Flame-retardant and thermally conductive structural acrylic adhesive

Abstract

A method of applying an adhesive to a substrate is provided, the method comprising mixing together the components of a two-part formulation of part A and part B. Part A and part B each independently include a methacrylate monomer and a conductive filler. The formulation additionally includes an impact modifier, an organometallic catalyst, a powdered rheological agent and a thixotropic agent, and a peroxide catalyst present in at least one of said part A and said part B or added thereto as an additional component. The parts A and B are combined together to form a thermally conductive adhesive mixture. The adhesive mixture is applied to a substrate. Also provided is a formulation of parts A and B. A bonded structure is provided in which the adhesive thus produced is an intermediate between the first substrate and the second substrate.

Description

[0001] Related Applications

[0002] This application claims the benefit of priority of U.S. Provisional Application Serial No. 63 / 604,362, filed Nov. 30, 2023; the content thereof is hereby incorporated by reference in its entirety. Technical Field

[0003] The present invention generally relates to adhesives and, more particularly, to free-radical curable adhesives that maintain strength after heating, which have the properties of flame retardancy, low toxicity, and high thermal conductivity compared to conventional products. Background Art

[0004] In many industries, manufacturers of mating components have switched to structural adhesives to replace conventional fastening techniques such as rivets, bolts, and welding. In theory, adhesives offer many attractive features, including improved product performance, aesthetics, some reduction in overall assembly time, and lower production costs. Additionally, adhesives avoid many stress point concentrations, corrosion, and component damage often seen in rivets, bolts, welding, and other traditional fastening methods. Compared to some traditional mechanical fastening methods, adhesives have made considerable progress in reducing assembly time, but depending on the application and assembly time, they can still be adversely affected due to the working life of the adhesive. In many applications, if the assembly is not completed before the material becomes a hard or gelled solid, the bonded joint will not provide the strength required to perform as designed. In many cases, if this occurs, it can result in expensive and time-consuming rework costs. To alleviate these problems, manufacturers can use materials with a longer working life. However, in doing so, the material will take longer to become strong enough to move on to the next step in the assembly, which is referred to as the "set time". Typically, for adhesives, as the working life increases, the set time can increase significantly.

[0005] Sufficient strength to move on to the next step in the production process is referred to as the set time of the adhesive. The bond strength to move on to another stage of the production process is uncertain because it depends largely on the production process and the specific circumstances of the product. Most often, the bond strength of metal joints is used to define the bond strength. The American Standard Test Method, ASTM D1002, "Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Bonded Metal Specimens by Tensile Loading (Metal-to-Metal)" is the accepted standard for testing bond strength. The set time can be defined as the time it takes for the adhesive to reach a defined bond strength.

[0006] Typically, acrylic adhesives are used in applications where the set time, or the time until the parts can be handled, is critical to production or repair. The set time can typically be improved by accelerating the adhesive through the use of a catalyst, increasing the curing agent or reducing agent. However, in doing so, the working life, or the time the material can be applied, is also shortened. If the working life is too short, the adhesive may be wasted and the mating parts may not adhere to each other properly. If the time until the parts can be handled (set time) is too long, repair or production time may be lost.

[0007] In the automotive industry, metal adhesive bonding typically involves steps such as thoroughly cleaning the mating surfaces of the substrates, lightly sanding the bonding surfaces, and using an adhesion promoter and / or primer. These steps are carried out to make the surfaces of the substrates as receptive to the adhesive as possible. Contaminants remaining on the surfaces can reduce the bond strength by interfering with the adhesive's ability to form a bond, creating weaker chemical bonds or reducing the bond area. Additionally, when the bond is stressed, the contaminants can provide sites for fracture initiation, again reducing the load the joint can withstand. Therefore, a cleaning step is typically required to remove possible contaminants from the bonding surfaces to ensure good adhesive bonding. Sanding the surfaces removes obvious surface defects, resulting in a consistent and tight contact of the bond interface thickness between the adhesive and the substrate. The primer can be an actual coating of another layer that provides a more consistent and bondable surface. An adhesion promoter can be used, which "activates" the surface, providing chemical groups to attach to the adhesive upon application. These preparations occur prior to the application of paint in an automotive factory, but not prior to applications such as hemming flange bonding.

[0008] Hemming flange bonding is carried out in the body shop of an assembly plant or prior to painting in a metal fabricating plant and is transported to the assembly plant. Typically galvanized steel body panels are stamped and formed, and the processing requires the application of various lubricants such as rolling oil and drawing lubricant, or pre-lubricating oil. When the adhesive is applied, one or more of these lubricants may be present, yet no cleaning step to remove the lubricants occurs, partly because the lubricants also serve to prevent metal oxidation.

[0009] During the hemming flange bonding process, after the adhesive is applied to the outer panel, the inner panel is placed and the outer panel is bent or curled around the inner panel to form a hemming flange. The bead size of the adhesive is carefully controlled to fill the bond interface but avoid extrusion. Adhesive escaping from the bond interface may contaminate the equipment and cause cleaning and maintenance problems in the manufacturing plant. A curing step, such as induction curing, can be introduced at this stage. The curing step can be a full cure or just sufficient to prevent any movement of the inner panel to the outer panel during subsequent processing. The body closure panels are attached to the frame and sent to the paint shop, where they are cleaned, primed, and painted. The curing of the adhesive is completed in the paint oven.

[0010] One of the reasons for using adhesives in flanged edges is to reduce or eliminate the use of spot welding to hold the inner and outer panels together. Spot welds are sometimes visible on the outer panel and require a finishing or polishing step before painting to make the spot welds nearly invisible. A few spot welds that still need to be retained act as peel stoppers, reducing the sensitivity of the adhesive to any peel load and holding the panels together until the adhesive cures. This processing step places new requirements on the adhesive related to weldability. First, the adhesive must not interfere with the integrity of the spot weld. Second, similar to the forming process, the adhesive must not escape from the joint and must not contaminate the welding equipment.

[0011] With the further use of adhesives in manufacturing, there is a need for improved adhesive formulations that are suitable for bonding metal substrates and can withstand various finishing processes, including painting, electrocoating (E-Coat) / electrostatic painting, and powder coating after baking. Existing adhesives further have problems with flammability, which complicates industrial handling and their use.

[0012] Compared with the use of conventional painting lines, electrostatic painting of various vehicle components presents an attractive and cost-effective solution. Electrostatic painting of vehicle parts, such as doors, hoods, fenders, and other vehicle skin parts, can be carried out routinely. Due to the high visibility and environmental exposure encountered by such vehicle parts, a high-quality painted finish surface is required, which has a high reflectivity and no visual defects. Electrostatic painting requires the part to be conductive and provides the required electrical potential on the part to attract the oppositely charged paint aerosol droplets to the part. Therefore, the bonding adhesives used to connect the parts to be painted are usually required to be conductive to ensure that the bonded components have the same electrical potential during the painting stage.

