Method for forming relief images and photosensitive material useful therein

Methods for forming relief images are disclosed employing photosensitive microcapsules; typically, the internal phase of the microcapsules includes a photohardenable composition such as an ethylenically unsaturated compound and a photoinitiator; release of the composition is controlled by exposure and the application of a uniform rupturing force such as pressure; in one embodiment, the released composition functions as a resist image for subsequent processing with an etching agent such as an acid.

BACKGROUND 
The present invention relates to a method for forming relief images such as 
letter press and, more particularly, intaglio printing plates. 
Processes for forming relief images are well known in the art. A wide 
variety of materials and methods are available. Typically a plate bearing 
a film of a photopolymerizable composition is image-wise exposed to 
actinic radiation. Exposure renders the film less soluble in a developing 
liquid (typically a solvent for the unpolymerized composition) with which 
the plate is washed to selectively remove the polymer film and yield 
polymeric resist images. Depending on the materials used, this product may 
represent a finished printing plate which is essentially ready for inking. 
Otherwise, the plate may be etched to carry the image into the surface of 
the plate as in the case of gravure printing. 
While numerous methods for forming relief images are known in the art, 
there is a need for alternative, efficient, and more simplified methods. 
SUMMARY OF THE INVENTION 
A principal object of the present invention is to provide a simplified 
method for the preparation of relief images. 
A related object of the present invention is to provide a method for 
forming relief images through the use of photosensitive microcapsules 
which have a discrete capsule wall and contain a photosensitive 
composition in the internal phase. 
Another object of the present invention is to provide a photosensitive 
material useful in forming relief images. 
Commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,846 to Sanders et al. 
disclose an imaging system which employs a microcapsule containing a 
photosensitive composition. The composition is one which changes in 
viscosity in response to actinic radiation. In the imaging system 
described in the patents, the microcapsules contain a color former, a 
substantially colorless compound which reacts with a developer compound to 
form a visible image. Typically, the color former is an electron donor and 
the developer is an electron acceptor. In contact with the developer, the 
color former transfers its electron and becomes visibly colored. An 
imaging sheet, which carries a layer of the microcapsules on its surface, 
is image-wise exposed to actinic radiation and subjected to a uniform 
rupturing force. This causes the microcapsules to rupture. As a result of 
differential hardening of the microcapsules achieved through exposure, the 
microcapsules image-wise release their contents for reaction with the 
developer. In the case of U.S. Pat. No. 4,399,209, the developer is on a 
separate sheet, and in the case of U.S. Pat. No. 4,440,846, the developer 
is on the same sheet as the microcapsules. A visible image is thereby 
formed. 
In accordance with the present invention, microcapsules containing 
photosensitive compositions which exhibit a change in viscosity, directly 
or indirectly, as a result of their exposure to actinic radiation are used 
in forming relief images. 
In accordance with one embodiment of the invention, a layer of 
microcapsules containing a photosensitive composition, as described above, 
is provided on an etchable support, such as a support useful in preparing 
a printing plate, a printed circuit, or the like. The layer of 
microcapsules is image-wise exposed to actinic radiation and subjected to 
a uniform rupturing force. This causes the microcapsules to rupture and 
image-wise release their contents as in the Sanders patents. When the 
photosensitive composition is a photohardenable composition, unhardened 
composition is released from the microcapsules in the unexposed areas 
whereas, in the exposed areas, the composition is hardened and is retained 
in the microcapsules. Where the microcapsules contain a photosoftenable 
composition, the opposite result is achieved. 
The released photosensitive composition is caused to migrate to a support 
where it can function as a resist image. This support can be the same 
support upon which the microcapsules are carried or it can be a separate 
support to which the photosensitive composition is transferred as by 
passing the support carrying the microcapsules and the support receiving 
the photosensitive composition between a pair of pressure rollers. An 
etching agent can be applied to the support which image-wise etches its 
surface. In the areas in which the photosensitive composition is released 
from the microcapsules, the composition protects the underlying surface 
and prevents it from being etched. Where the composition is not released, 
the etchant penetrates the microcapsule layer and etches the underlying 
surface. Subsequently, by washing the support to remove the etchant and 
the layer of microcapsules and/or the photosensitive composition, relief 
images in the form of the etched surface are obtained. 
