AND PROCESS FOR THE USE THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of United States Provisional Patent Application Serial No, 61/767,050 filed February 20, 20.13, which is incorporated herein by reference,

FIELD OF THE INVENTION

[0002] The present invention in general relates to adhesives and in particular to free-radical curing adhesives able to adhere to a variety of metal substrates and having a shelf stability of more than 300 days at 23°C.

BACKGROUND OF THE INVENTION

[0003] many industries, manufacturers of metal components have changed to structural adhesives to replace conventional fastening techniques such as rivets, bolts, and welding. Adhesives in theory offer many attractive properties that include improved product performance _* aesthetics, reduced overall assembly time, and lower production costs. Additionally, adhesives preclude much of the stress point concentration, corrosion, and component damage often seen with rivets, bolts, welding, and other traditional fastening methodologies,

[0004] While conventional structural adhesives have made considerable progress in. being able to bond a variety of substrates such as aluminum, cold-rolled steel, and carbon steel, conventional adhesives to cover loss of strength over time on galvanized steei substrates. As a result of conventional structural adhesives failure to retain strength on galvanized substrates, various industries reliant on galvanized materials have retained traditional joinders such as weidiog and mechanical fasteners while suffering ali the known limitations of these traditional processes.

[0005] Adhesive joinder of metal components has met with limited acceptance in various industries due to poor adhesion strength at elevated temperatures of 50°C, as well as low impact and yield strengths at ~40°C Additionally, conventional metal substrate joining adhesives tend to have inadequate shelf lives of six months or less at 20°C. Still further limitations of existing structural adhesives include low terminal lap shear strength and a slow build in handling strength that results in long fixture times that are contrary' ^" to efficient manufacturing throughput

[0006] Thus, there exists a need for a structural adhesive formulation with improved adhesion at elevated temperature while offering a longer shelf life and superior thermal stability. There further exists a need for such an adhesive formulation offering a more rapid build of handling strength and a higher terminal lap shear strength eve at reduced temperature so as to yield an adhesive abl to bond a variety of Structural substrates including galvanized metal.

SUMMARY OF THE INVENTION

[0007] A two-part adhesive formulation is provided that has an adhesive part A and an activator part B. The part A includes a monomer amount of a methacrySate ester monomer, a crosslinker amount of a polyfunctional monomer, a toughening agent, an impact modifier, a anti -oxidant, a free-radical polymerization inhibitor, and an adhesion promoter system to improve cured adhesive strength to a substrate, and free-radical polymerization initiator. The part B includes an activator monomer amount of the methacryfate ester monomer, and a free- radical polymerization accelerator and an impact modifier when the weight ratio the adhesive part A to activator part B is present in a 1:1 weight ratio. Each of the part A and the part B have separate storage stability of at least 300 clays at 23 °C. When the weight ratio of the adliesive part A to activator part B ar present in a 10:! weight ratio, the activator part B includes an butyl rubber, a thixotropic agent, and a free-radical polymerization accelerator; while retaining the property of storage stability of at least 300 clays at 23°C.

jOOOSJ A process of applying an adhesive to a substrate is provided that includes combining together the parts A and B to form an adhesive mixture. The adhesive mixture is then applied to the substrate and allowed to cure.

DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention has utility as a curing adhesive particularly well suited for bonding structural substrates. Structural substrates operatively bonded by an inventive adhesive illustratively include electro-galvanized steel, hot-dipped galvanized steel, cold-rolled steel, aluminum, aluminum alloys, acry!onitrile-butadiene-styrene (ABS), mild steel (MS), polyvinyl chloride (PVC), and fiberglass. An inventive adhesive formulation is appreciated to be operative to bond to like structural substrates, as well as to bond one such substrate to other substrates including other metals, other plasties, and to do so through a rapid handling strength during cure to facilitate handling and removal of fixturing devices in a manufacturing setting.

