EP0080144A1 - Process for fleece strengthening - Google Patents

Abstract

Process for the consolidation of a nonwoven made of more or less disoriented fibers, in which a crosslinkable binder is applied to the surface on one or both sides, optionally distributed in pattern form, freed of any carrier liquid that may be present, and crosslinked and consolidated by heating, which is different from the one that may be present Carrier liquid-freed binder is temporarily liquefied using pressure and heat and pressed into the nonwoven and the conditions used are maintained until the wetted fibers are spatially defined in the solid matrix formed by the crosslinking of the binder.

Description

The invention relates to a process for the consolidation of a nonwoven fabric made of more or less disoriented fibers, in which a crosslinkable binder is applied to the surface on one or both sides, optionally distributed in a pattern, is freed of any carrier liquid which may be present and is crosslinked and consolidated by heating.

Methods of the type specified above have long been known and common. The removal of the carrier liquid and the crosslinking of the binder are carried out at the same time in the course of heating, but binding migration, i.e. a relative depletion of binder in certain cross-sectional areas of the nonwoven must be accepted. The fibers of the nonwoven adhere to one another less firmly in these areas, which is equivalent to the fact that the degree of solidification which can be achieved per se is achieved only to an insufficient extent.

The procedure for producing spot-bonded nonwovens was corresponding. Was used in this case, a crosslinkable binder, a printing paste containing, and this was printed in tiny, closely adjacent _'surface areas on the nonwoven fabric, and optionally up to a certain degree pressed. The carrier liquid was then removed by final drying and at the same time the binder was crosslinked during its solidification. A uniform binder distribution, based on the cross-section of the nonwoven fabric, cannot be achieved here either, because the carrier liquid evaporating from the surface during drying sucks residual liquid from the interior of the fiber structure in the direction of the surfaces and thus at the same time a portion of the binder volume originally contained in the interior. For this reason, the fibers in the interior and possibly on the back of the nonwoven are not bonded to one another sufficiently tightly, which in addition to delamination phenomena can lead to poor pilling values on the back.

The above-mentioned problem becomes increasingly disruptive with increasing thickness of the nonwoven, and it has therefore already been proposed to increase the application amount while reducing the binder concentration and, if appropriate, to print the nonwoven to be treated both from the back and from the front . However, it has been shown that the methods are disadvantageous in terms of the smoothness of the fleece or in terms of practical implementation. In addition, no significant improvement in the strength values achieved was actually achieved.

The invention has for its object to develop an easy-to-implement method, preferably for the point consolidation of a nonwoven, which enables a uniform bonding of all fibers distributed over the cross section by means of a crosslinked binder and thus the achievement of an optimal strength.

This object is achieved in that the binder freed from the carrier liquid, if any, is temporarily liquefied using pressure and heat and pressed into the fleece and. that pressure and heat are maintained up to the spatial definition of the wetted fibers in the matrix formed by the crosslinking of the binder. Both the liquefaction and the solidification occur quite spontaneously during the crosslinking reaction of crosslinkable substances, which enables continuous work on a calender system. Although the crosslinking reaction is not yet complete when the binder is transferred from the liquid to the solid phase, the mechanical resistance of the formed However, the matrix is large enough to successfully counteract a subsequent change in the position of the bonded fibers, even if the pressure decreases. The final crosslinking of the binder can therefore take place without pressure, for example by heating as the nonwoven is passed through a tempering chamber.

The crosslinkable binder is preferably applied point by point to the nonwoven fabric to be consolidated, i.e. in the form of tiny, closely adjacent surface areas which can optionally also touch one another or which can also merge into one another. In these areas, the fibers are glued in the same way, based on the cross-section, and they lie more or less loosely on one another in the intermediate zones.

The binding technology described leads to the fact that the nonwoven in the areas containing the binder is thin and strongly compressed, whereas in the intermediate areas it is bulky and voluminous in accordance with the original thickness and properties of the nonwoven used. The intermediate areas can determine the overall impression of the finished nonwoven with a correspondingly fine design and correspondingly finer mutual assignment of the binder-containing areas and give it an extraordinarily soft feel.

With the proposed consolidation method, nonwovens made from natural and / or synthetic fibers can be treated.

