Description of the Prior Art In the manufacture of a tufted pile surface structure each of a plurality of pile yarns is drawn by a tufting needle through a backing to form face fiber elements and backstitch elements. The face fiber elements lie adjacent to the upper face of the backing while the backstitch elements are disposed along the lower face of the backing. Presently, the backstitch elements are secured by a thermoset or thermoplastic binder placed on the lower face of the backing. In actuality, only a small portion of the binder material serves to hold the backstitch elements in place, while a large portion of the binder material is wasted. Using very large quantities of binder to achieve deeper penetration of the binder through the backing to improve pull-out or unraveling resistance increases binder wastage, stiffens the carpet, and increases carpet weight.

Accordingly, it is believed advantageous to provide . a method of manufacture of a tufted pile surface structure that concentrates binder material on, through and in the vicinity of the backstitch elements to produce a lighter and more flexible carpet structure. Such a structure will also allow the direct deployment"hook- loop"attachment members on the back of the carpet.

SUMMARY OF THE INVENTION The present invention is directed to a pile surface structure and a process for manufacturing the same. Each of a plurality of pile yarns is tufted by a separate tufting needle through a plurality of needle insertion points in the backing to form face fiber elements that lie adjacent to the upper face of the backing and backstitch elements that overlay the lower face of the backing. The insertion points produced by the tufting needles form a pattern of parallel lines that extend longitudinally and transversely along the back face of the backing.

After tufting, a liquid binder material is applied to the backstitch elements. The binder material soaks into and through and collects in the vicinity of the backstitch elements. The pile surface structure is heat- treated to activate the binder material to hold the backstitch elements to the backing. Those portions of the lower face of the backing not overlaid by the backstitch elements are left substantially free of binder.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawings, which form a part of this application and in which: Figure 1 is a diagrammatic illustration of a tufting system for producing a tufted pile surface structure also in accordance with the present invention; Figure 2A is a stylized perspective view taken along view lines A-A of Figure 1 showing a pile surface structure in accordance with the present invention as produced within the tufting system of Figure 1 and prior to heat treatment, while Figure 2B is a stylized perspective view taken along view lines B-B of Figure 1 showing the pile surface structure in accordance with the present invention as produced at the output of the heat treating apparatus.

DESCRIPTION OF PREFERRED EMBODIMENT Throughout the following detailed description similar reference numerals refer to similar elements in all figures of the drawings.

Figure 1 is a diagrammatic illustration of an overall system 10 for producing and finishing a tufted pile surface structure in accordance with the present invention. The system 10 includes a conventional tufting apparatus generally indicated by the reference character 12 followed by a liquid binder dispenser 14. Downstream of the dispenser 14 is a heat finishing apparatus generally indicated by the reference character 16. The tufting apparatus 12, the dispenser 14 and/or the heat finishing apparatus 16 may be physically disposed in the same housing, if desired. Downstream of the heat finishing apparatus 14 is a compression roller 18. The temperature of the roller 16 is typically kept at room temperature.

The tufting apparatus 12 produces a conventional tufted pile surface structure generally indicated in Figure 2A by the reference 24. A liquid binder material is applied by the dispenser 14 to produce a tufted pile surface structure 28 in accordance with the present invention. The tufted pile surface structure 28 having the binder thereon is heat-treated in the finishing apparatus 16. The finished tufted pile surface structure in accordance with the present invention is generally indicated in Figure 2B by the reference character 32.

As shown in Figure 1 and 2A a primary backing P, having an upper face U and a lower face L, is dispensed from a roll 36 and is conveyed along a generally planar path of travel T through the tufting apparatus 12. The direction of travel of the primary backing P through the apparatus 12 is termed the "longitudinal"or the"machine"direction. The direction perpendicular to the longitudinal direction is termed the "transverse"direction. The primary backing P is conveyed in the longitudinal direction through the tufting apparatus 12 with its lower face L presented upwardly.

Within the tufting apparatus 12 a plurality of tufting needles N is carried by a movable needle bar M.

Each tufting needle N is supplied with a pile yarn Y dispensed from a creel (not shown). Each needle N is reciprocally movable in the directions R to tuft each of the pile yarns Y into the backing P at a plurality of spaced needle insertion points I (Figures 2A, 2B). The insertion points I produced by the reciprocating tufting needles N form a pattern of parallel lines LL, LT, that respectively extend in the longitudinal and in the transverse directions along the backing P.

As is well understood by those skilled in the art, during the basic operation of the tufting apparatus 12 the reciprocating insertion and retraction of the needles N form looped face fiber elements F that lie adjacent to the upper face U of the primary backing P. The face fiber F elements may be later cut, if desired. As the primary backing P is linearly advanced along the path of travel T lengths of yarn overlay the lower face L of the backing P between longitudinally adjacent needle insertion points I to define linear backstitch elements B shown in the foreground portion of Figure 2A.

