METHOD FOR MAKING A COMPOSITE WEB

Technical field

This invention relates to a method for making a composite web and, in particular, a composite web (for example, a non-woven web made from nonwoven fabric) comprising melted and blown fibres and particulate material, for example, absorbent or superabsorbent material.

Background art

Known in the prior art are methods for making composite webs which comprise melted and blown fibres, known as “meltblown” fibres, and spunbond, in which a particulate material, for example, in the form of discrete particles, is trapped.

The particulate material may be, for example, an absorbent or superabsorbent polymer material and examples of composite webs comprising meltblown fibres and discrete particles are described and illustrated in documents US6494974 and EP0156160.

By absorbent (or superabsorbent) material is meant a material that is capable of retaining any liquid or of filtering a fluid (liquid or gas) containing an extraneous substance (solid, liquid or gas).

As regards the production of composite webs comprising meltblown fibres in which discrete particles of particulate material are trapped, the need is felt to develop a method for making a web (meltblown or spunbond) which, with the same apparatus, allows modulating the capacity to retain the particulate material in the mass of meltblown fibres; that way, it is possible to make composite webs varying in their capacity to retain the particulate material, such composite webs thus being usable to make different products with different properties (for example: absorbent products for sanitary use, protective face masks, filtering elements for the medical sector, cigarette filters, antiparticulate filters for the automotive industry). Aim of the invention

In this context, the intention is to propose a method for making a composite web capable of meeting the above mentioned need.

More specifically, the aim of this invention is to provide a method for making a composite web which at least allows modulating the capacity to retain the particulate material in the mass of meltblown fibres.

This aim is achieved by a method for making a composite web comprising the technical features described in one or more of the accompanying claims. The dependent claims correspond to possible different embodiments of the invention.

According to a first aspect, the invention regards a method for making a composite web comprising at least a first layer comprising a mass of meltblown fibres formed from a first melted and blown thermoplastic material and a particulate material dispersed among the fibres and at least partly adherent thereto.

The method comprises a step, of melt blowing a first flow of thermoplastic material comprising the first thermoplastic material towards at least one collecting suction surface moving in a feed direction to obtain the first mass of meltblown fibres and a step of dispensing a flow of particulate material comprising the particulate material towards the collecting suction surface in such a way as to intercept the flow of thermoplastic material in an intercept zone.

According to an aspect, the first flow of thermoplastic material and the flow of particulate material intercept each other in the intercept zone at an intercept angle (a) of between 1 and 90 sexagesimal degrees, preferably between 15 and 40 sexagesimal degrees.

Advantageously, the intercept angle contributes to defining the intersection area between the two flows.

Generally speaking, increasing the intercept angle reduces the intersection area and improves the stability of the process and the distribution of the particulate material.

Advantageously, reducing the intercept angle results, for example, in a higher constraint factor of the particulate material.

According to an aspect, the flow of thermoplastic material and the flow of particulate material intercept each other in the intercept zone at an intercept height from the collecting suction surface which is greater than or equal to zero and less than 300 mm.

Advantageously, by increasing the intercept height, it is possible to retain all the particulate material and to stabilize the process without losing excessive quantities of particulate material.

According to an aspect, at the intercept zone, an entire section of the flow of particulate material, parallel to a feed direction of the collecting suction surface, has entered the first flow of thermoplastic material and/or an entire section of the flow of thermoplastic material, parallel to a feed direction of the collecting suction surface, has entered the first flow of particulate material.

According to an aspect, the flow of thermoplastic material is melt blown by at least one nozzle located at a dispensing distance, also referred to as “die to collector distance DCD” measured along a perpendicular to the collecting suction surface greater than 100 mm and less than 1200 mm, preferably between 250 mm and 400 mm.

The dispensing distance affects the temperature of the fibres in the intercept zone, hence the retention and distribution of the particulate material between the fibres.

According to an aspect, the flow of thermoplastic material has a distribution width, measured in a feed direction of the collecting suction surface, of between 1 mm and 200 mm, preferably between 5 mm and 100 mm.

According to an aspect, the flow of particulate material has a distribution width, measured in a feed direction of the collecting suction surface, of between 1 mm and 200 mm, preferably equal to 25 mm.

