Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/10—Oxidising
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
  • C23C22/74—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process for obtaining burned-in conversion coatings
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/1208—Oxides, e.g. ceramics
  • C23C18/1216—Metal oxides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1229—Composition of the substrate
  • C23C18/1241—Metallic substrates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1254—Sol or sol-gel processing
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/34—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing fluorides or complex fluorides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/20—Use of solutions containing silanes

Definitions

• This invention relates to methods and aqueous compositions for surface treatment.
• One purpose of the treatment is to increase the adhesion of subsequently applied coatings, such as paint, lacquer, varnish or adhesive.
• Another purpose is to decrease adhesion, i.e. to confer non-stick properties on the surface.
• Yet another purpose is to provide protection for the surface from mechanical and chemical damage.
• the invention is of application to solid surfaces generally, it is of major importance in relation to metals generally, and in particular to aluminium.
• Alocrom 100 is the Trade Mark of a commercially available chromium-based pretreatment applied to aluminium before coating with organic finishes such as lacquer on can stock or powder coating on architectural components. Excess chromium solution must be rinsed away before the organic coating is applied. This kind of pretreatment is known as conversion coating. Control of the chromium ions in the rinse water to prevent pollution can be a problem with this formulation.
• Accomet C is the Trade Mark of another commercially available chromium-based pretreatment, as described in US Patent 3706603.
• the composition is applied to a metal workpiece and dried in situ without washing; this is known as a no-rinse pretreatment.
• Accomet C avoids the chromium pollution problems of Alocrom 100, but is not used on can stock for food or beverages because of the danger of toxic chromates leaching out. It is used as a pretreatment for aluminium components that are to be adhesively bonded together, for example as described in British Patent Specification 2139540.
• Alocrom 404 is the Trade Mark of a commercially available pretreatment based on zirconium. This is a conversion coating which requires rinsing, but the absence of chromium reduces pollution problems. The protection is not as good as that provided by Accomet C or by Alocrom 100, but it does find some application in the food industry.
• Patent Specifications which describe metal pretreatment systems based on zirconium, often in the form of fluorozirconate, include US 3964936; 4191596; 4273592; 4339310; 4370177; and EPA 61911. (Some of these mention Ti, Si and Hf as alternatives for Zr.) All these are conversion coatings containing dissolved Zr.
• US Patent 4623591 describes a method of preparing metal surfaces for adhesive bonding by the application of a metal alkoxide solution, which hydrolyses on the surface to form an amorphous hydrated metal oxide layer.
• AI alkoxides are preferably used, though Ti, Zr, Fe and Ni alkoxides are mentioned as alternatives. Because these metal alkoxides hydrolyse in the presence of moisture, it is necessary to use them in solution in organic solvents such as toluene, which solutions have short shelf life and major handling, cost and environmental problems.
• GB 2107215 and 2134008 describe aqueous compositions based on inorganic sols containing refractory oxides for application to refractory substrates followed by firing to produce coatings for catalytic or electronic applications.
• EPA 273698 describes coating compositions to improve adhesion of paints etc, which compositions comprise a silica sol containing a dissolved aluminium or iron salt.
• U.S. Patent 4,271,210 describes forming a clear thin metal oxide layer on a glass substrate by applying a solution of partly hydrolysed aluminium alkoxide.
• Japanese Kokai 52-73138 describes sealing aluminium-plated steel members with an aqueous solution of aluminium biphosphate and/or magnesium biphosphate optionally containing also a silica or alumina sol.
• the invention provides a method which comprises applying to a solid surface an aqueous composition consisting essentially of an inorganic hydrous oxide sol containing an adhesion promoter selected from the class consisting of fluorozirconates, silane coupling agents, nitrilostrismethylene phosphonates, phosphoric acids, phosphate esters and oxidising agents for the surface and optionally also a passenger powder, but not containing toxic hexavalent chromium or molybdenum, and curing the composition to form a protective coating on the surface.
• an adhesion promoter selected from the class consisting of fluorozirconates, silane coupling agents, nitrilostrismethylene phosphonates, phosphoric acids, phosphate esters and oxidising agents for the surface and optionally also a passenger powder, but not containing toxic hexavalent chromium or molybdenum, and curing the composition to form a protective coating on the surface.
