Note: Descriptions are shown in the official language in which they were submitted.
~)70876
The invention relates to methods of developing,
gumming, gum etching, dampening during printing, cleaning
during and after printing, and treatment before storage,
of lithographic printing plates, and to compositions therefor
which utilize polyacrylamide polymers and blends thereof in
place of or as an extender for the traditional gum arabic.
The invention also relates to the treated lithographic plates.
Lithographic printing, which is a type of plano-
graphic printing, is a well known and established art. In
general, the process involves printing from a flat plate or
cylinder having substantially no surface relief (hence, the
term "planographic"), and depends upon different properties
of the image and non-image areas of the surface for printa-
bility. In lithography, the image to be reproduced is im-
parted to the plate by any one of several methods well known
to those skilled in the art in such a way that the non-image
areas are rendered hydrophilic while the image areas are
hydrophobic. A widely practiced technique employs a photo-
sensitive coating for this purpose. Following exposure of the
photosensitive coating to imagewise modulated light,
the latent image is developed and a portion of the coating
is removed from the plate. Next, the plate is treated with
a desensitizing solution to render the plate hydrophilic
in the areas from which the photo sensitive coating has
been removed. During the actual printing process, an
aqueous fountain solution is applied to the plate surface.
The fountain solution keeps moist all portions of the
surface not covered by the hydrophobic image. Furthermore,
the fountain solution prevents the plate from scumming,
i.e. it prevents the non-image areas from becoming at least
~ '.
1,,674B-F -1-
~g~70876
partially ink-receptive. The fountain solution may be
formulated to gradually etch the surface of the plate
just enough to keep the lines sharp and prevent rapid wear.
In a conventional system, the fountain solution is applied
S to the plate by one or more rollers. At least one
ink roller coated with an oil-based printing ink
then contacts the entire surface of the plate but deposits
the lithographic ink only on the image area since
the hydrophilic non-image areas repel the ink. Hence, for
each impression made during a run, the lithographic plate
is first dampened with the aqueous fountain solu~ion and
then inked with a lithographic ink. Alternatively, the
fountain solution and at least a portion of the oil-based
ink are applied to the plate simultaneously with a first
roller. In this latter system, other rollers,
usually smaller in diameter than the first, may contact
the plate subsequently to distribute the ink more evenly.
; Finally, the ink image is transferred directly to a paper
sheet or other receptive surface to be printed, or to an
offset blanket of rubber or synthetic material which in
turn transfers the print to the final copy surface.
Gum arabic has long been used in acidic aqueous
solutions in the preparation of lithographic plates. Gum arabic
has been used, for example, in solutions for developing a latent
image; as a desensitizing ingredient in a gumming solution --
sometimes in combination with an etchant, in which case the
solution is referred to as a gum etch -- to make the non-image
areas sharply defined and ink repellent, i.e. hydrophilic
rather than hydrophobic; in a fountain solution, again sometimes
in combination with an etchant, to keep the non-image
17,674B-F -2-
~70876
areas hydrophilic during the press run; as a protective
coating during idle periods on the press or even during
storage for weeks and months; and in plate cleaner formulations.
Gum arabic is a natural product obtained as an
exudate from acacia trees. While the precise structure of
gum arabic i8 not known, the main constituent apparently lies
somewhere between hemi-cellulose and the simple sugars.
Essentially, it is a mixture of calcium, magnesium, and
potassium salts of arabic acid. The average molecular weight
of the polymerized arabic acid is in the range of 200,000 to
270,000.
The disadvantages of gum arabic are well recognized
in the trade and a suitable substitute has long been sought.
As a natural product it is sub~ect to considerable variation
in quality, and it i8 also prone to contain foreign matter of
various kinds so that it must first be purified. The
fountain solutions of gum arabic employed during printing
to maintain the non-printing areas hydrophilic tend to
emulsify the ink. Excessive emulsification weakens the
resolution of the printing, causes scumming of the plate,
and stripping of the ink from the ink rollers. In addition
to the technological shortcomings of gum arabic, the con-
tinued assured availability of an adequate supply of the
product in the United States is in doubt, since nearly all
of the domestic supply is imported from the politically
unstable Middle East. U.S. Department of Commerce data
projects that for 1975, the quantity of gum arabic
imported will be only about one half that imported in
1972, and the unit price has more than doubled in the
same period. Thus, a substitute for gum arabic is
urgently needed.
17,674B-F -3-
- . , .
107V~376
Some of the compositions heretofore proposed as
gum arabic substitutes for the treatment of image-bearing
plates include oxalic acid (U.S. Patent No. 3,489,561),
homopolymers and copolymers of itaconic acid (U.S. Patent
No. 3,507,647), sodium carboxymethylcellulose (U.S. Patent
No. 3,166,421), the copolymer of methyl vinyl ether and
maleic anhydride (ibid.), polyacrylic acid (U.S. Patent
No. 3,211,686) and the sodium and ammonium salts thereof
(Japanese Patent Publication 49-6561 (1974)), alginic acid
and the sodium salt thereof, and polyvinyl alcohol (U.S.
Patent No. 3,607,255). None of these proposed substitutes
",
seem~ to ha~e realized overwhelming commercial acceptance,
at least to this date, as gum arabic continues to be the
composition of choice in industry, notwithstanding all of
its disadvantages.
Recently, alkaline solutions have been proposed and
used with some success as fountain solutions. However, most
contain a considerable proportion of surfactants, have a
tendency to foam, and cause some emulsification of the ink.
Consequently, they are not always suitable.
British Patent 1,055,711 teaches an improved
silver halide diffusion transfer process using a light
sensitive material comprising a silver halide emulsion
layer covered with a water-soluble colloid top layer.
The light sensitive material is exposed, developed, and
only then brought in contact with the metal comprising
the lithographic plate, for transfer of the image to the
plate. Includ~d in the list of colloids taught to be
suitable for use in the top layer are polyacrylamide and
polyacrylic acid. It is also taught that the top layer
1,,674B-F -4-
~C~7~87t;
may contain more than one of the colloids named in the
list. ~owever, the patent contains no suggestion to use
polyacrylamide or polyacrylic acid -- either separately
or together --- to render hydrophilic the non-image area
of the plate once the image has been transferred to the
plate: for that purpose, the patentees use carboxymethyl-
cellulose. Indeed, the patent contemplates the disappearance
of the colloid of the top layer after the transfer is
carried out. Moreover, the patent teaches no preference
for mixtures of polyacrylamide and polyacrylic acid over
the respective compounds employed separately, thereby
suggesting that in the process there described, no particular
advantage is obtained by employing the compounds in ad-
mixture. In contrast, in the hereindescribed processe~
for treating lithographic plates already having an image,
it has been found to be critical to employ an active polymer
component having the proper ratio of both amide and
carboxyl groups as illustrated by the numerous Examples
and Comparative Runs hereinafter set forth. Also, the
average molecular weight of the active polymer component
is critical in the present process.
In addition, the art contains several suggestions
to employ polyacrylic acid-containing or polyacrylamide-
-containing compositions in various ways as more or le~s
permanent components of the lithographic plate itself,
i.e. in compositions which form part of the plate even
before the plate contains an image. For example, Leonard
et al., U.S. Patent No. 3,265,504, apply a permanent
polyacrylamide-containing coating on the entire surface of
~7,674B-F -5-
t~7~876
the plate by contacting the plate with an abrasive poly-
acrylamide-containing slurry while simultaneously mech-
anically brush graining the surface. Dowdall et al., U.S.
