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Sunday, June 30, 2013

L*a*b* Production Tolerances for Colored Papers

Color Tolerances
With the use of color systems, the magnitude and direction of color difference between a sample and standard can easily be determined and understood. The Delta E* (∆E*) values are overall color difference values, which take into account lightness/darkness differences as well as chromatic differences. The intended object of these systems is for a color difference (∆E*) of 1.0 unit to be exactly the same visual color difference anywhere in color space. In practice, this objective is seldom realized; therefore, the establishment of tolerances based solely on ∆E* is not recommended. Individual tolerances on ∆L*, ∆a* and ∆b* should be employed for rigorous color control.  Likewise, the same tolerance on each of these parameters may be a simple approach, but is does not take into account the non-linearity of the color space.  Ideally, a variety of samples would be produced that vary from the customers perfect shade (standard) and the customer would be asked to accept or reject the different shades. This process would help establish tolerances based on the visual acceptability of the customer.   An excellent visual presentation of the L*, a*, b* color space is offered in the publication, “Prismatic II: A Visual Display of Measured Color Difference”. Two of those images follow to help give a better visual understanding of the variation in tolerances that may exist for more or less saturated colors.

Note: The following illustration uses Hunter L,a,b and ∆E, however, the concepts are still the same for CIE L*,a*, b* and ∆E*.

Figure 1 - Bone White
Bone White: The top of Figure 1 shows a standard in the center and 6 samples surrounding it. Each of the 6 samples differs from the standard by ∆E = 1 unit. However, the differences are only in one direction of color space. For example, the sample above the standard differs from the standard by ∆L = +1.0 unit (lighter than the standard). The sample below the standard differs from the standard by ∆L = -1.0 unit (darker than the standard).  Likewise, the other samples differ from the standard by ∆a = +1.0 unit (redder than the standard), ∆a = -1.0 unit (greener than the standard), ∆b = +1.0 unit (yellower than the standard), and ∆b = -1.0 unit (bluer than the standard).

The bottom of Figure 1 shows a standard in the center and 6 samples surrounding it. Each of the 6 samples differs from the standard by ∆E = 5 units. However, the differences are only in one direction of color space. For example, the sample above the standard differs from the standard by ∆L = +5.0 units (lighter than the standard). The sample below the standard differs from the standard by ∆L = -5.0 units (darker than the standard).  Likewise, the other samples differ from the standard by ∆a = +5.0 units (redder than the standard), ∆a = -5.0 units (greener than the standard), ∆b = +5.0 units (yellower than the standard), and ∆b = -5.0 units (bluer than the standard).

Obviously, the difference of 5.0 units is much more noticeable than the difference of 1.0 unit.

Figure 2 - Banner Red
Banner Red: Like the Bone White samples, the top of Figure 2 shows a standard in the center and 6 samples surrounding it; each of the 6 samples differs from the standard by ∆E = 1 unit.  The illustration at the right-bottom of the page shows a standard in the center and 6 samples surrounding it; each of the 6 samples differs from the standard by ∆E = 5 units.

Color Tolerances - Summary
The thing to take away from this is that the obvious difference that exists at 5 units of color difference on the white sample is not as obvious with 5 units of color difference on the red samples.  Also, the white samples with a 1.0 unit difference from the standard may or may not be acceptable, whereas, the red samples with 1.0 units of difference from the standard all appear to be acceptable.  This helps exhibit the non-linearity of the color space compared to visual observation. Typically, more saturated shades (further from a* = 0 and b* = 0) can have wider tolerances and still be visually acceptable.  Based on feedback from a variety of paper producers in North American tolerances can vary.

Near Neutral, Pastel Colors

Saturated Colors
L* ± 0.50

L* ± 0.50
a* ± 0.50

a* ± 0.80
b* ± 1.20

b* ± 1.80

Note: These are aggregate tolerances based on a variety of paper manufacturers.  These tolerances may or may not be acceptable depending on your application. The customer’s visual observation is always the best way to set these tolerances.

This is a common issue for companies that make a wide variety of colors. If you have additional questions email me Todd Popson.

Wednesday, June 26, 2013

West Linn Builds PROFILE/Plus System

West Linn Paper just outside Portland, OR recently ordered a PROFILE/Plus Caliper module. This instrument will be added along side their existing 
  • PROFILE/Plus Gloss
  • PROFILE/Plus Roughness/Porosity
to build an automated testing system.

Their primary goal was to get the instrumentation on the floor where the back tenders can do the testing in order to get the data to the operators more quickly.  This will help identify issues early and make corrective action much quicker and more effective. 

This information was provided by Rodger Segelstrom, US Sales Manager - Technidyne Corporation.

Monday, June 24, 2013

What is Specific Calibration?

In the late 1980's, customers in the kaolin industry were using the Technidyne Brightimeter S-4 and Micro S-5 to measure the brightness and color of kaolin.  These TAPPI geometry instruments had historically been used in the industry and provided slightly higher brightness results than the ISO or diffuse geometry instruments.  

Powder Press Apparatus
When measuring kaolin or other mineral pigments a sample suitable for measurement is made by putting the powdery substance in a 2" metal ring and pressing it against glass with a Powder Press Apparatus.  The resulting plaque is quite fragile, but must then be placed on the brightness tester and an average of 3-5 measurements is made.  However, since the TAPPI geometry instruments were oriented with the sample opening (for placement of the specimen) on the top of the instrument, the fragile plaque would break and some of the kaolin would fall into the optics of the instrument.