In accordance with another embodiment of the invention, the microcapsules 
may include a photosensitive composition and an etchant for the support. 
In this case, upon exposing and subjecting the layer of microcapsules to a 
uniform rupturing force, the etchant is imaqe-wise, selectively released 
from the capsules. In the areas in which it is released, it etches the 
underlying substrate. A relief image in the form of the differentially 
etched surface is again obtained. 
In another embodiment of the invention, the photosensitive material 
includes a support, a layer of a hardenable composition or resin such as 
gelatin, a polymer, or a prepolymer, and a layer of microcapsules 
containing a photosensitive composition and a hardening agent for the 
hardenable composition or resin. Exposure of the microcapsules and 
subjecting the microcapsules to a uniform rupturing force results in the 
hardening agent being image-wise released form the microcapsules. The 
hardening agent migrates to the underlying layer and hardens it through 
crosslinking, or further polymerization or the like. Subsequently, 
application of a solvent for the unhardened composition washes it away and 
leaves a resistant image. This image can be used for planographic 
printing, or, depending on the nature of the support, the support can be 
etched to provide an intaglio plate. 
In another embodiment of the invention, which is a variation of the 
foregoing embodiment, a layer of a composition is carried on the support 
which is softened by the agent released from the microcapsules.

DETAILED DESCRIPTION OF THE INVENTION 
The disclosures in commonly assigned U.S. Pat. Nos. 4,399,209 and 4,440,846 
relating to the preparation of microcapsules containing photosensitive 
compositions and the mechanisms by which they rupture, release their 
contents and yield images are incorporated herein by reference. 
FIG. 1 illustrates an embodiment of the invention wherein the internal 
phase of the microcapsules consists essentially of a photohardenable 
composition. There photosensitive material 100 includes a support 110 
having an etchable layer 112 on the surface thereof. The etchable layer 
112 may be provided as a separate layer or may simply be the surface of 
the support 110. In accordance with this embodiment of the invention, the 
etchable layer 112 is overcoated with a layer 114 of microcapsules 120 
having liquid internal phase 118. As mentioned earlier, a transfer 
technique analogous to that described in U.S. Pat. No. 4,399,209 could 
also be used, in which case the microcapsules would be carried on a 
separate support which is assembled with the support upon which the 
polymer image is to be formed after exposure, and the two are passed 
through the nip between a pair of pressure rollers. 
In FIG. 1B, the photosensitive material is shown being exposed through 
photomask or stencil M. In the exposed areas 16, the internal phase 118A 
of the microcapsules 120A is polymerized or crosslinked by the actinic 
radiation. The internal phase is shown as being solid. In fact, the 
internal phase 118A in the exposed areas 16 may actually be converted from 
a liquid to a less liquid form or from a semi-solid to more solid form. 
This is explained in more detail in U.S. Pat. No 4,399,209. In the 
unexposed areas 22, the internal phase 118B of the microcapsules 120B 
remains liquid. What is critical to the formation of the relief image is 
that upon subjecting the layer of microcapsules to the uniform rupturing 
force, the internal phase is released from the capsules in the unexposed 
or underexposed areas, whereas it is not released in the fully exposed 
areas. 
FIG. 1C is a schematic illustration of the product which results after 
subjecting the layer 114 of microcapsules 120A and 120B to a uniform 
rupturing force. This uniform rupturing force is most typically pressure 
which is applied to the layer of microcapsules by passing the 
photosensitive material through the nip between a pair of pressure 
rollers, however, forces other than pressure can be used. U.S. Pat. No. 
4,448,516, which is incorporated herein by reference, discloses the use of 
a fibrous developer roll to rupture the microcapsules. The use of a 
fibrous developer roll is advantageous because high line pressures are not 
required to obtain uniform development. In addition, microcapsules can be 
designed which are rupturable by forces such as ultrasonic energy and 
heating. 
