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METHOD OF BONDING SUBSTRATES

20240294804 ยท 2024-09-05

    Inventors

    Cpc classification

    International classification

    Abstract

    A method of bonding first and second substrates to each other the substrates having respective bonding surfaces to be bonded together, comprising: (a) applying to the bonding surface of at least the first substrate a redox-active metal catalyst primer to form a primed surface; (b) activating the primed bonding surface of the first substrate by exposing the primed bonding surface to actinic radiation; (c) applying, to the so activated bonding surface of the first substrate, and/or or to the bonding surface of the second substrate, a UV curable anaerobic adhesive; (d) mating the bonding surfaces together with the UV curable anaerobic adhesive therebetween; and (e) exposing the UV curable anaerobic adhesive between the mated surfaces to actinic UV radiation. The method is particularly suited for obtaining bonds with good tensile shear strength with electrical substrates coated with an insulating varnish.

    Claims

    1. A method of bonding first and second substrates to each other the substrates having respective bonding surfaces to be bonded together, comprising: (a) applying to the bonding surface of at least the first substrate a redox-active metal catalyst primer to form a primed surface; (b) activating the primed bonding surface of the first substrate by exposing the primed bonding surface to actinic radiation; (c) applying, to the so activated bonding surface of the first substrate, and/or or to the bonding surface of the second substrate, a UV curable anaerobic adhesive; (d) mating the bonding surfaces together with the UV curable anaerobic adhesive therebetween; and (e) exposing the UV curable anaerobic adhesive between the mated surfaces to actinic UV radiation.

    2. A method according to claim 1 wherein: step (a) comprises applying to the respective bonding surfaces of the first substrate and the second substrate a redox-active metal catalyst primer to form respective primed surfaces; and step (b) comprises activating the respective primed bonding surfaces of the first substrate and the second substrate by exposing those primed bonding surfaces to actinic radiation.

    3. A method according to claim 2 wherein step (c) comprises applying, to the so activated bonding surface of the first substrate, and to the so activated bonding surface of the second substrate, a UV curable anaerobic adhesive.

    4. A method according to claim 1 wherein the actinic radiation of step (b) has a wavelength of from about 10 nm to about 10,000 nm.

    5. A method according to claim 1 wherein the duration of the exposure to the actinic radiation of step (b) is from 1 to 300 seconds.

    6. A method according to claim 1 wherein the actinic radiation of step (b) has an intensity of 1 to 5000 mW/cm.sup.2.

    7. A method according to claim 1 wherein the total energy to which the primed bonding surface of the first substrate and/or the primed bonding surface of the second substrate is exposed during step (b) is from 1 to 300000 mJ/cm.sup.2.

    8. A method according to claim 1 wherein the actinic radiation of step (e) has a wavelength of from about 10 nm to about 10,000 nm.

    9. A method according to claim 1 wherein the duration of the exposure to the actinic radiation of step (e) is from 1 to 300 seconds.

    10. A method according to claim 1 wherein the actinic radiation of step (e) has an intensity of 1 to 5000 mW/cm.sup.2.

    11. A method according to claim 1 wherein the total energy to which the UV curable anaerobic adhesive is exposed during step (e) is from 1 to 300000 mJ/cm.sup.2.

    12. A method according to claim 1 wherein the redox-active metal catalyst primer comprises a redox-active metal catalyst selected from cobalt (II) naphthenate; copper carbonate; copper (II) acetylacetonate; silver nitrate; vanadium (III) acetylacetonate, iron (II) naphthenate, copper disodium ethylenediamine tetraacetic acid (EDTA.Math.2Na.Math.Cu(II)), vanadyl acetylacetonate, iron (II) acetate, or a combination thereof.

    13. A method according to claim 1 wherein the redox-active metal catalyst primer comprises a copper-based primer.

    14. A method according to claim 1 wherein the redox-active metal catalyst primer comprises at least one Cu II salt.

    15. A method according to claim 14 wherein the Cu II salt is selected from Cu acac (copper (II) acetylacetonate) and copper (II) ethyl hexanoate such as copper (II) 2-ethyl hexanoate and combinations thereof.

    16. A method according to claim 1 wherein the redox-active metal catalyst primer includes a the redox-active metal catalyst dissolved in a solvating agent, such as a reactive solvating agent for example a (meth)acrylate monomer such as hydroxy propyl methacrylate, methacrylic acid or propylene glycol dimethacrylate and combinations thereof.

