U.S. patent application number 13/586118 was filed with the patent office on 2012-12-06 for flexographic processing solution and use.
Invention is credited to M. Zaki Ali, Elsie A. Fohrenkamm, Michael B. Heller, Kevin M. Kidnie.
Application Number | 20120308935 13/586118 |
Document ID | / |
Family ID | 43806818 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120308935 |
Kind Code |
A1 |
Fohrenkamm; Elsie A. ; et
al. |
December 6, 2012 |
FLEXOGRAPHIC PROCESSING SOLUTION AND USE
Abstract
A flexographic printing plate can be prepared with relief images
using a processing solution. This processing solution includes one
or more esters of monobasic carboxylic acids represented by one or
both of the following Structures (I) and (II):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I) wherein R.sub.1
is an alkyl group having 1 to 5 carbon atoms, Ar.sub.1 is a
substituted or unsubstituted phenyl or naphthyl group, and n is 1
to 3, and H--C(.dbd.O)OR (II) wherein R is a hydrocarbon having 6
to 15 carbon atoms, and b. one or more aliphatic alcohols, or a
combination of one or more aliphatic alcohols and one or more
aromatic alcohols.
Inventors: |
Fohrenkamm; Elsie A.; (St.
Paul, MN) ; Ali; M. Zaki; (Mendota Heights, MN)
; Heller; Michael B.; (Iver Grove Heights, MN) ;
Kidnie; Kevin M.; (St. Paul, MN) |
Family ID: |
43806818 |
Appl. No.: |
13/586118 |
Filed: |
August 15, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12695190 |
Jan 28, 2010 |
|
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|
13586118 |
|
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Current U.S.
Class: |
430/306 |
Current CPC
Class: |
G03F 7/325 20130101 |
Class at
Publication: |
430/306 |
International
Class: |
G03F 7/20 20060101
G03F007/20 |
Claims
1. A method of providing a flexographic printing plate with a
relief image comprising imagewise exposing a flexographic printing
plate precursor comprising an imageable photopolymer layer to
provide exposed and non-exposed regions in an imaged flexographic
printing plate precursor, developing the imaged flexographic
printing plate precursor with a processing solution to remove
non-imaged photopolymer from the imageable photopolymer layer to
provide a relief image having an average depth that is from 2% to
100% of the original thickness of the imageable photopolymer layer,
to form a flexographic printing plate, wherein the processing
solution comprise: a. one or more esters of monobasic carboxylic
acids represented by one or both of the following Structures (I)
and (II): R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
wherein R.sub.1 is an alkyl group having 1 to 5 carbon atoms,
Ar.sub.1 is a substituted or unsubstituted phenyl or naphthyl
group, and n is 1 to 3, and H--C(.dbd.O)OR (II) wherein R is a
hydrocarbon having 6 to 15 carbon atoms, and b. one or more
aliphatic alcohols, or a combination of one or more aliphatic
alcohols and one or more aromatic alcohols.
2. The method of claim 1, further comprising drying the
flexographic printing plate.
3. The method of claim 1, wherein the imageable photopolymer layer
comprises a photopolymerizable elastomeric layer comprising an
elastomeric binder, a photoinitiator, at least one monomer, and
optionally a plasticizer, and the precursor is imagewise exposed
using actinic radiation.
4. The method of claim 1, wherein the one or more esters of
monobasic carboxylic acids are present in an amount of at least 5
weight % and up to and including 70 weight %, and the one or more
aliphatic alcohols, or combination of one or more aliphatic
alcohols and one or more aromatic alcohols, are present in an
amount of at least 5 weight % and up to and including 40 weight
%.
5. The method of claim 1, wherein the one or more esters of
monobasic carboxylic acids are present in an amount of from about
20 weight % to about 60 weight %, and the one or more aliphatic
alcohols, or combination of one or more aliphatic alcohols and one
or more aromatic alcohols, are present in an amount of from about
10 weight % to about 30 weight %.
6. The method of claim 1, wherein R.sub.1 is an alkyl having 1 to 3
carbon atoms, n is 1 or 2, and R is benzyl or citronellyl.
7. The method of claim 1, wherein the one or more esters of
monobasic carboxylic acids includes one of the more of benzyl
acetate, 2-phenylethyl acetate, 2-phenylethyl phenyl acetate,
2-phenylethyl isobutyrate, isobutyl phenyl acetate, benzyl
propionate, benzyl butyrate, benzyl pentanoate, benzyl formate, and
citronellyl formate.
8. The method of claim 1, wherein one or more aliphatic alcohols
includes one or more of n-butanol, 2-ethoxyethanol, a hexyl
alcohol, a heptyl alcohol, an octyl alcohol, a nonyl alcohol, a
decyl alcohol, alpha-terpineol, dipropylene glycol methyl ether,
2-butoxyethanol, isopropyl alcohol, and 2-(2-butoxyethoxy)ethanol,
substituted or unsubstituted cyclopentanol, substituted or
unsubstituted cyclohexanol, substituted or unsubstituted
cycloheptanol, cyclopentyl substituted alcohol, cyclohexyl
substituted alcohol, cycloheptyl substituted alcohol, and
citronellol, and the one or more aromatic alcohols include one or
more of benzyl alcohol, phenylethyl alcohol, isopropylbenzyl
alcohol, and phenylpropyl alcohol.
