Classifications

• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/58—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products
  • D01F6/62—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolycondensation products from polyesters

Definitions

• Poly (trimethylene terephthalate) polymer is a new polyester resin suitable for use in carpet, textile, and other thermoplastic resin applications.
• Poly (trimethylene terephthalate) (PTT) is chemically an aromatic polyester resin made by the polycondensation of 1, 3-propanediol (PDO) and terephthalic acid. Production of textile staple from PTT is possible on a wide variety of commercial processing eguipment .
• PET synthetic fiber staple production is often decoupled two-stage process.
• the first stage involves extrusion of Un- Drawn Yarn, which is stored for draw processing in the second stage.
• draw processes There are two main types of draw processes used in staple production Draw-Relax and Draw Anneal. The fundamental difference between these two processes is how fiber shrinkage is managed.
• draw relax staple production the shrinkage strategy is to pre-shrink the fibers in an oven after crimping to desired performance and properties.
• draw annealed staple production the shrinkage strategy is heat the fibers allowing for constant length crystallization before crimping.
• PTT staple fibre from polyethylene terephthalate (PET) has been produced and there are well established processes for doing so. It would be desirable to be able to produce PTT staple fibre on existing equipment. However, there are many differences between the two polymers which make the production of commercially useful staple fiber of PTT on existing staple production equipment difficult or unlikely. To understand how to produce PTT staple on existing equipment one needs to address several process questions:
• the present invention describes a two-stage staple production process using PTT.
• the first stage is extrusion of undrawn yarn (UDY) .
• UDY is converted to a staple fibre product in the second draw production stage.
• a process for making textile staple fibre from polytrimethylene terephthalate (PTT) on existing PET textile staple fibre making equipment which comprises: (a) melt extruding PTT polymer at 245 to 253° C, preferably 245 to 250 °C, (b) spinning the extruded PTT into yarn using at least one spinneret, (c) moving the spun yarn to a first takeup roll wherein the distance from the spinneret to the first takeup roll is from 16 to 20 feet, (d) cooling the spun yarn to less than 31°C, preferably less than 25 C, more preferably less than 20 C, before it reaches the first takeup roll, (e) optionally, storing the spun yarn in a climate controlled room at a temperature of no more than 31°C (both this step and the previous one are carried out to minimize premature shrinkage of the undrawn yarn prior to draw processing), (f) prior to the draw process, preconditioning the yarn under tension at a temperature of at least 60°C,
• the volume of the crimper may be increased 10 to 50, preferably 20 to 35 percent more than the crimper volume used to make PET in the existing equipment.
• the choice of conditions is based on the particular equipment and the desired yield.
• Figure 1 is a schematic of the process steps from resin to baled fibre whose critical elements will be described.
• Figure 2 is the tenacity elongation balance curve useful in helping assess the possible range of staple properties for PTT.
• Figure 3 shows a typical Stress / Strain Curve for as Spun Yarn Bundles.
• Figure 4 shows the effect of extrusion temperature on fiber drawability.
• Figure 5 shows the undrawn yarn shrinkage in water of different temperatures as a function of undrawn yarn spinning conditions .
• Figure 6 shows the orientation schematic describing the effect of fiber shrinkage.
• Figure 7 shows the effect of draw bath temperature and total orientation parameter on boil off shrinkage
• Figure 8 shows the effect of draw bath temperature and total orientation parameter on 125°C dry heat shrinkage.
• Figure 9 shows the effect of draw bath temperature and total orientation parameter on 140°C dry heat shrinkage.
• Figure 10 shows the effect of draw bath temperature and total orientation parameter on 175°C dry heat shrinkage.
• Figure 11 shows the effect of draw bath temperature and total orientation parameter on 197°C dry heat shrinkage.
• Figure 12 shows the effect of draw ratio and draw bath temperature on draw process relaxation factor.
• Figure 13 shows the predicted dry heat shrinkage as a function of drier (relaxer) oven temperature for free relax 1.4 Total Orientation Parameter and 75°C draw bath temperature.
