U.S. patent number 3,627,685 [Application Number 04/853,965] was granted by the patent office on 1971-12-14 for lithographic plate finishers and cleaners.
This patent grant is currently assigned to E. I. du Pont de Nemours and Company. Invention is credited to Frank Man-Kam Lam.
United States Patent |
3,627,685 |
Lam |
December 14, 1971 |
LITHOGRAPHIC PLATE FINISHERS AND CLEANERS
Abstract
This invention relates to the treatment and maintenance of
lithographic printing plates. More specifically, it is concerned
with finishing, cleaning, and dampening lithographic plates with
aqueous solutions containing an alkali metal-polyphosphate and an
inorganic oxidant to render the same more efficient.
Inventors: |
Lam; Frank Man-Kam (East
Brunswick, NJ) |
Assignee: |
E. I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
25317370 |
Appl.
No.: |
04/853,965 |
Filed: |
August 28, 1969 |
Current U.S.
Class: |
510/171; 134/2;
134/42; 252/186.36; 101/463.1; 134/3; 252/186.32; 252/186.44;
430/331 |
Current CPC
Class: |
B41N
3/08 (20130101) |
Current International
Class: |
C11D
7/60 (20060101); B41N 3/08 (20060101); B41N
3/00 (20060101); C11d 007/54 () |
Field of
Search: |
;252/100 ;134/2,3,42
;186/20,22 ;101/149.2 ;202/186 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Weinblatt; Mayer
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A lithographic plate finishing solution having a pH of 1- 5 and
consisting essentially of:
a 1-15 percent of an alkali metal polyphosphate of the formula
XMPO.sub.3 .sup.. YM.sub.2 O.sup.. ZO, where M is Na or K, X is an
integer of 2 to 20, Y is an integer of 1 to 5, and Z is 1 or 0,
b 2- 12 percent of phosphoric acid or citric acid,
c 1- 5 percent by weight of sodium or potassium nitrate,
perchlorate or persulfate, and
d about 95 to about 68 percent of water, the percentages being by
weight and based on the total weight of the composition.
2. A fountain solution consisting of 1 part by volume of the
finisher solution defined in claim 1, diluted with from 1 to 20
parts by volume of water.
Description
FIELD OF THE INVENTION
The efficiency of lithographic printing plates depends upon the
oleophilicity of the printing areas and hydrophilicity of
nonprinting areas. The "gumming" or finishing of lithographic
plates after image development is the standard way to enhance and
maintain the hydrophilicity of the nonprinting areas. Indeed
gumming of plates prior to long press stops and before plate
storage is the general practice to ensure the nonprinting areas
remain hydrophilic. The primary purpose of a fountain solution is
to dampen the plates during printing to maintain nonprinting areas
free of ink. A finishing solution is applied immediately following
development and press stops and plate storage. Accordingly the
efficiency of said solutions depends on the reactivity of the
support material and image with the same.
Various materials e.g., glass, wood, synthetic polyester films and
other suitable rigid or flexible materials have been used as
supports for lithographic compositions. Certain metals,
particularly those of zinc, stainless steel, aluminum, and aluminum
alloys, have been commercially accepted in the planographic
printing industry to support the lithographic element. However, it
is also well known that these metals are somewhat active and
readily oxidized. Therefore it is necessary to treat the surfaces
of such plates to avoid corrosion or oxidation which will cause the
plates to scum on press.
The light-sensitive, image-forming coating may be similar to the
diazo compounds disclosed in Schmidt et al., U.S Pat. No.
3,188,210, the combined diazides and interpolymeric resin type
taught in Neugebauer et al., U.S. Pat. No. 3,180,723 or the
photopolymerizable compositions of assignee's Alles, U.S. Ser. No.
560,889 filed June 27, 1966 abandoned, but photopolymerizable
subject matter first refiled as continuation-in-part application
Ser. No. 690,732, Dec. 15, 1967, U.S.P. 3,458,311, July 29, 1968
and assignee's Fan, U.S. Ser. No. 772,054 filed Oct. 30, 1968 U.S.
