Hybrid adhesive composition with high epoxy content

Abstract

A novel hybrid adhesive composition with high epoxy content and the method of making thereof.

Description

[0001] DI83926

[0002] Hybrid Adhesive Composition with High Epoxy Content

[0003] Background of the Invention

[0004] In the automotive industry, adhesives are used in the assembly of various components in which these components are bonded to each other or to other parts of the vehicle. In the assembly process of closures (doors, hoods and deck lids), some manufacturers require the adhesive to obtain handling strength via a room temperature curing process 15 minutes before the parts enter the high heat of the E-Coat ovens, which can cause part distortion of the panels that are not securely bonded. The adhesive joint must also withstand the high heat of the paint and E-Coat ovens during the assembly of the vehicle. It is a growing trend among automotive manufacturers to consider hem flange joints to be a crash critical component of the vehicle due to concerns from crash tests and real-world crash events. Therefore, room-temperature curing adhesives with heat resistance and impact peel strength are required for the closure application. Typically, the adhesive composition is a two-component epoxy-acrylic hybrid for attaining rapid cure and heat resistance. The hybrid composition is typically a mixture of two separately prepared components of Part A and Part B wherein Part A typically comprises at least one methacrylate monomer and Part B comprises at least one epoxy resin. In a prior patent application of PCT / US23 / 024257, incorporated herein in its entirety by reference, the inventor has disclosed that the optimum mix ratio of Part A to Part B for the hybrid composition is a volume mix ratio of 4 to 1 or greater to arrive at an epoxy resin content of the hybrid composition of about 3 to 6 wt.%. However, in some applications, it is desirable to have a higher epoxy resin content in the hybrid compositions, hence requiring a lower volume mix ratio between Part A and Part B of less than 4:1 .

[0005] Summary of the Invention

[0006] The present invention provides a novel two-component epoxy-acrylic hybrid adhesive composition having a Part A component and a Part B component. The Part A component comprises a) at least one methacrylate monomer; and b) at least one methacrylate-terminated toughener; and the DI83926

[0007] Part B component comprises at least one epoxy resin. It is found that by including at least one hydroxyethyl methacrylate (“HEMA”) phosphate diester in Part A component, a volume mix ratio of Part A to Part B of less than 4:1 , or even down to 2:1 , can be used in a hybrid composition and such composition can achieve a much higher epoxy resin weight content of about 11 to 13 wt.%, based on the total weight of the hybrid composition because more Part B is present in the hybrid composition. For example, in a preferred embodiment, the present invention provides a two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) at least one methacrylate monomer; and b) at least one methacrylate-terminated toughener; and the Part B component comprises at least one epoxy resin; and an oxidizing agent; and wherein the hybrid adhesive composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of less than 4:1 . In anther preferred embodiment, the present invention provides a two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) at least one methacrylate monomer; b) at least one methacrylate-terminated toughener; and c) a hydroxyethyl methacrylate phosphate diester; and the Part B component comprises at least one epoxy resin; and an oxidizing agent; and wherein the hybrid adhesive composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of about 2:1 and wherein the composition comprises 11 to 13 wt.% of epoxy resins based on the total weight of the composition.

[0008] Detailed Description of the Invention

[0009] The present invention provides an epoxy-acrylic adhesive composition having rapid curing at room temperature while having excellent impact peel strength with high epoxy resin content, even after exposure to high- temperature conditions, and with low odor. The two-component epoxy-acrylic adhesive composition of the present invention has two parts: Part A component and Part B component. DI83926

[0010] Part A component:

[0011] Part A of the adhesive composition comprises at least one methacrylate monomer. The methacrylate monomer is preferably one with low odor and very low vapor pressure typically less than 10 Pa at 20°C, preferably less than 8 Pa at 20°C, and more preferably less than 6 Pa at 20°C, and most preferably less than 5 Pa at 20°C. While any methacrylate monomers may be used in the present invention, in some preferred embodiments, the methacrylate monomers used in Part A will have the general chemical structure of either Formula I and / or Formula II:

[0012] In one preferred embodiment, the methacrylate monomer contains less than 0.5 wt. %, preferably less than 0.1 wt. %, and most preferably less than 0.01 wt. % of methacrylic acid based on the total weight of the methacrylate monomer.

