Note: Descriptions are shown in the official language in which they were submitted.
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Improvements in or relating to coatings
This inven-tion relates to -the coating of a backing or
substrate, for example an aluminium or aluminium alloy plain
bearing backing, with a layer or coating of polyarylene sulphide
resin. An object of the invention is to increase the bond of
the coating to the backing to produce a reliable bond for use
with engineering components as distinct from domestic holloware.
Polyarylene sulphides such as polyphenylene sulphide have high
temperature stability. The term polyarylene sulphide is further
meant not only to include homopolymers but also normally solid
arylene sulphide co-polymers and terpolymers.
- Polyphenylene sulphide is a crystalline material
prepared by the reaction of p-dichlorobenzene and sodium
sulphide in a polar solvent. The linear polymer so formed has
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a fair mechanical strength but it can be cured by heating in
air to be cross-linked and to be tough, ductile and extremely
insoluble with increased molecular weight and improved coating
characteristics. In this specification the term "polyphenylene
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sulphide" or the more generic term "polyarylene sulphide"
includes such polymers with varying degrees of cross-linking in
dependence on the heat treatment used.
A "base" is a term used in this specification to mean
any substan¢e capable of neutralizing acids.
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Polyphenylene sulphide as one form of polyarylene
sulphide is itse:Lf available in several forms - one form is the
raw polymer which has not been heat treated in air to improve
~- its characteristics. Other forms of polyphenylene sulphide can
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be heat treated in air to increase also the cross-linking. The
non-heat treated, or raw, forms of the polymer are unsuitable
for fluidised bed coatings because when -the powder melts the
coating runs and drips during curing. Similarly -the non-heat
treated polymers are unsuitable for providing a coating by
spreading the powder on the substrate because again the
viscosity is unsuitable and it tends to leave voids in the
coating or imperfections during heat processing. The grades
of polymer which have been heat treated either completel~ or
partially do not suffer from these defects when they are
-- applied as coatings and cured but tend to have worse bonding
characteristics than the untreated polymer. Nevertheless,
; the invention applies to improving the bond of polyarylene
sulphide to a backing whether the polymer has been so heat
treated or not.
Accordingly the invention provides a backing coated
with polyarylene sulphide resin incorporating a base which is
stable at least up to 300C.
In particular the present invention provides a plain
` 20 bearing comprising a backing of aluminium or aluminium alloy
and a coating on the backing and comprising a heat treated
-` polyarylene sulphide resin incorporating between 0.1 and 5.0
by weight of a strong base comprising a component of a metal
from Group I or ~roup II of the Periodic Table, said base being
stable at elevated temperatures up to at least 300C., for
establishing a bond between said backing and said coating.
Preferably the base is inorganic.
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According to another aspect the invention provides a
process for applying a coating of polyarylene sulphide polymer
to a backing of aluminium in which polymer is mixed with a com-
pound capable of producing a base cluring the process particularly
at the bond interface.
In particular, the present invention provides a method
of manufacturing a plain bearing in which a backing oE aluminium
or aluminium alloy has a bearing lining bonded to it by mixing
polyarylene sulphide resin with between 0.1 and 5.0~ by
weight of a strong base comprising a component of a metal from
Group I or Group II of the Periodic Table, applying the mixture
to the backing, and curing the polymer by heating at a temper-
ature of at least 300C for at least one hour.
Preferably the base is selected from a group comprising
hydroxides and carbonates of metals in Group I or II of the
Periodic Table, and preferably in a proportion of 1-10% by
- weight of the polyphenylene sulphide. The coating may be of
the order of .005-.015" thick. The base may be mixed with the~:
polymer or applied to the backing which is to be coated. 5% Of
- 20 calcium hydroxide is suitabla for example.
In one example of the pr~cess polyphenylene sulphide
is mixed intimately with a percentage of sodium carbonate
before coating is commenced. One method of achieving the
intimate mixing is by wetting the polyphenylene sulphide with
, an equal weight of water by stirring until a paste is formed.
The weighed quantity of sodium carbonate is dissolved in the
water before the mixing process. The optimum level of sodium
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carbonate has been found for one Eorm of polyphenylene sulphide
polymer to lie between l and 3 percent of the polyphenylene
sulphide when in the form of decahydrate crystals Na2(CO3 lOH2O).
In a further embodiment lithium hydroxide may be
used as an alternative to sodium carbonate.
of course, base producing compounds rather than bases
may be used, particularly if the use of those compounds or bases
leaves rather an inert residue in the coating after curing.
Sodium carbonate may, if not incorporated within the limits
of 1-3%, cause in the finished coating bubbling due to volatile
evolution. Lithium hydroxide may not have this disadvantage.
It is probable that the cause of bad bonding is the
presence of the very easily hydrolysed sulphur-aluminium bond~
Such bonds could arise from acid attack of the oxidised
aluminium surface from such species as H2S or a molecule con-
taining SH pendant or end groups. Such attack would be inhibited
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by alkaline conditions.
Thus it is probable that other base additives such
as the hydroxides and carbonates of all Group I and II metals
20 will be effective in preventing poor bonding when used at the
correct concentration and providing that these additives remain
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~- as stable alkalis during the coating and curing process, that
is, stable up to at least 300C.
Calcium hydroxide is a good base for providing a
sound bond and good bearing properties at the surfaae of the
coating/ ev~n if it is mixed with dry resin powder. Certain
examples will now be described.
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Example 1
1 Kilogram of heat treated polyphenylene sulphide
powder was added to 1 kilogram of aqueous solution containing
20 grams of sodium carbonate decahydrate crystals. The mixture
was stirred for 30 minutes until all the polymer had been
wetted to an even thick paste.
The thick paste was allowed to dry in a warm current
of air. After drying the powder was sieved through a BS.~4
sieve and placed in a fluidising tank.
Blanks with dimensions of 4" x 2" x 0.064" of an
aluminium alloy NS4 were abraded by brushing and coated in
fluidised bed and finally heated at 300C for 1 hour to cure
the resin and bond the coating to the backing.
The blanks were sawn into ~" strips.
~ Immediately after production all the coatings were
- well bonded and could not be picked off with a knife blade.
After boiling for 2 hours in water coatings were still firmly
~ bonded to the backings.
-- Blanks stored in air untouched for 5 days after
production were again tested and the bond was still firm.
Similar blanks coated using resin without the base
had their coatings easily lifted off with a knife after the
boiling and storiny described above.
Exa~mple 2
10 Grams of calcium hydroxide were dry mixed with
1 Kg of heat treated polyphenylene sulphide in a high speed
mixer and the mixture placed in a fluidising tank. Treatment
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was otherwise as in Example 1, and a very effective bond was
achieved.
: Example 3
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slanks were coated in several tests using instead
of calcium hydroxide, magnesium oxide fine powder in proportions
between 0.1% and 5% of the polymer and a good bond was achieved.
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