CA1293470C - Obtaining enhanced bonding between surfaces by laser beam and adhesive - Google Patents

Abstract

ABSTRACT

The invention is a method for making an article containing an adhesively bonded joint by first placing the surfaces to be bonded in the path of an intense energy beam, such as a laser beam, for a short duration to modify the surfaces. Then an adhesive is applied to the modified surfaces and the joint is completed. The inventive method results in stronger and more durable bonds relative to untreated surfaces and relative to prior surface treatments such as solvent cleaning. The invention is also an article made using the above method.

Description

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OBTAINING ENHANCED BONDING BETWEEN
SURFACES BY LASER BEAM AND ADHESIVE

The present invention relates to a method for making an impro~ed adhesive bond.
A need has long existed for a method of enhancing the adhesive bonding characteristics o~
various materials. This need ha~ extended to enhancing the bonding characteristics of materials which are essentially clean surfaces, e.g., solvent cleaned surfaces, as well as enhancing the bonding characteristics of contaminated surfaces, e.g., surfaces covered with a protective coating such as a wax or oil coated surface. These needs have developed for examp~e out of the automotive and aircraft industries' dissatisfaction with current surface treatment techniques and bonding results.
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An elegant explanation of material treatment using energy beams comprising laser beams is contained in U. S. Patent 4,122,240 granted to Banas et al.
Figure 1 therein shows a plot of absorbed power density versus interaction time. At relati-~ely low absorbed power density applied for relatively long times, mater-ials can be heated to appreciable depths without melt~
ing the surface and thus can be subjected to "trans-formation hardening." At very high absorbed power density applied for extremely short periods of time to a surface coated with a thin layer of preferably black paint (which enhances absorption of the laser beam) surface vaporization of the paint is so violent that a shock wave of su~ficient amplitude moves through the material that can result in "shock hardening" (see U.
S. Patent 4,401,477 to Clauer et al.). ~t mid-absorbed power density applied for intermediate time periods, the irradiated material can be vapoxized to a signifi-cant depth for "hole drilling" applications. At lower power density applied for longer time periods, the material can be melted to significant depths for "deep penetration welding." Using approximately the same absorbed power density as in "deep penetration welding,l' but for shorter periods of time, Banas et al. achieved "skin melting." In skin melting a thin layer of the material irradiated is melted but not vaporized and then rapidly self-cooled.

Langen et al. in U. S. Patent 4,368,080 apply 0.5 to 16 joules/cm2 per pulse and a pulse time of from 1 to 100 microseconds to clean rust from metallic objects prior to painting. The power density used by Langen et al. is relatively low to prevent melting or vaporization of the parent metal, but high enough to ~z~
3 6~693-3892 vaporize the rust or to conver~ the rust to a form not detrimental to subsequent paint performance.
In Japanese published Patent Application No. 55~119181, published September 12, 1980, by Iuchi et al.~ a laser is used to remove oil from steel plates prior to painting. The oil ls compounded wi~h ligh~ absorbing chemicals to improve the efficiency of conversion of the light energy into heating the oil fllm and only the oil is vaporized, not the underlying steel. In Japanese published Patent Application ~o. 56-116867, published 1~ September 12, 1981, by Maeda et al., zinc galvanized steel sheets are pollshed to remove the zinc coating, irradiated with a laser beam to remove residual ~inc, phosphate treated and then painted.
Patent No. 211,801 from the German Democra~lc Republic claims a process for the modification of surface propertie~ of se~i-finished products and molded materials made of olefin copolymers. Examples of the process use ionizing radiation, such as corona discharge and energy beams from an electron accelerator, to heat the surface to a temperatuxe between 340 and 410K. Other forms of ionizing radiation are suggested without examples, such 2Q as ultraviolet, X-ray, gamma or laser radlation and particle radiation such as alpha or beta radiation. Improvement of the adhesiveness, printability, metallizability and varnishability is taught in this patent.
The present invention is a new utili~y for surfaces modified by an energy beam, e.g., a laser beam. This new utility is enhanced bonding characteristics using an adhesive to bond together at leaqt two surfaces, enhanced relative to a comparable 9~
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untreated surface or surfaces. In many cases, enhanced bonding characteristics are also shown to be achieved relative to a comparahle solvent washed surface or surfaces. The term "enhanced bonding characteristic~"
refers to a bond having at least one of the following - enhanced properties: at least a 20 percent stxonger bond as demonstrated by-a standard lap shear test; a more durable bond upon exposure to a sodium chloride solution/h`igh humidity environment as demonstrated using the durability/lap shear test of Example 4; a more durable bond upon exposure to moisture as demon-strated by at least a 25 percent shorter crack exten-sion in a modified standard crack extension wedge test;
a stronger bond as demonstrated by at least a 25 per-cent shorter initial crack in a modified standard wedgetest; at least a 25 percent longer time of immersion in a boiling water bath before debonding in the test of : Example 29; at least a 20 percent higher pull strength as demonstrated by the ASTM 1876-72 peet test; at least a 20 percent higher impact strength as demonstrated by a modified ASTM D-256-81 impact test; at least a 20 percent higher torque strength using the torque test of Example 30; or at least a 25 percent reduction in the area of bond failure at the interface between the adhesive and the bonded surface in any of the tests above with a co~mensurate increase in failure within the adhesive itself or in the bonded material.

Prior techniques for enhancing the bonding characteristics of materials include sandblasting, shot peening, brushing, pickling with acid, anodizing and washing with solvents, see for example, "Adhesives Technology Handbook," A. H. Landrock, 1985, Noyes .

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Publications, ISBN 0-8155-1040-3. All of these tech-niques have undesirable features such as waste disposal of spent chemica~s. Nevertheless, surface treatment usually results in enhanced bondability. For example, galvanized steel sheets formed into automotive door panels are generally coated wi~h a lubricant prior to forming to extend forming die life and ~o preserve the surface finish of the panel. ~owever, before the panel can be fastened to other parts with an adhesive, the lubricant usually needs to be removed from the panel, e.g., by washing with a solvent, for yet improved bondability. Often, even better bondability can be obtained by additionally roughening or etching the panel surface to be bonded by sandblas-ting and/or chemical treatment, such as a phosphate treatment. The present invention cleans the surface of a material and can also be used to vaporize or melt the material itself or otherwise modify ~he surface, said modified surface especially suitable for adhesion purposes.

Terms The term "magnesium-containing material"
means (1) magnesium or (2) alloys having ma~nesium as the predominant component.

The term "aluminum-containing material" means (1) aluminum or (2) alloys having aluminum as the predominant component.

The term 'Icopper-containing material" means (l) copper or (2) alloys having copper as the predomi-nant component.

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The term "titanium-containing material" means (1) titani~m or (2) alloys having titanium as the predomina~t componen-t.
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The term "coact" means the adhesive inti-- 5 mately associates with the treated surface chemistry and/or topGgraphy. The-chemical association can include various chemical bonding phenomena and surface wetting phenomena. The topographical association can include load transfer between the adhesive ana the surface.

The term "stainless steel" refers to steel alloys having greater than lO percent chromium.

- The term "galvanized steel" refers to an alloy of iron which has been coated with a layer of zinc, cadmium or other similarly effective metal or metals in rontrolling the rate of corrosion of the steel itself.

The term "energy beam" refers to one or more electomagnetic radiation beams and/or one or more particle beams effective to modify the surface of a material. An example of an effective electromag~etic beam source in the invention is a laser. An example of a particle beam believed effective in the invention is an electron be~m.
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The term "material" relates to a solid sub-stance such as a metal, an alloy of metal, a metal composite, a metal laminate, a polymer, a polymer composite such as fiber reinforced polymer and com-~; posites comprising metals and p-olymers, as well as inorganic solids such as ceramics and semiconductors.

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-7- 1293~ ~0 Modi~ied surfaces having enhanced bonding characteristics have been observed to have one or more of the following surface modification effects: (a) a surface which has had any oil, wax, mold, release agent or other quch organic compound vaporized to produce a surface equivalent to a solvent washed surface; ~b) an altered surface of a metal or an inorganic material with the energy beam to produce a diminishme~t of surface carbon in excess of effect (a) above of at least 20 percent after said altering step as measured by x-ray photoelectron spectroscopy; ~c) an altered surface of a metal with the energy beam to vaporize at least 20 percent of the native metal oxide on the surface as measured by x-ray photoelectron spectroscopy; (d) a heated surface with an energy beam to melt the surface;
(e) a heated surface with an energy beam to not only melt the surface but also to vaporize it; (f) an altered surface with an energy beam to generate a roughened surface thereby generating load-bearing structures; (g) a heated surface to vaporize inorganic chemicals from the surface as measured by x-ray photoelectron spectroscopy; (h) an altered alloy composition of the surface as measured by x-ray photoelectron spectroscopy;
or (i) an increased oxide thickness by 20 percent or more after altering the surface as measured by x-ray photoelectron spectroscopy.
The invention is a method for making an article comprising an adhesive bond between at least two surfaces of said article, said method comprising the steps of: (a) placing at least one surface of said article in the path of an energy beam for a duration 32,850A-F -7-,, ~9;~ O

effective to modify said at least one surface; and ~b) contacting said at least one modi~ied surface with an adhesive comprising said adhesive bond, said adhesive being of a type effective to coact with said at least one modified surface to produce enhancement of the bonding characteristics of said adhesive bond.
A pre~erred energy beam source is a pulse laser and the specific energy density per pulse at the surface to be treated preferably is coordinated with the pulse time of the laser. For example, when the pulse time is between 1 and 100 nanoseconds, the energy density is preferably between 0.005 and 100 Joules/cm2 per pulse and more preferably between 0.05 and 10 Joules/om2 per pulse. Generally a 100 fo~d change in pulse time requires a corresponding 10 fold change in pre~erred energy density.
Another preferred energy beam source is a continuous wave laser and the specific energy density per time of treatment duration at the sur~ace to be treated preferably is coordinated with the treatment duration time for any one point treated on the surface.
For example, when the duration time is between 0.1 and 10 milliseconds, the energy density is preferably between 5 and 10,000 Joules/cm2 per duration time and more preferably between 50 and 1,000 Joules/cm2 per duration time. Generally, a 100 fold change in duration time requires a corresponding 10 ~old change in 3 preferred energy density.
Materials beneficially bonded by the method of the invention include polymers, metals and inorganic materials such as glass.

