Note: Descriptions are shown in the official language in which they were submitted.
32, ~66
3~7~
LITHOGRAPHIC SUBSTRATE AND ITg PE`(OCESS OF MANUFACTURE
BACKGROVND OF T~IE XNVEN'rION
Lithographic printing plates have been widely
used for many years. One of the basic concept~ utili~ed in
that technology is the establishment of differential
we~tabili~y between areas on the planographic printing
surace. This is most usually e~ected by providing a
substrate having a hydrophilic or water wettable surface
and coating that ~urface with an imageable (usually visible
li~ht or radiation sensitive) and developable grease
compatible ~oleophilic) and hydrophobic layer, After
imaging and developing of this layer9 the printin~ plate
imagewise exposes hydrophilic and hydrophobic surfaces.
When the plate is first wet with water and then coated with
grease or oil-based printing lnks, only the hydrophobic
areas of the image will hold the ink and provide a trans-
erred dark ima~e when pressed against a receiving surEace
such as paper.
This lithographic process has been able to
provide planographic printing plates whjcil are capable of
producing as few as hundreds of copies or as many as
several hundred thousand high quality copies. The
desirability of being able to produce large numbers of
copies from a single plate are quite apparent~ Only a
sin~le imaging and developing procedure must be performed,
and the printing press need not be shut down during
operation in order to change plates.
The investigation o means for lengthening the
running time of planographic printing pla~es has been the
ocus of many studies and research. It is also necessary
in the provision o~ more durable plates to maintain or
improve such o~her desirable or essential characteristics
o printing plates such as imagin~ speed r ease of
development, non-polluting chemistry, and shelf life.
,, . ~
7~ - 2-
Most o~ the research in providincJ longer running and
higher dura~ility planograpllic printin~ plates has
centered on the imageable and hydrophobic coating la~er on
the hydrophilic surEace of the ~ubstrate. As it is
usually the breakdown of this layer which causes failure
of the printing plate, the logic o~ that direction oE
research is apparent~
In general, the substrate provided for the image~
able layer is an alumin~n sheat which has been prepared for
coating by a variety of cleaning, mechanical, and chernical
treatments. For example, an alumin~n surface is usually
cleaned to remove oils and other contaminants. This
cleaning is then followed by a mechanical or electro-
chemical graining process, and finally an anodizing
15 process.
For example, U~S. Patent No. 3~963/594 discloses
the electrochemical etching of an aluminum substrate with
an aqueous solution of hydrochloric acid and glucGnic acidO
This provides a uni~ormly coarse surface texture to
the aluninum su~strate~ The process of ~hat patent
permits the use of lower current densities than were found
to be necessary when using only hydrochloric acid in the
bath. The treatment also complexad dissolved aluminum and
other impurities which ~orm in the etching bath. This
extended the liEe of the bath. Desmutting treatments were
also shown in co~nbination with the electrochemical
etching.
British Patent No. 1,439,12~ disclosas an
anodi~ treatlnent ~or alwninuJIl substrates in which the
30 anodizatiGn i8 performed in an aqueous sulfuric aci~ bath
at a telnperature in excess of 709C and with an anodizing
curr~nt density of at least 50 amps/sq. Et. This treat-
ment reduces the length of time in which the anodizing
step is performed. Other etching solution compositions
and electrical parameters are disclosed in U.S. Patents
Nos. 4,072,589 and 4,052,275 and French Patent No.
2,322,015.
~fter electrochemical or mechanical etchiny of
the alw~inurn surEace, an anodically oxidiziny treatment is
usually performed to rencler the aluininum surface both
corrosion resistant and wear resistant. This is shown in
aritish Patent 1,439,127 discussed above and in U.S.
Patent NO. 4,131,518. In this latter patent, aluminum
Eoil in the Eorm of a continuous web, particularly when
the aluminuln carries a polymeric coating on one sicle
thereof, is anodizecl so that energy requirements are
reduced and anodizing speeds are increased.
U.S. Patent No. 3,181,4~1 discloses an anodizing
process in which the sulfuric acid anodizing step is
~ollowed by trea~ment with an aqueous solution of sodium
silicate. This treatment seals the pores of the anodic
oxide surface and provides a hydrophilic, ink-repelling
surface layer.
German Patent (Offenlegungsschr1ft) 24 34 098
discusses firing a composition of aluminu~ phosphate and
silicon carbide particles onto a metal surface for the
purpose of inrreasing its wear resistance~ ~owever, this
invention of German Patent 24 34 098 is not suitable for
use on lithographic plates and is not coated on aluminum
surfaces.
The practice of treating lithographic substrates
o aluminum in order to increase surface areas and enable
ano~7ic coatings is well described in the art such as U.S.
Patents Nos. 3,935,080; 3,929,591; 3,980,539; and
3,98%,217.
Even though anoclizing has become the most common
means of providing an alulninum substrate for durable plano-
gra~hic printing plates, and even though some reduction of
eneryy rec~uirements has been made, the process still
re~uires large alnounts of electrical energy in its opera-
tion and also generates effluents that must be care~ully
disposed oE to avoid environmental pollution.
A novel Inethod for providing kexturecl surfaces
on lithoyraphic printing plate substrates of aluminum was
3t7~
~I:LSClOSe(3 in ~.S. Pal-ent NO. 3,210,184. A 1aYer OE
boehrnite (alulnlnum oxide monohydrate) was produced on the
alumillum substrate by bathing the aluminum in hot water or
steam in the presence of a weak organic base. Printing
plates using the textured substrate were shown to provide
increased numbers of copies under comparable conditions as
compared to printing plates using mechanically roughened
aluminurn substrates.
U~S. Patent Nos. 3,871,881 and 3,975~197 dis-
close another me~hod of enhancing the physical propertiesof aluminum surfaces, Various types of particulate
material are bonded to the surface of the aluminum by an
in_situ foLrned binder of aluminum hydroxyoxide, The
enhanced aluminum article is suggested Eor use as a
susbstrate ~or printing plates~
U~S. Patent No. 4,319,924 discloses an aqueous
coating cornposition comprisingg in coating forming propor-
tions; dissolved phosphate; dissolved dichromate;
dixsolved aluminu~; and ~ispersed solid particulate
material, preferably an aluminum-containing material.
