EP0805888A1

EP0805888A1 - Process for processing a cellulose fiber lap

Info

Publication number: EP0805888A1
Application number: EP96903044A
Authority: EP
Inventors: Jean-Louis Neveu; Bernard Louis Dit Picard
Original assignee: Individual
Current assignee: Essity Operations France SAS
Priority date: 1995-02-03
Filing date: 1996-02-02
Publication date: 1997-11-12
Anticipated expiration: 2016-02-02
Also published as: DE69601782D1; CA2212137C; ES2128833T3; ATE177796T1; GR3030204T3; WO1996023922A1; FR2730248B1; FR2730248A1; CA2212137A1; US5771517A; EP0805888B1; DE69601782T2

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

PROCESS FOR TREATING A TABLE OF CELLULOSIC FIBERS

The invention relates to a method of treating a web of natural fibers such as cotton fibers and is aimed in particular at the step during which the fibers are rinsed to remove the chemicals with which the web has previously been impregnated for its treatment.

For the preparation, for example, of hydrophilic cotton from unbleached cotton, the leaves, twigs or other foreign matter coming from the picking are first removed by mechanical means. Next, the fibers of their sheath of waxy and fatty materials are stripped by a chemical scouring treatment consisting in impregnating a sheet formed with the unbleached fibers by means, for example, of a soda-based liquor which is put in react by heating in a vaporizer. After treatment, the sheet is neutralized and then rinsed with water. Depending on requirements, it may be necessary to bleach the fibers and / or size them. For bleaching, the fibers are brought into contact with a solution of hydrogen peroxide which is left to act under an appropriate temperature before neutralizing and rinsing the fibers again with water. Scalding and bleaching can be carried out in batches in tanks containing the liquor. However, continuous processing methods have been developed in recent years with the aim of reducing costs when it comes to producing hydrophilic cotton in large quantities. Thus the Applicant has developed a continuous process making it possible to obtain a sheet having a certain cohesion which it is possible to use as it is in certain applications - cotton in packets, dressings or cosmetic pads for example - without having to rework mechanically the tablecloth, that is to say shred it to card it or put it in a tablecloth in another way, again.

Such a process has been described in patent application FR 90 04647. In this process, the steps of impregnation with the different liquors for scouring, bleaching or neutralizing rinsing, respectively, are carried out by pouring onto the sheet in the form liquid slides under conditions which allow both control of the quantity of liquid carried by the sheet and a uniform impregnation thereof. The general efficiency of the process is improved as well as the quality of the material after treatment, the characteristics of which vary little from one production to another. The application of a liquid in this form ensures at the same time a certain consolidation of the sheet, in particular due to the energy of the liquid communicated to it.

Attempts have been made to improve this process, in particular the efficiency of rinsing, since large amounts of water are required to remove the products. chemicals, in particular the surfactants necessary during the initial phase of impregnating unbleached cotton. Rinsing before refining or before final drying is particularly important in this respect because it is desirable to reduce the level of residual products as much as possible, in particular because of the Codex. In addition, in a constant concern to maintain and if possible improve the quality of the products without increasing costs, rinsing must not alter the mechanical characteristics of the sheet during treatment. 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 hydrophilic cotton or make-up removing pads.

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 liquor for treatment, for treatment, then for rinsing 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 a face of the sheet perpendicular to its direction of travel and communicating with the water table has an energy of between 2 and 100 h per tonne of product treated. The jets are produced by injectors as used in the hydrodynamic nonwoven bonding technology. each injector comprises, for example, an elongated chamber, closed over its length by a perforated plate, in one or more rows, with a large number of small diameter holes, of the order of 100 μm. The chamber is supplied with pressurized liquid which escapes through the orifices in the form of parallel fine jets of corresponding diameter; Thus, in one embodiment of the invention, an injector composed of 2 rows of 120 μm diameter holes, 0.6 mm apart, dissipate an energy from 2 to 58 h T, and distribute a quantity of rinsing water , respectively, from 9 to 41 m 3 per tonne of product treated. These energies correspond to injector use pressures 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

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 from 30 to 50%. These two indicators are representative of the residual quantity of treatment products. - As 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 make-up 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 using a 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 jet treatment produces a reinforcement of the sheet 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 93 00928.

