P.E.T material has characteristics
of good chemical effect tolerance, nice transparency,
and satisfied the food safety grade standard,
which has been used in many products, such as
mineral bottle, fruit juice bottle, carbonate
drink bottle..., etc. If it is used for cosmetic
containers, it is better to use P.E.T.G. material
since P.E.T.G has even better chemical effect
tolerance. unlike for acrylic container, which
the internal must fix with PP material container.
The biggest issue for P.E.T material is that
it absorbs humidity from the air, therefore, one
must dehumidify the material to be below 0.05%.
Otherwise, the product will become easily destroyable
with also crystal white finishing surface. Based
on this issue, a P.E.T injection machine must
come with a complete set of dehumidifier, which
dries the air between -29 to -40 degree, and for
dryer machine it's about 180°C. Furthermore, in
order to prevent the mold gets sweaty, the mold
must have dew preventing equipment, which normally
uses cool air to blow, but sometimes using dry/hot
air process system. The workshop should also include
air condition and dehumidifier.
In order to improve the production efficiency
and to prevent the beat break up, it is better
to design the machine using double loop controlling
type. That is, the mold can be opened during screw
charging action to shorten the cycle time. Also,
the mold side should be warped and dewy. Then,
it is important to design the injection screw
compression rate (L/D rate) to prevent heat break
up from strong friction heat.
The process of making a the mold is also not
a easy task, as it is difficult to make and expensive.
Without skilled mold design and structure, many
problem may occur. Therefore, one must purchase
a full equipment set and complete setting and
testing the mold to avoid trouble. Usually, a
full set includes P.E.T injection molding machine,
dehumidifier, hopper dryer, auto loader, water
chiller, mold, conveyer belt transmission system
and robotic arm..., etc. A blowing machine will
be required on two step injection machine, but
will not be required on P.E.T preform production;
additional injection molding machine and bottle
cap cutting machine will be required to produce
bottle cap.
There are two types for P.E.T injection machine:
single step type and double step type. For the
single step type, the mold rotates 180 degree
and blow the P.E.T preform after injection, before
cooling down to make the P.E.T bottle. As for
the double step type, the P.E.T injection machine
makes the P.E.T preform first. Then, it moves
the P.E.T preform to the blowing machine to be
heated up and blow to P.E.T bottle. So, the double
step requires a blowing machine. |