[0001] 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. Although the invention
is of application to solid surfaces generally, it is of major importance in relation
to metals generally, and in particular to aluminium.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] EPA 273698 describes coating compositions to improve adhesion of paints etc, which
compositions comprise a silica sol containing a dissolved aluminium or iron salt.
[0009] GB 1503934; GB 1411094; US 3248249; EPA 201228; and Chemical Abstract 1987 April
14 106545d: all describe coating compositions based on inorganic sols but which contain
hexavalent chromium or molybdenum.
[0010] 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.
[0011] 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.
[0012] There is a need for a pretreatment system for metal and other surfaces which does
not require rinsing and does not contain toxic material such as hexavalent chromium
or molybdenum, but which nevertheless improves the adhesion properties of the surface
for subsequently applied coatings such as paint, varnish, lacquer or adhesive. It
is an object of this invention to fulfil that need.
[0013] In one aspect 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.
[0014] In another aspect the invention provides a method which comprises applying to a solid
surface:
(i) an aqueous composition consisting essentially of an inorganic hydrous oxide sol,
an adhesion promoter and optionally also a passenger powder, but not containing toxic
hexavalent chromium or molybdenum, to form a layer on the surface,
(ii) a fluid which gels the layer on the surface,
the applications being made sequentially in either order, and curing the resulting
layer on the surface.
In another aspect the invention provides an aqueous composition for application to
solid surfaces to form a protective coating thereon, which composition contains no
toxic hexavalent chromium or molybdenum and consists essentially of:
a) an inorganic hydrous oxide sol and
b) an adhesion promoter selected form the class consisting of fluorozirconates, silane
coupling agents, nitrilotrismethylene phosphonates, phosphoric acids, phosphate esters
and oxidising agents for the surface, and optionally also
c) from 1 to 300 g/I of a passenger powder having an average primary particle size
in the range 3 - 250 nm,
[0015] 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. For example,
so far as subsequently applied adhesive is concerned, 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.
[0016] The inorganic sol is a stable, aqueous, colloidal dispersion containing primary particles
or aggregates of primary particles, which are smaller than 150 nm. Depending on the
nature of the basic colloidal unit, sols can be classified into three types; type
A, B and C.
[0017] 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) Th(IV): for example:
[0018] 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.
[0019] In the type C sol 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 sols formed from ultrafine powders prepared by vapour
phase techniques, i.e. flame hydrolysed powders, belong to this category.
[0020] Type A and B sols when dehydrated yield gels which are >45% of the theoretical density
of the oxide. The gels derived from a type C sol are porous and have a density <45%
of the theoretical density of the oxide.
[0021] 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. Examples
are zirconia sols, ceria sols, titania sols, hafnia sols, alumina sols, and iron oxyhydroxide
sols. Silica sols exemplify non-metal oxide sols.
[0022] 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.
[0023] Also applied to the surface, according to one aspect of the invention, is a fluid
which gels the layer and/or a passenger powder on the surface. For example, A1
20
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. More preferably, 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. Alternatively, 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.
[0024] 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).
[0025] Because the composition is intended for a no-rinse treatment, 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.
[0026] 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.
[0027] 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
2ZrFs, or a soluble fluorozirconate salt, in water; alternatively, a corresponding
acid or salt of Ti, Si or Hf, e.g. H
2TiFs, H
2SiF
6 or H
2HfF
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.
[0028] 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. In addition to the phosphoric acids and inorganic
phosphates, there are a number of 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.
[0029] 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. One or more of these or other classes of substantially
non-toxic dissolved adhesion-promoting and/or corrosion-inhibiting constituents, including
zirco-aluminates, and organo-metallic trivalent chromium compounds, may be used. The
terms fluorozirconate, phosphate etc. are used herein to include the free acid as
well as salts and esters thereof.
[0030] The adhesion promoter may be an oxidizing agent for the surface. Examples are 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.
[0031] 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.
[0032] Preferably 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
20
3 powder. When this fluid brings about gelation of the sol, the powder becomes incorporated
in the layer on the metal surface.