Patent No. 3,136,636, employ polyacrylic acid or water
soluble homologs thereof in a stratum between the surface
of the plate and the diazo coating. Similar teachings are
found in several other U.S. Patents such as No. 3,298,852.
In U.S. Patent No. 3,374,094, Wainer et al. describe a
binder for the photosensitive composition for 2 litho
graphic plate, the binder containing any of a number of
hydrophilic colloids, including polyacrylamide. No
attempt has been made, however, so far as the applicants
are aware, to utilize polyacrylamide compositions for the
treatment of lithographic plates already having an image
lS ~latent or developed) thereon, for example, in desensi-
tizing or fountain solutions.
The term "image" includes (1) both the hydrophobic,
oleophilic, ink receptive areas of a lithographic plate
produced, for example, on development on a photolithographic
plate following exposure to actinic light, and also (2) the
latent image produced in the light sensitive coating of such
a photolithographic plate after exposure of the plate to
actinic light but prior to development.
The term "non-image" refers to hydrophilic, oleo-
phobic, water receptive, ink repelling areas of a lithographic
printing plate.
By "image-bearing surface" is meant the entire
surface of the lithographic plate exposed to the paper or the
blanket in the printing process, including both the image and
non-image areas as hereinabove defined.
~7,674B-F -6-
: . . .
'~
~70876
"Scumming" refers to the condition that exists on
the printing plate or results in the printed image when
the water receptive areas of the prin~ing plate become at least
partially ink receptive.
The term "blinding" refers to the condition that
exists on the printing plate or results in the printed image
when the image areas of the printing plate become
at least partially water receptive and are not properly
ink receptive, e.g. the condition that is exhibited when
hydrophilic material from the fountain solution adheres to
the plate image instead of or in addition to the non-image
areas.
"Toning" or "tinting" refers to emulsification
o~ the ink as globule~ in water in the non-image areas which
lS results in ink transfer to the print in non-image areas.
"Desensitization" refers to the depositing in the
non-image areas of an adequate protective film of a
hydrophilic substance to prevent the plate from picking
up ink, in such areas, from the inking roller during
printing, or, during screening tests, from retaining
ink from a sponge or a tissue wiped across the plate
surface.
The term "chromium-anion providing agent" refers
to one or more compounds selected from the group consisting
of chromic acid and the alkali metal- and ammonium- chromates
and bichromates.
It is very difficult if not virtually impossible
to have an aqueous solution of polyacrylamide wherein all of
the carbonyl sites are amide moieties. The term "polyacrylamide"
therefore refers to a polymer comprised of at least 98 percent
7,674B-F _7_
11~70876
-ECH2CH 3--
,c~
H2N ~ O
combining units. Included within the meaning of polyacrylamide
are polymers containing 98 percent of the above combining
units, and up to 2 percent
2lH
MO O
combining units wherein M is a hydrogen, alkali metal, or
ammonium ion.
The terms ~active polymer(s) n and "active polymer-
component(s)" mean in a generic sense any one or more of the
members (a) through (e) of the Markush group further defined.
The term "caxboxyl group(s)" refers to the moiety
-COM wherein M i8 a hydrogen, alkali metal, or ammonium ion.
The term "alcohol," used in reference to the
fountain solutions of the present invention, refers
generically to lower alkyl mono- and polyhydric alcohols and
glycol ethers having a molecular weight of about 170 or less.
By "lower alkyl" is meant having no more than four
consecutive carbon atoms.
The abbreviation "cP" refers to the viscosity unit,
centipoise. Unless otherwise specified and except for the
viscosity measurements relating to characterization of
the hydroxypropyl methylcellulose, all viscosity measure-
ments were made at ambient temperature using a Brookfield
viscometer. Spindle sizes of 1 through 4 were employed
at rotations of from 6 to 60 revolutions per minute,
as appropriate for each particular solution.
7,674B-F -8-
1~70876
It has now been discovered that a highly sat-
isfactory method for treating and composition for rendering
hydrophilic the non-image areas of a lithographic plate
comprises: water and an active polymer component selected
from
la) a polyacrylamide-based polymer wherein
from about 3 to about 70 percent of the
carbonyl sites are carboxyl groups,
and the balance of said sites are amide
moieties;
(b) a physical blend comprised of from about
97 to about 30 weight percent polyacrylamide
and from about 3 to about 70 percent poly-
acrylic acid or an alkali metal or ammonium
salt thereof:
(c) a physical blend comprised of polyacrylamide,
or polyacrylic acid or an alkali metal or
ammonium salt thereof, and at least one
polyacrylamide-based polymer as described
in (a), said polymers being employed
in proportions such that of the total carbonyl
sites present in the blend, from about 3 to
about 70 percent are carboxyl groups and the
balance are amide moieties;
(d) a mixture of any two or more of the fore-
going;
the average molecular weight of each of said polyacrylamide-
-based polymer, polyacrylamide, and polyacrylic acid or salt
thereof being in the range of from about 5000 to about
1,000,000; or
./,674B-F -9-
1070~76
(e) a co-mixture of one or more of the
foregoing with up to about 30 weight
percent hydroxypropyl methylcellulose
based on the total weight of the co-
mixture, said hydroxypropyl methyl-
cellulose being of a type which produces
a 2 weight percent aqueous solution
having a viscosity of from about 1 to
about 100 cP when measured according
to ASTM Method D 2363-72.
By employing various concentrations of the above
described active component in an aqueous solution, and,
optionally, by employing in addition other components,
solutions and/or emulsions are provided for the developlng,
gumming, gum etching, cleaning, storage, and the like,
of lithographic plates. The method consists in applying
the compositions to an image-bearing plate. As a new
article, there is produced a lithographic plate bearing an
image and having a coating containing the recited
active polymer component.
In accordance with the foregoing, the present
invention also resides in an aqueous solution for rendering
hydrophilic, the non-image areas of an image-bearing litho-
graphic printing plate which comprises: water; a phosphate
compound selected from ~1) alkali metal phosphates, ammonium
phosphate, or mixtures thereof, and (2) phosphoric acid;
and the active pol~mer component.
The present invention further resides in a con-
centrated aqueous solution comprising: water; a phosphate
compound selected from (1) alkali metal phosphates,
17,674B-F -10-
1~'70~76
ammonium phosphate, or mixtures thereof, or (2) phosphoric
acid; and the active polymer component, said concentrate,
when diluted with additional water, providing a solution
containing from 0.001 to 30 weight percent of the active
polymer component, which diluted solution is suitable for
rendering hydrophilic the non-image areas of an image-
-bearing lithographic plate.
The present invention further resides in a composi-
tion for developing a latent image on a photolithographic
plate which has been exposed to imagewise modulated light,
of the emulsion type having
(1) a water immiscible phase containing a
solvent for ~electively removing the non-exposed areas
of a negative working photosensitive coating, or the
exposed areas of a positive working photosensitive coating,
without affecting the respective exposed or non-exposed
image areas, and
(2) an aqueous phase containing an agent for
rendering hydrophilic the non-image areas of the plate,
the aqueous phase comprising the active polymer component.
The invention also resides in a composition for
treating lithographic plates, of the emulsion type having
(i) a water immiscible phase for maintaining the
oleophilicity of the image areas of the
plate, containing asphaltum gum or gilsonite
and a solvent therefor, and
~ii) an aqueous phase containing an agent for
maintaining the hydrophilicity of the non-
-image areas of the plate,
the aqueous phase comprising the active polymer component.