According to an aspect, the flow of thermoplastic material comprises a corresponding compressed air flow and the flow of particulate material comprises a respective compressed air flow having the same compressed air flow speed as the compressed air flow speed of the thermoplastic material so that, advantageously, the process is balanced.

Furthermore, the sum of the air flows of the flow of thermoplastic material and of the flow of particulate material is preferably less than or equal to the flow of air sucked in by the collecting suction surface to stabilize the process. According to an aspect, the method comprises a step of forming a second layer of the composite web, again with meltblown technology.

The second layer is preferably formed on the collecting suction surface before making the first layer, which is thus formed on the second layer already present on the collecting suction surface.

The step of forming the second layer, on which the first layer will be deposited, comprises a step of meltblowing onto the collecting suction surface at least one flow of thermoplastic material comprising a second thermoplastic material, for example, the same thermoplastic material as the first layer, to form a second mass of meltblown fibres on the collecting suction surface.

As stated above, the step of meltblowing the flow of thermoplastic material of the second layer onto the collecting suction surface is carried out before the step of meltblowing the flow of thermoplastic material of the first layer. According to an aspect, the method comprises a step of forming a layer of the composite web, again with meltblown technology, on top of the first layer comprising the particulate material incorporated in the thermoplastic fibres. This layer is preferably formed on the first layer on the collecting suction surface after the first layer has been formed thereon.

The step of forming the layer of the composite web on top of the first layer comprises a step of meltblowing onto the first layer a flow of thermoplastic material comprising a second thermoplastic material, for example, the same thermoplastic material as the first layer, to form a second mass of meltblown fibres on the first layer. According to an aspect of the invention, the total flow of thermoplastic material for making the first layer may be composed of two flows of thermoplastic material which define a total flow and which intercept each other and intercept the flow of particulate material.

The two flows of thermoplastic material and the flow of particulate material intercept each other, at least partly, on a collecting suction surface.

According to an aspect of the invention, the total flow of thermoplastic material for making the first layer may be composed of two flows of thermoplastic material which define a total flow and which intercept each other and intercept the flow of particulate material on two collecting suction surfaces.

The two collecting suction surfaces face each other and define a passage for the flows of thermoplastic material and the flow of particulate material. Preferably, the flows of thermoplastic material and the flow of particulate material intercept each other, at least partly, upstream of that passage.

Advantageously, the suction of the collecting surfaces between which the flows pass allows spreading out the fibres of the material in transit to obtain an open-fibre material known as “high loff.

The size of the passage between the collecting surfaces, measured in a direction perpendicular to the first and the second collecting suction surface, is between 1 mm and 20 mm and adjusting this distance, together with adjusting the other process parameters, contributes to defining the capacity of the web to retain the particulate material.

The collecting suction surfaces are preferably in the form of suction drums with parallel axes and the passage is the gap between them.

According to an aspect, part of the first layer is formed on the first drum and part on the second and the two parts are combined in the passage.

According to an aspect, the method involves using a thermoplastic elastomer to obtain the fibres of the first layer so that the matrix is elastic. According to an aspect, the method involves adding a hydrophilic additive to the first thermoplastic material so as to obtain a matrix of hydrophilic fibres, particularly useful in the case where the particulate material is an absorbent or superabsorbent polymeric material.

Brief description of the drawings

Further features and advantages of the invention are more apparent in the exemplary, hence non-limiting description which follows of a preferred but non-exclusive embodiment of a method for making a composite web comprising at least a first layer which in turn comprises a first mass of meltblown fibres and a particulate material dispersed among the fibres and at least partly adherent thereto.

The description is set out below with reference to the accompanying drawings which are provided solely for purposes of illustration without restricting the scope of the invention and in which:

- Figure 1 schematically illustrates a portion, with some parts represented as blocks, of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figure 2 schematically illustrates a portion of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figure 3 schematically illustrates a portion of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figure 4 schematically illustrates a portion of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figure 5 schematically illustrates a portion of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figure 6 schematically illustrates a portion of a plant for implementing a possible embodiment of a method for making a composite web according to this disclosure;

- Figures 7 to 9 are schematic side views showing examples of a composite web comprising meltblown fibres and a particulate material dispersed therein, made with a method according to one or more aspects of this disclosure.

Detailed description of preferred embodiments of the invention

With reference to Figures 1 to 6, the reference numeral 1 generically denotes portions of a plant for implementing possible embodiments of a method for making a composite web according to this disclosure.

