Cleanrooms

JENI THOMAS, CONTENT AND COMMUNICATIONS LEADER AT CONNECT 2 CLEANROOMS (C2C), AND ALISDAIR WATSON, MD AT OPTIMOLD LIMITED, EXPLAIN HOW MODULAR CLEANROOMS SUPPORT MANUFACTURING PROCESS CONTROL FOR MEDICAL PLASTICS.

Modular cleanrooms supporting

PROCESS CONTROL FOR MEDICAL PLASTICS

There are certain challenges that plastics manufacturers face when producing molded parts for medical devices. Controlling air quality with a modular cleanroom protects the production of medical plastics.

The injection molding process—in particular the material conveying equipment—naturally creates a degree of particulate contamination. When molded parts are removed from the tool, the type of polymer and the process can also generate static, even with the use of an antistatic device. When combined, the particulate and static can cause problems for manufacturers who have tight AQL (Acceptable Quality Limit) sampling requirements. This is why the manufacture of medical devices must be performed within ISO 14644-1:2015 Class 5 to Class 8 cleanrooms.

CLEANROOMS AND PROCESSES ALIGNED TO CONTROL CONTAMINATION The way that the governing ISO standard looks at compliance is by minimizing the introduction, generation, and retention of particles. This can only be achieved through a partnership of cleanrooms and processes.

Cleanrooms stop the introduction of contamination through HEPA filtration. Controlling the generation of contamination is then down to organizations’ SOPs, protocols, and process controls. The responsibility of controlling the retention of particles comes back to cleanrooms again as they effectively flush that facility of contamination with appropriate air change rates.

Optimold Limited, the sister company to mold manufacturer Microsystems (UK) Limited, is a contract manufacturer producing injection molded components for medical devices, such as autoinjectors, asthma inhalers, drug delivery and blood diagnostics for both hospital and laboratory use. Over the past decade, C2C has supported Optimold with modular cleanrooms to facilitate growth in the medical device market.

STARTING CLEAN PRODUCTION To stay competitive, companies need to be able to incrementally grow their cleanroom offering in line with the growth of the company.

When Optimold won its first contract for medical device parts back in 2011, one machine out of the five they had at the time needed to be enclosed in an ISO Class 8 cleanroom. Converting the entire room which housed these machines into a cleanroom and encapsulating the whole area into a single level of control would have required a huge investment. The higher overheads would inevitably have driven up the cost of the parts that didn’t require cleanroom production.

The solution was simple. C2C installed a localized cleanroom to house an individual machine. As contracts grow or new work is won, machines can be upgraded with a cleanroom accordingly and, as freestanding units, they can easily be retrofitted to molding machines.

Optimold now has 13 injection molding machines, of which seven are enclosed in modular cleanrooms. The modular cleanrooms create a clean environment to prevent contamination issues and, when combined with the controls put in place, they manage contamination well within the requirements of customers’ AQL criteria.

ENERGY EFFICIENCY Modular cleanrooms give flexibility within the production environment, whilst still providing the customer with a quality product. Energy consumption in the manufacturing sector represents a huge proportion of overall consumption by industry and manufacturers need to do what they can to control usage. With the rising costs of energy, reducing energy consumption supports not only the environment but has a significant impact on overhead costs.

The primary cause of energy consumption within a cleanroom is the operation of the HVAC system to deliver the level of compliance. Using a localized approach to create clean environments, there is no overprocessing of air. Only the zone that needs to be controlled has the high air change rates required to deliver the particulate concentration limits according to its ISO class.

MOBILE CLEANROOMS OFFERING PART COVERAGE Part coverage of an injection molding machine means only the mold area and clamp end are covered by a cleanroom, leaving material conveying equipment external to the controlled environment.

The material conveying equipment can create a degree of particulate so separating it from the clean area makes a big difference to the overall cleanliness of the environment. In turn, a reduction in contamination generated within the cleanroom reduces the number of air changes that are required to keep within its classification. If machines were fully enclosed, a different method of conveying would have to be utilized.

Having the cleanrooms on castors means they can easily be wheeled away from the machine to give access to change tooling easily.

TEMPERATURE AND HUMIDITY CONTROLS Temperature variation can cause inconsistencies so certain products will run better when the process is kept at a consistent temperature. As Optimold have several injection molding machines in the same white room area, the external room is temperature-controlled. Each cleanroom features a ceiling-mounted HEPA fan filter unit that intakes air from the controlled surrounding environment. This keeps the temperature at acceptable limits within the cleanrooms.

Additional heat gains from operatives will affect this ambient temperature. For the most part, operators only need to enter the cleanrooms periodically to package parts or take samples for inspection, so this approach to HVAC delivers the appropriate parameters.

There is one unit, however, where a small amount of secondary work on components is performed within the cleanroom by an operator. Here comfort cooling is supplied to the cleanroom by a localized air conditioning unit. This unit supplies the cooled air to the fan filter unit, to provide terminal HEPA filtration and

ISO compliance.

WHEN TO INVEST The build of a new cleanroom can generally be delivered within the lead times of a new mold, so modular cleanrooms are fully scalable without the need to speculate to accumulate.

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MIKE RUST, GLOBAL DEVELOPMENT MANAGER – T-FIT INSULATION AT ZOTEFOAMS, CONSIDERS THE ISSUES AND DESCRIBES A TEST PROTOCOL DEVELOPED TO MEASURE THE PARTICULATE CONTRIBUTION OF THREE DIFFERENT TYPES OF INSULATION DURING TYPICAL CUTTING AND FITTING OPERATIONS WITHIN A CLEANROOM.

