Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02597361 2007-08-15
"A thread for synthetic grass turfs, die for
producing same related processes of manufacturing and
use, and synthetic grass turf including it"
***
The present invention relates to synthetic (or
"artificial") grass coverings.
Synthetic-grass coverings have been used for quite
some time now, in particular to provide areas of
greenery for urban decoration and similar amenities,
for areas for bordering swimming-pools, and, in
general, for replacing natural-grass cover in all those
conditions where the laying and maintenance of a
natural-grass cover may prove critical. The use of said
synthetic-grass coverings has received new impulse in
recent times in order to provide coverings for sports
facilities, for example, soccer pitches. The
corresponding literature is extremely extensive, as is
witnessed, at a patent level, by documents such as: US-
A-3 731 923, US-A-4 337 283, US-A-5 958 527, US-A-
5 961 389, US-A-5 976 645, JP-B-32 53 204, JP-A-
10037122, DE-A-44 44 030, EP-A-O 377 925, and EP-A-
1 158 099.
In particular, from the document mentioned last,
which is owned in the name of the owner of the present
application, a synthetic-grass structure is known,
which comprises a sheet-like substrate with a plurality
of filiform formations extending from the substrate for
simulating the grassy sward of natural turf, and a
particulate filling material, or infill, dispersed
between the filiform formations so as to keep the
filiform formations themselves in a substantially
upright condition. Specifically, the above synthetic-
grass covering is characterized in that the particulate
filling material (infill) is constituted by a
substantially homogeneous mass of a granular material
CA 02597361 2007-08-15
2
chosen in the group constituted by polyolefin-based
materials and by vinyl polymer-based materials.
Further advantageous developments of the above
solution are described in the documents EP-A-1 319 753,
EP-A-1 375 750, EP-A-1 371 779, as well as EP-A-1 486
613, and again the European patent application No.
05425957.7, all of said documents being owned by the
owner of the present application.
In the course of the last few years, as regards
application to the production of grass coverings for
sports facilities, the activity of innovation has been
aimed chiefly at the characteristics and modalities of
distribution of the filling material or infill.
As a whole, less attention has instead been paid
to the characteristics of the yarn used for making said
filiform formations. In this connection, reference may
be made, for example, to EP-A-0 259 940, which
describes, instead, the possibility of using, in a
synthetic-grass covering, a yarn obtained with the co-
extrusion of polymeric materials of different
composition, in particular with different coefficients
of friction.
A solution still widely used for making the
aforesaid filiform formations envisages resorting to a
yarn having a base of plastic material, such as
polyethylene. The material in question is initially
laminated so as to form a sheet or web of the thickness
of, for example, 200 - 300 micron. The sheet is then
subjected to a cutting operation, which divides the
sheet into a large number of strips of small width (for
example, 10 - 20 mm).
The cutting operation is usually followed by one
or more operations of longitudinal stretching and
fibrillation. For this purpose, the web is divided into
strips of given width, which are stretched and then
CA 02597361 2007-08-15
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pre-fibrillated, i.e., incisions are made in a
longitudinal direction, to give rise, during normal
use, to progressively thinner threads, in the direction
of the width. The material is gathered as a ribbon or
tape on a bobbin or reel, which usually passes it on to
a subsequent step of twisting of the thread, thus
enabling it to be treated in the subsequent processing
steps (e.g., tufting on the loom).
The above type of yarn is the first to have
asserted itself on the market on a large scale on
account of ease of production in all the steps of the
process. The final aesthetic appearance of the yarn is
not optimal as regards reproducing the appearance of
the sward of natural grass cover, but is considered
acceptable by the market. A practically inevitable
defect in this type of yarn lies in the fact that, when
four to five years have elapsed from its being laid,
the corresponding coverings manifest problems of wear
due to an excessive, uncontrolled and
uncontrollable fragmentation during use (breaking
of parts of thread, formation of very thin and brittle
strips, with the possible formation of dust on account
of the breaking-down/degradation of the thread, etc.).
An alternative technique envisages the formation
of a single-thread or single-strand yarn via the
formation of individual threads directly from a
threading die. The threads in question are stretched
and gathered with four, six or eight threads per tuft,
before passing on to the subsequent steps as described
above (gathering, twisting, tufting). This technique is
increasingly asserting its presence on the market
because it does not give rise to the problems of wear
described above in relation to a fibrillated yarn:
single-stranded yarn is not subject over time to
undesirable phenomena of splitting or fragmentation.
