U.S. patent number 3,808,000 [Application Number 05/238,933] was granted by the patent office on 1974-04-30 for printing plate and method of preparation.
This patent grant is currently assigned to W. R. Grace & Co.. Invention is credited to Arthur D. Ketley, Frank Magnotta.
United States Patent |
3,808,000 |
Magnotta , et al. |
April 30, 1974 |
PRINTING PLATE AND METHOD OF PREPARATION
Abstract
This invention relates to a printing plate of high-wear
resistance comprising an aluminum surface which is anodized with
sulphuric acid and stabilized in concentrated phosphoric acid and
having thereon an ink-receptive image layer. The aluminum surface
comprises a cellular structure of alumina-containing pores ranging
in size from about 5 to 100 angstroms in average diameter and also
comprises about 20 to 5000 mg./meter.sup.2 aluminum sulphate and
about 1 to 50 mg./meter.sup.2 aluminum phosphate. The stabilized
anodized aluminum is not only an excellent substrate for a
lithographic printing plate but also for letterpress printing
plates.
Inventors: |
Magnotta; Frank (Laurel,
MD), Ketley; Arthur D. (Columbia, MD) |
Assignee: |
W. R. Grace & Co. (New
York, NY)
|
Family
ID: |
22899920 |
Appl.
No.: |
05/238,933 |
Filed: |
March 28, 1972 |
Current U.S.
Class: |
430/155; 205/69;
205/324; 430/526; 430/274.1; 430/278.1; 101/459; 205/105;
205/328 |
Current CPC
Class: |
B41N
3/034 (20130101); C25D 11/24 (20130101) |
Current International
Class: |
C25D
11/18 (20060101); B41N 3/03 (20060101); C25D
11/24 (20060101); G03c 005/00 () |
Field of
Search: |
;96/35.1,115,86,33
;101/459 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; J. Travis
Assistant Examiner: Goodrow; John L.
Attorney, Agent or Firm: Plunkett; Richard P. Prince;
Kenneth E.
Claims
1. A printing plate comprising a support with an anodized aluminum
hydrophylic printing surface and an ink receptive coating layer
directly thereon, said anodized aluminum surface comprising a
cellular pattern of aluminum oxide having cells with pourous
openings of about 5 to 100 angstroms in average diameter and said
surface comprising about 20 to 5000 mg./meter.sup.2 aluminum
sulphate and about 1 to 50 mg./meter.sup.2 aluminum phosphate, said
ink receptive coating layer comprising an image forming material
selected from the group consisting of light sensitive
2. The printing plate of claim 1 wherein the light sensitive
material is a
3. The printing plate of claim 1 wherein the light sensitive
material is a photopolymer.
Description
This invention relates to an improved anodized aluminum
lithographic printing plate. More particularly this invention
relates to producing an anodized aluminum lithographic surface
which is highly water receptive and shows excellent abrasion
resistance and adhesion to photosensitive materials.
In the lithographic printing plate industry, aluminum is generally
used as a support for lithographic printing plates because of its
low cost, light weight, availability, flexibility and dimensional
stability. The water receptivity of the aluminum oxide surface is
further improved by anodizing the aluminum in an electrolytic
solution.
When an aluminum sheet is anodized in sulphuric acid, the surface
is covered by an anodic coating of alumina. This alumina is very
water receptive, due to the large number of small pores in the
surface, and shows excellent abrasion resistance and excellent
adhesion to photosensitive materials. Such a surface would be
excellent for a lithographic plate were it not that it is unstable,
being converted rapidly to boehmite, another form of alumina.
Experience has shown that H.sub.2 SO.sub.4 anodized, unstabilized
anodic coatings slowly "seal" under normal conditions (i.e.
68.degree.F, 35%RH) during a period of 6 months, the surface
impedance (Z) changing by at least doubling its initial value.
These surfaces can also be sealed rapidly by immersion into boiling
water for a period of no more than 15 minutes at which point the
surface impedance may increase to four times its original value.
Such sealed surfaces, because of their now low porosity (high
impedance) are no longer able to carry water efficiently or adhere
photosensitive materials. On the other hand, aluminum for
lithographic plates can be anodized normally using phosphoric acid
since the resulting anodic coating is stable. However, phosphoric
acid anodizing of aluminum leads to a coating with a small number
of relatively large pores which is hence less porous, less abrasion
resistant and less desirable.
One object of the instant invention is to produce a lithographic
printing plate containing a large number of small pores in the
surface. Another object of the instant invention is to produce a
litho-plate which is stable still another object is to provide an
improved process for the preparation of stabilized and highly
hydrophylic anodized lithographic printing plates. A yet further
object is to provide an improved anodized aluminum substrate
suitable for application of ink-receptive image patterns.
Surprizingly these and other objects have been achieved by
subjecting an aluminum plate to anodizing in a sulphuric acid bath
and thereafter stabilizing the thus anodized plate in a solution of
phosphoric acid. By this means one is thus able to combine the
enhanced porosity of the sulphuric acid anodized plate and the
stability of the phosphoric acid anodized plate in one element.
Lithographic plates prepared in the manner of the instant invention
show excellent adhesion on ink-receptive photopolymers and great
ability to carry water in the non-image areas. Their resistance to
abrasion and wear on the press is markedly enchanced relative to
conventional plates and especially those anodized in phosphoric
acid. Furthermore, photopolymer letter press plates prepared using
the same substrate also show greatly enhanced adhesion of the
polymer to the substrate. For the most part hereinafter the
invention will be explained in terms of forming a lithographic
printing plate.
Anodizing of aluminum substrates results in coatings that are
essentially aluminum oxide having a cellular structure in which the
aluminum surface is completely covered with the aluminum oxide
layer. However each cell of aluminum oxide contains a star shaped
pore which does not extend completely through the aluminum oxide
layer. The average pore size depends upon the electrolytic media
used in the anodizing step. To a lesser extent the conditions of
anodizing such as electrolytic concentration, voltage, temperature
and duration of anodizing can also effect pore size. Since these
conditions may be varied, the resulting surface is herein defined
in terms of average pore size of the resulting surface.
