FIELD OF THE INVENTION
[0001] 5 The present invention relates to a heat sensitive imaging element. More specifically
the invention is related to a heat sensitive imaging imaging element for preparing
a lithographic printing plate which can be imaged on the press.
BACKGROUND OF THE INVENTION
[0002] Lithography is the process of printing from specially prepared surfaces, some areas
of which are capable of accepting lithographic ink, whereas other areas, when moistened
with water, will not accept the ink. The areas which accept ink define the printing
image areas and the ink-rejecting areas define the background areas.
[0003] In the art of photolithography, a photographic material is made imagewise receptive
to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed
areas (positive-working) on a hydrophilic background.
[0004] In the production of common lithographic printing plates, also called surface litho
plates or planographic printing plates, a support that has affinity to water or obtains
such affinity by chemical treatment is coated with a thin layer of a photosensitive
composition. Coatings for that purpose include light-sensitive polymer layers containing
diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of
synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
[0005] Upon imagewise exposure of the light-sensitive layer the exposed image areas become
insoluble and the unexposed areas remain soluble. The plate is then developed with
a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
[0006] Alternatively, printing plates are known that include a photosensitive coating that
upon image-wise exposure is rendered soluble at the exposed areas. Subsequent development
then removes the exposed areas. A typical example of such photosensitive coating is
a quinone-diazide based coating.
[0007] Typically, the above described photographic materials from which the printing plates
are made are exposed in contact through a photographic film that contains the image
that is to be reproduced in a lithographic printing process. Such method of working
is cumbersome and labor intensive. However, on the other hand, the printing plates
thus obtained are of superior lithographic quality.
[0008] Attempts have thus been made to eliminate the need for a photographic film in the
above process and in particular to obtain a printing plate directly from computer
data representing the image to be reproduced. However the above mentioned photosensitive
coatings are not sensitive enough to be directly exposed to a laser. Therefor it has
been proposed to coat a silver halide layer on top of the photosensitive coating.
The silver halide can then directly be exposed by means of a laser under the control
of a computer. Subsequently, the silver halide layer is developed leaving a silver
image on top of the photosensitive coating. That silver image then serves as a mask
in an overall exposure of the photosensitive coating. After the overall exposure the
silver image is removed and the photosensitive coating is developed. Such method is
disclosed in for example
JP-A- 60- 61 752 but has the disadvantage that a complex development and associated developing liquids
are needed.
[0009] GB- 1 492 070 discloses a method wherein a metal layer or a layer containing carbon black is provided
on a photosensitive coating. This metal layer is then ablated by means of a laser
so that an image mask on the photosensitive layer is obtained. The photosensitive
layer is then overall exposed by UV-light through the image mask. After removal of
the image mask, the photosensitive layer is developed to obtain a printing plate.
This method however still has the disadvantage that the image mask has to be removed
prior to development of the photosensitive layer by a cumbersome processing.
[0010] Furthermore methods are known for making printing plates involving the use of imaging
elements that are heat-sensitive rather than photosensitive. A particular disadvantage
of photosensitive imaging elements such as described above for making a printing plate
is that they have to be shielded from the light. Furthermore they have a problem of
sensitivity in view of the storage stability and they show a lower dot crispness.
The trend towards heat mode printing plate precursors is clearly seen on the market.
[0011] EP-A- 444 786, JP- 63-208036,and
JP- 63-274592 disclose photopolymer resists that are sensitized to the near IR. So far, 5 none
has proved commercially viable and all require wet development to wash off the unexposed
regions.
EP-A- 514 145 describes a laser addressed plate in which heat generated by the laser exposure causes
particles in the plate coating to melt and coalescence and hence change their solubility
characteristics. Once again, wet development is required.
