Curable adhesive compositions with a low dielectric constant

Abstract

Curable adhesive compositions include a curable adhesive and a filler comprising expanded microspheres. Expanded microspheres are polymeric spheres with a central void. Curable adhesives include curable epoxy adhesives. The cured adhesive composition has a dielectric constant (Dk) of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%. The curable adhesive compositions can be used to form articles where one substrate is adhered to a second substrate with the cured adhesive composition between them.

Description

[0001] PA102801W002

[0002] CURABLE ADHESIVE COMPOSITIONS WITH A LOW DIELECTRIC

[0003] CONSTANT

[0004] Summary

[0005] Disclosed herein are curable adhesive compositions that upon curing have a low dielectric constant and yet do not have reduced adhesive properties. Also disclosed are articles that include the cured curable adhesive compositions.

[0006] In some embodiments, the curable adhesive composition comprises a curable adhesive and a filler comprising expanded microspheres comprising polymeric spheres with a central void. Curable adhesives include curable epoxy adhesives. The cured adhesive composition has a dielectric constant (Dk) of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%.

[0007] Also disclosed herein are articles. In some embodiments, the first substrate with a first major surface and a second major surface, a cured adhesive layer with a first major surface and a second major surface disposed on the second major surface of the first substrate such that the first major surface of the cured adhesive layer is in contact with the second major surface of first substrate, and a second substrate with a first major surface and a second major surface where the first major surface of the second substrate is in contact with the second major surface of the cured adhesive layer, wherein the cured adhesive layer is the cured layer of a curable adhesive composition. The curable adhesive compositions are described above.

[0008] Brief Description of the Drawings

[0009] The present application may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings.

[0010] Figure 1 is a cross sectional view of an article of this disclosure. Detailed Description

[0011] Electronics manufacturers are looking for high performance multifunctional polymeric adhesives and composites to enable low signal / noise ratio in high frequency communication devices. It has been observed that having a low dielectric constant (low Dk) adhesive in the device stack helps reduce signal / noise by 20-30%. The rest of the 70- 80% is controlled by device design. Reducing the Dk to below 3.0 has been cited as being beneficial to device performance, and even lower Dk values are better.

[0012] The adhesives used in the manufacture of these devices are often curable structural adhesives. Examples of suitable curable structural adhesive include epoxy adhesives, (meth)acrylate adhesives, silicone adhesives, and urethane adhesives. Epoxy adhesives are particularly suitable. Epoxy adhesives can be one-part adhesives that typically are cured by application of heat or actinic radiation, or two-part adhesives where the two parts are mixed and the mixture cures at room temperature. Epoxy adhesives typically have a dielectric constant (Dk) of around 3.3-3.6 upon curing. In order to reduce the Dk to a value of 3.0 or lower, often low-Dk fillers are added. These fillers lower the Dk of the cured adhesive.

[0013] Several low-Dk fillers include, but are not limited to, PTFE (polytetrafluorethylene) and glass bubbles. These fillers are commercially available and very effective in reducing Dk. However, they negatively impact the mechanical properties of the adhesive, particularly the elongation at break. In other words, to achieve the desired lowering of the Dk, the adhesive becomes more brittle and sacrifices mechanical properties such as elongation.

[0014] Therefore, a need remains for curable adhesive compositions that have a low Dk (a Dk of 3.0 or even lower) without sacrificing the mechanical properties of the cured adhesive. In this disclosure adhesive compositions are described that have a curable adhesive and filler, where the filler comprises expanded microspheres that are polymeric spheres with a central void. The cured adhesive composition has a dielectric constant (Dk) of less than the dielectric constant of the adhesive itself, generally a Dk of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%. Also disclosed are articles that include cured layers of these curable compositions.

[0015] The term “adhesive” as used herein refers to polymeric compositions useful to adhere together two adherends. Examples of adhesives are structural adhesives. Structural adhesives refer to adhesives that can bond other high strength materials (e.g., wood, composites, or metal) so that the adhesive bond strength is in excess of 6.0 MPa (1000 psi) at room temperature.

[0016] The terms “epoxy” and “epoxy composition” refer to curable compositions that include an epoxy resin and a curative. Epoxy resins are materials that contain one or more epoxy groups, that is to say oxirane rings.

[0017] The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25°C.

[0018] The terms “Tg” and “glass transition temperature” are used interchangeably. If measured, Tg values are determined by Differential Scanning Calorimetry (DSC) at a scan rate of 10°C / minute, unless otherwise indicated. Typically, Tg values for copolymers are not measured but are calculated using the well-known Fox Equation, using the monomer Tg values provided by the monomer supplier, as is understood by one of skill in the art.

[0019] The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

[0020] The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction.

[0021] The term “aliphatic” as used herein refers to groups that contain alkyl or alkylene groups or a combination thereof but do not contain unsaturation.

[0022] The term “aromatic” as used herein refers to groups that contain aryl groups, arylene groups or a combination thereof and may also include aliphatic groups.

[0023] The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl. The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

[0024] The term “alkylene” refers to a divalent group that is a radical of an alkane. The alkylene can be straight-chained, branched, cyclic, or combinations thereof. The alkylene often has 1 to 20 carbon atoms. In some embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylene can be on the same carbon atom (i.e., an alkylidene) or on different carbon atoms.

[0025] The term “arylene” refers to a divalent group that is carbocyclic and aromatic. The group has one to five rings that are connected, fused, or combinations thereof. The other rings can be aromatic, non-aromatic, or combinations thereof. In some embodiments, the arylene group has up to 5 rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromatic ring. For example, the arylene group can be phenylene.

[0026] The term “heteroalkylene” refers to a divalent group that includes at least two alkylene groups connected by a thio, oxy, or -NR- where R is alkyl. The heteroalkylene can be linear, branched, cyclic, substituted with alkyl groups, or combinations thereof. Some heteroalkylenes are poloxyyalkylenes where the heteroatom is oxygen such as for example, -CH2CH2(OCH2CH2)nOCH2CH2-.

[0027] The term “aralkyl” refers to a monovalent group that is an alkyl group substituted with an and group (e.g., as in a benzyl group). Tire term “alkaryl” refers to a monovalent group that is an aryl substituted with an alkyl group (e.g., as in a tolyl group). Unless otherwise indicated, for both groups, the alkyl portion often has 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms and an aryl portion often has 6 to 20 carbon atoms, 6 to 18 carbon atoms, 6 to 16 carbon atoms, 6 to 12 carbon atoms, or 6 to 10 carbon atoms.

