Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to the field of metal
substrates coating More particularly, one obJect of this
invention is a process for coating metal substrates with
plastics so as to provide multilayer metal-plastics pro-
ducts. This invention also encompasses the products obtai-
ned by such a process.
For decoration or anti-corrosion protection pur-
poses, the manufacturers were conduced to provide multi-
layer metalplastics composite products or complexes. The
method used therefor consisted in gluing, a plastics sheet
onto a metal strip continuously fed from a coil, or in
hot-rolling, in a calender or a rolling mill, a metal sheet
previously treated by application thereto of an adhesion
primer.
The metalsforming the metal sheet were usually
steel or galvanized steel, or else aluminium or an alu-
minium-based alloy.
The plastics used were principally polyvinyl
chloride and~ to a lesser extend, polyethylene
The present invention relates to the application
onto a metal substrate of one or more plastics layer, the
external layer being always o~ the polyamidic type.
Theob~ect of the invention is, on the one hand,
to provide a process more economical than the known proces-
ses starting from previously made films and, on the other
hand, to prov~e a process applicable to polyamides.
As a matter of fact, said polyamides are par-
ticularly valuable because of their resistances to tempe-
rature, abrasion and chemical agents, which are better
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~ i'7~5~1~
than those of the plastics used heretofore, such as PVC,
and afford full protection against corrosion to the basic
metal substrate.
One obJect of this invention is a process for
coating a metal substrate by application thereto of one
primer layer and at least one plastics layer, characte-
rized in that the primerlayer comprises a resin selected
from epoxy-phenolic resins, mixtures of epoxy resins and
phenolic resins and combinations of said resins and resin
mixtures, in that the last plastics layer is a layer of
polyamide applied under the form of a suspension, in an
organic liquid phase, of a polyamide powder having a
particle size lower than 40 ~, and in that the whole is
heated until fusion o~ the external polyamide layer and
obtention of a continuous coating.
The advantageous ~eatures of the~invention are
derived form the combined selection of the primer of the
external plastlcs layer, which is applied under the form
of a polyamide suspension,
The invention includes the application to the
substrate of an organic tack primer, having a structure
liable to be modified by heat.
In fact, it is indispensable that the metal
substrate to be covered with a polyamide suspension be
previously coated with a primer because, among its other
functions, said primer affords binding between the metal
and the polyamide coating, due to its very good adhesive-
ness to both metals and polyamides.
55~3
The primer acts to reinforce the metal protec-
tion afforded by the polyamidic coating, first by preven-
ting the see page between the metal and the polyamide of
gases such as oxygen, carbon dioxide, steam, and further
by adding its own protective action to¦that of the polya-
mide.
The causes for corrosion are multiple and will
differ according to the intended use for the coated metal
articles; for example, the following may be mentioned,
among others :
- boiling water and detergents in the case of
washers for clothes or for plates,
- various chemical agents if the metal-sheets
are used to construct storage tanks for such products,
- weathering agents if the coated articles
are used outside~
The provision o~ the primer is still more in-
dispensable when the metal sheet to be coated was not sub-
~ected to a preliminary treatment.
According to the present invention, the primer
contains an epoxy resln in an amount ranging from 1 to 20%
of the total primer weight, in association with a phenolic
resin in an amount ranging form 1 to 20% of the total pri-
mer weight, or an epoxyphenolic resin in an amount ranging
from 1 % to 20% of the total primer weight, or a mixture
of the above resins in the same amounts by weight, as re-
lated tOthe primer, as those mentioned above.
-- 4 --
According to the invention, the anti-corrosion ac-
tion afforded by the primer may be promoted by adding to
the primer corrosion-inhibiting chemical compounds such
as zinc phosphate, zinc tetrahydroxychromate, or strontium
chromate, those salts being usable alone or in mixture.