Upon subjecting the microcapsules to a uniform rupturing force, the 
microcapsules 120A in the fully exposed areas do not release their 
contents 118A, whereas the microcapsules 120B in the unexposed or 
underexposed areas release the internal phase 118B, as schematically 
shown. While the microcapsules 120A in the exposed areas are shown in FIG. 
1C as unruptured, as explained in more detail in U.S. Pat. No. 4,399,209, 
these capsules may actually be ruptured, but due to the polymerization of 
the internal phase 118A, the internal phase is not released from the 
capsules upon subjecting the microcapsules to the uniform rupturing force. 
Those skilled in the art will understand that two events are necessary to 
form the relief image. The microcapsules must rupture and the microcapsule 
must exude the internal phase. If either event is prevented through 
exposure, no image is formed. 
The intermediate shown in FIG. 1C can be processed by either of two routes 
depending upon the nature of the internal phase of the microcapsules. If 
the internal phase 118B released from the microcapsules is the type that 
is resistant to the etching agent that is used to develop the relief 
image, the etching agent can be applied directly to the intermediate 102 
shown in FIG. 1C. On the other hand, if the composition released from the 
microcapsules is the type which must be hardened, then it is necessary to 
harden the released composition. Since the composition released from the 
microcapsules is a photosensitive composition, one method for hardening 
the released composition 118B is to uniformly expose the photosensitive 
material to actinic radiation of the same type used to image-wise expose 
the microcapsules. Alternatively, the photosensitive material might be 
heated to harden the released photosensitive composition. The released 
composition could also be hardened chemically although this would be 
substantially less convenient. 
In FIG. 1D, the photosensitive material is shown after being uniformly 
exposed to actinic radiation. Exposure has the effect of cross-linking the 
released photosensitive composition and yielding a hardened polymer image 
128. 
Upon applying the etching agent to the surface of the intermediate 102 
shown in FIG. 1C or 104 shown in FIG. 1D, the etching agent readily 
penetrates the unruptured microcapsules 120A and removes the underlying 
etchable layer 112 in the areas 30 as shown in FIG. 1E to yield the 
intermediate 106. On the other hand, the polymeric image 128 is resistant 
to the etching agent and, as such, the etchable layer 112A is not removed 
in areas 32 which are protected by the image 128. 
Upon subsequent washing to remove the polymer image, a relief image 112A 
such as an intaglio plate 108 is formed as shown in FIG. 1F. 
FIG. 2 illustrates the embodiment of the invention wherein the 
microcapsules include both a photosensitive composition and an etching 
agent. In FIG. 2, a photosensitive material 200 includes a support 210, an 
etchable layer 212 and a layer 214 of microcapsules 220 containing a 
photosensitive composition and an etchant in the internal phase 218. 
The photosensitive material 201 is shown in FIG. 2B being exposed 
image-wise to actinic radiation through a photomask M. In the exposed 
areas 16, the internal phase 218A of the microcapsules 220A is shown as 
being hardened by the actinic radiation whereas in the unexposed areas 22, 
the internal phase 218B of the microcapsules 220B remains liquid. 
In accordance with this embodiment of the invention, upon subjecting the 
layer 214 of microcapsules 220A and 220 B to a uniform rupturing force, 
the microcapsules 220B in the unexposed areas rupture and release the 
etchant whereas the microcapsules 220A in the exposed areas do not. Thus, 
as shown in FIG. 2C, in the areas 22 in which the photosensitive material 
is not exposed, the etchant in the released phase 218B attacks the 
etchable layer 212 and removes it as shown at 225. On the other hand, in 
areas 16 in which the microcapsules 220A are exposed, the etchant is not 
released and the etchable layer 212A remains intact. Upon subsequently 
washing the photosensitive material 206 as shown in FIG. 1D, the product 
208 is obtained. 
In FIG. 3, the photosensitive material 300 comprises a support 310, an 
etchable layer 312 a layer of a chemically hardenable composition such as 
a hardenable polymer or prepolymer 340, and a layer 314 of photosensitive 
microcapsules 320 containing, as the internal phase 318, a photosensitive 
composition and an agent which is capable of reacting with the polymer or 
prepolymer in layer 340 and hardening it. The term "chemically 
hardenable," as used herein, is used in contrast to a photohardenable 
composition which is hardened via exposure to actinic radiation and refers 
to compositions which are hardened through the application of a chemical 
agent. Typically, these compositions are hardened through polymerization 
or crosslinking. 
