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
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/134—Plasma spraying
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
  • C23C4/12—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge characterised by the method of spraying
  • C23C4/137—Spraying in vacuum or in an inert atmosphere

Definitions

• the invention relates to an improved method of making a printing plate and an improved printing plate made in accordance with the method.
• the invention is applicable with particular advantage to the manufacture of plates for use in lithographic printing processes.
• a lithographic printing plate comprises a substrate including a surface layer upon which an image layer is created. It is created from a printing plate precursor comprising a substrate including a surface layer, upon which a layer of image material is formed. Image and non-image area will be created by exposing the image material to radiation. The exposure to radiation creates solubility differences in the image material of the image and non-image areas. Following development the soluble areas are removed leaving a pattern on the substrate corresponding to the image. This is the completed printing plate ready for use in a process. Preparation of the substrate base before the image material layer is applied or formed must be such that the material will bond to the base prior to image formation, but allows the release of the soluble image material after development.
• Suitable image materials for use in lithographic processes can include those based on diazonium/diazide materials, polymers which undergo depolymerisation or addition photo-polymerisation, and silver halide gelatin assemblies. Examples of suitable materials are disclosed in GB-1592281, GB-A-2031442.GB-A-2069164, GB-A-2080964, GB-A-2109573 and EP-A-377589.
• Substrates used in the printing industry commonly comprise an aluminium base layer, which has a layer of aluminium oxide on its surface, intermediate to the base material and a subsequently applied image layer, resulting from a controlled oxidation reaction conducted electrochemically.
• a cleaning treatment for example involving washing with alkali.
• the base layer is then subjected to a texture control treatment, for example involving an etching process, which increases the surface area of the substrate, which in turn controls the strength of the bond between the substrate and the image material and increases the ability of the substrate to hold water.
• This treatment can involve treatment with water, a solution of a phosphate or silicate salt, or a polycarboxylic acid.
• plasma spraying will be used to encompass any system which involves the generation of a plasma and the use of its thermal energy to melt solid particles, allowing them to be coated onto a base by simultaneously projecting the plasma. and solid particles towards the base.
• a plasma occurs due to the ionisation of a gas. It should be noted that since ionised particles recombine extremely quickly, it is likely that by the time the spray reaches the base, it will include very high temperature gas particles rather than plasma.
• plasma will be used to describe the spray even including recombined gas particles.
• Arc plasma processes for surface coating can be divided into two categories, those using a transferred arc and those using a non-transferred arc.
• a non-transferred arc process an arc is struck between a pair of electrodes with a torch so the gas through which the arc bums is ionised and becomes a plasma. The plasma is then projected beyond the arc (thus beyond the electrodes) towards the surface of the workpiece.
• a transferred arc process the workpiece becomes an electrode and the arc is struck between the torch and the workpiece itself. This requires that the environment between the workpiece and the torch consist of those gases which are to become the plasma.
• a major problem which arises is that no plasma spray gun will be 100% effective. Typically, the percentage of production time during which a viable product can be obtained from one spray gun is 97%. The problem is that as the number of spray units in a system increases, the percentage of time within which viable products can be obtained decreases. Since the capacity of any plasma system will be related not only to the number of guns but to their availability, it can be calculated that the total capacity will actually start to decrease once the number of spray units exceeds a threshold. It has been found that in a system where the percentage availability per unit is 97%, the optimum value is 33 spray units. However, it has been found that this has an overall availability of 37% so that of the time set aside for spraying only 37% produces viable products.
• a further problem which arises due to the plurality of tracks is that it is very difficult to produce even spraying since there is a danger of either a gap between adjacent tracks or the tracks overlapping too much or too little. If the tracks overlap too much, a thicker coating may be produced at that point. This can cause problems in the production of lithographic printing plates where accuracy and reliability are required.
• the plasma and associated molten particles have a heating effect on the base material which has a tendency to soften and warp the base material which means that the plate produced would have a low ultimate tensile strength.
• a method of manufacturing a lithographic printing plate precursor including the step of depositing upon a substrate a surface layer of particulate material by a plasma spray technique in which the plasma is sprayed onto the substrate into a low pressure environment at a pressure of less than 1.9984 x 10 4 Pa (150 torr).
