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Latex Glove Production

The Rubber Tree

Latex is a natural product that comes from rubber trees. Though rubber trees can live for up to 100 years, the prime time for latex rubber production is when they are between the ages of 6 and 30 years. Rubber trees are either native trees (that grow naturally) or hybrid trees that have been organized in a rubber plantation. Latex output is usually much greater from hybrid rubber trees. Some companies cut down rubber trees after they reach production maturity, replant new ones, and use the wood to fuel the factories that produce many latex-based products or sell the wood to local furniture producers.

 

Harvesting the Latex

Latex is a white, milky liquid that flows from the tree when the tree bark is scored (or shaved) and flows into a collection device that is attached to the tree. During the rainy season the trees are tapped every day after the rain has stopped. The rest of the year the trees are tapped every other day. On the average, the annual yield of latex from a rubber tree will produce only the equivalent of two boxes of exam gloves. The best time for tapping the trees is at night. Most latex farmers work at night, and sleep during the day (we pulled the farmer in the picture out of bed at 8:30 am). Usually one side of the tree is scored for four years, and then it’s switched to the other side.

 

Collection of the Latex

Since latex is a natural product, it can spoil. Therefore it needs to be collected quickly and stabilized. The collectors of the latex follow the farmers (kind of a second shift) usually between 6:00 a.m. and 8:00 a.m. and take the tapping cups, which are attached to the tree, and load the contents into larger, easy-to-carry containers. The latex needs to be treated with chemicals quickly or it hardens into a gum.

 

Collection Centers

This is where the fresh latex is processed. The collection centers are owned either by local dealers that have relationships with the rubber factories, or are part of company-owned cooperatives. At the collection center the latex is centrifuged to remove water, proteins and impurities. Ammonia is added to preserve the product for its trip to the factory and storage.

 

Quality Control

Although it seems obvious, the quality of the latex used has a direct impact on the quality of the glove produced. In fact, many of the early cases of latex protein allergy might be traced to latex that hadn’t been properly centrifuged (as well as to poor factory conditions). Today, improvements to latex quality such as pretreatment and additional centrifuging are done to remove as many of the remaining impurities and proteins as possible, ensuring a better quality of latex for production. The latex then moves to quality control and then in to storage.

 

Pre-Centrifugation

Some manufacturers are experimenting with the addition of proteolytic enzymes prior to centrifugation to break down proteins in the mix, and reduce the amount of available proteins in the final products.

 

Centrifugation

Centrifuging the latex concentrates the rubber content up to about 60 percent, but also reduces the protein content. Double centrifuging can reduce protein content even further.

 

Compounding

At this stage, up to a dozen chemical are added, including accelerators (which help control the later vulcanisation process) and antioxidants (which prevent deterioration of the rubber molecules in the final product by heat, moisture, and ozone).

 

Dipping and Coagulation

The hand-shaped formers are coated with coagulant (eg. calcium nitrate) and dipped into the latex to coat them with a thin film of latex. The coagulant converts the liquid latex film into a wet-gel on the former. Subsequent passage through a warm oven completes the coagulation process.

 

Pre-Vulcanisation leaching

Also known as "wet gel leaching", this is the process of immersing the latex-coated formers into a bath or spray of water, to wash out excess additives from previous stages, such as coagulant. Chemical and protein content can be reduced at this stage. The effectiveness of the process is dependent on the temperature of the water, the duration of the process, and the rate of water exchange.

 

Vulcanization

Vulcanization was one of the key discoveries in the manufacture of rubber products. In this stage, the latex film is heated, and the combination of sulfur, accelerator and heat cause cross-linking of the rubber, giving strength and elasticity to the film.

 

Stripping

This is the removal of the gloves from the formers, where they are turned inside out.

 

Post-Vulcanisation Leaching

Also called "dry-film" leaching, this process is similar to the wet-film leaching above, except it is carried out on the dry/vulcanized latex film. The effectiveness of the process in reducing water extractives is a function of time and temperature.

 

Lubrication

Hydrolyzed corn starch is added as a lubricant, to enable easy donning of the glove by tumbling the gloves in a slurry of starch and biocide.

 

Chlorination

Some gloves, especially NRL, are "chlorinated" during the process of stripping powder that was added during manufacturing. Chlorination makes the glove surface slippery, and therefore negates the requirement to add a powedered lubricant.

 

Checking and Packaging

Though the manufacturing processes for latex gloves vary greatly according to product, with many additional steps required for different products, most companies use a similar process. Liquid latex and some chemical additives are put into a large vat. Forms that are shaped liked hands (in different sizes) are then dipped into the latex. The latex hardens on the form, with the inside of the glove molded on the outside of the form. The gloves are then stripped from the form (some may be leached again), checked (some 100% air checked) and packaged.

 

 
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