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
  • B41C1/1058—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by providing a magnetic pattern, a ferroelectric pattern or a semiconductive pattern, e.g. by electrophotography
• • 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
  • B41N1/006—Printing plates or foils; Materials therefor made entirely of inorganic materials other than natural stone or metals, e.g. ceramics, carbide materials, ferroelectric materials

Definitions

• the invention relates to methods for producing an erasable printing form, methods for erasing the printing form, the printing form itself and its use as a coating on a roller.
• a photopolymer is applied to a hydrophilic (water-accepting) surface of the printing form, which is first exposed and then developed imagewise.
• hydrophobic (ink-accepting) image areas remain on the printing form surface while the photopolymer is removed at the non-image areas.
• the development step again exposes the surface of the material forming the printing form at the non-image points.
• the printing form is, for example, a roughened aluminum plate on which an aluminum oxide (Al2O3) layer has been applied anodically.
• Al2O3 aluminum oxide
• the aluminum oxide layer has a porous surface, which favors the adhesion of a hydrophobic coating and also stores dampening solution in the pores and thus improves the hydrophilic properties.
• this aluminum oxide layer has the disadvantage that it is very difficult to remove a polymer layer applied to it if the printing form is to be used several times.
• deep cleaning agents In order to clean the capillaries present in the surface of the aluminum oxide layer in such a way that they do not contain any residues that interfere with a subsequent printing process, deep cleaning agents must be used in a long-term cleaning process, which may also attack the aluminum oxide layer and reduce its service life.
• a printing form is known from DE 36 33 758 A1 on which hydrophobic and hydrophilic areas can be displayed and which Contains material with ferroelectric properties that can be locally polarized and depolarized or brought into the three different polarization states (positively or negatively polarized or depolarized).
• the printing form is polarized in that an electrical direct voltage is applied to an electrode and an electrically conductive layer underneath the ferroelectric material serves as the counter electrode.
• the printing form can be depolarized again by an AC voltage, the frequency of which is far above the resonance frequency of the ferroelectric, or by heating to a temperature above the Curie temperature, or polarized again uniformly by subsequent application of a DC voltage.
• barium titanate whose Curie temperature is 120 ° C. can be used as the ferroelectric material.
• other materials with ferroelectric properties can also be used, for example a composite material with hydrophobic properties, such as soft plastic mats, in which ferroelectric microcrystallites are enclosed.
• a disadvantage of the previously known methods for making printing forms with ferroelectric properties reusable for the offset process is, however, that either a current source and a counter electrode have to be brought up to the printing form or that a heat source is required. In order to avoid unnecessarily high electrical voltages, the ferroelectric layers must be thin.
• the invention provides a use of the layer with strong microdipoles as a coating of a roller in a dampening unit or an inking unit.
• An advantage of the invention is that the hydrophilicity of the hydrophilized areas is still retained even after more than 10,000 cylinder revolutions and that detachment of the material applied for masking the ink-accepting image areas during the printing process does not change the printed image, since the base material that comes to light when detached the printing form is hydrophobic. Even deliberate removal of the material applied to mark the ink-accepting image areas with solvents, such as Acetone, does not affect the printed image. However, if the material masking the image areas is retained, the hydrophilic areas can be refreshed at any time or can be continuously hydrophilized by additives in the dampening solution.
• a particular advantage of using a ferroelectric layer as a layer with strong microdipoles is that it can be permanently polarized and that hydrophilizing agents can be specifically bound in polarized areas. Since the non-polarized areas are hydrophobic, the coating does not have to be resistant to circulation. Nevertheless, ferroelectric layers can also be coated to produce the image areas. In the case of polarized material, the coating can also be refreshed at any time.
• the surface of the outer layer is very smooth, which can be achieved by polishing with a fine-grain polishing agent, and if it is pore-free.
• the hydrophilizing agent in the printing form according to the invention is held on the smooth, non-porous surface with strong electrostatic forces.
• a material that contains strong microdipoles is used to produce the printing form.
• the electrical fields of the disordered (non-polarized), yet effective microdipoles are sufficient to bind hydrophilizing substances so tightly to the surface that a hydrophilic layer that is difficult to remove during the printing process is formed. It is not necessary to apply an electrical field from the outside. Since only the microdipoles are necessary for adhesion, the material as a whole does not necessarily have to be polarizable, i.e. for example, be ferroelectric; it is sufficient that it has sufficiently strong microdipoles.
• Such a material, but not a ferromagnetic material is, for example, aluminum titanate.
• ferroelectric materials have strong microdipoles, for example barium titanate, lead zirconium titanates or, as a plastic material, polyvinylidene fluoride, which is a ferroelectric polymer.
• the outer layer of the printing form does not have to consist exclusively of a ferroelectric; it is rather sufficient if ferroelectric microcrystallites are embedded in a soft plastic material or a composite with non-ferroelectric material, e.g. Form glasses, hard plastics or ceramics.
• a sintered ceramic is preferably suitable as the ceramic, but dense ceramic layers produced by thermal spraying processes are also suitable. Overall, materials that are non-porous and have a smooth surface are suitable.
