides is often referred to as smoke suppressants. Examples of such smoke suppressants include, but are not limited to, aluminum trihydrate, aluminum oxide trihydrate (also sometimes referred to as aluminum hydroxide), and magnesium hydroxide.

The phosphorus-containing material may be selected from elemental red phosphorus, melamine phosphate, dimelamine phosphate, melamine pyrophosphate and inorganic phosphinates such as aluminum phosphinate.

According to some aspects, it may be advantageous to include a multifunctional acrylate accelerator in the composite structural adhesive. As used herein, the term "multifunctional acrylate" refers to a compound having at least two acrylate functionalities that are reactive under the conditions used to cure the composite structural adhesive, and at least one of the compounds is included in or formed by the curing reaction. As used herein, the term "acrylate functionality" refers to a functional group having the general structure:

wherein R can be any group that does not substantially interfere with or prevent the reaction of the multifunctional acrylate compound with the epoxy resin. In some aspects, R is independently H or a substituted or unsubstituted alkyl, aryl, oxyalkyl, arylalkyl, or oxyalkylaryl group. In a highly preferred aspect, each R is H.

Multifunctional acrylates may include aliphatic urethane acrylates, epoxy acrylates, melamine acrylates, methacrylates, and ethylenically unsaturated monomers and resins. Specific examples include, but are not limited to, trimethylolpropane triacrylate, 1, 6-hexanediol diacrylate, hexafunctional urethane acrylates, hexafunctional epoxy acrylates, tripropylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, propoxylated neopentyl glycol diacrylate, and mixtures thereof.

The composite structural adhesive may include an optional multifunctional acrylate accelerator in an amount of about 0.5 wt% to about 25 wt%, based on the total weight of the composite structural adhesive. In other aspects, the composite structural adhesive may include the optional multifunctional acrylate accelerator in an amount of from about 1 wt% to about 20 wt%, or from about 2 wt% to about 17.5 wt%, or even from about 3 wt% to about 15 wt%, based on the total weight of the composite structural adhesive.

In yet another aspect, the composite structural adhesives may also contain one or more other additives useful for their intended use. Optional additives useful for example in composite structural adhesives may include, but are not limited to, diluents, stabilizers, surfactants, flow modifiers, mold release agents, flatting agents, degassing agents, toughening agents (e.g., carboxyl terminated liquid butadiene acrylonitrile rubber (CTBN), acrylic terminated liquid butadiene acrylonitrile rubber (ATBN), epoxy terminated liquid butadiene acrylonitrile rubber (ETBN), Liquid Epoxy Resin (LER) adducts of elastomers and preformed core shell rubbers), cure initiators, cure inhibitors, wetting agents, processing aids, fluorescent compounds, UV stabilizers, antioxidants, impact modifiers, corrosion inhibitors, adhesion promoters, high density particulate fillers (e.g., various naturally occurring clays such as kaolin, bentonite, montmorillonite or modified montmorillonite, attapulgite (attapulgate), and Buckster fuller's clay; other naturally occurring or naturally derived materials such as mica, and/or mixtures thereof, Calcium carbonate and aluminum carbonate; various oxides such as iron oxide, titanium dioxide, calcium oxide, and silicon dioxide (e.g., sand); brick dust; various man-made materials such as precipitated calcium carbonate; and various waste materials such as crushed blast furnace slag) and mixtures thereof. In a particular aspect, the composite structural adhesive is substantially free of a blowing agent or toughening agent or tertiary amine or dicyandiamide or polyester or any combination thereof.

When present, the amount of additive included in the composite structural adhesive may be at least about 0.5 wt%, or at least 2 wt%, or at least 5 wt%, or at least 10 wt%, based on the total weight of the composite structural adhesive. In other aspects, the amount of additive included in the composite structural adhesive can be not greater than about 30 wt%, or not greater than 25 wt%, or not greater than 20 wt%, or not greater than 15 wt%, based on the total weight of the composite structural adhesive.

