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Monday, July 18, 2016

Legacy of TAPPI Opacity

The last BNL-3 to ever be sold was shipped from Technidyne Corporation (New Albany, Indiana, USA) last week.  Nearly 700 BNL-3 (and previous model BNL-2) TAPPI Opacity instruments have been manufactured and sold since 1978.

Developed in the 1930's, Bausch & Lomb was the original manufacturer of the TAPPI Opacity instrument. TAPPI T 425 was written around this instrument which was developed to measure of the hiding power of a material. In most applications, it is a sheet of paper or a single layer of flexible packaging.  The initial idea was to compare the reflectance of a single sheet backed with a black body to the reflectance of a single sheet backed with a white backing with the highest known reflectance.
Bausch & Lomb Opacimeter (gen. 2)

Magnesium oxide was the highest reflectance across the visible spectrum at the time of the development of brightness and opacity. Therefore, the reflectance of magnesium oxide was set as the 100% point on the brightness scale in the 1930's.  Likewise, magnesium oxide was going to be used as the white backing for the measurement of opacity.  The problem was that magnesium oxide was very unstable (it yellowed quickly when exposed to air) and it was a chalky material which would be affected when coming into intimate contact with paper.  The solution was to place a piece of glass between the magnesium oxide and the paper.  Magnesium oxide was replace with magnesium carbonate which was more stable. These two changes led to a white body with a reflectance that was 89% of the reflectance of magnesium oxide.
BNL-2 Opacimeter (2 piece design)

Bausch & Lomb sold the rights to the opacimeter to Diano Corporation (Woburn, MA, USA) around 1970. Diano also purchased the rights to the GE Brightness design originated by Kimberly-Clark and General Electric (the basis for TAPPI T 452) from Martin Sweets Company (Louisville, KY, USA).

Jerry Popson was an employee of both Martin Sweets and Diano. He was involved in design and sales of the equipment. He started Technidyne Corporation in 1974 with the opacimeter and brightness tester.  The BNL-2 Opacimeter™ was manufactured by Technidyne from 1978 to 1987. The BNL-3 Opacimeter™ was manufactured by Technidyne from 1987 to 2016.
TEST/Plus™ Opacity from Technidyne
A new generation of laboratory testing, TEST/Plus™, has an opacity testing instrument. TEST/Plus™ Opacity by Technidyne Corporation includes the key elements of the design of the original opacity instrument along with modern electronics and user interface. The TEST/Plus™ Opacity instrument is current available.

Tuesday, July 12, 2016

Tensile Testing Basics

Tensile breaking strength has always been considered the most fundamental strength test run in the Paper Industry. It is more complicated than it appears since it involves tensile, shear and flexural forces acting on the fibers and bonds in the sheet.

In a tensile measurement, a paper specimen of uniform width and length is clamped between two jaws.  The jaws are then separated to exert a tensile stress on the specimen, and the instrument indicates the tensile force when the specimen ruptures. Most modern instruments also indicate the stretch and tensile energy absorption (TEA). TEA is the area under the stress-strain curve. It is proportional to the energy that the paper can absorb up to the breaking point.

In the Paper Industry, vertical and horizontal tensile testers are most common. However, there is the pendulum-type tester as well. Sample width and length are important variables in the tensile test. Longer specimens give a greater chance for weak points to exist, provide initiation points for rupture, and result in lower tensile strengths. TAPPI Test Method T 494 specifies that the test specimen be 25 +/- 1 mm wide and long enough to be clamped in the jaws when they are 180 mm apart. Also, the specimen must have sides parallel within 0.1 mm. 

Tensile breaking strengths are reported as the force per unit width required to rupture the specimen. This is often reported as lb/in or 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. Tensile strength can vary dramatically from machine direction to cross machine direction.

Tensile Specimen Cutter
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 any paper that undergoes a web converting operation where it is subjected to tensile stresses during startup and while being pulled through the process. Printing papers are a primary example of this.

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 long fiber content of the furnish, and increasing the basis weight will all usually lead to improved tensile strength.

Do you see any change in the use of tensile tests and measurements?

Are there applications where a pendulum-type tester is preferred over a vertical or horizontal tensile tester? Why?


Is there a good way to estimate tensile with other tests?



Common Standards:
ISO 1924-2 Paper and board - Determination of tensile properties - Part 2: Constant rate of elongation method (20 mm/min) 
ISO 1924-3 Paper and board - Determination of tensile properties - Part 3: Constant rate of elongation method (100 mm/min) 

TAPPI T494 Tensile properties of paper and paperboard (using constant rate of elongation apparatus) 


NOTE: Tissue and wet tensile are discussed under a different blog post.


Reference: "Properties of Paper: An Introduction" - Scott, W.E & Trosset, S. p. 56-58 (1989)

Friday, July 1, 2016

Independence Day

Monday is the 4th of July, a holiday and celebration of independence in the USA.

Work and pray for the independence and freedom that has allowed us to be successful and strive to make our dreams a reality.

Technidyne appreciates the opportunities that have allowed us to exist, dream, work, and succeed.

All the best to everyone around the world on this holiday and remembrance of what was and what can be in the future...

Wednesday, June 29, 2016

To Tear or not to Tear

Tearing resistance of paper and paperboard has long been one of the standard physical tests performed by paper companies. However, as more paper companies move to automated laboratory and online testing, tear seems to be one property that is not being directly measured nearly as much. Most online and automated systems will correlate a series of tests to a tear value or estimate tear. There are some automated laboratory systems that do measure tear, however, they are not done the same as the traditional tearing resistance test.

The internal tearing resistance is the work done to tear paper through a fixed distance after the tear has been started. Tearing strength has long been widely used as a mill control test because it reflects the general nature of the fibers present in the paper as well as the degree of beating to which they have been subjected.

