GB2287482A - Synthetic paper pulp - Google Patents

Abstract

A synthetic paper pulp consists substantially of fibrillated polyethylenenaphthalatebibenzoate (PENBB) fibers. The steps according to the method of the invention include spinning multifilament PENBB fibers through a spinerette as shown adapted to maximize fibrillation by increasing the discontinuity of the flow extensional strain rate, stapling the fibers into staple lengths suitable for paper pulp formation, and mixing the staple fibers with water to form a fiber/water slurry. The method further includes the steps of refining the staple fibers in the slurry by processing the slurry through an attrition zone to fibrillate the fibers, forming a thin layer of fibrillated fibers on a support surface by screening the slurry to remove the water therefrom, and drying the screened fibers to form a paper sheet. <IMAGE>

Description

PENBB PAPER PULP, PAPER AND METHOD Technical Field and Backaround of the Invention This invention relates to paper formed substantially of fibrillated polyethylene-naphthalatebibenzoate (PENBB) fibers, and the associated method of manufacturing paper from PENBB fibers.

Of particular note is the characteristic of PENBB which causes PENBB fibers to fibrillate, i.e., to split into a multitude of fibrils by splitting along the axis of the fiber.

The ability of the fiber to fibrillate in this manner makes it possible to create paper. The ability to alter its fibrillating characteristics as described below permits a very wide range of uses, including circuit boards, filter media, electrical insulation, and other products common to papers and nonwovens.

PENBB fiber and its synthesis is described in applicant's published PCT Application No. WO 93/02122. Research into the properties and characteristics of PENBB has demonstrated that certain such properties and characteristics lend themselves to application in high performance tent fabrics and tents. PENBB fiber fabric exhibits many of the advantageous characteristics of polyethyleneteraphthalate (PET), such as light weight and good strength, while substantially exceeding other PET fiber characteristics which have heretofore been barriers to optimal fabric performance.

The term paper is traditionally applied to felted or matted sheets of cellulose fibers formed on a fine wire screen from a dilute water suspension, and bonded together as the water is removed and the sheet is dried. In current usage, paper may also include sheet materials produced from other types of fibers (particularly mineral or synthetic) formed and bonded by other means. The invention according to this application falls with this category of usage.

Its principal uses include high value-added applications where the unique qualities of the PENBB fiber are best put to advantage, as explained below.

Other fibrous materials, particularly some of the synthetic high polymers, are being used in papermaking. PENBB has qualities and characteristics which lend it to this type of application.

Paper manufacture is largely a mechanical operation, although the chemical aspects are important in determining the final sheet properties. The tendency of fibers to bond together when dried from a water suspension provides the basis of papermaking technology. Unmodified cellulose fibers, as obtained from pulping and bleaching operations, are generally unsuited for papermaking. They must first be refined. The refining operation is conducted mechanically in beaters or refiners such as hollander beaters. During refining, the pulp fibers are separated, crushed, frayed, fibrillated, and cut. They imbibe water and swell, becoming fore flexible and more pliable. Papers made from lightly beaten stocks are typically of low density, soft, and porous, whereas papers from heavily beaten stock are dense, hard and much stronger. With given pulps, final paper properties are largely controlled through the type and extent of refining action employed.

A major factor contributing to paper sheet strength is fiber-to-fiber bonding. These bonds, which may be largely but not exclusively on the hydrogen-bond type, develop as the wet, plasticized, swollen fibers are brought into intimate contact during the drainage, pressing, and drying processes. Many grades of paper receive some type of treatment after formation and drying in order to enhance certain desirable characteristics.

PENBB fibers have characteristics which permit the production of very high quality paper over a wide range of thicknesses, stiffnesses and the like, even to the point where the result is a paperboard-type product having a stiffness greater than can typically be achieved with a pulp or cotton sheet of similar thickness. The synthetic nature of the PENBB fibers and their manufacture under controlled conditions provide substantial benefits over use of wood pulp or cotton, as well as other synthetic papers such as polyethylene and polyolefin-based papers and wet-lay nonwovens.

Summarv of the Invention It is an object of the invention to provide a paper formed of fibrillated polyethylene-naphthalatebibenzoate (PENBB) fibers.

This and other objects of the present invention are achieved in the preferred embodiments disclosed below by providing a paper comprised of fibrillated polyethylene-naphthalatebibenzoate (PENBB) fibers.

