Process for multiple stage autodeposition of organic coatings onto metals

A multiple stage autodeposition of organic polymer coating compositions deposited onto metal substrates wherein the coating composition's thickness does not increase by more than about 20.DELTA. compared to a single dry coating. The coated metal substrates formed by the process of the instant invention are corrosion resistant.

BACKGROUND OF THE INVENTION 
The present invention is directed generally to a process for the 
application of organic polymer coatings to metal substrates. More 
specifically, the present invention relates to a multiple stage 
autodeposition of organic polymer coatings on metal substrates wherein the 
coated substrate as good barrier properties, adhesion, hardness and 
corrosion resistance. 
The use of organic polymers as coatings on metal surfaces has been 
practiced on a commercial scale for a number of years. One such method is 
referred to as the electrocoat or electrodeposit process which is either 
an anodic or cathodic process whereby an electrical current of high 
potential is passed through the coating system causing the composition to 
coagulate on the surface of the article being coated. However, this 
process is disadvantageous in that it employs a high energy input of 
electricity. Further, it is difficult to coat the edges and corners of 
complex metal articles employing the electrodeposit process. The anodic 
electrodeposit process is further disadvantageous in that serious damage 
to the substrate can result from the oxidation reactions which occur when 
the substrate is the anode. 
The dip coating process is a process in which the metal substrate for 
coating is immersed in the coating bath for a specified time and baked to 
cure the coating. This process is superior to the electrodeposition 
process in its ability to coat corners, edges and complex shapes. The dip 
coating process, however, is disadvantageous in that the coating on the 
substrate is thin, thus the coated substrate usually has poor corrosion 
resistance. Furthermore, due to the thin coating, pinholes readily form 
providing a pathway to the metal substrate for oxygen, water and various 
corrosion promoting ions. 
The autodeposition method is a process in which an article is immersed in 
an acidic coating bath composed of organic film-forming material, water, 
hydrogen ion, oxidizing agent, and an anion and then the article is 
withdrawn and optionally rinsed in a solution containing chromium to 
improve the corrosion resistance of the article over the dip coating 
process. This type of method is disclosed in U.S. Pat. No. 3,585,084 to 
Steinbrecher et al. This method is disadvantageous in that there are 
environmental and pollution problems involved in disposing the hazardous 
chromium containing waste solutions, while corrosion resistance in the 
absence of the chromium rinse is poor. 
Multiple stage autodepositions have been disclosed for increasing the 
thickness of the coating but not for improving the corrosion resistance 
without increasing the thickness of the coating. Multiple stage 
autodepositions for increasing the thickness of the coatings is 
disadvantageous in that some organic coating materials have poor intercoat 
adhesion and thus do not readily adhere to themselves causing peeling and 
poor corrosion resistance. 
It is therefore an object of this invention to provide a process for the 
multiple stage autodeposition of corrosion resistant organic polymer 
coatings on metal substrates. 
It is another object of this invention to provide corrosion resistant 
organic polymer coatings, by a multiple stage autodeposition process, 
which are thin, hard, highly adherent and resistant to impact shock. 
It is another object of this invention to provide a process for the 
multiple stage autodeposition of corrosion resistant organic polymer 
coatings in the absence of a chromium rinse treatment. 
These and other objects, together with advantages over known methods shall 
become apparent from the specification that follows and are accomplished 
by the invention as hereinafter described and claimed. 
SUMMARY OF THE INVENTION 
The invention relates to the multiple stage autodeposition of organic 
polymer coating compositions deposited onto metal substrates to form 
coated metal substrates that are highly corrosion resistant. The 
autodeposition process for applying an organic polymer coating composition 
onto a metal surface comprises immersing the metal substrate in an organic 
coating composition; withdrawing the coated substrate from the organic 
coating composition bath; rinsing the coated substrate in water; 
optionally drying the coating formed thereon; and then repeating the 
immersing, rinsing and optionally drying steps about 2 to about 10 times, 
wherein the thickness of the coated substrate does not increase by more 
than about 20 percent compared to a dried single coating; and finally 
baking the coated substrate. 
