Abstract:
A method using irradiation with optical light having a wavelength of 160 to 500 nanometers without higher wavelengths with cooling of the surface during the irradiation to modify the surface ( 12 A,  104 A,  202 A,  304 A,  402 A,  502 A) of a substrate ( 12, 104, 202, 304, 402, 502 ) is described. The light is filtered or the lamp ( 24, 106, 212, 306, 510 ) is restricted to the limited range to avoid the affects of the higher spectra. The light can be pulsed or continuous. The method is significantly enhanced by the presence of water ( 14, 124, 204, 306, 410, 508 ) on the surface, preferably also in the presence of ozone in the water. The treated surfaces are more paintable and bondable.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a process for treating surfaces of substrates using ultraviolet light along with cooling of the surface to produce surface activation. In particular, the present invention relates to a preferred process for pretreating surfaces of substrates by providing water to provide the cooling of the surface between the radiation and the substrate. The process is particularly useful when ozone is used to treat the surface, particularly with the water, since ozone is six times more soluble in water than oxygen. The treatment enhances surface activation, allows for surface modification in shorter time periods and preferably increases the wetting characteristics. 
     (2) Description of the Related Art 
     Manufactured surfaces of substrates always contain undesirable compounds or additives that limit or reduce adhesion to an adhesive or paint film. Hence, surface preparation, which includes cleaning and activation of the surfaces, of polymeric, polymer composite or metal substrates is carried out prior to applying protective paint films or adhesive bonding. Surface preparation determines the mechanical and durability characteristics of the composite created. Currently the techniques used for surface preparation are mechanical surface treatments (e.g. abrasion), solvent wash and chemical modification techniques like corona, plasma, flame treatment and acid etching. Each of the existing processes have shortcomings and thus, they are of limited use. Abrasion techniques are found to be time consuming, labor intensive and have the potential to damage the adherent surface. Use of organic solvents results in volatile organic chemical (VOC) emissions. Chemical techniques are costly and are of limited use with regard to treating three dimensional parts, can be a batch process (such as plasma, acid etching) and need tight control. 
     The use of lasers for surface treatment is known in the art. The focussed beams of the lasers make it difficult to treat a large surface. U.S. Pat. No. 4,803,021 to Werth et al describes such a method. U.S. Pat. No. 4,756,765 to Woodroffe describes paint removal with surface treatment using a laser. 
     Plasma treatment of surfaces is known in the art. Relatively expensive equipment is necessary for such treatments and plasmas are difficult to control. The surfaces are treated with vaporized water in the plasma. Illustrative of this art are U.S. Pat. No. 4,717,516 to Isaka et al., U.S. Pat. No. 5,019,210 to Chou et al., and U.S. Pat. No. 5,357,005 to Buchwalter et al. 
     A light based process which cleans a substrate surface also creates a beneficial chemistry on the surface for adhesive bonding and paintability is described in U.S. Pat. No. 5,512,123 to Cates et al. The process involves exposing the desired substrate surface to be treated to flashlamp radiation having a wavelength of 160 to 5000 nanometers. Ozone is used with the light to increase the wettability of the surface of the substrate being treated. Surfaces of substrates such as metals, polymers, polymer composites are cleaned by exposure to the flashlamp radiation. The problem with the Cates et al process is that the surface of the substrate is heated to a relatively high temperature, particularly by radiation above 500 nanometers and relatively long treatment times. Related patents to Cates et al are U.S. Pat. No. 3,890,176 to Bolon, U.S. Pat. No. 4,810,434 to Caines; U.S. Pat. No. 4,867,796 to Asmus et al; U.S. Pat. No. 5,281,798 to Hamm et al and U.S. Pat. No. 5,500,459 to Hagemever et al and U.K. Pat. No. 723,631 to British Cellophane. Non-patent references are: Bolon et al., “Ultraviolet Depolymerization of Photoresist Polymers”, Polymer Engineering and Science, Vol. 12 pages 109-111 (1972). M. J. Walzak et al., “UV and Ozone Treatment of Polypropylene and poly(ethylene terephthalate)”, In: Polymer Surface Modification: Relevance to Adhesion, K. L. Mittal (Editor), 253-272 (1995); M. Strobel et al., “A Comparison of gas-phase methods of modifying polymer surfaces”, Journal of Adhesion Science and Technology, 365-383 (1995); N. Dontula et al., “A study of polymer surface modification using ultraviolet radiation”, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, SC (1997); C. L. Weitzsacker et al., “Utilizing X-ray photoelectron spectroscopy to investigate modified polymer surfaces”, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); N. Dontula et al., “Ultraviolet light as an adhesive bonding surface pretreatment for polymers and polymer composites”, Proceedings of ACCE&#39;97, Detroit, Mich.; C. L. Weitzsacker et al., “Surface pretreatment of plastics and polymer composites using ultraviolet light”, Proceedings of ACT&#39;97, Detroit, Mich.; N. Dontula et al., “Surface activation of polymers using ultraviolet activation”, Proceedings of Society of Plastics Engineers ANTEC&#39;97, Toronto, Canada. Haack, L. P., et al., 22nd Adhesion Soc. Meeting (Feb. 22-24, 1999). 
     Non-pulsed UV lamps have been used by the prior art. These are described in: “Experimental Methods in Photochemistry”, Chapter 7, pages 686-705 (1982). U.S. Pat. No. 5,098,618 to Zelez is illustrative of the use of these types of lamps. 
     A disadvantage of the ultraviolet lamp treatments of the prior art is that they are time consuming and sometimes unreliable. To achieve suitable surface chemistries for adhesive bonding and painting purposes, exposure times for certain materials like polypropylene, thermoplastic olefins (TPO&#39;s) tend to be of the order of 5 to 60 minutes. In many cases there is a limit on the length of time to which one may expose the substrates to UV since there is a fear of degrading the substrate. There is a need for development of an environmentally friendly as well as cost effective and robust surface treatment process which can be used over a range of surfaces. 
     OBJECTS 
     It is therefore an object of the present invention to provide process and apparatus which are reliable and which can produce a highly active surface. It is further an object of the present invention to provide process and apparatus which are economical. These and other objects will become increasingly apparent by reference to the following description and the drawings. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an improved method for modifying a surface of a substrate by generating optical energy having ultraviolet wavelengths and irradiating the surface of the substrate, preferably comprising a polymer, with the optical energy which comprises: irradiating the surface with the optical energy to modify the surface, wherein the wavelengths are between about 160 nanometers and 500 nanometers without higher wavelengths with cooling of at least the surface of the substrate. The cooling of the surface is to temperatures less than 100° C., preferably between 0 and 50° C. 
     The present invention also relates to a preferred improved method for modifying a surface of a substrate, particularly a polymer surface, by generating optical energy and irradiating the surface of the substrate with the optical energy with an optical power density of sufficient intensity to modify the surface, which comprises: providing water on the surface to be modified prior to irradiating the surface to modify the surface and then irradiating the surface with the optical energy to modify the surface, wherein the wavelengths are between about 185 nanometers and 254 nanometers. 
     The present invention further relates to an apparatus for modifying a surface of a substrate comprising: an optical energy source for generating optical energy having ultraviolet wavelength components ranging from about 160 to 500 nanometers without higher wavelengths; a cooling means for cooling at least the surface of the substrate; and an electrical power supply operably coupled to power the energy source. 
     The present invention also relates to a preferred improved method for modifying a surface by irradiating the surface with optical energy at an intensity sufficient to modify the surface forming the surface, which comprises: providing water on the surface to be modified prior to irradiating the surface and then irradiating the surface with the optical energy to photodecompose organic materials present on the surface, preferably with ozone dissolved in the water, wherein the wavelengths are between about 160 nanometers and 500 nanometers without higher wavelengths. 
     The present invention further relates to a preferred improved method for modifying a surface by irradiating the surface with pulsed optical energy at an intensity sufficient to modify the metallic surface, which comprises: providing water on the surface to be modified prior to irradiating the surface and then irradiating the surface with the optical energy to modify any organic materials present on the surface, preferably with ozone dissolved in the water, wherein the wavelengths are between about 185 nanometers and 254 nanometers without higher wavelengths. 
     The present invention relates to an apparatus for modifying a surface of a substrate comprising: an optical energy source for generating optical energy having ultraviolet wavelength components ranging from about 160 to 500 nanometers without higher wavelengths; an electrical power supply operably coupled to power the energy source; and means for providing water on the surface for modifying the surface of the substrate when irradiated. 
     In the present invention it was discovered that if higher wavelengths of light above about 500 nm are used, a thermoplastic surface of the substrate is heated to above the glass transition temperature. This allows the newly formed chemically active groups to rotate into the melted surface thus, decreasing the activity of the surface. By limiting the wavelengths produced by the UV lamp or by the use of filters, the light above 500 nanometers can be largely eliminated with the cooling. 
     It is also necessary to cool the surface to freeze the chemically active groups to the outside of the substrate. This is a very unexpected finding, since the prior art is concerned only with heating the surface. The cooling can be by a cooling gas flushed over the surface and/or by using short durations (3 minutes or less) of the ultraviolet light with liquid cooling. 
     The process of the present invention is cost effective for pretreatment of surfaces of polymers, polymer composites and metals prior to adhesive bonding or painting. The process creates beneficial surface chemistries for adhesive bonding or painting. The advantages of this process over the existing prior art is that the process is cheaper than chemical modification techniques such as plasma and is not a batch process as with plasma and acid etching. Further, the new process can be used to treat three dimensional parts where corona and flame treatments have difficulty in treating. The process can also be used to treat large surface areas quicker than flame treatment. In addition, the substrates are not as sensitive to degradation as when exposed to flame, such as with flame treatment. The process is environmentally friendly as compared to solvent wash, acid etching and mechanical abrasion techniques. The process is much cheaper than processes using UV exciter lasers which are cost intensive and work on the principle of ablating the surface layers or roughening the surface or amorphizing the top surface layers. In comparison to the existing ultraviolet lamp techniques, the current process reduces the process times for treating various substrate surfaces (thus making it cheaper, and avoiding degradation of the substrates) and achieves surface modifications which were not possible. This invention can be used to tailor the chemistry of the substrate surface by using other cooling reactivating vapors (ozone, ammonium and nitrogen) in between the substrate surface and ultraviolet light. 
     The process of the present invention uses one step for cleaning the surface and functionalizing the surface so that the materials can be painted without the use of adhesion primers or the use of costly and environmentally unfriendly treatment steps. Further, this process can be used prior to adhesive bonding of polymers, polymer composites and metals, to achieve good bond strengths. 
     The process can be used for treating carbon fibers and carbon whiskers prior to their use in composites, for instance. An alternate use of the process is in the packaging industry where polymers are printed with ink. This process is an easier, flexible or alternate way for them to create materials with different barrier properties for solvents. 
    
