Agr’s Advanced Thin-wall Measurement for PET Bottles Helps Producers Get One Step Closer to Meeting Sustainability Goals
Home New Lightweight option for the Process Pilot® blowmolder management system affords the production of even lighter, more sustainable PET bottles With increasing focus on sustainability in packaging, Agr’s new Lightweight option for the Process Pilot® blowmolder management system gives brand owners and bottle manufactures another tool to meet this complex and growing challenge. The Process Pilot system, with the Lightweight option provides assurance that the limited material available for producing a light weight PET bottle is distributed exactly where it needs to be, and at the appropriate thickness, to ensure proper performance. There are many facets to this issue and improving the sustainability footprint of a product or brand can be a complex undertaking. Most avenues to sustainability are not under the direct control of the bottle manufacturer or brand owner. One option that is within their control however, is the reduction and optimization of the amount of resin that is used to manufacture the bottles. Resin (or weight) reduction per bottle does not need to be excessive to have an impact with regards to sustainability and financial benefits particularly when factoring in the quantity of bottles produced over a given period of time. Over the years, many PET bottle manufacturers have made great progress reducing excess material and moving towards lighter, more sustainable bottles. However, as weights continue to be reduced, the role of process variation and its effect on material distribution increasingly becomes a factor in the success of the weight-reduction program. Agr’s Process Pilot blowmolder management system was developed to address this issue and offers manufacturers a valuable tool to use in their weight reduction efforts. The Process Pilot system, with Agr Pilot Profiler® measurement technology installed inside the blowmolder, provides a means for manufacturers to accurately measure material distribution on every bottle (to 0.05mm), in real time, and proactively adjust the blowmolder to maintain proper distribution, countering the effect of process variation. In the push for more sustainable bottles, weights are being reduced even further and, with that, the sidewall thickness of the bottle. In order to process these bottles effectively and control the material distribution, additional measurement accuracy is required. The new Lightweight option, incorporated into the Pilot Profiler measurement component, offered with the Process Pilot system was developed to address this need for even greater measurement accuracy and control on very light bottles. With this option, a level of control is now available with the Process Pilot system that extends the measurement range to 0.025mm, with an accuracy of +0.01mm for PET bottle sidewall material. This added functionality delivers greater distribution control on bottles with very thin sidewalls or at specific locations on other types of bottles where precise material management is critical to meet performance and quality requirements. This capability removes one of the barriers to producing usable, lighter and more sustainable bottles. Agr’s Process Pilot automated blowmolder control systems are operating on over 400 PET bottle production lines. They have proven to be a vital tool in the production of light weight bottles while improving overall bottle performance and quality. The Process Pilot system is unique in that it manages the blowmolder based on direct bottle measurements, on every bottle produced. By controlling the blowmolder based on direct feedback from bottle measurements rather than just blowmolder performance indicators, the Agr system can ensure that the final product has the desired quality and performance attributes in spite of environmental, blowmolder or material variations that can occur during the production process. Now with the Lightweight option, the process can be controlled for even the lightest bottles. The option is currently available on all new production Process Pilot systems. To achieve these capabilities on existing systems, Agr also offers an upgrade package that can be easily installed in the field.
Real World Pressure Testing of PET Containers
Home PURPOSE Proper pressure testing of PET containers is an essential part of a smooth filling process and favourable downstream performance of carbonated soft drinks (CSD) and other pressure products. Whether we realize it or not, all PET containers used for pressure products are being pressure tested, both as they are filled in high-speed counter-pressure filling machines and in the distribution channels as they experience varying ambient temperature conditions. Relying on the filling equipment and downstream events of a container’s life cycle to verify container performance can be very costly and have undesirable implications on brand confidence. For this reason, state-of-the-art container manufacturers have adopted pressure testing protocols that simulate all of the conditions experienced by the container during the filling process and beyond. This paper will discuss the pressurized environments that a PET carbonated beverage is subjected to and the test methods used to ensure that commercial quality containers are produced. CONTAINER FILLING The typical filling process for a PET carbonated beverage container uses a counter-pressure technique. When the empty container is presented to the filling station, it is sealed and quickly charged with CO2. The CO2 located above the carbonated product in a holding bowl as well as in the container are pressurized higher than the desired product carbonation level to prevent the dissolved CO2 in the product from coming out of solution during filling. Typical counter pressures range from 60–100 psi for cold or ambient filling conditions. Gravity is used to transfer the carbonated product from the bowl into the container, and after the filling process is