[0013] In another preferred embodiment, Part A comprises two or more methacrylate monomers. The methacrylate monomer or monomers preferably represent 20-45 wt. %, preferably 28-38 wt.% of Part A, and more preferably 25-35 wt.%, all based on the total weight of Part A.

[0014] Part A also comprises at least one toughener, for example, methacrylate-terminated toughener as disclosed in PCT / US23 / 024257. In another preferred embodiment, the toughener can be selected from an elastomeric urethane toughener capped with hydroxy-functional methacrylate as disclosed in US 8,747,605, also incorporated herein in its entirety by reference, a methacrylate terminated butadiene-acrylonitrile liquid rubber, or DI83926 any core shell rubber, or a mixture thereof. In another preferred embodiment, the toughener comprises at least one polyether as part of its backbone.

[0015] In preferred embodiments, the toughener has a Tgof 0°C or less Tgof - 20°C or less, more preferably -40°C or less.

[0016] In one preferred embodiment, the at least one toughener is a toughener prepared by reacting a polyether polyol with a polyisocyanate in a ratio such that the resulting polymer is an NCO-capped polymer, followed by end-capping with a hydroxyalkyl ester of methacrylic acid. The polyether polyol may be a diol or triol, with diols being preferred. In another preferred embodiment, the polyol is a poly(C2-Ce-alkylene oxide) diol, with C2, C3 and C4 being preferred, and C4 being particularly preferred [i.e. poly(tetramethylene oxide)glycol or PTMEG].

[0017] In yet another preferred embodiment, the polyether polyol is selected from PTMEG’s having molecular weights from 1 ,000 to 3,000 Da, preferably from 1 ,500 to 2,500 Da, and more preferably about 2,000 Da. Equivalent and molecular weights are measured by gel permeation chromatography (GPC) using the method and equipment recited in the Examples section.

[0018] The toughener may also comprise a low molecular weight (< 250 Da) polyol having functionality of 3 or 4, such as trim ethylol propane. If present, the low molecular weight polyol is preferably used at 0.1-3 wt.%, more preferably 0.25-1 wt.%, particularly preferably 0.5 wt.%, based on the total weight of the toughener. In a preferred embodiment, the toughener comprises trimethylol propane at 0.1-3 wt.%, more preferably 0.25-1 wt.%, most preferably 0.5 wt.%, based on the total weight of the toughener.

[0019] The polyisocyanate may be aliphatic or aromatic, with aliphatic being preferred. In one embodiment, the polyisocyanate is a diisocyanate. In another embodiment, the polyisocyanate is an aliphatic diisocyanate. Examples include hexamethylene diisocyanate (HDI), isophorone diisocyanate, methylene dicyclohexyl diisocyanate.

[0020] The hydroxyalkyl ester of methacrylic acid used in end capping is preferably a C2-Ce-hydroxyalkyl ester, more preferably C2-C4-hydroxyalkyl, even more preferably C2-C3-hydroxyalkyl, with C2-hydroxyalkyl being the most preferred, in particular HEMA. DI83926

[0021] The toughener may also be made by reacting the polyether polyol with the polyisocyanate, in the presence of a polyurethane catalyst to produce an NCO-terminated prepolymer. The prepolymer is then reacted with a hydroxyalkyl ester of methacrylic acid, resulting in end-capping.

[0022] In a preferred embodiment, the toughener is made by reacting PTMEG with HDI, in the presence of a polyurethane catalyst to produce an NCO- terminated prepolymer. The prepolymer is then reacted with HEMA, resulting in end-capping.

