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
  • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F6/04—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyolefins
  • D01F6/06—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyolefins from polypropylene

Definitions

• the present invention relates, in general, to a polypropylene fiber and, more particularly, to a polypropylene fiber which is useful as a material for non-woven fabrics, thereby allowing the non-woven fabrics to be smooth and excellent in strength and providing workability and physical properties for the non-woven fabrics during after-processes. Also, the present invention is concerned with a method for preparing such fibers .
• staple fibers are prepared from polyolefin polymers, they have to undergo a series of processes: the polyolefin polymers are generally compounded with some amount of additives and the resulting mixtures are melt-extruded in ordinary commercial processes to give fibers, which are crimped and cut into predetermined lengths.
• polyolefin staples When being applied for the making of non-woven fabrics, polyolefin staples are typically processed in a carding machine to give non-woven webs which are then thermally bonded.
• calender rollers For thermal bonding, a pair of calender rollers, ultrasonification, or hot air is usually used. Particularly as for polypropylene filaments or staples, they are arranged after opening and carding processes, and bridged to afford webs. These webs are thermally bonded with the aid of a calender roller with diamond or delta type patterns to produce non-woven fabrics which are industrially useful in various fields.
• hot air may be utilized instead of calender rollers. In this case, after being allowed to undergo a carding process, webs are bonded to give non- woven fabrics by means of hot air which is circulated in a porous drum.
• Polypropylene non-woven fabrics find numerous applications in the disposable diaper, diaper for patients suffering from urinary incontinence, hygienic band, mask, and medical fabric industries. Although not demanding strength as high as that of woven fabrics, the non-woven fabrics used in these purposes have to be soft and satisfy the requirement of safety to skin because they are in direct contact with the skin.
• non-woven fabrics The strength of non-woven fabrics varies depending on their preparation processes as well as on physical properties of material fibers. With the aim of improving productivity, non-woven fabric producing manufacturers generally try to make high production speed. The high production speed, however, demands more excellent physical properties for the fibers for non-woven fabrics.
• polypropylene fibers for non-woven fabrics which can be applied to high-speed carding machines and guarantee the excellent strength and softness of the non- woven fabrics after thermal bonding. It is another object of the present invention to provide a method for preparing such polypropylene fibers.
• a non-woven fabric prepared from such polypropylene fibers It is a further object of the present invention to provide a non-woven fabric prepared from such polypropylene fibers.
• a polypropylene fiber which is obtained from an isotactic polypropylene homopolymer with an isotactic index of 90 to 99 % through melt- spmning or through drawing after melt-spmning, and shows two differential scanning calorimeter (DSC) endothermic peaks between 155 and 170 °C .
• DSC differential scanning calorimeter
• a method for preparing polypropylene fibers comprising the steps of: (a) melting an isotactic polypropylene homopolymer with an isotactic mdex of 90-99 %, a melting index (MI a ) of 10.0- 40.0, preferably 10.0-25.0 and a polydispersity index
• Fig. 1 is a DSC endothermic curve in which two endothermic peaks apparently appear in a polypropylene homopolymer fiber of the present invention as measured by a DSC;
• Fig. 2 is a DSC endothermic curve in which two endothermic peaks apparently appear with the secondary peak being in a shoulder form of the primary peak; and Fig. 3 is a DSC endothermic curve in which only one DSC endothermic peak appears in a conventional polypropylene homopolymer fiber.
• the present invention pertains to polypropylene fibers which are prepared from polypropylene homopolymers with an isotactic index of 90 to 99% by melt-spinning or by melt-spinning and drawing and have two differential scanning calorimeter (DSC) endothermic peaks in the range from 155 to 170 °C .
• the polypropylene fibers of the present invention show a primary endothermic peak at 160 ⁇ 3 °C and a secondary endothermic peak at 16513 C C .
• non-woven fabrics are prepared from the polypropylene fibers of the present invention by thermal bonding
• the above physical properties allow the non- woven fabrics to be smooth with excellent strength. This advantage is believed to result from the fact that, while the fibers thermally fused due to the heat or the heat and the pressure between rolls are solidified again, rapid recrystallization occurs in the regions which are high in melting points.
• Useful as materials to prepare the fibers of the present invention are polypropylene homopolymers with an isotactic index of 90 to 99 %.
