EP0805888B1 - Process for processing a cellulose fiber lap - Google Patents

Abstract

PCT No. PCT/FR96/00181 Sec. 371 Date Sep. 2, 1997 Sec. 102(e) Date Sep. 2, 1997 PCT Filed Feb. 2, 1996 PCT Pub. No. WO96/23922 PCT Pub. Date Aug. 8, 1996A process for treating natural cellulose fibers, in particular cotton fibers, comprising the stages of depositing the fibers on a continuously moving wire to form a lap evincing a specific surface weight of 100 to 800 g/m2, impregnation with a treating solution, treatment, and rinsing using an aqueous liquid, characterized in that rinsing is carried out by applying the liquid in the form of jets directed at one side of the lap perpendicularly to its direction of advance at an energy between 2 and 60 kwh/ton of treated product. The rinsing station (100) comprises at least one needle injector (105, 115) situated across the lap and applying highly pressurized water jets to its surface. The liquid is sucked in through a transverse slot communicating with a suction box (110, 125).

Description

The invention relates to a method for treating a sheet of fibers. natural fibers such as cotton fibers and particularly targets the step during which the fibers are rinsed to remove the chemicals with which the tablecloth was previously impregnated for its treatment.

For the preparation, for example, of hydrophilic cotton from cotton unbleached, the leaves are first removed by mechanical means, twigs or other foreign matter from the picking. Then we scour the fibers of their sheath of waxy and fatty materials by chemical treatment of scouring consisting in impregnating a sheet formed with the unbleached fibers using, for example, a soda liquor which is reacted with heating in a vaporizer. After treatment, the sheet is neutralized then rinsed at the water. Depending on requirements, it may be necessary to bleach the fibers and / or size. For bleaching, put the fibers in contact with a water solution oxygenated which is left to act at an appropriate temperature before neutralizing and rinse the fibers again with water.

Scouring and bleaching can be carried out in batches in tanks containing the liquor. However, continuous processing methods have been developed in recent years to lower costs when it comes to to produce cotton wool in large quantities. Thus the Applicant has put developed a continuous process to obtain a web having a certain cohesion that can be used as is in certain applications - cotton in packs, dressings or cosmetic pads for example - without having to mechanically rework the tablecloth, i.e. shred it for carding or tablecloth in another way, again.

Such a process has been described in patent application FR-A-2 660 942.

In this process, the steps of impregnation with the different liquors of scouring, bleaching or neutralizing rinse, respectively, are made by pouring onto the water table in the form of liquid slides in conditions which allow both a control of the quantity of liquid carried by the tablecloth and a homogeneous impregnation thereof. The general effectiveness of process is improved as well as the quality of the material after treatment whose characteristics vary little from one production to another. Liquid application in this form ensures at the same time a certain consolidation of the sheet in this is due in particular to the energy of the liquid communicated to it.

We tried to improve this process, in particular the efficiency of rinsing, because large amounts of water are needed to remove the products chemicals, in particular the surfactants required during the initial phase for impregnating unbleached cotton. Rinsing before finishing or before final drying is particularly important in this respect since it is desirable to reduce the rate of residual products as much as possible, in particular due to the Codex. In addition, with a constant concern to maintain and if possible improve the product quality without increasing costs, rinsing should not affect mechanical characteristics of the ply being treated. This condition only applies if you want to be able to use it after drying, without having to rework it, in the usual applications as cotton wool or cleansing pads.

Document FR-A-2 054 010 discloses a device using water jets for washing fibers.

The invention provides a method for treating natural cellulosic fibers, in particular cotton fibers, comprising the steps of depositing the fibers on a permeable fabric conveyor to form a sheet of 100 to 800 g / m ² , of impregnation with a treatment, treatment and then rinsing liquor by means of an aqueous liquid, characterized in that the rinsing is carried out by application of said liquid in the form of jets directed towards one face of the sheet perpendicular to its direction of travel and communicating with the water table has an energy of between 2 and 100 kWh per tonne of product treated.