Pat. No. 3,558,322, Jan. 26, 1971.
BACKGROUND OF THE INVENTION
Tremendous efforts have been directed toward remedying the inherent
disadvantages characteristic of metal support plates. The various
techniques involved chemical etching, mechanical graining or merely
degreasing the plate and predominantly desensitizing or finishing
with a suitable solution. Due to the difference between zinc and
aluminum in chemical activity, best desensitizing of each metal is
attained by using specific solutions for each metal. In this
instance we are particularly concerned with aluminum and alloys
thereof.
Earlier finishers or desensitizers generally comprised
water-soluble gums such as cellulose gum or gum arabic salts and
various other salts in water. Upon acidification and subsequent
release of acidic groups, the gum substance formed a strongly
adsorbing film with the metal surface. Each component having a
definite purpose when applied separately or combined to cofunction
with the others to provide a water-wettable surface.
The well-known practice of "gumming" does, in fact, modify the
surface of the metal to prevent formation of metallic oxide films
and imparts considerable corrosion resistance thereto, however, not
all of the inherent disadvantages or other difficulties
characteristic of lithography were overcome.
Conventional gums may be deficient and present at least one of a
variety of problems. Said gums may fail to adequately desensitize
the nonimage areas under certain circumstances. They may "blind" or
render the image area hydrophilic thus preventing ink acceptance.
Often such gums are incapable of desensitizing those areas which
have been inadvertently degraded prior to finishing e.g.,
contaminated or oxidized. They may leave too thin or weak a film to
protect the plate from being sensitized by picking up dirt, grease,
ink etc., during normal handling. In a similar manner certain gums
may not protect the plate during storage, and blinding or
deterioration may occur under slightly abnormal conditions. The
tendency for natural gums to coagulate and clog equipment upon
partial evaporation and phase separation limits the use of certain
gums in mechanical systems. The finishing solutions of the present
invention are capable of remedying all of the problems discussed
above.
It is the primary objective of the present invention to provide a
finishing solution which will render the nonprinting areas of a
lithographic plate more water acceptive and grease repellent while
the printing areas remain ink acceptive.
An objective of this invention is to provide a finishing solution
which will render the nonimage areas resistant to atmospheric
corrosion and any deleterious effects normally caused by prolonged
exposure in humid conditions. An objective of this invention is to
provide a gum-free fountain solution by which the hydrophobic
printing area and hydrophilic background areas in lithographic
printing plates are readily maintained.
An objective of this invention is to provide a finishing solution
which, when properly applied, will protect lithographic plates
during long storage.
An objective of this invention is to provide finishing solutions
which, when properly applied, can restore and desensitize
lithographic plates which have been inadvertently oxidized and show
scumming on the press.
An objective of this invention is to provide a finishing solution
which can also profitably be employed as a fountain solution.
SUMMARY OF THE INVENTION
The aqueous finisher-fountain solution for lithographic printing
plates contains an alkali metal polyphosphate, phosphoric or citric
acid, and sodium or potassium nitrate, perchlorate, permanganate,
or persulfate. Said solution should have a pH ranging from 1.0 to
5.0 and is applicable to systems involving manual or mechanical
processing of conventional lithographic elements. The fountain
solutions of this invention may contain additional ingredients to
further facilitate desensitizing of the nonprinting areas.
PREFERRED EMBODIMENTS
As briefly discussed above, any metal support may be used, for
example, aluminum, zinc, stainless steel, etc. Aluminum and
suitable alloys thereof have proven most efficient as conventional
photolithographic plate supports, and accordingly are the preferred
support materials used in practicing this invention. Since the
desired thickness is dependent upon the type of printing press and
the conditions incurred thereon, such support materials may be
obtained commercially, as foils, sheets, or laminates of various
thicknesses ranging from about 0.006-inch to 0.020-inch or more.
Also, said commercial support material may be available with a
treated surface to which an undercoating or the presensitized
lithographic composition may be applied.
