FRICTION SURFACE FOR PACKING FOIL OR LIKE WITH FRICTION SURFACE

MODE DE PRODUCTION DE SURFACE DE FROTTEMENT POUR PELLICULE D'EMBALLAGE OU AUTRE PRODUIT SIMILAIRE

English Abstract

Abstract
The invention relates to a friction surface comprising a
conventional foil (1), such as paper or plastic foil, and
hot melt bulges (2) and pattern formed by them made on the
foil surface by a screening technique. The foil (1) chosen to
be used should be such that it is most suitable for the
specific package, but the thickness of it should preferably be
more than 35 mm and it should at least temporarily endure the
heat of about 140 - 180° C, which the hot melt has. The bulges
made of hot melt are most advantageously made 50-150 µm high,
whereby their ability to adhere to other surfaces is excel-
lent. By using filling materials of the hot melts the friction
can be increased even more, but in such cases normally thicker
basic foil has to be used so as to prevent the foil from
tearing. By using a friction surface, considerably high piles
of packages can be made. Because the hot melt can be remelted,
the top packages can be bound together by spreading any kind
of foil on them, which can be attached on the friction surface
by heating.

Claims

The embodiments of the invention in which an exclusive
right or privilege is claimed are defined as follows:
1. A friction surface such as a foil made of plastics,
paper or other sheet or other material, having a friction
surface on the foil, characterized in that a coating of dot-
like projections, or projections of other shape, is provided
formed from a thermoplastic hot melt on that part or those
parts of the foil requiring improved friction.
2. A friction surface according to claim 1,
characterized in that the coating is either transparent or
colourless.
3. A friction surface according to claim 1,
characterized in that the coating is coloured.
4. A friction surface according to claim 1, 2 or 3
characterized in that the coating is in the form of a
plurality of dot-like projections, the height of which is
50-150 µm.
5. A friction surface according to claim 4,
characterized in that the coating is formed of a plurality
of dot-like projections with a form of truncated pyramids.
6. A friction surface according to one of claims 1, 2
or 3, characterized in that the square weight of the coating
is 2-15 g/m2.
7. A friction surface as claimed in one of claims 1, 2
or 3, characterized in that the coating of projections is
provided by using a screening technique.

8. A method of increasing the frictional
characteristics of a surface, such as a foil, comprises
applying a coating of thermoplastic material from a hot
melt, using a screen or other technique, to that part or
those parts of the surface requiring increased frictional
characteristics.

Description

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FRICTION SURFACE FOR PACKING FOIL OR LIKE
WITH FRICTION SURF~CE
The present invention relates to a friction foil of plastics,
paper or like material, which is provided with a friction
surface on the foil.
Difficulty can be experienced in stacking sheet-wrapped
packages which poorly remain on each other and such is often
overcome by providing an angular outer package of carton or
like strong material, which naturally raises the costs con-
siderably.
There have been proposed friction foils which include an
adhesive surface but such are expensive, because a substantial
area of adhesive is needed. Also, in dusty environments the
adhesive surface becomes covered with impurities and dust and
loses its good frictional qualities. A packaging foil with an
adhesive surface is also difficult to pack and use.
There has also been proposed the spreading of the plastics
foil chopped pieces of the same plastics in the production
stage which produces, without glue, a friction surface, which
has both high friction value and high mechanical strength in
different conditions. This type of manufacture is, however,
expensive and can be applied only with a very restricted
variety of foils. If all the piled packages have this type of
foil, it is difficult to bind the packages together even by
glueing foil on top of them, because the plastic pieces of the
friction foil disturb the attachment of the binding foil.
The main purpose of the invention is to avoid or minimize
said disadvantages. The friction surface according to the
invention is formed on a foil by a coating having thermo-
plastic hot melt spot-like or some other figures made by means
of a screening method.
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The coating is preferably transparent or colourless, but it
can also be coloured. Hot melt is used 2-15 g/m2, most prefe-
rably only about 3 g/m2. The friction foil is usable as a
finished product after a short cooling time, and it does not
require an evaporation line for any solvents or an expensive
method of packing, as do the friction surfaces coated with
adhesive material. The product does not have volatile sub-
stances, such as solvents of dispersion glue.
The friction foil according to the invention is very economic
to produce and therefore it can also be used as the packaging
for inexpensive materials, such as large food product pack-
ages, fertilizer sacks, timber covers, raw material sacks and
bulk material packayes. The piling of food product packages is
very difficult without a friction surface, and the products
packaged therein may break if they fall. The foil can also be
used as an anti-skid device in the transport.
By using the product according to the invention it is possible
to prevent, when filling a double-sack, the inner sack from
sliding during the filling, and the mouths of both sacks can
be glued by reheating the same coating only for a short
distance and no pressing is necessary, because the contacting
surface is large.
By using the screening method, very small amounts of hot melt
can be spread on the foil surface in a controlled manner,
whereby the production of a friction surface does not incur
great costs.
Because the coating in accordance with the invention is
carried out by means of a screening method or like method,
it is possible to coat the foil only on required parts, where-
by the costs can be further diminished and thus it is also
possible to print a text on the same foil after coating the
foil with the friction surface. Such is not possible, for