With reference to Figures 7 to 9, the reference numeral 100 denotes segments of a composite web obtainable with a method according to one or more aspects of this disclosure.

The web 100 comprises at least one layer 101 of the type known as meltblown or spunbond - that is to say, obtained by extruding and blowing thermoplastic material.

The layer 101 comprises a mass 102 of meltblown fibres 103.

The fibres 103 are, in particular, obtained by melting at least one thermoplastic material.

In a preferred embodiment, the fibres 103 are between 0.1 microns and 30 microns in diameter, preferably between 0.5 microns and 10 microns.

In a preferred embodiment, the fibres 103 are between 0.1 gsm and 300 gsm in gram weight, preferably between 1 gsm and 20 gsm.

The fibres 103 comprise a first meltblown thermoplastic material - that is, a first thermoplastic material that is placed in an extruder to make the layer 101.

In a preferred embodiment, the first thermoplastic material is preferably polymeric - for example, polypropylene (PP) or polyethylene (PE) and is present in the fibres 103 in a percentage between 0% and 99% by weight, preferably in a percentage between 70% and 95% by weight.

Preferably, the first thermoplastic material has a melt flow rate of between 1 and 2000, preferably 1200.

The fibres 103 comprise an elastomer, that is, a substance capable of reducing the elasticity of the fibres 103 in the sense of decreasing their resistance to deformation under mechanical stress.

The elastomer may be melted and blown individually (hence constituting all of the thermoplastic material), melted and blown together with a first thermoplastic material or melted and blown together with a first and a second thermoplastic material (that is, the elastomer is placed in the extruder to make the web 100 of meltblown type).

Generally speaking, the first thermoplastic material and the second thermoplastic material are thermoplastic materials suitable for being melted and blown. Preferably, the first thermoplastic material and the second thermoplastic material may be selected, by way of non-exhaustive example, from the following group of materials: Polypropylene and derivatives, polyethylene and derivatives, polylactic acid and derivatives, polyhydroxyalkanoates and derivatives, cellulose and derivatives, cellulose acetate and derivatives, starch and derivatives, polyesters (for example, polyethylene terephthalate), polyurethanes, polyamides, polycarbonates, thermoplastic biopolymers in general, polyoxymethylene and derivatives, polysulfone and derivatives, acrylates/methacrylates and derivatives.

Preferably, the particulate material may comprise one or more compounds that may be selected, by way of non-exhaustive example, from the following group of materials: absorbent or superabsorbent materials (either polymeric or not polymeric), graphene, odour eaters (such as, for example, activated carbon, zeolites, carbonates, silicates), chitosan, antibacterial or virucidal materials (such as, for example, titanium dioxide, zinc oxide, copper oxide, colloidal silver, polyethylene glycol).

When extruded together with at least the first thermoplastic material, that is, when it itself constitutes the thermoplastic material, the elastomer serves in particular to reduce the elasticity of the fibres 103, that is, to make them more flexible and pliable.

In a preferred embodiment, the elastomer is present in the fibres in a percentage between 0% and 99% by weight, preferably in a percentage between 5% and 30% by weight.

In practice, in a preferred embodiment, the fibres 103 may, as mentioned above, be made entirely from an elastomeric thermoplastic material - for example, Vistamaxx™ - so as to be particularly elastic.

In other words, in a preferred embodiment, the elastomer itself constitutes the first thermoplastic material, that is to say, the mass 102 may be made substantially entirely of elastomer.

In a preferred embodiment, the fibres 103 comprise a hydrophilic additive which is added in the extruder to make the fibres 103 hydrophilic.

If the hydrophilic additive is added in the extruder, the hydrophilic additive may be water based or non-water based.

The hydrophilic additive is present in the fibres 103 in a percentage between 1% and 10% by weight, preferably in a percentage between 3% and 6% by weight.

The layer 101 as a whole has a gram weight preferably between 50 and 1500 gsm.

The layer 101 also comprises a particulate material 104 dispersed among the fibres 103 and at least partly adherent thereto.

The particulate material is present in the composite web 1 with a gram weight of between 8 and 990 gsm, preferably between 50 and 700 gsm.

In a preferred embodiment, the particulate material 104 comprises an absorbent or superabsorbent material, for example, SAP such as Saviva B3.

