Note: Descriptions are shown in the official language in which they were submitted.
20 ~ 8954
METHOD OF DEVELOPING PHOTOPOLYMERIZABLE PRINTING PLATES
AND COMPOSITION THEREFOR
BACKGROUND OF THE INVENTION
The present invention relates to an improved method and
composition for developing a relief image by imagewise
exposing a photopolymerizable layer to actinic radiation
and subsequently removing the uncured material of the
photopolymerizable layer by use of a developer composition
to produce the relief image.
In the following description and claims, the term
"cured" and derivatives thereof shall be used to describe
material obtained by (1) the photopolymerization of mono-
meric or low molecular weight compounds, or (2) the cross-
linking of photocrosslinkable polymers. The term "uncured"
and derivatives thereof shall be used to describe material
which has not undergone photopolymerization or photocross-
linking.
The use of actinic radiation, such as ultraviolet
light, to form a relief pattern or image by the imagewise
curing of a photopolymerizable layer is well known in the
art and is typically used in preparing flexographic print-
ing plates and relief patterns on semiconductor layers.
These relief images or patterns are formed by placing an
image-bearing process transparency, for example, a line or
half-tone negative, over the photopolymerizable layer. The
negative is designed to transmit actinic radiation through
certain portions of it and to absorb or reflect actinic
radiation at other portions so that the photopolymerizable
layer underneath the negative is cured imagewise according
20 1 8954
to the portion of the negative that transmits the radia-
tion. A transparent protective film, called a slip film,
usually a polyamide resin film, is commonly provided be-
tween the negative and the photopolymerizable layer in
order to prevent the negative from damaging the photo-
polymerizable layer.
After the exposure to actinic radiation, the slip film
must be removed from the photopolymerizable layer and the
uncured material of the photopolymerizable layer must be
removed in order to produce the desired relief image or
pattern. Typically, a solvent or developer is used which
will solvate the portion of the photopolymerizable layer
that has not been cured by the actinic radiation, but will
not substantially affect the portion of the photo-
polymerizable layer which has been cured by the actinic
radiation. Typical developers used in such a process are
chlorohydrocarbons, such as chloroform, trichloroethylene,
tetrachloroethylene or trichloroethylene, either singly or
in a mixture with a suitable lower alcohol, such as n-
butanol; saturated cyclic or acyclic hydrocarbons, such as
petroleum ether, hexane, heptane, octane, cyclohexane or
methylcyclohexane; aromatic hydrocarbons, such as benzene,
toluene or xylene; or lower aliphatic ketones, such as
acetone, methylethyl ketone or methylisobutyl ketone.
In using the prior art developer compositions described
above, it usually takes a disadvantageously long time to
remove the portion of the photopolymerizable layer which
has not been cured. The cured relief patterns or images
swell or distort during the washing or removal of the
uncured portion of the photopolymerizable layer by the
developer composition. Further, under microscopic inspec-
tion, the printing surface may exhibit a nonsmooth surface
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due to cracks, crevices, bumps and other surface ir-
regularities and this may detrimentally affect the printing
quality. Additionally, these prior developers are toxic
and must be subjected to special handling procedures and
they have low flash points which makes the separation of
them from the removed or washed-out, uncured material very
difficult.
U.S. Patent No. 4 806 452 discloses a developer com-
position which contains, as an essential component, at
least one monoterpene and up to 40 % by weight of an ad-
ditional solvent.
Flexographic photopolymer printing plates can be made
of a variety of different materials, including:
1. block copolymers of styrene and butadiene or styrene
and isoprene (U.S. Patent Nos. 4 323 636, 4 323 637,
4 423 135 and 4 369 246),
2. a mixture of nitrile rubber, an addition photo-
polymerizable tri- or tetra-unsaturated ester of
acrylic or methacrylic acid and an addition
polymerization initiator activated by actinic radia-
tion (British Patent No. 1358062),
3. a mixture of a high molecular weight butadiene/
acrylonitrile copolymer containing carboxyl groups,
a low molecular weight butadiene polymer which may
or may not contain carboxyl groups, an ethylenically
unsaturated monomer and a free-radical generating
system (U.S. Patent No. 4 177 074), and
4. a mixture of a high molecular weight butadiene/
acrylonitrile copolymer containing carboxyl groups,
a high molecular weight butadiene/acrylonitrile co-
polymer which does not contain carboxyl groups, an
ethylenically unsaturated monomer and a free radical
generating system (U.S. Patent No. 4 517 279).
