EP0378957A1 - Process for making a non-woven web, non-woven web made by this process and use of the web as disposable absorbing sanitary product - Google Patents

Abstract

Process for the manufacture of a nonwoven web and such a nonwoven web obtained by the said process and an application of the said nonwoven web to disposable absorbent hygiene products such as especially nappies for babies or incontinent people, feminine hygiene products, products for facial care, cleaning products. According to the invention the process for the manufacture of a nonwoven web consisting at least of a mixture of absorbent fibres such as especially cellulose fibres and synthetic fibres is characterised in that: - a homogeneous mixture of the cellulose and synthetic fibres is produced to form a web in which at least the cellulose fibres are mutually oriented, - the fibre web thus formed is subjected to the effect of a microwave radiation, not disturbing the fibre orientation mechanically, allowing the synthetic fibres to melt in order to bond the cellulose fibres together so as to create a network of fibres, limiting the hot spots retaining the cellulose fibres to promote the absorption of the web, its resistance to tearing and its resilience.

Description

The invention relates to a process for manufacturing a nonwoven sheet, as well as to such a nonwoven sheet obtained by said process and an application of said nonwoven sheet to absorbent hygienic products for single use.

The present invention will find its application in the textile field of the manufacture of nonwovens as well as in particular in the field of the manufacture of hygienic articles and / or hygienic products for single use such as in particular diapers for babies or incontinence, products of feminine protection, facial care products, cleaning products.

In this field, it is known to produce such nonwoven webs from absorbent fibers such as cellulosic fibers obtained by defibration of cellulose wadding.

Thus, the sheet is formed by a mattress of short tangled but nonwoven fibers. The consistency of this layer depends essentially on the entanglement of the cellulosic fibers.

In certain use cases, for its absorbent function, said sheet is not subjected to mechanical stresses and gives completely satisfactory results. On the other hand, in other cases, the nonwoven web is subjected to crushing or tearing forces which disturb the arrangement of the fibers and modify the absorption qualities of the web.

We find ourselves in such a situation for the production of hygienic articles and / or diapers for babies or incontinence. In this regard, the latter articles generally consist of such an absorbent mattress sandwiched between two sheets, one consisting of a waterproof sheet, the other by a permeable veil.

During the use of such layers, the mattress is subjected to forces due to the movements of the wearer which cause the sheet to break and divide, which is detrimental for absorption, since these ruptures cause capillary arrest.

To overcome such drawbacks, attempts have been made to form a nonwoven web from a mixture of absorbent fibers and synthetic fibers, the latter serving as an inter-fiber bond to form a network.

In these processes, it is sought to melt the synthetic fibers and when using polyolefin type fibers whose melting point is between 100 ° C and 170 ° C, it is necessary to heat the fiber mat to a higher value to allow fusion.

For this, first tests were carried out by subjecting the nonwoven web to a forced air heated to a temperature in the region of 180 to 220 ° C. However, this process is not satisfactory because the pulsed air disturbs the mixture of fibers and the necessary temperature requires a very large energy, therefore, the efficiency of the installation is low.

To improve this first process, trials have been made of a combination of forced air and infrared heating. Such a method has advantages in terms of entanglement of the fibers and requires the use of significant energy. Furthermore, the temperatures required, above 180 ° C., to melt the polyolefin fibers such as polyethylene, are detrimental for safety since it must be remembered that there is a mattress made up of a mixture of fibers. defibrated cellulose wadding which ignites very easily and whose fines can even constitute an explosive mixture.

The aim of the present invention is to propose a process for manufacturing a nonwoven web, in particular made up of cellulosic fibers, which allows the implementation of a thermobonding using synthetic fibers while reducing the necessary energy consumption, and increasing efficiency as well as security.

One of the aims of the present invention is to propose a process for manufacturing a nonwoven web by which a network of fibers linked together is created by fusion of synthetic fibers while not "mechanically" disturbing the web during thermobonding and in which a concentrated heating is carried out mainly at the level of the synthetic fibers in a reduced bulk and at a high speed.

Furthermore, the manufacturing process of the present invention makes it possible to increase the efficiency rate of the welding of the fibers together and thus to increase the tear strength and the resistance of the nonwoven web thus produced.

This being the case, a sheet of absorbent fibers having a higher absorption rate than that of the sheets known to date linked by hot air blowing or heating will be produced. infrared.

