Oriented polyolefin tape yarns are commonly used in woven fabrics for applications such as carpet backing, geotextiles for soil stabilization and separation, and in coated fabrics such as housewrap, lumber wrap, and laminates for flexible packaging applications. In all these applications, the foamed, oriented tapes impart high strength and stiffness to the fabrics, and depending on the application, other essential properties. Foamed oriented tape yarns are also used as wire insulation and as crack arrestors in concrete.
Carpets
In the past, jute cloth was used as carpet backing for tufted carpets. More recently, woven fabrics of polypropylene tape yarns have been used for carpet backings.
Tufted carpets can be produced by a two-step process involving 1) stitching pile yarns made from synthetic or natural fibers through the primary backing then 2) fixing the stitches on the underside of the primary backing with a latex adhesive.
Tufted primary backings may have pile yarns that are loops, cut pile, or combinations of cut and loop pile. During the carpet manufacturing process, a second fabric, called the secondary backing may also be used. The latter fabric is laminated to the opposite side of the adhesive layer and contacts the floor. The secondary backing adds dimensional stability to the finished carpet. Typically the secondary backing is a woven fabric with tape yarns in the warp direction and spun yarns in the cross machine (or filling) direction.
Foamed Tapes for Carpet Backings
It is well known in the conventional art that polyolefin resins can be used as the stock materials for forming tape yarns for woven carpet backings. Specifically, it has been found that foamed, oriented polypropylene tape yarns can be used as the stock materials for woven backings. Such foamed tape yarns have ridged surfaces and internal voids. They typically contain less material than ordinary polypropylene tape yarns which are not formed by foaming methods. In addition to weighing less than conventional (unfoamed), oriented tape yarns, foamed, oriented tape yarns for primary carpet backing impart improved tuftability and surface appearance to tufted carpets. In secondary backings, foamed oriented tape yarns impart similar levels of dimensional stability to the finished carpet with less material than conventional (unfoamed) tape yarns.
Geotextiles
Many geotextiles are manufactured from oriented polyolefin tapes, including woven fabrics for separation and stabilization of soil layers in roadbeds and for containing soil particles (e.g., silt) at construction sites. Polyolefin tapes are also used in retaining wall fabrics, turf reinforcement mats, ground cover fabrics, geotubes, and erosion control blankets. Polypropylene tapes are used in many of these applications.
Foamed Tapes for Geotextiles
Woven geotextiles require high strength and stiffness, and specific levels of permeability to water. Often the strength of the starting tapes is diminished when they are woven into fabrics. In general, foamed, oriented tapes lose less strength in the weaving process than conventional (unfoamed) tapes, resulting in increased fabric strengths compared to fabrics woven from unfoamed tapes with the same starting tensile properties. For applications that require woven geotextiles to act as a filter, such as silt fence, foamed tapes generally have greater dimensions than conventional (unfoamed) tapes of similar weight, allowing less fabric to create the same opening size in the filter membrane.
Packaging
Oriented polyolefin tapes are commonly used to make reinforcing scrims in flexible packaging applications, such as lumber wrap, bale packaging for cotton and synthetic staple fiber, and retail packaging of food, seeds, and other granular material. The woven scrims are often extrusion coated with a layer of polyolefin resin to create a moisture-proof barrier and increase puncture resistance, strength and stiffness.
Foamed Oriented Polyolefin Tapes in Packaging
Woven fabrics for packaging often have critical requirements such as high coverage and strong adhesion of the extrusion coating to the woven scrim. Coverage, which refers to the extent of open area in the woven fabric, depends on the widths of the tapes and count of the tapes in the warp and fill direction. Compared to woven scrims made with conventional (unfoamed) oriented tapes, woven scrims with foamed, oriented tapes can have greater coverage for equal weight (or alternatively, equal coverage with less weight) and improved adhesion. As described in more detail below, improved adhesion is a consequence of the special ridged surface structure of the foamed, oriented tapes made by the method and system of this invention.
Housewrap
Housewrap is a moisture resistant, breathable fabric applied to residential and light commercial buildings prior to the installation of the exterior finish, such as shingles, brick, or siding. One purpose of housewrap is to conserve energy by reducing air infiltration. Many housewraps consist of extrusion coated woven scrims made from oriented, polyolefin tapes. They are similar to extrusion coated scrims for packaging, but often have less coverage (more open area in the scrim). These coated fabrics are often mechanically perforated to allow water vapor to pass through. Most housewraps made with woven polyolefin reinforcement easily pass the minimum requirements for tensile strength required by industry regulations.