• the term 'substrate' will be used to encompass any surface upon which a particulate material is to be deposited during the method, and is not limited to the conventional meaning of substrate recognised in lithography ie the surface upon which the light sensitive material is to be coated.
• a lithographic printing plate precursor made in accordance with the method according to the first aspect of the invention.
• the third and fourth aspects of the invention relate respectively to a method of manufacturing a lithographic printing plate, and a lithographic printing plate made from that method, in which the printing plate precursor is in accordance with the second aspect of the invention.
• the plasma spraying is carried out at a low pressure compared to atmospheric pressure (1.01325 x 10 5 Pa (760 torr)).
• the use of low pressure plasma spraying technique has a number of advantages. The first is that it produces a broad plasma stream in order to form a relatively uniform coating on the substrate.
• the effect is to produce a large pressure difference between the inside and the outside of the plasma gun used to create the plasma stream which creates a substantial shock pattern as the plasma stream comprising a mixture of gas and material being sprayed exits the plasma gun and travels to the substrate.
• the plasma stream quickly expands as it exits the plasma gun so as to form a large broad plume pattern particularly at substantial distances from the plasma gun.
• the track width is greater than 200mm. This gives increased capacity from a single unit, less spray units are required to approach target production capacity and there is therefore higher overall system availability with less unexpected downtime. At the same time, such plasma stream has the requisite energy to deposit uniform dense coatings on the substrate at distances which are considerably greater than those normally used in conventional plasma spraying applications.
• the pressure differential leads to an increase in velocity of the exhaust plasma gases and a length of plasma which is much longer than in atmospheric plasma spraying.
• the width of a deposited coated track from a single gun moving at a particular speed relative to a surface is related to the ambient pressure of the environment in which spraying is performed.
• different widths of the surface to be sprayed sometimes known as a web, can be accommodated by specifying particular conditions of powder feed rate, pressure, gun-workpiece distance and the speed of traverse of the gun relative to the web.
• Low Pressure Plasma Spraying can be used to obtain plasma spray streams with widths well in excess of those produced using atmospheric plasma spraying.
• the width of the stream produced depends on nozzle design and the pressure differential between the gun and the operating environment.
• the following information is based on a particular arrangement, namely an EPI Low Pressure Plasma Spraying system using an EPI-03 plasma gun and a diverging nozzle with a throat diameter of 12.5mm and an exit diameter of 19mm.
• the pressure of the environment during spraying will be less than 2.6664 x 10 3 Pa (20 torr) but greater than 1.3332 Pa (0.01 torr). More preferably, the pressure will be between 3.9996 x 10 2 Pa and 6.666 x 10 Pa (3-5 torr). The pressure within the plasma gun will typically be greater than 5.3329 x 10 4 Pa (400 torr).
• the arc used to generate the plasma is provided by a power supply or a combination of power supplies operating at a particular current and voltage giving a plasma arc having a power greater than 40 kW.
• the power is greater than 92 kW, more particularly between 110 and 120 kW.
• the relative speed of the gun to the web can vary from just over Oms' 1 but is preferably between 0.2 and 0.8 ms 1 .
• the gun or guns may move over the surface of the substrate or the substrate may be in the form of a moving web with stationary guns.
• the gas used to generate the plasma preferably consists of a mixture of primary and secondary gases.
• the primary gas is Argon and has a volumetric flow rate of between 30 and 200 litres per minute at standard temperature and pressure (ie standard litres) preferably between 60 and 140 standard litres per minute.
• the secondary gas may be Helium, Hydrogen or Nitrogen having a flow rate which is preferably greater than 3 standard litres per minutes and usually between 8 and 24 standard litres per minute but less than 40 standard litres per minute.
• the powder type used is a metallic or ceramic powder, preferably ceramic.
• the ceramic powder will comprise alumina.
• the particle size of the powder is preferably less than 20 ⁇ m, more preferably less than 12 ⁇ m, particularly between 3 and 10 ⁇ m.
• Each gun can be fed by a number of powder feed units, each unit using a flow of carrier gas to feed a certain mass flow rate of powder to the gun.
• a plurality of powder feed units attached to a gun.
• the gas used to carry the powder from the powder feed unit can have a volumetric flow rate greater than 5 standard litres per minute, preferably greater than 10 standard litres per minute, particularly around 20 standard litres per minute.
• the mass flow rate of powder fed into each earner gas stream will be at least 10gm per minute, preferably 30gm per minute.
• the gas used to carry the powder may be Argon.
• a single plasma gun capable of handling 120 kW power (compared to 40 kW in an atmospheric system) and operating in a chamber where a long spray distance can be realised (1300mm)
