Lidding foils for FORMPACK and thermoformed blister

[email protected] copyright 2007® 1/17

Lidding foils for FORMPACK and thermoformed blister

by Dr.E.Pasbrig; Director R&D Alcan Packaging Pharma Flexible Europe and Asia Summary: Lidding foils for blisters used for packaging of pharmaceutical products have been introduced since the 1960s. This article shall give an overview about the state-of-the-art of aluminium and the structure of the lidding foils in relation to the distinct application and quality criteria. Content: 1. Introduction 2. Aluminium foil - hard and soft tempered 2.1. Pinholes in Aluminium Foils 2.2 Mechanical properties of push-through foils 3. Types of opening 3.1. Push-through foil 3.2. Peelable lidding foil 3.3. Peel-push 4. Child resistance/senior friendliness (CR/SF) 5. Printability (in-line) 6. Quality tests on lidding foil 7. Closing remarks 1. Introduction Alcan Packaging Singen was the first company in the world to produce a rigid aluminium foil with a tight seal to hard PVC film which could be pushed through easily. It was introduced to the market in the beginning of the 60s. Numerous further developments have been carried out stemming from the "mother" of all push-through foils, a 20µm rigid aluminium foil heatsealable lacquered to PVC. Three categories are differentiated, dependent on the respective purpose: • Push-through for sealing to PVC, PP, PET and PE with the general structure: prelacquer 20 µm Al hard/soft tempered HSC prelacquer 25 µm Al hard/soft tempered HSC prelacquer 20 µm Al hard tempered PE extrusion

• Peel for sealing to PVC and PP with the general structure: paper PET 20 µm Al soft tempered HSC PET 20 µm Al soft tempered HSC paper 25 µm Al soft tempered HSC

• Peel-push for sealing to PVC and PP with the general structure: paper PET special adhesive 20 µm Al soft tempered HSC PET special adhesive 20 µm Al soft tempered HSC


Lidding foil for blisters (thermo-formed, FORMPACK) differ according to: 1. type of opening 2. child resistance 3. printability (in-line) 2. Aluminium foil - hard and soft tempered The structure of the grains of the rolling slab is being stretched when rolled down to a strip. The structure of the rolling slab and of the aluminium strip (soft recrystallization annealing) is being stretched during rolling. The aluminium grains take a longitudinal shape oriented in rolling direction. During the rolling process the technical properties change: Tensile strength increases and elongation diminishes. The recrystallized structure of the aluminium is achieved by intermediate and final annealing (table 1). Table 1: Formation of nuclei and growth of grains during recristallization (schematic). a) - d) are instantaneous exposures at constant temperature and increasing annealing time. a) Four recristallization nuclei developed in the microstructure (shortly after achieving the recristallization

temperature). b) More nuclei form whereas the first four nuclei have been growing into grain size. c)The grains continue to grow. Some of the recristallization nuclei touch and thus prevent each other´s growth. d) Primary recristallization is completed. The „recristallization structure“ was formed out of cold-formed grain

structure. (Table 1 from Altenpohl et. all; "Aluminium von innen betrachtet") After annealing the aluminium strip/foil will be of soft temper with lower tensile strength and higher elongation. Annealing is carried out at temperatures in the range of 250° and 400° C for several hours, depending on the type of alloy and gauge reduction during the cold-rolling process. During annealing process rolling aids on the surface of the aluminium foil will evaporate. These rolling oils and rolling additives prevent good adhesion of lacquers, adhesives and extrusion coatings as they are acting like separating agents. The laminating agent would have no adhesion to the aluminium thus paper / films would delaminate. After recrystallization annealing the aluminium foil is „lubricant-free“ and can be used for converting. Adhesion between aluminium - laminating agent - laminating substrate such as plastic films / paper is good thus there are no problems with delamination. There is one exception when lacquering hard as rolled (hard tempered) aluminium foils for push-through blisters. Here lacquers are used which can cope with part of the rolling additives. Application of protective lacquer is carried out in the first processing step of processing of push-through foil. Drying (removal of solvents) is carried out at high air temperature and with airflow. Due to these conditions a part of the rolling oil is also removed from the inner side of the material. Heatseal lacquering is carried out in the second processing step. The lacquer


