Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to printing methods and printing
ink compositions. More particularly, it relates to methods and
compositions for making sheets such as paper sheets or cards
covered with superimposed layers of print, the lower of which
comprises a "hidden" message which is masked from a reader
unless an~ until an upper coating is removed, e.g. by abrasion,
scratching and erasures.
Recently, the preparation and distribution of
promotional game cards, premium cards, lottery tickets and the
like, containing hidden messages or symbols has become popular
and widespread, in fund raising and product promotion. The
recipient of such a card must remove from the card a layer of
hiding coating in order to reveal a message or symbol. Such
items are, however, difficult to prepare and print in an
economical fashion, because of the technical specifications they
must fulfil.
Such a card bearing a hidden message normally has at
least two coating layers overlying a hidden message.
Imme~iately over the message, a transparent or translucent
protective layer is provided, through which the message can be
read. Over the protective layer, an opaque second layer is
applied in order to hide the message. The hiding layer can be
subsequently stripped away e.g. by scratching etc., to reveal
the message through the first coat.
It is necessary that there exists, as between the
protective coat or layer and the hiding coat or layer an
acceptable degree of adhesion or affinity, so that the hiding
- 2 - ~
coat remains in place and opaque to hide the message during
storage, shippi~g, packaging, and transportation of the cards~
Nevertheless, the hiding coat ("scratch off coat") must be
readily removable by abrasion by the user at the required time,
to render the message visible, leaving the first coat
substantially unaffected.
In the process according to the present invention, the
compositions may be applied lithographically, by letterpress,
web or dry offset or heat set techniques. The preferred process
is lithography. Adaptations of the ink compositions discussed
herein to suit the particular method of application will be
apparent to the skilled artisan.
The present invention provides a process, and
composition for use therein, whereby the hidden message and
other printed material are applied to the stock on a pigmented,
specifically formulated varnish-ink composition. The
film-forming resin system of the varnish-ink composition and
that of the hiding coat composition are substantially compatible
with one another. They are preferably deposited from a commmon
or at least mutually compatible solvent vehicle.
The present invention provides an improved process for
preparing printed or coated cards or similar items bearing
messages hidden under an opaque layer, by providing a
formulation which contains both pigment usable in printing of a
visible message on a substrate and varnish for the protection of
the message from abrasion and for compatibility with the hiding
layer whose base or vehicle is mutually compati~le with that of
the fvrmulated varnish-ink composition.
37
In the preferred process of the present invention~ both
the varnish-ink composition and the hiding coat may be applied
to the card lithographically. To facilitate this, the pigmented
varnish-ink coat formulation and the hiding coat formulation are
deposited from compatible solvent systems and contain mutually
compatible resin systems. Then the hiding coat, containing -~
opacifying pigments, can be applied as a thin layer, suitably
formulated to be applied by lithography, and still exhibit the
necessary hidiny power whilst being abrasively removable. ~n
addition, if desired, further patterns can be applied over the
hiding coat.
Previously proposed hiding coats have had to be
deposited by silk-screen methods in order to adhere
satisfactorily to the protective coat. This is inconvenient and
expensive, since it requires the use of different printing
machinery from that used to apply the other printing layers.
The pigmented varnish-ink formulation and the hiding
coat formulation of the present invention have film-forming
resin systems which are mutually compatible. Preferably they
comprise generally the same resins or types of resins in both
formulations.
Examples of suitable resins for use in both the
pigmented varnish-ink and the hiding coat formulation are
phenolic resins such as phenolic modified rosin esters,
hydrocarbon resins, alkyd resins such as linseed-isophthalic
alkyd and other unsaturated alkyds resins and the like, and
mixtures thereof. Such resin systems are curable with heavy
metal-organic salts such as manganese octoate and cobalt
octoate, to yield light coloured or transparent films. They can
be plasticised i~ desired, e.g. with waxes of the hydrocarbon
type. The pigmented varnish-ink formulation may contain other
ingredients in minor proportions to modify its surEace
properties. For example, small amounts of Montan wax, Carnuaba -
wax or another natural or synthetic wax of similar
characteristics, can be added to give a harder surface finish.
