Method of making a spunbond nonwoven laminate

Abstract

A spunbond nonwoven laminate has a plurality of stacked spunbond nonwoven layers, namely at least two and at most four spunbond nonwoven layers that have crimped continuous filaments or consist of crimped continuous filaments. The degree of crimping of the filaments is different in each of these spunbond nonwoven layers, and each of the crimped filaments of the spunbond nonwoven layers has a crimp with at least two, preferably at least three, and more preferably with at least four loops per centimeter of length. The crimped filaments of the spunbond nonwoven layers are multicomponent filaments, particularly bicomponent filaments, with a first plastic component and a second plastic component present in the respective filament in a proportion of at least 10 wt %.

Claims

1. A method of making a laminate having a plurality of stacked spunbond nonwoven layers, the method comprising the steps of: making at least two and at most four of these spunbond nonwoven layers with or from crimped continuous filaments with crimping of the continuous filaments in each of these spunbond nonwoven layers that is equal to at least three loops per centimeter of length and that is different from a degree of crimping of the continuous filaments in the other spunbond nonwoven layers; making the crimped continuous filaments of the spunbond nonwoven layers as multicomponent filaments each of a first plastic component that consists of only one first plastic and a second plastic component that is mixture of a second plastic and a third plastic with each of the two first and second plastic components being present in the multicomponent filaments in a proportion of at least 10 wt % and a mass of the third plastic relative to a mass of all the multicomponent filaments of the laminate being less than 25 wt %; and setting a molecular weight distribution of the third plastic greater than a molecular weight distribution of the first plastic and greater than a molecular weight distribution of the second plastic.

2. The method according to claim 1, further comprising the steps of: setting a melt flow rate of the first component 1.0 to 3 times greater than a melt flow rate of the second component, and/or setting a molecular weight distribution (M.sub.w/M.sub.n or M.sub.z/M.sub.w) of the first component smaller than the molecular weight distribution of the second component and/or the M.sub.w/M.sub.n value or M.sub.z/M.sub.w value of the second component at least 1.1 times greater than that of the first component, and/or setting a difference in melting point between the first and the second component is at least 10 C.

3. The method according to claim 1, further comprising the steps of: providing a respective supply unit for the first and second plastic components or for the first, second, and third plastics of a spunbond nonwoven layer, and changing an output rate of the plastic component and/or of the plastic by at least one supply unit during ongoing online operation in order to vary the crimping of the spunbond nonwoven layer by varying a speed of the supply unit.

4. The method according to claim 1, further comprising the steps of: associating a spinning pump with the plastic components for a spunbond nonwoven layer as a supply unit, and changing a feed rate of the plastic component by at least one spinning pump during ongoing online operation in order to vary crimping of the spunbond nonwoven layer by varying a speed of the spinning pump.

5. The method according to claim 1, further comprising the step of: varying a proportion of the third plastic during execution of the method in order to vary crimping of the respective spunbond nonwoven layer.

6. The method according to claim 5, further comprising the step of: varying a proportion of the second and/or of the third plastic during execution of the method.

7. The method according to claim 5, wherein the second plastic and/or the third plastic is polypropylene.

8. The method according to claim 1, further comprising the step of: calendering the laminate in at least one calender.

9. The method according to claim 1, further comprising the steps of: transferring the spunbond nonwoven laminate from a conveyor to a calender with rolls, setting a travel speed of the conveyor to less than a peripheral speed of the calender rolls, and setting a peripheral speed of the calender rolls to no more than 8% greater than a travel speed of the conveyor.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is a schematic side view of an apparatus for making the laminate of this invention;

(3) FIG. 1A is a large-scale view of the detail indicated in FIG. 1 at 1A;

(4) FIG. 2 is a large-scale view of the furthest upstream spinning/depositing subassembly of FIG. 1;

(5) FIG. 2A is a large-scale view of a detail of FIG. 2;

(6) FIGS. 3A, 3B, 3C, and 3D are large-scale sections through bicomponent filaments according to the invention;

(7) FIGS. 4A, 4B, and 4C are schematic simplified views illustrating three different laminated in accordance with the invention; and

(8) FIG. 5 is a photomicrograph taken using a 5 objective lens of an Olympus BX51 microscope with a USB camera.

SPECIFIC DESCRIPTION OF THE INVENTION

(9) As seen in FIG. 1. an apparatus according to the invention for making a spunbond nonwoven laminate S that here has three spunbond nonwoven layers L1, L2 and L3. Corresponding to the three spunbond nonwoven layers L1, L2 and L3, three spinning beams or spinnerets 1 are provided from which, preferably, filaments 3 are spun in the form of bicomponent filaments. After passing through a diffuser 11, the filaments 3 of each spunbond nonwoven layer L1, L2 and L3 are deposited on a mesh conveyor belt 13 to form the spunbond nonwoven layers L1, L2 and L3. Each spunbond nonwoven layer L1, L2, L3 is bonded by a respective a pair of compaction rollers 14. The finished three-layer spunbond nonwoven laminate S is then transferred from the mesh conveyor belt 13 to a calender 17 having two calender rolls 18, 19. FIG. 1 also shows an enlarged section of the transfer of the spunbond nonwoven laminate S from the mesh conveyor belt 13 to the calender 17. The mesh conveyor belt 13 is moved at a speed v.sub.1, while the calender rolls 18, 19 rotate at a peripheral speed v.sub.2. It lies within the scope of the invention if the peripheral speed v.sub.2 of the calender rolls 18, 19 is greater than the speed v.sub.1 of the mesh conveyor belt 13 by no more than 8%, preferably by no more than 5%.

