Note: Descriptions are shown in the official language in which they were submitted.
1337~45
METHOD AND COMPOSITION FOR SURFACE TREATMENT
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.
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
1 337 1 45
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 lO0, 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. Al 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.
1 337 1 45
20388-1648
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.
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.
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 effective concentration of an adhesion promoter
selected from the class consisting of fluorozirconates, silane
coupling agents, nitrilotrismethylene phosphonates, phosphate
esters, and Ce4 and permanganate oxidizing agents for the
surface, and optionally also a passenger powder, curing the
composition to form a protective coating at a coating weight of up
to 1.5 g/m on the surface, and applying an organic coating to the
protective coating.
One way of achieving this is by applying to the surface:
(i) an aqueous composition consisting essentially of an
inorganic hydrous oxide sol, an effective concentration of an
adhesion promoter and optionally also a passenger powder, to form
a layer on the surface,
1 337 1 45
20388-1648
(ii) a fluid which gels the sol on the surface,
the applications being made sequentially in either order, and
curing the resulting layer to form a protective coating at a
coating weight of up to 1.5 g/m on the surface.
The present invention also provides a method which
comprises applying to a solid surface an aqueous composition
comprising an inorganic hydrous oxide sol containing an adhesion
promoter selected from the class consisting of fluorozirconates,
silane coupling agents, nitrilotrismethylene phosphonates,
phosphate esters and Ce4 and permanganate oxidizing agents for
the surface, and curing the composition to form a protective
coating at a coating weight of up to 1.5 g/m2 on the surface.
In another aspect the invention provides an aqueous
composition for application to solid surfaces which composition
consists essentially of:
(a) an inorganic hydrous oxide sol, and
(b) an effective concentration of an adhesion promoter
selected from the class consisting of fluorozirconates, silane
coupling agents, nitrilotrismethylene phosphonates, phosphate
esters and Ce4 and permanganate oxidizing agents for the surface,
and optionally also
(c) from 1 to 300 g/l of a passenger powder having an
average primary particle size in the range 3 to 250 nm,
provided that the composition does not contain added hexavalent
chromium or molybdenum.
The aqueous composition of the present invention may
further comprise from 1 to 300 g/l of a passenger powder having an
1 337 1 45
-
20388-1648
average primary particle size in the range 3 to 250nm.
The method is suitable for the pretreatment of solid
surfaces such as non-metals and metals generally,
3b
4 1 337 1 45
including steel, titanium1 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.
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.
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 l:l. The polymeric
3 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 bonds. J. D. F. Ramsay "Neutron and Light
Scattering Studies of Aqueous Solutions of Polynuclear
1 337 1 45
-- 5
Ions. 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 the this paper by including those containing
Al(III) Fe(III) Zr(IV) Th(IV): for example:
A11304(0H)24 (H2)12
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
(Al(III) Zr(IV) Ce(IV) Ti(IV) Fe(III). Preparation of
Type B Al(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.
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.
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
3 density <45% of the theoretical density of the oxide.
The inorganic sol for use in this invention is a
hydrous oxide sol, preferably to 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.
1 33~ 1 45
- 6
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:
[Zr4(oH)l2(No3)2(H2o)4]n (N3)2n 2n 2 '
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.
Also applied to the surface, according to one
aspect of the invention, is a fluid which gels the sol
and/or a powder passenger on the surface. For
example, Al203 powder passenger 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,
- 1 337 1 45
-- 7
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
100C, 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
i i ) .
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.
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)
3 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
1337145
can be provided separately. They may conveniently
be provided by dissolving fluorozirconic acid H2ZrF6,
or a soluble fluorozirconate salt, in water;
alternatively, a corresponding acid or salt of Ti, Si
or Hf e 9. H2TiF6, H2SiF6 or H2HfF6, y
Fluorozirconate (or other fluoro complex) is preferably
present at a concentration of 0.1 to 200 gl~1,
particularly from 10 to 100 gl 1, 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 1, 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.
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
3 b~ 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,
1 337 1 45
20388-1648
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.
The adhesion promoter may be a Ce4 or permanganate
oxidizing agent for the surface. The Ce4 species may be provided
in the form of a hydrated ceria sol or as a dissolved ceric æalt.
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 composi-
tion, and should be used at a concentration designed to achieve
these ends.
The aqueous composition or the fluid may also contain a
powder passenger, 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 1, preferably 5 to 150
gl 1, more particularly 10 to 75 gl 1 are appropriate. The powder
may have an average particle size below 250 nm, e.g. in the range
3 to 150 nm, particularly 4 to 100 nm, and is preferably of sub-
stantially uniform particle size.
