Note: Descriptions are shown in the official language in which they were submitted.
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An Adhesive System for Applying Wrap-Around Labels
This invention relates to an adhesive system for applying wrap-
around labels to hollow containers and to a process for forming a readily
breakable bond between wrap-around labels and hollow containers using
this adhesive system.
At the present time, casein-based glues are mainly used for labeling
hollow containers, for example glass and polyethylene terephthalate
bottles. These aqueous formulations are mainly based on a casein
component and a tackifier resin along with certain additives. WO
93/03110, for example, is mentioned in this regard. This document
describes an adhesive based on casein, water-soluble extenders, fillers
and, optionally, other additives, the adhesive characteristically containing
resinic acid derivatives and alcohol. This provides for the satisfactory
labeling of wet glass bottles, even at temperatures of 15CC and even if the
casein content is well below the usual concentrations of more than 18% by
weight.
Unfortunately, the above-mentioned labeling adhesives containing a
casein component have the disadvantage that the labels are extremely
difficult to remove during cleaning. Thus, the following inter alia is stated inEuropean patent application 503 112, column 1, line 36 to column 2, line
52: ~Hitherto, the labels have been washed off with heated wash liquor
using large quantities of water. The soil content of the wastewater is
correspondingly diffficult to handle because not only is it necessary to filter
the waste- water to remove cellulose fibers, it is also particularly important
to eliminate metal components, more particularly aluminium compounds,
from the wastewater where they accumulate to a considerable extent from
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the print on the labels, i.e. from the pigment components of the labels. The
labels are removed in the bottle washing machine using an approximately
2.5% sodium hydroxide solution at an average temperature of 82~C.
During this removal process, parts of the paper coating and hence
pigments and lacquers from the print on the labels naturally pass over into
the sodium hydroxide solution. Labels thus contaminate the liquor with
soils which are now classified on the basis of chemical oxygen demand
(COD). Breweries have to pay their wastewater dues according to the
COD level."
In European patent application 503 112, it is proposed to solve the
problem by mechanically removing the label from the empties before
washing. This is made possible by inserting a separating layer between
the label and the original adhesive layer. The label can thus be removed
without tearing. However, the adhesive layer remains on the bottle and
has to be removed by wash liquor. Accordingly, the problem of completely
removing the labels is not solved.
According to DE-OS 34 34 141, the original adhesive (glue) is
replaced by an assembly or fixing adhesive. This adhesive is supposed to
have the property of not curing. Accordingly, a label applied to a bottle
with this adhesive can be completely removed at any time. What the
adhesive consists of is not disclosed. The adhesive is applied over the
entire area between the surface of the bottle and the label. However, it is a
disadvantage of fixing adhesives that they require a dry substrate.
In their prospectus entitled "Autosleeve", published in 1993, the
Automated Label Systems Company proposes a polyethylene wrap-around
label for labeling bottles which is drawn over the bottle in its expanded
state and, after contracting, applies itself firmly to the bottle. Accordingly,
no adhesive at all is used here. The label is cut through with a high-
pressure water jet in the same way as with a knife. Apparently the bottle is
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not damaged. However, the polyethylene label still has to be disposed of.
German patent 34 42 998 describes a process for applying a wrap-
around label to a container. In this process, a limited zone of the front part
of the label is initially attached to the wall of the container and, after
wrapping of the label around the container, a limited zone of the rear end
overlapping the front end is joined thereto. A thermoplastic, co-extruded
polymer with a foamed layer is used as the label. A viscous, solidifying
solution is formed on the foamed layer in the limited zone of the front label
by means of a solvent for the polymer for the purpose of establishing a
temporary connection between the limited zone of the foamed layer and
the wall of the container, which automatically weakens again on
evaporation of the solvent, the constituent material of the container being
unaffected by the solvent. The disadvantage of this process is that a low-
boiling solvent, for example methylene chloride, an aromatic or chlorinated
aliphatic hydrocarbon, has to be used for application.
German patent 34 42 997, which was filed on the same date at the
German Patent Offfice, relates to a similar process for applying a wrap-
around label to a container. In this process, however, a thermoplastic
polymer alone rather than a thermoplastic co-extruded polymer with a foam
layer is used for the label. In this process, too, ecologically unsafe, rapidly
evaporating chlorine-containing or aromatic solvents have to be used to
apply the wrap-around label.
