DE2528136C2 - Isotactic polypropylene filament bonded nonwoven fabric and method of making the same - Google Patents

Description

for this purpose the nonwoven fabric is broken down into X and M layers, and then the measurements are made performed optically on each layer and the results in relation to the weight of the layers dt-s nonwoven averaged XD / 45 is a measure of the total length of thread in the nonwoven fabric divided by the mean the entire length of the thread in the diagonal direction. The term MD / 45 is a measure of the whole Thread length in the nonwoven fabric divided by the mean value of the thread length in the Diagonal direction. In the above fractions, the denominator is not the angle value 45 °, but this Number is just a symbol for the length of the thread in the diagonal direction.

When producing the nonwovens, an unbonded thread fleece is created by successive laying down of layers of melt-spun urd stretched isotactic polypropylene threads are produced on a moving conveyor belt in such a way that the in Machine direction layer (M layer), on top of which is a cross machine direction Layer (X-Layer) and finally on top of the X-Layer a second layer running in the machine direction (M-layer) is laid down, the conditions of melt spinning, drawing and laying speed can be controlled so that the X layer is 40 to 60% by weight of the total weight of the nonwoven fabric and each layer consists essentially of 65 to 90% by weight of scaffolding threads and 10 to 35% by weight consists of binding threads or binding sections, and the threads are deposited depending on the direction that the thread fleece preferred direction values of at least 1.5 for MD / 45, at least 1.5 for XD / 45 and 3.5 up to 30 for (MD + XD) / 45, whereupon the fleece produced in this way is thermally limited under spatial delimitation is bound. The spinning and drawing process is controlled so that the framework threads of the M-layers have an average thread count of 6.6 to 22 dtex and a strength of at least 2.7 g / dtex and the framework threads of the X-layer have a mean thread denier of 29 to 66 dtex and one Strength of at least 3.3 g / den obtained, which is at least 10% higher than the strength of the Framework threads of each M-layer, and that the binding threads in all layers have an elongation at break of 400 to 800% received.

The thermally bonded nonwoven fabric according to the invention has because of its special combination of layers with special thread properties that combination of properties that for a carpet base for coniferous pile carpets are sought. In the X-layer, the scaffolding threads have one higher titre and higher strength, with the higher strength due to a higher molecular orientation is based. Because of their closer molecular orientation, the threads of the X-layer are compared to the The threads of the two M-layers are only moderately bound to one another. Therefore have in the bonded nonwoven fabric the threads of the X-layer have a high degree of mobility, so that they when the needles of the tufting machine penetrate through the nonwoven fabric, the needles can easily avoid it and worn needles cannot to be damaged. Furthermore, the combination of high thread denier and high strength favors the Structural threads of the X-layer increase the resistance of the needle-punch carpets to tearing in the Machine direction.

The scaffold threads in the two M layers of the bonded nonwoven fabric have a lower titer and moderate strength (moderate orientation). These threads have a moderate breaking strength and when setting nubs, it has a lower cut resistance compared to needles. A high cut resistance of the threads in the M-layers is not necessary because the nubbed needles are in the essentially parallel to the fields of the M-layers

ίο move and therefore a lower probability insists that they cut the threads. The moderately oriented framework threads of the M-layer can be easily bind to the binding threads and to each other, resulting in a high resistance to shrinkage and against the defibration results without the tear propagation resistance being significantly impaired as a result. the The use of moderately oriented scaffolding threads in the M-layers also enables lower ones to be used Temperatures and shorter treatment times for thermal bonding. Shrinkage resistance and Fiber resistance are very valuable properties for carpets that are to be dyed in the vat. The surface layers of the carpet base should be fiber-resistant. The proportionate The low denier of the threads in each M-layer also serves to improve the optical opacity of the layered one Nonwoven.

The binder in each layer of the bonded nonwoven fabric is molten or partially molten polypropylene, derived from the threads of poor orientation that are used in the binding process essentially melt. The unbonded nonwoven thread from which the nonwoven fabric is made contains Filaments with essentially three degrees of molecular orientation:

1. The binding threads of the M and X layers have a low degree of orientation,

2. the structural threads of the M-layers have a moderate degree of orientation, and

3. The framework threads of the X-layer have a high degree of orientation.

While the moderately and strongly oriented framework threads do not benefit from the thermal binding process are changed significantly, the threads of low degree of orientation melt completely during the binding process or partially.

