DE69716689T2 - Absorbent composite nonwoven fabric with a soft surface and a rough surface and method of manufacture - Google Patents

Description

Nowadays, a very large number of products based on fibrous materials for use in the household, clothing, hygiene, medical, industrial etc. sectors are manufactured from textile structures called "nonwovens".

Among these articles, apart from wiping materials, which are in the form of relatively fine sheets comparable to paper but with a very high absorbency, it has been proposed to produce genuine sponge substitutes, the dimensions of which (length, width and especially thickness) can vary widely depending on the intended use. By way of example, the thickness can be of the order of a few tenths of a millimetre when a wiping "rag" is produced, and can reach one centimetre or more for "sponge" type articles, the weight per square metre in turn varying from 30 g/m² to 200 g/m² or even more.

To manufacture these articles, one of the three processes for manufacturing nonwovens is used, namely the process known as dry process, which consists in producing a veil of fibres by mechanical or aerodynamic means using conventional textile machines such as rippers, cards, etc., or the process known as wet process, which is derived from the conventional manufacture of paper, and consists in producing a suspension of fibres which is laid down in the form of a sheet, or the process known as the "melt process", which consists in producing a web of continuous synthetic filaments arranged in a random arrangement with respect to one another, immediately at the exit from the nozzles for extruding the filaments.

It has long been proposed to use this arrangement for the manufacture of multilayer articles in order to obtain different properties on the two sides of the sheet formed, for example a printable or impermeable surface and a fibrous side, or an impermeable side and another side with a high absorbency.

The documents EP-A-0333211 and EP-A-0577156, the content of which is identical, describe a process for producing a nonwoven material which consists of interweaving or entanglement of the synthetic fibers of a first layer with the fibers of a second layer. According to these documents, the complex structure obtained can be subjected to a thermal bonding treatment which makes it possible to increase the hardness or resistance of the materials for bonding the fibers to one another without simultaneously deteriorating their structure.

The present invention relates to a novel type of absorbent composite nonwoven fabric consisting of at least two superimposed fiber webs or fiber layers which are bonded to one another by mutual penetration of the fibers in the thickness direction, characterized in that:

- the first web consists entirely or partially of heat-fusible synthetic fibres preferably selected from the class of polyolefins; advantageously, this web consists of a mixture of cellulose fibres or the like and heat-fusible synthetic fibres, the percentage of the latter in the layer being more than 30% and preferably more than 50%;

- the second layer consists of natural and/or artificial and/or synthetic fibres which have a higher melting temperature than the latter;

- the individual sheets are joined by subjecting them to a treatment which enables the synthetic fibres of the first sheet to be reorientated so that they are, on the one hand, intimately integrated into the structure of the second sheet and, on the other hand, have free ends or loops which are visible on one of the external faces of the composite material formed.

By subjecting the composite obtained to a treatment which allows the free ends of the synthetic fibres of the first web to melt, the latter is made abrasive by the formation of droplets at the point of melting.

The way in which the individual tracks are combined depends on the type of tracks.

By way of example, but not by way of limitation, this association can be carried out as follows:

- if the two individual webs are manufactured, for example, by the so-called wet or papermaking process, their manufacture takes place on a machine which enables two jets to be produced and superimposed, each corresponding to one of the webs; in this case, the superimposition takes place on the line, even before drying, and the joining is carried out by means of the action of jets of water under pressure;

- if the two individual strips are manufactured using the so-called dry process, also known as textile, they are also placed on top of each other and bonded together by a water-jet entanglement treatment;

- finally, if a composite is made from two sheets obtained by different processes, it is possible to bond one or the other of the sheets slightly beforehand by entangling them using water jets, avoiding blocking bonds of the chemical or thermal type; the two sheets are then placed one on top of the other and bonded by entangling them using water jets.