9. The method of claim 1, wherein the processing solution further
comprises an aliphatic hydrocarbon in an amount of from about 10 to
about 50 weight % of one or more hydrocarbon paraffins,
isoparaffins, naphthenic hydrocarbons, petroleum distillates,
de-aromatized petroleum distillates, terpene hydrocarbons, mixed
aromatic solvents, and halogenated hydrocarbon solvents.
10. The method of claim 9, wherein the processing solution further
comprises an aliphatic hydrocarbon that is one or more of
de-aromatized petroleum distillates, hydrocarbon paraffins and
iso-paraffins.
11. The method of claim 1, wherein the processing solution further
comprises one or more esters of monobasic carboxylic acids
represented by the following Structure (III):
Ar.sub.1--C(.dbd.O)O--R.sub.2 (III) wherein R.sub.2 is a saturated
hydrocarbon group having 1 to 10 carbon atoms and Ar.sub.1 is a
substituted or unsubstituted phenyl or naphthyl group.
12. The method of claim 11 wherein Ar.sub.1 in Structure (III) is a
substituted or unsubstituted phenyl group, and R.sub.2 is an alkyl
group having 1 to 3 carbon atoms or a cycloalkyl having 5 to 10
carbon atoms in the carbocyclic ring.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Divisional of application U.S. Ser. No. 12/695,190
filed Jan. 28, 2010 entitled "Flexographic Processing Solution and
Use", by Elsie A. Fohrenkamm, et al.
FIELD OF THE INVENTION
[0002] This invention relates to organic solutions that can be used
to "develop" or process imaged flexographic printing plates that
are formed by crosslinking a photosensitive relief-forming layer.
This invention also relates to a method of providing flexographic
printing plates using these organic solutions.
BACKGROUND OF THE INVENTION
[0003] The production of photopolymer relief images for
flexographic printing is generally carried out by imagewise
exposing the photosensitive layer of a flexographic printing plate
precursor using suitable imaging radiation such as UV radiation.
Unexposed areas of the photosensitive layer are washed off
(developed or "washed out") using a suitable developer or
processing solution while exposed, crosslinked areas are left
intact. Residual developer is generally removed by evaporation and
if necessary, the developed surface is treated to remove tackiness.
The flexographic printing plate is usually wrapped around a
cylinder on a printing press and used to transfer ink to a suitable
substrate such as papers, films, fabrics, ceramics, and other
materials.
[0004] While the non-exposed photopolymer may be soluble in a
variety of organic solutions, only some of those solutions are the
best developers that do not damage or swell the crosslinked
portions while cleanly removing the non-crosslinked portions.
Swelling will eventually cause the relief image to deteriorate in
the processing bath and the processing solution will have to be
changed frequently due to the build-up of sludge.
[0005] Suitable developers have generally comprised organic
solvents such as saturated hydrocarbons, aromatic hydrocarbons,
aliphatic ketones, terpenes, and chlorinated hydrocarbons such as
trichloroethylene, or mixtures of such solvents that may also
include lower molecular weight alcohols depending upon the polymer
binders used in the photosensitive layer.
[0006] Developers have been carefully formulated as mixtures of
organic solvents to overcome various problems such as acting too
slowly so that plate swelling occurs, solvent toxicity, safety
concerns, long drying times, and ineffective removal from the
developed printing plate. For example, U.S. Pat. No. 5,354,645
(Schober et al.) describes developers for flexographic printing
relief images that include one or more of diethylene glycol dialkyl
ethers, acetic acid esters or alcohols, carboxylic acid esters, and
esters of alkoxy substituted carboxylic acids.
[0007] The development or washout of imaged photopolymerizable
flexographic printing plate precursors is also described, for
example, in U.S. Pat. Nos. 6,162,593 (Wyatt et al) and 5,248,502
(Eklund) and U.S. Patent Application Publication 2005/0227182 (Ali
et al.), and the references cited in therein. Representative
processing solutions (developers) are also described in U.S. Pat.
No. 6,248,502 (Eklund). The photopolymer compositions used in the
flexographic printing plate precursors are generally carefully
matched to the desired processing solutions.
[0008] For example, U.S. Pat. No. 6,582,886 (Hendrickson et al.)
cites a number of publications that describe various "matched"
photosensitive layers and developers. This patent specifically
describes developers containing methyl esters alone or mixtures of
methyl esters and co-solvents such as various alcohols that are
soluble in the methyl ester(s). These developers can also include
various non-solvents such as petroleum distillates naphthas,
paraffinic solvents, and mineral oils.
[0009] Other known processing solutions include chlorohydrocarbons,
saturated cyclic or acyclic hydrocarbons, aromatic hydrocarbons,
lower aliphatic ketones, or terpene hydrocarbons. While these
processing solutions are effective for the intended purpose, they
have a number of disadvantages. They may act too slowly, causing
swelling in the printing plates and thus damage the fine detail in
the relief images, require long drying times, and have low
flashpoints resulting in dangerous situations. Many of these
solvents are also considered hazardous air pollutants (HAPS) and
are subject to stringent governmental reporting requirements. They
may also be too toxic for direct disposal into the environment or
create worker safety problems with strong odors or handling
problems.