The jets are produced by injectors as used in technology hydrodynamic nonwoven binding. each injector includes, for example, an elongated chamber, closed along its length by a perforated plate, in one or more rows, of a large number of small diameter holes, of the order 100 µm. The chamber is supplied with pressurized liquid which escapes through the orifices in the form of parallel fine jets of corresponding diameter; So in a embodiment of the invention, an injector composed of 2 rows of holes for diameter 120 µm, 0.6 mm apart, dissipate an energy from 2 to 58 kwh / T, and distribute a quantity of rinsing water, respectively, from 9 to 41 m3 per tonne of treated product. These energies correspond to pressures of use of injectors between 5 and 50 bars

According to the present invention, the jets are used for rinsing a sheet whose grammage can go up to 800 g / m ² , well beyond the grammages of the nonwovens for which they are generally used.

The level of energy to be supplied depends on the thickness of the sheet and its grammage. Preferably, the energy communicated to the water table will be less than 40 kwh / T. This will be the case, for example, for a sheet of 250 g / m ²

• L'efficacité du rinçage est nettement améliorée par rapport à un rinçage par déversement de liquide. Pour des niveaux d'énergie très faibles : 2,2 kwh/T, la hauteur de mousse devient nulle et le taux de substances solubles diminue de 30 à 50 %. Ces deux indicateurs sont représentatifs de la quantité résiduelle de produits de traitement.
• S'agissant d'un simple traitement d'une nappe de fibres dont le but est de fournir une nappe consolidée, destinée à être utilisée directement comme coton hydrophile en paquet ou bien comme pansement, tampon absorbant ou tampon à démaquiller sans autre transformation qu'une découpe et un conditionnement, il est important de ne pas trop réduire l'épaisseur de la nappe par ce mode de rinçage. Les résultats montrent de façon surprenante que dans la plage d'énergie définie, l'épaisseur du produit fini sortant du process après séchage, reste sensiblement constante et correspond à celle qu'elle présente dans le procédé mettant en oeuvre un rinçage par lames de liquide.
• Malgré la faible énergie des jets, on renforce dans une certaine mesure la résistance de la nappe. En particulier, la résistance au pelage et l'état de surface sont nettement améliorés. Il apparaít que ce traitement par jets produit un renforcement de la nappe dans les couches superficielles sans pour autant affecter les couches sous-jacentes. Ce procédé est particulièrement avantageux pour les nappes stratifiées comprenant une nappe centrale formée par voie aérodynamique entre deux voiles de carde, selon la demande de brevet FR-A-2 701 039.

It is surprising to note that the process makes it possible to obtain a very advantageous result on several levels:

• The effectiveness of rinsing is significantly improved compared to rinsing by liquid spillage. For very low energy levels: 2.2 kWh / T, the foam height becomes zero and the rate of soluble substances decreases by 30 to 50%. These two indicators are representative of the residual quantity of treatment products.
• In the case of a simple treatment of a sheet of fibers, the aim of which is to provide a consolidated sheet, intended to be used directly as hydrophilic cotton in a packet or else as a dressing, absorbent pad or pad for removing makeup without any other transformation than cutting and packaging, it is important not to reduce the thickness of the web too much by this rinsing mode. The results surprisingly show that in the defined energy range, the thickness of the finished product leaving the process after drying, remains substantially constant and corresponds to that which it presents in the process employing rinsing by liquid slides. .
• Despite the low energy of the jets, the resistance of the sheet is strengthened to a certain extent. In particular, the peel strength and the surface condition are significantly improved. It appears that this treatment by jets produces a strengthening of the web in the surface layers without affecting the underlying layers. This process is particularly advantageous for laminated plies comprising a central ply formed aerodynamically between two card webs, according to patent application FR-A-2 701 039.

According to another characteristic, the flow of liquid is understood between 8 and 40 m3 per ton of cotton.

