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Paper Properties

BASIS WEIGHT (GRAMMAGE)

The Basis weight of paper is the weight per unit area. This can be expressed as the weight in grams per square metre (Gsm or g/m2) or pounds per 1000 squares ft.

SIZING/COBB

Resistance towards the penetration of aqueous solution/water is measured by sizing or cobb values.
The cobb size tester measures the weight, in grams, of water absorbed in a given length of time, normally one minute (GSM/minute).

FORMATION

Formation is an indicator of how the fibers and fillers were distributed in the sheet.

BULK

Bulk is the volume of the paper per unit weight and is expressed as cc/gm. It is the reciprocal of density (weight per unit volume). It is calculated from caliper and basis weight.
Bulk = caliper in microns/Basis weight in GSM.

STIFFNESS

Stiffness is the measure of force required to bend a paper through a specified angle.

FOLDING ENDURANCE ( DOUBLE FOLDS)

Folding endurance is the paper’s capability of withstanding multiple folds before it breaks.
Fold test is also used as an indicator for aging properties of paper as it is a sensitive measure of influence tending to degrade fiber.

TEARING RESISTANCE

It is the amount of work done in tearing the paper through a fixed distance after an initial out. Tearing resistance is more in cross direction than machine director.

BURST STRENGTH/BURST FACTOR/BURST INDEX

The Bursting strength is the resistance to puncture by a blunt object. The results are reported in pounds per square inch or kgs. Per square centimeter or kilo pascals required to take the sample to rupture. Bursting strength indicates a composite of strength and toughness. Hence it is useful in testing for bag, wrapping papers and box boards where the paper is subjected to a stress similar to that exerted in the bursting tests.
Burst factor/burst Index are the terms used to indicate the strength of the paper irrespective of the basis weight of the sheet i.e. ratio of bursting strength in gms/cm2 or K. Pa to GSM.
Burst Index : Bursting Strength in K.Pa/ GSM.

TEARING STRENGTH/TEAR FACTOR/TEAR INDEX

Tear is the determination of the average gram force/milli Newton required to tear a single sheet of paper through a specified distance after an initial tear has been introduced.

TENSILE STRENGTH/BREAKING LENGTH/TENSILE INDEX

Tensile strength is a measure of the force per unit width required to break a specimen in either the machine or cross machine direction.
It is the strength (load) in Kgs. that a paper strip of 15mm in width and 180mm in length can withstand before it breaks. Tensile strength is more in MD than CD.

CRUSH TEST

The crust test is used to determine the compression strength of a material. The crush test also detects poor adhesive penetration, spotty adhesion and carton board with low board strength.

SIZING

The addition of material either to the stock (internal sizing) or to the surface or to the surface of a paper or board (surface sizing), generally in order to increase its surface strength and its resistance to the penetration and spreading of aqueous liquids, for example writing ink.

CALENDRING

Operation carried out by means of a calendar on the at least partially dried paper or board, with the aim of improving the finish.

MACHINE DECKLE

The Overall width of the wet web as it leaves the forming zone. It indicates total width of paper coming out of paper machine.

TWO-LAYER PAPER OR BOARD

Paper or board consisting of two furnish layers combined together during manufacture, while still moist, without the use of adhesive.

MACHINE-FINISHED (M.F.) PAPER OR BOARD

Paper or board treated mechanically on the making machine to improve the smoothness and uniformity of appearance on both sides.

MACHINE-GLAZED (M.G.) PAPER OR BOARD

Paper or board which has had one side made smooth and glossy by drying in contact with a heated, polished metal cylinder which forms part of the drying section of the machine. The other ide of the paper or board remains relatively rough.

SUM USEFUL CALCULATION

  1. REAM WT (kg) = Length (inches) x Breadth (inches) x Gram weight (gsm) / 3100
  2. To calculate gram weight (GSM)
    GRAM WEIGHT (gsm) = Weight (Kgs) x 3100 / Length (inches) x Breadth (inches)
  3. LENGTH OF PAPER (metres) = Weight of Reel (Kg) x 100000 / Reel Width (cm) x gsm
  4. SUBSTANCE (gsm) = Weight of Reel (Kg) x 20000 / Length (cms) x Width (cms)
  5. NO OF SHEETS = Weight of Reel (Kg) x 10000000 / Substance (gsm) x Width (cm) x Length (cm)
  6. BURST FACTOR = Bursting strength in kg/cm2 x 1000 / Gram Weight (gsm)

GRAIN

Paper has a definite grain direction due to greater orientation of fibers in the direction of travel of the paper machine. This grain direction is known as machine direction. The cross direction is the direction of paper at right angles to the machine direction.

LONG GRAIN AND SHORT GRAIN

The sheet is in long grain if the larger dimension is parallel to grain (MD) direction. The sheet is said to be in short grain if the larger dimension is parallel to cross direction (CD).

DETERMINATION OF GRAM DIRECTION OF THE SHEET


EXAMPLE

A: Short grain (SG): 76 x 102 cm
B: Long grain (LG): 51 x 76 cm


TECHNICAL SPECIFICATION

LINER PAPERS

They are usually referred to as the "inner" liner which faces the package contents and the "outer" liner which is exposed to the surrounding environment with the fluting sandwiched in between.

(A) KRAFT LINER

Kraft liner is made with mainly virgin fibre. The percentage of virgin to recycled material will vary between paper manufacturers, but generally, one would consider a Kraft liner to be one with at least 55% virgin material.
This paper will consist of mainly long fibres. The long fibres will give the board rigidity and strength, while the shorter fibre will give the paper a smoother surface for printability.

(B) TEST LINER

Test Liner is usually made entirely of recycled fibre and is usually weaker than Kraft Liner. Recycled paper, however, is significantly cheaper than Kraft Liner – making it a cost effective choice for most corrugated cartons.

(C) MULTI - LAYERED LINERS

Recent developments in papermaking technology have given manufacturers the ability to form the paper in layers, each with it's own characteristics of strength, moisture resistance, smoothness and colour.

(D) WHITE LINER

White liner is a multi layered paper that has a white outer facing made of bleached paper fibres. The base paper onto which the white layer is laid may be either Kraft or Test liner leading to their naming as White Top Test Liner (WTTL) and White Top Kraft Liner (WTKL).

FLUTING PAPERS

(A) MEDIUM (FLUTING) PAPERS

The fluting (or medium) in corrugated board is the wavy paper between the liners. Its “wavy” shape provides high compression resistance and strength characteristics to the corrugated board – making it the secret ingredient in the strength corrugated board. While liners generally have higher strength and moisture resistance, fluting has to be more pliable so that they can be formed into the characteristic wave shape. At the same time, however, the fluting cannot be too absorbent – otherwise it will soften and fail under humid conditions.

(B) HIGH PERFORMANCE FLUTING PAPER

High performance fluting is a relatively new development. These papers have been specifically manufactured to provide increased compression strength, reduced moisture absorption and consistent performance. Like high performance liners, the purpose of high performance fluting is to reduce the weight of packaging, without negatively impacting its strength.

(C) SEMI-CHEMICAL FLUTING PAPER

Semi-chemical fluting is used where hygienic considerations prohibit contact of the packaged goods with possible contaminants in recycled paper. This applies in packages which are in direct contact with products like food or other sensitive.

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Plot#. 10, Mukambika Nagar, Belgaum Road, Dharwad-580 008.
Karnataka. Tel/Fax : 0836-2444709
Email : srp@sunarapaperagencies.com