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Патент USA US2106368

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Jan. 25, v1938.
w. B. wEscoTT
2,105,358
SHEET ALUMINUM PLANQGRAPHIC PLATE
.Filed Nov. 8,- 1955 `
»jg/ffl '
~ /
/0
/0/
-
2,166,368
mentalen. 25, 193s _
UNITED STATES
PATENT
OFFICE
2,106,368
SHEET ALUMINUMl PLANOGBAPHIC PLATE
William B. Wescott, Dover, Mass., assignor, by '
mesne assignments, to Addressograph-Multi
graph Corporation, Cleveland, Ohio, a corpora
tion of Delaware
Application November s, 1935, serial No. 48,935
9 Claims.
This invention relates to a method of prepar
ing sheet aluminum for planographic printing
and to the product of said method; and it com
prises treating sheet aluminum in a hot aqueous
5 solution of an alkali aluminate and an alkali hy
’
droxide whereby all traces of grease are removed
(Cl.
148-8)
,
.
do not require the adsorption of a lyophilic col
1pm. when the image to be printed has been
directly delineated upon the printing surface by
means of crayon or the like, it is customary
then to “desensitize” the non-printing areas,
thereafter to wash out theV image with turpen
and both major surfaces of said sheet are pitted. tine, and to replace it with asphaltum or some
and sometimes, but not always, coated with a other image-forming material which will take a
layer of microporous oxide, and thereafter rins
firmer grip on the plate and hence betterwith
10 ing the said so-treated sheet aluminum and stand the attritional effect of the inking rolls
10
sometimes, but not always, washing the same to _during printing; thus assuring
the maintenanceA
remove any superficial scum which may‘result
from said treatment, and then drying the prod
uct; whereby are obtained sheet aluminum plan
of the. integrity of the image trirougnoutedinons
of many thousands of copies.
_
‘
Metal plates are vcustomarily roughened or
15 ographic printing plates, both major surfaces of V grained forl the purpose of minimizing the attri
which are “grained” with fine pits characterized _ tional effect of the ink rollers on the image and,
by a contained deposit of microporous oxide and perhaps more importantly, .for'the purpose of i
which surfaces are sometimes, but not always,
further characterized by a surface layer of mi
2o _croporous oxide comprising a trace of alkali, and
k which surfaces are basic in reaction and _highly
sensitized to direct image-forming materials
comprising free fatty acids; all as more fully
hereinafter described and claimed. -
25
The art of planographic printing from metal
preventing these rollers from too greatly reduc
ing the iìlm of moisture which must bel retained
.in order -to prevent ink contamination of the
non-printing image. 'I'his grain g 'operation is 20
customarily performed by gyrat
marbles over
ilne sand on the plate; and it is a costly, time
`consuming operation requiring much skill.
It isan object of -this invention to obviate the
plates depends, as does the older lithographie art, l necessity for mechanical graining of plano
upon the immiscibility of oil and water and upon ’ graphic plates. It is another object of this in
_the preferential retention of a greasy image
vention to obviate the heretofore necessary step
forming substance by the image areas, and a ofl “counter-etching”, or sensitization, by the
30 similar retention of an aqueous dampening ñuid planographic operator. _It is likewise an object
by the non-image areas. In order to> condition of this invention `to obtain a requisite grain and
A a metal printing plate for these preferential re
sensitization to ink solely by chemical treatment
tentions, it has heretofore been customary to of the plate. It is a further object of this in
remove all traces of grease and then to “counter
vention to prepare aluminum plates for plano
35 etch” the plate to provide a basic surface where- . graphic printing _by treatment with a single
with the fatty acid -,component of the greasy chemical reagent» whereby a plate is cleaned,
image-forming material might' react. A .so
treated metal plate is said to be "sensitized” vto
ink. The “sensitization" or “counter-etching”
40 operation has heretofore been performed by the
user and usually immediately preceding the de
lineation of the image on the plate. After the
greasy image has been delineated in known man
ner thereupon, the non-image areas are custom- .
45 arily “etched” o_r “desensitized” by treatment
with an aqueous solution adapted to at least neu
l. e., freed from that contamination by grease
which is inevitable -in the production of sheet-
aluminum, and is provided simultaneously with
an adequate grain and a highly grease-sensitive
surface.
