US 3223581 A
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D 1965 E. SOMMER ETAL 3,223,531
PROCESS FOR THE PRODUCTION OF A SHEET 0F SYNTHETIC POLYMER FIBROUS MATERIAL Filed Nov. 27, 1962 FIG! INVENTORS: ERWlN SOMMER KLAUS GERLACH HELMUT WERNER ATT'YS United States Patent 3,223,581 PROCESS FOR THE PRODUCTION OF A SHEET OF SYNTHETIC POLYMER FIBROUS MATERIAL Erwin Summer, Obernburg, Klaus Gerlach, Obernau, and
Helmut Werner, Elsenfeld, Germany, assignors to Vereinigte Glanzstotf-Fabriken A.G., Wuppertal-Elberfeld, Germany Filed Nov. 27, 1962, Ser. No. 240,342 Claims priority, application Germany, Nov. 30, 1961, V 21,700 5 Claims. (Cl. 162-157) The present invention is concerned with a process for producing sheet or paper-like structures of synthetic polymer fibers, and more particularly, the invention is concerned with an improvement in the formation of fibrous sheets or webs when laying or depositing fibers of a synthetic polymer from an aqueous dispersion onto a supporting surface and subsequently removing water from the fibrous web.
Many dilferent fibrous materials have been employed for the production of waterlaid sheet-like or paper-like structures according to the generally well-known papermaking process. Depending upon the exact nature of the initial fibrous material and the conditions under which the fibers are treated during the paper-making process, it is possible to obtain sheet-like products with different properties and characteristics. Thus, paper is produced when using cellulosic fibers, and many attempts have been made to produce a similar sheet material from fibers derived wholly from synthetic polymers.
In general, the over-all procedure for making paper or similar sheet materials is substantially the same in each case regardless of the particular fiber, although there may be a number of minor variations such as pretreatment of the fibers by heating or refining or the incorporation of additives such as binders, adhesives, thickening agents, fillers and the like.
Thus, in the usual paper-making process, the fibers are first dispersed in a liquid, preferably Water for obvious economical reasons, the dispersion of fibers being maintained by thorough mixing and/ or the addition of a suitable dispersing agent. The resulting pulp or fiber dispersion is then transferred or flowed onto a moving screen or sieve for removal of at least part of the water and formation of a fibrous Web or fleece. The moving screen employed for this purpose corresponds to one of two gen eral types, the Fourdrinier machine and the cylinder machine. After the fibrous web has been formed, it is transferred from the moving screen onto other suitable apparatus for removal of any remaining water and formation of a solid sheet by the application of heat and/or pressure and/or adhesives. L4
The paper-making process is particularly adapted to the manufacture of paper from cellulosic fibers, and it has been quite difficult to treat fibers of synthetic polymers by this same process. A waterlaid fleece or fibrous web of synthetic polymer fibers cannot be transferred from the Fourdrinier or similar moving screen without being torn or pulled apart, because there is very little cohesion between the individual polymer fibers. In contrast to natural cellulosic fibers which can be beaten into very fine fibers or fibrils, it has been practically impossible to provide synthetic polymer fibers with similar properties capable of forming a relatively strong and cohesive waterlaid fibrous web. This is partly due to the fact that it is very expensive to form fibrils from synthetic polymers, and partly due to the fact that synthetic polymer fibers have very low swelling values and a high degree of water-repellency.
In spite of numerous draw-backs, a number of attempts have been made to carry out processes for making sheet 3,223,581 Patented Dec. 14, 1965 materials containing synthetic polymer fibers in order to obtain the advantages of various physical and chemical properties from such polymers as polyamides, polyesters, polyolefines and the like. According to one known process, a sheet of synthetic polymer fibers is made by adding to the aqueous dispersion a relatively large proportion of cellulose fibers, for example, in amounts up to about 30% by weight. In the same manner, cellulosic fibers have been modified with minor amounts of synthetic polymer fibers in order to impart certain properties to the resulting paper product. It will be obvious that such procedures do not take full advantage of the preferred properties of the synthetic polymer fibers, and the admixture of very small amounts of a cellulose pulp does not overcome the disadvantages in working with the waterlaid fibrous web.
