Note: Descriptions are shown in the official language in which they were submitted.
CA 02225304 1997-12-19
METHOD AND APPARATUS FOR PRODUCING A
PRINTING IMAGE DISTRIBUTION
TECHNICAL FIELD
The invention relates to a method for producing an image on a
printing plate and, more particularly, to prod~lc.inp. such an image in a layer
ofthe plate comprisin~ therrn~lly activatable m~tPri~
BACKGROUND OF THE INVENTION
During the prod~Gti~)n of p.;,.l;~g forms, the pfinting and non-
g surface parts must be st~uctured in accordance with the
inform~tion to be printed Thus, it is known to convert therrn~lly
ch~n~e~ble coating applied to a base m~t~ri~l into oleophilic, ink-accepting
parts by he~ting the cOali~g using snit~ble means such as a laser beam.
15 The thprm~lly çh~ngeable coating m~tPri~l has hydrophilic properties.
r~ Li.lg forms work with a printing unit and can be of several types.
For eY~mr)le, the forms can be plates clamped onto a cylinder, which are
commonly used for off-set printing ~ltern~tively, they can be films in a
special prin*ng form image printing device or a sllrf~r,e of a m~r.hine
20 cylinder. In a flat bed lJ~ method using direct image 1~ e, a laser
is commonly used to write onto the printing forms. As a result of the input
of heat by means of the laser, a therm~lly activatable coating on the forms
has hydrophilic p~ Lies. It is converted or tr~nsformed from a
hydrophilic state to an oleophilic, ink-~ccepting state in response to heat
25 generated by applic~tion of the laser light to a spot-sized area (herein~ftPr the "image point").
The temperature applied to an image point ~n the therm~lly
activatable coating of a form must exceed a specific threshold value. This
means that the energy applied to the co~ting by the laser must locally
30 exceed a threshold value, which in tu~n generates thPrrn~l heat that raises
the temperature of the image point above an "image setting temperature."
This "image setting temperature" (e.g., 280 ~) must be exceede~l for a
predefined period of time such as one to two microseconds. The image
point is not set if this temperature versus time ch~racteristic is not
35 observed. This l~ )e,~ c versus time char~ct~ri~tic is pre~lçfined and
orient~l to the çh~nic~l and physical ~ropelLies of the th.~rm~lly
activatable m~teri~l
CA 02225304 1997-12-19
Writing printing forms by means of supplying heat is in this case
unable to structure the s~ce with respect to the informqtion to be printed
simply on the basis of a physical and/or chemir-q-l change to the coating
mqtçri~ql In this context, methods for image rrinting by means of thçrmql
5 abrasion are also known in which an image is created based on a point-by-
point energy input. Likewise, with a requirement that a limitin
lclll~e.dwc be excee~le~l for a ...i~ .. action time, removal of the
coqting mqterisl from the plate occurs, for example, by t~ ul~lion or by
restructuring of the plate caused by chqnges to the plate's volume.
In all of the methods described above for using laser rqdiqtion as a
source of heat energy to print images in a therm-q-lly açtivatable coating
m,qteriql the ~lclial must be heated to exceed a temp~"~lwc for a
predcle....i~-ed time interval. Depen~ling on the type of the image ~ -g
method and on the composition of the thPrm,q11y activatable coating
15 mstçri,ql relatively high laser powers must be employed. The lasers are
modlllqte~l to provide the ...i~-i...-~... time period required for he,q,tin~ each
image point, which has a negative effect on the mi.x;...l.... achievable speed
of writing precisely onto a large-format rrintin~ plate. In the case of this
thermql image y. ;..~ g method using laser radiation, however, it is not only
20 disadvqnt-q-geous to need high laser power that has to be mo~lnlq-te~l it is
also disadv~qntqgeous to require a high amount of thermql energy to be
applied to the plate. The higha the lcl~l)e.~lwe necessqry to set an image
in the thPrm~lly activatable coating, the greater the tempeMture dilrclcnce
between each image point and the region of the plate ~ullu~m~ling the point.
25 This large therm-ql gradient introduces stresses which can, for exqmple,
permqnently detach the coating and base m,q,teri,q,l or create deform~tions in
at least one of these two layers of mqtloriql~ It is also possible for a
specific type of thermqlly activatable coating m~teriql to have very good
th~rmql writing plOpcl ies but nevertheless be conci(lçred an lm~lesirable
30 image p~;..l;i-g mqt~i,q,l becq.~l~e it requires excessively high lcllll)clalulcs
that accentuate the p,~l~ms of mqtçri~l separation and/or deformation
caused by thermql stresses.