_
Another object of this invention is to provide
aluminum planographic _printing plates which
are highly _sensitized to direct image-forming
substances comprising fatty acidsand yet are
>equally serviceable for the retention of and print
tralize the basic condition previously produced, ' ing from photographically produced images. It
and preferably to render these areas lyophilic. l.is anotherobject to produce aluminum plano
In general _it has been the custom to "desensi
graphic printing .plates whereof both major sur
50 tize" by theuse of a weak acid and to .create a faces are conditioned for the reception and re
lyophilic condition by means of an adsorbable _ tention of planographlc printing images, and in
lyophillc colloîd, of which'gurn arabic is the most particular for such images when they are direct
~ commonly used example. It is also known that
ly delineated upon' the said surfaces, as by pen,
certain salts of the metal are preferentially wa
crayon, or typewriter. A still further .object is to
55 ter-wettable in themselves, and hence if present
produce planographic printing plates of sheet
2
2,106,368
aluminum of which both sides are conditioned
for use and may be stored indefinitely; and
which, after such storage and without further
preparation, will firmly retain an image delin
common practice, and thus their use affords much
saving of time and expense. Moreover, and by
reason of the firm retention of the image as orig
inally directly delineated on the plate, much less
eated with a greasy image-forming material _ skill is required than is requisite when the orig
comprising free fatty acid without the necessity inal work has to be washed out and redeveloped,
for any “counter-etching” or supplementary. as is the usual practice; and this is of material
treatment to sensitize said plates to grease for advantage. Other objects and advantages will
ima'ge reception and retention. It is yet another Vbecome apparent as the description proceeds.
In the acompanying drawing is illustrated more 10
object of this invention to provide planographic
printing plates of sheet aluminum characterized
by minute surface pits containing a. vdeposit of
microporous oxide of the metal> and further
characterized by an alkaline reacting surface. It>
15 is also an object to provide a ñnely pitted‘or
grained aluminum planographic printing plate
20
or less diagrammatically a plate formed in ac- ,
cordance with this invention;
^ Fig. 1 shows a portion of a plate I0 embodying
this invention having a character ii upon the
15
surface I2 thereof;
Figs. 2 and 3 are enlarged sectional views show
with a surface layer of relatively soft micropo
rous material comprising an oxide of the metal
and an alkali, whereby said plates are particu
ing theplate with pits i 5 therein and provided
with a coating or layer i6, in Fig. 2 the pits alone
being coated and in Fig. 3 both the pits and sur
larly sensitive to ordinary carbon paper.
face being coated; and
It is an object of this invention to provide a
process whereby sheet aluminum may be condi
tioned to receive and to retain a planographic
the plate.
printing image, and particularly a directly de
25 lineated image, by a treatment with a single
chemical reagent which simultaneously removes
all traces of’grease (both superficial grease and
>that ground into the metal during the rolling
process to which the sheet aluminum is subjected
in manufacture) and minutely pits or grains the
-surfaces and deposits within the pits an adherent
layer of relatively soft microporous material com
prising an oxide of the metal and an alkali. It is
an object of another embodiment of this inven
tion to provide aprocess as above described which,
in addition, will coat the said minutely pitted
_plates throughout their major surfaces with a
layer of the said microporous material.
y ,
Fig. 4 is an enlarged plan view of
_
20
a portion -of
-
Relatively pure aluminum is particularly suited
to the purposes of this invention; and it is pre
ferred to use aluminum in the higher grades of 25
purity, although that. alloy »of aluminum and
manganese designated by its manufacturers and
known to the trade as “38H” may be satisfactorily
used, and with particular advantage if a heavy
deposit in the pits of the plate or over the pitted
surface is desired.
A bath suitable for the practice of this inven-tion may be made by dissolving sodium aluminate
in ordinary tap water. The sodium aluminate
may be replaced either in part or in whole by
other alkali aluminates, such» as potassium alu
minate; but sodium aluminate alone is preferred.
While it has been found convenient to employ the
Among the advantages of the process of this ’ best commercial grade of sodium aluminate, so
40 invention may be mentioned the fact that the cost ,called white soluble 90% NaAlOz, the compounds
may however be made as required by well-known
of preparation of the sheet aluminum for plano
methods,` such as by the reaction of sodium hy
graphic printing is greatly reduced by the elimi
nation of the usual costly and tedious mechanical droxide with metallic aluminum or an aluminum
graining operation. Anothervadvantage of the salt.