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The developer compositions needed for development of these
different types of plates vary depending on the specific
composition of the plate employed. For example, a de-
veloper suitable for the development of Flex-Light type FL-
SKOR and Flex-Light type FL-KOR photopolymer plates (regis-
tered trademarks of W. R. Grace & Co.) may not be effective
in the development of Flex-Light type FL-1 and Flex-Light
type FL-AL photopolymer plates (registered trademarks of W.
R. Grace & Co.).
U.S. Patent No. 4 847 182 discloses a developer com-
position comprising a terpene which can be blended with a
nonsolvent, such as benzyl alcohol, which nonsolvent is
effective to promote the spontaneous separation of uncured
material from the developer solution after the plate has
been developed. Emulsifiers, such as polyethylene glycol
mono(nonylphenyl) ethers, can be incorporated in the de-
veloper composition so that the plate can be rinsed with
water prior to oven drying.
It is an object of the present invention to provide a
developer composition for use in the preparation of a
relief image or pattern by photopolymerization in which the
washout time and the drying time are substantially shorter
in comparison with conventional processes, the photo-
polymerized relief images or patterns do not undergo sig-
nificant permanent distortion or swelling during washout
with the developer composition and the developer composi-
tion can be economically recovered from the uncured photo-
polymerizable material without special handling procedures
or explosion problems.
It is a further object of the present invention to
provide a developer composition which has a low toxicity
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and volatility, is biodegradable and can be used for de-
veloping relief images or patterns produced on a wide
variety of types of photopolymer plates.
It is a still further object of the present invention
to provide a developer composition which will dissolve the
slip film during the development of the plate and thereby
eliminate the step of removing the slip film from the
photopolymer plate.
It is a still further object of the present invention
to provide a developer composition which enables the de-
veloped photopolymer plate to be rinsed with plain water
thereby eliminating the tackiness produced in the formed
image or pattern by the conventional solvent rinses and
allowing the easy disposal of waste rinse solution.
SUMMARY OF THE INVENTION
These and other objects of the present invention are
accomplished by providing a process and a developer com-
position for producing a relief image or pattern on a
photopolymerizable layer by removing the uncured portion of
the photopolymerizable layer by washing it with a developer
composition comprising a monoterpene and N-methyl-
pyrrolidone. An aromatic alcohol is employed in the
developer composition when a slip film is present on the
photopolymerizable layer.
In a second aspect of the present invention, the de-
veloper composition is a mixture of a monoterpene, N-
methylpyrrolidone, an aromatic alcohol and a nonionic sur-
factant. This latter composition is water-rinsable.
DETAILED DESCRIPTION OF THE INVENTION
According to the first, preferred embodiment of the
invention, the developer composition of the present inven-
tion comprises a monoterpene, N-methylpyrrolidone and an
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aromatic alcohol. As the monoterpene, p-methane, borneol,
menthone, D- and L-limonene, ~-terpineol, ~-terpinene,
~-terpinene, terpinolene, ~-pinene, ~-pinene, ~-pinene,
citronellol and mixtures of these monoterpenes can be used.
D-limonene is especially preferred. There can be used D-
limonene obtained from orange peel and/or pine needles. D-
limonene is nontoxic and has a boiling point of about
175C. The high boiling temperature and vapor pressure of
D-limonene enable it to be separated effectively and ef-
ficiently from the uncured photopolymerizable material that
is dissolved in the developer composition during the wash-
out step. The amount of the monoterpene component in the
developer composition is from 30 to 60 wt.%, preferably
from 35 to 50 wt.%, based on the total weight of the de-
veloper composition.
