Today’s environment for polymer dip molding has grown in size and complexity from the early 1980’s, when natural rubber latex was typically the polymer of choice for most dipped products. Natural rubber formulations were quite established during this period with compounding techniques varying little year to year for most manufacturers. However, today’s polymer dip molding environment in the decade of 1990 has seen many changes, new polymers, and continued scrutiny on the part of consumers and regulatory agencies, toward processing of natural rubber latex due to protein and powder related allergies.
Because of this changing technical, environment for barrier products made by the dip molding process , most established manufacturers of gloves, condoms, catheters, and related dipped products now own and operate some type of research laboratory dipping equipment. The advantage for research and development departments and chemists in using this equipment, are significant and can generally achieve payback benefits quickly, sometimes, in months. The key to justifying the acquisition of small-scale dipping units to simulate production conditions, lies in the understanding of the high volume environment within which most dip molders compete. The competitive production of gloves and condoms mandates production volumes in the millions of pieces, and sometimes billions of pieces annually. One day’s wasted production due to inferior compound management can easily justify the existence of a laboratory scale dipping machine to foster productive technological advancement for dip molders. Often, problems on the production floor can be minimized through proper and intelligent simulation on a practical scale, in the laboratory.
Dipping success
The primary key to dipping success is that of repeatability, and quality management within all aspects of the company, from sales, through research, engineering, production, quality control, and inventory management. Often, dip molders focus capital investment on the production aspect of the factory’, without recognizing the critical importance of advanced equipment technology in new product and formulation research. Frequently, you will find polymer chemists “hand dipping” samples for testing new formulations, new products, and/or producing size variations. That inferior level of accuracy detracts from the technical staff’s ability to introduce more consistent polymer products.
To obtain some element of accurate testing, the research staff is forced to experiment with new dipping and curing profiles on production scale machines. This technique is not only impractical for the latex chemist, but also forces production staff to reduce available production machine uptime which optimizes company profits. In most instances, the production team “wins” the argument on machine use, leaving the research & development department waiting for precious available machinery time to test new products and formulation adjustment.
The examination glove industry can be very competitive. Successful companies in this commodity market are those with established quality systems, and those who achieve a high level of production machine uptime of over 98%. It is therefore, absolutely mandatory to minimize production machine downtime to that of scheduled maintenance. Using production machines regularly for testing and product development will reduce overall company productivity. Fiscally and technically, this scenario is not a practical approach to R & D efforts in this industry.
The answer to this dilemma is investment in a Research Laboratory Scale Dipping machine. Most research lab dipping units are configured in “batch” dipping format (vertical indexing technology). In latex and condom glove manufacturing environments, most production plants are configured as continuous moving chain systems. However, this should not inhibit the chain plant user from investing in a laboratory scale batch system. Dip profiling and fluid disbursement routines can be simulated very effectively in batch lab format, when performing research for chain plants.
Any chain type laboratory dipping system normally must be justified as a “pilot plant”, and generally
must be configured in much larger space than that required of batch research dipping systems.
The design and selection of a lab scale unit should be objectively driven, based upon the intended purpose of the system. The following factors should be considered when identifying the proper type of system for purchase, and or construction:
1. Will the system be used to produce a modest amount of product samples or is its sole purpose formulation and process development?
Many times, a firm’s sales department will make efficient use of a lab scale dipping unit by introducing new products to the marketplace, produced on lab scale systems. Of course, if this is a primary objective, the system tends to grow in size and cost.
2. Will the system be used to dip only water-based emulsion products, or does the present and/ or future mandate possible testing with solvent based synthetics?
Systems designed for solvent based formulations will typically require 15% to 20% additional investment capital when compared with units designed for water based technology. This additional charge can be attributed to the need for explosion proof or air purged electrical motors (assuming the system employs electro-mechanical technology). Furthermore, some solvent systems may dictate the use of a machine enclosure and/or strong ventilation for operator protection.
Where as solvent based systems require these additional protective design measures, water based systems generally require additional stations to make an effective lab scale plant. For example, some natural rubber latex, nitrile, and neoprene lab scale systems will require up to five (5) or more dip tanks to accurately simulate production (latex, coagulant, leach, slurry, chlorination, polymer coating). Most solvent based systems require one (1) tank to make for an effective system (polyurethane, silicone, styrene butadiene). Lab scale units for PVC glove research are often scaled with one (1) or two (2) dip stations. In most cases, one or more ovens are part of the machine. A system with one oven, if designed with the proper controls, can enable the user to use the oven for multiple processing purposes (Curing, form heating, coagulant heating, pre-leach gel, etc.).
3. Does the unit require former rotation during testing?
Lab research units designed with no form spin capability may not be able to simulate chain plant dipping profiles accurately. For many latex products (gloves and condoms), designing the research lab dipping system with form spin capability throughout the process, will more effectively Simulate chain type dipping plants. The additional machine axis will add modest cost to the project. Electric motors or air motors for this function work well, but should be adjustable for rotation speeds.
