HAVE YOU EVER ASKED YOURSELF...
...HOW TO MAKE HIGH-PERFORMING IML FILM MOST EFFICIENTLY?
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 REASONS 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.
... WE KNOW HOW!
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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.
... 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.
... WE KNOW HOW!
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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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...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 in general
- 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 tend to delay in performance occasionally.
Possibilities to control electro-static charging are even more limited. All systems compatible with the orientation process (and Food Contact Regulations) are migratory in nature and require exposure to a certain level of moisture to perform as required. This makes testing for anti-static properties fairly difficult in a typical Q-lab and the necessary conditioning of the film adds 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 developing a "cloudy" and "greasy" appearance known as blooming and potential interference with the adhesion of metal layers (barrier film), printing inks, and adhesives. Optimizing additive incorporation is required.
... 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 HOW!
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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.
Quality needs require processing conditions to reflect the properties of the highest melting resin. The thermal stress this imposes on lower melting component tends to cause so-called "die drool".
Die drool is generally believed to be due to premature degradation of one of the components and leads to increased production costs by shortening the intervals between cleaning services at the line. 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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... 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? No need to worry: There are methods established that substitute for 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 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 ...