Patent Application
20220056624
The present invention relates to an apparatus and to a method for producing nonwovens in a drylaid process.
Apparatuses for producing nonwovens in a drylaid process generally comprise a section for forming a web or a fleece, said section comprising one or two cards, followed by a section for water-jet consolidation, generally over a plurality of rotary cylinders and a series of conveyors, then a section for extracting water using a high vacuum, most commonly, then a drying section and lastly a rolling-up unit.
These apparatuses for drylaid production are advantageous in that they produce lightweight nonwovens, generally from 20 to 80 g/m2, at high speeds from 150 to 350 m/minute. The nonwovens produced are of a high quality and are economical to produce, but their tensile strength in the machine direction is much greater than the tensile strength in the cross direction. This is because the webs are formed by direct carding. The machine direction/cross direction strength ratios are generally more than 3:1 or even 4:1; in other words, the tensile strength in the machine direction is four times greater than the tensile strength of the same nonwoven in the cross direction.
When nonwovens having very similar strength properties in both the machine direction and the cross direction are desired, it is customary to arrange a crosslapper between the card and the consolidation station. The crosslapper folds in layers and across the card web to impart tensile strength in the cross direction. However, the main disadvantage of this technique is that it is slow and is designed for heavy fleeces, or at the very least for fleeces that are heavier than with direct carding.
To produce lightweight fleeces of 40 to 60 g/m2, for example using a card followed by a crosslapper, it is necessary to keep to small number of folds (from one to three folds) and to draft the fleece at the outlet of the crosslapper using drafting rolls. These two factors (small number of folds and use of a drafting system) are detrimental to the homogeneity of the fleece and of the nonwoven produced. In addition, even with the best possible speed conditions, the production of lightweight nonwovens using a crosslapper is limited to around 180 to 200 kg/h and by metre of production width, and with fine fibres having a titre between 1.3 and 2.2 dtex.
According to the invention, an apparatus has been developed that makes it possible to produce nonwovens in a drylaid process that even have a basis weight between 40 and 80 g/m2 through direct carding, with high throughputs and machine direction/cross direction strength ratios of less than 2.5:1, less than 2:1, or even less than 1.5:1 and very close to 1.0, and that are well suited to high-quality markets, such as professional cleaning wipes or cosmetic masks, in which the nonwovens should be as lightweight as possible; this is provided that the rotational speeds of the components forming the apparatus are controlled as stipulated according to the invention.
Productivity is increased by 40 to 50% compared with an apparatus of the same width having a crosslapper and drafting system and producing lightweight nonwovens. In addition, the invention requires just one card and no other additional machines such as a lapper or a drafting system, needs much less investment, uses much fewer moving mechanical components (e.g. rolls, belts) and consumes less energy per kilo of product.
The apparatus for producing nonwovens in a drylaid process according to the invention comprises a card drum rotated in a first direction of rotation and at a first circumferential rotational speed by first driving means, producing a fibre web in the process. It is characterised in that it comprises, immediately downstream of the drum in the direction in which the fibres travel in the apparatus, a transfer cylinder rotated in a second direction of rotation, opposite to the first direction of rotation, and at a second circumferential rotational speed by second rotation means, the second speed being greater than the first speed, the transfer cylinder having, on the periphery, a lining comprising a plurality of teeth that are angled with respect to the radius of the cylinder and oriented in the second direction of rotation, and, immediately downstream of the transfer cylinder, a system that comprises, immediately sequentially in the upstream-downstream direction, at least one doffer, at least one condenser, at least one stripper roll, a first endless conveyor belt, a suction drum and a second endless conveyor belt, the suction drum being adjacent to the upper side of the first and second conveyor belts and ensuring the fibres pass from one to the other.
In this specification, “immediately downstream” should be understood to mean either that the component immediately downstream is adjacent to the component immediately upstream, or at least that there are no other rolls or drums between them.
Unexpectedly, this apparatus makes it possible to omit a crosslapper. What is particularly surprising is that the improvement in the isotropy of the nonwoven is apparent not just immediately after the toothed transfer cylinder, but also increasingly beyond it along the entire line.
If an apparatus not having the transfer cylinder is used and the speed ratios are varied according to the invention, in particular as specified in the table below, creases and visual flaws result in the nonwoven, without the machine direction/cross direction strength ratio improving sufficiently at the same time.
Preferably, the ratio of the second speed to the first speed is greater than or equal to 1.6 and even more preferably greater than or equal to 1.7.
When the rotational speed ratios between the various components of the apparatus are, preferably, as follows:
The invention also proposes a method for producing nonwovens, in which the apparatus according to the invention is operated according to the speed ratios according to the invention.
It is possible to obtain a nonwoven product based on artificial and/or synthetic fibres, such as viscose, lyocell, polyester or polypropylene, having a weight per square metre between 40 and 80 g/m2 and the fibres of which have a titre between 1.3 and 2.2 dtex and a length between 30 and 50 mm, the machine direction/cross direction tensile strength ratio is from 1.0 to 1.5, the elongation in the machine direction is between 35 and 70% and preferably between 40 and 60%, and the elongation in the cross direction is between 70 and 130% and preferably between 90 and 125%.
