U.S. patent application number 13/325130 was filed with the patent office on 2012-05-10 for processless development of printing plate.
This patent application is currently assigned to ANOCOIL CORPORATION. Invention is credited to Howard A. FROMSON, William J. ROZELL, William J. RYAN.
Application Number | 20120111214 13/325130 |
Document ID | / |
Family ID | 44904276 |
Filed Date | 2012-05-10 |
United States Patent
Application |
20120111214 |
Kind Code |
A1 |
FROMSON; Howard A. ; et
al. |
May 10, 2012 |
Processless Development of Printing Plate
Abstract
On-press development of an imaged printing plate on a plate
cylinder, in which ink is applied by an ink form roll, a blanket
roll is in contact with the plate, a rubber roll is opposed to the
blanket roll, and printable media passes between the blanket roll
and the rubber roll. The plate comprises a substrate carrying an
imaged coating and nonimage areas. The respective cohesive and
adhesive properties of the nonimage and image areas to the applied
ink, substrate, blanket roll and printable medium, and the ink to
the roll are such that the blanket roll pulls the ink from the
plate and the ink pulls the nonimage areas from the substrate as
undissolved particles that are transferred by the blanket with the
ink to the printable media.
Inventors: |
FROMSON; Howard A.;
(Stonington, CT) ; RYAN; William J.; (North
Granby, CT) ; ROZELL; William J.; (Simpsonville,
SC) |
Assignee: |
ANOCOIL CORPORATION
Rockville
CT
|
Family ID: |
44904276 |
Appl. No.: |
13/325130 |
Filed: |
December 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12799568 |
Apr 27, 2010 |
8137897 |
|
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13325130 |
|
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12586764 |
Sep 28, 2009 |
8133658 |
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12799568 |
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Current U.S.
Class: |
101/463.1 |
Current CPC
Class: |
B41C 2210/08 20130101;
B41C 1/1075 20130101; G03F 7/3035 20130101; B41C 2201/02 20130101;
B41C 2210/24 20130101; B41C 2210/04 20130101; B41C 1/1016 20130101;
B41C 1/1008 20130101 |
Class at
Publication: |
101/463.1 |
International
Class: |
B41N 3/00 20060101
B41N003/00 |
Claims
1. A process for developing a lithographic plate, comprising: (a)
selecting an imaged plate having (i) a substrate with a grained,
anodized, hydrophilic surface; (ii) a negative working, organic,
polymerizable coating in which all active components for
polymerization are insoluble in any of the group of fluids
consisting of water, fountain solution and ink; (iii) wherein said
coating is non-ionically bonded to the substrate and has been
imaged by polymerization in areas exposed to radiation, such that
the cohesion of the unimaged areas of the coating exceeds the
adhesion of the unimaged areas of the coating to the substrate; and
(b) subjecting the entire coating to mechanical forces while the
coating is in contact with one of said fluids, which forces disrupt
and remove only the unimaged areas of the coating from the
substrate surface in the form of particulate material and without
dispersing the unimaged areas of the coating into the fluid at the
substrate surface.
2. The process of claim 1, wherein the mechanical forces are
selected from the group consisting of compression, tension,
impulse, and piercing.
3. The process of claim 1, wherein the mechanical forces are
provided by pushing against the coating.
4. The process of claim 1, wherein the plate includes a top coat of
a water soluble oxygen barrier and after imaging the topcoat is
washed off with water before subjecting the entire coating to
mechanical forces according to step (b).
5. The process of claim 1, wherein the mechanical forces are
provided by pressurized water spray.
6. The process of claim 1, wherein the mechanical forces are
provided by rotating brushes in the presence of water.
7. A process for preparing a lithographic plate for offset
printing, comprising the sequence of: (a) selecting a plate having
an anodized, hydrophilic substrate and an overlying oleophilic,
radiation polymerizable, non-aqueous organic coating non-ionically
adhered to the substrate, wherein the cohesion of the coating to
itself is greater than the adhesion of the coating to the
substrate; (b) imagewise exposing the plate to radiation, thereby
producing a pattern of highly polymerized oleophilic imaged areas
and unimaged oleophilic areas; and (c) mechanically impinging the
entire coating in a water environment supplied by a source of
water, with sufficient energy to disrupt and dislodge the unimaged
areas from the substrate and thereby remove the unimaged areas from
the substrate in the form of discrete solid particles.
8. The process of claim 7, wherein the step of mechanically
impinging in step (c) is not performed by the source of water
itself.
9. The process of claim 8, wherein the discrete solid particles are
removed substantially by the water source after being dislodged
from the substrate.
10. The process of claim 7, wherein between steps (b) and (c), the
entire imagewise exposed plate is exposed to elevated temperature
in the range of between about 175 to 250 degrees F. for a time
period in the range of 5 to 15 seconds.
11. The process of claim 7, wherein step (c) is performed with a
high-pressure water spray.
12. The process of claim 7, wherein step (c) is performed with a
rotating brush.
13. A process for preparing a lithographic plate for offset
printing, comprising the sequence of: (a) selecting a plate having
an anodized, hydrophilic substrate and an overlying oleophilic,
radiation polymerizable, non-aqueous organic coating non-ionically
adhered to the substrate, wherein the cohesion of the coating to
itself is greater than the adhesion of the coating to the substrate
and the coating is not dispersible in any of the group of fluids
consisting of water, fountain solution and ink; (b) imagewise
exposing the plate to radiation, thereby producing a pattern of
highly polymerized oleophilic imaged areas and unimaged oleophilic
areas; and (c) mechanically impinging the entire coating in a water
environment with sufficient force to disrupt and dislodge the
unimaged areas from the surface of the substrate and thereby remove
the unimaged areas in the form of discrete solid particles.
14. The process of claim 13, wherein between steps (b) and (c), the
entire imagewise exposed plate is exposed to elevated temperature
in the range of between about 175 to 250 degrees F. for a time
period in the range of 5 to 15 seconds.
15. The process of claim 13, wherein step (c) is performed with a
high-pressure water spray.
16. The process of claim 13, wherein step (c) is performed with a
rotating brush.
Description
RELATED APPLICATIONS
[0001] This is a continuation of U.S. application Ser. No.
12/799,568 filed Apr. 27, 2010 for "Processless Development of
Printing Plate," which is a continuation-in-part of U.S.
application Ser. No. 12/586,764 filed Sep. 28, 2009 for
"Non-Chemical Development of Printing Plates", the complete
disclosures of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to imageable lithographic
plates for printing.
[0003] Plates of interest have a solvent-soluble,
radiation-polymerizable, oleophilic resin coating on a hydrophilic
substrate. In conventional practice, after image-wise exposure at
ultraviolet (UV), visible, or infrared (IR) wavelengths, the plates
are developed with solvent to remove the unexposed areas of the
coating by dissolution, thereby producing a substantially
planographic pattern of oleophilic and hydrophilic areas. The
developed plates are then ready for mounting on a cylinder of a
printing press, where the plates are subjected to fountain fluid
and ink for transfer of ink to a target surface according to the
pattern of oleophilic and hydrophilic areas on the plate.
[0004] Although a process is known for developing IR imaged plates
with water rather than solvent, the coating is not polymerized by
the imaging. Instead, the coating contains microspheres or beads of
thermally fusible material suspended in a water-soluble medium or
matrix. The plate is imaged at high energy levels (250-350
mj/cm.sup.2) such that the microspheres fuse to themselves and the
substrate. The imaged plates can be developed with water or
fountain fluid on-press, whereby the imaged, fused areas remains
intact whereas the unimaged, non-fused areas including microspheres
are removed via dissolution of the matrix.
[0005] Not only is a high level of energy required for imaging such
plates, but the rate of imaging is slow and the resolution is low.
Also, the dissolved matrix with microspheres is a chemical waste
that must be specially treated.
[0006] Thus, it should be appreciated that almost all existing
negative-working planographic lithographic printing plates, with
the exception of those produced by ablation in the imager, are
produced by laying down a continuous film of radiation-sensitive
coating on a suitable hydrophilic substrate such as grained,
anodized, and hydrophilized aluminum sheet, or its equivalent,
imaging the radiation-sensitive coating with actinic ultra-violet,
violet, or infra-red energy in an image-wise fashion, and
subsequently subtracting the non-irradiated portions of the imaged
plate by the process of solubilization or dispersion, thus
establishing oleophilic image areas and water receptive non-image
areas.