17,674B-F -ll-
1~70876
The present invention further resides in an image-
-bearing lithographic printing plate having a coating on the
non-image areas of the plate comprising the active polymer
component.
In the method of this invention, the foregoing
composition is applied to an image-bearing lithographic
plate to render hydrophilic the non-image areas, in aqueous
solutions of different concentrations, optionally in combina-
tion with other components, depending on the particular
function desired. Thus, a very dilute solution, e.g.,
0.001-0.5 weight percent active polymer, can be employed as
a fountain solution, whereas a more concentrated solution,
e.g., 3-30 weight percent active polymer can be employed
where the plate is to be desensitized initially, cleaned~ or
prepared for storage. The method encompasses application
of the solution to a plate manually or by automated means. The
composition is used either in an acid solution, in which
case it may be regarded as a substitute or extender for
gum arabic, in a solution of neutral pH, or in the more
recently developed lithographic plate treatment solutions
of the alkaline type. Aqueous solutions containing the
active polymer can also be employed as one phase of emulsions
for developing a latent image in an exposed photosensitive
coating on a lithographic plate, and for reconditioning a plate
after extended use. Concentrated aqueous solutions
comprising the active polymer component can be readily
stored and/or transported and then diluted with water
when needed for actual use. An image-bearing lithographic
printing plate having at least a partial coating comprising
the active polymer is also regarded as an aspect of this
invention.
17,674B-F -12-
~7~876
The method of the present invention is pre-
ferably practiced using ball grained, brush grained,
or anodized aluminum plates. The invention can also be
practiced, however, using copperized aluminum plates or
S trimetal chromium/copper/aluminum plates, as well as
offset master plates of steel, aluminum, or those having
zinc oxide/resin binder or titanium dioxide/resin binder
surfaces.
A. he Active Polymer
At the heart of all aspects of this invention
is the active polymer component.
The active polymer component may be a polyacryl-
amide-based polymer wherein from about 3 to about 70 percent
of the carbonyl sites are carboxyl groups and the balance
are amide moieties. The particular method by which the
polyacrylamide-based polymer is prepared is not critical.
It may be formed by copolymerization of acrylamide and acrylic
acid, or salts thereof, in proportions and conditions such that
of the carbonyl sites in the resulting copolymer, from about 3
to about 70 percent are carboxyl groups. Alternati~ely,
a suitable polyacrylamide-based polymer may be obtained
by hydrolysis of polyacrylamide. me preparation of
both partially hydrolyzed polyacrylamide and copolymers
of polyacrylic acid and acrylamide are well known
in the art. See, generally, "Acrylamide Polymers,"
Encyclopedia of Polymer Science and Technology, Volume I, pp. t
177ff, Interscience Publishers, N.Y., 1964.
The active polymer component need not be a single
polymeric substance, so long as the number of carboxyl
groups present in the entire active polymer component
17,674B-F -13-
.. ..
107{)~76
constitutes from about 3 to about 70 percent, preferably
about 5-50 percent, and most preferably about 5-25 percent,
of the total carbonyl sites, i.e., of the sum of the
carboxyl groups and amide moieties. Thus, the active
polymer component can be a physical blend of polyacrylamide
and polyacrylic acid, including the alkali metal and
ammonium salts thereof; or a physical blend of polyacrylamide
with a polyacrylamide-based polymer of the type described
in the preceding paragraph; or any other mixture of poly-
acrylamide, polyacrylic acid and the alkali metal and
ammonium salts thereof, and polyacrylamide-based polymers,
so long a~ the required percentage of carbonyl
sites are present as carboxyl groups.
An additional requirement is that each of the poly-
acrylamide, the polyacrylic acid or salt thereof, and the poly-
acrylamide-based polymers employed in the solution must
have an average molecular weight of from about 5000 to
about 1,000,000, preferably about 10,000-500,000, and most
preferably about 25,000-300,000. As a guide to those
practicing this invention, the average molecular weight of
the polymers and the perc~ntage of carbonyl sites as
car~oxyl groups should be considered together: although
the minimum acceptable percentage of carboxyl groups does
not appear to vary significantly with molecular weight,
the maximum percentage of carboxyl groups at which satisfactory
results are obtained generally declines with increasing
molecular weight.
Finally, the active polymer component may be a
co-mixture of any of the polyacrylamide-based polymers or
physical blends hereinabove described, with up to about 30
17,674B-F -14-
1~0876
weight percent hydroxypropyl methylcellulose, preferably
about 10-25 weight percent. In a typical process for the
manufacture of hydroxypropyl methylcellulose, cellulose
is reacted with propylene oxide and methyl chloride in the
presence of sodium hydroxide to obtain hydroxypropyl sub-
stitution on the anhydroglucose units. Hydroxypropyl
methylcellulose is a solid at room temperature, but is known
and commercially available in a variety of types which produce
2 weight percent solutions having viscosities of up to at least
about 75,000 cP when measured at 20C according to ASTM
Method D 2363-72. The type suitable for use herein
produces a 2 weight percent solution having a viscosity
of from about 1 cP to about 100 cP when measured according
to said Method.
B. Solutions Containing the Active Polymer
and ~heir Use
Having thus described the various forms which the
active polymer component may take, solutions containing the
active polymer component formulated to accomplish a particular
function will now be described. It is to be understood, of
course, that while a particular formulation may have another
primary function, such as developing a latent imaqe in an
exposed photosensitive coating, the active polymer component
of such a formulation is employed to render hydrophilic the
non-image areas of an imagebearing plate.
l. Developer Formulation
The active polymers of the present invention can
be used in the aqueous phase of emulsion type formulations
employed to develop a latent image on an exposed photo-
lithographic plate.
17,674B-F -15-
"
. . ; , ~ . ~
1~7~876
In the preparation of a photolithographic plate, a
plate having a photosensitive coating is exposed to imagewise
modulated light. For example, the plate can be exposed to
actinic light through an image-bearing transparency, whereby
light and shadow areas are cast upon the plate. The photo-
sensitive coating may be of a positive working type, wherein
the areas of the coating exposed to light are to be removed
from the plate while the shadowed portions of the coating remain
adhered to the plate. More frequently, a negative working
sensitive coating is employed, wherein the portions of the
coating exposed adhere to the plate and become the oleophilic
areas of the plate. Representative of the negative working
coating are those of the diazo and polyvinyl cinnamate type~.
Regardless of the particular type of photosensitive
coating employed, the plate is treated with a developer solution
after exposure. While a variety of formulations are employed
as developers depending on the particular .ype of photosensitive
coating employed, most comprise an emulsion containing at least
one water immiscible solvent for selectively removing the
photosensitized coating from only those areas of the plate
which are not intended to carry the printing ink. Thus, where
a negative working photosensitive composition is employed,
the solvent removes the shadowed areas of the coating, leaving
intact those areas which were actually exposed to light. Con-
versely, where the plate has a positive working coating, the
developer formulation contains a solvent which removes the
coating from the exposed area, leaving the shadowed areas
intact. A second phase of the developer emulsion comprises
an aqueous solution containing an agent for rendering hydro-
philic the non-image areas of the plate. The active polymers
17,674B-F -16-
1070876
of the present invention can be employed in the aqueous
phase of virtually any of such developer formulations in
lieu of, or in partial substitution for, the agents here-
tofore employed for this purpose, such as gum arabic. Since
the particular constituents employed in various developer
formulations do vary somewhat, however, it is recom-
mended that prior to preparing a large batch employing
the active polymer, the compatibility of the active
polymer with the remaining constituents be confirmed.
