Note: Descriptions are shown in the official language in which they were submitted.
21 57~5~
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Printing Ink
Description
The invention refers to a printing ink,
particularly for rotary printing processes and particularly
an ink for rotogravure and especially publication gravure,
which is printable in a liquidized state attained through
melting and hardenable through heat withdrawal, and which
contains a binding medium consisting of at least two groups
of components within each case at least one member. The
members of the first component group are crystalline
materials, which, when molten, act as solvents for the
members of the second component group. The members of the
second component group are amorphous thermoplastic
materials, which are solid at ambient temperature and are
softening, when temperature is raised to their respective
softening range.
The members of this second component group
dissolve in the members of the first component group by
application of heat up to a temperature above the melting
point of the members of the first component group and
further on up to the softening range of the members of the
second component group.
Upon withdrawal of heat, said members of the
second group, which are solute in the fused solvent made
out of the members of the first component group, resolidify
with inclusion of the members of the first group. Thereby
a new phase, namely a solid solution is created, which is
an amorphous glass consistent of at least a binary
homogeneous phase made up by the thermoplastic material of
the second group and the formerly crystalline component of
the first group.
By the term printing ink are here understood
printable substances with actual colouring effect as well
21~7453
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as printable non-coloured clear printing lacquers and non-
colouring printing-ink varnishes.
With conventional printing processes,
particularly with gravure printing, solvent based inks are
transferred from the printing form, i.e. from a printing
cylinder, which is preformed according to the printed
image, onto the web or substrate, which runs between the
printing cylinder and the counteracting impression rollers.
Subsequently, in an on-line drying section, the solvent of
the printing ink is driven off the substrate and the ink
film, which is printed on the substrate and partly
penetrating it in the case of paper webs or the like.
The term "solvent" in this context is to be
understood to mean those organic solvents, vegetable as
well as mineral oils included, which are conventionally
used in printing technology. Moreover, it means also water
or waterbased solvent, which is used to thin the so called
water-based or water thinn~hle printing inks.
This process, which is practiced at a very large
scale and with high productivity in printing industry and
particularly with the rotary printing techniques, depends
on great efforts regarding not only the actual print
production, but also the peripheral printing plant and the
enormous overall energy consumption. They have to be spent
to a large extent for
- The physically convective ink drying, which has to be completed during the run-time of the web
between every subsequent printing unit of the
printing machine. The time elapse which is left
to achieve this is extremely short due to the
running speed of rotary printing equipment.
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- The solvent recovery, which is performed close to
100~ or afterburning of the solvent, which means
its total loss. Either method is indispensable
to ensure an environmentally clean process.
- The fulfilment of the guidelines for clean and
health-convenient working areas as well as of the
regulations regarding the "threshold limit
values" (TLV), which apply for the solvents used
in the printing process, within all service areas
adjacent to the printing units.
- The observance of safety regulations, i.e. the
use of flame and explosion proof equipment in the
printing units and their periphery and also in
all service areas of the entire plant, which are
exposed to solvent vapours.
As compared to the spatial dimensions of the
aforementioned peripheric equipment, the dimensions of
those parts of the entire printing plant, which are
required for the immediate printing action itself are
small. This holds true especially for the large scale
printing processes, namely rotogravure and webbed offset
printing. The same relation is valid also for the capital
investment and the running costs of the printing machine
itself as compared to the capital expenditure and the
operating costs, which apply to those parts of the overall
plant which are needed for and involved with the connected
solvent technology.
The disadvantage mentioned, caused by the solvent
technology of the printing inks in the printing process,
can in principle be avoided through the use of solvent-free
meltable hot printing inks in printing machines with
heatable printing units. In this case the printing inks
are printed in a melted state and hardened through heat
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withdrawal.
