WO2002057321A1

WO2002057321A1 - Oil-activated sheet metal adhesive compositions

Info

Publication number: WO2002057321A1
Application number: PCT/US2001/047892
Authority: WO
Inventors: John G. Woods; Susanne D. Morrill; Anthony F. Jacobine; Thomas L. Labelle; Paul J. Rachielles
Original assignee: Henkel Loctite Corporation
Priority date: 2001-01-16
Filing date: 2001-12-13
Publication date: 2002-07-25

Abstract

This invention relates to oil-activated sheet metal adhesive composition systems, particularly well-suited for automotive panel closure.

Description

OIL-ACTIVATED SHEET METAL ADHESIVE COMPOSITIONS

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to oil-activated sheet metal adhesive composition systems, particularly well- suited for panel closure, such as vehicle or panel closure .

Brief Description of Related Technology

A need exists for a room temperature curing adhesive to bond the outer and inner panels of automobile body sheet-metal components stamped from oiled steel and aluminum stock. In conventional assembly processes for the bonding of the outer and inner panels of automobile body sheet-metal components stamped from oiled steel and aluminum stock, a bead of adhesive is ordinarily applied to the periphery of one or the other of the panel pair, with the second panel being aligned with the first and the edge of the joined pair folded and crimped in a hem- press. A sealer is then applied to the hemmed edge, with the entire process being referred to as closure. The assembly process is used to fabricate doors, hoods and trunk-lids of automobiles and trucks.

Rapid fixture of the inner and outer panels, such that they can be moved quickly to the next stage of the assembly process without loss of alignment of the panels, rupture of the adhesive bond or significant downtime, which would otherwise affect throughput, are all desirable attributes of the process.

In such conventional processes, two-part epoxy- based compositions and two-part acrylic-based compositions have been used as closure adhesives. However, these compositions do not cure sufficiently rapidly without a short heat cure cycle in an induction fixture. Not only does this additional heat cure cycle step add considerably to the cost of closure, but many vehicle manufacturers seek to eliminate this step by using rapid room temperature curing adhesive compositions .

Accordingly, the need exists for a curable adhesive composition that is capable of curing without such short heat cycle while being active on the surface of oiled panels.

SUMMARY OF THE INVENTION This invention relates to radical curable adhesive composition systems, whose cure is triggered by a catalyst disposed within a lubricating oil, such as those used in the metal stamping process. The catalyst is thus introduced to the adhesive composition by using the oil as a delivery medium therefor, as well as serving its primary role as a lubricant/protectant for the metal substrates on which it has been applied. That is, the invention relates to an adhesive composition system that is reacted by contact with a catalyst that has been disposed within a lubricating oil, under appropriate conditions, such as radiation curable conditions, anaerobic curable conditions, and/or heat curable conditions or combinations thereof.

The adhesive compositions are based on one or more (meth) acrylate monomers together with a radical cure-inducing component, together with a catalyst, such as transition metal complex, disposed in a lubricating oil that has been applied to a substrate.

The invention further provides a dual functioning sheet-metal lubricating oil composition, which serves to not only lubricate the stock metal prior to processing, such as stamping, but also to function as an adhesive activator for panel closure.

In addition the invention provides a bonded assembly of a first substrate; a second substrate; and a reaction product therebetween formed from the radical curable system, where a portion of the radical curable system was applied to at least a portion of a surface of at least one of the first or second substrate prior to joining the substrates.

The inventive compositions are desirable for use as oil-activated sheet metal adhesive compositions, particularly well-suited for vehicle panel closure. Desirable results are obtained when the catalyst-containing oil media and/or the reactivity of the adhesive composition is sufficiently high, so as to achieve appropriate bond strengths at room temperature within a commercial acceptable amount of time.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 depicts a curve showing the dependence of activator application rate on the concentration of the activator solution.

Figure 2 depicts a curve showing lap-shear adhesive strength of TA-2 versus copper (II) naphthenate ("CN") catalyst concentration in oil at standard application rate.

Figure 3 depicts a curve showing lap-shear adhesive strength of TA-2 versus room temperature ("RT") curing time for different catalyst levels at standard application rate.

Figure 4 depicts a curve showing the dependence of lap-shear adhesive strength on the on-part lifetime of CN catalyst/oil activator. Adhesive formulation TA-3, 10 mil gap, 30 minute RT cure; 2.5% CN in oil applied at standard application rate.

Figure 5 depicts a curve showing the effect of bondline gap on adhesive strength of TA-3 prototype adhesive after RT cure for 30 minutes.

Figure 6 depicts a curve showing the effect of bondline gap on adhesive strength of TA-3 prototype adhesive after RT cure for 2 hours (2.5% CN activator; 0.13 mg/cm² coverage).

