SURFACE TREATMENT

Abstract: The invention provides a process for treating a metallic or ceramic surface which comprises treating the surface with an organotitanate or zirconate or zircoaluminate or mixture thereof and exposing the treated surface to a laser.

Description: SURFACE TREATMENT The present invention relates to a process for treating a metallic or ceramic surface, particularly in order to improve its adhesion properties. Our published patent application WO96/23037 describes a process for treating cleaned aluminium surfaces in order to improve their adhesion properties which comprises treating the cleaned aluminium surface with an organosilane and exposing the surface to a laser. In a manufacturing environment it would be advantageous to provide improvements in adhesion without the requirement to first 'clean' the surface to be treated. Surprisingly it has now been found that pretreatment of a variety of cleaned or uncleaned metal surfaces with an organotitanate and/or an organozirconate or zircoaluminate in combination with laser treatment is valuable for the provision of improved adhesion. Accordingly the present invention provides a process for treating a metallic surface, which comprises treating the cleaned or uncleaned metallic surface with an organotitanate or organozirconate or zircoaluminate, or mixtures thereof, and exposing the surface to a laser. The clean or unclean metallic surface may be of any metal or metal alloy. Examples of suitable metals include steel, e.g. stainless steel, iron in ferrite form, aluminium, titanium, magnesium, copper, gold, nickel or chromium or an alloy of any of the said metals. The metallic surface may be treated with the organotitanate or organozirconate or zircoaluminate and the laser in either order. Preferably, however, an organotitanate or organozirconate or zircoaluminate is first applied to the metallic surface and the coated surface is exposed to a laser. - 2 - Also included within the present invention is a process wherein the metallic surface is exposed to a laser, coated with an organotitanate or organozirconate or zircoaluminate, or mixture thereof and then re-exposed to a laser. As herein before described the metallic surface used in the process of the present invention may be clean or unclean. For the avoidance of doubt, a cleaned metallic surface, as defined herein, means a degreased surface. Degreasing of a metallic surface may be achieved using any standard method including; wiping with a solvent such as acetone; vapour degreasing; dipping with or without ultrasonic treatment; or by using alkaline degreasing agents. The process of the invention can also be used to treat unclean metallic surfaces. An unclean metallic surface, as defined herein, means a surface which has not been subject to any specific cleansing regime, such as degreasing. Suitably 'unclean' metallic surfaces include soiled, dirty, oily, greasy, weathered and aged metallic surfaces. In addition to the metallic surfaces we have also found that the process according to the present invention is suitable for use in the treatment of ceramic surfaces prior to bonding or other adhesion properties of the surface are important. Ceramic as defined herein has its usual meaning and includes pottery, burnt clay, clay products and glass materials. Organotitanates suitable for use in the process of the present invention are compounds having the formula I: (RO) m — Ti — OXR 2 Y) n (I) Where: RO = monoalkoxy or chelate group X = carboxyl, phenyl, ethylene, sulphonyl, phosphate, pyrophoshate or phosphite group R 2 = isoheptadecyl, cumyl, ethylene, heptadecenyl, dioctyl, butyl octyl, butyl methyl, di-tridecyl, or octyl groups Y = methacryL acryl, aminoamino, amine, mercapto, vinyl or hydroxyl groups m = 1 or 4 n = 2 or 3 Preferred for use herein is the organo titanate having the following formula: O (C 8 H 17 0) 4 Ti HP(OCι 3 H 27 )J Zircoaluminates suitable for use in the process of the present invention are compounds of formula (II): | υ0ι HO /OH -Al ^ OH 0 0 RX (H) Where: X = primary amine, carboxy, mercapto, oleophilic, methacryloxy, or difunctional such as primary amine/hydroxy, methacryloxy/oleophilic, primary amine/secondary amine or mercapto/amine R = aliphatic chain -(CH 2 ) n - and n = 0 to 12 Preferred for use herein is the zircoaluminate having the following formula: - 4 - HO / \ / OH ~AI Zr OH c R(CH 2 ) 3 SH In the process of the present invention the organotitanate or organoizirconate or zircoaluminate, or mixture thereof, may be used in solution with water or an organic solvent. If water is used as the solvent and the organotitanate or zirconate or zircoaluminate is difficult to dissolve, a small amount of non ionic wetting agent may be added to the water before the organotitanate or zirconate or zircoaluminate addition. Alternatively, the organotitanate or zirconate or zircoaluminate may be used as