US 3097991 A
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I y 1963 w. A. MILLER ETAL 3,097,991
SYNTHETIC FIBROUS PRODUCTS Filed June 10, 1957 INVENTORS WALTER A. MILLER CHARLES N. MERRIAM,JR.
By M 4/6 A TORNEY 3,097,991 SYNTHETIC FIBROUS PRODUCTS Walter A. Miller, North Caldwell, and Charles N. Merrram, Jr., Florham Park, N.J., assigiors to Union Carbide Corporation, a corporation of New York Filed June 10, 1957, Ser. No. 664,772 6 Claims. (Cl. 162-157) The present invention relates generally to paper making and more particularly to specialty paper or paper-like products and to synthetic fiber pulps suitable for making paper containing synthetic fibers in combination with natural cellulosic paper making fibers.
During recent years a need has developed throughout industry for a better paper or paper product containing one or more types of synthetic fibers. Several synthetic fiber paper compositions and processes by which such paper can be made have been proposed. For certain rather limited and specialized purposes, the prior art compositions have been successful. However because the synthetic fibers contained in these compositions are not at all similar in structure to natural paper making fibers, the compositions have not been successful in the vast number of situations where a product is required which has essentially paper-like characteristics in addition to certain qualities not found in natural fiber paper. Such papers should have improved flexing qualities and crease resistance, high tensile and bursting strengths both when wet and when dry, be at least as resistant to high temperatures as natural fiber paper and be simply and economically produced.
One of the most critical points in making paper from synthetic fibers is in removing the web or water laid sheet from the forming screen in the case of a Fourdrinier type machine or the cylinder of a cylinder type machine. At this point the web must be strong enough to support itself though thoroughly wet. With natural fiber pulps, i.e., those made from any type of cellulosic material such as wood pulp, rags, or even straw, the web easily supports itself due to a high degree of interfelting of the fibers brought about by proper beating of the pulp. Heretofore, the synthetic fibers proposed for use in paper making have not been capable of interfeltin'g to any appreciable degree. As a consequence the paper made from these fibers had a low wet strength especially when only a small amount of the total fiber content was of the cellulosic type.
Interfelting is primarily due to an intertangling of microscopic fibrallae on the surface of a fiber with the fibrallae of other fibers. The synthetic fibers that have been proposed, prior to the present invention, for paper making have been extruded or spun through very small orifices either in solution on in the molten state to form long continuous fibers, the surfaces of which are quite smooth and slippery. As such they have no fibrallae to interfelt. Nor are they capable of being easily and uniformly dispersed in a water media or of fibrillating by being beaten while dispersed in water as is the case with natural fibers. A specific example of the difiiculty encountered with this type of fiber was demonstrated when an attempt was made to form a paper sheet from Dynel, a vinyl chloride-acrylonitrile copolymer. Whereas vinyl fibers in general, when woven into fabric, are known to Patented July 16, 1963 ice have a very high inter-fiber friction as compared to other extruded or spun synthetic fibers, Dynel fibers have in addition a highly irregular cross-section shape which increases inter-fiber friction. It is significant to note therefore, that when this resin was extruded into fine fibers, chopped into to A inch lengths, and sheeted in the conventional manner on a laboratory hand sheeting machine, the sheet produced could not 'be removed from the screen without tearing and was not self-sustaining.
To a certain extent the lack of fibrillae in synthetic fibers can be compensated for by causing the fibers to bond to each other in such a manner that the bonding forces are molecular rather than mechanical. subjecting a synthetic fiber web to the action of heat or a suitable solvent, or both, may bring about this bonding. The effect of either treatment is to soften the fibers to such an extent that fusion occurs at the points of contact of the fibers with each other. Such methods are usually difiicult to control, require the use of hazardous inflammable solvents, and to some extent destroy the molecular orientation frequently induced in the raw fibers to increase their strength and resistance to degeneration by ultra violet light.
Apart from the problem of wet strength of synthetic fiber paper, there exists the problem of producing raw fibers in the desired length and fineness for paper making. This is in large measure due to the difii-culty encountered in converting continuous extruded or spun fibers of suitable fineness into staple lengths for incorporation into paper.
