US3376370A - Vinylidene fluoride yarns and process for producing them - Google Patents

Description

United States Patent Ofilice 3,376,370 Patented Apr. 2, 1968 ABSTRACT OF THE DISCLOSURE A high-tenacity polyvinylidene fiuoride yarn is prepared by spinning a solution of polyvinylidene fluoride in a solvent consisting essentially of a mixture of an amide and a ketone into a coagulation bath consisting essentially of a mixture of water and a ketone wherein the polyvinylidene fluoride coagulates to form filaments, vaporizing all solvent and Water from the filaments, and orienting same by drawing.

This application is a divisional application of Serial Number 265,036, filed March 14, 1963, now abandoned.

This invention relates to novel textile yarns and to the process for producing them. In particular, the invention is directed to novel yarns of polyvinylidene fluoride and to a method of making such yarns by a novel solution spinning technique.

Yarns for textile and other uses have long been desired which would have high tenacity and resilience, would be resistant to chemicals and solvents, and which would withstand the effects of moisture, weathering sunlight, heat, cold and other environmental conditions. It is known that fluorocarbon resins are extremely resistant to chemicals and to weathering conditions, but the conversion of these materials to textile yarns is a diflicult task. Polytetrafluoroethylene, for example, is diflicult to manufacture into filaments because it can neither be spun from a solevent system nor can it be melt extruded as filaments. It requires a special spinning technique, and the resultant fibers are high priced because of the difficulties and poor economics of the manufacturing process. Likewise, with other polyfluorocarbon polymers, fibers fabrication techniques are difiicult. Polychlorotrifluoroethylene, for example, cannot be spun into filament from a solution system because of the insolubility of the polymer in all practical solvent systems. Therefore, special melt spinning techniques have been developed for making fibers of polychlorotrifluoroethylene polymer. These techniques require much control and are not economical.

Another fluorocarbon polymer which has recently become commercially available is polyvinylidene fluoride. Since this new polymer possesses many of the outstanding properties of the more difliculty fabricated fluoropolymers, it is desirable that it be converted to fibers and yarns. This has been accomplished in the laboratory by all three of the common methods of textile fibre manufacture-wet, dry, and melt spinning. However, the yarns obtained by each of these methods suffered certain deficiencies. The yarn obtained by melt spinning methods exhibited signs of incipient melt fracture and varying degrees of fibrillation. It was evident commercial polyvinylidene fluoride yarn production by melt spinning methods would require exacting control and special equipment and would necessarily be a costly process. Polyvinylidene fluoride yarn produced by solution spinning methods involved a relatively high boiling solvent system, since no true oi latent solvent is known which is a volatile liquid. Dry spinning of yarns required the removal by heat of the solvent as the fibers issued from the spinneret. In the case of polyvinylidene fluoride yarns the high boiling solvent which must be employed is difiicult to remove from the fibers. It requires the use of high temperatures, relatively long drying times, large and complicated drying equipment, and, most importantly, the operation is diflicult to control. All dry spun yarns experimentally produced have had the disadvantage of filament to filament adhesion; presumably because of insufficiently rapid solvent removal which allowed the surfaces of the filaments to remain tacky while the filaments were in contact with each other. Laboratory experiments have shown wet spinning methods for polyvinylidene fluoride yarn to be reasonably convenient and economical, but the yarns produced by conventional wet spinning methods have invariably had relatively low tenacities in the range of 2 grams per denier.

Therefore, an object of this invention is to prepare polyvinylidene fluoride fibers and yarns of improved physical properties, particularly more tenacious and more transparent fibers.

Another object of this invention is to provide solvent systems for spinning polyvinylidene fluoride polymers which contain substantial amounts of volatile solvents and which are miscible in all proportions with water. These solvent systems have also the ability to dissolve or suspend large proportions of polyvinylidene fluoride polymer yet remain sufliciently fluid to flow well through the orifices of a spinneret. I

A further object of this invention is to provide a substantially aqueous bath capable of rapidly coagulating streams of polyvinylidene fluoride polymer solution into filamentous form.

