Note: Descriptions are shown in the official language in which they were submitted.
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LATEX POLYMER BASED PRINTING INI~
Field of the Invention
The invention relates to latex polymer based printing ink.
Description of Related Art
In an attempt to eliminate volatile organic compounds (VOCs) in the pressroom,
water-based
alternatives are being sought for ink formulations. Water-based printing inks
for use in flexographic
printing processes are known in the prior art. This type of printing process
utilizes printing plates
wherein the printing images stand up in relief, i.e. the areas to be printed
are raised above the non-
printing areas. Printing by the flexographic process requires relatively low
pressure while sufficient
pressure is applied to transfer the ink from the face of the image carrier to
the surface of the substrate.
Examples of useful water-based flexographic printing inks are disclosed in U.
S. Patent No. 4,173,554
and The Printing Ink Manual, edited by R.H. Leach and R.J. Pierce, pages 571-
576, 5th edition,
(Blueprint, 1993).
Water-based inks for gravure printing are also well known. In the gravure
process, the printing
image is engraved into a cylinder in the form of cells which become filled
with ink. Printing is
achieved by passing the substrate between the gravure cylinder and impression
roller under pressure.
Examples of useful water-based gravure printing inks are disclosed in U.S.
Patent Nos. 4,954,556
and 5,098,478.
The offset lithographic printing process presents a unique challenge to ink
formulators since
such process utilizes a planographic printing plate, i.e. the image and non-
image areas are in the same
plane on the image carrier, and two fluids are concurrently utilized.
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It is fairly simple to define an image area by raising it above the background
as in the case of
the tlexographic printing plate or lowering it as in the case of the gravure
printing plate; avoidance of
ink adhering to the non-image area is not too difficult to achieve. However,
when all areas are on the
same level, techniques must be utilized to insure that ink adheres only to the
image area, and not to
the non-image area.
In conventional offset lithographic printing processes, the plate is damped
before it is inked
with an oil-based ink. Typically, the damping process utilizes a fountain
solution such as those
described in US patents 3,877,372, 4,278,467 and 4,854,969. Water will form a
film on the
hydrophilic areas (i.e. the non-image areas) of the printing plate, but will
contract into tiny droplets
on the oleophilic areas (i.e. the image areas). When an inked roller
containing the oil-based ink is
passed over the damped plate, it will be unable to ink the areas covered by
the water film (the non-
image areas), but will emulsify the droplets on the water-repellant areas (the
image areas) and these
will ink up. Such process is called offset lithography because the inked image
on the plate does not
directly print onto the paper substrate, but is first "offset" onto a rubber
blanket, and transferred
therefrom onto the paper substrate.
As mentioned above, conventional offset lithographic printing processes
entails the use of oil-
based inks and water-based fountain solutions. The ink/water balance is
critical and is quite
demanding of the pressman's skills. This issue is one of the several
disadvantages associated with
such printing processes as compared to flexographic and gravure printing
processes. Moreover, the
oil-based inks and aqueous fountain solutions typically employed in
conventional offset lithographic
printing processes contain fairly high levels of undesirable volatile organic
compounds ("VOCs").
U.S. Patent 3,356,030 discloses the use of a water-based printing ink in
respect to a method of
planographic printing utilizing a lithographic printing plate whose non-image
areas are coated with a
cured coating of a thermosetting silicone resin. However, the patented method
also entails the use of
a volatile hydrocarbon fountain solution which will coat the non-image areas
and which is re-applied
between successive printings. Of course, the use of a volatile hydrocarbon
fountain solution
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undermines the principal purpose of the water-based ink compositions of the
present invention, i.e.
the avoidance of the use of volatile organic compounds ("VOCs") during the
printing process.
Indeed, the water-based ink compositions of the present invention may be used
for offset lithographic
printing processes without any fountain solution whatsoever.
In the 1980s, a resurgence of interest occurred in respect to "waterless"
lithographic printing
processes. Both positive and negative waterless planographic printing plates
are commercially
available from Toray Industries of Japan. The image area of a waterless
planographic plate is a
photopolymer similar to that employed for the image area of a conventional
plate. However, the non-
image area is coated with a polymer such as a silicone which is ink repelIant.
Further information
about waterless printing plates and processes may be found in U.S. Patents
5,370,906 and 5,417,749.
The waterless printing process solved two issues: VOCs emanating from the
fountain
solutions and control of the inlc/water balance by the pressman. However, the
difference in surface
energy between the image and non-image areas of the conventional offset
lithographic printing plate
is typically 40 dynes/em is dramatically reduced to 20 dynes/cm in the case of
the waterless printing
plate. Therefore the latitude between scumming and poor print density is
considerably narrowed and
the issue of VOCs (emanating from the oil-based ink) still remains in respect
to waterless printing.
