Nonwoven material containing crimped multi-component fibers

Abstract

The present invention relates to nonwoven sheets comprising crimped multicomponent fibers.

Description

Technical Field

[0001] The present invention relates to a nonwoven sheet containing crimped multicomponent fibers.

Background Art

[0002] Flat sheets of nonwoven materials are used in the hygiene industry for the large-scale production of baby diapers and similar products. To improve the comfort and functionality of such products for the wearer, the industry has made efforts to enhance the softness and flexibility of the materials. Incorporating crimped multicomponent fibers instead of, or in addition to, straight single-component fibers is an approach widely described in the literature and practiced in the market to meet such demands. By using crimped fibers, the nonwoven becomes bulkier and less dense, and more flexible and soft. It closely resembles straight hair and curly hair. Generally, crimped multicomponent fibers contain two or more polymers with different physical properties that are asymmetrically distributed across their cross-section. The most common is the side-by-side configuration. In the case of spunbond fibers, this configuration causes the fibers to crimp when they are subjected to physical stress, such as during fiber stretching or rapid cooling.

[0003] One of the earliest patents related to this technology is US Patent No. 6,454,989, originally filed by the US company Kimberly-Clark. That document describes the basic principles related to spunbond, which was the industry standard for nonwoven materials for hygienic applications, and includes a long list of options where the polymers distributed across the fiber cross-section can vary. The options mentioned include, following the range of the degree of general differences, differences in melting point, differences in crystallization behavior, differences in melt elasticity, differences in molecular weight average or distribution, and many others. However, most of those options have not actually been tested, and since then, much research activity has been carried out to clarify the conditions under which they can be actually used and to clarify the configurations that provide materials with particularly desirable properties under various aspects. Patents resulting from these developments include European Patent No. 3165656, European Patent No. 3121314, European Patent No. 3246443, and European Patent No. 3246444, all of which date back to research conducted by the co-applicants of this application. However, despite such various improvements, the optimization and diversification of polymers that can be used to manufacture such materials are still necessary. Summary of the Invention

[0004] Against this background, the present invention provides a nonwoven sheet containing crimped multicomponent fibers, the fibers containing two different polymer components (A) and (B) distributed in a parallel arrangement across the cross-section of the fiber, wherein the line of the interface between the two polymer components (A) and (B) included in the radial plane of the fiber is curved, and the curvature (c) defined by the quotient (h) / (b) (wherein, the "length of the reference line" (b) is the length of the virtual straight line reference line connecting the two end points of the curved interface line, and the "height of the curvature" (h) is the distance from the reference line to the apex of the curved interface line) is between 0.05 and 0.25. The line of the interface has the shape of a single arc, i.e., it is not wavy, or more mathematically speaking, it has no inflection point where the sign of the curvature changes. Let us again describe the shape of the line of the interface included in any radial plane of the fiber, and thus the shape of the line of the interface visible when the fiber is cut in the radial direction. The radial plane is perpendicular to the longitudinal direction of the fiber, and thus forms an angle of 90° with the longitudinal axis of the fiber at any position. The shape of the line of the radial interface defining the present invention is the shape of the line of the interface included in this plane. This is to distinguish it from the contour of the interface along the longitudinal or diagonal line, which is naturally curved to some extent due to the geometric relationship in the crimped fiber. The curved nature of the line of the radial interface defining the present invention has no geometric relationship with the crimp of the fiber. Further studies aimed at a more fundamental understanding of the crimped bicomponent fibers have revealed that beneficial crimp behavior can be observed when the line of the radial interface between the components of the multicomponent fiber with the polymer components arranged in parallel has the specified curvature. In a preferred embodiment, the curvature (c) of the line of the radial interface is between 0.08 and 0.22, preferably between 0.10 and 0.20, more preferably between 0.12 and 0.18. Very advantageous crimp behavior has been observed in many cases where the curvature is within such a range.

[0005] For the purposes of the present application, the parallel arrangement of the polymer components (A) and (B) can be obtained with standard parallel fibers, but there can also be eccentric core-sheath fibers having a D-shaped core, the latter essentially corresponding to parallel fibers surrounded by a coating of either polymer. Nevertheless, the effect when the curvature is in the defined range is observed in particular in bicomponent parallel fibers containing only two polymer components distributed in a parallel arrangement across the cross-section. The effect is also observed with other fiber types such as staple fibers, but in a preferred embodiment, the nonwoven material of the invention is a spunbond material and the crimped multicomponent fibers are spunbond fibers. The sheet can contain, in addition to other fibers such as straight single-component fibers, bicomponent fibers according to the definition of the invention, or consist of bicomponent fibers according to the definition of the invention. In practice, since the millions of fibers formed for the nonwoven material are never always identical, the term "consisting of" must be understood in the sense that the fibers are all identical for each production and that the overwhelming majority of the fibers, for example more than 80% of the fibers, preferably more than 90% of the fibers, exhibit the characteristics of the invention to meet the requirement.