[0013] In addition, generally speaking, polymer compositions have lower thermal conductivity than metals, so any heat generated in these materials cannot be easily dissipated to the surrounding environment. Therefore, there is a need to increase the thermal conductivity of acrylic adhesives. There is a further need to ensure that such thermally conductive acrylic adhesives are non-toxic and non-flammable in order to reduce the potential health risks to adhesive users and promote shelf storage stability.

[0014] Therefore, there is a need for structural adhesive formulations that can be used to increase the working life while reducing the extension of the fixing time and are suitable for various finishing processes. There is a further need for structural adhesive formulations that are thermally conductive and / or conductive in order to bond parts that provide surfaces that are easily receptive to a highly uniform paint coating via electrostatic painting techniques and can dissipate heat to the surrounding environment. There is a further need to ensure that such thermally conductive acrylic adhesives are low-toxicity and flame-retardant in order to reduce the potential health risks to adhesive users and promote shelf storage stability. Summary of the Invention

[0015] A method of applying an adhesive to a substrate is provided, the method comprising mixing components of two-part formulations of Part A and Part B together. Part A and Part B each independently comprise a methacrylate monomer and a conductive filler. The formulation additionally comprises an impact modifier, an organometallic catalyst, and a peroxide catalyst, which are present in at least one of Part A and Part B or added thereto as additional components. The A and B parts are combined together to form a thermally conductive adhesive mixture. The adhesive mixture is applied to the substrate. A formulation for Part A and B is also provided. A bonded structure is provided, wherein the adhesive so produced is an intermediate between a first substrate and a second substrate. Brief Description of the Drawings

[0016] The subject matter regarded as the invention is particularly pointed out and distinctly claimed at the end of the specification. The foregoing and other objects, features, and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 is a graph showing the ASTM D1002 lap shear test of an adhesive formulation of the present invention comprising 85% thermally conductive filler, the adhesive formulation being applied and cured between two aluminum substrates;

[0018] Figure 2 is a graph showing the ASTM D1002 lap shear test of an adhesive formulation of the present invention comprising 75% thermally conductive filler, the adhesive formulation being applied and cured between two aluminum 6006 substrates;

[0019] Figure 3 is a graph showing the ASTM D1002 lap shear test of an adhesive formulation of the present invention comprising 85% thermally conductive filler, the adhesive formulation being applied and cured between two aluminum 6006 substrates;

[0020] Figure 4 is a graph showing the ASTM D1002 lap shear test of an adhesive formulation of the present invention comprising 85% thermally conductive filler, the adhesive formulation being applied and cured between two SS304 substrates; and

[0021] Figure 5 is a graph showing the test results of a dynamic mechanical analysis (DMA) test conducted on an adhesive formulation of the present invention comprising 85% thermally conductive filler. Detailed Description

[0022] The present invention has utility as a curable adhesive that is particularly well-suited for bonding structural substrates. Structural substrates that can be effectively bonded by the adhesives of the present invention can include electrogalvanized steel, hot-dip galvanized steel, cold-rolled steel, aluminum, aluminum alloys, acrylonitrile butadiene styrene (ABS), mild steel (MS), polyvinyl chloride (PVC), and fiberglass. The adhesive formulations of the present invention are understood to bond effectively to similar structural substrates, as well as to bond one such substrate to other substrates (including other metals, other plastics), and this is achieved by rapid handling strength during the curing process to facilitate handling and removal of fixtures in a manufacturing environment. A thermally conductive filler is incorporated into the adhesive formulation to control the thermal conductivity of the high-temperature adhesive. The inclusion of a thermally conductive filler in embodiments of the high-temperature adhesive provides a conductive adhesive that improves heat transfer between the cured materials being bonded, which is beneficial for heat dissipation.

[0023] As used herein, the thermally conductive portion is defined as being 0.1 to 2000 (W / m·K) higher than the cured material without the thermally conductive filler; and is conventionally measured by batch scanning with a hot disk method at a 5 mm probe depth.

[0024] As used herein, "V0" and "V1" refer to the fire ratings under the UL 94 standard, where "V0" indicates a higher level of fire resistance, meaning that the cured material will self-extinguish within 10 seconds when exposed to a flame, while "V1" means that it will self-extinguish within 30 seconds; where both ratings are tested on vertical samples and burning droplets are not allowed to ignite the cotton cloth below.

[0025] Embodiments of the adhesive formulations of the present invention are based on the following methacrylate monomers: benzyl methacrylate, methyl methacrylate, isobornyl methacrylate, methacrylic acid, tetrahydrofurfuryl methacrylate (THFMA), tetrahydrofurfuryl acrylate (THFA), 2-hydroxyethyl methacrylate phosphate (HEMA phosphate), 2-hydroxypropyl methacrylate (HPMA), lauryl methacrylate, or combinations thereof. Embodiments of the adhesive formulations of the present invention have a mixing ratio of 1:1, 4:1, or 10:1 ± 0.10%, which is convenient for the user and provides excellent adhesion to highly contaminated metal surfaces, even when associated with cutting oil and sampling oil, and in some embodiments without the use of a primer. Embodiments of the adhesive formulations of the present invention are suitable for bonding metal substrates and can withstand various processes, including painting and heating to temperatures up to 205°C (400°F), without adverse effects on adhesion or physical properties due to the thermally conductive filler loaded therein. Embodiments of the adhesive formulations of the present invention are very suitable for bonding flange joints on metal parts (such as doors on different vehicles), and also provide the ability to be manipulated to provide different working times to adapt to other transportation and general industrial applications.

[0026] Embodiments of the formulations of the present invention contain inhibitors, antioxidants, and stabilizers, which help increase the working life while reducing the extension of the setting time. Without being bound by a particular theory in terms of reagent selection, the setting time and working time characteristics are considered to be the result of a combination of thermodynamic and kinetic control processes.

[0027] It should be understood that in cases where a range of values is provided, the range is intended to cover not only the endpoint values of the range, but also the intermediate values within the range, as clearly included within the range and as modified by the trailing significant digit of the range. For example, the recited range of 1 to 4 is intended to include 1 - 2, 1 - 3, 2 - 4, 3 - 4, and 1 - 4.

[0028] For the purpose of defining and defining the strength that is considered sufficient for most production components, the setting time as used herein is the time to reach a strength of 1 MPa, as measured according to ASTM D1002, with a half - inch overlap and a bond gap of 0.03 inches.