[0010] An inventive formulation is provided as a two part formulation that includes an adhesive part that is synonymously referred to herein as part A. The adhesive part of the formulation includes a polymerizable monomer component, elastic material, reacts with an activator part that is synonymously referred to ^' herein as part B. The part B includes a rubber component and a polymerization accelerator. The following components of an inventive formulation are detailed as weight percentages of a formulated part A or part B inclusive ail components except non-reactive diluents, and non-reactive components under cure conditions illustratively including curing agents, corrosion inhibitors, chain transfer agents, pigments, spacers, fragrances, tillers, and fire retardants.

[0011] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from ί to 4 is intended to include 1-2, 1 -3, 2-4, 3-4, and 1-4.

[0012] An adhesive Part A includes in an adhesive embodiment a majority by active weight: percent of acrylate monomer, methacrylate monomer, or a combination thereof. In other embodiments of the present invention, such monomers represent at least 20 weight percent of an adhesive Part A (exclusive of non-reactive diluents). Acrylate monomers and methacrylate monomers operative in the present invention illustratively include etb yknethaerylate, Cj- C|(»alk l acrylate, C)-C _½ alkyi methacrylate, Cj-C^ hydroxy 1 alkylacrySates, CJ-CJ^ primer amine acrylates, CJ-CJ«; secondary amine acrylates, C j -Cj (tacrylosuifonic acids, and epoxy CJ-CK, acrylates or methacrylates. Specific acrylate and methacrylate monomers operative herein it) addition to aforementioned methylmethacrylate include methylacrylate, ethylacrylate, ethylmediacrylate, isoborny! methacrylate, butyiacrylate, oetylacrylate, ethyl hexyl acrylates, ethyl hexyl methacrylates, dodecyl methacryiaie, tetrahydro&rfuryi methacrylate, cyclohexyi methacrylate, 2-hyd.roxyl ethylacrylate, 2-hydroxyl methacrylate, 3 -hydroxy! propyJacrylate, 1- hydroxyl-2 amino propyl methacrylate, I -ainino-2-hydroxyl propyl methacrylate, acrylamide, 1- amino-3-hydroxy propyl methacrylate, 2-terbutyl amino ethyl methacrylate, 2-acry!amido-2- methyl propane sulfonic acid, gtycidyl methacrylate.

[0013] An inventive formulation also includes a di-methacrylate monomer, a txi-methacry!at monomer, earboxylie acid analogs thereof, or a combination thereof. These monomers are synonymously referred io herein as poly&netional monomers and illustratively a di- or tri- (meth)acrylate monomers, such as those selected from polyethylen glycol di(raeth)aerylates, bisphenol-A di(meth)acrylates- tefrahydrofurane di(meth)acrylates, hexanediol di(meth)acrylates, poiytbylene glycol di(niefh)acrylates, such as triethylene glycol di(meth)acrylate„ tripropylene glycol di(meth}acrylate _s tetraethylene glycol di(meth)a.crylate, diethylene glycol di(meth)acrylate, t ,4-butanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acry!ate, pentaerythritol tetra rneth)acryiate, irimethyioi. propane trifmetlijacrylate, triniethylol propane tri(meth)aerylate, di-p nlaerydiritoJmonohydroxypeirta(meth)acryla£e, peiHaerylhritol rri(meth)acrylate, eihoxylated bisphenol~A (ii(meth}acryiate ₅ ethox latedtrimethylol propane tri(ffieth)acrylates, triraethy!olpropanepropoxylaie tri(meth)aciylale$, or combinations thereof; and other such monomers as detailed in U.S. Patents 7,408,012; and US 5.376,746. in those embodiments of the present invention containing polyiunctionat monomers, the polyranctional monomer is typically present on a mole ratio relative to the aforementioned acrySaie monomers of 0.001-0.5:! with the ratio modifying the average chain length between cross linkages.