    17. A method according to claim 1 wherein the redox-active metal catalyst primer includes an organic solvent.

    18. A method according to claim 1 wherein the redox-active metal catalyst primer comprises from 0.01 to 0.4% by weight based on the total weight of the solution, of an active redox-active metal catalyst.

    19. A method according to claim 1 wherein at least one substrate is a substrate with a coating thereon and further wherein the coating is a coating applied by curing a curable coating composition on that substrate.

    20. A method according to claim 19 wherein the substrate is steel optionally wherein the substrate forms a part of an electric motor.

    21. A method according to claim 19 wherein the coating is formed from an epoxy resin, a phenolic resin, including phenol/formaldehyde resins, or a polyurethane resin or combinations thereof.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0093] Embodiments of the invention will be described, by way of example only, with reference to the accompanying drawings in which:

    [0094] FIG. 1 is a plot of tensile shear strength in N/mm.sup.2 for C5 E-steel lapshears with an epoxy coating. The cure time was 24 hours. As indicated on the X axis the tensile shear strength was tested using different adhesive/treatment of lapshears/activator/UV combinations. In this respect AA=anaerobic adhesive, Act=activator, UV=ultra violet irradiation, laps=lapshears, Hy indicates hybrid. All the numbers on the X axis are product codes for commercially available Loctite? products. These Loctite? products are available from Henkel Ireland and other Henkel sites.

    [0095] FIG. 2 is a plot of tensile shear strength in N/mm.sup.2 for the substrates indicated and giving both comparative results (without using a method of the invention and labelled as Loctite AA3510+UV only) and results using a method of the invention (labelled as 4 step primer/UV process).

    DETAILED DESCRIPTION

    [0096] Described below is a series of experiments highlighting a method to improve adhesion of substrates that are provided with an electrically insulating coating such as adhesion of an e-coat steel substrate to another e-coat steel substrate.

    [0097] A method of bonding according to the invention was carried out. Comparative tests/methods were also carried out.

    [0098] The method of the invention comprises bonding first and second substrates to each other the substrates having respective bonding surfaces to be bonded together, comprising: [0099] (a) applying to the bonding surface of at least the first substrate a redox-active metal catalyst primer to form a primed surface; [0100] (b) activating the primed bonding surface of the first substrate by exposing the primed bonding surface to actinic radiation; [0101] (c) applying, to the so activated bonding surface of the first substrate, and/or or to the bonding surface of the second substrate, a UV curable anaerobic adhesive; [0102] (d) mating the bonding surfaces together with the UV curable anaerobic adhesive therebetween; and [0103] (e) exposing the UV curable anaerobic adhesive between the mated surfaces to actinic UV radiation.

    [0104] One irradiation source used was a Light Hammer? 6 UV system. This is a device that emits UV light.

    [0105] In all aspects of the present invention where actinic radiation is referred to the actinic radiation is from a light source specifically arranged to irradiate the substrate to be bonded, for example the source is within 1 metre thereof, for example within 30 cm thereof. So exposure means exposure to the actinic radiation from such a light source and does not include ambient light such as natural light, light from overhead lights etc.

    [0106] The substrates bonded were e-coated steel. In particular substrates of the materials mentioned above were utilised: Waelzholz M310-65A according to EN10106supplied with mill certificate to EN 102043.1 Waelzholz 2? AN8C5 classified. EN 10106 conforming electrical steel strip grades are standard grades for many traditional applications. These grades are defined as non-grain-oriented, finally annealed electrical steel strip. The dimensional tolerances conform to EN 10106. Lapshears used in the experiments were made of the C-5 materials and were 2.0-6.0 ?m thick per side and had dimensions 100 mm?25 mm?0.5 mm. (Mill Test Certificate (MTC), or Mill Test Report (MTR), is issued by a manufacturer to certify the chemical and mechanical features of a product and its compliance to the applicable norms and technical specifications. Typically, mill test certificates conform to the EN 10204 standard and are related to steel products. Certification of steel plates rolled in Europe is generally to EN 10204. The actual certificate will depend on the plate offered but will either be 3.1 or 3.2. A 3.1 or 3.2 MTC means that the actual plate or heat sold will have been tested and a Mill Test Certificate (MTC) will accompany the plate. AN8 is a coating applied by Waelzholz.)

