Polycarbonate (PC) Water Bottles
Polycarbonate has high light-transmittance (88-91% as compared to 92% for
clear plate glass) and high resistance to stains by tea, coffee, lipstick,
inks, soap, detergent, and many other household materials. Its relatively
dense composition makes it resistant to odors, and its hard, smooth surface
facilitates easy removal of foodstuffs (Milhalick and Baccaro, 1986). For
these advantages, PC is the material of choice for returnable bottles.
Common bottle sizes are 3 and 5 gallons. The rectangular 3-gallon, an
exclusive bottle design of McKesson Water Products Company, is stackable.
Interlocking grooves on the sides allow the user to side-stack five
3-gallon bottles vertically to save space. These bottles, which have
identical non threaded finishes, are sealed by press-on polyethylene caps.
The 5-gallon round bottles is the basic bottle for the water bottling
Another popular PC bottle group includes bottles which are available for
sale to consumers at water-vending machine locations. These bottles are
designed with built-in handle, screw cap, and dispensing valve. Available
sizes are 1, 2, 3, and 5 gallons. The rectangular 2-gallon container with
its dispensing valve is a popular portable container. The 3 and 5-gallon
round bottles have integral handles and softer rib design to simplify
The two most important quality requirements for the returnable bottles are
aesthetic and sanitary conditions.
To optimize the bottle appearance, emphasis on the handling of the raw
resin and the regrind is essential. PC resin will absorb moisture upon
exposure to the air. To prevent silvery streaks, "chicken tracks",
or air bubbles, the resin feed stock has to be dried to the manufacturer's
specification. Regrind, the reusable plastic which is obtained from the
trimming of the flash from the pinch-off, handle, and neck finish areas,
should also be kept dry.
Both resin and regrind have to be processed within 20 minutes to be
effective. When using regrind in processing, the maximum allowable ratio
should not be more than 30 percent regrind to 70 percent virgin resin
(General Electric, 1992).
The manual trimming (around the spout and along the mold line) and the logo
silk- screening (on the side wall) should be done carefully.
Silk Screen Processing
Decorating process employing screen stencils. Silk screens were actually
once used in the methodology, hence, the name commonly used for the process.
Now, however, the process uses stencil screens of various
materials-especially fine wire mesh (The Packaging Institute International,
Blemishes are not permitted on the sealing surface of the bottle spout to
prevent leakage when full bottles are stored (3 and 5 gallon bottles are
stored sideways). A smooth spout helps the press-on cap to seal properly.
Delamination, degradation, and weak spots can be prevented by periodic
cleaning of the blow molding machine and mold (General Electric, 1990).
In the rectangular 2 and 3 gallon bottles, where thin wall corners are a
problem, the machine's mold vent should be clean at all times. An
unobstructed vent will permit uniform plastic stretch at the bottle corners
during blow molding.
To satisfy the federal Food and Drug Administration's (FDA) requirement for
a food product, all good manufacturing practices outlined in the Code of
Federal Regulations have to be followed. The returnable bottles have to be
cleaned and sanitized before the drinking water is bottled.
Bottles returned to the bottling plant are sorted before entering the
washer. Only the serviceable ones are reused. Others, with physical damages
or hardened foreign matter adhering to bottle walls, are discarded to the
recycling center. Inspections are performed at both ends of the washer.
At the entrance, an electronic vision system and inspection personnel
examine both the interior and exterior bottle walls for any foreign matter.
While the electronic "sniffer" detects bottles which were
contaminated with hydrocarbons (gasoline or petroleum products), alcohol, or
nitrogen-based contaminants (ammonia or solvents'. On the exit side of the
washer, the vision system and the inspection personnel again scrutinize the
bottles before allowing them to enter the bottling room. Daily calibration
of all inspection instruments is necessary to ensure a constant supply of
clean, sanitized bottles.
At the bottle washer, washing solutions from 49C (120F) to 60C (140F)
contact the bottles for five minutes. Although this
high temperature is
required for effective cleaning, it will shorten the bottle's life. Tests
show that continuous exposure in hot 65C (149F) water causes gradual
embrittlement in PC bottles (Machine Design, 1991). Hourly verification of
the washer solution's temperature, therefore, is essential during bottling.
Beside the temperature, the concentration of the cleaner and sanitizer
solutions are also tested hourly (bottles are washed with the cleaning
solution first, then rinsed with the sanitizer) to insure a thorough washing
Container and closure bacteriological tests are conducted quarterly to
verify the clean, sanitized condition of the washed bottles and their caps.
Randomly selected bottles and caps are rinsed with sterile water. A measured
sample of this solution is tested for the presence of bacteria.
Packaging the PC Water Bottles
The filled PC water bottles are packaged by two methods: crate and rack
systems. In the crate system, bottles enter the bottling room in their
individual plastic crates. The crated full bottles are stacked sideways onto
wood pallets for transport. A standard load is a 30-crate bottle pallet (two
rows of five-crates high, three-crates wide). The polyvinyl crate is
designed to cradle the bottle throughout the distribution cycle. The bottle
separates from its crate during two occasions: in the washing operation and
in the dispensing mode when the bottle is installed onto the water cooler.
Crates require maintenance and inspection on the return trip and they occupy
additional space in transport and in storage. As a result, modern bottling
plants are converting to the rack system.
In the rack system, bottles are filled without crates, then inserted into
metal racks for distribution. A standard size rack carries 30 bottles in the
same side-stacking arrangement as in a full pallet of crated bottles. The
rack system eliminates the need for plastic crates and simplifies handling.
However, a glossy and durable coating will be required and maintained on the
rack's supporting bars to reduce scratches on the bottles and to withstand
the outdoor exposure. Caring for the racks includes special truckbeds to
protect the rack and the periodic checking for the rack's structural