CA1050838A - Organic coating of metallic substrates - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Adherent organic coatings are applied under vacuum to a metallic substrate which has been coated with vacuum vapor deposited layers of zinc and a barrier material of a metal, alloy, or inorganic compound. The organic coatings may subsequently be polymerized in place by subjecting the coatings to radiation. The product of the process has superior corrosion resistance.

Description

33~3 T~e Invcrll:lon gencr~lly pertalns to a metllod oi' produclnc~ rcnt or~nlc coatlllgs on a inct~llllc sub~ltra~e uncler vacuum nnd tlle product thcreof. 'llle method comprlc,es applyln~ at leas~ two intermediat:e coatlngs on a metcllllc substrate pr:Lor to applicatlon of an organic layer. Th:ls procedure reslllts in an adherent organlc coating and an enh~neement of the corrosion resistance of the coated sub strate. ~11 coatings, except an organlc topcoat, are applied under pressures which are less tllan atmospheric pressure. In the method, a wire brushed substrate is first coated with a layer of vacuum vapor deposited zinc and then with at least one layer o~ a vacuum vapor deposited metal, ' alloy, inorganic compound or mixture thereof. Finally, a ~ -low volatility polymerizable organic primer coating is `
applied to the coated substrate while still under the influence of reduced pressure of vacuum. The organic coat~
ing is polymerized by radiation while still under the `~
influence of vacuum.
In order to enhance corrosion resistance for exterior applications, steel strip is commonly coated with ;`
an organic compound such as paint, plastic or lacquer.
Organic eoatings commonly comprise a primer and a topcoat.
A major percentage of such strip products are composed of hot dip galvanized material. Hot dip galvanized strip has proven to be very difficult to process through coil coating ~ ~`
lines because oi poor macro- and micro-uniformity of the galvani7ed surface. Such surface non-uniformities often prevent the satisfactory performance of the necessary clean- ~ -ing and inorganic pretreatment steps prior to paint applica- ~ ~ .
tion. In addition, even when galvanized strip has been ;~
s~tisf~lctorlly processed through a coil coatin~ line, eorrosion reslstance of the coated product is often ' m ;~

105~83~ l - ~ unsatlsfactory os a result of vnrLa~le llo~ clip g~lvaniæed -; surrace condi~ions. In any even~, when con~r~ d wlth ;
the llot dipled produc~s, ~he product of the lnventioll i8 `~
charactc~rl~ed by sl-perlor organic ~dhesion and generally :~ ;
better but at lcast equLvalent corrosion reslstance in the primed and topcoated s~;ate.
- The principal basis or the above statement o~
; comparative corrosion resistance properties resLdes in the results of salt spray tests. The tests were conducted upon steel substrates coated with layers of zinc, a barrier layer, a primer, and a heat curab]e topcoat. Topcoat formu~
lations were generally a thermosetting acrylic. These samples were compared with hot dip galvani~ed samples, ~ ~ :
conventionally pretreated, primed with a heat c-lrable epoxy primer and topcoated with the same thermosetting acrylic.
The coated panels were evaluated with respect to corrosion, blistering associated with corrosion, and loss ;~
of adhesion at scribed marks due to underc`utting in a `
corrosive environment. Prior to testing two intersecting scribes were cut to the metal substrate on a portion of the , surface of each specimen with a carbide-tipped tool. Salt -:
Spray ~Fog) Testing (ASTM Designation B 117-64) is an ac~elerated corrosion testing procedure. Inspections were ~ made after 250, 500, and 1,000 hours unless prior failure `~ had developed.
~` The invention, up to and alternatively includlng .
topcoating, is conducted entirely under vacuum in a continu-~us manner. This processing sequence is advantageous because ;~ ;
~wo separate operations in existing technology, i.e., hot dip galvanizing and coil coating, are combined. Also, much ~greater control can be exerted over the process so that a uniform product with superior properties can be produced.