[0028] Disclosed herein are curable adhesive compositions. In some embodiments, these curable adhesive compositions comprise a curable epoxy adhesive and a filler comprising expanded microspheres. Expanded microspheres are polymeric spheres with a central void. The curable compositions, when cured, have a dielectric constant (Dk) of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%. In some embodiments, the curable compositions, when cured have a dielectric constant (Dk) of 2.9 or less. In some embodiments, the curable composition, when cured have a shrinkage of 2% or less and an elongation of 2-100%.

[0029] The curable epoxy adhesive comprises a curable one-part epoxy adhesive or a curable two-part epoxy adhesive. The choice of a one-part or a two-part curable adhesive depends upon a variety of factors, including the desired used for the adhesive. One issue with two-part epoxy adhesives is that upon mixing there is a limited open time. “Open time” for one-part epoxy adhesives refers to the time after mixing in which the adhesive can be used before it hardens and is no longer usable as a curable adhesive.

[0030] In some embodiments, the curable adhesive composition is a one-part epoxy adhesive that cures at a temperature of 40°C or greater. Unlike two-part epoxy adhesives, one-part adhesives do not appreciably cure at room temperature, and thus do not have open time issues;.

[0031] Suitable adhesives include curable one-part epoxy / thiol adhesives. Particularly suitable curable one-part epoxy / thiol adhesives are those described in US Patent No. 11,584,823. These curable one-part epoxy / thiol adhesive comprise at least one epoxy resin having at least two epoxide groups per molecule, at least one thiol component that is a polythiol with at least two primary thiol groups per molecule, at least one nitrogencontaining catalyst, and at least one soluble substituted barbituric acid.

[0032] The curable epoxy / thiol resin compositions of this disclosure show improved storage stability at room temperature, particularly with respect to viscosity maintenance over time, as well as with extended working lives at room temperature, and relatively short curing times at elevated temperatures. In certain embodiments, the curable epoxy / thiol resin compositions are stable at room temperature for a period of at least 2 weeks, at least 4 weeks, or at least 2 months. In this context, “stable” means that the epoxy / thiol composition remains in a curable form.

[0033] It is believed a barbituric acid derivative prevents the nitrogen-containing catalyst and thiol curing agent from curing the epoxy resin for a period of time (e.g., at least 2 weeks) because the weakly acidic barbituric acid neutralizes any prematurely dissolved nitrogen-containing catalyst.

[0034] The curable epoxy / thiol resin compositions also possess good low temperature curability. In certain embodiments, the curable epoxy / thiol resin composition is curable at a temperature of at least 40°C. In certain embodiments, the curable epoxy / thiol resin composition is curable at a temperature of up to 80°C. In certain embodiments, the curable epoxy / thiol composition is curable at a temperature of 60-65°C.

[0035] Thus, curable epoxy / thiol resin compositions of the present disclosure are suitable for use in temperature sensitive bonding applications, particularly in the electronics industry, e.g., in cell phone assembly and bonding of plastic and metal parts. They may also be used in a variety of other applications, such as in the automotive and aerospace industries for parts bonding.

[0036] The epoxy resin component included in the curable epoxy / polythiol resin composition contains an epoxy resin that has at least two epoxy functional groups (i.e., oxirane groups) per molecule. As used herein, the term oxirane group refers to the following divalent group.

[0037] H H

[0038] O

[0039] The asterisks denote a site of attachment of the oxirane group to another group. If an oxirane group is at the terminal position of the epoxy resin, the oxirane group is typically bonded to a hydrogen atom.

[0040] This terminal oxirane group is often part of a glycidyl group.

[0041] The epoxy resin includes a resin with at least two oxirane groups per molecule. For example, an epoxy compound can have 2 to 10, 2 to 6, or 2 to 4 oxirane groups per molecule. The oxirane groups are usually part of a glycidyl group.

[0042] Epoxy resins can include a single material or mixture of materials (e.g., monomeric, oligomeric, or polymeric compounds) selected to provide the desired viscosity characteristics before curing and to provide the desired mechanical properties after curing. If the epoxy resin includes a mixture of materials, at least one of the epoxy resins in the mixture is usually selected to have at least two oxirane groups per molecule. For example, a first epoxy resin in the mixture can have two to four or more oxirane groups and a second epoxy resin in the mixture can have one to four oxirane groups. In some of these examples, the first epoxy resin is a first glycidyl ether with two to four glycidyl groups and the second epoxy resin is a second glycidyl ether with one to four glycidyl groups.

[0043] The portion of the epoxy resin that is not an oxirane group (i.e., an epoxy resin compound minus the oxirane groups) can be aromatic, aliphatic, or a combination thereof and can be linear, branched, cyclic, or a combination thereof. The aromatic and aliphatic portions of the epoxy resin can include heteroatoms or other groups that are not reactive with the oxirane groups. That is, the epoxy resin can include halo groups, oxy groups such as in an ether linkage group, thio groups such as in a thio ether linkage group, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. The epoxy resin can also be a silicone- based material such as a polydiorganosiloxane-based material.

[0044] Although the epoxy resin can have any suitable molecular weight, the weight average molecular weight is usually at least 100 grams / mole, at least 150 grams / mole, at least 175 grams / mole, at least 200 grams / mole, at least 250 grams / mole, or at least 300 grams / mole. The weight average molecular weight can be up to 50,000 grams / mole or even higher for polymeric epoxy resins. The weight average molecular weight is often up to 40,000 grams / mole, up to 20,000 grams / mole, up to 10,000 grams / mole, up to 5,000 grams / mole, up to 3,000 grams / mole, or up to 1,000 grams / mole. For example, the weight average molecular weight can be in the range of 100 to 50,000 grams / mole, in the range of 100 to 20,000 grams / mole, in the range of 10 to 10,000 grams / mole, in the range of 100 to 5,000 grams / mole, in the range of 200 to 5,000 grams / mole, in the range of 100 to 2,000 grams / mole, in the range of 200 to 2,000 grams / mole, in the range of 100 to 1,000 grams / mole, or in the range of 200 to 1,000 grams / mole.

[0045] Suitable epoxy resins are typically a liquid at room temperature; however, solid epoxy resins that can be dissolved in one of the other components of the composition, such as a liquid epoxy resin, can be used if desired. In most embodiments, the epoxy resin is a glycidyl ether. Exemplary glycidyl ethers can be of Formula (I).

[0046] In Formula (I), group R1is a polyvalent group that is aromatic, aliphatic, or a combination thereof. Group R1can be linear, branched, cyclic, or a combination thereof. Group R1can optionally include halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. Although the variable p can be any suitable integer greater than or equal to 2, p is often an integer in the range of 2 to 10, in the range of 2 to 6, or in the range of 2 to 4.

