Note: Descriptions are shown in the official language in which they were submitted.
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In-mould label film for blow-moulding, method for producing same and its use
The present invention relates to the use of an opaque film as in-mold label
for blow
molding.
Films made from thermoplastics have recently increasingly been used for
labeling
containers. The prior art discloses various labeling processes. The films
which are
suitable for use of this type must have a selected property profile, with
different
labeling processes requiring different film properties. This means that very
frequently
only a single good property does not enable the film to be used for the
proposed
purpose. Rather, only a multiplicity of properties, which must be achieved
simul-
taneously in a film, ensure that the film can be used for the proposed
purpose.
A known process is in-mold labeling during blow molding of plastic containers.
In this
process, a tube of a suitable polymer is extruded continuously or batchwise.
The
tube is laid in a multipart mold cavity, pinched off at the lower end and cut
off at the
upper end. A nozzle is inserted in a tight-fitting manner into the upper
opening which
remains, and air is blown in through this nozzle during the actual blowing
operation,
blowing up the extruded tube and bringing it into close contact with the wall
of the
mold. The mold is then opened, projecting tube residues of the demolded blow
molding are removed at the top and bottom, and the process started afresh.
Labeling by blow molding during production of containers is known in the prior
art
and is referred to as in-mold labeling. In this process, a label is laid in
the opened
blow mold, usually by a robot, in such a way that the printed outside of the
label is in
contact with the mold wall, and the unprinted inside is facing the blow
molding to be
shaped. During introduction of the tubular melt and shaping of the blow
molding by
the air pressure, the still-plastic surface of the polymer composition comes
into
intimate contact with the label and bonds thereto to give a labeled container.
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It must be ensured during this labeling process that the label lies against
the mold
wall in a flat and fold-free manner. This is achieved either by means of
vacuum
applied to fine aeration perforations in such a way that the perforations are
substantially sealed by the label, or by means of electrostatic forces between
the
electrostatically charged label and the earthed mold.
In the case of simple label shapes, the label is introduced in roll form and
cut to size
directly at the blow-molding machine (cut in place). In the case of more
complex
outlines, the label is cut to size in advance and away from the blow-molding
machine, stacked, segregated from the stack at the blow-molding machine (cut &
stack process) and introduced individually into the blow mold.
Th.e present invention provides an inexpensive label film which is
suitable for in-mold labeling in blow-moiding processes. On use for in-mold
labeling,
the film should give rise to a visually perfect, well-adhering label, and the
film must
be processable without problems in the process.
This is achieved by the use of an opaque, multilayered polypropylene film as
in-mold label in blow molding. The film has a base layer and at least two top
layers,
where the base layer contains vacuole-initiating fillers, the film has an
overall
thickness of at least 85 pm, and the base layer contains a combination of
tertiary
aliphatic amine and fatty acid amide. Both top layers contain antiblocking
agents, the
density of the film is in the range from 0.65 to 0.85 g/cm3, and the film has
been
corona- or flame-treated on both surfaces.
It has been found that the special additive formulation of the opaque film in
combination with the film thickness, and the selected density and surface
treatment
on both sides, ensures that it can be used for the purpose according to the
invention.
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For the purposes of the present invention, the term "opaque film" means a non-
transparent film whose transparency to light (ASTM-D 1003-77) is at most 70%,
preferably at most 50%.
The opaque base layer of the multilayered film essentially comprises a
polyolefin,
preferably a propylene polymer, and opacifying fillers and the stated
additives in
effective amounts in each case. In general, the base layer comprises at least
50% by
weight, preferably from 60 to 99% by weight, in particular from 70 to 98% by
weight,
of the polyolefin, in each case based on the weight of the layer.
Preferred polyolefins are propylene polymers. These propylene polymers
comprise
from 90 to 100% by weight, preferably from 95 to 100% by weight, in particular
from
98 to 100% by weight, of propylene units, have a melting point of 120 C or
above,
preferably from 150 to 170 C, and generally have a melt flow index of from 0.5
to
8 g/10 min, preferably from 2 to 5 g/10 min, at 230 C and a force of 21.6 N
(DIN
53735). Isotactic propylene homopolymer having an atactic content of 15% by
weight
or less, copolymers of ethylene and propylene having an ethylene content of 5%
by
weight or less, copolymers of propylene with C4-C8-olefins having an olefin
content of
5% by weight or less, terpolymers of propylene, ethylene and butylene having
an
ethylene content of 10% by weight or less and having a butylene content of 15%
by
weight or less are preferred propylene polymers for the base layer, with
isotactic
propylene homopolymer being particularly preferred. The stated percentages by
weight are based on the respective polymer.
