WO2001046298A2

WO2001046298A2 - Surface treatment of polymer or metal

Info

Publication number: WO2001046298A2
Application number: PCT/EP2000/012714
Authority: WO
Inventors: Petra Sandner
Original assignee: Vantico Ag
Priority date: 1999-12-22
Filing date: 2000-12-14
Publication date: 2001-06-28
Also published as: WO2001046298A3; AU3159001A

Abstract

The invention provides a process for treating the surface of substrate in order to improve its adhesion properties which comprises pretreating the surface with a primer composition containing (a) a radical precursor and (b) a laser radiation absorbing material having an absorption maximum in the vicinity of the wavelength of the laser light, and subsequently exposing the surface to a laser which produces an elevated temperature on the surface of the organic material.

Description

PLASTICS SURFACE TREATMENT

This invention relates to a process for treating the surface of a substrate in order to improve its adhesion properties and to a method of bonding the surface said substrate to another surface.

The production and use of high strength, light weight materials, e.g. aluminium or polymers and their composites, is of considerable commercial interest. For example, U.S. Patent Nos. 5,960,901 and 5,960,527 describe the fabrication of automobile parts from polymer materials. Other areas relate to home, aerospace, marine applications. Within this industry movement, there is the associated need to provide a means of adhering the above light weight metallic or polymeric articles to each other or to other polymeric composites or to metallic articles. Particularly, adhering low energy polymeric parts, which themselves can be readily fabricated and are stable for long term use, are of great interest. Adhering low energy surfaces to each other or to other materials is difficult to do usually, but much more so especially to reach stable, long term adhesion of a useful nature (i.e. achieving lap shear strengths > 3 MPa) .

Much art is available to change the surface of polymers to achieve better adhesion, using processes such as corona and plasma treatments. These are seen as aggressive treatments which may degrade the chemical and optical properties of the polymer materials. Application of carbon layers by sputtering (e.g. magnetron ) onto polymer surfaces (U.S. Patent No. 4,913,762) is claimed as a less aggressive technique.

A relatively new technique is the laser pretreatment of surfaces, prior to application of a suitable adhesive. WO 96/23037, WO 98/03600 and WO 99/37830 describe processes for treating metal surfaces which comprise coating the surface with an organosilane, -titanate, zirconate or -zircoaluminate and exposing the surface to a laser. According to GB-A-2321025, the treatment with an organosilane and subsequent laser processing can also be successfully applied to plastics surfaces.

Plastic surfaces can be treated with excimer lasers to ablate and fragment the top surface of e.g. polypropylene to produce higher energy polar species to which adhesives can anchor. NL 9001987 describes such UV excimer treatment of polymers for adhesion promotion. This procedure uses expensive bulky lasers.

There are now available low cost, high intensity, solid state lasers (e.g diode pumped YAG or YLF emitting at 1064 or 1055 nm directly or frequency doubled to emit at 532nm) and laser diodes/diode bars which can be easily used and replaced readily on production lines, thereby affording on-line or off-line laser treatments of low energy surfaces Furthermore, these lasers or laser diodes are available with a range of emission wavelengths (through frequency doubling or coupling to Er-doped fibres), giving considerable scope for tailoring the best surface treatment. Q-switched lasers in particular are of considerable interest because they produce high flux conditions of very short duration which surprisingly have been found to be most useful for the laser treatment of the low energy substrates.

