Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
  • B41N3/032—Graining by laser, arc or plasma means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N1/00—Printing plates or foils; Materials therefor
  • B41N1/12—Printing plates or foils; Materials therefor non-metallic other than stone, e.g. printing plates or foils comprising inorganic materials in an organic matrix
  • B41N1/14—Lithographic printing foils

Definitions

• the present invention relates to a lithographic base. More particularly the present invention relates to an improved adhesion of the hydrophilic lithographic layer to the support of the lithographic base.
• 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, generally hydrophobic areas, and the ink-rejecting areas form the background areas, generally hydrophilic 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 lithographic base that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition.
• compositions for that purpose include light-sensitive materials such as light-sensitive polymers, diazonium salts or resins, a photoconductive layer, a silver halide emulsion etc. These materials are then image-wise exposed to actinic radiation and processed in the appropriate manner so as to obtain a lithographic printing plate.
• a silver precipitating (nucleating) agent is located in or on top of the hydrophylic surface.
• An image is obtained on the precipitating layer according to the silver salt diffusion transfer process by contacting said precipitating layer with an exposed silver halide emulsion in the presence of a silver halide developing agent and a silver halide solvent.
• supports can be used for the manufacturing of a lithographic imaging printing plate.
• Common supports are for example organic resin supports, e.g.polyesters,and paper bases, e.g. polyolefin coated paper. These supports, if not sufficient hydrophilic by themselves, are first coated with a hydrophilic layer forming the hydrophilic lithographic background of the printing plate.
• hydrophilic layer in these systems a layer containing polyvinyl alcohol and hydrolyzed tetra(m)ethyl orthosilicate and preferably also silicium dioxide and/or titanium dioxide as described in e.g. GB-P-1419512, FR-P-2300354, US-P-3971660 and 4284705, EP-A-405016 and 450199 and U.S. Serial No. 07/881,718.
• an oleophilic (ink receptive) image is present on a hydrophilic background.
• the printing plate is continuously wetted with water and ink.
• the water is selectively taken up by the hydrophilic areas, the ink by the oleophilic areas of the printing surface.
• there occurs abrasion of the hydrophilic layer due to poor adhesion of this layer to the support either point by point or over the whole surface.
• the adhesion of the hydrophilic layer to the support is adversely influenced by a higher water adsorption and thus a less rigid hydrophilic layer. Due to said abrasion the hydrophobic support comes to the surface.This leads to ink acceptance in the non-printing areas, causing staining of the plate.
• the support is first coated with one or more subbing layers on which are coated in direct contact therewith the hydrophilic layer.
• said subbing layer(s) contain(s) organic compounds, the irreproducibility of which leads to adhesion problems between the subbed support and the hydrophilic layer.
• a decreased water absorption resulting in less emulgation with the ink and thereby an improved printing comfort and a sharper printed image is still wanted.
• Still further an improved dry start-up is also wanted.
• a method for obtaining a lithographic base comprising on a hydrophobic support a hydrophilic layer contiguous to said support containing a non-gelatineous hydrophilic (co)polymer or (co)polymer mixture, characterized in that said hydrophobic support is treated with a plasma treatment with an applied power density during the plasma treatment of at least 70 W min/m 2 before applying to said support said hydrophilic layer.
• plasma describes a partially ionized gas composed of ions, electrons and neutral species. This state of matter may be produced by the action of either very high temperatures, strong electric or radio frequency (R.F.) electromagnetic fields. High temperature or “hot” plasmas are represented by celestial light bodies, nuclear explosions and electric arcs. These are not suitable for the modification of polymeric materials. Glow discharge plasmas are produced by free electrons which are energized by an imposed direct current (DC) or R.F. electric fields and then collide with neutral molecules. These neutral molecule collisions transfer energy to the molecules and form a variety of active species including metastables, free radicals and ions.
• DC direct current
• R.F. electric fields imposed direct current
• a plasma is also called the fourth aggregation phase.