[0033] 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.
[0034] A particularly preferred aqueous composition comprises:
a) a zirconia sol of concentration 1 - 200 gl-1 metal oxide equivalent,
b) a silane coupling agent present at a concentration cf 0.05% to 10% by volume on
the volume of the sol, and
c) a passenger powder selected from silica, alumina, zirconia and titania, having
an average particle size in the range 3 - 150 nm, and present at a concentration of
5 - 150 gl-'.
[0035] The surface to which the aqueous composition is to be applied may be cleaned by conventional
means appropriate to the substrate concerned. For aluminium 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. Alternatively, 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.
[0036] By virtue of their small sol particle size, less than about 0.2 µm and typically
less than 10 nm, 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.
[0037] Addition of 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. Or the adhesion
promoter can be included in the gelling fluid ii).
[0038] If the 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. With 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.
[0039] The 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:
i) the interface between the substrate surface and the protective coating with which
this invention is concerned;
ii) the interface between this protective coating and the subsequently applied organic
coating.
[0040] By control over the microtexture of the protective coating, a number of options are
possible:
a) The substrate surface, to which the aqueous composition containing the sol is applied,
is clean and flat (or at least not deliberately profiled on a microscopic scale).
Although a sound interface i) can perfectly well be formed using the sol alone, it
may be advantageous to include an oxidizing agent or adhesion promoter in the aqueous
composition or in the gelling fluid ii). So far as interface ii) is concerned, it
is possible to give the protective coating some microtexture, by effecting controlled
flocculation of the sol and/or by incorporating a passenger powder in the aqueous
composition or the gelling fluid. This has the effect of increasing adhesive bond
strength, particularly peel strength. Or the protective coating may be made smooth
and featureless. This has the effect of reducing adhesive bond strength, particularly
peel strength. The coated surface may indeed have non-stick characteristics. Particularly
by control over the concentration and size of the passenger powder particles, the
adhesion properties of the coated surface can be optimised for its intended purpose.
b) The metal surface has been provided with a textured oxide film (or has itself been
profiled on a microscopic scale). So far as interface ii) is concerned, the use of
an oxidizing agent is possible but probably not advantageous. As noted above, the
protective coating formed is preferably so thin and uniform that the profiled surface
topography is maintained at interface ii). For this purpose it is generally preferred
that the sol be not flocculated and that a passenger powder be not present although
a dissolved adhesion promoter may be advantageous.
[0041] 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. For aluminium
strip, 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.
After application and drying, 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. For optimum adhesive bond strength, curing
temperatures in the range 50 - 100 ° C are preferred. For good adhesion combined with
good protection from corrosion, 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.
[0042] 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. There is increasing interest in the use of adhesively
bonded aluminium components as structures for motor vehicles. An example of a commercially
available epoxy adhesive suitable for this application is Permabond ESP105.
[0043] When the coating is intended for use as a protective coating in its own right, thicker
coatings e.g. of up to 5 gm-
2 may be preferred and passenger powders with average particle sizes up to 1 µm or
even up to 5 µm may be used.
[0044] The following examples illustrate the invention. Examples 1, 2 and 13 are comparative.
Examples 1 to 10
Zirconia sol preparation
[0045] In a typical preparation 2 kg of zirconium carbonate (44.8 w/v Zr0
2, 7.2 moles) was added with stirring to 0.91 of 8M HN03 (7.2 moles), the paste rapidly
dissolved (exothermic 43 ° C) to give a sol containing 444 gl
-1 Zr0
2 equivalent. When cooled to 20 ° C the dispersion (N0
3/Zr0
2 mole ratio = 1.0) has a viscosity of 16 cp and a density of 1.55 g/cm
3.
[0046] For pretreatment, 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.
[0047]
Sample Pretreatment
[0048] 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.
Preparation and Tensile Testing of Adhesive Joints
[0049] 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.
[0050] 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.
Preparation and Peel Testing of Adhesive Joints
[0051] 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.
