EP0524268B1 - Process for impregnating a textile fabric - Google Patents

Abstract

PCT No. PCT/FR91/00290 Sec. 371 Date Dec. 9, 1992 Sec. 102(e) Date Dec. 2, 1992 PCT Filed Apr. 10, 1991 PCT Pub. No. WO91/05622 PCT Pub. Date Oct. 17, 1991.The procedure for impregnating a woven or non-woven, knit, fiber sheet with an aqueous liquid, in particular of the kind containing a treatment agent, is characterized in that it consists of: (i) depositing the sheet 6 on a liquid-permeable, endless cloth 4, (ii) pouring by gravity the liquid in the form of a curtain or lamina onto the sheet and transversely to the direction of advance of this sheet, (iii) generating by means of a vacuum slit 13 mounted underneath the cloth sufficient pressure drop that at least part of said liquid shall pass through the sheet, the rate of poured liquid as defined in relation to the weight of the sheet moving underneath said curtain exceeding a specific value beyond which the entrainment rate is a function of said pressure drop but independent of the amount poured so as to make possible homogeneous impregnation and easy control of the entrainment rate.

Description

The invention relates to a method for continuously impregnating a fibrous web, such as a fabric. a knit or nonwoven, made of natural, synthetic, or artificial fibers. pure or mixed, unbound or bound. with an aqueous liquid, in particular of the type containing a treatment agent. latex, primer. dye. etc. and relates in particular to the impregnation of an unbleached cotton tablecloth with a view to a treatment, for example of scouring and / or bleaching.

The chemical treatment of unbleached cotton fibers begins with the scouring which consists, after opening and mechanical cleaning. to remove the sheath of waxy and fatty materials which envelops them, so as to make them hydrophilic. After rinsing and expressing, the chemical treatment is generally completed by a bleaching operation. So that until recently, the treatment of cotton was carried out in batches, discontinuously, we now seek to carry out all operations continuously, that is to say, to form a continuous sheet and convey cotton on a carpet through a succession of stations in which it is subjected, one after the other, to all the stages constituting its treatment.

One of the difficulties encountered with this type of process lies in carrying out the impregnation of the sheet with the various liquors. The quality of the finished product depends on the quality of the impregnation.

First of all, it involves incorporating a certain amount of scouring agent, for example soda, into the sheet, which is then reacted by heating in the vaporizer. In order for the scouring to be of maximum efficiency, it is desirable that the sheet is impregnated in a homogeneous manner with a controlled quantity of liquor. Indeed, the reaction time, the efficiency and the final properties depend on it. Furthermore, for all the fibers making up the sheet to be treated in a uniform manner, the impregnation must itself be homogeneous. Finally, it is desirable that the means of applying the liquid disturbs the organization of the fibers as little as possible, in order to obtain, at the end of the treatment, a product which can if necessary be used as which without having to rework the tablecloth.

The means known to the applicant do not allow these objectives to be achieved.

Thus, for example, it is possible to spray the treatment liquid on the moving sheet, by means of ramps of fluid jets. However, unless there is a high pressure of the jets which then modify the structure of the sheet, this development has the drawback of not allowing satisfactory wetting of the sheet if the fibers are not hydrophilic - which is the case. unbleached cotton - because the liquid then hardly penetrates and does not pass through it. In addition, it is not easy to achieve uniform spraying over the entire width of the sheet, which may be more abundant in the areas of overlap of the jets or, on the contrary, poorer in the intervals between the impacts of the jets. . To overcome these drawbacks, it is necessary to multiply the number of ramps, which makes the device complex.

Patent FR 1374161 describes an apparatus for washing fragile fabrics in which the fabric is supported on an endless porous fabric while the washing liquor is sprayed by means of a plurality of nozzles. It further comprises suction boxes placed under the fabric by which the liquor is sucked through the sheet facilitating the cleaning operation. This patent for cleaning only does not teach how to uniformly impregnate the tablecloth with a controlled quality of treatment liquor.

