1. Whiteness measurement
Optical properties of the paper have a high importance for printing and writing
papers. In order to achieve the desired result, we control the amount of raw material:
pulp, fillers, coloring additives, glue and brightening additives.
2. Measurement of print opacity
Opacity is the ability of paper to resist a passage of light. It is particularly important
with printing papers, in order to avoid the so-called a color piercing to the other side.
3. Measurement of color shade
Shades measurement of paper is used mainly in the production of colored papers.
The spectrophotometer measures individual coordinates of the color system, which
indicates the deviation in color compared to a standard sample.
4. Determination of basis weight
Basis weight is defined as the quotient of the weight of the examined material and
the respective surface area. It is one of the most important characteristics of the
paper. It is given in g/m2.
5. Determination of thickness
Paper thickness is the perpendicular distance between two opposing surfaces.
Measured with respect to the compressibility of fibrous structures established under
certain measuring pressure. The thickness affects almost all properties of the paper.
6. Determination of air permeability
Air permeability is understood as the ability of the paper to pass the air due to its
porous structure. Permeability decreases with an increase of milling, when disturbed
fibers overlap each other.
7. Determination of water absorption
This test determines the amount of water that is absorbed into the surface of the
sample
from
one
side.
Water absorption is an important feature especially during the printing process - as it
affects an acceptance and bleeding of color additive. It is also important when
considering on savings for printing inks - absorbency rate must be optimal for the
paper after the manufacturing.
8. Determination of tensile strength
Tensile strength of the paper is determined by the strength of individual fibers and
the links between them. During the testing process, the sample is subjected to the
action of an external load, causing its breakage. We record breaking length,
elongation at break and tearing load (tearing point).
Breaking Length (km)
It is an imaginary length of the paper, in which the free-hanging strip of paper breaks
at the point of suspension.
Elongation at break (%)
It is the relative elongation of a sample during a tensile test at the moment of
breakage.
Tensile loading (KNM)
It is a load at which a strip of paper (with determined length and width) breaks, under
specified conditions.
9. Determnination of tensile strength when wet
The destruction of the paper stability is caused when external mechanical forces
exceed the maximum strength. The tensile strength of the paper is determined by
the strength of individual fibers and the links between them. A soaking of the paper
decreases the strength to 10 % of its original condition. Hydrogen bonds are
disrupted with the effects of water. Wet tensile strength is important feature, e. g. in
shopping bags and wallpaper.
10. Determination of the number of double folds
Folding resistance is required for securities which are in practical world constantly
bent and crumpled. We determine a point of material disruption at which the paper
breaks.
High number of double folds is common with maps and banknotes.
11. Determination of stiffness
Stiffness of paper is its resistance against deformation by external forces. What is
important is the nature of the papermaking furnish from which the paper is made.
The rigidity is increased by using short-fiber pulp or by adding the starch. The
stiffness depends on the corresponding relative humidity and moisture content.
12. pH Identification of the aqueous extract
Determining pH of aqueous extract is important in order to establish the alkalinity or
acidity
of
paper.
The samples are extracted in cold or warm distilled water.
13. Determination of tear strength
It is an amount of strength and needed energy at pre-cut tear sample under specified
conditions. A significant drop in values may be due to overdrying of the paper.
Higher values can be achieved by increasing the pulp milling (but only up to the point
when fibers become too short).
14. Determination of surface strength
Surface strength is a measurement of the resistance of the paper surface against
pulling of the fibers (or coating force) when a perpendicular action is applied to the
surface.
Surface strength is an indicator of eligibility for printing as printing inks and rollers
cause (thanks to the influence of cohesion) to the fiber on the surface of the paper.
When insufficient strength occurs fibers, along with the bond are pulled from the
surface.
15. Determining of the ash content
The ash is non-combustible residue of the filler after a combustion of the paper is
completed at a temperature of 900 ± 25 °C.
16. Determination of roughness
Indication of smoothness (roughness) of the surface has great influence on the
choice of printing, following its quality, ... e. g. unprinted missing points. The purpose
of this test is to determine the thickness of the ink layer, necessary to fill even the
deepest points on the surface.
17. Calculation of smoothness
Smoothness expresses the mechanical state of the surface of the paper. The pulp
furnish has the major impact on the smoothness. It is possible to increase the
smoothness with additional milling, or by increasing the filler content.
18. Determination of grease-proof level
Grease-proofing of paper means resistance against penetration of fat, oil and wax.
The resistance of the paper to the penetration of fat is achieved by coating
substances on the surface of the paper, creating a continuous film that prevents a fat
to be absorbed to the paper.