an emulsion. Suitable organic solvents include alcohols, glycols, esters, ethers and aromatic hydrocarbons and mixtures thereof. Preferred alcohols are alkanols with 1 to 10 carbon atoms such as methanol, ethanol, propanol, hexanol and decanol. Preferred glycols are alkene glycols such as propylene glycol. Preferred esters are phthalate esters such as dioctyl phthalate. Preferred ethers are glycol ethers such as propylene glycol methyl ether. Preferred aromatic hydrocarbons are toluene or xylene. Water and/or carboxylic acid may also be added to suitable organic solvents as part of the solution. The solution may contain any concentration of organotitanate or zirconate or zircoaluminate preferably from 1 to 10% by weight of the organotitanate or zirconate or z coaluminate or mixture thereof, based on the total weight of the solution. The organotitanate or zirconate or zircoaluminate solution may be applied by any suitable method, for example, wiping, brushing or spraying on to the area(s) of the clean or unclean metallic surface to be treated. - 5 - Degreasing, when desired, of the metal surface, the application of organotitanate or zirconate or zircoaluminate solution and the laser treatment may all be carried out with automatic equipment such as robots. Any suitable laser may be used to treat the metallic surface either before or after the application of organotitanate or zirconate or zircoaluminate solution, e.g. at 400 mJ/pulse. Suitable lasers for use in the process of the present invention include, for example, excimer lasers and Q-switched Nd:YAG lasers. Others are well known in the literature and may be applied to the present process. For the avoidance of doubt a metallic surface may be pretreated as detailed herein and, provided, the treated surface is kept free from contamination, the laser treatment can be performed at a later time. For example, surfaces can be pretreated and left overnight before laser treatment. It has been found that it is advantageous, when using high treatment speeds (i.e. high energy conditions) to use an unfocussed laser . Selection of a unfocussed laser can limit damage to the metallic surface. The actual power level, of the laser, needed to avoid damaging the metallic surface depends on the actual particular under treatment and the specific laser used. This can be readily determined by simple experiment. After treatment of the metallic surface by the process of the invention, the surface is ready for bonding or other processing where the adhesion properties of the surface are important, for example coating or encapsulating. The bonding may be to another surface by means of adhesive or, by applying a coating to the surface. When bonding to another surface, that other surface may be metallic or non metallic. If the other surface is metallic, it too may be pretreated by the process of the present invention if desired. When the treated surface is bonded to another surface, this may be achieved using any adhesive such as 1 -component or 2-component epoxy or polyurethane adhesives. The process of the invention provides excellent joint performance, a fast treatment, a clean process, ecological advantages over conventional ''wet" processes and - 6 - sandblasting processes. Furthermore the process of the present invention allows for the use of a wide range of adhesives and makes local treatment of the areas to be bonded possible. A marked improvement in adhesion properties metallic surfaces can be obtained by the process of the invention. The present invention is illustrated by the following non-limiting Examples. Example 1 In this Example the metal used is an aluminium alloy (LI 65) in test strips (coupons) of 100mm x 25mm x 1.6mm which were tested using different surface conditions:- a) Uncleaned i.e. "as received" - this is the metal as dehvered from the supplier with no alteration of the surface at all. b) Clean i.e. "degreased" - the metal "as received" has undergone degreasing by means of a trichloroethylene vapour degreasing bath. Test coupons, suitable for lap shear specimens, mounted on the baseplate of a holding jig, were "primed" by the primer solution in a ~25mm stripe across one end of each row in the area to be bonded. The primer was a solution containing 90.0 parts by weight iso-propanol and 10.0 parts by weight of tetraoctyloxytitanium di(ditridecylphosphite) available from Kenrich Petrochem Inc., under the tradename KenReact KR46B (RTM). The primer was applied to the test coupons via a wipe with a pre-soaked paper towel. The primer was allowed to air-dry for 5 minutes at room temperature before being mounted on the X-Y stage of the laser. A jig was used to hold the specimens in place during exposure. The jig was mounted on a stage which moved at the given rate to expose a batch of 8 specimens in one pass. The laser used in this Example was a continuous wave Q-switched Nd-Yag laser (from