Patent application EP-A-0 97268 relates to an apparatus for applying foam to a sheet and comprises a dispensing member supplying a plurality of conduits connected to an application device with weir. This device is provided with a rounded sheet through which the foam pours into a continuous blade. Although ensuring a uniform deposit of foam, the device does not provide any means to control the amount incorporated into the sheet.

Another known means consists in impregnating the sheet in a tank containing the impregnation liquor, ensuring the wetting of the fibers and finally eliminating the excess liquid by passing through a scarf. This technique provides satisfactory impregnation, however when the textile web has no cohesion, there is a tendency to deform it by the mechanical action exerted on the fibers, and to produce irregularities, of air occlusions, which in the end do not allow its use as it is.

The object of the invention is to remedy these drawbacks and proposes a method of impregnating a textile sheet with an aqueous liquid, in particular of the type containing a treatment agent, according to which the sheet is deposited on an endless support mat permeable to liquids. , applying said liquid to the sheet and creating, by means of a suction slot located under the fabric, a depression sufficient to allow at least part of said liquid to pass through the sheet, characterized in that said liquid is poured by gravity onto the sheet in the form of a liquid blade transverse to the direction of movement of the latter and the rate of spilled liquid, defined relative to the weight of the sheet, passing under said blade, is greater than a ratio determined from which the carrying rate is a function of said depression and independent of the quantity spilled, so as to allow a homogeneous impregnation and easy control of the carrying rate.

• Il permet une imprégnation uniforme sur toute la largeur à traiter par l'application du liquide sous la forme d'une lame ou d'un rideau continu qui apporte la même quantité de liquide sur toute la largeur.
• La masse liquide, par son inertie, chasse de façon très efficace l'air emprisonné entre les fibres. Elle est assistée à cet effet par l'aspiration produite sous la toile. On assure ainsi le mouillage des fibres dans toute l'épaisseur.
• La fente d'aspiration remplit la fonction d'exprimage du liquide en excès de la nappe. Cet exprimage étant, contrairement au foulard classique, effectué sans pincement ni contact de pièces mécaniques, n'engendre aucun déplacement notable des fibres et ne perturbe pas leur organisation. Les risques de déformation de la nappe sont faibles.
• La fente, par sa disposition de préférence au droit de la lame liquide, exerce une force d'aspiration sur celui-ci et contribue à stabiliser son écoulement, et à garantir une répartition du flux sur toute la largeur de la nappe.
• Le flux liquide par son inertie, communique enfin une certaine énergie à la nappe, ce qui se traduit par un accroissement de la cohésion de cette dernière. On constate en effet, avec surprise, qu'une nappe constituée de fibres de coton initialement non liées peut subir sans dommages les manipulations accompagnant son traitement ultérieur. Elle ne se casse ni ne se déforme. L'aspect de la nappe et sa résistance mécanique à l'issue du traitement hydrophile et de blanchiment, sont tels qu'il est possible de l'utiliser comme produit fini ou semi-fini.
• Il permet de contrôler le taux d'emport de liquide par la nappe, appelé également taux d'exprimage. On rappelle que le taux d'exprimage est égal au taux de liquide résiduel après essorage par rapport au poids de la nappe. On réalise cet objectif en déversant sur la nappe une quantité de liquide telle que le taux du liquide déversé par rapport au poids de la nappe (voir sa définition plus loin, dans les exemples) est supérieur à un taux déterminé au-delà duquel le taux d'exprimage est fonction de la dépression créée par la fente d'aspiration et indépendant de la quantité déversée.

The process has the following advantages:

