U.S. patent application number 13/372060 was filed with the patent office on 2013-08-15 for integrated membrane lamination and uv exposure system and method of using the same.
The applicant listed for this patent is Kyle P. BALDWIN, Timothy GOTSICK, David A. RECCHIA. Invention is credited to Kyle P. BALDWIN, Timothy GOTSICK, David A. RECCHIA.
Application Number | 20130209939 13/372060 |
Document ID | / |
Family ID | 48945837 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130209939 |
Kind Code |
A1 |
RECCHIA; David A. ; et
al. |
August 15, 2013 |
Integrated Membrane Lamination and UV Exposure System and Method of
Using the Same
Abstract
A combined laminating and exposing apparatus for exposing a
photosensitive printing blank to actinic radiation in a printing
plate manufacturing system and a method of using the same are
disclosed. The photosensitive printing blank comprises a backing
layer, at least one photocurable layer disposed on the backing
layer, and a laser ablatable mask layer disposed on the at least
one photocurable layer, wherein the laser ablatable mask layer is
laser ablated to create an in situ negative in the laser ablatable
mask layer. The exposing apparatus comprises: (a) a laminating
apparatus for laminating an oxygen barrier layer to a top of the
laser ablated mask layer; (b) a conveyor; (c) a first exposing
device for imagewise exposing the at least one photocurable layer
to actinic radiation, and (d) a second exposing device for exposing
the at least one photocurable layer to actinic radiation through
the backing layer.
Inventors: |
RECCHIA; David A.; (Smyrna,
GA) ; BALDWIN; Kyle P.; (Acworth, GA) ;
GOTSICK; Timothy; (Acworth, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RECCHIA; David A.
BALDWIN; Kyle P.
GOTSICK; Timothy |
Smyrna
Acworth
Acworth |
GA
GA
GA |
US
US
US |
|
|
Family ID: |
48945837 |
Appl. No.: |
13/372060 |
Filed: |
February 13, 2012 |
Current U.S.
Class: |
430/296 ; 355/53;
430/306; 430/309 |
Current CPC
Class: |
G03F 7/202 20130101;
G03F 7/092 20130101; G03F 7/2035 20130101; G03F 7/2032
20130101 |
Class at
Publication: |
430/296 ; 355/53;
430/309; 430/306 |
International
Class: |
G03F 7/20 20060101
G03F007/20; G03B 27/42 20060101 G03B027/42 |
Claims
1. A method of exposing a photosensitive printing blank to actinic
radiation in a printing plate manufacturing process, wherein the
photosensitive printing blank comprises a backing layer, at least
one photocurable layer disposed on the backing layer, and a laser
ablatable mask layer disposed on the at least one photocurable
layer, wherein the laser ablatable mask layer is laser ablated to
create an in situ negative in the laser ablatable mask layer, the
method comprising the steps of: a) laminating an oxygen barrier
layer to a top of the laser ablated mask layer using heat and
pressure; b) conveying the photosensitive printing blank into an
exposing unit, wherein said exposing unit is capable of
crosslinking and curing portions of the at least one photocurable
layer not covered by the laser ablated mask layer and creating a
crosslinked floor layer in the at least one photocurable layer; and
c) at least substantially simultaneously (i) exposing the at least
one photocurable layer to actinic radiation from a first source of
actinic radiation through the laser ablated mask layer and the
oxygen barrier layer to selectively crosslink and cure portions of
the at least one photocurable layer not covered by the mask layer,
and (ii) exposing the at least one photocurable layer to actinic
radiation from a second source of actinic radiation through the
backing layer to create a crosslinked floor layer in the
photocurable layer.
2. The method according to claim 1, wherein the step of laminating
the oxygen barrier layer to the top of the laser ablated mask layer
comprises the steps of: a. supplying the photosensitive printing
blank to a nip formed between a heated laminating roller and a
second roller; b. supplying the oxygen barrier layer from a supply
roller over an outer surface of the heated laminating roller and
into the nip formed between the heated laminating roller and the
second roller; wherein the oxygen barrier layer contacts a top
surface of the photosensitive printing blank at a point where the
photosensitive printing blank advances through the nip; c. rotating
the heated laminating roller in a first direction and the second
roller in an opposite direction to advance the photosensitive
printing blank with the oxygen bather layer thereon through the
nip, thereby laminating the oxygen barrier film to the top of the
laser ablated mask layer.
3. The method according to claim 1, wherein after the oxygen
barrier layer is laminated to the top of the laser ablatable mask
layer and the photosensitive printing blank has been exposed to
actinic radiation, the method further comprises the step of
removing the oxygen barrier layer.
4. The method according to claim 3, further comprising the step of
developing the imaged and exposed photosensitive printing blank to
reveal a relief image therein, said relief image comprising a
plurality of relief dots; wherein the presence of the oxygen
barrier layer produces printing dots having at least one geometric
characteristic selected from the group consisting of planarity of a
top surface of the printing dots, shoulder angle of the printing
dots and edge sharpness of the printing dots, beneficially changed
in relation to dots formed without the use of the oxygen barrier
film.
5. The method according to claim 1, wherein the first source of
actinic radiation is selected from visible and UV sources including
carbon arcs, mercury-vapor arcs, fluorescent lamps, electron flash
units, electron beam units and photographic flood lamps.
6. The method according to claim 1, wherein the first source of
actinic radiation emits at a wavelength in the range of from about
250 nm to about 450 nm.
7. The method according to claim 5, wherein the first source of
actinic radiation emits at a wavelength in the range of from about
300 to about 400 nm.
