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A
Acid Free
A term describing paper and board that can be used
with anything that may be tarnished or otherwise harmed
by acid.
Alkaline Pulping
A general term, but usually applied to the kraft or
soda process as in contrast to the acid sulphite process.
Alkaline Sizing
Internal sizing under alkaline stock conditions.
Ambient Conditions
Prevailing conditions, (eg. temperature, humidity
in surrounding air or other media).
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B
Basis Weight (see also Grammage)
A measurement of paper mass per unit area, normally
expressed as grams per square metre.
Beating or Refining
The mechanical treatment of the fibres in water to
increase surface area, flexibility and promote bonding
when dried.
Blotting Paper
Very absorbent and bulky, woodfree, sometimes made
from a pulp of cotton or wool fibres 120-300gsm.
Brightness
Degree of reflection of a sheet of pulp or paper measured
under standardised conditions; used to indicate the
degree of whiteness. Originally was a judgement of
the amount of light reflected to the eye from the
surface of the paper, irrespective of the hue or saturation
of colour. Is now measured by optical comparators.
Many factors affect brightness, including the degree
of bleaching of pulp, addition of chemicals such as
titanium and fluorescent dyes. Top grades of test
and book papers with these chemicals have brightness
in the range 85-90+. Coated publication papers are
in the high 70's. Newsprint was traditionally around
60, but bleaching of mechanical pulps has allowed
newsprint brightness to be increased to 70+.
Broke
Paper or board that is discarded at any stage during
its manufacture and is usually repulped. There are
2 kinds - wet broke, which is accumulated at the wet
end of the papermaking machine; dry broke which is
accumulated at any stage on the dry end of the machine,
trimmings from the reeling, slitting and cutting operations,
as well as paper or board rejected during sorting.
Bulk
The number obtained by dividing the thickness, in
micrometres of paper or board, by its grammage. i.e.
mass per unit volume.
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C
Calender
A machine intended to smooth or otherwise finish the
paper and consisting essentially of a certain number
of superimposed rolls of which only one is power driven.
Caliper
Refers to the thickness of a paper sheet measured
under specified conditions and is generally expressed
in micrometres (microns).
Cellulose Fibre
The fibrous materials remaining after the non-fibrous
components of wood have been removed by pulping and
bleaching operations used in making paper.
Chemical Pulp
Pulp obtained by cooking wood with solutions of various
chemicals, usually under pressure and temperature.
The principal chemical processes are the sulphite,
sulphate (kraft) and soda processes.
CIE Whiteness
An internationally-recognised standard of paper brightness
developed in Europe by the Centre Internationale d'Eclairage
(CIE).
Clay Coated Boards
Cartonboard with a surface application of clay-based
coating that enables high quality printing.
Conditioning
Exposure of paper sample to a controlled environment
so that the moisture content of the sample will reach
equilibrium with a specified atmospheric condition
- Laboratory: The exposure of paper in accurately
controlled and specified atmospheric conditions so
that its moisture content may reach a reproducible
equilibrium. Press Room: Bringing the paper to the
appropriate temperature so that paper humidity environment
specified by the manufacturer will result in the best
Press Room performance.
Container Materials
Components used in the manufacture of corrugated fibre
containers and/or solid fibre combined boards. usually
two liners separated by a corrugated fluting or fillerboard.
Converting Paper
Any paper which may be converted by a separate operation,
to produce a paper of different characteristics or
to produce a product quite distinct from the original
paper. Thus, kraft paper is made and sold to be converte
into asphalt paper, waxed paper, gummed tape or paper
bags; writing paper is converted into envelopes and
alike.
Cotton
Linters
Cotton linters is a by-product of vegetable oil industry.
The fibre length is approximately 3 to 5mm, much shorter
than the cotton used for textiles which is around
25mm in length. Traditionally, paper making used cotton
rags to produce very strong papers with a "quality
feel" which was not present with papers produced with
wood pulp. This had led to the concept of cotton as
the premium fibre to be used for letterhead and stationery
papers. Cotton is the purest form of cellulose and
therefore retains its properties longer than wood
pulps. For this reason, a cotton content is normally
specified for archival papers.
Cracking
A defect in linerboards caused by the separation of
the liner ply and/or the formation of fissures (cracks)
in the surface of the liner during creasing.
Crinkles
A term applied to the crepe effect produced in fairly
heavy papers, the term ÔcrepeÕ generally being applied
to tissue and lightweight papers. Paper that is extensible
in both directions may be described as 'crinkled and
corrugated'.
