WO1992008615A1

WO1992008615A1 - Film net process

Info

Publication number: WO1992008615A1
Application number: PCT/US1991/008082
Authority: WO
Inventors: Hans O. Cedarblad
Original assignee: Leucadia, Inc.
Priority date: 1990-11-08
Filing date: 1991-10-31
Publication date: 1992-05-29

Abstract

A novel, economical, co-oriented reinforced film net laminate (20) comprised of a polymeric film (16) uniformly and firmly bonded to an extruded net (18) is produced by a new process involving orientation in both the machine and transverse direction. The film can be optionnally oriented in the machine direction while the net is typically stretched in both machine and transverse directions. The inventive process permits the film of the resultant laminate (20) to be manufactured thinner than most films currently employed in conventional reinforced film net structures. Among other applications, the laminate can be heat bonded onto carpet cushions which result in improved slip properties thereof.

Description

FILM NET PROCESS

Background Of the Invention

1. Field Of The Invention

This invention relates to a new process of forming a high strength, oriented film net composite by co-orienting and laminating together a polymeric film and an extruded net. The resultant oriented product is uniformly and firmly bonded throughout the netting network.

2. Description Of The Related Art

For purposes of the present invention, the terms laminate and composite are synonymous. Numerous patents exist describing films, netting, orientation or lamination. Existing technology does not include co-oriented composites of film and net forming an oriented film net laminate wherein the film can be manufactured thinner than most conventional films on the market, molecularly oriented and bonded throughout the netting network. It is known, according to United States Patent 3,474,952, to combine a film and a net by heat sealing a plastic trim around the edge of the film and net. The resultant product is not oriented or sealed throughout the netting structure.

United States patent 4,152,479 issued to R. Larsen, discusses a method of orienting sheet plastic net and is hereby incorporated by reference. The method discussed by Larsen involves an extruded thermoplastic netting having two sets of strands crossing each other at substantially right angles which are molecularly oriented first along one set of strands, and then along the other set to achieve improved heat stability.

In the carpet trade, a rebonded polyurethane cushion or foam is usually supplied with a carpet. This foam is typically constructed of various densities of polyurethane. A mono-extruded net and a film are individually and sequentially placed over the foam and bonded into the foam using hot rollers to provide for enhanced slip properties of the carpet foam. A carpet is placed over the cushion which is bonded with film and netting. Usually, the cushion or foam, the film and the net are inventoried separately. It is thus costly for carpet cushion manufacturers to maintain the necessary space and overhead in order to supply a final product to the customer. A need therefore exists to reduce inventory, space requirements and costs related to supplying all components associated with manufacturing the carpet cushion.

In cases involving mono-extruded films, it is preferred that the surface of the film be treated to possess suitable surface tension to bond to the intended substrates, ie. the netting or carpet cushion. Surface treatment is one consideration to ensure proper adhesion by inks and adhesives onto substrates. It may be necessary to treat the surface of a film in order to obtain increased bonding sites on the film prior to attaching the same to a substrate. Plastic films requiring surface treatment are normally those derived from hydrocarbons and have wax-like surfaces that resist wetting by solvents and adhesives. Typically, films are either chemically, electrically or flame treated to achieve the proper surface tension to facilitate adhesion to a particular substrate.

The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists. Summary Of The Invention

The present invention relates to a process of forming an oriented film net product and the article made by the disclosed process. For the purposes of this invention, orientation is defined as stretching the film in a predetermined direction. The terms orientation and stretch are interchangeable.

The concept of the invention involves co-orienting a film and an extruded net in order to produce a "film over net" oriented laminate composite. The film on the resultant composite is uniformly and firmly bonded throughout the netting network and is thinner and wider than the starting materials.

