Note: Descriptions are shown in the official language in which they were submitted.
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SPORTS SURFACE, ITS USE AND ITS METHOD OF
MANUFACTURING
Technical Field
[0001] The invention relates to a fibre-based sport surface and
a method of manufacturing a
fibre-based sports surface. The sports surface comprises a backing layer and a
pile layer and is
suited for a large variety of sports and recreational activities, including
field hockey, lawn bowls,
cricket, golf, tennis and paddle. The sports surface shows excellent
performance without irrigation
and is therefore particularly suited for use in its dry condition, i.e.,
without the addition of water.
Background Art
[0002] Sports surfaces need to fulfil certain performance
criteria to enable comfortable play
and/or to comply with norms and restrictions that have been set by
professional sports associations.
For example, restrictions may be provided to ensure a minimum or maximum ball-
roll distance,
specify ball bounce characteristics, or to enable a safe player sliding
performance. Natural turf is
one of the preferred surfaces for many sports but is frequently found too
costly to maintain for
everyday use. For this reason, artificial turf has become increasingly popular
and has developed
through multiple generations to achieve sports performance that is equal to or
even exceeds the
natural version. In general, artificial turf comprises a backing layer and a
pile layer, which are
connected together by tufting or weaving or the like. The pile layer forms the
playing surface.
[0003] The pile layer of the sports surface determines the performance of
the sports surface. It
may also be provided with infill materials to achieve the required resiliency
and other sports
performance characteristics. Features such as the pile height, yarn type,
fibre density and stiffness
all contribute to the ball's behaviour on the playing surface. For example, if
the friction between a
ball and the playing surface is very large, then the ball may not roll the
required distance. In general,
the development of pile has sought to mimic its natural equivalent by
providing different fibre shapes
and materials. WO 2006/091067 Al shows an example of an artificial grass turf
system specifically
intended for use as a sports field, in particular for soccer.
[0004] Fibre-based sports surfaces are widely used to play ball
sports like soccer and hockey,
but can have as a disadvantage that the friction at the playing surface is too
large. This can
negatively affect the sports performance and can lead to injuries of the
players when sliding. To
mitigate these negative effects, the sports surface can be wetted in order to
lower the friction at the
playing surface. This is especially applied on hockey fields and this solution
is commonly referred
to as a "water based field".
[0005] Although the described water based fields provide
excellent sports performance, the
required large volumes of water for wetting the field are not always readily
available. Moreover, it is
not environmentally friendly to use large amounts of water, especially in
periods of draught.
Preparing a water based field for a match can require as much as 20 000 litres
of water per period
of play. While such water based fields have become the standard for sports
such as hockey, their
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use has become untenable, since they put the sport out of reach for certain
groups of players and
nations with scarce water.
[0006] The present invention attempts to further improve on such sports
surfaces by providing a
field with a comparable or improved level of functionality while reducing the
required amount of
water to wet the field and/or entirely omitting the use of water.
Summary of Invention
[0007] Therefore, according to a first aspect of the invention,
there is provided a sports surface
comprising a backing layer and a pile layer, wherein the pile layer comprises
pile fibres, connected
to the backing layer to form loops and the loops are closely packed together
to form a substantially
continuous playing surface. The pile fibres can be formed by monofilaments,
fibrillated tapes, slit
tapes or the like. Preferably, the pile fibres are formed by monofilaments
i.e. fibres that have been
extruded as individual filaments.
[0008] Here the term "sports surface" is used to refer to a
specialized surface for carrying out
sports or other recreational activities, for example to play field hockey,
lawn bowls, cricket, golf,
tennis, paddle or soccer. It will be understood that in embodiments the sports
surface can be
adjusted to comply with norms set by professional sports associations
regarding certain
performance features such as ball roll distance or ball rebound height. The
sports surface according
to the present claims marks a significant departure from conventional thinking
in that it no longer
seeks to approximate natural turf but instead delivers a sports performance
that is inherently
different from natural turf and existing artificial turf.
[0009] The pile layer comprises a plurality of loops and the
playing surface is formed by an upper
part of the plurality of loops. The term "loop crest" is used to refer to the
upper and outer part of the
plurality of loops that forms the playing surface. Typically, each loop has a
loop base defined by the
points where the pile fibre extends from a top surface of the backing layer.
From the loop base, two
loop sides extend between the backing layer and the playing surface. The
playing surface is formed
by the loop crest that connects the two loop sides. It will be understood that
the loop is formed by a
continuous fibre and that the definition of what a loop side and a loop crest
is, may depend on the
momentary shape of the loop. The loop shape is for instance dependent on the
pressure currently
and/or previously applied to the playing surface, but may also depend on other
factors such as the
degree of packing of adjacent loops.
[0010] Traditional sports surfaces typically use cut-fibres in
the pile layer. In comparison to such
traditional cut-fibre sports fields, the resistance at the playing surface is
reduced. The loops provide
a better support for the same pile fibre volume and consequently the ball does
not sink into the field
as much. This may result in a smaller contact area between the pile fibres and
the ball, which can
reduce the friction between the ball or player's skin on the one hand, and the
playing surface on the
other hand. Less friction results in less deceleration of the ball and a lower
risk of skin abrasive
wounds when a player makes a sliding tackle. When a player slips or slides on
a playing surface
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with high frictional resistance, then locally high temperatures may develop
that can lead to friction
burns and skin abrasion.