It has now been discovered that the above objects may be accomplished and the disadvantages of conventional melt, wet, and dry spinning processes may be avoided by a spinning process which comprises dissolving polyvinylidene fluoride in certain solvents; passingthe solution through spinnerets into a spinning bath comprised of water and certain polar organic liquids, which bath c0- agulates the polyvinylidene fluoride filaments by a process of liquid-liquid extraction of the sol-vent until the filaments are sufficiently strong to be removed from the bath; and removing the remaining solvent by drying operations. The process of the present invention utilizesnthe general types of apparatus conventionally employed for wet spinning together with the polymeric solutions generally employed in dry spinning. It employs these in conjunction with a coagulating bath of carefully determined composition, which hardens the surface of the fibers by a process of liquid-liquid extraction of. a portion of the solvent. The process also involves'further drying of the yarn after it leaves the spinning bath in order to remove the remaining solvent. It is to be noted that the use of a coagulating bath normally used in wet spinning processes with the solvent removing drying step normally used in dry spinning is a novel feature of the present in vention. A further novel feature is the composition of the spinning baths used in. the practice of the invention. Other novel aspects are described in detail hereafter. The preparation and properties of the vinylidene fluoride polymer used in this invention are fully disclosed in US. Patent 2,435,537 which issued February 3,v 1948. I The general technique for wet spinning of multifilament yarns is described in many well known texts such as R. W. Moncrieft, Man-Made Fibers, 3rd ed., John Wiley and Sons, Inc., New York (1959) and J. J. Press, Man-Made Textile Encyclopedia, Textile Book Publishers, Inc, New York (1959).

It should be understood that'because it is commonpractice to alter the properties of polymers for particular textiles by copolymerization, the term polyvinylidene fluoride as used throughout this application will include homopolymers of polyvinyli dene fluoride and also copolymers containing at least 95 mole percent vinylidene fluoride monomer.

The significant steps involved in the process of this invention are:

(1) Substantially dissolving from to parts by weight of polyvinylidene fluoride in 100 parts by Weight of a select solvent system to form a spinning solution.

(2) The passage of the polyvinylidene fluoride solution at a controlled rate through a spinneret into a spinning bath consisting essentially of a mixture of water and an organic compound selected from the group consisting of: methanol, ethanol, glycol, glycerol, alcohols, ketones, polyglycol ethers, amides, and substituted amides. The preferred organic compounds include one or more of the following: acetone, methyl ethyl ketone, methanol, ethanol, propanol, isopropanol, dimethylformamide, dimethylacetamide, N-methyl-2-pyrolidone, and dimethylsulfoxide.

The polyvinylidene fluoride coagulates in said aqueous spinning bath containing the organic compound to form fibers (i.e., filaments) of polyvinylidene fluoride.

The above steps are followed by the more conventional steps listed below:

(3) The drying of the fibers in an air oven until the fiber surface appears substantially dry, and free from drippage.

(4) The further drying while maintaining suflicient tension on the yarn to align the filaments parallel to each other.

(5) The washing of the yarn in hot water to remove solvent remaining in the yarn and to remove any extraneous materials.

(6) The twisting of the yarn to facilitatehandling along with a drawing operation to orient the polymer and build strength into the yarn.

(7) The vacuum drying of the yarn to insure complete solvent and water removal from the yarn.

(8) The orientation and heat setting of the yarn to attain high tenacity with minimum shrinkage in the yarn.

In high speed commercial operations, Step 5, the washing of the yarn, and Step 7, the vacuum drying of the yarn, may be replaced with a more complete air drying under Step 4.

Steps 1 and 2 must be carried out by carefully regulating certain critical factors to obtain the high strength fibers of the present invention. These factors, each of which is discussed in detail hereafter, include:

(a) the solvents used to prepare the spinning solutions of Step 1 and their relative concentration.

(b) the amount of polyvinylidene fluoride in the spinning solution of Step 1.

(e) the composition of the spinning bath of Step 2 ineluding the type of additives and their concentration.

(d) the temperature of the spinning bath.

(e) the residence time of the filaments in the spinning bath.

The organic polar spinning solvents used in Step 1 to prepare the spinning solution of polyvinylidene fluoride are listed in List A.