[0023] In a preferred embodiment, the toughener has a number average molecular weight (Mn) of 6,119 Da. In another preferred embodiment, the PTMEG has a molecular weight of 2,000 Da, and the toughener has a number average molecular weight (Mn) of 6, 119 Da. In yet another preferred embodiment, the toughener has a weight average molecular weight (Mw) of 15,084 Da.

[0024] Part A typically comprises 7-30 wt.%, more preferably 15-28 wt.%, particularly preferably 17-25 wt.% of the toughener, based on the total weight of Part A. In a preferred embodiment, the toughener is made by reacting an aliphatic polyether diol with an aliphatic diisocyanate.

[0025] Part A may also comprise a phosphorus-containing compound which may be selected from monoesters of phosphonic, mono- and diesters of phosphonic and mono-, di- and tri-esters of phosphoric acid having one unit of vinyl or allylic unsaturation present.

[0026] In a preferred embodiment, Part A uses a diester HEMA phosphate monomer at an amount of about 5 to 15 wt.%, preferably about 6 to 12 wt.%, more preferably about 7 to 10 wt.%, and most preferably about 8 wt.% based on the total weight of Part A. In another preferred embodiment, Part A is substantially free or completely free of monoester HEMA phosphate. In those preferred embodiment, only diester HEMA phosphate is used.

[0027] Part A may also comprise other optional chemicals necessary and customary to a hybrid adhesive composition as further shown in the Examples and below disclose on Optional ingredients.

[0028] Part B component DI83926

[0029] Part B comprises at least one epoxy resin. Suitable epoxy resins include the diglycidyl ethers of polyhydric phenol compounds such as resorcinol, catechol, hydroquinone, bisphenol, bisphenol A, bisphenol AP (1 ,1- bis(4-hydroxylphenyl)-1 -phenyl ethane), bisphenol F, bisphenol K, bisphenol M, tetramethylbiphenol, diglycidyl ethers of aliphatic glycols and polyether glycols such as the diglycidyl ethers of C2-24 alkylene glycols and polyethylene oxide) or polypropylene oxide) glycols; polyglycidyl ethers of phenol-formaldehyde novolac resins, alkyl substituted phenol formaldehyde resins (epoxy novalac resins), phenolhydroxybenzaldehyde resins, cresolhydroxybenzaldehyde resins, dicyclopentadiene-phenol resins and dicyclopentadiene- substituted phenol resins, and any combination thereof. Suitable diglycidyl ethers include diglycidyl ethers of bisphenol A resins such as are sold by Olin Corporation under the designations D.E.R.®330, D.E.R.®331 , D.E.R.®332, D.E.R.®383, D.E.R.®661 and D.E.R.®662 resins.

[0030] In a preferred embodiment, the at least one epoxy resin comprises a reaction product of epichlorohydrin and bisphenol A. In another preferred embodiment, the at least one epoxy resin comprises a liquid reaction product of epichlorohydrin and bisphenol A.

[0031] In a preferred embodiment, the at least one epoxy resin comprises an epoxy resin that is a liquid reaction product of epichlorohydrin and bisphenol A, having an epoxide equivalent weight of 182-192 g / eq (as measured according to ASTM D-1652), an epoxide percentage of 22.4-23.6 % (as measured according to ASTM D-1652), an epoxide group content of 5,200- 5,500 mmol / kg (as measured according to ASTM D-1652), and a viscosity at 25°C of 11 ,000-14,000 mPas (as measured according to ASTM D-445).

[0032] In another preferred embodiment, the at least one epoxy resin comprises a bisphenol A-based epoxy resin with an epoxy equivalent weight of approximately 352.5 g / equivalent. In yet another preferred embodiment, Part B contains a mixture of at least two different epoxy resins.

[0033] Part B comprises 20 to 80 wt.%, preferably 20 to 60 wt.%, more preferably 25 to 50 wt.%, and most preferably 25-30 wt.% of the at least one epoxy resin, based on the total weight of Part B.

