BE1018052A3 - Multi-layer nonwoven fabric producing method for e.g. incontinence product, involves providing three composite layers of nonwoven layers to form stack, and interconnecting stack of nonwoven layers through air bonding - Google Patents

Abstract

The method involves providing three composite layers of nonwoven layers to form a stack, and interconnecting the stack of nonwoven layers through air bonding, where one of the nonwoven layers has a minimum tensile strength greater than 15N/5cm.

Description

Title

Method for manufacturing a multi-layer non-woven fabric, device for manufacturing a multi-layer non-woven fabric, multi-layer non-woven fabric.

State of the art

The invention relates to a method for manufacturing a multi-layer nonwoven fabric and to a device for manufacturing a multi-layer nonwoven fabric. The invention also relates to a multi-layer nonwoven fabric.

Multi-layer nonwoven fabrics contain a number of layers. The layers can be manufactured by web manufacturing methods such as carding and gameting.

U.S. Patent No. 4,883,707 describes a method for manufacturing a two-layer nonwoven fabric. US 4,883,707 describes how a first carded web is formed containing thermoplastic fibers with an average denier of 3 or more. A second web containing thermoplastic fibers with an average denier of 3 or less is formed. This second web is then superimposed over the first web to form a layered structure and the layered structure is contacted with a through air bonding surface to bond the structure. Through air bonding is a method in which hot air is blown through a nonwoven to activate thermoplastic and / or other binders. Such binders can be powder or mono-component or multi-component fibers. The TAB method makes it possible to manufacture non-woven structures with low density and high resistance, very suitable for controlling liquid flow. The liquid can be air, for filtration applications or for acoustic applications, but also liquids for liquid filtration or moisture, for example to increase the comfort for clothing or bed coverings.

Multi-layer structures offer advantages over single-layer structures. In many practical applications, single-layer structures fall short because, despite the fact that there is great freedom in choosing the composition for the single layer, it is often difficult to meet the many, sometimes opposing, functional requirements that are imposed. The limitations sometimes lie in the function of the layer, whereby the sometimes opposite requirements that are set in liquid management are important, and sometimes in the further processing steps that the nonwoven must undergo to deliver a usable product, which processing steps have the properties negative to influence.

In US 4,883,707, the two-layer structure comprises a soft viewing layer and an airy "lofty" second layer.

In addition to the substances from the method known from US 4,883,707, various multi-layer or stratified substances have been known to be developed using the so-called melt extrusion methods (Spunbond, meltblown or flash spun). Fusion extrusion processes greatly limit the ability to combine polymers or different fiber types in a single layer, making it difficult if not impossible to meet some functional requirements.

Conventionally, a multi-layer product is attempted to be produced by combining various manufacturing processes.

However, the inventors have realized that a combination of different layer manufacturing techniques can cause production problems or negatively influence the cohesion between layers.

For example, one loses the speed advantages of using a single technique and / or an intermediate glue layer must be used in a second step to ensure that there is sufficient bonding between layers. Such a second gluing process step usually causes a decline in technical properties of the multi-layer structure. The glue of the glue layer often has a negative influence on the passage of liquids through the structure. Compressive methods such as welding or hydrogen bonding do not have the drawback that a chemical substance must be added, but do have the property that the density of the substance is increased. An increased density and thereby reduced porosity negatively influence the flow properties of liquids through the structure and make it necessary to make further perforations.

Even more limiting in the known methods is the fact that combining separately produced layers always requires that these layers must be properly processable and thus must meet minimum strength requirements. This is, as the inventor has realized, an important contraction for the degrees of freedom of composition per layer as well as weight per layer and thus has an effect on the costs.

Summary of the invention

It is an object of the invention to provide a method for manufacturing a multi-layer fabric in which at least one or more of the above problems are reduced.

The method according to the invention is characterized in that a multi-layer non-woven fabric is manufactured, wherein at least three non-woven layers are produced, a stack of said non-woven layers is provided, and wherein the stack of non-woven layers is interconnected by means of air bonding, none of which the constituent non-woven layers has a minimum tensile strength greater than 15 N / 5 cm, and the multi-layer non-woven fabric has a minimum tensile strength greater than 15 N / 5 cm.

The multi-layer non-woven fabric contains at least three layers, the component layers being bonded by air bonding and none of the component layers itself has a minimum tensile strength greater than 15 N / 5 cm, the multi-layer non-woven fabric has a minimum tensile strength greater than 15 N / 5 cm .

The invention is based on the insight that the selection of a multi-layer structure makes it possible to have a large freedom in the choice of fibers and combinations of densities and weights.