Polyester, polyamide and / or cotton fibers and the like are particularly suitable. Synthetic fibers are generally preferred because of their higher wear resistance, their crimp and their elasticity.

The fibers are spread over a wide area using known methods, with the aim of uniform fiber density and distribution in all areas. The goal can be achieved particularly well by using a carding device, an air laying device or a direct spinning device. The fabric can be pre-consolidated and compacted immediately after being deposited, for example by needling and / or by passing it through a pair of heated rollers.

The preferred crosslinkable binders are self-crosslinking acrylic esters, self-crosslinking ethylene-vinyl acetate copolymers and self-crosslinking synthetic rubbers such as SBR and NBR.

Of course you can. binders are also used which require a crosslinking agent to crosslink. In order to partially apply a crosslinkable binder, a paste of an emulsion or the like is generally applied directly to the nonwoven fabric, for example with the aid of a rotary screen printing stencil or a doctor blade device.

Subsequently, the printed nonwoven fabric is preferably dried in a dryer, if possible not longer than 5 minutes at a temperature of at most 80 ° C., in order to remove the moisture contained while avoiding crosslinking reactions of the binder.

It is also possible not to print the binder directly onto the nonwoven fabric to be consolidated, but onto a removable rubber plate or rubber drum, to remove the moisture first and only then to transfer the remaining binder onto the surface of the nonwoven fabric.

Such a procedure makes it possible to prevent fine patterns of the binder from spreading, as a result of which particularly clearly and precisely delimited areas of binder are obtained in the nonwoven. Compared to a similar material on which the binder has been printed directly, this is softer to the touch and relatively free from such phenomena as leakage or bleeding of the binder pattern.

The nonwoven provided with the binder is then exposed to the action of heat and pressure in order to evenly distribute and crosslink and solidify the temporarily liquefying binder over the cross section of the nonwoven. When using a calender with a steel and a cotton roller, the temperatures required for this are between 150 and 250 ° C with a line pressure of maximum 50 kg / cm. The binder-containing parts of the nonwoven fabric are thereby compressed so that they are completely soaked through to the back of the temporarily liquefying binder which is initially only partially arranged on the surface of the nonwoven fabric. You will _. fixed in this form and then form thin and highly compressed surface areas.

The crosslinking process initiated during the calendering treatment is completed by a subsequent heat treatment, as a result of which the properties of the sheet material sought by the introduction of the binder undergo a lasting improvement, in particular an improvement in the washing and cleaning resistance with good softness and flexibility.

If, on the other hand, the calender conditions in a partially applied binder are set so sharply that the crosslinking reaction is already completed during the calendering process, the resulting nonwoven fabric as a whole has a significantly higher fiber density and a hard feel.

In the case of a nonwoven fabric partially consolidated by the proposed method, the unbound areas have almost their original density, and they are securely held in partially compressed, thin and bonded areas with a relatively reduced thickness. The non-bonded surface areas therefore have a very low bending resistance and they give the consolidated nonwoven a soft, textile-like feel. Since the bonded partial areas spring back in relief behind the unbound areas that essentially determine the surface, such a nonwoven fabric does not tend to show signs of dissolution when the surface is subjected to an abrasive load and is particularly resistant to washing and cleaning processes.

Due to the good integration of the unbound partial areas into the bound partial areas, the nonwoven fabric has a good inherent strength, which, with a correspondingly fine design and mutual assignment of the bound areas, enables the surface to be given a florally homogeneous appearance and a soft feel.

example 1

On a carding machine, polyester fleece with a denier of 1 denier and a staple length of 38 mm is used to produce a nonwoven fabric that has a basis weight of 30 g / m ² with a uniformly disordered fiber structure. The nonwoven fabric is then compressed and pre-consolidated by passing it through a steel calender, the rollers of which are at a mutual distance of 0.05 mm at a temperature of 150 ° C. The steel rollers exert a force of 30 kg / cm on the nonwoven fabric. This is then inherently firm, but only to the extent that a non-destructive removal of individual fibers is readily possible, for example under the influence of external forces.

Then, using a rotary screen printing stencil, a binder paste is applied to the nonwoven fabric in sub-areas that are spaced apart. The binder paste consists of a self-crosslinking acrylic ester emulsion and it has a viscosity of 15,000 cps at a 40% concentration.

