Molding conditions
Drying conditions
- Molding the resin without drying it will cause the viscosity to decrease due to hydrolysis. Be sure to dry the resin before molding. Amorphous resins (MA-2101M and MA-6101-3) should also be pre-dried.
- Use a dehumidifying dryer whenever possible.
- To prevent moisture absorption during molding, we recommend using a hopper dryer (preferably with dehumidification capability).
| Drying Temperature | Drying Time |
|---|---|
| 130℃ | 8 hours |
| 140℃ | 6 hours |
The amorphous resins should be pre-dried for 4 hours at 70°C.
Note: Even after the resin is dried, it can absorb moisture and cause problems if exposed to air for 15 minutes or more (especially during the rainy season). In addition, the crystalline resins can lose their physical properties and color if over dried (for 24 hours or more).
Example of injection molding conditions
| Item/Resin | Homogeneous Type | Copolymerization Type |
|---|---|---|
| Nozzle temperature | 270～290℃ | 255～275℃ |
| Cylinder front temperature | 270～290℃ | 260～280℃ |
| Cylinder middle temperature | 270～290℃ | 260～280℃ |
| Cylinder rear temperature | 250～270℃ | 250～270℃ |
| Injection pressure | 5.0MPa | 5.0MPa |
| Holding pressure | 4.0MPa | 4.0MPa |
| Back pressure | 0.5MPa | 0.5MPa |
| Mold clamping pressure | 15MPa | 15MPa |
| Injection time | 8sec | 8sec |
| Cooling time | 16sec | 16sec |
| Cycle time | 27sec | 27sec |
| Mold temperature (using chiller) | 15～30℃ | 15～25℃ |
| Screw speed | 150rpm | 150rpm |
(Updated on August 29, 2017)
Notes:
If the mold temperature exceeds 40°C, the molten material may fail to solidify completely, causing problems such as sprue breakage or ejector pin marks.
Molding PET resin using a mold with pin gates, which make it difficult to fill the mold, requires that the temperatures of the cylinder and nozzle be raised 10°C to 20°C higher than the specified temperatures to increase the fluidity.
In pin gate molding, the molten material easily solidifies in the gates to seal them due to oriented crystallization. For this reason, the first injection speed should be set high to fill the mold quickly. When using a multi-cavity mold, be careful that all cavities are filled simultaneously. Otherwise, some cavities may not be filled.
Additional notes
Note the following when recycling sprues, runners, and other materials.
- Resin left exposed must be re-dried because it will have absorbed moisture.
- Because the molding material is amorphous, it will soften and cause blocking at 70°C or higher, even if it is dried.
- Although blocking can be prevented by mixing the molding material with virgin material before drying, they will fuse together and cause blocking if the mixing ratio exceeds 20%.
- Ensure that the particle size of the crushed material is as uniform as possible, and remove any powder. Failure to do so may cause voids or unmelted material.
- As a guide, the mixing ratio should be 20% or less.