ES2237983B1 - POLYPROPYLENE FIBER AND PREPARATION OF THE SAME. - Google Patents

Abstract

Polypropylene fiber and preparation of the same.

A polypropylene fiber is disclosed which is obtained from an isotactic polypropylene homopolymer with an isotactic index of 90 to 99%, by fusion spinning or stretched after fusion spinning, and shows two spikes endothermic differential scanning calorimeter (DSC) between 155 and 170 ° C. When they thermally bond with each other, the fibers become transformed into nonwoven fabrics that have excellent strength In addition to softness. A high quality of the non-woven fabrics in high-speed card machines with excellent yields

Description

Polypropylene fiber and preparation of the same.

Background of the invention 1. Field of the invention

The present invention relates, in general, to a polypropylene fiber and, more particularly, to a fiber of Polypropylene that is useful as a material for nonwoven fabrics, allowing these nonwoven fabrics to be soft and present excellent resistance, providing capacity characteristics Handling and physical characteristics for nonwoven fabrics during subsequent processes. Also, the present invention it refers to a method for the preparation of said fibers.

2. Description of priorities

To prepare cut fibers from polyolefin polymers, the fibers have to undergo a series of processes: polyolefin polymers are combined in general with a certain amount of additives and the resulting mixtures are extruded in fusion in ordinary commercial processes for provide corrugated and length-cut fibers predetermined

When applied to fabric manufacturing, it does not woven, the polyolefins cut fibers are processed from typical way in a card machine, to get items nonwoven laminates that are then joined or agglomerated thermally

For thermal bonding or bonding, they are used usually a pair of calendering, ultrasonic or air rollers hot.

In particular, for polypropylene filaments or cut fibers, are arranged after the opening processes and carding, and overlap to get laminar elements. These laminar elements are bonded or thermally bonded with help of calendering rollers with diamond or delta type drawings, to produce nonwoven fabrics that can be used industrially in different sectors. Alternatively, it You can use hot air instead of calendering rollers. In This case, after receiving the carding process, the elements Layers are joined to get nonwoven fabrics by means of hot air that is circulated in a porous drum.

Non-woven polypropylene fabrics find numerous applications in the single-use diaper sector, diapers for patients suffering from urinary incontinence, bandages hygienic, masks, and in the fabric industry of medical application While they do not require such a high resistance as in woven fabrics, the non-woven fabrics used in these applications have to be smooth and must meet the safety requirements with respect to the skin, because it They find themselves in direct contact with it.

The resistance of nonwoven fabrics varies depending on your preparation process and also on the physical characteristics of the fibers of the material.

With the aim of improving productivity, nonwoven fabric manufacturers have generally tried to get high production speeds However, a high production speed requires more physical characteristics high for the fibers of nonwoven fabrics.

Characteristics of the invention.

To achieve the present invention, the intense and deep investigations in polypropylene fibers or cut fibers suitable for nonwoven fabrics, carried out by the present inventors to overcome the problems found in this technique that have been cited above, the discovery that polypropylene homopolymers isotactic, which show two endothermic peaks measured by a scanning calorimeter or differential scanning (DSC), allow the production of new fibers, which had not been disclosed still in the technique, and guarantee excellent resistance and softness in nonwoven fabrics prepared from such fibers In addition, the fibers that have this structure were observed which can be maintained by control of the melt indexes and of polydispersibility at each stage of the process throughout the process full.

Therefore, it is the objective of the present invention disclosing polypropylene fibers for non-woven fabrics fabrics that can be applied to high card machines speed and that guarantee the excellent strength and smoothness of Nonwoven fabrics after thermal bonding.

Another aspect of the present invention consists in disclose a method for the preparation of said fibers of Polypropylene.

Another additional objective of the present invention It consists of making known a non-woven fabric prepared from said polypropylene fibers.

