Chemical functionalization of material surfaces using optical energy and chemicals Number:7,094,451 from the United States Patent and Trademark Office (PTO) owispatent A method using irradiation with optical light in the presence of a chemical dissolved in a solvent which chemical reacts with the surface in the presence of the irradiation to modify the surface (12A, 104A, 202A, 304A, 402A, 502A) of a substrate (12, 104, 202, 304, 402, 502) is described. The light can be pulsed or continuous. The method is significantly enhanced by the presence of water (14, 124, 204, 308, 410, 508) as the solvent containing the dissolved chemical on the surface. The treated surfaces are more paintable and bondable.<H functionalization, chemicals, Chemical, functi, 7094451.html, Patent, pto, 7094451

Title: Chemical functionalization of material surfaces using optical energy and chemicals

Abstract: A method using irradiation with optical light in the presence of a chemical dissolved in a solvent which chemical reacts with the surface in the presence of the irradiation to modify the surface (12A, 104A, 202A, 304A, 402A, 502A) of a substrate (12, 104, 202, 304, 402, 502) is described. The light can be pulsed or continuous. The method is significantly enhanced by the presence of water (14, 124, 204, 308, 410, 508) as the solvent containing the dissolved chemical on the surface. The treated surfaces are more paintable and bondable.

Patent Number: 7,094,451 Issued on 08/22/2006 to Drzal, et al.

Inventors: Drzal; Lawrence T. (Okemos, MI), Tummala; Praveen (East Lansing, MI)
Assignee: Board of Trustees of Michigan State University (East Lansing, MI)

Appl. No.: 10/289,986

Filed: November 7, 2002

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
09287978	Apr., 1999	6565927

Current U.S. Class: 427/581 ; 250/492.1; 250/504R; 250/505.1; 427/515; 427/553; 427/558; 427/595

Current International Class: B05D 3/06 (20060101); C23C 18/14 (20060101)

Field of Search: 427/492,508,510,512,515,553,558,581,595,256,282,322,327,421,430.1 250/492.1,504R,505.1

References Cited [Referenced By]

U.S. Patent Documents


3890176	June 1975	Bolon
4717516	January 1988	Isaka et al.
4756765	July 1988	Woodroffe
4803021	February 1989	Werth et al.
4810434	March 1989	Caines
4867796	September 1989	Asmus et al.
4874672	October 1989	Etter et al.
4987032	January 1991	Miyasaka et al.
5019210	May 1991	Chou et al.
5098618	March 1992	Zelez
5200122	April 1993	Katoh et al.
5281798	January 1994	Hamm et al.
5357005	October 1994	Buchwalter et al.
5387462	February 1995	Debe
5464480	November 1995	Matthews
5500459	March 1996	Hagemeyer et al.
5512123	April 1996	Cates et al.
5755913	May 1998	Liaw et al.
5863333	January 1999	Kato et al.
5871823	February 1999	Anders et al.
5891530	April 1999	Wright
5948484	September 1999	Gudimenko et al.
6022596	February 2000	Baum et al.
6117497	September 2000	Murahara et al.
6197101	March 2001	Matsumura et al.
6245155	June 2001	Leon et al.
6565927	May 2003	Drzal et al.
2003/0194715	October 2003	Li et al.

Foreign Patent Documents


723631	Feb., 1955	GB
WO 95/20006	Jul., 1995	WO

Other References

Bolon et al., Ultraviolet Depolymerization of Photoresist Polymers, Polymer Eng. and Sci. vol. 12 pp. 109-111 (1972). cited by other .
M.J. Walzak et al., UV and Ozone Treatment . . . Polymer Surface Mod.: Relevance to Adhesion, K.L. Mittal (Editor), pp. 253-272 (1995). cited by other .
M. Strobel et al., A Comparison of gas-phase methods of modifying . . . , Journal of Adhesion Sci. and Tech. pp. 365-383 (1995). cited by other .
N. Dontula et al., A Study of Polymer Surface Mod . . . Proceedings of 20th Annual Adhesion Society Mtg., Hilton Head, SC (1997). cited by other .
N. Dontula et al., Surface activation of polymers using . . . , Proceedings of Society of Plastics Eng. ANTEC '97, Toronto, Canada. cited by other .
Haack, L.P., et al., 22nd Adhesion Soc. Meeting (Feb. 22-24, (1998). cited by other .
Experimental Methods in Photochemistry, Chapter 7, pp. 686-705 (1982). cit- ed by other.