The measurements for strength in the longitudinal direction (MD) and in the cross direction (CD) and for weight per m2 are taken in accordance with the ERT standards of the European Disposables And Nonwovens Association (EDANA), as follows:
a) Weight Per Square Metre:
b) Strength and Elongation in the Longitudinal Direction and the Cross Direction:
The invention also relates to a method for producing the above nonwoven product, in which the apparatus according to the invention is operated while imposing on its various components the rotational speeds for obtaining the desired ratios.
The diameter of the transfer cylinder is preferably less than that of the card drum. The ratio is, for example, between 0.40 and 0.50. Generally the card drum has a diameter between 900 and 1,500.
The tilt angle of the teeth with respect to the radius can be between 70° and 80°. The radial height of the teeth is advantageously between 0.7 and 1.5 mm. The teeth are distributed uniformly across the entire periphery of the transfer cylinder, the gap between two neighbouring teeth being between 1.3 and 2.3 mm. The width of the teeth at their base is between 0.70 and 1.2 mm. The distance between the card drum and the transfer cylinder is less than 1 mm, preferably being between 0.4 and 0.6 mm.
The side flanks of the teeth can be straight or curved.
The teeth are preferably pointed.
The transfer cylinder and its lining can be made of metal.
The card drum is formed in the same way as the transfer cylinder, having teeth angled by the same angle as the tilt of the teeth of the transfer cylinder in the opposite direction.
The teeth are angled in the direction of rotation.
Preferably, the anisotropy of the nonwoven is reduced further by a suction cylinder adjacent to the upper side of the second conveyor belt.
The apparatus comprises, generally at the end, a consolidation device on the suction cylinder and/or downstream thereof. The consolidation device can be provided by water jets, hot-air jets, calendering or needling, or can be implemented in a hot-air consolidation oven, or the like.
In the accompanying drawings, provided solely by way of example:
The apparatus in
The various rotating components of the apparatus are driven by their own motor, which are illustrated in
The distance between the drum 11 and the belt 9 and between the belt 11 and the cylinder 12 is between 2 and 15 mm.
In
The following examples illustrate the invention.
A fleece weighing approximately 60 g/m2, composed of 50% polyester fibres of 1.7 dtex measuring 38 mm in length and of 50% viscose fibres of 1.7 dtex measuring 40 mm in length, is produced at a speed of approximately 78 m/min at the cylinder 12.
For this test, the card is a conventional card without a drum 2 and is controlled according to the optimum production settings for producing nonwovens. The speeds of each component are set out in the table further below.
The bonding cylinder 12 is covered with a microperforated sleeve as described in French patent no. 2 734 285. The fleece is first wetted by an injector 13 that projects water jets of a diameter of 140 micrometres at a pressure of 10 bar, the jets being spaced apart from one another by 0.9 mm in two rows. The fleece thus wetted and slightly consolidated is then subjected to the action of a series of two hydraulic injectors 14 and 15 that project water jets of a diameter of 120 micrometres at increasing pressures of 70 bar and 90 bar, the jets being spaced apart from one another by 1.4 mm in two rows.
The bonding cylinder 12 is followed by another bonding cylinder (not shown), which is covered with the same microperforated sleeve as the cylinder 12 and fitted with an injector that projects, on the opposite face to the injectors 14 and 15, water jets of a diameter of 120 micrometres at a pressure of 100 bar.
The nonwoven thus obtained is then transferred to a suction belt connected to a vacuum generator, and then dried at a temperature of 140° C. in a through-air dryer.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance.
The conditions of example 1 are repeated using an apparatus according to the invention, which now comprises a cylinder 2, but the apparatus is operated at the speeds indicated in the table further below.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance but the MD/CD ratio is poor.
The conditions of example 2 are repeated. For this test, the speeds of the various components are modified according to the table further below.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance and a satisfactory MD/CD ratio.
The conditions of example 2 are repeated. For this test, the speeds of the various components are modified according to the table further below.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance and an even better MD/CD ratio than in example 3.
The conditions of example 2 are repeated. For this test, the speeds of the various components are modified according to the table further below.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance and an even better MD/CD ratio than in example 4.
The conditions of example 2 are repeated. For this test, the speeds of the various components are modified according to the table further below.
A nonwoven weighing approximately 60 g/m2 is obtained. The nonwoven has a uniform appearance and an MD/CD ratio of 1.2, which is altogether exceptional and unexpected.
Example 1 is repeated using a conventional card not having a transfer cylinder, while applying the speed ratios in example 5 for the doffers up to the cylinder 12. The nonwoven produced has numerous creases in the transverse direction and is unusable or unsellable.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19 00150 | Jan 2019 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/087194 | 12/31/2019 | WO | 00 |