Such a wax component may in fact migrate to the surface of the
coating after curing ("bloom") and then contribute to the
surface characteristics of the layer. The hiding coat
formulation should include a drying oil such as refined linseed
oil, and smaller amounts of curative, along with opacifying
agents, to yield a film of suitable hiding qualities and
compatibility with the pigmented varnish-ink film, yet readily
abrasively removable therefrom.
As noted, both the pigmented varnish-ink formulation
and the hiding coat formulation should be deposited from
compatible solvent systems, preferably from the same solvent
system. Hydrocarbon solvents (e.g. Magie oil, a mixture of
aliphatic and aromatic oils) are preferred. The pigmented
varnish-ink formulation will normally contain substantially
large proportions of solvent, and hence be of substantially
thinner consistency, than the hiding coat formulation. Both
formulations are nevertheless of a suitable consistency for
application preferably by lithography. The solvent used for the
hiding coat shGuld not be capable of penetrating the cured
~L9~87
pigmented varnish-ink coat to any significant extent, despite
the fact that the very same solvent may well have constituted
the vehicle for deposition of the uncured pigmented
varnish-ink. Accordingly, a fast drying varnish system is
chosen, which cures to a hard ~inish to prevent solvent and
pigment penetration thereof from the hiding coat, but which
nevertheless "traps" the subsequently applied hiding coat to the
necessary degree.
In order to be satisfactory for lithographic
application, an ink formulation must be adjusted in relation to
the printing machine speed, to adjust its rate of drying and
curing. On a high speed machine, the amount of heat generated
by the machine may cure the pigmented varnish-ink to such an
extent that the applied layer will not transfer from the plate
cylinder to the rubber blanket cylinder and on down the roller
train. Accordingly, depending upon the speed and nature of the
lithographic printing machine by means of which the pigmented
varnish-ink is to be applied, it may be necessary to retard the
drying or hardening rate of the pigmented varnish-ink as
compared with normal varnishes. When a slower speed of machine
is employed, such retardation may not be necessary.
With regard to the curing and the drying of the
pigmented varnish-ink, it has additionally been found that the
pigmented varnish-ink can be cured in a minimum amount of time.
Curing and drying of a pigmented varnish under an infra red
energy source can be completed in as little as 30 minutes. This
t7
provides additional time savings for operations of this type.
In the preferred process according to the present
invention, the card or paper stock is initially printed, in a
first colour, with the indicia to be subsequently covered with
the "scratch-off" hiding coat (the "hidden message") at the
appropriate location, lithographically. At the same tiDle and
from the same plate, any other areas of the stock may be
appropriately printed with the same colour, e.g. with text,
picture, design, etc. Normally, the first colour will be the
darkest colour to be applied, e.g. hlack or dark blue. The ink
composition used for the first lithographic applica~ion step may
be of the composition according to the invention, i.e. a
varnish-ink, or a standard conventional lithographic ink suited
to the base stock.
In the next step of the preferred process, the stock is
overprinted lithographically with a second colour, of a
varnish-ink according to the invention, at least in the area of
the "hidden message" t as a solid block covering it. This second
colour may be applied wet-on-wet over the first colour.
Preferably it is restricted to cover only the area of the
"hidden message", but may if desired be used to apply additional
text or colour to other are~s o~ the stock. Red is a suitable
choice for the second colour. The "hidden message" is still
readable through the applied second coat.
There then follow optional steps of lithographic
application of additional colour, to complete the printing of
the stock. If it is required to produce full-colour printing on
the stock, e.g~ with full colour illustration, two more colours,
e.g. green and yellow, are applied successively, wet-on-wet,
over the second colour by lithographic means~ Thus a standard
four-colour lithographic printing machine can be used. If any
of the subsequently applied colours are to cover the "hidden
message", t~en the composition of such colour must be a
varnish-ink according to the present invention. It is however
preferred to avoid further coating of the "hidden message" with
the subsequently applied colours, so tnat they catl be formulated
according to standard lithographic ink formulation, compatible
with the stock and the previously ap~lied coats. It ls however
to be emphasized that the third and fourth colour applications
are optional and not essential to the successful practice of the
process of the invention.
