Note: Descriptions are shown in the official language in which they were submitted.
69
PHOTOSENSITIVE llNILAYER FILM ST~UCTtTRE C~\~T FROM ~'\ rOL~
EMULSION DISPERSION
-
BACKGROUND OF THE INVENTION
The present invention relates generally to photo-
sensitive structures and more particular:ly to a photosensitive,
unilayer, film structure suitable for use in the manufacture of
water-processable printing plates and other graphic arts
elements.
Many different photosensitive systems are well-krlown in the
art for the manufacture and preparation of lithoqraphi.c plates.
Diazo compounds are, of course, frequently used as the
photosensitive component in such systems. The diazo compounds
can be formulated to possess several assets which make them
desirable for use in this field, including low-cost, long shelf-
like, water solubility, and good photosensitivity. However, the
ink receptivity of diazo compounds is seriously reduced when
they are contacted by water and the inherent durability of diazo
resins is relatively low. Accordingly, approaches to the
manufacture and preparation of printing plates utilizing diazo
compounds have sought to overcome this problem by using lacquer-
based developers, or overcoating the diazo with an ultra-violet
transmitting lacquer or other material. These approaches, while
enjoying some success, result in the loss of the simple water
processing of the diazo compound plates and in some instances
have required increased exposure times. Moreover, cliazo
compounds lack sufficient bond strengths to smoother substrates
and therefore it has been necessary to provide grained substrate
surfaces to increase the mechanical bonding oE these
photosensitive coatings, in order to achieve useful lengths of
press runs.
.~ .
69
Another popular photosensitive system employs photopolymers
which have both high ink receptivity and durability. These
systems however, generally require special solvents to develop
the plate, thereby increasing system complexity compared to
simple water processing and, in addition, presentlng undesirable
ecological waste problems.
SUMMARY OF THE INVENTION
In an attempt to overcome the problems and ex-tend the
performance features of prior art pho-tosensitive systems used in
the preparation oE printing plates and other graphic arts
articles, a new photosensitive film structure has beell
discovered which provides a highly desirable combination oE
properties in the various articles in which it finds
application.
Accordlngly, the present invention is direc-ted to a
unilayer film structure which includes a generally continuous
first or minor phase dispersed within a generally discontinuous
second or major phase. The :Eirst or minor phase comprises a
photosensitive material which changes solubility relative to a
selected solvent upon exposure to light, while the second or
major phase comprises a particulate material which is not
photosensitive and not soluble in the solvent.
More particularly the invention comprehends a
photosensitive unilayer film structure cas-t from a polymeric
emulsion dispersion comprising a generally continuous first
phase material dispersed with a generally discontinuous second
-2~
9~9
phase material. The first phase is a minor constituent by
weight of the structure and is composed o:E a photosensitive
material whose solubility with respect to a given solvent is
changed upon exposure to electromagnetic :radiation. The second
: phase is a major constituent by weight of the structure and is
composed oE a material which is substantially insoluble in the
solvent. The first phase material is a photosensitive material
of the group consisting of aromatic diazo compounds,
photopolymers, light sensitive dyestuffs, azo compounds,
dichromates and silver halide gelatin systems, and the second
phase material is a member of the group consisting of
polyacrylics, copolymers oE ace-tate and ethylene, copolymers oE
styrene and acrylates, polyvinyl aceta-tes and copolymers of
vinyl acetate and acrylates. The terms "generally continuous"
and "generally discontinuous" as used herein refer to the
overall character of the minor and.major phases, respectively.
Thus, while the minor phase may have random and remote
discontinuities, it will, over the film structure as a whole,
comprise a continuous unbroken material. Similarly, the major
phase may have a few particles joined to adjacent particl.es, yet
over the film structure as a whole the major phase will comprise
discrete particles separated by the minor phase.
It has been found that such a film structure may be made
selectively permeable through imagewise exposure to light and
~D 3
~LQ~ 9
thereafter used in a variety of graphic arts applications
wherein selective permeability to fluids is necessary or
desirable.