The average diameter of the pores in the aluminum oxide cells which
characterizes the anodized surface of the aluminum of our invention
ranges from about 5 to about 100 angstroms which is normal for
anodizing in sulphuric acid. The aluminum sulphate which
characterizes our improved aluminum lithographic surfaces
represents a concentration of from about 20 to about 5000 mg. or
more of aluminum sulphate per square meter. The aluminum phosphate
which characterizes our improved aluminum lithographic surfaces
represents a concentration of from about 1 to about 50 mg. or more
of aluminum phosphate per square meter.
In the instant invention an aluminum oxide layer is obtained by
anodizing the aluminum surface in an aqueous solution containing
sulphuric acid. The concentration of sulphuric acid can be varied
widely. Good results are achieved within the range 5 to 30 percent
sulphuric acid. Ordinarily, concentrations of 15 to 20 percent are
employed to mitigate repetitive replenishment of the
electrolyte.
Following the anodizing step, the sulphuric acid anodized layer is
water washed and then immersed into a solution of phosphoric acid
for stabilization. The concentration of the phosphoric acid bath
can be varied over a wide range. Excellent stabilization results
from an aqueous bath containing 3 to 35 percent phosphoric acid.
Generally, concentrations of 15 to 30 percent are used to defer
continuous replenishment of the acid in the bath.
Following the stabilization, if desired, a hydrophylic layer
sufficient to cover the anodic layer except for certain peaks in
the oxide layer extending through the hydrophylic layer may be
coated thereon. If desired or necessary, the coating may be of
sufficient dimension to overlie the peaks. In the practice of
applicants invention, however, it is not generally necessary to use
the hydrophylic layer due to the high water receptivity exhibited
by the stabilized anodized alumina. Should a hydrophylic layer be
employed, various conventional materials can be used including but
not limited to ethylene maleic anhydride; polyacrylic acid;
carboxymethylcellulose; methylvinyl ether/maleic anhydride
copolymer; poly[ vinybenzal-2,4-disulfonic acid] sodium salt; and
polyacrylamide and the like. These hydrophylic materials are
usually applied to whirl-coating in a suitable solvent to yield
concentrations in the range 5-100 mg./ft..sup.2.
After the anodic surface has been stabilized and whether or not a
hydrophylic coating is applied thereto, a light sensitive coating
or silver precipitating materials can be placed on the surface.
Thus, in addition to the light sensitive materials and silver
recipitating materials set out in U.S. Pat. No. 3,511,661 which are
operable herein, various other well-known photopolymerizable resins
may also be employed. One type of photopolymerizable resin is an
organic solvent-soluble ester of an unsaturated acid and a
polyalcohol. Examples of such photopolymerizable resins are
polyvinyl cinnamate, starch cinnamate, cellulous cinnamate, starch
furfurylacrylate, cellulous furfurylacrylate and polyvinyl
furfurylacrylate resins. One commercially available example of such
a resin is "Kodak Photo Resist" which is a polyvinyl cinnamate.
Another operable light sensitive system is that set out in U.S.
Pat. No. 2,760,863 wherein the photopolymerizable layer comprises
an addition polymerizable ethylenically unsaturated component and
an addition polymerization initiator therefor activatable by
actinic light. Still another light sensitive material operable
herein is a polyvinyl acetate latex stabilzed with polyvinyl
alcohol containing 0.01 to 1.0 part per hundred parts of NH.sub.4
.sup.+ or K.sup.+ dichromate after drying.
Photocurable compositions are also operable herein as the
ink-receptive image area. One such photocurable composition
operable is that set out in U.S. Pat. No. 3,627,529 assigned to the
same assignee incorporated herein by reference.
The crucial ingredients in the photocurable polymer composition
are:
1. 2 to 98 parts by weight of an ethylenically unsaturated polyene
containing two or more reactive unsaturated carbon to carbon bonds
per molecule;
2. 98 to 2 parts by weight of a polythiol containing at least 2
thiol groups per molecule; the total combined functionality of the
carbon to carbon bonds per molecule in the polyene and the thiol
groups per molecule in the polythiol being greater than 4; and
3. 0.0005 to 50 parts by weight of a photocuring rate accelerator
based upon 100 parts weight of (1) and (2) above. (Preferred range
of accelerator is about 0.005 to about 30 parts by weight).
The reactive carbon to carbon bonds of the polyenes are preferably
located terminally, near terminally, and/or pendant from the main
chain. The polythiols, preferably, contain two or more thiol groups
per molecule.
Included in the term "liquid," as used herein, are those
photocurable compositions which in the presence of inert solvent,
aqueous dispersion or plasticizer have a viscosity ranging from
essentially zero to about 20 million centipoises at
130.degree.C.
As used herein polyenes and polyynes refer to simple or complex
species of alkenes or alkynes having a multiplicity i.e., at least
2, "reactive" carbon to carbon unsaturated functional groups per
average molecule. For example, a diene is a polyene that has two
"reactive" carbon to carbon double bonds per average molecule,
while a diyne is a polyyne that contains in its structure two
"reactive" carbon to carbon triple bonds per average molecule.
Combinations of "reactive" triple bonds within the same molecule
are also operable. An example of this is monovinylacetylene, which
is a polyeneyne under our definition. For purposes of brevity all
these classes of compounds will be referred to herein as
polyenes.
As used herein the term "reactive" unsaturated carbon to carbon
groups means groups which will react under proper conditions as set
forth herein with thiol groups to yield the thioether linkage
##SPC1##
as contrasted to the term "unreactive" carbon to carbon
unsaturation which means ##SPC2##
groups when found in aromatic nucleii (cyclic structures
exemplified by benzene, pyridine, anthracene, and the like) which
do not under the same conditions react with thiols to give
thioether linkages. In the instant invention products from the
reaction of polyenes with polythiols which contain 2 or more thiol
groups per average molecule are called polythioether polymers or
polythioethers.