The German disclosure DE-OS 25 34 845 discloses
printing inks containing thermoplastic polymers. These
inks are thought for use in printing techniques of the
aforementioned kind, but in practice turn out to have too
high viscosities and tackiness. Inevitably and in
principle, a temperature rise of thermoplastic bodies or of
a mixture of them even up to temperatures far beyond their
respective thermoplastic softening points or even
approaching their decomposition temperatures, merely yields
a semifluid mass with high tackiness, which, mainly due to
its high viscosity and tack, cannot be used for printing
applications. The same findings generally apply to
thermoplastics and mixtures thereof, which are known by the
technical term "hotmelts".
The teaching of the German patent DE 42 05 713 C2
surpasses the above specified state of knowledge and gives
a doctrine, how in principle a hot printing ink is to be
composed to specially reach a ready to print viscosity, for
rotary printing techniques and especially a viscosity,
which is in fact suitable for gravure printing,
particularly for rotogravure and especially for publication
gravure upon application of heat. The binding medium of
the inks, which are disclosed therein, consists of a
mixture of at least two groups of components, amongst which
the components of the first group are crystalline materials
at normal ambient temperatures with melting points above
the usual application temperatures of printed products and
the components of the second group are solid amorphous
thermoplastic resins at room temperature.
When molten by application of heat, the members
of the first component group act as solvents for the
members of the second component group. Said members of the
second component group are soluble in the molten members of
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the first component group and furthermore are suitable as
binding agents of a printing ink. If such a mixture with
a proper choice of components is heated to a temperature
above the sharply defined melting point of the crystalline
components of the first group, the second group of
components dissolves in that molten fusion to yield a fluid
hot-printing ink with a viscosity, which is especially low
enough for rotogravure printing. This domain of low
viscosities is reached exclusively by the presence of the
molten members of the first group of components, which act
as a solvent for the components of the second group.
By the aid of this teaching, a suitable hot-
printing ink, which is especially suitable for rotogravure
and publication gravure printing, is obtained, which
becomes fluid within a small temperature range above the
typical temperatures of use of printed products by addition
of heat and in turn becomes solid again by heat withdrawal.
For the realization of this principle for the
preparation of hot printing inks suitable for printing
techniques and particularly suitable for photogravure and
publication gravure, in DE 42 05 713 C2 cetyl alcohol,
stearyl alcohol, and 12-hydroxy-stearic acid are offered as
examples of appropriate components for the first component
group. Additionally, a thermoplastic polyacrylate with
free hydroxyl functions is disclosed as a component of the
second component group.
Furthermore, it has been proposed that a third
group of components be admixed, whose members are dyes
and/or coloured pigments with colour-rendering ability, if
a colouring ink is to be designed, and/or additives, which
influence the printability and/or the application profile
of the hot-print inks and of the printed products.
When hot-print inks are prepared by fusion of a
21~7~53
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mixture of these components with the proportions specified
in DE 42 05 713 C2 and when these inks are printed on a
rotogravure printing unit by means of a conventionally
chrome-plated but heated printing cylinder, wetting
deficiencies come into the play of conventional immersion-
inking and subsequent doctor-blading of the printing
cylinder at higher printing speeds. Thereby, the ink film
is unevenly spread over the printing cylinder and is not
able to cover its entire printing surface. An uneven and
even fragmentary print may be the result.
Furthermore, if hot printing inks with the
specified components and in the specified mixture are
employed for printing at low- and medium-printing speeds,
then such inks are entirely satisfactory in their quality
for the eyes of the expert, provided that they are printed
on paper and cardboard, but exhibit, however, an
insufficient adhesion or staying on the print material when
printed on non-prelacquered metal foil or metallized foil,
both of which are important in the printing of packaging
materials.
From these deficiencies of DE 42 05 713 C 2 the
basic task of the present invention is deduced, namely to
prepare hot-print inks of the aforementioned type and for
the aforementioned applications, mainly gravure printing,
particularly rotogravure printing for magazine printing and
packaging and especially publication gravure, which however
exhibit an improved and satisfactory wetting behaviour both
towards the chromed surface of the printing cylinder and
metallic substrates as well as an increased and sufficient
adhesive capability when printed on and hardened on
metallic surfaces like aluminum foils or sheets and others.