In accordance with the realization of this invention, a polypropylene fiber is disclosed which is obtained from an isotactic polypropylene homopolymer with an isotactic index of 90 to 99%, by fusion spinning or stretched after fusion spinning, and shows two spikes endothermic differential scanning calorimeter (DSC) between 155 and 170 ° C.

In accordance with another embodiment of the present invention, a method for preparing fibers is disclosed Polypropylene, comprising the following steps: (a) melt an isotactic polypropylene homopolymer with an isotactic index of 90-99%, a melt index (MI_ {a}) of 10.0-40.0, preferably 10.0-25.0 and a polydispersibility index (PI_ {a}) of 2.5-6.0, preferably 2.8-5.0 and more preferably 3.5-4.3 to achieve a molten polymer having a melt index (MIb) with a ratio MI_ {b} / MI_ {a} between 1.01 and 1.50 and a narrower polydispersibility index (PI_ {b}) of the order of 10% or less than (PI_a); (b) spin the molten polymer to produce fibers with a melt index (MI_ {c}) of 16.5-80.0 and an index of polydispersability (PI c) narrower by 20% or less than PI_ {a}, the relationship MI_ {c} / MI_ {a} being understood between 1.65 to 7.50; and (c) optionally proceed to stretch the fibers

Brief description of the drawings

The previous and other objectives, the Features and other advantages of the present invention are will understand more easily from the following description detailed in relation to the attached drawings, in which:

Figure 1 is a DSC endothermic graph in the that apparently two endothermic peaks appear in a fiber of a polypropylene homopolymer of the present invention, measured by a DSC;

Figure 2 is a DSC endothermic graph in the apparently two endothermic peaks appear adopting the peak secondary form of primary peak step; Y

Figure 3 is a DSC endothermic graph in the which appears a DSC endothermic peak in a homopolymer fiber of conventional polyopropylene.

Detailed description of the invention

The present invention relates to fibers of polypropylene that are prepared from homopolymers of polypropylene with an isotactic index of 90 to 99%, by spinning in fusion or spinning in fusion and stretched and having two spikes endothermic (DSC) by differential scanning calorimeter in a range from 155 to 170 ° C. Preferably, polypropylene fibers of the present invention show a primary endothermic peak in 160 ± 3 ° C and a secondary endothermic peak at 165 ± 3 ° C.

In the case where the nonwoven fibers are prepared from the polypropylene fibers of the present invention by joining or thermal agglomeration, the characteristics The above physical properties allow to obtain non-woven fabrics Soft and with excellent resistance. This advantage is believed to result from the fact that, although thermally molten fibers are solidify again due to heat or heat action and pressure between rollers, rapid recrystallization takes place in areas that have high melting points.

They are useful as materials for the preparation of the fibers in the present invention the homopolymers of polypropylene 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 larger than the (MI_ {a}) of Isotactic polypropylene material.

Preferably, the polypropylene fibers of the present invention vary in the polydispersibility index (PI_), from 2.1 to 5.7 and, more preferably from 3.5 to 4.3 with a 20% narrower value than the PI_ {a} of the material isotactic polypropylene.

The preferred fineness of the fibers of Polypropylene of the present invention is comprised in a range from 1.0 to 80.0 deniers.

As for the isotactic polypropylene used in the present invention, it is preferably comprised in the melt indexes (MI_ {a}) from 10 to 40, and the index of polydispersibility (PIa) from 2.5 to 6.0.

When polypropylene is melted in a device extrusion or extruder, a stabilizer or a antioxidant preferably in an amount of 0.03 to 2.0% in weight, preferably 0.03 to 0.7% by weight, and more preferably from 0.03 to 0.4% by weight.

In addition to stabilizers or antioxidants, it can use for the preparation of the fibers of the present invention, ordinary additives in this technique, such as agents deoxidants, dyes, metal carboxylates, etc., for fiber preparation The metal carboxylate available in the The present invention is selected from the group consisting of salts of 2-ethylexanoic acid nickel, caprylic acid, decanoic acid and dodecanoic acid, salts of Fe, Co, Ca and Ba del 2-ethyl exanoic acid, and combinations of the same. As a deoxidizing or coloring agent, it can be selected calcium stearate, which is usually used to prepare polypropylene homopolymers in petrochemical factories. A series of additives available for the present invention can be find as reference in European patent 279,511.