By using three or more layers (instead of two), the differences in the multi-layer structure can become large on the one hand, while on the other hand the differences between adjacent layers can be kept relatively small. Too great a difference between layer properties, such as the layer composition or the length of the fibers in a layer, as the inventor has recognized, has a negative influence on the adhesion between adjacent layers and thus on the strength of the multi-layer structure.

Through air bonding makes it possible to interconnect layers that individually have a low minimum tensile strength to form a fabric with a high tensile strength without highly influencing the flow properties of the constituent non-woven layers to a large extent and without significantly reducing the low density of the non-woven fabrics negatively.

The method according to the invention makes it possible to manufacture a multi-layer structure with sufficient tensile strength that combines a relatively low density with desired flow properties.

US 4,883,707 mentions the possibility of using more than two layers. US 4,883,707 refers in this context to an article called "Multi-layer Nonwovens for Coverstock, Medical and other ends uses" by J. Pirkkanen in the November 1987 issue of "Nonwovens World". In said Pirkkanen article it is explicitly stated that for any lamination method it is essential that at least one of the layers is a reinforcing layer that resembles a conventional non-woven layer in order to provide the composition with sufficient rigidity and strength. Therefore, although the article by Pirkkanen and US 4,883,707 mentions the possibility of three layers, it concerns structures that are essentially composed as a structure that has at least one layer with the properties of a conventional non-woven layer and forms the backbone of the multi-layer structure on which other layers are applied. In the invention this convention is broken; each of the constituent layers has a relatively low tensile strength, the structure therefore lacks a reinforcing layer, which is necessary according to the article by Pirkkanen.

The inventor has realized that the said convention limits the freedom to provide desired features. A minimum tensile strength of 15 N / 5 cm, for example, is not feasible if a layer is used with a high content of inherently weak fibers such as super-absorbent fibers or split fibers. Such fibers require a high content of binding components in the layer. Very thin layers also often lack the required stated tensile strength. The inventor has recognized that through the use of through air bonding, although the constituent layers have a low minimum tensile strength, it is possible to provide a multilayer structure with a relatively high tensile strength without sacrificing other desirable properties such as the flow properties of the constituent layers or low density.

It is noted that the method according to the invention does impose limitations in comparison with conventional methods.

In a conventional method, layers from which a multi-layer structure will be constructed are separately fabricated, wound onto rollers or other winding means and transported in rolled state to the apparatus for manufacturing the multi-layer structure. Conventional non-woven layers are made, transported and processed in this standard manner. In or for the aforementioned device, the non-woven layers are wound, joined and bound together into a multi-layer structure. The joining of the non-woven layers is usually done by two or more free-standing conventional non-woven layers in a lamination process. Pirkkanen, and therefore also US 4,833,707, explicitly states that one of the non-woven layers is a reinforcing layer with the properties and strength of a conventional non-woven layer. However, such standard process steps are not possible with the method according to the invention since each of the non-woven layers is weaker than conventional layers and too weak to be a free-standing layer or to be wound back and forth. The constituent layers must therefore be made in situ, i.e. in the processing apparatus or directly coupled thereto. This requires, compared to standard methods in which layers are made in different ways, or at least at a different location and then transported to a central processing apparatus and unrolled and joined there, a very radical change in the method and arrangement of the layer manufacturing components.

In one embodiment, the multi-layer structure contains a gradient in denier. The invention makes it possible to apply a gradient in denier and also other fiber properties. This offers, for example, improved flow properties.

Brief description of the figures

These and further aspects of the invention are described below and illustrated with reference to the drawing:

In the drawing:

FIG. 1 a first implementation diagram for a method according to the invention; FIG. 2 a second implementation diagram for a method according to the invention;

FIG. 3 a third implementation diagram for a method according to the invention.

The figures are schematic exemplary figures and not drawn to scale, the same parts are generally designated with the same reference numerals.

Detailed description of preferred embodiments

Figures 1 to 3 schematically illustrate embodiments of the method according to the invention.

The following abbreviations and designations are used in the figures.

1 = Mixing and feeding devices 2 = web manufacturing devices: K = Carding or gamet device AL = airlay system or pneumatic carding device.

CL = cross-lapping device T = processing device unit (finish, embossing, perforation, smoothing ..), the use of such processing device is optional.

TAB Oven = the Through Air Bonding device with band or trammel systems CONV = converter device for bonded nonwovens (cutting, splitting, winding, applying to a coil, ..)