Another object of the present invention is to provide a nonwoven sheet, manufactured by said process, which will find its application in particular to the production of absorbent mattresses of disposable hygiene products such as in particular diapers for babies or incontinence, products feminine protection, facial care products, cleaning products, thus very significantly improving the absorption rate and the effectiveness of these articles.

Other objects and advantages of the present invention will appear during the description which follows which is however given only for information and which is not intended to limit it.

According to the invention, the process for manufacturing a nonwoven web, consisting at least of a mixture of absorbent fibers, such as in particular cellulosic fibers, and synthetic fibers, is characterized in that:
a homogeneous mixture of the cellulosic and synthetic fibers is produced to form a sheet in which the cellulose fibers at least are oriented relatively to each other,
- the sheet of fibers thus formed is subjected to the effect of microwave radiation, not mechanically disturbing for the orientation of the fibers, allowing the fusion of synthetic fibers to bond together the cellulose fibers in order to create a network of fibers, limiting hot spots, retaining cellulosic fibers, to promote the absorption of the sheet, its resistance to tearing and its resilience.

The invention will be better understood on reading the following description.

The invention relates to a method of manufacturing a nonwoven sheet, consisting at least of a mixture of absorbent fibers and synthetic fibers, as well as such a sheet and its application to the production of absorbent mattresses of hygienic products for single use, hygienic feminine protective articles, diapers for babies or incontinence, absorbent pads for facials or other hospital uses, cleaning products.

To make an absorbent mat for the retention of liquids, such as water, urine or other, commonly, a nonwoven formed of cellulosic fibers obtained from defibrated cellulose wadding is produced.

However, such a nonwoven poses certain problems of consistency of the material, especially when the latter is subjected to mechanical actions such as tearing and crushing.

According to the present invention, it is sought to increase the resistance to tearing and the resilience, which will have the implicit consequence of promoting the absorption of the nonwoven web.

For this, a consistency is given to the nonwoven web by thermobonding the fibers together.

First of all, a homogeneous mixture of cellulosic fibers, obtained by any traditional process such as dry defibration of cellulose wadding, and synthetic fibers is produced in order to form a sheet.

Long fibers are preferably used for the cellulose wadding and short fibers for the synthetic fibers and a preferential arrangement of the fibers is produced.

In fact, when the fibers are mixed and the sheet is formed, the cellulose fibers at least are oriented relatively to each other. This orientation will be such that the capillarity of the sheet thus formed is favored.

Then, the said sheet of fibers thus formed is subjected to the effect of microwave radiation, not mechanically disturbing for the orientation of the fibers; that is to say that, unlike forced air heating techniques, the fibers are not subjected to any force displacing the fibers relatively between them.

During this phase, the synthetic fibers are melted to bond together the cellulosic fibers in order to create a compact network of good tear resistance, good resilience in which the fibers are contained and maintained and whose absorption is improved thanks to the orientation and the bonding of the fibers together.

Thanks to the use of microwave radiation, a statically selective concentrated heating is authorized, which makes it possible to keep the relative arrangement of the fibers as it was made during the constitution of the sheet.

Furthermore, by microwave radiation, it is not no longer necessary to raise the temperature significantly, as is the case with hot pulsed air or infrared radiation, to obtain fusion; on the contrary, the heating is done punctually at the level of the synthetic fibers through the molecular agitation caused by the microwaves. This limits the hot spots in the water table.

In addition, such a technique allows a reduction in the power consumed because it avoids unnecessarily reheating the cellulosic fibers and the environment of the sheet thus formed.

In this regard, another important point of the process of the present invention lies in the fact that safety is increased because it minimizes any risk of fire and explosion, given the flammable and deflagrating nature of the materials treated and in particular cellulosic fibers.

However, according to the process of the present invention, good results are obtained with regard to the quality of the finished product by dispersing homogeneously 5 to 30% by weight of synthetic fibers in the web.

In addition, these synthetic fibers are dispersed so as to obtain a constant and homogeneous concentration in the three dimensions of the sheet and in particular in its thickness.

As far as the material itself is concerned, synthetic fibers of polyolefin type are used which are, for example, in the form of polyethylene treated, depending on the hydrophilic or hydrophobic case.

This example is not, however, limiting and one could use polypropylene fibers, ethylene-propylene copolymer, ethylene-alpha olefin copolymer.

These fibers can be added either before the defibration of the cellulose wadding, or after this defibration.

In the first case, the polyolefin fibers are then milled at the same time as the cellulose wadding until particles of between 0 and 40 mm are obtained.

