The process called “dip molding” has its roots in the USA and United Kingdom. Dip molding involves the lowering of a form or mandrel into a polymer bath, attracting a thin liquid film deposition onto the form or mandrel after raising from the bath. The film is dried for subsequent removal from the form, after which the form or mandrel returns to the start of the process. The dip molding process can take as few as 4 steps, or as mail), as over 50 steps to complete a dipping cycle.In addition to the main polymer dip, other tanks or steps are employed on the dipping line to finish the product including form cleaning stations, leaching tanks, powder application stations, Mold release stations, coagulant tanks, silicone coatings, ring rolling, rough texturing, cooling stations, and ovens. Most applications from the known beginning of dip molding in the 1930’s until 1985, involved the use of natural rubber latex or polyvinylchloride. Until 1985, clip molding was a slow growth industry residing primarily in the USA and Europe, in an oligopoly type Of industry with few players.
Dip molding found its advantages for high volume production with very consistent wall thickness performance for thin film products such as latex gloves and latex condoms. Furthermore, the performance of natural rubber for products such as breathing bags, toy balloons, and urinary catheters made the process of dip molding a very competitive one, in that tooling costs were generally low, and new product designs could be introduced quickly and inexpensively. Complex tubular products such as a Foley catheter could be made successfully With minimal tooling costs using the process of dipping.
By 1992, the overall dip molding market stabilized, as inferior quality suppliers liquidated, and the companies that had properly established operations with Sound capital equipment and quality systems were poised for future growth.
In 1993, the general awareness of latex anaphylactic shock entered the scene, as documented cases of latex allergies, some severe enough to Cause major medical problems for some individuals, grew at an alarming rate. Some users of latex gloves found themselves to be allergic to the donning powder applied to the glove as well. It was estimated that anywhere from 2% to 10% of the population had some form of allergy related to latex products exposure. The industry and the FDA was forced to respond to the issue in efforts to make thin film barrier products safe for consumer use.
The response by the dip molding industry was threefold;
1. A move was made to remove the donning powders from the end product. Powder-free gloves were introduced to the market place, accomplished through post-chlorination procedures which removed process powders and made for a frictionless Surface on the latex product.
2. A move was made to reduce extractable proteins from the natural rubber latex products through oil line protein removal stations in the dipping process. The same effort to reduce proteins was implemented into the latex centrifuging procedure, accomplished by Multiple cycles of the centrifuging process.
3. A growth cycle started in the dip molding industry for non-latex products. Polymers such as polyvinyl-chloride (PVC), polyurethane, nitrile, neoprene, and styrene butadiene were suddenly considered to be viable alternatives to natural rubber latex. All of these polymers had the advantage of being protein free materials, and considered more suitable and cornpatible for people suffering from latex allergies.
The reasons for dip molding as a process are:
- An accurate method of manufacturing thin wall barrier type products, with all thickness from 0.50 mill to 3.00 mm.
- For high volume production (6,000 to 60,000 pieces per hour), no other molding process can out-perform (fit) molding for speed and productivity.
- Generating tooling is fast and cost effective.
- Color changeover (i.e. toy balloons) is fast and cost effective.
- Parts such as medical brackets, metal rods, and cotton gloves call be dipped with a protective coating of polymer.
At the present time, the glove industry Continues to grow at a rate of 6% per year in the USA. For companies willing to implement the proper capital resources and quality procedures, the future looks promising. Further more, as more and more developing nations implement the same medical guidelines and Consumer standards as that of the USA, the world market is expected to grow simultaneously as that of the USA.
An intelligent path to prepare yourself for new dipping markets in the 21st century is to acquire an in house laboratory and research scale dipping system.
The strong industry trend for examination gloves is that of the powder free variety. Firms looking to expand or start operation in latex examination gloves would be wise to focus primarily on powder free product. The most common means of accomplishing this is through post-chlorination procedures. The process is somewhat labor intensive, but can be softened by careful consideration of oil line chlorination, which chlorinates one side of the glove on the dip molding line. This eliminates the costly “glove turning” step downstream during normal chlorination procedures. oil line chlorination must be properly engineered for ventilation. Otherwise, extreme damage to the dip line will occur.