• the polypropylene fibers of the present invention have a melt index (MI C ) of 16.5-80.0, which is preferably 1.65-7.50 times as large as that (MI a ) of the material isotactic polypropylene.
• the polypropylene fibers of the present invention range, in polydispersity index (PI C ), from 2.1 to 5.7 and, more preferably from 3.5 to 4.3 with a value being narrower by 20 % than the PI a of the material isotactic polypropylene.
• PI C polydispersity index
• the isotactic polypropylene used in the present invention preferably ranges, in melt index (MI a ) , from 10 to 40 and, in polydispersity index (PI a ), from 2.5 to 6.0.
• a stabilizer or an antioxidant is preferably formulated at an amount of 0.03 to 2.0 wt%, preferably 0.03 to 0.7 wt% and more preferably 0.03 to 0.4 wt% .
• a deoxidant agent such as 2- ethyl hexanoic acid, caprylic acid, decanoic acid, and dodecanoic acid, Fe, Co, Ca and Ba salts of 2-ethyl hexanoic acid, and combinations thereof.
• a deoxidant agent or the colorant calcium stearate, which is usually used to prepare polypropylene homopolymers in petrochemical plants, may be selected.
• a variety of additives available in the present invention may be referred to European patent No. 279,511.
• the isotactic polypropylene useful in the present invention preferably has a melt index (MI a ) of 10 to 40.
• MI a melt index
• the isotactic polypropylene has an MI a of greater than 40, the resulting fibers are not suitable for non-woven fabrics in terms of strength. Further, incompletion frequently occurs in the fulfillment of quenching after the spinning, leading to fusion between neighboring fibers.
• the fibers of the present invention include those which are obtained through melting, spinning, solidifying and taking-up processes as well as those which are obtained through a drawing process after melting and spinning processes and necessarily have undergone the processes of crimping, thermal fixing and cutting into staples.
• the fibers which experience melt-spinning are almost identical to those which further experience drawing in MI, PI and DSC endothermic peak.
• the material polymer is melted in an extruder to give a molten polymer which has a melt index (MI b ) with the ratio of Ml b MI a ranging from 1.01 to 1.50 and a polydispersity index (PI b ) being narrower by 10 % than PI a and more preferably by 5 %.
• MI b melt index
• PI b polydispersity index
• a preferable PIb falls in the range of 2.4 to 5.0.
• the polymer which has undergone an MI change the extruding process is allowed to be secondarily changed in MI.
• the MI change at a quenching step is determined depending on the temperature of the delayed quenched region, the atmosphere, the temperature, speed and quantity of quenching air.
• U.S. Pat. No. 4,193,961 describes the use of delay quenching and quenching air, which may also be referred to other documents, for example, M. Ahmed "Polypropylene Fibers-Science and Technology" sponsored by Society of Plastics Engineers, Inc.
• the fibers which experience the quenching step are preferably controlled to have a melt index (MI C ) 1.65- 7.50 times as large as the melt index (MI a ) of the material polymer and a polydispersity index (PI C ) narrower by 20 % or less than that (PI a ) of the material polymer
• the fibers preferably range, PI C , from 2.1 to 5.7, more preferably from 2.3 to 4.5 and most preferably from 3.0 to 4.0.
• PI C the strength of the grey yarns is deteriorated.
• the making of non- woven fabrics from the grey yarns suffers from poor workability because the non-woven fabrics are apt to be contaminated with card clothing and partially melted on the calender roll.
• the yarn has a too greatly decreased molecular weight and the quenching effect after the spinning from a nozzle is decreased to generate fusion between yarns.
• the strength of the grey yarn is improved, but it is difficult for such grey yarns to improve the thermal bonding index (hereinafter referred to as "TBI") to a desired extent. That is, the non-woven fabrics obtained show low TBI and feel harsh to the touch. Although the strength or TBI of the non-woven fabrics can be improved by increasing the temperature of the calender roll or the thermal bonding area, the non-woven fabrics still remain harsh.
• TBI thermal bonding index
• non-woven fabrics Upon the making of non-woven fabrics, their machine direction orientation and cross direction strengths vary depending on the kinds and arrangements of carding machines. Differences may be found m the machine direction and cross direction strengths of the non-woven fabrics which have passed through carding machines if these machines are manufactured by different manufacturers . Even in the carding machines manufactured by the same manufacturers, the non-woven fabrics show different physical properties in dependence on the shape and material of carding clothing and the presence of random rolls. In addition, the non-woven fabrics are different in plan weight, depending on the requirements for the after-process. The measured strength values of the non-woven fabrics represent simple tenacity and their units are characteristically different from one company to another.