Clean Lasersysteme GmbH) operating at a wavelength of 1064 nm; Traverse speed 950m/min; spot diameter 500 μm; scan width 35mm; average power 80W. The laser beam was raster scanned at a rate of 45Hz across the specimens to be treated using an attenuated mirror. A laser scan width of 35 mm translates to an area of 25 X 35 mm being exposed for each specimen (coupon). Three energy density levels of the laser, low, medium and high were used for each set of samples to give a spread of exposures. The energy density (fluence) was modified by altering the frequency of the laser. The following fluence figures were achieved: Frequency (Hz) Fluence (J/mm 2 ) Low power 30000 0.02 Medium power 22000 0.03 High power 16500 0.04 A jig was used to produce lap shear joints with consistent overlaps of 12.5mm x 25mm. The bondline thickness was controlled at 0.2mm using PTFE spacers. The adhesive was a one component epoxy paste adhesive which is butadiene- acrylonitrile rubber modified bisphenol- A epoxy resin using dicyandiamide and chlorotoluron as curing agents. All joints are given a cure of 30 minutes at 150°C. Control experiments without primer and laser pre-treatment were carried out to demonstrate the advantageous effect of the pre-treatment process of the present invention The lap shear strength of the prepared joints was determined according to ISO 4587 with the exception that the test speed is set at 10mm min "1 The lap shear strength was recorded and the failure mode recorded with reference to the descriptions given in ISO 10365. - 8 - The durability of the joints and the effect of the pre-treatment were also tested by carrying out an accelerated ageing test prior to determining the lap shear strength. The accelerated ageing technique employed is a 14 days Kataplasma Test which involves maintaining the samples at about 70°C under conditions of high humidity for 14 days followed by cooling to -20°C and storing for 2 hours after which the temperature of the samples is allowed to rise to ambient before being tested. In the tables presented below all the values quoted are in units of MPa for the lap shear strengths. A simple indication of the adhesive performance or bondability of the substrate can be obtained by observing the mode of failure of a lap shear joint. The following failure modes observed can indicate: AF - The indication of a poor interfacial adhesion between substrate and adhesive SCF - The interfacial adhesion is good and therefore the failure is nominally within the adhesive The following abbreviations were used describe the predominate type of failure observed for each set of test specimens in the following examples. AF = Adhesion Failure SCF = Special Cohesive Failure Control Experiment Results (Al alone) The results in Table I are expressed in terms of Nmm "2 (Mpa), with the failure modes noted as a percentage of the total bond area. Initial Kataplasma Clean LI 65 Al. 31.80 16.28 100% AF 100% AF Unclean LI 65 Al. 31.58 11.99 100% AF 100% AF Example 1 Results - Primed Metallic Surface + Laser Results - 9 The results in Table II are in units of Nmm " (MPa), with the failure modes noted as a percentage of the total bond area. TABLE II Clean L165 0.02 . mm '2 0.03 . mm "2 0.04 Jmm '2 Initial Kata Initial Kata Initial Kata KenReact KR46B 29.59 5.80 28.65 15.67 28.90 14.95 % SCF 75 0 60 30 90 20 % AF 25 100 40 70 10 80 Unclean LI 65 0.02 . mm "2 0.03 Jmm '2 0.04 Jmm "2 Initial Kata Initial Kata Initial Kata KenReact KR46B 27.72 11.05 30.02 7.12 27.20 9.26 % SCF 85 10 95 5 75 5 % AF 15 90 5 95 25 95 Example 2 In Example 2 the conditions of Example 1 were retained with the exception that the primer solution was a mercapto functional zirco aluminate, obtained from Rhone- Poulenc under the trade name MANCHEM S (RTM) in solution with acetone and methanol. The results in Table LU are in units of Nmm "2 (MPa) , with failure modes noted as a percentage of the total bond area. TABLE π Clean LI 65 0.02 : mm "2 0.03 . fmm "2 0.04 . fmm "2 Initial Kata Initial Kata Initial Kata Manchem S 15.40 6.70 25.77 16.30 29.66 18.45 % SCF 90 0 70 10 95 60 % AF 10 ϊδδ 30 90 5 40 Unclean LI 65 0.02 . fmm '2 0.03 . fmm "2 0.04 J mm '2 Initial Kata Initial Kata Initial Kata Manchem S 12.14 3.05 24.29 10.61 27.83 16.87 % SCF 90 0 60 20 100 30 % AF 10 100 40 80 0 70 Discussion of Experimental Results From Table I, it is clear that the samples that have had no primer or laser pre-treatment display adhesion failure (AF) throughout. It can be deduced that the interface between - 10 - the substrate and adhesive is not optimal for good adhesion and consequently the bond shows poor performance under accelerated ageing conditions, regardless of initial strength. The results obtained From Tables II and III it is clear that treatment of metallic surfaces via the process of the present invention imparts improvements in failure mode from AF to SCF, for the metal tested.