In particular, this flow is limited to 8 m3 / T, corresponding to levels low energy, less than 10 kWh / T, especially for cotton tablecloths intended for application as packaged cotton wool. Indeed, this flow already allows effective rinsing of the water table, and we are not looking, in this case, for a increase in the mechanical resistance of the sheet.

For cleansing pads, for example, the application of an energy of 4 to 30 kwh / T increases the resistance characteristics, without reducing the thickness of the sheet.

In accordance with another characteristic, the jets are also applied to the side opposite the first. A product is thus obtained whose surface condition is the same on both sides; it is symmetrical.

In accordance with another characteristic of the invention, there is incorporated in the tablecloth up to 30% of synthetic or artificial fibers. These fibers are advantageously mixed with the cellulosic fibers before the start of the treatment. he may be any fibers known per se in the field of woven textiles or nonwovens.

• la figure 1 représente schématiquement une installation de débouillissage et de blanchiment en continu, de fibres de coton conforme à l'enseignement de l'art antérieur.
• la figure la représente le détail du poste de rinçage conforme à l'invention.
• la figure 2 est un graphique représentant l'influence de la quantité d'énergie, ramenée à la tonne de produit traité, appliquée à la nappe par les jets d'eau sur son épaisseur en mm.
• la figure 3 est un graphique représentant l'influence du débit, ramené à la tonne de produit traité, sur la hauteur de mousse H, en mm, et le taux de matières solubles S, en pourcentage par rapport aux fibres.
• les figures 4 et 5 sont des graphiques représentant l'influence de la quantité d'énergie, ramenée à la tonne de produit traité, appliquée sur la nappe par les jets d'eau, sur les résistances à la rupture sens marche, respectivement sens travers de celle-ci.
• la figure 6 est un graphique représentant l'influence de la quantité d'énergie, ramenée à la tonne de produit traité, sur la résistance, en centi-newton, à la délamination d'une nappe de fibres stratifiée selon l'enseignement de la demande de brevet FR-A-2 701 040.

Other characteristics and advantages will appear on reading the description of a nonlimiting embodiment of the invention made with reference to the drawings in which

• Figure 1 schematically shows an installation for continuous scouring and bleaching of cotton fibers according to the teaching of the prior art.
• Figure la shows the detail of the rinsing station according to the invention.
• FIG. 2 is a graph representing the influence of the amount of energy, reduced to the ton of product treated, applied to the sheet by the water jets on its thickness in mm.
• FIG. 3 is a graph representing the influence of the flow rate, reduced to the ton of product treated, on the height of the foam H, in mm, and the rate of soluble materials S, in percentage relative to the fibers.
• Figures 4 and 5 are graphs representing the influence of the amount of energy, reduced to the tonne of product treated, applied to the sheet by the water jets, on the tensile strengths in the running direction, respectively in the cross direction of it.
• FIG. 6 is a graph representing the influence of the amount of energy, reduced to the ton of product treated, on the resistance, in centi-newton, to delamination of a layer of fiber laminated according to the teaching of patent application FR-A-2 701 040.

As shown in this figure, the installation may include a first station 2 for tableclothing the unbleached fibers which have been previously opened, mechanically cleaned, and possibly mixed if they are of different origins. The coating means can be of any form known to those skilled in the art: mechanical (carding) and / or pneumatic. A particular form of ply is described in patent application FR-A-2 701 039 or FR-A-2 701 040 where it comprises two layers formed of card webs on either side of a central layer obtained by pneumatic track. We thus deposit a sheet of 100 to 800 g / m ² depending on the application envisaged on the canvas of a conveyor which drives it at a constant and determined speed, for example 30 m / min. to an impregnation station 4. This can be of the type described in patent application FR-A-2 660 942 but any other impregnation means also falls within the scope of the present process.

The tablecloth loaded with boiling liquor (soda and wetting agent) is conducted to a vaporizer 5 heated to a temperature close to 100 ° C. where it stays, while remaining continuous thanks to an appropriate storage means, during the time required for the reaction. This depends on the liquor and the rate of carrying. Then. The tablecloth is rinsed, and the boiling juice is extracted with next station 6.

