EP0504368B1 - Hydraulically bound nonwoven and manufacturing method thereof - Google Patents

Abstract

PCT No. PCT/FR91/00783 Sec. 371 Date Jun. 8, 1992 Sec. 102(e) Date Jun. 8, 1992 PCT Filed Oct. 4, 1991 PCT Pub. No. WO92/06237 PCT Pub. Date Apr. 16, 1992.The invention relates to a method for forming a hydraulically bound web. A homogeneous mixture of wood pulp and synthetic fibers is blown on a forming surface. The web has a mixture of at least 70% wood pulp by weight of the mixture. The web is subjected to hydraulic bonding to form a stable fabric. The web is further heated to a temperature to cause partial melting of the synthetic fibers and further bonding of the fabric.

Description

The invention relates to an absorbent nonwoven product consisting mainly of short absorbent fibers, such as wood pulp fibers, and of longer synthetic fibers, the nonwoven being obtained by hydraulic bonding.

According to a common technique for manufacturing products based on paper fibers, a suspension of fibers in water is produced from which a sheet is formed. Depending on the nature of the fibers and the treatment of the sheet, various qualities of paper are obtained, including cellulose wadding. This one finds many applications like household paper, for the care of the body, the wiping, etc. However, the cellulose wadding presents a weak mechanical resistance especially in the wet state which does not allow its application in the field of industrial or household wiping for example.

According to another technique, known as the dry method, as described for example in patent GB 2015604 (KROYER), the fibers are suspended in a gas flow, and they are deposited in a sheet on a permeable fabric. The low humidity does not allow the constitution of interfiber bonds, it is necessary to add a binder, generally a latex, to ensure the cohesion of the sheet. This produces a product with better tear resistance than traditional paper while being very absorbent. This product has substantially the same applications as the latter. However, the incorporation of a binder such as latex has drawbacks. For example, it increases the rigidity of the product and can react chemically with the fluids with which it is likely to come into contact. This is particularly the case when it is desired to make wipes impregnated with a liquid such as toilet milk or the like.

Instead of using a binder of a chemical nature, it has been proposed to incorporate, into the sheet of absorbent fibers, thermoplastic synthetic fibers which perform the function of binder by thermal activation. Thus for example patent application EP 070164 (CHICOPEE) describes a thermally bonded absorbent nonwoven whose density is low, less than 0.15 g / cm3 (0.06 g / cm3 according to the examples reported), and composed of absorbent fibers of the papermaking type mixed with synthetic fibers conjugated to two components: polyethylene and polyester. The manufacturing process consists in preparing a sheet from a homogeneous mixture of absorbent fibers and conjugated fibers; then subjecting it to a heat treatment in the mass, under low pressure, at a temperature sufficient to melt the polyethylene located on the surface of the synthetic fibers but not the polyester. In this way, after cooling, a low density nonwoven is obtained, the synthetic material component of which has retained its fibrous character. The fact that synthetic fibers retain their integrity is an important factor according to the patent for obtaining a product of high mass volume, with high absorption capacity. The envisaged applications consequently aim to use in particular as an absorbent body in hygiene articles, periodic towel for example. However, a consolidation post-treatment (calendering, embossing), or the association with another more resistant veil, seems necessary if one wishes to use this nonwoven in an application such as wiping where the mechanical stresses are great.

Patent application EP 0326771 (JAMES RIVER) describes an absorbent and resistant nonwoven, composed of wood pulp fibers and textile fibers, free of any binder. This nonwoven is produced from one or more veils, previously formed by the wet method using the papermaking technique, and consisting of a homogeneous mixture of fibers containing 50 to 75% by weight of wood pulp and 25 to 50% by weight of synthetic fibers of textile length. The veil (s) have also been subjected to a binding treatment by water jets, known per se, with sufficient energy to form a relatively dense, uniform nonwoven fabric, with good cohesion of the fibers between them.

We also know the patent US 4442161 (KIRAYOGLU) which relates to a process for manufacturing a nonwoven bonded by water jets, consisting of synthetic fibers and wood pulp. The binding is carried out in particular from synthetic fibers in the form of a nonwoven veil of continuous filaments and wood pulp fibers in the form of a sheet. of paper. The treatment is carried out under conditions which make it possible to increase the liquid barrier properties of the nonwovens with a view in particular to an application as a linen for medical or surgical use.

US Patent 3620903 relates to a light nonwoven of the type bound by water jets, comprising at least 20% of synthetic fibers and up to 80% of paper fibers. It is noted that the grammage of the product is a maximum of 57 g / m ² and that it is intended for a textile application. This product compares favorably in terms of resistance, appearance and drape with conventional textiles for clothing items.