[0012] A somewhat different approach is disclosed in
US-P- 3 787 210, US-P- 3 962 513, EP-A- 001 068 and
JP- 04-140191. Heat generated by laser exposure of a donor sheet is used to physically transfer
a resinous material from the donor to a receptor held in intimate contact with the
donor. Provided the receptor surface has suitable hydrophilic properties, it can then
be used as a printing plate. This method has the advantage of not requiring wet processing,
but in order to achieve realistic write-times, a high power YAG (or similar) laser
is required, which has restricted the usefulness of the method
[0013] On the other hand polymer coatings which undergo a change in surface properties in
response to light exposure are known in the art.
WO- 92/09934 discloses imaging elements including coatings that become hydrophiliic as a result
of irradiation. The coatings 5 comprise an acid-sensitive polymer and a photochemical
source of strong acid, and in both cases the preferred acid-sensitive polymer is derived
from a cyclic acetal ester of acrylic or methacrylic acid, such as tetrahydropyranyl
(meth)acrylate.
[0014] WO- 92/02855 discloses that the acid-sensitive polymer is blended with a low-Tg polymer to produce
a coating that is initially non-tacky, but on irradiation undergoes phase separation
as a result of chemical conversion of the acid-sensitive polymer, and becomes tacky.
Although the possibility of laser exposure is mentioned, no details are given, and
there is no disclosure of IR-sensitivity, only UV/visible. However the same materials
were the subject of a paper entitled "Advances in Phototackification" presented as
Paper 1912-36 at the 1993 IS & T/SPIE Conference , Symposium on Electronic Science
and Technology, in which it was further disclosed that the photoacid generator could
be replaced by an IR dye (specifically a squarilium dye with thiopyrylium end groups)
and exposure effected with a diode laser device. The dye in question is not known
to have acid-generating properties. This technology is the subject of
US-P- 5 286 604.
[0015] WO- 92/09934 discloses that an acid-sensitive polymer is optionally blended with one or more photoacid
generators. Subsequent to imagewise exposure to UV/visible radiation, the exposed
areas are preferentially wettable by water, and the coatings may function as lithographic
printing plates requiring no wet processing. There is no disclosure of laser adress.
[0016] EP-A- 652 483 discloses a lithographic printing plate requiring no dissolution processing which
comprises a substrate bearing a heat-sensitive coating, which coating becomes relatively
more hydrophilic under the action of heat Said system yields a positive working printing
plate. An analogous system, however yielding a negative working printing plate is
not known.
[0017] EP-A- 507 008 provides homopolymers and copolymers containing aryldiazosulphonate units having
a maximal spectral sensitivity of at or above 320 nm. These polymers are especially
suitable for the production of printing plates.
[0018] US-P- 5 713 287 discloses a printing plate comprising hydrophobic polymers which turn into hydrophilic
polymers on heating, mixed with infra-red dyes.
[0019] GB-A- 1 195 841 discloses a thermal imaging element comprising a support and at least one layer containing
a radiation to heat converting substance and a thermally degradable polumer composed
of recurring units linked by azo groups.
OBJECTS OF THE INVENTION
[0020] It is an object of the invention to provide a non-ablative imaging element for preparing
a lithographic printing plate which is negative working.
[0021] It is also an object of the invention to provide a non-ablative imaging element for
preparing a lithographic printing plate which shows a good ink-uptake in the exposed
areas and no scumming in the non-exposed areas.
[0022] It is also an object of the invention to provide a non-ablative imaging element for
preparing a lithographic printing plate which can be exposed and developed on the
printing press.
[0023] Further objects of the invention will become clear from the description hereafter.
SUMMARY OF THE INVENTION
[0024] According to the present invention there is provided a heat-sensitive imaging element
for providing a lithographic printing plate, comprising a lithographic support with
a hydrophilic surface and a top layer wherein said top layer or a layer adjacent to
said top layer comprises a compound capable of converting light into heat,characterized
in that said top layer further comprises a polymer containing aryldiazosulphonate
units.