This composition is capable of being heat~cured at
elevated temperatures into a water-insoluble material.
The composition ~urther comprises diethanolamine in an
alnount suE~icient to reduce the temperature at which said
composition can be cured into the water-insoluble
material .
It is disclosed in the description of the
present invention that a novel process for treating
litho~raphic quality aluminum foil can provide a durable,
long-running substrate Eor lithographic plate construc-
tions. This process prov.ides a novel substrate which can
be ~esistant to the chernical action of the printing plate
~evelopers and press solvents. The novel substrate also
enables the bonding of many photoreactive imaging layers
~o the treated aluminum substrate without the need for
primer.s or other adhesion promoting agents.
7~
SUMMARY OF THE INVENTION
A process is disclosed for firing a slurry of particles and a phosphate
binder. The particles are preferably weakly basic or amphoteric non-metallic
particles and the composition is fired on an aluminum or aluminized substrate.
This process produces an aluminum substrate or aluminized surface of a sheet bea-
ring a textured layer of hard particles bonded together by a water resistant
phase, or phases, of a dehydration products of monobasic phosphates such as those
of aluminum and/or magnesium, alone or in combination with -the products of their
reaction with some or all of the particles, on at least one surface of the sheet.
This textured layer has been found to provide an excellent surface for adhesion
of organic ma-terials. In particular, the phosphates strongly bind and adhere the
particles into a layer having excellent adhesion for diazonium resins and photo-
polymeric compositions used in the printing art and particularly in the planogra-
phic printing art. This adhesion is enhanced by the surface texture and improved
chemical stability imparted by the particles.
DETAILED DESCRlPTION OF THE INVENTION
_
According to one aspect of the present invention there is provided a
process for preparing a photosensitive subs-trate comprising the steps of
A. Providing a ceramic layer on an aluminum substrate or aluminized
surface of a substrate which comprises applying a slurry of at least one mono-
basic phosphate and inorganic non-metallic particles on at least one surface of
the aluminum or aluminized substrate and firing the slurry at a temperature of at
least 230C to form a ceramic coating on said aluminum or aluminized surface;
B. Coating on said ceramic layer an organic photosensitive lithogra-
phic layer.
According to another aspect of -the present invention there is provided
a photosensitive article comprising:
-5-
~8~37~
A. an aluminum or aluminized subs-trate bearing on at least one alumi-
num or aluminized surface thereof a ceramic layer comprising 1) non-metallic in-
organic particles and 2) a water-resistan-t phase, or phases, of a dehydration
product of at least one monobasic phospha-te; and
B. a photosensitive lithographic coating over said ceramic layer.
The process of forming phosphate coatings on substra-tes according to
-the present invention provides a number of improvements over prior art processes
for producing substrates for photoimaging elemen-ts, particularly in -the con-tinu-
ous manufacture of subs-trates. Not only does the coated substrate of the present
invention have equivalent or improved properties as compared to materials of the
prior art, but also it provides significant economic advantages in its manufact-
ure. Apparatus used in the process consists of fewer separate items of equipment,
thus requiring a lower capital investment than conventional forms of continuous
substrate formation. The significant equipmen-t eliminated includes the anodizing
facility which is itself costly to operate because of high energy requirements
and the need for safe effluent
-5a-
~ G-
disposal. Such ec~uip~ent is desirably eliminated from a
substrate manufacturing line because oE a~sociated electro-
chemical corrosion problems oE other equipment on the same
production line. The coating layer produced according to
the present invention does not require e-tching or other
texturizing. Such othe-r texturizing may be optionally
perEormed to provide additional characteristics to the
surfaceO The elilnination oE such texturizing processes
provides a Eurther increment of cost reduction. The
process can be readily per~ormed in a continuous Eashion
and has been found to provide results subs~antially iden-
tical to those of a batch process.
A coating of a monobasic phosphate solution
E~rming a slurry with metal oxide particles is applied to
a clean aluminum or aluminiæed surface~ This coating is
fired at a temperature of at least 450F (230C),
preferably at leas~ 500 or 550~ (260 or 290C), to
produce a textured ceramic coating o~ a phosphate glass~
This may comprise non-metallic and especially meta~ oxide
particles embedded in a vitreous, water resistant phase or
phases o~ a dehydration product oE monobasic phosphates
such as those of aluminum and/or magnesium, alone or in
combination with the products of their reaction with some
or all oE the par-ticles. Other monobasic phosphates which
are acceptable include those of zinc, calcium~ iron, and
beryllium. When the metal oxide is alumina, the bondin~
phase between the phospha~e glass and the alumina is most
likely aluminum orthophosphate. The firing should be
~er~ormed for a long enou~h tilne at these temperatures to
insure substan~ially complete dehydration of the coating.
This Inay t~ke place in as li-ttle time as three seconds at
the descrihed temperature depending upon the thickness of
the coatiny and the temperature and other parameters oE
the Eiring process. The ceramic surface may be Eurther
treated as by e~ching to provide particularly desired
te~;~ures and properties to the surface, but the surEace
resulting Eroln the firiny already is textured. This
~ 7~
oç~tional treating is not critical or essential to the
present inver1tion anc~ is most generally performed in con-
junction witl1 imaging systems (e.g~, lithographic printing
L~lates~ wl1ich are optirnized hy a silicate treatment of the
substrate or sorne other analogous layer. Etching, for
example, can be accomplished s~y using known alkaline
silica~e solutions which will deposit a silicate coating
at the same time. Where no silicating is required or
where the subsequen~ly applied ligh~ sensitiv~ composition
would not be compatible with a silicate surface, the etch
may be performed in alkaline phosphate or aluminate solu-
tionsr Eor example. The aluminum or aluminized substrate
may initially have a texturized surface so that etching of
the cerarnic coating will expose the texture through the
ceramic coating. This is unnecessary, however, in the
practice o~ the present in~ention because of the natural
texture produced in ~he process. This natural texture,
which is a microscopic texturing visible by light
scattering or under magniEication, provides a physical
structure to which subsequently applied light sensitive
coating compositions may adhere.