The multiple stage autodeposition process of this invention can be used for 
industrial metal articles where corrosion protection properties are 
important such as in the automobile industry, appliance industry and 
machine parts industry and further where coating properties such as 
adhesion and hardness are important.

DETAILED DESCRIPTION OF THE INVENTION 
The invention described herein can be utilized to coat a variety of metal 
substrates. Typical metal substrates include but are not limited to cold 
rolled steel, phosphatized steel, tin free steel, zinc phosphate-treated 
steel, galvanized steel, iron, zinc, tin-plated steel, tin, copper, 
aluminum, brass and the like. The primary requirement of the substrate is 
that it produces sufficient ions to coagulate the particular coating 
composition on the metal substrate when it is immersed in the organic 
polymer coating composition bath. Autodeposition process is a mild etching 
of the metal substrate by the coating composition. In particular, the 
etching produces soluble, multi-valent metal ions, which cause a localized 
destabilzation of the coating bath in the immediate area of the metal 
substrate surface resulting in a continuous deposition of the coating 
composition onto the substrate. 
Various factors should be considered in determining whether the metal 
substrate should or should not be cleaned and the extent of cleaning, 
prior to contact with the autodeposition coating composition, including, 
for example the nature of foreign materials, if any, on the metal 
substrate and the desired quality of the coating. Foreign materials 
present on the surface of the metal substrate can lead to the formation of 
non-uniform coatings. Further, the adhesion and corrosion resistant 
properties of the coating may be adversely affected as a result of the 
presence of foreign materials on the metal substrate during the immersion 
steps. Generally, the cleaner the metal surface the better quality of 
coating can be obtained from the multiple stage autodeposition process. 
Types of cleaning agents and applications depend on the foreign material 
present and the metal substrate and are generally known and used in 
accordance with known technology. 
Compositions of coatings are generally well known in the art. Coating 
compositions which are effective in forming organic coatings are generally 
prepared in the form of emulsions, dispersions or solutions in an aqueous 
or organic medium. 
It is believed that the present invention will be used most widely in 
connection with coatings formed from organic polymers in particular, those 
polymers derived from ethylenically unsaturated compounds. Other organic 
polymers useful in the instant invention are those that can be obtained in 
a form suitable for compounding into an aqueous coating bath. 
Organic polymers which can be employed in the instant invention are, among 
others, those derived from ethylenically unsaturated compounds according 
to the following formula: 
EQU R.sub.1 R.sub.2 C=CR.sub.3 R.sub.4 
wherein R.sub.1, R.sub.2 R.sub.3 and R.sub.4 are each independently 
selected from: 
(1) hydrogen; 
(2) C.sub.1 --30 alkyl; 
(3) --(CH.sub.2).sub.p --CN wherein p is 0-3; 
(4) --(CH.sub.2).sub.q --OR.sub.5, wherein q is 0-30 and R.sub.5 is 
hydrogen, C.sub.1 --30 alkyl, C.sub.1 --30 cycloalkyl, C.sub.1 --30 aryl, 
C.sub.1 --30 alkylaryl or derivative thereof; and 
(5) --(CH.sub.2).sub.n --COOR.sub.6, wherein n is 0-5 and R.sub.6 is 
hydrogen, C.sub.1 --30 alkyl, C.sub.1 --30 cycloalkyl, C.sub.1 --30 aryl, 
C.sub.1 --30 alkylaryl or derivative thereof. 