While standards and specifications abound when it comes to the design features, apparel, and operator protocols necessary to minimize particulates as a contaminant in cleanrooms, there is little consideration of the part played by materials such as those used for insulation.

Wherever cleanroom manufacturing happens, the environment must be designed to ensure the safety and quality of products. Cleanroom design minimizes the introduction and circulation of potential contaminants, with control of particulate emissions essential to maintaining a secure, clean environment.

The construction of the cleanroom shell is subject to exacting engineering standards and specifications to maintain air quality in terms of particulate release. In 2016, ISO 14644, the recognized standard for cleanrooms, was expanded specifically to include the “assessment of suitability for use of equipment by airborne particle concentration” — although it did not extend to such important matters as the selection, testing or ease of cleaning of selected materials.

Thermal insulation — important but overlooked Amid all the attention paid to preventing, monitoring, and controlling particulates, one important aspect is often overlooked: the impact on particulate levels of the thermal insulation that controls the surface temperatures of process pipework and HVAC equipment in and around cleanrooms while conserving energy and providing personal protection for operators.

Whatever type of insulation is selected, during installation it will have to be cut to size and very likely manipulated to fit complex pipework runs in tightly confined spaces — all happening in situ. Post-installation, thermal insulation is not simply ‘fit and forget’: it is typically checked regularly as it is removed to facilitate pipeline maintenance and repair. And it is during removal that traditional thermal insulation products can pose the most danger in terms of emitting potentially hazardous particulates into the cleanroom environment.

Absence of independent testing So far as we can ascertain, there are no recognized independent tests that compare the particulate-emission performance of different insulation materials commonly used in a cleanroom — a situation that is no help to those charged with specifying appropriate insulation solutions.

With all the above in mind Zotefoams commissioned Occhnet, an occupational hygiene consultancy based in the UK, to design and conduct an independent test of T-FIT Clean foam insulation, produced from Zotefoams’ ZOTEK F highperformance PVDF closed cell foam. T-FIT Clean’s performance was tested against two traditional insulation products, manufactured respectively from foil-backed stone wool and flexible open cell melamine with a PVC jacket. The

testing measured the indicative concentrations of particulates released into the air during cutting of the material. The testing replicated the worst-case scenario — that of operators slicing and/or cutting the insulation within the cleanroom —simulating cutting-to-size operations during installation and replacement maintenance.

Each sample insulation material was placed into a sealed glovebox containing a particle counter. This ensured that, once the test samples and testing equipment were inside, no further particulate could be introduced. The glovebox did not contain an air exchange or filtering system.

To allow for the stabilization of the background particulate reading, the procedure started with a two-minute static period where there was no movement within the glovebox. Once that static period was completed, each test piece was subjected to three cuts at 90o and three at 45o. Cutting lasted one minute in duration, followed by a further two-minute static period. To measure any increases in background particles within the glovebox, differential µg/m3 readings were taken at particulate sizes of 0.5, 1.0, 3.0, 5.0 and 10.0 µm, at a flow rate of 2.83 l/m.

The results Measurement and comparison between the three materials produced results worthy of consideration by those charged with cleanroom design and operation.

T-FIT Clean: As Figure 2 (above) shows, the particle count fell steadily through the first two minutes of the static period. During cutting and manipulation and in the final two-minute static period there is a continued gradual decrease in particle count, indicating that T-FIT Clean does not emit particles within the measured particle size (0.3 to 10 micron). Occhnet concluded that “there was no detectable release of particulate during the cutting period.”

Flexible open cell melamine: When this typical melamine product, often installed in cleanrooms, was cut and manipulated, there was a significant increase in background particulates, indicating the materials added large amounts of particulates into the environment even before it is cut. Occhnet observed that a clean cut was difficult to achieve without compressing the material, which released air from the open-cell construction, coinciding with the rise in particulate count.

Foil-backed stone wool material: The particle count was stable during the static period but as soon as cutting commenced the particle count rose significantly, and particularly for larger particles. According to Occhnet, while a clean cut was possible without compressing the sample, “the material appeared friable and the rise in count was indicated to be associated with the cutting of the material.” It should be noted that this material incorporates a glue binding the fibers together, which is likely to deteriorate when the material is used in hightemperature applications, raising the prospect of particulate emissions increasing over time.

A different manufacturing process T-FIT Clean’s control of particulate emission lies in its three-stage foam manufacturing process that uses pure nitrogen as a foaming agent and produces materials with a consistent, fine closed cell structure. In Stage 1, pure PVDF polymer is extruded into a solid slab, then irradiated to create chemical bonds that join the polymer chains (crosslinking). This results in excellent thermal stability, high strength and toughness compared to non-crosslinked materials, and crosslinking via irradiation also prevents the shrinkage that is often associated with thermoplastic materials. Stage 2 applies extremely high pressures and temperatures to dissolve the nitrogen gas into the slabs. In Stage 3, the nitrogensaturated slabs are put through a second, high-temperature, lowerpressure cycle where the pressure is gradually released to allow the free expansion of the material into sheets of foam.

The result is a fine, completely closed cell structure that demonstrates exceptional performance across the board, not just in limiting particulate emissions but on all measures of cleanroom insulation efficiency. T-FIT Clean is also highly resistant to bacteria and mold growth and its ASTM G21-tested performance on zero fungal growth brings long-term protection against the risk of product contamination. Compared to open cell materials, T-FIT more effectively limits moisture and gas penetration because there is no continuous network through which substances can travel.

A wide temperature operating range — from -80oC to +160oC — combined with the durability of the material ensures thermal performance remains unimpaired in the long term, even where repeated cycling between chilled process temperatures and high cleaning temperatures (clean in place, sterilize in place) is involved.