It is also known that amorphous poly-a-olefins can be used as a
basis for hotmelt adhesives. Corresponding hotmelt adhesives are
distinguished by good adhesion to LDPE hlm and by firm fixing to porous
substrates so that they may be used in particular for sanitary articles
(diapers or the like). It is known that resins may be added to these basic
polymers, saturated resins of low polarity being the most compatible.
Compatible resins such as these generally act as tackifiers for amorphous
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poly-a-olefins. In addition, it is also known that waxes, such as
polyethylene, Fischer-Tropsch or microcrystalline waxes, are also
compatible with amorphous polyolefins and also bring about a reduction in
viscosity, a change in pot life and reduced penetration. However, the listed
examples of hotmelt adhesives show that the poly-a-olefin always has to
be used as the main component, optionally in conjunction with another
resin and/or another wax as secondary components.
The problem addressed by the present invention was to provide an
adhesive which would be suitable for applying wrap-around labels to
hollow containers, such as bottles, cans, etc., and which could be removed
easily and completely from the hollow container before cleaning. However,
neither the labeling process nor the handling of the labeled containers
would be adversely affected in any way and, in particular, labeling would
even be possible in high-performance machines.
This problem has been solved by an adhesive system which
contains two different hotmelt adhesives, namely one for permanently
bonding the overlap zone of the wrap-around label and one for temporarily
bonding the label during its pickup.
Accordingly, the present invention relates to an adhesive system for
applying wrap-around labels which comprises a pickup adhesive and an
overlap adhesive and which is characterized in that the pickup adhesive
has suffficient adhesive strength for labeling at its application temperature,
i.e. an adhesive strength of 0.005 to 0.03 N/mm2 at 80 to 200~C, and has
hardly any adhesive strength after it has set, more particularly at its
storage temperature of 5~C to 30~C.
The adhesive strength of the pickup adhesive at room temperature
is so low that the label can be easily and completely removed from the
hollow container, preferably without leaving any adhesive residues behind.
During application from the melt, the adhesive strength is suffficient to
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enable the label to be exactly positioned, even at high speeds. Because
the adhesive remains completely or partly on the label, there is no longer
any need for the complicated bottle washing process required in the prior
art where the wash liquor is soiled with label material and adhesive.
Accordingly, the washing of reusable bottles is barely affected, if at all, by
adhesives or even by label residues.
Whether and how much pickup adhesive remains on the container
after delabeling depends to a large extent on its surface characteristics. If
the adhesive strength at room temperature is substantially equal to or even
greater than that on the label surface, the adhesive will more or less
remain on the container, even though its adhesive strength according to
the invention is very low. Accordingly, the pickup adhesive is best also
alkali-soluble. Otherwise, it is sufficient if the pickup adhesive has hardly
any adhesive strength at room temperature, remains on the label and is
insoluble in alkalis.
In one preferred embodiment of the present invention, the alkali-
insoluble pickup adhesive in the adhesive system according to the
invention contains 10 to 100% by weight and preferably 30 to 35% by
weight of at least one amorphous poly-a-olefin, 0 to 40% by weight and
preferably 5 to 30% by weight of at least one plasticizer based on an
aromatic dicarboxylic acid ester, 0 to 50% by weight and preferably 15 to
40% by weight of at least one natural, chemically modified or synthetic wax
and typical auxiliaries and additives.
In the context of the invention, an amorphous poly-a-olefin which is
used as a component of the pickup adhesive forming part of the labeling
adhesive system according to the invention is understood to be a
homopolymer or copolymer of at least one of the comonomers ethylene,
propylene and 1-butene or 1-hexene. These monomers are normally
polymerized either individually or optionally in the form of a mixture under
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low pressure in the presence of a Ziegler-Natta catalyst. The poly-a-olefins
preferably have a molecular weight of around 30,000 to around 60,000
g/mole.
A plasticizer based on aromatic dicarboxylic acid esters, i.e. the
corresponding ester of phthalic acid, isophthalic acid or terephthalic acid, is
used as a potential component of the alkali-insoluble pickup adhesive of
the labeling adhesive system according to the invention. The alcohol
radical in these esters used as plasticizer normally contains 1 to 8 carbon
atoms.