Preferably, the olefinically unsaturated compounds comprise compounds 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently 
selected from: 
(1) hydrogen; 
(2) C.sub.1-10 alkyl; 
(3) --(CH.sub.2).sub.p --CN, wherein p is 0-2; and 
(4) --(CH.sub.2).sub.q --OR.sub.5, wherein q is 0-2 and R.sub.5 is 
hydrogen, methyl, ethyl, i-propyl, i-butyl, cyclohexyl, phenyl, or a 
derivative thereof; and 
(5) --(CH.sub.2).sub.n --COOR.sub.6 wherein n is 0-2 and R.sub.6 is 
hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, 
2-ethylhexyl, n-octyl, lauryl, stearyl, cyclohexyl, phenyl, hydroxymethyl, 
2-hydroxethyl, 2-ethoxyethyl or 2-(N,N-dimethylamino)-ethyl. 
Most preferably, the olefinically unsaturated compounds comprise compounds 
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently 
selected from hydrogen, methyl, ethyl, --(CH.sub.2).sub.p --CN, wherein p 
is 0-1, --(CH.sub.2).sub.n --COOR.sub.6 wherein n is 0-1, and mixtures 
thereof. 
Ethylenically unsaturated compounds include but are not limited to 
derivatives and homologues of acrylic acid, methacrylic acid, acrylic acid 
esters, methacrylic acid esters, amides, nitriles, vinyl esters, vinyl 
halides, vinylidene halides, vinyl aromatics, other ethylenically 
unsaturated compounds and the like. 
The acrylic acid esters include derivatives and homologues of 
methylacrylate, ethylacrylate, propylacrylate, n-butylacrylate, 
cyclohexylacrylate and the like. Most preferred are methylacrylate and 
ethylacrylate. 
The methacrylic acid esters include derivatives and homologues of methyl 
methacrylate, ethyl methacrylate, cyclohexyl methacrylate, phenyl 
methacrylate, n-butyl methacrylate and the like. The most preferred are 
methyl methacrylate, cyclohexyl methacrylate and phenyl methacrylate. 
The amides include derivatives and homologues of acrylamide, N-methyl 
acrylamide, N,N-dimethylacrylamide, N-butylacrylamide, N-octylacrylamide, 
methylenebis(acrylamide), N-methylolacrylamide, methacrylamide, 
N-methylmethacrylamide, N,N-dimethylmethacrylamide, diacetoneacrylamide 
and the like. Most preferred are N,N-dimethylacrylamide, N-butylacrylamide 
and N,N-dimethylmethacrylamide. 
The nitriles include derivatives and homologues of acrylonitrile, 
methacrylonitrile, tetracyanoethylene, itaconic acid nitrile, 
fumaronitrile and the like. Mosst preferred are acrylonitrile and 
methacrylonitrile. 
The vinyl esters include derivatives and homologues of vinyl acetate, vinyl 
stearate, vinyl butyrate, vinyl propionate and the like. Most preferred is 
vinyl acetate. 
The vinyl halides include derivatives and homologues of vinyl chloride, 
vinyl bromide, vinyl fluoride and the like. Most preferred is vinyl 
chloride. 
The vinylidene halides include derivatives and homologues of vinylidene 
chloride, vinylidene fluoride and the like. Most preferred are vinylidene 
chloride and vinylidene fluoride. 
The vinyl aromatics include derivatives and homologues of styrene, 
alpha-methylstyrene, p-methylstyrene, p-chlorostyrene, vinyl napthalene, 
o-methylstyrene, o-chlorostyrene, p-t-butylstyrene and the like. Most 
preferred are styrene and alpha-methyl styrene. 
Other ethylenically unsaturated compounds include derivatives and 
homologues of acrylic acid, methacrylic acid, indene, methylidene, 
vinylcyclohexane, isobutylene, propylene, maleic acid and its esters, 
fumaric acid and its esters and the like. Most preferred are acrylic acid, 
methacrylic acid, indene and isobutylene. 
The coating bath is an emulsion, dispersion or solution comprising the 
coating composition, water, fluoride ions and an oxidant. The water is 
used as a diluent to dilute the coating composition to a suitable solids 
content. Typically the solids content of the coating composition are 
diluted with water to about 5 g/l to about 100 g/l, preferably about 10 
g/l to about 50 g/l. 