DETAILED DESCRIPTION OF THE INVENTION
[0025] The image forming layer which becomes more hydrophobic under the influence of heat
comprises a polymer or copolymer which contains aryldiazosulphonate units. A photosensitive
polymer having aryldiazosulphonate units, also called aryldiazosulphonate resin, preferably
is a polymer having aryldiazosulphonate units corresponding to the following formula:
wherein R
0,1,2 each independently represent hydrogen, an alkyl group, a nitrile or a halogen, e.g.
Cl, L represents a divalent linking group, n represents 0 or 1, A represents an aryl
group and M represents a cation.
L preferably represents divalent linking group selected from the group consisting
of:
-(X)
t-CONR
3-, -(X)
t-COO-, -X- and -(X)
t-CO-, wherein t represents 0 or 1, R
3 represents hydrogen, an alkyl group or an aryl group, X represents an alkylene group,
an arylene group, an alkylenoxy group, an arylenoxy group, an alkylenethio group,
an arylenethio group, an alkylenamino group, an arylenamino group, oxygen,sulfur or
an aminogroup.
A preferably represents an unsubstituted aryl group, e.g. an unsubstituted phenyl
group or more preferably an aryl group, e.g. phenyl, substituted with one or more
alkyl group, aryl group, alkoxy group, aryloxy group or amino group.
M preferably represents a cation such as NH4
+ or a metal ion such as a cation of Al, Cu, Zn, an alkaline earth metal or alkali
metal.
A polymer having aryldiazosulphonate units is preferably obtained by radical polymerisation
of a corresponding monomer. Suitable monomers for use in accordance with the present
invention are disclosed in
EP-A- 339 393 and
EP-A- 507 008. Specific examples are:
Aryldiazosulphonate monomers, e.g. as disclosed above, can be 5 homopolymerised or
copolymerised with other aryldiazosulphonate monomers and/or with vinyl monomers such
as (meth)acrylic acid or esters thereof, (meth)acrylamide, acrylonitrile, vinylacetate,
vinylchloride, vinylidene chloride, styrene, alpha-methyl styrene etc.. In case of
copolymers however, care should be taken not to impair the water solubility of the
polymer. Preferably, the amount of aryldiazosulphonate comprising units in a copolymer
in connection with this invention is between 10 mol % and 60 mol %.
According to another embodiment in connection with the present invention, an aryldiazosulphonate
containing polymer may be prepared by reacting a polymer having e.g. acid groups or
acid halide groups with an amino or hydroxy substituted aryldiazosulphonate. Further
details on this procedure can be found in
EP-A- 507 008.
[0026] The image forming layer or a layer adjacent to said layer includes a compound capable
of converting light into heat. Suitable compounds capable of converting light into
heat are preferably infrared absorbing components although the wavelength of absorption
is not of particular importance as long as the absorption of the compound used is
in the wavelength range of the light source used for image-wise exposure. Particularly
useful compounds are for example dyes and in particular infrared absorbing dyes and
pigments and in particular infrared absorbing pigments. Examples of infrared absorbing
dyes are disclosed in
EP-A- 97 203 131.4. Examples of infrared absorbing pigments are carbon black, metal carbides, borides,
nitrides, carbonitrides, bronze-structured oxides and oxides structurally related
to the bronze family but lacking the A component e.g. WO
2.9. It is also possible to use conductive polymer dispersion such as polypyrrole or
polyaniline-based conductive polymer dispersions. Said compound capable of converting
light into heat is preferably present in the top layer but can also be included in
the adjacent layer.
[0027] Said compound capable of converting light into heat is present in the imaging element
preferably in an amount between 1 and 25 % by weight of the total weight of the image
forming layer, more preferably in an amount between 2 and 20 % by weight of the total
weight of the image forming layer. The compound capable of converting light into heat
is most preferably present in the imaging element in an amount to provide an optical
density at a wavelength between 800 nm and 1100nm of at least 0.35.
