Multi-Wall Sheet Extrusion: Resin Processing Parameters
Processing Bayer resins on extrusion lines requires an understanding of equipment settings as well as the properties of the specific resin. The following sections give an overview of the processing parameters for the two Bayer grades used for multi-wall sheet extrusion. Keep in mind that processing parameters can vary considerably, depending on the product to be manufactured and the plant technology available.
You can find more information about most grades and standard values in Bayer product information bulletins. See http://bayermaterialsciencenafta.com/products/index.cfm.
Moisture Content
Moisture in the resin adversely affects processing and the quality of the extruded material. Manage moisture levels for Bayer polycarbonates so the recommended moisture content of a specific resin is not exceeded.
If the Makrolon® 1243 and 1143 polycarbonate resins are not pre-dried, they can be degassed during extrusion. Degassing is often more economical than pre-drying because it allows you to maintain a higher extruder output. Even in regions with high humidity, degassing lowers the moisture content to recommended levels. Additional pre-drying is only necessary if the pellets have become moist due to improper storage.
Do not degas Makrolon® DP1-1852 polycarbonate, which can be coextruded with Makrolon® 1243 and 1143 resins for UV protection. Due to the volatility of the UV absorber, it is necessary to pre-dry Makrolon® DP1-1852 polycarbonate.
Please refer to the individual product information bulletins available for each grade for specific drying conditions.
Makrolon® 1243 and 1143 Polycarbonates
For extruding multi-wall sheets with Makrolon® 1243 and 1143 polycarbonates, use the following processing parameters. Depending on the product to be manufactured or the plant technology, processing parameters may vary considerably.
Extruder Temperatures
While most processing temperatures are the same for Makrolon® 1243 and 1143 polycarbonates, there are some differences.
Main Extruder Temperatures for Makrolon® 1243 Polycarbonate
Use a descending temperature profile of 535°F and 480°F (280°C to 250°C) from the feed hopper to the die. Reduce the temperature to approximately 464°F (240°C) in the degassing zone. Melt temperatures for Makrolon® 1243 polycarbonate should range between 450°F and 500°F (230°C and 260°C) at the end of the screw.Main Extruder Temperatures for Makrolon® 1143 Polycarbonate
Use a descending temperature profile of 570°F to 520°F (300°C to 270°C) from the feed hopper to the die. Reduce the temperatures to between 480°F and 500°F (250°C and 260°C) in the degassing zone. Melt temperatures for Makrolon® 1143 polycarbonate should range between 520°F and 570°F (270°C and 300°C) at the end of the screw.Coextruder Temperatures
The barrel temperature profile of the coextruder should be set so the melt temperature is approximately 70ºF (21ºC) lower than the base material. The melt temperature for Makrolon® DP1-1852 polycarbonate is 445°F to 500°F (230°C to 260°C). To reach this melt temperature, set the barrel temperature to 445°F to 480°F (230°C to 250°C). Keep the temperature constant throughout the entire barrel.Downstream Unit Temperatures
Temperatures of units downstream from the extruder, such as the screen exchanger, melt pump, coextrusion adapter, and sheet extrusion die, should be adjusted to the temperature of the last barrel zone.
Calibrator Temperatures
Calibrators have multiple zones that can be controlled individually for temperature. Generally, the temperatures range between 105°F and 212°F (40°C and 100°C). The temperature of an individual calibrator zone depends primarily on the thickness of the multi-wall sheet and the take-off speed. The front calibration zone is usually a lower temperature than the rear zone. At high take-off speeds, regulate the melt inflow zone separately and keep it at a relatively low temperature. If your sheets are uneven, set the temperature of the top calibrator zones hotter than the bottom temperatures.
Heating Device
A heating device, positioned after the take-off section, is equipped with infrared heating elements. If necessary, the multi-wall sheet can be reheated rapidly to eliminate internal stress, which could cause distortion.
Take-off Speeds
The maximum take-off speed of the sheet unit is usually limited by the calibration process and depends primarily on thickness of the multi-wall sheet and/or the weight per unit area.
| Table 1. Take-off speeds for various sheet thicknesses and weights per unit area | ||
| Sheet thickness in inches (mm) | Weight per unit area in lb/ft² (kg/m²) | Take-off speed in ft/min (m/min) |
| 0.178 (4.5) | 0.205 (1.0) | 6.6 to 13.2 (2.0 to 4.0) |
| 0.236 (6) | 0.266 (1.3) | 5.9 to 11.6 (1.8 to 3.5) |
| 0.394 (10) | 0.348 (1.7) | 4.3 to 9.9 (1.3 to 3.0) |
| 0.630 (16) | 0.553 (2.7) | 3.3 to 5.2 (1.0 to 1.6) |
| 0.984 (25) | 0.778 (3.8) | 2.0 to 3.3 (0.6 to 1.0) |
UV Stabilization
For outdoor applications and other applications that require increased UV stability, additional weathering protection is necessary. BMS developed Makrolon® DP1-1852 polycarbonate specifically for this purpose. Typically applied by coextrusion, Makrolon® DP1-1852 polycarbonate matches the processing properties of Makrolon® 1243 and 1143 polycarbonate resins. It provides excellent UV protection if the thickness of the coextruded layer is sufficient—usually 0.002 to 0.004 inches (0.05 to 0.10mm). This will vary depending on individual climate zones and expected weathering performance.
Product Stop/End of Production
In the case of a production stop, the extruder should be run until it is empty of the polycarbonate resin. Temperatures of all parts that come into contact with the polycarbonate melt (extruder barrel, screen exchanger, melt pump, adapter, and die) should be maintained at 320°F to 340°F (160°C to 170°C). If the extruder will be cleaned at the end of production, run the extruder until empty with high-viscosity polyethylene. This makes any subsequent mechanical cleaning much easier.
Process Optimization
Optimizing extrusion line processes typically involves increasing production speed while, at the same time, meeting quality criteria such as:
- Optical quality (cleanliness, minimal surface defects)
- Minimal transverse waviness
- Compliance with dimensional and weight tolerances
Some general recommendations can help you optimize your extrusion line:
- Keep melt temperatures as low as possible.
- Maintain a precise width setting of the upper and lower lip gap of the die.
- Minimize the space between the die and the calibrator.
- Set and maintain the partial vacuum in the first calibration zone as low as possible (boundary condition: adequate calibration).
- Set and maintain the temperature of first calibration zone as low as possible (boundary condition: adequate calibration).
If you have any questions about using Bayer polycarbonates on your extrusion equipment, you can reach the technical team at BMS using the Contact form.