In a preferred embodiment, the compositionof the
primer according to the invention includes one or more
compounds selected among the : -
- thermoplastic linear polyesters having a FP ran-
ging from lO0 to 150C, soluble in the solvent mixture
used, the content thereof preferably ranging from 10 to
25% of the total primer weight,
- blocked aliphatic or aromatic isocyanates which
are releasable from a temperature of 120C, the content
thereof ranging from 1 to 6% of the total primer weight,
- a corrosion-inhibiting mineral salt selected
from the group consisting of zinc phosphate, zinc tetrahy-
droxychromate, strontium chromate, used alone or in mixtu-
re~ the total content thereof ranging from O.S to 15% of
the primer weight.
The preparation of those primers may be readily
effected in usual mixing devices, such as those for paints,
it is recommended to use dispersing stirrers having impel-
lers with peripheral teeth particularly suited for prepa-
ring suspensions and pastes; it is advisable to previous-
ly mix the solid additives ~silica, mineral salts) or in-
soluble additives in a small porti~,of the solvents and
to add the resultant paste to remaining composition.
~ 1'7~ 5 ~ ~
These formulation techniques are within the range
of those skilled in the art and therefore require no fur-
ther description,
According to the invention, the second step of
the coating process consists in coating the primer with
a suspension of a fine polyamide-based thermoplastic
powder, in an organic solvent or a mixture of organic
solvents.
Once the metal substrate has been coated with the
primer, it is generally more advantageous to dry it be-
~ore applying the polyamide suspension. However, this
step is not compulsory as far as the final heating step
of the coating is liable to afford suitable bonding of
the primer to the substrate, The final heating step cau-
ses fusion o~ the polyamide particles and formation on
the substrate of a smooth continuous layer. This invol-
ves ln the polyamide layer a purely physical change occur-
ring under the effect o~ the temperature rise, e.g. in
a thermal treatment furnace. This ~eature is advantageous
and constitutes an important difference with the processes
of the prior art wherein the thermal treatment was inten-
ded to cause a chemical change comparable to cross-linking
within the final plastics layer,
On the contrary, according to the invention, the
final layer or ~inishinglayer is obtained by evaporating
the liquid phase having the polyamide particles suspended
therein and by fusing said particles to form the final
layer,
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According to an essential feature of the inven-
tion, the grain size of the polyamide powder corresponds
to a specific granulometry lying in a range lower than
about 40~ and preferably ranging from about 10 to 40 ~L,
more particularly from about 10 to 30 ~ .
The powders used in suspension are powders of
polyamides~ viz. resins of a hi~h molecular weight derived
from lactams or amino-acids wherein the hydrocarbon chain
has a number of carbon atoms ranging from 4 to 20 as~ for
example, caprolactam, oenantholactam, dodecalactam, unde-
canolac~amS dodecanolactam~ amino-undecanoic acid, 12-
amino-dodecanoic acid.
Thus the present invention provides in one aspect
the process for coating a metal substrate by application
thereto of one primer layer and at least one plastics layer,
characterized in that the primer layer comprises a resin
~elected from epoxy-phenolic resins, mixtures of epoxy resins
and phenolic resins and combinations of said resins
and resin mixtures, in that the last plastics layer is a layer
of polyamide applied in the form of a suspension, in an
organic liquid phase, of a polyamide powder having a particle
size lower than 40 ~, and in that the whole is heated until
fusion of the external polyamide layer and obtention of a
continuous coating, wherein, for the primer application, the
content of epoxy-phenolic resin or epoxy resin associated
with the phenolic resin ranges from 1 to 20% of the total
primer weight.
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ITI a preferred embodiment the process is charac-
terized in that the primer includes one or more compounds
selected from: ~
- thermoplastic linear polyesters with a FP ranging from
100 to 150C, soluble in the solvent mixture used, the content
thereof ranging from 10 to 25% of the total primer weight,
- blocked aliphatic or aromatic isocyanates releasable
from a temperature of 120C, the content thereof ranging from
1 to 6% of the total primer weight.