When so employed, the active poly~er component comprises
from about 0.1 to about 5 weight percent of the aqueous
phase of the emulsion, and the aqueous phase comprises
from about 5 to about 75 percent of the total emulsion,
by volume.
In addition to the water immiscible selective solvent
and the aqueous phase containing an active polymer as herein-
above described, the developer emulsion may also contain an
agent such as a dye or pigment for rendering easily visible
the oleophilic areas of the plate. Also frequently employed
in developers are agents for enhancing the properties of the
oleophilic areas of the plate, either with respect to dura-
~- bility, oleophilicity, or both. The aqueous solutions of the
present invention are compatible for use with any of these
optional components as well.
The inclusion in the developer of an agent for
rendering hydrophilic the non-image areas is not intended to
supplant use oE a separate so-called "straight gum" or "gum
etch" solution, or substitute, for desensitizing the plate
as hereinafter described. It does, however, provide pro-
tection against plate sensitization caused, for example, by
17,674B-F -17-
1070876
oxidation during the time between the exposure and a subse-
quent desensitizing step.
2. So- Called "Straight Gum'' Solutions
One type of aqueous solution referred to in the
trade as a "gum" or "straight gum" solution consists essentially
of water and a hydxophilic colloid. A widely used straight
gum solution is 14 Baumé (approximately 25%) gum arabic.
Such a solution naturally has a pH of from about 4 to about 5.
This type of solution can be used to desensitize a plate after
the plate has been exposed and developed, or after the plate has
been cleaned with a plate cleaning etch containing no hydro-
philic colloid. It can also be used to treat a plate for
storage.
A solution is now provided according to the
present invention to be used for substantially the same
purpose~ as a conventional straight gum solution, comprising
water and from about 3 to about 30 weight percent an active
polymer. Such a solution is approximately of neutral
pH, but may be slightly acidified with, for example, hydro-
chloric, phosphoric, or sulfuric acid, if desired. A
slightly basic straight gum type solution may be pre-
pared by including an alkali metal or ammonium phosphate.
A straight gum solution of the present invention is
generally characterized by a pH within the range of
from at least about 3 to about 9; similar solutions
having a pH either above or below the stated range are
generally regarded as "gum etch" solutions, hereinafter
described.
The amount of active polymer component employed
in solutions used as a substitute for a straight gum
7,674B-F -18-
,~
~070876
solution depends in part upon the molecular weight of
the polymers employed. Those skilled in the art will
recognize that within the above range of about 3-30 weight
percent, the quantity of a particular active polymer
component employed should be such that the viscosity of
the solution is from about 40-1000 cP, and preferably
from about 50-300 cP, in order to obtain a uniform
film on the plate. Where the active polymer component
employed is among those described above as preferred, i.e.,
with respect to molecular weight, percent carbonyl sites
as carboxyl groups, and the like, a preferred active
polymer concentration range for a solution to be used
in lieu of a conventional straight gum solution is from
about 5 to about 12 weight percent. ThuR, in most
instances, the preferred amount of active polymer com-
ponent employed is leRs than half the amount by weight
of gum arabic formerly used.
3. So-Called "Gum Etch" Solution
Another type of solution, known in the art as a
"gum etch" solution, typically comprises 32 parts by weight of
a straight gum solution, as hereinabove described, per part
of 85% phosphoric acid. Such a solution is employed, for
example, in lieu of a straight gum solution to desensitize a
plate after the plate has been exposed and developed, or to
desensitize a plate after the plate has been cleaned, or
to apply a protective coating prior to storage. The
distinction between a straight gum solution and a gum
etch solution is that the latter can also be used to
clean a scummed plate, in which case the two-step pro-
cedure of cleaning and thereafter regumming can be reduced
to one step.
17,674B-F -19-
. : . ~ . . ;. .
: , .. ,
107~)876
Both acidic and alkaline substitutes for a
conventional gum etch solution are provided by the
present invention. Each comprises from about 3 to
about 30 weight percent active polymer component and
from about 2 to about 4 weight percent (anhydrous basis)
of a compound selected from the group consisting of (1)
alkali metal and ammonium phosphates and mixtures thereof
and (2) phosphoric acid. The acidic gum etch type solution
contains phosphoric acid and is characterized by a pH of from
about 1 to about 3, whereas the alkaline gum etch type solution '
contains at least one alkali metal or ammonium phosphate and
is characterized by a pH of from at least about 9 to about
12.5.
With respect to both the acidic and the alkaline
lS solutions, a solution which has a pH which i9 too neutral
will not etch the plate sufficiently rapidly to be of any
practical use as a cleaning solution, though of course
such a solution can be employed as a straight gum type
solution, i.e., merely to desensitize a plate rather than
to clean or etch the plate. On the other hand, solutions
which are too acidic or too basic etch the plate too
rapidly, so that portions of the image areas of the plate
are destroyed or weakened.
The teachings presented above in describing
the substitute for conventional straight gum solutions
with respect to solution viscosity and preferred con-
centration, are applicable to solutions which are sub-
stitutes for conventional gum etch solutions a~ well. Thus,
a preferred active polymer component is preferably employed
in a concentration of about 5-12 weight percent of the
solution.
17,674B-F -20-
:1~7~876
As a concentrate, an aqueous solution is provided
comprising active polymer component, and phosphoric acid
or alkali metal or ammonium phosphates, in proportions so
that upon dilution with additional water, a solution is
obtained containing said compounds in the amounts hereinabove
described as required for the gum etch type solution of
this invention.
4. Fountain Solutions
Another category of solution require~ in lithographic
printing is a fountain solution. Normally, a plate will have
been desensitized with a straight gum or gum etch type
solution, or a substitute as provided herein, before a press
run is begun. A fountain solution contains water to moisten
the hydrophilic areas of the plate, and just enough selected
additional ingredients to keep the non-image areas of the plate
well defined and hydrophilic throughout the press run. On a
very short press run, water alone is sufficient since the
initially desensitized plate will remain desensitized for
at least a few printing cycles. As a practical matter, how-
ever, fountain solutions also contain, at the minimum, an
agent for maintaining the hydrophilicity of the non-image areas.
Thus, for example, a straight gum solution can be diluted and
used as a fountain solution. Often, a fountain solution
contains in addition phosphoric acid. Hence, an acidic gum
etch type solution can also be diluted to provide a fountain
solution. Where an acid fountain solution having a pH of
from about 3.5 to about 5.5 is employed, a solution regarded
as preferred in the art usually contains a metal nitrate
salt, phosphoric acid, and sometimes a chromium-anion
providing agent.
17,674B-F -21-
1~7~)876
The present invention embraces generally four
types of fountain solutions, grouped according to the pH
of the solution and the nature of the solvent system:
acidic aqueous, alkaline aqueous, acidic water/alcohol,
and alkaline water/alcohol. Each of the four types
comprises, by weight, at least about 97 percent solvent
and from about 0.001 to about 0.5 percent, preferably ! ,
from about 0.0025 to about 0.1 percent, active polymer.
Insufficient active polymer results in inadequate pro-
- tection of the plate during long press runs, while an excess
can result in an inordinate build-up of a glaze on the
rollers.
The solvent comprises at least about 75 volume
percent water. In the case of acidic aqueous and alkaline
aqueous fountain solutions, the solvent consists essentially
of water. ~
It is known in the art, however, that it is some- f
times desirable to include an alcohol in the fountain solution,
particularly when printing on high quality coated stock,
for example, when using a Dahlgren type dampening system.
