Maximum ink coverage and its control
One of the most important indicators in quality control is ink coverage and its control, which is expressed by TAC (Total Area Coverage) or TIC (Total Ink Coverage). This index is the sum of the four numbers used in CMYK for coloring a part of the file elements. If it exceeds a certain number, it may cause many problems during printing on the printing material. The maximum value of TAC is determined according to the printing machine and the type of printing material. You can check the same thing in black with BIL.
Excessive ink in this index can prevent the ink from drying quickly during printing and cause a "set-off" problem. In sheet-fed offset printing, set-off means the transfer of ink from the surface of the first material to the back of the second material. High ink coverage in offset-web printing can prevent the ink from drying on time or cause excessive darkness in shadows.
There are several ways to solve this problem, such as color separation, using color profiles, and adjusting color values in color palettes. In graphic design software like Photoshop and Illustrator, you can use these techniques to check and adjust ink coverage in different color areas.
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When we say "ink coverage is too high," it means there's more ink on the paper than is ideal. This can cause problems like smudging, color shifts, and incomplete drying.
To fix this, graphic designers use software like Photoshop and Illustrator. These programs have tools that allow designers to:
- Separate colors: Break down colors into their smaller components and adjust the amount of each component.
- Use color profiles: Choose a standard color profile for the printing device to ensure more accurate color reproduction.
- Adjust color palettes: Change the colors used in the design to reduce ink coverage.
By using these methods, a designer can control the amount of ink used in each part of the design and prevent problems caused by excessive ink coverage.
For example: Imagine you want to print a poster with very dark colors. If the ink coverage is too high in this poster, the ink might sit on top of each other and make the colors look muddy and dark. By using the methods mentioned above, the designer can make the colors slightly lighter or use complementary colors to reduce ink coverage and ultimately produce a higher quality poster.
For example, in Photoshop, you can use the Eyedropper tool to examine dark areas of the file and, if necessary, use commands like Hue/Saturation, Curves, and Channel Mixer for corrections. In Illustrator, you can select the object and change the CMYK values to achieve the desired level.
The amount of ink coverage
Typically, the TAC level is determined in coordination with the printing press and based on the printing material. However, as a general rule, we can consider a maximum ink coverage of 320% for glossy materials, 270% for plain paper, and 340% for plastic film. But as mentioned, all these numbers can be defined and modified under suitable conditions.
For example, you may define a number for ink coverage according to ISO standards and printing press guidelines, but you don't control the ink input, material quality, and cylinder pressure. In this case, you won't get the desired result.
In essence, while TAC is a crucial factor in print quality, it's just one piece of the puzzle. A combination of factors, including the printing process, material properties, and press settings, ultimately determines the final outcome.
Control the amount of ink
Up until now, we've discussed the general concept and role of maximum ink coverage in a file and its impact on printing. However, if we want to control this indicator within a file, manually adding up CMYK values using a calculator isn't a practical or accurate approach. Moreover, this calculation often extends to other factors like maximum black coverage, which has its own definition. Therefore, we need a better solution.
As mentioned, we can use Photoshop and the Eyedropper tool. But this is primarily effective for controlling TAC in dark areas. In highlights and midtones, the sum of the four CMYK values rarely exceeds 220%, which is generally manageable for most materials.
If your file contains a lot of dark areas or shadows, it's recommended to use Adobe Acrobat Pro. After exporting your file as a PDF, you can activate the "Total Area Coverage" option to visually highlight areas that exceed the maximum ink coverage limit.
Keep in mind that Acrobat is just one of the tools for controlling maximum ink coverage, and you can also use color profiles, Photoshop, Esko DeskPack, and other software to control or adjust this indicator.
Adobe Acrobat is popular due to its ease of use, speed, and rich features for troubleshooting and preflighting. It can handle various PDF files, addressing your needs beyond ink coverage control, including color channel management, color profile correction, overprint simulation, and specific printing requirements. However, if you need to control this directly within the original file, the Esko DeskPack plugin can be a more effective solution.
Remember that...
- TAC and material: The maximum amount of ink (TAC) that a material can handle varies based on its type. Glossy materials can typically handle more ink than regular writing paper.
- Flexibility of TAC: While there are general guidelines, the specific TAC for a job can be adjusted based on the desired outcome and the capabilities of the printing press.
- Factors affecting print quality: It's not just about setting a TAC. Other factors like ink input, material quality, and press pressure also play a significant role in achieving the desired print quality.
- Interconnected quality indicators: Various quality control metrics are interconnected. Relying on just one metric won't guarantee overall print quality.
Flexography vs. Offset
Flexography and offset printing processes differ significantly, impacting ink coverage and color management. Here's a breakdown of the key differences:
- Ink Viscosity: Flexographic inks are thinner and more fluid compared to offset inks, allowing for greater ink transfer and potentially higher ink coverage.
- Substrate: Flexography often involves printing on multi-layer plastic films, which can handle higher ink densities than traditional paper substrates used in offset printing.
- Ink Build-up: To achieve desired color saturation, flexography often employs the technique of overprinting a color multiple times (auxiliary colors) rather than relying solely on heavy ink deposits.
- TAC Values: Due to these factors, TAC values (total area coverage) can be higher in flexography compared to offset printing, typically reaching up to 400%.