contains resins which bind the residual rolling oil and which are characterized by a good adhesion to the surface. The heatseal lacquers are also checked for their sensitivity to humidity. For this test sealed strips of lidding foil and plastic are placed in water. The sealed seam strength decreases in case the lacquer does not have sufficient adhesion to the aluminium surface. Aluminium foil for lidding foils is double rolled. Double rolling is carried out by applying ( a liquid separation agent between the two aluminium strips. This avoids that the two foils stick together in the rolling slot – i.e. the slot between the plastic roller and the laminating roller. The inner side of the foil is roughened by means of the relative movement in the rolling slot. After separation of the two foils the outside is bright and the inner side is dull. The aluminium foil used for the push-through foil (Al 99, 20 and 25 µm) and for the peel-push- and peelable versions is chemically identical and is only characterised by another temper. The increased elongation of the soft aluminium foil will lead to a different push-through behaviour. Suitability of this material has to be tested by the manufacturer of pharmaceutical products. 2.1. Pinholes in Aluminium Foils The influence of pinholes in aluminium foil is a point of discussion related to water vapour and oxygen/gas barrier of aluminium lidding foils and alu-alu blister (coldform laminate). The barrier of a blister is related to the lidding and base material. In case of a thermoformed film absolute the main amount of transmission is through the cavity. Comparison of permeability alu-alu blister – barrier films (calculated)

material WVT (mg/d, 38°C; /90% RH) sealed seam

3 mm cavity blister

total ratio: alu-alu material = 1

250µm PVC/ 40 gsm PVDC 0.0087 0.0905 0.0992 62250µm PVC/ 60 gsm PVDC 0.0087 0.0664 0.0750 4715µm Aclar RX 160/200µm PVC 0.0058 0.0434 0.0493 3151µm Aclar UltRx 2000/200µm PVC 0.0058 0.0130 0.0188 12Alu-alu blister oPA/Al/60µm PVC 0.0016 0.0000 0.0016 1

In case of alu-alu blister and high grade Aclar® (UltRx 3000 and 4000) the cross migration through the sealed seam becomes relevant. The barrier of the lidding foil is related to the amount and size of pinholes in the aluminium foil. The following definitions are quotations from the standard EN 546-4, foils, part 4 – Special Property Requirements: 1. Pinholes Pinholes are holes with a maximum diameter of 0.20 mm, usually round or oval shaped, distributed randomly across foils with a thickness of 6 to 20 micron (picture 1). 2. Pinhole line Pinholes with a maximum diameter of < 0.20 mm which are distributed at random along the whole length of coil.


3. Rolling pores Pinholes with a maximum diameter of < 0.20 mm which are distributed in periodical intervals along the whole length of coil. 4. Application of checks of special properties Checks only have to be carried out if agreed upon between supplier and customer and stated in the order accordingly. The standard contains a table which stipulates the application of pinhole detection for thin, double-rolled converter foils (thickness 6 – 20 micron). Check for rolling pores is carried out for thin, double-rolled converter foils (thickness 6 – 70 micron). Pinhole detection is carried out by means of a light box. The translucent glass pane is illuminated by a source of light which provides a consistent lighting of 1 000 LUX to 1 5000 LUX. Lighting in the test room is reduced to 20 LUX to 50 LUX. The sample undergoes a visual check from a distance of approx. 0.5 m. The sample has to be selected according to one of the following procedures: a) Random selection: a sample of the size of 1 m² is selected at random b) Selection of the worst area: a sample of 1 dm² is selected from the area with the highest porosity (worst field) Number of pinholes, pinhole lines, or rolling pores in the sample is counted; whereas pinholes with a diameter of < 0.020 mm are not considered and thus not counted. The number of pinholes of the random sample is counted on a square of 1 m². The number of pinholes of the worst sample is counted on a square of 1 dm². The maximum number of pinholes, pinhole lines, and rolling pores acceptable has to be agreed upon between supplier and customer. This standard was issued in 1997. Feasibility of pinhole detection for foil thickness of maximum 20 micron results from the knowledge that foils of a thickness of > 20 micron are pinhole-free (considering a visual check on any sample). Visual checks for pinholes on samples of 1 m² to 3 m² usually result in no findings of pinholes for foils thickness ≥ 20 micron (check is carried out with uncoated aluminium foil after rolling, or after unwinding). Standard EN 546-4 does not stipulate porosity limits in dependence on foil thickness. Aluminium foil and thin strip with gauges ≥ 20 am are not completely free of pinholes. Single pinholes may occur randomly distributed in large distances. Therefore they are normally not detectable in the light table test. However, if at all, foil and thin strip ≥ 20 am show at least less than 0.5 pinholes/m2; typical average: less than 0.1 pinholes/m² Periodically occurring faults (rolling holes) are not acceptable. Definition of pinhole, testing method on light table and evaluation according to DIN EN 546-4. These limits refer to a visual check, and evaluation of the foil on the light box. The limit of pinholes/dm² was agreed upon based on the experiences from a 100 % check by means of a pinhole detector.


