Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
  • B41C1/1008—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials
  • B41C1/1033—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials by laser or spark ablation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
  • B41C1/1041—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by modification of the lithographic properties without removal or addition of material, e.g. by the mere generation of a lithographic pattern
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
  • B41M5/368—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties involving the creation of a soluble/insoluble or hydrophilic/hydrophobic permeability pattern; Peel development

Definitions

• the present invention relates to a heat sensitive imaging element.
• the invention is related to a heat sensitive wasteless imaging imaging element for preparing a lithographic printing plate which requires no dissolution processing.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the printing plates thus obtained are of superior lithographic quality.
• 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.
• EP-A- 444 786, JP- 63-208036, and JP- 63-274592 disclose photopolymer resists that are sensitized to the near IR. So far, 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.
• WO- 92/09934 discloses imaging elements including coatings that become hydrophiliic as a result of irradiation.
• the coatings 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.
• 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.
• 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 addresses.
• WO- 92/2855 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.
• 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
• 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.
• US-P- 5 713 287 discloses a printing plate comprising hydrophobic polymers which turn into hydrophilic polymers on heating, mixed with infra-red dyes.
• 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.
• a heat-sensitive imaging element for providing a lithographic printing plate, comprising a support and as top layer a heat switchable image forming layer comprising a hardened hydrophilic binder and a heat switchable polymer 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 heat switchable polymer is a polymer containing aryldiazosulphonate units.
• the image forming layer which becomes more hydrophobic under the influence of heat comprises a heat-switchable binder, a compound capable of transferring light into heat and a hardened hydrophilic binder.
• a heat-switchable binder is a polymer or copolymer which under the influence of heat undergoes a polarity transfer from hydrophilic to hydrophobic or vice versa.
• a switchable binder is used which is hydrophilic before heating and becomes hydrophobic by heating. This surface polarity difference is sufficient to prepare a classical offset printing plate.
• the switchable binders according to the invention are polymers or copolymers which contain aryldiazosulphonate units.
• a photosensitive polymer having aryldiazosulphonate units, also called aryldiazosulphonate resin preferably is a polymer having aryldiazosulphonate units corresponding to the following formula:
• Aryldiazosulphonate monomers can be homopolymerised or copolymerised with other aryldiazosulphonate monomers and/or with vinyl monomers such as (meth)acrylic acid or esters thereof, (meth)acrylamide, acrylonitrile, vinylacetate, vinyichloride, vinylidene chloride, styrene, alpha-methyl styrene etc..
• vinyl monomers such as (meth)acrylic acid or esters thereof, (meth)acrylamide, acrylonitrile, vinylacetate, vinyichloride, vinylidene chloride, styrene, alpha-methyl styrene etc.
• the amount of aryldiazosulphonate comprising units in a copolymer in connection with this invention is between 10 mol % and 60 mol %.
• 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 .
• the aryldiazosulphonate monomer is copolymerized with monomers which contain reactive groups capable of reacting with formaldehyde, glyoxal, polyisocyanates or a hydrolyzed tetraalkylorthosilicate.
• 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.
• 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.
• a particularly suitable hardened 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.
• a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetra-alkylorthosilicate, The latter is particularly preferred.
• hydrophilic binder there may be used hydrophilic (co)polymers such as for example, homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylate acid, methacrylate 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.
• 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.
• a cross-linked hydrophilic layer used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer.
• colloidal silica may be used.
• the 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,
• 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.
• 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.
• the image forming layer is preferably applied in an amount between 0.1 and 5 g/m 2 , more preferably in an amount between 0.25 and 3 g/m 2 .
• the support may be as well a hydrophobic as a hydrophilic support and as well a rigid as a flexible support
• the support can be an anodised aluminum
• a particularly preferred support is an electrochemically grained and anodised aluminum support
• the support is a flexible support, such as paper or plastic film.
• flexible support 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.
• the amount of silica in the adhesion improving layer is between 200 mg per m 2 and 750 mg per m 2 .
• 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.
• the imaging element can contain other layers such as subbing layers and antihalo layers.
• the imaging element can be prepared by applying the different layers according to any known technique.
• 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.
• Imaging in connection with the present invention is 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.
• a laser more preferably of a laser that operates in the infrared or near-infrared, i.e. wavelength range of 700-1500 nm.
• 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 ⁇ s and 20 ⁇ s.
• the imaging element After the exposure the imaging element is ready to be used as a lithographic printing plate.
• 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 printhead or a laser via a lead.
• 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.
• 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.
• the image-wise exposed imaging element 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).
• 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 and the ink rollers are dropped.
• the azogroups containing substances have to be protected from light e.g. by darkening the room or wrapping the flasks with aluminum foil.
• the reagents were obtained from Fluka and Aldrich, solvents were distilled before use.
• 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.
• 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.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Thermal Sciences (AREA)
• Printing Plates And Materials Therefor (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)

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Cited By (12)

Citations (6)

• 1999
  • 1999-03-18 EP EP19990200846 patent/EP0960729B1/de not_active Expired - Lifetime

Patent Citations (6)

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