[0011] In addition to a smaller contact area, the contact area
in the playing surface according to
the invention also has a lower roughness. A cut-fibre playing surface may have
sharp edges around
the cut cross-sections of the pile fibres, whereas the sides of the loop
crests that form the playing
field are typically much smoother. This additional smoothness contributes to a
further reduction of
the friction between the ball or player's skin on the one hand, and the
playing surface on the other
hand.
[0012] Consequent to the lower friction, it is typically not
needed to provide additional water on
the sports surface to further reduce the friction. From an environmental
perspective, this is a
significant advantage. Traditional water based fields used for field hockey,
for example, require
approximately 20,000 litres of water per hour of play for a single hockey
field.
[0013] The loops provide a significant amount of support and because the loops
can deform, the
resilience of the layer is improved. This results in increased player comfort
in comparison to cut pile
fibres and lower ball bounces as more energy is absorbed in the pile layer.
[0014] The loops further increase the rotational resistance of
the playing surface, leading to an
improved grip of the ball and player foot. This prevents a player from
accidentally slipping and falling
or becoming injured.
[0015] Further advantageous to the sports surface according to
the invention is the increased
longevity of the surface. Due to the relatively good flexibility of the loops,
pile fibre wear is reduced.
Moreover, pile fibre pull out is reduced because it requires more force to
pull out a loop than a single
cut pile fibre. In addition, the closed loops make it more difficult to damage
the pile fibres by splitting
them because there are no pile fibre ends extending to the surface that can be
damaged. This in
turn allows the fibre material to be adapted, since split resistance is no
longer paramount. It is thus
easier to tailor the fibre material to improved comfort or lower friction e.g.
by using softer materials
or coatings.
[0016] Finally, in most professional sports, consistency across
the surface is paramount to the
game. The loops are closely packed together to form a substantially continuous
playing surface.
The dense packing improves the consistency of the field. Due to the good
longevity of the field, the
consistency remains guaranteed over a longer period of time.
[0017] A close packing of the loops may help achieve the required support and
resilience of the
sports surface. In an embodiment, the pile layer has a pile density ratio of
at least 100 g/m2 per mm,
preferably at least 150 g/m2 per mm. Here the pile density ratio is defined as
the mass of the pile
layer [g/m2] per unit of height [mm] of the pile layer. The mass of the pile
layer may be determined
according to ISO 8543 and the pile height may be measured according to ISO
2549. Hence the unit
of the pile density ratio is grams per square meter per millimetre.
[0018] Alternatively, the close packing of the loops can be
defined by the number of loops per
square meter or the number of loops or filaments per square meter. In an
embodiment, at least
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40,000 loop bundles are provided per square meter, preferably at least 60,000
loop bundles per
square meter. The number of loop bundles may be measured according to the
standard ISO 1763.
[0019] In an embodiment, at least 400,000 individual loops are
provided per square meter,
preferably at least 600,000 loops per square meter. Here each loop is formed
by an individual
filament or fibre. A count of 600,000 loops is thus comparable to 1,200,000
filaments in a cut-fibre
pile layer. The number of filaments may be measured according to the standard
ISO 1763.
[0020] In an embodiment, the pile layer has a pile height
between 5 mm and 20 mm, preferably
between 8 mm and 10 mm. The pile height may be measured according to ISO 2549.
For a larger
pile height, the sports surface becomes more prone to damages as the
likelihood that part of a
player's shoe gets entangled in a loop increases. Larger loops therefore have
a higher risk of being
pulled out.
[0021] In an embodiment, the loops have an aspect ratio (H/VV)
of less than 3. The loop base is
generally determined by the manner in which the loop is formed. For a tufted
pile layer, the loop
base will be largely determined by the needle size and the bundle diameter
that is tufted. A loop, if
unconstrained will tend to have a curvature determined by the structural
properties of the fibre i.e.
the second moment of area. If the loops are packed closely together, the
adjacent loops may
support against each other, leading to narrower loops. In general, a maximum
loop width is obtained
within the pile layer at a position spaced from the top surface of the backing
layer. It is however not
excluded that other constructions may form loops having a greater width at
their base at the position
where the pile exits the backing layer.
[0022] In an embodiment, an aspect ratio may be at least 2.2,
preferably at least 2.4. For a tufted
pile layer the loop base is provided by a single opening in the backing layer.
In embodiments, the
loop base may be wider.
[0023] In an embodiment, the pile layer has a mass of at least 800 g/m2. The
mass may be
determined according to the standard ISO 8543.