A solution for this task consists herein, that at
least one out of the following group of materials
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- crystalline, bifunctional alcohols with
appropriate melting points, whose chemical nature
is made clear to the specialist by the mentioning
of 1,6-hexanediol as a typical representative of
this class of materials (melting point (M.P.)
technically 40 - 42~C);
- fatty-acid monoesters of multifunctional
alcohols, as for example glycerinmonostearate,
which is available under the trade mark Edenor
GMS as a trade product of Henkel KGaA (M.P.
technically 59~C), is used as a component of the
first component group. The use of materials
named here as members of the first component
group, alone, in combination with one another, or
in combination with the already known materials
of the first component group - cetyl alcohol,
stearl alcohol, and 12-hydroxy-stearic acid- , in
each case improves the moistening capability and
the adhesive capability on metallic surfaces.
This effect takes place also with the use of the
known polyacrylate as a member of the second
component group.
A further solution of the task of the invention
consists in planning at least one out of the following
group of materials as a component of the second component
group:
- non-crosslinking P(M)A copolymerisates, e.g.
polyacrylic acid-n-butylesters, which are
available under the trade mark Acronal 4F or in
a variation under the trade mark Acronal A 150F
from BASF AG, or for example n-butylmethacrylate-
copolymers, which are obtainable under the trade
mark Degalan LP AL 23 or LP AL 25 from Degussa,
or for example a n-Butylmeth-acrylate-copolymer,
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which can be obtained under the trade mark
Degalan LP 70/01 likewise from Degussa; in
addition, for example the trade product Jagotex~
AP 273 of Ernst Jager GmbH and/or the trade
product Paraloid~ B-44 of Rohm und Haas
Deutschland GmbH (the latter product is viscous
with a viscosity of ca. 1.500 mPas at room
temperature and is used preferably as an
auxiliary component with a relatively small
weight share in the second component group);
- thermoplastic polyamides, e.g. the
trade products Vestamelt~ 640 of Huls
AG and/or e.g. Reammide~ PAS 6 AP or
PAS 5059 of Chemplast SPA Milan and/or
Euremelt 930 or 2096 of Schering AG;
- thermoplastic polyester-polyamide-copolymers, e.g. the trade product Vestamelt~ 4380 of Huls
AG;
- thermoplastic rosin ester, e.g. the trade
products Filtrez~ 895 of Akzo Coatings Inc.,
and/or Burez~ 3099 of Akzo Nobel/EKA Nobel
Division;
- soluble polystyrenes, e.g. the trade products Kristalex~ F85 and/or F100, Piccotex~ 75 and/or
100, Piccolastic~ A75, all products of Hercules
BV.
Here too, the indicated components may be used
every each for its own or in combination with each other or
in combination with the already known hydroxy-
functionalized polyacrylate. The result is also a
distinguished improvement regarding wetting of and adhesive
cling to metallic surfaces.
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It is evident, that the latter approach to the
solution of the innovative task may be combined also with
the first one. I.e. every combination or at least one out
of said compounds of the second component group may be
combined with at least one member or a combination of said
members of the first component group to yield a hot-
printing ink according to the present invention. If such
a combination is not employed, the already disclosed
cetylic alcohol (technical, melting point (M.P. 49~C), but
also 1-octadeconal (technical, M.P. 56~C) and/or 1-
Eicosanol ttechnical, M.P. 63~C) and/or 1-Docosanol
(technical, M.P. 69~C) (trade products Nacol~ 16, Nacol 18,
Nacol 20 and Nacol 22 respectively of CONDEA Chemie GmbH.)
are suitable representatives of the first component group
and are able to fully or partially substitute the cetylic
alcohol.