A procedure called specific calibration was developed. This transferred calibration from a top-loading TAPPI geometry instrument to a bottom-loading ISO instrument.  In this instance, if the plaque failed the contents of the ring would not fall into the instrument.  Also, the diffuse instrument geometry did a better job of averaging the variation across the face of the 2" plaque.

Specific calibration is achieved by measuring a series of plaques of a given grade on the TAPPI geometry instrument and then forcing the ISO geometry instrument to read these same brightness and color values.  Technidyne offers software exclusively for this purpose.  There are limitations to this process:
  • The specific calibration will only maintain is linearity over a small brightness range, therefore, if multiple grades of material are to be measured, several specific calibrations may need to be used.
  • You must have both geometries (ISO and TAPPI) to achieve specific calibration; Technidyne often supplies testing services to those companies that only have one instrument.
  • Extreme care must be taken with these sensitive powdery substances, and many measurements must be made to ensure a good calibration.

For more information on Specific Calibration contact Tom Crawford at Technidyne.

Wednesday, June 19, 2013

Need Service in the Northeast US?

Russ Frazier, Northeast Service Technician, was in our International Headquarters this week for some training updates. Russ has over 15 years of pulp and paper experience in a variety of technical support and service positions with Voith, Valmet, Metso Automation, and Technidyne.

Russ is the primary service contact for Technidyne customers in: CT, DC, DE, MA, MD, ME, NH, NJ, NY, PA, RI, VA, VT and WV.  He lives in this area and is able to respond quickly to customers. 

See the Technidyne website for more information on the services Russ can provide.

Sunday, June 16, 2013

Kheops Measures Appearance for Graphic Packaging

Graphic Packaging is using the Kheops in place of the old appearance measurement device that was originally developed by a chemical supplier.  Graphic Packaging needed to continue to evaluate the variation in white appearance of its board, but it wanted independence from this old device.

The Kheops takes an image of the sample with the camera facing down 180 degrees from the sample
using neon light.  The measurement area is a 25mm square area.  Graphic Packaging coats the board with a white coating.  The problem is a variation in the white appearance due to flocs, fiber density, voids and other variations in the board.  This variation will show through the white coating and give an unappealing mottled look to the finished product.  The Kheops can measure this variation in the different white levels as well as provide a size class distribution of the white appearance variation.  The Kheops set up to measure two size families.   The higher the index number for these two families the worse the white appearance on the board.  Graphic Packaging uses these numbers to quantify production quality.

The next time you buy beer or cereal, thank the people at Graphic Packaging for using the Kheops to give you a nice looking package.

Thursday, June 13, 2013

FPInnovations Invests in Testing

I am visiting our office in Canada this week and have some meetings with FPInnovations, too.  FPInnovations recently purchased three new pieces of test equipment.  Technidyne Inc. (Canada) delivered the instruments to FPInnovations. I saw all three in the labs in Pointe Claire today.

Technidyne Color-Touch 2 - ISO conforming spectrophotometer for measuring color, brightness, opacity and fluorescence

Emtec Tissue Softness Analyzer - measures softness, elasticity and compressibility

Huygen Internal Bond Tester - Scott bond measurement

We discussed how they are going to use each instrument. I saw the PROFILE/Plus system which has been moved to a different lab (pictured below).

I am attending the PAPTAC Standard Methods Committee meeting at FPInnovations tomorrow.

Tuesday, June 11, 2013

Extended Wavelength Range

Traditional color measuring devices like the Color Touch™ measure from 400 to 700 nm. Some other color measuring devices measure lower than 400 nm and higher than 700 nm.  When doing normal color calculations of L*a*b* this extra data doesn't change the resulting data because the weighting factors from ASTM E308 are so small.

I have two questions:

What wavelength range do online color measuring devices measure?

If data is available below 400 nm and above 700 nm, is this data used for anything in particular?

Let me know...

Never a Dull Moment in Service

James Bruner - Service Manager
According to James Bruner, Service Manager, this week the Technidyne Service Department is especially busy.
  • Emergency Service Call in the Midwest
  • Training for a Service Technician in New Albany, IN
  • Training on the Techpap Morfi (fiber quality) for a customer in the South US
  • Preventative Maintenance in:
    • Western Canada
    • Northwestern US
    • Southwestern US

Sunday, June 9, 2013

What Do ERs and Paper Mills Have in Common?

A couple of weeks ago one of our employees was stricken with a medical emergency which forced him into the Emergency Room and a few nights in the Hospital.

Calibration and replacing deteriorating components
It reminded me of how the Preventative Maintenance program started at Technidyne.  In the early 1980's, two of Technidyne's service technicians had previous experience in the medical device industry. They realized that paper companies relied as heavily on their equipment as hospitals and emergency rooms. Neither was willing to accept equipment that had not been maintained and calibrated on a regular basis.  The Technidyne Preventative Maintenance program was born in 1985 to give paper companies the same confidence in the test equipment as the medical equipment patients and doctors rely on in hospitals.

Our employee is back on the track to recovery. However, your equipment should never have to endure this fate if a solid Preventative Maintenance program is in place for your critical instrumentation.

Monday, June 3, 2013

Made in America

Made in America has always had a connotation of quality products and service.

People don't automatically assume products labeled "Made in Sweden" are top shelf. Nor do customers clamor for products labeled "Made in Guyana."
Since it's inception Technidyne has been Made in America.  From research & development to production to phone support and preventative maintenance, Technidyne stands for quality.