, LIST A Gamma butyrolaetone, N,N-dimethylacetamide, cyclic butadienesulfone, tetramethylenesulfone, dimethylsulfolane, hexamethylenesulfone, diallylsulfoxide, dimethylsulfoxide, dicyanobutene, adiponitrile, ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, isobutylene carbonate, trimethylene carbonate, N,N-diethylformamide, N,N-dimethylformamide, N,N- dimethyl-gamma-hydroxyacetamide, N,N-dimethyl-gamma-hydroxybutyrarnide, N,N-dimethylaeetamide, N,N- dimethylmethoxyacetamide, N-methylacetamide, N-methylformamide, N,N-dimethylaniline, N,N-dimethylethanolamine, 2-piperidone, N-methyl-Z-piperidone, N-methyl- Z-pyrrolidone', N-ethyl-Z-pyrrolidone, N-isopropyl-2-pyrrolidone, 5-methyl-2-pyrrolidone, delta-valerolaetone, gamma-valerolactone, a-angelicalactone, B-angeliealactone, epsilon-caprolactone, and the derivatives of the gamma-butryolactone substituted by two alkyl radicals in alpha, beta and gamma, the gamma-valerolactone and the delta-valerolactone and also the derivatives of the delta-valerolactone substituted by alkyl radicals in delta, tetramethylurea, l-nitropropane, 2-nitropropane, acetonylacetone, acetophenon, acetylacetone, cyclohexanone, diacetone alcohol, dibutylketone, isophorone, mesityl oxide, methylamino ketone, 3-methylcyclohexanone, bis (methoxymethyl)urone, diethylphosphate, ethyl acetoacetate, methyl benzoate, methylene diaeetate, phenyl acetate, triethylphosphate, tris(morpholino) phosphine oxide, N-acetylmorpholine, N-acetylpiperidine, isoquinoline, quinoline, pyridene and tris(di-methylamido) phosphate.

Of the above liquids, dimethylformamide, dimethylacetamide, N-methylpyrrolidone and dimethylsulfoxicle are preferred because of their ability to apparently dissolve polyvinylidene fluoride at 20 to 25 C. The term apparently dissolve is used because 5% or greater concentrations of polyvinylidene fluoride in any of the above solvents show a haze. That is, light scattering or a Tyndall effect is evident, indicating that not all of the polyvinylidene fluoride is in true solution. Light scattering measurements show the presence of particles in the solutions, and microscopic observation shows that these particles range in size from approximately 0.1 micron to microns. Particles smaller than 0.1 micron probably are present, but they have not yet been observed and measured. Particles larger than approximately 100 microns are usually not present because particles larger than about 50 microns diameter settle out of the solution.

The particles present in the solutions are believed to be crystals composed of high molecular weight fractions of vinylidene fluoride which are not soluble at room temperature because of their high molecular weight. It is a characteristic of the present invention that by the special selection of solvent systems the percentage of such particles is reduced to a levelwhich permits the vinylidene fluoride spinning material to act as a true solution. The number of discontinuities caused by these insoluble particles is minimized by the practice of the present invention. In addition, the invention permits the use of higher molecular weight polyvinylidene fluoride than would otherwise be spinnable. Both of these factors contribute to provide vinylidene fluoride having higher tenacities and a higher thermal softening point than were previously obtainable.

The spinning solutions of the present invention are very nearly true Newtonian solutions. This is demonstrated by the fact that a plot ofthe logarithm of the viscosity versus the concentration of polyvinylidine fluoride in the spinning solution is a straight line function over the range from 0 to above 20% by weight of polyvinylidene fluoride. The film and fiber forming properties of the. spinning solutions are further evidence that the solutions behave generally as true solutions instead of suspensions. If such a spinning solution is spread on a flat surface and the solvent allowed to evaporate at room temperature, a continuous film of polyvinylidene fluoride is formed. However, if a dispersion of polyvinylidene fluoride particles in a non-solvent or latent solvent is similarly spread on a fiat surface and allowed to dry, a layer of white particles with no physical continuity results. Analogously, a filament as long as ten feet may be drawn by dipping a rod into a polyvinylidene fluoride solution and withdrawing the rod slowly at constant velocity allowing the soltuion to pull out into a low strength filament. Suspensions of polyvinylidene fluoride, in contrast, have no ability to act as fiber-forming substances.

Of the liquids included in List A, above, the liquid most useful in spinning solutions for polyvinylidene fluoride fibers is dimethylacetamide, but its use alone does not lend itself to an entirely satisfactory procedure. One of the problems involved is that the fibers retain 20% or more of their weight in solvent after they emerge from the spinning bath. This causes difficulties such as adsorption of water from their surfaces and retention of one to nine percent of their weight of solvent after subsequent drying steps. It has now been discovered that a specific co-solvent combination of a liquid amide, such as dimethylformamide, with an aliphatic liquid ketone, such as acetone, or methyl ethyl ketone, permits a spinning solution of polyvinylidene fluoride to be formed which, when the fibers are coagulated in the spinning bath, unexpectedly results in practically no solvent retention or water absorption. Thus, although the process of this invention is operative with solutions of polyvinylidene fluoride in a single solvent such as the preferred N-methyl-2- pyrrolidone, dimethyl sulfoxide, dimethylformamide and dimethylacetamide, the use of co-solvent solutions is still dene fluoride in the spinning solution. The proportions of the solvents used in these co-solvent systems may vary widely and may consist of a preponderance of either one of the components. A preponderance of the ketone may be used, or a preponderance of the amide may be used, depending on the solution viscosity and solubility of the particular type of polyvinylidene fluoride used.