One advantage of an alcohol is that it changes the wetting
angle so that the fountain solution can be carried from
the fountain reservoir to the plate surface on rollers
of metal, rubber or the like, having no water absorbent
wrapping, such as cloth or paper. The fountain solutions
of this invention having a water/alcohol solvent system
are similar in all respects to the corresponding aqueous
fountain solutions, except that an equal amount, by
volume, of a low molecular weight (about 170 or less)
lower alkyl mono- or polyhydric alcohol or glycol ether is
17,674B-F -22-
- - ~ .,, , ; .
.. ~ . . . .
1~7~876
employed in lieu of up to about 25 volume percent of the
water. Examples of such compounds are isopropanol, propylene
glycol, glycerine, and diethylene glycol ethyl ether.
~epending on the nature and concentration of the active
polymer component and the compound selected for use as a
solvent in lieu of some of the water, those skilled in the
art will recognize that in some instances the water:alcohol
ratio must be greater, i.e., more water, than 75:25 lest
precipitation of the active polymer component occur. Usually,
of course, no more alcohol will be employed than is required
to achieve the performance desired, if for no other reason
than cost. In this respect, an advantage of the acidic
water/alcohol fountain solutions of the present invontion is
that a significantly lower proportion of alcohol is generally
required to achieve a desired performance than in comparable
fountain solutions based on gum arabic.
The acidic fountain solutions of this invention,
regardless whether the solvent system consists of water or
includes an alcohol, may contain, in addition to the active
polymer: a metal nitrate in an amount up to about 0.25
weight percent of the solution, calculated on an anhydrous
basis, preferably from about 0.02 to about 0.15 weight
percent, and most preferably from about 0.04 to about 0.1
weight percent; phosphoric acid in an amount up to about
0.05 weight percent of the solution, preferably from about
0.004 to about 0.03 percent, and most preferably about 0.008
to about 0.018 weight percent; and a chromium-anion providing
agent in an amount up to about 0.02 weight percent of the
solution, calculated on an anhydrous basis, preferably
from about 0.01 to about 0.02 percent. Ammonium bichromate
17,674B-F -23-
1~7~876
is the preferred chromium-anion providing agent. Preferably
the pH of the acidic fountain solutions is maintained
within the range of from about 3.5 to about 5.5.
Metal nitrates suitable for use in the acidic
fountain solutions described herein are those nitrates,
the corresponding hydroxide compound of which, e.g.,
Mg(OH)2, has a solubility product in water at 25C of from
about 10 5 to about 10 35, and preferably about 10 10
to about 10 20. Included by way of example are the nitrates
of magnesium, calcium, cadmium, berylliumt aluminum, tin,
zirconium, nickel, manganese, iron (Fe 2 only), chromium,
copper, and lead. Preferably, the metal has a standard
reduction potential negative with respect to hydrogen.
Magne~ium and zinc nitrates are most preferred. Those
skilled in the art will recognize that where some of the
aforementioned metal nitrates are employed, within the
above limits the concentrations of the various ingredients
and the pH of the solution should be selected so that
precipitation detrimental to the quality of the printed
image or to the smooth operation of the press is avoided.
It has been found that when the acidic fountain
solutions of the present invention are employed, less fountain
solution is required to maintain the proper ink-water balance
than when corresponding solutions of gum arabic are
employed. When an insufficient supply of fountain solution
is provided, the plate will not be moistened sufficiently,
and scumming occurs. When too much moisture is applied,
carryback of the fountain solution occurs on the ink
rollers, which leads to uneven ink distribution on the
rollers and on the plate. Since the use of less fountain
17,674B-F -24-
0876
solution ultimately results in less moisture being
transferred from the plate to the surface being printed,
faster press speeds are possible with fountain solutions
of the present invention than with gum arabic fountain
solutions. Moreover, there is less lint accumulation
on the press rollers resulting in less frequent shut
down for cleaning the press.
Finally, the alkaline fountain solutions employed
herein have a pH of from about 7.5 to about 12, preferably
from about 8.5 to about 10. In addition to the solvent
and the active polymer, the alkaline fountain solutions
contain sufficient alkali metal or ammonium phoqphate or
mixtures thereof to maintain the pH within a preselected
range. Usually, this requires in the solution from
about 0.01 to about 0.06 weight percent of the phosphate
salt. Generally, the greater the quantity of active
polymer employed in the solution, the lower the pH can be
maintained with satisfactory results; however, by em~loying
somewhat lower amounts of active polymer and operating at
somewhat higher pH levels, the press can be restarted with
fewer spoiled impressions following periods of brief shut
down, such as where a correction must be made on one of the
plates on a four color press in the midst of a run.
Since no surfactants of the type which have heretofore caused
foaming in conventional alkaline fountains are required in
the present invention, a preferred alkaline fountain solution
consists essentially of water, the active poIymer component,
and the alkali metal or ammonium phosphate in proportions
set ~orth above.
17,674B-F -25-
11[)70876
!
Concentrates of each of the four types of
fountain solutions are provided for convenient transport
and storage. These concentrates contain appropriate
ingredients in the requisite amounts and proportions
80 that upon dilution of the concentrates with water,
or with water and an alcohol, fountain solutions as described
herein are obtained.
5. Asphaltum ~um Emulsion
When plates are employed in a long press run,
or are reused in several runs of more moderate duration,
the image areas sometimes tend to deteriorate. When this
occurs, the practice in the art has been to treat the plate
with an asphaltum gum emulsion comprised of from about 25
to about 75 percent by volume an aqueous phase, and the
balance (exclusive of emulsion stabilizers) a water
immiscible phase containing asphaltum or other solid tar such
as gilsonite, and a solvent therefor such as turpentine or
a suitable mineral spirit, e.g. naptha. The asphaltum (or
equivalent) enhances the oleophilicity of the image areas
of the plate and the aqueous phase, which includes a
suitable agent for such purpose, simultaneously imparts a
coating to the non-image areas to maintain and/or revitalize
the hydrophilicity of such areas.
An asphaltum gum emulsion prepared according to the
present invention comprises as the aqueous phase of an emulsion
of the type just described, a solution containing from about 3
to about 30 weight percent, preferably about 5-12 percent,
active polymer component, and up to about 4 percent, pre-
ferably about 2 to about 4 percent, phosphoric acid. When
plates are treated with such an emulsion, impressions of
premium quality can once again be obtained from the plates. r
7,674B-F -26-
~76)876
V. Examples and Comparative Runs
The following examples further illustrate the present
invention, and in particular illustrate the use of solutions
containing the hereinabove described polymers, copolymers,
blends and co-mixtures for treating in various ways image-
-bearing lithographic plates. The examples are illustrative
only and are not to be construed so as to limit the scope of
the invention. In the tables, "Example" is abbrevia~ed "Ex.",
"Comparative Run" is abbreviated "C.R.", and all perc~nts
relating to solution concentrations are by weight unless
otherwise specified.
A test procedure, hereinafter referred to as the
"laboratory scumming test," was devised to evaluate the
effectiveness of a composition as a desensitizing or
gumming solution. Generally, if a composition adequately
protects a plate against scumming in such a test, it will,
as a rule, also perform adequately in any other plate
treatment application, e.g., in a developer emulsion, in
an asphaltum gum emulsion, or when diluted as a fountain
solution. In the test, an exposed and developed plate was
treated with the solution being evaluated, inked, rinsed
with water, and examined for scumming, blinding, or
tinting. In particular, brush grained aluminum sheets were
coated with a diazo type photosensitive coating. Although
the solutions of this invention can be employed with any
diazo or other photosensitive coating, the particular diazo
coating employed was formed by applying to the plate a
solution made up by initially admixing two grams of
"Wipe-on Coating Powder" with 56 grams "Negative Wipe-On
Coating Solution", each of which was obtained as an item
17,674B-F -27-
. . .. . . .
