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Monday, March 17, 2014

Paper Machine Control Strategies: Color Matching (Part 1)

There are predominantly two approaches to color control in the Paper Industry.

The first approach is to control color separately from fluorescence.  This method looks a the color components with the ultraviolet (UV) light excluded from the light source thus eliminating the affect of optical brighteners.  The color is then adjusted and controlled only with the dyes and possibly by adjusting the pulp.  The amount of optical brightener added is then adjusted by the amount of brightness gain that is measured with the proper amount of UV energy from the source applied to the paper compared to the brightness value obtained with the UV excluded measurement.
Pros and cons:

This method helps prevent metamerism because the color is controlled independently of the optical brightener used.  This provides more consistent color control over time and within a run.  This also is a simpler strategy - with a three-dye system there are only 10 variables to control.

This method may be more expensive than the second approach since it does not allow for reduction in the optical brightener level when pulp brightness is improved or higher retention provides more scattering and increased brightness.


TABLE 1 - Control variables for Grade 1 using UV excluded measurements to
separate controls for Color and Fluorescence




Dye 1
Dye 2
Dye 3
OBA
L*
variable 1
variable 2
variable 3

a*
variable 4
variable 5
variable 6

b*
variable 7
variable 8
variable 9

Fluorescent component



variable 10


Part 2 of this discussion on approaches to control color in the Paper Industry will revolve around controlling color and fluorescence simultaneously.

If you have questions or comments, please contact me at toddp@technidyne.com.