Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for the Manufacture of Aluminum Supports for Planographic
Printing Plates by Electrochemical Roughening of the Plate Surfaces
The present invention reLates to a process for the electrochemi-
cal roughening of the surfaces of aluminum plates which are to be used
as supporting materials for planographic printing plates.
The use of aluminum supports for planographic printing plates has
generally been accepted and proved to be advantageous.
It is known to subject the surfaces of aluminum supports for
planographic printing plates to a pre-treatment in order to improve the
adhesion of the image-carrying layer and the hydrophilic properties of f
the aluminum support.
Thus, mechanical treatments have been proposed, for example I ~ -
brushing with wire brushes or wet-brushing with abrasives. Recently, I -
electrochemical roughening, followed, if desired, by anodic oxidation,
has increasingly gained importance. Preferably, the roughening process ' -
is continuously operated, i.e. the materials to be roughened are in the
form of webs.
Satisfactory qualities are achieved by mechanical roughening f
processes. Among the known processes, wire brushing yieids a direc-
tionally oriented surface which still has a silvery luster. Brushing with
the aid of graining abrasives and water produces a dull gray surface
which in only exceptional cases shows a directional orientation. By
far the most favorable results are produced by electrochemical roughen-
ing in acid baths. The uniformity of the roughening thus produced is
achieved by no other known method.
As a rule, acid-containing electrolytes are used for roughening.
The rinsing solutions and spent baths resulting from this treatment must
be decontaminated at considerable expense. Handling, storage and
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equipment must be adapted to the corrosive media, which also
causes large costs.
Further, it has been proposed to manufacture foils
for electrolytic condensers by subjecting aluminum surfaces to
an electrochemical treatment with neutral or only slightly cor-
rosive solutions. Being intended for a different purpose,
these foils require surfaces which are quite different from
those of planographic printing plates.
Apart from the use of acids, British Patent No.
467,024, also discloses the use of sodium chloride in an alter-
nating current circuit arrangement for the production of a
surface which is considerably increased by pores and craters.
French Patent No. 1,248,959, discloses a process for
the manufacture of condenser foils by using pulsating direct
current in an anodic arrangement and aqueous solutions of the
chlorides, bromides, iodides or nitrates of sodium, potassium,
magnesium or ammvnium.
According to German Patent No. 1,144,562, a useful
condenser foil of aluminum may be produced by using pulsating
direct current in an anodic circuit arrangement and solutions
of the chlorides, iodides, bromides or chlorates of alkali metals
to which hydrochloric acid is added.
In a process for the manufacture of a condenser foil
disclosed in German Auslegeschrift No. 1,262,721, sodium chlor-
ide is used together with sodium bisulfate in an anodic circuit
arrangement at a low pH value and high temperatures, the desired
pH range being adjusted by the continuous addition of sulfuric
acid.
German Offenlegungsschrift No. 1,496,731, published
July 31, 1969 to Rosenthal and Degenhardt discloses the use of
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halide ions and electric current Eor roughening a condenser
foil.
German Offenlegungsschrift No. 1,496,725, published
September 10, 1970 to Martin, discloses the use of chlorides in
admixture with sulfates and the application of direct
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current in an anodic circuit arrangement, stating, at the same
time, that the most favourable working range is immediately below
the boiling point of the electrolyte.
The object of all these processes was to modify the
aluminum in a manner such that pores of maximum depth were formed
by which a maximum increase of the aluminum surface was produced.
A surface treated in this manner is not very suitable,
however, for use as a support for planographic printing plates.
Too deep, and often irregularly distributed, cavities impede pro-
cessing at all stages.
Normally, a very uniform, directionally non-oriented
roughening of medium depth is desired for planographic printing
plate supports. Above all, it should guarantee a good adhesion
of the light-sensitive layer to be applied thereto and good hydro-
philic properties during the printing process.
On the other hand, however, it is desirable in the
manufacture of planographic printing plate supports to have avail-
able, in addition to surfaces which may be used for many purposes,
also other surfaces which are adapted to special purposes and
which differ from the former surfaces in a characteristic manner,
for example by their depth of roughening, number and size of pores,
distribution of the pore sizes, and other parameters. The demand
for such different types of surfaces is determined by the nature
of the light-sensitive layer, the run to be printed, the printing
technique to be employed, and other factors. So far, it was known
only that for producing surfaces of different types, electrolytes
of different compositions had to be selected. This means that
time-consuming changeover operations were invariably necessary -
when it was desired to successively produce, in one and the same
plant, aluminum webs with different types of roughening.
