IL28165A - Method for producing metal-non metal fiber webs and the product - Google Patents

Description

SPECIFICATION sip¾ »nanp vfr ~ nsno »a»o Witt ns 1? rupm METHOD FOR PRODUCING METAL-NON METAL FIBER. WEBS AND PRODUCT THE MEAD CORPORATION, a corporation duly organized under the laws of the State of Ohio, of 118 West First Street, Dayton, State of Ohio, U.S.A., DECLARE the nature of this invention and in what manner the same is to be performed This invention relates to new and improved methods for producing webs comprising a major portion of metal fibers, and to the products produced thereby. More particularly, the method of the invention permits the production over extended time periods of continuous metal fiber webs of improved strength using methods analogous to papermaking.

The production of metal fiber webs, wherein the metal fibers are deposited from liquid dispersions is known, and may embody deposition from dispersions containing only metal fibers, or alternatively, may employ dispersions of metal fibers containing suspending fibers of other types, as shown in prior United States Patent No. 2,971,877, granted February 14, 1961. In either case, machines of the type used for papermaking may be employed wherein the metal fiber dispersion is flowed, as by a head box, onto a continuous forming wire.

Following deposition and removal of free liquid through the forming wire, the wet web may be compacted by press rollers, dried, and subjected to such other treatments as may be desired to produce a finished product having properties adapting it to a particular use.

It has now been found that deposition of dispersions comprising metal fibers, whether or not suspending fibers are used, results in the entanglement of some of the metal fibers in the meshes of the forming wire on which they are deposited. Unlike cellulose fibers, which are flexible and may be washed out of the meshes of the forming wire by water jets, metal fibers Ing above and/or below the plane of the wire, are bent or crimped into a "U" shape around the strands making up the forming wire as it passes around the various rolls around which it is trained to complete its travel loop. Once a metal fiber has been so crimped, it is effectively locked in place and can no longer be washed out of the forming wire mesh, even by high velocity water jets.

In a relatively short period of operation, the number of metal fibers so lodged in the forming wire builds up to the point where liquid drainage through the wire is greatly impeded, and operation must be interrupted to replace the forming wire with a new one. Such wires are expensive, and their replacement requires a shutdown of the papermachine and loss of production.

According to the present invention, the entanglement of metal fibers in the meshes of the forming wire is greatly reduced or substantially eliminated so that continuous production may be attained over much greater time periods and the useful life of the forming wires is greatly extended. This is accomplished, according to this invention, by depositing a primary layer of carrier fibers on the forming wire prior to the deposition of the metal fiber dispersion. In one embodiment of the invention, the primary layer of carrier fibers is delivered to the forming wire by means of the first head box of a papermachine, while the metal fiber dispersion is distributed, by means of a secondary head box, on top of the pre-formed primary layer. Not only does this primary layer effectively prevent or greatly r d nt n e t o m tal fib s th es f t forming wire, it also provides additional strength and support to the wet, weak metal fiber web, thus reducing web-breaks and generally improving operating efficiency.

Accordingly, it is a principai object of this invention to provide an improved pioce-is for the manufacture of metal fiber webs wherein forming wire life is extended by preventing or substantially reducing entanglement of metal fibers in the meshes of the forming wire.

A further object is to provide additional support to a metal fiber web to improve its handling properties during its manufacturing steps.

Yet another object is to provide a metal fiber web having a layer of supporting fibers on at least one surface thereof.

Still another object is to provide a method whereby metal fiber webs thinner than was heretofore possible may be produced.

Other objects will become apparent from the description to follow, the appended drawings and the claims.

In the drawings: Figure 1 is a diagrammatic elevation view of one form of apparatus for carrying out the method of the invention; Figure 2 is a schematic cross-section, highly magnified, of one embodiment of the product of the invention; and magnified, of another embodiment of the product of the invention.

Generally speaking, the process of the invention may be carried out on a variety of types of known paper-making machines, in many cases with little or no modification required. Conventional fourdriniers, rotoformers and up-hill wire machines are especially well-adapted to the method, and other known types can be converted, usually at modest cost, to perform the process. The primary requirement resides in the provision of means to deposit a metal fiber dispersion onto a primary layer of supporting fibers, the primary layer being deposited prior to the deposition of the metal fibers.