CA 02225304 1997-12-19
SUMMARY AND OB.TECTS OF THE INVENTION
The ~lilll&l~ aim of the present invention is, therefore, to provide a
method and a~ lus for producing a distributed prinhng image on a
thçrmfl1ly activated ~ul~ lt; in such a way that the above-mentioned
5 disadv~nt~es are avoided and reliable stmctnring of the base and coating
m~tçriflls for a p~ g pl~te or form are re~ ed
The invention is based on direct im~ing processes and a device for
direct im~ging using the1m~l activatedlconvertible m~tçrial i.e. l";~
plates or printin~ molds, having a co~ting that can be altered at an image
10 point by applying therm~l energy in a m~nner described hereinfl~çr.
According to the invention, the thPrm~l gradient around an image
point fixed by thermfll action is red~lced by he~ting the region around the
point to an intermediate temp~alule below the temperature for f~xing or
setting the image point. By hPating the region ~ ullding the image point
15 to be set, the re-lnGed th~prmal gradient mitig~tes the separation and
deform~tion problems that plague the prior art approaches. Preferably, the
invention employs a two-stage heflting action on the mfltPri~l to be printed
First, the therm~l mfltPrifll of the plate or prinhng form is prehe~ted to a
lel-l~)el~ e below the process l~mp~lalule for setting or fixing an image
20 point. Second, the image is generated on a point-by-point basis by hç~ting
the plate using a modnl~ted laser beam in keeping with the required
lelll~)el~Lule and time profile for setting each of the image points.
The prehç~ting of the region around the image point to be set or
fixed can be the entire plate or printing form. In this case, the entire
25 printing plate or printin~ form is heated and ~ ed at a le",~ alu~e
below the limitin~ or process lell~ luLe envisioned for the image printing
process. This preh~ting can be performed, for exflmple, by an electric
he~ting device that is constructed as an oven for the plate.
In an ~ltçrnfltive approach for practicing the invention, a small
30 region immediately ~ uu~ding the image point is hç~ted This local
prehçflting of the plate or printing form can also be pe.ro....ed by an
electrical h~flting element~ using a fan to direct the heat to a loc~li7çd area
o~ ding the image point. As an ~lt~rnfltive, howev~r, prçh~flting can be
accomplished by a dispersed laser beam, which irradiates the plate or
35 printing form in an apprûp,ialely sized regiûn arûund the image point as it
is being set. In this a~r~ ~,h the rate a writing head traverses the plate or
CA 02225304 1997-12-19
form is controlled such that the lelll~ lu,e of the region stabilizes before
the image point is set.
One advantage of inc~ , the local temperature around the image
point being fixed is that it is not necess~-y for the entire printing plate or
5 printing form to be brought to a high le~)elalule level, w_ich has a
disadvantage of overall thennal P~xpansion of the plate or form. As an
allf~ e to local preheating using a widened laser beam, prPhe~ting by a
lacuna with a heatin~ elP-mPnt or by an infrared radiation source would also
provide suitable locali7~d he~ting to an intermediate temperature.
Other objects and advanta~s will become a~pa~ l from the
following detailed dP~scriI~tion when taken in conjunction with the
dlawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a exemplary and ideali7ed temperature profile for
heatin~ a plate or printin~ form m~tP~ri~l in accordance with co~ iona
practice;
FIG. 2 is an exemrl~ry and i~ali7ed tempe alu~c profile for heating
a plate or printing form mat~Prial in accordance with one embodiment of the
invention, where the entire plate or printing form is prehP~ted to an
intPrmediate lelll~ e Tz;
FIG. 3 is an exemplary and ide~ ed temperature profile for he~ting
a plate or ~ lling fonn m~teri~l in accordance with an ~ltern~tive
embodiment of the invention, where a local region of the plate or printing
form is prPhP~ted and the local region moves with the laser beam that sets
or iixes the image points;
FIG. 4 is a schPm~tic represent?tion of a writing head with a laser
and a thPrm~l pre-w~mi~lg device in accordance with the invention for
generating both the therm~l set point and the therm~l prehe~ting of the
~wl~wlding region of a flat plate;
FIG. 5 is a schem~tic represent~tion of the writing head of FIG. 4
applied to wlili~g to a therm~l printin~ layer on a plate or form mounted to
a cylinder;
FIG. 6 is a schem~tic diagram of a system for driving the writing
head of FIGS. 5, incl~ldin~ a rail on which the head is mounted for
f~ilit~ting the sc~nning of the head over the surface of the plate or form in
conjunction and synchronization with the rotation of the cylinder;
..