[0006] To facilitate the spinning of the spunbond multicomponent fibers of the invention, the spunbond machine must be able to flow the directly adjacent streams of two different polymers in parallel on the scale of a single fiber. The streams merge just before leaving the spinneret (die plate). The formation of the curved interface and the degree of curvature depend on the polymers used and the process conditions during fiber stretching and quenching. In this situation, at least one of the polymer components (A) or (B) is preferably a polyolefin polymer. More preferably, both the polymer component (A) and the polymer component (B) are polyolefin polymers. Among polyolefin polymers, propylene homopolymers, ethylene homopolymers, and copolymers of propylene or ethylene with other α-olefins, particularly propylene-α-olefin copolymers such as propylene-ethylene copolymers or propylene-C4-C8-copolymers, are preferred. In one embodiment, a propylene-ethylene copolymer is most preferred. In a given situation, a homopolymer is defined as a polymer having a comonomer content of less than 1 mass percent, preferably less than 0.5 mass percent. The comonomer content of the copolymer of propylene or ethylene with other α-olefins is preferably between 1.0 and 5.5 mass percent. The copolymer is preferably a random copolymer.

[0007] In a specifically preferred embodiment, one polymer component (A) is a propylene homopolymer and the other polymer component (B) is a propylene-α-olefin copolymer, and the comonomer content of the propylene-α-olefin copolymer is preferably between 1.0 and 5.5 mass percent. Furthermore, in this situation, the difference in the crystallization temperature T c of the two polymer components has been confirmed to be the most important parameter. In a preferred embodiment, the absolute value of the difference between the crystallization temperature [T c (A)] of the polymer component (A) and the crystallization temperature [T c (B)] of the polymer component (B) is more than 0 °C and less than 30 °C, preferably more than 10 °C and less than 25 °C, when measured by differential scanning calorimetry (DSC, ISO 11357-1 and -2).

[0008] When the polymer component (A) is a propylene homopolymer and the polymer component (B) is a propylene-α-olefin copolymer, the crystallization temperature [T c(A) preferably has a crystallization temperature [T c (B)] that is higher to such an extent. In one embodiment, the line of the curved radial interface curves, preferably towards the polymer component with the lower crystallization temperature, more preferably towards the propylene-α-olefin copolymer. The polymer component with the higher crystallization temperature, preferably the homopolypropylene, has a more compact cross-section. The crystallization temperature [T c (A)] of the polymer component (A) with the higher crystallization temperature preferably has an absolute value in the range of 90 °C to 135 °C, more preferably in the range of 100 °C to 125 °C. The crystallization temperature [T c (B)] of the polymer component (B) with the lower crystallization temperature preferably has an absolute value in the range of 80 °C to 125 °C, more preferably in the range of 90 °C to 115 °C.

[0009] The crystallization temperatures T c of polymers (A) and (B) are related to the chemical properties of the polymers and vary, for example, depending on the comonomer content, stereoregularity, or molecular weight distribution in the propylene-α-olefin copolymer. The crystallization behavior and kinetics can further influence each other and be balanced by adding a nucleating agent to one or both of the polymer components (A) and (B). The nucleating agent increases the number of sites where crystal nuclei start to form and thus promotes crystallization. Suitable nucleating agents include nonitol-based or sorbitol-based nucleating agents. In a preferred embodiment, the nucleating agent is an α-nucleating agent. Suitable α-nucleating agents include salts of monocarboxylic acids and polycarboxylic acids (e.g., sodium benzoate or aluminum tert-butylbenzoate), dibenzylidene sorbitol (e.g., 1,3:2,4-dibenzylidene sorbitol), C1-C8-alkyl-substituted dibenzylidene sorbitol derivatives (e.g., methyldibenzylidene sorbitol such as 1,3:2,4-di(methylbenzylidene) sorbitol, ethyldibenzylidene sorbitol, or dimethyldibenzylidene sorbitol), or substituted nonitol derivatives (e.g., 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol), salts of phosphoric acid diesters, such as sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl) phosphate or aluminum-hydroxy-bis[2,2'-methylene-bis(4,6-di-t-butylphenyl) phosphate], vinyl cycloalkane polymers, and vinyl alkane polymers. Dibenzylidene sorbitol (e.g., 1,3:2,4-dibenzylidene sorbitol), dibenzylidene sorbitol derivatives, preferably dimethyldibenzylidene sorbitol (e.g., 1,3:2,4-di(methylbenzylidene) sorbitol), or substituted nonitol derivatives, such as 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol, sodium 2,2'-methylenebis(4,6-di-tert-butylphenyl) phosphate, vinyl cycloalkane polymers, or vinyl alkane polymers, etc. may be most preferred.

