TYRE CORD PROCESSING.pptx

TYRE CORD REINFORCEMENT
Dr.K.RAVICHANDRAN
Professor
Department of Rubber and Plastics
Technology
MIT Campus Anna University Chennai

Tyre is a Structural Composites
Reinforcement of Textile Fabrics in rubber
composites:
O Impart loading carrying capacity
O Serve as a medium of stress transmission
O Provide dimensional stability
O Determines basic strength and durability
O Also Carbon black / Silica in rubber
composites improves rubber modulus

Requirements for Reinforcing Materials
Rubber composites used for Dynamic flexing
Applications ( Tyre Carcass):
O Modulus
O Tensile strength
O Dimensional stability
O Fatigue resistance
O Hysteresis
O Adhesion

Requirements for Reinforcing Materials
O Rubber composites used for Tyre Belt
Applications (In addition to carcass):
O Compression modulus
O Moisture content
O Chemical stability
O Impact strength
O Less brittleness

Truck Radial Tyre Casing Components

Hysteresis loops of four different textile cords, loaded by the
force of 20 N and then unloaded

Tyre Structure
O The term tyre structure defines the number,
location and dimension of the various
components used in it’s composition.
O The primary components which govern the
performance of the tyre are the casing plies,
bead construction, belts, sidewall and tread.
O The secondary components are chaffers,
flippers and overlays, which are strips of
fabric located in the bead and crown areas,
protect the primary components by minimising
stress concentration

CORD ANGLE
O ANGLE OF THE CORD PATH TO THE
CENTRE LINE THE TYRE, THE
PREDOMINANT FACTOR AFFECTING THE
TYRE SHAPE OR CONTOUR
O The term equilibrium shape or neutral-
contour shape is used in conjunction with cord
angle to describe specific tire dimensions

Functions and Requirements of Tyre cords
Functions
O Maintain durability against bruise and impact
O Support inertial load and contain inflating gas
O Provide tire rigidity for acceleration, cornering, braking
O Provide dimensional stability for uniformity, ride,
handling.
Cord Requirements
O Large length to diameter ratio , eg, long filaments
O High axial orientation for axial stiffness and strength
O Good lateral flexibility (low bending stiffness)
O Twist to allow filaments to exert axial strength in
concert with other filaments in the bundle
O Twist and tire design to prevent cord from operating in
compression.

Ideal cord properties for a radial tire
belt
O High tensile strength
O High bending modulus
O High stiffness
O High compression modulus
O High adhesion to rubber
O Good resistance to chemical attack

Cord reinforcement for different Tyres

Reinforcement and Tyre Properties

Textile Terminology
O Cord Structure: consisting of two or more strands
when used as plied yarn or an end product.
O Denier: The weight of cord expressed in grams per
9000 meters.
O EPI: Ends of cord per inch width of fabric.
O Fibers: Linear macromolecules orientated along
the length of the fiber axis.
O Filaments: Smallest continuous element of textile,
or steel, in a strand.
O Filling: Light threads that run right angles to the
warp (also referred to as the "pick") that serves to
hold the fabric together.
O LASE: Load at a specified elongation or strain

Textile Terminology
O Length of lay: Axial distance an element or
strand requires to make a 360 ~ revolution in
a cord.
O Ply twisting: Twisting of the tire yarn onto itself
the required number of turns per inch; two or
more spools of twisted yarn are then twisted
again into a cord: for example,
O if two 840-denier nylon cords are twisted
together, an 840/2 nylon cord construction is
formed;
O if three 1300-denier polyester cords are
twisted together,they give a 1300/3 cord
construction.
O Rivit Distance: between cords in a fabric; high
rivet typically describes a fabric with a low
EPI.

Textile Terminology
O Tenacity: Cord strength, frequently expressed
in grams per denier.
O Tex: Cord weight expressed in grams per
1000 meters.
O Twist: Number of turns per unit length in a
cord or yarn; direction of twist can be either
clockwise ("S" twist) or counterclockwise ("Z"
twist); twist imparts durability and fatigue
resistance to the cord, though tensile strength
can be reduced.
O Warp: Cords in a tire fabric that run
lengthwise.
O Weft: Cords in a fabric running crosswise.
O Yarn: Assembly of filaments.