A polymeric film and an extruded net are fed into a standard netting machine direction (MD) orientor comprising a series of hot and cold rollers and nip idler rolls which aid in bonding and co- orienting the two structures together. The film is optionally oriented in the machine direction while the net is typically oriented in the machine direction. After machine direction orientation, the composite film and net is carried to and through a tenter frame where it is stretched in the transverse direction. The film net laminate can be applied to substrates of varying porosities. For example, it may be placed on rebonded foam for carpet backing, furniture coverings or insulation, paper, foil, woven or non-woven fabrics. Among other benefits, the film net laminate acts to increase the integrity and improve the bond strength of the article to which it is applied. Brief Description Of The Drawings

Figures 1 and 2 illustrate varying threadpath configurations for the draft mechanism. Figure 3 illustrates a side view of the tentering mechanism.

Figure 4 illustrates a top view of the tentering mechanism with the ovens removed for clarity. Description Of The Preferred Embodiments

While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.

This invention relates to a process of forming an oriented film net composite and an article produced by said process. The process involves the use of a polymeric, stretchable film and a polymeric, stretchable extruded net which are fed into a standard netting orientor in which the composite is co-oriented first in the machine direction and then in the transverse direction. The resultant laminate is firmly bonded throughout the netting structure and can be placed onto substrates of varying porosities. An objective of the present invention is to provide a unitary film and net for placement over rebonded caφet foam to improve the slip properties of the same. The invention bonds firmly and uniformly to rebonded caφet foam and enhances the tensile strength, elongation, compression load deflection (CLD), cutting resistance and slip properties of the foam. The cushion is also protected from caφet abrasion with the addition of the film net laminate. Although the above identified properties are achieved with current caφet cushion lamination technology, the present invention accomplishes the same with a unitary product.

The present invention permits thinner films to be used with caφet foam than are traditionally employed. Standard film utilized in the caφet cushion industry for enhanced slip properties of the cushion is typically greater than 0.6 mils thick. The present invention allows the film to be produced less than 0.6 mils thick, if desired although the actual thickness of the film in any particular instance is based upon the application of interest.

Producing the Film Net Machine Direction Orientation:

Figures 1 and 2 illustrate examples of varying threadpath configurations for the machine direction orientation process. It is understood that these examples are for illustrative puφoses only, and that varying threadpath configurations are possible to achieve the oriented laminate described herein.

The term "drafting" is used when the composite is stretched in the machine direction. The term "tentering" is used when the composite is stretched in the transverse direction.

The MD orienting device 10, shown in Figures 1 and 2 and utilized for the drafting mechanism consists of a frame (not shown) supporting a series of nip rollers 12 and 14 which serve to isolate tension of the laminate 20, prevent slippage of the same and apply pressure to the composite. The draft rate defines the speed with which laminate 20 is being stretched. This rate is determined by the length between nip rolls 12 and 14. The length between nip rolls is also referred to as stretch gap. The draft rate is further determined by the drive speed of rolls 30, 32 and 36, and the draft ratio which is the ratio of roll speeds 36 and 30. Typical machine direction orientation draft ratios are 2.5-6.0. A preferred ratio is 3.3. The value is determined by product design and operating conditions such as line speed and netting utilized. Laminate 20 comprises film 16 and net 18.

Machine direction orientor 10 further consists of a series of idler rolls 22, 24, 26 and 28 which serve as guide rollers for the laminate 20 as it is processed through MD orientor 10, and the variably driven hot and cold rolls 30, 32, 34 and 36 respectively. Typically rolls 30, 32, 34 and 36 are motor driven, however in the present invention, hot roll 32 is optionally motor driven. Undriven, roll 32 can serve as a heated idler roll. The speed with which laminate 20 travels over hot rolls 30 and 32 is controlled by the natural stretch properties of laminate 20. By allowing roll 32 to serve as an idler roll, the natural stretch ratio distribution of the composite is achieved. At least one hot and cold roll is required for the present invention. However, it is understood that various rolls can be used and that those shown are for illustrative purposes. Holders 38 and 40 serve to unwind film 16 and net 18 respectively as they are fed through the drafting mechanism.