The preferred direction of the threads in the various layers is also important. An XD / 45 value (as defined below) of less than 1.5 leads to a reduction in the tufted tear strength by the tongue method, while an MD / 45 value of less than 1.5 results in more shrinkage when dyeing or otherwise Heat treatment process leads. It was also found that the desired combination of little Shrinkage and high tear strength is not achieved if the weight of the X-layer or the The total weight of the M layers is 70% of the total weight of the nonwoven fabric. As mentioned above, is hence the X-layer in the layered fleece stole according to the invention to 40 to 60% of the total weight of the nonwoven, while each M-layer contributes 20 to 30% of the total weight of the nonwoven is.

In order to complete the description of the procedure according to the

To simplify the invention, letters are used to indicate the order in which the Layers of the thread fleece are deposited, whereby the deposit begins with the bottom layer and up to top layer is continued. Since the product can be viewed from both sides, Marking the product only the relative position of the layers is important. According to this system MXM means that first the M-layer, then the X-layer on top of the M-layer and finally another M-layer is deposited on top of the X-layer. Every single M- or X-layer can with the help of a large Number of nozzles are deposited, which are distributed across the width of the depositing belt. Furthermore can several successive rows of nozzles can be used. When the threads come out of consecutive If rows of nozzles are deposited in the same general direction, the deposited material can be used as one only layer to be considered.

To further explain the invention, reference is made to the drawings.

F i g. 1 is a schematic section through a melt-spinning and cooling device with which the Polypropylene threads of high denier and high degree of orientation for the nonwovens according to Invention are made.

F i g. Figure 2 is a schematic representation of an apparatus for stretching and laying a Thread ribbon on a running belt.

F i g. 3 is a perspective view of four air jet devices for deflecting the filaments in FIG Form of layers with a directional pattern.

A general description of devices used for making a nonwoven fabric according to the invention are suitable, can be found in US-PS 35 63 838. However, for the melt spinning and cooling of the polypropylene filaments of the X-layer of the nonwoven fabric preferably uses an improved mechanism. In particular the flow of cooling air is carefully controlled in such a way that that rapid cooling takes place without breaking the running threads. The device according to FIG. 1 is a Modification of the device described in US-PS 37 05 227. This device can optionally can also be used to make the threads of the M-layers, but is of particular value for the manufacture of the threads of the X-layer. As shown in Fig. 1, melt-spun polypropylene filaments are used 4 from the spinneret plate 1, in which openings (not shown) are arranged in circles. The threads are running through a radial cooling device 2 to the conveyor roller 22. An air deflector 3 is located on the spinneret plate in FIG Attached in the shape of an inverted cone. At the top and at the bottom of the cooling device 2 are Flow diaphragms 5 and 6 attached In this particular, modified embodiment, the The flow diaphragms are intended for spinning of highly oriented, high-denier filaments elliptical and are in such a position that from any point on the outer Circle the spinneret orifices a straight line (with only minor deviations) through a point on the innermost surface of the flow diaphragm 5 and a similar point of the flow diaphragm 6 to the first Conveyor roller 22 of the thread drawing device can be pulled. At the same time, the big ones lie Axes of the elliptical surfaces of the flow diaphragms 5 and 6 in one to the surface of the roller 22 tangential plane. This allows a better adaptation to the natural shape of the running threads. This special design of the device according to US-PS 37 05 227 enables an extraordinary effective cooling, which prevents threads from sticking together and the formation of highly oriented Threads of high titer at high spinning speeds is favored.

The openings at the top and bottom of the

ίο Cooling devices have such sizes that the main resistance to the air flow occurs at the lower end of the cooling device and most of the cooling air is forced to leave the cooling device through the upper end. The cooling air is supplied through the inlet 7 and, as described below, distributed so that it flows radially inward against the running threads entering the cooling chamber, whereupon the flow diaphragms 5 and 6 force the greater part of the air out of the upper end of the To flow out cooling chamber 2 and briefly upwards through the middle of the hollow thread bundle 4. Then the air hits the conical deflecting member 3 and is deflected back radially outward through the running thread bundle. The length of the conical flow deflector and the cooling air speeds depend on many factors, such as the number of threads, the throughput per spinning hole, the spinning temperature, etc.
A smoke extractor is normally used in melt spinning polypropylene which contains certain stabilizing additives which sublime or decompose at the spinning temperatures to form smoke on the spinneret face. This device also improves the cooling process.

