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

Definitions

• the invention relates to a plate, film or ribbon-shaped carrier material for offset printing plates made of aluminum or its alloys with a surface roughened on one or both sides, the structure of which has a combination of 6 parameters. It also relates to a method for producing this structure and the use of these materials for producing offset printing plates carrying at least one radiation-sensitive layer, from which reproductions of halftone originals can be produced without rastering.
• This grid then breaks down the individual tonal values into points of different sizes.
• the rastering is used almost universally in photomechanical printing, in which prints are required in large numbers. Nevertheless, this method sometimes leaves something to be desired, since some of the sharpness, color purity and detail of the original image are lost due to the rastering.
• the rasters have about ten lines per mm, ie a line spacing of 100 pm for a relatively high quality print. All tonal values are reduced and the final proofs cannot withstand the details in comparison with the original.
• Another disadvantage of the autotypical process is the so-called Moire effect, which can occur if the alignment of the grid deviates slightly from the alignment of a regular pattern on the image and / or if there are slight deviations in the accuracy of fit of at least two rastered patterns when copied over one another Images are present. This affects the reproduction of the original in a way that is usually undesirable.
• Another disadvantage is that the production of the necessary raster films is relatively expensive.
• No. 3,282,208 describes a printing plate with a positive-working radiation-sensitive layer, which is irradiated with light from a halftone original without an interposed grid. After development, the printing plate is treated with printing ink in such a way that images result which have semitones corresponding to the original. It is stated that the exposure time is an important parameter that must be determined for each special case; Great importance is also attached to the composition of the developer, for example its effect on the pH; further factors for the feasibility of transferring halftone images without rastering the original are particularly thin radiation-sensitive layers and special printing inks. Mechanically roughened aluminum foils are mostly used as carrier materials for the printing plates, but anodized aluminum is also used.
• a radiation-sensitive reproduction material is known, the radiation-sensitive layer of which is provided in a dense arrangement with depressions whose extents on the surface of the copying layer have a diameter of 1 to 50 ⁇ m, preferably 5 to 10 ⁇ m, and with Approach to the base of the copying layer become smaller.
• a surface modification is complex because. they are an additional feature in the large-scale production of precoated printing plates, but also in the coating of substrates with the consumer himself passageway required.
• Aluminum either smooth or roughened to a roughness depth of about 2 ⁇ m, is used as the carrier material. Due to the presence of the depressions, a true-to-tone transmission of halftone images should be possible without rastering the original.
• the height of the elevations should be at least one third of their diameter, in particular from 2 to 6 ⁇ m.
• the surface structure of the aluminum substrate materials, which are mechanically roughened by conventional methods, must be leveled, for example by thermal melting or by polishing; a scraping or embossing technique is proposed as a variant, ie likewise processes which are too complex on an industrial scale or too slow for continuously running belt systems.
• an electrochemical roughening method also mentioned in aqueous electrolytes containing alkali metal gluconate and alkali hydroxide, which leads to shiny structures with pear-shell patterns, is unsuitable for a continuously operating process and, moreover, does not lead to a practical roughening topography. Due to the presence of the special roughening structure after application of a radiation sensitive layer, a tone-true transfer of halftone images without rastering the original.
• GB-B 1 591 988 describes a process for the production of printing forms, of which printing can be carried out in such a way that a true-to-tone reproduction of halftone originals is possible without rastering the original.
• the process necessarily comprises two stages, namely a) the application of a positive-working radiation-sensitive layer containing naphthoquinonediazide esters and an alkali-soluble resin in a ratio of 1: 1 to 1: 6.5 to a roughened support, and b) development of the exposed layer with a developer containing 75 to 99.5 vol .-% of an aqueous alkaline solution and Contains 0.5 to 25 vol .-% of a water-miscible organic solvent.
• the carrier material is roughened electrochemically and has a surface roughness of 2.5 to 12 m 2 per m 2 (measured by gas adsorption). Anodic oxidation can also be added to the electrochemical roughening stage.
• the object of the present invention is to propose a carrier material on the basis of aluminum, with which, after application of a radiation-sensitive coating, a reproduction material is produced which makes it possible to use templates having halftones. reproduce true to tone without rasterization. It should be possible to be able to produce the carrier material in modern continuously operating belt systems, and also not to be too restricted with regard to the selection of the radiation-sensitive layer to be applied, i. H. for example, to be able to use both negative- and positive-working radiation-sensitive layers in which commercially available radiation-sensitive compounds, resins and / or other auxiliaries can be used.
