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Monday, January 25, 2016

What is paper formation and why is it important?

Less uniform sheet                                             More uniform sheet
The uniformity with which fibers and other solid components are distributed in paper determines the "formation" of paper. In practice, the term "formation" refers to the appearance of the sheet when viewed by transmitted light.  Formation is an important property for printing papers - a poor or wild formation will produce nonuniform printing. There is no ISO Standard or TAPPI Test Method for formation measurement since there are so many different ways to evaluate this parameter.

Nonuniformity of paper within a length scale of 2-20 mm is most frequently associated with a tendency of fibers to form flocs. It is important to keep in mind that a certain degree of fiber flocculation can be expected, regardless of chemical conditions in a papermaking furnish. The flocculation occurs because a typical papermaking fibers have length-to-thickness ratios between about 50 and 100. That means that the fibers tend to collide with each other and become somewhat entangled. At the same time, hydrodynamic shear also tends to break down the fiber flocs, and the degree of flocculation can be understood as a dynamic equilibrium between these two tendencies.

Papermakers employ the following kinds of strategies to try to minimize the level of fiber flocculation in the paper: (a) adjustments of the papermaking equipment, (b) selection of fibers or manipulation of mechanical aspects of the furnish, and (c) adjustment of the chemical environment.

There is an interrelationship among roughness, porosity, and optical formation measurements. Those regions that are calendered the heaviest will be smoother, denser, and will have lower opacity than the adjacent regions that are calendered lightly. Local variations in opacity will show up as having poor formation on optical formation testers. A rough surface will absorb more ink, and that same rough surface will be more porous, as it received less calendering action. The more porous region will also absorb more ink into its interstices. When printers correlate poor printing with poor formation, perhaps it is the roughness and porosity variations that are the culprits, and the formation tester is one additional piece of test equipment that verifies the root of the problem. These formation problems occur on a small scale, smaller than what a basis weight process control system will discriminate. Formation problems are perhaps quite detectable by analyzing the standard deviation of porosity and roughness measurements within a small region. The roughness and porosity variations caused by fiber flocs are much smaller than the test area of either the roughness or porosity measuring heads. There can be other reasons for high standard deviations, such as non-uniform sizing, which may also be caused by the localized absorbency properties in the region of fiber flocs.

References:

  • Scott, William & Trosset, Stanley, "Properties of Paper: An Introduction", 1989.
  • Hubbe, Martin, "Formation Uniformity", http://www4.ncsu.edu/~hubbe/TShoot/G_Formn.htm

Friday, January 22, 2016

Brazil Agent Receives Service Certification

Filipi on a John Deere tractor at a farm in Indiana
Filipi Nic├ício of Poli Instrumentos, Technidyne's exclusive sales and service agent in Brazil, was in for updated training this week.

Filipi received the latest training techniques on classic Technidyne instruments like the Micro TB-1C, Color Touch 2, and Color Touch PC.  He also received information and training on the PROFILE/Plus™Color Touch X and TEST/Plus™ products. He also received information and training on several new products that will be released to the Pulp and Paper Industry in the coming months. In addition  to Technidyne, Poli represents Mocon, Dansensor, Brugger, Haug Quality Equipment, M/K Systems, RDM Test Equipment and TMI. In 2015, Rodrigo from Poli also received service certification from Technidyne.

Technidyne has used Poli Instrumentos and principal, Mr. Richard Machoczek, as its exclusive agent for over 20 years.  Poli Instrumentos offers high quality testing equipment from around the world as well as technical support and complete after-sales services to the Pulp, Paper, Printing, Packaging and Pharmaceutical Industries. Poli is a provider of calibration materials for optical tests (via Technidyne). 

Monday, January 18, 2016

Should color tolerances be the same for near-white as for saturated colors?

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.

Thursday, January 14, 2016

Join the Team

As we put the finishing touches on another successful fiscal year in 2015, we turn our attention to the possibilities and goals set for 2016. 