Foamed Oriented Polyolefin Tapes in Housewrap
Foamed, oriented tapes have sufficient strength to produce housewraps that meet industry standards. They also have a ridged surface that imparts improved adhesion of the polyolefin coating to the tapes, another important property for these products. Scrims made from foamed, oriented tapes require less resin than scrims made from similar conventional (unfoamed) tapes while still delivering fully satisfactory tensile properties to the final product.
Other Applications
Oriented polyolefin tapes are used for other applications such as netting for produce bags, open knitted fabrics for curing meat, and for wire insulation. Polyolefin tapes that are cut into 1 to 2-inch lengths are also used as crack arrestors in concrete mixtures.
Foamed Oriented Polyolefin Tapes in Other Applications
Foamed, oriented tapes for other applications, can include, but are not limited to netting applications and open knitted fabrics because foamed tapes impart sufficient strength and stiffness at lower weight than conventional, unfoamed tapes. When used as wire wrap, foamed, oriented tapes impart improved insulation properties because of their increased thickness compared to conventional (unfoamed), oriented tapes. As crack arrestors in concrete, chopped foamed tapes made by the system and process of this invention have surface characteristics that lead to improved mechanical bonding between the foamed, chopped tape and cement mixture compared to an unfoamed, chopped tape of similar length.
Limitations of Conventional Thermoplastic Foaming Processes
While the conventional art describes the advantages of foamed, oriented polypropylene tapes in the above applications, much of the conventional art does not articulate how these foamed tapes can be manufactured. Most of the conventional art only describes the mechanical properties of the end products (i.e., the tapes and woven fabrics) and fails to provide any information on a sequence of specific steps and/or processes for producing such foamed, oriented tapes. Furthermore, the surface characteristics of the foamed oriented tapes are not described.
Some of the conventional art mentions specific information on a few, isolated steps that can be used in processes for making foamed, oriented polyolefin tapes for use in primary carpet backings. However, the conventional art does not provide a complete set of steps which would allow one of ordinary skill in the art to produce repeatable and accurate results for manufacturing foamed, oriented polyolefin tapes for carpet backings. Specifically, the conventional art does not provide discrete steps that describe how to manufacture foamed, oriented polyolefin tapes economically and efficiently at high line speeds, such as speeds at or above 850 feet per minute. For efficient production, the number of end breaks in the process must be low—preferably less than about 5% per hour and more preferably less than about 2% per hour.
The conventional art also mentions the use of certain equipment for making foamed polyolefin profiles, such as fence posts, moldings, and sheets for thermoforming. FIG. 1A shows a high density foam exiting a die 106 and expanding into a shaping device or calibrator 106B. The purpose of the calibrator 106B is to fix the dimensions of the expanding foam profile at it cools. While this is needed for thick section parts, it is very difficult to implement with thin sheets for tapes that are produced at faster extrusion speeds, since the opening (interior height dimension) within the calibrator for thin sheets would be very small, leading to frequent clogging and tearing of the foam sheet.
In conventional art, a set of stack smooth rolls (not shown) is sometimes used to control the thickness and smoothness of an extruded foam sheet. Since foaming processes with stacked rolls are typically run at lower extrusion speeds than the tapes of this invention and are designed to create a smooth surface on the cooled foamed sheet, they are also not well suited for making the tapes of this invention, which have a unique surface structure.
FIG. 1B shows another method for making foamed, thick section profiles. In FIG. 1B, the foamable resin 107 is spun into filaments through a spinneret die 220. The extruded filaments coalesce into a thick section that is further shaped by a calibrator 106C. The calibrator creates a smooth surface on the coalesced filaments. In the method of this invention, a smooth surface is not required or desired. Consequently, the conventional processes of shaping a foamable extrudate, either by a calibrator or stack of smooth calendar rolls do not provide much useful information about how to make the thin, foamed tapes with ridged surfaces that are the end products of the inventive method and system.
Accordingly, there is a need in the art for a method and system that describes the discrete steps and equipment that can be used to produce foamed, oriented polyolefin tape yarns for the above applications. Specifically, there is a further need in the art for a method and system that describes how such foamed, oriented polyolefin tapes can be manufactured efficiently at line speeds that allow them to be a lower cost alternative to conventional (unfoamed) tapes of similar dimensions.