Methods of preparing various polyenes useful within the scope of
this invention are disclosed in U.S. Pat. No. 3,627,529 assigned to
the same assignee. Some of the useful polyenes are prepared in the
detailed examples, set forth in the following specification.
One group of polyene compositions are those polyene compositions
have a -ene or -yne functionality of at least two which are formed
by reacting either:
A. An organic epoxide containing at least two ##SPC3##
groups in its structure with a member of the group consisting of
hydrazine, primary amines, secondary amines, tertiary amine salts,
organic acids wherein said group members contain at least one
organic substituent containing a reactive ethylenically or
ethylynically unsaturated group; or
B. An organic epoxide containing at least one organic substituent
containing a reactive ethylenically or ethylynically unsaturated
group with a member of the group consisting of hydrazine and an
organic material containing at least two active hydrogen functions
from the group consisting of: ##SPC4##
A second group of polyenes operable in the instant invention is
that taught in British Patent No. 1215591 assigned to the same
assignee. This group includes those having a molecular weight in
the range of 50 to 20,000 a viscosity ranging from 0 to 20 million
centipoises at 70.degree.C. of the general formula: [A--X).sub.m
wherein X is a member of the group consisting of ##SPC5##
and R--C.tbd.C--; m is at least 2; R is independently selected from
the group consisting of hydrogen, halogen, aryl, substituted aryl,
cycloalkyl, substituted cycloalkyl, aralkyl, substituted aralkyl
and alkyl and substituted alkyl groups containing one to 16 carbon
atoms and A is a polyvalent organic moiety free of (1 ) reactive
carbon to carbon unsaturation and (2) unsaturated groups in
conjugation with the reactive ene or yne groups of X. Thus A may
contain cyclic groupings and minor amounts of hetero atoms such as
N, S, P or O but contains primarily carbon-carbon, carbon-oxygen or
silicon-oxygen containing chain linkages without any reactive
carbon to carbon unsaturation.
In this second group, the polyenes are simple or complex species of
alkenes or alkyenes having a multiplicity of pendant, teminally or
near terminally positioned "reactive" carbon to carbon unsaturated
functional groups per average molecule. As used herein for
determining the position of the reactive functional carbon to
carbon unsaturation, the term "terminal" means that said functional
unsaturation is at an end of the main chain in the molecule;
whereas by "near terminal" is meant that the functional
unsaturation is more than 16 carbon atoms away from an end of the
main chain in the molecule. The term "pendant" means that the
reactive carbon to carbon unsaturation is located terminally or
near terminally in a branch of the main chain as contrasted to a
position at or near the ends of the main chain. For purposes of
brevity all of these positions will be referred to generally as
"terminal unsaturation."
The liquid polyenes operable in this second group contain one or
more of the following types of non-aromatic and non-conjugated
"reactive" carbon to carbon unsaturation: ##SPC6##
These functional groups as shown in 1-8 supra are situated in a
position either which is pendant, terminal or near terminal with
respect to the main chain but are free of terminal conjugation. As
used herein the phrase "free of terminal conjugation" means that
the terminal "reactive" unsaturated groupings may not be linked
directly to non-reactive unsaturated species such as ##SPC7##
and the like so as to form a conjugated system of unsaturated bonds
exemplified by the following structure: ##SPC8##
etc. On the average the polyenes must contain two or more
"reactive" unsaturated carbon to carbon bonds/molecule and have a
viscosity in the range from slightly above 0 to about 20 million
centipoises at 70.degree.C. Included in the term "polyenes" as used
herein are those materials which in the presence of an inert
solvent, aqueous dispersion or plasticizer fall within the
viscosity range set out above at 70.degree.C. Operable polyenes in
the instant invention have molecular weights in the range of about
50 to about 20,000, preferably about 500 to about 10,000.
Examples of operable polyenes from this second group include, but
are not limited to:
1. crotyl-terminated polyurethanes which contain two "reactive"
double bonds per average molecule in a near terminal position of
the average general formula: ##SPC9##
where x is at least 1,
2. ethylene/propylene/non-conjugated diene terpolymers, such as
"Nordel 1040" manufactured by E. I. duPont de Nemours and Co.,
Inc., which contains pendant "reactive" double bonds of the
formula: --CH.sub.2 CH=CH--CH.sub.3,
3. the following structure which contains terminal "reactive"
double bonds: ##SPC10##
where x is at least 1.
4. The following structure which contains near terminal "reactive"
double bonds ##SPC11##
where x is at least 1.
A third group of operable polyenes includes those unsaturated
polymers in which the double or triple bonds occur primarily within
the main chain of the molecules. Examples include conventional
elastomers (derived primarily from standard diene monomers) such as
polyisoprene, polybutadiene, styrene-butadiene rubber,
isobutylene-iosprene rubber, polychloroprene,
styrene-butadiene-acrylonitrile rubber and the like; unsaturated
polyesters, polyamides, and polyurethanes derived from monomers
containing "reactive" unsaturation, e.g.; adipic acid-butenediol,
1,6-hexanediamine-fumaric acid and 2,4-tolylene
diisocyanate-butenediol condensation polymers and the like.
A fourth group of polyenes operable in this invention includes
those polyenes in which the reactive unsaturated carbon to carbon
bonds are conjugated with adjacent unsaturated groupings. Examples
of operable conjugated reactive ene systems include but are not
limited to the following: ##SPC12##
A few typical examples of polymeric polyenes which contain
conjugated reactive double bond groupings such as those described
above are poly(oxyethylene) glycol (600 M.W.) diacrylate,
poly(oxytetramethylene) glycol (1000 M.W.) dimethylacrylate, the
triacrylate of the reaction product of trimethylolpropane with 20
moles of ethylene oxide, and the like.
As used herein, the term polythiols refers to simple or complex
organic compounds having a multiplicity of pendant or terminally
positioned --SH functional groups per average molecule.
