Offset Printing Plate Research Articles

B115 スペックル計測を用いたオフセット印刷版の表面濡れ状態の評価

In this paper, a technique of speckle measurement has been developed for evaluating the wetting state on a surface of offset printing plate. The present method can provide not the amount of water supplied to a printing plate, but the information of the wetting state on the plate to automate the system for water supplying in offset printing machine. The experimental results demonstrate that the speckle intensity increases for the wetting state suitable for better offset printing as compared with that for short or excessive water supplying.

Synthesis, characterization and photocross-linking of copolymers of furan and aliphatic hydroxyethylesters prepared by transesterification

Mild experimental conditions were applied to the synthesis of furan-aliphatic photoreactive copolymers by bulk transesterification, which called upon potassium carbonate as the catalyst, reaction times of about 30 h and temperatures ranging from 95 to 120 °C. The ensuing copolymers contained 3–10% of furan photoreactive monomer units, which absorbed at 308 nm, and had molecular weights of about 8000. They were semi-crystalline materials with glass transition temperatures of −51 to −62 °C and were stable up to 225 °C. The irradiation in the near-UV of concentrated solutions or thin films of these copolymers resulted in their cross-linking and suggested their possible use as photoresists, particularly in offset printing plates.

Trends in making offset printing forms

This paper presents new technologies for making offset printing plates, new materials for inplate manuifacturing and new screening technologies.

Investigation of the influence of cementation of chromium onto aluminium on the characteristics of non-printing elements of an offset printing plate

The possibility of the electro less deposition of chromium onto aluminum was investigated in order to improve non-printing element properties. It was determined that the electrochemical deposition of trivalent chromium was possible from alkaline solutions. The presence of chromium was confirmed by the EDAX procedure in three different laboratories. The influence of chromium on the wet ability of the nonprinting elements of the printing form was examined by drop spreading. Specimens were examined by pouring distilled water in drops onto the surface of the specimen. The picture of the drop was taken by a digital camera from two directions, in order to measure the diameter of the spreaded drop (a measuring gauge was recorded together with the drop) and contact angle. The chromium-treated samples showed increased wettability compared with the non-chromium-treated samples. Improvement of the non-printing elements was confirmed during a printing test that was performed under real printing conditions. The purity of the prints made by two types of printing forms was analyzed in two ways: based on densitometric measurements and based on statistical analysis of the scanned print. Both methods of analysis of the control prints showed that the control prints made from chromium-treated specimens were purer than the prints made from the non-chromium-treated specimens. Considering that all the conditions of making the printing forms and the printing conditions, except the electro less deposition procedure were the same, it could be concluded that the electro less deposited layer of chromium improved the printing properties of the offset printing form because of the increased wettability.

Using Machine Vision Based System for Benchmarking Various Printing Plate Surfaces

Traditionally a dot meter or an optical microscope fitted with a camera is used to analyze the dot position and dot area fraction of offset plates. Dot meters do not provide valuable information such as dot raggedness and dot positioning. These features are important when the plates are exposed digitally using laser diodes. The alignment of individual laser diodes is very important for controlling the position of the dots and in turn controlling the moire patterns appearing the final full color prints. Dot position verifies diode quality, alignment, and ensures output quality.The optical microscope system that was used by Presstek in the past could capture optimal contrast images only of metallic plates. Also, the software that had been used for analysis was only capable of measuring dot percentage and a few dot quality parameters, and could not provide enough useful information about other plate and print quality features. To achieve accurate dot percentage results, the threshold values had to be changed manually for each nominal dot area fraction value. After each analysis, the measurement result of the actual dot area percentage had to be saved manually to a file from the software.Presstek (a manufacturer of wide range of specialty offset printing plates) deals with plates of different materials, many of which are unique, so a new image inspection system was required to provide the quality assurance necessary across the various product lines. It was recognized that this system needed to be able to successfully measure on various plate media, and be able to adjust threshold values, store images, and save results to a file automatically. It was also necessary for the system to be able to perform various plate and print quality analyses including dot area fraction, dot position, feature location, etc.An ImageXpert system with a 3-CCD color camera and high magnification optics is now in use. The combination of camera and ring light illumination source is capable of capturing images from various plate materials with excellent contrast. In addition, when co-axial illumination is necessary, images can be captured using our existing microscope and can be imported into ImageXpert for analysis. The software provided with the system is capable of measuring dot area percentage (even in the difficult 50% dot area range) with automatic thresholding, and it can measure dot positions, various dot quality attributes, and perform printability analysis on printed sheet as well as imaged plates.