In the threadpath configuration of Figure 1 , the film 16 and net 18 are fed from holders 38 and 40 into MD orientor 10. Film 16 and net 18 meet under idler roll 22, are carried over hot roll 30 maintaining net 18 directly next to hot roll 30. Film 16 is overlayed and in direct contact with net 18 throughout the drafting and tentering mechanism. Typically, net 18 is directly against hot rollers 30 and 32 for heat transfer to film 16, softening the film allowing it to bond to net 18. However, it is possible to place the film in direct contact with hot rolls 30 and 32. The temperature of hot rolls 30 and 32 is a critical consideration in the drafting process and must be maintained at a level to avoid melting and decomposition of film 16. Laminate 20 is carried over hot roll 32, idler rolls 24 and 28, nip roll 14 and over cold rolls 36 and 34 finally be guided under idler roll 26 and fed into the tenter frame shown in Figures 3 and 4.

The manner of introducing film 16 and net 18 into the MD orientation process as well as the location of nip rollers 12 and 14 are important as they determine the percent orientation of the film relative to the net. Orientation of film 16 in the machine direction is optional. Film 16 can be wholly, partially or not oriented in the machine direction, ie. the film can be stretched from 0% to about 100% relative to the net. The film stretch can be varied by varying the stretch gap of the MD orientor 10. Whole orientation involves orienting film 16 to the same degree as net 18. Partial orientation involves orienting film 16 to a degree less than that for net 18. As the film and/or net are oriented in the machine direction, the thickness thereof is subsequently reduced.

The configuration of Figure 1 illustrates whole orientation of film 16. The polymeric film and net can be either mono or co-extruded when full MD orientation is employed. Film 16 and net 18 are jointly stretched in the machine direction as they enter orientor 10, passing under nip roll 12 and over hot roll 30. Approximately 95% of the machine direction orientation of laminate 20 occurs before passage over roll 32, as shown in the threadpath configuration of Figure 1. The remaining orientation in the machine direction occurs as laminate 20 is carried from idler roll 24 to cold roll 36.

The threadpath configuration shown in Figure 2 is preferred and illustrates partial machine direction orientation of film 16 relative to net 18. The threadpath configuration of Figure 2 involves feeding film 16 and net 18 separately into the drafting mechanism. Bonding film 16 to net 18 can occur without orientation in the MD however, some machine direction orientation is recommended to enhance bonding the film to the netting and eliminate any possible film wrinkling. It is possible to bond film 16 to net 18 by softening the film sufficiently to attach to the net. Orientation of the film in the machine direction exposes greater surface area of the film, thus enhancing the bonding mechanism to a netting structure. In the configuration of Figure 2, net 18 is fed into the draft mechanism at hot roll 30 and meets film 16 at hot roll 32. The drafting process then proceeds as illustrated in Figure 1.

In the case where partial or no machine direction orientation is desired for film 16, it is recommended to utilize a co-extruded film or net, i.e., a film or net containing an adhesive to aid in the bonding mechanism. It is important to have the film securely bonded to the netting structure before the laminate enters the tentering mechanism. If the film and net are not securely bonded during the machine direction orientation process, they will de-laminate during the tentering phase with subsequent film breakage. Secure bonding of film 16 and net 18 also facilitates web handling through the draft and tentering processes and maintains the integrity of laminate 20 during the tentering phase.

The temperature of the hot rolls depends on the film and net utilized and the application of interest as well as the particular equipment. In the present invention the hot rolls were typically covered with 'Teflon'¹® coated fabric or its equivalent to serve as a release surface to prevent composite 20 from sticking to the rolls. When utilizing polypropylene net and polyethylene film, hot rolls 30 and 32 were maintained at approximately 270°F.

Transverse Direction Orientation: After exiting from the drafting section and the various rolls supported therein, the film and net are transported to and through the tentering mechanism illustrated in Figures 3 and 4. Figure 3 illustrates a side view of the tentering mechanism while Figure 4 illustrates a top plan of the same. The tentering mechanism 70 comprises an oven 44 containing generally three sections as indicated by the reference characters 74, 76, and 78 and chain members 50 and 52. Sections 74, 76 and 78 are heated by any suitable means including, for example a hot gas blowing mechanism. Horizontally disposed, endless chain members 50 and 52 have grippers (not shown) for gripping the edges of laminate 20 for transporting the same through oven 44 and for pulling laminate 20 laterally. As laminate 20 is pulled through the tentering phase, it is softened and stretched in the cross direction. This action allows film 16 to be further bonded to net 18 while fully supported and carried by net 18 through the tentering mechanism. After exiting from tentering mechanism 70, laminate 20 is carried by members 50 and 52 over a cooling section 80 which optionally blows cool air onto laminate 20. Laminate 20 then passes over suitable idler rolls as illustrated in Figure 3, i.e., rolls 62 and 64, and is taken up on the roll 60 of the take-up section 58. Roll 60 is formed on a shaft 66 which is driven by a mechanism, not shown, to take up laminate 20.