In FIG. 3B, the photosensitive material 302 is shown after exposure to 
actinic radiation through a photomask M. As in FIG. 1 and FIG. 2, the 
microcapsules 320A are shown as having a solid internal phase 318A in the 
exposed areas 16 and the microcapsules 320B are shown as having a liquid 
internal phase 318B in the unexposed areas 22. 
Upon subjecting the microcapsules 320A and 320B to a uniform rupturing 
force, as shown in FIG. 3C, the microcapsules 320B rupture and release the 
composition 318B containing the hardening agent to the underlying layer of 
polymer or prepolymer 340. This hardens the layer 340 in the areas 330. 
The microcapsules 320A in the exposed areas do not release the hardening 
agent and, as such, the layer 340 remains unhardened in the areas 332. 
Upon washing the intermediate 302 shown in FIG. 3C in a solvent for the 
polymer or prepolymer in layer 340, the polymer is removed from the areas 
332, but a hardened polymeric image 334 remains in the areas 330 as shown 
in FIG. 3D. 
The intermediate 304 shown in FIG. 3D will be useful in certain 
applications, depending upon the materials which are selected for the 
support 310 and the polymer or prepolymer layer 340. For example, the 
intermediate shown in FIG. 3D may be useful as a planographic printing 
plate. In accordance with other embodiments of the invention, however, the 
intermediate shown in FIG. 3D may be further processed using an etching 
agent. In accordance with these embodiments, an etching agent is applied 
to remove the etchable layer in the areas 332 which are not protected by 
the polymeric image 334 as shown in FIG. 3E. The layer 312 remains intact 
in the areas 312B which are protected. Upon washing the intermediate 306 
to remove the etchant and the polymeric image, a relief 308 as shown in 
FIG. 3F is obtained. It will be appreciated that this method is 
positive-working. 
In a further embodiment of the present invention, the hardenable 
composition layer 340 is replaced by a layer of a chemically softenable 
composition such as a novolak resin. In this embodiment, a softening agent 
for th layer 340 is released from the microcapsules. Whereas the 
photoimaging material illustrated in FIG. 3 is positive working, the 
analogous material employing a chemically softenable composition is 
negative working. 
In FIGS. 1-3 the invention has been illustrated for embodiments in which 
the microcapsule layer is formed directly on the support on which the 
relief image is desired. Those skilled in the art will appreciate that the 
microcapsule layer can be carried on a separate support to provide a 
transfer sheet which is assembled with the support on which the relief is 
desired before or after exposure. In this case an image-wise transfer of 
the contents of the microcapsules is effected by subjecting the transfer 
sheet in contact with the support which is to bear the relief to a uniform 
rupturing force. 
The photosensitive compositions used in of the present invention can be 
designed to be sensitive to ultraviolet, infrared, visible, X-ray, ion 
beam radiation and the like. This is accomplished through a judicious 
selection of the composition and the photoinitiator. Furthermore, while 
photohardenable compositions are usually employed in the microcapsules, 
embodiments are also possible wherein photosoftenable compositions are 
used. 
The photohardenable compositions used in the present invention can be 
selected from among photohardenable compositions which are well known in 
the art. The most typical examples of such compositions are compositions 
including ethylenically unsaturated compounds. These compounds contain at 
least one terminal ethylene group per molecule. Typically, liquid 
ethylenically unsaturated compounds having two or more terminal ethylene 
groups per molecule are preferred. Examples of this preferred group are 
ethylenically unsaturated acid esters of polyhydric alcohols such as 
ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 
trimethylolpropane triacrylate (TMPTA) and trimethyolpropane 
trimethacrylate (TMPTMA), styrene, divinylbenzene and derivatives thereof. 
Another example of a useful radiation sensitive composition is an acrylate 
prepolymer derived from the partial reaction of pentaerythritol with 
acrylic acid, methacrylic acid, or acrylic or methacrylic acid esters. 