A further solution consists in planning at least
one out of the following group of materials:
- 2,4,7,9-tetramethyl-5-decin-4,7-diol (M.P.
technically ca. 37 C), available under the trade
mark Surfynol 104 of Air Products and Chemicals
Inc.i
- Butin-2-diol-1,4 (technical, M.P. 55-58~C),
available as an intermediate compound from BASF
AG;
- (4-Oxo-6,7-Epoxi-Heptyl)-Trimethoxy-Silan,
available as Dow Corning~ PA 25, a trade product
of Dow Corning, which is a highly viscous fluid;
as an additive component of a third component group, which
may be optionally introduced into the overall ink-mixture
at a level of 0.5 to 5% by weight as an order of magnitude
and which upon heat withdrawal form the new phase with the
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members of the first and second group in the same way as it
is described above for the combination of the components of
the first and second group, namely to form a solid
solution.
Use of these additional third components can be
made with those me~mbers of the first and second component
group, which are known by the teaching of DE 42 05 713 C2
as well as with the members of the first and second group
disclosed for the first time by the present teaching.
In the interest of a very low ink-viscosity of 5
to 15 mPas, which is typical mainly for today's high-speed
publication gravure printing, a very fluid hot printing
ink, which completely fulfils the dem~n~ of the present
invention is advantageously made by a combination of group
1 and optionally group 3 components with a thermoplastic
hydrocarbon-resin and a thermoplastic rosin ester or a
combination thereof as members of the second component
group. Particularly suitable for this aim are Burez~ 3099,
a rosin ester and Hercures~ A101, a hydrocarbon resin both
with a softening point of 100~C. They are available as
trade products from Akzo Nobel/EKA Nobel Division and
Hercules BV respectively.
As a rule, the me~m~bers of the first as well as
those of the third component group are in a solid state at
ambient temperatures. However, according to this teaching,
they may be even liquid or viscous at a~m~bient temperature
for themselves or may have a melting point below the normal
application temperatures of printed products, as long as
provision can be made, that they will enter into a solid
solution with the members of the second group of components
at a temperature above said range of usual life-
temperatures of printed products.
As a special and surprising advantage of the
21S7~53
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printing inks according to the present invention it was
found, that these inks excel in their de-inkability. This
technical term means the ability of printing inks and
general colorants on paper substrate, to be removed from
these substrates under the conditions of de-inking
procedures prior to recycling of the cellulose fibres.
This property, which is demandatory today for every printed
paper product or cardboard, is fulfilled in a favourable
manner by the present printing inks.
In the following, preferable and appropriate
formulations of hot-printing inks according to the present
invention are given with an improved wetting of chromed
printing cylinder surfaces as well as improved adhesion on
metallic print substrates, such as and especially on non-
lacquered all]mlnl]m foils.
In the listing of these examples, the components
belonging to the first component group are in each case
indicated by K1, the components belonging to the second
component group by K2, and components of a third component
group by K3.
Example 1:
Kristalex F 100 45g K2
Acronol 4F lOg K2
Nacol 18 40g K1
12-hydroxy-stearic acid 5 g K1
Example 2:
Kristalex F 100 30g K2
Degalan LP 70/01 20g K2
Degalan LP AL 23 8g K2
Nacol 20 42g K1
Example 3:
Piccotex 100 45g K2
Nacol 18 48.5g K1
1,6-hexanediol 5.0g K1
Surfyanol 104 1.5g K3
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Example 4:
Vestamelt 640 40g K2
Vestamelt 4380 lOg K2
Edenor GMS 50g K1
An especially good de-inkability for the printing
inks according to the invention can be achieved through the
use of a 4-nonylphenol-polyglycol ether, which is
obtainable under the trade mark Arkopal N-230 of Hoechst AG
and exhibits ca. 23 ethylene oxide units in the polyglycol
ether chain.
In the following, an example of a formulation for
a hot-printing ink with especially good deinkability is
given:
Example 5:
Filtrez 895 30g K2
Kristalex F100 20g K2
Nacol 18 49.5g K1
Arkopel N-230 0.5g K3
The following gives an example of a coloured
printing ink for publication gravure, which prints with a
dynamic viscosity of 7 mPas at 110~C and exhibits improved
wetting properties to chromed printing surfaces for high
speed publication gravure printing:
Example 6:
Burex 3099 25.0g K2
Hercures A 101 20.0g K2
Mannox 280 Iron Blue 4.0 5.0g K3 Colouring Pigment
Nacol 20 49.0g K1
Edenor GMS l.Og K1
In DE 42 05 713 C2 it was suggested, among other
things, that the hot printing inks be capable of being
delivered to the printing machines in the form of rolled
films. Printing practice proves that such a procedure is
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especially advantageous for the realization of a proof
process.
