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
  • B41C1/1016—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 characterised by structural details, e.g. protective layers, backcoat layers or several 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
  • B41C2210/02—Positive working, i.e. the exposed (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
  • B41C2210/06—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
  • B41C2210/14—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 preparing a lithographic printing plate using a heat mode imaging element whereby the capacity of the top layer of being penetrated and/or solubilised by an aqueous developer is changed upon exposure.
• the invention is related to a method for preparing a lithographic printing plate using a heat mode imaging element by developing with an alkaline solution having a pH of at least 12 and a surface tension of at least 30 mN/m..
• 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 material is made imagewise receptive to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophilic background.
• lithographic printing plates also called surface litho plates or planographic printing plates
• a support that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition.
• Coatings for that purpose include light-sensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
• the exposed image areas become insoluble and the unexposed areas remain soluble.
• the plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
• printing plates are known that include a photosensitive coating that upon image-wise exposure is rendered soluble at the exposed areas. Subsequent development then removes the exposed areas.
• a typical example of such photosensitive coating is a quinone-diazide based coating.
• the above described photographic materials from which the printing plates are made are camera-exposed through a photographic film that contains the image that is to be reproduced in a lithographic printing process.
• Such method of working is cumbersome and labor intensive.
• the printing plates thus obtained are of superior lithographic quality.
• GB-1 492 070 discloses a method wherein a metal layer or a layer containing carbon black is provided on a photosensitive coating. This metal layer is then ablated by means of a laser so that an image mask on the photosensitive layer is obtained The photosensitive layer is then overall exposed by UV-light through the image mask. After removal of the image mask, the photosensitive layer is developed to obtain a printing plate. This method however still has the disadvantage that the image mask has to be removed prior to development of the photosensitive layer by a cumbersome processing.
• 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.
• US-P- 4 708 925 discloses imaging elements including a photosensitive composition comprising an alkali-soluble novolac resin and an onium-salt. This composition may optionally contain an IR-sensitizer. After image-wise exposing said imaging element to UV - visible - or IR-radiation followed by a development step with an aqueous alkali liquid there is obtained a positive or negative working printing plate. The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.
• EP-A- 625 728 discloses an imaging element comprising a layer which is sensitive to UV- and IR-irradiation and which may 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.
• EP-A- 678 380 discloses a method wherein a protective layer is provided on a grained metal support underlying a laser-ablatable surface layer. Upon image-wise exposure the surface layer is fully ablated as well as some parts of the protective layer. The printing plate is then treated with a cleaning solution to remove the residu of the protective layer and thereby exposing the hydrophilic surface layer.
• EP-A- 97 200 588.8 discloses a heat mode imaging element for making lithographic printing plates comprising on a lithographic base having a hydrophilic surface an intermediate layer comprising a polymer, soluble in an aqueous alkaline solution and a top layer that is sensitive to IR-radiation wherein said top layer upon exposure to IR-radiation has a decreased or increased capacity for being penetrated and/or solubilised by an aqueous alkaline solution.
• Said polymer soluble in an alkaline solution is preferably a novolac.
• the image differentation between exposed and non exposed materials is based on an increased wettability or penetration on the exposed areas. It was observed that the properties of the obtained lithographic plate were deficient in many cases certainly regarding the dot rendering, making said plates unsuitable for high quality printing. So an amelioration of said property is requested.
• the top layer is also called the second layer.
• the first layer and the top layer are different.
• a method for making lithographic printing plates including the following steps:
• the top layer in accordance with the present invention comprises an IR-dye and a binder resin.
• a mixture of IR-dyes may be used, but it is preferred to use only one IR-dye.
• IR-dyes are IR-cyanines dyes.
• Particularly useful IR-cyanine dyes are cyanines dyes with two acid groups, more preferably with two sulphonic groups .
• the top layer may preferably comprise as binder a water insoluble polymer such as a cellulose ester, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, silicone resins, etc.
• a water insoluble polymer such as a cellulose ester, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, silicone resins, etc.
• the ratio between the total amount of IR-cyanine dyes and resin binder preferably ranges from 1:99 to 100:0, more preferably from 5:95 to 95:5.
• the total amount of the top layer preferably ranges from 0.1 to 10 g/m 2 more preferably from 0.3 to 2 g/m 2 .
