Drum for a production unit for a non-woven material, method for production of a non-woven material and non-woven material obtained thus

Holder (s):

® Representative (s): CABINET FLECHNER.

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DRUM FOR PLANT FOR THE PRODUCTION OF A NON-WOVEN TABLECLOTH, PROCESS FOR THE PRODUCTION OF A NON-WOVEN TABLECLOTH AND OBTAINED NON-WOVEN TABLECLOTH

The present invention relates to nonwoven webs and their production methods and installations.

US Patent 6,321,425 describes a process for manufacturing a nonwoven web which consists in sending a web, resulting from a spunbond tower which normally comprises successively from top to bottom a generator of a curtain of filaments, in particular of filaments in plastic material, a slit alternator device for drawing the filaments of the curtain, a diffuser and a conveyor for receiving the filaments, to a calender which consolidates the blank sheet formed, then to a water jet entanglement drum. This process has the drawback of altering the uniformity of the formation of the web and of orienting the filaments preferentially in the machine direction by the stretching which is applied thereto.

The invention overcomes this drawback by making it possible to obtain a nonwoven web whose properties are substantially isotropic, that is to say substantially identical whether in the machine direction or in the transverse direction.

This is achieved by a drum comprising a fixed cylindrical body with a perforated lateral surface surrounded by a perforated sleeve driven in rotation with respect to the axis of the cylindrical body, and means intended to create a depression inside the body. According to the invention, a waterproof partition subdivides the interior of the body into two compartments delimited by the partition and by respectively a first and a second part of the lateral surface and both put in a vacuum by the means intended for it. to create.

The first compartment of the drum according to the invention makes it possible to bring onto the drum a blank sheet lying on an associated conveyor, substantially tangent to the drum at a so-called point of contact (this is the point where the conveyor and the drum are closer to each other without touching each other), even if this blank sheet blank is still poorly consolidated, as is the case when it comes to the sheet coming from a spunbond tower, without first needing to calendar the blank sheet or to subject it to other operations involving stretching which permanently affect the isotropy of the properties of the nonwoven sheet finally obtained.

Preferably, the first compartment begins opposite the point of contact of the conveyor tangent to the drum and ends opposite a point on the lateral surface downstream, in the direction of rotation of the sleeve, from the point of contact. As soon as the blanket blank has thus been applied to the drum by the vacuum prevailing in the first compartment, it is subjected to entanglement by water jets.

According to one embodiment, the first compartment extends over a cylindrical sector of the body defined, in the cross-sectional view of the cylindrical body, substantially by two spokes perpendicular to each other, the first compartment thus occupying substantially a quarter of the interior. from the body. Preferably, the cylindrical sector occupied by the first compartment is placed in the second dial between three and six o'clock.

The means intended to create a depression may be common to the two compartments but, according to a preferred embodiment, each compartment has its own means for creating a depression and, preferably, the depression is greater in the first compartment than in the first compartment. the second. In particular, it is possible to create in the first compartment a depression of between 30 and 400 mbar and in the second compartment a depression of between 30 and 300 mbar.

In order for the drum to pick up the blanket blank properly, it is better that the ratio of the total area of ​​the perforations, per unit area, to the area of ​​the side surface where they are located, is greater for the first compartment than for the second. This ratio may be for the first compartment between 5% and 30%, while for the second compartment it is between 2% and 15%.

The perforations of the side surface facing the second compartment are in particular slots which are located facing pressurized water injectors on the part of the sleeve which passes just opposite the part of the side surface of the second compartment. The pressure of the jets is generally between 30 and 400 bars and the diameter of each jet between 75 and 200 microns. A rigid rotating perforated cylinder is mounted on the outside of the stationary cylindrical body and its inside diameter is adjusted to the outside diameter of the cylindrical body so that the minimum clearance thus maintained allows rotation while minimizing air leakage. According to the technical solution adopted for the manufacture of this rotary cylinder, it is planned to use plastic battens mounted on springs to improve the sealing of the separation of the two compartments. This rotating cylinder can be a simple perforated sheet, a bronze or stainless steel cylinder pierced with holes arranged in a helix, a honeycomb cylinder. It may be a rolled perforated sheet tube coated with a coarse metal fabric drainage sleeve which ensures good uniformity of water extraction. This rotating cylinder supports a thinner perforated sleeve which effectively supports the filaments and fibers of the nonwoven during hydraulic entanglement. The distribution of the holes in the sleeve can be random. The holes can also be ordered by being aligned or staggered. The holes in the sleeve can also be distributed in small areas of ordered perforations distributed randomly on the surface of the sleeve. The sleeve can be made of a metallic fabric or synthetic material or a mixture of metallic fabric and synthetic material. It is preferred that the diameter of the holes in the sleeve is between 50 and 500 microns. Provision can be made, in order to obtain patterns on the web, also to put a perforated sheath on the sleeve, the openings of which have at least one dimension greater than 2 mm.

The invention also relates to an installation for producing a nonwoven web comprising a spunbond tower with conveyor leading to a drum according to the invention. Preferably, the tower conveyor and the conveyor tangent to the drum are one and the same conveyor, but it is also possible to provide two separate conveyors.

According to a particularly preferred embodiment, the drum is mounted directly downstream of the tower. By directly downstream is meant, in the present specification, without the interposition of a device causing the stretching of the web. So there is no calender, but there may be a compactor roller.

