Reinforced primary backing for carpet

A reinforced polypropylene primary backing for carpets and carpet tiles in which the polypropylene warp yarns have another synthetic yarn woven into the warp in order to increase the strength in the warp direction. The reinforcing yarn is a synthetic yarn which is non-stretchable or at least less stretchable than polypropylene when exposed to the temperatures developed during a hot melt resin process step during the manufacturing of tufted carpet.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a new and novel reinforced primary backing 
made primarily of woven polypropylene where the backing is reinforced in 
the warp direction by weaving yarns other than polypropylene into the 
backing at predetermined intervals across the width. The other yarn in 
order to impart the requisite improved dimensional stability to the 
backing will either be non-stretchable or less stretchable than 
polypropylene. 
2. Description of the Prior Art 
In recent years, tufted pile fabrics utilizing primary and secondary 
backings made from synthetic plastic materials have been developed for use 
indoors and outdoors. These carpets have utilized synthetic plastic 
primary and secondary backings in order to provide stability to the carpet 
structure and to eliminate the problems encountered previously by carpets 
which have been made from natural fibers. Carpets made from natural fibers 
are subject to shrinking and rotting in abnormal weather conditions and 
when liquids are spilled thereon. Additionally, such carpets are subject 
to excessive staining and require frequent removal and cleaning. 
In U.S. Pat. No. 3,110,905 issued Nov. 19, 1963 to Rhodes and U.S. Pat. No. 
3,336,178 issued Aug. 15, 1976 to Levitch, and both assigned to the same 
assignee as the instant application, namely, Burlington Industries, Inc., 
there are disclosed tufted pile fabrics utilizing synthetic plastic 
backings and pile yarn also made from synthetic plastic or man-made 
fibers. While the tufted pile fabric disclosed in these two patents have 
been commercially successful for installations wherein the floor covering 
is subjected to rotting conditions, moisture conditions from rain or 
spillage of liquids, they have not been completely satisfactory when used 
in situations wherein the carpeting is to be substantially permanently 
installed by adhesively securing the same to a floor structure, 
particularly when the primary and secondary backings are bonded together 
with a hot melt adhesive. With the advent of the use of hot melt adhesives 
and the application of such technology to the disclosures in these two 
patents and particularly to the disclosure in Levitch, the resulting 
tufted pile fabric provided greatly improved adhesion between the 
synthetic primary and secondary backings, effectively preventing 
separation of the primary and the carpet face from the secondary, when the 
secondary is bonded to a floor structure. Additionally, the hot melt 
adhesive greatly improves pile bind, effectively preventing removal of 
carpet tufts from the carpet face by pulling or snagging. 
U.S. Pat. No. 3,110,905 to Rhodes discloses the basic woven synthetic 
primary carpet backing. In essence, such a primary backing is formed of a 
flat weave of synthetic yarns in which every point on the primary backing 
is of substantially uniform thickness. While, Rhodes teaches the use of 
any synthetic yarn capable of being spun, extruded, or shaped into a 
flattened or rectangular shape, polypropylene and polyethylene are 
disclosed as most suitable. Other suitable synthetic yarns which are 
listed in the Rhodes patent are acrylic, modacrylic, polyester, nylon, 
rayon, acetate, triacetate, cellulosic, vinyl, vinylidene, chloride and 
polyvinyl chloride. However, in actuality, the most commonly used woven 
synthetic primary backings are made entirely of polypropylene yarns 
employed for both the warp and weft. 
As discussed hereinabove, polypropylene primary backings are used in 
various hot melt processes. During the course of applying hot melt resins 
to carpets having polypropylene primary backings the heat from the hot 
resin renders the polypropylene primary backing susceptible to stretchings 
in the machine direction, i.e., length direction, during subsequent 
process steps thereby losing a portion of its dimensional stability. 
The stretching imparts instability to the carpet product particulary when 
the carpet is cut and sold as carpet tiles. This instability, in turn, 
leads to excess shrinkage, cupping and domeing of the carpet or carpet 
tiles. 
While there have been various attempts to improve the dimensional stability 
of backings, e.g., U.S. Pat. Nos. 4,296,159, 4,242,394, 4,123,577 and 
4,131,704, none of these appear to have efficiently and economically 
solved the stretching of polypropylene backings caused by a hot melt resin 
application. 
Therefore, it is the object of the present invention to overcome the 
stretching problem and the resultant decrease in dimensional stability 
discussed hereinabove. 
