BACKGROUND ART
Field of the invention
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The present invention relates to a spreading line or plant
for adhesive films.
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As known, spreading plants for adhesive film are laid out
in various ways according to use requirements and to the nature
of the adhesives and of the release agents used.
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Figs. 1 and 2, which represent diagrammatic elevation side
views of prior art plants, illustrate two of such exemplary
spreading plants.
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Fig. 1 shows a spreading line for films with a solvent-based
release agent and "hot-melt" adhesive.
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A film P, supplied on reels, is unwound on the right hand-side
of the line and initially goes through a station A1 where
the solvent-based release agent is delivered. After the release
agent has been spread on one side of the film, the film is
guided towards the top part of the line, where it continues its
journey inside a horizontal linear oven F.
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During the journey inside the oven F, the solvent-based
release agent is dried to the required degree.
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At the exit from the oven F, the film is guided downwards
and then into the spreading station A2, where the film is coated
with a thin layer of hot-melt adhesive, on the opposite side to
that of the release agent.
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Finally, the film is conditioned (cooled) and rewound on a
reel in a terminal station A3.
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Fig. 2 illustrates instead a plant for spreading an
acrylic-based or water-based adhesive on a polypropylene film.
In this case the adhesive, which is applied at the beginning of
the line, is water-based and the drying journey hence is
necessarily longer (the film travelling speed being equal) than
the one for the drying of a solvent-based release agent.
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As can be realised from the drawing, a plastic film of
polypropylene P is unwound off a reel, made to pass through a
station where the water-based adhesive A4 is applied, and then
into a horizontal linear oven F.
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At the exit from the oven, the film P passes through a
rewinding station A5 where it is rewound on a reel in the
terminal station A6.
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It must be noted that, compared to the plant employing a
solvent-based release agent and hot-melt adhesive, this latter
plant has a remarkably longer oven, because longer are the
drying times of water-based solutions.
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This consideration immediately leads to the guessing that
plants employing water-based release agents or adhesives have
the disadvantage of considerable linear dimensions. Although the
oven is located in the top part of the plant, exploitation of
the bottom part of the plant - as can be seen in fig. 2 - is not
fully achieved.
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Both these plants are substantially designed for a single
use and dedicated to a specific function: as such, they are
consequently little flexible.
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Therefrom derives the fact that, should a user need to
produce an adhesive film with a water-based adhesive or a
solvent-based release agent and hot-melt adhesive, he is
presently forced to purchase both plants, although the one for
water-based adhesive (typically for polypropylene films) has a
useful oven length which is theoretically suitable for a
solvent-based release agent, too.
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Furthermore, a plant designed exclusively for a solvent-based
release agent and hot-melt adhesive, such as the one shown
in fig. 1, is intended to be more and more limited or to face
high manufacturing and maintenance costs, due to the strict
environmental requirements which must be observed during solvent
treatment. Consequently, resorting to plants with a long linear
oven will be more and more unavoidable in order to treat water-based
substances, unless the film travelling speed is
drastically reduced with detriment of its throughput.
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However, as already said above, due to the oven linear
length, use of ground space in these plants is a reason for
dissatisfaction, especially in users who - up until now - were
used to achieving similar results with a more compact plant (the
one in fig. 1 for solvent-based release agents and hot-melt
adhesives), especially if employing vertical ovens of the
rotogravure type.
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Finally, it must be noted that in some individual cases,
for example in the masking-tape treatment, the film to be coated
with the adhesive does not even require prior treatment with a
release agent, because it arrives already treated by the
manufacturer. In this case, a large part of the plant - at least
all the length occupied by the oven - is substantially not used,
although it occupies productive space inside the treatment
premises.
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It would hence be desirable to provide a plant which
exploits more effectively the linear dimensions typical of the
manufacturing area.
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It is hence an object of the present invention to provide a
spreading plant to coat the film with adhesive, which plant is
equipped with a substantially linear and horizontal drying oven,
which is more flexible and allows a better exploitation of
ground space than those offered by the prior art.
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Such objects are achieved through a spreading plant as
described in its essential features in the attached main claim.
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Other inventive aspects of the apparatus are described in
the depending claims.
