7. Molding Conditions
General nozzle and cylinder temperatures are shown in Table 7-1 and they are recommended as standard conditions. Temperatures be changed within a range of 10°C to 20°C depending on molding conditions. In order to prevent stringiness and drooling, nozzle temperature can be lowered 10°C to 20°C. However, it is advised to pay attention to the following remarks.
If unstable metering occurs, setting as shown below is recommended for cylinder temperature distribution.
(Example) In case of E130i:
(NH) 350°C - 350°C - 350°C - 350°C (Flat)
(NH) 350°C - 350°C - 360°C - 370°C (Raise temperature at rear section)
Table 7-1 Recommended Cylinder Temperature Setting of Each Grade
It is generally recommended to set mold temperature in a range of 50°C to 120°C when molding LAPEROS. Mold temperature of 50°C rarely causes problems normally. However, if there is any problem in appearance such as surface roughness or gloss, a higher mold temperature is recommended.
Generally, screw rotational speed is approximately 100 rpm. Higher screw rotational speed is allowable for reduction of cycle time or metering stability. It is recommended to set back pressure at approximately 0 MPa to 2 MPa to prevent drooling and fiber breakage.
Each LAPEROS grade has very low melt viscosity and, therefore, can be molded at much lower pressure than those applied for other thermoplastic polymers. In most cases, a resin pressure of 15 MPa to 45 MPa can be adopted for molding. Furthermore, as LAPEROS has fast solidifying speed, fast injection speed may produce better results in most cases.
(1) Stopping the Molding Machine
After purging of LAPEROS remaining in the cylinder at the molding temperature of LAPEROS, the cylinder should be purged with a resin which is the same molding temperature as LAPEROS and has good thermal stability. (Commercially available glass-fiber reinforced polycarbonate, high-density polyethylene or acrylic type purging materials are recommended.) If LAPEROS is to be subsequently molded, the cylinder can be purged with LAPEROS.
(2) Starting the Molding Machine
In starting up a machine containing another resin that is stable within the LAPEROS molding temperature range, cylinder temperature can be raised to this level and purging can be done with LAPEROS. However, LAPEROS has a very low melt viscosity, which makes purging of the remaining resin in the cylinder difficult, so extremely thorough purging is required. It is efficient to purge cylinders with glass-fiber reinforced polycarbonate first, and then purge with LAPEROS.
When the resin remaining in the cylinder has a different molding temperature range, the following steps should be carried out:
In general, when LAPEROS is the resin remaining in the cylinder, it is possible to raise the cylinder temperature to the LAPEROS molding level and to purge with LAPEROS. However, as the molding temperature ranges of LAPEROS differ depending on the grade, it is necessary to confirm the molding temperature ranges of the remaining LAPEROS grade and the replacement LAPEROS grade prior to purging. When the molding temperature range of the remaining LAPEROS grade is different from that of replacement LAPEROS grade, the purging should be done according to the instructions when the case that the resin remaining in the cylinder has a different molding temperature range.
(3) Changing the molding material
When the resin has the same molding temperature range as LAPEROS, the cylinder can be purged at the molding temperature, following the same procedures used in starting and stopping the molding machine.
When the resin cannot be replaced under the same molding condition, it is recommended to purge the cylinder with a resin that can be used at the molding temperatures of both LAPEROS and the replacement, and has good thermal stability (e.g. glass-fiber reinforced polycarbonate or high-density polyethylene). Then, set the cylinder temperature at the replacement resin molding level.
Especially when the resin remaining in the cylinder has a higher viscosity than that of LAPEROS, it is quite difficult to replace it with LAPEROS. Very thorough purging is required.
If LAPEROS remains in the cylinder for a long time, degradation and contamination may occur. In such a case, extremely thorough purging is required.
When it is difficult to purge dark colored materials such as black coloring materials, purging should be done with glass-fiber (GF) reinforced polycarbonate, then with polyethylene. Repeat purging with GF reinforced polycarbonate and polyethylene alternately is recommended. It is more effective if the new purging material is fed into the cylinder after completely purging the previous material.
Note: Make sure to read purging material SDS prior to use.