The threads run down through the cooling chamber, the walls of which are made of a cylindrical, permeable Organ 16 exist. The air chamber 19 is through the inlet 7 with air or another cooling gas fed under slight overpressure in order to

To achieve ßige radial flow of cooling gas into the cooling chamber through the permeable organ.

Behind the flow diaphragm 6, the thread bundle 4 has an elliptical shape; the major axis of the ellipse lies in a plane tangential to the surface of the roller 22. F i g. 1 shows a section along the small one Axes of the ellipses at 5 and 6. The major axes of the ellipses are parallel to the axis of the roller 22.

Like F i g. 2 shows the elliptical thread bundle 4 is made into a band as it passes the roller 22 parallel threads. Then the yarn runs one after the other over the rollers 23, 24, 25, 26 and 27. This increases the speed of the yarn run from roller to roller. The highest speed increase takes place in each case between a hot roll and the subsequent cold roll instead of the stretching process is supported in that the threads or parts thereof on the grooved roller 25 and optionally on the smooth roller 23 are heated. As the roller 23 is a smooth, cylindrical roller, takes place between the Rolls 23 and 24 a uniform stretching instead. The roller 25, on the other hand, has grooves that are in axial direction Direction across their surface. Those sections of the yarn that touch the hot roll surface touch between the grooves are additionally stretched, whereas those thread sections that bridge the grooves, are not additionally stretched to a significant extent. The one from the Roller 25 coming threads show their length

alternating strongly oriented and less oriented sections. The tape of stretched in sections Threads run from roller 27 to guide 28.

When walking past the target stick of a corona charger 29, as described in US Pat. No. 3,163,753. the threads become electrostatic charged. The band of electrostatically charged filaments is inserted into the inlet opening of the slot nozzle 30 (the type of which is shown in Fig. 6 of US-PS 35 63 838) and emerges from the slot nozzle outlet for storage on the running belt 32. F i g. 2 shows the arrangement, from the front end of the Discarding tape 32 seen here. If multiple nozzles are used, the sides 41 of the conveyor belt of course, be further apart. NVie Fig. 2 shows, the thread tape 31 is used as an X-layer filed. At the nozzle outlet, the thread tape is driven by an air pulse that alternates from one side and then fed in from the other side of the running thread tape, alternately back and forth deflected forward so that the threads are deposited oriented predominantly transversely to the machine direction.

The general arrangement of the multiple delivery nozzles over the depositing belt is shown in FIG. 3, the four can be seen Slot nozzles shows, each of which conveys a thread tape 31 to the porous depositing tape 32, which is in the through the direction shown by arrow 40 advances. The two front nozzles 30 extend in the width direction their slots across the width of the filing tape. The two rear nozzles 34 are directed so that their Slot width in the machine direction 40 has. The in F i g. 3 arrangement is used to store Layers in MX order. For an MXM deposit there would be another one behind the nozzles 34 further assembly of nozzles is required, which would have the same direction as the nozzles 30. if If a wider carpet is to be made, a larger number of nozzles are used over across the width of the machine.

F i g. Figure 3 also shows the arrangement of the threads in the product according to the invention. The threads of the M-layer 38 are generally in the machine direction. However, part of each thread runs in others Directions because the direction is reversed at each end of the reciprocating motion in the M direction must become. Similarly, the threads in the X-layer 39 are oriented generally in the cross-machine direction, but their length has parts that are oriented in other directions. Finally, threads become is deposited downstream of the conveying direction to a further M-layer (not shown in FIG. 3).

In the manufacture of the nonwoven fabrics according to the invention, threads are relatively small Titer spun, drawn and by the jets of air oscillating back and forth in the machine direction filed, while high-denier threads are spun, drawn, and swayed by the reciprocating Air jets are deposited across the machine direction. Also, the threads that later to form the M-layers, in sections to a lower degree of molecular orientation stretched than the threads that will later form the X-layer. The difference in the thread count and in the Molecular orientation of the drawn thread sections in the M-layers and the X-layer is thereby achieves that the spinning speed, the draw ratio between the smooth rollers 23 and 24 and regulates the stretching ratio between the grooved roller 25 and the smooth roller 26. The amount of Molecular orientation in the binding sections of the threads is primarily determined by the relative Speeds of rollers 23 and 24. The percentage of binding sections in the M and X-layers is determined by the ratio of the sum of the groove widths to the total circumference of the Grooved roller 25.