BRIEF DESCRIPTION OF THE DRAWINGS
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Further features and advantages of the plant according to
the invention will in any case be clearer from the following
detailed description, given by way of example and illustrated in
the accompanying drawings, wherein:
- fig. 1, as already mentioned, is an elevation side view of
a prior art plant for a solvent-based release agent and hot-melt
adhesive;
- fig. 2, as already mentioned, is an elevation side view of
a prior art plant for water-based adhesive;
- fig. 3A is a diagrammatic elevation side view of a plant
according to the invention;
- fig. 3B is a top plan view of the plant of fig. 3A; and
- fig. 3C is an elevation front view of the plant of fig. 3A.
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DESCRIPTION OF A PREFERRED EMBODIMENT
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A spreading plant comprises, in a manner known per se, a
bridge-like structure 1, above which are mounted a series of
oven modules 2a-2d (four in the drawings), mutually linearly
adjacent. In the present description the oven module - which is
well-visible also in fig. 3C both in its open and closed
position - will not be described in further detail, since it is
well-known to a skilled person in the field.
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Below the bridge-like structure 1 a series of processing
stations is housed.
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At the plant entrance (for example, the right-hand end in
fig. 3A), an unwinding and coating station 3 is provided which
also delivers water-based substances. A film P is unwound off a
reel and made to pass through such station in different ways,
which will be illustrated further on.
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Typically, this station consists of an unwinding unit 3a of
film reels to be treated, a calender stabilising unit 3b, and a
proper spreading or coating head 3c.
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It should be noted that the plant of the invention is
designed to be able to treat in this front-end station at least
one plastic film with a water-based substance: therefore, the
length of the linear oven described above must be such as to be
capable of completing the drying of this substance in a way
adequate to the work speed to which it is destined.
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According to the invention, at the opposite exit of the
plant (the left hand-side one in fig. 3A) at least one spreading
station applying the hot-melt adhesive, and one rewinding
station are provided.
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In particular, it is provided a winding device 4 - capable
of rewinding a polypropylene film P, which arrives coated with
water-based adhesive - and a spreading device 5 for hot-melt
adhesive.
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The plant is completed by a second rewinding station 6,
arranged between the front-end station 3 and the hot-melt
spreading device 5, where a winder is mounted to form a reel of
film which is fully treated with release agent and hot-melt
adhesive.
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Advantageously, upstream of the spreading device 5 a
further unwinding unit 7 is provided specifically for masking
tape or for the unwinding of other films to be coupled, whose
usefulness will be shown later on.
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The general layout of each individual station is known per
se and will hence not be described in further detail here.
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Now the possible ways of use of the plant according to the
invention will be described, so as to highlight the flexibility
and the advantages which it carries.
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In the front-end station 3, a reel of polypropylene plastic
film can be loaded, which is treated in the stabilising station
3b and onto which a water-based adhesive is applied in the head
3c.
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This film P is then dried in the oven 2 and finally rewound
in the rewinder 4 at the opposite end of the plant.
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Alternatively, in the front-end station 3, a plastic film
can be loaded, onto which hot-melt adhesive is to be applied. In
such case, through the same head 3c, a water-based or solvent-based
release agent is initially applied, which is then suitably
dried in the oven 2. In this case the film P, after having
passed onto cooling calenders 8, is deviated towards the station
5, where it is coated with adhesive. Finally, the film is
rewound in the rewinder 6.
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In these two ways, the plant of the invention is exploited
fully.
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Advantageously, moreover, in case it is necessary to coat a
masking tape with hot-melt adhesive, it is possible to mount the
corresponding reel on the additional unwinder 7, have the tape
travel through the hot-melt adhesive spreading head 5, and then
rewind it in the rewinder 6.
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For this last specific operation, as can be well
understood, only a small portion of the plant is occupied. It is
hence possible to perform simultaneously, exploiting the same
plant, the coating of polypropylene with masking tape and with
water-based adhesive: this further increases productivity and
versatility of the plant according to the invention, fully
achieving the objects set forth in the preliminary remarks.
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Thanks to the layout of the plant according to the
invention, good flexibility of use can be achieved at the same
time for various processes requiring an oven for drying water-based
solutions - be they a release agent for subsequent
spreading of hot-melt adhesive, or directly a water-based
adhesive - as well as an efficient exploitation of the ground
space, in the case that two mutually compatible processed are
performed simultaneously (specifically, coating polypropylene
with a water-based adhesive and coating masking tape with a hot-melt
adhesive).
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It is understood, however, that the scope of the invention
described above is not limited to the particular embodiment
illustrated, but extends to any other construction variant which
is comprised in the object of the attached claims.