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It is the object of the present invention to provide
a process for the electrochemical roughening of aluminum surfaces,
which may be operated with as little environmental pollution as
possible and which renders it possible to produce surfaces with
different types of roughening by changing easily variable process
parameters.
The present invention provides a process for the
manufacture of a printing plate that can be processed into a
planographic printing form, which process comprises:
(a) electrochemically roughening one or more surfaces
of a support comprising aluminum in an electrolyte comprising a
neutral aqueous solution of a salt in a concentration of 200 g
per litre to the saturation point, and having a pH of from 5 to
8, the salt, the type of electrolysis current and whether the
support is the anode or cathode being so selected that substan-
tially no insoluble deposits are formed on said surfaces of the
support; and
(b) applying a light-sensitive layer to one or more
roughened surfaces of the support.
"Neutral salt solutions" according to the present
invention are generally those having a pH value between about 5
and 8, preferably from about 6 to 8. On the other hand, devia-
tions from this range by up to one pH unit, especially to the
more acid region, amy at least temporarily occur during operation
of the process without detracting from the advantages thereof.
The inventive process has the advantage that only very
little of the electrolyte used is consumed. Consequently, it has
the further advantage that only very small quantities of spent
electrolyte solutions result to be disposed of, without damage
to the environment. At the pH values preferred for the inventive
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process, the aluminum dissolved during the electrochemical
roughening process precipitates in the form of aluminum hydroxide
or aluminum oxide hydrate and thus may be continuously removed
from the mixture by filtration or centrifuging.
Prior to electrochemical roughening, the aluminum is
normally pickled in the conventional manner with an aqueous-
alkaline solution in order to clean and degrease the surface
thereof.
The usability of the electrolyte solutions employed
according to the present invention is practically unlimited.
Other than in the case of
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acid-containing electrolytes, only those components must be replaced
which are lost by entrainment. This means a considerable rationaliza-
tion in the storage and handling of the chemicals used.
The pH value remains practically unchanged during operation of
the process. It does not deviate from the preferred range around the
neutral point.
Preferred electrolytes are the chlorides and nitrates of alkali
metals. Normally, they are used in concentrations of from about 50 g,
preferably from 200 g per liter, to the saturation poine.
According to one embodiment of the invention, the aluminum is
first degreased with an alkaline pickling solution and then treated for
30 to 60 seconds with direct current between Z,000 and 9,000 C/dm2
(70 - 150 A/dm2) in a cathodic circuit arrangement. A silvery surface
with a dull finish is produced which very much resembles that of a di-
rectionally unoriented, wire-brushed surface ~Type A). The depths of
roughening of the material thus obtained range from about 9 to 12~m.
The good contrast between the support and the light-sensitive layer
applied thereto allows an effective visual control during processing of
the resulting printing plate.
A transition between surfaces of Type A and those of Type B (to
be described hereafter) is obtained by an intermittent cathodic and
anodic treatment. The surfaces thus produced are of a dull gray and
more closely resemble Type B. An almost identical effect is achieved
by subjecting an already roughened surface of Type B to an alkaline
pickling treatment.
When the process described for Type A is applied, using however
direct current in an anodic circuit arrangement, a dull gray, visually
uniform surface is produced which resembles known surfaces produced
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by electrochemical treatment with acid electrolytes (Type B). The depth
of roughening of surfaces of this type may range from about 7 to about
20~4m, depending upon the electrolyte selected, the current density,
and the like.
If alternating current is applied, a more pitted surface results
which does not appear as uniform to the eye but is nevertheless very
suitable for the manufacture of an offset printing plate (Type C). In
this case, the depth of roughening is in the range of about 15 to 20~1~m.
(In all cases, the depth of roughening was measured by means of a
"Perthometer" type S 10 D.)
If a surface of Type A is produced, the cation is the essential
and effective component of the electrolyte. Alkali cations are by far
preferred. Their concentration may range between about 30 grams per ~ -
liter and the saturation point.
In principle, all alkali metal salts may be employed for produc~
ing a surface of type A (cathodic treatment, direct current), because
immediately after discharge of the metal ions at the cathode, a reaction
to the hydroxide takes place with a corresponding attack upon the alumi-
num. The ammonium ion is unsuitable for this application.
Alkaline earth metal salts and aluminum salts are not suitable
for this type of use because they form oxide or hydroxide layers of poor
solubility. The same applies to the salts of heavy metals, e.g. the ni-
trates and chlorides of zinc, iron, nickel, chromium and copper, which
form metal deposits of very poor adhesion with this type of circuit
arrangement.