~0~70876
of commerce from RBP Chemical Corporation, Milwaukee,
Wisconsin. After the diazo coating had sufficiently dried
in warm air, the plate was exposed to a mercury arc 5 KW
ultraviolet lamp at a distance of 38 inches (about 96.5 cm)
through a 65-screen combination negative with half tone~
and line copy in a vacuum printer. The resulting latent
image was developed and rinsed with water according to
the manufacturer's directions using Sure Dot brand wipe-on
developer, also obtain~d from RBP Chemical Corporation. An
aqueous solution of the substance being evaluated was
applied to at least a section of the wet plate with a paper
tissue. In some runs, two or more substances were applied to
different sections of the plate for simultaneoug evaluation.
me plate was buffed dry and maintained at ambient temper-
ature for a duration of, in some runs one hour and in others
24 hours, 72 hours, 96 hours, or longer as hereinafter
specified. The plate was then dampened with water and
lightly buffed with a moist sponge after which a grease
based ink was applied and evenly distributed over the
plate. Finally, the plate was rinsed wi$h water and
buffed with a wet sponge to remove ink from the non-image
areas. The plate was examined under low power magnification
for evidence of scumming, blinding, or tinting.
Comparison Run 1
A 14 Baume aqueous solution of gum arabic
(equivalent to about 25 weight percent solids) having ;
a pH of 4.7 and a viscosity of about 55 cP was evaluated
using the laboratory scumming test. The non-image area of the
treated plate was of good quality, showing no scumming
after 72 hours.
17,674B-F -28-
.
107~876
Examples 1-3 and Comparison Run 2
Aqueous solutions of a polyacrylamide-based
polymer having an average molecular weight of about 250,000,
obtained by hydrolysis of approximately 10 percent of the
carbonyl sites of a corresponding polyacrylamide polymer,
were prepared and acidified with sulfuric acid as follows:
TABLE I
Percent Poly- Solution Vis-
acrylamide-based cosity, Ambient
Run PolymerTemperature pH
Ex. 1 5 50 cP 4.5
Ex. 2 8.5 235 4.5
Ex. 3 12 880 cP 4.5
C.R. 2 20 15,000 cP 4.5
The solutions of Examples 1-3 were evaluated using the
laboratory scumming test. In each instance, a sharp,
clean image of excellent quality was obtained both on
plates inked after one hour and after 72 hours. No
scumming was observed in either line copy, solids, or
half tones. The plates of Examples 1-3 were judged to
be of even better overall quality than those obtained
in Comparison Run 1 using gum arabic. The solution of
Comparison Run 2 was ~ound to be too viscous to spread uni-
formly over the plate at ambient temperature.
Example 4
A 26 percent aqueous solution of a polyacrylamide-
-based polymer obtained by copolymerization of equal parts
acrylamide and acrylic acid and having an average molecular
weight of about 25,000 was prepared and the p~ adjusted to
4.3 with sulfuric acid. The visco~ity of the solution was '
:'
17,674B-F -29-
1~70~376
measured as 120 cP. No scumming was observed in the lab-
oratory scumming test when the plate was inked after 72 hours.
Comparison Runs 3 and 4
In Comparison Run 3, a 15 percent aqueous solution
of polyacrylamide (less than 2 percent hydrolysis) having an
average molecular weight of 25,000 was prepared and the pH
adjusted to 4.3. The viscosity of the solution was measured
as 80 cP. Upon evaluation using the laboratory scumming test,
scumming was observed when the plate was inked a~ter 72
hours. Similarly, in Comparison Run 4, an 8 percent aqueous
solution of polyacrylamide having an average molecular weight
of about 250,000 was prepared and adjusted to pH 4.5. The
solution had a viscosity of 190 cP, and did not adequately
protect the plate against scumming in the laboratory scumming
test. Comparison Runs 3 and 4 demonstrate that polyacrylamide
alone having substantially no carboxyl groups at the carbonyl
sites is not as effective in a gumming solution as either gum
arabic or the compositions of the invention described herein
and therefore is not commercially acceptable for such use.
Comparison Runs 5 and 6
In Comparison Run 5, a 0.4 percent aqueous solution
having a pH adjusted to 4.5 and a viscosity of 215 cP was
prepared from a polyacrylamide-based polymer having an
average molecular weight somewhat in excess of about 1,000,000
and having carboxyl groups at about 30 percent of the carbonyl
sites. The solution was evaluated using the laboratory
scumming test. One hour after the solution was applied to
the plate, it was found the plate inked readily, but some
scumming was observed. More severe scumming was observed
when a still higher molecular weight (1.5 to 2 x 106) poly-
mer was tested.
17,674B-F -30-
1~70~76
In Comparison Run 6, a series of solutions having a
pH adjusted to about 4 and polymer concentrations ranging
from about 6 to about 25 percent was prepared from poly-
acrylamide and polyacrylamide based polymers having in
each instance, molecular weights less than about 5000. None
of the compositions performed as well as gum arabic in the
laboratory scumming test.
Comparison Runs 5 and 6 demonstrate that solutions
based on polymers having an average molecular weight less
than about 5000 or more than about 1,000,000 are not as
effective as gumming solutions containing similar polymers
having average molecular weights within the above range
and are not suitable for use as gum arabic sub~titutes.
Examples 5 and 6
In Example 5, an 8 percent aqueous solution was pre-
pared from a polyacrylamide based polymer having an average
molecular weight of from about 200,000 to about 250,000,
and acidified to a pH of about 4.5 with sulfuric acid.
The polymer had been prepared by copolymerization of
acrylamide and acrylic acid using proportions such that about
10 percent of the carbonyl sites in the copolymer were
carboxyl groups.
I~ Example 6, a similar solution was prepared from
`~ a polyacrylamide based polymer having an average molecular
weight of 250,000, and approximately the same proportion
of amide:carboxyl groups as in Example 5. The polymer in
Example 6, however, was obtained not by copolymerization,
but rather by hydrolysis of polyacrylamide.
Each solution was applied to two plates, according
to the laboratory scumming test procedure. One pair
17 ! 674B-F -31-
.. . . .
~C~7~ 76
of plates was inked after one hour, and the other was
inked after 96 hours. None of the plates showed any
scumming, thereby demonstrating that the method used
to provide carboxyl groups in the active polymer component
is not critical.
Comparison Run 7
A solution was prepared as described in Examples
5 and 6, except that in lieu of the polyacrylamide-based
polymer there was used unhydrolyzed polyacrylamide similar
to that which had been hydrolyzed to produce the polym~r
used in Example 6. The solution proved unsatisfactory
in the laboratory scumming test.
Examples 7-11 and Comparison Run 8
Example 7 shows the use of a solution containing
27 weight percent polyacrylamide-based polymer having
an average molecular weight of 25,000 obtained by
copolymerization of equal parts acrylic acid and acrylamide.
The pH of the solution was 4.5, and the viscosity was
65 cP. Aliquots of the solution of Example 7 were used
as "Solution B" in preparing the various physical blends
of Examples 8-11 as set forth in Table II. Used as "Solution
A" for Examples 8-11 were aliquots of the solution used in
Comparison Run 8, which is of substantially the same composition
as the solution described hereinabove in Comparison Run 4,
i.e., polyacrylamide having less than 2 percent hydrolysis.