After the desired number of colour coats have been thus
lithographically applied, the printed stock is allowed to dry,
and then the scratch-off hiding coat is applied lithographically
to the "hidden message" area. Drying of the colour coats
normally takes from 6 to 24 hours, so that the hiding coat
application is conveniently conducted the following day. The
hiding coat, of formulation previously described, is
lithographically applied over the "hidden message" area, in one,
two or three wet-on-wet applications using a standard
lithographic plate and printlng machine. Then the hiding coat
is dried. It is found that the hidin~ coat successsfuly adheres
to the coating over the "hidden message" so as to render it
indecipherable, and is sufficiently adhesive and durable to
withstand normal handling and transporation of the printed
stock. Nevertheless it can be readily scratched off, to reveal
the "hidden message" throuc~h the coating of the second colour.
The varnish which, along with any desired pigment, is
used to formulate the pigmented varnish-ink of the present
invention, is preferably as follows, the ingredients being
expressed as percentaqes by weight:
Components % Ran~e
Magie oil (solvent) 30-35
Phenolic modified rosin ester 16-20
Hydrocarbon resin (e.g. of the PICCOPALE* type) 13-17
Linseed-isophthalic alkyd 10-13
Hydrocarbon plasticizer (e.g. of the DUTREX* type) 7-10
Montan wax 3-6
Calcium perborate 1.5-3
Manganese octoate 1.5-2
Cobalt octoate 0.5-1
Gelling agent 0.5-0.7
Chinawood oil 0.3-0~5
*Trade mark
In this formulation, cobalt octoate, manganese octoate
and calcium perborate constitute the curing system. The calcium
perborate helps to cure the chinawood oil~ by supplying oxygen
thereto. Similar hydrocarbon flexibilizer may be used in place
of DUTREX as the plasticizer. Also similar hydeocarbon rosins
may be used in place of PICCOPALE. The chinawood oil (tung oil)
is optionally added, to adjust the consistency and taclciness o~
the surface. The gelling agent also adjusts the consistency of
the formulation. As gelling agent, there can be used any
suitable product from the reaction of an unsaturated fat~ty acid,
a solvent and calcium octoate. Alternatively, thickeners such
as fumed silica may be used as or instead of a gelLing agent.
In order to formulate the pigmented varnish of the
present invention for application by lithography 15-25% of the
normal pigment (ink) vehicle usually employed in lithographic
printing, is substituted by the varnish identified above. The
varnish may be substituted in any colour of ink in order to
formulate the pigmented varnish. In this way, a large number o~
colours may be used to print the message and any other pattern
required on the card. A number of layers of differently
coloured pigmented varnishes may be applied in succession, in
order to print a multi-coloured pattern and/or message on the
card. It is, of course, necessary that in such cases, the
colour of the second layer and any additional layer be chosen so
as to maintain visibility of the message printed by the first
layer.
Formulation of the pigmented varnish of the present
invention for use with other printing methods may require
incorporation into the varnish identified above, of inks which
are typically used in those printing methods.
In formulating the pigmented varnish, the extent of the
-- 10 --
varnish substitution for normal ink vehicle is dependent on the
colour sequence used in the printing process. It is most
desirable that the uppermost layer of piqmented varnish contains
a higher percentage of the varnish than the lower layers so as
to provide optimum communication between the pigmented varnish
and the hiding layer.
The following is a preferred general formulation for
the pigmented varnish-ink for lithographic use in the present
invention. The amollnts of ingredients are expressèd as parts by
weight:
Components % Range
Magiè oil (paraffin based solvent) 20-28
Phenolic modified rosin ester 14-18
Hydrocarbon resin (e.g. of the PICCOPALE* type) 8-12
Linseed-isophthalic alkyd 6-10
Hydrocarbon plasticizer ~e.g. of the DUTREX* type) 6-8
Isophorone diamine 0.5-105
Texanol isobutyrate 2-5
Montan wax 2-5
Calcium perborate 1 5
Manganese octoate 1-2
Cobalt octoate 0.5-1
Gelling agent 0.3-0.6
Chinawood oil 0~3-0-5
Pigment 16-25
*Trade mark
-- 11 --
a8~
It should be noted that the pigmented varnish may also
be prepared by mixing known inks of desired colour directly with
the varnish. In this case, it will be evident that dilution of
the pigment will result. Additional pigment may be added to
retrieve the original intensity of the ink, if desired.