It has been observed that the temperature of 45
said process lies in the fact that the aluminum
is thereby both “grained” and sensitized, whereby the bath, the concentration of alkali in the bath,
the necessity for "counter-etching” or sensitizing the time of treatment, together with the ratio
by the user is avoided. Still another advantage of aluminum surface to bath volume are to some
is that both sides of the plates of ,this invention extent compensating variables. Thus,-differences
are simultaneously prepared for use and this in concentration can be offset and substantially 50
the same result obtained by inverse adjustment'
without resort to building up laminated struc
ofthe temperature or time of treatment, or both;
tures as has been heretofore suggested.
Among the advantagesv of the plates of this and also by varying the ratio of surface tobath
invention may be mentioned the fact that they volume.
In general, a bath is preferred which contains 55.
are useful for the reception and retention of im
ages directly delineated by greasy image-forming five grams of the 90% sodium aluminate referred
materials comprising fatty acids, and for photo
graphicimages as well. Another advantage of
the said plates is that the high sensitivity to fatty
acids imparted by the process of this invention
is not diminished by long storage, and yet their
grease-sensitive surfaces may be readily desensi
tized by such weakly acidic etches as are buñered
at or about the isoelectric point of usual photo
graphic image-forming' materials. Still another
advantage of the plates of this invention is that
they are particularly retentive of poorly coherent
greasy image-forming materials‘such as the more
or less pulverulent coating of ordinary carbon
70 paper. -A still further advantage of the said
plates is that they *arev adapted to print from an
image, as directly. delineated in crayon or the.
like, without the necessity of washing out the
original image forming material and the replace
75 ment thereof with asphaltum or the like as is
to above for every 100 cc. of water. Best results
are obtained when the bath is maintained at a
temperature slightly below the boiling point. A
temperature of 195° F. plus or minus 5° has been
found satisfactory. When operating continuous
ly, a ratio of one square foot of aluminum surface
to every five gallons of the preferred solution and
an immersion time of 11/2 minutes provide a satis
factory relationship.4 A substantially equivalent 05
relationship for processing by the batch method
consists of a ratio of one square foot of aluminum
surface to every two and one-half gallons of
solution, and an immersion time of 11/2 minutes
with a pause between batches of 11/2 minutes. If 70
there -were nopause between batches,- the rela
tionship would- be the same as that given for the
continuous operation, for reasons which will later
become apparent.
One of the desirable effects of treating alumi
3
:2,106,368l
num in a bathof an alkali aluminate is an ero-v
mersed in such a freshly made solution; the mol.
sion or pitting of the surface of the metal. This , percent of sodium hydroxide drops rapidly as' the
erosion is accompanied by loss of Weight and loss aluminum reacts therewith; and then; as hydrol
of thickness of the sheet aluminum. 'I'he treat
ysis is in some unknown way stimulated as a
ment is-considered >to be at itsOptimum when consequence of this reaction, the mol. percent of
-maximum pitting occurs with minimum loss of.' sodium hydroxide rises again. By adjustment of u
thickness. The optimum treatment of sheet one or more ofthe several mentioned variables,
aluminum according to this invention may be the mol. percent of sodium hydroxide may be <
obtained over a wide range of concentrations of maintained within the range of that of the bath
10 sodium aluminate by adjusting the above-men
as freshly made; and, as stated, a molal concen-l
tioned variables, as stated. This adjustment is tration of I15% of sodium hydroxide has been 10
_not critical in so 'far as the production of a found convenient and satisfactory. Thus, when
satisfactory pitting or graining is concerned, and there is kept immersed about one square foot of
approaches the critical only when it is desired aluminum surface in five gallons of solution con-y
15 so to balance all the variables that the loss of
taining flve grams of sodium aluminate for every
thickness is held to a consistently low value. The „ 100 cc. of water and maintained at about 195° F 15
above-given example of a practical relationship the bath will remain in substantial equilibrium
between concentration, temperature, treatment at about 15 mol. percent sodium hydroxide con
time and ratio of aluminum surface to solution centration and the optimum treatment of the Y,
volume, is given by way of illustration partly aluminum surface will obtain in about 11/2 min- `
because adherence to'these conditions has yielded » utes. The loss of weight of aluminum is direct _20
25
`satisfactory results in practice, and partly be- » `ly proportional to the time of immersion; and,
cause they are particularly convenient.
under the stated conditions, _the loss of weight
The behavior of hot alkali alumlnate baths, asf per square foot of immersed surface lies in the
influenced by reaction with commercial _alurni
close vicinity of two grams. When the described
num, is not wholly understood: but certain theo
retical considerations are-hereinafter given as
being useful in clarifying the probable relation
Aship of several factors, although not relied upon
conditions have been closely maintained, the
deviation' from the mean loss of weight has in
practice been found to be of t-he _order of plus
as factual.
y
or minus 0.1 gram.l
.