Other future opportunities in dip Molding reside in the non-latex filed. Synthetic polymers such as nitrite latex and neoprene are being used in the glove industry. Nitrile gloves present a major opportunity for growth. The process to make nitrite gloves is very similar to that of natural rubber latex, making conversion of existing latex lines a very practical option. In, a related field, supported nitrile industrial gloves are growing in use.
The plastisol dipping market (PVC) which involves products such as caps, grips, and covers, has been demonstrating between 6% and 10% growth annually in the USA. Dip molding machinery call be implemented with far less capital investment than that of the glove and condom market. Furthermore, PVC processing is less demanding with respect to formulation management than that of natural rubber or nitrile. The key factor to consider in this market is the ready availability of raw materials.
There are several polymers that call be dip molded. Natural rubber latex remains the dominant one, covering approximately 65% of all dipping operations. This has dropped in recent years due to the latex sensitivity issues, which are more of concern in the US market than in other countries. Providing that manufacturers properly lower protein content in gloves (100 mg levels as established by the FDA), natural rubber latex will continue to be the dominant choice of buyers due to favorable properties and favorable price.
Firms looking to expand or start operation in latex examination gloves would be wise to focus primarily on powder-free product
The key to success in the dip molding industry relies in the concept of repeatability. From the time the raw material arrives until the final product leaves the plant, the supervisors will have established a proper document and procedure trail throughout the plant. The establishment of ISO 9000 quality procedures is a must for serious manufacturers who wish to maintain a profitable position into the 21st century.
What are the future trends in the dip molding operations and how to make them a success?
1. The successful plants in the 21st century will have multiple lines of smaller capacity, to allow for product differentiality.
In today’s marketplace for gloves and condoms, there are several more styles of products, most varying slightly from the baseline product of the 1980’s. By establishing machines with productive capacities of between 6,000 and 10,000 pieces per hour, the dip molding operation would be better equipped to changeover to different styles of gloves or condoms more readily than larger lines.
2. Growth in batch dipping equipment
There are essentially two primary types of dip molding lines – continuous chain and batch indexing systems Continuous chain systems are advantageous for higher production quantities, generally for a single type of product design, and used in water based dipping operations. Batch dipping lines have the advantage of being more flexible, but with lower throughput capability than continuous chain systems.
3. Growth in establishment of pilot scale and research scale machines.
An intelligent path to prepare yourself for new dipping markets into the 21st century, is to acquire an in house laboratory and research scale dipping system. Generally designed as a batch dipping unit, this machine can be invaluable for not only new product development, but also to improve existing formulations and test new dipping profiles for improved product characteristics. New products can be tested and developed on a research scale unit without interrupting production lines. These units can be designed for dipping between 1 and 4 mandrels during a single cycle, or alternatively, be scaled tip to accommodate higher volumes in the range of between 100 and 300 pieces per hour.
4. More Automation will be employed in the process.
Today’s natural rubber dip molding plants in the USA are highly automated throughout the entire process. Automatic stripping of most dipped articles from molds is proven technology today, and can be employed if justifiable. As growing economies, such as Malaysia, continue to experience higher labor costs more and more automation will be employed to reduce the labor content in the product line.
5. Powder free manufacturing:
Especially related to the glove industry, this trend has already begun. A few states in the USA have banned the use of powdered latex products front use in its medical facilities. Glove plants in the 21st century should be prepared to respond to this growing demand.
6. Latex alternative products:
The possibility exists, though improbable, that natural rubber latex could lose its number one position as polymer of choice for dip molding. It is imperative that the dip molder be prepared for alternative materials. Popular choices would be nitrile and neoprene, as both are water based and similar in process to natural rubber latex. It is the writer’s opinion that natural rubber will survive the challenge, providing that manufacturers continue their prudent efforts towards protein reduction in manufacturing.
However, for firms who can successfully diversify their product line to include product differentiation in polymers as well as types of natural rubber products, the long term risk is lowered.
The process of dip molding continues to offer new opportunities for existing and new dip molding firms prepared to invest in a long term strategy of sound quality procedures and ample capital equipment. A strong technical staff to manage the day to day formulation management factor within the factory, is imperative to a successful dip molding operation.