US3378514A - Process for making polycarbonamide yarns - Google Patents

Description

United States Patent 3,378,514 PROCESS FOR MAKHNG POLYCARBON- AlifliDE YARNS Liiburn Lafayette Norton, Seaford, Del, assignor to E. I. du Pont de Nemours and Company, Wilmington, Deb, a corporation of Delaware No Drawing. Fiied Feb. 9, 1965, Ser. No. 431,447 7 Claims. (Cl. 265-37) ABSTRACT OF THE DISCLOSURE Polycarbonamides having reduced friction in yarn form are made by carrying out the polymerization in the presence of kaolinite then melt extruding the mixture. The tendency for excessive buildup of spinnerette pack pressure during spinning caused by accumulation of solids in the pack can be reduced by pretreating the kaolinite to deposit aluminum oxide on the surface thereof.

This invention relates to an improvement in kaolinitemodified synthetic, fiber-forming polycarbonamides. More particularly it relates to such an improvement for reducing certain processing difiiculties in the melt-spinning of low friction filaments therefrom.

Ordinarily, melt-spun polycarbonamide filaments are characterized by a relatively smooth surface which gives high friction when yarn thereof is passed into contact with various guides used in the processing of the yarn into end products. Particularly in the production of yarn by the newer coupled process, i.e., where the filaments are extrudcd, quenched and drawn in a continuous operation without intermediate packaging before drawing, the filaments tend to have an extremely smooth surface such that the yarn-to-guide friction is even higher than previously encountered. Increased friction results in higher and more variable tension, which in turn causes undesirable nonuniformities such as streaks in a fabric produced from the yarn.

One attempt to reduce yarn friction is described in Belgian Patent 646,680, dated May 15, 1964, and involves polymerization of the polycarbonamide forming constituents in the presence of an aqueous slurry of kaolinite and a heat stable defiocculant. Upon melt-spinning and drawing filaments of such a kaolinite-modified polymer, a surface roughness is developed in the form of numerous bumps elongated in the direction of the fiber axis. The reduced fiber surface that is available to contact yarn guides and the like accounts for a marked decrease in friction. An attendant disadvantage of the use of such kaolinite-modified polycarbonamides, however, is that there is often a tendency for excessive build-up of spinneret pack pressure during spinning, i.e., as caused by an unduly high amount of filtered solids accumulating in the spinneret pack. Where the life of the spinneret packs is thereby materially reduced, the economies of the spinnin g operation suffer accordingly.

In accordance with the present invention it has been found that kaolinite-modified polycarbonamides exhibiting reduced friction in the form of yarn can be produced by the use of pretreated kaolinite so as to minimize the aforementioned processing difiiculties; namely, of excessive build-up of spinneret pack pressure. In particular it has been found that these difiiculties can be largely overcome if the polymerization of the polycarbonamide is conducted in the presence of an aqueous slurry containing finely-divided kaolinite particles and a heat stable defiocculating agent, the finely-divided kaolinite particles having been pretreated by the steps of adding thereto in aqueous medium a fluocculating agent and an alkali metal aluminate, acidifying to precipitate aluminum hydroxide on the kaolinite particles, and separating and washing the particles. Sodium aluminate is preferred for use in the process of the invention but other water soluble alkali metal aluminates, e.g. potassium aluminate, may be used in lieu thereof.

The aluminum hydroxide thus deposited upon the surface of the kaolinite particles is converted to aluminum oxide by dehydration as water is removed from the polymerizate. Evidence tends to indicate thatthe aluminum oxide on the surface of the kaolinite particles may tend to reduce interaction with the polymer prior to filtration and in this way reduce gel-formation in the polymer and facilitate filtration. It will be understood that a number of other factors, e.g. the scale of the operation and the type of filter used, will also have some influence upon the pressure rise encountered during filtration.

In the pretreatment of the kaolinite, a slurry thereof in aqueous medium should contain about 0.1 to 1.0% by weight, based on the kaolinite, of magnesium sulfate or other flocculating agent for kaolinite and about 0.1 to 1.5% by weight, based on the kaolinite, of the aluminate salt. Other suitable fiocculating agents include zinc sulfate and the alkali metal sulfates, e.g. sodium and potassium sulfate.

