When it comes to liquid rubber emulsion dipping products, a series of process steps need to be completed to ensure proper molding, vulcanization and surface treatment to meet customer needs in the final application.
Dip molding can manufacture durable medical equipment parts of various shapes, sizes and wall thicknesses, including probe covers, bellows, neck seals, surgeon gloves, heart balloons and other unique parts.
Natural rubber has excellent resilience and high tensile strength, but it also carries a protein that can cause allergic reactions in the human body. In contrast, synthetic neoprene and synthetic polyisoprene do not cause allergies. Neoprene can withstand the test of many factors; it is resistant to fire, oil (medium), weathering, ozone cracking, abrasion and flex cracking, alkali and acid resistance. In terms of feel and flexibility, polyisoprene is a close substitute for natural rubber and has better weather resistance than natural rubber latex. However, polyisoprene does sacrifice some tensile strength, tear resistance, and compression set.
The term “impregnation” relates to the operation in the form of impregnation. In fact, as the sequence is executed, the table will be immersed in the material. It is very important to ensure that the rubber formulation complies with the FDA medical device guidelines and requirements.
The impregnation process can be characterized as a conversion sequence: the rubber is converted from a liquid to a solid, and then chemically converted into a vulcanized molecular network. More importantly, the chemical process transforms the rubber from a very fragile film into a network of molecules that can be stretched and deformed, and still return to its original shape.
The solidification process is not always necessary for all “dipping” processes, but it is critical to our processing sequence. Rubber can be changed from liquid to solid by air drying, but this takes a long time. Some thin-walled parts are produced in this way. The solidification process uses chemicals to force this physical state to change.
The coagulant is a mixture or solution of salt, surfactant, thickener, and release agent in a solvent (usually water). In some processes, alcohol can also be used as a solvent. The alcohol evaporates quickly and there is little residue. Some water-based coagulants require the help of an oven or other methods to dry the coagulant.
The main component of the coagulant is salt (calcium nitrate), which is an inexpensive material that provides the best coagulation uniformity in the impregnated form.
The surfactant is used to wet the impregnated form and ensure that a smooth, uniform coating of coagulant is formed on the form.
A release agent, such as calcium carbonate, is used in the coagulant formulation to help remove the cured rubber part from the dipped form.
The key to coagulant performance includes uniform coating, rapid evaporation, material temperature, entry and recovery speed, and easy modification or maintenance of calcium concentration.
This is the stage where the rubber changes from liquid to solid. The chemical agent that promotes coagulation, the coagulant, is now applied to the impregnated form and is dry.
The form is “placed”, or immersed in a liquid rubber tank. When the rubber comes into physical contact with the coagulant, the calcium in the coagulant will cause the rubber to become unstable and change from liquid to solid. The longer the model is immersed, the thicker the wall. This chemical reaction will continue until all the calcium is consumed from the coagulant.
The key to latex dipping includes inlet and outlet speed, latex temperature, uniformity of the coagulant coating, and control of the pH, viscosity and total solids content of the rubber.
The leaching process is the most effective stage for removing unwanted water-based chemicals from the final product. The best time to remove unwanted materials from the impregnated film is leaching before curing.
The main material components include coagulant (calcium nitrate) and rubber (natural (NR); neoprene (CR); polyisoporene (IR); nitrile (NBR)). Insufficient leaching can lead to “sweat”, sticky films on the finished product, and increased risk of adhesion failure and allergic reactions.
The key to leaching performance includes water quality, water temperature, residence time and water flow.
This step is a two-step activity. The water in the rubber film is removed, and over time, the temperature of the oven will activate the accelerator and begin the curing or vulcanization process. When optimizing the best physical properties of different types of rubber, curing time and curing temperature are the key.
There are many options for treating the surface of the dipped parts so that the parts will not stick. Options include powdered parts, polyurethane coating, silicone wash, chlorination and soap wash. It’s about what customers want or need to make their products successful.
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Post time: Aug-16-2021
