Applications for Dipped Goods

Robert Craves, Andrew Lanham, and Karen Spenceley, Synthoner Ltd, Harlow, UK 

In another guise, the dipping technique can be used to produce flexible, thin-walled articles from natural or synthetic polymers. The various types of synthetic polymer used for dipping are discussed in the next section. In the dipping process, a suitable shape, called in the industry a mold , form or former , is dipped with an appropriate dwell time into a liquid containing the polymer. The coated former is then heated to dry and cure the polymer as necessary. Finally, the article is removed from the former, whose shape it retains. The dipping process therefore provides the means to make seamless thin-walled items with predetermined, perhaps complex, shapes. 

The thin walled, flexible products normally associated with this process are gloves, condoms, balloons, catheters and feeder teats and soothers for babies. The polymers from which they are made often include additives to produce the desired physical properties. One example of this is the use of curing agents to produce elastomeric properties, where the final article exhibits the abihty to recover its original dimensions after the removal of an applied stress. 

This book is concerned with synthetic emulsion polymers, and it has to be said that at the start of the 21st century their use in the production of dipped goods is relatively limited. The area is dominated by the use of natural rabber for gloves and condoms. Matching the strength, modulus, tear resistance and dipping characteristics of natural mbber has provided a formidable challenge to the synthetic polymer chemist 

Balloons and catheters remain the domain of natural rubber, with the very minor exception of the use of some high modulus synthetic emulsion polymer as a reinforcing material for catheters. 

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Other than tire use, there are few other significantly large application areas for natural mbber that can be identified, as indicated in Table 10. The use of natural mbber in latex products covers items such as gloves, condoms, balloons, catheters and other dipped goods, latex thread, foam and carpet backing, and rubberized coir and hair. In total, latex goods consume about 11% of world mbber production. Thereafter, there are four categories footwear,... 

Traditional applications for laiices arc adhesives, binders for libers and paniculate matter, protective and decorative coatings, dipped goods, loam, paper coatings, hackings for carpet and upholstery, modifiers for bitumens and concrele. thread, and textile modifiers. More recent applications include biomedical applications as protein immobilizers, visual detectors in immunoassays, as release agents, in electronic applications as photoresists for circuit boards, in batteries, conductive paint, copy machines, and as key components in molecular electronic devices. 

The largest use of natural rubber is in the manufacture of tires. Over 70 percent of its consumption is in this area. The next largest use is as latex in dipped goods, adhesives, rubber thread, and foam. These uses account for approximately another 10 percent. The remainder is used in a variety of applications such as conveyor belts, hoses, gaskets, footwear, and antivibration devices such as engine mounts. 

A study on application of radiation vulcanized NR latex already be done. The most possible application is for production of rubber dipped goods rubber gloves, condom etc. Unfortunately the consumption of latex for producing these materials are relatively very low. Consumption of NR latex in Indonesia is about 6,000 tonnes annually, mainly for the production of rubber foam, and only a small amount is for producing dipping rubber goods. 

Polyvinyl chloride (PVC) is often produced by suspension or emulsion polymerisation. It is used extensively in producing PVC pipes for construction. Impact modifiers are often added to strengthen the material. PVC is also used in plastisols for dipped coatings, in shower curtains, and in vinyl leather. Nonvolatile plasticisers are necessary in such applications where the material must remain flexible. Because PVC is a very hydrophobic polymer with good barrier properties, it makes an effective obstacle to oxygen and water vapour in packaging films. 

A good way to remember the applications for latex is to follow the first six letters of the alphabet A, adhesives B, binders C, coatings D, dipped goods E, elasticizers and F, foam. 

RhGOlogy. Flow properties of latices are important during processing and in many latex applications such as dipped goods, paint, and fabric coatings. Rheology is used to characterize the stability of latices (45). For dilute, nonionic latices, the relative latex viscosity is a power-law expansion of the particle volume fraction. The terms in the expansion account for flow aroimd the particles and particle-particle interactions. For ionic latices, electrostatic contributions to the flow around the diffuse double layer and enhanced particle-particle interactions must be considered (46). A relative viscosity relationship for concentrated latices was first presented in 1972 (47). A review of empirical relative viscosity models is available (46). In practice, latex viscosity measurements are carried out with rotational viscometers (see Rheological Measurements). 

Malaysian and Indonesian natural rubber growers have established a system based on technical characteristics. A summary of the standard technical specification scheme shown in Table 4 for natural rubber can be foimd in ISO 2000 (14,15). In addition to the solid form of natural rubber, it is available as a suspension in water and is known as latex. Synthetic rubbers are also available in latex form. Latex has become an important commodity used in the manufacture of dipped goods for pharmaceutical applications. The principal uses of natural rubber are as follows tires and tire retreading, 70% latex (eg, gloves), 12% mechanical goods, 9% load-bearing components, 4% and other, 5%. 

Atomic force microscope tips can also be used to deposit matter on a surface at nanometer scale. The reference example is dip-pen nanolithography where molecules deposited on the tip diffuse to the surface when in contact and define patterns with dimensions as small as 15 nm. An extension is the so-called NADIS technique, for which a nanochannel drilled at the tip apex is used to deposit liquid from a reservoir defined on the top of the cantilever (for a review of these methods refer to chapter 12). Besides its applications for nanopatterning, the NADIS method is a unique method to study liquids at submicron scale and, more particularly, liquid meniscus with controlled dimensions. The capillary force curve experienced by the tip during the deposition and measured with AFM is a good way to assess calculation methods and finally to get more insight into the liquid transfer mechanism from the reservoir to the surface. ... 

The huge variety of applications continues into the area of soHd plastic materials -impact modifiers are added to improve the properties of plastic materials. Dipping goods, e.g. gloves, and latex foams for mattresses are polymeric materials which are made directly from polymer dispersions. 

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