The deposited threads are thermally bonded, preferably by being passed through saturated water vapor in a binding device as described in US Pat. No. 3,313,002. After tying a finish is applied in order to avoid excessive thread breaks when setting nubs. as

A polysiloxane is preferably used for the finish. as described in US Pat. No. 3,322,607. Too much shrinkage is caused by spatially delimiting Prevents the fleece from being clamped during the binding process. The degree of binding influences the properties of the Nonwoven. As the binding temperature rises, the tendency of the pile carpet to shrink decreases. Simultaneously run through the values for the tufted tear strength according to the as the binding temperature rises Tongue method a maximum and then decrease again. There is compensation for a carpet base required between shrinkage and tufted tear strength. The aim is to produce products which shrink by 1 to 5%, preferably by 1 to 3%. The effect of excessive mechanical pressure should be avoided when using the binding device according to US-PS 33 13 002, so that the fiber mobility is retained in the X-layer. It is especially important to avoid exposure to too high a Avoid mechanical pressure when any of the outer M-layers have more than 20% binder contains because the binder easily melts under the action of heat and pressure and into the X-layer can run into it, whereby the fiber mobility is reduced. The fiber mobility is but necessary for achieving a high tufted tear strength of cut pile carpets. At the The structure of the nonwoven fabric should take into account that it is closest to the source of water vapor M-layer a higher heat absorption takes place.

Therefore, even if in the same amount of binder has been used for each M-layer.

_Μ test methods

The direction, the tufted tear strength, the percentage run-in, the binder concentration, the titer of the framework threads and the thread strength are determined according to US Pat. No. 3,821,062 The thread strength can also be determined on thread samples taken directly from the nozzles be removed, whereby there is a 10 percent decrease in strength when going through the heat-bonding process bills

Tear resistance of cut pile carpets

A cut pile carpet using a bonded nonwoven fabric as the carpet backing is used for this experiment Old, worn needles are used to manufacture the carpet. The non-woven fabric is provided with 2 percent by weight of polymethylhydrogensiloxane as a lubricant. Lengthwise (in the machine direction) becomes a sample of the with the lubricant

provided nonwoven fabric cut out so that 20.3 cm wide strips are obtained. These strips are in a 5/32 gauge cut pile nub setting machine (where the needles are 0.396 cm) Arranged so that a strip 15.3 cm wide, with the help of old needles (taken from a Stock of needles that have been used for about 1000 hours can be randomly selected) is trimmed with pile. All needles are "Eisbar 1269/350" needles with an insertion end 0.318 cm thick. The nonwoven fabric is made in the machine direction using a twisted polyamide staple yarn (two-wire yarn made from single capillaries with a worsted number of 2.25) with a density of 6.5 tufts each 2.54 cm occupied with Fior, so that a cut pile carpet with a pile height of 1.27 cm arises and on each side of the part covered with pile a 2.5 cm wide unoccupied nonwoven strip is exposed remain. The nonwovens covered with pile and with the 2.54 cm wide selvedge on each side are turned into (in the Machine direction) cut 8 inch strips. The tufted tear resistance of the cut pile carpets is then determined by the tongue method in the same way as for knobbed pile carpets happens by tearing in the machine direction.

Fiber resistance

This test is a modification of ASTM Test Standard D 1375, Part C, Brush and Sponge Method. the end Square samples are cut out of the bonded nonwoven fabric, in the M-direction and in the X direction are each 25.4 cm long. The samples are wrapped around flat sample holders made of galvanized steel be rectangular in shape (10.8 cm by 29.2 cm). The side to be examined faces outwards. The keepers are covered with No. 100 sandpaper to prevent the specimens from sliding during the test, and the specimens are attached to the holders with magnets. The total weight of the steel strip and magnet is 550 ± 5 g. The samples are then placed face down on the upright bristles of the The pilling test device is attached and the fibrillation brush is placed under the samples for 10 seconds run. The next step in the ASTM test procedure, which is the circular rubbing of the samples with a sponge to roll up the free fiber ends into fiber balls is omitted. The appearance of the nonwoven fabric is assessed visually by comparison with standard samples Samples received brush fray values from 1 to 5, with 1 being extremely fibrous and 5 practically free of Fibers means. The nonwovens according to the invention have a relatively high degree of shrinkage compared to the previously known products with the same degree of enema high fiber resistance.