According to yet another preferred embodiment of the invention, the synthetic paper may be used in electrical insulation or a fluid filter medium.

An embodiment of the method of manufacturing paper from PENBB fibers according to the present invention comprises the steps of spinning PENBB filaments through a capillary adapted to maximize fiber fibrillation potential by increasing the degree of discontinuity of the polymer flow extensional strain rate, and cutting into staple filament fibers into staple lengths suitable for paper pulp information, and mixing the staple fibers with water to form a fiber/water slurry. The method further includes the steps of refining the staple fibers are refined in the slurry by processing the slurry through an attrition zone to fibrillate the fibers forming a thick layer of fibrillated fibers on a support surface by screening the slurry to remove the water therefrom, and drying the dewatered fibers to form a paper sheet.

Brief DescriDtion of the Drawings Some of the objects of the invention have been set forth above. Other objects and advantages of the invention will appear as the invention proceeds when taken in conjunction with the following drawings, in which: Figures 1-3 are diagrams of spinnerette profiles illustrating designs which enhance fibril formation during the pulpmaking process; Figure 4 is a diagram of fibril formation during refining of the fibers in the attrition zone of the papermaking process.

Description of the Preferred Embodiment and Best Mode Polyethylenenaphthalatebibenzoate (PENBB) fibers are formed using a conventional polyester fiber spinning process, with the exception that the spinnerette has been designed to maximize fibrillation of the fibers during downstream processing. As noted above in the general discussion of the papermaking process, fibrillation is a key to the manufacture of paper. Fibrillation greatly increases the fiber surface area available for fiber-tofiber bonding. It has been observed that PENBB fibers can be made in such a way as to enhance the fibrillation process and thus create a fiber slurry with a vastly increased number of fiber-to-fiber bonding sites.

To accomplish this, the capillary of the spinnerette is configured to increase the degree of discontinuity in the flow extensional strain rate. Referring to Figures 1, 2 and 3 of the drawings, Figures 1 and 2 illustrate suitable profiles for spinnerettes used to extrude PENBB filaments specifically intended for paper production. Figure 3 illustrates a spinnerette profile which would minimize fibril formation during downstream processing. Note the rather severe, straight line taper to the spinnerette orifice in Figures 1 and 2 in contrast to the gradual taper shown in Figure 3. The gradual taper shown in Figure 3 produces areas of increased, continuous strain running in a longitudinal direction along the filament shaft. To optimize the fibrilization potential of the PENBB fiber the spinnerette orifice needs to introduce a discontinuation of the strain rate in the direction of the polymer flow such as in Figures 1 and 2.

The continuous filament fiber produced at the spinnerette must be cut into an appropriate staple length such as .25 inches (6 mm) before the paper formation process begins. This is typically done by winding the tow band around a cutter wheel as pressure is applied to the tow band. The cutter wheel creates a weakness area transverse to the longitudinal axis of the fiber shaft. The pressure applied to the tow band causes the fiber shaft to separate at the weakness areas. Staple length can vary considerably depending on determined end product characteristics, but a staple length of .25 to .50 inches (6 mm to 12 mm) is typical for PENBB fibers used in the present invention.

Since the process of cutting the continuous filament tow bands into staple lengths is conventional, further discussion is unnecessary.

As described generally above, fibers are formed into a suitable pulp for papermaking by mechanical work on the fiber.

The characteristics of PENBB as enhanced by spinnerette configuration, described above with reference to Figures 1, 2 and 3, lend themselves to the manufacture of papers of enhanced quality. PENBB is fibrillated during the refining process, preferably by use of a disc refiner. A beater or jordan can also be used.

The refining process includes running a fiber/water slurry through an attrition zone. The fiber to water ratio depends on the device used, i.e. disc refiner, beater, etc., but can be from less than one percent fiber to as much as 20 percent fiber, or more.

Referring now to Figure 4, a PENBB fiber 10 is shown (300X).

Note a plurality of fibrils 11, which are not yet separated from the shaft of the fiber 10. A shearing action on the fibers created by the disc refiner or beater splits the fiber 10 into fibrils 11. In other words, the fiber 10 splits into longitudinal strips which may be the same length as the length of the staple fiber, but of much small diameter, or may form only on the ends of the fiber, extending some portion but not all of the length of the fiber.