Sources of fluoride ions and procedures to add fluoride ions to the coating 
bath are generally well-known in the art. Typical sources of fluoride ions 
include but are not limited to ammonium fluoride, hydrofluoric acid and 
its solubule or partially soluble salts such as sodium, potassium, cesium, 
iron (III), tin (II), tin (IV), copper (II) and zinc salts and the like. 
Ammonium fluoride, hydrofluoric acid and mixtures thereof are the most 
preferred sources of fluoride ions. Generally, the fluoride ions source is 
present in the range of about 0.5 g/l to about 10 g/l, preferably about 
1.0 g/l to about 4.0 g/l of the coating bath. 
Oxidants and the use of oxidants are generally well known in the art. The 
oxidants may be any oxidizing compound which is solubule in the coating 
composition bath which include but are not limited to nitric acid, 
peroxides and peroxydisulfates, and the like. Preferred oxidants are 
hydrogen peroxides, ammonium, peroxydisulfates and potassium 
peroxydisulfate and mixtures thereof. The oxidant is present at a 
concentration of about 0.5 g/l to about 10 g/l, preferably about 1.0 g/l 
to about 4.0 g/l of the coating bath. 
The pH of the coating bath may range from about pH 1.0 to about pH 8.5, 
preferably from about pH 2 to about pH 6, and most preferably from about 
pH 2.5 to about pH 4.5. Generally, the procedure to adjust the pH by the 
additions of acids, buffers and the like to the coating bath is well known 
in the art. Typical examples of acid additives include but are not limited 
to hydrochloric acid, hydrobromic acid, sulfuric acid, formic acid, acetic 
acid, oxalic acid, malonic acid and the like. Typical examples of 
buffering agents include but are not limited to sodium acetate, potassium 
tartrate and the like. 
It will be readily apparent to those skilled in the art that the coating 
bath may be further modified by the addition of surfactants, chelating 
agents, plasticizers, pigments, thickners and the like. The coating bath 
may also optionally contain modifiers that enhance the stability of the 
coating bath, modify the coating bath rheology and/or provide special 
properties to the final coating. All these additives and the use thereof 
are well known in the art and do not require extensive discussion, it 
being understood that any additive employed can be used so long as they do 
not deleteriously affect the coating bath and do not adversely affect the 
characteristics of the coating. 
The metal substrate is immersed in a coating bath that has an operating 
temperature between about 15.degree. C. to about 50.degree. C., preferably 
about 20.degree. C. to about 45.degree. C. The bath temperature is kept 
relatively constant. Any suitable means can be used to contact the coating 
bath with a heat exchange medium. For example, tubes through which water 
are circulated can be immersed in the composition or the bath container 
holding the composition can be jacketed with tubes through which an 
appropriate heat exchange material is pumped. 
The coating composition is contacted with the metal substrate by immersing 
the metal substrate in the coating bath. The metal substrate is immersed 
in the coating bath for a period of time within the range of about 5 
seconds to about 10 min., preferably from about 10 sec. to about 120 sec. 
Agitating the coating composition in the bath while immersing the metal 
substrate aids in maintaining the uniformity of the coating formed. This 
may be accomplished, for example, by stirring the composition with a 
mixer, by moving the substrate in the coating bath and the like. 
After withdrawing the coated metal substrate from the coating bath, the 
coating is rinsed with water for about 5 seconds to about 60 seconds. 
Following the water rinse step the coating can optionally be dried at 
temperatures in the range of about 20.degree. C. to about 260.degree. C., 
preferably 22.degree. C. to about 200.degree. C. 
The metal substrate is then reimmersed in the coating bath for about 5 
seconds to about 10 minutes, preferably 10 seconds to 120 seconds. The 
different immersion steps may all be the same length of time or different 
lengths of time. The cycle of immersion, rinsing with water and optionally 
drying is repeated about 2 to about 10 times, preferably about 3 to about 
7 times and most preferably from about 4 to about 5 times. The thickness 
of the coated metal substrate does not increase by the cyclic process more 
than about 20 percent compared to a dried single coat. 