[0014] It is appreciated that the methacrylate ester monomer is present solely in adhesive part A in some embodiments while in other embodiments methacrylate ester monomer is present in both parts A and B of an inventive formulation. An inventive formulation includes a quantity of a butyl rubber component present in quantities to promote a cohesive failure mode. Without intending to be bound to a particular theory, it is believed that crack propagation of a cured inventive adhesive is inhibited by the presence of such rubber domains thereby changing the failure mode of the resultant adhesive, in specific embodiments of the present invention in which parts A and B are present in a 10: 1 ratio, the butyl rubber is present in both the adhesive part as well as the activator part while in other inventive embodiments, the butyl rubber is segregated to only one of these two inventive formulation parts. As used herein, the term butyl rubber is intended to encompass SB rubber, isoprene rubber, polyisobutylene rubber, isobutylene Isoprene rubber, and combinations thereof.

[0015] An impact modifier operative herein illustratively includes methacrylate butadiene sryrene, nitiiie rubber, a block copolymer of styrene and butadiene, high rubber graft having 60 percent rubber, ABS, natural rubber, and combinations thereof. While the loading of an impact modifier depends on factors including weight ratio between adhesive part and activator part, impact modifier mo.lecu.1ar weight, and impact modifier modulus. Typical impact modifier loadings in adhesive; activator weight ratio formulation range from 10 to 37 total weight percent for a 10: 1 ratio formulation and from 12 to 50 total weight percent for a 1 : 1 ratio inventive formulation. In certain inventive embodiments, a butyl rubber is preseiit as a rubber component in combination with the impact modifier. In still other embodiments, the butyl rubber is segregated into an activator, part B of an inventive formulation, yet still serves to modify the failure mode of the cured adhesive.

[0016] An inventive fonnulatton also includes a toughening agent, A toughening agent is distinguished from rubber component in the present invention in having low Tg and can significantly improve the performance of cured adiiesives at low temperatures such as -40 °p (- ί it

40 C) and at. the same time does not cause a negative impact on the performance of cured adhesives at elevated temperatures such as 180 °F whereas the rubber component used in this invention are the core-shell structured impact modifiers and provide not only excellent impact strength but also non-sag, excellent thixotropic property and improved anti-sliding performance. Toughening agents operative hereto illustratively can be chosen from a wide variety of elastomeric materials that form discrete particles or biphasic domains in a continuous resin matrix. For example, pre~reacted particles of polyacrylate, styrene/butadiene/styiene (SBS) copolymers, styrene/ isoprene/ styrene (SIS) copolymers, sryrene/butadiene (SBR) copolymers, as well as other pre-reacted materials may be added i pailicuiate form to the resin composition. A partial listing of -useful pre-reacted elastomer rubbers includes pre-reacted elastomer particles selected from the group consisting of aerylate-butadiene, butadiene, ehloroprene, ethylene- propylene, ethylene-propylene-diene, isoprene, isobutylene, isobuty!ene-isoprene (butyl rubber), styrene-butadiene, styrene-isopretie, acrylonitrile-butadiene, acrylomtriie-chlotopfeue, vmylpyridine-butadiene, vmyipyridine-styrene-butadiene. carboxyiic-styrene-butadiene, cSiioro- isobutylene-isoprene (chiorobutyl rubber), bromo-isobutylene-isoprene (brornobutyl rubber), dialkysiioxane, polyipropylene oxide), polyester urethanes, polyether urethanes, and. mixtures thereof. Moreover, reactive liquid -polymers (RLP's) also can be incorporated as the toughening component, RLP's contain functional groups, usually on their terminal ends but occasionally as pendant groups, and react with the resin in situ to form elastomeric domains. Examples, of RLP's include, without limitation, carboxyl-tenninated butadiene nitrite (CTBN), amine-terminated butadiene nitrite (ATB ), hydroxy! -terminated butadiene nitrite (HTBN), epoxy-termmated butadiene nitrile (ETB ), mercapto-terminated butadiene nitrile (MT.PN), and phenoxy- terminated butadiene nitrile (PTBN). In specific embodiments of the present invention, the toughening agent includes chloro-su!phonated polyethylene, neoprene, copolymers of ethylene acrylic elastomer, poly (methyl methacrylate)~grafted rubber, Styrene acry!omtrile copolymer or combinations thereof. It is appreciated that a toughening agent is present as a component of an adhesive part, an activator part, or both parts of an inventive fonnulation. In specific embodiments of the present invention, a toughening agent is present only in an adhesive part but it is appreciated that the amount of toughening agent present depends on characteristics of the toughening agent as well as the weight ratio between adhesive: activator parts, typical loadings of toughening agent in a fully formulated inventive adhesive range from 7-20 total weight percent for a 10: 1 weight ratio formulation and I 0-40total weight percent in a 1:1 adhesive; activator formulation.