• top layer a difference in the capacity of being penetrated and/or solubilised by the aqueous alkaline solution is generated upon image-wise exposure for an alkaline developer according to the invention.
• the said capacity is increased upon image-wise IR exposure to such degree that the imaged parts will be cleaned out during development without solubilising and/or damaging the non-imaged parts.
• the development with the aqueous alkaline solution is preferably done within an interval of 5 to 120 seconds.
• the present invention comprises a first layer soluble in an aqueous developing solution, more preferably an aqueous alkaline developing solution with preferentially a pH between 7.5 and 14.
• Said layer is preferably contiguous to the top layer but other layers may be present between the top layer and the first layer.
• the alkali soluble binders used in this layer are preferably hydrophobic binders as used in conventional positive or negative working PS-plates e.g. novolac, polyvinyl phenols, carboxy substituted polymers etc. Typical examples of these polymers are descibed in DE-A- 4 007 428, DE-A- 4 027 301 and DE-A- 4 445 820 .
• the hydrophobic binder used in connection with the present invention is further characterised by insolubility in water and partial solubility/swellability in an alkaline solution and/or partial solubility in water when combined with a cosolvent.
• this aqueous alkali soluble layer is preferably a visible light- and UV-light desensitised layer Said layer is preferably thermally hardenable.
• This preferably visible light- and UV-desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• Said first layer preferably also includes a low molecular acid, preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• a low molecular acid preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• the ratio between the total amount of low molecular acid or benzophenone and polymer in the first layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 20:80.
• the total amount of said first layer preferably ranges from 0.1 to 10 g/m 2 , more preferably from 0.3 to 2 g/m 2 .
• the lithographic base may be an anodised aluminum for all embodiments.
• a particularly preferred lithographic base is an electrochemically grained and anodised aluminum support.
• the anodised aluminum support may be treated to improve the hydrophilic properties of its surface.
• 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 may be carried out at a slightly elevated temperature of about 30 to 50°C.
• a further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution.
• 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 for all embodiments.
• a particularly suitable cross-linked hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetra-alkylorthosilicate. The latter is particularly preferred.
• 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, more preferably between 0 5 and 5 parts by weight, most preferably between 1.0 parts by weight and 3 parts by weight.
• a cross-linked hydrophilic layer 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 may 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 m 2 and 750 mg per m 2 .
• the ratio of silica to hydrophilic binder is preferably more than 1 and the surface area of the colloidal silica is preferably at least 300 m 2 per gram, more preferably at least 500 m 2 per gram.
• the top layer in accordance with the present invention comprises an organic quaternary ammonium salt.
• a mixture of organic quaternary ammonium salts may be used, but it is preferred to use only one organic quaternary ammonium salt.
• Said organic quaternary ammonium salt may be a low molecular compound, preferably containing at least a C 6 carbon chain, more preferably containing at least a C 12 carbon groep, still more preferably at least a C 12 aliphatic group.
• Most preferable said organic quaternary ammonium salt is a polymer, particularly preferable a poly-p-vinylbenzyltrimethylammonium salt.
• the top layer may comprise as binder a water insoluble polymer such as a cellulose ester, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, silicone resins, etc.
• a water insoluble polymer such as a cellulose ester, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, silicone resins, etc.
• the top layer may comprises as a binder resin in accordance with the present invention preferably a water soluble polymer.
• a water soluble polymer a protein, preferably gelatin may be used.
• synthetic, semi-synthetic, or natural water soluble polymers may be used.
• Synthetic polymers are e.g. polyvinyl alcohol, poly-N-vinyl pyrrolidone, polyvinyl imidazole, polyvinyl pyrazole, polyacrylamide, polyacrylic acid, and derivatives thereof, in particular copolymers thereof.
• Natural substitutes for gelatin are e.g. other proteins such as zein, albumin and casein, cellulose, saccharides, starch, and alginates.
• the semi-synthetic substitutes for gelatin are modified natural products e.g. gelatin derivatives obtained by conversion of gelatin with alkylating or acylating agents or by grafting of polymerizable monomers on gelatin, and cellulose derivatives such as hydroxyalkyl cellulose, carboxymethyl cellulose, phthaloyl cellulose, and cellulose sulphates.