In Figure 1, a dispersion of supporting fibers is delivered from primary head box 10 onto forming wire 11 of a fourdrinier papermachine. The supporting fibers are formed into a web by drainage of the dispersing liquid, usually water, therefrom, through the action of gravity, table rolls 12 and suction boxes 13, all as well known in the art. A dispersion of metal fibers is delivered by secondary head box 14 onto the primary layer of supporting fibers at 15 and formed into an interfelted layer thereon by removal of the dispersing liquid by means of suction boxes 16 and suction applied by suction couch roll 17. As the metal fiber dispersion is deposited on the primary layer of supporting fibers, there is some intermingling of the metal fibers with the supporting fibers, but this is insufficient to extend through the primary layer, and the metal fibers are enerall revented from comin int direct contact ■with forming wire 11.

Alternatively, the metal fiber dispersion can be deposited on the primary layer of supporting fibers at a point after the primary layer has been removed from forming wire 11, as by up-hill applicator head box 20. The up-hill applicator embodies an endless wire screen 21 trained around rolls 22 , 23, 24 so as to give an upwardly inclined run of screen as shown between rolls 22 and 24, Suction means 25 is located to remove liquid from the metal fiber dispersion through the primary layer and the screen. By using the up-hill applicator for deposition of the metal fiber layer, any possibility of contact between the metal fibers and forming wire 11 is eliminated. Also, intermingling of the metal fibers with supporting fibers in the primary layer is reduced, since the water content of the primary layer is lower in this instance, although some intermingling does occur, and this is desired, since it unites the primary layer with the metal fiber layer into a unitary structure of significantly improved strength compared to that attainable with interfelted metal fibers, either alone or admixed with other suspending fibers.

Following the deposition of the metal fiber layer onto the primary layer, the composite web may be compacted by pressing, by means of press rolls 30» 31 to the desired density and drying or such other manufacturing steps as may be dictated by the intended end use of the metal fiber web. Such steps may involve any one or chemical treatment and the like.

If desired, a three or more layered structure may be produced by depositing a primary layer by means of head box 10, a metal fiber layer or layers by means of one or more secondary head boxes 14, and a top supporting layer by means of up-hill applicator head box 20.

Referring to Figure 2, a diagrammatic sectional view of the product of the invention is shown, wherein the primary layer of supporting fibers is indicated by 40, the metal fiber layer by 4l, and the zone of intermingled metal and supporting fibers by 42.

In similar manner, Figure 3» shows a three layer structure wherein a primary layer is shown at 5, a metal fiber layer at 46 and a top supporting layer at 47. In this instance a first zone of intermingling of metal fibers and supporting fibers is indicated at 48 and a second zone of intermingling of metal fibers and supporting fibers is indicated at 49. Such a product exhibits still higher strength, and has the added advantage of reducing abrasion of press and calender rolls which operate in contact with the composite metal fiber web.

Supporting fibers used for the primary layer may be selected from a wide range of papermaking fibers. Cellulosic < fibers such as rag or wood pulp are generally preferred because of their relatively low cost, but vegetable fibers such as cotton linters, ramie, hemp, sisal, mitsumata and the like are effective, as also are and the like. Sub-micron glass fibers may also be used, since such fibers, with a diameter ranging from 0.2 to 1.0 microns, deposit into a web of adequate strength for this use and will also prevent or minimize entanglement of metal fibers in the meshes of the forming wire. To a degree, the subsequent processing steps and the end use of the metal fiber web will govern the choice of the fibers to be used in the primary layer.

Cellulosic fibers such as rag are well-suited for use when the finished product is to be a sintered metal fiber web free of organic matter, as these can be completely removed in the sintering operation.

The thickness or weight of the primary layer may fall within fairly wide limits, and again, the end use requirements and type of metal fiber used will govern the acceptable or preferred range. In most instances, the primary layer should be of a minimum thickness to protect the forming wire and provide adequate strength for handling the composite metal fiber web through the remaining steps of the process. Generally, primary layers weighing from 6 to 10 pounds, dry basis, per ream of 3000 square feet are effective, although higher weights per ream than this may be desired for some purposes. The higher ream weights are preferred for use with relatively short metal fibers of relatively large cross sectional area, while the lower ream weights are preferred for use with relatively long metal fibers of relatively small cross sectional area. Likewise, the thickness or weight per unit area of the metal fiber for the supporting layer, the thicker metal fiber layers generally permitting the use of thicker primary layers.