Cross-Direction (CD)
The direction at right angles to the direction of
running a paper machine.
Curl
Tendency of paper by itself to bend or partly wrap
around the axis of one of its directions. Usually
caused by changes in weather, faulty drying on the
paper machine or in a multi-ply sheet with differing
ply composition.
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D
Dandy Roll
A skeleton cylinder covered with a woven wire cloth.
The dandy roll is one method of applying watermarks
to paper while wet. Used for smoothing the surface
and ÔclosingÕ the formation. It is positioned after
the forming area of the wire and usually after the
second flowbox.
Deckle
The untrimmed edge of paper as it comes off the machine.
(Also used to denote the width of the web).
Density
Density generally is the ratio of the weight of paper
to the volume (ie. high density paper has a high weight
to volume ratio).
Dimensional Stability
Paper or board changes in its dimension and flatness
with variation in its moisture content and it's termed
dimensionally stable when such changes are of a low
order.
Duplex
A term which, when applied to a paper or board, may
refer to texture, finish, or colour:
(a) A duplex texture may be produced by a multi-ply
machine, using two different stocks or by lining a
board with two kinds of stock:it may also be obtained
by pasting (laminating) together two papers or boards
of different texture.
(b) Duplex finish is a finish which is rough on one
side and smooth on the other (eg. a machine glazed
finish). A paper may have a linen finish on one side
and a burlap finish on the other, or any other combination
may be used.
(c) Duplex colour may be produced by pasting together
two papers or boards with different colour, by staining
one side and not the other, or by coating the two
sides with different colours.
(d) A general term applied to a paperstock or board
having two or more plies.
(e) In the bag industry, the use of two separate sheets
in the manufacture of a bag.
(f) When applied to a cutter, means two cutting stations
on the machine.
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E
Embossed
A finish imparted to paper by means of raised or depressed
engravings on steel rolls so as to leave a visible
surface design on the paper. Normally a conversion
process.
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F
Formation
The manner in which the fibres of a sheet of paper
or board are distributed, disposed and intermixed
to constitute the sheet.
Fourdrinier
The terms applied to the standard type of paper machine
which was produced by Fourdrinier about 1800.
Furnish
The specific mixture of raw materials, both pulp and
chemicals, from which a particular grade is manufactured.
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G
Ghosting
A printed image can also be seen on the reverse side
of a sheet, caused by the vapourisation of the ink
solvent.
Gloss
Refers to the specular reflection of light and occurs
when specular reflection exceeds the diffuse reflection
from various viewing angles. Paper gloss can be measured
with various geometrics of illumination. For most
printing papers, gloss is measured at an angle of
85 degrees to a plane normal to the surface.
Grain
In machine-made papers, the direction in which the
majority of the fibres are aligned, (ie. the machine
direction). Long grain is synonymous with Òmachine
directionÓ and short grain with "cross direction".
Grammage (GSM)(see also Basis Weight).
Weight per unit of a paper i.e. basis weight in grams
per square metre.
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H
Hard-sized
Refers to a type of paper which has been treated with
considerable size to resist moisture penetration.
Opposite of "slack sized".
Hickies
Specks of dust or dirt adhering to the printing plate
or blanket cause spots of colour with a halo around
them in print.
Humidity
The moisture condition of the air. Actual humidity
is the number of grains of moisture in the air at
any given time. Relative humidity is the percent of
moisture relative to the maximum which air at any
given temperature can retain without precipitation.
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I
Intaglio
A printing process where the image is etched below
the surface of the plate, ink fills these grooves
and then the sheet is printed. Gravure is a common
example of this process.
Internal Bond Strength
A measure of the internal strength of paper and paperboard.
Also, the bond between body stock and coating as measured
by DennisonÕs Graded Waxes. Low internal bond strength
could lead to picking the clay from the paper when
tacky inks are used.
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K
Kraft Paper
A strong pulp produced by the sulphate process by
digestion of wood with sodium hydroxide and sodium
sulphide.
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L
Laid
Papers with a ribbed appearance produced by a mould
or dandy roll which has wires parallel to each other
and not woven.
Letterpress
In this form of printing the image is raised, then
inked and printed.
Lignin
An organic compound which is the main non-cellulosic
constituent of wood. It bonds the cellulose fibres
together. During pulping, chemicals dissolve the lignin,
thus releasing the cellulose fibres as pulp.
Linerboard
Boards used as facing materials in the manufacture
of paperboard containers as for the outer layers of
plaster building boards.