An optional post-firing etch may remove whatever
amount of the dehydrated ceramic coating is necessary to
pro~ide the character required in the texture of the
substr~te. As little as five percent and as much as sixty
percent by weight or more oE the ceramic coating may be
relnoved. Irhe length oE -time oE the etch is regulated by
the temperature and pF of the etching environment. Higher
ternperatures and higher p~I le~els provide ~aster etches.
The pH may be controlled by the addition of alkaline
hydroxides such as sodiurn hydroxide. Replenishing solu-
tions Inay be adde~ durin~ the continuous proCeSSinCJ oper~-
tion to replace any material, such as the alkali
colnponent, which is deple-ted during the etch. The
coms~ined etch and silicating solutions are generally
optisnized to emphasize the silicating treatment, since the
silicate etch has a wider performance latitude than
'7~
phosphate or alulnlnate etching solutions. The silicates
used Eor the combined etching and silicating ~aths are
~referably at the high silica content end of the com~ r-
~ cially av~ilable materials. Such materials as "Kasil ~1"
or "S-35" of the Philadelphia Quartz Co~ or mixtures of
"S-35" ~7ith a fine silica sol (e~g., Sol~ 1115 of Nalco
Chemical Co~ are particularly useful when diluted with
water to give solutions having approximately one percent
silica on a dry weight basis.
The texturized substrates produced on the
ceramic coated aluminum or aluminized substrate by the
firing step may then be coated with a llght sensitive
composition either directly or with an intermediate
sublayer. An oligomeric diazonium resin andjor an organic
negative or positive acting photosensitive composition may
be desirably appli~d to the textured surface.
A broad range of photosensitive compositions
having va~ious diEEerent fields of utility are known to
those oE ordinary skill. The types of photosensitive
coatings useful in the practice oE the present in~ention
are those which would ordinarily be considered for use in
the printing plate art, and speciically, lithographic and
relief compositions. These compositions wGuld include
both ~egative and positive acting lithographic composi-
tions and negative acting relief compositions.
Neyative acting compositions ordinarily perEormby having a photopolymerizable composition which becornes
less soluble and/or more highly polymeri~.ed when struck by
actil~ic radiation in an imagewise pattern. This is
ordinarily acco~plished by havin~ a mixture of materials
including such various ingredients as binders, polymeriz-
able Inaterials ~mono!ners, oligomers and polymers~, photo-
initiator catalysts Eor the polymerizable materlals,
sensitizers Eor the photocatalysts, and various other
ingredients such as oleophilicity enhancers, pigments,
surfactants, coating aids and other ingredients known in
the art. Afte~ i~nagewise exposure to actinic radiation,
~ ~ r~
~ ~q¢~ 7
the unreacted, ~nore soluble are~s of the coating corn-
position are ren~oved by washing with various solvents
includin.3 water, aqueous alkaline solutions and organic
developers. Amongst the most common materials used in the
forrnation of negative acting lithographic printing
compositions are ethylenically unsaturated monomers and
photoinitiated free radical generators.
Organic and methacrylic polymerizable materials
are tne most frequently utilized components, but all other
ethylenically unsaturated materials and copol~merizable
ingredients are useul and known in the artO See, for
example, U.S. Patent Nos. 4~ 315,9~9, 4,228,232,
3,895,949, 3,887,450, and 3,~7~955.
Positive acting lithographic compositions
ordinarily comprise a binder of thermoplastic or partially
crosslinked compcsitions which con~ain a por~itive acting
photosensitizer which, when struck by light, becomes more
soluble in selected solvents than the non-light exposed
sensi~izer. The most common photosensitizers used in the
art are o-quinone diazide compounds and polymers. Various
binders such as acrylic resins, phenol formaldehyde resins
(particularly novolaks)l polyvinyl acetal resins, and
cellulosic esters are also yPnerally known in the art Eor
use ~ith this type of photosensitizerO See, for example~
U.S. Patent Nos. 4,1g3,797; 4,189,320; 4llÇ9,732 and
4,247,616.
Negative acting relief compositions work in
similar fa~shion to negative acting lithographic systems,
except that the layers are considerably thicker and that
molds and embossing are often used to impress the surface
structure when forming the relief image.
The cera~nic surf~c~ provided on the al ulninurn
substrate is hi~hly water receptive and has been shown to
be at least as hydrophilic as anodized aluminum. The
sur~ace provides excellent adhesion Eor polymeric and
oligomeric compositions. The surface has been found to
provide parti~ùlarly excellen~ adhesion for positive
3,~ 7~7 -1o-
acting photosensitive compositions such as those
containing diazo oxides and diazo sulfides, and provides
good resistance to the developiny solutions use-3 which are
generally highly alkaline.
The thickness oE the ceramic coating can readily
be varied as desired, Eor example, between 002 and 15
microTneters. Preferably, for use as a substrate for plano
graphic printing plates~ the coatlng layer is between 0.3
an~ 10 micrometers and more preferably is between 0.5 and
5 micrometars.
The firiny temperatures used in the practice of
the present invention must b~ hi~her than 450 or 500~F
(230 or 260C~ and preferably are at least 550~ (285C).
Telnperatures higher than 700F (370C) do nvt ofEer any
significant advantages and raise the energy requirements
of the process and may distort or weaken the substrate.
These temperatures refer to the surface temperature of the
coatin~, measured by contacting the coating surEace with
the bare junction of a thermocouple. It will be under-
stood that many dif~erent types of ovens having a variety
oE control characteristics may be used Eor achieving the
required surface temperatures. The control temperature
may in fact difEer substantially Erom the surface
temperature measured in the manner described above~
The particulate matter added to the monobasic
phosphate to Eorm a slurry may have a considerable range
and constitute substantially any non-metallic inorganic
particle. By non metallic, it is meant that the particle
s~lould not have such a high proportion of free metal
~greater than 25% by weight on the surface~ as would
interEere with lithographic colnpositions.