Fabric reinforced in rubber
Square woven linen fabric
Cords embedded in rubber

Tyre Cord Construction
O To use the range of fibers for tire
applications, the yarns must be twisted
and processed into cords.
O First, yarn is twisted on itself to give a
defined number of turns per inch, i.e., ply
twisting.
O Two or more spools of twisted yarn are
then twisted into a cord.
O Generally, the direction of the twist is
opposite to that of the yarn; this is termed
a balanced twist .

PLY TWISTING
The plies are twisted on itself and with
another ply before it is formed into a cord.
The ply twisting directions are denoted by “Z”
and “S”.
If the direction of twist is from right to left,
then it is called “Z” twist and if the direction
of twist is from left to right, then it is called
“S” twist.
Usually, the individual ply is twisted in the “z”
direction and two plies are twisted together
in “s” direction to form a cord

Designation of twist direction

Reasons for Twisting of Tyre Cord
1. Twist imparts durability and fatigue resistance
to the cord, though tensile strength can be
reduced.
2. Without twist, the compressive forces would
cause the cord outer filaments to buckle.
3. Increasing twist in a cord further reduces
filament buckling by increasing the extensibility
of the filament bundle.
4. If the twist is irregular, the phenomenon of
“bird caging” or filament un-winding can occur,
where the cord is flexed during in-service tire
rotation

Tyre Cord Twisting
O Durability reaches a maximum and then
begins to decrease with increasing twist.
This can be explained by the effect of
stresses on the cord as the twist
increases.
O As the twist increases, the helix angle or
the angle between the filament axis and
the cord axis, increases.
O In addition to twist, the cord size may be
varied to allow for different strengths,
depending on the application or tire line.

Twist multiplier
O The amount of twist relates to both tenacity and
compression fatigue resistance.
O To obtain equivalent fatigue performance in a product when
changing cord size, cords must be twisted to the same helix
angle using a “twist multiplier” relationship:
O For the same material:
Cord Atpi x √Cord A denier = Cord B tpi x √Cord B denier.
O [For example: Cord A of 2000/2 construction at 8 tpi would
be equal to Cord B of 1000/2 at 11.3 tpi.]
O For different materials specific gravity must also be
considered Cord Atpi x √Cord A denier/ √Cord ASpGr =
Cord B tpi x √Cord B
denier/√Cord B SpGr.
O [For example, an 840/2 nylon (1.14 SpGr) at 11.0 tpi would
have the same helix angle as a 1100/2 aramid (1.44 SpGr)
at 11.3 tpi.]

Weaving
O After twisting yarns into cords, 1000 to 1500 cords are
woven into a coherent sheet using a very light “pick” fabric
as the weft at a very low fill count of one to two picks per
inch.
O Rolls of this fabric (which is about 1.5 to 1.75 meters wide -
the practical width of rubber-cord calenders) are transferred
for further operations.
O The function of the pick is to maintain a uniform warp cord
spacing during the downstream operations, such as,
shipping, adhesive dipping and heat treating, calendering,
tire building and lifting.
O The core ensures uniform cord distribution as the tire is
shaped and the sheath holds the cord spacing during
adhesive treatment and calendering but breaks readily
during tire lifting and shaping.

O Generally, three-ply cords have the greatest durability. After
cable twisting, the cords are woven into a fabric, using small fill
threads. These threads are also referred to as picks
O This weaving process introduces an additional construction
variable, i.e., the number of cords per inch or EPI (ends per
inch) that are woven into the fabric.
O High-end-count fabric gives greater plunger strength or
penetration resistance.
O Low-end-count fabrics have more rivet (distance between
cords) and give better separation resistance because of the
greater rubber penetration around the cords.
O In addition, the weight savings may enable reductions in rolling
resistance with equivalent tire strength factors

O Normally all fabric will have a balanced twist which
means that S and Z twists will be equal.
O The usually given twists in turns per meter are
O 840/2 —- 472 TPM (turns per metre)
O 1260/2 — 394 TPM
O 1680/2 — 335 TPM
O by twisting, we lose tensile strength but gain flex
fatigue resistance.
O Hence the twist factor must by decided by striking
a compromise between tensile strength and flex
fatigue resistance.
O By twisting, the cord acts as a single unit, and
gains good abrasion resistance.