Preferably, the hiding coat contains pigments or
opacifying agents which render the finished coat not only
visibly opaque but also opaque to all other forms and
wavelengths of radiation also, so that the "hidden message"
cannot be prematurely revealed e.g. by ~-rays, UV lic3ht etc.
For this purpose the hiding coat formulation should contain a
powdered metal such as powdered aluminum, carbon ~lack, dyes etc.
A suitable such hiding coat for use by lithographic
application is as follows, with the amounts of ingredients
expressed as percentages by weight:
Components ~ Ran~e
Titanium dioxide 28-35
Aluminum powder 15-~0
Phenolic modified resin ester 15-18
Linseed oil refined 9-11
~lack pigment (carbon black) 7-8
Linseed-isophthalic alkyd 5-8
Magie solvent 5_7
Cobalt octoate 0.5-1
Chinawood oil 0.5-1
Hydrocarbon resin 0.5-1
- 12 -
Polyethylene wax 0.3-0.5
Fischer-Tropsch wax 0.2-0.5
Gelling agent 0.5-1
The hiding coat formulations for use in the present
invention may be the same as described above or may contain an
additional ingredient. It has been found that incorporation of
one or more species of long chain fatty amides, of which may be
mentioned erucamicle, erucyl stearamide and erucyl erucamide,
will improve the scratch-off properties of the hidng coat
without impairing its integrity durin~ the normal handling and
storage. Incorporation of the long chain fatty amides with the
above mentioned hiding coat formulation in a preferred range of
about 10-20% by weight has been found to provide easier removal
thereof by abrasion by the user and improved clarity oE the
uncovered message.
It will be noted that the above hiding coat formulation
has the same basic resin system and solvent as the pigmented
varnish-ink formulation. It differs, however, in the amount of
solvent and hence consistency, in the amount of curing system,
and in the presence of opacifying agents of those mentioned in
the specific formulations. Other suitable unsaturated oils may
be used instead of linseed oil, and instead of chinawood oil.
The gelling agent is as described in connection with the
pigmented varnish-ink coat. The presence of some such
unsaturated oil is high~y advantageous in providing the best
"scratch-off" properties. The linseed-isophthalic alkyd resin
in both formulations is
~ 13 -
8'7
represented in a large variety of available such materials, and
substantially any other unsaturated alkyd could be used
instead. IsophthaLics are preferred, however.
The pigmented varnish-ink coat is suitably applied to a
printed card stock by sheet fed or web lithograph methods. The
aforementioned formulations are most suitable for sheet fed -
lithography. The consistency of the formulations needs
adjustment to render them more suitable for web lithography.
The pigmented varnish-ink layees, suitably 2-4 in
number, wherein each layer may be the same or a different
colour, may be applied wet-on-wet, i.e. without waiting for the
previously applied layer of pigmented varnish to dry and cure.
The total pigmented varnish coat must however, as mentioned, be
dried and cured before the hiding coat is applied. Then the
hiding coat is also suitably applied to the stock, over the
pigmented varnish, in one or several wet-on-wet layers, and then
allowed to dry and cure.
The resulting hiding coat is durable not only to
withstand normal storage and handling, but also to receive
further overprintings with additional hiding layers, patterns or
printed information, should this be required. The scratch-off
portion can be readily removed by the user's fingernails9
without abrasives, coins, files, erasers or the like, to show
clearly the overprinted hidden messageO
The invention is further illustrated in the following
specific examples.
Example 1:
The following specific pigmented varnish-ink
formulatlon (a red ink) and hiding coat formulation were made
up, with ingredients listed as weight percentages:
RED VARNISH-INK FORMULATION
Components ~_Ran~e
Magie oil (paraffin based solvent) 25
Phenolic modified rosin ester 15
Hydrocarhon resin (e.g. of the PICCOP~LE* type) 14
Linseed-isophthalic alkyd 8
Hydrocarbon plasticizer (e.g. of the DUTREX* type) 6
Isophorone diamine
Texanol isobutyrate 4
Montan wax 3
Calcium perborate 2.2
Manganese octoate 0.3
Cobalt octoate 0.5
Gelling agent 0,5
Chinawood oil 0.5
Pigment (Permanent Carmine FBB02 (CI, 12485) 20
*Trade mark
- 15 -
'7
HIDING COAT FORMULATION
~ onents
Titanium dioxide (TIOXIDE*~ 32
Aluminum powder 18
PhenoLic modified resin ester 16
I.inseed oil refined 10
Black pigment ~carbon black)
L,.inseed-isophthalic alkyd 5
Magie solvent 6
Cobalt octoate 0.6
Chinawood oil 0.6
Hydrocarbon resin (PICCOPALE type)
Polyethylene wax 0.3
Fischer-Tropsch wax 0~3
Gelling agent 0.6
* Trade Mark
The red varnish-ink formulation was applied, by sheet
fed lithographically using a standard printing machine, to a
card stock bearing indicia previously printed with a standard
black ink known for use in lithographic printing. The card
contained an area with a printed message which was to be
hidden. The carmine pigmented ink formulation was applied
lithographically over the message area such that the entire
- 16 -
, ~,
message was covered by a solid rectangular block of the red
varnish-ink~ The message was clearly visible and legible
through the red varnish-ink coat. The applied red varnish-ink
coat was allowed to dry and cure for one day.
