In manufacturing environments that use dip coating, compliance with VOC (Volatile Organic Compound) regulations is an unavoidable challenge. To reduce environmental impact while meeting regulatory standards, two primary approaches are commonly used:
Fundamental measures, which include changing the coating material itself, and
treatment-based measures, which control or process VOC emissions after they occur.
This article explains the main VOC countermeasures in dip coating and outlines practical methods for implementation.
Switching Coatings to Comply with VOC Regulations
Fundamental Measures That Eliminate Emissions at the Source
The most effective way to fundamentally reduce VOC emissions from coating solvents is to replace conventional coatings with materials that contain little or no VOCs. Changing the coating material helps eliminate the need for exhaust treatment running costs and directly contributes to improving the working environment.
Types of Low-VOC Coatings and Their Characteristics
The main low-VOC coating options used for VOC control are as follows:
- Water-based coatings
It uses water instead of organic solvents (VOC) as the primary component. This is the most common alternative, but drying often takes longer, potentially requiring a larger drying oven and tighter temperature control. - High-solid coatings
It reduces solvent content by significantly increasing the ratio of resin solids. While comparable coating performance to solvent-based types is easier to maintain, the viscosity tends to be higher, making dip-coating condition adjustments (e.g., withdrawal speed) more critical. - Powder coatings
It contains no solvent at all, so VOC emissions are zero. However, dip-coating requires specialized immersion tanks designed for electrostatic powder application as well as curing equipment, often resulting in significant capital investment.
How Should Exhaust Treatment Be Managed in Dip Coating?
Option for Maintaining Current Quality
In many cases, switching from solvent-based coatings to low-VOC coatings is difficult due to accumulated expertise, established process know-how, or product quality requirements. In such situations, emission treatment systems are an effective solution that enables regulatory compliance without changing the existing dip coating process or coating material.
This approach focuses on neutralizing only the VOC gases after they are emitted while keeping the current quality and process unchanged.
Typical Treatment Systems: Combustion and Adsorption
When solvent-based coatings continue to be used, VOC gases in the exhaust stream are typically treated using one of the following two systems:
- Combustion Systems (e.g. RTO, deodorizing furnaces)
Combustion systems heat exhaust gas containing VOCs to a high temperature (typically 700–800 °C) to decompose them into less harmful carbon dioxide (CO₂) and water (H₂O). They offer very high treatment efficiency (over 98 percent) and can handle fluctuations in exhaust gas concentration.
However, installation costs are high, and significant thermal energy is required during operation, leading to higher running costs. - Adsorption Systems
In adsorption systems, VOCs pass through adsorbent materials such as activated carbon or zeolite, where only the VOC components are captured and removed. These systems are relatively simple and have lower initial cost.
However, once the adsorbent becomes saturated, replacement or regeneration is required. Because replacement and regeneration incur maintenance costs and require energy, these systems are generally suited to situations where VOC concentrations are relatively low.
Summary
The optimal VOC control strategy for dip coating depends on the specific circumstances of each company.
If the goal is to fundamentally eliminate VOC emissions, coating material replacement should be considered. If maintaining existing product quality and process conditions is the highest priority, installing an exhaust treatment system is the more suitable approach.
It is essential to compare both advantages and disadvantages of each option, including cost, quality, and environmental impact. The appropriate measure should align with the company’s production system and management strategy.
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