Figure 7 depicts a curve showing the effect of lap-shear test results for various adhesives after curing 4 hours at RT and 1 hour at 200°C

Error bars on these figures represent standard deviation of mean stress for 5 specimens. DETAILED DESCRIPTION OF THE INVENTION

As noted above, the inventive adhesive compositions are based on radical-curable (meth) acrylate monomers together with a radical cure-inducing composition. The polymerization of these adhesive compositions is initiated by highly reactive oil- compatible catalysts that are effective at low concentrations and have good oxidative stability. More particularly, these catalysts include transition metal complexes that are dissolved or dispersed in lubricating oils. The adhesive compositions may be cured through one or more of a variety of curing mechanisms, such as radiation curing, anaerobic curing, and/or heat curing. It is particularly desirable to cure the adhesive composition by exposure to one or the other or both of radiation curing and anaerobic curing conditions, and allowing for further adhesive properties to develop through a secondary heat cure that occurs during the assembly of the vehicle into which the panel is to be used.

The adhesive composition is ordinarily applied to at least one substrate prior to bonding that substrate with another substrate with the oil-based activator applied to either or both of the substrates. The substrates are then mated and exposed to conditions effective to promote curing of the adhesive composition. The (meth) acrylate monomer suitable for use in the present invention may be chosen from a wide variety of materials. For instance, mono (meth) acrylates represented by H₂C=CGC0₂Rι, where G may be hydrogen, halogen or alkyl of 1 to about 4 carbon atoms, and Ri may be selected from alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl or aryl groups of 1 to about 16 carbon atoms, any of which may be optionally substituted or interrupted as the case may be with silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbamate, amine, amide, sulfur, sulfonate, sulfone and the like, may be used. Particular examples include methyl (meth) acrylate, butyl (meth) acrylate, lauryl (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and benzyl (meth) acrylate . Such

(meth) acrylate monomers are particularly well-suited for applications in which it is desirable for the composition to possess oil-cutting properties.

In addition, di- or poly- (meth) acrylates may be used. For instance, monomers that may be used herein include polyethylene glycol di (meth) acrylates, bisphenol- A di (meth) acrylates, such as ethoxylated bisphenol-A (meth) acrylate ("EBIPMA"), and tetrahydrofurfuryl (meth) acrylates and di (meth) acrylates, citronellyl acrylate and citronellyl methacrylate, hydroxypropyl

(meth) acrylate, hexanediol di (meth) acrylate, trimethylol propane tri (meth) acrylate, tetrahydrodicyclopentadienyl (meth) acrylate, ethoxylated trimethylol propane triacrylate ("ETMPTA"), triethylene glycol acrylate and triethylene glycol methacrylate ("TRIEG A"), and an acrylate ester corresponding to structure I as shown below:

where Rg may be selected from hydrogen, alkyl of 1 to about 4 carbon atoms, hydroxyalkyl of 1 to about 4 carbon atoms or

0

-C H, 0 C C =C H,

R7 may be selected from hydrogen, halogen, and alkyl of 1 to about 4 carbon atoms;

Rg may be selected from hydrogen, hydroxy and

- H, -C C=CH,

m is an integer equal to at least 1, e.g., from 1 to about 8 or higher, for instance, from 1 to about 4; n is an integer equal to at least 1, e.g., 1 to about 20 or more; and

Of course, combinations of these (meth) acrylate monomers may also be used.

The (meth) acrylate monomer should be of an oil- cutting nature; that is, it should be able to develop adhesive strength without regard to whether the surface of the substrate (s) with which it is used has been prepared by removing any oil therefrom. To that end, mono (meth) acrylate monomers are particularly desirable, such as those set forth above. The (meth) acrylate component should be present in the inventive compositions in an amount within the range of from about 10 to about 90, such as about 50 parts per hundred ("phr").

A variety of additives may be included in the adhesive composition, depending on the physical properties one wishes to develop for the uncured and/or cured adhesive, and/or the cure profile of the adhesive composition. For instance, rubber toughening agents, thixotropy-conferring agents, plasticizers, dyes, pigments, fillers, may be included.

The rubber-toughening agent may be selected from a wide range of rubbers, such as (a) homopolymers of alkyl esters of acrylic acid; (b) copolymers of lower alkenes, with an alkyl or alkoxy ester of acrylic acid; (c) copolymers of alkyl or alkoxy esters of acrylic acid; (d) copolymers of styrene, butadiene, and/or acrylonitrile; and combinations thereof. Additional polymerizable unsaturated monomers which may be copolymerized with the alkyl and alkoxy esters of acrylic include dienes, polymerizable halogen-containing olefins and alkylies and acrylamides . For instance, core-shell rubbers, polymers and copolymers of vinyl ethers, maleates, fumarates, urethane elastomers, polyester elastomers, butyl rubbers and other elastomers that are typically used to toughen adhesives are well suited, as are acrylonitrile-butadiene-styrene terpolymers, styrene- isoprene copolymers and the like. Of the acrylic rubbers, copolymers of methyl acrylate and ethylene, manufactured by Du Pont, under the tradename of VAMAC, such as VAMAC N123 and VAMAC B124, are desirable. Other desirable acrylic rubbers include copolymers of ethyl acrylate and 2-chloroethyl vinyl ether in a molecular ratio of about 95:5, respectively. One such acrylic rubber is manufactured by B.F. Goodrich Company, and is sold under the tradename HYCAR, such as HYCAR 4021.