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The superlor propcrtles are n result of the fact tha~ organic pretreatlnCElt i5 nchlevcd slmply by the controlled evaporation of a thin barrier layer which aclheres wlth no dlfEic~llty to the previously deposited zlnc coating. Thus, it can be seen that there is no requirement of cleanlng and complex sur~ace reactions wlth an aqueous solution as i8 the case or conven-tional processlng of coa~ed steel strip. The application and subsequent adhesion of the organic coating to the barrler layer is achieved with minimal difficulty because the surface composition and topography have been controlled through the steps of the vacu~lm vapor deposition of zinc and the barrier material.
It has been recently disclosed in United States Patent No. 3,674,445 that metallic substrates coated with vacuum vapor deposited zinc can be coated with an adherent organic coa~ing. However, such product does not include a vacuum vapor deposited layer of a metal, alloy, or inorganic compound between the zinc and organic layers. This additional layer provi~es a barrier or chemical effect and results in improved corrosion resistance and equivalent organic adhesion characteristics when contrasted to the product of United States Patent No. 3,674~445.
As ~ay be apparent from the foregoing description of the prior art, the product of the invention is superior .. .. ~ ~
to hot dip galvanized material from the standpoint o~ organic .: .
adhesion and superior to vacuom vapor coated material, from the standpoint of corrosion resistance. Thus, the product ~ of the invention possesses a combination of the most `~ desirable features of the prior art.
; 30 It is an ob~ect of the invention to provide a process in which strongly adherent organic coatings can be applied to metallic substrates.

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~ ` It 1~ ~ further obJect to conduc~ ~ process which providcs strongly adhcrent or~anic coatlngs on metalllc substrates en~irely under tlle influence of vacuum.
- It i5 an additiollal ob~ect to provide s~rongly adherent organic coatlngs upon a metallic s~lbstrate whlch has been successively coated with vacuum vapor deposited æinc and a barrier material.
It is an object of ~he invention to produce a strongly corrosion resistant organic coated product which 10 . is superior to that produced by conventional hot dip galvan-iæing and coil coating as well as that produced by the direct application of an organic coating upon a vacuum vapor zinc coated metallic substrate. --;
These and other objects and advantages of the preisent invention will appear from the following description o f the invention.
Figure 1 is a schematic illustration of one form of apparatus suitable for use in producing a product having ~;
an organic primer coating. As depicted by this ~igure, a metallic coil, such as steel, is passed into an evacuated : , . .
- chambeir, subjected to wire brushing, two vacuum vapor layer ~ ~;
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deposi~ions, roll cooling, organic primer layer application, -radiation polymerization, and passed Erom the evacuated chamber.
Figure 2 is a schematic illustration of one form of apparatus suitable for use in producing a product having :
organic primer and organic topcoat layers. As depicted by ;~
~, the Figure, a metallic coil is processed with tke use of apparatus similar to that shown in Figure 1. However, the :.: . ,:
. 30 cured primer coated substrate is also coated with an org~anic topcoat layer and cured by radiatlon prior to passing from ~:
~ the evacuated chamber. ~ ~