[0024] In an embodiment, the backing layer has an upper surface
and a lower surface, the pile
fibres passing through the backing layer and extending along the lower surface
of the backing layer,
wherein the pile fibres at the lower surface of the backing layer have been
heated to weaken or
destructure the material. It will be understood that the pile fibres are
generally drawn down during
extrusion in order to orientate the polymer material. Heating the material to
the softening
temperature can cause the orientation to be lost and the fibre strength to be
reduced. VVhen a large
pulling force is exerted on one of the loops in the pile layer, the loop may
be pulled out, while
breaking the yarn at the weakened lower side of the backing. Consequently, the
effects of laddering,
i.e., loss of consecutive loops from the same column or row if one loop is
pulled out, and fraying,
i.e., loss and damage of pile fibres from the cut edge, may be reduced or
fully prevented.
[0025] It is believed that attempts have been made in the past
to use loop pile constructions for
sports surfaces but these have failed due to the tendency of loops to become
snagged and cause
unacceptable laddering. Cutting of the loops to provide cut-pile sports
surfaces was seen as the
only solution to this problem. In an embodiment, the present disclosure
teaches a way of
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overcoming the problem of laddering by providing a point of weakness in the
pile fibres that avoids
laddering.
[0026] In an embodiment, the pile fibres at the lower surface of
the backing layer are at least
partially melted. The pile fibres may be partially melted or fused entirely.
The term "fusing" is used
to refer to the situation where two components or fibres are fully melted
together i.e. to form an
integral component. Melting may merely cause one component to mould around the
other
component without actual bonding or fusing taking place. In this case, once
cooled, there may be
merely a mechanical bonding of the two components e.g. the pile fibres and the
woven backing
layer. Melting the pile fibres together may lead to bundles of fibres at the
lower surface of the
backing layers which have a higher pull out strength. The melted bundles of
filaments are more
difficult to pull out than a single filament but can nevertheless not easily
ladder.
[0027] In an embodiment, the sports surface further comprises a
locking layer provided at a lower
surface of the backing layer for locking the pile fibres to the backing layer
and/or mitigate laddering.
The locking layer prevents pull-out of the pile fibres from the backing layer
and may further reduce
the effects of laddering due to the enhanced pull out strength.
[0028] In an embodiment, the locking layer comprises one of the
following: a hot melt adhesive,
a powder melt adhesive, a coating layer or a laminated film. The coating layer
may for example be
a latex or polyurethane coating. In embodiments, a combination may be applied;
for example
application of both a powder melt adhesive and a laminated film.
[0029] Additional layers may be provided below the backing layer, both for
locking and other
purposes. Woven layers or needled felt layers may be provided to add strength
and durability or to
enhance shock absorption. The sports surface may thus be produced with an
integral shock pad.
[0030] In an embodiment, the pile layer further comprises a
plurality of cut loops. Such cut loops
preferably have a similar pile height or a lower pile height than the loops,
such that the playing
surface is at least partially formed by the looped pile fibres. In
embodiments, all loops are uncut. A
combination of both cut loops and uncut loops can be used to optimize the
sports performance
characteristics of the sports field. In addition, cut loops can be provided to
mitigate the effects of
"fraying", and "laddering" as cutting the loops reduces the length of
consecutive loops so that less
loops are pulled out. Alternatively, the effects of laddering and fraying may
be mitigated by cutting
the pile fibres at a lower surface of the backing layer.
[0031] In an embodiment, at least 70 wt. `3/0 of the pile layer
consists of uncut loops, preferably
wherein at least 90 wt. % of the pile layer consists of uncut loops. The term
'uncut' loops in this
context is understood to refer to them not being cut within the pile layer,
i.e., above the top surface
of the backing layer.
[0032] In an embodiment, the pile fibres comprise a polymeric material,
preferably a polyethylene
material. The polymeric material may be extruded and oriented by drawing.
Polyethylene, in
particular low density polyethylene is a preferred material due to its good
resilience and is therefore
most suited to achieve the required sports performance. Alternatively, for
example polypropylene
or polyamide material can be used to form the pile layer. As noted above, due
to the use of loops
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and the absence of cut ends that may be prone to fraying and splitting, softer
materials may be
used that have been conventionally used in artificial turf.
[0033] In an embodiment, the pile fibres forming the loops are
arranged in bundles. Preferably,
each bundle comprises 3 to 30, preferably from 6 to 12 monofilaments,
fibrillated tapes, or bundles
of slit tapes. Application of the pile in bundles is efficient from a
production standpoint and the skilled
person will understand the trade-offs between bundle size and processability.
In embodiments, the
bundles of pile fibres have a linear density between 2000 dtex and 20000 dtex,
preferably between
6000 dtex and 10000 dtex.
[0034] According to an aspect of the invention, the fibres
within the bundle have a linear density
between 500 dtex and 2000 dtex, preferably between 800 dtex and 1200 dtex. It
will be understood
that this is not comparable with carpet materials e.g. for indoor use, which
may also be formed with
a loop pile but have dtex values far below 100 dtex.
[0035] In an embodiment, the pile layer further comprises
texturized yarns. The texturized yarns
may be formed as looped pile fibres or can be cut pile fibres. The texturized
yarns may have the
same pile height or be shorter and provided to form a resilient thatch layer.
