HAVE YOU EVER ASKED YOURSELF ...
... HOW TO COMPLY WITH DEMANDS FOR PRODUCTS FROM SUSTAINABLE RESIN WITHOUT DISRUPTING MANUFACTURING EFFICIENCY?
Most observers believe that the recent revival of the demand for sustainability will not fall silent easily. As a consequence, to support this trend and their own “green” claims, brand owners and retailers will insist that their suppliers can at least plausibly demonstrate preparedness and possibly show-off first projects and applications. However, volumes of resin from suitable origin, whether bio-based or from recycling of plastic waste, are still limited since investments in facilities of practically relevant capacity are still scarce. One reason seems to be that the technology is not yet mature enough to take the risk of hundreds of millions of failed expenditure.
Under these conditions it would be a shame if converters wasted such significantly higher-priced resins during line re-starts and product change-overs or for physically separating sustainable from non-sustainable products.
To make best use of these precious materials the concept of mass balance has been developed. This concept stipulates that a converter must establish a procedure by which it is ensured and documented that in any given period of time there will not be more product produced and sold than can be made from the amount of sustainable resin purchased, considering as well any percentage of material that is to be expected to be lost by previous experience. This concept has been tuned to account for most of the obstacles and any imponderability a manufacturer of plastic articles has to deal with: Short-term call-off of volumes scheduled for later, delays of resin supplies for reasons beyond the scope of the converters responsibility, re-utilization of volumes of sustainable resin that has been reclaimed internally. You are afraid that tracking and documentation will be too complex to implement and handle for your lean organization?
WE CAN SHOW YOU HOW TO COMPLY WITH THE RULES EFFICIENTLY ...
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... HOW TO BALANCE APPARENTLY INCOMPATIBLE SPECIFICATIONS FOR HIGH PERFORMANCE IML FILM MOST EFFECTIVELY?
In-mould labelling of all kinds of containers is a market segment that shows dynamic growth in all regions of the global BOPP market. The technology requires a number of conversion steps including cutting sheets from a roll of film, high quality printing of the sheets, cutting and stacking of the printed labels as well as de-stacking and electrical charging of the labels, and precise positioning in the mould at the moulding machine, to finally stick fast to the container walls without any blisters and creases after the container has been formed.
Entry barriers are comparatively high since stacking and de-stacking, printing and handling properties of the film substrate as well as the ready-made labels, not to forget: appearance (colour, gloss at various angles) must comply perfectly with technical requirements that appear to be incompatible in part.
Besides the complex and highly specific formulation, a number of processing conditions must be carefully observed to meet the quality standards of the IML market regarding appearance, printing, and handling properties by balancing
- unit weight against stiffness,
- good adhesion against reliable cutting,
- slip and electrostatic properties not only against the costs of additives and masterbatches but also against printability,
- low static on de-stacking and stacking during printing and before, against sufficient static charging for reliable transfer to, the mould,
- precise positioning and, during injection of the melt, anchorage inside the mould.
For consistent performance and acceptance static properties must be controlled during the whole value chain, starting with film manufacture.
WE KNOW HOW …
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... HOW TO BROADEN THE RANGE OF INKS SUITABLE FOR BOPP, ENHANCE AND PROLONG PRINTABILITY AS WELL AS ADHESIVE ANCHORAGE?
BoPP film is highly appreciated not only for its natural moisture barrier, but also for its dimensional stability in printing and lamination. However, there is a major disadvantage: BoPP requires corona or plasma treatment to prepare for, and ensure, appropriate spreading (or “wetting”) and adhesion of specific inks optimized for this purpose and even this will work for a limited time only since treatment fades quite rapidly: Printability is usually warranted for no more than six months. This is acceptable only for printers typically specializing in BoPP printing who have learnt how to “refresh” the treatment by investing in corona treaters in-line with the press or laminator.
On the other hand, the packaging industry is a mature market and the converters tend to squeeze margins in a way that innovative film manufacturers are well advised to look out for other markets, making the film fit i.e. for digital printing technologies, “narrow width” luxury label printing or, i.e., the specific needs of the pressure sensitive label (PSL) industry. To comply with those needs, meaning ensure compatibility with a wide range of inks, excellent print quality and ink adhesion as well as long-term printability (two or three years or more), opens the door to replace other materials like paper in high-priced applications. Among special applications are labels that require durability as for drums and other bulk containers for i.e. the chemical industry, or compatibility with polyolefin based substrates to accomplish the status of single-material solutions for easy recycling. But how to get there?
WE KNOW HOW …
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... HOW TO ACCOMPLISH A NEXT-GENERATION ULTRA-HIGH BARRIER METALLIZED BOPP FILM?