It has been found surprisingly that high intensity laser conditions as observed in laser thermal applications provide the best conditions of both photon flux and higher temperature environments, necessary for photothermographic breakdown of the radical precursors and the reactions of these radicals with low energy polymers. U.S. Patent No. 5,945,249 describes the interaction of reducing agents with photoreducible laser absorbing dyes to produce imaging articles: there is no mention of the use of the products of the laser induced reaction for reaction with the polymer surface to change adhesion characteristics. U.S. Patent No. 5756689 describes the laser thermal decomposition of diazo compounds and their use as propellants to effect laser ablation transfer; there is no mention of using any decomposition products for altering the surfaces of low energy polymers

The present invention relates to a process for treating the surface of a substrate in order to improve its adhesion properties which comprises pretreating the surface with a primer composition containing

(a) a radical precursor and

(b) a laser radiation absorbing material having an absorption maximum in the vicinity of the wavelength of the laser light, and subsequently exposing the surface to a laser which produces an elevated temperature on the surface of the substrate

The claimed process can basically be applied to any inorganic materials, like metals, and organic materials, like wood and, in particular, natural or synthetic polymeric materials Examples of suitable natural or synthetic polymeric materials are the following:

1. Polymers of monoolefins and diolefins, for example polypropylene, polyisobutylene, polybut-1 -ene, poly-4-methylpent-1 -ene, polyisoprene or polybutadiene, as well as polymers of cycloolefins, for instance of cyclopentene or norbornene, polyethylene (which optionally can be crosslinked), for example high density polyethylene (HDPE), high density and high molecular weight polyethylene (HDPE-HMW), high density and ultrahigh molecular weight polyethylene (HDPE-UHMW), medium density polyethylene (MDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), branched low density polyethylene (BLDPE).

Polyolefins, i.e. the polymers of monoolefins exemplified in the preceding paragraph, preferably polyethylene and polypropylene, can be prepared by different, and especially by the following, methods: a) radical polymerisation (normally under high pressure and at elevated temperature). b) catalytic polymerisation using a catalyst that normally contains one or more than one metal of groups I V b, V b, V I B or V III of the Periodic Table. These metals usually have one or more than one ligand, typically oxides, halides, alcoholates, esters, ethers, amines, alkyls, alkenyls and/or aryls that may be either π- or σ - coordinated. These metal complexes may be in the free form or fixed on substrates, typically on activated magnesium chloride, titanium (III) chloride, alumina or silicon oxide. The catalysts can be used by themselves in the polymerisation or further activators may be used, typically metal alkyls, metal hydrides, metal alkyl halides, metal alkyl oxides or metal alkyloxanes, said metals being elements of groups la, lla and/or Ilia of the Periodic Table. The activators may be modified conventiently with further ester, ether, amine or silyl ether groups. These catalyst systems are usually termed Phillips, Standard Oil Indiana, Ziegler (-Natta), TNZ (Du Pont), metallocene or single site catalysts (SSC).

2. Mixtures of the polymers mentioned under 1 ), for example mixtures of polypropylene with polyisobutylene, polypropylene with polyethylene (for example PP/HDPE, PP/LDPE) and mixtures of different types of polyethylene (for example LDPE HDPE).

3. Copolymers of monoolefins and diolefins with each other or with other vinyl monomers, for example ethylene/propylene copolymers, linear low density polyethylene (LLDPE) and mixtures thereof with low density polyethylene (LDPE), propylene/but-1 -ene copolymers, propylene/isobutylene copolymers, ethylene/but-1-ene copolymers, ethylene/hexene copolymers, ethylene/methylpentene copolymers, ethylene/heptene copolymers, ethylene/octene copolymers, propylene/butadiene copolymers, isobutylene/- isoprene copolymers, ethylene/alkyl acrylate copolymers, ethylene/alkyl methacrylate copolymers, ethylene/vinyl acetate copolymers and their copolymers with carbon monooxide or ethylene/acrylic acid copolymers and their salts (ionomers) as well as terpolymers of ethylene with propylene and a diene such as hexadiene, dicyclopentadiene or ethylene- norbornene; and mixtures of such copolymers with one other and with polymers mentioned in 1) above, for example polypropylene/ethylene-propylene copolymers (EAA), LLDPE/EVA, LLDPE/EAA and alternating or random polyalkylene/carbon monoxide copolymers and mixtures thereof with other polymers, for example poiyamides.

