Note: Descriptions are shown in the official language in which they were submitted.
BRIEF D~SCRIPTION OF THE INVENTION
Field of the Invention
This invention relates to a process for the production of
partial or full color images, pictures, scenes or the like on
5 articles o~ aluminum or aluminum alloys which have been
previously specially anodized in order to obtain products
which are useful for all types of industrial, commercial and
consumer use. The products include decorative panels,
nameplates, belt buckles, instrument panels, trophy articles,
10 and others.
Prior Art
Many attempts have been made to economically produce
multicolor images on aluminum. For example, U.S. Patent
3,264,158 describes a process wherein oil soluble dyes are
15 applied to a decal and an unsealed, anodized surface is then
wetted with a solvent to cause dissolved dye to stain the
surface. U.9. Patent 3,258,381 describes a similar process.
U.S. Patent 3,218,243 discloses a method wherein water-soluble
dyes are used. U.S. Patent 3,242,037 describes yet another
20 process using a dye film on a solvent wetted anodic surface.
Another U.S. Patent 3,193,416, discloses a vat dye and
compatible solvents. Another approach ~as taken in U.S.
Patent 3,515,598 whexein a silk screening type ink is utilized
for screen printing dyes onto an anodized surface. A system
25 for coloring an anodized surEace was disclosed in U~S. Patent
3,718,548 wherein a meltable organic coloring matter is
brought in contact with an anodized surface and is then melted
into the oxide pores. Finally, U.S. Patent 3,079,309
discloses a system whexein a water base ink is manufactured
using water soluble dyes and pigments. This is applied to an
oxide surface wherein the surface is stained. None of these
5 prior art patents disclose a process capable of producing
crisp, sharp images, or of producing pictures on a mass
production basis, or of producing images having adequate
clarity or durability. In addition, the processes of these
prior art patents are cumbersome to practice and are not
10 capable of producing durable, full color photographs on
aluminum which are comparable to those taken by a quality
camera and printed on photographic paper.
U.S. Patent 3,363,557 discloses a heat transfer of
indicia containing sublimable coloring agent. The process
; 15 of this patent is particularly directed to printing inks for
textile coloring and those inks, in accordance with the
invention, comprise an organic resinous binder which when
deposited supplies a dry solid film which remains solid and
dry upon exposure to elevated temperatures. This patent is
20 directed to and provides great detail about using
; sublimation type transfers for coloring cellulose and other
organic materials used in the textile, carpet, plastic and
garment industries. The patent gives several examples, each
of which is concerned with placing images on textiles. In
25 addition, the patent mentions that images can be provided on
~Imetallic surfaces especially anodized aluminum". While the
patent is clearly principally directed to the coloring of
organic materials and the process disclosed will not provide
any image on most metallic surfaces, it is disclosed that an
image can be Eormed on an unsealed, anodized surface.
However, unless the anodic coating is of a very specific
type, not disclosed in the patent, the image produced is
fugitive, subject to fading and of limited or no commercial
value. Attempts over the past few years to use the standard
commercial anodizing processes, which are in general
practice throughout the world, have resulted in colored
10 products which at first appeared satisfactory but later,
thxough natural weathering and exposure to sunlight, proved
valueless. The coatings produced by the heat transfers
evaporated ~resublimed) or were destroyed by the natural or
artificial ultra violet radiation.
We have now discovered that the use of a special
anodizing techrlique produces a superior, extremely dense and
hard anodic coating optimally suited to application of single
or multiple colors by transfers produced as described in U.S.
Patent 3~363,557. It has been found that the anodizing system
20 disclosed in U.S. Patent 3,52~,799 can be modified to produce
an ideal surface for subsequent coloring. This patented
anodizing system was developed for produlcing- a white surface
on space vehicles and was not intended to receive coloring.
In fact, the stark white surface was absolutely required to
25 reflect heat encountered by space vehicles and rockets.
