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EP0849090A2 - Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties - Google Patents

Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties Download PDF

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Publication number
EP0849090A2
EP0849090A2 EP96203632A EP96203632A EP0849090A2 EP 0849090 A2 EP0849090 A2 EP 0849090A2 EP 96203632 A EP96203632 A EP 96203632A EP 96203632 A EP96203632 A EP 96203632A EP 0849090 A2 EP0849090 A2 EP 0849090A2
Authority
EP
European Patent Office
Prior art keywords
imaging element
outermost layer
layer
image
element according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP96203632A
Other languages
German (de)
French (fr)
Other versions
EP0849090A3 (en
Inventor
Joan Vermeersch
Geert Defieuw
Marc Van Damme
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Agfa Gevaert NV
Original Assignee
Agfa Gevaert NV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Agfa Gevaert NV filed Critical Agfa Gevaert NV
Priority to EP96203632A priority Critical patent/EP0849090A3/en
Priority to JP36390797A priority patent/JPH10193824A/en
Publication of EP0849090A2 publication Critical patent/EP0849090A2/en
Publication of EP0849090A3 publication Critical patent/EP0849090A3/en
Ceased legal-status Critical Current

Links

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
    • B41C1/1025—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 using materials comprising a polymeric matrix containing a polymeric particulate material, e.g. hydrophobic heat coalescing particles
    • 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
    • B41M5/366—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 using materials comprising a polymeric matrix containing a polymeric particulate material, e.g. hydrophobic heat coalescing particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
    • B41C2201/04—Intermediate layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
    • B41C2201/14—Location, type or constituents of the non-imaging layers in lithographic printing formes characterised by macromolecular organic compounds, e.g. binder, adhesives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/06—Developable by an alkaline solution
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/08—Developable by water or the fountain solution
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/14—Multiple imaging layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/20—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by inorganic additives, e.g. pigments, salts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/22—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by organic non-macromolecular additives, e.g. dyes, UV-absorbers, plasticisers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/24—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by a macromolecular compound or binder obtained by reactions involving carbon-to-carbon unsaturated bonds, e.g. acrylics, vinyl polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/26—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by a macromolecular compound or binder obtained by reactions not involving carbon-to-carbon unsaturated bonds
    • B41C2210/262—Phenolic condensation polymers, e.g. novolacs, resols