The composition of the co-solvents system will be determined by the solubility of the particular vinylidene fluoride polymer to be spun. 'Higher molecular weight polymers are generally less soluble and require more of the amide in the solvent system. It is desirable to use as large an amount of ketone as possible, since the ketone is more volatile and is more easily removed during the drying operation. Also, the ketone is generally less expensive than the amide.

In general, the co-solvent system will contain from 0 to 75 percent by weight of the ketone. When the preferred concentration of polyvinylidene fluoride as discussed hereafter is employed, the ketone will be from 0 to about 60% by weight of the co-solvent system and preferably 30 to about 50% by weight of the co-solvent system.

The concentration of polyvinylidene fluoride in the spinning solution is critical. Unless a concentration range from about to 50 parts of polyvinylidene fluoride to 100 parts by weight of solvent system is employed, satisfactory fibers are not obtained.

The preferred range of polyvinylidene fluoride concentration is from to about parts by weight. The optimum conditions for any given system depend on the viscosity of the spinning solution. Solutions whose viscosities are as low as 100 cps. are inoperable, as are solutions whose viscosities are on the order of 500,000 cps. Sucessful operations has been obtained with solutions whose viscosities ranged between 1000 and 250,000 cps., but a viscosity range between about 10,000 and 100,000 cps. is preferred. -It is to be understood that there may exist certain conditions or certain types of polymer which will permit solutions to be used which are somewhat out of this range.

The spinneret used in the practice of this invention will generally be conventional in design with from two to over 5,000 orifices, and preferably with from about 20 to 150 orifices for most purposes. The orifices will generally have diameters of from 0.003 to about 0.020 inch, limited only by the abilities of available commercial extrusion equipment.

The spinnerets are immersed in the spinning bath, preferably with the face of the spinneret facing upward to permit the fibers to be withdrawn vertically so that drippage falls back into the spinning bath.

The composition of the spinning bath used in Step 2 is also critical. Water, in spite of its low wetting power on polyvinylidene fluoride, has :been discovered to be the most effective coagulating medium for the spinning bath. The use of baths composed entirely of organic liquids results in the formation of soft, sticky filament. However, it has been discovered that satisfactory fiber formation requires that certain organic liquid additives be used in the water of the spinning bath. These additives have the dual function of increasing the wetting power of water on the filaments and of reducing the surface tension and viscosity of the water. Suitable additives have been found to be polar organic compounds such as methanol, ethanol, propanol, butanol, pentanol, glycol, glycerol, ketones, polyglycol ethers, amides, and substituted amides. Especia'lly preferred additives are acetone, methyl ethyl ketone, dimethylacetamide, dimethylformamide, N-methyl-Z-pyrrolidone, and dimethylsulfoxide.

The most useful and practical additives for the spinning bath in accordance with this invention have been found to be the solvent systems used to dissolve polyvinyliene fluoride. These solvent systems have the greatest wetting and surface effect on polyvinylidene fluoride filaments because of their solvating action. Their use is particularly practical and economical because they can be stripped out of the spinning bath and reused to make more spinning solution.

The concentration of these additives varies widely, depending on the agent used. Concentrations of various materials have been found to be useful in the range of 0.05 to 50% by volume in water, but the preferred range is from 10 to about 25% by volume of additives.

In operation, the bath is thus preferably composed of water and solvent system. As the spinning process begins, the spinning bath contains between 10 and about 25% by volume of solvent system in Water. During the spinning process the solvent system is continuously extracted from the filaments, and its concentration in the spinning bath increases. Its concentration in the spinning bath is maintained within the 10 to 20% range by the continuous addition of water. At the conclusion of the spinning operation, a portion of the spinning bath is retained for future spinning runs, and the remainder is distilled to recover the solvents. The recovered solvents are used to prepare more spinning solution. During continuous spinning operations, a portion of the spinning bath is continuously removed, and the requisite amount of Water is added to maintain the concentration of solvents in water within the 10 to about 25 range.

Commercial wetting agents, textile softeners, lubricating agents, and anti-static agents may also be used in the coagulating bath. These improve the handling properties of the polyvinylidene fluoride yarns produced.

