EP0637641A1 - Nonwoven containing an acid lactic polymer derivate, process of making and use thereof - Google Patents

Abstract

The subject of the present invention is a nonwoven based on polymers derived from lactic acid, the process for the production of and the use of such a nonwoven. Nonwoven consisting of filaments of a polymer material, characterised in that all the filaments composing it are made entirely from a polymer or from a polymer mixture derived from lactic acid. <IMAGE>

Description

The present invention relates to the field of nonwovens, in particular nonwovens at least partially degradable, and relates to a nonwoven which is completely degradable and assimilable by the environment, its manufacturing process and its various uses.

Currently, most of the nonwovens produced are made from synthetic polymers, such as propylene, polyethylene, polyesters or polyamides, which are practically non-degradable, in particular non-biodegradable, all the more so since they Often incorporate stabilizers or other additives that extend their life.

In an attempt to overcome this drawback, it has been proposed to include photosensitive agents in the composition of the filaments of nonwovens in order to trigger a photo-oxidation reaction.

It has also been proposed to produce nonwovens from thermoplastic polymers derived from starch or else based on polycaprolactones or polyhydroxybutyrates / polyhydroxyvalerates.

However, the nonwoven products obtained do not have sufficiently satisfactory properties (mechanical strengths, physicochemical properties) allowing their use and, moreover, their cost price is too high compared to synthetic polymers.

In addition, the filaments obtained from these materials always have high titers, rarely less than 10 dtex, due to the nature and characteristics of the materials used.

The problem posed in the present invention therefore consists in designing a fully biodegradable, compostable and assimilable by the environment nonwoven, the filaments of which have a very low titer and the production costs of which are low and the mechanical and physico-chemical properties substantially equivalent to those of synthetic polymers.

For this purpose the present invention relates to a nonwoven consisting of filaments of a polymeric material, characterized in that all of the filaments which compose it are made entirely of a polymer or of a mixture of polymers, derived from 'Lactic acid.

The subject of the invention is also a process for producing a nonwoven as mentioned above, characterized in that it essentially consists in introducing a solid mass of polymers or a mixture of polymers, derivative ( s) lactic acid, in a heated extruder, to heat said mass in a controlled manner by working it, in order to obtain a homogeneous melt and having a determined viscosity, then to transport said melt to a device die for the formation of filaments, to cool and stretch the filaments thus obtained, to deposit said filaments, without preferential orientation, on a circulating collecting mat, so as to form a sheet or a non-woven veil and, finally, the case where appropriate, to secure said filaments of said web or of said web to each other at at least part of their mutual crossing points and / or to treat said filaments of said e tablecloth by immersion, coating, impregnation or spraying.

• la figure 1 représente schématiquement un ensemble extrudeuse-filière pour la mise en oeuvre du procédé conforme à l'invention;
• la figure 2 représente un dispositif pour la mise en oeuvre du procédé selon un premier mode de réalisation de l'invention;
• la figure 3 représente un dispositif pour la mise en oeuvre du procédé selon un second mode de réalisation de l'invention;
• les figures 4 et 5 représentent des courbes montrant, respectivement, l'évolution de la viscosité et de la contrainte de cisaillement en fonction du taux de cisaillement pour deux polymères dérivés de l'acide lactique et utilisés pour la réalisation d'un non-tissé selon l'invention.

The invention will be better understood from the description below, which relates to preferred embodiments, given by way of nonlimiting examples, and explained with reference to the appended schematic drawings, in which:

• FIG. 1 schematically represents an extruder-die assembly for implementing the method according to the invention;
• FIG. 2 represents a device for implementing the method according to a first embodiment of the invention;
• FIG. 3 represents a device for implementing the method according to a second embodiment of the invention;
• Figures 4 and 5 show curves showing, respectively, the change in viscosity and shear stress as a function of the shear rate for two polymers derived from lactic acid and used for the production of a nonwoven according to the invention.

In accordance with the latter, all the filaments making up the nonwoven are produced entirely (100% of their composition) in a polymer or in a mixture of polymers, derived from lactic acid.

According to a first characteristic of the invention, said polymer or polymers constituting said filaments is (are) derived from lactic acid L or lactic acid D or from a mixture of lactic acids L and D.

Said polymer or said mixture of polymers derived from lactic acid advantageously has a molecular mass of between 100,000 g / mol and 200,000 g / mol and a polydispersity index of between approximately 1 and approximately 3.