The composite structural adhesive may be prepared by stirring and mixing the materials in a state of heating the materials, if necessary, without particular limitation. In some aspects, the composite structural adhesives of the present disclosure may be multi-component (e.g., two-component) adhesives, wherein at least two components of the composite structural adhesive are separately prepared and packaged in separate containers (or appliances), and the composite structural adhesive is obtained by mixing two or more separately prepared components together, in some aspects immediately prior to use. For example, according to one aspect, a two-part includes part a (which is an epoxy resin) and part B (which is a hardener), and a low-density particulate filler and optional materials are added to part a, part B, or both part a and part B. Parts a and B are mixed together in a predetermined ratio before use. The amount of part a and part B mixed together will depend on the desired molar ratio of epoxy to hardener-reactive hydrogen in the composite structural adhesive. In some aspects, part a and part B may be mixed in a weight ratio of about 0.1:1 to about 3:1, or about 0.2:1 to about 2:1, or about 0.5:1 to about 1.5:1, or even still about 1: 1. In other aspects, the epoxy resin and hardener are combined such that the ratio of the number of equivalents of reactive hydrogen in the hardener to the number of equivalents of epoxide present in the composite structural adhesive is from about 0.2 to about 2, or from about 0.3 to about 1.5, or even from about 0.4 to about 1, or even still from about 0.5 to about 0.85, and in some cases from about 0.6 to about 0.8, and in another case from about 0.65 to about 0.75.

According to a particular aspect, the composite structural adhesive is a two-component adhesive, wherein: part a comprises from about 10 wt% to about 90 wt% of an epoxy resin, from about 5 wt% to about 80 wt% of a low density particulate filler, and from about 5 wt% to about 60 wt% of a flame retardant, wherein the wt% is based on the total weight of part a; and part B comprises from about 10 wt% to about 90 wt% of a hardener, from about 5 wt% to about 80 wt% of a low density particulate filler, and from about 5 wt% to about 60 wt% of a flame retardant, wherein the wt% is based on the total weight of part B, and wherein a cured material is provided by mixing part a and part B together to form a composite structural adhesive and curing, the material exhibiting at least the following well-balanced properties: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi. According to yet another particular aspect, part a may include about 15 wt% to about 70 wt% epoxy resin, about 10 wt% to about 30 wt% low density particulate filler, about 3 wt% to about 20 wt% multifunctional acrylate, and about 5 wt% to about 40 wt% flame retardant, where the wt% is based on the total weight of part a; and part B includes from about 15 wt% to about 80 wt% of a hardener, from about 10 wt% to about 30 wt% of a low density particulate filler, and from about 5 wt% to about 40 wt% of a flame retardant, wherein the wt% is based on the total weight of part B.

In still other aspects, kits suitable for use in making portions of composite structural adhesives are provided. Such a kit comprises at least two parts, part a comprising an epoxy resin and part B comprising a hardener, and wherein at least one of the parts a and B of the kit further comprises a low density particulate filler. In some aspects, the low density particulate filler may be included in part a and part B. The parts of the kit may be packaged and sold in cartridges, such as dual cartridges similar to a caulking gun, or in drums or large containers, and then dispensed using a metered mixing device, or packaged and sold in glass or film capsules.

In yet another aspect, the composite structural adhesive may be a "one-component" composite structural adhesive, wherein all of the materials are pre-mixed and stored in a container, and wherein the reactive components do not readily react under ambient or low temperature conditions, such as about-18 ℃, but instead react only upon activation by an external energy source. After all the materials have been combined and mixed, the mixture may be degassed and then sealed in a closed container. The order of mixing is not critical, i.e., the materials may be mixed in any order. In the absence of activation from an external energy source, the composite structural adhesive will remain largely unreacted for a long period of time until use. It has been surprisingly found that the one-part composite structural adhesives of the present disclosure are stable (i.e., remain largely unreacted) for at least 18 months when stored under low temperature conditions, such as about-18 ℃. External energy sources that may be used to promote the curing reaction include, for example, radiation (i.e., actinic radiation such as ultraviolet light) and/or heat. As further defined herein, "ambient conditions" generally refer to temperatures of about 10 ℃ to about 25 ℃, while cryogenic conditions are temperatures below 0 ℃ and above-40 ℃.

According to a particular aspect, the composite structural adhesive is a one-component composite structural adhesive comprising from about 10 wt% to about 70 wt% of an epoxy resin, from about 2 wt% to about 50 wt% of a low-density particulate filler, and up to about 45 wt% of a hardener, wherein the wt% is based on the total weight of the composite structural adhesive, and wherein the one-component composite structural adhesive exhibits at least the following well-balanced properties when cured: (i) density less than 1g/cm³(ii) a (ii) The compression modulus is more than 500 MPa; and (iii) a lap shear strength greater than 750 psi. In yet another particular aspect, the one-part composite structural adhesive comprises from about 20 wt% to about 40 wt% of an epoxy resin, from about 10 wt% to about 30 wt% of a low density particulate filler, and up to about 30 wt% of a hardener, and optionally up to about 40 wt% of a flame retardant, where the wt% is based on the total weight of the composite structural adhesive.