Inasmuch as some water is lost by evaporation
-
A freshly prepared solution ‘of sodium alumi , and some solution is entrained with the metal
nate in the preferred concentration of five grams when it is removed from the bath, it is periodical
of the commercial substance to every 100 cc. of ly necessary to replace both. It has been found ‘
water appears to bel substantially stable over a _convenient to replace lost water by such additions
period of lmany hours. When such a hot solution as Will maintain an approximately constant solu
is reacted with commercial aluminum- (as for in
tion level, and to replace the alkali periodically 35
stance that grade designated by its makers as
“3SH”), the bath loses its initial stability and the
sodium aluminate hydrolyzes to form aluminum
hydroxide or oxide, and sodium hydroxide. The
by addition of sodium aluminate in an amount
which is indicated by titration. In general, a loss
of solution corresponding to 10% of the original
total alkali `is permissible._ It has been found in
practice that such lossmay occur in from three (0
to six hours of operation depending upon whether
former is precipitated, for the most part, as a
sediment; the latter is deemed to be the active
agent -of the bath, and it reacts with the alumi
the operation is continuous or discontinuous. The
num to form sodium aluminate. In so `doing it discontinuous, or batch, operation involves use
erodes or pits the metal and correspondingly ex
of holding means for the individual aluminum
hausts itself. For any given initial concentration sheets and hence results in the entrainment of 45
of sodium aluminate, the amount of sodium hy
more solution than is occasioned by drawing a droxide in the bath at any time, after hydrolysis continuous ribbon of sheet aluminum through a- ‘
has been initiated by the reactive presence there
bath. Continuous operation is preferred.
in of metallic aluminum and under otherwise con
When operating by the batch method, the indi
stant conditions, depends upon the ratio of the vidual sheets of aluminum are preferably main so
surface of 'aluminum immersed in the bath to the‘ tained in a substantially vertical position“ and
volume of the bath.
.
Disregarding such small amounts of impurities
as there may be, alkali is present in the bath as
sodium hydroxide and as sodium aluminate, and
each canbe determined as such by titration. It
is convenient to express the concentration of
sodium hydroxide in terms of mol. percent; that
that is to say that the ratio of the mols of sodium
hydroxide to the mols of total alkali present
may be expressed in percentage.
While satis
factory> plate surface treatment is obtainable
from alkali aluminate baths over a wide range
of molal concentrations of sodium hydroxide, it
has been found that about 15 mol. percent sodium
hydroxide concentration corresponds to substan
tial equilibrium at an expedientrate of treatment
and at a convenient ratio of bath volume to im
70
mersed aluminum surface.
'
spaced apart by at least two inches. In continu
ous operation the -desired substantially verticall
position of the- aluminum is suñîciently obtained
by feeding thegribbon of metal through the bath
in one or more loops such that for the most part
-the ribbon is vertically pendant therein.
Pjor certain purposes, such as forming a direct
image by means of a greasy substance compris
ing very little free fatty acid or a substance of
such friable‘or pulverulent a nature as topoorly
contact the plate'surface, it has been found de
sirable as part of this invention to substanti-ally
coat the entire surface of the plate with' such
microporous material as is discernibly retained 65
only in the pits of the plates made as above de
scribed.
,
‘
/
ns a means of coatingthe entire surface of
sheet aluminum with the said microporous ma
Freshly made solutions of commercial 90% so- ' terial and as a means particularly effective when
dium aluminate containing five grams of the ma
terial to every 100 cc. of water were found by
titration to have between 1l and`16 mol. percentl
sodium hydroxide. When aluminum is first im
relatively thick coatings are desired, i. e., coat-_
ings as thick as between two ‘and three vone
thousandths of a millimeter, the sheet aluminum
may be simultaneously pitted y'and coated in a 75
2,106,368
It w111 be obvious to those skilled in the art
that the process of this invention is, as stated,>
susceptible of wide variation and it is to be un
tween 5 and 10 percent, with an immersion time of . derstood that the examples of the preferred rela
ten minutes. Under these conditions, the loss of tionship of the several variables are given by way
weight is of the order of one "gram per square of illustration only.
