Note: Descriptions are shown in the official language in which they were submitted.
842
DEMETALLIZING APPARATUS
The present invention relates to formation of
packaging material by selectively demetallizing
metallized film and apparatus for effecting the same.
In my United States Patent No. 4,398,994, I have
described a continuous method of forming decorative
patterns of aluminized plastic film and the use of such
patterned film in packaging. As is described therein,
a web of aluminized poiymer film is printed with a
lO pattern of etchant-resistant material, corresponding to
the pattern desired on the aluminized surface. Aqueous
sodium hydroxide solution having a concentration of up
to about 25 wt.% is applied, at a temperature of about
15~ to about 100C, across the whole width of the web
to contact the pattern on the web. The sodium
hydroxide solution is allowed to remain in contact with
the web as it is conveyed for about 0.1 to about 10
seconds to permit the sodium hydroxide to dissolve
aluminum only from areas of the web not having the
2(j pattern of etchant-resistant material applied thereto.
The spent sodium hydroxide solution is washed from the
web to leave the pattern of etchant-resistant material
on the transparent polymeric film. The various steps
of the operation are effected consecutively at a web
~5 speed of up to about 1000 ft/min.
The apparatus illustrated in the aforementioned
patent utilizes rollers dipping into baths of liquid to
effect the various steps. This manner of application
of etchant and of wash water has been found to be
~0 somewhat inefficient in ensuring a consistent product
at high speeds of operation and also to be uneconomical
with respect to utilization of sodium hydroxide
etchant.
In an attempt to overcome those difficulties, in
'5 my U.S. Patent No. 4,551,614, I have described a
procedure in which the etchant is spray applied to the
film to impinge thereon, scrapers may be used to assist
in removal of etched material, warm water sprays wash
the spent etchant from the film surface, the washed
2 ~4
film is hot air dried and the air-dried film is
chilled-roll cooled. By proceeding in this manner,
high speed operations may be effected to produce a
consistent product with economical use of etchant.
However, the latter operation requires an initial
step of applying a pattern of etchant-resistant
material to the aluminized surface, the application of
an etchant solution over the patterned surface, and the
recovery and recycle of etchant solution.
n It has also previously been proposed in U.S.
Patent No. 3,647,508 to provide patterns on aluminized
plastic film by a procedure which involves printing a
pattern of etchant material onto a web of aluminized
plastic film using a printing medium comprising a
15 mixture of an etchant, a body-forming member and a
volatile carrier. Following printing of the pattern,
the volatile carrier is removed to form a spongelike
trap for the etchant limiting its spread to the pattern
area. Subsequently, the aluminum is washed away to
?~) provide the pattern in the etched areas.
Essential to this prior art procedure is the
utilization of a volatile carrier for the etchant and
some form of heating means to remove the volatile
carrier from the etchant. The purpose of the volatile
carrier is to enable the pattern to be set and prevent
its spread.
In accordance with one aspect of the present
invention, there is provided a method of forming a
pattern on a metallized film, which comprises printing
~0 onto ~he metallized surface of the film a pattern of a
water-based varnish having an etchant dissolved
therein; permitting the pattern to remain in contact
with the metallized surface for a period of time
sufficient to etch the pattern into the metallized
:'5 surface; washing spent etchant from the film; and
drying the resulting washed film.
In this invention, therefore, a pattern is printed
onto the metallized film using a water-based printing
varnish having an etchant dissolved therein. By using
,, .
this medium for printing the image, rapid and effective
etching is achieved and the spent etchant is readily
removed by washing. This procedure contrasts markedly
with that described in the prior art wherein printing
5 of the image requires a printing medium including a
volatile solvent and substantially immediate
volatilization of the solvent to fix the image.
In particular, the invention is concerned with
printing repetitive images on continuous webs of
10 aluminized polymeric film. For aluminum, the etchant
usually is sodium hydroxide dissolved in the
water-based printing varnish. In such continuous
operation, the image is conveniently printed on the
aluminized film using a gravure printing roll with a
]5 water-based gravure printing varnish, preferably an
acrylic-based aqueous gravure printing varnish.
By using a water-based conventional gravure
printing varnish, the desired image is easily and
reproducibly printed onto the aluminized surface in
?ij such a manner that the dissolved etchant rapidly etches
the desired image, without any undesired spreading or
the necessity to dry the etchant to prevent spreading.