32,850A-F -8-.... .

` ` 9 ~334`~a3 The invention also includes an article made using the method of the invention.

The invention is also a method for preparing a surface formed of a material of a type capable of being treated to produce an enhanced bondable surface by using the method below, said method comprising the steps of: placing said surface in the path of a beam of electromagnetic radiation having an energy density selected to produce beneficial enhancement of the bonding characteristics of the surface; applying said beam for a duration effecive to modify the surface; and applying an adhesive of a type effective to coact with the treated surface to produce a stronger bond than with respect to the nontreated surface.

Brief Description of The Drawinqs Figure 1 shows an apparatus useful for the method of the invention.

Figure 2 shows photomicrographs of laser treated aluminum of Example 9.

Figure 3 shows photomicrographs of laser treated titanium of Example 12.

Figure 4 shows photomicrographs of laser treated silicone rubber of Example 19.

Figure 5 shows photomicrographs of laser treated tin of Example 20.

Figure 6 shows photomicrographs of laser treated graphite fiber reinforced epoxy composite of Example 21.
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Figure 7 shows photomicrographs of laser treated cold rolled steel of Example 22.

Fiyure 8 shows photomicrographs of laser treated copper of Example 23.

Figure-9 shows photomicrographs of laser treated molybdenum of Example 24.
'' ' Figure 10 shows photomicrographs of laser treated tungsten of Example 25.

Figure 11 shows photomicrographs of laser treated glass of Example 30.

An apparatus useful for modifying surfaces to be bonded accor~ing to the method of the invention is typically illustrated in Figure 1 and involves a laser 10 and means 14, 16 and 26 for guiding the beam rom the laser to the surface of the object to be treated.
:~ . A preferred laser 10 is a Q-switched Nd:YAG laser, but other lasers which are preferred include gas lasers, C2 lasers, and excimer lasers. The Kirk-Othmer "Encyclopedia of Chemical Technology," Third Edition, Volume 154, pages 42~81, John Wiley & Sons, New York : (1979), describes various types of lasers and their uses. The apparatus of thP invention may also comprise ;. one or more lasers or a laser with beam splitting means adapted for the purposes of the invention.
', The beam 34 issuing from laser 10 ca~ be altered by a harmonic generator 12 capable of reducing the wavelength of the beam proportional to a selected ~ .
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integral factor, and optical components, such as a prism 14 to spacially separate differing frequencies of the laser beam, a right-angle prism 16, and a preferred cylindrical focusing lens 26 which focuses the laser beam onto a surface to be'treated 30 and results in a - generally elliptical shaped area of surface treatment at any one time.- The length of said ellipse is deter-mined by the diameter of the laser beam and can be made longer by placin~ a dive~rging lens, not show~, in th~
laser beam 34 as is well known in the a'rt. The dotted line 34 between laser 10 and lens 26 can further repre-sent an optical fiber for directing the beam 34 at the surface to be treated.

- A power meter 24 can be disposed between the rlght-angle prism 16 and the ~ocusing lens 26. The power meter essentially has two parts, a detector head 18 integrally connected by means 22 with a con-ventional analog readout meter 20. The detector head 18 can be placed in the path of the laser beam to ` 20, detect the average power of the laser beam.

The cylindrical focusing lens 26 is disposed on a translation stage 28. The translation stage 28 includes a track for moving the l'èns 26 parallel to the path of the beam to focus and defocus the beam at the sample surface 30 to be treated. The translation stage 28 can be manually operated or operated by xobotic means or by a motor.

The sample to be treated 30 is disposed on a sample translation stage 32. The sample surface 30 is moved on the translation stage 32 relative to the ~, 3~L~JC~

beam 34. Preferably, the sample surface 30 is moved perpendicular to the beam 34. The translation stage 32 can be operated by a stepping motor 38 or, alterna-tively, by a robotic means or by manual means (not shown). Preferably the translation stage 32 is a - controlled X-Y translational stage or a combination -g translation stage-rotating wheel. SUCh items are easily available commercially, for example, from Velme~
Company in Bloo~field, New York. Other means of moving the energy beam relative to the surface to be treated can include optical fibers attached to robot arms that have 2-6 degrees axis of freedom or industrial grade X-Y-Z gantry style platforms. It is convenient to control translation stage 32 with a driver 40 which in turn is operated by a computer ~2. The computer 42 can easily control the number of pulses per area or the treatment duration when using a continuous wave laser on the surface 30 and the amount of overlap between successive areas treated may be easily regulated. As long as the energy density for treating the surface is maintained, the relative movement between the laser beam path and the surface to be treated can be as fast as possible. Preferably, each area treated overlaps at least somewhat with the area treated previously. In many embodiments of the invention where there is a visible change in the surface resulting from the laser treatment, it is preferable that there is an overlap of the visibly affected areas from those areas previously treated. In ~he case of polymer materials, it is generally believed that the depth of apparent vapor-ization of the polymer is preferably deep enough to (a) remove any mold release agents, (b) roughen the surface, or (c) expose the fibers which can then bene-ficially interlock with the applied adhesive. Once the 13 3L ~3~'~

sample 30 has passed through the beam 3a~ a beam block 36 can be used to trap the beam 34. The invention can also incorporate more than one energy beam, e.g., two or more lasers.

- 5 The energy beam or beams can be site-specific, that is, focused on a se-lected area of a surface, such as a metal surface with a high degree of accuracy to insure that the beams do not affect the appearance and/or other characteristics of neighboring surface~areas, namely, of areas which do not require any treatment or whose treatment is already completed. The amount of energy transferred to an area of surface may be controlled by focusing or defocusing the energy beam, controlling the - exposure time of the beam and adjusting the output power of the energy beam source. Any vaporized material may be easily exhausted from the treatment area using conventional exhaust, so as not to affect the health and/or comfort of the attendants and not to contribute to the pollution of the surrounding atmosphere.
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The energy beam source must satisfy certain criteria. The first criterion is that the enersy beam source must be capable of producing an extremely high energy density at the surface to be treated. For this invention, the critical parameter is absorbed energy rather than incident energy. However, absorbed energy is difficult to quantify and for the case where a laser is used as the beam source, the proportion of energy absorbed varies widely, for example, with differences in the material to be treated and the condition of the surface to be treated. The second criterion is that the absorbed energy must be converted into sufficient thermal .

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energy to vaporize and/or melt a surface layer of said material or to otherwise modify the topography and/or chemistry of the surface. The third criterion is that the energy beam applied to any specific area of the material must be applied for a relatively short time to control the depth of any melting or charring of the material. This ~riteria must be observ~d to preven~
melt through or burn through of the material to be treated.

Using either a pulsed laser or a continuous wave laser, or a plurality of lasers, the exposure time o~ the laser onto the object may be used to control the amount of energy directed to the surface of the object.
- The optimal exposure time and energy content of the energy beam depends upon the chemical composition of the surface of the object, the shape of the surace of the object, the surface roughness of the object, the movement of the surface of the object relative to the beam, the angle the beam strikes the surface of the object, the type of laser being used, and on the ulti-mate application desired for the object being treated.

The preferred type of laser used in the invention depends on the specific application. Among the preferred lasers for metal and polymer surfaces is a Q-switched Nd:YAG laser. Among the preferred lasers for ceramic and polymer surfaces is a pulsed or con-tinuous wave Co2 laser. It is believed that an excimer laser is also preferred for metal, polymer and ceramic surfaces.
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Generally when a longer pulse time laser is used, the amount of laser energy focused onto a given -15~ 3~

area per pulse needs ~o be increased. When using a laser having a pulse time between 1 and 100 nanoseconds, preferably the enersy density of each la~er pulse is in the range of from 0.005 to 100 joules/cm2, and more preferably in the range of from 0.05 to 10 joules/cm2 per pulse. When using a pulsed laser having a pulse time between 100 and 10,000 nanoseconds, prefer-ably the energy density of each laser pulse is in the range of from 0.05 to 1,000 joules/ cm2 per pulse and more preferably in the range of from 0.5 to :L00 joules/cm2 per pulse. When using a laser having a pulse time between lO and 1,000 microseconds, preferably the energy density of each laser pulse is in the r~nge of from 5 and 10,000 joules/cm2 per pulse and more pre~er-- 15 ably from 50 to 1,000 joules/cm2 per pulse. When us:Lng a laser having a pulse time between 1 and 100 micxo-seconds, preferably the energy density of each laser pulse is in the range of from 5 to 10,000 joules/cm2 per pulse and more preferably from 50 to 1,000 joules/cm2 per pulse. Similarly, when using a pulsed laser having a pulse time of 0.1 nanoseconds, it is believed that the preferred energy density of each laser pulse is in the range of from about 0.001 to about 5 joules/cm2, and more preferably from 0.01 to 1 joules/cm2 per pulse. When using a continuous wave laser, the relative rate of movement between the laser beam and the surface to be modified and the intensity of the beam need to be controlled to similarly achieve beneficial modification. When using a continuous wave laser and a duration of treatment between 0.1 and 10 milliseconds, preferably the energy density is between 5 and 10,000 joules/cm2 per duration time, and more preferably between 50 and 1,000 joules/cm2 per duxation time. When using a continuous wave laser and -16- ~Z9347~