[0017] ϊ« order to formulate an inventive adhesive formulation that achieves high strength without the need for a separate surface treatment prior to application of an in venti ve formulation, an adhesion promoter system is provided within an inventive formulation.. ^' The adhesion promoter system includes an etching agent and an adhesion promoter to facilitate adhesion of a fully cured formulation of various substrates including galvanized substrates. A adhesion promoter system is readily formulated into either an adhesive part, an activator part, or both parts of an inventive formulation, in specific embodiments, the adhesion promoter system is found only in the adhesive part. Specific adhesion promoters operated in an inventi e formulation illustratively include phosphate esters, mono-functional phosphates, difunetionai phosphates, and combinations thereof. Typical loadings of adhesion promoter in an. inventive formulation, are from 1. to 5 total weight percent of a fully formulated adhesive with the amount being largely independent of the weight ratio between adhesive part: acti vator pari. Etching agents operative herein illustratively include inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, perchloric acid, phosphoric acid, or monophosphate; and organic acids such as acetic acid, tannic acid or formic acid. Typical loadings of etching agent in an inventive formulation are from 0.2 to 1 total weight percent of a fully formulated adhesive with the amount being largely independent of the weight ratio betwee adhesi ve part: activator part.

[0018] A polymerization initiator present in an adhesive Part A is limited only by the desired kinetics of f ee-radical polymerization desired and compatibility with other inventive composition components. Initiators operative herein illustratively include /ert-Bntyi peroxylbenzoate, eumene hydroperoxide, tert-butyi hydroperoxide, and combinations thereof. Typical loadings of initiator in an inventive formulation are from 0.0001 to 2 total weight percent of a fully formu!ated adhesi ve.

[0019] A polymerization accelerator present in an activator Part B is limited only by the desired kinetics of tree-radical polymerization desired and compatibility with other inventive composition components. Accelerators operative herein illustratively include terr-pyridme derivatives, butaraldehyde aniline condensate, , -dimethyianiline, N,N~dime†hyitoludiene, N,N-4iethyHoUidiene, Copper acetyl, acetonate (Metal acetyl acetonates). and combinations thereof. o ical loading of initiator in an inventive formulation is from 1 to 10 total weight percent of a fully formulated adhesive.

[0020] An inventive formulation in certain embodiments also includes various chelating agents, corrosion inhibitors, chain transfer agents, pigments, spacers, fragrances, fillers, fire retardanis, and combinations thereof. Such additives are limited only by the requirement, of compatibility with the other components of an inventive formulation. Such additives are provided to balance or otherwise .modify at least one property of an inventi e formulation as to handling, storage, cure rate, or adhesive properties. An inventive formulation in certain embodiments also includes various oxidizing agents, reducing agents, thickeners, pigments, thixotropic agents, plasticizers, antioxidants, fillers, and combinations thereof. Such additives are limited only by the requirement of compatibility with the other components of an inventive formulation. Such additives are provided to balance or otherwise modify at least one property of an inventive formulation as to handling, storage, cure rate, or adhesive properties. Typical components amounts for an inventive adhesive are provided in Tables IA and IB for parts A and B, respectively.