Therefore, various objects of the present invention
include providing a unique photosensitive film structure which
may be made selectively permeable to fluids upon exposure to
light; one wherein the photosensitive phase cons-titutes a minor
fraction of the film's mass and volume, thereby offering
considerable performance latitude and improvement, and cost
reductions as well and one which may be developed by water
subse~uent to imagewise exposure to ligl~t, withou~ tl~e use o~
the organic or inorganic solvents. The film is su:itable ~or use
in the manufacture and provision of lithographic or offset
printiny plates in which the ink receptivity and durability of
the imaging areas are relatively independent of the exposure
techni~ue and the development compositions used in making the
finished plate.
Other objects of the invention are -to provide a unique
photoresist material and to provide a photosensitive film
structure having a high bond s-trength to a variety of surfaces.
A BRIEF DESCRIPTION OF THE DRAWINGS
The novel features which are believed to be characteristic
of the present invention are set forth in the appended
claims. The invention itself, however, together with
L9~i9
forthcoming objects and attendant advantages will be
best understood by referring to the following description taken
in connection with the accompanying drawings in which FIGURES 1,
2 and 3 are enlarged cross-sectional schematic views, each
illustrating an emhodiment of the film structure of the present
invention. It should be noted, however, that these schematic
representations only serve to illustrate the structure and
mechanism of the present invention and are not intended to limit
- the scope thereof.
10 DETAILED DESCRIPTION OF THE INVENTION
The photosensitive unilayer film composition of the present
invention comprises a first (minor) phase material dispersed
within a second (major) phase material.
The first or minor phase is photosensitive, generally
continuous throughout the structure and capable of changing
solubility with respect to a given solvent. The second or major
phase comprises discontinuous (discrete particular) material
which is not photosensitive and chosen to be relatively
insoluble in the solvent for the minor phase. Thus, -the "two
phase" concept of the present invention relates to the physical
structure of the phases, one being continuous and the other
being discontinuous and the solubility of the phases, Olle heillg
selectively soluble in a given solvent of the imagewise exposure
to light while the other phase is insoluble in the solvent
irrespective of light exposure. The photosensitive unilayer
film structure of the present invention may be best dcscribed as
a lattice cast from an emulsion-dispersion. Several lattices
formed from these emulsion-dispersions have been identified,
each of which offers various performance features.
-5-
6~
One of the lattices which embodies the concepts of the
present invention is illustrated schematically in FIGURE 1.
This lattice is cast from a dispersion of substantially
monodimensional coa-ted spheres and is shown as it might
typically be utilized, as a coating on a suitable substrate.
Thus, in this system the generally continuous photosensitive
minor phase cons~itutes a coating for the generally
discontinuous major phase material.
The minor phase material chosen to wet and coat the major
phase particles is soluble in the selected solvent whereas the
major phase is insoluble in this solvent. After actinic
exposure, however, the minor phase is, Eor example, rendered
insoluble. Thus, after imagewise exposure of the photosensitive
structure and upon application of the selected solvent thereto,
the unexposed areas of the lattice may be wetted and permeated
by the solvent due to the con-tinuing solubility of the minor
phase coating in those areas. Significantly, ~liS permeatioll of
the lattice permits the physical removal of bo-th the first and
second phase materials from the substrate by mechanical
techniques such as wiping, brushing, or the like.
The wettability and spreading characteristics oE the
substrate with water and the capillary pressures at the lattice/
substrate interface are believed to assist in this "development"
process and may thereby offer additional system control.
Another lattice embodying the concepts of
the present invention is illustrated schematically in FIGURE 2.
