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Published: May 11, 2010
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Transitioning from Preformed Trays to In-Line HFFS Machinery

When volume supports the investment and packaging design warrants it, significant cost savings can be gained by thermoforming, loading and sealing trays in-line rather than purchasing preformed trays, handling them individually and then sealing after loading on a tray sealer. The factors to consider when making the transition to in-line horizontal-form-fill-seal process are examined.

By: J.P. Merritt, Oliver-Tolas Healthcare Packaging, Suzhou, Jiangsu Province, China

Factors for success

The best way to package many medical devices is in rigid trays. In general, rigid tray packaging has a higher cost than flexible packaging, but there are applications for which rigid trays are most appropriate, these are:
  • high profile products
  • products requiring special protection against shock and movement
  • procedural trays, where there are multiple components and the sequencing of component access needs to be controlled.
Medical device manufacturers take two approaches to rigid packaging.
  • Where volumes are small or the forming application is extremely difficult, preformed trays and die cut lids are brought together on a tray sealer and sealed by the medical device manufacturer or packager.
  • Where volumes are extremely large and forming requirements allow it, the manufacturer often opts for in-line horizontal-form-fill-seal (HFFS) machinery to reduce packaging costs.
In the medical device industry, companies often launch new products in preformed trays and then after the product has matured and the volume increased, transition to HFFS machinery. For this transition to be successful, it is important to understand the different characteristics of rigid packaging produced by these two methods.
 
Preformed tray applications
FIGURE 1: Four station tray sealer. Courtesy of Sealed Air Ltd.
As mentioned, preformed trays are typically used in small volume applications or where the challenges of forming preclude the use of HFFS machinery. The degree of difficulty in forming depends on the depth of the tray, the ratio of the depth to the draw area and the number and shape of compartments in the tray. The complexity of the tray design depends on the number and nature of the components to be packaged. For instruments where abrasion or product movement is of concern, the tray may have snap locks to hold the product in place. The design of snap locks and their execution can be challenging. Poor design or inconsistent forming allows excessive vibration and can generate particulates during transportation.
 
In general, the combined cost of the sealing machinery, moulds and other tooling for preformed tray operations, each purchased separately from the machine fabricator, the tray former and the lid supplier, are much less expensive than the investment required for sophisticated HFFS machinery. The basic elements of tooling and machinery for the application of preformed trays falls into the following areas.
  • Thermoforming moulds. The size and cost of the mould depends on the volume of trays to be produced per cycle and the complexity of the design. Trays are formed in large arrays and then die cut into individual trays, which are sent to the device manufacturer for use.
  • Cutting dies for trays and lids. In addition to the cutting dies used for the blister, cutting dies also are required for the precut lids.
  • Tray sealer. Tray sealers come in a variety of designs and a wide range of costs. Simple tabletop tray sealers are the lowest cost alternative for lower volume applications. Shuttle sealers and rotary tray sealers are used for higher volume applications (Figure 1). 
HFFS applications
Where volume can support the investment and packaging design warrants it, there are significant cost savings in thermoforming, loading and sealing trays in-line as opposed to purchasing performed trays and lids, handling them individually and then sealing after loading on a tray sealer. HFFS machinery takes roll stock, forms a rigid tray in-line, allows for product loading, seals a lidding stock to the formed and loaded tray, cuts the final package and discharges the packaged product.
 
FIGURE 2: Thermoforming with a male mould. Courtesy of Sealed Air Ltd.
The HFFS machine will perform the same functions as the preformed tray system, that is, forming, cutting and sealing. The challenges of building one machine that is capable of addressing all of the special requirements, which are addressed separately by the dedicated tray supplier, the dedicated lidding supplier and a focused machine builder, are intuitively obvious. However, some of the specific challenges are worth discussing.
 
Common challenges for both processes
There are performance challenges common to rigid tray applications, whether in preformed or in-line systems.
  •  Flex cracking. Typically, this is the result of repetitive shock and corners can often develop small cracks or pin holes that compromise sterility.
  • Abrasion. This is the result of vibration and causes issues relating to particulate contamination and possible pinholes. This is a common challenge with instruments used for less invasive surgical procedures, staplers and similar types of device.
  • Cold flex. Large rigid trays can be challenged by extremes of temperature, particularly by cold flex; seals can fail when the package is subjected to shock and vibration under extremely cold conditions. Resistance to this challenge will vary among sealing systems and it is wise to explore alternatives should this be a concern.
  • Tearing of the lid upon opening. Tearing always represents a potential breach of sterility; large rigid trays are more difficult to open and inconsistent seal strengths can further aggravate this problem.
  • Product presentation. It is essential that products can be easily removed from their packaging and removed in the proper sequence. 
Transition design considerations
FIGURE 3: Thermoforming with a female mould. Courtesy of Sealed Air Ltd.
The transition from preformed trays to in-line HFFS trays involves some specific challenges. Building the same rigid package on a HFFS machine that will perform in a similar way to packages produced using preformed trays, die cut lids and a tray sealer requires a number of design considerations. The goal is to produce a package that will perform and appear to the nurse or practitioner to be the same as a preformed tray. Yet, the two processes involve subtle differences in the design and the processes used to produce them have dramatic differences.
 