a duration of treatment between 10 and 1,000 milli-seconds, preferably the energy density is between 10 and 20,000 joules/cm2 per duration time and more pre-ferably between 100 and 2,000 joules/cm2 per duration time. When using a continuous wa~e laser and a dura-- tion of treatment between 0.001 and 0.1 millisecond, preferably the energy density is between 0.5 and 1,000 joules/cm2 per duration time and more preferably be~ween 5 and 100 joules/cm2 per duration timè. When using a continuous wave laser and a duration of treat-ment between 0.01 and 1 microsecond, preferably the energy density is between 0.05 and 1,000 joules/cm2 per duration time and more preferably between 0.5 and 100 joules/cm2 per duration time.
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The determination of joules/cm2 per pulse is made by interrelating two measurements. The first measurement is a determination of the specific laser beam energy per laser beam pulse. This measurement includes the use of a laser optical power meter as is well known in the art. Generally, laser power meters ; show the average power of the laser beam in average watts. The number of average watts reported by the ; laser power meter is divided by the number of laser beam pulses per second to obtain the number of joules per pulse. The pulse time is that time over which about 66 percent of the beam energy is emitted by the laser. The second measurement is a determination of the area on the surface to be modified that is impacted i~ by the laser beam. This measurement is made by placing ii^ 30 Zap-It brand laser thermal sensitive paper (Kentek Inc., ~anchester, New Hampshire), or an equivalent paper, on the surface to be treated followed by * -r~ ~ ~ J~ ~f~ ~ ~

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examination of the resulting visible effect of a singl~
laser pulse. An envelope is dxawn around the visibly affected area of the pulse and the area of the envelope is calculated as is well known in the art of geometry.
Finally, the number of joules ~er pulse is divided by - the affected area in cm2 to obtain the joules/cm2 per pulse. - -The determina~ion of joules/cm2 per unit of treatment time for any one point a continuous wave laser is made by interrelating two measurements. The first measurement is a determination of the laser beam power per cm2. Using a laser optical power meter, the number of watts reported is divided by the area of the - surface treated by the laser at any one time as deter-mined above to obtain watts per cm2. The second measurement is a calculation of the duration o~
exposure o any one point. The width of the treated area in cm at any one time in the direction of surface movement relative to the laser beam is divided by the relative movement velocity in cm per second. Then the watts per cmZ is multiplied by the treatment duration to obtain the joules/cm2 per unit of treatment dura-tion.

The method of the invention can be used for enhancing the adhesion performance of any surface ~ormed of a material of a type capable of being treated with an energy beam to produce an enhanced bondable surface, such as a metallic sheet-forming surface, a polymer or a ceramic. Examples of such a surface include galvanized steel, an aluminum-containing material, or a magnesium-containing material. The .

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method has been generally observed to enhance metallic surfaces in the tests conducted by the inventors without being limited to a particular metal.

In some applications it is desirable to - 5 modify only one surface for enhanced bonding. For example, when bonding dissimilar surfaces, one~surface may reguire modification to enhance its performance to a level approximately equal to the other surface.
Additionally, it is sometimes desirable to modify only one surface to predispose a bond to fail in a pre-dictable and beneficial manner not unlike the desire ~ for rolled cellophane~adhesive tape to come off its - roll with the adheslve layer bonded to only one side of - the cellophane.

The invention can be used to bond different materials where both surfaces are treated. As an example, it is not generally possible to spot weld aluminum to steel while the present invention can be used to enhance the adhesive bonding of aluminum to steel, galvanized steel to glass fiber reinforced plastic (SMC), aluminum to SMC, and other dissimilar materials generally without limitation.

The specific àdhesive used is not critical in the invention as long as said adhesive coacts with the modified surface to produce an enhanced bond. Pre-ferred a~hesives which work within the scope of the in~ention include urethanes, acrylics and epoxies.
Gther adhesives which work within the scope of the invention include silicone adhesives, cyanoacrylates and thermoplastic hot melts like polyimides. Alter-natively, other hot melts, may work within the scope and teaching of the invention.
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The specific curing conditlons for the a &e-sive used in the invention are not critical. Generally, the curing conditions are recommended by the manufa--turer of the adhesive for a given application. Prefer-ably, the adhesive is applied to the mo,~ified surfacewith a minimum of delay in time. However, tests indi-cate that when a modified surface was k~pt covered (in a drawer), enhanced bonding performance was observed even when the adhesive ~as applied one week and later after surface modification.

With respect to the temperature at which enhanced bonding is proved by lap shear or wedge test-ing, said testing is generally done at room temperature - but can also be done at temperatures higher or lower than room temperature, e.g., at 180F or at 0F.

Wikh respect to the examples, the treated surface generally has appeared amenable to a wide variety of adhesives rather than appearing adhesive specific to particular adhesives.

Urethane based adhesives are well known and widely used to adhere plastic and/or metal adherends together. The choice o~ urethane adhesives over other adhesives is based in part upon their outstanding characteristics with respect to bond strength, chemical inertness, tensile strength and handling character-istics.

One component of a urethane based adhesive generally is an isocyanate-terminated prepolymer com-pound. Such a compound is normally prepared by react-- 30 ing a polyisocyanate with a polyhydroxy compound or .

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other compound containing labile hydrogen atoms that will give a positive Zerewitinoff test. The isocyanate group reacts with the labile hydrogen atom to form a urethane group. A molar excess of the isocyanate is added so that the resulting compound contains fre~
isocyanate groups.

The other component of the urethane based adhesive is generally a cross-linking mixture compris-ing an admixture of polyhydroxy compound free of iso-cyanate groups and selected urethane catalysts. Whenthe two components are admixed, for example, in a high shear mixing head and then applied to a surface, a reactive hydrogen can interact with a free isocyanate - group chain extended and cross-linked with an isocyanate~
terminated prepolymer to form a cured adhesive.

Other adhes.ives which work within ~he scope and teachings of the present invention include epoxy adhesives. A variety of epoxy adhesives work within the scope of the present invention including those which are rapidly curable at elevated temperatures and espe-cially adapted ~or use on automotive assembly lines to adhesively bond metal and/or polymeric parts. Numerous t~pes of epoxy adhesives exist on the market, such as the epoxy described in U. S. Pate~ts 4,459,398;
4,467,071; and 4,485,229. Epoxies and epoxy resins which have increased adhesive strength contemplated for use within the present invention include epoxy resin formulations which are either pure or contain additives which enhance the properties of the epoxy resin.
Exemplary enhanced epoxy resin compositions include those described in U. S. Patents 4,002,598i 4,011,281;
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4,139,524; 4,1g6,701; 4,147,857; 4,178,426; and 4,219,638. Curable epoxy resins which are polymerized by ionic addition mechanisms and ofter. reguire high curing temperatures and long setting times can be used within the scope and teachings of the invention.
Essentially, any epoxy adhesive capable of fQrming a tight polymer network, ~haracterized-bv durability, good adhesion, good water, chemical and/or heat-resistant qualities can be used within the scope of the invention.

Additionally, combinations of epoxies and -acrylic based adhesives can be used. For example, the adhesive described in U. S. Patent 3,684,617 dealing with an adhesive mixture of acrylic based monomer and epoxy resin can be used within the scope o~ the inven-tion. Also, a nonreactive composite adhesive described in U. S. Patent 3,994,764 may be used within the scope of the invention.

Acrylic adhesives can work within the scope and teachinss of the present invention. Acrylic adhe-sives which include polymers and copolymers formed from acryli~ and methacrylic acids and their derivatives can be applied to the laser treated surface and provide the enhanced bonding properties. It is anticipated that a variety o~ other adhesives will also have utility within the defined invention. These adhesives include carboxylic polymeric adhesives, polysulfide adhesives, phenolic resin adhesives, amino resin adhesives, ethyl-ene copolymer based hot melt adhesives, polyvinyl acetal adhesives, anaerobic adhesives, polyamide adhesives and polyethylenimine based adhesives.

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These adhesives can optionally contain other materials. Other optional ingredients which can be added to either component include thickeners~
stabili~ers, flame retardants, metal particles, fibers, fillers, thixotropes and the like. The adhesives which are usable within the scope and teachings of the present invention can be prepared by a variety of methods, e.g., one and/or two-part components using a variety of curing processes.
Adhesive materials can in ~ome cases be used in conjunction with a primer as is well known in the art. Here and in the claims such primers are considered to be adhesive materials.
Thc adhesive coating disposed on the surface of the material and treaSed in accordance with the inventive method, can Porm a more durable bond, as well as a stronger bond.
The invention can be carried out in alter-native environments, such as a protective atmosphere composed of nitrogen, or alternatively, an environment containing an inert gas, such as argon or alternatively ; 25 in an environment containing a reactive gas such as hydrogen. It is contemplated that the inventive method could be practiced in an atmosphere containing a mixture of gases which would enhance the treatment of the surface for enhanced bonding.
The novel features which are considered as characteristic of the invention are set forth in particular in appended claims. The apparatus for the 32,850A-F -22--23- ~93~ '~

practice of the method, both as to its construction and its mode of operation, together with additional features and advantages of the metnod will be best understood upon perusal of the follo~ing detailed description of certain specific embodiments with reference to the accompanying drawings as shown in the following examples and comparative- examples.