In the mixing and feeding devices, fiber material is mixed and supplied to produce the web for the construction in the three or more layers. Three mixing and feeding devices 1a, 1b and 1c are used in the diagram of Figure 1. A first layer is carded in carding device 2Ka, a next layer is applied over the clarified layer and the two layers are carded together in carding device 2Kb, this step is repeated in carding device 2Kc. After an optional post-treatment in processing device T1, the combined multilayer structure is guided to TAB oven. In the TAB oven, the layers are bonded to a multi-layer structure, resulting in a multi-layer structure with sufficient tensile strength.

Figure 2 illustrates a variation on the diagram of Figure 1. The difference is that one of the carding devices has been replaced by an airlay device is AL.

Figure 3 illustrates a further embodiment of the method according to the invention. The difference with the diagram of Figure 1 is that two carded layers are cross-laid in cross-lapping device CL. "Cross-laid" or "cross-lapped" means that the layers are explained in lanes across the production direction. This is intended to produce higher weights in the middle layer. But these layers have insufficient strength properties in their transverse direction. According to the principle of the invention, sufficient strength is obtained in the process direction of the multi-layer structure.

The layers of the examples contain a proportion of bicomponent fibers that ensure bonding within the layer and between the layers. In the examples, the bicomponent fibers are core / sheath types (sheath / core). However, other bicomponent fibers such as side-by-side and eccentric can also be used within the scope of the invention. The fibers can take many forms, such as hollow or profiled forms (trilobal, pentalobal, etc.). In the examples given, the layers contain two types of fibers. Fibers with or for certain functions can be used or added such as absorbent fibers to absorb moisture, spreading fibers to disperse moisture, fibers with active substances such as anti-fungal or odor-absorbing or even odor-spreading fibers, etc. The properties of the fibers can be strengthened or adjusted by used ensimage (high wetting, hydrophilic and / or hydrophobic)

The following examples, made using three carding devices, illustrate embodiments of the invention.

The following abbreviations have been used: PET = Polyethylene Terephthalate coPET = copolymer Polyethylene Terephthalate PE = Polyethylene PP = Polypropylene coPP = copolymer Polypropylene solid = solid fiber hollow = hollow fiber pentalobal = five-lobed fiber

The percentages are expressed in weight percentage. An indication (b) after a fiber indicates that this fiber is a bonding fiber.

The numbers represent the denier (dn) of the fibers. The tensile strength is expressed in units of N / 5 cm.

Table 1.

Table 1 shows a number of layers that do not have sufficient minimum tensile strength. The columns "tensile strength" give averages for the tensile strength and minimum tensile strength at a weight of 20 g / cm 2.

All layers above contain non-binding fibers in addition to binding fibers such as PET / PE. This is an illustration of the advantage that the selection of a multilayer structure makes it possible to have a great freedom of choice of fibers and combinations of densities and weights, and because the inventor has realized that it is not necessary that all layers have a sufficiently minimal strength, this freedom is further increased. The thermoplastic component for use as or in a binder fiber can be selected from the group consisting of the polyesters, olefins, polyamides and other thermoplastic polymers. They can be used in staple fiber, in various forms (see US Patents 5,277,976 to Hogle et al. And US 5,466,410 to Hills) and in monocomponent or multicomponent composition. These latter multicomponent or conjugate fibers are described, for example, in US Patents 5,336,552 to Strack or US 5,108,827 to Gessner, as well as in textbook "Polymer blends and Composites" by John A. Mansan, 1976 plenum Press ISBN 0-306-30831-2 page 273 to 277.

In order to withstand normal conventional treatments, such as rolling up and down on rollers or use as a free-standing layer, a layer must have a minimum tensile strength of at least 15 N / 5 cm. None of the above layers meets this condition.

Still, using through air bonding, the composite multi-layer structures do show a high tensile strength, as shown in Table 2.

Table 2

The three-layer structures have a high tensile strength. It is important to note that using through air bonding the properties such as the density of the constituent layers are not or hardly affected, as is the case with compressing techniques. The adhesion between the layers is good, without, as in the case of the use of an intermediate adhesive layer, the adhesion layer between two component layers adversely affecting the passage of liquid. In several examples, the multi-layer structure contains a layer with a composition containing less than 50% of binder fibers. The invention makes it possible to use layers with a small percentage of binder fibers. The properties of the non-binding fibers can therefore be better utilized. This is an illustration of the fact that the invention allows great freedom in the choice of fibers and combinations of densities and weights.

In these examples, all layers contain non-binding fibers in addition to binding fibers.

The above examples show examples where the denier shows a gradient.