17,674B-F -32-
10~0876
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17, 674B--F --33--
1070876
Plates were treated with each of the solutions described
in Table II according to the laboratory scumming test
procedure. When inked after seven days at ambient temperature
and humidity, the plates of Examples 7-11 showed no scumming,
while that of Comparison Run 8 showed severe scumming.
Example 12
Another blend comparable to that described in
Examples 8-11 was successfully employed in the same manner.
The blend contained 4 weight percent each of polyacrylamide
and partially (10 percent) hydrolyzed polyacrylamide, each
having an average molecular weight of 250,000. Thus, of
the total carbonyl sites in the blend, about 5 percent were
carboxyl groups. Solution viscosity was 120 cP.
Example 13
A 4 percent solution of a polyacrylamide-based
polymer having an average molecular weight of about 750,000
and about 20 percent of the carbonyl sites as carboxyl was
prepared and acidified to pH 4.5. Viscosity of the solution
was about 120 cP. Plates were treated and inked as per the
laboratory scumming test. No scumming was observed on the
plate when inked after 1 and 96 hour intervals. While
certainly usable within the scope of this invention, the
polymer solution was somewhat stringy and is not considered
a perferred embodiment.
Examples 14-17
Aqueous solutions each containing approximately
the same weight percent of polyacrylamide hydrolyzed to
various degrees, were prepared and successfully employed
in the laboratory scumming test. The solutions are
summarized ln Table III.
17,674B-F -34-
- , -, .
.~, ..
~1 ~70876
TABLE III
Ex.14 Ex.15 Ex.16Ex.17
Percent Hydrolysis 8.7 14.2 19.5 28.9
Percent Active7 7 7 7.5
Polymer
Solution Viscosity 105 110 115 155
Polymer3Ave.M.Wt. 250 250 250 250
X 10
Bxamples 18-20 and Comparison Runs 9 and 10
The series of Examples and Comparison Runs in-
cluded under this caption relate to the actual use in a
lithographic printing process of solutions coming within
the scope of the present invention. A separate Example
or Comparison Run number has been designated for each
~olution employed. The solutions will be described first,
followed by a description of their application.
The solutions shown in Table IV were prepared
for use as straight gum type solutions. The gum arabic
solution of Comparison Run 9 naturally has a pH of about
4.5. The solutions of Examples 8-20 were adjusted to their
respective hydrogen ion concentrations using sulfuric acid.
` ;,
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~7,674B-F -35-
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17, 674 3-F -36
876
Substitute solutions for conventional gum etch
solutions, designated as Examples 18-GE, l9~GB, and
20-GE respectively were prepared by mixing 32 parts by
weight of the respective gumming solutions of Examples 18,
19, and 20, with one part of 85 weight percent phosphoric acid.
A control gum etch solution, Comparison Run 10, contained 32
- parts of 7 Baumé gum arabic and one part of 85 weight percent
phosphoric acid.
Four different fountain solutions, designated as
Examples 18-F, l9-F, 20-F, and Comparison Run 9-F, were pre-
pared by diluting to one gallon (3.78 liters): 1 fluid
ounce (29.6 ml) of the respective desensitizing solutions of
Examples 18-20 and Comparison Run 9, and 2 fluid ounces
(59.1 ml) of a so-called etch concentrate. The particular
etch concentrate employed was an aqueous solution consisting
of (in addition to water), per liter, 90 grams of zinc
nitrate and 8.5 ml of 85 weight per cent phosphoric acid.
; Having described the solutions employed, the press
runs will now be described.
A series of latent images was established on a com-
mercially available aluminum plate having a presenqitized diazo
coating, by exposing the coating to an ultraviolet light source
through a negative comprised of solids, 120 line screen,
a screen step wedge, and a 40 percent tint scale. The plate
was developed with the recommended chemicals for this commercial
plate. The plate was divided into four parallel sections.
To each of the four sections was applied a different desensi-
tizing solution described above as Examples 18-20 and Com-
parison Run 9. The plate was maintained for 16 hours at ambient
temperature and humidity and was then mounted on a Miehle
7,674B-F -37-
~70876
Favorite litho press for scumming tests. To simulate varying
rates of wear on the plates, paper packing of 0.008 inch,
0.0055 inch, 0.004 inch, and 0.002 inch thicknesses was in-
terposed between the plate and the plate roller in such a
manner that the four sections of the plate which had been
treated with four different desensitizing solutions would
each be subjected to four different printing pressures. Thus,
16 different combinations of plate treatment and pressure
were evaluated simultaneously. The dampening solution con-
sisted only of water in order to provide a rigorous test
for the desensitizing composition. The paper printed upon
was Mountie brand Offset Enamel #70, sold by the Northwest r
Paper Company. The ink employed was Hanco Offset Super Nax
Arid Black BK 4664 Litho manufactured by Handschy Chemical
Company. The test cycle was comprised of 10 cycles of inking
and cleaning the plate with water, followed by the printing
of 100 sheets. A total of 180 test cycles, each of 100
sheets, was run.
Scumming occurred throughout most of the press run
in all of the sections of the plate under the excess pressure
of the 0.008 inch packing, but after 180 test cycles, all the
sections printed under normal press conditions (0.004 inch
packing) were printing cleanly and showed no scumming.
Similarly, substantially no difference was observed in the
performance of the four desensitizing solutions in the
portions of the plate having the 0.002 inch and 0.0055 inch
paper packing. The sections of the plate treated with the
solutions of Examples 18-20 were equivalent or better in
print quality to that treated with the gum arabic solution
of Comparison Run 9.
l7,674B-F -38-
lG70876
The portions of each of the four plate sections
upon which scumming had developed were cleaned with the
respective gum etch type solutions of Examples 18-GE through
20-GE and Comparison Run 10. The scum cleaned off with equal
ease in all sections, and clean, high quality printed images
were once again obtained from the plate, demonstrating that
the active polymers of the present invention can be employed
as a substitute for gum arabic in plate cleaning solutions.
Another test employing some of the same specific
solutions hereinabove described under this caption was per-
formed as follows. Four plates were exposed and developed
in the same manner as described in the preceding press test.
Each plate was desensitized using, in four parallel sections
on the plate, the gum etch type solutions of Examples 18-GE
through 20-GE and Comparison Run 10. The four identically
prepared plates were maintained under ambient conditions for
40 hours and each was then mounted on the press for successive
:
; runs. For each run a different one of the four fountain
solutions of Examples 18-F through 20-F and Comparison
Run 10 was employed. The pressure applied to different
` parts of the plates was again varied using different
thicknesses of paper between the plate roller and the plate
itself as hereinabove described.
On initial inking, the image areas in those portions
of the plates desen~itized with the substitute gum etch
solutions of Examples 18-GE through 20-GE accepted ink
more readily than those portions treated with the gum arabic
counterpart, Comparison Run 10; i.e. there was less initial
blinding with the compositions of the present invention.
With each fountain solution, 5000 sheets were printed at
a press speed of 4000 sheets per hour.
17,674B-F -39-
~070876
With the gum arabic fountain solution, satisfactory
results were obtained in 15 of the 16 parts of the plate.
In that portion of the plate which was desensitized with
the gum ara~ic solution of Comparison 10 and which was
subjected to the highest pressure during the prass run, con-
siderable scumming occurred in the half tones.