Example 1 The apparatus for treating an object for ' 10 enhanced adhesion includes a Q-switched Quanta-Ray~
Nd:YAG model no. DCR-2 laser which produces 30 pulses per second. The laser produces radiation at a wave-length of 1.06 microns with a maximum average power of - about ~8 watts.

The laser beam is directed at the object to be treated by a system of optical compo~ents. The components route and focus the beam. The components are constructed of high ~uality quartz, Sl- W grade.
The beam is directed by 90 degree prisms ESCO model no. 1125250 and focused to a line image about 1/2 inch long by a cylindrical 50 cm focal length lens, ESC0 model no. Bl-20100.

The objects to be treated, 1 x 4 inch solvent cleaned (the term "solvent cleaned" in this and all examples herein means rinsing three times with methyl-ene chloride unless otherwise indicated) 2024-T3 alu-minum alloy panels 1/16 o~ an inch thick, are placed in a holder on a translation stage synchronized with the laser pulse repetition rate and translated through the - 30 beam. The translation apparatus includes a Velmex ~ 'T~ ~. J~

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, ~
Unislide AgO00 series translation stage. The slide of the translation apparatus is driven by a stepping motor from Superior Electric, model M061-FD08. The stepping motor is controlle~ by a Superior Electric~model STM 103 controller and the controller is operated by a Commodore 64 computer for co~plex maneuvers or manually operated.

The panels are translated through ~le laser beam path at 18 mm/sec and the final 1/2 inch portion of each panel is treated. The lens to panel distance is 35 cm.

Four pairs of panels are treated at each of several energy density levels between 0.14 and 2.16 - joules/cm2 per pulse. Each panel pair is then bonded together applying a high strength two-part urethane 15 adhesive cured at 135C for 45 minutes (Dow~XPR no.
0544-00923-05-1 urethane adhesive systems) containing ; 0.5 percent, 0.004 inch diameter glass beads to insure an evenly spaced "glue line" as is wel- known in the art, only to the treated portion of each panel with a 1/2 x 1 inch lap joint of the panel ends. Table I
lists the lap shear strength (measured using ASTM test D-1002) of each pan~l pair so bonded in relation to laser energy density. The lap shear str~ngth of the panels treated with 0.8 to 2.3 joules/cm2 per pulse is about 50 percent higher than those with no treatment.
The lap shear strength shown in Table I is an average of four tests and generally such tests show a statis-tical variation ~relative standard deviation) of about ilO percent. Unless otherwise indicated, all examples herein involved testing in quadruplicate at any one laser energy density treatment.
~c/~ .,k .

-25- ~93~ ~

TABLE I
, hAP SHEAR TESTING OF LASER TREATED ALUMINUM
PANELS ~ONDED TOGETHER WITH A URE~NE ADHESIVE

~aser Energy Density, Joules/cm2 per pulse La~Shear Stren~h, psi O 2,300 0 4 2,200 0~6 2,500 0.8 3,300 1.0 3,800 - 1.2 3,~00 1.7 3,500 2.3 3,600 Exam~le 2 The apparatus of Example 1 is used in conjunction with 1 x 4 inch solvent cleaned magnesium panels 1/16 inch thick prepared as cold chamber die-cast magnesium alloys of type AZ 91B produced by The Dow Chemical Company. This alloy contains 9 percent alu-minum and 1 percent æinc. The sample to lens distance is 25 cm.

The samples are moved through the beam at a rate of 15 mm/sec. These magnesium alloy panels are then bonded and tested as in Example 1. The results listed in Table II show that lap shear strength increases with increased laser energy density. The bond stxength increases approximately 60 percent over that obtained from the untreated panels.

~. .

-~6- 12~

TABLE II

LAP SHEAR TESTING OF LASER TREATED MAGNESIUM
PANELS BONDED TOGETHER WITH A URE~NE ADHESIVE

Laser Energy Density, - 5 Joules/cm2_per ~ se La~ Shear Streng~h, :.
O - 1,200 0.1 1,600 0.3 1,700 0.4 2,000 0.8 1,800 1.2 2,200 Exam~le 3 The apparatus of Example 1 is used in connec-tion with 1 ~ 4 inch hot dip zinc galvanized steel panels (Deep DQSK, G-60 automotive grade) 1/33 inch thick. The panels are immersed in a water based oil emulsion, H. A. Montgomery no. DF-4285 and allowed to drain for a period of 15 to 45 minutes. The panels are translated through the laser beam at 7.4 mm/sec.
The sample to lens distance was SO cm.

These galvanized steel panels are then bonded and tested as in Example 1. The lap shear strength of the bonded panels versus the laser energy density is listed in Table III. Laser treatment in the energy density range of from 1.2 to 5.2 joules/cm2 per pulse produced an increase in bond strength of almost an order of magnitude over that of the untreated material.
.
.

, 27- 1~934'~

As the laser power increases to 1.2 joules/cm2 per pulse, the lap shear strength increases to about 2,000 psi and remains at about that level for higher laser energy densities. The lap shear strength of non-oiled solvent cleaned panels of galvanized steel isabout 1,300 psi.
.

TABLE III
.
LAP SHEAR TESTING OF LASER
TREATED OILED GALVANIZED STEEL PANELS
BONDED TOGETHER WITH A URETHANE ADHESIVE
Laser Energy Density, Joules/cm2 per pulse_ Lap Shear Strength, psi 1.2 1,000 1.4 2,100 . 1.9 1,700 .4 2,000 2.8 . 1,900 3.3 ~,100 5.2 2,000 Example 4 The apparatus of Example 1 also can be used to improve ~he durability of bonding. Thirty-two sets of 4 hot dip zinc galvanized steel panels axe first pre-:~ 25 treated with an oil emulsion as in Example 3. Two of the panels of galvanized steel in each set are then translated through the laser beam at 7.4 mm/sec using a sample to lens distance of 50 cm and a laser ener~y :;

-28- 1Z~3~

density of approximately 1.60 joules/cm2 per pulse.
The other two panels of each set are not treated with the laser and instead are solvent cleaned to remove the oil. Table IV shows the bond strength of laser treated and solvent cleaned panels bonded together as in Ex~nple 1 versus the length of time the panels are exposed to a - moist salty environment in a test known as the Generai Motors Scab Corrosion Test. This test is performed over a period of 32 days and involves testin-g the lap shear strength of the panels bonded as in Example 1.
This experiment involves 32 cycles, where for each cycle, the bonded panels are placed for 22.5 hours in a cabinet with a relative humidity of 85 percent and a temperature of 145F, followed by 0.25 hour immersion - 15 in a 5 weight percent NaCl solution in water and then 1~25 hours in a dry, room temperature area follcwed by a test of lap shear strength. After 7 cycles, the test results reveal that the untreated panels lost all lap shear strength and fell apart. In contrast, the laser treated panels maintain a bond for 32 days at a strength . of at least 500-600 psi.

-29~ 34~;~

TABLE IV

BOND DURABILITY UPON EXPOSURE TO
MOISTURE AND SALT FOR ~ASER TREATED AND
SOLVENT CLEANED GALVANIZED STEEL PANEL~

Lap Shear Strength Lap Shear Strength Days ofin psi for the in psi for the a Exposure Solvent Cleaned Panelsa Laser Treated Panels -0 1,30~ ~,000 1 600 1,400 4 600 1,400 7 0 1,300 14 0 1,300 1~ 28 0 500 a- Note, these data are the average of 2-3 determina-- tions.
~, Example 5 The apparatus of Example 1 is used in conjunc-tion with hot dip zinc galvanized steel panels (Deep DQSK, G-60 automotive grade) and an acrylic adhesive.
; (Hardman~red/white two-part acrylic adhesive, ~ured at - 325F for 30 minutes). The galvanized steel panels are treated with an oil emulsion as in Example 3 prior to laser treatment. The sample to lens distance is 35 cm, the sample translation is 15 mm/sec through the laser ~ T,'~Je _30_ ~29~

beam and the laser energy density is 0.6 joules/cm2 per pulse. The oily galvanized panels with no laser treat-ment before bonding have a bond strength of about 900 psi. The laser treated panels have a bond strength of approximately 1,600 psi. This result represents over a 75 percent increase in bond strength for the laser treated panels bonded with acrylic: adhesive in comparison with untreated panels bonded with acrylic adhesive.

Example 6 The apparatus of Example 1 is used in connec-tion with treating 1 x 4 inch panels of sheet molding compound (calcium carbonate/glass fiber filled poly-- ester resin containing zinc stearate as a mold release agent) 1/16 inch thick bonded with Hardman red/white two-part acrylic adhesive, containing 0.5 percent, 0.020 inch diameter glass beads, cured according to label directions. The panels are laser treated without any application of oil or other material to the surface 2Q of the panels. The lens to sample distance is 35 cm, the sample translation speed is 16 mm/sec and the laser ; energy density is 0.6 joules/cm2 per pulse. Polymer panels bonded without laser treatment have bond strengths of about 100 psi. The laser treated panels show a lap shear strength of about 500 psi. The increase in lap shear strength is greater than S00 percent for laser treated glass fiber filled polymer panels as compared to the untreated panels. Examina-tion of the laser treated surface by x-ray photoelec-tron spectroscopy indicated that substantially all ofthe mold release agent was removed by the laser treat-ment as measured by the diminishment of zinc from the surface after laser treatment.

