TECHNOLOGY
Plastics vie for printing plate market Daily newspapers offer largest potential market for plastic plates from Carbide, Du Pont, and Grace "Daily newspapers are the largest potential market for plastic printing plates," Wallace Sadauskas, market development manager of the plastics development division of Union Carbide, declares. Carbide is developing a plastic plate system which has been used experimentally by the nation's largest newspaper. At least two other chemical companies would be quick to agree with Mr. Sadauskas' evaluation of this tempting market. Du Pont, in 1960, aimed part of its Dycril plate effort at the newspaper market. And W. R. Grace set Wall Street aflutter this spring with the news that it had also developed a plastic printing plate for newspapers. Grace will say only that three newspapers are now experimenting with its Letterflex plates, that they can be used with existing equipment, and that it expects to have a commercial product in the fall of 1968. Like Dycril, W. R. Grace's Letterflex plate is probably based on a photopolymer reaction. In these systems, ultraviolet light passes through a film negative of the page to be printed and strikes the coated plate. The light causes polymerization ( photopolymerization) or cross-linking (photocrosslinking) of the surface coating. In a second step, unsensitized or unpolymerized material is washed away leaving a plastic image in relief. With
Dr. Julius L. Silver A truly planographic offset plate
Dycril, the relief or height of the type is about 40 thousandths of an inch. There are a number of other photopolymerization letterpress printing plates in development but only Grace and Du Pont seem to have stressed newspaper markets in the U.S. (C&EN, March 4, page 4 6 ) . Time, Inc., has developed a nylon printing plate with long life for its magazine's long press runs. Both West Germany's Farbenfabriken Bayer and Badische Anilin-& Soda-Fabrik have photopoly-
The page of C&EN you are now reading was printed on a web rotary letterpress from a continuous roil of paper. The metal type that produced this line was coated with ink and pressed against the paper to leave an imprint in much the same way a rubber stamp leaves a word on a page. About 135,000 copies of C&EN were printed this week. The plate that made this page required many process steps (see opposite page) and was finally electroplated with nickel so that the type would withstand the abrasion of paper whizzing through the press at almost 800 feet per minute. Most daily newspapers are also printed on web rotary letterpresses. However, newspaper plates are made from lead-alloy in a simpler process since each plate is required to make only about 50,000 impressions under tight newspaper printing schedules. There is another kind of printing, called offset or lithography, which uses a different principle to transfer an image to paper. In lithography, a printing plate is prepared which contains an image which is oleophilic. That is, it holds ink. The substrate or nonimage portion
62 C&EN AUG. 26, 1968
mer letterpress plates. BASF says its Nyloprint has been used by daily newspapers in Germany. Bayer's plate uses an unsaturated polyester coating that is cross-linked by light. Eastman produces a letterpress plate based on silver emulsion chemistry to produce a light-sensitive resist. Reichhold Chemicals, in a different approach, has sponsored the development of a plastic printing plate system using its polyester resins. This kind of plate is not photosensitive and is molded in much the same way that lead-alloy plates are made. Their advantage is light weight and compatibility with existing letterpress systems. While the nation's daily newspapers present an inviting target for chemical companies that can develop an economical plastic plate, there are some very good reasons for viewing the market with caution. The large metropolitan dailies are printed on letterpress. To prepare a printing plate, each column line is cast in a single slug of lead alloy type on a Linotype machine. The lines are locked in a frame from which a papiermâché mold is made. The mold is placed in a casting machine that produces a lead-alloy plate about 0.5 inch thick. The time required to make this plate is less than a minute and the stereo, as the plate is called, is good for 50,000 impressions
of the plate is hydrophilic (it holds water). Both water and ink rollers contact the plate. The image is then transferred to a rubber roller rather than directly to the paper. The rubber blanket covering the offset cylinder transfers the inked image it carries to the paper. There are many differences between offset and letterpress operations and the economics of which to use for a particular printing job have to be studied on an individual basis. Offset printing is rapidly replacing letterpress in this country. Wh/Je 80% of the 1960 daily newspapers in the U.S. are letterpress, about half of the 10,000 weekly newspapers are now printed on offset presses. Last year, for the first time, offset printing surpassed letterpress in dollar value in this country. Bolstering the swing to offset printing has been the acceptance by the printing industry of photocomposition systems. The offset plate can be made from a photograph negative. Such a negative can be made through optical systems without ever having to cast type. The use of photopolymers for letterpress plates will increase if metropolitan newspapers accept photocomposition.
