Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVEI~TIO~
The present invention relates to a composition for deve-
loping reproduction layers. More specifically, the pre-
sent invention relates to a method of developing printing
plates and similar elements. More particularly, the
invention relates to aqueous alkaline developing compo-
sitions suitable for use with such elements.
The art of lithographic printing depends upon the immi-
scibility of grease and water, upon the preferential re-
tention of a greasy image-forming substance by an image
area, and upon the similar retention of an aqueous dam-
pening fluid by a non-image area. When a greasy image is
imprinted upon a suitable surface and the entire surface
is then moistened with an aqueous solution, the image
area will repel the water and the non-image area will
retain the water. Upon subsequent application of greasy
ink, the image portion retains ink whereas the moistened
non-image area repels it. The ink on the image area is
then transferred to the surface of a material on which
the image is to be reproduced, such as paper, cloth and
the like, via an intermediary, a so called offset or
blanket cylinder, which is necessary to prevent mirror-
image printing.
The most common type of lithographic plate to which the
present invention is directed has a coating of a light-
sensitive substance that is adherent to an aluminum base
sheetO Depending upon the nature of the photosensitive
coating employed, the treated plate may be -utilized to
3~
reproduce directly the image to which it is exposed, in
which case it is termed a positive-acting plate, or to
produce an image complementary to the one to which it is
exposed, in which case it is termed a negative-acting
plate. In either case the image area of the developed
plate is oleophilic and the non image is hydrophilic.
In the case of a negative plate that is exposed to light
through a negative transparency, the light sensitive
material, commonly a diazo compound, is caused to harden
and thereby become insoluble in a desensitizing solution
applied to the plates after light exposure for the pur-
pose of removing that part of the light sensitive coating
which, because it was protected i-rom the light by the
negative, was not light hardened. The light hardened sur-
face of a negative plate will be the oleophilic surface
compatible with the greasy ink and is called the "image-
area". The surface from which the non-hardened light sen-
sitive material has been removed by a desensitizer will
be, or can be, converted to a hydrophilic surface having
lit~le affinity for the greasy ink and is called the
"non-image" area. t
The present invention provides a developer for negative-
working lithographic printing plates.
Most developing compositions for negative-working
printing plates disadvantageously contan strong organic
solvents. These are bcth expensive and ecologically not
favoured. ~n recent years certain aqueous alkaline deve-
loping compositions have been developed and employed for
~ ~31~
such purposes. While they are less costly and dangerous
to the environment, they do pose several technical prob-
lems. Specifically, they tend to corrode aluminum, foam
and precipitate when used in developing machinery and
additionally have a relatively slow development speed.
The present invention provides a developing composition
which substantially alleviates these problems.
A developer which comprises components a) to e) of the
present invention is described in Canadian Patent appli-
cation No. 432 42~-5, filed July 14th, 1983, having an
earlier priority date and being not pre-published (com-
pared with the present invention).
_._._.
3~6
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SUMMA~Y OF THE INVENTION
The invention provides an aqueous-alkaline developer for
an irradiated radiation-sensitive negative-working repro-
duction layer, which developer is based on water, an
anionic surfactant, at least one inorganic salt having an
alkaline reaction and at least one alkanoic diacid or a
salt thereof, wherein the developer has a pH of from
about 8 to 12 and comprises
a) 0.05 to 10 % by weight of a sodium, potassium
or lithium sulfate salt of octyl, decyl or
dodecyl alcohol;
b) 0.001 to 5 % by weight of a sodium, lithium
or potassium metasilicate salt;
c) 0.1 to 15 % by weight of a lithium, potassium
or sodium borate salt;
d) 0O01 to 5 % by weight of an alkanoic diacid,
or sodium or potassium salt thereof having
from 2 to 6 carbon atoms;
e) 0.5 to 12 U/o by weight of di- or tri-sodium or
potassium phosphate;
f) 0.02 to 10 % by weight of a substituted or
unsubstituted benzoic acid, or the sodium,
potassium, lithium or ammonium salt thereof;
and
76
g) 0~5 to 5 % by weight of an ethylene glycol
monoether or an ethylene glycol diether,
and the weight ratio of sodium ions to potassium ions in
the developer ranges from 1:1 to 1.4:1.
It is, therefore, an object of the present invention to
provide a negative-working lithographic printing plate
developer which is an aqueous alkaline solution.
It is a further object of the present invention to pro-
vide a negative-working lithographic printing plate which
alleviates the hereinbefore mentioned problems.
These and other objects of the instant invention will be
in part discussed and in part apparent upon consideration
of the detailed description of the preferred embodiment.