For aluminium foil with thickness 9 to 45 µm following limits are acceptable:

thickness (µm) maximum amount of pinholes average 9 - 13 500/dm² -

15 200/dm² < 0.5/dm² 20 0.5/m² < 0.1/dm² 25 0.4/m² < 0.08/m² 30 0.3/m² < 0.06/m² 45 0.1/m² < 0.02/m²

Following examples of pinholes in 9 µm Al foil. As said, in 20 µm pinholes are very seldom and difficult to find.

Pinhole in the aluminium (9 µm)


The measurement of transmission of water vapour and oxygen is done in accordance to standards: oxygen: ASTM D 3985-81 (25°C; 50% RH) < 0.005 cc/m² x d x bar water vapour: ASTM F 1249-90 (25°C; 100% RH) < 0.01 g/m² x d A pinhole is not a straight breakout in the aluminium foil. The hole will be smaller in the middle compared to the outer side. This can be measured with transmitted light.

Dr.Pasbrig, [email protected]

effective defect

normally seen

effective defect < normally seen



Lidding foil is lacquered from both sides, or laminated with paper, paper/PET and on the other side is heatseal lacquer.

heatseal lacquer

PET

pinhole

pinhole

pinhole

aluminum

aluminum

aluminum

pre-lacquer

heatseal lacquer

heatseal lacquer

adhesive

PET

paper

adhesive

adhesive

Pinhole in Al and influence after converting

The permeation rate through a pinhole of 20 µm (314 µm²) covered by 5 µm PVC-lacquer would be 20 x 10-9 g/d (20 ng/d). The permeation rate would be 750 times lower than the limit of detection with the currently available test equipment. In the past test were done with aluminium foils (9 – 12 µm) in laminates for packaging coffee powder. The result was that aluminium foil with thickness of 9 µm protects the product sufficient. roasted and ground coffee, 500 g, vacuum packaging 1:

PET 12 µm reverse printed adhesive Al-foil 7 µm adhesive LDPE 80 µm

over lacquer printing oPP 35 µm metallization adhesive LDPE 80 µm

PET 12 µm printing adhesive coex 80 gsm PE-tie- EVOH 10 µm tie-PE

BOPP 25 µm printing adhesive metallization PE-tie 18 µm EVOH 8 µm tie 3 µm PE 18 µm intermediate layer PE 30 µm PE 20 µm

WVTR (g/m²) 23/85% RH < 0.2 0.2 4.8 < 0.2 O2-permeability (ml/d x m² x bar)

< 0.02 0.4 0.2 < 0.2

filling good shelf life at 25°C > 2 year 2 year 2 year > 2 year xxxxxxxx = barrier layer