Long Fibre Pulp (LF)
A general term given to pulps produced from soft woods
such as pine. The fibre length of the pulps is long
compared with that of hardwood.
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M
Machine Coating
Applying coating to paper on the paper machine on
which the paper is made. Can be done by several processes,
the most successful of which are the doctor coaters
such as the 'trailing blade coater' or the 'air-knife'
method.
Machine Direction (MD)
Direction of forward movement on the paper machine.
Also called "with the grain". The direction at right
angles to this is called the "cross direction" or
"cross grain".
Machine Finish (MF)
The finish applied on the paper or board machine,
commonly referred to as MF.
Machine Glazed (MG)
The finish produce din glaze on wire side of a sheet
as it is passed in contact over a single, large diameter,
steam heated cylinder. The finish is commonly referred
to as MG.
Mechanical Pulp
Pulp produced by separating fibres from wood by abrasive
(grinding) mechanical action only. This pulp is usually
called "groundwood" pulp and the fibre strength within
the pulp can be varied by using stones of different
surfaces. Pulp can also be produced from chips processed
through refiners.
Moire Pattern
A pattern of coloured dots can be seen, especially
in a printed photo- graphic image. This is caused
by incorrect screen angles of halftone dots, thus
causing an obvious grid of dots in the image.
Moisture Content
The percentage of moisture found in paper or pulp.
Misregister
When printing more than one colour, the succeeding
plate fails to register to the previous printed sheet.
Mottle (paper)
Non-uniform colour of a paper sheet, whether accidental
or intentional.
Mottle (printing)
When a printed area, especially a solid area of colour,
looks uneven or spotty due to varying degrees of the
absorption of ink.
m2 Yield/Tonne
A measure of the surface area of paper or paperboard
which is obtained from a tonne of product.
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N
Newsprint
A generic term used to describe paper of the type
generally used in the publications of newspapers.
Often referred to as mechanical pulp, this paper normally
has a very high "groundwood" content.
Nominal Grammage
The aim grammage for a grade when conditioned at specified
humidity and temperature.
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O
Offset Lithography
The method of printing where the image is transferred
first from the plate to a rubber covered cylinder
(blanket) from where it is printed.
Opacity
Property of a paper which prevents "show-through"
of printing from one side of sheet to the other. The
opposite of transparency.
Out-of-Square
Paper which is trimmed improperly so the corners are
not true 90 degrees. This will result in difficulty
when the presser does not have a good guide edge to
work from for accurate register.
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P
pH
Measure of the hydrogen ion concentration and the
degree of acidity or alkalinity on a scale ranging
from 0 to 14. Neutral points is 7.0 with 7.0 to 0
being increasingly acid and 7.0 to 14 increasingly
alkaline.
Picking
Fibres in the paper which tend to pull away from the
surface during the printing process. This occurs when
the tack or pull of the ink is greater than the surface
strength of the paper.
Pin Holes
Small holes in paper due to fibres being drawn through
the mesh of the wire by excessive suction. Small holes
in paper caused by fine particles of sand or similar,
when the paper is calendered, the particles are crushed
and fall out leaving a hole.
Piping
A type of creasing or ribbing in paper due to irregular
tension and drying.
Ply
The separate webs which make up the sheet formed on
a multi-ply machine. Each formed ply adds one web
which is pressed to the other, the plies adhering
firmly upon drying.
Porosity
Property of containing connected air voids. The porosity
of paper is evaluated by measuring the air permeability
under standardised conditions.
Profile
An outline of the variation in a measured property.
Usually a graph showing the variations in basis weight,
moisture content or other property from point to point
in a paper web, either in the machine direction or
cross-direction.
Pulping
To remove lignin or mechanically grind in refiners
in the first stage of transforming wood into paper.
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R
Ream
A term denoting a number of sheets of paper ranging
from 480 to 516, most commonly 500.
Reel Hardness
A measure of web tension in a reel (related to grammage
and thickness).
Reel Set
MD curl induced into paper or board when winding or
reeling a web into a roll. Usually occurs near the
core.
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S
Set Off
When a printed image is accidently transferred or
smudged on to the back of the following printed sheet
within a stack. This usually occurs if the ink has
not had enough time to dry and if the sheets are stacked
too high or too tightly.
Semi-chemical Pulp (NSSC)
Pulps originally used in making corrugating medium
but recently used in bleached papers. Wood chips are
partially cooked in sodium sulphite and then reduced
to fibre by the mechanical action of an abrasive mill.
