Polyester-based spandex filament and process for its preparation

Abstract: A polyester-based spandex filament or film is provided. The filaments when used in swim-wear fabrics provide the fabrics with increased resistance to mildew-induced degradation. The filaments are formed from a spandex derived substantially from a poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate)­ glycol having no more than 15 milliequivalents of glycol acidity per kilogram of glycol, which glycol is capped with an organic diisocyanate and then chain-extended with an aliphatic diamine.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an elastic filament formed from a spandex polymer derived from a hindered polyester, an organic diisocyanate and an aliphatic diamine chain extender. The invention particularly concerns such a filament wherein the polyester is derivable from 2,2-dimethyl-1,3-propane diol (neopentyl glycol) and 1,12-dodecanedioic acid. The spandex filaments of the invention have improved resistance to degradation by mildew attack. Description of the Prior Art Elastic filaments of polyester-based spandex polymer can be prepared from a hydroxyl-terminated polyester which is capped with an organic diisocyanate and then reacted with an aliphatic diamine chain extender. The polyester forms what is called the "soft segment" of the polymer; the diisocyanate and diamine form the so-called " hard segment". The polymer can then be formed into filaments or films by known techniques. For example, filaments may be formed by dry spinning. Many such polyester-based spandex filaments are known. Some have enjoyed considerable commercial success, but their value could be further enhanced by certain improvements. For example, in swim-wear fabrics, although such filaments usually have adequate resistance to attack by swimming-pool chlorine, the filaments often degrade because of mildew attack. Accordingly, an object of the present invention is to provide a polyester-based spandex filament that has satisfactory elastic and tensile characteristics and satisfactory chlorine-resistance, but that also resists degradation caused by mildew attack. Many hydroxyl-terminated polyesters made from α,ω-dicarboxylic acids and glycols have been disclosed for use in making the polyester-based spandex polymers. Generally, a preference is disclosed for acids that contain ten or fewer carbon atoms. However, none of the disclosures address the problem of mildew resistance or specifically mention poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) as a soft segment of a polyester-based spandex filament. For example, United States Patents 3,009,762 (Kohrn et al) and 3,009,765 (Slovin et al) disclose such hydroxyl-terminated polyesters derived from glycols and saturated organic dicarboxylic acids, the glycols and acids each having from 4 to 20 carbon atoms. These patents disclose that preferred polyesters precursors have a molecular weight of 1500 to 3000 and an acid value of less than 1. An acid value of 1 is equal to a glycol acidity of about 17.6 milliequivalents per kilogram (meq/kg). Among the polyesters specifically mentioned, though not exemplified, is a hindered polyester, poly(neopentyl sebacate). United States Patent 3,097,192 (Schilit) discloses elastic filaments of polyester-based spandex polymers and states that when the ester function is hindered, as with polyesters made with 2,5-hexane diol or 2,2-dimethyl-1,3-propane diol, the hydrolytic stability of the polymer is enhanced. In Examples II and IX, Schilit discloses a polyester-based spandex filament made with a polyester soft segment formed from sebacyl chloride and 2,2-dimethyl-1,3-propane diol. However, the tensile and elastic characteristics of the disclosed filaments are clearly in need of significant improvement. Among the many other patents that disclose hydroxyl-terminated polyesters for segments of spandex filaments are United States Patents 2,621,166 (Schmidt), 2,956,961 (Kibler et al), 3,211,701 (Muller et al), 3,481,905 (Weiden et al), 3,496,144 (Kunde et al), 3,506,617 (Collardeau et al) and 3,907,863 (Voss). From a practical standpoint, some degradation of the spandex filament from mildew attack can be tolerated without it being objectionable to users of the fabrics containing the filaments. However, the utility of the polyester-based spandex filaments would be much improved by increases in their mildew resistance. SUMMARY OF THE INVENTION The present invention provides an improved elastic filament or film formed from a spandex polymer having a hindered polyester soft segment and a hard segment derived from an organic diisocyanate and a diamine chain extender selected from aliphatic diamines, tetrachlorometa-xylylene diamine and tetrachloro-para-xylylene diamine. The hindered polyester segment is made from a poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) glycol including up to 25% of copolymerised units of other aliphatic diacids and/or glycols and having a molecular weight in the range of 1700 to 3000, preferably in the range of 2200 to 2700, most preferably in the range of 2300 to 2600, and a glycol acidity, measured by the method of ASTM-1638-67T, of no more than 15 milliequivalents per kilogram, preferably no more than 10 meq/kg and most preferably no more than 5 meq/kg. The spandex polymer is such that an as-spun elastic filament thereof has a set of less than 25%, an unload power of at least 0.027 gram per effective denier (gped) and a break elongation of at least 400%, as determined in accordance with the method of ASTM D 2731-72 as described herein. There is also provided a process for making a spandex filament or film of the invention, wherein in the presence of an inert organic solvent 2,2-dimethyl-1,3-propanediol is reacted with 1,12-dodecanedioic acid to form a hydroxyl-terminated polyester having a molecular weight in the range of 2200 to 2700 and a glycol acidity of no more than 15 meq/kg, the thusly formed polyester is reacted with an organic diisocyanate to form an isocyanate-terminated polyester having an isocyanate end-group content in the range 2.2 to 3.3%, the isocyanate-terminated polyester is then chain-extended with an aliphatic diamine to provide a viscous spandex polymer solution having a relative viscosity in the range of 1.5 to 1.9 (as determined with a 0.5% concentration of the polymer in N,N-dimethylacetamide solvent), and the polymer solution is formed into filaments or film. In the process of the invention, the organic diisocyanate is preferably an aromatic diisocyanate, most preferably methylene bis(4-phenyl isocyanate), and the diamine chain extender is preferably a mixture of ethylene diamine and 1,3-diaminocyclohexane. Preferred heat-set elastic filaments of the invention have, in addition to improved mildew resistance and satisfactory chlorine resistance, tensile and elastic characteristics that include a set of no more than 25%, an unload power of at least 0.036 gped and a break elongation of at least 300%. BRIEF DESCRIPTION OF THE DRAWING The invention will be more readily understood by reference to the drawing which presents a graph of the heat-set unload power and percent set of a filament of the invention as a function of the glycol acidity of a hydroxyl-terminated poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) used to form the soft segment of the filament spandex polymer. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As used herein, the term "fiber" includes staple fibers and/or continuous filaments. "Spandex" has its usual definition; that is, a long chain synthetic polymer that comprises at least 85% by weight segmented polyurethane. The terms "soft segment" and "hard segment" refer to specific portions of the spandex polymer chains. The soft segments are the polyester portions of the segmented polyurethane polymer and the hard segments refer to the portions of the polymer chains that are derived from the reaction of an organic diisocyanate with a diamine chain extender. Glycol acidity, as used herein, refers to end groups, such as acid end groups, of the polyester glycol precursor which do not react with organic diisocyanates under conventional urethane-forming conditions, such as those illustrated in the examples below. The isocyanate end group content of a polymer may be referred to as the NCO content. As noted, the spandex polymer for use in the present invention comprises a soft segment made substantially from a poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) glycol having a certain maximum glycol acidity. The term, "substantially made from", is intended to include in the glycol a small portion (i.e. up to as much as 25%) of copolymerized units of other aliphatic diacids and/or glycols, so long as these other acids and/or glycols do not detrimentally affect the mildew resistance, tensile and elastic properties of the final filaments or films. In accordance with the present invention, a polyester-based spandex filament of improved mildew resistance is provided when a particular hindered polyester soft segment is included in the spandex polymer chains. The particular soft segment is poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate). For ease of manufacture, the polyester soft segment usually is prepared from the corresponding hydroxyl-terminated polyester. Conventional methods, such as those described in R. Hill, " Fibres from Synthetic Polymers", Elsevier Publishing Co., New York, p.144ff (1953), are satisfactory for synthesizing the polyester that will subsequently form the soft segment of the spandex polymer of the fibers. These methods include: (a) direct esterification of an acid (i.e., in this case, 1,12-dodecanedioic