The isotactic polypropylene used in the The present invention, as indicated above, has preferably a melt index (MI_) of 10 to 40. example, when the (MI_ {a}) is less than 10, a increase in the pressure in the spindle nozzle head, leading to decreased productivity. One is required great contribution of heat to the melt spinning of said polypropylene, resulting in increased consumption of Energy. In addition, the fibers obtained under these conditions of high heat input show greater toughness, so which are not suitable for the uses of nonwoven fabrics They require softness. Moreover, when polypropylene isotactic has a (MI_) greater than 40, the fibers resulting are not suitable for nonwoven fabrics in terms of resistance. In addition, a shutdown or incomplete quenching after spinning, which leads to fusion between adjacent fibers.

It should be noted that the fibers of the present invention include those that are obtained by fusion, spinning, solidification and collection, and also those obtained by stretching processes after melting and spinning and that necessarily have suffered the processes of undulation, fixed thermal and cut to get short fibers. The fibers that they experience fusion spinning are almost identical to those that they also experience stretching at the endothermic peak MI, PI and DSC.

In an embodiment of the preparation of polypropylene filaments or fibers according to the present invention, The polymer material is melted in an extruder to get a molten polymer that has a melt index (MI_ {b}) with a proportion of MI_ {b} / MI_ {a} between 1.01 and 1.50 and a polydispersibility index (PI_ {b}) more narrow in 10% than the PI a and more preferably in 5%. A Preferred PI_ is in a range of 2.4 to 5.0.

For example, if MI_ {b} exceeds 1.5 times the MI_ {a}, the polypropylene molecular chain is so fractional that its intrinsic resistance cannot be maintained. In addition, said fractionation leads to insufficient viscosity so that the molecular chains are oriented in a nozzle, and nor can an adequate pressure for spinning be maintained. In addition, the fibers obtained have little resistance, so that nonwoven fabrics prepared from fibers are rough touch. As a result, productivity is reduced. A MI change of the order of 1% or higher occurs naturally in polypropylene when extrusion takes place. When MI_ {b} is changed to less than 1.01 times MI_ {a}, they appear serious difficulties in the fiber preparation process. Particularly, a high viscosity appears in the nozzle increasing the pressure on it, making the process of very unstable spinning. Accordingly, the performance of the production decreases with a serious deviation in the quality of fibers

When controlling cooling conditions abrupt or "off" after spinning, the polymer that has underwent an MI change in the extrusion process, it can be changed secondarily in MI. The change of MI at a stage of rough cooling is determined depending on the temperature of delayed shutdown zone, atmosphere, temperature, speed and amount of shutdown air. US Patent 4,193,961 describes the use of delayed shutdown and shutdown air, to which reference can also be found in other documents, for example, M. Ahmed "Polypropilene Fibers-Science and Technology "sponsored by the Society of Plastics Engineers, Inc.

In accordance with the preparation of this invention, the fibers undergoing the cooling stage rough are preferably controlled so that they have a melt index (MI_ {c}) 1.65-7.50 times in melt index (MI_) of the polymer material and an index of polydispersibility (PI c) narrower than 20% or less than the (PI_ {a}) of the polymer (ie in magnitudes of 0.80xPI_ {a} or wider). The fibers preferably vary, in their value of PI_ {c}, between 2.1 to 5.7, more preferably between 2.3 to 4.5 and more preferably between 3.0 to 4.0.

