Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
The present invention relates in general to coverin~s
with grain effects and the like (for example, marbling
or veining) and has been developed with particular
attention to its possible use in the field of coverings
o~ rubber or of synthetic or artificial materials
usable, for example, as floor coverings.
In this field, it is current practice to produce sheet
coverings of rubber, polyvinyl chloride or other
thermoplastic or thermosetting materials which have
undergone an operation to give them a marbled or veined
effect by producing more or less regular, sharp or
blurred marks and lines on the covering material to
create an effect more or less comparable to that of the
veining of marble or wood.
The coverings are usually formed by the calendering of
an extruded mass produced from materials of different
colours. A marbling effect oriented substantially in
the direction of the calendering operation is thus
obtained. In practice, this means that the marks and
lines characteristic of this effect may be longer or
shorter, and more or less close together, but are
alwa~s oriented in a predominant direction which is
that in which the calendering operation takes place.
Moreover, it is known, for example, in the production
o linoleum, to divide the material output from the
calendering operation into thin longitudinal strips
whilst it is still plastic and to rearrange the strips
transverse the length of the sheet and then subject the
whole to a further calendering operation.
This method is rather complex and does not eliminate
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the problem indicated above since it simply achieves a
different orientation of the predominant direction of
the grain.
Another solution sometimes used is to incorporatè
granules of various shapes, consistencies and colours
directly into the mixture used to form the covering
sheet. More precisely, the sheet is produced by a
calendering operation followed by a surface-finishing
of the calendered sheet in order to produce a pattern
or effec~ represented by the granules on the surface.
Finally, another solution is to form granules or small
cubes of various shapes and colours and then deposit
them on a substrate and subject the composite thus
produced to a pressing operation to produce a final
product with an appearance approximately similar to
that of a grained covering.
For various reasons, this technique is quite complex to
carry out.
In the first place, the distribution o~ the granules
has to be regulated very precisely in crder to produce
a uniform final product.
In the second place, the air in the spaces between the
granules has to be el;~;nAted during the pressing
without giving rise to residual porosity which could
promote the accumulation of dirt on the covering and
make it more difficult to clean.
Moreover, particularly with intrinsically plastic
materials (e.g. rubber), it is very difficult to
produce the granules, except by fairly sophisticated
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processes (for example, the formation of small cubes in
a cooled environment). ~urthermore, once khey have
been granulated, these materials have an intrinsic
tendency to clump which makes their deposition even
more difficult.
Finally, the aesthetic effect achieved cannot be said
to be wholly satisfactory, since the grain pattern is
constituted essentially by separate areas of different
colours without the gradual colour changes, blurring or
mixing achieved in some natural grains.
The particular object of the present invention is to
provide means for producing coverings with grain
effects and the like (for example marbling or veining)
which are substantially free of directional
characteristics and the other defects mentioned above,
all by means of an intrinsically simple operation which
does not require substantial modification of the
equipment and devices already in use for producing
covering sheets.
According to the present invention, this object is
achieved by virtue of a method having the
characteristics recited in the following claims.
A further subject of the present invention is a device
which can carry out the method.
The invention will now be described, purely by way of
non-limiting example, with reference to the appended
drawings, in which:
Figure 1 is a schematic, side elevational view o the
structure of a device for producing sheet coverings
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according to the invention,
Figure 2 is a section taken on the line II-II of Figure
1, on an enlarged scale,
Figure 3 is a section taken on the line III-III of
Figure 2, on an enlarged scale, and
Figur~es 4 and 5 show the characteristics of two
covering sheets at two successive stages of the method
according to the invention.
In the drawing, a device for treating calendered sheet
materials is generally indicated 1 and may, to
advantage, be connected, as an output stage, to a
calendering line (of known type, not shown in the
drawings) for the continuous or substantially
continuous production of a sheet of covering material A
which is intended to be used as the starting material
for the method according to the invention.
The starting sheet A preferably, but not strictly
necessarily, already has marbling or veining produced
by a known technique. The marbling or veining of a
sheet of this type thus extends generally
longitudinally, that is, in the direction in which the
calendering operation by which it is produced takes
place. An example of the surface appearance of such a
sheet A is shown in Figure 1.
The sheet A passes (downwardly in the embodiment shown)
around a first roller, indicated 2, with a horizontal
axis so as to be directed towards a further, return
roller 3 also with a horizontal axis.
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A further roller 4 with a horizontal axis, opposite the
first roller 2, has tooth-like formations which, in
general, have cutting edges and are of a length
~measured radially of the roller 4 and in relation to
the thickness of the sheet ~ and the distance apart of
the surfaces of the rollers 2 and 4) such that the
formations 5 can penetrate the sheet A slightly so as
to achieve a distinct scraping (milling) effect
thereon.
For example, as shown in Figures 2 and 3, the teeth 5
may be grouped on a plurality of s~raight blades 8 (for
example, four blades3 disposed in respective recesses 9
spaced uniformly around the periphery of the roller 4
and extending along respective generatrices thereof.
The blades 8 are generally crenellated, so to speak,
the teeth 5 constituting the crenellations.