Another process suggested by the prior art consists in the addition of certain adhesives or viscosity-increasing agents to the fiber dispersion in order to increase the strength of the fibrous web. A typical example of this procedure is the addition of carboxymethyl cellulose in an amount of about 0.1-5 by weight to the aqueous dispersion of the fibers. It will be evident that the fiber dispersion then contains about parts by weight or more of the additive for each part by weight of fibers. Since the additive, such as carboxymethyl cellulose, is generally at least partly soluble in water, large amounts of the additive will 'be removed as the fibrous web is drained or dewatered, and it is therefore essential to recirculate the water in order to avoid substantial loss of the additive. Furthermore, the carboxymethyl cellulose or other additive remaining in the fibrous web must be washed out during subsequent processing steps or at least removed from the finished product, since such additives impair the quality, color, or other desirable properties of the final product.
Still another technique which has been suggested for the production of sheet structures of synthetic polymer fibers is the addition to the fiber dispersion of so-called fibrids. These fibrids may be characterized as ultra-fine fibers which can be obtained, for example, when a solution of a synthetic polymer is sprayed with high velocity onto the surface of a precipitation bath. The production of these fibrids and their use in the formation of waterlaid fibrous Webs from aqueous dispersions is described in detail in US. Patent No. 3,062,702. The use of such fibrids in the paper-making process does result in a stronger and more easily handled fibrous web, and it is possible in this manner to produce a sheet composed solely of synthetic polymer fibers. However, the methods required for the production of the fibrids are quite complicated and very expensive, particularly because large amounts of solvents and precipitating agents must be circulated and treated during production and recovery of the fibrids.
Finally, processes have been developed for the socalled fibrillation of synthetic polymer fibers. In this case, an attempt is made to duplicate the effect of the beater in the usual paper-making process wherein cellulose fibers are beaten in order to fibrillate and hydrate the pulp material. However, synthetic polymer fibers cannot be hydrated, and any fibrillation is achieved only by using very expensive beating methods. Furthermore, as in the production of fibrids, it may be necessary to deviate substantially from the usual filament spinning processes in order to achieve satisfactory fibrillation.
Although it has been possible with prior processes to produce fibrous fleeces or waterlaid webs which can be transferred from the paper-making machine without being torn or pulled apart, the various disadvantages of these processes prevent a practical or economical production of a synthetic polymer fibrous sheet material.
A primary object of the present invention is to provide a new and improved process for the production of a sheet of synthetic polymer fibrous material wherein the waterlaid fleece or web of fibers is sufliciently strong so that it can be transferred from the screen of the paper-making machine and otherwise handled during subsequent treatment without being ruptured or pulled apart.
Another object of the invention is to provide a commercially practical and economical process for the felting or waterlaying of synthetic polymer fibers in which it is possible to obtain the advantages of conventional filament spinning methods and paper-making processes.
Still another object of the invention is to provide a waterlaid or felted product consisting substantially or wholly of synthetic polymer fibers in the form of a strong, continuous water-containing web or fleece, and it is also an object of the invention to produce this product without employing special adhesives or thickening agents.
These and other objects and advantages of the invention will become more apparent from the following detailed description and the accompanying drawing where- FIGS. 1 and 2 represent a cross-section of intercontacting synthetic polymer fibers as employed for the purposes of this invention; and
FIG. 3 is a schematic representation of suitable papermaking apparatus for carrying out the process of this invention.