• the invention provides a method which comprises applying to a solid surface:
• the method is suitable for the pretreatment of solid surfaces such as non-metals and metals generally, including steel, titanium, copper, zinc and, particularly aluminium, which term is used herein to include the pure metal and its alloys.
• the method can be arranged to improve the adhesion properties of the pretreated surface, by improving the adhesion thereto of a subsequently applied coating such as paint, varnish, lacquer or adhesive.
• the pretreatment may improve either the initial adhesion of the subsequently applied coating to the surface or the maintenance of such adhesive properties in service, or both the initial adhesion and maintenance of adhesives properties.
• the benefits of the invention may be shown mainly not in the initial adhesive strength obtained, but in the maintenance of adhesive strength in hostile or corrosive environments.
• the inorganic sol is a stable, aqueous, colloidal dispersion containing primary particles or aggregates of primary particles, which are smaller than 150 nm.
• sols can be classified into three types; type A, B and C.
• Type A sols consist of basic units which are polynuclear ions which form an 'inorganic polymer' and are formed by hydrolysis and polymerisation of monomeric cations.
• the molecular weight of the polynuclear cations will depend on the degree of hydrolysis but these sols normally have an anion to metal ratio of approximately 1:1.
• the polymeric species are not large enough to scatter light efficiently, so the sol and the resultant gel are optically clear.
• the gel has a high density, low porosity and the x-ray diffraction pattern consists of very broad bands.
• J. D. F. Ramsay “Neutron and Light Scattering Studies of Aqueous Solutions of Polynuclear lons. Water and Aqueous Solutions", 207-218 1986 (ed G. W. Neilson and J. E. Enderby: Bristol. Adam Hilger).
• Type A sols may be formed from the polynuclear ions listed in this paper including those containing AI(III) Fe(III) Zr(IV)
• Type B sols consist of basic units with a definite shape, e.g. spherical, rod or plate-like, and are amorphous or microcrystalline.
• the sol is formed by extensive hydrolysis of a salt and has a low anion to metal atom ratio of approximately 0.3:1.
• the sols can also be prepared by peptization of fresh precipitates.
• the colloidal units are not aggregated and the sol and the resultant gel are both clear.
• Type B sols include (AI(III) Zr(IV) Ce(IV) Ti(IV) Fe(III).
• Preparation of Type B AI(III) sols is described in GB 1,174,648.
• Preparation of Ce Type B sol is described in GB 1,342,893.
• Type B Alumina Sols are available commercially.
• the basic colloidal units are aggregated. They are crystalline and the gels formed by removal of water have a low density. These sols scatter light and are therefore opaque.
• the gels derived from a type C sol are porous and have a density ⁇ 45% of the theoretical density of the oxide.
• the inorganic sol for use in this invention is a hydrous oxide sol, preferably a hydrous metal oxide sol, that is to say a Type A or Type B (but not Type C) sol.
• a hydrous oxide sol preferably a hydrous metal oxide sol, that is to say a Type A or Type B (but not Type C) sol.
• examples are zirconia sols, ceria sols, titania sols, hafnia sols, alumina sols, and iron oxyhydroxide sols.
• Silica sols exemplify non-metal oxide sols.
• Zirconia sols are readily formed by peptising basic zirconium carbonate in mineral acid.
• the constitution of zirconia sols when the associated anion is nitrate or bromide or chloride is discussed in a UKAEA Research Group Report, reference AERE - R5257 (1966) by J.L. Woodhead and J.M. Fletcher.
• Zirconia sols contain extensively hyrolysed inorganic polymers with a primary particle size of less than 10 nm. The polymer is thought to be built up of hydrated oxy-hydroxide species of zirconium. When nitric acid is used, the species is believed to have the formula: where n is thought to be approximately one in dilute sols and greater than one at higher concentrations.
• Ceria and titania and other hydrous metal oxide sols may be formed by peptising the corresponding hydrated metal oxide with a mineral acid.
• a fluid which gels the layer and/or a passenger powder on the surface.
• A1 2 0 3 passenger powder may be gelled on the surface by phosphoric acid.
• This fluid may be in vapour phase, for example a low molecular weight amine such as ethylamine or preferably ammonia, which is applied after the aqueous composition and simply serves to gel and thereby fix the layer on the surface.
