Note: Descriptions are shown in the official language in which they were submitted.
CA 02487195 1995-05-09
1
MIRRORS HAVING A SILVER COATING AT A SURFACE OF
A VITREOUS SUBSTRATE
This application is a division of Canadian Patent Application No
2,148,955 filed on May 9, 1995. The invention has particular reference to
glass
substrates bearing a continuous reflective coating. It is envisaged that the
invention
will find greatest use when the coating is applied to a flat glass substrate.
The coating
may be fully reflective, thus forming a mirror-coating. Conventionally, silver
mirrors
are produced as follows. The glass is first of all polished and then
sensitised, typically
using an aqueous solution of SnC12. After rinsing, the surface of the glass is
usually
activated by means of an ammoniacal silver nitrate treatment. The silvering
solution is
then applied in order to form an opaque coating of silver. This silver coating
is then
covered with a protective layer of copper and then one or more coats of paint
in order
to produce the finished mirror.
The silver coating does not always adhere sufficiently to the substrate.
In the case of certain prior products, it has been observed that the silver
coating comes
away spontaneously from the glass substrate. This is, for example, the case
when
silvered microbeads manufactured in a normal manner are incorporated in a
plastics
matrix.
According to one aspect of the invention, there is provided a silver
mirror comprising a silver coating which is not covered with a protective
layer of
copper, comprising in the order recited:
(a) a flat glass substrate in the form of a glass sheet,
(b) tin at a surface of the glass sheet,
(c) a silver coating at the surface of the glass sheet,
(d) at least one paint layer covering the silver coating, wherein the
silver mirror exhibits an average number of white specks of less than 10 per
dm2, after
having been subjected to at least one of the following tests:
(i) a 120 hour accelerated ageing CASS Test; and
(ii) a 480 hour Salt Fog Test.
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According to another aspect of the invention, there is provided a silver
mirror comprising in the order recited:
(a) a flat glass substrate in the form of a glass sheet,
(b) tin and at least one material selected from the group consisting of
palladium, bismuth, chromium, gold, indium, nickel, platinum, rhodium,
ruthenium,
titanium, vanadium, and zinc at a surface of the glass sheet,
(c) a silver coating on the surface of the glass sheet, and
(d) at least one paint layer,
wherein the silver mirror is a domestic mirror or a vehicle rear-view
mirror.
According to another aspect of the invention, there is provided a silver
mirror comprising in the order recited:
(a) a flat glass substrate in the form of a glass sheet,
(b) tin and at least one material selected from the group consisting of
palladium, bismuth, chromium, gold, indium, nickel, platinum, rhodium,
ruthenium,
titanium, vanadium, and zinc at a surface of the glass sheet,
(c) a silver coating on said surface of the glass sheet,
(d) a layer of copper; and
(e) at least one paint layer,
wherein said silver mirror is a domestic mirror or a vehicle rear-view
mirror.
A characteristic of embodiments of the invention is to "activate" the
substrate by treating it with a specific activating solution before silvering.
It has been observed that the treatment of glass using an activating
solution according to the present invention improves the adhesion of the
silver coating.
A sensitising step may contribute to improving the adherence of the
silver coating and therefore its durability. Preferably the sensitising step
is carried out
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3
before said silvering step. This sensitising step is typically carried out
with a
sensitising solution comprising tin (II) chloride.
Preferably, said sensitising step is carried out prior to the activating
step. We have observed that the order of the steps is important to obtain good
durability. This observation is very surprising because the activation
treatment does
not really produce a distinct continuous layer containing bismuth (III),
chromium (II),
gold (III), indium (III), nickel (II), palladium (II), platinum (II), rhodium
(III),
ruthenium (III), titanium (III), vanadium (III) or zinc (II), but they are in
the form of
islets on the surface of the glass. An analysis of the surface of glass
treated with a
sensitising solution containing tin (II) chloride followed by an activating
solution
containing palladium (II) shows the presence of a certain proportion of
palladium
atoms with respect to tin atoms at the glass surface. Typically, one finds
about 0.4
atoms of palladium per atom of tin, and 0.3 atoms of tin per atom of Si at the
surface
of the glass.
The invention can also be implemented on flat glass substrates, and it is
believed that the invention will be particularly useful for this type of
substrate.
