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Home > A to Z of Paper > Paper Tests

Paper Tests

Important Parameters for Paper & Paperboard

Physical Properties    
  Grammage
Moisture Content
Surface Strength (Wax Pick)

Thickness (Calliper)
Water Absorption (COBB)
Water Absorption (WICK)
 
Strength Properties    
  Bending Resistance (L&W)
Bursting Strength
Compressibility
Elongation
Hardness
Ply Bond/ Scott Bond
Resiliency

Stiffness (Taber)
Tearing Resistance
Tensile Strength
 
Optical Properties  
  Brightness
Colour
Gloss
Opacity
Whiteness
 
Printing Properties  
  Printability
Print Quality
 










 

 

 

Important Parameters for Paper & Paperboard

All tests are carried out at 23C + 1C and 50 + 2% relative humidity which is a TAPPI standard.

Grammage
Weight per unit area expressed in g/m2. The standard procedure is laid out in ISO 536, Tappi T 410.




Moisture Content
The absolute moisture content, expressed as a % of the paper/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.


 

Surface Strength (Wax Pick)
A measure of the surface strength of the sample or surface resistance to picking. Pick occurs due to poor internal bonding strength, making it susceptible to adherance to grade wax sticks (Dennison). This test is valid only for uncoated board or paper. For Coated stock IGT pick test is applicable.



Thickness (Calliper)
The perpendicular distance between the two surface of the board / paper, expressed in mm or m, measured with a micrometer. The standard procedures are explained in Tappi T 411.




 

Water Absorption (COBB)
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 (WICK)
Water absorption at the edge, expressed in kg/m2, using Wick Test. Board surface is sealed with waterproof tape on both sides, weighed, placed in water @ 80F for 20 minutes and weighed again to measure the water absorbed by wicking. It is an important test for measuring the water absorption capacity of cupstock grade, which is used for the manufacture of soft drink cups.




Bending Resistance/ Stiffness
It is a measure of the resistance offered to a bending force by a rectangular sample, expressed in mN (milli newtons).

The instruments used are:
(i) Taber Stiffness tester
(ii) L & W tester

The standards are as per Tappi T 556.

 

 

Bursting Strength
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 standards are as per Tappi T 403

 

 

Compressibility
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 relevant in gravure and letterpress printing. Compressibility is measured as a ratio of roughness under to different standard pressures in a Parker Print Surf tester

 

 

Elongation
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.

 

 

Hardness
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 tester with load on the measuring head.

 

 

Ply Bond/ Scott Bond
The interlayer strength of the paperboard, measured on Scott Bond Tester, expressed in J/m2. The standard procedures are explained in Tappi T 403. In paper, it is a measure of the internal strength of the sheet.

 

 

Resiliency
The ability of paper to recover its original thickness and surface contour after release of the compressive forces of printing nips.

 

 

Stiffness (Taber)
A measure of flexural rigidity, Stiffness is the bending moment (g-cm or mNm) required to deflect the free and of a 1.5 in wide vertically clamped sample 15° 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.

 

Tearing Resistance
Tearing resistance/ strengths is the ability of the paper to withstand any tearing force when it is subjected to. It is measure in both MD & CD, expressed in mN (millinewtons). The procedural standards are explained in Tappi T 414.

 

 

Tensile Strength
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.





Brightness
It is the percentage of blue light reflected of a sample measured at an effective wavelength of 457nm.

Measured with to 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 standards are as per Tappi T 452.




Colour
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 illuminance and varies from 100 for perfect white to 0 for perfect black.
a - redness to greenness.
b - yellowness to blueness.




Gloss
It is the specular reflection of light, which is reflected at an equal and opposite angle. Normally measured at 75 or 20. Generally, gloss of unprinted sheet/ board is measured at 75 (except for cast coated papers). Printed and varnished surfaces are measured at 60 angle. The standard procedures are laid out in Tappi T 480.

 

 

Opacity
The property of a substrate to resist passage of light. It is measured as the percentage of light absorbed by a sheet of paper. Important in book printing where both sides of paper are printed. The procedural standards are explained in ISO 2471.

Whiteness
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.


 

 

Printability
The extent to which properties of paper lends them 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.

 

 

Print Quality
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.




 
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