In this lattice system the interstices of the discontlnuous
major phase material, or void space, is filled with the
continuous minor phase pho-tosensitive material. The
~r -
96~
close packing of the spherical major phase particles as shown in
FIGURE 2, results in a void volume of approximately 25% when the
spheres are of substantially uniform size. This theoretical
void space is independent of actual sphere size so long as
uniformity of sphere size is main~ained. In accordance with
this la-ttice structure, the interstices between the major phase
particles may be filled with a variety of photosensitive
materials, such as silver-halide/gelatin, dichromated colloids,
photopolymers, diazo-colloid systems and the like.
Using this lattice system, imagewise exposure produces in
the exposed areas an effective bonding medium for the major
phase material, whereas unexposed areas remain water soluble
and, therefore, accommodate the desired solvent permeation and
subsequent development.
Still another lattice useful in -the practice of the present
invention is illustrated in FIGURE 3. The la-ttice again
includes a generally continuous photosensitive minor phase
material as disclosed for the previously mentioned systems
interdispersed with a generally discontinuous major phase
comprising polydimensional spheres.
As noted above, a matrix of monodimensional spheres
will have a void space of approximately 25%. The use of
polydimensional spheres results in a reduction of this
void space, thereby enabling the use of smaller quantities
of the minor phase material in the manufacture of photo-
sensitive structures. This, of course, may be highly
FD -7-
6~
desirable in terms of lower costs and in permitting the physical
and chemical characteristics of the major phase to dominate to
an even greater extent the properties of the entire film
structure.
The photosensitive materials useful as the minor phase in
the practice of the instant invention include any photosensitive
compound wherein exposure to electromagnetic radiation creates
a change in solubility characteristics in a selected solvent.
Photosensitive compounds which may be used in the present
invention include aromatic diazo compounds, light sensitive
dyestuffs, azo compounds, dichromates, photopolymers, and
silver halide gelatin systems. Further useful minor phase
materials may be found in the disclosures of U.S. patents Nos.
2,063,631 and 2,679,478 and in Light Sensitive SYstems
authored by J. Kosar and published by John Wiley & Sons (1965).
Particularly preferred minor phase materials include
condensation products of carbonyl compounds, such as
formaldehyde or paraformaldehyde, and a diazo compound such as
4-diazo-1, l'-diphenylamine. Such condensation products are
available under the trade names DiazoT~ No. 4 and Diazo No.
~L from the Fairmont Chemical Co., Newark, New Jersey.
The major phase of the film structures of
the present invention may be chosen to tailor
F ~D
~IL43~9~9
the physical and chemical properties of the final produc-t for a
given application. These properties include, among others:
durability or physical toughness, the ability to adhere to
substrates, water repellency (and therefore ink receptivity),
permeability, solvent resistance, particle size, viscosity,
solids content, heat sealing characteristics, film forming
characteristics and molecular weight.
Some of the homopolymers and copolymers, in emulsion-
dispersion form, which are suitable for use as the major
phase of the present invention include, amonr~] others: aclyllcs,
copolymers of acetate and ethylene, copolymers of s-tyrene and
acrylates, polyvinyl acetates, and copolymers of vinyl acetate
and acrylates. Each of these may be used with or without
protective colloids, wetting agents, plasticizers and o-ther
modifying agents.
In accordance with one preferred embodiment of the
present invention the photosensitive film structure may be
formed by casting, either as a self-supporting film or onto a
suitable substrate, an emulsion containing water, a suitable
diazo compound, and a PVA-acrylate emulsion. Upon drying, the
resulting film structure comprises a con-tinuous diazo compound
minor phase which coats the discontinuous PVA-acrylate major
phase spheres and/or fills -the interstices thereof. This major
phase material is known to form a water insoluble film which
is non-emulsifiable whereas the diazo compounds only become
water insoluble upon exposure to light.
, .~
g_
~a~ 69
A most important application of the present invention is
in the field of lithoyraphic offset printing. Offset
printing plates can be prepared usinq a hydrophylic subs-trate
such as silicated aluminum and the like with the composition of
the present invention molded or cast as a film on its
surface. The aforementioned copolymer of vinyl acetate and a
long chain acrylate provides a flexible, non re-emulsifiable
film with high water repellency.