Photopolymerizable prepolymers are also useful in the present invention. 
Suitable prepolymers can be selected from commercially available acrylate 
terminated polyurethanes, polyesters and polyethers. Typically, these 
compounds are prepared by end capping isocyanate terminated prepolymers 
with acrylic or methacrylic acid. The prepolymers can range up to about 
16,000 in molecular weight, but in most cases do not exceed about 1,000 to 
3,000 in molecular weight. If the molecular weight of the prepolymer is 
too high, it may be too viscous to be adequately emulsified for 
encapsulation and released from the microcapsules. However, higher 
molecular weight prepolymers can be used in the present invention if they 
are diluted with low molecular weight reactive monomers such as TMPTA. 
Representative examples of acrylate terminated urethane prepolymers which 
may be useful in the present invention include Chempol 19-4832 and Chempol 
19-4833 available from Freeman Chemical Corporation; Uvithane 893, 788, 
782 and 783 available from Thiokol Corporation; Ebercryl 220, 204, 210 and 
240 available from Virginia Chemicals, Inc.; etc. Examples of epoxy 
acrylate prepolymers include Chempol 19-4824 and Chempol 19-4825 from 
Freeman Chemical Corp.; Celrad 3200, 3700 and 3701 from Celanese Corp.; 
Ebercryl 600 series prepolymers from Virginia Chemicals, Inc.; etc. 
It is particularly desirable to use a mixture of a multifunctional acrylic 
monomer such as TMPTA and an acrylate-capped prepolymer such as an 
acrylate-capped polyurethane in the photosensitive composition. One such 
composition is made up of 60% of a diacrylate-capped pre-polymer, 30-40% 
of a monomeric, low molecular weight diacrylate, and up to 10% of TMPTA. 
For certain applications, it may be desirable to modify the photohardenable 
composition to enhance the oleophilic nature of the polymer image that is 
formed. In particular, ethylenically unsaturated monomers such as TMPTA 
are relatively hydrophilic. To enhance oleophilicity, it is sometimes 
desirable to use oleophilic additives such as waxes, cellulose acetate, 
cellulose nitrate, polybutadiene, and the like. The function of these 
additives is to enhance the affinity of the polymer image for printing ink 
in preference to water. 
While the present invention will typically be practiced using 
photohardenable compositions in the microcapsules, embodiments are also 
possible in which photosoftenable compositions are used. In this case, 
exposure will result in the internal phase being released from the capsule 
instead of being retained as with a photohardenable composition. Examples 
of photosoftenable compositions are described in U.S. Pat. No. 4,399,209. 
Another particularly useful type of photosensitive composition is described 
in commonly assigned U.S. patent application Ser. No. 118,016, filed June 
7, 1984, which is incorporated herein by reference. These compositions 
include a photosensitive precursor of a polymerization inhibitor such as 
6-nitroveratraldehyde. These compositions are image-wise exposed to 
generate the inhibitor which prevents them from polymerizing in the 
exposed areas when they are subsequently given a uniform exposure at a 
different wavelength of radiation which otherwise hardens the composition. 
Within the context of the present invention, photohardenable compositions 
are negative working. This modification provides a positive working 
system. 
In most cases, the photosensitive composition includes a photoinitiator. It 
is possible to use either homolytic photoinitiators which are converted to 
an active species by radiation and generate a radical by abstracting 
hydrogen from a hydrogen donor, or photoinitiators which complex with a 
sensitizer to produce a free radical generating species, or 
photoinitiators which otherwise generate radicals in the presence of a 
sensitizer. If the system relies upon ionic polymerization, the 
photoinitiator may be the anion or cation generating type depending on the 
nature of the polymerization. 
Examples of photoinitiators useful in the present invention include diaryl 
ketone derivatives, and benzoin alkyl ethers. The photoinitiator is 
selected based on the sensitivity of the system that is desired. Where 
ultraviolet sensitivity is desired, suitable photoinitiators include 
alkoxy phenyl ketones, O-acylated oximinoketones, polycyclic quinones, 
benzophenones and substituted benzophenones, xanthones, thioxanthones, 
halogenated compounds such as chlorosulfonyl and chloromethyl polynuclear 
aromatic compounds, chlorosulfonyl and chloromethyl heterocyclic 
compounds, chlorosulfonyl and chloromethyl benzophenones and fluorenones, 
and haloalkanes. 