Although metallized barrier BoPP films are broadly used for decades there is always a need for improvement: appearance, printability of the metal layer, metal adhesion, barrier / shelf-life. Improving metal adhesion and barrier through treatment of the polypropylene surface has apparently been exploited to the limits: even the plasma treatment in modified atmosphere, be it in-line with manufacture of the film or in-line with deposition of the metal, never met expectations due to occasional short plasma trips resulting in small patches of untreated film among other issues. There are several patents in place on BoPP film with a chemically modified surface that look promising, however, for now they block the entry to a number of attractive markets.
WE KNOW WHAT NEEDS TO BE DONE …
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... HOW TO INCREASE OUT-PUT OF BOPP LINES LIMITED BY HEAT TRANSFER IN MDO OR TDO?
The out-put and capabilities of BOPP lines is often limited by the amount of heat you can transfer to the film to make it ductile enough for efficient and safe stretching. The most obvious solution, adding to the number of heat transfer rollers before MDO or to the length of the pre-heat zone in the TDO oven will hardly ever work for a simple reason: No space, or, if you were to add to them, there wouldn’t be enough space for operators and engineers to do their work during start-up, breaks or maintenance.
Another problem associated with limitations in heat transfer is a pronounced differential in mechanical properties between web centre and edge. A revamp of heat transfer nozzles or up-grade of the air blowers would require a maintenance stop of several weeks and is, thus, no option.
If only there were equipment that you could move in an out as required or if you could make use of the ample space on the side of MDO and oven entry or if technology were available that selectively compensated local deficiencies in heating power – or is there?
WE KNOW THERE IS AND HOW TO MAKE USE OF IT …
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... HOW TO MAKE TRANSPARENT BOPP FILM WITH ULTRA-HIGH BARRIER?
High and ultra-high oxygen barrier films that are aluminium coated, or metallized, are reliable and well established in the market. However, the aluminium layer prevents viewing the packed good and the “clean” metal look is not always what product managers and packaging engineers are looking for. Further, the metal may prevent correct sorting of the package in the post-consumer waste stream and causes a grey or greyish appearance of second-life products made from post-consumer recycled resin. Finally, consumers confuse the metal look with aluminium foil and, thus, associate it with waste of energy and with reports on aluminium possibly furthering dementia.
None of these disadvantages apply to coatings of amorphous aluminium oxide (AlOx) or, simply, AlOx. However, attractive barrier properties could not be reproduced in the industrial reality. A lot of work has been invested to figure out why: Is it a poor adhesion between the brittle AlOx and the BoPP surface, poor control of the aluminium / oxygen ratio, chemical processes associated with post-oxidation when the film leaves the chamber, or pin-holes? We believe it’s not much what’s missing.
WE KNOW WHAT NEEDS TO BE DONE …
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... HOW TO MAKE USE OF SPECIAL OFFERS OF BASE RESIN BY TUNING THEIR STRETCH PROPERTIES?
Today resin manufacturers typically provide no more by-lot QC data than melt flow rate (MFR) and yellowness index. However, in the case of BoPP the MFR is only one of three of the most important parameters to describe the performance as base layer material in the orientation process, the other two being xylene (or heptane) solubles (XS or HS) and the width of the chain length distribution, represented by i.e. the melt flow ratio (for example MFR (230 °C / 10 kg) / MFR (230 °C / 2.16 kg)). Thus, if you desire to save on resin cost by employing typical low XS tape resin grades you need to adjust stretchability in order to run your line efficiently.
You think that measuring xylene solubles (XS) yourselves is too cumbersome, and, involving solvents, too dangerous and won't help since there is no way to adjust XS other than employing expensive hard resin masterbatches? Not necessarily: There are methods established that substitute for the real XS testing. And to correct for the low XS, there are resins available that improve stretchability without raising issues with extractables and overall migration limit – you may even have them on site. How would you do that?
JUST ASK US …
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... HOW TO AVOID UNINTENDED STATIC CHARGING OF, e.g., IML FILM MOST EFFECTIVELY?
In-mould labelling of all kinds of containers is a market segment that shows dynamic growth in all regions of the global BOPP market. The technology involves a number of conversion steps that require a strict control of the electrostatic properties in a way that appears to be a "mission impossible": On the one hand, high static charging of the unwinding web, of the sheets and the labels when de-stacked and stacked in the press and at the moulding machine, respectively, entail safety hazards and interfere with smooth operations. On the other hand, the efficiency and reliability of the moulding depends on the transfer and retention of static charges of both polarities for the time it takes to transfer and position the label and fill the mould.