The final step after the immersion, rinse and optionally dry cycles is 
baking the coated metal substrate. The metal substrate is baked to cure 
the coating on the metal substrate at a temperature from about 100.degree. 
C. to about 260.degree. C., preferably from about 180.degree. C. to about 
230.degree. C. 
Generally the coated metal substrate has a coating thickness of from about 
0.05 mil to about 5 mil, preferably from about 0.1 mil to about 2 mil. The 
thickness of the coated substrate dos not increase in thickness by more 
than 20 percent compared to a dried single coating. It is theorized that 
the coating does not increase in thickness by more than 20 percent of a 
single dry coating because of the interval rinsing steps and/or drying 
steps. During the rinsing steps the coating is washed substantially free 
of the metal ions and during the drying steps the free water contained in 
the coating which is a transport medium for the metal ions is removed. 
Thus, through rinsing and/or drying the metal ions from the substrate 
through the coating are greatly reduced. Therefore, reimmersion of the 
metal substrate in the coating bath results in preferential deposition of 
the coating composition to the areas where the coating bath has access to 
the metal substrate which liberate ions, such as pinholes, defects, pores 
and thin areas of the first coating layer. Accordingly, there is no more 
than about 120 percent the thickness of a dry single immersion coating in 
the subsequent stages of the autodeposition process of the instant 
invention. 
It has been observed that the metal substrates coated according to the 
process of this invention have outstanding qualities with respect to 
corrosion resistance and adhesion. 
SPECIFIC EMBODIMENTS 
The outstanding results that can be obtained from the utilization of the 
present invention will become apparent from the examples set forth 
hereinafter. 
PREATION OF ORGANIC COATING COMPOSITION 
A clean dry, 7 oz. crown cap bottle was charged with about 0.62 g of Gafac 
RE-610 (surfactant, available from GAF Corp. New York, N.Y.) and about 65 
g of water. This solution was agitated by magnetic stirrer to dissolve the 
surfactant. About 15.08 g of a 70/30 butadiene/acrylonitrile copolymer 
elastomer emulsion of 27.8 percent solids was diluted with about 18.18 g 
of water. The diluted elastomer emulsion was added dropwise to the rapidly 
agitated surfactant solution. About 0.61 g of pentaerythritol 
tetra(3-mercaptopropinate) was dissolved in a mixture of about 30 g of 
acrylonitrile and about 10 g of methylacrylate resulting in a 
monomer/chain transfer agent solution, which solution was added to the 
reaction bottle. 
The reaction bottle was sealed with a rubber lined, perforated crown cap. 
The bottle was purged for about 10 minutes with nitrogen by means of about 
a 12 inch hypodermic needle inserted through the cap and with an inserted 
shorter needle as a vent. A nominal 5 psig nitrogen pressure was left in 
the reaction bottle after the nitrogen purge. The reaction bottle was then 
placed in a safety cage. 
A solution of about 0.055 g of potassium persulfate in about 9.6 ml of 
water was prepared and about 4.8 ml of this initiator solution was 
injected by a syringe into the reaction bottle. The reaction bottle was 
then rotated in about a 56.degree. C. constant temperature water bath for 
about 6.25 hours. The resulting latex was filtered through a double layer 
of cheezecloth to remove the coagulum. 
The latex product contained about 29.8 percent solids and exhibited the 
following characteristics; 3.7 pH, 2140 .ANG. average particle size, 78 wt 
percent acrylonitrile content, 1.69.times.10.sup.5 weight average 
molecular weight and 4.5 Mw/Mn (polydispersity index). This latex was used 
in the organic polymer coating composition. 