    [0107] As above the coatings are filled organic and inorganic based varnishes typically applied to steel for increased insulation properties, resistance against annealing and/or improved weldability. Typical applications for these coatings are machines undergoing treatments like welding, Al-die casting or annealing.

    [0108] The UV curable anaerobic adhesive used in the testing was Loctite? AA 3510. (AA=anaerobic adhesive.)

    [0109] The redox-active metal catalyst primer used was Loctite? 7091. It includes an organocopper compound and reactive methacrylate monomer as solvent.

    [0110] The tests were carried out according to the following standards: [0111] (i) ASTM D1002-05 (Oct. 1, 2005) Strength Properties of Adhesives in Shear by Tension Loading (Metal-to-Metal) [0112] (ii) ASTM D3163 Strength Properties of Adhesively Bonded Rigid Plastic Lap-Shear Joints in Shear by Tension Loading [0113] (iii) ISO 4587 Adhesives-Determination of Tensile Lap-Shear Strength of High Strength Adhesive Bonds 5.1.4 DIN EN 1465 Adhesives-Determination of Tensile Lap-Shear Strength of Rigid-to-rigid Bonded Assemblies.

    [0114] For the tests above M310-65A C5 lapshears were used.

    [0115] The Light Hammer? 6 was used as an actinic UV radiation source. The Light Hammer? 6 was used for step (b) and (e) where indicated (Tables 1 to 3).

    [0116] Loctite? 7091 was applied to both lapshears to prime their respective surfaces.

    [0117] The Light Hammer? 6 was used to irradiate and activate the primed surfaces. Each primed surface was irradiated for 60 seconds at an intensity of approx. 5 W/cm.sup.2. It was used in the same way for step (e) where indicated (Tables 1 to 3). The output from the Light Hammer? 6 was measured using a Power Puck? as 5 W/cm.sup.2 in total (UVV 2.6 W/cm.sup.2; UVA 1.8 W/cm.sup.2; UVB 0.7 W/cm.sup.2; UVC 0.1 W/cm.sup.2.

    [0118] Loctite? 3510 was applied to one of the activated surfaces and the lapshears were mated together to form a mated laps shear assembly.

    [0119] Where indicated (Table 4) for step (b) and step (e) the UV source was a Loctite? UVALOC 1000 UV Cure Chamber. The mated laps shear assembly was placed in the Loctite? UVALOC 1000 UV Cure Chamber (UVALOC 1000). The bonded assembly was arranged so that the bond line on each side of the lapshears was irradiated for 60 seconds at an intensity of 200 mW/cm.sup.2.

    [0120] A series of tests were carried out as set out below.

    TABLE-US-00002 TABLE 1 (Comparative Examples) ACM-DUB-0031-52-02 ACM-DUB-0031-52-04 ACM-DUB-0031-52-01 1) Applied 3510 to 1) Applied 7091 primer ACM-DUB-0031-52-05 1) Applied 3510 to lapshears to lapshear 1) Applied 7091 primer lapshears 2) Clamped bonds and 2) Irradiated primed followed by Loctite 2) Clamped bonds and irradiate lapshear 3510 and clamp bonds. left to cure 3) Left to cure 3) Applied 3510 and 2) Left to cure overnight overnight clamped, left overnight overnight. No UV Sample 24 h @ RT N/mm.sup.2 1 1.53 0.62 5.32 2.88 2 1.42 1.03 6.19 2.74 3 1.19 1.12 7.95 2.90 Avg. 1.38 0.92 6.49 2.84 In Table 1 above: the ACM . . . codes are an identifier reference/code for respective tests. 3510 and 7091 are shorthand for the respective Loctite? products 3510 and 7091 discussed above. Each test was performed with three samples as labelled by Sample 1-3 above. The tensile shear strength results over the three tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-52-01 is a comparative test where the Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and left for 24 hours before testing. This test omits priming and all UV exposure steps. ACM-DUB-0031-52-02 is a comparative test where the Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2 and then left for 24 hours before testing. This test omits priming and UV activation of the primed surface steps. ACM-DUB-0031-52-03 is a comparative test where the Loctite? 7091 primer is applied to the lapshears. The primed lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is then applied to the activated primed lapshears and the lapshears are clamped together and then left for 24 hours before testing. This test omits irradiation of the lapshears after they have been brought together. ACM-DUB-0031-52-04 is a comparative test where the Loctite? 7091 primer is applied to the lapshears and the Loctite? 3510 is applied to the primed lapshears and the lapshears are clamped together and left for 24 hours before testing. This test omits all UV exposure steps.