1 H.Schroeder; H.Richarz, Grevenbroich; SAR/RSA/SAR 1/1981


Result of test for limit of O2 and water vapour (≥20 µm hard tempered Al-foil: 1 g/m² lacquer/ Al/ 7 g/m² heatseal lacquer): O2: ASTM D 3985-81 (25°C; 50 % RH) < 0.005 cc/sqm x d bar H2O: ASTM F 1249-90 (25°C; 100 % RH) < 0.01 g/sqm x d. 2.2. Mechanical Properties of push-through foils Mechanical properties (elongation A10 and tensile strength - Rm-) of push-through foils are described. The test as to elongation and tensile strength are no parameters which would affect the quality of further converting and thus do not underlie permanent checks. Thus these are no statistical values but only individual values. Due to the temperature which is required for drying of the lacquers it is possible that the aluminium foil has a decreased rigidity (partly crystallisation) and the state is between soft and rigid. The degree of decreased rigidity depends on the technological treatment during rolling process and the annealing after rolling of the aluminium strip. Rigid aluminium foil, 20µm should be set technologically in such a way that it is resistant/stable to temperature after the last rolling pass (double rolling). Thus the influence of heat during the drying process of the lacquer does not completely decrease the rigidity of the metal. The metal maintains an intermediate rigidity with "rigid character" (temper 24). The crystal structure of the soft aluminium foil is re-crystallized completely during annealing and results in temper 01. Internal stipulations for the tensile strength of aluminium foils are as follows:

alloy tensile strength (N/mm²) Al 99 / 24 100 - 120 Al 99 / 01 050 - 075

The table below depicts the individually measured values of elongation:

plain lacquered on both sides

lacquered on both sides

Al elongation (%)

unprinted printed alloy temper thickness (µm)

maximum

x Al 99 19 25 1 – 1.5

x Al 99 01 25 > 4,0 x Al 99 01 25 > 4.5

x Al 99 19 20 1 – 1.5 x Al 99 24 20 > 2.0 x Al 99 24 20 > 2,0

x Al 99 01 20 > 4,0 x Al 99 01 20 > 4,5

- temper: 01 = soft; temper 19 = hard as rolled; temper 24 = rigid lacquered; - these data are measured and no statistical value.


3. Types of opening There are the following types of opening for blisters: 1. push-through 2. peelable 3. peel-push The lidding foils are sealable to PVC, PVDC-coated PVC, PP and PET. 3.1. Push-through foil This type of lidding material is applied the most. The thickness of the aluminium used varies from 15 to 30 µm (mainly depending on the countries’ "thoughts on safety", child resistance, type of sealing medium). Here both soft- and hard tempered aluminium foils are used. Preference is given to the 20 µm hard tempered foil. Foil with 25 µm is mainly used in the USA (1 mil = 25.4 mm 25.4 µm). The 5 µm difference in thickness does not mean the 25 µm foil is more resistant to occurrence of pinholes during rolling process. Soft tempered 25 µm foil is mainly used for CR application in Germany. The GSM of the sealing lacquer/coating is dependent on the type of sealing layer as well as on the packing machine (age). The coating weight of lacquers for sealing to PVC has at present been reduced from 12 gsm to 6 to 9 gsm, whereby 7.0 +/- 1.5 gsm (4 s tolerance) are mainly used. The diagram in table 1 shows the sealed-seam strength of push-through foils for sealing to PVC. The minimum sealed seam strength of 7 N/15 mm (request of the pharmaceutical industry) will be achieved with 0.3 sec. at 140 °C. This means that on fast running blister machines a tight seal can be achieved without increasing the temperature too much. The sealing temperature on the machines depends on the kind of sealing as well. For intermittent sealing temperature is 150 °C and has to increase if dwell time will be shorter. For rotary sealing with low speed the sealing temperature is approx. 160 °C and for the fast running lines (up to 14 m/min) max. 240°C. Table 1: Influence of dwell time on sealing strength (PVC-foil)

6

7

8

9

10

11

12

13

14

140 160 180 200 220

sealing temperature (°C)

seal

str

engt

h (N

/15

mm

)

0.3 sec. 0.5 sec.