• a plasma can be obtained by adding to a gas enough energy. Plasma's which are used to functionalize the surface of a support are preferentially created by means of an electric field. By exposing a polymeric support to a plasma, there are introduced a variety on functional groups on the surface. The bulk of the polymer remains unchanged.
• a lithographic base prepared by applying on a hydrophobic support which is plasma treated under the conditions given above a non-gelatineous hydrophilic layer contiguous to said support has improved properties qua adhesion of the hydrophilic layer to the support, qua water absorption and qua dry upstart.
• the power during the plasma treatment is preferably at least 120 W min/m 2 , more preferably at least 175 W min/m 2 .
• hydrophobic supports may be used in the lithographic base in connection with the present invention.
• examples of such supports are organic resin supports e.g. cellulose acetate films and polyolefin (e.g. polyethylene) coated paper.
• a preferred support is polyethylene naphthalenedicarboxylate, a more preferred support is polyethylene therephthalate film.
• Said support has preferably a thickness between 40 and 500 ⁇ m, more preferably between 100 and 350 ⁇ m.
• hydrophilic (co)polymers in the hydrophilic layer of the lithographic base in connection with the present invention a non-gelatineous, preferably a non-proteinic (co)polymer is used.
• the hydrophilicity of the (co)polymer or (co)polymer mixture used is the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 80 percent by weight, preferably 95 percent by weight. Most preferably polyvinyl alcohol is used in the hydrophilic layer in connection with the present invention.
• the hydrophilic layer of the lithographic base is preferably hardened.
• Preferred hardening agents are those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone type e.g. 1,3-vinylsulphonyl-2-propanol, aldehydes e.g. formaldehyde, glyoxal, and glutaraldehyde, N-methylol compounds e.g. dimethylolurea and methyloldimethylhydantoin, dioxan derivatives e.g. 2,3-dihydroxy-dioxan, active vinyl compounds e.g.
• 1,3,5-triacryloyl-hexahydro-s-triazine 1,3,5-triacryloyl-hexahydro-s-triazine, active halogen compounds e.g. 2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic acids e.g. mucochloric acid and mucophenoxychloric acid.
• active halogen compounds e.g. 2,4-dichloro-6-hydroxy-s-triazine
• mucohalogenic acids e.g. mucochloric acid and mucophenoxychloric acid.
• These hardeners can be used alone or in combination.
• the binders can also be hardened with fast-reacting hardeners such as carbamoylpyridinium salts of the type, described in US-P-4,063,952.
• Preferably used hardening agents are tetraalkyl orthosilicate crosslinking agents.
• tetraalkyl orthosilicate crosslinking agents are hydrolyzed tetraethyl orthosilicate and hydrolyzed tetramethyl orthosilicate.
• the amount of tetraalkyl orthosilicate crosslinking agent is at least 0.2 parts by weight per part by weight of hydrophilic (co)polymer, preferably between 0.5 and 5 parts by weight, most preferably between 1 and 3 parts by weight.
• the lithographic base can comprise only one hydrophilic layer. However the lithographic base can also include more than one hydrophilic layer, the hydrophilic layer contiguous to the support then being a part of the hydrophilic element of the lithographic base.
• the hydrophilic layer or layers not contiguous to the hydrophobic support differs from the hydrophilic layer contiguous to the hydrophobic support either in the nature of the hydrophilic (co)polymer and/or the nature of the crosslinking agent and/or the ratio between the hydrophilic (co)polymer and the crosslinking agent.
• the hydrophilic layer or layers of the lithographic base 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 upto 40 nm, e.g. 20 nm.
• inert particles of larger size than the colloidal silica can be added e.g. silica prepared according to Stober 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 100nm which are particles of titanium dioxide or other heavy metal oxides.
• the surface of the layer is given a uniform rough texture consisting of microscopic hills and valleys, which serve as storage places for water in background areas.
• the hydrophilic lithographic base in accordance with the present invention may be coated with a thin layer of a heat- or photosensitive composition.
• the heat- or photosensitive composition can also be present partially or completely in the hydrophilic layer used in accordance with the present invention.