Surprisingly, the addition of the diazo resin with this
major phase material results in the ability to wash th:in layers
of the film structure from the substrate subsequent to
imagewise exposure to light. Those areas of the film which
have been exposed to light are not removed Erom the subs-trate
during the water wash/scrub processl whereas those portions of
the film which are not exposed to light may be removed.
Moreover/ the light exposed areas exhibit desirable ink
receptive properties and efficient bonding even to non-porous
surfaces such as silicated, ungrained aluminum.
It is believed that the film structures of the presen-t
invention are rendered selectively permeable -to a given
solvent upon imagewise exposure to light due to the unique
physical arran~ement of the minor and major phases. Thus, in
the case of a diazo-PV~/acrylate composition, upon exposure -to
a light image the diazo will become insoluble in those portions
of the film exposed to light thereby making the entire film in
those portions impermeable to water. On the other hand, the
--10--
h ~ ^
9~9
diazo in those portions oE the film not exposed to light will
remain water soluble thereby permitting water to permeate the
film structure. The permeation of water may create hiqh interllal
stresses permitting a film splitting failure or it may simply
provide access to the substrate promoting adhesive failure.
Thus, the photosensitive film structure of the present invention
discussed herein is made selectively permeable to water through
exposure to a light image.
When such a photosensitive film structure as described
herein is utilized with a hydrophylic substrate in the
manufacture of lithographic printing plates, those portions of
the structure not exposed to light are easily removed durin~ the
water development step. It is believed that the water
insoluble major phase is capable of removal Erom the subs-tra-te
due partly to the action oE water at the film substrate
interface, as previously stated, which water has reached this
interface due to the permeability of the non-exposed portions of
the film. Since the PVA-acrylate copolymer major phase is
hydrophobic (and oleophilic), the photosensitive film structures
of the present invention are ideally suited for use in
lithographic offset printing processes. Moreover, since these
major phase material is not light sensitive and are not affected
by the light exposure and developing processes, i~ may be
selected largly for the purpose of optimizing the ink
receptivity, durability, and bonding properties of the resulting
plates~
It will be appreciated from the foregoing that films made
in accord with the present invention, because of their two
phase structure, may be compounded from a wide variety of
materials to optimize both developmel)t and performallcc
characteristics. The photosensitive phase, being a relatively
minor constituent, does not interfere wi-th the performance
characteristics of the film and may be chosen largly for
desirable development properties; while the major phase may be
chosen to optimize the film's physical and chemical properties
- 1 1 -
3LIQ~969
such as durability for a given application without regard to
development. In addition, since the photosensitve phase is a
minor constituent, the particles of the ma~or phase material
will be ciosely packed in the film structure, as illustrated
schematically in the drawings. Thus, the particles of the major
phase are sufficiently proximate to one another to permit their
coalescence by means of heat of chemical treatment after the
film has been developed. Such post development coalescence has
been found to significantly enhance the performance of
lithographic printlng plates made in accord with the present
invention.
By proper choice of the major phase material, thickness and
substrate, it is possible to create both hydrophobic and
hydrophilic characteristics in the film itself, which are
relatively independent of those of the substrate. In such
cases, after imagewise exposure, the photosensitive minor phase
of the film retains its solubility in the unexposed areas such
that a porous surface can be obtained by leaching with the
selected solvent. sy developing the film withou-t scrubbing or
brushing, the major phase material retains substantial
structural continuity over the substrate. Thus, the unexposed,
porous areas thereof may thereafter be mechanically wetted with
water, whereas the exposed areas are non-porous and exhibi-t
hydrophobic characteristics. This "wet-tability" di~ferential
over the surface of the film has been found suitable for
lithographic printing and thereby frees the manufacturer to
choose any low cost substrate material for use therein.