Definitions

  • the present invention relates to a method for making a lithographic printing plate involving the use of a heat-sensitive imaging element.
  • it concerns improvements in imaging properties due to its surface in contact with the heat source having a particular composition.
  • Lithographic printing is the process of printing from specially prepared surfaces, some areas of which are capable of accepting ink, whereas other areas will not accept ink.
  • a photographic material is made imagewise receptive to oily or greasy ink in the photo-exposed (negative working) or in the non-exposed areas (positive working) on a ink-repelling background.
  • lithographic 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.
  • thermoplastic polymer particles By image-wise exposure to an infrared laser, the thermoplastic polymer particles are image-wise coagulated thereby rendering the surface of the imaging element at these areas ink acceptant without any further development.
  • a disadvantage of this method is that the printing plate obtained is easily damaged since the non-printing areas may become ink-accepting when some pressure is applied thereto. Moreover, under critical conditions, the lithographic performance of such a printing plate may be poor and accordingly such printing plate has little lithographic printing latitude.
  • EP-A-514145 discloses a heat-sensitive imaging element including a coating comprising core-shell particles having a water insoluble heat softenable core component and a shell component which is soluble or swellable in an aqueous alkaline medium.
  • Red or infrared laser light directed image-wise at said imaging element causes selected particles to coalesce, at least partially, to form an image and the non-coalesced particles are then selectively removed by means of an aqueous alkaline developer. Afterwards a baking step is performed.
  • the printing endurance of a so obtained printing plate is low.
  • EP-A-599510 discloses a heat-sensitive imaging element which comprises a substrate coated with (i) a layer which comprises (1) a disperse phase comprising a water-insoluble heat softenable component A and (2) a binder or continuous phase consisting of a component B which is soluble or swellable in aqueous, preferably aqueous alkaline medium, at least one of components A and B including a reactive group or precursor therefor, such that insolubilisation of the layer occurs at elevated temperature and/or on exposure to actinic radiation , and (ii) a substance capable of strongly absorbing radiation and transferring the energy thus obtained as heat to the disperse phase so that at least partial coalescence of the coating occurs.
  • EP-A 952022871.0, 952022872.8, 952022873.6 and 952022874.4 disclose a method for making a lithographic printing plate comprising the steps of (1) image-wise exposing to light a heat-sensitive imaging element comprising (i) on a hydrophilic surface of a lithographic base an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and (ii) a compound capable of converting light to heat, said compound being comprised in said image-forming layer or a layer adjacent thereto; (2) and developing a thus obtained image-wise exposed element by rinsing it with plain water.
  • thermosensitive imaging systems can also be used as direct thermosensitive imaging elements for a recording process wherein images are generated by the use of imagewise modulated thermal energy.
  • the presence of a compound capable of converting light into heat in said image-forming layer or a layer adjacent thereto is not necessary.
  • thermosensitive imaging element suitable for imaging with a thermal head with excellent transporting properties and developable in a convenient ecological way.
  • thermosensitive imaging element which has no soiling or abrasive effects on the thermal head and shows no smearing after the thermographic imaging process.
  • an imaging element for making a lithographic printing plate comprising on a flexible support (i) an ink-repellant layer containing a crosslinked hydrophilic binder and (ii) a thermosensitive layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder, characterized in that an outermost layer is present on top of said layers of said imaging element, said outermost layer comprising at least a solid or liquid lubricant in a hydrophilic binder.
  • a thermal image forming process is realized, wherein the heat source is a thin or thick film thermal head.
  • the lubricant may be liquid or solid.
  • the solid lubricant may be thermomeltable or not.
  • a lubricant is called thermomeltable when its melting point is below 200 °C.
  • Non-thermomeltable lubricants such as teflon or inorganic particles can be added to the outermost layer. The addition of inorganic particles is especially recommended. It is advantageous that they protrude through the surface of said outermost layer to reduce building up of debris on the thermal head.
  • Inorganic particles such as silica or salts derived from silica such as e.g. talc, clay, china clay, mica, chlorite, silica, or carbonates such as calcium carbonate, magnesium carbonate or calcium magnesium carbonate (dolomite) can be added to the outermost layer in accordance with the invention.
  • a mixture of talc and dolomite or talc and silica particles is highly preferred.
  • thermomeltable lubricant has a melting point below 150 °C.
  • solid lubricants having a melting point below 110°C, with solid lubricants with a molecular weight below 1000 being particularly preferred.
  • solid lubricants are defined as those lubricants being solid at 20 °C.
  • Solid thermomeltable lubricants which can be used according to the present invention are polyolefin waxes e.g. polypropylene waxes, ester waxes e.g. fatty acid esters, polyolefin-polyether block copolymers, amide waxes e.g. fatty acid amides, polyglycols e.g. polyethylene glycol, fatty acids, fatty alcohols, natural waxes and solid phosphoric acid ester derivatives.
  • polyolefin waxes e.g. polypropylene waxes
  • ester waxes e.g. fatty acid esters
  • polyolefin-polyether block copolymers amide waxes e.g. fatty acid amides
  • polyglycols e.g. polyethylene glycol
  • fatty acids fatty alcohols
  • natural waxes and solid phosphoric acid ester derivatives.
  • Preferred solid thermomeltable lubricants are selected from the group consisting of fatty acid esters, fatty acid amides and phosphoric acid esters.
  • Preferred fatty acid esters are glycerine monostearate, glycerine monopalmitate and mixtures of glycerine monostearate and glycerine monopalmitate.
  • Preferred fatty acid amides are selected from the group consisting of ethylenebisstearamide, stearamide, oleamide, myristamide and erucamide.
  • Suitable solid non-phosphoric acid ester derivative lubricants according to the present invention with their melting points are: Melting point [°C] SL01 ethylenebisstearamide (CeridustTM 3910 from Hoechst AG) 141 SL02 myristamide 106 SL03 stearamide 104 SL04 glycerine monostearate 81 SL05 erucamide 80 SL06 oleamide 73 SL07 glycerine tristearate 55-73 SL08 MobilcerTM Q (a paraffin wax) 67 SL09 glycerine monotallow acid ester (RilanitTM GMS from Henkel AG) 55-60 SL10 sorbitan monostearate (SPANTM 60 from ICI PLC) 55 SL11 sorbitan tristearate (SPANTM 65 from ICI PLC) 48-53 SL12 sorbitan monopalmitate (SPANTM 40 from ICI PLC) 44-47 SL13 POE-(4)-sorbitan monoste
  • PSL solid phosphoric acid ester derivative solid lubricants
  • PSL melting point
  • PSL01 ServoxylTM VPAZ 100 from Servo Delden BV mixture of monolauryl and dilauryl phosphates
  • PSL02 ServoxylTM VPRZ 100 from Servo Delden BV mixture of monocetyl and monostearyl phosphates
  • PSL03 potassium alkyl phosphate CrafolTM AP37 from Henkel AG
  • Liquid lubricants which can be used according to the present invention include silicon oils, functionalized silicon oils, silicon block polymers such as polyalkyleneoxide-polysiloxane copolymers, glycerol esters, liquid phosphoric ester derivatives and the like . Liquid phosphoric ester derivatives are preferred among the liquid lubricants.
  • non-phosphoric acid ester derivative liquid lubricants (LL) are:
  • PLL phosphoric acid ester derivative liquid lubricants
  • the outermost layer on top of the imaging layers of the imaging element comprises a hydrophilic binder.
  • Suitable hydrophilic binders for said outermost layer are, for example, gelatin, polyvinylalcohol, cellulose derivatives or other polysaccharides, hydroxyethylcellulose, hydroxypropylcellulose etc., with binders having a glass transition temperature above 100 °C being preferred and polyvinylalcohol being particularly preferred.
  • additives or fillers can also be incorporated in the outermost layer e.g. colloidal particles such as colloidal silica.
  • hardening of the binder may affect the water processability of the imaging element, a low degree of hardening can improve the thermostability of the outermost layer.
  • the thickness of the outermost layer on top of the imaging layer of the imaging element may be any thickness to obtain sufficient protection of the image and the thermal head.
  • the thickness of the outermost layer is 0.1 to 10 ⁇ m more preferably 0.2 to 5 ⁇ m.
  • An intermediate layer between the outermost layer and the thermosensitive layer may be used to improve the development properties of the imaging element or to improve the adhesion between the outermost layer and the thermosensitive layer.
  • the binder for said intermediate layer is preferably hydrophilic and the thickness of said layer may be 0.05 to 5 ⁇ m.
  • An intermediate layer may be especially usefull when a slightly crosslinked hydrophilic binder is used in the outermost layer.
  • a heat-sensitive imaging element comprising on a hydrophilic surface of a lithographic base an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder.
  • the hydrophilic binder in the image-forming layer used in connection with the present invention is preferably not crosslinked or only slightly crosslinked.
  • the imaging element may further include a compound capable of converting light into heat. This compound is comprised in the image-forming layer or a layer adjacent thereto.
  • the lithographic base comprises a flexible support, such as e.g. paper or plastic film, provided with a cross-linked hydrophilic layer.
  • a particularly suitable cross-linked rough hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or preferably a hydrolysed tetra-alkylorthosilicate.
  • 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.
  • 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.
  • a cross-linked hydrophilic layer on a flexible support used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer e.g. colloidal silica.