    
     The substance and advantages of the present invention will become increasingly apparent by reference to the following drawings and the description. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic side view of a conveyor system  10  for applying a spray of water droplets  14  onto a surface  12 A of a substrate  12 , then irradiating the substrate  12  with the water droplets  14  on it using a UV lamp  24  and then drying the substrate  12  to remove traces of the water droplets  14  with an electric heater  36  without melting the surface. 
     FIG. 2 is a schematic perspective view of a conveyor system  100  of a second embodiment for a substrate  104  wherein moist air is introduced into a chamber  108  containing the substrate  104  to place droplets  124  on the surface  104 A and then irradiated with a UV lamp  106 . The surface  104 A is then air-dried upon removal from the chamber  108 . 
     FIG. 3 is a schematic side view of a conveyor system  200  of a third embodiment with a substrate  202  with a layer of water  204  held in place by a dam  227  on surface  202 A while the surface  202 A is irradiated by a UV lamp  212 , then the substrate surface  202 A is air dried by air from a diffuser  224 . 
     FIG. 4 is a perspective view of an x-y movable table  302  of a fourth embodiment supporting a substrate  304  with water droplets  308  on surface  304 A so that the position of the substrate  304  is varied under the housing  306  containing lamp (not shown) as a function of time. The position of the housing  306  containing the lamp (not shown) can also be varied. 
     FIG. 5 is a schematic side view of a conveyor system  400  of a fifth embodiment with substrate  402  with a layer of water  410  on surface  402 A and with a transparent layer  412  to filter out infrared light. A cooling plate  404  is provided for the substrate  402 . 
     FIG. 6 is a schematic perspective view of a system  500  of a sixth embodiment wherein a substrate  502  with an opaque mask  504  having cutouts  506  forming the word “MASK” to the substrate  502  which are filled with water  508 . The cutouts  506  are irradiated with a UV lamp  510 . 
     FIG. 7 is a schematic representation of a PATTI tester  600 . 
     FIG. 8 are graphs showing x-ray photoelectron spectroscopy (XPS; percent composition) and contact angle (cos θ) measurements with water for polycarbonate. A: control; B: UV@t=2.25 min, d=2 cms; C: UV@t=2.25 min, d=1 cm; D: UV@t=2.25 min, d=2 cms, ozone from generator; E: UV@t=2.25 min, d=1 cm, and water droplets on surface and F: UV@t=2.25 min, d=1 cm, ozone from generator. 
     FIG. 9 is a graph showing C1s curve fits on XPS measurements of polycarbonate surfaces treated with UV and water. 
     FIG. 10 is a graph showing C1s curve fits on XPS measurements of polycarbonate surfaces treated with UV and ozone. 
     FIG. 11A is an AFM image of a control (baseline) sample of polycarbonate. 
     FIG. 11B is an AFM image of UV treated polycarbonate. UV treatment conditions were t=2.25 min, d=1 cm. 
     FIG. 12A is a surface plot of the polycarbonate control sample AFM image (FIG.  11 A). 
     FIG. 12B is a surface plot of the UV treated polycarbonate AFM image (FIG.  11 B). 
     FIG. 13 is a graph showing the effect of UV treatment on adhesive bond strength and contact angle with water (cos θ) for polycarbonate. 
     FIGS. 14A to  14 D are ESEM images of the molded surfaces of mechanical grade TPO (FIGS. 14A and 14B) and reactor grade TPO (FIGS.  14 C and  14 D). 
     FIGS. 15A and 15B are ESEM images of the molded surfaces of toluene etched mechanical grade TPO (FIG. 15A) and reactor grade TPO (FIG. 15B) samples. 
     FIG. 16 is a graph showing the effect of UV treatment on wettability (cos θ) and adhesive bond strength of reactor grade TPO (without UV stabilizers). 
     FIG. 17 is a graph showing the effect of UV treatment on adhesive bond strength of mechanically blended grade TPO (without UV stabilizers). 
     FIG. 18 are graphs showing the effect of UV treatment on wettability (cos θ) and adhesive bond strength of polypropylene (without UV stabilizers). 
     FIGS. 19A to  19 D are ESEM images of PATTI tested failure surfaces of baseline MTPO (without UV stabilizers). 
     FIGS. 20A to  20 F are ESEM images of PATTI tested failure surfaces of UV treated MTPO (without UV stabilizers). V treatment conditions were t=4 min at d=2 cms. 
     FIGS. 21A to  21 D are ESEM images of PATTI tested failure surfaces of baseline RTPO (without UV stabilizers). 
     FIGS. 22A to  22 D are ESEM images of PATTI tested failure surfaces of ozone treated RTPO (without UV stabilizers). Ozone treatment conditions were t=30 min at d=2 cms. 
     FIGS. 23A to  23 D are ESEM images of PATTI tested failure surfaces of UV treated RTPO (without UV stabilizers). The UV treatment was done in presence of water for t=4 min at d=2 cms. 
     FIGS. 24 and 25 are graphs showing contact angle measurements for the epoxy paint. 
     FIGS. 26 and 27 are graphs showing pull test measurements. 
     FIG. 28 is a graph showing contact angle change prior to and after UV/Ozone treatment 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 A 
                 Baseline 
               
               
                 B 
                 t = 2 mins, d = 2 cm 
               
               
                 C 
                 t = 2 mins, d = 2 cm with ozone 
               
               
                 D 
                 t = 4 mins, d = 2 cm with ozone 
               
               
                 E 
                 t = 4 mins, d = 1 m with ozone 
               
               
                   
               
             
          
         
       
     