4. Hydrocarbon resins (for example C₅-C₉) including hydrogenated modifications thereof (e.g. tackifiers) and mixtures of polyalkylenes and starch.

5. Polystyrene, poly(p-methylstyrene), poly(α-methylstyrene).

6. Copolymers of styrene or α-methylstyrene with dienes or acrylic derivatives, for example styrene/butadiene, styrene/acrylonitrile, styrene/alkyl methacrylate, styrene/butadiene/alkyl acrylate, styrene/butadiene/alkyl methacrylate, styrene/maleic anhydride, styrene/acrylonitrile/methyl acrylate; mixtures of high impact strength of styrene copolymers and another polymer, for example a polyacrylate, a diene polymers or an ethylene/-propyiene(diene terpolymer; and block copolymers of styrene such as styrene/butadieneAstyrene, styrene/isoprene/styrene, styrene/ethylene/butylene/styrene or styrene/ethylene/-propylene/styrene.

7. Graft copolymers of styrene or α-methylstyrene, for example styrene on polybutadiene, styrene on polybutadiene-styrene or polybutadiene-acrylonitrile copolymers; styrene and actylonitrile (or methacrylonitirle) on polybutadiene; styrene, acrylonitrile and methyl methacrylate on polybutadiene; styrene and maleic anhydride on polybutadiene; styrene, acylonitrile and maleic anhydride or maleimide on polybutadiene; styrene and maleimide on polybutadiene; styrene and alkyl acrylates or methacrylates on polybutadiene; styrene and acrylonitrile on ethylene/propylene/diene terpolymers; styrene and acrylonitrile on polyalkyl acrylates or polyalkyl methacrylates, styrene and acrylonitrile on acrylate/butadiene copolymers, as well as mixtures thereof with the copolymers listed under 6), for example the copolymer mxitures known as ABS, MBS, ASA or AES polymers

8 Halogen-containing polymers such as polychloroprene, chlorinated rubbers, chlorinated and brominated copolymer of isobutylene-isoprene (halobutyl rubber), chlorinated or sulfochloπnated polyethylene, copolymers of ethylene and chlorinated ethylene, epichlorohydπn homo- and copolymers, especially polymers of halogen-containing vinyl compounds, for example polyvinyl chloride, polvinyhdene chloride, polyvinyl fluoride, polyviny dene fluoride, as well as copolymers thereof such as vinyl chloride/viny dene chloride, vinyl chloride/vinyl acetate or vinyhdene chloride/vinyl acetate copolymers

9 Polymers derived from α, β-unsaturated acids and derivatives thereof such as polyacrylates and polymethyacrylates, polymethyl methacrylates, polyacrylamides and polyacrylonitπles, impact-modified with butyl acrylate

10 Copolymers of the monomers mentioned under 9) with each other or with other unsaturated monomers, for example acrylonitnle/butadiene copolymers, acrylonιtrιle/-alkyl acrylate copolymers, acrylonitπle/alkoxyalkyl acrylate or acrylonitrile/vinyl halide copolymers or acrylonitπle/alkyl methacrylate/butadiene terpolymers

11 Polymers derived from unsaturated alcohols and amines or the acyl derivatives or acetals thereof, for example polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate, polyvinyl butyral, polyallyl phthalate or polyallyl melamine, as well as their copolymers with olefins mentioned in 1 ) above

12 Homopolymers and copolymers of cyclic ethers such as polyalkylene glycols, polyethylene oxide, polypropylene oxide or copolymers thereof with bisglycidyl ethers

13 Polyacetals such as polyoxymethylene and those poiyoxymethyienes which contain ethylene oxide as a comonomer, polyacetals modified with thermoplastic polyurethanes, acrylates or MBS

14 Polyphenylene oxides and sulfides, and mixtures of polyphenylene oxides with styrene polymers or polyamides 15. Polyurethanes derived from hydroxyl-terminated polyethers, polyesters or polybutadienes on the one hand and aliphatic or aromatic polyisocyanates on the other, as well as precursors thereof.

16. Polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from ammocarboxylics acids or the corresponding lactams, for example polyamide 4, poly- amide 6, polyamide 6/6, 6/10, 6/9, 6/12, 4/6, 12/12, polyamide 11 , polyamide 12, aromatic polyamides starting from an m-xylene diamine and adipic acid; polyamides prepared from hexamethylenediamine and isophtha c or/and terephthalic acid and with or without an elastomer as modifier, for example poly-2,4,4,-tπmethylhexamethylene terephthalamide or poly-m-phenylene isophthalamide; and also block copolymers of the aforementioned or poly- m-phenylene isophthalamide; and also block copolymers of the aforementioned polyamides with polyolefins, olefin copolymers, lonomers or chemically bonded or grafted elastomers; or with polyethers, e.g. with polyethylene glycol, polypropylene glycol or polytetramethylene glycol; as well as polyamides or copolyamides modified with EPDM or ABS; and polyamides condensed during processing (RIM polyamide systems).

17. Polyureas, polyimides, polyamide-imides, polyetherimids, polyesterimids, polyhydantoins and polybenzimidazoles.

18. Polyesters derived from dicarboxylic acids and diols and/or from hydroxycarboxylic acids or the corresponding lactones, for example polyethylene terephthalate, polybutylene terephthalate, poly-1 , 4-dιmethylolcyclohexane terephthalate and polyhydroxybenzoates, as well as block copolyether esters derived from hydroxyl-terminated polyethers; and also polyesters modified with polycarbonates or MBS.

19. Polycarbonates and polyester carbonates.

20. Polysulfones, polyether sulfones and polyether ketones.

21. Crosslinked polymers derived from aldehydes on the one hand and phenols, ureas and melamines on the other hand, such as phenol/formaldehydes resins, urea/formaldehyde resins and melamine/formaldehyde resins 22. Drying and non-drying alkyd resins.

23. Unsaturated polyester resins derived from copoiyesters of saturated and unsaturated dicarboxylic acids with polyhydric alcohols and vinyl compounds as crosslinking agents, and also halogen-containing modifications thereof of low flammability.

24. Crosslinkable acrylic resins derived from substituted acrylates, for example epoxy acrylates, urethane acrylates or polyester acrylates.

25. Alkyd resins, polyester resins and acrylate resins crosslinked with melamine resins, urea resins, isocyanates, isocyanurates, polyisocyanates or epoxy resins.

26. Crosslinked epoxy resins derived from aliphatic, cycloaliphatic, heterocyclic or aromatic glycidyl compounds, e.g. products of diglycidyl ethers of bisphenol A and bisphenol F, which are crosslinked with customary hardeners such as anhydrides or amines, with or without accelerators.

27. Natural polymers such as cellolose, rubber, gelatin and chemically modified homologous derivatives thereof, for example cellulose acetates, cellulose propionates and cellulose butyrates, or the cellulose ethers such as methyl cellolose; as well as rosins and their derivatives.

28. Blends of the aforementioned polymers (polyblends), for example PP/EPDM, Poly- amide/EPDM or ABS, PVC/EVA, PVC/ABS, PVC/MBS, PC/ABS, PBTP/ABS, PC/ASA, PC/PBT, PVC/CPE, PVC/acrylates, POM/thermoplastic PUR, PC/thermoplastic PUR, POM/acrylate, POM/MBS, PPO/HIPS, PPO/PA 6.6 and copolymers, PA/HDPE, PA/PP, PA PPO, PBT/PC/ABS or PBT/PEP/PC.