By the term 'particulate,l as used in the
practice of the present invention, it is understood that
particles within a broad size range are useful. Particles
smaL1 enough to Eorm colloidal dispersions, e.g.~ as small
as average si~es of 5 x 10-3 microme~ers and pre~erably no
smaller ~han 1 x 10-3 microme~ers ara quite useful up ~o
3;1'7~ 1 :L
~5 microlneters. The preEerred size rancJe is between 10-2
and 45 micrometers, and the most preferred range is
between lo-2 and 5 micrometers. If highly reactive
particles are used, they will in effect dissolve away (in
whole or in part) by reaction of material from the sur~ace
of the par~icle. Thus, surprisingly large particles can
be used which would no~ interfere with the physical
properties oE the surEace. Agglomerated particles having
an effective large size which can be broken down during
processing may also be used.
The metal oxides, Eor example, may include
alumina (in various phases such a~ alpha, betaJ theta, and
gamrna alumina), chromia, titania~ zirconia, zinc oxide,
stannous oxide, stannic oxide, beryllia, boriay silica, '
magnesium oxide, etc. Certai~ oxides and even certain
different phases of the oxides or mixtures thereof perEorm
better than others. For example, the use oE mixtures of
alpha alumina and certain reactive transition aluminas
such as the theta and gamma alumina provides a surface
having improved properties over that obtained wi~h
particles of a single alumina phase. The presence of the
alpha phase in the slurry provides a ceramic coating with
increased wear resistance and the presence of the other
phases, or other metal oxide particles, tends to provide a
more Einely textured surface than alpha alumina by itself.
By 'reactive' it is meant that the oxide reac~s with mono-
basic phosphate during firing conditions.
Particulate materials which react with the acid
or rnonobasic phosphate ~ive more alkali-resistant binder
compositions. When such materials are added in excess of
the amount that will react Eully with phosphate, they may
additionally contribute to the surface texture oE the
Eired coating. If they are in a Eorm that reacts slowly
or not at all at room temperature, they may contribute to
the consistency or viscosity oE the slurry, giving a
Eormulation that may be particularly well-adapted Eor
L~articular coating methods. Furthermore, some of these
7~;7
mate~rials detract ~rom or add to the hydrophilicity of the
phosphate coating in a controlled way. In summary, then,
there can be added to the slurry a blend of reactive~
fine, particulate ma erials that maximize resistance to
alkaline attack, optimize slurry consistency for the
slurry solids fraction and the paxticular coating process,
and give the hydrophilicity and microtexture that are most
compatible with the intended image coating system.
A reactive inorganic material most desirably
present is a magnesium compound. Magnesium carbonate,
rnagnesium oxide r magnesium hydroxide, and monomagnesium
phospha~e have been used, and the characteristic,
desirable, contribution to alkali resistance was obtained
in each case. Zinc oxide, zinc carbonate or zinc
phospha~e could be substituted for the magnesium compound~
though slightly poorer alkali resistance was obtained with
the zinc compounds than with the magnesium compounds.
The arnount of magnesia, i.e. t magnesium oxide or
magnesiuln hydroxide, generally a~ded is not enough to
yield a fully tribasic ~dehydrated) phospha~e composition
upon Eiring, so additions oE other materials supplying
polyvalent cations will in general give Eurther alkali
resistance~ Hydrated or transition aluminas, sols of rnany
metal oxides, or blends of these materials, may be added,
generally together with magnesia and generally in such
proportions as to optirnize the coating as noted abo,ve.
The graded gamma~theta alurrlina designated "G~ 2500~ by its
supplier, the Micro A~rasives Co~p. oE Westfieldt Mass~,
the hydrated alumina "Hydral 71~; supplied by the ~luminum
Co. of ~me~ica, the predominantly boehmite product,
"Dispural'~ supplied by Condea Chemie G ~ H, 2000 Hambur~J
13, West Germany; the "Aluminum Oxide C" of Degussa
Pigrnents Division, D-6000 FrankEurt 1, West Germany; and
the alumina, chrornia, yttria, ~irconia, an~ ceria sols
supplied by Nyacol Inc., Ashland, Mass., are examples o~
reactive materials use~ul in combination with the sug-
~ested ,nagnesium compounds. This list is intended ~o be
t/~ ~,D~-
7t7 -1 3-
sugyestive rather than exhaustive. Many other compounds
are expectd to be useful as reactive materials in the
~orm of sols or ine powders: compounds such as titanium
~ioxide, calcium hydroxide, calcium oxide~ calcium
fluoride, or calcium phosphate, beryllium oxide, ammonillm
fluorotitanate, and tungstic oxide are suggested by the
li-terature as useful constituents of phosphate glasses.
The resulting fired slurries tolerated moderate
levels of alkali metal oxides, such that commercial or
technical gra~es of materials are gener~lly acceptable;
however, compounds containing majo~ amounts of alkali
metal cations are not recommended. When silica sol is
added, compensatin~ extra metallic oxide should also be
a~ded to optimize alkali resistance.
In addition to reactive inorganic particulate
materials or some blend thereof~ particles of hard, wear-
resistant materials may be added with good effect. In
general these ar~ expected to react only superficially
with the phosphate bonding material~ and not to contribute
subs~antially to insolubilization. Graded alpha alumina
o the type of "331200 Alundum'l~ supplied by ~he Norton
Co. of Troy, N.Y., Gr "WSK l200" white alumina supplied by
Tr~ibacher GMBH of Treibach, Austria, and various grades
o~ "WCA" alumina supplied by Micro ~brasives Corp., are
~seful. It is necessary to burn off organic contaminants,
as hy kiln Eiring, ~rom some of these ma~erials~ Graded
tin oxide supplied by Transelco~ Inc. of Penn Yan, N.Y.,
was substituted for or blended with alumina in several
propor-tions witllout loss of properties. Graded fine sands
of other hard ~aterials such as quartz, amorphous silica,
cerium oxide, zirconia, zircon, spinel, aluminum silicate
(mullite), and even hydrophobic particles such as silicon
carbide, among many others, would be expected to function
sa~isfac~orily, though perhaps (as compared to alu~ina) ~o
have less attractive co~t or availability as closely-sized
powders. It is preEerred to use hydrophilic parti~le~ in
the practice of the present invention, and especially
metal o~ides.