SUMMARY OF THE INVENTION
[0007] In one general aspect, the invention is directed to a
process for developing a lithographic plate, in which a first step
is selecting an imaged plate having (i) a substrate with a grained,
anodized, hydrophilic surface and (ii) a negative working, organic,
polymerizable coating in which all active components for
polymerization are insoluble in any of water, fountain solution,
ink or similar fluids, wherein the coating is non-ionically bonded
to the substrate and has been imaged by polymerization in areas
exposed to radiation, such that the cohesion of the unimaged areas
of the coating exceeds the adhesion of the unimaged areas of the
coating to the substrate. In a subsequent step, the entire coating
is subjected to mechanical forces, preferably while the coating is
in contact with one of the fluids, which forces disrupt and remove
only the unimaged areas of the coating from the substrate surface
in the form of particulate material, without dispersing the
unimaged areas of the coating into the fluid at the substrate
surface.
[0008] We disclose an embodiment in which a planographic
lithographic printing plate is produced by laying down a film of
radiation-sensitive organic coating on a suitably hydrophilic
substrate, such as grained, anodized and hydrophilized coating, or
its equivalent, imaging the radiation-sensitive coating with
actinic UV, violet, or IR radiation to highly polymerize the image
areas and subsequently removing the non-image areas of the imaged
plate by mechanically disturbing the planar coating with either the
hydraulic energy of a high-pressure water spray, or by bristled
brushes rotating rapidly under pressure in an aqueous bath against
the plate surface, thus fracturing the coating in the non-image
areas into discrete insoluble particles of resin. The fractured
particles suspended in water are preferably captured by a powered,
rapidly-circulating filter system at a rate at least equal to the
particle generation rate.
[0009] This state of water insolubility is achieved by composing
the organic radiation-sensitive film only of active components that
are insoluble in water. The fracturing phenomenon of the imaged
organic film is achieved by making certain that the adhesion of the
as-coated unimaged organic film to the substrate is less than the
internal cohesion of the imaged film. The generation of the removal
of the unimaged film in particulate form only is thus attributable
to the combined factors that the as-coated coating is not soluble
in water and is designed to have an adhesion to the substrate that
is less than the cohesion of the as-coated organic layer.
[0010] Because the fractured particles, generated by compressive
forces in the processor, have not undergone solubilization, they do
not adhere to each other to form agglomerates in the processor, nor
do they adhere to the rubber, polymer, or metal of the processor or
the plate.
[0011] In another embodiment, wherein a suitably-coated and imaged
plate is to be developed on press, the topcoat of polyvinyl alcohol
on the imaged plate is removed in water and the plate is mounted on
press in either visible or yellow light. On-press the high-tack
press inks adhere very well to the imaged plate surfaces, in both
the imaged and unimaged areas. During start-up, when the blanket
compresses against the inked surface of the imaged plate, the
high-tack adhesion of the ink to the blanket exceeds the adhesion
of the unimaged areas of the plate, and the cohesion of the
unimaged areas of the plate also exceeds the adhesion to the plate,
so the fractured non-image particles are pulled onto the blanket
and deposited on the paper web by the blanket and eventually end up
in the initial start-up paper waste. The imaged areas have both
adhesion and cohesion greater than the ink. On-press the ink film
deposited by the ink form roll onto the plate splits between the
imaged areas of the plate and the ink form roll.
[0012] According to the present innovation, a solvent-soluble,
radiation-polymerizable, oleophilic resin coating non-ionically
adhered on a hydrophilic substrate can be imagewise exposed to
polymerizing radiation and then directly processed by application
of mechanical force that removes the non-exposed areas of the
coating as particulates, either pre-press or on press, without
dissolution of the coating material. By subjecting the entire
imaged surface to mechanical forces (such as steady compression or
tension, or a series of impulses or impacts), the unimaged areas of
the coating are mechanically dislodged from the substrate in the
form of particulate matter, without any solubilization or
dispersion process.
[0013] The mechanical force can be applied by piercing, scraping,
pushing or pulling. When applied pre-press at a dedicated
developing station or step, such pressure can be in the form of
impacts by a pressurized spray of neutral water, or by rapidly
rotating bristle brushes, with or without water spray. On press,
the tack of ink applied to a newly-installed plate provides
sufficient pulling force. In the on-press embodiment, the cohesion
of the coating in the unimaged areas exceeds its adhesion to the
substrate, and the adhesion of the unimaged coating to the ink is
greater than the adhesion to the substrate, such that the blanket
pulls the unimaged areas off the substrate and deposits them on the
blanket waste.
[0014] It should be appreciated that, whereas the active
ingredients in the dried, unimaged areas of the coating are only
soluble in a non-aqueous solvent, these areas are removed (i.e.,
the plate is "developed") without use of any such solvent. In this
context, "active" means an ingredient that participates in the
radiation induced polymerization in the imaged areas. This
generally means the active ingredients are a polymer, a monomer
and/or oligomer, at least one polymerization or cross link
initiator, and a dye.
[0015] The most evident advantage is that no separate developing
equipment or step is required between the imager and the press. A
second significant advantage, whether or not the plate is passed
through a pre-press water processor, is that there is little or no
chemical treatment required of the waste stream associated with
developing the plate. A third significant advantage is that because
dissolution of the polymer resin is not relied upon for processing
the plate, higher molecular weight resins can be used in the
imageable coating, thereby producing more durable oleophilic areas
and longer plate life on press.
[0016] Two factors play an important role in enabling the removal
of the unimaged areas without any solvent or dissolution. First,
the imageable coating as initially applied and dried on the
substrate, has a relatively low degree of adhesion to the
substrate. This is preferably achieved by using a substrate having
a grained, positively charged (anionic) hydrophilic surface to
which the coating mildly adheres non-ionically as a result of
drying. Such substrate can be a grained aluminum sheet treated with
silicate or other known hydrophilizing agents. Drying produces a
mild degree of cohesion, such that the bottom surface of the
coating mechanically interengages and thus adheres to the
irregularities in the grained surface of the substrate, and the
body of the coating achieves sufficient cohesion to permit further
handling, shipment, and imaging of the plates. For on-press
development, the cohesion of the dried, unimaged coating is greater
than its adhesion to the substrate and its tack or adhesion to the
ink and blanket roll is greater than its adhesion to the substrate,
but the adhesion of the imaged coating to the substrate is greater
than its adhesion to the ink.
[0017] Second, upon imaging of the plates, the radiation induced
polymerization causes the adhesion and cohesion of the imaged areas
to become much higher than the adhesion and cohesion of the
unimaged areas. Diazo compounds have been used by some
practitioners to increase the adhesion of imaged areas in
essentially photopolymerizable coatings. However, the coatings for
use in the present invention must be diazo-free, because with diazo
based coatings (whether applied in aqueous or non-aqueous solution)
the dry coating bonds ionically to the substrate and can only be
removed via chemical reaction with non-aqueous (organic)
solvent.
[0018] Without limiting the scope of the claims corresponding to
the inventive concept, we can ascribe the best results at least in
part to a combination of non-diazo based resins and associated
polymerization initiating agents, which produce low adhesion to the
substrate in the manufactured plate yet can quickly produce high
adhesion where radiation imaged.
[0019] Practitioners in this field had no reason to investigate or
optimize the difference in adhesion of non-aqueous
photopolymerizable resins as a basis for non-chemical, and
especially mechanical, removal of the nonimage areas. Because it
was the established practice that nonimage areas of the imaged
plate could be substantially completely dissolved by the non
aqueous developer solution, the main objective for improving
coatings has been to increase the adhesion, cohesion, and
durability of the imaged areas and thereby enable the plate to
better withstand the rigors of the printing press. Any desired
relationship between the imaged and unimaged areas was based on
relative solubility, not relative mechanical adhesion, to minimize
incidental dissolution of any of the exposed surface the imaged
areas while the developer solution dissolved substantially all of
the non image areas.
[0020] With the present invention, several techniques are available
for facilitating or increasing the speed of the removal of the
unimaged areas in solidus, i.e., without dissolution or
dispersion.