The effect of the described treatment is three
foot of surface and the loss in thickness is negli- .
fold: it removes not only the superficial grease
gibly small. While baths of higher sodium alumi
but also that grease which has been ground into
nate content may be adjusted to yield satisfac
10 torily coated plates, less concentrated baths are metal in the process of rolling it into sheet form; _
not in general desirable because they may be, and it so pits thesurface as to provide a ñne “grain”;
usually are, ineñective to remove completely from y and it leaves the surface in an alkaline-reacting
state.- The complete absence of grease is of
. the metal the grease commonly associated there
single bath made up of 1.5
of sodium
aluminate to every 100 cc. of Water and adjusted
to a molal concentration of sodium hydroxide be
with.
15
.
As stated, aluminum hydroxide is precipitated
as a sediment; and it is`convenient to allow this
sediment to collect in the bottom- of the tank
and to remove it at daily intervals. Best'results
are obtained when the ‘sediment is not agitated,
20 although avoidance of agitation is not essential.
It is, however, essential for uniform results and
therefore desirable that the metalbeing treated
should be kept from contact with the concentrated Í
sediment’. The treating solution is conveniently
heated by jacketing the treating tank in known
manner.A
,
'I'he treated sheet aluminum should be rinsed
in running water immediately after treatment
course of vital importance because any residual
trace of grease would actas an ink-receptive
image and would print a tone in the non-printed
areas. Of vital importance also is the alkalinity
of the resultant surface, because upon this alka
A15 '
linity depends that sensitivity to fatty acids
which is necessary to the retention of direct 20
images under printing conditions and for long
editions. The “grain” constituted by the pits,
while not a prime essential, is nevertheless highly
desirable because the dampening solution (with
which the plate is wet between successive inking's 25
during printing) is better retained by the plate
when the surface continuity of its plane surface
is broken up by suchv “grain” as is provided by
the pits of this invention; and also,'although less
importantly, because this “grain” provides a 30
“tooth” which is of advantage when a direct
image is delineated in pencil or crayon. 0n the
in order to remove the entrained solution. If
30 rinsing is deferred, an unsightly brown'discolora
tion of the metal sometimes occurs; and while
this discoloration seems not to adversely affect the
behavior of the aluminum as a printing plate, it other hand, the “grain” ofthe plates of this
is unsightly, as stated, and for' that reason its .invention is of so ñne a texture that it is not35 formation is preferably prevented. After rins » objectionable when the image is formed photo 35
- ing, the aluminum is swabbedwith a soft rubber graphically from even the ñnest halftones.
_While it is feasible to print 4from aluminum
-sponge or with cotton wadding. When aluminum
alloyed with manganese (that known to .the plates which have been treated by the process of
--trade as “3SH”) is treated in the alkali baths of vthis invention merely tothe extent of removing>
-this invention, it becomes loosely coated with a the grease and of rendering the surface alkaline 40.
dark grayish deposit which is readily removed by reacting but without any substantial pitting, such
swabbing. Drying of, or pressure against this limited treatment is not recommended because
gray coating should be avoided inasmuch as its not all the advantages of this invention are fully
- removal is thereby rendered more diillcult.
The
45 purer grades of aluminum do not show this gray
deposit but are preferably swabbed to remove any
realized when printing from plates wholly devoid
of "grain”. These advantages are most fully 45
realized when the-pitted area constitutes between
loose precipitate that may survive the 'rinsing 40 and 70% of the total surface. Under the con
operation. After the rinsing and swabbing, the ditions of the examples above given, the follow
ing relationship obtains. The number of the pits
sheet aluminum is dried in any convenient man
50 ner and is then ready for use without any further
treatment.
.