Advantageously, if an elastomer is present in the fibres 103 or itself constitutes them, the fibres 103 are particularly sticky, especially during the meltblowing process.

That way, the particulate material 104 adheres better to, and is retained by, the fibres.

Reference is hereinafter made to a preferred embodiment in which the particulate material is a superabsorbent material (SAP) and the web obtained an absorbent web, without thereby losing in generality.

A method for making a composite web comprising the layer 101 comprises the step of melt blowing, for example, with an extruder 2, a first flow F1 of thermoplastic material comprising the first thermoplastic material towards at least one collecting suction surface 3 moving in a feed direction V to obtain the mass 102 of meltblown fibres.

The step of melt blowing the flow F1 is performed along a main trajectory T1 where by “trajectory” is meant the bisector of the angle that is formed by dispensing through each nozzle 5 of the extruder 2.

The flow F1 is preferably supported by or comprises a respective air flow A1.

The flow F1 of thermoplastic material is melt blown by at least one nozzle 5 located at a dispensing distance hi measured along a perpendicular to the surface 3 greater than 100 mm and less than 1200 mm, preferably between 250 mm and 400 mm.

The flow F1 has a distribution width d1 , measured in a feed direction of the surface 3, of between 1 mm and 200 mm, preferably between 5 mm and 100 mm.

The method comprises a step of dispensing a flow FP of particulate material comprising the particulate material 104, for example, through a dispenser 4. The step of dispensing the flow of particulate material is performed along a main trajectory TP where by “trajectory” is meant the bisector of the angle that is formed by dispensing through the dispenser 4.

The flow FP is preferably supported by or comprises a respective air flow AP.

Preferably, the flow A1 and the flow AP are equal in speed so that neither prevails over the other and both contribute to creating a balanced process. Furthermore, the sum of the air flows of A1 and AP is preferably less than or equal to the flow of air sucked in by the collecting surface 3 to stabilize the process.

The flow FP has a distribution width d2, measured in a feed direction of the surface 3, of between 1 mm and 200 mm, preferably equal to 25 mm.

Advantageously, adjusting d2 modifies the distribution of the particulate material; in the case of SAP, it is possible to control what is known as “free swell” because the fibres capture the SAP, preventing it from agglomerating. In an embodiment, the SAP is also extruded with an extruder of its own and contributes to forming the fibres which will themselves be absorbent.

The flow FP is dispensed towards the collecting suction surface 3 in such a way as to intercept the flow F1 of thermoplastic material in an intercept zone Z.

With reference in particular to Figure 3, it may be observed that in the zone Z, an entire section of the flow FP has preferably entered the flow F1 .

More specifically, at the intercept zone Z, an entire cross section of the flow FP of particulate material, parallel to a feed direction of the collecting suction surface 3, has entered the flow F1 of thermoplastic material.

In another way, at the intercept zone Z, an entire cross section of the flow F1 of thermoplastic material, parallel to a feed direction of the collecting suction surface 3, has entered the flow FP of particulate material.

The aforementioned height hi affects the temperature of the fibres in the zone Z and the type of motion of the flow F1 ; increasing hi lowers the temperature of the fibres in the zone Z and reduces the bond between fibres and particulate material. In the case of SAP, a lower constraint factor goes hand in hand with poorer dry and wet integrity.

As schematically illustrated in Figure 3, the flow F1 and the flow of particulate material intercept each other in the zone Z at an intercept angle a.

Preferably, the angle is between 1 and 90 sexagesimal degrees and, more preferably, between 15 and 40 sexagesimal degrees.

The intercept angle a determines the intersection area 6 of the flows F1 and FP; when the other process parameters are set - for example, the height at which the flows intersect, that is, the height of the zone Z relative to the collecting surface - the lower the value of a, the greater the area 6.

Increasing the intersection time and space advantageously allows increasing the bonds between the fibres and the particulate material, thus constraining the particulate material to a greater extent.

In the case of superabsorbent material, if a is reduced below a certain value, the SAP is excessively constrained, thus reducing the free swell of the absorbent web, hence its absorption capacity.

If a is raised above a certain value, the process can become turbulent, leading to non-uniform distribution of the particulate material.

For simplicity of process setup, we can refer to the trajectories T1 and TP and consider that these trajectories intersect at the angle a.