[0034] Part B may also comprise an oxidizing agent as disclosed in PCT / US23 / 024257. Examples of such oxidizing agents include organic DI83926 peroxides, such as benzoyl peroxide and other diacyl peroxides, hydroperoxides such as cumene hydroperoxide, peresters such as - butylperoxybenzoate; ketone hydroperoxides such as methyl ethyl ketone hydroperoxide, organic salts of transition metals such as cobalt naphthenate, and compounds containing a labile chlorine such as sulfonyl chloride. The most preferred oxidizing agent is benzoyl peroxide.

[0035] The oxidizing agent, preferably organic peroxide such as benzoyl peroxide, is preferably present in Part B at 3-10 wt.%, more preferably 5-9 wt.%, based on the total weight of Part B.

[0036] Optional ingredients

[0037] The adhesive composition of the present invention may contain additional optional ingredients, such as, for example: stabilizers / free-radical scavengers being added to both Part A and Part B, to extend shelf-life of the unmixed parts. Examples of stabilizers / free-radical scavengers include 1 , 3, 5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, diethylhydroxy amine (DE HA), butylated hydroxy toluene (BHT), methyl ether of hydroquinone, hydroquinone, benzoquinone, naphthoquinone, hydroxyl amine, and nitrile oxides. The optional ingredients may also include fillers such as wollastonite, talc, fumed silica, calcium carbonate and glass.

[0038] Part A may optionally comprise cross-linkers, such as divalent metal salts of methacrylic acid, such as zinc dimethacrylate, calcium dimethacrylate, magnesium di methacrylate, or mixtures of these. As disclosed above, Part A may also optionally comprise an additional toughener. Suitable additional tougheners are rubber based, such as acrylate-based tougheners, butadiene- based tougheners, acrylonitrile-butadiene-based tougheners, chlorinated or chlorosulphonated polyethylenes, block copolymers of styrene and conjugated dienes (SBS, SIS), ethylene acrylic elastomers, core-shell graft copolymers. Specific examples can be a copolymer of 2-propeneoic acid, 2- methyl-, methyl ester with 1 ,3-butadiene.

[0039] If used, the additional rubber-based toughener is preferably used in Part A at 2-24 wt.%, more preferably 7.5-18.5 wt.%, more particularly preferably 10-15.75 wt.%, based on the total weight of Part A. DI83926

[0040] Additional optional ingredients may include, for example, adhesion promoters, pigments, thixotropic agents, wetting agents, reactive diluents, antioxidants, inhibitors, and stabilizers. These ingredients may be used in an amount commonly known to one skilled in the art to achieve their intended purposes.

[0041] Examples and testing methods

[0042] Part A preparation

[0043] The at least one toughener, e.g. methacrylate-terminated toughener, is manufactured by a method as disclosed in PCT / US23 / 024257 which includes the steps: (1) mixing a polyetherpolyol and a polyisocyanate; (2) adding a catalyst capable of catalyzing the reaction of a hydroxyl group with an isocyanate group, to form an isocyanate terminated prepolymer; and (3) reacting the isocyanate prepolymer is then reacted with a hydroxyalkyl ester of methacrylic acid, such that the isocyanate groups are capped with the hydroxyalkyl ester of methacrylic acid. The reactions in steps (2) and (3) are typically carried out under vacuum or under a neutral atmosphere, such as nitrogen or argon. The catalyst is preferably selected from Lewis bases and Lewis acids. Suitable catalysts include tertiary amines, including diazabicyclo[2.2.2]octane, 2,4,6-tris((dimethylamino)methyl)phenol, DM DEE (2,2'-Dimorpholinodiethylether), imidazoles, such as 4-methylimidazole), triethanolamine, and organometallic catalysts, in particular organotin compounds, such as dibutyl tin dilaurate, dioctyltindineodecanoate, and other metal catalysts such as tetrabutyltitanate, zirconium acetylacetonate, and bismuthneodecanoate. Part A may also comprise a tertiary amine radical initiator as disclosed in PCT / US23 / 024257. Preferred examples include N,N- dimethyl aniline, N,N-dimethylaminomethylphenol and N,N-dimethyl-p- toluidine.