Advantageous and in practice according to the invention are:

- the synthetic fibres present in the composition of the first web preferably polypropylene or polyethylene fibres:

- with a linear density of more than 5 dtex, the upper limit being directly related to the fluid pressure used for entangling in order to ensure the coherence of the fibres with the rest of the web; the upper limit of fibres is determined by commercial availability, which currently allows fibres with a linear density of 17 dtex;

- whose length exceeds 5 mm, the upper limit depending essentially on the manufacturing process; a finer linear density therefore leads to the use of shorter fibres and the wet process requires a shorter cut than the dry process;

- whose surface is as rounded as possible; therefore, preference is given to using fibres that are multilobed or fibril-forming or have a flattened cross-section and are much more susceptible to the action of the fluid jets for entangling;

- although the use of polyolefin fibres, which have the characteristic of having a density of less than 1, is preferable, the use of other types of fibres may also be envisaged, for example fibres made from a copolymer of vinyl chloride (85%) and vinyl acetate (15%) having a melting temperature of the order of 160°C and a density of 1.37 g/cm 5;

- any type of fibre which allows an absorbent character to be obtained, such as wood pulp, cotton, linters, viscose, may be used as natural and/or synthetic fibres; in the case of a synthetic fibre, it may have a multilobed cross-section or be fibrillatable in order to optimise the action of the liquid jets;

- if synthetic structural fibres are incorporated into the second web, they have a higher melting point than those present in the composition of the first web; for example, fibres made of polyester or polyamide 6.6 (preferably over polyamide 6) are used, optionally crimped;

- if necessary, it is possible to add to one or the other of the webs a certain percentage of so-called binding fibres, for example bicomponent fibres, part or all of which, during a heat treatment, flows onto the neighbouring fibres, thus making it possible to achieve a "bonding" which makes the fibres integral; in such a case, the melting point of the binding part of these binding fibres is lower than the melting point of the structural fibres mentioned above, but may be lower or higher than that of the fibres of the first web intended to provide the "scratching" or "scouring" effect;

- after the two sheets have been superimposed, the resulting composite material is subjected to a heat treatment designed, on the one hand, to bring out the binding capacity of the binding fibres that may be introduced and, on the other hand and in particular, to melt the free ends of the synthetic fibres of the first sheet in order to increase the "scratching" effect;

- before or after a heat treatment, it may be possible to carry out additional mechanical treatments, such as creping or Application of a Micrex type device to supple the product, or chemical treatments such as:

- Additions of latex-type polymer emulsions intended to mechanically reinforce the product,

- Addition of chemical associating agents,

- Addition of hydrophilic agents,

- Impregnation of degreasing liquids (dishwashing liquid type), skin protection agents, release agents, etc.

The respective weights per square metre of the two layers are adjusted according to the applications, these weights per square metre being able to range from 15 to 200 g/m² for the second web and from 10 to 70 g/m² for the first web. The invention also relates to a process for producing such a product, the process consisting in producing two layers of single fibres, the two layers being bonded together downstream of the formation zone by a needling treatment using a fluid jet acting at least against the surface of the web comprising the thermofusible fibres intended to form the "scratching" surface of the finished composite article.

The composite nonwoven fabric formed is then dried and receives a supplementary heat treatment which allows the partial melting of the ends of the chemical fibres of the first layer, which remain bonded to the base composite nonwoven fabric.

For example, to implement such a process, it is possible to use a conventional machine for producing a nonwoven fabric by wet means, such as a VOITH hydroformer machine, at the outlet of which is arranged a hydraulic binding unit, also of a known type, such as a TCBT-PERFOJET "Jet Lace" type water jet treatment machine, this machine being regulated so that the jets act preferentially on the side of the multilayer material consisting of the web containing the heat-fusible synthetic fibers; this allows the fibers to be reoriented in the Z direction of the sheet so that they are "driven" into it.

If the two individual layers are produced by the wet method, they are united on the draining sieve before being treated by means of fluid jets.

It is also possible to provide for this second layer to be produced dry, the unification being carried out at the end of the formation of this layer by applying to its surface, on the side/on which the action of the fluid jets for the entangling is to take place, the first sheet produced wet or dry. In such a case, the two superimposed layers are preferably re-moistened before being subjected to the action of the jets for entangling.