• Figure 14 shows the effect of relaxer oven temperature and applied yarn stretch on 175°C dry heat shrinkage for 100% PTT yarns .
• Figure 15 shows the effect of relaxer oven temperature and applied yarn stretch on 175°C dry heat shrinkage for 100% PET yarns .
• Figure 16 shows the comparison of PTT and PET spun yarn 175°C dry heat shrinkage at two yarn heat set temperatures.
• Figure 17 shows the effect of relaxer oven temperature and applied yarn stretch on 175°C dry heat shrinkage for 50:50 PTT: Cotton yarns.
• Figure 18 shows the comparison of PTT and PET spun yarn boil off shrinkage at two heat set temperatures.
• Figure 19 shows the comparison of PTT and PET spun yarn load at 5% strain at two yarn heat set temperatures.
• Figure 20 shows the comparison of PTT and PET spun yarn 2 minute percent stress decay at two spun yarn heat set temperatures .
• Figure 21 shows the comparison of PTT and PET spun yarn percent strain recovery (2 minute extension) at two spun yarn heat set temperatures.
• Polymer textile staple is feasible using existing facilities. Since the equipment used by different companies varies greatly, there will be differences in how the processes are carried out. Once the staple producer tailors its settings to the unique properties of PTT, it is possible to produce a wide variety of staple products suitable for use in spun yarn and non-woven textiles. Textile staple produced from PTT offers excellent loft and drape providing softness, bulk, compatibility in blends, easy-care, and shape retention in textile products.
• a typical melt preparation system includes an extruder, spin beam, melt pump, and spin pack.
• the key is to establish a uniform, optimum polymer melt viscosity by minimizing melt process temperature and residence time.
• Commercial production of PTT UDY with both twin screw and single screw extruders is straightforward. In twin screw extruders it may be necessary to reduce the extruder melt pressure by as much as 25-50% (from PET conditions) to avoid excessive shear degradation of the polymer melt.
• Commercial production of PTT UDY uses extruder melt temperatures ranging from 245°C to 270°C. Care must be taken when producing PTT UDY at melt temperatures between 260 to 270°C to avoid excessive degradation of polymer melt and subsequent UDY properties.
• the optimal staple extrusion melt temperature for PTT is 245 to 253°C, preferably 245 to 250°C. Future PTT resins with lower intrinsic viscosity will likely require lower temperatures. Figure 4 shows that better drawability is obtained when the polymer is extruded at 250°C rather than at 240°C or 260°C. 2.0 UNDRAWN YARN (UDY) SPINNING
• Staple extrusion systems are engineered for a specific range of resin viscosity, throughput, melt temperature, and residence time.
• the hole-throughput needed to make PTT staple is usually 20-30% lower than that for PET products of comparable denier. This essentially increases the residence time for PTT extruded with PET staple production equipment. The increase in melt residence time can lead to degradation if melt temperatures are higher than 260°C. Transfer line and spin beam heating systems should equal the extruder outlet polymer temperature if possible.
• PTT staple can use standard PET spinneret designs for similar products.
• PTT staple generally requires smaller capillary diametres for low denier products when compared to PET staple production.
• PTT resins have an upper shear rate limit of 7500-9000 reciprocal seconds for round cross sections depending on melt extrusion conditions.
• spin finishes are fibre coatings that provide lubrication, cohesion, and additive protection to the PTT fibre during staple production and down stream processing. Both multi-component phosphate and mineral oil based finishes have been used successfully in the production of PTT staple. Proven PET spin finish chemistries and application methods are satisfactory for initial PTT staple products. Spin finish formulations and application methods can then be changed based on customer feedback on staple processing.
• PTT UDY completes over 90% of its ageing process within 8 hours of extrusion.
• UDY draw properties stabilize within 24 hours and no significant change in draw properties is observed after 2-4 months of storage at constant temperature.
• PTT UDY has the potential to shrink more easily and at lower temperatures than PET UDY. Storage conditions warmer than 25-30°C should be avoided because they trigger UDY shrinkage.