Primary Examiner: Meeks; Timothy
Assistant Examiner: Markham; Wesley D.
Attorney, Agent or Firm: McLeod; Ian C.

Parent Case Text

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 09/287,978, filed Apr. 7, 1999 now U.S. Pat. No. 6,565,927.

Claims

We claim:

1. A method for modifying a surface of a polymer or polymer composite substrate, the improvement which comprises: (a) providing a surface of a polymer or polymer composite substrate; (b) providing a lamp for generating optical energy; (c) providing a layer of water between the surface of the substrate and the lamp; (d) providing an aqueous silane solution on the polymer or polymer composite substrate surface to be modified comprising at least one silane of the formula Si(OR').sub.4-n(R'').sub.n where n is 1, 2, or 3, R' is an alkyl group of 1 to 8 carbon atoms, and R'' is an organic moiety comprising a member selected from the group consisting of a metal, vinyl, cyano, amino, mercapto, halogen, aldehyde, ketone, and acid, the silane being dissolved in water, wherein a silyl group of the silane reacts with hydroxyl groups on the polymer or polymer composite surface in the presence of the optical energy; and (e) irradiating the surface with the optical energy at wavelengths between about 185 nanometers and 254 nanometers which is provided to the surface by irradiating through the layer of water to filter out any longer wavelengths in an infrared region so that the substrate does not overheat, such that the intensity of the optical energy reaching the surface is sufficient to modify the surface while the surface is exposed to the silane, so that the silyl group with the organic moiety is covalently bonded to the surface.

2. The method of claim 1 wherein the surface is irradiated with the optical energy which is generated by a xenon flashlamp energized by current pulses.

3. The method of claim 1 or 2 wherein the irradiating the surface is in a predetermined pattern with the optical energy.

4. The method of claim 1 or 2 wherein the surface comprises a glass fiber-reinforced PET.

5. The method of claim 1 or 2 wherein the surface is treated with ozone prior to irradiating the surface.

6. The method of claim 1 or 2 wherein the silane is an amino silane which forms an amino silyl group on the surface.

7. The method of claim 1 wherein the layer of water is provided as liquid on a transparent tray between the surface and the lamp to filter out the longer wavelengths.

8. A method for modifying a surface of a polymer or polymer composite substrate, the improvement which comprises: (a) providing a surface of a polymer or polymer composite substrate; (b) providing a lamp for generating optical energy; (c) providing a layer of water between the surface of the substrate and the lamp; (d) irradiating the polymer or polymer composite surface through the layer of water with optical energy from the lamp at wavelengths between about 185 nanometers and 254 nanometers which is provided to the surface by irradiating through the layer of water to filter out any longer wavelengths in an infrared region so that the substrate does not overheat, while the surface is exposed to ozone dissolved in water on the surface, at an intensity sufficient to render the surface reactive with at least one silane of the formula Si(OR').sub.4-n(R'').sub.n where n is 1, 2, or 3, R' is an alkyl group of 1 to 8 carbon atoms, and R'' is an organic moiety and comprises a member selected from the group consisting of a metal, vinyl, cyano, amino, mercapto, halogen, aldehyde, ketone, and acid; and (e) providing on the irradiated surface the silane dissolved in water which reacts with hydroxyl groups on the irradiated polymer or polymer composite surface to covalently bond a silyl group with the organic moiety to the surface.

9. The method of claim 8 wherein the surface is irradiated with the optical energy which is generated by a xenon flashlamp energized by current pulses.

10. The method of claim 8 or 9 wherein the irradiating the surface is in a predetermined pattern with the optical energy.

11. The method of claim 8 or 9 wherein the surface comprises a glass fiber-reinforced PET.

12. The method of claim 8 or 9 wherein the silane is an amino silane which forms an amino silyl group on the surface.

13. The method of claim 8 wherein the layer of water is provided as a liquid on a transparent tray between the surface and the lamp to filter out the longer wavelengths.

14. The method of claim 7 or 13 wherein the transparent tray is quartz or fused silica.

15. The method of claim 7 or 13 further comprising cooling the surface of the polymer or polymer composite substrate during the irradiation with a cooling plate upon which the substrate is mounted.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

Reference to a "Computer Listing Appendix Submitted on a Compact Disc"

Not Applicable.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a process for treating surfaces of substrates coated with a chemical in a solvent using optical energy to produce surfaces with the chemical bonded to it. In particular, the present invention relates to a preferred process for pretreating surfaces of substrates by providing water containing the chemical between the optical energy source and the substrate.

