FR2655361A1 - Process for the manufacture of hydrophilic nonwovens comprising natural fibres, in particular unbleached cotton, and the nonwovens obtained - Google Patents

Abstract

The method of manufacturing a nonwoven fabric from unbleached cotton, or other natural lignocellulosic fibers comprising on the surface a layer of materials making the fiber hydrophobic, comprising the following steps: - forming a web of fibers, unbound, on a fabric permeable to water, - entanglement of the fibers of the web by means of a plurality of water jets from injector ramps, arranged transversely with respect to the direction of movement of the support is characterized in that the total energy communicated to the web by all of the jets is at least equal to a minimum threshold corresponding to the value at which said web becomes hydrophilic. The invention also relates to a hydrophilic nonwoven made by hydraulic bonding from unbleached and chemically untreated cotton.

Description

 The invention relates to the manufacture by hydraulic bonding of hydrophilic nonwoven fabrics based on unbleached cotton fibers, or other natural non-chemically treated lignocellulosic fibers, and to the products obtained according to the process.

 The purpose of the hydraulic bonding technique is to provide a certain mechanical resistance to a sheet of initially unrelated fibers, independently of any binder supply. The binding process involves subjecting these fibers to the action of very thin streams of liquid - for example water - under pressure. Usually, these jets are arranged along ramps spaced apart from each other and directed on the fiber web which is supported by a permeable fabric traveling at a predetermined speed. Passing under these ramps, the fibers are driven by the jets of fluid that pass through the sheet. These will bounce off the web and produce entanglement of fibers by interaction. The bonds thus created ensure the cohesion of the sheet.

 By this method, it is possible to obtain nonwoven fabrics from fibers of various origins: synthetic, natural, long or short, alone or in mixture, which one chooses according to the use for which they are intended . The products obtained generally have a drapery, a softness and a smoothness of touch superior to those of nonwovens manufactured by other techniques.

 European Patent Application EP 132028, in particular, discloses a method of manufacturing non-woven fabrics from unbleached cotton, comprising subjecting a veil of unbleached cotton fibers, initially unbound, to entanglement by oscillating water jets. at low pressure and then to complete the treatment, before drying, by a scouring and bleaching step according to any known technique, for example by dipping in an autoclave at 120 ° C. in a solution based on caustic soda and hydrogen peroxide.

 This last phase of the process is, according to this patent, made necessary, in particular, by the use of unbleached cotton. Indeed, it is raw cotton having undergone further cleaning that mechanical possibly, and whose fibers have a primary layer consisting of waxes and greases, it is to eliminate to make them hydrophilic. Thus the scouring has for object, in particular, to ensure the saponification of fats.

 The invention is based on the discovery that it is possible, by applying a consolidation treatment by jets of water, to confer on a sheet of natural fibers such as unbleached cotton, the property of absorbing liquids, the water in particular, without any chemical treatment.

The method according to the invention for manufacturing a nonwoven fabric from unbleached cotton fibers, or other natural lignocellulosic fibers having on the surface a layer of material making the fiber hydrophobic, comprises the following steps
- formation by any suitable method of a non-bonded web of fibers on a water-permeable support fabric
- Entanglement of the fibers of the sheet by means of a plurality of water jets from nozzle ramps, arranged transversely to the direction of movement of the support. It is characterized in that the total energy imparted to the ply by all the jets is at least equal to a minimum threshold corresponding to the value at which said ply becomes hydrophilic.

 This threshold depends in particular on the nature and the origin of the fibers (new cotton or recovery fibers: stripping, combing blouse, etc ...) of the structure of the web (superimposed card webs, pneumatically obtained webs). ) weight and thickness of the web.

 It has been found, surprisingly, that from a certain threshold of kinetic energy imparted by the jets of water to the fibers, to ensure their entanglement, an action breaking their initial hydrophobic character occurred.

 It has been found, for example, that for an ecru cotton of the combing type, of micronaire 3 to 5, or of the new cotton type, of micronaire 3 to 8, this threshold of energy dissipated by the injector was between 0.4 and 1.1 kwh per kilogram of treated fibers, for webs having a basis weight of between 25 and 200 g / m 2 and preferably between 30 and 100 g / m 2.

 Thus, for example, when the wettability of an unbleached cotton veil is evaluated by measuring the time it takes to sink into the water after having deposited it on the surface, it is not measurable for a veil of untreated fibers, that is to say, not bonded by water jet, because the sheet floats on the surface. By cons, it becomes when the same veil has undergone the treatment of the invention, that is to say, it has absorbed the minimum energy required.