[0036] In an embodiment, the pile fibres are tufted into the
backing layer. The skilled person will
be familiar with the procedure for tufting such loops. The tufts may be
straight or may be arranged
in a zig-zag fashion. It has been found that a slight zig-zag is useful in
avoiding an overly linear
pattern of the loops, which could lead to directionality in the playing
surface. Alternatively, the pile
fibres may be integrated in the backing layer in a different way such as by
knitting, weaving, or
needling.
[0037] In an embodiment, the loops have a pull-out strength of
at least 35 N, preferably at least
50 N. The pull-out strength may be determined by the minimum withdrawal force
as defined
according to ISO norm 4919 for loops. Where the loop comprises a plurality of
fibres in a bundle,
this is the pull-out strength of the bundle. Such a strength is typically
required by sports associations
as a minimum. The sports field according to the invention can be configured to
comply with norms
set by sports associations.
[0038] In an embodiment, the pile fibres have a cross section
with an aspect ratio (wit) of not
greater than 5, preferably not greater than 4. The person skilled in the art
will understand that this
is relatively thick for conventional artificial grass blades. In the present
case however, the fibre is
no longer functioning as an upstanding blade, intending to mimic grass. The
shape instead provides
the pile fibre with structural strength in the form of a bowed arch.
[0039] In an embodiment, the pile fibres may have a
substantially circular, elliptical, oval,
lenticular, diamond or rectangular cross-sectional shape.
[0040] In another embodiment, the pile fibres may have a plurality of
elongated ribs extending
along the elongated direction of the pile fibres. Disadvantageous to a smooth
circumferential
surface of the pile fibres is a potential glaring when the light is bright.
Roughening the surface of
the pile fibres by providing elongated ribs along the pile fibres can mitigate
glare and provide a more
natural appearance.
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[0041] In an embodiment, the sports surface is suited for ball
sports, in particular for field hockey,
lawn bowls, cricket, golf, tennis or paddle. It will be understood that the
pile layer may be adjusted
to comply with the norms and requirements for a specific sports application.
It will further be
understood that the sports surface may also be used for other recreational
activities without a ball.
[0042] In an embodiment, the sports surface is suited for use without
irrigating the surface. As
explained above, conventional fields are often used in combination with water
to enhance sports
performance. The water reduces the resistance of the playing surface thereby
improving sports
performance. For the sports surface according to the invention, it has
surprisingly been found that
no water is required for good sports performance as the resistance is
naturally lower.
[0043] In an embodiment, the backing layer comprises polymeric material.
For example, the
backing layer may be made of polypropylene, which exhibits excellent stability
to outdoor
conditions, shows high creep resistance and has excellent longevity. Stability
of the backing layer
is important because temperatures on a pitch may vary between below freezing
and up to 85
degrees Celsius if exposed to direct sun without suitable cooling provisions.
Sufficient creep
resistance is especially important for sports surfaces applied on sports
fields with even a minor
slope for drainage, where static forces can otherwise lead to deformation over
time of the sports
surface. Alternatively, the backing layer may be made of another polymeric
material such as
polyethylene and preferably a high density polyethylene. A high density
polyethylene material may
also be used to manufacture a backing that exhibits excellent stability to
outdoor conditions, shows
high creep resistance and has excellent longevity. Moreover, providing both
the backing layer and
the pile fibres of a polyethylene material enhances the ability to recycle the
product at end of life.
[0044] Preferably, the backing layer is made of a polymeric
material having a higher melting
temperature than the pile fibres. In an embodiment, the backing layer
comprises a polymeric
material having a first melting temperature and the pile fibres comprise a
polymeric material having
a second melting temperature, wherein the difference between the first and
second melting
temperature is at least 2 degrees Celsius, preferably at least 3 degrees
Celsius and may be more
than 5 degrees Celsius. The different melting temperature enables the pile
fibres to be secured in
the backing layer through melting of the pile fibres without affecting the
filaments of the backing
layer.
[0045] In an embodiment, the sports surface has been heat-stabilized. For
heat stabilization the
sports surface is heated above the maximum temperature that can be expected
during play. Heat
stabilization may improve the dimensional stability of the sports surface. The
backing layer may be
a woven fabric and the heat-stabilization relaxes the strain developed in the
filaments of the backing
layer during the weaving process. It will be understood that weaving generally
takes place at
ambient temperatures at which the filaments have a given modulus. The weaving
action creates
bends and twists in the filaments, which remain once the process is completed.
If the temperature
of the backing layer is elevated, the induced strain can recover by relaxation
and straightening of
bends in the filaments. As a side-effect of the heat-stabilization, the height
of the pile layer may be
reduced by approximately 20%.
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[0046] The heat-stabilization may be performed using a variety
of different methods. In an
embodiment, heat-stabilization takes place by feeding the substrate along a
body having a heated
surface, a first surface of the backing layer being arranged to contact the
heated surface. The
heated surface may be a roller or calendar as is generally known in the art.
In another embodiment,
the heat-stabilization is performed by guiding the backing layer through an
oven or ovens without
direct contact with a heated surface. For example, a tenter frame may be used
to guide the backing
layer through the oven.
[0047] According to a second aspect of the invention and in accordance with
the advantages and
effects described herein above, use of a sports surface according to the
invention for a ball sport is
disclosed, preferably for field hockey, lawn bowls, cricket, golf, tennis or
paddle.