• the PTT UDY creel is stored in an air-conditioned environment to help avoid shrinkage. The exact temperature that triggers PTT UDY shrinkage depends on UDY extrusion, quench, take-up and storage conditions. Even if the PTT UDY shrinks it is possible to convert this UDY into a first grade commercial staple product during draw processing with minor impact on product quality.
• the creel size for PTT staple is determined by the size of the production crimper. In general the creel size for PTT staple is roughly 60% of an equivalent PET staple product because of the higher bulk of PTT fibres. A 600,000 denier drawn tow will satisfactorily feed a 110 mm wide by 20 mm high crimper. This may change as crimper size increases and/or draw production rates increase above 100-130 metres per minute. Since most draw production lines have a maximum line speed of 250-300 m/min, increasing the volume of the crimping chamber is another way to improve draw line productivity.
• PTT staple has been manufactured on draw-relax and draw- anneal process configurations.
• the staple In the draw relax process the staple is heat treated and dried under zero tension to reduce shrinkage. This process produces a low modulus fibre suitable for PTT spun yarns and blending with low modulus fibres like wool and acrylic.
• the draw anneal process heat treats the tow on rolls under high tension and produces a higher modulus fibre more suitable for blending with minor amounts of rayon, cotton or other higher modulus fibre.
• the initial draw point of the UDY tow in the first draw stage should occur under water heated to a minimum of 60°C, preferably 60 to 100°C. Keeping the draw point hot improves draw process performance by significantly reducing the impact of extrusion conditions on production draw ratios.
• the second draw stage is hotter than the first draw stage up to a practical maximum of the melting point of the yarn, preferably 60 to 160°C, most preferably 80-100°C. Unlike PET, PTT will not turn harsh in heated draw baths. Additional draw zones are optional and usually extend the total machine draw ratio slightly. The major draw ratio should be taken in the first stage.
• Annealing or relaxing PTT staple tow with a 3% roll relaxation across a set of 100-130°C calendar rolls increases the initial modulus of the final PTT staple by 12-14%. This process produces a high modulus fibre suitable for PTT spun yarns and blending with high modulus fibres like cotton, rayon, and PET. Initial modulus increases about 4% for every 10°C from 130-150°C when the relaxation across the roll set is held at 3%. Annealing PTT tow above 150°C may require increasing the relaxation across the calendar rolls to avoid excessive filament breakage. Spin finish is often applied to make up for spin finish lost in draw processing using a dip bath or front/back kiss roll application just before the crimping stage .
• PTT tow bends very easily compared to PET tow given its low bending modulus. This low modulus also gives PTT excellent hand and softness. Additionally, PTT is much more bulky than PET. Low bending modulus and high bulk require the following changes in crimping conditions:
• Feed tow denier must be decreased or crimper volume increased because of PTT' s higher bulk.
• the increased bulkmess of PTT can be accounted for by either decreasing the amount of tow denier feeding to the crimper by most preferably 10 to 60 percent, preferably 40 to 60 percent, all by denier.
• Another way is to increase the volume of the crimper by 10 to 50 percent, preferably 20 to 35 percent, all by volume. Also, a combination of these two methods can be used.
• the crimper should be equipped with steam and spin finish injection to better control crimping chamber temperature.
• Crimp stability and take up improve significantly when the crimper chamber is at least 85°C and at 300 kPa (3 bar) of gate pressure. Crimp frequency may be higher and crimp amplitude lower than comparable PET staple. Crimp stability and take up improves as crimper temperature increases. The crimper should not be heated too much because, as crimp stability increases, so does staple cohesion, which can increase defects m carding. 3.6 Drying, Cutting, and Packaging
• the commercial draw relax process typically uses a 70°C first draw and a 100°C second draw.
• the commercial annealed staple process typically uses a 70°C first draw, a 100°C second draw, and 130°C calendar rolls with a 0.95 relaxation .