After production, the composite nonwoven fabric formed is dried and then, if necessary, impregnated with chemical binders based on acrylic (copolymerized if necessary), ethylene-vinyl acetate, polyurethane or similar, as well as with various additives that allow the reinforcement of specific properties such as hydrophilicity, flexibility, etc.

After drying, a heat treatment is preferably carried out on the same machine, which allows the partial melting of the ends of the chemical fibres of the upper layer, which remain bonded to the base composite nonwoven fabric, the melted ends increasing and enhancing the roughening effect.

However, a better understanding of the invention and the advantages it provides will be obtained from the embodiments given below by way of example, but not by way of limitation.

These examples were produced on a conventional papermaking machine of the type Hydroformer VOTTH, which is designed with two separate feeders for suspensions, thus allowing the production of a multi-layer sheet.

At the exit of this machine there is a station for mixing fluid jets, sold by ICBT-PERFOJET under the name JET-LACE, which has four rows of nozzles that allow the composite to be subjected to the action of jets/needles obtained from water at a pressure of between 10 bar and 125 bar. The number of jets/needles per meter of width of each row can vary from 800 to 1700 and is advantageously of the order of 1000, with the diameter of each spray nozzle opening is substantially between 100 and 140 µm, but may optionally reach a value of 300 µm.

example 1

On a papermaking machine of the type mentioned above, a composite nonwoven fabric according to the invention is produced starting from two fiber suspensions with the following compositions:

for the upper layer, which is ultimately subjected to the preferential action of the needle jets and represents a total of 23% of the total fibre mass of the composite after its formation, a suspension of a mixture comprising:

- 50% polypropylene fibres (titer 6.7 dtex, cutting length 6 mm, round cross-section); these fibres are dyed into the material, which allows the different layers of the finished product to be identified visually.

- 50% cellulose fibres, consisting of long papermaking fibres from pine.

- for the lower layer, which forms the second, flexible and advantageously absorbent web and represents a total of 77% of the total fibre mass in the finished composite, a suspension comprising:

- 67% long cellulose fibres from pine,

- 33% polyester fibres (titer 1.7 dtex - cutting length 18 mm - round cross-section).

The two sheets are superimposed so that the sheet comprising the polypropylene fibres is in the upper section and, before drying, the composite is subjected to the action of water jets for entangling, the four successive series of jets being obtained with water under increasing pressure, which can reach 23 bar for the first series, 27 bar for the second series, 55 bar for the third series and also 55 bar for the fourth series.

The action of the water jets modifies the initial position of the fusible and rigid fibers, which originally lie completely in the plane of the sheet, by reorienting the fibers along the Z-axis of the sheet and their end as a result the tangled knot becomes visible, even in the longest fibers, which form loops between the tangled knots.

The composite is then dried and subjected to a heat treatment inside a tunnel oven heated to 400ºC (the burner temperature if the fibres to be melted are of the polypropylene type). This heat treatment causes partial melting of the polypropylene fibres visible on the surface of the web, making it abrasive by the formation of droplets at the melting point. Although the effective temperature inside the oven is 190ºC, i.e. above the melting point of polypropylene, the speed of passage of the web inside the oven is such that the fibres only partially melt, the other synthetic fibres (except for the binding fibres, if present) present in the composition of the composite not being affected by this heat treatment, thus making it possible to preserve the flexibility of the article. For example, the speed of passage of the web inside the oven is of the order of 90 m/min. the oven has an "effective" length of six meters; the nonwoven fabric is then preheated to a temperature of 140ºC.

Note that these values for temperature and speed are not limiting, since a higher speed can be compensated by a longer useful length of the oven or a higher temperature, or a different type of fiber requires an adjustment of the selected temperatures.

At the machine exit, a sheet weighing 40 g/m² is obtained, with one side being flexible and absorbent and the other side having abrasive properties due to the exposed ends of the polypropylene fibres.

In this regard, it should be noted that the choice of polyolefin fibres for forming the visible scratching side of the article facilitates its manufacture since, during the suspension to form the web, said fibres, which have a density of less than 1, remain on the surface during wet formation.

Depending on the desired application, this sheet can either be used as is or it can be additionally treated on the line with a binding agent tel, in this case an acrylic polymer/vinyl acetate emulsion applied in a ratio of 10 g/m².