In the second case, the synthetic fibers and the cellulose fibers are mixed after grinding the latter, the fibers having dimensions ranging from 0 to 40 mm also.

When this homogeneous mixture of constant concentration has been produced, the sheet of mixed fibers is then passed through a microwave dryer at least equipped with a fixed microwave emission source and means of linear scrolling of said sheet in the microwave field.

Such a device is advantageous for the manufacture of a sheet since it is possible to envisage linear speeds of travel of the sheet ranging up to 150 m / min or even more.

For example, we use a type of microwave dryer, known from the prior art, in which the wave is progressive, that is to say sent and then damped at the end, or uses a resonant wave system in which the transmitted wave travels back and forth. The microwave emission will advantageously be done longitudinally, with respect to the movement of the tablecloth in order to guarantee the homogeneity of the "cooking".

These machines allow drying on a moving conveyor belt, with continuous scrolling, thanks to a phase shift of the waves and an arrangement of several successive waveguides.

However, in certain cases, to increase the efficiency of the microwave device and improve the bonding of the fibers to one another by the fusion of the synthetic fibers, prior to the submission of the web to the effect of microwaves, one can increase the humidity of said tablecloth; for example by spraying it.

The sheet thus obtained will have very good mechanical strength and will be advantageously used for the production of the absorbent mattress of any disposable hygiene article such as hygienic article and / or diaper for babies or incontinence.

For these latter articles, it will be sandwiched between an inner sheet and an outer sheet, the first being produced by a permeable comfort veil, the second generally consisting of a liquid-tight sheet such as a polyethylene film.

The use of the sheet produced by the process of the present invention is advantageous for such absorbent articles since the performance of the product is appreciably increased in terms of retention and absorption by the constitution of the network of fibers linked between them, and capillary breaks are avoided by mechanical destruction, that is to say by separation of the fibers. Finally, the resilience of the mattress is such that it contributes to the improvement of absorption.

Furthermore, it should be noted that, in certain cases, the nonwoven product obtained will make it possible to avoid the use of a complementary nonwoven commonly called a "fabric" surrounding the sheet of absorbent material.

On the other hand, the constitution of such a network makes it possible to advantageously fix in position in the three dimensions other elements inside the sheet, such as super-absorbent for example. This fact makes it possible to improve the absorption and retention characteristics, in terms of statistical average value of performance in particular.

Naturally, other implementations of the present invention, as well as other applications, within the reach of ordinary skill in the art, could have been envisaged without departing from the scope of the present application.

Claims (10)

1. Method for manufacturing a nonwoven web, consisting at least of a mixture of absorbent fibers, such as in particular cellulosic fibers, and synthetic fibers, characterized in that:
a homogeneous mixture of the cellulosic and synthetic fibers is produced to form a sheet in which the cellulose fibers at least are oriented relatively to each other,
- submitting the sheet of fibers thus formed to the effect of microwave radiation, not mechanically disturbing for the orientation of the fibers, allowing the fusion of synthetic fibers to bond together the cellulose fibers in order to create a network of fibers, limiting hot spots, retaining cellulosic fibers, to promote the absorption of the web, its tear resistance and its resilience. 2. The manufacturing method according to claim 1, characterized in that 5 to 30% by weight of synthetic fibers are dispersed in a homogeneous manner in the sheet. 3. Manufacturing process according to claim 1, characterized in that polyolefin fibers such as polymers are used as binding fibers. 4. The manufacturing method according to claim 2, characterized in that the synthetic fibers are dispersed so as to obtain a constant and homogeneous concentration in the three dimensions of the sheet. 5. The manufacturing method according to claim 2, characterized in that the synthetic fibers and the cellulose fibers are mixed after grinding the latter. 6. The manufacturing method according to claim 2, characterized in that the synthetic fibers are added before defibering the cellulose wadding and the synthetic fibers are ground during the defibration of the wadding. 7. The manufacturing method according to claim 1, characterized in that the web of mixed fibers is scrolled in a microwave dryer equipped with a source of emission of fixed microwaves and scrolling means linear of the tablecloth in the microwave field. 8. The manufacturing method according to claim 1, characterized in that, prior to the submission of the sheet to the effect of microwaves, the humidity of said sheet is increased to favor the action of microwaves. 9. Nonwoven tablecloth, manufactured by the method according to any one of the preceding claims. 10. Application of the nonwoven web according to claim 9 to the production of the absorbent mattress of hygienic articles and absorbent hygienic products for single use.