PENBB has characteristics which permit it to fibrillate into many fibrils at the end of the fiber. This provides an enormous increase in surface area. In effect, the fiber strand is "peeled"--the fibrils being the portions of the strand which are peeled all or partially away from the main filament shaft. The degree of fibrillation is substantially higher than other synthetic fibers, such as polyethylene (PE), polyethylenenapthalate (PEN), polyethyleneteraphthalate (PET), and polypropylene (PP).

PENBB pulp made by the process described above is dispersed in water via a hydropulper or other agitator system commonly found in paper or wet lay nonwovens manufacturing facilities.

Consistency at this point is generally in the range of 0.5 percent to 6 percent. The slurry is then pumped to a mix chest or stock chest and diluted generally to a consistency of 0.1 percent to 1 percent. Depending on the arrangement of the stock system, additional intermediate chests may be used. Final dilution to the head box is generally in the rage of 0.01 percent to 0.2 percent. The slurry is then formed into a web by dewatering onto a moving porous screen in the typical manner of paper or wet laid nonwovens. The wet web is then dried and taken up as a continuous roll.

Overall, the process of producing paper from PENBB fiber is conventional, and those of ordinary skill in the art will recognize that the characteristics of the paper products manufactured from PENBB fiber can be optimized or varied by alterations in the processing carried out during pulp preparation and refining, as with other fibers.

Referring now to Figure 5, a circuit board 20 is shown, the substrate of which being manufactured from PENBB paper. The paper is processed in such a way as to provide a very thin and lightweight, yet relatively stiff paper suitable for carrying electronic circuitry. The thermal, physical and chemical properties of PENBB, including its dielectric capacity, lends it to use in environments where electrical insulation is necessary.

The PENBB may be coated or impregnated with an epoxy or thermosetting resin to provide stiffness and a uniform surface.

The thinness and low weight combined with stiffness and strength are particularly important in the fabrication of new, lightweight computers, such as laptop and notebook computers where weight and space-saving are critical.

Referring to Figure 6, PENBB paper fabricated for use as electrical insulation is illustrated. Of course, numerous applications are possible, including fabrication of the PENBB paper into sheets, strips, tapes, batt coverings and backings.

In Figure 6, the PENBB paper is shown as an insulative tape covering an electrically conductive wire 30. The PENBB paper tape shown in Figure 6 is formed by a slitting process carried out after paper formation. When used as electrical insulation, the PENBB paper may be typically slit into widths of between 0.25 and 0.5 inches (6-12 mm).

Figure 7 illustrates the use of PENBB paper as a filter medium 40. In this application, the paper would be processed to be Qas permeable, with the fibers, filaments and fibrils acting as traps for accumulating particulate matter entrained in a moving gas stream on the upstream side of the filter medium. The degree of porosity is determined according to the size and quantity of the material to be filtered. The hydrophobic nature of the PENBB fiber permits the material to be used to filter liquids, as well.

A PENBB paper pulp, paper and method of producing PENBB paper is described above. Various details of the invention may be changed without departing from its scope. Furthermore, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation--the invention being defined by the claims.

Claims (6)

We claim:

1. A synthetic paper pulp comprised substantially of fibrillated polyethylenenaphthalatebibenzoate (PENBB) fibers.

2. A synthetic paper comprised substantially of fibrillated polyethylenenaphthalatebibenzoate (PENBB) fibers.

3. A synthetic paper according to claim 2, wherein said fibers are staple fibers and have a staple length of between approximately .25 inches and 2 inches (6 mm and 50 mm).

4. A synthetic paper according to claim 2, and characterized by being relatively strong, lightweight and flexible.

5. A synthetic paper according to claim 2, wherein said synthetic paper comprises electrical insulation in the form of a wrapped tape for wrapping around electrically conductive wire.

6. A method of manufacturing synthetic paper from PENBB fibers, comprising the steps of: (a) spinning multifilament PENBB fibers through a capillary adapted to maximize fiber fibrillation by increasing the degree of discontinuity of the flow extensional strain rate; (b) cutting stapling multifilament PENBB fibers into staple lengths suitable for paper pulp formation; (c) mixing said staple fibers with water to form a fiber/water slurry; (d) refining said staple fibers in said slurry by processing said slurry through an attrition zone to fibrillate the fibers in the slurry; (e) forming a thin layer of fibrillated fibers on a support surface by screening the slurry to remove the water therefrom; and (f) drying the screened fibers to form a paper sheet.