  • colloidal silica inert particles of larger size than the colloidal silica can 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. Incorporation of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys.
  • the thickness of the cross-linked hydrophilic layer may vary in the range of 0.2 to 25 ⁇ m and is preferably 1 to 10 ⁇ m.
  • cross-linked hydrophilic layers for use in accordance with the present invention are disclosed in EP-A 601240, GB-P-1419512, FR-P-2300354, US-P-3971660, US-P-4284705 and EP-A 514490.
  • plastic film e.g. substrated polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film etc.
  • the plastic film support may be opaque or transparent.
  • An image-forming layer in connection with the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.
  • Suitable hydrophilic binders for use in an image-forming layer in connection with this invention are water soluble (co)polymers for example synthetic homo- or copolymers such as polyvinylalcohol, a poly(meth)acrylic acid, a poly(meth)acrylamide, a polyhydroxyethyl(meth)acrylate, a polyvinylmethylether or natural binders such as gelatin, a polysaccharide such as e.g. dextran, pullulan, cellulose, arabic gum, alginic acid.
  • water soluble (co)polymers for example synthetic homo- or copolymers such as polyvinylalcohol, a poly(meth)acrylic acid, a poly(meth)acrylamide, a polyhydroxyethyl(meth)acrylate, a polyvinylmethylether or natural binders such as gelatin, a polysaccharide such as e.g. dextran, pullulan, cellulose, arabic gum,
  • the hydrophilic binder can also be a water insoluble, alkali soluble or swellable resin having phenolic hydroxy groups and/or carboxyl groups.
  • the water insoluble, alkali soluble or swellable resin used in connection with the present invention comprises phenolic hydroxy groups.
  • Suitable water insoluble, alkali soluble or swellable resins for use in an image-forming layer in connection with this invention are for example synthetic novolac resins such as ALNOVOL, a registered trade mark of Reichold Hoechst and DUREZ, a registered trade mark of OxyChem and synthetic polyvinylfenols such as MARUKA LYNCUR M, a registered trade mark of Dyno Cyanamid.
  • the hydrophilic binder of the image-forming layer used in connection with the present invention is preferably not cross-linked or only slightly cross-linked.
  • thermoplastic polymer particles preferred in the embodiment of this invention are hydrophobic polymer particles.
  • the hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50°C and more preferably above 70°C. Coagulation may result from softening or melting of the thermoplastic polymer particles under the influence of heat.
  • There is no specific upper limit to the coagulation temperature of the thermoplastic hydrophobic polymer particles however the temperature should be sufficiently below the decomposition temperature of the polymer particles.
  • the coagulation temperature is at least 10°C below the temperature at which the decomposition of the polymer particles occurs.
  • said polymer particles When said polymer particles are subjected to a temperature above the coagulation temperature they coagulate to form a hydrophobic agglomerate in the hydrophilic layer so that at these parts the hydrophilic layer becomes insoluble in plain water or an aqueous liquid.
  • hydrophobic polymer particles for use in connection with the present invention having preferably a Tg above 80°C are preferably polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole etc., copolymers or mixtures thereof. Most preferably used are polystyrene, polymethylmethacrylate or copolymers thereof.
  • the weight average molecular weight of the polymers may range from 5,000 to 1,000,000g/mol as determined by GPC relative to polystyrene standards.
  • the hydrophobic particles may have a particle size from 0.01 ⁇ m to 50 ⁇ m, more preferably between 0.05 ⁇ m and 10 ⁇ m and most preferably between 0.05 ⁇ m and 2 ⁇ m.
  • the polymer particles are present as a dispersion in the aqueous coating liquid of the image-forming layer and may be prepared by the methods disclosed in US-P-3,476,937. Another method especially suitable for preparing an aqueous dispersion of the thermoplastic polymer particles comprises:
  • the amount of hydrophobic thermoplastic polymer particles contained in the image-forming layer is preferably at least 30% by weight and more preferably at least 45% by weight and most preferably at least 60% by weight.
  • the image-forming layer can also comprise crosslinking agents although this is not necessary.
  • Preferred crosslinking agents are low molecular weight substances comprising a methylol group such as for example melamine-formaldehyde resins, glycoluril-formaldehyde resins, thiourea-formaldehyde resins, guanamine-formaldehyde resins, benzoguanamine-formaldehyde resins.
  • a number of said melamine-formaldehyde resins and glycoluril-formaldehyde resins are commercially available under the trade names of CYMEL (Dyno Cyanamid Co., Ltd.) and NIKALAC (Sanwa Chemical Co., Ltd.).
  • the imaging element may further include a compound capable of converting light to heat.
  • This compound is preferably comprised in the image-forming layer but can also be provided in a layer adjacent to the image-forming layer.
  • Suitable compounds capable of converting light into heat are preferably infrared absorbing components.
  • Particularly useful compounds are for example dyes and in particular infrared dyes, 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 .
  • a light-to-heat converting compound in connection with the present invention is most preferably added to the image-forming layer but at least part of the light-to-heat converting compound may also be comprised in a neighbouring layer.
  • the image forming layer may further comprise a diazonium salt, diazo resin or aryldiazosulfonate resin.
  • a diazonium salt, diazo resin or aryldiazosulfonate resin Such offers the advantage that subsequent to image-wise heating and development the printing properties, in particular the ink uptake by the image-areas, can be improved by applying an overall UV exposure to the developed imaging element. Such practice will however only be practical in case of off-line exposure and development rather than in an on-press development.
  • diazo resins useful in the present invention include condensation products of an aromatic diazonium salt as the light-sensitive substance.
  • condensation products are known and are described, for example, in German Pat. no. 1214086. They are in general prepared by condensation of a polynuclear aromatic diazonium compound, preferably of substituted or unsubstituted diphenylamine-4-diazonium salts, with active carbonyl compounds, preferably formaldehyde, in a strongly acid medium.
  • the imaging element is image-wise heated with a thermal head, e.g. in a thermal printer, and subsequently developed with water or an aqueous solution.
  • the imaging element is image-wise heated with a thermal head, e.g. in a thermal printer, and subsequently mounted on a print cylinder of a printing press.
  • 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.
  • the dampener rollers that supply dampening liquid are dropped on the imaging element and subsequent thereto the ink rollers are dropped.
  • the first clear and useful prints are obtained.
  • the ink rollers and dampener rollers may be dropped simultaneously or the ink rollers may be dropped first.
  • 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.
  • 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.
  • imaging element after image-wise heating said imaging element 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 may remove some non-image areas and/or the outermost layer.
  • a cotton pad or sponge soaked with water e.g. a cotton pad or sponge soaked with water
  • the imaging element is first mounted on the print cylinder of the printing press and then image-wise heated directly on the press. Subsequent to heating, the imaging element can be developed as described above.
  • This embodiment requires that a thermal head is build-in the printing press and offers the advantage of shorting total processing time between paste-up of the orginal (e.g. prepared on a computer) and actual printing of copies.
  • the imaging element may be image-wise heated and subsequently developed with plain water or an aqueous liquid.
  • the obtained dispersion was coated on a polyethyleneterephthalate film support (coated with a hydrophilic adhesion layer) to a wet coating thickness of 50 g/m 2 , dried at 30 °C, and subsequently hardened by subjecting it to a temperature of 57 °C for 1 week.
  • thermosensitive layer Preparation of the thermosensitive layer.
  • thermosensitive layer was produced by preparing the following coating composition and coating it to the above described lithographic base in an amount of 30 g/m 2 (wet coating amount) and drying it at 30°C. resulting in a heat-sensitive layer.
  • the above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer with an average printing power of 60 mWatt per dot (300 dpi) (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press.
  • thermosensitive layer The preparation of the lithographic base and the thermosensitive layer was identical with these described in example 1.
  • An outermost layer was produced by preparing the following coating composition and coating it to the above described heat-sensitive-layer in an amount of 40 g/m 2 (wet coating amount) and drying it at 30°C.
  • the above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press. Printing was carried out on an AB Dick 360 offsetpress equipped with a VARN TM KOMPAC II dampening system. As ink, VanSon RB2329 TM and as dampening liquid G671c (3% in water) commercially available from Agfa-Gevaert N.V. were used. Good prints were obtained with the appropriate dimensions and without any ink uptake in the non-image areas. Smearing of the image did not occur.
  • thermosensitive layer The preparation of the lithographic base and the thermosensitive layer was identical with these described in example 1.
  • An outermost layer was produced by preparing the following coating composition and coating it to the above described heat-sensitive-layer in an amount of 40 g/m 2 (wet coating amount) and drying it at 30°C.
  • the above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press. Printing was carried out on an AB Dick 360 offsetpress equipped with a VARN TM KOMPAC II dampening system. As ink, VanSon RB2329 TM and as dampening liquid G671c (3% in water) commercially available from Agfa-Gevaert N.V. were used. Good prints were obtained with the appropriate dimensions and without any ink uptake in the non-image areas.