Consequently, the activation treatment is preferably effected on a flat glass
substrate,
such as a glass sheet.
The treatment is preferably applied to glass substrates onto which a
thick opaque silver coating is subsequently applied in order to form a mirror.
Such
embodiments of the invention, where the product is a mirror, are used for
example as
domestic mirrors or as vehicle rear-view mirrors. The invention makes it
possible to
produce mirrors on which the silver coating has an improved adhesion to the
glass
and/or a desired resistance to ageing. Thus according to another embodiment
the
thickness of the layer of silver formed in said silvering step is between 70
nm and 100
nm.
According to the present invention, the activation of the glass is
effected before silvering by treating the glass substrate with a specified
activating
solution. It is observed that the silver coating of the mirror produced in
this way has
CA 02487195 1995-05-09
4
better adhesion than that of a mirror manufactured by the conventional process
and/or
desired resistance to ageing.
The improvement of the adhesion of the silver coating obtained by the
process according to the present invention is observed in different ways.
The adhesion of a silver coating to its glass substrate may be assessed
quickly by testing using adhesive tape: an adhesive tape is applied to the
silver coating
and then pulled off. If the silver coating is not adhering well to the glass,
it comes
away from the glass when the tape is pulled off.
The degree of adhesion of the silver coating to the glass can also be
observed by subjecting the product to an accelerated ageing test such as the
CASS Test
or Salt Fog Test. It is sometimes found that the product subjected to such
tests has a
certain edge corrosion and/or light diffusing specks ("white specks").
The activation treatment according to the invention affords another
advantage. We have observed that the silvering reaction on glass activated
according
to the invention is more effective, that is to say the reaction yield is
greater. It is
possible to achieve yields improved by around 15% compared with silvering
effected
on a glass activated in a conventional manner, with a solution of ammoniacal
silver
nitrate. This presents advantages from the economic point of view since one
can use
less reagents to form the same thickness of silver coating and also from the
environmental point of view since the quantity of waste from the silvering
reaction to
be eliminated can be reduced.
It is conventional to protect the silver coating with an overcoating of
copper to retard tarnishing of the silver layer. The copper layer is itself
protected from
abrasion and corrosion by a layer of paint. Those paint formulations which
afford the
best protection against corrosion of the copper layer contain lead pigments.
Unfortunately lead pigments are toxic and their use is being increasingly
discourage
for reasons of environmental health.
It has recently been proposed to protect the silver coating by treatment
with an acidified aqueous solution of Sn (II) salt (see British patent
application GB
CA 02487195 1995-05-09
2252568). According to another recent proposal, the silver coating is
protected by
treatment with a solution containing at least one of Cr (II), V(II or III), Ti
(II or III), Fe
(II), In (I or II), Cu (I) and Al (III) (see British patent application GB
2254339). We
have observed that the activation treatment according to the present invention
is
5 particularly useful for the manufacture of such products. One important
application of
the protection treatments according to GB 2252568 and GB 2254339 is the
formation
of silver mirrors which do not include a conventional protective layer of
copper. Such
mirrors can be protected with lead-free paints. The activation treatment
according to
the present invention is particularly advantageous for the manufacture of such
mirrors.
This is because the activation treatment of the glass during the manufacture
of mirrors
protected with such treatment significantly improves the adhesion of the
silver coating
of such mirrors and therefore their durability. Consequently, the invention
applies
preferably to the manufacture of mirrors with no copper layer, and in
particular to
mirrors formed by a process in which the silver coating is subsequently
contacted with
a solution containing ions of at least one of the group consisting of Cr (II),
V(II or III),
Ti (11 or III), Fe (II), In (I or II), Sn (II), Cu (I) and Al (III).
The glass substrate may be brought into contact with the activating
solution by dipping in a tank containing an activating solution but,
preferably, the glass
substrate is brought into contact with the activating solution by spraying
with an
activating solution. This is particularly efficacious and practical in the
case of flat
glass substrates, for example during the industrial manufacture of flat
mirrors, in
which sheets of glass pass through successive stations where sensitisation,
activation
and then silvering reagents are sprayed.
We have observed that the glass substrate may be effectively activated
by a rapid treatment using the specified activating solution. It has been
observed that
the glass/activating solution contact time may be very short, for example
around a few
seconds only. In practice, in the industrial production of flat mirrors, the
sheet of glass
moves along a mirror production line on which the glass passes through an
activation
station where the activating solution is sprayed, then through a rinsing
station and
afterwards through the silvering station.
