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| Title: |
Film Negative and Plate Quality Control (QC) Tools |
| Submitted By: |
Catherine Haynes, APR's Director of Training |
| Date Submitted: |
08/04/04 |
Film Negative and Plate Quality Control (QC) Tools
Listed are three key quality control (QC) tools that should be included on every film negative for every job through the plate making and, if possible, the printing process.
- Fine Rule (Microline)
- Tonal Patches (HL/SID)
- Cylinder Repeat Rule
The fine rule (microline) must be free standing/floating and at least a couple inches in length. This is an excellent quick reference tool for the plate maker to check the plate exposure, as it should be straight after the plate is finished. If the line appears wavy or distorted, this would be a quick indication that the plate was not exposed correctly. Not every job includes freestanding microlines in the main art and the fine lines may not be thin enough to use as an exposure guide.
The FTA recommends the following guidelines for microlines used as exposure guides:
Line Screen (LPI)
55 lpi / 22 lpcm
65-85 lpi / 26-33 lpcm
100-120 lpi / 39-47 lpcm
133-175 lpi / 52-69 lpcm
200 lpi / 79 lpcm
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Microline Width
0.22 pts. / 3.0 mils / 0.078 mm
0.18 pts. / 2.5 mils / 0.064 mm
0.14 pts. / 2.0 mils / 0.049 mm
0.11 pts. / 1.5 mils / 0.039 mm
0.09 pts. / 1.3 mils / 0.032 mm
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A solid and highlight (HL) tonal patch should be included on all jobs even if the art does not include highlight screens. The solid patch is used to check the D-max of the film which should have a base orthochromatic density no greater than 0.05. The highlight patch should be the minimum dot that can be consistently maintained from film output through plate making, for these two processes are what really determine the minimum dot that can be printed. Make sure the HL patch is not cut back to compensate for dot gain. Additional screen patches may also be added. These screen patches are ideal for checking dot tolerances in the film negatives before plate making.
The FTA recommends the following guidelines for dot tolerances for film negatives:
2%
±0.5% |
10%
±0.75% |
25%
±1.0% |
30%
±1.0% |
50%
±2.0% |
70%
±2.0% |
75%
±2.0% |
The HL patch should also be measured in plate making to determine if there has been sufficient exposure or excessive dot gain. The solid patch can be used to check the finished plate thickness and shoulder angle.
A cylinder repeat rule is a line that runs in the web direction (circumferential) and measures the length of the cylinder repeat. The distorted cylinder repeat or distortion percentage should be included in the job jacket provided to the QC inspectors. They can then quickly measure the cylinder repeat rule to determine if the job has been output with the correct distortion.
Not every job will include these elements and it is often difficult for the QC inspector to find and take measurements within the art of a given product. So it is critical to set these tools up as part of your standard operating procedures to be included on all negatives for all jobs. They can then be used for quick and easy, continuous or random QC measurements for film negatives and plate making. Since these tools can also be used to evaluate the print try to find a way to include them in the printable area. They can be hidden in the bearer bars, waste matrix, trim, or folds of a job. Many print buyers are beginning to understand the value in these tools and will allow these elements to be incorporated in the art. Worst-case scenario, they can be opaqued on the film negatives before plating or cut off the plates before mounting.
Another helpful tool for both the film negative and plate QC inspectors is a distorted positive template or die line. They can use the distorted template to check the films, plates, and distorted proofs (usually analog proofs).
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