When MI_ {c} is above values indicated, the resistance of the raw fibers it deteriorates. The manufacture of non-woven fabrics from raw threads suffers from reduced handling capacity because nonwoven fabrics are likely to be contaminated with Card cloth and partially melt on the calendering roller. In more detail, if the MI_ {c} deviates from the upper limit, the thread has a molecular weight too reduced and the effect of rapid cooling after spinning of a nozzle decreases generating fusion between threads. When the threads are used to prepare nonwoven fabrics after being prepared so forced despite the conditions indicated above, it generates a lot of dust from defective threads in a process of opening and card, which has a negative influence on the fabrication process. In addition, certain heat sensitive parts of the defective threads are stopped by melting in the calendering, fouling the surface of the calendering roller, which plays a  certain role in the union or thermal agglomeration of fabrics non-woven

On the other hand, if the MI_ {c} is more beyond the lower limit, the resistance of the raw threads is improvement but it is difficult for these raw threads to improve the index thermal bonding (referred to below as "TBI" to the desired extent). That is, nonwoven fabrics obtained show a low BIT and have a rough touch. Although the Strength or TBI of nonwoven fabrics can be improved increasing the temperature of the calendering roller or the area of thermal bond, non-woven fabrics remain rough.

In the manufacture of nonwoven fabrics, its resistance in machine direction and direction transversal vary depending on the types and dispositions of the card machines. Differences can be found in the resistance in the machine direction and in the transverse direction of the non-woven fabrics that have passed through the card machines if These machines are manufactured by different manufacturers. Even in card machines manufactured by the same manufacturers, the non-woven fabrics show different physical characteristics depending on the shape and material of the card fittings and the presence of random rollers. In addition, non-woven fabrics they are different in their flat weight, depending on the demands of the  subsequent process The measured values of the resistance of the non-woven fabrics represent simple tenacity and their units are characteristically different from one company to another. Thus, since the case can be presented in which you cannot discriminate superiority between them, simple tenacity is not adequate to determine if the physical characteristics of the fabrics Nonwovens have been improved. However, the structure and inherent physical characteristics of the yarn or cut fiber are can compare the influence of nonwoven fabrics making reference to the indexes of union of the nonwoven fabrics prepared although there may be a difference in the types or provisions of loading machines.

In the precise determination of the influence of the physical characteristics of threads or fibers cut with respect to fabrics from them, it is recognized as appropriate the concept of TBI. TBI is described in detail in an article referring to polypropylene fibers or textile products, which was given to be announced at the fourth international conference of "The Plastics and Rubber Institute. "Certainly, the BIT is introduced into the present invention as the most valuable parameter to determine comparatively the influence of the physical characteristics of threads or fibers on nonwoven fabrics.

Of the fibers of the present invention, they can be manufacture nonwoven fabrics that have a value of 2.0 or higher in TBI, with satisfactory smoothness.

The present invention will be better understood in based on the following examples that are illustrative, but not limiting of the present invention.

In the following examples, fibers will be analyzed and nonwoven fabrics of the type suggested in the present invention in terms of its physical characteristics.

DSC endothermic peaks : fiber samples were sufficiently washed to remove oily agents. After air drying for 30 minutes, the samples were dried under vacuum for 1 hour in a desiccator and cut to a length of 2-4 mm. The cut samples of 5 mg were placed on a measuring cuvette which was then subjected to thermal analysis using the Perkin Elmer 7 thermal analysis system in which the temperature was increased at a rate of 5 ° C / min from 30 ° C to 190 ° C, at effects of obtaining endothermic curves. Other features of this measurement were adapted to ASTM method 3418-82. Conventional polypropylene homopolymer fibers showed unique endothermic peaks while the fibers of the present invention have double endothermic peaks, as seen in the accompanying drawings. Figure 1 shows two apparent DSC endothermic peaks of the fiber according to the present invention, and Figure 2 shows the appearance of a stepped secondary DSC endothermic peak of a primary DSC endothermic peak. Figure 3 is an endothermic curve showing that only one endothermic type DSC appears in a conventional fiber.

Denier of the threads and fibers : measured using Vibroskop, manufactured by Lenzing.