8. The method according to claim 7, wherein the first source of
actinic radiation emits at a wavelength in the range of from about
320 to about 380 nm.
9. The method according to claim 1, wherein the second source of
actinic radiation is selected from visible and UV sources including
carbon arcs, mercury-vapor arcs, fluorescent lamps, electron flash
units, electron beam units and photographic flood lamps.
10. The method according to claim 1, wherein the second source of
actinic radiation emits at a wavelength in the range of from about
250 nm to about 450 nm.
11. The method according to claim 8, wherein the second source of
actinic radiation is attenuated, wherein the at least one
photocurable layer absorbs 80% to 99% of the actinic radiation
emitted by the second source of actinic radiation
12. The method according to claim 11, wherein the second source of
actinic radiation is attenuated by a method selected from the group
consisting of positioning a shutter between the second source of
actinic radiation and the backing layer, by positioning a filter
between the second source of actinic radiation and the backing
layer, by use of a second source of actinic radiation that emits at
a less efficient UV wavelength, by use of a backing layer that
absorbs a portion of the actinic radiation emitted by the second
source of actinic radiation and combinations of one or more of the
foregoing.
13. The method according to claim 12, wherein the second source of
actinic radiation is attenuated by positioning a shutter between
the second source of actinic radiation and the backing layer.
14. The method according to claim 12, wherein the second source of
actinic radiation is attenuated by positioning a filter between the
second source of actinic radiation and the backing layer.
15. The method according to claim 12, wherein the second source of
actinic radiation is of a less efficient UV wavelength.
16. The method according to claim 12, wherein the second source of
actinic radiation is attenuated by using a backing layer that
absorbs a portion of the actinic radiation emitted by the second
source of actinic radiation.
17. The method according to claim 16, wherein the backing layer
comprises polyethylene naphthalate or doped polyethylene
terephthalate.
18. The method according to claim 1, wherein the first source of
actinic radiation and the second source of actinic radiation emit
at substantially the same wavelength.
19. The method according to claim 1, wherein the first source of
actinic radiation and the second source of actinic radiation emit
at different wavelengths.
20. The method according to claim 2, wherein the oxygen barrier
layer comprises a material selected from the group consisting of
polyamides, polyvinyl alcohol, hydroxyalkyl cellulose, copolymers
of ethylene and vinyl acetate, amphoteric interpolymers, cellulose
acetate butyrate, alkyl cellulose, butyral, cyclic rubbers,
polypropylene, polyethylene, polyvinyl chloride, polyester and
combinations of one or more of the foregoing.
21. The method according to claim 20, where the oxygen barrier
layer has an oxygen diffusion coefficient of less than
6.9.times.10.sup.-9 m.sup.2/sec.
22. The method according to claim 20, wherein the oxygen barrier
layer has a thickness of between about 5 and about 300 microns.
23. The method according to claim 20, wherein the oxygen barrier
layer has an optical transparency of at least about 50%.
24. The method according to claim 1, wherein the conveying speed of
the photosensitive printing blank through the laminating step and
the exposing unit is between about 0.5 and 5.0 feet per minute.
25. The method according to claim 1, wherein the photosensitive
printing blank is exposed to actinic radiation from the first
source of actinic radiation through the in situ negative and the
oxygen barrier layer for between about 1 and 20 minutes.
26. The method according to claim 1, wherein the photosensitive
printing blank is exposed to actinic radiation through the backing
layer from the second source of actinic radiation for between about
1 and 5 minutes.
27. An exposing apparatus for exposing a photosensitive printing
blank to actinic radiation in a printing plate manufacturing
system, wherein the photosensitive printing blank comprises a
backing layer, at least one photocurable layer disposed on the
backing layer, and a laser ablatable mask layer disposed on the at
least one photocurable layer, wherein the laser ablatable mask
layer is laser ablated to create an in situ negative in the laser
ablatable mask layer, the exposing apparatus comprising: a) a
laminating apparatus for laminating an oxygen bather layer to a top
of the laser ablated mask layer; a conveyor for conveying the
photosensitive printing blank through the exposing apparatus; c) a
first exposing device for exposing the at least one photocurable
layer to actinic radiation from the first exposing device through
the laser ablated mask layer and the oxygen barrier layer to
selectively crosslink and cure portions of the at least one
photocurable layer not covered by the mask layer, and d) a second
exposing device for exposing the at least one photocurable layer to
actinic radiation from the second exposing device through the
backing layer to create a crosslinked floor layer in the
photocurable layer, wherein said first exposing device and said
second exposing device operate substantially simultaneously.
28. The exposing apparatus according to claim 27, wherein the first
exposing device is selected from visible and UV sources including
carbon arcs, mercury-vapor arcs, fluorescent lamps, electron flash
units, electron beam units and photographic flood lamps.
29. The exposing apparatus according to claim 27, wherein the
second exposing device is selected from visible and UV sources
including carbon arcs, mercury-vapor arcs, fluorescent lamps,
electron flash units, electron beam units and photographic flood
lamps.
30. The exposing apparatus according to claim 27, further
comprising an attenuating mechanism for the second exposure device,
whereby an intensity in the actinic radiation from the second
exposing device is reduced.
31. The exposing apparatus according to claim 30, wherein the
attenuating mechanism comprises a shutter.
32. The exposing apparatus according to claim 30, wherein the
attenuating mechanism comprises a filter.