• It allows a uniform impregnation over the entire width to be treated by applying the liquid in the form of a blade or a continuous curtain which provides the same amount of liquid over the entire width.
• The liquid mass, by its inertia, very effectively expels the air trapped between the fibers. It is assisted for this purpose by the suction produced under the fabric. This ensures the wetting of the fibers throughout the thickness.
• The suction slot fulfills the function of expressing excess liquid from the web. This expression being, unlike the conventional scarf, carried out without pinching or contacting mechanical parts, does not cause any significant displacement of the fibers and does not disturb their organization. The risks of deformation of the sheet are low.
• The slot, by its arrangement preferably in line with the liquid blade, exerts a suction force on it and helps to stabilize its flow, and to guarantee a distribution of the flow over the entire width of the sheet.
• The liquid flow by its inertia, finally communicates a certain energy to the sheet, which results in an increase in the cohesion of the latter. It is found, in fact, with surprise, that a tablecloth made of cotton fibers initially unbound can undergo without damage the manipulations accompanying its subsequent treatment. It does not break or deform. The appearance of the sheet and its mechanical resistance after the hydrophilic and bleaching treatment are such that it can be used as a finished or semi-finished product.
• It makes it possible to control the rate of liquid transport by the tablecloth, also called expressing rate. It is recalled that the rate of expression is equal to the rate of residual liquid after spinning relative to the weight of the sheet. This objective is achieved by pouring a quantity of liquid onto the sheet such that the rate of the liquid spilled relative to the weight of the sheet (see its definition below, in the examples) is greater than a rate determined beyond which the rate of expression is a function of the depression created by the suction slot and independent of the quantity spilled.

It has indeed been surprisingly found that beyond a certain quantity of liquid poured onto the sheet, the rate of expression no longer depends on the quantity of liquid supplied but only on depression. Depending on a single parameter, it can thus be more easily controlled, especially within an interval between 40% and 400%. By regulating the poured rate beyond this threshold, one thus controls in a very satisfactory way the impregnation and the regularity of the treatment which follows. If, for example, the speed of travel of the sheet undergoes untimely variations, the spilled rate varies but not the carrying rate. It is the same if the mass of the sheet is not constant.

In practice, this threshold is determined experimentally. It corresponds to a spilled rate between 300% and 1500%. For the same liquid, it depends on the nature of the fibers, the weight of the tablecloth and its presentation: compressed or open, fabric, knitted or nonwoven. For example, for a carded tablecloth of unbleached cotton of 250 g / m², impregnated with an aqueous scouring solution, it corresponds to a rate of the order of 600%.

On an unbonded fibrous web such as an unbleached cotton web, the carrying rate can then be varied between 150% and 400%, preferably between 250% and 300%.

The process essentially aims at impregnating a textile sheet composed of unbound fibers, with a grammage between 20 and 1000 g / m². The fibers can be of all kinds: natural, synthetic or artificial, alone or in a mixture. The sheet can be formed by any suitable means, mechanical or pneumatic. The ply may optionally be composite and obtained from two or more card webs associated or not with pneumatically formed webs. In addition to the unbound fibrous webs, the process is also suitable for impregnating bonded textiles: fabrics, knits or others.

Another object of the invention is to provide a liquid distribution device ensuring the formation of a continuous and as regular blade as possible. This is achieved with a liquid dispensing member provided with a weir with a portion of flow surface oriented towards the sheet, of width at least equal to that of the area to be impregnated.

According to a preferred embodiment, the weir consists of a sheet with a convex cylindrical profile, the downstream edge of which is serrated in order to facilitate detachment of the liquid blade.

In particular, the laminar flow is improved by providing grooves in the region of the lateral edges.

Another object of the invention is to improve the impregnation of a sheet made up of unbound fibers, deposited on a porous mat, by mechanical or pneumatic means. This is achieved by compressing the web, in particular by mechanical means, so as to reduce its thickness before it passes under the liquid slide.

According to a particular embodiment, said compacting means is constituted by a pressure roller.

The compaction of the sheet is further improved by having a vacuum slot immediately downstream of the compacting member so as to avoid relaxation of the sheet before it passes through the impregnation means.

Another object of the invention is to design a continuous scouring and bleaching process of unbleached cotton fibers, making it possible to obtain a treated cotton sheet, having sufficient mechanical strength and regularity so that the tablecloth can be used as is, without any mechanical treatment other than cutting or other operation of transformation into finished product.

This object is achieved by performing at least one of the impregnation operations according to the technique according to the invention.

In particular, provision is made to carry out according to this technique, at least the first impregnation provided in the treatment with a liquor containing a scouring agent. Thanks to the process of the invention, it not only ensures a homogeneous impregnation at a controlled rate of expression but also the sheet is consolidated, before any other treatment, by the action of the blade on the fibers, as has been reported above, without disturbing the quality of the topping produced by the upstream formatter.