[0048] In an embodiment, the sports surface is used without
purposely watering the surface in
advance, to improve play. Here "purposely watering the surface in advance, to
improve play" refers
to the common practice to water hockey fields to enhance their performance. It
will be understood
that water may naturally be added to outdoor fields when it rains, or possibly
when a field is cleaned
or for cooling purposes. The sports surface according to the invention can be
used without watering
and still meet the desired performance criteria.
[0049] According to a further aspect of the invention and in accordance with
the advantages and
effects described herein above there is provided a method of manufacturing a
sports surface, the
method comprising providing a backing layer, the backing layer have an upper
surface and a lower
surface; integrating a plurality of pile fibres into the backing layer to be
upstanding as loops from
the upper surface, the loops being connected to each other at the lower
surface of the backing
layer; and forming a substantially continuous playing surface by providing a
close packing of loops.
[0050] In an embodiment, the method further comprises weakening
the pile fibres at the lower
surface of the backing layer to prevent laddering.
[0051] In an embodiment, the method further comprises at least partially
melting the pile fibres
at the lower surface of the backing layer to disrupt or reduce the molecular
orientation of the fibre
material to prevent laddering and/or prevent fibre pull-out.
[0052] In an embodiment, the method further comprises heat-
stabilizing the sports surface.
Brief Description of Drawings
[0053] Embodiments will now be described, by way of example
only, with reference to the
accompanying schematic drawings in which corresponding reference symbols
indicate
corresponding parts. In the drawings, like numerals designate like elements.
Multiple instances of
an element may each include separate letters appended to the reference number.
For example,
two instances of a particular element "20" may be labelled as "20a" and "20b".
The reference
number may be used without an appended letter (e.g. "20") to generally refer
to an unspecified
instance or to all instances of that element, while the reference number will
include an appended
letter (e.g. "202") to refer to a specific instance of the element.
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[0054] Figure 1A schematically shows a cross-sectional side view
of a sports surface according
to a first embodiment.
[0055] Figure 1B shows a detail of a looped pile fibre in the
sports surface according to Fig. 1A.
[0056] Figure 2 shows a cross-sectional view of a filament in a
pile fibre according to a first
embodiment.
[0057] Figure 3 shows a first embodiment of an apparatus that
can be used to heat-stabilize the
sports surface and/or to provide the pile fibres with an anti-laddering
treatment.
[0058] Figure 4A schematically shows a cross-sectional side view
of a hockey ball arranged on
the sports surface according to an embodiment of the invention.
[0059] Figure 4B schematically shows a cross-sectional side view of a
hockey ball arranged on
a prior art water field with cut pile fibres.
[0060] The figures are meant for illustrative purposes only, and
do not serve as restriction of the
scope or the protection as laid down by the claims.
Description of Embodiments
[0061] The following is a description of certain embodiments of
the invention, given by way of
example only and with reference to the figures.
[0062] Figure 1A schematically shows a cross-sectional side view
of a first embodiment of a
sports surface 10 comprising a backing layer 1 having a lower surface 11 and a
top surface 12, a
pile layer 2 with loop bundles 20, a locking layer 3 and a playing surface 15.
The loop bundles 20
are formed by bundles of pile fibres 27 formed as monofilaments. Each
monofilament forms an
individual loop 21, having loop sides 22, a loop crest 23 and a loop base 24.
[0063] The backing layer 1 is a woven fabric having warp tapes and weft tapes
through which
the loops 21 have been tufted. The backing layer 1 is made of polypropylene
and has a fabric weight
of approximately 250 g/m2. The backing layer 1 comprises two sub layers 13 and
14 that are stitched
together to form the primary backing layer 1. Nevertheless, it will be
understood that also a single
layer backing layer, or a backing layer made of another material may be used
in other embodiments.
The polypropylene backing layer 1 has a melting point of approximately 160
degrees Celsius.
[0064] The pile layer 2 comprises a plurality of closely packed
loop bundles 20, each formed by
ten loops 21 extending from the top surface 12 of the backing layer 1 to the
playing surface 15.
Each loop 21 has two loop sides 22a, 22b, and a loop crest 23, wherein the
loop sides 22 are
connected to each other by the loop crest 23. The loop crests 23 of all loops
21 together form the
playing surface 15 of the sports surface 10. The playing surface 15 may
support a ball or a player
during play.
[0065] At the lower surface 11 of the backing layer 1, the fibres 27 are
continuous between
consecutive loop bundles 20. The portions of fibre 27 that extends along the
lower surface 11 of
the backing layer 1 is locked to the backing layer 1 by the locking layer 3.
The locking layer 3
comprises a latex coating with a weight of approximately 1000 g/m2.
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[0066] Figure 1B shows a detail of a single loop 21 within a
loop bundle 20. The loop sides 22
each extend approximately over a pile height H from the top surface 11 of the
backing layer 1. The
loop base 24 is here defined as the point where the loop 21 intersects the top
surface 12 of the
backing layer 1. The loop 21 is widest at a distance of approximately 2/3 of
the pile height from the
loop base 24. The loop 21 has an aspect ratio (H/VV) of approximately 2.5.