• the parameters a) D a are in the range from 0.5 to 3.0 ⁇ m, in particular from 1.0 to 3.0 ⁇ m, b) D 99 at a maximum of 8 ⁇ m, c) D d at a maximum of 5% , d) A at a maximum of 10%, e) R in the range from 0.8 to 1.2 ⁇ m and f) R d at a maximum of 5%.
• at least 95% of all holes should have a diameter D 95 of at most 8 ⁇ m, in particular of at most 6 ⁇ m.
• the radiation-sensitive layer should preferably have an extraordinarily extensive range of tonal values, the production of such layers being known.
• the tonal range is only one of several criteria that must be considered if printing is to take place without the interposition of a grid.
• a high resolution must also occur within each gray level, and the printing form must be able to print for a relatively long time without any appreciable deterioration in the image.
• a very decisive factor for the production of a printing plate in line with the market in the field of rasterless offset printing is obviously the surface topography of the carrier material.
• the parameters characterizing the carrier material according to the invention are therefore to be explained in more detail below.
• the roughening of the surface can be analyzed and measured using various methods.
• the standard methods include observation under a scanning electron microscope and instrument measurements, such as B. with a profilometer that scans a linear path on the plate with a highly sensitive needle.
• the diameters of the holes created by the roughening are determined on the basis of photos which are taken at 1000 to 2000 times magnification using a scanning electron microscope with an electron beam incident perpendicular to the aluminum surface.
• a representative quadra is used for each sample table area with at least one thousand holes selected for the measurement.
• the diameter of each hole is measured in the plane of the surface both parallel and perpendicular to the rolling axis or strip direction of the aluminum.
• the maximum length measured across the hole on the respective axis is assumed and recorded as the diameter. All diameters under 0.5 ⁇ m are not taken into account in the subsequent parameter determinations.
• the arithmetic mean of the diameters in the parallel and vertical directions are calculated separately.
• the arithmetic mean D a of the distribution of the hole diameters is calculated from the arithmetic mean of the hole diameters in the parallel and perpendicular directions and the directional dependence D d of the hole diameters as the percentage difference between these two arithmetic means of the hole diameters.
• D 95 is the maximum diameter that 95% of all holes reach in parallel and vertical directions; accordingly D 99 denotes the diameter that 99% of all holes reach to the maximum.
• Areas that are clearly free of holes or that have holes with a diameter of less than 0.5 ⁇ m on each of the two axes are also determined and added. A is then the percentage of these added areas in the total surface.
• the surface roughness (see for example DIN 4768 in the version from October 1970) is measured with a profilometer over a representative distance of at least 2 mm both parallel and perpendicular to the rolling axis sen.
• the mean roughness values are calculated from the two measurements as the arithmetic mean of the absolute distance of all points on the surface separated from the center line.
• the average center-line roughness value R a is calculated as the average value of the center-line roughness values in the parallel and perpendicular directions and the directional dependence R d of the roughness profile as the percentage difference between these two center-line roughness values.
• the parameters which characterize the invention are therefore the hole diameters, their size distribution and directional dependence, the surface roughness and their directional dependence and the extent of the hole-free or only very small areas.
• the surface of the plate must always be roughened if you want to ensure that the coatings to be applied are adequately anchored and thus want to obtain a plate that can be used in practice. It has also been written in the past that plates were made without any roughening, but these plates are not practical because coatings do not adhere sufficiently to their surfaces.
• the surface In the quality plates produced according to the invention, the surface must have very fine holes, i.e. H. Hole diameter and depth are limited; the carrier material must be roughened very uniformly over its entire surface, and the roughening structure must not run preferably or even exclusively in a certain direction.
• the aluminum to be used as the carrier material does not have to be of a particularly special quality, the grain orientation is not very important, i.e. the base grain of the plate can even have a preferred direction.
• This directional grain is the result of the rolling process in which the aluminum is stretched and then wound on a core. A thick aluminum bar is squeezed together with rollers working under high pressure until a very long, thin aluminum strip (sheet) is formed. This process imprints a directional pattern on the strip that runs parallel to the rolling direction. If this tape is now roughened, the holes that are formed tend to follow the course of this directional pattern.