0.7 sec. 0.9 sec.

lidding: 20 µm Al hard/7 gsm HSC - LA 2404; PVC-film: PH 177 transperant; angle of opening: 180°;


There is also an influence of the type of PVC film (PH 170 and 177) used. If the PVC is coloured, e.g. white, the sealing strength is slightly higher (table 2). This can be related to the morphology of the surface or minor changes in the recipe. Table 2: Influence of the type of PVC on the sealing strength

PVDC coated PVC is used as barrier to water vapour. Compared to PVC the sealing strength is approximately 2 N/15 mm higher (table 3). The assumption: The more lacquer the higher the impermeability of the blister is incorrect, provided the sealing tools function properly. The impermeability of a blister, related to the sealing, is influenced mainly mechanically through non-parallel sealing tools and temperature fluctuations within the sealing plates or sealing rollers and soiled surfaces of the sealing tool. Always provided that the appropriate heatseal lacquer is used and that the lacquering is faultless. Table 3: Sealing strength of PVDC

6

7

8

9

10

11

12

13

14

140 160 180 200 220sealing temperature (°C)

seal

str

engt

h (N

/15

mm

)

DD 21 - PH 170 - white

DD 21 - PH 177 - transparent

lidding: 20 µm Al hard/HSC - LA 2404; 7.0 gsm; angle of opening: 180°; dwell time: 0.5 sec.

6

7

8

9

10

11

12

13

140 160 180 200 220sealing temperature (°C)

seal

str

engt

h (N

/15

mm

)

60 PVDC 90 PVDC

120 PVDC PVC PH 177

lidding: 20 µm Al hard/HSC - LA 2404 - 7.0 gsm; angle of opening: 180°; dwell time: 0.5 sec.;


3.1.1. Defects of sealing Defects of the sealing tool, faulty lidding foil and bottom material foil might lead to leaky blisters. Channels are detected by means of a vacuum test (blue bath test). It is important to be aware of the reasons. One method to determine these reasons is scanning with the electron microscope (REM). Hereunder please find this type of determination (table 4) Faulty cavities can be detected by the snake-like channel from the edge of the blister to the cavity detected by transmitted light microscopy (table 4/a). In the electron microscope one can easily detect the channel after removal of the push-through foil (table 4/b in the centre from above leading below and in detail in table 4/c). Comparison to a good area (table 4/d). Table 4/c depicts the bottom of the channel which is the plastic surface without sealing lacquer; beginning of the sealing is detectable at the edges of the cavity. Table 4: REM picture of channel

picture 4/a: overview picture 4/b: REM overview of channel

picture 4/c: REM detail of channel picture 4/d: REM overview of good sealing


Parts of the sealing with micro-channels will cause problems of stability over the time. This defect is normally not detected by the vacuum test. Table 5 shows REM pictures of a tight sealing and one with micro-channels (same blister). Table 5: blister with and without micro channel

good sealing micro-channel The composition of the heatseal lacquers is dependent on the type of plastic material which is to be sealed: • PVC and PVDC-coated PVC : copolymers of vinyl chloride and vinyl acrylate • PP : copolymers of polypropylene • PET : polyester resins or PVCA/acrylate • PE : PE extrusion A very good seal to the bottom material and adherence to the surface of the aluminium foil is achieved by this "chemical" coordination. The outside, preferably the dull side of the aluminium foil, is protective lacquered and/or printed and overlacquered. When the bright side is printed, the typography and writing can be difficult to read. The term "printing primer" is also used instead of protective lacquer. These terms explain at the same time the need for lacquering the outside. If the hard or soft-tempered aluminium foil is not lacquered, the surface of the aluminium can be rubbed off during the packing process and even more so during transport. This results in a black coloured bottom of the cavities, i.e. on the areas which are in contact with the blisters stacked below ("aluminium corrosion"). Further disadvantages are deteriorated adherence of the printing inks and insufficient gliding movement of the bottom foil against the aluminium foil (sticking when stacked) in the packaging machine/cardboard packer. The printing overlacquers are applied because of their higher temperature stability and to avoid ink-smearing when reel-winding. The heat stability is especially necessary for rotary sealing due to the higher sealing temperatures and sealing pressures of this procedure.