[0021] According to one such technique, the coating also includes
as a non-active ingredient, a solvent soluble, partially water
soluble, organic compound that is not photosensitive (i.e., it does
not harden via photopolymer or photochemical reaction to imaging
radiation).
[0022] According to another technique, the plates are heated after
imaging to increase the difference in cohesion and adhesion of the
coating to the substrate as between the imaged and unimaged areas,
such that a greater force can be applied to the plates to dislodge
only the unimaged areas. In particular, a thermally imageable
negative working plate can be exposed to heat for a short period of
time after imaging, whereby the imaged portions become more stable
and tougher, while the portions of the coating that are to be
removed are not significantly affected. The heating step
preferably, but not necessarily, immediately follows the imaging
step, but can be at a different location from the imaging step.
[0023] With yet another technique, any water applied to the plate
is at elevated temperature.
[0024] In a further preference, the water soluble top coat
conventionally used to protect photosensitive (PS) coatings is
washed off the PS coating after imaging (and after any subsequent
heating step) and the plates stored temporarily until mounted on
press. The top coat is typically a water soluble film former (such
as PVOH) that prevents atmospheric oxygen from diffusing into the
coating and quenching the free radicals necessary for inducing
polymerization. The removal of this topcoat has been found to
substantially immunize the imaged coating from further
polymerization in the unimaged areas due to ambient light. Thus,
the plates need not be handled in yellow or other special light
between imaging and mounting on press.
[0025] The combination of water with pressure produces faster
removal of the unimaged areas. Although the mechanism is not known
with certainty, it is believed that the coating as applied and
dried (and as found in the unimaged areas) inherently contains
molecular level interstices that provide paths by which the water
can penetrate into the coating and ultimately to the substrate.
These interstices may very well be associated with the residual or
tail solvent in the dried coating, which can be up to about 5% of
the coating by weight. For example, water is miscible with DMF,
which if used as a component of the coating solution applied to the
substrate, can provide interstices of miscibility in the dried
coating. These interstices likely disappear in the imaged areas as
a result of the high degree of polymerization. The application of
mechanical pressure with water on the relatively soft unimaged
areas appears to significantly open up these interstices, and the
use of hot water renders the unimaged areas even softer and more
easily removable. The paths for water penetration through the
interstices of miscibility do not depend on the (optional) presence
of a partially water soluble compound in the coating.
[0026] In another aspect, the invention is directed to a process
for preparing a lithographic plate for offset printing. The steps
include selecting a plate having a hydrophilic substrate and an
overlying oleophilic, radiation sensitive coating, which coating
cross links where exposed to radiation in a particular wavelength
range, and imagewise exposing the plate to radiation in that
particular wavelength range, thereby producing a pattern of cross
linked, highly cohesive oleophilic areas and less cohesive
oleophilic areas. The entire coating is then exposed to mechanical
force, thereby overcoming the adhesion of and completely dislodging
the unimaged areas from the substrate to form a printing plate
having an image pattern of cross linked, oleophilic areas of the
coating and hydrophilic areas of the substrate.
[0027] In yet another aspect, the invention is directed to a
printing process in which the imaged plates are developed on press,
including selecting a plate having a hydrophilic substrate and an
overlying oleophilic, radiation sensitive coating, which coating
cross links where exposed to radiation in a particular wavelength
range. The next step is imagewise exposing the plate to radiation
in that particular wavelength range, thereby producing a pattern of
highly cross linked, highly cohesive and highly adhesive oleophilic
areas and less cohesive and adhesive oleophilic areas. The plate is
mounted on a lithographic printing press cylinder or roll in
opposition to an ink cylinder or roll and a blanket roll. Contact
of the inked coating with the blanket pulls the ink and less
adhesive areas from the plate to form a printing plate having an
image pattern of highly cross linked, highly adhesive oleophilic
areas of the coating and hydrophilic areas of the substrate.
[0028] In a preferred embodiment, the plate is imaged and then
passed through a processor in which a high pressure stream of
neutral water with optional brush mechanically removes the non
imaged areas to achieve accurate pixels densities from about 1%
highlights to at least about 95% shadows. The plate is then mounted
on press and the combination of ink and blanket roll mechanically
cleans out the remaining non imaged areas to achieve accurate
shadow densities approaching 99%. The coating removed in the
processor is in the form of particles, which are filtered and the
water recycled in the spray.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 schematically shows a printing system comprising
plate stack, imager, and press;
[0030] FIG. 2 is a schematic plate cross section showing an
imageable coating directly supported on a substrate;
[0031] FIG. 3 is a schematic plate cross section showing an
imageable plate with a subcoat and top coat;
[0032] FIG. 4 is a schematic plate cross section upon exposure to
radiation;
[0033] FIG. 5 is a schematic of on-press development of an imaged
plate;
[0034] FIG. 6 is a schematic plate cross section showing the
pattern of remaining oleophilic imaged areas of the coating and the
hydrophilic substrate surface areas where the unimaged areas have
been removed in solidus;
[0035] FIG. 7 is a schematic of one embodiment of a pre-press water
processor;
[0036] FIG. 8 is a schematic representation of the interface
between the imaged plate and the blanket roll during development
on-press;
[0037] FIG. 9 is a schematic representation of the interface
between the imaged plate and the blanket roll as the roll pulls off
the unimaged areas during development on-press;
[0038] FIG. 10 is a schematic representation of the interface
between the blanket roll and the printable media as the ink and
unimaged material is transferred to a waste leader during
development on-press; and
[0039] FIG. 11 is a matrix showing the relationships of the
adhesion and cohesion among the unimaged coating, imaged coating,
substrate, ink, ink roll, blanket roll, and printable media during
the on press development represented in FIGS. 8-10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Printing Press Process
[0040] FIG. 1 shows a schematic of a printing plant 10, such as for
newspaper printing, in which a stack of radiation imageable plates
12 is situated upstream of an imager 14, where the coating on the
plates is selectively highly cross linked by selective exposure to
radiation to form a pattern of highly cohesive and adhesive areas,
and areas that exhibit less cohesion and adhesion. The plate
substrate is hydrophilic, whereas the coating is oleophilic. The
radiation exposure produces high internal cohesion, and high
adhesion to the plate. In a conventional negative working system,
the original (unimaged) coating is soluble in a specified developer
solvent, so the imaged plate must be developed with such solvent to
remove the non-exposed areas and thus produce a plate usable in the
press. The developer solutions most frequently used contain either
some amount of an organic solvent (typically benzyl alcohol) or
have an elevated pH (alkaline).
[0041] Unlike conventional systems, the present invention delivers
the imaged plates directly from the imager 14 to the press 16,
wherein contact with the ink form roll 20 and blanket roll (not
shown) remove the non-image areas. In another embodiment fountain
fluid 18 may also be employed 20. The unimaged coating material is
quickly dislodged to reveal areas of the underlying substrate,
which have an affinity for fountain fluid, and the retained imaged
areas, which have an affinity for ink. Once developed in this
manner, the resulting printing plates can be run in the
conventional fashion to produce the printed product, which is
output at 22.
[0042] As an optional configuration, the imaged plates may be sent
to a processing station 24, where no special treatment is required
other than contact with a spray of pH neutral water (e.g., tap
water). A preferred spray can be achieved with a nozzle pressure
over about 1000 psi, but if accompanied by brushing or similar
wiping action the water pressure can be lower. This wiping can be
achieved as part of or immediately after the water processing at
24. The plates can then be dried and stacked, before a fully or
substantially fully processed plate is sent to the press 16.
[0043] The most evident advantages of the foregoing process, are
that no separate developing equipment or step is required between
the imager 14 and the press 16, and no resin is dissolved or
dispersed into the process water. Rather, all or most of this
coating detaches from the substrate in sufficiently large pieces
that can be readily removed by filtration and relatively easily
disposed of.
Imageable Plate
[0044] FIGS. 2-6 illustrate schematically, the physical attributes
of a plate according to the present invention. FIG. 2 is a
schematic section view of the basic embodiment 26, consisting of a
substrate or carrier S on which an organic, non-aqueous
solvent-based coating C has been applied and dried. The substrate S
is preferably a grained, anodized aluminum sheet. The substrate is
preferably post treated with a hydrophilizing agent prior to
coating. Such post treatments are well known in the art, and
include silicate solutions, polyvinylphosphonic acid (PVPA) or
amino trimethylenephosphonic acid (ATMPA). The coating C is applied
from a solvent soluble composition comprising one or more
components capable of cross linking by free radical polymerization.