The temperature of the spinning bath of Step 2 is also critical. It affects the viscosity of the spinning solution and the strength of the filaments formed as the spinning solution emerges from the spinneret which is submerged in the spinning bath. The temperature also influences the rate at which the solvents are extracted from the filaments as they form. The temperature of the spinning bath thus partially determines the rate at which the surfaces of the filaments harden.

The temperature of the spinning bath influences the amount of water which may diffuse into the filaments, and this affects the physical properties of the filaments and yarns. Although yarn can be made with the spinning bath at temperatures from room temperature to the boiling temperature of the lowest boiling component of the spinning solution, the yarns of higher tenacities which are the subject of this invention are obtained at temperatures of to 135 F. The narrow range of to F. is the preferred condition for the operation of this invention.

One of the most important features of the invention is the close control of the residence time of the fibers in the spinning bath. It must be sufficiently long to cause enough hardening of the outer portion of the fibers to permit the withdrawing of the fibers from the bath and be sulficiently short to prevent a degradation or loss of fiber strength. It has been discovered that fibers which remain in the bath too long become white, opaque, and low in tenacity and elasticity. The tenacity of such filaments could not be increased beyond 2.1 to 2.3 grams per denier regardless of subsequent processing steps. The cause of the low strength of the filaments has been postulated to be water absorbed into the filament during spinning causing discontinuities or destruction of the normal morphological makeup of the filament. Regardless of the physical cause of this decrease in strength, it has been discovered that it can be avoided by using relatively short residence times in the spinning bath. This differentiates the process of this invention from normal wet spinning processes in which longer residence times are used to remove a large portion of the solvent from the filaments. These residence times will be determined for each individual polymeric solution as discussed below.

It is essential to the process of this invention as indicated, that the fibers be kept in the spinning bath long enough to harden the surface of the fibers, but not long enough to allow the fibers to become White and opaque. It has been found that this time period varies with both the temperature and the rate at which the liquid Within the spinning bath is circulated or agitated. At the optimum temperature range of 115 to 125 F. it has been found that a residence time of 0.1 to 0.5 sec. in the bath is the operable range, presuming agitation sufficient to maintain the to solvent concentration in the region of the spinneret. The preferred residence time for the filaments in the bath is 0.2 to about 0.3 second.

In Step 3, the partially hardened filament is drawn from the spinning bath through an oven whose temperature is 180 to 250 F. This oven is preferably so mounted that the fiber travels vertically to permit maximum draining of spinning solution from the filament. Forced convection through this oven is desirable to hasten the drying operation. The apparatus may consist of a forced hot air chamber, or of a radiant heat tunnel and may be heated to temperatures up to about 400 R, if close control of the filament throughput is maintained. The filament is pulled through the first oven by godet wheels.

In Step 4, the filament passes through a second oven maintained at a temperature of 500 to 800 F. The filament is pulled through this second oven by a second set of godet wheels running at a rate about 10% higher than the first set. The higher rate of speed of the second set of godet wheels, coupled with the shrinkage of the filament which accompanies the drying process, places the yarn under tension. Yarn leaving the second oven is substantially dry but may contain significant amounts of solvent. If solvent removal is not sufficiently complete, the yarn may be passed through a bath of water at about 200 F. and may additionally be passed through a vacuum drying chamber for final solvent removal.

In Step 5, the yarn is washed in water by any conventional means, generally at a temperature of from 100 F. to 180 F.

In Step 6, the yarn passes through a conventional twisting device which applies approximately 1 to about 12 twists per inch.

In Step 7, the yarn may optionally be vacuum dried to insure rapid and complete removal of solvents and water from the yarn.

The polymeric structure is oriented in Step 8 by drawing the yarn with additional sets of godet wheels. The draw ratio for most polyvinylidene fluoride yarns will be from about 3 to about 10 to 1, with most commercial applications falling within the range of from about 4.5 to about 6.5. Optimum draw ratio for any individual yarn will depend on the strength of the individual filaments and on the purpose for which the yarn will be used. Orientation is accomplished in ovens in order to heat the yarn to permit greater freedom of movement of individual molecules and to obtain more uniform orientation. The temperature of the oven will vary with the rate of throughput but in general will be from about 250 to about 400 F. at throughput rates offrom 10 to 50 yards per minute.

The yarns of this invention have properties as shown in Table I below. These properties have made fabrics 8 manufactured from these yarns useful for a variety of purposes such as filter cloth, chemical and solvent resistant cloth, and dimensionally stable cloth which has no water absorption and which is unaffected by changes in.

relative humidity in the atmosphere. By the practice of this invention it is possible to fabricate yarns containing one or a multiplicity of filaments with tenacities of above 2.5 grams per denier.