In particular, as shown schematically in ~roken outline
ln Figure 2, the teeth 5 of two successive blades 8 are
offset so that the teeth of a given blade act on
regions of the sheet A which are not affected by the
action of the teeth of the blade immediately upstream.
The teeth S may be mounted in various ways, however,
according to techniques used, for example, in rotary
mills, planing machines, etc.
The profiles of the teeth 5 (in a plane transverse the
axis of the roller 4) usually have a front cutting edge
lO which is intended to act on the sheet A, with a
frontal undercut surface 11 (of cylindrical profile)
and a dorsal undercut surface 12, respectively. The
shapes of the undercut surfaces 11 and 12, as well as
the width of the tooth 5 (axially of the drum 4), may
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be varied selectively, however, in dependence on ~he
final result to be achieved, particularly as regards
its aesthetic appearance~
The senses (and speeds) of rotation of the rollers 2
and 4 are selected so that the formations 5 effectively
move relative to the sheet A so as to form and remove
therefrom shavings 6 which fall freely onto the
underlying pass of the sheet A against which they are
then compressed. After it has passed around the
return roller 3, the sheet A advances further
substantially in the direction in which it advanced
into the device 1 and continues towards a pair of
further, contrarotating rollers 7 arranged above and
below the sheet respectively, or towards a continuous
vulcanising (rotocure) unit, so that the shavings 6 are
compressed or pressed against the surface of the sheet
A which was scraped or milled by the teeth 5.
For this purpose (that is, in order to facilitate the
incorporation of the shavings 6 into the sheet), the
rollers 7 may, to advantage, be heated so as at least
partially to melt the shavings 6 which are thus
anchored firmly to the body of the sheet. The surface
of the sheet B output by the pair of pressing rollers 7
(or the rotocure unit) thus has a grain effect more or
less comparable to that shown in Figure 5.
This effect is achieved essentially as a result of the
shavings 6 falling freely and consequently being
reincorporated into the sheet. This pro~uces an
overall grain effect which, unlike that of the starting
sheet A, has na directional characteristics or
appearance longitudinally of the sheet.
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The fact that the shavings 6 which have just been
formed fall freely in order to be compressed against
the underlying sheet ensures completely uniform
distribution without the need for complex metering
operations.
In the second place, the shavings can be produced
easily by scraping ~milling) even from very plastic
materials (e.g. rubber), even when operating at ambient
temperature. Their immediate deposition on the
underlying sheet creates neither storage and
accumulation problems nor the consequent risks of
clumping.
Moreover, the shavings 6 produced by scraping are quite
thin (of the order of tenths of a millimeter), and
hence extremely flexible, and can consequently be
compressed very easily without the risk o trapping
quantities of air.
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Finally, the final aesthetic effect is that of a grain
with many colour-change effects and much blurring and
mi~ing of di~ferent colours.
Furthermore, it should be noted that, although it is
preferred, the solution of reincorporating the shavings
6 scraped or milled from the sheet A into the sheet
from which they were formed is not strictly essential
in order put the invention into practice. In fact, one
could consider a solution in which the shavings 6
produced by scraping or milling are deposited on a
different substrate in order to produce the desired
final result, or even a solution in which the shavings
6 are compressed to produce a covering sheet directly
without the use of a substrate.
- As already stated, the final characteristics of the
grain of the sheet B (that is, essentially, the
lengths, orientations, shapes and characteristics of
the marks or lines which give rise to the grain effect)
depend on the shapes of the shavings 6 produced by the
teeth 5. This shape depends in turn on a sexies of
factors, amongst which may be mentioned:
- the shapes of the teeth 5,
- the dimensions of the teeth,
- the distribution thereof (their so-called density) on
the external surfac~ of the roller 4,
- the speed at which the scraping operation is carried
out, and
- the depths of the incisions.
In the embodiment to which Figure 1 relates the
starting sheet A which passes around the roller 2
advances at a linear velocity ~that is, a velocity
tangential to the roller 2) of the order of 0.6
m/minute. The sense of rotation of the roller 2,
which, from the viewpoint of Figure 1, is clockwise, is
such that the starting sheet A advances from left to
right.
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The roller 4, however, is rotated anticlockwise (by a
respective motor, not shown) at a speed such that the
teeth 5 have a linear velocity (tangential to the
roller 4) of the order of lO0 m/minute and hence
substantially faster than the speed of advance of the
sheet A.
In an embodiment which has been found particularly
advantageous, the teeth 5 penetrate the sheet A to a
depth of the order of 1 mm (for example, 0.6-1.2 mm).
In tests carried out by the Applicant, sheets such as
linoleum sheets 2-2.5 and 3.2 mm thick were used as the
starting sheet A and already had marbling or veining
such as that shown ln Figure 4.
The teeth 5 used had front cutting edges 10 about 4 mm
long (with the teeth 6 mm apart) axially of the roller
4. The tools 5 were distributed on the roller 4 on
four blades 8 angularly spaced 90 apart around its
periphery.
Naturally, the principle of the invention remaining the
same, the details of construction and forms of
embodiment may be varied widely with respect to those
described and illustrated, without thereby departing
form the scope of the present invention.
