Lidding foils for FORMPACK and thermoformed blister_e_1

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 alu-
minium 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)
erwin.pasbrig@alcan.com copyright® 1/12

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
Pinholes are material faults; their form is usually round or oval with a size of approx. 0.020
mm to 0.200 mm (DIN EN 546-4). Material faults of sizes > 0.200 mm are described as
holes; if occurring at regular intervals they are called „rolling holes“ as they are caused by
rolling. These are immediately detected during visual check against through-light as they
occur periodically in short intervals.
Pinholes in aluminium foils are caused by faults of the foil stock (gas bubbles, inclusions of
aluminium oxide and aluminium oxihydrate), lattice defects (alloying elements, grain
refinement elements) and/or faults occurring during rolling process.
Pinholes form during rolling when the size of the fault is bigger than the thickness of the
aluminium foil. It is self-evident that the number of pinholes is increasing with decreasing foil
thickness. Aluminium foils with thickness of 20 µm and above almost never show pinholes.
Check for pinholes is usually carried out by counting of pinholes (foil is put over a source of
light, pinholes can be counted). For this check a square with the most pinholes is selected
and the number of pinholes is counted on 10 cm².
Check of aluminium foils with 20 µm and 25 µm thickness was carried out by a in-process
pinhole detector installed after separation of double rolled strips using IR light. Only single
pinholes were detected with this method. This means that foil of this thickness processed by
ALCAN Packaging can be described as "technically free of pinholes". We warrant that the
average number of pinholes is approx. 1 pinhole/sqm. Our foil 9 to 14.9 µm has max. 7
pinholes per sqm.
2.2 Mechanical Properties of push-through foils
Mechanical properties (elongation and tensile strength - Rm-) of the push-through foils
applied at ALCAN Packaging 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 is set technologically in such a way at ALCAN Packaging 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 recrystalized completely during annealing
and results in temper 01.
Internal Stipulations for the tensile strength of aluminium foils are as follows:
alloy 158/24 (Al 99) 100 - 120 N/mm²
alloy 158/01 (Al 99) 50 - 75 N/mm²
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 158 19 25 1 – 1.5
x 158 01 25 > 4,0
x 158 01 25 > 4.5
x 158 19 20 1 – 1.5
x 158 24 20 > 2.0
x 158 24 20 > 2,0
x 158 01 20 > 4,0
x 158 01 20 > 4,5
Temper: 01 = soft; 19 = hard as rolled; 24 = rigid lacquered; alloy.: 158 = Al 99;
These data are measured values and are 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)
sealstrength(N/15mm)
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 177transperant; 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
6
7
8
9
10
11
12
13
14
140 160 180 200 220
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.

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
140 160 180 200 220
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).
picture 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 rotative 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
0
1
2
3
4
5
6
180 200 220 240 260 280
peelingforce(N/15mm)
0,5 sec.; 90°
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.
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

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.
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 50
sealing bar temperature above °C 150 200
sealing bar temperature below °C RT RT
sealing 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 rotative 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
prelacquers for the lidding foils were developed in the plants.
Dr.Pasbrig, Erwin
Director R&D Pharmaceutical Europe
Director R&D Pharmaceutical Asia
office:
Alusingen Platz 01
78221 Singen
Germany
phone: +49 7731 802510
mobile: +49 1733163932

Lidding foils for FORMPACK and thermoformed blister_e_1

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (10)

Similaire à Lidding foils for FORMPACK and thermoformed blister_e_1

Similaire à Lidding foils for FORMPACK and thermoformed blister_e_1 (20)

Lidding foils for FORMPACK and thermoformed blister_e_1