The concentration of kaolinite in the slurry is preferably from about 200 grams/liter to about 400 grams/ liter. The slurry is desirably substantially neutral (pH 6.5-7.5) prior to addition of the magnesium sulfate and sodium aluminate. After addition of the sodium aluminate, the solution becomes alkaline and acid is added to neutralize the slurry and precipitate the aluminum as aluminum hydroxide. The pH of the slurry should be adjusted to the range of 6.5-7.5 to effect maximum precipitation of the aluminum as the hydroxide. The aluminum hydroxide is adsorbed on the surface of the kaolinite where it is later converted toaluminum oxide by dehydration.

De-ionizcd Water should be used to prepare the slurry I and to wash the precipitate. The water may be de-ionized by distillation or by passage through a de-ionizing column as is common practice in the purification of water for various purposes.

The term kaolinite refers to thin, hexagonal platelets of Al O -2SiO -2H O having the kaolinite crystal structure described by C. E. Marshall in The Colloid Chemistry of the Silicate Minerals, Academic Press, Inc., New York, N.Y., 1949, pp. 49 and 72. For the purposes of this invention, it is necessary to use a purified kaolinite which is substantially free of all metal oxides other than those of aluminum and silicon. It is desirable to use a kaolinite in which the platelets have an average maximum dimension of from 0.2-2.0 microns and which is substantially free of platelets larger than 5 microns. The presence of particles larger than about 5 microns results in the plugging of sand packs in the melt spinning operation. On the other hand, particles smaller than about 0.2 micron do not give the filament surface roughening effect which is necessary for reduced running tensions.

The aqueous slurry of kaolinite which is added to the polymer is preferably prepared by mixing a sufficient quantity of the pretreated kaolinite with water to give a 20-75% by weight slurry thereof. A heat stable defiocculant in an amount of from ODS-3% by weight based on the weight of kaolinite is also added. Preferably, the acidiiy of the slurry is adjusted to give a pH of 6 to 10. The slurry is stirred for at least 1 hour, preferably 4 hours, and then diluted to 10-40% solids-and allowed to stand until the larger particles have settled, preferably about 20 hours. After settling, the slurry is decanted from the settled material, again stirred and sutficient wafer added to adjust the concentration to the desired level for introduction into the polymerization system. Usually a slurry concentration of -25% by weight is preferred when the polymer is to contain 0.5-2% by weight kaolinite. Amounts of kaolinite up to 17% by weight, based on polymer, may be used. After adjusting the concentration, the slurry is passed through a filter having a mean porosity rating of 5 microns (Cuno Filter, Cuno Engineering Corporation, Meriden, Conn.) and thus made ready for injection into the polymerization system.

By heat stable deflocculant is meant a material which promotes dispersion of kaolinite in water by breaking agglomerates to an average equivalent spherical diamefer of 0.3-1 micron, preferably about 0.5 micron. Furthermore, it does not lead to discoloration. Illustrative of the reagents suitable in the process of this invention are tetrasodium pyrophosphate, sodium siIicate, sodium hexametaphosphate, collodial silica, lithium hydroxide, low molecular weight sulfonated naphthalene-formaldehyde condensates, and certain amines and amides. The presence of a suitable defiocculant in the correct amount is essential to provide defiocculation of the kaolinite particles in the aqueous slurry and to prevent agglomeration of particles during the polymerization process.

The size or maximum dimension of the kaolinite particles is determined by means of the electron microscope (ASTM E20-51T) but may also be determined by light scattering techniques.

The prepared kaolinite slurry is incorporated in the pol 'mer by addition to the aqueous solution of nylon salt, either at the beginning of the polymerization or at some later point during the polymerization procedure. Preferably, the slurry is added after polymerization has started but before an appreciable viscosity change has een realized according to the general procedure of H00? in U.S. Patent No. 2,278.878. In continuous polymerization procedures, it is preferred that the kaolinite slurry be added according to the method of Heckert, as described in US. Patent No. 2,689,839.

Following the addition of the slurry to the polymerization mixture, the process is continued in the conventional manner to give a fiber-forming polymer. The polymer may be forwarded in the molten state through conduils to a spinning machine and there melt-spun into filaments which are subsequently drawn to give strong textile fibers. Alternatively, the polymer may be extruded as a ribbon, quenched, cut to flake and subsequently remelted for spinning into textile fibers on conventional melt-spinning equipment.