`
-
per square millimeter of surface lies between two 50
and ñve thousand. .The individual pits are gen
While the plates of this invention may be made erally spaced apart although occasionally they
encroach upon each other, and they are of gen
under widely variant conditions of bath, the opti
erally rounded and approximately circular con
mum treatment, for consistent results, will ob
tour. The mean diameter of the pits varies over 55
55 tain when the molal concentration of alkali hy
droxide in the bath is maintained a constant; that the range lying between something less than 0.001
is, when the rate of the consumption of alkali and 0.015 millimeter; It is observed that in gen
hydroxide is equal to the ratev of its liberation
through hydrolysis -of the alkali aluminate. Al
though high molal concentrations of alkali hy
droxide cause rapid loss of weight, equilibrium
of thebath at these concentrations requires a
low ratio of surface area to~vo1ume; and di'
eral the average of the mean diameters of the pits
in a given area is roughly inversely proportional
to the concentration of pits in that area. Thus
when the number of _pits per square millimeter is
of the -order of ñve thousand, the average of their
. mean diameters is of the order of 0.008 milli
minishing returns result. In fact, it has been - meter; and when there are but two thousand pits
found that the productivity of a bath (atleast. per square millimeter, the average of their mean
in the lower ranges of both the molal concentra ¿diameters is of the order of 0.012 millimeter. The
tión' of alkali hydroxide and th‘e concentration ratio of pitted to non-pitted areas appears to vary
of total alkali) .is inversely proportional to the much less than does the concentration of pits
equilibrium of molal concentration. Hence, it is from one minute area to the next. The depth of
70 in general preferred so to adjust the severalï the pits Vappears to be roughly proportional to
variables as to -maintain a relatively low equi- _' their mean diameter. The “grain” constituted
by the pits as described and within the above
librium' of molal concentration of alkali hydrox
ide, since under these conditions the vmaximum limits is very fine when compared to the “grain”
yield of treated surface per unit of bath volume - which is obtained by abrasive attrition under gy
75 in unit time is approximated.
rating marbles, as is the common practice; and 'l y
‘2,106,868
5
yet it is fully e?'ective to retain, against the ,
'I'he microporous deposits on thev plates of this
squeegee action of the ink rollers, a sufficiency of invention may be distinguished from both normal
dampening solution. It is one of the advantages atmospheric oxide and from anodic aluminum
of the plates of this invention that less dampen
oxide by two distinct characteristics. Thus,
ing solution is required to maintain the non
when scratched with a needlepoint, the said de
printing portions clear from tone than is re
posit appears under the microscope and at- a
quired by plates with the finest grain mechani
magnification of 100 diameters or so, to consist
cally obtainable. This advantageous behavior is of whitish particles suggestive of a relatively
thought to be due to the'high moisture retentivity delicate and iinely crystalline ~material and dis
1.o of the open-textured or microporous material de tinctly not comparable to the powdery product
posited in the pits and sometimes over the entire of a similarly scratched hard amorphous mass,
surface.` The presence of this microporous ma.
such as the relatively dense aluminum oxide pro
_ terial, in contrast to the extremely thin normal duced by anodic deposition. It is thought that
oxide, may be readily observed by microscopic in- . the expression "microporous crystalline oxide” is
spection. If the microporous deposit is limited to -useful in distinguishing the oxide deposited by
the pitted areas of the plate, its presence though the process of this invention both from normal
not its porosity may be observed by inspection of -atmospheric oxide and from oxide produced
a microtomed section under vertical incident il
anodically.
lumination. If the deposit extends beyond the
The second distinguishing characteristic is
20 pitted areas, it may be discerned without section
vthat the microporous crystalline oxide deposited
ing, by microscopic inspection under~ vertical in`
by the process of this invention is alkaline re
cident illumination. In, either case, whether lim
acting. whereas normal atmospheric and anodicited to the .pitted areas or extended over the en
oxides are acid reacting. Whether the alkali is
tire surface of the plate, the relative thickness merely entrained by, or occluded in, ` the mi
of the deposit may be estimated microscopically cropores of the crystalline oxide, or whether it
under incident dark field illumination. '
is a component of a compound comprising the
The microporosity of the deposit may be dem
oxide, is not known; but the` presence of the
onstrated in terms of its high adsorptive capacity alkali in the deposited material is of prime ad-for finely -divided pigment, as carbon black for vantage. One of the advantages of the alkaline
30
instance, by the following procedure, which also
serves to show the contrasting behavior of the
normal oxide coating on the non-pitted areas
when the latter are free from the microporous de
posit of the process of this invention. Usual
' black lithographie ink is first well rolled onto a
restricted area of the plate and then washed out
with an appropriate solvent, as carbon tetrachlo
ride for instance.