• a deposited track with a width of 300mm can be obtained the gun moves at a speed of 0.5m/s relative to the surface to be sprayed.
• the weight of the deposited coating in the latter case can be controlled within a range of 2-10g/m 2 , which contains the weight range of an anodic film produced by conventional electrochemical means.
• the potential capacity from a single gun using this method is 540 m /hr, more than 5 times that available by pushing atmospheric plasma spraying (100m 2 /hr) to its limits (a 10mm track deposited at 3m/s).
• a multi-unit system using Low Pressure Plasma Spraying as a basis would need only 3 guns to give a yearly coated output of 10 million m 2 , compared to the 33 needed using atmospheric plasma spraying which only attains the maximum production figure of 9 million m 2 /yr.
• the overall system availability of a 3 unit system is 91% (disregarding possible failures within the vacuum pumping system) compared to the figure of 37% obtained using a 33 gun atmospheric system.
• the Drawing is a schematic view of the apparatus
• Table 2 sets out the alterations to Table 1 used in Example 3;
• Table 4 sets out the conditions used in Example 5.
• the sample to be coated (3) is cut into a. rectangular section and mounted on a backing plate toward the bottom of the chamber a certain vertical distance below the plasma torch (2).
• the torch can be oscillated around a fixed centre of rotation.
• the angular velocity of the torch controls the linear speed at which the spray traverses the workpiece.
• a single pass occurs when the spray has wholly traversed the workpiece.
• the torch can be manipulated such that the spray moves a certain horizontal distance, or raster step, perpendicular to the direction of traverse.
• the plasma power supply (6) provides the electrical power required to strike the arc within the plasma torch.
• the plasma gas source (5) provides the various primary and secondary gases required to form the plasma.
• the cooling water source (7) is necessary to prevent the heat generated in the plasma from destroying the plasma torch.
• a powder source (8) consisting of a dehydrated powder and a carrier gas, is necessary to introduce the coating material into the plasma spray. More than one powder source per torch can be used. In the following examples, standard EPI apparatus is used, the torch being an EPI-03 type fitted with a divergent nozzle having a 13mm throat diameter and a 19mm exit diameter.
• Table 1 gives the conditions used to spray the A1 2 0 3 powder onto the sheet.
• the substrate was used to produce a printing plate by bar coating in the laboratory with a light sensitive material of the type which is applied by Horsell Graphic Industries Limited to light sensitive lithographic printing plates sold by them under the trade mark CAPRICORN at a coating weight of 2g/m 2 .
• a substrate for use as a printing plate was produced using similar conditions to those given in example 1 , but using a sheet of aluminium alloy AA3104 which had been treated by (i) dipping in a 5% w/w solution of NaOH and (ii) dipping in a 7% w/w solution of HNO 3 .
• a printing plate was made from the substrate using the technique described in Example 1.
• a substrate for use as a printing plate was produced using similar conditions to those given in example 1 , apart from the alterations in Table 2.
• a printing plate was made from the substrate using the technique described in example 1.
• a substrate for use as a printing plate was produced using similar conditions to those given in example 1 , but using A1 2 0 3 powder supplied by Abrasive Developments Ltd with the designation F600/9 and a mean particle size of 9.3 ⁇ m.
• further alterations were made, shown in Table 3.
• a printing plate was made from the substrate using the technique described in example 1.
• a substrate for use as a lithographic printing plate was made by using the apparatus described above to spray.
• the A1 2 0 3 powder was supplied by Fulton Abrasive Systems Inc with the description 800 mesh and had a mean particles size of 7 ⁇ m. It is necessary to dehydrate the powder by preheating in an oven at 200°C for 24 hours prior to spraying. The sheet was cut to size (711mmx457mm) before mounting on the backing plate.
• Table 4 gives the conditions used to spray the A1 2 O 3 powder onto the sheet.
• Powder unit carrier gas flow 231.min '1 (@ stp)
• the substrate was used to produce a printing plate by bar coating in the laboratory with a light sensitive material of the type which is applied by Horsell Graphic Industries Limited to light sensitive lithographic printing plates sold by them under the trademark CAPRICORN at a coating weight of 2g/m 2 .
• a substrate for use as a printing plate was produced using similar conditions to those given in example 5, but using a sheet of aluminium alloy AA3104 which had been treated by dipping in a 5% w/w solution of NaOH.
• a printing plate was made from the substrate using the technique described in Example 5.

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• Engineering & Computer Science (AREA)
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• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Optics & Photonics (AREA)
• Printing Plates And Materials Therefor (AREA)
• Materials For Photolithography (AREA)

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• 1995
  • 1995-08-17 AU AU32301/95A patent/AU3230195A/en not_active Abandoned
  • 1995-08-17 JP JP8507862A patent/JPH10504605A/ja active Pending
  • 1995-08-17 WO PCT/GB1995/001960 patent/WO1996006200A1/en not_active Application Discontinuation
  • 1995-08-17 EP EP95928587A patent/EP0771367A1/de not_active Withdrawn

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