Also suitable is a mixture of said propylene homopolymers and/or copolymers
and/or
terpolymers with other polyolefins, in particular made from monomers having 2
to 6
carbon atoms, where the mixture comprises at least 50% by weight, in
particular at
least 75% by weight, of propylene polymer. Suitable other polyolefins in the
polymer
mixture are polyethylenes, in particular HDPE, LDPE, VLDPE and LLDPE, where
the
proportion of these polyolefins is in each case not in excess of 15% by
weight, based
on the polymer mixture.
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The opaque base layer of the film comprises fillers in an amount of at most
40% by
weight, preferably from 1 to 30% by weight, in particular from 2 to 20% by
weight,
based on the weight of the opaque layer. For the purposes of the present
invention,
the fillers are pigments and/or vacuole-initiating particles.
For the purposes of the present invention, pigments are incompatible particles
and
essentially do not result in vacuole formation when the film is stretched. The
coloring
action of the pigments is caused by the particles themselves. The term
"pigments" is
generally associated with a mean particle diameter in the range from 0.01 to a
maximum of 1 pm and covers both so-called "white pigments", which color the
films
white, and "colored pigments", which give the film a colored or black color.
In
general, the mean particle diameter of the pigments is in the range from 0.01
to
1 pm, preferably from 0.01 to 0.7 pm, in particular from 0.01 to 0.4 pm.
Conventional pigments are materials such as, for example, aluminum oxide,
aluminum sulfate, barium sulfate, calcium carbonate, magnesium carbonate,
silicates, such as aluminum silicate (kaolin clay) and magnesium silicate
(talc),
silicon dioxide and titanium dioxide, of which white pigments, such as calcium
carbonate, silicon dioxide, titanium dioxide and barium sulfate, are
preferably
employed.
The titanium dioxide particles generally comprise at least 95% by weight of
rutile and
are preferably employed with a coating of inorganic oxides and/or of organic
compounds containing polar and nonpolar groups. Ti02 coatings of this type are
known in the prior art.
For the purposes of the present invention, "vacuole-initiating fillers" are
solid particles
which are incompatible with the polymer matrix and result in the formation of
vacuole-like cavities when the films are stretched, with the size, nature and
number
of the vacuoles being dependent on the size of the solid particles and the
stretching
conditions, such as stretching ratio and stretching temperature. The vacuoles
reduce
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the density and give the films a characteristic pearl-like opaque appearance
caused
by light scattering at the "vacuole/polymer matrix" interfaces. The light
scattering at
the solid particles themselves generally makes relatively little contribution
toward the
5 opacity of the film. In general, the vacuole-initiating fillers have a
minimum size of
1 pm in order to result in an effective, i.e. opacifying amount of vacuoles.
In general,
the mean particle diameter of the particles is from 1 to 6 pm, preferably from
1.5 to
5 pm. The chemical character of the particles plays a secondary role.
Conventional vacuole-initiating fillers are inorganic and/or organic,
polypropylene-
incompatible materials, such as aluminum oxide, aluminum sulfate, barium
sulfate,
calcium carbonate, magnesium carbonate, silicates, such as aluminum silicate
(kaolin clay) and magnesium silicate (talc), and silicon dioxide, of which
calcium
carbonate and silicon dioxide are preferred. Suitable organic fillers are the
conventional polymers which are incompatible with the polymer of the base
layer, in
particular those such as HDPE, copolymers of cyclic olefins, such as norbomene
or
tetracyclododecene, with ethylene or propene (COC), as described in
EP-A-0 623 463, polyesters, polystyrenes, polyamides and halogenated organic
polymers, preference being given to polyesters, such as, for example,
polybutylene
terephthalate, and cycloolefin copolymers. For the purposes of the present
invention,
"incompatible materials or incompatible polymers" means that the material or
polymer is in the film in the form of a separate particle or separate phase.
The base layer preferably comprises pigments in an amount of from 0.5 to 10%
by
weight, preferably from 1 to 8% by weight, in particular from 1 to 5% by
weight.