[0010] Copending and commonly assigned U.S. Ser. No. 12/545,268
filed Aug. 21, 2009 by Bradford and based on Provisional
Application 61/097,358 (filed Sep. 19, 2008 by Bradford) describes
flexographic printing plate washout or processing solutions
containing dipropylene glycol dimethyl ether (DME) alone or in
combination with various co-solvents such as alcohols and aliphatic
dibasic acid ethers.
[0011] U.S. Pat. No. 6,162,593 (noted above) describes the use of
diisopropylbenzene (DIPB) alone or with alcohol co-solvents in
processing solutions.
[0012] Whether the processing solutions are reclaimed or not, there
is a need for more environmentally friendly developing solutions
that offer improvements in handling, disposal, low odor, and low
levels of volatility (lower level of "volatile organic chemicals",
or "VOC" content) while still providing the effective cleanout (or
washout) of non-polymerized material in an imaged flexographic
printing plate precursor. It is also desirable that the processing
solution be useful for a variety of photopolymer compositions so
that the processing solution is versatile for multiple uses.
[0013] While many of the known developers are effective for
removing non-crosslinked materials in the imaged flexographic
printing plate precursor, the developers are not necessarily
environmentally friendly or free of health hazards (toxicity).
Thus, there continues to be a need to provide improved flexographic
printing plate developers that are non-hazardous, non-flammable,
and environmentally friendly especially to aquatic life, and have
low odor and a reduced level of VOC.
SUMMARY OF THE INVENTION
[0014] This invention provides a processing solution useful for
providing flexographic relief images, comprising:
[0015] a. one or more esters of monobasic carboxylic acids
represented by one or both of the following Structures (I) and
(II):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
wherein R.sub.1 is an alkyl group having 1 to 5 carbon atoms,
Ar.sub.1 is a substituted or unsubstituted phenyl or naphthyl
group, and n is 1 to 3, and
H--C(.dbd.O)OR (II)
wherein R is a hydrocarbon having 6 to 15 carbon atoms, and
[0016] b. one or more aliphatic alcohols, or a combination of one
or more aliphatic alcohols and one or more aromatic alcohols.
[0017] Some embodiments of this invention include a processing
solution useful for providing flexographic relief images,
comprising:
[0018] a. one or more esters of monobasic carboxylic acids
represented by the following Structure (I):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
wherein R.sub.1 is an alkyl group having 1 to 5 carbon atoms,
Ar.sub.1 is a substituted or unsubstituted phenyl or naphthyl
group, and n is 1 to 3, and
[0019] b. one or more aliphatic alcohols, or a combination of one
or more aliphatic alcohols and one or more aromatic alcohols.
[0020] More specific flexographic developers of this invention
consisting essentially of:
[0021] a. from about 5 to about 70 weight % of benzyl acetate or
propionate,
[0022] b. from about 5 to about 40 weight % of 2-ethylhexyl
alcohol, octyl alcohol, or benzyl alcohol, and
[0023] c. from about 5 to about 50 weight % of a petroleum
distillate.
[0024] This invention also provides a method of providing a
flexographic printing plate with a relief image comprising
[0025] developing an imaged flexographic printing plate precursor
comprising an imageable photopolymer layer with the processing
solution of this invention to remove non-imaged photopolymer.
[0026] More specifically, a method for providing a flexographic
printing plate comprises:
[0027] A) imagewise exposing a flexographic printing plate
precursor to provide exposed and non-exposed regions,
[0028] B) removing the non-exposed regions with the processing
solution of this invention to provide a relief image in a
flexographic printing plate, and
[0029] C) optionally, drying the processed flexographic printing
plate.
[0030] The present invention provides improved developers
(processing solutions) for imaged flexographic printing plate
precursors, which developers are more environmentally friendly,
less toxic or hazardous to users, and non-flammable, and have
reduced VOC and odor. These features are achieved using the unique
combination of specific solvents described herein.
DETAILED DESCRIPTION OF THE INVENTION
[0031] "VOC" refers to "volatile organic chemicals".
[0032] Unless otherwise indicated, the terms "processing solution",
"developer", "washout solution" all refer to the compositions of
this invention.
[0033] In addition, all percentages of processing solutions, unless
otherwise noted, represent weight %.
[0034] The processing solution of this invention includes one or
more esters of monobasic carboxylic acids. The esters of monobasic
carboxylic acids used in the present invention generally have low
vapor pressure. For example, both benzyl acetate and benzyl
propionate have a vapor pressure of less than 0.1 mm Hg at ambient
temperature (20.degree. C.), which is desirable to reduce exposure
of vapors around printing plate processing units. Unlike these
solvents, the esters solvents known in the prior art, such as
2-ethylhexyl acetate as disclosed in U.S. Pat. No. 5,534,645, has a
vapor pressure of 0.4 mm Hg. The esters used in the practice of the
present invention do not have any objectionable odor. Usually, only
one of these compounds is present.