N-methylpyrrolidone is contained in the developer
composition, according to the invention, and it is un-
expectedly effective to increase the versatility of the
developer composition so that a very wide variety of dif-
ferent types of photopolymer printing plates can be washed
by the developer composition with good results and with
improved plate quality. Particularly, the developer com-
position can be effectively used in the development of all
commercially available flexographic photopolymer printing
plates, including Flex-Light type FL-l and Flex-Light type
FL-AL acrylic ester photopolymer plates (registered trade-
marks of W. R. Grace & Co.) which have heretofore required
the use of a developer containing a chlorinated hydro-
carbon. The amount of N-methylpyrrolidone present in the
invention composition is from 10 to 50 wt.%, preferably
from 20 to 40 wt.%, based on the total weight of the de-
veloper composition. The amount of N-methylpyrrolidone is
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less than the amount of the monoterpene component. Prefer-
ably, the weight ratio of N-methylpyrrolidone/monoterpene
is from about 0.95 to about 0.5, more preferably, from
about 0.8 to about 0.6. N-methylpyrrolidone has a boiling
point of about 202C so that it has a relatively high flash
point and it can be easily separated from the uncured
photopolymerizable material.
The aromatic alcohol contained in the developer com-
position of the present invention enables the slip film
covering the photopolymerizable material to be dissolved
during the development step without there being needed a
separate step of peeling off the slip film from the photo-
polymerizable layer. Of the aromatic alcohols, benzyl
alcohol has proven to be particularly effective for dis-
solving the slip film without any attendant negative ef-
fects on the photopolymerized relief pattern or image. The
content of benzyl alcohol is in the developer composition
of the present invention in the range of from 1 to 35 wt.%,
preferably from about 10 to about 20 wt.%, based on the
total weight of the developer composition. The amount of
benzyl alcohol is less than the amount of N-methyl-
pyrrolidone. Preferably, the weight ratio of N-methyl-
pyrrolidone/benzyl alcohol is from 4 to about 1, more
preferably about 2.5 to about 1.5. Benzyl alcohol has a
boiling point of about 205C and it can be easily separated
from the uncured material.
In the event that the photopolymerizable plate does not
have a slip film or it is removed in a different way, then
the benzyl alcohol can be omitted from the developer com-
position.
In a second, preferred embodiment of the present inven-
tion, the developer composition additionally comprises a
nonionic surfactant. It has been found that the presence
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of a nonionic surfactant in the developer composition
enables the developed photopolymer layer to be rinsed with
water before the layer is dried. This reduces the perma-
nent distortion or swelling of the developed relief image
or pattern during drying. Additionally, the nonionic
surfactant emulsifies the ingredients of the developer
composition and the uncured material of the photopolymer
plate and enables the waste aqueous rinse solution to be
sewered or disposed of in another environmentally safe
manner. The nonionic surfactant preferably used in the
present invention is nonylphenolpolyethylene glycol ethers
in which about 6.0 to 9.5 moles of ethylene oxide are
condensed with one mole of nonylphenol. It is especially
preferred that the nonionic surfactant composition is a
blend of nonylphenolpolyethylene (9.5) glycol ether and
nonylphenolpolyethylene (6.0) glycol ether in 2:1 weight
ratio. The nonionic surfactant is contained in the de-
veloper composition of the present invention in an amount
of from 5 to 12 wt.%, based on the total weight of the
developer composition, preferably about 8 to 10 wt.%.
Preferably, the amount of the nonionic surfacant is less
than the amount of benzyl alcohol.
The presently most preferred, water-rinsable developer
composition of the present invention consists of 30 wt.% of
N-methylpyrrolidone, 50 wt.% of D-limonene, 11 wt.% of
benzyl alcohol, 6 wt.% of nonylphenolpolyethylene (9.5)
glycol ether and 3 wt.% of nonylphenolpolyethylene (6.0)
glycol ether.
The developer composition of the present invention can
be used to develop all presently known types of photo-
polymer plates, is nontoxic, eliminates the step of remov-
ing the slip film and can be more efficiently recovered
because of the high temperature and vapor pressure of its
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g
components, including the monoterpene. These and other
advantages of the present invention are shown in the fol-
lowing examples.
In the following examples, the equipment used to per-
form the exposure, washing and drying of the photopolymer
plates was the Anderson & Vreeland Photopolymer System,
commercially available from Anderson & Vreeland, Inc.,
Bryan, Ohio. The washing equipment was of two types,
namely,
1. a 12 inch x 15 inch flat bed for receiving the
photopolymer plate and in which a brush is
disposed above the plate and is moved in an
orbital pattern so that its bristles contact
and remove uncured material from the plate, and
2. a 30 inch x 44 inch unit in which the photo-
polymer plate is mounted on an oscillatable
drum and 4 rotary brushes are disposed in as-
sociation with the drum so that their bristles
contact and remove uncured material from the
plate.