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

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

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

According to another characteristic, the jets are also applied to the face opposite the first. A product is thus obtained, the surface condition of which is the same on both sides; it is symmetrical.

According to another characteristic of the invention, up to 30% of synthetic or artificial fibers are incorporated into the sheet. These fibers are advantageously mixed with the cellulosic fibers before the start of the treatment. They can be any fibers known per se in the field of woven or non-woven textiles. 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 - FIG. 1 schematically represents an installation for continuous scouring and bleaching of fibers cotton according to the teaching of the prior art.

- Figure la shows the detail of the rinsing station according to the invention.

- Figure 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.

- Figure 3 is a graph representing the influence of the flow rate, reduced to the ton of product treated, on the height of foam H, in mm, and the rate of soluble matter S, in percentage relative to the fibers. - Figures 4 and 5 are graphs representing the influence of the amount of energy, reduced to the ton of product treated, applied to the water table by the water jets, on the tensile strengths in running direction, respectively direction through 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 93 03964.

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 93 00928 or FR 93 03964 where it comprises two layers formed of card webs on either side of a central layer obtained by pneumatic means. A sheet of 100 to 800 g / m ^{2 is} thus deposited according to the application envisaged on the canvas of a conveyor which drives it at a constant and determined speed, for example of 30 m / min. to an impregnation station 4. This may be of the type described in patent application FR 90 04647 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 led to a vaporizer 5 heated to a temperature close to 100 ° C. where it remains, while remaining continuous thanks to an appropriate storage means, for the time necessary for the reaction. This depends on the liquor and the rate of carrying. Then. The tablecloth is rinsed, and the boiling juice is extracted at the following station 6.

If the fibers are to be bleached, the hydrophilic scoured sheet is impregnated at 8 with a bleaching solution comprising, for example, hydrogen peroxide, then the sheet is again introduced into a vaporizer 10 heated to a temperature close to 100 ° C in which it remains for a sufficient time for the bleaching to be effective.

Rinsing and neutralization are then carried out at 12 to remove all traces 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 following step or before drying, to sizing the fibers by any means known to those skilled in the art. The tablecloth resulting from the process can be used directly for the manufacture of hydrophilic cotton or any other application in which the 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, generally water, such as those used in the techniques for manufacturing nonwovens by hydraulic needling of the fibers, well known in the field under the designation "jetlace". We could, for example, use an installation provided by the company PERFOJET.

Thus, the station 100 for rinsing with water jets, represented in FIG. 1a, comprises a needle injector 105 disposed across the sheet and which applies jets of water at high pressure on its surface. The water jets are small, 120 μm, 0.6 mm apart and arranged in two parallel rows spaced apart from each other. The liquid passes through the sheet and the permeable support fabric. It is sucked through a transverse slot parallel to the line of jets communicating with a suction box 110. In the example shown, the installation comprises a second injector 115 for treating the opposite face of the sheet. This is deposited on a metallic cylinder 120, driven in rotation about an axis perpendicular to the direction of travel of the sheet; the cylinder is porous and covered, for example, with a fine metallic fabric. The needle injector 1 15 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 so as to pass in line with the jets for rinsing, then is taken up by the conveyor . It is brought to a high vacuum slot for the expression of liquids, before being dried in a hot air oven, for example as in previous installation. Finally the sheet 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 are highlighted 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 leaving the process: After passing under the water jets, at a running speed set to

30 m / min., The supply pressure of the needle injector of which has been varied from 0 to 50 bars, corresponding to energies from 0 to 57 kwh / T and water flows from 8.9 to 42 m3 / T, the thickness of the sheet was measured under a load of 5 g / cm ² , the values were plotted on a graph (cf. FIG. 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:

The sheet was passed under the jets of water, at a running speed set at 30 m / min. The supply pressure of the needle injector was varied from 0 to 50 bars, corresponding to energies from 0 to 57 kwh / T and water flow rates from 8.9 to 42 m3 / T. We verified the existence of residual products according to Codex methods by measuring the height of foam and the rate of substances soluble in water, we plotted these values on a graph, cf. Figure 3. With the abscissa, the water flow rate per tonne of product treated, and on the ordinate, on the one hand, the foam height in mm, on the other hand, the percentage of water-soluble substances in percentage. relative to the weight of the cotton.