[0035] The esters of monobasic carboxylic acids can be defined by
either or both of Structures (I) and (II):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
H--C(.dbd.O)OR (II).
[0036] The compounds represented by Structure (I) are particularly
useful.
[0037] R.sub.1 is a substituted or unsubstituted alkyl group having
1 to 5 carbon atoms (such as methyl, ethyl, n-propyl, iso-propyl,
iso-butyl, t-butyl, and n-pentyl). Ar.sub.1 is a substituted or
unsubstituted phenyl or naphthyl group, and n is 1 to 4. R is a
substituted or unsubstituted hydrocarbon (such as a substituted or
unsubstituted alkyl or cycloalkyl group) having 6 to 15 carbon
atoms. For example, R.sub.1 can be an alkyl having 1 to 3 carbon
atoms, n is 1 or 2, and R is benzyl or citronellyl.
[0038] Examples of useful esters of monobasic carboxylic acids
include one of the more of benzyl acetate, 2-phenylethyl acetate,
2-phenylethyl phenyl acetate, 2-phenylethyl isobutyrate, isobutyl
phenyl acetate, benzyl propionate, benzyl butyrate, benzyl
pentanoate, benzyl formate, and citronellyl formate.
[0039] The one or more esters of monobasic carboxylic acids are
present in the processing solution in an amount of at least 5 and
up to and including 70 weight %, or from about 20 to about 60
weight %.
[0040] The useful esters of monobasic carboxylic acids can be
obtained from a number of commercial sources.
[0041] Optionally, the processing solution can include one or more
esters of monobasic carboxylic acids represented by the following
Structure (III):
Ar.sub.1--C(.dbd.O)O--R.sub.2 (III)
wherein R.sub.2 is a substituted or unsubstituted saturated
hydrocarbon group having 1 to 10 carbon atoms and Ar.sub.1 is a
substituted or unsubstituted phenyl or naphthyl group. Ar.sub.1 is
particularly a substituted or unsubstituted phenyl group, and
R.sub.2 is an alkyl group having 1 to 3 carbon atoms.
Representative compounds defined by Structure (III) include but are
not limited to, methyl benzoate or ethyl benzoate, or both. When
such compounds are present, the amount is from about 5 to about 30
weight %.
[0042] In addition, the processing solution includes one or more
aliphatic alcohols, or a combination of one or more aliphatic
alcohols and one or more aromatic alcohols. The total amount of
both types of alcohols is at least 5 and up to and including 40
weight %, or particularly from about 10 to about 30 weight %. These
alcohols are generally available from various commercial
sources.
[0043] Useful aliphatic alcohols include but are not limited to,
n-butanol, 2-ethoxyethanol, a hexyl alcohol, a heptyl alcohol, an
octyl alcohol, a nonyl alcohol, a decyl alcohol, alpha-terpineol,
dipropylene glycol methyl ether, 2-butoxyethanol, isopropyl
alcohol, and 2-(2-butoxyethoxy)ethanol, substituted or
unsubstituted cyclopentanol, substituted or unsubstituted
cyclohexanol, substituted or unsubstituted cycloheptanol,
cyclopentyl substituted alcohol, cyclohexyl substituted alcohol,
and cycloheptyl substituted alcohol.
[0044] Useful aromatic alcohols include but are not limited to,
benzyl alcohol, 2-phenylethyl alcohol, and isopropylbenzyl
alcohol.
[0045] Three particularly useful alcohol co-solvents include
2-ethylhexyl alcohol, benzyl alcohol, n-octyl alcohol, and mixtures
thereof.
[0046] The processing solution can also include one or more
aliphatic hydrocarbons in an amount of up to 50 weight %. Useful
compounds of this type include but are not limited to, hydrocarbon
paraffins, isoparaffins, naphthenic hydrocarbons, petroleum
distillates, terpene hydrocarbons, mixed aromatic solvents, or
halogenated hydrocarbon solvents. An advantage of the present
invention is that substituted or unsubstituted aromatic
hydrocarbons, which are usually found to be marine pollutants, and
are not generally needed for effective development of many
photopolymer-containing flexographic printing plate precursors.
[0047] After its use to develop imaged flexographic printing plate
precursors, the processing solution of this invention can be
reclaimed in a suitable fashion or disposed of in an
environmentally proper manner.
[0048] Some useful flexographic printing plate precursors are
described in numerous publications including but not limited to,
U.S. Patent Application Publication 2005/0227182 (noted above) and
U.S. Pat. No. 7,226,709 (Kidnie et al.) and U.S. Pat. No. 7,326,353
(Hendrickson et al.), all of which are incorporated herein by
reference.
[0049] For example, the precursors are generally composed of a
photopolymerizable elastomer or elastomeric layer composition
disposed on a suitable support. By the term "photopolymerizable",
we mean that the composition is polymerizable or crosslinkable
using suitable radiation, or both polymerizable and crosslinkable.