Next, using the same sheet fed lithographic printing
machine, the hiding coat was applied directly over the cured
varnish-ink coat. Four layers were applied, wet on wet, and
then the hiding coat was allowed to dry.
The hiding coat so formed completely obliterated the
underlying message. It was durable enough to withstand normal
handling and packaging. Nevertheless, it was removable by
scratching with a fingernail, to reveal the varnish coat
substantially unaffected, through which the printed message was
clearly visible.
EXAMPLE 2
By replacing the carmine pigment component in the
varnish-ink formulation o example 1, black pigmented, yellow
pigmented, and blue pigmented varnish-ink were prepared. The
carmine varnish-ink was also prepared as per example 1.
Using the black-pigmented varnish-ink, a first layer
was printed on a black substrate by a sheet-fed lithographic
press having four printing stations in serial arrangement. This
first black layer marked characters on the blank substrate
including the indicia which were to be hidden, i.e. the
"message".
The indicia-bearing substrate was passed, while still
"wet" to a second pressing station on the same lithographic
press where the carmine pigmented varnish-ink was applied such
that the entire area encompassing the message was covered or
"masked by the carmine ink-varnish. Other areas were printed on
the substrate at this same station and with the same carmine
pigmented varnish ink in this printing step in order to add
colour to the characters on the card outside the area containing
the message. The masking provides a surface over the message
which enables the hiding layer to be reversibly trapped within
the area of the maskin~. The message was clearly vislble and
legible through the carmine layer.
A third layer of yellow-pigmented varnish-ink was then
applied at the next station on the same lithographic press to
the substrate on areas outside of the message area. This
additiona] layer served to add colur to the characters on the
face of the card.
To provide an even more colourful card the substrate
was passed from the yellow-pigmented printing station to the
fourth and final printing station on the press where the
blue-pigmented varnish-ink was appropriately layered on areas
outside the message area.
Although it is within the scope of the invention to
apply either or both of the yellow and blue-pigmented varnishes
into the masked area at the subsequent printing stations it will
be realized that, since the carmine layer i.e. the first masking
layer will fulfill the aforementioned requirements of releasably
- 18 -
trapping the hiding layer, savings on ink consumed in the
printing process can be obtained by omitting the application of
more than one b1ocking layer.
After the final fourth layer was printed, the substrate
was removed and allowed to cure until the next day. Means for
reducing the curing time can be used to accelerate the curing~ --
process, if desired, such as an infra red energy source, etc.
The substrate with the cured varnish-ink layers was
then introduced into a lithoc3raphic press having, agaill, four
printing stations, each oE which contained a hiding coat
formulation as e~emplified in example 1~ The hiding coat was
applied directly over the carmine pigmented area blocking the
message at each successive station.
The layers were applied wet-on-wet. After passing
through the press the card was removed and allowed to dry.
The following day, it was found that the hiding coat
layer was completely removeable to reveal the hidden message by
scratching with a fingernail.
Whilst according to the invention, it is preferred to
apply the varnish coat and the hiding coat lithographically, it
is nevertheless possible to apply the varnish-ink coat by
letterpress application or by other methods kno~n in the art and
the hiding coat lithographically, thus providing the advantage,
of avoiding silk screen application. In application by
-letterpress, the hydrocarbon rosin component is omitted from the
varnish-ink formulation.
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