The claimed process is especially useful for the treatment of thermoplastic polymers, in particular thermoplastic polymers selected from polyethylene, polypropylene, polyethylene/polypropylene-copolymers, polycarbonate, polyphenylenesulfide and polyetherimide. The process according to the invention can also be advantageously applied to the surface of any metal or metal alloy

Examples of suitable metals include steel, e.g. stainless steel, iron, titanium, magnesium, copper, gold, nickel, chromium and, in particular, aluminium

The metallic surface may be clean; for example, it may be degreased, generally using any standard method such as wiping with a solvent such as acetone, vapour degreasing, dipping with or without ultrasonic treatment or by using alkaline degreasing agents. The process of the invention can also be used to treat the metallic surface when it is not clean, for example when it is oily or when it is aged

As component (a) in the process according to the invention any compound known in the art as initiator for radical reactions can be employed. Generally, these are compounds which decompose under the influence of heat or radiation thus yielding free radicals

Suitable radical precursors are peroxides and azo compounds.

Di-tert.-butylperoxide, tert.-butylhydroperoxide, dibenzoylperoxide, azobiscyclohexanecarbonitπle and 2,2-azobιsιsobutyronιtrile are particularly preferred

The choice of the laser radiation absorbing material (b) depends on the wavelength of the laser used in the process. The proviso "having an absorption maximum in the vicinity of the wavelength of the laser light" within the scope of the invention means that the absorption maximum of the absorbing material is not more than 50 nm, preferably not more than 30 nm, below or above the laser wavelength.

In case a Q-switched Nd-YAG laser is used emitting a 532 nm radiation, rhodamine dyes are the preferred absorbing materials. Such dyes are known and commercially available, for example rhodamine B, rhodamine S and rhodamine 6G

Other suitable dyes are, for example, the cyanine borates described in U.S. Patents Nos 4,895,880 and 5,151 ,520 as well as the onium salts disclosed in U.SA. Patent No. 5,998,496. Specific examples for suitable dyes are Rose Bengal and Sudan Red 7B (Aldπch Catalogue). The primer composition may be used in solution in water or, preferably, in an organic solvent.

Suitable organic solvents include alcohols, esters, ethers, ketones and chlorinated hydrocarbons. Preferred alcohols are alkanols with 1 to 10 carbon atoms such as methanol, ethanol, propanol, hexanol and decanol. Preferred esters are d - C alkyl esters of C - C₄ aliphatic carboxylic acids such as methyl acetate, ethyl acetate, butyl acetate and methyl propionate. Preferred ethers are dialkyl ethers such as diethyl ether, butoxyethanol and cyclic ethers such as tetrahydrofuran. Preferred chlorinated hydrocarbons are dichloromethane, 1 ,2-dichloroethane, and trichloromethane.

Preferred ketones are lower aliphatic ketones such as acetone and methyl ethyl ketone. Mixtures of these solvents may be used if desired. The most preferred solvents are polar solvents such as alcohols, especially ethanol. Water and/or a carboxylic acid may also be added to suitable organic solvents as part of the solution.

The solvent may be chosen to ensure good wetting of the plastics substrate, but also to ensure no damage to the surface.

The concentration of components (a) and (b) in the primer solutions may vary within wide ranges. Preferably, the primer solution contains 0.1 to 15 % by weight, in particular 0.5 % by weight to 10.0 % by weight, of component (a) and 0.01 to 5.0 % by weight, in particular 0.02 % by weight to 2.0 % by weight, of component (b) based on the total weight of the solution.

The primer solution may be applied by any suitable method, for example, wiping, brushing or spraying on to the areas to be treated.

The application of the primer solution may be carried out with automatic equipment such as robots.

Any suitable laser may be used, e.g. at 400 mJ/pulse. Suitable lasers include, for example excimer lasers, CO₂ lasers, Nd-YAG lasers and Q-switched Nd-YAG lasers. Others are well known in the literature. For high treatment speeds and not to damage the plastics surface through unacceptable high energy concentrations, good results can be obtained using an unfocussed laser.

The actual power level needed to avoid damaging the plastics surface depends on the actual surface being treated and on the specific laser used. This can be readily determined by simple experiment.