[0010] Suitable addition amounts are in the range of 0.01 to 5000 ppm, preferably 0.05 to 4500 ppm, more preferably 0.15 to 3000 ppm, such as 0.1 to 4000 ppm, based on the total mass of each polymer component. The difference in the melting points T m of the two polymer components has been confirmed to be an important parameter. The melting temperature T mis preferably in the range of 155 °C to 164 °C (when determined by DSC, ISO 11357-1 and -2). The melting temperature T of the polymer component (B) with the lower crystallization (and melting) temperature m of the absolute value is preferably in the range of 142 °C to 155 °C (when determined by DSC, ISO 11357-1 and -2).

[0011] Other relevant properties of the polymer include melt flow rate MFR and molecular weight distribution. The melt flow rate of at least one, more preferably both, of the two polymer components (A) and (B) is in the range of 15 to 120 g / 10 min (when determined at 230 °C and 2.16 kg in accordance with ISO 1133). At least, the preferred melt flow rate of the component with the higher melt flow rate, in the embodiment, the propylene homopolymer is less than 60 g / 10 min. The polydispersity (M w / M n ) of at least one, more preferably both, of the two polymer components (A) and (B) is in the range of 4.5 to 10.0 (when measured by size exclusion chromatography in accordance with ISO 16014), preferably in the range of 5.0 to 9.0, more preferably in the range of 5.5 to 8.5. The absolute value of the difference in polydispersity of the two polymer components is preferably 0.3 or more. When the polymer component (A) is a propylene homopolymer and the polymer component (B) is a propylene-α-olefin copolymer, it is preferable that the polydispersity of the propylene homopolymer (A) is lower than the polydispersity of the propylene-α-olefin copolymer (B).

[0012] Also, the difference in melt viscosity at a given temperature can also be a relevant parameter in a given situation. When the polymer component (A) is a propylene homopolymer and the polymer component (B) is a propylene-α-olefin copolymer, it is preferable that the melt viscosity of the propylene homopolymer (A) is lower than the melt viscosity of the propylene-α-olefin copolymer (B). In a further embodiment, the low-temperature xylene-soluble content (XCS) of at least one, more preferably both, of the two polymer components (A) and (B) is in the range of 1.5 to 10.0% by mass, more preferably in the range of 1.5 to 8.0% by mass. The amount of such low-temperature xylene-soluble content (XCS) represents a low content in any elastomeric polymer component such as ethylene-propylene rubber, and thus a low content in a single-phase polymer component in which the elastomeric phase is not dispersed at all. Such a system is characterized by a rather high low-temperature xylene-soluble content. In one embodiment, one or both of the polymer components (A) and (B) are visbroken. Visbreaking refers to the controlled cracking of polymer chains by adding a visbreaking additive to the polymer component. The cracking of the polymer chains occurs at a high temperature when the polymer component melts and is extruded from the spinneret of the spunbond machine. Suitable visbreaking additives include organic peroxides, organic hydroxylamine esters, or mercaptan compounds as a source of free radicals. A suitable addition amount is between 100 ppm and 500 ppm. Visbreaking can be used to affect the viscosity, adjust the polydispersity, and further adjust the melting and crystallization behaviors of the two polymer components (A) and (B) with respect to each other.

[0013] In a specific embodiment of the present invention, only one of the propylene polymers (A and B) is visbroken, and the absolute value of the difference in M z / M w between propylene polymers A and B is 0.3 to 10.0, preferably 0.5 to 8.5, more preferably 1.0 to 5.5, and still more preferably 1.5 to 4.0. In another embodiment of the present invention, both of the propylene polymers (A and B) are visbroken, and the absolute value of the difference in M z / M w between propylene polymers A and B is between 0.0 and 0.3, preferably between 0.00 and 0.25, more preferably between 0.00 and 0.22, and still more preferably between 0.00 and 0.15.

[0014] The findings of the present invention are not limited to fibers in which two polymer components (A) and (B) arranged in parallel are used at a mass ratio of 50:50 within the fiber. Rather, the findings can be applied to a wide range of mass ratios such as 90:10 to 10:90. However, the preferred mass ratios that result in prominent crimp are between 80:20 and 20:80, more preferably between 70:30 and 30:70, and even more preferably between 60:40 and 40:60.

