Note: Descriptions are shown in the official language in which they were submitted.
TRANSPARENTLY BONDED POLYESTER FILM AND
CONTAINERS PROVIDED WITH A FINISH OF THOSE FILMS
Background of the Invention
Field of the Invention
5The invention relates to transparently bonded
polyester films which are useful as all-around labels for
containers, the transparency of the bond zone being
retained even under the action of heat and in a humid
atmosphere. The invention also relates to containers
10provided with a finish based on these films.
Description of Related Art
It is known to print some types of plastic films in
transparent form and to bond these using an adhesive to
give tubes or the like, without haviny to accept losses
15in transparency in the bonded overlap zone of the films.
Film tubes of this type are used, inter alia, as all-
around labels, safety seals or sheaths for providing
containers, such as bottles, tubes, jars, and similar
articles, with a finish which is effective for
20advertising purposes.
Films based on polyvinyl chloride (PVC), polystyrene
(PS) and polypropylene (PP) are very suitable for this
purpose since they can be bonded easily and the bonding
zones also are clean and, above all, transparent and,
25thus, do not have an adverse effect on the optical impact
of a bonded 360 all-around label.
Currently, polyester containers are finding
increasing acceptance in the market, since these give
rise to fewer problems with regard to environmental
30pollution. It is true that containers of this type based
on polyester can be provided without any problem with the
above-mentioned container finishes based on PVC, PS or PP
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film, but this has the concomitant disadvantaye that the
polyester containers finished in this way are no longer
of a single material type, i.e., they no longer consist
of a single raw material and thus are virtually no longer
recyclable.
There is therefore a need to find polyester films
useful as the finishing films of containers, particularly
polyester containers, which films are in no way inferior
to the PVC, PS or PP films, and in particular, that can
be bonded with retention of the transparency in the
bonding zone.
This was not possible hitherto since, to date, it was
only possible to bond transparent polyester films in a
manner that resulted in clearly optically visible
cloudiness as a result of crystallization streaks.
It is true that bonded colored, non-transparent
polyester films are known for applications not requiring
stringent optical requirements, but these are not
adequate for use as finish and decoration material.
Summarv of the Invention
An object of the present invention was, therefore,
to find a method that allows for transparent polyester
films to be firmly bonded with adhesives while retaining
the transparency in the bonded film zone. A further
object of the invention was to carry out this bonding in
such a way that the transparency in the bonding zone is
retained even in the case of a subsequent heat treatment,
for example, shrinkage or pasteurization.
A further object of the present invention is to
provide a polyester tube that retains its transparency
even in the region of overlap of the initial film.
It is further an object of the invention to provide
a manner of forming and using such a tube, and to provide
a container that has been provided with finish of such a
tube.
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In accomplishing the foregoing objectives, there has
been provided, in accordance with a first aspect of the
present invention, a hollow article comprising a
polyester film haviny an overlapped, transparent,
adhesively bonded seam region, wherein said polyester
film comprises a polyester containing reactive groups.
In accordance with another aspect of the present
invention, there is provided a container that is
surrounded with an article as described above.
In accordance with another aspect of the invention
there has been provided a process for the production of
a container provided with a film-finish comprising the
steps of:
a) placing a film comprising a polyester containing
reactive groups around the container so that the ends of
the film overlap at a seam,
b) applying a solvent-based adhesive to the film
in the seam, and
c) removing the solvent and with the application
of pressure and optionally heat, sealing the overlapping
ends of the film, so as to form a film finish around the
container.
There has been provided a further process for the
production of a container provided with a film-finish
comprising the steps of:
a) forming a film comprising a polyester containing
reactive groups into an article such as a hollow cylinder
or hollow truncated cone by bonding two overlapping ends
with an adhesive,
b) placing the article around the container, and
c) shrinking the article onto the container by the
action of heat.
Further objects, features and advantages of the
present invention will become apparent from the detailed
description of preferred embodiments which folIows.
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Detailed Description of the Preferred Embodiments
According to the present invention, a reactive group-
modified polyester film, that has a bond seam and a
partial overlap in the seam region where it is bonded by
means of an adhesive, allows for the zone bonded by means
of an adhesive to be and remain transparent.
The polymer films are useful, for example, as all-
around labels, safety seals or sheaths and in other
applications where transparency is a desired
characteristic.
The polyester film according to the invention may be
any known polyester, preferably transparent polyester
films such as those based on polyethylene terephthalate
(PET). Preferably the film contains more than 90% by
weight of polyester, the polyester preferably being PET.