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The single-thread technique presents, however, various
weakpoints. There exists in the first place a
difficulty of production in gathering the individual
threads (even though they are grouped together in
groups of four, six or eight threads) on the reels, as
well as a similar, if not greater, difficulty in the
twisting operation. In the end product the
strength/toughness of anchorage of the threads to the
substrate of the synthetic-grass covering, albeit
accepted by the market and in compliance with the
existing technical requirements, is not comparable to
that of the "fibrillated" material described
previously. This is explicable by the fact that the
individual (single) threads that make up a single tuft
have the possibility of sliding on one another also at
the point where the loop is fixed to the substrate
(usually with a latex).
For the sake of completeness, it should again be
recalled that there exists yet a third type of yarn
constituting a sort of hybrid between the preceding
ones, defined as "monotape". For the manufacturing
process, the production cycle indicated for the
fibrillated product described at the start is in
practice followed, cutting from the original sheet or
web strips of smaller width, without using any process
of pre-fibrillation, then gathering together the four,
six or eight strands per tuft and passing on to the
subsequent operations, etc. This technique, which
presents various problems, has had little commercial
success and is in fact disappearing from the market.
From WO-A-2004/106601, taken as model for the
preamble of Claim 1, a technique is known, in which a
multilayer strip is obtained from a film extruded from
a threading die through a nozzle provided with
projections. The projections form in the strip grooves
CA 02597361 2007-08-15
designed to form preferential sites of splitting of the
strip during fibrillation. In this way, it is claimed,
a subsequent random post-fibrillation of the yarn such
as to reduce the resilience of the synthetic-grass
5 covering, would be prevented.
As has already been mentioned, whatever the
technique of production adopted, the yarn is usually
wound on reels used for supplying workstations that
produce the basic structure of a synthetic-grass
covering of the type described previously, i.e., with
the filiform formations that extend from a sheetlike
substrate. Said workstations operate typically with
known techniques resembling techniques of tufting or
the like.
In particular, said techniques aim at "implanting"
in a sheetlike substrate (which is either continuous or
substantially continuous, for example, because it is
provided with draining holes) yarn formations having a
general U-shaped configuration. Each formation
basically constitutes a sort of tuft with a looped part
that passes underneath the substrate and two lateral
branches that extend vertically above the substrate, to
simulate blades of grass. In the case of the single
thread, the tuft is constituted by four, six or else
eight strands or blades according to the thicknets
and/or width of each blade.
Albeit as a whole satisfactory, these traditional
techniques leave room for further improvements,
oriented in various directions.
In particular, there has been felt the need for a
technique for producing yarn for grass coverings that,
substantially, combines within it the positive aspects
of the various techniques described previously, without
sharing their drawbacks, and in particular presents the
stability and resistance to subsequent fragmentation
CA 02597361 2007-08-15
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typical of single-stranded yarn, thus preventing the
critical aspects linked to the need to combine a
plurality of (single) threads to form a single tuft,
and ensuring at the same time the strength/toughness of
anchorage to the substrate typical of fibrillated yarn,
this being achieved within the context of a process of
production, which is moreover simple, reliable and
efficient and affords the possibility of achieving a
further improvement as regards the faithfulness in the
reproduction of the appearance of the sward of natural
grass cover.
According to the present invention, this need is
met thanks to a yarn having the characteristics
referred to specifically in the ensuing claims. The
invention also relates to a corresponding process for
manufacturing said yarn, as well as a corresponding
process of use for the purpose of making a synthetic-
grass covering (either with or without infill).
The claims form an integral part of the technical
disclosure provided herein in relation to the
invention.
The invention will now be described, purely by way
of a non-limiting example, with reference to the
annexed plate of drawings, in which:
- Figure 1 is a functional block diagram of a
plant for the production of a yarn of the type
described herein;
- Figure 2 is a plan view of a portion of a
threading die used for forming a yarn of the type
described herein;
- Figures 3 and 4 illustrate the yarn in question
in two subsequent steps of the manufacturing process;
- Figure 5 is a schematic illustration of the
criteria with which the yarn described herein can be
CA 02597361 2007-08-15
7
used for making a synthetic (or "artificial") grass
covering; and
- Figures 6 and 7 illustrate a yarn of the type
described herein, respectively immediately after
production and in a subsequent step, after application
of mechanical stress.
In Figure 1, the reference number 10 designates
as a whole a plant that can be used for producing a
yarn that is to be used for the production of
synthetic-grass coverings.
The plant 10 is represented in the form of a set
of processing stations that are here supposed as being
located in a single site and designed to carry out a
processing cycle comprising different operations of
treatment performed in cascaded fashion one after the
other. Persons skilled in the sector will moreover
appreciate that the aforesaid operations can, however,
be performed in different premises or contexts and at
different times, after prior storage and/or transfer of
the intermediate products of the various processing
steps illustrated.