If surfaces of Type B and Type C are produced, the anion is the
essential component of the electrolyte. Chlorides and nitrates are par-
ticularly suitable for this purpose, but bromides, chlorates and nitrites
also cause a very satisfactory roughening.
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Phosphates form a deposit on the roughened surface and
thus are less suitable. Sulfates and bisulfates lead to anodic
barrier layers without roughening. Sulfites and bisulfites have
the same effect. The addition of this type of ions to other ions
with a strong roughening effect (for example Cl ) may be of ad-
vantage, however, in order to influence conductivity and reactiv-
ity.
The cation may be derived in this case from alkalies,
alkaline earths, aluminum, ammonium or even from heavy metals.
Ammonium salts are particularly useful for increasing
the concentration of the desired anion after the saturation limit
of, e.g., the alkali salt has been reached.
Urea, for example in the form of the chloride or
nitrate, was found suitable as the anion carrier. The inhibiting
action of this compound, which is known from conventional cor-
rosion tests, is not so effective in the electrochemical treat-
ment of aluminum as to prevent roughening. The strongly acidic
solutions of urea salts (pH 0.4 to 0.5) produce an effect which
resembles that of the known roughening by means of acids. If
these solutions have been previously neutralized, i.e. adjusted
to pH values of ahout 5 to 8, they may be successfully used with-
in the scope of the present process.
The salts of organic carboxylic acids, e.g., of acetic
acid, oxalic acid, or citric acid, are unsuitable for use in a
circuit arrangement of this type either because their conductiv-
ity is insufficient, or because they form sparingly soluble
aluminum salts. Nor do the corresponding alkali metal salts pro-
duce any advantages with any circuit arrangement.
The process according to the invention may be applied
to single sheets in a simple trough equipped with the necessary
circulating and current supply devices, or to webs in appropriate-
ly designed continuously
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operating plants. The current transfer in these plants may be
either by contact rollers or by the neutral-wire method.
Suitable apparatuses for performing the process of
the invention are disclosed, for example, in German Offenlegungs-
schriften No. 2,234,424, published January 31, 1974 to Idstein
and No. 2,228,424, published December 20, 1973 to Stroszynski.
Of course, these apparatuses must be provided with
temperature control and adjusting devices. The working range of
the inventive process extends normally from room temperature
(20C) to the boiling point of the solution used. The application
of lower temperatures, even approaching the solidifying point of
the solution, is possible but not recommended in view of the high
cooling costs.
In the case of a cathodic circuit arrangement, a
relatively high reaction temperature within the range stated,
i.e. between about 40 and 80C, preferably between 50 and 60 C,
is normally preferred.
In the case of an anodic arrangement and an alternating
current circuit, temperatures between 20 and 35C are normally
preferred.
In order to facilitate the heat exchange and flow of
material at the aluminum surface, the electrolyte solution is
stirred or circulated by pumping. The velocity of flow is ad-
vantageously maintained between about 0.1 and 5 m/sec., prefer-
ably between 0.8 and 1.5 m/sec. These values refer to a perform-
ance of the inventive process on a technical scale, especially
in a continuous operation treating continuously fed webs of
aluminum. Part of the experiments described in the examples
below were made on a laboratory scale so that the values stated
in the examples may deviate from the optimum values. -
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If the current densities applied fall substantially
below the values stated above and an equivalent current quantity
is achieved by prolonging the reaction time, poorer results are
normally achieved.
Likewise, it is not always advisable to increase the
current density while at the same time shortening the reaction
time. In most cases, this results in a heavy removal of metal
and produces very smooth, almost electropolished surfaces.
The voltage required depends largely on the distance
between the electrodes. For this reason, this distance should be
made as small as possible. In order to guarantee the necessary
exchange of material, distances ranging from about 0.5 to 5 cm,
preferably from 0.6 to 1.5 cm, are preferred. Wider distances
are possible, but require higher voltages. The examples describe
a number of experiments in which test plants were used in which
the distance between the electrodes did not correspond to the
above optimum values.
The surfaces roughened by the process of the invention
may be either directly provided with a light-sensitive layer or
first anodized.
If copying layers based on diazo compounds are used,
non-anodized surfaces of Type A yield 10,000 to 30,000 copies of
good quality and non-anodized surfaces of Types B and C yield
about 50,000 copies. Subsequently anodized plates yield runs
which correspond to a multiple of the above values, the increase
being more conspicuous in the case of Types B and C than in the
case of surfaces of Type A.
