At High Level Medical, we have some of the most highly technical personnel on our team. We know unsupported gloves manufacturing process inside out. Gloves manufacturing is not as complex as some of the high-tech manufacturing, in fact is a relative simple process. The difficulties of gloves manufacturing largely depends on the process control and the understanding each stage of the process. It is imperative for a buyer to be able to source from a manufacturer that can produce a consistent quality at a minimal cost.
Making unsupported disposable gloves is a multi-stage process. Only gloves that meet required Accepted Quality Level (AQL) will be market as medical grade gloves and those that failed the medical grade are generally downgrade to disposable or general use gloves. The quality of gloves will differ based on how the factories treat each manufacturing stage. The illustration below gives an idea to how the unsupported gloves are manufactured today. The differences between manufacturing natural rubber and synthetic gloves are minimal. The required processes are relatively the same albeit different dipping line would requires different operating parameters.
In this segment, we would like to introduce manufacturing processes to gloves buyers who may or may not understand its each process function. There are no “One Size Fits All” to produce gloves, although the glove may be seem similar outside but the physical properties, glove donning feel, strength, and many more may vastly differ from one manufacturer to another.
The process begins with incoming materials inspection ensuring the latex and chemical are within required specification. Next, latex, chemicals, and color pigments will be compounded accordingly to required gloves specification.
Formers Cleaning and Drying
Unlike traditional dipping line where formers need to be removed from the line to be brushed, new dipping lines today are generally equipped with online brushing mechanism. This process does not only clean the formers but also ensure the quality of the latex adhesion to the formers during latex dipping. When the formers are not cleaned thoroughly, defects such as pin holes can occurs. This presents major quality issue in respect to quality of the barrier protection. Formers are cleaned by acid bath to remove organic materials, then alkaline bath to remove inorganic materials. Formers then would pass through series of brushes to scrub the former surface before rinsing it with clean water. Although the present dipping lines are equipped with online brushing, formers must be taken out periodically for manual cleaning and inspection for any crack that may have formed on the formers. After formers are cleaned, it would be enter a dryer oven before coagulant dipping.
Coagulant Dipping and Drying
This process involves formers to be dipped into coagulant solution primarily consist of calcium nitrate and calcium carbonate. Coagulant can determine the quality of latex adhesion and the thickness of the gloves. Calcium nitrate assists the latex adhesion to the formers, where as calcium carbonate act as former releasing agent during stripping process as well as preventing gloves from sticking to each other. Failure to maintain proper TSC at all time and agitation to prevent sedimentation of ingredients particularly when powder is used in the mixture, could cause weight variation and weak spot on the gloves. After formers dipped into coagulant solution, formers will enter drying oven before proceed to latex dipping.
The formers that are coated with coagulant will now dip into latex tank that contains compounded matured latex. Traditionally, manufacturers only dipped once but in the recent year newer dipping lines enable manufacturer to dip twice, hence reducing the risk of pin holes. Regardless single-dipping or double-dipping, consistencies in the total solids (TSC), dry rubber content (DRC), temperature, and latex agitation flow should be maintained at pre-determined uniform level. Failure to maintain consistency would cause a host of defects such as weight variation and pin holes.
Formers that coated with latex will now enter a pre-vulcanization oven where latex film forming takes place when the small particles of the polymer come together and fuse into a coherent mass. One condition that absolutely important in this process is the Minimum Film Forming Temperature (MFFT), this is the minimum temperature at which the polymer particles will coalesce together.
Once all required conditions are met, the liquid latex form on the formers began a transformation into “wet-gel” form. At this point – the “wet-gel” point -- the film will have a measure of strength, although well below that which will eventually be attained. The wet-gel strength is very much dependent on the base polymer as well as the dipping conditions. Natural rubber typically can have good wet-gel strength whilst that of nitrile rubber can be very weak.
