Abstract:
A rigid thermoformable recyclable nonwoven liner material is formed by a wet process on a papermaking machine. The rigid thermoformable nonwoven liner material is intended to be laminated to a woven fabric and then thermomolded around a wooden panel to form an office partition. The wet-laying process may consist entirely of conventional steps. The fiber furnish includes polyester matrix fibers and co-polyester/polyester bicomponent binder fibers. The web of fibers coming off the papermaking machine is passed through a foam press, which applies a water-based medium having polyvinyl chloride binder dispersed therein. The web is dried, treated again with a water-based medium having polyvinyl chloride binder dispersed therein and then dried again. The final product can be molded in a wide range of temperatures ranging from 225° to 300° F.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/115,218, filed Jan. 8, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to synthetic nonwoven materials fabricated by wet-laid processes. In particular, the invention relates to a paper-like web made with polyester fibers which is useful as a thermoformable liner material for framed structures, such as an office partition. 
     BACKGROUND OF THE INVENTION 
     A typical office partition construction involves laminating several different components together, with each component providing a specific functionality to the structure. Most of such structures use fiberglass mats which have been impregnated with phenolic or other thermosetting saturants to impart the desired rigidity to the structure. Such laminated structures are unnecessarily complicated and are not completely recyclable. There is a need for an improved office partition construction having fewer components. 
     An improved office partition comprises a rigid frame, e.g., a wooden panel, and a woven fabric which is attached to the wooden panel. There is a need for completely recyclable and environmentally friendly means for attaching the woven fabric to the wooden panel. 
     SUMMARY OF THE INVENTION 
     The present invention is a rigid thermoformable recyclable nonwoven liner material which is formed by a wet process on a papermaking machine. The wet-laying process is most suitable for this application as compared to other existing forming technologies due to the resulting uniformity in structure and tight construction. This invention also has the benefit of eliminating the manufacturing costs associated with dry web formation. The rigid thermoformable nonwoven liner material is intended to be laminated to a woven fabric and then thermomolded around a wooden panel to form an office partition. The paper-like construction is most beneficial in order to meet the tackability (i.e., tack-holding) requirement for the substrate. 
     The wet-laying process may consist entirely of conventional steps. The fiber furnish includes thermoplastic matrix fibers and thermoplastic binder fibers. In accordance with the preferred embodiment, the matrix fibers are made of polyester and the binder fibers are bicomponent fibers having co-polyester sheaths and polyester cores. The use of polyester is advantageous in that polyester is considered to be flame retardant in nature. The bicomponent fibers serve two purposes. First, the low melting point of the co-polyester enables bonding and therefore provides sufficient strength for on-line processing and handling during substrate manufacture. Second, the co-polyester sheath material is moldable at a lower temperature compared to the matrix polyester fibers. 
     In accordance with one preferred embodiment of the method of manufacturing a nonwoven liner material for use as a thermoformable liner in an office partition, the web of fibers coming off the papermaking machine is passed through a first binder application station, which applies a water-based solution, emulsion or foam having binder dispersed therein to one side of the web. In accordance with the preferred embodiment, the binder consists of polyvinyl chloride. The polyvinyl chloride binder features a curing mechanism which is activated by heat. The curing temperature of polyvinyl chloride is in the range of 225° to 280° F. Curing above 250° F. imparts the wet strength and the rigidity desired for the product. Alternatively, the binder can be polyvinylidene chloride or polyester. 
     The treated web exits the first binder application station and enters an infrared dryer comprising a plurality of infrared heaters which remove moisture from the web. Additional moisture is removed by passing the web through a first section of dryer cans. The dryer cans are heated to a temperature of about 300° F. Since the polyester sheath of the binder fiber has a melting point in the range of 225° to 240° F., the binder fibers are activated, i.e., the sheaths are melted, as the web passes over the dryer cans. Also the binder, which has a film forming temperature of 150° F. and a curing temperature ranging from 225° to 240° F., is activated. 
     After drying in the first section of dryer cans, the web passes through a second binder application station, which again applies a water-based solution, emulsion or foam to the web. The water-based solution, emulsion or foam has the same type of binder particles as those applied during the first binder application. The web is then passed through a second section of dryer cans to again remove moisture. The temperature of the dryer cans in the second section is about 300° F. Again the binder fiber sheath material is melted and the binder is activated as the web passes over the dryer cans. Upon cooling of the web, the binder fiber sheath material is fused to neighboring matrix fibers. The web is then wound on a winder roll. Optionally, the dried web is calendered using unheated calender rolls prior to winding. 