• the halftone dots in the image areas resulting from the radiation-sensitive layer bridge these aligned holes without major disadvantages.
• this is a serious problem for rasterless offset printing because the image consists of layer particles that are much smaller than dots can be.
• the carrier material has the parameters according to the invention, these problems do not arise.
• Aluminum alloys with an aluminum content of at least 98.5% are most suitable as the starting material for the carrier material according to the invention; alloys with an aluminum content of more than 99.5% are preferred; these alloys contain, for example, proportions of Si, Fe, Ti, Cu and Zn.
• the carrier materials according to the invention a plate, film or tape-shaped material is assumed which must have a maximum average roughness R of 0.10 pm, i.e. H. the surface of the aluminum must be specially treated before roughening. Accordingly, the average roughness on such a surface must have values of at most 0.10 ⁇ m, in particular of at most 0.08 ⁇ m and preferably of at most 0.05 ⁇ m, both on the parallel and on the vertical axis. The average roughness value in the vertical direction is given because it is the larger of the two values.
• the aluminum surface Before and / or after polishing, the aluminum surface can be cleaned and / or degreased and / or etched using conventional methods. These methods include, for example, treatment with aqueous NaOH solution with or without degreasing agent and / or chelating agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains. This processing step usually takes about 15 seconds to 5 minutes. The pre-cleaned and polished surface is then roughened very uniformly using known methods. The roughening is expediently carried out by mechanical and / or electrochemical processes.
• the preferred electrochemical roughening can be carried out in an electrolyte which contains acids, such as, in particular, nitric and / or hydrochloric acid, which may have been admixed with further additives, such as boric acid, hydrogen peroxide, aluminum chloride and aluminum nitrate, in order, for example, to contribute to a uniform processing result and that improve electrical conductivity of the electrolyte; however, neutral salt solutions are also known as electrolytes.
• the nitric or hydrochloric acid is normally contained in the aqueous electrolyte in a proportion of about 1 to 20 g / l, which is kept at a temperature of about 20 to 60 ° C.
• the current preferably alternating current
• the current density is approximately 0.1 to 200 A / dm 2 .
• the roughening process lasts from about 0.1 seconds to 5 minutes.
• the roughened carrier is then preferably anodically oxidized by one of the various known methods in order, for example, to improve the mechanical properties of the surface.
• aqueous solutions containing sulfuric, phosphoric and / or oxalic acid in concentrations up to about 200 g / l at temperatures of about 20 to 40 ° C. are used as electrolytes.
• the current density is up to about 30 A / dm 2 , and this results in an oxide film of up to about 10 g / m 2.
• the aluminum oxide layer can then be treated in a hydrophilizing manner by chemical (dipping) or electrochemical means with a hydrophilizing agent, such as As polyvinyl phosphonic acid or sodium silicate, is brought into contact.
• the carrier produced according to this invention and having a specific surface topography has proven to be very advantageous in the production of the most varied of printing plates, but is particularly suitable for the field of rasterless offset printing.
• a radiation-sensitive coating must be applied to the support, which results in an extremely long tonal range.
• Many such coatings are known which are suitable for coating the carrier materials according to the invention.
• these coatings are used as photosensitizers diazo compounds such.
• At least 7, but preferably at least 12 to 13 gray levels in the Stauffer step wedge are expected from the radiation-sensitive coating.
• An image with such a broad tonal range can be achieved by many coating variants, including, for example, the addition of UV absorbers to the coating, an increase in the dry layer weight per unit area of the plate and changes in the composition of the developer solutions used to develop the exposed layers.
• Suitable radiation-sensitive compounds are, for example, a polycondensation product of 3-methoxydiphenylamine-4-diazonium salt and 4,4'-bismethoxymethyldiphenyl ether, precipitated as mesitylene sulfonate, azides such as 2,6-di (4'-azidobenzal) cyclohexanone and o-quinonediazides such as Esters of naphthoquinone (1,2) diazide (2) -5-sulfonic acid and 2,3,4-trihydroxybenzophenone or 2,2'-dihydroxy-dinaphthyl- (1,1 ') - methane.