The utilization of the improved photosensitive, unilayer
film structures of the present invention has been illustrated
above in the context of the manufacture and preparation of
lithographic offset printing plates. It is to be understood,
however, that the scope of the present invention is not
intended to be so limited. The pho-tosensi-tive film structures
of the presen-t invention may be utilized in other
applications wherein selective permeability to a given fluld or
-12-
69
solvent is desirable. For example, the photosensitive film
structures of the present invention may be cast as a self-
supporting film and subse~uen-t]y exposed to a light image and
developed without destroying the structural integrity of the ma-
trix. In this manner, a skeletal template is obtained which is
selectively permeable to certain fluids. Such a template may
then be used for any number of diverse purposes such as the ap-
plication of designs, patterns, or images, on an underlying sur-
face by means of inks or the like wllicll are cap.~le o E perlllc-
ating the template.
For example, numerous photoresist applications may also be
practicable with the photosensitive structures of the :Lnstant
invention. Of course, the major phase material may be chosen
and tailored to the appropriate environment. Thus, resistance
to certain acids or bases or a necessary dielectric constant for
plating resist applications wlll point those skilled ln the art
to the selection of a particular major phase material. Once
chosen a compatible photosensitive phase may be added and the
desired performance obtained.
It will be appreciated that development ease for -the photo-
sensitive structures of the present invention is proportionally
related to the concentration of the minor phase material; -that
is, easier development occurs at higher minor phase concentra-
tion. On the other hand, it is often preEerable to minimize the
concentration oE the minor phase, since the major phase material
provides the improved durability, bonding properties and print-
ing characteristics which form an important part of the present
invention. Accordingly, the relative amounts of the first and
second phase materials utilized will depend upon the properties
sought to be obtained in the given photosensitve structure. By
way of illustration, however, the amount of minor phase diazo
material utilized in Example III set forth in detail below may
range from 0.03 to 10 weight percent without signiEicantly
affecting the final product. Similarly by way oE further
FD -13-
6~
illustra-tion of the amount of minor ph~se in the diazo/polyvinyl
acetate system utilized in Example IV (which allows ~or post
development coalescence of the major phase by heat of chemical
treatment to provide for greater durability), the minor phase
preferably constitutes less than about 10 percent, by weight of
the film and most preferably between about 2 and 6 percent, by
weight, of the film. Although such quantitative analyses are
dependent upon the size of the particulate material comprising
the major phase, it will nevertheless be appreciated by tllose
skilled in the art that the quantity of minor phase material is
preferably sufficiently small to allow post development
coalescence of the major phase. Otherwise, the physical and
chemical properties of the major phase would not dominate the
film structures characteristics.
The thickness of the photosensitive Eilm compositioll also
affects the developmen-t of the pho-tosensi-tive structure, since
the solvent must permeate a greater distance to reach the
substrate when thicker films are employed. Photosensitive films
having a thickness from about 0.5 to 25 microns have been found
generally suitable. However, the particle size of the major
phase material and the type of lattice structure employed may
influence the ap~ropriate thickness limits Eor a give
application.
The pho-tosensitive film struc-tures of the present invention
also exhibit improved light sensitivity as compared to many
prior art systems. For example, the photosensitive printing
plates described herein may be "activated" by actinic exposure
about 3 - 5 times faster than conventional wipe-on diazo plates.
This improved photosensitive responsiveness oEfers further
advantages. For example, since development efficacy is
influenced significantly by the wettability and pe~leabili-ty of
the surface of -the film, a brief actinic exposure which acts
--l'i--
~La5~69
only at the surface or near-surface levels has proven efEective
in permittlng selective permeation and development. Such a
brief exposure technique may be preferred particularly in those
instances where heat is used subsequent to development since in
such cases the finished structure's ink receptivity and
durability bear no relationship to exposure.
The following examples, while not intended to be taken as
limiting the scope of the present invention, will serve to
illustrate the process and compositions for making the
photosensitive structures of the present invention.