It is to be understood that various idler rolls may be used in the tentering phase and that those shown are for illustrative puφoses only since requirements of space and equipment may require different paths of travel for laminate 20. The transverse direction orientation process is important to the invention as this allows for film orientation between each bonded netting strand. It is also during the tentering phase whereby the width of laminate 20 is increased. As the width of laminate 20 increases, the thickness of film 16 decreases. High film tension concentrations which may potentially cause the film to split is prevented by controlling the tentering process and by isolating the film tension between strands of the netting to reduce breaking. Isolation of film tension between strands occurs during the drafting phase by firmly bonding film 16 to net 18. This isolation of film tension is especially important when reducing film thickness.

For a polypropylene net/polyethylene film combination, the temperature in the tenter oven was maintained at approximately 270° F. The temperature chosen for the tenter oven will vary based on the film and netting utilized. The optimum orientation temperature for the netting is a specific consideration in determining the temperature for the tentering process. Additional factors to consider in determining temperature are the thickness of the starting film, the desired thickness of the processed film and the melt strength of the film chosen. Other factors include the temperature at which the film will soften and bond to the netting, the line speed of the laminate through the tentering process, and the transverse direction orientation ratio which is the ratio between the outfeed and infeed width of the tenter frame.

Typical transverse direction orientation ratios are 3.0-6.5. Transverse direction orientation ratios are determined by design of the netting, for example, the strand count and netting orientation considerations. With the present invention, by varying the temperature of the transverse direction orientation process, films can be made continuous or discontinuous, ie. with or without holes, depending on the application of interest. Utilizing a thin film or a film which possesses a low melt strength and increasing the process temperature results in a discontinuous film net containing openings therein. A discontinuous film net will contain partial film coverage around the individual strands of the netting. Utilizing increased film thickness results in a continuous film net, or one without holes over the netting thus providing 100% film coverage over the net. Total coverage is typically desired for most applications. Net Selection

A mono- or co-extruded net can be utilized in the present invention. The net can be of any thermoplastic, stretchable, orientable material, provided that the temperature parameters are equal to or greater than the corresponding properties of the film. The net must be able to be stretched in both the machine and transverse direction. Co- orientation of the film and net occurs best when the melting point of the film is below that of the netting. If the film and net chosen have the same or similar melting points, a co-extruded net, ie. with adhesive, is required to bond the two together. If inadequate bonding is obtained between a mono-extruded film and net at the machine direction orientation phase, the following options may be utilized: 1) use of a co-extruded film or net containing a thermoplastic adhesive, or 2) blending or co-extruding the mono-extruded film or net desired with a functionalized resin.

Advantages of the melting point difference between film and net chosen are improved adhesion between the film and the net, and reduced strength of the film so that minimal tension develops in the film during the orientation procedure.

Examples of suitable nets for use in the co-orientation process include but are not limited to polypropylene, polyethylene, polyester, nylon or blends thereof.

Film Selection Any orientable, stretchable polymeric film can be used in the present invention. Desirable film properties include: a) toughness, high melt strength, b) puncture resistance, c) possession of good bonding characteristics to desired substrate for lamination puφoses and d) the ability to stretch in the machine direction. Necessary film properties for co-orientation according to the present invention include: a) an orientation and stretch temperature which is compatible with the net orientation temperature, typically, but not necessarily, being lower than the corresponding temperature for the net chosen, and b) the ability to stretch in the transverse direction. EΞxamples of suitable films for use in the film net co-orientation process include but are not limited to polyethylene, polypropylene or blends thereof.