• modified natural products e.g. gelatin derivatives obtained by conversion of gelatin with alkylating or acylating agents or by grafting of polymerizable monomers on gelatin
• cellulose derivatives such as hydroxyalkyl cellulose, carboxymethyl cellulose, phthaloyl cellulose, and cellulose sulphates.
• the total amount of the top layer preferably ranges from 0.1 to 10 g/m 2 more preferably from 0.3 to 2 g/m 2 .
• top layer a difference in the capacity of being penetrated and/or solubilised by the aqueous alkaline solution is generated upon image-wise exposure for an alkaline developer according to the invention.
• the said capacity is increased upon image-wise exposure to actinic light to such degree that the imaged parts will be cleaned out during development without solubilising and/or damaging the non-imaged parts.
• the development with the aqueous alkaline solution is preferably done within an interval of 5 to 120 seconds.
• the top layer or the layer just underlying said top layer includes a compound capable of converting light to heat.
• Suitable compounds capable of converting light into heat are preferably infrared absorbing components although the wavelength of absorption is not of particular importance as long as the absorption of the compound used is in the wavelength range of the light source used for image-wise exposure.
• Particularly useful compounds are for example dyes and in particular infrared 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 .
• conductive polymer dispersion Such as polypyrrole or polyaniline-based conductive polymer dispersions.
• the lithographic performance and in particular the print endurance obtained depends on the heat-sensitivity of the imaging element. In this respect it has been found that carbon black yields very good and favorable results.
• IR-cyanine dyes are IR-cyanine dyes.
• a mixture of IR-cyanine dyes may be used, but it is preferred to use only one IR-cyanine dye.
• Particularly useful IR-cyanine dyes are cyanines dyes with two acid groups, more preferably with two sulphonic groups . Still more preferably are cyanines dyes with two indolenine and two sulphonic acid groups. Most preferably is compound I with the structure as indicated
• the ratio in weight between the organic quaternary ammonium salt and the compound capable of converting light into heat is preferably between 98:2 to 20:80, more preferably between 95:5 to 50:50.
• the present invention comprises a first layer soluble in an aqueous developing solution, more preferably an aqueous alkaline developing solution with preferentially a pH between 7.5 and 14.
• Said layer is preferably contiguous to the top layer but other hydrophilic layers may be present between the top layer and the first layer.
• the alkali soluble binders used in this layer are preferably hydrophobic binders as used in conventional positive or negative working PS-plates e.g. novolac, polyvinyl phenols, carboxy substituted polymers etc. Typical examples of these polymers are descibed in DE-A- 4 007 428, DE-A- 4 027 301 and DE-A- 4 445 820.
• the hydrophobic binder used in connection with the present invention is further characterised by insolubility in water and partial solubility/swellability in an alkaline solution and/or partial solubility in water when combined with a cosolvent.
• this aqueous alkali soluble layer is preferably a visible light- or UV-light desensitised layer.
• Still further said layer is preferably thermally hardenable.
• This preferably visible light- or UV-light desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• Said first layer preferably also includes a low molecular acid, preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• a low molecular acid preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• the weight ratio between the total amount of low molecular acid or benzophenone and polymer in the first layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 20:80.
• the total amount of said first layer preferably ranges from 0.1 to 10 g/m 2 , more preferably from 0.3 to 2 g/m 2 .
• the top layer in accordance with the present invention consists of an IR-dye and preferably of an IR-dye and a binder resin.
• a mixture of IR-dyes may be used, but it is preferred to use only one IR-dye.
• Suitable IR-dyes are known since a long time and belong to several different chemical classes, e.g.
• indoaniline dyes oxonol dyes, porphine derivatives, anthraquinone dyes, merostyryl dyes, pyrylium compounds and sqarylium derivatives
• said IR-dyes especially for irradiation with a laser source with an emission spectrum of about 1060 nm belongs to the scope of the general formula of the German patent application DE- 4. 31 162 .
• This general formula (I) is represented by :
• R1, R2, R17 and R18 have the same meaning as R3, and B1, B2, the other R symbols, T, and the D symbols are defined as hereinbefore, and ⁇ is 0 or 1.