-31- ~293470 In addi~ion, 1 x 4 inch panels of acrylonitri~e-butadiene-styrene (ABS) plastic sheet, 1/16 inch thick, are laser treated as above and bonded with either a Dow two-part urethane adhesive as in Example 1 cured at 150F for 30 minutes or bonded with Hardman red/white two-part acrylic adhesive cured at room temperature, containing 0.5 percent, 0.020 inch diameter glass beads, cured according to label directions. The lap shear strength of the laser treated panels is so high that the panels themselves break in testing at about a lap shear strength of 900 psi and for comparison the lap shear strength of the panels without laser treatment is about 400 psi.

- Example 7 In Examples 1-6 the test method is ASTM
D-1002 for lap shear strength. In this example and in many of the following examples the test method is wedge test ASTM D-3762, modified as describ~d below. In the modified ASTM D-3762 test, 1 x 4 inch metal panels 1/16 inch thick are bonded together with an adhesive and then a wedge is forced between the panels as sho-~n in Figure 3. The initial crack length is a function of several factors including the tensile strength of the \ bond. The bond strength can be so poor that the test panels fall apart, i.e., an initial crack length in excess of 3 inches. After measuring the initial crack length, the wedged panels, with wedge in place, are placed in a 49C, 100 percent relative'humidity envi-ronment for 75 minutes and then the crack growth after exposure (herein termed "crack extension") is measured.
If the bond has poor resistance to moisture, then the crack extension can be large and again if large enough the test panels can fall apart. The percent relative :: `

-32~ 3 ~t~'~

standard deviation precision of the wedse test is generally believed to be about ~ 12 percent.

The system of Example 1 is used to laser treat solvent clean~d 2024-T3 aluminum alloy p~nels.
The cylindrical lens is changed to one having a 25 cm focal length and the panels are placed-21 cm fEom this lens. Between the laser and the cylindrical lçns is placed a polarizing filter. By~adjusting the polar izing filter, different laser power can be directed upon the panels while operating the laser itself at full power (18 watts).

The panels are translated back and forth - through the laser beam at 12 mm/sec to completely treat one side of each panel with about a lSO percent overlap of each pulse treated area. The treated surace of each panel is then coated with American Cyanamid~epoxy primer no. BR-127, cured at 250F for 1 hour and bonded to an identically treated panel with 3M~epoxy adhesive no. AF-163-2, OST, Grade 5, cured at 250F for 1.5 hours under vacuum at 100 psi and wedge tested.
:
As listed in Table V, with no laser treatment the initial crack is about 37 mm and this crack grew about 30 mm upon exposure to moisture. At 0.7 to 1.6 joules/cm2 of laser energy per pulse, the initial crack is significantly reduced and the crack grew only about 2 mm to about 5 mm upon exposure to moisture; a signif-icant improvement in both bond strength and bond dur-ability upon exposure to moisture according to the wedge test.
7rcr Je Oarrk .
.

.

-33~ ~93 TABLE V

WED'~E TESTING OF LASER TREATED ALUMINUM
PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE

~ Laser Energy Density, Initial Crack Crack Joules/cm2 per pulse Length~ mm Extension, mm 0.0 37 30 0.7 12 ~ 5 0.8 12 2 1.1 13 2 1.4 12 2 1.6 12 2 Example 8 This is a comparative example of several prior axt surface preparation techniques. Panels of solvent cleaned 2024-T3 aluminum alloy are sanded with 80, 320 or 600 grit sandpaper (190, 29 and 17 microns, respectively), polished with 5 ~ alumina, sandblasted with 54 grit aluminum oxide, or wire brushed with 13 mil wire. The soxhlet cleaned panels are placed in a Whatman*LTD cel-lulose soxhlet thimble and sox~let extracted with tol-uene for 4 hours (~37 rinse cycles). The panels are then coated with American Cyanamid epoxy primer no.
BR-127 and bonded together with 3M epoxy a &esive no.
: AF-163-2 as in Example 7 and then wedge tested, see Table VI.
~ ~T,Qd~ ~nc"k _34- ~2~3~

TABLE VI

WEDGE TESTING OF SEVERAL PRIOR ART
SURFACE PREPARATION TECHNIQUES FOR ALUMINUM
PANELS BONDED TOGETHER WIT~ AN EPOXY ADHESIVE

Surface Treatn.ent Initial Crack Length ra k Extension 80 Grit Sandpaper 24 mm 21 mm 320 Grit Sandpaper 22 mm 22 mm 600 Grit Sandpaper 17 mm 15 mm Polished Surface 49 mm >27 mma-10 Sandblasted 15 mm 14 mm Wire Brushed 20 mm 15 mm - Solvent Cleaned 36 mm >41 mma-Soxhlet Cleaned 30 mm >~7 mma' a- Panels ~ell apart in the humidity cabinet.

The data in Table VI, when compared to the results obtained using the present invention, see Example 7, demonstrate the superiority of the present invention over the surface treatments listed in Table VI
; as indicated by the wedge test.

Exam~le 9 The system of Example 7 is used to again treat ; solvent cleaned 2024-T3 aluminum alloy panels except that the polarizing filter is removed and the laser power is adjusted as in Example 1. The panels are placed about 25 cm from the 25 cm focal length cylin-; drical lens.
.

_35_ ~ 2~ 3 ~7~

, The degree of overlap of the area covered by each laser pulse is about 150 percent. The pulse time of the laser depends on the power setting, being about 10 nanoseconds above 6 watts and from 10 to 40 nano~
: 5 seconds between 1/2 watt and 6 watts, see Table VII.

: TABLE VII

PULSE TIME OF THE LASER USED AS A
: FUNCTION OF ENERGY DENSITY AND o~rpuT POWER
, : Laser Power Laser Energy Density,Pulse Time in 10 in Watts/Sec Joules/cm2 per pulseNanoseconds 0.5 0.7 40 l 0.8 25 2 l.1 20 3 1.4 16 4 1.6 12 1.9 11 . 6 2.2 10 ` 10 3.3 10 ~: 15 4.7 10 18 5.5 10 :~
The data in Table VII is pro~ided to allow ~ conversion from laser power to energy density and pulse :~ time for the conditions described above. The following Table VIII shows example data of enhanced bonding char-acteristics.

`""' ' .

-36~

The treated aluminum panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M epoxy adhesive no. AF-163-2 as in Example 7 and -then wedge tested, see Table VIII.

TABLE VIII

WEDGE TESTIN~ OF LASER TREATED-.ALUMINUM
PANELS BONDED TOGEl~R WITH AN EP~.XY ADHESIVE

Laser Energy Density,Initial Crack Crack Joul~s/cm2 ~er pulseLen~th, mm Extenslon, mm 10 0.0 40 30 0.7 19 20 0.8 12 1.4 11 15 1.9 12 ~ 207 11 3 The data in Table VIII indicate that even at a laser energy density of 0.7 joules/cm2 per pulse, the bond strength and durability is improved relative to the nonlaser treated panels.

Figure 2 shows electron photomicrographs of aluminum treated with: (a) a single 0.8 joules/cm2 pulse, shown at 3,000X magnification; and (b) an alu-minum surface showing overlapping 2.7 joules/cmZ pulses, ~ 25 shown at 1500X magnification. These photomicrographs :~ show evi.dence o~ surface vaporization and/or surface ~`

-37~ 3~

melting along with roughening of the surface. X-ray photoelectron spectroscopy of the treated surfaces listed in Table VIII indicates that even at 0.7 joules/cmZ per pulse of laser energy density, the percent carbon on the surface of the aluminum is sig-nificantly diminished versus the untreated surface.

Optimization of economic factors using the invention can result from using full laser powex with a defocused laser beam to treat a larger~area of surface with each pulse. In this event, the linear velocity of relative movement between the laser beam and the surface to be treated can be higher and still effectively treat the surface for enhanced bonding characteristics.

Example 10 The system of Example 9 is used to treat panels o~ solvent cleaned 304 grade stainless stee~.
The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table IX.

~,~
~ TABLE IX

.
WEDGE TESTING OF LASER TREATED STAINLESS STEEL
PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE
.
Laser Energy Density, Initial Crack Crack ~ 25 Joules/cm2 per Pulse Length, mm Extenslon, mm ,~ .

1.4 17 7 2.7 8 5.5 17 3 ~38-~3~

The data in Table IX show that optimum bond strength as indicated by initial crack length requires a specific treatment power range while bond durability as indicated by crack extension is improved at all laser power levels tes~ed.
.
ExamPle 1-~
The system of Example 9 is used to treat panels of solvent cleaned hot dip zinc galvanized steel (Deep DQSK, G-60 automotive grade~. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table X.

TABLE X

WEDGE TESTING OF LASER TREATED GALVANIZED STEEL
PANELS BONDED TOGETEER WITH AN EPOXY ADHESIVE

Laser Ener~y Densit~, Initial Crack Crack Joules/cm2 per pulse Len~th, mm Extension, mm 0.0 11 2 . 1.~ 2 0.3 .2.7 2 0.2 5.5 4 0.3 The data in Table X show laser treatment improves both initial crack length and crack e~tension for galvanized steel under the condikions studiedO How-ever, it should be noted that the laser treated panels ,:

-39~

curled back upon wedge entry and thus the only conclu-sion believed to be shown by the data in Table X is t~at laser treatment improved bond strength.

