DAK Americas Laser+ W 4000 K42A - Manual (Page 2)

Laser+
®
W 4000 (K42A) Product Information
polyethylene terephthalate resin
DAK Americas LLC
Gateway Corporate Center, Suite 210
223 Wilmington W Chester Pike• Chadds Ford, PA 19317
1-888-738- 2002 • fax: 610-558-7385 • www.dakamericas.com
PDS-K42A 140303KH
DAK Americas
ISO 9001:2008
#10004457
Material Drying
Proper drying of polyethylene terephthalate (PET) is essential to produce a high quality part (container, film, etc.) with optimum
physical properties. PET is hygroscopic, meaning that when it is exposed to humid atmospheres, it will absorb moisture. In
PET the moisture is not only on the surface but diffuses slowly through the whole pellet and is firmly held by molecular
attraction. Before processing the PET, this moisture must be removed. Carefully controlled drying of all PET is an essential
requirement for optimum processing performance and final product properties. If drying is not carried out properly, to the
known requirements of the type of PET in use, then deficiencies in process and product will results. The deficiencies will be
impossible to remedy by later process changes. These defects arise in the injection molding or extrusion processes because
at PET melt temperature (250°-280° C) any water present causes hydrolytic degradation of the PET, almost instantaneously,
with the resultant loss in intrinsic viscosity (IV). Significant drops in IV cause loss of process control and reductions in end
product properties.
Drying of PET polymer involves the diffusion of absorbed moisture from the interior of the polymer chip to its surroundings and,
subsequently the removal of moisture from the bulk of polymer chips. Moisture removal can be achieved by heating the
polymer chip under dry air or vacuum. In an air drying system, heated dehumidified air flows up through a chip bed and
returns to the dehumidifier. The key requirements for a reliable drying process are:
Drying temperature: The ACTUAL chip temperature should achieve between 300° and 330° F measured at the dryer exit.
Dehumidified air temperature: Correctly designed equipment should operate at temperatures up to 340° F measured on entry
to the dryer hopper, with an absolute maximum of 350° F to prevent possible discoloration.
Dehumidified air dew point: This should not be allowed to rise above
–34° F and should preferably be –40° F or lower,
measure after the desiccant bed. Always check the correct regeneration temperatures are being used.
Dehumidified air flow through the chip bed: Most dryers operate at around 1 CFM of airflow per 1lb/hr of PET chip as a
minimum requirement, with the airflow at the correct temperature and dew point.
Chip residence time (drying time): DAK recommends a chip residence time for Laser+
®
PET of not less than four hours and
preferably six hours. This is the theoretical drying time, which is calculated by dividing dryer capacity in lbs. by throughput in
lb./hr. Extended periods of high temperature can adversely affect the polymer processing conditions. In the event of a
stoppage for an extended period, dry polymer can be stored in the dryer-hopper by reducing the air temperature to 240° F (or
even lower).
Important Start-Up and Shut-Down Procedures:
Dryer Start-Up Conditions
 When beginning to dry a “wet” load of pellets, start drying at reduced temperatures 135 to 150 ⁰C (275 to 300⁰F) for 2 hours

Raise the drying temperature to a maximum of 165 ⁰C (330⁰F) for a single stage drying system for the remaining start-up drying time
(2-4 additional hours)
Dryer Running Conditions

When running the injection molding machine, it is recommended to not exceed 170 ⁰C (340⁰F)

Absolute maximum drying condition is 175 ⁰C (350⁰F).
 When higher operational temperatures are used, care should be taken if the machine stops production (idle time of 20+ minutes) to
reduce the drying temperature down to a maximum of 165
⁰C (330⁰F) and preferred to be at or below 150⁰C (300⁰F).
Shutting Down Dryers

Ensure pellet temperature is cooled to below 120 ⁰C (250⁰F) prior to shutting down process air blower

Time required to reduce the pellet temperature varies on ambient conditions, equipment configuration, and air flow capacity

If pellets reside in drying vessel above the recommended cooled pellet temperature, degradation can occur (IV loss and yellowing)
Note: When a stoppage occurs for an extended period of time, dry resin pellets may be stored in the drying vessel at a reduced air
temperature of 115
⁰ C (240 ⁰ F). Drying of these pellets will not then be necessary, only increasing of the pellet temperature will be required to
restart the system.