     The final product is a 100% recyclable, 100% thermoplastic nonwoven liner material. Being 100% thermoplastic in nature, the final product can be molded in a wide range of temperatures ranging from 225° to 300° F. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of apparatus for preparation of stock or furnish for manufacture of the composite material of the invention. 
     FIG. 2 is a diagrammatic view of apparatus for formation of a web by the wet-laying process and a first application of a binder. 
     FIG. 3 is a diagrammatic view of apparatus for drying the web and a second application of binder in accordance with the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with a first preferred embodiment of the invention, the fiber furnish comprises 20 wt. % of 2.0 denier×5 mm Type N-720H bicomponent (co-polyester sheath/polyester core) binder fiber supplied by Kuraray (sheath melting temp. 225° F.); 20 wt. % 1.5-denier×0.5″ Type 103 polyester staple fibers supplied by Hoechst/Celanese (melting temp. 480° F.); 40 wt. % 6.0-denier×1.0″ Type 103 polyester staple fibers supplied by Hoechst/Celanese (melting temp. 480° F.); and 20 wt. % 15.0-denier×1.5″ Type 103 polyester staple fibers supplied by Hoechst/Celanese (melting temp. 480° F.). All of the foregoing fiber types are sized by the respective manufacturer. It will be readily appreciated, however, that other polyester staple fibers could be used in place of the Hoechst/Celanese fibers specified above. Also the fiber deniers and lengths can be varied from those set forth above. Strength and porosity characteristics are imparted to the composite by the combination of polyester fibers employed in the invention. In particular, the strength of the composite can be improved by varying the polyester fiber content in accordance with the following functional relations: (a) as the polyester denier increases at constant length and amount, the porosity, bulk and stiffness of the composite increase and the amount of fiber entanglement decreases; and (b) as the polyester length increases at constant denier and amount, the tensile and tear strengths in the MD and CD directions and the Mullen burst strength increase and the stiffness decreases. 
     In accordance with other preferred embodiments, the amount of 2.0 denier×5 mm Type N-720H bicomponent binder fiber can be varied from about 0 to about 40 wt. %; the amount of 1.5 denier×0.5″ Type 103 polyester staple fibers can be varied from about 10 to about 30 wt. %; the amount of 6.0 denier×1.0″ Type 103 polyester staple fibers can be varied from about 20 to about 60 wt. %; and the amount of 15.0 denier×1.5″ Type 103 polyester staple fibers can be varied from 0 to about 60 wt. %. 
     Using a fiber furnish of the type described above, a high-strength nonwoven material is formed by a wet-laying process on a conventional papermaking machine. FIG. 1 illustrates an apparatus for preparation of stock or furnish for manufacture of the composite material. The wet-laid forming process begins with stock preparation to make an evenly dispersed mixture of the polymeric fibers. The polymeric fibers are opened (separated) and dispersed in a mixing tank  10 . The mixing tank  10  is equipped with an agitator which provides the shear energy required to effect good fiber separation and dispersion throughout the mix volume. Water, chemicals and fibers are added to the mixing tank  10  in controlled amounts to obtain a desired stock consistency. From an operational point of view, thicker stock consistencies are desirable to minimize preparation time and save on chemical usage. The consistency level should be chosen so that the forming process can be operated at its optimal speed for a particular grade of fabric. 
     With the completion of the stock preparation, the thick stock furnish is transferred to a holding or surge tank  12 , so that the next batch of stock can be prepared. The surge tank  12  is equipped with an agitator to keep the thick stock uniformly mixed. The surge tank  12  meters stock into a web forming machine via a pump  14 . The web forming machine  22  (shown in FIG. 2) may be of the type known as a Fourdrinier or a Rotoformer. The stock is fed to a head box  24  in the forming machine  22  where it is diluted with water to a lower consistency and brought to a forming zone of an endless wire (mesh)  26  moving in a machine direction. In the forming zone, water from the diluted stock is applied to the wire  26  is drawn through the wire, leaving behind the fiber web or sheet. The drained water is then recirculated through a primary water circuit. The temperature to which the polymeric fibers are exposed on the wet-laying machine  22  lies in the range of 325-365° F. During the wet-laying process, the co-polyester sheath materials of the N-720H bicomponent binder fibers (which sheath material has a melting point of 225° F.) melts and then fuses upon cooling to lend strength to the web during further processing. 