33. The exposing apparatus according to claim 27, wherein the
laminating apparatus comprises: a. a heated laminating roller and a
second roller, wherein said heated laminating roller and said
second roller are opposably mounted and form a nip therebetween for
receiving the photosensitive printing blank to be laminated; b. a
drive mechanism for rotating the heated laminating roller and
second roller, wherein the heated laminating roller is rotated in a
first direction and the second roller is rotated in an opposite
direction to advance the photosensitive printing blank through the
nip formed between the heated laminating roller and second roller;
and c. a supply roller adapted to support a roll of oxygen bather
layer and supply the oxygen barrier layer over an outer surface of
the heated laminating roller and into the nip formed between the
heated laminating roller and the second roller, wherein the oxygen
barrier layer is contactable with a top surface of the
photosensitive printing blank at a point where the photosensitive
printing blank advances through the nip.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a combined
lamination and exposure system for use in manufacturing relief
image printing elements.
BACKGROUND OF THE INVENTION
[0002] Flexography is a method of printing that is commonly used
for high-volume runs. Flexography is employed for printing on a
variety of substrates such as paper, paperboard stock, corrugated
board, films, foils and laminates. Newspapers and grocery bags are
prominent examples. Coarse surfaces and stretch films can be
economically printed only by means of flexography. Flexographic
printing plates are relief plates with image elements raised above
open areas. Generally, the plate is somewhat soft, and flexible
enough to wrap around a printing cylinder, and durable enough to
print over a million copies. Such plates offer a number of
advantages to the printer, based chiefly on their durability and
the ease with which they can be made.
[0003] A typical flexographic printing plate as delivered by its
manufacturer is a multilayered article made of, in order, a backing
or support layer; one or more unexposed photocurable layers;
optionally a protective layer or slip film; and often, a protective
cover sheet.
[0004] The support (or backing) layer lends support to the plate.
The support layer can be formed from a transparent or opaque
material such as paper, cellulose film, plastic, or metal.
Preferred materials include sheets made from synthetic polymeric
materials such as polyesters, polystyrene, polyolefins, polyamides,
and the like. One widely used support layer is a flexible film of
polyethylene terephthalate.
[0005] The photocurable layer(s) can include any of the known
photopolymers, monomers, initiators, reactive or non-reactive
diluents, fillers, and dyes. The term "photocurable" refers to a
composition which undergoes polymerization, cross-linking, or any
other curing or hardening reaction in response to actinic radiation
with the result that the unexposed portions of the material can be
selectively separated and removed from the exposed (cured) portions
to form a three-dimensional or relief pattern of cured material.
Exemplary photocurable materials are disclosed in European Patent
Application Nos. 0 456 336 A2 and 0 640 878 A1 to Goss, et al.,
British Patent No. 1,366,769, U.S. Pat. No. 5,223,375 to Berrier,
et al., U.S. Pat. No. 3,867,153 to MacLahan, U.S. Pat. No.
4,264,705 to Allen, U.S. Pat. Nos. 4,323,636, 4,323,637, 4,369,246,
and 4,423,135 all to Chen, et al., U.S. Pat. No. 3,265,765 to
Holden, et al., U.S. Pat. No. 4,320,188 to Heinz, et al., U.S. Pat.
No. 4,427,759 to Gruetzmacher, et al., U.S. Pat. No. 4,622,088 to
Min, and U.S. Pat. No. 5,135,827 to Bohm, et al., the subject
matter of each of which is herein incorporated by reference in its
entirety. More than one photocurable layer may also be used.
[0006] Photocurable materials generally cross-link (cure) and
harden through radical polymerization in at least some actinic
wavelength region. As used herein, the term "photocurable material"
refers to a solid composition which undergoes polymerization,
cross-linking, or any other curing or hardening reaction in
response to actinic radiation with the result that the unexposed
portions of the material can be selectively separated and removed
from the exposed (cured) portions to form a three dimensional or
relief pattern of cured material. As used herein, "actinic
radiation" is radiation capable of polymerizing, crosslinking or
curing the photocurable layer. Actinic radiation includes, for
example, amplified (e.g., laser) and non-amplified light,
particularly in the UV and violet wavelength regions.
[0007] The slip film is a thin layer, which protects the
photopolymer from dust and increases its ease of handling. In a
conventional ("analog") plate making process, the slip film is
transparent to UV light, and the printer peels the cover sheet off
the printing plate blank, and places a negative on top of the slip
film layer. The plate and negative are then subjected to
flood-exposure by UV light through the negative. The areas exposed
to the light cure, or harden, and the unexposed areas are removed
(developed) to create the relief image on the printing plate.
[0008] In a "digital" or "direct to plate" plate making process, a
laser is guided by an image stored in an electronic data file, and
is used to create an in situ negative in a digital (i.e., laser
ablatable) masking layer, which is generally a slip film which has
been modified to include a radiation opaque material. Portions of
the laser ablatable layer are then ablated by exposing the masking
layer to laser radiation at a selected wavelength and power of the
laser. Examples of laser ablatable layers are disclosed, for
example, in U.S. Pat. No. 5,925,500 to Yang, et al., and U.S. Pat.
Nos. 5,262,275 and 6,238,837 to Fan, the subject matter of each of
which is herein incorporated by reference in its entirety.
[0009] Processing steps for forming relief image printing elements
typically include the following: [0010] 1) Image generation, which
may be mask ablation for digital "computer to plate" plates or
negative production for conventional analog plates; [0011] 2) Back
exposure to create a floor layer in the photocurable layer and
establish the depth of relief; [0012] 3) Face exposure through the
mask (or negative) to selectively crosslink and cure portions of
the photocurable layer not covered by the mask, thereby creating
the relief image; [0013] 4) Developing to remove unexposed
photopolymer by solvent (including water) or thermal development;
and [0014] 5) If necessary, post exposure and detackification.