Tray characteristics
Preformed tray producers are better able to take advantage of a wider range of mould designs and techniques, which are not practical on HFFS machinery. For example, male mould designs are seldom used on HFFS machinery, but are commonly used by tray suppliers. The two different thermo-forming techniques produce trays with fundamentally different characteristics.
 
A male mould, one where the material is formed over a contoured form, will produce trays with better inside dimensional precision and will be more likely to have a thicker bottom and sides. Conversely, trays produced on male moulds generally have thinner and less consistent flanges (Figure).
 
A female mould, one in which material is pulled into a cavity and formed, will produce blisters with more precise outside dimensions and consistent flanges. Conversely, these blisters will have thinner walls towards the bottom of the tray and thinner corners (Figure 3).
 
Preformed trays sometimes use stepped flanges to reduce tearing on opening by not sealing the Tyvek (DuPont, www.dupont.com) all the way to the edge of the blister. A stepped flange is also utilised to separate the lidding and the tray at the peel tab to facilitate opening. It is not practical to use stepped flanges on HFFS machinery. However, similar effects can be gained by other techniques such as building an unsealed zone longitudinally between blisters (Figure 4).
 
Tray design considerations
Once these characteristics for preformed trays and trays formed in-line on a HFFS machine are understood, the following specific points should be considered when transitioning from preformed trays to HFFS packaging.
  • The packaging engineer must be clear about how the material is to be distributed: are thicker walls required, thicker corners or thicker flanges?
  • It is important to pay close attention to snap locks when transitioning from male moulds to female moulds; parts formed on female moulds have less precise internal dimensions and it is those dimensions that are most critical to holding the part in place when using snap locks.
  • Stepped flanges are not practical on HFFS machinery; to minimise tearing, a similar effect can be achieved by leaving an unsealed area between each blister.
 
Lid characteristics
FIGURE 4: Stepped flanges. Courtesy of Sealed Air Ltd.
The blister and the lid sealed together provide a sterile barrier that must survive manufacturing, distribution and storage. But once in the hands of the nurse or practitioner, the package must open without tearing and allow appropriate product presentation. Sealing and cutting techniques can have an affect on the ability of the lid to tear efficiently on opening.
 
Preformed trays most often use die cut lids. Die cut lids commonly have radiused corners with cleaner cuts than those made on in-line HFFS machines. This is because the cutting die for the lidding is only cutting one homogenous material, whereas the cutting mechanisms on HFFS machinery must cut through the Tyvek as well as the thermoformed film.
Die cut lids are quite often produced in sheet form, printed on smaller offset presses and then cut to dimensions. Offset printing can handle smaller typefaces and provide consistent print placement. Print registration on HFFS machinery can be problematic regardless of whether or not preprinted roll stock or blank stock printed on the HFFS machine with an in-line printer is used.
 
Lidding design considerations
Understanding the implications of the two alternative approaches to rigid packaging, the following specific points for lidding should be considered in the transition from preformed trays to HFFS packaging.
  • If the original preformed tray uses stepped flanges, consider the impact of changing to flat flanges when transitioning to in-line HFFS machinery. As mentioned above, an unsealed area can be placed in between individual packages to provide a similar effect, but this will increase the area required for forming.
  • Anticipate more variation in print location on in-line HFFS machinery.
  •  Build adequate seal width, anticipating that cutting location varies on HFFS machinery and in some cases cutting into the seal area can reduce seal width.
 
Achieve a collective solution
Considering these design elements early on in the transition from preformed trays to in-line form-fill-seal can eliminate the most common pitfalls that can cause problems for the packaging engineer. As always, an open and early dialogue among the major parties is essential. This allows for the development of a collective solution that utlises the strengths that the different material and machine provide and minimises the risk associated with the limitations of the various entities involved. 
 
Further reading
1. “Implications of Material Selection to the Design of HFFS Machinery,” Medical Device Technology, March/April 2009, www.emdt.co.uk/article/implications-material.
2. “The Intricacies of Print Registration on Horizontal Form Fill Seal Machinery,” Pharmaceutical and Medical Packaging, November 2005.
3. “3-D Packaging for Medical Products,” Medical Device & Diagnostic Industry, October 2003, www.mddionline.com/article/3-d-packaging-medical-products.
 
John P. Merritt BA, MBA, MSME, CPP
is International Managing Director, Oliver-Tolas Healthcare Packaging, Building 9, Suite B, No.5 Chun Hui Road, Suzhou Industrial Park
Suzhou, Jiangsu Province, China 215021
tel. +86 512 6956 0016
e-mail: jmerritt@oliver-tolas.com
www.oliver-tolas.com
 
 
 
 
 

 

Published in European Medical Device Technology, May 2010, Volume 1, No. 5



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