     After formation, the web W is transported to a first binder application station  30  by a transfer wire  28 . The first binder application station may comprise any conventional means for applying a water-based solution, emulsion or foam having binder dispersed therein, e.g., a saturator or a foam press. 
     In accordance with preferred embodiments of the invention, the binder is polyvinyl chloride. A preferred water-based emulsion of polyvinyl chloride is Vycar 460×95 (50% solids), which is commercially available from B.F. Goodrich Chemical Company. The Vycar 460×95 polyvinyl chloride binder has a curing temperature of 250-260° F. TN-810 or equivalent polyvinyl chloride binder can be used. The TN-810 polyvinyl chloride binder is commercially available from B.F. Goodrich Chemical Company and has a glass transition temperature greater than 130° F. The TN-810 is moldable in a temperature range of 225° to 300° F. Alternatively, the binder can be polyvinylidene chloride or polyester having a melting point lower than the melting point of the polyester matrix fibers. 
     Referring to FIG. 3, the foam-treated web exits the first binder application station  30  and enters an infrared dryer  32  comprising a plurality of infrared heaters which remove moisture from the web. Then the web is passed through a dryer section  34  comprising a multiplicity of dryer cans  54 , where additional moisture is removed. The dryer cans are heated to a temperature of about 300° F. Since the polyester sheath of the binder fiber has a melting point in the range of 225° to 240° F., the binder fibers are activated, i.e., the sheaths are melted, as the web passes over the dryer cans. Also the binder, which cures at a temperature of 225° to 280° F., are activated. After drying in the first section of dryer cans, the web passes through a second binder application station  38 , which applies a water-based solution, emulsion or foam of binder to the web. The same binder is applied by the first and second binder application stations. 
     The web W is then passed through a second section  40  of dryer cans  36  to again remove moisture following the second binder application. The temperature of the dryer cans in the second section is about 300° F. Again the co-polyester binder fiber sheath material is melted and the polyvinyl chloride binder is activated as the web passes over the dryer cans. Upon cooling of the web, the binder bonds to neighboring matrix fibers. The web is then wound up on a reel  48  for further processing. Optionally, the dried web is calendered, prior to winding, in a calendering section  42  using unheated calender rolls  44  and  46 . 
     The final product is a 100% recyclable, 100% thermoplastic nonwoven liner material. Being 100% thermoplastic in nature, the final product can be molded in a wide range of temperatures ranging from 225° to 300° F. The amount of polyvinyl chloride binder in the final product can be in the range of 25 to 40 wt. % of the total weight of the fibers in the nonwoven web. The first preferred embodiment (described above) has 40 wt. % binder add-on. In this case, with the base furnish weighing 4 oz./yd 2 , the final weight is around 5.6 oz./yd 2 . When samples of the first preferred embodiment were manufactured, the samples had an average stiffness in the machine direction of 2,308.5 mg. 
     The foregoing preferred embodiments have been described for the purpose of illustration only and are not intended to limit the scope of the claims hereinafter. Variations and modifications of the composition and method of manufacture may be devised which are nevertheless within the scope and spirit of the claims appended hereto. For example, the deniers of the various polyester matrix fibers can be varied depending on the molding conditions to be employed. In other words, the invention does not require the specific combination of deniers used in the preferred embodiments described above. Also a lower-melting-point polyester fiber, e.g., made of undrawn or amorphous polyester, can be used as the binder fiber, instead of polyester/copolyester bicomponent fiber, in a proportion from 0-40 wt. % of the total fiber furnish. In addition, bicomponent fibers having geometries other than the sheath/core geometry can be utilized. Depending on the degree of rigidity desired, a small amount of cross-linking agent (up to 10 wt. % of the binder) may be added to the polyester binder. If very high rigidity is desired, a B-stageable formaldehyde-free binder, such as HF-O5 supplied by Rohm &amp; Haas Company, could be used. Other variations in web composition will be apparent to persons skilled in the art.