[0015] In one embodiment, the mass ratio of the polymer component (A) with the higher crystallization temperature, preferably a propylene homopolymer, to the polymer component (B) with the lower crystallization temperature, preferably a propylene-α-olefin copolymer, is less than 50:50, which means that the polymer component (B) with the lower crystallization temperature is present in excess in the fiber. This has been found to potentially enhance crimp. In an alternative embodiment, the mass ratio of the polymer component (A) with the higher crystallization temperature, preferably a propylene homopolymer, to the polymer component (B) with the lower crystallization temperature, preferably a propylene-α-olefin copolymer, is greater than 50:50, which means that the polymer component (A) with the higher crystallization temperature is present in excess in the fiber. This has been found to potentially enhance the stability of the manufacturing process. The crimp bicomponent fiber is typically helically crimped. In one embodiment, the average number of crimps of the crimp multicomponent fiber is in the range of at least 7 crimps, preferably at least 10 crimps per centimeter of the fiber when measured under a tensile preload of 2 mg / denier in accordance with Japanese Standard JIS L-1015-1981. The amplitude of the crimp is preferably less than 0.30 mm, preferably in the range between 0.20 and 0.30 mm when measured under a tensile preload of 2 mg / denier in accordance with JIS L-1015-1981.

[0016] The linear mass density of the fiber is preferably in the range between 1.0 and 2.2 denier, preferably between 1.2 and 2.0 denier. The basis weight of each spunbond layer in the multilayer sheet is 4 to 40 g / m2 Preferably between 5 and 25 g / m 2 It may also be in between. The density of the nonwoven sheet is preferably less than 60 mg / cm 3 Preferably less than 50 mg / cm 3 These are typical values for nonwoven fabrics having crimped fibers and high bulkiness. By comparison, the density of nonwoven fabrics having non-crimped fibers and standard bulkiness is typically above 60 - 70 mg / cm 3 Exceeds. The thickness of the nonwoven sheet, in accordance with WSP.120.6, Option A, when measured at a pressure of 0.5 kPa on a 2500 mm 2 plate, for a basis weight of 20 g / m 2 or more, preferably exceeds 0.35 mm.

[0017] In one embodiment, the spunbond sheet forms one layer of a multilayer sheet that includes, in addition to the spunbond sheet according to the present invention, one or more additional layers. The additional layer may be a nonwoven material such as an additional spunbond sheet or a meltblown sheet, or another sheet such as a polymer film or a woven fabric. A preferred embodiment is an S n type structure (such as SS, SSS, etc.) that includes a combination of the sheet according to the present invention with at least one additional spunbond nonwoven sheet, preferably a spunbond nonwoven sheet formed from non-crimped fibers such as single-component fibers, or any SM type structure or SMS type structure (such as SSMS, SMMS, SSMMS, etc.) in which the sheet according to the present invention is combined with one or more layers of meltblown nonwoven sheets and further combined with at least one layer of spunbond nonwoven sheet, preferably a spunbond nonwoven sheet formed from non-crimped fibers. For a multilayer sheet including the nonwoven sheet according to the present invention, it is preferred that the nonwoven sheet according to the present invention forms the outer layer of the multilayer sheet.

[0018] In one embodiment, the nonwoven sheet or multilayer sheet includes a bonding pattern introduced by calendar rolls during manufacturing. In one embodiment, the bonding pattern has a bonding area of 10 - 16% and / or a dot density of 20 - 45 dots / cm 2 and / or a dot size of 0.35 - 0.55 mm per dot. Such a relatively open bonding pattern is typical for sheets containing a highly bulky spunbond material formed from crimped fibers. 2

[0019] The basis weight of each spunbond layer within the multilayer sheet may be between 3 - 25 g / m 2 preferably between 4 - 20 g / m 2 . The basis weight of the meltblown layer may be between 0.5 - 5 g / m 2 preferably between 1 - 4 g / m 2 . The present invention further relates to a method for manufacturing a spunbond nonwoven sheet or multilayer as defined above. The spunbond nonwoven sheet is manufactured by a device comprising at least two extruders having a spinneret, a stretching channel, and a moving belt, in which the fibers are spun by the spinneret, stretched in the stretching channel, and placed on the moving belt, and the device comprises a pressurized process air chamber that guides process air through the stretching channel to stretch the fibers. The stretching channel may comprise a plurality of sections. The stretching channel or sections of the stretching channel may become narrower as the distance from the spinneret increases. In one embodiment, the convergence angle can be adjusted. The device may form a sealed assembly extending at least from the point of inflow of the process air to the end of the stretching channel, so that air cannot flow in from the outside and the supplied process air cannot escape to the outside. In one embodiment, the device comprises at least one diffuser disposed between the end of the stretching channel and the moving belt.