The average denier runs over the layers as follows:

In the context of the invention, "a gradient" is understood to mean that the average denier increases or decreases monotonically over the layer structure. All the above combination except III + II + VI meet this condition.

Examples C and D illustrate further embodiments of the invention.

Example C:

The compositions of the layers are:

Layer 1 = 60% PET / copet 2dn (b) + 40% coPP 2dn

Layer 2 = 40% PET / copet 6dn (b) + 30% coPP 4dn + 30% PET hollow 6dn

Layer 3 = 40% PET / copet 2dn (b) + 30% coPP 2dn + 30% PET pentalobal 6dn

Example D:

The compositions of the layers are:

Layer 1 = 60% PET / copet 2dn (b) + 40% coPP 2dn

Layer 2 = 40% PET / copet 6dn (b) + 30% coPP 4dn + 30% PET hollow 6dn

Layer 3 = 40% PET / copet 2dn (b) + 30% coPP 2dn + 30% PET hollow 12dn

Also in Examples C and D, the three-layer structures have a high tensile strength.

In these examples too, all layers have both binder fibers and non-binder fibers. Also in these examples, at least one of the layers contains less than 50% binder fiber.

A variation on three-layer structures C and D in which the three-layers of approximately equal weight were used showed equivalent values for tensile strength and minimum tensile strength.

For comparison, three-layer structures have been made in which first layer was made of the following material: 50% PET / PE 3 (b), 50% PET / PE 2 (b) such a layer has a tensile strength of 26 at a weight of 20 g / m2 74 and a minimum tensile strength of 18.60, therefore above 15 N / 5 cm. Such a layer, in contrast to the layers for a composition according to the invention, does have sufficient minimum tensile strength to be rolled up and down. This layer consists entirely of binding fibers and is relatively heavy.

Combinations of this layer with layers as described above yielded three-layer structures with similar strengths, but were stiffer and had a negative influence on the liquid flow properties through the three-layer structure.

The invention also relates to a multi-layer nonwoven wherein the multi-layer nonwoven contains at least three layers, each of the layers containing both binder fibers and non-binder fibers.

The denier preferably has a gradient over the layers.

The multi-layer nonwoven structures according to the invention are particularly suitable for moisture absorption and distribution layers in absorbent products for ladies' hygiene or light incontinence, as well as for airflow control (filtration and / or acoustics).

It is noted that "liquid" is mentioned above. "Liquid" must be understood in a broad sense as "fluid". The fluid may, for example, be perspiration for a comfort-enhancing layer in clothing, sleeping bag or mattress. It can also be urine for a fluid uptake and spread layer used in absorbent hygiene products (such as diapers or incontinence products or pantyliners). It can also be air flow or liquid flow that needs to be filtered and therefore offers lower resistance less resistance but remains strong enough in multiple layers. This can also be a coalescence filter for liquid mixtures. This fluid can also be sound (pressure waves from air) so that a sound absorption or resonance can be achieved. Here the invention makes it possible to provide fewer binding fibers in the individual layers (thus too weak to be able to be used alone) and to use more active or functional fibers that have this specific cross-sectional profile or fineness in order to be able to contribute more to such acoustic performance ( much binding fiber alone - prior art - could not achieve this). This applies similarly to achieving a certain level of absorption: the binding fibers for strength have this property far too little or even not. The invention makes it possible to use relatively much more absorbent fiber (cellulose types, superabsorber types, extra hydrophilic & profiled types) that cannot contribute to achieving the necessary strength in single-layered non-woven fabrics according to the prior art. The invention also makes it possible to make less use of binder fiber types in order to achieve higher levels of comfort such as softness and drapability, which for instance offers possibilities for clothing insulation.

Further examples of three-layer structures according to the invention are:

Further example 1:

Layer 1: 1 lg: 50% PET / PE 3 (b) + 50% PET / PE 2 (b)

Layer 2: 14.5g: 30% PET / PE 3 (b) + 40% PET / PE (b) + 30% Hollow PET 6 Layer 3: 14.5g: 30% PET / PE 3 (b) + 40% PET / PE 9 (b) + 30% Hollow PET 6dn

In this example, layers 2 and 3 have the same composition, but are distinguishable as separate layers. The designation 1 lg means a weight of 11 grams / m2. In this example, the first layer contains 100% bonding fibers. However, the layer is so light that it does not have sufficient strength to be rolled up or unrolled.