acid) and a glycol (i.e., in this case, 2,2-dimethyl-1,3-propane diol); (b) ester interchange between the glycol and an ester of the acid; (c) reaction of the glycol with the corresponding acid chloride; and (d) reaction of the diacetate of the glycol with the acid or its ester. To prepare spandex polymer for the filaments or films of the invention, the soft-segment precursor, in the form of a polyester diol, has a molecular weight in the range of 1,700 to 3,000, preferably in the range of 2,200 to 2,700, and most preferably in the range of 2,300 to 2,600. In addition, the polyester diol must have a glycol acidity of no more than 15, preferably no more than 10, and most preferably less than 5 meq/kg. As shown in the drawing, which is derived from the data of Example 2, low glycol acidity in the polyester diol results in superior properties in the final spandex filament. In particular, lower percent set and higher unload power are obtained. To form the spandex polymer for the filaments or films of the invention, the above-described polyester soft-segment precursor is reacted (or "capped" as it is sometimes called) in a conventional manner with an excess of an organic diisocyanate to form an isocyanate-terminated polyester which is then chain-extended with an aliphatic diamine. Suitable diisocyanates are methylene bis(4-phenyl isocyanate), tolylene-2,4-diisocyanate, p-phenylene-2,6-diisocyanate and the like, with the first-mentioned diisocyanate being preferred. The capping reaction preferably is carried out so that the isocyanate end group content of the capped polyester is in the range of 2.2 to 3.3 weight percent, most preferably 2.4 to 3.1. The preferred ranges of NCO contents result in a preferred combination of elongation, unload power and set in the final spandex filaments. Suitable aliphatic diamine chain extenders include ethylene diamine("EDA", also known as 1,2-diamino ethane), hydrogenated meta-phenylene diamine ("HMPD", also known as 1,3-diaminocyclohexane), propylene diamine, mixtures thereof and the like. The preferred chain extender is a mixture of EPA and HMPD, particularly preferred in a weight ratio of 80 to 20 parts, or 90 to 10 parts, respectively. The polymerization reactions are generally carried out in an inert solvent, such as dimethylacetamide, dimethylformamide or the like. The thusly prepared spandex polymer, which has a relative viscosity in the range of 1.5 to 1.9 (determined by the method indicated hereinafter), can then be dry spun into filaments or formed into films, usually from the same solvent as was used for the polymerization. Dry-spun filaments or formed films can then be heat-set by maintaining them for 2 to 10 minutes at a temperature in the range of 145 to 165°C while stretched to 1.5 to 3.5 times their original length and then being immersed in boiling water in a relaxed condition for at least 20 minutes. Of course, higher setting temperatures for shorter times (e.g., at 195°C for 30 seconds) can be employed satisfactorily. The filaments and films of the present invention have an unexpectedly good resistance to mildew. In addition, the filaments resist degradation due to swimming-pool chlorine, have excellent hydrolytic stability, especially in acid environments, and have satisfactory elastic and tensile properties. As a result, filaments of the present invention are particularly useful for swim-wear fabrics. The resistance of polyester-based spandex filaments and films to chlorine-induced degradation can be further improved by using a spandex formed from the poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate)glycol employed in the spandex of the present invention and the functionally non-aromatic diisocyanates and functionally non-aromatic diamines disclosed by Altau and Stiehl in United States Patent 3,994,881, such as tetrachloro-(meta and/or para)-xylylene diisocyanate, tetrachloro-(meta and/or para)-xylylene diamine, or the like. The following test procedures were used in the Examples and Comparisons below for measuring various parameters and properties. Glycol acidity, which is defined herein as the concentration of ends, such as acid ends, in the polyester precursor which do not react with isocyanates under conventional urethane-forming conditions, such as those illustrated in the examples below. The glycol acidity of the hydroxyl-terminated polyester was measured by the method of ASTM-1638-67T and is reported herein in milliequivalents per kilogram of the hydroxyl-terminated polyester. The molecular weights reported herein are number average molecular weights of the polyester diols. Each was determined from the hydroxyl number of the polyester diol, which was measured by the imideazolepyridine catalyst method described by S. L. Wellon et al, "Determination of Hydroxyl Content of Polyurethane Polyols and Other Alcohols", Analytical