[0020] ​The pressure difference between the ambient pressure and the pressure inside the process air cabin is usually higher than 2000 Pascals. It has been observed that within a reasonable overall range, the higher the cabin pressure, the more likely it is to result in the desired range of curvature and have a favorable effect on crimping. Therefore, in a preferred embodiment, the cabin pressure is higher than 2500 Pascals, more preferably higher than 3000 Pascals, or even more preferably higher than 3500 Pascals. For the stability of the process, at the upper limit, the cabin pressure is preferably less than 6000 Pascals, preferably less than 5000 Pascals. A suitable process air temperature is usually higher than 10°C. However, within a reasonable overall range, it has been observed that the higher the process air temperature, the more likely it is to result in the desired range of curvature and have a favorable effect on crimping. Therefore, in a preferred embodiment, the process air temperature is higher than 20°C, more preferably higher than 25°C. At the upper limit, the process air temperature is preferably less than 60°C. When process air at two different temperatures is applied to the fibers during stretching, the above description relates to the process temperature of the air that first contacts the filaments. The maximum air velocity in the stretching channel is usually higher than 50 m / s. Furthermore, the present invention relates to a sanitary product comprising a non-woven sheet or a multi-layer sheet according to the present invention. The sheet of the present invention can be used as a non-woven sheet in sanitary products in the sanitary industry, such as adult incontinence products, baby diapers, sanitary napkins, etc. Further details and advantages of the present invention will become apparent from the figures and examples described below.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0022] FIG. 1 shows a schematic diagram of a cross-section of a two-component parallel fiber. The fiber F includes first and second polymer components A and B arranged in parallel. The arrangement extends over the entire length of the fiber. FIG. 2 is a schematic diagram of a part of the crimped fiber F included in the nonwoven fabric sheet of the present invention. The fiber is curved and has a certain crimp radius and a certain number of crimps. FIG. 3 shows a spinning machine 100 suitable for manufacturing the spunbond nonwoven fabric according to the present invention. The spunbond nonwoven fabric NW is manufactured from continuous fibers F of a thermoplastic material. The continuous fibers F are spun from a spinneret 101 and then passed through a cooling device 102. A monomer suction device 104 for removing gases in the form of decomposition products, monomers, oligomers, etc. generated during the spinning of the fibers F is arranged between the spinneret 101 and the cooling device 102. The monomer extraction device 4 is provided with a suction port or a suction gap. In the cooling device 102, the process air is applied to the fiber curtain exiting from the spinneret 101 from both opposite sides. The cooling device 102 is divided into two compartments 102a and 102b, which are arranged in series along the flow direction of the fibers. Thus, the process air at a relatively higher temperature (e.g., 60°C) can be applied to the fibers at the earlier stage within the chamber compartment 102a, and the process air at a relatively lower temperature (e.g., 30°C) can be applied to the fibers at the later stage within the chamber compartment 102b. The supply of the process air is performed via air supply chambers 105a and 105b, respectively. The cabin pressures within the chambers 105a and 105b can be made the same, for example, about 3000 pascals above the ambient pressure.

[0023] The drawing device 106 for pulling and stretching the fibers 103 is arranged below the cooling device 102. The drawing device includes an intermediate channel 107, which preferably converges and narrows as the distance from the spinneret 101 increases. In one embodiment, the convergence angle of the intermediate channel 107 can be adjusted. After the intermediate channel 107, the fiber curtain enters the lower channel 108. The cooling device 102 and the drawing device 106, including the intermediate channel 107 and the lower channel 108, are formed together as a sealed assembly, which means that a major air flow from the outside cannot flow in over the entire length of the assembly, and the major process air supplied into the cooling device 102 cannot escape to the outside. Some fume extraction devices for taking out a small volume of air can be incorporated directly below the spinneret. Subsequently, the fiber 103 exiting the stretching device 106 is passed through the placement unit 109. This placement unit 109 includes two diffusors 110 and 111 arranged continuously. The diffusor 110 has a diverging portion, and the diffusor 111 has a converging portion and an adjacent diverging portion. The angles of the diffusors, particularly the angles of the diffusors in the diverging regions of the diffusors 110 and 111, are adjustable. There is a gap 115 between the diffusors 110 and 111, through which the surrounding air is sucked into the fiber flow space.