PILE LAYER - EXAMPLE 1
[0067] According to a first embodiment of the pile layer 2, the
loops 21 have a height of
approximately 8 mm, measured as the distance between the top surface 11 of the
pile layer 2 and
the average height of the loop crests 23. The loops 21 are provided at a stich
rate of approximately
375 stiches per meter across a length direction of the sports surface 10 and a
gauge of
approximately 4 mm along the width direction of the sports surface. In this
way, approximately
100,000 bundles of loops are provided per square meter of sports surface 10.
[0068] Each bundle has a linear density of 8000 dtex, consisting
of 10 monofilaments of 800 dtex
each. Consequently, the sports surface 10 comprises approximately 2 million
filaments per square
meter, wherein each loop side 22 is counted as a separate filament. Hence the
loops 21 are packed
closely together to form the playing surface 15. The pile layer 2 has a total
pile mass of
approximately 2000 g/m2.
[0069] The pile height is approximately 8mm, leading to a pile
density ratio of 250 g/m2 per mm
of height. The aspect ratio (H/VV) is approximately 2.5.
PILE LAYER - EXAMPLES 2- 5
[0070] Table 1 shows the characteristics of four further
examples for the pile layer 2. Features in
the pile layer 2 that have already been described above with reference to the
first example may
also be present in examples 2-5 and will not all be discussed here again. For
example, the loop
shape and loop aspect ratio (H/VV) are approximately the same as in Example 1.
Table 1
Property Method Unit Example 2 Example 3 Example 4
Example 5
Pile height ISO 2549 mm 8 mm 8 mm 8 mm 8
mm
Stitch rate ISO 1763 /m 450 450 250 250
Gauge ISO 1763 /m 252 252 252 252
Filaments ISO 1763 # 2,3 million 2,3 million 1,3
million 1,3 million
per m2
Pile mass ISO 8543 g/m2 2200 2200 1220
1220
PILE LAYER - EXAMPLE 6
[0071] According to a second embodiment of the pile layer 2, the loops 21 have
a height of 9mm.
The loops 21 are provided at a stitch rate of approximately 450 stiches per
meter across a length
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direction of the sports surface and a gauge of approximately 4 mm along the
width direction of the
sports surface. In this way, approximately 115,000 bundles of loops are
provided per square meter
of sports surface 10.
[0072] The bundles are formed by two different types of filaments. Each bundle
has a linear
density of 8000 dtex, comprising 4 fibres of a first straight filament of 1000
dtex and 5 fibres of a
texturized filament of 800 dtex. The pile layer 2 has a total pile mass of
approximately 2400 g/m2,
leading to a pile density ratio of approximately 260 g/m2 per mm of height.
MATERIAL OF THE PILE FIBRE FILAMENTS
[0073] The pile fibres of each of examples 1-6 are made of a polyethylene
(PE) material as this
can provide the desired sports performance. The filaments may further comprise
one or more
additives preferably selected from the group comprising antioxidants, UV
stabilizers, pigments,
processing aids, acid scavengers, lubricants, antistatic agents, fillers,
nucleating agents, and
clarifying agents.
[0074] In each of the examples, approximately 90.5 wt.% of the filaments is
made of PE and the
remaining 9.5 wt.% is provided by additives. For example, 6 wt.% of pigments,
3 wt.% of calcium
carbonate and 0.5 wt.% of processing aids. It will be understood, however,
that different
compositions may be used in other embodiments.
[0075] According to a first embodiment of the PE composition, used in examples
2 and 4 of the
pile layer, the filaments of the pile fibres are made of a low density
polyethylene material formed
from monomers having four carbon atoms, i.e., butene based PE, here referred
to as a C4 grade
PE. The C4 grade PE has a melt flow index (MFI) of approximately 2 and a
density of 918 kg/m3.
The straight pile fibres of Example 6 are also of C4 grade PE.
[0076] According to a second embodiment of the PE composition, used in
examples 3 and 5 of
the pile layer, the filaments of the pile fibres are made of a low density
polyethylene material formed
from monomers having six carbon atoms, i.e., a hexene based PE, here referred
to as a C6 grade
PE. The C6 grade PE has a higher toughness and higher flexibility than the C4
grade PE. The C6
grade PE has a melt flow index (MFI) of approximately 3.5 and a density of 918
kg/m3. The
texturized filaments of Example 6 are also of this polymer grade.
[0077] According to a third embodiment of the PE composition, used in example
1, the filaments
of the pile fibres are made of a C4 grade PE and C6 grade PE blend.
Approximately 85 wt.% of the
PE blend consists of a C4 grade of PE and 15 wt.% of the PE blend consists of
a C6 grade of PE.
[0078] Typically, in a conventional sports surface with cut pile
fibres a higher grade PE is used
to increases the toughness. The pile fibres are prone to damage if the
material is soft, such as a
C4 grade PE, mainly due to the grass blades splitting from their top surface.
By providing closed
loops in the pile layer of the sports surface according to the invention,
splitting of the pile fibres is
prevented and softer 04 grade PE can be used without adverse consequences.