[0029] As used herein, the working life is defined as the time from the first mixing of the material until it reaches a gel state, which is defined by the time point when the storage modulus (G’) and the loss modulus (G”) are equal, as defined by the time it takes for beads of the material (about 20 grams) dispensed from a cartridge and mixed by a tip mixer and then manually checked with a tongue depressor for the adhesive to start thickening.

[0030] As used herein, the maintenance of bond strength at elevated temperatures is defined as within 20% of the room - temperature strength measured immediately after curing.

[0031] The present invention uses an acrylic adhesive in a two-part adhesive formulation. It is provided in a binary system that includes an adhesive part A and an activator part B. Part A includes the following methacrylate monomers: benzyl methacrylate, methyl methacrylate, isobornyl (meth)acrylate, methacrylic acid, tetrahydrofurfuryl methacrylate (THFMA), tetrahydrofurfuryl acrylate (THFA), 2-hydroxyethyl methacrylate phosphate (HEMA phosphate), 2-hydroxypropyl methacrylate (HPMA), lauryl methacrylate, or a combination thereof, as monomers; and conductive fillers. In some embodiments of the present invention, a pre-reacted elastomeric rubber or a reactive liquid polymer (RLP) is also present in part A. Part B includes the methacrylate monomers of part A, which are high flash point acrylate monomers according to the embodiments; and conductive fillers, provided that an impact modifier, an organometallic catalyst, a powdered rheology agent, a thixotropic additive, and a peroxide catalyst are each present as separate parts in the fully mixed curable formulation or in at least one of part A or part B. In some embodiments, the part B methacrylate monomers are the same monomers or a combination of monomers as those present in part A. In other embodiments of the present invention, a pre-reacted elastomeric rubber or a reactive liquid polymer (RLP) is also present in part B. Optionally, in at least one of part A and part B, a free radical polymerization inhibitor, a toughening agent, a adhesion promoter, an antioxidant, a polymerization accelerator, an additive, or a combination thereof is present in the formulation.

[0032] Various additives can be included to improve the handling characteristics of the formulations of the present invention. Although the present invention has been described in detail herein with respect to a 4:1 weight ratio mixture of part A:part B, it should be understood that other mixing ratios in the range of 1:1 to 10:1 ± 10% of part A:part B can also be compounded without departing from the spirit of the present invention. The components common to parts A and B, such as monomer reactants, fillers, antioxidants, elastomeric rubbers, and additives, can be the same or present as different compounds in the two parts to impart the desired properties to the resulting adhesive.

[0033] In some embodiments of the present invention, part B does not contain polymerizable monomers and includes a peroxide catalyst; and optionally at least one of a plasticizer, an impact modifier, and a thermal conductive filler. The resulting formulation is very suitable for forming a part A:part B ratio of 10:1 ± 10%.

[0034] A method of applying an adhesive to a substrate is provided, the method comprising combining parts A and B together to form an adhesive mixture, and applying the mixture to the substrate and curing the applied mixture.

[0035] According to an embodiment, the methacrylate monomer includes secondary monomers that are present in an amount not exceeding 10 monomer percent by weight of the total combined amount of methacrylate monomers present. When present, a typical lower limit is 1 monomer percent by weight (if present). Illustrative secondary monomers used herein include: lauryl methacrylate, 2-hydroxyethyl methacrylate (HEMA), 2-ethylhexyl methacrylate, trimethylolpropane trimethacrylate, benzyl 2-methylpent-2-enoate, benzyl (E)-2-methylhex-2-enoate, benzyl (2E)-2-vinylpent-2,4-dienoate, 5-O-benzyl 1-O-methyl (E)-pent-2-enedioate, benzyl (E)-2-methyl-4-prop-2-enoxybut-2-enoate, benzyl prop-2-enoate, methyl (E)-2-methylene-9-phenyloxynon-3-enoate, benzyl (E)-3-methoxy-2-methylprop-2-enoate, ethyl 2-methyl-5-phenyloxypent-2-enoate, benzyl (2E)-2-methylhex-2,5-dienoate, 4-phenyloxylbutyl 2-methylprop-2-enoate, benzyl (2E,4E)-5-fluoro-2-methylhex-2,4-dienoate, benzyl (2E)-2-vinyl-3-methylpent-2,4-dienoate, fluorobenzyl methacrylate, 2-(perfluorooctyl)ethyl acrylate, (perfluoroheptyl)methyl methacrylate, 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate, 2-(perfluorohexyl)ethyl methacrylate, 2-(perfluoroisononyl)ethyl acrylate, or combinations thereof. The typical loading range of the methacrylate monomer in Part A of the adhesive of the present invention is 7 - 15 total weight percent, and in Part B it is in the range of 8 - 16 total weight percent.

[0036] The thermally conductive fillers used in the present invention illustratively include expanded graphite, coke graphite, flake graphite, synthetic graphite, hexagonal boron nitride, zinc oxide, magnesium oxide, alumina (spherical, round, flake), silane-treated and non-silane-treated alumina, aluminum hydroxide, aluminum oxide, aluminum trihydroxide (ATH), aluminum nitride (AlN), Al 2 O 3 / hexagonal boron nitride (HBNNT) and at least one of their combinations. Factors related to the selection of particulate fillers illustratively include filler cost, resulting flow characteristic viscosity, resulting shrinkage rate, surface finish weight, flammability, and chemical resistance of the thermosetting formulation. The typical filler size is from 0.01 to 130 microns. In a 4:1 adhesive:activator formulation, the typical loading of particulate fillers in the formulation of the present invention is 70 to 90 total weight percent. It should be understood that some of these thermally conductive fillers also provide flame retardant properties, and if also referred to as body fillers, the amount of body fillers is included within the amount of the thermally conductive fillers.

[0037] In some embodiments of the present invention, 40% of the total weight of the curing material being ATH can achieve V0 - level flame retardancy, but in the absence of other thermal conductive fillers with an additional loading amount, a thermal conductivity of >0.8 W / m·K cannot be produced. These other thermal conductive fillers illustratively include Al 2 O 3 , AlN, or combinations thereof.

