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Reproductive Health |
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The Latex Condom: Recent Advances, Future DirectionsChapter 4 sidebar: How a Latex Condom Is Made |
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Latex comes primarily from the tropical rubber tree (Hevea brasiliensis), with the best quality found in Malaysia and Thailand. Latex is a natural elastomer and has the chemical name of cis-polyisoprene. Most other elastomers are synthetic. The liquid latex lies between the tree's bark and wood and is collected by making a series of slashes through the tree bark, which allows the latex to flow out of the tree. During collection, a small amount of ammonia is added to the raw latex to counteract the acid production of waste products from the bacteria that naturally feed on the latex and can cause the liquid latex to curdle. From this stage, latex is held in stainless steel tanks and processed with tools that are made only from stainless steel or other inert ingredients. Liquid latex is actually a dispersion of rubber particles in water. Fresh raw latex consists of about 70 percent water and 30 percent rubber cells. The fresh latex is centrifuged, which concentrates it to approximately 60 percent solids. Concentrating latex reduces the cost of transport to the condom manufacturer and decreases the amount of time it takes to manufacture a condom. (Murphy) The liquid latex is mixed with other chemicals to make a latex formulation for manufacturing. The latex formulation includes the liquid latex dispersion and various chemicals, including an antioxidant, a sulfur-based vulcanizing agent, and a vulcanizing accelerator. Accelerators are chemicals that increase both the rate and extent of cross-linking in the latex compound during vulcanization. Latex condoms are produced by dipping plastic, ceramic, stainless-steel or glass mandrels mounted on a conveyor into a latex formulation.* The mandrel, most often glass, is dipped into the latex formulation in either a vertical or horizontal fashion, with virtually all manufacturers currently using a vertical dip. The mandrels go through a series of dips, rotating to spread the latex evenly. Between dips, each coat of latex is partially cured on the mandrel via hot-air drying in a carefully controlled tunnel-like oven on a conveyor system. Successive coats of latex are used to build the condom to the required thickness, with most manufacturers using two dips. Brushes or water jets then roll up a section of the condom's open end to form the rim roll at the base of the condom, which stays in place because the rolled latex adheres to itself. Then, the condoms, still on mandrels, are dipped into one or more hot baths of either water or a caustic agent such as sodium hydroxide or potassium hydroxide. This removes some of the latex proteins from the condom, a process called leaching. Another round of curing is completed in a drying tunnel. The condoms are then removed from the mandrels using brushes or water jets, placed in an appliance similar to a clothes washing machine and washed with a powder slurry, usually cornstarch. After washing, the condoms are dried in a large appliance similar to a clothes dryer, which removes the liquid but leaves the dry powder on the condom to serve as a dry lubricant for further processing. Each condom is tested electronically for the presence of any holes. The condom is then rolled into its final configuration and placed between two layers of packaging material. If the condom is to be lubricated, a specified amount of lubricant and/or spermicide is put on the condom, and the two layers of packaging are then sealed. Most are lubricated with silicone or a water-based lubricant, which may or may not include a spermicide. The most commonly used spermicide is N-9, a water-soluble detergent (surfactant) that interacts with the cell membranes, killing sperm, bacteria and some viruses. Latex condoms are manufactured in different shapes, textures, colors, thicknesses, widths and lengths. A reservoir tip may or may not be included at the closed end of the condom. Some condom surfaces are smooth, while some are textured, sometimes in a design on the outside or inside surface. Most condoms are a dull opaque tan, although some are colored. Some condoms are manufactured with scent, flavoring (strawberry, mint and others), or other features. Currently the two most common condom shapes are straight-sided and contoured/form-fitting. A straight-sided condom has basically the same diameter at its open and closed ends. A contoured condom is similar to a straight-sided condom, but with a slightly smaller width just below where the head of the penis would be. A third shape is tapered from the closed end to a smaller diameter at the open end, and a fourth has a bulbous tip at the closed end. The open-end diameter is about the same size for all shapes. Condom dimensions vary. In terms of film thickness, almost all latex condoms are between 0.01 mm and 0.09 mm. Those made in the U.S. are generally from 0.03 mm to 0.07 mm (Hatcher) while those in Japan are generally 0.01 mm to 0.03 mm. (Concar) The lay-flat widths, corresponding to diameter, range from 47 mm to 55 mm, with most measuring 52 mm. Latex condom lengths range from 160 mm to 210 mm, with the majority measuring between 170 mm and 190 mm. *Latex is a liquid, and the condom material is technically "latex rubber." In this monograph, as in common usage, we refer to the "latex" condom rather than the "latex rubber" condom. by Caroline E. Gilmore References
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