Chemistry , Vol. 52, No. 8, pp. 1374-1376 (July 1980). The NCO content of isocyanate-capped hindered polyester was measured by the method of S. Siggia, "Quantitative Organic Analysis via Functional Group", 3rd Edition, Wiley & Sons, New York, pages 559-561 (1963). Relative viscosity of the spandex polymer was determined with a 0.5% concentration solution of the polymer in N,N-dimethylacetamide solvent. Relative viscosity is defined as the ratio of the flow times of solution to solvent at 25°C in a capillary viscometer. Strength and elastic properties of the spandex filaments were measured in accordance with the general method of ASTM D 2731-72. Three filaments, a 2-inch (5-cm) gauge length and a zero-to-300% elongation cycle were used for each of the measurements. "Unload Power" (i.e., the stress at an elongation of 100%) and "Set" were measured after the samples had been cycled five times at an constant elongation rate of 800% per minute and then held at the 300% extension for half a minute after the fifth extension. Stress, on unloading from this last extension, was measured and expressed as grams per effective denier at 100% elongation. At the end of the fifth cycle and after the sample had been allowed to recover for a half minute, the measured length of the sample was then used to calculate the set, which was expressed as a percentage of the original length of the sample. The percent elongation and tenacity at break were measured on the sixth extension cycle. Tenacity is reported in grams per denier or grams per dtex. Effective denier is the denier of the filament at 100% elongation. Resistance to attack by chlorine was measured by the method described in United States Patent 4,340,527, column 4, lines 7 through 25. The method involves immersing a test yarn, while extended to 150% of its original length, in a water bath maintained at a temperature of 22°C, at a pH of 7.5 by addition of hydrochloric acid, and at an active chlorine concentration of 3 parts per million by addition of sodium hypochlorite solution. After the exposure, the yarn is dried and its physical properties are measured, as described in the preceding paragraph. After-exposure yarn properties were then compared to the properties before exposure to determine that amount of degradation. Resistance to attack by mildew was measured by the general method of ASTM D-1924-70. An aqueous dispersion of aspergillus niger spores was employed. The test was performed on single-knit (four feed hosiery machine) hosiery panty fabric made with 50-denier,17 filament nylon as companion fibers to the spandex test filaments. The spandex filaments were knitted in every fourth course without plaiting with the nylon. Before mildew testing, the fabric was washed with one half cup of laundry detergent in a home laundry washing machine set for a normal wash and rinse cycle, followed by drying in a home laundry dryer set for a permapress cycle. Square samples of the fabric measuring 3 inches (7.6 cm) on each side were then fastened under light tension over cylindrical polystyrene dishes. The samples were then inoculated with the aqueous spore dispersion. Days to first failure were then measured. Failure was recorded as the time at which a hole was evident in the fabric sample. In each test, a similar control fabric made with commercial polyester-based spandex filaments was exposed under the same conditions. The comercial polyester-based spandex yarn was Type-128 "LYCRA" spandex, available from E. I. du Pont de Nemours and Company. The polymer of the commercial yarn was formed from a 3,400-molecular-weight polyester glycol that was derived from the reaction of a 60/40 ethylene glycol/1,4-butanediol mixture with adipic acid and then capped with methylene bis(4-phenyl isocyanate) and extended with ethylene diamine. EXAMPLE 1 This example illustrates the manufacture of an elastic filament of the invention made from a spandex polymer having a poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) soft segment. Compared to commercial filaments in which the dicarboxylic acid portion of the soft segment is derived from adipic acid and a glycol portion that is not hindered, the filaments of this example have surprisingly superior resistance to chlorine and mildew attack. A hydroxy-terminated polyester having a molecular weight of 2499 and a glycol acidity of 3.6 meq/kg was prepared from 1,12-dodecanedioic acid and 2,2-dimethyl-1,3-propane diol. A weight of 82.8 grams of this polyester glycol was mixed with one drop of phosphoric acid and 5 ml of cyclohexane. The mixture was stirred while being heated to a temperature of 85°C in a nitrogen-blanketed vessel. After thirty minutes of heating, the mixture was allowed to cool to 40°C. Then, the polyester glycol was capped with an aromatic diisocyanate by adding 17.2 grams of methylene