The influence of electroless plated chromium on printing properties of aluminium offset printing plate

A method for the improvement of the printing properties of offset printing forms is presented. Specimens of technical aluminum were electrochemically roughened and treated in different alkaline solutions of chromium chloride in order to chemically deposit a chromium layer. The composition of the surface layer was investigated by EDAX. Chromium was found on the specimens that had been treated in an alkaline solution of chromium chloride, while no chromium was found on chemically untreated specimens or on specimens that had been treated in an alkaline solution without chromium chloride. The spectral reflectance from treated and non-treated specimens was also measured. The chromium-treated specimens were brighter than the non-chromium-treated ones. The wettability of the chromium- treated samples was compared with the wettability of the non-chromium treated samples by measuring the contact angle with water and the wetted area. The chromium-treated samples showed increased wettability compared with the non-chromium-treated samples.A printing test was performed under real printing conditions. Control prints was analyzed densitometrically and statistically. The chromium-treated printing forms gave clearer prints than the non-chromium-treated printing forms under all printing conditions.

Screened Offset Plates: A Contact Angle Study

Many studies about offset printing plate surface energetics have dealt with determinations of the difference between image and non-image areas through contact angle measurements. On another hand, contact angle hysteresis studies have highlighted the influence of surface state and/or heterogeneity. The novel approach of Shanahan and Di Meglio expresses hysteresis as a function of surface defects parameters. In the case of offset printing plates we have considered screen dots as defects, and we have evaluated the corresponding hysteresis energy by the use of some liquids such as pure water, glycerol and a series of fountain solutions. The experimental results turned out to validate this approach and to show the way this energy is linked to the screen geometry and the relative dot area. In parallel with this new approach, we have also shown that the classical Cassie and Baxter model of averaging effects may be applied to liquids on screened areas.

IR-empfindliche Schichten zur Herstellung von Offset-Druckplatten

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Ellipsometric Study of Silicate Treatment of Aluminum Offset Printing Plates

The silicate treatment of aluminum offset printing plates has been studied by ellipsometry. Aluminum is very reactive with oxygen and the aluminum surface is easily oxidized in the atmosphere. The presence of the oxide layer on the aluminum surface brings about some ambiguities in the analysis of the ellipsometric data of the overlaid film. Few researchers have estimated the thickness of a siliceous film on aluminum plates as far as we know. However their estimations are very vague, ranging from one monolayer (∼0.3 nm) to 1 µm.1,2) We carried out a series of experiments to determine the thickness of a siliceous film on an aluminum surface by means of ellipsometry. The thicknesses of the siliceous films on the aluminum film surface were successfully estimated by applying Bruggeman's effective medium approximation to the composite layer of the aluminum and the aluminum oxide. In our experiments, the thicknesses of the composite layer and the siliceous film were estimated to be in the range from 1.3 nm to 1.6 nm and about 0.7 nm, respectively.

Modification of the aluminum for making offset printing plates

Aluminum as the base of offset printing plates should make good contact with wetting agents and the light sensitive layer and should be resistant to wear and cracking. In order to achieve this, the aluminum is roughened and eventually anodized. A thin, electrochemically deposited chromium layer is used as the non-printing element in bimetallic offset printing forms. Chromium shows excellent wettability and wear resistance. The possibility of chemical deposition of chromium on aluminum from an alkaline solution is examined in this paper. The presence of chromium was confirmed and measured by EDAX. A difference in the spectral reflection characteristic between chromium-treated and non-treated specimens was also detected. An influence of a chromium layer on an aluminum surface was examined by water drop spreading. Chromium-treated samples showed better wettability than non-treated samples, but they are less wettable than anodized samples.

Application of Laser to Digital Printing. High Definition Image Printed by Laser Thermal Transfer.

For development of computer-to-plate direct exposure system, it is necessary to develop a dry and high definition recording process connected to the computer system. In the wax melt-type laser thermal transfer printing, the laser diode irradiation is absorbed as heat in the thermal transfer ribbon that results in local melting and transfer of the ink to the receiving sheet. In this research, the ink image was transferred to the paper and an aluminum plate by laser heating technology for making the high definition image and offset printing plate directly. The fundamental characteristics such as the shape of printed pixel, printing energy and optimization of printing condition were discussed in the melt-type thermal printing by laser heating.