The term synthetic linear polycarbonamide is intended to include any linear polymer having recurring units of the formula I: l H :l R O as integral parts of the main polymer chain, wherein R is hydrogen or a monovalent hydrocarbon radical, the average number of carbon atoms separating the amide groups being at least 2. The polycarbonamide should be fiber forming as indicated by having an intrinsic viscosity of at least about 0.4, as defined in US. Patent No. 2,130,948. Particular polycarbonamides included among those which are useful in this invention are as follows: polyhexamethylene adipamide, polyhexamethylene sebacamide, polymerized 6-aminocaproic acid (or the corresponding lactam), polytetramethylene sebacamide, polytetramethylene adipamide, polymetaxylylene adipamide, the polyamide from bis(4-aminocyclohexyl)methane and azelaic, sebacic or decamethylene-1,10-dicarboxylic acid, and the polyamide from Z-methylhexamethylene diamine and terephthalic acid. The invention is also applicable to various copolymers, either block or random, such as the copolymer of polyhexamethylene adipamide with polyhexaa methylene isophthalamide, the copolymer of polyhexamethylene adipamide with polyhexamethylene-t-butyl isophthalamide and the tcrpolymer of polyhexamcthyleue adipamide with polyhexamethylene sebacamide and po- 4 lymerized G-aminocaproic acid. Other polycarbonamides suitable for use in the present invention are disclosed in U.S. Patents Nos. 2,071,251 and 2,071,253.

The following example further illustrates the practice of the invention. It is not intended to limit it in any way.

Example Commercially available kaolinite powder, purified by the ultrafiotation process (US. Patent 2,990,958) to substantially eliminate metal oxides other than aluminum and silicon oxide and classified by centrifugation to provide an average maximum dimension of 0.55 micron, is added to de-ionized water to form a slurry containing 300 grams per liter of the kaolinite powder. The pH of the slurry is 6.8. As a fiuocculating agent, sufficient magnesium sulfate solution (50 grams MgSO '7H O per liter H O) is added to the slurry to provide a concentration of 0.3% lvlgSO -7H O based on the weight of kaolinite powder. The slurry, which now has a pH of 6.1-6.2 is mixed for minutes. Suflicient sodium aluminate solution in H 0 (320 grams/liter sodium aluminate calculated as Al O is added to provide a concentration equivalent to 1% A1 9 based on the weight of the kaolinite powder and the slurry which now has a pH of 11.8-11.9 is mixed for 30 minutes. The pH of the slurry is then adjusted to 7.0 with concentrated sulfuric acid and the slurry heated to 60, followeod by additional mixing for 1 hour. The slurry is then filtered and the wet filter cake of kaolinite washed with hot de-ionized water to remove soluble salts, the washing being continued until the filtrate shows a minimum of 7,000 ohms resistance as measured with a conventional conductivity meter.

The wet filter cake is mixed with die-ionized water containing 0.3/ by weight sodium silicate, based on kaolinite, in a high shear mixing mill to form a slurry containing two hundred parts of kaoiinite (dry basis) and 300 parts water. After milling for 1 hour, the mixture is diluted with 300 parts de-ionizcd water, transferred to a tank, adjusted to pH 9 by addition of sulfuric acid or ammonium hydroxide and stirred for 24 hours. After mixing, the slurry is allowed to settle for hours, then decanted from the settled material and diluted with water to a concentraion of 20% by weight total solids. The diluted slurry is then passed through a standard commercial filter having an average pore size of 5 microns and continuously stirred until used.

Polymer containing kaolinite from the above-prepared slurry is prepared in a stainless steel autoclave modified as in US. Patent 2,278,878. The autoclave is charged with 467 parts by weight of an aqueous solution containing 47% by weight hexamethylene diammonium adipate and 2.1 parts by weight of an aqueous solution containing 25% by weight acetic acid, purged of air, filled with nitrogen and heated until its temperature reaches approximately 215 C. at 250 p.s.i. At this stage, bleeding off of water vapor is begun and an appropriate amount of the previously-prepared kaolinite slurry is added to give a concentration of 2% by weight in the final polymer. The kaolinite slurry is pumped into the autoclave over a period of ten minutes. The polymerization cycle is continued as described in Example I of US. Patent 2,163,636, giving a molten fiber forming polymer having a relative viscosity of 42 (measured at 25 C. as 8% by weight solution in 90% formic acid). The polymer is extruded in the form of a ribbon upon a casting wheel, quenched, and cut into chips suitable for remelting and melt-spinning as taught in Example 1 of US. Patent 2,289,774.

