Product and process
United States Patent Guinn et al.  
 [ Apr. 15, 1975 PRODUCT AND PROCESS Inventors: Gail Crolley Guinn, Gastonia, NC; Joseph W. Jenny, Jr., Camden, S.C.  
 Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.  
 Filed: Apr. 26, 1973 Appl. No.: 354,792  
 Related U.S. Application Data Continuation-impart of Ser. No. 89,918, Nov. 16, I970, abandoned.  
 U.S. Cl. 260/793 MU; 28/72; 260/793 R; 264/l82; 264/290 Int. Cl C08f 15/40; C08f 47/00 Field of Search 260/793 R, 79.3 MU; 264/182 References Cited UNITED STATES PATENTS 6/l958 Millhiser 260/793 3,097,415 7/1963 Davis 23/82 3,380,976 4/1968 lzumi 3,560,603 2/197] Ryan, .lr 264/168 Primary ExaminerChristopher A. Henderson 3 Claims, 1 Drawing Figure PRODUCT AND PROCESS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of application Ser. No. 89,918, filed Nov. 16, 1970, and now abandoned.  
  The present invention relates to a tow of a new acrylic homofiber (single component) fiber useful in knitwear.  
  Acrylic staple fiber yarns are used in many forms of knitwear. In this use it is desirable for the fiber to have a shrinkage in boiling water of at least 13% and most perferably 13 to 26%.  
  Conventionally such acrylic staple fibers may be formed on a Turbo Stapler, a conventional device wherein a tow of acrylic fibers is drawn and immediately broken. The drawing step in the Turbo Stapler should give the fiber the desired break elongation to process properly (break) in the second step breaking of the filaments into staple over breaker bars, and also imparts stresses in the filament to yield the desired shrinkage in the staple. The product of the Turbo Stapler is a sliver of fibers resulting from the drawing and stretch breaking of the tow of filaments fed to it.  
  An acrylic tow which can be directly broken into staple without employing the Turbo Stapler is provided by the present invention. The filaments in such tow consist essentially of 93-95% acrylonitrile, 7% methylacrylate and up to 0.5% sodium styrene sulfonate. The filaments have an X-ray porosity index of less than about 1.5 in the void size range of each 45-90A and 90-140A, a molecular orientation of greater than about 66.5%, a break elongation of 8 to 18%, a shrinkage in boiling water of 13 to 26% and a tenacity of above about 3.6 gpd. Preferably the sodium styrene sulfonate will be present in an amount between about 0.1% and 0.5%. Preferably also the tow is in the form of a ball warp having a density of filaments of 35 to 55 lbs./ft. Alternatively, the tow can be packaged in a carton to the same density.  
  The present invention also comprehends a process for stretching acrylic filaments under conditions which will increase their tenacity and reduce their X-ray po-&#39; rosity index. This process involves spinning acrylic filaments from solution, i.e., dry or wet spinning, washing said filaments, drawing said filaments in a first draw step between about 4 and 5X in an aqueous bath, drying said filaments in a heated gas under relaxed conditions at a temperature of 135l45 C. to yield filaments having less than 2% moisture, and subsequently drawing said filaments in a second draw stepat least 1.4X in a zone at a temperature of at least 121C. for at least 1.7 seconds and cooling the filaments. In the preferred embodiment, the filament consists essentially of 93-95% acrylonitrile, 57% methylacrylate and up to 0.5% sodium styrene sulfonate.  
 THE INVENTION IN MORE DETAIL The critical aspects of the instant process arise after the fibers have beenspun, wash-drawn, and dried in the relaxed state. The dried fiber in accordance with this invention is then drawn at least 1.4X in a hot zone for a period of at least 1.7 seconds.  
  The degree of draw should be at least 1.4X. The upper limit of draw is governed by the number of broken filaments found acceptable in processing.  
  The temperature in the hot draw zone will normally be at least 121C., but it is to be understood that the maximum suitable temperature will be related to the residence time of the filament in the hot draw zone.  
  Preferably, the temperature of the hot draw zone will be between 133190C.  
  The residence time of the filaments in the draw zone should be at least 1.7 seconds. Residence time, of course, will be related to the temperature of the hot draw zone as stated above and will be such that excessive degradation and discoloration of the polymer is avoided.  
  For the preferred composition 9395% acrylonitrile, 5-7% methylacrylate and up to 0.5% sodium styrene sulfonate the filaments are drawn 1.4-2.0X and preferably 1.5-7X at a temperature in the hot draw zone of between 135C. and 190C.  
  Before the tow is packaged it must be cooled to below about 70C. to avoid shrinkage problems involving shrinkage of the filaments in the package on further cooling. Until this temperature is reached the filaments are held under tension sufficient to prevent relaxation.  