Tire cord processing
O Downstream cord processing of tire cords can profoundly influence tire
performance and dimensional stability of the cords through the various
environments
O Dipping, adhesive baking, heat stretching, relaxation, and tire
vulcanization- is necessary to control and predict variations in such
factors as tire size, tire uniformity, cord-to-cord uniformity, flat spotting,
side-wall indentations, and creep during operation.
O Steel, aramid and rayon are minimally affected during cord processing
while the thermoplastic fibers, nylon and polyester, must be very carefully
controlled.
O The radial tire with its high-modulus restrictive belt has greatly alleviated
many of the cord growth problems previously seen in bias tires, leading
for example to tread groove cracking.
O A goal of process engineers concerned with dimensional stability when
working with the thermoplastic cords is to maximize tensile modulus
(often characterized by EASL - elongation at specified load) while
minimizing thermal shrinkage.
O Care must be taken to optimize tensile strength and fatigue properties in
these procedures.

Rayon and aramid cord processing
O The processing of these cords is relatively simple since
they are thermally stable and do not change significantly in
downstream operations.
O Rayon must be carefully protected from moisture regain at
all processing stages, especially at roll ends to avoid
uneven shrinkage across a fabric roll.
O An optimum treatment for processing rayon has been
reported .Rayon cord made with a higher than specification
twist is dipped in cord adhesive under relaxed conditions to
open the twist for good dip penetration and to completely
wet the cord with the aqueous adhesive.
O The cord is then tensioned to achieve the specification twist
and dried at 130-150C before being baked under tension at
155-175C to cure the adhesive.
O Heat treatment for aramid 230-260C is generally at low
tension (8.8cN/tex) and with very low stretch to standardize
modulus. As with polyester, adhesive application is a two
step procedure.

Nylon and polyester cord processing
O Thermoplastic fibers, such as nylon and polyester, are
considered to be composed of a mixture of crystallites,
extended (aligned) non-crystalline molecules, and
amorphous “tie” molecules.
O Crystallization occurs principally during fiber drawing.
O Cord processing, carried out below the crystal melting
temperature, modifies the non-crystalline portion.
O In the process of applying and baking a cord adhesive
the amorphous portion of a thermoplastic cord will tend
to become less oriented, resulting in shrinkage which
will, in turn, adversely affect tire uniformity.

Heat treatment
O Heat treatment temperatures can cause polymer flow
and molecular weight degradation.
O Heat treatment of nylon, for example, varies in
temperature between 177oC and 246oC, between 7%
and 16% stretch, and between 20 and 60 seconds
residence time.
O For Polyester cord recommended a treatment
temperature of 246oC, 4% stretch in the first zone
and 3% relaxation in the second zone, with 90
seconds residence time in both zones for optimum
fatigue resistance.
O Nylon is generally used at 3-7% net stretch, and
polyester at 0 - 4%.

Stretching
O Shrinkage is partially controlled by stretching the
fabric in the heat-setting zone and relaxing it under
controlled tension in a second zone.
O In general, higher relaxation results in lower
shrinkage.
O Net stretch (the difference between stretch in the first
zone and relaxation in the second) is often used as a
measure of shrinkage and growth potential. This can
be deceptive, however, for a number of reasons:
O Additional crystallinity can occur that will lower
shrinkage and/or growth potential,
O Equilibrium orientation is seldom reached in allotted
treatment times, especially with heavy cords