The polymerization arises as a result of imaging with ultraviolet,
visible or infrared radiation. As such, the coating may further
comprise radiation absorbers and/or initiators to facilitate the
cross linking efficiency. None of these active components is
soluble in water. Preferred coating compositions further comprise a
polymeric material to enhance the oleophilicity and durability of
the coating in the ink receptive printing areas.
[0045] FIG. 3 is a schematic section view of a plate according to
an alternative embodiment where a subcoat SC has been applied to
the substrate S, the imageable coating C is applied over the
subcoat, and a topcoat TC is applied over the imageable coating.
The top coat TC is typically a water soluble film forming layer
such as polyvinyl alcohol (PVOH) that serves to prevent atmospheric
oxygen from diffusing into the coating and quenching the free
radicals. Without the topcoat, the polymerization efficiency is
dramatically decreased. The subcoat SC is a water soluble material
that facilitates the release of the coating from the substrate in
the unimaged areas. The subcoat SC must not adversely impact the
adhesion of the coating to the substrate in the imaged areas of the
coating. 4-hydroxybenzene sulfonic acid, sodium salt has been found
to be particularly suitable as a subcoat.
[0046] FIG. 4 corresponds to FIG. 2, and illustrates the effect on
the coating of exposure to imaging radiation. The radiation source
is preferably a digitally controlled laser, which produces exposure
pixels such that a pattern of unexposed coating 38a, 30b, and 30c
and exposed coating 32a and 32b covers substantially all of the
plate. However, any of the sources of incident imaging radiation
used in the art to form selectively written surfaces can be used.
The selective imaging results in relatively distinct boundaries 34
at the interface between the imaged and unimaged areas. It should
be appreciated that the Figures are not to scale, especially as to
relative thickness of the coating and substrate, but are merely
illustrative. For the illustrated negative working plate, the
exposed coating in areas 32a, 32b becomes highly cross linked,
thereby creating areas that have sufficient cohesion and adhesion
such that they are not removable by subjecting these areas to
substantial mechanical forces or pressure. The unexposed areas 30a,
30b, and 30c retain the original characteristics and properties of
the dried coating before imaging. This material is not highly cross
linked, and lacks the adhesion to withstand substantial mechanical
forces or pressure.
[0047] FIG. 5 illustrates the context of development on press 100.
The imaged plate 102 has been mounted to a plate cylinder 104 in
contact opposition to an ink form roll 106 and a blanket roll 108.
The ink roll is generally made of rubber and the ink is generally
supplied to the ink roll from a source 110 as an emulsion of water
in a continuous ink medium. A fountain fluid distributor 112 is
provided for the plate cylinder 104 and a rubber roll 114 is in
opposition to the blanket roll 108.
[0048] During normal printing with a developed printing plate, ink
is applied to the rotating plate 102 and it immediately splits,
with the ink portion attracted to the oleophilic areas and the
water portion attracted to the hydrophilic areas. Fountain fluid is
deposited on the upper portion of the plate 102, to further assure
that the ink portion and water find the oleophilic and hydrophilic
areas, respectively, thereby defining the image pattern of ink to
be printed on the target medium (e.g., paper). This pattern of ink
is first transferred to the blanket 108, which transfers the ink to
the paper 116 as the paper passes between the blanket 108 and the
opposed rubber roll 114.
[0049] With the present invention, after a new plate 102 is mounted
on the plate cylinder 104, the plate cylinder is rotated and the
ink form roll 106 is activated, without activation of the fountain
fluid supply 112. A film of ink emulsion arises between the ink
roll cylinder 106 and the entire surface of the plate 102. The
continuous ink medium adheres to the entire (oleophilic) surface of
the plate, exhibiting sufficient cohesion and adhesion to detach
the ink from the ink roll 106. However, the adhesion of the
unimaged areas of the plate 102 to the substrate is so low that the
blanket 108 pulls the unimaged areas off the substrate, as
frangible particles. Thus, the mechanical removal forces are
applied by the blanket roll puling ink and unimaged coating
material adhered to the ink, off the substrate. For this to occur,
in the unimaged areas the adhesion (tack) and cohesion of the ink
exceed both the cohesion of the coating and its adhesion to the
substrate, and the adhesion of the ink to the blanket exceeds the
adhesion of the unimaged areas to the substrate. These particles
are transferred by the blanket roll 108 to the paper 116. As with
conventional startup of a newly installed plate, a paper leader or
sacrificial paper sheets are passed through the press during up to
a few hundred startup revolutions of the plate roll 104. With the
present invention, these startup revolutions completely remove the
non-image areas, with all of the removed coating material
transferred to the sacrificial sheets 116. These can be disposed of
as solid waste, without chemical treatment. After startup, the
fountain supply 112 is activated and normal printing begins on the
developed plate.
[0050] FIG. 6 shows a portion the resulting plate 26 (flattened for
convenience) ready for production runs with areas 32a and 32b
representing the oleophilic coating areas that pick up ink and 42a,
42b, and 42c representing the hydrophilic substrate surfaces that
carry the fountain fluid. It is to be understood that the plates
and process described herein are essentially planographic and, as
noted above, the relative thickness of the areas and surfaces shown
in the figures should not be considered as in scale.
[0051] FIG. 7 is a schematic of the operative components of one
possible processor 200 for the pre-press water development of an
imaged plate in a system as depicted in FIG. 1 (where the water
processor is indicated at 24). The imaged plate 202 is conveyed
over a basin or tank 204 onto a platen 206 or the like. A high
pressure spray 208 impinges on the plate surface and mechanically
removes the unimaged areas from the substrate, as particles. This
removal can be facilitated by the use of hot water in the spray. A
rotary brush 210 in combination with water at any pressure or flow
rate can provide all or additional impingement on the coating
surface. The overflowing water with removed particles is captured
in the basin or sump 204 and continuously drained and delivered via
line 212 to particle filter 214. The filtered water is recirculated
back to the spray nozzle 218 by pump 216 and return line 218. The
resinous material removed as particles is trapped in the filter, so
there is little or no chemical treatment required of the waste
stream associated with developing the plate.
[0052] One significant advantage arising from the present invention
is that the unimaged areas of the plate have less tendency to
retain ink receptive coating residue than on a conventionally
developed plate. With conventional development, the coating must be
completely dissolved and removed in the developing step. It is
sometimes problematic to ensure that all coating is removed from
the interstices of the substrate grain. Any residual will remain
during the printing process and cause some level of ink pick-up in
the background. With the present invention, the coating in the
background areas is non-ionically and only mildly adhered to the
substrate, so is fully removable. In any event, even a residual of
coating material will be removed soon after printing start-up,
resulting in a cleaner background.
[0053] Another significant advantage of the present invention is
that the integrity of the imaged coating is not adversely affected
by the processing liquid, i.e., water or fountain fluid. For
conventional plates, the imaging process causes a change in the
solubility of the coating in the developer. The change is never
100% efficient; that is, even the imaged coating will have some
level of solubility in the developer. This residual solubility may
significantly alter the adhesive and/or cohesive integrity of the
coating. The present invention does not suffer from this
problem.
Coating of Representative Embodiment
[0054] In one particular embodiment of the invention having the
basic configuration shown in FIG. 2, the coating comprises from
about 5 to about 30 wt % based on solids content, of a polymer that
is generally considered by practitioners of applied chemistry, as
insoluble in water. The polymer material may be selected from a
wide range of types such as but not limited to acrylates,
siloxanes, and styrene maleic anhydrides.
[0055] Advantageously, the coating comprises from about 35 to about
75 wt % based on solids content, of a polymerizable monomer, a
polymerizable oligomer, or combination thereof that is similarly
insoluble in water. Some suitable radically polymerizable (cross
linkable) materials are a multifunctional acrylate such as Sartomer
399 and Sartomer 295 commercially available from Sartomer Co.
[0056] The coating comprises a non-water-soluble initiator system
capable of initiating a polymerization reaction upon exposure to
imaging radiation. Some suitable initiator systems comprise a free
radical generator such as a triazine or an onium salt.