Of the styrene-butadiene copolymer rubber toughening agents, STEREON 840A, commercially available from Firestone Synthetic Rubber, is particularly desirable. STEREON 840A is a copolymer of butadiene and styrene.

The amount of rubber toughening agent chosen should range from about 1 to about 50 percent by weight, such as about 5 to about 40 percent by weight, based on the weight of the composition. Radical cure-inducing compositions may be chosen from those which initiate cure through radiation initiated (such as electron-beam, ultra-violet and visible light) cure mechanisms, anaerobic cure mechanisms and/or heat cure mechanisms. Radiation initiated cure mechanisms may be triggered through photoinitiators, which may be chosen from a variety of materials, such as those commercially available from Ciba Specialty Chemicals Corp., Tarrytown, New York under the tradename "IRGACURE" and "DAROCUR". Or radiation initiated cure mechanisms, such as E-beam or radio frequency, may not require the use of photoinitiators . Anaerobic cure mechanisms are triggered by anaerobic cure-inducing compositions, which typically include a variety of components, such as amine oxides, sulfonamides and triazines, for instance saccharin, toluidenes, such as N, N-diethyl-p-toluidene and N,N- dimethyl-o-toluidene, and acetyl phenylhydrazine ("APH"). Acidic materials, such as maleic acid, may also be included. Of course, other materials known to induce or initiate anaerobic cure may also be included or substituted therefor, such as cumene hydroperoxide ("CHP"), para-menthane hydroperoxide, t-butyl hydroperoxide ("TBH") and t-butyl perbenzoate. See e.g. U.S. Patent Nos . 3,218,305 (Krieble) , 4,180,640 (Melody), 4,287,330 (Rich) and 4,321,349 (Rich). Quinones, such as naphthoquinone and anthraquinone, may also be included to scavenge free radicals which may form.

The radical cure-inducing composition should be present generally within the range of from about 0.001 phr to about 10 phr, such as from about 0.1 phr to about 5 phr.

The lubricating, stamping, mill or drawing oils (collectively, "lubricating oils") are typically petroleum lubricants used to provide corrosion protection, surface preparation and lubricity to steel and aluminum alloys during production and processing.

They are available as oils, or emulsions or suspensions of oils dispersed in water, and may contain surfactants and dye tracers.

For instance, PARCO PRE-LUBE MP-404, available commercially from Henkel Corporation, Madison Heights, MI, is a petroleum lubricant for use as a mill applied prelubricant and drawing oil. It is reported to contain about 10-30 weight percent of each of hydrotreated light naphthenic petroleum distillates, hydrotreated heavy naphthenic petroleum distillates, and calcium petroleum sulfonate. It is promoted for use on plain steel, free zinc, zinc alloy coated steels, and aluminum.

Another particularly desirable lubricating oil is MONTGOMERY DB-4265-C, available commercially from Fuchs Lubricants Co., Harvey, IL.

Into the lubricating oils is disposed a catalyst, such as a transition metal complex. In order to be effective for use herein, the transition metal complex is to be active in causing reaction of the (meth) acrylate component of the adhesive composition, and exhibit solubility in the lubricating oil.

For instance, The transition metal complex may be chosen from a variety of organometallic materials or metallocenes . Those materials of particular interest herein may be represented by metallocenes within structure II:

M_e

II where R₂ and R₃ may be the same or different and may occur at least once and up to as many four times on each ring in the event of a five-membered ring and up to as many as five times on each ring in the event of a six-membered ring;

R₂ and R₃ may be selected from H; any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms, such as CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, C(CH₃)₃ or the like; acetyl; vinyl; allyl; hydroxyl; carboxyl; -(CH₂)_n-OH, where n may be an integer in the range of 1 to about 8; - (CH₂) _n-COOR , where n may be an integer in the range of 1 to about 8 and R₄ may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; H; Li; or Na; -(CH₂)_n-ORs, wherein n may be an integer in the range of 1 to about 8 and R₅ may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; or - (CH₂)_nN⁺ (CH₃) ₃ X^", where n may be an integer in the range of 1 to about 8 and X may be Cl^", Br^", I^", C10₄ ^" or BF₄ ^";

Yi and Y₂ may not be present at all, but when at least one is present they may be the same or different and may be selected from H, Cl^~, Br^~, I^", cyano, methoxy, acetyl, hydroxy, nitro, trialkylamines, triaryamines, trialkylphosphines, triphenylamine, tosyl and the like;

A and A' may be the same or different and may be C or N; m and m' may be the same or different and may be 1 or 2 ; and

M_e is Fe, Ti, Ru, Co, Ni, Cr, Cu, Mn, Pd, Ag, Rh, Pt, Zr, Hf, Nb, V, Mo and the like.