• Compositions for that purpose include heat- or light-sensitive substances such as heat-or light-sensitive polymers, diazonium salts or resins, quinonediazides, photoconductive layers, silver halide emulsions etc. These materials are then imagewise exposed to actinic radiation and processed in the appropriate manner so as to obtain a lithographic printing plate.
• an imaging element is prepared by applying a layer comprising a photopolymerizable composition and a silver halide emulsion layer to the lithographic base of the present invention. After imagewise exposure of the silver halide emulsion layer and subsequent development a silver image is obtained. The thus obtained silver image is subsequently employed as a mask for the photopolymerizable composition during an overall exposure of the imaging element. Finally the silver image and the non-exposed photopolymerizable composition are removed so that a lithographic printing plate is obtained.
• an imaging element is prepared by applying a layer comprising a o-naphtoquinonediazide compound and an alkali soluble resin to the lithographic base of the present invention. After imagewise exposure of the photosensitive element and subsequent development a lithographic printing plate is obtained.
• a lithographic printing plate is produced by the following steps :
• a heat recording material comprising the hydrophilic lithographic base of the present invention containing in homogeneously distributed state throughout the entire hydrophilic layer hydrophobic thermoplastic polymer particles having a softening or melting temperature of more than 30°C and that are capable of coagulating when brought above their softening or melting temperature, forming a hydrophobic agglomerate in the hydrophilic layer so that at these parts the hydrophilic layer becomes sufficiently hydrophobic to accept a greasy ink in lithographic printing wherein a dampening liquid is used.
• hydrophobic polymer particles for use in connection with the present invention are e.g.polyethylene,polyvinyl chloride, polymethyl(meth)acrylate, polyethyl (meth)acrylate, polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole, polystyrene etc. or copolymers thereof.
• the molecular weight of the polymers may range from 5,000 to 1,000,000.
• 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 larger the polymer particles are the less the resolving power of the heat recording material will be.
• the polymer particles are present as a dispersion in the aqueous coating liquid 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 hydrophilic layer is preferably between 20% by weight and 65% by weight and more prerably between 25% by weight and 55% by weight and most preferably between 30% by weight and 45% by weight.
• the hydrophobicity produced at the exposed areas may be too small and as a consequence ink acceptance will be poor in these areas whereas too large amounts of the hydrophobic thermoplastic polymer particles may result in ink acceptance in the non-image areas due to a too large overall hydrophobicity of the hydrophilic layer.
• the above described heat recording material can be exposed by actinic radiation while in contact with an original that contains a pattern of areas that are capable of converting the radiation into heat at these areas so that the hydrophobic thermoplastic polymer particles in the hydrophilic layer are softened or melted and coagulate in the exposed areas thereby increasing the hydrobicity of the hydrophilic layer at these areas.
• An especially suitable radiation is e.g. infrared or near infrared radiation.
• an original there may be used e.g. an imaged silver halide photographic material.
• a light-sensitive material comprising a diazonium salt or resin, contained in homogeneously distributed state throughout or preferably coated from a hydrophilic solution over the hydrophilic lithographic base of the present invention.
• 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 DE-P-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.
• Said light-sensitive layer preferably also contains a binder e.g. polyvinyl alcohol and may be applied to the lithographic base in a thickness of 0.2 ⁇ m to 5 ⁇ m.
• Said presensitized imaging element advantageously contains water-soluble dyes such as rhodamines, sudan blue, methylen blue, eosin or triphenylmethane dyes such as crystal violet, victoria pure blue, malachite green, methylviolet and fuchsin or dye pigments which are essentially water insoluble.
• Said dyes and/or dye pigments may be present in any layer comprised on the support of said presensitized imaging element but are preferably present in said hydrophilic layer and/or light-sensitive layer.
• Exposure of the presensitized imaging element advantageously proceeds with ultraviolet light optionally in combination with blue light in the wavelength range of 250 to 500 nm.