If you want to whiten the fibers, you can impregnate the scorched layer at 8 hydrophilic with a bleaching solution comprising, for example, water oxygenated, then the web is again introduced into a vaporizer 10 heated to a temperature close to 100 ° C. in which it remains for a sufficient time for money laundering to be effective.

We then proceed to rinsing and neutralization at 12 to eliminate all trace of reagent, the liquids are expressed, and the sheet is dried in an oven 14 which is preferably through air. If necessary, we can proceed in a next step or before drying, sizing the fibers by any known means of the skilled person. The tablecloth from the process can be used directly for the manufacture of hydrophilic cotton or any other application in which cotton comes into contact with the skin.

According to the invention, the rinsing step before drying is advantageously carried out by means of jets of liquid, water generally, such than those used in nonwoven manufacturing techniques by hydraulic needling of fibers, well known in the art under the designation "jetlace". We could, for example, use an installation provided by the company PERFOJET.

Thus, the station 100 for rinsing by jets of water, represented in FIG. includes a needle injector 105 arranged across the web and which applies high pressure water jets on its surface. The water jets are weak diameter, 120 µm, 0.6 mm apart and arranged in two parallel rows slightly spaced from each other. The liquid passes through the tablecloth and the support fabric permeable. It is sucked through a transverse slit parallel to the line jets communicating with a suction box 110. In the example shown, the installation includes a second injector 115 for the treatment of the face opposite of the tablecloth. This is placed on a metal cylinder 120, driven in rotation about an axis perpendicular to the direction of travel of the web; the cylinder is porous and covered, for example, with a fine metallic fabric. The needle injector 115 is placed along a generator of the cylinder. The injectors 105 and 115 are supplied by a high pressure pump, not shown.

A suction box 125 is placed inside the cylinder and collects the water coming from the injector 115. The sheet is guided around the cylinder of so as to pass to the right of the jets for rinsing, then is taken up by the conveyor. It is brought to a slot with high depression for the expression of liquids, before being dried in a hot air oven, for example as in previous installation. Finally the tablecloth is taken up to be, for example, cut and assembled.

Tests were carried out on a cotton ply of 250 g / m ² formed from a central ply by pneumatic route, framed by two isotropic card webs. This sheet was previously bleached and dried according to a process of the prior art.

The thickness of the sheet is 4.5 mm measured under a load of 5 g / cm ² . It still contains surfactants in small quantities which we highlight by measuring, according to the methods recommended by the French Pharmacopoeia, 10th edition, the height of the foam formed, and by determining its rate of substances soluble in water. . For the sheet used in the test, these values were 1 mm and 0.3% respectively.

Influence of energy on the thickness of the product at the end of the process:

After passing under the water jets, at a running speed set at 30 m / min., The supply pressure of the needle injector of which was varied from 0 to 50 bars, corresponding to energies of 0 to 57 kwh / T and water flows from 8.9 to 42 m3 / T, the thickness of the water table was measured under a load of 5 g / cm ² , the values are plotted on a graph ( see figure 2). It can be seen that the thickness of the sheet remains substantially constant, up to an energy of around 40 kWh / T, then it begins to drop.

Treatment effectiveness:

We passed the tablecloth under the water jets, at a running speed set at 30 m / min. The needle injector supply pressure was varied from 0 to 50 bars, corresponding to energies from 0 to 57 kwh / T and flow rates of water from 8.9 to 42 m3 / T. We verified the existence of residual products according to the Codex methods by measuring foam height and level of substances soluble in water these values have been plotted on a graph, cf. figure 3. with in abscissa, the flow of water related to the ton of product treated, and on the ordinate, of a firstly the height of the foam in mm, secondly the rate of soluble substances in water as a percentage of the weight of cotton.

