JPS61165759A - Correction for gravure printing plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION A gravure printing plate surface consists of a number of cells defined by cell walls and placed on a plate which may be lithographic or cylindrical. These cells may be independent cells or may be grooves. For example, the cells on a gravure cylindrical plate may be helical grooves. Various methods for manufacturing cells are well known and include engraving by various mechanical methods or by applying a laser to the surface. Scrape the ink from the top of the cell, leaving ink only inside the cell.

The proof sheet to be printed is placed against the plate, which attracts ink from the cells. The capacity of the cell determines the amount of ink to be adsorbed and therefore the density of the print.

If the proof print is sufficient, the plate is then used in a printing run. Otherwise, the cell must be changed. For example, it is often necessary to change the density of the print over part or all of the plate surface. To increase the density of the print, the cells must be deepened, and this is called positive chip correction.

If very large areas of the plate are not to be positively modified, it is difficult to accurately register the plate to the machine, program it, and operate it, and the original mechanical or radiographic engraving should be avoided. Carving by repetition is not practical.

Another method for modifying plates is by chemical etching. In this method, the entire surface of the plate is coated with a chemical resist, a protective ink that does not normally get into the cells. The ink is then dried and the areas that do not need to be touched up are covered with a layer of bitumen or other protective material that penetrates into the cells and provides a layer of cell wall mud. Then from other parts of the edition,
Etching solution retained within the cell is wiped away as much as necessary to provide the desired modification. The protective coating and resist are then washed away.

This method requires that the etchant be left in contact with the cells for varying lengths of time, so it is not suitable for feathering corrections, i.e. corrections where adjacent areas require different amounts of correction. It's inconvenient. This is generally accomplished by repeating the process several times, varying the area covered by the protective coating each time, thereby controlling the exposure of the cell to the entraining agent. .

A development of this process is described in Yoguchi-Soba Patent No. 0031646, in which the etching agent is temperature sensitive. In this method, the etching agent etches the plate at high temperatures and does not etch at the lower ambient temperatures at which the etching agent is applied to the plate. By heating the areas differently to obtain the feathering effect, it can be easily carried out in a one-step process. Also, the speed at which the cells are machined and sown can be more easily controlled than in previous processes.

Chemical etching methods for positive correction are suitable for metal printing plates because the etching and sowing agents are not necessarily too harsh. Unfortunately, printing plates made of synthetic resin,
They are often very chemically inert, so suitable chemical etchants must be extremely harsh, with the most commonly used etchants being 85%
It is sulfuric acid. Conventional etching agents are generally not harsh enough to attack the ridge ink resist and protective coating, or if they are inert enough to withstand the etching agents, the positive retouching process is Extremely difficult to remove when finished. Additionally, chemical etching agents are environmentally hazardous and corrosive, making them difficult to use and expensive to dispose of.

Therefore, currently gravure printing provides the desired properties in a quick and easy way, uses inexpensive, readily available materials that are not harmful to the environment, and is also suitable for the modification of resin plates. A new version of Bozitibu rash corrective method is needed.

A method of positively modifying a gravure printing plate according to the present invention includes applying a physical resist on top of the cell walls of the plate, deepening the cells within the plate by abrasion by a jet of abrasive particles in a fluid; This method of the invention, which then involves removing the physical resist, can be used on plates with metal or synthetic surfaces. It has been shown that the method of the present invention is particularly useful for fixing plates with continuous resin surfaces, which have extremely high chemical resistance and are difficult to repair using normal chemical processes. discovered. Any resin suitable for use as a continuous surface of a gravure printing surface can be used. Various resins have been proposed in the literature, especially acetal resins and epoxy resins. For example, British patent 1544748.2034636.2071011
and 2071574 - Preferably the plate has a printing surface consisting of a resin system based on epoxy novolak, most preferably as described in European Patent No. 0094142. The process of the invention also provides that the plates and cells of soft metal, for example copper or aluminum, are preformed from the metal and that, prior to engraving,
A physical resist that is effective for such plates that are filled with removable resin must have properties that protect the cell walls against polishing while deepening the cells by polishing. . The physical resist may be completely resistant to polishing, in which case the amount on top of the cell wall is extremely small, or the physical resist may be polished to some extent by polishing, and this In this case, the volume at the top of the cell wall must be such that it has sufficient thickness so that the top of the cell wall is sufficiently covered by the physical resist throughout the polishing process.

The physical resist generally consists of an abrasion resistant, elastic material, most preferably a urethane-based elastomer.

The resist is generally applied as a liquid using a soft, eg rubber, roller by conventional winding techniques. The resist can be applied in several layers, especially if the resist is sacrificial and therefore generally fairly thick. The rheology of the resist when applied must be such that the top of the cell wall is completely covered. In general, the liquid will not penetrate to the bottom of the cell, but some penetration may occur if the amount of resist at the bottom of the cell is sufficiently strong that the resist can be polished while the cell walls remain protected. good. The liquid is then hardened to a solid by conventional methods including polymerization, such as heating, evaporation of the solvent or exposure to ultraviolet light, or cooling if the resist is applied as a melt.