• IR-dyes especially for irradiation with a laser source with an emission spectrum of about 830 nm belong to the scope of the following general formulas. wherein X, X'each independently represents O, S
• the charge of the dyes may be compensated by any (intermolecular or intramolecular) counterion.
• binder resin in the top layer gelatin cellulose, cellulose esters e.g. cellulose acetate, polyvinyl alcohol, polyvinyl pyrrolidone, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, nitrocellulose, silicone resins etc.
• binder resin are hydrophobic binder resins, more preferably phenolic resins e.g. novolacs and vinyl phenols.
• the IR-dyes are present preferably in an amount between 10 and 80 parts by weight of the total amount of said IR-sensitive top layer.
• the total amount of the top layer preferably ranges from 0.1 to 10 g/m2 more preferably from 0.3 to 2 g/m2.
• top layer a difference in the capacity of being penetrated and/or solubilised by the aqueous alkaline solution is generated upon image-wise exposure according to the invention.
• the said capacity is increased upon image-wise IR exposure to such degree that the imaged parts of the top layer and the underlying areas of the first layer will be cleaned out during development without solubilising and/or damaging the non-imaged parts.
• the development with the aqueous alkaline solution is preferably done within an interval of 5 to 120 seconds.
• the present invention comprises a first layer soluble in an aqueous developing solution, more preferably an aqueous alkaline developing solution with a pH between 7.5 and 14. Said layer is preferably contiguous to the top layer.
• the alkali soluble polymers used in this layer are preferably hydrophobic and ink accepting polymers as used in conventional positive or negative working PS-plates e.g. novolac, polyvinyl phenols, carboxy substituted polymers etc. Typical examples of these polymers are descibed in DE-A- 4 007 428, DE-A- 4 027 301 and DE-A- 4 445 820.
• the hydrophobic polymer used in connection with the present invention is further characterised by insolubility in water and at least partial solubility/swellability in an alkaline solution and/or at least partial solubility in water when combined with a cosolvent.
• this aqueous alkali soluble layer is preferably a visible light- and UV-light desensitised layer. Said layer is preferably thermally hardenable.
• This preferably visible light- and UV-light desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• Said first layer preferably also includes a low molecular acid, preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• a low molecular acid preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• the ratio between the total amount of low molecular acid or benzophenone and polymer in the first layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 20:80.
• the total amount of said first layer preferably ranges from 0.1 to 10 g/m2, more preferably from 0.3 to 2 g/m2.
• the top layer in accordance with the present invention comprises an IR-absorbing compound and a binder resin.
• IR-absorbing compounds are for example infrared dyes, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the A component e.g. W02.9.
• carbon black is used as the IR-absorbing compound.
• a binder resin gelatin, cellulose, cellulose esters e.g. cellulose acetate, polyvinyl alcohol, polyvinyl pyrrolidone, a copolymer of vinylidene chloride and acrylonitrile, poly(meth)acrylates, polyvinyl chloride, silicone resins etc. may be used.
• binder resin is nitrocellulose.
• a difference in the capacity of being penetrated and/or solubilised by the aqueous alkaline solution is generated upon image-wise exposure.
• a difference in the capacity of the top layer to be penetrated and/or solubilised by a developing solution may be obtained by a thermally induced physical or chemical transformation. Examples of thermally induced physical transformations which generate a difference in said capacity are: the above cited embodiments which creates an increase in the capacity of being penetrated and/or solubilised in the exposed areas and laser induced removal of material which creates an increase in the capacity in the exposed areas of the layer for penetration and/or solubilisation by the developing solution.
• thermally induced chemical transformations which generate a difference in the capacity of the layer for penetration and/or solubilisation by a developer are: laser induced change in polarity which increases the said capacity in the exposed areas.
• the change in said capacity created upon laser exposure should be high enough to allow a complete clean-out without damaging and/or solubilising the resulting image upon development with an aqueous alkaline solution.
• the imaged parts will be cleaned out during development without solubilising and/or damaging the non-imaged parts.
• the development with the aqueous alkaline solution is preferably done within an interval of 5 to 120 seconds.
• the present invention comprises a layer soluble in an aqueous developing solution more preferably an aqueous alkaline developing solution with preferentially a pH between 7.5 and 14.