These hard par~icles contribute wear resistance
and coarse roughness to the fired coating. 'rhe amount and
size to be added depends on development of optimum com-
patibility with the desired image coating system, to the
extent such compatibility depends on coarse roughness,
measurable as "Arithmetic Average Roughness" using a
profile measuring instrument. ~xamples o~ such instru
ments are the Federal Products Corp~ (Providence, R.I~)
~ "Surfanalyzer"~ and the Bendix Co. (Ann Arbor~ Mich.)
"ProEicorder"~
It is well known that diferent lithographic
substrate texturizi~g processes and he variation of
conditions within these processes provide diferent ranges
oE ~rithmetic average roughness and difEerent combinations
of arithmetic average roughness and specific surface area.
The optimum combina~ion oE ~hese characteristics depends
upon the type o~ use to which the final lithographic plate
is subjected and the particular photosensitive composition
applied thereto. Important characteristics to be
considered with reyard to selecting combinations of these
charact~ri~tics with specific photosensitive compositions
include the mechanical adhesion and release properties
(e.g., developability) of the imaged coating. By
adjusting the size~ type, fraction, and mix oE particles
in the coating composition, the coating process o~ the
present invention can provide substrates over most of the
range of roughness and specific surEace areas produced hy
all of the prior art processes. The present process is
highly El~xible and can be readily al~ered to provide
substrates which fit changed r~quirements.
It should be noted that one can practice the
present invention by Eorming monoalumin~n phosphate or
other acid phosphates in situ during the Eiring step.
This can be accomplished, or example, by coating a slurry
oE phosphoric acid and a stoichiometric excess o~ reactive
alumind onto the alulninum or aluminized surEace to be
Eired. Aluminum phosphate is ~enerated durin~ the initial
~rh~e ~
firing period, an~ with a stoichiome~ric excess of alurnina
present, reactive alumina particulate material will remain
in the reactive composition during the continued firing.
This is sufficient to provide coatings according to the
present invention, and the formation cf monoaluminum phos-
phate or other aluminum phosphates or mixed phosphates of
aluminum and other metals in situ is contemplated as being
within the scope o~ practicing the present invention.
In addition to the ~oregoing in situ formation
by reaction oE excess metal oxide or hydroxide with
phosphoric acid, it is also possible to form monoaluminum
phosphate in situ or mixed phosphates of alwninum and
other metals in situ by reacting stoichiometrically
ey~i~alent amounts of reactive alumina~ i.e. 9 aluminum
oxide or aluminwm hydroxide, wi~h either pho~phoric acid
or an alkaline earth acid phosphate such as monomagnesium
phosphate solution. The interchang~ability of mono-
alulninum phosphate with a reaction mixture containing
alulnina and phosphoric acid or an alkaline earth acid
phosphate is shown by ~he following equivalences:
3Ca(H2PO4)2 ~ A123 = 2~1(H2PO4)3 ~ 3Ca~
3MgtH2PO4)2 + ~12O3 = 2Al(H2PO4)3 ~ 3MgO
Al(OH)3 ~ 3H3PO~1 = A1(H2PO4)3 + 3H20
1~1203 ~r 61~3P04 = 2Al(H2po4)3 t 3~20
The foregoing reactions are not necessarily of practical
si~niEicance.
3~ Further, alkaline earth acid phosphates may be
created in solution by mixing an appropriate alkaline
~arth tribasic phosphate with phosphoric acid. For
example,
Ca3(PO4)2 ~ 4H3PO4 - 3Ca(H2pO4)2
Mg3(po4)2 -~ 41I3PO4 = 3M~(~3~PO~)2
Mg3(po4)2 + H3PO4 - 3MgHPO4
~ lG
The ~ollowincJ reactions dernonstrate the
processes which create orthophosphates during firing with
phosphoric acid and/or a suitable acidic phosphate
starting material:
2H3PO4 + A123 ~ 2AlPO~ + 3H20
Al(H2PO4~3 + A12O3 ~---, 3~1PO~ ~ 3H20
Al(H2PO~)3 + 3MgO -~ AlPO4 + Mg3(po4)2 + 3~2~
3,~g(~l2PO4~2 + 2A1203 - ~ 4AlPO4 -~ Mg3(po4)2 ~ ~2
GCa(QH)2 + 3Mg(H2Po4~2 ~ 2Ca3(PO4)2 ~ Mg3(po4)2 + 12~20
It has been Eound that addition oE calcium-
containing inorganic compounds to the slurry reduces the
necessity Eor close monitoring o the firing temperature,
by providing a mixture that i5 efEectively dehydra~ed at
somewhat lower temperatures or shorter times. The calcium
addition is preferably in the ~orm of calcium hydroxide,
calcium ca~bonate, calcîum oxide, calcium phosphate, or
mixtures thereof. To achieve this useful result it is
also desirable to add the magnesium-containin~ compound as
a soluble phosphate and the aluminum-containing compound
in an ultraEine and/or dissolved condition.
It has also been ound that addition of calcium-
containing inorganic compounds to the slurry contributes
to a coating colnposition that may be fired at a lower
3Q tempera~ure or in less time, while retaining lithographic
-~uality at yreater coating thicknesses than previously
L~ossil~le. The alulninum-con~aining compound may be a ~umed
alumina, e.g. that produced by flame hydrolysis of
anl)ydrous alulninulll chloride, having mean ultimate parkicle
diameter less than 20 nanometers. When all the consti-
tuents which are required to react to form an intimately
dispersed, uniforrn phosphate phase are in the most rapidly
~ 17~
r:edutive ~orms currently available as chemical raw
materials, better functional properties at the lower
Eiring times and/or temperatures are obtained. It should
be noted that too great a stoichiometric excess of
reactive cation-supplying materials over anion supplying
materials, i~e~ phosphate and silicatel tends to weaken
the coating mechanically, giving less abrasion resistance
of the type described by ~NSI ASTM tests C501-66 and
D1044-76, or a test combining some of the features o each
of tl~e two standard tes~s.