• Example 1 Controlling Shrinkage of Undrawn Yarn During Extrusion and Storage
• Drawn fibre shrinkage decreases with increasing draw bath temperature, but the effect is fairly small at temperatures above 60°C. Shrinkage also decreases with increasing total orientation (Draw Ratio) , but the effect is very minimal at the higher draw bath temperatures.
• Drawn fibre shrinkage is insensitive to spinning and drawing settings, crimping becomes more stable, and the product less variable. Drawing at temperatures above 60°C is recommended and should provide stable crimping operation.
• Predicted relaxation factors for crimping and drying/relaxing as a function of drier/relaxation temperature were prepared from the shrinkage data. Although the shape of the curve is correct and can be used for extrapolation of known data, the magnitude of the factor appears too high.
• shrinkage is a much more sophisticated probe of fibre structure, and is affected by orientation and, more importantly, by crystallinity .
• a model that has proven useful for PET has the following premises:
• Glass transition temperature is defined as that temperature at which unrestrained amorphous chains are free to deorient, as required by the second law of thermodynamics.
• Amorphous areas are those which are not crystalline.
• Crystalline areas are those which do not deorient at this temperature.
• the length, orientation diagram in Figure 6 can be used to illustrate the process. This diagram represents what happens when you draw a fibre from its length at zero birefringence to the sample fibre length, l f . When this fibre is heated to temperature Tl it loses length to i because all the amorphous areas deorientate and all crystals that are not stable to T melt and also deorientate.
• the fibre does not deorientate completely, because there are still crystals that are stable at T When the temperature is raised to T , additional crystals melt, become amorphous, deorientate, and the length decreases further.
• T time
• additional crystals melt, become amorphous, deorientate, and the length decreases further.
• S n is % Strain at the Natural Draw Strain
• NDR l d / Is (2)
• I d is the length at the natural draw point of inflection
• l s is the length of the spun sample.
• the first step is to establish what variables are statistically significant in predicting shrinkage at a given temperature.
• the procedure was to use the stepwise forward and stepwise backward regression procedures in Sigma Stat 2.0 with F to enter >4.0 and P to reject ⁇ 0.05. Results summarised in Table III indicate:
• Figures 7 through 11 are plots of Boil Off Shrinkage, and Dry Heat Shrinkage at 125,140, 175, and 197°C, for the three draw bath temperatures used. It is clear that there is a large mechanism change between 45 and 60°C, the next higher temperature tested. At temperatures greater than 60°C shrinkage is nearly independent of orientation, and relatively insensitive to bath temperature.
• Figure 12 shows the relationship between oven temperature and relaxation factor for drawn ropes. At draw bath temperatures above 60°C a line through the top grouping of data points should approximate the relaxation factor. This is a good starting point, but the value may be too high (shrinkage too low) because the shrinkage method uses a small weight on the sample so it is not completely free to relax as it would in a typical plant drier/relaxer . However, the curve should have the correct shape and therefore be good enough to extrapolate the temperature effect when more machine specific data is obtained.
• the shrinkage may be expressed m the following way:
• the first shrinkage is what the fibre experiences in the relaxer, and the second shrinkage is the residual shrinkage in the relaxed product.
• PET follows these assumptions so it is possible to estimate relaxed product shrinkage from the dry heat shrinkage of drawn ribbons.
• ⁇ p S (% shrinkage of sample shrunk at T when shrunk at T 2 ) / 100 (5)
• the expected product shrinkage at T 2 after an oven relaxation at Ti can be calculated.
• Figure 13 is a plot of predicted shrinkage for the technical useful case of high orientation, and high bath temperature. It appears that the predicted fibre shrinkages after a given oven relaxation are much too low. This indicates that significant crystalline change in addition to simple deorientation occurs in the drier/relaxer .
• Example 3 Evaluation of PTT Staple Fiber Heat Setting on the Properties on PTT Spun Yarn Properties under Heated Strain Conditions: Yarns Evaluated included PTT, PTT/PET Blend, PTT/Cotton Blend, and PET (Table IV) Breakage of filaments during the extrusion of PTT synthetic fibres severely limits production productivity and product quality.