Vacuole-initiating fillers are preferably present in an amount of from 0.5 to
25% by
weight, preferably from 1 to 15% by weight, in particular from 1 to 10% by
weight.
The data are based on the weight of the base layer.
The vacuole-initiating fillers reduce the density of the film. It has been
found that the
density of the film must be kept within narrow limits in order to ensure that
the film is
highly suitable for use as an in-mold label in blow molding. The density of
the film
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must be in the range from 0.65 to 0.85 g/cm3. Films having a density of less
than
0.65 g/cm3 exhibit optical defects on use as in-mold labels in blow molding,
usually in
the form of the so-called orange-peel effect, where the label film is deformed
on the
surface with formation of millimeter-sized bubbles, which result in a visually
unacceptable appearance. If the density is greater than 0.85 g/cm3, the
adhesion to
the container is poor. The poor adhesion at a film density of greater than
0.85 g/cm3
could be connected with the fact that the label film, with only slightly
reduced density,
is too inflexible at the surface and does not come into sufficiently intimate
contact
with the blow molding being formed. It is therefore essential to the invention
that the
density is in the range from 0.65 to 0.85 g/cm3, preferably from 0.7 to 0.8
g/cm3.
The overall thickness of the film is furthermore essential to the invention
and is at
least 85 pm, preferably from 87 to 120 pm, in particular from 90 to 100 pm. It
has
been found that films having an overall thickness of less than 85 pm cannot be
employed as in-mold label in the blow-molding process since on use of films
which
are thinner than 85 pm, relatively large bubbles form between the label and
blow
molding which frequently appear to be bulging or blown up. This is presumably
caused by air being included between the blow molding being formed and the
label
and being compressed under the increasing blowing pressure on a narrowing
area.
After demolding of the still-warm blow molding, the included air expands still
further,
with arching of the label.
Besides the opaque base layer, the film according to the invention comprises
top
layers on both sides. For the purposes of the present invention, top layers
are outer
layers whose outer surface forms the film surface.
The top layer of the multilayered film generally comprises at least 70% by
weight,
preferably from 75 to < 100% by weight, in particular from 90 to 98% by
weight, of a
propylene polymer and antiblocking agents and, if desired, further
conventional
additives, such as stabilizers and/or lubricants, for example fatty acid
amides, in
effective amounts in each case. Preference is given to embodiments of the top
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layers which additionally comprise fatty acid amides. The above data in % by
weight
are based on the weight of the top layer.
The propylene polymer of the top layer is preferably a copolymer of propylene
and
ethylene or propylene and butylene or propylene and another olefin having from
5 to
carbon atoms. Also suitable for the purposes of the invention are terpolymers
of
ethylene and propylene and butylene or ethylene and propylene and another
olefin
having 5 to 10 carbon atoms. It is also possible to employ mixtures or blends
of two
10 or more of said copolymers and terpolymers.
For the top layer, preference is given to ethylene-propylene copolymers and
ethylene-propylene-butylene terpolymers, in particular random ethylene-
propylene
copolymers having an ethylene content of from 2 to 10% by weight, preferably
from
5 to 8% by weight, or random ethylene-propylene-1-butylene terpolymers having
an
ethylene content of from 1 to 10% by weight, preferably from 2 to 6% by
weight, and
a 1 -butylene content of from 3 to 20% by weight, preferably from 8 to 10% by
weight,
in each case based on the weight of the copolymer or terpolymer.
The copolymers and terpolymers described above generally have a melt flow
index
of from 1.5 to 30 g/10 min, preferably from 3 to 15 g/10 min. The melting
point is in
the range from 120 to 140 C. The blend of copolymers and terpolymers described
above have a melt flow index of from 5 to 9 g/10 min and a melting point of
from 120
to 150 C. All the melt flow indices given above are measured at 230 C and a
force of
21.6 N (DIN 53735).
The film according to the invention has at least three layers and comprises,
as
essential coextruded layers, always the opaque base layer and at least one top
layer
on both sides. If desired, 4- and 5-layered embodiments are also possible, in
which
the opaque layer forms the base layer of the film, and an interlayer has been
applied
to the surfaces of the base layer on one or both sides.