Results
[0052] The results of the tests are set out in Table 2. These show that high initial tensile
bond-strengths and good bond-strength retentions were obtained both with and without
an adhesion promoter. Particularly with fluorozirconate as the adhesion promoter,
the compositions led to protective coatings of exceptionally uniform thickness containing
uniformly sized particles, well adapted to allow underlying profiled surfaces to show
through. Use of a silane coupling agent as adhesion promoter resulted in exceptionally
high initial tensile bond strengths and bond strength retention. The peel strengths
reflect the fact that the protective coatings had a smooth finish without microtexture.
Example 11
[0053] 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.
Example 12
[0054] 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.)
[0055] The coatings were microtextured.
Examples 13 to 19
[0056] Various 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.
Silica - Aerosil 380, crystallite size 7 nm Aerosil 200, crystallite size 12 nm
Alumina - Degussa, flame hydrolysed powder, crystallite size 20nm (Alumina C).
Zirconia - Tosoh TZO powder, crystallite size 27 nm, aggregate particle size 400 nm.
[0057] 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.
Preparation of a Ceria Sol
[0058] 250g of 99-grade, 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.
[0059] For pretreatment 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.
Preparation of a Titania Sol
[0060] 201 of dilute (0.3M Ti) titanium IV chloride solution was added with stirring to
2001 of 0.175M NH
4OH (22 ° C). The gelatinous precipitate was allowed to settle (2hr), the supernatent
decanted off, and the precipitate washed with 2201 of demineralized water. To remove
adsorbed ammonium ions the pH of the washed slurry was adjusted to 3.3 with IM HN0
3 (approx. 401) with a pH of 3.8 and a conductivity of 1.3x10
2 umhos. This slurry was then deaggregated by adding 0.751 HN0
3 (pH of slurry 2.3) and allowing to age for 14 days at 23 ° C. The dilute sol was
then evaporated at 20 ° C to yield a redispersible gel with a characteristic 'glitter'.
The gel contains 80.8% Ti0
2.
[0061] For pretreatment a 5wt% titania sol was prepared by dispersing the gel in deionised
water. The stock sol was dilute further for use in formulation 5.
Zirconia Sol and Oxidising Agent
[0062] 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.
EXAMPLE 20
[0063]
(a) (Comparison). A 1.5% zirconia sol was prepared by methods described in Examples
1 to 10. 10% by weight on the weight of the diluted sol of silica powder (aerosil
380, particle size 7 nm) was mixed in to the sol. The resulting mixture was roll coated
onto a clean aluminium surface and dried at 200 ° C. The value of the coating as a
base for adhesive was determined as described above, using a single part epoxy adhesive.
The peel strength was measured at 33N.
(b) (This example). The zirconia sol/silica powder mixture of (a) was roll coated
onto cleaned aluminium metal and dried at room temperature to form a layer on the
surface. A 7.5% aqueous solution of aluminium dihydrogen phosphate was roll coated
onto that layer. The resulting layer was cured at 200 ° C to form a protective coating on the metal surface. The adhesive peel strength obtained
using this protective surface was measured at 65N.
[0064] Application of the 7.5% aluminium dihydrogen phosphate solution gelled the zirconia
sol in the layer on the metal surface. If that solution had been added to the sol
in bulk, uncontrolled flocculation would have taken place and the resulting composition
would not have been useful for metal treatment.
EXAMPLE 21
[0065] A 2.25% aqueous solution of aluminium dihydrogen phosphate, (AI(H
2P0
4)a, was roll coated onto cleaned aluminium metal (AA5251 canning alloy) and dried
at room temperature. An aqueous dispersion consisting of 1 volume % zirconia sol and
7 weight % silica powder (Aerosil 200 (supplied by Degussa), particle size 12 nm)
was then applied by roller coating on the phosphate coated metal. The resulting coating
was cured at 80
° C for 3 minutes.
[0066] 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.
[0067] After tests, each sample was assessed for performance and marked semi-quantitatively.