Table I.Properties of polyvinylidene fluoride yarn No. of ends1 to 100 Yarn denier12 to 1500 Filament denier-5 to 20 Yarn tenacity (at room temperature) 2.5 to 3.5 g./d.

I-LT. yarn- 3.0 to 3.5)

Tenacity at 210 F.2 to 2.5 g./d.

Tensile strength (avg. filament) lb./ sq. in.60,000 to 75,000 p.s.i.

Shrinkage (1 hr. in boiling water)2 to 10% Elongation at rupture-12 to 22% Softening range-275 to 300 F.

Melting range325 to 335 F.

Specific gravity-1.77

Water absorption (moisture regain)-0.5%

Refractive indexl.42 (11 Specific heat, cal./g. 1 C.-0.33

Thermal conductivity, cal./sec./cm. C./cm.--

Elastic recovery-(100% up to 10% extension-estimated) Elastic modulus (lbs./sq. in.)150,000 to 550,000

Relative stiffness, g./d.--20 to 45 (estimated) Relative toughness-0.3 to 0.6 (estimated) Coefficient of friction0-O.1

Resistance to abrasion-good Resistance to aging-excellent Resistance to sunlightexcellent Resistance to biological attackexcellent Resistance to chemicals-very good (resistance to all common acids, alkalis, oxidants and solvents. Degraded by fuming sulfuric acid and alkylamines. Partially dissolved by acetone, dioxane, dimethylacetamide, dimethylformamide, dimethylsulfoxide, and N-methyl-2-pyrrolidone Life of yarn at 212 F.unlimited Usable temperature range: to 275 F.

Flammability-chars; does not burn The following examples numbered IV through X illustrate the polyvinylidene fluoride yarn and the process for producing it by this invention. Examples I, II and III illustrate the differences between the well known wet, dry and melt spinning processes and the process of this invention.

Example l.Wet spinning of polyvinylidene fluoride yarn The following wet spinning experiment demonstrates the inability of vinylidene fluoride to be wet spun into yarns having strengths as high, as 2.5 grams/denier even when close supervision and control are exercised over each step of the process.

350 g. of polyvinylidene fluoride polymer is added slowly with continuous stirring to g. of dimethylacetamide at C. The solution is stirred until it cools to room temperature, then filtered under 45 lbs. per sq. in. pressure through a 2 in. (uncompressed and dry) hat of absorbent cotton. The solution has an initial viscosity of 125,000 centipoises which increases on standing and varies from batch to batch prepared by the same procedure. The viscosities generally range between 125,000 and maximum 1 of 150,000 centipoises.

The solution is placed in the reservoir of the spinning ameter. The fiber emerging from the spinneret is passed horizontally through a four-foot-long bath of water maintained at 65 C. and wound on a paper tube at the rate of 4 ft./min. The 20 end yarn obtained is air dried by standing at room temperature. When dry, the yarn is fed at the rate of 3 ft./min. into an eight foot long bath at glycerin maintained at 137 C. The yarn is pulled out of the bath at 9 ft./min. thus drawing it to three times its original length. Experimentation shows that this is the maximum extent to which the yarn can be drawn. The yarn is washed thoroughly with water, dried, and examined. The yarn is white and opaque. Microscopic observation shows essentially circular fibers with a milky color. The denier is measured at 135, and the tenacity is found to be 2.15 g./d. The elongation at rupture is 16%.

Example 2.-Dry spinning of polyvinylidene fluoride yarn The following example illustrates the inability of vinylidene fluoride to be dry spun into yarns having tenacities as high as 2.5 g./d. even under close control.

A polyvinylidene fluoride polymer solution is prepared and filtered by the methods described in Example 1. The composition of the solution is 400 g. polyvinylidene fluoride, 667 g. dimethylacetamide, and 333 g. acetone. The viscosity of this solution is 74,133 cps, The solution is spun in the same manner through the same spinning apparatus used in Example 1. The spinneret assembly is pointed downward, and a four foot long heated oven is mounted below the spinneret enclosing the spinneret. The filaments are drawn downward through the oven onto a take-up tube at the rate at which they extruded from the spinneret orifice. The oven temperature is 145 F., and the spinning rate is 5 cc./min.

The resulting yarn is examined and is found to contain both a large number of broken filaments and many sections in which the filaments are fused together. No physical properties can be measured.

Example 3.Melt spinning of polyvinylidene fluoride yarn The following example illustrates the inability of vinylidene fluoride to be melt spun into satisfactory yarns having strengths of 2.5 g./d. and freedom from excessive filament breakage.

