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All Paperboard tests are to be done after conditioning
samples. The steps in conditioning are
1. Pre dry the samples at 60° C for 30 Minutes
in a drying chamber with air circulation
2. Condition the samples at 23° C + 10 C and 50
+ 2 % relative humidity at least for 3 hours
Commonly referred to as “Stiffness” incorrectly
is a measure of the resistance offered to a bending
force by a rectangular sample, expressed in mN (millinewtons).
The commonly used instrument is a L & W tester
which consists of a clamp which can pivot about a
vertical axis.The sample is held between the clamp
and a knife connected to a transducer and the force
measured after the clamp is pivoted through 15º
for paperboards. The Procedural standards are as per
Tappi T 556.
The percentage of blue light reflectance of a sample
measured at an effective wavelength of 457nm, to provide
an indication of the amount of bleaching; generally,
the higher the reflectance, the brighter the sample
appears.
Measured with two different standards – Tappi/GE
and ISO. Though there is no direct correlation, ISO
brightness of a sample is usually lower by 1 –1.5
units over GE brightness. The procedural standards
are as per Tappi T 452
The maximum hydrostatic pressure required to rupture
the sample by constantly increasing the pressure applied
through a rubber diaphragm on 1.20 inch diameter sample.
The sample is initially held flat & rigid and
allowed to bulge during the test. B.S is expressed
in kPa or psi. The procedure is laid out in Tappi
t 403.
Burst Factor = Burst, g/cm2 / Grammage, g/m2
Burst Ratio = Burst , Psi/Basis Weight, lb/ream
Burst Factor = Burst, g/cm2 / Grammage , g/m²
Related to perception and therefore measured or specified
in terms of colour space. A commonly used system is
the CIE L,a,b system. This is based on the idea of
colour opposites.
L – measure of whiteness and varies from 100
for perfect white to 0 for perfect black
a – redness to greenness
b - yellowness to blueness
See chart below
The reduction in thickness under compressive forces
or pressure. It influences the ability of paper to
change its surface contour and to conform to and make
contact with the printing plate or blanket during
printing impression. This is highly relevent in gravure
and letter press printing. Compressibility is measured
as a ratio of roughness under two different standard
pressure in a Parker Print Surf tester.
The tensile strain developed in a test sample at maximum
tensile strength before rupture, measure as the %
increase in the length of the sample to the original
length. The standard procedures are laid out in Tappi
T 404.
It is the specular reflection of light which is reflected
at an equal and opposite angle. Normally measured
at 75°or 20°. It is advisable to measure high
gloss surfaces at 20° angle. Printed and varnished
surfaces are measured at 60° angle. The standard
procedures are laid out in Tappi T 480
Weight per unit area expressed in g/m2. The standard
procedures are laid out in ISO 536, Tappi T 410.
The degree to which paper will resist indentation
by some other material such as a stylus, pen or printing
plate. Hardness is measured with the help of bendtsen
smoothness by tester with load on the measuring head.
The absolute moisture content, expressed as a % of
the paperboard weight. The sample is generally not
conditioned while doing this test. The standard procedures
are laid out in Tappi T 412 and ISO 287.
The property of a substrate to resist passage of light.
Important in book printing where both sides of paper
are printed. The procedural standards are explained
in ISO 2471.
The extent to which properties of paper lend themselves
to the true reproduction of the original artwork.
This is influenced by the printing process and can
be evaluated in terms of – dot reproduction,
dot gain, print gloss, hue shift and print uniformity.
The degree to which the appearance and other properties
of a print approach a desired result. Lot of parameters
in paper surface like roughness, gloss, ink absorption,
whiteness, brightness affect this.
The interlayer strength of the paperboard, measured
on Scott Bond Tester, expressed in J/m2. The standard
procedures are explained in Tappi T 403.
The ability of paper to recover its original thickness
and surface contour after release of the compressive
forces of printing nips.
A measure of flexural rigidity, Stiffness is the bending
moment (g-cm or mNm ) required to deflect the free
end of a 1.5 in wide vertically clamped sample 150
from its center line when load is applied 50 mm away
from the clamp; measured in MD & CD. The procedural
standards are explained in Tappi T 489 and ISO 2491.
A measure of the surface strength of the sample or
surface resistance to picking. Pick occurs due to
blisters or coating substance adhering to graded waxsticks(Dennison).
This test is valid only for uncoated board or paper.
For Coated stock IGT pick is used.
The force required to tear a paperboard, measure in
both MD & CD, expressed in mN(millinewtons). The
procedural standards are explained in Tappi T 414.
The tensile force required to produce a rupture in
a strip of paperboard, measured in MD & CD, expressed
in kN/m. The procedural standards are explained in
Tappi T 404.
The perpendicular distance between the two surfaces
of the board / paper, expressed in mm / mm, measured
with a micrometer. The standard procedures are explained
in Tappi T 411.
The surface water absorption over 60 seconds , expressed
in g/m2, measured by Cobb Test . The procedural Standards
are explained in Tappi T 441.
Water absorption at the edges, expressed in kg/m2,
using Wick Test. Board surface is sealed with waterproof
tape on both sides, weighed, placed in water @ 800F
for 20 minutes and weighed again to measure the water
absorbed by wicking.
Printing ink / Glue adherence to the board surface
is influenced by wettability, measured as the surface
tension of the liquid, expressed in dynes/cm.
The extent that paper diffusely reflects light of
all wavelengths throughout the visible spectrum i.e.
the magnitude & uniformity of spectral reflectance
measured as the percent light reflectance for the
whole wavelength range. The procedural standards are
explained in ISO 11475. |
