EP0518003B1 - Spun-bonded, non-woven fabric continuous thermoplastic filaments and method of manufacturing the same - Google Patents

Abstract

A spunbonded fabric comprises continuous thermoplastic filaments, which adhere to one another at their intersecting points without binder, and whose material comprises at least 50 weight % biodegradable polycaprolactone having a mean molecular weight of from 35,000 to 70,000. In the production process of the spunbonded fabric, no additional stabilization step is necessary after the filaments are deposited.

Description

The present invention relates to a spunbonded nonwoven fabric made from continuous thermoplastic filaments and to a method for its production according to the preamble of claims 1 and 5, known for example from DE-A-3 932 877.

Biodegradable nonwovens made from staple fibers are known: the use of viscose fibers is described in I. MARINI, General. Nonwovens Report (1986) Vol. 14, No. 4, 214 f.

These biodegradable fibers are natural fibers and natural fiber derivatives. Areas of application are disposable consumer goods such as Children's and incontinence diapers, bed pads, surgical gowns and surgical drapes and plasters.

Biodegradable is to be understood here and in the following to mean that the fiber or nonwoven material is completely destroyed by microorganisms. These microorganisms are bacteria and fungi that are present in the soil, among other things.

A disadvantage of the known biodegradable nonwoven fabrics is the anisotropy inherent in all staple fiber products, which is particularly evident in the mechanical properties, e.g. the strength, makes it disadvantageously noticeable: this is different in the longitudinal and transverse directions, and it is easy to see that this limits and makes the properties of use more difficult. Another criterion is the consolidation of the biodegradable short fibers, which usually has to be done with additional binders, since natural fibers are known to have no thermoplastic properties. Such binders are critical because of possible skin irritation or problems with wound tolerance; moreover, they are usually not biodegradable.

Often, therefore, preference will be given to spunbond nonwovens made from continuous polymer filaments, which have the same strength properties in all directions, are often more hygienic in use because of the smooth surface of the polymers and because of the thermoplastic properties, they can be easily connected to one another by heat, ie welded together. The production is described for example in DE-PS 31 51 322, the filament polymer being polypropylene.

Biodegradable polymers, for example thermoplastic cellulose derivatives, previously used for melt spinning to form continuous filaments present difficulties in this process: Just above the melting temperature, these polymers remain so viscous that they cannot be spun into filaments; if the temperature is increased further, decomposition usually occurs immediately. There is therefore only a very narrow temperature band within which spinning can be carried out.

DE-A-3 932 877 discloses an erosion protection and / or substrate stabilization mat made of at least predominantly degradable synthetic polymer threads. The mat can be made of nonwoven. The state of the art states that the polymer threads can be connected, welded or glued together at their crossing points.

Starting from the latter prior art and from the inadequate heat stability of biodegradable polymers during spinning, it was the object of the present invention to provide an improved generic spunbonded nonwoven whose biodegradable filaments can be spun in a conventional manner without the problem of the temperature influence mentioned. It should be possible to dispense with a binder when the nonwoven is consolidated, and the filaments should also be able to be colored and hydrophilic.

The solution to this problem consists in a spunbonded nonwoven made of thermoplastic filaments according to the preamble of the first claim, supplemented by its characteristic features. Preferred embodiments and the manufacturing method are specified in the subclaims.

All solution variants have in common that the polymer forming the filaments consists of at least 50% by weight polycaprolactone with an average molecular weight of 35,000 to 70,000 and that the welding of the filaments at their crossing point is autogenous, i.e. solely through their thermoplastic, sticky properties during the placement on each other.

The biodegradability of polycaprolactone has been known for a long time, but so far this material has only been used for the production of surgical sutures, i.e. relatively coarse yarns, with a melted thread being quenched in water. This process has nothing in common with melt spinning technology.

The type of polycaprolactone mentioned is surprisingly processable on conventional melt spinning devices to form endless polymer threads, the process steps of melting, pumping to the nozzles, drawing and cooling by means of tempered air and laying down the finished filaments within the scope of manual skill on the thermal properties of the polymer can be matched. However, a conventional melt spinning plant can be used in any case. It is essential that a finished, consolidated spunbonded nonwoven fabric is already present in the manufacturing process, after deposition, ie no subsequent consolidation step is required, for example by embossing rollers or the like. By simply optimizing the melting temperature and the drawing air temperature, it can be achieved that at the time of depositing the freshly spun filaments, the polymer is still in the state of incomplete crystallization, which together with the sufficiently high surface temperature of the filaments leads to such a stickiness that thermoplastic welding occurs automatically at the filament crossing points.

This is surprising because with conventional thermoplastic fibers, e.g. Polypropylene, polyethylene, polyamide or polyester, always solidification by subsequent heating and embossing is necessary; only the polycaprolactone specified above in a proportion of at least 50% by weight in the filament-forming polymer allows subsequent thermal consolidation to be dispensed with.

The solution to the problem as well as the advantage just mentioned can be achieved in a simple manner in that the filament material consists of the polycaprolactone mentioned. It is easily spinnable to form a continuous filament at 150 to 220 ° C, with no decomposition; furthermore, this material is stretchable after spinning out of the nozzles, a property that other biodegradable polymers do not have.

The limits of the molecular weight are given by the fact that at smaller values the mass is too wax-like to be still spinnable and at molecular weights over 70,000 the material becomes brittle.