In addition, said polymer (s) derived from lactic acid has a glass transition temperature between 45 ° C and 55 ° C and a melting temperature between 165 ° C and 180 ° C.

By way of example, a polymer A, which can be used for the production of a nonwoven according to the invention, can be obtained by reacting in a lactic acid reactor with a catalyst, under the form of stannous octoate mixed with said lactic acid at a rate of 0.11% by weight.

The above polymer, having at the outlet of the reactor a temperature of 209 ° C., has a weight-average molecular mass of 132,000 g / mol, a polydispersity index of 1.9, a glass transition temperature of 51, 5 ° C and a melting temperature of 170.3 ° C.

It is also possible to obtain, with the operating conditions indicated above, a polymer B, derived from lactic acid and which can be used for the production of a nonwoven according to the invention, said polymer B having a weight average molecular weight of 158,000 g / mol, a polydispersity index of 2.1, a glass transition temperature of 49 ° C and a melting temperature of 171.6 ° C.

Certain other characteristics of polymers A and B will appear to a person skilled in the art on seeing FIGS. 4 and 5 of the accompanying drawings.

The abovementioned polymers A and B, as well as other polymers derived from lactic acid and capable of serving as a base material for the production of nonwovens in accordance with the invention, are described in more detail with regard to obtaining them and their characteristics, in the Finnish patent application n ° 923167 filed on July 9, 1992 by the company Nesté Oy.

According to another characteristic of the invention, the titer of the filaments constituting the nonwoven is between 0.5 and 10 dtex, advantageously between 1 and 5 dtex and preferably between 2.5 and 4.5 dtex, said non woven fabric which, moreover, with a view to increasing the mechanical strength and the resistance of the web or of the nonwoven web, may include welds of different geometries between filaments over approximately 5% to 50% of its surface, obtained by calendering hot, preferably on 12%, 24% or 48%.

Furthermore, the filaments constituting the nonwoven according to the invention can also be treated with a view to acquiring specific physicochemical properties and, for example, having hydrophilic or hydrophobic properties, obtained by impregnation or spraying. surfactants.

The nonwoven fabric according to the invention, as described above, may advantageously be used as a partial component or as a single constituent of a disposable article, in particular for single use, and more particularly, following treatment. adapted, in as a hydrophilic component, in particular a surface veil, of a disposable hygiene product, for example a disposable diaper or towel or as a hydrophobic component, in particular a barrier surface, of a product disposable hygiene, for example a diaper or a disposable sanitary napkin, by making a nonwoven on the basis of the aforementioned polymer A.

With the aid of the abovementioned polymer B, it will be possible to produce a nonwoven which can be used as mulch or protective veil for crops.

The subject of the invention is also, as shown in FIGS. 1, 2 and 3 of the appended drawings, a process for producing a nonwoven as described above, said process essentially consisting in introducing, from a reservoir, for example, and in granular or powdery form, a solid mass of polymers or of a mixture of polymers, derived from lactic acid, in a heated extruder 2, to heat said mass in a controlled manner working it, in order to obtain a homogeneous melt and having a determined viscosity, then transporting said melt to a spinneret device 3, 3 ′ for the formation of filaments, cooling and drawing the filaments thus obtained, depositing said filaments, without preferential orientation, on a circulating collecting mat 4, so as to form a sheet or a non-woven veil and, finally, if necessary, securing said filaments of said sheet e ntre them at at least part of their mutual crossing points and / or to treat said filaments of said web by immersion, coating, impregnation or spraying, this via, if necessary, a post calendering 5 and / or a corresponding treatment station 6 through which the web or the nonwoven web can pass after its formation.

Of course, the fleece or the nonwoven web is finally made in width and rolled up at a suitable winding station 7.

The extruder 2 used advantageously has a single screw 2 ′ (see FIGS. 2 and 3) and its body is surrounded by a plurality of heating collars delimiting, in said body, heating zones Z1 to Z5 (see figure 1) which may have increasing values of temperature between the feed inlet of the extruder 2, connected to the reservoir 1, and the outlet of said extruder 2.

According to a first alternative embodiment of the invention, and as shown in FIG. 2 of the accompanying drawings, the method consists in pushing the molten material coming from the extruder 2 through a die 3 composed of several fields, advantageously seven, then to cool the filaments from each field by an air flow 8, then to stretch said filaments, by Venturi effect, in nozzles 9 and, finally, to deposit the drawn filaments on a collecting mat 4 circulating without preferential orientation and homogeneously, using separators 10.