• the alkali soluble binders used in this layer are preferably hydrophobic binders as used in conventional positive or negative working PS-plates e.g. novolac, polyvinyl phenols, carboxy substituted polymers etc. Typical examples of these polymers are descibed in DE-A-4007428, DE-A-4027301 and DE-A-4445820.
• the hydrophobic binder used in connection with the present invention is further characterised by insolubility in water and partial solubility/swellability in an alkaline solution and/or partial solubility in water when combined with a cosolvent.
• this aqueous alkali soluble layer is preferably a visible light- and UV-desensitised layer that is thermally hardenable and ink-accepting.
• This visible light- and UV-desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• the IR-radiation sensitive top layer may be partially solubilised in the aqueous alkali soluble layer upon exposure.
• Said first layer preferably also includes a low molecular acid, preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• a low molecular acid preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzophenone.
• the ratio between the total amount of low molecular acid or benzophenone and polymer in the first layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 20:80.
• the total amount of said first layer preferably ranges from 0.1 to 10 g/m2, more preferably from 0.3 to 2 g/m2.
• the first layer and the second layer are the same.
• a method for making lithographic printing plates including the following steps
• the IR-sensitive layer in accordance with the present invention comprises an IR-dye and a polymer, soluble in an aqueous alkaline solution.
• a mixture of IR-dyes may be used, but it is preferred to use only one IR-dye.
• Suitable IR-dyes are those mentioned above in the third embodiment of the first group.
• the IR-dyes are present preferably in an amount between 1 and 60 parts, more preferably between 3 and 50 parts by weight of the total amount of said IR-sensitive top layer.
• the alkali soluble polymers used in this layer are preferably hydrophobic and ink accepting polymers as used in conventional positive or negative working PS-plates e.g. carboxy substituted polymers etc. More preferably is a phenolic resin such as polyvinylfenol or a novolac polymer. Most preferred is a novolac polymer. Typical examples of these polymers are descibed in DE-A- 4 007 428 , DE-A- 4 027 301 and DE-A- 4 445 820 .
• the hydrophobic polymer used in connection with the present invention is further characterised by insolubility in water and at least partial solubility/swellability in an alkaline solution and/or at least partial solubility in water when combined with a cosolvent.
• this IR-sensitive layer is preferably a visible light- and UV-light desensitised layer. Still further said layer is preferably thermally hardenable.
• This preferably visible light- and UV-light desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• Said IR-sensitive layer preferably also includes a low molecular acid, more preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzofenone, more preferably trihydroxybenzofenone
• the ratio between the total amount of low molecular acid or benzofenone and polymer in the IR-sensitive layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 30:70.
• the total amount of said IR-sensitive layer preferably ranges from 0.1 to 10 g/m 2 , more preferably from 0.3 to 2 g/m 2 .
• a difference in the capacity of being penetrated and/or solubilised by the alkaline developer is generated upon image-wise exposure for an alkaline developer according to the invention.
• the IR-sensitive layer in accordance with the present invention comprises an IR-absorbing pigment and a polymer, soluble in an aqueous alkaline solution.
• a mixture of IR-absorbing pigments may be used, but it is preferred to use only one IR-absorbing pigment.
• Particularly useful IR-absorbing pigments are carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the A component e.g. W02.9.
• conductive polymer dispersion such as polypyrrole or polyaniline-based conductive polymer dispersions.
• the lithographic performance and in particular the print endurance obtained depends on the heat-sensitivity of the imaging element. In this respect it has been found that carbon black yields very good and favorable results.
• the IR-absorbing pigments are present preferably in an amount between 1 and 60 parts, more preferably between 3 and 50 parts by weight of the total amount of said IR-sensitive top layer.
• the alkali soluble polymers used in this layer are preferably hydrophobic and ink accepting polymers as used in conventional positive or negative working PS-plates e.g. carboxy substituted polymers etc. More preferably is a phenolic resin such as polyvinylfenol or a novolac polymer. Most preferred is a novolac polymer. Typical examples of these polymers are descibed in DE-A- 4 007 428, DE-A- 4 027 301 and DE-A- 4 445 820 .
• the hydrophobic polymer used in connection with the present invention is further characterised by insolubility in water and at least partial solubility/swellability in an alkaline solution and/or at least partial solubility in water when combined with a cosolvent.