A typical composition may be of the type previously discussed or a
photoactivable system such as that disclosed in assignees Chang et
al., U.S. Ser. No. 731,733 now U.S. Pat. No. 3,549,367 or Fan, U.S.
Ser. No. 722,054 now U.S. Pat. No. 3,558,322. Said compositions,
essentially comprising a monomer, photoinitiator, and sensitizer(s)
dispersed in a soluble polymeric binder, are coated on the aluminum
support. When thoroughly dried, the lithographic plates may be
exposed and processed in the conventional manner.
Upon sufficient exposure to high-energy actinic radiation for 20 to
120 seconds ore more through a suitable image-bearing negative, the
exposed areas become hardened and insoluble.
Adequate development may be achieved by gently applying a
conventional aqueous-alkali solution to the just exposed
lithographic composition for 10 to 120 seconds at 65 to 95.degree.
F. and thoroughly washing the same immediately thereafter. Such a
developer may be the type disclosed in assignee's application, Lam
U.S. Ser. No. 801,740 comprising an aqueous solution of an alkali
metal silicate and a water-miscible organic solvent.
The aqueous finishing solutions may contain alkali metal
polyphosphates in amounts from about 1 percent to the limit of
solubility, phosphoric or citric acid in amounts of 1 to 20
percent, and the oxidizing agents in amounts of 1 to 5 percent or
more, although quantities exceeding 5 percent are usually no more
effective, the balance is mainly water, and the percentages are by
weight of the total weight of the solution.
Preferred concentration ranges are 1 to 15 percent of alkali metal
polyphosphates, 2 to 12 percent of the phosphoric or citric acid,
and 1 to 15 percent of sodium or potassium nitrate, perchlorate,
permangate, or persulfate.
Accordingly, the suitable alkali metal polyphosphates are those
having the general formula XMPO.sub.3 .sup.. YM.sub.2 O.sup.. ZO,
wherein M is an alkali metal, preferably those of sodium or
potassium, X is an integer of 2 to 20, Y is an integer of 1 to 5,
and Z is 1 or 0.
Phosphoric and citric acids have been found to be the only two
acids useable in this invention. Preferably, the acids are added in
an amount between 2 to 12 percent or more of the total weight of
the intended volume. Acid concentrations are adjusted within the
prescribed range to avoid reaction beyond that normally required to
adequately form the ink-repellent surface in the nonimage
areas.
Many adjuvants e.g., accelerators, buffers, preservatives wetting
agents etc., may be incorporated in the instant solutions to
slightly alter process activity. However, inorganic oxidizers such
as the sodium or potassium nitrates, perchlorates, permanganates,
persulfates and other suitable salts thereof are preferred. A
particular salt or suitable combination thereof is added in amount
of approximately 2 percent by weight. Since these oxidizers act as
catalysts, their precise concentrations are not critical and can be
varied within the limits given above.
Proper application of the finisher composition of the instant
invention results in desensitization of the background or
nonprinting areas only of an aluminum, aluminum alloy or stainless
steel supported printing plate bearing a conventional lithographic
element. Accordingly the desensitized areas become water-receptive
and resistant to the greasy lithographic ink, as the image areas
remain oleophilic, upon adequate treatment with a solution of the
preferred acid, alkali metal polyphosphate, and inorganic oxidant.
Also the conditioned plates are stable during storage. In a manner
similar to that of any commercially accepted multipurpose process
solution, the preferred solutions herein are readily adaptable to
both manual and mechanical systems.
Sufficient conditioning may be achieved by any conventional manual
method such as gentle application of the finishing-cleaning
solution over the entire plate surface with a cotton pad, sponge,
or squeegee and immediate buffing down to dryness. The solution may
be applied at room temperature.
Conventional mechanical systems may involve subjecting the
processed plate to a gentle to moderate spraying of the solution
followed by squeegee roller treatment and blower drying.