[0028] The image forming layer is preferably applied in an amount between 0.1 and 5 g/m
2, more preferably in an amount between 0.5 and 3 g/m
2.
[0029] In the imaging element according to the present invention, the lithographic base
may be an anodised aluminum. A particularly preferred lithographic base is an electrochemically
grained and anodised aluminum support. The anodised aluminum support may be treated
to improve the hydrophilic properties of its surface. For example, the aluminum support
may be silicated by treating its surface with sodium silicate solution at elevated
temperature, e.g. 95°C. Alternatively, a phosphate treatment may be applied which
involves treating the aluminum oxide surface with a phosphate solution that may further
contain an inorganic fluoride. Further, the aluminum oxide surface may be rinsed with
a citric acid or citrate solution. This treatment may be carried out at room temperature
or may be carried out at a slightly elevated temperature of about 30 to 50°C. A further
interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate
solution. Still further, the aluminum oxide surface may be treated with polyvinylphosphonic
acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol,
polyvinylsulphonic acid, polyvinylbenzenesulphonic acid, sulphuric acid esters of
polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulphonated
aliphatic aldehyde It is further evident that one or more of these post treatments
may be carried out alone or in combination. More detailed descriptions of these treatments
are given in
GB-A- 1 084 070, DE-A- 4 423 140, DE-A- 4 417 907, EP-A- 659 909, EP-A- 537 633, DE-A-
4 001 466, EP-A- 292 801, EP-A- 291 760 and
US-P- 4 458 005.
[0030] According to another mode in connection with the present invention, the lithographic
base having a hydrophilic surface comprises a flexible support, such as e.g. paper
or plastic film, provided with a cross-linked hydrophilic layer. A particularly suitable
cross-linked hydrophilic layer may be obtained from a hydrophilic binder cross-linked
with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed
tetra-alkylorthosilicate. The latter is particularly preferred.
[0031] As hydrophilic binder there may be used hydrophilic (co)polymers such as for example,
homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol
methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl
methacrylate or maleic anhydride/vinylmethylether copolymers. The hydrophilicity of
the (co)polymer or (co)polymer mixture used is preferably the same as or higher than
the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60 percent
by weight, preferably 80 percent by weight.
[0032] The amount of crosslinking agent, in particular of tetraalkyl orthosilicate, is preferably
at least 0.2 parts by weight per part by weight of hydrophilic binder, more preferably
between 0.5 and 5 parts by weight, most preferably between 1.0 parts by weight and
3 parts by weight.
[0033] A cross-linked hydrophilic layer in a lithographic base used in accordance with the
present embodiment preferably also contains substances that increase the mechanical
strength and the porosity of the layer. For this purpose colloidal silica may be used.
The 5 colloidal silica employed may be in the form of any commercially available water-dispersion
of colloidal silica for example having an average particle size up to 40 nm, e.g.
20 nm. In addition inert particles of larger size than the colloidal silica may be
added e.g. silica prepared according to Stöber as described in J. Colloid and Interface
Sci., Vol. 26, 1968, pages 62 to 69 or alumina particles or particles having an average
diameter of at least 100 nm which are particles of titanium dioxide or other heavy
metal oxides. By incorporating these particles the surface of the cross-linked hydrophilic
layer is given a uniform rough texture consisting of microscopic hills and valleys,
which serve as storage places for water in background areas.
[0034] The thickness of a cross-linked hydrophilic layer in a lithographic base in accordance
with this embodiment may vary in the range of 0.2 to 25 µm and is preferably 1 to
10 µm.
[0035] Particular examples of suitable cross-linked hydrophilic layers for use in accordance
with the present invention are disclosed in
EP-A- 601 240, GB-P- 1 419 512, FR-P- 2 300 354, US-P- 3 971 660, US-P- 4 284 705 and
EP-A- 514 490.
