Woven fabric from splittable ribbons

A fabric, useful as a primary carpet backing, woven in both the warp and weft directions from filmy elements in the form of longitudinally-oriented, splittable ribbons formed from a blend of a major amount of polyester and a minor amount of a polyolefin. The ribbons split longitudinally when punctured by a tufting needle, thus providing for a more secure grip on the tufted carpet yarn than that given by conventional polyester backings. The use of polyester as a principal component overcomes certain drawbacks of polypropylene backings. Alternative processes for making these fabrics, each involving a heat-treating step at a temperature of at least 150.degree. F. (66.degree. C.) for a sufficient period of time to render the ribbons splittable, are also disclosed.

BACKGROUND OF THE INVENTION 
This invention involves a low cost, high value woven fabric useful as a 
primary backing for tufted pile carpets. More specifically, the invention 
pertains to a woven fabric composed in both the warp and the weft 
directions of filmy elements in the form of longitudinally-oriented 
splittable ribbons formed from a blend of a major amount of polyester and 
a minor amount of a polyolefin, said elements having been heat-treated at 
a temperature of at least 150.degree. F. (66.degree. C.) for a sufficient 
time to render the elements splittable. Preferably the polyester is 
polyethylene terephthalate and the polyolefin is polyethylene. An 
advantage of the invention is that inexpensive polyester such as that 
recoverable from waste bottles, fibers and films is abundantly available 
and provides a satisfactory source of raw material. 
Woven jute carpet backing has been replaced to a large extent in recent 
years by products made from synthetic materials. Carpet backings woven 
from ribbons of polypropylene, such as those disclosed in Rhodes U.S. Pat. 
No. 3,110,905, are the current industry standard, partly because they are 
strong yet inexpensive, and partly because they split longitudinally when 
penetrated by a carpet tufting needle. The ability to split longitudinally 
is highly desirable, because split ribbons close and grip the yarn 
securely after the needle retracts, keeping the yarn tufts firmly in 
position. The splitting prevents the ribbons from being severed 
transversely or from being severely weakened in the longitudinal direction 
by the penetration and removal of the tufting needles. While such products 
have been successful to a large extent, polypropylene has not altogether 
been satisfactory as the material forming the ribbons as it has the 
disadvantage of not being dyeable by standard carpet dyes, thus making the 
backing more visible and the carpet less attractive. In addition, 
polypropylene has a tendency to shrink at temperatures used for forming 
automotive carpets to desired contours and at temperatures used in bonding 
carpet tiles. 
Polyester backings, readily dyeable with dispersed dyes and thermally 
stable at higher temperatures, largely overcome these particular 
deficiencies, and indeed spunbonded polyester backings are currently used 
for both automotive carpets and carpet tiles. These backings, however, are 
less satisfactory than those of polypropylene because they often do not 
grip the tufts with adequate force, and they are quite expensive. The 
Rhodes patent referred to above and Dionne U.S. Pat. No. 3,317,366 each 
describe all-polyester backings, but both tend to have the same tufting 
deficiencies as spunbonded backings. Rhodes discloses fabrics woven from 
ribbons in both directions, but the ribbons are not said to be splittable. 
The Dionne backing is made from flat warp ribbons and multifilament weft 
yarns. No mention is made of the splittable or nonsplittable nature of the 
warp ribbons. Without the advantages created by splittable ribbons, these 
polyester backings will not perform as well as polypropylene backings in 
firmly securing the fiber tufts in place. 
Various backings which are more splittable have been suggested in an 
attempt to overcome the disadvantages of polypropylene while maintaining 
its positive features. Stitch bonded backings, made by stitching layers of 
splittable film or by stitching layers of a splittable film and a 
nonwoven, are disclosed in Ploch et al., U.S. Pat. No. 3,769,815 and 
Kumar, U.S. Statutory Invention Registration H90 respectively. However, 
these materials have high cost and poor strength in the fill or cross 
machine direction. A woven backing made from a blend of 80% to 65% 
polyamide with 20 to 35% polyester is shown in Ramsauer et al., U.S. Pat. 
No. 4,010,303. This is primarily a polyamide backing and has several 
drawbacks: (1) it is very susceptible to moisture; and (2) the ribbons, if 
not splittable (particularly those in the weft direction), rupture 
transversely when impacted by a tufting needle. This makes for an 
expensive and deficient backing.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention overcomes the problems of the patents discussed 
above. In one embodiment, a fabric is woven in both the warp and weft 
directions from filmy elements in the form of longitudinally-oriented, 
splittable ribbons. The ribbons are slit from a film made by extruding and 
drawing a blend composed of a major amount of polyester with a minor 
amount of a polyolefin. splittability is achieved both by the use of the 
polyolefin and by heat-treating, either singly or in combination, the 
extruded film, the slit ribbons, or the woven fabric. 
As used herein the term splittability refers to the tendency of the film or 
the ribbons to split longitudinally when penetrated by an object such as a 
tufting needle. Without this tendency the film or ribbon would be left 
with a hole about the size of the object penetrating it or larger. When 
woven in a flat weave to make a fabric useful as a carpet backing, 
non-splittable ribbons rupture on tufting and are incapable of holding 
tufts adequately. On the other hand, backings made from splittable ribbons 
retain their integrity and hold tufts well. The ribbons tear 
longitudinally but do not tend to rupture transversely. The weave keeps 
the ribbons in place. 