Applicants have now been able to produce a superior pulp and a paper product made therefrom containing, in combination with natural fibers conventionally used in paper pulps, a substantial percentage of synthetic fibers. The actual ratio of synthetic to natural fibers may vary over a wide range depending primarily on the chemical composition of the synthetic fiber used and the use to which the paper or paper-like product is to be put. These new paper products are characterized by having synthetic fibers whose surface and ends are frayed into minute tendrils or fibrillae. The physical structure of these fibers being similar to that of natural fibers, a much higher degree of interfelting occurs than in pulps made from synthetic fibers by prior known methods.
With the improved interfelting qualities of the paper product coming within the scope of the present invention, there is no longer any need to incorporate synthetic fibers having a softening point low enough to be rendered tacky at temperatures below C. Synthetic fibers having either a high or a low softening point may be used or a combination of the two, depending on the properties required in the finished paper.
This invention utilizes as a base material to form feltable paper forming fibers, stretch oriented synthetic monofilaments prepared by the extrusion of a mixture of two or more linear polymeric thermoplastic materials, mutually incompatible with each other, through a single orifice die forming a composite monofilament product. By the term monofilament as used in the invention is meant the product obtained by melt extrusion of a mixture of two or more incompatible thermoplastic resins, said monofiiament after extrusion having been stretch oriented. This monofilament is composed of individual fibrils having longitudinal axes essentially parallel to each other and are weakly attached in a lateral direction, i.e., contact of one fibril with another is along a line running longitudinally along the outer surface of the fibrils. Fibril groups, comprised of several fibrils of each of the incompatible resin making up the monofilament, when split off from the monofilament are designated as fibers. The number of fibrils comprising each fiber may be in the range of about 2 to 100.
Such monofilaments may be produced according to the following generalized process steps. Two or more incompatible resins may be blended by mixing them on heated differential rolls, in a kneader, or with a Banbury mixer, or any other suitable means for obtaining an intimate mixture, such as dissolving them in a solvent and then evaporating the solvent. When mechanical mixing is employed, the temperatures used for mixing will vary but should be sufiicient to give a well dispersed mixture but not high enough to induce decomposition. The fiuxed sheets are cooled, granulated to a suitable size, and fed to an extruder.
The mixture may be extruded in any conventional extruder operated at a temperature low enough to prevent decomposition and high enough to be consistent with processing viscosity. It is not necessary to heat the resin mixture hot enough to maintain all components in a molten state. One or more components may be heated only enough to achieve workable plasticity while the remaining components are molten. Hot drawing of the plastic mixture as it emerges from the extruder is not necessary but may be done if a reduction in size of the monofilament is desired. Cold drawing to induce molecular orientation in the fibrils comprising the monofilament is necessary however if a product which will fibrillate readily is to be produced. The optimum degree of orientation induced will vary depending on the composition of the monofilament. Generally 350 to 550 percent orientation is adequate but orientation up to 2,000 percent may sometimes be advantageous. Aside from facilitating fibrillation, molecular orientation imparts improved physical properties to a large number of fiber forming polymers such as polyamides, polyesters, polyurethanes, and vinyl and acrylic type polymers, and as a consequence, improves the paper made from them.
Fibrillation of the monofilaments produced when two or more incompatible plastic materials are extruded by a process of which Examples I and II are typical, can be advantageously carried out by mechanical beating or working. Chopped monofilament A to inch in length are generally suitable for any of the numerous mechanical methods available.
A typical fibrillation operation may be carried out in a commercial Holland paper beater which consists of a cylinder of knives or bars and an adjustable bed plate. Chopped monofilament in a water media is circulated repeatedly under the beater roll by flowing around a circular trough. The filaments immediately begin to break up and within a few hours the plastic pulp resembles normal cellulose pulp.
In the drawing the photomicrographs permit a comparison of the fibers proposed by prior art and those proposed by the present invention for use in making paper and paper-like products. FIG. 1 is an enlargement (100x) of synthetic fibers of the type utilized in the present invention. These fibers were produced by fibrillating an extruded composite monofilament consisting of 80 parts by weight of a vinyl acetate-vinyl chloride copolymer (Bakelite Co.s VMCH) and 20 parts by weight of a solid polyethylene (Bakelite Co.s DYNH). The large number of fibrallae available for interfelting is typical. FIG. 2 shows a loose mat of extruded Dynel (a commercial vinyl chloride-acrylonitrile copolymer) fibers enlarged 100 times. The smooth surface of the fibers and the small number of contact points the fibers make with 4 one another are typical of the synthetic fibers in prior art paper products.