Of course, depending on valence state, the element represented by M_e may have additional ligands — Yi and Y₂ -- associated therewith beyond the carboxylic ligands depicted above (for instance, where M_e is Ti and Yi and Y₂ are Cl^") .

Alternatively, metallocene structure I_I may be modified to include materials such as those within structure III below:

III

where R₂, R₃, Yi, Y₂, A, A¹, m, m' and M_e are as defined above .

A particularly desirable example of such a material is where R₂ and R₃ are each H; Yi and Y₂ are each Cl; A and A' are each N; m and m' are each 2 and M_e is Ru ,

Within metallocene structure I_I, well-suited metallocene materials may be chosen from within metallocene structure IV:

IV where R₂, R₃ and M_e are as defined above.

Particularly well-suited metallocene materials from within structure I_I may be chosen where R_x, R₂, Y_lf Y₂, m and m' are as defined above, and M_e is chosen from Ti, Cr, Cu, Mn, Ag, Zr, Hf, Nb, V and Mo. Examples of such metallocenes include ferrocenes (i.e., where M_e is Fe) , such as ferrocene, vinyl ferrocenes, ferrocene derivatives, such as butyl ferrocenes or diarylphosphino metal-complexed ferrocenes [e.g. , 1,1-bis (diphenylphosphino) ferrocene-palladium dichloride] , titanocenes (i.e., where M_e is Ti), such as bis (D⁵-2, 4-cyclopentadien-l-yl) -bis- [2, 6-difluoro-3- (1H- pyrrol-1-yl) phenyl] titanium which is available commercially from Ciba Specialty Chemicals, Tarrytown, New York under the tradename "IRGACURE" 784DC, and combinations thereof. A particularly desirable metallocene is ferrocene.

And bis-alkylmetallocenes, for instance, bis- alkylferrocenes (such as diferrocenyl ethane, propanes, butanes and the like) are also desirable for use herein, particularly since about half of the equivalent weight of the material (as compared to a non-bis-metallocene) may be employed to obtain the sought-after results, all else being unchanged. Of these materials, diferrocenyl ethane is particularly desirable.

Other materials well-suited for use herein include M_e [CW₃-CO-CH=C (0^") -CW ' ₃] ₂, where M_e is as defined above, and W and W may be the same or different and may be selected from H, and halogens, such as F and Cl . Examples of such materials include platinum (II) acetylacetonate ("PtACAC"), cobalt (II) acetylacetonate ("Co (II) ACAC") , cobalt (III) acetylacetonate ("Co(III)ACAC") , nickel (II) acetylacetonate ("NiACAC"), iron (II) acetylacetonate ( "Fe (II) ACAC" ) , iron (III) acetylacetonate ( "Fe (III) ACAC" ) , chromium (II) acetylacetonate ( "Cr (II) ACAC" ) , chromium (III) acetylacetonate ( "Cr (III) ACAC") , manganese (II) acetylacetonate ( "Mn (II) ACAC" ) , manganese (III) acetylacetonate ( "Mn (III ) ACAC") and copper (II) acetylacetonate ("CuACAC") .

Generally, transition metal carboxylate salts, some examples of which are give above, are suitable for use herein. Other examples include copper (II) naphthenate and copper (II) 2-ethylhexanoate, cobalt (II) naphthenate and cobalt (II) 2-ethylhexanoate, and iron (II) naphthenate and iron (II) 2-ethylhexanoate. Metal phenolate salts, such as copper (II) phenolate, may also be used.

Of course, combinations of these transition metal complexes may also be employed.

When oil dispersions in water are used, it may also be desirable to include one or more surfactants in an amount sufficient to ensure the physical stability of the suspension or emulsion.

Stabilizers and inhibitors (such as phenols including hydroquinone and quinones) may also be employed to control and prevent premature peroxide decomposition and polymerization of the composition of the present invention, as well as chelating agents [such as diethylenetriamine pentaacetic acid ("DTPA") or the tetrasodium salt of ethylenediamine tetraacetic acid ("EDTA")] to remove trace amounts of metal contaminants therefrom.

The compositions of the present invention may be prepared using conventional methods, which are well known to those persons of skill in the art. For instance, the components of the inventive compositions may be combined together with mixing in any convenient order consistent with the roles and functions the components are to perform in the compositions. Conventional mixing techniques using known apparatus may be employed.

More particularly, the invention relates to an oil-cutting, toughened acrylic composition, which is curable between metal panels having an oil-activated coating thereon. The oil-activated coating includes a catalyst capable of triggering a rapid curing of the adhesive composition.