- 4 - 9912-72
Summary of the Invention
The present invention provides a method of decorating
articles of aluminum comprising the steps of:
anodizing said aluminum in an aqueous acid electrolyte
consisting essentially of from about 165 to 250 grams per liter
sulfuric acid, from about 10 to 30 milliliters per liter of an
organic carboxylic acid containing at least one reactive group
in the alpha-position wherein said reactive group is a hydroxy,
amino, keto or carboxyl group, and from about 10 to 30 milliliters
per liter of a polyhydric alcohol of from 3 to 6 carbon atoms,
with the temperature of the electrolyte being main~ained at be-
tween about 15C and 24C and the current density being maintained
at bet,ween about 200 to 535 amps per square meter so as to form
an anodized layer on the surface of said aluminum article, said
layer having a thickness of between about 10 and 26 microns;
pla~ing a dry film in intimate contact with said
anodized layer, said dry film containing a dye capable of
subliming when heated;
heating said dry film while in intimate contact with
said anodized layer for a time sufficient to cause at least a
portion of said dye to sublime and condense within said anodized
layer; and !
thereafter sealing said anodized layer on the surface
of said aluminum article.
According to the present invention, a novel process
is disclosed for the production of full color, partial color, or
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- 5 - 9912-72
any mixture of colors on aluminum or aluminum alloys. This
includes but is not restricted to full color pictures, designs,
images, and the like. The anodi~ing is carried out in a sulfuric
acid electrolyte containing a polyhydric alcohol of 3 to 6 carbon
atoms and an organic carboxylic acid containing at least one
reactive group in the alpha-position. The preferred polyhydric
alcohol is glycerine and the pre-ferred carboxylic acid is hydroxy
acetic acid. Anodizing optimally is carried out with a current
density of about 330 amps per square meter, with sufficient
anodizing time to produce an anodic film thickness of between
about 10 and 26 microns, The anodically formed aluminum oxide
is then carefully washed to remove the electrolyte and is allowed
to air dry. During the drying operation, care must be taken to
keep the surface clean so that the pores in the anodic film will
remain open. ~ heat transfer sheet, previously prepared by
printing or hand painting using colorants which are capable of
subliming when heated, is placed on the unsealed film and heated
usually to about 160 to 220C during which time the image from
the sheet is transferred into the pores of the anodic film in
vivid detail. The completed rendering is then sealed.
DET~ILED DESCRIPTION
In order to obtain a durable anld desirable colorless
hard anodic coating with its peculiar pore structure, it is
absolutely critical that the anodic layer be maintained between
10 and 26 microns. It is preferable that the anodic layer is
formed at a current density of between about 220 and 440 amps per
- 5a ~ 9912-72
square meter, with the optimum current density being 330 amps
per square meter and the optimum film thickness being 15 microns.
Further, the anodizing electrolyte must be maintained at a
temperature of between 15 and 24C with the optimum being 21C
and its chemistry as disclosed in Table l.
TABLE 1
Minimum Optimum Maximum
Sulfuric ~cid 165 grams/liter 200 g/l 250 g/l
Hydroxy Acetic Acid 10 milliliters/liter 20 ml/l 30 ml/l
Glycerine 10 milliliters/liter 20 ml/l 30 ml/l
It should be noted that the electrolyte of Table l is
similar to that disclosed in U.S. Patent 3,524,799, but without
any titanic acid salt being included. It has been found -that the
titanic acid salt acts as a pigment resulting in some pore closure
in the anodic film and a non-desirable surface for accepting the
sublimation dyes from the heat transfer.
The transfers may be printed on any suitable substrate
material, with paper being preferred and inks used for the pre-
paration of transfers for the te~tile industry, such as are dis-
closed in U.S. Patent 3,363,557 are accept~ble. The transfers
may be printed by means of offset or gravure printing, for example.
Also, transfers can be hand painted
~'
using these inks and the rendering so painted can then be
transferred to aluminum in accordance with the present
invention. Other printing or screening methods may also be
used to produce the transfers.
To illustrate this unique and novel technology and to
also compare it with val~eless technology, the following
examples are provided:
Example 1
Heat transfers were produced by offset printing using
10 color separations made from a 35 millimeter slide of a lion
taken in a jungle. The full color picture was printed on
standard quality printing paper of size about 6.35 centimeters
by 11.43 centimeters. The sublimation printing ink used was
made by Colonial Printing Ink Company of New Jersey who
15 manufactures this type ink for making heat transfers for the
garment and carpet industry. ~ transfer was placed tightly
against a clean, steel surface and the surface was heated
190C for 2 minutes. No image was formed on the steel.