Rapid fibrillation can be accomplished by ball milling the chopped mixed strand with water. An air micronizer or a micropulverizer or other machines such as a Jordan or a Sutherland mill perform this operation equally well. The mention of these specific means is not intended to exclude other equivalent means which perform the operation with equal facility and still are within the scope of the invention.
The dimensions of the staple fibers, i.e., those fibers relatively short in length produced from chopped filament, depend somewhat on the fibrillation method employed and are normally in the range of 1 to microns in diameter. Fibers with diameters in the range of 10 to 30 microns are easily produced in a Holland paper beater. For instance chopped monofilaments produced in subsequent Examples I and II were fed into the beater in the ratio of 2 pounds of filament to 4 gallons of water and beaten for S to 8 hours. Since beating to some extent breaks the staple fibers laterally as well as longitudinally, the fibers in each case had an average length somewhat shorter than their original M; to A inch length. This length however always remains many fold larger than the diameter which averaged about 20 microns.
Typical extrusion processes in which stretch oriented filaments of a suitable nature for use in the product of this invention are shown in Examples I and II. Unless otherwise stated, all parts recited in the following examples are to be understood as being parts by weight.
The use of specifically defined polymers and copolymers in the foregoing examples are not intended to limit the scope of the invention. Owing to the fact that operable polymers are defined by physical properties more than by chemical composition, a vast number of varied polymers are applicable. Thus, in general, normally solid fiber forming resins are applicable so long as pairs or groups are so chosen that at least two incompatible polymers, copolymers or mixtures are extruded as a monofilament. These may include among others, polyamides or the various nylon resins; polyvinyl compositions and copolymers such as Saran (vinylidene chloride-vinyl chloride), Vinyon HH (vinyl chloride-vinyl acetate); polyethylene; polyesters such as Dacron (polyethylene terephthalate); and polyurethanes such as Perlon U.
EXAMPLE I Fifty five parts of polystyrene (M. Wt. 70,000 to 80,- 000) and 45 parts of polyethylene (M. Wt. 20,000 to 22,000) in the form of inch pellets were tumbled together in a conical blender and the resultant mixture fed to a 1 /4 inch bore extruder. The extruder temperature conditions were: die, 450 to 470 F.; front half, 430 to 450 F.; rear half, to F. The polymer mixture was fed to the extruder at a rate of 4 to 5 pounds per hour, extruded through a /8 inch diameter die at the rate of 5 to 10 ft./min. The extruded filament was hot drawn on a conventional hot draw godet and passed through a bath of ethylene glycol heated to about 270 to 285 F. to bring the filament to the proper temperature for stretch orientation. The orientation godet traveled at the rate of 600 ft./min. as did the wind up roll. The resulting filament was about 20 to 30 mils in diameter and oriented 500 percent.
. EXAMPLE II Fifty parts polystyrene (M. Wt. 70,000 to 80,000) and 50 parts of a hard tough interpolymer consisting of 70 parts styrene and 30 parts acrylonitrile (M. Wt. 70,000 to 80,000) in the form of inch pellets were tumbled together in a conical blender and the resultant mixture fed to a 1% inch extruder. The extruder temperature conditions were: die, 470 to 490 F.; front half, 470 to 480 F.; rear half, 210 to 220 F. The polymer mixture was fed to the extruder at a rate of 4 to 5 pounds per hour, extruded through a inch diameter die at the rate of 5 to 10 ft./min., and the filament ultimately wound at 600 ft./ min. Elongation and orientation of the filament was accomplished by the same apparatus as described in Example I except that the ethylene glycol bath was heated to 280 to 300 F. The resulting monofilament was about 20 to 30 mils in diameter and oriented 500 percent.