The exposure unit employed W fluorescent-type lamps. When
the plate was subjected to "back exposure", that is, uni-
form exposure on the back without a negative, the back side
of the photopolymer was uniformly cured to a selected depth
to form a so-called "floor" underneath the relief areas.
When the plate was subjected to "face exposure", that is,
imagewise exposure on the face with a negative, latent
relief areas of a selected depth were formed in the face of
the photopolymer layer. A W. R. Grace test negative was
used. Development of the photopolymer plate with the
solution removed the uncured material whereby to form
relief areas projecting from the floor. In those cases in
which no back exposure and no face exposure were conducted,
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the test measured the resistance to dissolving of the
uncured photopolymer material in the developing solution.
Example 1
A developer solution was prepared by mixing 30 parts by
weight of N-methylpyrrolidone, 50 parts by weight of D-
limonene, 11 parts by weight of benzyl alcohol, 6 parts by
weight of nonylphenolpolyethylene (9.5) glycol ether and 3
parts by weight of nonylphenolpolyethylene (6.0) glycol
ether.
The solution was added to a 12 inch x 15 inch,-orbital
brush, flat bed plate processor. A photopolymer plate
having a photopolymer layer having a thickness of 0.067
inch (KOR~ available from W. R. Grace & Co.) was uniformly
pre-exposed on the back for 20 seconds and then was exposed
imagewise through a photographic negative placed on the
protective layer for 5 minutes and 20 seconds. The plate
was then washed with the above-described solution for 4~
minutes in the plate processor. The plate was rinsed with
plain tap water and then was dried at 150F for 1 hour.
The depth of the floor (uniformly cured back of the plate)
was 0.030 inches. The relief was 0.037 inches deep. The
sidewall structure of the image elements was good. Under-
mining of the sidewalls and rounding of the edges was not
observed.
Additional commercially available photopolymer plates
were processed in similar fashion. The following table
lists the processing conditions and results. All the tests
were conducted with the 12 inch x 15 inch flat bed washing
unit.
TM- Trade-mark
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TABLE I
Photopoly- Wash- Depth of
mer Layer Back Face ing ~ Relief
Thickness Expo- Expo- Time Areas
Plate Type (inches) sure sure (mins.) (inches)
Grace FL-ALr~ 0.067 None None 10 0.031
Grace FL-AL 0.067 None None 12 0.035
DuPont Cyrel LPT~ 0.067 None None 5 0.040
BASFT~ 0.067 None None 4 0.046
DuPont Cyrel LP7~ 0.067 None None 10 O.045
DuPont Cyrel LP 0.067 None None 4 0.042
Grace FL-1~ 0.090 None None 15 0.046
Example 2
A developer solution was prepared by mixing 32 parts by
weight of N-methylpyrrolidone, 37 parts of D-limonene, 22
parts of benzyl alcohol and 9 parts of nonylphenolpoly-
ethylene/9.S glycol ether.
The solution was added to the 30 inch x 44 inch washing
unit described above. The following table lists the pro-
cessing results and conditions.
TM - Trade-mark
20 1 ~9 5 4
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TABLE II
Photopoly- Wash- Depth of
mer Layer Back Face ing Relief
Thickness Expo- Expo- Time Areas
Plate Type (inches) sure sure (mins.) (inches)
FL-Grace KOR 0.067 10 5 6 0.030
secs. mins.
FL-Grace KOR 0.250 5 10 5 0.035
mins. mins.
FL-Grace KOR 0.250 5 10 10 0.070
mins. mins.
FL-Grace KOR 0.250 5 10 15 0.107
mins. mins.
FL-Grace KOR 0.250 5 10 20 0.135
mins. mins.
FL-Grace KOR 0.250None None 20 0.150
DuPont Cyrel LP 0.250 2 10 6 0.040
mins. mins.
Grace FL-l 0.0g0 1~ 8 12 0.030
mins. mlns.
The components of the developer composed can be easily
separated from the uncured photopolymer contained therein,
for example, by steam distillation or vacuum distillation.
It would be obvious to those skilled in the art that
many modifications may be made within the scope of the
present invention without departing from the spirit there-
of, and the invention includes all such modifications.