• PTT resins with IV in the range of 0.55-1.0 are preferred, more preferably those with IV range of 0.675-0.92, and most preferably those with IV range of 0.72-0.82.
• Producing PTT synthetic fibres with an intrinsic viscosity range of 0.72-0.82 helps improve synthetic fibre production operability and product quality without a significant reduction in final fibre properties.
• Staple yarns made from PTT are surprisingly elastic - having recoverable elasticity when extended up to 15-25% of the original yarn length. This elasticity is also present in staple yarns produced from intimate and non-intimate fibre blends where PTT is the major fibre component by weight and/or length. Further, this elasticity is recoverable after several hundred cycles. The elasticity is sufficient enough to enhance the shape retention characteristics of textile fabrics produced from PTT staple yarns and blended staple yarns. Properly constructed and finished fabrics that contain a majority of PTT staple spun yarn (by weight of length percent) can have surprisingly high elastic recovery in woven and knit fabrics (tested with over 500 cycles by hand and 200 by instrument) .
• the present invention covers the formation of staple spun yarns by conversion of staple into a twisted yarn structure by any method.
• the spun yarn can be made by hand, spinning wheel, ring-spinning, open-end spinning, air-jet spinning or other types of staple to yarn conversion equipment.
• Staple yarns made from cotton, wool, acrylic, PET are not elastic.
• the industry commonly has to add an elastic continuous filament either internally to the yarn or fabric to give the final textile product elastic properties.
• These solutions are more expensive than a basic staple spun yarn made from PTT.
• the value of the present invention is that people with basic staple spun yarn technologies can produce an elastic spun yarn of commercial value without investing in more expensive core spun yarn equipment or incorporating elastic continuous filaments into the fabric structures, which then complicates how the fabric is dyed and finished.
• PTT stress decay was independent of heat set temperature and decreased linearly with increasing applied stretch (0.5% reduction in stress decay / 1% applied stretch in heat setting) .
• PET stress decay decreased with increasing oven temperature and linearly with increasing applied stretch.
• the applied stretch effect is considerably stronger than with PTT (-0.9% per % applied stretch).
• the orientation In a semi crystalline polymer fiber with significant orientation, the orientation resides in two areas, the crystalline areas, and the amorphous areas connecting the crystalline domains. There is usually a range of crystal sizes, and the orientation of crystalline regions can vary.
• the second route is exclusively used, because as we will see later, preshrinking reduces fiber modulus.
• Specialty fibers, particularly for wool blends, use the first route because strength and modulus are not important issues, but the better dyeability offered by route 1 is an advantage. At this juncture, it is not clear which is the better route for PTT.
• Fibers are twisted at a helix angle which reduces the effect of fiber shrinkage on the yarn
• PTT is a wonderful substrate that follows all the rules of the total orientation model.
• PET behaves in a similar manner, Figure 15. Because it is an annealed, and not a relaxed fiber, shrinkage of the control yarn decreases with increasing oven temperature even at 100°C. Because it is high modulus, at high stretch and low oven temperature the fibers do not stretch, but slip in the yarns so the shrinkage increase is not so great as for PTT. For oven temperatures above 130 °C PET dry heat shrinkage increases about 0.55% per 1% applied stretch. This is somewhat higher that PTT, but a good rule of thumb for both is ⁇ % shrinkage increase for each % stretch.
• Figure 16 compares PTT and PET yarn shrinkage for the highest and lowest heat set temperatures.
• PTT has about 2 to 2
• the PTT / Cotton blend is similar to the PET blend (Figure 17) with shrinkage increasing with decreased oven temperature and increasing applied stretch.
• the increase with applied stretch is fairly linear and shrinkage increases roughly 0.47 % per 1% applied stretch.
• Shrinkage of the cotton blends is approximately 1% less than the PET blend for similar conditions. For this sample set a good rule of thumb is that 1% applied stretch increases dry heat shrinkage %.