[0024] After passing through the placement unit 109, the fiber F is deposited as a non-woven web NW on a rotating belt 113 formed from a breathable web. The suction device 116 is arranged below the placement area of the rotating belt 113 to suck the process air indicated by the arrow 117 in FIG. 3. Once the non-woven web NW is deposited, it is first guided through the gap between a pair of preliminary consolidation rollers 114 for preliminary consolidating the non-woven web NW.

[0025] FIG. 4 shows a production line 200 for manufacturing the SMS-type non-woven laminated sheet NWLS of the present invention. Specifically, the machine is configured to manufacture an SMS-type non-woven laminated sheet NWLS, specifically SMMS H in the form of a sheet. Here, "S" represents a normal spunbond layer, that is, a layer formed from non-crimped fibers, "M" represents a meltblown layer, and "S H " represents a highly bulky spunbond layer formed from crimped bicomponent fibers. The layer "S H " in this fabric is the layer according to the present invention. The spunbond structure on one side of the internal meltblown structure has high bulkiness, and the spunbond structure on one side of the internal meltblown structure is a normal spunbond sheet. The SMS-type sheet is known as a somewhat bulky structure. The normal S layer provides mechanical stability, the M layer improves liquid barrier properties, and the bulky S layer enhances the softness and flexibility of the fabric. The production line 200 is S HIt is equipped with a spinning machine 100 for manufacturing layers, and this spinning machine is configured as shown in FIG. 3. Two storage tanks 118a and 118b contain two different polymer components A and B used for the spinning of bicomponent fibers. The attached storage tank 119 may include a masterbatch having additives such as a nucleating agent or a bisbreaking additive.

[0026] Furthermore, the production line 200 includes a rotating belt 213, a first spinning machine 220 for forming a normal S layer that is configured to spin single-component fibers with only one polymer storage tank 218, and two meltblowing machines 230 for forming an MM double-layer meltblown structure. Machines 220, 230, and 100 are continuously arranged along the rotating belt 213. Downstream of each of the spinning machines 220 and 100, a pair of preliminary consolidation rollers 214 and 114 are arranged. Downstream of the last spinning machine, a calendar / embossing roll 240 for firmly bonding the layers of the laminated sheet NWLS is arranged. FIG. 5 shows an SEM (scanning electron microscope) photograph of a cross-section of a bicomponent fiber having a line of a curved interface between polymer components. The photograph in FIG. 5 was taken by the method described below, and generally, it is a method suitable for measuring the curvature that defines the present invention. Curvature is, in principle, an absolute geometric property of the fiber and does not depend on the measurement method. Naturally, there is some variation in curvature along the length of a single fiber, and not all fibers in a fabric sheet are the same. For practical purposes, it is most preferable to extract at least 10 fibers from the nonwoven fabric sheet, measure the curvature of each of the extracted fibers at randomly selected length positions, and use the average value.

[0027] When measuring from a non-woven sheet, first the machine direction is identified, and the sheet is encapsulated in a polyester resin or an epoxy resin and decomposed. Next, the obtained polymer block is cut in a plane transverse to the machine direction perpendicular to the plane of the encapsulated non-woven sheet. The cut surface is polished so that the interface can be visually recognized after etching. The cross-sections of the fibers exposed on the polished cut surface are etched to remove the more amorphous of the polymer components. The fiber ends having the most circular cross-sections and thus being oriented as precisely as possible in the machine direction at the cut surface are selected for measurement. A slight deviation in direction can be corrected as strain. In practice, useful fiber cross-sections are ellipses with a ratio of major axis to minor axis of less than 1.2. Preferably, the fibers appear circular. After taking SEM photos by a method generally known to those skilled in the art, the curvature can be obtained using a photo-based measurement system such as DatInf measure of DatInf GmbH.

[0028] It can be seen that the interface between the two polymers is curved. More specifically, the line of the interface has the shape of a single arc and has no inflection point where the sign of the curvature changes. In the example of FIG. 5, the polymer on the left is a propylene-α-olefin copolymer with a relatively low crystallization temperature, and the polymer on the right is a propylene homopolymer with a relatively high crystallization temperature. The curved interface draws an arc towards the left, that is, towards the propylene-α-olefin copolymer with a relatively low crystallization temperature. The polymer component with a higher crystallization temperature has a more compact cross-section.