[0015] Removable coversheets are typically provided to protect the
photocurable printing element from damage during transport and
handling. Prior to processing the printing elements, the
coversheet(s) are removed and the photosensitive surface is exposed
to actinic radiation in an imagewise fashion. Upon imagewise
exposure to actinic radiation, polymerization, and hence,
insolubilization of the photopolymerizable layer occurs in the
exposed areas. Treatment with a suitable developer (or thermal
development) removes the unexposed areas of the photopolymerizable
layer, leaving a printing relief that can be used for flexographic
printing.
[0016] As used herein "back exposure" is a blanket exposure to
actinic radiation of the photopolymerizable layer on the side
opposite that which does, or ultimately will, bear the relief. This
step is typically accomplished through a transparent support layer
and is used to create a shallow layer of photocured material, i.e.,
the "floor," on the support side of the photocurable layer. The
purpose of the floor is generally to sensitize the photocurable
layer and to establish the depth of relief.
[0017] Following this brief back exposure step (i.e., typically
brief as compared to the imagewise exposure step which follows), an
imagewise exposure is performed utilizing a digitally-imaged mask
or a photographic negative mask, which is in contact with the
photocurable layer and through which actinic radiation is
directed.
[0018] The type of radiation used is dependent on the type of
photoinitiator in the photopolymerizable layer. The
digitally-imaged mask or photographic negative prevents the
material beneath from being exposed to the actinic radiation and
hence those areas covered by the mask do not polymerize. The areas
not covered by the mask are exposed to actinic radiation and
polymerize. Any conventional sources of actinic radiation can be
used for this exposure step. Examples of suitable visible and UV
sources include carbon arcs, mercury-vapor arcs, fluorescent lamps,
electron flash units, electron beam units and photographic flood
lamps.
[0019] After imaging, the photosensitive printing element is
developed to remove the unpolymerized portions of the layer of
photocurable material and reveal the crosslinked relief image in
the cured photosensitive printing element. Typical methods of
development include washing with various solvents or water, often
with a brush. Other possibilities for development include the use
of an air knife or heat plus a blotter. The resulting surface has a
relief pattern that reproduces the image to be printed. The relief
pattern typically comprises a plurality of dots, and the shape of
the dots and the depth of the relief, among other factors, affect
the quality of the printed image. After the relief image is
developed, the relief image printing element may be mounted on a
press and printing commenced.
[0020] The shape of the dots and the depth of the relief, among
other factors, affect the quality of the printed image. It is very
difficult to print small graphic elements such as fine dots, lines
and even text using flexographic printing plates while maintaining
open reverse text and shadows. In the lightest areas of the image
(commonly referred to as highlights) the density of the image is
represented by the total area of dots in a halftone screen
representation of a continuous tone image. For Amplitude Modulated
(AM) screening, this involves shrinking a plurality of halftone
dots located on a fixed periodic grid to a very small size, the
density of the highlight being represented by the area of the dots.
For Frequency Modulated (FM) screening, the size of the halftone
dots is generally maintained at some fixed value, and the number of
randomly or pseudo-randomly placed dots represent the density of
the image. In both cases, it is necessary to print very small dot
sizes to adequately represent the highlight areas.
[0021] Maintaining small dots on flexographic plates can be very
difficult due to the nature of the platemaking process. In digital
platemaking processes that use a UV-opaque mask layer, the
combination of the mask and UV exposure produces relief dots that
have a generally conical shape. The smallest of these dots are
prone to being removed during processing, which means no ink is
transferred to these areas during printing (the dot is not "held"
on plate and/or on press). Alternatively, if the dots survive
processing they are susceptible to damage on press. For example
small dots often fold over and/or partially break off during
printing, causing either excess ink or no ink to be
transferred.
[0022] Furthermore, photocurable resin compositions typically cure
through radical polymerization upon exposure to actinic radiation.
However, the curing reaction can be inhibited by molecular oxygen,
which is typically dissolved in the resin compositions, because the
oxygen functions as a radical scavenger. It is therefore highly
desirable for the dissolved oxygen to be removed from the resin
composition before image-wise exposure so that the photocurable
resin composition can be more rapidly and uniformly cured.
[0023] As described in related patent application Ser. No.
12/571,523 to Recchia and Ser. No. 12/660,451 to Recchia et al.,
the subject matter of each of which is herein incorporated by
reference in its entirety, it has been found that a particular set
of geometric characteristics define a flexo dot shape that yields
superior printing performance, including but not limited to (1)
planarity of the dot surface; (2) shoulder angle of the dot; (3)
depth of relief between the dots; and (4) sharpness of the edge at
the point where the dot top transitions to the dot shoulder. An
important method of beneficially changing and/or tailoring the
shape of printing dots formed on a printing element is accomplished
by limiting the diffusion of air into the photocurable layer. As
described in related patent application Ser. No. 13/205,107 to
Gotsick et al., the subject matter of which is herein incorporated
by reference in its entirety, the use of a barrier layer, such as
an oxygen barrier membrane during the imaging and exposing steps
produces printing dots having at least one of the particular set of
geometric characteristic that is beneficially changed in relation
to dots formed without the use of a barrier layer.
[0024] The inventors of the present invention have determined that
it would be desirable to automate the exposure process to reduce
the time requirement of the platemaking process and to create
printing dots having desirable geometric characteristics and other
features.