Preferably the powder passenger is present in the
aqueous composition containing the inorganic sol. It is possible
to incorporate the powder passenger in the fluid (ii), provided
that the fluid does not react and/or destabilize the powder
passenger, as for example when phosphoric acid is added to an
Al2O3 powder. When this fluid brings about gelation of the sol,
the powder becomes incorporated in the layer on the metal surface.
1 337 1 45
~ o
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:
a) a zirconia sol cf concentration 1 - 200 9l~1 metal
oxide equivalent,
b) a silane coupling agent present at a concentration
cf C.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 1.
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 b~ 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 treatmerts with sulphuric, chromic or
3 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
1 3371 45
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.
By virtue of their small sol particle size, less
than about 0.2 microns 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.
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).
If the adhesion promoter is added in a less
controlled manner, irreversible flocculation occurs and
3 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.
1337145
- 12 -
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.
By control over the microtexture of the protective
coating, a nun,ber 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 adhesicn
promoter in the aqueous compcsition 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 prctective coating
m~ 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
3 cver the concentration and size of the passenger powder
particles, the adhesion prGperties of the coated
surface can be optimised for its intenced purpose.
b) The metal surf2ce has been provided with a textured
1 `33~1 45
- 13 -
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.
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. rhe 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 700C,
usually (though not always) below those required to
fully sinter the particles, and may typically be in the
range 50 to 400C. Calcination of the coating at
temperatures above 400C is possible but not usually
necessary. For optimum adhesive bond strength, curing
temperatures in the range 50 - 100C are preferred.
For good adhesion combined with good protection from
corrosion, curing temperatures in the range 100C to
400C are preferred. Removal of water takes place
progressively and is still not complete at 400C.
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
14 l 337 1 45
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
B is Permabond ESP105 ~
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 micron or
even up to 5 microns may be used.
The following examples illustrate the invention.
Examples 1 to lO
Zirconia sol preparation
In a typical preparation 2 kg of zirconium
carbonate (44.8 w/v ZrO2, 7.2 moles) was added with
stirring to O.9l of 8M HN03 (7.2 moles), the paste
rapidly dissolved (exothermic 43C) to give a sol
containing 444 gl 1 ZrO2 equivalent. When cooled to
20C the dispersion (N03/ZrO2 mole ratio = 1.0) has a
viscosity of 16 cp and a density of 1.55 g/cm .
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
3 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.
1 3 3 7 1 45
TABLE l
Pretreatment Solutions Prepared for Adhesive Bonding
EXAMPLE
l) 2% Zirconia Sol
2) 10% Zirconia Sol
3) 10~ Zirconia Sol and 1% (v/v) Silane coùpling
agent Al100 (3-aminopropyltriethoxysilane)
4) 2% Zirconia Sol and 0.5% (v/v) Silane coupling
agent A1100.
5) 10% Zirconia Sol and lO~ (v/v) Fluorozirconic Acid
6) 10% Zirconia Sol and 4X (v/v) Fluorozirconic Acid
7) 10% Zirconia Sol and 0.1~ (v/v) Phosphoric Acid
8) 2~ Zirconia Sol and 0.1~ (v/v) Phosphoric Acid
9) 2% Zirconia Sol and 0.01~ (v/v) Phosphoric Acid
lO) lO~ Zirconia Sol and 0.1~ (v/v) NTMP (nitrilotris-
methylene phosphonic acid)
Sample Pretreatment
300 x lO0 panel of 5251 alloy were vapour0 degreased and then acid cleaned by a 1 minute immersion
B in Ridolene 124~acid cleaner at a temperature of
between 55 and 60C. 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
200C for 1 minute. Additional samples of metal
pretreated with the additive-free formulations were
dried at 100C.
Preparation and Tensile Testing of Adhesive Joints
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
~T~de~ k
1 3371 45
- 16 -
a jig giving 10 mm overlap, clipped together, and sub-
sequently removed from the jig and cured at 180C for a
time of 30 minutes, commencing from the time the sample
temperature reached 175C. 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 60C 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
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
d 60mm long bondline. These were peeled at Smm/min on
an Instron 1115 tensile tester and the steady-state
peel load was recorded during the peel event.