During the transformation, water evaporates from the wet film, the volume is shrinking and the particles are forced closer together. During this phase if required conditions are not met, coalescent of polymer will be resisted by the dispersant or surfactant system which is used to keep particles apart during preparation of the compound. However, if the required conditions are met, eventually the forces acting on the particles, as they are gradually pushed together, will overcome these dispersant forces and the particles come into contact. At this stage, the inter-particle boundaries will start to disappear and any substances incompatible with the bulk polymer will be pushed, together with residual water, towards the film surface. Typically, these will include the dispersant, non-rubber content, and other chemicals that were used to compound the latex.
Recent gloves are generally beaded at the cuff. This process does not only provide better aesthetic look to the gloves but also enhance the cuff strength.
This process generally right after the formers exited the pre-vulcanization oven and dipped into temperature regulated water tanks. The latex at this phase is still in the wet-gel form, the non-rubber materials such as the surfactants, colloid stabilizers, coagulant and other components of the system begin forming on the surface of the glove. During this process, formers pass through a series of hot water tank, dissolving out the water-soluble residues and other chemicals. Proper leaching of the gloves will usually improve the strength of the film but not without proper changeover of water to prevent build-up of extracted chemicals. Turbulent flow and increase rate of incoming fresh water would significantly increase the extraction efficiency. Leaching is extremely important for natural rubber gloves because it reduces the protein content on the gloves that would cause allergic reaction to some people.
Main Vulcanization Oven
Vulcanization process is the heart of glove manufacturing, a complete cross-linking of the polymer will create strong rubber gloves. The internal temperature, formers dwell time, humidity, and air-flow, just to name few are the key operation parameters. The understanding of each functional is imperative to ensure optimum level of cross-linking within the polymers. The most common defect if the parameters are not control optimally would be sticky gloves, which means insufficient cross-linking took place causing inferior gloves performance.
The polymer cross-linking is probably at 80% to 90% complete at this stage and the rubber will continue to vulcanize even after it was stripped from the formers. Therefore, good manufacturing practice would require glove to be aerated for at least two days to further enhance the strength of the film.
Gloves are dipped into chlorination solution generally to produce powder free gloves. This is at present the most popular methods of manufacturing such gloves. Chlorination removes tackiness by hardening the glove surface to reduce surface friction, thus facilitate easier donning. In natural rubber gloves production, it is widely believe that chlorination breaks down latex proteins to make them insoluble by reacting with amino groups, thus disrupting their structure and any reactive units they potentially possess. However, poorly managed chlorination processes could cause detrimental effects on the physical properties of the gloves, including decreased shelf life, decreased elasticity and decreased strength. Excessive chlorination could lead to yellowish discoloration that generally occurs on natural rubber gloves. Some manufacturers would substitute chlorination with polymer coating.
Post-leaching is almost similar to the pre-leaching process. This process serves two major purposes, neutralize gloves from chlorination and remove additional chemical residue that are previously still trapped between the polymer matrices. In short, this is the last process to thoroughly clean the gloves before final coating.
Slurry Dipping and Drying
In the recent year’s, market have moved towards powder-free gloves. Slurry dipping is the final process of applying silicone coating to enhance the donning, a very important aspect of powder-free gloves. Depending on customer requirements manufacturer could also apply anti-microbial or moisturizing agent at this stage of process. Formers would be dried in the oven before heading for stripping.
New dipping lines are now semi automated with partial stripping capability, thus enable the line to run at speed that is impossible for conventional dipping line. Mechanical stripping also poses risk of cuff tearing; therefore the operator that lays the gloves must be trained to spot such defect. Gloves at this point should be layered on top of each other. Excellent manufacturer would have good air movement in the stripping area to remove as much humidity as possible from the area. Proper cover-up of the operators is essential to reduce the risk of gloves contamination.
Testing and Packing
After gloves are stripped from the formers, a random sampling will take place to ensure compliance with ASTM and USFDA standards. Sample gloves will then subject to physical property test and water barrier test to determine Accepted Quality Level (AQL), USFDA mandate a minimum of AQL 2.5 for medical examination grade. Only gloves that pass the AQL will then approved for packing. Gloves are then moved to a clean environment room to be weight and pack into individual dispensers. They hygiene and cleanliness of the packing room is essential to reduce the risk of contamination on the gloves