Etching of the aluminized film occurs immediately
upon printing and is rapidly complete, so that washing
can rapidly follow the printing step, thus enabling the
printing, washing and drying operations to be effected
in a compact piece of equipment.
In one particularly preferred embodiment of the
invention, the washing step is effected in such manner
~0 that only the etched surface of the film is contacted
with wash water. This procedure significantly
decreases the quantity of water which needs to be
removed from the washed film to dry the same.
In the latter embodiment, it is preferred to
?5 effect the washing by passing the etched film in tight
engagement with the surface of a first roll and with
the etched face exposed, into a bath of wash water to
remove the spent etchant, then through the nip between
~~ 4 ~2~842
the first roll and a second roll and finally tightly
about the surface of the second roll.
By having the tight engagement between the etched
film and the first roll, the etched side of the film
5 only is exposed to the wash water and by having the
washed film then pass between the nip between the first
and second roll and tightly about the second roll, a
considerable amount of the wash water adhering to the
film is squeezed off, thereby decreasing further the
10 volume of water that needs to be removed by drying.
The invention has particular application to
metallized polymeric films and will be described more
particularly with reference thereto, but the invention
may be employed with any other metallized film, for
lS example, metallized water- and etchant-resistant paper.
The present invention also includes apparatus to
effect the method aspect of the invention.
Accordingly, another aspect of the invention provides
an apparatus for effecting continuous formation of a
?() repetitive pattern on a web of metallized film, which
comprises feed means for continuously feeding the web
of metallized film; and flow path defining means
defining the flow path of the web through the
apparatus; the flow path defining means sequentially
~5 defining printing station means for printing the web
with a pattern of a water-based varnish having an
etchant dissolved therein as the web passes
therethrough; washing station means for applying wash
water to the web to remove spent etchant-solution
~0 therefrom as the web passes therethrough; and drying
station means for drying the washed web as the washed
web passes therethrough.
The invention is described further, by way of
illustration, with reference to the accompanying
'5 drawing, in which:
The sole Figure of the accompanying drawing is a
schematic representation of an embodiment of an
apparatus for carrying out the present invention.
5 1z3884z
Referring to the drawing, there is schematically
illustrated therein a demetallizing machine 10 for
select.ive demetallizing of a web 12 of metallized
plastic film drawn from a roll 14 thereof. The
5 substrate polymer film may be any convenient flexible
polymeric material chemically resistant to the etchant
and typically is a polyester material, for example,
that sold under the trade mark "Mylar". The polymer
material usually is transparent but may be translucent.
lO The metal film adhered to the plastic film, as the
lower surface in the illustration, may be any
convenient metal which can be removed from the surface
of the substrate by chemical etching. The metal
usually is aluminum, but other metals, such as copper,
~5 may be used. The thickness of the metal film may vary
widely within the range of about 10 to about 1000 A,
preferably about 300 to 600 A, and may vary in
appearance from opaque to transparent. In the case of
aluminum, the chemical etchant commonly is aqueous
2~J sodium hydroxide solution and the description of the
preferred embodiment which follows is directed to this
combination.
The web 12 of metallized plastic film is drawn
over a first roll 16 to a printing station 18. The
~5 printing station 18 comprises an etched gravure
printing roll 20 and a backing roll 22 which serves to
maintain the web in contact with printing roll 20. The
gravure printing roll 20 bears the image to be formed
on the web 14.
~0 The printing roll 20 dips into and rotates through
an etchant bath 24 housed in a suitable tank 26. The
etchant bath comprises a water-based gravure printing
varnish having sodium hydroxide dissolved therein. A
doctor blade 28 is used to wipe excess printing varnish
~5 from the surface of the gravure roll 20 and leave
printing varnish only in the recessed portions of the
gravure roll, corresponding to the image to be printed
on the web 12.
6 ~23~8~2
As the web 12 engages the wetted image of the
gravure roller the etchant-containing printing varnish
commences etching of the aluminized 2urface of the web
12 in the pattern as it appears on the gravure roller.
5 The water-based gravure printing varnish ensures that
etching occurs only in the desired areas and does not
run into the adjacent areas. In this way, the etched
image is sharp and has the desired appearance.