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

Abstract

The present invention provides an imaging element for making a lithographic printing plate comprising on a flexible support (i) an ink repellant layer containing a crosslinked hydrophilic binder and (ii) a thermosensitive layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder, characterized in that an outermost layer is present on top of said imaging element on the opposite side of the support, said outermost layer comprising at least a solid or liquid lubricant in a hydrophilic binder.

Description

1. Field of the invention.
The present invention relates to a method for making a lithographic printing plate involving the use of a heat-sensitive imaging element. In particular, it concerns improvements in imaging properties due to its surface in contact with the heat source having a particular composition.
2. Background of the invention.
Lithographic printing is the process of printing from specially prepared surfaces, some areas of which are capable of accepting ink, whereas other areas will not accept ink.
In the art of photolithography, a photographic material is made imagewise receptive to oily or greasy ink in the photo-exposed (negative working) or in the non-exposed areas (positive working) on a ink-repelling background.
In the production of common lithographic 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.
Upon imagewise exposure of such 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.
On the other hand, 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. The trend towards heat-sensitive printing plate precursors is clearly seen on the market.
For example, Research Disclosure no. 33303 of January 1992 discloses a heat-sensitive imaging element comprising on a support a cross-linked hydrophilic layer containing thermoplastic polymer particles and an infrared absorbing pigment such as e.g. carbon black. By image-wise exposure to an infrared laser, the thermoplastic polymer particles are image-wise coagulated thereby rendering the surface of the imaging element at these areas ink acceptant without any further development. A disadvantage of this method is that the printing plate obtained is easily damaged since the non-printing areas may become ink-accepting when some pressure is applied thereto. Moreover, under critical conditions, the lithographic performance of such a printing plate may be poor and accordingly such printing plate has little lithographic printing latitude.
EP-A-514145 discloses a heat-sensitive imaging element including a coating comprising core-shell particles having a water insoluble heat softenable core component and a shell component which is soluble or swellable in an aqueous alkaline medium. Red or infrared laser light directed image-wise at said imaging element causes selected particles to coalesce, at least partially, to form an image and the non-coalesced particles are then selectively removed by means of an aqueous alkaline developer. Afterwards a baking step is performed. However the printing endurance of a so obtained printing plate is low.
EP-A-599510 discloses a heat-sensitive imaging element which comprises a substrate coated with (i) a layer which comprises (1) a disperse phase comprising a water-insoluble heat softenable component A and (2) a binder or continuous phase consisting of a component B which is soluble or swellable in aqueous, preferably aqueous alkaline medium, at least one of components A and B including a reactive group or precursor therefor, such that insolubilisation of the layer occurs at elevated temperature and/or on exposure to actinic radiation , and (ii) a substance capable of strongly absorbing radiation and transferring the energy thus obtained as heat to the disperse phase so that at least partial coalescence of the coating occurs. After image-wise irradiation of the imaging element and developing the image-wise irradiated plate, said plate is heated and/or subjected to actinic irradiation to effect insolubilisation. However the printing endurance of a so obtained printing plate is low.
Furthermore EP-A 952022871.0, 952022872.8, 952022873.6 and 952022874.4 disclose a method for making a lithographic printing plate comprising the steps of (1) image-wise exposing to light a heat-sensitive imaging element comprising (i) on a hydrophilic surface of a lithographic base an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and (ii) a compound capable of converting light to heat, said compound being comprised in said image-forming layer or a layer adjacent thereto; (2) and developing a thus obtained image-wise exposed element by rinsing it with plain water.
The above discussed heat-sensitive imaging systems can also be used as direct thermosensitive imaging elements for a recording process wherein images are generated by the use of imagewise modulated thermal energy. In this case the presence of a compound capable of converting light into heat in said image-forming layer or a layer adjacent thereto is not necessary.
In this process the imaging is effected by transporting the heat-sensitive imaging element over a thermal head which generate an image. However the transport of said heat-sensitive imaging element over said thermal head is not adequate so that the image generated on said heat-sensitive imaging system is distorted, damaged and smeared. This latter smearing can occur since the thermoplastic particles melt during the heating process and are transported in the printing direction. Supplementary the thermal head becomes polluted.
3. Summary of the invention.
It is an object of the present invention to provide a thermosensitive imaging element suitable for imaging with a thermal head with excellent transporting properties and developable in a convenient ecological way.
It is another object of the printing invention to provide a thermosensitive imaging element which has no soiling or abrasive effects on the thermal head and shows no smearing after the thermographic imaging process.
It is still another object of the present invention to provide a method for making a lithographic printing plate having excellent printing properties, and without distortion in the direction of the transport of the imaging element during imaging.
Further objects of the present invention will become clear from the description hereinafter.
According to the present invention there is provided an imaging element for making a lithographic printing plate comprising on a flexible support (i) an ink-repellant layer containing a crosslinked hydrophilic binder and (ii) a thermosensitive layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder, characterized in that an outermost layer is present on top of said layers of said imaging element, said outermost layer comprising at least a solid or liquid lubricant in a hydrophilic binder.
Furthermore there is provided according to the present invention a method for making a lithographic printing plate comprising the steps of:
  • (1) image-wise heating by means of a thermal head an imaging element as described above on the side of said outermost layer
  • (2) developing a thus obtained image-wise heated imaging element with water or an aqueous liquid.
    • 4. Detailed description of the invention.
    It has been found that according to the present invention, using an imaging element as described above, the transport of said imaging element over a thermal head is excellent and a lithographic printing plate is obtained with the appropriate dimensions. Moreover, smearing of the image and soiling of the thermal head is avoided.
    According to a preferred embodiment a thermal image forming process, according to the present invention, is realized, wherein the heat source is a thin or thick film thermal head.
    According to the invention the lubricant may be liquid or solid. The solid lubricant may be thermomeltable or not. A lubricant is called thermomeltable when its melting point is below 200 °C. Non-thermomeltable lubricants, such as teflon or inorganic particles can be added to the outermost layer. The addition of inorganic particles is especially recommended. It is advantageous that they protrude through the surface of said outermost layer to reduce building up of debris on the thermal head.
    Inorganic particles such as silica or salts derived from silica such as e.g. talc, clay, china clay, mica, chlorite, silica, or carbonates such as calcium carbonate, magnesium carbonate or calcium magnesium carbonate (dolomite) can be added to the outermost layer in accordance with the invention.
    It is highly preferred to add mixtures of inorganic particles to the outermost layer having a Mohs hardness below 2.7.
    A mixture of talc and dolomite or talc and silica particles is highly preferred.
    According to a preferred embodiment, the thermomeltable lubricant has a melting point below 150 °C. Preferred are solid lubricants having a melting point below 110°C, with solid lubricants with a molecular weight below 1000 being particularly preferred. For the purposes of the present invention solid lubricants are defined as those lubricants being solid at 20 °C.
    Solid thermomeltable lubricants which can be used according to the present invention are polyolefin waxes e.g. polypropylene waxes, ester waxes e.g. fatty acid esters, polyolefin-polyether block copolymers, amide waxes e.g. fatty acid amides, polyglycols e.g. polyethylene glycol, fatty acids, fatty alcohols, natural waxes and solid phosphoric acid ester derivatives.
    Preferred solid thermomeltable lubricants are selected from the group consisting of fatty acid esters, fatty acid amides and phosphoric acid esters. Preferred fatty acid esters are glycerine monostearate, glycerine monopalmitate and mixtures of glycerine monostearate and glycerine monopalmitate. Preferred fatty acid amides are selected from the group consisting of ethylenebisstearamide, stearamide, oleamide, myristamide and erucamide.
    Examples of suitable solid non-phosphoric acid ester derivative lubricants according to the present invention with their melting points are:
    Melting point [°C]
    SL01 ethylenebisstearamide (Ceridust™ 3910 from Hoechst AG) 141
    SL02 myristamide 106
    SL03 stearamide 104
    SL04 glycerine monostearate 81
    SL05 erucamide 80
    SL06 oleamide 73
    SL07 glycerine tristearate 55-73
    SL08 Mobilcer™ Q (a paraffin wax) 67
    SL09 glycerine monotallow acid ester (Rilanit™ GMS from Henkel AG) 55-60
    SL10 sorbitan monostearate (SPAN™ 60 from ICI PLC) 55
    SL11 sorbitan tristearate (SPAN™ 65 from ICI PLC) 48-53
    SL12 sorbitan monopalmitate (SPAN™ 40 from ICI PLC) 44-47