An overall impression of performance was obtained from the total marks. For any test,
if there were no defects a score of 0 was given and for the word performance a score
of 4 was given. Each testing system generates a score from 0 to 16 and the four together
generates a score from 0 (best) to 64 (worst). Results are set out in Table 4. A low
score is a good result in these tests.
[0068] The pretreatment applied on a lacquered surface prevents 'feathering'. Feathering
refers to the degree of detachment of a lacquer film from a surface in a ring-pull-tab
configuration.
[0069] 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.
EXAMPLE 22
[0070] A pretreatment formulation containing 3 components (i.e. the sol, the adhesion promoter
and the passenger powder) was prepared as follows:
8 ml of silane (3-aminopropyltriethoxysilane) was added with stirring to 11 of deionised
water. 10 ml of conc. zirconia sol (containing 444gl-1 ZR2 equivalent) was then added dropwise with stirring in the silane solution. 40g of
silica powder (Aerosil 380) was finally blended in and the mixture was homogenised
for 1 hour in a Siliverson high shear blender to ensure good dispersion.
[0071] 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.
[0072] The pretratment formulations were applied on precleaned aluminium by roller coating
and dried at 80
° C for 3 mins. The 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).
EXAMPLE 23
[0073] 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.
EXAMPLE 24
[0074] CR2 steel was precleaned by degreasing, abrading and degreasing again. A pretreatment
formulation containing 4% Zr0
2 sol, 2% Amino silane and 7% A200 silica and prepared according to the procedure described
in Example 22 (formulation 1), was roller coated on the steel surface. The coating
was dehydrated at 180°C for 3 mins. 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.
EXAMPLE 25
[0075] 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.
EXAMPLE 26
[0076] 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].
EXAMPLE 27
[0077] A pretreatment formulation consisting of 3.1% Zr0
2 sol and 1% silane [N (β-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.
[0078] A lacquer performance test on the pretreated panels gave the following results:
[0079] It should be noted that the phosphoric acid anodised surface was prepared two years
ago. Electron microscopy showed that the surface topography remained unchanged after
storage, but it is possible that surface contamination during strorage is responsible
for the poor lacquer adhesion results prior to pretreatment.
1. 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.
2. A method which comprises applying to a solid surface:
(i) an aqueous composition consisting essentially of an inorganic hydrous oxide sol,
an adhesion promoter and optionally also a passenger powder, but not containing toxic
hexavalent chromium or molybdenum, to form a layer on the surface,
(ii) a fluid which gels the layer on the surface,
the applications being made sequentially in either order, and curing the resulting
layer on the surface.
3. A method as claimed in claim 1 or claim 2, wherein the inorganic sol is a hydrous
metal oxide sol.
4. A method as claimed in any one of claims 1 to 3, wherein the sol is a zirconia
sol.
5. A method as claimed in any one of claims 1 to 4, wherein the surface is a metal
surface.
6. A method as claimed in any one of claims 1 to 5, wherein the surface is of aluminium
or titanium which has been pre-treated to form thereon an artificially applied oxide
layer.
7. A method as claimed in any one of claims 2 to 6, wherein the adhesion promoter
is selected from fluorozirconates, silane coupling agents, nitrilotrismethylene phosphonates,
phosphates, and oxidising agents for the surface.
8. A method as claimed in any one of claims 1 to 7, wherein the aqueous composition
and/or the fluid contains from 1 to 300 g/I of a passenger powder.
9. A method as claimed in claim 8, wherein the passenger powder is selected from silica,
alumina, zirconia and titania having an average primary particle size in the range
3 - 150 nm.
10. A method as claimed in any one of claims 1 to 9, wherein the aqueous composition
contains a silane coupling agent as an adhesion promoter and a passenger powder.
11. A method as claimed in any one of claims 1 to 10, wherein the composition is cured
by heating to a temperature of from 50 ° C to 400 ° C.
12. A method as claimed in any one of claims 1 to 11, including the additional step
of applying an organic coating to the protective coating.