    [0121] While some of the results are better than others the conclusion from Table 1 is that the tensile shear strengths are relatively low and it is desirable to achieve better tensile shear strengths. For example, it is desirable is to achieve a tensile shear strength greater than 10 N/mm.sup.2.

    [0122] Some further testing was carried out as set out in Table 2. Table 2 includes comparative examples and an example of the invention.

    TABLE-US-00003 TABLE 2 * ACM-DUB-0031-53-04 * ACM-DUB-0031-53-01 ACM-DUB-0031-53-02 1) Applied 7091 to 1) Irradiated lapshears 1) Irradiated the lapshears ACM-DUB-0031-53-03 lapshears for 60 s for 60 s 1) Applied 7091 primer to 2)Irradiated the primed 2) Applied 3510 and clamp 2) Applied 3510 and clamp lapshear lapshears bonds bonds 2) Irradiated primed 3) Applied 3510 and 3)Clamped bonds are left 3) Irradiated clamped lapshear clamped bonds overnight to cure - NO UV bondsfor 60 s, left 3) Applied 3510 and 4) irradiated bonds for 60 s of clamped bonds overnight to cure clamped, left overnight and left overnight to cure Sample 24 h @ RT N/mm.sup.2 1 1.71 1.55 4.67 12.70 2 1.71 1.76 6.06 10.00 3 2.05 1.41 5.54 10.70 4 1.49 4.05 5.96 9.40 5 3.76 4.62 12.10 Avg. 1.74 2.51 5.37 10.98 In Table 2 above: the ACM . . . codes are an identifier reference/code for respective tests. 3510 and 7091 are shorthand for the respective Loctite? products 3510 and 7091 discussed above. Each test was performed with four/five samples as labelled by Sample 1-5 above. The tensile shear strength results over the four/five tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-53-01 is a comparative test where the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and left for 24 hours before testing. This test omits priming and omits irradiation of the lapshears after they have been brought together. ACM-DUB-0031-53-02 is a comparative test where the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2 and then left for 24 hours before testing. This test omits priming. ACM-DUB-0031-53-03 is a comparative test where Loctite? 7091 primer is applied to the lapshears and the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and then left for 24 hours before testing. This test omits irradiation of the lapshears after they have been brought together. ACM-DUB-0031-53-04 is a test which is within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears and the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention.

    [0123] Some further testing was carried out as set out in Table 3 which includes a comparative example and an example of the invention.

    TABLE-US-00004 TABLE 3 ACM-DUB-0031-54-02 ACM-DUB-0031-54-01 1) Applied 7091 to lapshears 1) Irradiated the 2)Irradiated the primed lapshears for 60 s lapshears 2) Applied 3510 and 3) Applied 3510, clamped clamped bonds and bonds and irradiated bonds irradiated bonds for for 60 s and left overnight to 60 s, left overnight cure Sample 24 h @ RT N/mm2 1 3.57 9.21 2 3.22 10.40 3 3.75 13.50 4 3.67 12.90 5 3.02 10.60 Avg. 3.45 11.32 In Table 3 above: the ACM . . . codes are an identifier reference/code for respective tests. 3510 and 7091 are shorthand for the respective Loctite? products 3510 and 7091 discussed above. Each test was performed with five samples as labelled by Sample 1-5 above. The tensile shear strength results over the five tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-54-01 is a comparative test where the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2 and then left for 24 hours before testing. This test omits priming. This test is essentially a repeat of example ACM-DUB-0031-53-02. ACM-DUB-0031-54-02 is a test which is within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears and the lapshears are irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. This is essentially a repeat of example ACM-DUB-0031-53-04.

    Comments/Conclusions

    [0124] It can be seen that utilising a method of the invention a skilled person can achieve a target of at least 10 N/mm.sup.2. In tests carried out within the present invention there was instant fixture between the substrates.

    Further Testing

    [0125] In order to show that a range of intensities can be used, the inventors investigated using different a different UV source. The Light Hammer? 6 is a high intensity UV system. A UVALOC system is lower intensity. The aim was to illustrate a wide range of intensities (W/cm.sup.2), energy of total exposure (J/cm.sup.2) can be used to achieve high bond strength (>10 N/mm.sup.2).

