Classifications

• • 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
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/46—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography characterised by the light-to-heat converting means; characterised by the heat or radiation filtering or absorbing means or layers
  • B41M5/465—Infrared radiation-absorbing materials, e.g. dyes, metals, silicates, C black
• • 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
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/04—Negative working, i.e. the non-exposed (non-imaged) areas are removed
• • 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
  • B41C2210/22—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

Definitions

• the present invention relates to a heat sensitive material for making a lithographic printing plate.
• the present invention further relates to a method for preparing a printing plate from said heat sensitive material.
• 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 form the printing image areas and the ink-rejecting areas form the background areas.
• a photographic materials 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 hydrophilic 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- 514 145 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 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- 599 510 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.
• said plate 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.
• the printing endurance of a so obtained printing plate is low.
• EP-A- 625 728 discloses an imaging element comprising a layer which is sensitive to UV- and IR-irradiation and which can be positive or negative working.
• This layer comprises a resole resin a novolac resin, a latent Bronsted acid and an IR-absorbing substance.
• the printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
• US-P- 5 340 699 is almost identical with EP-A- 625 728 but discloses the method for obtaining a negative working IR-laser recording imaging element.
• the IR-sensitive layer comprises a resole resin,a novolac resin, a latent Bronsted acid and an IR-absorbing substance.
• the printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
• US-P- 4 708 925 discloses a positive working imaging element including a photosensitive composition comprising an alkali-soluble novolac resin and an onium-salt. This composition can optionally contain an IR-sensitizer. After image-wise exposing said imaging element to UV - visible - or eventually IR-radiation followed by a development step with an aqueous alkali liquid there is obtained a positive working printing plate. The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
• EP-A-0 800 928 discloses 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 water insoluble alkali soluble or swellable resin and a compound capable of converting light into heat, said compound being present in said image forming layer or a layer adjacent thereto, wherein said alkali swellable or soluble resin comprises phenolic hydroxy groups and/or carboxyl groups.
• said alkali swellable or soluble resin comprises phenolic hydroxy groups and/or carboxyl groups.
• Analogous imaging elements comprising on a hydrophilic surface of a lithographic base an image forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a water or alkali soluble or swellable resin and a compound capable of converting light into heat, said compound being present in said image forming layer or a layer adjacent thereto are disclosed in e.g.
• EP-A 0 832 739, EP-A 0 839 648, EP-A 0 839 647 and EP-A 0 849 091 belong to the prior art according to Article 54(3)(4) EPC.
• poly(meth)acrylate latices are used as thermoplastic polymer particles and no specific hydrophilic resin is mentioned
• carbon black or an IR-dye are mentioned as the compound capable of converting light into heat.
• IR-dyes should be used. Carbon black causes indeed a soiling on the press when removing the unexposed areas. On the other hand when using IR-dyes the unexposed areas are not completely dissolved when developing on the press resulting in scumming.
• a heat sensitive imaging element comprising on a lithographic base with a hydrophilic surface an image forming layer including thermoplastic particles of a homopolymer or a copolymer of styrene and a hydrophilic polymer containing carboxyl groups, characterized in that said imaging element further contains an anionic IR- cyanine dye being present in said image forming layer or a layer adjacent thereto,
• lithographic printing plates of high quality, giving prints with excellent ink acceptance can be obtained according to the method of the present invention using an imaging element as described above. More precisely it has been found that said printing plates are of high quality and are provided in a convenient way, thereby offering economical and ecological advantages.
• the image forming layer or a layer adjacent thereto comprises in accordance with the present invention an anionic IR-cyanine dye, which serves as light to heat converting compound.