     FIG. 29 is a graph showing wettability change presence/absence water during UV/Ozone treatment. 
     FIG. 30 is a graph showing the correlation of contact angle and adhesion change. 
     FIG. 31 is a graph showing the affect of water and ozone on adhesion. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferably, the surface of the substrate is exposed to a UV flashlamp emitting the radiation in the required wavelength range (180 nm-500 nm). The substrate surface to be treated is preferably constructed of a polymer, polymer composite or a metal. Prior to exposing the substrate to UV radiation, water droplets or a sheet of water are preferably placed on the substrate surface. Process times are regulated by the distance of the UV lamp or flashlamp from the substrate surface, ambient temperature or condition and the extent of surface modification needed. The distance of the UV lamp or flashlamp from the substrate surface determines the intensity of UV radiation at the surface substrate and the time required to evaporate the water if present on the surface. Ambient conditions are important depending on whether air, nitrogen or ozone are present. Surface modifications are characterized using contact angle measurements which are done using a Rame-Hart goniometer apparatus with deionized water. The present process creates surfaces which wet better than if they were exposed solely to UV radiation (180 nm-500 nm), creates similar substrate surfaces in a shorter time than that achieved using only UV or ozone and is cheaper than using only UV or ozone. 
     In an alternate embodiment, a film of water is placed on a quartz or fused silica tray above the substrate to filter out longer wavelengths in infrared region (over ≈1200 nm). In this embodiment, only UV is allowed to interact with the substrate surface. 
     The process can also be used in a continuous process by either having a falling film of water on the substrate or by immersing the substrate in water and then exposing the substrate to UV radiation (FIG.  3 ). The lamp could be moving over a row of substrates or the substrate surface could be moving under a bank of lamps (FIG.  4 ). The lamps could be arranged to irradiate all surfaces, such as a tunnel of lamps. Alternatively, the current process can also be used in a continuous process by dispersing water in the form of fine droplets using an atomizer or any other technique between the lamp and the substrate surface (FIG.  1 ). In any of the embodiments, either the lamp or the substrate surface can be moving. In addition, to use this process as a continuous process, air or ozone or other gases can be bubbled through water at various flow rates which may be introduced onto the substrate. 
     FIG. 1 shows a preferred system  10  of the present invention for irradiating a substrate  12  which has a coating of water droplets  14 . The substrate  12  is provided on a conveyor belt  16  supported for rotation on belt tensioning rollers  18  and  20 . Conveyor belt  16  moves from left to right as indicated by the arrow. At a first station A, a spray nozzle  22  disperses droplets  14  of the water onto the surface  12 A of the substrate  12 . The substrate  12  is then moved to station B where the surface  12 A is irradiated with UV light from a lamp  24  in a housing  24 A mounted in a hood  26  which is opaque to the light to prevent eye damage. The lamp  24  is controlled by a pulse modulator  27  and operated by a power supply  28 . Insulators  30  and  32  are provided for wires  34  leading from the hood  26 . Upon irradiating the surface  12 A, the substrate  12  is moved to station C where the surface  12 A is dried by an electric heater  36  operated by a power supply  38 . Insulators  40  pass wires  42  through the hood  26 . The substrate  12  is then removed taking care to keep surface  12 A clean. The surface  12 A is then painted or otherwise treated in a conventional manner (not shown). The hood  26  is provided with a blower  44  which removes volatilized products from the hood  26  through line  46 . 
     In operation, the system  10  moves the substrate  12  through stations A, B and C for treatment. The substrate  12  is provided with water  14  at station A. irradiated at station B, dried at station C and then removed from the system  10  for subsequent treatment. 
     FIG. 2 shows a system  100  wherein a conveyor belt  102  provides a substrate  104  to be irradiated by lamp  106  in housing  106 A. The conveyor moves from right to left as indicated by the arrow. The lamp  106  is powered by power supply (not shown) and pulse modulator (not shown) similar to power supply  28  and pulse modulator  27  as shown in FIG.  1 . The substrate  104  is surrounded by a chamber  108  which confines the substrate  104  and moist air is introduced via line  110  into the chamber  108 . The line  110  is supported from a vessel  112  containing water  114 . Air is bubbled into the water  114  by pump  116 . If designated, the water  114  or air is also ozonated by generator  118 . The chamber  108  is vented by blower  120  which draws the moisture laden air through the chamber  108 . Upon removal of the substrate  104  from the chamber  108 , the surface  104 A is air-dried by air directed at the surface  104 A by a blower (not shown). 
     In operation, the system  100  provides air on the surface  104 A of the substrate  104 . The substrate  104  can be cooled to encourage moisture to condense as droplets  124  on the surface  104 A. The substrate  104  is irradiated by the UV lamp  106  and then air-dried upon removal from the chamber  108 . The substrate surface  104 A is then painted or otherwise treated, taking care to prevent contamination. 
     FIG. 3 is a schematic view of a variation of the system  10  of FIG. 1 wherein the system  200  is provided with a substrate  202  having a layer of water  204  on a surface  202 A which is spread on the surface  202 A. As before, the substrate  202  is supported on a conveyor belt  206  on tensioning rollers  208  and  210 . The belt  206  moves from left to right as indicated by the arrow. The substrate surface  202 A is irradiated by lamp  212  in housing  212 A through the layer of water  204  at station A. As before, the lamp  212  is provided in a hood  214  with a blower  216  connected by line  218  to the hood  214 . At station B an air blower  220  supplies dry air into the hood  214  via line  222  and diffuser  224  held in place by a dam  227  to dry the surface  202 A of the substrate  202 . The substrate  202  with dam  227  is then removed from the conveyor belt  206 . In station B, the drain  227  can be removed for drying by the air from blower  220 . 
     FIG. 4 shows a system  300  for moving a table  302  in the x-y direction. The substrate  304  under a housing  306  containing a lamp (not shown). The table  302  indexes the substrate  304  under the housing  306 . Droplets  308  of water are provided on the surface  304 A of the substrate  304 . Alternatively, the housing  306  can be moved as shown by the dotted lines. The lamp in the housing  306  is supplied by a power supply and pulse modulator (not shown). via wires  310 , as shown in FIG.  1 . 
     FIG. 5 shows a system  400  wherein the substrate  402  is mounted on a cooling plate  404  provided with a channel  404 A supplied with a coolant by a pump or compressor  406  and line  408 . A layer of water  410  held in place by a transparent layer or tray, such as quartz. The surface  402 A of the substrate  402  is irradiated through the layer  412  and water  410  by lamp  414  in housing  414 A. As before, the lamp  414  is powered by a power supply and modulated by a modulator (not shown) by lines  416  through insulators  418 . In this embodiment, the transparent layer  412  holds the water  410  in place. The filtering of the infrared light by the water  410 /layer  412  (quartz) assures that the substrate  402  does not overheat. This system  400  can be incorporated into any one of the other systems  10 ,  100 ,  200  or  300 . 
     FIG. 6 shows a system  500  wherein the substrate  502  is protected by an opaque mask  504 . The mask  504  has cutouts  506  spelling the word MASK which goes to the surface  502 A of the substrate  502 . The cutouts  506  are provided with water  508 . The mask  504  is irradiated with a lamp  510  in a housing  510 A powered by a power supply and pulse modulator (not shown) as in FIG. 1 via lines  512 . In this embodiment, the surface  502 A is treated to make the cutouts  506  receptive to further treatment. 
     In the following Examples 1 to 12, a pulsed xenon lamp from Xenon Corporation, located in Woburn, Mass. is capable of providing the emission at wavelengths below 225 nm is used in the experiments. The materials used in the experiments were: (1) polypropylene based thermoplastic olefins (TPO), both reactor grade and mechanically blended with different amounts of UV stabilizers and sheet molding compound (SMC), both standardized and flexibilized, (2) aluminum alloy sheets (A1 5754, A1 5052 and A1 6061), (3) polycarbonate, and (4) vinyl ester. Polycarbonate was selected as a model base amorphous polymer. The experiments show that the nature of the substrate is an important factor in determining the extent of modification by UV radiation. 
     To study ozone&#39;s effect on the extent of surface modification, an ozone generator was included in the experimental setup. The other variables that play a role in the extent of modification of the substrate surfaces by UV are: distance of lamp from the substrate surface (d), exposure time (t), effect of humidity surrounding the substrate, intensity of lamp radiation, presence of UV stabilizers in the substrate, the nature of the substrate surface and cooling of the surface. 
     Normally, the environment between the lamp and the surface of the material being treated is normal ambient air. During some experiments, an external ozone generator (Ozotech, Eureka, Calif. 96097) was used to increase the concentration of ozone over the sample surface over what is generated in air by the UV light. The ozone flow rate used during experimentation was 30 std.cu.ft./hr. The other variables were the time of exposure, the distance between the sample and the UV source and the glass plate used to isolate the lamp tube from the sample. A pulsed lamp is preferred to prevent overheating of the substrate. Two types of glass plates were used: SUPRASIL™ (fused silica) and PYREX®. The glass plates act as filters and have different transmission characteristics. SUPRASIL™ transmits light in the UVC region and has a 10% transmission at 170 nm. PYREX® transmits light primarily in the UVB region (280 nm and higher) and filters the high frequency UVC radiation. Pyrex has 10% transmission at a frequency of 280 nm. 
     Moisture can be added in a variety of ways. The incoming air can be saturated with moisture to near 100% relative humidity by bubbling the air or nitrogen or another gas through water to saturate it. Alternatively, water can be sprayed onto the surface using a common atomizer prior to introducing the surface to the UV radiation under the lamp. The spraying process creates very small droplets, less than 1 micron in diameter on the surface. In addition, the sample can be covered with a very thin, continuous layer of water. 
     The experiments show that the treatment enhances the substrate&#39;s surface wettability, with the degree of enhancement depending on the substrate characteristics and the treatment processing conditions used. The substrates are characterized prior to and after UV treatment using contact angle measurements to determine wettability. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy with the attenuated total reflectance (FTIR-ATR) setup is used to characterize the surface chemical composition of the substrates. XPS results show an increase in the oxygen content of the polycarbonate substrates after UV treatment (FIG.  8 ). Atomic force microscopy (AFM) is used to characterize and compare the control substrate surfaces with the UV treated surfaces (FIGS.  11 A and  11 B). Also, environmental scanning electron microscopy (ESEM) is being used to determine the effect initial substrate morphology has on UV treatment (FIGS. 14A to  14 D). Stability studies on the UV treated polycarbonate surfaces show that the surfaces are stable in time at room temperature. Adhesion measurements have been conducted using a pneumatic adhesion tensile testing instrument. 
     On exposure to various treatments the substrates were characterized for wettability, surface chemical composition, morphology and stability. Wettability was determined by measuring contact angles of de-ionized water using the Rame-Hart goniometer apparatus. Except where specified, the contact angles (θ) were measured immediately after UV exposure. At least ten measurements of contact angles were taken for each sample and the averages are reported here. To correlate the change in wettability to a change in surface chemical composition, Fourier transform infrared spectroscopy (FTIR) with the ATR cell was used. Measurements using zinc selenide crystal at sampling depths of 1-2 microns and germanium crystal at a sampling depth of 0.5 microns were carried out. The FTIR-ATR spectra did not show any significant change in the polymer samples after UV treatment. Thus, it was concluded that the changes caused by UV on the polymers were confined to a few atomic layers near the surface and FTIR-ATR was seeing the polymer to depths of a few microns. 
     X-ray photoelectron spectroscopy (XPS) was used to characterize the substrate surfaces for a change in chemical composition after UV treatment. A Perkin-Elmer Physical Electronics PHI5400 ESCA Spectrometer equipped with both a standard Mg Kα 1,2  X-ray source, and a monochromated Al Kα 1,2  X-ray source, and an electron flood gun for neutralization was used. The instrument uses a 180° hemispherical energy analyzer operated in the fixed analyzer mode and a position sensitive detector. The instrument has variable apertures available from spot sizes of 250 μm to a rectangle of 1.5×5 mm. The optimum spot size for the conditions used in these experiments is the 1.00 mm diameter aperture. Resolution settings for collecting data are 89.45 eV for survey (wide window) scans, 35.75 eV for utility resolution and 17.90 eV for high resolution scans. 
     Use of the monochromatic source on a non-conducting sample necessitates the use of a neutralization source. This instrument utilizes a low energy electron flood gun. Prior to establishing the baseline chemistry of untreated polymers, the neutralizer operating conditions had to be optimized. This was accomplished by first aligning the neutralizer with mylar, followed by using these conditions on the baseline TPO and polycarbonate samples. The peak shape of the C1s was used to assess the neutralizer operation. An asymmetric C1s peak was initially observed. To determine if this was real or due to the neutralizer, the specimen was analyzed using the standard Mg source set to 150 W, 15 kV. Lower power was used to minimize damage that may occur when the non-monochromatic source is used. It was concluded that the asymmetry was an artifact of the neutralizer. The operating conditions were adjusted through several iterations until the C1s peak shape was symmetric. A molybdenum mask was employed to assist in neutralizing the charging occurring in the samples, where the mask attracts electron and causes a distribution of electrons to spread across the sample surface. Use of the mask has improved the reproducibility of neutralizing, allowing the same neutralizer setting to be used from sample to sample. 
     To determine whether surface topography had changed due to UV treatment, atomic force microscopy (AFM) of the polymer samples was done using a Nanoscope III made by Digital Instruments (FIGS. 11A and 11B. Along with AFM, environmental scanning electron microscopy (ESEM) was also used to characterize surface morphology prior to and after UV treatment (FIGS. 14A to  14 D and  15 A to  15 B). Also, ESEM was used to determine if there was any relationship between extent of modification and initial morphology of the substrate. The ESEM used for the morphological study was an Electroscan 2020. 
     A pneumatic adhesion tensile testing instrument (PATTI) was used to measure adhesion properties as a function of UV treatment (FIG.  7 ). This instrument (PATTI-2A) is made by SEMicro division, M. E. Taylor Engineering, Inc. This instrument uses compressed inert gas to apply a continuous load to a 0.5 inch (outer diameter) aluminum pull stub which is bonded to the rest surface with an adhesive. Once the pull stub has been bonded and the adhesive cured, the stub is attached to a piston. The piston design assures uniaxial alignment with the pull stub axis for “true tensile testing”. A continuous load is applied perpendicular to the pull stub until failure occurs. The PATTI instrument and method conforms to ASTM D4541, “Pull-off strength of coatings using portable adhesion testers”. 
     EXAMPLE 1 
     Polymer samples (control and UV treated) were bonded to aluminum stubs using an epoxy structural adhesive, ARALDITE AW106 with hardener HV953 (from Ciba Geigy Corporation). 30 micron sized glass bubbles from 3M Corporation (S60/10000, 3M Scotchlite Glass Bubbles) were used to control the adhesive bond line thickness. In order to attain its full strength, the adhesive was allowed to cure for more than 15 hours at room temperature. Five or more samples were tested for control and each treatment condition. ESEM was used to characterize the polymer side of the PATTI test in order to determine the locus of failure. The following paragraphs summarize the results of the UV experiments for various polymers. 
     Table 1 shows the effect of UV treatment with the xenon lamp on samples of polycarbonate where d=distance of lamp from the substrate surface and t=exposure time. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Contact angle measurements on polycarbonate 
               