• the fluid is a liquid, particularly an aqueous liquid containing a gelling agent for the sol. This liquid may be applied to the surface to deposit the gelling agent thereon, prior to application of the inorganic sol.
• the liquid can be applied to the surface already carrying a layer of the inorganic sol. It is preferred, though not essential, that the layer of inorganic sol be dried prior to application of the gelling fluid. Gelling of the layer causes or may cause shrinkage, and care may need to be taken to prevent cracking of the layer at this stage. Drying may be effected at temperatures below 100°C, conveniently at ambient temperature.
• Either the aqueous composition i) or the fluid ii) may contain an adhesion promoter. These materials may also act as gelling agents for the sol.
• the two step method of this invention allows the incorporation of high concentrations of these reagents into the fluid ii).
• the dissolved adhesion promoting constituent should preferably be substantially non-toxic.
• the constituent promotes adhesion, for example by providing suitable links to the underlying substrate and to the overlying organic layer, or by inhibiting corrosion at the organic coating/substrate interface. It is believed that adhesive bond strength falls on exposure to water or more aggressive agents because of corrosion or hydration at this interface. Inhibition of this corrosion helps to retain adhesive bond strength.
• Adhesion promoters are known and employed to enhance the joint strength, or more commonly to enhance the environmental resistance of the substrate surface/adhesive interface to attack by moisture. Adhesion promoters were described by P.E.Cassidy et al in Ind. Eng. Chem. Prod. Res. Development, Vol 11, No.2 (1972) pages 170-7; and by A.J.Kinlock in J. Mat. Sci., 15 (1980) pages 2141-66 at page 2159. But these articles do not discuss coating compositions.
• the adhesion promoter may comprise fluoride values and one or more of Ti, Si, Hf and Zr values. These can be provided separately. They may conveniently be provided by dissolving fluorozirconic acid H 2 ZrFs, or a soluble fluorozirconate salt, in water; alternatively, a corresponding acid or salt of Ti, Si or Hf, e.g. H 2 TiFs, H 2 SiF 6 or H 2 HfF 6 , may be used.
• Fluorozirconate (or other fluoro complex) is preferably present at a concentration of 0.1 to 200 gl-', particularly from 10 to 100 gl-', of the fluid ii). When provided separately, the fluoride and zirconium (or other) values are preferably sufficient to give a fluorozirconate (or other fluoro complex) concentration in this range.
• the adhesion promoter may comprise phosphate or phosphonate, preferably in a concentration of 0.05 to 200 gl-', particularly 10 to 100 gl -1 , of the fluid.
• Phosphate esters are known to bond well onto aluminium surfaces and to be able to inhibit corrosion.
• organic phosphorus-containing compounds which may be used, examples being amino-phosphates for example nitrilotris (methylene) phosphonic acid (NTMP) or other nitrilo-substituted phosphonic acids or phosphate esters such as bis-(nonyl phenyl ethylene oxide) phosphate.
• the adhesion promoter may comprise one or more silane coupling agents which are organosilanes, for example glycidoxypropyltrimethoxy silane or aminopropyltriethoxy silane, which may act to promote adhesion, preferably in a concentration of 0.05% to 10% by volume on the volume of the fluid.
• silane coupling agents which are organosilanes, for example glycidoxypropyltrimethoxy silane or aminopropyltriethoxy silane, which may act to promote adhesion, preferably in a concentration of 0.05% to 10% by volume on the volume of the fluid.
• organosilanes for example glycidoxypropyltrimethoxy silane or aminopropyltriethoxy silane, which may act to promote adhesion, preferably in a concentration of 0.05% to 10% by volume on the volume of the fluid.
• organosilanes for example glycidoxypropyltrimethoxy silane or aminopropyltrie
• the adhesion promoter may be an oxidizing agent for the surface.
• the Ce 4+ species which may be provided in the form of a hydrated ceria sol or as a dissolved ceric salt, and permanganate.
• the oxidizing agent acts on the aluminium or other metal (e.g. iron or steel) or non-metal surface, improves adhesion of the surface to the protective coating formed by drying the composition, and should be used at a concentration designed to achieve these ends.