[0025] In addition, the inventors of the present invention have
also determined that it would be desirable to combine a laminating
step with the automated exposure process to further streamline the
platemaking process and to produce relief image printing elements
having desirable geometric characteristics and other features.
SUMMARY OF THE INVENTION
[0026] It is an object of the present invention to automate
production of digital relief image printing elements by means of a
simultaneous face and back exposures step.
[0027] It is another object of the present invention to allow for
the simultaneous face and back exposure of digital relief image
printing elements after lamination of an oxygen barrier layer to a
relief image printing element.
[0028] It is another object of the present invention to provide a
combined laminating and exposure system comprising a laminating
station and an exposure station capable of simultaneously
performing front and back exposure of a relief image printing
element.
[0029] It is still another object of the present invention to
create printing dots having desirable geometric
characteristics.
[0030] It is still another object of the present invention to
provide means of attenuating the actinic radiation in the back
exposure step in order to reduce the intensity of the actinic
radiation.
[0031] To that end, in one embodiment, the present invention
relates generally to a method of exposing a photosensitive printing
blank to actinic radiation in a printing plate manufacturing
process, wherein the photosensitive printing blank comprises a
backing layer, at least one photocurable layer disposed on the
backing layer, and a laser ablatable mask layer disposed on the at
least one photocurable layer, wherein the laser ablatable mask
layer is laser ablated to create an in situ negative in the laser
ablatable mask layer, the method comprising the steps of: [0032] a)
laminating an oxygen barrier layer to a top of the laser ablated
mask layer using heat and pressure; [0033] b) conveying the
photosensitive printing blank into an exposing unit, wherein said
exposing unit is capable of crosslinking and curing portions of the
at least one photocurable layer not covered by the laser ablated
mask layer and creating a crosslinked floor layer in the at least
one photocurable layer; and [0034] c) at least substantially
simultaneously (i) exposing the at least one photocurable layer to
actinic radiation from a first source of actinic radiation through
the laser ablated mask layer and the oxygen barrier layer to
selectively crosslink and cure portions of the at least one
photocurable layer not covered by the mask layer, and (ii) exposing
the at least one photocurable layer to actinic radiation from a
second source of actinic radiation through the backing layer to
create a crosslinked floor layer in the photocurable layer.
[0035] In another embodiment, the present invention relates
generally to an exposing apparatus for exposing a photosensitive
printing blank to actinic radiation in a printing plate
manufacturing system, wherein the photosensitive printing blank
comprises a backing layer, at least one photocurable layer disposed
on the backing layer, and a laser ablatable mask layer disposed on
the at least one photocurable layer, wherein the laser ablatable
mask layer is laser ablated to create an in situ negative in the
laser ablatable mask layer, the exposing apparatus comprising:
[0036] a) a laminating apparatus for laminating an oxygen barrier
layer to a top of the laser ablated mask layer; [0037] b) a
conveyor for conveying the photosensitive printing blank through
the exposing apparatus; [0038] c) a first exposing device for
exposing the at least one photocurable layer to actinic radiation
from the first exposing device through the laser ablated mask layer
and the oxygen barrier layer to selectively crosslink and cure
portions of the at least one photocurable layer not covered by the
mask layer, and [0039] d) a second exposing device for exposing the
at least one photocurable layer to actinic radiation from the
second exposing device through the backing layer to create a
crosslinked floor layer in the photocurable layer,
[0040] wherein said first exposing device and said second exposing
device operate substantially simultaneously.
BRIEF DESCRIPTION OF THE FIGURES
[0041] The above set forth and other features of the invention are
made more apparent in the ensuing Detailed Description of the
Preferred Embodiments when read in conjunction with the attached
Drawings, wherein:
[0042] FIG. 1 depicts an exposure step with a simultaneous face and
back exposure step in accordance with the present invention.
[0043] FIG. 2 depicts an integrated laminating and exposure system
in accordance with the present invention.
[0044] FIG. 3 depicts a photosensitive printing blank that is
processible through the laminating and exposure system of the
present invention.
[0045] FIG. 4 depicts a photosensitive printing blank with an
oxygen barrier layer laminated thereon that is processible through
the exposure system of the present invention.
[0046] Identical reference numerals in the figures are intended to
indicate like parts, although not every feature in every figure may
be called out with a reference numeral.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] The present invention describes a conveyorized exposure
system that is capable of at least substantially simultaneously
performing both a face exposure and a back exposure of a
photosensitive printing blank in a flexographic platemaking process
and a method of using the same. Furthermore, the present invention
also describes a combined laminating and exposure system to further
streamline the platemaking process and to create printing dots
having desirable geometric characteristics and a method of using
the same.
[0048] In one preferred embodiment, the present invention relates
generally to a method of exposing a photosensitive printing blank
to actinic radiation in a printing plate manufacturing process to
crosslink and cure portions of the at least one photocurable layer,
thereby creating the relief layer while simultaneously back
exposing the at least one photocurable layer to actinic radiation
through the backing layer to create a floor layer and set the depth
of relief.
[0049] The photosensitive printing blank comprises a backing layer,
at least one photocurable layer disposed on the backing layer, and
a laser ablatable mask layer disposed on the at least one
photocurable layer, and the laser ablatable mask layer is laser
ablated to create an in situ negative in the laser ablatable mask
layer.
[0050] The laser ablatable mask layer can be any photoablative mask
layer known in the art. Such mask layers include those that can be
ablated by any type of laser known to those skilled in the art such
as, for example, UV-type Eximer lasers typically operating at
wavelengths of about 300 to 400 nm; IR-type lasers such as, for
example, CO.sub.2 lasers typically operating at a wavelength of
about 10,640 nm; Nd-YAG lasers typically operating at a wavelength
of about 1064 nm; and diode array lasers typically operating at a
wavelength of about 830 nm.