After treatment of the plastics surface by the process of the invention, the surface is ready for bonding or other processing where the adhesion properties of the surface are important, for example coating or encapsulating. The bonding may be to another surface by means of an adhesive or by applying a coating to the surface. When bonding to another surface, that other surface may be metallic or non metallic. The other surface may also be pretreated by the same process as described above if desired, whether it is metallic or non-metallic.

When the treated surface is bonded to another surface, this may be achieved using various adhesives such as 1 -component or 2-component epoxy adhesives, and 2-component polyurethane adhesives.

The process of the invention provides excellent joint performance, a fast treatment, a clean process, low running costs, allows for the use of a wide range of adhesives and makes local treatment of the areas to be bonded possible.

The following examples are illustrative of the present invention and are therefore not intended as a limitation on the scope thereof.

Materials and Methods

The following substrates are surface-treated by the process according to the invention. PC- Apec HT KU 1 -9350, high temperature type polycarbonate (Bayer AG), an unfilled system but unlike conventional grades not transparent; PPS- Ryton R-4(XT), polyphenylene sulfide containing 40% glass fibres (Phillips

Petroleum Chemicals), linear structured engineering plastic having an improved ductility and impact behaviour. PEI: Ultem 2300, 30% glass fibre filled polyethenmide, amorphous thermoplast with good mechanical properties, shows even greater stiffness and dimensional stability than standard PEI; PP-HP: polypropylene homopolymer (manufactured by PLASTECH); PP-CP: polypropylene copolymer with a 5-10% content of polyethylene in blocks

(manufactured by PLASTECH), the addition of polyethylene increases the flexibility of polypropylene homopolymer, ALU. aluminium alloy L165

In the cases of PC, PPS and PEI the specimens are injection moulded strips with a thickness of 3mm and a width of 12.5 mm. The overlap in the bonding trials is 12.5 mm. The PP specimens are cut out of extruded sheets and have an average width of 15 mm and thickness of 3 mm. The overlap is 10mm. The overlap of every sample is measured before testing the lap shear strength. A jig is used to produce ALU lap shear joints with consistent overlaps of 12.5 mm x 25 mm.

Laser absorber: Rhodamine 6G (Aidnch);

Rhodamine S (Hopkin&Williams Ltd.); radical precursor. AIBN (azobisisobutylnitπle) from Fisher Scientific;

ACCN (azobiscyclohexanecarbonitnle) from Aidnch;

The laser system used is a Q-switched Nd-YAG laser from Quanta Systems. It has a maximum power output of 500 mJ at 1064 nm. It also allows frequency-doubling to obtain 532 nm. The systems runs in the pulse mode with a pulse width of ca.9 ns Th e following adhesives are selected for the trials:

EP-AD1 Araldite 2012 (Ciba Specialty Chemicals), is a rapid cure (5mιn), multi-purpose, room temperature curing, high viscosity liquid 2-component epoxy adhesive of high strength and toughness. It is suitable for binding wide variety of metals, ceramics, glass, rubber, rigid plastics and most other materials. PU-AD1 ^• Araldite 2018 (Ciba Specialty Chemicals), is a two component room temperature curing, pale coloured, lightly thixotropic liquid polyurethane adhesive for thermoplastic bonding. PU-AD2: XD 4700/XD4701 (Ciba Specialty Chemicals), is a fast curing transparent two component polyurethane system for bonding thermoplastics and glass.

To achieve the same lap shear strength, independent of the time after bonding, a post cure at 40°C for 16 hours is used with all adhesives

General Formulation and Test Conditions

SET A: The laser absorber (e.g. 0.4% Rhodamine 6G) is dissolved in ethyl alcohol. SET B: Subsequently a radical precursor (e.g. 5% of tert. Butyl-Hydroperoxide, AIBN) is added to the mixture from SET A and stirred. Other absorbers or radical precursor might require other solvents or mixtures thereof. The solution might also contain a surface active agent to improve the wettability of the substrate surface.