13. An aqueous composition for application to solid surfaces to form a protective
coating thereon, which composition contains no toxic hexavalent chromium or molybdenum
and consists essentially of:
a) an inorganic hydrous oxide sol and
b) an adhesion promoter selected from the class consisting of fluorozirconates, silane
coupling agents, nitrilotrismethylene phosphonates, phosphoric acids, phosphate esters
and oxidising agents for the surface, and optionally also
c) from 1 to 300 g/I of a passenger powder having an average primary particle size
in the range 3 - 250 nm.
14. A composition as claimed in claim 13, wherein component a) is a hydrous metal
oxide sol of concentration 1 - 200 g/I metal oxide equivalent.
15. A composition as claimed in claim 13 or claim 14, wherein component b) is a silane
coupling agent present at a concentration of 0.05% to 10% by volume on the volume
of the sol.
16. A composition as claimed in any one of claims 13 to 15, comprising:
a) a zirconia sol of concentration 1 - 200 g/I metal oxide equivalent,
b) a silane coupling agent present at a concentration of 0.05% to 10% by volume on
the volume of the sol, and
c) a passenger powder selected from silica, alumina, zirconia and titania, having
an average particle size in the range 3 - 150 nm, and present at a concentration of
5 - 150 g/I.
17. A particulate solid formed by drying the composition of any one of claims 13 to
16 and having the property of being re-dispersable in water to form the composition
of any one of claims 13 to 16.
1. Verfahren, wobei man auf eine feste Oberfläche eine wässrige Zusammensetzung aus
im wesentlichen einem anorganischen wasserhaltigen Oxid-Sol aufträgt, die ein Haftungsförderungsmittel,
ausgewählt aus der Klasse, bestehend aus Fluorzirkonaten, Silan-Kupplungsmitteln,
Nitrilotrismethylenphosphonaten, Phosphorsäuren, Phosphatestern und oxidierenden Mitteln
für die Oberfläche, sowie gegebenenfalls auch ein Passagier-Pulver, jedoch kein toxisches
sechswertiges Chrom oder Molybdän enthält, und wobei man die Zusammensetzung zur Bildung
eines Schutzüberzugs auf der Oberfläche härtet.
2. Verfahren, wobei man auf eine feste Oberfläche aufträgt:
(i) eine wässrige Zusammensetzung, bestehend im wesentlichen aus einem anorganischen
wasserhaltigen Oxid-Sol, einem Haftungsförderungsmittel und ggf. auch aus einem Passagier-Pulver,
welche jedoch kein toxisches sechswertiges Chrom oder Molybdän enthält, um eine Schicht
auf der Oberfläche zu bilden,
(ii) ein fluides Mittel, daß die Schicht auf der Oberfläche geliert,
wobei die Aufbringungen nacheinander in jeder der beiden Reihenfolgen durchgeführt
werden können, und wobei man die entstehende Schicht auf der Oberfläche härtet.
3. Verfahren gemäß Anspruch 1 oder 2,
worin das anorganische Sol ein wasserhaltiges Metalloxid-Sol ist.
4. Verfahren gemäß jedem Anspruch 1 bis 3,
worin das Sol ein Zirkonoxid-Sol ist.
5. Verfahren gemäß jedem Anspruch 1 bis 4,
worin die Oberfläche eine Metalloberfläche ist.
6. Verfahren gemäß jedem Anspruch 1 bis 5,
worin die Oberfläche aus Aluminium oder Titan ist, welche vorbehandelt worden ist,
um darauf eine künstlich aufgetragene Oxidschicht auszubilden.
7. Verfahren gemäß jedem Anspruch 2 bis 6,
worin das Haftungsförderungsmittel aus Fluorzirkonaten, Silan-Kupplungsmitteln, Nitrilotrismethylenphosphonaten,
Phosphaten und oxidierenden Mitteln für die Oberfläche ausgewählt ist.
8. Verfahren gemäß jedem Anspruch 1 bis 7,
worin die wässrige Zusammensetzung und/oder das fluide Mittel 1 bis 300 g/I eines
Passagier-Pulvers enthalten.