On the average the polythiols must contain two or more --SH
groups/molecule. They usually have a viscosity range of slightly
above 0 to about 20 million centipoises (cps) at 70.degree.C, as
measured by a Brookfield Viscometer. Included in the term
"polythiols" as used herein are those materials which in the
presence of an inert solvent, aqueous dispersion or plasticizer
fall within the viscosity range set out above at 70.degree.C.
Operable polythiols in the instant invention usually have molecular
weights in the range about 50 to about 20,000 preferably about 100
to about 10,000.
The polythiols operable in the instant invention can be exemplified
by the general formula: R.sub.8 --SH).sub.n where n is at least 2
and R.sub.8 is a polyvalent organic moiety free from "reactive"
carbon to carbon unsaturation. Thus R.sub.8 may contain cyclic
groupings and minor amounts of hetero atoms such as N, S, P or O
but primarily contains carbon-hydrogen, carbon-oxygen, or
silicon-oxygen containing chain linkages free of any "reactive"
carbon to carbon unsaturation.
One class of polythiols operable with polyenes in the instant
invention to obtain essentially odorless cured polythioether
printing plates are esters of thiol-containing acids of the general
formula: HS-R.sub.9 --COOH where R.sub.9 is an organic moiety
containing no "reactive" carbon to carbon unsaturation with
polyhydroxy compounds of the general structure: R.sub.10
--OH).sub.n where R.sub.10 is an organic moiety containing no
"reactive" carbon to carbon unsaturation and n is 2 or greater.
These components will react under suitable conditions to give a
polythiol having the general formula: ##SPC13##
where R.sub.9 and R.sub.10 are organic moieties containing no
"reactive" carbon to carbon unsaturation and n is 2 or greater.
Certain polythiols such as the aliphatic monomeric polythiols
(ethane dithiol, hexamethylene dithiol, decamethylene dithiol,
tolylene-2,4-dithiol, etc.) and some polymeric polythiols such as a
thiol-terminated ethylcyclohexyl dimercaptan polymer, etc. and
similar polythiols which are conveniently and ordinarily
synthesized on a commercial basis, although having obnoxious odors,
are operable in this invention. Examples of the polythiol compounds
preferred for this invention because of their relatively low odor
level and fast curing rate include but are not limited to esters
thioglycolic acid (HS-CH.sub.2 COOH), .alpha. -mercaptopropionic
acid (HS--CH(CH.sub.3)--COOH) and .beta. -mercaptopropionic acid
(HS--CH.sub.2 CH.sub.2 COOH) with polyhydroxy compounds such as
glycols, triols, tetraols, pentaols, hexaols, etc. Specific
examples of the preferred polythiols include but are not limited to
ethylene glycol bis(thioglycolate), ethylene glycol bis (.beta.
-mercaptopropionate), trimethylolpropane tris (.beta.
-mercaptopropionate), pentaerythritol tetrakis (thioglycolate) and
pentaerythritol tetrakis (.beta. -mercaptopropionate), all of which
are commercially available. A specific example of a preferred
polythiol is polypropylene ether glycol bis (.beta.
-mercaptopropionate) which is prepared from polypropylene-ether
glycol (e.g., Pluracol P2010, Wyandotte Chemical Corp.) and .beta.
-mercaptopropionic acid by esterification.
The preferred polythiol compounds are characterized by a low level
of mercaptan-like odor initially, and after reaction, give
essentially odorless cured polythioether end products which are
commercially useful resins or elastomers for printing plates.
As used herein the term "odorless" means the substantial absence of
the well-known offensive and sometimes obnoxious odors that are
characteristic of hydrogen sulfide and the derivative family of
compounds known as mercaptans.
The term "functionality" as used herein refers to the average
number of ene or thiol groups per molecule in the polyene or
polythiol, respectively. For example, a triene is a polyene with an
average of three "reactive" carbon to carbon unsaturated groups per
molecule and thus has a functionality (f) of three. A dithiol is a
polythiol with an average of two thiol groups per molecule and thus
has a functionality (f) of two.
It is further understood and implied in the above definitions that
in these systems, the functionality of the polyene and the
polythiol component is commonly expressed in whole numbers although
in practice the actual functionality may be fractional. For
example, a polyene component having a nominal functionality of 2
(from theoretical considerations alone) may in fact have an
effective functionality of somewhat less than 2. In an attempted
synthesis of a diene from a glycol in which the reaction proceeds
to 100 percent of the theoretical value for complete reaction, the
functionality (assuming 100 percent pure starting materials) would
be 2.0. If, however, the reaction were carried to only 95 percent
of theory for complete reaction, about 10 percent of the molecules
present would have only one ene functional group, and there may be
a trace of material that would have no ene functional group, and
there may be a trace of material that would have no ene functional
groups at all. Approximately 90 percent of the molecules, however,
would have the desired diene structure and the product as a whole
then would have an actual functionality of 1.9. Such a product is
useful in the instant invention and is referred to herein as having
a functionality of 2.
The aforesaid polyenes and polythiols can if desired, be formed or
generated in situ and still fall within the scope of the instant
invention.
To obtain the maximum strength, solvent resistance, creep
resistance, heat resistance and freedom from tackiness, the
reaction components consisting of the polyenes and polythiols of
this invention generally are formulated in such a manner as to give
solid, crosslinked, three dimensional network polythioether polymer
systems on curing. In order to achieve such infinite network
formation the individual polyenes and polythiols must each have a
functionality of at least 2 and the sum of the functionalities of
the polyene and polythiol components must always be greater than 4.
Blends and mixtures of the polyenes and the polythiols containing
said functionality are also operable herein.
