Secondary Processing Technology of Medical Injection Molding Parts

Medical injection molded parts often require secondary molding after extrusion, injection molding, surface treatment and other procedures are completed. At present, the commonly used secondary processing technologies for medical injection molded parts include connection, assembly, punching, thermoforming, printing, and laser engraving, surface modification, tube end forming, butt welding of tube body.

Ⅰ. Connection of medical injection molded parts

1. Adhesive connection

Adhesive sticks to the surface of the plastic molded parts to complete the connection, which is a widely used bonding method. It has the characteristics of simple process, continuous stress distribution, light weight, or sealing, and low temperature in most processes. Gluing is particularly suitable for the connection of different materials, different thicknesses, ultra-thin specifications and complex components. This is a bonding technology with the fastest development in modern times and a wide range of applications.

Advantages: uniform stress distribution, maximum fatigue resistance, (vibration absorption); good sealing.

Disadvantages: limited assembly speed, toxic gas may be generated during operation, uncertainty in connection strength, difficulty in recovery, and surface treatment.

2. Solvent connection

The solvent dissolves the surface of the plastic part to mix the materials between the surfaces. When the solvent evaporates, a connection is formed.

Advantages: cheap, uniform stress distribution, weight reduction;

Disadvantages: limited assembly speed, toxic gas, uncertainty in connection strength.

3. Hot melt welding

A heating plate or a heating wire is used to melt the butt surface of the plastic part to be welded, and then the butt surface is connected by pressure to achieve the purpose of firm welding. Hot-melt welding is often used in the production of medical plastic molding products and medical packaging bags with a circular welding surface. For example, the mouth of medical plastic infusion bottles, medical plastic or paper-plastic composite packaging bags, etc.

4. High frequency welding

High-frequency welding of plastic injection molding medical parts is the use of thermoplastics between high-frequency electrodes due to molecular polarization and electric field changes. Friction occurs between the molecules to convert electrical energy into heat. The plastic itself generates heat until it melts, thereby achieving the purpose of connection. High-frequency welding is often used in the production of blood bags, drainage bags, urine bags and other medical bags and the sealing of some medical packaging bags.

① Advantages: uniform heating inside the welding material; fast welding speed; beautiful welding surface. For large-area welding; special-shaped welding has obvious advantages.

② Disadvantages: Material limitation-PVC is the main material.

5. Ultrasonic welding

Ultrasonic welding has been used in the production of hemodialysis machines, plasma collectors and other medical products, such as the welding of the cup body and gland of the plasma apheresis centrifugal separator. This welding method is used to replace chemical bonding and solve the problem of high-speed centrifugal cups. The melting of the adhesive caused by the rotation has achieved good results. In addition, this method is often used in the manufacturing process of medical protective masks, protective clothing, infusion sets, and balloon dilatation catheters.

① Advantages: no curing time, clean air, high efficiency.

② Disadvantages: limited by compatibility and thermoplastics, noise, area and shape limitations;

③ The main factors affecting the welding effect:

A. For materials with water absorption characteristics such as nylon, polycarbonate, polysulfone, etc., they should be treated before welding to ensure that the product is welded firmly;

B. Put it in a sealed environment;

C. Bake the other parts before ultrasonic welding;

D. Ultrasonic welding immediately after injection.

④ The scope of application of different materials

6. Vibration welding

Vibration welding has many advantages such as fast welding speed, automatic adjustment of welding temperature, no overheating of the weld, and few impurities in the weld area. It is widely used in medical device plastic injection molding products. It is especially suitable for long linear joints that are not easy to achieve by ultrasonic welding and joints that require a long time to complete for hot plate welding.

Ⅱ. Plug-in connection of medical injection molded parts

1. Plug-in connection method:

Generally refers to the connection of plastic pipes and joints; the connection is realized by tolerance matching and bonding, and is mostly used for pipeline products.

Advantages: Convenient connection, suitable for mass production, and there is no limit to the length of the connecting piece.

Disadvantages: suitable for the connection of pipe fittings.

Factors affecting external plug connection method:

①The inner diameter, wall thickness, tolerance and hardness of the plastic pipe.

③The maximum and minimum diameter of the connecting part of the joint and the plastic pipe.

④There is no axial joint film line at the end of the joint.

⑤The height of the joint film line is too high, which is easy to cause leakage.

⑥Formulation of connection technology, method of interspersing joints, quality of cassette, and tools for tightening cassettes.

2. Molding of multiple parts

Rotating, molding threads, tapping threads, hot air, vibration, induction, electromagnetic, laser, fasteners, inserts, hinges, hot plates, snaps, etc.