    SL13 POE-(4)-sorbitan monostearate (TWEEN™ 61 from ICI) 36-40
    Examples of suitable solid phosphoric acid ester derivative solid lubricants (PSL) according to the present invention with their melting points are:
    Melting point [°C]
    PSL01 Servoxyl™ VPAZ 100 from Servo Delden BV (mixture of monolauryl and dilauryl phosphates) 33
    PSL02 Servoxyl™ VPRZ 100 from Servo Delden BV (mixture of monocetyl and monostearyl phosphates) 50
    PSL03 potassium alkyl phosphate (Crafol™ AP37 from Henkel AG) 62
    Liquid lubricants which can be used according to the present invention include silicon oils, functionalized silicon oils, silicon block polymers such as polyalkyleneoxide-polysiloxane copolymers, glycerol esters, liquid phosphoric ester derivatives and the like . Liquid phosphoric ester derivatives are preferred among the liquid lubricants.
    Examples of suitable non-phosphoric acid ester derivative liquid lubricants (LL) according to the present invention are:
    LL01:
    glycerine trioleate
    LL02:
    sorbitan monooleate (SPAN™ 80 from Henkel AG)
    LL03:
    sorbitan trioleate (SPAN™ 85 from Henkel AG)
    LL04:
    Tegoglide™ ZG 400 from TEGO-chemie
    Examples of suitable phosphoric acid ester derivative liquid lubricants (PLL) according to the present invention are:
    PLL01:
    Servoxyl™ VPDZ 3 100 from Servo Delden BV {mono[isotridecyl polyglycolether (3 EO)]phosphate}
    PLL02:
    Servoxyl™ VPRZ 6 100 from Servo Delden BV {mono[isotridecyl polyglycolether (6 EO)]phosphate}
    PLL03:
    Servoxyl™ VPFZ 7 100 from Servo Delden BV {mono[oleyl polyglycolether (7 EO)]phosphate}
    PLL04:
    Sermul™ EA224 (= Servoxyl™ VPFZ 7 100) from Servo Delden BV {mono[oleyl polyglycolether (7 EO)]phosphate}
    The use of a mixture of a solid and a liquid lubricant is preferred. Especially preferred are mixtures of liquid and thermomeltable solid lubricants.
    According to the present invention the outermost layer on top of the imaging layers of the imaging element comprises a hydrophilic binder. Suitable hydrophilic binders for said outermost layer are, for example, gelatin, polyvinylalcohol, cellulose derivatives or other polysaccharides, hydroxyethylcellulose, hydroxypropylcellulose etc., with binders having a glass transition temperature above 100 °C being preferred and polyvinylalcohol being particularly preferred.
    Other additives or fillers can also be incorporated in the outermost layer e.g. colloidal particles such as colloidal silica.
    Although hardening of the binder may affect the water processability of the imaging element, a low degree of hardening can improve the thermostability of the outermost layer.
    The thickness of the outermost layer on top of the imaging layer of the imaging element may be any thickness to obtain sufficient protection of the image and the thermal head. Preferably, the thickness of the outermost layer is 0.1 to 10 µm more preferably 0.2 to 5 µm.
    An intermediate layer between the outermost layer and the thermosensitive layer may be used to improve the development properties of the imaging element or to improve the adhesion between the outermost layer and the thermosensitive layer. The binder for said intermediate layer is preferably hydrophilic and the thickness of said layer may be 0.05 to 5 µm. An intermediate layer may be especially usefull when a slightly crosslinked hydrophilic binder is used in the outermost layer.
    In the present invention a heat-sensitive imaging element is used comprising on a hydrophilic surface of a lithographic base an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder. The hydrophilic binder in the image-forming layer used in connection with the present invention is preferably not crosslinked or only slightly crosslinked. The imaging element may further include a compound capable of converting light into heat. This compound is comprised in the image-forming layer or a layer adjacent thereto.
    According to the present invention, the lithographic base comprises a flexible support, such as e.g. paper or plastic film, provided with a cross-linked hydrophilic layer. A particularly suitable cross-linked rough hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or preferably a hydrolysed tetra-alkylorthosilicate.
    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.
    A cross-linked hydrophilic layer on a flexible support used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer e.g. colloidal silica. In addition inert particles of larger size than the colloidal silica can 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. Incorporation of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys.
    The thickness of the cross-linked hydrophilic layer may vary in the range of 0.2 to 25 µm and is preferably 1 to 10 µm.
    Particular examples of suitable cross-linked hydrophilic layers for use in accordance with the present invention are disclosed in EP-A 601240, GB-P-1419512, FR-P-2300354, US-P-3971660, US-P-4284705 and EP-A 514490.
    As flexible support of a crosslinked hydrophilic layer in connection with the present embodiment it is particularly preferred to use a plastic film e.g. substrated polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film etc... The plastic film support may be opaque or transparent.
    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 619524, EP-A 620502 and EP-A 619525.
    Optionally, there may be provided one or more intermediate layers between the hydrophilic base and the image-forming layer. An image-forming layer in connection with the present invention comprises thermoplastic polymer particles dispersed in a hydrophilic binder.
    Suitable hydrophilic binders for use in an image-forming layer in connection with this invention are water soluble (co)polymers for example synthetic homo- or copolymers such as polyvinylalcohol, a poly(meth)acrylic acid, a poly(meth)acrylamide, a polyhydroxyethyl(meth)acrylate, a polyvinylmethylether or natural binders such as gelatin, a polysaccharide such as e.g. dextran, pullulan, cellulose, arabic gum, alginic acid.
    The hydrophilic binder can also be a water insoluble, alkali soluble or swellable resin having phenolic hydroxy groups and/or carboxyl groups.
    Preferably the water insoluble, alkali soluble or swellable resin used in connection with the present invention comprises phenolic hydroxy groups. Suitable water insoluble, alkali soluble or swellable resins for use in an image-forming layer in connection with this invention are for example synthetic novolac resins such as ALNOVOL, a registered trade mark of Reichold Hoechst and DUREZ, a registered trade mark of OxyChem and synthetic polyvinylfenols such as MARUKA LYNCUR M, a registered trade mark of Dyno Cyanamid.
    The hydrophilic binder of the image-forming layer used in connection with the present invention is preferably not cross-linked or only slightly cross-linked.
    The thermoplastic polymer particles preferred in the embodiment of this invention are hydrophobic polymer particles. The hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50°C and more preferably above 70°C. Coagulation may result from softening or melting of the thermoplastic polymer particles under the influence of heat. There is no specific upper limit to the coagulation temperature of the thermoplastic hydrophobic polymer particles, however the temperature should be sufficiently below the decomposition temperature of the polymer particles. Preferably the coagulation temperature is at least 10°C below the temperature at which the decomposition of the polymer particles occurs. When said polymer particles are subjected to a temperature above the coagulation temperature they coagulate to form a hydrophobic agglomerate in the hydrophilic layer so that at these parts the hydrophilic layer becomes insoluble in plain water or an aqueous liquid.
    Specific examples of hydrophobic polymer particles for use in connection with the present invention having preferably a Tg above 80°C are preferably polyvinyl chloride, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole etc., copolymers or mixtures thereof. Most preferably used are polystyrene, polymethylmethacrylate or copolymers thereof.
    The weight average molecular weight of the polymers may range from 5,000 to 1,000,000g/mol as determined by GPC relative to polystyrene standards.
    The hydrophobic particles may have a particle size from 0.01 µm to 50 µm, more preferably between 0.05 µm and 10 µm and most preferably between 0.05 µm and 2 µm.
    The polymer particles are present as a dispersion in the aqueous coating liquid of the image-forming layer and may be prepared by the methods disclosed in US-P-3,476,937. Another method especially suitable for preparing an aqueous dispersion of the thermoplastic polymer particles comprises:
    • dissolving the hydrophobic thermoplastic polymer in an organic water immiscible solvent,
    • dispersing the thus obtained solution in water or in an aqueous medium and
    • removing the organic solvent by evaporation.
    The amount of hydrophobic thermoplastic polymer particles contained in the image-forming layer is preferably at least 30% by weight and more preferably at least 45% by weight and most preferably at least 60% by weight.
    The image-forming layer can also comprise crosslinking agents although this is not necessary. Preferred crosslinking agents are low molecular weight substances comprising a methylol group such as for example melamine-formaldehyde resins, glycoluril-formaldehyde resins, thiourea-formaldehyde resins, guanamine-formaldehyde resins, benzoguanamine-formaldehyde resins. A number of said melamine-formaldehyde resins and glycoluril-formaldehyde resins are commercially available under the trade names of CYMEL (Dyno Cyanamid Co., Ltd.) and NIKALAC (Sanwa Chemical Co., Ltd.).
    The imaging element may further include a compound capable of converting light to heat. This compound is preferably comprised in the image-forming layer but can also be provided in a layer adjacent to the image-forming layer. Suitable compounds capable of converting light into heat are preferably infrared absorbing components. Particularly useful compounds are for example dyes and in particular infrared dyes, 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. WO2.9. It is also possible to use conductive polymer dispersion such as polypyrrole or polyaniline-based conductive polymer dispersions. A light-to-heat converting compound in connection with the present invention is most preferably added to the image-forming layer but at least part of the light-to-heat converting compound may also be comprised in a neighbouring layer.