It can happen, that during the sealing process steam comes out of the sealing tool. This steam will condense on cooler parts of the machine and over the time yellow to brown drops form. These may drop on the lidding foil of the sealed blister strip and the print will be removed partly. The reason for this is mainly the ink for printing and/or the protective lacquer. If it contains monomer plasticizer (dibutyl-phthalate or dioctyle-phtalate) they will partly evaporate during sealing process. The printing inks which are applied at ALCAN Packaging contain polymeric plasticizer and do not show the mentioned problem. Print on the inner side Calender packs require also a print on the inner side of the lidding foil. Other specifications are coloured on the inside (Marketing). Now we have to cope with the requirement of the FDA that all substances which come into contact with pharmaceuticals have to be approved according to the FDA list. As to colours: Only natural pigments (white and brown/gold) comply to these requirements. All synthetical colours may not have direct contact with the filling good and have to be protected by means of a plastic film. A compromise can be made for printing of the material: Colour opacity < 5% and printing not in the area of the cavities. The printing ink may be NC-based. Sealable printing inks have to be used for colour opacity >= 5% and printing is carried out in critical areas of the sealing (land area; between the cavities). The resulting printing quality is for the most part not as good as if it were printed on a prelacquer (unevenness of HSC surface). To be on the safe side printing should be carried out on a prelacquer (approx. 1.0 gsm). In this case also the risk is lower that the printing ink is pushed aside during sealing or that the print merges into one another (blurred print design). The print is overlacquered with HSC in a subsequent processing step. 3.2. Peelable lidding foil Peelable sealing means that easy opening is achieved with the same impermeability as with push-through foil. Differences exist between rigid and soft peel but there are no limit values for the sealed seam strength. Peelable lidding foils are applied to achieve child resistance further for filling goods which are sensitive to pressure. The peeling is achieved through - special heatseal lacquers which are "softer" than those applied for push-through foil. - structure of the support foil/laminate. The opening angle which is used when peeling off the lidding foil has a decisive influence on the measured sealed seam strength. The diagram in table 5 shows the results for sealing of FORMPACK material to lidding foil with the following structure: 50gsm paper/12 µm PET film/20 µm soft aluminium foil/7 gsm heatseal lacquer.


Table 5: Peelable lidding foil - influence of the opening angle on the peeling force

With an opening angle of 180° steady values are achieved which range about 4.5 N/15 mm, an opening angle of 90° results in values of approximately 2.5 N/15 mm. This constant is a characteristic sign of peel lacquers at distinct sealing temperatures and times. Both of these limiting values will not occur in practice. The opening angle is at about 130°. In contrast to the non-peelable sealing no increase of sealed seam strength can be achieved by a further increase of the sealing temperature. As the lacquers applied here are „soft“ they flow more the higher the temperature. This might result in the following: The lacquer is squeezed aside so much that channels form thus the sealing is leaky. 3.3. Peel-push This type of lidding foil is applied for CR/SF blisters. These blisters are opened by peeling the PET film or paper-PET-laminate off the aluminium foil. The tablet/capsule can be pressed through afterwards. In comparison to the aluminium surface, the PET film has only a minor adhesion and can therefore be peeled off without tearing. When sealing peelable lidding foils and the peel-push version, attention must be paid to the fact that the composites require a higher sealing temperature than lacquered aluminium foils (push-through). Paper, PET film and the laminate paper/PET work as insulators for the diffusion of warmth. It is therefore better to warm the top foil first (preheating station or contact with the sealing roller) before it is processed in the sealing station. 4. Child resistance/senior friendliness (CR/SF) The laws regarding child safety vary from country to country. Attention is to be paid to the fact that patients, especially elderly, are able to take the tablets out of the package without problems (test for seniors). The type of opening and CR/SF can be seen in close connection with one another. In Germany and the USA blister packs are applied the most where child resistance is required. In Germany it is generally to be said that the tablets should not be visible, which is why white opaque or dark coloured foils are used for thermo-formed blisters.