Percentage optical opacity

This is a photometric test to determine the opacity of the nonwovens. There will be separate Measurements of the of a white background, that of a black background, of that of the nonwoven fabric in contact with the white background and the one with the black background in Touching the same part of the nonwoven fabric to be examined, the amount of light reflected is carried out. The measurements are made on at least five different parts of each test nonwoven. Man uses a commercially available device that consists of a cable connected to a meter connected locator (including light source, optical system and photocells), a power source and tax organs. The percent optical opacity is derived from the measured reflectivity calculated according to the following equation:

10

15th

20th

Percentage optical opacity = (l - χ iOO,

V Rwb ~ Ebb J

Rwb = reflectivity of the white background (for which the meter is calibrated to show 100),

Rbb = reflectivity of the black background (for which the measuring device is calibrated to display 0),

Rfwb = reflectivity of the nonwoven fabric against the white background,

Rfbb = reflectivity of the nonwoven fabric against the black background.

The nonwovens according to the invention have, for a given basis weight, compared to the previous ones Known nonwovens have a high optical opacity. For comparison purposes, the nonwovens made of threads the same color depth and shade can be produced.

Examples 1 to 5

An experimental device similar to that according to FIG. 1 and 2 is used to produce five nonwovens used according to the invention. The details of the spinning, drawing and laying process are for each example given in Table I. As a result of the

Transitioning over the grooved roller 25, which is heated to 135 to 140 ⁰ C have the threads greatly stretched projecting skeleton portion and less strongly stretched binding portions.
In all examples, the amount of nonwoven waste

Steering adjusted so that the M and X layers are in the middle ones used for sampling Areas have the prescribed percentage by weight of fibers. The sampling areas lie in the middle of the width of the nonwovens and

contain representative portions of each of the deposited M and X layers. On the margins parts of the nonwovens located in the area are not used for sampling. The structure of the five nonwovens is summarized in Table II The properties of

Bound nonwovens on their own and when used as basic carpet materials are shown in the table III.

In all examples, the filaments are made from the melt of a polypropylene with a melt index

of 3.2 ± 0.4, determined according to ASTM test standard D 1238-65T, spun, the 0.068 to 0.078% carbon black as Contains pigment. The spun threads are gray and have the same depth of color and the same hue

on. Nonwovens with an MXM construction are produced by using the melt-spun polypropylene threads are deposited from three spinnerets arranged in a row above the depositing belt. Every The spinneret feeds a separate suction nozzle. The individual spinnerets are ejected one after the other deposited on a moving conveyor belt. First, there is an M-layer on the leading end of the filing tape deposited, then an X-layer and finally another M-layer is deposited. The belt speed to speed is set so that nonwovens with the values listed in Table II! given area weights arise.

As Table II shows, the nonwovens in the X-layer have the threads of higher titer and in the M-layers on the threads of lower titer. The threads in the X-layer have a higher orientation than the threads in the M layers. The high degree of orientation is reflected in the high strength of the Threads reflected.

The properties of the carpet bases and carpets made from the nonwovens according to Table II result from Table III. The thread webs described in Table II are bound by be passed through the steam binding device according to US-PS 33 13 002. The discarded threads and the filing tape run out of the filing area directly through this binding device. The steam temperature in the binding device is adjusted so that a nonwoven fabric is produced that is less than 5%, preferably by less than 3%. The tendency to shrinkage increases with use Temperatures decreased. However, the temperature is kept so low that the tear strength is off The knobbed pile carpets made of the nonwovens

kg

was at least 0.24 ϊ,;. In these examples

g / m- ^r

temperatures in the range from 148 to 152 ° C are used. (If you work with higher belt speeds, higher temperatures are necessary for a sufficient bond.) From Table III it can be seen that the carpet base materials thus obtained at basis weights of 98 to 125 g / m ^{2 have} a fiberization value of at least 3.0 and preferably of at least 4.0 on at least one surface and an opacity of at least 77%.