Postcure inflation
O On release from the tire curing press, viscoelastic cords in the hot
tire are almost completely free to shrink.
O Postcure inflation (PCI) is therefore employed to stabilize tire size
and uniformity.
O All-steel or all-rayon tires do not require a postcure treatment.
Because the postcure inflating equipment is expensive to install and
maintain, some companies have minimized or eliminated PCI for
their radial tires by predictive mold sizing, control of cord properties,
and controlled cooling. The use of PCI entails the following:
O Passenger and light truck tires are automatically ejected from the
press after the usual 12 to 24 minute cure time, depending on size,
and then immediately loaded onto a postcure inflator which re-
inflates the tire to 200 to 400 kPa (30 - 60 psi).
O This loads and stretches the hot cords. Post inflating controls the
size, shape, uniformity, and growth of the finished tire.
O However, the results depend on the time, temperature and load
applied to the cords during the inflation process.
O Moreover, the cords should be cooled evenly to below their glass
transition temperature before release from the inflator

Postcure inflation
O Lim has reported on studies that simulate PCI and non-PCI
conditions by measuring EASL (elongation at specified load -
the inverse of modulus).
O For Rayon the modulus is constant for cords heated to 177C
under 0.06N/tex and cooled to RT with or without tension. No
modulus change took place.
O Under the same conditions Nylon showed a 20% increase in
modulus and PET a 30% increase. Equilibrium times for the
cords were 30 minutes.
O A practical cooling time for factory tires is usually about two
cure cycles. Also, it should be noted that uneven cooling, e.g.,
from one side to the other, can result in tire distortion, so that
tires may be rotated during the PCI treatment.
O Skolnik has reported a “coefficient of retraction” for loaded
cords in a simulated postcure inflation study. Cords were
loaded to 0.9 g/den., heated to 165C, and cooled to various
temperatures where the load was released. The coefficient of
retraction (CR) is the percent length change per degree C.

Cord Construction
O Depending on the speed rating of the tire,
the overlay can take one of several lay-
ups,
O a) One layer or two layers
O b) Covering the immediate top belt
O c) Full belt coverage and partially
extending over the shoulder wedge

O one layer or ply of textile
O is used (as is generally the case) each ply
will only contribute approximately 70-80%
of its
O strength as measured before
incorporation into the composite.

Designation: D 885 – 03
O Standard Test Methods for
O Tire Cords, Tire Cord Fabrics, and
Industrial Filament Yarns
O Made from Manufactured Organic-Base
Fibers1

Choice of a textile cord
O Chemical composition of textile
O Cost per unit length and weight (cost in
tire)
O Denier – filament size and strength
O Cord construction – number of yarn plies
O Cord twist
O Number of cords per unit length in ply
O Number of plies in the tire

Cotton
O Cotton is a natural fibre, consisting of the
seed hairs of a range of plant species in
the
O Mallow family (Genus Gossypium). The
plants are grown, mainly as an annual
crop, in many countries around the world
between latitudes 40°N and 40°S.

Rayon
O Rayon is a man-made fibre, based on regenerated
cellulose
O Rayon is used as a body ply cord or belt
reinforcement made from cellulose produced by wet
spinning. It is often used in Europe and in some run-
flat tires as body ply material.
O Advantages: Stable dimensions; heat resistant; good
handling characteristics.
O Disadvantages: Expensive; more sensitive to
moisture; environmental manufacturing issues.
O Rayon is used in both carcass and belt of passenger
radial tires but lacks strength for durable heavy-duty
tires

Rayon
Rayon - Tire cord strength has been improved 300% since its
introduction by improved coagulation and heat treatment.
The low- shrink, high-modulus, good-adhesion properties of
rayon make it an excellent choice for use in passenger tires.
However, rayon has lost market share to polyester due to
higher cost and environmental concerns with production
facilities.
Rayon had historically been used in truck tires but has been
displaced by nylon with higher strength and impact resistance.
Rayon is used for racing tires and has gained renewed interest
in the development of an extended-mobility self-supporting
passenger tire.