[0029] The curvature "c" is measured and calculated according to the following description. First, the distance "b" between the intersections on the polymer surface is measured by a line drawn between the intersections of the polymer on the fiber surface. This line is a virtual reference line. In the example shown, b is 540 pixels. Next, the height "h" of the curvature is measured by drawing a line perpendicular from the reference line (usually the middle of the reference line) to the apex of the line of the curved interface. The length of that line corresponds to the height "h" of the curvature, and in the example shown it is 111 pixels. Then, the curvature is obtained as 111 / 540 = 0.206. Therefore, FIG. 5 shows a fiber having a curvature within the range required by the present invention. FIG. 6 shows how the teachings of the present invention are also applicable to eccentric core-sheath fibers having a D-shaped core.

Example

[0030] A series of options with two polymers configured in parallel were processed with a machine as shown in FIG. 3. For all options, the basis weight of the spunbond nonwoven material sheet was 20 g / m 2 . The specific polymer throughput of the spinneret 101 was approximately 0.52 g of polymer per hole per minute. The cabin pressure was kept substantially constant at 4000 Pascals. Other process settings were kept within the normal range for the production of crimped fibers. For example, the ceramic pre-consolidation roller 114 in contact with the rotating belt on the beam outlet side was operated at a temperature of 50 to 70 °C. The calender (not shown in FIG. 3 but located downstream of the pre-consolidation roller 114) was a standard open dot calender having a bonding area of 12% and 25 circular bond points per 1 cm 2 . The temperature of the calender was in the range of 135 to 145 °C. A wide variety of different polymer combinations were tested. The main focus was on the combination with propylene homopolymer as Polymer A and propylene-α-olefin copolymer as Polymer B. The varying parameter was mainly the difference in crystallization temperature. The configurations of the individual examples are summarized in Table 1 below.

[0031]

Table 1

[0032] Preparation of Mg alkoxide compound An Mg alkoxide solution was prepared by adding a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg of butoxypropanol to 11 kg of a 20% by mass solution of butylethylmagnesium (Mg(Bu)(Et)) in toluene while stirring (70 rpm) in a 20 l stainless steel reactor. During the addition, the contents of the reactor were maintained below 45 °C. After the addition was complete, the mixing of the reaction mixture (70 rpm) was continued at 60 °C for 30 minutes. After cooling to room temperature, 2.3 kg of bis(2-ethylhexyl) citraconate, which is a donor, was added to the Mg alkoxide solution while maintaining the temperature below 25 °C. Mixing was continued for 15 minutes with stirring (70 rpm).

[0033] Preparation of Solid Catalyst Component 20.3 kg of TiCl4 and 1.1 kg of toluene were added to a 20 l stainless steel reactor. The mixture was stirred at 350 rpm, and while maintaining the temperature at 0 °C, 14.5 kg of the Mg alkoxy compound prepared in Example 1 was added over 1.5 hours. 1.7 l of Viscoplex (registered trademark) 1-254 and 7.5 kg of heptane were added, and after mixing at 0 °C for 1 hour, the temperature of the formed emulsion was raised to 90 °C within 1 hour. After 30 minutes, the mixing was stopped, the catalyst droplets were solidified, and the formed catalyst particles were allowed to settle. After settling (1 hour), the supernatant was suctioned off. Subsequently, the catalyst particles were washed with 45 kg of toluene at 90 °C for 20 minutes, followed by two heptane washes (30 kg, 15 minutes). The temperature was lowered to 50 °C during the first heptane wash and to room temperature during the second wash. The catalyst thus obtained was used together with triethylaluminum (TEAL) as a co-catalyst and dicyclopentyldimethoxysilane donor (D-donor) as an external donor. The polymerization was carried out in a Borstar PP type polypropylene (PP) pilot plant equipped with one loop reactor and one gas phase reactor. The polymerization conditions for the PP3 base polymer are shown in Table 2.

[0034]

Table 2

[0035]

Table 3

Table 4

[0036]

Table 5

[0037]

Table 6

[0038] Figure 7 shows a graph plotting the thickness of the material (thickness of 20 g / m 2 material) correlated with bulkiness and fiber crimp against the curvature "c" (determined as described above) for Examples IE1 - IE6 and some additional examples. Since the thickness of a standard 20 g / m 2 spunbond nonwoven fabric without crimped fibers and bonded with the same calendar is approximately 0.28 mm, the reference line was drawn at 0.30 mm. It becomes clear that when the value of the curvature "c" is between approximately 0.05 and approximately 0.25 and the peak is between approximately 0.12 and approximately 0.20, the bulkiness, and thus the fiber crimp, is most prominent. This holds regardless of whether the mass ratio of polymers A and B in the fiber is 50:50, 40:60, 60:40, or 70:30.

