3. FILLERS
Essentially fillers are added to formulations to
reduce costs, although they may offer other advantages – such as opacity,
resistance to blocking, reduced plate-out, improved dry blending. On the other
side, fillers can reduce tensile and tear strength, reduce elongation, cause
stress whitening, reduce low temperature perforance.
The most common fillers used with PVC are calcined
clays, and water-ground and precipitated calcium carbonates of particle size
around 3 micrometers. Other fillers are silicas and talcs.
4. LUBRICANTS
These materials are of prime importance in
PVC processing. They are decribed below.
⑴ Improve the internal flow characteristics
of the compound.
⑵ Reduce the tendency for the compound to
stick to the process machinery
⑶ Improve the surface smoothness of the
finished product
⑷ Improve heat stability by lowering
internal and/or external friction
Examples of lubricants, with which
you may be familiar, are stearic acid, calcium stearate, Wax E, polythylene AC
617.
5. PROCESSING AIDS
These may be regarded as low-melt viscosity,
compatable solid plasticizers. They are added to lower processing temperatue,
improve roll release on calenders, reduce plate-out, promote fusion.
They are usually added at concentration of 5.0%. The
most widely used processing aids are acylic resins of which acrylic K 120N is
an example.
6. OTHER ADDITIVES
There are
several other addtives which we will list and comment on briefly.
⑴ Impact Modifiers: These are usd in rigid
vinyls to improve impact resistance. These are usually acrylic or ABS polymers
used at 10-15 phr levels. Examples are Kureha BTA 111, Blendex 301.
⑵ Light Stabilizers: for resistance to
ultraviolet radiation. They are used in low concentrations 0.5-1.5 phr.
⑶ Flame Retardants: PVC is inherently
self-extinguishing However, the plasticizers and additives are not. Therefore,
flame retardants are added. The most widely known one is antimon tri-oxide.
⑷ Anti-Static Agents
⑸ Fungicides: Vinyzene BP-5
⑹ Foaming Agents: Chemicals that decompose
at predetermined temperature to produce a certain volume of gas within the
molten vinyl and thereby create foam.
⑺ Colorants: Both pigments and dyes can be
used. However, dyes, which are soluble organic substances,are used sparingly de
to their tendency toward migration and extract ability. Heat resistance of
colorants must be carefully evaluated.
In summary, we have seen that a vinyl
compound consists of following components: PVC resin, plasticizer, heat
stabilizer, lubricant, special additive, colorants.