 Without wishing to be limited to an interpretation, it appears that the jets of water have an unexpected mechanical effect and additional stripping on the fibers. Surprisingly, from a certain amount of energy absorbed, the effect is sufficient to cause at least a partial detachment of the hydrophobic sheath, possibly with the release of fibrils, making the hydrophilic parts of the fibers accessible to liquids. water in particular.

In addition, this stripping action causes no deterioration of the mechanical properties of the resulting nonwoven, since there is a continuous improvement in the breaking strength of the product obtained. It should be noted that this treatment does not necessarily lead to the elimination of the materials constituting the hydrophobic sheath. These can be retained between the fibers, or remain attached by zones. There is no significant modification of the chemical functions of the fibers after water jet treatment as shown by the infrared peaks, although the nonwoven has become hydrophilic.

 The solution of the invention thus has the advantage of allowing in a single step the production of water-jetted products having a marked absorbent character, from unbleached cotton fibers, without requiring complex chemical treatment intended to confer a hydrophilic nature to the fibers such as scouring.

 The method is applicable to all lignocellulosic fibers having a hydrophobic character in the natural state due to the presence on the surface of waxy or fatty mineral matter, which is reduced by treating them chemically. Among the raw materials, unbleached cotton is the material primarily targeted by the process, but other fibers such as flax, for example, are not excluded.

 Another advantage is to allow the recovery of recovery fibers such as spinning waste for example so the process allows the treatment of fibers consisting of combing residues which are relatively short fibers, length between 5 and 25 mm.

The products resulting from the process of the invention have multiple applications, for example in the fields
- Industrial or domestic wiping: rags, tea towels, tea towels
- toilet: gloves, towels
- table linen: tablecloths, towels
- bedding: bed sheets, pillowcases, bolster covers, etc ...

 - protective clothing.

 Although in general the product is sufficiently resistant to be handled, it is possible to continue the treatment beyond the minimum threshold required for hydrophilicity until the improvement of the mechanical tensile strength properties reaches a minimum. bearing. Hydrophilicity properties are not increased in the same proportion.

 According to another aspect of the invention, it is also possible to incorporate in the web a certain amount of synthetic fibers, in particular binder or hot melt fibers, which after appropriate treatment - thermal and / or mechanical if necessary - increase the resistance mechanics of the nonwoven web, especially in the wet state.

 For example, up to 30% of thermoplastic fibers can be incorporated - based on polyethylene, polypropylene or the like and, after the removal of water, passing the veil in a heated oven at a temperature sufficient to melt them at least partially. . The softened material constitutes bonding zones forming bonds between the cotton fibers after cooling to room temperature.

 The invention also relates to a hydrophilic nonwoven comprising in majority natural lignocellulosic fibers entangled according to a hydraulic bonding process characterized in that said fibers have not undergone any chemical treatment to render them hydrophilic.

 In particular a nonwoven according to the invention comprises at least 70% unbleached cotton and is free of any wetting agent, surfactant product or other. In spite of this, it has an absorption capacity of aqueous liquids such that its immersion time, measured according to the method reported below, is less than 30 seconds. In addition, its absorption coefficient is greater than 9 g / g of nonwovens.

 Finally, according to a particular embodiment, the nonwoven comprises up to 30% of synthetic fibers.

Other features and advantages of the method will appear on reading the description which follows, of a non-limiting embodiment of the invention, accompanied by the appended drawings on which
FIG. 1 represents a hydraulic binding installation for implementing the method of the invention
FIG. 2 is a graphical representation of the breaking strength of the treated product, as a function of the quantity of energy released by the successive injectors, per kilogram of product treated;
FIG. 3 is a graphic representation of the immersion time of the product treated in the example as a function of the quantity of energy released by the successive injectors per kilogram of treated product;
FIGS. 4A and B are photomicrographs of the ecru cotton fibers before treatment
- Figures 4 C and D are microphotographs of the same fibers shown in Figures 4 A and B, after the treatment of the invention, and extracted from the nonwoven.

 Figure 1 shows a hydraulic binding system of the type developed by the PERFOJET Company. It comprises a first hydraulic binding unit (10) with an endless web (12) stretched between horizontal rollers (14) so as to form a loop. The web is driven in the direction of the arrow at a predetermined constant speed of scrolling. It comprises an upper portion at which a first battery of injector ramps (16) is placed, fed with pressurized liquid and oriented vertically in the direction of the fabric. The ramps are arranged perpendicular to the running direction of the web, and have injection orifices distributed over the entire width of the web. The number of ramps is variable and chosen according to the desired pressure leveling. Preferably it will be between 3 and 10.

 Next to the ramps, under the fabric, suction boxes (18), communicating with a source of vacuum, have the function of recovering water from the injectors, which has passed through the fabric.

