Anilox Line Screen
By: Harper GraphicSolutions
Line screen indicates the number of cells per linear inch on an anilox roll, and is a major component when specifying an anilox roll.
Line screen is chosen in direct correlation to anilox volume. For example, an anilox volume of 3.2 BCMs, requires a line screen of approximately 500. If an anilox volume of 3.2 BCM was engraved at 1000 line screen, cells would be much too deep. In correlation, a 3.2 BCM anilox at 120 line screen anilox would result in cells being much too shallow.
With increased ink strength and lower anilox volumes, higher line screen anilox rolls can now be used. These higher line screen rolls give printers the opportunity to reach for higher graphics with finer vignettes, line and type, and process work. Following, is a rough outline of printing applications matched with appropriate line screens and cell volumes:
|Application||Appropriate Anilox Line Screen||Appropriate Anilox Volume|
|Heavy line and solids||180 - 330||9 - 4 BCMs|
|Line and type||200 - 400||8 - 3 BCMs|
|Vignettes||360 - 500||3.6 - 2.8 BCMs|
|Process||500 - 1200||2.8 - 0.9 BCMs|
Impact on Graphic Quality As shown in the table above, different printing applications require different line screen counts. The reasoning behind this is that lower line screen anilox rolls typically have higher volumes and carry larger amounts of ink or thicker ink films. These thick ink films do not produce the graphic quality necessary for high-end process work. Therefore, a 330 line screen anilox roll will not be adequate when printing process flexo.
On the other hand, a high line screen anilox roll (800-1200) is not capable of laying down enough ink for a block solid job. The printer will not get enough density or coverage from such small cells. Most importantly, a printer must choose the best line screen for their anilox roll to meet the needs of the specific job he or she is printing. One helpful tool for determining the line screen needed is a banded roll.
A banded roll contains actual bands of different line screen and volume combinations. A banded roll test helps determine the correct line screen and volume combination for printing the thinnest ink film possible and still delivering the color strength you need. You Harper Technical Account Manager can help you run and interpret a banded roll test at your facility if you are interested.
Surface Geometry Other than random patterns, anilox cell angles include the 60° hex pattern, the 30° hex pattern, and the 45° diamond pattern.
Today, the 60° hex pattern is recommended for most flexo printing applications for the following reasons:
- Cells can be nested more tightly together, allowing for approximately 15% more cells in a given area.
- Post areas are eliminated due to the placement of the cells during laser engraving.
- Cells can be shallower while still releasing the same amount of ink because more cells fit into a square inch area.
- Channeling is avoided (as compared to the 30°) because the straight side of the cell wall is not positioned horizontally.
- The 60° hex pattern is most easily reproducible from a manufacturing standpoint. Therefore, you will see greater consistency from roll to roll.
45° and 30° patterns may be preferable in non-printing flexo applications (such as coatings, laminations, and specialty printing), but ordinarily are not recommended for general flexo printing applications.
Calculating the Number of Cells per Square Inch There are two calculations for determining the number of cells per square inch of your anilox roll. One calculation is specifically for 45° cell patterns, and the other accounts for both 60° or 30° anilox configurations. Following are the calculations:
For 45° Cell Patterns:
Line Screen X Line Screen = # of Cells per Square Inch
Example: For a 500 Line Screen, 45° anilox roll:500 line screen X 500 line screen = 250,000 cells per sq. inch
For 60° and 30° Cell Patterns:
(Line Screen X Line Screen) X 1.15 = # of Cells per Square Inch
Example: For a 500 Line Screen 60° or 30° anilox roll: (500 line screen X 500 line screen) X 1.15= 287,500 cells per sq. inch
Conclusion In today's flexo marketplace, it is vital that you understand the impact of your anilox line screen and cell geometry.
In addition, you need a basic understanding of the carrying capacity of the cell or cell volume. Knowledge of these three components will give you the ability to choose the anilox inventory best suited to your printing operation. If you have further questions, please do not hesitate to e-mail technical service department, or call Harper at 800-438-3111 / 704-588-3371
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