EP0464400A1 - Method for making needled nonwoven fabrics - Google Patents

Abstract

Process for the production of needled spunbonded nonwovens made of thermoplastic fibers, in which the nonwoven fabric coming from the spinning plant is thermally sealed to the surfaces and a lubricant is added before the needling.

Description

The invention relates to a process for the production of needled spunbonded nonwovens, in which a nonwoven consisting of deposited continuous filaments is thermally sealed only on the surface of the nonwoven and needled with a lubricant.

As already known from DE-PS 30 09 116, in order to achieve favorable nonwoven properties, in particular to achieve high nonwoven strength and uniformity, it is essential to finish the nonwoven prior to needling. By treating the nonwovens with a finishing agent before needling, the sliding properties are improved, which on the one hand prevents needle breaks during needling and on the other hand damages the threads. The finish was applied by means of nozzles or by diving. When applied by means of nozzles, however, the jet effect showed the disadvantage that the fleece structure of the still loose and unconsolidated fleece webs was partially destroyed and the cohesion of the fleece was broken. The fleece structure was also destroyed when the loose laid scrim was immersed, for example in a liquid lubricant bath or in foam. It was therefore necessary to fix the fleece slightly before needling with a light pre-needling. However, this had the disadvantage that the production speed had to be greatly reduced in order to avoid excessive damage to the non-finished nonwoven and to avoid needle breaks.

According to DE-PS 30 09 116 this disadvantageous process step of pre-needling can be eliminated by placing the still unconsolidated nonwoven coming from the spinning system on a rotating screen drum on which the finishing agent is sucked through the nonwoven in the form of a mist by means of negative pressure and over several suction zones are sucked through the inside of the sieve drum. The main disadvantage of this already improved method is that the It is still unsatisfactory that the fleece is uniform in weight per unit area, that high production speeds are not possible and that a relatively complicated depositing device with the aid of negative pressure and complicated regulations is required.

The object of the invention was to avoid the disadvantages described and above all to provide a method with which a uniform nonwoven with good mechanical properties can be produced at high production speed. The solution to the problem was found in that the fleece coming from the spinning plant is thermally sealed only on the surfaces.

• a) an beiden Vliesoberflächen thermisch angesiegelt,
• b) mit einem Gleitmittel versetzt und
• c) durch Vernadelung verfestigt werden, wobei auch die Versinterung an den Kreuzungspunkten der Fäden auf den angesiegelten Vliesoberflächen wieder gelöst wird.

The invention accordingly relates to a process for the production of needled spunbonded nonwovens made from thermoplastic fibers, which is characterized in that the threads coming from the spinning system are drawn and laid down to form a nonwoven

• a) thermally sealed on both fleece surfaces,
• b) mixed with a lubricant and
• c) are solidified by needling, the sintering at the crossing points of the threads on the sealed nonwoven surfaces also being released.

With the aid of the method it is possible to transport the fleece, which is only lightly sealed on the surface, without destroying the fleece structure and to add lubricant. The lubricant penetrates the fleece through the sealed fleece surfaces and provides good impregnation that is suitable for subsequent needling even at high production speeds. According to the method, spunbonded nonwovens with good basis weight uniformity can be produced approximately twice, in special cases also with higher production speeds compared to known methods. According to the invention, speeds of up to about 40 m / min and, in special cases, up to about 60 m / min can be achieved, depending on the nonwoven weight. With conventional Processes for producing needled spunbonded nonwovens have a maximum production speed of about 20 m / min. The high production speeds according to the invention are possible, in particular, due to the replacement of the limiting process steps of pre-needling or of finishing on the screen drum by means of negative pressure due to the much faster process step of thermal sealing. Due to the thermal sealing of the fleece surfaces, the threads lying on the surface are easily sintered together at their crossing points without the threads melting. The surfaces of these fibers lying on the nonwoven surface are softened without melting, a kind of sintering effect being achieved at the crossing points of the fibers. The connection of the threads by sealing is reversible and is loosened again when needling, so that finally the end product is a nonwoven that is only solidified by needling and not by thermal fusion.

The thermal sealing of the nonwovens according to the invention only on their surfaces, the core zone of the nonwovens remaining unconsolidated, results in sufficiently load-bearing, transportable and age-capable scrims, the structure of which is not destroyed during the application of the lubricant. As a result, a uniform fleece is obtained after the needling, in which the sealed surface layers are dissolved again. The uniformity of the nonwovens was indicated in the examples by the coefficient of variation c _V according to DIN 53854.

The two nonwoven surfaces are preferably sealed only to a maximum depth of 0.2 mm.

The thermal sealing can for example by means of heated rollers, belts, plates or surfaces or by radiant heaters, e.g. B. IR emitters. Heated rolls are preferably used; the nonwoven is particularly preferably passed through the nip of two calender rolls. The roller temperature and the surface temperature of the fleece are below the Melting point of the thermoplastic threads used. In the case of, for example, polypropylene nonwovens (melting point 165 ° C.), the calender rolls are preferably heated to approximately 120-140 ° C. The advantage of using a calender is that the sintering effect on the softened, non-melted fibers at the crossing points is increased by the roller pressure. Both the size of the nip and the roller pressure can be optimally adapted to the respective fleece weights, the thread count, the temperature, the thermoplastic threads used and the production speed.

The process according to the invention is suitable for producing nonwovens from all thermoplastics suitable for spunbonding technology. It is preferred for the production of spunbonded fabrics from polyolefin threads, such as. B. polyethylene or polypropylene threads, polyamide threads or polyester threads are used. Polypropylene threads are particularly preferably used, both threads made of polypropylene homopolymers and propylene-ethylene copolymers being possible. The basis weights of the nonwovens produced are approximately 30 to 2500 g / m², preferably approximately 100 to 2000 g / m².