             
          
           
               
                 Sample/Treatment Conditions 
                 Water Contact Angle (degrees) 
               
               
                   
               
               
                 Control 
                 78 
               
               
                 UV @ t = 1 min, d = 2 cms 
                 64 
               
               
                 UV @ t = 1 min, d = 1.4 cms 
                 49 
               
               
                 UV @ t = 2.25 min, d = 1 cm 
                 35 
               
               
                 UV @ t = 2.25 min, d = 1 cm, 
                 20 
               
               
                 with water droplets on the 
               
               
                 surface 
               
               
                 UV @ t = 2.25 min, d = 1 cm 
                 21 
               
               
                 and ozone from ozone generator 
               
               
                   
               
             
          
         
       
     
     It was observed that polycarbonate is significantly modified by UV radiation. From Table 1, it is also observed that the same synergistic effect of water is seen for polycarbonate as was noted for reactor grade TPO. Also, decreasing the distance between the lamp surface and the substrate or increasing the ambient ozone concentration was observed to enhance the surface wettability. 
     FIG. 8 is a plot of the carbon and oxygen content on the polycarbonate surface as a function of various UV treatment conditions. This was obtained using XPS. Also plotted in the same FIG. 8 is the cosine of the contact angle (θ) against the UV treatment conditions. With increase in the intensity of UV treatment (either due to decreasing distance between lamp and substrate or presence of water droplets on the surface or presence of ozone from ozone generator in the ambient) there is an increase in the oxygen content on the surface (increases from 15% to 31%) and also there is a corresponding increase in the wettability of the substrate (cos(θ)) approaches a value of 1 which corresponds to θ equal to 0 or the substrate being perfectly wettable). Thus, XPS is able to detect changes in surface chemical composition after UV treatment. 
     Chemical information indicating changes in the surface treated polycarbonates was further investigated by curve fitting the C1s spectra. Curve fitting defines and interprets the carbon chemistry as detected at the sample surface by allowing the user to distinguish overlapping features with a carbon is spectral envelope. Using a curve fit model, the surface chemical composition for control and various treated polycarbonate samples were compared. FIG. 9 compares the effect of the distance from the UV lamp, and the presence of water during UV exposure on surface chemical composition. Upon surface treatment, oxygen functional groups have been added to the polycarbonate surface. There is a marked increase in the C—O, and oxygen functionality&#39;s such as C═O, COOH and COOR. The carbonate peak has decreased and this is consistent through all the UV treated polycarbonate samples. FIG. 10 shows that UV used along with ozone also showed an increase in the oxygen functionality. FIG. 10 also shows that there is no change in the polycarbonate chemistry within experimental error when exposed to ozone only for 5 minutes. 
     AFM was used to determine if UV treatment altered the substrate topography. The surface topography of polycarbonate was studied as a function of UV treatment. FIGS. 11A and 11B are a comparison of images obtained from AFM for control and UV treated polycarbonate. It was observed that the topography is different. The image for the UV treated polycarbonate shows regions which are lighter in gray scale. This corresponds to peaks on the substrate surface. An analysis of these images in terms of surface plots, show the UV treated polycarbonate surface to have a number of peaks (corresponds to white regions in gray scale) and troughs (corresponds to dark regions in gray scale). This is shown in FIGS. 12A and 12B. The frequency of these peaks and troughs was found to depend on the intensity of the UV treatment. Intensity increased with a decrease in the distance between the lamp and the substrate and also with the presence of water droplets on the substrate surface. 
     FIG. 13 shows the effect of UV treatment on wettability and bond strength for polycarbonate. UV and ozone treatments increased the wettability, and enhanced adhesive bond strengths. The extent to which the bond strength increases is dependent on the UV treatment condition and the nature of the polymer after UV treatment with bond strength increases of 200% for polycarbonate. Besides affecting bond strength, failure mode was observed to have changed from control samples to different UV treatment conditions. The locus of failure can be evaluated by characterizing the tested samples using XPS or ESEM. A main use of this process is as a surface pretreatment for polymers, composites or metals prior to the painting or adhesive bonding step. Thus, it was necessary to know what changes occurred on the UV treated surfaces as a function of time, temperature and moisture after the UV treatment. In Tables 2, 3 and 4, contact angle measurements for the preliminary time and moisture stability studies conducted on polycarbonate at room temperature are listed. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Contact angle measurements on UV treated polycarbonate. UV 
               
               
                 treatment was for t = 2.25 min at d = 2 cms 
               
             
          
           
               
                   
                 Water 
               
               
                 Sample Conditions 
                 Contact Angle (degrees) 
               
               
                   
               
               
                 control (analyzed immediately after UV) 
                 51 
               
               
                 aged for 2 hours at room temperature 
                 47 
               
               
                 aged for 4 hours at room temperature 
                 49 
               
               
                 aged for a day at room temperature 
                 48 
               
               
                 aged for 7 days at room temperature 
                 48 
               
               
                 rinsed in deionized water for 5 min 
                 54 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Contact angle measurements on UV treated polycarbonate. UV 
               
               
                 treatment was for t = 2.25 min at d = 1 cm. 
               
             
          
           
               
                   
                 Water 
               
               
                 Sample Conditions 
                 Contact Angle (degrees) 
               
               
                   
               
               
                 control (analyzed immediately after UV) 
                 35 
               
               
                 aged for 2 hours at room temperature 
                 29 
               
               
                 aged for 4 hours at room temperature 
                 27 
               
               
                 aged for a day at room temperature 
                 31 
               
               
                 aged for 7 days at room temperature 
                 33 
               
               
                 rinsed in deionized water for 5 min 
                 54 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Contact angle measurements on UV treated polycarbonate. UV treatment 
               
               
                 was for t = 2.25 min at d = 1 cm with water droplets on the surface. 
               
             
          
           
               
                   
                 Water 
               
               
                 Sample Conditions 
                 Contact Angle (degrees) 
               
               
                   
               
               
                 control (analyzed immediately after UV) 
                 20 
               
               
                 aged for 2 hours at room temperature 
                 27 
               
               
                 aged for 4 hours at room temperature 
                 26 
               
               
                 aged for a day at room temperature 
                 28 
               
               
                 aged for 7 days at room temperature 
                 30 
               
               
                 rinsed in deionized water for 5 min 
                 55 
               
               
                   
               
             
          
         
       
     
     It was observed that the contact angle made by de-ionized water on the substrates does not change significantly over the span of 7 days. This means that the UV treated polycarbonate surfaces are stable at room temperature. On rinsing the UV treated samples for 5 minutes in de-ionized water with slight agitation and then drying on a KIMWIPE®, the measured contact angles were found to be higher than the control sample for that particular UV treatment. These measured contact angles were lower than those obtained for the untreated polycarbonate (78%). From this it may be reasoned that though UV modifies polycarbonate, it might also create low molecular weight species on the surface which are dislodged during rinsing. More experiments need to be done to verify this hypothesis and determine the moisture stability of UV treated surfaces. 
     EXAMPLE 2 
     UV treatment on reactor grade and mechanically blended TPO without UV stabilizers showed that wettability of reactor grade TPO could be improved while not that of the mechanically blended TPO. It was also shown that water droplets on the surface of reactor grade TPO enhanced the extent of modification and modification rates. 
     Table 5 compares the UV radiation exposure effects for reactor grade TPO&#39;s without UV stabilizers against those that contain UV stabilizers. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Contact angle measurements on reactor grade thermoplastic olefin 
               
             
          
           
               
                   
                 Water Contact Angle (degrees) 
                   
               
             
          
           
               
                   
                   
                 TPO control + UV 
               
               
                 Sample/Treatment Conditions 
                 TPO control 
                 stabilizer 
               
               
                   