It has now been found, in accordance with the invention, that a sheet or paper-like structure can be readily produced from fibers of synthetic polymers, by forming a fibrous web on a supporting surface, such as the usual screen or sieve of a paper-making machine, the fibrous web being formed with individual fibers which consist predominantly of synthetic polymer strands having smooth and flat surfaces, whereby the individual fibers are in contact with each other along these flat surfaces. After initial formation of the fibrous web and before its trans fer from the supporting screen, it is essential to withdraw water therefrom to a residual moisture content of about A 30 to 85% by weight with reference to the wet web.
In general, the process steps correspond to the usual paper-making procedure in which the fibers are first trans ferred from an aqueous dispersion to a screen or similar supporting surface of a paper-making machine, water is then withdrawn from the waterlaid and interlaced fibers to form a fibrous web or fleece on the supporting surface, and the web is then removed from the supporting surface and finally formed into a solid sheet of bonded fibrous material by heating, applying pressure and/or applying various well-known sprays, plastic or resin dispersions, adhesives or the like. The web containing a 30-85% residual moisture content can be more fully dried with removal of part or all of the remaining water just prior to solidification of the web, or the residual moisture can i also be removed during or after solidification or bonding of the fibers in the web. However, a residual moisture content of 30-85% is essential in combination with the particular synthetic polymer strands of the invention in order to produce a waterlaid web or sheet on the papermaking machine with suflicient strength or cohesiveness for subsequent removal of the web from the supporting screen without tearing or otherwise substantially damaging the web.
The exact form or shape of the individual fibrous strands is a critical feature of the present invention, since it is essential that the synthetic polymer strands have a large area of surface contact with each other in the waterlaid fibrous web. FIGS. 1 and 2 of the drawing illustrate two types of such synthetic polymer strands which meet the necessary conditions of the invention with respect to surface area and shape. FIG. 1 illustrates fibers in the form of bands or tapes, having a substantially rectangular cross-section, and it is apparent how the fiat surfaces of these small bands contact each other in the waterlaid sheet. The same result is achieved with fibers as represented in cross-section in FIG. 2, wherein the strands have an approximately triangular cross-section. It will be self-evident that fibrous synthetic polymer strands of other types are also suitable provided that they present essentially smooth and flat or planar surfaces, thereby providing a large area of contact between fiber surfaces. Of course, the most favorable conditions will exist when the ratio of the cross-sectional circumference to the cross-sectional area is as great as possible.
In general, all fiber-forming or film-forming synthetic polymers can be used in order to form the flat-surfaced strands required for the purposes of this invention. For example, such polymers include polyamides such as nylon and polycaprolactam, polyesters such as polyethylene terephthalate, polyolefines such as polyethylene and polypropylene, and polymers or copolymers of acrylonitrile, vinyl chloride, vinylidine chloride and the like. It will be recognized that the structure or shape of the synthetic polymer fibrous strand is the important consideration, and the chemical composition of the polymer is important only because synthetic polymer fibers as a class cannot be hydrated or subjected to fibrillation according to the usual paper-making procedure with natural or artificial cellulose fibers.
Synthetic polymer fibrous strands having the required shape or form can be obtained quite easily by spinning the molten polymer through a nozzle orifice or opening having the desired cross-sectional shape. For example, strands, having the shape shown in FIG. l can be obtained by extrusion through a nozzle with a substantially rectangular slit-shaped opening. A triangular nozzle opening will produce the cross-section of the fibrous strand in FIG. 2, e.g., an isosceles triangle. Furthermore, it is possible to obtain such fibrous strands by cutting up thin foils or films of the synthetic polymer. As indicated by the drawing, the cross-sectional shape of the polymer strand need not be absolutely uniform or correspond to an exact geometric configuration, and slight variations are permitted within the scope of the invention, e.g., rounded edges or somewhat irregular surfaces. Thus, as other examples of suitable structures, the strands may have the form of flattened ovals or equilateral triangles or narrow trapezoids. The most favorable results are obtained when the polymer strand has two oppositely disposed flat faces or planar surfaces and relatively smaller or narrower edges separating the two faces. Also, the length of the cross-section should be relatively large by comparison to the width, and it is preferred to have a ratio of maximum length to maximum width of the cross-section of at least 3:1 or more. In general, this ratio of maximum length to maximum width should fall within a range of 3:1 to 10:1.