This invention will be further illustrated by examples of processed
photopolymerizable elements finished with the essential
acidic-alkali metal polyphosphate-oxidant solutions and various
modifications disclosed herein. Also said solutions may be applied
to the plates as a fountain solution. However, it is not intended
that the scope of the present invention be limited to the
examples.
EXAMPLE I
Several photopolymer lithographic printing plates were processed in
preparation for comparative-finishing tests with a preferred
solution of the present invention and several conventional gums. A
free-radical photopolymerizable composition similar to that
described in Chang and Fan, Ser. No. 731,733 filed May 24, 1968,
wherein lophine dimers are combined with Michler's ketone
(4,4'bisdimethylaminobenzophenone) was coated on an aluminum plate.
Said composition was thoroughly mixed, and a uniform layer of the
same of about 35 to 50 mg. per dm.sup.2 was coated on a
brush-grained aluminum sheet approximately 12 mil thick.
The photopolymerizable plates were then dried and subjected to
appropriate light exposures of 20 to 50 seconds through a suitable
negative process transparency. Exposures were made on standard
equipment, such as the carbon arc or nuArc "Flip Top" Plate Maker,
Model FT26L to the xenon light source. Several of the exposed
plates were then developed in an aqueous alkali metal silicate
solution such as that taught in Assignee's copending application,
Lam U.S. Ser. No. 801,740, filed Feb. 24, 1969. Upon completion of
development, the image-bearing elements were treated with a
preferred solution or one of several conventional gum finishers
prior to printability tests. The finishers were applied immediately
after development and thorough rinsing by gently swabbing over the
entire plate surface with a sponge. The commercially available
finishers, identified as "A" and "B", essentially comprised gum and
phosphoric acid in combination with various conventional
ingredients. All finishers were applied at room temperature, and
the preferred solution "C" had the following formula:
Components Amount Distilled water 100 ml. Sodium hexametaphosphate
15 g. Sodium nitrate 2 g. Phosphoric acid 2 g. *Octyl phenoxy
polyethoxy ethanol containing 9-10 ethoxy groups (10 percent
solution) and a pH of 2.00. 4 drops * This ingredient is optional
and may be replaced by other similar surfactants.
Shortly thereafter the plates were buffed down to dryness and
stored under various conditions for two weeks. Said conditions were
room temperature, tropical oven and high humidity. Following the
storage period, the plates were mounted on a Heidelberg KOR
single-color offset press for printing with black offset ink. Upon
close examination, of several samples, representative of many
prints obtained therefrom results were as recorded below:
---------------------------------------------------------------------------
TABLE 1
Conditions Finisher A B C
__________________________________________________________________________
Room Clean Clean Clean Temperature Background Background Background
Tropical Oven Clean Heavy Clean (120.degree. F. & 80%
Background Scumming Background Relative Humidity) High Humidity
Slight Severe Clean (85.degree. & 90 percent Scumming Scumming
Background or more Relative Humidity)
As indicated by the table, the plate finished with the preferred
solution (C) yielded prints comparable and, at times, superior to
those obtained from similar plates finished with commercially
accepted gums, A and B. Unlike both gums following the two week
exposure to high humidity and the tropical oven in the instance of
gum B, the preferred solution did not scum. Significant oxidation
was prevented. Accordingly said solution rendered the image-bearing
plate more storable and continuous reproduction of a sharp image in
excess of 2,000 prints was evident of lasting, good
printability.
EXAMPLES II-XIV
A quantity of lithographic printing plates bearing a free-radical
photopolymerizable composition similar to that of Example I was
prepared for printability tests in the manner described in Example
I using various preferred solutions and operable modifications
thereof. The particular formulas and the results obtained therefrom
are recorded as follows:
As disclosed in table 2 below, the above-identified solutions
except that of Example XII, proved readily applicable as finishers
to be employed when practicing this invention. There was no
scumming, and after several thousand prints, the same tones
characteristic of the original were reproduced.