• the simple tenacity is unsuitable to determine whether the physical properties of the non-woven fabrics are improved.
• the structure and inherent physical properties of the yarn or staple can be compared as to the influence on the non-woven fabrics by reference to the bonding indexes of the non-woven fabrics prepared although a difference may exist in kinds or arrangements of the carding machines.
• TBI TBI is recognized as very proper. A detail of TBI is described in an article concerning Polypropylene Fibres and Textiles, reported in the Fourth International Conference held by The Plastics and Rubber Institute. Indeed, TBI is introduced in the present invention as the most valuable parameter to comparatively determine the influence of the physical properties of yarns or staples on the non-woven fabrics .
• the non- woven fabrics can be made which are 2.0 or higher in TBI with good softness.
• DSC endothermic Peaks fiber samples were sufficiently washed to remove oiling agents. After being dried for 30 min in the air, the samples were vacuum- dried for 1 hour in a decicater and cut into a length of 2-4 mm. The cut samples of 5mg were put on a measuring pan which was then subjected to thermal analysis using the Perkin Elmer 7 series Thermal Analysis System in which the temperature was elevated at a rate of 5 °C/min
• Fig. 1 shows two apparent DSC endothermic peaks of the fiber according to the present invention and Fig. 2 shows that a secondary DSC endothermic peak appears in a shoulder form of a primary DSC endothermic peak.
• Fig. 3 is an endothermic curve showing that only one DSC endothermic peak appears in a conventional fiber.
• Denier of Yarn and Staple measured using Vibroskop, manufactured by Lenzing.
• MI Melt Index
• Polydispersity Index (PI): using Model RMS-800 ( Disk; parallel plate) of Rheometrics, U.S.A., G c was measured at 200 °C at a shear rate of 0.1-100 under a 10% strain condition and substituted into the following equation.
• G c is a modulus of a point at which a storage modulus (G' ) and a loss modulus (G") are crossed with each other at two to six frequencies in a frequency range of 5-250 Hz. When there occurred no cross points, G c was determined by extrapolation.
• TAI Thermal Bonding Index
• MD is a machine direction strength (kg/50 mm)
• CD is a cross direction strength (kg/50 mm)
• plan weight is a weight per area of a non-woven fabric.
• Softness the feeling to the touch was graded: 1 very harsh; 2 harsh; 3 ordinary; 4 soft; 5 very soft.
• MI isotactic polypropylene homopolymers with an isotatic index of 97% and MI as indicated in Table 1, below, containing an antioxidant and stabilizer at an amount of 0.09 wt%, were melt-spun at an extruder temperature from 250 to 290 °C while the heating in the range from the extruder to the nozzle was controlled in the range of 285-310 °C by means of a heating medium to allow the melt to have MI b as indicated in Table 1, below.
• a bypass was set to take the samples
• the melt was extruded at a spinning rate of 1,500 m/min through a spinneret, passed through a heat reserving zone for delayed quench -1 ng and then quenched to afford primary yarns of 2.4 deniers, which had Mic, Pic and DSC endothermic peaks as shown in Table 1.
• the primary yarns thus obtained were collected in a bundle and drawn at a drawing ratio of 1.5 times while being crimped in a crimper, following cutting them to staples 40 mm long.
• the staples were applied to the carding machines according to manufacturers .
• the upper roll used for the preparation of non-woven fabrics was of a diamond type with a sealing area amounting to 22 % while the calender roll performed its function at 147 °C with a pressure of 95 kg/cm.
• the non-woven fabrics obtained are described concerning plan weight, strength of machine direction and cross direction, TBI and softness in Table 3, below.
• the non-woven fabrics which are prepared by thermally bonding the isotactic polypropylene homopolymer fibers having two DSC endothermic peaks in accordance with the present invention, show excellent strength in addition to being soft.
• the non-woven fabrics can be produced in high speed carding machines. Consequently, the present invention allows the production of high quality non-woven fabrics with a high yield.
• the present invention has been described in an illustrative manner, and it is to be understood that the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Artificial Filaments (AREA)
• Nonwoven Fabrics (AREA)

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