complete, pressure is relieved from the container. A schematic of this technique can be seen in Figure 1.0. INITIAL PRESSURIZATION Of particular note in the filling process is the speed of initial pressurization of the PET container, by far the most important step as it relates to the ongoing performance of the container. The initial pressurization found in normal filling machines occurs in approximately 500 milliseconds, as the ambient air in the container is replaced with CO2. BRITTLE FAILURES This rapid, non-linear pressurization in PET containers can trigger brittle failures, especially in the base. Excess amorphous material that remains in the base of the container after the blowing process creates a region, with high concentrations of stress, between the oriented and amorphous material. The material in this region is brittle and can fracture easily when the container is pressurized. Many of these early failures occur well below the pressure level used in the counter-pressure filling process. Conversely, pressure testing containers with slow initial pressurization characteristics is not sufficient to identify when the blowing process is making containers that will not survive this first step of the filling process (figure 2.0). VOLUME EXPANSION A container that survives the initial rapid pressurization still may not provide acceptable performance. After the counter-pressure has been applied, the container is subjected to a pressure hold for approximately 13 seconds (figure 3.0). Understanding volume expansion behaviour of the container during this hold time provides an important data point about how the container will react throughout the commercial life cycle. A container with a weak overall structure or lower levels of material orientation may expand beyond acceptable levels, causing thinning of the wall thickness, faster loss of carbonation and a higher risk for side wall failures. To ensure that the filled container will ultimately perform for the consumer, a quality pressure testing method must include the pressure hold at a value that simulates the real-world experience of the bottle. PROCESSING HISTORY ON INHERENT MATERIAL PROPERTIES The ultimate material properties of a finished PET container are the cumulative result of multiple factors including the time and temperature profiles for heating the preform, along with the stretching and blowing profiles in the formation of the container itself. A change in any of these variables will affect many factors, including the pressure at which the container will experience an unrecoverable yield or deformation. The natural frequency and potential impact of these processing changes drive the need to regularly pressure test containers to determine how a given production run will perform under filling and down-stream conditions. PRESSURE TESTING For over 25 years, PET containers have been pressure tested with the intent of understanding how well a container will perform under real-world filling, storage, transportation, shelf-life and consumer-use conditions. When PET, as a material, is tested using a tensile tester, a stretching force is applied to determine the amount of force required to reach the yield point (where material is permanently deformed) and is continued until failure (point where the material stops stretching and breaks). With a container, this can be equated to the application of internal pressure expanding the container volume and stretching the material to the point where the PET yields, and then a continuation of pressurization to container failure (burst). Yield and burst are the two key material failure modes experienced by a PET bottle. This simple ramp approach is acceptable for use only after the 13 second hold spoken of earlier. To simulate actual conditions, a complex test is warranted that subjects the container to the same abrupt, non-linear pressure dynamic (counter-pressures) seen in the filling process, then held at actual filling pressures for the appropriate filling time, and then subjected to a continuously increasing pressure ramp to identify the container yield point and ultimate failure. Testing PET containers in this manner provides the manufacturer with the information required to understand how the containers will perform in the filling operation and throughout the commercial life cycle. An example of a testing system that provides the capabilities to simulate the complex pressure profile of the filling operation is the Agr PPT3000TM. The PPT3000 accurately represents the counter-pressure filling simulation by providing a precise pressure profile that simulates a true filling environment. This pressure profile has been dubbed the “Fill Ramp”, where the container is subjected to an abrupt, ~500 millisecond non-linear pressurization, up to the test pressure hold level (60–100psi). It is held at that test pressure for 13 seconds,
Bringing Shelf-life Testing to the Production Line
Home As soon as the bottle is filled and capped, the countdown begins. Single layer PET bottles, though they appear to be impermeable, are slightly porous, and over time CO2 escapes and/or O2 permeates through the material. How fast this process happens determines the “shelf-life”. In today’s fast-paced environment, it can take less than an hour from preform to case packer. Products show up on the grocer’s shelf within a few short days. Bottles that under perform with regards to shelf-life can affect a consumer’s experience, impact future sales and ultimately damage the brand image. With the trend for bottle self-manufacture by brand owners and increased emphasis on light weighting, bottle shelf-life properties are increasingly impacted by the production process. Faster production processes with lighter bottles dictate a new approach towards shelf-life management. One such approach is the M-RULE® container performance model for analyzing shelf-life in PET beverage bottles. The M-RULE model is notable because of the speed of the tests, and the reproducibility of the result, all at a