By this consolidation, the sheet can be handled, transferred, treated, rinsed, expressed without risk of breakage or deformation. In addition, thanks to the quality of its appearance, it is it can be transformed directly into a finished product without having to card it again or rework it.

• la figure 1 représente schématiquement un procédé d'imprégnation d'une nappe de coton
• la figure 2 est une représentation en perspective d'un dispositif de distribution de liquide
• la figure 3 représente schématiquement une installation de débouillissage et de blanchiment de fibres de coton écru.

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

• Figure 1 schematically shows a method of impregnating a cotton web
• Figure 2 is a perspective representation of a liquid dispensing device
• FIG. 3 schematically represents an installation for scalding and bleaching unbleached cotton fibers.

In the diagram of FIG. 1, an impregnation installation according to the invention is shown, applied to the treatment of a sheet of unbound fibers of unbleached cotton, for example.

A forming system shown diagrammatically by the block (2) deposits the open and individualized fibers on an endless belt (4), driven in a plane translational movement according to the arrow. The carpet is porous; it may be a suitably perforated waterproof material or a canvas. The carpet is stretched between horizontal rollers, one of which is powered. The sheet (6) from the former is relatively thick and uniform.

Downstream, a pressure roller (7) rotatably mounted about a horizontal axis, transverse to the direction of movement, cooperating with a counter-roller (8) placed on the canvas, has the function of partially expelling the air from the tablecloth by reducing its thickness. It is important to expel this air, because it forms pockets opposing the subsequent penetration of the liquid. Immediately downstream of the compacting means, provision is made for the implementation of a vacuum under the sheet by means of a first suction slot (9), to prevent it from naturally re-inflating under the effect of elastic restoring forces exerted by the fibers themselves. In addition, the depression presses the fibers against the fabric and promotes the action of the liquid afterwards. The slot (9) is in communication with a vacuum source, not shown. The sheet resulting from this compacting means has undergone no other deformation than a reduction in height. Its homogeneity is not broken. For example, a tablecloth of unbleached cotton having, initially according to the grammage and the mode of forming, a thickness comprised between 40 and 150 mm, is thus compacted up to a height between 10 and 30 mm. For compaction, instead of a mechanical means, the effect of a vacuum created under the sheet can also be used.

Then, the ply passes into the actual impregnation device (10). This (10) is composed of two elements: a distributor (11) of the liquid and a suction member (13).

The dispensing member (10) is designed to deliver the liquid in the form of a curtain, or blade, transverse to the direction of movement of the sheet, the liquid being set in motion by the action of simple gravity. By blade or curtain, we understand a uniform distribution of the liquid crosswise, with no continuity. Above the liquid impact zone, a suction member (13) is provided, consisting of a suction slot of determined width, the vacuum height of which is chosen so as to be able to control the rate for expressing the liquid in the sheet.

Referring to Figure (2), which is a perspective representation of the device (10) cut in the direction of movement of the belt (4), it is noted that the dispenser (11) includes a liquid accumulation zone , separated into two compartments (113, 114) by a transverse partition (112) pierced with orifices connecting the 2 compartments (113,114). The first compartment is supplied with liquid by a pipe and supplies the compartment (114). This arrangement makes it possible to reduce turbulence inside this latter compartment. On its outer wall, there is provided a weir (115) of convex cylindrical shape, whose generatrices are horizontal and oriented perpendicular to the direction of travel of the web. The free edge of the weir is serrated, that is to say it is provided with pointed projections (115 ') in the extension of its surface, in order to facilitate the detachment of the liquid from the surface of the weir. The curvature of the weir is chosen so that the liquid flowing from the overflow from the compartment (114) forms a laminar flow with streams of current as parallel as possible. The tangent of the weir at its free edge is preferably substantially vertical. The surface condition is also a factor to take into consideration; it is chosen smooth to reduce disturbances. The flow from the weir thus forms a curtain, or blade, a continuous liquid in its transverse direction and substantially planar. In order to reduce the narrowing of the liquid blade between the weir and its impact on the web, provision may be made, near the lateral edges, for fine grooves on the surface of the weir, oriented in the direction of the fluid threads, or else lamellae guide along which the fluid threads remain glued.