7~
DETAILED ~ESCRIPTION OF TH~ PREFERR~D ~MBODIMENT
In the production of a photographic element, a sheet
substrate, preferably aluminum and the alloys thereof
especially those aluminum compositions sui-table for the
manufacture of lithographic printing plates such as Alcoa
3003 and Alcoa 1100 which may or may not have been pre-
treated by standard graining and/or etching and/or ano-
dizing techniques as are well known in the art, may be
coated by spraying, brushing, dipping or other means with
a composition suitable for use as an interlayer for
lithographic plates. Standard metal substrate pretreat-
ments include electrolytically anodizing in sulfuric
and/or phosphoric acids, electrolytically etching in
hydrochloric acid, and chemical or mechanical graining by
well known methods, which are all known to the skilled
worker. Interlayer compositions employable in the prac-
tice of this invention include aqueous solutions of
alkali silicate and polyvinyl phosphonic acid~
Said substrate is then coated by means well known in the
art with a radiation-sensitive (photosensitive) coating
which comprises a negative working diazo photosensitizer
arld may contain suitable colorants, resins, acid stabili-
zers and other art recognized ingredients. AEter drying,
the coated substrate is exposed to ultraviolet radiation
through a photographic mask in a known manner.
The exposed photographic element is then developed to
remove the non-image areas by cleaning with the deve]oper
solution provided in this invention.
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The developer employed is an aqueous based solution which
has an alkaline pH in the range of from about 8 to about
12, more preferably from about 9 to about 11 and most
preferably from about 9.5 to about 10.5
The composition contains a surfactant which is a sodium,
potassium or lithium sulfate salt of octyl, decyl or
dodecyl alcohol and most preferably octyl. These surfac-
tants provide a stable solution at low temperatures. The
surfactant concentration ranges from about 0.05 % to
about 10 % by weight, preferably 0.5 % to 6 % and most
preferably 1.0 % to ~ %. The solution also contains, as a
corrosion inhibiting silicate compound, a metasilicate.
Useful silicates include sodium, potassium or lithium
metasilicate in an amount of from about 0.001 % to about
5.0 % by weight, preferably 0.005 % to 0.5 % and most
preferably 0.01 % to 0.1 %. The composition further con-
tains a borate, preferably a tetraborate or pentaborate
in the form of its lithium, potassium or sodium salt~ The
borate, which aids corrosion resistance and desensitizes
aluminum background areas, is present in an amount
ranging from about 0.1 % to about 15 % by weight, pre-
ferably 0.5 % to 8 % and most preferably 1.0 % to ~ %.
The composition also contains an alkanoic acid having
from 2 to 6 carbon atoms or the salts thereof. These
include oxalic, malonic, succinic, glutaric and adipic
acids or the salts thereof such as the lithium, potassium
or sodium salts thereof. A preferred salt is potassium
oxalate. This ingredient is present in an amount of from
about 0.01 % to about 5 % by weight, preferably from 0.1 %
to ~ % and most preferably from 0.5 % to 3 %. The compo-
~2~
sition further contains a phosphate salt. Such includesodium and potassium phosphate, preferably di- and tri-
potassium and sodium phosphate salts. Such may be present
in an amount of from about 0.5 % to 12 %, preferably
0.75 % to ~ % and most preferably 1.0 % to 4 %. The com-
position also contains a benzoic acid or -the above indi-
cated salts thereof in an amount of from about 0.02 % to
about 10.0 %, more preEerably from 0.2 % to 5.0 %; if the
benzoic acid is substituted its substituents include pre-
ferably alkyl from C1 to Cs, halogeno, amino, hydroxy or
alkoxy from C1 to Cs. The composition further contains an
ethylene glycol mono or diether, preferably having as
ether substituents alkyl from C1 to Cs or unsubstituted
or substituted phenyl, its substituents including espe-
cially the substituents mentioned before; particularly
2-phenoxy-ethanol in an amount of from about 0.5 % to
5.0 %, more preferably from 1.0 % to 3.0 %, which
increases the speed of development, especially of older
plates. The benzoic acid or the salt thereof lowers the
amount of 2-phenoxy-ethanol required for good development
and helps prevent precipitation of the composition at
relatively low tempera~ures. All parts herein are by
weight.
In the preferred embodiment, it is most advantageo~ls that
a ratio exist between the elemental sodium and potassium
within the composition. A most advantageous balance bet-
ween developability and storage stability exists when the
ratio of sodium to potassium ranges Erom about
1.0~ 1, more preferably 1.1-1 .3:1, and most preferably
1.15-1.25-1. This aids storage at temperatures below
7~
lO C by substantially reducing or preventing solution
precipitation.
The following examples illustrate the invention.
Example l
A developer is prepared having the following ingredients.
All parts are anhydrous.
% (WIW)
H2O (deionized) ~7.23
sodium octyl sulfate 2.50
sodium metasilicate0.07
disodium phosphate1.50
trisodium phosphate1.50
potassium oxalate 1.70
potassium tetraborate 1.00
sodium benzoate 2.50
2-phenoxy-ethanol 2.00
The developer is found to have a solid content of 12.77 %
and a pH of 9.8. When corrosion tests are conducted for
300 hours using aluminum a 0.002 % gain in weight is
noted. At -3 C no precipitation or crystal formation is
observed. The solution is then frozen and allowed to re-
turn to room temperature. At room temperature, a clear
solution is observed in which there is no insoluble
material.