The process of the invention involves the preparation of a woven fabric by 
the steps of (1) forming a film by extruding a blend comprised of a major 
amount of polyester and a minor amount of a polyolefin; (2) drawing the 
film to give it a longitudinal orientation; (3) slitting the film to form 
ribbons; and (4) weaving the fabric using the ribbons in both the warp and 
fill directions. As noted above, there is also a heat-treating step which 
is necessary for achieving acceptable splittability. This step may be 
performed either by heating the film, the ribbons, the fabric, or some 
combination of the three to a temperature of at least 150.degree. F. 
(66.degree. C.) for a period of time sufficient to impart splittability. 
More specifically, the film is made by extruding and drawing, preferably 
uniaxially, a blend of polyester, such as polyethylene terephthalate, and 
a polyolefin, preferably low density polyethylene, according to standard 
techniques in ratios of about 90:10 to about 75:25. The film may be drawn 
to thicknesses as low as about 1.8 to 2 mils (0.045 mm to 0.05 mm). Draw 
temperatures ranging from about 90.degree. C. to about 150.degree. C. may 
be used, although in general lower draw temperatures result in improved 
splittability. The higher the amount of polyolefin, the greater the 
splittability of the film. 
The addition of polyolefin is essential to making the film and the ribbons 
more splittable, as is proper heat treatment. This heat-treating may be 
effected for about one minute or more at temperatures ranging from 
150.degree. F. (66.degree. C.) to 350.degree. F. (177.degree. C.). The 
choice of heat-treating temperature within this range is not critical, 
provided that it is above the melting point of the polyolefin used and 
below the melting point of the film. The proper duration for heat-treating 
at any given temperature can be determined experimentally by puncturing 
the film or the ribbons with a tufting needle and noting the degree of 
longitudinal splitting. 
A preferred film for making a suitable backing has the following 
properties: 
______________________________________ 
Thickness 2.5 to 3.0 mils (0.06 mm to 0.075 mm) 
Tensile Strength 
&gt;50 lbs (22.7 kg) (using test method 
as per ASTM D1682-75 except that 
test is run using rate of extension 
of 40%/minute until breaking, 
rather than measuring force needed 
to break within 20 .+-. 3 seconds) 
Elongation &gt;20% 
Shrinkage 0% at 300.degree. F. (149.degree. C.) 
&lt;0.2% at 350.degree. F. (177.degree. C.) 
&lt;0.5% at 350.degree. F. (177.degree. C.) to 400.degree. F. 
(204.degree. C.) 
______________________________________ 
This film is slit in the direction of preferential orientation and then 
woven into a backing with a flat weave. Preferred constructions depend on 
the tufter gauge and on the needle size. In a typical construction, the 
weft ribbon is about twice the width of the warp because the tufting 
needle tips are larger in this dimension. Warp ribbons may be about 0.05 
inch (1.3 mm) in width, while the typical weft width is about 0.10 inch 
(2.5 mm). The fabric may be lubricated with silicone oil for smoother 
entry of the tufting needles. When nylon bulked continuous filament carpet 
yarn is tufted into the woven backing, there is no transverse rupturing of 
the ribbons, and the tufts are gripped as readily as they are in a 
standard polypropylene backing. 
In contrast with polypropylene backings, fabrics of the present invention 
tend to be thermally stable at temperatures of 300.degree. F. (149.degree. 
C.) to 400.degree. F. (204.degree. C.). At 300.degree. F. (149.degree. C.) 
where polypropylene backings shrink, and at 350.degree. F. (177.degree. 
C.) where they melt, the fabrics of this invention are generally 
unaffected. The fabrics can thus be used in temperature sensitive 
applications such as molded automotive carpets and carpet tiles. 
While primarily useful as a primary carpet backing, the fabrics of this 
invention can also be used in geotextile, roofing and other applications. 
A further advantage of the invention is that the polyester may be scrap 
recovered from bottles or other waste forms of products, thus greatly 
reducing the cost of raw materials. 
EXAMPLES 
In the Examples discussed below, parts and percentages are by weight unless 
otherwise specified. 
Several 12 mil undrawn films are extruded from a blend of recovered 
polyethylene terephthalate bottle waste and polyethylene resin at 10, 15 
and 20% levels. These films are drawn uniaxially 4X to produce a 
longitudinally oriented film with a thickness of about 3 mils. 
Polyethylene resins used are Du Pont "Alathon" 20 and "Alathon" 2020 with 
melt flow indices of 1.9 and 1.1 respectively. 
The drawn films are next slit and woven by conventional techniques into 
fabrics at 15 X 6.5 picks (ribbons per inch). The fabrics are wet-coated 
with a typical silicone finish and tufted on a table-top tufter. During 
tufting the ribbons rupture transversely without splitting, making it 
impossible to form a carpet. 
The same backings are then heat-treated at 300.degree. F. (149.degree. C.) 
for one minute. When tufted on a table-top tufter, the ribbons split 
longitudinally and tuft problem-free.