0

1

2

3

4

5

6

180 200 220 240 260 280

sealing temperature (°C)

peel

ing

forc

e (N

/15

mm

)

0,5 sec.; 90° 0,5 sec.; 180° 1,0 sec.; 90° 1,0 sec.; 180°

50 paper/12 PET/20 Al soft/HSC LA 2475 - 60 PVC/45 Al/25 oPA


Child resistance can be achieved by means of the packaging material (lidding foil and base material) and the blister design. Related to CR/SF a separate paper will be published. 5. Printability (in-line) When choosing lidding foils heed is to be given to the fact that they can also be printed on the packing machine. Printing might comprise variable details (lot no., expiration date) or a complete print design. The following printing systems are available on the market: printing inks on a solvent base ultraviolet hardening printing inks laser print ink jet process thermo transfer print laser marking Certain matters have to be taken into consideration, e.g. the printing primers (protective lacquer), print overlacquers, paper and polyester films must guarantee sufficient adhesion of the printing inks. If adhesion is too low the printing ink might come off in the sealing station (sticking on the sealing tool), or could be rubbed off when being stacked, so that in both cases printing can no longer be read properly. In-line printing with solvent-based inks is the exemption in Europe and USA. More or less it is changed to UV curing inks and laser printing. 6. Quality tests on lidding foil Coating weight of lacquer (pre-lacquer and heatseal lacquer): The coating weight is generally determined during running production at the end of the reel on the left and right edge of the reel. Additional manual measurements across reel length are not possible as for this the process would have to be stopped, loose its stability and additional waste would be caused. Special bulk productions in campaigns are only checked at random. Huge lacquering lines for bulk productions are equipped with an IR camera; this IR camera measures the coating weight of the lacquer traversally across the reel width. A control system regulates the lacquering plant (= SPC). Coating weight of printing ink and lacquer: The lacquered reels are subsequently printed. The exact determination of the coating weight of printing ink and lacquer can only be carried out if silicon paper has been applied to the material during printing process. By help of this paper the coating weight of printing ink and lacquer can be determined. As this is a complicated process on the printing machine this determination is only carried out once per reel. As printing ink and printing overlacquer are applied by help of cylinders, the coating weight is already predefined by the depth of the cavities of these cylinders. In case viscosity and share of solid parts are adjusted correctly one achieves an exact and homogeneous coating weight which does not have to be checked by means of further tests. Tests after reel slitting are only possible to a limited extent. The only definite test which could be carried out is the measurement of the coating weight of the heatseal lacquer. Check of


print, lacquer and coating weight of the pre-lacquer cannot be carried out any more. Only the total weight of pre-lacquer, printing ink and overlacquer can be determined. Sealed seam strength Determination of sealed seam strength is the quality criterion for tight sealing. For this determination the lidding foil and the appropriate bottom material (thermoformed; FORMPACK) are sealed against each other.

Sealing conditions tight seal peel sealing pressure N/cm² 50 50sealing bar temperature above °C 150 200sealing bar temperature below °C RT RTsealing time sec. 0.5 1.0

The sealed strips are pulled apart by means of a testing device. The result (average of the peeling force) given in N/15 mm is the reference number for the quality. There is no national or international standard for the sealed seam strength of push-through foils. Nevertheless unwritten the following limits are accepted in Europe: The value should not be below 7 N/15 mm. For peelable openings there are no set values, generally they range between 3 and 8 N/15 mm. 7. Closing remarks Due to the ever increasing efficiency of production lidding foils have to be processable on fast running packaging lines with platen sealing and rotary sealing. Thus for sealability it must be possible to decrease the minimum required sealing temperatures of the heatseal lacquers whereas the hot tack has to remain constant or might be increased. ALCAN Packaging can offer types of lidding foils for all applications. We comprise lacquer development and production in our plants in Germany (SINGEN) and Switzerland (Kreuzlingen). We can consequently react quickly to market requirements. For example, the heatseal- and pre-lacquers for the lidding foils were developed in the plants.

Lidding foils for FORMPACK and thermoformed blister

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