[0036] As flexible support of a lithographic base in connection with the present embodiment
it is particularly preferred to use a plastic film e.g. substrated polyethylene terephthalate
film, cellulose acetate film, polystyrene film, polycarbonate film etc... The plastic
film support may be opaque or transparent.
[0037] It is particularly preferred to use a polyester film support to which an adhesion
improving layer has been provided. Particularly suitable adhesion improving layers
for use in accordance with the present invention comprise a hydrophilic binder and
colloidal silica as disclosed in
EP-A- 619 524, EP-A- 620 502 and
EP-A- 619 525. Preferably, the amount of silica in the adhesion improving layer is between 200 mg
per m
2 and 750 mg per m
2. Further, the ratio of silica to hydrophilic binder is preferably more than 1 and
the surface area of the colloidal silica is preferably at least 300 m
2 per gram, more preferably at least 500 m
2 per gram.
[0038] Between the support and the top layer the imaging element can contain other layers
such as subbing layers and antihalo layers.
[0039] The imaging element can be prepared by applying the different layers according to
any known technique. Alternatively said imaging element may be prepared on the press
with the support already on the press by a coater or coaters placed in the immediate
vicinity of the press.
[0040] Imaging in connection with the present invention is preferably done with an image-wise
scanning exposure, involving the use of a laser, more preferably of a laser that operates
in the infrared or near-infrared, i.e. wavelength range of 700-1500 nm. Most preferred
are laser diodes emitting in the near-infrared. Exposure of the imaging element can
be performed with lasers with a short as well as with lasers with a long pixel dwell
time. Preferred are lasers with a pixel dwell time between 0.005 µs and 20 µs.
[0041] In another embodiment of the invention the exposure of the imaging element can be
carried out with the imaging element already on the press. A computer or other information
source supplies graphics and textual information to the laser via a lead.
[0042] The printing plate of the present invention can also be used in the printing process
as a seamless sleeve printing plate. This cylindrical printing plate has such a diameter
that it can be slided on the print cylinder. More details on sleeves are given in
"Grafisch Nieuws" ed. Keesing, 15, 1995, page 4 to 6.
[0043] The printing plate of the present invention can also be used in the printing process
as a seamless sleeve printing plate. This cylindrical printing plate which has as
diameter the diameter of the print cylinder is slided on the print cylinder instead
of applying in a classical way a classically formed printing plate. More details on
sleeves are given in "Grafisch Nieuws" ed. Keesing, 15, 1995, page 4 to 6.
[0044] Subsequent to image-wise exposure, the image-wise exposed imaging element can be
developed by washing with plain water or an aqueous solution. The plate is then ready
for printing and can be mounted on the press. However, to improve durability it is
still possible to bake said plate at a temperature between 200°C and 300°C for a period
of 30 seconds to 5 minutes. Also the imaging element can be subjected to an overall
post-exposure to UV-radiation to harden the image in order to increase the run lenght
of the printing plate.
[0045] More preferably the image-wise exposed imaging element after optional wiping is mounted
on a print cylinder of a printing press with the backside of the imaging element (side
of the support opposite to the side having the photosensitive layer). According to
a preferred embodiment, the printing press is then started and while the print cylinder
with the imaging element mounted thereon rotates, the dampener rollers that supply
dampening liquid are dropped on the imaging element and subsequent thereto the ink
rollers are dropped. Generally, after about 10 revolutions of the print cylinder the
first clear and useful prints are obtained. According to an alternative method, the
ink rollers and dampener rollers may be dropped simultaneously or the ink rollers
may be dropped first.
[0046] Preferably, the photosensitive layer of an image-wise exposed imaging element in
accordance with the present invention is wiped with e.g. a cotton pad or sponge soaked
with water before mounting the imaging element on the press or at least before the
printing press starts running. This will remove some unexposed aryldiazosulphonate
resin but will not actually develop the imaging element. However, it has the advantage
that possible substantial contamination of the dampening system of the press and ink
used is avoided.