bis(4-phenylisocyanate) (MDI) to the mixture and heating the mixture at 90°C for two hours. The capped polyester had a 3.04% concentration of isocyanate groups. After being allowed to cool to about 25°C, the mixture was dissolved in 110.6 grams of N,N-dimethylacetamide. The isocyanate-capped polyester, while still in solution, was then reacted with 70.9 grams of a mixture of aliphatic diamine chain extenders and a chain terminator in N,N-dimethylacetamide carrier. The mixture of aliphatic diamines consisted of 0.796 gram of 1,3-diaminocyclohexane (HMPD), 1.675 grams of 1,2-diaminoethane (EDA), 0.184 gram of diethylamine and 69.245 grams of N,N-dimethylacetamide. A half gram of 1,1-bis(6-methyl-3-tertiary-butyl-4-hydroxyphenyl)butane stabilizer was added to the resultant viscous polymer solution. The polymer had a relative viscosity of 1.6. Elastic filaments were formed from the polymer solution by conventional dry spinning techniques. Filaments of 66 denier (73 dtex) were wound up at a speed of 150 yards per minute (137 meters/min). The filaments had the following satisfactory tensile characteristics: Fifth cycle unload power at 100% elongation 0.029 g/edtex Fifth cycle set 24% Break tenacity (sixth cycle) 0.72 gram/dtex Break elongation 482% Other filaments made substantially according to the procedures of this example were tested for mildew and chlorine resistance by the test procedures described hereinbefore. The tests were performed on as-spun filaments and on filaments that had been heat set for 3 minutes at 150°C while being held at an elongation of 150% and then immersed in boiling water in a relaxed condition for 30 minutes. The filaments also were tested for hydrolytic stability by immersing the filaments in water of pH 3 at 70°C for one hour and then measuring the tenacity of the filaments. In each of these tests, the results on the filaments of the invention were compared to those obtained with a commercial non-hindered polyester-based control yarn (i.e.,Type-128 "LYCRA" spandex) tested under the same conditions. The test samples made according to this example exhibited four to ten times greater resistance to mildew attack than did the commercial polyester-based spandex yarns. Furthermore, the samples with the commercial yarn control exhibited a much higher severity of failure (i.e., many failure sites) at the recorded time of first failure, in contrast to the fabrics having yarns of the invention which exhibited only one small hole at time of recorded failure. In the chlorine resistance tests, the samples made in accordance with this example exhibited about the same or somewhat better resistance to chlorine attack than did samples containing the commercial control spandex yarn. In the hydrolytic stability test, the samples of commercial spandex filaments lost all of their tenacity, whereas those of the example retained more than 40% of their tenacity. EXAMPLE 2 This example illustrates how filament mechanical properties are affected by the free acidity of the poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate) glycol used to manufacture hindered polyester-based spandex filaments of the invention and demonstrates the requirement for a glycol acidity in the polyester glycol of no more than 15 meq/kg. A series of spandex filaments was made according to the general procedures of Example 1 with a soft segment derived from poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate)glycol having a molecular weight of 2,400. As in Example 1, the glycol was capped with MDI to form an isocyanate-terminated polyester having a 3.1% concentration of NCO groups which was then chain extended with an 80/20 EDA/HMPD mixture. A series of the polyester glycols, each glycol having a different free acidity, was prepared by heating the glycol with a small amount of water for different times. The thusly prepared spandex polymers were dry-spun into filaments, as in Example 1. The filaments then were heat set at 150°C for 3 minutes while being held at a 200% elongation and then immersed in boiling water for 30 minutes while in a relaxed condition. The heat-set and boiled-off filaments had the tensile and elastic properties listed below. Note that the first three samples are of the invention; the last two are comparisons, outside the invention. Glycol acidity meq/kg Filament Characteristics dtex % set unload g/edtex tenacity g/dtex elongation, % 4.4 43 21 0.041 0.97 336 11.1 40 23 0.037 1.01 354 14.9 43 24 0.032 0.77 349 19.9 49 23 0.030 0.90 373 26.7 47 25 0.029 0.69 351 The data given above, as well as other such data, show the desirability of low glycol acidity in the polyester glycol used to prepare the soft segment of the spandex filaments. Low acidity generally results in filaments having lower set and higher unload power. The attached drawing graphically illustrates these results.