The features and properties of the sheets produced are summarized in the table below.

The measurements of the characteristics of the products are carried out under the following conditions.

Weight per square metre: according to EDANA 40.3-90 method

Thickness: according to AFNOR NF Q 03 + 016 method

Permeability: according to method EDANA 140.1-81

Fracture: according to method EDANA 20.2-89 (modified)

Distance between jaws: 127 mm

Pulling speed: 25.4 mm/min

Elongation: according to method EDANA 20.2-89 (modified)

Distance between jaws: 127 mm Pulling speed: 25.4 mm/min Detection at 75% of the max. tear strength

Wet fracture: according to the same procedure as dry fracture, but after a dwell time of the test strips of 10 min under 20 mm distilled water at 20ºC

Tearing: according to method EDANA 70.3-96

Stiffness: with the device "HANDLE-O-Meter"

Absorbency: according to method EDANA 10.2-96.

From the above examples it can be seen that the non-impregnated product has a higher absorbency, is much more flexible, and has relatively low mechanical strength properties, which could possibly be compensated by incorporating a certain percentage of hot-melt fibers, as indicated above.

Such products are particularly suitable for the manufacture of semi-etching or highly absorbent wiping products, but could also be used in other areas, such as the food and agricultural sectors, solvent media, laboratory workbenches, etc.

The same product, when impregnated with a polymeric binder, is particularly suitable for the production of:

Wiping products impregnated with dishwashing liquid for single use (camping, etc.),

towels impregnated with degreasing and softening agents for workers (workshops, etc.),

windscreen wipers impregnated with an appropriate liquid for vehicles (dried insects, bird droppings), for household use, etc.,

Mopping products for DIY (cleaning railings, dusting outside the house, etc.).

Example 2

A composite material according to the invention is produced by combining a nonwoven fabric obtained by wet processing on the one hand and a nonwoven fabric obtained by dry processing on the other hand.

The wet-processed fleece, produced on the same machine as the previous example, has only a single jet, which represents approximately 50% of the total mass of fibers in the final product.

This web is manufactured from a fibre suspension which has:

- 33% polypropylene fibers with titre 6.7 dtex, cut length of 6 mm, round cross-section;

- 67% cellulose (wood pulp) from long fibers (softwood).

This first web is applied to a carding veil, representing 50% of the total fibre weight, consisting of crimped polyester fibres with a titre of 1.7 dtex and a cutting length of 38 mm, before being treated by the fluid jet unit. This carding veil is preferably slightly disturbed beforehand with water jets in order to ensure its cohesion and to facilitate its handling.

The carding veil is placed under the veil obtained by the wet method, the whole being moistened again before being subjected to the action of the tangling jets, which are carried out in the same way as in Example 1.

After the composite has been manufactured, the product is subjected to a heat treatment as in the previous example, which leads to a partial melting of the polypropylene fibres, making the surface where they are present abrasive.

A composite product is obtained whose properties are listed in the table below.

Square meter weight 68.4 g/m²

Thickness: 255 um under 100 kPa

Permeability. 1160 L/m²/S under 196 Pa

Longitudinal fracture 1920 N/M

Fracture in transverse direction 690 N/M

Elongation in longitudinal direction 29%

Elongation in transverse direction 30%

Wet fracture in longitudinal direction 1600 N/M

Wet fracture in transverse direction 550 N/M

Longitudinal tear 1330 cN

Tear in transverse direction 2810 cN

Longitudinal stiffness 31 cN (Handle-O-Meter)

Transverse stiffness 5 cN (" " ")

Absorbency 402%

Such a product, having a compliant side consisting of the polyester fibers and a rough side, is particularly suitable for use as various wiping materials similar to those mentioned in Example 1, which also have greatly improved compliance.

It should be noted that the invention is not limited to the previously described embodiments, but extends to all variants produced according to the same basic ideas.

It is therefore possible to treat the product in order to incorporate various additives, such as surface-active products such as the alkyl sulfonates currently used in dishwashing liquids, these products being added either alone or mixed with a binder. It would also be conceivable to add associating, degreasing, insecticidal, bactericidal, flame-retardant products and solvents.

