( 1 ) The Toray System

	Waterless vs. Conventional Printing Plates

The Toray waterless printing system is comprised of three main components, these are the waterless plate, specially formulated waterless inks and press equipment outfitted with a temperature control system.

The Toray Waterless Plate is based on a laminate design. Aluminum is used as the base material. Light sensitive photopolymer material is bonded to the aluminum and a two micron coating of silicone rubber is applied to the photopolymer.

Depending upon the type of Toray plate used, run lengths for the plates range from 150,000 to more than 600,000 impressions. These run lengths are based on use with a #1 or #2 coated paper. The use of more abrasive stocks will significantly reduce maximum run lengths. Toray waterless plates are recyclable and are not differentiated from conventional aluminum plate material in recycling. Toray plates will fit all popular sheetfed and web presses.

The main difference between waterless and conventional inks is in the resins or vehicles that are used. Vehicles for waterless inks are selected for their rheological properties and tend to have higher viscosities than resins used in conventional ink systems.

The theory behind waterless printing is that the silicone material which makes up the non-image area of the plate has a very low surface energy. This material will resist ink provided the ink's viscosity is such that it has a greater affinity for itself than it does for the silicone.

One factor that will affect viscosity is temperature. By removing the water from the offset process, there is a loss of it's cooling effect on the surface of the plate. This will tend to cause a primary temperature increase at the plate cylinder due to friction. Because of the higher initial viscosities of the waterless inks there is also a secondary heat generation in the roller train caused by the friction of milling the ink through the rollers.

	A typical press color unit temperature control system. Systems and presses will vary in terms of the number of ink vibrators which receive temperature control.

This heat is why press temperature control systems are required to allow for the precise control of temperature within the printing unit. The most popular systems use vibrator cooling, in which coolant is pumped through hollow core vibrator rollers in the inker. This type of system has been in use in high speed web presses for many years. The technology has been refined and is now being applied to sheetfed equipment as well. Almost all sheetfed press manufacturers offer hollow core ink vibrators which can then accept the after-market temperature control systems.

The function of the temperature control system is to circulate enough coolant through the roller train to carry away the heat that is generated by the mechanical actions in the printing unit.

As with other PostScript based systems, proofing can be handled by a variety of digital proofing options such as the Iris ink jet and the 3M Rainbow.