In many cases it is advantageous to use a combination of compounds to 
provide a photoinitiator system. Useful systems include co-initiators such 
as tertiary amines and, more particularly, N,N-dimethylanilines. It is 
particularly desirable to include a compound such as ethyl 
p-dimethylaminobenzoate in the initiator composition. The 3-substituted 
coumarin compounds described in U.S. Pat. No. 4,147,552 are also useful. A 
combination of Michler's ketone and benzoin methyl ether (ratio 2:5) may 
be used. A combination of 2,2'-dimethoxy-2-phenylacetophenone, 
isopropylxanthone and ethyl p-dimethylaminobenzoate (Quanticure EPD); or a 
combination of Quanticure EPD, Irgacure 651 and 2-chlorothioxanthane can 
also be used. 
The amount of photoinitiator used in the photosensitive composition depends 
on the particular photohardenable composition selected. It should be 
present in an amount sufficient to initiate photopolymerization within a 
reasonably short exposure time. The photoinitiator may also be used to 
sequester oxygen, which is present in the microcapsules and inhibits 
photopolymerization. In some cases it is desirable to conduct a 
non-imaging, oxygen sequestering pre-exposure or co-exposure to sequester 
the oxygen in the microcapsules before conducting the image-wise exposure. 
See U.S. Pat. No. 4,482,624. When the photoinitiator is also relied upon 
to sequester oxygen, it must be used in amounts sufficient to fulfill both 
this function and its imaging function. 
To obtain improved film speed, it may be desirable to incorporate certain 
prepolymers in the microcapsules such as a diallylo-phthalate prepolymer. 
Prepolymers such as this are believed to enhance film speed by 
accelerating the rate with which the viscosity of the internal phase 
builds upon exposure. Waxes can also be used for this purpose. 
In addition to the foregoing materials, certain photohardenable 
compositions conventionally used in making printing plates may be 
microencapsulated and used in the present invention, provided of course, 
that these compositions can be satisfactorily encapsulated. Typical 
examples include photosensitive phenol-formaldehyde novolak resins, diazo 
compounds, etc. 
The microcapsules used in the present invention are characterized in that 
they include a discrete capsule wall. Conventional techniques such as 
coacervation, liquid-liquid phase separation, interfacial polymerization 
and the like can be used to form the microcapsules. 
The photosensitive compositions are usually oleophilic and therefore 
preferably encapsulated in hydrophilic wall-forming materials such as 
gelatin-type materials (see U.S. Pat. Nos. 2,730,456 and 2,800,457 to 
Green et al.) including gum arabic, polyvinyl alcohol, 
carboxymethyl-cellulose; resorcinol-formaldehyde wall formers (see U.S. 
Pat. No. 3,755,190 to Hart et al.); isocyanate wall-formers (see U.S. Pat. 
No. 3,914,511 to Vassiliades); isocyanate-polyol wall-formers (see U.S. 
Pat. No. 3,796,669 to Kirintani et al.); urea formaldehyde wall-formers 
(see U.S. Pat. Nos. 4,001,140, 4,087,376 and 4,089,802 to Foris et al.); 
particularly urea-resorcinol-formaldehyde in which oleophilicity is 
enhanced by the addition of resorcinol and melamine-formaldehyde 
wall-formers and hydroxypropyl cellulose (see commonly assigned U.S. Pat. 
No. 4,025,455 to Shackle). One method for forming microcapsules that is 
particularly useful is described in U.S. Pat. No. 4,353,809. 
It has been found that the microcapsules desirably range from about 3 to 15 
microns in diameter. The microcapsules can be coated on a support to form 
the transfer sheet using conventional coating techniques such as blade 
coating, air-knife coating, curtain coating, etc. The microcapsules can be 
applied to the support neat, e.g., dispersed in water, however, it may be 
desirable to include a small amount of an adhesive such as polyvinyl 
alcohol or Rohm & Haas latex P-310 with the microcapsules to improve their 
adhesion to the substrate. Of course, the system must be constructed such 
that the microcapsule layer is permeable to any developing solution that 
is used. The microcapsules are preferably coated in a capsule coating 
weight (solids) of about 1.5 to 5 lbs. per 3000 sq. ft. 
