Dry Offset Halftone Screening for Rosette Elimination
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Solution Overview
Problem
Current Dry Offset printing technologies face issues with loss of print contrast and ink contamination due to the overlap of wet ink colors, resulting in a flat, muddy image and visible rosette patterns, especially when using coarse line screen rulings, which limits the number of colors that can be effectively printed and maintains poor print consistency over the run length.
Innovation Solution
The Stealth Screening method converts original files into a continuous tone color space using RGB to CMYK or Pantone colors with maximum ink density and Gray Component Replacement, applying specific print angles and processing steps to eliminate rosette patterns and maximize ink coverage, allowing for the use of coarser line screen rulings while maintaining high print quality and consistency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional halftone screening with four printing angles (45°, 75°, 90°, 105°) is used to avoid moiré patterns, then moiré patterns are reduced, but rosette patterns become visible and ink contamination increases
Solution Approach 1:
The patent inverts the conventional approach by using only two printing angles (45° and 75°) instead of four, and by positioning halftone dots of different colors at the same location rather than distributing them at different angles. This inversion eliminates the rosette pattern formation while maintaining moiré pattern avoidance, and prevents ink contamination by ensuring dots of different colors do not overlap.
Solution Approach 2:
The patent applies different angle assignments strategically: 45° angles are used for colors that need to be printed first (such as cyan and magenta), while 75° angles are used for colors printed later (such as yellow and black). This local differentiation in angle assignment optimizes ink transfer and prevents contamination at specific locations on the blanket.
2Productivity
If coarse line screen rulings are used in Dry Offset printing, then printing speed and productivity are improved, but rosette patterns become more visible and fine image detail is lost
Solution Approach 1:
The patent inverts the conventional relationship between line screen ruling fineness and pattern visibility. By using the two-angle system with co-located dots, the patent achieves continuous-tone appearance and eliminates rosette patterns even at coarse line screen rulings (e.g., 85 lines per inch), thereby maintaining fine image detail while preserving high printing speed.
3Productivity
If multiple wet ink colors are transferred on top of each other on the common blanket, then multi-colored copy can be printed in a single operation, but print contrast is lost and ink contamination occurs
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-positioning halftone dots of different colors at the exact same location on the printing plate. This preliminary dot placement ensures that when wet inks are transferred sequentially, the dots align perfectly and do not overlap, preventing ink contamination and maintaining print contrast while enabling multi-colored printing in a single operation.
Solution Approach 2:
The patent changes the spatial parameter of halftone dot positioning from the conventional distributed angular arrangement to a co-located arrangement. This parameter change fundamentally alters ink transfer behavior, allowing wet inks to be applied sequentially without contamination, thereby maintaining print contrast and color vibrancy while preserving productivity.
4Object-generated harmful factors
If Frequency Modulated (FM) Stochastic Screening with fine random dots is used, then moiré patterns and rosette patterns are reduced, but ink contamination increases and print consistency control becomes difficult
Solution Approach 1:
The patent changes the deterministic parameter of halftone dot positioning from random stochastic distribution to a calculated co-located arrangement based on two specific angles (45° and 75°). This parameter change eliminates the need for fine random dots, prevents ink contamination through proper angle assignment, and maintains print consistency by ensuring reproducible dot placement across the entire print run.
Data Source
AI summary
A method of file preparation, ripping and plate making for high end graphics printed on cylindrical products utilizing Dry Offset printing presses. While utilizing two inverse angle techniques and one fixed angle on the Black, with virtually unlimited color pluralities, encompassing a majority of all open areas of the common printing blanket without any ink overlap. The nesting of the halftone dots at even coarse line screen rulings eliminating a dot rosette pattern and creating a continuous tone appearance. Print contrast is increased to that of offset printing quality and ink contamination over the course of the run length is virtually eliminated. This current invention also increases the ability to print white with colors as opposed to needing white coating done in advanced to transparent plastics and metallic surfaces.