significantly lower cost than traditional methods. Are all PET Bottles of the Same Design Alike? When a bottle is designed, considerable effort is put into optimizing the mechanical and aesthetic properties of the container. For a given bottle design, the shelf-life is primarily determined by the surface area and effective thickness of the package sidewall, which in turn determines the weight of that package. Because cost is a key objective, the package weight is usually the minimum needed to achieve the targeted shelf-life. In theory, if you get everything right and every bottle is produced by a uniform process, then every bottle should exhibit the same shelf-life properties. In reality, this is not the case. Variations that affect the bottle blowing process continually occur. Differences in preform moisture content and temperature, material properties, blow molder anomalies, plant environmental changes, operator experience… to name a few, all impact material distribution and affect sidewall thickness, the property that is so crucial to shelf-life performance. Why is this so critical now? In the past, variations in the blowing process were masked by heavy sidewalls and extra material. Bottles were over-engineered, and their shelf-life exceeded the minimum targets. As a result, minor variations in material distribution had no impact on product quality. Light weight bottles are the game changer. The processing window on a light weight bottle is very narrow, and the target shelf-life is achieved only in bottles with optimal material distribution. Minor deviations in material distribution and wall thickness that normally would have little impact in the past, now can result in significant production that does not meet shelf-life specifications. With the reality of variability in the process inputs, the only way to ensure consistency in shelf-life is to tightly control, monitor and continually adjust the blowing process. And, by pro-actively managing variations in material distribution and thickness, shelf-life performance can be managed as part of this process. However, even with the various process monitoring techniques in practice today, shelf-life is one aspect that is not typically incorporated into the routine process monitoring and response programs. This is because, until recently, monitoring shelf-life properties on the production floor has not been a simple matter. Traditional shelf-life testing methods can take as long as 8–24 weeks, hardly practical when timely and accurate data is necessary to make process related decisions. Furthermore, these tests require intensive laboratory preparation prior to testing, continual monitoring and attention during the test, and have limitations that can result in testing inaccuracies. Variations in bottle to bottle dosing, fill level, temperature control of the testing environment and so forth affect test results, making it difficult to predict shelf-life with confidence using these methods. “There are a lot of things you can do to compromise a CO2 test…. It is sometimes like throwing dice” claims a bottle development engineer at a major beverage producer. An Alternative to Traditional Shelf-life Testing using the M-Rule Model Container Science Inc, Atlanta GA, offers a very tangible solution to the shelf-life dilemma with its M-RULE container performance model for analyzing shelf-life in PET beverage bottles. Commercially available since 2002, the model has been validated repeatedly by brand owners, converters and technology developers. This model overcomes the variability of traditional testing by providing a means to evaluate bottles using standardized data, testing and environmental conditions, resulting in a very repeatable method. And, with results available within seconds, it overcomes the critical issue of timeliness. The M-RULE container performance model for beverages is a web based predictive tool. It operates by integrating the fundamentals of permeation with critically evaluated physical data for the materials in a given package (bottle and closure) and other pertinent data affecting the permeability of a container, such as temperature and pressure. The M-RULE model takes into account a host of parameters and bottle attributes as part of the shelf-life determination, such as surface area, material distribution (wall thickness), base design, filling conditions, storage and distribution conditions, etc. The impact of material properties such as construction of the sidewall, resin, orientation of the material, crystallinity, the modulus of the resin and scavenging activity can also be tested. The model simultaneously predicts CO2, O2, N2, and H2O permeation based on first-principles calculation of the diffusion and solubility of these gasses, along with the impact of stress, temperature, crystallinity and modulus on these parameters. For this reason, the model can accurately predict bottle performance under a wide range of conditions. Package-specific performance is determined by applying bottle parameters such as surface area, weight, base design, finish, volume and filling conditions. All calculations include the impact of the closure on package performance. Below are three examples of the model’s predictive capability vs. two different traditional test methods. When specific bottle/package details are entered into the model, a very accurate determination of shelf-life can be made. This is accomplished without the influence of many of the issues that compromise the results of traditional tests such as: Precision of initial test carbonation Test control parameters and precision over the
A Journey into the Unknown