• the outer layer is given a smooth surface, for example, by being polished with a polishing agent with a grain size of less than 20 ⁇ m.
• an erasable printing form is produced in that, by rubbing with a hydrophilizing agent, the non-image areas of a hydrophobic printing form imaged at the image areas with a covering material are hydrophilized with a layer according to the invention with strong microdipoles will.
• the hydrophilizing agent is preferably a plate cleaner customary in offset technology.
• plate cleaners are known for example from SU 42 97 485 A or from DE 31 17 358 A1 and DE 34 01 159 A1.
• the plate cleaners contain, for example, orthophosphoric acid, silicates, non-ionic surfactants and long-chain hydrocarbons. Such plate cleaners have so far only been used for cleaning pre-coated aluminum offset printing plates.
• a plate cleaner is applied as a hydrophilizing agent to the non-image parts of a printing form containing strong microdipoles, it becomes hydrophilic and its hydrophilicity is maintained during an entire printing process. This also applies to long print runs, for example, when more than 10,000 cylinder revolutions.
• the surface of the printing form has a low sensitivity to fluctuations in the pH of the dampening solution. Pure tap water can even be used without any additives, e.g. use as dampening solution.
• the image areas are deleted by removing any cover material that may still be present at the image points and by reversing the hydrophilization of the non-image areas.
• the process of hydrophilizing the surface of the printing surface to produce the non-image areas can easily be reversed by treatment with a non-polar solvent.
• the solvents for liquid toners known from electrophotography are suitable, which essentially consist of a mixture of long-chain, branched aliphatic, liquid, i.e. isoparaffinic, hydrocarbons.
• a reversibly hydrophilizable and hydrophobizable surface of a printing form is created which is erasable and thus reusable.
• highly polished printing forms made of ferroelectric material are often reusable.
• a printing form is prepared for the printing process by imagewise covering material on the hydrophobic, ink-accepting surface of the outer layer is applied. All methods are suitable for this, in which a material application to the surface takes place for image differentiation.
• the cover material is preferably itself hydrophobic. Examples of this include processes such as thermal transfer, ink jet coating, electrostatic toner transfer, in which thermoplastic layers, inks that accept ink through heat input, or charged toner particles are transferred and then fixed by attachment to electrically charged surfaces, and also application of photopolymers with subsequent image-differentiated layer removal during development .
• the non-imaged portions of the surface are then hydrophilized by the hydrophilizing agent.
• a special property of the ferroelectric layer is that its surface is initially hydrophobic before it is treated.
• the image unit therefore only has to prevent the hydrophilizing agent from covering the image areas for the hydrophilization process, which is unique for each printing process.
• the printing form is hydrophilized by the hydrophilizing agent, e.g. a plate cleaner, is sprayed onto the outer layer from nozzles.
• the hydrophilizing agent is rubbed on the outer layer.
• a hydrophilizing agent for example as an additive to the fountain solution, can also be applied to the printing form during the production run in order to improve the print quality.
• the printing form as a whole can be cleaned with a solvent, for example acetone, and returned to its original hydrophobic state using a non-polar solvent, for example an isoparaffinic hydrocarbon.
• a solvent for example acetone
• a non-polar solvent for example an isoparaffinic hydrocarbon
• the printing form is either designed as a plate that can be clamped onto a forme cylinder or as a cylindrical sleeve of a channelless forme cylinder.
• the printing form has a particularly long service life due to the hard, abrasion-resistant ceramic surface.
• An erasable printing form which has strong microdipoles at least in its outer layer, can also be produced for the dry offset printing process, cover material being applied imagewise and non-image areas subsequently being rendered oleophobic by an oleophobic medium.
• an oleophobic medium e.g. a liquid silicone.
• the ability to deposit electrically active substances on a ferroelectric layer also permits applications in which the effect of the top layer on a surface is decisive for the surface properties.
• These are e.g. Surface properties such as surface tension, stickiness or adhesion, which can be controlled within certain limits by targeted attachment and possibly. can be made regenerable.
• the effect of the dampening solution on dampening unit rollers or that of the printing ink on the inking unit rollers can also be controlled.
• the printing form preferably surrounds the Entire lateral surface of the forme cylinder so that it does not have a clamping channel.
• the properties of the dampening solution for example its pH value, can fluctuate over a wide range without reducing the print quality.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Inorganic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Printing Plates And Materials Therefor (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)
• Ink Jet Recording Methods And Recording Media Thereof (AREA)
• Ink Jet (AREA)
• Cleaning In Electrography (AREA)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (2)

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Citations (7)

Family Cites Families (9)

• 1992
  • 1992-10-20 DE DE4235242A patent/DE4235242C1/de not_active Expired - Fee Related
• 1993
  • 1993-10-18 DE DE59306781T patent/DE59306781D1/de not_active Expired - Fee Related
  • 1993-10-18 EP EP93116766A patent/EP0594097B1/fr not_active Expired - Lifetime
  • 1993-10-20 CA CA002108862A patent/CA2108862C/fr not_active Expired - Fee Related
  • 1993-10-20 JP JP5262317A patent/JPH06191004A/ja active Pending
  • 1993-10-20 US US08/139,527 patent/US5454318A/en not_active Expired - Lifetime
• 1995
  • 1995-06-05 US US08/465,132 patent/US5555809A/en not_active Expired - Lifetime

Patent Citations (7)

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