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The thickness of the top layers is preferably in the range from 0.5 to 5 pm,
in particu-
lar from 1.5 to 3 pm, preferably from 2 to 3 pm. Within the scope of the
present
invention, it has been found that comparatively thick top layers are
advantageous for
the film appearance, in particular for the quality of the print image on the
printed
outside of the label film. It has been found that, for opaque base layers
having a
layer thickness of up to 70 pm, the top layer thickness is comparatively
unimportant.
It has been found that a uniform appearance is particularly difficult to
achieve with
very thick opaque base layers of greater than 80 pm. This problem has been
solved
by providing the thick opaque base layer with particularly thick top layers of
greater
than 1.5 pm. Advantages have furthermore arisen with respect to the adhesion
of the
label to the blow molding if the layer thickness of the inner top layer, i.e.
the side
facing the blow molding, is greater than 1.0 pm, preferably greater than 1.5
pm.
Finally, particularly good flat lying during processing of the film (printing,
stacking and
segregation) arose if the top layers are of identical or virtually identical
thickness on
both sides.
In accordance with the prior art, BOPP films are frequently corona- or flame-
treated
on one side in order to anchor printing inks, metal layers or adhesives to be
applied.
The opposite side usually remains untreated. It has been found that, on use in
the
cut & stack process, the in-mold label film according to the invention can be
segregated particularly simply and reliably if the film is subjected to corona-
or flame-
pretreatment on both sides.
In accordance with the invention, the base layer contains a tertiary aliphatic
amine in
an amount of from 0.02 to 0.3% by weight, preferably from 0.05 to 0.2% by
weight,
and fatty acid amides in an amount of from 0.04 to 0.4% by weight, preferably
from
0.07 to 0.25% by weight, and, if desired, glycerol monostearate in an amount
of from
0.05 to 0.4% by weight, preferably from 0.10 to 0.25% by weight.
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Tertiary aliphatic amines include compounds of the general formula R3N, in
which R
is a fatty acid radical or a C12-C18-alkyl radical or a hydroxyl-substituted
alkyl radical,
where the radicals R may be identical or different. Hydroxyl-substituted alkyl
radicals
are preferably hydroxyethyl, hydroxypropyl or hydroxybutyl radicals.
Particular prefe-
rence is given to N, N-bis(2-hydroxyethyl)alkylamines. In industry, use is
frequently
made of mixtures of differently substituted tertiary aliphatic amines, which
may also
contain hydroxyalkyl chains extended by oxyalkylidene groups. In addition, N,N-
bis-
hydroxyalkyl fatty acid esters may also be used.
The carboxylic acid amides include amides of a water-soluble carboxylic acid
having
8 to 24 carbon atoms, or mixtures of these amides. Particular preference is
given to
erucamide, oleamide, stearamide and the like.
Suitable glycerol monostearates may, if desired, be substance mixtures which,
besides the stearyl radical, may also contain further fatty acid radicals and
differ with
respect to the substitution pattern on the glycerol radical. Particularly
advantageous
mixtures are those having a high proportion of alpha-glycerol monostearate.
As part of the present invention, it has been found that films having a
thickness of
greater than 85 pm and a density of from 0.65 to 0.85 g/cm3 and the additive
formulation described can be processed without bubbles and without increased
shrinkage and do not have an orange-peel effect. It is therefore preferred for
the film
to have shrinkage values of < 4% in both directions. The shrinkage is
preferably from
0.5 to 3%, in particular 1-2%, in both directions. The shrinkage values are
determined by the OPMA shrinkage test, in which the film is kept in an oven at
a
temperature of 130 for 10 minutes.
In order to set/improve certain properties of the polypropylene film according
to the
invention for the production and processing of the film and for use, both the
base
layer and the top layers may comprise further additives in an effective amount
in
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each case, preferably stabilizers and/or neutralizers which are compatible
with the
polymers of the base layer and of the top layer(s).
5 Neutralizers are preferably calcium stearate and/or calcium carbonate having
a
mean particle size of at most 0.7 pm, an absolute particle size of less than
10 pm
and a specific surface area of at least 40 m2/g. Other neutralizers, such as
DHT 4A,
have also proven successful.