Like the roughening process, anodization may be per-
formed in known manner and either individual sheets or endless
webs may be treated. Appropriate apparatuses are described, for
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example, in German Offenlegungsschriften No. 2,420,704, published
December 5, 1974 to Fromson, and No. 1,906,538, published
November 20, 1969 to Suzuki.
The following examples describe the inventive roughen-
ing of aluminum in different electrolytes. In all examples, a
smooth rolled aluminum web with an aluminum content of 99.5 per -
cent was used. Prior to electrochemical roughening, the web was
subjected for 30 seconds, at a temperature of 50 to 60C, to an
alkaline pickling treatment
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in an aqueous solution containing 20 g of NaOH per liter of water. About
3 g of aluminum per square meterwere thus removed.
All percentages are by weight unless otherwise stated.
Example 1
Electrolyte: 220 g of sodium chloride and 150 g of ammonium
chloride per liter of softened water.
Circuit Current Tempe- Time, Appearance
Arrangement Density rature, (secs.)
(A/dm2) ( C)
~ , . .. . .
Anodic 70 25 30 dull dark gray
Cathodic 100 50 60 dull, silvery finish
Alternating 25 60 dull dark gray
current (50 Hz) 70
.
Distance between electrodes: 1 - 2 cm.
Flow velocity of electrolyte: 0.8 - 1 m/sec.
pH value of the solution: 6.5 - 7.5
Alternatively, a solution may be used which contains 200 g of
sodium nitrate and 100 g of ammonium nitrate per liter. In this case,
however, the dull surfaces obtained with an anodic circuit arrangement
and alternating current are of a somewhat lighter shade of gray.
Example 2
Electrolyte: 250 g of potassium chloride per liter of
softened water.
Circuit Current Tempe- Time, Appearance
Arrangement Density rature, (secs.)
(A/dm ) ( o C)
.
Anodic 100 25 30 dull gray
Cathodic 100 50 60 dull finish
Alternating 100 25 30 dull dark gray
current (50 Hz)
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1077433 K-2 4 0 6
Distance between electrodes: 5 cm
Flow velocity of electrolyte: 0.3 - 0.4 m/sec.
pH value of the solution: 6 - 8.
Example 3
Electrolyte: 250 g of magnesium chloride per liter of
softened water.
Circuit Current Temper- Time, Appearance
ArrangementDensit2Y ature, (secs.)
(A/dm ) ( C )
.
Anodic 100 25 30 dull dark gray
Cathodic 100 25 30 no corrosion,
formation of
oxide deposit,
Alternating
current t50 Hz) 100 25 30 dull dark graY
Distance between electrodes: 5 cm
Flow velocity of electrolyte: 0.3 m/sec.
pH value of the solution: 6 - 8.
Calcium chloride and barium chloride behave in a similar manner.
The nitrates of the metals mentioned have the same effect. In this case,
however, the roughening produced with an anodic circuit arrangement
and alternating current is of a lighter gray than when using a magnesium
2 0 salt .
Example 4
Electrolyte: 250 g of sodium chloride per liter of
softened water.
Circuit Current Tempe- Time, Appearance
ArrangementDensity rature, (secs . )
(A/dm~) ( C )
Anodic 70-100 25 30 dull dark gray
Cathodic 150 20 60 dull metallic
finish
Alternating70-100 25 60 dull dark gray
current (50 Hz)
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Distance between electrodes: 1 cm.
Flow velocity of electrolyte: 0.8 m/sec.
pH value of the solution: 6 - 8.
Example 5
Electrolyte: 250 g of sodium nitrate per liter of
softened water.
Circuit Current Tempe- Time, Appearance
ArrangementDensity rature, (secs . )
(A/dm2) ( C)
. :
Anodic 100 25 30 dull gray
Cathodic 150 50 30 dull, metallic
finish
Alternating 100 25 60 dull gray
current (S0 Hz)
,
Distance between electrodes: 5 cm.
Flow velocity of electrolyte: 0.3 m/sec.
pH value of the solution: 6 - 8.
When using an anodic circuit arrangement and alternating current, I -
- a weak oxide deposit is formed which is dissolved away during subse- ;
quent anodization and does not cause any difficulty.
Example_6
Electrolyte: 100 g of sodium chloride and 300 g of
sodium nitrate per liter of softened water.
Circuit Current Tempe- Time, Appearance
ArrangementDensity rature, (secs.)
rA,/dm2 ) ( C )
Anodic 100 30 30 dull light gray
Cathodic 150 60 30 dull silvery
finish
Alternating
current (50 Hz) 100 30 30 dull light gray
. . . ~
Distance between electrodes: 5 cm.
