(57) Method for the production of yarn for fields of articicial grass by extruding polymer
granulate to bands or to a film, cutting the film into bands and stretching the bands,
in which the bands having a width of 1.5-4 mm are stretched at a stretching ratio
of 1 to 2-3 to bands having a width of 0.75-3 mm whilst the thickness is 50-80% of
the thickness of the extruded bandand then 5-10 bands are twisted into the yarn
[0001] The invention relates to a method for producing yarn for fields of artificial grass
by extruding polymer granulate to bands or to a film, cutting the film to bands and
stretching the bands. The invention also relates to the grass fields produced with
this yarn.
[0002] From "De Tex" 27 (1968) number 12, pages 638-643 it is known from an article "Staplefibres
and continuous yarns of fibrillated polypropylene film" of Dr. G. Schuur to produce
fibred yarns from polypropylene by extruding the granulate to a film, stretching the
film at a stretching ratio of 1:6 to 1:12 especially at 1:10, cutting the stretched
film to bands and modifying these bands to fibres. It also is possible to cut the
film to bands before stretching, after which the bands are stretched. Besides the
general use of such fibres for cloths, carpets and technical backings, it also is
mentioned that it can be used for "artificial lawn".
[0003] From "The Textile Manufacturer", July 1971, pages 263-268 "Fibrillated polypropylene
fibre" W.H. Badrian and J.H.L. Choufoer it is known that it is difficult to directly
extrude polypropylene fibres with additions from a spinneret, if this polypropylene
comprises a relatively high amount of additives such as pigments and fillers. For
this reason it is suggested to extrude the granulate to a film, to stretch this film
and to cut bands from the stretched film. The value as such mentioned for the stretching
ration is 1:8. The produced fibres have a low dtex-value of 6 and 42 denier, such
as indicated in the table on page 266. The use of these fibres for articicial grass
has not been mentioned in this article.
[0004] In practice one produces yarn for fields of artificial grass, as disclosed in European
patent 0 263 566 by extruding polymer granulates such as polypropylene, to a film
having a width of about 750 mm and a thickness of about 100 µm. This film is cut to
bands of a width of about 30 mm, which bands are stretched to a stretch ratio of 1:4
or more, to a width of about 15 mm and a thickness of about 50 µm. In order to twist
these bands, they are provided with cuts, so that a reticulated structure is produced,
which structure facilitates twisting. When fields of artificial grass are made of
said yarn, a disadvantage of a field of such artificial grass is that an after-fibrillation
is caused, as a result of which the tufted yarn wears out. The inventor carried out
an intensive research in order to improve the fields of artificial grass, during which
research experiments have been directed to improve the resistence to wearing out.
From these experiments it appeared that at a relatively high stretching ratio the
strength of the fibers is high, but the resistence against wearing can be improved
at a lower value for the stretching ratio. For this reason a new process has now been
developed, in which one returned to a process that was no longer used in the production
of yarns for fields or artificial grass. This process according to the invention as
disclosed in the preamble is characterized by the fact that the bands having a width
of 1.5-4 mm are stretched at a stretching ratio of 1:2-3, to bands having a width
of 0.75-3 mm while the thickness is 50-80% of the thickness of the extruded band,
and then 5-10 bands are twisted to yarn. Preferably the bands have after extrusion
a width of 2-3 mm and after stetching, during which the thickness of the band is 50-70%
of the original thickness, a width of 1-2 mm. Besides this it is preferred that the
bands have a yarn number of 900-1350 dtex and that beside polypropylene a blockcopolymer
is used as sold by Solvay, Belgium. According to the process of the invention, the
cutting of the bands from the film and the stretching can be reversed, so that it
is possible to stretch bands as well as to stretch the film.
[0005] It might be true that it is known from US patent 4,253,299 to produce fibres from
films by cutting the films and to stretch the fibres at a stretching ratio of about
3.0, but then much lighter fibres are produced of about 132 denier per fibre, which
fibres are entangled in a jet. On basis of such fibres no useful fields of artificial
grass can be produced.
[0006] On basis of the results of experiments as carried out, it is clear that the fields
of artificial grass with a tufted yarn according to the invention is less subject
to after fibrillation, which can be proved by a wheel experiment, with which a clearly
improved result can be obtained after visual inspection. From the Taber test, of which
the results have been indicated in the table given here below, it appears that the
fibre loss has been strongly decreased of 70‰ , for fields of artificial grass on
basis of yarns as used for fields as disclosed in European patent 0,263,566, to 20‰
for fields of artificial grass, produced on basis of yarns according to the invention.
TABLE
| material for artificial grass |
method as used |
dtex |
stretching ratio |
wearing |
| polypropylene |
bands of 15 mm with cuts *) |
6600 |
1:4 |
70‰ |
| polypropylene + silicon oil |
bands of 15 mm with cuts *) |
8000 |
1:4 |
50‰ |
| polypropylene |
according to the invention |
6600/6 bands |
1:2.5 |
40‰ |
| polypropylene + silicon oil |
according to the invention |
8000/7 bands |
1:2.5 |
20‰ |
| *) 4 cuts per 10 mm width. |
[0007] From this table it also appears that the application of a silicon derivative such
as silicon oil on the field of artificial grass, to lower the coefficient of friction,
decreases the wearing.
[0008] Instead of the production of a film that is cut into bands of 2-3 mm it also is possible
to produce directly the bands with the indicated width from the spinneret. The melt
then is pressed through a spinneret having openings which are dimensioned such that
the bands can be obtained directly after which they are cooled, this contrary to the
expectation as given in the article of W.A. Badrian as above mentioned, because now
one produces according to the invention heavier fibres than aimed according to that
article.
[0009] The invention is explained in more detail with reference to the following examples.
Example I
[0010] An extruder is fed with propylene having a melting index of 2. From this a film is
produced having a width of 750 mm and a thickness of 100 µm. Said film is cut into
bands being 2-3 mm width, while the thickness is maintained. Stretching takes place
at a temperature of about 130 °C at a stretching ratio of 1:2.5. It also is possible
to stretch at first the film and to cut bands from the stretched film. A hot-blast
furnace is used for the stretching operation. After relaxation, cooling and shrinking,
bands are obtained, having a width of 1.5 mm and a thickness of 60 µm. Eight of these
bands are twisted in a yarn which can be processed into a carpet for a field of artificial
grass by means of a tufting operation.
Example II
[0011] The method of example I was repeated whereby instead of polypropylene a blockcopolymer
was used consisting of polypropylene and polyethylene marketed by Solvay, Belgium.
1. Method for the production of yarn for fields of artificial grass by extruding polymer
granulate to bands or to a film, cutting the film into bands and stretching the bands,
characterized in that the bands having a width of 1.5-4 mm are stretched at a stretching
ratio of 1 to 2-3 to bands having a width of 0.75-3 mm whilst the thickness is 50-80%
of the thickness of the extruded band and then 5-10 bands are twisted into the yarn.
2. Method according to claim 1, characterized in that after extrusion the bands have
a width of 2-3 mm, and after stretching, during which the thickness of the band becomes
50-70% of the original thickness, the width of the bands is 1-2 mm.
3. Method according to claims 1-2, characterized in that as the polymer granulate
a propylene comprising blockcopolymer is used.
4. Method according to claims 1-3, characterized in that the bands as used have a
yarn number of 900-1350 dtex.
5. Field of artificial grass from yarn material, characterized in that the yarn material
as used is produced according to a method as disclosed in claims 1-4.
6. Field of artificial grass according to claim 5 characterized in that on the yarn
material a substance has been applied in order to decrease the coefficient of friction
such as a silicon derivative.