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Flgure 3 is a scllemntlc illus~ration o~ ano~her form of npparatus su:Ltable for usr. ln producing a product havln~ orgnnic prlmer and organlc topcoat layers. As shown in thls F~gure, a met~lllc coil i8 processed with use of thc same general apparatus that is shown in Figure 2. The dlfference is that tlle topcoat layer is applled and cured under atmospheric pressure upon exiting from the evacuated chamber.
Figure 4 is an illustration of a metallic sub~
strate, SUCll as steel, upon which four layers have been applied. The first two layers are vacuum vapor deposited zinc and a barrier material. The final two layers are an organic primer and organic topcoat.
Figure 5 is an illustration oE a metallic sub-strate, such as steel, upon which five layers have been applied. The fira~ layer is vacuum vapor deposited zinc and the second and third layers are vacuum deposited barrier material. The final two layers are an organic primer and ~-. organic topcoat.
The method of the present invention generally com-prises the steps of passing a metallic substrate into an ' evacuated chamber, wire brushing the substrate, vacuum vapor depositing a layer of zinc onto the brushed substrate surface, vacuum vapor depositing at least one barrier material layer upon the previously deposited zlnc layer, and applying a low volatility, polymerizable organic primer coating onto the barrier layer, and passing the coated substrate from the evacuated chamber. The organic coating is polymerized by the action of radiatlon prior to ex~t from the chamber. An .~ .
organic topcoat layer may be subsequently applied over the primer layer. The topcoat may be applied and polymerlzed ln the evacuated chamber or thereafter under atmospheric pressure.
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Ttle produc~ ~roduce~ by the nbove method comprises a metallic substrate whlch contalns intermedlate vacuum vapor deposlted layers of ~inc and at least one barrler matcrial an~ a layer or layers of an organic compound. The barrier material may be elther a metal, alloy, inorganlc compound, or mlxture tllereof.
A suitable apparatus for applying an organic primer layer is sche~atically illustrated in Figure 1. Metallic strip 1 is passed through evacuated chamber 2 from uncoiling reel 4 and collected on coiling reel S. Strip entry is accomplished by passage through seal rolls 6 and 7. Reel 5 is driven so as to continually move strip 1 at a desired rate of travel. Chamber 2 is evacuated through outlet 3 by means of suitable vacuum pumps, not shown. A suitable chamber vacuum level ranges on the order oE about 5 x 10 5 to about 5 x 10 4 mm Hg. Upon entry into the chamber, the strip is -~ mechanically abraded by rotary wire brush 10 in order to abrasively clean the strip and to place it in proper condi-tion for subsequent vacuum vapor zinc deposition. A pool of molten zinc is maintained in crucible 11 and heated tb vapoT-~ ization by appropriate means which may include an electron i beam gun or resistance heater. A pool of molten barrier layer material is maintained in crucible 12 for vacuum vapor deposition upon the prevlously deposited zinc layer. `~
~; Inorganic materials such as oxides may be conveniently ; vaporized through the electron beam bombardment of pre-sintered oxide discs. Crucible 12 may also be heated by electron beam bombardment or a resistance heater. Roll 13 -~
is arranged in such a manner that suitable roll cooling of ~ ~;
-~ 30 the coated strip may be effected through contact with thè
roll surface. Although one roll is shown, it should be under-stood that one or more roll surfaces may be utilized. Roll . ' ' ~
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coollng serves to permlt nd~us~mcrl~ of thc str:lp tem~erature to an extc~t that is compntible wL~`h appllcatlon of an organic coati~g. Appllcator roll 14 iB u~llized to roller coat a layer oE an organlc compo~lnd OI~O the barrier layer.
Roll 15 changes the `pass line direction al~d fl~ally, the organlc coated strlp is cured by radlatlon emitted by electron beam gun 16 before exiting from chamber 2 through seal rolls 8 and 9. It ls to be understood that one or both sldes of the strip may be coated through rearrangement of or 10 . additions to the above apparatus.
The system illustrated in Figure 2 indicates suitable apparatus for applying and polymerizing prlmer and topcoat organic layers within evacuated chamber 2, The primer is applied in the same fashion as in Figure 1. The organic topcoat is applled by reverse rollcoat applicator 17 and the dlrection o~ travel of strip 1 is changed ~y means of roll 18 in order to pass over topcoat electron beam curing gun 19. The gun is typically operated at low voltages (< 150KV). After curing or polymerizing the top~
coat, the coated strip is passed from cha~ber 2 through seal rolls 8 and 9.
Figure 3 illustrates a suitable apparatus syst-em ~::
for applying and polymerizing primer and topcoat organic layers that is an alternative to the system shown in Figure 2. The primer layer is applied and polymerized ln a similar manner, however, the topcoat layer is applied by ; reverse rollcoat applicator 20 at a location outside of ~-evacuated chzmber 2. After strip travel is changed in direction by roll 21, electron beam gun 22 is used to poly~
~0 merize the topcoat under atmospheric pressure The gun~is typlcally operated at high voltages (> 250KV~. ~
Upon entry into the evacuated system9 the metallic ~;