  The tow of this invention need not be crimped, thus avoiding a process step typically present in providing tow for breaking into staple.  
 THE DRAWING The preferred apparatus for carrying out the drawing step of the process after the filament has been spun, wash-drawn and dried in the relaxed state is shown in the attached schematic drawing. It is basically a drawing zone such as found in Turbo Tow Processor, 1, coupled to a ball warper 2 modified to provide a uniform traverse of the tow on the package. The apparatus is shown with a tow, T, threaded therethrough. The tow first extends around a group of guide bars 10 followed by the first set of nip rolls, commonly called the input rolls, l2, 12&#39;. The tow then passes around the first set of cascade rolls 14 and thence between the first set of heater plates 16 and to the second set of cascade rolls 18. Tow ispulled to this point by means of a second set of nip rolls, commonly called intermediate rolls, 20, 20&#39; and is stretched the desired amount by means of a preselected speed differential between this second set of nip rolls and the first set l2, 12&#39;. Two more sets of heater plates 22,22 and 24, 24&#39; are followed by a cooling plate 26, a guide roll 28, a cooling drum 30 and the third set of nip rolls 32, 32&#39;. Tow is advanced by differential speed between roll set 32, 32 and set 20, 20&#39;. Heating and subsequent partial cooling are possible in this region. The tow then extends through stationary guide 34 and thence to traverse guide 36 which is driven by traverse guide drive mechanism 38. Tow then is wound on a core 40 by means of drive roll 42 thus forming the ball warp package 44. Alternatively, the very high density package of this invention may be prepared in a closed free standing container by substituting for the ball warper the type of container and apparatus conventionally used in such packaging.  
  The filaments of the tow of this invention have a tenacity at least 3.6 and a porosity index of less than 1.5 in each of the void size ranges of 45-90A and -l40A which is believed related to improved uniformity of dye due to slower initial dye uptake. In addition these fibers have a break elongation of between 8-18% and a shrinkage in boiling water of l3-26%.  
  The shrinkage range is desirable for staple fiber in knitwear. The break elongation is desirable for direct cold breaking of the tow into staple. As shown in Table I, when this elongation is exceeded the directly coldbroken sliver is of poor quality.  
  The denier of the tow processed in accord with the invention is not critical. It may range between 100,000 and 1,000,000 or more in denier. The filaments may have a denier of between 1 to 10.  
 DEFINITION S Acrylic filaments refers to filaments consisting essentially of polymer containing at least 85% by weight of acrylonitrile.  
  Acrylic filaments as used herein, included filaments of any long chain synthetic polymer composed of acrylonitrile units of the formula in the polymer chain. As is well understood, the term includes the homopolymer of acrylonitrile (i.e., polyacrylonitrile) and copolymers of acrylonitrile and one or more suitable monoethylenically unsaturated monomers copolymerizable with acrylonitrile. Among the typical addition monomers as exemplary of those which are copolymerizable with polyacrylonitrile are methyl acrylate, methyl methacrylate, vinyl acetate, styrene, methacrylamide, methacrylonitrile, vinyl chloride, vinylidene chloride, methyl vinyl ketone and the like as well as any of the available vinyl pyridines. The preferred compounds include methyl acrylate, vinyl acetate, styrene and the vinyl pyridines.  
  Among the copolymerizable sulfonates are the sulfonated styrenes, vinyl sulfonate, ally] sulfonate, methallyl sulfonate and their alkali-metal or alkaline-earthmetal salts, and the like, it being necessary only that the compound chosen from this class be copolymerizable with acrylonitrile to the desired extent. The preferred compounds are the sulfonated styrenes.  
  Molecular orientation and X-ray porosity refer to structural features of the filaments comprising the tow as measured by tests as follows:  
  Molecular orientation and porosity indices were obtained from X-ray diffraction measurements made in a conventional manner. [For example, generally as described by Statton in A.S.T.M. Spec. Tech. Bull. No. 247 (1958)].  
  Yarn test samples of about re gm. were uniformly wound on a stainless steel card (1% X 1% X l/32 inch) with a 4 inch diameter aperture. The thus arranged specimen was mounted in the spinning or stepped rotation holder of the diffractometer. Thus, wide angle, crystalline, diffraction pattern was used for measuring orientation and the small angle scattering for porosity. Commercial Philips Electronic Instruments Co. instrumentation was used to provide and make the required intensity measurements on the X-ray diffraction patterns. The X-ray source comprised a copper target with a 40KV, ma power supply. The monochromator employed A divergence and receiving slits along with a 1 pre-slit.  
