US3094454A - Paper making with synthetic fibers - Google Patents

Description

June 18, 1963 c. B. MOORE 3,094,454

PAPER MAKING WITH SYNTHETIC FIBERS Filed Jan. 5. 1961 United States Patent 3,094,454 PAPER MAKING WITH SYNTHETIC FIBERS Charles B. Moore, Scituate, Mass., assignor to W. R.

Grace & (10., Cambridge, Mass, a corporation of Connecticut Filed Jan. 3, 1961, Ser. No. 80,431 4 Claims. (Cl. 162-157) This invention is concerned with the manufacture of paper and similar materials from thermoplastic fibers which are not amenable to being handled in conventional paper-making equipment.

Cellulose fibers coated with a polyolefin have recently become available. For example, see Belgian Patent No. 575,559, dated February 10, 1959, issued in the name of National Lead Company. These fibers are hydrophobic and display no, or very little, fiber-to-fiber bonding or cohesiveness when formed as a Wet web in a conventional paper-making manner. There is, however, a desideratum for forming paper in large volumes from these fibers because of their unusual properties, e.g. chemical inertness, pore structure, and thermoplasticity.

In brief compass, the present invention is a paper-making process comprising forming an aqueous slurry or papermaking stock of a surfactant and hydrophobic polyolefin coated cellulose fibers in the head box of a paper-making machine. The paper-making machine is conventional and has a moving endless filter screen. The filter screen supports a smooth surface fabric felt having a relatively low drain time. The stock is flowed on to the felt and the water is drained therefrom through the felt and screen, forming a web of the fibers on the felt. The web so formed is then dried of water, while still supported by the felt. Mechanical compaction of the web and felt is avoided as much as possible. The dried web is immediately thereafter heated to a softening temperature in the range of 250 F. to 350 F. to fuse the polyolefin and impart coherency to the web. The web is thereafter cooled and stripped from the felt to obtain a self-supporting web of the polyolefin coated fibers that could not be obtained in any other manner at comparable production rates.

This invention will become clear from the following discussion and description of the drawing attached to and forming a part of this specification. The drawing illustrates the application of the principles of this inventlon to the formation of a coherent web of thermoplastic fibers using one type of cylinder paper-making machine.

The fibers used in the present invention are basically cellulose fibers coated with a polyolefin such as a polystyrene, polybutadiene or polyisoprene, but preferably a polyethylene, a polypropylene, or mixtures thereof. The cellulose fibers give shape to the polyolefin. The cellulose typically has an average length of about 1 to 20 milli meters although any length that can be formed into a paper can be used. The cellulose fibers can be any of those conventionally used for paper-making such as bleached or unbleached hard or soft wood sulphites or sulphates, soda-flock, cotton linters, manila hemp and synthetic fibers. The polyolefin can be placed on the fibers through the use of solvents, but it is preferred to form the polyolefin in situ by first impregnating the cellulose, while carried in finely divided form in an anhydrous hydrocarbon liquid with a polymerization catalyst, such as a titanium or zirconium compound, followed by contact with the monoolefin under polymerization conditions. The polyolefin comprises to 75 weight percent of the reaction product and the remainder is cellulose. The polyolefin preferably has a softening point in the range of 250 F. to 350 F. The polyolefin essentially coats all of the fibers and some of it will usually appear as nodules on the fibers.

A paper-making slurry is formed from the thermoplastic ice fibers by the use of a surfactant, since the fibers are hydrophobic. Such surfactants as polyethylene glycol terdodecyl thioether (Nonic 218), polyoxyethylated fatty alcohols (Emulphor ON-870) and the dioctyl ester of sodium sulfosuccinic acid (Aerosol OT) are satisfactory. The amount of surfactant used will vary, but will usually be in the range of 0.05 to 0.1 Weight percent based on dry fibers. The consistency of the stock is about 0.01 to 1 percent, preferably 0.01 to 0.1 percent (dry basis). The fibers do not respond to mechanical action such as heating in a conventional manner. They can be dispersed in water by simple agitation, with any lumps being mechanically dispersed as is necessary. The fibers are very loose, usually giving freeness readings above 700 cubic centimeters Canadian Standard. No additional binders, such as glue and starch, are necessary or desirable.