Surface‐activated photopolymer microgels

Enhancement of the sensitivity of photopolymers is needed if photopolymers are to find more extensive applications in the printing and microlithography industries. A new concept is presented for sensitivity enhancement: the use of surface‐activated microgels as a heterogeneous polymer matrix. The preparation of the microgels and their effect on the polymerization rate and the sensitivity are described. Examples are given of applications of microgel‐based photopolymers as offset printing plates and photographic film.

Chemical Aspects of Offset Printing

In the last ten years, offset printing has achieved the broadest application on the printing market due to its inherent advantages. Light sensitive offset plates for contact UV exposure are mainly used at present. The chemistry of these plates are based on the photoreactions of quinone diazides, diazo resins and radical photopolymers. For the further development of offset printing plates the improvement of the light sensitivity and extension of spectral sensitivity to the visible range is a market-driven requirement to realize transfer of computer stored informations by laser. For this requirement electrophotographic systems, systems based on silver halides and photoinduced polymerizations are most important. New literature data dealing with these systems in relation to printing plates are summarized.

Identification of Wrinkled and Charred Counterfeit Currency Offset Printing Plate by Infrared Examination

Abstract Badly charred and burned material present unique and difficult identification problems for the document examiner. When these qualities are coupled with badly bent and wrinkled metal objects, the problems are compounded. This paper describes how a badly wrinkled and burned sheet of aluminum metal was identified as being a 20-dollar bill counterfeit money plate. The identification was made by use of an infrared viewer and infrared film.

Chalcogenide Glasses as Sensitizing Layer for Offset Printing Plates

Etude des possibilites de sensibilisation des plaques d'impression offset par des couches evaporees de verre de chalcogenure. On determine l'influence du traitement du substrat aluminium sur les qualites des plaques offset. Il est montre que des plaques offset sensibilisees par des couches evaporees de As 2 S 3 presentent des qualites elevees, permettent des tirages importants et que leur traitement est facile et non critique, ce qui les rend particulierement bien adaptees aux applications pratiques

MEASUREMENT OF PHOTOCHEMICAL CHANGES OF PRESENSITIZED OFFSET PRINTING PLATES BY FOURIER TRANSFORM INFRARED PHOTOACOUSTIC SPECTROSCOPY

Abstract Fourier transform infrared photoacoustic spectroscopy(FTIR-PAS) was applied to the measurement of photochemical changes of presensitized offset printing plates. FTIR-PAS was found to be a useful method for obtaining direct information on structural changes of photosensitive resins on roughened metal surface.

ARSENIC SULPHIDE AS EVAPORATED DRY PHOTORESIST

Most amorphous substances change their physical and chemical properties on illumination. The photosensitive solubility permits the use of amorphous arsenic sulphide as evaporated photoresist. An appropriate solvent was found which fully dissolves the exposed areas without affecting the unexposed ones. Thus extremely thin layers of evaporated amorphous arsenic sulphide can be used as sensitive photoresist with high resolution for the production of chromium masks and sensitized offset printing plates.

The Alternating Current Etching of Aluminium Lithographic Sheet

SummaryElectrolytic etching has for some time been used to produce a ‘grained’ or uniformly roughened surface on aluminium sheet for offset lithographic printing plates. The process commonly employed involves alternating current etching in 1–2% HCl. The effect of etching variables such as etching time, temperature, current density and electrolyte usage is described. Etching is found to be accompanied by the formation of a surface film and electrochemical studies have shown that within the potential range -700 to -850 mV SCE passivity occurs. On the basis of these results a mechanism is proposed for the etching process. Uniformity of pitting and pit depths are thought to arise from the use of alternating current, which allows passivation of etch pits during etching and thus produces a redistribution of attack.

Screenless Offset Printing Process Using Presensitized Printing Plates

The report starts with the definitions and the advantages and disadvantages of offset printing with un-screened (= continuous tone) and with screened photographic originals. This is followed by the description of the historical development of screenless offset printing from the phototype or collotype process to the present art, which is characterized in that the presensitized offset printing plates known nowadays have too steep a gradation for this field of application.First results obtained with a novel presensitized offset printing plate for screenless printing are graphically represented in the Goldberg-Jones diagram.

Graining of Aluminum Offset Printing plates

Graining of Aluminum Offset Printing plates