Plumb with the weir (115). under the carpet (4) there is provided a suction slot (13) which is parallel to it, communicating with a source of vacuum. The size of the opening of the slit is determined so as to exert a suction of sufficient duration when the sheet passes at its level. It therefore extends downstream of the weir over a distance determined as a function of the nature of movement of the sheet.

The depression generated by the slot is chosen so as to be sufficient to wring out the sheet. Furthermore, it has been found that it is possible to control the rate of expression of the sheet by adjusting only the level of vacuum, when the liquid flow rate exceeds a threshold.

This property is illustrated by the following examples:

Example 1 :

A cotton tablecloth with a width of 0.56 m (L), the dry grammage (M) of which was 250-260 g / m², was prepared and laid on a carpet moving at a speed (V) of 25 m / min. Lightly colored water was poured out with the device described. The suction slot was 30 mm wide and the vacuum was 90 mb (relative vacuum). The flow rate (D) of the discharged water was gradually varied. It can be seen that from a spilled rate threshold (Td) corresponding to around 600%, the expressing rate (E), or take-up rate. varies very little. The curve Td = f (E) becomes asymptotic.

$$\text{E =}\frac{\text{Masse humide - masse sèche x 100}}{\text{Masse sèche}}$$

The spilled rate (Td) is the ratio expressed as a percentage between the mass of liquid spilled and the mass of fibers traveling under the mass of said liquid. $$\text{Td =}\frac{\text{D x 1000 x 100}}{\text{60 x L x V x M}}$$

$$\text{E =}\frac{\text{Wet mass - dry mass x 100}}{\text{Dry mass}}$$

Example 2 :

A needled nonwoven of viscose fibers was treated in the same way as in Example 1.
M = 145 g / m²
V = 25 m / min
Depression: 85 mb

The variation in the rate of expression (E) as a function of the rate spilled is reported in the following table:

By plotting the curve E = f (Td) we can determine the threshold from which E varies only very slightly. In this example, it is 1000% - 1200%.

Example 3 :

A cotton jersey was treated in the same way as in Example 1
M = 140 g / m²
V = 25 m / min
Depression: 90 mb

Graphically, it is determined that the threshold is around Td = 600%.

Example 4 :

Solution

: Eau + agent mouillant (5 g/l)

Débit

: 1200 l/h, largeur 0.5 m

Vitesse

: 3 m/min

Fente

: 30 mm soit un temps d'aspiration de 0.6 s. Au-delà de cette valeur la durée d'aspiration n'a pratiquement plus d'in- fluence sur le taux d'exprimage.

The following examples illustrate how we can control the rate of squeezing or take-up (in%) as a function of the depression (δP) created under the tablecloth, for 3 different types of tablecloth.

Solution

: Water + wetting agent (5 g / l)

Debit

Speed: 1200 l / h, width 0.5 m

Speed

: 3 m / min

Slot

: 30 mm i.e. a suction time of 0.6 s. Beyond this value, the suction duration has practically no more influence on the rate of expression.

CANVAS OF 115 g / m² Dumped rate: 1390%

140 g / m² KNIT Dumped rate: 1140 %

ECRU COTTON TABLECLOTH OF 250 g / m² Dumped rate: 570%

A complete installation for bleaching unbleached cotton fibers using the impregnation process of the invention is described below, in relation to FIG. 3.

The bleaching process consists of opening, cleaning, if necessary blending cotton of different origins and qualities, and in forming (21) a sheet of between 50 and 1000 g / m², preferably between 100 and 600 g / m² by any suitable means, mechanical (carding) and / or pneumatic.

This sheet is supported and driven by a belt through the various treatment stations.

It is impregnated in (22) according to the means of the invention with a scouring solution (soda with wetting agent) while controlling the rate of expression by the vacuum created at the suction slot. The vacuum is around 100 mbar:

The tablecloth is introduced into a vaporizer (23) heated to a temperature close to 100 ° C. in which it remains, while remaining continuous thanks to an appropriate storage means, for a determined period depending on the liquor and the take-up rate. .