[0047] In some embodiments, the epoxy resin is a polyglycidyl ether of a polyhydric phenol, such as polyglycidyl ethers of bisphenol A, bisphenol F, bisphenol AD, catechol, and resorcinol. In some embodiments, the epoxy resin is a reaction product of a polyhydric alcohol with epichlorohydrin. Exemplary polyhydric alcohols include butanediol, polyethylene glycol, and glycerin. In some embodiments, the epoxy resin is an epoxidised (poly)olefmic resin, epoxidised phenolic novolac resin, epoxidised cresol novolac resin, and cycloaliphatic epoxy resin. In some embodiments, the epoxy resin is a glycidyl ether ester, such as that which can be obtained by reacting a hydroxycarboxylic acid with epichlorohydrin, or a polyglycidyl ester, such as that which can be obtained by reacting a polycarboxylic acid with epichlorohydrin. In some embodiments, the epoxy resin is a urethane -modified epoxy resin. Various combinations of two or more epoxy resins can be used if desired.

[0048] In some exemplary epoxy resins of Formula (I), the variable p is equal to 2 (i.e., the epoxy resin is a diglycidyl ether) and R1includes an alkylene (i.e., an alkylene is a divalent radical of an alkane and can be referred to as an alkane-diyl), heteroalkylene (i.e., a heteroalkylene is a divalent radical of a heteroalkane and can be referred to as a heteroalkane-diyl), arylene (i.e., a divalent radical of an arene compound), or combination thereof. Suitable alkylene groups often have 1 to 20 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms. Suitable heteroalkylene groups often have 2 to 50 carbon atoms, 2 to 40 carbon atoms, 2 to 30 carbon atoms, 2 to 20 carbon atoms, 2 to 10 carbon atoms, or 2 to 6 carbon atoms with 1 to 10 heteroatoms, 1 to 6 heteroatoms, or 1 to 4 heteroatoms. The heteroatoms in the heteroalkylene can be selected from oxy, thio, or -NH- groups but are often oxy groups. Suitable arylene groups often have 6 to 18 carbon atoms or 6 to 12 carbon atoms. For example, the arylene can be phenylene, fluorenylene, or biphenylene. Group R1can further optionally include halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. The variable p is usually an integer in the range of 2 to 4.

[0049] Some epoxy resins of Formula (I) are diglycidyl ethers where R1includes (a) an arylene group or (b) an arylene group in combination with an alkylene, heteroalkylene, or both. Group R1can further include optional groups such as halo groups, oxy groups, thio groups, carbonyl groups, carbonyloxy groups, carbonylimino groups, phosphono groups, sulfono groups, nitro groups, nitrile groups, and the like. These epoxy resins can be prepared, for example, by reacting an aromatic compound having at least two hydroxyl groups with an excess of epichlorohydrin. Examples of useful aromatic compounds having at least two hydroxyl groups include, but are not limited to, resorcinol, catechol, hydroquinone, p,p’ -dihydroxydibenzyl, p,p’ -dihydroxyphenylsulfone, p,p’- dihydroxybenzophenone, 2,2 ’-dihydroxyphenyl sulfone, p,p’ -dihydroxybenzophenone, and 9,9-(4-hydroxyphenol)fluorene. Still other examples include the 2,2’, 2,3’, 2,4’, 3,3’,

[0050] 3,4’, and 4,4’ isomers of dihydroxydiphenylmethane, dihydroxydiphenyldimethylmethane, dihydroxydiphenylethylmethylmethane, dihydroxydiphenylmethylpropylmethane, dihydroxydiphenylethylphenylmethane, dihydroxydiphenylpropylenphenylmethane, dihydroxydiphenylbutylphenylmethane, dihydroxydiphenyltolylethane, dihydroxydiphenyltolylmethylmethane, dihydroxydiphenyldicyclohexylmethane, and dihydroxy diphenylcyclohexane .

[0051] Some commercially available diglycidyl ether epoxy resins of Formula (I) are derived from bisphenol A (i.e., bisphenol A is 4,4 ’-dihydroxydiphenylmethane). Examples include, but are not limited to, those available under the trade designation EPON (e.g., EPON 1510, EPON 1310, EPON 828, EPON 872, EPON 1001, EPON 1004, and EPON 2004) from Momentive Specialty Chemicals, Inc. (Columbus, OH), those available under the trade designation DER (e.g., DER 331, DER 332, DER 336, and DER 439) from Olin Epoxy Co. (St. Louis, MO), and those available under the trade designation EPICLON (e.g., EPICLON 850) from Dainippon Ink and Chemicals, Inc. (Parsippany, NJ). Other commercially available diglycidyl ether epoxy resins are derived from bisphenol F (i.e., bisphenol F is 2,2 ’-dihydroxydiphenylmethane). Examples include, but are not limited to, those available under the trade designation DER (e.g., DER 334) from Olin Epoxy Co. (St. Louis, MO), those available under the trade designation EPICLON (e.g., EPICLON 830) from Dainippon Ink and Chemicals, Inc. (Parsippany, NJ), and those available under the trade designation ARALDITE (e.g., ARALDITE 281) from Huntsman Corporation (The Woodlands, TX).

[0052] Other epoxy resins of Formula (I) are diglycidyl ethers of a poly(alkylene oxide) diol. These epoxy resins also can be referred to as diglycidyl ethers of a poly(alkylene glycol) diol. The variable p is equal to 2 and R1is a heteroalkylene having oxygen heteroatoms. The poly (alkylene glycol) portion can be a copolymer or homopolymer and often includes alkylene units having 1 to 4 carbon atoms. Examples include, but are not limited to, diglycidyl ethers of polyethylene oxide) diol, diglycidyl ethers of polypropylene oxide) diol, and diglycidyl ethers of poly(tetramethylene oxide) diol. Epoxy resins of this type are commercially available from Polysciences, Inc. (Warrington, PA) such as those derived from a polyethylene oxide) diol or from a polypropylene oxide) diol having a weight average molecular weight of 400 grams / mole, about 600 grams / mole, or about 1000 grams / mole.

[0053] Still other epoxy resins of Formula (I) are diglycidyl ethers of an alkane diol (R1is an alkylene and the variable p is equal to 2). Examples include a diglycidyl ether of 1,4- dimethanol cyclohexyl, diglycidyl ether of 1,4-butanediol, and a diglycidyl ether of the cycloaliphatic diol formed from a hydrogenated bisphenol A such as those commercially available under the trade designation EPONEX (e.g., EPONEX 1510) from Hexion Specialty Chemicals, Inc. (Columbus, OH) and under the trade designation EP ALLOY (e.g., EP ALLOY 5001) from CVC Thermoset Specialties (Moorestown, NJ).