Table 1A and IB. Typical component amounts for adhesive (part A) and activator (part B), where amounts are given in weight percentages unless otherwise noted:

Table IA. ADHESIVE (Part-A)

ACTI VATOR Part B

fOOlS] A process is provided for producing an adhesive formulation produced by tre radical polymerization that bonds well to the aforementioned substrates. An inventive formulation is a two-part formulation that is either premised to initiate a time period pot life, or alternatively the two parts are co-applied to a substrate under conditions for polymerization to occur between the various monomers, A pot life of 5 to 7 minutes is provided for in certain embodiments to achieve an adhesive product that has a rapid cure time and possesses superior thermal stability over a wide temperature range of -40°€ - !20°C ₅ as compared to preexisting adhesive*. Additionally, the separate parts of an inventive formulation provide a shelf iife of more than 300 days at 23 °C in specific inventive embodiments, polymerization occurs at 28*C in ambient atmosphere on other embodiments, polymerization is initiated by energy inputs such as heating, ultraviolet radiation exposure or other free radical formation mechanisms. In certain inventive embodiments in which the adhesive part. A, and activator, part B are present in a 1 1 weight ratio 10%, storage stability of more than 300 days at 23°C is obtained. This is in contrast to conventional adhesives that have working ratios of 10:1, 4:1, or 2:1 yet still are unable to achieve storage shelf life of more than six months unde like storage condi ions.

fOwUi] Regardless of the form of an inventive formulation, upo induction of pot life for the formulation, the formulation is present in simultaneous contact with two of more substrates with the substrates held in contact with the curing inventive formulation for an amount of time sufficient to achieve a bond between the substrates. While an inventive formulation is particularly well-suited for bonding gal vanized substrates such electro gal vanized to one another, substrates in simultaneous contact with a polymerizing inventive formulation need not be the same and an inventi ve formulation is also well -suited for joinder of other substrates illustratively including cold rolled steel, aluminum, PYC, ABS, mild steel vinyl polymers, wood, and fiberglass. Two such substrates can be brought together to form various adjoined structures such as a lap joint, butt joint, comer joint, edge joint, and T-jokvt In still other embodiments, an inventive formulation is applied to a single substrate and allowed to cure to form a coating that offers substrate protection or is operati ve as a primer for subsequent material applications. As an inventive formulation cures through a free-radical mechanism, an inventive formulation can be appiied to a variety of thicknesses and still achieve polymerization throughout. Typical thicknesses of an inventive formulation between substrates range from 0.00 i -4mm.

|ββΙ7| The present invention is further described with respect to the following non-limiting examples. These examples are intended to illustrate specific formulations according to the present invention and should not be construed as limitation as to the scope of the present invention.

Example 1. Compounding of two-part formulation.

fuulS] Adhesive part A is produced by mixing 51.9 g (grams) of roethaerylate ester monomer, 4.5 g of methyl methaaerylic acid, 1.0 g of ditri-decyl-thiodipiX pioaaaie (DTDTDP). 2,0g of buty!ated hydroxy! toluene with 0.03 g of benzoqu none in a reaction kettle equipped with a mechanical stirrer and nitrogen gas blanketing. The components are mixed under a nitrogen blanket for 1.5 minutes at room temperature under swirling conditions. 2.52 g of phosphate esters and ! .05g of phosphoric acid are added to the mixture with stirring at 500 revolutions per minute (rpm) for 15 minutes. 7.5 g of chloro-sulphonated polyethylene and 10 g of SAN copolymer is added slowly to the mixture with stirring continuing for an additional 30 minutes until a homogeneous mixture is achieved. Stir speed is then raised to 800 rpm for ten minutes to assure homogeneity. 15 g of SBS and 3g methacrylate butadiene styrene are added over a period of 10 minutes with stirring at 800 rpm. Thereafter, the mixture is allowed to rest for 2 hours under the nitrogen blanket without agitation. ^' Thereafter, the mass is stirred for 30 minutes at 1,000 rpm and stirrer speed is reduced to 200 rpm. i.5 g of t -butyl peroxylbenzoate is added drop wise to the reaction mass with stirring continuing at 200 rpm. The reaction kettle is then evacuated for 20 minutes under vacuum of 600 ramBg to degas th adhesive part A. Th resultant adhesive pari A is packed under a nitrogen atmosphere to achieve a storage siabiiiiy of mor than one year at 23°C