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1~;i0~38 substratc is mecha~ically abraded to the extent that an actlvnted surace condltion is ob~ained. S~lch surEace con-dition will lead ~o the creation of a vacuum vapor depositcd zinc layer havin~ superior adherence. ~ sultable technique for activating the surface of metallic substrates is shown in British Patent No. 1,222,198.
Followin~ surface preparation of the substrate, a layer of zinc is vacuum vapor deposited upon the substrate s~rface. This step may be accomplished by heating a liquid 10 zinc containing source in vacuum and condensing the zinc vapors generated by the source upon the moving substrate.
These steps, i.e., surface preparation and deposition, result in a zinc surface morphology that is generally smooth, clean, and free of adherence-offsetting second phases. The zinc surface has platelet texture which is very favorable for subsequent organic adhesion because of the creation of num-erous locking ~sites on a micro-scale.
Vacuum vapor deposited zinc layers of a thickness greater than about 0.1 mil develop a topographical texture of platelets which favor the subsequent excellent adhesion af organic compounds. In this regard, it has also been discovered that strip temperatures in excess of 250F. at ;
the completion of zinc vapor deposition also favor the ;~
development of a platelet texture which is sufficiently coarse ;
to promote adhesion.
We have discovered that the favorable effect of zinc surface =orphology can be retained if an intermediate layer of a barrier material is interposed between the zinc and organic layers. The barrier layer should be of a thick- -ness which is controlled to be a~ least sufficient to cover ~ the zinc layer but yet not of a thickness which will ; essentially change the favorable vacuum vapor deposited ~ -8-:

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133~1 zinr ~urface morpllolo~y. As may be appreci~ed by those skillcd in the art, the upper thlckness range is thus a function Or thc particular zinc texture and, hence, can be expected to vary somewhat according to the zince deposition practice followed in a given instance. Whlle not diminislling the favorable effect upon subsequent organic adhesion, the barrier layer functions to markedly improve the corrosion resistance of the final product.
The barrier layer materlal may comprise vapor deposited metal, alloy, inorganic compound or combination ~ ~
thereof. Exemplary materials include tin, aluminum, aiumin- ~ !
um base alloys, aluminum-tin alloys, silicon oxides, and similar oxides. Silicon oxide coatings perform well when applied as an individual coating or as a second coating in combination with an initial aluminum coating.
Silicon oxide coatings are applied by the evapor~
ation of SiO2. The SiO2 vapor becomes somewhat lean in oxygen during passage from the source to the substrate under the reduced pressure in the chamber. Thus, the deposited silicon oxide layer contains somewhat less than the stoichiometric amount of oxygen. Silicon oxide coatings of a thickness appreciably greater than 25 microinches are not -; desirable. This ls due to a substantial loss of organic adhesion which is because of brittleness which develops in - silicon oxide layers greater than 25 microinch thicknesses. ~ ~' . :
Following deposition of the barrier layer, the strip temperature may be adJusted through roll cooling. The purpose of this step is to adJust the strip temperature to ~ ~ a range which is compatible with the application of a given ~;