It's vexing and galling that you can spend a lot of money for anti-static additives or active or passive discharging, however, nothing works reliably. The reason is all these measures cure the symptoms, not the root cause. You wonder what's at the bottom and how to fix it?
We know both reason and cure …
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... WHAT A POOR CONTROL OF THE THICKNESS OF INDIVIDUAL LAYERS MAY IMPLY AND HOW TO CHECK?
The thickness of the individual layers of a multi-layer film is affected by the over-all out-put per layer, the design of the die’s interior melt channels, the flowability (primarily the melt flow rate, MFR) of the different raw materials and their blends (including recycled production scrap), the melt temperatures as well as the die temperature and some other processing conditions. In the best case, lack of control means wasting of expensive materials (sealing resin, masterbatches) in order to maintain product specifications over the width of the web. In the worst case, “having too much of a good thing” may seriously affect the film quality.
First thing, however not trivial, is to determine the thickness profiles of the film layers under well-documented conditions. Depending on the findings a number of corrective actions may be considered including re-specifying raw materials, changing line settings, and re-checking the die design.
WE KNOW HOW …
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... HOW TO MAKE METALLIZED FILM OF BRILLIANT APPEARANCE?
Besides for their barrier properties, metallized films are selected for their clean and “technical” appearance. Any kind of optical defect tolerable in standard coex is readily visible after metallisation. A number of processing conditions from positioning and operating conditions of the air knife via surface conditions of rollers (ridges as well as deposits) to temperatures and stretching ratios in MDO and TDO, and rotational velocity ratios in MDO and pull roll stand must be observed very carefully. Detailed documentation of all line settings are mandatory to reproduce successful operations. However, with all due diligence applied the variation in resin properties is wide enough to require an adjustment of manufacturing conditions. A decent understanding of the factors at work is mandatory to ensure reliable production.
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... HOW BEST TO CONTROL COSTS OF MAKING HIGH QUALITY MATT FILMS?
BOPP film grades with a matt face are mainly sold for their specific appearance. The matt appearance is basically provided by a blend of resins that separate from each other in domains of micron size on the one hand but stick to each other on the other hand. The quality of the “velvet” or “paper” or “non-plastic” look and the homogeneity of the appearance depend on the perfect homogeneity of the spatial distribution of the domains of the resin blend which strongly depends on the homogeneity and, therefore, on an intense mixing of the melt blend.
Unfortunately, when manufacturing matt film times of continuous operation of a BOPP line are limited by the formation of what is called “die drool”. Die drool has been analysed to consist of degraded resin that forms deposits on the outside of the die lip. These deposits cause mark lines on the film which deteriorate the homogeneous appearance and may even cause breaks when the bigger ones drop onto the film.
Using different types of resins requires compromising in the choice of processing conditions. The processing temperature must exceed the melting temperature of all components to create the homogeneous melt from which those resins segregate to form a film surface of controlled roughness. Unfortunately, however, the components of such blends are based on resins, which, by their nature, provide considerably different thermal stability. This is believed to be the root cause for die drool.
To prevent degradation masterbatchers tend to employ high levels of stabilizers that require more complex considerations with respect to food contact regulations than e.g. a standard coex film
Considering that, in general, matt blends are used in fairly thick layers in bulk as opposed to a typical masterbatch, such compounds of at best still fair performance are among the most costly BOPP raw materials offered by the masterbatch industry.
For all these reasons it is mandatory to minimize the thermal stress applied to the blend resins, limit the level of stabilizers, and save costs without compromising on the quality of the film product.
WE KNOW HOW …
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... WHY SURFACE TENSION OF METALLIZED FILM OCCASIONALLY DROPS TO LEVELS INCOMPATIBLE WITH PRINTING AND HOW TO FIX IT?
Besides for their barrier properties, metallized films are selected for their clean and “technical” appearance. Consequentially, the ease and appearance of the printing are crucial for the acceptance of metallised film by the converters.
Disregarding the so-called “revers” printing / lamination process, printing onto the metallized surface is mandatory in the manufacture of metal-look flexible packages. This as such is not a major issue since suitable printing inks are available that anchor well to the clean metal surface. However, like in every printing technology the surface energies of substrate and printing inks have to match in order to facilitate a proper spreading of the ink and prevent contraction of the individual ink droplets before curing. Low surface tension contamination of the metal surface, unevitably, results in poor appearance as well as poor anchorage of the printing.
Unfortunately the dyne level of metallized BOPP film surfaces often drops rapidly to critically low values, occasionally even within a couple of weeks, much quicker than corona treated BOPP film. This effect can be avoided by selection of suitable PP resins for the manufacture of the metallizable base film.