- - -
- 13 -
An electrochemically grained and anodized plate is coated
with a light sensitive diazo compound disclosed in US
Patent 3,849,392 and is exposed ~2~0 mJ/cm2) using a
negative test mask. The plate is developed using the com-
position of this example by immersion and light agitation
for 60 seconds. A 21-step Stouffer Step Wedge, which is
part of the test mask is inked and found to give a solid
5 and two ghost steps. Such a result is preferred and
would be expected from a proper developer.
Another plate is likewise developed and after rinsing has
a finishing film applied using the subject developer. A
printing press roll-up test is conducted after 1 week of
storage and was compared to a plate developed with the
same developer but finished with a standard solution COIl-
sisting essentially of tapioca dextrin as the Eilm
former. Both plates had similar roll-up characteristics
with no hint of blinding or toning on the test plate.
Comparison Example Cl
A commercially available developer having a total solids
content of 23 %, of which 12 % is sodium benzoate, is
tested in a similar manner as detailed in Example 1.
After 300 hours, a weight loss of 5.1 % is measured. At
10 C the solution begins to form a precipitate that only
returns into solution at room temperature with agitation.
A plate is processed and only after extensive development
time appears to be desensitized. A solid 7 and seven
ghost steps are realized after inking.
~ ~ L~
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Comparision Example C2
Another commercially available developer having a solid
con~ent of 16 % (> 11 % organics) is tested in similar
manner as described in Example 1. The results of the
corrosion test after 300 hours indicated that 17.2 % of
the aluminum is dissolved. The plate developed with this
developer is seen to be insufficiently desensitized in
the background. A solid 9 and eight ghost steps are
measured.
Examples 2 and 3 and Comparison Examples C3 to C9
The following examples demonstrate the results stemming
from variations made in the inventive product.
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~3~76
- 16 -
Comparison Example C3
This Example repeats Example 1 except that the potassium
oxalate is omitted. The pH is 10.44 and there is no pre-
cipitation at low temperatures. A plate is exposed
(240 mJ/cm2) and developed. Upon inking, the background
appeared to be desensitized but the Step Wedge giv~ a
solid 7 and four ghost steps. Such a result is unaccep-
table and demonstrates the utility of the oxalate.
Comparison Example C4
This Example repeats Example 1 except the potassium
tetraborate is omitted. The pH is 11.25. An exposed plate
is developed and upon inkin~ gives a solid 5 and three
ghost steps. An aging test for corrosion shows after 300
hours that 3.47 ~O is lost due to the inability of the
silicate alone to prevent corrosion. It can be seen that
the tetraborate aids in desensitization and corrosion
inhibition.
Comparison Example C5
This Example repeats Rxample 1 except that the sodium
silicate is omitted. The pH is 10.37. An exposed plate is
developed and upon inking gives results identical to
those obtained when the silicate is present. After 300
hours, the corrosion study indicates that a 3.7 % growth
had occurred due to the continued deposition of salts~
This example clearly demonstrates that the silicate and
8~6
tetraborate should be present together so as to result in
an essentially zero net change in weight gain or loss,
C parison Example C6
This Example uses the mole ratio equivalent amount of di
and tripotassium phosphate as is used for the sodium
salts in Example 1. The results are all the same except
that at ~ C, the developer is crystallized into a solid
mass. Here the sodium to potassium ratio is ~,16 to 1.~.
Example 2
This Example uses the acids and hydroxides in lieu of the
salts to demonstrate an alternative embodiment. The de-
veloper, when tested, is substantially identical with the
developer of Example 1.
Comparison Example C7
A developer similar to that of Example 1 is made except
that 2-phenoxy ethanol is omitted. The developer is ob-
served to be slow in removing the non-image areas of the
plate after exposure with an indication of only partial
development. When the developer is stored at low tempe-
ratures , severe non-reversible precipitation occurs.
Example 3
This Example uses the stoichiometric equivalent amount of
potassium succinate ~or comparison. The results are
:~2L~31~76
- - -
18 -
essentially identical in all respects as those obtained
from the developer containing potassium oxalate.
Comparison Example C8
A developer similar to that of Example 1 is made except
that sodium benzoate is omitted. The developer is
observed to have good development speed but inadequate
background desensitizing capability. Additionally, the
solution at room temperature is not stable since the
2-phenoxy ethanol phases out of solution.
Comparison Example C9
This Example repeats Example 1 except that the sodium
benzoate, sodium salt and 2-phenoxy ethanol are oMitted.
Plates can only be slowly developed, and older plates
cannot be satisfactorily developed.
_ . _ . _, _ .