• this IR-sensitive layer is preferably a visible light- and UV-light desensitised layer. Still further said layer is preferably thermally hardenable.
• This preferably visible light- and UV-light desensitised layer does not comprise photosensitive ingredients such as diazo compounds, photoacids, photoinitiators, quinone diazides, sensitisers etc. which absorb in the wavelength range of 250nm to 650nm. In this way a daylight stable printing plate may be obtained.
• Said IR-sensitive layer preferably also includes a low molecular acid, more preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzofenone, more preferably trihydroxybenzofenone.
• a low molecular acid more preferably a carboxylic acid, still more preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic acid or a benzofenone, more preferably trihydroxybenzofenone.
• the ratio between the total amount of low molecular acid or benzofenone and polymer in the IR-sensitive layer preferably ranges from 2:98 to 40:60, more preferably from 5:95 to 30:70.
• the total amount of said IR-sensitive layer preferably ranges from 0.05 to 10 g/m 2 , more preferably from 0.1 to 2 g/m 2
• Image-wise exposure in connection with the present invention is an image-wise scanning exposure involving the use of a laser that operates in the infrared or near-infrared, i.e. wavelength range of 700-1500 nm. Most preferred are laser diodes emitting in the near-infrared. Exposure of the imaging element may be performed with lasers with a short as well as with lasers with a long pixel dwell time. Preferred are lasers with a pixel dwell time between 0.005 ⁇ s and 20 ⁇ s.
• the heat mode imaging element is developed by rinsing it with an alkaline developer.
• the alkaline developer used in the present invention have a pH of at least 12 and a surface tension of at least 30mN/m, more preferably of at least 35 mN/m.
• the development of the image-wise exposed imaging element is carried out between 15 and 45°C, more preferably between 22 and 35°C.
• the composition of the developer used is very important.
• the developers and replenishers for developer used in the invention are preferably aqueous solutions mainly composed of alkali metal silicates and alkali metal hydroxides represented by MOH or their oxyde, represented by M 2 O; more preferably, wherein said developer comprises SiO 2 and M 2 O in a molar ratio of 0.5 to 1.5 and a concentration of SiO 2 of 0.5 to 5% by weight.
• alkali metal silicates preferably used are, for instance, sodium silicate, potassium silicate, lithium silicate and sodium metasilicate.
• alkali metal hydroxides preferred are sodium hydroxide, potassium hydroxide and lithium hydroxide.
• the developers used in the invention may simultaneously contain other alkaline agents.
• other alkaline agents include such inorganic alkaline agents as ammonium hydroxide, sodium tertiary phosphate, sodium secondary phosphate, potassium tertiary phosphate, potassium secondary phosphate, ammonium tertiary phosphate, ammonium secondary phosphate, sodium bicarbonate, sodium carbonate, potassium carbonate and ammonium carbonate; and such organic alkaline agents as mono-, di- or triethanolamine, mono-, di- or trimethylamine, mono-, di- or triethylamine, mono- or diisopropylamine, n-butylamine, mono-, di- or triisopropanolamine, ethyleneimine, ethylenediimine and tetramethylammonium hydroxide.
• the concentration of SiO 2 in the developer and replenisher preferably ranges from 1 to 6% by weight. Such limitation of the concentration of SiO 2 makes it possible to stably provide lithographic printing plates having good finishing qualities even when a large amount of plates according to the invention are processed for a long time period.
• an aqueous solution of an alkali metal silicate having a molar ratio [SiO 2 ] / [M 2 O], which ranges from 1.0 to 1.5 and a concentration of SiO 2 of 1 to 6% by weight is used as a developer.
• a replenisher having alkali strength equal to or more than that of the developer is employed.
• a molar ratio, [SiO 2 ] / [M 2 O] of the replenisher is equal to or smaller than that of the developer, or that a concentration of SiO 2 is high if the molar ratio of the developer is equal to that of the replenisher.
• organic solvents having solubility in water at 20 °C of not more than 10 % by weight according to need.