    According to a particular embodiment in connection with the present invention, the image forming layer may further comprise a diazonium salt, diazo resin or aryldiazosulfonate resin. Such offers the advantage that subsequent to image-wise heating and development the printing properties, in particular the ink uptake by the image-areas, can be improved by applying an overall UV exposure to the developed imaging element. Such practice will however only be practical in case of off-line exposure and development rather than in an on-press development.
    Examples of low-molecular weight diazonium salt for use in the present invention include: benzidine tetrazoniumchloride, 3,3'-dimethylbenzidine tetrazoniumchloride, 3,3'-dimethoxybenzidine tetrazoniumchloride, 4,4'-diaminodiphenylamine tetrazoniumchloride, 3,3'-diethylbenzidine tetrazoniumsulfate, 4-aminodiphenylamine diazoniumsulfate, 4-aminodiphenylamine diazoniumchloride, 4-piperidino aniline diazoniumsulfate, 4-diethylamino aniline diazoniumsulfate and oligomeric condensation products of diazodiphenylamine and formaldehyde.
    Examples of diazo resins useful in the present invention include condensation products of an aromatic diazonium salt as the light-sensitive substance. Such condensation products are known and are described, for example, in German Pat. no. 1214086. They are in general prepared by condensation of a polynuclear aromatic diazonium compound, preferably of substituted or unsubstituted diphenylamine-4-diazonium salts, with active carbonyl compounds, preferably formaldehyde, in a strongly acid medium.
    Examples of aryldiazolsulfonate resins are disclosed in EP-A 339393 and EP-A 507008, the teaching of which is incorporated herein by reference.
    In accordance with a method of the present invention for obtaining a printing plate, the imaging element is image-wise heated with a thermal head, e.g. in a thermal printer, and subsequently developed with water or an aqueous solution.
    In accordance with a preferred method of the present invention for obtaining a printing plate, the imaging element is image-wise heated with a thermal head, e.g. in a thermal printer, and subsequently mounted on a print cylinder of a printing press. 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.
    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. 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.
    It may be advantageous to wipe the imaging element after image-wise heating said imaging element 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 may remove some non-image areas and/or the outermost layer. However, it has the advantage that possible substantial contamination of the dampening system of the press and ink used is avoided.
    According to an alternative method, the imaging element is first mounted on the print cylinder of the printing press and then image-wise heated directly on the press. Subsequent to heating, the imaging element can be developed as described above. This embodiment requires that a thermal head is build-in the printing press and offers the advantage of shorting total processing time between paste-up of the orginal (e.g. prepared on a computer) and actual printing of copies.
    According to a still further method in connection with the present invention, the imaging element may be image-wise heated and subsequently developed with plain water or an aqueous liquid.
    The invention will now be illustrated by way of the following examples without however the intention to limit the invention thereto. All parts are by weight unless otherwise specified.
    EXAMPLE 1 Preparation of a lithographic base.
    To 398 g of a dispersion containing 21.5 % TiO2 (average particle size 0.3 to 0.4 µm) and 2.5 % polyvinyl alcohol in deionized water were subsequently added, while stirring, 195 g of a hydrolyzed 22 % tetramethylorthosilicate emulsion in water and 12 g of a 10 % solution of a wetting agent. To this mixture was added 395 g of deionized water and the pH was adjusted to pH = 4. The obtained dispersion was coated on a polyethyleneterephthalate film support (coated with a hydrophilic adhesion layer) to a wet coating thickness of 50 g/m2, dried at 30 °C, and subsequently hardened by subjecting it to a temperature of 57 °C for 1 week.
    Preparation of the thermosensitive layer.
    The thermosensitive layer was produced by preparing the following coating composition and coating it to the above described lithographic base in an amount of 30 g/m2 (wet coating amount) and drying it at 30°C. resulting in a heat-sensitive layer.
    Preparation of the coating composition for the thermosensitive layer.
    To 105 g of a 20 % dispersion of polymethylmethacrylate/polystyrene (80/20) copolymer (particle diameter of 100 nm) stabilized with Hostapal B (available from Hoechst) in deionized water was subsequently added, while stirring, 20 g of a 15 % dispersion of Printex L6 (a carbon black dispersion available form Degussa) stabilized with Ultravon W (available from Ciba-Geigy), 120 g of a 5 % solution of a 98 % hydrolized polyvinylacetate, having a weight average molecular weight of 200000 g/mol (MOWIOL 56-98 available from Hoechst), in water, 745 ml of water and 10 g of a 10 % solution of a wetting agent.
    Preparation of the outermost layer.
    The outermost layer was produced by preparing the following coating composition and coating it to the above described heat-sensitive-layer in an amount of 40 g/m2 (wet coating amount) and drying it at 30°C.
    Preparation of the coating composition of the outermost layer
    To 535,6 g of water was subsequently added, while stirring, 387,5 g of a 5 % solution of a 98 % hydrolized polyvinylacetate, having a weight average molecular weight of 200 000 g/mol (MOWIOL 56-98 available from Hoechst) in water, 1,9 g of Servoxyl VPDZ3/100 (available from Servo Delden BV) and 75 g of a 5 % dispersion of Rilanit GMS (available from Henkel) stabilized with Gafac RM710 (available from GAF) in water.
    Preparation of a printing plate and making copies of the original.
    The above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer with an average printing power of 60 mWatt per dot (300 dpi) (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press.
    Printing was carried out on an AB Dick 360 offsetpress equipped with a VARN ™ KOMPAC II dampening system. As ink, VanSon RB2329™ and as dampening liquid G 671c (3% in water) commercially available from Agfa-Gevaert N.V. were used.
    Good prints were obtained with the appropriate dimensions and without any ink uptake in the non-image areas.
    EXAMPLE 2 :
    The preparation of the lithographic base and the thermosensitive layer was identical with these described in example 1.
    Preparation of the outermost layer.
    An outermost layer was produced by preparing the following coating composition and coating it to the above described heat-sensitive-layer in an amount of 40 g/m2 (wet coating amount) and drying it at 30°C.
    Preparation of the coating composition for the outermost layer.
    To 366,5 g of water was subsequently added, while stirring, 18 g of a 5 % solution of Ultravon W - acidic form (Ultravon W available from Ciba-Geigy) in water, 454,5 g of a 5 % solution of a 98,5 % hydrolized polyvinylacetate, having a weight average molecular weight of 90 000 g/mol (POLYVIOL WX 48/20 available from Wacker), in water, 45 g of a dispersion containing 2 % of Servoxyl VPDZ3/100 (available from Servo Delden BV), 2 % of Servoxyl VPAZ 100 (available from Servo Delden BV), 2,4 % of Syloid 72 (available from Grace GMBH), 1,2 % of Steamic 00S (available from Talc de Luzenac) and 3 % of a 98,5 % hydrolized polyvinylacetate, having a weight average molecular weight of 90 000 g/mol (POLYVIOL WX 48/20 available from Wacker), stabilized with Gafac RM710 (available from GAF) in water, 36 g of a 5 % dispersion of Rilanit GMS (available from Henkel) stabilized with Gafac RM710 (available from GAF) and 80 g Kieselsol 500F (available from Bayer).
    Preparation of a printing plate and making copies of the original.
    The above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press. Printing was carried out on an AB Dick 360 offsetpress equipped with a VARN ™ KOMPAC II dampening system. As ink, VanSon RB2329 ™ and as dampening liquid G671c (3% in water) commercially available from Agfa-Gevaert N.V. were used.
    Good prints were obtained with the appropriate dimensions and without any ink uptake in the non-image areas. Smearing of the image did not occur.
    EXAMPLE 3 :
    The preparation of the lithographic base and the thermosensitive layer was identical with these described in example 1.
    Preparation of the outermost layer.
    An outermost layer was produced by preparing the following coating composition and coating it to the above described heat-sensitive-layer in an amount of 40 g/m2 (wet coating amount) and drying it at 30°C.
    Preparation of the coating composition for the outermost layer.
    To 366,5 g of water was subsequently added, while stirring, 18 g of a 5 % Solution of Ultravon W - acidic form (Ultravon W available from Ciba-Geigy) in water, 454,5 g of a 5 % solution of a 98,5 % hydrolized polyvinylacetate, having a weight average molecular weight of 90 000 g/mol (POLYVIOL WX 48/20 available from Wacker), in water, 45 g of a dispersion containing 2 % of Servoxyl VPDZ3/100 (available from Servo Delden BV), 2 % of Servoxyl VPAZ 100 (available from Servo Delden BV), 2,4 % of Syloid 72 (available from Grace GMBH), 1,2 % of Steamic 00S (available from Talc de Luzenac) and 3 % of a 98,5 % hydrolized polyvinylacetate, having a weight average molecular weight of 90 000 g/mol (POLYVIOL WX 48/20 available from Wacker), stabilized with Gafac RM710 (available from GAF) in water and 36 g of a 5 % dispersion of Rilanit GMS (available from Henkel) stabilized with Gafac RM710 (available from GAF).
    Preparation of a printing plate and making copies of the original.
    The above described imaging element was printed (exposed) in a DRYSTAR 2000 thermal printer (commercially available from Agfa) and hereafter the unexposed parts are washed-off manually or on press. Printing was carried out on an AB Dick 360 offsetpress equipped with a VARN ™ KOMPAC II dampening system. As ink, VanSon RB2329 ™ and as dampening liquid G671c (3% in water) commercially available from Agfa-Gevaert N.V. were used. Good prints were obtained with the appropriate dimensions and without any ink uptake in the non-image areas.