  Measurements of diffracted radiation intensity were made by means of a scintillation counter with pulse height analyzer. Determinations of intensity were made in terms of the reciprocal of the time required for a specified number (usually 500) of counts for each angular position. For determining the porosity indices, intensity was determined at discrete diffraction angle (20) steps of A from a value of 26 of% to 1 for the -140A index and 1 to 2 for the 45-90A index. These measurements were extended to a 20 value of 36 for normalization computations. For orientation measurements, intensity was determined at azimuthal (ill) angle intervals of 2 extending from 0 through 180 for a constant, preselected, 20 value equal to 168.  
  Raw intensity values were corrected by subtracting air and electronic noise background. The raw air background values were first corrected by multiplying by sample transparency values before then subtracting. In addition normalized corrected intensity values were computed in order to correct for small variations in the amount of sample in the beam. This was accomplished by multiplying by a factor found necessary to achieve a value of l for the integrated area under the corrected intensity versus 26 curve from 26 equal to 6 to 36. Sample transparency, the zero (20) angle intensity reduction was determined by using nine Ni filters each 0.007 inch thick and measuring beam intensity with and without the sample for 500 sec. as I and I respectively. Transparency values were then computed as the ratio l/l Molecular orientation was computed from the azimuthal intensity variations curve according to the equation: Orientation (90 d \11 A/2/90 The value of d ill m is obtained from the corrected intensity vs. ll! curve by first determining the total area, A, under the curve, computing the value A/2, and then finding that width, d 111 in degrees, of the intensity peak selected, symmetrically around the peak, so that the area under the peak confined by this width is equal to A/2.  
  The two porosity indices were computed from the normalized corrected intensity vs. diffraction angle data according to the following expressions:  
 P(45-90A) 100 X Area (200 1 to 2) P(90-l40A) 100 X Area (26 4 to 1).  
  Thus these indices are indicative of the relative number of pores (inhomogeneities) which contribute to the X-ray scattering over a certain range of the intensity vs. 20 curve.  
  Elongation and tenacity are measured by the Instron tester in accord with ASTM D-540-64 after the filaments have been conditioned as per ASTM D-l776.  
  Shrinkage refers to the reduction in length of the fiber after immersion in boiling water for 30 minutes as determined by tests hereinafter described. Percent shrinkage is calculated as L, L /L X100 wherein L is the length of fiber before immersion in boiling water and L is the length of fiber after 30 minutes immersion in boiling water.  
  In the following examples all parts are by weight unless otherwise indicated.  
 EXAMPLE 1 Acrylic filaments of the following composition, 93.9% of acrylonitrile, 6% methylacrylate and 0.1% sodium styrene sulfonate was spun from dimethylformamide solution in conventional manner, wash-drawn 4.5X at 96C. in an aqueous bath and dried in a relaxed mal textile testing conditions of 65% R.I-1., 70F.&#39;  
 (21C.), and then tested for tensile properties and loop properties by means of well known lnstron (Product of the lnstron Engineering Co., Canton, Mass.) tensile tester by the tests set forth above. Similar specimens were tested for shrinkage in boiling water by the test set forth above.  
  Processing conditions and product properties for the different samples of this example and controls are shown in Table I below. The ultimate acceptability of each sample was judged on the basis of its processability into staple sliver on a Turbo Stapler. This latter machine was operated according to accepted standard practice except that the heater plates were held open and not heated and no significant stretch (about 1.15X) was imposed on the tow in the initial sections merely to attenuate kinks in the tow. All of the samples prepared by the process of the present invention processed well into sliver. The control samples processed poorly.  
  Continued EXAMPLE 2 To demonstrate the very high package density of filaments of this invention, a sample of the tow was first spun, wash-drawn and dried as described in Example 1 and was given a second draw as follows at yards/- min. as measured at rolls 20, 21 in the Figure on the apparatus above described. The heater plate temperatures were as follows:  
 Heater plate temperatures:  
 1st heater: 180C. (l6, 16&#39; in the Figure) 2nd heater: 180C. (22, 22 in the Figure) 3rd heater: 180C. (24, 24 in the Figure) Draw Ratios:  
 1st stage draw: 1.309X (at heater plates 16, 16  
 2nd stage draw: 1.260X (at heater plates 22, 22, 24,  
 Residence time in the draw zone is calculated on the same basis as Example 1, to be 2.15 seconds.  