In general, it is preferred, especially at or near the operable
lower limits of functionality in the polyene and polythiol, to use
the polythiol and the polyene compounds in such amounts that there
is one thiol group present for each double bond, it being
understood that the total functionality of the system must be
greater than four, and the functionality of the thiol and the diene
must each be at least two. For example, if two moles of a triene
are used, and a dithiol is used as the curing agent, making the
total functionality have a value of five, it is preferable to use
three moles of the dithiol. If much less than this amount of the
thiol is used, the curing rate will be lower and the product will
be weaker because of the reduced crosslink density. If much more
than the stoichiometric amount of the thiol is used, the rate of
cure may be higher, if that is desirable, although excessive
amounts can lead to a plasticized crosslinked product which may not
have the desired properties. However, it is within the scope of
this invention to adjust the relative amounts of polyenes and
polythiols to any values above the minimum scope disclosed herein
which give desirable properties to the cured polythioether.
The photocurable compositions of this invention can be modified so
that relatively oleophilic material, such as, stearic acid, are
present in the surface areas of the photocured image areas. Other
variations include using allyl stearate as a co-curable additive;
using resins which are more oleophilic in character than the
bisphenol-A used in several of the specific examples; using allyl
alcohol or trimethylol propane diallyl ether in place of diallyl
amine to terminate the diepoxide resins, the former being the least
water sensitive (hydrophilic); and using oleophilic fillers, e.g.,
powered polyethylene, which are transparent to U. V. light, thereby
not interferring with the photocure.
The photocuring element should be exposed to actinic radiation
containing a substantial amount of ultraviolet radiation until
substantial photocuring takes place in the exposed areas.
The photocuring reaction can be initiated by U. V. radiation
contained in actinic radiation from sunlight or obtained from
special light sources which emit significant amounts of U. V.
light. Thus it is possible merely to expose the polyene and
polythiol admixture to actinic radiation under ambient conditions
or otherwise and obtain a cured solid elastomeric or resinous
product useful as image production material. But this approach to
the problem results in extremely long exposure times which causes
the process in the vask bulk of applications to be commercially
unfeasible. Chemical photocuring rate accelerators (photoinitiators
or sensitizers or activators) serve to drastically reduce the
imaging exposure times and thereby when used in conjunction with
various forms of energetic radiation (containing U.V. radiation)
yield very rapid, commercially practical cures by the practice of
the instant invention. Useful photocuring rate accelerators include
benzophenone, acetophenone, acenapthene-quinone, methyl ethyl
ketone, thioxanthen-9-one, xanthen-9-one, 7-H-Benz [de]
anthracen-7-one, dibenzosuberone, 1-naphthaldehyde,
4,4'-bis-(dimethylamino) benzophenone, fluorene-9-one,
1'-acetonaphthone, 2'-acetonaphthone, 2,3-butanedione,
anthraquinone, 1-indanone, 2-tert-butyl anthraquinone,
valerophenone, hexanophenone, 8-phenylbutyrophenone,
p-morpholinopropiophenone, 4-morpholinobenzophenone,
4'-morpholinoseoxybenzoin, p-diacetylbenzene, 4-aminobenzophenone,
4'-methoxyacetophenone, benzaldhyde, .alpha.-tetralone,
9-acetylphenanthrene, 2-acetylphenanthrene, 10-thioxanthenone,
3-acetylphenanthrene, 3-acetylindole, 1,3,5,-triacetylbenzene, etc.
and blends thereof. The photocuring rate accelerators (the third
crucial ingredient) are added in an amount ranging from about
0.0005 to about 50 percent by weight of the polyene and polythiol
components in the instant invention. Benzophenone is the preferred
photocuring rate accelerator. Useful U. V. radiation has a wave
length in the range of about 2000 to 4000 angstrom units.
The compositions to be photocured, i.e., converted to a solid
continuous tone lithographic printing plate, in accord with the
present invention may, if desired, include such additives as
natural or synthetic resins, antioxidants, dyes, inhibitors,
activators, fillers, pigments, antistatic agents, flame-retardant
agents, thickeners, thixotropic agents, surface-active agents,
light scattering agents, viscosity modifiers, extending oils,
plasticizers, tackifiers and the like within the scope of this
invention. Such additives are usually preblended with the polyene
or polythiol prior to or during the compounding step. As is the
case with any material which is added to the photocurable polymer
composition useful within the scope of the invention, one should
take care that it does not affect the oleophilic or hydrophobic
characteristics thereof in a manner which is undesired. Operable
fillers include natural and synthetic resins, carbon black, glass
fibers, wood flour, clay, alumina, carbonates, e.g., an oxide,
e.g., titanium dioxide, hydroxides, silicates, glass flakes, glass
beads, borates, phosphates, diatomaceous earth, calcium sulfate, a
calcium carbonate, antimony oxide, colloidal carbon, titanium
dioxide, various colored pigments, various organophilic silicas,
powdered glass, and the like. The aforesaid additives may be
present in quantities up to 500 parts or more per 100 parts
photocurable polymer composition by weight and preferably 0.0005 to
300 parts on the same basis.
The type and concentration of additives must be selected with great
care so that the final composition remains photo-curable under
practical conditions of exposure and with commerically feasible
time cycles maintained throughout the operation. Additives which
block out the passage of U. V. light or which detract from the
stability of the photo-curable composition must be avoided.
The compounding of the components prior to curing can be carried
out in several ways. One useful method of compounding is to prepare
by conventional mixing techniques (but in the absence of actinic
radiation) a composition consisting of polyene, polythiol, U.V.
sensitizer or photoinitiator, and other inert additives. This
composition generally can be stored in the dark for extended
periods of time. It could be charged to an aerosol can, drum, tube
or cartridge for subsequent use.
Conventional curing inhibitors or retarders operable in the instant
invention include but are not limited to hydroquinone p-tert-butyl
catechol; 2.6-ditert-butyl-p-methylphenol phenothiazine and
N-phenyl-2-napthylamine. The majority of the commercially available
monomers and polymers used in the photocurable compositions
normally contain minor amounts (about 50 to 5000 parts per million
by weight) of inhibitors to prevent spontaneous polymerization
prior to use in making a printing plate. The presence of these
inhibitors in optimum amounts causes no undesirable results in the
photocurable layer of this invention.
The molecular weight of the polyenes of the instant invention can
be measured by various conventional methods including solution
viscosity, osmotic pressure and gel permeation chromatography.