3o
- 17 - 1 337 1 45
-
TABLE 2
Effect of Storage at 60C in water for 200 hours
Tensile Adhesive Bond Strength kN
ExampleStored in Dry Stored in Wet ~ Retention Dry Peel
Environment Environment of Adhesion Strength
(N)
1) Dried 200C 4.80 + 0.29 3.63 + 0.15 75.6 23 + 1.5
2) Dried 200C 4.63 _ 0.16 3.45 + 0.20 74.5 20 + 0.6_
1) Dried 100C 5.58 + 0.78 3.73 + 0.27 66.7 21 + 1.0
2) Dried 100C 4.31 + 0.10 3.41 + 0.35 79.1 19 + 0.6
3) 4.72 + 0.21 4.22 + 0.25 89.4 22 + 1.0
4) 5.38 + 0.07 5.00 + 0.19 92.9 30 + 1.1
5) 3.64 _ 0.03 1.65 + 0.18 45.3
6) 3.44 + 0.26 2.37 + 0.15 68.9 24 + 1.1
7) 4.41 + 0.04 3.73 + 0.12 84.5 21 + 1
8) 4.81 + 0.17 3.85 + 0.24 80.0 28 + 7.2
9) 4 70 + 0.09 3.55 + 0.04 75.5 27 + 6.9
10) 4.79 + 0.10 3.27 + 0.11 68.3 20 + 0.6
Etched * 5.44 + 0.02 3.34 + 0.08 61.4 34.26
(comparative)
* Vapour degreased and acid cleaned as above.
1 337 1 45
- 18
Results
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 ll
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
Treatment solutions containing silane adhesion
promoters were prepared and applied as described in
Example ll except that the silane was diluted to 0.5
volume percentage by adding water to the silane AlllO.
(The recommended procedure is to add the silane to
water.)
The coatings were microtextured.
3 Examples 13 to l9
Various aqueous compositions according to the
invention were made up by the general procedure given
in Examples l to lO. Sample pretreatment and
preparation and testing of adhesive joints were also as
described in Examples 1 to lO. Details of
19 1 3371 45
formulations and peel strengths ~re set out in Table 3
below.
B 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.
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.
Ceria sol - Oxidising sol
Ce(S04)2, KMN04 - Oxidising agents (salts).
Preparation of a Ceria Sol
2509 of 99-grade, Rhone-Poulenc Ceria hydrate
(typically 70.9 wt~ oxide) was slurried in distilled
water. 16ml of conc. HN03 in 34ml of water was added
to the slurry and stirred thoroughly. The mixture was
heated to 70C 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 9l~l concentration.
For pretreatment the sol was diluted to 10% or 2%
of the original concentration. O.lM 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.
~r k
- - 20 - 1337145
Preparation of a Titania Sol
201 of dilute (0.3M Ti) titanium IV chloride
solution was added with stirring to 2001 of 0.175M
NH40H (22C). 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 HN03 (approx. 401)
with a pH of 3.8 and a conductivity of 1 3x102 umhos.
This slurry was then deaggregated by adding 0.751 HN03
(pH of slurry 2.3) and allowing to age for 14 days at
23C. The dilute sol was then evaporated at 20C to
yield a redispersible gel with a characteristic
'glitter'. The gel contains 80.8~ TiO2.
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
The zirconia sol was diluted to 10% of the
original conc. O.lM KMnO4 solution was added dropwise
to the sol while stirring rapidly such that minimal
flocculation occurred. The 1.5% silica powder was
added finally.
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TABLE 3
Example Pretreatment Dry Peel Strength (N)
13 2% Zirconia Sol 51.6 + 2.7
2.5% (w/v) Silica
14 2% Zirconia Sol 58.3 + 13.9
0.5% (v/v) Silane
2.5% (w/v) Silica
10% Zirconia Sol 62.9 + 3.9
O. 1% (v/v)
Phosporic Acid
2.5% (w/v) Silica
16 2% Zirconia Sol 62.6 + 1.2
0.5X (v/v) Silane
1.5X (w/v) Alumina
17 10% Ceria Sol 58.7 + 1.8
1.5% (w/v) Silica
18 2% Ceria Sol 60.4 + 4.4
0.2% (v/v) O.lM
Ce(S04)2
1.5% (w/v) Silica
19 10% Zirconia Sol 54.8 + 6.8
1% (v/v) O.lM KMN04
3 1.5% (w/v) Silica
2% Alocrom 404 32 + 0
(Commercial pretreatment)
l337145
EXAMPLE 20
(a) (Prior method). 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
200C. 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 invention). 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 200C to
form a protective coating on the metal surface. The
adhesive peel strength obtained using this protective
surface was measured at 65N.
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
A 2.25% aqueous solution of aluminium dihydrogen
phosphate, (Al(H2P04)3, was roll coated onto cleaned
3 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 80C
for 3 minutes.
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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.
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 worst 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.
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.
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 130C for l 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.