[0057] Optionally but not necessarily, the coating comprises from
about 5 to about 15 wt % based on solids content of a "stabilizer"
that is soluble in organic solvents and only partially soluble in
water. This option may be used when the plates are developed with
water pre-press, especially if no brushing is performed. Some
suitable stabilizers include a substituted aromatic compound, such
as DTTDA (an allyl amide derived from tartaric acid) and tetra
methyl tartaramide. The water solubility must not be so great as to
overcome the hardening of the imaged areas and compromise the
ability of these areas to remain on the plate in the presence a
high pressure water spray. The water solubility should be
sufficient to facilitate the penetration of water through the
unimaged areas.
[0058] Additional optional components include dyes that absorb the
imaging radiation (e.g. infrared absorbing dyes) and pigments or
dyes that serve as colorants in the coating.
[0059] The coating advantageously comprises a "release agent" such
as 4-hydroxybenzene sulfonic acid, sodium salt 4-HBSA,
4-hydroxybenzoic acid or sodium benzoate. In a different embodiment
the release agent is disposed as a sub-coating between the
hydrophilic substrate and the imageable coating.
EXAMPLES
[0060] In a first trial at a commercial newspaper printing
facility, a negative working, photopolymerizable plate was imaged
with IR radiation at 90 mj/cm.sup.2 and developed on press during
startup as described above, then used in the normal manner to print
over 100,000 high quality newspaper sheets. The plate was
constituted as follows:
[0061] (a) grained, hydrophilized aluminum substrate
[0062] (b) imageable coating comprising the raw materials [0063]
(i) organic solvent [0064] (ii) polyvinyl butyral polymer resin
[0065] (iii) penta functional acrylate monomer [0066] (iv) pigment
dispersion [0067] (v) stabilizer [0068] (vi) IR dye [0069] (vii)
organo-borate catalyst [0070] (vii) onium salt catalyst [0071]
(viii) partially water soluble additive (DTTDA)
[0072] (c) PVOH topcoat
[0073] After thermal imaging, the plate was post-heated. It is
believed this step produces further cross linking in the imaged
areas but not in the unimaged areas. After cooling, the topcoat was
washed off with tap water. Several hours after the topcoat was
removed, the plate was mounted on the plate cylinder of a
commercial newspaper printing press, with standard news paper, ink
roll, blanket roll and rubber roll set up. During startup only the
ink roll was active, and the plate was developed and background
areas satisfactorily cleaned out within about 300 revolutions of
the plate cylinder.
[0074] Another trial press run was made with a plate that was
identical to that of the first run, except for the omission of the
partially water soluble organic compound (DTTDA). The results
showed no significant difference.
[0075] These trials support the conclusion that unimaged areas can
be cleaned out on press corresponding to print dot (pixel) density
targets between 0 percent to at least about 98 percent, and most
likely at least 99 percent.
[0076] If the plates are developed off-press with water and
brushing or other devise that impinges or impacts, the targets are
achieved between about 0 percent to about 97 percent. The remaining
unimaged coating is not a thin layer, but rather in the form of
small clumps that cling to the substrate at the corners of certain
imaged letters, numbers, and symbols. This remaining material is
cleaned out with the ink roll onto the blanket and paper on
press.
[0077] FIGS. 8-11 disclose in greater detail the manner in which
the unimaged coating is removed from the substrate (i.e., the plate
is "developed") on press. FIG. 8 is a schematic representation of
the interface between the imaged plate and the blanket roll during
development; FIG. 9 is a schematic representation of the interface
between the imaged plate and the separating blanket roll during
development; FIG. 10 is a schematic representation of the transfer
of ink and unimaged coating from the blanket roll to the printable
media; and FIG. 11 is a matrix showing the relationships of the
adhesion and cohesion among the unimaged coating, imaged coating,
substrate, ink, ink roll, blanket roll, and printable media during
the on press development represented in FIGS. 8-10. In these
Figures, arrows with alphanumeric identifiers point to either the
inside of a given material (to indicate cohesion) or to the
interface between two materials (to indicate adhesion). "A"
indicates adhesion and "C" indicates cohesion.
[0078] FIG. 11 shows the desired relationships among the adhesions
and cohesions, to be understood by first selecting an A or C entry
in the first column and then finding its relationship to another A
or C at the intersection of the row of the first selection and the
column of the other A or C. For example, C1 is greater than A1 and
C1 is less than A3 (which is equivalent to A1 less than C1 and A3
greater than C1).
[0079] FIG. 8 shows the condition on press, after the ink has been
applied to the imaged plate and the inked plate has been rotated
into contact with the blanket. Whether pure ink or an emulsion of
water in pure ink was applied (collectively, "ink"), the ink
adheres to the entire coating, because at this point the entire
coating is oleophilic.
[0080] FIG. 9 shows a subsequent point in time, at which the imaged
plate on the plate cylinder is separating from contact with the
blanket. In the unimaged regions the tack and cohesion of the ink
exceeds the adhesion of the coating to the substrate, and the
cohesion of the coating exceeds its adhesion to the substrate. The
split in the unimaged regions occurs between the coating and the
substrate. The unimaged regions are removed in solidus from the
substrate along with the overlying ink, while attached to the
surface of the ink and without dispersing into the ink. No
dissolution of the coating should occur or the split would take
place within the coating and leave some coating on the substrate.
In the imaged regions, the adhesion of the coating to the substrate
and its cohesion exceed the cohesion of the ink, thus causing the
ink to split within itself, such that some ink remains on the
imaged regions of the coating and some remains on the blanket.
[0081] FIG. 10 depicts the interaction of the blanket after
separation from the plate, with the sacrificial paper or leader on
which the removed coating material is transferred for disposal. The
ink and attached particles of unimaged coating preferentially
adhere to the paper, which goes to waste disposal. The area of the
blanket where such transfer occurred is returned into contact with
the plate as depicted in FIG. 8. This is repeated until all the
unimaged coating has been removed from the entire plate, thus
"developing" the plate. The developed plate has a pattern of areas
of hardened, oleophilic coating material and hydrophilic substrate,
which are compatible with conventional wet lithographic printing
presses.
[0082] It should be appreciated that whether development is fully
or partially implemented pre-press or on-press, the coating is not
dispersible in water (or equivalent fountain solution) or ink,
i.e., the mere immersion of the coating in water pre-press or in
fountain solution or ink on-press, does not produce a suspension or
solution of coating material in the water, fountain, or ink. Only
after the application of mechanical force (with or without the
presence of water or ink) do particles of unimaged coating release
from the substrate.
[0083] If development is undertaken in a two step embodiment,
whereby approximately 95% or more of the unimaged coating is
removed by high pressure water spray or water deposition with
brushes upstream of the press and the residual unimaged coating is
removed by the tack of the ink on press, the particles are
initially removed as a result of active disturbance. Relatively
large particles are dislodged from the substrate, and are carried
away from the plate surface by the flow of water. However, the
particles do not distribute or mix in the water flow, but rather
are merely swept away such that any water with entrained particles
drawn from such flow into a vessel will separate as by settling at
the bottom of the vessel or floating. The residual unimaged coating
removed on-press by the ink and blanket in the second step remains
adhered to the surface of the ink during removal from the substrate
and transfer to the blanket and sacrificial leader paper, without
any dispersion.
[0084] To the extent the particles entrained in the flow are to be
filtered for reuse of the water, it is preferred that such flow be
agitated (as by pumping) to thereby temporarily disperse the
particles so that they can be more uniformly filtered across the
full cross section of the filtering means.
[0085] Thus, the mechanical forces imparted by or during contact
with a fluid such as water, fountain solution or ink, disrupt and
remove only the unimaged areas of the coating from the substrate
surface in the form of undissolved particulate material, without
dispersing the unimaged areas of the coating into the fluid at the
substrate surface as a mechanism of removal from the substrate. The
fluid can be the agent by which the coating material removed from
the surface of the substrate is transferred from the plate to
another operation, such as a filter in the first step or the
blanket of the second step.
[0086] With the pre-press developing embodiment, the brushes remove
the coating whereas the water is merely a flushing agent to carry
away the removed solid particles. Water alone (without high
pressure spray) cannot remove the unimaged coating. For the few
seconds in which the plate is immersed in water before being
subjected to the brushes, there may be an infinitesimal or
negligible undercutting via interstitial seepage, but the water
cannot be considered a significant factor in the coating removal.