Patent EP 171 806 relates to a nonwoven, comprising at least 10% of conjugated fibers, bound by water jets and having undergone heating up to the partial melting temperature thereof. The other fibers can be any, synthetic or natural, short or long (6 to 50 mm).

The invention relates to a method of manufacturing an absorbent nonwoven consisting of wood pulp fibers and synthetic fibers, using a binding treatment using water jets. The invention is characterized in that the binding treatment by water jets is carried out on a sheet, consisting of a homogeneous mixture of unbound fibers of wood pulp and synthetic fibers, hot-melt at least in part and of length less than 20 mm, formed by air flow and in that the nonwoven is then subjected to heating at a temperature sufficient to cause at least partial fusion of the synthetic fibers.

In fact, unlike the prior art which consists of nonwoven sails having undergone a prior binding, it has been found that, by applying the process of the invention, it is possible to obtain a product having good breaking strength characteristics. , both wet and dry, and absorption speed.

The formation of the web is ensured by any conventional method known to those skilled in the art. It consists in preparing metered quantities, on the one hand of synthetic fibers by opening and individualizing them, on the other hand of paper fibers obtained by dry defibration of paper pulp; then driving them by air, suspended in an air flow in a cyclone type mixer for example. The homogeneous mixture resulting from the latter is then entrained, still in suspension in an air flow, towards a head for forming the sheet from which the fibers are deposited uniformly on a support fabric traveling at a determined continuous speed.

The mixture produced will preferably comprise at least 70% by weight of wood pulp fibers, the remainder consisting of synthetic fibers. An advantageous mixture will be composed of 70 to 90% by weight of wood pulp fibers and 30 to 10% of synthetic fibers. If you introduce too little fiber synthetic in the mass of wood pulp fibers, it is difficult to obtain a homogeneous dispersion, and the grammage of the tablecloth lacks regularity. In addition, the subsequent binding is not carried out satisfactorily. Synthetic fibers can be of various natures; they will preferably have a length less than 20 mm and a titer between 1.2 and 3.3 dtex.

The binding treatment by water jets is also known per se to those skilled in the art. An example of a process is described in patents US 3,485,706 (EVANS) or US 3,560,326 (BUNTING). It consists in passing through fine jets of high energy liquid through the fibrous sheet to be treated which is arranged by a support, in horizontal displacement, consisting of a perforated plate or else of a suitably chosen woven fabric. The intertwining of the fibers produced by the action of the water jets, leads to consolidating the sheet and gives it a textile appearance.

The process allows the production of a nonwoven having a basis weight between 20 and 200 g / m ² , preferably it will be 40 to 100 g / m ² . In fact, the upper limit will depend on the ability of the water jets to cross the sheet and interleave the fibers.

The tear resistance is improved by choosing thermoplastic synthetic fibers, and by subjecting the nonwoven, originating from the hydraulic bonding station, to a thermal bonding treatment by which the thermoplastic fibers are melted, partially at least, and ensure, after cooling , the formation of bonding zones between the fibers. Advantageously, these fibers are two-component fibers of which the one with the lowest melting point is at the surface. The heating temperature is determined so as to be sufficient to melt that of the two components which is at a lower melting point but not the other. These fibers thus allow a lower thermobonding temperature and the fibrous structure is preserved.

The process therefore makes it possible to obtain a product having a textile appearance, absorbent, resistant to tearing, and therefore the surface does not tend to fluff. It can be used as a disposable or short-term product, as a household, industrial wiping cloth or in catering. By its absence of any chemical binder, it can serve as a support for impregnating liquids: toilet milk, lanolin, wax, etc., and can be used as an impregnated wipe. It can also be used in the medical, surgical, or hygienic field, if necessary, it is possible to subject the nonwoven to a chemical or mechanical softening post-treatment.

Other characteristics and advantages will appear in the following description of a non-exhaustive embodiment of the invention with reference to the drawings in which:

FIG. 1 represents an installation allowing the implementation of the method of the invention.

Figures 2 and 3 are graphs illustrating the tensile strength of nonwovens obtained according to the method of the invention.

FIG. 4 is a graph illustrating a comparative test with a dry bonded nonwoven by latex and a thermally bonded nonwoven.

The installation shown in Figure 1 comprises a receiving station for synthetic fibers (2) with a loader to feed a card (4) necessary when the fibers must be opened. The card itself feeds a mixer (5) which can be of the cyclone type. The mixer is also supplied with wood pulp fibers from a station (3) for dry defibering of paper pulp which is delivered in the form of sheets in a roll. The fibers, intimately mixed in the cyclone, are suspended in an air flow which carries them towards a head for forming the sheet (6).