[0038] In some embodiments of the present invention, the thermal conductive filler has a bimodal size distribution, or the second of the above - mentioned thermal conductive fillers is sized to promote gap filling of the voids between adjacent particles of the thermal conductive filler by smaller particles of the thermal conductive filler. For example, four coplanar 18 - micron filler particles filled in a matrix formed from the composition of the present invention create a gap with a diameter of 7.4 microns. Smaller filler particles with an average diameter of 5 microns are well - suited to fill the 7.4 - micron gap. A person skilled in the art can calculate the gap size through geometric techniques related to crystallography. Assuming that the thermal conductive filler particles have an average radius r, for a set of consecutive particles forming a gap where four spheres intersect, the size of the filler particles capable of filling the gap is less than or equal to a diameter D, which is given by the following formula:

[0039] D ≤ 2SQRT(2r²)-2r

[0040] In some embodiments of the present invention, the thermal conductive filler has a bimodal size distribution, or the second of the above - mentioned thermal conductive fillers is sized to promote gap filling of the voids between adjacent particles of the thermal conductive filler by smaller particles of the thermal conductive filler. For example, four coplanar 18 - micron filler particles filled in a matrix formed from the composition of the present invention create a gap with a diameter of 7.4 microns. Smaller filler particles with an average diameter of 5 microns are well - suited to fill the 7.4 - micron gap. A person skilled in the art can calculate the gap size through geometric techniques related to crystallography. Assuming that the thermal conductive filler particles have an average radius r, for a set of consecutive particles forming a gap where four spheres intersect, the size of the filler particles capable of filling the gap is given by the formula detailed in the priority application.

[0041] While not intended to be bound by a particular theory, it is speculated that the gap dispersion of small particles within a set of larger particles inhibits the formation of non - uniform regions rich in filler. It is believed that non - uniform filler regions with relatively weak interactions with the surrounding cured matrix will promote crack propagation and thereby weaken the resulting article.

[0042] The specific ratio range of large to small thermally conductive filler particles is from 50 to 80 total weight percent of large-sized thermally conductive filler and 20 to 50 total weight percent of smaller-sized thermally conductive filler. In some other embodiments, the ratio range of large to small thermally conductive filler particles is from 50 to 90 total weight percent of large-sized thermally conductive filler and 10 to 50 total weight percent of smaller-sized thermally conductive filler, with the proviso that the formulation contains less than 2 total weight percent of graphite.

[0043] To the extent that the above thermally conductive filler is also electrically conductive, the loading of the thermally conductive filler is adjusted to maintain a resistivity (ρ) of at least 10 Ohm·m. As should be understood, the resistance can vary in direction, and ρ, as used herein, is the minimum value obtained based on ASTM F1529-02, regardless of whether the volume or surface is measured.

[0044] According to embodiments, impact modifiers used herein illustratively include styrene-block-butadiene copolymer modifiers, maleic anhydride-capped polymers, vinyl-capped nitrile, epoxy-capped nitrile, amino-capped nitrile, methyl methacrylate-butadiene-styrene, nitrile rubber, styrene or alpha-methyl styrene block copolymers with butadiene or hydrogenated butadiene (wherein having a high rubber graft of 50 percent rubber or higher), ABS, natural rubber, or combinations thereof. Further, it should be understood that any of the above methyl methacrylate-capped forms can also be used as impact modifiers herein, which crosslink with the matrix formed by monomer / oligomer curing. The loading of the impact modifier depends on multiple factors, including the weight ratio between adhesive part A and activator part B, the impact modifier molecular weight, and the impact modifier modulus. For the formulations of the present invention of 1:1, 4:1, or 10:1, the typical impact modifier loading range is from 1 - 5 total weight percent. In some embodiments of the present invention, the impact modifier is present as a rubber component in combination with a toughening agent (e.g., in the form of core-shell rubber particles). In some other embodiments, the impact modifier is separated into the activator, part B of the formulation of the present invention, but is still used to change the failure mode of the cured adhesive. In some embodiments of the present invention, the impact modifier is present in both part A and part B.

[0045] According to embodiments, the pre-reacted elastomeric rubbers used herein include bifunctional ethoxylated bisphenol A methacrylate, methyl methacrylate - butadiene - styrene - copolymer (MBS), polychloroprene paraffin additives, acrylate butadiene; butadiene; chloroprene; ethylene - propylene; ethylene - propylene - diene; isoprene; isobutene; isobutene isoprene (butyl rubber); styrene - butadiene; styrene - isoprene; acrylonitrile - butadiene; acrylonitrile - chloroprene; vinyl - terminated polybutadiene, such as vinyl pyridine - butadiene, vinyl pyridine - styrene - butadiene; carboxy - styrene butadiene; chloro - isobutene - isoprene (chlorobutyl rubber); bromo - isobutene - isoprene (bromobutyl rubber); dialkyl siloxane, polypropylene oxide); polyester urethane; polyether urethane; and mixtures thereof. In specific embodiments of the present invention, the pre-reacted elastomeric rubber is present in adhesive part A, activator part B, or a combination thereof. In each part of the formulated adhesive of the present invention, the typical loading range of the pre-reacted elastomeric rubber is from 0.05 to 4 total weight percent.

[0046] According to embodiments, the organometallic catalysts used herein include copper, tin, bismuth, zinc, potassium. In specific embodiments of the present invention, the organometallic catalyst is only present in activator part B; however, in some embodiments, the organometallic catalyst is present in both part A and part B. The typical loading range of the organometallic catalyst in the total formulated adhesive of the present invention is from 0 to 0.005 total weight percent.

[0047] According to some embodiments of the present invention, thixotropic agents illustratively include fumed silica, organoclays, organophilic phyllosilicates, inorganic clays, and precipitated silica. The thixotropic agent is present in an amount from 0 to 10 weight percent. In some embodiments, the organophilic phyllosilicate additive acts as a thixotropic agent and is defined as a material obtained by reacting a phyllosilicate that is completely colloidal and cation-exchanged in water with an organic onium salt in an aqueous suspension, followed by subsequent mechanical removal of water without drying by heating.

[0048] According to an embodiment, the peroxide catalysts used herein include acidic p-toluenesulfonyl chloride catalyst, tert-butyl peroxybenzoate aromatic perester peroxide, 1,2-dichlorobenzene peroxide, 1,3- and 1,4-bis(tert-butylperoxyisopropyl)benzene peroxide. In a specific embodiment of the present invention, the peroxide catalyst is only present in adhesive part A; however, in some embodiments, the organometallic catalyst is present in both part A and part B. The typical loading range of the peroxide catalyst in the total formulated adhesive of the present invention is from 0.1 to 0.7 total weight percentage.

[0049] In some exemplary embodiments of the present invention, after mixing parts A and B, ultra-high molecular weight polyethylene (UHMW-PE) is present at 1-3 total weight percentage, methacrylate is present at no more than 10 total weight percentage, and there is no curable monomer having a flash point less than 65 °C at standard temperature and pressure (STP). In some other embodiments of the present invention, a toughening agent is present in part A, part B, or both part A and part B.