SUMMARY OF THE INVENTION 
Even though the Rhodes and Levitch patent, U.S. Pat. Nos. 3,110,903 and 
3,336,178, respectively, were assigned to the instant assignee, Burlington 
Industries, Inc., it has heretofore been impossible to prevent the 
stretching problem caused by the application of hot melt resin to woven 
polypropylene carpet primary backings. Now, however, it has been 
discovered that by adding to the polypropylene warp yarns certain other 
synthetic yarns, the primary backing's susceptibility to stretching is 
significantly reduced. In fact, the dimensional stability of a primary 
backing of the present invention is such that problems associated with and 
caused by such stretching are virtually eliminated. 
The reinforced primary backing of the present invention comprises a woven 
polypropylene backing wherein synthetic yarns which are non-stretchable or 
less stretchable than the polypropylene yarns, at the temperatures reached 
by the hot melt resin application, are woven into the backing as warp 
yarns together with the polypropylene warp yarns. The synthetic yarns 
which are preferred for purposes of reinforcement are nylon, polyester and 
fiberglass. In addition, the reinforcement yarns should have the following 
physical characteristics: 
(1) Continuous filament, non crimped; 
(2) about 500 denier or greater, or in the case of fiberglass the denier 
equivalent; 
(3) high tenacity of about 7.5 grams per denier or greater; and 
(4) low elongation with the elongation at the break point being no more 
than about 25%. 
The increase in strength of the reinforced primary backing will depend on 
the type of reinforcing yarn employed and the amount of such yarn woven 
into the backing, but the strength should be increased by at least about 
20% to be effective. The improvement in the strength of the final carpet 
product will vary considerably depending upon the laminate used with the 
backing. However, with a thermoplastic laminate system the dimensional 
stability of the final carpet product should be improved by at least about 
40%.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE INVENTION 
Referring to the drawings, FIG. 1 is a bottom view of a woven primary 
polypropylene backing where the warp and weft yarns are interwoven at one 
to one weave. 
The primary backing 20 comprises a series of polypropylene warp yarns 22-36 
which are interwoven in a one to one weave with a series of polypropylene 
weft yarns 38-68. The relatively even thickness and width of the 
polypropylene warp and weft yarns results in a substantially uniform woven 
backing material having a thickness equivalent to yarn strands at every 
point in the fabric. It is, however, understood that the present invention 
is applicable with any synthetic woven backing material and that the 
thickness and width of the warp and weft yarns of the backing have no 
effect on the present invention. Therefore, the present invention can be 
employed using warp and weft yarns having any range of dimensions and 
weaving ratios. 
Moreover, the present invention is suitable for use with any synthetic 
yarns. 
FIG. 2 illustrates a reinforced backing of the present invention wherein 
synthetic yarns less susceptible to stretching deformation than 
polypropylene yarn in a subsequent hot melt resin application are added as 
reinforcement to the polypropylene warp yarns. 
The reinforced primary backing 70 has polypropylene weft yarns 72-102 and 
polypropylene warp yarns 104-130 woven at a one to one weave. Woven as 
warp yarns at predetermined intervals are a series of synthetic yarn less 
stretchable than polypropylene when subject to the heat imparted to the 
yarns from a hot melt resin application. These warp yarns 132, 134 and 136 
can be any synthetic yarn which is non-stretchable or less stetchable than 
the polypropylene yarns under the conditions discussed hereinabove and are 
preferably nylon, polyester and fiber glass. 
In another embodiment, the reinforcing yarns simply replace a predetermined 
number of the polypropylene warp yarns and are made an integral part of 
the one-to-one weave (not shown). 
Moreover, the reinforcing yarn in order to function effectively should have 
the following physical properties. The yarn is preferably a noncrimped 
continuous filament having a denier preferable to at least about 500, and 
in the case of fiber glass, the denier equivalent. The yarn is of high 
tenacity with a preferred tenacity of at least about 7.5 grams per denier. 
Finally, it should have a low elongation with preferably an elongation at 
break point of no more than about 25%. 
The reinforced primary backing of the present inventor, in order to 
function effectively, should have an increased strength in the warp 
direction of at least about 20% greater than that of a normal primary 
backing consisting of only polypropylene warp and weft yarns. The strength 
in the warp direction is a function of several factors including, inter 
alia, the synthetic yarn selected as the reinforcing material, the 
physical properties and dimensions of the reinforcing yarn as woven into 
the backing, and the spacing of the reinforcing yarns as they are woven 
into the backing. These various factors are dependent upon the specific 
requirements of the particular carpet or carpet tile being manufactured. 
Once these factors are analyzed the appropriate reinforcing yarn can be 
selected and woven into the polypropylene backing at predetermined 
intervals.