Hot printing inks which exhibit the desired
elasticity and mechanical tensile strength for use in the
form of drawn, cast, or extruded foils can be formulated by
the use of an appropriate P(M)A-copolymerisate, which is to
be obtained under the trade mark Jagotex AP 578 of Ernst
Jager GmBH & Co. OHG.
Additionally, softening agents for acrylate
systems can be put in which have a synergistic effect
toward that purpose. Appropriate, are commercial
polyesters of adipic acid and butandiol, in particular
Palamoll~ 654 of BASF AG.
Hot printing inks with especial suitability for
the form of mechanically stressed foils are made by the
following prescriptions:
Example 7:
Jagotex AP 578 45g K2
Acronal 150 F 15g K2
Edenor GMS 35g K1
12-hydroxy-stearic acid 5g K1
Example 8:
Jagotex AP 578 50g K2
Acronal 150 F 15g K2
Edenor GMS 28g K1
12-hydroxy-stearic acid 5g K1
Palamoll 654 2g K1
The manufacturing of hot printing inks according
to the invention takes place through the heating of the
entire mixture of the components of the formulation to a
temperature above the highest melting point of the first
component group, and furthermore above the highest solution
temperature of the binding medium components of the second
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component group in the melt of the first binding medium
components. This solution temperature typically amounts to
ca. 100 to 110~C for the mixtures given as examples.
If the intention is to prepare a coloured
printing ink - a black ink included -, at least one colour
rendering component is added, be it a soluble dye or an
insoluble pigment.
The melted solution of first and second (and
third if applicable) components is then homogenized or
dispersed by the conventional methods.
When manufacturing a hot-print ink, the molten
homogeneous system or the molten dispersion may be cast
into molds before solidification, or, alternatively,
extruded or cast as thin film to a width fitting the
standard width of printing machines. The cast bodies
coming out off the casting molds may be used as a
practicable delivery form as well as granulates or powders
or flakes, which are made therefrom or from a cast layer.
The thin films, which are manufactured as an
alternative application form are rolled onto rollers and
delivered to the printing machine for further processing at
the printers site.
Hot printing inks belonging to this type
distinguish themselves by the fact that the thermoplastic
binders of the second component group separate themselves
out of the melt of the first component group upon a slight
lowering of the temperature below the solution temperature
and during this process bind the components of the first
group (and if applicable also the components of the third
group) as a so-called solid solution.
This typical behaviour, which generates a new
21~7~ ~33
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solid glassy phase during cooling down to temperatures
still far above the melting point of the first component
group, allows for the fact, that compounds and additives be
chosen as individuals of the first and third group of
components, which by themselves are fluid or viscous at
normal ambient temperatures or which may have a melting
point, which ranges below the usual life temperatures of
printed products. The solid solutions which appear in the
course of cooling down the molten solutions are amorphous
and typically have softening intervals in the range of 60
to 80~C. This holds true especially for the examples given
herein. This temperature range makes it possible to safely
handle the printed products without danger of the ink
becoming soft, whenever the products be exposed to extreme
temperatures, which rarely may occur during the normal
lifetime of a print.
The above mentioned, relatively high
resolidification temperatures of said hot-printing inks,
which congeal as solid solutions and the low heat content
of the thin printed ink layers are both responsible for an
extremely fast resolidification of the printed ink
immediately after transfer to the running web of a rotary
printing unit or to the sheets of a sheet-fed printing
machine.