Having a greater
proportion of C4 grade PE in the fibre material leads to a much softer fibre
that is more comfortable
for players in use.
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CROSS SECTIONAL SHAPE OF THE FILAMENTS
[0079] The filaments may be provided in many different shapes
such as substantially circular,
oval, lenticular, diamond shaped, rectangular, or shaped as a capital letter
"C" or" D". The closed
loop protects the pile fibre from splitting as no separate blade ends are
provided and therefore the
cross-sectional shape has less need for a special shape to prevent splitting
of the pile fibres.
[0080] Figure 2 depicts the cross-sectional shape of a fibre 27
as used in the pile layer 2
according to Example 1. The cross section has a lenticular shape with a
maximum width w of
approximately 0.75 mm and a maximum thickness t of approximately 200 pm. Hence
the aspect
ratio (w/t) is approximately 3.75. The thicker filaments forming the loops
provide a good ratio
between the contact area versus the cross-sectional area of the pile fibre and
ensure that the loop
is structurally more resilient due to the higher second moment of area of the
fibre.
[0081] The surface of the fibre 27 is relatively smooth, which
reduces the friction at the contact
surface. This has several advantageous effects and in particular reduces the
risk of skin abrasions
when a player falls or slides along the playing surface 15.
[0082] The surface of the fibre 27 is provided with a plurality of
elongated ribs 25 that extend
along the elongated direction of the fibre 27. The ribs 25 along the surface
reduce the glare from
the surface in bright areas. It will be understood that the ribs 25 may be
omitted if the reduction of
glare is not required, for example for indoor use. Examples 2-6 have filaments
or fibres with a similar
lenticular shape, yet no ribs 25 have been provided.
HEAT STABILIZATION AND HEAT TREATMENT
[0083] The sports surface 10 according to each of examples 1 to 6 has been
heat stabilized
before use by guiding the sports surface 10 through an oven using a tenter
frame during application
of the latex coating. This process is well known to the skilled person for
drying of the latex material
and also leads to a reduction in the pile height from the initially tufted
condition.
[0084] In addition to heat stabilization of the overall sports
surface, the fibres 27 at the lower
surface 11 of the backing layer 1 may undergo an additional heat treatment
step to prevent
laddering.
[0085] Fig. 3 shows an exemplary embodiment of an apparatus 30 that can be
used to carry out
the heat treatment. The sports surface 10 is provided to a feed roller 31 and
guided through the
apparatus 30 using a plurality of guiding rollers 32. The sports surface 10 is
carried through the
machine at a speed between 1 and 30 m/min and guided along the heated surface
35 of a roller
34. In the case of the polypropylene backing layer described in relation to
Example 1, the melting
temperature of the PP backing layer 1 is at least 25 C above the temperature
at which the pile fibres
27 are softened. By heating to the point at which the pile fibres 27 at the
lower surface 11 of the
backing layer 1 are melted, the fibres 27 become weakened at this point and
will break prior to
laddering when subjected to a sufficient force. The weakening of the pile
fibres 27 may be sufficient
that the breaking strength of the fibre is lower than the pull out force of an
individual fibre.
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[0086] The heat treatment may be combined with the heat
stabilization or carried out separately.
The heat treatment may further be combined with the application of a locking
layer. For example, a
hot melt adhesive or powder melt may be applied to further increase the pull-
out strength. A device
33, for instance a sprinkling device, may be arranged in the apparatus 30. The
device 33 may
sprinkle hot melt adhesive powder on the lower surface 11 of the backing layer
1 before the sports
surface 10 is carried along the heated roller 34.
SPORTS PERFORMANCE
[0087] The sports surface 10 has enhanced sports performance properties in
comparison to a
prior art sports surface 80 used on water based fields. Figures 4A and 48
schematically depict a
hockey ball 7 arranged on top of the playing surface 15 of the sports surface
10 according to the
invention, and of a prior art sports surface 80, respectively. The drawings
are highly schematic and
it will be understood by the skilled person that in reality a hockey ball is
significantly larger than a
few loops or cut pile fibres.
[0088] At each of the sports surfaces 10, 80, frictional resistance occurs
between the ball 7 and
the surface from rolling and when skidding. Both actions are interrelated and
the transition from
skidding to rolling is a key property in many games. The 'rolling resistance'
is considerably less than
the resistance to skidding, but depending on the velocity and spin applied to
the ball the transition
between the two can differ. In this context, skidding is used to refer to the
movement of a ball, which
moves along the surface without rotation. Reverse rotation may also be
present.
[0089] Roll resistance is defined as the force acting at the
point of contact between the ball and
surface whose direction is opposite to that of the motion and thus causes
deceleration of the ball
as it moves across the surface. Friction between the ball and the surface is
responsible for variations
in speed, direction and rate of rotation. The type of surface can dramatically
influence friction.
Differences in pile height, yarn type, fibre density and stiffness (amongst
others) all contribute to
the ball's behaviour. If the friction between a ball and the surface is too
large, then the ball will not
roll the required distance.