German Offenlegungsschrift DE 41 19 348 A1 pertains to a moistureless offset
printing
method and a water-based printing ink. The ink described therein is one which
will adhere to
hydrophilic materials, but not to hydrophobic materials, and contains a dye,
water, 5-50% water-
soluble macromolecular binder and a hygroscopic liquid, preferably a
multihydric alcohol.
U.S. Patent 5,725,646 disclosed an invention eliminating the principal
disadvantages of
conventional offset lithographic printing inks, viz. high levels of VOCs
emanating from the oil-based
ink and the aqueous fountain solution and the difficulty in controlling the
ink/water balance, while
preserving the principal advantage of the conventional lithographic printing
process, i.e. high surface
energy differential between the image and non-image areas of the printing
plate.
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U.S. Patent 5,725,646, teaches a method for making a water based offset
lithographic printing
ink based predominantly on a rosin ester salt (neutralized to be in a pH range
of 7.5-10). Smaller
amounts of aqueous emulsion polymers (0-20%) were also present. That invention
comprised a
water-based printing ink, based predominantly on a rosin ester salt, that is
to be used in offset
lithographic newspaper printing processes without the need for any
accompanying fountain solutions.
While the method described in U.S. Patent No. 5,725,646 is satisfactory up to
a press speed of
1,000 feet per minute, the method is not optimal for higher print speeds. For
faster printing speeds
up to 3,000 feet per minute, the rosin salts do not release the neutralizing
amines fast enough for
drying to occur. Additionally, large quantities of the modified rosin salts
result in unacceptably high
tack for high speed printing. Although a lower tack of the composition can be
obtained by increasing
the emulsion polymer content beyond 20%, an unacceptable drying up on
conventional offset press
ink trains, e.g., typically containing 5 or more transfer rolls, will occur.
An object of the present invention is to provide a fast drying offset
lithographic printing ink
which eliminates the disadvantages of present water based lithographic
printing inks by permitting
fast drying for acceptable high speed printing.
General Description of the Invention
Tt has been found that it is possible to incorporate large amounts of certain
latex polymers and
reduce the use of soluble resins thus obtaining fast drying waterbased offset
inks. These
compositions are stable on conventional ink trains. The general requirement
for these class of latex
polymers seems to be a particle size average of less than .03 micron,
preferably O1. to 0.2 micron.
The invention generally comprises a latex polymer based ink comprising:
(a) water; (b) a latex polymer; (c) pigment; (d) an acid neutralization agent;
and (e) a rewetting agent.
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In another embodiment, a modified rosin polymer may be included. The modified
rosin polymer
may be comprised of: (i) resin soluble in water regardless of the pH of the
water,(ii) resin rosin salts
soluble in water at a pH ranging from about 7.5 to about 10, and (iii) aqueous
emulsions resins.
Detailed Description of the Invention
The printing plates for use with the newspaper printing ink of the present
invention should
be such that the image areas thereof are hydrophilic in nature, while the non-
image areas are
hydrophobic in nature. An example of a suitable printing plate is the
"waterless" Toray type
discussed above. However, the image area of the plate need not contain a
photopolymer. The
image area of the plate may comprise, e.g. a grained aluminum surface which
has no coating
thereon, but is hydrophilic in nature. The non-image area of the plate must,
of course, be
hydrophobic in nature. However, the non-image area may be covered with any
type of
hydrophobic material, provided that such hydrophobic material adheres to the
non-images area of
the plate during the printing process.
The latex polymers employed in the present invention are those of a particle
sign of less than
.03 micron. Preferably, the particle size of the latex polymers is 0.1 to 0.2
micron. Suitable
examples of such latex polymers are urethane latex polymers or acrylic latex
polymers such as an
acrylic latex polymer from S. C. Johnson Joncryl 537.
The pigment may be any of those which are suitable for formulating offset
lithographic
printing inks such as CI Pigment Yellows 1, 3, 4, 5, 12, 13, 14, 17, S5, 65,
73, 83, 97 and 98; CI
Pigment Oranges 13, 16 and 46; CI Pigment Reds 2, 3, 4, 10, 12, 48, 48:1,
48:2, 53, 57:2, 81, 104,
146, 170 and 176; CI Pigment Greens 2, 7 and 36; CI Pigment Blues 1, 15:1,
15:2, 15:3, 15:6, 16, 29,
56 and 61; CI Pigment Violets 3, 23 and 37; CI Pigment Blacks 6 and 7; and CI
Pigment Whites 6, 7,
18 and 26.
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Examples of rewetting agents for water based printing inks are well known in
the art and
may be employed in accordance with the present invention, however, the
preferred rewetting agent is
hydroxyethylethylene urea. Similarly, examples of acid neutralization agents
for use in water based
printing inks are equally well known in the art, however, the preferred acid
neutralization agent is
monoethanolamine.