Nylon
O Nylon type 6 and 6,6 tire cords are synthetic
long chain polymers produced by continuous
polymerization/spinning or melt spinning. The
most common usage in radial passenger tires
is as cap, or overlay ply, or belt edge cap strip
material, with some limited applications as
body plies.
O Advantages: Good heat resistance and
strength; less sensitive to moisture.
O Disadvantages: Heat set occurs during
cooling (flatspotting); long term service growth
.

Nylon Fabrics
O Nylon fabric comes in different deniers
like 840/2, 1260/2, 1680/2, and 1260/3.
O The nomenclature can be explained by
taking an example.
O If we take 1260/2, it means that two plies
make one cord (represented by the digit 2
in the denominator) and 9,000 meters of
one yarn will weigh 1260 grams.

Flatspotting
O In instances where nylon 6 is used, the tire will show
“flat spotting”, i.e., when the vehicle is parked,
particularly in hotter environments, the loaded tire
footprint will flatten.
O On start-up, the vehicle driver will experience severe
vibration, due to this distorted section of the rotating
tire.
O As the tire continues in service, the increase in
operating temperature will allow the nylon 6 cords to
relax and the temporary distortion in the tire may be
mitigated.
O High-end tires tend to use overlays with a 1400 × 2
construction, whereas broad-market tires use overlay
reinforcements, such as 840 × 2.

Nylon Cap ply
O Nylon finds use in the tire overlay or cap ply.
When the new tire is cured, the nylon overlay
will shrink, thereby locking the belts in place.
O Under high-speed tire service conditions, the
belts show strong centrifugal forces but with a
firmly positioned overlay, so that such forces
are contained, the long-term durability of the
tire is improved.
O The key properties for an overlay fabric are
tensile strength and modulus, adhesion,
shrinkage, and heat and fatigue resistance.
For these reasons, nylon 6,6 is preferred

Polyester
O Polyester tire cords are also synthetic, long
chain polymers produced by continuous
polymerization/spinning or melt spinning.
O The most common usage is in radial body
plies with some limited applications as belt
plies.
O Advantages: High strength with low shrinkage
and low service growth; low heat set; low cost.
O Disadvantages: Not as heat resistant as nylon
or rayon

Polyester
O Polyester Tyre Cord Fabrics are used as
reinforcing materials for tyres and designed to
keep tyres in shape and support vehicle
weight, having a significant impact on tyre
performance.
O
Nylon has high strength and excellent fatigue
resistance. However, owing to its low glass
transition temperature and lower modulus, it is
not suited for high-speed application.
O Polyester on the other hand, being superior to
nylon tyre cord fabric in these respects, is
preferred in radial and high-speed tyres.
Polyester tyre cord fabrics are available in
1000/2,1300/2,1500/2 and 2000/2

Polyester
O General comments on cord usage in various types of tires
O Polyester – Polyester is the condensation polymerization
product of ethylene glycol and terephthalic acid.
O Newer modifications resulting from increased molecular
weight and revised processing are called DSP-PET
(dimensionally stable PET), with 50% increased modulus
and 50% reduced shrinkage, bringing it close to rayon for
dimensional stability. It has become relatively inexpensive
making it a good choice for passenger and small light truck
tires.
O Polyester must be used with carefully designed rubber
adhesion systems and carcass rubber compounds to
prevent cord deterioration in use.
O Polyester cord is not recommended for use in high-
load/high-speed/ high-temperature applications, as in truck,
aircraft and racing tires, because of rapid loss in properties
at tire temperatures above about 120C.

Aramid
O Aramid is a synthetic, high tenacity organic
fiber produced by solvent spinning. It is 2 to 3
times stronger than polyester and nylon. It can
be used for belt or stabilizer ply material as a
light weight alternative to steel cord.
O Advantages: Very high strength and stiffness;
heat resistant.
O Disadvantages: Cost; processing constraints
(difficult to cut).

