Method for accurate exposure of small dots on a heat-sensitive positive-working lithographic printing plate material
US7467587B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Apr 21, 2005 |
| Grant date | Dec 23, 2008 |
| Priority date | — |
| Expiry date | Apr 21, 2025 |
Classification
- Technology area (CPC B)Performing Operations; Transporting
- CPC primaryB41C2210/262
- WIPO fieldTextile and paper machines
- WIPO sectorMechanical engineering
Abstract
A method is disclosed for accurate reproduction of high-quality halftone images comprising microdots by means of lithographic plate materials which comprise a heat-sensitive positive-working coating that requires wet processing. Such microdots have a dot size ≦25 μm and may be obtained by stochastic screening or by amplitude-modulated screening at a ruling of not less than 150 lpi. It has been established that the “physical right exposure energy density” (physical REED) lies in the range from CP to 1.5*CP, wherein the physical REED is defined as the energy density at which the physical area on the plate, occupied by a microdot corresponding to a 50% halftone in the image data, coincides with the 50% target value; and wherein CP is the clearing point of the plate which is defined as the minimum energy density that is required to obtain, after processing, a dissolution of 95% of the coating. An accurate reproduction of microdots can therefore be achieved by exposing the material with light having an energy density in the range from CP to 1.5*CP. Loss of microdots by overexposure is thereby avoided.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.