The so-treated area, when
5
10
15
20
25
reaction of the deposit is that it provides a pre 30
sensitized surface, i. e.,. a surface with which the
fatty acids of direct image-forming materialsv
may react; vand thus is avoided the necessity for
sensitizing or counter-etching by the user. An
other advantage is manifested by the substan .35.
tially greater life under printing conditions of
an image derived directly from a greasy image
forming substance containing a free fatty acid
microscopically viewed` at a magnification of reactive with said alkali over the life of any
about 100 diameters, will be observed to be of direct image obtainable in the absence of said 40
undiminished metallic brilliancy in the non
alkaline component in the deposit.
pitted areas and dark gray in the pitted areas,
If a restricted portion ofa plate of this inven
Repeated washings with solvent are not eñ'ective tion be treated with acid, as dilute phosphoric
to appreciably lighten the grayness of the pitted acid for instance; and it be then thoroughly
areas; from which observation'it is concluded ,washed and dried, and an image thereafter di 45
that the pigment of the ink'is iìrmly adsorbed rectly delineated upon both the normal surface within micropores of the deposit on the pits.
' and the acid-'treated surface .under like Vcondi
When the microporous deposit covers th‘e non
tions, it will be found that the printing life of
pitted as well as the pitted areas, the above
the image on the normal surface greatly exceeds
described procedure aifords a test for the con
that of the corresponding image on the acid» -5o`
tinuity of the deposit as well as for` its micro
treated surface. That the relative capacities for
porosity. If the deposit is continuous over the 'direct-image retention on the surface of a plate ~ I
entire surface, the demarcation of the inked area, which is sensitized by the process of this inven
after washing the ink therefrom, will still be ' tion and of a portion of that surface as modi
.. macroscopically discernible; although contrast flecl by desensitization with acid indicate not
between these and the surrounding normal areas merely a'difference vin degree in sensitivity but a
of the plate surface will be very much weaker. diiference in kind 'of surface may be demon
When viewed microscopically, the entire inked strated by a simple and expeditious bench test.
and washed area will appear markedly darker Thus,_if a plate of this invention be desensitized
in color than the surrounding normal plate sur
over part of _its area with an acid, as phos 60
face and will comprise at least two distinct phoric for instance; and if, after thorough Wash
shades; the darker of these shades will appear as ing and drying, it be rolled up with a usual litho
isolated small patches against a continuous back
graphic ink and then flooded with a weakly
ground of a lighter- and sometimes slightly vary
acidic etch, comprising .an acid phosphate such
.-ing shade. In Figure 4 of the drawing, the ' as that disclosed in U. S. Patent No. 2,003,268, 65
darker areas- of the coating, corresponding to it will be observed that after standing fora few
the pits I5, are indicated by the numeral I'I andl minutes the ink over the desensitized area will
the lighter areas by the numeral I8. . ‘I'he ap
withdraw from the plate and expose minute areas
parent density of the coloring, residual after the of bare metal. It lwill be further observedthat
70 above-described inking and solvent treatment, is these ink-denuded areas gradually increase in
believed to be proportional to the thickness of size until they become connected with their ad 70
the coating, whichis greatest in the isolated jacent neighbors; and that the plate becomes
areas overlying the deeper pits and is least in> substantially freed from ink without mechanical
the expanses of the unpitted or very slightly intervention, unless theink has been rolled up
pitted areas lying therebetween.
very thickly, in which case the last traces of ink 75
6
2,108,388
may require gentle swabbing for their complete `an alkali aluminate until the surface of said
removal.
The ink on the sensitized or normal
aluminum is freed from grease, is minutely pitted.
surface of the plate will be found to be undis
turbed by the acidic etch. It is believed that the
retention of the ink by the surface of the plates
of this invention, against the action of the acidic
etch, is due to chemical reaction between the
fatty acids of the ink and the alkali component
of the oxide ñlm coating the surface of these
and is sensitized to fatty acids.
plates.
poë'ous aluminum oxide comprising a trace of
10
>
The presence of alkali, as a component of the
oxide deposited on the surface of these plates,
may be demonstrated colorimetrically; but, be
cause of the extremely small amount of deposited
15 oxide, this determination is tedious and difficult.