[0047] An exposed imaging element in accordance with the present invention is preferably
mounted on a printing press and used to print shortly after the exposure. It is however
possible to store an exposed imaging element for some time in the dark before using
it on a printing press to print copies.
[0048] Suitable dampening liquids that can be used in connection with the present invention
are aqueous liquids generally having an acidic pH and comprising an alcohol such as
isopropanol and silica. With regard to dampening liquids useful in the present invention,
there is no particular limitation and commercially available dampening liquids, also
known as fountain solutions, can be used. The invention will now be illustrated by
the following examples without however the intention to limit the invention thereto.
All parts are by weight unless stated otherwise.
EXAMPLES 1
Preparation of the lithographic base
[0049] 5 A 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous
solution containing 5 g/l of sodium hydroxide at 50°C and rinsed with demineralized
water. The foil was then electrochemically grained using an alternating current in
an aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of hydroboric acid
and 5 g/l of aluminum ions at a temperature of 35°C and a current density of 1200
A/m
2 to form a surface topography with an average center-line roughness Ra of 0.5 µm.
[0050] After rinsing with demineralized water the aluminum foil was then etched with an
aqueous solution containing 300 g/l of sulfuric acid at 60°C for 180 seconds and rinsed
with demineralized water at 25°C for 30 seconds.
[0051] The foil was subsequently subjected to anodic oxidation in an aqueous solution containing
200 g/l of sulfuric acid at a temperature of 45°C, a voltage of about 10 V and a current
density of 150 A/m
2 for about 300 seconds to form an anodic oxidation film of 3.00 g/m
2 of Al
2O
3 then washed with demineralized water, posttreated with a solution containing polyvinylphosphonic
acid and subsequently with a solution containing aluminum trichloride, rinsed with
demineralized water at 20°C during 120 seconds and dried.
Preparation of the imaging element
[0052] To 9.367 g of a methanol solution was subsequently added, while stirring, 0.670 g
of the azosulphonate copolymer P20 and 0.063 g of an IR absorbing dye IR-1.
[0053] The obtained solution was coated on the lithographic base to a wet coating thickness
of 30 µm and dried at 30°C.
[0054] This plate was imaged on a CREO 3244 TRENDSETTER ™ (available from Creo) at 2400
dpi. operating at a drum speed of 60 rpm and a laser output of 11 Watt.
[0055] After imaging the plate was mounted on a GTO46 press using Van Son Rubberbase ink
and water with 10% isopranol and 5% G671c ™ (silica containing fountain from Agfa
Gevaert Belgium) as fountain.
[0056] Subsequently the press was started by allowing the print cylinder with the imaging
element mounted thereon to rotate. The dampener rollers of the press were then dropped
on the imaging element so as to supply dampening liquid to the imaging element and
after 10 revolutions of the print cylinder, the ink rollers were dropped to supply
ink. After 10 further revolutions clear prints were obtained with no ink uptake in
the non-image parts.
Synthesis of diazosulphonate containing polymer P20
Synthesis of monomer A
[0057] The azogroups containing substances have to be protected from light e.g. by darkening
the room or wrapping the flasks with aluminum foil.
[0058] The reagents were obtained from Fluka and Aldrich, solvents were distilled before
use.
a) preparation of 3 solutions
[0059]
1 24 g sodium sulfite and 40 g sodium carbonate are dissolved in 250 ml of water
2 15,02 g of p.-aminoacetanilide are diluted in 100 ml water and 36,8 ml concentrated
HCl (32%) and cooled to 0-5°C with a cooling bath.