Home Agr helps beverage brand owners manufacturing PET containers In many beverage plants, the decision to self-manufacture PET bottles is a journey not just into the unknown, but the unknown unknown. Agr’s Process Performance Optimization Group (PPOG) consultants help processors navigate this unfamiliar terrain. The new millennium has seen tremendous advances in PET bottle blowing technology, from block or integrated blow-fill machines to the breakthrough Process Pilot automated blowmoulder control system introduced by Agr International. At the same time, there’s been an absence of demand growth for carbonated beverages, a consequence of the increasing consumer appetite for a healthier diet as evidenced by tremendous demand growth for bottled water. Several big-name converters have consolidated, changed focus, or exited the business. Not surprisingly, the industry saw a wave of retirements among plastics engineers. All this was unfolding against the backdrop of mounting environmental concerns that prompted fillers to rethink the need to ship empty bottles hundreds of miles to their plants. The beverage industry responded with a logical solution: bring blowmoulding in-house. The numbers pencil out, and it makes sense from the sustainability perspective. Making bottles on demand at the point of filling also offers the advantages of increased flexibility and closer control. According to Paul DiZinno, Manager of Agr’s Process Performance Optimization Group, brand owners have invested in hundreds of blowmoulding lines over the past decade. The seismic shift to self-manufacturing has spread far beyond the U.S. to beverage operations around the globe. But as one major CSD processor in Germany found out, there’s a lot to learn about the blowmoulding process. Labeller trouble Opening in 2018, the German plant was designed and equipped for efficiency and productivity, with the Agr Process Pilot installed inside the 20-mould KHS blow-fill machine. Prior to installation of Agr’s Process Pilot system, container handling issues were observed on the high-speed line producing 42,000 bph. Sometimes, the bottles seemed to wobble in the labeller, as though they weren’t sitting well in the cup. Further downstream, labels would pop off as the containers were going into pallets. New to blowmoulding, plant personnel didn’t know how to track down the cause of the skewed labels. Nor did they suspect that it was the symptom of a much more significant problem. As a long-term supplier of critical measuring instruments and productivity tools to the plastic packaging industry, Agr was keenly aware of the industry shift to self-manufacturing – and its pitfalls. PET bottle making is extremely sensitive to a host of variables. Dynamics like temperature, humidity, preform composition, machine condition, or even operator skill can impact material distribution, the key factor in bottle performance. Process Pilot takes and analyses real-time measurements of the thickness of the sidewall of every single bottle, then adjusts the blowmoulder control parameters if material distribution starts trending out of spec. The result is an optimised blowing process that ensures consistent container quality and performance. PPOG supplements Agr’s Process Pilot by providing plants with fundamental process knowledge. Brand owners have discovered a shortage of knowledgeable plastics personnel in the job market. The PPOG engineers, veterans with a long history in bottle manufacturing operations, have deep expertise in the blowmoulding process. They also take a holistic view of the vast chain of interrelationships throughout the production cycle. All these elements must be coordinated to achieve sustainable improvements in stability, uniformity, and productivity. Turn down the heat The issue of the wobbling bottles came up when PPOG Process Engineer Consultant Damon Choate was in the German plant for phased commissioning of the Process Pilot. Without on-site equipment to do qualitative bottle testing, Choate sent samples to the Agr service depot in Italy for analysis. There, bottle volume expansion and maximum burst pressure data, provided by Agr’s PPT3000 Packaging Pressure Tester, revealed that the bottles were subject to frequent base stress crack failures. “Half the sample bottles burst in the base just a few seconds into the test,” Choate relates. “The ones that didn’t fail had over 40 per cent volume expansion. The resin wasn’t being distributed properly, which is why the bottles wobbled and didn’t fit in the label cup.” “Agr is well known for our ability to test volume expansion,” DiZinno observes. “We were the first to do the 13-second expansion test. This is the number-one parameter PPOG engineers look at. Even if the weights are exactly centered, we can tell whether the problem resides with the material, the process, or the design.” With the PPT results indicating room for improvement in the process, the engineers reviewed the bottle recipe, or blowmoulder settings. It was clear to them that too many oven lamps were directed to turn on during blowing. The process was running too hot, and the preform temperature was higher than necessary to produce the ideal stretch and orientation of the PET molecules. “In general, when making PET bottles, the colder you can make the process, the better,” explains Choate. “The goal in blowing is to get the very best orientation of the PET, both vertically and horizontally. This gives the best container strength.” It’s true that high heat makes the PET more pliable and easier to stretch, but all stretching is not equal, he points out. Cold forces the molecules to align better vertically and horizontally. Reducing the preform temperature specified in the recipe by a few degrees will produce better overall resin distribution and better strength and rigidity, a critical attribute for shelf life. Gas permeation through the walls and resistance to volume expansion also improve with the proper orientation of molecules in a colder blow. In all, the PPOG engineers reduced the number of lamps that turned on in the oven by 15, from 69 from the original recipe to 54 in the revised one. They also lowered the preform temperature setpoint by four degrees. With these two changes, the bottle volume expansion went down to the most desirable rate of 12 to 13 per cent, from 40 per cent prior to the engagement, “a vast improvement,” DiZinno notes. Additionally,