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6
The activating solution preferably comprises a source of palladium,
most preferably a palladium (II) salt in aqueous solution, in particular PdC12
in
acidified aqueous solution.
The activating solution may be used very simply and economically.
The PdC12 solution may have a concentration of from 5 to 130 mg/1. We have
observed that bringing the glass substrate into contact with a quantity of
from 1 to 23
mg, preferably at least 5 mg of PdC12, per square metre of glass is entirely
sufficient to
activate the glass substrate effectively. In fact, we have observed that the
use of
quantities of PdC12 higher than about 5 or 6 mg PdCl2 / m2 does not afford any
significant improvement. Therefore it is preferred to treat the glass
substrate with
about 5 or 6 mg of PdC12 per square metre of glass.
We have found that best results can be obtained when the pH of said
activating solution is from 2.0 to 7.0, most preferably from 3.0 to 5Ø This
pH range
allows solutions to be formed which are both stable and effective for
activating the
glass. For example, when using palladium, below pH = 3.0 the level of
palladium
deposited on the glass substrate may be reduced, leading to a poor quality
product.
Above pH = 5.0, there is a risk of precipitation of palladium hydroxide.
The silver coating may be covered with one or more protective paint
layers and according to a preferred aspect of this invention such a paint is
free, or
substantially free, of lead. Where more than one such paint layer is used, the
paint
layers other than the uppenmost paint layer may contain lead. However, for
environmental health reasons, lead sulphate and lead carbonate in the lower
paint
layers are,preferably absent so that where lead is present in these lower
layers it is
preferably in the form of lead oxide.
The invention will now be further described, purely by way of example,
in the following examples.
Example 1 + Control 1
Mirrors are manufactured on a conventional mirror production line in
which sheets of glass are conveyed along a path by a roller conveyor.
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7
The sheets of glass are first of all polished, rinsed and then sensitised
by means of a tin chloride solution, in the normal manner, and then rinsed.
An acidic aqueous solution of PdC12 is then sprayed onto the sheets of
glass. This solution is prepared from a starting solution containing 6 g of
PdC12/1
acidified with HCl in order to obtain a pH of approximately 1, and diluted
with
demineralised water in order to feed spray nozzles which direct the dilute
solution,
which contains 60 mg PdC12/1, onto the sheets of glass, so as to spray
approximately
11 mg of PdC12/m2 of glass.
The sheets of glass thus activated then pass to a rinsing station where
demineralised water is sprayed, and then to the silvering station where a
traditional
silvering solution is sprayed, comprising a silver salt and a reducing agent.
This is
achieved by simultaneously spraying a solution A containing ammoniacal silver
nitrate
and heptagluconic acid and a solution B containing ammoniacal sodium
hydroxide.
The flow rate and concentration of the solutions sprayed onto the glass are
controlled
so as to form, under conventional production conditions, a layer containing
approximately 800-850 mg/m2 of silver. It is observed that the mass of silver
deposited is higher by approximately 135 mg/m2 of silver, ie approximately 935-
985
mg/m2 of silver.
A coppering solution of a usual composition is sprayed onto the silver
coating in order to form a coating containing approximately 300 mg/m2 of
copper.
This is achieved by simultaneously spraying a solution A and a solution B.
Solution A
is prepared by mixing an ammonia solution with a solution containing copper
sulphate
and hydroxylamine sulphate. Solution B contains citric acid and sulphuric
acid. The
glass is then rinsed, dried and covered with a Levis epoxy paint. This paint
comprises
a first coat of approximately 25 gm of epoxy and a second coat of
approximately 30
m of alkyd. Mirrors are allowed to rest for 5 days to ensure complete curing
of the
paint layers.
Mirrors manufactured in this manner are subjected to various
accelerated ageing tests.
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One indication of the resistance to ageing of a mirror incorporating a
metallic film can be given by subjecting it to a copper-accelerated acetic
acid salt spray
test known as the CASS Test in which the mirror is placed in a testing chamber
at
50 C and is subjected to the action of a fog formed by spraying an aqueous
solution
containing 50 g/l sodium chloride, 0.2 g/l anhydrous cuprous chloride with
sufficient
glacial acetic acid to bring the pH of the sprayed solution to between 3.0 and
3.1. Full
details of this test are set out in International Standard ISO 3770-1976.