Another potential component of the alkali-insoluble pickup adhesive
of the labeling adhesive according to the invention is at least one natural,
chemically modified or synthetic wax. Any waxes compatible with
amorphous poly-a-olefins may be used for this purpose. The natural
waxes may be vegetable waxes, animal waxes, mineral waxes or
petrochemical waxes. The chemically modified waxes include hard waxes,
such as montan ester waxes, Sarsol waxes, etc. The synthetic waxes
used are polyalkylene waxes and also polyethylene glycol waxes. For
economic reasons, petrochemical waxes, such as petrolatum, paraffin
waxes, microwaxes and synthetic waxes, especially polyethylene waxes
with melting points of 85 to 140~C and molecular weights of 500 to 3,500,
paraffin waxes with melting points of 45 to 70~C and molecular weights of
225 to 500, microcrystalline waxes with melting points of 60 to 95~C and
synthetic Fischer-Tropsch waxes with melting points of 100 to 115~C, are
preferably used.
In addition, typical auxiliaries and additives may be incorporated in
the alkali-insoluble pickup adhesive. These include above all stabilizers of
which the function is to prevent the reactive monomers from entering into
an unwanted or premature reaction and to protect the polymers against
decomposition during processing. Antioxidants are particularly suitable for
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this purpose. They are normally added to the pickup adhesive in quantities
of up to 3% by weight and preferably in quantities of around 0.5% by
weight.
In one preferred embodiment, the pickup adhesive according to the
invention is also soluble in alkalis, i.e. it saponifies and dissolves
completely in a 1% sodium hydroxide solution at 50~C up to a
concentration of 10% by weight within 24 hours, preferably within 3 hours
and above all within 20 minutes. Accordingly, the pickup adhesive
remaining on the container generally also dissolves during washing in a
wash liquor. The wash liquors are generally water-containing media with a
pH value of 8 to 14.
A ~water-containing medium" in the context of the invention is
understood to be a solution, dispersion or emulsion of an organic or
inorganic alkaline water-containing substance which is capable of
dissolving organic substances containing hydrolyzable or salt-forming
groups. Examples of organic bases are alkanolamines, more especially
(poly)ethanolamines, while examples of inorganic substances are alkali
metal hydroxides, alkali metal carbonates and alkali metal
sesquicarbonates, but especially the corresponding sodium and potassium
compounds. Sodium hydroxide and potassium hydroxide are particularly
preferred, normally being used in the form of aqueous solutions with
concentrations of 0.5 to 40% by weight.
In one preferred embodiment of the present invention, the pickup
adhesive contains
1. 20 to 98% by weight of at least one alkali-soluble polymer which
serves as the backbone poly~mer,
Il. 1 to 70% by weight of at least one resin based on functional hydro-
carbon resins and optionally modihed natural resins,
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Ill. 0.5 to 30% by weight of at least one plasticizer and
IV. 0 to 3% by weight of at least one typical auxiliary and additive.
The backbone polymer essentially determines cohesion and
temperature behavior. It is used in a quantity of, preferably, 30 to 70% by
weight and, more preferably, 50 to 65% by weight. The backbone polymer
is selected from
a) saturated and/or unsaturated polyesters, above all based on
aromatic dicarboxylic acids, such as phthalic acid or terephthalic
acid, more particularly from polyesters of phthalic acid, neopentyl
glycol and glycerol or pentaerythritol,
b) polyacrylic and/or polymethacrylic acid alkyl esters containing 1 to
18 and, more particularly, 1 to 4 carbon atoms,
c) acrylic acid homopolymers and/or copolymers,
d) vinyl polymers, for example polyvinyl alcohol with a molecular
weight above 1,000, polyvinyl pyrrolidone, vinyl pyrrolidone/vinyl
acetate copolymers, polyvinyl ethers, more particularly polyvinyl
alkyl ethers containing 1 to 4 carbon atoms in the alkyl group, for
example polyvinyl methyl ether or polyvinyl ethyl ether.
The resin is intended to tackify the backbone polymer and to
improve the compatibility of the hotmelt adhesive components. It is
preferably used in a quantity of 1 to 15% by weight or 15 to 70% by weight.