Such a process is more generally known under the designation LURGI in the production of conventional nonwovens.

According to the invention, the extruder 2 is preferably maintained at a temperature between 185 ° C and 204 ° C, giving the mass of polymer (s) derived from lactic acid a determined viscosity allowing its handling and its transport, without however altering the constituent (s).

According to a second alternative embodiment of the invention, and as shown in FIG. 3 of the accompanying drawings, the method can also consist in pushing the molten material coming from the extruder 2 through a monobloc die 3 ′, then in cooling the filaments obtained by means of an air flow 8 and in stretching them in a slot 11 and, finally, in depositing said stretched filaments on said collecting mat 4 or scrolling, without preferential orientation and in a homogeneous manner.

In addition, a suction device 11 'is located under the collecting mat 4, creating a suction effect at the level of the latter, intended to press the filaments against it.

Such a process is more generally known under the designation S-Tex for the production of synthetic nonwovens.

According to a characteristic of the invention, the temperature of the extruder 2 is advantageously included, for this second embodiment, between 245 ° C and 295 ° C.

According to a third alternative embodiment of the invention, not shown in the accompanying drawings, the method according to the invention may also consist in pushing the molten material through a die having a multitude of holes in line, then in drawing the filaments obtained by means of hot air currents circulating around the die and in the direction of the collecting mat, and, finally, projecting said filaments, without preferential orientation and homogeneously, onto said moving collecting mat.

Advantageously, the temperature of the molten material from the extruder 2 is fixed, on the one hand, by a first heating circuit 12 comprising a first heat transfer fluid, during its transport from the extruder 2 to the die 3 , 3 'and, on the other hand, by a second heating circuit 13 comprising a second heat transfer fluid, distinct from said first devices and fluids, at the level of the die 3, 3', said molten material thus being able to be brought to temperatures different depending on the operations to be performed.

The first heat transfer fluid, for example of the type known under the designation marlo, can give the melt a sufficient temperature for its transfer from the extruder 2 to the die 3, 3 ', while the second heat transfer fluid, for example type known under the designation dyphil, will bring said melt to a higher temperature allowing its spinning.

In order to guarantee a constant quality of the veil or of the nonwoven web, it is preferable to supply the die 3, 3 ′ by means of positive displacement pumps 14 connected to the outlet of the extruder 2 (FIGS. 2 and 3 ) or via a booster pump 15 (Figure 1).

According to a characteristic of the invention, the rate of stretching of the filaments is advantageously between 100% and 1000%, and the veil or the sheet of nonwoven obtained can be treated by impregnation or by spraying of surfactants.

TABLEAU 2 Nature des paramètres Lieu/objet concerné Unités Valeurs vitesse extrudeuse (vis) t/mn 15 à 80 pompes volumét. t/mn 4 à 22 tapis m/mn 5 à 200 débit Kg/h < 140 température zone 1 °C 250±5 zone 2 °C 290±5 zone 3 °C 290±5 zone 4 °C 290±5 zone 5 °C 290±5 1° circ. chauffe °C 200±5 filière °C 240±5 2° circ. chauffe °C 245±5 pression extrudeuse bars 37 surpression bars 46 pompes volum. bars 24 filière bars 18 aspiration mm de CE 50 vit. filament. étirage m/s 2 < < 30 taux d'étirage % 150 < < 900 T° picots °C 132±5 T° lisse calandre °C 132±5 pression daN/cm 50 vitesse gommage traitement m/mn 3 taux prod. actif imprégnation % 12 type / silvet As a practical example of implementing the process according to the invention, the values of the various essential operating parameters involved in the process for manufacturing the nonwovens according to the invention obtained according to the first variant are indicated below. of embodiment (Table 1) or according to the second alternative embodiment, mentioned above (Table 2), mentioned above.