    Claims (10)

    1. An imaging element for making a lithographic printing plate comprising on a flexible support (i) an ink repellant layer containing a crosslinked hydrophilic binder and (ii) a thermosensitive layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder, characterized in that an outermost layer is present on top of said layers of said imaging element, said outermost layer comprising at least a solid or liquid lubricant in a hydrophilic binder.
    2. An imaging element according to claim 1, wherein said lubricant is a thermomeltable solid or a liquid.
    3. An imaging element according to claim 1 or 2 wherein said outermost layer comprises a mixture of a thermomeltable solid lubricant and a liquid lubricant.
    4. An imaging element according to any of the preceding claims, wherein said solid lubricant is selected from the group consisting of fatty acid esters, fatty acid amides and phosphoric acid ester derivatives.
    5. An imaging element according to any of claims 1 to 3,wherein said liquid lubricant is a phosphoric acid ester derivative
    6. An imaging element according to any of the preceding claims, wherein said outermost layer has a thickness between 0.1 and 10 µm.
    7. An imaging element according to any of the preceding claims, wherein said outermost layer further comprises inorganic particles protruding from the surface of said outermost layer.
    8. An imaging element according to any of the preceding claims, wherein said outermost layer further comprises a colloidal filler.
    9. A method for making a lithographic printing plate comprising the steps of:
      (1) image-wise heating by means of a thermal head an imaging element according to one of the claims 1 to 8:
      (2) developing a thus obtained image-wise heated imaging element with water or an aqueous liquid.
    10. A method for making a lithographic printing plate comprising the steps of:
      (1) mounting an imaging element according to one of the claims 1 to 8 on a print cylinder of a printing press;
      (2) image-wise heating said imaging element by means of a thermal head;
      (3) and developing a thus obtained image-wise heated imaging element by supplying an aqueous dampening liquid and/or ink to said image forming layer while rotating said print cylinder.
    EP96203632A 1996-12-19 1996-12-19 Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties Ceased EP0849090A3 (en)