The resin is selected from
a) hydroabietyl alcohol and esters thereof, more especially esters with
aromatic carboxylic acids, such as terephthalic acid and phthalic
acid,
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b) preferably modified natural resins, such as resinic acids of balsam
resin, tallol resin or wood rosin, for example fully saponified balsam
resin or alkyl esters of optionally partly hydrogenated colophony with
low softening ranges, for example methyl, diethylene glycol, glycerol
and pentaerythritol esters,
c) acrylic acid copolymers, preferably styrene/acrylic acid copolymers,
and
d) a resin based on functional hydrocarbon resins.
An alkyl ester of partly hydrogenated colophony is preferably used as the
tackifying resin, the alkyl group preferably containing 1 to 6 carbon atoms.
The plasticizer is preferably present in the hotmelt adhesive in a
concentration of 5 to 20% by weight. Suitable plasticizers are monohydric
or polyhydric alcohols, preferably glycol monophenyl ether, hexamethylene
glycol, glycerol and, in particular, polyalkylene glycols with a molecular
weight of 200 to 6,000. Polyethylene glycols with a molecular weight of up
to about 1,000 and preferably up to about 600 are preferred.
Polypropylene glycol, polybutylene glycol and polymethylene glycol are
also suitable. Esters, for example liquid polyesters and glycerol esters,
such as glycerol diacetate and glycerol triacetate, and neopentyl glycol
dibenzoate, glyceryl tribenzoate, pentaerythritol tetrabenzoate and 1,4-
cyclohexane dimethanol dibenzoate, are fit for use as the plasticizers.
Finally, alkyl monoamines and fatty acids preferably containing 8 to 36
carbon atoms may also be used.
Stabilizers and antioxidants, for example tris-(nonylphenyl)-
phosphite, are mentioned as typical auxiliaries and additives.
The above-mentioned components form the alkali-soluble hotmelt
adhesive according to the invention. It is insoluble in water, even if
individual components should be soluble. Accordingly, it is distinguished
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for example by high resistance to condensation.
The thermal stability of the hotmelt adhesive according to the
invention is sufficient in practice for permanent use (multishift working) at
application temperatures of up to 160~C. This is surprising in view of the
thermal instability of individual raw materials, for example polyethers and
saponifiable polyesters.
The viscosity of the hotmelt adhesive according to the invention,
which is at most 1 to 2 Pas at 140~C (Brookfield, Thermacell RVT ll, ASTM
D3236-88), is remarkably low in view of the high polar forces of individual
raw materials. Accordingly, the hotmelt adhesive according to the
invention may be used in a variety of installations.
The adhesive properties of the hotmelt adhesive according to the
invention depend to a very large extent upon the composit on of the raw
materials mentioned above and, accordingly, may readily be adapted to
the particular problem to be solved on the basis of specialist knowledge.
Thus, permanently tacky hotmelt adhesives can be obtained by a high
concentration of plasticizer. Hotmelt adhesives with sufficient tackiness for
labeling and with very poor adhesion at room temperature can be obtained
by a low concentration of plasticizer, particularly the polyol. Adhesives
such as these are suitable as pickup adhesives for wrap-around labels
because the labels are thus easy to remove before washing of the
container. Because its adhesive properties can be varied by varying the
formulation, the adhesive according to the invention is suitable not only as
a pickup adhesive for wrap-around labels, but also for bonding paper,
board, plastics and nonwovens.
The overlap adhesive used is a standard labeling adhesive with
adequate flexibility. It performs an equalizing function in the event of
expansion of the bottle through the emission of carbon dioxide from bottles
of thermoplastics at elevated temperature. The overlap adhesive contains
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tackifying resins as its principal component, plasticizers and polymers as
secondary components and typical auxiliaries and additives. Compared
with the pickup adhesive, the overlap adhesive has more or less uniform
tackiness over a broad temperature range of -10 to 2005C. When the
overlap adhesive is applied, however, it is important to ensure that it does
not come into contact with the container, more particularly the bottle.
If the containers in question, more particularly bottles, do not
demand such flexibility, the above-mentioned pickup adhesive itself may
also be used as the overlap adhesive.