In particular, the reference number 12 designates
an extruder for plastic materials which operates with a
vertical axis. A plastic material in the molten state
is fed into the extruder 12 through an inlet duct 14,
to undergo extrusion in a threading die 16 constituted,
for example, by a die with an annular profile.
In particular, in the examplary of embodiment
illustrated herein, which is provided merely by way of
example, the annular threading die 16 is constituted by
a certain number of arched portions 160, separated from
one another by a distance, for example of 1 - 2 cm.
Each portion of a threading die 160 is designed to
produce a respective strip B and has the profile
illustrated in Figure 2. For instance, Figure 2 can be
CA 02597361 2007-08-15
8
considered as a plan view from beneath of the single
arched portion 160 of a threading die, as ideally
viewed from beneath, i.e., from the area in which the
respective strip B drops as it comes out of the
threading die.
In practice, the single portion of a threading die
160 has a certain length (for example, 50 - 60 mm,
typically 56.4 mm) measured along its arched path of
extension and comprises a certain number of segments
162 (eight in number, in the example illustrated).
Each segment 162 has then a length (once again
measured along the arched path of extension of the
portion of a threading die 160 of which the segment
forms part) in the region of 6.7 mm and is connected to
the adjacent segments 162 (or to the adjacent segment,
in the case of the two end segments 162 in the portion
of a threading die 160) by a thin portion or stretch
164.
Each thin portion 164 has a length, for example,
of 0.4 mm, and a width or thickness (dimension in the
radial direction with respect to the path of extension
of the portion of a threading die 160) of, for example,
0.15 mm.
An important characteristic of the segments 162 is
that they have a U-shaped cross section, hence one with
two wider end parts or branches 1620 (once again the
dimension in the radial direction with respect to the
arched path of extension of the portion of a threading
die 160) with respect to the central part 1622.
For simplicity of illustration, in Figure 2 the
widened end parts 1620 and the central part 1622, which
is narrower, are designated expressly by the
corresponding reference numbers only in the segments
162 that occupy the end positions within the portion of
a threading die 160 illustrated.
CA 02597361 2007-08-15
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It will on the other hand be appreciated that the
U shape is not to be considered imperative, since the
characteristic of the end parts 1620 that are wider
than the central part 1622 can be achieved also with
other shapes (for example, a "bone" shape).
Purely by way of example, the end parts 1620 can
present a width or thickness (once again the dimension
in the radial direction with respect to the arched path
of extension of the portion of a threading die 160) of
0.67 mm as against a width or thickness of the central
part 1622 of 0.46 mm.
It is on the other hand evident that all the
dimensional values mentioned previously are given
purely by way of example and are not to be interpreted
in a way that might in any sense limit the scope of the
invention described herein.
At output from the threading die 16, there are
hence present a plurality of strips B, each of which
has, if viewed in cross section, the profile
represented in Figure 3: this is, in other words, a
profile complementary to the profile of the portion of
a threading die 160 described previously with reference
to Figure 2, hence a profile in which it is possible to
distinguish a certain number (eight, in the example
illustrated) of segments B1 connected to one another by
slender portions B2, with each segment Bl presenting a
profile (roughly U-shaped, in the example illustrated
herein) with end parts that are wider than the central
part.
The material used for forming the strips B is
usually a polyolefin-based material, such as a material
chosen from the group constituted by polyethylene,
polypropylene and/or mixes and/or copolymers thereof,
polyethylene representing the currently preferred
choice.
CA 02597361 2007-08-15
The material in question is usually pigmented so
as to present en masse a colouring such as typically a
green colouring, it being evident that this
characteristic is not to be understood as in any sense
5 limiting the scope of the invention.
Usually, the strips B coming from the threading
die 16 are subjected to cooling by being dipped in a
cooling bath contained in a tank 18 so as to enable
their consolidation.
10 As has already been mentioned, each of the strips
B reproduces the profile of drawing conferred upon it
by the respective portion of a threading die 160, and
is thus in the form of a strip constituted by a
plurality of (for example, eight) filiform elements B1
(with widened ends, hence thickened with respect to the
central part), set alongside one another and connected
together by more slender connection portions B2.
Usually, as it is lowered into the cooling bath
18, each strip B tends to stretch out so that the
substantial identity of shape with the portion of a
threading die 160 does not usually correspond to an
identity of dimensions. For example, the strip B can
present a width in the region of 20 mm, with the
segments B1 and the slender portions B2 that have
homologous dimensions of width, respectively of 2.4 mm
and 0.12 mm.