               
               
                 baseline 
                 93 
                 101  
               
               
                 UV @ t = 4 min, d = 2 cms 
                 85 
                 94 
               
               
                 UV @ t = 4 min, d = 2 cms 
                 78 
                 N.D.* 
               
               
                 with water droplets on the 
               
               
                 surface 
               
               
                 UV @ t = 6 min, d = 2 cms 
                 N.D.* 
                 93 
               
               
                 with water droplets on the 
               
               
                 surface 
               
               
                 UV @ t = 4 min, d = 2 cms 
                 89 
                 88 
               
               
                 and ozone from ozone 
               
               
                 generator 
               
               
                 UV @ t = 4 min, d = 2 cms 
                 76 
                 82 
               
               
                 and ozone from ozone 
               
               
                 generator 
               
               
                   
               
               
                 *Not determined  
               
             
          
         
       
     
     It is noted that the initial value of the de-ionized water contact angle is higher for the TPO containing UV stabilizers. It was also observed that UV modifies the substrates containing the UV stabilizers, although to a slightly lesser extent. The contact angles achieved after UV treatment of the reactor grade TPO&#39;s are similar to those obtained using propane flame treatment (76°) on reactor grade TPO&#39;s. 
     From the above listed tables, it is noted that water has a synergistic effect with UV radiation for certain polymer substrates. Thus, some experiments were carried out to determine whether any other chemicals other than water, in the presence of UV, causes an increase in the substrate&#39;s wettability. Tables 6 and 7 list the preliminary results for the effect of droplets of different strengths of hydrogen peroxide solution on mechanical and reactor grade TPO substrate surfaces. Standard hydrogen peroxide solution is in water and is available at 30% strength. Preliminary conclusions from these experiments show that dilute solutions of hydrogen peroxide enhances UV modification slightly. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Effect of hydrogen peroxide in the presence of UV on contact angle 
               
               
                 measurements for mechanical grade thermoplastic olefin 
               
             
          
           
               
                 Sample/Treatment Conditions 
                 Water Contact Angle (degrees) 
               
               
                   
               
               
                 control 
                 90 
               
               
                 UV @ t = 6.75 min, d = 2 cms 
                 93 
               
               
                 UV @ t = 6.75 min, d = 2 cms, 
                 88 
               
               
                 with 8.5% strength hydrogen 
               
               
                 peroxide droplets on the surface 
               
               
                 UV @ t = 6 min, d = 2 cms, with 
                 88 
               
               
                 15% strength hydrogen peroxide 
               
               
                 droplets on the surface 
               
               
                 UV @ t = 6 min, d = 2 cms, with 
                 84 
               
               
                 6% strength hydrogen peroxide 
               
               
                 droplets on the surface 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Effect of hydrogen peroxide in the presence of UV on contact angle 
               
               
                 measurements for reactor grade thermoplastic olefin 
               
             
          
           
               
                 Sample/Treatment Conditions 
                 Water Contact Angle (degrees) 
               
               
                   
               
             
          
           
               
                 control 
                 93 
               
               
                 UV @ t = 4 min, d = 2 cms 
                 85 
               
               
                 UV @ t = 30 min, d = 2 cms 
                 86 
               
               
                 UV @ t = 4.5 min, d = 2 cms, 
                 83 
               
               
                 with 3% strength hydrogen peroxide 
               
               
                 droplets on the surface 
               
               
                 UV @ t = 5 min, d = 2 cms, with 
                 85 
               
               
                 6% strength hydrogen peroxide 
               
               
                 droplets on the surface 
               
               
                 UV @ t = 6.0 min, d = 2 cms, 
                 88.5 
               
               
                 with 15% strength hydrogen 
               
               
                 peroxide droplets on the surface 
               
               
                   
               
             
          
         
       
     
     FIGS. 14A to  14 D are the ESEM images for reactor grade TPO and mechanical grade TPO samples. The images are of the top surface of the injection molded substrates. The ESEM images show that except for the reactor grade TPO&#39;s surface which appears to be rougher, there are no significant differences between the two grades of TPO. Also from FIGS. 14A to  14 D, it is not possible to distinguish the dispersed elastomer phase from the polypropylene matrix. Even when the ESEM was operated in the back-scattered mode, the two phases were not able to be distinguished from each other. To distinguish the elastomer phase from the polypropylene, the TPO samples were placed in toluene for different times at room temperature. Toluene selectively etches the elastomer phase, and one is able to distinguish the two phases. This is shown in FIGS. 15A to  15 B. The ESEM images are of the top surface of the injection id s molded TPO substrates. On toluene etching, it is observed that the resultant morphology for the two grades of TPO are different. 
     To determine whether UV treatment affected. adhesive bond strength, PATTI experiments were carried out on reactor and mechanically blended grades of TPO as shown in FIGS. 16 and 17. FIG. 16 is a plot of adhesive bond strength and wettability versus treatment conditions. In reactor grade PTO, wettability in this figure is indicated by the cosine of the contact angle (cos(θ)) made by de-ionized water. From FIG. 16, it is observed that for certain conditions the adhesive bond strength improved even if the wettability did not improve. 
     FIG. 17 is a plot of mechanically blended grade TPO&#39;s adhesive bond strength for different UV treatment conditions. Wettability has not been plotted in FIG. 17, since it was documented in the previous reports that wettability represented by the equilibrium contract angle did not change with UV treatment. Though wettability did not improve, FIG. 17 shows that the adhesive bond strength improves. 
     Even if wettability did not change for certain UV treatment conditions, the adhesive bond strength showed improvement. The TPO&#39;s being studied here are made up of a polypropylene matrix in which an elastomer is dispersed. To identify the role played by the polypropylene matrix during UV treatments of TPO, PATTI tests were conducted on control and UV treated polypropylene samples. FIG. 18 shows a plot of adhesion strength and wettability versus UV treatment conditions for polypropylene. It was observed that for the conditions studied, though the wettability did not significantly increase, the adhesive bond strength has improved after UV treatment. 
     The polypropylene and TPO samples contain an anti-oxidant package. These anti-oxidant materials may be preventing nascent oxygen from attacking the sites where surface bonds are broken by UV radiation. Due to this, wettability of the substrates might not have improved significantly. The other possible reason is that in polypropylene based materials, a competing mechanism like cross-linking of the substrate surface might be occurring. Due to this, the weak boundary layer might have cross-linked in polypropylene and hence the adhesive bond strength might have improved. Similarly in the case of injection molded TPO&#39;s, the dispersed elastomer migrates from surface and the surface (or skin) is dominated by polypropylene. Hence even for TPO&#39;s, it may be hypothesized that under some conditions surface cross-linking occurs. ESEM is also being used to characterize the failure surfaces of the PATTI tested samples and determine the locus of failure. XPS will be used to confirm the results obtained from ESEM. The following paragraphs discuss the same typical ESEM results obtained after scanning the substrate (polymer) side. 
     FIGS. 19A to  19 D are the ESEM images for PATTI tested baseline mechanical grade TPO. These images are taken of the polymer side after the PATTI test. It is observed that the failure is clean and it seems to occur at the adhesive-polymer interface. The condition of the TPO for this test resulted in poor bond strength. FIGS. 20A to  20 F show typical ESEM images for UV treated mechanical grade TPO. These images have been taken from the edge of the adhesive joint to the center of the joint. One observes that the failure mode has changed after UV treatment of the TPO. From the images in FIGS. 20A to  20 F, one observes polymer pull-out. This is seen to be more near the edge of the adhesive joint. A hypothesis on how the failure occurred may be: that the crack initiated near the edge of the adhesive joint below the interface and then propagated inward towards the interface. Hence one sees more polymer pull-out near the edge of the adhesive joint. 
     FIGS. 21A to  21 D are ESEM images of PATTI tested baseline reactor grade TPO samples. The images taken are of the polymer side of the PATTI test. It is observed that the failure is clean and the condition corresponds to poor adhesive bond strength of reactor grade TPO. FIGS. 22A to  22 D show the ESEM images of the ozone treated reactor grade TPO samples which have been PATTI tested. It is observed that the failure surfaces seem different from that of the baseline sample of reactor grade TPO and also bond strengths registered for ozone treated TPO are higher than for baseline reactor grade TPO. Since glass beads which were used as spacers to control adhesive bond line thickness and also epoxy (adhesive used) residue are not observed on the polymer failure side, one can postulate that the failure is occurring in the interphase. FIGS. 23A to  23 D show ESEM images of the polymer failure side of UV treated reactor grade TPO. It is observed that the failure surface appears to be different from that of ozone treated or the baseline reactor grade TPO. It is seen from FIGS. 23A to  23 D that the failure has occurred in the polymer substrate. Thus, the failure mode has changed after UV treatment. XPS may be used to determine the exact location of the failure surface. 
     Overall, from the PATTI tests it was observed that UV treatment caused enhancement in the adhesive bond strength and also a change in the failure mode. PATTI tests and a preliminary ESEM analysis of failure surfaces revealed that mechanically blended TPO and reactor grade TPO failed differently. This may be correlated to the morphology of the TPO which in turn is a function of how they are manufactured and processed. PATTI tests carried out on polypropylene highlight that UV treatment enhances bond strength. 
     The wettability of polymeric substrates like polycarbonate, reactor grade thermoplastic olefin (TPO), polypropylene and vinyl ester matrix was increased after UV modification. This was indicated by a decrease in the contact angle of de-ionized water. The extent of UV modification was found to be dependent on distance (d) between lamp and substrate (i.e. intensity of radiation falling on the substrate), exposure time (t), ozone concentration, presence of water droplets, presence of UV stabilizers and nature of the substrate. 
     The presence of water droplets on the substrate surface was found to enhance the UV modification of certain polymers as well as increase the UV modification rates. This was found to be true for both reactor grade TPO and polycarbonate. The extent of improvement for polypropylene was to a lesser extent, while for mechanical grade TPO, the presence of water did not make any difference. 
     Experiments with hydrogen peroxide solution were undertaken to explore the effect of the presence of other fluids during UV radiation of polymeric substrates. The presence of hydrogen peroxide solution droplets on substrate surfaces of reactor and mechanical grade TPO&#39;s and polypropylene was found to affect UV treatment. Preliminary findings showed that the lower the concentration of hydrogen peroxide solution, the larger was the UV modifications of the substrate surfaces. 
     Besides wettability and surface chemical composition being altered, AFM of UV treated polycarbonate samples showed a change in surface morphology (FIG.  12 B). This change was seen as an increase in the number of peaks and valleys as a function of the intensity of UV treatment condition. 
     The adhesive bond between the polymer substrate surface and the aluminum stub showed varying strengths for different UV treatment conditions. In most cases, the UV treated samples showed higher bond strengths than baseline samples. The increase in adhesive bond strength was as high as 200-600%. This was found to be the case for polycarbonate, reactor and mechanical grade TPO, and polypropylene samples. 
     UV treatment was found to be stable over time for polycarbonate. On washing/rinsing these UV treated samples in de-ionized water, the substrate surfaces did change their contact angles. Yet, the resultant contact angle was found to be smaller (or surface more wettable) than those of the baseline samples. 
     ESEM of TPO has shown that the morphology of reactor grade TPO might be different from mechanical grade TPO. This might explain why UV treatment shows a different effect on them. ESEM has also been used to characterize polymer surfaces after PATTI testing to determine nature and locus of failure. 
     EXAMPLE 3 
     This example shows the effect of adding supplemental ozone to the environment under the UV lamp on tire rubber. Rubber samples were cut into 1 inch×1 inch squares prior to treatment. The distance between the sample surface and the UV lamp was kept at 20 mm. Treatment times ranging from 30 seconds to 4 minutes were evaluated. After treatment, the contact angle of pure deionized water with the rubber was measured using a contact angle goniometer (Rame-Hart Inc.). All the contact angle measurements were performed one (1) hour after treatment. 
     The treatment was evaluated for different environments like air, ozone and water for various times. The ozone was fed into the treatment area directly from the ozone generator via a tube. To keep the sample temperature low and prevent thermal damage to the polymer, the samples were exposed to UV light in stages. This is off and on pulsed where the sample is exposed for a certain amount of time, the light is turned off and the sample is allowed to cool. This step is repeated till the required amount of total exposure is achieved. 
     The various treatment conditions used and the results are tabulated in Table 8. A reduction in contact angle was observed in all samples exposed to UV light. The reduction in contact angles was seen to be directly dependent on the treatment time. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Various UV Treatment Conditions Used for Cured 
               