TABLE 2 Nature of parameters Place / object concerned Units Values speed extruder (screw) rpm 15 to 80 volumet pumps. rpm 4 to 22 carpet m / min 5 to 200 debit Kg / h <140 temperature zone 1 ° C 250 ± 5 zone 2 ° C 290 ± 5 zone 3 ° C 290 ± 5 zone 4 ° C 290 ± 5 zone 5 ° C 290 ± 5 1st circ. heated ° C 200 ± 5 Faculty ° C 240 ± 5 2nd circ. heated ° C 245 ± 5 pressure extruder bars 37 overpressure bars 46 volum pumps. bars 24 Faculty bars 18 aspiration mm of CE 50 lives. filament. drawing m / s 2 <<30 stretch rate % 150 <<900 T ° pins ° C 132 ± 5 Smooth temperature grille ° C 132 ± 5 pressure daN / cm 50 scrub speed treatment m / min 3 production rate active impregnation % 12 type / silvet

The median values of the operating parameters indicated in Table 1 make it possible to obtain nonwovens which can be used for agricultural and hygienic applications and which have the characteristics mentioned in Tables 3 and 4 below, depending on the polymer. , respectively A (table 3) and B (table 4), used for their realization. TABLE 3 weight g / m² 20 25 voltage md N / 5cm 22 26.5 CD N / 5cm 8.5 10 elongation md % 2.5 2.5 CD % 2.5 2.4 air permeability (10 pa) 1 / m² / s 1500 1300 absorption time s <3 <3 filament title dtex 2.2 2.5 mfr (I2 190 ° C) / / 400 weight g / m² 50 100 voltage md N / 5cm 60.2 110.5 CD N / 5cm 23.5 40.5 elongation md % 3.1 3.5 CD % 2.9 3.5 air permeability (10 pa) 1 / m² / s 650 300 absorption time s <3 <3 filaments title dtex 2.2 2.2 mfr (I2 190 ° C) / 400 400

Tables 3 and 4 above indicate, in addition to the conventional characteristics such as weight, tensile strength and elongation (in the machine direction: md and perpendicular to the latter: cd) and the title of the filaments of the nonwoven obtained, certain characteristics particular of said nonwoven such as air permeability (under a vacuum of 10 Pascal), absorption coefficient (time of passage of 5 cm³ of urine through the veil or nonwoven web - Edam 150 standard -1-90) or even the fluidity index (mfr - Standard ISO 1133 at T = 190 ° C).

The four nonwovens described in Tables 3 and 4 were treated, as shown in Table 1 above, using a surfactant known under the designation SILVET (brand) by the company Union Carbide.

In order to test the degree and speed of degradability of the nonwovens in accordance with the invention, samples having the characteristics mentioned in table 3, intended more particularly for hygiene articles, were mixed with vegetable food waste and transformed into compost and humus in a reactor of the composter type.

For eight days, the temperature in the reactor was fixed at 55 ° C., the humidity of the mixture maintained at 50% and the supply of air ensured.

After this period, it was found that the nonwoven had deteriorated considerably and that only a few filaments were still visible.

The compost was then extracted from the reactor and spread in the open air for 10 weeks. At the end of this second period no more filament was visible and the decomposition of the nonwoven was complete.

Likewise, nonwovens having the characteristics mentioned in Table 4 were used as mulch sails in vegetable and horticultural crops to control weeds, in place of phytosanitary products.

• contrôle des mauvaises herbes sans utilisation d'herbicides (examen du nombre d'adventices et de leur taille),
• activation des microorganismes du sol, les non-tissés constituant un excellent substrat de culture,
• limitation de l'évaporation (hygrométrie supérieure à 80% à 22°C).

By testing these nonwovens on young coniferous and lettuce plants, the following properties were found:

• weed control without the use of herbicides (examination of the number of weeds and their size),
• activation of soil microorganisms, nonwovens constituting an excellent growing medium,
• limitation of evaporation (humidity higher than 80% at 22 ° C).

The degradability of the nonwoven is ensured by watering, rain and the activity of microorganisms.

The samples taken from the sails under test revealed that the mechanical properties fell by 10% in 2 months.

Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings. Modifications remain possible, in particular from the point of view of the constitution of the various elements, or by substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims (22)