  The ball warp thus produced was weighed and dimensions measured. The ball weighed 656 lbs. Cylin- 3O drical dimensions of this package were: length 40 in.,  
 TABLE I Stretch break Product Properties Processing to Fiber Silver Evalua- Prucess Conditions Loop Work tion of Sliver T.P. Draw Heater plate Ten. Elong. Mod. to Break Shrinkage Produced item Speed Ratio Tcmp.C. g/d) (7r) g/d) g.cm) (&#39;7!) (den.-cm.)  
  a 4 131/126 190 4.5 14.2 98.9 0.01 14.2 Good b 1 1.31/1.26 190 4.1 16.6 83.8 0.01 16.6 do. 0 4 1.31/1.26 180 4.2 15.5 90.4 0.01 20.5 do. (1 4 1.31/1.26 4.2 14.1 94.2 0.01 22.9 do. e 4 1.12/1.12 190 3.5 24.5 76.5 0.06 16.4 Poor f 2 l.55/1.26 190 4.8 11.7 97 0.01 17.5 Good g 1 1.55/1.26 4.8 12.7 103.8 0.01 15.2 do. h 2 1.55/1.26 180 4.7 11.1 107.2 0.01 18.1 do. i 2 131/126 180 3.5 12.8 83.6 0.01 19.0 do. j 1 1.31/1.26 170 4.0 14.3 90.9 0.01 18.2 do. k 2 1.12/1.12 170 3.5 24.2 77.4 0.06 15.2 Poor 1 4 1.12/1.12 180 3.1 24.3 73.0 0.07 16.0 do. in 1 1.12/1.12 180 3.2 25.7 73.2 0.07 11.8 do. n 2 1.12/1.12 3.1 26.7 73.9 0.09 13.1 do.  
 &#34; Speed 1 20 yd./min., 2 30 yd.ln1in.. 4 60 ydJmin. at intermediate r0115. 20. 21 in the Figure.  
  Temperature of heater plates. 16. 16&#39;. 22. 22&#39;. 24. 24 in the Figure.  
 3&#39;06 &#34;:0 an g-gu outer dimensions 27 in. and inner diameter 5 in. The computed package density was, therefore, 51.4 lb./cu.  
  In an identical run, tow temperture readings were 60 taken by means of an infrared thermometer. Results were:  
 210F. (99C.) at exit of heater plate 16, 16&#39; in the Figure 260F. (127C.) at exit of heater plate 24, 24&#39; in the Figure 240F. (116C.) at entrance to cooling drum 30 in the Figure 165 F. (75C.) at exit from machine to wind up at 32,  
  32&#39; in the Figure. Fiber characterization for this run showed tenacity 3.7 gm./den., elongation 14%, modulus 86 gm./den. and shrinkage 21.5%.  
 EXAMPLE 3 A. A sample of tow was first spun, wash-drawn and relaxed as described in Example 1 and was dry stretched on the apparatus above described between heater plates at 60 ypm. as measured at rolls 20, of the Figure. The tow wasdrawn in two stages. The first stage draw occurred between heater plates l6, l6 and the second stage between heater plates 22, 22&#39; and 24, 24&#39;. The first stage draw was 1.309X and the second stage draw was 1.230X. Each set of heater plates is at 149C. Residence time in the draw zone is calculated to be, on the same basis as Example 1, 2.18 seconds for item A and 6.54 seconds for item B. The tow was packaged as a ball warp of a density about 45 lbs./cu. ft. Fiber specimens were taken from the tow before dry relaxing and from the ball warped tow.  
  B. Experiment A was repeated but drawing speed measured at rolls 20, 20&#39; of the Figure was 20 yds./min.  
  The specimens were characterized by the above described X-ray scattering techinques to give first an index of porosity of the internal structure and secondly a measure of molecular orientation.  
  Table ll records the values of porosity index and orientation for these samples and also fiber properties. Table ll records the values of porosity index and orientation for a control sample (the sample of tow before the additional stretching).  
  The product has been shown to have important utility in its direct processability into sliver in the second stage of the Turbo Stapler machine (breaking).  
 TABLE 11 Test Test Control A B Porosity lndex -14OA 3.87 1.35 1.18 Orientation 58.8 68.9 73.8 Tenacity (gpd) 4.0 4.0 Elongation 14.6 15.2 Modulus (gpd) 92.1 95.0 Shrinkage 16.6 14.7  
  The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described for obvious modifications will occur to those skilled in the art.  
  The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
  1. A tow of acrylic filaments, said acrylic filaments consisting essentially of 93.9% acrylonitrile, 6% methylacrylate and 0.1% sodium styrene sulfonate, the filaments have an X-ray porosity index of 1.27-1.47 in the void size range of 45-90A and 1.18-1.35 in the void size range of 90-140A, a molecular orientation of 68.973.8%, a brake elongation of 14.6-15.2%, a shrinkage in boiling water of 14.7-16.6% and a break tenacity of about 4.0 gpd.  
  2. The tow of claim 1 in the form of a ball warp having a density of filaments of 45 lbs./ft.  
 3. A carton of the tow of claim 1, said tow having a density of filaments of 45 lbs/ft.