Further example 2:

Layer 1: 1 lg: 100% PP / PE 1.5 (b)

Layer 2: 14.5g: 70% PP / PE 3 (b) + 30% Hollow PET 6 Layer 3: 14.5g: 70% PP / PE 3 (b) + 30% Hollow PET 6

Further example 3:

Layer 1: 1 lg: 100% PP / PE 1.5 (b)

Layer 2: 14.5g: 70% PP / PE 3 (b) + 30% Hollow PET 6 Layer 3: 14.5g: 70% PP / PE 3 (b) + 30% pentalobal PET 6

Further example 4:

Layer 1: 15g: 75% PP / PE 1.5 (b) + 25% coPP 2 Layer 2: 20g: 60% PP / PE 3 (b) + 40% Hollow PET 6 Layer 3: 30g: 50% PP / PE 3 (b) + 50% flat Viscose 2

Further example 5:

Layer 1: 15g: 75% PP / PE 1.5 (b) + 25% coPP 2 Layer 2: 20g: 60% PP / PE 3 (b) + 40% Hollow PET 6

Layer 3: 30g: 50% PP / PE 3 (b) + 50% SAF 10 with SAF = Super Absorbent Fiber Further example 6:

Layer 1: 20g: 35% PET / copes 4 (b) + 65% solid PET 3 Layer 2: 20g: 40% PET / copes 4 (b) + 60% pentalobal PET 6 Layer 3: 20g: 50% PET / copes 4 (b) + 50% hollow PET 12

Further example 7:

Layer 1: 20g: 35% PET / copes 4 (b) + 65% solid PET 3 Layer 2: 20g: 40% PET / copes 4 (b) + 60% pentalobal PET 6 Layer 3: 30g: 50% PET / copes 4 (b) + 50% SAF 10

Further examples 3 to 7 show embodiments in which all non-woven layers do not contain binder fibers. Further examples 6 and 7 show examples in which at least one of the, in these further examples 6 and 7, even two of the non-woven layers contains less than 50% binder fibers.

The invention can be briefly described as follows:

A multi-layer non-woven comprising at least three non-woven layers is produced by means of through air bonding. The constituent non-woven layers have too low a pulling force to be rolled up or unrolled as an independent non-woven fabric. Although this limits the method of manufacture, it makes it possible to provide great freedom in properties in the component layers.

It will be clear that many variations are possible within the scope of the invention and that the invention is not limited to the examples given above.

Claims (18)

A method for manufacturing a multi-layer non-woven fabric, characterized in that at least three non-woven layers are produced, a stack of said non-woven layers is provided, and that the stack of non-woven layers is interconnected by means of air bonding, none of the component nonwoven layers has a minimum tensile strength greater than 15 N / 5 cm, and the multi-layer non woven fabric has a minimum tensile strength greater than 15 N / 5 cm. A method according to claim 1, wherein a gradient in denier occurs over the multi-layer nonwoven fabric. Method according to claim 1 or 2, characterized in that each non-woven layer contains both binder fibers and non-binder fibers. Method according to one of the preceding claims, characterized in that at least one of the non-woven layers contains less than 80% binder fibers. Method according to claim 4, characterized in that at least one of the non-woven layers contains less than 50% binder fibers. 6. Device for manufacturing a multi-layer non-woven fabric wherein the device is adapted to produce at least three layers of non-woven fabric, wherein none of the three layers is rolled up or moved independently, the device is adapted to superimpose the at least three non-woven layers and the device comprises a through air bonding oven (TAB oven) for interconnecting the at least three non-woven layers into a multi-layer structure by means of through air bonding. Device according to claim 6, characterized in that the device comprises three carding devices (2Ka, 2Kb, 2Kc). Device according to claim 6 or 7, characterized in that the device comprises two carding devices and an airlay device (AL). Device according to one of claims 6 to 8, characterized in that the device comprises a cross-lapping device (CL). 10. Multi-layer non-woven fabric wherein the fabric contains at least three non-woven layers, wherein each of the non-woven layers contains both binder fibers and non-binder fibers and the multi-layer non-woven fabric is produced by air bonding. The multi-layer nonwoven fabric according to claim 10, characterized in that the average denier of the layers has a gradient over the multi-layer nonwoven fabric. A multi-layer nonwoven fabric according to claim 10 or 11, characterized in that at least one of the nonwoven layers contains less than 80% binder fibers. A multi-layer nonwoven fabric according to claim 12, characterized in that at least one of the nonwoven layers contains less than 50% binder fibers. A product containing a multi-layer nonwoven fabric according to any one of claims 10 to 13. Product according to claim 14, characterized in that the product is an incontinence product. A product according to claim 14, characterized in that it is a ladies' hygiene product. A product according to claim 14, characterized in that the product is a gas flow regulating product. A product according to claim 10, characterized in that the product is an acoustically efficient product