Where the microcapsules are carried on a transfer sheet, various substrates 
can be used including both transparent and opaque substrates such as paper 
and plastic films such as polyethylene terephthalate. The latter are 
useful when the transfer sheet is pre-assembled with the printing plate 
support since they permit the microcapsules to be exposed from the 
support-side of the transfer sheet. 
The transfer sheet can be exposed in an assembled or unassembled condition 
with the printing plate support. Exposure can be conducted using 
conventional radiation sources. Among the exposure techniques that can be 
used are exposure through a mask using ultraviolet or visible radiation, 
e.g., using a mercury, carbon, or xenon arc or a tungsten lamp; or 
exposure with an ultraviolet laser, a visible laser, or an argon ion 
laser. 
The present invention can be used to provide relief images on supports 
conventionally used for this purpose in the art. The present invention is 
particularly useful in manufacturing printing plates, but those skilled in 
the art will appreciate that these teachings can also be applied in other 
applications where relief images are desired including the production of 
certain printed circuits. 
Printing plate supports can be selected from among the supports 
conventionally used in the art. A support will be selected which exhibits 
the desired hydrophilic characteristic and good adhesion for the 
photohardenable composition released from the microcapsules. A preferred 
support is the anodized aluminum support treated with an alkali metal 
silicate as described in U.S. Pat. No. 3,181,461. Other useful printing 
plates supports include oxidized aluminum, stainless steel, cobalt-plated 
steel, copper-coated steel, chrome-plated steel, coated papers such as 
polyolefin coated paper, polymeric substrates such as polyethylene 
terephthalate, copper-coated epoxy, etc. 
Conventional etchants and etchable supports can be used herein. Typical 
examples of etchable supports include acid etchable or alkali etchable 
metallic layers such as copper, aluminum, zinc, or silicon dioxide. 
Typical examples of etchants useful in conjunction therewith include 
ferric chloride to etch copper; hydrochloric, phosphoric or acetic acid to 
etch aluminum or zinc; and hydrofluoric acid to etch silicon dioxide. 
The embodiment shown in FIG. 3 relies upon a combination of a chemically 
hardenable composition such as a curable or hardenable polymer or 
prepolymer layer and a chemical hardening agent. An example of a 
hardenable polymer is gelatin. Hardeners for gelatin are well known. 
Representative examples are dialdehydes such as glutaraldehyde, glyoxal, 
and succinaldehyde; and diketones such as 2,5-hexandione, 
3-hexane-2,5-dione, and p-benzoquinone. It is also envisioned that the 
hardenable layer can be a layer of poly(cis-isoprene) which is image-wise 
crosslinked by the release of an encapsulated but photolysed 
bis(arylazide). 
In the alternative embodiment to FIG. 3, in which the layer on the support 
is selectively solubilized by the agent released from the microcapsules, a 
layer of a novolak resin can be rendered soluble in water by the release 
of an organic acid from the microcapsules such as indene carboxylic acid 
or a derivative thereof. 
A number of techniques can be used to rupture the microcapsules. The most 
common is application of a pressure roller. The amount of pressure applied 
should be adjusted such that the microcapsules in the unexposed or 
underexposed areas are forced to rupture and exude their contents. It is 
not clear whether this force actually ruptures the microcapsules in the 
fully exposed areas or not. If the force applied does rupture the fully 
exposed capsules it should not force these microcapsules to transfer their 
contents to the printing plate as this will produce background coloring 
and spotting. In addition to pressure, the microcapsules can be designed 
to be ruptured by heating or ultrasonically. A fibrous developer roller of 
the type described in U.S. Pat. No. 4,448,516 can also be used. 
Having described the invention in detail and by reference to specific 
embodiments thereof, it will be apparent that numerous modifications and 
variations are possible without departing from the spirit and scope of the 
invention as defined by the following claims.