• Useful exposure sources are high or medium pressure halogen mercury vapour lamps, e.g. of 1000 W. Since most lithography is done by the offset process, the imaging element is exposed in such a way that the image obtained thereon is right reading.
• the exposure may be an exposure using optics or a contact exposure.
• the diazo resin or diazonium salts are converted upon exposure from water soluble to water insoluble (due to the destruction of the diazonium groups) and additionally the photolysis products of the diazo may induce an advancement in the level of crosslinking of the polymeric binder or diazo resin, thereby selectively converting the surface, in an image pattern, from water soluble to water insoluble.
• the unexposed areas remain unchanged, i.e. water soluble.
• the printing plate When mounted on a printing press the printing plate is first washed with an aqueous fountain solution. To prevent this fountain solution from being contaminated by residual non-exposed diazo the unexposed diazo resin or diazonium salt should be removed from the printing plate before mounting it on a printing press. This removal can be achieved by rinsing or washing the imaging element with water or an aqueous solution.
• the hydrophilic lithographic base in accordance with the present invention is used as an image-receiving element for a heat- or photosensitive composition.
• the lithographic base in accordance with the present invention may be used as a receiving element in a thermal transfer process where a hydrophobic substance or composition is information-wise transferred from a donor element to said lithographic base.
• a thermal transfer process where a hydrophobic substance or composition is information-wise transferred from a donor element to said lithographic base.
• a toner image may be transferred to the lithographic base of the present invention during an electrophotographic process as disclosed in e.g. US-P-3,971,660 and EP-A-405,016.
• a layer of physical development nuclei may be applied to the lithographic base of the present invention.
• Suitable physical development nuclei for use in accordance with the present invention are e.g. colloidal silver, heavy metal sulphides e.g. silver sulphide, nickel sulphide, palladium sulphide, cobalt sulphide, zinc sulphide, silver nickel sulphide etc.
• the layer of physical development nuclei may contain a hydrophilic binder but preferably does not contain a binder.
• the physical development nuclei contained in the image receiving layer can also be present partially or completely in the hydrophilic layer used in accordance with the present invention.
• a thus prepared element can be used as the image-receiving element in a DTR-process.
• an image-wise exposed photographic material comprising a silver halide emulsion layer is contacted with said image-receiving element and developed in the presence of a silver halide solvent e.g. thiosulphate or thiocyanate and one or more developing agents.
• a silver halide solvent e.g. thiosulphate or thiocyanate
• Both elements are subsequently separated and a silver image is formed in the layer of physical development nuclei comprised on the image-receiving element. More details about this process for obtaining a silver image in said receiving layer can be found in e.g. US-P-4.649.096 or EP-A-397926.
• Said silver image is oleophilic while the background of the image-receiving element is oleophobic so that a lithographic printing plate results. It may however be advantageous to improve the oleophilicity of the silver image by treating the silver image with so-called hydrophobizing agents.
• US-P-3,776,728 describes the use of heterocyclic mercapto-compounds, e.g. a 2-mercapto-1,3,4-oxadiazole derivative as hydrophobizing agents
• US-P-4,563,410 discloses hydrophobizing liquids containing one or more mercaptotriazole or mercaptotetrazole derivatives.
• the adhesion was determined as follows:
• the amount of water absorption, expressed in g/m 2 was determined as follows:
• the dry start-up is measured as follows:
• a lithographic base obtained from a support that has undergone plasma treatment has one or more of the following advantages when compared with a lithographic based obtained from a subbed support: adhesion, water absorption and or dry start-up.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Optics & Photonics (AREA)
• Plasma & Fusion (AREA)
• Printing Plates And Materials Therefor (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)

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Cited By (2)

Citations (4)

• 1997
  • 1997-07-04 DE DE1997603879 patent/DE69703879T2/de not_active Expired - Fee Related
  • 1997-07-04 EP EP19970202034 patent/EP0889364B1/de not_active Expired - Lifetime
• 1998
  • 1998-06-30 JP JP19812498A patent/JPH1134526A/ja active Pending

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