The water-based gravure printing varnish is a
l~ conventional unpigmented water-based printing ink
useful in gravure printing. These materials generally
comprise water and a water-soluble binder, which may be
acrylic-based. The sodium hydroxide is dissolved in
the aqueous base to provide the etchant medium. The
lS quantity of sodium hydroxide employed may vary widely,
although is generally relatively low, below about 15
wt.% of the varnish. Pre~erably, the concentration of
sodium hydroxide is in the range of about 5 to about lO
wt.%.
2() Although the process will operate satisfactorily
at ambient temperatures, it is preferable to use the
aqueous etch medium at an elevated temperature, to
increase the speed of etching and to provide thereby
for an increased throughput of film and speed of
operation. Elevated temperatures of about 50 to about
95C preferably are employed and may be achieved by
heating the bath 24.
By the utilization of the water-based printing
varnish with the gravure roll, etching of the metal on
~0 the web occurs in the same pattern as appears on the
gravure roll to provide a sharply-outlined image. A
visible pattern of metallized and demetallized area
results.
The web 12 passes from the printing station 18 to
~5 a washing station 29 wherein the etched image is washed
free from spent etchant. The temperature and
concentration of etchant solution are coordinated with
web speed to ensure that etching of the metal in the
~!~
7 lZ38842
printed pattern is substantially complete by the time
the web 12 reaches the washing station 26.
In the washing station 29, the web 14 first
engages an idle roll 30 before passing into engagement
5 with the lower one 31 of a pair of rolls to be guided
through a bath 32 of wash water in a suitable tank 34.
The web 14 is tightly wrapped around roll 31, passes
through the nip 36 between the lower roll 31 and upper
roll 38 and then passes tightly around the upper roll
n 38. The size of the roll 31 and the depth to which it
is submerged in the bath 32 are chosen, in combination
with the tight wrapping of web 12 about roll 31, to
ensure that only the surface of the web 12 which is
contacted with etchant comes into contact with the wash
15 water. In this way, the amount of water which needs to
be removed from the film during drying is significantly
decreased.
In continuous operation, the wash water in the
water bath 32 is constantly changed to ensure as high a
~(J cleanliness of washed web as possible.
As the web 12 passes through the nip 36 between
the rolls 31 and 38 and the washed surface of the web
comes into engagement with roll 38, water is squeezed
from the washed surface, leaving little water adhered
to the washed surface. The web next is guided past a
drier 40 which removes the residual water, such as by
hot air or infra-red heat.
The dried web may be reeled up or may be subjected
to a single or multiple one-color printings, as
~0 described.
Utilizing the procedure outlined above, etching of
the aluminum film by the image printed from the gravure
roller occurs rapidly and high speed operation, usually
up to about 1000 ft/min can be achieved in a compact
~5 demetallizing machine, preferably about 100 to about
700 ft/min.
The demetallizing machine 10 illustrated in the
drawings is capable of operating at speeds which are
compatible with those of flexographic and gravure
8 ~2388~2
printing presses, so that the demetallizing operation
may be run on-line with subsequent color printing of
the film on modern film-printing machinery.
The roll of clean dried patterned film which
5 results from the demetallizing operation may be used as
is or color printed as a packaging material for a
variety of products. The patterned film often is
laminated with another, often polymeric, film to impart
desirable properties thereto, for example, heat sealing
n properties and improved strength properties, prior to
use of the laminate as a packaging material.
When lamination with the patterned web is to be
effected, such operation may be carried out separately
on a roll of the patterned web or may be effected
lS on-line with the demetallizing operation following the
drying of the patterned web, optionally in combination
with multiple color printing.
The demetallizing machine 10 illustrated in the
drawings may be used efficiently to remove any desired
2() proportion of the metal present on the web surface,
depending on the pattern desired, by use of the
appropriately-patterned gravure plate. The web speed
and other operating parameters, for example, sodium
hydroxide concentration and temperature may be adjusted
to take into account varying thicknesses of metal film.
In summary of this disclosure, the present
invention provides an improved method and apparatus for
selectively etching a metallized film to achieve
continuous reliable high speed operation.
~0 Modifications are possible within the scope of this
invention.
? 5
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