As schematically illustrated in Figures 1 and 2, the flow F1 and the flow FP intercept each other, in the terms set out above, at an intercept height h greater than or equal to zero, measured perpendicularly to the collecting surface 3.

In simpler terms, an entire cross section of the flow FP of particulate material, preferably parallel to a feed direction of the collecting suction surface 3, enters the flow F1 of thermoplastic material at a height h which is greater than or equal to zero.

In a preferred embodiment, the flow FP of particulate material is at a right angle to the collecting suction surface 3.

With reference to Figures 8 and 9, it is noted that in a preferred embodiment of it, a composite web 100 comprises at least a second layer 105, also meltblown or spunbond and, looking at the drawings, located under the first layer 101 .

The layer 105 comprises, for example, a mass 106 of meltblown fibres 107. In a preferred embodiment of the method, the layer 105 is made “in process”, that is to say, directly on the collecting suction surface 3 before the layer 101 is formed. The web of Figure 8 is, for example, made with the plant illustrated in Figure 4, and the related method comprises a step of melt blowing onto the collecting suction surface 3 a flow F2 of thermoplastic material,, for example, through a corresponding extruder 7.

The mass 106, hence the layer 105 on which the first layer 101 of the composite web 100 is placed, is formed on the surface 3 by the flow F2.

The step of melt blowing the flow F2 is carried out before the step of melt blowing the flow F1 , that is to say, the extruder 7 is located upstream of the extruder 2 and of the dispenser 4 in the feed direction V of the surface 3.

Thus, the first layer 101 is superposed on the second layer 105, thereby contributing to retaining the particulate material, specifically SAP, without constraining it.

As illustrated in Figure 9, the composite web 100 might comprise a further layer 108, placed on top of the layer 101 (as illustrated in Figure 9).

The layer 108 comprises, for example, a mass 109 of meltblown fibres obtained by a step, not illustrated, of melt blowing onto the first layer 101 a flow of thermoplastic material comprising a thermoplastic material to form the mass 109 of meltblown fibres on the layer 101 .

In an embodiment, illustrated in Figure 5, the method comprises a step of melt blowing a flow F3 of thermoplastic material dispensed, for example, by a respective nozzle 8 and preferably comprising the first thermoplastic material, towards the collecting suction surface 3 to contribute to forming the mass 102 of fibres 103.

The flow F3 intercepts the flow F1 , forming a total flow of thermoplastic material, and the flow FP of particulate material in the intercept, zone preferably positioned as described above.

As illustrated in Figure 6, the flows F1 , F3 and FP move towards two collecting suction surfaces 9, 10 positioned relative to each other in such a way as to define a passage 1 1 for the total flow of thermoplastic material and the flow of particulate material; preferably, the flows F1 , F3 and FP intercept each other, at least partly, upstream of the passage 1 1 . The size d of the passage 1 1 , measured in a direction perpendicular to the surfaces 9 and 10, is between 1 and 20 mm.

Generally speaking, forming the mass 102 with a pair of flows of thermoplastic material improves the balance of the air flows and helps trapping the particulate material more effectively.

In the preferred embodiment illustrated, the surface 9 is in the form of a collecting suction drum with an axis of rotation R9 and the surface 10 is in the form of a collecting suction drum with an axis of rotation R10 which is parallel to the axis R9.

The passage 1 1 is defined between an outer cylindrical collecting surface of the drum 9 and an outer cylindrical collecting surface of the drum 10.

Advantageously, by adjusting the distance d and the suction of the drums or, generally speaking, of the collecting surfaces, it is possible to spread out the material passing through to obtain a more open mass of fibres.

The method as described allows optimizing the use of the particulate material (reducing the quantity of particulate material lost during production) and reducing its constraint factor; if the particulate material is absorbent or superabsorbent polymeric material, the method allows obtaining absorbent products characterised by higher absorption capacity (for the same quantity of absorbent material used).

This invention also has for an object a method for making an article, preferably for sanitary, biomedical or antiparticulate use, comprising a segment of a composite web 100 made according to the method described herein.

Preferably, the biomedical article is a protective mask for the face, preferably with virucidal and/or bactericidal action.

In an embodiment, the article is a smoking article and/or a semifinished product for the tobacco industry, preferably a cigarette filter.