[0051] The method generally comprises the steps of: [0052] a)
laminating an oxygen barrier layer to a top of the laser ablated
mask layer using heat and pressure; [0053] b) conveying the
photosensitive printing blank into an exposing unit, wherein said
exposing unit is capable of crosslinking and curing portions of the
at least one photocurable layer not covered by the laser ablated
mask layer and creating a crosslinked floor layer in the at least
one photocurable layer; and [0054] c) at least substantially
simultaneously: [0055] (i) exposing the at least one photocurable
layer to actinic radiation from a first source of actinic radiation
through the laser ablated mask layer and the oxygen barrier layer
to selectively cross link and cure portions of the at least one
photocurable layer not covered by the mask layer, and [0056] (ii)
exposing the at least one photocurable layer to actinic radiation
from a second source of actinic radiation through the backing layer
to create a crosslinked floor layer in the photocurable layer.
[0057] As described herein, the oxygen barrier layer is laminated
to the top of the laser ablated mask layer using heat and pressure
prior to the step of exposing the at least one photocurable layer
to actinic radiation. The photosensitive printing blank is thus
exposed to actinic radiation from the first source of actinic
radiation through the laser ablated mask layer and the oxygen
barrier layer.
[0058] The laminating step typically comprises the steps of: [0059]
a) supplying the photosensitive printing blank to a nip formed
between a heated laminating roller and a second roller; [0060] b)
supplying the oxygen barrier layer from a oxygen barrier layer
supply roller over an outer surface of the heated laminating roller
and into the nip formed between the heated laminating roller and
the second roller; wherein the oxygen barrier layer contacts a top
surface of the photosensitive printing blank at a point where the
photosensitive printing blank advances through the nip; and [0061]
c) rotating the heated laminating roller in a first direction and
the second roller in an opposite direction to advance the
photosensitive printing blank with the oxygen barrier layer thereon
through the nip, thereby laminating the oxygen barrier layer to the
top of the laser ablated mask layer.
[0062] After the oxygen barrier layer is laminated to the top of
the laser ablatable mask layer and the photosensitive printing
blank has been exposed to actinic radiation, the oxygen barrier
layer is removed. It is also generally preferred that the oxygen
barrier layer be removed prior to the development step.
[0063] The conveying speed of the photosensitive printing blank
through the laminating step and the exposing unit is typically
between about 0.5 and 5 feet per minute.
[0064] Next, the imaged and exposed photosensitive printing blank
is developed to reveal the relief image therein that comprises a
plurality of relief dots. Development may be accomplished by
various methods, including water development, solvent development
and thermal development, by way of example and not limitation.
Finally, the relief image printing element is mounted on a printing
cylinder of a printing press and printing is commenced.
[0065] As described in related application Ser. No. 12/571,523 to
Recchia and Ser. No. 12/660,451 to Recchia et al., the presence of
the oxygen barrier layer produces printing dots having at least one
geometric characteristic selected from the group consisting of
planarity of a top surface of the printing dots, shoulder angle of
the printing dots and edge sharpness of the printing dots,
beneficially changed in relation to dots formed without the use of
a barrier layer.
[0066] The photocurable materials of the invention should
cross-link (cure) and, thereby, harden in at least some actinic
wavelength region. As used herein, actinic radiation is radiation
capable of effecting a chemical change in an exposed moiety.
[0067] In one embodiment, the first source of actinic radiation is
selected from visible and UV sources including carbon arcs,
mercury-vapor arcs, fluorescent lamps, electron flash units,
electron beam units and photographic flood lamps, although other
similar sources of actinic radiation that emit at a wavelength in
the desired range would also be usable in the practice of the
invention. Preferred actinic wavelength regions are from about 250
nm to about 450 nm, more preferably from about 300 nm to about 400
nm, even more preferably from about 320 nm to about 380 nm.
Furthermore, the intensity of flood exposure lamps used in the
curing of flexographic printing plates is typically in the range of
about 5-25 milliwatts/cm.sup.2, but intensities can be as high as
50 milliwatts/cm.sup.2.
[0068] The second source of actinic radiation is also preferably
selected from visible and UV sources including carbon arcs,
mercury-vapor arcs, fluorescent lamps, electron flash units,
electron beam units and photographic flood lamps. As with the first
source of actinic radiation, other similar sources of actinic
radiation that emit at a wavelength in the desired range would also
be usable in the practice of the invention. The second source of
actinic radiation also preferably emits at a wavelength in the
range of from about 250 nm to about 450 nm.
[0069] As described herein, the photosensitive printing blank is
exposed to actinic radiation from the first source of actinic
radiation through the in situ negative. In a preferred embodiment,
the photosensitive printing blank is exposed to actinic radiation
for between about 1 and about 20 minutes, more preferably, for
between about 4 and about 10 minutes. In addition, the
photosensitive printing blank is exposed to actinic radiation
through the backing layer from the second source of actinic
radiation for between about 0.5 and about 5 minutes, more
preferably for between about 1 and about 3 minutes.