In one particularly desirable commercial application, an adhesive prepared in accordance with this invention is useful for the bonding and sealing of automobile panel closure joints, in which the adhesive catalyst is formulated as a constituent component of the drawing oil. The blended mixture of oil and catalyst is then utilized as both a lubricating oil and an adhesive activator .

The inventive adhesive systems are characterized by rapid curing and strength development at room temperature, good oil cutting properties, excellent on-part activator lifetimes and acceptable ultimate strengths after exposure at elevated temperatures. The adhesive system meets the cure speed and adhesive performance properties at 10-mil gap (0.25 mm), which are 400 psi (2.8 mPa) after about one half hour at ambient temperature conditions, but may require longer times to attain minimum adhesive strength when the bondline gap is increased to 30 mils (0.75 mm).

Unlike activators containing aldehyde-aniline condensates, thin films of the inventive composition remain stable, even following prolonged exposure to air. The materials are therefore suitable for applications where on-part activator lifetimes exceed 24 hours. In addition, the new adhesive system is sensitive to curing at relatively low levels of active catalyst. This permits thin oily films of drawing oil to be utilized as a medium for the delivery of activator without increasing the standard oil application rates for automotive panel assembly operations. Low catalyst levels also result in low additional costs. The cost requirement is critical, as it is proposed to coat the entire component panel with the oil-activator, but to utilize only a very small fraction (typically, less than 1/200) of the applied catalyst amount, to affect the curing of the adhesive in a peripheral bondline of the jointed panels.

Among other things, the inventive compositions yield improved ultimate adhesive strength after thermal aging, as contrasted with the adhesive strength developed after say 30 minutes.

The inventive activator-containing lubricating oil shows shelf life stability comparable to that of lubricating oils, without added activator.

While the invention has been described above in terms of panel closure applications, it may be used as well in body structure applications, and a-pillar, fa- pillars, c-pillars, floor pans, firewalls, and the like, all of which are stamped followed by an assembly operation that welds and/or bonds together the substrates. Therefore, for automotive applications, the present invention may be used on any metal part that has been stamped using a lubricating oil, whether aqueous or non-acqueos . In addition, the present invention may be used in non-automotive applications, such as furniture assembly, such as desks and cabinets, as well as heat registers . The present invention will be described in further detail by the following illustrative non-limiting examples .

EXAMPLES

PARCO 404 drawing oil supplied by Henkel Corporation was used throughout these examples. Copper naphthenate ("CN"; 77% in mineral spirits; 8% Cu) and copper (II) 2-ethylhexanoate ("CEH") were used as catalysts. Both of these salts are readily soluble in the 404 oil and solutions of varying concentrations were prepared. Activator-oils were applied by dip coating specimens from heptane solution to ensure uniform and reproducible coverage over the application range that is typical encountered in the industrial application of - drawing oils.

Lap-shear adhesive strength tests were performed on an Instron tensile test machine fitted with a 1 or 5 KN load cell operating at a strain rate of 12.7 mm/min., according to standard test method ASTM D1002. Aluminum alloy 2024-T3 lap-shear panels were used. The panels were cleaned by rinsing with acetone and isopropanol .and dried by wiping with clean tissue paper. Bondline gaps were set by means of a V-shaped small strip of wire of appropriate diameter that was placed between the overlapping substrates. The mean stress at maximum load of 5 specimens was determined in each case.

Two experimental adhesive formulations were prepared by blending together the components listed in Table 1. Table 1

Adhesive Formulations for Cu-based Oil Activator

TA-2 TA-3

Component

% by weight % by weight

Cyclohexyl methacrylate (CHM) 56.00 52.00

STEREON 840A 26.00 30.00

Methacrylic acid 10.00 10.00

Acrylic acid 2.00 2.00

1,3-Butyleneglycol dimethacrylate 2.00 2.00

Cumene hydroperoxide 2.00 2.00 l-Acetyl-2-phenylhydrazine (APH) 1.00 1.00

Propylene glycol 0.59 0.59

Poly(ethylene glycol) dimethacrylate, Mn = 340 0.19 0.19

Water 0.18 0.18

Tetrasodium ethylenediamine tetraacetate 0.03 0.03

1 ,4-Naphthoquinone 0.01 0.01

The copolymer was initially dissolved in the monomer blend by stirring under low shear at ambient temperature over about 4 hours to give a moderately viscous solution (high shear mixing resulted in a temperature increase and loss of volatile CHM) . Finally, CHP was added to give the active adhesive formulations .

Product profile

The inventive adhesive composition system should yield:

(a) rapid adhesive strength development at room temperature, achieving about 400 psi lap-shear strength at a 10 mil gap after 30 minutes on oiled aluminum and steel alloys;

(b) an on-part activator life-time of at least about 30 days under ambient storage conditions; (c) good cure through depth up to 30 mils; and

(d) lap-shear strength of at least about 1500 psi after a paint bake cycle of a temperature of 200°C for 1 hour. The adhesive composition as well as the oil- based activator should have good storage stability, low toxicity/odor and be inexpensive to produce.