If desired, the part adjacent to the part to be modified may be sufficiently insulated, ie the cell may be filled with a resist (K) to prevent polishing before the polishing step.

Polishing may be by dry polishing methods where the particle-carrying fluid is air or other gas. However, if the particles are very fine or relatively inflexible, this may provide fairly severe abrasiveness. To more easily control the degree of modification, the jet of abrasive particles is preferably a slurry of particles in a liquid, usually an aqueous liquid, generally water.

Abrasives include finely divided particles of, for example, silica, pumice or Merck. The particle size is general K.

The thickness is 0.5 to 20μ, preferably 1 to 5μ.

The slurry generally has a solids content of 2 to 50 parts by volume, preferably 5 to 20 parts by volume, and usually about 10 parts by volume.

The slurry may contain other agents, for example, a slurry used to polish a metal surface may further contain a chemical etching agent to facilitate the engraving process. The etching agent may be a conventional chemical etching agent. For slurries using very fine abrasives, such as talc, it is advantageous to include a dispersant, such as a low molecular weight polymeric dispersant.

Suitably, the particles are jetted from a conventional type of hand-held or automatically redirected gun. Abrasives are generally supplied to the gun as a thicker slurry or as a finely divided solid, and liquids or other fluids are supplied to the gun separately. Abrasive material is typically collected and recycled.

The engraving depth is determined by the jet pressure, the distance of the gun from the plate surface, the residence time and the size of the abrasive particles.
The depth will of course also depend on the nature of the plate, and the zero jet pressure is usually between 300 and 1000 kPa, preferably 45
0-600kPa.

Often 480-550 kPa. The gun generally has a nozzle with a diameter of 1 to 5α, preferably about 2.5 cm, and 1 to 20 cm, preferably 2 to 20 cm, from the surface of the plate.
It is held at 10crn. The residence time of the jet on the part to be modified is from a few seconds to a few minutes. The plate is generally rinsed after the polishing step.

For rinsing, usually use the same liquid as the one containing the slurry,
This is done by simply turning off the supply of abrasive to the gun.

After polishing and desired rinsing steps, the resist is generally removed by dissolving it with a suitable solvent. Toluene and other aromatic hydrocarbons will dissolve many suitable elastomers.

The plate may then be processed through conventional processing steps. The metal plate can also be coated, for example with chromium, to give a harder surface.

The method of the invention is particularly suitable for feathering correction because it is easy to create sections where there is a gradual increase and/or decrease in the residence time of the abrasive jet.

The method of the invention allows the use of reagents and abrasives that are not environmentally harmful and do not require special precautions in their use. The resist does not need to be chemically resistant, so it is easier to find a suitable resist. In accordance with the method of the invention, it has been found that the inner surfaces of the cells have suitable surface suitability and provide reasonable properties with respect to releasing ink during printing.

The reagents used in this method are reusable and in any case inexpensive. The equipment used to carry out the method of the invention is readily available or can be modified from readily available, inexpensive equipment. - By way of example, an epoxy novolak gravure cylindrical plate can be formed, laser engraved and protected as in European Patent 94142. In areas where positive modification is required, the urethane elastomer can be rolled applied over the top of the cell walls and cured. A 10% slurry of pumice with a particle size smaller than 5μ in water was added at a distance of 10α from the plate from a nozzle with a diameter of 2.5 cm into a cell requiring modification at a rate of approximately 50 kP.
Jet at a pressure of about 1 minute. This time should be sufficient to obtain the desired depth without exposing the top of the cell walls. The plate is then washed with water and the elastomer is removed by application of toluene.

Margin below

Claims (1)

[Claims] 1. A method for positive modification of a gravure printing plate comprising applying a resist to cover the upper part of the cell walls of the plate, deepening the cells in the plate, and removing the resist. A method characterized in that the resist is a physical resist and the cells are deepened by abrasion by a jet of abrasive particles in a fluid. 2. The method according to claim 1, wherein the fluid is a liquid. 3. The method according to claim 1, wherein the fluid is water. 4. The method according to any one of claims 1 to 3, wherein the abrasive particles have an average diameter of 1 to 5 microns. 5. The method according to any one of claims 1 to 4, wherein the abrasive particles are pumice or silica. 6. A method according to any of claims 1 to 5, wherein the physical resist is an elastic polymer, preferably a urethane-based polymer. 7. A method according to any of claims 1 to 6, wherein the resist is applied to the plate as a liquid and then cured to a solid. 8. The method according to any one of claims 1 to 7, wherein the gravure printing plate is previously engraved with a laser. 9. The method according to any one of claims 1 to 8, wherein the surface of the gravure printing plate on which cells are formed is a resin, preferably an epoxy novolac resin. 10. The method according to any one of claims 1 to 9, wherein the plate is a cylindrical plate.