Aramid
O Aramid is a wholly aromatic polyamide. The most common
commercial material is poly(p-phenylene terephthalamide), eg,
Kevlar™ or Twaron™.
O Aramid cords have very high strength, high modulus, and low
elongation.
O The relatively high cost has slowed adoption as a general radial
belt material where steel cord is performing well.
O It is particularly suited where weight is important, such as in the
belts of radial aircraft tires or in overlay plies for premium high-
speed tires.
O In a multiply carcass construction, aramid’s low elongation will
prevent the outer ply from adjusting to the average curvature,
thus placing the inner plies into compression. This reduces the
contribution of the inner plies to the total strength, but, more
seriously, early failures of the inner ply are encountered due to
the poor dynamic fatigue resistance of aramid in compression.

Glass fiber
O Glass fiber – fiber glass was introduced to the US tire industry in the
1960s with Goodyear’s development of a belted-bias tire.
O This tire was soon replaced by the radial tire, however. Some
attempts were made to use fiber glass in the belts of radial tires but
in spite of its excellent credentials, fiber glass quickly lost out to
steel as the premier belt material.
O Premature failures were encountered, both in cold weather use and
with inappropriate tread designs that put the top belt into
compression.
O However, a review of its properties gives glass fiber an excellent
rating as a belt material if proper tread design and latex adhesive
dips are used. Its specific stiffness and strength are equal to those
of steel, whereas the specific gravity is only 2.54 compared to 7.85
for steel.
O The initial modulus is 2150 cN/tex compared to 1500 for steel.
Rubber adhesion is excellent with no problems with rusting due to
water in the belt. Each filament of fiber glass is coated with a latex
dip before the filaments are twisted into a yarn. It has been
established that this latex must be formulated from a low glass
transition polymer to prevent the premature glass breakage seen in
the early glass fiber development

Polyethylene Naphthalate (PEN)
O Polyethylene Naphthalate (PEN) - PEN is similar to
the standard polyethylene terephthalate (PET)
polyester, being a copolymer of ethylene glycol and
naphthalic acid.
O This new textile has been developed by Allied-Signal
(presently Honeywell High Performance Fibers) and
is being evaluated for tires. Its properties have been
reported by Rim . It is claimed to surpass DSP-PET
for use in the carcass of passenger car tires, having
lower shrinkage, higher modulus, and higher Tg
(120C vs. 80C).
O It also has potential as a restrictive overlay belt for
light truck and high-speed passenger tires, replacing
nylon overlays. A disadvantage is the high price,
about 2.5 times that of polyester.

Chafer Fabrics
O Chafer Fabrics are speciality fabrics used in
manufacture of heavy duty tyres, specially to
protect the side wall of tyres.
O The fabric is offered in both wicking and non
wicking types in construction of 420, 840 and
1260 denier.
O It protects the tyre from damages during the
fitting or removal operations by Rim and
Wheel assembly, also by the tools during
these operations.
O

Advantages
O Advantages
O It saves tyres from damages during fitting or removal
operations by rim and wheel assembly, also by the tools
used during these operations.
O It saves tyres bead area from chafing effects and damages
caused by rim.
O It saves tyres carcass plies from damage from rim friction.
O Additionally, the chafer fabric should ensure that
pressurized air inside the tubeless tyres does not wick
through it.
O Our wide range of chafer fabric meets the performance
requirements of all kinds of tyres, be it passenger tyres or
light and heavy duty truck / bus tyres or aircraft tyre besides
industrial and agricultural tyres.

Steel Cord
O Steel cord is carbon steel wire coated with
brass that has been drawn, plated, twisted
and wound into multiple-filament bundles. It is
the principal belt ply material used in radial
passenger tires.
O Advantages: High belt strength and belt
stiffness improves wear and handling.
O Disadvantages: Requires special processing
(see figure 1.16); more sensitive to moisture.