Claims: - 11 - Claims 1. A process for treating a metallic surface, which comprises treating the surface with an organotitanate or zirconate or zircoaluminate or mixture thereof and exposing the treated surface to a laser. 2. A process according to claim 1 in which the metallic surface is of steel, iron in ferrite form, titanium, aluminium, magnesium, copper, gold, nickel, or chromium or mixture thereof or an alloy of any of these metals or a mixture of these metal alloys. 3. A process according to claim 1 or 2 in which an organotitanate or zirconate or zircoaluminate or mixture thereof first applied to the metallic surface and the coated surface is then exposed to a laser. 4. A process according to any of Claims 1 to 3 in which the organotitanate has the following general formula (RO) m — Ti ( OXR 2 Y) n wherein: RO is a monoalkoxy or chelate group; X is a carboxyl, phenyl, ethylene, sulphonyl, phosphate, pyrophoshate or phosphite group; R 2 is a isoheptadecyl, cumyl, ethylene, heptadecenyl, dioctyl, butyl octyl, butyl methyl, di-tridecyl, or octyl group; Y is a methacryl, acryl, aminoamino, amine, mercapto, vinyl or hydroxyl group; m is equal to 1 or 4 and n is equal to 2 or 3. 5. A process according to any of Claims 1 to 4 in which the organozirconate has the following general formula 12 - HO / \ -OH -Al Z \ OH 0 \ ,' 0 C RX (H) wherein: X is a primary amine, carboxy, mercapto, oleophilic, methacryloxy, or difunctional group such as primary amine/hydroxy, methacryloxy/oleophilic, primary amine secondary amine or mercapto/amine; R is an aliphatic chain -(CH 2 ) n - and n is equal to from 0 to 12 6. A process according to any of Claims 1 to 5 in which the organo titanate or organozirconate or zircoaluminate or mixture thereof is used in solution in water and or organic solvent or mixture thereof. 7. A process according to Claim 6 in which the said solution contains from 1 to 10% by weight of organotitanate or zirconate or zircoaluminate or mixture thereof. 8. A process according to any of Claims 1 to 7 in which the metallic surface is a non- clean surface. 9. A process according to any of Claims 1 to 7 in which the metallic surface is of aluminium or an alloy thereof. 10. A process according to any of Claims 1 to 7 in which the metallic surface is of stainless steel. 11. A process according to any of claims 1 to 7 in which the metallic surface is of iron in ferrite form. 12. A process according to any of claims 1 to 7 in which the metallic surface is of titanium or an alloy thereof. - 13 - 13. A process according to any of Claims 1 to 7 in which the metallic surface is of magnesium or an alloy thereof. 14. A process according to any of Claims 1 to 7 in which the metallic surface is of copper or an alloy thereof. 15. A process according to any of Claims 1 to 7 in which the metallic surface is of gold or an alloy thereof. 16. A process according to any of Claims 1 to 7 in which the metallic surface is of nickel or an alloy thereof. 17. A process according to any of Claims 1 to 7 in which the metallic surface is of chromium or an alloy thereof. 18. A method of bonding a metallic surface to another surface which comprises treating the metallic surface by a process as claimed in any of Claims 1 to 7 followed by bonding the treated metallic surface to another surface with an adhesive. 19. A method according to any of Claim 18 in which the other surface is metallic or non-metallic. 20. A method as claimed in claim 18, in which the other surface is metallic and is a surface treated by a process as claimed in any one of claims 1 to 7. 21. A method of improving the adhesion properties of a metallic surface which comprises treating the metallic surface by a process as claimed in any one of claims 1 to 7 and then applying a coating to the treated surface. - 14 - 22. A process for treating a ceramic surface, which comprises treating the surface with an organotitanate or zirconate or zircoaluminate or mixture thereof and exposing the treated surface to a laser.

Inventors: BROAD RICHARD MARTIN, FRENCH ALBERT JOHN, BROAD, RICHARD, MARTIN, FRENCH, ALBERT, JOHN
Applicants: CIBA GEIGY AG, CIBA SPECIALTY CHEMICALS HOLDING INC.
Application year: 1999
Main classification: C23C30
IPC codes: C09J5, C23C26