[0044] The following steps are carried out to prepare the Part A component in the Examples. All ingredients are shown in Table 1. DI83926

[0045] 1 . The above prepared toughener was first preheated to 60°C. All monomers and stabilizers were first pre-blended with the core shell rubber in a mixing cup to mix at about 2,300 rpm for about 4 minutes;

[0046] 2. the mixed mixture was allowed to cool to room temperature and then mixed again for 2 minutes at 2,300 rpm. Visual homogeneity was checked and the cooling and mixing cycles were repeated until the sample became homogenous;

[0047] 3. while mixture is still warm, half of the required cross linker, such as ETHOXYLATED BIS-A DIMETHACRYLATE were added to the mixture and speed mixed for 2 minutes at 2,300 rpm;

[0048] 4. Half of the preheated toughener was then added to the mixing cup to be mixed for 2 minutes at 2300 rpm. Then the remaining toughener was added along with all remaining fillers and speed mixed for 2 minutes at 2,300 rpm;

[0049] 5. Hydroxyethyl methacrylate (“HEMA”) phosphate, silane, and methacrylic acid were then added to mixing cup and mixed for 2 minutes at 2100 rpm;

[0050] 6. Amine radical initiator, e.g. toluidine and glass beads were then added to the speed mixing cup and mixed for 25 seconds at 800rpm and ended with additional 1 minute mixing at 2000 rpm; and

[0051] 7. The content of the mixing cup was vacuumed and mixed at 30 mbar and 1 ,800 rpm for 3 minutes.

[0052] Part B preparation

[0053] 1. Epoxy resin and butylated hydroxy toluene (“BHT”) were first preblended in a speed mixing cup. The mixing cup was heated to 90°C for 1 hour to dissolve BHT. The mixing cup was then cooled to 70C before the content was speed mixed for 2 minutes at 2100 rpm;

[0054] 2. The above pre-blend, additional epoxy resins and fillers were mixed for 2 minutes at 2100 rpm;

[0055] 3. The content was mixed again for 2 minutes before cooled down to room temperature; and DI83926

[0056] 4. Peroxide was added to the speed mixing cup and mixed for 25 seconds at 800rpm with an additional 1 minute mixing at 2000 rpm. The content was then vacuum Speed mixed at 30 mbar and 1800 rpm for 3 minutes and then cooled to a temperature below 40C.

[0057] Hybrid adhesive composition

[0058] During application, Part A and Part B components are mixed to homogeneity and applied to a substrate immediately. The volume mixing ratio of Part A to Part B is preferably 1.5:1 to less than 4: 1 , with 2:1 being particularly preferred. In the combined hybrid adhesive composition of Part A and Part B, the weight percent of epoxy resin is about 3% to 20%, preferably 8% to 15%, and most preferably 11 to 13 wt.%, based on the total weight of the hybrid composition.

[0059] Suitable substrates include, for example, electrogalvanized steel, hot dipped galvanized steel, cold rolled steel, and aluminum.

[0060] Ingredient details of Inventive and Comparative Examples

[0061] Part A and Part B components were first separately prepared using the ingredients and the amounts listed in Table 1 below. Both Parts A of the Inventive Examples used HEMA phosphate diester while Part A of the Comparative Example used HEMA phosphate monoester, all at about 8 wt.% based on the weight of Part A. Parts B of all Examples are the same.