The sheet or felt used to support the web until it is rendered coherent in accordance with this invention can be a woven material such as a cheese cloth, or it can be a nonwoven material. It has a relatively smooth surface to prevent undue adhesion of the fibers to the web. The felt is relatively open and does not materially alter the water drainage rate and the rate of paper formation from that obtained with the screen alone. The felt should allow 400 cubic centimeters of air to pass through 8 plies in 4 to 10 seconds as measured with a Gurley densimeter equipped with a 5 ounce cylinder and A inch diameter orifice. Slower draining felts have been used, however, by slowing the machine down sufficiently to compensate for the slow drainage. It is preferred to use felts made from nonwovens because they are inexpensive and can be discarded after several passes through the machine. While a continuous self-returning belt of Woven fabric might possibly be used, it is mechanically difiicult to provide for the extreme lengths necessary to support the web from the head box to the final heating and fusion step.

Either a Fourdrinier or a cylinder machine can be used. The supporting felt is placed onto the Wire screen of the paper-making machine prior to the laying down of the stock. The stock is flowed onto the web in an amount sufiicient to obtain the desired thickness, usually 10 to 400 pounds of fiber per 3000 square feet, and is drained and at least partially dried before the fusion step.

It is the custom in most paper-making processes to mechanically press the Web to squeeze Water therefrom before resorting to heat drying. This results in some compaction of the Web, and in the present process, some intermingling of the web fibers with the felt, making the final stripping or separating of the felt and web more difficult. It is preferred, therefore, not to subject the webfelt strip to severe mechanical compaction or compression by rolling or similar methods prior to the fusion step.

The web is set or fused as by running it over a heated roller or can through an infrared unit or through an air or festoon dryer, and heating it to a temperature sufiicient to permit contiguous fiber bonding. Total fusion of the fibers need not be carried out at this point. It is satisfactory if sufficient bonding takes place to give the web enough coherency to be self-supporting under whatever additional treatment may be desired. After the web fusion step, the webis allowed to cool and is then separated from the felt by simple stripping.

The papers thus obtained can be fabricated into excellent battery separators by pressing between heated plates having the desired configuration. Depending on the polyolefin content, the paper will also find use per se as a filter medium, especially for corrosive materials, as a coating base, and as a cushioning or packing material. The papers of relatively high polyolefin content can readily be molded into disposable cups and dishes, milk bottles, and floor tiles.

Example A polyethylene coated cellulose is prepared as follows.

Reactants: Weight percent Solka-Floc 47.0 Toluene 23.7 TiCl 11.8 CH MgBr 17.5

Disperse the Solka-Floc (a pure alpha cellulose) in the toluene (anhydrous), and react the titanium tetrachloride therewith for one hour at room temperature under a nitrogen atmosphere. Add the methyl magnesium bromide and raise the temperature to 131 F. Bubble ethylene therethrough at a pressure of 25 pounds per square inchuntil an-amount by weight about equal to the cellulose has been added. Cool the solution and add an equal volume of methanol. Follow by filtering and washing with additional methanol. A white powdery fiber containing about 50 weight percent polyethylene is obtained after desiccation. The preparation of the thermoplastic fibers is known to the prior art and is not part of the present invention.

A stock'having the consistency of two percent is made from the fibers using 0.1 weight percent on dry fibers of sodium dioctyl sulfosuccinateas a dispersant, by simple admixing in a pulper. The stock has a freeness of about 760 cubic centimeters Canadian Standard. The stock is then diluted to a consistency of 0.05 percent.