CA 02225304 1997-12-19
FIG. 7 is a plan view of a th~rm~lly writable printing form
illustrating the location of an exemplary few lines of image points in a
matrix of image point c ~lid~tçs, which matrix is used as a map to locate
image points to be set or _xed by the writing head;
FIG. 8 is a block diagram of a controller for the drive system and
laser of the writing head as illu~ d in FIG. 6; and
FIG. 9 is a high level flow diagram of the steps executed by the
drive system in order to write the image points in precise loc~ti~ n~ on the
th~rm~l layer by following the matrix map of FIG. 7.
0 While the invention is susceptible to various moflific~tions and
;v~ constructions, a certain illustrated embo~liment thereof is shown
in the drawings and will be described below in detail. It should be
understood, however, that there is no intention to limit the invention to the
speci_c form disclosed. To the conll~y, the int~ntion is to cover all
15 modi_c~tic)n~ t~rn~tive constructions and equivalents falling within the
spirit and scope of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to the drawings and .ere";"g first to FIGS. 1-3, the
exçmrl~ry temperature versus time profiles for a point (i.e., dot) on the
20 therm~lly writable snrf~ce of a printing plate or form (herein~flPr "plate")
is set by a modnl~t~d laser which scans the plate on a line-by-line basis in a
conventional m~nner as ç~p1~ined more fillly herein~fler. In this regard, a
writing head tr~n~s~ g a focused laser beam onto the plate is moved line
by line over the plate. In this case, the plate can be clamped on a flat
25 substrate as illustrated in FIG. 4 or it can be wlillen to when it is in place
on a cylinder as illusll~led in FIG. 6.
The tempcralule versus time plot in FIG. 1 of the d ~wings
illu~ s a conventional le~ elalule profile at the image point to be set or
fixed. The image point is the exclusive region of the plate that is subjected
30 to heat. The heat from the laser raises the temperature of the image point
from an ambient leml)elalu,e Tp to the temperature of the limiting or
process temperature TG in accordance with the lellll)c;,~ e profile in
FIGURE 1. Depending on the relative speed of the movement between the
writing head and the plate, the thPrm~lly activatable m~teri~l is heated to a
35 temperature above the limitin~ or process temperature TG for a time
interval ~T. After the laser beam has moved away from the image point,
CA 02225304 1997-12-19
the L~ e~ c of the th~m~lly act,ivatable m~tçn~1 drops once more to
the ambient temperature Tp as su~ested in the tPrmin~1 portion of the
profile in FIGURE l.
The limitin~ or process lel~ e TG is exceeded for a predefined
5 ,.,;..;..,~.. time interval ~T, wherein both the temperature and time intervaldepend on the particular composition of the therm~1 act,ivatable coating
material of the plate or form. Only when t,he lel"~e~ c TG is exceeded
for the pre~fined ...;~ .. time interval ~T does a perm~nçnt physical
andlor çhemi~.~1 conversion of the th~,rm~lly activat,able plate or form
occur. Thus, the speed of the writing head must be cont,rolled accordingly.
In accordance with the invention, FIG. 2 illust,rates a temperat,ure
versus time plot in which the entire plate is prehe~ted by a hç~tin~ device
from the ambient temperature Tp to an intçrrnediate lellll)elalulc Tz, which
is below the 1imiting or process lelll~el~ c TG. When the writing head is
moved over the surface of the plate, the therm~11y act,ivatable layer is
heated to a temperature above the 1imiting or process lel.l~elalu,e TG for
the predefined time interval ~T, in subsPnti~11y the same way as described
above in connect,ion with FIGURE l. However, the starting temperat,ure is
now the intçrmediate le~ e.~ c Tz. Consequently, a lesser amount of
heat is required to further raise the temperature of the point to the 1imiting
or process temperature TG. Bec~n~e less of a temperature rise is necessary
to i;x or set the image point, a lesser amount of laser power is required to
be applied at the plate.
In cont,rast to the red~1ced power requirements of the invention as
illustrated in FIG. 2, the convtq.ntion~1 he~tin~ profile in FIGURE 1 requires
the laser beam to provide sufficient power to the image point so as to raise
the temperature an addit,ional amount Tz minus Tp, which often causes
def~rm~tion or layer separation as described above in the foregoiLIg
"Background" section.
The exPmr1~ry le~ )elalulc profile of FIG. 3 illustrates an
z~1tçrn~tive embodiment of the invention wherein the image point is
prehç~tçd only for a time i_mediately precedin3~ the he~tinf~ of the point to
the limitin~ or process l~ cralule TG. In this ~lt~.fn~tive embo-liment, the
advantages of preh~ting are re~ ed while prehe~ting only the image point
and an area imme~ tely around the image point for a time period related to
CA 02225304 1997-12-19
the time period required to fix or set the point rather than the much longer
time period for setting the points for the entire plate.