The slurries or solu~ions generally contain
between 85 and 95% (by volume) of material that i5
vola~ile upon firing, the actual amount being that
re~uired to yield a satisfactory coating weight and
satisfactory coatability with the chosen coating tech~
nique. A mix~ure of so% aqueous monoaluminu~ phosphate
solution with an equal weiyht of water, ~alls easily in
this range, as do slurries which contain a greater number
oE additives. The volatile material is generally water,
although water-miscihle volatile liquids such as alcohols
may be added in substantial partO The volume of volatile
material stated above includes bo~h the volatile material
added as solvent or diluent, and that generated by reac-
tions such as pyrolysis of organics or acid-base metathesis~
The second largest constituent of the slurries
or solutions, which constituent may or may not be present,
is a Eorm of hard particles, such as the alpha aluminas
men~ioned previously. These may comprise between zero and
55~ of the volume oE ~he non-volatile portion. The size,
shape, volume and type oE hard partic]es is varled as
needed to accolnmodate the intended specific use o the
ceramic-coated materialO ~ coating containing more than
65% hard particles by volume will be too lean in binder
material with the result that the hard particles will not
35 be securely bonded, and ~he voids between them may tend to
trap ink in areas required to remain free of ink when the
Co,ltill~ is used as a lithographic substrate. A fired ~ilm
containillg 45-60% by volume hard p~rticles is dominated by
relatively coarse features. This -~ype of surface is
desirable for use with sorne image coatings. Fired films
containing less than 50~ by volume hard particles may have
their surfaces increasingly dominated by ultrafine
featur~s, because the relative volume of hard particles
declines, while the relative volume of ultrafine particles
increases. The ultrafine features are more desirable Eor
use with some image coatings~ Sedimentation and agglomera-
tion of hard particles may be a source of coating problems.Where a formulation i~s required wherein the main charac-
teristic is ease of coating with simple apparatus, the
reduc~ion of the volume of, or ~he complete elimination
oE, ~he coarser particles may be preferableO The hard
particles considered for use in this invention react so
slowly with phosphate solu~ions that they are presumed to
undergo negligible reaction during firing
The remaining consl-ituent of the slurry ~ormula-
tion is a matrix or bonding constituent. In the simplest
form, phosphorîc acid alone may be coated and fired; how-
ever, useEul properties are enhanc~d by using acid phos-
phates, such as monoaluminum phosphate, and/or reactive
particles, such as alumina.
Greater chemical resistance than can be obtained
with a coating derived from phosphoric acid employed by
it~lf is essential or at least preferred. To obtain
greater chesnical resistance, reactive particles which
yield metal ions should he added to khe pho.sphate solution
in quantities sufficient ~hat an orthophosphate or mixture
30 of orthophosphates is created upon firing.
Where the reactive particles are of a chemical
species which yield calcium ions, a quantity ranging Erom
about 0 to about 20% of the arnount ~hat would combine with
the available phosphate ions to give calciu~n ortho~
35 phosphate is used~ Calcium additions in excess of 20~
result in coagulation of the slurry, and are li]cely to
result in a decline in acid resistance oE the final
article. Quantities in the range of about 4 to about 7%
give the rnaximum reduction oE firing temperature with no
noticeable degradation of acid resistance or slurry
viscosity. A solution o~ monocalcium phosphate, rather
than particles which yield calcium ions~ may be used to
provide the calcium content.
Where the reactive particles are of a chemical
species which yield magnesium ions, a quantity ranging
from about 0 to about 35~ oE the amount that would combine
with the available phosphate to give magnesium
orthophosphate, is used. Quantities in the range of about
10 to about 20% are preferred. Where magnesium-containing
particles are added at a level greater than 35% to
monvalulninum phosphate, the resulting coating will flake
lS away from the aluminum substrate upon cooling down rom
the ~iring temperature. ~nounts of magnesium at lower
than the 10% level are found to provide a less than
optirnum contribution ~o alkali resistance. Comlnercial
monomagnesium phosphate solution, containing 5.3% MgO and
32.6~P205 by weight, may be used to provide magnesium
ions since the amounts of magnesium and phosphate provided
by this solu~ion, witn no other phosphate addition, give a
magnesium ion addition oE 19.1~ of the amount required to
yield magnesium orthophosphate.
~ Reactive particles yielding aluminum ions may be
added in quantities ranging ~rom about 0 to about 200% of
the amount which, in combination with all other metal and
phosphate ions present or liberated during firing, would
give ~oichiometric orthophosphate. The pre~erred range
is 100-150~. For example, if the quantity of calcium-
containing material in the phosphate solution slurry were
5% oE the a,nount that would give calcium orthophosphate,
and if the quantit~ of Inagnesium-containing material in
the phosphate solution slurry were 15% of the amount that
would give magnesium orthophosphate, then the preEerre~
alnount o aluminwn ion-containing material to be added
would be in the range oE 80-130% of the amount that would
-20-
3~
yiel~ aluminum orthophosph~te. I another reactive cation
were present, sufficient additional aluminum ion would
have to be provided in excess o~ the 100-150~ orthophos-
phate level to form the other reactive cation's ortho-
cornpound for the preferred compositions (e~g. f if theotner cation were silica, then sufficient additional
aluminu,-n ion-containing material would have to be provided
to form aluminum orthosilicate). Aluminum contents below
100~ result in coatinys lacking chemical resistance, and
alurninum contents above 150%, in combination with a
typical loading of hard particles, result in decreased
wear resistance of the coating. The excess oE unr~acted
fine particles have utility as a filler or flatting agent,
imparting a useful rnicrotexture or chemical character to
the surface of the Eired ~ilm. It is concei~able that the
total fine aluminum reactive parkicle content could be
raised into the 150-200g range, with the resul~ing improve-
ment in anchorage ~or the overcoated material compensating
~or the loss of basic abrasion resistance.