[0050] In some embodiments of the present invention, a polymerization initiator is provided, which is sulfonyl chloride. The sulfonyl chlorides used herein illustratively include chlorosulfonated polyethylene, p-toluenesulfonyl chloride, methanesulfonyl chloride, benzenesulfonyl chloride, C 2 -C 14 alkylsulfonyl chloride and C 7 -C 14 arylsulfonyl chloride or a combination thereof, wherein the alkyl is intended to include straight-chain, branched-chain, cyclic structures, and the above structures having side groups therein, and the aryl includes diaryl and monoaryl containing side groups. The sulfonyl chloride is present in part A of the present invention in an unprotected or encapsulated form, while the sulfonyl chloride is only present in part B in an encapsulated form. For a 1:1, 4:1, or 10:1 volume ratio of part A: part B, the typical loading range of the sulfonyl chloride (if present) is from 0 to 1 total weight percentage of the combined parts A and B (excluding any encapsulating agent). It should be understood that the sulfonyl chloride can be used in combination with a halogen chain transfer agent and / or a multifunctional chain transfer agent to adjust the working time of the resulting formulation. It should be understood that if chlorosulfonated polyethylene (CSPE) is used instead of p-toluenesulfonyl chloride, the loading may be higher because the MW per mole of sulfonyl chloride in CSPE is much higher, for a 1:1, 4:1, or 10:1 volume ratio of part A: part B, wherein the amount of CSPE ranges from 0 to 8 total weight percentage of the combined parts A and B (excluding any encapsulating agent).

[0051] The encapsulating agent used herein is detailed in US 3,396,116, the details of which are hereby incorporated by reference.

[0052] In some embodiments of the present invention, the formulations of the present invention further include a toughening agent. The difference between the toughening agent and the impact modifier in the present invention is that the resin is blended or dissolved and forms a miscible blend / solution with the monomer, and can significantly improve the performance of the adhesive cured at low temperatures such as -40°F (-40°C), and at the same time will not have a negative impact on the performance of the cured adhesive at elevated temperatures such as 180°F, while the core-shell structured impact modifier as a rubber particle dispersion not only provides excellent impact strength but also provides non-sagging, excellent thixotropic properties and improved anti-slip performance. The toughening agent used herein can illustratively be selected from a variety of elastomeric materials that form discrete particles or biphasic domains in a continuous resin matrix. For example, pre-reacted particles, butadiene-acrylonitrile copolymers, styrene / ethylene / styrene, α-methylstyrene / ethylene / α-methylstyrene, α-methylstyrene / butadiene / α-methylstyrene, styrene / butadiene / styrene (SBS) copolymers, styrene / isoprene / styrene (SIS) copolymers, styrene / ethylene / butadiene / styrene (SEBS) copolymers, styrene / butadiene (SBR) copolymers, styrene acrylonitrile (SAN), vinyl-terminated butadiene co-acrylonitrile, glycidyl methacrylate-functionalized butadiene co-acrylonitrile, hydroxy-functionalized butadiene, isocyanate-functionalized butadiene, amine-terminated butadiene, epoxy-terminated butadiene, melanized poly-butadiene or -isoprene, or copolymers thereof. US 6,660,805 includes examples of such maleated polymers and copolymers, as well as other pre-reacted materials that can be added to the resin composition in particulate form. The typical loading range of the toughening agent (if present) is from 0 to 4 total weight percent of the combined Part A and Part B. In some embodiments of the present invention, the toughening agent is present in only one of Part A or Part B, while according to other embodiments, the toughening agent is present in both Part A and Part B.

[0053] In addition, a reactive liquid polymer (RLP) can also be incorporated as a toughening component. The RLP contains functional groups, typically at its ends but occasionally as side groups, and reacts in situ with the resin to form elastomeric domains. Examples of RLP include, but are not limited to, vinyl-terminated butadiene acrylonitrile (VTBN), carboxyl-terminated butadiene acrylonitrile (CTBN), amine-terminated butadiene acrylonitrile (ATBN), hydroxyl-terminated butadiene acrylonitrile (HTBN), epoxy-terminated butadiene acrylonitrile (ETBN), mercapto-terminated butadiene acrylonitrile (MTPN), vinyl-terminated butadiene (VTB), maleated butadiene, phenoxy-terminated butadiene acrylonitrile (PTBN). In a specific embodiment of the present invention, the toughening agent includes ultra-high molecular weight polyethylene (UHMW-PE), chlorosulfonated polyethylene, chloroprene rubber, copolymers of ethylene acrylic elastomers, poly(methyl methacrylate)-grafted rubber, butadiene styrene acrylonitrile copolymer, or combinations thereof. It should be further understood that any of the above methyl methacrylate-terminated forms can also be used as toughening agents herein, which crosslink with the matrix formed by monomer / oligomer curing.

[0054] In order to formulate an adhesive formulation of the present invention that achieves high strength without the need for a separate surface treatment prior to application of the formulation of the present invention, and in accordance with some embodiments, an adhesion promoter is provided within the formulation of the present invention. The adhesion promoter promotes the adhesion of a fully cured formulation to various substrates, including galvanized substrates. The adhesion promoter is readily formulated into the adhesive portion, the activator portion, or both portions of the formulation of the present invention. In a particular embodiment, the adhesion promoter is found only in the adhesive portion. Specific adhesion promoters effective in the formulation of the present invention illustratively include phosphate esters, monofunctional phosphate esters, difunctional phosphate esters, polymerized phosphate ester-functionalized polymers, (meth)acrylic acid, polymeric materials having organic acid functional groups, maleic acid, acid-functionalized polymers such as maleated polybutadiene, citric acid di- or tri-methacrylate, polymethacrylated oligomeric maleic acid, polymethacrylated poly maleic acid, polymethacrylated polymethacrylic acid, silanes, or combinations thereof. Silane adhesion promoters used herein illustratively include: 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, (3-glycidoxypropyl)bis(trimethylsilyloxy)methylsilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyl)dimethylethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, methacryloxymethyltriethoxysilane, methacryloxymethyltrimethoxysilane, methacryloxypropyl dimethylethoxysilane, methacryloxypropyl dimethylmethoxysilane, methacryloxypropyltrimethoxysilane, ethylacryloxypropylmethyldimethoxysilane, methacryloxypropyltriethoxysilane, methoxymethyltrimethylsilane, 3-methoxypropyltrimethoxysilane, 3-methacryloxypropyl dimethylchlorosilane, methacryloxypropylmethyldichlorosilane, methacryloxypropyltrichlorosilane, 3-isocyanatopropyl dimethylchlorosilane, 3-isocyanatopropyltriethoxysilane, bis(3-triethoxysilylpropyl)tetrasulfide, and combinations thereof. In a 1:1, 4:1, or 10:1 adhesive:activator formulation, the typical loading of the adhesion promoter in the formulation of the present invention is from 0 to 1 total weight percent.