• a mixture of anionic IR-cyanine dyes may be used, but it is preferred to use only one anionic IR-cyanine dye.
• Particularly useful anionic IR-cyanine dyes are IR-cyanines dyes with at least two sulphonic groups. Still more preferably are IR-cyanines dyes with two indolenine and at least two sulphonic acid groups. Most preferable is compound I with the structures as indicated. Compound II with the structure as indicated gives also very good results.
• the amount of anionic IR-cyanine dye contained in the image forming layer is preferably between 1% by weight and 40% by weight and more preferably between 2% by weight and 30% by weight and most preferably between 5% by weight and 20% by weight of said image forming layer.
• the lithographic base having a hydrophilic surface can be an anodised aluminum.
• a particularly preferred lithographic base having a hydrophilic surface is an electrochemically grained and anodised aluminum support.
• said aluminum support is grained in nitric acid, yielding imaging elements with a higher sensitivity.
• an anodised aluminum support may be treated to improve the hydrophilic properties of its surface.
• the aluminum support may be silicated by treating its surface with sodium silicate solution at elevated temperature, e.g. 95°C.
• a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution that may further contain an inorganic fluoride.
• the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or can be carried out at a slightly elevated temperature of about 30 to 50°C.
• a further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution.
• the aluminum oxide surface may be treated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulphonic acid, polyvinylbenzenesulphonic acid, sulphuric acid esters of polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulphonated aliphatic aldehyde. It is further evident that one or more of these post treatments may be carried out alone or in combination.
• the lithographic base having a hydrophilic surface comprises a flexible support, such as e.g. paper or plastic film, provided with a cross-linked hydrophilic layer.
• a particularly suitable cross-linked hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetraalkylorthosilicate. 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, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• the hydrophilicity of the (co)polymer or (co)polymer mixture used is preferably the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60 percent by weight, preferably 80 percent by weight.
• 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, preferably between 0.5 and 5 parts by weight, more preferably between 1.0 parts by weight and 3 parts by weight.
• a cross-linked hydrophilic layer in a lithographic base used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer.
• 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 can be added e.g. silica prepared according to Stöber as described in J. Colloid and Interface Sci., Vol.
• 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 thickness of a cross-linked hydrophilic layer in a lithographic base in accordance with this embodiment may vary in the range of 0.2 to 25 ⁇ m and is preferably 1 to 10 ⁇ m.
• 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 m2 and 750 mg per m2.
• 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 m2 per gram, more preferably at least 500 m2 per gram.
• the hydrophobic thermoplastic polymer latices used in connection with the present invention are copolymers or preferably homopolymers of styrene and 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 latices under the influence of heat.
• the coagulation temperature of the thermoplastic hydrophobic polymer latices there is no specific upper limit to the coagulation temperature of the thermoplastic hydrophobic polymer latices, however the temperature should be sufficiently below the decomposition temperature of the polymer latices.
• the coagulation temperature is at least 10°C below the temperature at which the decomposition of the polymer latices occurs.
• the weight average molecular weight of the hydrophobic thermoplastic polymer may range from 5,000 to 1,000,000g/mol.
• the hydrophobic thermoplastic polymer latex may have a particle size from 0.01 ⁇ m to 50 ⁇ m, more preferably between 0.01 mm and 10 mm, still more preferably between 0.01 ⁇ m and 1 ⁇ m and most preferably between 0.02 ⁇ m and 0.15 ⁇ m.
• thermoplastic polymer latex is 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 latex comprises:
• the amount of hydrophobic thermoplastic polymer latex contained in the image forming layer is preferably between 20% by weight and 95% by weight and more preferably between 40% by weight and 90% by weight and most preferably between 50% by weight and 85% by weight of said image forming layer.
• the image forming layer also contains as binder a hydrophilic polymer containing carboxyl groups.
• a hydrophilic polymer containing carboxyl groups is a homo- or copolymer of poly(meth)acrylate.