[0054] For some applications, the epoxy resins chosen for use in the curable coating compositions are novolac epoxy resins, which are glycidyl ethers of phenolic novolac resins. These resins can be prepared, for example, by reaction of phenols with an excess of formaldehyde in the presence of an acidic catalyst to produce the phenolic novolac resin. Novolac epoxy resins are then prepared by reacting the phenolic novolac resin with epichlorihydrin in the presence of sodium hydroxide. The resulting novolac epoxy resins typically have more than two oxirane groups and can be used to produce cured coating compositions with a high crosslinking density. The use of novolac epoxy resins can be particularly desirable in applications where corrosion resistance, water resistance, chemical resistance, or a combination thereof is desired. One such novolac epoxy resin is poly [(phenyl glycidyl ether)-co-formaldehyde] . Other suitable novolac resins are commercially available under the trade designation ARALDITE (e.g., ARALDITE GY289, ARALDITE EPN 1183, ARALDITE EP 1179, ARALDITE EPN 1139, and ARALDITE EPN 1138) from Huntsman Corporation (The Woodlands, TX), under the trade designation EPALLOY (e.g., EP ALLOY 8230) from CVC Thermoset Specialties (Moorestown, NJ), and under the trade designation DEN (e.g., DEN 424 and DEN 431) from Olin Epoxy Co. (St. Louis, MO).

[0055] Yet other epoxy resins include silicone resins with at least two glycidyl groups and flame retardant epoxy resins with at least two glycidyl groups (e.g., a brominated bisphenol-type epoxy resin having at least two glycidyl groups such as that commercially available from Dow Chemical Co. (Midland, MI) under the trade designation DER 580).

[0056] The epoxy resin component is often a mixture of materials. For example, the epoxy resins can be selected to be a mixture that provides the desired viscosity or flow characteristics prior to curing. For example, within the epoxy resin may be reactive diluents that include monofimctional or certain multifunctional epoxy resins. The reactive diluent should have a viscosity which is lower than that of the epoxy resin having at least two epoxy groups. Ordinarily, the reactive diluent should have a viscosity less than 250 mPa s (cPs). The reactive diluent tends to lower the viscosity of the epoxy / polythiol resin composition and often has either a branched backbone that is saturated or a cyclic backbone that is saturated or unsaturated. Particularly suitable reactive diluents have only one functional group (i.e., oxirane group) such as various monoglycidyl ethers. Some exemplary monofimctional epoxy resins include, but are not limited to, those with an alkyl group having 6 to 28 carbon atoms, such as (C6-C28)alkyl glycidyl ethers, (C6-C28)fatty acid glycidyl esters, (C6-C28)alkylphenol glycidyl ethers, and combinations thereof. In the event a monofimctional epoxy resin is the reactive diluent, such monofimctional epoxy resin should be employed in an amount of up to 50 parts based on the total of the epoxy resin component.

[0057] In some embodiments, the curable adhesive compositions typically include at least 20 weight percent (wt-%), at least 25 wt-%, at least 30 wt-%, at least 35 wt-%, at least 40 wt-%, or at least 45 wt-%, epoxy resin component, based on a total weight of the curable adhesive composition. If lower levels are used, the cured composition may not contain enough polymeric material (e.g., epoxy resin) to provide desired coating characteristics. In some embodiments, the curable epoxy / thiol resin compositions include up to 80 wt-%, up to 75 wt-%, or up to 70 wt-%, epoxy resin component, based on a total weight of the curable epoxy / thiol resin composition.

[0058] The curable adhesive composition also comprises at least one thiol. A thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl or mercapto (-C-SH) group. Suitable polythiols are selected from a wide variety of compounds that have two or more thiol groups per molecule, and that function as curatives for epoxy resins.

[0059] Examples of suitable polythiols include trimethylolpropane tris(beta- mercaptopropionate), trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(beta-mercaptopropionate), dipentaerythritol poly(beta-mercaptopropionate), ethylene glycol bis(beta-mercaptopropionate), a (Cl- C12)alkyl polythiol (e.g., butane- 1,4-dithiol and hexane- 1 ,6-dithiol), a (C6-C12)aromatic polythiol (e.g., p-xylenedithiol and 1,3,5-tris (mercaptomethyl) benzene). Combinations of polythiols can be used if desired.

[0060] In some embodiments, the curable epoxy / thiol compositions typically include at least 25 wt-%, at least 30 wt-%, or at least 35 wt-%, thiol component, based on a total weight of the curable epoxy / thiol resin composition. In some embodiments, the curable epoxy / thiol compositions include up to 70 wt-%, up to 65 wt-%, up to 60 wt-%, up to 55 wt-%, up to 50 wt-%, up to 45 wt-%, or up to 40 wt-%, thiol component, based on a total weight of the curable epoxy / thiol resin composition. Various combinations of two or more polythiols can be used if desired.

[0061] In some embodiments, the ratio of the epoxy component to the thiol component in the curable epoxy / thiol resin compositions of the present disclosure is from 0.5: 1 to 1.5: 1, or 0.75: 1 to 1.3: 1 (epoxy:thiol equivalents).

[0062] Systems containing epoxy resins and polythiols suitable for use in the present disclosure are disclosed in U.S. Pat. No. 5,430,112 (Sakata et al.).

[0063] The curable adhesive compositions of the present disclosure include at least one nitrogen-containing catalyst. Such catalysts are typically of the heat activated class. In certain embodiments, the nitrogen-containing catalyst is capable of activation at temperatures at or above 40°C to effect the thermal curing of the epoxy resin.

[0064] Suitable nitrogen-containing catalysts are typically a solid at room temperature, and not soluble in the other components of the epoxy / thiol resin compositions of the present disclosure. In certain embodiments, the nitrogen-containing catalysts are in particle form having a particle size (i.e., the largest dimension of the particles, such as the diameter of a sphere) of at least 100 micrometers.

[0065] As used herein, the term “nitrogen-containing catalyst” refers to any nitrogencontaining compound that catalyzes the curing of the epoxy resin. The term does not imply or suggest a certain mechanism or reaction for curing. The nitrogen -containing catalyst can directly react with the oxirane ring of the epoxy resin, can catalyze or accelerate the reaction of the polythiol compound with the epoxy resin, or can catalyze or accelerate the self-polymerization of the epoxy resin.

[0066] In certain embodiments, the nitrogen-containing catalysts are amine -containing catalysts. Some amine-containing catalysts have at least two groups of formula -NR2H, wherein R2is selected from hydrogen, alkyl, aryl, alkaryl, or aralkyl. Suitable alkyl groups often have 1 to 12 carbon atoms, 1 to 8 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms. The alkyl group can be cyclic, branched, linear, or a combination thereof. Suitable aryl groups usually have 6 to 12 carbon atom such as a phenyl or biphenyl group. Suitable alkaryl groups can include the same aryl and alkyl groups discussed above.

