Today PP Thermoforming has become popular due to availability of machines, adequate knowledge of process, technology, proper grade of raw materials etc. Though internationally well accepted, PP Thermoforming was uncommon in Indian disposable and packaging market till recent times.
Thanks to Wonderpack for the innovative pioneering efforts to develop and establish PP Thermoforming. Even before the advent of proper raw material, Wonderpack, an enterprise, committed for innovative developments and an undisputed thermoforming leader, was equipped with the apt technology & machines. After an extensive in-house R&D, Wonderpack, as a tradition, has brought to Indian thermoforming market an indigenously developed PP line with a reliable technology.
Properties of PP
a. Strength to weight ratio: High strength to weight ratio and lightest resin, hence, preferred over other thermoplastics.
b. Hinge properties: Has good hinge properties and hence, ideal for stationery.
c. High heat resistance: Hence, suitable for hot filling.
d. High surface finish: Hence, suitable for packaging. High stress-crack resistance: Hence, does not creep & crack, unlike other formable plastics.
e. High clarity: High clarity can be achieved by using clarifying agents, hence, possible to make transparent containers.
f. High chemical resistance: Hence, used for making inert containers.
g. Good barrier for oxygen / moisture: Hence, used for food packing to keep it fresh.
Process
The PP extrusion and forming process, though critical, is machine dependent and needs sophisticated machinery. The sheet line needs to have a precisely designed screw barrel. The geometry of screw, type of temperature controller, heating-cooling system, roll stack design etc is of extreme importance.
The thermoformer needs to have precise and accurate heat control, suitably designed heat tunnel, two station (preheating) gradual heating, pressure forming with plug & vacuum assist. Accurate forming station is critical. Cutting tolerances and design of mould is also critical.
The PP sheet forming is carried out approximately at temperature of 150 degree to 165 degrees, depending upon type and grade of material.
The sheet is first gradually heated, which is stress relaxation and then rapidly to the final forming temperature. To avoid excessive sagging, suitable and possible precaution should be provided.
The sheet sag is often a strong indication of sheet attaining its forming temperature. Pre-stretching the sheet is always advantageous.
The speed of plug movement also plays very significant role for orientation of sidewall thickness. Wonderpack recommends servo assist plug.
Considering the process, forming and extrusion criticalities, Wonderpack has developed a tailor made PP line to suit various demands of processor at an affordable price with highest level of sophistication.
A rare combination of innovation, speed, technology and reliability is N series of fully automatic thermoforming machine. This is the latest trend setting development and a-state-of-the-art machine, with dual crankshaft mechanism, driven by Servo motor for platen movement. [The plug movement, sheet indexing and platen movement all can be actuated by servo (optional)]. The control can be PLC/ PC based with
PID heat control. The Servomotor, controlled through servo drive and suitable software, gives the processor a complete control over the entire forming cycle at the fingertips. Most important, the machine runs up to 45 cycles / minute, which is revolution of sorts, as it sets a trend for next generation thermoforming machinery.
Applications
PP will continue to be a privileged raw material in thermoforming industry due to its inherent properties and achievable economics. Few of notable and important applications are mentioned as below:
(a) Conventional forming applications:
The main forming applications are dairy containers, drinking cups, plates and trays are taking a bigger share of market along with tea/coffee cups. With new range of microwave, disposable market shall be dominated by PP in future.
Fruits and vegetable packages are produced of clarified PP, which offer clarity, rigidity and impact strength.
The thermoformed flowerpots and handling trays have an increasing share in horticulture industry.
Packaging applications
Blister packs for pharmaceutical packaging, cosmetic / toiletries, bakery products, personal appliances, thermoform disposable stationery etc is becoming popular.
Packaged mineral water in 200-ml clear glass with top foil is most popular and growing application.
(b) Non conventional for-ming applications:
Photo frame, figures of gods & goddesses, clocks housing and dials (even metallized), decorative plant pots, blister for unit pack of shampoos as a substitute for sachets are few untapped applications.
SOME Distinct Benefits of PP over other resins
a) Lightest among all formable plastics excluding foam ones, hence, economic.
b) Withstands temperature as high as 140 deg, hence, can sterilize & hot fill.
c) Has good rigidity and unbreakable.
d) It can be glass clear and transparent.
-The author is with Wonderpack Ind P Ltd, Mumbai and he can be reached at mangesh@wonderpackindustries.com