Letterpress printing plates

Manufacturing process of nylon letterpress printing plates using photoinduced chain reactions... 

The thiol-ene system is used mostly in the production of letterpress printing plates. Since both components are liquid, they are mixed with appropriate sensitizers, and the mixture is coated on aluminium or steel plates and then covered with protective foils. Exposure through a negative film causes the exposure area to solidify. Air is then blown onto the exposed plate to remove the remaining liquid. The resultant relief plate is developed, washed, and re-exposed to give a strong letterpress plate ready for use. 

During the past decades, photosensitive polymer printing plates have largely displaced the classical letterpress printing plates made of metals such as lead [47-51]. This technological revolution commenced in the 1950s [52], when the Dy-... 

Japanese Patent (Toray Industries), Photopolymer Printing Plate Precurser, Its Manufacturing Method of Plastic Letterpress Printing Plate Using It. JP 2005326442. 

Letterpress. This is the oldest printing process stiU in use. It continues to be replaced by newer printing processes. Printing is conducted from a raised image area of the printing plate. Inks in the printing process are transferred directly from a raised area to a substrate. The printing plates contain a thick layer of photopolymer (often a mixture with polymer such as poly(vinyl alcohol) deposited over a plastic or aluminum base. 

Printing is conducted with a printing plate similar to letterpress. However, the chemistry of the photopolymer is somewhat different in order to... 

The general configuration of rollers from the ink duct to the printing plate is common in those processes which use paste inks, that is, letterpress, intaglio, and lithography. A typical arrangement is shown in Figure 99. 

In the context of printing plastics, the Nyloprint photo-polymer plate appears to be the most popular in the areas of narrow-web rotary-letterpress label printing and rotary-offset letterpress printing of plastic tubs and tubes. 

This is the basis of the Larocque letterpress quality test wherein 2 g/m2 of ink is used on the printing plate. At this ink level the fractional coverage varies from 0.3 to 0.6 for rough and smooth newsprint, respectively. 

Figure 8. Transfer of letterpress inks and oil vehicles to smooth mylar as a function of weight of ink or oil on the printing plate and of printing speed.

Letterpress and lithographic inks can be formulated from these thermally-catalyzed vehicles. Their main advantage is that they can be cured with the present flame or hot-air dryers, to give carbon dioxide and water plus small amounts of alcohols and formaldehyde. Moreover, the properties of these inks films are very good, particularly their reds-tance to scuffing, abrasion, or scratchiig. In addition, they handle well on the press distribtion system or on the printing plate, and their shelf life is adequate (3-6 months). 

Quantity to be produced—If only running a few hundred cartons of one particular type, then choose the process with the cheapest plates and shortest make ready that will be the cheapest, e.g. one colour flexographic or letterpress printing. At the other end of the scale, if you wish to produce four colour process printing with screens and tones and produce them by the tens of millions then either offset litho or gravure printing is the choice. 

---