The dimensions of thickness can instead be
approximately 300 micron and approximately 30 micron,
respectively, for the segments B1 (maximum thickness in
an area corresponding to the thickened ends) and for
the slender portions B2.
Once again it is recalled that all the dimensional
values, as quoted throughout the present description
are provided purely by way of example and are not to be
CA 02597361 2007-08-15
l~
interpreted as in any sense limiting the scope of the
invention described herein.
In any case, the slender connection portions B2
preferably have a thickness sufficient to cause them
not to be brittle in normal conditions of manipulation
of the strip B, where by "normal conditions of
manipulation" is meant the conditions corresponding to
the fact that the strip B is gripped by a person with
his hand and felt, for example, by winding it around
his fingers.
The strip B or each strip B consolidated by
cooling (the solution herein represented, which
envisages the simultaneous formation of a number of
strips B, constitutes only a preferred, but non-
imperative, embodiment of the invention) is then to be
fed into a drawing assembly, for example, with motor-
driven rollers, designated as a whole by 20.
The strip or strips B can be taken up in the
course of a process that is either continuous (and in
this case there will usually be provided one drawing
assembly 20 for each strip B) or else discontinuous, in
this case envisaging a gradual emptying from the tank
18 of the web/strips B that gradually accumulate
therein.
It will likewise be appreciated that recourse to a
technique of cooling by dipping constitutes just one
from among the many choices possible for achieving the
desired result of cooling/consolidation of the strip or
strips B. Other techniques for achieving cooling are
represented, for example, by exposure to the
environment or else by exposure to jets of air or
aeriform for cooling upon exit from the threading die
16.
Starting from the drawing assembly 20, the strip
or strips B (in what follows reference will be made to
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just one strip, for reasons of simplicity of treatment)
is/are sent on to an assembly for longitudinal
stretching 22.
In a way in itself known, this assembly is
normally constituted by an oven for heating the
material and two or more sets of motor-driven rollers,
each comprising two counter-rotating rollers, between
which the strip B is made to advance (from left to
right as viewed in Figure 1) in conditions in which the
peripheral or tangential speed of the pairs of rollers
(hence the speed imparted upon the strip B) increases
gradually.
In this way, the strip B is subjected, in one or
more stages, to an overall action of longitudinal
stretching. For example, it is possible to operate (in
a way in itself known) so as to apply a ratio of
stretching of between 4:1 and 5:1 understood as the
ratio between the rate of advance after and before the
heating/stretching oven.
The overall effect of this stretching is
represented in Figure 4, where the reference B'
designates the strip at output from the stretching unit
22.
The strip B' subjected to stretching (in what
follows also referred to, for reasons of brevity, as
"yarn") has a width and a thickness that are smaller
than that of the starting strip B, having, however,
preserved in a practically unaltered way (for well-
known physical reasons) its cross-sectional profile
during stretching.
Consequently, also the yarn B' deriving from
stretching is obtained, if viewed in cross section as
represented in Figure 3, in the form of a strip of the
width of, for example, 9-10 mm constituted (as in the
case of the "length" of strip B from which it has been
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obtained) by a plurality of filiform segments Bl' set
alongside one another and connected together by more
slender connection portions B2', with the segments B1'
that have thickened end parts.
For example, in the case of the yarn B', the
segments B1' can have a width of 1.1 - 1.3 mm and a
thickness (maximum, in an area corresponding to the
thickened ends) of 130 - 150 micron. The slender
connection portions B2' can instead typically have a
width of approximately 30 micron and a thickness of
10 micron in the thinnest area.
Once again it is recalled that the aforesaid
dimensional values are provided purely by way of
example and are not to be interpreted as in any sense
limiting the scope of the invention described herein.
In any case, the slender portions B2' are very
brittle, so that the single yarn B' can be easily
fibrillated, i.e., split into individual threads, each
corresponding to one of the segments Bl', by breaking
the slender portions B2' with a modest stress such as
the one deriving from the operation of twisting
normally performed for winding the yarn B' onto reels R
according to the modalities and for the purposes
described in the introductory part of the present
description. The strip B' thus behaves as a true strip,
with all the resulting advantages, until the operation
of twisting, when the strip then divides up into the
individual strands.
In Figure 1, the reference number 24 indicates a
processing station, which, operating according to
criteria in themselves known (i.e., basically according
to techniques of tufting or the like) enables
formation, starting from the yarn B' wound on reels R,
of a synthetic-grass covering designated as a whole by
S.
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This is basically a synthetic-grass structure S
that comprises a sheetlike substrate K, from which
there extends a plurality of filiform formations
(constituted by the yarn B') that simulate the grassy
sward of natural grass cover.