EXAMPLES XV-XVI
Additional solutions comprising essentially the same ingredients,
but of lesser concentrations, as the preferred formulation in
Example I were prepared for use as fountain solutions on a Harris
Intertype Sheet-Fed press. Respective working strength of said
solution, XV and XVI, were 10 and 25 percent of the above-mentioned
preferred solution of Example I. Said press is equipped with a
reservoir having a partially immersed driver-roll so positioned to
transfer fountain solution to the printing roll by means of a
series of contiguously situated rolls. In this instance, processed
photopolymerized litho plates such as that described in Example I
were used with Litho Spark-Dri Black ink. None of the problems
associated with dampening systems were incurred.
The diluted acidic-alkali metal polyphosphate and sodium nitrate
solutions having a small amount of ##SPC1## octyl phenoxy
polyethoxy ethanol therein proved efficient as fountain solutions.
Solutions XV and XVI sufficiently dampened the press roll thereby
maintaining the desired printable plate surface throughout the run.
Printing was suspended for one-half hour and resumed without
treating the plates with additional preferred finisher.
Nevertheless, it was apparent as several thousand scum-free prints
were made, the fountain solution dried down on the plate during the
press stop protected the plate from contamination and oxidation
which usually occur with conventional dampening solution.
EXAMPLE XVII
A number of lithographic printing plates, similar to those of
Example I, were exposed and developed as in Example I with
appropriate developer. Oxidation was intentionally promoted on the
plates by placing on the plates damp paper towels which were
allowed to dry in contact with the plates. Several plates were then
finished with a preferred solution, such as that disclosed in
Example I, or a conventional commercial gum, and prepared for
printability tests in the prescribed manner. Prints obtained from
those plates finished with the finisher of Example I did not show
oxidation scumming, whereas, the other plates showed various
degrees of scumming. This illustrates the ability of solution of
this invention to desensitize oxidized background, thereby
preventing scumming on press.
EXAMPLE XVIII
A stainless steel lithographic plate was cleaned with a
conventional trisodium phosphate cleaning solution, prepared for
coating, and coated as in Example I. After exposure and by
processing, as in Example I, a portion of the plate was treated
with the finisher composition of Example I. The untreated portion
scummed badly, while the treated portion was free of scum when
tested on the Heidelburg press.
In addition to the foregoing examples, the compositions were used
to finish a diazo composition on an aluminum wipe-on plate, as well
as other commercial presensitized lithographic plates on aluminum
supports, including grained and silicated supports. On all such
plates, the advantages of the invention were realized.
When applied in the prescribed manner, the preferred finisher
offers several advantages over those compositions designed for the
same purpose in addition to providing an economic means of
desensitizing the nonprinting areas and rendering the same
hydrophilic.
The preferred finisher-cleaning solution offers an advantage in
that it penetrates or solubilizes any treatment layer or residual
development film to attack the metal surface of the background
areas only. Hence, the efficiency of these solutions is not
appreciably altered by any conventional presensitized lithographic
element or subcoatings thereof. Accordingly finisher activity is
not hindered by any treated stainless steel or treated aluminum
surface, e.g., brushed-grained, silicated, anodized etc., or any
layer applied thereon.
Another advantage is that said solutions are nontoxic and do not
present the potential hazards characteristic of certain
commercially accepted compositions, such as the fluorides or
chromate/dichromate combination.
Another advantage is that these acidic-alkali metal polyphosphates
desensitize areas very well even after oxidation has occurred.
Another advantage provided upon use of said solutions is the
greater resistance to abnormally high humidity and atmospheric
oxidation which permits increased plate storage life.
An additional advantage is the lasting homogeneity of these
solutions. The ingredients of said solutions do not decompose and
remain soluble. Accordingly the preferred solutions do not "scale"
or precipitate and are readily adaptable to use in automatic
processors. These solutions are also immune to bacteriological
deterioration which is a distinct drawback associated with
conventional compositions containing various types of natural
gums.
One part by volume of the finisher solution may be diluted from 1
to 20 parts by volume of water to form a solution.
* * * * *