Additionally, the molecular weight can be sometimes calculated from
the known molecular weight of the reactants. The viscosity of the
polyenes and polythiols was measured on a Brookfield Viscometer at
30.degree. or 70.degree.C. in accord with the instructions
thereof.
The photocurable composition at ambient temperatures can vary from
a liquid to a solid state, including a gel or elastomeric state.
The photocurable composition may also contain a thickening agent to
increase the viscosity of the photocurable liquid polymer. For
example, cellulosic derivatives, finely divided silicas, and finely
ground fibrous asbestos materials may be used, but it is preferable
that a filler be used which will volatilize when the cured
photocurable composition is thermally decomposed. The preferred
photocurable compositions of the instant invention have viscosities
in the range of about 0.25 to about 350 poises and preferably from
about 5 to about 150 at or below 130.degree.C. The photocurable
compositions can also be added as an aqueous emulsion.
The light sensitive materials operable herein can be liquid or
solids. They are usually applied to the anodized aluminum surface
in solution and then the solvent is evaporated off.
Other suitable radiation sensitive layers which may be employed
include silver halide emulsions, bichromated colloids, diazonium
compounds and the like.
In the process of the instant invention a grained or ungrained
aluminum or aluminum alloy sheet may be employed. A grained sheet
is preferred since this provides better water receptivity.
Preferably the sheet should have a surface which has been
mechanically or electrochemically roughened so that the
non-printing areas of the resulting printing plate retain the
fountain solution during printing more easily.
To process a presensitized printing plate made by the process of
the instant invention it should be placed under an image bearing
transparency and exposed to a source of actinic radiation for
example a carbon arc, pulsed xexon lamp or mercury xexon lamp or
any other lamp containing a high proportion of U.V. light for
periods ranging from 1/2 to 6 minutes depending on the distance of
the light source from the plate. After exposure, the image is
formed by dissolving away or washing away the unexposed portion of
the light-sensitive material with a suitable developer. The plate
is then treated with a desensitizing solution of gum arabic to
prevent the background areas from accepting ink. If desired, the
image may be made visible by the use of a lacquer, developing ink
or colorant before being used for printing on the press. The plate
is now ready for use on a lithographic printing press.
The following examples are intended to illustrate but in no way
limit the instant invention. Unless otherwise noted all parts and
percentages are by weight. In order to test the plates as rapidly
as possible for wear resistance an accelerated wear test was
devised. Said test consisted of: overpacking a non-compressible
blanket on the press to 7 mils over bearers in combination with an
abrasive ink commercially available from Capitol Printing Ink Co.,
Washington, D.C. under the tradename "Abrasive Black No. 15745."
Said ink consisted of a standard black offset printing ink
containing granulated lime of greater than 10 microns in diameter
in an amount equal to 1.0 oz. lime/pound ink. When printed under
the conditions of this test, plates showed the same wear in 20,000
impressions as they would have done in 200,000 impressions with the
press run normally packed and with non-abrasive ink.
EXAMPLE 1
An 18 inch .times. 23 inch .times. 12 mil sheet of grained aluminum
was anodized by immersing the sheet to serve as an anode in a tank
containing a 15 percent sulfuric acid electrolyte at a temperature
of 24.degree.C and wherein an 18 inch .times. 23 inch .times. 12
mil sheet of lead served as the cathode. Current was applied to the
elctrodes at a density of 20 amps per square feet for 11/2 minutes.
The anodized aluminum sheet was removed from the bath and
thoroughly rinsed with water at room temperature and then dried.
Analysis of the surface anodized layer indicated the presence of
about 221 mg/m.sup.2 of aluminum sulphate. The pore size of the
oxide coating was found from electron microscopy to be less than 50
angstroms. The dried anodized aluminum sheet was immediately coated
with a composition made up in the following manner. 458 G. (0.23
mole) of a commercially available liquid polymeric diisocyanate
sold under the tradename "Adiprene L-100" by E. I. Dupont de
Nemours and Co., were charged to a dry resin kettle maintained
under a nitrogen atmosphere and equipped with a condenser, stirrer,
thermometer and gas inlet and outlet. 37.8 g. (0.65 mole) of allyl
alcohol were charged to the kettle and the reaction was continued
for 17 hours with stirring at 100.degree.C. Thereafter the nitrogen
atmosphere was removed and the kettle was evacuated 8 hours at
100.degree.C. 50 cc. dry benzene were added to the kettle and the
reaction product was azeotroped with benzene to remove the
unreacted alcohol. This allyl terminated liquid polyene prepolymer
had a molecular weight of approximately 2100 and will herein after
be referred to as prepolymer A. 2 grams of prepolymer A along with
0.6 grams of dibenzosuberone (photosensitizer) and 0.23 grams of
pentaerythritol tetrakis (.beta. -mercaptopropionate) commercially
available from Carlisle Chemical Company under the tradename "Q-43"
were dissolved in 13.3 grams of 2-methoxyethyl ether. The
photocurable composition was wiped on the anodized aluminum sheet
with a cloth until dry. The plate was then contact exposed through
a half-tone negative for one minute to a carbon lamp at a distance
of 38 inch and thereafter swab-developed with an aqueous solution
consisting of 8 parts "Triton X-100" in 100 parts water. The plate
was then printed on a Harris Model L 125 B 19 .times. 25 inch
offset press using 60 pound long grain Scott offset paper. The
quality of the plate was excellent and it ran for 23,000
"accelerated wear" impressions with no sign of wear. This example
shows the ability of a sulfuric acid anodized plate to print
effectively if it is used immediately before the surface becomes
unstable.
EXAMPLE 2
A grained aluminum plate was anodized, rinsed and dried according
to Example 1, and then cut in half. One half was stabilized for two
minutes in a 15 percent phosphoric acid solution giving 39
mg./m.sup.2 of aluminum phosphate and the other half was untreated.