Strength and elongation of thread and fibers : measured by the use of a Vibrodyn device, manufactured by Lenzing, in accordance with ASTM D 638.

Melt index (MI) : measured using Tinius Olsen MP 993 model, in accordance with ASTM D 1238. For the measurement of MI, fiber samples were washed with plenty of water, centrifuged, dried at 105 ° C for 15 min. in a stove and cut to length of 1 cm.

Polydispersibility index (PI) : using the RMS-800 (disk; parallel plate) of Rheometrics, USA, G c was measured at 200 ° C with a hard shear of 0.1-100 under resistance characteristics of 10 % and replaced in the following equation

PI = \ frac {10 6} {G_ {c}}

in which G_ {c} is the module of a point at which the storage module (G ') and the module loss (G '') cross each other on two to six frequencies in one 5-250 Hz frequency range. When they do not occur crossing points, G_ {c} is determined by extrapolation.

Isotactic index (II) : A sample of polypropylene homopolymer was cut in a length of 5 mm, washed with water, and dried at 105 ° C for 1 hour in an oven. After taking about 5 g and its exact weight, a portion of the dried sample was boiled for about 5 hours in heptane for extraction purposes. After completion of the extraction, the sample was sufficiently washed with water, washed at 105 ° C for 1 hour in an oven and then weighed. Weights measured before and after extraction were replaced in the following equation to achieve the isotactic index.

\ text {Index isotactic (%)} = \ frac {\ text {Weight after extraction}} {\ text {Weight before extraction}} \ x \ 100

Thermal bond index (BIT) of a non-woven fabric : calculated according to the following equation:

TBI = (MD x CD) ^ {1/3} x \ frac {20} {\ text {Weight in flat}}

in this formula, MD indicates the resistance in the machine direction (kg / 50 mm), CD is the resistance in the transverse direction (kg / 50 mm), and in weight in flat is a weight per area of the fabric not woven

Resistance of the non-woven fabric : samples with a dimension of 50 mm in width and 140 mm in length with a tensile speed of 100 mm / minute were measured using an instron apparatus.

Softness : touch sensation is graduated: 1 very rough; 2 coarse; 3 ordinary; 4 soft; 5 very soft.

Examples from 1 to 7

Comparative Examples 1 to 7

Polymers of fusion polymers were spun Isotactic polypropylene with an isotactic index of 97% and MI such as indicated in table 1, below, containing a antioxidant and a stabilizer in an amount of 0.09% by weight, at an extruder temperature of 250 to 290 ° C, while the heating between the nozzle extruder was controlled in a range of 285-310ºC through a conduit of heating allowing the fusion to have such a MI_ {b} as indicated below in table 1. For comparison of MI between the raw material and the fusion product before the nozzle, a bypass was arranged to take the samples while arranged a pressure reduction just before the pump gears that served to constantly feed the product in fusion to the nozzle.

Then the molten material was extruded at a spinning speed of 1,500 m / min through a fine nozzle head, was passed through an area of thermal reserve for delayed shutdown and then it was made  quenching or quenching to get primary threads of 2.4 deniers, which had Mic, PIc and DSC endothermic peaks that they are shown in table 1.

The primary threads obtained that way were collected in a beam and stretched with a proportion of stretched 1.5 times while rippling in a corrugated device, following the cutting of the same in fibers 40 mm long.

Table 2 shows the MI values, PI, fiber resistance, number of undulations and peaks Endothermic DSC of the cut fibers obtained.

In order to prepare nonwoven fabrics, the Cut fibers were applied to card machines according to their Manufacturers The top roller used for the preparation of the nonwoven fabrics were diamond type with an area of tightness that reached 22% while the roller calendering carried out its function at 147 ° C with a pressure of 95 kg / cm

The nonwoven fabrics obtained are described with with respect to the flat weight, resistance in machine direction and in transverse direction, TBI and smoothness in the following table 3.