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1337145
- 24 -
TABLE 4 - LACQUER TESTS
PRETREATMENT SCORE
LACQUER FEATHERING
1) Degreased and acid cleaned 40~ 4
2) ALOCROM 4040 (a commercial 34 4
nonchromate pretreatment
manufactured by AMCHEM
supplied by ICI)
3) 1st coat : 2.25~ Al(H2P04)3 18~ 2
2nd coat : 1% ZnO2 sol + 7
silica powder
4) 0 5X ZrO2 sol 30 2
1~ Glycidoxy silane
7~ Zirconia powder
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EXAMPLE 22
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 4449l~1 Zr2 equivalent) was
then added dropwise with stirring in the silane
solution. 409 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.
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
80C 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 60C, 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 120C
3 for 3 mins., as recommended by the supplier (ICI).
1 337~45
- - 26 -
TABLE 5
FORMULATION CONC. OFTENSILE ADHESIVE BOND STRENGTH DRY PEEL
(KN)
CONSTITUENTS DRY 200h 1000h STRENGTH ('~
1 lX ZrO2 sol 4.5 4.1 4.1 73
0.8% Amino silane
4X Silica A380
2 5% Zr2 sol 4.0 3.9 3.9 78
0.5% Amino silane
4X Silica A380
3 lX ZrO2 sol 4.3 4.2 4.2 74
0.5X Amino silane
6X Alumina 'C'
4 0.5X ZrO2 sol 4.9 4.4 - 55
1X Glycidoxysilane
10% Silica A200
1.3% TiO2 sol 4.8 4.4 42
1% Glycidoxysilane
7~ Alumina 'C'
6 1.4% CeO2 sol 4.4 3.9
4X Alumina 'C'
z lX ZrO2 sol 4.4 3.9 3.6 39
0.25X Ce(S04)2
6X Silica A380
8 Alocrom 4040 3.7 1.9 1.4 56
(- No data available)
` - 27 - l 337 1 45
EXAMPLE 23
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
5% zirconia sol was roller coated on aluminium
foil which had been precleaned by vapour degreasing and
acid etching. The coating was cured at 450C for 3
mins.
The coated foil was then used to line a petri dish
and 209 of 1~ Oxalic acid was heated in the lined
container at 50C for 1 hour. A control experiment
with uncoated aluminium foil was also carried out. The
Al content in the processed oxalic acid is shown in the
following table. (Table 6).
TABLE 6
ALUMINIUM FOIL CONC. OF Al (ppm) CONC. OF Zr (ppm)
Uncoated 24 1.8
3 Zirconia coated 7 1.7
~ - 28 - 1 3371 45
EXAMPLE 25
CR2 steel was precleaned by degreasing,
abrading and degreasing again. A pretreatment
formulation containing 4% ZrO2 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 180C for 3 mins. Single lap adhesive
joints were prepared with the pretreated metal and the
joints exposed to neutral salt spray (5% NaCl)
maintained at 43C. 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 7.
LAP SHEAR JOINT STRENGTH (KN)
PRETREATMENT O 1 2 4 7.5 (weeks of
Exposure)
4% Zr2 sol 3.9 3.1 2.6 2.5 1.6
2% Amino silane
7% Silica
Electrogalvanising 3.9 2.6 2.0 1.7 1.2
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1 337 1 45
,
- 29 -
EXAMPLE 26
The integrity of the pretreatment film on the
aluminium surface was measured by immersing the
pretreated coupon in acidified copper sulphate
solution. The time taken for copper to electroplate on
the aluminium surface was measured. The results are
shown in Table 8.
TABLE 8
PRETREATMENT COPPER DEPOSITION TIME (SEC)
untreated 36
1.5% Flame hydrolysed alumina 60
(1.59 Al203/100 ml H20)
tTYPE C sol~ -
2.5% Zirconia sol 192
(1.19 ZrO2/100ml H20)
[TYPE A sol]
Longer copper deposition time (hence better corrosion
protection) resulted from the Type A sol.
EXAMPLE 27
A pretreatment formulation consisting of 1X
Zr2 sol, 0.8% amino silane and 4% silica prepared as
described in Example 22 (formulation 1), was roller
3 coated on aluminium foil, and heated to 200C 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
13371 ~5
- 30 -
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 28
A pretreatment consisting of 1% ZrO2 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 29
A pretreatment formulation consisting of 3.1%
Zr2 sol and 1% silane [N (~-aminoethyl)
-y-aminopropyltrimethoxy silane] was roll coated on
aluminium metal and dried at 80C 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
3 section also revealed that the pretreament had
penetrated the anodic film and formed a dense layer
adjacent to the metal surface.
A lacquer performance test on the pretreated
panels gave the following results:
7~145
PRETREATMENT TOTAL SCORE* FEATHERIN~
(A) Phosphoric acid anodising 25 4
(B) 3.1% ZrO2 26 2
1% silane
(A) and (B) 18
(* Low score indicates good performance)
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.
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