The polymer chips obtained above are melt-s ,un into -filament yarn using a spinning pack containing a sand filter of the general type described in US. 2,266,363. The filter consists of an upper layer of sand of porosity five times greater than -80 mesh sand, followed by a layer of 150-200 mesh sand, the two layers being supported by a sintered metal disc of porosity intermediate between -150 mesh and -200 mesh sand. The

5, filaments are quenched and drawn to form a 70-denier yarn in the conventional manner. The drawing of the filaments develops reduced frictional properties by the creation of a roughened surface of numerous small size bumps on the surface of the filaments.

During the spinning of the polymer, it is noted that the pressure required to force the polymer through the spinning packs increases at an average rate of 11 lbsi/ sq. in./hr. (0.77 kg./sq. cm./hr.) for the first 36 hours. By comparison, a pressure rise of 25.5 lbs/sq. in./hr. (1.79 kg./sq. cm./hr.) is found for polymer prepare-d in an identical fashion except that the pretreatment ofthe kaolinite particles is omitted.

The yarn containing pretreated kaolinite exhibits reduced friction and reduced surface luster as compared to yarns produced without the kaolinite. When yarn is processed into fabric, the running tensions are lower and more uniform than experienced in the absence of the kaolinite and the fabric is found to be improved with respect to quille barre, long-length tension streaks and short-length uniformity.

As many widely different embodiments of this invention may be made without departing from the'spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

What is claimed is: a

1. In a process for the prepration of a fiber-forming synthetic linear polycarbon-amide having recurring units of the formula N IC [1. a l

as an integral part of the main polymer chain, wherein R is hydrogen or a monovalent hydrocarbon radical, the average number of carbon atoms separating the amide groups being at least 2,

which process comprises polymerizing the polycarbonamide in the presence of an aqueous slurry containing (1) kaolinite platelets having an average maximum dimension of from 0.2 to 2.0 microns, substantially none of the platelets having a dimension larger than 5 microns, and (2) a heat stable defiocculating agent selected from the group consisting of tetrasodi-um pyrophospha'te, sodium silicate, sodium hexametaphosphate, colloidal silica, lithium hydroxide and low molecular weight sulfonated naphthalene-formaldehyde condensates whereby the polycarbonamide exhibits reduced friction in the form of yarn,

the improvement wherein the kaolinite platelets are pretreated by the steps of (A) adding thereto in aqueous medium (1) a flocculating agent selected from the group consisting of magnesium sulfate, zinc sulfate, sodium sulfate, and potassium sulfate, and (2) an aluminate selected from the group consisting of sodium aluminate and potassium aluminate, (B) acidifying to a pH in the range of about 6.5-7.5 to precipitate aluminum hydroxide on the kaolinite platelets then (C). separating and washing the platelets.

2. Process of claim 1 wherein the polycarbonamide is polyhexamethylene adipainide.

3. Process of claim 1 wherein the kaolinite is substantially free of metal oxides other than those of aluminum and silicon.

4. Process of claim 1 wherein the defiocculant is present in the slurry at a concentration of from 0.05 to 3% by weight based on kaolinite..

5. Process of claim 1 further comprising the step of melt spinning filaments from the polycarbonamide.

6. Process of claim 1 wherein, in the pretreatment of the kaolinite, the concentration of kaolinite in the aqueous medium is about 200 to about 400 grams/liter, and the amounts of fiocculating agent and aluminate added are, respectively, about 0.1 to 1.0% by weight and about 0.1 to 1.5% by weight, based on the kaolinite.

7. Process of claim 6 wherein the aqueous slurry contains 10 to 40% by weight of total solids including 0.05 to 3% by weight of the defiocculant, based on kaolinite, and wherein, in the polymerization step, the concentration of kaolinite is 0.5 to 17% by weight based on the polycarbonamide.

References Cited UNITED STATES PATENTS 2,205,722 6/ 1940 Graves 26037 2,341,759 2/ 1944 Catlin 260-37 2,385,890 10/1945 Spanagle 26037 2,387,534 10/1945 Seidel 106308 3,151,993 10/1964 Bundy 106-288 MORRIS LIEBMAN, Primary Examiner. JULIUS FROME, Examiner.

S. L. FOX, Assistant Examiner.