In another embodiment the present invention pro-
vides a process as above characterized in that the organic
liquid phase containing the polyamide powder in suspension
comprises a solvent or a mixture of solvents including one or
more of the materials from the group consisting of:
- the product sold by American Cyanamid Company under the
Trade Mark CYMBL 303, and which is a hexamethoxy methyl
melamine,
- the product sold by Bayer Company under the Trade Mark
SILICONE OL which is a surfactant,
- the product sold by Esso Company under the Trade Mark
SOLVBSSO 150 which is an aromatic solvent with 9 carbon atoms,
- the product sold by the Rohm and Haas Company under the
Trade Marks PARALOID B 48 and DM 54, said products facilitat-
ing the mixing and the adhesion of the dispersion on a
substrate.
In still another embodiment the invention provides
such a process wherein the organic liquid phase contains the
polyamide powder in suspension and includes a solvent or
r 9
A 7a -
11'7955~
or solvent mixture containing at least one c~mponent from the
group consisting of:
- hexamethoxy methyl melamine, polymethyl siloxane, an
aromatic hydrocarbon solvent, a thermoplastic acrylic ester,
and a thermoplastic acrylic resin.
The polyamlde may also be a condensation product
of a dicarboxylic acid with a diamine such as, for example,
the 6.6~ 6.9, 6 10, 6.12, 9.6 polyamides, which are conden-
sation products of hexamethylene diamine with adipic acid,
azelaic acid, sebacic acid, 1.12 dodecanedioic acid and
of nonamethyl~ne diamine with adipic acid
Of course, the powders may consist of copolyamidesresulting from a polymerization of the various above-
recited monomers.
Particularly suitable in practizing the process
are the powders of :
Polyamide 6, obtained by polymerization of
-caprolactam~
Polyamide 11, obtained by polycondensation of
ll-aminoundecanoic acid.
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7~SS~3
Polyamide 12, obtained by polycondensation o~ 12
aminododecanoic acid or of dodecano-lactam ,
or of copolyamides obtained by interpolymerization of two
or three of the above-mentioned monomers
Valuable copolyamides are derived from a polyconden-
sation of ~-caprolactam , of amino-undecanoic acid and/or
of lauryl lactam.
The higher the molecular weight of the polyamidic
component of the powders, the better their resistance to
ageing and their mechanical prsperties. However, their
fusion viscosity is all the more high, this being detri-
mental to their spreading onto the substrate upon fusion;
according to the present invention, the suspension may con-
tain ad~uvants adapted to promote spreading of the fused
polyamide in spite of a high fusion viscosity. Conversely,
the lower the molecular weight, the higher the ~luidity of
the coating in the ~used state to the pre~udice of its
mechanlcal properties and its resistance to ageing and to
weathering agents,
In general, the Inherent viscosity (as measured at
20C ~or a solution of 0.5g in 100 ml of metacresol) of
the polyamide powders, which reflects their molecular mass,
ranges between values of 0 75-1.40; the nature of the poly-
amide and final use intended for the coated substrate are
the determinant parameters ~or selecting the most favora-
ble value.
5~i~
The organic liquid phase, which contains suspended
polyamide powder, includes a solvent or mixture of sol-
vents selected from the group consisting of alcohols, es-
ters, cetones and aromatic hydrocarbons, as it is known
by man skilled in the art in view of choosing an appro-
priate solvent for the polyamides.
Specific examples of appropriate solvents are ben-
zyl alcohol, ethylglycol acetate, dibutylglycol acetate,
N-methylpyrrolldone and the mixtures available under the
trade name Solvesso 100 and 150.
The polyamide powder based suspension may contain
various additives providing the formation of the suspen-
sion, such as expanded silica (for example the compound
available under the trade name Aerosil) or additivesacting
as tensio_actives, such additives being known from the
man skilled in the art for preparing paints and lacquers.