A one inch extruder is fitted with a die holder and a die plate containing eight orifices equally spaced in a A; in.-diameter circle. The orifice diameter is 0.028 in. The channel through which the polymer melt passes within the die holder is conical, tapering from 1 in. at the breaker plate to A-inch. in a distance of 1 /2 in. The channel bends 90 downward at the apex of the cone and continues to the die plate. The entrance to the die plate is also an inverted cone, increasing in dameter from A in. to 1 in. in 1 /2 in. The polymer melt is distributed to the die orifices by a cone fabricated from stainless steel and attached to the inner face of the die plate. This cone is A-inch in diameter tapering to a point in 1% inches.

The extruder is operated at a rate suflicient to extrude /2 lb. of polyvinylidene fluoride per hour. The die temperature is maintained at 550 F.

The resulting eight filament yarn consists of rough filaments with evidence of melt fracture. That is, fissures and fracture are present in the filaments, presumably caused by greater shear rates than the molten polymer can Withstand without forming voids in the melt. The filaments cannot be drawn to increase their strength and decrease their diameter without excessive filament breakage.

Example IV.-Po1yvinylidene fluoride spun by the method of the present invention The spinneret assembly described in Example 1 is mounted on a %-inch I.D. pipe immersed in a ten-gallon container. The spinneret used has 100 jets, 0.010 in diameter. The ten gallon container is filled with 8.0 gallons of distilled water and 1 gallon of acetone. The solution 10 is stirred by a laboratory stirrer with a 3 bladed propeller 2 in. in diameter at the rate of 300 r.p.m. The solution is heated and maintained at 120 F. The spinneret assembly is adjusted so that the face of the spinneret faces upward four inches below the surface of the bath.

A solution of polyvinylidene fluoride is prepared using polymer which has been washed with an equal weight of absolute methanol in a one gallon capacity blender, filtered on a Buchner funnel, sucked dry, and dried 24 hours at 110 C. and mm. pressure. Dimethylacetamide is treated with activated charcoal and filtered. A solution using 4800 g. polyvinylidene fluoride, 9600 g. dimethylacetamide, and 6400 g. cps. acetone, is made and filtered as in Example 1. After standing one week the viscosity of the solution at room temperature was 28,000 cps.

The solution is spun through the spinneret at the rate of 17 cc./rnin. The yarn is pulled upward 3 ft. over a system of wiper bars and around a 2 in. pulley. The yarn then is pulled horizontally through a 4 ft. long air oven maintained at 230 to 235 F. The yarn is pulled by godet wheels at the rate of 3 yd./'min. The yarn is pulled through a second oven 32 inches long by a second set of godet wheels running at the rate of 3.3 yd./min. The oven is maintained at 750 F. at the entry end graduated in four zones to 650 F. at the exit end. The yarn is pulled through the oven for a second pass at 3.3 yd./min. The yarn then is pulled through a wash bath containing water at 200 F. The yarn is stretched 3 to 1 in this bath over a distance of 9 yd. The yarn is finally taken up on 2 in. diameter paper tubes at 10 yd./min.

After taking the yarn onto the tubes, the tubes are mounted vertically on a rotating spindle and the yarn taken off the end through an eyelet to uptwist it. The yarn is twisted one twist per inch and fed over 8 inch diameter drawing rolls at the rate of 14.4 yd./min. It is then passed through an oven 6 ft. long and onto a second set of drawing rolls at 18.1 yd./min. The yarn then-is passed through a secondoven 2 ft. long and passed onto a third set of drawing rolls at 16.5 yd./ min. The first oven is maintained at 398 F. and the second at 405 to 425 F. The yarn is taken up onto 2" paper tubes and dried 16 hrs. at C. and 200 mm. pressure (absolute).

The yarn is then finally oriented and heat set by passing it through the twisting and drawing procedures described above. Feed rate is 15 yd./min. Twist is one turn per inch of S twist. Draw ratio is 1.4 to 1. Heat setting ratio is 1.0 to 1. Drawing oven temperature was 330 F. Heat set oven temperature is 405 to 429 F.

The physical properties of the finished yarn are: denter-983, load at rupture'3092, tenacity3.l5'g./d., g./d., elongation at rupture-15%.

Example V.Polyvinylidene fluoride spun by the method of the present invention Example four is repeated to determine the reproducibility of the method and apparatus of the present invention. The physical properties of the resulting yarn are denier-l055, load at rupture3293 g., tenacity-3.12 g./d., elongation at rupture-15%.