[0070] In order for the face exposure step and the back exposure
step to be performed at least substantially simultaneously and to
adequate crosslink and cure both the floor layer and the relief
layer, the second source of actinic radiation is preferably
attenuated. In this instance, it is desirable that the at least one
photocurable layer absorbs 80% to 99% of the actinic radiation
emitted by the second source of actinic radiation
[0071] The second source of actinic radiation may be attenuated by
any one of a variety of methods. For example, the second source of
actinic radiation may be attenuated by a method selected from the
group consisting of positioning a shutter between the second source
of actinic radiation and the backing layer, by positioning a filter
between the second source of actinic radiation and the backing
layer, by use of a second source of actinic radiation that emits at
a less efficient UV wavelength, by use of a backing layer that
absorbs a portion of the actinic radiation emitted by the second
source of actinic radiation and combinations of one or more of the
foregoing.
[0072] In one embodiment, the second source of actinic radiation is
attenuated by positioning a shutter between the second source of
actinic radiation and the backing layer. For example, the shutter
may be any material opaque to actinic radiation that has the
physical properties needed for repeated exposure to actinic
radiation and mechanical properties needed for being positioned
between the actinic radiation source and the photopolymer plate.
General examples of suitable shutter designs would be retractable
shields that accordion or roll up when not in use, or louver-type
shutters that remain in place, but can be mechanically manipulated
so that very little actinic radiation is blocked when they are
`open`. A suitable shutter for use in the practice of the invention
would be light duty commercial louvers, available from North Coast
Tool (Erie, Pa.).
[0073] In another embodiment, the second source of actinic
radiation is attenuated by positioning a filter between the second
source of actinic radiation and the backing layer. In particular, a
light attenuating filter may be used which adjusts the amount
(intensity) of light illuminated on the backing layer. The light
attenuating filter is selected so as to have a particular
transmittance. For example, the light attenuating filter may have a
transmittance of 80% so that the light passing through the filter
is attenuated by 20%. A suitable light attenuating filter for use
in the practice of the invention would be a UV-blocking PET film,
available from DuPont Teijin Films under the tradename Melinex
626.
[0074] In yet another embodiment, the second source of actinic
radiation is of a different, less efficient UV wavelength to allow
the use of a non-UV-blocking polyester as the backing layer on the
plate because attenuation would no longer be needed.
Photoinitiators dispersed in the at least one photocurable layer
typically have a wavelength (or range of wavelengths) at which they
are effective. Choosing a wavelength for the second source of
actinic radiation that is less efficient allows for the use of
additional non-UV-blocking backing layers to be used.
[0075] In still another embodiment, the second source of actinic
radiation is attenuated by using a backing or support layer that
absorbs a portion of the actinic radiation emitted by the second
source of actinic radiation. As described in U.S. Pat. No. RE39,835
to Kanga, the subject matter of which is herein incorporated by
reference in its entirety, a modification may be made to the
support layer, to allow printers to better control floor-formation
in digital platemaking processes.
[0076] As described above, the support layer of the photocurable
element is preferably formed from a variety of flexible,
transparent materials. The support layer may be made UV-absorbing
either by forming the support layer from a material that is
inherently UV-absorbing, i.e., attenuates actinic radiation itself,
or by adding a dopant to the material forming the support
layer.
[0077] Support layers that are inherently UV-absorbing include
polyethylene naphthalate (PEN) (for example, Kaladex 1030 and
Kaladex 2000 commercially available from DuPont PET, Hopewell,
Va.). When an inherently UV-absorbing support layer is used, the
percent of actinic radiation that is absorbed is a function of the
thickness of the support layer. For example, a PEN support layer
having a thickness of about 5 mils typically absorbs about 97
percent of actinic radiation; a PEN support layer having a
thickness of about 3 mils typically absorbs about 95 percent of
actinic radiation.
[0078] Support layers that contain a UV-absorbing material
typically have a UV-absorbing dopant added to the support layer
during manufacture. The spectral range of the flood-exposure lamps
used in many applications is about 300-400 nm. Based thereon, the
UV absorbing dopant should typically be active in this range.
Preferably, the presence of the UV absorber changes a normally UV
transparent support layer into an attenuation tool that absorbs at
least a portion of the UV radiation that passes through it.
Preferably, the support absorbs between about 80 to 99%, more
preferably between about 85 to about 95%, and most preferably about
88% of actinic radiation.
[0079] Depending on the method selected for attenuating the second
source of actinic radiation, first source of actinic radiation and
the second source of actinic radiation may emit at substantially
the same wavelength or may emit at different wavelengths.
[0080] A wide range of materials can serve as the oxygen barrier
layer, including various oxygen barrier films and membranes. Three
qualities that have been identified in producing effective oxygen
barrier layer include optical transparency, low thickness and
oxygen transport inhibition. Oxygen transport inhibition is measure
in terms of a low oxygen diffusion coefficient. As noted, the
oxygen diffusion coefficient of the oxygen barrier layer should be
less than 6.9.times.10.sup.-9 m.sup.2/sec., preferably less than
6.9.times.10.sup.-10 m.sup.2/sec. and most preferably less than
6.9.times.10.sup.-11 m.sup.2/sec.
[0081] Examples of materials which are suitable for use as the
oxygen barrier layer include those materials that are
conventionally used as a release layer in flexographic printing
elements, such as polyamides, polyvinyl alcohol, hydroxyalkyl
cellulose, copolymers of ethylene and vinyl acetate, amphoteric
interpolymers, cellulose acetate butyrate, alkyl cellulose,
butyral, cyclic rubbers, and combinations of one or more of the
foregoing. In addition, films such as polypropylene, polyethylene,
polyvinyl chloride, polyester and similar clear films can also
serve well as barrier layers. In one preferred embodiment, the
oxygen barrier layer comprises a polypropylene film or a
polyethylene terephthalate film.