It is then rinsed and the boiling juice is extracted by means of a second liquid blade (24) and a vacuum slot associated with a medium vacuum (100 to 350 mbar).

The hydrophilic scoured sheet is impregnated with a bleaching solution (hydrogen peroxide with sodium hydroxide essentially) by means of a third device with a liquid blade and a vacuum slit (25).

The sheet is again introduced into a vaporizer (26) heated to a temperature close to 100 ° C. in which it stays thanks to an appropriate storage means, for a time long enough for the bleaching to be effective.

Then the sheet is rinsed by means of a succession of liquid blades associated with suction slots (27).

Finally, the maximum amount of water contained in the sheet is extracted at (28), and it is dried in an oven (29) which is preferably through air.

The tablecloth can be used directly for the manufacture of packaged hydrophilic cotton or else be transformed into fibers after shredding for the production of nonwoven products.

The invention is not limited to the embodiments shown. It includes all equivalents and all applications within the reach of the skilled person.

Claims (12)

1. Process for impregnating a fibrous woven, knitted or nonwoven sheet with an aqueous liquid notably of the type containing a treatment agent, according to which the sheet is deposited on an endless web permeable to liquids, the said liquid is applied to the sheet and, by means of a vacuum slot disposed below the web, a negative pressure is created sufficient for at least some of the said liquid to pass through the sheet, characterised in that the liquid is poured by gravity onto the sheet in the form of a liquid sheet or curtain transverse to the direction of travel of the sheet and the amount of liquid poured, defined with respect to the weight of the sheet passing under the said curtain, is greater than a given value as from which the carrying capacity is a function of the said negative pressure and independent of the quantity poured, so as to allow a homogeneous impregnation and easy control of the carrying capacity.
2. Process according to Claim 1, characterised in that the liquid sheet is obtained by means of a liquid distribution device provided with an overflow of a width at least equal to the width of the sheet to be impregnated, by which the liquid is spread out in the form of a continuous curtain.
3. Process according to Claim 2, characterised in that the said overflow is formed by a metal sheet with a convex cylindrical profile, the downstream edge of which is serrated in order to facilitate the detachment of the liquid curtain.
4. Process according to one of Claims 2 and 3, characterised in that the overflow has grooves oriented in the direction of flow of the liquid, provided close to the lateral edges.
5. Process according to one of the preceding claims, characterised in that the said value of the amount of liquid poured is between 300% and 1500%.
6. Impregnation process according to Claim 5, characterised in that the carrying capacity is between 40% and 400%.
7. Process according to Claim 6 for impregnating an unbound fibrous sheet such as a raw cotton sheet, characterised in that the carrying capacity is between 150% and 400% and preferably between 250% and 300%.
8. Process according to one of the preceding claims for impregnating an unbound fibrous sheet such as a raw cotton sheet, characterised in that it consists, before effecting the said impregnation, of:

   - forming a sheet by mechanical and/or air means from bulk fibres and depositing it on the said endless web conveyor,

   - reducing the thickness of the sheet by a compacting means, notably a mechanical means, or by the effect of a negative pressure created below the sheet.
9. Process according to Claim 8, characterised in that the sheet has a weight of between 20 and 1000 g/m².
10. Process according to Claim 8, characterised in that the compacting is effected by the application of a pressure cylinder.
11. Process according to one of Claims 8 or 10, characterised in that a negative pressure is created underneath the sheet in the gap between the compacting means and the impregnation means.
12. Process according to one of Claims 1 to 11 for the continuous treatment of raw cotton fibres, which notably comprises the stages of:

    - opening and mechanical cleaning of the fibres

    - formation of a sheet and its conveyance by endless belt

    - impregnation with a boiling solution

    - boiling

    - rinsing, elimination of liquid

    - impregnation with a bleaching solution

    - bleaching

    - rinsing, elimination of liquid

    - oiling where necessary

    - drying

    characterised in that it is applied to at least one of the said impregnation and rinsing operations.

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