; ~ 30 organic formulation. It is to be understood that, in ~ome ~ ;
ins~ances, temperature ad~stment may be unnecessary because ` ~;
the strip will inherentl~ arrive at a suitable temperature ~ ~
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" wi~ho~lt the need for roll cooLIng. Tllus, this s~ep i~
regarded a~ optiollal ln the sense related above. Roll cool-ing may also nclvantageously be employed :Ln order to reduce the tlme or travel space needed for the strip to cool to thc desired coating temperat~lre. In general, however, the processing of strip in vacuum systems is often limited because of the difficulty in ex~racting heat from the strip in lower temperature ranges where radiation cooling is not effective. Cooling by heat conduction from the strip to a heat sink such as a roll is often a necessary expedient.
In the context of this invention, roll cooling !~ of a metallic strip which has been coated with zinc and a thin barrier layer may be rapidly cooled in a manner which ~ does not appreciab].y disturb the surface morphology of the j~ coated substrate and, as a consequence, does not interfere with the basic process and results described herein.
Roll cooling of the intermediately coated strip can be accomplished in an efficient manner. Por example~
~; a 27" diameter water-cooled turn~around roll (180 wrap) ,. 20 has been effective to reduce strip temperature from 450~F.
to 150F. in less than two seconds. When continuous roll contact is not made because of poor strip shape and lo~
strip tension, the majority of cooling will be due to r`adiation which is ineffective in this temperature range.
In such instances it becomes necessary to employ high strip ~; tension in order to ensure that strip having poor shape is ~; pulled flat over the cooling roll and that good roll con-eact is made over the full width of the strip. It is also preferred that the cooling roll be of as large diameter as ~`
practical and that ~he wrap angle be as large as posslble.
Both of the above features will maximize cooling due to increased contact times. The cooling roll should be smoothly , . .
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finlsll~d to maxlmlY.e con~ac~ Wi~ he COflting protrUSlonB
and sllould also have suEf:lcient wnter coollng ~rom the roll interlor to remove tl3e heat transferred to the roll body from the strip. Also, the roll should be located to make the lnit:Lal contact with the freshly deposited surface so that coating protrusions can be deformed to make good contact with the smooth rol]. surface.
The total amount of heat removed due to roll cooling can be monitored through measurement of water flow and inlet and outlet water temperatures. With a knowledge or strip speed, gauge, width, and initial strip temperature, - the strip temperature upon roll cooling can be calculated.
Such calculation thus permits control of final s~rip temp~
erature to be achieved through the use of controlled water inlet temperature to the cooling roll interior.
Following roll coolin~ o~ vacuum vapor deposition of the barrier layer, as the case may be, the substrate is coated with a low volatility organic material while still under the influence of vacuum. Application of the coating ~ `~
while still under vacuum ofers the advantage that there can be no contamination of the strip other than possible gas absorption. On the other hand, the application of organic materials in environments outside of the vacuum - chamber obviously increases the risk that harmful contamin-ation will occur. ;~
At this stage in the process, the preparation o the intermediate product has been carefully controlled in such a manner that a product having superior organic coat-- ing adhesion and corrosion properties may be obtained, ;~j 30 The preparation of the coated substrate for application of ::, . .
^; the organic material has been controlled from two stand-i points. Pirst of all, the coated surface morphology is oi .~ ~ ' ,, mJ~I

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the desired plaLelet topogr~lphy. Secondly, t~lnpcrature oE
thc strip is controlled to allow for ~low and leveling of the organic materlal on a macroscalc ncrosY the vapor deposlted sur~cc while ~he vacuu~ envlron~oent allows unim-peded flow between the plate]et texture on a mlcroscale.
This set of conditions ensure~ superlor organic adhe~ion and superior corrosion resistance when the coating layer is subsequently polymerized.
A preferred organic primer thickness range is from about 0.2 to 0.3 mils and thickness ranging from about 0.15 to 0.4 mils are generally suitable. As the barrier coated zinc plate]et peaks are generally on the order of 0.15 mils in height, this amount of organic thickness is usually necessary to satisfy the porosity of the coated substra~e and to cover the surface up to the peaks. Hence, minimal thickness should be approximately 0.2 mils in order to ensure that the substrate is adequately coated with the organic material so as to ensure the attainment of superior corrosion properties. On the other hand, corrosion resist-ance does not appreciably improve at prinler thicknesses of over 0.3 mils and there is little advantage in producing primer coatings above this thickness value. Primer coatings are generally applied in thickness of about 0.25 mils.
Roller coating is a satisfactory method for application of the organic coating. This general type of coating technique is conventionally utilized for coatlng moving substrates and need not be aescribed further~ Other methods such as extrusion, curtain or powder coating are also applicable for use in this invention.
After application, the or~anic layer is polymer- ;`
i~ed in place by exposure to radiation such as electron beam ~ -or ultraviole~ radiation. Polymerization is acco~pllshed m~p/
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~L~35~838 - ~hi]~ the co.lted E~rlp ls stJIl wi~l-in thc cvucuated cbamber ~ince lo~ beam voltages can be used to advnnta~c. Radlatlon curing or polymerlza~ion `o org~nlc coaLcd materlnls is known in the art. Illustrative patellts wl~ich discuss this tcchnlque include Unlted States ratent No. 3,547,683 and Brl~ish Patent Nos. 801,479 and 94~,192. As radlation polymeriza~ion is a conventlonal technlque, no urther discussion of this step ls believed to be necessary.
For a coil coated product to be of maximum utillty, it should contain both prlmer and topcoat organic layers.
Primer coats usually contain an inhibitlve pigment which chemically aids in suppressing underfilm corrosion and may be formulated to maximi~e adhesion to the substrate. As noted above, primers are generally applied at thicknesses on the order of 0.25 mils. At this thickness level and con- ;~
sidering the relatively low pigment contents utilized in ~;
primers, primers generally have poor hiding ability as well as poor resistance to the degrading effects of sunlight. ~ -Thus, in order to achieve reproducible color coatings which are not dependent upon substrate and primer coloration, a ;
topcoat is required. Topcoat thicknesses generally are greater than 0.7 mils and are, preferably, on the order of 1.0 mil in order to obtain complete hiding of the substrate color. Topcoats generally have higher pigment contents than primers and thus are superior with regard to hiding and resistance to the degrading effects of sunlight and moisture.
Topcoats should also be deformable and exhibit good adhesion ~ -to the primer coatlng. In order to obtain good formlng properties, the ma~ority of coil coating topcoats have thick-nesses no greater ~han about 1.0 mil.
A rather wide range of topcoat formulations are ~; suitable for the practice of the invention. Such formula . :