The denier of the fibers or strands according to the invention should be as low as possible and should amount to not more than about 3 denier, preferably about 0.8 to 2.0 denier. The length of the individual strands is dependent upon the properties or characteristics desired in the finished sheet product. In general, however, the synthetic polymer strands should have a length of about 1 to 10 mm., preferably 2 to 6 mm.
The web or fleece which is waterlaid from an aqueous dispersion should consist predominantly of fibrous strands having the above-described shapes or configurations, and it will be obvious that one may use mixtures of difierently shaped fibers as well as mixtures of fibers prepared from different synthetic polymers. The present invention is especially useful for producing waterlaid webs or fleeces which consist wholly of synthetic polymer fibers. In any case, the invention is directed especially to waterlaid webs containing at least 90% by weight and preferably 95% by weight of synthetic polymer fibers with respect to the total weight of fibers in the web.
Although consisting wholly or substantially wholly of synthetic polymer fibers, the waterlaid web and the finished sheet product may alsocontain small amounts of other fibers or such materials as fillers, binders, pigments or the like. However, such additives should ordinarily be. present in amounts of not more than and preferably not more than 5% by weight with reference to the dry web. With the process of the invention, it is unnecessary to add any adhesive or bonding agents .until after the waterlaid web has been formed and transferred from the screen or sieve of the paper-making machine onto .other apparatus for solidification into a A permanent sheet material.
If the spinning process for the production of the synfiber pulp which is to be transferred to the paper-making The actual manner in which the synthetic polymer strands are formed into a sheet structure according to the invention can be described as follows. About 0.01 to 0.5 and preferably 0.05 to 0.1 parts by weight of the polymer strands are firstdispersed in 100 parts by weight of water, in a conventional mixing box or pulp tank 1. The fibrous dispersion is preferably achieved by the addition of a small amount of any conventional dispersing agent together with intense mixing or rapid agitation of the pulp. The alkane sulfonate type of dispersing agent can be readily employed, these agents being characterized by a sulfonate group attached to a long chain aliphatic radical as the hydrophobic group.
Such compounds are typical anionic surface active agents as .described, for example, in chapter 4 of Surface Active Agents, by Schwartz and Perry, Interscience Publishers, Inc. (1949). The alkane sulfonates having an ester intermediate linkage are especially useful, for example in which a sulfonated lower alkanol is esterified with a long chain alphatic carboxylic acid such as oleic,
stearic and palmitic acids or other fatty acids and their closely related derivatives. In general, these dispersing agents are obtained commercially in the form of their sodium salts of the formula RCOOC H SO Na in which R is the residue of a fatty acid such as oleic acid. These dispersing agents are sold under the trade name Igepon A, AP andAP Extra. Other suitable dispersing agents for the purposes of this invention are the nonionic compounds which .are obtained by the action of ethylene oxide on highmolecular alcohols (e.g., oleyl alcohol) and which have the. formula R(OC H ,OH
where R is a long chain aliphatic residue and n is a number between 9 and 20. Such compounds are wellknown under the trade names Emulphor O, Emullat, Cirrasol SF, and Peregal G, for example.
The aqueous dispersion or fiber pulp is discharged or poured from the mixing box 1 through a slit-shaped or elongated opening 2 onto the so-called wire or endless screen belt 3 of a conventional paper-making machine such as the Fourdrinier. A Fourdrinier machine is preferred with its vibrating or shaking action which tends to orient the synthetic polymer strands so as to align and intercontact the flat surfaces thereof. As the layer of fiber pulp is conveyed as a fleece or web F by the wire or endless screen or any similar perforated supporting surface, water is drained off by means of suitable suction boxes 4 and squeeze rollers 5. If desired, other rollers may also be provided to work the fibrous pulp into a relatively uniform waterlaid fleece or web.