[0067] The nitrogen-containing catalyst minus the at least two amino groups (i.e., the portion of the catalyst that is not an amino group) can be any suitable aromatic group, aliphatic group, or combination thereof.

[0068] Exemplary nitrogen-containing catalysts for use herein include a reaction product of phthalic anhydride and an aliphatic polyamine, more particularly a reaction product of approximately equimolar proportions of phthalic acid and diethylamine triamine, as described in British Patent 1,121,196 (Ciba Geigy AG). A catalyst of this type is available commercially from Ciba Geigy AG under the tradename CIBA HT 9506.

[0069] Yet another type of nitrogen-containing catalyst is a reaction product of: (i) a polyfiinctional epoxy compound; (ii) an imidazole compound, such as 2-ethyl-4- methylimidazole; and (iii) phthalic anhydride. The polyfiinctional epoxy compound may be a compound having two or more epoxy groups in the molecule as described in U.S. Pat. No. 4,546,155 (Hirose et al.). A catalyst of this type is commercially available from Ajinomoto Co. Inc. (Tokyo, Japan) under the tradename AJICURE PN-23, which is believed to be an adduct of EPON 828 (bisphenol type epoxy resin epoxy equivalent 184- 194, commercially available from Hexion Specialty Chemicals, Inc. (Columbus, OH)), 2- ethyl-4-methylimidazole, and phthalic anhydride.

[0070] Other suitable nitrogen-containing catalysts include the reaction product of a compound having one or more isocyanate groups in its molecule with a compound having at least one primary or secondary amino group in its molecule. Additional nitrogencontaining catalysts include 2-heptadeoylimidazole, 2-phenyl-4,5- dihydroxymethylimidazole, 2-phenyl-4-methyl-5 -hydroxymethylimidazole, 2 -phenyl -4- benzyl-5-hydroxymethylimidazole, 2,4-diamino-8-2-methylimidazolyl-(l)-ethyl-5- triazine, or a combination therof, as well as products of triazine with isocyanuric acid, succinohydrazide, adipohydrazide, isophtholohydrazide, o-oxybenzohydrazide, salicylohydrazide, or a combination thereof.

[0071] Nitrogen-containing catalysts are commercially available from sources such as Ajinomoto Co. Inc. (Tokyo, Japan) under the tradenames AMICURE MY-24, AMICURE GG-216 and AMICURE ATU CARBAMATE, from Hexion Specialty Chemicals, Inc. (Columbus, OH) under the tradename EPIKURE P-101, from T&K Toka (Chikumazawa, Miyoshi-Machi, Iruma-Gun, Saitama, Japan) under the tradenames FXR-1020, FXR-1081, and FXR-1121, from Shikoku (Marugame, Kagawa Prefecture, Japan) under the tradenames CUREDUCT P-2070 and P-2080, from Air Products and Chemicals (Allentown, PA) under the tradenames ANCAMINE 2441 and 2442, from AC Catalysts (Linden, NJ) under the tradenames TECHNICURE LC80 and LC100, and from Asahi Kasei Kogyo, K.K. (Japan) under the tradename NOVACURE HX-372.

[0072] Other suitable nitrogen-containing catalysts are those described in U.S. Pat. No. 5,077,376 (Dooley et al.) and U.S. Pat. No. 5,430,112 (Sakata et al.) referred to as “amine adduct latent accelerators.” Other exemplary nitrogen-containing catalysts are described, for example, in British Patent 1,121,196 (Ciba Geigy AG), European Patent Application No. 138465A (Ajinomoto Co.), and European Patent Application No. 193068A (Asahi Chemical).

[0073] In some embodiments, the curable epoxy / thiol resin compositions typically include at least 1 part, at least 2 parts, at least 3 parts, at least 4 parts, or at least 5 parts, of a nitrogen-containing catalyst, per 100 parts of the epoxy resin component. In some embodiments, the curable epoxy / thiol compositions typically include up to 45 parts, up to 40 parts, up to 35 parts, up to 30 parts, up to 25 parts, or up to 20 parts, of a nitrogencontaining catalyst, per 100 parts of the epoxy resin component. Various combinations of two or more nitrogen-containing catalysts can be used if desired.

[0074] The curable adhesive compositions also comprise a barbituric acid derivative. The barbituric acid derivatives useful in the curable epoxy / thiol resin compositions of the present disclosure include those that are soluble in the epoxy / thiol resin compositions of the present disclosure.

[0075] In this context, a barbituric acid derivative “soluble in the epoxy / thiol resin composition” (i.e., a “soluble” barbituric acid derivative) refers to a barbituric acid derivative which, when incorporated in an epoxy / thiol resin composition in an amount of 5 wt-%, produces an epoxy / thiol resin composition with at least 80% clarity and / or at least 80% transmission, as evaluated according to the Stabilizer Solubility Test in the Examples Section. In certain embodiments, the clarity of a curable epoxy / thiol resin composition that includes 5 wt-% of a “soluble” barbituric acid derivative is at least 85%, at least 90%, or at least 95%. In certain embodiments, the transmission of a curable epoxy / thiol resin composition that includes 5 wt-% of a “soluble” barbituric acid derivative is at least 85%, or at least 90%.

[0076] A soluble barbituric acid derivative is used in an epoxy / thiol resin composition in an amount that allows the epoxy / thiol resin composition to remain curable for at least 72 hours at room temperature such that there is no doubling in viscosity. Typically, this is an amount of at least 0.01 wt-%, based on the total weight of the curable epoxy / thiol resin composition.

[0077] The greater the amount of a soluble barbituric acid derivative used in an epoxy / thiol resin composition, generally the longer the shelf life of the curable epoxy / thiol composition. The greater the amount of a soluble barbituric acid derivative used in an epoxy / thiol resin composition, generally the longer the time required to cure and / or the higher the temperature required to cure the curable epoxy / thiol composition. Thus, depending on the use of the curable composition, there is a balance between shelf life and cure time / temperature. Typically, for a reasonable shelf life, cure time, and cure temperature, the amount of soluble barbituric acid derivative used is up to 1 wt-%, or up to 0.5 wt-%.

[0078] Herein, the barbituric acid “derivatives” include those barbituric acid compounds substituted at one or more of the 1, 3, and / or 5 N positions, or at the 1 and / or 3 N positions and optionally at the 5 N position, with an aliphatic, cycloaliphatic, or aromatic group. In certain embodiments, the barbituric acid derivatives include those of Formula (II): wherein one or more of the R3, R4, and R5groups are represented by hydrogen, an aliphatic group, a cycloaliphatic group, or an aromatic group (e.g., phenyl), optionally further substituted in any position with one or more of (Cl-C4)alkyl, -OH, halide (F, Br, Cl, I), phenyl, (Cl-C4)alkylphenyl, (Cl-C4)alkenylphenyl, nitro, or -OR6where R6is phenyl, a carboxylic group, a carbonyl group, or an aromatic group and R6is optionally substituted with (Cl-C4)alkyl, -OH, or halide; and further wherein at least one of the R3, R4, and R5groups is not hydrogen. In certain embodiments, at least two of the R3, R4, and R5groups are not hydrogen.