The elastomeric layer composition generally includes a
thermoplastic binder, at least one monomer and an initiator
(photoinitiator) that is sensitive to suitable radiation such as
actinic radiation (for example, UV radiation). Various polymeric
binders are known in the art as described in the publications noted
in the preceding paragraph. Poly(styrene/isoprene/styrene) and
poly(styrene/butadiene/styrene) block copolymers are useful, as
well as various synthetic or natural polymers of conjugated
hydrocarbons, including polyisoprene, 1,2-polybutadiene, and
butadiene/acrylonitrile.
[0050] The "monomer" is generally considered a compound that is
compatible with the polymeric binder and is capable of addition
polymerization in response to irradiation with actinic radiation.
There can be a mixture of monomers if desired. They typically have
a molecular weight less than 5000 although compounds with higher
molecular weight can be used if desired. Useful monomers include
various acrylates, methacrylates, mono- and polyesters of alcohols
and polyols such as polyacrylates and polymethacrylates.
Photoinitiators can include but are not limited to, compounds that
generate free radicals upon exposure to actinic radiation such as
quinones, benzophenones, benzoin ethers, aryl ketones, peroxides,
biimidazoles, benzyl dimethyl ketal, and others known in the
art.
[0051] The elastomeric layer composition can also include various
additives such as colorants, processing aids, antioxidants, and
antiozonants as are known in the art.
[0052] Additionally, a protective cover sheet can be placed over
the photosensitive elastomeric composition layer, which cover sheet
contains a protective polymer that is soluble or dispersible in the
solvent(s) that is capable of dissolving or dispersing the uncured
photosensitive elastomeric composition. Generally, the protective
layer is transparent and has little tackiness before irradiation.
It can be washed away or removed using the processing solutions
described herein. Examples of polymers suitable for preparing this
cover sheet include but are not limited to, polyamides and
cellulose esters such as cellulose acetate butyrate and cellulose
acetate propionate (for example, see U.S. Pat. No. 6,030,749 of
Takahashi et al., Cols. 4-8).
[0053] The flexographic printing plate precursors that can be
processed according to this invention in general comprise a
photopolymerizable elastomeric layer comprising an elastomeric
binder, a photoinitiator, at least one compound that is free
radical crosslinkable with actinic radiation (such as a monomer),
and optionally a plasticizer.
[0054] Such flexographic printing plate precursors can be imaged by
exposure to curing radiation through a suitable mask image to form
an imaged element. In this step, the curing radiation is projected
onto the photosensitive composition through the mask image that
blocks some of the radiation. The exposed regions are hardened or
cured. Exposure through the mask image can be accomplished by
floodwise exposure from suitable irradiation sources (visible or UV
radiation). For example, curing radiation may be at a radiation at
a wavelength of from about 340 to about 400 nm from a suitable
irradiation source. The time for exposure through the mask image
will depend upon the nature and thickness of the flexographic
printing plate precursor and the source of the radiation. For
example, useful commercial flexographic printing plate precursors
such as Eastman Kodak's FLEXCEL brand precursors and DuPont's
Cyrel.RTM. brand precursors can be imaged on commercial apparatus
such as a Mekrom processor, model 302 EDLF.
[0055] The processing solution can be applied to an imaged
flexographic printing plate precursor in any suitable manner
including but not limited to spraying, brushing, rolling, dipping
(immersing), or any combination thereof. This removes uncured or
non-polymerized regions of the photopolymerizable composition.
Development or processing is usually carried out under conventional
conditions such as for from about 5 to about 20 minutes and at from
about 23 to about 32.degree. C. The specific development conditions
will be dictated by the type of apparatus used and the specific
processing solution.
[0056] Post-developing processing of the relief image may be
suitable under some circumstances. Typical post-development
processing includes drying the relief image to remove any excess
processing solution and post-curing by exposing the relief image to
curing radiation to cause further hardening or crosslinking. The
conditions for these processes are well known to those skilled in
the art. For example, the relief image may be blotted or wiped dry
or dried in a forced air or infrared oven. Drying times and
temperatures would be readily apparent to one skilled in the
art.
[0057] Detackification can be carried out if the flexographic
printing plate is still tacky after drying. Such treatments, for
example, by treatment with bromide or chlorine solutions or
exposure to UV or visible radiation, are well known to a skilled
artisan.
[0058] The resulting relief image may have a depth of from about 2%
to about 100% (typically from about 10 to about 80%) of the
original thickness of the radiation-sensitive composition in the
flexographic printing plate precursor. For example, if the
radiation-sensitive composition is disposed on a non-photosensitive
support, up to 100% of the radiation-sensitive composition can be
removed in the relief image. The relief image depth may be from
about 150 to about 2000 .mu.m.
[0059] The flexographic printing plates can be used to advantage in
the formation of seamless, continuous flexographic printing
elements, or they can be formed as flat sheets that can be wrapped
around a cylinder form, for example as a printing sleeve or the
printing cylinder itself. Alternatively, the radiation-sensitive
composition can be mounted around a cylindrical form for imaging
and development.