The surface impedance as measured by a Z scope was 1.47 K.OMEGA.
for the untreated sample and 1.40 K.OMEGA. for the stabilized
sample. After one week storage, the stabilized plate was still at
1.40 K.OMEGA. while the unstabilized plate had increased to 2.45
K.OMEGA.. At the end of the one week period the phosphoric acid
treated plate was coated with the photocurable composition used in
Example 1. Following the exposure and development technique of
Example 1 the stabilized plate was run on the Harris press for
25,000 "accelerated wear" impressions without any sign of wear.
The untreated plate was coated and exposed under the same
conditions as in Example 1. An attempt to develop the plate as in
Example 1 resulted in the plate failing to adhere the cured
photopolymer. That is, both the cured exposed and the uncured
unexposed areas were removed and no imaged plate was obtained. This
example shows the stability of the plate produced by the instant
invention over one anodized in sulfuric acid.
EXAMPLE 3
An aluminum plate was anodized according to Example 1 and cut in
half. One half was treated for 2 minutes in an aqueous 15 percent
phosphoric acid bath and the other half was untreated. Both halves
were placed in water at 100.degree.C for 15 minutes. After drying,
the phosphoric acid treated plate was unchanged (and had a Z of
1.40 K.OMEGA.) and could still be used as a plate base whereas the
untreated base (with a Z of 10.5 K.OMEGA.) was "sealed" (as
determined by impedance measurements (Z scope) and no longer
adhered polymer.
EXAMPLE 4
An aluminum plate was anodized in sulfuric acid according to the
procedure of Example 1. The plate was washed in water, dried and
then immersed in a aqueous 15 percent phosphoric acid bath for two
minutes, followed by a rinse in deionized water. After drying it
was coated with the photocurable composition of Example 1 pigmented
with 0.15 grams phthalocyanine blue. The plate was imaged and
developed as in Example 1. Following the printing procedure of
Example 1, 25,000 "accelerated wear" impressions were obtained
without any sign of wear on the plate.
For a comparison an aluminum plate, anodized in phosphoric acid
without any subsequent treatment, resulting in an aluminum oxide
coating having a pore size of in the range 150 - 500 angstroms. The
anodized aluminum surface layer contained about 97 mg./m.sup.2 of
aluminum phosphate and was exposed and developed as above using the
same photocurable composition. When run under the same conditions
on the Harris press, the plate showed signs of wear after 15,000
"accelerated wear" impressions.
EXAMPLE 5
An 18 inch .times. 23 inch .times. 12 mil sheet of grained aluminum
was anodized by immersing the sheet to serve as an anode in a tank
containing a 15 percent sulfuric acid electrolyte at a temperature
of 24.degree.C and wherein an 18 inch .times. 23 inch .times. 12
mil sheet of lead served as the cathode. Current was applied to the
electrodes at a density of 20 amps per square feet for 1 1/2
minutes. The anodized aluminum sheet was removed from the bath and
thoroughly rinsed with water at room temperature and then dried.
The anodized sheet was then stabilized by immersion in a bath of 25
percent phosphoric acid maintained at room temperature for a period
of 3 minutes. The thus stabilized sheet was removed from the bath
and rinsed in deionized water and then dried. Analysis of the
surface anodized layer indicated the presence of about 395
mg./m.sup.2 of aluminum sulphate and about 48.5 mg./m.sup.2 of
aluminum phosphate. The pore size of the oxide coating was found
from electron microscopy to be less than 50 angstroms. The dried
anodized aluminum sheet was coated with a composition made up in
the following manner. 897.8 gms (3.8 moles) of commercially
available trimethylolpropane diallylether, sold by Proctor Chemical
Company, and 6.2 gms stannous octoate (catalyst) was charged to a
dry resin kettle maintained under a nitrogen atmosphere and
equipped with a condenser, stirrer, thermometer, dropping funnel
and gas inlet and outlet. 348 gms. (2 moles) of commercially
available toluene diisocyanate was charged to the dropping funnel
and dripped into the resin kettle at a rate to maintain the
temperature between 70.degree.C-80.degree.C. After addition, the
reaction was allowed to stir at 70.degree.C-80.degree.C. for an
additional 2 hours under nitrogen. This allyl terminated liquid
polyene prepolymer had a molecular weight of 602 and will be
referred to herein after as Prepolymer B. 2 grams of prepolymer B
along with 1.1 grams dibenzosuberone (photosensitizer) and 1.63
grams of pentaerythritol tetrakis (.beta. -mercaptopropionate)
commercially available from Carlisle Chemical Company under the
tradename "Q-43" were dissolved in 27.8 grams of 2-methoxyethyl
ether. The photocurable composition was wiped on the anodized
aluminum sheet with a cloth until dry. The plate was then contact
exposed through a half-tone negative for one minute to a carbon
lamp at a distance of 38 inch and thereafter swab-developed with an
aqueous solution consisting of 8 parts "Triton X-100" in 100 parts
water. The plate was then printed on a Harris Model L 125 B 19
.times. 25 inch offset press using 60 pound long grain Scott offset
paper. The quality of the plate was excellent and it ran for 25,000
"accelerated wear" impressions with no sign of wear.
EXAMPLE 6
An aluminum plate was anodized and rinsed according to Example 1,
and then cut in half. One half was stabilized for 3 minutes in an
18 percent phosphoric acid solution, rinsed and dried and the other
unstabilized half only dried. Both plates were stored for one week
after which time both were hand coated with full strength Kodak
Photo Resist (KPR) and wiped dry. The plates were contact exposed
to a carbon lamp at a distance of 38 inch through a halftone
negative for 1 minute and developed with 1:2 KPR Developer/KPR
Thinner followed by 1:1 KPR Developer/Denatured Alcohol, then
desensitized with 1:1 LTF Post Nital Solution/Desensitizing Etch.
Attempts to rub up the plate with P.D.I. Spray Rub UP ink gave a
completely scummed background to the untreated sample while the
phosphoric acid treated sample rubbed up normally and went on to
print 23,000 "accelerated wear" impressions with no sign of
sharpening or scumming.
