Who Measures Board Stiffness and Crease Resistance?
Board stiffness and crease resistance are important measures that indicate how a finished carton will run on an automated glueing, filling or packaging line.
Substrate manufacturers, printers, converters and any manufacturer who fills or packs products in cartons can use this measurement to optimise production.
QA departments use these instruments to check the running attributes of finished cartons are prior to conversion and filling, reducing lost production time from slow running or difficult to convert packaging.
Carton manufacturers and designers can use a CBT1 crease and board stiffness tester with a Hanatek Carton Crease Proofer to test different substrate and crease combinations in the laboratory without committing valuable production time.
Why is board stiffness and crease resistance important?
A printed sheet or roll of carton board is die-cut and creased into a preformed carton board blank.
This blank is then often glued and erected before being filled on an automated packaging line, these processes all interact mechanically with the blank to convert it into a three dimensional object.
To be most cost effective, it is important this convertion is performed at the maximum speed possible without causing misfeeds and blockages in the process.
It is also important that the finished material has the required dimensional strength to hold and protect the packaged product.
Board stiffness and crease resistance are important parameters that help determine maximum conversion and packaging speeds, they can also be related to the final dimensional stability of the finished product.
Board stiffness is determined by the physical makeup of the substrate i.e. - its thickness, fibre mix, coating and manufacturing method. It is determined by measuring the resistance of a cut sample to a force applied through a pre-determined angle.
Crease resistance is a similar measure of resistance which is made across a preformed crease in the carton blank.
How is board stiffness and crease resistance measured?
The method for stiffness measurement is outlined in several international standards. These standards describe cutting a sample of pre-determined size either from a sheet of virgin material or from a pre-formed carton blank.
The sample is griped in jaws and rotated through a set angle, the force transmitted through the sample is measured. This force is quoted in grams for comparative measurements or g/cm2 -an absolute value for the tested substrate. Some instruments may also quote the value in mN or mN/m2.
Manual or Fully Automated Testing
The Hanatek CBT1 crease and stiffness tester is a low cost manual instrument for testing board stiffness and crease resistance, the sample is clamped into the test jaws and the sample is rotated manually. The instrument displays the force measurement in grams and unlike other similar instruments on the market, it automatically calculates the crease to board stiffnes ratio. If multiple tests are conducted, batch statistics are displayed. These can be printed for documented traceability.
For improved ease of use, a fully automated carton force analyser(CFA) should be considered, the instrument clamps the sample in electronically operated jaws and rotates the sample automatically at a pre-determined speed with pre-set dwell times.
The use of these operator independent test methods vastly improves the repeatability of the results. The CFA also graphically displays the developing forces which gives added information on the physical changes that take place during bending.
Interpreting Crease and Board Stiffness Rests
The key to manufacturing fast running packaging lies in producing carton blanks with certain stiffness/crease ratios as described in BS6965