Before you start creating the characteristic curve, you should get an overview of papers. It is vital in this context to categorize the papers according to the criteria influencing the paper stretch. The best way is to set up a table.
What are the categories to apply to the papers?
Basically, there are two paper categories you must consider:
•Grain direction (short grain/long grain)
•Paper grade (coated/uncoated)
There are other properties that affect the paper stretch. The more categories you assign to your papers, the better will be the print result later on. In turn, the more categories you use, the more time is required to create a characteristic curve. In a first step, we recommend that you simply differentiate between grain direction and paper grade. In the past, this gave very good results. You can create more characteristic curves if you realize later that there are higher quality requirements for some papers.
Other factors can be:
•Machine
As a rule, stretching is different on every machine. Even machines of the same size do not behave fully identical.
•Grammage
As a rule, papers need not be categorized by their grammage. APSC automatically considers the grammage used. If one of your papers has a very low or very high grammage (e.g. 80 g - 300 g), the difference in stretching may be too great. In this case, you can create two characteristic curves (e.g. 80 g - 190 g and 190 g - 300 g) later.
•Paper manufacturer
Stretching may depend on the paper manufacturer.
The table below shows an example of paper categories "grain direction" and "paper grade". In this example, two papers are being compensated.
The available grammages of each paper are also specified in addition to the grain direction and the paper grade. The grammages are relevant when the test jobs are created later.
Example for paper categories
This table also helps you identify the number of required characteristic curves. This overview is especially useful when many paper variants are used.
2 characteristic curves (one for the front, one for the back) are required for each paper variant. For this reason, 4 characteristic curves must be created for the above example.