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example, for such friction surfaee, whieh is made by blowing
chopped pleces of plastics foil during the produetion stage on
the plastics foil. The spreading unit for the hot melt ean
operate as a part of a press or as an extension of it, whereby
the increase in the production costs to produce the friction
surface is considerably small.
The application of a thermoplastic melt on a packaging foil is
known as such and disclosed, for example, in Finnish patent
publication 71263.
The eoefficient of friction of totally smooth plastics foils
of some plastics types is generally high, but even slight
impurities, sueh as concrete dust, aggregate dust or pollen
dust may reduce the friction coefficient considerably. With
the saek packages it is not even possible to produce smooth
surface which would be against eaeh other. The frietion at
least doubles when a coated foil aceording to the invention is
against an uneoated foil, and when two frietion foils are
against each other, the total frietion is even higher, and
approaching, in the most preferable eonditions, the value of
1.
It is possible to use, for example, eorundum as filling ma-
terial of the thermoplastic melt, when the packing foil is
thiek, or, for example, ealeium phosphate, magnesium silieate,
silieon dioxide or eombination thereof; the filling material
is known as sueh from US patent publieation 3,691,120.
The sereening surfaee ean be varied by a known method on the
top and bottom surfaees, the total effeet of whieh gives an
advantageous binding as a result.
If the paeking foil is sensitive, a form of sereening dot is
ehosen which does not break the surfaee of -the foil, for
example, hemispherieal dots in a uniformly distributed pat-
tern.

The invention will be described further, by way of example,
with reference to the accompanying drawirl~, in which:-
ig. 1 is a sectional view of a friction foil inaccordance with the invention
ig. 2 is a fragmentary plan view of the friction foil of
Fig. 1, and
ig. 3 is a schematic illustration of the manufacture of
the foil according to the invention.
In the drawings, a foil 1 is coated with coating 2 comprising
a plurality of conical projections of dots each having a flat
top. The dots are provided by means of a screening technique,
as illustrated in Fig. 3. A screening roll 3 is provided with
cup-like recesses 4 and is partly immerged in a hot melt 6
contained in a vat 5. When the screening roll 3 rotates it
raises hot melt from the vat, whereby the melt in the cups ~
is brought into communication with the foil 1 running between
a press roll 7 and the screening roll 3, and the melt adheres
on the surface of the foil forming a dot-like coating of
projections. By means of a scraper 8, any excess hot melt is
removed from the surface of the screening roll. The screening
cups are dimensioned in such a way that the hot melt forms
projections on the foil surface, the height of which pro-
jections is about 50-150 ~ m and which form the desired
pattern.
E~ample
A low density polythene foil, the thickness of which was 0,2
mm, was coated using an apparatus according to Fig. 3 with hot
melt mainly consisting of ethyl-vinyl acetate, the viscosity
of which was 1000 cP in the temperature of 140 C. The depth

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of the screening cups 4 was 0,12 mm and their diameter 1 mm.
The distance of the dot-like projections from each other was 4
mm. The finished product may be used in the manufacture of
sacks.

Representative Drawing