The polyamide powders used according to the inven~
tion can be obtained by all sorts of techniques known to
those skilled in the art, e.g. by grinding of polyamide
pellets previously cooled with liquid nitrogen, or by hot
dissolution of such pellet~ in solvents and precipitation
by cooling, among others.
Methods involving anionic polymerizationof the mono-
mer or monomers in solvents, wherein the polymers are
separated under powder from the reaction medium wherein
they became insoluble, are recommended and, more particu-
larly, those described in FR patents 1,601,194, 1,601,195
and 1,602,751; in fact, the particles forming the powder
* Trade mark.
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~:~795~i8
are small spheres especially suitable to provide satis-
factory suspensions and smooth coatings after fusion onto
the metal sheet,
Such powders may be in their naturally occurring
state and therefore provide colorless coatings, or be
pigmented, with possible introductionof the pigment or
pigments in the suspension through a blending resin spe-
cifically selected for this purpose, this representing
a further advantage of the invention.
According to the invention, it is possible to coat
the most diversified metal substrates, in particular
sheets or plates of steel, galvanized steel, aluminium or
aluminium-based alloys, It is to be noted that coating
may be effected either on one or on both sides of such a
metal-sheet, The process may be applied most advantageous-
ly to metal strips of a thickness ranging from about 0,2
mm to about 2 mm, In this case, the thickness of the ex-
ternal finishing polyamidic layer ranges ~rom about 20~to
about 50 ~,
The process according to the invention will now be
illustrated by no way of limitation by the following exam-
ples and description, with reference to the appended dra-
wings wherein.
Fig, l diagrammatically shows a process for conti-
nUouscoating of a metal strip,
Fig, 2 shows an alternate embodiment of the pri-
mer application step,
Referring to figure l, there may be seen at le~t
side thereoff the strip uncoiling station, This station
includes a coil l and an accumulator la adapted to take
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~17955~3
up the variations in length and tension caused by coil-
replacements. Numeral 2 generally designates a surface-
treatment step which in fact includes several stations,
viz.
- rough pickling
- brushing
- fine pickling
- hot rinsing
- phosphatizing
- chromizing
- cold rinsing
- chromic rinsing.
Said stations consist of separate vats through which the
strip is fed.
The strip then enters a primer-application station
3, As schematically illustrated in figure 1, station 3
comprises a two-high mill operating according to the
known so-called "reverse roll" technique. An alternative
embodiment of this primary application step is shown in
figure 2. This figure diagrammatically shows a coating
step by the so-called rotogravure technique. In this case,
the solution to be applied is contained in a vat 10 and de-
posited onto the strip by a two-high mill 11, 12.
Of course, for coating the two sides of the strip,
another coating station of the same type is to be provi-
ded.
Usually, a final thickness of 6-7 microns is deemed
sufficient for the primer.
~L~ 7~5~3
Referring again to figure 1, numeral 4 generally
designates a furnace for drying and cross-linking the
primer deposited at station 3. The temperature to be
reached in furnace 4 will of course depend upon the natu-
re of the primer. In practice, the temperature reached by
the strip metal (called peak metal temperature or PMT) is
used as a measure of the real primer curing temperature.
The plant shown in figure 1 for practizing the
process of the invention further includes a station 5
for pulsed air cooling of the primer-coated strip. Station
6 servesto apply on the strip already coated with the pri-
mer a layer of a dispersion of a fine polyamidic powder
according to the invention. As illustrated, station 6 com-
prises a two-high mill operating according to the roto-
gravure principle (similar to figure 2). A drying and ge-
lifying furnace 7 is used to remove the solvents compri-
sing the organic phase and to fuse the fine powder parti-
cles into a continuous layer, When issuing from furnace
7, the strip goes through a cooling station 8, then to a
coiler 9 preceded by its accumulator 9a.
The temperature conditions in furnace 7 will depend
upon the nature of the polyamides used.