Due to the fact, that the thermal mass of the
unit area of web is large compared to the thermal mass of
hot-print ink, which is printed on this unit area and due
to the short time of contact (impression-time) between the
web and the printing cylinder, the temperature equilibrium
between the running web and the printing cylinder is never
reached. Thus, the web acts as a very effective heat sink
with a high cooling capacity for the freshly printed ink
and speeds up its immediate solidification. The web itself
is scarcely warmed when running past the print cylinders.
21574 S~
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Technically, this stands in particularly
advantageous contrast with printing methods practiced with
printing ink containing solvents, especially for gravure
and flexographic printing, with which the drying comes
about through heated jets with considerable heating of the
running print-substrate, whose temperature may easily reach
80~C. By this heating changes of the dimensions of the
running print-substrate come into play, which in the case
of polymeric films are due to their stretchability and the
influence of temperature thereon. In the case of paper-
web, besides the latter effect, the dimensional changes are
caused also by a loss of moisture of the web. If the usual
four colours shall be printed by passing the web through
four consecutive printing units, these remarkable
elongations and shrinking effects of both the length and
width of the printing substrate make it necessary to use a
complex control of the register and the print position as
well. In the case of printing on paper-web, measures have
to be taken to remoisture the web through vapour-nozzles.
By this, the dimensional changes are compensated and other
print-deficiencies, which are equally due to the lack of
moisture of the paper may be eliminated.
With the use of hot printing inks, such
dimensional changes of the substrate are of less concern as
is the loss of moisture in a paper-web. The reasons have
been explained above: The short dwell-time of the web or
substrate in the printing nip does not allow for the
establishment of a temperature-equilibrium between the
printing cylinder and the web. Thus, the register and
print alignment can be handled with much lower efforts.
A plot of the temperature-viscosity path, which
is followed by a hot print ink during preparation and
melting resolidification of the finished ink is displayed
schematically for the formulation #2 above in the diagram
enclosed herewith. The initial hysteresis of the path is
- 17 - 21~7~3
typical for the formation and resolidification of the solid
solution, which is essentially responsible for the
advantages of this new ink-system regarding print
technology.
The diagram displays the plot of the dynamic
viscosity (mPas) versus temperature (~C) of formulation #2
as an example of a mixture according to the present
invention.
Region 1 is the domain of a conglomerate
consisting of a component group, namely Degalan, and a
component of the first group, namely Nacol 20. As
indicated by the arrows, this initial conglomerate is
heated. Of course, the viscosity displayed for this
mixture is not a real homogeneous property, because as long
as the state of the dry mixture prevails and even at the
softening temperature of Degalan at 60~C and at the melting
point of Nacol 20 at 63~C the mixture is not a homogeneous
phase.
This inhomogenity still holds on in the branch 2
of the diagram, but viscosity comes down very steeply by
the melting of the component of the first group, Nacol 20.
The component of the second group, Degalan, continues to
soften up to a temperature of 80~C, where the second
component completely disappears to form a homogeneous
solution in the molten first component.
Branch 3 displays the domain of the homogeneous
fusion of both components with a very low viscosity as a
function of still growing temperature. The temperature of
the molten solution is to be increased up to about 110~C,
where a viscosity of about 5 to 10 mPas is typically
reached. This viscosity is low enough for publication
graw re printing. Hence, 110~C in this case could be the
printing temperature for publication gravure, whereas
2157~53
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temperatures even lower than this may be enough to reach
viscosities, which range slightly higher up to 15 to 25
mPas and thus are suitable for general gravure and
rotogravure printing.
Cooling down the fused solution means, that
branch 3 is followed backwards down to the solution
temperature of 80~C, where the molten solution is turned
into a solid solution of the first component (Nacol 20) in
the second component (Degalan). When temperature slightly
falls short this point, viscosity comes up with a very
steep slope and behaves reversible upon variation of
temperature within a relatively narrow range of
fluidization or solidification. Solidification is complete
at a temperature slightly below 80~C and thus well above
the typical life-temperatures of printed products.
Of course, this temperature should not be
surpassed for a printed product, so that during its
lifetime the reversibility of the fluidization and
solidification along the branches 3 and 4 of the diagram is
of no concern.