• azides such as 2,6-di (4'-azidobenzal) cyclohexanone
• o-quinonediazides such as Esters of naphthoquinone (1,2) diazide (2) -5-sulfonic acid and 2,3,4-trihydroxybenzophenone or 2,2'-d
• Typical binders are novolaks, polyisoprene, alkylphenol or polyvinyl formal resins.
• Suitable UV-absorbing dyes are, for example, benzotriazoles, benzophenones, cinnamates and salicylates, such as 2 - [ «2'-hydroxyphenyl) imino) methyl] phenol, 2-hydroxy-4-methoxybenzophenone, 2,2 ', 4,4'- Tetrahydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2 (2'-hydroxy-5'-methylphenyl) benzotriazole or phenyl salicylate.
• Preferred developers are solutions which contain, for example, the following constituents: sodium metasilicate, trisodium phosphate, monosodium phosphate and / or alkali metal hydroxides in water for quinonediazide layers, n-propa nol in water for diazonium salt layers and benzene for azide layers.
• the carrier materials according to the invention are distinguished by the fact that after application of a suitable radiation-sensitive coating, a reproduction material is produced which makes it possible to reproduce templates having halftones faithfully without rastering.
• the carrier materials can be produced in modern, continuously operating conveyor systems without major additional effort, i.e. in particular, no processing of already roughened, anodized and / or radiation-sensitive coated strips, plates or foils is required.
• a strip is made from an aluminum alloy with the following composition: 0.12% Cu, 1.20% Mn and 98.68% Al and cut into plates.
• the average roughness R a is about 0.25 ⁇ m on both sides of the material.
• One side of these plates is mechanically polished for 15 minutes with an aluminum oxide paste which has an average particle diameter of 0.05 ⁇ m, after which the R a value of the polished side is 0.01 ⁇ m.
• the aluminum plate thus polished is first briefly trichlorethylene, acetone and at room temperature then methanol and then immersed in an aqueous solution containing 40 g / l of NaOH for 1 min at a temperature of 25 ° C.
• the polished side of the plate is electrochemically roughened at 25 ° C in an aqueous solution containing 20 g / 1 of concentrated HN0 3 , being subjected to a current density of 100 A / dm 2 from alternating current at 50 Hz for 15 seconds ; the counter electrode is made of stainless steel.
• a strip is made from an aluminum alloy with the following composition: 0.01% Fe and 99.99% Al and cut into plates.
• R a is approximately 0.8 ⁇ m on both sides of the material.
• Two of these plates are briefly at room temperature in trichlorethylene, acetone and then methanol and then for 3 min at 70 ° C in an aqueous solution of 200 g / 1 of concentrated H 3 P0 4 (concentration: 33.5 to 36, 5%), 200 g / l of concentrated H 2 S0 4 and 20 g / 1 of concentrated HN0 3 .
• the two chemically treated (polished) plates have R a values of about 0.09 ⁇ m on both sides.
• the plates thus treated are immersed in an aqueous solution containing 40 g / l of NaOH at 25 ° C. for 1 minute.
• the two plates form the electrodes;
• a current density of 75 A / dm 2 from alternating current at 50 Hz is applied for a period of 20 sec.
• One of the roughened sides is then anodized at 25 ° C. in an aqueous solution containing 150 g / l of H 3 PO 4 , with 40 V DC being applied for 4 minutes.
• a tape is made from an aluminum alloy with the composition and surface quality according to the information in Example 2.
• a plate cut from this tape is briefly immersed in trichlorethylene, acetone and then in methanol at room temperature and then anodized at 25 ° C. in a methanolic solution containing 7% of HClO 4 , with a direct current of 20 V for 1 min is applied.
• the electrochemically treated (polished) surface has an R a value of 0.07 ⁇ m.
• the plate treated in this way is then immersed in an aqueous solution containing 40 g / l of NaOH for 3 minutes at 25 ° C. It is then electrochemically roughened on one side at 30 ° C.
• a tape is made from an aluminum alloy of the following composition: 0.70% Si, 0.41% Fe, 0.11% Cu, 0.01% Mn, 0.01% Mg, 0.01% Zn, 0, 02% Ti and 98.73% Al. Both sides of the material have average roughness values R a of about 0.29 ⁇ m.
• the tape is further cold stretched until it is 0.31 mm thick and has an R a of 0.04 ⁇ m on one side.