• the aqueous composition or the fluid may also contain a passenger powder, which can be used to give the protective coating a desired surface topography.
• the powder is preferably an inert metal oxide such as silica, zirconia, titania or alumina. This may be a type C sol, or a powder produced by comminution, for example. Powder loadings of 1 to 300 gl-', preferably 5 - 150 gl-', more particularly 10 - 75 gl- 1 are appropriate.
• the powder may have an average primary particle size below 250 nm, e.g. in the range 3-150 nm, particularly 4 - 100 nm, and is preferably of substantially uniform particle size.
• the passenger powder is present in the aqueous composition containing the inorganic sol. It is possible to incorporate the passenger powder in the fluid ii), provided that the fluid does not react and/or destabilise the passenger powder, as for example when phosphoric acid is added to an A1 2 0 3 powder. When this fluid brings about gelation of the sol, the powder becomes incorporated in the layer on the metal surface.
• the aqueous composition generally has an acid pH, typically in the range 1 .5 to 7. Sol concentration is chosen to achieve a convenient application viscosity.
• the sol may typically contain from 1 to 200 gl- 1 metal oxide equivalent.
• the adhesion promoting constituent when used in the aqueous composition may be present in conventional concentrations, for example from 0.001 % to 10% by volume.
• a particularly preferred aqueous composition comprises:
• the surface to which the aqueous composition is to be applied may be cleaned by conventional means appropriate to the substrate concerned.
• this may be an acid or alkaline cleaning treatment, using commercially available chemicals such as those sold by ICI under the trade marks Ridolene 124 and 124E.
• the (aluminium or titanium) metal surface may be pre-treated to form thereon an artificially applied oxide layer.
• Such treatments include acid etching (Forest Products Laboratories), and anodizing treatments with sulphuric, chromic or phosphoric acid, the latter being particularly effective in terms of bond strength and durablity. It has been shown by means of transmissions electron microscopy that phosphoric acid anodizing treatment produces fine oxide protrusions of greater length and magnitude than other surface treatments. These whiskers are believed to account for the strength enhancement achieved with joints made using phosphoric acid anodized adherends. Thus, mechanical interlocking by whisker reinforcement of an adhesive appears to play a role in enhancing adhesive bonding.
• the aqueous compositions of this invention can be applied to such profiled surfaces in layers so thin and uniform that the profiled surface topography is substantially maintained. It is believed that the artificially applied oxide layer provides improved initial adhesion for subsequently applied artificial coatings by mechanical interlocking; and that the protective coatings applied according to this invention ensure that the initial excellent adhesion properties are not reduced on prolonged exposure to humid or corrosive environments.
• an adhesion promoter to the sol in a controlled manner, i.e. slowly with stirring, results in a clear, homogenous sol with no apparent flocculation.
• the coating produced by such a pretreatment is therefore smooth and featureless.
• the adhesion promoter can be included in the gelling fluid ii).
• adhesion promoter is added in a less controlled manner, irreversible flocculation occurs and a turbid pretreatment sol is obtained. Consequently, the coating deposited on the surface is more textured.
• silane coupling agents addition of water to the silane (rather than the recommended procedure of adding the silane reagent to water) results in the formation of condensed polysiloxanes which also contribute to surface microtexturing.
• adhesion to non-metal or metal substrate of subsequently applied organic coatings such as paint, lacquer, varnish or adhesive, depends substantially upon the properties of two interfaces:
• the composition may be applied to the substrate surface (optionally carrying an artificially applied oxide layer with a profiled surface) by any convenient technique, such as spin coating, immersion, flow or roller coating, brushing, or by spraying.
• roller coating is likely to be an attractive option.
• the formulation may need to be adjusted to provide a convenient viscosity for application by the desired method.
• the coating on the surface is cured.
• Curing temperatures are from ambient up to 700 ° C, usually (though not always) below those required to fully sinter the particles, and may typically be in the range 50 to 400 ° C. Calcination of the coating at temperatures above 400 ° C is possible but not usually necessary.
• curing temperatures in the range 50 - 100 ° C are preferred.
• curing temperatures in the range 100 ° C to 400 ° C are preferred. Removal of water takes place progressively and is still not complete at 400 ° C.
