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How Should Oily Plastic Resin Drying Be Done Before Injection Molding?

2026/09/21 By le zhan

How Should Oily Plastic Resin Drying Be Done Before Injection Molding

When volatile, oil-based additives enter the dry-air circulation system, manufacturers should use specialized oil-resistant dehumidifiers for oily plastic resin drying instead of conventional 3-in-1 dryers. Operators should also follow the material supplier’s recommendations when setting the resin temperature and residence time to control oil contamination while maintaining stable, low-dew-point airflow. For applications involving oily plastic resins, the dryer should have enhanced dehumidification capacity and be equipped with an oil-discharge blower and an oil filtration system. The purpose is not only to raise the pellet temperature but also to continuously remove moisture while preventing released oil from contaminating the drying circuit.

Which Additives Make Oily Plastic Resin Drying More Difficult?

The first step in oily plastic resin drying is to identify the source of the oil. The resin itself may not initially contain high levels of oil; in many injection molding facilities, processors introduce various additives during the mixing, color matching, recycling, or production preparation stages.

Common sources of oil include oil-based release agents, diffusion oils, certain flame retardant formulations, and modifying oils or lubricants.

During the heated drying process, the volatile or semi-volatile components of these additives migrate from the pellets into the circulating air. Subsequently, the dehumidifying dryer recirculates this contaminated air back into the system, where it passes through filters, fans, heat exchangers, ductwork, and the dehumidification unit.

Which Additives Make Oily Plastic Resin Drying More Difficult

Oily Plastic Resin Drying Starts With Understanding the Material Formulation

Before starting the drying process, operators should first confirm whether the material contains oily substances or whether someone has mixed them into the material, as these substances may volatilize when heated. This is particularly important when drying equipment that was previously operating normally begins to exhibit oily deposits following adjustments to the formulation or additives. If oily residues build up in the return air ducts, filters, blower assemblies, or dehumidification units, operators should address the problem as part of the oily plastic resin drying process rather than treating it as a routine filter maintenance issue.

Oily Plastic Resin Drying Starts With Understanding the Material Formulation

Why Do Standard Honeycomb 3-in-1 Dryers Become Contaminated?

Traditional compact honeycomb 3-in-1 dehumidifying dryers primarily focus on moisture control. The dehumidification system removes moisture from the return air, reheats the dry air, and then circulates it back through the drying system. This closed-loop design is highly efficient when handling ordinary resins. However, for materials with high oil content, it causes oil vapors and residues to circulate repeatedly within the system.

We understand that oil molecules released during the drying process enter the recirculation system and accumulate on filters, heat exchangers, ductwork, and dehumidification components. This disrupts airflow and reduces the stability of long-term drying.

The oil contamination problem is most severe around the honeycomb and desiccant components. Once oily residues coat the moisture-absorbing surfaces, standard dryers cannot operate properly. Oil contamination may also migrate toward the blower. If residues continue to accumulate, the blower will face increased resistance; in severe cases, this may lead to seizure or mechanical damage.

Why Do Standard Honeycomb 3-in-1 Dryers Become Contaminated

How Should Oily Plastic Resin Drying Be Controlled, and Which Parameters Matter Most?

Effective oily plastic resin drying requires two conditions: stable dehumidification and active oil management.

For dehumidifying dryers that must meet oil-resistance requirements, Topstar employs an expanded dehumidification structure and enhances the processing capacity for makeup air (fresh air) and compressed air. The goal is to ensure that the air entering the drying hopper maintains an extremely low moisture content (i.e., an extremely low dew point) even after coming into contact with an oil-containing process environment.

The key performance parameters for Topstar’s oil-resistant dehumidifying dryers are as follows (Note: The process air dew point may vary depending on the model and configuration):

Makeup-air dew point: as low as approximately −57°C

Process-air dew point at the material: approximately −27°C

However, operators should not focus on the dew point alone. They also need to consider the following three key process parameters.

How Should Oily Plastic Resin Drying Be Controlled, and Which Parameters Matter Most

Three Key Process Parameters and Oil Content Control for Oily Plastic Resin Drying

The drying temperature should follow the recommendations of the specific resin grade and additive suppliers. Simply raising the temperature to accelerate drying may cause additives to volatilize or damage heat-sensitive materials.

  1. The residence time of the material must be sufficiently long:
    to ensure that internal moisture can diffuse out of hygroscopic particles. Simply supplying air with a low dew point does not achieve instant drying.
  2. The airflow through the material bed must remain stable:
    Oil buildup can clog the filters or contaminate the blower, reducing the actual airflow even when the temperature and dew point readings appear normal.
  3. The dew point reflects the dehumidification capacity of the dry air. During prolonged production runs, the dew point should remain stable and should not gradually rise.

Additionally, for oily plastic resins, special attention must be paid to oil accumulation.

Topstar’s oil-resistant 3-in-1 dehumidifying dryer addresses this issue through two specialized features. The blower uses an oil drain port to remove accumulated residue from the blower area. This design helps prevent gradual buildup that could cause sticking or damage the equipment. Furthermore, a high-efficiency oil filter removes oil contaminants from the circulating drying air before they can spread throughout the system. In addition, during actual operation, operators should not only monitor the dryer’s temperature and dew point but also pay attention to the blower’s condition, the degree of filter contamination, airflow stability, and the amount of oil collected at the drain port.

When Is an Oil-Resistant 3-in-1 Dehumidifying Dryer Necessary?

Not all resins containing processing aids require a dedicated oil-resistant dehumidifying dryer. The decision to use one should depend on the material’s characteristics during the heated drying process and the impact on the dryer over time.

The use of an oil-resistant dehumidifying dryer is essential when the following recurring issues occur during the process: visible oily residues in the air circuit, rapid filter contamination, unstable airflow or dew point, the need for frequent blower cleaning, blower jamming, recurring instability in the drying process after the introduction of oily additives, or the long-term, heavy use of oil-containing compounds.

In particular, oil-resistant 3-in-1 dehumidifying dryers are especially suitable when release agents, diffusion oils, flame retardant packages, or modified oils added by the customer release residues sufficient to contaminate conventional closed-loop dryers.

Solving Oily Plastic Resin Drying Problems

Therefore, the optimal drying approach is clear:

Identify the source of oily substances → Follow the resin’s specified drying temperature and time → Maintain an adequate airflow with a low dew point → Continuously remove oil from the air circuit → Verify the resin’s moisture content before molding when quality requirements are stringent.

For ordinary materials, a standard honeycomb rotor dryer is fully adequate. However, for materials that repeatedly release oily contaminants during the drying process, a specialized oil-resistant three-in-one dehumidifying dryer is required. By combining moisture control with oil management, this approach fundamentally resolves the issue. When both consistent injection molding quality and long-term, stable dryer operation are required, this is the most appropriate method for drying oil-containing plastic resins.

 

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