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Monday, May 23, 2016

How are Opacity and Transparency Different?

When light strikes an object, it is reflected (specular), refracted (scattering & non-specular reflection), transmitted and/or absorbed.  Parallel rays of light which are reflected or transmitted as parallel rays are said to be specularly reflected or specularly transmitted.  Light which is scattered before it is reflected or transmitted is said to be diffusely reflected or diffusely transmitted.  In general, incident light that is specularly reflected determines the gloss of an object and that part which is diffusely reflected determines its color (and brightness).  Finally, that part of the incident light which is transmitted determines the opacity and transparency.

Opacity is determined by the total transmitted light while transparency is determined by the amount of light which is transmitted without scattering.  When the light is scattered and diffusely transmitted, the object is translucent. Nearly all papers are translucent because they permit the passage of mainly diffusely transmitted light.
Transmission (without scattering)
Transmission (scattering)














Transparency is important in tracing, reproduction and packaging papers.  A completely transparent paper would be one that transmitted, without scattering, all of the light falling on it, and a clear view of an object would be had when the paper was placed between the object and the viewer, regardless of the distance between the paper and the object.  If, on the other hand, a paper has a tendency to scatter light, its transparency will depend upon the distance between the paper and any object being viewed through it.

Reference: "Properties of Paper: An Introduction" - Scott, W.E & Trosset, S. p. 84 (1989)

Thursday, May 19, 2016

New Paper Stock for Calibration Standards

Please be aware that the 80-range, brightness calibration paper for Directional (Brightimeter S-4M and Micro S-5) and Diffuse (Technibrite Micro TB-1C) instruments has changed this month.


The new paper is a neutral white, 32# text with brightness values closer to 85 brightness. This means there about 10 points of brightness between the the 60’s, 70’s, 80’s and 90’s/Fluorescent range papers. Overall the change made in paper being used should improve the linearity of the calibrations. It also provides a broader range of paper values for calibration and verification.

Questions, contact our Lab Manager - Nick Riggs.

Tuesday, May 10, 2016

Setting Tolerances (Color)

Customers ask all the time, "What is the best way to determine a production tolerances?" I'll use color as an example to help answer this question.

Generally speaking in the Paper Industry we are normally dealing with near-white colors. In that case, we often use the rule of thumb that +/- 0.3 in L*, a* or b* is visually perceptible. However, when we start to look at more saturated colors the question becomes much more difficult.


L*a*b* color tolerance
Color tolerance vs. Visual acceptability
If we set a tolerance based on L* a* b*, the color space we are looking at is cubical. However, when we plot actual visual acceptability it is more ellipsoidal-shaped.  See at the right, the black shading represents numerical acceptance, but visually unacceptability.

Obviously, there is a difference here. If we look at the ΔEcmc tolerancing which is based on ellipsoidal tolerances, this does a much better job of matching visual and numerical acceptability.  Looking at a particular cross-section of the a* b* space (below), we can see that the visually acceptable ellipses vary in size depending on the position in color space. The ellipses in the orange area of color space are longer and narrower than the broad and rounder in the green area. The shape of the ellipses are larger as the color increases in chroma (away from a*=0, b*=0).

This means that visually acceptable differences in L*, a* and b* differ depending where we are in color space.  A Δa*=0.5 would be noticeable on a near-white, but Δa*=5.0 on a red may not be noticeable.

The best advice is to give your customer a series of samples that vary from the target by different amounts. Let them visually analyze the samples and tell you which ones they would accept and which ones they would reject.  You can measure all of the samples and help define tolerances based on their feedback.  It may also be helpful to keep an archive of samples (over time) that they have rejected. This will help you hone the tolerances based on complaints, returns or rejects.


This same concept can be used for many other measurable quantities as well. Brightness, Gloss, Opacity, Smoothness, Softness, Tensile, Formation, Burst and many more parameters can have tolerances set around them. Giving your customer a say in the matter and then keeping a record of their historical actions can build a strong quality program. Also, it is important to set tolerances that are reasonable. All instrumentation has limits. Setting tolerances is a balance between what the customer sees as objectionable and what the precision and accuracy of the instrumentation.


If you have more questions about this topic, contact me at toddp@technidyne.com.