(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 Hagemeyer et al. and U.K. Patent 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 20.sup.th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); C. L. Weitzsacker et al., "Utilizing X-ray photoelectron spectroscopy to investigate modified polymer surfaces", Proceedings of 20.sup.th 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'97, Detroit, Mich.; C. L. Weitzsacker et al., "Surface pretreatment of plastics and polymer composites using ultraviolet light", Proceedings of ACT'97, Detroit, Mich.; N. Dontula et al., "Surface activation of polymers using ultraviolet activation", Proceedings of Society of Plastics Engineers ANTEC'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'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 a process which bonds a chemical to the surface of a substrate.

It is further an object of the present invention to provide a process which is 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 provides a method using irradiation with optical light in the presence of a chemical dissolved in a solvent which chemical reacts with the surface in the presence of the irradiation to modify the surface of a substrate. The light can be pulsed or continuous. The method is significantly enhanced by the presence of water as the solvent containing the dissolved chemical on the surface. The treated surfaces are more paintable and bondable.

Therefore, the present invention provides a method for modifying a surface, the improvement which comprises (a) providing a solvent on the surface to be modified comprising at least one chemical dissolved in the solvent which reacts with the surface in the presence of optical energy; and (b) irradiating the surface with the optical energy at an intensity sufficient to modify the surface by reacting the chemical with the surface.

The present invention further provides a method for modifying a surface, the improvement which comprises (a) irradiating the surface with an optical energy at an intensity sufficient to render the surface reactive with at least one chemical; and (b) providing on the irradiated surface a solvent comprising the chemical dissolved in the solvent which reacts with the irradiated surface to modify the surface.

In a further embodiment of the above method, the surface is irradiated with the optical energy which is generated by a xenon flashlamp energized by current pulses.

In a further embodiment of the above method, the surface is exposed to ozone dissolved in the solvent during the irradiation.

In a further embodiment of the above method, the irradiating the surface is in a predetermined pattern with the optical energy.

In a further embodiment of the above method, wherein the surface is comprised of a polymer.

In a further embodiment of the above method, the surface comprises a composite material.

In a further embodiment of the above method, the surface comprises a metallic material.

In a further embodiment of the above method, the solvent is water.

In a further embodiment of the above method, the water is provided on the surface by spraying or by humidity in air adjacent to the surface or as a thin sheet of water on the surface.

In a further embodiment of the above method, the surface is treated with ozone prior to irradiating the surface.

In a further embodiment of the above method, the optical energy is at a wavelength between about 185 nanometers and 254 nanometers, without higher wavelengths.

In a further embodiment of the above method, the surface is a polymer with hydroxyl groups and wherein the chemical reacts with the hydroxyl groups to form a covalent bond with the polymer.

In a further embodiment of the above method, the surface is a polymer with hydroxyl groups and the chemical is silane which reacts with the hydroxyl group to form a silyl group on the polymer.

In a further embodiment of the above method, the chemical is a silane of the formula XSi where X is a functional group which is co-linked on the polymer after the reaction with the polymer.

In a further embodiment of the above method, the chemical is an amino silane which forms an amino silyl group on the surface.

In further embodiments, it is desirable to cool the surface with the solvent to freeze the chemically active groups on 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 include that the process is cheaper than chemical modification techniques such as plasma and that it is not a batch process as with plasma and acid etching. Further, the 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 excimer 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 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. The 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 of the present invention 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. The process is an easier, flexible or alternate way for the packaging industry 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 12A 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 104A and then irradiated with a UV lamp 106. The surface 104A 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 202A while the surface 202A is irradiated by a UV lamp 212, then the substrate surface 202A 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 304A 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 402A 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 .theta.) 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 Cls curve fits on XPS measurements of polycarbonate surfaces treated with UV and water.

FIG. 10 is a graph showing Cls 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. 11A).

FIG. 12B is a surface plot of the UV treated polycarbonate AFM image (FIG. 11B).

FIG. 13 is a graph showing the effect of UV treatment on adhesive bond strength and contact angle with water (cos .theta.) for polycarbonate.