The film can optionally contain conventional additives
such as stabilizers, lubricants, antistatic agents or the
like in the customary proportion depending on their
purpose, i.e., generally up to about 10% by weight of the
film.
The reactive group can be present anywhere along the
polyester and be any reactive group known in the art.
Preferably, reactive group-modified polyester films are
used which have terminal reactive groups such as OH, CHO
or COOH groups. Alkanediol-modified PET films, such as
1,3-propanediol-modified or ethylene glycol-modified PET
films, have proved particularly suitable. Films of this
type are obtainable, for example, under the name
PETCLEARYL (Hagner, Dornstatten, Germany) or VILLPET
PETG films type 1003 (Stager, Muri, Switzerland).
The polyester films can be single layer or
multilayer; they can be unstretched or monoaxially or
biaxially stretched; and they can be printed or
unprinted.
The adhesive used to bond the overlap region is
generally a solvent-based adhesive (i.e. an organic
solvent) that has an affinity for the reactive groups
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present on the polyester film surface. Furthermore, this
adhesive should not cause substantial crystallization of
the incipiently dissolved polyester. Solvents from the
yroup comprisiny esters, alcohols, ketones, furans,
hydrocarbons such as chlorinated hydrocarbons and
aliphatic and cyclic hydrocarbons and mixtures of these
substances with one another have proved particularly
suitable. For example, esters that can be used are ethyl
acetate or methyl acetate, alcohols that can be used are
ethanol or propanol, ketones that can be used are methyl
ethyl ketone, cyclohexane or acetone, furans that can be
used are tetrahydrofuran or lower alkyl-substituted THF,
chlorinated hydrocarbons that can be used are methylene
chloride or 2,2-dichloroethane, and aliphatic or cyclic
hydrocarbons that can be used are pentane, hexane or
cyclohexane.
Surprisingly, it has been found that the reactive
yroup-modified polyester films and in particular the
alkanediol-modified PET films can be permanently bonded,
with retention of the transparency of the bond zone,
usiny solvent-based adhesives. The bond zones remain
transparent even under the action of heat, such as is
applied when shrinking such films onto containers. It was
exceptionally surprising that no change in the
transparency occurs even in a humid, warm atmosphere,
such as occurs for example in pasteurization.
In this context, transparency is intended to signify
that no cloudiness arises, for example, because of
crystallization phenomena. The transparency can be
measured or assessed, for example, by means of light
scattering measurement (ASTM-D 1003-61, method A). In the
case of the polyester films bonded according to the
invention the transparency is generally in the range from
75 to 90%, preferably in the range from 80 to 90%
(determined in accordance with ASTM-D 1003-61, method A).
The film of the present invention can be used in any
desired application, and is particularly useful where it
is desired to have a transparent film. When used for
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all-around labeling, the best procedure for making the
article is to place an appropriately sized, optionally
printed polyester film strip as described above around
the container to be labeled, for example, a bottle, so
that the two ends of the film somewhat overlap. The
length of the overlap zone is not critical but is in
general 1 to 10 mm, preferably 3 to 7 mm. The solvent-
based adhesive is applied to the film surface on one or
both sides in this overlap zone and the seam is sealed,
after evaporation of the solvent from the adhesive, with
the application of pressure and, where appropriate, of
heat.
In a further embodiment of the process, a tubular
sleeve is first formed by shaping, and bonding, the film
in the form of a hollow cylinder or, optionally, a hollow
truncated cone with an overlapping seam. This tubular
sleeve is then slipped around the container. The all-
around label is then shrunk on to the container by the
action of heat, for example, by means of hot air.
The container can be composed of any desired
material, such as glass, metal or plastic, such as PVC,
PS or PP, but preferably is made from the same material
as the film so as to facilitate recycling. Thus, the
container is preferably polyethylene terephthalate.
The invention is illustrated below with the aid of
examples:
Example 1
A single-layer PET film monoaxially oriented in the
transverse direction (PETCLEARYL, P100; Hagner,
Dornstatten, Germany) was shaped to give a tube with a
3 mm overlap seam. One side of the seam was coated with
THF and following a period of 1 to 5 sec for the solvent
to evaporate, the seam was pressed together. After
drying, the bond zone had a transparency of 80% (ASTM-D
1003-61, method A).
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Example 2
The PET film shaped and bonded to form a tube, from
Example 1, was shrunk on to a cylindrical bottle in a
stream of hot air. The temperature of the hot air was 120
to 130C (treatment time 4 sec). The bonded seam was
transparent (80% according to ASTM-D 1003-61, method A)
even after this shrinkage process.
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