Dispersants such as gluconic acid may also be
added to the slurry. Alkaline dispersants such as sodium
tripolyphosphates are not preferred even though they do
not destroy the Eunction of the present invention.
Pre~reatment oE the coarsest particles as with colloidal
silicar may make the resulting slurries more stable
a~ainst sedimentation.
Lithographically useEul compositions may, of
course, be coated on the cerarnic surEace. Such composi-
~ions would comprise 1) oligomeric diazonium resins,
2) positive acting diazo oxides or esters, 3) photopoly-
merizable organlc compositions (particularly such as
ethylenically unsaturated ma~erials in the presence of
ree radical photoinitiators~, 4) oligomeric diazonium
resin undercoats with photopolymerizable organic composi-
tion overcoats, and 5) any other various well known litho-
~raphically useful photosensitive compositions.
Tllese and other aspects oE the present invention
will beco~ne apparent ~roln the ~ollowing examples.
7t~ ~L_
Example 1
A precleaned aluminum oil was coa'ced with a
solu~ion of 50 weight percent monoaluminum phosphate in
water and dried below 100C to a coating thickness of
about 3 micrometers. The surface temperature of the
coating was raised to 550F (260C) in ninety seconds in
an oven and removed after thirty seconds at khat tempera-
ture. A positive acting photosensitive composition as
described in Example 3 of U.S. Patent No. 4,247,616 was
coated onto the treated surface a~ter rinsing and drying.
The composition adhered to the substrate and developed off
cleanly after exposure.
Example_2
lS A precleaned alumin~n foil was coated with a
composition comprising, by weight, 1~ transition alumina
(nominally 0~ 5 micrometers diameter of gamma or theta -
phase alumina), 15% monoaluminum phosphate~ 0.75%
magnesium oxide tparticle size less than 200 mesh~, and
72.25~ water. The coatiny was dried to a thickness of
about 3 ~nicrometers.
The coated foil was placed in an oven and the
surface tempera~ure of the coating was raised to 550F
(260C) in thirty seconds. Dwell time in the oven was one
and one half minutes~ The coated ~oil was co~led, rinsed,
and dried, then rolled up.
The foil was subsequently unrolled and coated
with the positive acting photosen.sitive composition of the
~revious example~ The photosensitive layer adhered well
to ~he substrate and developed o~f cleanly with no undesir-
able undercuttin~ of the half tone image. The background
areas were less readily attacked by alkaline developer
than was the ~ubstrate oE Example 1. There was also
better adhesion on press because of reduced undercutting
and a Eurther increase in adhesion due ~o surface texture
provided.
22-
~ rhe procedure oE Example 2 was repeated except
that 1% æinc oxide was used in place of the magnesium
oxide and correspondingly less water was used. The coated
aluminum was found to be somewha less resistant to
developer chemicals than ~he sheet of Example 2, but still
provided excellent adherenee to the photosensltive layer
and provided a useful prin~ing plate surface.
Example ~
The procedure of Example 2 was repeated, using
the same coating composition, but with iring effected at
600F (310C~. No differences wer~ obs2rved between the
mechanical or chemical properties of the materials. Both
were presumed to be ~ully dehydrated.
The procedure of Example 2 was repeated using a
coating composition having 8 percent reactive (e.g., theta
transition alumina~ alumina (nominally 0.5 microns
diameter), 0.5 percent dead-burned magnesia (parkicle size
less than 200 mesh~, and 4.0 percent alpha alumina
(nominally 1.0 microns average diameter) ~hese were
dispersed as a 30% raw solids slurry in 0~5 percent
aqueous gluconic acid. A water and monoaluminum phosphate
solution was used to provide the above weight percentages
of metal oxides and 15 percent by weight of monoalu~inum
phosphate and 66 percent water. The alpha alumina content
conferred additional wear resistance and a higher arithmetic
average roughnes~ to the fired coating~ These additional
properties are advantageous in many image coating systems.
Example 6
The ~ired substrate of Example 2 was immersed
eor 2-1/2 Ininutes in a solution containing 5% by weight
Phila. Quartz Co. "Star" brand sodium silicate solution at
95C, then rinsed in a deionized water spray and dried.
~ 7 -23-
.~t was coatecl with a negative o]..igomeric diazonium resin
and an ~ ~nicron dried thickness coating of the negative
~hotopolymeric composition of Example 2 oE U~. Serial No.
103,712, filed December 14, lg79. The image develoepd
cleanly upon conventional exposure and development. It
gave Inany thousands of good inked impressions during an
accelerated press wear test, at least equalling the wear
performance of the same image material on conventional
c3rained and anodized aluminum.
Example 7
A slurry was prepared consisting of l~o 1~ (wt~ )
Norton Co. "~381200 Alundum~' brand alpha alumina (prior to
ad~ition it had been cleaned by firing overnight in air at
600C); 2.4% Alcoa "Hydral 710" alumina trihydrate; 0 75
Condea Chemie l'Dispural 10/2" alumina monohydrate, 0.36%
Martin Marietta "MagChem 10" magnesia, and 14.4% 50~
monoal~minum phosphate solution, plus some surface-active
materials as ~ollows. The dry powders were milled
~ogether as a 30~ solids slurry~ First the alpha alumina
was milled alone in a solution containing all the water o~
the 30% slurry and 2~ oE ~he weight of alumina as Nalco
"Nalcoag 1115" colloidal silica, for one hour. Then
enough 50~ yluconic acid was added to make the aqueous
phase 0.5% acid, and the balance of the dry solids were
ad~ed, and milling continued for 12 hours~ A weighed
sample of the 30% slurry was added to a container with
enough additional distilled water and 50% rnonoaluminum
phospila~e solution to yield th~ above ~roportions, and the
combination stirred with a propellor mixer and roll coated
onto sheets o~ alulninum alloy cleaned by trisodium
i~hosphate (3% solution at 160F) etching, rinsing, and
desmutting in 50~ HNO3, r.insing, and drying. The coated
sheets dried in roorn air, and were fired 2 min. in an oven
35 wl~ose circulating air temperature was ~iven by the oven
colltroL thermolneter as 650F. (~rhis thermal exposure had
E>reviou~ly been Eound to yield a sur~ace te~lnpera~ure oE
~ 3 ~ 2~-
550F duriny the final 30 sec.) When cooled and coated
with a positive-working image composition of -the diazo
oxide-phenolic resin type well known in the art, the
resulting lithoyrapllic plate was capable of state-of-
the-art performance, with regard to image contrast,
developer resistance, and wear life, as determined b~
accelerated wear tests.