• organic solvents are such carboxilic acid esters as ethyl acetate, propyl acetate, butyl acetate, amyl acetate, benzyl acetate, ethylene glycol monobutyl acetate, butyl lactate and butyl levulinate; such ketones as ethyl butyl ketone, methyl isobutyl ketone and cyclohexanone; such alcohols as ethylene glycol monobutyl ether, ethylene glycol benzyl ether, ethylene glycol monophenyl ether, benzyl alcohol, methylphenylcarbinol, n-amyl alcohol and methylamyl alcohol; such alkyl-substituted aromatic hydrocarbons as xylene; and such halogenated hydrocarbons
• organic solvents may be used alone or in combination. Particularly preferred is benzyl alcohol in the invention. These organic solvents are added to the developer or replenisher therefor generally in an amount of not more than 5 % by weight and preferably not more than 4 % by weight.
• Examples of such compounds are neutral salts such as NaCl, KCl and KBr as disclosed in JN-A- 58- 75 152 ; chelating agents such as EDTA and NTA as disclosed in JN-A- 58- 190 952 (U.S-A- 4 469 776) , complexes such as [Co(NH3)6]Cl3 as disclosed in JN-A- 59- 121 336 (US-A- 4 606 995); ionizable compounds of elements of the group IIa, IIIa or IIIb of the Periodic Table such as those disclosed in JN-A- 55- 25 100; tetramethyldecyne diol as disclosed in US-A- 4 374 920 ; cationic polymers such as methyl chloride quaternary products of p-dimethylaminomethyl polystyrene as disclosed in JN-A- 55- 95 946 ; amphoteric polyelectrolytes such as copolymer of vinylbenzy
• any known means of supplementing a replenisher for developer may be employed.
• Examples of such methods preferably used are a method for intermittently or continuously supplementing a replenisher as a function of the amount of PS plates processed and time as disclosed in JN-A- 55- 115 039 and GB-A- 2 046 931 , a method comprising disposing a sensor for detecting the degree of light-sensitive layer dissolved out in the middle portion of a developing zone and supplementing the replenisher in proportion to the detected degree of the light-sensitive layer dissolved out as disclosed in JN-A- 58- 95 349 (US-A- 4 537 496); a method comprising determining the impedance value of a developer and processing the detected impedance value by a computer to perform supplementation of a replenisher as disclosed in GB-A- 2 208 249 .
• the printing plates of the present invention may also be used in the printing process as seamless sleeve printing plates.
• the printing plate is soldered in a cylindrical form by means of a laser.
• This cylindrical printing plate which has as diameter the diameter of the print cylinder is slided on the print cylinder instead of applying in a classical way a classically formed printing plate. More details on sleeves are given in "Grafisch Nieuws" ed. Keesing, 15, 1995, page 4 to 6.
• the plate After the development of an image-wise exposed imaging element with an alkaline developer and drying, the plate is preferably rinsed with water. The plate is then dried and preferably gummed. The obtained plate may then be used as a printing plate as such. However, to improve durability it is still possible to bake said plate at a temperature between 200°C and 300°C for a period of 30 seconds to 5 minutes. Also the imaging element may be subjected to an overall post-exposure to UV-radiation to harden the image in order to increase the run lenght of the printing plate.
• 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/m 2 for about 300 seconds to form an anodic oxidation film of 3.00 g/m 2 of A12O3 then washed with demineralized water, posttreated with a solution containing polyvinylphosphonic acid and subsequently with a solution containing aluminum trichloride, rinsed with demineralized water at 20°C during 120 seconds and dried.
• the IR-sensitive layer was coated onto the above described lithographic base from a 4.9 % wt solution in ethyl-/buthylacetate 60/40 with a wet thickness of 25 ⁇ m.
• the resulting IR-sensitive layer contained 22.3 % of carbon black (Special Schwarz 250), 8.3 % of 3,4,5-trimethoxybenzoic acid, 61.1 % of Alnovol PN 452, 0.5% Solsperse 5000, 2.2 % Solsperse 28000 and 2.2 % Nitrocellulose E950.
• the coating was then dried at 110 °C
• This material was imaged with a GERBER C42T TM internal drum platesetter at 12,000 rpm (367 m/s, pixel dwell time 0.032 ⁇ s) and 2540 dpi.
• the power level of the laser in the image plane was 4.8 W.