. X-ray photoelectron spectrosc:opy of the 0 and 1.4 joules/cm2 per pulse treated panels indicates that b~fore laser treatment the surface contains about 70 percent carbon, and ~hat after treat~ent the surface is essentially 100 percent zi~c oxide.

Example 12 The system of Example 9 is used to treat panels of wire brushed and nonbrushed solvent cleaned Ti6Al4 titanium alloy. The treated panels are then - coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M epoxy adhesive no. AF-163-2 and then wedge ~ested, see Table XI.

T~BLE XI

: WEDGE TESTING OF LASER TREATED TITANIUM
PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE

Laser Energy Density, Initial CrackCrack ~;20 Joules/cm2 per pulse Lenqth, mmExtension, mm O O O 24a 36a-0.0 2ob- 8b.

2.7 22 4 5.5 24 11 :
Not wire brushed.
b- Wire brushed.

' ~' .

-40- ~3~

The data in Table XI show no improvement in bond strength at the laser powers tested as indicated by initial crack length. However, an improvement in bond durability is seen at 1.4 and 2.7 joules/cm2 per pulse of laser energy as indicated by the crack exten-sion data in Table XI.

Figure 3 shows electron photomicrographs of:
(a) the titanium alloy before laser tre~tment at 3,000X
magnification; and (b~ aftex laser treatment with a single 1.4 joules/cm2 pulse at 2,900X magnification that also shows evidence of apparent surface melting.
.

X-ray photoelectron spectroscopy of the 0 and - 3 watt treated panels indicates that before laser treatment the surface contains about 50 percent carbon and only about 2 percent titanium. After treatment the surface contains about 15 percent carbon and 19 percent titanium (present as titanium dioxide).

- Example 13 The system of Example 9 is used to treat panels of solvent cleaned 15 microinch surface ground cold rolled steel. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded to an identically treated panel with 3M epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table XII.

:~ :

,. ...

-41~

TABLE XII

WEDGE TESTING OF LASER TREATED COLD ROLLED STEEL
PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE

Laser Energy Density,Initial Crack Crack 5 Joules/~mZ per pulse Length, mm Exte~siGn, mm 2.2 22 2.7 2~ 6 3.8 23 7 5.5 22 7 The data in r~able XII show no significant improvement in either initial crack lenyth or in crack extension under the conditions studied. When the sol-vent cleaned ground cold rolled steel panels are treated as listed in Table XII, bonded using a urethane adhesive as in Example 1 and subjected to the lap shear testr no significant improvement in lap shear strength results.
Example 22 describes wedge testing of laser treated cold rolled steel panels and Example 28 describes lap shear testing of laser treated oily cold rolled steel panels.

Photo~icrographs o~ the 5.5 joules/cm2 per pulse laser treated ground steel surface showed a general smoothing of the surface, relative to the untreated ground surface, with evidence of overall apparent surface melting.

.

-42- ~g3~

E~ample 14 The system of Example 9 is used to laser treat panels of solvent cleaned mirror smooth chrome plated steel. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M epoxy adhesive no. AF-163-2 as in - Example 7 and then wedge tested, see Table XIII.
.

TABLE XIII

WEDGE TESTING OF LASER TREATED CHROME PLATED
STEEL PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE
Laser Energy Density, Initial Crack Crack Joules/cm2 per pulse_ Lenqth, mm Extension, mm 0.0 45 13 0~8 6 0 1.4 6 0 2.7 14 3 5.5 16 6 The data in Table XIII show that under the conditions studied both bond strength and bond dur-ability are improved by laser treatment as indicatedby the wedge test.

Example 15 The laser of Example 9 is replaced with an excimer laser having a waveleng~h of 0.249 micron, a pulse width of about 10 nanoseconds, a pulse frequency of 30 Hertz and a maximum power of 6 wat-ts. The excimer '' ~ 3 ~7~

laser is used to treat panels of aluminum, stainless steel and copper at a laser energy density of approxi-mately 10 and 0 joules/cm2 per pulse. The treated surface of each panel is then coated with ~merican Cyanamid epoxy primer no. BR-127 and bonded to an identically treated panel of the same metal with 3M
epoxy a &esive no. AF-163-2 and then wedge tested.
In each case, the laser treatment significantly enhances the bonding characteristics of the panels as indicated by the wedge test.

Example 16 The system of Example 9 is used to treat panels of solvent cleaned 2024-T3 aluminum alloy panels.
- In this example the Q-switch of the laser is turned off and as a result the laser pulse length is about 100 microseconds. The cylindrical lens is replaced with a conventional converging lens and the laser pulse is focused to a spot 0.6 mm in diameter on the object to be treated in order to compensate for the longer laser pulse length. The translation stage is controlled so that there is about 150 percent coverage of the panel surface with the laser pulses. The treated panels are then coated with American Cyanamid epoxy primer no.
, BR-127 and bonded to an identically treated panel wi-th 3M epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table XIV.

.. .- - . , .,, ~., _4g- ~293~70~

TABLE XIV

WEDGE TESTING OF LASER TREATED ALUMINUM
PANELS BONDED TOGEl~IER WITH AN EPO~ ADHES IVE

Laser Energy Density,Initial Crack Crack Joules/cm2 per pulse Len~th, mm Extension; mm S

140 3~ L8 .
The data in Table XIV indicate that signif-icant enhancement of bond characteristics was observed at the highest laser power studied as indicated by the wedge test. This example demonstrates the success~ul use of a relatively long pulse length laser in the invention.

15. Comparing the data in Table XIV (Q-switch off3 with the data in Table VIII and Table VIII (Q-switch on~
indicate that delivering a given laser energy density in a xelatively short pulse (Q-switch on) is more efficient than a relatively long pulse (Q-switch off).

Example 17 The s.ystem of Example 9 is used to treat ~ .
panels of solvent cleaned 2024-T3 aluminum alloy panels.
;~ The treated panels are then bonded together with Locktite Super Bonder~495 cyanoacrylate-type adhesive containing . .
0.5 percent, 0.004 inch diameter glass beads to insure an evenly spaced "glue line" as is well known in the art.
s~Trc~d~ ~,k .
. .
,: ,, .

., ..... , , .... .-`

TABLE XV

WEDGE TESTING OF LASER TREATED ALUMINUM PANELS
BONDED TOGETHER WITH A CYANOACRYLATE ADHESIVE

Laser Energy Density, Initial Crack Crack -Joules/cm2 per pulse_ Length, mm Extension, mm 0.0 54 ~ >23a 1.5 36 3 a- Panels fell apart in the humidity cabinet.

- The data in Table XV show that both the initial crack length and crack extension are improved with the laser treatment.
i Exa~le 18 The system of Example 9 is used to treat panels of solvent cleaned, Bonderized, ~phosphate treated) electrogalvanized steel. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 ; and bonded to an identically treated panel with 3M
epo~y adhesi~e no. AF-163-2 as in Example 7 and then wedge tested, see Table XVI.

-46~ 34~

TABLE_XVI

WEDGE TESTING OE LASER TREATED
BONDERIZED ELECTROGAr.VANIZED STEEL PANELS
BONDED TGGETHER WITH AN EPOXY ADHESIVE

- - S Laser Energy ~ensity,Initial Crack - Crack Joules/cm2 per Pulse Length, mm Extension, mm .
0.0 8.0 - 2.2 0.8 7.6 0.7 1.4 8.1 0.0 2.7 8.~ 0.0 5.5 6.7 0.4 The data in Table XVI indicate tha~ although bond strength was not significan~ly improved by laser treatment as indicated by the initial crack length, bond durability was significantly improved as indicated by the crack extension under the conditions studied.
.
Example 19 The system of Example 9 is used to treat detergent washed panels of Duro Inc. 50A red silicone rubber. The test panels are not the usual 1 x 4 x 1/16 inch, but rather are 1 x 4 x 1/8 inch. The . treated panels are then bonded together with 3M
icotch-Weld no. 2216 B/A flexible a &esive (3 parts "A" to 2 parts "B" by volume) cured 1 hour at room temperature and 1 hour at 180F and then subjected to the ASTM D-1876-72 peel test, see Table XVII.
~Tr~c/e ~ rk.

_47- ~2~3~ ~

TABLE XVII

PEEL TESTING OF LASER TREATED SILICONE RUBBER
PANELS BONDED TOGETHER WITH SCOTCH-WELD ADHESIVE

Laser Energy Density,Peel Strength Pounds Joules/cm2 per pul-seper Linear Inch - o . o 0 . 1 1.35 ~ a.3 5.5 13.6 The data in Table XVII indicate that the bond strength as indicated by the peel test was significantly improved after laser treatment.

Figure 4 shows 400X magnification electron photomicrographs of silicone rubber: (a) before laser treatment; (b) after overa~l treatment with 1.4 joules/-cm2 per pulse of laser energy; and (c) after overalltreatment with 5.5 joules/cm2 per pulse of laser energy.
Figure 4 shows evidence o~ apparent surface vaporiza-tion. Figure 4(c) shows evidence of general overall apparent surface vaporization and roughening.

Example 20 The system of Example 9 is used to laser treat panels of solvent cleaned pure tin. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M
epoxy adhesive no. AF-163-2 as in Example 7 and then peel tested using the ASTM 1876-72 peel test, see Table XVIII.

~ '.

-48- ~2~34~

TABLE XVI I I

PEEL TESTING OF LASER TREATED TIN PANELS
BONDED TOGETHER WIl~ AN EPOXY ADHESIVE

Laser Energy Density, Peel Strength, Pounds `oules/cmZ per pulse per Linear Inch ` 3 . 6 `
1.4 8.9 :~ 2-7 7.0 5.5 3.5 - 10 The data in Table.XVIII show that at the intermediate laser energy densities per pulse, the peel strength is significantly improved relative to no laser treatment.