(10) FIG. 2 shows a portion of the apparatus according to the invention near a spinning beam or spinneret 1. A spunbond nonwoven layer L1 or L2 or L3 is made with this part of the apparatus. Preferably, the filaments 3 are spun in the form of bicomponent filaments by the spinneret 1 and subsequently passed through a cooler 2 in order to cool the filaments 3. It is recommended that a monomer extractor 4 be provided between the spinneret 1 and the cooler 2 so that extraction from the filament formation region is done directly below the spinneret 1. In addition to air, especially the gases generated during the spinning of the filaments 3 in the form of decomposition products, monomers, oligomers, and the like are removed here from the system.

(11) In the cooler 2, cooling air is preferably applied from opposite sides to the filament curtain that is being guided from the spinneret 1 to the filament placement area. According to a preferred embodiment shown in FIG. 1A, the cooler is divided into at least two cooling chambers 2a, 2b follow each other in the direction of flow of the filaments 3 and in which process air of different temperatures can be supplied. For instance, low-temperature process air (for example, 20 C.) can be fed into the upstream cooling chamber 2a and process air or cooling air with a higher temperature (for example, 25 C.) can be supplied to the downstream chamber 2b provided below it in the direction of flow. The cooling air is advantageously supplied via air supply cabins 5a and 5b.

(12) A stretcher 6 is provided downstream of or below the cooler 2 with which the filaments 3 passing through the cooler 2 are elongated or stretched. Preferably, the intermediate passage 7 preferably embodied so as to converge toward the deposition area of the filaments 3 and/or to run together in the manner of a wedge, is provided immediately adjacent the cooler 2. Advantageously, the filament curtain enters the down-stretch passage 8 of the stretcher 6 after the intermediate passage 7.

(13) According to a highly recommended embodiment of the invention, the subassembly of the cooler 2 and the stretcher 6 (intermediate passage 7 and down-stretch passage 8) is a closed assembly. The term closed assembly means that, in addition to the supply of process air and/or cooling air in the cooler, no additional air is supplied to this unit and the unit is thus designed so as to be closed to the outside. Such a closed assembly is advantageously implemented in the apparatus according to the invention for all parts of the apparatus with spinning beams or spinnerets 1 of making crimped filaments 3.

(14) Preferably, the filaments 3 emerging from the stretcher 6 are guided through a deposition unit 9 that has at least one diffuser 10, 11. Preferably, two diffusers 10, 11 are provided, one downstream of the other. Recommendably, after passing through the deposition unit 9, the filaments 3 deposited on the conveyor or on the mesh conveyor belt 13 to form the nonwoven web 12 and/or the spunbond nonwoven layers L1, L2, and L3. The mesh conveyor belt 13 is preferably a continuous belt.

(15) Advantageously, process air is aspirated down through the mesh conveyor belt 13 in the area where the filaments 3 or nonwoven web 12 are deposited as illustrated in FIGS. 1 and 2 by the arrow A. Recommendably, the deposited nonwoven web 12 or the deposited spunbond nonwoven layers L1, L2, and L3 are initially conducted by the mesh conveyor belt through the gap of a pair of compaction rollers 14 for bonding. As indicated in FIG. 1, the spunbond nonwoven laminate S formed from the spunbond nonwoven layers L1, L2, L3 moves from calender rolls 18, 19 for bonding by a calender 17.

(16) The enlarged section in FIG. 2A shows two extruders E1 and E2 with which the two plastic components I and II of the spinneret 1 are supplied. The plastic component II is a blend (mixture) of plastics, particularly of polypropylenes according to the recommended embodiment. Two metering screws D1 and D2 are provided upstream of the extruder E2 associated with this plastic component II, with one of the two plastics of the blend being fed to the extruder E2 by a respective one of the metering screws D1 and D2. Recommendably, the speed of the metering screw D1 and/or D2 can be controlled with or without feedback online or during execution of the method without switching off the apparatus. Hardware components and/or software components corresponding thereto, not shown, are provided for this purpose. A respective spinning pump P1 and P2 is provided downstream from each of the extruders E1 and E2 for each plastic component I and II with which the mass flow rate of the plastic components I and II can be controlled with or without feedback. It lies within the scope of the invention if this mass flow rate of the two plastic components I and II is controlled online or during execution of the method.

(17) FIG. 3A-3D show typical cross sections for bicomponent filaments that are preferably made using the method according to the invention or by the apparatus according to the invention. Crimped filaments 3 can be made with these filament cross sections of the bicomponent filaments. FIG. 3A shows a typical side-by-side configuration of crimpable bicomponent filaments. A plastic component I or II is provided on each side of this filament cross section. FIG. 3B shows an eccentric core/sheath configuration for crimpable bicomponent filaments. FIG. 3C shows a trilobal cross section for crimpable bicomponent filaments. Finally, FIG. 3D shows a tubular filament 3 in a side-by-side configuration. All of these filament cross sections are suitable of making crimpable bicomponent filaments.

(18) FIGS. 4A-4C show three spunbond nonwoven laminates S that can be made by the method according to the invention. In all of the examples, the lowermost spunbond nonwoven layer L1 has the least crimp, and the middle spunbond nonwoven layer L2 has greater crimp in comparison. Consequently, the degree of crimping increases from bottom to top in the spunbond nonwoven laminate S. In the spunbond nonwoven laminate S according to FIG. 4A, a low/high/high crimp sequence is observed, while in the example of FIG. 4B, a low/medium/high crimp sequence is observed from bottom to top. Finally, the embodiment according to FIG. 4c shows a crimp sequence of low/high/low.