[0090] A ball will continue to skid across the surface until its
linear velocity parallel to the playing
surface 15 has been reduced and the angular velocity of the ball 7 has
increased to the point where
rolling occurs. For smooth rolling there can be no skidding between the ball
and surface, therefore,
a balance between the forward velocity and rate of rotation at the point of
contact with the surface
is required for pure rolling. The transition between the Rolling friction (RF)
and Skidding friction (SF)
is impacted by a range of variables of the sports surface 15, specifically by
the pile layer 2.
[0091] Advantageous to the use of the loops 21 in the pile layer
2 is that they naturally have a
lower skidding friction than the conventional cut pile sports surface 80. The
ball 7 is supported by
the loop crests 23 and the loop crests 23 are formed by the sides of the
filament forming the loop
21. Therefore the contact area between the ball 7 and the playing surface 15
is relatively smooth.
[0092] In contrast, the cut pile fibres 81 in the pile layer of
the prior art surface 80 have sharp
edges, providing a contact area which is not smooth. In addition, the hockey
ball 7 does not sink as
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deep within the pile layer 2 as the loops provide more support than the cut
pile fibres for the same
pile fibre volume. Consequently, the contact area of the ball 7 with the pile
fibres is reduced. Hence
the roll and skidding resistance provided at the playing surface 15 is
significantly larger in the prior
art system for the same pile fibre volume.
[0093] In prior art systems, for example for field hockey surfaces, water
is applied to reduce the
friction at the playing surface, especially skidding friction. By providing
the loops 21, the skidding
friction is already naturally lower, providing good sports performance also
when no water is applied.
The ball roll distance is approximately a factor two larger in the sports
surface according to the
invention in comparison to a dry sports surface of the fields currently used
as water based fields.
[0094] Table 2 provides an overview of the performance characteristics of the
sports surface
according to examples 1-6 in comparison to a reference water based sports
surface with cut pile
fibres. For the reference surface, the pile height is 13 mm, provided at a
stich rate of 360 stitches
per m, a gauge of 210 per m, and approximately 75,000 tufts per surface. Each
tuft comprising
8000 dtex bundle with 10 texturized filaments of 800 dtex each.
Table 2
Property Method Unit Reference Example
1 2 3 4 5
6
Ball roll distance (dry) EN 12235 mm 14 29 >25 >26
22 >23 22
(1.0 m)
Rot. resistance (dry) EN 15301-1 Nm 35-38 38-40 41-
44 46-48 33-35 39-42 41-43
Rot. resistance (wet) EN 15301-1 Nm 37 38 43 44 34
40 41
Ball rebound (dry)* EN 12235 mm 500 440 440 390
540 480 420
[0095] Besides the rolling and skidding resistance, ball bounce
characteristics are important for
sports performance of a field. The loops 21 absorb more energy than cut-pile
fibres, thereby
resulting in a lower ball rebound. It will be understood that dependent on the
sports application this
is preferable. For example for field hockey, a lower ball bounce is
advantageous. For a similar pile
fibre volume, the ball rebound height is up to 15% lower for the dry sports
surface according to the
invention in comparison to the prior art system with cut pile fibres. It is to
be noted that the ball
rebound value is based on a solid concrete undersurface for comparison
purposes only. In actual
use, the sports surface 10 would be installed on a shock pad or provided with
additional cushioning
to achieve the required specifications.
[0096] Further important for sports performance is the
rotational resistance experienced by the
ball 7. The rotational resistance has an effect on the grip and is
approximately 5 % higher on the
dry sports surface according to the invention in comparison to a wetted prior
art system with cut pile
fibres.
[0097] Finally, in ball sports consistency across the surface is
paramount to the game. The
playing surface 15 comprising loop crests 23 is very consistent due to the
high density of the loops.
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Moreover since the pull-out strength very good, the consistence of the sports
surface remains good
for a long time. Each of examples 1-5 has a pull-out strength of at least 50
N. Example 6 has a pull-
out strength of approximately 45 N.
[0098] Additionally, as a consequence of the present loop based system, extra
fibre mass can
be used without risking the fibre integrity of the system. In prior art cut-
pile systems, the bundle size
was limited by the ability to successfully lock in all of the fibres within a
bundle. A common failure
mode was the loss of individual filaments which compromised the strength of
the bundle. Were a
less well held fibre to be pulled out from the middle of a bundle, the
remaining fibres would become
loose and soon also pull out. In the case of a loop-based system, even if a
single fibre is partially
pulled, it is not removed and does not therefore affect the remaining fibres
in the bundle.
[0099] Although the sports surface 10 according to the above described
examples has been
designed for field hockey, the skilled person will understand that the field
may also be suited for use
in a variety of different ball sports, for example lawn bowls, cricket, golf,
tennis or paddle, or for
other recreational purposes.
[00100] The present invention may be embodied in other specific forms without
departing from its
spirit or essential characteristics. The described embodiments are to be
considered in all respects
only as illustrative and not restrictive. The scope of the invention is,
therefore, indicated by the
appended claims rather than by the foregoing description. It will be apparent
to the person skilled
in the art that alternative and equivalent embodiments of the invention can be
conceived and
reduced to practice. All changes which come within the meaning and range of
equivalency of the
claims are to be embraced within their scope.
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