-15-
6~
EXAMPLE I
100 ml of Rhoplex AC-388 (an acrylic emulsion vehicle
available from Rohm & Haas, Philadelphia, Pa.), 10 ml oE wa-ter,
and 2 grams of Diazo 4L are hlended for about 5 minutes or until
well mixed. This admixture is then used to charge a roller-
coater and applied to a brush grained alwninum substrate -to form
a dry film having a thickness of about 5 microns. Air drying
occurs in about 2 minutes. The sensitized pla-te is then placed
in vacuum contact with a film negative and exposed for 15
seconds to the output of a 2 KW Xenon source. After exposure
the plate is developed with ordinary tap water and gummed. The
plate is then mounted on an offset press using conventional
fountain solutions and inks. Up to 80,000 high quality copies
are obtained with minimal image deterioration.
EXAMPLE II
100 ml of Elvace 1875 (a water based ace-ta-te/e-thylene
copolymer emulsion available from DuPon-t, Wilmington, Del.), 5
ml of water, and 1 gram of Diazo (a light sensitive material
available from Graf-Com Co., Easton, Maryland) are blended until
well-mixed or about 2 minutes in a conventional stir-mixer.
This admixture is then wiped onto a brush grained aluminum
substrate and dried to a film -thickness of about 2 microns. Air
- 16 -
~3~6~
drying occurs in about 1 minute. The sensitized p:late is then
- placed in vacuum contact with a film negative and exposed for
about 30 seconds to the output of a 2 KW Xenon source. Af-ter
exposure the plate is developed wi-th tap water and gummed
conventionally. The plate is then mounted on an offset press
(e.g., 1250 Addressograph/Multigraph) and printed using a
conventional alkaline fountain solution and an ink. Several
thousand copies were obtained.
EXAMPLE III
100 ml of GelvaT TS 100 (a water based polyvin~ cet.llo,~lo~
chain acrylate copolymer emulsion available from Monsanto Corp.,
Newport Beach, Cal.), lO ml of water, and 4 grams of Diazo ~L
are blended until well mixed. This admixture is applied to an
ungrained silicated aluminum substrate and dried to a thickness
of about 5 microns. Air drying occurs in about 2 minu-tes. The
sensitized plate is then placed in vacuum contact wi-th a film
negative and exposed for 5 seconds to the output oE a 3 liW
Mercury Vapor source. Af-ter exposure the plate is developed
with ordinary tap water. Af-ter developmen-t -the plate is mounted
onto an offset press and printed using conventional press
materials. Six thousand high quality copies were obtained with
no apparent image wear.
- 17 -
69
EXAMPLE IV
100 ml oE Gelva TS 30 and 100 ml of Gelva S 52 (both water based
polyvinyl ace-tate emulsions available from ~lonsanto ~orp.,
Newport Beach, Cal.) and 2 grams of Diazo are blended for about
2 minutes. This admixture is applied to a brush grained
aluminum substrate and dried to a film thickness of about 10
microns. Two sensi-tized pla-tes made as disclosed ahove are then
placed in vacuum contact with a film negative and exposed for 60
seconds to the output of a 3 KW Xenon source. After exposure
the plates are deveLoped with tap water and gummed. One plate
is then placed in a convection oven set at 250F for 2 minutes.
Comparison testin~ reveals much greater durability and higher
ink receptivity of the hea-ted sample. Both plates, however,
provide high quality copies. About 50,000 copies were obtained
with the unheated plate, and over 200,000 copies were obtained
with the heated plate.
EXAMPLE V
100 ml of Gelva TS 100, 50 ml of wa-ter, and 1 clm cf Diazo
4L are blended until well mixed (abou-t 1 minu-te). This
admix-ture is then applied to a telurium clad MYI.AR ~ substrate
and dried to a film thickness of about 2 microns. Air
drying occurs in about I minu-te. The sensitized plate is
then placed in vacuum contac-t with a film negative and
exposed for 10 seconds to the output of a 3 KW Mercury
Vapor source. After exposure the pla-te is dip developed
- 18 -
. . . ~
969
in an aqueous solution of NaOCL and NaOH ~ithout scrubbing
or brushing. Inspection of the plate reveals that the
tellurium has been etched by the solution in the unexposed
areas and that the film coating of the plate is intact.