There is great room for optimism in 2016. Two new products, the Color Touch X and the TEST/Plus Gloss, released in 2015, and there are far more products coming to the market in 2016. The establishment of CalStandards.com as a resource for people looking online for lab standards and tools will continue to develop. Our staff continues to grow geographically to help us continue to respond quickly to customer demands, especially in North America. Partnerships with Techpap, ACA and emtec/AFG resulted in our best overall performance for their unique solutions and increasing coverage for service.

We have set our goals for 2016. We are excited and energized by the continued possibilities. We have great employees who get to work with outstanding agents and engaging customers around the world.

If you or someone you know fits our DNA:

Technidyne's passion for customer satisfaction
drives us to be the best in the world at
providing economical and creative solutions.

Contact us to see how you may help Technidyne reach even higher in 2016 to meet the challenges of our customers around the world.

Monday, January 11, 2016

Opacity Calibration: What is the value of paper calibration versus the opal standards?


This time of the year most customers have renewed their paper calibration subscriptions for the next 12 months. Others forgot to renew and start to wonder, do I really need paper calibration standards since I have opal glass standards?

During primary calibration the paper calibration standard is used to adjust the white body for proper calibration. The opal glass is a different material and that difference is important for verifying translucency.  This allows for confirming calibration and verification of  opacity from paper to opal and back. In other words, this process is used to make sure the opal glass is a valid way of doing day to day calibrations since the tile is mineral and the end use product is paper (or flexible packaging). Lamp position, chromatic output, focus, and so forth all affect the relationship between paper and the tile. The biggest single item is the chromatic output (amount of light and spectral response).  The lamp age and position are the critical factors related to the chromatic output of the lamp. The paper standard is required for full primary calibration and should be done monthly regardless of how often or when Preventative Maintenance is performed.


The question to ask is, "how critical is the accuracy of your day to day measurements?" If a paper calibration is performed, and this if followed by measurement with opal glass, the opal glass will keep the calibration close even if monthly, paper primary calibrations are not performed. However, if a lamp is changed or if there is a noticeable shift in performance then primary calibration to the paper standard is vital to ensuring accuracy when measuring paper products (or flexible packaging). Paper standards degrade with time. That’s why paper standards are only certified for 6 weeks from the issue date when unopened, or 3 weeks after opening. A quarterly subscription will keep you close, but a monthly subscription will keep you fully TAPPI T 425 compliant.

Forward any of you calibration question or concerns.

Monday, January 4, 2016

Which gloss measurement should I use, 75° or 20°?

When light strikes a sheet of paper, three types of reflectance can occur. In one extreme case, all of the light that strikes the surface is diffusely reflected in all directions equally (A, above).  In another extreme case, all of the light is reflected in an equal but opposite angle of its incident direction (C, above).  Paper is neither totally specular nor totally diffuse, it is a combination of the two (B, above). However, only the specular component is measured as gloss.

The two specular angles which are most commonly used in the paper industry are 75° and 20° (measured with respect to a perpendicular to the surface of the sheet). These angles were selected on the basis of best correlation between measured values and visual assessment of gloss.  The image above shows that for intermediate ranges of gloss, numerical gloss values measured at a specular angle of 75° provide a nearly linear relationship with visual gloss assessment.  For very low or very high gloss  materials, however, large observable changes in gloss result in very small changes in the measured numerical values.  For measurements of high gloss materials such as cast coated papers, high gloss inks, etc. which have a 75° gloss value greater than 85, a steeper angle such as 20°, may provide better discrimination.  As seen above there is a better spread of numerical gloss values in the high gloss region for 20° measurements than for 75° measurements. Sixty degree gloss is commonly employed in other industries for products such as paint and plastics, but it is seldom encountered in the paper industry.

Related standards:
  - 75° gloss: TAPPI T480, ISO 8254-1, PAPTAC E.3 [intermediate ranges of gloss]
  - 20° gloss: TAPPI T563, ISO 8254-3 [high gloss range]