Monday, April 25, 2016

Comparison of Two Variables of Common Roughness/Smoothness Testers

Flow restrictor used to calibrate air-leak instruments
There are numerous published inter-conversions of data between various roughness/smoothness testers. These should be used with the understanding that the only way to achieve unequivocally valid data of a particular instrument type is to use the specified instrument for the required testing. There are strong proponents for each of the instruments discussed here, as well as additional instruments familiar in different parts of the world. The user must make the decision which instrument is most useful for a specific property measurement task.

The following chart shows some smoothness values for different papers measured with the Sheffield, Gurley and Bekk testers.

Source: Abbott, J.C., "A Training Presentation Prepared for Technidyne Corporation", April 4 & 5, 2000.

Friday, April 22, 2016

Technidyne Survey

Please let us know how we are doing. The Technidyne Customer Survey is on our website.

Technidyne strives to become a trusted partner with each of its customers. In order to do this there must be open communication and a willingness to work together. In an effort to address weaknesses and understand strengths in the Technidyne approach we must have honest feedback.

It also helps us understand the expectations our customers have in terms of:

  • Customer need & innovation
  • Price & ROI
  • Support
  • Product quality & reliability
  • Contact achievement
  • Mill success
  • Outstanding employees
We always welcome your feedback to make Technidyne Corporation a better partner for you and other customers.

Go to the survey HERE, or go the Technidyne website and under "Contact Us", you will see the link to the survey.

Monday, April 18, 2016

From the Testing Lab: Tensile

Most tensile testers today are vertical or horizontal and subject the specimen to a constant rate of elongation.

Units of Reported Values
     Tensile breaking strengths are reported as the force per unit width required to rupture the specimen. Some of the common units for reporting tensile breaking strength are lb/in and kN/m. Tensile breaking strength corrected for grammage is called the tensile index.
     A similar quantity, called the breaking length, is also used for reporting grammage-corrected tensile strength. Breaking length is defined as the length of a strip of given paper that will cause it to break under its own weight. It is calculated by dividing the tensile breaking strength by the grammage. The tensile strength may be expressed in kilograms force per meter for this calculation or one can use customary basis weight and tensile units.

Why is Tensile Breaking Strength Important?
     Tensile strength is a direct indication of the durability and potential end use performance of a number of papers that receive direct tensile stresses in use, such as wrapping, bag, gummed, tape, cable wrapping, twisting papers, and printing papers.
     In general, a certain minimum tensile strength is required of an paper that undergoes a web converting operation where it is subjected to tensile stresses while being pulled through the process. Printing papers are a primary example of this.
Tensile property data for several different grades of paper
How is Tensile Strength Increased?
     There are several ways to increase the tensile strength of paper. For example, increasing beating or refining, increasing wet pressing, adding a beater adhesive, increasing the long fiber content of the furnish, and increasing the basis weight will all usually lead to an improvement in tensile strength.

Source: Scott, William E., Trosset, Stanley, Properties of Paper: An Introduction. TAPPI Press, 1989.

Tuesday, April 5, 2016

Where does the term Elrepho come from?

Elrepho with liquid cooling unit
The Zeiss Elrepho was introduced in the 1950's by the Carl Zeiss Company of Oberkochen, West Germany.  It was a diffuse (sphere) geometry brightness instrument developed for the Paper Industry. The instrument had a needle read out and the lamp was so hot, it required a liquid cooling unit.  The term Elrepho was a shortened version of Electro-recording photometer.

The Elrepho with its integrating sphere (diffuse) geometry was adopted by the European and Canadian Paper Industries and ISO created ISO 2469 as the standard for measuring brightness. The Elrepho remained the only instrument manufactured in accordance with European, Canadian and ISO standards until Technidyne Corporation introduced the Technibrite TB-1 in 1980.

Since that time Technidyne has developed and manufactured several generations of diffuse instrumentation according to ISO 2469 (Technibrite TB-1 [2-piece], Technibrite Micro TB-1C, Technibrite TB-1 [1-piece] & Color Touch family). The Color Touch was initially released in 1994. This instrument changed the capabilities of diffuse instruments with unique features such as automatic calibration (no manual data entry), an internal swing-in standard and an integrated computer with touch screen interface. These are all still uniquely Technidyne Color Touch™ features.

1950's - Zeiss Elrepho
1980 - Technibrite TB-1 [2-piece]
1984 - Technibrite Micro TB-1C
1990 - Technibrite TB-1 [1-piece]
1994 - Color Touch
1998 - Color Touch™ 2
2001 - Color Touch™ PC
2002 - PROFILE/Plus Color Touch
2015 - Color Touch™ X