Application of the primer:

The solution is applied with a brush on the substrate being treated and allowed to dry until the solvent has evaporated

Laser treatment (Nd-YAG Laser):

The samples are mounted on an automated x-y stage. The travel speed of the stage is set as follows: in x direction the pulse overlaps half the area of the previous pulse; and in y- direction less than a quarter of the area of the previous pulse line overlap.

The energy density of the laser treatment is calculated by the spot area and the laser output measured with a power meter. Bonding procedure:

In all cases single overlap lap shear samples are prepared. Both substrates are of the same polymeric material and both bond areas are pre-treated in the same way. The overlap is

10 mm for the polypropylene samples and 12.5 mm for all other materials.

After the pre-treatment the adhesive is applied with a wooden spatula. After alignment the specimens are fixed with thumbscrews and cured at 40 °C for 16 hours. The bond line thickness varies from 0.01 to 0.03 mm.

Test procedure:

The cured specimens are tested with a tensile tester at a speed of 10 mm/min at room temperature. The results are summarised in Table 1 :

Table 1:

Conclusions:

1 ) Laser or no laser address or sandblasted on completely untreated substrates give poor adhesion: see Comparison Examples 1 ,2, 3, 5, 7, 9, 10, 11 ,13, 14, 15, 30,32,36, 37, 39, 41. Examples 7 and 11 show that at very high energy levels (E>60), there may be some adhesion improvement, this requires excessive energy requirement.

2) Simple treatment with peroxide or AIBN on the substrates, with no laser treatment, gives poor adhesion: see Comparison Examples 18, 19, 20, 21 , 22, 23, 26,27, 28, 29.

3) Treatment with Laser Absorber Dye and Laser Treatment gives much improved adhesion: See Invention Examples 4, 8, 12,16, 17.

4) Treatment with laser absorber dye and peroxide or AIBN (radical precursors) give very good (surprising) adhesion: see Invention Examples 24, 25,31 , 33, 43, 35,38, 40, 42.

Claims

1. A process for treating the surface of a substrate in order to improve its adhesion properties which comprises pretreating the surface with a primer composition containing

(a) a radical precursor and

(b) a laser radiation absorbing material having an absorption maximum in the vicinity of the wavelength of the laser light, and subsequently exposing the surface to a laser which produces an elevated temperature on the surface of the substrate.

2. A process according to claim 1 wherein the substrate is an organic material.

3. A process according to claim 2 wherein the organic material is a natural or synthetic polymeric material.

4. A process according to claim 3 wherein the organic material essentially consists of a thermoplastic polymer.

5. A process according to claim 3 wherein the organic material essentially consists of polyethylene, polypropylene, polyethylene/polypropylene-copolymer, polycarbonate, polyphenylenesufide or polyetherimide.

6. A process according to claim 1 wherein the substrate is a metal.

7. A process according to claim 6, wherein the metal is aluminium or an aluminium alloy.

8. A process according to claim 1 wherein the primer composition contains a peroxide or an azo compound.

9. A process according to claim 8 wherein the primer composition contains di-tert.-butylperoxide, tert.-butylhydroperoxide, dibenzoylperoxide, azobiscyclohexanecarbonitrile or 2,2-azobisisobutyronitriie as component (a).

10. A process according to claim 1 wherein the primer composition contains a rhodamine dye as component (b).

11. A process according to claim 1 wherein the primer composition is applied as a solution containing 0.1 to 10 % by weight of component (a) and 0.01 to 5.0 % by weight of component (b) in an organic solvent.

12. A method of bonding the surface of a substrate to another surface which comprises treating the surface of the substrate by a process according to claim 1 followed by bonding the treated surface to another surface with an adhesive.

13. A method according to claim 12 wherein the adhesive is an epoxy or a polyurethane adhesive.