Mirrors may
be subjected to the action of the saline fog for different lengths of time,
whereafter the
reflective properties of the artificially aged mirror may be compared with the
reflective
properties of the freshly formed mirror. We find that an exposure time of 120
hours
gives a useful indication of the resistance of a mirror to ageing. We perform
the CASS
Test on 10 cm square mirror tiles, and after exposure to the copper-
accelerated acetic
acid salt spray for 120 hours, each tile is subjected to microscopic
examination. The
principal visible evidence of corrosion is a darkening of the silver layer and
peeling of
the paint around the margins of the mirror. The extent of corrosion is noted
at five
regularly spaced sites on each of two opposed edges of the tile and the mean
of these
ten measurements is calculated. One can also measure the maximum corrosion
present
at the margin of the tile to obtain a result which is again measured in
micrometres.
A second indication of the resistance to ageing of a mirror
incorporating a metallic film can be given by subjecting it to a Salt Fog Test
which
consists in subjecting the mirror to the action, in a chamber maintained at 35
C, of a
salt fog formed by spraying an aqueous solution containing 50 g/l sodium
chloride.
We find that an exposure time of 480 hours to the Salt Fog Test gives a useful
indication of the resistance of a mirror to ageing. The mirror is again
subjected to
microscopic examination, and the corrosion present at the margin of the tile
is
measured to obtain a result in micrometres, in the same way as in the CASS
Test.
Mirrors measuring 10 cm square manufactured according to Example I
are subjected to the CASS and salt fog tests, along with Control samples not
according
to the invention.
These Control samples are manufactured from sheets of glass as
described in Example 1, except that the PdC12 activation stage followed by a
rinsing is
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omitted. This step is replaced by a traditional activation step, by spraying
with an
ammoniacal solution of silver nitrate.
The results of the two ageing tests on the mirror of Example 1 and the
Control sample 1 are as set out in the following TABLE I:
TABLE I
CASS test Salt fog test Density of white specks
average in m average in m average number/dm2
Example 1 334 97 0
Control 1 480 153 0
The mirrors according to Example 1 and Control 1 do not show any
white specks after these two tests.
The treatment consisting of the activation of the glass with palladium
(II) chloride before silvering according to Example 1 therefore reduced the
corrosion at
the edges of the mirror, which shows better adhesion of the silver, compared
with a
mirror on which the glass has been activated in a conventional manner with
ammoniacal silver nitrate.
Examples 2 and 3 & Controls 2 and 3
Mirrors according to the invention are manufactured on a conventional
mirror production line in which sheets of glass are conveyed along a path by a
roller
conveyor.
The sheets of glass are first of all polished, rinsed and then sensitised
by means of a tin chloride solution, in the usual manner, and then rinsed.
An acidic aqueous solution of PdC12 is then sprayed onto the sheets of
glass. This solution is prepared from a starting solution containing 6 g of
PdC12/1
acidified with HCI in order to obtain a pH of approximately 1, and diluted
with
demineralised water in order to feed spray nozzles which direct the dilute
solution,
which contains about 30 mg PdC12/1, onto the sheets of glass, so as to spray
CA 02487195 2006-11-29
approximately 5.5 mg of PdC12/m2 of glass. The contact time of the
palladium chloride on the surface of the sensitised glass is approximately 15
seconds.
The sheets of glass thus activated then pass to a rinsing station where
demineralised water is sprayed, and then to the silvering station where a
traditional
5 silvering solution is sprayed, comprising a silver salt and a reducing
agent. The flow rate
and concentration of the silvering solution sprayed onto the glass are
controlled so as to
form, under conventional production conditions, a layer containing
approximately 800-850
mg/m2 of silver. It is observed that the mass of silver deposited is higher by
approximately
100 mg/m2 of silver, ie approximately 900-950 mg/m2 of silver.
10 The glass is then rinsed. Directly after the rinsing of the silver coating,
a
freshly formed acidified solution of tin chloride is sprayed onto the silvered
glass sheets
moving forward, as described in patent application GB 2252568.
The mirrors are then treated by spraying with a solution containing 0.1% by
volume of y-aminopropyl triethoxysilane (Silane A 1100 from Union Carbide).