• the aluminum strip is then cleaned, degreased and lightly etched, which is done by treating for about 1.5 minutes at about 50 to 70 ° C in aqueous alkaline solutions containing about 20 g / 1 sodium hydroxide, aluminum ions and a degreasing agent.
• the smooth side of the tape is then electrochemically roughened at 40 ° C. in an aqueous solution containing 20 g / l of concentrated HNO 3 (concentration: 69.0 to 71.0%), with a current density of 70 A. / dm 2 from alternating current at 60 Hz for 4 sec is created; then it is switched off for 20 seconds, the current is again applied for 4 seconds, switched off for 20 seconds and applied again for 4 seconds; the counter electrode is made of lead.
• the roughened side is then in an aqueous solution with a content of about 150 g / 1 of concentrated H 2 S0 4 (concentration: 95.0 to 98.0%) and about 5 g / 1 of Al 2 (SO 4) 3 ⁇ 18 H 2 0 anodized at 45 ° C.
• the direct current density of 26 A / dm 2 is switched on and off alternately for a total operating time of 10 seconds.
• the tape is immersed for 1 min at 60 ° C. in an aqueous solution containing 2.2 g / l of polyvinylphosphonic acid for hydrophilization.
• the plate is then rubbed by hand with printing ink and rubberized.
• the printing form is clamped in an offset printing machine and it is printed with black ink on coated paper, with about 60,000 flawless prints being achieved.
• An aluminum alloy ribbon is made with the following composition: 0.12% Si, 0.27% Fe, 0.01% Zn, 0.02% Ti and 99.58% Al. On both On the material side, the average roughness values R a are approximately 0.15 ⁇ m. The tape is further cold stretched until it has a thickness of 0.20 mm and an R a value of 0.10 ⁇ m on one side. The aluminum strip is cleaned, degreased and lightly etched with an aqueous solution containing 20 g / l of NaOH, aluminum ions and a degreasing agent at a temperature of about 60 to 70 ° C. for about 1 minute.
• the smooth side of the tape is then electrochemically roughened in an aqueous solution containing about 16 g / l of concentrated HNO 3 and aluminum ions at about 40 ° C., with a current density of 123 A / dm 2 from alternating current at 60 for 8 sec Hz acts; the counter electrode consists of lead.
• the roughened page is then stored at 40 ° C, about 5 g / 1 3 ⁇ 18 H 2 0 anodically oxidized to Al 2 (SO 4) in an aqueous solution with a content of about 150 g / 1 of concentrated H 2 S0 4 and whereby DC current with a current density of 10 A / dm 2 is applied for 8 sec.
• the radiation-sensitive printing plate thus produced is exposed through a positive, rastered original (12 lines / mm) with a metal halide lamp in such a way that stage 3 on the Stauffer step wedge is the first non-blackened step and 4 gray steps result during printing. It is developed in a cuvette with swiveling device for 2 min with the developer according to the information in Example 7 at 22 ° C. Then it is rubbed by hand with printing ink and rubberized. The printing form is printed on coated paper on a magenta offset printing machine. It delivers around 150,000 flawless prints.
• a positive-working radiation-sensitive coating according to the instructions in Example 9 is spun onto a plate and, after drying, has a layer weight of 2.5 g / m 2 .
• The. radiation-sensitive printing plate is a positive, non-rastered halftone with a D ichtebine of 0.80 using a metal halide lamp illuminated. It is then placed in an immersion container with an aqueous solution containing 3.79% of sodium metasilicate and enough NaOH for 30 seconds that the aqueous solution has a pH of 13.2.
• the plate is then heat-treated at 100 ° C. for 5 minutes, rubbed in by hand with printing ink and rubberized.
• the printing form is used for printing on an offset printing machine with alcohol dampening. It is printed on coated paper with black ink, producing approximately 200,000 flawless prints. There are 7 gray steps in the Stauffer step wedge.
• the pressure plate labeled ® Ozasol P3S with the D a , D d and R a values lies inside and with the D 99 , A and R d values outside
• all of the carrier materials produced in the above examples lie in all 6 parameters within the claimed values or value ranges.

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Citations (5)

• 1983
  • 1983-02-16 EP EP19830101472 patent/EP0088899B1/fr not_active Expired
  • 1983-02-16 DE DE8383101472T patent/DE3365765D1/de not_active Expired

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