Its advantage is that it makes a relatively strong
pulp from hardwoods.
Shadow Mark (paper quality)
A defect in paper appearance which looks like the
drilling pattern in a suction roll. It is due to opacity
effects caused by areas of vacuum and pressure as
the wet web passes over a suction roll.
Shadow Mark
Otherwise known as an embossed mark, the design is
pressed directly into the wire covering of the dandy
roll using a two-piece (male and female) die. The
embossed mark is pressed into the surface of the dandy
roll and produces a mark which is darker than the
background. A shadow mark can also be debossed, which
produces a mark that is lighter than the background,
therefore a combination of embossing and debossing
can be used to create a tone effect.
Sheet Fed
A printing press which is fed paper in single sheets
rather than from a ream.
Short Fibres (SF)
A general term relating to pulp made from hardwoods,
(eg. eucalypt) because of their short fibre length
relative to the fibre length of softwoods(eg. short-fibred
pulp).
Silk Screen
A form of printing were a frame or screen is stretched
with silk material and ink is passed through the screen,
under pressure, via a soft rubber blade onto the sheet
below.
Size
A material added to the stock or to the surface of
the sheet to impart water-resistance to the sheet.
Smoothness
The texture of the surface of the paper. Also called
its "finish". Generally determined with a tester which
measures the time required for a given volume of air
to flow between the surfaces of the paper sample and
a piece of optically-flat glass under standard loading
conditions.
Stiffness
Rigidity, resistance to bending, inflexibility.
Strike-through
In printing, the ink soaks through the sheet of paper
to the reverse side. This is related to the absorbency
of the paper and consistency of the ink.
Surface Sized
Paper that has been treated with starch or other sizing
material at the size press of the paper machine.
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T
Tensile Strength
The force parallel to the plane of the specimen required
to produce failure in a specimen of given width and
length under specified conditions of loading.
Top Side
Paper web side that has not been in contact with the
wire during manufacture. Also termed "felt side".
Translucency
Ability to transmit light without being transparent.
Two Sidedness
Difference in properties between two sides of the
same sheet, (ie. front and back) in colour, formation
or finish.
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W
Watermark
Design formed among the fibres of a sheet as a result
of the wet paper web coming into contact with the
pattern of the dandy roll. The paper becomes thinner
and more translucent where the fibres are displaced
by the raised design.
Wire Mark
Traditionally, wire was sewn onto the dandy roll to
form a pattern, logo or signature. Today, we utilise
electrotype, the design of which is created by computer,
engraved into beeÕs wax and immersed into an electrolysis
bath. The resultant electrotype is coated with solder
and affixed to the dandy roll using a soldering iron.
A wire mark sits proud of the dandy roll and produces
a mark which is lighter than the background.
Wavy Edges
A warping effect in paper which is the result of the
edges of the sheet having picked-up moisture and expanded.
This will normally happen only in a pile which prevents
the centre of the sheets from picking-up the same
amount of moisture and levelling-out or ÒcocklingÓ.
It is usually a warm weather problem. It is caused
by improper balance between the moisture content of
the paper or too high humidity in the air.
Web Fed
A printing press which prints from a ream of paper
rather than from single sheets.
Wire Side
The side of the sheet of paper which was originally
in contact with the forming wire or fabric.
Woodfree
Paper made entirely from chemical pulps, (eg. kraft
pulps) as distinct form papers incorporating mechanical
pulp or groundwood. Usually applied to fine papers.
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UNITS
Bending Resistance CD - MN
Bending resistance measures the stiffness of the paper
or board, more often applied to Board grades. CD refers
to cross direction, and MD to machine direction, bend
resistance is higher in the machine direction. The
higher the value the stiffer the paper.
Bending Resistance
MD - MN
Bending resistance measures the stiffness of the paper
or board, more often applied to Board grades. CD refers
to cross direction, and MD to machine direction, bend
resistance is higher in the machine direction. The
higher the value the stiffer the paper.
Burst - KPa
Burst measures the internal strength of the paper.
Paper is held against a flexible membrane and pressure
is applied to the membrane forcing it to expand against
the paper. The pressure required to burst the paper
is the Burst figure quoted. The higher the figure
the stronger the paper.
Brightness -
%
Brightness is a measurement of the reflectance of
a sheet of paper, particularly in the blue region
of the spectrum. It is sometimes used as an indication
of how white the sheet is but in general CIE whiteness
is a better measurement.