    Priority Applications (2)

    Application Number Priority Date Filing Date Title
    EP96203632A EP0849090A3 (en) 1996-12-19 1996-12-19 Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties
    JP36390797A JPH10193824A (en) 1996-12-19 1997-12-18 Heat-sensitive image forming element for manufacturing lithographic printing plate having improved transfer characteristic

    Applications Claiming Priority (1)

    Application Number Priority Date Filing Date Title
    EP96203632A EP0849090A3 (en) 1996-12-19 1996-12-19 Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties

    Publications (2)

    Publication Number Publication Date
    EP0849090A2 true EP0849090A2 (en) 1998-06-24
    EP0849090A3 EP0849090A3 (en) 1998-07-01

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    EP96203632A Ceased EP0849090A3 (en) 1996-12-19 1996-12-19 Thermosensitive imaging element for the preparation of lithographic printing plates with improved transporting properties

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    WO1998051496A1 (en) * 1997-05-10 1998-11-19 Agfa-Gevaert Naamloze Vennootschap Improvements in or relating to the formation of images
    EP1065049A1 (en) * 1999-06-29 2001-01-03 Agfa-Gevaert N.V. Heat-sensitive imaging element with cover layer for providing a lithographic printing plate
    US6503684B1 (en) 1999-06-29 2003-01-07 Agfa-Gevaert Processless thermal printing plate with cover layer containing compounds with cationic groups
    US6551757B1 (en) 2001-05-24 2003-04-22 Eastman Kodak Company Negative-working thermal imaging member and methods of imaging and printing
    EP1334841A3 (en) * 2002-02-06 2004-08-25 Konica Corporation Planographic printing plate precursor and printing method employing the same
    EP1685957A3 (en) * 2005-01-26 2006-08-16 Fuji Photo Film Co., Ltd. Lithographic printing plate precursor, lithographic printing method and packaged body of lithographic printing plate precursors
    WO2006133741A1 (en) * 2005-06-17 2006-12-21 Agfa Graphics Nv Method for making a negative-working lithographic printing plate precursor.
    EP1777067A1 (en) * 2005-10-20 2007-04-25 Agfa Graphics N.V. A method for making a lithographic printing plate precursor
    EP2065211A1 (en) 2007-11-30 2009-06-03 Agfa Graphics N.V. A method for treating a lithographic printing plate
    EP2098376A1 (en) 2008-03-04 2009-09-09 Agfa Graphics N.V. A method for making a lithographic printing plate support
    EP2106924A1 (en) 2008-03-31 2009-10-07 Agfa Graphics N.V. A method for treating a lithographic printing plate
    US8419923B2 (en) 2006-08-03 2013-04-16 Agfa Graphics Nv Lithographic printing plate support
    US8679726B2 (en) 2012-05-29 2014-03-25 Eastman Kodak Company Negative-working lithographic printing plate precursors
    EP3032334A1 (en) 2014-12-08 2016-06-15 Agfa Graphics Nv A system for reducing ablation debris
    WO2017157572A1 (en) 2016-03-16 2017-09-21 Agfa Graphics Nv Apparatus for processing a lithographic printing plate and corresponding method
    EP3637188A1 (en) 2018-10-08 2020-04-15 Agfa Nv An effervescent developer precursor for processing a lithographic printing plate precursor
    CN111471508A (en) * 2020-05-09 2020-07-31 中国乐凯集团有限公司 Lubricant and preparation method thereof, direct thermal imaging material and preparation method thereof
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    JP4558907B2 (en) * 2000-08-31 2010-10-06 株式会社きもと Lithographic printing plate material and plate making method using the same
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    WO1998051496A1 (en) * 1997-05-10 1998-11-19 Agfa-Gevaert Naamloze Vennootschap Improvements in or relating to the formation of images
    EP1065049A1 (en) * 1999-06-29 2001-01-03 Agfa-Gevaert N.V. Heat-sensitive imaging element with cover layer for providing a lithographic printing plate
    US6503684B1 (en) 1999-06-29 2003-01-07 Agfa-Gevaert Processless thermal printing plate with cover layer containing compounds with cationic groups
    US6551757B1 (en) 2001-05-24 2003-04-22 Eastman Kodak Company Negative-working thermal imaging member and methods of imaging and printing
    EP1334841A3 (en) * 2002-02-06 2004-08-25 Konica Corporation Planographic printing plate precursor and printing method employing the same
    EP1685957A3 (en) * 2005-01-26 2006-08-16 Fuji Photo Film Co., Ltd. Lithographic printing plate precursor, lithographic printing method and packaged body of lithographic printing plate precursors
    US7910286B2 (en) 2005-01-26 2011-03-22 Fujifilm Corporation Lithographic printing plate precursor, lithographic printing method and packaged body of lithographic printing plate precursors
    US7767384B2 (en) 2005-06-17 2010-08-03 Agfa Graphics Nv Method for making a negative-working lithographic printing plate precursor
    WO2006133741A1 (en) * 2005-06-17 2006-12-21 Agfa Graphics Nv Method for making a negative-working lithographic printing plate precursor.
    US7867572B2 (en) 2005-10-20 2011-01-11 Agfa Graphics Nv Method for making a lithographic printing plate precursor
    CN101287603B (en) * 2005-10-20 2010-04-14 爱克发印艺公司 Method for making lithographic printing plate precursor and lithographic printing plate
    WO2007045607A1 (en) * 2005-10-20 2007-04-26 Agfa Graphics Nv A method for making a lithographic printing plate precursor
    EP1777067A1 (en) * 2005-10-20 2007-04-25 Agfa Graphics N.V. A method for making a lithographic printing plate precursor
    US8419923B2 (en) 2006-08-03 2013-04-16 Agfa Graphics Nv Lithographic printing plate support
    EP2065211A1 (en) 2007-11-30 2009-06-03 Agfa Graphics N.V. A method for treating a lithographic printing plate
    EP2098376A1 (en) 2008-03-04 2009-09-09 Agfa Graphics N.V. A method for making a lithographic printing plate support
    EP2106924A1 (en) 2008-03-31 2009-10-07 Agfa Graphics N.V. A method for treating a lithographic printing plate
    US8679726B2 (en) 2012-05-29 2014-03-25 Eastman Kodak Company Negative-working lithographic printing plate precursors
    EP3032334A1 (en) 2014-12-08 2016-06-15 Agfa Graphics Nv A system for reducing ablation debris
    WO2017157571A1 (en) 2016-03-16 2017-09-21 Agfa Graphics Nv Method and apparatus for processing a lithographic printing plate
    WO2017157572A1 (en) 2016-03-16 2017-09-21 Agfa Graphics Nv Apparatus for processing a lithographic printing plate and corresponding method
    WO2017157579A1 (en) 2016-03-16 2017-09-21 Agfa Graphics Nv Method for processing a lithographic printing plate
    WO2017157576A1 (en) 2016-03-16 2017-09-21 Agfa Graphics Nv Method for processing a lithographic printing plate
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    WO2020074258A1 (en) 2018-10-08 2020-04-16 Agfa Nv An effervescent developer precursor for processing a lithographic printing plate precursor
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