10 Stabilizers which can be employed are the conventional stabilizing
compounds for
ethylene, propylene and other olefin polymers. Their added amount is between
0.05
and 2% by weight. Particularly suitable are phenolic stabiiizers, also in
combination
with phosphitic co-stabilizers, alkali metal / alkaline earth metal stearates
and/or
alkali metal/alkaline earth metal carbonates. Phenolic stabilizers are
employed in an
amount of from 0.1 to 0.6% by weight, in particular from 0.15 to 0.3% by
weight; in
combination with phosphitic co-stabilizers, like the latter themselves, they
are
employed in an amount of from 0.04 to 0.2%, in particular from 0.05 to 0.15%.
Preference is given to stabilizers and co-stabilizers which have a molar mass
of
greater than 500 g/mol. Pentaerythrityl tetrakis[3-(3,5-di-tertiary-butyl-4-
hydroxy-
phenyl)propionate] and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tertiarybutyl-4-
hydroxy-
benzyl)benzene, if desired in combination with (*Ultranox 626 or Irgafos 168),
are
particularly advantageous.
In accordance with the invention, antiblocking agents and preferably also
fatty acid
amides are added to the top layers. The effective amount of antiblocking agent
is in
the range from 0.05 to 2% by weight, preferably from 0.15 to 0.6% by weight.
Fatty
acid amides may be present in the top layer in an amount of from 0.05 to 0.3%
by
weight. In addition, the top layers may also comprise siloxanes in an amount
of from
0.05 to 1.0 /a by weight, preferably from 0.1 to 0.5% by weight, siloxane only
being
added to the layer which is subsequently not intended for printing.
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Suitable antiblocking agents are inorganic additives, such as silicon dioxide,
calcium
carbonate, magnesium silicate, aluminum silicate, calcium phosphate and the
like,
and/or incompatible organic polymers, such as polyamides, polyesters, poly-
carbonates, and/or crosslinked organic polymers, such as polymethacrylates and
polysiloxanes and the like, preference being given to benzoguanamine-
formaldehyde
polymers, silicon dioxide and calcium carbonate. The mean particle size is
between
1 and 6 pm, in particular between 2 and 5 pm, particles having a spherical
shape, as
described in EP-A-0 236 945 and DE-A-38 01 535, being particularly suitable.
The invention furthermore relates to a process for the production of the
multilayered
film according to the invention by the coextrusion process, which is known per
se.
This process is carried out by coextruding the melts corresponding to the
individual
layers of the film through a flat-film die, taking off the resultant film over
one or more
rolls for solidification, subsequently, if desired, biaxially stretching
(orienting) the
film, heat-setting the optionally biaxially stretched film, and corona- or
flame-treating
the film on one side, preferably on both surface layers.
Biaxial stretching (orientation) is preferred and can be carried out
simultaneously or
consecutively, with consecutive biaxial stretching, in which stretching is
firstly carried
out longitudinally (in the machine direction) and then transversely
(perpendicular to
the machine direction), being particularly favorable.
As is conventional in the coextrusion process, the polymer or polymer mixture
of the
individual layers is firstly compressed and liquefied in an extruder, it being
possible
for any additives added already to be present in the polymer. The melts are
then
forced simultaneously through a flat-film die (slot die), and the extruded
multilayered
film is taken off on one or more take-off rolls, during which it cools and
solidifies.
The film obtained in this way is preferably then stretched longitudinally and
transversely to the extrusion direction, which results in alignment of the
molecule
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chains. The stretching is preferably carried out in a ratio of from 4:1 to 7:1
in the
longitudinal direction and in a ratio of from 6:1 to 11:1 in the transverse
direction. The
longitudinal stretching is advantageously carried out with the aid of two
rolls running
at different speeds corresponding to the desired stretching ratio, and the
transverse
stretching is advantageously carried out with the aid of an appropriate tenter
frame.
The biaxial stretching of the film is followed by heat-setting (heat
treatment) thereof,
in which the film is held at a temperature from 110 to 150 C for from about
0.5 to 10
seconds. The film is subsequently wound up in a conventional manner by means
of
a wind-up unit.
It has proven particularly favorable to keep the take-off roll or rolls, by
means of
which the extruded film is cooled and solidified, at a temperature from 10 to
90 C,
preferably from 20 to 60 C.
In addition, the longitudinal stretching is advantageously carried out at a
temperature
below 140 C, preferably in the range from 110 to 125 C, and the transverse
stretching is advantageously carried out at a temperature above 140 C,
preferably
from 145 to 160 C.