[0019] Activator part B is produced by adding together 70 g of butyl rubber and 25 g of butaraldeliycle aniline condensate and 0,005 a of metal acetyl acetonate in a reaction kettle equipped with a mechanical stirrer and nitrogen gas blanketing equipment. The components are mixed for 20 minutes at room temperature with the stirrer operating to achieve swirling. And 4.995 g of (fumed silica thixotropi.e agent) are added to the mixture with stirring for 60 minutes at 1 ,000 rpm t achieve homogeneity. The reaction kettle is evacuated for 20 minutes under a vacuum of 600 mm Hg to degas the activator part B. The activator part B is then packed under a nitrogen atmosphere to achieve storage stability of more than 1 year at 23°C.

[0020] Part A and part B are combined in weight ratios of 10: 1 ± 10% and used in subsequent testing.

Example 2. Thermal stability testing.

[0021] 1:1 system: Uneured samples are kepi at 50° ± ^■ 1 °C for 28 days and observed to change in viscosity by less than 40% relative to initial viscosity. Pot life, mechanical strength, and bonding capability to gal vanized surfaces and rate of strength development for the resulting adhesive remained within 85% relative io initially formulated samples showing two substrates during the test, period. Further, product performance and lap shear strength are found io h within 80% even after aging the samples at 5Q°C for 28 days.

[0622] 10: 1 system: Uticured samples are kept, at 50° ± P ^' C for 28 days and observed to change in viscosity b less than 40% relative to initial viscosity. Pot life, mechanical strength, and bonding capability to galvanized surfaces and rate of strength development for the resulting adhesive remained withi 85% relative io initially formulated samples showing two substrates during the test period. Further, product performance and lap shear strength are found to be within 80% even after aging the samples at 50°C for 28 days.

[0023] Uncured samples of the 10: 1 system parts A and B are also kept at 60 ± 1°C for 5 days and observed to change in viscosity by less than 40% relative to initial viscosity. Mechanical properties and cure profiles also remained within 85% relative to initially formulated samples. This data is extrapolated with conventional models to a shelf life of 23 "C of at least 300 days (10 months).

Example 3. Properties of inventive formulations.

[0024] The various properties of inventive formulations are provided in Table 2fbr the part A and part B of example 1 with the respective methodology used for determining properties of a fully cured adhesive so formed along with the respecti ve values.

[0025] Duplicate lap joints are formed between strips of various substrates as iioted in Table 2 with the substrate strips having a thickness of 1.6 mm and an adhesive thickness of between 0.03 and 0.06 mm earing at a temperature of 23.5°C. Surface preparation prior to application is performed with an isopropanoi wipe. The strip dimensions are 101.6 mm x 25.4 ramxl .6 mm with an overlap of 25.4 mm x 12,5 mm, with a ramp rate of 1.3 mm per minute. The strips are coated with a formulation of example 1 at either J 0:1 or 1 : 1 ratios between adhesive

part A: activator part B.

Table 2, Properties of inventive formulation and resultant fully cured adhesive.

[0026] Lap joints of Example 3 are repeated with comparative conventional adhesives noted herein as reference 1 and reference 2 that are beyond the inventive formulation compositions. The properties tor these comparative examples are provided in Table 3 along with data from the above Table 2 for an inventive 10: 1 formulation.

Table 3. Comparative properties of inventive adhesion and. reference conventional adhesives.

[0027] Patents and references ci ted in the above application are indicati ve of the skill in the art. Each of these patents and references is hereby mcorporated by reference to the same extent as .if each reference was individually incorporated by reference.