9. Verfahren gemäß Anspruch 8,
worin das Passagier-Pulver aus Silizium-, Aluminium-, Zirkon- und Titanoxid mit einer
durchschnittlichen Primärpartikelgröße im Bereich von 3 bis 150 nm ausgewählt ist.
10. Verfahren gemäß jedem Anspruch 1 bis 9,
worin die wässrige Zusammensetzung ein Silan-Kupplungsmittel als ein Haftungsförderungsmittel
sowie ein Passagier-Pulver enthält.
11. Verfahren gemäß jedem Anspruch 1 bis 10,
worin die Zusammensetzung durch Erhitzen auf eine Temperatur von 50 bis 400 ° C gehärtet wird.
12. Verfahren gemäß jedem Anspruch 1 bis 11,
wobei die zusätzliche Stufe der Aufbringung eines organischen Überzugs auf den Schutzüberzug
eingeschlossen ist.
13. Wässrige Zusammensetzung zur Aufbringung auf feste Oberflächen, um darauf einen
Schutzüberzug zu bilden, wobei die Zusammensetzung kein toxisches sechswertiges Chrom
oder Molybdän enthält und im wesentlichen besteht aus:
(a) einem anorganischen wasserhaltigen Oxid-Sol und
(b) einem Haftungsförderungsmittel, ausgewählt aus der Klasse, bestehend aus Fluorzirkonaten,
Silan-Kupplungsmitteln, Nitrilotrismethylenphosphonaten, Phosphorsäuren, Phosphatestern
und oxidierenden Mitteln für die Oberfläche, sowie gegebenenfalls auch aus
(c) 1 bis 300 g/I eines Passagier-Pulvers mit einer durchschnittlichen Primärteilchengröße
im Bereich von 3 bis 250 nm.
14. Zusammensetzung gemäß Anspruch 13, worin Komponente (a) ein wasserhaltiges Metalloxid-Sol
einer Konzentration von 1 bis 200 g/I Metalloxid-Äquivalent ist.
15. Zusammensetzung gemäß Anspruch 13 oder 14, worin Komponente (b) ein Silan-Kupplungsmittel
ist, das in einer Konzentration von 0,05 bis 10 Vol.% vorliegt, bezogen auf das Volumen
des Sols.
16. Zusammensetzung gemäß jedem Anspruch 13 bis 15, enthaltend:
a) ein Zirkonoxid-Sol einer Konzentration von 1 bis 200 g/I Metalloxid-Äquivalent,
b) ein Silan-Kupplungsmittel, das in einer Konzentration von 0,05 bis 10 Vol.% vorhanden
ist, bezogen auf das Volumen des Sols, sowie
c) ein Passagier-Pulver, ausgewählt aus Silizium-, Aluminium-, Zirkon- und Titanoxid,
mit einer Durchschnittsteilchengröße im Bereich von 3 bis 150 nm, welches in einer
Konzentration von 5 bis 150 g/I vorhanden ist.
17. Teilchenförmiger Feststoff, der durch Trocknung der Zusammensetzung eines jeden
Anspruchs 13 bis 16 gebildet ist und die Eigenschaft aufweist, in Wasser redispergierbar
zu sein, um die Zusammensetzung eines jeden Anspruchs 13 bis 16 zu bilden.
1. Procédé qui consiste :
à appliquer à une surface solide une composition aqueuse consistant essentiellement
en un sol d'oxyde minéral hydraté contenant un agent d'amélioration de l'adhérence
choisi parmi les fluorozirconates, les agents de couplage au silane, les phosphonates
de nitrilotrisméthylène, les acides phosphoriques, les phosphates et les agents oxydants
pour la surface et aussi facultativement, une poudre transitoire, mais ne contenant
pas de chrome ou de molybdène hexavalent toxique et à faire durcir la composition
pour former un revêtement protecteur sur la surface.