Example 8
A slurry was prepared~ coated and fired
similarly to that of Example 7 except that the proportions
were grade 1200 alpha alumina, 17~8%; Alcoa l'~ydral 710",
3.2%; Condea "Dispural 10i2" 0O7%; MgO, 0.38%; the ~nilling
tir~es were 30 min. for alpha alumina in silica 501, and ~
hours ~or all solids at 40% solids; the phosphate addition
was 15.4% 50% monoaluminum phosphate solution. The
resulting slurry was readily roll coatable on etched and
desmutted alulninum, and also onto lithographic aluminum
alloy precleaned by brushi~g with a motor-driven
cylindrical "Scotch-brite" Type A Very Fine ~l~p brush,
while being sprayed with 150F~ 3% solution of Oakite
"#166" metal cleaner, then rinsing and air drying. The
resulting lithoplates conformed to the standards
established ~or Example 7.
Example 9
The slurry of Example B was roll coated onto
Bethlehem Steel Co9 "Duraskin" sheet, which is steel sheet
plated with a predominately alwninum,
aluminum-zinc-silicon alloy, and rerolled to .010 in.
thickness. The "Duraskin"~sheet was precleaned using the
same "Scotch-brite" brushing technique described in Ex-
ample 8. The fired material functioned very well as the
substrate for either neyative- or positive working, long-
wear life, lithographic plates; no significant differencesbeiny observed between it and the lithoplates of Example 8
in its image contrast or resolution, or its wear characteristics.
~ t~,~
25-
A slurry was prepared consisting of 19.05~
(w~/wt) of "Imsil ~-10~ amorphous silica, said by the
Illinois Minerals Co. oE Cairo, Ill~, to have a mean
particle diameter of 2.2 micrometers; 0.65% `'~luminum
Oxide C", said by the Degussa Pigments Division of
Frankfurt, Germany to have a mean particle diameter oE
0.02 rnicrometers; 32.9% deionized water; and 47O4% of the
Mobil Chemical Co. 50~ monoaluminum phosphate solution~
The silica and colloidal alumina were Eirst mixed together
in the water, then the phosphate solution was added. This
slurry was coated onto the subs~r~e o Example 7 and
fired as in the same Example It was then immersed 25
se~onds in an 80C solution containing 4.8 wt. % "Kasil
No. 1" potassium silicate solution available from the
Philadelphia Quartæ Co., rinsed in deionized water and air
dried. The resulting sheet was primed with a negative-
working diazo compound and overcoated with a neyative-
working photopolymer of a type well-known in the art. The
resulting printing plate was exposed to a tes~ negative
and developed with 3M Subtractive Developer. It was found
to have commercially acceptable photospeed, contrast,
resolution, and press life.
Example_ll
A slurry was prepared consistiny of 15.08~ (wt.)
Norton Co. "~381200 ~lundum" brand alpha alumina (prior to
addition it has been cleaned by firing overnight in air at
600C), 0~45~ (wt.) "Nalcoag 1115" 15% aqueous colloidal
30 silica suspension, 0.45~ (wt.) 50~ aqueous gluconic acid
solution, 62.12% (wt.) deionized water, 2.72~ (wt.)
"Aluminum Oxide C", manufactured by Deyussa Pigments
Division of Frankfurt, Germany, 0.96~ (wt.) Condea Chemie
"Dispural 10/2" alumina monohydrate, 4.13~ (wt.) 50
aq~eous monoaluminum phosphate solution from Mobil
Chemiccll Co., 13.48% (wt.) coMmercial magnesium phosphate
solution containing 3.3~ magnesium and 140 2% phosphorus
t ~e~
26-
from ~obil Chemical Co., and 0.61~ (wt.) reagent calcium
hydroxide. This ~ormulation was coated onto lithographic
aluioinum at a coatiny weight in the range oE 325 to 400
mg~square foot and fired at a temperature of approximately
550F for one minute. When cooled and coated with a posi-
tive working composition of the diazo oxide-phenolic resin
type well known in the art, the resulting lithographic
plate was capable o state-of-the-art perEormance, with
regard to resolution, ink/water balance, and wear life, as
determined by accelerated wear tests.
Example 12
___
A slurry was prepared consis~ing of 18.64% (wt.)
Trc-ibacher "WSK" F1200 alumina (prior to addition it had
been cleaned by calcinin~ at 600C) 0O56% (wt.) "Nalcoag
lllS" 15~ aqueous colloidal silica suspension, 0.44% ~wt.)
50% aqueou~ gluconic acid solution, 58.64~ (wt.) deionized
water, 4.21~ (wt.) "Aluminum Oxide C~', manufactured by
Degussa Pigments Division of Frank~urt, Germany, 17.00~
(wt.) cornmercial magnesium phosphate solution containing
3.3~ magnesium and 14.2% phosphorus ~rom Mobil Chemical
Co., and 0.51% (wt.) reagenk calcium hydroxide~ This
formulation was coated onto lithographic aluminum at a
coating weight in the range oE 325 to 400 mg/square foot
and fired at a temperature of approximately 550F for one
Ininute. When cooled and coated with a positive working
composition of the diazo oxide-phenolic resin type well
known in the art, the resulting litho~raphic plate was
capable oE state~o~-the-art performance, with regard to
resolution~ ink/water balance, and wear life, as deter-
mined by accelerated wear tests.