With-reference to the drawing, the diluted stock is added to the head box 1 of a cylinder machine 2, eg a Rotoformer (trademarkofSandy Hill Iron and Brass Works). The cylinder carries a screen having a diameter of about 48 inches. The cylinder is equipped with suction boxes 3. The cylinder forms a paper strip 29 inches wide at a rate of 20' feet per minute. The dry weight of the paper web is 220 pounds per 3000 square feet (500 sheets, 24 inches by 3 6 inches) The felt is picked up by the cylinder from feed roll 4 prior to the head box. The felt passes between the head box apron and the cylinder wire, the web is deposited thereon and the continuous web-felt sheet then passes under a light couch roll 5. The felt is a nonwoven, formed from air laid cotton and nylon fibers over /2 inch long, and bonded together with a small amount of butadiene-styrene elastomer. It has a ream weight of 36 pounds (500- sheets 24 inches by 36 inches), at caliper of 0.011 inch, and an S-ply Gurley densimeter t me of 4.2

seconds (5 ounce cylinder, 400 cubic centimeters, 4 inch opening). This nonwoven is commercially available as Lantuck 4400T Prebond sold by West Point Manufacturing Company.

The strip is passed from cylinder 2 to a series of twenty drying drums'7, only a part of which isshown and heated to about 300 F. The drums are four feet in diameter. The moisture content of the web is reduced by the drying to about three percent. The web is then passed to fusion rolls 8 where the web is heated momentarily to a temperature of 325 F. It is then allowed to cool while passing over roller 10 which is water cooled. A high velocity jet dryer has also been used to dry and set the web.

The web-felt strip is then passed through stripper rolls 11 with the felt being Wound up on roll 13 for reuse. The total linear distance of travel from the head box to the stripping rolls is about 130 feet. The twenty feet per minute rate of this example is low compared to commercial practice. At commercial speeds it would be impractical to provide for continuous return of the felt. Conventional splicing arrangements are provided at feed roll 4 to provide continuous addition of the felt to the process.

The web stripped from the felt is shown as being wound on wind-up roll 14. It ma, however, be directly passed on to whatever further conventional treatment may be desired, such as calendering, impregnation, or coating. The web obtained as described is buff colored and has a caliper of mils.

While the preparation of a fairly heavy paper has been described, it will be appreciated that the process of this invention also permits relatively thin papers to be formed from the polyolefin coated fibers without difficulty because of the support given by the felt.

\ Conventional pulps, especially of long fibers (10 to 20 millimeters average length) can be added to the stock in amounts up to 20 weight percent of the coated cellulose, which is insufficient to give self-supporting characteristics to the wet web.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. A paper-making process comprising flowing an aqueous paper-making stock of a surfactant and hydrophobic polyolefin coated cellulose fibers from the head box of a paper-making machine having a moving, endless filter screen onto a relatively smooth surfaced felt supported by said screen, drawing the water thereof through said felt and screen forming thereby a Web of said fibers on said felt, drying and fusing the polyolefin content of said fibers by heating said web while supported by said felt and prior to any appreciable mechanical compaction thereof to a temperature in the range of 250 F. to 350 F., cooling the web, and stripping said web now in coherent form from said felt.

2. The process of claim 1 wherein said polyolefin is polyethylene formed in situ on said cellulose by the catalytic polymerization of ethylene on catalyst impregnated cellulose fibers carried in an anhydrous liquid hydrocarbon, said polyethylene amounting to about 10 to weight percent of the fibers.

3. The process of claim 2 wherein said felt is an air laid nonwoven material comprised of cotton and nylon fibers bonded together with a minor amount of an elastomer.

References Cited in the file of this patent UNITED STATES PATENTS Milkey Apr. 19, 1932 Hanson Sept. 13, 1949

Claims (1)

1. A PAPER-MAKING PROCESS COMPRISING FLOWING AN AQUEOUS PAPER-,AKING STOCK OF A SURFACTANT AND HYDROPHOBIC POLYOLEFIN COATED CELLULOSE FIBERS FROM THE HEAD BOX OF A PAPER-MAKING MACHINE HAVING A MOVING, ENDLES FILTER SCREEN ONTO A RELATIVELY SMOOTH SURFACED FELT SUPPORTED BY SAID SCREEN, DRAWING THE WATER THERETO THROUGH SAID FELT AND SCREEN FORMING THEREBY A WEB OF SAID FIBERS ON SAID FELT, DRYING AND FUSING THE POLYOLEFIN CONTACT OF SAID

Images