After
rinsing and drying, the mirrors are covered with a Levis paint. This paint
comprises a first
coat of approximately 25 m of epoxy and a second coat of approximately 30 m
of alkyd
(Example 2).
In a variant (Example 3), the mirrors are covered not with a Levis paint but
with MerckensTM paint in two coats of alkyd with a total thickness of
approximately 50 m.
The two coats of paint were specifically an undercoating of MerckensTM SK 8055
and the
overcoating was MerckensTM SK 7925. These two coats contain lead. The mirrors
are
allowed to rest for 5 days to ensure complete curing of the paint layers.
Mirrors manufactured in this way are subjected to CASS accelerated ageing
and salt fog tests.
Two Control samples not in accordance with the invention are also subjected
to the same tests.
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11
These Control samples are manufactured from sheets of glass as
described above, except that the step consisting of activation with PdC12
followed by
rinsing is omitted. This step is replaced by a traditional activation step, by
spraying
with an ammoniacal solution of silver nitrate.
The results of the ageing tests on the mirrors of Examples 2 and 3 and
the Control samples 2 and 3 are as set out in the following TABLE II:
TABLE II
CASS test Salt fog test Density of white specks
average in m average in m average number/dm2
Example 2 140 30 0.7
Control 2 170 110 20 to 50
Example 3 100 < 6 1.0
Control 3 130 58 20 to 50
The "white speck" defect is observed after the two tests. This is a point
where the silver coating is coming away locally, accompanied by the formation
of
agglomerations of silver, which appear as a speck diffusing light. These
defects are
circular in shape, and the average size is between 40 m and 80 m. The
"density of
white specks" value given above is the average number of white specks per dm2
of
glass which are observed after the salt fog test and after the CASS test.
In fact, the number of white specks measured after each of the two tests
are generally fairly close to each other. This is probably because this "white
specks"
defect appears when the mirrors are brought in contact with water (in vapour
or liquid
phase). The CASS test and salt fog test consist of subjecting the mirror to
the action
of a mist of an aqueous solution: an aqueous solution of NaCI for the salt
fog, an
aqueous solution containing sodium chloride, copper (I) chloride and acetic
acid in the
CASS test. It is therefore not surprising if the number of white specks after
each of
these tests is relatively similar.
The treatment consisting of the activation of the glass with palladium
(II) chloride before silvering according to Examples 2 and 3 therefore reduces
the
CA 02487195 1995-05-09
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corrosion of the edges of the mirror, compared with a mirror on which the
glass has
been activated in a conventional manner with ammoniacal silver nitrate. In
addition,
these mirrors according to Examples 2 and 3 have a very appreciable decrease
in the
number of white specks after the CASS and salt fog tests. The adhesion of the
silver
on the glass is therefore greatly improved compared with mirrors on which the
glass
has been activated in a conventional manner, with silver nitrate.
Examples 4, 5 and 6
Mirrors are manufactured as described in Example 2, varying the
quantity of palladium chloride sprayed onto the glass. The starting solution
containing
6 g of PdC12/1, with a pH of approximately 1, is diluted to varying extents in
the spray
manifold as follows:
Example 4: 12 mg PdC12/1 to yield 2.2 mg of PdC12 per m2 of glass;
Example 5: about 30 mg PdC12/l to yield 5.6 mg of PdC12 per m2 of glass;
and
Example 6: 60 mg PdC12/1 to yield 11 mg of PdC12 per m2 of glass.
The results of the ageing tests on the mirrors according to these
Examples 4, 5 and 6 are as set out in the following TABLE III:
TABLE III
CASS test Salt fog test Density of white specks
average in m average in m average number/dm2
Example 4 181 60 18
Example 5 166 16 1
Example 6 163 16 1
The "white speck" defect is observed only after the CASS test. The
number of "white specks" after salt fog was not measured.
It is therefore observed that the activation of the glass by spraying with
2.2 mg of PdC12 per m2 of glass provides a mirror which resists ageing tests
relatively
well. However, the density of white specks after the CASS test diminishes
CA 02487195 1995-05-09
13
spectacularly if not 2.2 but 5.6 mg of PdC12 /m2 of glass is sprayed. The
spraying of
higher quantities of PdC12 (cf Example 6: 11 mg of PdC12/m2 of glass) does not
afford any significant improvement.
