UV Laser Marking Ideal for Medical Devices and Pharmaceuticals

 

Marking is used in a wide range of industries and products, from bar codes on milk cartons to alphanumeric batch numbers on microelectronic packages.  Infrared lasers are well-proven as a superior option to traditional ink printing in many uses, but both technologies still present significant disadvantages in some important applications, particularly in the medical device and pharmaceutical industries.  Although ultraviolet (UV) laser marking is proven to avoid the limitations of both ink and IR lasers, their higher cost of ownership have previously limited their adoption, even in high value applications like medical devices, disposables and pharmaceuticals.  Fortunately, advances in the reliability and cost of ownership of ultraviolet lasers have changed this situation.  This article explains how and why UV laser marking is now poised for fast growth in these markets.

 

The Special Needs of Medical Marking

 

Manufacturers of medical devices and implants need to mark their products to enhance traceability – for economic reasons and for long-term quality control, to prevent counterfeiting, fraudulent returns and unregulated distribution, and to comply with increasingly strict government regulations.  For example, some countries already require all medical device manufacturers to mark their products with some type of UDI (unique device identification), including when and where each was made.  Marking also allows tracking; if any part is found to be defective, the entire batch can be flagged and recalled if necessary.  Anti-counterfeit is a growing concern as all kinds of medical devices (and drugs) are targets for highly organized groups. 

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As a consequence, device and implant manufacturers have several marking requirements.  First the mark must be permanent.  Second, the mark must not interfere with product functionality, including avoidance of contamination or introduction of allergens.  And third, the mark ideally should be hard to counterfeit.

 

Pills (tablets, capsules and caplets) and their packaging also need to be marked for much the same reasons.  Typically, this includes a product identifier, the manufacturer’s logo, and possibly the date of manufacture or lot number. 

 

The Limitations of Traditional Marking Methods

 

The dominant method for marking pharmaceuticals, medical devices and their associated packaging has long been ink printing.  Pills have traditionally been imprinted using one of two methods.  In the first method, a mark is molded into a pill during the compression of the powder in the manufacturing process. This method is limited, however, as it allows only for marks that are simple and large, usually containing two to five characters or an elementary symbol.  The second traditional method is offset rotogravure printing, which has significant drawbacks such as cleanliness of operation, the use of solvents, and extra downtime to clean and maintain equipment.  Also, any type of ink printing that involves mechanical pressure can be a problem for the newer soft gel formats.  The overall print quality is poor, often limiting the amount of information that can be encoded. Packaging and wrapping have also traditionally been ink marked — usually by inkjet or pad printing.  In terms of costs, printing is attractive to manufacturers because the capital equipment cost is relatively low.  However, the ongoing cost of consumables (ink) is often substantial. 

 

For medical applications, the main drawback of printing is that it is often easy to remove or alter printed marks (especially if they’re on a paper label).  This means that marks can become difficult to read after shipping, handling or storage, and also permits purposeful counterfeiting.  In addition, although the inks themselves are usually non-toxic, high speed printing involves mechanical handling that may require lubricants or solvents that could possibly contaminate the product.

 

Medical devices and disposables are commonly made of metal and/or plastic components.  Although these can be printed, conventional ink printing will generally not make a very permanent mark and is mainly used with implants and disposables to mark the sterile sealed packaging. 

 

Medical products have been directly marked for some time using infrared lasers.  Laser marking is a non-contact method that involves either producing a color change on a surface or within the bulk of the material, or a change in surface relief (e.g. engraving) or texture that is easily visible.  Laser marking usually employs (CO2, solid state, or fiber) lasers operating in the infrared.  The marking process itself is a thermal interaction; material is heated until it bleaches, carbonizes or ablates in order to produce a color contrast.  Nearly all plastics directly absorb the far infrared CO2 output; absorptive additives are sometimes used to facilitate this process with near in

 

Medical products have been directly marked for some time using infrared lasers.  Laser marking is a non-contact method that involves either producing a color change on a surface or within the bulk of the material, or a change in surface relief (e.g. engraving) or texture that is easily visible.  Laser marking usually employs (CO2, solid state, or fiber) lasers operating in the infrared.  The marking process itself is a thermal interaction; material is heated until it bleaches, carbonizes or ablates in order to produce a color contrast.  Nearly all plastics directly absorb the far infrared CO2 output; absorptive additives are sometimes used to facilitate this process with near infrared, solid state or fiber lasers.  However, this heating can alter the chemical structure of the material in the heat-affected zone (HAZ) such as charring, and also produces some surface relief.  This texture can offer a place for bacteria to settle and grow, and may be difficult to clean.  Laser engraving cannot be used with most metal (or plastic) medical devices for this reason, because it deliberately creates surface relief.