• Boil off shrinkage behaves in the same way as dry heat, except that the amorphous orientation available is that present in the fiber plus all crystals which melt between the glass transition and 100°C, so it is much less than the dry heat shrinkage. In some fibers where the plastization effect of water is high, this shrinkage can be considerable. Fibers produce by a draw relax process with relaxation temperatures above 100°C generally have very low boil off shrinkages. Annealed fibers generally have relatively high boil off shrinkage because they are heated under tension and there is always amorphous orientation present.
• the PTT control yarn had a shrinkage of 2% even though the fibers which went into it were oven relaxed at 100 C. This indicates that some cold drawing occurred in processing, probably during carding. This is not unexpected, given PTT' s low modulus.
• PTT yarn shrinkage increased about 0.38% per I % applied stretch.
• the control PET yarn had considerably higher shrinkage than PTT (4.5 vs 2%) because it is produced by the annealing process.
• Yarn shrinkage increased 0.47% per 1% applied stretch. In general PTT yarns have approximately 1% less dry heat shrinkage than PET yarns given similar yarn heat setting conditions (Figure 18).
• the PTT/PET blend yarns had a shrinkage increase of 0.44% per 1% applied stretch, and the PTT/Cotton yarn hand an increase of 0.417.
• a good rule of thumb for boil off shrinkage is that it increases about 0.4% per 1% applied stretch for all conditions tested.
• load at 5% strain is nearly independent of oven temperature, and is linearly related to applied stretch increasing O.Olgpd per 1% increase in applied stretch. This means that yarn stretch decreases as the yarn is drawn during heat setting. Note for the PTT data that the control yarn, which was produced from fibers relaxed at 100100% has essentially the same load at 5% strain as that heat set at 0 stretch and 100°C.
• PET yarns behaved in a similar manner. In this case there was a considerable change for the control yarn vs yarn heat set at 100°C and 0 applied stretch because the feed fibers were annealed, not relaxed. PET load at 5% elongation increases an order of magnitude higher than PTT with applied stretch, 0.1 gpd/1% applied stretch.
• Figure 19 compares the behavior of PTT and PET, and PTT' s stretch advantage is strikingly apparent. Not only is the force required for 5% strain a factor of 3 lower with no applied stretch, the response to applied stretch is much less, which means applied stretch can be used in heat setting PTT yarns without paying an excessive price in yarn stretch. Interestingly the highest applied stretch PTT item (7.5%) requires 45% less force at 5% strain than a PET sample which is relaxed 7.5%.
• This spun yarn stress decay experiment involved straining the yarn 5%, then holding the spun yarn at length for 2 minutes and allowing the yarn to recover to zero stress. Stress decay was calculated manually from the test charts, and is somewhat less accurate than machine calculated numbers from computerized analysis methods. Stress decay and recovery are two separate phenomena and are discussed separately.
• PTT recovery was not affected by oven temperature and increased linearly with increasing applied stretch (0.9 % recovery per 1% applied stretch) .
• PET recovery increased marginally with increase in oven temperature but the principal effect was applied stretch. Its response is much more pronounced than for PTT with an increase of 2.2 % recovery for each 1% applied stretch.
• PTT generally has 5-10% higher recovery than PET except where PET has had high levels of applied stretch in a high temperature oven.
• the PTT / PET blend yarn responded like pure PTT with no oven temperature dependence and a strong response to applies stretch (1.7% increase in recovery for each 1% applied stretch.
• PTT / Cotton blend results were erratic with both higher oven temper and higher applied stretch increasing recovery.
• Example 4 Lowering Resin PTT Resin IV from 0.92 to 0.82 Provides Improved Extrusion Reliability in PTT Staple Production
• PTT resin with 0.92 IV requires more severe spin pack filtration systems to maintain marginal yields in extrusion. It also helps improve production operability by decreasing the number of broken filaments during production. It allows one to run the product with cooler extrusion temperatures for extruded filaments having less than 2-denier per filament. PTT is known to degrade at melt extrusion temperature above 260°C.

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• Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
• Artificial Filaments (AREA)
• Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
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