Although polypropylene is particularly suitable for the manufacture of the scratching side of the article, polyethylene fibres may also be used, or, where appropriate, other fibres such as those derived from polyvinyl chloride, whose melting point allows heat treatment to be carried out without deteriorating the characteristics of the fibres present in the structure of the composite material. The choice of polypropylene as a material particularly suitable for the application of the invention rial is explained by the fact that, at the date of the present application, it is the product which has the best price/properties ratio (solvent resistance, rigidity, abrasiveness, contact with skin and food).

Furthermore, it could be envisaged to manufacture products with a much higher weight per square metre than those indicated in the previous description.

Finally, the web constituting the preferably absorbent, flexible layer is formed from fibers that are preferably selected depending on the properties sought. For example, if a flexible and highly absorbent side is desired, viscose or cotton are preferably used; if an article with good tear resistance is desired, polyamide fiber is preferably used; and if it is desired to improve the feel, acetate or cellulose fibers (rayon) are preferably used.

Claims (10)

Absorbent composite nonwoven material consisting of at least two superimposed webs or layers bonded together by mutual penetration of the fibers in the thickness direction, wherein: - the first web consists entirely or partly of heat-fusible synthetic fibres, preferably selected from the class of polyolefins; - the second web is made of natural and/or artificial and/or synthetic fibres which have a higher melting temperature than the latter; - the individual sheets are joined by subjecting them to a treatment which enables the synthetic fibres of the first sheet to be reorientated so that they are, on the one hand, intimately integrated into the structure of the second sheet and, on the other hand, have free ends or loops which are visible on one of the external faces of the composite material formed; characterized in that: - the composite obtained is subjected to a heat treatment which allows the free ends of the synthetic fibres of the first web to melt, thus rendering the latter abrasive by the formation of droplets at the point of melting. 2. Material according to claim 1, characterized in that the first web consists of a mixture of cellulose fibers or the like and heat-fusible synthetic fibers, the percentage of the latter in the web being higher than 30% and preferably higher than 50%. 3. Material according to one of claims 1 and 2, characterized in that the synthetic fibers present in the composition of the first web are polypropylene or polyethylene fibers. 4. Material according to claim 3, characterized in that the fibers have a titre of more than 5 dtex and a length of more than 5 mm. 5. Material according to one of claims 1 to 4, characterized in that the natural and/or synthetic fibers which allow the retention of the absorbency property are papermaking fibers, viscose fibers or the like. 6. Material according to one of claims 1 to 5, characterized in that the synthetic fibers present in the composition of the second web are polyester or polyamide fibers, optionally crimped, and having a melting point higher than that of those present in the composition of the first web. 7. Material according to one of claims 1 to 6, characterized in that the composite undergoes an additional treatment such as creping, treatment with wetting agents enabling an improvement of its hydrophilicity, impregnation with a more or less aggressive liquid such as dishwashing liquid. 8. Material according to one of claims 1 to 7, characterized in that the square meter weight of the second web is between 15 and 200 g/m², and that of the first web is between 10 and 70 g/m². 9. Process for producing a material according to one of claims 1 to 8, in which two sheets of single fibers are produced, the two sheets being bonded together downstream of the formation zone by a needling treatment using fluid jets acting at least against the surface of the first sheet, characterized in that the composite nonwoven fabric formed is then dried and receives a supplementary heat treatment which makes it possible to cause the partial melting of the ends of the chemical fibers of the first layer which remain bonded to the base composite nonwoven fabric. 10. Process according to claim 9, characterized in that the two individual layers are produced by wet means, their combination on the draining sieve being carried out before treatment by means of fluid jets. Process according to claim 9, characterized in that the second web is manufactured by the process known as "dry method", the joining of the two individual webs at the end of the formation of this web being carried out dry method by applying to their surface, on the side on which the action of the fluid jets for entangling is to take place, the first veil manufactured wet method, the two superimposed webs preferably being re-moistened before being subjected to the action of the jets for entangling.