• the weight average molecular weight of the hydrophilic polymer may range from 2,000 to 1,000,000g/mol, more preferably from 5000 to 500,000 g:mol, most preferably from 10,000 to 100,000 g/mol.
• 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.)
• An anionic IR-cyanine dye in connection with the present invention is most preferably added to the image forming layer but at least part of the anionic IR-cyanine dye may also be comprised in a neighbouring layer.
• Such layer can be for example the cross-linked hydrophilic layer of the lithographic base according to the second embodiment of lithographic bases explained above.
• the imaging element is image-wise exposed to IR-light and subsequently developed with an aqueous solution having a pH between 3.5 and 13, most preferably between 4 and 8.
• Image-wise exposure in connection with the present invention is preferably an image-wise scanning exposure involving the use of a laser or L.E.D.. It is highly preferred in connection with the present invention to use a laser emitting in the infrared (IR) and/or near-infrared, i.e. emitting in the wavelength range 700-1500nm. Particularly preferred for use in connection with the present invention are laser diodes emitting in the near-infrared.
• IR infrared
• near-infrared i.e. emitting in the wavelength range 700-1500nm.
• laser diodes emitting in the near-infrared are particularly preferred for use in connection with the present invention.
• the exposure of the imaging element can be carried out with the imaging element 'already on the press.
• a computer or other information source supplies graphics and textual information to a L.E.D.or a laser via a 'lead.
• the imaging element is image-wise exposed and subsequently is 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.
• 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.
• an image-wise exposed imaging element e.g. a cotton pad or sponge soaked with water before mounting the imaging element on the press or at least before the printing press starts running. This will remove some non-image areas but will not actually develop the imaging element.
• it has the advantage that possible substantial contamination of the dampening system of the press and ink used is avoided.
• a 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution containing 5 g/l of sodium hydroxide at 50°C and rinsed with demineralized water.
• the foil was then electrochemically grained using an alternating current in an aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of hydroboric acid and 5 g/l of aluminum ions at a temperature of 35°C and a current density of 1200 A/m 2 to form a surface topography with an average center-line roughness Ra of 0.5 mm.
• the aluminum foil was then etched with an aqueous solution containing 300 g/l of sulfuric acid at 60°C for 180 seconds and rinsed with demineralized water at 25°C for 30 seconds.
• the foil was subsequently subjected to anodic oxidation in an aqueous solution containing 200 g/l of sulfuric acid at a temperature of 45°C, a voltage of about 10 V and a current density of 150 A/m2 for about 300 seconds to form an anodic oxidation film of 3.00 g/m2 of Al2O3, then washed with demineralized water and posttreated with a solution containin g polyvinylphosphonic acid , rinsed with demineralized water at 20°C during 120 seconds and dried.
• An imaging element according to the invention was produced by preparing the following coating composition 1 and coating it to the above described lithographic base in an amount of 30 g/m 2 (wet coating amount) and drying it at 35°C.
• Imaging elements 2-3-4 were produced by preparing the coating compositions 2-3-4 and coating them to the above described lithographic base in an amount of 30 g/m 2 (wet coating amount) and drying it at 35°C.
• a lithographic base was prepared as described in example 1.
• An imaging element 5 according to the invention was produced by preparing the coating composition 5 and coating it to the above described lithographic base in an amount of 30 g/m 2 (wet coating amount) and drying it at 35°C.
• Other imaging elements 6-7-8 were produced by preparing the coating compositions 6-7-8 and coating them to the above described lithographic base in an amount of 30 g/m 2 (wet coating amount) and drying it at 35°C.
• Imaging element 5-8 as described above were imaged with a Creo 3244T thermal platesetter using 830nm laser diodes (scanspeed 75 rpm at 2540dpi and the total power on the plate surface was 11 W).

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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)
• Photosensitive Polymer And Photoresist Processing (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (2)

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Family Applications (1)

Country Status (3)

Cited By (68)

Families Citing this family (80)

Family Cites Families (4)

• 1998
  • 1998-01-23 EP EP19980200187 patent/EP0931647B1/en not_active Expired - Lifetime
  • 1998-01-23 DE DE69812871T patent/DE69812871T2/de not_active Expired - Lifetime
• 1999
  • 1999-01-20 JP JP1190899A patent/JPH11265062A/ja active Pending

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