Application of catalyst solution

The oil-activator mixture was applied to the substrates by dip coating from heptane solution. We found that this application method provided uniform and reproducible coverage and allowed the application rate to be accurately varied within the specification range by controlling the concentration of the oil/catalyst blend (activator) in the solvent. The average application rate is 0.11 mg/cm² and the maximum value is 0.22 mg/cm². An initial experiment was performed to determine the application rate dependence on the concentration of activator in solution. A blend of 5% CN catalyst in oil was prepared and diluted with varying concentrations of heptane to give a series of solutions for dip-coating. Cleaned and dried aluminum lap-shear panels were weighed and dipped once into the various solutions, removed and dried to constant weight. The average weight increase was determined for six panels in a range of activator solutions. The correlation of application rate with _N solution concentration is shown in Figure 1. A dip-solution concentration of about 10% by weight provides an activator coverage corresponding to the average application rate, while the maximum rate coverage is obtained from an activator solution of about 15% by weight. For the purposes of the current tests, a solution concentration of 11.27% activator by weight, corresponding to an application rate of 0.13 mg/cm² was employed. Cure speed

The adhesive, when used for panel closure, should cure rapidly and develop strength at room temperature. The specification requires a minimum of 400 psi (2.8 MPa) after about one half hour. A series of 30 minute RT cured lap-shear adhesive strength tests were performed in order to determine the minimum concentration of CN catalyst in oil that is required to meet this minimum value. Cleaned aluminum substrates were dip- coated at the standard application rate of 0.13 mg/cm² with oil-activator solutions containing varying amounts of CN catalyst. The prototype adhesive formulation TA-3 was used and the bondline gap was set at 10 mils. The results, presented in Figure 2, indicate that a catalyst concentration of about 1.25 % is needed to achieve the minimum specified lap-shear adhesive strength value (400 psi; 2.8 MPa) . The data also shows that the adhesive strength increases sharply with increasing levels of catalyst up to about 2.5% but becomes less sensitive to changes in concentration above this value.

Reference to Figure 2 demonstrates that the rapid curing and high adhesive sensitivity to relatively low concentrations of applied catalyst. In contrast, the corresponding adhesive with a commercially available aldehyde-aniline condensate, Loctite Activator 7380, exhibits a comparable cure speed when about 50% by weight of dissolved activator is used with the oil-activator solution applied at the same rate.

In order to estimate the curing rates and the ultimate adhesive strength that can be attained at ambient temperature, lap-shear tests were conducted on adhesive formulation TA-2 in combination with CN-oil based-activators over a four-hour period. In all cases the activators were applied at the standard rate by dip- coating and the bondline gap was set at 10 mils. The data (shown in Figure 3) shows that curing rates and the extent of cure increase with catalyst concentration. The results further highlight the sensitivity of the curing system to relatively low levels of catalyst. At catalysts levels of as low as about 0.5% by weight of oil, the specified strength can be obtained in slightly over 1 hour at room temperature. At 10 mil gap, the volume fraction of oil- activator, applied at standard rate (0.13 mg/cm²), to the combined adhesive and activator is approximately 0.5% (assuming all densities are 1 g/cm³) . Since the catalyst concentration in the oil is in the range of about 0.5 to 5.0%, the effective catalyst concentration in the curing adhesive is in the range 25-250 ppm. For CN, which contains 8% Cu, the corresponding metal concentration is about 2 to 20 ppm. As the bondline gap increases, the metal concentration is further decreased, since the application rate of the activator remains constant.

Catalyst on-part life

On-part activator lifetime for panel closure is specified by the end user, and in some cases is 30 days under ambient conditions. Accordingly, since the inventive composition, which is applied ordinarily as a thin layer (about 1-2 μm) , should be stable with respect to atmospheric oxidation and humidity, and inert with respect to the drawing oil and the metal surface of the panel.

To determine the extent of catalyst activity loss in CN/oil films, a solution of 2.5% CN in PARCO 404 was applied to aluminum lap-shear panels at the standard application rate (0.13 mg/cm²) by dip-coating. The panels were then stored under ambient conditions for up to four weeks. At various intervals adhesive joints were assembled using the prototype TA-3 adhesive at bondline gap of 10 mils and the lap-shear strength determined after 30 minutes RT curing. The results are shown in Figure 4.

Although a small reduction in adhesive strength was observed over the duration of the test, the results indicate the CN catalyst retains most of its original activity over the duration of the 28-day test period. Clearly it is resistant to oxidation and stable to normal levels of humidity under ambient storage conditions in thin film form. Although the adhesive strength falls slightly below the specified value of 400 psi after 4 weeks, it is expected that this can be adjusted by increasing the CN concentration or by modifying the adhesive formulation.