The stirring/mixing method for preparing the composite structural adhesive is not particularly limited. For example, known or customary stirring/mixing units such as mixers (e.g. dissolvers, homogenizers or static mixers), kneaders, rollers, bead mills or planetary stirring devices or even manual mixing can be used. After stirring and mixing, the mixture may be subjected to deaeration under vacuum, if desired.

The composite structural adhesive of the present disclosure may be used to supplement or eliminate welding and/or mechanical fasteners altogether by applying the composite structural adhesive between two or more substrates to be joined and curing the composite structural adhesive to form a bonded joint. The composite structural adhesive may be applied to any substrate. Substrates include, but are not limited to, metals, carbon fibers, glass, polymeric materials such as hard plastics, cellulose containing materials, epoxy fiber composites, and mixtures thereof. Metals include, but are not limited to, titanium, ferrous metals, aluminum alloys, copper, and other metal and alloy substrates. Non-limiting examples of steel include cold rolled steel, galvanized (zinc coated) steel, electrogalvanized steel, stainless steel, pickled steel, zinc-iron alloys such as

Steel and combinations thereof. Examples of cellulose-containing materials include paper, paperboard, cardboard, plywood and compressed fiberboard, hardwood, softwood, plywood, particle board, oriented strand board, and fiberboard. Such materials may be made entirely of wood, such as pine, oak, maple, mahogany, cherry, and the like. In some cases, however, the material may comprise a combination of wood with another material, such as a resinous material, i.e., wood/resin composites, e.g., phenolic composites, composites of wood fibers and thermoplastic polymers, and wood composites reinforced with a cement, fiber or plastic coating.

According to a particular aspect, at least one of the substrates is a metal. In another aspect, the substrates may be the same or different.

The composite structural adhesive may be applied as a liquid, a paste, and a semi-solid or solid that can liquefy upon heating. In some particular aspects, the composite structural adhesive is in the form of a liquid or paste. The composite structural adhesive may be applied to the surface of the substrate in a continuous bead, a middle point, a stripe, a diagonal line, or any other geometric form.

The composite structural adhesive may be applied by any known technique, such as dipping, brushing, spraying, die coating, roll coating, extrusion, injection, and contact by mixing and dispersing the substrate with a bath containing the composite structural adhesive manually and/or via an automated machine.

It is conventional, although not necessary, to remove foreign matter from the surface of one or more substrates by thoroughly cleaning and degreasing the surface prior to applying the composite structural adhesive to the surface of the one or more substrates. Such cleaning is typically performed after the substrate is formed into a final shape. The surface of the substrate may be cleaned by physical or chemical means, such as mechanically abrading the surface or cleaning/degreasing with commercially available alkaline or acidic cleaners such as sodium metasilicate and sodium hydroxide well known to those skilled in the art.

After the cleaning step, the substrate may be rinsed with deionized water or an aqueous solution of a rinsing agent to remove any residue. The substrate may be air dried, for example, by using an air knife, by flashing off water by briefly exposing the substrate to elevated temperatures, or by passing the substrate between squeeze rollers.

The surface of the substrate on which the adhesive of the present disclosure is to be applied may be a bare, clean surface; it may be oily, pretreated with one or more pretreatment compositions, and/or precoated with one or more coating compositions, primers, and the like, applied by any method, including but not limited to electrodeposition, spray coating, dip coating, roll coating, curtain coating, and the like.

Although not required in some aspects, the composite structural adhesive placement option may be enhanced by welding or mechanical fastening. The welding may occur as spot welding, continuous seam welding, or any other welding that may cooperate with the composite structural adhesive to form a mechanically sound joint.

According to one aspect, the composite structural adhesive may be used as a structural adhesive for vehicle components, such as components for marine vehicles, aircraft vehicles, railway vehicles, or automotive vehicles such as cars and motorcycles, or bicycles. In other aspects, the composite structural adhesive may be used as a structural adhesive for construction or household and industrial applications.

In still other aspects, the composite structural adhesive may be used as a welding additive.

The present disclosure also provides a method of making a composite article comprising applying the composite structural adhesive of the present disclosure to a surface of a substrate and curing the adhesive to form a composite article.