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tlon3 lnclud~ botil conventional and heat curabl~ topcoats such as ncrylics, sIliconI7.ed acryllc~, and fluorocarbons as well as electron beam c~rable acryllcs. At this Juncture, it i9 pointed out tl1at appl-lcation o~ the topcoat layer over the primer may be accomplished ln three ways. They are:
~l) application and curing undex vacuum, (2) application in line after strip exit from the vacuum chamber and curing with an atmosphere electron beam apparatus, and (3) appli-cation and curing by conventional means in a separate facility.
During the vacuum application and curing of top-coats, such as illustrated in Figure 2, the previous]y applied primer coating is subjected to very light electron ~-beam radiation prior to topcoat application. This procedure is followed so that the topcoat can be applied over a primer which is cured to the degree that mixing of the respective organic layers does not occur. The undercured primer, how-ever, provides for good intercoat adhesion. Because the ;
topcoat is applied in thicknesses greater than the primer and with a uniform smooth surface, reverse roll coating is a preferred application technique. Other methods such as curtain or extrusion coating are ~easible but are considered `
to be relatively more difficul~ to conduct under vacuum.
Curing of the topcoat may be accomplished by a low voltage - (< 150KV) electron beam. Complete curing of the primer and topcoat are simultaneously effected at t-his stage of the process. ;
In contrast with topcoat application and curing under vacuum, primer coating should be cured to a greater degree when in-line application of the topcoat after exit.
~from the evacuated chamber is used. This is because the primer requires a considerably greater degree of.curing to m~/
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~ enablc lt to be passed thro~l~il tlle seal rolls. Once the prime coated ma~erial exlt~ from th'e evucnated chamber, thc topcoa~ layer is applied by reverse roll coating and curing -is effectc(l by e]ectron bcam cur:lng at high voltages (>250KV~.
Such applicatloll and cur~ng techniqlles arc conventional. As in the case of the process embodlrnent in which topcoat appli-cation and curing was conducted under vacuum, full curlng of the primer and topcoat would be accomp].ished slmultaneously.
Although one could consider the possibility of placing a conventional heat curing topcoat system in-line with the ~ ~
vacuum system to produce a fully, coated product, process con- ~ ' trol would be quite difficult due to the necessity to ~' balance the slower line speed of the topcoat curing system with ; the faster line speed of the vacuum system. This factor is '`
not signiEicant when an electron beam topcoat curing system " ' ' is employed.
For oùt-of-line topcoat application and curing, the r;
vacuum primed coated substrate is fed into conventionally "
available solvent-containing heat-carable topcoat fac,illties.
No cleaning or phosphating facilities are necessary.
A suitable primer material, for use in the invention should be of a low volatility to be applied under vacuum environment and should also be capable of polymerization under radiation such as electron beam or ultraviolet radiation. "
5uch organic materials include acrylics, epoxies, and sili~
conized versions of these formulations. An acrylic ester is ',`
a preferred formulation.
As can be seen from the above discussion of the ~ ', process, there are a wide range of variables relati~g to the invention. The following speclfic conditions were found to be suitable for obtainlng a highly adherent and corrosion resistant primer coating of an acrylic ester.