After the biaxial stretching, one, preferably both, surface(s) of the film is
(are), as
mentioned above, preferably usually corona- or flame-treated by one of the
known
methods.
For the corona treatment, the film is passed between two conductor elements
serving as electrodes, with such a high voltage, usually an alternating
voltage (about
10000 V and 10000 Hz), being applied between the electrodes that spray or
corona
discharges can occur. Due to the spray or corona discharge, the air above the
film
surface is ionized and reacts with the molecules of the film surface, causing
formation of polar inclusions in the essentially non-polar polymer matrix. The
treatment intensities are in the usual range, preferably from 38 to 45 rnN/m.
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The opaque multilayered film is highly suitable in accordance with the
invention for
the in-mold labeling process. The ready-labeled blow molding exhibits an
optically
sparkling appearance without optical defects due to the orange-peel effect or
bubbles. When used in accordance with the invention, the film can be processed
and
handled extremely well. In particular, the film can, after cutting to size and
stacking,
be segregated very well and without errors at high speed. None of the measures
for
optimizing this use impair the other important properties, such as gloss and
good
printability. In addition, the cut-to-size label has a very low curl tendency,
which
enables the label stack to be handled very well.
The film can be used particularly advantageously in accordance with the
invention
for the labeling of blow moldings or containers made from polyethylene.
The invention is now explained by the examples below.
Example 1
A three-layer film having an ABA layer structure, i.e. a top layer A had been
applied
to both sides of the base layer B, was extruded as the sum by the coextrusion
method from a flat-film die at an extrusion temperature of 260 C. Both top
layers A
were corona-treated.
The essentially components of the base layer B were the following:
92.70% by weight of a propylene homopolymer (PP) having an n-heptane-soluble
content of 4.5% by weight (based on 100% PP) and a melting point of 165 C; the
melt flow index of the propylene homopolymer is 3.2 g/ 10 min at 230 C and a
load
of 21.6 N (DIN 53 735);
6.0% by weight of Ti02 via masterbatch P 8555 LM, supplier Schulman GmbH,
Huttenstraf3e 211, D-54578 Kerpen;
0.10% by weight of N,N-bis(2-hydroxyethyl)(Clo-C2o)alkylamine ( Armostat 300)
0.25% by weight of erucamide
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5% by weight of calcium carbonate having a mean particle size of 3 pm
The top layers A consisted of
50% by weight of a random ethylene-propylene copolymer from Solvay (EltexTM
PKS 409), having an ethylene content of 4.5% by weight, and
0.1 % by weight of antiblocking agent ( Syloblock 45) as well as
0.1 % by weight of erucamide.
The melting point of the copolymer was 134 C, and the melt flow index was
7.0 g/10 min.
AII layers contained 0.12% by weight of pentaerythrityl tetrakis[4-(3,5-di-
tertiary-
butyl-4-hydroxyphenyl)propionate] ( Irganox 1010) as stabilizer and 0.06% by
weight of calcium stearate as neutralizer.
After coextrusion, the extruded three-layer film was, via the corresponding
process
steps, taken off and cooled via a first take-off roll and a further trio of
rolls,
subsequently stretched longitudinally, stretched transversely, set and corona-
treated
on both sides, with the following conditions, in detail, being selected:
Extrusion: extrusion temperature 260 C
Longitudinal stretching: stretching roll T = 135 C
Longitudinal stretching by a factor of 4.5
Transverse stretching: heating fields T = 180 C
Stretching fields T = 177 C
Transverse stretching by a factor of 8
Setting: temperature T = 155 C
Corona treatment: voltage: 10,000 V
frequency: 10, 000 Hz
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The multilayered film produced in this way had a surface tension of from 40 to
41
mN/m on both sides directly after production. The film had a thickness of
5 approximately 90 pm, with the thickness of the top layers being about 1.8
pm. The
film had a density of 0.72 g/cm3.
The film was printed, cut into label shape and stacked. The label stacks were
provided in the usual manner at the blow-molding machine, and the stacks were
10 prepared for removal of the labels. The equipment and operations necessary
for this
purpose are known in the prior art and are described, for example, in company
publications by Hoechst Trespaphan.
A blow-molding machine with automatic label feed was charged with HD-PE blow-
15 molding material and run under the usual processing conditions for HD-PE.