By way of illustration but not by way of limiting the invention, the following specific examples are given: Example 1 Cotton rag pulp, beaten to a freeness of 280 ml (Canadian standard) and at a consistency of 0.5$ was delivered to the primary head box of a fourdrinier papemachine and a web formed therefrom having a basis weight (dry basis) of 8 lb. per ream of 3000 square feet. Concomitantly, nickel fibers dispersed in water at a concentration of 5% by weight were delivered to the secondary head box of the same papermachine. The nickel fibers were deposited as an interfelted web weighing 260 lb., dry basis, per ream of 3000 square feet. The composite web, weighing 268 lb. (dry basis) per 3000 square feet, and having a bottom primary layer of supporting rag fibers and a metal fiber layer of nickel fibers was pressed and dried. Examination of the product showed a zone of intermingling of the rag and nickel fibers in the region where the two layers came together, and the structure was unitary, in the sense that the two layers could not be separated without destroying the web structure of the layers. Subsequently, the composite web was sintered in an inert atmosphere whereby the supporting layer was substantially completely burned away. The sintered nickel web was suitable for use as a battery electrode.

Examination of the forming wire of the paper- dujpation, revealed only an insignificant number of nickel fibers entangled in its meshes.

Example 2 1.5 denier acrylic fibers of papermaking length were suspended in water at a consistency of 0,1% and delivered to the primary head box of a fourdrinier papermachine and a primary layer formed therefrom having a basis weight (dry basis) of 10 lb. per ream of 3000 square feet. A dispersion of stainless steel metal fibers containing 7.5$ by weight (dry basis) of highly beaten rag fibers and having a total fiber concentration in the dispersion of 8 by weight was delivered to the head box of an up-hill applicator located between the wire section and the press section of the same fourdrinier machine. A layer of stainless steel fibers having rag fibers intermixed therewith was deposited on top of the primary layer of acrylic fibers. This stainless steel fiber layer weighed 600 lb. (dry basis) per 3000 square feet. The resulting composite web was pressed and dried, and had adequate strength for the handling required in its further processing. Examination of the product revealed a zone between the acrylic primary layer and the stainless steel fiber layer wherein there was intermingling of the fibers making up the two layers. In this example, the stainless steel fibers were added to the system at a point beyond the fourdrinier forming wire section, so there was no possibility for entanglement of the stainless steel fibers in the meshes of the forming wire. Likewise, the pre-formed entanglement of stainless steel fibers in the wire screen of the up-hill applicator.

Claims (11)

Ρ.Α. 28165/1 WHAT IS CLAIMED ISt - non metal

1. Process for producing metal/fiber webs comprising the steps of depositing on a wire screen of a papermaking machine an aqueous slurry of nonmetalllc fibers* draining the aqueous dispersing agent from the nonmetalllc fibers deposited on said wire screen, depositing on the resulting web of nonmetalllc fibers an aqueous dispersion of metallic fibers,, draining from the resulting web the aqueous dispersing, agent, thereby producing a composite web composed of metallic and nonmetalllc fibers.

2. The method of claim 1 wherein the supporting ibers are rag fibers.

3. · The method of claim 1 wherein the supporting fibers are synthetic organic fibers.

4. The method of claim 3 wherein the synthetic organic fibers are acrylic fibers.

5. · The method of claim 1 wherein the supporting fibers are glass fibers having a diameter of from 0.2 to 1.0 microns.

6. * The method of claim 1 wherein the primary layer of supporting fibers amounts to 6 to 10 pounds (dry basis) per 3000 square feet.

7. The method of claim 1 wherein supporting fibers in the top of the primary layer intermingle with metal fibers in the bottom of the metal fiber layer, so as to produce a zone of intermingled supporting fibers and metal fibers.

8. A composite metallic-nonmetallic fiber web comprising a primary supporting laye of nonmetalllc fibers o which is a secondary layer of metallic fibers wherein / the fibers of said primary and said secondary layers are intermingled at the point of contact of the two layers.

9. The composite metal fiber web of claim 8 wherein there is a zone of Intermingled supporting fibers and metal fibers between said primary layer and eaid secondary layer. ',''■ ' . ·

10. The composite metal fiber web of claim 8 wherein the primary layer amounts to 6 to 10 pounds, dry basisj per 3000 square feet.

11. Δ method of producing webs substantially as described and set forth in the foregoing description. ¾2. A composite metal fiber web substantially as described' and illustrated in the accompanying drawings.