Thus, no removal occurred but rather only a selective permeation.
EXA~PLE VI
50 ml of Gelva TS 100, 50 ml of water, and 2 grams of
Diazo are blended until well mixed (about 2 minutes in a
stir-mixer). This admixture is then applied to a ball
grained non-s~licated aluminum substrate and dried to
a film thickness of about 2 microns. Air drying occurs
in about 2 minutes. The sensitized plate is then placed
in vacuum contact with a Eilm negative and expased for
30 seconds to the output of a 2 KW Xenon source. After
exposure the plate is developed via simple tap water wetting
and rinsing. No wiping is used and the coating remains intact.
The plate ls then tested for differential wetting and inking
by wetting with a conventional fountain solution and inking
with a cotton swab and ink. Selective imagewise inking is
observed and confirms the fact that the unexposed areas are
rendered water wettable due to the leached diazo and resulting
porosity.
-- 19 --
1969
EXAMPLE VII
50 ml of TS 30 and 50 ml oE TS 98 (both polyvinyl acetate,
water based emulsions from Monsanto Corp., Newport Beach, Cal.)
and 2 grams Diazo 4L are blended until well mixed (about 2
minutes in a conventional stir-mixer). This admixture is then,
applied to a shallow grained and a deep grained aluminum
substrate. The films are dried in air in about 3 minutes to a
thickness of about 8 microns. The sensitized plates are then
placed in vacuum contact with a film negative and ~xposed for 90
seconds to the output of a 3 KW Xenon source. After exposure the
plates are developed using tap water and gentle scrubbing and
then gummed. Both plates are subjected to a heat treatment at
250F for 2 minutes and then mounted on a commercial web
lithographic press. No signs of image wear are observed after
printing over 150,000 impressions on either the shallow grain
plate or the deeper grained plate.
- 20 -
'~
6~
It should be understood -that various changes and
modifications of the invention as described herein will be
apparent to those skilled in the art. Such changes and
modifications can be made without departing from the spirit and
scope of the invention and without diminishing its attendant
advantages. For example, many variatio.ns of the lattice designs
described herein above are possible when viewed within the
spirit and scope of this invention. In addition, passive fill
materials may be used to improve shelf life to enhance color or
to provide special photo, magnetic or electrical prope:rties. It
is therefore intended that such changes and modifications be
covered by the following claims:
~D -21-
SUPPLEMENTARY DISCl:.OSUl~
It has been previously noted that the thickness oE the
photosensitive film composition also affects development of
the photosensitive structure, since the solvent must permeate a
greater distance to reach the substrate when thicker films
are employed. Moreover, the particle size of the major phase
material influences the development rate, since for a given film
thickness smaller major phase particles result in a more tortuous
or circuitous development path as the minor phase solvent per-
meates to the substrate. Accordingly, a :Eilm thickness less thanabout 10 times the average diameter of the major phase particles
is preferred in the practice of the present invention since dev-
elopment time otherwise becomes excessive. Preferably, the film
thickness is less than about five times the average diameter of
the ma~or phase particles. By way of example, many of the major
phase materials listed in the principal disclosure and herein
are composed of particles with average diameters in the range of
0.5 to 3.0 microns. For film structures using such major phase
materials, a maximum film thickness less than about 10 microns
is preferred. The verv thin photosensi-tive film structures
minimize the cost of expensive compound used in the formation of
these structures. Nevertheless, these thin film structures are
surprisingly durable and resistant to abrasion due -to the fact
that major phase materials may be employed -to optimize these
properties.
As noted in the originally framed disclosure, the photo-
sensitive film structure of the invention also exhibit improved
light sensitivity compared to many prior art systems. Since relat-
ively thin films are employed, enhanced image quali-ty and resolu-t-
ion are obtained in producing lithographic printing plates.