Example 2
The procedure was repeated as discussed in Example 1 with
the transfer being placed tightly against clean metallic
surfaces of tin, nickel chromium, zinc alnd anodized aluminum
as used in the architectural and building industry. No image
was formed on any of these metallic surfaces even when the
25 time of contact and the ~emperature of contact were varied.
It appears images were not formed on the metallic surfaces
because there were no pores available to accept the dye as it
sublimed from the printed paper. Conse~uently, the dye just
evaporated into the air.
~xample 3
Anodized aluminum pieces of size 7.62 centimeters by 12.7
5 centimeters were produced in a standard sulfuric acid
electrolyte conventionally used throughout the world. This
electrolyte is normally 175 grams per liter sulfuric acid
maintained at 22~. Anodizing is carried out at a current
density of about 130 amps per square meter. More detail of
10 the process is described in the Metal Finishing Guidebook and
Directory published by Metal and Plastics Publications, Inc.,
Hackensack, New Jersey. An anodic film of a thickness of
about 15 microns was produced by anodizing in the conventional
electrolyte at 130 amps per square meter for 35 minutes. The
15 aluminum pieces were rinsed free oE electrolyte with tap water
and allowed to air dry. Care was taken not to touch or dirty
the surface. Lion picture heat transfers produced as
described in E~ample 1 were placed in intimate contact with
the anodized surfaces and were heated to 190C. The
20 temperature was maintained for 2 minutes. The heat transfers
were immediately removed and perfect im~es of the lion were
faithfully reproduced on the unsealed anodized surface; the
colors apparently having penetrated at least partially into
the pores o~ the anodic film. These samples were then further
25 processed as follows:
Piece A was left, as decorated, in normal room light.
After 3 months, the image was apparently lighter. After
months, the i~age was approximately half vivid and after one
year the lion could hardly be discerned and the green jungle
grass background was completely faded out.
Piece B was placed in 8~C water as used by some
5 anodizers to seal anodic surfaces. After 15 minutes, the
piece was removed and the lion picture was observed. It was
practically bleached out and the picture was unacceptable for
any practical use.
Piece C was placed in a closed steam chamber, similar to
10 those commonly used for steam sealing of anodic coatings.
Saturated steam was formed in the chamber and the piece was
sealed for 15 minutes. The picture of the lion, while not
greatly faded, was streaked by dye which had run from the
anodic film pores. The picture was worthless.
Piece D was sealed in a water solution of nickel acetate
at a temperature of 93C and concentration of 5 grams per
liter. Time of sealing was 15 minutes, in accordance with
standard practices in the anodizing industry. The lion
picture was apparently as bright as it was prior to sealing
ZO but the surface of the picture had a slight velvet-like
coating. This was easily removed by rubbing with a cloth.
The image appeared satisfactory. Several other samples were
prepared in this manner and were tested as follows:
1. A sample was placed on a roof with a southern
25 exposure~ The image on the sample was noticeably faded in 5
days, and almost completely faded in 30 days. The picture was
therefore unacceptable for commercial or decorative use.
~ . Samples were made into belt buckles that were worn by
adults and youth. Periodically, during an 18 month time
period, they were observed. The surface on all of the buckles
was seriously scratched and light to heavy fading of the image
was noted.
It is apparent from the above tests that the standard
sulfuric acid anodizing process produces an unsatisfactory
surface for coloring using sublimation dye heat transfer
techniques. Further, it is also apparent that most metallic
surfaces are also worthless as surfaces upon which a picture
may be transferred. Based on the testing conducted, it became
apparent that even conventionally anodized aluminum surfaces
would not be satisfactory for use with aluminum. Hard
anodizing processes including those used for engineering and
industrial purposes were also considered. All known processes
produced an integrally colored surface varying in color from
light bronze to gray and black. These dark surfaces were
obviously unsuited for decorating with bright colors, pastel
shades, etc. Even non-standard, European anodizing processes
20 which utilize oxalic acid or mixtures of o~alic acid and
sulfuric acid ~ere tried. These processes produced gray or
dark surfaces unsuitable for decorating.! Chromic acid
anodizing was also considered and tried but it also resulted
in a gray surface. Further research was made with the
standard sulfuric acid anodizing processes, attempting to
obtain a more dense, durable surface. It was thought that by
cooling the eleçtrolyte and increasing the current density
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- 10 - g912-72
from the normal 130 amps per s~uare meter, a satisfactory surface
might result. This was tried, but a gray surface resulted.