Claims

Claim 1: A spunbond nonwoven sheet comprising spunbonded crimped multicomponent fibers, the fibers comprising two different polymer components (A) and (B) distributed in a parallel arrangement across the cross-section of the fiber, wherein the line of the interface between the two polymer components (A) and (B) contained in the radial plane of the fiber is curved, and the curvature (c) thereof is 【Number 1】 (wherein the length of the reference line (b) is the length of the virtual straight reference line connecting the two end points of the curved interface line, and the height of the curvature (h) is the distance from the reference line to the apex of the curved interface line) and the line of the interface has the shape of a single arc without an inflection point where the sign of the curvature changes, the absolute value of the difference between the crystallization temperature [T c (A)] of the polymer component (A) and the crystallization temperature [T c (B)] of the polymer component (B) is more than 5 °C and less than 30 °C when measured by DSC according to ISO 11357-1 and -2, and the curved radial interface line draws an arc towards the polymer component with the lower crystallization temperature, and the polymer component with the higher crystallization temperature has a more compact cross-section, characterized in that it is a nonwoven sheet. Claim 2 The curvature (c) of the line of the interface is 【Number 2】 as defined in Claim 1, the nonwoven sheet according to Claim 1. Claim 3 One polymer component (A) is a propylene homopolymer, and the other polymer component (B) is a propylene-α-olefin copolymer, and the comonomer content of the propylene-α-olefin copolymer is preferably between 1.0 and 5.5 mass percent, the nonwoven sheet according to Claim 1. Claim 4 The crystallization temperature of the polymer component (A) [T c (A)] and the crystallization temperature [T c (B)] is greater than 10° C. and less than 25° C. when measured by DSC in accordance with ISO 11357-1 and -2. Claim 5 The absolute value of the crystallization temperature [T c (A)] of the polymer component (A) with the higher crystallization temperature is preferably in the range between 90°C and 135°C when measured by DSC according to ISO 11357-1 and -2. The nonwoven fabric sheet according to claim 1. Claim 6: The absolute value of the crystallization temperature [T c (B)] of the polymer component (B) with the lower crystallization temperature is preferably in the range of 80 °C to 125 °C when measured by DSC according to ISO 11357-1 and -2, the nonwoven sheet according to Claim 1. Claim 7 One or both of the polymer components (A) and (B) contain a nucleating agent, preferably a nonitol-based or sorbitol-based nucleating agent, and the nucleating agent is preferably present in an amount between 0.15 ppm and 3000 ppm, the nonwoven sheet according to Claim 1. Claim 8 The melting temperature of the polymer component (A) with a higher melting temperature [T m (A)] is preferably in the range between 155°C and 164°C when measured by DSC according to ISO 11357-1 and -2, and the melting temperature of the polymer component (B) with a lower melting temperature [T m (B)] is preferably in the range between 142°C and 155°C when measured by DSC according to ISO 11357-1 and -2. The nonwoven sheet according to claim 1. Claim 9 The melt flow rate of one or both of the polymer components (A) and (B) is 15 to 120 g / 10 min (measured at 230 °C and 2.16 kg in accordance with ISO 1133), and / or the polydispersity (M w / M n ) of one or both of the polymer components (A) and (B) is 2.5 to 10.0 (measured by size exclusion chromatography in accordance with ISO 16014), preferably, the absolute value of the difference in polydispersity of the two polymer components is preferably 0.3 or more. The nonwoven sheet according to claim 1. Claim 10 The nonwoven sheet according to claim 1, wherein one or both of the polymer components (A) and (B) contain a bis-breaking additive, preferably an organic peroxide or an organic hydroxylamine ester, and the bis-breaking additive is preferably present in an amount between 100 ppm and 500 ppm.

11. The nonwoven sheet according to claim 1, wherein the mass ratio of the two polymer components (A) and (B) is between 80:20 and 20:80, more preferably between 60:40 and 40:

60.

12. The nonwoven sheet according to claim 1, wherein the polymer component (B) having the lower crystallization temperature is present in excess in the multi-component fiber.

13. A spunbond nonwoven sheet according to any one of claims 1 to 12, and a multi-layer sheet further comprising at least one layer of a spunbond nonwoven sheet and / or at least one layer of a meltblown nonwoven sheet.

14. A method for manufacturing a spunbond nonwoven sheet according to any one of claims 1 to 12, the method comprising manufacturing the spunbond nonwoven sheet using a device having at least two extruders with a spinneret, a stretching channel, and a moving belt, in which device the fibers are spun by the spinneret, stretched in the stretching channel, and placed on the moving belt, and the device comprises a pressurized process air cabin for guiding process air through the stretching channel to stretch the fibers.

15. A sanitary product comprising the spunbond nonwoven sheet according to any one of claims 1 to 12.

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