[0079] Such soluble acids function as stabilizers of the nitrogen-containing catalyst in the epoxy / thiol resin compositions of the present disclosure. Desirably, the nitrogencontaining catalyst is stabilized against curing the epoxy resin at room temperature for a period of at least 2 weeks, at least 4 weeks, or at least 2 months.

[0080] Examples of suitable substituted barbituric acid derivatives include l-benzyl-5- phenylbarbituric acid, l-cycloheyl-5 -ethylbarbituric acid (available from Chemische Fabrik Berg, Bitterfeld-Wolfen, Germany), 1,3 -dimethylbarbituric acid (available from Alfa Aesar, Tewksbury, MA), and combinations thereof.

[0081] U.S. Pat. No. 6,653,371 (Bums et al.) teaches that a substantially insoluble solid organic acid is required for epoxy / thiol resin compositions to stabilize the composition. Surprisingly, it was found that the use of a soluble organic acid, in particular, barbituric acid derivatives that are functionalized to make them more soluble, result in better stabilization of the epoxy / thiol resin composition than the use of substantially insoluble organic acids. Also, U.S. Pat. No. 6,653,371 (Bums et al.) teaches that stabilizer effectiveness is directly affected by particle size of the stabilizing component added into the system. A benefit of using soluble barbituric acid derivatives as stabilizers is that the initial particle size does not alter stabilizer performance, at least because the stabilizer is fully dissolved throughout the curable epoxy / thiol resin compositions.

[0082] In some embodiments, the curable adhesive composition comprises:

[0083] 20 wt-% to 80 wt-%, based on the total weight of the curable adhesive composition of at least one epoxy resin component comprising: a polyglycidyl ether of a polyhydric phenol, a reaction product of a polyhydric alcohol with epichlorohydrin, an epoxidised (poly)olefinic resin, an epoxidised phenolic novolac resin, an epoxidised cresol novolac resin, a cycloaliphatic epoxy resin, a glycidyl ether ester, a polyglycidyl ester, a urethane modified epoxy resin, or a combination of two or more thereof;

[0084] 25 wt-% to 70 wt-%, based on a total weight of the curable adhesive composition of at least one polythiol component comprising: trimethylolpropane tris(beta- mercaptopropionate), trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(beta-mercaptopropionate), dipentaerythritol poly(beta-mercaptopropionate), ethylene glycol bis(beta-mercaptopropionate), a (Cl- C12)alkyl polythiol, a (C6-C12)aromatic polythiol, or a combination of two or more thereof;

[0085] 1 part to 45 parts per 100 parts of the epoxy resin component of an amine catalyst that is a solid at room temperature; and

[0086] 0.01 wt-% to 1 wt-%, based on the total weight of the curable adhesive composition of at least one soluble substituted barbituric acid comprising: l-benzyl-5-phenylbarbituric acid, l-cycloheyl-5 -ethylbarbituric acid, 1,3 -dimethylbarbituric acid, and a combination thereof.

[0087] In addition to the components described above, the curable compositions of this disclosure can include various optional additives as long as the additives do not adversely affect the desirable properties of the curable adhesive composition. Examples of suitable additives include toughening agents, non-reactive plasticizers, flow control agents, thickeners, adhesion promoters, inorganic fdlers, reactive or unreactive diluents, dyes, pigments, or a combination thereof. Toughening agents can be added to provide the desired overlap shear, peel resistance, and impact strength. Useful toughening agents are polymeric materials that may react with the epoxy resin and that may be cross-linked. Suitable toughening agents include polymeric compounds having both a rubbery phase and a thermoplastic phase or compounds which are capable of forming, with the epoxide resin, both a rubbery phase and a thermoplastic phase on curing. Polymers useful as toughening agents are generally selected to inhibit cracking of the cured epoxy composition.

[0088] Some polymeric toughening agents that have both a rubbery phase and a thermoplastic phase are acrylic core-shell polymers wherein the core is an acrylic copolymer having a glass transition temperature below 0°C. Such core polymers may include polybutyl acrylate, polyisooctyl acrylate, polybutadiene-polystyrene in a shell comprised of an acrylic polymer having a glass transition temperature above 25 °C, such as polymethylmethacrylate. Commercially available core-shell polymers include those available as a dry powder under the trade designations ACRYLOID KM 323, ACRYLOID KM 330, and PARALOID BTA 731, from Dow Chemical Co., and KANE ACE B-564 from Kaneka Corporation (Osaka, Japan). These core-shell polymers may also be available as a predispersed blend with a diglycidyl ether of bisphenol A at, for example, a ratio of 12 to 37 parts by weight of the core -shell polymer and are available under the trade designations KANE ACE (e.g., KANE ACE MX 157, KANE ACE MX 257, and KANE ACE MX 125) from Kaneka Corporation (Japan).

[0089] Another class of polymeric toughening agents that are capable of forming, with the epoxide group-containing material, a rubbery phase on curing, are carboxyl-terminated butadiene acrylonitrile compounds. Commercially available carboxyl-terminated butadiene acrylonitrile compounds include those available under the trade designations HYCAR (e.g., HYCAR 1300X8, HYCAR 1300X13, and HYCAR 1300X17) from Lubrizol Advanced Materials, Inc. (Cleveland, Ohio) and under the trade designation PARALOID (e.g., PARALOID EXL-2650) from Dow Chemical (Midland, MI).

[0090] Other polymeric toughening agents are graft polymers, which have both a rubbery phase and a thermoplastic phase, such as those disclosed in US Patent No. 3,496,250 (Czerwinski). These graft polymers have a rubbery backbone with thereto thermoplastic polymer segments grafted thereto. Examples of such graft polymers include, for example, (meth)acrylate-butadiene-styrene, and acrylonitrile / butadiene-styrene polymers. The rubbery backbone is generally prepared so as to constitute from 95 wt-% to 40 wt-% of the total graft polymer, so that the polymerized thermoplastic portion constitutes from 5 wt-% to 60 wt-% of the graft polymer.

[0091] Still other polymeric toughening agents are polyether sulfones such as those commercially available from BASF (Florham Park, NJ) under the trade designation ULTRASON (e.g., ULTRASON E 2020 P SR MICRO).