The coating could be removed by the brushes alone but for
convenience the brushes are in the water environment for the
desired flushing action. With pre-press development, the brushes
are relatively coarse and that is why some non-imaged material
remains on the plate, which material is later removed on press via
the tack of the ink. This does not imply that the tack of the ink
must apply a greater force than the brushes.
[0087] In newspaper presses, it is customary that the ink roll is
dropped first before water or fountain is initiated, to assure that
the paper remains relatively dry and does not tear as a result of
too much moisture. However, if fountain or water is sprayed on the
undeveloped plate or on the ink roll, on-press development will not
occur via interaction with the water or fountain. Rather, on-press
development occurs via the ink having been applied to the plate
such that the tack of the ink in contact with the blanket pulls the
unimaged material off the plate. There cannot be simple water or
fountain development on press without the ink roll on the plate. It
should be understood that the term "ink" is used herein according
to the conventional meaning when discussing lithographic printing,
whereby the ink is typically an emulsion of water entrained in a
continuous ink phase. Reference herein to the "tack" or "adhesion"
of the ink encompasses pure ink and such ink emulsion.
[0088] In a facility where the development is on press, a pre-press
water/brush station or localized steam discharge may desirably be
adapted to process only an edge or corners of the plate where
reference numbers or markers were imaged. The pre-press step will
reveal the markers to the press operator for confirmation that the
correct plate is to be mounted and properly aligned in the press.
Preferably the entire plate includes a top coat of a water soluble
oxygen barrier as well as at least one imaged region of the coating
defining a latent reference mark at a margin of the plate. After
imaging of the plate, the topcoat is washed off with water and the
unimaged areas of only the margin are removed with water to reveal
the reference mark before subjecting the remaining coating to
mechanical forces development forces on press.
Coating Chemistry Including Enhancement for Water Penetration
[0089] The following tables contain descriptions of the coating
constituents and variations in the percentage content, associated
with multiple examples in which the coating contained a
non-photosensitive, solvent soluble, organic compound that is
partially soluble in water. The imaged plates were developed by
immersion in water and then wiped with a cloth. Although these
tests were not performed in a system as depicted in FIGS. 1 and 5
with only mechanical force as the developing agent, the effects of
varying the ingredients in a laboratory are believed applicable for
optimizing performance in a production setting where mechanical
force is proved by a high pressure spray. It should be appreciated,
however, that with development according to the invention in a
water spray processor or on press, there would be much less
tendency of redeposition of removed coating material as reported
for some tests.
[0090] In each instance, the plates were prepared in a conventional
manner in a laboratory, with conventional coating weight of 100
mg/sq.ft., drawn down with a wire wound stainless steel rod, and
dried for two minutes at 90.degree. C. All plates had a topcoat of
PVOH at 140 mg/sq.ft. All plates having triazine were imageable
with UV, and all plates with a dye sensitive to 830 nm light
source, such as the KF-1151, were imageable with IR. The results
reported with each table are based on conventional IR imaging at
about 90-100 mj/sq.cm. A dash in a column indicates that the wt %
value is the same as the entry in the previous column of the same
row.
[0091] If the plates are to be processed in a dedicated station
upstream of the press by immersion in water and a wiping action
milder than what a plate experiences on-press, the coating could be
augmented by a release agent, as shown in Table 1.
[0092] Table 2 shows that for a given polymer (Clar. Poly 123) and
monomer (Sartomer 399) combination, the relative weight percent is
a significant variable. Ratios of monomer to polymer in the range
of at least about 1:1 to about 5:1, preferably about 2:1 to about
4:1 are likely to work well, given that the ratio of 0.5:1 (Plate
#4) produced only fair results, the ratio of 4:1 (Plate #3)
produced excellent results, and the ratio of about 9:1 (Plate #2)
produced only fair results.
[0093] Table 3 shows the result that satisfactory plates can be
made from polymer resins that do not necessarily have a reaction to
radiation exposure. The coatings of Plates #1 and #3 have reactive
resins that produced good results, and the coatings of Plates #4
and #5 have non-reactive resins that produced good to fair results.
The potential for use of non-reactive resins opens the door for use
of resins having a much higher molecular weight than presently used
resins.
[0094] Table 4 demonstrates that not all monomers at a given weight
percent of the coating, produce equivalent results, with some
producing poor results. Similarly, Table 5 demonstrates that
potential stabilizers other than DTTDA that are soluble in the
non-aqueous solution and are partially soluble in water, do not
necessarily produce satisfactory results.
[0095] Table 6 demonstrates that potential release agents other
than 4-HBSA that are fully soluble in both non-aqueous solutions
and water can be successfully utilized.
[0096] Table 7 demonstrates that a coating that is sensitive to
both UV and IR radiation can be successfully imaged and processed
in water according to the invention.
[0097] Table 8 demonstrates that good results do not depend on use
of only one kind of initiator.
[0098] Table 9 shows that the use of coinitiator compounds and/or
post-imaging heating, can improve the performance of the
plates.
[0099] In Table 9 the organo-borate compound is P3B, made by Showa
Denko K.K., headquartered in Tokyo, Japan. The P3B can be used as
the sole initiator. It is believed that used individually, the
listed initiators would rank from strongest to weakest as Diphenyl
Iodonium hexaflouro phosphate, Triazine AC, and P3B. The reason for
using a coinitiator system rather then increasing a single
initiator is that there is a synergistic effect between the
organo-borate and either the triazine or onium catalyst. Given a
fixed amount of energy the initiators individually (at their
optimum level) will only produce a certain amount of free radicals.
However, when the organo-borate is combined with one of the other
catalysts, free radicals are generated at a faster rate by the
triazine or onium catalyst while free radicals are still generated
(at a normal rate) from the organo-borate. Therefore the efficiency
of the system is increased in both rate and population. By using
this combination, a much higher degree of cross-linking is
realized, which improves both adhesion and cohesion of the image.
With an increase in adhesion and cohesion, an increased amount of
release agent can be used, thereby providing for better
development.
[0100] Depending on the type of equipment used for the post-imaging
thermal enhancement, a different range of times and temperatures
should be used. With a convection oven, both the temperature and
dwell time are greater than with a small preheat oven unit (where
the plate comes in direct contact with the heating element). As a
rough guide, 200 deg. F. at 1 minute in a convection oven has
approximately the same effect as 175 deg. F. for 7 seconds in a
preheat oven. With a typical commercially available preheat unit,
the window would be 175 to 250 deg. F. for a time period of 5 to 15
seconds.
[0101] Tests were also run on the six formulations shown in Table
9, for comparison of UV versus IR exposures. Previous formulations
which did not contain the organo-borate co-initiator system were UV
sensitive only when they contained the Triazine AC. The onium salt
by itself was not UV sensitive. Incorporating the organo-borate
into the formulation rendered the formulations that contained the
onium salt UV sensitive. All six of the formulations that contained
the co-initiator system produced a good image when exposed to
either IR or UV. In order to simplify the testing formulation #5
was chosen for testing in UV exposures.
[0102] Using an Ugra scale for comparison, plates were exposed for
250, 125 and 62.5 mjs. The plates were then developed through a
water bath with two molleton socks at 4 feet per minute at 75
degrees F. The resulting step wedges were 250 mj--solid 9 steps
with 2 gray steps to a total of 11, 125 mj--solid 7 steps with 2
gray steps to a total of 9 and 62.5 mj--solid 5 steps with 2 gray
steps to a total of 7. All of the images from the different
exposures exhibited very good solvent resistance. The best
resolution that was received was at 62.5 mjs, which yielded an open
15 micron line target and good screen values from 2% to 99%.