Examples VI to X To further check the reproducibility of the method and to demonstrate a colored, low static electricity yarn, Example IV is repeated as follows.

A solution is prepared, containing:

5000 g. Ll8-6203-9 Kynar polyvinylidene fluoride 10,000 g. N,N-dimethylacetamide 6,000 g. acetone 1.5 g. Brilliant Blue BGS dye Five lb. samples of yarn are prepared using the following conditions:

Spinning conditions Twisting and drying conditions Twist rate0.8 to 0.9 t.p.i.

Feed rate--14.4 yd./-min.

Drawing oven temperature-389 to 394 F. Drawing rate15.8 yd./min.

Heat set oven temperature-640 to 545 F.

3rd drawing roll ratel5.8 yd./min.

Draw ratio 1.08 to 1.12

Vacuum drying16 hrs. at 110 C. and 200 mm.

Orientation and heat set conditions Feed rate for orientation-14.4 to 14.5 yd./min. Orientation oven-341 to 343 F.

Drawing rate-43 to 44 yd./min.

Orientation drawing ratio-2.99 to 3.07/1

Heat set temperature-405 to 429 F.

Heat set rate-43 to 44 yd./min.

Twist-0.89 to 0.96 t.p.i. (s)

' The resulting yarn was uniformly colored throughout the filaments. Microscopic observation showed the dye to be distributed uniformly through the interior of each filament, but to be occluded instead of dissolved. When the yarn is held loosely in a skein after removing it from a denier reel, there is very little ballooning or repulsion among the several strands of yarn. Undyed polyvinylidene fluoride yarns such as described in Examples IV and V have a tendency to accumulate a large static electrical charge, and they balloon as do the leaves of a charged electroscope when they are held loosely.

The physical properties of the yarns produced in EX- amples VI to X were:

Breaking load Tenacity in Elongation at Example Denier in grams g./denier Rupture,

Percent 12 Example XI A polyvinylidene fluoride yarn is produced exactly according to the methods used in Examples VI to X except that no twisting is done to the yarn. After all other steps have been completed, the individual filaments are separated and are tested according to the methods used to establish the physical properties in Examples VI through X. Each of the individual monofilament yarns is found to have a tenacity greater than 3.0 grams per denier.

It is to be understood that the foregoing embodiments of the invention are for purposes of illustration only and that the invention is not limited thereto.

We claim:

1. A process for the manufacture of polyvinylidene fluoride yarn having a tenacity of at least 2.5 grams per denier which comprises the steps of spinning a solution of from 10 to 50 parts by weight of polyvinylidene fluoride in 100- parts by weight of solvent consisting essentially of a mixture of (a) an amide selected from the group con- Sisting of dimethylformamide and dimethylacetamide and ('b) a ketone selected from the group consisting of acetone and methyl ethyl ketone into a coagulation bath having a temperature of from about 100 F. to about 135 F. and consisting essentially of a mixture of 75% to by volume of water and from 10% to 25% by volume of a ketone selected from the group consisting of acetone and methyl ethyl ketone, passing the polyvinylidene fluoride filaments thereby formed into an evaporative zone to evaporate all solvents and water therefrom, and orienting the filaments by drawing.

2. The process of claim 1 wherein the spinning solution has a viscosity of from 1000 to 250,000 centipoises.

3. The process of chaim 1 wherein the spinning bath is at a temperature of from to F.

4. A multi-filament high-tenacity polyvinylidene fluoride yarn consisting of filaments of polyvinylidene fluoride produced by the process of claim 1.

References Cited UNITED STATES PATENTS 2,531,406 11/1960 D'Alelio. 2,405,008 7/ 1946 Berry 18-1155 2,821,459 1/ 1958 Morris 18-54 FOREIGN PATENTS 845,634 8/ 1960 Great Britain.

ALEXANDER H. BRODMERKEL, Rrinwry Examiner.

H. W. LUCKOWER, Examiner.

I. H. WOO, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,376,370 April 2, 1968 Francis P. Koblitz et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 19, "solvent" should read solvents line 39, solevent" should read solvent line 47, "filament" should read H filaments line 63, after "evident" insert H that Column 5, line 15, after "still" insert more preferred to maintain a high concentration of vinyliline 48 "S ucessful" should read Successful line 71 "filament" should read filaments Column 10, line 52, cancel "g./d. Column 12, line 33, "chaim" should read claim Signed and sealed this 29th day of July 1969.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. A: testing Officer Commissioner of Patents