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~ pOll sur~ac~ Rctlva~ion by wlre brushlng~ the vacuum vapor dcposl~ed ~inc layer should be greater than about 0.1 mll in thickn~ss in orcler to de,velop a surface morphology of platele~s avorable for organic adhesion. In connection with this requirement, strlp temperatures about '~
250F. at the completlon of zinc vapor deposition also favor the devclopment of platelet texture which is sufficiently coarse to promote adhesion.
Coating performance is enhanced by the vacuum vapor deposition of a thin alumlnum layer directly upon the previously deposited ~inc layer. The aluminum layer should be on the order of 10 to 20 micro-inches in thickness.
Although not quite as effective ln pramoting adhesion as the aluminum layer, a 15 to 25 microinch layer o~ silicon oxide deposited from a source of SiO2 performs satisfactorlly either as a substitute layer for aluminum or as an additional layer which is vapor deposited over the aluminum layer. ~ ~;
A strip temperature range which is preferred for roller coating of acrylic esters is between about 15QF. and 250F. This temperature range is suitable to ensure that organic deposition and levelling will properly take place ' ' prior to curing. Roll cooling of the strip is necessary to ;
obtain proper strip temperature in this instance. For the application of acrylic ester coatings in the thickness range of 0,15 to 0.4 mil it is suitable to heat the organic formu-lation to app~oximately 170F. in order to obtain the desired viscosity for flow-ou~ and levelling.
A specific example of the process as applied to a 12-inch wide strip of low carbon steel is described below.
The 0.018-inch thick strip was passed through an evacuated chamber at a speed of lOQ ft.Imin.
A dry, cleaned strip having a temperature of 130~F.

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was passed into an evl~cuated chamber. l'he strlp entry temperaturc was ~ue to hcat rc~aincd from tlle cleaning ba~h.
. The 8 trip was then wire bruslled with a bru~h drlven at 7 amps by a no load 500 RPM, 440-volt, three-phase motor. Brush rotntion was counter-curren~ wlth thè
; ~, direction of strip travel. Strip temperature lncreased ~rom ,;
130F. to 220F. due to brush ~rict:lon.
A 0.6 mil layer of zinc was vacuum vapor deposited upon the brushed strip. A graphite resistance heated source ;~
was employed. This procedure resulted in a strip tempera-ture increase to b30F.
An 0.020 mil (20 microns) layer of aluminum was `
vacuum vapor deposited upon the zinc layer. An electron beam heated source was utilized. This procedure resul.ted in a temperature increase to 450F.
The coated strip was then passed around a 27-inch diameter water cooled ro~l at a wrap angle of 180F. Contact time was 2 seconds. This resulted in a reduction of strip temperat~re ~rom 450F. to 150F.
A 0.25 mil coating of an acrylic ester was applied to the coated strip by direct roll coating at about 150F.
Finally, the coated strip was cured or polymerized ~ith the use oE radiation emitted from a 150 KV, 10 ma electron beam generator which scanned the strip at 100 cycles/
second.
This application is a division of copending Canadian application Serial No. 208,961, filed September 11, 1974. :~
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Claims (2)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composite article of manufacture, comprising:
a. a steel substrate;
b. a vacuum vapor deposited layer of zinc of a thick-ness of at least about 0.1 mil;
c. a vacuum vapor deposited layer of aluminum of a thickness of from about 10 to 20 microinches; and d. an at least partially polymerized acrylic ester coating of a thickness of about 0.2 to 0.3 mils.

2. A composite article of manufacture, comprising:
a. a steel substrate;
b. a vacuum vapor deposited layer of zinc of a thick-ness of at least about 0.1 mil;
c. a vacuum vapor deposited layer of aluminum of a thickness of from about 10 to 20 microinches;
d. a polymerized acrylic ester coating of a thickness of about 0.2 to 0.3 mils; and e. a polymerized layer of an organic compound selected from the group consisting of acrylics, polyesters, siliconized versions of acrylics and polyesters, and mixtures thereof of a thickness of at least about 0.7 mils.