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Method and system for manufacturing foamed polyolefin tapes at cost effective line speeds

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Method and system for manufacturing foamed polyolefin tapes at cost effective line speeds


Making foamed polyeolefin tapes include combining a polyolefin resin and a chemical blowing agent to form a mixture. This mixture can then be heated in an extruder to create a supersaturated solution of gas within the polyolefin resin. A cooling device can be positioned adjacent to a die at a set distance for receiving extruded resin and for allowing exposure of the extruded resin to ambient air. This space between the cooling device and die outlet allows bubbles to grow in the extruded resin and to be shaped such that voids or empty spaces can be generated within the extruded polyolefin resin. The voids allow the formation of tapes which use less material but have adequate strength for various applications, such as carpet backings, geotextiles, packaging, housewrap, bags, wire insulation, and reinforcement elements in concrete.

Inventors: Hugh C. Gardner, Josef Uesbeck, Andy Rakovac, Philippe Combier, Kam Lui
USPTO Applicaton #: #20120276358 - Class: 428220 (USPTO) - 11/01/12 - Class 428 
Stock Material Or Miscellaneous Articles > Structurally Defined Web Or Sheet (e.g., Overall Dimension, Etc.) >Physical Dimension Specified

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The Patent Description & Claims data below is from USPTO Patent Application 20120276358, Method and system for manufacturing foamed polyolefin tapes at cost effective line speeds.

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STATEMENT REGARDING RELATED APPLICATIONS

The present application claims priority to provisional patent application entitled, “Method and System for Manufacturing Foamed Polyolefin Tapes at Cost Effective Line Speeds,” filed on Nov. 1, 2007 and assigned U.S. Application Ser. No. 60/984,564, the entire contents of which are hereby incorporated by reference.

FIELD OF INVENTION

This invention generally relates to foamed, oriented tape yarns used in carpet backing, geotextiles, packaging, housewrap, and similar applications. More particularly, the invention relates to a high speed process for producing foamed, oriented polyolefin tapes for such applications.

BACKGROUND OF THE INVENTION

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.

SUMMARY

OF THE INVENTION

A method and system for manufacturing foamed polyolefin tapes with line speeds at or in excess of 850 feet per minute can include combining a polyolefin resin and a chemical blowing agent to form a mixture. This mixture can then be heated in an extruder to create a supersaturated solution of gas within the polyolefin resin.

Pressure within the extruder containing the mixture can be applied such that the gas within the polyolefin resin mixture remains dissolved. Next, the solution can be fed through the die.

A cooling device can be positioned adjacent to an outlet of the die at a predetermined distance for receiving the extruded resin and for allowing exposure of the foamed extruded resin to ambient air during its movement through the predetermined distance between the die outlet and the cooling device. This predetermined distance or space between the cooling device and die outlet allows bubbles to grow in the extruded resin such that voids or empty spaces can be generated within the extruded polyolefin resin. This predetermined distance can be between from about 0.2 to about 6.0 inches.

According to one exemplary aspect of the inventive system and method, in addition to the predetermined spacing or distance between the cooling device and die, the time in which the extruded resin is exposed to air can be increased by using a die with a particular design. Such a die may include an area within a lip of the die allows expansion of the extruded foamed resin sheet mixture before it exits the die.

The cooling device in one exemplary embodiment can include a quenching bath in which the extruded resin is submerged in a liquid such as water. The cooling device according to another exemplary embodiment can include a chill roll. The chill roll can be maintained at a temperature much lower than that of the die and receives the extruded resin, which is allowed to contact and move with the chill roll. The chill roll can rotate at a slightly higher speed than the exit speed of the resin from the die and can transport the extruded resin to the next stage in the process. When the extruded resin contacts the chill roll, the temperature of the extruded resin changes such that its temperature is lowered.

If the cooling device used in the process includes a quenching bath, then liquid that remains on the extruded resin sheet can be removed with various mechanisms. One mechanism includes vacuum devices. Each vacuum device can be provided with a particular design such that the extruded resin sheet is spread evenly across slots of the vacuum devices. The particular design of a vacuum device can include a diverging array of grooves that originate from the entrance to the main vacuum source. The grooves can have a tapering cross-section that can accelerate the air stream and entrain more moisture so that more liquid is pulled through the slots into the vacuum device and away from the extruded resin sheet.

If a liquid quenching bath is used, another mechanism for removing water from the extruded resin sheet and pulling the sheet away from the die is a pair of nip rolls positioned above the quenching bath. At least one of the rolls in the pair is driven. Various combinations of vacuum devices and pairs of nip rolls can be used to remove liquid that may be left on the sheet from a liquid quenching bath.

Next the extruded resin can be slit into tapes. The tapes can then be heated and oriented to increase their length-wise or longitudinal dimension. The tapes are then optionally annealed, depending on their end use application. The tapes can then be taken up on individual bobbins that are present in a winder bank. At this last stage of the inventive process, the line speed is maintained in excess of 850 feet per minute. The term “line speed” refers to the take-up speed of the yarn on the bobbins in a winder bank.

The inventive method and system can produce thin, lightly foamed tape at a speed that is much higher than is used for conventional foaming processes. Typical foamed, oriented tape dimensions are about 1.0 to about 4.0 mils thick when measured according to test method ASTM 3218, and 20 to 400 mils wide. In contrast to many extruded foam profiles, the tapes of the invention are not shaped by a calibrating device such as 106B in FIG. 1A or 106C in FIG. 1B, and the foamed sheet is not passed through a stack of polished rolls while still molten, as is commonly done when a foamed sheet is produced.

With the inventive system and method, the internal void content is not typically as high as what would be calculated if all the gas resulting from decomposition of the blowing agent were allowed to form a closed cell foam. This can be attributed to the high haul off speed, rapid cooling of the foamed sheet in contact with the cooling devices, such as a quench bath or chill roll, and the high surface to volume ratio of the thin, unoriented sheet prior to quenching. The tapes can have void contents between about 20 and about 150%. At least one surface has multiple longitudinal ridges that result from expansion of the entrained gaseous decomposition products. The tapes can be produced without extreme difficulty and have very good property profiles for the various applications described above. Those applications include, but are not limited to, carpet backings, geotextiles, packaging, housewrap, netting for bags or containers, netting for food stuffs, and insulation for wires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a high density foam freely expanded and shaped in a calibrator or shaping die that is commonly used with conventional foaming processes.

FIG. 1B illustrates a foamed resin produced using a spinnerette die at the exit of an extruder in combination with a calibrator or shaping die that is commonly used with conventional foaming processes.

FIG. 2A illustrates one exemplary system for manufacturing foamed polyolefin tapes according to one exemplary embodiment of the invention.

FIG. 2B illustrates another exemplary system for manufacturing foamed polyolefin tapes according to an alternate exemplary embodiment of the invention.

FIG. 2C illustrates further details of an exemplary high-density foam extruder system and gear pump that can be employed in the systems of FIGS. 1A and 1B according to one exemplary embodiment of the invention.

FIG. 3 illustrates an exemplary method for manufacturing foamed polyolefin tapes with increased line speeds according to one exemplary embodiment of the invention.



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stats Patent Info
Application #
US 20120276358 A1
Publish Date
11/01/2012
Document #
13483472
File Date
05/30/2012
USPTO Class
428220
Other USPTO Classes
264 54, 4253781, 521143
International Class
/
Drawings
11



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