    [0126] To do so they utilised the Loctite? UVALOC 1000 UV Cure Chamber, which is a high-performance modular curing system consisting of a cure chamber, lamp housing, and controller. The chamber has four rack levels to accommodate a slide-in tray that allows for easy positioning of parts of various heights at the level of optimum exposure. A perforated aluminium plate allows positioning of customized part holders. The lamp is shielded by a timed control shutter that eliminates UV exposure to operators during loading or unloading of parts. A door safety switch prevents opening while exposure is in progress. The cure time is controlled by the built-in timer and can be operated in a continuous or timed mode. The exposure cycle is triggered by footswitch, panel-mount start button, or PLC interface.

    [0127] Tests within the method of the invention and comparative tests were repeated using the UVALOC 1000 where for both irradiation steps the assembly was placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 for both steps. This achieved a desirable average tensile shear strength of 14.74 N/mm.sup.2.

    TABLE-US-00005 TABLE 4 ACM-DUB-0031-57-03 ACM-DUB-0031-57-04 ACM-DUB-0031-57-01 ACM-DUB-0031-57-02 1) Apply Loctite 7091 + 1) Irradiate lapshears for 60 s 1) Loctite 3510 - clamp 1)Loctite 7091 + Loctite Loctite AA 3510 2) Apply Loctite AA3510, bonds. No irradiation AA 3510 -no irradiation of 2) Irradiate clamped bond clamp bond and irradiate of lapshears clamped bond for 60 s for 60 s 2) Leave for 24 h @ 2)Leave for 24 h @ 3) Leave for 24 h @ 3) Leave for 24 h @ RT before testing RT before testing RT before testing RT before testing Sample 24 h @ RT N/mm.sup.2 1 1.84 2.22 5.24 2.12 2 0.77 2.50 2.47 3.36 3 1.12 1.96 3.63 0.97 4 2.47 6.71 1.61 5 1.54 6.49 1.25 Avg. 1.24 2.14 4.91 1.86 Std. 0.55 0.40 1.83 0.94 ACM-DUB-0031-57-05 1) Apply Loctite 7091 ACM-DUB-0031-57-06 2) Irradiate lapshears for 60 s 1) Apply Loctite 7091 3) Apply Loctite AA3510, 2) Irradiate lapshears for 60 s clamp bond and irradiate for 60 s 3) Apply Loctite AA3510, 4) Leave for 24 h @ clamp bond RT before testing 4) Leave for 24 h @ Sample 24 h @ RT N/mm.sup.2 RT before testing 1 14.80 9.87 2 15.20 9.34 3 15.30 6.47 4 15.90 5 12.50 Avg. 14.74 8.56 Std. 1.31 1.83 In Table 4 above: the ACM . . . codes are an identifier reference/code for respective tests. Loctite 3510 and Loctite AA 3510 are the same product. (AA = anaerobic adhesive). Loctite? products 3510 and 7091 are those discussed above. Each test was performed with three or five samples as labelled by Sample 1-5 above. The tensile shear strength results over the three/five tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-57-01 is a comparative test where the Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and the assembly was placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test omits priming and UV activation of the primed surface steps. It is comparable to test ACM-DUB-0031-52-02. ACM-DUB-0031-57-02 is a comparative test where the Loctite? 7091 primer is applied to the lapshears and the Loctite? 3510 is applied to the primed lapshears and the lapshears are clamped together and left for 24 hours before testing. This test omits all UV exposure steps. It is comparable to test ACM-DUB-0031-52-04. ACM-DUB-0031-57-03 is a comparative test where Loctite? 7091 primer is applied to the lapshears and the lapshears were placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and then left for 24 hours before testing. This test omits irradiation of the lapshears after they have been brought together. It is comparable to test ACM-DUB-0031-53-03 ACM-DUB-0031-57-04 is a comparative test where the lapshears were placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and irradiated using the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test omits priming. It is comparable to test ACM-DUB-0031-53-02. ACM-DUB-0031-57-05 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. It is comparable to test ACM-DUB-0031-53-04. ACM-DUB-0031-57-06 is a comparative test where Loctite? 7091 primer is applied to the lapshears and the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and then left for 24 hours before testing. This test omits irradiation of the lapshears after they have been brought together. It is comparable to test ACM-DUB-0031-53-03.

    [0128] By using a more directed UV irradiation step for the bonded assembly in particular it has been found that the tensile shear strengths can be even further improved.