The containers to be labeled in the context of the invention are in
particular hollow containers, such as bottles, cans, drums, tubes or car-
tridges. They consist essentially of optionally plated or galvanized metal,
for example tin plate or aluminium, glass or thermoplastics, such as
polyethylene terephthalate, polycarbonate, polyethylene, polypropylene,
polyvinyl chloride or polystyrene. A polar plastic, more particularly a
polyester, is preferably used. Corresponding hollow containers are used in
particular for mineral waters and refreshing drinks.
The labels consist on the one hand of thermoplastics, such as
polyethylene, polypropylene, polystyrene, polyvinyl chloride or cellophane.
It is preferred to use labels of a film based on nonpolar plastics, more
particularly oriented polypropylene (OPP). In that case, a pickup adhesive
based on poly-a-olefin is preferably used. However, the wrap-around
labels may also be based on paper, optionally in combination with a
polymer. Depending on the material and the production process, the
following labels, for example, may be used: simple labels of nonfinished
paper, labels of surface-finished paper, high-gloss labels of cast-coated
label papers, labels of papers coated with aluminium by vapor deposition
and labels of aluminium-lined papers.
The shape of the labels does not have to meet any particular
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requirements although the labels must be wrap-around labels.
The present invention also relates to a process for applying wrap-
around labels optionally containing perforations to containers, more
particularly hollow containers, using an adhesive system of the type
described above, characterized in that it comprises the following steps:
a. transferring a pickup adhesive to at least part of the back of a wrap-
around label or to the bottle at temperatures of 80 to 200~C and
preferably 120 to 1 80~C in the case of alkali-insoluble hotmelt
adhesives based on poly-a-olefins and at temperatures of 90 to
160~C in the case of alkali-soluble ester-based hotmelt adhesives,
b. applying the wrap-around label and joining the back of one end to
the front of the other end by the overlap adhesive and
c. Ieaving the wrap-around label to cool.
The present invention also relates to a process for removing the
wrap-around labels applied in accordance with the invention from hollow
containers, characterized in that, after it has been cut through, optionally at
the perforations, the wrap-around label is removed from the hollow
container by light mechanical force. This is preferably done by removing
the wrap-around label from the hollow container by light mechanical force
after it has been cut through, but especially by applying compressed air,
contrarotating rollers which pull the label off the bottle or water pressure as
the mechanical force. Accordingly, the adhesive system according to the
invention is particularly suitable for recyclable hollow containers in the
sense of returnable containers and general recycling.
Finally, the present invention relates to the use of the labeling
adhesive system according to the invention for labeling hollow containers,
more particularly bottles of glass, metal and/or plastics, with wrap-around
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labels.
The adhesive system according to the invention is also suitable for
high-performance machines capable, for example, of applying 10 labels
per second.
The invention is illustrated by the following Examples.
A) Hotmelt adhesive based on poly-a-olefins
Production Example A1:
27 Parts by weight of the plasticizer phthalic acid dicyclohexylester,
38.5 parts by weight of a polyethylene wax and 0.5 part by weight of an
antoxidant are mixed at 150~C until a homogeneous mixture is obtained.
34 Parts by weight of an amorphous poly-a-olefin with a molecular weight
of around 35,000 g/mole are then added to the resulting mixture.
A 100 llm thick and 1 cm wide film of the above-described pickup
adhesive was applied to a Kofler bench, after which a 1 cm wide label film
of oriented polypropylene was placed on the adhesive and subjected to
light pressure. The bonded area measured 1 cm x 1 cm. The film was
peeled off by a tensile tester. The necessary force was read off from the
tensile tester. Tackiness and hence the pickup properties were evaluated
by rolling a bottle over the label with adhesive on the Kofler bench, the
following adhesive strength values being obtained:
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Tempera- 60 70 80 90 100 1 10 120 130 140 150
ture ( C)
Adhesive 0.000 0.000 0.000 0.000 0.008 0.020 0.016 0.004 0.004 0.002
strength
(N/mm2)
Production Example A2:
A standard overlap hotmelt adhesive for labeling cans, glass and
polyethylene terephthalate bottles was produced, for example, in
accordance with the teaching of US 4,749,739 by reacting 50 parts by
weight of an amorphous poly-cc-olefin, 20 parts by weight of a synthetic
polycarbonate resin, 20 parts by weight of a glycerol ester of partly
hydrogenated colophony, 10 parts of a synthetic hard wax based on a
polyethylene wax, which had been obtained by the Fischer-Tropsch
process, and 0.4 parts by weight of antioxidants at elevated temperature.