EXAMPLE III Eighty parts by weight of a vinyl copolymer consisting of 85 to 88 weight percent vinyl chloride, 11 to 14.3 percent vinyl acetate, 0.7 to 1.0 interpolymerized maleic anhydride and 20 parts normally solid polyethylene having an average molecular weight of 20,000 and 4 parts basic lead silicate (Tribase) were compounded to a smooth sheet on differential rolls heated to 140 C. The time of compounding was about 10 minutes for a forty pound batch. The sheet was granulated to about inch pellets and fed to a 1% inch extruder. The feed end of the extruder was water cooled (30 C.) and the die end of the extruder heated to about 250 F. The die 4; inch diameter was heated to about 270 to 280 F. The pellets were fed to the extruder through the die at a rate of 13 to 14 pounds per hour and passed between draw rolls, situated about 2 /2 feet from the end of the die, running at a speed of 28 ft./ min. The filament then passed through a bath of hot water (100 C.) to godet rolls traveling at a speed of 185 feet per minute, and fromthere to wind up rolls. The resulting filament was about 40 to 60 mils in diameter and oriented about 550 percent over the hot drawn length.
EXAMPLE IV Thirty five parts by weight polyethylene (M. Wt. 20,000 to 22,000) and 65 parts by weight Saran 281-S905 in the form of A inch pellets were tumbled together in a conical blender and the resultant mixture fed to a 1% inch Hartig extruder. The extruder temperature conditions were: die, 330F.; front barrel, 330 F. The polymer mixture was fed to the extruder at a rate of 4 to pounds per hour, and extruded through a A; inch diameter die at the rate of 5 to ft./min. The extruded filament was hot drawn at the rate of 25 ft./min. and cold drawn at room temperature at a rate suflicient to impart a molecular orientation of between 350 and 400 percent.
EXAMPLE V The extruded filament in Example III was used for the preparation of a heat scalable paper. The filaments were chopped into 4; inch to inch lengths, charged with water, in the ratio of 1 pound chopped filament to 3 gallons of water, into a paper beater, and beaten for 3 to 4 hours. Sufiicient pulp prepared from a standard Tappi cellulosic blotting paper was added to give a mixed pulp having equal weight percentage of synthetic fiber and natural fiber. The mixed pulp was then sheeted in the known manner on a Fourdrinier machine and dried at a temperature below the softening point of the plastic. It was found that the dried sheet could be sealed electronically at 250 F.
EXAMPLE VI The extruded filament in Example III was chopped into inch to A inch lengths and beaten for 3 to 4 hours with water in the proportion of 1 pound chopped filament to 3 gallons of water. A hand sheet was formed from this pulp which could be removed from the screen without tearing.
EXAMPLE VII Filaments having the same composition and made according to the process described in Examples I and II were chopped and beaten for 5 to 8 hours with water in the proportion of 2 pounds chopped filament to 4 gallons of water. The fibers resulting were A; inch to inch in length and had an average diameter of 20 microns. Portions of these synthetic fiber pulps were mixed with varying amounts of paper pulp made from a standard 6 Tappi blotting paper. These mixed pulps were then sheeted in the known manner on a Fourdrinier machine and dried over drying rolls heated to 225 -F. Sheets cut to measure 8 inches by 8 inches and were pressed under a pressure of 250 psi. at to C. before testing. The results of the tests are shown in the tables below:
Table I POLYSTYRENE-POLYETHYLENE PULP PLUS BLEAOHED SULFITE CELLULOSE PULP Sample No 1 2 3 4 Weight percent plastic fiber pulp 1 0 10 25 50 Weight percent bleached sulfite cellulose pulp 100 90 75 50 Dry mullen 2 (bursting strength) 13.0 16.8 18.2 15.4 Wet Mullen 2.0 7.7 8. 5 10. 2
1 Plastic pulp from Example I. z Tappi 403-M-53.
Table II POLYSTYRENE AND STYRENE-ACRYLONITRILE CO- PULP PLUS BLEACHED SULFITE CELLULOSE The extruded filament from Example I was chopped into inch to /1 inch lengths, charged with water in the ratio of one pound chopped filament to three gallons of water into a conventional paper beater and beaten for 3 to 4 hours. Sufi'icient pulp prepared from a bleached hardwood sulphite cellulose was added to form a pulp having the following weight ratios of synthetic fiber to natural fiber:
Cellulose Synthetic Pulp Fiber Pulp The pulps were mixed 10 minutes and sheeted in the known manner on a. Fourdrinier machine. In all sheets there was sufficient interfelting of the synthetic fibers with each other and with cellulosic fibers to permit removal of the sheets from the screen without tearing.