before it has to be replaced. The advantage of the system is that a number of stereos for duplicate presses can be made in very little time once the mold is prepared. The lead is melted and used again. These plates cost about 35 cents per sq. ft. to produce. Paul Smith, manager of printing plates in Du Pont's photo products department, lists some of the problems that have to be overcome before plas-
tic plates can be used on newspaper letterpresses: • Newspapers are not geared now to making a photographic negative of their pages. Photocomposition systems would have to replace hot metal composition before the full advantage of photopolymer plates could be realized. • Photopolymer plates would have to sell for under $1.00 per sq. ft. to be competitive.
(1) Locked-up page of type and its plastic mat are preheated
• Plastic plates take longer to make than stereos, a big disadvantage to deadline conscious newspaper editors. • Finally, plastic plates do not have the weight and thickness of stereos and will not fit existing presses. A special saddle must be made to fit the plates on the press and tolerances are very critical. Du Pont has experimented with a number of newspapers on the East
(6) Lead is poured into the shell to form the printing plate
(4) The mat goes next to the electrolysis bath where the final mold is formed
(5) The shell, an opposite relief of the original type, is now ready
(2) After molding, the plastic mat is removed from the type face
(7) The plate is curved and then routed out to remove extraneous matter
(3) A silver nitrate solution is then sprayed onto the mat
AUG. 26, 1968 C&EN 63
QUSO MICRO-FINE PRECIPITATED SILICA . . .
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The ultimate particles are extremely fine, about 12 milli-microns, or even finer than the particles that are airborne of cigarette smoke. QUSO has immense adsorptive surface and capacity. With an external surface area in about two ounces roughly equivalent to the playing space of two football fields, or about 8360 square meters, it can adsorb over twice its weight of water or oil and still remain free flowing.
Pressure Temperature Crystallization
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Sales Manager for QUSO: (215) MA 7-7200. P h i l a d e l p h i a Quartz C o m p a n y 1162 Public Ledger Building, Philadelphia, Pa. 19106
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Name_ Company. Address— City 64 C&EN AUG. 26, 1968
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Coast in the use of Dycril, but is not optimistic over the future for these plates in the newspaper field. Newspapers simply do not need to pay for the long life inherent in Dycril plates since their press runs are relatively short. Photopolymer plates are also poised to enter the offset printing plate business. Du Pont's Lydel, for example, is an outgrowth of the firm's development of the photopolymerization letterpress plate, according to Mr. Smith. A different concept in polymer technology was harnessed by Dr. Julius L. Silver at Union Carbide's Bound Brook, N.J., lab to make a new family of offset plates. Union Carbide has licensed the technology to Rogers Corp. and Dr. Silver will become a research associate for the Rogers, Conn., firm. In the Rogers plate, aluminum is coated with a thin layer of an ethylene oxide polymer and phenolic resin that are associated through hydrogen bonding. A sensitizer is then applied to this polymer film. When light shines through a negative of the image to be produced, the sensitizer causes the coating struck by light to become ink receptive. Unlighted areas remain water sensitive. The plate is truly planographic. While the image can be seen, it is not raised. After unreacted sensitizer is washed off with water, the plate is ready fo^ mounting on the press. Dr. Silver estimates that when processing cost* are considered the plate may be 509f less expensive to use than competitiv< offset plates. He also lists some other advantage for the plate: • It is very long wearing. Chemic preparation steps after exposure a eliminated. • Unexposed portions of the pli can be coated with sensitizer and us again.