Cure through gap

While the average bondline gap after panel closure is 10 mils (0.25 mm), the specification requires curing and adhesive performance at gaps up to 30 mils (0.76 mm) . All of the adhesive tests described above were performed with the bondline gap set at 10 mil. To evaluate the influence of bondline gap on the adhesive strength, testing of the prototype adhesive TA-3 with CN/oil catalyst was also performed over a range of different gap sizes from 5 to 30 mils following 30 minutes RT cure. The results obtained for activator containing 2.5% CN in oil are presented in Figure 5. As expected, the strength decreases with increasing gap size and falls below the specified value of 400 psi when the gap exceeds about 11 mils.

By extrapolation of the plot in Figure 5, it can be predicted that no strength would be obtained for a bondline gap of 30 mil after curing under these conditions. However, if the curing time is extended to 2 hours, then values in excess of 300 psi can be obtained at a gap of 30 mils. (See Figure 6.)

In terms of the curing time required to meet the minimum specified strength, the cure-through-gap properties of the adhesive system TA-3 and activator 2.5% CN applied at standard rate is 11 mils after 30 minutes and 27 mils after 2 hours.

Thermal stability and ultimate strength

The adhesive should have a cured strength greater than 1500 psi after processing through a thermal paint-bake cycle of 1 hour at 200°C. To test conformance of the new adhesive systems to this requirement, lap- shear joints at 10 mil gaps were assembled; allowed to cure at RT for four hours and then heated at 200°C for 1 hour. After cooling to ambient temperature the adhesive strength was determined in the usual manner. Formulations TA-2 and TA-3 were evaluated with dilute oil solutions of catalysts CN and CEH applied at standard rate by dip-coating, and compared with Product 332 (a commercially available toughened acrylic adhesive from Loctite Corporation, which is included here for comparative purposes) and Product 7380, which was applied at the same rate but without oil. The results are presented in Figure 7.

The experimental composition TA-2 fails to meet the minimum requirement of 1500 psi after heating 1 hour at 200°C, irrespective of the catalyst or catalyst level employed (formulations A, B, and C) . However, experimental composition TA-3 in combination with 5% CN catalyst (formulation D) , exceeds the minimum value and demonstrates that the inventive adhesive composition system can meet the requirements of the paint-bake cycle. The effectiveness and reactivity of the new product is clearly demonstrated by comparing the formulations A-D to the control sample (formulation E) in which Product 7380 is applied without oil, i.e., at 100% level. In all cases, the adhesive strengths of the new materials are within about 80-95% of the value of 332/DHP system, but employ levels of activator/catalysts that are 20-40 times lower than the standard product. This data also shows that both the 332/DHP and TA-3/CN systems exceed the minimum value by only a small margin.

Stability tests

The 82°C stability of TA-3 was found to be 2-3 hours at 82°C. The common value specified for anaerobic adhesives is 2 hours. Therefore, the inventive compositions have acceptable shelf life for commercial applications .

The inventive adhesive composition conforms to the requirements for activator on-part lifetime, thermal resistance and ultimate strength when the activator is applied at levels that are typical for drawing/stamping oils. In addition, the adhesive meets the 30-minute room temperature cure speed and adhesive strength development at a bondline gap of 10 mils. However, when the gap size is increased, cure speed and strength development decrease. At 20-mil gap, a RT cure time of about 1-hour is required to develop 400 psi of lap-shear strength. At 30-mil gap, the equivalent time is in excess of 2 hours. Preliminary accelerated testing indicates that the prototype products have sufficient shelf-stability under ambient storage.

The spirit and scope of the invention is defined by the claims.

Claims

What is Claimed is :

1. A radical curable system, comprising:

(a) a first component, comprising a reactive composition, comprising

(i) a (meth) acrylate component, and (ii) a radical cure-inducing composition; and

(b) a second component, comprising (i) a lubricating oil, and (ii) a catalyst.

2. The radical curable system according to Claim 1, wherein the second component is applied to at least one substrate prior to bonding the at least one substrate with an other substrate with the first component which is applied to at least a portion of either or both of the at least one substrate or the other substrate .

3. The radical curable system according to Claim 1, wherein the (meth) acrylate component is represented by H₂C=CGCO_Rι, wherein G is a member selected from the group consisting of hydrogen, halogen or alkyl of 1 to about 4 carbon atoms, and Ri is a member selected from the group consisting of alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkaryl, aralkyl and aryl groups having from 1 to about 16 carbon atoms, any of which may be optionally substituted or interrupted with a member selected from the group consisting of silane, silicon, oxygen, halogen, carbonyl, hydroxyl, ester, carboxylic acid, urea, urethane, carbamate, amine, amide, sulfur, sulfonate and sulfone.