The invention also relates to a method for producing a nonwoven web, which consists in using an installation according to the invention, and in adjusting the speed of the conveyor of the tower or of the tangent conveyor to a value greater than the linear speed of the drum. (counted around the perimeter of the drum). A nonwoven web is thus obtained in which the ratio of the breaking strength in the machine direction to that in the cross direction may be less than 1 because of this speed difference. When the speeds are substantially the same, it is possible to obtain a ratio of the breaking strength in the machine direction to that in the cross direction of the nonwoven web according to the invention of less than 1.2 and in particular of about 1, so that the nonwoven web according to the invention is particularly well isotropic.

In the accompanying drawings, given by way of example:

Figure 1 is a perspective view with cut away of an installation according to the invention Figure 2 and Figure 3 are two perspective views with cut away of a drum according to the invention and Figures 4 and 5 are two schematic views of two variants of the installation according to the invention.

The drum shown schematically in Figure 1 comprises an inner body 1 composed of a fixed cylinder with a diameter of 400 mm and a sheet forming the side surface. The lateral surface is perforated with perforations with a diameter of 8 mm in a part which will delimit what will later be called the first compartment and the lateral surface is pierced with several slots, in particular facing the injectors in a part which will delimit what will be called the first compartment. will call the second compartment later. The ratio (void rate) of the sum of the areas of the perforations to the total area of ​​the lateral surface is between 5% and 30% in the first compartment and between 2% and 15% in the second compartment. A perforated rotary cylinder 4 is slipped over the body 1 and is driven in rotation by a belt drive device 2. Cylinder 4 has a hole. The ratio of the sum of the surface areas of the holes to the surface area of ​​the total lateral surface of the cylinder 4 is between 30% and 90% and preferably between 40% and 80%. The cylinder 4 has a thickness of between 1.5 and 30 mm and is generally made of stainless steel or bronze. A sleeve 5 is slipped over the rotary cylinder 4. The ratio of the sum of the surface areas of the holes to the total lateral surface area of ​​the sleeve 5 is between 5% and 20% and preferably between 5% and 15%. The sleeve 5 is obtained by electroplating nickel. It is microperforated with holes with a diameter ranging from 50 to 500 microns and preferably between 200 and 400 microns. It has a thickness between 0.1 and 0.6 mm and preferably between 0.2 and 0.4 mm. The interior of the drum 1 communicates with a pipe 7 for extracting air and water. Two injectors 8 and 9 send respectively along generatrices of the body 1 jets of water in the direction of the sleeve 5.

Fig. 2 is a perspective view better illustrating one embodiment of the drum. It consists of the inner cylinder 1 of axis O which is split as well as the sheet forming the lateral surface along two slots 11 arranged between spacers 12 and located in the dial from 1 to 3 o'clock. In the dial from 3 o'clock to 6 o'clock is formed a partition consisting of two sheets 13,14 together forming a cylinder sector. The two sheets 13,14 extend in a cross-sectional view perpendicular to the axis O along substantially two radii. They are waterproof. They delimit between them with the part 15 of the lateral surface located between 3 o'clock and 6 o'clock a first compartment 16 while the partition 13,14 defines with the rest of the body 1 a second compartment 17 into which the slots 11 open. Rows of holes 18 made on part 15 of the lateral surface open into the first compartment 16. The first compartment 16 is connected to means making it possible to put it under negative pressure. They are of the same type as conduit 7, but are distinct from it. The vacuum rate of part 15 is 16%. It is larger than that corresponding to the slots 11. In a variant, the first compartment also comprises a slot (not shown), placed at 6 o'clock opposite the point of tangency of the conveyor transporting the nonwoven blank with the cylinder. The purpose of this slot is to facilitate the transfer of the sheet of filaments onto the portion of the cylinder opposite the first compartment.

The embodiment shown in Figure 3 is identical to that of Figure 2, except that the rows of holes 18 of part 15 are replaced by slots 19 which are not parallel to the axis O.

The installation shown in FIG. 4 comprises a spunbond tower 21 with conveyor 22 leading, optionally with the interposition of a pressure roller 23, to a drum 24 according to the invention. The conveyor 22 is tangent to the drum 24 at the lowest point thereof. Two water injectors 25 are provided facing the side surface portion of the second compartment. One of the water injectors 25 is arranged angularly immediately adjacent to the first compartment 26, which means that one of the radial walls defining the second compartment 26 is in a position corresponding substantially to 4 o'clock while the first injector is in a position a little before 4 o'clock. The blank of the nonwoven web which is deposited on the conveyor 22 is sucked on the drum 24 thanks to the suction provided by the first compartment 26, is hydraulically entangled by the injectors 25 and leaves the drum 24 to pass over an inclined conveyor 27 before entering an oven 28, then leaving it to wind up on a reel 29.

In Figure 5, we again recognize a spunbond tower 31 which deposits a blank of nonwoven web 32, which is taken by a first drum 33 according to the invention having an injector 34 and which is sent by a conveyor 35 15 to a second drum 36 according to the invention.

In Figure 6, we recognize a variant of Figure 4 in which the filament web is transferred to additional drums 41 and 42 to give it additional consolidation and patterns before entering the through-air drying oven.