WE KNOW WHY, AND HOW TO FIX IT …
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... WHY IT IS SO DIFFICULT TO PROVIDE CONSISTENT SLIP PROPERTIES IN STANDARD COEX FILMS?
Food contact regulations limit the range of chemicals to select from to modify the properties of plastic articles. Chemical agents modifying the slip properties may serve as an example to point out these limitations:
- Siloxanes provide good slip properties but interfere with printing, sealing, and metallizing under certain conditions
- Certain anti-blocking agents provide acceptable slip properties on their own or may at least be used as slip synergists but require a close control of the top layer thickness and –last but not least– are fairly expensive.
- So-called migratory additives like traditional amide slip agents are still most cost efficient, however, tend to delay in performance occasionally.
The situation is even worse in controlling electro-static charging: The technical possibilities are even more limited. All systems compatible with the orientation process and food contact regulations are migratory in nature and require some aging time. Even worse, test results strongly depend on a prefect control of the level of moisture and observing a minimum exposure time to ensure equilibrium. This makes testing for anti-static properties fairly difficult in a typical Q-lab and the times needed for aging and equilibration add to the working capital costs.
For this, most BOPP manufacturers tend to add such additives generously, wasting money and, even worse, lay the seed for a greasy or cloudy appearance caused by “blooming”. This and interference with the adhesion of metal layers (barrier film), printing inks, and adhesives are comparatively frequent causes for customer claims. Optimizing additive incorporation is required.
WE KNOW WHY, AND HOW TO FIX IT …
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... HOW TO ENSURE HIGHEST QUALITY STANDARDS IN STANDARD COEX FILM MANUFACTURE?
“Standard Coex” is the kind of BOPP film with the biggest share in volume. Especially the market for grades designed for standard packaging applications is extremely competitive. To be profitable it is mandatory to control the internal rejection rates. On the other hand, convertors and brand owners are very sensitive to any kind of quality deficiencies especially all kinds of optical defects with “stretch bows” or “unstretched areas” and “triangles”, easily visible and therefore among those that are most frequently claimed.
All these defects are known to be related to the MDO stretching conditions and at the same time to be difficult to control even if operating conditions proven successful are most carefully documented and reproduced. Another piece of the puzzle is that before and after a cleaning service when restarting the line with the same lots of raw material and the same operating parameters the appearance of the product has been found to be quite different.
Such observations strongly suggest that there are one or more hidden factors at work that are apparently outside the control of the operator team. Careful analysis of many incidents of this kind led to strategies for adjusting the line settings that are against intuition.
WE KNOW HOW …
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... HOW TO IDENTIFY SUITABLE BASE RESIN BEFORE SPENDING MONEY ON PLANT TRIALS?
The response of the BOPP film-in-process to the processing conditions depends of the properties of the base resin and of the top layer material: The level of stretching resistance is dominated by the properties of the base resin and the temperature, grip and stretching efficiency in the MDO are dominated by the properties of the top layer material and the additive package – dominated, but by far not completely defined.
Combining no more than half a dozen of analytical methods for a side-by-side resin test saves extended phase-in procedures in the BOPP plant and enables short-cutting the approval processes. The total costs for such tests of less than 10 000 € (depending on what can be tested in-house) pay off easily compared to, let’s say, 4 hours of lost production time. Please note that some of these methods need specific interpretation regarding the resin supplier’s manufacturing technology.
Such methods can be used also to determine simple-to-test resin properties. Using these methods in incoming goods control it is possible to save resin costs by selectively up-grading cost-efficient resin grades such as offered for tape production by blending them with base resins of high ductility to enhance processability.
Based on the same general approach the assessment of top layer materials in a multi-source purchasing strategy seems possible but needs to be validated on a broader data base.
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... HOW TO MAKE HIGH-SHRINK TOBACCO OVER-WRAP FILM?
High shrink BOPP film is used in applications like cigarette hard packs where a tight fit of the over-wrap film gives the pack the appearance of high value. Top specifications amount to >13% shrink in MD. Such levels are achievable by combining certain additives and specific processing conditions (“hard stretching”) in addition to well controlled annealing conditions. With properly selected additives at adequate levels it is also possible to enhance processability (crucial in this segment!) and water vapour barrier. Unfortunately, such additives add considerably to the formulation costs.
These extra costs can be held at bay by using a special kind of base resin that act synergistic with the shrink additives. By this, the concentration levels of the additives can be lowered considerably without major change in processing conditions. As an extra bonus, film quality improves leading to lower rates of internal rejections adding up to several tens per cent of savings. Other key properties of such shrink films match well to the traditional bench-mark grades.
Transfer of these achievements into the segment of printed shrink wrap film is expected to be feasible.
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