Both water and the finishing agents customary in textile technology, such as are described, for example, in DE-PS 30 09 116, can be used as lubricants. The lubricant can by conventional methods such. B. be applied by spraying or by means of impregnation rollers.

The subsequent needling is carried out on known needling machines, for example as described in DE-PS 30 09 116, where solidification is carried out all at once or in stages up to the desired degree of needling.

Example 1:

Polypropylene with an MFI (melt flow index at 230 ° C and 2.16 kg load according to DIN 53735) of 17-21 and a molecular mass distribution of 2.3-2.7 was melted in an extruder at 230-260 ° C a 1 m wide test spinning system spun into fibers by means of spinnerets, drawn off via an aerodynamic take-off system, stretched to 8-12 dtex fineness and placed on a spinning belt to form a tangled thread structure. At a belt speed of 25 m / min, a fleece with a basis weight of 110 g / m² was produced. The as yet unconsolidated sheet was then introduced into a two-roll calender via an infeed belt. At 125 ° C - 130 ° C surface temperature of the oil-heated calender rolls and an applied line pressure of 30 - 35 N / mm, the loose fleece structure was reversibly consolidated, whereby only the fibers located on the fleece surfaces were caught and softened by the temperature influence, as well as by the roller pressure were pressed together, a kind of sintering effect being achieved at the crossing points of the fibers. Sufficiently viable surface layers were created on the top and bottom sides of the fleece, which can be redissolved in the later process, the layer thickness being less than 0.1 mm. The core area of the fleece, here at least 80% of the fibers, remained unconsolidated.

This preliminary fleece was then wetted with a lubricant on a roll pad. The sealed and finished nonwoven was then fed to a two-stage needling (80 punctures / cm 2 in each case), the sealed nonwoven surface being completely dissolved.

The fleece obtained had the following properties:

Grammage (DIN 53 854) 110 g / m2 Weight per unit area c _V (DIN 53854) 8th % Strip tensile strength (DIN 53 857/2) 780 N / 10 cm Stamp puncture resistance x (DIN 54 307) 1320 N.

Example 2:

Analogously to Example 1, a fleece with a basis weight of 1000 g / m² was produced at a belt speed of 3 m / min. The pre-consolidation was carried out at 120 ° C - 125 ° C roller surface temperature and 35 - 40 N / mm line pressure. The thickness of the sealed surface layer was 0.2 mm, at least 90-95% of the fibers remained unconsolidated.

Nonwoven properties:

Basis weight 1000 g / m² Uniformity of basis weight 4% Strip tensile strength 5200 N / 10 cm Stamp puncture resistance 6800 N

Example 3:

Analogously to Example 1, a web with a basis weight of 70 g / m 2 was produced at a belt speed of 35 m / min. The pre-consolidation was carried out at 130 - 135 ° C roller surface temperature and 20 - 30 N / mm line pressure. The thickness of the sealed surface layer was 0.05 mm, at least 60% of the fibers remained unconsolidated.

Nonwoven properties:

Basis weight 70 g / m² Uniformity of basis weight 9% Strip tensile strength 430 N / 10 cm Stamp puncture resistance 840 N.

Example 4:

Analogously to Example 1, polyester with an MFI (280 ° C / 2.16 kg) of 40-45 and a relative viscosity of 1.3-1.4 at 280-300 ° C were fibers with a fineness of 2-8 dtex spun and at a production speed of 27 m / min a fleece with a basis weight of 100 g / m² is produced. The calender was pre-consolidated at a roller surface temperature of 180 - 190 ° C and 25 - 30 N / mm line pressure.

Nonwoven properties:

Basis weight 100 g / m² Uniformity of basis weight 8th % Strip tensile strength 680 N / 10 cm Stamp puncture resistance 1140 N.

Example 5:

Analogously to Example 1, fibers with a fineness of 6-8 dtex were spun from polyamide 6 with a relative viscosity of 2.4-2.5 at 300-310 ° C. and a nonwoven with a basis weight at a production speed of 10 m / min of 250 g / m². The calender was pre-consolidated at a roll surface temperature of 190 - 200 ° C and 30 - 35 N / mm line pressure.

Nonwoven properties:

Basis weight 250 g / m² Uniformity of basis weight 6% Strip tensile strength 1710 N / 10 cm Stamp puncture resistance 2800 N

Example 6:

Analogously to Example 1, fibers with a fineness of 8-12 dtex were spun from polyethylene (HDPE) with an MFI (190 ° C./2.16 kg) of 12-14 at 210-240 ° C. and at a production speed of 25 m / min a fleece with a basis weight of 110 g / m² is produced. The calender was pre-consolidated at a roll surface temperature of 90 - 100 ° C and 25 - 30 N / mm line pressure.

Nonwoven properties:

Basis weight 110 g / m² Uniformity of basis weight 8th % Strip tensile strength 550 N / 10 cm Stamp puncture resistance 920 N.

Claims (6)

Process for the production of needled spunbonded nonwovens made of thermoplastic fibers, characterized in that the threads coming from the spinning installation are drawn and laid to form a nonwoven a) thermally sealed on both fleece surfaces, b) mixed with a lubricant and c) are solidified by needling, the sintering at the crossing points of the threads on the sealed nonwoven surfaces also being released. A method according to claim 1, characterized in that the two fleece surfaces are sealed up to a depth of 0.2 mm. A method according to claim 1 or 2, characterized in that the fleece surfaces are sealed by means of heated rollers. A method according to claim 3, characterized in that the fleece surfaces are sealed by means of heated calender rolls. Method according to one of claims 1 to 4, characterized in that the thermoplastic threads consist of polyolefin threads, polyamide threads or polyester threads. A method according to claim 5, characterized in that the thermoplastic threads consist of polypropylene.