• Alkaline developer 1 comprises sodium silicate (0.3 mole/l) in water and the pH is obtained by adding sodium hydroxide.
• Alkaline developer 2 is identical with alkaline developer 1 except that the surface tension was obtained by adding octylsulphate.
• a lithographic base was prepared as described in example 1.
• the IR-sensitive layer was coated onto the above described lithographic base from a 5.60% wt solution in ethyl-/butylacetate 58/42 with a wet thickness of 25 ⁇ m.
• the resulting IR-sensitive layer contained 4.3 % of carbon black Special Schwarz 250, 7.3% of Naphtoquinondiazide CP3171, 2.0% of Trihydroxybenzoic acid, 5.8 % of 3,4,5-trimethoxybenzoic acid, 76.6 % of Alnovol PN 452, 0.1% Solsperse 5000, 0.4 % Solsperse 28000, 0.4 % Nitrocellulose E950 and 3.0 % Fluorad FC431. The coating was dried at 110 °C.
• This material was imaged with a GERBER C42T TM internal drum platesetter at 12,000 rpm (376 m/s, pixel dwell time 0.032 ⁇ s) and 2540 dpi.
• the power level of the laser in the image plane was 4.4 W.
• Element 3 Alkaline developer 1(85%) 2(85%) pH 13.1 13.1 Surface tension 64 mN/m 27 mN/m Dmax 0.38 0.35 Dmin 0.00 0.01 Dot rendering (200 lpi) 3-98 5-98 Dot rendering 40% 40 35 Dot rendering 50% 50 44 Dot rendering 70% 71 66
• a lithographic base was prepared as described in examples 1 and 2.
• the resulting layer contained 88.0% of Alnovol PN452 and 12.0% of 3,4,5-trimethoxybenzoic acid and was dried at 110°C.
• Upon this layer was then coated, with a wet coating thickness of 25 ⁇ m, the IR-sensitive layer from a 3 % wt solution in ethyl/butylacetate 60/40.
• the resulting IR-sensitive layer contained 66.0 % of Alnovol PN452, 14.0% of an esterificationproduct of 1,2-Naphtoquinone-2-diazido-5-sulphonylchloride and p-tert.butyl phenol/formaldehyde copolymer (PR12 available from PCAS), 3.8% of Trihydroxybenzoic acid, 8.6% of Special Schwarz 250, 0.9% of Nitrocellulose E950, 0.2% of Solsperse 5000, 0.8% of Solsperse 28000 and 5.7% of Fluorad FC431. This second coating was dried at 120°C.
• This material was imaged with a GERBER C42T TM internal drum platesetter at 12,000 rpm (367 m/s, pixel dwell time 0.032 ⁇ s) and 2540 dpi.
• the power level of the laser in the image plane was 4.0 W.
• the plates were both printed on a Heidelberg GTO46 printing machine with a conventional ink (A B Dick 1020) and fountain solution (Rotamatic), resulting in prints without any scumming in IR-exposed areas and good ink-uptake in the unexposed areas, however the dot rendering on print was favorable for element 5: 3% dot is rendered on print while element 6 only rendered the 6% dot on print.
• a lithographic base was prepared as described in examples 1-3.
• the IR-sensitive layer was coated onto the above described lithographic base from a 11 % wt solution in tetrahydrofuran/propylene glycol 1-methyl ether 1/1.
• the resulting IR-sensitive layer had a coating thickness of 2 ⁇ m and contained 6.7% of Carbon black, 70.3% of a cresol-formaldehyde novolak, 3% of 2,4-dihydroxybenzo-phenone and 20% of an esterification product of 2,3,4-trihydroxybenzophenone and 1,2-naphthoquinone-2-diazido-5-sulphonyl chloride.
• the coating was dried for 2 minutes at 100 °C.
• This material was imaged with a GERBER C42T TM internal drum platesetter at 12,000 rpm (367 m/s, pixel dwell time 0.032 ⁇ s) and 2540 dpi.
• the power level of the laser in the image plane was 4.4 W.
• Alkaline developer 3 comprises sodium silicate (0.3 mole/l) in water and the pH is obtained by adding sodium hydroxide.
• Alkaline developer 4 is identical with alkaline developer 3 except that the surface tension was obtained by adding octylsulphate.

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• 1998
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