FIGS. 14A to 14D are ESEM images of the molded surfaces of mechanical grade TPO (FIGS. 14A and 14B) and reactor grade TPO (FIGS. 14C and 14D).

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 .theta.) and adhesive bond strength of reactor grade TPO (without UV stabilizers).

FIG. 18 are graphs showing the effect of UV treatment on wettability (cos .theta.) and adhesive bond strength of polypropylene (without UV stabilizers).

FIGS. 18A to 18D are ESEM images of PATTI tested failure surfaces of baseline MTPO (without UV stabilizers).

FIGS. 19A to 19F are ESEM images of PATTI tested failure surfaces of UV treated MTPO (without UV stabilizers) UV treatment conditions were t=4 min at d=2 cms.

FIGS. 20A to 20D are ESEM images of PATTI tested failure surfaces of baseline RTPO (without UV stabilizers).

FIGS. 21A to 21D 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. 22A to 22D 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. 18 and 19 are graphs showing contact angle measurements for the epoxy paint.

FIGS. 20 and 21 are graphs showing pull test measurements.

FIG. 22 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. 23 is a graph showing wettability change presence/absence water during UV/Ozone treatment.

FIG. 24 is a graph showing the correlation of contact angle and adhesion change.

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. 25 is a graph showing the affect of water and ozone on adhesion.

FIG. 26 is a graph comparing the PATTI results of UV/ozone treated Ticona to UV/ozone treated Ticona immersed in silane.

FIG. 27 is a graph showing the PATTI results for UV treated Ticona through silane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

All patents, patent applications, government publications, government regulations, and literature references cited in this specification are hereby incorporated herein by reference in their entirety. In case of conflict, the present description, including definitions, will control.

Preferably, the surface of the substrate is exposed to an optical energy source provided by an ultraviolet (UV) lamp or 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 or provided by humidity in the air adjacent to the substrate surface.

In a further embodiment of the present invention, a method is provided for covalently bonding one or more chemicals to the surface of a substrate surface. A solvent comprising at least one chemical dissolved therein is placed on the substrate surface in the form of droplets, a sheet, or humidity which is then irradiated with optical energy of sufficient intensity and duration that the chemical becomes covalently bonded to groups on the substrate surface thereby modifying the surface of the substrate. Preferably, the solvent is water. Alternatively, the surface of the substrate is irradiated with the optical energy to render the surface reactive with at least one chemical and then the solvent comprising the chemical dissolved therein is placed on the irradiated surface in the form of droplets, a sheet, or humidity wherein the chemical in the solvent reacts with the irradiated surface to become bound thereon.

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 or bond the chemical when present in the water to 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 .apprxeq.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. In a further embodiment of the above processes for modifying the surface of a substrate, the water comprises one or more chemicals dissolved therein which reacts with the surface of the substrate when exposed to the UV radiation of sufficient intensity and duration to bond the chemical to a group on the surface of the substrate. Alternatively, the one or more chemicals are in a solvent other than the water.

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 12A of the substrate 12. The substrate 12 is then moved to station B where the surface 12A is irradiated with UV light from a lamp 24 in a housing 24A 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 12A, the substrate 12 is moved to station C where the surface 12A 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 12A clean. The surface 12A 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 106A. 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 104A is air-dried by air directed at the surface 104A by a blower (not shown).

In operation, the system 100 provides air on the surface 104A of the substrate 104. The substrate 104 can be cooled to encourage moisture to condense as droplets 124 on the surface 104A. The substrate 104 is irradiated by the UV lamp 106 and then air-dried upon removal from the chamber 108. The substrate surface 104A 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 202A which is spread on the surface 202A. 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 202A is irradiated by lamp 212 in housing 212A 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 202A 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 304A 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 404A 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 402A of the substrate 402 is irradiated through the layer 412 and water 410 by lamp 414 in housing 414A. 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 502A of the substrate 502. The cutouts 506 are provided with water 508. The mask 504 is irradiated with a lamp 510 in a housing 510A powered by a power supply and pulse modulator (not shown) as in FIG. 1 via lines 512. In this embodiment, the surface 502A 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'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.TM. fused silica (Heraeus) and PYREX.RTM. glass (Corning). The glass plates act as filters and have different transmission characteristics. SUPRASIL.TM. fused silica transmits light in the UVC region and has a 10% transmission at 170 nm. PYREX.RTM. glass transmits light primarily in the UVB region (280 nm and higher) and filters the high frequency UVC radiation. PYREX.RTM. glass 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'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. 11A and 11B). Also, environmental scanning electron microscopy (ESEM) is being used to determine the effect initial substrate morphology has on UV treatment (FIGS. 14A to 14D). 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 (.theta.) 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 K.alpha..sub.1,2 X-ray source, and a monochromated Al K.alpha..sub.1,2 X-ray source, and an electron flood gun for neutralization was used. The instrument uses a 180.degree. 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 .mu.m to a rectangle of 1.5.times.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 Cls was used to assess the neutralizer operation. An asymmetric Cls 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 Cls 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 14D and 15A to 15B). 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 test 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".