It may be a device of the type described in patent application EP 032772 (SCANWEB), or an equivalent device. This consists of two rotary cylinders (61,62), parallel, perforated wall, and arranged transversely relative to an endless receiving fabric (8), which is itself permeable to air. Inside each cylinder, there is a rod (63) for stirring the fibers provided with fins rubbing against their internal wall when they are rotating. The fluidized fibrous material is introduced inside the cylinders (61, 62) by one end, and is sucked through their perforated wall by a depression generated by a vacuum box (10) disposed under the receiving fabric (8 ) opposite the training head (6). The stirring rods ensure the progression of the mass of fibers axially inside the cylinders, and help in the division of the aggregates possibly formed as well as in the passage of the fibers to the through walls. Sheets (65,66), arranged on either side of the cylinders, channel the gas flow towards the fabric (8). The fibers are thus received on the movable fabric in a continuous sheet which is entrained towards the binding station by water jets (20).

This station comprises an endless cloth (21) stretched horizontally between rollers (22), at least one of which is driven by suitable means. The mesh of the canvas, made of metal or plastic threads, is chosen in particular according to the texture, open or not, desired for the nonwoven; a perforated continuous sheet is also suitable. The canvas conveys the sheet through a set of ramps of water jets oriented transversely to its direction of movement. The number of ramps depends on the chosen stage of pressures. In the example produced on equipment supplied by the Perfojet Company, there are four. The water jets are produced from tubular distributors (24,26,28,30), arranged across the top of the fabric. Each distributor feeds a ramp of 40 to 60 injectors consisting of a plate pierced with calibrated orifices. The distributors are supplied with pressurized water and deliver high energy water jets on the fibrous web. After having dissipated its energy through the tablecloth, the water is recovered by suction boxes (25,27,29,31) arranged under the fabric opposite each ramp.

The sheet, after having been tied, is wrung by passage over vacuum slots and is then drawn to a drying device (40). The one shown in the figure is a through-blowing oven, the temperature of the heating gas of which can be adjusted so as to be able to ensure, in addition to drying, if necessary, the melting of the thermoplastic fibers contained in the sheet.

EXAMPLE 1

"Danaklon ESF" :

bicomposants PE/PP, type side/side, frisée longueur 12mm, titre 3,3 dtex

"Danaklon ESHF" 6mm :

bicomposants PE/PP, type side/side, frisée longueur 6mm

"Danaklon ESHF" 12mm :

bicomposants PE/PP, type side/side frisée longueur 12mm.

Nonwovens were produced according to the process of the invention with mixtures at different levels of synthetic fibers (Table I). TABLE I MIXTURES AT B VS D E F Wood pulp: "ITT Rayonier JLD" not treated 80% 70% Vigor 90% 80% 90% 80% Synthetic fibers: "Danaklon ESF" 12mm 20% 30% "Danaklon ESHF" 6mm 10% 20% "Danaklon ESHF" 12mm 10% 20%

"Danaklon ESF":

two-component PE / PP, side / side type, curly length 12mm, title 3.3 dtex

"Danaklon ESHF" 6mm:

two-component PE / PP, side / side type, crimped length 6mm

"Danaklon ESHF" 12mm:

two-component PE / PP, curly side / side type, length 12mm.

After having put the different mixtures A to F in the form of sheets, as indicated above, their bonding was carried out by water jets followed by a thermal bonding. The conditions of this binding are reported in Table II below: Table II Support canvas: Metal grid (the texture and the diameter of the metal wires ensure better interlacing of the sheet) Scrolling speed under the injectors: 25 m / min Injectors: 4 injector pumps Orifice diameter: 100 - 140 µm Water jet pressure: 30/50/70/90 bars for mixture A measured at the supply line 30/60/80/100 bars for mixtures B 30/40/60/80 bars for mixtures C and E Air temperature in the hot air oven 145 to 150 ° C

The heating conditions in the oven were chosen so as to allow the drying of the nonwoven and the melting of the polyethylene of the synthetic fibers but not that of the polypropylenes In this way, the latter have retained their integrity, while ensuring the bonding of the fibers which are in contact with them.

The breaking strength and absorption characteristics of the nonwovens obtained according to the method were measured. They are reported in Table III below:

The measurements were made according to EDANA standards. For example, the test for measuring the breaking strength 20.2-89 consists in subjecting the nonwoven to a tensile force at constant speed (100 mm / min) and in measuring the maximum load before breaking. The elongation corresponds to the extension of the sample measured at this point. The absorption capacity measurement test 10.1-72 consists in measuring, on the one hand, the time necessary for a nonwoven to be completely impregnated with a liquid, and on the other hand, the quantity of liquid absorbed during a determined time reduced to the weight of the nonwoven.