[0060] The present invention provides at least the following
embodiments and combinations thereof:
[0061] 1. A processing solution useful for providing flexographic
relief images, comprising:
[0062] a. one or more esters of monobasic carboxylic acids
represented by one or both of the following Structures (I) and
(II):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
wherein R.sub.1 is an alkyl group having 1 to 5 carbon atoms,
Ar.sub.1 is a substituted or unsubstituted phenyl or naphthyl
group, and n is 1 to 3, and
H--C(.dbd.O)OR (II)
wherein R is a hydrocarbon having 6 to 15 carbon atoms, and
[0063] b. one or more aliphatic alcohols, or a combination of one
or more aliphatic alcohols and one or more aromatic alcohols.
[0064] 2. The solution of embodiment 1 wherein the one or more
esters of monobasic carboxylic acids are present in an amount of at
least 5 and up to and including 70 weight %, and the one or more
aliphatic alcohols, or combination of one or more aliphatic
alcohols and one or more aromatic alcohols, are present in an
amount of at least 5 and up to and including 40 weight %.
[0065] 3. The solution of embodiment 1 or 2 wherein the one or more
esters of monobasic carboxylic acids are present in an amount of
from about 20 to about 60 weight %, and the one or more aliphatic
alcohols, or combination of one or more aliphatic alcohols and one
or more aromatic alcohols, are present in an amount of from about
10 to about 30 weight %.
[0066] 4. The solution of any of embodiments 1 to 3 wherein R.sub.1
is an alkyl having 1 to 3 carbon atoms, n is 1 or 2, and R is
benzyl or citronellyl.
[0067] 5. The solution of any of embodiments 1 to 4 wherein the one
or more esters of monobasic carboxylic acids includes one of the
more of benzyl acetate, 2-phenylethyl acetate, 2-phenylethyl phenyl
acetate, 2-phenylethyl isobutyrate, isobutyl phenyl acetate, benzyl
propionate, benzyl butyrate, benzyl pentanoate, benzyl formate, and
citronellyl formate.
[0068] 6. The solution of any of embodiments 1 to 5 wherein one or
more aliphatic alcohols includes one or more of n-butanol,
2-ethoxyethanol, a hexyl alcohol, a heptyl alcohol, an octyl
alcohol, a nonyl alcohol, a decyl alcohol, alpha-terpineol,
dipropylene glycol methyl ether, 2-butoxyethanol, isopropyl
alcohol, and 2-(2-butoxyethoxy)ethanol, substituted or
unsubstituted cyclopentanol, substituted or unsubstituted
cyclohexanol, substituted or unsubstituted cycloheptanol,
cyclopentyl substituted alcohol, cyclohexyl substituted alcohol,
cycloheptyl substituted alcohol, and citronellol,
[0069] the one or more aromatic alcohols include one or more of
benzyl alcohol, phenylethyl alcohol, isopropylbenzyl alcohol, and
phenylpropyl alcohol.
[0070] 7. The solution of any of embodiments 1 to 6 further
comprising an aliphatic hydrocarbon in an amount of from about 10
to about 50 weight % of one or more hydrocarbon paraffins,
isoparaffins, naphthenic hydrocarbons, petroleum distillates,
de-aromatized petroleum distillates, terpene hydrocarbons, mixed
aromatic solvents, and halogenated hydrocarbon solvents.
[0071] 8. The solution of embodiment 7 wherein the aliphatic
hydrocarbon is one or more of de-aromatized petroleum distillates,
hydrocarbon paraffins and iso-paraffins.
[0072] 9. The solution of any of embodiments 1 to 8 further
comprising one or more esters of monobasic carboxylic acids
represented by the following Structure (III):
Ar.sub.1--C(.dbd.O)O--R.sub.2 (III)
wherein R.sub.2 is a saturated hydrocarbon group having 1 to 10
carbon atoms and Ar.sub.1 is a substituted or unsubstituted phenyl
or naphthyl group.
[0073] 10. The solution of embodiment 9 wherein Ar.sub.1 in
Structure (III) is a substituted or unsubstituted phenyl group, and
R.sub.2 is an alkyl group having 1 to 3 carbon atoms or a
cycloalkyl having 5 to 10 carbon atoms in the carbocyclic ring.
[0074] 11. A processing solution useful for providing flexographic
relief images, comprising:
[0075] a. one or more esters of monobasic carboxylic acids
represented by the following Structure (I):
R.sub.1--C(.dbd.O)O--(CH.sub.2).sub.n--Ar.sub.1 (I)
wherein R.sub.1 is an alkyl group having 1 to 5 carbon atoms,
Ar.sub.1 is a substituted or unsubstituted phenyl or naphthyl
group, and n is 1 to 3, and
[0076] b. one or more aliphatic alcohols, or a combination of one
or more aliphatic alcohols and one or more aromatic alcohols.