Alternatively, as also appreciated by those skilled in the art, in addition to being vertically reciprocable the needle bar M may also. be transversely movable with respect to the backing P in the directions V. In this event, as the primary backing P is linearly advanced along the path of travel T backstitch elements B'are formed that diagonally overlay the lower face L of the backing P across one or more longitudinal lines LL of adjacent needle insertion points I. The backstitch elements B'are shown in the background portion of Figures 2A, 2B.

As noted the conventional tufted pile structure produced by the tufting apparatus 12 is indicated in the drawings by the reference character 24. However, the tufted pile surface structure 28 in accordance with this invention includes a binder material therein. The binder material 38 is applied

after the tufting operation in the form of a liquid coating using the dispenser 14. The dispenser 14 includes a kiss roller 14R positioned at the mouth of a trough 14T. The dispenser is adjusted above the lower surface L of the pile surface structure 24 such that the kiss roller 14R contacts the backstitch elements B, B'and applies a coating, indicated by the character 42, of the liquid binder to the top surfaces thereof.

The pile surface structure 28 having the binder material applied onto the backstitches B, B'thereof is conveyed to the finishing apparatus 16. However, as the structure 28 advances toward the finishing apparatus 16 the liquid binder diffuses into the yarn forming the backstitch elements B, B', as is progressively indicated schematically at the reference characters 42', 42". By the time the pile surface structure 28 reaches the heat-treating apparatus 16 the binder has soaked through the backstitches B, B'so that binder material is on, through and is collected in the vicinity of the backstitches B, B'. This condition is illustrated by the reference character 44 in Figure 2A.

As noted earlier, located downstream of the dispenser 14 is a finishing apparatus 16 that heat-treats the tufted pile surface structure 28 to activate the binder material therein. The application of heat from the lower face L activates the binder and causes the backstitch elements B, B'and the primary backing P to fuse together.

The finished pile surface structure 32 having the activated binder thereon is illustrated in Figure 2B. The activated binder material, indicated in selective locations in Figure 2B by the reference character 46, is disposed on, through and in the vicinity of the backstitch elements B, B' to holds the same to the backing P. However, those portions of the lower face L of the backing P not overlaid by the backstitch elements B, B'are left substantially free of binder. These binder-free areas are selectively illustrated in Figure 2B by the reference character 48.

As seen from Figure 1 a secondary backing 50 may be optionally applied to the pile surface structure 28 (prior to activation of the binder). The secondary backing 50 is drawn from a roll 52 as the pile surface structure 28 enters the finishing apparatus 14. Depending upon the denier of pile yarn, the viscosity of the binder and the pressure applied during binder activation, binder material that flows through and about the backstitch elements B, B'may be used to attach the secondary backing 50 to the pile surface structure 28/32 without the need of any additional binder. The roller 18 can be useful to press together the binder material, the backstitch elements B, B', and the secondary backing 50.

Depending upon the nature of the binder the roller 18 may be located before, within, or after the heating apparatus 16.

Figure 1, wherein the roller 18 is located after of the heating apparatus 16, is the preferred arrangement for thermoplastic binders.

Suitable liquid binder materials include latex dispersions, thermoplastic particles dispersed in liquids, and binders dissolved in solvents. The dispersion or solution must be chosen to have suitable viscosity and affinity to the backstitch elements and the primary backing (and secondary backing, if any) to diffuse and adhere as discussed.

The finished pile surface structure 32 in accordance with the present invention is believed to provide significant advantages over conventional tufted pile surface structures. Since substantial areas on the lower surface L of the backing P are left binder-free (i. e. the binder is concentrated in discrete areas in, through and in the vicinity of the backstitches B, B') the finished pile surface structure 32 is lighter in weight than a conventional tufted pile surface structure. Because of the discrete bonding pattern that leaves binder-free areas 48 on the lower surface of the backing P the finished pile surface structure 32 is also softer than conventional tufted pile surface structures.

Since the lower face of the backing is left substantially binder-free, pins or hooks can easily penetrate through the binder-free areas of the primary and/or secondary backings to aid installation. Also, since a secondary backing is bonded to the primary with a discrete pattern of bonds leaving binder-free areas the secondary backing may itself have"loops"allowing a "hook-loop"installation system.

Moreover, since the heat required to set the discretely located binder material is less than that required to cure conventional latex, the finishing/bonding operation in the heat-treatment apparatus 16 may be performed in line with the tufting operation.