Application Example A1:
A pickup adhesive according to Example 1 was applied in a quantity
of 50 g/m2 at 145~C to the back of labels in a Contiroll labeling machine
(manufactured by the Krones company of Neutraubling, FRG) and served
to pick up the label and to hold it in place on the bottle pending application
of the overlap adhesive. An overlap adhesive according to Production
Example 2 was then applied to the front part of the back of the label, but in
such a way that it did not come into direct contact with the bottle.
After the polyethylene terephthalate bottle including the wrap-
around label had left the labeling machine, a label positioned firmly on the
bottle by the overlap bond was obtained after cooling.
Delabeling itself was carried out by cutting the label open at the
perforations present, if any. In this way, the label is held solely by the
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pickup adhesive 1 although, as shown in Example 1 above, the pickup
adhesive is only very slightly tacky when cold, i.e. at room temperature or
20CC to 40~C, so that the label can be removed from the bottle by light
mechanical force. The adhesive remains completely on the label. The
same applies even when the labeled bottle has been stored under typical
conditions (40~C, rain) before delabeling.
B) Alkali-soluble hotmelt adhesives
Production Example B1:
Production of an alkali-soluble pickup adhesive with better adhesion at the
application temperature than at room temperature.
A pickup adhesive was prepared by mixing and homogenizing
59.0% by weight of the saturated aromatic polyester Phthalopal~NP (an oil-
free phthalate resin marketed by BASF AG) based on phthalic acid,
pentaerythritol and neopentyl glycol,
20.0% by weight of a styrene/acrylic acid copolymer (ACX 12-436),
10.0% by weight of a colophony alkyl ester (Herkolyn~D marketed by
Hercules Inc.), more particularly a methyl ester of partly hydrogenated
colophony,
10.0% by weight of a polyethylene glycol with a molecular weight of 400
(Polydiol 400) and
1.0% by weight of a stabilizer (Irgafos~TNPP, marketed by Ciba Geigy)
based on tris-(nonylphenyl)-phosphite
at elevated temperature.
Production Example 2:
A standard overlap hotmelt adhesive for labeling cans, glass and
polyethylene bottles was produced, for example, in accordance with the
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teaching of US 4,749,739 by reacting 50 parts by weight of an amorphous
poly-oc-olefin (Vestoplast V3649 marketed by Huls AG), 20 parts by weight
of a synthetic polyterpene resin (Wingtack~95, Goodyear Tire & Rubber
Company), 20 parts by weight of a glycerol ester of partly hydrogenated
colophony (Fhoral~85, Hercules Inc.), 10 parts by weight of a synthetic
hard wax based on a polyethylene wax, which had been obtained by the
Fischer-Tropsch process (Vestowax A 616, Huls AG), and 0.2 part by
weight of each of the antioxidants Irganox~1010 (Ciba-Geigy) and
Irganox~PS 802 (Ciba-Geigy) at elevated temperature.
Application Example B1:
The pickup adhesive was applied to a bottle of polycarbonate at 120
to 150~C and had sufficient tackiness at that temperature to pick up the
wrap-around label of polypropylene from the label box. The label was then
held on the bottle until it fitted sufficiently firmly thereon following the
application of an overlap adhesive according to Example 2 to the back of
the label end.
For small bottles with minimal volume expansion and for paper
labels, the pickup adhesive of Example 1 may also be used for the overlap
bond, i.e. as the overlap adhesive.
The pickup adhesive is disintguished in particular by the fact that it
is only slightly tacky when cold or in storage (room temperature) so that,
after it has been cut open, for example with a knife, it can be removed very
easily from the bottle. No tearing occurs, particularly in the case of paper
labels, which has the advantage over the standard known process that the
label is thus completely removed before the bottle washing machine.
Accordingly, the wash liquor is not soiled by paper residues. After the
labels have been removed by light mechanical force, the adhesive remains
largely on the bottle, but dissolves very quickly, i.e. in 2 to 10 minutes, and
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completely in the following wash liquor, for example a 1% sodium
hydroxide solution, at 80~C. The pickup adhesive according to the
invention is substantially non-hygroscopic and does not penetrate even
uncoated paper labels.
