2. Surface
sizing
Surface sizing is an ancient operation as old as papermaking itself
Effect of surface sizing on the Properties of Paper
Surface sizing agent is applied to the surface of the paper
It cements the fiber to the body of the paper and deposited
continuous film on the surface
Advantages
Will not catch the pen when the paper is written on (writing and
printing paper)
Increased oil resistance---- surface pores of the paper are
sealed
Surface sizing is more important than internal sizing in writing and
printing paper
3. Types of
surface sizing
agent
Starch: is commercially used as sizing agent
Other sizing agents: Animal glue; methyl cellulose, CMC,
polyvinyl alcohol; wax emulsion; and resin polymer
Surface sizing agent can be
applied in
Size press or in size tub
Spraying
As a foam
At calenders (heavy paper)
Surface sizing is mainly concerned with surface film
4. Effect of
surface sizing
on Water
resistance
• Starch----Not increase water resistance but
animal glue slightly increase water resistance
• Some cases: starch increases time of penetration
of test inks------increase in water resistance (Two
sided paper with high filler content on felt side)
• Low water resistance due to low angle of contact
with water
• Although, starch and animal glue do not impart
water resistance but some newer sizing agent
• Alkaliprooof papers for use of soap wrapper
• Sizing prevent the alkali in the soap from
destroying the rosin in the sheet
5. Effect of surface sizing on penetration of Oils
• The penetration of oil into papers to be important for high gloss
ink, paper to be coated with paraffin or paper used for greasy
food
• The paper have very low porosity or surface sized with oil-
resistant material
• Material increase the contact angle against oil and provide
relatively continuous and non porous film-----oil can not be
penetrate
• Oil penetration can be Measured by the time required for an
oily test liquid to penetrate through the paper (turpentine is used
to speed up the test)
6. Effect of Surface sizing on Writing qualities
• It is important in bond, ledger, tablet envelope chart paper
and business form
• Sized with starch or animal glue
• Improves the writing quality------the effect in increasing
the contact angle; Increasing the smoothness; and reducing
the porosity of the paper
• Measure by “pen-and-ink test”
• --carried out by drawing several lines on paper in one
direction and several in opposite direction
• Some cases---0.08% solution of malachite green is used
7. Effect on erasibility
• Defined as: property of paper that permits writing to
be removed from the paper by ensure without
excessive erosion of the paper.
• Important in ledgers, bond, stationery and drawing---
such paper must permit writing over erased area
• The erasibility of paper can be studied by mechanical
abrasion test
8. Effect on
physical
properties
• Improve the strength of the paper
• Enough penetration of sizing agent into the
paper to increase the fiber bonding and he
dependent properties such as; bursting, tensile
and folding strength
• If the sheet is porous and adsorbent, the
surface sizing operation may be regarded as an
impregnation and the strength improvement
can be vary great
9. Surface sizing with Size press
• The size press consist of two rolls between which he paper
travels while it receives the surface-sizing solution
• Vertical Type
• top roll is usually dead hard rubber covered roll (brass
roll or Stonite roll)
• Bottom roll is usually softer rubber covered roll (20-30
plastometer)
• Horizontal Type
• The size is introduced in the nip at the center of he
sheet and flows from the centre of the sheet towards
both ends
https://www.convergencetraining.com/size-presses.html
10. • Size presses: Up until the 1980s, the conventional two-roll size press was
standard equipment used for fine paper and board surface sizing and low solids
pigmenting. Attempts at high-quality pigment coating for magazine paper
grades led to a wide variety of film transfer roll coaters.
• This development started on production scale in 1933 and was based on the
utilization of a large number of rolls in pre-metering. This development gave
way in the 1960s to the well-known gate-roll coater. Even though the gate roll
enjoyed great success in surface sizing of fine papers and precoating of various
paper grades, the invention of the blade coater prevented stronger interest in
this field of technology.
11. • Two-roll size press
• To improve printing and strength properties, the conventional size press holds
no great qualitative disadvantage in fine paper surface sizing applications.
Bone-dry size amount is easy to control through size solids content to a wide
extent.
• In the pond and/or nip, size deeply penetrates the sheet, which has normally
been considered beneficial for paper quality. The two-roll size press is also
reliable: it requires little maintenance, and paper quality is constant. At lower
speeds, the runnability is reasonably good
• However, at higher speeds (over 800 m min-I), the size press is the bottleneck
for the fine papermaking process because of an unacceptably high number of
web breaks. Even though high-speed problems relating to pond splashing Were
quite eliminated through, for example, the Sym-Roll size press, it was
impossible to reduce the number of breaks at high speeds.
12. • The break reasons can be explained by at least three different mechanisms.
• 1. Hydrodynamic forces in the pond rupture weak spots in the web.
• 2. Holes and impurities in the paper web entering the size press can collec
excessive amounts of size from the pond, causing sticking to the top roll, thus
tearing the web.
• 3. The paper gets so wet in the size press that its strength is too low in the
afterdryer section
Gate-roll size press/coater
• Quality wise, the gate-roll size press is good for applications where very low size
amounts are needed, such as in newsprint surface sizing. The major disadvantage
is the impossibility to achieve sufficient size penetration for many applications.