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Flow velocity of electrolyte: 0.3 m/sec.
pH value of the solution: 6 - 8.
Other than in Example 5, the mixed electrolyte used in Example
6 yielded surfaces free from deposits with all types of circuit arrange-
ments .
Example 7
Electrolyte: 220 g of sodium chloride and 50 g of
sodium sulfate per liter of softened water.
Circuit Current Tempe- Time, Appearance
Arrangement Density rature, (secs . )
(A/dm ) (C)
. _ ,
Anodic 80 25 30 dull gray
Cathodic 150 50 60 dull silvery
finish
Alternating
current (50 Hz) lQ0 25 30 dull gray
.
Distance between electrodes: 1 cm.
Flow velocity of electrolyte: 0.8 m/sec.
pH value of the solution: 6 - 8.
The aluminum hydroxide precipitating during operation was con-
tinuously removed from the electrolyte solution by pressure filtration,
2 0 Exa mp le 8
The aluminum foils roughened in accordance with Examples 1 to
7 are anodized in sulfuric acid (130 g per liter). A lead plate serves as
the cathode. Current density 2.5 A/dm2. Temperature 25 C. Reaction
time 3 minutes. Compressed air is used to circulate the bath. After
thorough rinsing with water and drying, the plate may be coated.
Example 9
Roughened and possibly anodized aluminum plates are coated
with a solution containing 2 per cent of the naphthoquinone-(l,2)-
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diazide-(2)-5-sulfonic acid ester of 2,3,4-trihydroxy-benzophen-
one, 5 per cent of novolak, and 0.1 per cent of polyvinyl acetate
in ethylene glycol monoethyl ether.
The novolak used is a neutral phenol resin of the
novolak type with a melting range of about 108 - 118C. The
polyvinyl acetate is a resin with a softening range between 140
and 160C which has a viscosity of 110 to 150 Cp at 20 C as a 20
per cent ethyl acetate solution.
The solution thus applied is dried by means of hot
air. The resulting material may be stored for several months in
the absence of light without suffering any damage. For use it
is exposed under a suitable positive transparency and then devel-
oped with a 3 per cent aqueous solution of trisodium phosphate.
The exposed areas of the layer are dissolved away. After rinsing
with water and wiping with l per cent aqueous phosphoric acid,
the material is inked up with greasy ink. In the case of an off-
set printing form pretreated as in Example 7 and sensitized as
described, about 50,000 copies of good quality may be printed.
A printing form which had been prepared as described
in Example 7 and then anodized as described in Example 8 yielded
about 150,000 copies of good quality after being processed as
described in Example 9.
Alternatively, the plates may be coated and further
processed as described in German Offenlegungsschrift No. 1,447,011
published January 2, 1969 to Schell and Uhlig.
Example 10
A base material which had been roughened as described
in Example 7, using an anodic circuit arrangement and direct
current, is provided with an anodic oxide layer (about 3 g/m2) as
described in Example 8. The resulting material i8 immersed for
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30 seconds at 80C in an aqueous solution containing 1.5 per cent
of polyvinyl phosphonic acid and 0.2 per cent of vinyl phosphonic
acid. After rinsing with water and -~
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drying, the material is coated with a solution containing 0.8 part by
weight of a condensate of paraformaldehyde and diphenylamine-4-dia-
zonium chloride and 0.5 part by weight of polyvinyl acetate in 100 parts
by weight of ethyleneglycol monomethyl ether.
After drying with hot air, the material is converted into a print-
ing form by exposure under a negative photographic transparency and
development with an aqueous solution containing ~ per cent of gum ara-
bic and 2 per cent of magnesium nitrate. The areas of the Layer not hard-
ened by light action are removed by the developer. After inking up with
greasy ink, the printing form may be used for printing long runs of very
good quality.
Exam~le 11
Electrolyte: 250 g of ammonium chloride per liter of
partially softened water.
Circuit Current Tempe- Time, Appearance
ArrangementDensity rature, (secs.)
(A/dm2) ( C)
Anodic 70 25 30 dull dark gray
Cathodic 70 50 30 no corrosion
Alternating 70 25 30 dull dark gray
current 0
Distance between electrodes: 5 cm.
Flow velocity of electrolyte: 0 . 3 m/sec .
pH value of the solution: 4.5 - 5.
Similar results are obtained when using ammonium nitrate. In
this case, the surfaces are of a lighter shade of gray, however.
It will be obvious to those skilled in the art that many modifi-
cations may be made within the scope of the present invention without
departing from the spirit thereof, and the invention includes all such
modifications.
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