[0062] Table I. Ingredients for both Comparative and Inventive Examples

[0063] Inve ntive Inve ntive Comp arative Exarr iple 1 Exarr iple 2 Exai nple

[0064] We ght Vie ght We ght

[0065] Part A Ingredients 3 % a % g %

[0066] Zinc Dimethacrylate 3 60 1.20 3 60 1 20 3 60 1.20

[0067] CHMA 97.041 32.347 97.041 32 347 97.041 32.347

[0068] NOVEL ELASTOMERIC URETHANE TOUGHENER CAPPED HYDROXY76.50 25.50 76.50 25.50 0.00 0.00 FUNCTIONAL METHACRYLATE Methacrylate Terminated Butadiene- Acry lonitrile liquid rubber 0.00 0.00 0.00 0 00 76.50 25.50 MBS core shell rubber 39 00 13 00 39 00 13 00 39 00 13 00 DI83926

[0069] Details of these ingredients and their functions in the components are provided below in Table 2:

[0070] Table 2. Ingredients used in Examples, and their sources DI83926

[0071] Testing methods

[0072] Lap Shear Procedures - Lap Shear specimens were prepared and tested according to the ISO Standard ISO 4587. The substrate used was 1 .5 mm thick electrogalvanized steel. Test coupons were cut into 1 in. X 4 in. strips. The V2inch bonding overlap section of each coupon was cleaned with acetone. Part A and Part B components were combined in a 2:1 ratio by volume using a static mixer to form the adhesive. The adhesive was applied to the bonding section of the coupon. Another coupon was laid on top, and the DI83926 specimen was assembled in a fixture yielding a V2 inch overlap. The edges of the assembly were scraped clean using a spatula and held together with binder clips while curing at room temperature for 16 hours followed by a 10- minute oven bake at 163°C (metal temperature). The loads to failure of the Lap Shears were measured using an Instron® 5500R Materials Testing System (Instron Corporation) at room temperature. Mechanical grips were used to hold the Lap Shear samples in place. The distance between the grips was seven inches. The crosshead speed was 0.5 in. / min. The computer measured the load as a function of crosshead displacement and loads were converted to pounds of force per square inch of bond area. After each Lap Shear was tested to failure, a failure mode was assigned by visual evaluation. Failure modes were classified as either adhesive failure or cohesive failure.

[0073] Hot Lap Shear Procedures - Lap Shear specimens were prepared and tested according to the ISO Standard ISO 4587. The substrate used was 1 .5 mm thick electrogalvanized steel. Test coupons were cut into 1 in. X 4 in. strips. The 3 inch bonding overlap section of each coupon was cleaned with acetone. Part A and Part B components were combined to form the adhesive in a 2:1 ratio by volume using a static mixer. The adhesive was applied to the bonding section of the coupon. Another coupon was laid on top, and the specimen was assembled in a fixture yielding a 34 inch overlap. The edges of the assembly were scraped clean using a spatula and held together with binder clips while curing at room temperature for 3 hours. Lap Shear specimens were then placed in a pre-heated Instron test chamber at 190°C. Once the chamber recovered to 190°C after opening & closing the door to add specimens, the loads to failure of the Lap Shears were measured using an Instron® 5500R Materials Testing System (Instron Corporation) at 190°C. Mechanical grips were used to hold the Lap Shear samples in place. The distance between the grips was seven inches. The crosshead speed was 0.5 in. / min. The computer measured the load as a function of crosshead displacement and loads were converted to pounds of force per square inch of bond area. After each Lap Shear was tested to failure, a failure mode was assigned by visual evaluation. Failure modes were classified as either adhesive failure or cohesive failure. DI83926

[0074] T-Peel Procedures - T-Peel samples were prepared and tested according to ISO Standard ISO 11339. The substrate used was 0.8 mm thick electrogalvanized steel. 1 inch by 4 inch substrate strips were bent at a 90° angle yielding a 3 inch bonding section. The bonding overlap section of each coupon was cleaned with acetone. Part A and Part B components were combined, to form the adhesive, in a 2:1 ratio by volume using a static mixer. A second strip was placed on the adhesive to create the T-Peel joint assembly. The assembly was held with clips and cured at room temperature for 16 hours followed by a 10-minute oven bake at 163°C (metal temperature). After curing the samples were tested on an Instron at a pull rate of 100 mm per minute to develop a load curve. The average load was taken to give the Newtons of force per linear mm of substrate. Failure modes were classified as either adhesive failure or cohesive failure.