• the surface preferably carries the coating at a rate of from 0.01 to 5 gm- 2 , preferably between 0.02 and 0.7 gm- 2 , and most preferably from 0.05 to 0.3 gm- 2 .
• Thinner coatings up to 1.5 gm- 2 will normally be preferred when the metal surface has been provided with an underlying artificially applied oxide layer.
• the invention envisages as an additional method step the application to the protective coating of an organic coating such as paint, lacquer, varnish or adhesive.
• an organic coating such as paint, lacquer, varnish or adhesive.
• An example of a commercially available epoxy adhesive suitable for this application is Permabond ESP105.
• thicker coatings e.g. of up to 5 gm- 2 may be preferred and passenger powders with average particle sizes up to 1 ⁇ m or even up to 5 ⁇ m may be used.
• the sol was diluted to 10% or 2% of the original concentration. Further dilution also occurred as a result of mixing the sols with equal volumes of solutions of the adhesion promoters. This mixing was effected by dropwise addition with stirring, thus without significant sol flocculation, and as a result the protective coating had a smooth, glassy appearance under the microscope. Volumes used are summarised in Table 1.
• 300 x 100 panel of 5251 alloy were vapour degreased and then acid cleaned by a 1 minute immersion in Ridolene 124 acid cleaner at a temperature of between 55 and 60 °C. Following cleaning, the samples were thoroughly rinsed in deionised water and pretreated by spin coating. Surfaces were thoroughly wetted with the pretreatment solution prior to spin coating. All pretreatments were dried in an oven at 200 °C for 1 minute. Additional samples of metal pretreated with the additive-free formulations were dried at 100 ° C.
• Samples were cut to a width of 20 mm, stacked (ca 12 samples) and cut to a length of 90 mm.
• a single part epoxy adhesive containing 1% ballotini was applied to one end of two specimens.
• Specimens were mounted in a jig giving 10 mm overlap, clipped together, and subsequently removed from the jig and cured at 180 ° C for a time of 30 minutes, commencing from the time the sample temperature reached 175 ° C. Following curing, excess adhesive was filed off the edges of the sample and, finally the same edges were smoothed with emery cloth.
• Samples for accelerated testing were immersed in deionised water at 60 ° C for 200 hours. All samples were tested on a Zwick tensile tester using a crosshead speed of 2 mm min -1 .
• Pretreated sheets were then cut to form 20mm x 100mm coupons, bent to form L-shaped adherends and bonded, with a standard heat-cure single-part structural epoxy adhesive, to give T-shaped joints with a 60mm long bondline. These were peeled at 5mm/min on an Instron 1115 tensile tester and the steady-state peel load was recorded during the peel event.
• Treatment solutions were prepared and coated as described in Examples 1 to 10 except that dilution with the adhesion promoter was done quickly causing some flocculation of the sol. Coatings produced from the treatments were microtextured.
• Treatment solutions containing silane adhesion promoters were prepared and applied as described in Example 11 except that the silane was diluted to 0.5 volume percentage by adding water to the silane A1110. (The recommended procedure is to add the silane to water.)
• the coatings were microtextured.
• aqueous compositions according to the invention were made up by the general procedure given in Examples 1 to 10. Sample pretreatment and preparation and testing of adhesive joints were also as described in Examples 1 to 10. Details of formulations and peel strengths are set out in Table 3 below.
• the powder was always the last constituent to be added, i.e. it was added to the final sol/adhesion promoter or sol/oxidising agent mixture, with mixing for 1 hour in a Silverson high shear blender to ensure good dispersion.
• Rhone-Poulenc Ceria hydrate (typically 70.9 wt% oxide) was slurried in distilled water. 16ml of conc. HN0 3 in 34ml of water was added to the slurry and stirred thoroughly. The mixture was heated to 70 ° C for 30 minutes allowed to cool and then to settle. The supernate was decanted and water added to the residue to give a final volume of 417ml. The residue immediately disperses to give a stable sol of 425 gl -1 concentration.
• the sol was diluted to 10% or 2% of the original concentration.
• 0.1 M ceric salt, Ce-(S04) 2 was added dropwise to the ceria sol, while stirring rapidly, such that minimal flocculation occured.
• the 1.5% silica was added finally.
• a 5wt% titania sol was prepared by dispersing the gel in deionised water.
