Automated medical device coating systems are a versatile, high-throughput platform made to apply a protective layer of coatings to medical device surfaces. These systems are made up of different components or modules. The most common modules are the surface preparation module, coating application module, curing module, and more.
The system’s coating application module applies or allows a controlled deposition of liquid medical coating onto the device surface. There are several different types of coating application modules, such as dip coating, spray coating, meniscus coating, etc.. The one used is chosen based on the specific device type and requirements.
Dip coating machines (present as application modules) are used frequently in high-volume, medical device manufacturing lines. This is due to the method’s ease of use, reliability, compatibility with a variety of coating chemistries, and more. Such a module is ideal for medical devices such as catheters, guidewires, and introducers.
Drawing on Hydromer®’s 40 years of experience in advanced coatings, this article explores the benefits of dip coating equipment (otherwise known as the dip coating module) when used for an automated medical coating system. Our goal is to understand this coating equipment better. We will dive deep into different components, types, and critical parameters of a dip coater. If you are involved in medical device production or engineering you will want to read this article to the end.
Dip Coating Equipment For Automated Medical Device Coating Systems: Overview
Medical devices can be coated using a variety of application methods. These include dip, spin, spray, flow, meniscus, etc. The right choice among them depends upon the coating chemistry, the device’s complexity, the compatible curing method, and more.
The most popular coating application process in automated equipment is dip coating. In this process, a substrate is immersed in a liquid coating solution at a controlled speed. Both the immersion and withdrawal speeds need to be controlled precisely for the best results. As such, for this purpose, an automated machine known as the dip coater is used.
A dip coater enhances the performance of semi- or fully-automated coating systems by enabling repeatable, production-ready coatings within a compact footprint.
How Does Medical Dip Coating Equipment Work?
Dip coating is one of the simplest methods used to apply coatings to devices. It is based on the Landau-Levich regime. This describes the formation of a thin, uniform liquid film on the surface of a solid substrate withdrawn from a bath of solution at a consistent speed.
Steps of the Dip Coating Process
In general, the dip coating process includes three steps:
- Immersion: A substrate is carefully cleaned and dried, then immersed in a bath of coating at a controlled speed. As soon as it is immersed, the liquid coating starts wetting its surface.
- Dwelling: In this step, the substrate is held inside the bath to ensure the coating solution is spread across the entire surface.
- Withdrawal: Several high-performance servos and actuators are used to pull the substrate at controlled speeds. During this withdrawal, the draining and entertaining forces ensure the application of a thin layer of coating on the surface of the substrate. The Draining force removes the excess liquid solution and draws it back towards the bath. Similarly, the entertaining forces work to retain coating on the surface.
Any failure to maintain consistency during these steps can cause runs, edge thickening, un-uniformity, and beading.
Critical Process Parameters in Dip Coating Equipment
There are key factors affecting the film thickness and properties of the applied coating. These include withdrawal and immersion speeds, coating solution viscosity, surface tension, and gravity. All parameters except gravity can be precisely controlled within the automated coating equipment to achieve the desired film thickness.
Here is a set of critical process parameters in dip coating:
- Withdrawal Speed: The most important parameter controlling the coating thickness. Typically, it is maintained between 0.1 and 500 mm/min for optimal results. This rate will depend on the specific requirements.
- Dwell Time: The total time the substrate remains immersed in the bath drastically affects the coating thickness. If the time is too short, it results in incomplete wetting, air bubbles, and more critical problems.
- Viscosity: Coating solution viscosity determines how liquid is entrained during withdrawal. Lower viscosity produces thinner films. Higher viscosity results in thicker coatings. Advanced dip coating equipment feature temperature-controlled tanks, inline viscometers, and closed-loop, solvent replenishment. These all help maintain optimal viscosity.
- Surface Tension: Film stability and leveling are strongly influenced by surface tension. High surface tension produces a thin, smooth coating.
- Surface Energy: When it comes to substrate surface, the surface energy is used to ensure proper wetting and adhesion. If the surface energy is low, it may lead to poor wetting and peeling.
- Temperature: The temperature of the coating solution and the dip coater must be precisely maintained to prevent issues with viscosity, evaporation, and chemical stability. Even small variations of ±1–2°C can significantly affect coating thickness.
Key Components of Dip Coating Equipment in Automated Medical Devices
A dip coater is a precision-controlled module within semi- or fully-automated coating systems. It consists of several key submodules, which are discussed in more detail below.
1. Coating Reservoir
The coating reservoir, or dip tank, stores the coating solution and maintains its chemical stability. The substrate is immersed in this solution during the medical device coating process.
At Hydromer®, Inc., we use stainless steel, glass-lined, or fluoropolymer-lined reservoirs for liquid coatings. Stainless steel is standard, while glass- or PTFE-lined reservoirs are used for aggressive chemistries.
2. Motion Control System
The motion control system manages precise immersion and withdrawal of substrates. This system uses servo motors, linear actuators, encoders, and PLC modules. It is the core subsystem of a dip coater.
Its primary function is to ensure controlled vertical movement of the substrate using programmable motion profiles. The PLC and HMI serve as the control center of the dip coater.
3. Coating Solution Management System
Maintaining the chemical and physical stability of the liquid coating is essential for precise application. Advanced dip coaters include micron-level filtration, recirculation pumps, and viscosity control systems. This system also ensures contamination-free storage of the liquid coating.
4. Part Holding System
The part holding system is designed to ensure correct orientation and uniform coating application. The dip coater uses racks and trays to hold parts or substrates. The parts are precisely transferred between modules by the motion control system.
5. Environment Control System
Both the internal and external environments around the dip coater must be maintained at specified levels to prevent dust and airborne contamination.
The dip coater employs HEPA-filtered laminar airflow, temperature and humidity sensors, and an airtight chamber to maintain a controlled environment.
6. Safety System
Solvent-based coating chemistries generate hazardous fumes from alcohols, ketones, and other volatile compounds (VOCs). Therefore, all dip coaters must include a safety or exhaust system to protect operators.
Such a safety system must support immediate interlocks and emergency stops as required. Compliance mandates the inclusion of such systems.
Inline vs. Batch Dip Coating Machines: Which is Best?
Inline and batch are the two types of dip coaters that are used in a semi- or fully-automatic medical coating system.
1. Batch Dip Coaters
Batch dip coaters are ideal for small-scale production. They coat groups of parts in each cycle. They typically operate as standalone units and are mainly used for R&D or coating small batches of medical devices.
All parts are mounted on racks and trays simultaneously and moved with precision. However, even while the immersion and withdrawal speeds are controlled, variations may occur in large-scale applications.
2. Inline Dip Coaters
Inline dip coaters can be fully integrated into automated production lines. They use conveyors or transport systems to coat parts continuously. This makes them ideal for large-scale production.
An inline dip coater can process hundreds or thousands of pieces per hour. As such, they offer much higher throughput than batch systems. They are the best choice for scalable production.
Compatible Coating Chemistries For Dip Coating Equipment
Various medical device coatings are available for different applications, and most liquid or powder-based coatings are compatible with dip coaters. Selection of a coating should be based on viscosity, volatility, reactivity, and wetting behavior for optimal results.
Below are the most popular coating chemistries for a medical device dip coating equipment:
- Medical Device Hydrophilic Coatings: These lubricious coatings are widely used due to their multifunctional benefits. They can be customized for drug-eluting, antimicrobial, and thromboresistant properties. These are fully compatible with dip coaters as part of a larger hydrophilic coating system.
- Silicone Coatings: Silicone coatings provide smooth, safe insertion and navigation for medical devices. Their moderate viscosity makes them suitable for dip coating applications.
- Hydrogels: These coatings have a three-dimensional structure composed of natural or synthetic polymers. They can retain significant amounts of water or biological fluids, depending on application requirements.
Hydromer®: Hydrophilic Medical Coating Manufacturer and Coating Equipment Supplier
Hydromer®, Inc. has over 40 years of experience manufacturing and supplying advanced hydrophilic coatings. In addition, we offer a full portfolio of coating equipment, which includes high-performance semi- and fully-automated coating systems, friction testing machines, and custom-built equipment.
We have served startups, OEMs, and CMOs for decades. Our automated systems integrate with multiple coating application methods and curing processes, including Hydromer®’s proprietary UV curing technology, HydrUV™.
Our goal is to enable our customer to achieve efficient, high-volume device production. Hydromer® collaborates closely with clients, providing support throughout the entire product lifecycle. We also offer a full range of coating services, including contract R&D, coating formulation, analytical testing, and more.
Medical Coating Equipment Available From Hydromer®, Inc
Our two most popular automated coating applications solutions are:
- Hydrophilic Coating System: This automated system features integrated UV curing and is designed for applying hydrophilic coatings to medical devices. It requires only one or two operators and supports an annual capacity of 200,000 to 300,000 units.
- Fully Automated Coating System: This end-to-end solution is suitable for industrial applications and compatible with various medical-grade coatings. It requires a single operator and is ideal for large-scale production of complex devices such as catheters and guidewires.
- Friction Testing Equipment: Through years of manufacturing experience, we have developed a high-performance vertical and desktop friction tester. It is compliant with the industry standard YY/T 1898-2024. The equipment has been proven to measure the lubricity and durability of hydrophilic coatings accurately.
To learn more about Hydromer automated coating systems, visit our coating equipment product page or contact us.
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