 The installation comprises a second hydraulic binding unit (20) with an endless cloth (22) for processing the second face. It comprises a second battery of injector ramps (26) supplied with pressurized liquid by unrepresented conduits. The ramps are associated with suction boxes (28) for recovering the liquid after its entanglement work.

 As seen in the figure the fiber web is deposited on the web (12) from a formation station of the web, not shown.

 Before being conveyed to this tablecloth forming station, the cotton is first cleaned and freed from most of its impurities such as seeds, leaf debris and dust, on conventional textile material, for example opener, cleaner, etc. ... The fiber flakes are then sent on topping material: carding, pneumatic lapping, etc.

 Cardes of any type can be used. For light nonwovens weighing less than 100 g / m 2, a card with a sail jammer is preferably chosen, which makes it possible to obtain good strength ratios in the cross direction.

 The number of carding sails to be superimposed depends on the weight per m2 desired. For example for a basis weight of 65 g / m 2, 4 card veils are superimposed.

 Instead of forming the web by carding, it is also possible to use pneumatic means of the RANDO type, especially for the higher grammages, up to 200 g / m2.

 The web thus formed is deposited on the web (12), moving at a predetermined speed, from where it is driven to the battery of injector ramps (16) for processing on a first face. To ensure the prewetting of the haze (necessary because of the hydrophobicity of the fibers used), it is possible, for example, to use an injector whose pressure is set at a low level (30 bar), without disturbing the arrangement of the fibers. The other injectors are set at pressures ranging from 40 to 250 bar, to ensure the entanglement of the fibers. Then, the web, having undergone a first consolidation on the first face, can be driven to the second binding unit where it will be taken up by a fabric so as to present its second face to the battery of injectors (26). For example, the second face is treated identically to the first. The nonwoven passes then on a last empty slot which makes it possible to evacuate most of the water. It is then dried, for example on a through air dryer or on drying drums, not shown. If necessary it is subjected to a heat treatment if it is planned to incorporate thermofoil fibers in the veil.

 One can also provide, if desired, a hydraulic structuring station disposed before drying of course.

Example
This process has been treated with a sheet of unkempt cotton fibers of the combing type. The average length of the fibers was 12 to 14 mm with a micron number 4. The final nonwoven material, 65 g / m2, consisted of 4 superposed card webs.

Each hydraulic binding unit consisted of 4 injectors with pressures of 30, 95, 125 and 125 bar, respectively. At the machine speed of 30 meters per minute, the energy released successively by the injectors and measured at the pumps, per kilogram of nonwovens, is reported in the table below.

<tb> INJECTORS <SEP> PRESSURE <SEP> (bars) <SEP> ENERGY <SEP> BY <SEP> ENERGY <SEP> DISSIPATED
<tb><SEP> RAMP <SEP> OF INJECTORS <SEP> (KWH / KG)
<tb><SEP> 1 <SEP> 30 <SEP> 0.03 <SEP> 0.03
<tb><SEP> 2 <SEP> 95 <SEP> 0.16 <SEP> 0.19 <SEP>
<tb><SEP> 3 <SEP> 125 <SEP> 0.19 <SEP> 0.38
<tb><SEP> 4 <SEP> 125 <SEP> 0.19 <SEP> 0.57
<tb><SEP> 5 <SEP> 30 <SEP> 0.03 <SEP> 0.60
<tb><SEP> 6 <SEP> 95 <SEP> 0.16 <SEP> 0.76
<tb><SEP> 7 <SEP> 125 <SEP> 0.19 <SEP> 0.95
<tb><SEP> 8 <SEP> 125 <SEP> 0.19 <SEP> 1.14
<Tb>
A nonwoven was obtained with the following characteristics
- weight per mZ: 65 g
- thickness: 0.42 mm
- breaking strength SM: 55 N
a test piece of 5cm ST: 33 N
wide
- immersion time: 30 s
- absorption coefficient:> 9 g / g
FIG. 2 shows the evolution of the breaking strength of the web as a function of the energy imparted to the lap by the successive injectors. It can be seen that the resistance, both in direction and cross direction, increases as a function of the energy received by the sheet so as to reach, with respect to the cross-directional resistance, a plateau after 0.9 kWh per kg of nonwovens.

 FIG. 3 shows for the example under consideration the evolution of immersion time representative of the wettability, as a function of this same quantity of energy. It can be seen that the time taken by the sample to sink into the water becomes measurable from a minimum energy threshold of 0.7 kWh per kg of nonwovens for the example under consideration.

 The table below shows the immersion time values relative to the nonwoven of the example on the one hand and for a nonwoven of the same weight obtained by mechanical needling from the same veils of unbleached cotton card on the other hand .

Immersion times greater than 300 seconds mean that after that time, the nonwoven still floated on the water and did not get wet.

