PVC Injection Molding
PVC material has special properties, and special attention needs to be paid to temperature control, mold design, and stability requirements during the injection molding process.
Medical Device Injection Molding Requirements
Medical device injection molding is the mainstream process used by injection molding manufacturers to produce medical equipment, bringing extremely high hygiene and precision standards. Its main process is to melt medical-grade plastic, then reshape and mold it into the shape required for medical devices. This additive manufacturing process produces sturdy and durable medical injection parts with high-quality surface finish and high dimensional accuracy. In addition, due to the lower processing cost of plastic parts, this technology is suitable for large-scale production of disposable medical devices, while reducing the production cost of injection molding. In addition, PVC injection molding accounts for as much as 28% of the manufacturing in the medical field.
The Advantages of Injection Molding in The Medical Device
Medical device injection molding is an automated process that enables the rapid manufacturing of components for medical devices. Its advantages surpass other additive manufacturing technologies in the same industry, such as plastic extrusion, which include:
- Meet Industry Standards
Components manufactured by injection molding using the medical device are suitable for the medical industry because their high quality meets regulatory requirements. All devices must meet a series of safety, aseptic, and cleaning requirements established by the FDA. Unlike metals and other materials, these special plastics are easy to clean and disinfect, resistant to pollution, and have low precision processing requirements, making them very suitable for the medical industry.
- Compatibility with Multiple Materials
The medical device injection molding process provides mechanics with a variety of materials to choose from. This technology applies to plastics, fibers, composite materials, etc. However, even though we have streamlined the materials required for plastic injection molding in the medical industry, this process is compatible with almost all medical-grade plastics.
- High Precision and Accuracy
The medical industry requires its device to have excellent dimensional accuracy because it needs to handle various internal structures of blood and the human body. A simple deviation of a few millimeters and inches can pose serious risks to patients, meaning that injection molding is very suitable for achieving maximum dimensional accuracy and strict tolerances in plastic manufacturing. In addition, as an automated process, the error caused by human influence is smaller, which eliminates the serious consequences caused by external interference.
- Very Little or No material Waste
Like any manufacturing technology, injection molding of the medical device generates waste – during the manufacturing of parts, this process releases some excess waste. Compared to other technologies, the advantage of this technology is that it allows you to regrind and melt these excess parts, and reuse them for the manufacture of other parts, reducing waste and costs. Therefore, the waste generated after manufacturing medical prototypes can be almost negligible.
- Strength and Durability
The special plastics used for manufacturing medical injection components must combine significant mechanical properties related to strength, stiffness, and durability. The key to designing components for the healthcare sector is to avoid using fragile plastics that are prone to breakage. Instead, use impact-resistant and high-strength thermoplastic materials that will serve their creative purposes for the long term.
- Ability to Withstand Sterilization Conditions
Many medical devices require sterility, meaning they do not contain any pollutants or microorganisms that may cause harm to patients. That is to say, the sterilization process involves exposing these medical devices to extreme conditions, such as; High temperature, radiation, or chemicals. Therefore, even after exposure to these extreme environments, plastic polymers used for manufacturing instruments that require sterilization must maintain their dimensional accuracy and not change.
Characteristics and Requirements of Medical Device Injection Molding
With the continuous progress of medical technology and changes in market demand, medical device injection molding is developing towards higher precision, efficiency, and intelligence. Meanwhile, with the application of new materials and technologies, the improvement of the performance of injection molding molds for medical device has become increasingly important, including:
- Simple and Beautiful Appearance Design: The basic requirements for modern medical product design are simplicity and aesthetics. Medical device injection molding molds should pursue simplicity in product design, color, material, and process.
- High Precision: For designers of injection molding molds for medical devices, it is crucial to grasp the accuracy of plastic part dimensions and mold dimensions.
- Easy to Operate and Maintain: Mold design should consider the level of cognitive ability of different users, and the operation should be from the user’s perspective, easy to understand， and remember, while ensuring that the product is durable, easy to use, and maintain.
Common Plastic Materials and Applications for Medical Device Injection Molding
Plastic rubber has long become one of the important raw materials for a medical device and pharmaceutical packaging. With the booming development of the industry, various high-performance plastics and technologies applied to medical devices are constantly emerging. In addition to traditional medical plastics such as PP, PVC, PE, silicone rubber, etc., which are commonly used in the medical device industry, some high-performance materials such as polyether ether ketone (PEEK), biocompatible polycarbonate (PC), thermoplastic elastomers (TPE), etc. are important materials for promoting the development of the medical device industry.
- Polyvinyl Chloride (PVC)
Currently, plastic medical products made of PVC account for 25% of the market. Mainly due to the low cost, wide application range, and low processing requirements of PVC. PVC products used in the medical field include hemodialysis tubing, respiratory masks, oxygen tubes, etc.
- Polyethylene (PE)
PE can become an ideal material for artificial hip, knee, and shoulder connectors mainly due to its high impact strength, low friction, stress cracking resistance, and good energy absorption characteristics.
- Polypropylene (PP)
PP materials used in medical devices have high transparency, good barrier properties, and radiation resistance, making them widely used in the medical device and packaging industry. Non-PVC material with PP as the main body is currently a widely used alternative to PVC material.
- Polystyrene (PS) and K resin
PS is the third largest plastic variety, second only to polyvinyl chloride and polyethylene. Due to its lightweight, transparency, easy dyeing, and good molding and processing performance, it is usually used as a single-component plastic for processing and application.
K resin is formed by copolymerization of styrene and butadiene. It is an amorphous polymer, transparent, odorless, non-toxic, with a density of about 1.01g/cm3 (lower than PS and AS). Its impact resistance is higher than that of PS, and its transparency (80-90%) is good. The hot deformation temperature is 77 ℃, and the amount of butadiene content in K material varies. Due to its good fluidity and wide processing temperature range, its processing performance is good.
These two materials are widely used in fields such as pharmaceutical packaging products.
- Acrylonitrile Butadiene Styrene Copolymer (ABS)
ABS is mainly used in medical applications as surgical tools, roller clips, plastic needles, toolboxes, diagnostic devices, and hearing aid casings, especially for some large medical device casings. This depends on the rigidity, hardness, impact resistance, chemical resistance, radiation resistance, and resistance to ethylene oxide disinfection properties of ABS.
- Polycarbonate (PC)
The typical characteristics of PC are toughness, strength, rigidity, and excellent heat resistance for steam disinfection. These characteristics make PC a preferred raw material for making blood dialysis filters, surgical tool handles, and oxygen tanks (which can remove carbon dioxide from the blood and increase oxygen during cardiac surgery). The application of PC in medicine also includes needleless injection systems, perfusion instruments, blood centrifuge bowls, and pistons. Due to its high transparency, PC is also used for myopia glasses.
- Polytetrafluoroethylene (PTFE)
PTFE has good performance, low friction coefficient, and good biocompatibility in plastic materials, making it suitable for making instruments directly implanted into the human body, such as artificial blood vessels.
Maintenance of Injection Molding Machines for Medical Device
Developing good operating habits for medical device injection molding machines is beneficial for improving machine life and production safety.
Before Turning on:
- Check if water or oil is entering the electrical control box. If the electrical appliances are damp, do not turn them on. Electrical components should be blown dry by maintenance personnel before starting up.
- Check if the power supply voltage is within the normal range, generally not exceeding ± 15%.
- Check if the emergency stop switch is intact and if the front and rear safety door switches are functioning properly. Verify if the rotation direction of the electric motor and oil pump is consistent.
- Check whether each cooling pipeline is unobstructed and unobstructed, and inject cooling water into the cooling water jacket at the oil cooler and the end of the machine barrel.
- Check if there is lubricating oil (grease) in each moving part. If it is below the normal level, it is necessary to add enough lubricating oil.
- Turn on the electric heating and heat each section of the barrel. When the temperature of each section meets the requirements, keep it warm for another period to stabilize the machine temperature. The insulation time varies depending on the requirements of different devices and plastic materials.
- Add enough plastic to the hopper. According to the requirements for injecting different plastics, some raw materials are best dried first.
- It is necessary to cover the insulation cover on the cylinder, which can not only save electricity, but also extend the life of the electric heating coil and current contactor, and prevent aging.
During the Operation Process:
- Do not cancel the function of the safety door for convenience.
- Pay attention to the temperature of the pressure oil and ensure that the oil temperature does not exceed the specified range. The ideal working temperature of hydraulic oil should be maintained between 45~50 ℃, generally suitable within the range of 35~60 ℃.
- Pay attention to adjusting the limit switches of each stroke to avoid mechanical damage caused by collisions and friction during machine operation.
At the End of Work:
Before shutting down, the remaining materials inside the machine barrel should be cleaned up to prevent oxidation or long-term thermal decomposition of the remaining materials, which may affect the new materials and increase costs.
- The mold should be opened to keep the elbow mechanism in a locked state for a long time.
- The workshop must be equipped with a lifting device. When assembling and disassembling bulky components such as molds, great caution should be exercised to ensure production safety.
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