COATING COMPOSITION BATH FORMULATION 
About 75 g of the latex was added to approximately 1 liter of distilled 
water. About 10 ml of 30 percent aqueous hydrogen peroxide and about 
3 g of 50 percent aqueous hydrofluoric acid were added to the diluted latex 
with agitation to form the autodeposition coating bath. The coating bath 
had a pH of about 3.46. 
TEST PANELS 
The coating compositions were coated onto the following two types of 4 
inch.times.6 inch 20 gauge test panels; 
Q-panels which are polished, cold rolled steel from Q-Panel Co., Cleveland, 
Ohio, and 
B-40 panels which are cold rolled zinc phosphate pretreated steel panels 
from Parker Co., Detroit, Mich. 
The test panels were washed with acetone and dried prior to being employed. 
TEST METHOD 
Test panels 1 and 2, respectively, a Q panel and a B-40 panel, were 
immersed in the coating composition bath for about 10 seconds, withdrawn 
from the bath, rinsed with water for about 10 seconds, and air dried. The 
process was repeated with immersion time, respectively, of about 30, about 
60, about 90 and about 110 seconds. After the final coat was deposited, 
the panels were rinsed with water and baked for about 10 minutes at about 
200.degree. C. The test results are shown in Table I. 
Test panels 3 and 4, a Q panel and a B-40 panel, respectively, were 
immersed in the coating composition bath for about 10 seconds, withdrawn 
from the bath, rinsed with water for about 10 seconds, and baked for about 
10 minutes at about 200.degree. C. The process was repeated with the 
immersion time of the coats, respectively, at about 30, about 60, about 90 
and about 110 seconds. The test results are shown in Table I. 
B-40 test panels 5,6,7 and 8 were immersed in the coating composition bath, 
rinsed with water and air dried after each coating application. The 
process was repeated with the immersion time of the cycles respectively, 
as follows: example 5, about 10, about 30 and about 60 seconds; example 6, 
about 10, about 30, about 60 and about 90 seconds; example 7, about 10, 
about 30, about 200, about 90 and about 110 seconds; and example 8, about 
10, about 30, about 60, about 90 and about 110. After the final coat was 
deposited on the test panels in examples 5-8 were baked for about 10 
minutes at about 200.degree. C. The test results are shown in Table II. 
Comparative examples 9 Q panel, 10 Q panel and 11 B-40 panel, were immersed 
in the coating composition bath for, respectively 1 minute, 3 minutes and 
3 minutes, and then baked for about 10 minutes at 200.degree. C. The 
comparative results are shown in Table I. 
Comparative example 12, B-40 test panel was immersed in the coating 
composition bath for about 180 seconds, withdrawn from the bath, rinsed 
with water for about 10 seconds, air dried and then baked for about 10 
minutes to about 200.degree. C. The comparative results are shown in Table 
II. 
In each case, ASTM standard adhesion (tape test), hardness (pencil), 
reversed impact, creepback and salt fog (rust) testing of the coated metal 
substrate was carried out. 
The thicknesses of the cured dry coatings are non-destructively measured by 
an electronic probe based on magnetic conduction and eddy current. 
The adhesion tape test (ASTM D 3359-78) was carried out by applying a strip 
of standard tape to a cross-cut section in the coated substrate, 
previously made by a sharp tool in the coated substrate. The tape was then 
removed by briskly snapping it off. The adhesion is denoted as the percent 
of the cross-cut squares of which the coating remains intact. 
The hardness test measures the rigidity of the organic coating applied to 
rigid substrates such as metal panels. The hardness test, (ASTM D 3363-74) 
was carried out by forcing pencil leads of increasing hardness values 
against the coated surface in a precisely defined manner, until one lead 
mars the surface. Surface hardness is defined by the hardest pencil lead 
which just fails to mar the coated surface. Test ranges are 6B, 4B, 2B, 
HB, 2H, 4H, 6H and 8H with 8H being excellent, that is, the hardest lead 
failed to mar the coating. 