• the stock sol was dilute further for use in formulation 5.
• the zirconia sol was diluted to 10% of the original conc. 0.1 M KMn0 4 solution was added dropwise to the sol while stirring rapidly such that minimal flocculation occurred. The 1.5% silica powder was added finally.
• Lacquers were applied to the treated panels and then drawn into standard shaped cans.
• the four lacquer systems applied and the adhesion test conditions used are standard in the field.
• Feathering refers to the degree of detachment of a lacquer film from a surface in a ring-pull-tab configuration.
• the feathering test was carried out by applying an organosol lacquer on the pretreated surface of an aluminium coupon.
• the lacquered coupon was sterilised in water at 130 ° C for 1 hour.
• Parallel lines were scribed on the reverse side of the metal and the metal was then scrolled back along the scribes.
• Feathering was assessed by noting the extent of detachment of lacquer along the metal edge. A score of 0 indicates best performance (i.e. no feathering) and a score of 4 indicates poor performance. Results are set out in Table 4.
• a pretreatment formulation containing 3 components i.e. the sol, the adhesion promoter and the passenger powder
• 3 components i.e. the sol, the adhesion promoter and the passenger powder
• a second formulation containing a higher sol concentration and a lower silane concentration and a series of other formulations containing a range of chemistries were prepared in a similar manner.
• the pretratment formulations were applied on precleaned aluminium by roller coating and dried at 80 ° C for 3 mins.
• concentration of constituents in the respective formulations, the peel strength of resultant adhesive joints (using a modified epoxy adhesive), the tensile adhesive bond strength and bond strength after 200 hours and 1000 hours of immersion in water maintained at 60 °C, are given in Table 5.
• the results are compared with Alocrom 4040, a commercial pretreatment based on fluorozirconic acid and applied by dip coating at 30 for 10 mins. and dried at 120 ° C for 3 mins., as recommended by the supplier (ICI).
• Formulation 3 described in Table 5 was used to prepare single lap adhesive joints which were stressed to 8MPa by means of a calibrated spring arrangement and exposed to condensing humidity of 98-100%, in a test cabinet. The joints remained intact after 100 days of testing. Comparison joints made using Accomet C failed after 87 days.
• CR2 steel was precleaned by degreasing, abrading and degreasing again.
• Single lap adhesive joints were prepared with the pretreated metal and the joints exposed to neutral salt spray (5% NaCI) maintained at 43 ° C.
• the lap shear strength of the joints were measured at various intervals and compared with lap shear strengths of adhesive joints prepared with electrogalvanised steel.
• the sol pretreatment resulted in superior performance. The results are given in Table 6.
• a pretreatment formulation consisting of 1% Zr0 2 sol, 0.8% amino silane and 4% silica prepared as described in Example 22 (formulation 1), was roller coated on aluminium foil, and heated to 200 ° C for 3 mins. The coated foil was immersed in liquid Nitrogen to cause embrittlement of the coating and then bent through 180°. Scanning election microscopy revealed that the pretreatment layer did not delaminate under these conditions. The sol component formed a flexible skin adjacent to the metal surface and deformed with the metal. Cracking was observed in the pretreatment layer when a similar test was carried out on Alocrom 4040 pretreated aluminium.
• a pretreatment consisting of 1% Zr0 2 sol 0.5% aminosilane and 6% alumina (Example 22 formulation 3) was dehydrated by either spray drying or tray drying.
• the tray dried powder was redispersed in water and used to pretreat aluminium.
• the peel strength of the resultant metal:adherend joint was 55N. [The peel strength of a joint prepared with the original formulation, prior to dehydration and reconstitution was 74N].
• a pretreatment formulation consisting of 3.1% Zr0 2 sol and 1% silane [N ( ⁇ -aminoethyl) -y-aminopropyltrimethoxy silane] was roll coated on aluminium metal and dried at 80 ° C for 3 mins. Scanning election microscopy revealed a smooth, featureless coating on the metal surface. The same pretreatment was also roller coated on phosphoric acid anodised metal. Scanning electron microscopy showed that the pretreatment coated the alumina whiskers while maintaining the open, porous topography. A cross section also revealed that the pretreament had penetrated the anodic film and formed a dense layer adjacent to the metal surface.

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