The results of the experiment are described in the table below.
Example 2
Example 1 was repeated, with the base layer containing, as lubricant and
antistatic,
0.15% by weight of glycerol monostearate
0.05% by weight of N,N-bis(2-hydroxyethyl)(Clo-C20)alkylamine ( Armostat 300)
0.05% by weight of erucamide.
Comparative Example 3
Example 1 was repeated, with the thickness of the film being 80 pm.
Comparative Example 4
Example 1 was repeated, with the thickness of the top layers being 0.7 pm.
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Comparative Example 5
Example 1 was repeated, with the density of the film being 0.62 g/cm'.
Comparative Example 6
Example 1 was repeated, with the density of the film being 0.86 g/cm'.
Comparative Example 7
Example 1 was repeated, with only one outside of the film being corona-
treated. The
treated side was on the outside on laying in the blow mold.
Comparative Example 8
Example 1 was repeated, with the thickness of the top layer on the outside
being
0.5 pm.
The raw materials and films were characterized using the following measurement
methods:
Melt flow index
The melt flow index was measured in accordance with DIN 53 735 at a load of
21.6 N and at 230 C.
Melting point
DSC measurement, maxima of the melting curve, heating rate 20 K/min.
Density
The density is determined in accordance with DIN 53 479, Method A.
Assessment of the handling properties:
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Curl tendency: a film sheet in DIN A4 format is laid with either the underside
or the
upper side on a flat substrate. After any static charge has dissipated,
whether and to
what extent the edges of the film lift up from the substrate is assessed and,
where
appropriate, measured. The curl tendency is regarded as good if the edge
height is
less than 1 mm, moderate if it is up to 2 mm.
Segregation ability: the frequency with which a handling machine takes more
than
one film sheet from the stack during loading of a sheet offset printing
machine or the
blow-molding machine is assessed. The destackability is regarded as good at an
incorrect removal rate of less than 1:10,000, poor at greater than 1:5000.
Mold charging: the error rate on laying the label in the blow mold is
assessed.
Frequent errors are folding, turned-in edges and, in the case of electrostatic
location,
incorrect positioning due to movement in the mold. The charging ability is
regarded
as good at an error rate of less than 1:10,000, and poor at greater than
1:5000.
Adhesion: it is assessed (A) whether the edge of the label can be lifted from
the
container without using a tool, (B) whether a film detached from the substrate
at the
edge can be peeled off without destruction, and (C) whether the label detaches
from
the substrate after flexural stressing at a flexural radius of less than 3 cm.
It is
regarded as poor if (A) the edge spontaneously detaches from more than 1 in
100
blow moldings, if (B) the label detached at the edge can be peeled off without
destruction from more than 1 in 100 blow moldings or if (C) the label detaches
from
the substrate after flexural stressing at a flexural radius of less than 3 cm.
Appearance of the labeled bottle: the number and size of raised bubbles is
assessed, and in addition the bubbles are classified by type and size.
Orange-peel effect: the appearance of a labeled bottle is classified as good
if less
than 30 bubbles of the orange-peel type are evident on the label with an area
of
100 cm2 and as moderate if more than 200 bubbles are evident.
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Large bubbles: the appearance of a labeled bottle is classified as good if not
more
than 3 bubbles of not greater than 3 mm in diameter and not greater than 0.5
mm in
height are evident on a label area of 100 cm2. The appearance is regarded as
poor if
more than 15 smaller bubbles of not greater than 3 mm in diameter and not
greater
than 0.5 mm in height or one bubble of greater than 10 mm in diameter or 2 mm
in
height are evident. The bottles that count are the worst ones.
The table below shows the properties of the in-mold-labeled, blow-molded
bottles
from the examples.
Handling Adhesion Appearance
Example 1 good good good
Example 2 good good good
Comparative good good in the areas in large bulging bubbles
Example 3 contact
Comparative good poor (detaches at the poor gloss
Example 4 edge, flexural test poor)
Comparative still good good poor (orange-peel effect)
Example 5
Comparative very good poor (detaches at the poor (waved appearance
Example 6 edge, can be peeled off after spontaneous
with substantially no detachment from the
destruction) blow molding)
Comparative moderate good good
Example 7 (segregation
flawed)
Comparative poor (tendency good good
Example 8 to curl during
printing)