Bead wire
O Bead wire is carbon steel wire coated
with bronze that has been produced by
drawing and plating. Filaments are wound
into two hoops, one on each side of the
tire, in various configurations that serve to
anchor the inflated tire to the rim

Shear Strain on Radial Tyre Belt
(greater at the edges of the belt)

Change in Tyre Shape When Under Load

O Gum Strips: These are different types of
rubber strips, all made of the same
compound, located at belt endings, ply
endings, and other component endings,
and serving as a transition compound
between two different tire parts. They
provide a modulus gradient, improve
component-to-component adhesion, and
minimize potential for crack formation and
propagationThe

Cord-rubber adhesion
O The adhesion of rayon, nylon, polyester, and aramids has been reviewed
extensively. Takeyama and Matsui (24) reviewed adhesives for rayon, nylon,
and polyester. Solomon (25) updated this work in 1985 to include aramid
adhesion and the effects of environmental exposure on degradation of
adhesion. Chawla (17) summarized both cord processing and adhesive dip
treatments. Dipping and baking of the adhesive is intimately tied in with cord
stretching and relaxation procedures.
O There are many variations in cord dipping procedures, e.g., one-step vs two-
step dipping, dipping in the tire-plant vs in the cord-plant, surface activation of
the cord, etc. We consider here only the goal of using adhesives, general
operating procedures, and potential problem areas.
O The prime goal of the cord adhesive is to avoid separation at the cord-
adhesive interface, at the rubber-adhesive interface, or within the adhesive
itself. This objective is achieved by using proper dipping procedures. Tire
carcass failures that were initially attributed to failure at the adhesive interface
were often shown on microscopic examination to be due either to fatigue
failure of rubber close to the cord, caused by high stresses resulting from
improper construction or irregular cord spacing, or to cord fatigue from
excessive compressive stresses

Mechanism of cord-rubber adhesion
O It is generally accepted that the adhesive provides
both chemical bonding between the rubber and the
cord surface and by mechanical interlocking as the
rubber penetrates within the cord interstices. The
adhesive must also accommodate the large
differences in the two materials:
O -high-polarity polymers in cords vs. low polarity of
rubber
O - high modulus of cords vs. low modulus of rubber.
O -Good adhesive durability is achieved by minimizing
the abrupt change in modulus at the cord-rubber
interface by introducing an adhesive layer of
intermediate modulus

Requirements for cord-to-rubber
adhesives
O Good bonding to both cord and rubber
Intermediate modulus between cord and
rubber
O Rapid rate of bond formation
O High fatigue resistance in the cured adhesive
O No chemical deterioration of cord by the
adhesive
O Compatibility with a range of rubber
compounds No brittleness or flaking in
processing

resorcinol-formaldehyde-rubber latex system (RFL)
O The resorcinol-formaldehyde-rubber latex system (RFL) developed
in the 1940s for use with nylon and rayon is still used throughout
the tire industry.
O A synthetic 2-vinyl pyridine-butadiene-styrene copolymer latex,
developed for nylon, has replaced the natural rubber latex originally
used for rayon, in all modern dips. Resorcinol and formadehyde
react in the dip to give a strong polar polymer with good adhesion
the polar tire cord, while the rubber component of the latex provides
good bonding to the rubber.
O RFL is used for rayon and nylon exclusively and as the outer dip for
polyester and aramid cords.
O Typically, rescorcinol and formaldehyde are mixed and “matured”
for up to 24 hours. The latex is blended and the cord is dipped
before tensioning. Dip formulations contain 2 5% total solids and dip
pickup is controlled to about 6 - 8%. The cord is then tensioned and
baked.
O Complete total wetting of the cord is necessary to prevent spotty
adhesion. Good dip penetration is important for good adhesion and
cord compaction. Dip penetration of 2 - 3 filament layers is optimal.

O Polyester and aramid polymers are much less reactive to
standard RFL and must be pretreated to obtain good
adhesion. A common practice is to employ a multistage
dipping process.
O The cord is first dipped in an aqueous solution of a reactive
chemical, such as an epoxide, e.g., the diglycidyl ether of
glycerol or a blocked isocyanate, e.g., phenol-blocked
polyisocyanate [“Hylene MP”], along with a small amount of
wetting agent to give uniform dip pickup.
O After tensioning and baking the cord is again dipped in a
standard RFL for final baking and relaxation. Processing
times through each of the steps is generally 30-60 seconds.

