Masks: the hot topic on – or rather over – everyone’s lips at the moment. They have become the focus of huge attention due to the worldwide spread of coronavirus. But protective masks, respiratory masks, sleep masks and diving masks have been vital pieces of equipment for a long time. We look at the important role that liquid silicone plays in producing this equipment.
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Emergency services, hospitals and research institutes began using protective masks a long time ago. They are also increasingly being used at home for the treatment of conditions such as sleep apnea. Liquid silicone rubber (LSR) is often the material of choice as it ensures a very comfortable fit. LSR is also frequently combined with other materials in mask design. For instance, the housing might be made from thermoplastic and the mouth and nose area from silicone, and the mask could feature a replaceable or insertable filter system. Masks have many different applications and can be produced in lots of different ways. The RICO GROUP has been manufacturing injection molds and silicone masks for its customers for over three decades. It uses both one-component and multi-component injection molding technology in its production operations. LSR combines outstanding material properties and reliability in the production process. The material is a true all-rounder, excelling due to its biocompatibility, allergy friendliness, neutral odor and taste, and heat resistance (-50°C to +250°C), as well as allowing for a high degree of design flexibility and making complex geometries and material combinations feasible.
Multi-component injection molding
Liquid silicone can be processed using 2K or multi-component technology, enabling combinations of LSRs of different shore hardnesses, or of LSR with thermoplastics. Mask designs featuring high-performance and engineering plastics such as PEEK, PPS, PSU, PBT, PA, PMMA, PET and PC have proved particularly successful, but bonding to glass, fiberglass and metal is also possible. Other advantages of LSR are high tear resistance, a low compression set and good resilience. And what’s more, it can be dyed any color and illuminated.
From thick silicone for functional elements to delicate face coverings
The special requirements associated with mask design and functionality continually present new challenges for mold making and material processing. Comfort and varying face shapes both have to be taken into consideration. This results in the use of 3D freeform elements for the mouth and nose areas, which need to be incorporated in the mold. For silicone-only (1K) masks, the thickness of the silicone often varies greatly in different parts of the mask. It may be thick in areas with a functional purpose, but supple and soft where the mask comes into contact with the face. This means that the mask will be very thin and membrane-like in some areas. Differences in texture can also lead to complexity in production. Low-viscosity materials, such as 5 Shore materials, are especially challenging in terms of both mold making and production. Working with these materials calls for particularly close attention to repeatability, process stability and achieving outstanding quality.
Challenging production process
Mask production is extremely difficult to plan. With 3D freeform elements, it is very hard to make calculations for the flow front in materials. Although the design and demolding can be simulated, the experience of the RICO GROUP’s application engineers is essential to overcome the final hurdles on the way to creating a perfect product. If the parts are manufactured fully automatically, they require space: in the handling during demolding and when positioning on the conveyor belt, as well as in the post curing oven and at the packaging stage. There also needs to be a sufficient supply of materials for unmanned, automated production at night.
New LSR masks
The coronavirus crisis has demonstrated that masks which need to be supplied in a hurry are rarely made from silicone. The development time required for the production of high-quality LSR masks is longer than for other materials and the production concepts need to be highly sophisticated. Preventing rejects is vital due to the high cost of materials and in order to comply with the RICO GROUP’s environmental protection requirements. Silicone is a unique material that is ideal for the production of masks and is also perfectly aligned with the RICO GROUP’s sustainability strategy.
Liquid silicone in mask production – the main advantages:
• Biocompatible, allergy-friendly, neutral odor and taste
• Resistant to water, alcohol, polar solvents and weak acids
• High temperature resistance and flexible at low temperatures (-50°C to +250°C)
• Pleasant feel against the skin and comfortable to wear thanks to soft material (up to 5 Shore)
• Differences in thickness and texture possible in different areas of the mask
• Well suited to 2K injection molding (e.g. LSR+LSR or LSR+thermoplastic)
• Enhanced design flexibility