For many applications such as painting, corrosion protection, adhesive bonding, and the like, the surfaces of substrates have to be treated to alter their native chemistry to one that is beneficial for the intended application. Because of the need to reduce or eliminate volatile organic compounds from the air and organic liquid and vapor wastes, a simple, inexpensive method was needed for treating the surfaces of the substrates which was environmentally benign. The further embodiment of the present invention wherein a solvent comprising one or more chemicals reactive with the surface of the substrate when the surface is irradiated with an optical energy source as mentioned previously satisfies the above need.

Thus, by treating the surface of the substrate (which includes polymers, metals, ceramics, or composites, as a solid film, fiber, or particle) in the manner disclosed above but wherein one or more chemicals dissolved in a solvent, preferably water, is in contact with the surface of the substrate during or following irradiation with the optical energy source to modify the surface. In either arrangement, the surface of the substrate is modified by reaction of the one or more chemicals with the surface of the substrate to produce a substrate with a modified surface with improved wettability, chemical compatibility, and adhesiveness. This further embodiment of the present invention provides a substantial improvement (up to about 500%) in adhesion through the addition of specific chemical groups to the surface of substrates. This embodiment is particularly remarkable because of its easy implementation, simplicity, ease of use, cleanliness, and minimal use of solvents or chemical compounds.

The advantages of this embodiment for modifying surfaces of substrates include the short treatment times needed to modify the surface with a chemical, the ability of the method to be conducted at ambient temperatures and pressures, that the method does not involve the use of caustic acids or solutions, that it is environmentally acceptable, that it can be used with any shape substrate (for example, film, fiber, particle, or the like), and that it is economically competitive or superior to the methods currently being used. Further advantages include that any functional chemical or compound soluble in water can be applied to the surface; the water allows the UV light to pass through it without attenuation; the surface of the substrate being treated remains low; and the treatment times are short. For example, metalization of plastic surfaces can be conducted without the use of electrolytic cells, strong acidic or caustic solutions, and without solutions containing metal wastes. Likewise, polymers can be grafted onto metallic surfaces to provide corrosion protection to the metallic surfaces. Thus, this embodiment of the present invention would be of interest to the U.S. government and to American, British, Canadian, French, German, and Asian companies. It would be of particular interest to the automobile and structural sectors of the above companies.

In a preferred embodiment, the optical energy source is preferably high intensity ultraviolet light. The substrate surface to be treated is immersed in a thin solution of one or more water soluble chemicals or compounds covering the surface to a depth of preferably about 1 to 5 mm wherein the one or more chemicals has a desirable chemical functionality in water. The surface is then irradiated with the optical energy source, preferably short wavelength UV light from about 180 to 300 nm wavelength. The radiation from the optical energy source interacts with the one or more chemicals in the water to induce a chemical reaction between a group on the one or more chemicals and a group (such as a hydroxyl group or the like) on surface of the substrate in which the one or more chemicals becomes covalently bonded to the surface or the radiation from the optical energy source interacts with the substrate surface to disrupt and change chemical bonds to create a surface with reactive groups favorable to covalently bond a group on the one or more chemicals to the surface, or both. Alternatively, the substrate surface is irradiated with the optical energy source, preferably with short wavelength UV light from about 180 to 300 nm wavelength, and optionally in the presence of ozone, to render the surface reactive to one or more chemicals. After irradiation, the irradiated surface is immersed in a solution comprising the one or more water soluble chemicals to covalently bond the one or more chemicals to the surface of the substrate.