[0077] 12. The solution of embodiment 11 wherein the one or more
esters of monobasic carboxylic acids includes one of the more of
benzyl acetate, 2-phenylethyl acetate, 2-phenylethyl phenyl
acetate, 2-phenylethyl isobutyrate, isobutyl phenyl acetate, benzyl
propionate, benzyl butyrate, benzyl pentanoate, benzyl formate, and
citronellyl formate,
[0078] the one or more aliphatic alcohols includes one or more of
n-butanol, 2-ethoxyethanol, a hexyl alcohol, a heptyl alcohol, an
octyl alcohol, a nonyl alcohol, a decyl alcohol, alpha-terpineol,
dipropylene glycol methyl ether, 2-butoxyethanol, isopropyl
alcohol, and 2-(2-butoxyethoxy)ethanol, substituted or
unsubstituted cyclopentanol, substituted or unsubstituted
cyclohexanol, substituted or unsubstituted cycloheptanol,
cyclopentyl substituted alcohol, cyclohexyl substituted alcohol,
cycloheptyl substituted alcohol, and citronellol, and
[0079] the one or more aromatic alcohols include one or more of
benzyl alcohol, phenylethyl alcohol, isopropylbenzyl alcohol, and
phenylpropyl alcohol.
[0080] 13. A flexographic developer consisting essentially of:
[0081] a. from about 5 to about 70 weight % of benzyl acetate or
propionate,
[0082] b. from about 5 to about 40 weight % of 2-ethylhexyl
alcohol, octyl alcohol, or benzyl alcohol, and
[0083] c. from about 5 to about 50 weight % of a petroleum
distillate.
[0084] 14. A method of providing a flexographic printing plate with
a relief image comprising
[0085] developing an imaged flexographic printing plate precursor
comprising an imageable photopolymer layer with the processing
solution of any of embodiments 1 to 13 to remove non-imaged
photopolymer.
[0086] 15. A method for providing a flexographic printing plate
comprising:
[0087] A) imagewise exposing a flexographic printing plate
precursor to provide exposed and non-exposed regions,
[0088] B) removing the non-exposed regions with the processing
solution of any of embodiments 1 to 13 to provide a relief image in
a flexographic printing plate, and
[0089] C) optionally, drying the processed flexographic printing
plate.
[0090] 16. The method of embodiment 14 or 15 wherein the
flexographic printing plate precursor comprises a
photopolymerizable elastomeric layer comprising an elastomeric
binder, a photoinitiator, at least one monomer, and optionally a
plasticizer, and the precursor is imagewise exposed using actinic
radiation.
[0091] The following Examples are provided to illustrate the
practice of this invention but not to limit it in any manner.
Invention Examples 1-4 and Comparative Examples 1-4
[0092] Several flexographic plate developer solutions of this
invention were prepared and compared to several developer solutions
of the prior art, as shown below in TABLE I. To judge the
effectiveness of the developer solutions to remove the
un-crosslinked polymers in the imaged flexographic printing plate
precursors, the following procedure was followed:
[0093] A fixed amount (20 g) of each developer solution was placed
in a jar. Each solution contained 50 weight % of an ester solvent,
20 weight % of an aliphatic hydrocarbon (Marathon 142 Solvent, from
Marathon), and 30 weight % of an aliphatic alcohol (Exxal 8
isooctyl alcohol, obtained from Exxon Mobil). A flexographic
printing plate precursor (Flexcel.RTM. SRH, 1.70 mm, from Eastman
Kodak Company) was cut into small pieces (3''.times.5/8'', or
7.6.times.1.6 cm), the cover sheet was removed, and then the
flexographic printing plate precursor sample was precisely weighed
in an analytical balance. Each sample was then placed inside a jar
containing a developing solution and the jar lid was closed. The
bottle was then shaken for an hour in a mechanical shaker. Each
sample was then carefully removed by tweezers and was then was
placed on a cardboard with the polyethylene terephthalate) support
side down. The wet imaged printing plate was then placed in an oven
set at 66.degree. C. and dried for one hour. The dried printing
plates were brought to room temperature and weighed again on the
analytical balance. The difference in the weight of the printing
plate after development and before development was indicative of
the efficiency of the developer solution. Thus, a larger weight
loss indicates more efficient removal of the un-crosslinked polymer
by the developer solution. For Comparative Examples 2 and 3,
solvent mixtures were prepared using ethyl nonanoate (nonanoic acid
ethyl ester) and ethyl octanoate (octanoic acid ethyl ester), as
described in U.S. Pat. No. 5,354,645 (noted above). A commercially
available developer solution that is known to contain nonyl acetate
and benzyl alcohol (Optisol.RTM. Rotary from DuPont) as described
in U.S. Pat. No. 5,354,645, was also tested as a Comparative
example.
[0094] It is clearly evident from these data in TABLE I that the
developer solutions of the present invention are very efficient in
removing the un-crosslinked photopolymer from the imaged
flexographic printing plate precursors. Invention Example 4 shows
that a combination of an aliphatic alcohol and an aromatic alcohol
further enhances the efficiency of the removal of un-crosslinked
polymer. Comparative Example 1 performed well but had an
objectionable odor.