Examples 7 to 11 and Control 4
Mirrors are formed as described in Example 3, by varying the quantity
of palladium chloride which is sprayed onto the glass. Initially, the solution
contains 6
g PdC12/l, with a pH of 1. This solution is diluted as set out in the
following TABLE
IV:
TABLE IV
Solution Spraying level
EXAMPLE mg PdC12/1 mg PdC12/m2
Example 7 6 1.1
Example 8 12 2.2
Example 9 30 5.5
Example 10 60 11
Example 11 120 22
The mirrors which were formed in this manner were subjected to CASS
tests and salt fog tests. At the same time a control sample, not according to
the present
invention, was subjected to the same tests. The control sample was formed from
glass
sheets as described in Example 3, save that the activation step with PdC12 was
omitted. This step was replaced by a usual activation step by spraying with
ammoniacal silver nitrate.
The "white speck" observation is made after the CASS test and after the
Salt Fog Test. The results were as set out in TABLES Va and Vb.
TABLE Va
CASS test White specks
EXAMPLE average in m average / dm2
Control 4 124 47
Example 7 254 40
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14
Example 8 156 24
Example 9 101 3
Example 10 102 3
Example 11 129 2
TABLE Vb
Salt fog test White specks
EXAMPLE average in m average / dm2
Control 4 41 10
Example 7 87 41
Example 8 52 7
Example 9 13 1
Example 10 13 1
Example 11 5 1
From these results it is apparent that the activation of the glass by
spraying 1.1 or 2.2 mg PdCl2/m2 of glass results in a mirror which resists the
ageing
tests relatively well. Furthermore, the density of white specks after the CASS
test
becomes very low if the level of PdC12 is increased to 5.5 mg/m2 of glass.
Higher
levels of PdC12 (for example as used in Examples 10 and. 11) do not lead to a
significant further improvement.
Examples 12 to 15 and Control 5
Mirrors are formed as described in Example 3, with the following
variations:
Example 12: About 6 mg PdC12/m2 is sprayed onto glass, instead of 5.5 mg
PdC12/m2. The quantity of PdC12 is also increased to about 6
mg PdC12/m2 of glass in Examples 13 to 15.
Example 13: The sensitisation step with stannous chloride is omitted.
Example 14: The activation step with PdC12 is carried out before the
sensitisation step with stannous chloride.
Example 15: The step of protecting the silver coating by treatment with a
freshly formed acidified solution of stannous chloride was not
CA 02487195 2006-11-29
carried out. The silvered sheets of glass were directly covered with
MerckensTM paint.
Control 5: Mirrors not according to the invention were formed as described
in Example 12 except that the activation step with PdC12 followed by rinsing
is replaced by
5 a traditional activation step, by spraying an ammoniacal solution of silver
nitrate.
The mirrors fonned according to Examples 12 to 15 and Control 5 were
subjected to an accelerated CASS ageing test. Corrosion of the margins and the
density of
white specks after this test were as set out in the following TABLE VIa:
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16
TABLE VIa
CASS test White specks
EXAMPLE average in m average / dm2
Control 5 395 32
Example 12 165 2
Example 13 2700 *
Example 14 650 46
Example 15 3200 55
* The silver coating was so destroyed at the glass/silver interface that
the identification of white specks was not possible.
The mirrors formed according to Examples 12, 13, 14 and 15, and
Control 5 are subjected to the Salt Fog Test. The corrosion of the margins and
the
density of white specks after the Salt Fog Test were as set out in the
following TABLE
VIb:
TABLE VIb
Salt fog test White specks
EXAMPLE average in m average / dm2
Control 5 70 47
Example 12 41 2
Example 13 760 *
Example 14 93 46
Example 15 132 >125
* The silver coating was so destroyed at the glass/silver interface that
the identification of white specks was not possible.
It can be seen, by comparison of the results of Examples 12 and 13, that
it is important to sensitise the glass before activation with PdC12. The order
of the
sensitisation and activation steps is very important: when activation is
carried out
CA 02487195 1995-05-09
17
before sensitisation worse ageing results are achieved (see Example 14).
Example 15
shows that it is important to protect the silver coating before painting.