EXAMPLE 7
Two aluminum plates, one anodized and stabilized and the other only
anodized as in Example 6 were coated with Harold M. Pitman Co. --
ST Diazo material and dried. After contact exposure to a carbon arc
under a half-toned negative for 100 seconds, the plates were
developed with Pitman Co. ST Super D + developer. Again, the
untreated plate scummed badly in the background areas while the
H.sub.3 PO.sub.4 treated plate produced a clean background area
with a well defined image area. This plate was subjected to 20,000
"accelerated wear" impressions with little loss of image fidelity
and no background scumming.
EXAMPLE 8
Two uncoated aluminum plates, one anodized and stabilized and the
other only anodized according to Example 6 were coated with
polyvinyl alcohol stabilized polyvinyl acetate latex sensitized
with 0.1 percent ammonium dichromate and dried. After contact
exposure to a carbon lamp for 2 minutes through a halftone
negative, the plates were developed with tap water and desensitized
with normal pressman's desensitizing etch. Both were then rubbed up
with P.D.I. spray rub-up ink at which point the untreated plate
again showed scum in the background area, indicating imcomplete
removal or possible precuring of unexposed photosensitive material.
The H.sub.3 PO.sub.4 stabilized plate was subjected to 35,000
"accelerated wear" impressions without any sign of wear or
failure.
EXAMPLE 9
Two aluminum plates, one anodized and stabilized, the other only
anodized by the procedure of Example 6 were coated in a darkroom
with a silver halide aqueous emulsion containing 25 percent Ag
NO.sub.3, 0.8% photographic grade gelatin and 0.02% K.sub.2
Cr.sub.2 O.sub.7 by soaking for 1 minute, squeegeeing off the
excess, and drying. Then both plates were soaked for 1 minute in an
aqueous solution of 5% each KBr and K.sub.2 Cr.sub.2 O.sub.7,
rinsed well under running water and dried at 40.degree.C for 1/2
hour. After exposure to visible light for 20 seconds under a
half-tone negative, both plates were developed using a normal
silver halide type film developer. The untreated plate showed a
general background fog while the H.sub.3 PO.sub.4 treated plate did
not. The treated plate printed 10,000 "accelerated wear"
impressions without loss of image fidelty.
The following example will show the use of the instant invention in
producing a letter press printing plate.
EXAMPLE 10
A grained aluminum plate anodized and stabilized as in Example 2
was used as a substrate for a 20 mil thick layer of the
photocurable composition of Example 5 except that no 2-methoxyethyl
ether was added as a solvent. The layer was exposed through a line
and half-tone negative with an air gap of 12 mils between the
surface of the photocurable composition and the negative to actinic
light from a 4,000 watt Ascorlux pulsed xenon arc printing lamp,
commercially available from American Speed Light Corporation placed
30 inches above the negative. The exposure was for 1 1/2 minutes
during which time the liquid photocurable composition solidified in
the image areas. The plate was developed in an aqueous solution
consisting of 8 parts "Triton X-100" in 100 parts water in a bath
ultrasonically activated to the degree necessary to cause
cavitation, i.e. in the energy level range of 18-40 kilocycles/sec.
at a temperature of 60.degree.C to remove the uncured material. The
cured imaged areas obtained had outstanding adhesion to the
aluminum plate. The plate was inked and employed in letter press
printing on a Davidson Press Model 816 manufactured by Davidson
Corporation, Chicago, Illinois. The printing resulted in distinct
and separate lines and the dots in the half-tone areas had
excellent definition.
To show the wear resistance of the stabilized anodized aluminum
plate of the instant invention as compared to other aluminum plates
anodized by other procedures the following comparisons were
made.
EXAMPLE 11
8 inch .times. 8 inch .times. 12 mil sheets of grained aluminum
were subjected to the following treatment:
Sheet A was immersed as a anode in a tank containing a 15 percent
sulfuric acid electrolyte at a temperature of 40.degree.C employing
a lead cathode of the same dimensions. Current was applied to the
electrodes at a density of 50 amps per square foot for 1.5 minutes.
The sheet was removed from the bath, thoroughly rinsed with water
and dried. Analysis of the surface indicated the presence of 1109
mg./m.sup.2 aluminum sulphate. The sheet was cut in a 6 inch
diameter circle and weighed.
Sheet B was immersed to serve as an anode in a tank containing 42
percent phosphoric acid electrolyte at a temperature of 25.degree.C
using a lead cathode of the same dimensions. A current density of
24 amps per square foot was applied for 6 minutes. The sheet was
removed, rinsed thoroughly in water and dried. Analysis of the
surface indicated the presence of 97 mg./m.sup.2 aluminum
phosphate. The sheet was cut in a 6 inch diameter circle and
weighed.
Sheet C was anodized by immersing the sheet to serve as an anode in
a tank containing a 15 percent sulfuric acid electrolyte at a
temperature of 21.degree.C using a lead cathode of the same
dimensions. Current was applied to the electrodes at a density of
27 amps per square foot for 2 minutes. The sheet was removed from
the bath, thoroughly rinsed with water and then stabilized by
immersion in a bath of 25 percent phosphoric acid at room
temperature for a period of 3 minutes. The sheet was removed from
the bath, rinsed thoroughly in water and dried. Analysis of the
surface indicated the presence of 520 mg./m.sup.2 aluminum sulphate
and 50 mg./m.sup.2 aluminum phosphate. The sheet was cut in a 6
inch diameter circle and weighed.
The sheets were individually subjected to a wear resistant test in
accord with ASTM D 1044-56 using a Taber caliber CS-17 abrading
wheel with a 250 gram counter balanced weight on the arms. A
refacing disc (180 J Al.sub.2 0.sub.3) on cloth was used to reface
the wheels for 10 cycles after every 50 cycles. The samples were
run 150 cycles and were weighed after every 50 cycles. The results
showed that after 150 cycles, sheet A lost 1.8 mg; sheet B lost 1.4
mg. and sheet C lost 0.3 mg.
* * * * *