WHY DIPPING ?

Raw fabric as received is having very poor adhesion to the
rubber compound and has poor dimensional stability. During
dipping process, an adhesive coating (resorcinol ,
formaldehyde ,V.P Latex) is applied to the surface of the
fabric to improve the adhesion. The fabric is also stretched
and heat set to increase the dimensional stability.

Textile treatment systems

The adequate bonding of textile fibres to elastomeric matrices is
important for the satisfactory performance of many heavy duty
mechanical rubber products like tires.

Most popular adhesive systems are

1) Resorcinol-Formalde hyde-Latex (RFL) system
2) Poly isocyante-latex system

The RFL is preferred over the latter primarly due to

1) Difficulty in getting adequate textile to rubber adhesion
2) Cost aspects
3) Difficulty in handling chemicals



Requirements for an adhesive
system

a) Rapid rate of adhesive formation.
b) High fatigue resistance, compatibility with many types of rubber
compounds.
c) No adverse effect on cord properties.
d) Heat resistance.
e) Ageing resistance in tire service.
f) Mechanical stability.
g) Aqueous medium

Adhesive system for NYLON-6

•Resorcinol Formaldehyde Latex(RFL) based solution system is
the preferred adhesive system for NYLON.
•The RFL system is prepared by dissolving resorcinol in water and
then adding formaldehyde and an alkaline ( NaOH) catalyst. On
formation of resin ( at definite time and temperature) latex is added
under slow stirring and the whole solution is matured for definite
time at a specified temperature before use.

Dip Solution formulation

Material Parts
Water 270.87
Resorcinol 11.00
Formaldehyde 16.20
Caustic Soda 0.30
VP latex 242.42
Ammonia 11.85

RFL -FUNCTION OF INGREDIENTS

Sodium Hydroxide -Used as a catalyst
Ammonium Hydroxide- Use as preservative and improve adhesion

Resorcinol & formaldehyde- For condensation polymerization
.
V.P.Latex -For RFL structure

Water-Aqueous medium


DIP SOLUTION -MIXING PROCEDURE

Preparation of RF Solution (Resin Master)
1. Fill the tank with the required quantity of water.Set the temp to 75°F and
start the stirrer
2. Dissolve the Caustic soda (NaOH) in the required quantity of water and
keep aside
3. Weigh the required amount of Resorcinol & Formaldehyde and keep ready
4. After the set temperature is attained ,Add the dissolvedCaustic soda
5. Add the Resorcinol & Formaldehyde

6. Continue stirring maintain the temperature.between 70-80°F by
controlling the circulation of chilled water.
7. After 4 hrs take sample and give to lab for approval.



DIP SOLUTION -MIXING PROCEDURE

Preparation of RFL (Final dip solution)
1. Fill the tank with the required quantity of latex
2. Transfer the RF solution @ 20 Liters per Minute to the Latex
3. Add the required Quantity of Ammonia.
4. Stirr for 15 Minutes
5. Give sample to Laboratory for Approval

Dip solution properties

•PH (Controls adhesion and solution wastage) 10.5±0.5
•Total Solids (Controls DPU,adhesion & solution wastage) 21.2 ±0.5%
• BF Viscosity (Controls DPU) 4.5±0.5 cps




Factors affecting Dipped cord adhesion

Effect of Resin to Latex Ratio

If too low a level of resin is used the
film strength of the dip will be low due to
insufficient cross links. Also since the resin preferentially
bonds to the fiber portion of the fiber -- rubber composite,
a decrease in adhesion to the fiber will be noted

If too high a level of resin is used, the dipped cord will be
too stiff due to the excessively high modulus of the
cured RFL film. Also since the latex preferentially bonds to
the rubber portion, a decrease in adhesion is observed.

For dip solution the Resin to Latex Ratio
is around 5.7

Effect of Formaldehyde to Resorcinol Ratio

The rate ofmethylol reaction is accelerated with increasing
amounts of formaldehyde.It is determined about 2 moles of
formaldehyde per mole of resorcinol completes
the reaction.

If the ratio is 3 :1, increase in viscosity is very sharp and onset of
gelation is very rapid.

The best values are obtained with the ratio of 2 :1

Dip solution the Resorcinol to formaldehyde Ratio
is 2:1

Effect of VP content

The Vinyl Pyridine Latex is 70 % Polybutadiene
15 % Vinyl Pyridine and 15 % Stirene
The Adhesion values are the best with 15 % VP content
The VP latex used by ATL contains 15 % VP

Effect of Dip Pick up

The dip Penetration should be about 2--3 filaments into the fiber
bundle to give enough anchorage. The balance of the dip on the
surface of the fibre is then available for bonding to the rubber

Higher dip pick up contributes increased stiffness and H- adhesion
to the cord.

But the observation is that the
Calendered Strip adhesion and coverage drops with increase in
Dip pick up

The Dip Pick up maintained is 4.25 ±1.25 %

Dipping process for Nylon-6

Dipping is essentially a 3T process where in, Time,
Temperature and Tension are carefully controlled to
get desired technological characteristics to Nylon cord
fabric for engineering applications like tire
manufacturing.

The dipped fabric is exposed to hot air environment of
120°C for 3 minutes in the drier.
The fabric, after the drier, is stretched so as to adjust the
technological properties in heat oven at a temperature,
which can be between 205°C and 212°C depending upon
the yarn denier.

To account for the thermal shrinkage characteristics and
to achieve the dimensional stability required for post
dipping processing, a shrinkage (-2.5%) is induced in the
normalizing zone under controlled condition of
temperature ranging from 210°C to 213°C.