4. The radical curable system according to Claim 1, wherein the (meth) acrylate component is a member selected from the group consisting of polyethylene glycol di (meth) acrylates, citronellyl methacrylate, bisphenol-A di (meth) acrylates, citronellyl acrylate, tetrahydrofurane (meth) acrylates, tetrahydrofurane di (meth) acrylates, hydroxypropyl (meth) acrylate, hexanediol di (meth) acrylate, trimethylol propane tri (meth) acrylate, tetrahydrodicyclopentadienyl (meth) acrylate, ethoxylated trimethylol propane triacrylate, triethylene glycol acrylate, triethylene glycol methacrylate, and an acrylate ester corresponding to

wherein Rg is a member selected from the group consisting of hydrogen, and alkyl and hydroxyalkyl groups having from 1 to about 4 carbon atoms and

-C H, 0 c C ==C H_;

R₇ is a member selected from the group consisting of hydrogen, halogen, and alkyl groups having from 1 to about 4 carbon atoms;

R₈ is a member selected from the group consisting of hydrogen, hydroxy and

m is an integer equal to at least 1; n is an integer equal to at least 1; and v is 0 or 1, and combinations thereof.

5. The radical curable system according to Claim 1, wherein the radical cure-inducing composition is selected from the group consisting of anaerobic cure- inducing compositions, photoinitiators, heat cure catalysts, and combinations thereof.

6. The radical curable system according to Claim 5, wherein the anaerobic cure-inducing composition comprises one or more of saccharin, toluidenes, acetyl phenylhydrazine, cumene hydroperoxide and maleic acid.

7. The radical curable system according to Claim 1, wherein the lubricating oil of the second component is selected from the group consisting of drawing oils, stamping oils, and lubricating oils.

8. The radical curable system according to Claim 1, wherein the catalyst of the second component is a transition metal complex.

9. The radical curable system according to Claim 1, wherein the catalyst of the second component is a transition metal complex selected from the group consisting of

II wherein R₂ and R₃ may be the same or different and may occur at least once and up to as many four times on each ring in the event of a five-membered ring and up to as many as five times on each ring in the event of a six- membered ring;

R₂ and R₃ may be selected from H; any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms, such as CH₃, CH₂CH₃, CH₂CH₂CH₃, CH(CH₃)₂, C(CH₃)₃ or the like; acetyl; vinyl; allyl; hydroxyl; carboxyl;

-(CH₂)_n-OH, wherein n may be an integer in the range of 1 to about 8; - (CH₂) _n-COOR₄, wherein n may be an integer in the range of 1 to about 8 and R₄ may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; H; Li; Na; -(CH₂)_n-ORs, wherein n may be an integer in the range of 1 to about 8 and R₅ may be any straight- or branched-chain alkyl constituent having from 1 to about 8 carbon atoms; or - (CH₂) _nN⁺ (CH₃) ₃ X^", where n may be an integer in the range of 1 to about 8 and X may be Cl^", Br^", I^", C10₄ ^" or BF₄ ^";

Yi and Y₂ may not be present at all, but when at least one is present they may be the same or different and may be selected from H, Cl^", Br^", I^", cyano, methoxy, acetyl, hydroxy, nitro, trialkylamines, triaryamines, trialkylphospines, triphenylamine, tosyl and the like;

A and A' may be the same or different and may be C or N; m and m' may be the same or different and may be 1 or 2; and

M_e is Fe, Ti, Ru, Co, Ni, Cr, Cu, Mn, Pd, Ag, Rh, Pt, Zr, Hf, Nb, V, and Mo;

III

wherein R₂, R₃, Yi, Y₂, A, A', m, m' and M_e are as defined above;

IV wherein R₂, R₃ and M_e are as defined above; and M_e[CW₃-CO- CH=C (0^") -CW'₃] ₂, wherein M_e is as defined above, and W and W' may be the same or different and may be selected from H, and halogens.

10. The radical curable system according to Claim 9, wherein the transition metal complex is a member selected from the group consisting of platinum (II) acetylacetonate; cobalt (II) acetylacetonate; cobalt (III) acetylacetonate; nickel (II) acetylacetonate; copper (II) acetylacetonate; iron (II) acetylacetonate; iron (III) acetylacetonate; chromium (II) acetylacetonate; chromium (III) acetylacetonate; manganese (II) acetylacetonate; manganese (III) acetylacetonate; copper (II) acetylacetonate; and combinations thereof.

11. The radical curable system according to Claim 9, wherein the transition metal complex is a member selected from the group consisting of copper naphthenate; copper (II) 2-ethylhexanoate; iron naphthenate; iron (II) 2-ethylhexanoate; cobalt (II) naphthenate; cobalt (II) 2- ethylhexanoate; and combinations thereof.

12. Reaction products formed from the radical curable system according to Claim 1, upon exposure to conditions in which air is substantially excluded therefrom under ambient temperature conditions.

13. A bonded assembly comprising:

(a) a first substrate;

(b) a second substrate; and

(c) a reaction product therebetween formed from the radical curable system according to Claim 1, wherein a portion of the radical curable system was applied to at least a portion of a surface of at least one of the first or second substrate prior to joining the substrates.