3 6,8 g sodium nitrite are diluted in 15 ml water
[0060] Solution 3 is added dropwise to solution 2 while cooling (below 5°C), then it is
stirred for 10 minutes. After filtration the solution is poured quickly into solution
1 under intensive stirring. Then the solution is stirred for 30 minutes. The solution
may be red at the beginning but the colour turns to yellow after some minutes. The
solid product is filtered off from the solution and used without further purification.
b)
[0061] The product is dissolved in 150 ml water, 8 g NaOH are added, then the solution is
heated to 50°C for one hour and afterwards cooled down to 0°C. While still cooling,
19,66 ml concentrated HCl (32%) are added to the solution. Then 100 ml 1% picrinic
acid and a solution of 33,6 sodium carbonate in about 350 ml water are poured into
the mixture. Before adding the methacrylic acid chloride the temperature of the solution
has to be below 5°C. From a dropping funnel 15 ml of methacrylic acid chloride is
very slowly dropped to the solution (heavy foaming). The mixture needs to be stirred
for 1 hour at 0-5°C and after that for another hour at room temperature. Then 300
ml of a saturated solution of sodium acetate are added and the solution is stored
in a refrigerator (about 4°C) overnight. The solid product is filtered and dried for
17 hours at 50°C under vacuum. To remove inorganic salts the product is dissolved
in 150 ml DMF and stirred for at least 2 hours at room temperature and filtered. For
precipitation the filtrate is poured into 2 l of diethylether and then filtered. To
realize a very low contents of water (2.5 %) drying for three days at 50°C under vacuum
is necessary.
Synthesis of the polymer P 20
[0062] Firstly 2.11 g monomer 1 is diluted in 10 ml of water,3.1 g methyl methacrylate and
0.300 g of azo-bis-isobutyronitrile as well as 40 ml of dioxane are added. In order
to remove oxygen, the solution has to be degassed several times. Afterwards the solution
(protected from light) is stirred for 17 hours at 70°C. The polymerisation is stopped
by adding a small amount of hydroquinone, the solvent is evaporated and the polymer
is redissolved in 80 ml methanol. The solution is dropped to 2 l of diethylether and
then dried at 50°C under vacuum over phosphor pentoxide. After drying for 3 days,
one obtains a polymer with a water content of 2.5%.
1. Ein wärmeempfindliches Bilderzeugungselement zur Herstellung einer lithografischen
Druckplatte, das einen lithografischen Träger mit einer hydrophilen Oberfläche und
eine Deckschicht enthält, wobei die Deckschicht oder eine an die Deckschicht grenzende
Schicht eine Licht in Wärme umwandelnde Verbindung enthält, dadurch gekennzeichnet, daß die Deckschicht weiterhin ein Aryldiazosulfonateinheiten enthaltendes Polymer enthält.
2. Ein wärmeempfindliches Bilderzeugungselement nach Anspruch 1, dadurch gekennzeichnet, daß die Menge Aryldiazosulfonateinheiten im Polymer zwischen 10 mol-% und 60 mol-% liegt.
3. Ein wärmeempfindliches Bilderzeugungselement nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Aryldiazosulfonateinheiten enthaltende Polymer ein Copolymer mit einem Monomer
aus der Gruppe bestehend aus (Meth)acrylsäure oder deren daraus gebildeten Estern,
(Meth)acrylamid, Acrylnitril, Vinylacetat, Vinylchlorid, Vinylidenchlorid, Styrol
und α-Methylstyrol ist.
4. Ein wärmeempfindliches Bilderzeugungselement nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß die Aryldiazosulfonateinheiten substituierte Aryldiazosulfonateinheiten sind.
5. Ein wärmeempfindliches Bilderzeugungselement nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Verbindung, die Licht in Wärme umzuwandeln vermag, eine infrarotabsorbierende
Komponente ist.
6. Ein wärmeempfindliches Bilderzeugungselement nach Anspruch 5, dadurch gekennzeichnet, daß die infrarotabsorbierende Komponente ein infrarotabsorbierender Farbstoff ist.
7. Ein wärmeempfindliches Bilderzeugungselement nach Anspruch 5, dadurch gekennzeichnet, daß die infrarotabsorbierende Komponente ein infrarotabsorbierendes Pigment ist.