4. What funds are available for the project?
Unfortunately for the R & D staff, this often is the driving factor towards machine selection. However, as technology has advanced, commercially available systems from suppliers such as DipTech Systems, Inc., have become much more affordable. For example, a lab dipping unit with simply a programmable vertical axis can often be sufficient for the task, by manually switching tanks beneath the single axis. Further addition of a pallet rotate axis can be added economically to provide the user with further flexibility.
Past versions of lab scale dipping units utilized “air” or “hydraulic” technology. However, today’s systems are best configured with electromechanical technology, using computer controlled stepper motors, and in larger applications, servo motors. This technology not only represents the most repeatable and accurate system today, but also is equally competitive in price to air or hydraulic systems.
Process Control
A key consideration for research scale dipping units, is that of defining desired level of process control functions for the unit. The most critical programmable features for any lab scale system would be that of the vertical, pallet rotate, and form spin axes. Units today feature the ability to extract formers very accurately at speeds as slow as .025 mm per second. For the vertical axis, the unit should be designed with multiple profiling capability, so that speeds can be adjusted during the entry and exit profiles, in blended fashion for smooth transition. Programmable dwell time is also mandatory.
Secondly, the system oven should ideally be able to simulate all production line oven temperature profiles. It is not absolutely necessary to include the oven within the automated lab unit, to accurately simulate production conditions. However, by doing so more accurate data can be obtained from lab trails. Most commercially available lab ovens today can be purchased with programmable “ramp and soak” controllers, to simulate those production lines that have multiple zoned cure ovens. As previously mentioned, if the oven is included in the automatic lab dipping cycle, the machine can be designed easily to allow one oven to function as several production line oven stations, such as curing, form heating, coag, drying, and pre-leach latex gelling.
Thirdly, automatic tank heating can be crucial to ensure accurate simulation conditions on the production line. Systems today can be supplied with tank heating/cooling loops whereby temperatures for solutions are set and maintained automatically by hot/cold water supply systems. In conjunction with tank temperature, adequate tank agitation (air, magnetic, or electric stirrers) will be advised for most water based formulations. Most solvent based formulations tend towards higher viscosities (500 to 3000 cps) and can often be managed accurately on the lab scale level without on going solution mixing.
The last consideration is the decision whether or not to include automatic bead (ring) rolling as part of the laboratory scale system. Today’s more sophisticated systems can actually operate without the presence of an operator. After starting the machine cycle, the completely automated system can run unattended. However, for unsupported gloves and condoms, bead (ring) rolling is generally a requirement.
Automatic product take off systems for lab scale units are seldom considered. Most firms who wish to experiment with automatic product take off techniques will set up this research independently of the research laboratory scale dipping machine.
Robotic Machine
As for any robotic or automatic motion machine, the equipment should be designed with proper safeties and emergency features. Enclosed systems work well, but must carefully consider the ramifications of thermal conditions. If a lab unit enclosed with a constant opening oven door, temperatures within the chamber can elevate perhaps beyond that desired. A small temperature control unit can often be added to the equipment to ensure proper temperature control of the environment surrounding the process. An enclosure also aids in cleanliness within the dipping operation area
The typical laboratory scale dipping machine for gloves and condoms is normally configured with spatial pallet capability of from I to 6 moulds. Some pilot plants utilize pallet sizes of up to 1 meter square, containing perhaps up to 36 glove moulds per pallet. However, this requires a significant investment, normally only feasible for the world’s largest 5 to 10 dip molding firms.
Consideration of these factors will allow the dip molder’s research and development staff to easily identify, features necessary for a sensible investment in research laboratory scale dipping technology. Advances in formulation management are key to long term survival in this changing industry. Proper selection and use of this type of equipment will not only benefit production efficiencies, but also can enable the sales department to be equipped with improved new product samples to distribute to the marketplace. However, the dynamic hidden benefit in acquisition of a Laboratory Scale Dipping machine is that this investment may actually be the catalyst for sales, manufacturing, and research departments to work more closely together.
For the interested buyer of Research Scale Laboratory Dipping Machines, DipTech Systems®, Inc., Kent, Ohio USA, offers three (3) different standard models, all available with many options. All systems feature computerized programmable controls for ease of programmer adjustment, and superb repeatability. The standard product line for Research Scale Laboratory Dipping Machines includes:
- “Diplomat®” – A two axis (vertical, pallet rotate) programmable table top unit with a single dip tank station.
- “Diplomat® HD” – A three axis (vertical, pallet rotate, former rotate; programmable unit with a single dip tank station.
- “Diplomat® XL” – Up to 4 axis available (vertical, horizontal, pallet rotate, former rotate), this model can be equipped with any desired number of dip tank stations, bead roller, and oven. This system employs the use of a “pick and place” robotic manipulator.
DipTech Systems® has also designed and built customized systems for pilot scale research, batch and continuous.