Examples 16 to 21
Mirrors are formed as described in Example 2, except that the
activation solution is poured over the glass instead of being sprayed. 500 ml
of
acidified solution is poured over 0.5 m2 of glass. The contact time of the
solution on
the surface of the sensitised glass is approximately 30 seconds. The following
activation solutions were used:
Example 16: an acidified aqueous solution containing 6 mg/1 PdCI2. The pH
was 3.8
Example 17: an acidified aqueous solution containing 10.0 mg/1 AuC13 (pH =
4.1).
Example 18: an acidified aqueous solution containing 10.2 mg/1 PtC12 (pH =
4.0).
Example 19: an acidified aqueous solution containing 6.7 mg/1 RuC13 (pH =
4.0).
Example 20: an acidified aqueous solution containing 8.1 mg/1 NiC12.6H20
(pH = 4.3).
Example 21: an acidified aqueous solution containing 3.6 mg/l CrC12 (pH =
4.2).
The mirrors formed in Examples 16 to 21 were subjected to accelerated
CASS ageing and salt fog tests. Corrosion of the edges and the density of
white
specks after these tests were as set out in the following TABLEs VIIa and
VIIb:
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18
TABLE VIIa
CASS test White specks
EXAMPLE average in m average / dm2
Control6# 477 0
16 (PdC12) 143 7
17 (AuCI3) 262 55
18 (Pt02) 204 *
19 (RuC13) 187 8
20 (NiC12.6H20) 298 34
21 (CrC12) 180 3
TABLE VIIb
Salt fog test White specks
EXAMPLE average in m average / dm2
Control6" 214 0
16 (PdC12) 53 5
17 (AuC13) 117 73
18 (PtC12) 107 *
19 (RuC13) 53 6
(NiC12.6H20) 82 46
20 21 (CrC12) 39 10
# Control 6 is a mirror similar to Control 1, that is a traditionally
formed silver mirror carrying a coating of copper to protect the silver layer.
* The surface of the silver coating showed a number of aligned faults
indicating separation of the silver.
It can be seen that all the salts used for the activation solutions used in
Examples 16 to 21 give improved results from the point of view of marginal
corrosion
following the CASS test compared with traditionally produced mirrors carrying
a
coating of copper. Best results were obtained with Pd (II), Cr (II), and Ru
(III).
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Examples 22 to 24
Example 3 was followed except that in Example 22 the two coats of paint
were specifically an undercoating of MerckensTM SK9085 (a lead-containing
paint in which
the lead is in the form of lead oxide) and the overcoating was MerckensTM
SK8950 (lead-
free). The results obtained were compared with a modification (Example 23) in
which the
undercoating was MerckensTM SK9135 (a lead-containing paint in which the lead
is present
in the form of oxide) and the overcoating was MerckensTM SK8950 (lead-free)
and in a
second modification (Example 24) in which the undercoating was MerckensTM
SK8055 (a
lead-containing paint in which the lead is present in the form of carbonate,
sulphate and
oxide) and the overcoating was MerckensTM SK8950. The results of the tests on
the
products obtained are set out in the following TABLE VIIIa and VIIIb:
TABLE VIIIa
CASS test White specks
EXAMPLE average in gm average / dm2
Example 22 164 1
Example 23 85 0
Example 24 118 2
TABLE VIIIb
Salt fog test White specks
EXAMPLE average in m average / dm2
Example 22 19 0.5
Example 23 22 0
Example 24 22 0.5
Examples 25 to 27
The procedure of Example 2 was followed except that the activating solution
was acidified with various different amounts of hydrochloric acid to give
dilute solutions
(i.e. solutions sprayed on the glass) with different pHs. The samples obtained
were tested
with the CASS test and the Salt fog test and were also analyzed to determine
the level of
palladium deposited on the substrate in the activation step. In
CA 02487195 1995-05-09
the following tables of results (TABLES IXa and IXb), the level of palladium
is
expressed as the atomic ratio to silicon. The presence of those palladium
atoms, and
their proportion in relation to the silicon atoms present on the glass may be
estimated
by an X-ray bombardment technique which causes the ejection of electrons from
a
5 surface stratum of the glass. From the X-ray beam energy and the energy of
the
emitted electrons, it is possible to calculate the binding energy of the
electrons so that
they may be apportioned between specific electron shells of different atomic
species.
The atomic ratios of palladium and silicon may then readily be calculated.