A further improvement in the spinning behavior and the self-solidification during deposition is achieved by processing it in admixture with other thermoplastic polymers instead of the pure polycaprolactone. Preference will be given to two-component polymer mixtures, the polycaprolactone being present at least 50%, based on the total weight. Biodegradable two-component systems in the above sense are those which contain polyhydroxybutyrate, polyhydroxybutyrate hydroxyvalerate copolymer, a polylactide or polyester urethane as the second polymer component. Although the materials of these second components are biodegradable, they cannot be spun as a pure substance or only with great technical effort. Only the combination with polycaprolactone makes the mass suitable for conventional melt spinning processes and solves the requirements mentioned in the task.

Furthermore, it has surprisingly been found that conventional, spinnable polymers, such as polyethylene, polypropylene, polyamide or polyester, are self-setting after spinning in a mixture with polycaprolactone.

This combination of materials also completely solves the task, particularly with regard to degradability, since the resulting polymer mixture surprisingly proves to be largely biodegradable, in contrast to the pure polyolefins, polyamides or polyesters, which are inert in this regard demonstrate.

All of the polymer mixtures mentioned and the pure polycaprolactone are easy to dye, have an extensibility of at least 50% and impart a textile character to the spunbonded nonwoven.

It is possible to vary the basis weights of the finished spunbonded nonwoven from 10 to 120 g / m.

Further advantages are permanent hydrophilicity and thus an antistatic behavior.

In addition to hygiene and medicine, the following areas of application are possible: covering fleeces for horticulture and agriculture; adhesion-promoting adhesive fleece and adhesive between polar and non-polar polymers, for example between polyethylene and polypropylene or polyester and polyamide; iron-on interlining nonwovens in the outer clothing area because of the anisotropic stretching property; technical applications in which permanent hydrophilic properties or antistatic properties are required, e.g. filter materials.

Example 1: Manufacture of a polycaprolactone nonwoven

Polycaprolactone with a melting point of around 60 ° C and an MFI (melt flow index) of 10 g / 10 min at 130 ° C / 2.16 kg is melted at an extruder temperature of 185 ° C. The melt temperature of the polymer melt is 203 ° C. The air required to stretch the polymer melt emerging from the spinnerets has a temperature of 50 ° C.

The drawn continuous filaments are caught on a screen belt and wound up without further consolidation. The basis weight of the polycaprolactone spunbonded nonwoven is 22 g / m.

Example 2: Preparation of a polycaprolactone-polyhydroxybutyrate-hydroxyvalerate spunbonded nonwoven

A polymer mixture of 90% polycaprolactone and 10% polyhydroxybutyrate-hydroxyvalerate copolymer with an MFI value of 34 g / 10 min at 190 ° C / 2.16 kg is melted at 182 ° C. The polymer melt emerging from the spinnerets is stretched with air at a temperature of around 40 ° C. The drawn continuous filaments are caught on a conveyor belt and the nonwoven is wound up without further consolidation. The basis weight of the nonwoven is 23 g / m.

Example 3: Production of a polycaprolactone-polyethylene spunbonded nonwoven

A polymer mixture of 75% polycaprolactone and 25% polyethylene is processed to a spunbonded nonwoven under the same conditions as described in Example 2.

All spunbonded nonwovens of Examples 1 to 3 are suitable for applications in hygiene products, e.g. as a diaper covering fleece, in agriculture as a mulch film, as an adhesive fleece for the production of textile laminates or for technical applications such as Filter materials.

Claims (5)

1. A spunbonded nonwoven fabric formed of continuous thermoplastic filaments which is composed to the extent of at least 50% by weight of biodegradable polymer and the filaments of which are fused to one another at their points of intersection, characterized in that the biodegradable polymer is composed of polycaprolactone of an average molecular weight of 35,000 to 70,000 and in that the fusing of the filaments at their points of intersection is brought about solely by the thermoplasticity of the filament polymer, without the presence of an additional binder.
2. A spunbonded nonwoven fabric according to claim 1, characterized in that the continuous filaments are entirely composed of polycaprolactone.
3. A spunbonded nonwoven fabric according to claim 1, characterized in that the continuous filaments are composed of a two-component polymer mixture, the one component being the polycaprolactone, the other being biodegradable polyhydroxybutyrate, polyhydroxybutyrate-hydroxyvalerate copolymer, a polylactide or a polyester-urethane.
4. A spunbonded nonwoven fabric according to claim 1, characterized in that the continuous filaments are composed of a two-component polymer mixture, of which one component is the polycaprolactone, of which other component is polyethylene, polypropylene, polyamide or a polyester.
5. A method of manufacturing a spunbonded nonwoven fabric according to any of claims 1 to 4, the polymeric material used or the material mixture being melted, fed by means of pumps to the spinnerets, spun by means of the spinnerets, stretched and cooled by temperature-controlled air and laid down as filaments to form a spunbonded nonwoven, characterized in that a polymeric material or a material mixture which contains at least 50% by weight of biodegradable polycaprolactone of an average molecular weight of 35,000 to 70,000 is melted, and in that the melting temperature and the stretching-air temperature are set such that the filaments still have at the time of laying down such a high surface temperature, and hence tackiness, that a thermoplastic fusing at the points of filament intersection occurs of its own accord, without an additional bonding step taking place after the laying down.