               
                 (Vulcanized) Tire Rubber and Resulting Contact Angles 
               
             
          
           
               
                   
                 Treatment Conditions 
                 Contact 
                   
               
             
          
           
               
                   
                 Distance 
                 Time 
                 Environment 
                 Angle 
                 Temperature 
               
               
                   
                   
               
               
                   
                   
                   
                 untreated 
                 121  
                 25 C 
               
               
                   
                 20 mm 
                 2 min 
                 UV + Ozone 
                 31 
                 101 C  
               
               
                   
                 20 mm 
                 2 min 
                 UV + Ozone 
                 20 
                 74 C 
               
               
                   
                   
                   
                 30 sec 
               
               
                   
                   
                   
                 on/30 sec 
               
               
                   
                   
                   
                 off Pulsed 
               
               
                   
                   
               
             
          
         
       
     
     The following Examples 4, 5 and 6 show the effect of adding supplemental ozone to the environment under the UV lamp illuminating the sample surface and short illumination times. 
     EXAMPLE 4 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 UV Treatment of Polyimide (Kapton 500-HN) 
               
             
          
           
               
                   
                 Treatment 
                 Contact Angle 
                 Cos (θ) 
               
               
                   
                   
               
               
                   
                 Control 
                 61.75 ± 3.75  
                 0.473 
               
               
                   
                 UV (30s) 
                 56.4 ± 11.1 
                 0.553 
               
               
                   
                 UV (60s) 
                 47.8 ± 2.3  
                 0.672 
               
               
                   
                 UV (120s) 
                 45.6 ± 8.45 
                 0.699 
               
               
                   
                 UV &amp; Ozone (30s) 
                 49.2 ± 10.3 
                 0.653 
               
               
                   
                 UV &amp; Ozone (60s) 
                 35.75 ± 2.6  
                 0.811 
               
               
                   
                 UV &amp; Ozone (120s) 
                 31.8 ± 3.34 
                 0.849 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 5 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 10 
               
             
             
               
                   
               
               
                 UV Treatment of Ultra-High Molecular 
               
               
                 Weight Polyethylene 
               
             
          
           
               
                   
                   
                   
                   
                 Pull-off 
               
               
                   
                   
                 Contact 
                   
                 Strength 
               
               
                   
                 Treatment 
                 Angle 
                 Cos (θ) 
                 (psi) 
               
               
                   
                   
               
               
                   
                 Control 
                 100.2 ± 8.1  
                 −0.177 
                 145 ± 20 
               
               
                   
                 UV (30s) 
                  94.6 ± 2.05 
                 −0.080 
               
               
                   
                 UV (60s) 
                 98.25 ± 3.9  
                 −0.143 
               
               
                   
                 UV (120s) 
                 98.6 ± 5.8 
                 −0.149 
               
               
                   
                 UV &amp; Ozone (30s) 
                 97.2 ± 4.1 
                 −0.125 
               
               
                   
                 UV &amp; Ozone (60s) 
                 93.5 ± 3.2 
                 −0.061 
               
               
                   
                 UV &amp; Ozone (120s) 
                 88.11 ± 2.0  
                  0.032 
                 390 ± 55 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 6 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 11 
               
             
             
               
                   
               
               
                 Ultra-High Molecular Weight Polyethylene 
               
               
                 Debond Strength 
               
             
          
           
               
                   
                   
                 Pull-off Strength 
               
               
                   
                 Treatment 
                 (psi) 
               
               
                   
                   
               
               
                   
                 Control 
                 145 ± 20 
               
               
                   
                 UV &amp; Ozone (120s) 
                 390 ± 55 
               
               
                   
                 UV &amp; Ozone (180s) 
                 320 ± 80 
               
               
                   
                 UV &amp; Ozone (240s) 
                  400 ± 120 
               
               
                   
                   
               
             
          
         
       
     
     The following Examples 7, 8 and 9 show the effect of ultraviolet light and short time treatments on metals. 
     EXAMPLE 7 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Contact Angles of 110 Copper 
               
               
                 UV and Ozone Treatment 
               
             
          
           
               
                 Treatment 
                   
                   
               
               
                 Time(s) 
                 Contact Angle 
                 Cos (θ) 
               
               
                   
               
             
          
           
               
                 0 
                 (Control) 
                 85.4 ± 1.0 
                 0.080 
               
               
                 10 
                   
                 80.0 ± 4.6 
                 0.174 
               
               
                 15 
                   
                 65.7 ± 2.3 
                 0.411 
               
               
                 30 
                   
                 56.1 ± 2.7 
                 0.558 
               
               
                 45 
                   
                 39.4 ± 3.9 
                 0.773 
               
               
                 60 
                   
                 37.0 ± 2.9 
                 0.798 
               
               
                 90 
                   
                 26.4 ± 6.2 
                 0.896 
               
               
                 120 
                   
                 23.1 ± 2.8 
                 0.920 
               
               
                 150 
                   
                 34.9 ± 4.4 
                 0.820 
               
               
                 180 
                   
                 17.1 ± 0.9 
                 0.956 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 8 
     Contact Angles of Commercially Oxidized Copper UV and Ozone Treatment 
     Brown Oxide 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 13 
               
               
                   
               
               
                 Treatment 
                   
                   
               
               
                 Time (s) 
                 Contact Angle 
                 Cos (θ) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 (Control) 
                 128.4 ± 6.2 
                 −0.621 
               
               
                 5 
                   
                 115.8 ± 8.1 
                 −0.435 
               
               
                 15 
                   
                  7.0 ± 2.3 
                  0.992 
               
               
                 30 
                   
                 Complete Wetting 
                 — 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 9 
     Contact Angles of Commercially Oxidized Copper UV and Ozone Treatment 
     Black Oxide (Light Side) 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 14 
               
               
                   
               
               
                 Treatment 
                   
                   
               
               
                 Time (s) 
                 Contact Angle 
                 Cos (θ) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 Control) 
                 95.0 ± 3.2 
                 −0.087 
               
               
                 15 
                   
                 40.1 ± 5.6 
                 −0.765 
               
               
                 30 
                   
                 13.1 ± 2.4 
                  0.973 
               
               
                 45 
                   
                 Complete Wetting 
                 — 
               
               
                   
               
             
          
         
       
     
     EXAMPLE 10 
     Contact Angles of UV and Ozone Treatment of Polypropylene (PP), Mechanical Grade Thermoplastic Polyolefin (MTPO) and Reactor Grade Thermoplastic Polyolefin (RTPO) 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 15 
               
               
                   
                   
               
               
                   
                 Specimen 
                 Contact Angle (θ) 
                 Cos θ) 
               
               
                   
                   
               
             
             
               
                   
                 PP Control 
                 96.0 ± 3.1 
                 −0.104 
               
               
                   
                 PP (120s) 
                 84.6 ± 2.3 
                  0.094 
               
               
                   
                 PP (240s) 
                 89.9 ± 3.5 
                  0.003 
               
               
                   
                 MTPO Control 
                 90.2 ± 1.5 
                 −0.003 
               
               
                   
                 MTPO (120s) 
                 89.7 ± 1.0 
                  0.005 
               
               
                   
                 MTPO (240s) 
                 82.9 ± 1.8 
                  0.124 
               
               
                   
                 RTPO Control 
                 93.7 ± 2.3 
                 −0.052 
               
               
                   
                 RTPO (120s) 
                 92.0 ± 3.8 
                 −0.035 
               
               
                   