Sufiicient water is removed from the fleece or web F so that by the time it leaves the endless screen 3, for example at point 6, it has a residual moisture content of 30 to 85% by weight, and preferably 60 to 75% by weight, with reference to the weight of the wet fleece. With this residual moisture content, the fleece is then transferred to a second conveyor belt in the form of a second enddoes not tear apart. .be solidified by bonding the individual polymer strands does it tear. of apparatus not represented in the drawing and conto each other by conventional means not shown in the drawing. This solidification can be easily accomplished by the application of pressure and/or heat with or without the application of various adhesive or bonding agents which are well-known in the art. Fillers, pigments or the like may also be added at the same time that the waterlaid fibrous web is solidified. The term solidification is employed herein with reference to the permanentbonding of the individual strands to each other as distinct from the solidification of a molten material or the adherence of the water-coated flat surfaces of the individual fibrous strands in the waterlaid web.
The process of the invention is further illustrated with additional detail by the following examples. Parts and percentages in-these examples are by weight unless otherwise indicated. It will be understood that the examples are illustrative only and that the invention should not be limited thereby.
Example 1 Polycaprolactam is melted in the usual manner and is spun through a 36-hole nozzle with a rectangular crosssection of each hole or opening of x 600 my. The drawing-off speed of the extruded strands is 1000 m./min. After stretching in a ratio .of 1:3, the resulting strands have an individual fiber denier of 2 and a cross-section as shown in FIG. 1. The strands are then freed from excess spinning preparation by washing with a soap solution and are cut to a length of 5 mm.
A 0.05% aqueous fiber dispersion is prepared by mixing the strands in water together with several cubic centimeters of a 10% aqueous solution of a sodium salt of a higher aliphatic sulfonic acid of the formula as a dispersing agent. The dispersion is homogenized by intense agitation and is then processed with the apparatus shown schematically in FIG. 3. The fiber dispersion is first discharged from mixing box 1, through slit-shaped opening 2 ontothe moving endless screen 3, on which the fiber pulp is worked into a fleece or web F. The screen is equipped with'suction boxes 4 and squeeze rollers 5. By means of this apparatus, water is removed from the fleece so that is 6, i.e., upon leaving the screen 3, the fleece has a residual moisture content of 65% (with reference to the weight of the wet fleece). The fleece is now transferred to a second conveyor screen 7, and during this transfer, the fleece does not lengthen nor Further processing takes place by means sists of spraying the fleece with a 10% aqueous dispersion of polyvinyl chloride, and drying the fleece .or web without application of pressure at about 'C. A soft liner material is obtained as the final resin-bonded fibrous sheet.
Example 2 Corresponding to the data of Example 1, polyethylene terephthalate is spun from the melt with the use of a 36-hole nozzle. The rectangular cross-section of the nozzle openings is 60 x 800 my. The drawing-01f speed amounts to 500 m./min. Stretching is carried out in a ratio of 1:4, and the resulting strands are obtained with an individual fiber denier of 1.2, the cross-section again appearing as in FIG. 1. After washing with a soap solution to remove adherent spinning preparations or finishing agents, the strands are cut to a length of 6 mm.
With addition of the dispersing agent described in Example 1, a 0.05 aqueous fiber dispersion is prepared and is further processed on the paper-making machine according to the data of Example 1. The fiber fleece leaving the Fourdrinier screen has a residual moisture content of 70% (with reference to the weight of the wet fleece). After being transferred to the second conveyor screen, the fleece is sprayed with a aqueous dispersion of polymethacrylic acid ester. The fleece or web is finally dried without application of pressure at a temperature of about 110 C. so as to provide a soft liner material consisting of a bonded fibrous sheet.
Example 3 A polyamide of adipic acid and hexamethylene diamine (nylon) is spun from the melt and stretched under the same conditions described in Example 2. The strands in this case likewise have an individual fiber denier of 1.2 and are cut to a length of 6 mm.