The impact (ASMT D 2794-82) test measures the tendency for a coating to 
crack after being deformed by an impacting force. A falling stainless 
steel dart ball weight hits a panel with the coated side down for the 
reverse impact test. The height of the fall in inches multiplied by the 
dropping weight in pounds is the impact energy. To pass the test, a 
standard tape is applied to the impact area and snapped off and the 
coating must remain intact. 
Examples 1-8 and comparative examples 9-12 were applied to duplicate panels 
and tested as described above. The duplicate panels were subjected to salt 
exposure (ASTM B 117) testing. Salt fog testing was carried out by masking 
with black tape coated portions of the panel and then a large X is scribed 
in the dried coated panel. The panel is placed in a salt-fog cabinet for a 
given period of time. The coating compositions were exposed to at least 24 
hours of salt fog environment. A rating is given based on the degree of 
rusting of the samples. Test ranges are 0 to 10, with a 0 rating for all 
rust and a 10 rating for no appreciable rust; furthermore, the scale is 
logarthmic between the two extreme endpoints. 
Creepback (ASTM-0-1654) was also measured on the test panels subjected to 
salt exposure testing. Creepback determines the wet adhesion of the 
coating by measuring in millimeters (mm) how wide the large X mark 
originally scribed in the test panel has grown after exposure to the salt 
fog cabinet. The number identified is the number of millimeters the mark 
has grown with 0 meaning no creepback. 
The test results reported in Table I demonstrate multiple stage 
autodeposited coatings have excellent corrosion resistance at 24 hours and 
very good corrosion resistance at 100 hours whereas the comparative 
coating produced by the single dip process have very poor results to 
failure at 24 hours of salt fog exposure. 
The results of the hardness and adhesion tests demonstrate that the 
multiple stage auto deposition coatings are as good as the single dip 
coatings. The results of the reverse impact test demonstrates that 
coatings prepared by Applicant's multiple stage autodeposition process are 
as good as, or better than, the coatings prepared by the single dip 
process. 
The test results reported in Table II demonstrate that a multiple stage 
autodeposited coating has superior hardness, adhesion, reverse impact and 
corrosion resistance than a coating prepared by a single dip process. 
Although the invention has been described in detail through the preceeding 
examples, these examples are for the purpose of illustration only, and it 
is understood that variations and modifications can be made by one skilled 
in the art without departing from the spirit and the scope of the 
invention. 
TABLE I 
__________________________________________________________________________ 
Multiple vs. Single Autodeposited Coatings 
Reverse 
Coating Impact 
Rust Rating 
Example 
Thickness (mil) 
Hardness 
Adhesion Percent 
(in-lbs) 
24 hrs. 
100 hrs. 
200 hrs. 
__________________________________________________________________________ 
1 3.1 4B 80 0 4 3 -- 
2 0.6 2H 0 0 9 7 7 
3 0.6 HB 100 0 8 2 -- 
4 Unknown* 
2H 100 160 9 5 -- 
C9 0.4 4H 0 0 0 
C10 0.3 2H 100 20 1 
C11 0.6 2H 100 60 0 
__________________________________________________________________________ 
*The coating thickness was difficult to measure due to the porous nature 
of the metal substrate surface. 
TABLE II 
__________________________________________________________________________ 
Effect of Number of Autodeposition Stages 
Reverse 
Number of Impact 
Rust Rating 
Creep Back 
Example 
Autodeposition Cycles 
Hardness 
Adhesion Percent 
(in-lbs) 
24 hrs. 
100 hrs. 
24 hrs. 
100 hrs. 
__________________________________________________________________________ 
5 3 4H 100 140 2 1 0 -- 
6 4 4H 100 60 9 6 0 0 
7 5 8H 100 60 6 5 0 0 
8 5 8H 100 50 8 6 0.2 0 
C12 1 * * * 0 0 0 0 
__________________________________________________________________________ 
*Coating was too poor for meaningful evaluation.