Nonwoven consisting of filaments of a polymeric material, characterized in that all of the filaments that compose it are made entirely of a polymer or of a mixture of polymers, derived from lactic acid. Nonwoven fabric according to claim 1, characterized in that said polymer (s) constituting said filaments is (are) derived from L or D lactic acid. Nonwoven according to claim 1, characterized in that the said polymer or polymers constituting the said filaments are obtained from a mixture of lactic acids L and D. Nonwoven according to any one of claims 1 to 3, characterized in that said polymer or said mixture of polymers derived from lactic acid has a molecular weight of between 100,000 g / mol and 200,000 g / mol and a polydispersity index of between approximately 1 and approximately 3. Nonwoven according to any one of Claims 1 to 4, characterized in that the said polymer or polymers have a glass transition temperature between 45 ° C and 55 ° C and a melting temperature between 165 ° C and 180 ° C. Nonwoven according to any one of Claims 1 to 5, characterized in that the titer of the filaments constituting said nonwoven is between 0.5 and 10 dtex, advantageously between 1 and 5 dtex and preferably between 2.5 and 4.5 dtex. Nonwoven fabric according to any one of Claims 1 to 6, characterized in that it has welds of different geometries between filaments over approximately 5% to 50% of its surface, obtained by hot calendering. Nonwoven according to any one of claims 1 to 7, characterized in that the filaments have hydrophilic or hydrophobic properties, obtained by impregnation or spraying with surface-active agents. Process for the manufacture of a nonwoven according to any one of Claims 1 to 8, characterized in that it essentially consists in introducing a solid mass of polymers or of a mixture of polymers, derived from the lactic acid, in a heated extruder (2), heating said mass in a controlled manner by working it, in order to obtain a homogeneous melt and having a determined viscosity, then transporting said melt to a die device ( 3, 3 ') for the formation of filaments, to cool and stretch the filaments thus obtained, to deposit said filaments, without preferential orientation, on a collector mat (4) circulating, so as to form a non-woven web or web woven and, finally, where appropriate, securing said filaments of said ply to one another at at least part of their mutual crossing points and / or treating said filaments of said ply by immersion, e nduction, impregnation or spraying. Method according to claim 9, characterized in that it consists in pushing the molten material coming from the extruder (2) through a die (3) composed of several fields, advantageously seven, then cooling the filaments coming from each field by an air flow (8), to then stretch said filaments, by Venturi effect, in nozzles (9) and, finally, to deposit the drawn filaments on a collecting mat (4) circulating without preferential orientation and in a homogeneous manner , via separators (10). Process according to claim 10, characterized in that it consists in maintaining the extruder (2) at a temperature between 185 ° C and 205 ° C. Method according to claim 9, characterized in that it consists in pushing the molten material from the extruder (2) through a monobloc die (3 '), then in cooling the filaments obtained by means of a flow of air (8) and to stretch them in a slot (11) under the action of a suction generated by a device (14) adapted under the collecting mat (4) at the level of the slot (11) and, finally, depositing said stretched filaments on said collecting mat (4) or running, without preferential orientation and in a homogeneous manner. Method according to claim 12, characterized in that it consists in maintaining the extruder (2) at a temperature between 245 ° C and 295 ° C. Method according to claim 9, characterized in that it consists in pushing the molten material through a die having a multitude of holes in line, then in drawing the filaments obtained by means of hot air currents circulating around the die and in the direction of the collecting mat, and, finally, to project said filament, without preferential orientation and in a homogeneous manner, onto said moving collecting mat. Method according to any one of Claims 9 to 14, characterized in that the temperature of the molten material coming from the extruder (2) is fixed, on the one hand, by a first heating circuit (12) comprising a first heat transfer fluid, during its transport from the extruder (2) to the die (3, 3 ') and, on the other hand, by a second heating circuit (13) comprising a second heat transfer fluid, distinct from said first devices and fluids, at the level of the die (3, 3 '), said molten material thus being able to be brought to different temperatures depending on the operations to be undergone. Method according to any one of Claims 9 to 15, characterized in that it consists in supplying the die (3, 3 ') by means of positive displacement pumps (14) connected to the outlet of the extruder (2) or by via a booster pump (15). Process according to any one of Claims 9 to 16, characterized in that the rate of stretching of the filaments is between 100% and 1000%. Method according to any one of Claims 9 to 17, characterized in that the nonwoven web obtained is treated by impregnation or by spraying with surface-active agents. Use of a nonwoven according to any one of claims 1 to 8 as a partial component or as a single constituent of a disposable article, in particular for single use. Use of a nonwoven fabric according to any one of Claims 1 to 8 as a hydrophilic component, in particular surface fleece, of a disposable hygiene product, for example a diaper or a periodic towel Disposable. Use of a nonwoven according to any one of Claims 1 to 8 as a hydrophobic component, in particular a barrier surface, of a disposable hygiene product, for example a diaper or a periodic towel for use unique. Use of a nonwoven according to any one of claims 1 to 8 as mulch or protective veil for crops.

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