8. Ein durch die nachstehenden Schritte gekennzeichnetes Verfahren zum Bereitstellen
einer lithografischen Druckplatte :
- bildmäßige Belichtung eines Bilderzeugungselements nach einem der Ansprüche 1 bis
7,
- Entwicklung des belichteten Bilderzeugungselements mit Leitungswasser oder einer
wäßrigen Lösung.
9. Ein Verfahren nach Anspruch 8, das weiterhin die vollflächige UV-Belichtung des entwickelten
Bilderzeugungselements umfaßt.
10. Ein durch die nachstehenden Schritte gekennzeichnetes Druckverfahren :
- Belichtung eines Bilderzeugungselements nach einem der Ansprüche 1 bis 7,
- Aufspannen des belichteten Bilderzeugungselements auf eine Druckpresse,
- Zuführen von Druckfarbe und Feuchtwasser auf das Bilderzeugungselement und
- Drucken mit dem Bilderzeugungselement.
1. Élément de formation d'image thermosensible pour procurer un cliché d'impression lithographique
comprenant un support lithographique muni d'une surface hydrophile et d'une couche
de protection, dans lequel ladite couche de protection ou une couche adjacente à ladite
couche de protection comprend un composé capable de transformer de la lumière en chaleur,
caractérisé en ce que ladite couche de protection comprend en outre un polymère contenant des unités d'aryldiazosulfonates.
2. Élément de formation d'image thermosensible selon la revendication 1, dans lequel
la quantité des unités structurales d'aryldiazosulfonates dans ledit polymère se situe
entre 10 moles % et 60 moles %.
3. Élément de formation d'image thermosensible selon la revendication 1 ou 2, dans lequel
ledit polymère comprenant des unités d'aryldiazosulfonates est un copolymère avec
un monomère choisi parmi le groupe constitué par l'acide (méth)acrylique ou ses esters,
le (méth)acrylamide, l'acrylonitrile, l'acétate de vinyle, le chlorure de vinyle,
le chlorure de vinylidène, le styrène, l'alpha-méthylstyrène.
4. Élément de formation d'image thermosensible selon l'une quelconque des revendications
1 à 3, dans lequel lesdites unités d'aryldiazosulfonates sont des unités d'aryldiazosulfonates
substitués.
5. Élément de formation d'image thermosensible selon l'une quelconque des revendications
1 à 4, dans lequel le composé capable de transformer de la lumière en chaleur est
un composant absorbant dans le domaine infrarouge du spectre.
6. Élément de formation d'image thermosensible selon la revendication 5, dans lequel
ledit composant absorbant dans le domaine infrarouge du spectre est un colorant absorbant
dans le domaine infrarouge du spectre.
7. Élément de formation d'image thermosensible selon la revendication 5, dans lequel
ledit composant absorbant dans le domaine infrarouge du spectre est un pigment absorbant
dans le domaine infrarouge du spectre.
8. Procédé pour procurer un cliché d'impression lithographique, comprenant les étapes
ci-après consistant à:
- exposer en forme d'image un élément de formation d'image selon l'une quelconque
des revendications 1 à 7 ;
- développer ledit élément de formation d'image à l'état exposé avec de l'eau ordinaire
ou avec une solution aqueuse.
9. Procédé d'impression selon la revendication 8, comprenant en outre le fait d'exposer
globalement par exposition à un rayonnement ultraviolet, l'élément développé formant
une image.
10. Procédé d'impression comprenant les étapes indiquées ci-après consistant à :
- exposer un élément de formation d'image selon l'une quelconque des revendications
1 à 7 ;
- monter sur une presse l'élément de formation d'image exposé ;
- appliquer de l'encre et une solution de mouillage sur l'élément de formation d'image
; et
- imprimer à partir dudit élément de formation d'image.