[0055] According to some embodiments, antioxidants are present in the binder and illustratively include hydroquinone (HQ), butylated hydroxytoluene (BHT), 1,4-naphthoquinone, 2,6-di-tert-butyl-4-(dimethylaminomethyl)phenol, (2,2,6,6-tetramethylpiperidin-1-yl)oxy or commonly known as TEMPO, 4-hydroxy-TEMPO or TEMPOL, butylated hydroxyanisole, 2,6-di-tert-butylcresol, 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-thiobis(6-tert-butyl-4-methylphenol), tert-butylhydroquinone, di-tert-butylhydroquinone, di-tert-amylhydroquinone, methylhydroquinone, p-methoxyphenol, tetrakis[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate]methane, N-(2-aminoethyl)-3-[3,5-bis(tert-butyl)-4-hydroxyphenyl]propanamide, 5,7-di-tert-butyl-3-(3,4-dimethylphenyl)-3H-benzofuran-2-one, dilauryl thiodipropionate, dimyristyl thiodipropionate, tris(nonylphenyl)phosphite, and combinations thereof. In a 1:1, 4:1, or 10:1 binder:activator formulation, the typical loading of the antioxidant in the formulations of the present invention is from 0 to 1 total weight percent.

[0056] The polymerization accelerators present in activator portion B are limited only by the desired kinetics of the desired free radical polymerization and compatibility with other components of the compositions of the present invention. Accelerators used herein illustratively include dimethylaminopyridine; polyethyleneimine, N,N-dimethylaniline, modified dihydropyridines such as 3,5-diethyl-1,2-dihydro-1-phenyl-2-propylpyridine, 2-methylimidazole, 2-hydroxyethyl p-toluidine, ethanolamine, diethanolamine, diethylethanolamine, methyldiethanolamine, butyldiethanolamine, diethylamine, triethylamine, n-butylamine, 2,2-bipyridine, 1,10-phenanthroline, ammonia, alkylidene malonates, δ-iminomalonates, ethylenediamine (ethylazan), aniline, benzylamine, 1-benzofuran-2-amine, 4-aminoquinoline, pentane-1,2,5-triamine, benzene-1,2,4,5-tetraamine, bis(2-chloroethyl)amine, butyl(ethyl)methylamine, (2-chloroethyl)(propyl)amine, hexane-1-imine, isopropylideneamine, ethane-1,2-diimine, carbodiimide, o-acetylhydroxylamine, o-carboxyhydroxylamine, hydroxylamine-o-sulfonic acid, o-hydroxyaniline, phenylpropanolamine hydrochloride, catecholamine, indolamine, or polyacrylamide and combinations thereof. In a 1:1, 4:1, or 10:1 binder:activator formulation, the typical loading of the accelerator in the formulations of the present invention is from 0 to 1 total weight percent. Without being bound by a particular theory, it is believed that the accelerators react to decompose the organic peroxide and increase the cure rate of the binder.

[0057] In certain embodiments of the adhesive, the formulations of the present invention further include various bulk fillers that are flame retardant and / or fire resistant and have good application properties. The inorganic hydrate fillers used herein include aluminum trihydrate (ATH); its geological sources, such as gibbsite; dolomite (mainly Mg 3 Ca(CO 3 ) 4 );magnesite (mainly Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O); AlN; Al 2 O 3 / HBNNT; sepiolite clay (Mg 4 Si 6 O 15 (OH) 2 ·6H 2 O); SbO 3 ; or combinations thereof. Provided that dolomite is present in the form of a mixture with magnesite. It should be understood that the surface energy of the inorganic hydrate filler is reduced by treating the inorganic hydrate filler with silane to make the filler more compatible with the resin. The silane (if present) is typically present in an amount of 0.1 to 1 weight percent of the inorganic hydrate filler and is included as part of the weight of the hydrate filler if present. In specific embodiments of the present invention, the flame retardant and / or fire resistant filler is only aluminum trihydrate (ATH), AlN or Al 2 O 3 / HBNNT. The inorganic hydrate filler releases hydrated water upon heating related to fire, thereby providing a cooling effect to inhibit combustion. The flame retardant and / or fire resistant properties of the bulk fillers of the present invention are formulated for embodiments of the adhesive while maintaining the fire safety rating.

[0058] In some embodiments of the present invention, the sepiolite clay is 0.5% to 3% by weight of ATH in the unexpectedly effective carbon layer. As a result, the V1 performance of the given material of the present invention is enhanced by shortening the self-extinguishing time to 20 seconds or even shorter, or the material even reaches the V0 classification.

[0059] Embodiments of the adhesive of the present invention containing ATH, AlN or Al 2 O 3 / HBNNT as the inorganic hydrate filler show good application properties, and in some cases, compared with those without ATH, AlN or Al 2 O 3Match the properties of the control binder for / HBNNT. The inorganic hydrate filler can be formulated to achieve different working times, from 4 to 30 minutes, depending on the specific application.

[0060] Examples of the binder of the present invention containing ATH burn for a very short time of less than 20 seconds and then the fire self-extinguishes to meet the V1 classification. In a specific example of the present invention, 8 - 15 / 48 - 61 total weight percentage% of Al 2 O 3 is combined with ATH to produce a low - density fully flame - retardant material.

[0061] It has also been unexpectedly found that an AlN / ATH loading of 22 - 38 / 22 - 38 total weight% produces a fully V0 flame - retardant material, where the same formulation using Al 2 O 3 requires more than 45% of ATH to produce a fully V0 system. At the same amount (22 - 38 total weight% of ATH), when ATH is the only flame - retardant component, the material cured with Al 2 O 3 can only pass UL - 94 - V1.

[0062] In certain embodiments of the present invention, when SbO 3 is present, a conventional bromide flame - retardant is also present, and this combination provides unexpectedly good fire - proof characteristics relative to SbO 3 alone.

[0063] In certain embodiments, the formulations of the present invention also include various additives such as chelating agents, corrosion inhibitors, thickeners, pigments, thixotropic agents, plasticizers, viscosity regulators, and combinations thereof. Such additives are only limited by the requirement of compatibility with other components of the formulations of the present invention. Such additives are provided to balance or otherwise alter at least one property of the formulations of the present invention regarding handling, storage, cure rate, or adhesion characteristics. In 1:1, 4:1, or 10:1 binder:activator formulations, the typical loading of each additive in the formulations of the present invention is independently 0 to 5 total weight percentage.

[0064] Typical component amounts of part A and part B of the binder of the present invention are provided in Tables 1A and 1B respectively.