• Size metering is based on hydrodynamic forces and SO only by high viscosities is
it possible to achieve thick size films on the applicator rolls
13. • Blade surface sizing
• In blade coater surface sizing, the size solids have to be twice as high as in pond
surface sizing to achieve the same bone-dry size amount. The blade mainly fills
up the surface roughness of the sheet, and so the applied wet size amount is
very low. The quality of the paper surface is quite similar to that of the gate-roll
surface sized sheet.
• With blade/roll process, size staying on the surface has a benefit in a better
surface strength than is achieved with the same bone-dry size amount with a
pond size press. The other blade/roll surface sizing benefits are the much lower
water content to evaporate in the after dryer section, and, in board production,
10% lower density compared with the pond size press
15. Surface sizing
with size tub
• Surface sizing utilizes a tub for holding the
size into which the sheet is dipped
• The time of contact of the paper with the
size depends on the speed of the machine,
dimensions of the tub, and the area of the
sheet dipped
• Size tub is located in the dryer section----
sheet is partially dried before reaching the
tub
16. Factors affecting Surface sizing
• Moisture content
• Internal sizing
• Basis weight
• Sheet density and
smoothness
• Viscosity, solid content and
Temp of the size
17. Size-press pick-up
The following interactions affect the pick-up of the size-press formulation and
the final location of the surface size in the finished sheet:
• type of surface applicator (film-transfer or puddle size press);
• moisture content and degree of internal size of the sheet entering the size
press;
• temperature, viscosity and concentration of the size-press formulation, extent
of recirculation and foam formation;
• mechanical conditions at the size press (for example, nip pressure, type of roll)
and papermachine speed;
• conditions in the size-press after dryers (for example, drying time and
temperature profile);
• post-treatments such as calendering and off-machine coating.
18. Fixation and distribution of the size
• Not only is the amount of surface size applied important but also where it
ends up on the surface, how it is distributed within the starch and whether
there is penetration of the surface size into the sheet.
• The anionic surface sizes are fixed to the fibre by hydrogen bonds or by
cationic bridges formed by alum or polymers and so this mechanism will also
affect the distribution.
• Some surface sizes such as the solution polymers have surface active
properties, whereas the emulsion polymers do not.
• The surface active properties are responsible for the tendency to foam but
also affect the distribution of the surface size within the starch.
• The distribution of the surface size on and in the paper sheet is the subject of
current research.
19. Influence of post-treatment
• After the surface size has been applied at the size press it normally passes through after
dryers; this may be followed by calendering or coating treatments.
• The drying regime affects the final form of the surface size, and if the profile or type of
heating is inappropriate for the surface size applied there can be problems from deposit
formation at the dryers.
• A higher concentration of size-press chemicals will be applied using a film-transfer size
press and these will penetrate less into the sheet. Often infra-red dryers are used in this
case since there is less water to be removed and there is less risk of deposit formation.
• The softening point or the glass transition temperature of the emulsion polymers can be
modified according to drying conditions.
• For instance, with a film-transfer size press followed by infra-red post-drying, a low
softening point polymer may be preferred to increase the spreading of the polymer
across the surface of the sheet and give a more even coverage of the polymer. Conversely,
with a conventional size press followed by contact drying to remove the larger amount of
water present it may be better to use a higher softening point polymer to avoid the risk of
deposit formation at the drying cylinders.
23. Surface sizing with Starch
Chemically Modified Starch
• Oxidised starches
• Superior to other types
• Oxidised starch is made by starch manufacture; by treating a slurry of native
starch with alkaline sodium hypochlorite at temp. not higher than 54o
C.
• Then removed by filtering and washing
• Hydroxyethyl ether starch is made by reacting starch with ethylene oxide in
alkaline medium.
• Cationic starches ---Modified viscosities
• They are substantive to the paper fiber
• They do not penetrate the web
• Reduce the BOD load
24. Surface sizing with Starch
Enzyme Modified Starch
• Enzyme—biocatalyst and sold in liquid, powdered, pellets, and capsule form
• Starch is made into a slurry with a cold water at the desired concentration
• pH of the slurry maintained at 6.5 to 7.5
• Correct amount of enzyme (0.05 to 0. 6%) is added, heat is applied
• Temp should be raised to 95-97oC and hold for 10 min to inactive the enzyme
• Another method to inactive; use of copper sulfate, formaldehyde, alkalies,
etc.
25. Surface sizing with Starch
Thermal Modified Starch
• Inclusion of acid compound into the starch-----viscosity is reduced
• Device is used to create back pressure so that temp reached to 160-165oC
26. Calender sizing with starch
• Starch is widely used for calender sizing of paperboard
• In this process, Starch solution is run in one or more boxes on the calender
stack to increase the finish of the board and improve the printing properties
of the board.
• When starch is properly applied, it is possible to reduce the penetration of
printing ink and thereby improve the sharpness of the printing
• Bothe high and low viscosity starches used in the calender sizing
• In the calender sizing of cylinder machine board, the viscosity oof the
solution is determine by the type and character of the liner stock-----If long,
slow stock is used in the liner– a solution of relatively high viscosity can be
used without trouble.
27. Surface sizing with animal glue
• Used for high quality papers
• Protein derived from animal bones (ossein) or from animal skin
• The raw protein is insoluble in water, but after treatment of acid/alkali, they
became soluble in hot water
• Preparation of Glue:
29. Surface sizing with other film forming material
• CMC
• Methyl cellulose
• Polyvinyl alcohol
• Alginate