It is admitted that the area lying between the cur-
ve of the temperatures recorded on the metal strip bet-
ween the furnace inlet and outlet, the abscissae axis
(indifferentlygraduated in terms of spa ce or time) and the
two verticals corresponding to the inlet and the outlet
of the furnace represents the energy used to effect the
~7~5~3
steps of solvent removal~ and polyamidic powder fusion.
Experience showed that according to the intended
use, to the sought properties and to their degree of in-
tenseness, the above PMT's could be varied in the range
from 230 to 260.C. These directions to those skilled in
the art are merely illustrative and it will be unter-
stoodthat departure therefrom may be comtemplated within
the scope of the invention
It will thus be appreciated that the process of
the invention makes it possible to treat metal substrates
under coil form, by means of a continuous production li-
ne of the kind shown in figure 1.
In the ~ollowing, merely illustrative examples, the-
re were used various formulations for the primer and the
finishing polyamidic layer(s). In these examples, all
parts are given by weight, unless otherwise, stated, and
the various components are recited in the order wherein
they operate and are introduced within the composition.
FORMULA I (primer) % by weight
Dynapol L 441 17
tthermoplastic linear polyester
o~ Dynamit Nobel)
Ethylglycol acetate 10.5
*
Solvesso 100 10.5
( a solvent of Esso)
Aerosil 300 0.3
tmicronized dispersant silica of
the firm Degussa)
* Trade Mark.
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.~
~1'7~55~3
FORMULA I (primer) % bY weight
Zinc phosphate 7.5
Titanium dioxide 11
Phenolic Resin PR 897 6
(unplastified phenolic condensate
of the firm Hoechst)
Epikote 1001 1.5
(polycondensate of epichlorhy-
drine and diphenylolpropane of
the firm Shell)
Solution of lOX phosphoric acid
in butanol
Ethyl glycol acetate 34.7
100
This primer is characterized by being wholly free
o~ yellowing and having good flexibility due to the pre-
sence of polyester; however, its boiling water strength
is poor.
FORMULA II (Primer) X by weicht
Phenoxy PK HH 12
~polycondensate of epochlorhy-
drine and diphenylolpropane
manufactured by Union Carbide)
Zinc tetrahydroxychromate 10
Aerosil 300 0~5
Ethyl glycol 25
Toluene 29,S
Phenolic resin PR 897 2
Desmodur L 2248 2
(blocked aliphatic isocyanate of
Bayer)
* Trade Mark.
14 -
13l7~55~
FORMULA II (primer) X by weight
Ethylglycol acetate 19
This primer is also characterized by being free of
yellowing :
FORMULA III lprimer) % by weight
Ethyl glycol acetate 8
Phenolic resin PR 897 12
Dimethyl formamide 6.5
Titanium dioxide 3B
Strontium chromate 3.8
Ethylglycol acetate 3.1
Solvesso 100 3.1
(solvent of the firm ESSO~
Epikote 1007 4.3
(polycondensate of epichlorhydrine
and diphenylolpropane o~ the firm Shell)
Ethylglycol acetate 4.3
Solution of 10% phosphoric acid in
butanol 2.5
Phenoxy resine PK HH 2.4
(polycondensate of epichlorhydrine and
diphenylolpropane of a high molecular
weight manufactured by Union Carbide)
Ethylglycol acetate 12
100
This primer is characterized by a good boiling water
strength. It is thus clear that the primer formulation
may be adapted to the final use of the coated metal-sheet.
* Trade Mark.
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~17955~3
Thus, the formulas disclosed in examples I and II
will be recommended for their non-yellowing properties.
Yellowing is undesirable in some applications, since the
sub-layer may sometimes be visible by transparent effect
through the polyamide coating On the other hand, their
boiling water strength is not very good.
The contrary is true in the case of the primer of
Example III which is yellow but has very good resistance
to hot water, at 750C!