[0065] Tables 1A and 1B. Typical component amounts of the binder (part A) and activator (part B), where amounts are given in weight percentage unless otherwise specified:

[0066] Table 1A. Binder (part - A)

[0067]

[0068] Table 1B. Activator (Part B)

[0069]

[0070]

[0071] A method for producing an adhesive formulation is provided. The adhesive formulation is produced by free radical polymerization and adheres well to the above-mentioned substrate. The formulation of the present invention is a two-part formulation, which is either pre-mixed to initiate a pot life for a period of time, or alternatively, the two parts are applied to the substrate together under conditions where polymerization occurs between different monomers. In a specific embodiment of the present invention, the polymerization occurs at 24 °C in an ambient atmosphere. In other embodiments, the polymerization is initiated by an energy input such as heating, exposure to ultraviolet radiation, or other free radical formation mechanisms. In certain embodiments of the present invention where the adhesive part A and the activator part B are present in a volume ratio of 1:1, 4:1, or 10:1 ± 10%, a storage stability greater than 180 days at 23 °C is obtained. The typical viscosities of parts A and B are independently between 20,000 and 500,000 cPs. In some embodiments of the present invention, the viscosities of the individual parts A and B are within ±50% of each other to facilitate mixing between them.

[0072] Regardless of the form of the formulation of the present invention, when inducing the pot life of the formulation, the formulation is in contact with two or more substrates simultaneously, where the substrates remain in contact with the curing formulation of the present invention for a time period sufficient to achieve bonding between the substrates. The formulation of the present invention is very suitable for bonding galvanized substrates, cold-rolled steel, aluminum, PVC, ABS, low-carbon steel, vinyl polymers, wood, and fiberglass. Two such substrates can be joined together to form various adjacent structures, such as lap joints, butt joints, corner joints, edge joints, and T-joints. In other embodiments, the formulation of the present invention is applied to a single substrate and cured to form a coating that provides substrate protection or is effective as a primer for subsequent material application. Since the formulation of the present invention cures by a free radical mechanism, the formulation of the present invention can be applied in various thicknesses and still achieve polymerization throughout. The typical thickness range of the formulation of the present invention between substrates is 0.001 - 25 mm.

[0073] In some embodiments, the adhesive of the present invention builds strength rapidly to facilitate handling, as measured by lap shear on 5 mm thick low-carbon steel, which reaches a strength of 0.34 MPa within 30 to 35 minutes and a strength of 3 to 5 MPa at 50 minutes.

[0074] According to an embodiment, the adhesive of the present invention has a measured thermal conductivity of 0.8 to 4 W / m / K. This cured material allows the user to not only adhere to its substrate, but also dissipate thermal energy during the process, and it is non-flammable and non-toxic.

[0075] Example 1

[0076] An adhesive formulation of the present invention comprising 85% thermally conductive filler was applied and cured between two aluminum substrates to form three identical samples. The samples were subjected to an ASTM D1002 lap shear test where the lap shear was 0.05” / min. The results are as Figure 1 shown in the graph and Table 2 below. The average lap shear strength of the adhesive formulation of the present invention comprising 85% thermally conductive filler on aluminum 6006 is 782 PSI.

[0077] Table 2. Lap shear data.

[0078]

[0079] Example 2

[0080] An adhesive formulation of the present invention comprising 75% thermally conductive filler was applied and cured between two aluminum substrates. The samples were subjected to an ASTM D1002 lap shear test where the lap shear was 0.05” / min. The results are as Figure 2 shown in the graph and the associated Table 3 below. The average lap shear strength of the adhesive formulation of the present invention comprising 85% thermally conductive filler on aluminum is 1845 PSI.

[0081] Table 3. Lap shear data.

[0082]

[0083] Example 3

[0084] An adhesive formulation of the present invention comprising 74% thermally conductive filler DG-TC-ADH was applied and cured between two aluminum 6006 substrates. The samples were subjected to an ASTM D1002 lap shear test where the lap shear was 0.05” / min. The results are as Figure 3 shown in the graph and the associated Table 4 below. The average lap shear strength of the adhesive formulation of the present invention comprising 74% thermally conductive filler on aluminum 6006 is 1019 PSI.

[0085] Table 4. Lap shear data.

[0086]

[0087] Example 4

[0088] The adhesive formulation of the present invention comprising 74% thermally conductive filler DG-TC-ADH was applied and cured between two SS304 (Type 304 stainless steel) substrates. The samples were subjected to ASTM D1002 lap shear testing with a lap shear of 0.05” / min. The results are as shown in the graph of Figure 4 and the associated Table 5. The average lap shear strength of the adhesive formulation of the present invention comprising 80% thermally conductive filler on SS304 is 1020 PSI.

[0089] Table 5. Lap shear data.

[0090]

[0091] Example 5

[0092] A formulation of the adhesive of the present invention was prepared and its thermal conductivity was tested. The results are shown in Table 6 below.

[0093] Table 6. Thermal conductivity of the adhesives of the present invention with different amounts of thermally conductive filler

[0094]

[0095] Example 6

[0096] A dynamic mechanical analysis (DMA) test was performed on the adhesive formulation of the present invention comprising 85% thermally conductive filler. The results are as shown in the graph of Figure 5 . The DMA results show that the cured material is not brittle and has a very high storage modulus capacity for highly filled acrylic adhesives. This indicates that despite being highly filled, this cured material is not brittle. This is also important because most of the impact modifiers have been removed, and impact modifiers are the components that impart more elastic properties to this cured material and reduce brittleness.

[0097] The results also show that adding thermally conductive fillers (e.g., HBN) helps reduce the flammability of the formulation. This means that only a small addition of about 4% - 5% will significantly improve the flame retardancy.

[0098] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are numerous variations. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit in any way the scope, applicability, or configuration of the described embodiments. On the contrary, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing one or more exemplary embodiments. It should be understood that various changes can be made to the function and arrangement of the elements without departing from the scope as set forth in the appended claims and their legal equivalents.

Claims

1. A two-part adhesive formulation comprising: an adhesive part A, the adhesive part A comprising: a part A methacrylate monomer and a part A thermally conductive filler, the part A methacrylate monomer being benzyl methacrylate, methyl methacrylate, isobornyl methacrylate, methacrylic acid, tetrahydrofurfuryl methacrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl methacrylate phosphate, 2-hydroxypropyl methacrylate (HPMA), lauryl methacrylate, or a combination thereof; and An activator part B, the activator part B comprising: a part B methacrylate monomer and a part B thermal conductive filler, the part B methacrylate monomer being benzyl methacrylate, methyl methacrylate, isobornyl methacrylate, methacrylic acid, tetrahydrofurfuryl methacrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl methacrylate phosphate, 2-hydroxypropyl methacrylate, lauryl methacrylate or a combination thereof; in, An impact modifier, an organometallic catalyst, and a peroxide catalyst are each present in at least one of the part A and the part B or added thereto as an additional component.

