METHOD FOR PRODUCING SYNTHETIC NON-WOVEN REINFORCED NATURAL FIBER SUBSTRATES

CLAIM OF PRIORITY The present application claims the benefit of priority under the Paris

Convention to U.S. Patent Applications Serial No. 60/717,913, filed on September 16, 2005, Serial No. 60/819,309, filed on July 7, 2006, and Serial No. 60/819,575, filed on July 10, 2006, the entire contents of which are hereby incorporated by reference.

TECHNICALFBELD This invention relates to manufacture of flexible substrates, and more particularly to the manufacture of paper products. BACKGROUND

Reinforced paper substrates are important in several applications, including the manufacture of bank notes. Because bank notes experience significant wear and tear, there is a desire to reinforce such substrates to be more resistant. Currently, attempts have been made to produce such a substrate. Two main methods include gluing and incorporating loose fibers.

The gluing method essentially brings a paper/non-woven/paper "sandwich" together either by adhesives or by utilizing a non-woven that is made up of bi- component fibers, whereas the sheath of the fibers are comprised of a low melt polymer that can be heated to melt and adhere the two individual paper substrates together. United States Patent Application Serial No. 11/266,475 discloses a process which takes a synthetic web roll, two cotton/paper rolls where the three separate rolls are evenly fed together through a series of heated rolls or a heated press which melts the sheath material and essentially glues the three separate substrates together.

Although this is an improvement over plain natural fiber substrates, this process does not solve problems with delamination.

Others incorporate loose reinforcing fibers into the pulp that are then formed into the substrate. It is important to note that these loose fibers are not cross-linked with themselves, and hence only have a limited ability to catch and prevent tearing. SUMMARY

Embodiments of the present invention produce an improved substrate, comprising a core of non-woven synthetic materials encapsulated by regular paper. The encapsulation occurs during the wet paper pulp stage. This encapsulation

provided the same look and feel as normal paper substrates, but many increased strengths also.

Alternative embodiments of the present invention produce normal substrate but with non-woven synthetic inclusions. These inclusions may be used as security devices that are incorporated into the substrate of a security paper. They may have some visual effect such as iridescence, fluorescence, etc. The incorporation of the inclusions into the paper may also occur during the wet paper pulp stage. This incorporation allows the otherwise standard paper new and interesting features such as tactile feel, novel optical features and even other, more covert security features. In regard to the substrate, embodiments of the present invention produce a natural or synthetic fiber (or combination of both) substrate that is stronger and lasts longer, while exhibiting similar printing characteristics as typical paper substrates. Such substrates are useful in many markets, including the currency market. The inclusion of a synthetic cross-linked component (such as a non- woven) within a natural fiber matrix augments an ability to incorporate more advanced security features to thwart counterfeiting efforts, both foreign and domestic. It also enables the inclusion of anti-bacterial components to sustain cleanliness, if so desired.

Embodiments of the present invention further solve delaminating problems as • the synthetic substrate and natural fibers essentially become a single substrate that looks and feels like a normal paper/cotton substrate, but possessing strength properties associated with the polymer core of the substrate. This strength enhancement produces a stronger substrate product that exhibits superior longevity.

Synthetic non-wovens of embodiments of the present invention have a capability of being printed or modified (such as die cut) prior to being incorporated into a natural fiber slurry. This enables a clear and recognizable overt security feature to be incorporated within a natural substrate, which cannot be duplicated. Further, other typical security features may be deployed within the fibers of the non-woven, which may not be able to be implemented into the paper itself.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. IA illustrates a synthetic substrate;

FIG. IB illustrates entangling of fibers in the substrate;

FIG. 1C illustrates the entangled substrate "sandwiched" between encapsulating paper slurry;

FIG. ID illustrates the product of FIG. 1C after being rolled;

FIG. 2A illustrates a headbox;

FIG. 2B illustrates a split headbox;

FIG. 3 illustrates a cut-away view of an embodiment of the present invention; FIG. 4 illustrates an alternative embodiment of the present invention; and