It can be seen that the height of the foam is brought to 0 mm from 8.9 m3 / T or 2.2 kwh / T, and that the rate of soluble material is reduced simultaneously to 0.1%. Influence of the energy on the direction of resistance of the water table: The water table 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 was varied 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 values of energy by pulling on test pieces, cut from the sheet, until they break, on an INSTRON device. The characteristics of the test are as follows:

- speed of spacing of the jaws of the Instron: 100 mm / min; - width of the 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 the energy in kwh / T on the abscissa, energy referred to the tonne of product treated.

It is noted that the resistance in the running direction progresses little up to 25 kwh / T and then increases.

Energy influence on cross resistance:

We proceeded as before, we measured the resistance crosswise, in newton, and we plotted these values on a graph (cf. figure 5).

It is noted that the cross direction resistance increases appreciably up to 4.4 kwh / T then weakly up to 25.6 kwh / T, to increase again appreciably 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 93 00968 mentioned above. The water table was treated with water jets as above. The force required to separate one of the surface veils from the central layer is measured. 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, on the abscissa, the different values of the energy of the jets with which the water table has been treated (cf. FIG. 6).

It can be seen that the resistance to fluff increases very appreciably 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 of 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 ^ 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 π by ton of product treated.

The values of the measurements carried out are reported in the table below. TABLECLOTH 250 g / m ² SPEED OF 30 mmn WITH 2 INJECTORS - 1 PER SIDE

ΔP by ENERGIE Deb injector. rsm water. min rsm. nuxi RSM rst. mini rst. max RST. EP./5G EP./20G Weight WEIGHT SS.EAU Bar K-vh / T 3 tonne NNNNNN mm mm g / m ¹ H, mm S.%

0 0 6.8 12.2 9.4 6 7.7 6.4 4 2.4 248 1 0.28

5 2.2 8.9 7.5 10.4 9.1 6.8 8.9 8.1 4.8 3.1 272 0 0.11

10 4.4 18.6 8.1 13.9 10.9 7.9 10.9 9.5 4.4 4,274 0 0.11

15 9.8 21.9 11 9.2 4.5 0 0.12

20 15.2 25.3 10.5 15.1 13 8.6 10 9.3 4.4 3.9 277 0 0.14

25 20.4 28.6 10.8 13.8 12.3 9.5 10.3 9.9 4.6 3.7 269 0 0.13

30 25.6 32 13.2 17.6 15.2 9.8 13.8 M.2 4.5 3.6 264 0 0.12

35 32.8 34.4 15.2 24.9 21.8 9.1 12.2 10.9 4.7 3.9 271 0 0.12

40 40 36.9 22.1 28.6 24.6 10 16.4 13.8 4.4 3.3 270 0 0.11

45 48.4 39.1 27 35.9 29.3 12.4 15.9 14 4.3 3.7 256 0 0.11

50 56.8 41.3 32.6 48.4 40.1 15.7 19.9 18.7 3.5 3.1 252 0 0.09

rsm: resistance in running direction

RSM: average resistance in direction of travel rst: resistance in cross direction

RST: average resistance cross direction

EP: thickness under a load of 5g / cm ² respectively 20 g / cm ²

Claims

1) Process for treating natural cellulosic fibers, in particular cotton fibers, comprising the steps of depositing the fibers on a canvas in continuous movement to form a sheet of 100 to 800 g / m ² , of impregnation with a treatment solution , of treatment, then of rinsing 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 a face of the sheet perpendicular to its direction of travel with an energy of 2 to 60 kh per tonne of product treated.

2) Method according to claim 1, in particular for the manufacture of packaged hydrophilic cotton, characterized in that the amount of energy is between 2 and 10 kWh per ton of product treated.

3) Method according to claim 2, characterized in that the flow rate is between 8 and 22 m3 per tonne of product treated.

4) Method according to claim 1, in particular for the manufacture of make-up removing pads or other similar product, characterized in that the level of said energy is between 2 and 40 kwh / T, preferably between 10 and 40 kwh / T. 5) Method according to claim 4, characterized in that the flow rate is between 8 and 37 m3 per tonne of product treated.

6) Method according to one of the preceding claims characterized in that the jets are also applied to the face opposite to said face.

7) Method according to one of the preceding claims, characterized in that up to 30% of synthetic fibers are incorporated into said sheet.