CIE Whiteness - (D65/10°)
CIE Whiteness is a international standard for measurement
of Whiteness and is used to compare the whiteness
of papers. It attempts to match the way the humans
perceive white by measuring the reflectance of the
paper with a bias towards the blue region of the spectrum
as a blueish white is generally perceived as being
whiter than a neutral white. A perfect white surface
reflects all the light which shines on it and has
a whiteness of 100. Many paper grades have a whiteness
well above 100 due to the addition of Fluorescent
whitening agents. These absorb UV light and re-emit
it as blue light.
Cobb 1min. (multisheet) - Mls/sqm
This is a measure of how much water will absorb into
the paper in grams per square metre per minute. If
you have an 80gsm sheet of paper and it has a cobb
of 30gsm, it means that 30gsm of water have absorbed
into the paper over a minute. The cobb test has traditionally
been a useful measure to approximate how quickly liquids
such as ink and glues will absorb into the paper.
Cobb values of 50gsm are considered high.
Colour a*
This is a measure of how Green or Red the sheet of
paper is. A value of zero is neither green nor red.
The more positive a number goes the more red the paper
becomes. The more negative the number goes the more
green the paper becomes.
Colour b*
This is a measure of how Blue or Yellow the sheet
of paper is. A value of zero is neither blue nor yellow.
The more positive a number goes the more yellow the
paper becomes. The more negative the number goes the
more blue paper becomes.
Colour L*
This is measure an alternative measure of lightness
and varies from 100 for perfect white to 0 for absolute
black. Copy paper grades can typically be around 93.
Density - G/cm³
Density is calculated by dividing the grammage of
the paper by its thickness. A high density sheet (>0.9)
will be relatively thin at a given grammage while
a low density sheet will be more bulky.
Droop Rigidity CD - mm
Droop rigidity measures the stiffness of the paper
or board, more often applied to lighter weight grades.
CD refers to cross direction, and MD to machine direction,
Droop rigidity is higher in the machine direction.
The higher the value the stiffer the paper.
Droop Rigidity MD
- mm
Droop rigidity measures the stiffness of the paper
or board, more often applied to lighter weight grades.
CD refers to cross direction, and MD to machine direction,
Droop rigidity is higher in the machine direction.
The higher the value the stiffer the paper.
Fluorescence
Fluorescence measures the amount of fluorescent whitening
agent present in the paper. Optical brightening agent
absorbs UV light and re-emits it as visible blue light.
Under lighting with a UV component this makes the
paper appear more blue and brighter. All high white
grades have high levels of optical brightener. Less
than 5 fluorescence indicates very little optical
brightener is present.
Gloss
Gloss is a measurement of the mirror like reflection
of light which gives the paper a glossy appearance.
In high gloss papers light is reflected from the paper
at the same angle as it approached. This is most apparent
in smooth coated papers. Uncoated papers tend to have
a rougher surface and reflect light in all directions.
Grammage - g/m²
Weight per unit area of paper (ie basis weight) in
grams per square metre. Gsm is a primary property
that describes paper. If a lower gsm product is used,
paper properties such as stiffness and opacity are
normally lower.
IGT - m/s
IGT is a measurement of the surface strength of the
paper. A tacky ink is applied to sample of the paper
at an increasing speed. As the speed increases the
peeling force applied to the paper also increases
and the speed at which the fibres begin to be pulled
from the sheet is recorded as the IGT. A high IGT
(>300) indicates a strong surface strength suitable
for demanding offset applications.
Moisture - %
This is the percentage of moisture or water in paper
when it is made. As a general rule higher moisture
(7%) suits offset printing and lower moisture (5%)
suits laser printing. Letterhead papers normally go
through offset and laser processes so the moisture
content is in between. Care should be taken when storing
and handling paper not to allow it to pick up or lose
moisture as this will usually cause curl.
Opacity - %
Opacity is a measure of how easy it is to see through
a piece of paper. Fibre properties refining, the shade
of the paper, the grammage, and the amount of filler
used, all contribute to the final opacity developed
in a sheet of paper. High opacity is important for
most printing papers and office papers to ensure that
print from the opposite side of the sheet is not visible
and that print from a printed sheet below is not visible.
Parker Print Surf
Parker print surf is a surface smoothness measurement
particularly good for very smooth papers. A lower
value indicates a smoother surface.
Porosity
(Bendtsen)
Porosity can be measured by a number of methods including
Sheffield and Bendsten. These measure the rate at
which air will pass through a sheet of paper at a
set pressure. A high porosity indicates the paper
allows the air to travel through relatively easily.
