Lens moulders set sights on global growth with the help of Sumitomo (SHI) Demag. Today, there are estimated to be 125 million global wearers of contact lenses in a sector that’s worth nearly US$15 billion. Sumitomo (SHI) Demag is a major player in supplying the machinery that produces the moulds that make the contact lenses.
Contact Lenses
Because no two eyes are the same, there is a broad spectrum of styles and parameters to meet when producing lenses. Every contact lens that is produced requires a bespoke mould, which is where Sumitomo (SHI) Demag’s injection moulding expertise comes in.
The process starts with the injection moulding of a front and base curve mould. This mould is then filled with a monomer (a molecule that can be bonded to other identical molecules to form a polymer) and is then closed and cured before the lens is then hydrated and packed. Every single mould used to make a contact lens is produced to a very high level of precision and cannot be reused.
Nigel Flowers, managing director of Sumitomo (SHI) Demag UK explained: “Because the final lenses are moulded against a surface that has already been injection-moulded, any imperfection within the mould will find its way into the lens.”
A variety of moulds is used in the production of contact lenses, representing the different magnification levels (graded in quarter diopters) that are prescribed for each lens. The differences are in the variation in the space thickness between the front and rear of the mould, which dictates the thickness of the lens. There are a finite number of combinations and a standard number of magnifications and variations on the curve. Nevertheless, production must still be carefully controlled.
To accomplish this required quality and accuracy, Sumitomo (SHI) Demag installs its activeFlowBalance technology into its all-electric IntElect machines. This helps to combat uneven filling of multi-cavity moulds.
“When we’ve got to a certain part of the fill and the materials are moving under their own inertia, we stop pushing and let the mould fill naturally. We are not forcing it in at high pressures and forces,” explained Flowers.
“The key is to ensure that the manufacturers that specialise in making contact lens moulds can do it repeatedly and with the highest precision in order to mass-produce the moulds cost efficiently.”
Typically, there are between eight and 16 cavities in each moulding tool.
While contact lens moulds are not technically classed as medical devices, any airborne contaminants, such as dust and particles from the raw materials, as well as human contaminants like bacteria, could affect the lens function.
For the production of lens moulds, both all-electric and hydraulic injection moulding machines are used – with the bias heavily weighted (90% to 10%) towards all-electric. Repeatability is the main rationale, as well as meeting ISO Class 8 cleanroom standards.
Moulders venturing into this specialist sector may also opt for a self-contained cleanroom moulding and packing system which are fully compliant with any GAMP and FDA requirements and have the required DQ, IQ and OQ documentation.
Automation plays an equally big role in maintaining cleanliness and efficiency levels, as each mould is typically produced in under three seconds. Tasks undertaken by these robots include unloading the mould tool and packing into sterile carriers.
Currently, only one Sumitomo (SHI) Demag UK customer automates the entire lens production process. Here, the company’s IntElect injection moulding machine forms just one small part of a huge production line whereby raw material is put in and, when it comes out the other end, the final product is packed and ready to ship.
“Packing and sealing the lens at the point of manufacture reduces the risk of contamination during moving and storage,” said Flowers, who noted that complexity, investment costs and potential downtime issues are the downside to this approach.
Batchmaking the moulds and then shipping to local markets where the lenses are produced offers more flexibility and operators have the ability to stop the injection moulding machine and compensate somewhere else in the system. In both instances preventative maintenance and management of downtime has to be well managed.
So what’s next? Bifocal lenses are now manufactured on a larger scale to correct both near and far vision. Asia is one of the fastest growing regions for cosmetic coloured lenses. The next milestone could be smart lenses that monitor a user’s health through a series of circuits, sensors and wireless technology.
“Breakthroughs are happening all the time. For this reason, moulders will typically upgrade their machines every five years with new drive systems, controllers and other key components to ensure their hardware is one step ahead and meeting future global consumer demands,” added Flowers.