[0075] Open Time Procedure - Open time was measured by first combining Part A and Part B components of the adhesive in a 2:1 ratio by volume using a static mixer. An adhesive bead was then dispensed on a sheet of paper with the bead dimensions approximately 8cm long and 8mm wide by 5mm high. The bead was checked with a tongue depressor at various time intervals to determine when the center of the adhesive bead transitioned from a soft paste to a hard solid. The open time recorded is the time when the center of the bead cures to a solid.

[0076] Testing results and discussions

[0077] Test results of the Inventive Examples and Comparative Example are summarized in Table 3.

[0078] Table 3. Testing results. DI83926

[0079] As shown in Table 3, by using a diester HEMA phosphate monomer, Inventive Examples 1 & 2 are able to achieve a more desirable performance than the Comparative Example that uses a monoester HEMA phosphate at the same concentration. Specifically, the open time and hot lap shear strength are greatly improved. For this technology, open times in the range of 60 minutes are the most desirable. The hot lap shear strength indicates that the Inventive Examples are able to provide a higher level of strength at a test temperature of 190°C with only 3 hours of room temperature curing. The Comparative Example does not cure during this time.

Claims

DI83926Claims1 . A two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) at least one methacrylate monomer; and b) at least one methacrylate-terminated toughener; the Part B component comprises at least one epoxy resin; and an oxidizing agent; wherein the hybrid adhesive composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of less than 4:1 .

2. The adhesive composition of Claim 1 wherein the Part A component further comprising a phosphorus-containing compound selected from monoesters of phosphonic, mono and diesters of phosphonic and phosphoric acids.

3. The adhesive composition of Claim 2 wherein the Part A component comprises a hydroxyethyl methacrylate phosphate diester.

4. The adhesive composition of Claim 3 wherein the Part A component is substantially free of hydroxyethyl methacrylate phosphate monoester.

5. The adhesive composition of any one of the preceding claims wherein the Part A component comprises 20-45 wt.% of methacrylate monomer, based on the total weight of Part A component.

6. The adhesive composition of any one of the preceding claims wherein the methacrylate monomer has chemical structure of one of Formula I or IIDI83926 Sx7. The adhesive composition of any one of the preceding claims wherein the toughener comprises at least one polyether as part of its backbone.

8. The adhesive composition of any one of the preceding claims wherein the at least one epoxy resin comprises a reaction product of epichlorohydrin and bisphenol A.

9. The adhesive composition of any one of the preceding claims wherein Part B component comprises 20 to 80 wt.% of the at least one epoxy resin, based on the total weight of Part B component.

10. The adhesive composition of any one of the preceding claims wherein Part B component comprises 25 to 30 wt.% of the at least one epoxy resin, based on the total weight of Part B component11 . The adhesive composition of any one of the preceding claims wherein the composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of more than 1.5:1.

12. The adhesive composition of claim 11 wherein the composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of about 2:1.

13. The adhesive composition of claim 1 wherein the composition comprises 8 to 15 wt.% of epoxy resins based on the total weight of theDI83926 composition.

14. The adhesive composition of claim 13 wherein the composition comprises 11 to 13 wt.% of epoxy resins based on the total weight of the composition.

15. A two-component epoxy-acrylic hybrid adhesive composition, comprising a Part A component and a Part B component wherein the Part A component comprises a) at least one methacrylate monomer; b) at least one methacrylate-terminated toughener; and c) a hydroxyethyl methacrylate phosphate diester; and the Part B component comprises at least one epoxy resin; and an oxidizing agent; wherein the hybrid adhesive composition is formed by combining Part A and Part B with a volume ratio between Part A and Part B of about 2: 1 and wherein the composition comprises 11 to 13 wt.% of epoxy resins based on the total weight of the composition.

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