A 0.05% aqueous dispersion of these strands is prepared with the same dispersing agent mentioned in Example 1. After leaving the screen 3 of the paper-making machine, the residual moisture content of the waterlaid fleece is 75%. The solidification of the fleece is accomplished by spraying With a 5% methanolic copolyamide solution (the copolyamide consisting of 60% hexamethylene diamine adipate and caprolactarn). Drying is then carried out at about 70 C., and the web is subsequently pressed at about 120 C. and a pressure of 5 kg./cm. The final sheet product has a smooth paper-like structure.
Example 4 A melt of polypropylene is spun through a 36-hole nozzle with a rectangular cross-section of the nozzle openings of x 800 my. at a drawing-off speed of 500 m./rnin. Stretching is carried out in a ratio of 1:3, and the resulting strands have an individual fiber denier of 1.3 and are cut to a length of 5 mm.
From these strands, there is prepared a 0.08% aqueous dispersion, making use of the dispersing agent described in Example 1. The fibrous dispersion is then processed on the paper-making apparatus as in Example 1 to a residual moisture content of The fleece is finally sprayed with a 10% aqueous dispersion of :polyrnethacrylic acid ester, dried at about C. and thereupon pressed at C. and under a pressure of 5 kg./cm. A smooth, soft, paper-like web is obtained in which the individual strands are bonded together.
From the foregoing examples, it will be apparent that the present invention permits a very economical production of sheet or paper-like structures of synthetic polymer fibrous materials while using conventional papermaking apparatus. The intermediate waterlaid fibrous fleece or web is characterized by its unusual strength and resistance to deformation so that subsequent treatment steps such as drying and solidification by bonding can be carried out without any difficulties. Because of this ease in handling the waterlaid web, the final or finished product in the form of a solidified sheet or paper-like structure has a much more uniform quality and strength than could be achieved in prior processes. The process of the invention thus provides a greater opportunity for making useful articles which consist wholly or at least predominantly of waterlaid and bonded synthetic polymer fibers.
The invention is hereby claimed as follows:
1. In a process for the production of a sheet of synthetic polymer fibrous material wherein an aqueous dispersion of synthetic polymer fibers is transferred to a supporting surface, water is withdrawn to form a fibrous web on said supporting surface, and the web is then removed from said supporting surface and formed into a bonded sheet of fibrous material, the improvement which comprises: forming a fibrous web on said supporting surface with individual fibers which consist predominantly of melt-spun, non-fibrillated synthetic polymer strands, each of said strands having a solid elongated cross-section in which the ratio of maximum length to maximum width is at least 3:1 and each of said strands also having smooth and fiat surfaces, whereby said individual fibers are in contact with each other along said flat surfaces; withdrawing water from said fibrous web to a residual moisture content of 30 to 85% by weight with reference to the wet web; and removing said fibrous web with said moisture content from the supporting surface.
2. A process as claimed in claim 1 wherein the length of the individual strands is about 2 to 6 mm.
3. A process as claimed in claim 1 wherein the individual synthetic polymer strands have a denier of not more than about 3.
4. A process as claimed in claim 1 wherein the individual synthetic polymer strands have the shape of a band with an elongated, substantially rectangular crosssection.
5. A process as claimed in claim 1 wherein the individual synthetic polymer strands have the shape of a band with an elongated substantially triangular crosssection.
References Cited by the Examiner UNITED STATES PATENTS 2,810,646 10/1957 Wooding et a1. 162-146 2,999,788 9/1961 Morgan 162157 3,002,880 10/1961 Schonberg et al. 162157 3,068,527 12/1962 Morgan 162-146 3,081,519 3/1963 Blades et a1. 162-157 OTHER REFERENCES Calkin, Modern Pulp and Paper Making, 3rd edition, 1957, Reinhold Publication Corp., New York, page 312.
DONALL H. SYLVESTER, Primary Examiner.
' MORRIS o. WOLK, Examiner.