                 RTPO (240s) 
                 81.8 ± 1.9 
                  0.143 
               
               
                   
                   
               
             
          
         
       
     
     Contact Angles of UV and Ozone Intermittent Treatment of Polypropylene, Mechanical Grade Thermoplastic Polyolefin and Reactor Grade Thermoplastic Polyolefin 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 16 
               
               
                   
                   
               
               
                   
                   
                 Contact Angle 
                 Contact Angle 
               
               
                   
                   
                 (120 second 
                 (240 second 
               
               
                   
                 Material 
                 Exposure) 
                 Exposure) 
               
               
                   
                   
               
             
             
               
                   
                 PP 
                 84.6 ± 2.8 
                 89.9 ± 2.7 
               
               
                   
                 MTPO 
                 89.7 ± 0.4 
                 82.9 ± 2.0 
               
               
                   
                 RTPO 
                 92.0 ± 3.2 
                 81.8 ± 1.6 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 11 
     Ultraviolet light irradiation offers promise as a method to treat metallic surfaces in preparation for subsequent operations involving adhesive bonding or priming and coating. In a series of laboratory investigations, three aluminum compounds were investigated for changes in surface wettability following exposure to ultraviolet light irradiation. Aluminum 1100 is pure aluminum, alloy 6061 is a specialty alloy used in many aerospace applications, and A356 is a cast alloy used in auto wheels. The samples were subjected to ultraviolet irradiation from a pulsed xenon lamp for various time periods. One series of experiments was carried out in ambient air, and another set of exposures were completed with an ozone enriched atmosphere. The contact angle with water was used to evaluate changes in surface properties as a function of ultraviolet light treatment. Data are reported in Table 9. In all cases the contact angle was observed to decrease following UV irradiation. The ability of UV irradiation to lower the contact angle of water on aluminum substrates was enhanced in the presence of ozone. In one ongoing study, the contact angle of A356 is substantially lower following two weeks aging after treatment. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 17 
               
             
             
               
                   
               
               
                 Effect of UV treatment time on the contact 
               
               
                 angle of water on aluminum substrates 1 . 
               
             
          
           
               
                   
                   
                   
                 Treatment Atmosphere 
                   
               
               
                   
                   
                   
                 Air Ozone 2   
               
               
                   
                   
                 UV Exposure 
                 Contact Angle 
               
               
                   
                 Alloy 
                 Time minutes 
                 degrees 
               
               
                   
                   
               
             
          
           
               
                   
                 Aluminum 1100 
                 0 
                 85.8 
                 82.5 
               
               
                   
                   
                 1 
                 71.9 
                 67.0 
               
               
                   
                   
                 3 
                 73.2 
                 35.3 
               
               
                   
                   
                 5 
                 63.7 
                 24.0 
               
               
                   
                   
                 10  
                 22.7 
                 19.8 
               
               
                   
                 Aluminum 6061 
                 0 
                 37.6 
                 36.2 
               
               
                   
                   
                 1 
                 28.1 
                 19.3 
               
               
                   
                   
                 3 
                 27.0 
                 16.8 
               
               
                   
                   
                 5 
                 26.7 
                 18.3 
               
               
                   
                   
                 10  
                 25.0 
                 16.7 
               
               
                   
                 Aluminum A356 
                 0 
                 65.4 
                 57.8 
               
               
                   
                   
                 1 
                 50.1 
                 29.9 
               
               
                   
                   
                 3 
                 33.3 
                 23.1 
               
               
                   
                   
                 5 
                 28.8 
                 23.9 
               
               
                   
                   
                 10  
                 17.1 
                 14.6 
               
             
          
           
               
                   
                 A356 10 min UV Treatment in Ozone, 
                 38.0 
               
               
                   
                 following 2 weeks aging after 
               
               
                   
                 treatment 
               
               
                   
                   
               
               
                   
                   1 Xenon pulsed lamp, quartz filter, lamp to surface distance of 2 cm; contact angle measurements collected immediately following treatment, except as noted.  
               
               
                   
                   2 Ozone flow rate of 30 standard cubic feet per hour.  
               
             
          
         
       
     
     EXAMPLE 12 
     This example details how laboratory-controlled surface modifications of epoxy coatings with UV/ozone treatments can be utilized to beneficially affect paint adhesion. Previous studies demonstrated that surface modifications, brought about by gaseous species present in a bake oven cure environment, can effect the surface chemistry of urethane-crosslinked epoxy coatings, and favorably influence their adhesion to applied melamine-crosslinked polyester coatings. In the present invention, epoxy-coated panels were subjected to varying degrees of UV/ozone exposure, and the effects of the treatments on adhesion to the polyester coating was then evaluated. X-ray photoelectron spectroscopy (XPS) was used to characterize the reacted epoxy surfaces, and interfacially-generated epoxy/polyester surfaces, as a function of UV/ozone exposure time in order to gain a chemical insight as to how the surface treatments beneficially effect adhesion. It was revealed that polyester/epoxy adhesion improves noticeably with exposure to ozone alone, and dramatically under exposures to UV/ozone. XPS identified that increased UV/ozone exposure of the epoxy resulted in higher amounts of surface carboxylate species, and a depletion in a polyether surface-segregated overlayer present on the epoxy coating. Lesser amounts of polyether material were present at the interfaces of coating systems exhibiting better intercoat adhesion. 
     Additives are routinely incorporated into paint formulations to improve properties such as appearance and rheology. Surface segregation of these additives can occur during the cure process. The amount of segregation is influenced by the nature of the polymers comprising the coating and the manner in which the coating is processed. This phenomenon can produce deleterious effects on adhesions to the subsequently applied paint layer. One example is a polyether crater-control additive (CCA) found in some commercial epoxy-based paints. This CCA surface-segregates when the paint is cured, creating a surface of relatively low polarity with poor adhesion characteristics. A previous study revealed that this surface overlayer is partially removed, when the paint is cured using a gas-fired oven, by a reaction with nitrogen oxides produced in the combustion of methane with air. The adhesion properties of this “surface-modified” epoxy were significantly improved over the same paint cured using an electric oven (where the surface CCA remains intact after cure in the “inert” air environment). However, it is not necessarily desirable to rely on fortuitous chemistry occurring during bake oven cure to insure proper intercoat adhesion in multi-layered paint systems. 
     Controlled laboratory UV/ozone treatments were used to enhance the adhesion properties of a commercial epoxy-based paint (cured using an electric oven). Epoxy-coated panels were subjected to varying degrees of UV/ozone exposure, and the effects of the treatments on adhesion to an applied polyester coating were then evaluated. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical changes present on the reacted epoxy surfaces and interfacially-generated epoxy-polyester surfaces as a function of UV/ozone exposure time. The experiments provided a chemical insight as to how the surface treatments enhance adhesion performance. In addition, contact angle measurements were made to assess the effects of the UV/ozone treatments on surface wettability. Both the XPS and contact angle measurements were correlated to adhesion/tape pull results obtained on polyester applied to epoxy-based paints. 
     UV/ozone treatments were accomplished using a 180-320 mn wavelength xenon flashlamp (Xenon Corporation) with an external ozone generator (Ozotech Corporation) using oxygen as the source gas. Chemical characterizations by XPS were made using an AXIS 165 Electron Spectrometer manufactured by Kratos Analytical, Manchester, England, using a monochromatic Al Kα (1486.6 eV) X-ray source. Contact angle measurements were carried out using a Rame-Hart goniometer with deionized water as the testing liquid. Scribe and cross-hatch adhesion/tape-pull testing (FLTM BI 106-01) was conducted on complete paint systems consisting of commercial epoxy, polyester and urethane base-coat/top-coat layers. 
     The polyether CCA is high in ether content. 
     An increased amount of ether is observed on the surface of the electric-oven cured epoxy relative to the bulk epoxy, which itself has ether moieties due to its epoxy formulation. Gas-oven cure removes much of the CCA without actually oxidizing the surface, as is revealed in a reduced ether content without an enhancement in carboxylate. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 18 
               
             
             
               
                   
               
               
                 Contact angle measurements of epoxy paint 
               
               
                 after UV/ozone exposure 
               
             
          
           
               
                   
                 Treatment 
                 (θ) 
               
               
                   
                   
               
               
                   
                 Initial 
                 68.7 
               
               
                   
                 60s ozone 
                 68.7 
               
               
                   
                 15s UV/ozone 
                 62.6 
               
               
                   
                 30s UV/ozone 
                 59.5 
               
               
                   
                 60s UV/ozone 
                 51.5 
               
               
                   
                   
               
             
          
         
       
     
     Scribe and cross-hatch adhesion/tape pull testing (PATTI) revealed that the polyester paint easily delaminates from the initial untreated electric-oven cured epoxy surface only partial delamination occurs after exposure to ozone alone. After exposure to UV/ozone, it was not possible to generate the epoxy/polyester interface at room temperature. The system could only be forced to fracture after applying artificial stresses through immersion in liquid nitrogen (See FIGS. 24 to  27 ). Comparing interfaces generated from the initial, 60s ozone, and 15s UV/ozone exposed samples (data not shown), XPS identified an excess amount of ether at the interfacial surfaces, which was attributed to the CCA. The level of ether (CCA) measured varied inversely relative to the observed epoxy/polyester intercoat adhesion strengths. 
     Exposure of the electric-oven cured epoxy to ozone alone improves adhesion to the polyester paint, while UV/ozone exposure improves adhesion to the point where interfacial paint failure cannot be generated. XPS surface characterization reveals that UV/ozone oxidatively removes the polyether-based CCA overlayer from the electric-oven cured epoxy paint. The majority of the carboxylate debris formed is not cross-linked into the bulk epoxy, since it can be removed by a base rinse. Improved adhesion properties of the epoxy can be attributed both to removal of surface CCA, and to the production of some polar surface carboxylate species that remain cross-linked into the bulk epoxy. 
     EXAMPLE 13 
     The focus of this experiment is to study the influence of ozone on UV treatment of glass fiber filled (PET) composite and to optimize process times to make this process effective. 
     Procedure 
     A pulsed Xenon lamp and powder supply (Xenon Corporation) was used as a source for UV radiation. It is capable of providing emissions below 185 nm. Changes in the ambient were introduced through presence of ozone from an external ozone generator (Ozotech, Inc.). Photons, usually those with low wavelength, are energetic species which are used to activate many chemical reactions. The mechanisms for ozone formation and destruction in the presence of UV light are as follows: 
     