This
analysis is generally realised on the activated glass before silvering and
painting. The
10 presence of palladium (or other atom according to the type of activation
solution used)
may also be analyzed by Secondary Ion Mass Spectroscopy.
TABLE IXa
ExampleActivator Pd/Si CASS test White specks
(pH 0.5) ratio average in gm average / dm2
15 Example 25 PdC12 (3.5) 0.12 71 0
Example 26 PdC12 (4.5) 0.16 65 1
Example 27 PdC12 (2.5) 0.03 76 2
TABLE IXb
ExampleActivator Pd/Si Salt fog test White Specks
20 (pH 0.5) ratio average in m average / dm2
Example 25 PdC12 (3.5) 0.12 15 0.5
Example 26 PdC12 (4.5) 0.16 18 0
Example 27 PdC12 (2.5) 0.03 76 9
These results show that if the pH is low, the level of palladium fixed on
the substrate is low and the results are less good. If the pH is higher than
5, a
precipitate of palladium hydroxide may result in blockages of the apparatus.
Examples 28 to 43
Using the procedure as described in connection with Examples 16 to
21, a number of activating solutions were used as follows.
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21
Exam lp e 28: acidified aqueous solution containing 10.7 mg/1 AuC13 (pH =
4.6).
Example 29: acidified aqueous solution containing 5.9 mg/1 PtC12 (pH = 3.5).
Example 30: acidified aqueous solution containing 8.2 mg/1 NiC12.6H20 (pH
= 4.6).
Example 31: acidified aqueous solution containing 5.9 mg/1 PdC12 (pH =
4.6).
Example 32: acidified aqueous solution containing 5.9 mg/1 PdC12 (pH =
4.1).
Example 33: acidified aqueous solution containing 8.3 mg/1 InC13 (pH = 4.6).
Example 34: acidified aqueous solution containing 8.3 mg/1 InC13 (pH = 4.1).
Example 35: acidified aqueous solution containing 4.4 mg/1 ZnC12 (pH =
4.6).
Example 36: acidified aqueous solution containing 4.4 mg/1 ZnCl2 (pH =
4.1).
Example 37: acidified aqueous solution containing 54.6 mg/1 BiCl3 (pH =
4.6). Note that BiC13 is only slightly soluble.
Example 38: acidified aqueous solution containing 54.6 mg/1 BiC13 (pH =
3.5).
Example 39: acidified aqueous solution containing 7.8 mg/1 RhC13.3H20
(pH = 4.6).
Example 40: acidified aqueous solution containing 7.8 mg/1 RhC13.3H20
(pH = 4.1).
Example 41: acidified aqueous solution containing 5.4 mg/1 VC13 (pH = 4.6).
Example 42: acidified aqueous solution containing 5.4 mg/i VC13 (pH = 4.1).
Example 43: acidified aqueous solution containing 5.8 mg/1 TiC13 (pH =
4.5).
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The mirrors were subjected to the CASS test. Some metal/silicon ratios
were estimated on activated glass. The results were as follows.
TABLE X
CASS test White specks Ratio
Example No average in m average/dm2 Me/Si
28(AuCI3 pH = 4.6) 219 1 0.03
29(PtC12 pH = 3.5) 131 20 0.007
30(NiC12.6H20 pH = 4.6) 144 19 0.028
31(PdC12 pH = 4.6) 161 1.5 0.032
32(PdC12 pH = 4.1) 106 0 0.076
33(InCl3 pH = 4.6) 127 3
34(InC13 pH = 4.1) 123 10 0.045
35(ZnC12 pH = 4.6) 141 9
36(ZnCI2 pH = 4.1) 126 11 0.006
37(BiCl3 pH = 4.6) 155 11
38(BiC13 pH = 3.5) 180 13
39(RhCI3.3H20 pH = 4.6) 149 29
40(RhC13.31120 pH = 4.1) 167 8.5 0.016
41(VC13 pH = 4.6) 164 2
42(VC13 pH = 4.1) 179 4.5 0.014
43(TiC13 pH = 4.5) 256 33.5 0.012
Best results are obtained with the use of AuC13, PdC12, InC13, VC13:
the mirrors exhibit an average number of white specks of less than 5 per dm2.
With
ZnC12 or RhC13.3H20, the mirrors exhibit an average number of white specks
comprised between 5 and 10 per dm2.