FORMULA IV (polyamide)
Polyamide dispersion
Polyamide powder with 25% o~ TiO2
~iller 40%
Benzyl alcohol 60X
lOOX
In this same type o~ ~ormula, the benzyl alcohol may be
replaced by the ~ollowing solvents :
- isophorone
~ éthylglycol acetate
- dibutylglycol acetate
The polyamide powder may, according to the contemplated
applications, be present in the dispersion at a concentra-
tion ranging ~rom 20X to 50%.
FOflMULA V (polyamide)
The components being added, as previously stated ~or
the primer, in the order indicated below, the ~ormula is
as ~ollows :
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Component Amount % Possible Nature
range %
benzyl alcohol 20
Paraloid
DM54(1) 2 0-6 thermoplastic
acrylic resin
polyamide powder
with 25% TiO2
filler 38 25-45
Paraloid B 48(2)1.5 0-6 thermoplastic
acrylic ester
benzyl alcohol 38.5
100 parts
~1) promotes wetting and adherence
~2) promotes adherence to the primer
. supplier : Rohm and Haas
FORMULA Vl (Polyamide)
Component Amount % Possible ~ture
range %
N-methylpyrrolldo-
ne 40
Epikote 1001(1) 3 0-8 polycondensate of
eplchlorhydrine
and diphenylpro-
pane
Silicone OL (2) 0.1 polymethylsilo-
Disperbyk (3) 0,3 barium salt of a
polycarboxylic
acid
polyamide powder with
25% of TiO2 filler 40 25-45
* Trade Mark.
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~7~?SS~3
Component Amount X Possible Nature
range %
Cymel 303(4) 0.3 0-1 hexamethoxyme-
thylmelamine
N-methyl pyrro- 16.3
lidone
100
(l) product of SHELL
(2) product of UAYER - a surfactant promoting spreading
(3) product of MALLINCKRODT - a dispersion-stabilizing
agent
(4) product of AMERICAN CYANAMID - an agent for cross-
linking the Epikote resin.
The latter also serves as a blending resin to
carry the various additives or further fillers for co-
lor-ad~ustment of the finishing layer.
EXAMPLE 1
A continuous strip of mild steel having a~thickness
o~ 0,7 mm, previously sub~ected to a preliminary surface
treatment, for the twofold purpose o~ anti-corrosion
protection and adhesion promotion, with the commercial
product designated BONDERITE 914 o~ the firm PARKER, i~
fed to the primer application station 3 at a velocity
o~ about 30 m/mn,
It is provided therein with a layer of primer accor-
ding to abOve formula III having a 7-microns thickness in
the dry state, resides in furnace 4 for a time period of
about 30-60 seconds and reaches a Peak Metal Temperature
(PMT) of 241 C. It goes through cooler 5 before reaching
* Trade Mark.
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li7~35S~3
the inlet of coating station 6 where it receives a
layer of polyamide 11 according to formula IV ha~ing
a 30-micro~ thickness in the dry state. In furnace 7,
the strip reaches a PMT of 230C before cooled and
colled.
The resulting metalloplastic multilayer complex
is capable of successfully undergoing, without suffering
stripping of the plastic coating, the test oflOOO_hours
immersion in boiling water on samples provided with
crossed slits in the coating.
EXAMPLE 2
A continuous aluminium strip having a 0.5 mm thick-
ness, previously sub~ected to a preliminary surface treat-
ment wlth the commercial product designated COLARDIN
6204 of the firm C.F.P.I., is provided at priming station
3 with a layer of primer according to formula II, having
a thickness of 4-5 microns ln the dry state, and reaches
in furnace 4 a PMT of 249C. Similarly, in the second fur-
nace 7, the strip also reaches a PMT of 249C after ap-
plication thereto of a coat of formula VI, wherein the
polyamide is a polyamide 12. The residual thickness cf
the polyamide coating after drying is of 25 microns.
* Trade Mark.
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