The carpet raw materials explained in Table III are, as indicated in the test methods, for Used in the manufacture of knobbed pile carpets and cut pile carpets. These nonwovens according to Invention have a high tufted tear strength in tufted pile carpets. These are also suitable Basic materials for the production of cut pile carpets and are less sensitive to the texture the knobbed setting needles. Table III shows that the cut pile carpets made with old needles are a Have tufted tear strength greater than 20.4 kg. This feature in combination with the high The resistance to shredding and the high coverage make the carpet base very valuable Product.

Table I.

Procedure conditions of the examples

example 1

Surface speed of roller 26
M layers, m / min
X layers, m / min

Draw ratio of the drawn
Sections *)

M layers
X-layer

Elongation at break of the undrawn
Sections **)

M layers,%

X layers,%

660 660 505 505 660 537 645 537 495 537 1.8 1.8 1.8 1.8 1.8 3.5 4.0 3.6 3.3 3.5 466 481 478 524 548 595 551 577 637 595

Remarks

*) The draw ratio is determined from the ratio of the surface speed of the roller 26 to the surface speed the roller 22 is calculated.

**) The mean elongation at break is determined on sections of high titer, those from threads deposited on the conveyor belt have been cut out before binding.

200 threads per spinneret are deposited in each M-layer, 150 threads per spinneret in each X-layer, with the exception of example 2, in which only 100 threads are deposited in the X-layer per spinneret.

in det 13th ^a ) 25th 28 136 14th Table II Examples Nonwoven construction

example 2 3 4th 5 1 Framework thread denier (1 den = 1.1 dtex) 13.3 11.5 14.5 14.0 M-layer 14.2 47.1 35.3 33.6 33.6 X layer 32.5 12.0 14.5 14.4 10.3 M-layer 12.8 Framework thread strength, g / den ^b ) 2.4 2.6 2.4 2.8 M-layer 2.7 3.7 3.5 3.6 3.6 X layer 3.7 2.4 2.7 2.9 2.8 M-layer 2.2 Binder in the layers,% by weight ^c ) 12th 12th 12th 32 M-layer 12th 12th 12th 23 12th X layer 12th 12th 12th 12th 32 M-layer 12th Characteristic values for the filament orientation ^d ) 2.8 2.6 2.4 2.6 MD / 45 ° 2.0 2.9 2.6 1.5 2.8 XD / 45 ° 2.9 5.7 5.2 3.9 5.4 (MD + XD) / 45 ° 4.9

Remarks

^a ) In each example, the weight of each M-layer is 25% and the weight of the X-layer is 50% of the total weight of the nonwoven fabric.

^b ) The thread samples are taken from the threads coming from the nozzles or the bound nonwovens. From the strength values of the thread samples coming from the nozzles 10% are subtracted in order to increase the effectiveness of the binding; To take into account.

^c ) Calculated as percent by weight of non-drawn thread sections according to the equation

Total arc length of the grooves

% undrawn = ^Ξ x 100

Total circumference of the grooved roller

^d ) Determined by the random meter method.

Table III

Properties of the basic carpet fabrics and carpets of the examples

example 2 3 4th 5 1 Carpet base 125 98 102 119 Basis weight, g / m ² 125 80 80 81 77 Opacity,% 79 Defibration value of the M-layers 4.6 5.0 5.0 4.4 first layer treated with steam 4.7 4.1 3.5 4.0 3.3 other layer 4.5