Anodizing temperatures of 20 up to 24C were tried with increased
current density but all the anodic films produced became smutty
and powdered off. The following examples are illustrative of use
of the anodizing system of the invention as disclosed in Table l.
Example 4
Pieces of aluminum allo~ 5052 were anodized at 330 amps
per square meter using the electrolyte disclosed in Table l, having
a minimum concentration of chemicals. Electrolyte temperature was
20C and the anodic film was about lO microns thick. The lion was
heat transferred to the clean air dried anodic film at a temper-
ature of 190C by holding the transfer in contact with the anodic
~ilm for 1 minute using a hand flat iron. An almost perfect copy
of the lion resulted. Its colors were just a shade light.
Example 5
An aluminum sample, decorated with the lion was prepared
as discussed in Example 4 except the optimum anodizing electrolyte
was used as disclosed in Table l. The electrolyte temperature was
21C. The anodic film thickness was about 15 microns The copy of
the lion obtained matched the original 35 millimeter slide from
which it was copied.
Example 6
An aluminum sampe was decorated as discussed in Example
5, except the anodic film thickness was about 26 microns. The
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- 11 - 9912-72
lion picture was acceptable. However, it was not quite as bright
as the one prepared per Example 5. It i5 believed that the pores
in the thicker anodic film are smaller because of the thicker
coating and thus cannot as readily accept the vaporized dye.
Example 7
An aluminumsample as decorated with the lion as
discussed in Example 4 except an electrolyte temperature of 24C
was used and the maximum electrolyte strength was used as shown
in Table 1. The anodizing current density was 440 amps per square
meter, the anodization being carried out long enough to produce a
film thickness of about 15 microns. A perfect picture of the lion
resulted. The inventors observed that the anodic film seemed
slightly softer than the previous samples when tested by drawing
a metal working file across the surface.
Example 8
An aluminumsample was decorated with the lion as per
Example 7, except a current density of 220 amps per s~uare meter
was used. The picture of the lion was perfect except the anodic
film seemed slightly softer as tested in Example 7
Example 9
An aluminumsample was decorated with a lion as per
Example 7, except that a current density of 48 amps per square
meter was used. The picture of the lion was perfect except the
anodic film seemed soft when tested with a file per Example 7.
The anodic film appeared to be on the verge of burning (chalking).
~ ~1
12
Many decorated aluminum samples of the lion were prepared
as discussed in Examples 4 through 9. They were accomplished
on aluminum alloy 5052. Some were sealed in the nickel
acetate solution per Example 3, piece D. Others were left
5 unsealed. Part of the 2 l/2 by 4 inch lion samples were
converted to belt buckles and the others left as decorated
aluminum plates. These articles were then kested for 18
months. The test results are summarized in Tables 2 and 3.
TABLE 2
10 Decorated Samples Per Examples--Fading Observation*
Image Treatment/Exposure Examples
4 5 6 7 8 9
Unsealed-inside exposure SF SF SF SF GF GF
Sealed-inside exposure NF NF NF NF SF SF
15 Outdoor Southern exposure-sealed GF SF GF SF GF GF
Outdoor Southern exposure-unsealed LI GF GF GF LI LI
Worn as belt buckles-sealed NF NF NF NF SF SF
Worn as belt buckles-sealed GF SF GF GF GF GF
*LI = Loss of Image
SF = Slight Fading
GF = Grea~ Fading
NF = No Noticeable Fading
TABLE 3
Decorated Samples Per Examples--Abrasion/Scratch Resistance*
25 Image Treatment/Exposure Examples
4 l5 6 7 8 9
Worn as belt buckles-unsealed SS NS NS SS MS MS
Worn as belt buckles-sealed SS NS NS NS SS MS
*NS = No appreciable scratches
SS = Slight scratches
MS = Many deep scratches and abrasions
From the tests conducted, it is apparent that the limits
for the ancdizing electrolyte chemistry and film thickness are
established for satisfactory practicing of the invention. It
is evident that practicing the invention within the limits
establishe~ produces highly acceptable products and is of
great value while images produced by other anodizing
techniques have no commercial or practical value.