Polyolefin films which include but are not limited to polypropylene and polyethylene films have been the polymeric films of choice for use in the present invention. Standard laminating grade Linear Low Density Polyethylene (LLDPE) film is preferred as the starting film. Laminating grade film has been pre-surface treated on at least one side using either chemical, electrical or flame treatment to expose reactive sites and promote good bonding of the film to the desired substrate, ie. the netting. The surface tension of LLDPE film can be improved by blending with a high surface tension polymer such as Ethylene Methyl Acrylate (EMA) or Ethylene Vinyl Acetate (EVA). Composites made from films of LLDPE blended with EVA resins and polypropylene netting have been found to offer the best combination of cost savings and performance. Bonding was achieved at all strands of the net.

It is preferred that the film chosen for use have at least one side surface treated to expose reactive sites and enhance bonding to the netting. Often times, even with laminating grade films, the surface of the film will need to be further treated prior to entering the drafting mechanism and/or again upon exit from the tentering frame. It is possible to incorporate a surface treater into the drafting process by placing a treater at the film unwind point; referring to Figure 1 , the surface treater would be located between holder 38 and idler roll 22; in Figure 2, location of the surface treater would be between holder 40 and idler roll 24. The film can be surface treated to obtain a sufficiently high level of surface tension whereby processing through the drafting and tentering mechanism does not eliminate all surface tension on the film. A suitable surface tension range is 45-50 dyne/cm. However this range may vary based on the film and net utilized in the process. Artisans can determine surface tension ranges outside of 45-50 dyne/cm through routine experimentation. Treating the film to a high level of surface tension at the beginning of the drafting process may eliminate the need to retreat the laminate upon exit from the tentering frame. The laminate however, may optionally be treated upon exit from the tentering mechanism to further increase the surface tension thereof.

Advantages of Film Net Advantages of the present invention over other film and net composites include a) a composite which is co-oriented, b) fully and uniformly bonded together, c) the ability to utilize a film thinner than possible with conventional unsupported film orientation methods, d) providing an alternative to co-extrusion of a netting with adhesive resin to produce an adhesive net which is thermally activated for use in bonding to various substrates, e) the use of a wider range of polymeric films to function as adhesives when laminating the composite to varying substrates, f) allowing up to 100% active bonding sites when bonding a netting to any substrate resulting in increased substrate selection, e.g. tissue, paper, film, foil, fabric, foam, non-woven are available as substrates of choice, g) the ability to fuse the film into the desired substrate resulting in improved substrate penetration and bond, h) having the net support the film in the orientation process allowing the film thickness to be reduced significantly over an unsupported web, i) space savings in the caφet cushion industry due to the ability to store a unitary product which includes a film and a net. Instead of caφet cushion manufactures stocking film and netting separately, a unitary sheet of both film and net is available with cost advantages which arise from the use of a thinner film. The resultant oriented composite can also be laminated directly onto rebonded foam or caφet cushion.

This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.

Claims

WHAT IS CLAIMED IS:

1. An extruded film net composite comprised of at least two materials laminated together: material one comprising an orientable, stretchable, polymeric film; material two comprising a thermoplastic, orientable stretchable extruded net, the net possessing temperature parameters including softening temperature, melting temperature, optimum orientation temperature and optimum heat seal temperature equal to or greater than the corresponding properties of the film; the film being heat sealed throughout the netting structure and bonded to the net; and, the composite being substantially oriented in both the machine direction and the transverse direction.

2. An extruded film net composite comprised of at least two materials laminated together: material one comprising an orientable, stretchable, polymeric film; material two comprising a thermoplastic, orientable stretchable extruded net, the net possessing temperature parameters including softening temperature, melting temperature, optimum orientation temperature and optimum heat seal temperature equal to or greater than the corresponding properties of the film; the film being sealed throughout the netting structure and bonded to the net; and, the composite being substantially oriented in the transverse direction.

3. A film net composite according to claim 1 wherein the film is less than about 0.6 mil thick.

4. A film net composite according to claim 1 wherein the filmed net comprises a continuous composite having complete film coverage over the net.