In yet another aspect, a method of forming a bonded joint between at least two or more substrates is provided that includes applying a composite structural adhesive of the present disclosure to a surface of at least one of the two or more substrates, joining the two or more substrates such that the composite structural adhesive is sandwiched between at least two of the two or more substrates, and curing the composite structural adhesive to form a bonded joint between the two or more substrates.

The composite structural adhesives of the present disclosure may have at least the following properties when cured: density less than 1g/cm³The compressive modulus is at least 500MPa and the lap shear strength is greater than 750psi, as measured in accordance with the examples section below.

In some aspects, the density of the composite structural adhesive when cured may be less than 0.95g/cm³Or less than 0.9g/cm³Or less than 0.85g/cm³Or less than 0.8g/cm³Or less than 0.75g/cm³Or even less than 0.7g/cm³. In still other aspects, the density of the composite structural adhesive when cured can be at least 0.4g/cm³To less than 1g/cm³E.g., about 0.50g/cm³To about 0.95g/cm³Or about 0.6g/cm³To about 0.85g/cm³Or about 0.65g/cm³To about 0.75g/cm³。

According to some aspects, the compressive modulus of the composite structural adhesive when cured may be greater than 750MPa, or greater than 1000MPa, or greater than 1500MPa, or greater than 2000MPa, or even greater than 2250 MPa.

In still other aspects, the lap shear strength of the composite structural adhesive when cured may be greater than 800psi, or greater than 1000psi, or greater than 1250psi, or greater than 1500psi, or greater than 1750psi, or even greater than 2000 psi.

Examples

Test method

Lap shear strength-ASTM D1002

Lap shear strength is measured using ASTM D1002, which is incorporated herein by reference in its entirety. The two metal plates were bonded together with the sample and cured as specified. The assembly was then cut into lap shear specimens of uniform width. The test specimen was then placed in the clamp of a universal testing machine and pulled at 1.3mm/min (0.05in/min) until rupture occurred.

Compressive Strength and compressive modulus-ASTM D695

Compressive strength and compressive modulus were measured using ASTM D695, which is incorporated herein by reference in its entirety. The sample was placed between compression plates parallel to the surface. The sample was then compressed at a uniform rate. The maximum load is recorded along with the stress-strain data. The compression modulus was measured using an extensometer attached to the front of the clamp.

Density-ASTM D792 and ASTM D1622

The density is measured using ASTM D792 and ASTM D1622, which are incorporated herein by reference in their entirety. The samples were weighed in air and then when immersed in distilled water at 23 ℃, using sinkers and wires to keep the samples completely submerged as required. The samples were also weighed and then sized with calipers. The density is calculated from these values.

Gel time and working life

(a) For the two-component system, the working life or gel time is determined as follows:

50.0g or 100.0g of the epoxy resin component is combined with an appropriate amount of the hardener component. The mixture was then blended for 2-3 minutes and allowed to sit at (77 ° ± 2 °) F. Gel time or working life is reported as the amount of time that elapses from the start of blending to the initial formation of the non-fluid substance.

(b) For the single component system, the working life was determined as follows:

the samples were placed in a 6 ounce (150mL) cartridge (Semco number 250-C6 or equivalent). The cartridge has no nozzle. An air pressure of 75psig to 85psig was used to squeeze out the 2-3 inch sample to remove trapped air. The extruded material was then placed on a tared piece of paper for about 10 seconds with a sealant gun running at full speed. Although the time can be adjusted depending on how fast the tube empties, the nearest second is measured. The extruded compound was then weighed and the extrudability was calculated as follows:

extrudability (g/min) ═ weight extruded (g) × 60(s/min) ]/flow time(s)

Smoke Density and vertical burning test-FAA Title 14 CFR/JAR/CS part 25 appendix F

Smoke density and vertical burn were measured using FAA Title 14 CFR/JAR/CS part 25 appendix F, which is incorporated herein by reference in its entirety. The sample was placed vertically in the chamber and exposed to radiant heat (non-combustible mode) or flame (combustion mode), and the smoke density was measured as optical density by analyzing the decrease in light transmittance as the smoke collects.

The samples were aligned vertically and their lower edges were exposed to a small Bunsen burner flame. The flame was applied for 12 or 60 seconds and then pulled away from the sample. If the sample continues to have a flame, the flame time is recorded, as well as any combustion drops that may have occurred. After the test was completed, the burning length was measured.