<tb><SEP> ENERGY <SEP> RELEASED <SEP> BY <SEP> TIME <SEP> IMMERSION
<tb><SEP> NONTISSE <SEP><SEP> INJECTORS <SEP> (seconds)
<tb><SEP> Kwh / kg
<tb> LIE <SEP> MECHANICALLY <SEP> - <SEP><SEP> 300
<tb><SEP> 0.03 <SEP><SEP> 300
<tb><SEP> LIE <SEP> 0.19 <SEP><SEP> 300
<tb><SEP> 0.38 <SEP><SEP> 300
<tb><SEP> BY
<tb><SEP> 0.57 <SEP><SEP> 300
<tb><SEP> JETS <SEP> 0.60 <SEP><SEP> 300
<tb><SEP> 0.76 <SEP> 95
<tb><SEP> WATER
<tb><SEP> 0.95 <SEP> 37
<tb><SEP> 1.14 <SEP> 27
<Tb>

 This measurement of immersion time is used in the pharmacopoeia as a measure of the wettability of the hydrophilic cotton.

The method is as follows
- Using a cylindrical basket, previously dried, consisting of copper son with a diameter of about 0.4 mm.

This basket has a height of 8.0 cm, a diameter of 5.0 cm and mesh width of 1.5 to 2.0 cm. Its mass is 2.7 + 0.3 g.

 We weigh the basket (m1). 1 g of nonwoven material is taken at 5 different places in the sample. We introduce the 5 g without packing into the basket that is weighed (m2). On the other hand, a container of 11 cm to 12 cm in diameter filled with water at about 200 ° C. over a height of 10 cm is prepared. The basket is presented horizontally above the water and dropped from a height of 10 mm. The time is measured by the stopwatch to sink into the water. It is this time in seconds that is reported in Figure 3.

The absorption coefficient is determined from the previous test. The basket is removed from the water, allowed to drain for 30 seconds and then placed in a tared container (m3) and weighed (m4). The water absorption coefficient per gram of cotton reported earlier in the example is given by the formula
m4 - (m + m,)
C 2
m2 -m1
The photos made with a scanning electron microscope show the stripping action of the jets on the primary layer of the fibers. Photomicrographs A and B show that the pre-treatment fibers are smooth and intact while the C and D photomicrographs carried out after treatment reveal the presence of fibrils attached to the fibers which have not been otherwise deteriorated.

 Infrared spectrophotometry was also performed.

 At the level of the infrared peaks there is an evolution between two spectra made one before treatment the other after treatment. However, this evolution is not sufficient to allow conclusions to be drawn about the disappearance of the materials conferring hydrophobic properties on the fiber.

Claims (12)

 A method of manufacturing a nonwoven fabric from unbleached cotton, or other natural lignocellulosic fibers having on the surface a layer of materials rendering the fiber hydrophobic, comprising the following steps  forming an unbonded sheet of fibers on a water permeable fabric,  entanglement of the fibers of the sheet by means of a plurality of jets of water coming from nozzle ramps, arranged transversely with respect to the direction of displacement of the support, characterized in that the total energy imparted to the sheet by the the set of jets is at least equal to a minimum threshold corresponding to the value at which said ply becomes hydrophilic.  2. A method of manufacturing a nonwoven fabric from unbleached cotton according to claim 1 characterized in that the energy threshold is between 0.4 and 1.1 kwh per kg of treated fibers.  3. Method according to one of claims 1 and 2 characterized in that said web has a basis weight between 25 and 200 g / m2, preferably between 30 and 100 g / m2.  4. Method according to one of the preceding claims characterized in that it consists in successively treating both sides of the web.  5. Method according to the preceding claim characterized in that the number of injectors is between 3 and 10 for each face.  6. Method according to one of claims 4 and 5 characterized in that the first injector is at low pressure so as to ensure the wetting of the web without moving the fibers.  7. Method according to one of claims 4 to 6 characterized in that the bonding treatment is carried out by jets of water whose pressure at the injector outlet is set to a mean or high value, between 40 and 250 bar.  8. Hydrophilic nonwoven comprising predominantly natural lignocellulosic fibers, entangled according to a hydraulic bonding process characterized in that said fibers have not undergone any chemical treatment to render them hydrophilic.  9. Hydrophilic nonwoven according to claim 8 characterized in that it comprises at least 70% unbleached cotton and is free of any wetting agent.  10. Hydrophilic nonwoven according to claim 9 characterized in that it has a wettability such that the immersion time of a sample is less than 90 seconds and preferably 30 seconds.  11. Hydrophilic nonwoven according to one of claims 9 and 10 characterized in that its absorption coefficient is greater than 9 g / g.  12. Nonwoven according to one of claims 8 to 11 characterized in that it comprises up to 30% of synthetic fibers.