The advanced technology disclosed in this specification
was further evaluated by producing full-color samples of elk,
aircraft, automobiles, mountain scenes, science fiction
pictures, etc. Various aluminum alloys were used including
1100, 3003, 6061, 5005 and 2024. The rendering varied from a
size of about 5 centimeters by 6.5 centimeters to about 38 by
38 centimeters. The anodic coating ~ilm was produced in the
optimum electrolyte per Table 1. A curren-t density of 330
amps per s~uare meter was used and anodizing time was
sufficient to produce a film thickness of about 15 microns.
15 The electrolyte temperature was held between 20 and 22C.
The heat transfers were produced on an offset, full color
printing press using Colonial Heat transfer inks developed
Eor the textile and carpet industries. Transfer temperature
was 190C using a hand flat iron and also a standard heat
20 transfer press utilized in the "T" shixt heat transfer
industry. Transfer time was from 1 to 2 minutes. The
optimum time was dependent on the size gf the aluminum sheet
and its thickness. The sheet thickness varied from about
0.08 centimeters to 0.3 centimeters. The completed work was
25 sealed by various means with results shown in Table 4, below.
14
TABLE 4
Results of Sealing the Colored Image
Perfect Slight Fading
Image of Image
5 Saturated Steam--15 min. X
88C Water--15 min. X
5g/1 Nickel Acetate Solution--15 min.
(93C) X
It should be noted that nickel acetate sealing is the
preferred method to seal images produced by this invention.
Example 10
An anodic film was produced on aluminum alloy 3003 in
accordance with the optimum conditions described for producing
the elk, aircraft, mountain scenes, etc. The clean dry film
was then contacted with a hard painted landscape scene which
was painted on heavy news print type paper using Colonial ~eat
Transfer inks. The artist mixed the colors on a palette as if
they were oil paints. The paper heat transfer and the
prepared aluminum sheet were placed in a "T" shirt heat
transfer press at a temperature of 190C for 2 minutes. A
perfect permanent metal scene of the previously painted
rendering resulted; the color and clarity being preserved.
The rendering was then sealed in the previously described
nickel acetate solution for 15 minutes.
Laboratory and metallurgical work ~as accomplished to
determine why this invention produc~s highly satisfactorv,
beautiful long lasting decorating work while a standard
anodizing system is worthless. Taber abraser tests were made
on film thicknesses of about 15 microns produced on aluminum
alloy 5052 by this process~ The normal sulfuric acid
anodizing process is used for comparison with the process
disclosed in this invention because all other processes
produce colored or otherwise unacceptable films. Results are
depicted in Table 5.
_ABLE 5
Taber Abraser Tests*
Milligram Weight
Loss for 3000 Cycles
Sample anodized at 330 amps per s~uare
me~er at 21C per this invention 11.6
Sample anodized at 130 amps per square
meter at 21C standard sulfuric
process 22.9
Sample anodized at 200 amps per square
meter at 21C per this invention 15.7
Sample anodized at 530 amps per square
meter at 21C per this invention 16.1
*Details on this test method are
found in U.S. Military Specification
MIL-A-8625
In addition to the Taber abraser tests, the weight of the
; anodic films was determined by the method outlined in U.S.
Military Spacification MIL-~-8625. The results are shown in
Table 6.
TABLE 6
Average Anodic Film Weight in
Milligrams Per Square Foot
330 amps per square meter anodizing per!this invention 2920
130 amps per square meter standard sulfuric acid anodizing
30 process 840
It appears that the process of the present invention
produces outstanding decorated items and that those produced
by other anodizing processes are unsatisfactory. The superior
t~
16
anodic coating produced in accordance with the invention
protects the colors deep inside the anodic coating pores from
abrasion and it is believed that this dense film also shields
the colors from degrada~ion by ultraviolet radiation coming
from the sun or other sources.
Although a preEerred form of our invention has been
herein disclosed, it is to be understood that the present
disclosure is by way of example and that variations are
possible without departing from the subject matter coming
within the scope of the following claims, which subject matter
we regard as our invention.