TABLE 1

one

       \ vskip1.000000 \ baselineskip
    

TABLE 1 (continued)

2

TABLE 2

3

       \ vskip1.000000 \ baselineskip
    

TABLE 3

4

As is evident from previous examples, nonwoven fabrics, which are prepared by thermal bonding of isotactic polypropylene homopolymer fibers having two DSC endothermic peaks according to the present invention, It shows excellent resistance as well as softness. Also, the non-woven fabrics can be produced in high card machines speed. As a consequence, the present invention allows production of high quality nonwoven fabrics with high performance.

The present invention has been described in a manner illustrative, and it should be understood that the terminology used It is intended to have a descriptive nature rather than a limitation. Many modifications and variations of this are possible invention in the light of the teachings that emerge from the previous description. Therefore, it should be understood that within within the scope of the appended claims, the invention It can be practiced differently than described specifically.

Claims (18)

1. Polypropylene fiber, obtained from an isotactic polypropylene homopolymer, with an index isotactic from 90 to 99%, by melting or stretching spinning after fusion spinning, and shows two DSC endothermic peaks to differential scanning calorimeter between 155 and 170 ° C. 2. Polypropylene fiber according to claim 1, in which the two DSC endothermic peaks to the calorimeter of differential scan are composed of an endothermic peak primary that appears at 160 ± 3 ° C and a second endothermic peak secondary that appears at 165 ± 3 ° C. 3. Polypropylene fiber according to claim 1, in which the fiber has a melt index (MI_ {c}) of 16.5-80.0. 4. Polypropylene fiber according to claim 1, in which the fiber has a polydispersibility index (PI_ {c}) of 2.1-5.7. 5. Polypropylene fiber according to claim 1, in which the fiber has a fineness of 1.0-80.0 deniers per filament. 6. Polypropylene fiber according to claim 4, in which the fiber has a PI_ {c} of 2.3-4.5. 7. Polypropylene fiber according to claim 1, in which it further comprises a stabilizer and / or an antioxidant in an amount of 0.03 to 2.0% by weight. 8. Polypropylene fiber according to claim 7, in which the stabilizer and / or an antioxidant are contained in an amount of 0.03 to 0.7% by weight. 9. Polypropylene fiber according to claim 8, in which the stabilizer and / or an antioxidant are contained in a proportion of 0.03 to 0.4% by weight. 10. Method for preparing fibers of polypropylene, which comprises the following phases: (a) fusion of a polypropylene homopolymer isotactic with an isotactic index of 90-99%, a melt index (MI_ {a}) of 10.0-40.0 and an index of polydispersibility (PI_) of 2.5-6.0 for provide a molten polymer that has a melt index (MI_ {b}) with a ratio MI_ {b} / MI_ {a} between 1.01 and 1.50 and a polydispersibility index (PI_ {b}) more narrow of 10% or less than PI_ {a}; (b) proceed to spin the molten polymer to produce fibers with a melt index (MI_ {c}) of 16.5-80.0 and a polydispersibility index (PI_ {c}) narrower than 20% or less than PI_ {a}, being including the proportion of MI_ {c} / MI_ {a} between 1.65 and 7.50; Y (c) optionally stretching the fibers. 11. Method according to claim 10, wherein the polypropylene homopolymer contains a stabilizer and / or a antioxidant with a proportion of 0.03-2.0% in weight in stage (a). 12. Method according to claim 10, wherein the value of MI_ {a} is between 10 and 30. 13. Method according to claim 10, wherein the value PI_ {a} is between 2.8 and 5.0. 14. Method according to claim 13, wherein the value of PI_ {a} is between 3.5 and 4.3. 15. Method according to claim 10, wherein the fibers are comprised, in fineness, between 1.0 and 80.0 deniers by filament 16. Method according to claim 10, wherein MI_ {b} is between 10.1 and 41.0. 17. Method according to claim 10, wherein the fibers have a value of PI_ {c} between 2.1 and 5.7. 18. Method according to claim 17, wherein the fiber has a value of PI_ {c} between 2.3 and 4,5.