~ Figure 5 shows 3, 000X magnification electron :~ 15, photomicrographs of tin: (a) before laser treatment;
:~ (b) after overlapping treatment with 1.~ joules/cm2 ~` laser pulses; and (c) after overlapping txeatment with 2 . 7 joules/cm2 laser pulses. Although there is no signifi,cant apparent difference between Figure 5(a) and 5(b), the data in Table XVIII indicates that the surface shown in Figure 5~b~ was apparently beneficially modi-fied even though,there is no apparent surface melting ;~ and roughening o~ the type shown in Figure 3(b) or Figure 2~a). Figure 5(c) does show evidence of apparent ~ ~ 25 surface melting and/or vaporization.

: .

~ '' ' .
~ .

~Z~3~

Exam~le 21 - The system of Example 9 is used to laser treat panels of solvent cleanec. aircraft grade graphite fiber reinforced epoxy composite panels, 4 x 1 x 0.040 ~- 5 inches, ~60 volume percent Hercules IM-6 graphite fibers, 40 volu~e percent epoxy resin~. The treated panels are bonded together with Hardman blue~beige urethane adhesive, containing 0.5 percent, 0.020 inch -glass spheres, and tested for lap shear strength using the ASTM D-1002 lap shear test. Another set of treated panels are ~onded together with Hardman yellow epoxy adhesive containing 0.5 percent, 0.020 inch diameter glass spheres, and tested for lap shear strength using the same test. The test results are shown in Table XIX.

~ Tr~ c/e /q'~a~iÇ

~50- 12~

TABLE XIX

LAP SHEAR TESTING OF IASER TREATED GRAPHITE FIBER
REINFORCED EPOXY COMPOSITE PANELS BONDED TOGETH~R
WITH A URETHANE ADHESIVE OR AN EPOXY ADHESI~E

-~ Lap Shear Lap Shear Laser Energy Density, Strength, psi Strength, psi Joules/cm2 per pulse_ Urethane Adhesive Epoxy Adhesive 0.0 2,800 1,845 1.4 3,020 --5.5 3,010 ~,350 The data in Table ~IX indicate that the laser treatment resulted in stronger bonds as indicated by the lap shear test or both adhesives at all laser energy densities per pulse studied but with a signficant improvement in lap shear strength shown only for the epoxy adhesive. Using the urethane adhesive without - laser treatment shows most of the bond failure at the interface between the adhesive and the panel, whereas with laser treatment the bond failure occurred mostly in the adhesive. Therefore, it is believed that the use of a stronger urethane adhesive would have resulted ln even higher lap shear test results than shown in Table XIX.
.
~` Figure 6 shows electron photomicrographs of the graphite fiber reinforced epoxy composite panels:
(a) before laser treatment at 400X ma~nification; (b) after overlapping treatment with 1.4 joules/cm2 pulses .
.

-51~

at 400X magnification; (c) after overlapping treatment with 5.5 joules/cm2 pulses at 400X magniXication; and (d) the same treatment as (b) above but at 3,000X
magnification.

Figure 6(a) sho~s the graphite fibers just under the surface-of the -epoxy resin. Figure 6~b) shows the expo-sure of the fibers, apparently due to vaporization of the epoxy resin around the fibers. Figure 6~c) shows in addition to the exposure of the fibers some apparent fiber damage that nevertheless does not appear to detract from bonding performance.

Example 22 - The system of Example 9 is used to laser -treat panels of solvent cleaned mill finish cold rolled steel ~surface not ground). The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded togethex with 3M epoxy adhesive no.
AF-163-2 as in Example 7 and then wedge tested, see Table XX.

,.
WEDGE TESTING OF LASER TREATED COLD ROLLED STEEL
PANELS BONDED TOGETHER WITH AN EPOXY ADHESIVE

Laser Energy Density, Initial Crack Crack Joules/cm2 per PuIseLen~th, mm _Extension, mm .
250.~ 26 24 0.8 13 2 1.4 12 2.7 12 2 5.5 ll 4 -52- lZ~3~7~

The data in Table XX indicate that the laser treatments studied resulted in stronger and more dur-able bonds as indicated by the wedge test relative to no laser treatment.

- 5 Figure 7 shows electron photomicrographs of the steel panels: (a) before laser treatmen~ at 400X;
(b) after treatment with overlapping 2.7 joules/cm2 pulses at 400X; (c) before laser trea~ment at 3,000X-magnification; and (d) after treatment with overlapping 2.7 joules/cm2 pulses at 3,000X magnification. Figure 7(b) and (d) show apparent surface melting and roughen-iny unlike the surface discussed in Example 13 and it is believed that the roughening shown in Figure 7(b) - and (d) may be partly responsible ~or the improved performance shown in Table XXI with laser treatment.

Example 23 The system of Example 9 is used to treat panels of solvent cleaned copper. In this example the ; panels are 1/8 inch thick instead of the more usual 1/16 inch thickness. The treated 1 x 4 inch panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded to an identically treated panel with 3M epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table XXI.

.

~53~ ~29~4~

TABLE XXI

WEDGE TESTING OF LASER TREATED COPPER
PANELS BONDED TOGETHER WIT~ AN EPOXY ADHESIVE

Laser Energy Density,Initial Crack Crack 5 -Joules/cm2 per pulseLen~th, mmExtension, mm 1.~ 47 3 2.7 30 8 5.5 47 12 - 10 The data in Table XXI show that optimum bond strength as indicated by initial crack length rec~uires a specific power range while bond durability as indi-cated by crack extension is improved at all laser power levels tested. In the wedge test, low yield strength materials such as copper require thicker panels (than the usual 1~16 inch thick panels) to prevent the panels from simply curling back as the wedge is inserted between ~ the bonded panels.
:
Figure 8 shows 3,000X magnification electron - 20 photomicrographs of the copper panels: (a) after laser treatment with a single 1.4 joules/cm2 pulse; and (b) after laser treatment with overlapping 1.4 joules/cmZ
pulses. Figure 8(a) and (b) show apparent surface melting and roughening after laser treatment.

_54- ~Z~3~ ~

Exam le 24 The system of Example 9 is used to laser treat panels of solvent cleaned pure molybdenum. The treated panels are then coated with American Cyanamid epoxy primer no. BR-127 and bonded together with 3M
epoxy adhesive no. AF-163-2 as in Examp:Le 7 and then ; wedge tested, see Table XXII.

TABLE XXII

WEDGF TESTING OF LASER TREATED MOLYBDENUM
PANELS BONDED TOGETHER WIT~ AN EPOXY ADHESIVE
Laser Energy Density,Initial Crack Crack Joules/cm2 per pulseLenqth, mm Extension, mm .
48 a.
1.4 23 a-152.7 35 a-a- Panels fell apart in the humidity cabinet.

The data in Table XXII indicate an optimum in bond strength enhancement at an energy density of 1.4 ioules/cm2 per pulse under the conditions studied as indicated by the initial crack length of the wedge test.

Figure 9 shows 400X ma~nification electron photomicrographs of the molybdenum panels: (a) before laser treatment; and (b) after laser treatment with 1.4 joules/cm2 pulses. Figure 9(b) shows apparent surface melting and roughening after laser trea~ment.

-55- ~ 29 3~ 3 Exam~le 25 The system of Example 9 is used to laser treat panels of solvent cleaned pure tungsten. The treated panels are then coated with American Cyanamid S epoxy primer no. BR-127 and bonded together with 3M
epoxy adhesive no. AF-163-2 as in Example 7 and then wedge tested, see Table XXIII. ' ~~

TABLE XXIII

WEDGE TESTING OF LASER TREATED TUNGSTEN

Laser Energy Density,Initial Crack Crack Joules/cm2 per PulseLength, mm Extension, mm -62 a.
2.7 47 a-a- Panels fell apart in the h~midity cabinet.

The data in Table XX~II indicate almost exactly a 25 percent reduction in initial crack length after laser treatment.

Figure 10 shows 1,500X magnification electron photomicrographs of the tungsten panels: (a) before laser treatment; and ~b) after a single 2.7 joules/cm2 pulse. Figure 10(b) shows apparent surface melting and roughening after laser treatment.

-56~ 3~7 Example 26 The system of Example g is used to treat 0O006 inch thick solvent cleaned aluminum foil panels.
The treated panels are bonded together with Dow Corning Silastic~732 RTV adhesive cured at room temperature for - 3 days at 70 percent relative humidity or with 3M
-Scotch Weld 2216 B/A epo~y adhesive cured for 1 hour at room temperature and l.hour at 180F both containing 0.5 percent, 0.004 inch diameter glass spheres, and then peel tested, see Table XXIV.

TABLE XXIV

- PEEL TESTING OF LASER TREATED
AL~MINUM FOIL BONDED TOGETHER WITH A
SILICONE ADHESIVE OR AN EPOXY ADHESIVE

Peel Strength Peel Strength Pounds per Pounds per Laser Energy Density, Linear Inch, Linear Inch, Joules/cm2 per pulse Silicone Adhesive Epox~ A &esive 0.0 0.2 8.0 1.4 7.2 13.8 The data in Table XXIV show that laser treat-ment significantly improves bond strength as indicated by the peel test for both adhesives tested.

Example 27 The system of Example 9 i5 used to treat 0.055 inch thick panels of solvent cleaned Ti6A14 titanium alloy with overlapping 1.4 joules/cm2 pulses.