[0092] The curable composition can additionally contain a non-reactive plasticizer to modify rheological properties. Commercially available plasticizers include those available under the trade designation BENZOFLEX 131 from Eastman Chemical (Kingsport, TN), JAYFLEX DINA available from ExxonMobil Chemical (Houston, TX), and PLASTOMOLL (e.g., diisononyl adipate) from BASF (Florham Park, NJ).

[0093] The curable composition optionally contains a flow control agent or thickener, to provide the desired rheological characteristics to the composition. Suitable flow control agents include fumed silica, such as treated fumed silica, available under the trade designation CAB-O-SIL TS 720, and untreated fumed silica available under the trade designation CAB-O-SIL M5, from Cabot Corp. (Alpharetta, GA). Also suitable are liquid thixotropic agents such as RHEOBYK 7410ET and RHEOBYK R606 from BYK.

[0094] In some embodiments, the curable composition may optionally also comprise expandable microspheres in addition to the expanded microspheres described below. Expandable microspheres are well understood in the art. The expandable microspheres expand upon the curing of the curable composition. It should be understood that these expandable microspheres are different from the expanded microspheres described below.

[0095] In some embodiments, the curable composition optimally contains adhesion promoters to enhance the bond to the substrate. The specific type of adhesion promoter may vary depending upon the composition of the surface to which it will be adhered. Adhesion promoters that have been found to be particularly useful for surfaces coated with ionic type lubricants used to facilitate the drawing of metal stock during processing include, for example, dihydric phenolic compounds such as catechol and thiophenol.

[0096] The curable composition optionally may also contain one or more conventional additives such as fillers (e.g., aluminum powder, carbon black, glass bubbles, talc, clay, calcium carbonate, barium sulfate, titanium dioxide, silica such as fused silica, silicates, glass beads, and mica), pigments, flexibilizers, reactive diluents, non-reactive diluents, fire retardants, antistatic materials, thermally and / or electrically conductive particles. Particulate fillers can be in the form of flakes, rods, spheres, and the like. Additives are typically added in amounts to produce the desired effect in the resulting adhesive.

[0097] The amount and type of such additives may be selected by one skilled in the art, depending on the intended end use of the composition.

[0098] As described above, the curable adhesive composition also comprises expanded microspheres. These expanded microspheres are polymeric spheres with a central void. Unlike expandable microspheres wherein the expandable microspheres are added to the curable composition and expand during the curing process, the expanded microspheres of the curable compositions of this disclosure are expanded prior to incorporation into the curable adhesive composition.

[0099] Examples of suitable expanded microspheres include EXPANCEL thermoplastic microspheres from Nouryon, DUALITE Expanded Microspheres from Chase Corporation, MFL-81GCA from Matsumoto, and . PHENOLIC MICROBALLOONS from MAS EPOXIES

[0100] The amount of expanded microspheres present in the adhesive composition can vary widely. Some embodiments comprise at least 0.5 % by weight of expanded microspheres based on the total weight of the curable adhesive composition. In some embodiments, the adhesive composition comprises up to 10% by weight of expanded microspheres based on the total weight of the curable adhesive composition. In some embodiments the adhesive composition comprises from 1-4% by weight of expanded microspheres based on the total weight of the curable adhesive composition.

[0101] Also disclosed herein are articles. In some embodiments, the article comprises a first substrate with a first major surface and a second major surface, a cured adhesive layer with a first major surface and a second major surface disposed on the second major surface of the first substrate such that the first major surface of the cured adhesive layer is in contact with the second major surface of first substrate, and a second substrate with a first major surface and a second major surface where the first major surface of the second substrate is in contact with the second major surface of the cured adhesive layer. The cured adhesive layer is the cured layer of the curable adhesive compositions described above. The curable adhesive compositions comprise a curable epoxy adhesive and a filler comprising expanded microspheres comprising polymeric spheres with a central void. The cured adhesive composition has a dielectric constant (Dk) of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%. As described above, in some embodiments the cured adhesive composition has a dielectric constant (Dk) of 2.9 or less and / or a shrinkage of less than 2.0% and / or an elongation of 2-100%.

[0102] A wide variety of substrates are suitable for use in the articles of this disclosure. In some embodiments, the first and second substrate independently comprise a metal substrate, a polymeric substrate, or a glass substrate. In some embodiments, the first substrate comprises a metal substrate and the second substrate comprises a glass substrate.

[0103] In some embodiments, at least one of the first and second substrate comprises a polymeric film substrate. Polymeric film substrates are those substrates prepared polymeric materials. The polymeric film substrates may be relatively thin and flexible or may be relatively thick and rigid.

[0104] An article of this disclosure is shown in Figure 1. Figure 1 shows first substrate 100, second substrate 300, and cured adhesive layer 200 between first substrate 100 and second substrate 300. First substrate 100 and second substrate 300 can be the same or different. Cured adhesive layer 200 is prepared from the curable adhesive compositions described above and contains a cured epoxy adhesive with expanded microsphere filler.

[0105] Examples

[0106] These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. Solvents and other reagents used were obtained from Sigma-Aldrich Chemical Company; Milwaukee, Wisconsin unless otherwise noted. The following abbreviations are used: mm = millimeters; cm = centimeters; in = inch; RPM = revolutions per minute; min = minutes; hrs = hours; sec = seconds; Hz = Hertz; CTH = Controlled Temperature and Relative Humidity. The terms “weight %”, “% by weight”, and “wt%” are used interchangeably.

[0107] Table of Abbreviations

[0108] Test Methods

[0109] Tensile Test With Optical Extensometer

[0110] This test method used was ASTM D638. Three replicate samples were prepared and cured at 65°C for 1 hour and then dwelled for 24 hours in a CTH room at 23°C / 50% RH. The test samples were dog bone Type IV that were die-cut with a pneumatic press. Sample thickness was 0.5 mm. Gauge length was 2.5 in (6.35 cm). Testing speed: lOOmm / min. Modulus was calculated by fitting strain 0.1% to 1%. Full field DIC with virtual extensometer. Strain calculated by averaging deformation gauge area. Sample images / inspection was used for documentation and to identify defects. Tensile DMA Temperature Sweep

[0111] The test method used was ASTM D4065. Film samples of 0.5 mm thickness were prepared and cured at 65°C for 1 hour and then dwelled for 24 hours in a CTH room at 23°C / 50% RH. Films strips of 5 mm x 30 mm strips were placed on a TA Instruments DHR3 Rheometer and the sample was tested at 1 Hz tensile oscillation. Temperature was ramped from -30°C to 100°C at 2.5°C / min.