In this ~ltçrnstive embodimçnt of the invention, provision is made
for the speed of movement of the writing head Co~ g the laser device
5 to be m~tched to the heating power of the prehe~tin~ system in such a way
that a temp-_,ulwc state results which is steady over time with respect to the
intermediate ~ ~alwc Tz. Then, as in the P~empl~ry embodiment
according to FIG. 2, the therm~lly activatable m~tçri~l of the plate is
brought to a temperature above the limiting process temperature TG
10 according to the envisio~ed ~ .. action time ~T by means of the
mod~ ted laser beam. After the image point has been set, the heat
sir~te~ and the lel-l~c;ldtwe cools to the intçrmediate temperature Tz.
The point will stabilize at the intermediate lelllpel~lwc Tz until the
region~l he~tin~ of the plate no longer incl~ldes the area around the set or
15 fixed point. Thus, the t,~ c;lalwc will pl~te~ll at the intermediate
tempelalwc Tz until the printing head moves farther away, which results in
the region of prehe~ting moving off the set image point and, therefore, the
le~ )elutw~ retums to the ambient temperature Tp.
As can be seen from the fo~cgoiug description, there is provided a
20 method and ap~alus for prehç~ting th~rm~lly writable y~ plates or
forms, which enables the amount of laser power applied to set image points
to be lessened with respect to the methods of the prior art. By applying a
redllced amount of laser power to write onto the plate, the problems of
deformation or layer separation are dramatically reduced, which results in
25 higher quality p.i~ g plates that in turn provide higher quality prints.
FIG. 4 illu~llal~s a laser 2 focused on an image point 4 of a plate. In
kçeping with the invention, a prehe~tin~ device 6 such as an i~cd
radiator or a hot air blower pl~hcd~ an area or zone S ~wl- ullding the
image point 4. The laser 2 is of a collv~nLional construction for producing
30 a modnl~ted laser beam 3. The preh~tin~ device can be also of
convçntion~l design for producing a directed beam of infrared r~ tion 7
or simply generating an air flow of heated air directed to the region 5.
In FIG. 4, the printin~ plate is in a planar configuration. In a
conventional m~nn~r, the laser 2 and prçhe~t ng device 6 are mounted
35 togetller in a writing head, which in turn is mounted to a drive system for
increm~ont~lly moving the writing head to discrete image points on the
CA 02225304 1997-12-19
plates that form an array. By he~tin~ selective ones of the image points in
the array, the writing head forms an image on the therm~lly actn~t~ble
surface of the plate In a collv~ ;on~l m~nner, writing head moves
increment~lly along a rail (not shown) for Il~V~l~g the plates. A second
5 rail (also not shown) increments the transverse rail from the top to bottom
of the plate so that the writing head scans the entire plate and is
positionable over each of the available image points on the plate .
As an ~ltern~tive to printing on a flat plate as illustrated in FIG. 4,
the invention also co~ ...pl~tes writing in a convention~l m~nner on a plate
10 mounted to a printing cylinder 13 as illustrated in FII~r. 5. The three
cylinders 13, 15 and 17 illustrated in FIG. 5 are collv~nlional cylinders in a
printing unit for off-set printing of a p~ g sheet 19. In this regard, the
P~ e sheet 19 is directed into a nip formed between a counter-pl~s~ule
cylinder 17 and a rubber blanket cylinder 15. The image printed onto the
15 l..;..l;..g sheet 19, is ~ressed onto the rubber blanket cylinder 15 by the
plate cylinder 13 in a conv~ntion~1 m~nner As illustrated in FIG. 5, the
writing head 21 for pe.ro....ill~ the method ofthe invention is mounted to
an a~yal~lus for coor~lin~ting the transverse movement of the writing head
21 along the length of the cylinder 13 and coor 1in~tin that movement with
the rot~tion~l movement of the cylinder.