In some applications a low porosity may be required,
such as if the paper is processed using a vacuum,
a low porosity paper forms a better seal against the
vacuum.
Porosity (Sheffield) - Sheffield
Units
Porosity can be measured by a number of methods including
Sheffield and Bendsten. These measure the rate at
which air will pass through a sheet of paper at a
set pressure. A high porosity indicates the paper
allows the air to travel through relatively easily.
In some applications a low porosity may be required,
such as if the paper is processed using a vacuum,
a low porosity paper forms a better seal against the
vacuum.
Roughness (Bendtsen)
Bendsten and Sheffield Roughness are similar methods
used to measure how smooth the surface is. Roughness
is a key property that describes the surface texture
of the paper. A low roughness paper (smooth) allows
finer details to be printed. A high Roughness paper
gives the paper a tactile quality. The test unit involves
the measurement of airflow under a very uniform metal
ring that is placed on the paper's surface. If the
surface is rough, more air escapes and you obtain
a higher airflow. The higher the number the rougher
the sheet.
Roughness (Sheffield)
Bendsten and Sheffield Roughness are similar methods
used to measure how smooth the surface is. Roughness
is a key property that describes the surface texture
of the paper. A low roughness paper (smooth) allows
finer details to be printed. A high Roughness paper
gives the paper a tactile quality. The test unit involves
the measurement of airflow under a very uniform metal
ring that is placed on the paper's surface. If the
surface is rough, more air escapes and you obtain
a higher airflow. The higher the number the rougher
the sheet.
Stretch CD
Stretch is a measure of the degree to which a paper
will stretch before breaking under a tensile force.
Stretch MD
Stretch is a measure of the degree to which a paper
will stretch before breaking under a tensile force.
TEA CD
TEA is the Tensile Energy Absorption, ie the amount
of work required to break the sheet under tension.
.
TEA MD
TEA is the Tensile Energy Absorption, ie the amount
of work required to break the sheet under tension.
Tear Resistance CD
Tear measures the amount of energy required to tear
a sheet of paper. Low tear papers have a brittle feel
and will snap fairly easily once a tear is started.
High tear papers are tougher.
Tear Resistance MD
Tear measures the amount of energy required to tear
a sheet of paper. Low tear papers have a brittle feel
and will snap fairly easily once a tear is started.
High tear papers are tougher.
Tensile Strength CD
Tensile strength measures the amount of force required
to break a strip of paper. Tensile is important where
high stresses are applied to the paper during processing.
Tensile Strength MD
Tensile strength measures the amount of force required
to break a strip of paper. Tensile is important where
high stresses are applied to the paper during processing.
Thickness - Microns
(µ)
This is the thickness of a sheet of paper measured
in micrometres (or microns for short). These are sometimes
referred to as "ums". 0ne thousand microns is one
millimeter. 80gsm copy paper is around 100 microns
thick so a ream of 500 sheets will be about 50mm thick.
At a given grammage a thicker sheet is normally rougher
and stiffer.
Wax Pick - Wax Pick Number
This is a measure of paper surface strength. A melted
wax stick is inverted and pressed against a sheet
of paper until the wax cools. The wax stick is pulled
away from the sheet of paper. If the papers surface
fibres are pulled out of the sheet then the paper
has failed the test. Wax sticks are available at many
adhesion levels from 2 to 26. The higher the wax pick
number the better the paper's surface strength. Critical
wax strength number (CWSN) is the way test data should
be presented. This means that a particular paper showed
no surface/fibre pick when tested with a wax stick
of number of say 14. Higher numbers can of uncoated
papers can indicate that product will be less prone
to dusting. However, slit edge quality is an important
property also for minimal dust buildup.
Wet Burst
Wet burst refers to the burst strength when the paper
has been saturated. It is normally compared to the
normal burst strength to indicate the proportion of
the sheets strength that is lost when it is wet. Some
grades have wet strength agents added to retain more
of the sheets strength when wet.
Wet Burst Retention
Wet burst retention is the ratio of wet burst to normal
burst it indicates the proportion of the sheets strength
that is lost when it is wet. Some grades have wet
strength agents added to retain more of the sheets
strength when wet.
Wet Tensile Retention
Wet tensile retention is the ratio of the tensile
strength of a wet sheet of paper to normal tensile
strength. It indicates the proportion of the sheets
strength that is lost when it is wet. Some grades
have wet strength agents added to retain more of the
sheets strength when wet.
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