It should be noted that other fibers, than those retained for the example, are conceivable. Among the two-component fibers of the S / C (sheath / core) type, mention may be made of polyethylene / polyester fibers such as those sold under the brand name CELANESE reference K 56 (uncrimped, 10 mm, 2.2 dtex) or else under the SOLSTAR brand (uncrimped, 10 mm, 2.2 dtex) or Polyester / polyester fibers as sold under the brand DUPONT reference 271P (uncrimped, 12 mm, 2.2 dtex) or under the brand UNITIKA reference Melty ( crimped, 10-15 mm, 1.5 / 2 dtex) or polyethylene / polypropylene fibers as sold under the brand DAIWABO reference NBF (uncrimped, 10 mm, 2 dtex). Among the fibers of the S / S type (side / side), mention may also be made of polyethylene / polypropylene fibers sold under the brand DAIWABO under the reference ESF (crimped, 6 mm, 3.3 dtex). Among the single-component fibers, one can note a polyethylene fiber sold under the brand STEEN reference Polysteen (uncrimped, 12 mm, 2.8 dtex).

EXAMPLE 2

From each of the mixtures A and B of the previous example, three different nonwovens, hydraulically linked, were produced.

For the first case, drying was carried out at moderate temperature so as to remove the water without modifying the structure of the fibers (tests E21A and E21B).

In the second case, the nonwoven from the binding by jets of water was also calendered at moderate temperature (tests E22A and E22B).

In the third case, the conditions of Example 1 were reproduced (tests E23A and E23B).

The graphs in FIGS. 2 and 3 representing the breaking strength of a 5 cm wide (gf / 5 cm), direction of travel (SM) and cross direction (ST) specimen, both in dry and in wet conditions show a very clear improvement by heat treatment up to the melting temperature.

EXAMPLE 3

Comparative tests were carried out on three nonwovens of the same grammage. The first E31 is a dry type product, the bond between the fibers was obtained by spraying with latex. The nonwoven contains 20% by weight of binder. The second E32 is a nonwoven, of the dry process type bonded by embossing, with a binder consisting of DANAKLON ESF thermoplastic fibers (see example 1) at a rate of 20%. The third E33 is a product produced under the conditions of Example 1 with mixture A.

It can be seen in the graph in FIG. 4, representing the tensile strength in the running direction (SM) and transverse direction (ST), both in dry and in wet conditions, that the process of the invention leads to much more efficient.

EXAMPLE 4

A comparative absorption-retention-resilience test was carried out between the nonwovens of Example 1 obtained from mixtures D, E and F according to the process of the invention and a dry nonwoven bonded with latex (15%) as sold under the brand HOMECEL reference P050.

The test consisted in particular in placing a sample on an absorption plate made of porous sintered glass through which it is moistened. The tray is connected by a flexible tube to a tank placed on a scale, and it can be moved along a vertical rail. The measurements are taken from the weight indications by the balance, the absorption capacity of the sample of which can be calculated in grams of liquid per gram of sample, after a determined time, and also the speed of initial absorption.

For retention, the frit is moved along the rail so that the sample releases the liquid, due to the pressure negative created by the difference in level between the frit and the tank. Table IV PRODUCTS MIX D MIX E MIX F HOMECEL Weight 75.2 72.3 68.4 50.2 Dry bouffant (cc / g) 9.4 9.9 9.3 15.2 Absorption (g / g) 7.3 7.3 7.3 9.4 Initial absorption rate (100 xg / g / sec) 186 217 230 175 Retention (g / g) 4.38 4.44 4.40 5.56 Absorption at 10 kPa (g / g) 5.1 5.1 5.2 4.9 Reabsorption (g / g) 5.9 6.0 6.0 6.8 Resilience% 17.6 16.1 16.0 30.9 Compression% 31.3 33.5 30.9 54.8

This test reported in Table IV shows in particular that the product has an excellent initial absorption rate.

Claims (4)

1. Process for manufacturing an absorbent nonwoven consisting of wood pulp fibres and no more than 30 % synthetic fibres using a known binding treatment by means of water jets, characterized in that the binding treatment by means of water jets is carried out on a lap, consisting of a homogeneous mixture of unbound wood pulp fibres and at least partly of heat fusible synthetic fibres with a length of less than 20 mm, formed by an aeraulic process and in that the nonwoven is then subjected to heating at a temperature sufficient to bring about at least partial fusion of the synthetic fibres.
2. Process according to one of the preceding claims characterized in that the synthetic fibres comprise bi-component fibres.
3. Process according to one of the preceding claims characterized in that the nonwoven has a grammage of between 20 and 200 g/m², and preferably 40 to 100 g/m².
4. Process according to claim 2 characterized in that the temperature is sufficient to bring about fusion of the component which has a lower fusion temperature but not the other component.

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