Claims: An elastic filament or film formed from a spandex polymer having a hindered polyester soft segment and a hard segment derived from an organic diisocyanate and a diamine chain extender selected from aliphatic diamines, tetrachloro-meta-xylylene diamine and tetrachloro-para-xylylene diamine; characterised in that the hindered polyester segment is made from a poly(2,2-dimethyl-1,3-propylene 1,12-dodecanedioate)glycol including up to 25% of copolymerised units of other aliphatic diacids and/or glycols and having a molecular weight in the range of 1700 to 3000 and a glycol acidity, measured by the method of ASTM-1638-67T, of no more than 15 milliequivalents per kilogram, and wherein the spandex polymer is such that an as-spun elastic filament thereof has a set of less than 25%, an unload power of at least 0.027 gped and a break elongation of at least 400%, as determined in accordance with the method of ASTM D 2731-72 as described herein. A filament or film as claimed in claim 1, wherein the hindered polyester glycol has a molecular weight in the range of 2200 to 2700 and a glycol acidity of no more than 10 meq/kg. A filament or film as claimed in claim 1, wherein the hindered polyester glycol has a molecular weight in the range of 2300 to 2600 and a glycol acidity of no more than 5 meq/kg. A filament or film as claimed in any one of the preceding claims wherein the diisocyanate is methylene bis(4-phenyl isocyanate) and the chain extender is a mixture of ethylene diamine and 1,3-diaminocyclohexane. A filament or film as claimed in any one of claims 1 to 3 wherein the diisocyanate is the functionally non-aromatic diisocyanate tetrachloro-(meta and/or para)-xylylene diisocyanate, and/or the chain extender is the functionally non-aromatic diamine tetrachloro-(meta and/or para)-xylylene diamine. A heat-set elastic filament of the polymer as claimed in any one of claims 1 to 5, characterised by a set of no more than 25%, an unload power of at least 0.036 gped and a break elongation of at least 300%, as determined in accordance with the method of ASTM D 2731-72 as described herein. A process for making a spandex filament or film as claimed in claim 1, wherein in the presence of an inert organic solvent 2,2-dimethyl-1,3-propanediol is reacted with 1,12-dodecanedioic acid to form a hydroxyl-terminated polyester having a molecular weight in the range of 2200 to 2700 and a glycol acidity of no more than 15 meq/kg, the thusly formed polyester is reacted with an organic diisocyanate to form an isocyanate-terminated polyester having an isocyanate end-group content in the range 2.2 to 3.3% by weight, the isocyanate-terminated polyester is then chain-extended with an aliphatic diamine to provide a viscous spandex polymer solution having a relative viscosity in the range of 1.5 to 1.9 (as determined at 25°C with a 0.5% concentration of the polymer in N,N-dimethylacetamide solvent), and the polymer solution is formed into filaments or film. A process as claimed in claim 7, wherein the polyester is formed with a molecular weight in the range of 2300 to 2600 and a glycol acidity of no more than 10 meq/kg and the isocyanate-terminated polyester is formed with an NCO content in the range of 2.4 to 3.1%. A process as claimed in claim 7 or claim 8, wherein the organic diisocyanate is methylene bis(4-phenyl isocyanate) and the diamine chain extender is a mixture of ethylene diamine and 1,3-diaminocyclohexane.

Inventors: LODOEN GARY ARTHUR, LODOEN, GARY ARTHUR
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1987
Main classification: C08G18
IPC codes: D01D5, D01F6, C08G18, C08J5, C08G63