2. Procédé qui consiste à appliquer à une surface solide :
(i) une composition aqueuse consistant essentiellement en un sol minéral d'oxyde hydraté,
un agent d'amélioration de l'adhérence et aussi facultativement une poudre transitoire,
mais ne contenant pas de chrome ou molybdène hexavalent toxique, afin d'établir une
couche à la surface,
(ii) un fluide qui gélifie la couche à la surface,
les applications étant effectuées successivement dans un ordre quelconque et à faire
durcir la couche résultante sur la surface.
3. Procédé selon la revendication 1 ou 2, dans lequel le sol minéral est un sol d'oxyde
métallique hydraté.
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel le sol est
un sol de zircone.
5. Procédé selon l'une quelconque des revendications 1 à 4, dans lequel la surface
est une surface métallique.
6. Procédé selon l'une quelconque des revendications 1 à 5, dans lequel la surface
est en aluminium ou en titane ayant subi un pré-traitement pour établir sur lui une
couche d'oxyde artifiellement appliquée.
7. Procédé selon l'une quelconque des revendications 2 à 6, dans lequel l'agent d'amélioration
de l'adhérence est choisi parmi les fluorozirconates, les agents de couplage au silane,
les phosphonates de nitrilotrisméthylène, les phosphates et les agents oxydants pour
la surface.
8. Procédé selon l'une quelconque des revendications 1 à 7, dans lequel la composition
aqueuse et/ou le fluide contiennent de 1 à 300 g/I d'une poudre transitoire.
9. Procédé selon la revendication 8, dans lequel la poudre transitoire est choisie
parmi la silice, l'alumine, la zircone et le bioxyde de titane ayant une granulométrie
primaire moyenne de 3 à 150 nm.
10. Procédé selon l'une quelconque des revendications 1 à 9, dans lequel la composition
aqueuse contient un agent de couplage au silane à titre d'agent d'amélioration de
l'adhérence et une poudre transitoire.
11. Procédé selon l'une quelconque des revendications 1 à 10, dans lequel on fait
durcir la composition en chauffant à une température comprise entre 50 et 400 ° C.
12. Procédé selon l'une quelconque des revendications 1 à 11, qui comprend le stade
supplémentaire d'application d'un enduit organique sur le revêtement protecteur.
13. Composition aqueuse pour application à des surfaces solides afin de former un
revêtement protecteur sur celles-ci, composition qui ne contient pas de chrome ou
molybdène hexavalent toxique et qui consiste essentiellement en :
(a) un sol d'hydroxyde minéral hydraté et
(b) un agent d'amélioration de l'adhérence choisi parmi les fluorozirconates, les
agents de couplage au silane, les phosphonates de nitrilotrisméthylène, les acides
phosphoriques, les phosphates et les agents oxydants pour la surface, ainsi que, facultativement,
(c) de 1 à 300 g/I d'une poudre transitoire présentant une granulométrie primaire
moyenne de 3 à 250 nm.
14. Composition selon la revendication 13, dans laquelle le composant (a) est un sol
d'oxyde métallique hydraté ayant une concentration de 1 à 200 g/I d'équivalent d'oxyde
métallique.
15. Composition selon la revendication 13 ou 14, dans laquelle le composant (b) est
un agent de couplage au silane présent en une cncentration de 0,05 à 10% en volume,
par rapport au volume du sol.
16. Composition selon l'une quelconque des revendications 13 à 15, qui comprend :
(a) un sol de zircone d'une concentration de 1 à 200 g/I d'équivalent d'oxyde métallique,
(b) un agent de couplage au silane en une concentration de 0,05 à 10% en volume par
rapport au volume du sol, et
(c) une poudre transitoire choisie parmi la silice, l'alumine, la zircone et le bioxyde
de titane, ayant une granulométrie moyenne de 3 à 150 nm et présente en une concentration
de 5 à 150 g/I.
17. Solide particulaire formé par séchage de la composition selon l'une quelconque
des revendications 13 à 16 et possédant la propriété d'être redispersable dans l'eau
pour former la composition selon l'une quelconque des revendications 13 à 16.