Tearing strength has particular significance in the evaluation of paper and paperboard which is subjected to tearing strains during converting and end use. This includes paper used for bags, wrapping, tissue, books, and magazines.

Do you see less reliance on tear testing and measurements?

If so, what other tests are used to predict the same action that tear has traditionally been used for?


Is there a good way to estimate tear with other tests?



Reference: "Properties of Paper: An Introduction" - Scott, W.E & Trosset, S. p. 61 (1989)

Monday, June 20, 2016

Comparison of Paper and Board Burst Tests

Bursting strength is measured by a test methods where a specimen is held between annular clamps and subjected to pressure from one side. The portion of the specimen exposed between the openings is the test area. The portion of the specimen around the test area is clamped rigidly so that it does not slip as the test area bulges under the increasing pressure during the test. Pressure is applied to the underside of the specimen by a rubber diaphragm which is expanded by hydraulic pressure at a controlled constant rate. The bursting test value is the maximum pressure, above atmospheric pressure, in pounds per square inch (or kilonewtons per square meter or kilopascals) required to produce rupture of the specimen. There are separate test methods for paper burst and board burst.

TAPPI T 403 & ISO 2758 TAPPI T 807, T 810 & ISO 2759
Mullen Model C Mullen Model A
Application paper & paper products T 807 linerboard
T 810 single & double wall corrugated
Diaphragm 30 - 35 kPa to distend 160 - 210 kPa to distend
0.375 in (9 mm) 0.375 in (9.53 mm)
Diaphragm opening (diameter) 1.2 in (30.5 mm) 1.24 in (31.5 mm)
"Upper" Clamping Plates (minimum diameter) 48 mm 3.75 in (95.3 mm)
Rate of pressure increase 1.6 mL/s [96 mL/min] 170 mL/min (5.75 oz/min)
Clamp pressure   Adjustable 600 - 1000 kPa
Measurement Range (bursting strength) 50 - 1200 kPa ( 7 - 175 psi) 350 kPa (51 psi) and up

There are some small differences in the TAPPI and ISO Standards, but they have been minimized over the years to make them as close as possible. The primary take away is that there are two different devices for measuring paper and board burst. Each has its own requirements for clamping size, clamping force and diaphragm.

Thursday, June 16, 2016

More than just brightness...

Technidyne has been known as the brightness company for years. Most in the Paper Industry think of optical tests such as brightness, color, opacity, gloss, fluorescence and whiteness. However, Technidyne has been manufacturing surface and physical testing equipment for years.

1998 Acquired Hagerty Technologies
         Roughness
         Porosity

2000 Parker Print Surf (PPS)
2001 PROFILE/Plus Roughness
           PROFILE/Plus Porosity
2003 PROFILE/Plus Grammage
2004 PROFILE/Plus Tensile Strength Alignment
           (fiber orientation)
2006 PROFILE/Plus Burst
2008 PROFILE/Plus Tensile
2009 PROFILE/Plus Formation

Technidyne also represents ACA, Emtec/AFG and Techpap for sales and service in North America. Some notable products include:

ACA RoQ (roll hardness)
ACA Permi (online porosity)

Techpap Morfi Compact (fiber morphology)**
Techpap 2D (formation)**
Techpap Simpatic (dirt & shives)**
Techpap Kheops (print mottle)
Techpap Pulp Inspector
                (automated pulp measurement
                - morphology, brightness, color,
                freeness, dirt & shives)

Emtec TSA (tissue softness)
Emtec EST 12 (surface and sizing tester)
Emtec PDA (dynamic penetration)

AFG CAS Touch! (charge analysis)
AFG FPA (fiber potential)
AFG DFA (dynamic filtration)


Get the same high quality customer service and support for all of your tests. Technidyne does more than brightness!

**available in lab and online

Tuesday, June 14, 2016

Technical Basics of Bursting Strength

Vintage Mullen Burst Tester
Bursting strength is measured by a test methods where a specimen is held between annular clamps and subjected to pressure from one side. The portion of the specimen exposed between the openings is the test area. The portion of the specimen around the test area is clamped rigidly so that it does not slip as the test area bulges under the increasing pressure during the test. Pressure is applied to the underside of the specimen by a rubber diaphragm which is expanded by hydraulic pressure at a controlled constant rate. The bursting test value is the maximum pressure, above atmospheric pressure, in pounds per square inch (or kilonewtons per square meter or kilopascals) required to produce rupture of the specimen. There are separate test methods for paper burst and board burst.









It is sometimes said that the bursting strength is very closely related to machine direction tensile strength. The basis for this statement lies in the distribution of stresses within the specimen during the test. Prior to rupture, the rigidly clamped specimen stretches due to the stress applied by the expanded diaphragm. The strain is approximately equal in all directions. But, since the paper will not withstand stretch equally in all directions, unequal stresses build up and eventually produce rupture. In most cases, the line of rupture will be perpendicular to the machine direction because the paper stretches least in that direction. At other times, there is no principal rupture line. Consequently, the burst test can be used to determine the machine direction of a specimen whenever a principal line of rupture occurs during the test.

Bursting strength is of importance as a paper mill control test for linerboards for shipping containers. Conformity of the finished shipping containers with the test specifications required by Uniform Freight Classification Rule 41 is dependent on the bursting strength of the finished corrugated paperboard, which is controlled by the bursting strength of the linerboard.
Modern PROFILE/Plus Burst


Common Standards:
ISO 2758 Paper. Determination of bursting strength 
ISO 2759 Board. Determination of bursting strength 

TAPPI T403 Bursting Strength of Paper 
TAPPI T807 Bursting Strength of Paperboard and Linerboard 
TAPPI T810 Bursting Strength of Corrugated and Solid Fiberboard