Reference Table of Drying Temperature and Time for Common Plastic Raw Materials
Reference Table of Drying Temperature and Time for Common Plastic Raw Materials In injection molding production, moisture in raw materials is the main inducement for silver streaks, bubbles, water marks and hydrolytic embrittlement of plastic parts. Different plastic raw materials have great differences in moisture absorption characteristics. Most general plastics have low water absorption, while engineering plastics and special plastics can easily absorb water vapor in the air and must be dried in accordance with specifications before molding. Setting appropriate drying temperature and duration can control the moisture content of raw materials within qualified range, and avoid yellowing, degradation and particle agglomeration caused by excessive temperature or overlong drying time. This table summarizes reference parameters for drying common plastic raw materials in injection molding industry, together with notes for drying operations for quick reference in workshop process.
1. Reference of drying temperature and time for common raw materials
| Raw Material | Drying Temperature | Drying Time | Remarks |
|---|---|---|---|
| ABS | 80~85℃ | 2~4 hours | Suitable for plastic parts such as home appliance shells. Dehumidifying dryer is recommended for transparent and high-gloss parts, and the moisture content shall be controlled within 0.1%. |
| HIPS/PS | 70~75℃ | 1.5~2 hours | Sealed original materials generally do not need drying. Drying is recommended when reclaimed runner materials are added or produced in high humidity environment. |
| PC | 110~120℃ | 3~5 hours | PC absorbs water quickly. Transparent parts must be fully dried. The dried raw materials should be used up within 4 hours to prevent re-moisture absorption. |
| PC/ABS Alloy | 90~100℃ | 3~4 hours | It takes into account the characteristics of the two materials. Extend drying time for precision appearance parts. |
| PA6 | 90~100℃ | 4~6 hours | Nylon has extremely strong moisture absorption. Vacuum dehumidifying drying is preferred. Appropriately extend drying time for thick-wall and glass fiber reinforced versions. |
| PA66 | 100~105℃ | 4~6 hours | The temperature shall not exceed 110℃, otherwise the material is easy to turn yellow and the toughness decreases. |
| POM | 80~85℃ | 2~3 hours | POM cannot resist high temperature. Long-time high-temperature baking is forbidden to prevent raw material decomposition and irritating gas. |
| PBT | 120~130℃ | 3~4 hours | Polyester materials are easy to hydrolyze at high temperature, and dehumidifying drying is the first choice. |
| PET | 130~140℃ | 4~6 hours | It has strict requirements for moisture content. Thin-wall and high-strength products must be fully dried. |
| TPU | 75~85℃ | 2~3 hours | The drying temperature of soft TPU cannot be too high to avoid particle adhesion and agglomeration. |
| PMMA | 70~80℃ | 2~4 hours | Moisture in acrylic raw materials will directly cause internal white haze inside products. Transparent parts have high requirements for drying control. |
| PP, PE | 60~70℃ | 0.5~1 hour | Drying is basically unnecessary under conventional environment. Simple low-temperature drying is recommended in humid rainy season. |
| PEEK | 150~160℃ | 3~4 hours | It is special high-temperature engineering plastic. Vacuum drying is adopted to remove deeply adsorbed moisture. |
2. Selection points of drying equipment
For low moisture absorption raw materials such as PP, PE and HIPS, ordinary hot air dryer can meet the requirements. For high moisture absorption materials such as PC, PA, PBT, PET and TPU, dehumidifying dryer or vacuum dryer is recommended. Ordinary hot air drying can hardly reach target moisture content under high humidity environment. The thickness of raw material layer during drying shall be controlled at 30 to 40 millimeters. Too thick material layer leads to uneven heating, the surface layer is dried while moisture at the bottom cannot be discharged. Maintain stable circulating hot air volume to ensure uniform temperature inside the oven.
3. On-site control notes for drying operations
The drying temperature cannot be increased blindly. If the temperature exceeds the temperature resistance limit of raw materials, polymer degradation will occur, resulting in reduced product strength and discoloration. After drying, moisture-absorbing raw materials should be produced within the specified time limit. Materials such as nylon and PC will quickly absorb water again when exposed to air, and need re-drying after secondary moisture absorption. The higher the proportion of reclaimed runner materials, the longer the drying time needs to be extended. Crushed runner materials have larger surface area and absorb water vapor more easily. Check whether the raw material package is damaged before drying. Raw materials with damaged packages have higher risk of moisture absorption. Sampling test of moisture content is preferred. Different materials are prohibited from drying in the same oven to prevent cross-contamination of raw material dust and conflict of temperature requirements of different materials. Clean the filter screen of dryer regularly. Blocked filter screen will lead to insufficient air volume and reduce drying efficiency.
4. Rapid defect judgment and adjustment
If silver streaks and bubbles appear during production, check the drying status of raw materials first and confirm whether temperature and duration meet standards. Yellowing and brittle cracking of products are mostly caused by excessively high drying temperature or overlong baking time. It is necessary to lower temperature and shorten drying time. White haze on the surface of transparent parts is mostly caused by excessive moisture of PC and PMMA, increase dehumidifying drying time.
Summary
Drying of plastic raw materials is the pre-process foundation of injection molding. The same set of parameters cannot be applied universally. Weak moisture absorption raw materials such as PP and PE can simplify drying process. Engineering plastics such as nylon, PC and polyester must strictly implement dehumidifying drying standards. Adjust the drying scheme combined with raw material type, product wall thickness, glass fiber filling and on-site environmental humidity, control raw material moisture content, reduce molding defects related to moisture, stabilize the appearance and mechanical properties of plastic parts, and reduce the reject rate in trial production and mass production.