The chemical in the solution can be any chemical with a reactive group including, but not limited to, organic silanes, aldehydes, ketones, hydroxy acids, acid halides, alcohols, thiols, esters, amides, ethers, epoxies, and the like, which will react with the substrate surface. The preferred solvent for the chemical is water; however, for particular chemicals such as epoxies, the preferred solvent is an organic solvent. Thus, as an example, when the surface is a polymer with hydroxyl groups, the reactive group of the chemical in the solvent or water reacts with the hydroxyl groups when the surface is irradiated with the optical energy while the surface is immersed in the solution comprising the chemical or immersed in the solution comprising the chemical following the exposure to the optical energy to covalently bond the chemical to the surface.

In a further example, the surface is a polymer with hydroxyl groups and the chemical in the solvent or water is an organic silane which reacts with the hydroxyl groups when the surface is irradiated with the optical energy source, preferably UV light, while the surface is immersed in the solution comprising the chemical or immersed in the solution comprising the chemical following the exposure to the optical energy source to form a silyl group on the surface. The Si atom of the silyl group can be bound to one hydroxyl group or bridge two or three hydroxyl groups.

In a further example, when the surface is a polymer with hydroxyl groups and the chemical in the solvent or water is an XSi organic silane where X is a functional group which becomes co-linked on the polymer when irradiated with the optical energy source, preferably UV light, while the surface is immersed in the solution comprising the chemical or immersed in the solution comprising the chemical following the exposure to the optical energy source. Thus, the overall effect of the method is the rapid reaction between the chemical and the substrate surface.

Thus, the organic silanes and XSi organic silanes which are useful are those which react with the reactive groups on the surface of the substrate. Included are the preferred silanes of the formula: (RO).sub.3SiR.sub.1 where R is a lower alkyl group (1 to 8 carbon atoms) and R.sub.1 can be an organic group which can be an alkyl, alkoxy, alkenyl or alkynyl, cycloaliphatic, aromatic group containing 1 to 25 carbon atoms. R.sub.1 can include substituents of O, N, or S and can provide a hydroxide, an aldehyde, acid, base, sulfide, cyanide, mercaptan, and the like. Examples of basic moieties especially useful as catalysts include amines and pyridyl groups. Useful acidic functionalities include carboxylic acids, sulfonic acids, and furoinated sulfonic acids. R.sub.1 can contain a halogen selected from the group consisting of F, I, Br, and Cl and the R.sub.1 group can be further reacted at the halogen group. The particularly useful R.sub.1 contains moieties which are metal binding to provide selective adsorption of metal ions to the surface, which is particularly useful for polymeric substrates which are to be coated with a metal. Especially useful metal trapping agents include organic groups containing chelating ligands such as ethylene diamines, ethylene diamine tri- and tetra acetate, cyclic and bicyclic polyethers known as crown ethers and cryptans and the like. The mixed metal alkoxides and organic-alkoxy silanes can be obtained commercially. Alternatively, they may be specifically prepared for use in modifying particular surfaces. For instance, desired mixed metal alkoxides may be prepared by reaction of the parent alkoxides in desired molar ratios under reflux for 3 4 hours. Functional organosilanes can be prepared by hydrosilylation of olefins.

Other preferred silanes are of the class RO.sub.2Si(R.sub.2).sub.2 where R.sub.2 can be the same as R.sub.1. The general formula is Si(OR).sub.4-n(R).sub.n where n is 1, 2, or 3. Preferably, R.sub.1 or R.sub.2 contains a functional group selected from a metal, vinyl, cyano, amino, mercapto, halogen (usually Cl or Br), aldehyde, ketone acid (including sulfuric and F-sulfuric acid or base group). The metals help form structures where the metal is removable and provides increased receptivity to the metal removed. Preferably R.sub.1 or R.sub.2 is a functional group.

Examples of commercially available functional silanes which can be used are: 3-(N-allylamino)propyltrimethoxy-silane; O-allyloxy(polyethyleneoxy)-trimethylsilane; N-(2-aminoethyl)-3-aminopropylmethyl-dimethoxysilane; N-(2-aminoethyl)-3-aminopropyltri-methoxysilane N-[3-(trimethoxysilyl)propyl]ethylenediamine; N-(6-aminohexyl)aminopropyl-trimethoxysilane; 2-[Methoxy(polyethyleneoxy)propyl]trimethoxysilane; (3-Trimethoxysilylpropyl)diethylene-triamine 95%; Trivinylmeth