    [0129] Further testing was carried out as follows (with results shown in FIG. 1): Each test was performed with three samples. All samples were allowed to cure at room temperature for 24 hours before testing. The average tensile shear strength results over the three tests were calculated and are shown in FIG. 1. Appropriate units for tensile shear tests are N/mm.sup.2. Each lap shear was of Waelzholz M310-65A and the overlap (bond area) is 322 mm.sup.2 unless otherwise stated. All lapshears were clamped together unless otherwise stated. The results shown in FIG. 1 are for the following tests in the same order. [0130] Loctite? AA 3510 is used as a control (without any UV exposure or priming). Loctite? AA 3510 has been applied to Waelzholz M310-65A as received and allowed to cure. As can be seen from FIG. 1 the tensile shear strength is low at less than 2 N/mm.sup.2. [0131] Loctite? AA 3510 and Loctite? 3038-part BLoctite? 3038 is a two-component acrylic adhesive designed to cure on low activity plastics such as polyethylene. The part B has been combined with Loctite? AA 3510 to investigate if there is any improvement in performance. Loctite? AA 3510 and Loctite 3038-part B were applied to different lap shear within a pair of Waelzholz M310-65A lap shears as received. The compositions were brought together when the lapshears were brought together and clamped together and allowed to cure. As can be seen from FIG. 1 the tensile shear strength is still low at less than 2 N/mm.sup.2. [0132] Loctite? AA 3510 with UV primed lap shear with Loctite? 3038-part BLoctite? 3038 is 2 component acrylic designed to cure on low activity plastics such as polyethylene. The part B component has been combined with Loctite AA 3510 to investigate if there is any improvement in performance. This differs from the previous test insofar as both Waelzholz M310-65A lap shears have been primed with Loctite? 3038 part B and exposed to UV light using the Light Hammer? 6 for 60 seconds at an intensity of approx. 5 W/cm.sup.2. Loctite? AA 3510 is then applied, clamped and allowed to cure for 24 hours. As can be seen from FIG. 1 the tensile shear strength is still low at about 7 N/mm.sup.2. [0133] Loctite? AA 3510 with Loctite? 7091 UV primed lap shear both sides Loctite? 7091 primer is applied to the lapshears and the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together, exposed to UV light from the sides in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2, clamped and then left for 24 hours before testing. This is a test that follows a method of the invention and as can be seen from FIG. 1 the tensile shear strength is much better at about 15 N/mm.sup.2. [0134] Loctite? AA 3510 with plasma treated lap shears-Both Lap shears have been plasma treated before bonding using a Tantec? Plasma treatment system. The lap shears have been exposed to the plasma for 0.5 seconds and 1 cm away from the tip. Loctite? AA 3510 has been applied to one of the pre-treated lap shears, the lap shears were clamped and allowed to cure for 24 hours. As can be seen from FIG. 1 the tensile shear strength is relatively low at less than 8 N/mm.sup.2. Furthermore, such treatment is undesirable as it tends to remove the insulation coating. [0135] Loctite? AA 3510 with grit-blasted lap shear specimens-Both lap shears have been grit-blasted before bonding. Loctite? AA 3510 has been applied to one of the pre-treated lap shears, the lap shears were clamped and allowed to cure for 24 hours. As can be seen from FIG. 1 the tensile shear strength is above the target value of 10 N/mm.sup.2, however such treatment is undesirable as it tends to remove the insulation coating. Loctite? HY 4070 is a two-component cyanoacrylate/acrylic hybrid with excellent bonding to a variety of plastics and metals. This has been used is used as a control (without any UV exposure or priming).

    [0136] It will be noted that using a UV anaerobic primer Loctite? AA 7091 and Loctite? 3510 with UV treatment in accordance with a method of the invention can improve bond strength on substrates for example e-coated C5 steel such as e-coated steelWaelzholz M310-65A according to EN10106supplied with mill certificate to EN 102043.1 Waelzholz 2? AN8C5 classified2.0-6.0 ?m thick per side 100 mm?25 mm

    [0137] E-coated steel to E-coat steel bonded with standard adhesive products produce low strengths as compared to those bonded using the method of the invention.

    [0138] Tests within the method of the invention and comparative tests were repeated using the UVALOC 1000 where for both irradiation steps the assembly was placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 for both steps.

    [0139] Various e-coated substrates were tested to compare with original e-coat Waelzholz M310-65A substrate.

