Development of modern medical technology has made plastics widely used in the field of medicine. From general pharmaceutical, pharmaceutical packaging, disposable medical devices, to multiple precision and high-tech medical meters, surgical instruments, medical plastics play an important role in improving level of medical technology. Because medical devices have special requirements for hygienic safety, smooth surface, and corrosion resistance, medical plastic injection molding play an important role in production process of their products. Plastic molding is an important indicator to measure level of manufacturing of a country’s medical plastic products, which largely determines quality, efficiency and development ability of new products. With gradual improvement of China’s medical care system, demand for disposable medical device supplies has grown rapidly. Higher requirements are placed on mould manufacturing, product production equipment and processes for medical devices, especially for disposable medical devices.
(1) Strict selection of plastic molding materials
Most disposable medical device products use medical grade polyvinyl chloride (PVC) and polycarbonate (PC). Because PVC has better corrosion resistance than steel, PC has higher hardness, so there are strict requirements for selection of plastic molding materials. It is recommended that domestic plastic mold makers use Sweden-Shengbai S136H or Japan Datong NAR-80 steel, which have strong corrosion resistance and high polishing performance.
(2) Heat treatment process to control hardness
Because medical grade PVC material has good fluidity, parting surface is deformed due to softness of mold material during use of plastic molding, which leads to flash burrs in injection process, so hardness of mold material has high requirements. Heat treatment process used in mould manufacturing process is to carry out quenching and tempering treatment after rough processing of template, and hardness is controlled at HRC32-36; after mold test sample is qualified, hollow type, movable mold and core are vacuum quenched and hardness is controlled at HRC58-620.
(3) Reasonable and accurate structural design
Transparent products should choose hot runners as much as possible to reduce signs of converging; when using cold runners, soft PVC should minimize size of runners; since disposable medical devices are small in size and large in volume, automatic unloading and shear gate should be adopted to ensure production efficiency and quality; disposable medical device products have more transparent tubular parts. In the design, we should pay more attention to gate feeding position and dynamic model Z fixed way to avoid improper selection due to gate position and core fixing method, material flow is uneven during injection, core to be elastically deformed, and product is not uniform or can not be filled. Length of tube shape product should pay attention to adopt appropriate exhaust method. Inlet channel of feed inlet should be constructed according to product forming condition and avoid difficulty of forming products due to gas shut down; mold cooling system should adopt multiple sets of separate cooling channels to reasonably control dynamic mold temperature to control deformation of product.
(4) High precision in mould manufacturing
In manufacturing process of medical plastic products, parting surface is required to be tight. Precision of plastic molding should be ensured by means of equipment processing. Gap of parting surface should be less than 0.01mm, and matching gap between push rod and push tube of ejector system should be less than 0.01mm. Take push plate ejection structure, push plate should ensure a certain hardness.
Fixed mold and dynamic model core of transparent product should be polished to ensure that Ra value is 0.20 or more, and liquid polishing means can be adopted if necessary.
(5) Exquisite injection molding machine and parts selection
Injection molding machine should use a small screw to ensure accuracy of plastic molding, and adopt automatic unloading device. Plastic molding can be used for gas-assisted unloading when mold is ejected. Machine tool installs robot to realize automatic process of product molding to packaging, and minimize pollution link; Injection mechanism of injection molding machine should take closed vacuum feeding, adopt closed storage tank, arrange feeding pipe to each injection molding machine, and install automatic metering vacuum feeding device at injection port of injection molding machine to ensure raw materials not contaminated before enter injection molding machine.
(6) Plastic molding workshop should be cleaned up
Production workshop should be fully enclosed, install high-power air-conditioner ventilator, remove harmful gases in time to ensure workshop constant temperature and air cleaning in the production process. It is strictly prohibited to use mold release agent and rust remover to ensure that product is not contaminated. In the production process, melting temperature should be strictly controlled to avoid excessive temperature of sub-material and long-term residence in the barrel to decompose raw materials to produce harmful gases. When stopping machine, screw and barrel should be cleaned immediately to avoid damage to screw of injection molding machine. Implement GMP standard and strictly follow IS0 9000 quality management system to ensure that there are no problems at all points in production process.