 

The Unique Advantages of UV Laser Marking

 

An alternative method is to employ the UV (355 nm) output of a frequency tripled, diode-pumped, solid-state (DPSS) laser.  UV light is absorbed more strongly than longer wavelengths by most materials.  Moreover, the laser photons directly break interatomic bonds in the plastic substrate causing a cold, photochemical interaction with any fillers or pigments, thus eliminating any heat affected zone (HAZ) or changes to the surrounding material.  For most plastics that appear white, this pigment is TiO2, which strongly absorbs the UV light and then undergoes a change in crystalline structure.  This renders the substance dark, producing a smooth, highly legible mark within the bulk material, rather than at the surface. 

 

Because the mark is actually subsurface, it doesn’t provide a possible home for bacteria, and it is nearly impossible to alter or deface without destroying the material itself.  And, the higher absorption in the UV means that material can be processed with lower laser power (or pulse energy).  Finally, since UV light can be more tightly focused than IR, ultraviolet lasers support complex, high-resolution marks, such as 2D barcodes. 

 

이러한 장점에도 불구하고 UV 레이저는 비용 때문에 과거에는 의료 마킹 응용 분야에 널리 사용되지 않았습니다. 그러나 지난 10년 동안 Coherent와 같은 회사는 UV 레이저 수명, 신뢰성 및 출력에서 ​​상당한 개선을 이루었습니다. 이는 레이저 설계, 재료의 개선 및 생산 중 엄격한 클린룸 절차의 구현을 통해 달성되었습니다. 또한 자동화된 조립 방법과 판매량 증가에 따른 규모의 경제는 이 기간 동안 UV 레이저 가격을 거의 5배까지 낮추는 데 도움이 되었습니다. 또한 일부 제조업체는 비용에 민감한 마킹 응용 분야에 맞게 특별히 최적화된 UV DPSS 레이저를 개발했습니다.

 

일부 표시 예

 

코히런트 응용 연구실(독일 뤼벡)에는 자외선 마킹 레이저(MATRIX 355)를 비롯한 여러 레이저가 장착되어 있습니다. 의료 기기 및 일회용품에 일반적으로 사용되는 여러 가지 재료를 표시하는 데 사용되었습니다. 여기에 몇 가지 예가 나와 있습니다.

 

실리콘 고무는 일반적으로 투명 및 불투명 흰색 형태로 의료 기기에 사용됩니다. UV 마킹의 장점 중 하나는 투명 기판 내부에 레이저를 집중시키는 기능입니다. 이것은 튜브의 내부 표면에 표시를 할 수 있기 때문에 삽관 또는 기타 정맥 적용에 사용되는 실리콘 튜브에 유용합니다. 치수 정보 외에도 마크에는 원래 보관 날짜가 포함되어야 합니다. 미국 및 기타 국가에서는 이 날짜로부터 3년 이내에 튜브를 사용해야 합니다. 프로세스가 적절하게 최적화되면 외부 표면(환자와 접촉하는 표면)에 영향을 미치지 않고 시인성이 높은 마크를 생성합니다.

 

알약은 속도와 처리량이 마킹 품질만큼 중요한 대량 생산 문제를 나타냅니다. 달성 가능한 최대 마킹 속도를 결정하기 위해 다양한 유형의 소프트젤 및 하드젤 캡슐에 테스트 마킹을 수행했습니다. 소프트젤 캡슐의 1.5mm 높이 문자의 경우 최고 속도는 <0.024초/문자였습니다. 마크 가독성은 모든 경우에 우수했습니다. 하드젤 캡슐의 경우 1mm x 1mm의 2D 바코드를 0.2초 미만으로 재현할 수 있습니다. 대조적으로, 잉크 마킹은 빠를 수 있지만 알약을 마킹을 더럽히지 않고 취급하려면 1-2초의 건조 시간이 필요합니다.

 

MATRIX 355 레이저를 사용하여 생성된 두 개의 다른 마크가 여기에 표시됩니다. 그림 3은 고밀도 폴리에틸렌(HDPE)으로 만든 구부러진 약병에서 단 2초 만에 생성된 고대비 2D 바코드(8mm x 8mm)의 예입니다. 그림 4는 의약품용 최신 '블리스터' 포장에 사용되는 유형의 젤라틴에 대한 영숫자 표시를 보여줍니다. 이 마크는 1.3m/s의 스캔 속도로 30% 깊이(0.58mm 두께의 0.17mm)로 생성되었습니다. 색상 변경 표시는 재료 제거 없이 양호한 대비를 보여줍니다.  

 

요약

 

요약하면 UV 레이저 마킹은 의료 기기, 일회용품, 제약 및 관련 관련 포장에 적용할 수 있는 우수한 솔루션인 것으로 나타났습니다. 이러한 마킹 응용 분야에 최적화된 DPSS 레이저의 등장으로 이제 UV 마킹이 경제적으로 매력적입니다.