We note that the foam height is brought to 0 mm from 8.9 m3 / T, i.e. 2.2 kwh / T, and that the rate of soluble matter is reduced simultaneously to 0.1%.

Influence of energy on the direction of resistance of the water table:

• vitesse d'écartement des machoires de l'Instron : 100 mm/min ;
• largeur de l'éprouvette : 50 mm ; et
• longueur de l'éprouvette : 100 mm.

The sheet of 250 g / m ² was passed under the water jets, one injector per side, at a running speed set at 30 m / min., And the supply pressure of the injector-needles from 0 to 50 bars, corresponding to energies from 0 to 57 kWh / T and water flows from 8.9 to 42 m3 / T. We tested its resistance in the running direction, in newton, for increasing energy values by pulling on test pieces, cut from the sheet, until their rupture, on an INSTRON device. The characteristics of the test are as follows:

• spacing speed of the Instron jaws: 100 mm / min;
• width of test piece: 50 mm; and
• length of test piece: 100 mm.

These values have been plotted on the ordinate on a graph (cf. FIG. 4), with on the abscissa the energy in kwh / T, energy related to the ton of product treated.

We note that the direction-of-use resistance progresses little up to 25 kwh / T and then increases.

Energy influence on cross resistance:

We proceeded as before, we measured the cross direction resistance, in Newton, and we have plotted these values on a graph (see Figure 5).

We note that the cross direction resistance increases appreciably up to 4.4kwhfr then weakly up to 25.6 kwh / T, to increase again substantially up to 57 kwh / T.

Influence of energy on the delamination resistance of the surface veil:

We take into account the fact that the sheet is laminated, of the type manufactured according to patent application FR-A-2 701 039 mentioned above. We treated the tablecloth by water jets as before. We measure the force necessary to separate one of the surface veils of the central layer. The test is carried out on a device INSTRON. The characteristics of the test are the same as before:

The values of the resistance to delamination, expressed in centi-newton, have been plotted on the ordinate on a graph with the different abscissas energy values of the jets with which the water table has been treated (see Figure 6).

It can be seen that the resistance to lint increases very appreciably at from 15 kwh / T.

Thus, with these tests, it is shown that the method of the invention makes it possible to obtain an effective rinsing, without modifying the structure of the sheet while controlling the improvement in its resistance. For the manufacture of cotton wool packets, an energy level of between 2 and 10 kwh / T is chosen and a flow rate preferably between 8 and 22 m ³ per tonne of product treated. For the manufacture of products of the make-up removing pads type which must have a certain resistance, the mechanical resistance of the sheet is increased by positioning preferably between 10 and 40 kwh / T, the flow rate being between 8 and 37 m ³ per tonne of product treated.

The values of the measurements carried out are reported in the table below.

Claims (7)

1. Process for treating natural cellulose fibres, in particular cotton fibres, comprising the steps of depositing fibres on a continuously moving cloth to form a 100 to 800 g/m² lap, of impregnating with a treatment solution, treating, then rinsing it with an aqueous liquid, characterized in that rinsing is carried out by applying the said liquid in the form of jets directed towards one face of the lap perpendicularly to its direction of motion with an energy value of 2 to 60 kwh per tonne of product treated.
2. Process according to claim 1, in particular for the manufacture of packaged hydrophillic cotton, characterized in that the quantity of energy is between 2 and 10 kwh per tonne of product treated.
3. Product according to claim 2, characterized in that the flow rate is between 8 and 22 m³ per tonne of product treated.
4. Process according to claim 1, in particular for the manufacture of cosmetic removal pads or other similar product, characterized in that the level of the said energy is between 2 and 40 kwh/T, preferably between 10 and 40 kwh/T.
5. Process according to claim 4, characterized in that the flow rate is between 8 and 37 m³ per tonne of product treated.
6. Process according to one of the preceding claims, characterized in that the jets are also applied to the face opposite the said face.
7. Process according to one of the preceding claims, characterized in that up to 30 % of synthetic fibres are incorporated in the said lap.

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