5. A film net composite according to claim 1 wherein the film net comprises a dis-continuous composite having an apertured film that has less than complete film coverage over the net.

6. A film net composite according to claim 1 wherein the net is mono-extruded.

7. A film net composite according to claim 1 wherein the net is co-extruded with an adhesive or functionalized resin.

8. A film net composite according to claim 7 wherein the net is co-extruded with ethylene vinyl acetate.

9. A film net composite according to claim 7 wherein the net is co-extruded with ethylene methyl aery late.

10. A film net composite according to claim 1 wherein the extruded net is polypropylene, polyethylene, polyester, nylon or blends thereof.

11. A film net composite according to claim 1 wherein the polymeric film is a polyolefin polymer.

12. A film net composite according to claim 11 wherein the polyolefin polymer is polypropylene, polyethylene or blends thereof.

13. A film net composite according to claim 1 wherein the polymeric film is blended with ethylene vinyl acetate.

14. A film net composite according to claim 1 wherein the polymeric film is blended with ethylene methyl acrylate.

15. A film net composite according to claim 1 wherein the polymeric net is polypropylene and the extruded film is polyethylene.

16. A film net composite according to claim 1 wherein the polymeric film is surface treated on at least one side thereof.

17. A film net composite according to claim 1 wherein the resultant composite is surface treated on at least one side thereof.

18. A method of producing an oriented film net composite comprising: a) feeding a length of a polymeric, orientable, stretchable film and a length of thermoplastic, orientable, stretchable extruded net through a drafting frame having a series of variably motor driven hot and cold rollers along with nip and idler rollers; b) stretching and heating the film and net as they pass over the hot roller and under the nip roll in the machine direction resulting in bonding of the film and net together; c) transferring the bonded film and net to a tentering frame comprising a series of heating sections, followed by cooling sections and chain members with grippers which pass therethrough whereby the bonded film and net are gripped and stretched in the transverse direction as the film and net is carried through the tentering frame; and, d) optionally surface treating the bonded film and net upon exit from the tentering frame.

19. A method of producing an oriented film net composite comprising: a) feeding a length of thermoplastic, orientable, stretchable extruded net through a drafting frame having a series of variably motor driven hot and cold rollers along with nip and idler rollers; b) stretching and heating the net as it passes over the hot roller and under the nip roll in the machine direction; c) feeding a length of polymeric, orientable, stretchable film through said drafting frame whereby said film joins said net after passage over the hot roller and nip roller; d) binding said film and net; e) transferring the bonded film and net to a tentering frame comprising a series of heating sections, followed by cooling sections and chain members with grippers which pass therethrough whereby the bonded film and net are gripped and stretched in the transverse direction as the film and net is carried through the tentering frame; and, f) optionally surface treating the bonded film and net upon exit from the tentering frame.

20. A method according to claim 18 wherein the temperature parameters of the extruded netting are equal to or greater than those of the polymeric film.

21. A method according to claim 19 wherein the temperature parameters of the extruded netting are equal to or greater than those of the polymeric film.

22. A method according to claim 18 wherein the drafting frame includes two hot rollers and two cold rollers in series with two each of nip and idler rolls.

23. A method according to claim 22 wherein at least one hot roller is optionally motor driven.

24. A method according to claim 18 wherein the drafting frame includes at least one optionally motor driven hot roller.

25. A film net composite according to claim 1 laminated onto a polyurethane foam substrate.

26. A method according to claim 18 wherein the draft frame includes an entry and exit point, a surface treater for enhancing surface tension of plastics being placed at the entry of the draft frame to treat the surface of said plastics prior to processing the same through the drafting frame.

27. A method of surface treating plastics utilizing a drafting frame and a surface treater, said frame having an entry and exit point, placing the surface treater at the entry point of the drafting frame and treating the surface of the plastic with the surface treater prior to processing of the same through the drafting frame.

28. A method according to claim 26 wherein the plastic is processed through a drafting and tentering frame, said plastic being treated to a sufficiently high level at the entry point of the draft frame to eliminate the need for surface treatment thereon upon exit from the tenter frame.

29. A method according to claim 28 wherein the plastic is surface treated upon exit from the tentering frame.