The mech~nicm for controlling the movement of the writing head 21
and coor~lil-~l;,-g that movement with the rotational movement of the
cylinder 13 is illustrated in FIG. 6. The writing head 21 is mounted for
reciprocating movement on a rail 23 that m~int~in~ the writing head in
proper ~lignmpnt with the therm~lly writable printing form 11 on the
cylinder 13 for setting image points. A system drive 24 controls the
reciprocating movement of the writing head 21 on the rail 23 in a m~nner
such that the writing head moves in increments from one end of the
cylinder to the other. As su~ested by the illustration of the printin~ form
11 in FIG. 7, the cylinder 13 in FIG. 6 is held static by a rotational drive 25
while the writing head 21 is moved along the rail 23 from one end of the
cylinder to the other in order to set selected ones of the image points 4,
which create a distribution of the set points that form an image when
viewed as a composite. Rotational drive 25 may be a motor such as a
stepper motor whose step resolution complement~ the ~mll~rily of ~he
image points as suggested by their spacing in the illustration of FIG. 7. In
CA 02225304 1997-12-19
this regard, one transverse pass of the writing head 21 allows the head to
set selected ones of the image points 4, in a line of an array of points as
illustrated in FIG. 7.
In order to increment the writing head 21 to the next line, a drive 27
5 for the cylinder 13 in FIG. 6 rotates the cylinder by an incrPmPnt~l amount
that rotates the therm~lly writable printing form 11 mounted to the cylinder
by an amount that aligns an ~dj~cent line of image points with the writing
head. Like the drive 25, the drive 27 may be a motor such as a stepper
motor whose step resolution comrlPment~ the gr~mll~rity of the lines as
10 sll~ested by the sp~cing of the lines in the illustration of FIG. 7. The
cylinder 13 is mounted for rotation on support structures 28A and 28B.
The cylinder 13 is mounted for rotation on a shaft 30, which is driven by
the drive 27.
In a conventional manner, the drive system 24 for the drives 25 and
15 27 coordinates the rot~tionn1 movement of the cylinder 13 and the
reciprocating movement of the writing head 21 on the rail 23. Also, the
drive system provides control signal to the laser 2, c~l1sing it to modulate
its laser beam so as to set only those image points 4 desired to create the
overall image to be printed on the p~ g sheet 19. The haldw~e of the
20 drive system 24 is shown in FIG. 8 and the methodology executed by the
hal.lw~uc for sc~nnin~ the printing form 11 in a line-by-line basis is
illu~ led in a flow diagram in FIG. 9.
The drive system 24 inchldes a microcontroller 31 as illustrated in
FIG. 8, which is in ch.. l~.ications with a memory 33 that contains a file
25 of the image. The image file is form~t~ed to complementc the physical
matrix format of the image points 4 placed on the form 11. In this regard,
the file of the image can be a simple matrix itself' with each cell
corresponding to one of the image points. Each cell can inclnde a data
field that is illlel~leled by the micro controller for the purpose of providing
30 an a~plopliate control signal for mod~ ting the laser to set selected ones of the points. The microcontroller 31 also is in co.~ ic~tion~ with a
program memory 35, which contains executable files for controlling the
movement of the drives 25 and 27 and the laser 2 In a convention~l
m~nner, an int~ ce 37 co.~.~..l.l-ic~tes control signals from the
35 microcontroller 31 to ~he drives 25 and 27 and the laser 2.
CA 02225304 1997-12-19
- 10-
Turning to the flow diagram of FIG. 9, the drive system 24 scans the
image points 4 in a lc~ ive m~nner, be~innin~ with a first point in the
matrix of image points (see FIG. 7) to the last point in the m~trix Starting
at step 41, the microcontroller 31 reads the image points to be set from the
5 point distribution memory 33. Pursuant to the program memory 35, the
microcontroller 31 executes the rem~ining steps in the flow diagram of
FIG. 9 in a recursive m~nner.
Specifically, the microcontroller 31 sets the drives 25 and 27 such
that the writing head 21 is initially align~l with the _rst line and _rst point
10 in that line at steps 43 and 45, respectively. Pursuant to the program in
memory 35, the _rst line is thclc~lcl scanned on a point-by-point basis in
steps 47, 49, 51 and 53 until the last point in the line is id~ntified in step
51. When the last image point 4 is identified in the line at step 51, the
program 35 controlling the microcontroller 31 branches to step 55 to
15 del~ e whether a next line exists. If the line just scanned is the last line,the program 35 exits and releases control of the microcontroller to other
operations. Otherwise, the program 35 increments to the next line by
driving the driver 27 by an increm~nt~l amount at step 57. The program 35
then returns to step 45 as illustrated in the flow diagraIn of FIG. 9 and
20 repeats the steps for 45, 47, 49, 51 and 53 in a recursive m~nner. After all
of the lines have been scanned and selected ones of the image points 4 have
been set in keeping with the data in the point distribution memory 33, the
desired image is then completely written to the form 11, which is now
ready for use in an off-set prinling process as illustrated in FIG. 5.