    [0140] The following C5 e-coated steel substrates were comparatively tested using a method not within the present invention and then using a method of the invention: [0141] NO30-1500A Suralac 7000 [0142] M270-50AA Backlack Suralack 9000 (EB549) [0143] M270-35AA Backlack Suralack 9000 (EB549) [0144] M330-50 Backlack 2? PE 75 W [0145] Waelzholz M310-65A-blue/grey substrate [0146] Waelzholz M310-65A-Original

    TABLE-US-00006 TABLE 5 (Comparative tests) E-coated C5 substrate: NO30-1500A Suralac 7000 M270-35AA Backlack Suralack 9000 (EB549) M270-50AA Backlack Suralack 9000 (EB549) Reference ACM-DUB-0031-81-02 ACM-DUB-0031-82-02 ACM-DUB-0031-83-02 1) Loctite 3510 - clamp bonds. 1) Loctite 3510 - clamp bonds. 1) Loctite 3510 - clamp bonds. 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 3) Leave for 24 h @ RT before testing 3) Leave for 24 h @ RT before testing 3) Leave for 24 h @ RT before testing Sample 24 h @ RT N/mm.sup.2 1 0.07 3.88 6.47 2 0.31 3.43 3.18 3 0.56 2.43 3.02 Avg. 0.31 3.25 4.22 Std. 0.25 0.74 1.95 E-coated C5 substrate: M330-50 Backlack 2x PE 75 W Waelzholz M310-65A - blue/grey Waelzholz M310-65A Reference ACM-DUB-0031-84-02 ACM-DUB-0031-85-02 ACM-DUB-0031-86-02 1) Loctite 3510 - clamp bonds. 1) Loctite 3510 - clamp bonds. 1) Loctite 3510 - clamp bonds. 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 3) Leave for 24 h @ RT before testing 3) Leave for 24 h @ RT before testing 3) Leave for 24 h @ RT before testing Sample 24 h @ RT N/mm.sup.2 1 8.52 3.29 0.75 2 6.99 3.51 4.70 3 8.96 2.97 3.35 Avg. 8.16 3.26 2.93 Std. 1.03 0.27 2.01 In Table 5 above: the ACM . . . codes are an identifier reference/code for respective tests. Loctite 3510 and Loctite AA 3510 are the same product. (AA = anaerobic adhesive). Each test was performed with three as labelled by Sample 1-3 above. The tensile shear strength results over the three tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-81-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is a comparative C5 e-coated lapshear, NO30-1500A Suralac 7000. The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-52-02. ACM-DUB-0031-82-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is a comparative C5 e-coated substrate, M270-50AA Backlack Suralack 9000 (EB549). The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-81-02. ACM-DUB-0031-83-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is a comparative C5 e-coated substrate, M270-35AA Backlack Suralack 9000 (EB549). The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-81-02. ACM-DUB-0031-84-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is a comparative C5 e-coated substrate, M330-50 Backlack 2x PE 75 W. The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-81-02. ACM-DUB-0031-85-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is a comparative C5 e-coated substrate, Waelzholz M310-65A -blue/grey substrate. The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-81-02. ACM-DUB-0031-86-02 is a comparative test where Loctite? 3510 is applied to the lapshears and the lapshears are clamped together. The substrate is the original C5 e-coated substrate, Waelzholz M310-65A used in previous experiments described above. The clamped bond is exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm2 and left for 24 hours before testing. This test omits the primer and irradiation of the primed substrate. It is comparable to test ACM-DUB-0031-52-02.

    [0147] Tests within the method of the invention (which can be compared to those in Table 5) were repeated using the UVALOC 1000 where for both irradiation steps the assembly was placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 for both steps.

    [0148] Various e-coated substrates were tested to compare with original e-coat Waelzholz M310-65A substrate.

    [0149] The following C5 e-coated steel substrates were tested: [0150] NO30-1500A Suralac 7000 [0151] M270-50AA Backlack Suralack 9000 (EB549) [0152] M270-35AA Backlack Suralack 9000 (EB549) [0153] M330-50 Backlack 2? PE 75 W [0154] Waelzholz M310-65A-blue/grey substrate [0155] Waelzholz M310-65A-Original