TABLE-US-00001 TABLE I Composition Initial Weight Final Weight
Weight % Un-crosslinked Example (% by weight) of plate (g) of plate
(g) loss (g) polymer removed Invention 1 Benzyl acetate: 50% 2.1171
1.0388 1.0783 50.93% Marathon 142 Solvent: 20% Exxal 8: 30%
Invention 2 Benzyl Formate: 50% 2.1394 1.0948 1.0446 48.83%
Marathon 142 Solvent: 20% Exxal 8: 30% Invention 3 Benzyl
Propionate: 50% 2.2170 1.1192 1.0978 49.5% Marathon 142 Solvent:
20% Exxal 8: 30% Comparative 1 Methyl Benzoate: 50% 2.1299 1.0522
1.0777 50.60% Marathon 142 Solvent: 20% Exxal 8: 30% Comparative 2
Ethyl Nonanoate: 50% 2.1404 1.8991 .2413 11.27% Marathon 142
Solvent: 20% Exxal 8: 30% Comparative 3 Ethyl Octanoate: 50% 2.1770
1.7764 .4006 18.40% Marathon 142 Solvent: 20% Exxal 8: 30%
Comparative 4 Optisol .RTM. Rotary solution 2.2014 1.5508 .6505
29.55% Invention 4 Benzyl Acetate: 40% 2.1327 .8130 1.3227 61.93%
Marathon 142 Solvent: 40% Exxal 8: 10% Benzyl Alcohol: 10%
Invention Examples 5-6 and Comparative Example 5
[0095] Two embodiments of the present invention were compared to
the use of the commercially available Optisol.RTM. Rotary (Dupont)
as Comparative Example 5, to prepare flexographic printing plates
in a commercially available Kelleigh 310 processing unit.
[0096] An unexposed commercially available 0.067 inch (0.17 cm)
thick photopolymer flexographic printing plate precursor (Kodak
Flexcel.RTM. SRH) was cut into sample strips measuring 2
inch.times.12 inch (5.1 cm.times.30.5 cm) and the sample strips
were clamped 8 abreast along the width of the Kelleigh processing
drum. The brush pressure in the processor was adjusted to a setting
of 3.5 and the processing was started. Beginning at 8 minutes of
processing, the printing plate samples were removed one every 2
minutes. Each sample strip was blotted dry with a non-lint plate
wipe fabric and placed in the Kelleigh drying section set to
60.degree. C. After drying for 2 hours, the plates were removed
from the drying section. The dried printing plate samples were then
finished for 10 minutes exposure to UVC light and 3 minutes
exposure to UVA light. Measurements were made with an Ono-Sokki
model EG-225 digital caliper by comparing the unexposed washed out
area of each sample to the original sample caliper (0.067 inch,
0.17 cm). The difference between the unexposed washed out plate
sample and the original plate sample caliper was recorded as the
relief image depth. The relief image depth was plotted verses
processing times for each processing solution that was tested. The
point where processing time intersects a 0.040 inch (0.10 cm)
relief image depth is listed in TABLE II as "Wash-out Time."
[0097] A commercially available 0.067 inch (0.17 cm) thick
photopolymer flexographic printing plate precursor (Kodak
Flexcel.RTM. SRH) was first back exposed by a UV light source for
40 seconds with a commercially available Kelleigh model 310
exposure/processor/drier/finisher unit. The top of the printing
plate precursor was then exposed to UV light for 15 minutes through
a negative film (mask) made from commercially available Kodak
Flexcel.RTM. NX thermal imaging layer. The images on the mask
contained multiple repeating sections, small halftone dots of
various line rulings as well as fine line and text images to
determine image quality. The mask also contained D.sub.min areas to
generate fully crosslinked patches on the precursor for caliper
measurements to determine drying time. The mask was removed from
the printing plate precursor that was then processed in the
Kelleigh model 310 processor for a predetermined length of time
based on the processing time test. After processing, the printing
plates were blotted dry using a non-lint plate wipe fabric and
placed in the drying section of the Kelleigh processor. Caliper
measurements of the printing plates in the fully exposed area were
made at 10 minute intervals using an Ono-Sokki model EG-225 digital
caliper. "Dry Times" listed in TABLE II were determined when the
printing plates reached a steady state where no thickness decrease
was measurable.
[0098] The dried printing plates were then finished by 10 minutes
exposure to UVC light and 3 minutes exposure to UVA light using the
Kelleigh model 310 processor. The plates were then examined under a
60X stereo microscope to determine image quality by examining the
areas of small dots and looking for misshapen or missing dots. The
fine line rulings and text areas were examined for shoulder angle
and structure. The results of the microscopic examination are
listed as "Image Quality" in TABLE II.
TABLE-US-00002 TABLE II Processing Drying Processing Time Time
Image Example Solution (min.) (min) Quality Comparative 5 DuPont
Rotary 20.0 90 Excellent Optisol .RTM. Invention 5 Marathon 142
11.5 120 Excellent solvent: 50% Benzyl Acetate: 30% Benzyl Alcohol:
10% Exxal 8, 10% Invention 6 Marathon 142 10 120 Excellent solvent:
50% Benzyl Acetate: 30% Benzyl Alcohol: 5% Exxal 8: 15%
[0099] It is evident from the data in TABLE II that the processing
solutions of this invention containing the noted ester solvents
washed out the un-crosslinked photopolymer more efficiently than
the prior art processing solution, and are capable of producing
high image quality flexographic printing plates required for
commercial applications. Although the drying time was a little
longer than for the Comparative Example 5 processing solution, the
drying time was a commercially acceptable time.
[0100] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *