Selection of Raw Materials for Medical Plastic Injection Molding Parts

 

 

In recent years, the use of Plastic injection molded parts in the medical field has increased significantly. Because these parts come into contact with medications or the human body, the basic requirements for medical plastics are chemical stability and biocompatibility. So, how should one choose plastic raw materials when customizing medical plastic injection molded parts? HUIWEN Plastics lists the following points:

 

1. Polyvinyl Chloride (PVC)

 

PVC is one of the world's most produced plastic varieties. PVC resin is a white or light yellow powder. Pure PVC has a random structure, is hard and brittle, and is rarely used. Different additives can be added depending on the application, giving PVC Plastic Parts different physical and mechanical properties. Adding appropriate amounts of plasticizer to PVC resin can produce various rigid, flexible, and transparent products. Rigid PVC contains little or no plasticizer and has good tensile, bending, compressive, and impact resistance properties, and can be used alone as a structural material. Flexible PVC contains more plasticizer, increasing its flexibility, elongation at break, and cold resistance, but decreasing its brittleness, hardness, and tensile strength. The density of pure PVC is 1.4 g/cm³, while the density of PVC plastic parts with added plasticizers and fillers generally ranges from 1.15 to 2.00 g/cm³.

 

Market estimates suggest that approximately 25% of medical plastic products are PVC. This is mainly due to the resin's low cost, wide range of applications, and ease of processing. PVC products used in medical applications include hemodialysis tubing, breathing masks, and oxygen tubing.

 

2. Polyethylene (PE)

 

Polyethylene plastic is the most widely produced variety in the plastics industry. It is a milky white, tasteless, odorless, and non-toxic glossy waxy granule. Its characteristics include low price and good performance, making it widely used in industry, agriculture, packaging, and everyday industrial applications, holding a crucial position in the plastics industry.

 

PE mainly includes low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHDPE). HDPE has fewer branches on its polymer chains, resulting in higher relative molecular mass, crystallinity, and density. It also has greater hardness and strength, poorer opacity, and a higher melting point, making it commonly used in injection molded parts. LDPE has many branches, resulting in a smaller relative molecular mass, lower crystallinity and density. It offers better flexibility, impact resistance, and transparency, and is commonly used in blown film production, making it a widely used alternative to PVC. HDPE and LDPE can also be mixed depending on performance requirements. UHDPE possesses high impact strength, low friction, stress cracking resistance, and good energy absorption properties, making it an ideal material for artificial hip, knee, and shoulder connectors.

 

3. Polypropylene (PP) Polypropylene is colorless, odorless, and non-toxic. It resembles polyethylene in appearance but is more transparent and lighter. PP is a high-performance thermoplastic with advantages such as low specific gravity (0.9 g/cm³), non-toxicity, easy processing, impact resistance, and flexural strength. PP has wide applications in daily life, including woven bags, films, turnover boxes, wire shielding materials, toys, car bumpers, fibers, washing machines, etc. Medical-grade PP has high transparency, good barrier properties, and radiation resistance, making it widely used in medical equipment and packaging. Non-PVC materials based on PP are currently widely used alternatives to PVC.

 

4. Polystyrene (PS) and K resin

 

PS is the third largest plastic after polyvinyl chloride and polyethylene. It is usually processed and used as a single-component plastic. Its main characteristics are light weight, transparency, easy dyeing, and good molding and processing performance, so it is widely used in daily-use plastics, electrical parts, optical instruments, and stationery. However, it is hard and brittle with a high coefficient of thermal expansion, which limits its engineering applications. In recent decades, modified polystyrene and styrene-based copolymers have been developed, overcoming some of the shortcomings of polystyrene. K resin is one such example.

 

K resin is a copolymer of styrene and butadiene. It is an amorphous polymer, transparent, odorless, and non-toxic, with a density of approximately 1.01 g/cm³ (lower than PS and AS). It has higher impact resistance than PS, good transparency (80-90%), and a heat distortion temperature of 77℃. The hardness varies depending on the amount of butadiene in K resin. Due to its good flowability and wide processing temperature range, K resin has excellent processing performance.

 

Its main applications in daily life include cups, lids, bottles, cosmetic packaging, hangers, toys, PVC substitutes, food packaging, and pharmaceutical packaging.

 

 

Qingjin Portable Dental X-ray Machine

 

5. ABS, Acrylonitrile Butadiene Styrene Copolymers

ABS possesses certain rigidity, hardness, impact resistance, chemical resistance, radiation resistance, and resistance to ethylene oxide sterilization. ABS is primarily used in the medical field for surgical instruments, roller clamps, plastic needles, tool cases, diagnostic devices, and hearing aid housings, especially for the housings of some large medical devices.

 

6. Polycarbonate (PC) PC's typical properties include toughness, strength, rigidity, and resistance to heat steam sterilization. These characteristics make PC a preferred choice for blood dialysis filters, surgical tool handles, and oxygen cylinders (in cardiac surgery, these instruments remove carbon dioxide from the blood and increase oxygen). PC's medical applications also include needle-free injection systems, perfusion instruments, blood centrifuge bowls, and pistons. Due to its high transparency, it is commonly used in eyeglasses for nearsightedness.

 

7. PTFE (Polytetrafluoroethylene) Polytetrafluoroethylene resin is a white powder with a waxy, smooth, and non-sticky appearance. It is an important type of plastic. PTFE possesses superior properties unmatched by most thermoplastics, hence its nickname "King of Plastics." Its coefficient of friction is among the lowest of plastics, exhibiting excellent biocompatibility, making it suitable for manufacturing implantable devices such as artificial blood vessels.

 

HUIWEN Plastics is a group enterprise specializing in mold design, manufacturing, and injection molding for many years. The company focuses on providing customers with complete solutions, from product design, mold manufacturing, injection molding and assembly, to after-sales service. Its products are widely used in household appliance housings and accessories, medical device injection molding parts, and medical molds.