Specifically, the weaving station 24 operates by
"implanting" in the sheetlike substrate K formations
each comprising a sort of tuft of yarn B' having a
looped part L that passes underneath the substrate K
and two lateral branches that extend vertically above
the substrate K, simulating blades of grass.
The synthetic-grass structure S is suited to
receiving (once again according to altogether known
criteria) a filling with particulate material F
dispersed between the filiform formations so as to keep
the filiform formations themselves in a substantially
upright condition. For example, the particulate filling
material (infill) F in question may be constituted by a
substantially homogeneous mass of a granular material
chosen from the group constituted by materials with a
base of polyolefin and by materials with a base of
vinyl polymer.
In any case, the characteristics of operation of
the weaving station 24 and the criteria of production
of the synthetic-grass covering S do not constitute
elements of specific importance for the purposes of an
understanding and implementatioon of the present
invention. The solution according to the invention is
suited in fact to being used also in the context of
synthetic-grass coverings made according to criteria
different from the ones represented in Figure 4.
For example (and without evidently wishing to
limit the scope of the invention in any way), the
filiform formations that extend above the sheetlike
substrate K, instead of having their distal ends free
CA 02597361 2007-08-15
(according to the plush or velvety configuration,
represented in Figure 4) can instead be connected to
one another, creating loop formations.
Figures 6 and 7 illustrate the appearance of a
5 length of yarn B', respectively before and after
separation of the individual segments Bl' deriving from
breaking of the slender portions B2' originally
connecting the segments themselves. After their
separation, the segments B1' preserve their
10 individuality precisely, without undergoing further
fragmentation.
Unlike what happens in fibrillation treatments of
a traditional type, the structure of the yarn B' means
that the yarn B' itself gives rise to a plurality of
15 filiform elements B1', the characteristics of which are
defined precisely, for example, so that (according to a
currently preferred, but non-imperative, embodiment)
the filiform elements B1' are substantially the same as
one another.
The expression "currently preferred, but non-
imperative, embodiment" is intended to take into
account the fact that, in some applications, the fact
that the filiform segments Bl' (and hence the segments
B1 of Figure 3 and the segments 1600 of the portion of
a threading die 160), which are not the same as one
another, but present different dimensions (being, for
example, alternatively, "wide" and "narrow"), may be
considered preferable.
Whatever the choice adopted, the solution
described herein in any case prevents one of the
traditional drawbacks of the operations of
fibrillation, namely, the fragmentation of each blade
of yarn in an irregular (in effect random) way, with
the consequent formation of fibrils of different width,
frequently so thin as to break up and crumble under
CA 02597361 2007-08-15
16
minimum stress. At the same time, the solution
described herein does not alter appreciably the
criteria of production of the synthetic-grass covering
S, in particular as regards the development of the
operation of "weaving" of the synthetic-grass covering.
In particular, the (somewhat burdensome) operation,
inevitably required by single-thread techniques, namely
of having to aggregate a certain number of single
threads to form a tuft, is avoided.
Persons skilled in the sector will likewise
appreciate that the operation of separation of the
segments B1' (i.e., breaking of the slender portions
B2') is not in any way indissolubly linked to the
possible re-twisting of the yarn B'.
Purely by way of example, the operation of
separation of the segments B1' (breaking of the slender
portions B2') can be performed or completed after the
yarn B' has been woven with the substrate K, for
example, with an operation of brushing of the
synthetic-grass covering formed by the yarn B',
performed, for instance, with a rotary brush that
subjects the yarn B' to mechanical stress, bringing
about fragmentation of the yarn itself in an area
corresponding to the slender portions B2'.
Albeit without wishing to be tied down to any
specific theory in this connection, the present
applicant has reasons to believe that the precision
with which the segments B1' are separated from one
another, for example, following upon mere twisting of
the strip or strip B' of which the segments themselves
originally form part, as well as the fact that, after
separation, the segments preserve precisely their own
individuality, without undergoing further
fragmentation, are indissolubly linked to the mechanism
of formation of the aforesaid strip B' (and of the
CA 02597361 2007-08-15
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strip B from which the same is obtained by stretching),
i.e., to the fact that the segments Bl' (and B1)
present end parts (between which there extend the
slender portions B2' and, respectively, B2) thickened
with respect to the central part, a fact which in turn
derives from the portions of a threading die 160, in
which the segments 162 have end parts 1620 that are
wider than the central part 1622.
Of course, without prejudice to the principle of
the invention, the details of construction and the
embodiments may vary, even extensively, with respect to
what is described and illustrated herein purely by way
of non-limiting example, without thereby departing from
the scope of the invention as defined by the annexed
claims.