FIG. 5 illustrates a process in accordance with an embodiment of the present invention.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION Embodiments of the present invention use a melt blown or spun-bond synthetic web being fed at some point into a slurry flow of a typical paper manufacturing method, possibly within a "headbox" or between a "split headbox." The substrate material may thus be a "nonwoven," which as the name implies, are fibers formed and bonded together without interweaving them. The individual fibers may be structured fibers or multi-component fibers. The fibers may have an inner core made of one material (nylon) with an outer sheath made from another (polylactic acid or PLA). Virtually any polymer may be used, which may depend upon the application and how the material is to be used and what characteristics of the material are to be achieved. Utilizing multi-component technology allows one to be able to have fibers that are made from a high viscosity polymer (nylon) for strength and a low viscosity polymer (PLA) that may be used for adhesion or for softness. By varying the ratio of the high and low viscosity polymers allows one to dictate how much strength and how soft the fibers are. Also, considerations for the specific gravity of the polymer may be a factor. Other polymers that may be used are polyester, polypropylene, co-polyester, and polyethylene. Further, tertiary materials, such as our phosphors or fluorescent materials, may be added into the core with the surrounding sheath protecting them from the external environment. These can give long life. Additives or sheath/core configurations may be added as the application needs; nylon

may be used where the need is a long lasting component, or PLA where the need is of thermosoftening materials.

FIG. IA illustrates a porous non- woven synthetic substrate 101. Referring to FIG. IB, synthetic web material (or substrate) 101 may be exposed to sonication in the presence of some amount of paper slurry (step 501 in FIG. 5). This forces some of the paper slurry into the open pores of the substrate 101, mechanically entangling fibers 102 of the paper slurry within the synthetic web 101. This increases the bonding between the encapsulating paper 103 and the internal non- woven materials 101.

Referring to FIGS.2A and 5, in step 502, the synthetic web and fiber substrate 120 is evenly distributed or fed into a headbox 203 in such a way that the paper slurry 204 can migrate underneath and above the synthetic substrate 120, as in a typical paper making process. As illustrated in FIG. 1C, this allows the natural fibers 103 to become entangled with the synthetic fibers of the non- woven substrate 101, as well as the web-entrained paper fibers 102, which may be located or placed in the top, middle or bottom of the final natural/synthetic product 104. As the paper making process progresses, in step 503, the water is removed from the slurry by vacuum boxes and rollers 207 located downstream. This vacuum process draws the natural fibers into the synthetic web and causes even further entanglement as shown in FIG. ID. Alternatively, a "split" headbox 209, 210 method may also be used as illustrated in FIG. 2B in a manner similar to FIG. 2A. Single and split headboxes for making paper are well known in the art.

FIG. 3 illustrates a substrate 104 manufactured in accordance with an embodiment of the present invention. The substrate 104 is shown in a cut-away view where the natural paper 103 is cut away to show the non-woven synthetic core 101, 120 inbetween.

Referring to FIG. 4, in a similar manner, the incorporation of large pieces of the non- woven material 403 into the substrate 401 can occur, where these large inclusions may support many security features. These inclusions may be loose from each other, or only connected in a very tenuous manner in the form of a daisy-chain. The embedded inclusions403, may be formed of the same non-woven materials as used in the substratelOl. There are various methods of forming them from the substrates. They include:

1. Die cutting them from a continuous web. This inexpensive process produces many individual inclusions for incorporation into the paper. However, care

must now be taken in order for them to be correctly placed within the substrate, if that is so desired.

2. Forming daisy-chain lengths of the material by die-cutting. This is accomplished by cutting away unwanted areas of the continuous non-woven web, leaving the non-woven structure connected in a tenuous manner. This allows for easier handling and ensures that the security feature are positioned relative to each other corrected.

3. Forming daisy-chain lengths of the material by insertion of obstacles. During the original formation of the continuous non-woven web, pointed-obstacles are placed upon the surface of formation. The non-woven web cannot form on those obstacles, leaving user-defined "holes." This is a very efficient method and does not require a large amount of cutting. It is also a standard industry process.

Further, the synthetic web may be produced as a bi-component spun-bond web in which the sheath is comprised of a specific ratio of a lower melt temperature polymer such as PLA (polylactide), PVA (Poly(vinyl acetate)), or EVA (Ethylene vinyl acetate). This allows for even further adhesion when subjected to a roll heat source 207 that is set at or above the sheath polymer melt temperature. Further, a chemical reaction between non-woven sheath material and pulp may further increase bonding. A number of embodiments of the invention have been described.

Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.