[0112] Dielectric Property Measurements

[0113] The test method used was IEC 61189-2-721. Samples were 6.5 in x 5.5 in (16.5 cm x 14.0 cm) with a thickness of 0.5 mm. Measurements were performed in accordance with the standard IEC 61189-2-721, utilizing a 2.5GHz split post dielectric resonator (SPDR) designed by QWED.

[0114] Viscosity / Shear sweep on Rheometer

[0115] The test method used was ASTM D7867. Testing was carried out on a TA Instruments DHR3 Rheometer with 40 mm, 2° SUS cone and Peltier plate set to 25°C. The test was carried out with a 1 min equilibration time + 1 min pre-shear at 20 Hz. The Shear Sweep was 0.01 to 100 Hz collecting 3 points per decade (e.g. 1, 2, and 5 Hz) and using steady state sensing (2 min max equilibration time, 5 sec sample period, 5% tolerance, consecutive within 3 periods).

[0116] Examples E1-E5 and Comparative Examples CE1-CE2

[0117] Sample preparation

[0118] All resin ingredients described in Table 1 and 2 below were homogenized using a speed mixer at 2000 rpm for 2 min. All amounts are in weight %. Fillers were added and the formulation was degassed at 3 torr (400 Pascals), 1000 rpm, 8 min. Catalyst was then added and the formulation was mixed and degassed at 1000 rpm, 3 torr (400 Pascals), 5 min. Formulations are stored in a freezer at -20°C. Films and cured samples were made by curing at 65°C for 1 hr in a heated oven. The examples were also tested using the test methods described above. Table 1

[0119] Table 2

Claims

What is claimed is:

1. A curable adhesive composition comprising: a curable adhesive; and a fdler comprising expanded microspheres comprising polymeric spheres with a central void, wherein the cured adhesive composition has a dielectric constant (Dk) of 3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%.

2. The curable adhesive composition of claim 1, wherein the curable adhesive comprises a curable epoxy adhesive.

3. The curable adhesive composition of claim 1, wherein the cured adhesive composition has a dielectric constant (Dk) of 2.9 or less.

4. The curable adhesive composition of claim 1, wherein the cured adhesive composition has a shrinkage of less than 2%.

5. The curable adhesive composition of claim 1, wherein the curable adhesive comprises a curable one-part epoxy adhesive that cures at a temperature of 40°C or greater.

6. The curable adhesive composition of claim 1, wherein the curable adhesive comprises a curable one-part epoxy / thiol adhesive, wherein the curable one-part epoxy / thiol adhesive comprises: at least one epoxy resin having at least two epoxide groups per molecule; at least one thiol component that is a polythiol with at least two primary thiol groups per molecule; at least one nitrogen-containing catalyst; at least one soluble substituted barbituric acid.

7. The curable adhesive composition of claim 6, wherein the curable epoxy adhesive comprises:20 wt-% to 80 wt-%, based on the total weight of the curable adhesive composition of atleast one epoxy resin component comprising: a polyglycidyl ether of a polyhydric phenol, a reaction product of a polyhydric alcohol with epichlorohydrin, an epoxidised (poly)olefinic resin, an epoxidised phenolic novolac resin, an epoxidised cresol novolac resin, a cycloaliphatic epoxy resin, a glycidyl ether ester, a polyglycidyl ester, a urethane modified epoxy resin, or a combination of two or more thereof;25 wt-% to 70 wt-%, based on a total weight of the curable adhesive composition of at least one polythiol component comprising: trimethylolpropane tris(beta- mercaptopropionate), trimethylolpropane tris(thioglycolate), pentaerythritol tetrakis(thioglycolate), pentaerythritol tetrakis(beta-mercaptopropionate), dipentaerythritol poly(beta-mercaptopropionate), ethylene glycol bis(beta- mercaptopropionate), a (Cl-C12)alkyl polythiol, a (C6-C12)aromatic polythiol, or a combination of two or more thereof;1 part to 45 parts per 100 parts of the epoxy resin component of an amine catalyst that is a solid at room temperature; and0.01 wt-% to 1 wt-%, based on the total weight of the curable adhesive composition of at least one soluble substituted barbituric acid comprising: l-benzyl-5-phenylbarbituric acid, l-cycloheyl-5 -ethylbarbituric acid, 1,3 -dimethylbarbituric acid, and a combination thereof.

8. The curable adhesive composition of claim 1, wherein the adhesive composition further comprises at least one additive selected from toughening agents, non-reactive plasticizers, flow control agents, thickeners, expandable microspheres, adhesion promoters, inorganic fdlers, reactive or unreactive diluents, or a combination thereof.

9. The curable adhesive composition of claim 1, wherein the adhesive composition comprises at least 0.5 % by weight of the filler comprising expanded microspheres.

10. An article comprising: a first substrate with a first major surface and a second major surface; a cured adhesive layer with a first major surface and a second major surface disposed on the second major surface of the first substrate such that the first major surface of the cured adhesive layer is in contact with the second major surface of first substrate; anda second substrate with a first major surface and a second major surface where the first major surface of the second substrate is in contact with the second major surface of the cured adhesive layer, wherein the cured adhesive layer is cured layer of a curable adhesive composition comprising: a curable adhesive; and a filler comprising expanded microspheres comprising polymeric spheres with a central void, wherein the cured adhesive composition has a dielectric constant (Dk) of3.0 or less, a shrinkage of less than 4.5%, and an elongation of 2-400%.

11. The article of claim 10, wherein the first and second substrate independently comprise a metal substrate, a polymeric substrate, or a glass substrate.

12. The article of claim 10, wherein the first substrate comprises a metal substrate and the second substrate comprises a glass substrate.

13. The article of claim 10, wherein at least one of the first and second substrate comprises a polymeric film substrate.

14. The article of claim 10, wherein the cured adhesive layer has a shrinkage of less thanZ 90 / / o.

15. The article of claim 10, wherein the curable adhesive comprises a curable one-part epoxy adhesive that cures at a temperature of 40°C or greater.

16. The article of claim 10, wherein the curable adhesive comprises a curable one-part epoxy / thiol adhesive.

17. The article of claim 10, wherein the curable adhesive comprises a curable one-part epoxy / thiol adhesive, wherein the curable one-part epoxy / thiol adhesive comprises: at least one epoxy resin having at least two epoxide groups per molecule;at least one thiol component that is a polythiol with at least two primary thiol groups per molecule; at least one nitrogen-containing catalyst; at least one soluble substituted barbituric acid.

18. The article of claim 10, wherein the adhesive composition further comprises at least one additive selected from toughening agents, non-reactive plasticizers, flow control agents, thickeners, adhesion promoters, inorganic fdlers, reactive or unreactive diluents, organic fdlers, or a combination thereof.

19. The article of claim 10, wherein the adhesive composition comprises at least 0.5 % by weight of the fdler comprising expanded microspheres

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