A characteristic difference between the normal
alkaline surface of the plates of this invention
and such surface after desensitization by an acid
“etch” may otherwise be demonstrated by observ
20 ing the relative wettability of these surfaces by
aqueous ethyl alcohol comprising 50 to 55% of
water. A drop of this mixture will spread im
~
3. 'I'he process of preparing vphanographic
printing plates from sheet aluminum which com
prises immersing said sheet aluminum in a solu
tion of an alkali aluminate until the surface of
said aluminum is` freed »from grease, and is
grained with minute pits coated with a micro- '
al ali.
‘
4. The process of preparing planographic
printing plates from sheet aluminum which com
prises immersing said sheet aluminum in a so
lution of an alkali aluminate until the surface of 15
said aluminum is freed from grease, is grained
with minute pits, and is coated with'a micropo
rous aluminum oxide comprising a trace of a1
kali.
~
5. A planographic printing plate of sheet 20
aluminum characterized by minute pits of the
order of from two to ilve thousand per square
mediately when applied to the normalA surface of millimeter and of generally .rounded contour in
the plate, but will not spread when applied to an otherwise substantially plane surface, the
vprinting _surface of said plate being alkaline re
25 the desensitized or acid-treated/ surface.
While the planographic printing plates of this acting and highly sensitive to fatty acids.
6. A planographic printing plate of sheet
invention which have their entire surfaces cov
aluminum characterized by minute pits of the
ered with a. continuous layer of microporous de
posit (see Fig. 3) are particularlyuseful for the order of from two to five thousand per square
30 reception and retention of images formed from_ millimeter and of generally rounded contour in 30
the less reactive grades of carbon paper and for vvan otherwise substantially plane surface, said
free hand work with the drier grades of crayon, pits being partially filled with a deposit of micro
porous oxide and said surface being alkaline re
lthey are not particularly satisfactory for photo
acting and highly sensitive to fatty acids.
graphic reproduction. Because of the very open
7. A planographic printing plate of sheet alu-‘_
35 textured surfacing, which advantageously retains
minum characterized by minute pits of the o_rder
dampening solution, the unexposed photo-sensi
tive material with which they are sensitized for ~ of from two to ilve thousand per square millime
photographic reproduction cannot be wholly . ter and of generally rounded' contour inI an other
wise substantially plane surface, said pits and
washed out of the porous surface layer on devel
opment; and hence the obtainment fromvsuch surface'being coated with a deposit of crystalline
plates of clear tone-free whites in the non-print
lng areas is generally diflicult and more particu
larly so with fine halftones. When an image or
part of an image is to be formed photographically
on plates of this invention, itis preferable to use
plates on the surfaces of which the microporous
deposit is segregated within the pits and gen
erally below the level of the non-pitted areas
(see Fig. 2) , It is believed that even though some
of the unexposed photosensitive material may
remain in the micropores of the deposit within
the pits, the dampening solution is so firmly re
tained in the pits against the squeegee action ‘
of the ink rolls as to eifectively protect from ink
contamination such traces of photosensitive ma
terial as may have been there retained.
I claim:
'
'
.
'
1. In aprocess of preparing planographic print
ing plates from sheet aluminum, that step which
-microporous oxide thicker in the pits than over
the substantially plane surface comprising a
trace of alkali and being highly sensitive to fatty
acids.
‘
>
,
8. A planographic printing plate of sheet alu
minum characterized by between two and ñve
thousand minute pits of generally rounded con
tour to the _square millimeter in an otherwise sub
stantially plane surface, said pits having a mean
diameter o_f the order of five one-thousandths of
va millimeter and said surface being alkaline re
acting and highly sensitive to fatty acids.
,
9. A planographic‘printing plate of sheet alu
minum characterized by between two and ilve
thousand minute pits of generally rounded con
tour to the square millimeter in anotherwise'sub
stantially plane surface,`said pits having a mean _
diameter of the order of ilve one-thousandths of a
millimeter and said pits and surface being coated
comprises reacting saidaluminum with an alkali ' with a deposit of a crystalline microporous oxide
05
hydroxide in hot solution with an alkali alu
minate, whereby the surface of said aluminum is
freed from grease and is sensitized to fatty acids.
comprising a trace of alkali and being highly
sensitive to fatty acids, said deposit h’aving a
f
thousandths of a millimeter.
2. 'I'he process of preparing planographic print
mean thickness of between one and three one
'
.
ing plates from sheet aluminum which comprises
immersing said sheet aluminum in a solution-of
WILLIAM B. WESCOTI‘.
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