    TABLE-US-00007 TABLE 6 (method of the invention) E-coated C5 substrate NO38-1500A Suralac 7000 M270-35AA Backlack Suralack 9000 (E8549) M270-50AA Backlack Suralack 9000 (EB549) Reference ACM-DUB-0031-81-06 ACM-DUB-0031-82-06 ACM-DUB-0031-83-06 1) Apply Loctite 7091 1) Apply Loctite 7091 1) Apply Loctite 7091 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 3) Apply Loctite AA3510, clamp 3) Apply Loctite AA3510, clamp 3) Apply Loctite AA3510, clamp bond and irradiate for 60 s bond and irradiate for 60 s bond and irradiate for 60 s 4) Leave for 24 h @ RT 4) Leave for 24 h @ RT 4) Leave for 24 h @ RT before testing before testing before testing Sample 24 h @ RT N/mm.sup.2 1 10.90 13.50 20.20 2 11.30 13.50 19.30 3 11.00 13.40 19.30 Avg. 11.07 13.47 19.60 Std. 0.21 0.06 0.52 E-coated C5 substrate M330-50 Backlack 2x PE 75 W Waelholz M310-65A - blue/grey Waelzholz M310-65A Reference ACM-DUB-0031-84-06 ACM-DUB-0031-85-06 ACM-DUB-0031-86-06 1) Apply Loctite 7091 1) Apply Loctite 7091 1) Apply Loctite 7091 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 2) Irradiate lapshears for 60 s 3) Apply Loctite AA3510, clamp 3) Apply Loctite AA3510, clamp 3) Apply Loctite AA3510, clamp bond and irradiate for 60 s bond and irradiate for 60 s bond and irradiate for 60 s 4) Leave for 24 h @ RT 4) Leave for 24 h @ RT 4) Leave for 24 h @ RT before testing before testing before testing Sample 24 h @ RT N/mm.sup.2 1 9.90 17.00 15.40 2 10.25 16.20 15.10 3 11.00 16.20 12.90 Avg. 10.38 16.47 14.47 Std. 0.56 0.46 1.37 In Table 6 above: the ACM . . . codes are an identifier reference/code for respective tests. Loctite 3510 and Loctite AA 3510 are the same product. (AA = anaerobic adhesive). Loctite? products 3510 and 7091 are those discussed above. Each test was performed with three or five samples as labelled by Sample 1-5 above. The tensile shear strength results over the three/five tests were averaged as indicated by Avg.. 24 hr@ RT N/mm.sup.2 indicates the tensile shear strength in N/mm.sup.2 after 24 hours at room temperature. ACM-DUB-0031-81-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. NO30-1500A Suralac 7000 is a comparative C5 e-coated substrate that was tested in this experiment. It is comparable to test ACM-DUB-0031-57-05. ACM-DUB-0031-82-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. M270-50AA Backlack Suralack 9000 (EB549) is a comparative C5 e-coated substrate that was tested in this experiment. It is comparable to test ACM-DUB-0031-57-05. ACM-DUB-0031-83-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. M270-35AA Backlack Suralack 9000 (EB549) is a comparative C5 e-coated substrate that was tested in this experiment. It is comparable to test ACM-DUB-0031-57-05. ACM-DUB-0031-84-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. M330-50 Backlack 2x PE 75 W is a comparative C5 e-coated substrate that was tested in this experiment. It is comparable to test ACM-DUB-0031-57-05. ACM-DUB-0031-85-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. Waelzholz M310-65A -blue/grey substrate is a comparative C5 e-coated substrate that was tested in this experiment. It is comparable to test ACM-DUB-0031-57-05. ACM-DUB-0031-85-06 is a test which falls within the scope of the present invention where Loctite? 7091 primer is applied to the lapshears which were then placed in the UVALOC 1000 and exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2. Loctite? 3510 is applied to the lapshears and the lapshears are clamped together and within the UVALOC 1000 are exposed to the irradiation for 60 seconds at an intensity of 200 mW/cm.sup.2 and then left for 24 hours before testing. This test includes all steps of the method of the present invention. Waelzholz M310-65A - Original is a comparative C5 e-coated substrate that was tested in this experiment. It is a repeat test of ACM-DUB-0031-57-05.

    [0156] The results of the testing above is shown in FIG. 2. In FIG. 2 the comparative results (from Table 5) are those shown on the left in each pair of columns while the results from using a method of the invention (from Table 6) are those shown on the right in each pair of columns. As can be clearly seen the results using a method of the invention are clearly better in all cases in achieving better tensile strengths.

    [0157] The above tests demonstrate that the process of the invention significantly improves tensile strength performance on a range of C5 e-coated steel substrates.

    [0158] The words comprises/comprising and the words having/including when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

    [0159] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.