[0082] The thickness of the oxygen barrier layer should be
consistent with the structural needs for handling of the film and
the film/photopolymer plate combination. Barrier thicknesses
between about 5 and 300 microns are preferred, more preferably
between about 10 to about 200 microns and most preferably between
about 1 to about 20 microns.
[0083] The oxygen barrier layer also needs to have a sufficient
optical transparency so that the oxygen barrier membrane will not
detrimentally absorb or deflect the actinic radiation used to
expose the photosensitive printing blank. As such it is preferable
that the oxygen barrier layer have an optical transparency of at
least 50%, most preferably at least 75%.
[0084] The oxygen barrier layer also needs to be sufficiently
impermeable to oxygen diffusion so that it can effectively limit
diffusion of oxygen into the photocurable layer during exposure to
actinic radiation.
[0085] As discussed above, related patent application Ser. No.
12/571,523 to Recchia, Ser. No. 12/660,451 to Recchia et al., and
Ser. No. 13/205,107 to Gotsick et al., the subject matter of each
of which is herein incorporated by reference in its entirety,
describe the particular set of geometric characteristics define a
flexo dot shape that yields superior printing performance,
including but not limited to (1) planarity of the dot surface; (2)
shoulder angle of the dot; (3) depth of relief between the dots;
and (4) sharpness of the edge at the point where the dot top
transitions to the dot shoulder.
[0086] In another preferred embodiment, the present invention also
relates generally to a combined laminating and exposing apparatus
for exposing a photosensitive printing blank to actinic radiation
in a platemaking system. As described above, the photosensitive
printing blank comprises a backing layer, at least one photocurable
layer disposed on the backing layer, and a laser ablatable mask
layer disposed on the at least one photocurable layer, and the
laser ablatable mask layer is laser ablated to create an in situ
negative in the laser ablatable mask layer.
[0087] As shown in FIGS. 1 and 2, the exposing apparatus 10
preferably comprises: [0088] a) a laminating apparatus 30 for
laminating an oxygen barrier layer 24 to a top of the laser ablated
mask layer 22; [0089] b) a conveyor 12 for conveying the
photosensitive printing blank 14 through the exposing apparatus;
[0090] c) a first exposing device 16 for exposing the at least one
photocurable layer 20 (shown in FIG. 3) to actinic radiation from
the first exposing device 16 through the laser ablated mask layer
22 and the oxygen barrier layer 24 to selectively crosslink and
cure portions of the at least one photocurable layer 20 not covered
by the mask layer 22, and [0091] d) a second exposing device 18 for
exposing the at least one photocurable layer 20 to actinic
radiation from the second exposing device 18 through the backing
layer 28 to create a crosslinked floor layer in the photocurable
layer 20,
[0092] wherein said first exposing device 16 and said second
exposing device 18 operate substantially simultaneously.
[0093] As described herein, the second exposure device 18 may
comprise an attenuating mechanism for the second exposure device,
whereby an intensity in the actinic radiation from the second
exposing device is reduced.
[0094] In one embodiment, the attenuating mechanism may comprise a
shutter. One suitable shutter is a light duty commercial louver,
available from North Coast Tool (Erie, Pa.). Other suitable
shutters that are capable of attenuating the intensity of actinic
radiation from the second exposing device, including for example
any material opaque to actinic radiation that has the physical
properties needed for repeated exposure to actinic radiation and
mechanical properties needed for being positioned between the
actinic radiation source and the photopolymer plate. General
examples of suitable shutter designs would be retractable shields
that accordion or roll up when not in use, or louver-type shutters
that remain in place, but can be mechanically manipulated so that
very little actinic radiation is blocked when they are `open`,
would also be usable in the practice of the invention.
[0095] In another embodiment, the attenuating mechanism may
comprise a filter. One suitable filter is available from DuPont
Teijin Films under the tradename Melinex 628 Other suitable filters
that are capable of attenuating the intensity of actinic radiation
from the second exposing device, including for example a matte or
translucent film would also be usable in the practice of the
invention.
[0096] As shown in FIG. 4, the photosensitive printing blank 14
with the oxygen barrier layer 24 mounted thereon thus comprises a
backing layer 28, at least one photocurable layer 20 disposed on
the backing layer 28 and a laser ablatable mask layer 22 disposed
on the at least one photocurable layer 20.
[0097] As shown in FIG. 2, the laminating apparatus 30 typically
comprises: [0098] a. a heated laminating roller 32 and a second
roller 34, wherein said heated laminating roller 32 and said second
roller 34 are opposably mounted and form a nip 36 therebetween for
receiving the photosensitive printing blank 14 to be laminated;
[0099] b. a drive mechanism for rotating the heated laminating
roller 32 and second roller 34, wherein the heated laminating
roller 32 is rotated in a first direction and the second roller 34
is rotated in an opposite direction to advance the photosensitive
printing blank 14 through the nip 36 formed between the heated
laminating roller 32 and second roller 34; and [0100] c. a supply
roller 38 adapted to support the roll of oxygen barrier layer 24
and supply the oxygen barrier layer 24 over an outer surface of the
heated laminating roller 32 and into the nip 36 formed between the
heated laminating roller 32 and the second roller 34, wherein the
oxygen barrier layer 24 is contactable with a top surface of the
photosensitive printing blank 14 at a point where the
photosensitive printing blank 14 advances through the nip 36.
[0101] The present invention allows for the full automation of
simultaneous exposure along with the production of flat top dots.
The present invention can also be used to automate the production
of standard digital relief image printing elements by means of a
simultaneous face and back exposure.
* * * * *