TABLE-US-00001 TABLE 1 Coating Compositions With Partially Water
Soluble Stabilizer As the Significant Variable 4-Hydroxy B S A and
DTTDA #1 #2 #3 #4 #5 #6 Meth. Prop. .sup.(a) 92.39% 91.99% 92.27%
91.77% 91.77% 91.77% Sartomer 399 .sup.(b) 2.31% 2.31% 2.31% 2.31%
2.31% 2.31% Clariant Poly 123 .sup.(c) 0.46% 0.46% 0.46% 0.46%
0.46% 0.46% Triazine AC .sup.(d) 0.45% 0.45% 0.45% 0.45% 0.45%
0.45% DTTDA .sup.(e) 0.00% 0.40% 0.00% 0.40% 0.52% 0.00% 4-HBSA
.sup.(f) 0.00% 0.00% 0.12% 0.12% 0.00% 0.52% KF-1151 .sup.(g) 0.05%
0.05% 0.05% 0.05% 0.05% 0.05% Pigment Disp. .sup.(h) 4.34% 4.34%
4.34% 4.34% 4.34% 4.34% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
.sup.(a) Solvent (1-Methoxy-2-Propanol, Propylene Glycol Methyl
Ether available from Arco Chemical Company) .sup.(b) Monomer
(Dipentaerythritol Monohydroxypentaacrylate available from Sartomer
Company, West Chester, Penn.) .sup.(c) Polymer .sup.(d) Initiator
.sup.(e) Stabilizer .sup.(f) Release Agent .sup.(g) Dye .sup.(h)
Pigment RESULTS #1 Plate would not develop #2 Plate showed slight
signs of development #3 Plate had partial development with heavy
redeposition #4 Plate developed very easily producing an image with
good adhesion, good dot reproduction and a clean background. #5
Plate did not develop any better than plate #2 #6 Plate developed
in a very non uniform way yielding a weak image and
redeposition
TABLE-US-00002 TABLE 2 Coating Compositions With Monomer/Polymer
Ratio as the Significant Variable Monomer/Polymer Ratio #1 #2 #3 #4
#5 #6 Meth. Prop. 92.39% -- -- -- -- -- Sartomer 399 2.77% 2.49%
2.21% 1.85% 0.92% 0.00% Clar. Poly 123 0.00% 0.28% 0.56% 0.92%
1.85% 2.77% Triazine AC 0.45% -- -- -- -- -- DTTDA 0.40% -- -- --
-- -- 4-HBSA 0.12% -- -- -- -- -- KF-1151 0.05% -- -- -- -- --
Pigment Disp. 4.34% -- -- -- -- -- 100.0 100.0 100.0 100.0 100.0
100.0 Results: #1 Plate produced a good image but the plate was
easily over developed. The coating was slow in speed and had poor
adhesion to the substrate. #2 Produced a better image than #1 with
faster speed but it was still easy to over develop but with better
adhesion. #3 Produced a strong image with good adhesion. The
coating developed very easily with good dot reproduction and clean
background. #4 Produced a very strong image with great adhesion.
The coating was more difficult than #3 to develop but had good dot
reproduction and a clean background. There was also some evidence
of redeposition. #5 Plate showed only very slight development. #6
Plate had no development.
TABLE-US-00003 TABLE 3 Coating Compositions With Radiation
Sensitive Resin As the Significant Variable Reactive and Non
Reactive Resins #1 #2 #3 #4 #5 #6 Meth. Prop. 92.39% -- -- -- -- --
Sartomer 399 2.21% -- -- -- -- -- Triazine AC 0.45% -- -- -- -- --
DTTDA 0.40% -- -- -- -- -- 4-HBSA 0.12% -- -- -- -- -- KF-1151
0.05% -- -- -- -- -- Pigment Disp. 4.34% -- -- -- -- -- Clar. Poly
123 0.56% -- -- -- -- -- Jaylink 106 -- 0.56% -- -- -- -- NK-P1002
-- -- 0.56% -- -- -- Dow Corning 62230 -- -- -- 0.56% -- --
Sartomer PRO5542 -- -- -- -- 0.56% -- 4-vinylphenol/MMac. -- -- --
-- -- 0.56% 100.0 100.0 100.0 100.0 100.0 100.0 Results: #1
Produced an image with good dot reproduction and adhesion along
with a clean background. Coating was easy to develop. #2 Coating
was difficult to develop and produced a broken image with poor
adhesion. The background of the plate was clean. #3 The coating was
slightly more difficult to develop then #1 but produced an image
with good adhesion but significant coating re-deposited on the
image. The background area of the plate was clean. #4 This resin
(non photo reactive) produced a coating that was easy to develop.
The image had good dot reproduction and good adhesion. The image
was prone to over development. The background areas of the plate
were clean. #5 This resin (non photo reactive) produced a coating
that was easy to develop without being over sensitive. The image
had good dot reproduction and good adhesion. The background areas
of the plate were clean. #6 This resin (non photo reactive)
produced a coating that was very difficult to develop. Could not
get good dot reproduction or a clean background.
TABLE-US-00004 TABLE 4 Coating Compositions With Monomer Type as
the Significant Variable Monomers #1 #2 #3 #4 #5 #6 Meth. Prop.
92.39% -- -- -- -- -- Clar. Poly 123 0.28% -- -- -- -- -- Triazine
AC 0.45% -- -- -- -- -- DTTDA 0.40% -- -- -- -- -- 4-HBSA 0.12% --
-- -- -- -- KF-1151 0.05% -- -- -- -- -- Pigment Disp. 4.34% -- --
-- -- -- SR-399 2.49% -- -- -- -- -- SR-454 -- 2.49% -- -- -- --
SR-350 -- -- 2.49% -- -- -- SR-295 -- -- -- 2.49% -- -- CD-580 --
-- -- -- 2.49% -- SR-348 -- -- -- -- -- 2.49% 100.0 100.0 100.0
100.0 100.0 100.0 Results: #1 (SR-399 Dipentaerythritol
Pentaacrylate) This monomer produced a coating that was easy to
develop. The image was strong with good dot reproduction and good
adhesion. The background area was very clean. The image was
slightly sensitive to overdevelopment. #2 (SR-454 Ethoxylated
Trimethylolpropane Triacrylate) This monomer produced a coating
that was very easy to develop but had a weak image and a dirty
background. #3 (SR-350 Trimethylolpropane Triacrylate) This monomer
produced a coating that was somewhat difficult to develop. The
resulting image was strong but with heavy retention in Background.
#4 (SR-295 Pentaerythritol Triacrylate and Tetraacrylate) This
Mixture of monomers produced a coating that was almost as As easy
as #1 to develop. The image was slightly weaker then#1 but the
background was clean. #5 (CD-580 Alkoxylated Cyclohexane Dimethanol
Diacrylate) This monomer produced a coating that did not develop.
#6 (SR-348 Ethoxylated Bisphenol A Dimethacrylate) This monomer
produced a coating that was very difficult to get any
development.
TABLE-US-00005 TABLE 5 Coating Compositions With DTTDA and other
Partially Soluble Stabilizers As the Significant Variable DTTDA and
Analogous Compounds #1 #2 #3 #4 #5 #6 Meth. Prop. 92.39 -- -- -- --
-- Sartomer 399 2.31 -- -- -- -- -- Clar. Poly 123 0.46 -- -- -- --
-- Triazine AC 0.45 -- -- -- -- -- 4-HBSA 0.12 -- -- -- -- --
KF-1151 0.05 -- -- -- -- -- Pigment Disp. 4.34 -- -- -- -- -- DTTDA
0.40 -- -- -- -- -- Dimethyl Tartrate -- 0.40 -- -- -- -- Di allyl
Maleate -- -- 0.40 -- -- -- Di allyl Succinate -- -- -- 0.40 -- --
Dimethyl Maleate -- -- -- -- 0.40 -- Tetra Methyl Tartaramide -- --
-- -- -- 0.40 100.0 100.0 100.0 100.0 100.0 100.0 Results: #1 Good
development, good image and clean background. #2 Hard to develop,
strong image and dirty background. #3 Very slight development. #4
No development #5 No development #6 As good as #1
TABLE-US-00006 TABLE 6 Coating Compositions With 4HBSA and Other
Soluble Release Agents As the Significant Variable 4-Hydroxy B.S.A.
and Analogous compounds #1 #2 #3 #4 Meth. Prop. 92.39 -- -- --
Sartomer 399 2.31 -- -- -- Clar. Poly 123 0.46 -- -- -- Triazine AC
0.45 -- -- -- DTTDA 0.40 -- -- -- KF-1151 0.05 -- -- -- Pigment
Disp. 4.34 -- -- -- 4-HBSA 0.12 -- -- -- Benzene Sul. Acid -- 0.12
-- -- 4-Hydroxy Benzoic Acid -- -- 0.12 -- Sodium Benzoate -- -- --
0.12 100.0 100.0 100.0 100.0 Results: #1) Control formula -
produced a coating that was easy to develop. The image was strong
and the background was clean. #2) The coating was not as easy to
develop but the image was strong and the background was somewhat
clean. #3) This material produced a coating that was as good or
better than the control. #4) This coating was equivalent to #2.