Knobbed carpet Tufted tear strength, kg kg

g / m ³ shrinkage,%

Cut pile carpet, made with worn needles, tufted tear resistance. ka

47 0.38

1.7 24

41

21

24
η κ

25 0.34 1.7 24

46

r \ tr

2.2 23

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1. Bound nonwoven made of isotactic polypropylene threads, which has a layer M running in the machine direction on each of its two surfaces, while a layer X running transversely to the machine direction makes up 40 to 60% of the total weight of the nonwoven, each layer being essentially 65 to 90% by weight .-% of scaffold fibers and from 10 to 35Gew .-% of isotactic polyp ^r opylen as a binder is, and the threads arranged in each layer so that the characteristic values for the filament orientation of the nonwoven fabric for at least 1.5 MD / 45, at least 1.5 for XD / 45 and 3.5 to 30 for (MD + XD) / 45, where MD and XD are the mean values of the ic machine direction or filament length sections of the framework threads running in the transverse direction of the nonwoven and the expressions MD / 45, XD / 45 or (MD + XD) / 45 mean the ratio of the corresponding mean values to the mean value of the filament length sections in the diagonal direction, characterized in that the framework threads one each M-layer has an average titer of 6.6 to 22 dtex and a strength of at least 1.8 g / dtex and the framework threads of the X-layer have an average titer of 29 to 66 dtex and a strength of at least 2.7 g / dtex, which is at least 10% higher than the strength of the framework threads of each M-layer. 2. Bound nonwoven fabric according to claim 1, characterized in that each M-layer is closed about 20 to 30% of the total weight of the nonwoven is involved. The invention relates to improved nonwovens which are particularly suitable for use as a carpet base for According to the preamble of claim 1, needle-cut pile carpets are suitable. The US-PS 35 02 538 describes a nonwoven made of polypropylene thread existing carpet base. The bonded nonwoven fabric is made from nonwovens that Contain threads or thread sections which differ in their orientation (i.e. birefringence) from one another differentiate. The less strongly oriented threads or thread sections are called binding threads and the more oriented as scaffolding threads. The degree of orientation is determined by the extent of the stretching controlled, which the threads experience before they turn into a random thread fleece on a laying surface be filed. In US-PS 35 63 838 a process for the production of carpet base from nonwovens is described, which consist of the framework and binding threads made of polypropylene described above. These nonwovens are made up of at least two layers. In one layer, the threads are mainly in the Machine direction (i.e. in the general direction of the longitudinal dimension of the nonwoven fabric, which is also the Corresponds to the direction of the running belt on which these nonwovens are produced); this layer will referred to as the M-layer. In the adjacent layer, the threads are predominantly perpendicular to the M-layer directional threads, d. H. across the machine direction; this type of layer is called X-layer denotes Furthermore, the layers of these nonwovens contain a small proportion of threads that oblique to the machine direction and to the cross direction. The patent describes nonwovens with an MX sequence of layers as well as nonwovens with an MXM sequence of layers. When these nonwovens are bonded in saturated steam, basic carpets are obtained from high tufted tear resistance using the tongue method, which only minimally shrinks into the dye vat demonstrate. From DE-OS 23 07 829 a carpet base in the form of a layered polypropylene thread nonwoven is known which means an improvement over the carpet raw materials disclosed in US Pat. No. 3,563,838 Scaffolding threads as well as in the distribution of binding and scaffolding threads. The bonded product shows relatively little shrinkage in the dyeing tub and, after the usual coating with latex, which is required in the manufacture of tufted carpets, has a high tear resistance; Furthermore, even after the latex has been applied, it retains a large part of its tear ^resistance: at relatively low weights per unit area, however, these nonwovens show insufficient optical coverage Although the two polypropylene thread nonwovens described above suitable as a carpet base for certain types of coniferous pile carpets their use for the production of cut pile carpets highlighted certain disadvantages. At the This is because the needles wear out when the hook removes the carpet yarn from the needle withdraws. These worn or burred needles then often cut the carpet, when he advances against the needle. It has also been found that some of the known carpet base nonwovens tend to form fibrils (or fibrils) in the vat when the carpet is dyed (what hereinafter referred to as defibration). When the usual second back is applied, form these fiber globules put mi! insufficient resistance to stripping The object of the invention is to avoid these disadvantages and to provide a carpet base which has a better resistance to being cut by sharpened needles during the Tufted and has a high resistance to lint formation during dyeing. The solution to this task is in specified in the claims. The filament orientation is determined according to the »random meter method«. This method is based on the principle that only those incident light rays that hit the filament axis perpendicularly, are reflected perpendicular to the filament axis. So if a bundle of parallel rays of light hits you If nonwoven fabric is directed at an angle of incidence of less than 90 °, e.g. 60 °, then the light comes from is emitted perpendicular to the plane of the fleece, only from filaments which are perpendicular to the incident light in the Fleece plane are oriented. The intensity of this light is a measure of the total length of the filament segments that perpendicular to the incident light. By turning the fleece, the filament segments for each Direction can be determined, and from this determination the filament orientation can be determined. to