The following additional examples of exemplary embodimentsof the invention, while not intended to limi-t the scope of the
invention, will serve to illus-trate further the process for making
the photoscnsitive filn~ str~lcture of the illVelltiOIl.
L96~
EXAMPLE5 VIII - XII
Example Emulsion-Dispersion Photosensitive Material
VIII 100 parts by weight 0.5 parts by weight
Gelva TS65 (water based Anthraquinone B-Sulfonic
polyvinyl acetate available Acid Sodium Salt (AQS)
from Monsanto Corp.)
IX Same 0.6 parts by weight
AQS + Ferric Ammonium
Citrate
10 X Same 0.6 parts by weight
AQS ~ P-Toluene
Sulfonic Acid
XI Same 0.6 parts by weight
AQS + Acryl Phosphate
XII Same 0.6 parts by weight
AQS ~ 4, 4'-Diazide
Stilbene 2, 2'-Disulfonic
Acid, Sodium Salt
Each of these formulations was blended until wel] mixed and
then whirl coated onto a grained aluminum substrate and dried
at 45C for about five minutes. The samples were then
exposed from about 15 to 40 seconds at 15cm to the radiation
from a 450 watt chemical lamp. After exposure, each sample
was developed in tap water at 15-20C for a few seconds with
light mechanical action (rubbing). The resulting lithographic
plates were then inked and found to provide quality lithographic
performance.
EXAMPLE XIII
150 ml of Polyco 218~ (a water based polyvinyl acetate co-
polymer emulsion having a solids concentration of 50% and
marketed by the Borden Chemical Co.), 35 ml of water and
8 grams of (NH4)2 Cr2 O7 are blended until well mixed and
hand coated using a conventional draw bar technique onto an
aluminum substrate. The cast emulsion was dried with forced
air flow at room temperature for about 30 seconds, exposed to
a 3KWA~I mercury vapor source for 10 seconds and then developed
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96~33
with tap water at room temperature. The resulting lithographic
plate provided excellent lithographic performance.
EXAMPLE XIV
50 parts by weight Gelva TS 65 (see Examples VIII-XII)
and 1 part by weight of a mixture of 100 parts water and 1
part photopolymer (disclosed in United States Patent No.
3,801,328 issued to Takimoto) are blended until well mixed and
draw bar coated onto an aluminum substrate. The cast emulsion
is dried by forced air flow at room temperature, exposed to a
3KW radiation source for 60 seconds and then water developed
at room temperature. The resulting imaged plate provides
excellent lithographic performance.
EXAMPLE XV
~ mixture (A) of Polyco 2186, carbon black, water and a surfactant
was ball milled for 8 hours. To this was added a mixture (B)
of a Polyco 2186, water and diazo 4L and milled for an additional
8 hours. The following proportions were used:
50 g Polyco 2186
9 g Carbon black
Mix A
35 g H2O
3 g Surfactant
300 g Polyco 2186
Mix B
60 g H2O
10 g 4L
The resulting emulsion was cast on a synthetic paper (such
as a polyethelene paper marketed under the trade name Kimdura
by Kimberly-Clark), dried, exposed to a 2-5KW light source for
30 seconds and water developed. The dried article exhibited
- good abrasion resistance and high contrast images useful for
proofing purposes.
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.
11;9
EXAMPLE XVI
A mixture of 9 grams Phthalocyanine Blue pigment, 80 ml of
water and a surfactant was milled for 4 hours. 300 ml of 81 B
Cascokes (a water based polyvinyl acetate and acrylic copolymer
emulsion marketed by the Bordon Co.) and 10 grams of Diazo ~L
were added, and the mixture milled an additional 2 hours. The
resulting emulsion was cast on mylar, dried, light exposed
and developed with water. The resulting transparent article
exhibits high abrasion resistance and is useful as a color proof.
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