~-rf c~ C~ ~ ~Y1" ~ k ~2~3~

The panels are bonded together with Langley Research Center Thermoplastic Polyimide primer and adhesive resin and tested for lap shear strength~ The primer coated panels are cured for 1 hour at 3~5F prior to applying the adhesive to the panels which is heated for 105 hours at 625F under vacuum at 200 psi to bond the panels together. For comparison, addi-t.ional panels are chromic acid anodized according to airc:raft industry standards and bonded together and tested as above. ~f all the prior art treatments for titanium alloy, the chromic acid anodizing process is o~ten preferred despite waste disposal considerations for the spent chromic acid bath liquors. The comparative data is shown in Table XXV.

TABLE XXV

LAP SHEAR TESTING OF hASER TREATED TITANIUM
PANELS AND CHROMIC ACID ANODIZED TITANIUM PANELS
BONDED TOGETHER WITH A THERMOPLASTIC POLYIMIDE ADHESIVE

Treatment Lap Shear Strenqth, psi Laser 4,640 Anodized 4,430 The data in Table XXV show that the laser treatment provides a stronger bond than the anodizing treatment but not a significantly stronger bond.
Importantly, the data show that the present invention approximately equals the best of the prior treatments for titanium alloy with regard to lap shear testing - without a problem of waste disposal of spent bath liquors.

~ . .

-58~ 3 ~70 The system of Example 1 is used to laser treat panels of oiled cold rolled steel. The panels are bonded together with a urethane adhesive as in Example 1 and then tested for la~ shear strength, see . Table XXVI.

- TABLE XXVI
.
LAP SHEAR TESTING OF LASER TREATED
OILY COLD ROLLED STEEL PANELS
BONDED TOGETHER WITH A URETHANE ADHESIVE
Laser Energy Density, Lap Shear - Joules/cm2 per Pulse Strength, psi 2.,200 0.8 2,500 1.1 3,600 1.4 4,200 1.6 5,500 1.9 4,200 2.2 5,200 2.7 5,000 3-3 4,200 4.0 3,200 .

The data in Table XXVI indicate that above a laser power density of about 1 joule/cmZ, a significant improvement in bond strength is observed with an apparent optimum in improvement around 2 joules/cm2. The lap - shear strength of solvent cleaned and nonlaser treated ' :, .~

~lZ~39,t7~

panels is about 4,500 psi. Therefore, tne improvements in bond strength shown in Table XXVI are believed to be at least partly attributed to a vaporization of the oil from the surface of t~e steel with the laser treatment.

Example 2g - - The laser of Exam~le 28 is replaced with a-100 watt (maximum) CO2 continuous wave :Laser. The cylindri~al lens is removed from the system and the -laser beam is instead focu~ed to a spot approximately OoO1 inches in diameter. The translation stage is adjusted to move the sample to be treated at a velocity of about 5 inches per second. The laser is adjusted for 50 watt output and thus the energy density of the - laser beam directed to any one spot on the sample to be treated is about 160 joules/cm2. The duration of exposure for any one spot to be treated is calculated to be about 2 milliseconds.

The above system-is used to laser treat 1 x 4 x 1/8 inch panels of plate glass with overlapping coverage of the treated areas (about 150 percent cover-age). The laser treated panels are bonded together with Hardman Kalex "Blue Urethane" two-part urethane adhesive with 0.5 percent, 0.020 inch diameter glass beads added to insure an evenly spaced "glue line." This adhesive is recommended by the manufacturer for use with glass and is rated as having a very good resistance to water.

The bonded panels are immersed into boiling water and examined periodically. After 24 hours of this exposure, none of the laser treated and bonded panels fell apart and could not be pulled apart by hand. For comparison, nonlaser treated panels bonded ~* If aJe ~1~k ~60- 1Z~3~ ~

as a~ove fell apart in the boiling water after 0.6 to 2 hours.

Example 30 The system of Example 29 is used to laser treat 1 x 4 x 1/4 inch panels of plate glass. A
stainless steel, General Motors approved automotive interior windshield mirror mount is bonded to the laser ~ treated glass surfac~ with ~ardman "Orange" two-part epoxy adhesive (which is recommended by the manufac-turer for bonding stainless steel to glass and is rated as having good water resistance) premixed with glass beads as in Example 29. A 1 x 4 x 1/16 inch carbon steel panel is bonded to the other side of the glass - panel with the same adhesive as above.

The bonded assembly above is immersed into boiling water for 4.5 hours and then subjected to the industry specified torque test, i.e., a torque wrench is attached to the mirror mount and the torque required to peel the mirror mount away from the glass is measured.
The mount could not be peeled away from the glass without actually breaking the glass (at about 150 inch pounds of torque) with failure occurring in the glass .itself with no failure at ~he a & esive/glass interface.
For comparison, a nonlaser treated glass panel was bonded, boiled and tested as above. The mirror mount cleanly peeled away from the glass at about 70 inch pounds of torque.

Figure 11 shows electron photomicrographs of the lasex treated glass panels: (a) before laser treatment at 400X magnification; ~b) after laser treat-ment at lOOX magnification; (c) before laser treatment ~ rrc~ Je YY~a rk , .

-61- 1293~ ~

at 3,000X magnific2tion; and (d) after laser treatme~t at 4,000X magnification. Figure ll(b) and (d) show apparent surface roughening.

Example 31 The system of Example 29 is used to laser treat 1 ~ 4 x ;/8 inch panels of Ashland Chemical Co.- -"phase alpha" sheet molding compound and the panels are bonded together with ~ardman ~'blue" acrylic adhesive which is recommended by the manufacturer for bonding fiber reinforced plastics. The adhesive is premixed with 0.5 percent, 0.02 inch (O.51 mm) diameter glass beads and the adhesive is cured for 1 hour at room temperature and then at 250F ~121C) for 1 hour. The bonded panels are tested for lap shear strength which averages 450 pounds per square inch (3.1 MPa) ancl the panel itself breaks without bond failure. Panels not laser treated but bonded as above have lap shear strengths averaging 160 pounds per square inch ~1.1 MPa) and the bond fails at the interface between the adhesive and the panel.

Exam~le 32 The system of Example 9 is used to laser ; txeat panels of 2024-T3 aluminum at a laser energy density of 1.4 joules/cm2 per pulse. The panels are bonded together (1/2 x 1 inch [12 x 25 mm] overlap of the ends of the panels as in a lap shear test) with -Hardman "blue/beige" two-part urethane adhesive, con-taining 0.5 percent, 0.004 inch (0.1 mm) diameter glass ~- beads cured as in Example 31. The bonded panels are then impact tested by General Motors side impact test ~modified from the ASTM D-256-81 impact test) wherein the pendulum impact head strikes at right angles to the ~ , .

-62~ lZ~347~

bond. The bonded panels show an average impact strength of more than 5 foot pounds. Nonlaser treated panels bonded as above show an average impact strength of 0.4 foot pounds.
Example 33 The system of Example 9 is used to laser treat 1/2 x 4 x 0.022 inch panels of gold clad Kovar~M
alloy at a la~er energy density of 1.4 Joules/cm2 per pulse. The gold thickness is 0.0025 inches (24 carat gold). The laser treated gold surface of the panels are bonded together with Dow Corning Sila~tic RTV-732 silicone adhesive containing 0.5 percent, 0.020 inch diameter glass spheres and allowed to cure for 2 days at room temperature and peel tested at a crosshead speed o~
2 inche~ per minute. The peel strength is 5.5 pounds per linear inch.
Without laser treatment but bonding as 2~ above, the peel strength is 2.0 pounds per linear inch.
Example 34 ~
A Gentec Model DD-250 TEA C02 laser is focused with a spherical ZnSe lens of focal length 100 mm to achieve the energy density indicated in Table XXVII. The pulse length of this laser has a peak including approximately 50 percent of the energy of 0.1 microsecond in length. The remainder of the energy is included in a tail approximately 1.0 microsecond in length. The results in Table XXVII indicate no improvement in initial crack, durability, or mode of failure with laser treatment approximately 5 Joules/cm2 per pulse.

32,850A-F -62-,~
, ~
~.~., --63- ~293~

TABLE XXVII
Laser Energy Density, Initial Crack Crack Material Joules/cm2 p~r pulse L~ mm Extension, mm Aluminum 0 36.1 3405 5.2 3~.8 42 _____________________ _______ __ _______________________ Cold 0 40 8.5 Rolled 5.2 40 7.6 Steel lO The following will reveal the gist of the present invention that others can, by applying current knowledge, be readily adapted for various applications without admitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this contribution to the art and, therefore, such adaptions should and are intended to be comprehended within the meaning and range or equivalence of the appended claims.

Claims (6)

1. A method for enhancing the bonding characteristics of an adhesive between two surfaces wherein one of them is a metal surface by modifying at least the metal surface with an energy beam generated by a pulsed laser to generate a roughened surface having load-bearing structures characterized in that the energy beam has a pulse time between 1 and 10,000 ns and the energy density is between 0.05 and 100 Joules/cm2 per pulse to melt and vaporize the surface and to control the depth of any melting or charring of the materials.

2. The method of Claim 1, wherein different materials are bonded and both surfaces are treated.

3. The method of Claim 1 or 2, wherein the second surface is a polymer.

4. The method of Claim 1 or 2, wherein the second surface is a metal.

5. The method of Claim 1 or 2, wherein the second surface is an inorganic material.

6. An article comprising an adhesive bond between at least two surfaces of said article prepared by a method according to Claim 1 or 2.
32,850A-F -64-