The rotary screen printing stencil for applying the binder paste has a zigzag-shaped, rectangular pattern, each rectangle being 0.9 x 0.6 mm in size. After the printing process, the binder plastic covers 15% of the total area of the printed fabric. It contains 13 g of pure binder per square meter.

The nonwoven fabric with the binder paste printed thereon is transferred to a dryer and dried at a temperature of 80 ° C. for about 5 minutes, the moisture contained in the binder emulsion being removed while avoiding a crosslinking reaction.

The nonwoven fabric is then transferred to a calender which has a steel and a cotton roller. These are heated to a temperature of 190 ° C. and are in contact with the nonwoven fabric with a force of 30 kp / cm, the crosslinkable binder initially on the surface being temporarily liquefied and pressed into the interior of the nonwoven fabric. The binder completely penetrates the nonwoven fabric to the back in a distribution corresponding to the original print pattern, and it is crosslinked and solidified in this form and distribution. The crosslinking process is completed by a final heat treatment at 150 ° C for a period of 5 minutes.

The fibers in the unbound areas return to their original shape after a short period of time.

The finished nonwoven thus returns to its original thickness and is characterized by good suppleness, a firm bond, high wash resistance and good cleaning resistance.

Example 2

A binder of self-crosslinking acrylic ester emulsion was partially applied to a 70 g / m ² non-woven fabric made of polyester fibers with a thickness of 1.5 denier and a cutting length of 51 mm, as described in Example 1. The binder had a 49% concentration and a viscosity of 15000 cps.

The rotary screen printing stencil used to apply the binder emulsion had a rectangular zigzag pattern, with each rectangle measuring 2.5 x 0.4 mm. The areas printed with binder emulsion then covered 15% of the total area. They contained 30 g of pure binder per square meter.

To remove the moisture contained in the binder emulsion, the nonwoven fabric was then subjected to drying under the conditions of Example 1 and then transferred to the same calender. The calender conditions were characterized by a temperature of 190 ° C and a line pressure of 40 kp / cm.

A heat treatment at 150 ° C. was then carried out for 10 minutes. As a result, a highly supple fleece was obtained with a very precisely structured unevenness between the bound and the unbound parts. Then the fleece was roughened with emery paper of 240 grit. The result was a product with a well patterned pile, fine appearance and good grip.

Example 3

A binder paste print made of self-crosslinking acrylic ester emulsion was applied to a detachable silicone conveyor belt. The concentration and viscosity of the binding medium, the sieve pattern, the binding surface and the dry weight of the binding medium corresponded to the information from Example 2. The moisture from the binding paste print was completely removed by using a dryer with a temperature of 80 ° C., careful care being taken that cross-linking reactions did not occur. A nonwoven fabric with a basis weight of 70 g / m ^{2 was then} applied to the top. The nonwoven fabric consisted of rayon staple fibers with a titer of 1.5 denier and a cutting length of 51 mm. Both fabrics were then transferred together in a calender and exposed to a line pressure of 3 kp / cm at 100 ° C. As a result, the binder was transferred to the nonwoven in a distribution corresponding to the shape of the screen pattern, the two sheets were separated from one another, and the nonwoven provided with the binder imprint was under subjected to the conditions of Example 2, a calendar treatment and a final heat treatment at 150 ° C.

As a result, a bonded nonwoven was obtained. This was characterized by a particularly good water absorption capacity and a high resistance to abrasion, which makes it particularly suitable as a wipe for cleaning purposes.

Claims (3)

1. A process for the consolidation of a nonwoven made of more or less disoriented fibers, in which a crosslinkable binder is applied to the surface on one or both sides, if appropriate distributed in a pattern, is freed of any carrier liquid and crosslinked and consolidated by heating, characterized in that the binder freed from the carrier liquid, if any, is temporarily liquefied using pressure and heat and pressed into the fleece, and that pressure and heat are maintained until the wetting fibers are spatially defined in the matrix formed by the crosslinking of the binder. 2. The method according to claim 1, characterized in that the crosslinking of the binder is completed by a subsequent heating, optionally carried out without pressure. 3. The method according to claim 1 to 2, characterized in that the binder is distributed in a pattern on the nonwoven.