O The dip formulation, amount of dip pickup and the curing
conditions can all affect adhesion and must be optimized.
Strict quality control must be implemented once optimum
conditions are established. Problems that must be avoided
are: inadequate wetting of the cord, inadequate dip pickup,
excessive dip pickup (which can result in flaking off of the
adhesive), or overbaking during heat treatment. Any of
these conditions can reduce adhesion. The finished cord
must be protected from nitrous oxides (if gas or oil heating
ovens are used) and from exposure to sunlight, humidity, or
ozone if the cords are stored or shipped before being
calendered with rubber. The treated cords are generally
protected by storing them in polypropylene cloth liners and
sealing them in black polyethylene film

FABRIC PRODUCTION
O The most critical stage in preparing a cord or
fabric for use in tires is fabric treatment, which
consists of applying an adhesive under
controlled conditions of time, temperature,
and tension . Required properties are:
O 1.Adhesion for bonding to rubber
O 2. Optimization of the physical properties of
strength, durability, growth, and elongation of
the cord for tire application
O 3. Stabilization of the fabric
O 4. Equalization of differences resulting from
the source of supply of the fiber

Processing consists of passing the fabric through a series of
zones
O 1. Adhesive application zone or first dip
zone
O 2. First drying zone
O 3. First heat treatment zone
O 4. Second dip zone
O 5. Second drying zone and then second
heat treatment zone
O 6. Final cooling zone

O To obtain optimum cord properties of strength,
growth, shrinkage, and modulus, specific
temperatures and tensions are set at various
exposure times within the fabric processing unit.
O The temperature and tensions determine, in part, the
ratio of crystalline and amorphous areas within the
fiber, and the orientation of the crystallites, which, in
turn, determines the physical properties of the cord.
O For example, polyester, when heated, tends to revert
to its un-orientated form and the cord shrinks.
O Stretching the cord in the first heating zone and then
allowing the cord to relax in a controlled manner in
the second heat treatment zone, i.e., stretch
relaxation, will control shrinkage

O An increase in temperatures can decrease
cord tensile strength and modulus but will
improve fatigue life which may be necessary
for some tire constructions. However, not all
cord properties behave similarly with changes
in processing conditions. It is thus necessary
to determine the processing conditions that
optimize the specific cord properties needed
forthe required tire end use. When two or
more diametrically opposed properties have to
be optimized, more complex processing
operations could be required

CORD-TO-RUBBER COMPOUND ADHESIVE
O There are three aspects to adhesion of tire cord to the elastomer
treatment: molecular, chemical, and mechanical.
O Molecular bonding is due to absorption of adhesive chemicals from
the adhesive dip or elastomer coating onto the fiber surface by
diffusion and could be achieved by hydrogen bonding and van der
Waals forces.
O Chemical bonding is achieved through chemical reactions between
the adhesive and the fabric and rubber, i.e., crosslinking and resin
network formation.
O Mechanical adhesion is a function of the quality of coverage of the
cord by the rubber coating compound; the greater the coverage, the
better the adhesion. The fiber properties of primary importance to
adhesion are reactivity, surface characteristics, and finish.
O Rayon has many reactive hydroxyl groups.
O Nylon is less reactive but contains highly polar amide linkages,
whereas polyester is quite inert. Thus, an adhesive system must be
designed for each type of fiber.

adhesive system must conform to a rigid set of
requirements:
O 1. Rapid rate of adhesion formation
O 2. Compatibility with many types of compounds
O 3. No adverse effect on cord properties
O 4. Heat resistance
O 5. Aging resistance
O 6. Good tack
O 7. Mechanical stability
O The adhesive bond between the rubber and cord is
achieved during the tire vulcanization cycle. The
rate of adhesive formation should give maximum
adhesion at the point of pressure release in the
cure cycle

TYRE CORD PROCESSING.pptx

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