EXAMPLE IX A low softening composite, fibrous monofilament consisting of polyvinyl acetate and polyethylene was prepared as follows: 80 parts of polyvinyl acetate (Bakelite Co.s AYAT) and 20 parts polyethylene (DYNB) were milled together on rolls heated to 280 F. The mill sheet was cooled, dried, and fed to an extruder and extruded under the following temperature conditions:
Back barrel of extruder F 220 Front barrel of extruder F" 250 Nozzle F 300 Hot draw it lrnin-.. 25 Cold draw (180 F.) percent 450 The filament when chopped and beaten in a conventional paper beater fibrillated readily. The pulp formed in the beater was mixed with equal parts by weight of a standard Tappi cellulose pulp and sheeted in the known manner on a Fourdrinier machine.
What is claimed is:
1. As an article of manufacture a fibrous pulp comprising inert liquid dispersed molecularly oriented composite fibers of synthetic plastic material having lateral surfaces and ends frayed into microscopic fibrillate and having diameters from 0.2 to 100 microns and lengths from to A; inch, said fibers comprising one or more fibrils of each of two or more normally solid, mutually incompatible, synthetic thermoplastic resins.
2. As an article of manufacture a pulp suitable for paper making comprising an inert liquid dispersed interfelted mixture of beaten cellulosic fibers and molecularly oriented composite fibers comprising one or more fibrils of each of two or more normally solid, mutually incompatible, synthetic thermoplastic resin materials hav: ing diameters from 0.2 to 100 microns and lengths from ,5 to 4; inch and having surfaces and ends frayed into microscopic tendrils. .l
3. As an article of manufacture a fibrous pulp suitable for making paper-like products comprising'an inert'liquid dispersed mixture of fibers said mixture comprising from 5 to 75 percent by weight-molecularlyoriented composite fibers comprising one or more fibrils of each of two or more normally solid, mutually incompatible,-synthetic thermoplastic resin materials, said synthetic fibers having lateral surfaces and ends frayed into microscopic fibrillae and 25 to 95 percent by weight of natural cellulosic paper making fibers. a
4. As an article of manufacture a paper product comprising cellulosic fibers and interfelted molecularly oriented composite fibers comprising one or more of each of two or more normally solid, mutually incompatible, synthetic thermoplastic resin materials, said synthetic fibers having microscopic tendrils protruding from ends and lateral surfaces.
5. As an article of manufacture a paper product comprising an interfelted mixture of beaten cellulosic fibers and molecularly oriented composite fibers comprising one or more of each of two or more normally solid, mutually incompatible, synthetic thermoplastic resin materials, said synthetic fibers having diameters of between 0.2 and 100 microns and lengths of between 3& and inch and having ends and lateral surfaces frayed into microscopic tendrils.
6. As an article of manufacture a paper product comprising an interfelted mixture of beaten cellulosic fibers and molecularly oriented composite fibers comprising one or more of each of two or more normally solid, mutually incompatible, synthetic thermoplastic resin materials, said synthetic fibers having ends and lateral surfaces frayed into microscopic fibrillae, and said synthetic fibers having diameters of between 0.2 and 100 microns and lengths of between and inch, and constituting between 5 and percent by weight of the fiber content of said product.
References Cited in the file of this patent UNITED STATES PATENTS 2,351,090 Alles June 13, 1944 2,443,711 Sisson June 22, 1948 2,531,234 Seckel Nov. 21, 1950 2,533,145 Schorger Dec. 5, 1950 2,545,869 Bailey Mar. 20, 1951 2,558,730 Cresswell July 3, 1951 2,579,589 Lehrnberg Dec. 25, 1951 2,736,946 Stanton Mar. 6, 1956 2,795,821 William June 18, 1957 2,796,656 Schappel June 25, 1957 2,810,646 Wooding Oct. 22, 1957 2,816,851 Arledter Dec. 17, 1957 FOREIGN PATENTS 687,041 Great Britain Feb. 4, 1953