2. The preparation according to claim 1, wherein The monomers of part A or part B each independently further comprise at least one secondary monomer selected from the group consisting of lauryl methacrylate, hydroxyethyl methacrylate, 2-ethylhexyl methacrylate, trimethylolpropane trimethacrylate, benzyl 2-methylpent-2-enoate, benzyl (E)-2-methylhex-2-enoate, benzyl (2E)-2-vinylpent-2,4-dienoate, 5-O-benzyl 1-O-methyl (E)-pent-2-enoate, benzyl (E)-2-methyl-4-prop-2-enyloxybut-2-enoate, benzyl prop-2-enoate, methyl (E)-2-methylene-9-phenylmethoxynon-3-enoate, methyl (E)-3- benzyl methoxy-2-methylprop-2-enoate, ethyl 2-methyl-5-phenylmethoxypent-2-enoate, benzyl (2E)-2-methylhexa-2,5-dienoate, 4-phenylmethoxybutyl 2-methylprop-2-enoate, benzyl (2E,4E)-5-fluoro-2-methylhexa-2,4-dienoate, benzyl (2E)-2-vinyl-3-methylpenta-2,4-dienoate, fluorobenzyl methacrylate, 2-(perfluorooctyl)ethyl acrylate, (perfluoroheptyl)methyl methacrylate, 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate, 2-(perfluorohexyl)ethyl methacrylate, 2-(perfluoroisononyl)ethyl acrylate, or a combination thereof.

3. The preparation according to claim 1, wherein The part A thermally conductive filler and the part B thermally conductive filler are each independently at least one of expanded graphite, coke graphite, flake graphite, synthetic graphite, hexagonal boron nitride, zinc oxide, magnesium oxide, aluminum oxide (spherical, round, flake), silane-treated and non-silane-treated aluminum oxide, aluminum hydroxide, aluminum oxide (Al2O3), aluminum oxide trihydrate (ATH), aluminum nitride (AlN), Al2O3 / hexagonal boron nitride and combinations thereof.

4. The preparation according to claim 1, wherein The Part A conductive filler and the Part B conductive filler are present in 70-90 total weight percent of the Part A and the Part B, respectively.

5. The formulation of claim 1, wherein At least one of the Part A conductive filler or the Part B conductive filler has a ratio of 50 to 80 total weight percent of the large particle size thermally conductive filler and 20 to 50 total weight percent of the smaller particle size thermally conductive filler.

6. The formulation of claim 1, wherein At least one of the Part A thermally conductive filler or the Part B thermally conductive filler has a ratio of large to small thermally conductive filler particles of 50 to 90 total weight percent of large particle size thermally conductive filler and 10 to 50 total weight percent of smaller particle size thermally conductive filler, with the proviso that the formulation contains less than 2 total weight percent of graphite.

7. The formulation of claim 1 further comprising a part A pre-reacted elastomeric rubber or reactive liquid polymer or a part B pre-reacted elastomeric rubber or reactive liquid polymer.

8. The formulation of claim 7, wherein The pre-reacted elastomeric rubber of Part A is present in an amount of 0.05 to 4 total weight percent of Part A; and The part B pre-reacted elastomeric rubber is present in an amount of 0.03 to 3 total weight percent of the part B.

9. The formulation of claim 1, wherein The impact modifier is present in the fully formulated adhesive at 1 to 5 total weight percent after the Part A and the Part B are mixed.

10. The formulation of claim 1 further comprising a thixotropic agent, wherein the thixotropic agent is an organophilic phyllosilicate additive present in the fully formulated adhesive at 1 to 10 total weight percent after mixing of the part A with the part B.

11. The formulation of claim 1, wherein The peroxide catalyst is present in the fully formulated adhesive at 0.1 to 0.7 total weight percent after the Part A and the Part B are mixed.

12. The formulation of claim 1, further comprising one or more of the following: a polymerization initiator, said polymerization initiator being present in the fully formulated adhesive at 0 to 1 total weight percent after said part A is mixed with said part B; a toughening agent, said toughening agent being present in the fully formulated adhesive at 0 to 4 total weight percent after said part A is mixed with said part B; an adhesion promoter, said adhesion promoter being present in the fully formulated adhesive at 0 to 2 total weight percent after said part A is mixed with said part B; an antioxidant, said antioxidant being present in the fully formulated adhesive at 0 to 2 total weight percent after said part A is mixed with said part B; as well as A polymerization accelerator, said polymerization accelerator being present in the fully formulated adhesive at 0 to 1 total weight percent after said Part A and said Part B are mixed.

13. The formulation of claim 1 further comprising a bulk filler present in an amount to impart a V0 or V1 flame retardant rating to the cured material of the formulation.

14. The formulation of claim 13, wherein The bulk filler is ATH, gibbsite, magnesite, hydromagnesite, AlN, Al2O3 / HBNNT, sepiolite clay, SbO3, or a combination thereof.

15. The formulation of claim 13, wherein There was 8-15 / 48-61 total weight % Al2O3 / ATH or 22-38 / 22-38 total weight % loading of AlN / ATH.

16. The formulation of claim 1, wherein ATH is present, and further comprises sepiolite clay present in an amount of 0.5% to 3% by weight of ATH.

17. A two-part adhesive formulation consisting essentially of: an adhesive part A, the adhesive part A comprising: a part A methacrylate monomer and a part A thermally conductive filler, the part A methacrylate monomer being benzyl methacrylate, methyl methacrylate, isobornyl methacrylate, methacrylic acid, tetrahydrofurfuryl methacrylate, tetrahydrofurfuryl acrylate, 2-hydroxyethyl methacrylate phosphate, 2-hydroxypropyl methacrylate (HPMA), lauryl methacrylate, or a combination thereof; and An activator part B consisting of a peroxide catalyst, and optionally at least one of a part B thermally conductive filler, a plasticizer, or an impact modifier.

18. A method of applying the two-part adhesive formulation of claim 1 to a substrate, the method comprising: Mixing the adhesive part A and the activator part B together; combining the impact modifier, the organometallic catalyst, and the peroxide catalyst with the combined binder part A and activator part B if the impact modifier, the organometallic catalyst, and the peroxide catalyst are not already present in the binder part A and the activator part B; applying the adhesive mixture to the substrate; as well as The adhesive mixture is allowed to cure into an adhesive.

19. The method of claim 18, wherein: The volume ratio of the binder part A to the activator part B is from 1:1±0.10% to 10:1±0.10%.

20. The method of claim 18, further comprising securing the substrate and the second substrate in a fixture in a joint position and in contact with the mixture during free radical curing for a period of 5 to 180 minutes, and then releasing the substrate and the second substrate from the fixture.

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