The modified rosin polymer according to the present invention may be a malefic
modified
rosin esterified with pentaerithrytol. Examples of suitable modified rosin
polymers which are soluble
in the water phase of the ink regardless of the pH of the water phase include:
carboxymethyl-
cellulose, hydroxyethylcellulose, hydroxypropyl-cellulose,
hydroxybutylmethylcellulose, poly(C,-
C~) alkylene oxides, polyethyleneimine, polyvinyl alcohol, polyvinyl acetate,
polyvinylpyrollidone,
polyvinyl-oxazolidone and polyacrylamide polymers.
Preferably, the modified rosin polymers present in the ink are only those
modif ed rosin
polymers which are soluble in the water at pH ranging from about 7.5 to about
10. Suitable examples
of such resin rosin salt binders include methacrylic resins; styrene-acrylic
resins; rosin salts; and
polystyrene- sulfonic acid and their salts. Ammonia or an organic amine such
as monoethanolamine
or N,N-diethanolamine may be added to the water phase in order to adjust the
pH to the preferred
value (a mineral acid or an organic acid such as acetic acid may be used to
adjust the pH to a value in
the range of about 2.5 to about~6.5).
Suitable examples of the modified rosin polymers comprising aqueous emulsions
include
acrylic or vinyl emulsion polymers prepared from monomers selected from the
group consisting of
acrylic acid esters, methacrylic acid esters, acrylic acid esters of
polyhydric alcohols, methyl
methacrylate, styrene, vinyl styrene and vinyl acetate.
In the latex polymer based printing ink of the present invention the water is
present in
amounts of 25 to 60 wt.%; and more preferably 35 to 50 wt.%. The latex polymer
is present in
amounts of 10 to 50 wt.%, and more preferable 15 - 40 wt.%. The pigment is
present in amounts of
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to 25 wt.%. The acid neutralization agent is present in amounts of 0.5 - 2
wt.%. Finally, the
rewetting agent is present in amounts from 0.5 to 10 wt.%. It is also
preferred that when a modified
rosin polymer is used, it be present in amounts of 10 to 70 wt.%; and more
preferably 30 to 60 wt.%;
and most preferably the macromolecular resin binder is a composite having up
to 5 wt.% of a resin
binder soluble in water regardless of the pH of the water; 10 to 70 wt.% of a
resin binder soluble in
water at a pH ranging from 7.5 to 10; and up to 20 wt.% of an aqueous emulsion
resin binder.
If desired, the usual adjuvants such as waxes, anti-foam agents, biocides,
surfactants,
corrosion inhibitors, etc. may be incorporated in the inks of the present
invention. In a preferred
embodiment of the water-based offset lithographic printing ink of the present
invention a non-ionic
surfactant is employed in the amount of up to 5 wt.%. Suitable examples of the
surfactant include
acetylenic glycols, ethoxylated glycols and sorbitan esters.
The latex polymer based printing ink of the present invention are further
illustrated by the
following non-limiting examples in which all parts and percentages are by
weight, unless otherwise
indicated.
Example 1
A black water based offset ink was prepared as follows, and made with the
following
compositions:
Carbon black 40%
Water soluble alkyl 35
Surfynol 420 3
Hydroxyethyl ethylene 20
urea
(75% solids)
Monoethanol amine 2
Total: 100%
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From the above formulation, a water based ink was made as follows:
Black base 50%
Urethane Latex polymer 30%
Modified Rosin polymer 20%
Total: 100%
The latex polymer was a urethane type containing 40% solids and 60% water. The
composition was stable on a conventional ink train on a Heidelberg press and
gave dry prints
comparable to magic oil based inks. In addition, the ink was easily washed off
from the press rollers
with plain tap water.
Example 2
A black water based offset ink was prepared as follows, and made with the
following
compositions:
Carbon black 40%
Water soluble alkyl 35
Surfynol 420 3
Hydroxyethyl ethylene urea 20
(75% solids)
Monoethanol amine 2
Total: 100%
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From the above formulation, a water based ink was made as follows:
Black base SO%
Acrylic Latex polymer 30%
Modified Rosin polymer 20%
Total: 100%
A composition similar to Example 1 was made replacing the urethane latex
polymer with an acrylic
latex polymer from S.C. Johnson Joncryl 537.
The latex polymer was an acrylic type from S.C. Johnson having the trade name
Joncryi S37.
The composition was stable on a conventional ink train on a Heidelberg press
and gave dry prints
comparable to magic oil based inks. In addition, the ink was easily washed off
from the press rollers
with plain tap water.
The present invention has been described in detail, including the preferred
embodiments
thereof. However, it will be appreciated that those skilled in the art, upon
consideration of the
present disclosure, may make modifications and/or improvements on the
invention that fall within
the scope and spirit of this invention as set forth in the following claims.