The fountain solutions of the Examples performed
in a manner comparable to one another, and each proved
- superior to the gum arabic fountain solution. Less fountain
solution of the Examples was required to maintain the proper
ink~water balance, and cleaner, better quality half tones
were obtained, especially in the high pressure areas, than
with the gum arabic fountain solution.
Example 21
A fountain solution similar to that of Example 18-F
was employed in a press run of 60,000 impression6 on newspaper
stock using a Harris Cottrell 15A web offset press. Prints
of excellent quality were obtained throughout the run. No
foaming of the fountain solution occurred, nor was there any
indication that the ink was emulsified by the fountain
solution. A suitable fountain solution may also obtained by
substituting, for example, an equal amount by volume of
isopropyl alcohol, propylene glycol, glycerine, diethylene
glycol ethyl ether, and the like, for up to about 25 percent
`25 of the water employed in solutions such as those described
in Examples 18-F through 20-F. In particular, a press run
of 60,000 impressions was made on a Harris Cottrell LTZ
printing press using a fountain solution such as Example
18-F except that isopropanol was substituted for about 25
percent of the water.
17,674B-F -40-
~070876
Examples 22-27
Several alkaline concentrate and fountain solutions
were prepared as summarized in Table V. The particular
source of the active polymer component was an 8 percent
aqueous solution of partially hydrolyzed (approximately 10
percent) polyacrylamide having a molecular weight of about
250,000, although any of the polymers, copolymers, and
blends hereinabove described may be used as well. The
fountain solution of Example 26 was successfully employed
in a press run of 300,000 impressions on newspaper stock.
The fountain solutions of Examples 22-25 and 27 can be
employed in a similar manner.
17,674B-F -41-
~0876
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17, 674B-F -42-
1070876
Exampl ~ n Runs 11-14
Solutions containing a blend of hydroxypropyl
methylcellulose ("HPMC" in the table which follows) and par-
tially hydrolyzed (about 10 percent) polyacrylamide having
a molecular weight of about 250,000 were prepared, adjusted
to a pH of 4.5 with sulfuric acid, and evaluated using
the laboratory scumming test. Results are tabulated in
'~ Table VI.
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17,674B-F -43-
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17, 674B-F -44-
1CI37~876
Example 36
Fountain solutions containing hydroxypropyl methyl-
cellulose are prepared in a manner similar to the fountain
solutions described in Examples 18-F through 20-F by
employing solutions such as those of Examples 28-35 in lieu
of the solutions in Examples 18-20. As a specific example,
0.5 ounce (14.8 ml) of a solution such as that of Example
29, except containing 8 percent solids and having a viscosity
of 165 cP, was admixed in 1 gallon (3.785 liters) of water
with 1 fluid ounce (29.6 ml) of an etch concentrate com-
parable to that described in the preparation of Examples
18-F through 20-F, to form a fountain solution which was
used in the printing of excellent quality prints of an
ANPA Faximile Test Sheet on an offset press.
Example 37
Another fountain solution is prepared by dissolving
in 1 liter of water, about 4 milliliters of an "A" solution,
hereinafter described, and about 8 milliliters of a
"B" solution, also hereinafter described, and about
4 milliliters of the solutions of any of Examples 1-17,
18, 19, 20, and 28-35. The ~A" solution comprises 1
liter of water, about 45 grams of ammonium bichromate,
and about 24 ml of 85~ phosphoric acid. The "B" solution
comprises about 120 grams of magnesium or zinc nitrate
dissolved in 1 liter of water.
Example 38
A plate was treated as described in the laboratory
scumming test with a solution such as that of Example 31, except
containing 8 percent total active polymer component and having
a solution viscosity of 165 cP. After storage for one month
17,674B-F -45-
~70876 r
at ambient temperature and humidity, the plate was inked.
No scumming was detected.
Examples 39-42
An "A" solution having a pH of 12.3 was prepared
S by dissolving 7 grams of Na3PO4-12H2O in 100 grams water.
A "B" solution having a pH of 10.65 was prepared by dissolving
6 grams Na3PO4-12H2O in 100 grams of an aqueous solution
initially adjusted to pH 4.5 and containing 6.5 weight
percent partially (about 10%~ hydrolyzed polyacrylamide
having an average molecular weight of about 250,000. Four
alkaline aqueous fountain concentrates were prepared by
combining solutions "A" and "B" in different proportions as
summarized in Table VII.
TABLE VII
Weight Ratio
A/B pH
Ex. 3910/1 12.15
Ex. 4010/3 12.0
Ex. 412/1 11.85
Ex. 421/1 11.6
Sixteen fountain solutions were prepared by diluting 0.5
fluid ounce (14.8 ml), 1 oz (29.6 ml), 2 oz (59.1 ml),
and 3 oz (88.7 ml) of each of the four concentrates to
1 gallon (3.785 liters) with water. The pH of each of
the resulting fountain solutions is shown in Table VIII.
TABLE VIII
Amount of Each Source of
Concentrate ---Concentrate---
Diluted to
One Gallon Ex.39 Ex.40 Ex.41 Ex.42
0.5 oz 11 10.87 10.7 10.58
1 oz 11.35 11.28 11.15 11
2 oz 11.6 11.55 11.45 11.28
3 oz 11.73 11.65 11.55 11.38
17,674B-F -46-
~7~876
Example 43
An alkali solution comparable to that prepared
as described in the preceding set of examples by diluting
one ounce of the concentrate of Example 39 to one gallon
was employed as the fountain solution throughout a press
run of about 300,000 impressions on newspaper stock using
a Harris Cottrel 15A web offset press. Impressions of high
quality were obtained throughout the run, except for a
small quantity of unsatisfactory impressions obtained
immediately after periods of brief shut down which is
normal for alkaline fountain solutions. No significant
foaming of the fountain solution was encounted during the
run.
Comparison Runs 15 and 16
In Example 2 of British Patent 1,055,711, here-
inabove discussed, an approximately 1 weight percent
solution of medium viscosity polyacrylamide was employed
to form the colloid top layer described therein. A 5
percent aqueous solution of the polyacrylamide of the type
employed therein was taught to have a viscosity at 25C
of between 280 and 600 cP.
For Comparison Run 15, a 5 weight percent
aqueous solution of polyacrylamide was prepared, which
had a viscosity of 3 55 cP at ambient temperature. The
pH of the solution was 7.19. For Comparison Run 16,
a portion of the solution of Comparison Run 15 was diluted
with water to obtain a 1 weight percent solution. The
latter had a viscosity of 15 cP and a pH of 7.15.
Two substantially identical image-bearing plates
were treated according to the laboratory scumming test
17,674B-F -47-
1~70876
procedure with the respective compositions of Comparison
Runs 15 and 16. To assure that any scumming which might
be observed with the Comparison compositions could not
be attributed to defects in the plates or other extraneous
S factors, a third substantially identical image-bearing
plate was treated with a composition which was substantially
that of Example 6, i.e., an 8 weight percent solution of
a polyacrylamide-based polymer having a carboxyl group
at approximately 10 percent of the carbonyl sites. When
inked 24 hours later, the plate treated with the 5 percent
solution of Comparison Run 15 showed severe scumming,
and that treated with the 1 percent solution of Comparison
Run 16 was much worse still. That plate treated according
to the present invention showed no evidence of scumming
whatsoever.
Although the solution employed according to the
present invention happened to be an 8 percent solution
whereas those employed in the Comparison Runs were but 5
and 1 percent, that alone does not account for the
remarkable difference in performance since as is
described in Example 13, no scumming was observed, even
after 96 hours, when a plate was treated with a 4 percent
solution according to the present invention.
17,674B-F -48-