       
         O 2   +h ν(184.9 nm)→O 2 * 
       
     
     
       
         O 2 *→2O 
       
     
     
       
         2O+O 2 →O 3   
       
     
     
       
         O 3   +h ν(253.7 nm)→O+O 2   
       
     
     Active atomic oxygen and ozone are capable of reacting with substrate and increasing its surface energy. 
     The material to be evaluated in this study was Rynite 530, a 30% glass reinforced modified PET composite from DuPont (Wilmington, Del.). Equilibrium contact angle of water prior to and after UV treatment were measured using the Rame-Hart goniometer apparatus. Adhesive bonding properties were decided using the PATTI (pneumatic adhesion tensile testing instrument) tester. Surface chemistry change were given by XPS results. 
     Results 
     PET surface wettability as a function of various UV treatments is shown in Table 20. It was observed that PET control sample does not wet. UV exposure did help increase the wettability of the surface. Addition of applying ozone and exposing UV was seen more significantly improving the surface wetting characteristics. The longer the exposure time is, the lower the contact angle becomes. 
     The contact angle measurement results were correlated to adhesion bonding improvement. The polymer samples were bonded to aluminum stubs using an epoxy structural adhesive, ARALDITE AW106 with hardener HV953 (from Ciba Geigy Corporation). As shown in Table 21, the adhesion bonding first increases with increasing of wettability, then decrease with further increasing of wettability. It seems that over UV exposure will not benefit the adhesion improvement. 
     Surface chemistry composition change were detected via XPS. From Table 22 it is seen that the C/O ratio increased due to the UV exposure indicating more oxygen contained functional group formed on the surface. The XPS results showed that the reason for the adhesion improvement was because the increase of polar functional group on the surface caused by UV ozone exposure. Table 23 lists the distribution of surface functional group change prior to and after the UV treatment. Good adhesion corresponded to a high C—O and C—OOH group concentrations. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 20 
               
             
             
               
                   
               
               
                 Contact angle measurements for Rynite 530. 
               
             
          
           
               
                   
                   
                 Contact angle 
               
               
                   
                 Sample 
                 (degree) 
               
               
                   
                   
               
               
                   
                 Control 
                 75 
               
               
                   
                 t = 2 min, d = 2 cm 
                 62 
               
               
                   
                 t = 2 min, d = 2 cm with ozone 
                 58 
               
               
                   
                 t = 4 min, d = 2 cm with ozone 
                 57 
               
               
                   
                 t = 4 min, d = 1 cm with ozone 
                 46 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 21 
               
             
             
               
                   
               
               
                 Adhesion Bonding for Rynite 530 via PATTI 
               
               
                 Test. 
               
             
          
           
               
                   
                   
                 Pull-off Tensile 
               
               
                   
                   
                 Strength 
               
               
                   
                 Sample 
                 (psi) 
               
               
                   
                   
               
               
                   
                 control 
                 564 
               
               
                   
                 t = 2 min, d = 2 cm 
                 810 
               
               
                   
                 t = 2 min, d = 2 cm with ozone 
                 908 
               
               
                   
                 t = 4 min, d = 2 cm with ozone 
                 973 
               
               
                   
                 t = 4 min, d = 1 cm with ozone 
                 851 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 22 
               
             
             
               
                   
               
               
                 Surface Composition C/O Ratio for Rynite 530 
               
               
                 Via XPS. 
               
             
          
           
               
                   
                 Sample 
                 C/O 
               
               
                   
                   
               
               
                   
                 control 
                 0.35 
               
               
                   
                 t = 4 mi, d = 2 cm with ozone 
                 0.53 
               
               
                   
                 t = 4 min, d = 1 cm with ozone 
                 0.52 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 23 
               
             
             
               
                   
               
               
                 Surface Functional Group Distribution Based on 
               
               
                 C 1s Curve Fitting 
               
             
          
           
               
                   
                   
                 t = 4 min, 
                 t = 4 min, 
               
               
                   
                   
                 d = 2 cm 
                 d = 1 cm 
               
               
                   
                 Control 
                 with ozone 
                 with ozone 
               
               
                   
                   
               
             
          
           
               
                   
                 CHX 
                 67.4 
                 47.6 
                 56.6 
               
               
                   
                 C—O 
                 20.4 
                 32.1 
                 21.1 
               
               
                   
                 C═O 
                 1.89 
                 2.1 
                 3.6 
               
               
                   
                 COOH 
                 9.1 
                 17.1 
                 17.2 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE 14 
     A pulsed Xenon lamp and power supply obtained from Xenon Corporation was used as a source for UV radiation. It was capable of providing emissions below 185 nm. Changes in the ambient were introduced through presence of ozone from an external ozone generator (Ozotech, Inc.) and water. The other variables that might affect the extent of polymer surface modification were: distance of the lamp from the substrate surface (d), radiation exposure time (t), intensity of lamp radiation. The material evaluated in this experiment was Rynite 530, a 30% glass reinforced modified PET composite from DuPont. 
     On exposure to various UV treatments the substrate was characterized for wettability, surface chemical composition, and adhesive bonding. Contact angle measurements, a measure of wettability were carried out using a Rame-Hart goniometer with de-ionized water as the testing liquid. For each condition, 9-10 measurements of the contact angle were taken. Contact angle measurements were only sensitive to changes in the top 2 nm of the surface, and they do not reveal much about the surface chemical composition. Hence, X-ray photoelectron spectroscopy (XPS) was carried out on the control and the UV treated samples. The instruments used for the characterizations was a Perkin-Elmer Physical Electronics PHI5400 ESCA Spectrometer equipped with both a standard Mg Kα 1,2  X-ray source and a monochromated Al Kα 1,2  X-ray source, and an electron flood gun for neutralization. The instrument used a 180° hemispherical energy analyzer operated in the fixed analyzer mode and a position sensitive detector. The optimum spot size for the conditions used was the 1.00 mm diameter aperture. The monochromic source was used since it provides better resolution for data collection. A molybdenum mask was also employed to assist in neutralizing the charging. 
     The substrate surfaces prior to and after UV treatment were also characterized for adhesive bonding properties using a PATTI (pneumatic adhesion tensile testing instrument) tester. The tests were carried out using PATTI-2A made by SEMicro division, M. E. Taylor Engineering, Inc. The PATTI instrument and method confirms to ASTM D4541, “Pull-off strength of coatings using portable adhesion tests”. The polymer samples were bonded to aluminum stubs using an epoxy structural adhesive. ARALDITE AW106 with hardener HV953 (from Ciba Geigy Corporation). The adhesive was allowed to cure for more than 15 hours at room temperature. Five or more samples were tested for each condition. Results from the adhesion tests were correlated to the contact angle measurements. 
     FIG. 28 is a plot of cosine of the contact angle (θ) versus treatment conditions for PET with or without ozone presence. Here, modification is measured by the substrate&#39;s wettability. A surface is said to be perfectly wettable if θ is equal to zero. As θ increases, the degree of wettability decreases. It was observed that PET control sample did not wet. UV exposure did help increase the wettability of the surface. Addition of applying ozone was seen more significantly improving the surface wetting characteristics. An increase in the intensity of radiation (obtained by decreasing the distance between the substrate and the lamp surface) or an increase in the exposure time, increased the extent of modification. 
     The ozone influence of UV treatment was enhanced by applying water droplets on the substrate surface. Ozone is 12.5 times more soluble in water than oxygen. Decomposition of ozone in water, as shown immediately below, produces free radicals (HO 2 . and HO.) which can react with substrate surface. 
     
       
         O 3 +H 2 O→HO 3 +OH −   (5) 
       
     
     
       
         HO 3 +OH→2HO 2   (6) 
       
     
     
       
         O 3 +HO 2 →HO+2O 2   (7) 
       
     
     Water droplets caused uneven treated surfaces unless dispensed on the surface in very small droplets. An uniform thin water layer saturated with ozone on the substrate significantly increased the extent of modification if a correct UV exposure time was used and a much more uniform modified surface was obtained. FIG. 29 is a plot comparing the wettability change with or without water under same UV exposure condition. Presence of water droplets dramatically decreased the contact angle, inhomogeneous surface was obtained (as shown in error bar). A thin layer of water layer saturated with ozone generated a more uniform surface. However, longer UV exposure time was needed to create the same modification. UV exposure shorter than necessary did not effect the contact angle change. 
     The contact angle measurement results were correlated to adhesion bonding improvement. The polymer samples were bonded to aluminum stubs using an epoxy structural adhesive, ARALDITE AW106 with hardener HV953 (from Ciba Geigy Corporation). As shown in FIG. 30, adhesion tensile strength increased with increasing of wettability, then decreased with further increasing of wettability due to the over UV exposure of the surface. 
     Although the presence of water droplets showed positive effect on wettability improvement, adhesion property did not show as much difference. All the UV treated samples gave excellent adhesion. Samples showed cohesive failure at PET matrix. The results are shown in FIG.  31 . 
     UV/ozone as a high speed, low cost surface modification method showed a positive surface bonding improvement on PET/glass fiber enforced composites. The intensity of radiation, exposure time and presence of water will all influence the surface treatment results. Surface chemistry change is detected after UV exposure. UV exposure will benefit the interfacial bonding because of the increase of polar functional group on the surface. 
     It is intended that the foregoing description be only illustrative of the present invention and that the present invention be limited only by the hereinafter appended claims.