TABLE-US-00007 TABLE 7 Coating Compositions With Various Infrared
Sensitive Dyes As the Significant Variable Various 830 Dyes #1 #2
#3 #4 Meth. Prop. 92.39 -- -- -- Sartomer 399 2.31 -- -- -- Clar.
Poly 123 0.46 -- -- -- Triazine AC 0.45 -- -- -- DTTDA 0.40 -- --
-- 4-HBSA 0.12 -- -- -- Pigment Disp. 4.34 -- -- -- KF-1151 0.05 --
-- -- ADS-WS -- 0.05 -- -- Few Chem S0456 -- -- 0.05 -- Few Chem
S0306 -- -- -- 0.05 100.0 100.0 100.0 100.0 Results: #1) This is
the control coating which developed easily and produced a good
image and clean background. #2) This coating was equivalent to #1
except that the image was not quite as strong. #3) This coating
developed easily but did not produce any image. #4) This coating
developed easily but produced a very weak image.
[0103] Observation; Although not all of the coatings produced an
image in the IR all of them did produce strong images in the
UV.
TABLE-US-00008 [0103] TABLE 8 Coating Compositions With Triazine
vs. Onium Salts As the Significant Variable for Cross Linking
Initiators Initiators: Triazine Vs. Onium Salts #1 #2 #3 Meth.
Prop. 92.39 -- -- Sartomer 399 2.31 -- -- Clar. Poly 123 0.46 -- --
DTTDA 0.40 -- -- 4-HBSA 0.12 -- -- KF-1151 0.05 -- -- Pigment Disp.
4.34 -- -- Triazine AC 0.45 -- -- Diphenyl lod. PF6 -- 0.45 --
CD1012 -- -- 0.45 100.0 100.0 100.0 Results: #1) This is the
control formulation which was easy to develop and produced a strong
image with a clean background. #2) This formula (with
Diphenyliodonium Hexafluorophosphate) developed easier then the
control and still produced a strong image with a clean background.
#3) This formulation was slightly more difficult to develop than
the control. It produced a strong image but a slightly dirty
background. (Diaryliodonium Hexaflouroantimonate)
TABLE-US-00009 TABLE 9 Post-Imaging Thermal Enhancement and Coating
Compositions with Co-Initiators #1 #2 #3 #4 #5 #6 Meth. Prop.
91.87% 91.77% 91.25% 91.87% 91.77% 91.25% Sartomer 399 2.46% 2.46%
2.46% 2.46% 2.46% 2.46% Clar. Poly 123 0.31% 0.31% 0.31% 0.31%
0.31% 0.31% DTTDA 0.40% 0.40% 0.80% 0.40% 0.40% 0.80% 4-HBSA 0.12%
0.12% 0.24% 0.12% 0.12% 0.24% KF-1151 0.05% 0.05% 0.05% 0.05% 0.05%
0.05% Pigment Disp. 4.34% 4.34% 4.34% 4.34% 4.34% 4.34% Showa D.
3PB -- 0.10% 0.10% -- 0.10% 0.10% Triazine AC 0.45% 0.45% 0.45% --
-- -- Diphnly Iod. PF6 -- -- -- 0.45% 0.45% 0.45% Total 100.0 100.0
100.0 100.0 100.0 100.0 Results: #1a This is a control type coating
formula which developed easily and produced a good image and clean
background. The run length of this image was very susceptible to
press type and conditions. #1b Using the same coating formula the
plate was put through a pre-heat of 100 degrees C. for 1 minute
prior to being mounted on press. The plate still had good
development (slightly less then #1a) but had an image that was less
susceptible to the type of press and its condition. #2a This is the
control formulation but with the addition of a small amount of an
organo-borate compound (Showa D. 3PB) used as a co-initiator. This
plate took longer to develop than plates 1a or 1b but had a much
more durable image. This coating was much less sensitive to press
type or conditions and also had better run length than 1b. #2b
Using the same coating formula as 2a the plate was put through a
pre-heat of 100 degrees C. for 1 minute prior to being mounted on
press. The plate was slower to develop than 2a and although the
image was much tougher the background was not as clean causing the
plate to print with a background tone. #3a This coating was the
same as #2 but the amount of DTTDA and 4-HBSA was doubled, which
with the use of the organo-borate allowed the plate to have good
development characteristics along with a good image. This made it
easier to develop then 2a but it did not have as tough an image.
#3b This is coating 3a but the plate was exposed to a pre-heat of
100 degrees C. (for 1 minute) prior to being mounted on the press.
This plate had a very tough image but was slower to develop then 3a
and did not have a completely clean background. #4a This is the
same as formula #1 but the Triazine AC was replaced with the onium
salt Diphenyl Iodonium Hexa-Flouro Phosphate. This change not only
allowed the plate to develop faster on press but it also produced a
slightly better image then #1 with a good clean background. #4b
This is coating 4a except the plate was exposed to a pre-heat of
100 degrees C. for 1 minute prior to mounting on press. The plate
developed as fast as #1 having a strong image with good integrity.
The plate had a decent run but was still somewhat susceptible to
press conditions. #5a This is the same as coating 4a except for the
organo-borate. The plate produced from this coating was slower to
develop than plate 4a. It had a good image with a clean background.
#5b This is coating 5a with a preheat of 100 degrees C. for 1
minute prior to mounting on press. This coating developed at
approximately the same speed as 5a. The image was very strong with
good integrity but the background printed with a very slight tone.
#6a This is coating formula #5 with double the amount of the DTTDA
and 4-HBSA. These plates had a good roll up on press with a clean
background. The image was sound but not quite as strong as #5. #6b
These plates were coated with the formula of #6 but were exposed to
a pre-heat prior to being mounted on press. In the previous
pre-heat trials the plates could not exceed a temperature of 100
degrees C. without either losing a clean background or loss of
development altogether. With the increase in the developing aids
the plates were able to take a pre-heat of 120 degrees C. for 1
minute and still maintain good development with a strong image and
a clean background.
Coating Chemistry without Enhancement for Water Penetration
[0104] Although the Tables above were based on varying the
components of a composition which included a solvent soluble,
partially water soluble organic compound, the effects of these
variations are likely to be instructive for compositions without
such organic compound. It should be appreciated that a key aspect
of the embodiment without the partially water soluble organic
compound, is that the cohesion of the unimaged coating is greater
than the adhesion of the unimaged coating to the substrate. Some
compositions in the foregoing tables that show promise (because of
the efficacy of the partially soluble compound) may not be suitable
for this embodiment if the adhesion is not less than the cohesion,
however, one of ordinary skill in the art can readily select and
optimize many of the compositions in the Tables by omitting the
partially water soluble organic compound.
[0105] There are many types of resins, oligomers and monomers that
can be used to produce coatings that would have properties suitable
for use in the present invention. It is believed that the monomer
to polymer ratio in the range of 2-4 and the use of an
organo-borate catalyst with an onium salt catalyst are important
preferences. A wide mixture of functionalities can be used but
cured coatings with better adhesion and cohesion are achieved with
multi functional monomers and oligomers (functionality of 3 or
higher). It is not necessary to use a resin which contains
unsaturated groups but in the majority of the cases the cured film
will exhibit better adhesion and integrity. Types of resins can
include poly vinyls (poly vinyl acetate, poly vinyl butyral, etc),
cellulosic, epoxies, acrylics and others as long as the resin does
not produce a strong adhesive bond with the substrate. Monomers and
oligomers should be somewhat viscous liquids and can be
polyester/polyether, epoxy, urethane acrylates or methacrylates
(such as polyether acrylate, polyester acrylate, modified epoxy
acrylate, aliphatic urethane methacrylate, aliphatic urethane
acrylate oligomers, polyester acrylate oligomers, aromatic urethane
acrylate, dipentaerythritol pentaacrylate, pentaacrylate ester,
etc.).
* * * * *